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http://math.stackexchange.com/questions/215297/suppose-i-said-x-spans-w
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# Suppose I said “$X$ spans $W$”…
So I've seen two definitions of this:
Let $V$ be a vector space with subspace $W$. We say that $X \subseteq V$ spans $W$ if and only if
(Definition 1): Every $\vec{w} \in W$ can be written as a linear combination of vectors in $X$.
(Definition 2): $span(X) = W$.
I don't think the two definitions are equivalent are they? Clearly the condition in Def. 2 implies the condition in Def. 1, but not the other way round.
For example take $V$ to be the vector space of ordered pairs over $\mathbb{Z}_2$, then if $W = \{(0,0),(1,1)\}$ and $X=\{(0,1),(1,0)\}$, $X$ spans $W$ according to the first definition, but not the second.
What then would you have understood if I were to tell you that "$X$ spans $W$"? Would you have agreed or disagreed with me?
I know the usual drill is "clarify your definitions from the start" in whatever work you're doing, and that as long as you do that it will be fine, but I'm just wanting to know what peoples' immediate interpretation would be. Because it does impact a little on the reading and understanding process.
(For the record I'm a fan of Definition 1.)
-
One usually understands $X$ spans $W$ to include the condition that $X$ is a subset of $W$. – Gerry Myerson Oct 17 '12 at 1:22
I would vote for definition 2. – Bitwise Oct 17 '12 at 1:57
My feeling for this terminology is that the phrase "$X$ spans $W$" should be consistent with the phrase "the span of $X$ is $W$". It is standard to define "the span" of a set, and so the first definition, which implies that $X$ could span distinct subspaces, is inconsistent with "the span".
Probably a good definition is: if $V$ is a vector space and $X\subseteq V$ is a set then we say that $X$ spans $V$ if every $v\in V$ can be written as a linear combination of elements of $X$. This way you have to refer to a set of vectors within a vector space.
So in this case to say that $X$ spans $W$ only makes sense in the case that $X\subseteq W$. It is as if $V$ ceased to exist for a brief moment of mathematical thought.
|
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https://code.bioconductor.org/browse/bsseq/blob/RELEASE_3_9/man/BSseq-class.Rd
|
\name{BSseq-class}
\Rdversion{1.1}
\docType{class}
\alias{BSseq-class}
\alias{[,BSseq-method}
\alias{combine,BSseq,BSseq-method}
\alias{combineList}
\alias{length,BSseq-method}
\alias{pData,BSseq-method}
\alias{pData<-,BSseq,data.frame-method}
\alias{pData<-,BSseq,DataFrame-method}
\alias{sampleNames,BSseq-method}
\alias{sampleNames<-,BSseq,ANY-method}
\alias{updateObject,BSseq-method}
\alias{assays,BSseq-method}
\alias{assayNames,BSseq-method}
\alias{show,BSseq-method}
\alias{getBSseq}
\alias{collapseBSseq}
\alias{strandCollapse}
\alias{orderBSseq}
\alias{chrSelectBSseq}
\alias{hasBeenSmoothed}
\title{Class BSseq}
\description{
A class for representing whole-genome or capture bisulfite sequencing
data.
}
\section{Objects from the Class}{
An object from the class links together several pieces of information.
(1) genomic locations stored as a \code{GRanges} object, a location by
samples matrix of M values, a location by samples matrix of Cov
(coverage) values and phenodata information. In addition, there are
slots for representing smoothed data. This class is an extension of
}
\section{Slots}{
\describe{
\item{\code{trans}:}{Object of class \code{function}. This
function transforms the \code{coef} slot from the scale the
smoothing was done to the 0-1 methylation scale.}
\item{\code{parameters}:}{Object of class \code{list}. A list of
parameters representing for example how the data was smoothed.}
}
}
\section{Methods}{
\describe{
\item{[}{\code{signature(x = "BSseq")}: Subsetting by location
(using integer indices) or sample (using integers or sample
names).}
\item{length}{Unlike for \code{RangedSummarizedExperiment},
\code{length()} is the number of methylation loci (equal to
\code{length(granges(x))}).}
\item{sampleNames,sampleNames<-}{Sample names and its replacement
function for the object. This is an alias for \code{colnames}.}
\item{pData,pData<-}{Obtain and replace the \code{pData} slot of the
\code{phenoData} slot. This is an alias for \code{colData}.}
\item{show}{The show method.}
\item{combine}{This function combines two \code{BSSeq} objects.
The genomic locations of the new object is the union of the
genomic locations of the individual objects. In addition, the
methylation data matrices are placed next to each other (as
appropriate wrt. the new genomic locations) and zeros are entered
into the matrices as needed.}
}}
\section{Utilities}{
This class extends \linkS4class{RangedSummarizedExperiment} and therefore
inherits a number of useful \code{GRanges} methods that operate on the
\code{rowRanges} slot, used for accessing and setting the genomic locations
and also do \code{subsetByOverlaps}.
There are a number of almost methods-like functions for operating on
objects of class \code{BSseq}, including \code{getBSseq},
\code{collapseBSseq}, and \code{orderBSseq}. They are detailed below.
\describe{
\item{\code{collapseBSseq(BSseq, columns)}}{
is used to collapse an object of class \code{BSseq}. By
collapsing we simply mean that certain columns (samples) are merge
together by summing up the methylation evidence and coverage.
This is a useful function if you start by reading in a dataset
based on say flowcells and you (after QC) want to simply add a
number of flowcells into one sample. The argument \code{columns}
specify which samples are to be merged, in the following way: it
is a character vector of new sample names, and the names of the
column vector indicates which samples in the \code{BSseq} object
are to be collapsed. If \code{columns} have the same length as
the number of rows of \code{BSseq} (and has no names) it is
assumed that the ordering corresponds to the sample ordering in
\code{BSseq}.}
\item{\code{orderBSseq(BSseq, seqOrder = NULL)}}{
simply orders an object of class \code{BSseq} according to
(increasing) genomic locations. The \code{seqOrder} vector is a
character vector of \code{seqnames(BSseq)} describing the order of
the chromosomes. This is useful for ordering \code{chr1} before
\code{chr10}.}
\item{\code{chrSelectBSseq(BSseq, seqnames = NULL, order = FALSE)}}{
subsets and optionally reorders an object of class \code{BSseq}.
The \code{seqnames} vector is a character vector of
\code{seqnames(BSseq)} describing which chromosomes should be
retained. If \code{order} is \code{TRUE}, the chromosomes are
also re-ordered using \code{orderBSseq}.}
\item{\code{getBSseq(BSseq, type = c("Cov", "M", "gr", "coef",
"se.coef", "trans", "parameters"))}}{
is a general accessor: is used to obtain a specific slot of an
object of class \code{BSseq}. It is primarily intended for
internal use in the package, for users we recommend \code{granges}
to get the genomic locations, \code{getCoverage} to get the
coverage slots and \code{getMeth} to get the smoothed values (if
they exist). }
\item{\code{hasBeenSmoothed(BSseq)}}{
This function returns a logical depending on whether or not the
\code{BSseq} object has been smoothed using \code{BSmooth}. }
\item{\code{combineList(list, BACKEND = NULL)}}{
This function function is a faster way of using \code{combine} on
multiple \linkS4class{BSseq} objects. The input is a list, with each
component an object of class \linkS4class{BSseq}. The (slower)
alternative is to use \code{Reduce(combine, list)}.
The \code{BACKEND} argument determines which backend should be used for
the 'M' and 'Cov' matrices and, if present, the 'coef' and 'se.coef'
matrices (the latter two can only be combined if all objects have the
same rowRanges). The default, \code{BACKEND = NULL}, corresponds to using
alternative backends.
}
\item{\code{strandCollapse(BSseq, shift = TRUE)}}{
This function operates on a \code{BSseq} objects which has
stranded loci (i.e. loci where the strand is one of \sQuote{+} or
\sQuote{-}). It will collapse the methylation and coverage
information across the two strands, unstranding the loci in the process
and potentially re-ordering them.
The argument \code{shift} indicates whether the positions for the loci
on the reverse strand should be shifted one (i.e. the positions for
these loci are the positions of the \sQuote{G} in the
\sQuote{CpG}; this is the case for Bismark output for example).}
}
}
\section{Coercion}{
Package versions 1.5.2 and 1.11.1 introduced a new version of representing
\sQuote{BSseq} objects. You can update old serialized (saved)
objects by invoking \code{x <- updateObject(x)}.
}
\section{Assays}{
This class overrides the default implementation of \code{assays} to
make it faster. Per default, no names are added to the returned data
matrices.
Assay names can conveniently be obtained by the function
\code{assayNames(x)}
}
\author{
Kasper Daniel Hansen \email{[email protected]}
}
\seealso{
The package vignette. \code{\link{BSseq}} for the constructor
data stored in the object and finally \code{\link{BSmooth}} for
smoothing the bisulfite sequence data.
}
\examples{
M <- matrix(1:9, 3,3)
colnames(M) <- c("A1", "A2", "A3")
BStest <- BSseq(pos = 1:3, chr = c("chr1", "chr2", "chr1"), M = M, Cov = M + 2)
chrSelectBSseq(BStest, seqnames = "chr1", order = TRUE)
collapseBSseq(BStest, group = c("A", "A", "B"))
#-------------------------------------------------------------------------------
# An example using a HDF5-backed BSseq object
#
hdf5_BStest <- realize(BStest, "HDF5Array")
chrSelectBSseq(hdf5_BStest, seqnames = "chr1", order = TRUE)
collapseBSseq(
BSseq = hdf5_BStest,
group = c("A", "A", "B"),
BACKEND = "HDF5Array",
type = "integer")
}
\keyword{classes}
|
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|
https://www.theochem.ru.nl/~pwormer/Knowino/knowino.org/wiki/Rotation_matrix.html
|
# Rotation matrix
In mathematics and physics a rotation matrix is synonymous with a 3×3 orthogonal matrix, which is a real 3×3 matrix R satisfying
$\mathbf{R}^\mathrm{T} = \mathbf{R}^{-1},$
where T stands for the transposed matrix and R−1 is the inverse of R.
## Connection of an orthogonal matrix to a rotation
In general a motion of a rigid body (which is equivalent to an angle and distance preserving transformation of affine space) can be described as a translation of the body followed by a rotation. By a translation all points of the body are displaced, while under a rotation at least one point of the body stays in place. Let the the fixed point be O. By Euler's theorem follows that then not only the point is fixed but also an axis—the rotation axis— through the fixed point. Write $\hat{n}$ for the unit vector along the rotation axis and φ for the angle over which the body is rotated, then the rotation operator on ℝ3 is written as ℛ(φ, ).
Erect three Cartesian coordinate axes with the origin in the fixed point O and take unit vectors $\hat{e}_x,\;\hat{e}_y,\;\hat{e}_z$ along the axes, then the 3×3 rotation matrix $\mathbf{R}(\varphi, \hat{n})$ is defined by its elements $R_{ji}(\varphi, \hat{n})$ :
$\mathcal{R}(\varphi, \hat{n})(\hat{e}_i) = \sum_{j=x,y,x} \hat{e}_j R_{ji}(\varphi, \hat{n}) \quad\hbox{for}\quad i=x,y,z.$
In a more condensed notation this equation can be written as
$\mathcal{R}(\varphi, \hat{n})\left(\hat{e}_x,\;\hat{e}_y,\;\hat{e}_z\right) = \left(\hat{e}_x,\;\hat{e}_y,\;\hat{e}_z\right) \; \mathbf{R}(\varphi, \hat{n}).$
Given a basis of the linear space ℝ3, the association between a linear map and its matrix is one-to-one.
A rotation $\mathcal{R}$ (for convenience sake the rotation axis and angle are suppressed in the notation) leaves the shape of a rotated rigid body intact, so that all distances within the body are invariant. If the body is 3-dimensional—it contains three linearly independent vectors with origins in the invariant point—it holds that for any pair of vectors $\vec{a}$ and $\vec{b}$ in ℝ3 the inner product is invariant, that is,
$\left(\mathcal{R}(\vec{a}),\;\mathcal{R}(\vec{b}) \right) = \left(\vec{a},\;\vec{b}\right).$
A linear map with this property is called orthogonal. It is easily shown that a similar vector-matrix relation holds. First we define column vectors (stacked triplets of real numbers given in bold face):
$\vec{a} =\left(\hat{e}_x,\;\hat{e}_y,\;\hat{e}_z\right)\begin{pmatrix}a_x\\a_y\\a_z\end{pmatrix} \;\stackrel{\mathrm{def}}{=}\; \left(\hat{e}_x,\;\hat{e}_y,\;\hat{e}_z\right) \mathbf{a} \quad\hbox{and}\quad \vec{b} =\left(\hat{e}_x,\;\hat{e}_y,\;\hat{e}_z\right)\begin{pmatrix}b_x\\b_y\\b_z\end{pmatrix} \;\stackrel{\mathrm{def}}{=}\; \left(\hat{e}_x,\;\hat{e}_y,\;\hat{e}_z\right) \mathbf{b}$
and observe that the inner product becomes by virtue of the orthonormality of the basis vectors
$\left( \vec{a},\; \vec{b} \right) = \mathbf{a}^\mathrm{T} \mathbf{b}\equiv \left(a_x,\;a_y,\;a_z\right) \begin{pmatrix}b_x\\b_y\\b_z\end{pmatrix} \equiv a_xb_x+a_yb_y+a_zb_z.$
The invariance of the inner product under the rotation operator $\mathcal{R}$ leads to
$\mathbf{a}^\mathrm{T}\; \mathbf{b} =\big(\mathbf{R}\mathbf{a}\big)^\mathrm{T}\; \mathbf{R}\mathbf{b} = \mathbf{a}^\mathrm{T} \mathbf{R}^\mathrm{T}\; \mathbf{R}\mathbf{b},$
since this holds for any pair a and b it follows that a rotation matrix satisfies
$\mathbf{R}^\mathrm{T} \mathbf{R} = \mathbf{E},$
where E is the 3×3 identity matrix. For finite-dimensional matrices one shows easily
$\mathbf{R}^\mathrm{T} \mathbf{R} = \mathbf{E} \quad \Longleftrightarrow\quad\mathbf{R}\mathbf{R}^\mathrm{T} = \mathbf{E}.$
A matrix with this property is called orthogonal. So, a rotation gives rise to a unique orthogonal matrix.
Conversely, consider an arbitrary point P in the body and let the vector $\overrightarrow{OP}$ connect the fixed point O with P. Expressing this vector with respect to a Cartesian frame in O gives the column vector p (three stacked real numbers). Multiply p by the orthogonal matrix R, then p′ = Rp represents the rotated point P′ (or, more precisely, the vector $\overrightarrow{OP'}$ is represented by column vector p′ with respect to the same Cartesian frame). If we map all points P of the body by the same matrix R in this manner, we have rotated the body. Thus, an orthogonal matrix leads to a unique rotation.
Note that the Cartesian frame is fixed here and that points of the body are rotated, this is known as an active rotation. Instead, the rigid body could have been left invariant and the Cartesian frame could have been rotated, this also leads to new column vectors of the form p′ ≡ Rp, such rotations are referred to as passive.
## Properties of an orthogonal matrix
Writing out matrix products it follows that both the rows and the columns of the matrix are orthonormal (normalized and orthogonal). Indeed,
\begin{align} \mathbf{R}^\mathrm{T} \mathbf{R} &= \mathbf{E} \quad\Longleftrightarrow\quad \sum_{k=1}^{3} R_{ki}\, R_{kj} =\delta_{ij} \quad\hbox{(columns)} \\ \mathbf{R} \mathbf{R}^\mathrm{T} &= \mathbf{E} \quad\Longleftrightarrow\quad \sum_{k=1}^{3} R_{ik}\, R_{jk} =\delta_{ij} \quad\hbox{(rows)} \\ \end{align}
where δij is the Kronecker delta.
Orthogonal matrices come in two flavors: proper (det = 1) and improper (det = −1) rotations. Indeed, invoking some properties of determinants, one can prove
$1=\det(\mathbf{E})=\det(\mathbf{R}^\mathrm{T}\mathbf{R}) = \det(\mathbf{R}^\mathrm{T})\det(\mathbf{R}) = \det(\mathbf{R})^2 \quad\Longrightarrow \quad \det(\mathbf{R}) = \pm 1.$
### Compact notation
A compact way of presenting the same results is the following. Designate the columns of R by r1, r2, r3, i.e.,
$\mathbf{R} = \left(\mathbf{r}_1,\, \mathbf{r}_2,\, \mathbf{r}_3 \right)$.
The matrix R is orthogonal if
$\mathbf{r}_i^\mathrm{T} \mathbf{r}_j \equiv \mathbf{r}_i \cdot \mathbf{r}_j = \delta_{ij}, \quad i,j = 1,2,3 .$
The matrix R is a proper rotation matrix, if it is orthogonal and if r1, r2, r3 form a right-handed set, i.e.,
$\mathbf{r}_i \times \mathbf{r}_j = \sum_{k=1}^3 \, \varepsilon_{ijk} \mathbf{r}_k .$
Here the symbol × indicates a cross product and $\varepsilon_{ijk}$ is the antisymmetric Levi-Civita symbol,
\begin{align} \varepsilon_{123} =&\; \varepsilon_{312} = \varepsilon_{231} = 1 \\ \varepsilon_{213} =&\; \varepsilon_{321} = \varepsilon_{132} = -1 \end{align}
and $\varepsilon_{ijk} = 0$ if two or more indices are equal.
The matrix R is an improper rotation matrix if its column vectors form a left-handed set, i.e.,
$\mathbf{r}_i \times \mathbf{r}_j = - \sum_{k=1}^3 \, \varepsilon_{ijk} \mathbf{r}_k \; .$
The last two equations can be condensed into one equation
$\mathbf{r}_i \times \mathbf{r}_j = \det(\mathbf{R}) \sum_{k=1}^3 \; \varepsilon_{ijk} \mathbf{r}_k$
by virtue of the the fact that the determinant of a proper rotation matrix is 1 and of an improper rotation −1. This was proved above, an alternative proof is the following: The determinant of a 3×3 matrix with column vectors a, b, and c can be written as scalar triple product
$\det\left(\mathbf{a},\,\mathbf{b},\, \mathbf{c}\right) = \mathbf{a} \cdot (\mathbf{b}\times\mathbf{c})$.
It was just shown that for a proper rotation the columns of R are orthonormal and satisfy,
$\mathbf{r}_1 \cdot (\mathbf{r}_2 \times \mathbf{r}_3 ) = \mathbf{r}_1 \cdot\left(\sum_{k=1}^3 \, \varepsilon_{23k} \, \mathbf{r}_k \right) = \varepsilon_{231} = 1 .$
Likewise the determinant is −1 for an improper rotation.
## Explicit expression of rotation operator
Rotation of vector $\scriptstyle \vec{r}$ around over φ.
(i) The red vectors and black axis are in the plane of the screen.
(ii) The blue vectors are obtained by rotation into the screen.
(iii) The green cross product in x-y plane is perpendicular to the screen, pointing away from the reader.
Let $\overrightarrow{OP} \equiv \vec{r}$ be a vector pointing from the fixed point O of a rigid body to an arbitrary point P of the body. A rotation of this arbitrary vector around the unit vector over an angle φ can be written as
\begin{align} \mathcal{R}(\varphi, \hat{n})(\vec{r}\,)&= \vec{r}\,' = \\ & \vec{r}\;\cos\varphi + \hat{n} (\hat{n}\cdot\vec{r}\,)\; (1- \cos\varphi) + (\hat{n} \times \vec{r}\,) \sin\varphi . \\ \end{align}
where • indicates an inner product and the symbol × a cross product.
It is easy to derive this result. Indeed, decompose the vector to be rotated into two components, one along the rotation axis and one perpendicular to it (see the figure on the right)
$\vec{r} = \vec{r}_\parallel + \vec{r}_\perp\quad\hbox{with}\quad \vec{r}_\parallel = \hat{n} (\hat{n}\cdot\vec{r}\,),$
and
$\vec{r}_\perp = \vec{r} - \vec{r}_\parallel =\vec{r}- \hat{n} (\hat{n}\cdot\vec{r}\,),$
so that, in view of || = 1,
$|\vec{r}_\perp|^2 = r^2 - (\hat{n}\cdot\vec{r}\,)^2$
and from |a×b|2 = a2b2 − (ab)2 follows
$|\hat{n} \times \vec{r}\,|^2 = r^2 - (\hat{n}\cdot\vec{r}\,)^2.$
Upon rotation, the component of the rotated vector along the rotation axis is invariant, only its component orthogonal to the rotation axis changes. By virtue of the following fact (in words: length of basis vector along x-axis is length of basis vector along y-axis):
$|\vec{r}_\perp| = |\hat{n} \times \vec{r}\,| = \sqrt{|\vec{r}\,|^2 - (\hat{n}\cdot\vec{r}\,)^2},$
the rotation property simply is
$\vec{r}_\perp \mapsto \vec{r}\,'_\perp = \cos\varphi\;\vec{r}_\perp + \sin\varphi\;(\hat{n}\times\vec{r}\,).$
Hence
$\vec{r}\,' = \hat{n} (\hat{n}\cdot\vec{r}\,) + \left[\vec{r}- (\hat{n}\cdot\vec{r}\,) \hat{n}\right]\cos\varphi+(\hat{n}\times\vec{r}\,)\sin\varphi.$
Some reshuffling of the terms gives the required result.
## Explicit expression of rotation matrix
It will be shown that
$\mathbf{R}(\varphi, \hat{n}) = \mathbf{E} + \sin\varphi \mathbf{N} +(1-\cos\varphi)\mathbf{N}^2,$
where (see cross product for more details)
$\mathbf{N} \equiv \begin{pmatrix} 0 & -n_z & n_y \\ n_z& 0 & -n_x \\ -n_y& n_x & 0 \end{pmatrix}\quad\hbox{and}\quad \hat{n} \equiv (\hat{e}_x,\;\hat{e}_y,\;\hat{e}_z\,) \begin{pmatrix} n_x \\ n_y \\ n_z \\ \end{pmatrix} \equiv (\hat{e}_x,\;\hat{e}_y,\;\hat{e}_z\,) \; \hat{\mathbf{n}}$
Note further that the dyadic product satisfies (as can be shown by squaring N),
$\hat{\mathbf{n}}\otimes\hat{\mathbf{n}} = \mathbf{N}^2 + \mathbf{E}, \quad\hbox{with}\quad |\hat{\mathbf{n}}| = 1$
and that
$\hat{n} (\hat{n}\cdot\vec{r}\,) \leftrightarrow (\hat{\mathbf{n}}\otimes\hat{\mathbf{n}})\;\mathbf{r} = \left(\mathbf{N}^2 + \mathbf{E}\right) \mathbf{r}.$
Translating the result of the previous section to coordinate vectors and substituting these results gives
\begin{align} \mathbf{r}' &= \left[\cos\varphi\; \mathbf{E} +(1-\cos\varphi)(\mathbf{N}^2 + \mathbf{E}) + \sin\varphi \mathbf{N} \right] \mathbf{r} \\ &= \left[\mathbf{E} + (1-\cos\varphi) \mathbf{N}^2 + \sin\varphi \mathbf{N}\right] \mathbf{r}, \qquad\qquad\qquad\qquad\qquad(1) \end{align}
which gives the desired result for the rotation matrix. This equation is identical to Eq. (2.6) of Biedenharn and Louck[1], who give credit to Leonhard Euler (ca. 1770) for this result.
For the special case φ = π (rotation over 180°), equation (1) can be simplified to
$\mathbf{R}(\pi, \hat{n}) = \mathbf{E} + 2 \mathbf{N}^2 = -\mathbf{E} +2\, \hat{\mathbf{n}}\otimes\hat{\mathbf{n}}$
so that
$\mathbf{R}(\pi, \hat{n})\, \mathbf{r} = -\mathbf{r} +2\; \hat{\mathbf{n}}\; (\hat{\mathbf{n}} \cdot\mathbf{r}),$
which sometimes[2] is referred to as reflection over a line, although it is not a reflection.
Equation (1) is a special case of the transformation properties given on p. 7 of the classical work (first edition 1904) of Whittaker[3]. To see the correspondence with Whittaker's formula, which includes also a translation over a displacement d and who rotates the vector (xa, yb, zc), we must put equal to zero: a, b, c, and d in Whittaker's equation. Furthermore Whittaker uses that the components of the unit vector n are the direction cosines of the rotation axis:
$n_x \equiv \cos\alpha,\quad n_y \equiv\cos\beta,\quad n_z\equiv\cos\gamma.$
Under these conditions the rotation becomes
\begin{align} x' &= x-(1-\cos\varphi)\left[x\;\sin^2\alpha - y\;\cos\alpha\cos\beta - z\;\cos\alpha\cos\gamma\right] +\left[z\;\cos\beta- y\;\cos\gamma\right]\sin\varphi \\ y' &= y-(1-\cos\varphi)\left[y\;\sin^2\beta - z\;\cos\beta\cos\gamma - x\;\cos\beta\cos\alpha\right] +\left[x\;\cos\gamma- z\;\cos\alpha\right]\sin\varphi \\ z' &= z-(1-\cos\varphi)\left[z\;\sin^2\gamma - x\;\cos\gamma\cos\alpha - y\;\cos\gamma\cos\beta\right] +\left[y\;\cos\alpha- x\;\cos\beta\right]\sin\varphi \\ \end{align}
## Vector rotation
Sometimes it is necessary to rotate a rigid body so that a given vector in the body (for instance an oriented chemical bond in a molecule) is lined-up with an external vector (for instance a vector along a coordinate axis).
Let the vector in the body be f (the "from" vector) and the vector to which f must be rotated be t (the "to" vector). Let both vectors be unit vectors (have length 1). From the definition of the inner product and the cross product follows that
$\mathbf{f} \cdot \mathbf{t} = \cos\varphi,\quad |\mathbf{f}\times\mathbf{t}| = \sin\varphi,$
where φ is the angle (< 180°) between the two vectors. Since the cross product f × t is a vector perpendicular to the plane of both vectors, it is easily seen that a rotation around the cross product vector over an angle φ moves f to t.
Write
$\mathbf{u} = \mathbf{f}\times\mathbf{t}\quad \Longrightarrow\quad \mathbf{u} = \sin\varphi\hat{\mathbf{n}},$
where $\hat{\mathbf{n}}$ is a unit vector. Define accordingly
$\mathbf{U} \; \stackrel{\mathrm{def}}{=} \; \sin\varphi \mathbf{N}= \sin\varphi \begin{pmatrix} 0 & -n_z & n_y \\ n_z& 0 & -n_x \\ -n_y& n_x & 0 \end{pmatrix}= \begin{pmatrix} 0 & -u_z & u_y \\ u_z& 0 & -u_x \\ -u_y& u_x & 0 \end{pmatrix} ,$
so that
\begin{align} \mathbf{R}(\varphi, \hat{n})&= \mathbf{E} + \mathbf{U} + \frac{1-\cos\varphi}{\sin^2\varphi} \mathbf{U}^2 \\ &= \mathbf{E} + \mathbf{U} + \frac{1}{1+\cos\varphi} \mathbf{U}^2 \qquad\qquad\qquad\qquad\qquad\qquad\qquad(2)\\ &= \cos\varphi\,\mathbf{E}+ \mathbf{U} + \frac{1}{1+\cos\varphi} \mathbf{u}\otimes\mathbf{u}\\ \end{align}
The last equation, which follows from U2 = uu − sin2φ E, is Eq. (3) of Ref. [4] after substitution of
$\frac{1-\cos\varphi}{\sin^2\varphi} =\frac{1-\cos\varphi}{1-\cos^2\varphi} = \frac{1}{1+\cos\varphi} .$
Indeed, write the rotation matrix in full, using the short-hand notations c = cos φ and h = (1-c)/(1-c2)
$\mathbf{R}(\varphi, \hat{n}) = \begin{pmatrix} c+hu_x^2 & h u_xu_y - u_z & h u_x u_z + u_y \\ h u_x u_y + u_z & c + h u_y^2 & h u_y u_z - u_x \\ h u_x u_z -u_y & h u_y u_z + u_x & c + h u_z^2 \\ \end{pmatrix},$
which is the matrix in Eq. (3) of Ref. [4]. If the vectors are parallel, f = t, then u = 0, U = 0 and ft = cosφ = 1, so that the equation is well-defined—it gives R(φ, n) = E, as expected. Provided f and t are not anti-parallel, the matrix $\mathbf{R}(\varphi, \hat{n})$ can be computed easily and quickly. It requires not much more than the computation of the inner and cross product of f and t.
### Case that "from" and "to" vectors are anti-parallel
If the vectors f and t are nearly anti-parallel, f ≈ − t, then ft = cosφ ≈ − 1, and the denominator in Eq. (2) becomes zero, so that Eq. (2) is not applicable. The vector defining the rotation axis is nearly zero: uf × tf × (−f) ≈ 0.
Clearly, a two-fold rotation (angle 180°) around any rotation axis perpendicular to f will map f onto −f. This freedom in choice of the two-fold axis is consistent with the indeterminacy in the equation that occurs for cosφ = −1.
Since −E (inversion) sends f to −f, one could naively assume that all position vectors of the rigid body may be inverted by −E. However, if the rigid body is not symmetric under inversion (does not have a symmetry center), inversion turns the body into a non-equivalent one. For instance, if the body is a right-hand glove, inversion sends it into a left-hand glove; it is well-known that a right-hand and a left-hand glove are different.
Recall that f is a unit vector. If f is on the z-axis, |fz| = 1, then the following rotation around the y-axis turns f into −f:
$\mathbf{R}(\pi, \hat{e}_{y}) \mathbf{f} = \begin{pmatrix} -1 & 0 & 0 \\ 0 & 1 & 0 \\ 0 & 0 & -1 \\ \end{pmatrix} \begin{pmatrix} 0 \\ 0 \\\pm 1 \end{pmatrix} = \begin{pmatrix} 0 \\ 0 \\\mp 1 \end{pmatrix}$
If f is not on the z-axis, fz ≠ 1, then the following orthogonal matrix sends f to −f and hence gives a 180° rotation of the rigid body
$\mathbf{R}(\pi, \hat{e}_{y'}) \mathbf{f} = \frac{1}{1-f^2_z} \begin{pmatrix} -(f^2_x-f^2_y) & -2f_xf_y & 0 \\ -2f_xf_y &(f^2_x-f^2_y) & 0 \\ 0 & 0 & -(1-f^2_z) \\ \end{pmatrix} \begin{pmatrix} f_x \\ f_y \\ f_z \end{pmatrix} = \begin{pmatrix} -f_x \\ -f_y \\ -f_z \end{pmatrix}$
To show this we insert
$\hat{\mathbf{n}} = \frac{1}{1-f^2_z} \begin{pmatrix} f_y \\-f_x \\0 \end{pmatrix}$
into the expression for rotation over 180° introduced earlier:
$\mathbf{R}(\pi, \hat{e}_{y'}) = -\mathbf{E} +2 \hat{\mathbf{n}}\otimes \hat{\mathbf{n}} .$
Note that the vector $\hat{\mathbf{n}}$ is normalized, because f is normalized, and that it lies in the x-y plane normal to the plane spanned by the z-axis and f; it is in fact a unit vector along a rotated y-axis obtained by rotation around the z-axis.
Given f = (fx, fy, fz), the matrix $\mathbf{R}(\pi, \hat{e}_{y'})$ is easily and quickly calculated. The matrix rotates the body over 180° sending f to −f exactly. When −f and t are close, but not exactly equal, the earlier rotation formula Eq. (2), may be used to perform the final (small) rotation of the body that lets −f and t coincide exactly.
## Change of rotation axis
Euler's theorem states that a rotation is characterized by a unique axis (an eigenvector with unit eigenvalue) and a unique angle. As a corollary of the theorem follows that the trace of a rotation matrix is equal to
$\mathrm{Tr}[\mathbf{R}(\varphi, \hat{n})] = 2\cos\varphi +1,$
and hence the trace depends only on the rotation angle and is independent of the axis. Let A be an orthogonal 3×3 matrix (not equal to E), then, because cyclic permutation of matrices under the trace is allowed (i.e., leaves the trace invariant),
$\mathrm{Tr}[\mathbf{A} \mathbf{R}(\varphi, \hat{n}) \mathbf{A}^\mathrm{T}] = \mathrm{Tr}[ \mathbf{R}(\varphi, \hat{n}) \mathbf{A}^\mathrm{T}\mathbf{A}] = \mathrm{Tr}[\mathbf{R}(\varphi, \hat{n})] .$
As a consequence it follows that the two matrices
$\mathbf{R}(\varphi, \hat{n})\quad \hbox{and}\quad \mathbf{A} \mathbf{R}(\varphi, \hat{n}) \mathbf{A}^\mathrm{T}$
describe a rotation over the same angle φ but around different axes. The eigenvalue equation can be transformed
$\mathbf{R}(\varphi, \hat{n})\;\hat{n} = \hat{n} \;\Longrightarrow\; \left(\mathbf{A}\,\mathbf{R}(\varphi, \hat{n})\,\mathbf{A}^\mathrm{T}\right) \;\mathbf{A}\hat{n} = \mathbf{A}\hat{n}$
which shows that the transformed eigenvector is the rotation axis of the transformed matrix, or
$\mathbf{R}(\varphi, \mathbf{A}\hat{n})= \mathbf{A}\,\mathbf{R}(\varphi, \hat{n})\,\mathbf{A}^\mathrm{T} .$
## References
1. L. C. Biedenharn and J. D. Louck, Angular Momentum in Quantum Physics, Addison-Wesley, Reading, Mass. (1981) ISBN 0-201-13507-8
2. Wikipedia Retrieved July 20, 2009
3. E. T. Whittaker, A Treatise on the Dynamics of Particles and Rigid Bodies, Cambridge University Press (1965)
4. 4.0 4.1 T. Möller and J. F. Hughes, J. Graphics Tools, 4 pp. 1–4 (1999).
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http://mathhelpforum.com/algebra/67656-urgent-help-needed-solve-equation-print.html
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# Urgent Help needed to solve equation.
• January 11th 2009, 02:49 AM
den
1 Attachment(s)
Urgent Help needed to solve equation.
Urgent Help needed to solve equation.
• January 11th 2009, 03:37 AM
Prove It
Quote:
Originally Posted by den
Urgent Help needed to solve equation.
Complete the square on the bottom.
• January 11th 2009, 04:02 AM
den
What I cannot figure out is how we get
0.46y2 + 1.84y + 1.84 = 2.87
• January 11th 2009, 04:06 AM
Prove It
Quote:
Originally Posted by den
What I cannot figure out is how we get
0.46y2 + 1.84y + 1.84 = 2.87
Are you trying to solve this? Just get everything on one side and use the Quadratic formula...
• January 11th 2009, 04:16 AM
den
When I multiply I get different figures than 0.46y2 + 1.84y + 1.84 = 2.87.
• January 11th 2009, 05:31 AM
running-gag
Hi
Double posting is forbidden on MHF
http://www.mathhelpforum.com/math-he...lp-needed.html
What is your problem exactly ?
• January 11th 2009, 05:41 AM
den
Missing line/calulation
What I cannot figure out is how we get
0.46y2 + 1.84y + 1.84 = 2.87
• January 11th 2009, 06:05 AM
running-gag
Starting from
$0.080 = 0.051 \,\frac{56.25}{5.76 y^2 + 23.04 y + 23.04}$
You just have to multiply 0.080 par the denominator
$0.080 \,(5.76 y^2 + 23.04 y + 23.04) = 0.051 \,\, 56.25 = 2.87$
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https://www.physicsforums.com/threads/finding-a-formula-for-a-sequence-with-recurring-digits.623732/
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# Finding a formula for a sequence with recurring digits
1. Jul 26, 2012
### spiritzavior
how do i determine the formula for the sequence below?
1,1,2,2,2,2,3,3,3,3,3,4,4,4,4,4,4,4,4,...,n,n,n,n,n,...,n,...
need some instructions. thanks in advance
2. Jul 26, 2012
### Dickfore
Ok, there are subsequences of equal entries (increasing by one) in a row, and the numbers of equal entries in each of them form the following sequence:
2, 4, 5, 8, ...
I can't see any regularity. Sorry.
3. Jul 26, 2012
### haruspex
I can't see a pattern here: you have two 1s, four 2s, five 3s and eight 4s. Can you confirm that you've written it out correctly?
4. Jul 27, 2012
### ramsey2879
Seems like one too many 2's with n-1 repeated F(n+1) times for n = 2,3,4,5,... .
Last edited: Jul 27, 2012
5. Jul 28, 2012
### spiritzavior
sorry, i've typed it incorrectly, it should be:
1,1,2,2,2,2,3,3,3,3,3,3,4,4,4,4,4,4,4,4,...
two 1s, four 2s, six 3s, eight 4s,...
6. Jul 28, 2012
### haruspex
If you don't mind the use of [] (integer part of) it's [1/2 +√(n-3/4)]
7. Jul 28, 2012
### Dickfore
So, there are $2 n$ n's. The total number of elements no smaller than n is:
$$\sum_{k = 1}^{n}{2 k} = n(n + 1)$$
Thus, all the elements with an index k that satisfies:
$$(n - 1) n < k \le n (n + 1)$$
are equal to $x_k = n$ (why?). Can you find n, given k from the above inequalities?
$$n^2 + n - k \ge 0 \Rightarrow n \ge -\frac{1}{2} + \sqrt{k + \frac{1}{4}}$$
$$n^2 - n - k < 0 \Rightarrow n < \frac{1}{2} + \sqrt{k + \frac{1}{4}}$$
If you know the [STRIKE]floor[/STRIKE] floor function, which is the same as integer part for positive integers, you should be able to deduce:
$$x_k = \mathrm{Ceiling} \left[ \sqrt{k + \frac{1}{4}} - \frac{1}{2}\right]$$
Last edited: Jul 28, 2012
8. Jul 28, 2012
### acabus
$a(n) = round(\sqrt{n})$ seems to work, not that I could prove it.
This is where a(1) is the first entry in the sequence.
9. Jul 28, 2012
### Anti-Crackpot
Good intuition abacus...
A000194 n appears 2n times; also nearest integer to square root of n
http://oeis.org/A000194
If one desires that digits are repeated 2n - 1 times, that's an easy one: floor [sqrt n]
10. Jul 28, 2012
### Dickfore
The definition of ceiling and round functions is:
$$\mathrm{Ceiling}(x) \equiv n, \ n \le x < n + 1$$
$$\mathrm{Round}(x) \equiv m, \ \vert x - m \vert < 1/2$$
(the last definition is ambiguous if the argument is half-integer, but there can never happen for acabus's argument)
We want to know for what x, and y, $\mathrm{Ceiling}(x) \stackrel{?}{=} \mathrm{Round}(y) = n$. From the above definitions, this happens when:
$$n \le x < n + 1, \ n - 1/2 < y < n + 1/2$$
or, if we rewrite these inequalities for n, we get:
$$x - 1 < n \le x, \ y - 1/2 < n < y + 1/2$$
Then, a necessary and sufficient (why?) condition is:
$$x - 1 < y + 1/2, \ y - 1/2 < x$$
In our case, $x = \sqrt{k + 1/4} - 1/2$, and $y= \sqrt{k}$, so we have:
$$\sqrt{k + 1/4} - 1/2 - 1 < \sqrt{k} + 1/2 \Leftrightarrow \sqrt{k + 1/4} - \sqrt{k} < 2$$
$$\sqrt{k} - 1/2 < \sqrt{k + 1/4} - 1/2 \Leftrightarrow \sqrt{k + 1/4} - \sqrt{k} > 0$$
The second inequality is surely true, but the first is proven as follows:
$$\begin{array}{l} \sqrt{k + 1/4} - \sqrt{k} \stackrel{?}{<} 2 \\ 0 < \sqrt{k + 1/4} \stackrel{?}{<} \sqrt{k} + 2 \\ k + 1/4 \stackrel{?}{<} k + 4 \sqrt{k} + 4 \\ 0 \stackrel{\surd}{<} \sqrt{k} + 15/16 \end{array}$$
This is surely true. Therefore, both the formulas give the same output for all positive integers.
11. Jul 28, 2012
### spiritzavior
Similar Discussions: Finding a formula for a sequence with recurring digits
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https://hippocampus-garden.com/best_papers_2020/
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# Hippocampus's Garden
Under the sea, in the hippocampus's garden...
Search by
Best Machine Learning Papers of 2020 | Hippocampus's Garden
# Best Machine Learning Papers of 2020
January 02, 2021 | 12 min read | 831 views
Happy New Year!🎉🎉
In 2020, the Machine Learning community has seen a lot of new achievements. I believe winter vacation is a good time to look back on the year, so this post will cover 10 representative papers that I found interesting and worth reading.
## Best Papers
Here are the 10 best ML papers of 2020 that I chose (in chronological order).
1. Rigging the Lottery: Making All Tickets Winners
2. PIFuHD: Multi-Level Pixel-Aligned Implicit Function for High-Resolution 3D Human Digitization
3. Jukebox: A Generative Model for Music
4. Language Models are Few-Shot Learners
5. Bootstrap Your Own Latent: A New Approach to Self-Supervised Learning
6. Implicit Neural Representations with Periodic Activation Functions
7. Graph Structure of Neural Networks
8. Towards Faster and Stabilized GAN Training for High-fidelity Few-shot Image Synthesis
9. An Image is Worth 16x16 Words: Transformers for Image Recognition at Scale
10. Pre-training without Natural Images
### Rigging the Lottery: Making All Tickets Winners
• Authors: Utku Evci, Trevor Gale, Jacob Menick, Pablo Samuel Castro, Erich Elsen
• Released in: November 2019
• Accepted to: ICML 2020
The lottery ticket hypothesis [1,2] argues that training neural networks is like a lottery. According to [1], network pruning is feasible because:
Dense, randomly-initialized, feed-forward networks contain subnetworks (“winning tickets”) that - when trained in isolation - reach test accuracy comparable to the original network in a similar number of iterations.
So, should we always start with a large network, aiming to draw a winning ticket and drop losing tickets (unnecessary subnetworks) after the winner announcement (training & validation)? This paper answers no. The authors introduce a method to train sparse neural networks by iteratively dropping and growing connections with the model size fixed throughout the training. The proposed training strategy is named RigL, as it “rigs the lottery ticket hypothesis.” The algorithm of RigL is summarized as below:
RigL achieves higher test accuracy with fewer training FLOPs and parameter counts than pruning on various networks and datasets (e.g., ResNet-50/MobileNet on ImageNet and GRU on WikiText-103).
### PIFuHD: Multi-Level Pixel-Aligned Implicit Function for High-Resolution 3D Human Digitization
PIFuHD is an updated version of PIFu (Pixel-aligned Implicit Function) [4], a deep learning method for reconstructing a 3D human shape from a single image. I chose this paper because it’s fun! Not only are the result remarkable (see the image below), but the authors provide a Colab demo that you can try out with your own images instantly.
Many people have tried this demo and uploaded their results to #pifuhd. One of my favorites is the video of G7 leaders dancing to a song by Sakanaction.
For technical details, I’d like to recommend the excellent presentation video by the authors.
### Jukebox: A Generative Model for Music
• Authors: Prafulla Dhariwal, Heewoo Jun, Christine Payne, Jong Wook Kim, Alec Radford, Ilya Sutskever
• Released in: May 2020
Generating realistic images is no longer surprising, but generating realistic music remains a hard challenge due to its extremely long-range dependency. Specifically, a 4-minute song at CD quality (44 kHz) has more than 10 million timestamps with high-level semantics (c.f., intro, verse, chorus). OpenAI boldly tackled the generation of raw audio in a variety of genres, and their Jukebox succeeded in producing pretty impressive music!
Here are the non cherry-picked 7,131 samples. They are conditioned on specific genres and artists, some of which are also conditioned on lyrics. For example, this sample is a continuation of I Just Call To Say I Love You by Stevie Wonder. It sounds like a new song after 10 seconds, while reasonably maintaining the style of the singer and the song.
What is inside this magic? Inspired by VQ-VAE-2 [5], the authors use hierarchical VQ-VAE to handle long-range dependency. As for the prior (or, the generator), they use Sparse Transformer [6], an efficient Transformer that succeeded in generating 64x64 sized images and raw audio waveforms, as already mentioned in my earlier post.
The details are explained with informative GIFs in the official blog post.
The appendix of the paper is also worth reading. The figure below is a t-SNE plot of (artist, genre) embeddings learned by Jukebox. I agree that ELO is similar to The Beatles😉
### Language Models are Few-Shot Learners
• Authors: Tom B. Brown, Benjamin Mann, Nick Ryder, Melanie Subbiah, Jared Kaplan, Prafulla Dhariwal, Arvind Neelakantan, Pranav Shyam, Girish Sastry, Amanda Askell, Sandhini Agarwal, Ariel Herbert-Voss, Gretchen Krueger, Tom Henighan, Rewon Child, Aditya Ramesh, Daniel M. Ziegler, Jeffrey Wu, Clemens Winter, Christopher Hesse, Mark Chen, Eric Sigler, Mateusz Litwin, Scott Gray, Benjamin Chess, Jack Clark, Christopher Berner, Sam McCandlish, Alec Radford, Ilya Sutskever, Dario Amodei
• Released in: May 2020
• Accepted to: NeurIPS 2020
GPT-3, the latest version of GPT [6,7], is a pre-trained language model that has as many as 175B parameters (10 times larger than Turing-NLG!) and is trained with 300B tokens. The authors found that scaling up the model significantly improves the performance of few-shot learning without fine-tuning, which they call in-context learning. The following figure compares in-context learning with traditional fine-tuning.
In short, in their in-context few-shot learning, the model sees the input containing task description, a few examples, and prompt only at inference time and predicts the answer. There is no training or fine-tuning. GPT-3 can deal with a variety of tasks such as translation, text generation, summarization, question answering, and even arithmetic. Sometimes it outperforms fine-tuned models.
More surprisingly, it is reported that GPT-3 can translate English into JSX code. Indeed, quantitative changes transform to qualitative changes.
OpenAI releases the GPT-3 model as an API instead of pre-trained weights. If you wish to use it, join the waitlist for the beta version.
### Bootstrap Your Own Latent: A New Approach to Self-Supervised Learning
• Authors: Jean-Bastien Grill, Florian Strub, Florent Altché, Corentin Tallec, Pierre H. Richemond, Elena Buchatskaya, Carl Doersch, Bernardo Avila Pires, Zhaohan Daniel Guo, Mohammad Gheshlaghi Azar, Bilal Piot, Koray Kavukcuoglu, Rémi Munos, Michal Valko
• Released in: June 2020
• Accepted to: NeurIPS 2020
Contrastive learning, a variant of self-supervised learning algorithm that leverages information from negative samples, was probably one of the hottest research topics in 2020. Many methods such as MoCo, SimCLR, and InfoMin, competed for the higher accuracy on ImageNet classification [8-10]. They are based on the assumption that the distance between representations of different augmented views of the same image should be small while the distance between different images should be large.
As opposed to them, the proposed Bootstrap Your Own Latent (BYOL) does not use negative pairs at all and outperformed all the contrastive learning methods, closing the gap between self-supervised and supervised learning.
As shown in the figure below, BYOL uses two networks: online ($\theta$) and target ($\xi$), where the target network is simply the exponential (slow-)moving average of the online network.
An input image $x$ is transformed into two views $v$ and $v'$ with different augmentations ($t$ and $t'$), which are then fed into the online and the target network respectively. BYOL is trained to minimize the L2 distance between the prediction by the online network ($q_{\theta}(z_{\theta})$) and the projected representation by the target network ($\mathrm{sg}(z'_{\xi})$), where $\mathrm{sg}$ means the stop-gradient operator. This is how BYOL bootstraps its latent.
An additional benefit of BYOL is the robustness to the choice of batch size and the set of image augmentations compared to the contrastive baselines. Also, there is a discussion on how to avoid collapsed solutions in the paper. Please check it out if you are interested.
### Implicit Neural Representations with Periodic Activation Functions
• Authors: Vincent Sitzmann, Julien N. P. Martel, Alexander W. Bergman, David B. Lindell, Gordon Wetzstein
• Released in: June 2020
• Accepted to: NeurIPS 2020
Many scientific problems fall into the learning of implicit neural representations. For instance, implicit neural representations can model images, audio signals, and 3D shapes and can solve boundary value problems. However, the popular ReLU-MLP networks fail to represent fine details in the signals and their derivatives well, partly because the second derivative of ReLU is zero everywhere. Other nonlinearities such as tanh or softplus can represent higher-order derivatives, but they also fail to represent fine details.
To address this issue, the authors present neural networks that leverage periodic, $n$-times differentiable $\sin(\cdot)$ activation, which is named sinusoidal representation networks (SIREN). The benefits of sinusoidal activation are best illustrated in the figure below, which compares different implicit networks fitted to the ground truth image. Unlike other activations, SIREN is able to learn by itself the Gaussian and Laplacian well.
This property of SIREN seems particularly beneficial when modeling 3D shapes.
One may wonder “why no one has ever come up with this simple solution?” Well, periodic activation functions have been studied for more than 10 years, but I guess there two factors that make this work still new in 2020. First, it hasn’t been explored very much how to apply periodic activations to implicit neural representations. Second, SIREN requires a special initialization scheme. To preserve the distribution of activations through the network, the initial weights of SIREN have to be drawn from a carefully designed uniform distribution.
More samples including audio and differential equations and their presentation video can be found on the project page.
### Graph Structure of Neural Networks
This exciting work was done by a collaboration between graph and computer vision researchers.
What do neural networks with good predictive performance have in common? To answer this question, this paper analyzes neural networks from the point of view of graph theory. First, the authors define a novel graph-based representation of neural networks called relational graph (a,b). Then, they design a graph generator that systematically explores the design space of relational graphs. The idea of relational graphs enables neural networks to be characterized by two graph statistics: average path length and clustering coefficient (c). Finally, they conducted an extensive study on the relationship between the predictive performance of generated neural networks and the graph statistics of the corresponding relational graphs (d).
Their observations include:
• there is a sweet spot in the design space that leads to significantly better predictive performance
• predictive performance of neural networks can be approximated by a smooth function of the clustering coefficient and average path length of its relational graph
• the graph statistics of top-performing neural networks are similar to those of macaque’s.
### Towards Faster and Stabilized GAN Training for High-fidelity Few-shot Image Synthesis
There is no doubt that StyleGAN2 is great and successful [11], but it still has a problem of requiring a huge amount of data and computation. In fact, for learning to generate 1024x1024 sized FFHQ face images, StyleGAN2 used 8 Tesla V100 GPUs and 70,000 images, and it took 9 days for the entire training process. This is almost impossible for small laboratories and companies who want to reproduce the results. Also, that huge demand limits the potential applications of GANs in production.
This limitation was quite obvious, and 6 months after the publication of StyleGAN2, the authors released StyleGAN2-ADA (StyleGAN2 with adaptive discriminator augmentation) [12]. They introduced a new technique in data augmentation for the discriminator, allowing StyleGAN2 to generate as fine images as the original model with a few thousand training images.
The authors of this paper made a step even further. This paper proposes the so-called Lightweight GAN, which adopts skip-layer excitation modules and an autoencoder-like discriminator to generate FFHQ images by training for a few hours with a few hundred images on a single RTX-2080 GPU!
And fortunately, Phil Wang released a beautiful and easy-to-use implementation of Lightweight GAN at GitHub. Now, using Colaboratory or any GPU at your disposal, it’s possible to generate almost any image you like. They indeed democratized GANs!
I tried it out to train Lightweight GAN with just 200 sushi images. After training, it generated fairly realistic sushi images as shown below. The generated images are also displayed at ”This Sushi Does Not Exist”. So, what GANs do you want to create?
For more details, please refer to the original paper and my previous post.
### An Image is Worth 16x16 Words: Transformers for Image Recognition at Scale
• Authors: Alexey Dosovitskiy, Lucas Beyer, Alexander Kolesnikov, Dirk Weissenborn, Xiaohua Zhai, Thomas Unterthiner, Mostafa Dehghani, Matthias Minderer, Georg Heigold, Sylvain Gelly, Jakob Uszkoreit, Neil Houlsby
• Released in: October 2020
• Accepted to: ICLR 2021
This year has seen a lot of attempts to apply Transformers to computer vision tasks. Cordonnier et al. investigated the equivalence of self-attention and convolutional layers [13]. Chen et al. used GPT to generate images in an autoregressive way [14]. Carion et al. applied Transformers to object detection [15]. With such studies in mind, it’s not unnatural to create a Transformer-based pre-trained model for image classification.
Motivated by this, a team from Google Research trained Vision Transformer (ViT), achieving the new state-of-the-art over CNN baselines such as Big Transfer (BiT) and Noisy Student. Let’s get an overview of ViT from the figure below, because “a picture is worth a thousand words”.
As the title implies, images are split into small patches (16x16) and fed into the projection layer with position embeddings, in the same way that the tokens are embedded and fed into the encoder in the vanilla Transformer. The entire model is trained to minimize the classification loss (so, it is supervised learning).
The authors report that ViT does not generalize well when trained with “mid-sized” ImageNet dataset due to its smaller inductive bias, but it outperforms CNN baselines when trained with 300 times larger JFT-300M dataset. Nevertheless, ViT uses up significantly fewer computational resources than BiT and Noisy Student.
Now that it is found that supervised pre-training works for image classification with a huge Transformer model, I guess a self-supervised version will appear this year.
### Pre-training without Natural Images
Pre-training with large datasets proved to be the key better accuracy. However, such datasets often involve issues such as mistaken labels, copyright violation, privacy violation, and unethical biases. To address these, this paper shows that artificial images can be used for pre-training.
Specifically, the authors prepared Fractal Database (FractalDB) by a certain algorithm and pre-trained ResNet-50 with it.
The model pre-trained with FractalDB does not outperform the ones pre-trained with ImageNet-1k, but the result is promising. Considering the issues listed above, FractalDB can be a good option.
## Concluding Remarks
There are other interesting papers that I could not include here. If you have any recommendations, please feel free to comment.
Thanks for reading this long post. Hope you have a good one!
## References
[1] Jonathan Frankle, Michael Carbin. ”The Lottery Ticket Hypothesis: Finding Sparse, Trainable Neural Networks“. ICLR. 2019.
[2] Madison May. ”Comparing Rewinding and Fine-tuning in Neural Network Pruning“. ICLR. 2020.
[3] Shunsuke Saito, Zeng Huang, Ryota Natsume, Shigeo Morishima, Angjoo Kanazawa, Hao Li. ”PIFu: Pixel-Aligned Implicit Function for High-Resolution Clothed Human Digitization“. ICCV. 2019.
[4] Ali Razavi, Aaron van den Oord, Oriol Vinyals. ”Generating Diverse High-Fidelity Images with VQ-VAE-2“. NeurIPS. 2019.
[5] Rewon Child, Scott Gray, Alec Radford, Ilya Sutskever. ”Generating Long Sequences with Sparse Transformers”. 2019.
[6] Alec Radford, Karthik Narasimhan, Tim Salimans, Ilya Sutskever. ”Improving Language Understanding by Generative Pre-Training”. 2018.
[7] Alec Radford, Jeffrey Wu, Rewon Child, David Luan, Dario Amodei, Ilya Sutskever. ”Language Models are Unsupervised Multitask Learners”. 2019.
[8] Kaiming He, Haoqi Fan, Yuxin Wu, Saining Xie, Ross Girshick. ”Momentum Contrast for Unsupervised Visual Representation Learning“. CVPR. 2020.
[9] Ting Chen, Simon Kornblith, Mohammad Norouzi, Geoffrey Hinton. ”A Simple Framework for Contrastive Learning of Visual Representations“. ICML. 2020.
[10] Yonglong Tian, Chen Sun, Ben Poole, Dilip Krishnan, Cordelia Schmid, Phillip Isola. ”What Makes for Good Views for Contrastive Learning?“. NeurIPS. 2020.
[11] Tero Karras, Samuli Laine, Miika Aittala, Janne Hellsten, Jaakko Lehtinen, Timo Aila. ”Analyzing and Improving the Image Quality of StyleGAN“. CVPR. 2020.
[12] Tero Karras, Miika Aittala, Janne Hellsten, Samuli Laine, Jaakko Lehtinen, Timo Aila. ”Training Generative Adversarial Networks with Limited Data“. NeurIPS. 2020.
[13] Jean-Baptiste Cordonnier, Andreas Loukas, Martin Jaggi. ”On the Relationship between Self-Attention and Convolutional Layers“. ICLR. 2020.
[14] Mark Chen, Alec Radford, Rewon Child, Jeff Wu, Heewoo Jun, Prafulla Dhariwal, David Luan, Ilya Sutskever. ”Generative Pretraining from Pixels“. ICML 2020.
[15] Alexander Kolesnikov, Lucas Beyer, Xiaohua Zhai, Joan Puigcerver, Jessica Yung, Sylvain Gelly, Neil Houlsby. ”Big Transfer (BiT): General Visual Representation Learning“. ECCV. 2020.
[16] Qizhe Xie, Minh-Thang Luong, Eduard Hovy, Quoc V. Le. ”Self-training with Noisy Student improves ImageNet classification“. CVPR. 2020.
[17] Nicolas Carion, Francisco Massa, Gabriel Synnaeve, Nicolas Usunier, Alexander Kirillov, Sergey Zagoruyko. ”End-to-End Object Detection with Transformers“. ECCV. 2020.
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https://ftp.aimsciences.org/article/doi/10.3934/cpaa.2014.13.1337
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# American Institute of Mathematical Sciences
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On the blow-up criterion of smooth solutions for Hall-magnetohydrodynamics system with partial viscosity
May 2014, 13(3): 1337-1345. doi: 10.3934/cpaa.2014.13.1337
## Global existence of strong solutions to incompressible MHD
1 The Institute of Mathematical Sciences, University of Science and Technology of China, Anhui, 230026 2 The Institute of Mathematical Sciences, The Chinese University of Hong Kong
Received September 2013 Revised November 2013 Published December 2013
We establish the global existence and uniqueness of strong solutions to the initial boundary value problem for the incompressible MHD equations in bounded smooth domains of $\mathbb R^3$ under some suitable smallness conditions. The initial density is allowed to have vacuum, in particular, it can vanish in a set of positive Lebessgue measure. More precisely, under the assumption that the production of the quantities $\|\sqrt\rho_0u_0\|_{L^2(\Omega)}^2+\|H_0\|_{L^2(\Omega)}^2$ and $\|\nabla u_0\|_{L^2(\Omega)}^2+\|\nabla H_0\|_{L^2(\Omega)}^2$ is suitably small, with the smallness depending only on the bound of the initial density and the domain, we prove that there is a unique strong solution to the Dirichlet problem of the incompressible MHD system.
Citation: Huajun Gong, Jinkai Li. Global existence of strong solutions to incompressible MHD. Communications on Pure & Applied Analysis, 2014, 13 (3) : 1337-1345. doi: 10.3934/cpaa.2014.13.1337
##### References:
[1] A. G. Kulikovskiy and G. A. Lyubimov, Magnetohydrodynamics, Addison–Wesley, Reading, MA, 1965. Google Scholar [2] L. D. Landau and E. M. Lifchitz, Electrodynamics of Continuous Media, 2nd ed., Pergamon, New York, 1984. Google Scholar [3] M. Sermange and R. Temam, Some mathematical questions related to the MHD equations, Comm. Pure Appl. Math., 36 (1983), 635-664. doi: 10.1002/cpa.3160360506. Google Scholar [4] G. Duvaut and J. L. Lions, Inequations en thermoelasticite et magnetohydrodynamique, Ach.Rational Mech. Anal., 46 (1972), 241-279. Google Scholar [5] J. F. Gerbeau and C. Le Bris, Existence of solution for a density-dependent magnetohydrodynamic equation, Adv. Differential Equations, 2 (1997), 427-452. Google Scholar [6] P. L. Lions, Mathematical Topics in Fluid Mechanics. Vol. 1. Incompressible Models, Oxford Lecture Series in Mathematics and its Applications, 3. Oxford Science Publications. The Clarendon Press, Oxford University Press, New York, 1996. Google Scholar [7] P. L. Lions, Mathematical topics in fluid mechanics. Vol. 2. Compressible models, Oxford Lecture Series in Mathematics and its Applications, 10. Oxford Science Publications. The Clarendon Press, Oxford University Press, New York, 1998. Google Scholar [8] X. P. Hu and D. H. Wang, Global existence and large-time behavior of solutions to the three-dimensional equations of compressible Magnetohydrodynamic flows, Arch. Rational Mech. Anal., 197 (2010), 203-238. doi: 10.1007/s00205-010-0295-9. Google Scholar [9] X. P. Hu and D. H. Wang, Global solutions to the three-dimensional full compressible Magnetohydrodynamic flows, Commun. Math. Phys., 283 (2008), 255-284. doi: 10.1007/s00220-008-0497-2. Google Scholar [10] J. S. Fan and W. H. Yu, Global variational solutions to the compressible magnetohydrodynamic equations, Nonlinear Analysis, 69 (2008), 3637-3660. doi: 10.1016/j.na.2007.10.005. Google Scholar [11] E. Feireisl, Dynamics of viscous compressible fluids, Oxford Lecture Series in Mathematics and its Applications, 26. Oxford University Press, Oxford, 2004. Google Scholar [12] E. Feireisl, A. Novotný and H. Petzeltová, On the existence of globally defined weak solutions to the Navier-Stokes equations, J. Math. Fluid Mech., 3 (2001), 358-392. doi: 10.1007/PL00000976. Google Scholar [13] B. Ducomet and E. Feireisl, The equation of Magnetohydrodynamics: on the interaction between matter and ration in the evolution of gaseous stars, Commun. Math. Phys., 266 (2006), 595-629. doi: 10.1007/s00220-006-0052-y. Google Scholar [14] Q. Chen, Z. Tan and Y. J. Wang, Strong solutions to the incompressible magnetohydrodynamic equations, Math. Methods Appl. Sci., 34 (2011), 94-107. doi: 10.1002/mma.1338. Google Scholar [15] H. W. Wu, Strong solutions to the incompressible magnetohydrodynamic equations with vacuum, Comput. Math. Appl., 61 (2011), 2742-2753. doi: 10.1016/j.camwa.2011.03.033. Google Scholar [16] X. D. Huang and Y. Wang, Global strong solution to the 2D nonhomogeneous incompressible MHD system, J. Differential Equations, 254 (2013), 511-527. doi: 10.1016/j.jde.2012.08.029. Google Scholar [17] J. S. Fan and W. H. Yu, Strong solution to the compressible magnetohydrodynamic equations with vacuum, Nonlinear Anal. Real World Appl., 10 (2009), 392-409. doi: 10.1016/j.nonrwa.2007.10.001. Google Scholar [18] X. L. Li, N. Su, and D. H. Wang, Local strong solution to the compressible magnetohydrodynamic flow with large data, J. Hyperbolic Differ. Equ., 8 (2011), 415-436. doi: 10.1142/S0219891611002457. Google Scholar [19] X. L. Li and D. H. Wang, Global strong solution to the three-dimensional density-dependent incompressible magnetohydrodynamic flows, J. Differential Equations, 251 (2011), 1580-1615. doi: 10.1016/j.jde.2011.06.004. Google Scholar [20] W. Von Wahl, Estimating $\nabla u$ by $\text{div} u$ and $\text{curl}u$, Math. Methods Appl. Sci., 15 (1992), 123-143. doi: 10.1002/mma.1670150206. Google Scholar [21] Y. Zhou, Remarks on regularities for the 3D MHD equations, Discrete Contin. Dyn. Syst., 12 (2005), 881-886. doi: 10.3934/dcds.2005.12.881. Google Scholar [22] Y. Zhou, Regularity criteria for the 3D MHD equations in terms of the pressure, Internat. J. Non-Linear Mech., 41 (2006), 1174-1180. doi: 10.1016/j.ijnonlinmec.2006.12.001. Google Scholar [23] Y. Zhou, Regularity criteria for the generalized viscous MHD equations, Ann. Inst. H. Poincaré Anal. Non Linéaire, 24 (2007), 491-505. doi: 10.1016/j.anihpc.2006.03.014. Google Scholar
show all references
##### References:
[1] A. G. Kulikovskiy and G. A. Lyubimov, Magnetohydrodynamics, Addison–Wesley, Reading, MA, 1965. Google Scholar [2] L. D. Landau and E. M. Lifchitz, Electrodynamics of Continuous Media, 2nd ed., Pergamon, New York, 1984. Google Scholar [3] M. Sermange and R. Temam, Some mathematical questions related to the MHD equations, Comm. Pure Appl. Math., 36 (1983), 635-664. doi: 10.1002/cpa.3160360506. Google Scholar [4] G. Duvaut and J. L. Lions, Inequations en thermoelasticite et magnetohydrodynamique, Ach.Rational Mech. Anal., 46 (1972), 241-279. Google Scholar [5] J. F. Gerbeau and C. Le Bris, Existence of solution for a density-dependent magnetohydrodynamic equation, Adv. Differential Equations, 2 (1997), 427-452. Google Scholar [6] P. L. Lions, Mathematical Topics in Fluid Mechanics. Vol. 1. Incompressible Models, Oxford Lecture Series in Mathematics and its Applications, 3. Oxford Science Publications. The Clarendon Press, Oxford University Press, New York, 1996. Google Scholar [7] P. L. Lions, Mathematical topics in fluid mechanics. Vol. 2. Compressible models, Oxford Lecture Series in Mathematics and its Applications, 10. Oxford Science Publications. The Clarendon Press, Oxford University Press, New York, 1998. Google Scholar [8] X. P. Hu and D. H. Wang, Global existence and large-time behavior of solutions to the three-dimensional equations of compressible Magnetohydrodynamic flows, Arch. Rational Mech. Anal., 197 (2010), 203-238. doi: 10.1007/s00205-010-0295-9. Google Scholar [9] X. P. Hu and D. H. Wang, Global solutions to the three-dimensional full compressible Magnetohydrodynamic flows, Commun. Math. Phys., 283 (2008), 255-284. doi: 10.1007/s00220-008-0497-2. Google Scholar [10] J. S. Fan and W. H. Yu, Global variational solutions to the compressible magnetohydrodynamic equations, Nonlinear Analysis, 69 (2008), 3637-3660. doi: 10.1016/j.na.2007.10.005. Google Scholar [11] E. Feireisl, Dynamics of viscous compressible fluids, Oxford Lecture Series in Mathematics and its Applications, 26. Oxford University Press, Oxford, 2004. Google Scholar [12] E. Feireisl, A. Novotný and H. Petzeltová, On the existence of globally defined weak solutions to the Navier-Stokes equations, J. Math. Fluid Mech., 3 (2001), 358-392. doi: 10.1007/PL00000976. Google Scholar [13] B. Ducomet and E. Feireisl, The equation of Magnetohydrodynamics: on the interaction between matter and ration in the evolution of gaseous stars, Commun. Math. Phys., 266 (2006), 595-629. doi: 10.1007/s00220-006-0052-y. Google Scholar [14] Q. Chen, Z. Tan and Y. J. Wang, Strong solutions to the incompressible magnetohydrodynamic equations, Math. Methods Appl. Sci., 34 (2011), 94-107. doi: 10.1002/mma.1338. Google Scholar [15] H. W. Wu, Strong solutions to the incompressible magnetohydrodynamic equations with vacuum, Comput. Math. Appl., 61 (2011), 2742-2753. doi: 10.1016/j.camwa.2011.03.033. Google Scholar [16] X. D. Huang and Y. Wang, Global strong solution to the 2D nonhomogeneous incompressible MHD system, J. Differential Equations, 254 (2013), 511-527. doi: 10.1016/j.jde.2012.08.029. Google Scholar [17] J. S. Fan and W. H. Yu, Strong solution to the compressible magnetohydrodynamic equations with vacuum, Nonlinear Anal. Real World Appl., 10 (2009), 392-409. doi: 10.1016/j.nonrwa.2007.10.001. Google Scholar [18] X. L. Li, N. Su, and D. H. Wang, Local strong solution to the compressible magnetohydrodynamic flow with large data, J. Hyperbolic Differ. Equ., 8 (2011), 415-436. doi: 10.1142/S0219891611002457. Google Scholar [19] X. L. Li and D. H. Wang, Global strong solution to the three-dimensional density-dependent incompressible magnetohydrodynamic flows, J. Differential Equations, 251 (2011), 1580-1615. doi: 10.1016/j.jde.2011.06.004. Google Scholar [20] W. Von Wahl, Estimating $\nabla u$ by $\text{div} u$ and $\text{curl}u$, Math. Methods Appl. Sci., 15 (1992), 123-143. doi: 10.1002/mma.1670150206. Google Scholar [21] Y. Zhou, Remarks on regularities for the 3D MHD equations, Discrete Contin. Dyn. Syst., 12 (2005), 881-886. doi: 10.3934/dcds.2005.12.881. Google Scholar [22] Y. Zhou, Regularity criteria for the 3D MHD equations in terms of the pressure, Internat. J. Non-Linear Mech., 41 (2006), 1174-1180. doi: 10.1016/j.ijnonlinmec.2006.12.001. Google Scholar [23] Y. Zhou, Regularity criteria for the generalized viscous MHD equations, Ann. Inst. H. Poincaré Anal. Non Linéaire, 24 (2007), 491-505. doi: 10.1016/j.anihpc.2006.03.014. Google Scholar
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2020 Impact Factor: 1.916
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https://blog.jungsoo.kim/laser-population-inversion-2state/
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I reviewed some basic laser physics from a class. Laser requires a gain medium with state > 2. Here's a quick analysis behind why.
Following Einstein's conventions, 3 things can happen in the system: spontaneous emission, stimulated emission, and photon absorption.
Let's look into each component.
1.Spontaneous emission
$$\Bigg(\frac{dN_2}{dt}\Bigg)_{spontaneous} = -A_{21} N_{2}$$
$$\Bigg(\frac{dN_1}{dt}\Bigg)_{spontaneous} = A_{21} N_{2}$$
2.Stimulated emission
$$\Bigg(\frac{dN_1}{dt}\Bigg)_{- absorption} = B_{21} N_{2} \rho(v)$$
3.Photon absorption
$$\Bigg(\frac{dN_1}{dt}\Bigg)_{+ absorption} = -B_{12} N_{1} \rho(v)$$
Combining the above and since Einstein showed that $$B_{12} = B_{21}$$ because of thermodynamics,
$$\frac{dN_1}{dt} = A_{21} N_2 + B N_2 \rho(v) - B N_1 \rho(v)$$
$$\frac{dN_2}{dt} = - A_{21} N_1 + B N_1 \rho(v) - B N_2 \rho(v)$$
Simplifying,
$$\frac{dN_1}{dt} = A_{21} N_2 + \rho(v) B (N_2-N_1)$$
$$\frac{dN_2}{dt} = - A_{21} N_2 + \rho(v) B (N_1-N_2)$$
At steady state $$\frac{dN_1}{dt} = \frac{dN_2}{dt} = 0$$,
$$0 = 2 \rho(v) B (N_1 - N_2) - 2 A_{21} N_2$$
$$\frac{N_1 - N_2}{N_2} = \frac{A_{21}}{\rho(v)B}$$
$$\frac{N_1}{N_2} = \frac{A_{21}}{\rho(v) B} + 1$$
$$\frac{N_2}{N_1} = \frac{\rho(v) B}{A_{21} +\rho(v) B}$$
$$\frac{N_2 + N_2}{N_1 + N_2} = \frac{\rho(v) B}{A_{21} +\rho(v) B}$$
$$\frac{N_2}{N_1 + N_2} = \frac{\rho(v) B}{2(A_{21} +\rho(v) B)}$$
Now $$\frac{N_2}{N_1 + N_2}$$ is the fraction of state 2 out of total (state 1 + state 2). In order for the population inversion to happen, this ratio needs to be greater than 1/2.
Now let's take a limit where $$\frac{B}{A_{21}}\to\infty$$ i.e. pumping the gain medium:
$$\lim_{\frac{B}{A_{21}}\to\infty} \frac{\rho(v) B}{2(A_{21} +\rho(v) B)} = 1/2$$
The result of the limit shows that the maximum achievable ratio is 1/2, which means that population inversion is not theoretically possible in a 2-state gain medium.
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https://math.stackexchange.com/questions/3008406/show-that-a-given-measure-is-equal-to-the-lebesgue-measure-on-borel-subsets-on
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# Show that a given measure is equal to the Lebesgue measure on Borel subsets on $\mathbb{R}$
Suppose we have a measure $$\mu$$ on $$\left( \mathbb{R},\mathcal{B}(\mathbb{R}) \right)$$ with $$\mu((0,1])=1$$, and $$\mu$$ invariant under translations i.e. $$\mu(A) = \mu(A+c)$$ for every $$c \in \mathbb{R}$$ and Borel set $$A \subseteq \mathbb{R}$$.
Now letting $$\lambda$$ be the Lebesgue measure, in the first part of the question I was able to show that for any interval $$A=(a,b]$$ with $$b-a \in \mathbb{Q}$$ that $$\mu(A) = \lambda(A)$$.
The second part of the question asks to extend this to all Borel sets, i.e. $$\forall A \in \mathcal{B}(\mathbb{R})$$ we get that$$\mu(A) = \lambda(A)$$, but I am really struggling to think of a practical way of achieving this.
Clearly using the first part of the question is the correct approach, so I was attempting to come up with some ways of using this.
The first thing I thought of was maybe to approximate all of the intervals in $$\mathcal{B}(\mathbb{R})$$ by these rational intervals in the first part of the question, but I could not think of a rigorous way of doing this and I do not think this is the correct approach.
My next thought was to potentially show that the intervals from the first part form a $$\pi$$-system of some sort and maybe generate the Borel sets and so agreeing only on these intervals is sufficient to show they agree on the whole space, but I am not too confident in arguing this so any help would be appreciated thanks.
Having $$\mu (a,b]=b-a$$ for rational $$a,b$$ gives $$\mu (a,b)=b-a$$ for all real $$a Proof: Write $$(a,b)$$ as the increasing union of $$(a_n,b_n]$$ for appropritate rational $$a_n,b_n.$$ Standard measure theory with your result for rationals then gives the result.
Since every open set in $$\mathbb R$$ is the disjoint union of open intervals, we see $$\mu(U) = \lambda (U)$$ for all open $$U\subset \mathbb R.$$
• Hi thanks for the comment, I was thinking about this approach at first but had some concerns about the fact that it's not neccesary that $a_n$ and $b_n$ are rationals, since only their difference need be rational - is there still a way to make this method work? – UsernameInvalid Nov 21 '18 at 22:09
• But if both $a_n,b_n$ are rational, you have it covered. – zhw. Nov 21 '18 at 22:11
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http://math.stackexchange.com/questions/421647/whats-the-best-way-to-calculate-all-of-the-points-for-a-curve-given-only-a-few
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# What's the best way to calculate all of the points for a curve given only a few points?
I've been reading up on curves, polynomials, splines, knots, etc., and I could definitely use some help. (I'm writing open source code, if that makes a difference.)
Given two end points and any number of control points (including e.g. $0$ and $100$), I need to calculate many different points for curve. This curve must pass through all points, including the end points.
I'm not sure if this means that there is even a difference between the end points and the control points or not; I guess the difference would be that the end points don't have any points on the "outside", and thus they are different in that regard.
I have tried and succeeded with the "De Casteljau's algorithm" method, but the curve it generates doesn't (necessarily) pass through the control points (unless on a straight line or something).
I have also looked into solving for the curve's equation using a generic polynomial curve equation, e.g.:
$y = a + b x + c x ^ 2 + \dots + j x ^ 9$
plugging points into it, and then solving systematic equations. The problem with this approach is that it solves for a function, so then the curve wouldn't be able to go "backwards" any, right (unless it's a "multivalued" function maybe)?
Based on browsing through Wikipedia, I think what I might want is to calculate a spline curve, but even though I know some Calculus I'm having trouble understanding the math behind it.
I asked this question in the Mathematics section because I'm expecting a mathematical answer, but if the solution is easier to explain with pseudocode or something then I'll take that too. :)
Thanks!
• Andrew
Update: I'm looking to curve fit using Spline (low-degree) polynomial interpolation given some points. Order matters (as marty cohen explained it), and I want each polynomial to be continuous in position, tangent, and curvature. I also want minimalized wiggles and to avoid high degree polynomials if possible. :D
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What do you mean about "Backwards" and "the end points don't have any points on the outside? – Zeta.Investigator Jun 16 '13 at 5:31
Have you seen these pages? en.wikipedia.org/wiki/Interpolation and en.wikipedia.org/wiki/Extrapolation – Zeta.Investigator Jun 16 '13 at 5:34
This is what I consider going "backwards": i.imgur.com/j5ldhFu.png Notice how the curve goes outside the minimal bounding rectangle (based off of the provided points) and goes back over the same x value with a different y value. I said "the end points don't have any points on the outside" in reference to the fact that they are in fact end points. If you were to add another point outside an end point, it would no longer be an end point, etc. This could very well then change the slope of the tangent line on that point (that used to be the end point). – Andrew Jun 16 '13 at 5:47
@PooyaM : He means that you cannot draw the curve on the plane with a parametrization of the form $\vec v(t) = (t,f(t))$ because there are at least two points on the curve who have the same $x$-coordinate but distinct $y$-coordinates. – Patrick Da Silva Jun 16 '13 at 5:53
@Andrew : Do you have an example of a curve you want to plot, with the control points? Because I think mathematically your description is a bit vague ; maybe in your terms it will be easier to understand! – Patrick Da Silva Jun 16 '13 at 5:54
It looks like your set of endpoints and control points can be any set of points in the plane. This means that the $order$ of the points is critical, so that the generated curve goes through the points in a specified order.
This is much different than the ordinary interpolation problem, where the points of the form $(x_i, y_i)$ are ordered so that $x_i < x_{i+1}$.
As I read your desire, if you gave a set of points on a circle ordered by the angle of the line from the center to each point, you would want the result to be a curve close to the circle.
There are a number of ways this could be done. I will assume that you have $n+1$ points and your points are $(x_i, y_i)_{i=0}^n$.
The first way I would do this is to separately parameterize the curve by arc length, with $d_i = \sqrt{(x_i-x_{i-1})^2+(y_i-y_{i-1})^2}$ for $i=1$ to $n$, so $d_i$ is the distance from the $i-1$-th point to the $i$-th point.
For a linear fit, for each $i$ from $1$ to $n$, let $t$ go from $0$ to $d_i$ and construct separate curves $X_i(t)$ and $Y_i(t)$ such that $X_i(0) = x_{i-1}$, $X_i(d_i) = x_i$, and $Y_i(0) = y_{i-1}$, $Y_i(d_i) = y_i$. Then piece these together.
For a smoother fit, do a spline curve through each of $(T_i, x_i)$ and $(T_i, y_i)$ for $i=0$ to $n$, where $T_0 = 0$ and $T_i = T_{i-1}+d_i$. To get a point for any $t$ from $0$ to $T_n$, find the $i$ such that $T_{i-1} \le t \le T_i$ and then, using the spline fits for $x$ and $y$ (instead of the linear fit), get the $x$ and $y$ values from their fits.
Note that $T_i$ is the cumulative length from $(x_0, y_0)$ to $(x_i, y_i)$, and $T_n$ is the total length of the line segments joining the consecutive points.
To keep the curves from not getting too wild, you might look up "splines under tension".
Until you get more precise, this is as far as I can go.
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What you said about ordering and the circle is correct. Could you clarify what d_i and i_i mean? I am looking to generate spline curves. – Andrew Jun 16 '13 at 6:19
That's a typo. I will fix. – marty cohen Jun 16 '13 at 6:34
Ahh. Much better. :) So... i is the resulting point number that goes from 0/1 to n, t is the point number for each individual polynomial that goes from 0 to d_i, d_i is the linear distance between each end/control point, and X_i and Y_i are the sets of resulting points? What are T_0 and T_i then, and why are they being paired with x_i and y_i for spline curves? What's confusing is that T_i is the first in each pair. Thanks. – Andrew Jun 16 '13 at 7:18
I added some more explanation. – marty cohen Jun 16 '13 at 17:32
Well, you have some points of a "curve" of unknown type and you want to know which set of points would that curve passes.
Suppose you know the price of gold in US market at time 10:00AM . You also know that price at 11:00 AM. Does it mean that "given mere two points,you can predict the exact price at any time later?"
Here comes the concepts of Interpolation and Extrapolation and Fitting methods.
From Wikipedia:
In the mathematical field of numerical analysis, interpolation is a method of constructing new data points within the range of a discrete set of known data points.
In engineering and science, one often has a number of data points, obtained by sampling or experimentation, which represent the values of a function for a limited number of values of the independent variable. It is often required to interpolate (i.e. estimate) the value of that function for an intermediate value of the independent variable. This may be achieved by curve fitting or regression analysis.
In mathematics, extrapolation is the process of estimating, beyond the original observation interval, the value of a variable on the basis of its relationship with another variable. It is similar to interpolation, which produces estimates between known observations, but extrapolation is subject to greater uncertainty and a higher risk of producing meaningless results
For example in Interpolation, If you want that curve to be polynomial there is a Lagrange polynomials method and a Newton Finite difference method. See this paper about XY Interpolation Algorithms:
http://goldberg.berkeley.edu/pubs/XY-Interpolation-Algorithms.pdf
You can find some useful information in these pages:
http://en.wikipedia.org/wiki/Interpolation#Polynomial_interpolation
http://en.wikipedia.org/wiki/Extrapolation http://en.wikipedia.org/wiki/Polynomial_interpolation http://en.wikipedia.org/wiki/Newton_series#Newton_series
Hope this helps...
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I'm looking to curve fit using Spline (low-degree) polynomial interpolation given some points, and I don't understand Wikipedia's math. – Andrew Jun 16 '13 at 6:09
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https://www.zbmath.org/?q=ut%3Afuzzy+temporal+reasoning
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## Found 41 Documents (Results 1–41)
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### Is time fuzzy? (English)Zbl 1451.62167
Kreinovich, Vladik (ed.), Statistical and fuzzy approaches to data processing, with applications to econometrics and other areas. In honor of Hung T. Nguyen’s 75th birthday. Cham: Springer. Stud. Comput. Intell. 892, 47-54 (2021).
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### Aggregation of infinite chains of intuitionistic fuzzy sets and their application to choices with temporal intuitionistic fuzzy information. (English)Zbl 1457.68259
MSC: 68T37 03E72
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### Fuzzy spatio-temporal ontologies and formal construction based on fuzzy Petri nets. (English)Zbl 1427.68301
MSC: 68T30 68Q85 68T37
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### Consistencies of fuzzy spatiotemporal data in XML documents. (English)Zbl 1397.68036
MSC: 68P05 62H11 68T37
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### Quantitative model checking of linear-time properties based on generalized possibility measures. (English)Zbl 1382.68143
MSC: 68Q60 03B44 68T37
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MSC: 68T37
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### A fuzzy spatio-temporal description logic F-ALCT($$D_{\mathrm{fst}}$$). (Chinese. English summary)Zbl 1374.68538
MSC: 68T27 68T30 68T37
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### New integral approach to the specification of STPU-solutions. (English)Zbl 1358.68286
Rutkowski, Leszek (ed.) et al., Artificial intelligence and soft computing. 15th international conference, ICAISC 2016, Zakopane, Poland, June 12–16, 2016. Proceedings. Part II. Cham: Springer (ISBN 978-3-319-39383-4/pbk; 978-3-319-39384-1/ebook). Lecture Notes in Computer Science 9693. Lecture Notes in Artificial Intelligence, 317-328 (2016).
MSC: 68T37 03B52 68T27
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### Model checking fuzzy computation tree logic. (English)Zbl 1360.68595
MSC: 68Q60 03B44 68T37
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MSC: 68T37
### On temporal intuitionistic fuzzy cognitive maps. (English)Zbl 1324.03017
MSC: 03E72 68T37
### Dual tableaux. Foundations, methodology, case studies. (English)Zbl 1210.03001
MSC: 03-02 03Bxx 03F07
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### Characterizing an extended fuzzy logic system with temporal attributes for real-time expert systems. (English)Zbl 1339.68247
Mastorakis, N. (ed.) et al., New aspects of systems theory and scientific computation. 10th WSEAS international conference on systems theory and scientific computation (ISTASC ’10), Taipei, Taiwan, August 20–22, 2010. Athens: WSEAS Press (ISBN 978-960-474-218-9/hbk; 978-960-474-219-6/cd-rom). Mathematics and Computers in Science and Engineering, 159-165 (2010).
MSC: 68T35 03B52 68T37
### Dynamic aspects for virtual organizations based on intelligent agent technology. (English)Zbl 1231.68253
Kallel, Ali (ed.) et al., Mathematical methods, computational techniques, intelligent systems. 12th WSEAS international conference (MAMECTIS ’10), Kantaoui, Sousse, Tunia, May 3–6, 2010. Athens: World Scientific and Engineering Academy and Society (WSEAS) (ISBN 978-960-474-191-5/CD-ROM; 978-960-474-188-5/hbk). Electrical and Computer Engineering Series. A Series of Reference Books and Textbooks, 61-66 (2010).
MSC: 68T35 68T37 68T42
### On metric temporal Łukasiewicz logic. (English)Zbl 1348.03023
Falaschi, Moreno (ed.), Proceedings of the 17th international workshop on functional and (constraint) logic programming (WFLP 2008), Siena, Italy, July 3–4, 2008. Amsterdam: Elsevier. Electronic Notes in Theoretical Computer Science 246, 71-85 (2009).
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### Rough set theory: a temporal logic view. (English)Zbl 1268.03070
Chakraborty, Mihir K. (ed.) et al., Logic, Navya-Nyāya and applications. Homage to Bimal Krishna Matilal. Selected papers from the international conference on logic, Navya-Nyāya and applications, Kolkata, India, January 3–7, 2007. London: College Publications (ISBN 978-1-904987-44-4/pbk). Studies in Logic (London) 15, 1-20 (2008).
MSC: 68T37
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### Solving temporal over-constrained problems using fuzzy techniques. (English)Zbl 1152.90518
MSC: 90B99 90C70
### Imprecise temporal interval relations. (English)Zbl 1168.68582
Bloch, Isabelle (ed.) et al., Fuzzy logic and applications. 6th international workshop, WILF 2005, Crema, Italy, September 15–17, 2005. Revised selected papers. Berlin: Springer (ISBN 978-3-540-32529-1/pbk). Lecture Notes in Computer Science 3849. Lecture Notes in Artificial Intelligence, 108-113 (2006).
MSC: 68T37
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### The algebra $$\text{IA}^{\text{fuz}}$$: a framework for qualitative fuzzy temporal reasoning. (English)Zbl 1131.68530
MSC: 68T27 68T20 68T37
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### A generalized time quantifier approach to approximate reasoning. (English)Zbl 1068.68146
MSC: 68T37 03B52
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### Fuzzy constraint networks for signal pattern recognition. (English)Zbl 1082.68792
MSC: 68T10 68T20
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### Temporal granulation and its application to signal analysis. (English)Zbl 1006.68651
MSC: 68U99 68T37 94A12
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MSC: 68P10
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### Object-oriented implementation of a model for fuzzy temporal reasoning. (English)Zbl 1009.68115
Bouchon-Meunier, Bernadette (ed.) et al., Technologies for constructing intelligent systems. 1: Tasks. Heidelberg: Physica-Verlag. Stud. Fuzziness Soft Comput. 89, 85-98 (2002).
MSC: 68T01
MSC: 68T10
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### Temporal representation and reasoning in artificial intelligence: A review. (English)Zbl 0990.68109
MSC: 68T01 68T30
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### A temporal many-valued logic for real time control systems. (English)Zbl 0973.68562
Cerri, Stefano A. (ed.) et al., Artificial intelligence: methodology, systems, and applications. 9th international conference, AIMSA 2000, Varna, Bulgaria, September 20-23, 2000. Proceedings. Berlin: Springer. Lect. Notes Comput. Sci. 1904, 91-100 (2000).
MSC: 68T35 93C41 93C42
### Approximate reasoning with time. (English)Zbl 0940.68144
MSC: 68T37 68T27 03B52
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### Reasoning with fuzzy temporal rules on Petri nets. (English)Zbl 0947.68104
Cardoso, Janette (ed.) et al., Fuzziness in Petri nets. Heidelberg: Physica-Verlag. Stud. Fuzziness Soft Comput. 22, 174-201 (1999).
MSC: 68Q85 68T37
### Obtaining solutions in fuzzy constraint networks. (English)Zbl 0939.68116
MSC: 68T37 68T20 03E72
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### A strategy of problem solving in a fuzzy reasoning network. (English)Zbl 0679.68179
MSC: 68T20 68T15
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### Non-standard logics for automated reasoning. (English)Zbl 0669.03002
London etc.: Academic Press, Inc. x, 334 p. £19.00 (1988).
Reviewer: S.Gottwald
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https://www.physicsforums.com/threads/injective-proof.408789/
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# Homework Help: Injective proof
1. Jun 8, 2010
### rallycar18
Prove that:
If f : X → Y is injective, g, h : W → X, and f ∘ g = f ∘ h, then g = h.
2. Jun 8, 2010
### Tedjn
What is your progress on this problem?
3. Jun 8, 2010
### rallycar18
Definition of injective for If f : X → Y :
For all y $$\in$$ Y, there exists at most one x $$\in$$ X such that f(x) = y
Because f : X → Y and g, h : W → X,
f ∘ g : W → X → Y and f ∘ h : W → X → Y
so f ∘ g, f ∘ h : W → Y
that's where I get stuck.
4. Jun 8, 2010
### lanedance
note that an injective function is a function that preserves distinctness... so you can consider the inverse of f
5. Jun 8, 2010
### rallycar18
Then f^(-1) : Y → X is also injective.. but I don't see what I can do from that.
6. Jun 8, 2010
### Tedjn
It may be easier to see via contradiction. If there is w in W such that g(w) is not equal to h(w), what happens to (f ∘ g)(w) and (f ∘ h)(w)?
7. Jun 8, 2010
### lanedance
or if f o g = f o h, then apply f-1
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https://repository.uantwerpen.be/link/irua/88644
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Publication
Title
Au@MOF-5 and $Au/Mo_{x}@MOF-5$ (M = Zn, Ti; x = 1, 2) : preparation and microstructural characterisation
Author
Abstract
The Zn-carboxylate-based porous coordination polymer MOF-5 [Zn4O(bdc)3] and the metal oxide loaded materials ZnO@MOF-5 and TiO2@MOF-5 were loaded in a second step with the precursor [ClAuCO] to yield intermediate materials denoted as [ClAuCO]@MOF-5, [ClAuCO]/ZnO@MOF-5 and [ClAuCO]/TiO2@MOF-5. These composites were decomposed to Au@MOF-5, Au/ZnO@MOF-5 and Au/TiO2@MOF-5 under hydrogen at 100 °C. The nanoparticle-loaded hybrid materials were characterised by powder X-ray diffraction (PXRD), IR spectroscopy, X-ray photoelectron spectroscopy (XPS) and N2 sorption measurements, which reveal an intact MOF-5 structure that maintains a high specific surface area. For Au@MOF-5, crystalline Au nanoparticles were distributed over the MOF matrix in a homogeneous fashion with a size of ca. 13 nm, evidenced by high resolution transmission electron microscopy. In the case of Au/ZnO@MOF-5, the Au and metal oxide particles of a few nm in size were coexistent in a given volume of the MOF-5 matrix and were not separated in different crystalline MOF particles. For the TiO2 loaded materials the oxide is preferentially located near the outer surface of the MOF particles, leading to an increase of larger exterior Au particles in comparison to very small interior Au particles as observed for the other materials. Au@MOF-5, Au/ZnO@MOF-5 and Au/TiO2@MOF-5 were tested in liquid-phase oxidation of alcohols. Preliminary results show a high activity for the Au loaded materials in this reaction. This observation is attributed to the microstructure of the composites with very small Au particles distributed homogeneously over the MOF matrix.
Language
English
Source (journal)
European journal of inorganic chemistry. - Weinheim, 1998, currens
Publication
Weinheim : 2011
ISSN
1434-1948 [print]
1099-0682 [online]
Volume/pages
12 (2011) , p. 1876-1887
ISI
000289644300004
Full text (Publisher's DOI)
UAntwerpen
Faculty/Department Research group Publication type Subject Affiliation Publications with a UAntwerp address
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https://asmedigitalcollection.asme.org/memagazineselect/article/124/11/50/379574/Organ-on-the-WallAn-English-Doctor-Consults-a-Four
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This article reviews liver surgeon, Rory McCloy’s operations that are guided by a four-foot, three-dimensional virtual profile of a patient’s liver that rotates at his command on the operating room wall in front of him. Using a specially outfitted mouse and his lap top computer, McCloy can manipulate the virtual liver to find the exact location and extent of a tumor before he makes even one incision in the patient’s actual liver on the table below. The high-powered graphic are available to McCloy by remote access on his decidedly non-supercomputer, with the help of a software called OpenGL Vizserver, also from SGI, which allows the data from the supercomputer to be shifted to other computers, even much less powerful ones, via a network link. The trick in making the technology useful for the operating room lay in finding a way to manipulate the images with one hand while performing the surgery with the other of the school’s computing center.
## Article
These days, liver surgeon Rory McCloy's operations are guide d by a four-foot, three-dimensional virtual profile of a patient's liver that rotates at his command on the operating room wall in front of him. Using a specially outfitted mouse and his lap top computer, McCloy can manipulate the virtual liver to find the exact lo cation and extent of a tumor before he makes even one incision in the patient's actual liver on the table below.
This virtual medical technology isn't ahead of its time, McCloy said. Instead, it has been slow to be adopted by the medical establishment and he, for one, aims to speed the pace. McCloy is a surgeon at the Manchester Royal Infirmary at the University of Manchester in England.
In the past 20 years, virtual reality and virtual imaging have revolutionized the way physicians practice medicine, McCloy said. Magnetic resonance imaging, computer-aided tomography scans, and ultrasound images give doctors a vital peek into the inner workings of a patient's body in a way that X-rays cannot. Not only can these imaging tools diagnose disease, tumors, and the like, but they serve as a map to each person's unique body. Just as people are different on the outside-though they all have a nose, two eyes, and two ears-internal organs are also unique. Being able to see exactly what an organ looks like before operating allows doctors to perform closer and more precise work.
McCloy is charged with cutting tumors from the liver and the pancreas. Nicking the tumor during surgery can release cancerous cells into the organ, so he needs to map his cuts.
But MRI, CT, and ultrasound techniques only touch on what technology is capable of now, McCloy said. The shame of it is that more virtual reality technology isn't exploited for the medical environment, he said.
As a doctor long interested in virtual reality, McCloy has gone to meetings and conferences on that subject for the past eight years and has seen firsthand me feasibility of using 3-D scans for more than just diagnostic purposes. The scans could be used in the operating arena to take the place of the X-rays hung around the room to help guide his knife.
"Here I am at a state-of-the-art teaching hospital in the U.K., one of the biggest hospitals in Europe, and I'm still given X-ray films or CT scans that are slices, like slices of salami," he said. "I have to reconstruct in my mind, in the operating room, the 3-D image."
In fact, many hospitals in the United States digitally reconstruct a patient's body or organ in 3-D by use of a CT scan across the body, he said. But those reconstructions are often available only at a computer workstation in the X-ray room.
"The surgeons go down there and look at it and then vanish to the operating theater, and still have to remember where the tumor is," he said. "And while they're very good at remembering, it's the difference between cutting here or cutting three millimeters away in hitting cancer or not hitting cancer."
McCloy likens his operations to extracting an entire plum from a pie with only a few knife slices allowed. It would be easier to do that if you were guided by images in three dimensions that exactly mirrored the pie, rather than looking at slices and trying to figure out how big the plum was and exactly where it was situated.
''I'm busy in my mind during operations trying to put the X-rays into 3-D and going into the patient's body and trying to figure out where this tumor is, and it's all a bit demanding," McCloy said. "Since we're in the digital age, wouldn't it be nice to use all the digits?"
Before using the virtual reality technology, which he and Nigel John, a computer scientist at the university, prepared for the operating room, McCloy studied patients' CT scans and X-rays before surgery to decide how to best operate. During surgery, he didn't have access to the CT scan, because it needed to reside on a computer and the images often didn't load fast enough to really help a doctor.
"On the X-ray, I can see the tumor on one slide and then on another slide, and I can work out that it's several millimeters long," he said. "The X-ray doctors are happy to look at the slide and see that there's a tumor there at that particular part of the liver.
That's the diagnosis. But I'm faced with six pounds of liver or the pancreas, which is the size of the banana and buried deep in the body, and you can't see it because it's hidden behind a lot of other structures.
"I know the tumor is there because the X-ray doctors told me it was there," McCloy continued. "But it's a bit like a lucky dip. You put your hand into a barrel and pick out the sweeties. With the X-ray, you know there are six packages of sweeties in the barrel, but you don't know exactly where they are. Only it's not a barrel, it's a liver that bleeds when you cut it. And I have to remove the cancer whole because if I cut into it, the cells spread around the body."
## Why Can't I See A Liver In 3-D
Because of his affiliation with John and because he has attended conferences on virtual reality, McCloy knew that the technology he sought was available. However, he had to find his own way to make it available to him, to get it to meet his own needs. John helped with that.
"My frustration was sheer frustration that people kept giving me these X-ray films while the data h as been there for years just sitting on the scanners," he said. " It's okay to look at a lovely 3-D image, but why can't I have that while I'm operating? I'm the guy that has to get the 3-D tumor out."
Because the amount of data contained in a series of CT scans is too large for the graphics card on a personal computer to handle, McCloy couldn't simply bring a computer into the operating room and refer to the patient's CT while operating. The scan would take forever to load. So he and John found a way to send the CT information to a supercomputer at the University of Manchester computing center more than a mile from the hospital. The supercomputer was then networked with a laptop McCloy used in his operating room.
The team used an Onyx 300 visualization computer from SG!, formerly Silicon Graphics Inc., of Mountain View, Calif. The machine is specially configured for high-powered graphics imaging by use of the company's Infinite Reality graphics capability. It simultaneously processes two-dimensional images, 3-D graphics-in this case, the CT scan-and data in real time. A team at the on-campus Manchester Visualisation Centre wrote the software that allows the raw 50 to 80 megabytes of data from the CT images to be graphically visualized.
View, Calif. The machine is specially configured for high-powered graphics imaging by use of the company's Infinite Reality graphics capability. It simultaneously processes two-dimensional images, 3-D graphics-in this case, the CT scan-and data in real time. A team at the on-campus Manchester Visualisation Centre wrote the software that allows the raw 50 to 80 megabytes of data from the CT images to be graphically visualized
The high-powered graphic are available to McCloy by remote access on his decidedly non-supercomputer, thanks to software called OpenGL Vizserver, also from SGI, which allows the data from the supercomputer to be shifted to other computers, even much less powerful ones, via a network link. In this case, the laptop in McCloy's operating room serves as a remote station that lets him see and manipulate the CT in 3-D while operating.
Because the images take no time to load, he can manipulate them in real time. For instance, he can rotate the image of the liver.
To keep the files small for negligible loading time, only the pixels of the graphics are transmitted to the laptop, not the graphics themselves. The computer generates about 20 images a second. McCloy uses a common projector, the same one he uses for PowerPoint presentations, to display the image on the wall.
Because the graphic is what's called a volume reconstruction of the entire data set--in this case, an image of the entire liver, both inside and out, McCloy can slice the image--the liver--for a 2-D look inside the organ to mirror the X-rays he formerly saw. He likened the technology to a 3-D anatomy book customized for each patient and projected at a height of six feet on the operating- room wall. The wall is, in McCloy's words, a tasteful shade of pale green and the images show up clearly even under the bright operating-room lights.
## Practicing Before Operating
McCloy performed his first liver surgery using the technology in April , a second in May, and a third in July. The next surgery will be done on a pancreas rather than on a liver. And he's been using the technology to plan surgeries before going into the operating room.
"But the exciting bit is getting the scan on the wall while operating," he said.
Still, McCloy runs through the surgery on another laptop computer before going into the operating theater.
"I can practice before I make the cut," he said. "I can say to myself, 'If I cut it at this angle, will it work?' And I can see on-screen that it won't. Then, I can cut through it another way and see that, yes, I can get it out this way."
Still, the scan won't accurately reflect the shape of the real liver McCloy will see because organs aren't rigidly Conformed inside the body. They move around a bit and spread, or are contracted by other organs and their shape changes accordingly, he said.
"When I actually have the patient's organ in front of me, it may not be in the same shape or at the same angle it is on screen," he added. "Bu t I can rotate the organ on screen so it shows up at the same angle."
A joystick works fine encased in plastic. John's team is now linking an $18 joystick, the type used for computer gaming, to the software program. Many university teaching hospitals have been working with SGI to find uses for visualization technology, according to Chodi McReynolds, director of marketing at the SGI sciences division. One area of continued study, for example, is pairing a CT scan with customized graphics of the patient's blood flow through veins and arteries provided courtesy of computational fluid dynamics software, McReynolds said. The pairing of a patient's body scan with graphics that depict blood flow could be used to study how surgery would affect that particular person. " If they wanted to do a bypass in one spot, they could do that on the image, and it would show how blood flow to the leg would be affected," she said. For their part, McCloy and John hope to network their supercomputer to other lap tops in operating rooms throughout the United Kingdom. First, McCloy will use the technology during 30 surgeries over the next year to document its usefulness. In the next few weeks, a gynecologist colleague will begin looking at ways a digitized and projected CT scan of the pelvis, ovaries, and uterus rnight be used during surgery. T he visual technology that McCloy and John implemented was funded by a$25 million grant from the Department of Education in the U.K.
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http://simbad.u-strasbg.fr/simbad/sim-ref?querymethod=bib&simbo=on&submit=submit+bibcode&bibcode=2005A%26A...438..841M
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# 2005A&A...438..841M
other querymodes : Identifierquery Coordinatequery Criteriaquery Referencequery Basicquery Scriptsubmission TAP Outputoptions Help
Query : 2005A&A...438..841M
2005A&A...438..841M - Astronomy and Astrophysics, volume 438, 841-853 (2005/8-2)
Late-epoch optical and near-infrared observations of the GRB 000911 afterglow and its host galaxy.
MASETTI N., PALAZZI E., PIAN E., HUNT L., FYNBO J.P.U., GOROSABEL J., KLOSE S., BENETTI S., FALOMO R., ZEH A., AMATI L., ANDERSEN M.I., CASTRO-TIRADO A.J., CASTRO CERON J.M., DANZIGER J., FRONTERA F., FRUCHTER A.S., GREINER J., HJORTH J., JENSEN B.L., KAPER L., KOUVELIOTOU C., LEVAN A., MAGAZZU A., MOLLER P., NICASTRO L., PEDERSEN H., TANVIR N.R., VREESWIJK P.M., WIJERS R.A.M.J. and VAN DEN HEUVEL E.P.J.
Abstract (from CDS):
We present the results of an optical and near-infrared (NIR) monitoring campaign of the counterpart of Gamma-Ray Burst (GRB) 000911, located at redshift z=1.06, from 5-days to more than 13-months after explosion. Our extensive dataset is a factor of 2 larger and spans a time interval ∼4 times longer than the ones considered previously for this GRB afterglow; this allows a more thorough analysis of its light curve and of the GRB host galaxy properties. The afterglow light curves show a single power-law temporal decline, modified at late times by light from a host galaxy with moderate intrinsic extinction, and possibly by an emerging supernova (SN). The afterglow evolution is interpreted within the classical fireball'' scenario as a weakly collimated adiabatic shock propagating in the interstellar medium. The presence of a SN light curve superimposed on the non-thermal afterglow emission is investigated: while in the optical bands no significant contribution to the total light is found from a SN, the NIR J-band data show an excess which is consistent with a SN as bright as the known hypernova SN1998bw. If the SN interpretation is true, this would be the farthest GRB-associated SN, as well as the farthest core-collapse SN, discovered to date. However, other possible explanations of this NIR excess are also investigated. Finally, we studied the photometric properties of the host, and found that it is likely to be a slightly reddened, subluminous, extreme starburst compact galaxy, with luminosity ∼0.1L*, an age of ∼0.5Gyr and a specific Star Formation Rate (SFR) of ≃30M/yr/(L/L*). This is the highest specific SFR value for a GRB host inferred from optical/NIR data.
Journal keyword(s): gamma rays: bursts - supernovae: general - radiation mechanisms: non-thermal - cosmology: observations - galaxies: high-redshift - Galaxy: fundamental parameters
Full paper
Number of rows : 16
N Identifier Otype ICRS (J2000)
RA
ICRS (J2000)
DEC
Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2023
#notes
1 NAME SMC G 00 52 38.0 -72 48 01 2.79 2.2 ~ 10530 1
2 SN 2002ap SN* 01 36 23.85 +15 45 13.2 13.11 14.54 SNIc-BL 547 1
3 M 74 G 01 36 41.7451236624 +15 47 01.107512304 10.52 10.00 9.46 9.16 ~ 1612 1
4 SN 2003gd SN* 01 36 42.65 +15 44 19.9 13.2 SNIIP 232 2
5 GRB 000210 gB 01 59 15 -40 40.0 ~ 167 0
6 [PBK2002] GRB 000911 Host Galaxy G 02 18 34.360 +07 44 27.65 ~ 7 0
7 GRB 000911 gB 02 18 42 +07 48.0 ~ 150 0
8 CPD-69 177 WD* 03 10 31.0195960176 -68 36 03.380768388 10.757 11.413 11.394 11.47 11.558 DA3.0 255 0
9 NAME LMC G 05 23 34.6 -69 45 22 0.4 ~ 16509 1
10 SN 2003lw SN* 08 02 30.1 -39 51 03 20.23 SNIc: 526 0
11 SN 2002lt SN* 08 08 59.858 +06 43 37.52 SNIc: 345 1
12 SN 2003dh SN* 10 44 50.030 +21 31 18.15 16.2 SNIcpec 1177 1
13 SN 1994D SN* 12 34 02.395 +07 42 05.70 11.75 12.03 SNIa 536 1
14 SN 1994I SN* 13 29 54.072 +47 11 30.50 12.9 SNIc 610 1
15 GRB 020405 gB 13 58 03.12 -31 22 22.2 21.9 21.5 ~ 242 1
16 SN 1998bw SN* 19 35 03.17 -52 50 46.1 14.09 SNIc 1764 2
To bookmark this query, right click on this link: simbad:objects in 2005A&A...438..841M and select 'bookmark this link' or equivalent in the popup menu
2023.01.31-08:32:40
© Université de Strasbourg/CNRS
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https://datascience.stackexchange.com/questions/61850/numpy-arithmetic-operation-between-two-columns
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# Numpy arithmetic operation between two columns
Below is the numpy array. I need to perform two operations on this array.
1. Add one column with value [column 1] - [column 3].
2. Add another column with value [column 1] - [previous value of column1].
I can do this using normal list operations, but is it possible to use numpy or pandas? If so, how can it be done?
Input data:
[['78' '3412' '98' '3441']
['106' '3412' '127' '3434']
['139' '3411' '160' '3434']
['170' '3411' '191' '3442']
]
These types of operations can easily be done using both numpy or pandas. However, in this case I would recommend pandas since it is more intuitive. Using the example array we can create a pandas dataframe:
arr = np.array([[78, 3412, 98, 3441], [106, 3412, 127, 3434], [139, 3411, 160, 3434], [170, 3411, 191, 3442]])
df = pd.DataFrame(arr, columns=['a', 'b', 'c', 'd'])
The two new columns can now be added as follows:
df['e'] = df['a'] - df['c']
df['f'] = df['a'].diff(1)
Directly using numpy, one possible way would be to do:
arr = np.c_[ arr, arr[:,0] - arr[:,2], np.append(np.NaN, arr[1:, 0] - arr[:-1, 0]) ]
• Thanks. It will help to me – Rajesh das Oct 18 '19 at 13:14
• @Rajeshdas Happy to help :) – Shaido Oct 18 '19 at 15:50
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http://physics.stackexchange.com/questions/16939/capacitance-of-non-concentric-spheres/33165
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# Capacitance of Non-concentric Spheres
We all know how to obtain the capacitance $C=\frac{ab}{b-a}$ (ignoring constants) for two concentric spheres of radii $a,b$.
I was just thinking to myself, what would happen to the capacitance for non-concentric spheres?
Suppose we perturbed the inner sphere off the origin. Does capacitance increase? Ideally I would be looking for an explicit calculation (under sufficiently nice assumptions) but I am also guessing it would be a rather ugly formula.
-
We know that the system is unstable. After you perturb the inner sphere, it'll move all the way until it touches the outer sphere. Since the potential energy is $\frac{Q^2}{2C}$, and it's decreasing along the way -> the capacitance increases – pcr Nov 14 '11 at 6:09
Here is my estimate for the change in potential energy $\approx U_0 (\frac{\delta}{b})^2$ (I got this from the change in $\frac12 E^2 2\pi b^2 \delta$). This gives us $\frac{\delta C}{C}\approx (\frac{\delta}{b})^2$. Not sure – pcr Nov 14 '11 at 6:38
@pcr: I do not see why the system is unstable... Irregardless, I am defining my region, with boundaries of the conductors! So everything is held fixed! – Chris Gerig Nov 14 '11 at 20:57
I cheated by using Earnshaw theorem =) (the system is unstable if you don't nail down the conductors). Alternatively, you can also argue by drawing the E-field line: the lines in the "forward pole" region (using Georg's convention) are denser than those in the "backward pole" region, which suggests an attraction. – pcr Nov 14 '11 at 21:14
Check section III and figures 5 to 9 of this note. – mmc Nov 14 '11 at 23:25
Important notice: My previous result was a little bit incorrect. I found the factor $1/2$ by comparison with the textbook V.V. Batygin, I.N. Toptygin «Problems in electrodynamics».
Let's denote the radius of the inner sphere $S_1$ as $a$, the radius of the outer sphere $S_2$ as $b$ and the displacement as $c$, so that $c\ll a,b$. We choose the origin of the coordinate system to be in the center of the inner sphere. Then, up to the second order in $c$ the distance from the origin to the outer sphere has the form: $$R\left( \theta\right) =b+c\cos\theta.$$ Therefore, the potential in the space between them can be found as $$\phi=\left( \alpha_{1}+\frac{\beta_{1}}{r}\right) +c\left( \alpha _{2}r+\frac{\beta_{2}}{r^{2}}\right) \cos\theta,$$ where $\alpha_{i}$ and $\beta_{i}$ are constant which should be found from the boundary conditions: $$\left. \phi\right\vert _{S_{1}}=const,\quad\left. \phi\right\vert _{S_{2} }=0,\quad \oint_{S_{1}} \mathrm{d}S\,\mathbf{n}\cdot\mathbf{\nabla}\phi=-4\pi Q,\,$$ where $\mathbf{n}=\mathbf{r}/r$. Hence the potential reads as follows: $$\phi=Q\left( \frac{1}{r}-\frac{1}{b}\right) +\frac{Qc}{b^{3}-c^{3}}\left( r-\frac{a^{3}}{r^{2}}\right) \cos\theta.$$ Therefore the potential on the inner sphere doesn't depend on $c$ up to the second order: $$\left. \phi\right\vert _{S_{1}}=Q\,\frac{b-a}{ab}.$$ The charge distribution on the inner sphere can be found as follows: $$\sigma=-\frac{1}{4\pi}\left( \mathbf{n}\cdot\mathbf{\nabla}\phi\right) =-\frac{1}{4\pi}\left. \frac{\partial}{\partial r}\,\phi\right\vert _{r=a}=\frac{Q}{4\pi a^{2}}\left( 1-\frac{3a^{2}c}{b^{3}-c^{3}}\cos \theta\right) .$$ Hence, the force acting on the inner sphere has the form: $$\mathbf{F}=-\frac{1}{2}\oint_{S_{1}} \mathrm{d}S\,\sigma\mathbf{\nabla}\phi,$$ $$F =-\frac{Q^{2}}{4}\int_{-1}^{1}\mathrm{d}\cos\theta\,\left( 1-\frac{3ca^{2}}{b^{3}-c^{3}}\cos\theta\right) \left. \frac{\partial }{\partial z}\left[ \frac{1}{r}+\frac{c}{b^{3}-c^{3}}\left( 1-\frac{a^{3} }{r^{3}}\right) z\right] \right\vert _{r=a}\\ =-\,\frac{Q^{2}c}{b^{3}-c^{3}},$$ where I use the trivial identity: $$\frac{\partial}{\partial z}\frac{1}{r^{n}}=-\frac{nz}{r^{3}}.$$ The capacity $C$ can be found from the potential energy: $$U=\frac{CV^{2}}{2}\quad\Rightarrow\quad F=-\frac{\Delta U}{\Delta c} =-\frac{\phi^{2}}{2}\frac{\Delta C}{\Delta c},$$ thus $$\frac{\Delta C}{\Delta c}=-\frac{2F}{\phi^{2}}=\frac{2ca^{2}b^{2}}{\left( b^{3}-a^{3}\right) \left( a-b\right) ^{2}}.$$ Finally, we obtain $$C=\frac{ab}{b-a}+\frac{a^{2}b^{2}c^{2}}{\left( b^{3}-a^{3}\right) \left( a-b\right) ^{2}}\quad\quad (1)$$
UPDATE: The comments given above give the reference to the article of «Capacitance Bounds for Geometries Corresponding to an Advanced Simulator Design» by M.I. Sancer and A.D. Varvatsis. The article in turn contains the reference to the book:
W. R. Smythe, Static and Dynamic Electricity, McGraw-Hill, New York, 1950
where the following exact result for the capacitance is presented: $$C=ab\sinh\alpha\sum_{n=1}^{\infty}\frac{1}{b\sinh n\alpha-a\sinh\left( n-1\right) \alpha},\quad\quad\left( 2\right)$$ so that $$\quad\cosh\alpha=\frac{a^{2}+b^{2}-c^{2}}{2ab}.$$ Sancer and Varvatsis claim that they found the approximation of the exact result in the $c\rightarrow0$ limit: $$C=\frac{ab}{b-a}\left[ \frac{1}{2}\left( \sqrt{\frac{1-y^{2}/\left( 1+x\right) ^{2}}{1-y^{2}/\left( 1-x\right)^{2}}}+1\right) + \frac{x}{2}\left( \sqrt{\frac{1-y^{2}/\left( 1+x\right) ^{2}}{1-y^{2}/\left( 1-x\right) ^{2}}}-1\right) \right] ,\quad\quad\left( 3\right)$$ where $$x=\frac{a}{b},\quad y=\frac{c}{b}.$$ It is easy to see that the expansion of the result (3) doesn't coincide with mine result (1). The numerical comparison of all three results presented in the figure below:
One can see that the result (3) of Sancer and Varvatsis is incorrect.
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In one of the above comments, a paper was referenced, and it shows that: Letting $d$ denote the distance between the spheres' centers, $C\sim 4\pi\varepsilon\frac{ab}{b-a}\cdot F$, where $F=\frac{1}{2}[\sqrt{\frac{1-(\frac{d}{a+b})^2}{1-(\frac{d}{b-a})^2}}+1]+\frac{1}{2}\frac{a}{b}[\sqrt{\frac{1-(\frac{d}{a+b})^2}{1-(\frac{d}{b-a})^2}}-1]$. Does your approximation fit with this? Sorry I'm being lazy. – Chris Gerig Jul 31 '12 at 1:11
@ChrisGerig I added the comparison with the article you mentioned. – Grisha Kirilin Aug 1 '12 at 14:27
AWESOME, thanks for the comparison! – Chris Gerig Aug 1 '12 at 17:02
+1, nice answer! Although you leave the limit of large c undiscussed. – Ron Maimon Aug 11 '12 at 10:06
The whole system is unstable (you can convince yourself by Earnshaw theorem or by drawing the field lines). After you perturb the inner sphere, it'll move all the way until it touches the outer sphere. Since the potential energy is $\frac{Q^2}{2C}$, and it's decreasing along the way -> the capacitance increases.
Here is my estimate for the change in potential energy $\approx -U_0 \frac{b-a}{a}(\frac{\delta}{b})^2$ .
I got this from the change in bulk electrostatic energy $\frac12 E^2 2\pi b^2\delta$
Here I shift the outer conductor because it is easier to follow my calculation this way. The shift is exaggerated for clarity's sake.
Initially, the electrostatic energy comes from region 1 and 2. After the shift, it comes from region 2 and 3. We can roughly see that the energy in region 3 is less than the one in region 1: region 1 is nearer to the inner conductor than region 3.
Clearly the change in energy is
$$U_3 - U_1 = \frac12 (E_3^2 -E_1^2) 2\pi b^2 \delta$$ with $$E_3^2 - E_1^2 \approx 2E_1 \frac{dE}{dr} \delta \approx -4 E_1^2 \frac{\delta}b$$
we get $$U_3 - U_1 = - \frac{e^2}{4\pi b} (\frac{\delta}b)^2= U_0 \frac{b-a}a (\frac{\delta}b)^2$$
This gives us $-\frac{\Delta U}{U}=\frac{\Delta C}C\approx\frac{b-a}{a}(\frac{\delta}{b})^2$.
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See my comment above, I do not see how Earnshaw is sufficiently applied, because there are not only electrostatic forces here... And the field lines argument is not rigorous so it could be incorrect. But in addition, I would like to see your energy change calculation as well. – Chris Gerig Nov 14 '11 at 21:40
@pcr, I erased my comment when I realized that Chris knows better than any answer, especially when he wrote ""especially when these are rings moving in weird ways (or just rings moving towards the other sphere?) and not planes moving closer to each other..."". He lacks imagination of the one-dimensional nature of the problem. – Georg Nov 15 '11 at 11:36
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http://tex.stackexchange.com/questions/58363/how-to-change-hyperlink-target-of-frame-titles-in-beamer
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# How to change hyperlink target of frame titles in Beamer? [closed]
The default behaviour is that clicking on frame titles takes you to the next slide. I would like to change that behaviour but I can't seem to workout how it is achieved when reading the Beamer source code.
How do you change the hyperlink target of frame titles in Beamer?
Edit
I was hardcoding hyperlinks into the titles as follows:
\documentclass{beamer}
\begin{document}
\begin{frame}
\frametitle{\href{http://www.yahoo.com}{Yahoo}}
Blah
\end{frame}
\begin{frame}{\href{http://www.google.com}{Google}}
Blah
\end{frame}
\begin{frame}{\href{http://www.bing.com}{Bing}}
Blah
\end{frame}
\end{document}
And it wasn't working. I thought my hyperlink behaviour was somehow being overwritten by Beamer but it turns out that it was just the PDF viewer misbehaving.
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## closed as not a real question by Claudio Fiandrino, lockstep, Marco Daniel, Joseph Wright♦Jun 3 '12 at 20:59
It's difficult to tell what is being asked here. This question is ambiguous, vague, incomplete, overly broad, or rhetorical and cannot be reasonably answered in its current form. For help clarifying this question so that it can be reopened, visit the help center.If this question can be reworded to fit the rules in the help center, please edit the question.
Can you please add to your question some minimal and complete document reproducing the mentioned behaviour? Hyperlinks usually take you to the right frame... so I don't quite understand your question. – Gonzalo Medina Jun 3 '12 at 2:49
How exactly would you like to change the hyperlink behaviour? – Gonzalo Medina Jun 3 '12 at 2:58
It is difficult understand what you are wondering because it's not true that you go in the next slide just clicking on the title. Try to click in another point of the frame: you will go to next slide. – Claudio Fiandrino Jun 3 '12 at 6:04
The default behaviour is not broken, I would just like it to link somewhere else. Start of the section, for example... – Dale Roberts Jun 3 '12 at 9:53
If you want to point to the start of a section you can, for example, choose a theme that made use of the navigation bar then click on it. One example: the Frankfurt theme. – Claudio Fiandrino Jun 3 '12 at 13:22
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http://mathhelpforum.com/new-users/220978-integrating-trignometric-functions-print.html
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# Integrating Trignometric Functions
• August 1st 2013, 12:57 AM
reindeer7
Integrating Trignometric Functions
I know that to integrate functions like cos(x) you search for the expression which gave cos(x) as its derivative in the first place so the integral of cos(x) will be sin(x).So i should think that the integral of cos(2x) should be sin(2x) but is that correct? Afterall maybe z=2x and the integarl of cos(z) will be sin(z).but i have seen a different expression for the integrals of those trignometric functions which have a coefficient>1 with x,in their domain.i did not really understand what they did and please also give some simple reasoning as to why sin(2x) will be incorrect.
And similarly how will I integrate functions like cos(3x+1) , cos(3x^2) , cos(x^(2x+4)) , cos((3x+4)^99).What is the underling principle behind all of them?
• August 1st 2013, 01:08 AM
MarkFL
Re: Integrating Trignometric Functions
Consider:
$\int\cos(ax+b)\,dx$ where $a,b$ are constants.
If we use the substitution:
$u=ax+b\,\therefore\,du=a\,dx$
then we have:
$\frac{1}{a}\int\cos(u)\,du=\frac{1}{a}\sin(u)+C= \frac{1}{a}\sin(ax+b)+C$
If the argument of the cosine function is non-linear, that is, its derivative is not constant, then you will need a function that is a constant times this derivative as a factor to the cosine function within the integrand in order to use this substitution technique.
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https://hackage.haskell.org/package/effet-0.4.0.0/docs/Control-Effect-RWS-Strict.html
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effet-0.4.0.0: An Effect System based on Type Classes
Copyright (c) Michael Szvetits 2020 BSD3 (see the file LICENSE) [email protected] stable portable None Haskell2010
Control.Effect.RWS.Strict
Description
Strict interpretations of the RWS' effect.
If you don't require disambiguation of multiple RWS effects (i.e., you only have one RWS effect in your monadic context), you usually need the untagged interpretations.
Synopsis
# Interpreter Type
data RWST r w s m a Source #
The strict interpreter of the RWS effect. This type implements the RWS' type class in a strict manner.
When interpreting the effect, you usually don't interact with this type directly, but instead use one of its corresponding interpretation functions.
#### Instances
Instances details
# Tagged Interpretations
Arguments
:: forall tag r w s m a. (Functor m, Monoid w) => r The initial environment. -> s The initial state. -> ('[RWS' tag r w s, Reader' tag r, Writer' tag w, State' tag s] EachVia RWST r w s) m a The program whose RWS effect should be handled. -> m (w, a) The program with its RWS effect handled, producing the final output w and the result a.
Runs the RWS effect and discards the final state.
Arguments
:: forall tag r w s m a. (Functor m, Monoid w) => r The initial environment. -> s The initial state. -> ('[RWS' tag r w s, Reader' tag r, Writer' tag w, State' tag s] EachVia RWST r w s) m a The program whose RWS effect should be handled. -> m (w, s) The program with its RWS effect handled, producing the final output w and the final state s.
Runs the RWS effect and discards the result of the interpreted program.
Arguments
:: forall tag r w s m a. (Functor m, Monoid w) => r The initial environment. -> s The initial state. -> ('[RWS' tag r w s, Reader' tag r, Writer' tag w, State' tag s] EachVia RWST r w s) m a The program whose RWS effect should be handled. -> m (w, s, a) The program with its RWS effect handled, producing the final output w, the final state s and the result a.
Runs the RWS effect and returns the final output, the final state and the result of the interpreted program.
# Untagged Interpretations
evalRWS :: (Functor m, Monoid w) => r -> s -> ('[RWS r w s, Reader r, Writer w, State s] EachVia RWST r w s) m a -> m (w, a) Source #
execRWS :: (Functor m, Monoid w) => r -> s -> ('[RWS r w s, Reader r, Writer w, State s] EachVia RWST r w s) m a -> m (w, s) Source #
runRWS :: (Functor m, Monoid w) => r -> s -> ('[RWS r w s, Reader r, Writer w, State s] EachVia RWST r w s) m a -> m (w, s, a) Source #
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https://math.stackexchange.com/questions/3539273/topology-induced-by-a-norm
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# Topology induced by a norm
I came across the notion of a $$\textit{topology induced by a norm}$$.
If $$(X,\Vert\ . \Vert)$$ is a normed space w.r.t a norm $$\Vert\ . \Vert: X \to \mathbb{R}$$. Most sources define the topology $$\tau$$ on $$X$$ induced by $$\Vert\ . \Vert$$ as the sets $$U \subset X$$ open w.r.t. the metric $$d: X \times X \to \mathbb{R}$$ given by $$d(x,y) = \Vert x - y \Vert$$.
But would I be correct in assuming that an equivalent definition would be $$\tau = \{\Vert\ . \Vert^{-1}(U) \mid U \subset \mathbb{R}\ \textrm{open} \}$$?
• Note that the preimage of U would be a subset of $X\times X$, not $X$ – Ottavio Bartenor Feb 8 at 17:42
• Wouldnt you be applying the norm preimage to a real number (representing the norm) and trying to get the original set which has that value as a norm back out? Or am I misreading? – SquishyRhode Feb 8 at 17:46
• We know topologies are induced by metrics. But norms induce metrics too. So a norm should imply a metric, which then implies a topology. Assuming all other criteria are met. – SquishyRhode Feb 8 at 17:48
• @BrianMoehring My bad, didn't pay enough attention – Ottavio Bartenor Feb 8 at 17:48
• I think you only get a neighborhood basis at $0$ with this definition, but that uniquely determines the topology, so in a sense it is sufficient. – TSU Feb 8 at 17:48
With your version and $$\Bbb R$$ with norm $$|\cdot|$$, the set $$(-3,-2)\cup(2,3)$$ would be open, but $$(2,3)$$ not.
Note that your sets $$U'=\|\cdot\|^{-1}[U]$$ are always symmetrical in that $$x \in U$$ implies $$-x \in U'$$. Not all open sets will obey that. These sets will give the open balls around the origin for $$U$$ that are symmetric around $$0$$, but not all other translated balls.
In fact $$\tau$$ is the topology induced by $$\{ \lVert. \rVert^{-1}(U): U\subseteq \mathbb{R} \ \ \text{is Open} \ \}$$
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http://itknowledgeexchange.techtarget.com/itanswers/outlook-express-compacting/?watch=22199
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15 pts.
Outlook Express Compacting
Hi All, I have a peculire problem here, I am using outlook express to access our emails, A while before one of my colleage complained that the emails for last three months are removed from deleted folder of outlook express after the system finished the compacting folders ??? I checked the maintinance tab, there isn't any option seleted to delete the email to compact the folders, however the compacting is set run if there is 5% of wasted space. Now the question is how the emails are deleted? and Can I restore them? Any help will be highly appriciated. Thanking You and Best Regards.
Software/Hardware used:
ASKED: December 15, 2005 7:49 AM
UPDATED: February 8, 2006 10:49 AM
Hi !! Check out the following tool. I installed it after i read ur post. It works. http://www.office-addins.com/-outlook-express-addins/restore-deleted-from-outlook-express.html Let me know if it helped you. Regards, Nilesh.
Last Wiki Answer Submitted: December 15, 2005 8:48 am by Nileshroy 0 pts.
All Answer Wiki Contributors: Nileshroy 0 pts.
Discuss This Question:
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The first reply is a good way to get the email messages back. You might want to think about moving to Outlook (not outlook express) you get the option to backup your folders, to a .pst file (example Dec2005.pst) if something goes wrong, you can restore the individual folders, and there is an option for no duplicates, I would look into this option, or create a folder called ‘holdtemp’, and then only send messages to delete that you are sure you want deleted.
0 pts.
Oulook Express store messages into a *.DBX files. Each folder has its DBX file(ie Inbox.dbx, sent.DBX, ect) search for all *.DBX files and make comparison to see.
Another thing, its possible that the autmatic Archiving has been enabled and after some certains days, the process will automatically archive the items to another DBX file… in Outlook 2000 and greater version, this option exist(for PST files).
0 pts.
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http://openstudy.com/updates/55e4e749e4b0819646d808d9
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## clara1223 one year ago find the limit as x approaches 1 of abs(x-1)/x-1 Delete Cancel Submit
• This Question is Closed
1. clara1223
• one year ago
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$\lim_{x \rightarrow 1}\frac{ \left| x-1 \right| }{ x-1 }$
2. random231
• one year ago
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okay what is the first thing you check for when you solve a limit?
3. dinamix
• one year ago
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its 1 or -1
4. clara1223
• one year ago
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@random231 you plug it in to see if you get 0/0
5. random231
• one year ago
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1
nope dinamix i dont think you got it!
6. clara1223
• one year ago
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2
@random231 and if so you have to simplify
7. random231
• one year ago
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1
no clara the first thing you have to check whether the limit exists or not!
8. jdoe0001
• one year ago
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$$\large { \lim\limits_{x\to 1}\ \cfrac{|x-1|}{x-1}\implies \begin{cases} \lim\limits_{x\to 1^{\color{red}{ +}}}\ \cfrac{+(x-1)}{x-1} \\ \quad \\ \lim\limits_{x\to 1^{\color{red}{ -}}}\ \cfrac{-(x-1)}{x-1} \end{cases} }$$
9. dinamix
• one year ago
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0
$\lim_{x \rightarrow 1^+} = \frac{ x-1 }{ x-1 } = 1$
10. random231
• one year ago
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1
that is you put in a value immediate to the left of 1 in one case and to the right in the other case. if both of them give the same value then the limit exists.
11. dinamix
• one year ago
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yup @ what i said @random231 its 1 and -1
12. dinamix
• one year ago
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13. random231
• one year ago
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nope there cant be two values
14. clara1223
• one year ago
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@dinamix if thats the case then doesn't the limit not exist? if theyre two different numbers?
15. random231
• one year ago
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exactly
16. jdoe0001
• one year ago
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notice the values found for the two one-sided limits they differ thus the two-sided limit of $$\lim\limits_{x\to 1}\ \cfrac{|x-1|}{x-1}\impliedby \textit{does not exist}$$
17. dinamix
• one year ago
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|dw:1441065218850:dw| this is graph of function now we understand everything i think i am right about my graph draw it @clara1223 , @random231
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https://greprepclub.com/forum/until-recently-astronomers-have-been-puzzled-by-the-fate-of-12386.html
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# Until recently astronomers have been puzzled by the fate of
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Until recently astronomers have been puzzled by the fate of [#permalink] 10 Feb 2019, 02:19
Expert's post
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Question Stats:
33% (04:53) correct 66% (10:07) wrong based on 6 sessions
Until recently astronomers have been puzzled by the fate of red giant and supergiant stars. When the core of a giant star whose mass surpasses 1.4 times the present mass of our Sun ($$M \odot$$) exhausts its nuclear fuel, it is unable to support its own weight and collapses into a tiny neutron star. The gravitational energy released during this implosion of the core blows off the remainder of the star in a gigantic explosion, or a supernova. Since around 50 percent of all stars are believed to begin their lives with masses greater than 1.4 $$M \odot$$ we might expect that one out of every two stars would die as a supernova. But in fact, only one star in thirty dies such a violent death. The rest expire much more peacefully as planetary nebulas. Apparently most massive stars manage to lose sufficient material that their masses drop below the critical value of 1.4 $$M \odot$$ before they exhaust their nuclear fuel.
Evidence supporting this view comes from observations of IRC + 10216, a pulsating giant star located 700 light-years away from Earth. A huge rate of mass loss (One $$M \odot$$ every 10,000 years) has been deduced from infrared observations of ammonia ($$NH_3$$) molecules located in the circumstellar cloud around IRC + 10216. Recent microwave observations of carbon monoxide $$(CO)$$ molecules indicate a similar rate of mass loss and demonstrate that the escaping material extends outward from the star for a distance of at least one light-year. Because we know the size of the cloud around IRC + 10216 and can use our observations of either $$NH_3$$ or CO to measure the outflow velocity, we can calculate an age for the circumstellar cloud. IRC + 10216 has apparently expelled, in the form of molecules and dust grains, a mass equal to that of our entire Sun within the past ten thousand years. This implies that some stars can shed huge amounts of the matter very quickly and thus may never expire as supernovas. Theoretical models, as well as statistics on supernovas and planetary nebulas, suggest that stars that begin their lives with masses around 6 $$M \odot$$ shed sufficient material to drop below the critical value of 1.4 $$M \odot$$. IRC + 10216, for example, should do this in a mere 50,000 years from its birth, only an instant in the life of a star.
But what place does IRC + 10216 have in stellar evolution? Astronomers suggest that stars like IRC + 10216 are actually "protoplanetary nebulas"—old giant stars whose dense cores have almost but not quite rid themselves of the fluffy envelopes of gas around them. Once the star has lost the entire envelope, its exposed core becomes the central star of the planetary nebula and heats and ionizes the last vestiges of the envelope as it flows away into space. This configuration is a full-fledged planetary nebula, long familiar to optical astronomers.
21. The primary purpose of the passage is to
(A) offer a method of calculating the age of circumstellar clouds
(B) describe the conditions that result in a star's expiring as a supernova
(C) discuss new evidence concerning the composition of planetary nebulas
(D) explain why fewer stars than predicted expire supernovas
(E) survey conflicting theories concerning the composition of circumstellar clouds
[Reveal] Spoiler: OA
D
22. The passage implies that at the beginning of the life of IRC + 10216, its mass was approximately
(A) 7.0 $$M \odot$$
(B) 6.0 $$M \odot$$
(C) 5.0 $$M \odot$$
(D) 1.4 $$M \odot$$
(E) 1.0 $$M \odot$$
[Reveal] Spoiler: OA
B
23. The view to which Evidence supporting this view comes from refers serves to
(B) undermine a previously held theory
(C) take into account data previously held to be insignificant
(D) resolve a controversy
(E) question new methods of gathering data
[Reveal] Spoiler: OA
A
24. It can be inferred from the passage that the author assumes which of the following in the discussion of the rate at which IRC + 10216 loses mass?
(A) The circumstellar cloud surrounding IRC + 10216 consists only of CO and $$NH_3$$ molecules.
(B) The circumstellar cloud surrounding IRC + 10216 consists of material expelled from that star.
(C) The age of a star is equal to that of its circumstellar cloud.
(D) The rate at which IRC + 10216 loses mass varies significantly from year to year.
(E) Stars with a mass greater than 6 $$M \odot$$ lose mass at a rate faster than stars with a mass less than 6 $$M \odot$$ do.
[Reveal] Spoiler: OA
B
25. According to information provided by the passage, which of the following stars would astronomers most likely describe as a planetary nebula?
(A) A star that began its life with a mass of 5.5 $$M \odot$$, has exhausted its nuclear fuel, and has a core that is visible to astronomers
(B) A star that began its life with a mass of 6 $$M \odot$$, lost mass at a rate of 1 $$M \odot$$ per 10,000 years, and exhausted its nuclear fuel in 40,000 years
(C) A star that has exhausted its nuclear fuel, has a mass of 1.2 $$M \odot$$, and is surrounded by a circumstellar cloud that obscures its core from view
(D) A star that began its life with a mass greater than 6 $$M \odot$$, has just recently exhausted its nuclear fuel, and is in the process of releasing massive amounts of gravitational energy
(E) A star that began its life with a mass of 5.5 $$M \odot$$, has yet to exhaust its nuclear fuel, and exhibits a rate of mass loss similar to that of IRC + 10216
[Reveal] Spoiler: OA
A
26. Which of the following statements would be most likely to follow the last sentence of the passage?
(A) Supernovas are not necessarily the most spectacular events that astronomers have occasion to observe.
(B) Apparently, stars that have a mass of greater than 6 $$M \odot$$ are somewhat rare.
(C) Recent studies of CO and $$NH_3$$ in the circum-stellar clouds of stars similar to IRC + 10216 have led astronomers to believe that the formation of planetary nebulas precedes the development of supernovas.
(D) It appears, then, that IRC + 10216 actually represents an intermediate step in the evolution of a giant star into a planetary nebula.
(E) Astronomers have yet to develop a consistently accurate method for measuring the rate at which a star exhausts its nuclear fuel.
[Reveal] Spoiler: OA
D
27. Which of the following titles best summarizes the content of the passage?
(A) New Methods of Calculating the Age of Circumstellar Clouds
(B) New Evidence Concerning the Composition of Planetary Nebulas
(C) Protoplanetary Nebula: A Rarely Observed Phenomenon
(D) Planetary Nebulas: An Enigma to Astronomers
(E) The Diminution of a Star's Mass: A Crucial Factor in Stellar Evolution
[Reveal] Spoiler: OA
E
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Re: Until recently astronomers have been puzzled by the fate of [#permalink] 14 Feb 2019, 20:53
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This was a very tough one
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Re: Until recently astronomers have been puzzled by the fate of [#permalink] 23 Feb 2019, 20:04
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21. The primary purpose is introduced in the first paragraph. The central problem is: "we might expect that one out of every two stars would die as a supernova. But in fact, only one star in thirty dies such a violent death." How do we explain that paradox? The passage attempts to explain one possible theory. D is the best choice.
22. Here's the relevant portion: "Theoretical models, as well as statistics on supernovas and planetary nebulas, suggest that stars that begin their lives with masses around 6 M⊙ shed sufficient material to drop below the critical value of 1.4 M⊙. IRC + 10216, for example, should do this in a mere 50,000 years from its birth, only an instant in the life of a star." IRC + 10216 is given as an illustration of a star who begins its life with a mass around 6 M⊙ and sheds down to below 1.4 M⊙ by the end of its life. Hence, IRC + 10216 must have started its life at around 6 M⊙.
23. The pronoun "this" in "this view" refers to the fact that "most massive stars manage to lose sufficient material that their masses drop below the critical value of 1.4 M⊙ before they exhaust their nuclear fuel." The fact is mentioned as an explanation of the paradox that most stars are born larger than 1.4 M⊙ but do not end as supernovas. Since such large stars should create supernovas, the mentioned view serves to reconcile the seemingly contradictory facts.
24. The rate of matter loss is measured by observing the circumstellar cloud. The point here is that matter lossed by the star becomes part of the cloud. If the cloud does not consist of material expelled by the star, then the composition of the cloud would not relate to the star itself.
25. Here's the relevant portion: "Once the star has lost the entire envelope, its exposed core becomes the central star of the planetary nebula and heats and ionizes the last vestiges of the envelope as it flows away into space. This configuration is a full-fledged planetary nebula, long familiar to optical astronomers." If it is familiar to optical astronomers, that means it must be able to be seen. A planetary nebula occurs when a star finishes it's life cycle (running out of nuclear fuel) and is now just an exposed core. This correlates best with choice A.
26. The final paragraph labels IRC + 10216 as a "protoplanetary nebulas" that has almost, but not quite, used up its fuel. It thus falls between a normal giant star and a full-fledged planetary nebula. Choice D fits bets with this assessment, summing up the contents of the final paragraph.
27. Since we're summarizing the content, this is kind of like a primary purpose question. Crucially, the passage is attempting to answer a question: Why do most stars, despite their size, end as nebulas instead of supernovas? Certainly, the passage is not just about methods of calculation, nor is it primarily concerned with composition, eliminating A and B. We have no evidence that protoplanetary nebulas are rare, eliminating C. Between D and E, choice D does not address the passages main question, while E does. The answer to the question is that stars get smaller with time, and that's the big point the passage is making.
Last edited by MagooshStudentHelp on 15 Mar 2019, 09:42, edited 1 time in total.
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Re: Until recently astronomers have been puzzled by the fate of [#permalink] 14 Mar 2019, 21:49
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Re: Until recently astronomers have been puzzled by the fate of [#permalink] 14 Mar 2019, 21:49
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https://docs.daml.com/2.0.0-snapshot.20220215.9307.0.55fef9cf/ops/connect/auth0.html
|
Setting Up Auth0¶
In this section, we will walk through a complete setup of an entire Daml system using Auth0 as its authentication provider.
Note
These instructions include detailed steps to be performed through the Auth0 UI, which we do not control. They have been tested on 2021-11-02. It is possible Auth0 has updated their UI since then in ways that invalidate parts of the instructions here; if you notice any discrepancy, please report it on the forum.
Authentication v. Authorization¶
In a complete Daml system, the Daml components only concern themselves with authorization: requests are accompanied by a (signed) token that claims a number of rights (such as the right to act as a given party). The Daml system will check the signature of the token, but will not perform any further verification of the claims themselves.
On the other side of the fence, the authentication system needs to verify a client’s identity and, based on the result, provide them with an appropriate token. It also needs to record the mapping of client identity to Daml party (or parties), such that the same external identity keeps mapping to the same on-ledger party over time.
Note that we need bidirectional communication between the Daml driver and the authentication system: the authentication system needs to contact the Daml driver to allocate new parties when a new user logs in, and the Daml driver needs to contact the authentication system to fetch the public key used to verify token signatures.
In the context of this section, the authentication system is Auth0. For more information on the Daml side, see the Authorization page.
Prerequisites¶
In order to follow along this guide, you will need:
• An Auth0 tenant. See Auth0 documentation for how to create one if you don’t have one already. You should get a free, dev-only one when you create an Auth0 account.
• A DNS (or IP address) that Auth0 can reach, and on which you (will) run a JSON API instance. This will be used to create parties. Auth0 uses a known set of IP addresses that depends on the location you chose for your tenant, so if your application is not meant to be public you can use network rules to only let requests from these IPs through.
• To know the ledgerId your ledger self-identifies as. Refer to your specific driver’s documentation for how to set the ledgerId value.
• To be running SDK 1.17.0 or later. Before 1.17.0, the JSON API required an extra token, the setup of which is not covered here. If you are somehow unable to upgrade but still want to use Auth0, please contact us for assistance.
• An application you want to deploy on your Daml system. This is not, strictly speaking, required, but the whole experience is going to be a lot less satisfying if you don’t end up with something actually running on your Daml system. In this guide, we’ll use the create-daml-app template, which as of Daml SDK 1.17.0 supports Auth0 out-of-the-box on its UI side.
Generating Party Allocation Credentials¶
Since Auth0 will be in charge of requesting the allocation of parties, the first logical step is to make it generate a token that can be used to allocate parties. This may seem recursive at first, but the token used to allocate parties only needs to have the admin field set to true; it does not require any preexisting party and does not need any actAs or readAs privileges.
In Auth0 concepts, we first need to register an API. To do so, from the Auth0 Dashboard, open up the Applications -> APIs page from the menu on the left and click Create API in the top right.
You can choose any name for the API; for the purposes of this document, we’ll assume this API is named API_NAME. The other parameters, however, are not free to set: the API identifier has to be https://daml.com/ledger-api, and the signing algorithm has to be RS256 (which should be selected by default). Creating the API should automatically create a Machine-to-Machine application “API_NAME (Test Application)”, which we will be using to generate our tokens. You can change its name to a more appropriate one; for the remainder of this document, we will assume it is called ADMIN_TOKEN_APP.
Navigate to that application’s settings page (menu on the left: Applications > Applications page, then click on the application’s name). This is where you can rename the application and find out about its Client ID and Client Secret, which we’ll need later on.
Now that we have an API and an application, we can generate a token with the appropriate claims. In order to do that, we need to make an Auth0 Action.
In the menu on the left, navigate to Actions > Library, then click on Build Custom in the top right. You can choose an appropriate name for your action; we’ll call it ADMIN_TOKEN_ACTION. Set the Trigger field to “M2M/Client-Credentials”, and leave the version of Node to the recommended one. (These instructions have been tested with Node 16.)
This will open a text editor where you can add JavaScript code that will trigger on M2M (machine to machine) connections. Replace the entire text box content with:
exports.onExecuteCredentialsExchange = async (event, api) => {
api.accessToken.setCustomClaim(
"https://daml.com/ledger-api",
{
"ledgerId": "%%LEDGER_ID%%",
"participantId": null,
"applicationId": "party-creation",
"actAs": []
}
);
}
};
You need to replace %%ADMIN_TOKEN_ID%% with the Client ID of the ADMIN_TOKEN_APP application, and %%LEDGER_ID%% with your actual ledgerId value. You can freely choose the applicationId value, and should set an appropriate participantId if your Daml driver requires it.
You then need to click on Deploy in the top right to save this Action. Despite the text on the button, this does not (yet) deploy it anywhere.
In order to actually deploy it, we need to make that Action part of a Flow. In the menu on the left, navigate through Actions > Flows, then choose Machine to Machine. Drag the “ADMIN_TOKEN_ACTION” (in the “Custom” tab) box on the right in-between the “Start” and “Complete” black circles in the middle. Click Apply. Now your Action is “deployed” and, should you modify it, clicking on the Deploy button would directly affect your live setup.
At this point you should be able to verify, using the curl command from the “Quick Start” tab of the M2M application, that you get a token. You should also be able to check that the token has the expected claims. You can do that by piping the result of the curl command through:
cat curl-result.json | jq -r '.access_token' | sed 's/.*\.$$.*$$\..*/\1/' | base64 -d
JWKS Endpoint¶
In order to verify the tokens it receives, the Daml driver needs to know the public key that matches the secret key used to sign them. Daml drivers use a standard protocol for that called JWKS; in practice, this means giving the Daml driver an HTTP URL it can query to get the keys. In the case of Auth0, that URL is located at /.well-known/jwks.json on the tenant.
https://%%AUTH0_DOMAIN%%/.well-known/jwks.json
You can find the value for %%AUTH0_DOMAIN%% in the Domain field of the settings page for the ADMIN_TOKEN_APP application (or any other application on the same tenant).
Dynamic Party Allocation¶
At this point, we can generate an admin token, and the Daml driver can check its signature and thus accept it. The next step is to actually allocate parties when people connect for the first time.
First, we need to create a new application, of type “Single Page Web Applications”. We’ll be calling it LOGIN_APP. Open up the Settings tab and scroll down to “Allowed Callback URLs”. There, add your application’s origin (scheme, domain or IP, and port) to all three of Allowed Callback URLs, Allowed Logout URLs and Allowed Web Origins. Scroll all the way down and click “Save Changes”.
Create a new Action (left menu > Actions > Library, top-right Build Custom button). As usual, you can choose the name; we’ll call it LOGIN_ACTION. Its type should be “Login / Post Login”.
Replace the default code with the following JavaScript:
const axios = require('axios');
// only required if JSON API is behind self-signed cert
// const https = require('https');
exports.onExecutePostLogin = async (event, api) => {
async function getParty() {
} else {
const tokenResponse = await axios.request({
"method": "post",
"data": {
"audience": "https://daml.com/ledger-api",
"grant_type": "client_credentials"
},
"Content-Type": "application/json",
"Accept": "application/json"
}
});
const token = tokenResponse.data.access_token;
const partyResponse = await axios.request({
"url": "%%ORIGIN%%/v1/parties/allocate",
"method": "post",
"Content-Type": "application/json",
"Accept": "application/json",
"Authorization": "Bearer " + token
},
"data": {}
// only required if JSON API is behind self-signed cert
//, httpsAgent: new https.Agent({ rejectUnauthorized: false })
});
const party = partyResponse.data.result.identifier;
// optional one-time setup like creating contracts etc. here
return party;
}
};
function setToken(party, actAs = [party], readAs = [party], applicationId = event.client.name) {
api.idToken.setCustomClaim("https://daml.com/ledger-api", party);
api.accessToken.setCustomClaim(
"https://daml.com/ledger-api",
{
"ledgerId": "%%LEDGER_ID%%",
"participantId": null,
"applicationId": applicationId,
"actAs": actAs,
});
};
const party = await getParty();
setToken(party);
}
};
where you need to replace %%LOGIN_ID%% with the Client ID of the LOGIN_APP application; %%ADMIN_TOKEN_URL%%, %%ADMIN_TOKEN_ID%% and %%ADMIN_TOKEN_SECRET%% with, respectively, the URL, client_id and client_secret values that you can find on the curl example from the Quick Start of the ADMIN_TOKEN_APP application; %%ORIGIN%% by the domain (or IP address) and port where Auth0 can reach your JSON API instance; and %%LEDGER_ID%% by the ledgerId you’re passing into your Daml driver.
Before we can click on Deploy to save (but not deploy) this snippet, we need to do one more thing. This snippet is using a library called axios to make HTTP calls; we need to tell Auth0 about that, so it can provision the library at runtime.
To do that, click on the little box icon to the left of code editor, then on the button Add Module that just got revealed, and type in axios for the name and 0.21.1 for the version. Then, click the Create button, and then the Deploy button.
Now you need to go to Actions > Flows, choose the Login flow, and drag the LOGIN_ACTION action in-between the two black circles Start and Complete.
Click Apply. You now have a working Auth0 system that automatically allocates new parties upon first login, and remembers the mapping for future logins (that happens by setting the party in the “app metadata”, which Auth0 persists).
Note
If you are hosting your JSON API instance behind a self-signed certificate (Auth0 absolutely requires TLS, but can be made to work with a self-signed cert), you’ll need to uncomment the https import and the httpsAgent line above. The https module does not require extra setup (unlike the axios one).
Token Refresh for Trigger Service¶
If you want your users to be able to run triggers, you can run an instance of the Trigger Service and expose it through the same HTTP URL. Because the Trigger Service (via the Auth Middleware) will need “refreshable” tokens, though, we need a bit of extra setup for that to work.
The first step on that front is to actually allow our tokens to be refreshed. Go to the settings tab of the API_NAME API (menu on the left > Applications > API > API_NAME) and scroll down. Towards the bottom of the page there should be a “Allow Offline Access” toggle, which is off by default. Turn it on, and save.
Next, we need to create a second “Machine-to-Machine Application”, which we’ll call OAUTH_APP, to register the OAuth2 Middleware which will refresh tokens for the Trigger service. When creating such an application, you’ll be asked for its authorized APIs; select API_NAME. Once the application is created, go to its settings tab and add %%ORIGIN%%/auth/cb as a callback URL.
You also need to scroll all the way down to the Advanced Settings section, open the Grant Types tab, and enable “Authorization Code”. Don’t forget to save your changes.
Finally, we need to extend our LOGIN_ACTION to respond to requests from the OAuth2 Middleware. Navigate back to the Action code (left menu > Actions > Library > Custom > click on LOGIN_ACTION) and add a second branch to the main if (new code starting on the line with CHANGES START HERE; everything before that should remain unchanged).
const axios = require('axios');
// only required if JSON API is behind self-signed cert
// const https = require('https');
exports.onExecutePostLogin = async (event, api) => {
async function getParty() {
// unchanged
};
function setToken(party, actAs = [party], readAs = [party], applicationId = event.client.name) {
// unchanged
};
const party = await getParty();
setToken(party);
// CHANGES START HERE
} else if (event.client.client_id === "%%OAUTH_ID%%") {
const party = await getParty();
const actAs = [];
let appId = undefined;
event.transaction.requested_scopes.forEach(s => {
api.access.deny("Current user is not authorized for admin token.");
} else {
}
} else if (s.startsWith("actAs:")) {
const requested_act = s.slice(6);
if (requested_act === party) {
actAs.push(requested_act);
} else {
api.access.deny("Requested unauthorized actAs: " + requested_act)
}
} else if (s.startsWith("applicationId:")) {
appId = s.slice(14);
}
});
}
};
Where %%OAUTH_ID%% is the Client ID of the OAUTH_APP. The OAuth2 Middleware will send a request with a number of requested scopes; the above code shows how to walk through them as well as a simple approach to handling them. You can change this code to fit your application’s requirements.
Don’t forget to click on Deploy to save your changes. This time, as the Action is already part of a Flow, clicking the Deploy button really deploys the Action and there is no further action needed.
You may have an application already. In that case, use that. For the purposes of illustration, here we’re going to work with a modified version of create-daml-app.
daml new --template=gsg-trigger my-project
If your app was based on the create-daml-app template using a Daml SDK version prior to 1.17.0, you may need to adapt your ui/src/config.ts and ui/src/components/LoginScreen.tsx files. See this commit for guidance.
The next step is to build the Daml code:
cd my-project
daml build
daml codegen js .daml/dist/my-project-0.1.0.dar -o ui/daml.js
Next, we’ll build our frontend code, but first we’re going to make a small change to let us demonstrate interactions with the Trigger Service.
We’ll need the package ID of the main DAR for the next step, so first collect it by running:
daml damlc inspect .daml/dist/my-project-0.1.0.dar | head -1
from the root of the project. In the following, we’ll refer to it as %%PACKAGE_ID%%.
Open up ui/src/components/MainView.tsx and add the Button component to the existing imports from semantic-ui-react:
import { Container, Grid, Header, Icon, Segment, Divider, Button } from 'semantic-ui-react';
Scroll down a little bit, and add the following code after the USERS_END tag (around line 18):
const trig = (url: string, req: object) => async () => {
const resp = await fetch(url, req);
if (resp.status === 401) {
const challenge = await resp.json();
console.log(Unauthorized ${JSON.stringify(challenge)}); var loginUrl = new URL(challenge.login); loginUrl.searchParams.append("redirect_uri", window.location.href); window.location.replace(loginUrl.href); } else { const body = await resp.text(); console.log((${resp.status}) ${body}); } } const list = trig("/trigger/v1/triggers?party=" + username, {}); const start = trig("/trigger/v1/triggers", { method: "POST", body: JSON.stringify({ triggerName: "%%PACKAGE_ID%%:ChatBot:autoReply", party: username, applicationId: "frontend" }), headers: { 'Content-Type': 'application/json' }}); where %%PACKAGE_ID%% is the package ID of the main DAR file, as explained above. Finally, scroll down to the end of the Grid.Column tag, and add: // ... </Segment> <Segment> <Button primary fluid onClick={list}>List triggers</Button> <Button primary fluid onClick={start}>Start autoReply</Button> </Segment> </Grid.Column> Now, build your frontend with (starting at the root): cd ui npm install REACT_APP_AUTH=auth0 \ REACT_APP_AUTH0_DOMAIN=%%AUTH0_DOMAIN%% \ REACT_APP_AUTH0_CLIENT_ID=%%LOGIN_ID%% \ npm run-script build As before, %%AUTH0_DOMAIN%% and %%LOGIN_ID%% need to be replaced. Now, we need to expose the JSON API and our static files. We’ll use nginx for that, but you can use any HTTP server you (and your security team) are comfortable with, as long as it can serve static files and proxy some paths. First, create a file nginx/nginx.conf.sh with the following content next to your app folder, i.e. in our example nginx is a sibling to my-project. #!/usr/bin/env bash set -euo pipefail openssl req -x509 \ -newkey rsa:4096 \ -keyout /etc/ssl/private/nginx-selfsigned.key \ -out /etc/ssl/certs/nginx-selfsigned.crt \ -days 365 \ -nodes \ -subj "/C=US/ST=Oregon/L=Portland/O=Company Name/OU=Org/CN=${FRONTEND_IP}"
openssl dhparam -out /etc/ssl/certs/dhparam.pem 2048
cat <<NGINX_CONFIG > /etc/nginx/nginx.conf
worker_processes auto;
pid /run/nginx.pid;
events {
worker_connections 768;
}
http {
sendfile on;
tcp_nopush on;
tcp_nodelay on;
keepalive_timeout 65;
types_hash_max_size 2048;
include /etc/nginx/mime.types;
default_type application/octet-stream;
access_log /var/log/nginx/access.log;
error_log /var/log/nginx/error.log;
gzip on;
ssl_certificate /etc/ssl/certs/nginx-selfsigned.crt;
ssl_certificate_key /etc/ssl/private/nginx-selfsigned.key;
ssl_protocols TLSv1 TLSv1.1 TLSv1.2;
ssl_prefer_server_ciphers on;
ssl_ciphers "EECDH+AESGCM:EDH+AESGCM:AES256+EECDH:AES256+EDH";
ssl_ecdh_curve secp384r1;
ssl_session_cache shared:SSL:10m;
ssl_session_tickets off;
ssl_stapling on;
ssl_stapling_verify on;
resolver 8.8.8.8 8.8.4.4 valid=300s;
resolver_timeout 5s;
ssl_dhparam /etc/ssl/certs/dhparam.pem;
server {
listen 80;
return 302 https://${FRONTEND_IP}\$request_uri;
}
server {
listen 443 ssl http2;
location /v1/stream {
proxy_pass http://${JSON_IP}; proxy_http_version 1.1; proxy_set_header Upgrade \$http_upgrade;
proxy_set_header X-Forwarded-For \$proxy_add_x_forwarded_for; } location /v1 { proxy_pass http://${JSON_IP};
proxy_set_header X-Forwarded-For \$proxy_add_x_forwarded_for; } location /auth/ { proxy_pass http://${AUTH_IP}/;
proxy_set_header X-Forwarded-For \$proxy_add_x_forwarded_for; } location /trigger/ { proxy_pass http://${TRIGGER_IP}/;
proxy_set_header X-Forwarded-For \$proxy_add_x_forwarded_for; } root /app/ui; index index.html; location / { # for development, uncomment proxy_pass and comment the try_files line #proxy_pass http://localhost:3000/; try_files \$uri \$uri/ =404; } } } NGINX_CONFIG Next, create a file nginx/Dockerfile with this content: FROM nginx:1.21.0 COPY build /app/ui COPY nginx.conf.sh /app/nginx.conf.sh RUN chmod +x /app/nginx.conf.sh CMD /app/nginx.conf.sh && exec nginx -g 'daemon off;' Finally, we can build the Docker container with the following, starting in the folder that contains both nginx and my-project: cp -r my-project/ui/build nginx/build cd nginx docker build -t frontend . And that’s it for building the application. We now have a DAR file that is ready to be deployed to a ledger, as well as a Docker container ready to serve our frontend. All we need now is to get a Daml system up and running. We document two paths forward here: one that relies on the Helm chart included in Daml Enterprise, and a manual setup using only the Open Source SDK. Using the Daml Helm Chart¶ For simplicity, we assume that you have access to a server with a public IP address that both you and Auth0 can reach. Furthermore, we assume that you have access to Daml Enterprise credentials to download the Docker images. We also assume you can create a local cluster with minikube on the remote machine. Finally, we assume that you have downloaded the Helm chart in a folder called daml-connect. First, start a new cluster: minikube start Next, load up your credentials as explained in the Daml Helm Chart section. We assume they are loaded under the secret named daml-docker-credentials. Create a file called values.yaml with the following content: imagePullSecret: daml-docker-credentials authUrl: "https://%%AUTH0_DOMAIN%%/.well-known/jwks.json" oauthMiddleware: create: true oauthAuth: "https://%%AUTH0_DOMAIN%%/authorize" oauthToken: "https://%%AUTH0_DOMAIN%%/oauth/token" callback: "https://%%DOMAIN%%/auth/cb" clientId: "%%OAUTH_ID%%" clientSecret: "%%OAUTH_SECRET%%" triggerService: create: true authExternal: "https://%%DOMAIN%%/auth" authCallback: "https://%%DOMAIN%%/trigger/cb" where, as before: • %%AUTH0_DOMAIN%% is the domain of your Auth0 tenant, displayed as the “Domain” property of any app within the tenant. • %%DOMAIN%% is the domain on which your frontend will be exposed, and in particular here the domain to which Auth0 needs to redirect after the OAuth handshake. • %%OAUTH_ID%% is, as before, the OAUTH_APP application’s Client ID. • %%OAUTH_SECRET is the same application’s Client Secret. Assuming that you have your Artifactory credentials in the environment variables ARTIFACTORY_USERNAME (user name) and ARTIFACTORY_PASSWORD (API key), you can add the Helm repository with: helm repo add daml \ https://digitalasset.jfrog.io/artifactory/connect-helm-chart \ --username$ARTIFACTORY_USERNAME \
--password $ARTIFACTORY_PASSWORD And now, you can deploy your cluster: helm install dm daml/daml-connect --devel --values values.yaml which will start the demo, non-production mode of the Helm chart. You can now start your application with: PROXY="$(minikube ip):$(kubectl get svc dm-daml-connect-reverse-proxy --output=json | jq '.spec.ports[0].nodePort')" docker run -e JSON_IP=$PROXY \
-e AUTH_IP=$PROXY/auth \ -e TRIGGER_IP=$PROXY/trigger \
-e FRONTEND_IP=$DOMAIN \ --network=host \ frontend where $DOMAIN is assumed to be an environment variable set to the public domain on which your server is exposed. And voilà! Your application is up and running. You should be able to log in with Auth0, exchange messages, and set up an auto-reply trigger, all by connecting your browser to https://$DOMAIN/. Manually Setting Up the Daml Components¶ For simplicity, we assume that all of the Daml components will run on a single machine (they can find each other on localhost) and that this machine has either a public IP or a public DNS that Auth0 can reach (hereafter assumed to be set as the DOMAIN env var). Furthermore, we assume that IP/DNS is what you’ve configured as the callback URL in the Auth0 configuration above. Finally, we assume that you can SSH into that machine and run daml and docker commands on it. The rest of this section happens on that remote server. First, we need to start the Daml driver. For this example we’ll use the sandbox, but with --implicit-party-allocation false it should behave like a production ledger (minus persistence). daml sandbox --ledgerid %%LEDGER_ID%% \ --auth-jwt-rs256-jwks https://%%AUTH0_DOMAIN%%/.well-known/jwks.json \ --implicit-party-allocation false \ --dar .daml/dist/my-project-0.1.0.dar As before, you need to replace %%LEDGER_ID%% with a value of your choosing (the same one you used when configuring Auth0), and %%AUTH0_DOMAIN%% with your Auth0 domain, which you can find as the Domain field at the top of the Settings tab for any app in the tenant. Next, you need to start a JSON API instance. cd my-project daml json-api --ledger-port 6865 \ --ledger-host localhost \ --http-port 4000 If you are using a Daml SDK version prior to 1.17.0, you’ll need to find a way to supply the JSON API with a valid, refreshing token file. We recommend upgrading to 1.17.0 or later. Then, we want to start the Trigger Service and OAuth2 middleware, which we will put respectively under /trigger and /auth. First, the middleware: DAML_CLIENT_ID=%%OAUTH_APP_ID%% \ DAML_CLIENT_SECRET=%%OAUTH_APP_SECRET%% \ daml oauth2-middleware \ --address localhost \ --http-port 5000 \ --oauth-auth "https://%%AUTH0_DOMAIN%%/authorize" \ --oauth-token "https://%%AUTH0_DOMAIN%%/oauth/token" \ --auth-jwt-rs256-jwks "https://%%AUTH0_DOMAIN%%/.well-known/jwks.json" \ --callback %%ORIGIN%%/auth/cb where, as before, you need to replace: • %%OAUTH_APP_ID%% with the Client ID value you can find at the top of the settings tab for the OAUTH_APP we just created. • %%OAUTH_APP_SECRET%% with the Client Secret value you can find at the top of the settings tab for the OAUTH_APP we just created. • %%AUTH0_DOMAIN%% with your tenant domain. • %%ORIGIN%% with the full domain-name-or-ip & port, including scheme, under which you expose your server. Now, the trigger service: daml trigger-service \ --address localhost \ --http-port 6000 \ --ledger-host localhost \ --ledger-port 6865 \ --auth-internal http://localhost:5000 \ --auth-external %%ORIGIN%%/auth \ --auth-callback %%ORIGIN%%/trigger/cb \ --dar .daml/dist/my-project-0.1.0.dar where %%ORIGIN%% is, as per the Auth0 configuration, https://$DOMAIN.
And that’s all the Daml components. You can now start your frontend application with:
docker run -e JSON_IP=localhost:4000 \
-e AUTH_IP=localhost:5000 \
-e TRIGGER_IP=localhost:6000 \
-e FRONTEND_IP=\$DOMAIN \
--network=host frontend
This runs a “production build” of your frontend code. If instead you want to develop frontend code against the rest of this setup, you can uncomment the last proxy_pass directive in nginx.conf.sh, comment the try_files line after it, and start a reloading development server with:
cd ui
npm install
REACT_APP_AUTH=auth0 \
REACT_APP_AUTH0_DOMAIN=%%AUTH0_DOMAIN%% \
|
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|
https://docs.idmod.org/projects/emod-hiv/en/2.20_a/model-vaccination.html
|
# Vaccination and herd immunity¶
In a basic compartmental model, we often assume all individuals are susceptible before the importation of an outbreak. However, vaccination is the one of the most effective ways to prevent or contain a disease outbreak.
Starting from the traditional SIR equation:
\begin{split}\begin{aligned} \frac{dS}{dt} & = -\frac{\beta SI}{N}\\ \frac{dI}{dt} & = \frac{\beta SI}{N} - \gamma I\\ \frac{dR}{dt} & = \gamma I \end{aligned}\end{split}
For an outbreak to start, the following condition needs to be satisfied:
$\frac{dI}{dt} = \frac{\beta SI}{N} - \gamma I > 0$
If a vaccination campaign with coverage p $$\in$$ [0, 1] is performed before the outbreak, only a fraction of susceptible people move to the recovered compartment. If the vaccine take is e $$\in$$ [0, 1], representing the probability of being protected after receiving a vaccine dose, the fraction of immune people due to vaccination is ep. Therefore, the previous condition can be reduced to:
\begin{split}\begin{aligned} \left(\beta (1 - e p) - \gamma\right) I & > 0\\ R_0 (1 - e p) & > 1\\ R_{eff} & > 1 \end{aligned}\end{split}
Reff is also called the effective reproductive number. Vaccination can reduce the disease’s ability to spread, and the outbreak can be prevented or stopped with less than 100% coverage. When Reff= 1, there exists a minimum vaccination coverage that can prevent a disease outbreak. This minimum coverage required to prevent an outbreak is usually called herd immunity (represented as Pherd). Therefore, the analytical form of Pherd can be derived based on the previous condition:
$p_{herd} = \frac{1}{e}\left(1-\frac{1}{R_0}\right)$
## Multiple rounds of vaccinations¶
If multiple vaccine interventions are performed in the same area, people are selected on a binomial basis and all individuals have the same probability of being included. If the vaccine coverage is p, every individual has a probability p of being selected in a given round. After the first round, the fraction of non-vaccinated is 1-p, and after n rounds this fraction is (1 - p)n. Therefore, the fraction of people getting at least 1 dose is:
$1-(1-p)^n$
For example, the fraction of people getting at least one vaccination with a 50% campaign coverage is shown in the following table. After a few rounds, the coverage increases significantly with the number of campaigns.
Number of campaigns
Covered percentage (>=1 dose)
1
50%
2
75%
3
87.5%
4
93.75%
5
96.875%
The following graphs show a baseline SIR outbreak and then the effect of a vaccination campaign distributed to the entire population. The vaccination campaign is repeated three times, seven days apart. The vaccine has 100% take and 50% demographic coverage. With this configuration, the fraction of immune people is above herd immunity and the outbreak does not spread.
Figure 1: Baseline SIR outbreak
Figure 2: Broad vaccination campaign achieving herd immunity
However, this is usually not the case. In recent polio eradication campaigns, the number of supplemental immunization activity (SIA) campaigns planned in certain high-risk districts is greater than 6 per year, but poliovirus still persists in the area due to certain groups that are chronically missed. This can be caused by low accessibility, exclusion from SIA microplans, or vaccine refusal. Reff has not been driven below 1 because these susceptible people in the chronically missed groups are still in contact with the rest of population. In some modeling simulations, this assumption has to be included.
In this second example, the same 50% campaign coverage is repeated so that the same amount of vaccine is used. However, 30% of the population is not accessible to any vaccine campaigns. Although the number of vaccine doses used is the same as the previous example, the overall coverage is much lower. Creating campaigns that target interventions is described in more detail in Targeting interventions to nodes or individuals.
Number of campaigns
Covered percentage of total population
Covered percentage of groups with access
Covered percentage of groups without access
1
50%
71.43%
0%
2
29%
91.84%
0%
3
68.37%
97.67%
0%
4
69.53%
99.33%
0%
5
69.87%
99.81%
0%
The following graph shows the same SIR outbreak when 30% of the population is chronically missed by the vaccination campaign, allowing the outbreak to persist.
Figure 3: Vaccination campaign that misses 30% of the population
|
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|
http://www.cjmenet.com.cn/CN/Y2011/V47/I24/177
|
• CN：11-2187/TH
• ISSN：0577-6686
›› 2011, Vol. 47 ›› Issue (24): 177-185.
• 论文 •
强冲击条件下MEMS封装可靠性有限元分析
1. 北京航空航天大学可靠性与系统工程学院
• 发布日期:2011-12-20
Finite Element Analysis of MEMS Package under High Impact
CUI Jiuzheng;SUN Bo;FENG Qiang
1. School of Reliability and Systems Engineering, Beihang University
• Published:2011-12-20
Abstract: Under high-g (104g or above, g is the acceleration of gravity) impact load conditions, onboard micro electro-mechanical system (MEMS) (such as gyroscopes or accelerometer) and electronics package and interconnection are critical concern that influence the reliability of total projectile. A research on this problem is conducted to reveal the influencing factors and assess package reliability using finite element modeling and simulation method. A finite element modeling (FEM) dynamic analysis is conducted on a typical leadless chip carrier (LCC) package. In order to be closer to the engineering practice, the bilinear kinematic hardening model is chosen for the solder joints. Several sensitive factors that influence the reliability of solder joint are analyzed in detail, and several suggestions are given to improve the reliability of MEMS package.
|
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|
https://proceedings.neurips.cc/paper/2019/file/3a0844cee4fcf57de0c71e9ad3035478-MetaReview.html
|
NeurIPS 2019
Sun Dec 8th through Sat the 14th, 2019 at Vancouver Convention Center
This paper proposes extending temporal matrix factorization to incorporate neural network regularization for time series forecasting. The intuition is to capture global and local structure to make forecasts. The work is interesting because it bridges more classical forecasting ideas with new state of the art deep learning approaches. The ideas presented in this paper seem novel as the authors take existing building blocks for deep learning and combine them in a creative way to capture interesting structure of time series. This is in contrast to simply applying an existing deep learning approach such as seq2seq. There were some criticisms of the experimental evaluation which the authors seem to have addressed in their response and will include new comparisons that the reviewers asked for. The outstanding concern is in regards to understanding what each component of the proposed model is contributing to the increased performance as the current experiments do not elucidate this. However, I think that the ideas presented in this paper are very interesting and that the improved forecasting abilities of the model are good enough for publication now with a deeper understanding being followup work.
|
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|
http://gmatclub.com/forum/how-many-five-digit-numbers-can-be-formed-using-digits-91597.html?kudos=1
|
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# How many five-digit numbers can be formed using digits
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How many five digit numbers can be formed using digits 0,1,2,3,4,5, Which are divisible by 3, whithout any of the digits repeating?
A. 15
B. 96
C. 120
D. 181
E. 216
[Reveal] Spoiler: OA
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TheRob wrote:
How many five digit numbers can be formed using digits 0,1,2,3,4,5, Which are divisible by 3, whithout any of the digits repeating?
A. 15
B. 96
C. 120
D. 181
E. 216
First step:
We should determine which 5 digits from given 6, would form the 5 digit number divisible by 3.
We have six digits: 0,1,2,3,4,5. Their sum=15.
For a number to be divisible by 3 the sum of the digits must be divisible by 3. As the sum of the six given numbers is 15 (divisible by 3) only 5 digits good to form our 5 digit number would be 15-0={1, 2, 3, 4, 5} and 15-3={0, 1, 2, 4, 5}. Meaning that no other 5 from given six will total the number divisible by 3.
Second step:
We have two set of numbers:
{1, 2, 3, 4, 5} and {0, 1, 2, 4, 5}. How many 5 digit numbers can be formed using this two sets:
{1, 2, 3, 4, 5} --> 5! as any combination of these digits would give us 5 digit number divisible by 3. 5!=120.
{0, 1, 2, 4, 5} --> here we can not use 0 as the first digit, otherwise number won't be any more 5 digit and become 4 digit. So, total combinations 5!, minus combinations with 0 as the first digit (combination of 4) 4! --> 5!-4!=96
120+96=216
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06 Jan 2012, 07:48
3
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A number is divisible by 3 if sum of its digits is a multiple of 3.
With the given set of digits, there are two possible combinations of 5 digits each-
A. [1,2,3,4,5] No. of possible 5 digit numbers: 5!= 120
B. [0,1,2,4,5] No. of possible 5 digit numbers: 4*4!=96 [the number can't start with a 0]
A+B= 120+96= 216
E
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Last edited by blink005 on 06 Jan 2012, 09:27, edited 1 time in total.
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26 Oct 2009, 06:21
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Only 2 sets are possible
case (1) 1,2,3,4,5
case (2) 0,1,2,4,5.
case (1) : there will 5! ways to form the number = 120
case (2) ; there will 4*4*3*2*1 = 96 ways
So total no.of ways = 120+96 = 216 ways
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29 Apr 2010, 23:51
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By the property of divisibility by 3 i.e "a no: is divisible by 3, if the sum of the digits is divisible by 3"(e.g= 12-->1+2=3)
so from 0,1,2,3,4,5 the set of 5 digit no:s that can be formed which is divisible by 3 are 0,1,2,4,5(sum=12) & 1,2,3,4,5(sum=15)
from first set(0,1,2,4,5) no:s formed are 96 i.e first digit can be formed from any 4 no: except 0, second digit from 4 no: except digit used at first place,3rd from rest 3 , 4th from rest 2 no: and in fifth remaining digit since no repetition allowed.
from second set(1,2,3,4,5) no:s formed are 120 i.e first digit can be formed from any 5 digits, second digit from 4 no: except digit used at first place,3rd from rest 3 , 4th from rest 2 no: and in fifth remaining digit since no repetition allowed.
so total 120+96=216
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06 Feb 2011, 15:18
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Expert's post
ajit257 wrote:
so lets say we were asked a multiple of 5 so in that case we would have to withdraw the digit 5 ..is that correct ?
5 or 0, as 0 is also a multiple of 5.
AGAIN: we have (sum of 6 digits)=(multiple of 3). Question what digit should we withdraw so that the sum of the remaining 5 digits remain a multiple of 3? Answer: the digit which is itself a multiple of 3.
Below might help to understand this concept better.
If integers $$a$$ and $$b$$ are both multiples of some integer $$k>1$$ (divisible by $$k$$), then their sum and difference will also be a multiple of $$k$$ (divisible by $$k$$):
Example: $$a=6$$ and $$b=9$$, both divisible by 3 ---> $$a+b=15$$ and $$a-b=-3$$, again both divisible by 3.
If out of integers $$a$$ and $$b$$ one is a multiple of some integer $$k>1$$ and another is not, then their sum and difference will NOT be a multiple of $$k$$ (divisible by $$k$$):
Example: $$a=6$$, divisible by 3 and $$b=5$$, not divisible by 3 ---> $$a+b=11$$ and $$a-b=1$$, neither is divisible by 3.
If integers $$a$$ and $$b$$ both are NOT multiples of some integer $$k>1$$ (divisible by $$k$$), then their sum and difference may or may not be a multiple of $$k$$ (divisible by $$k$$):
Example: $$a=5$$ and $$b=4$$, neither is divisible by 3 ---> $$a+b=9$$, is divisible by 3 and $$a-b=1$$, is not divisible by 3;
OR: $$a=6$$ and $$b=3$$, neither is divisible by 5 ---> $$a+b=9$$ and $$a-b=3$$, neither is divisible by 5;
OR: $$a=2$$ and $$b=2$$, neither is divisible by 4 ---> $$a+b=4$$ and $$a-b=0$$, both are divisible by 4.
Hope it's clear.
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07 Feb 2011, 04:39
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0,1,2,3,4,5
One digit will have to remain out for all 5 digit numbers;
if 0 is out; Leftover digits will be 1,2,3,4,5 = Sum(1,2,3,4,5)=15.
5! = 120 numbers
if 1 is out; Leftover digits will be 0,2,3,4,5 = Sum(0,2,3,4,5)=14. Ignore(Not divisible by 3)
if 3 is out; Leftover digits will be 0,1,2,4,5 = Sum(0,1,2,4,5)=12.
4*4! = 4*24 = 96
if 4 is out; Leftover digits will be 0,1,2,3,5 = Sum(0,1,2,3,5)=11. Ignore
if 5 is out; Leftover digits will be 0,1,2,3,4 = Sum(0,1,2,3,4)=10. Ignore
Total count of numbers divisible by 3 = 120+96 = 216
Ans: "E"
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Re: How many five-digit numbers can be formed using digits [#permalink]
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28 Dec 2012, 06:54
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TheRob wrote:
How many five digit numbers can be formed using digits 0,1,2,3,4,5, Which are divisible by 3, whithout any of the digits repeating?
A. 15
B. 96
C. 120
D. 181
E. 216
0 + 1 + 2 + 3 + 4 + 5 = 15
To form 5-digit number, we can remove a digit and the sum should still be divisible by 3.
15 - 1 = 14
15 - 2 = 13
15 - 3 = 12 BINGO!
15 - 4 = 11
15 - 5 = 10
Possible = {5,4,3,2,1} and {5,4,0,2,1}
There are 5! = 120 ways to arrange {5,4,3,2,1}
There are 5! - 5!/5 = 96 ways to arrange {5,4,0,2,1} since 0 cannot start the five number digit.
120 + 96 = 216
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Re: How many five-digit numbers can be formed using digits [#permalink]
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14 Jan 2013, 00:40
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I did in 1 min 18 sec.
At first I wanted to choose a set of five digits, but started to worry about the complications with the leading zero.
Then I thought that the last digits could always be chosen in only two ways so as to ensure divisibility by three - however, I quickly realized that I would not get all different digits.
Then I realized that once I get a number I can keep permuting the digits while still getting valid numbers.
In an attempt to avoid the leading zero I tried 12345 and noticed that it was divisible by 3. Thus, I've got 5!=120 answers and immediately eliminated two answers, A and B.
Then I addressed the case of a leading zero. Since I wanted to preserve divisibility by 3, I quickly saw that I could only use 0 instead of 3. Thus, the only other possible set was {0, 1, 2, 4, 5}. I tried adding another 5! and got 240, so the answer was slightly less than that.
After that I knew I had to subtract 4!=24 to account for all the possibilities with a leading zero, which left me with 240-24=216. This is how I do such problems...
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16 Jun 2014, 23:11
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Expert's post
ronr34 wrote:
I tried to do as follows:
take all 5 digit numbers possible : 5 *5*4*3*2
divide by 3 to get all numbers divisible by 3.
What is wrong with this logic?
We cannot do this because we have the asymmetric 0 as one of the digits. The number of 5 digit numbers that can be formed with 0, 1, 2, 3 and 4 is different from the number of 5 digit numbers that can be formed with 1, 2, 3, 4 and 5 (because 0 cannot be the first digit).
Had the digits been 1, 2, 3, 4, 5 and 6, then your method would have been correct.
If 0 is included:
{0, 1, 2, 3, 4} --> 96 5-digit numbers possible with this set.
{0, 1, 2, 3, 5} --> 96 5-digit numbers possible with this set.
{0, 1, 2, 4, 5} --> 96 5-digit numbers possible with this set. - All these numbers are divisible by 3
{0, 1, 3, 4, 5} --> 96 5-digit numbers possible with this set.
{0, 2, 3, 4, 5} --> 96 5-digit numbers possible with this set.
{1, 2, 3, 4, 5} --> 120 5-digit numbers possible with this set. - All these numbers are divisible by 3
The number of 5 digit numbers in these sets is not the same - Sets with 0 have fewer numbers
If 0 is not included:
{1, 2, 3, 4, 5} --> 120 5-digit numbers possible with this set.
{1, 2, 3, 4, 6} --> 120 5-digit numbers possible with this set.
{1, 2, 3, 5, 6} --> 120 5-digit numbers possible with this set. - All these numbers are divisible by 3
{1, 2, 4, 5, 6} --> 120 5-digit numbers possible with this set.
{1, 3, 4, 5, 6} --> 120 5-digit numbers possible with this set.
{2, 3, 4, 5, 6} --> 120 5-digit numbers possible with this set. - All these numbers are divisible by 3
Here exactly 1/3rd of the numbers will be divisible by 3.
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22 Oct 2009, 15:14
Thanks Bunuel for the great explanation . +1 Kudos...
Why don't I borrow your math brain for my GMAT LOL
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24 Oct 2009, 00:06
srini123 wrote:
Thanks Bunuel for the great explanation . +1 Kudos...
Why don't I borrow your math brain for my GMAT LOL
I have been thinking the same for quite some days!
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25 Oct 2009, 14:42
YOu're awesome Bunuel !!
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20 Mar 2010, 03:02
aramjung wrote:
How many five-digit numbers can be formed using the digits 0, 1, 2, 3, 4 and 5 which are divisible by 3, without repeating the digits?
(C) 2008 GMAT Club - m04#32
15
96
120
181
216
HOW DO YOU SOLVE THIS, I CAN'T UNDERSTAND IT
For a number to be divisible by 3 sum of its digits should be divisible by 3, so in 0,1,2,3,4,5 set of digits that can be together
1,2,3,4,5, and 0,1,2,4,5 (drop one digit at a time and sum rest of the others to find this )
in first set numbers that can be there = 5*4*3*2*1
in second set = 4*4*3*2*1 (since zero cannot be the last digit)
total = 5*4*3*2*1 + 4*4*3*2*1 = 4! * (5+4) = 24 * 9 = 216, hence 216 is the answer.
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thank you sooo much!!!!!!!!
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06 Feb 2011, 14:48
For a number to be divisible by 3 the sum of the digits must be divisible by 3. As the sum of the six given numbers is 15 (divisible by 3) only 5 digits good to form our 5 digit number would be 15-0={1, 2, 3, 4, 5} and 15-3={0, 1, 2, 4, 5}. Meaning that no other 5 from given six will total the number divisible by 3.
i understood the first part but did not get the second part 15-3={0, 1, 2, 4, 5}. Meaning that no other 5 from given six will total the number divisible by 3. ..Could you please explain it in a little bit more detail. Thanks
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06 Feb 2011, 14:55
Expert's post
ajit257 wrote:
For a number to be divisible by 3 the sum of the digits must be divisible by 3. As the sum of the six given numbers is 15 (divisible by 3) only 5 digits good to form our 5 digit number would be 15-0={1, 2, 3, 4, 5} and 15-3={0, 1, 2, 4, 5}. Meaning that no other 5 from given six will total the number divisible by 3.
i understood the first part but did not get the second part 15-3={0, 1, 2, 4, 5}. Meaning that no other 5 from given six will total the number divisible by 3. ..Could you please explain it in a little bit more detail. Thanks
The sum of the given digits is already a multiple of 3 (15), in order the sum of 5 digits to be a multiple of 3 you must withdraw a digit which is itself a multiple of 3, otherwise (multiple of 3) - (non-multiple of 3) = (non-multiple of 3).
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06 Feb 2011, 14:59
so lets say we were asked a multiple of 5 so in that case we would have to withdraw the digit 5 ..is that correct ?
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06 Feb 2011, 15:20
Bunuel...awesome ..thanks a ton!
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How many five digit numbers can be formed using digits 0,1,2,3,4 [#permalink]
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13 Nov 2012, 19:31
12345
and
01234
are the two set of numbers which are divisible by 3 when added.
12345->5.4.3.2.1 ways = 120
01234->4.4.3.2.1 ways = 96
Total 216
How many five digit numbers can be formed using digits 0,1,2,3,4 [#permalink] 13 Nov 2012, 19:31
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### [NTG-context] vertical bar spacing in Antykwa-Poltawskiego
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### Re: [NTG-context] vertical bar spacing in Antykwa-Poltawskiego
Am 23.07.2013 um 13:20 schrieb Alan Bowen [email protected]: I am using Antykwa-Poltawskiego to set a French text that includes ancient Greek. In the Greek text, there is a vertical bar (to mark the end of a column). The custom is to set the spacing about the bar so that (a) when
### Re: [NTG-context] vertical bar spacing in Antykwa-Poltawskiego
On 7/23/2013 1:32 PM, Wolfgang Schuster wrote: Am 23.07.2013 um 13:20 schrieb Alan Bowen [email protected]: I am using Antykwa-Poltawskiego to set a French text that includes ancient Greek. In the Greek text, there is a vertical bar (to mark the end of a column). The custom is to set
### Re: [NTG-context] vertical bar spacing in Antykwa-Poltawskiego
Wolfgang, Hans—many thanks to you both! Part of the problem was that i was using \| instead of \textbar. I now have: \setupbodyfont[antykwa-poltawskiego] \def\test {\ifnum\lastnodetype=\gluenodecode \| \else \textbar \fi} \setcharacterspacing[frenchpunctuation] \starttext
### Re: [NTG-context] vertical bar spacing in Antykwa-Poltawskiego
Am 23.07.2013 um 15:42 schrieb Alan Bowen [email protected]: Wolfgang, Hans—many thanks to you both! Part of the problem was that i was using \| instead of \textbar. I now have: \setupbodyfont[antykwa-poltawskiego] \def\test {\ifnum\lastnodetype=\gluenodecode \| \else
### Re: [NTG-context] vertical bar spacing in Antykwa-Poltawskiego
Thanks, Wolfgang. I will start experimenting. Alan On Tue, Jul 23, 2013 at 10:25 AM, Wolfgang Schuster [email protected] wrote: Am 23.07.2013 um 15:42 schrieb Alan Bowen [email protected]: Wolfgang, Hans—many thanks to you both! Part of the problem was that i was using
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John Culleton wrote: I use slackware linux 14, the 64 bit version. What is the proper code for opening quotes in context? Wolfgang Schuster wrote: Use “quoted word” or \quotation{quoted word}. Since you're using Linux: if you set your keyboard layout to `English (international AltGr dead
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Russell Urquhart [email protected] writes: On Sun, Jul 21, 2013 at 11:19:27PM -0700, David Rogers wrote: To summarize: A page header with page number and guide word (the guide word showing which chapter of which book of the Bible begins on this page), two columns of regular text,
### Re: [NTG-context] Can this layout be done in Context
On 7/23/2013 9:47 PM, David Rogers wrote: Russell Urquhart [email protected] writes: On Sun, Jul 21, 2013 at 11:19:27PM -0700, David Rogers wrote: To summarize: A page header with page number and guide word (the guide word showing which chapter of which book of the Bible begins on
### Re: [NTG-context] footnotes on wrong page
On 7/23/2013 9:22 PM, Alan Bowen wrote: What is the setting that forces ConTeXt to keep footnotes on the page where they are called? In the following example, \setupinteraction[state=start] \setupnotation[footnote][interaction=yes,way=bytext] \setupnotation[footnote][split=verystrict]
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# AP Calculus BC : Geometric Series
## Example Questions
### Example Question #1 : Series Of Constants
Consider: . Will the series converge or diverge? If converges, where does this coverge to?
Explanation:
This is a geometric series. Use the following formula, where is the first term of the series, and is the ratio that must be less than 1. If is greater than 1, the series diverges.
Rationalize the denominator.
### Example Question #2 : Series Of Constants
Consider the following summation: . Does this converge or diverge? If it converges, where does it approach?
Explanation:
The problem can be reconverted using a summation symbol, and it can be seen that this is geometric.
Since the ratio is less than 1, this series will converge. The formula for geometric series is:
where is the first term, and is the common ratio. Substitute these values and solve.
### Example Question #3 : Series Of Constants
A worm crawls up a wall during the day and slides down slowly during the night. The first day the worm crawls one meter up the wall. The first night the worm slides down a third of a meter. The second day the worm regains one third of the lost progress and slides down one third of that distance regained on the second night. This pattern of motion continues...
Which of the following is a geometric sum representing the distance the worm has travelled after 12-hour periods of motion? (Assuming day and night are both 12 hour periods).
Explanation:
The sum must be alternating, and after one period you should have the worm at 1m. After two periods, the worm should be at 2/3m. There is only one sum for which that is true.
### Example Question #1 : Geometric Series
Determine whether the following series converges or diverges. If it converges, what does it converge to?
Explanation:
First, we reduce the series into a simpler form.
We know this series converges because
By the Geometric Series Theorem, the sum of this series is given by
### Example Question #1 : Geometric Series
Calculate the sum of a geometric series with the following values:,,. Round the answer to the nearest integer.
Explanation:
This is a geometric series.
The sum of a geometric series can be calculated with the following formula,
, where n is the number of terms to sum up, r is the common ratio, and is the value of the first term.
For this question, we are given all of the information we need.
Solution:
Rounding,
### Example Question #6 : Series Of Constants
Calculate the sum, rounded to the nearest integer, of the first 16 terms of the following geometric series:
Explanation:
This is a geometric series.
The sum of a geometric series can be calculated with the following formula,
, where n is the number of terms to sum up, r is the common ratio, and is the value of the first term.
We have and n and we just need to find r before calculating the sum.
Solution:
### Example Question #7 : Series Of Constants
Calculate the sum of a geometric series with the following values:
,, ,
rounded to the nearest integer.
Explanation:
This is a geometric series.
The sum of a geometric series can be calculated with the following formula,
, where n is the number of terms to sum up, r is the common ratio, and is the value of the first term.
For this question, we are given all of the information we need.
Solution:
Rounding,
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https://asmedigitalcollection.asme.org/IDETC-CIE/proceedings-abstract/IDETC-CIE2004/46954/407/306455
|
This paper shows how the instantaneous invariants for time-independent motions can be obtained from time-dependent motions. Relationships are derived between those parameters that define a time-dependent motion and the parameters that define its geometrically equivalent time-independent motion. The time-independent formulations have the advantage of being simpler than the time dependent ones, and thereby lead to more elegant and parsimonious descriptions of motions properties. The paper starts with a review of the choice of canonical coordinate systems and instantaneous invariants for time-based spherical and spatial motions. It then shows how to convert these descriptions to time-independent motions with the same geometric trajectories. New equations are given that allow the computation of the geometric invariants from time-based invariants. The paper concludes with a detailed example of the third-order motion analysis of the trajectories of an open, spatial R-R chain.
This content is only available via PDF.
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https://www.atlantis-press.com/proceedings/isees-19/125914148
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# Assessment of Hydrocarbon State of Soil and Bottom Sediments of Arctic Zone of Yakuti
Authors
S.Kh. Lifshits, Yu.S. Glyaznetsova, O.N. Chalaya, I.N. Zueva, L.A. Erofeevskaya
Corresponding Author
S.Kh. Lifshits
Available Online August 2019.
DOI
https://doi.org/10.2991/isees-19.2019.15How to use a DOI?
Keywords
geochemical background; oil pollution; chloroform extract; bottom river and sea sediments; hydrocarbon oxidizing microorganisms; soil self-regeneration.
Abstract
The study of soil samples and bottom sediments from the Arctic region of the Sakha Republic (Yakutia) in the coastal zone of the East Siberian Sea (Nizhnekolymsky region) was conducted. The yield of chloroform extracts and the nature of the IR spectra were used to evaluate the hydrocarbon composition of the samples taken. The localized areas with high levels of pollution were identified. All of them were located within the territories of man-made objects. The remaining territories correspond to the background indicators or have insignificant traces of pollution. Following the results of microbiological studies the degree of enrichment with microorganisms of studied soil and bottom sediment samples belong to the category of poorly enriched. It was possible to identify hydrocarbon oxidizing microorganisms, which differ only by their poor qualitative and quantitative composition in some oil-contaminated samples. The low activity of hydrocarbon oxidizing microflora against poor soil enrichment with microorganisms indicates the sluggishly ongoing self-healing processes of soils of the Arctic region.
Open Access
TY - CONF
AU - S.Kh. Lifshits
AU - Yu.S. Glyaznetsova
AU - O.N. Chalaya
AU - I.N. Zueva
AU - L.A. Erofeevskaya
PY - 2019/08
DA - 2019/08
TI - Assessment of Hydrocarbon State of Soil and Bottom Sediments of Arctic Zone of Yakuti
BT - Proceedings of the International Symposium "Engineering and Earth Sciences: Applied and Fundamental Research" dedicated to the 85th anniversary of H.I. Ibragimov (ISEES 2019)
PB - Atlantis Press
SP - 755
EP - 759
SN - 2590-3217
UR - https://doi.org/10.2991/isees-19.2019.15
DO - https://doi.org/10.2991/isees-19.2019.15
ID - Lifshits2019/08
ER -
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|
http://tex.stackexchange.com/questions/16088/ledpar-ignores-startstanzahook-not-able-to-put-extra-space-between-stanzas
|
# ledpar ignores \startstanzahook (not able to put extra space between stanzas)
The ledmac/-par manual says that I may use \startstanzahook to get extra space between stanzas. But it works only in normal verses an not in parallel typsetting. The following example may give a better idea what I mean:
% XETEX-DOCUMENT
\documentclass{scrartcl}
\usepackage{xltxtra}
\usepackage{ledmac,ledpar}
\maxchunks{100}
\newcommand*{\startstanzahook}{\vspace{\baselineskip}}
\begin{document}
% works (vspace between stanzas):
\beginnumbering
\setstanzaindents{2,0,0}
\stanza
Non ego Caesareas, non arma virumque, &
sed chitaram plectrumque cano nec inutile numen
\&
\stanza
Doctus in Arcadiis vivebat musicus oris, &
clarus circa urbes et famae voce lyraeque.
\&
\endnumbering
% doesn't work (no vspace):
\begin{pages}
\begin{Leftside}
\beginnumbering
\setstanzaindents{2,0,0}
\stanza
Non ego Caesareas, non arma virumque, &
et lyricam poterit, nisi centum vocibus, artem?
\&
\stanza
Doctus in Arcadiis vivebat musicus oris, &
vicina quondam late celebratus in urbe
\&
\endnumbering
\end{Leftside}
\begin{Rightside}
\beginnumbering
\setstanzaindents{2,0,0}
\stanza
Non ego Caesareas, non arma virumque, &
et lyricam poterit, nisi centum vocibus, artem?
\&
\stanza
Doctus in Arcadiis vivebat musicus oris, &
vicina quondam late celebratus in urbe
\&
\endnumbering
\end{Rightside}
\Pages
\end{pages}
\end{document}
Is there any way to instert extra space between stanzas in parallel-mode?
-
The trick is to include the material to be inserted between the stanzas into a seperate \pstart ... \pend construct, otherwise it won't be processed by the delayed output routine of ledpar. So you'll have to replace
\newcommand*{\startstanzahook}{\vspace{\baselineskip}}
by
\def\endstanzaextra{\pstart\skipnumbering\strut\pend}
in order to add one extra line between the stanzas (with the \strut macro). Note that this hook triggers at the end of each stanza, not at the beginning. This is because the extra line is included in the line numbering by default - in order to avoid this, \skipnumbering is called, which is only possible at the end of the stanza.
-
Thank you very much! That works. I wonder why something like that isn’t mentioned in the manual—or did I overlook something? – Tobi Apr 19 '11 at 18:44
@Tobi Well, I found this solution with the help of example A.3 (p. 82-86) in the ledpar manual where \endstanzaextra is used in order to insert a dash between the stanzas. I fear, however, that you can only find it there if you're explicitly looking for it... It would be worth mentioning it directly, especially because the trouble with ledpar is that you never know which features of ledmac still work and which don't. – diabonas Apr 19 '11 at 18:59
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|
http://tex.stackexchange.com/questions/44693/polyline-shading-in-tikz?answertab=oldest
|
Is it possible to apply a shading effect on one side of a polyline in TikZ? I have the following simple code
\begin{tikzpicture}
\draw (1.06,9.56) -- (1.44,9.78) -- (1.78,9.56) -- (2.14,9.79) -- (2.48,9.29)
-- (2.83,9.79) -- (3.17,9.54) -- (3.54,9.76) -- (3.87,9.56);
\draw (1.06,8.94) -- (1.44,8.72) -- (1.78,8.93) -- (2.14,8.71) -- (2.48,9.21)
-- (2.83,8.72) -- (3.17,8.96) -- (3.54,8.74) -- (3.87,8.94);
\end{tikzpicture}
I want some shading above the upper line and below the lower line, as the lines represent air-solid boundaries and I need to convey this graphically.
-
I believe that a fill or shade requires a closed path up to some \MaxY and down to some \MinY so you can just create one. Below I used a macro to define the \TopPath and \BottomPath so that we can use it twice: Once to draw the line, then to specify the closed area.
\documentclass[border=2pt]{standalone}
\usepackage{tikz}
\begin{document}
\newcommand*{\MaxX}{3.87}%
\newcommand*{\MinX}{1.06}%
\newcommand*{\MaxY}{10.0}%
\newcommand*{\MinY}{8.50}%
\newcommand*{\TopPath}{(\MinX,9.56) -- (1.44,9.78) -- (1.78,9.56) -- (2.14,9.79) -- (2.48,9.29) -- (2.83,9.79) -- (3.17,9.54) -- (3.54,9.76) -- (\MaxX,9.56)}%
\newcommand*{\BottomPath}{(\MinX,8.94) -- (1.44,8.72) -- (1.78,8.93) -- (2.14,8.71) -- (2.48,9.21) -- (2.83,8.72) -- (3.17,8.96) -- (3.54,8.74) -- (\MaxX,8.94)}%
\begin{tikzpicture}
\shade [top color= white, bottom color=brown] \TopPath
-- (\MaxX,\MaxY) -- (\MinX,\MaxY) -- cycle;
\draw [thick] \TopPath;
\shade [top color= blue, bottom color=white] \BottomPath
-- (\MaxX,\MinY) -- (\MinX,\MinY) -- cycle;
\draw [thick] \BottomPath;
\end{tikzpicture}
\end{document}
-
I see what you did here, that's what I need! – MindV0rtex Feb 15 '12 at 23:44
@MindV0rtex: Have updated it so that you can reuse the coordinates without having to specify them twice. – Peter Grill Feb 16 '12 at 0:17
I know that an answer has already been accepted, but I will still give mine.
This answer uses a clip, to remove parts of the boundaries that are drawn (the outside parts). With this approach a path only has to be entered and used once.
Here is the code
\documentclass{article}
\usepackage{tikz}
\usetikzlibrary{calc}
\begin{document}
\begin{tikzpicture}
\begin{scope} %only to make sure the clip doesn't act on anything else
\clip ($(0,0)+2*(\pgflinewidth,\pgflinewidth)$) rectangle ($(5,3)-2*(\pgflinewidth,\pgflinewidth)$);
\draw[ultra thick,bottom color=gray,top color = white] (0,2.5) -- (1,2.7) -- (2,2.4) -- (3,2.6) -- (4,2.5) -- (5,2.6) -- (5,3) -- (0,3) -- cycle;
\draw[ultra thick,bottom color=white,top color = gray] (0,0.5) -- (1,0.6) -- (2,0.4) -- (3,0.6) -- (4,0.5) -- (5,0.4) -- (5,0) -- (0,0) -- cycle;
\end{scope}
\end{tikzpicture}
\end{document}
The result is
-
|
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|
https://www.aimsciences.org/article/doi/10.3934/dcds.2015.35.5107
|
# American Institute of Mathematical Sciences
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October 2015, 35(10): 5107-5131. doi: 10.3934/dcds.2015.35.5107
## Monotonicity, asymptotics and uniqueness of travelling wave solution of a non-local delayed lattice dynamical system
1 Department of Mathematics, Shanghai Jiao Tong University, Shanghai, 200240, China 2 College of Science, University of Shanghai for Science and Technology, Shanghai, 200093, China
Received May 2014 Revised January 2015 Published April 2015
A delayed lattice dynamical system with non-local diffusion and interaction is considered in this paper. The exact asymptotics of the wave profile at both wave tails is derived, and all the wave profiles are shown to be strictly increasing. Moreover, we prove that the wave profile with a given admissible speed is unique up to translation. These results generalize earlier monotonicity, asymptotics and uniqueness results in the literature.
Citation: Zhaoquan Xu, Jiying Ma. Monotonicity, asymptotics and uniqueness of travelling wave solution of a non-local delayed lattice dynamical system. Discrete & Continuous Dynamical Systems - A, 2015, 35 (10) : 5107-5131. doi: 10.3934/dcds.2015.35.5107
##### References:
show all references
##### References:
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2019 Impact Factor: 1.338
## Metrics
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• Cited by (3)
• on AIMS
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https://tex.stackexchange.com/questions/234487/polyglossia-and-hookrightarrow/234491
|
Polyglossia and hookrightarrow
Can someone explain why there is a gap between the tail and the head of \hookrightarrow when I load polyglossia with French support ? I'm using LuaLaTeX for producing the .pdf.
\documentclass{article}
\usepackage{polyglossia}
\setdefaultlanguage{french}
\begin{document}
\Huge $\hookrightarrow$
\end{document}
Here is the output:
Thank you.
• For me it works when using babel instead of polyglossia, so if that’s a compromise you’re willing to do, go for it. – user74027 Mar 22 '15 at 15:52
• french treats punctuation differently -- adds space(s) around some punctuation marks. \lhook (the leftmost piece of \hookrightarrow) has the misfortune to be defined (in fontmath.ltx) as \DeclareMathSymbol{\lhook}{\mathrel}{letters}{"2C}, and "2C is in the same location as a comma in a text font. how to fix it? don't know ... – barbara beeton Mar 22 '15 at 16:02
• @DavidCarlisle -- that may not be the cause (and egreg has just identified the actual cause), but the coincidence was just too great to ignore, and led to a truly delightfully devious workaround. so i'm not displeased with my conjecture. – barbara beeton Mar 22 '15 at 16:39
• @barbarabeeton yes I deleted my comment (and unfortunately had to vote for egreg:( – David Carlisle Mar 22 '15 at 16:41
• I opened an issue at GitHub: github.com/reutenauer/polyglossia/issues/92 – egreg Mar 22 '15 at 17:16
The callback used by LuaTeX for inserting the penalties and spaces after punctuation should be disabled in math mode, but apparently it isn't.
Workaround until a fix is shipped out:
\documentclass{article}
\usepackage{ifluatex}
\usepackage{polyglossia}
\setdefaultlanguage{french}
\ifluatex
\makeatletter
\let\latex@lhook\lhook
\renewrobustcmd{\lhook}{%
\mathrel{\mathpalette\do@lhook\relax}%
}
\newcommand{\do@lhook}[2]{%
\hbox{\directlua{polyglossia.desactivate_frpt()}$\m@th#1\latex@lhook$}%
}
\makeatother
\fi
\begin{document}
$\hookrightarrow$
\end{document}
Of course this won't be necessary if unicode-math is used.
The problem, as hinted by Barbara Beeton (but not getting the real problem), is that the right arrow happens to occupy the position of exclamation mark in the ASCII code, so LuaTeX blindly applies the penalty and spacing also before it as if it were in text.
The same problem could arise for other math symbols sharing their code point with punctuation symbols.
The characters involved for the OML encoding are
• \lhook in the position of ,
• \omega in the position of !
• the period in the position of :
• \star in the position of ?
• the comma, in the position of ;
• > in the same position as itself.
However, only \lhook and \omega seem to be affected; more tests with different character combinations should be performed.
In the OMS encoding we have
• \Leftrightarrow in the position of ,
• \rightarrow in the position of !
• \lnot in the position of :
• \bot in the position of ?
• \emptyset in the position of ;
• \top in the position of >
Curiously enough, here \rightarrow, \lnot, \bot and \emptyset are affected.
Here's the output of
X${\lhook}{\omega}{.}{\star}{,}{>} {\Leftrightarrow}{\rightarrow}{\lnot}{\bot}{\emptyset}{\top}$X
\selectlanguage{english}
X${\lhook}{\omega}{.}{\star}{,}{>} {\Leftrightarrow}{\rightarrow}{\lnot}{\bot}{\emptyset}{\top}$X
used for making the comparison
I'm quite afraid to see what happens with the OMX encoding: I guess that
• \mapsto is also problematic. – BigDawg Mar 22 '15 at 20:37
• @BigDawg I came to the conclusion that \rightarrow is the culprit in \hookrightarrow and not \lhook. But the principle is the same. And this explains \mapsto that has \rightarrow in it. – egreg Mar 22 '15 at 23:29
• I know this answer is years old, but I ran into this (actually for \mapsto), and this workaround seems to desactivate french spacing in all document. So, what I did is \renewcommand{\mapsto}{\mathrel{\mathord{\mapstochar}\mathord{\rightarrow}}}. But let us be honest: I have no idea what I'm doing and this is probably not the right way. – Armand Koenig Apr 4 at 15:17
• @ArmandKoenig Oh, that's possible. Support for French has changed quite a lot, in the past years. – egreg Apr 4 at 15:46
Here is a nasty fix following barbara beeton's comment, if someone has better...
\documentclass{article}
\usepackage{polyglossia}
\setdefaultlanguage{french}
\setotherlanguage{english}
\begin{document}
\Huge \begin{english}$\hookrightarrow$\end{english}$\hookrightarrow$
\end{document}
• definitely evil! (good idea, though.) – barbara beeton Mar 22 '15 at 16:26
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https://www.physicsforums.com/threads/centrifical-force-of-earth.96153/
|
# Centrifical force of earth
1. Oct 22, 2005
### Petrikovski
How long would a day be if the Earth were rotating so fast that objects at the equator had no weight?
I do Fcnet = m(v^2/r) --> mg = m(v^2/r) --> g = (v^2/r)
g = (v^2/r)
but g = 0 right? so then how do i do this problem? that would make v = 0 and ya...
2. Oct 22, 2005
### Janus
Staff Emeritus
g is the acceleration due to gravity. Its value is independent of any spin of the Earth.
3. Oct 22, 2005
### Petrikovski
ok thanks. unfortunately the answer isnt given so idk if im right until monday. i did:
g = (v^2)/r
9.8 = (v^2)/6.38e6
v =7907
40086722 (distance of Earth in m)/7907 = 5069 seconds
= 1.4 hours per day.
i have one more question and then im done.
A train traveling at a constant speed rounds a curve of radius 275m. A pendulum suspende dfrom the ceiling swings out to an anglr of 17.5 throughot the turn. What is the speed of the train?
Fcnet = m(v^2/r)
Fk = m (v^2/r)
coeff of friction * mg = m(v^2/r)
i dont know the coefficient of friction or v. im supposed to solve for v. am i not supposed to use friction as the force? and how do i factor the 17.5 degree swing fo the pendulum into this?
thanks a lot for the help
4. Oct 23, 2005
### Staff: Mentor
train problem
First figure out the acceleration of the train by analyzing the forces on the pendulum.
5. Oct 23, 2005
### Petrikovski
would this be correct then?
Fnet=ma
mg(cos17.5)=ma
9.8(cos17.5)=a
9.34=a
(v^2)/r = a
(v^2)/275 = 9.34
v^2 = 2568
v = 50.7 m/s
6. Oct 23, 2005
### Staff: Mentor
No. Start by identifying the forces acting on the pendulum mass. (There are two forces.) Then apply Newton's 2nd law to the vertical and horizontal components.
Similar Discussions: Centrifical force of earth
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http://math.stackexchange.com/questions/221128/what-is-left-delta-ab-right-1?answertab=votes
|
# What is $\left(\delta_{ab}\right)^{-1}$?
I have an expression that involves the Wigner 3j coefficient:
$$\left(\matrix{a&b&0\\0&0&0}\right)^{-1}$$
This simplifies to:
$$\left[\frac{\left(-1\right)^{a}\delta_{ab}}{\sqrt{2a+1}}\right]^{-1}$$
Which, in turn would be:
$$\frac{\sqrt{2a+1}}{\left(-1\right)^{a}\delta_{ab}}$$
What I'm unsure about is how the Kronecker Delta behaves when it's in the denominator. This would seem to me to indicate that the expression is finite when $a=b$ and infinite otherwise, is that correct?
-
Whether it makes sense to regard the value of expression as infinite will depend on the context; in some contexts "undefined" might be a better description. It usually makes sense to regard something as infinite when it approaches infinity, e.g. $1/r$ as $r$ approaches $0$ from above; but in this case there's no approach, and in particular there's no reason to prefer calling this $+\infty$ over calling it $-\infty$. This has nothing specific to do with the Kronecker symbol, which is just a convenient notation that captures the fact that this Wigner $3$-$j$ symbol vanishes unless $a=b$.
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|
https://nigerianscholars.com/tutorials/chemical-bonding/summarizing-formal-charges-and-resonance/
|
Chemistry » Chemical Bonding » Formal Charges and Resonance
# Summarizing Formal Charges and Resonance
## Key Concepts and Summary
In a Lewis structure, formal charges can be assigned to each atom by treating each bond as if one-half of the electrons are assigned to each atom. These hypothetical formal charges are a guide to determining the most appropriate Lewis structure. A structure in which the formal charges are as close to zero as possible is preferred.
Resonance occurs in cases where two or more Lewis structures with identical arrangements of atoms but different distributions of electrons can be written. The actual distribution of electrons (the resonance hybrid) is an average of the distribution indicated by the individual Lewis structures (the resonance forms).
## Key Equations
• $$\text{formal charge}\phantom{\rule{0.2em}{0ex}}=\text{# valence shell electrons (free atom)}\phantom{\rule{0.1em}{0ex}}-\phantom{\rule{0.2em}{0ex}}\text{# one pair electrons}\phantom{\rule{0.2em}{0ex}}-\phantom{\rule{0.2em}{0ex}}\frac{1}{2}\phantom{\rule{0.3em}{0ex}}\text{# bonding electrons}$$
## Glossary
### formal charge
charge that would result on an atom by taking the number of valence electrons on the neutral atom and subtracting the nonbonding electrons and the number of bonds (one-half of the bonding electrons)
### molecular structure
arrangement of atoms in a molecule or ion
### resonance
situation in which one Lewis structure is insufficient to describe the bonding in a molecule and the average of multiple structures is observed
### resonance forms
two or more Lewis structures that have the same arrangement of atoms but different arrangements of electrons
### resonance hybrid
average of the resonance forms shown by the individual Lewis structures
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|
http://www.gradesaver.com/textbooks/science/physics/physics-principles-with-applications-7th-edition/chapter-3-kinematics-in-two-dimensions-vectors-problems-page-70/36
|
## Physics: Principles with Applications (7th Edition)
Choose x = 0 and y = 0 to be the point of launch with speed v and initial angle $\theta$, and upward to be the positive y direction. Assume the boy in the tree starts at x = d, y = h. The vertical acceleration is $-9.8 \frac{m}{s^{2}}$, negative because it is directed downward. Write the equations of motion for the balloon and for the boy. $$x_{balloon} = (v cos \theta)(t)$$ $$y_{balloon} = 0 + (v sin \theta)(t) – 0.5 g t^{2}$$ $$y_{boy} = h – 0.5 g t^{2}$$ Use the balloon's horizontal motion to find the time for the balloon to travel a distance d. $$t = \frac{d}{(v cos \theta)}$$ Use that time and find the balloon’s vertical position. Use the same time to find the boy’s vertical position. They are exactly the same, showing that the boy is splashed by the balloon.
|
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|
https://zenodo.org/record/1235764/export/schemaorg_jsonld
|
Journal article Open Access
# RT-PCR/electrospray ionization mass spectrometry approach in detection and characterization of influenza viruses
Deyde, Varough M.; Sampath, Rangarajan; Gubareva, Larisa V.
### JSON-LD (schema.org) Export
{
"description": "Reverse-transcription PCR (RT-PCR) coupled with electrospray ionization mass spectrometry (ESI-MS) is a high-throughput nucleic acid-based technology that relies on the accurate measurement of the molecular weight of PCR amplicons that can be used to deduce the base counts (number of As, Gs, Cs and Ts) of DNA. These amplicons represent highly variable regions with information-rich sequences, which are flanked by broad-range primers designed based on highly conserved loci. This technology was first introduced in 2005 for microbial identification and subtyping, and was later applied to influenza virus detection and identification. The influenza RT-PCR/ESI-MS assay allows analysis of approximately 300 samples per 24 h, and aids in the characterization of influenza viruses based on their 'core' gene signatures. Notably, this assay was used to identify one of the first cases of the 2009 H1N1 pandemic viruses. One of the main advantages of the RT-PCR/ESI-MS technology is its universality and adaptability for pathogen characterization. Efforts are being made to customize the currently used influenza surveillance assay for use in the diagnosis of the H1N1 pandemic virus. In this article, we provide a summary of known applications of the RT-PCR/ESI-MS assay in the field of influenza.",
"creator": [
{
"@type": "Person",
"name": "Deyde, Varough M."
},
{
"@type": "Person",
"name": "Sampath, Rangarajan"
},
{
"@type": "Person",
"name": "Gubareva, Larisa V."
}
],
"headline": "RT-PCR/electrospray ionization mass spectrometry approach in detection and characterization of influenza viruses",
"datePublished": "2011-01-01",
"url": "https://zenodo.org/record/1235764",
"@context": "https://schema.org/",
"identifier": "https://doi.org/10.1586/erm.10.107",
"@id": "https://doi.org/10.1586/erm.10.107",
"@type": "ScholarlyArticle",
"name": "RT-PCR/electrospray ionization mass spectrometry approach in detection and characterization of influenza viruses"
}
121
133
views
|
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|
http://mathhelpforum.com/advanced-algebra/221480-semi-direct-product-proof-print.html
|
# Semi-Direct product proof
• August 28th 2013, 09:43 PM
akarimi
Semi-Direct product proof
Suppose N is a normal subgroup of G and H is a subgroup of G, and G is the semi-direct product of N and H.
Then is there a nice way to prove that N(and)H = {1}
Thanks.
• August 28th 2013, 09:48 PM
Drexel28
Re: Semi-Direct product proof
I'm confused by your question. I'm going to assume by your wording that you're considering groups of the form $G=N\rtimes_\varphi H$? Then, we identify $N$ with $N\times\{1\}$ inside $N\times H$ and similarly for $H$. In this context, your question should be easily solved.
If this is not what you mean, could you please elaborate?
• August 28th 2013, 10:07 PM
akarimi
Re: Semi-Direct product proof
Hmm I'm not sure if it's the same as what you're saying but it could just be my lack of knowledge, this is my first time reading about semi-direct products but I have yet to see their connection to cross products.
The question I asked was part of a bigger Lemma: Let N <| G and H < G. Then G = N ><| H if and only if G = NH and N(and)H = {1}.
The part I'm having trouble with is using the fact that G = N ><| H to implicate that N(and)H = {1}.
I Hope I've made it a bit clearer.
• September 4th 2013, 05:46 PM
Deveno
Re: Semi-Direct product proof
Hint: Show the mapping G → Nx|H given by nh → (n,h) is an isomorphism iff G = NH and N∩H = {e}.
|
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https://metacpan.org/pod/release/PYTHIAN/DBD-Oracle-1.54/lib/DBD/Oracle/Troubleshooting/Win32.pod
|
++ed by:
11 PAUSE users
10 non-PAUSE users.
Pythian Remote DBA
and 4 contributors
# NAME
DBD::Oracle::Troubleshooting::Win32 - Tips and Hints to Troubleshoot DBD::Oracle on Win32
version 1.54
# GENERAL INFO
In general, on Windows, it's best to just use ActiveState Perl and the PPM package manager to install a pre-built version of DBD::Oracle however only version 1.17 is available there.
# Oracle Instant Client 11.1.0.6.0 Notes
So far I have managed to get it to Makefile and compile test and install and work. However it seems one needs to set "NLS_LANG" to a valid value in the environment variables.
As well IC 11 seems to have trouble finding the .ORA files. A quick fix for this is to add "TNS_ADMIN" to the environment variables and point it to where your .ORA files are.
# Other information, some of which is out of date ---
`````` DBD-Oracle for Windows and Oracle Instantclient and 10XE (Express Edition)
By: John Scoles
The Pythian Group``````
The preferred method of getting DBD::Oracle is to use a pre-built version from the ActiveState repository, which can be installed with PPM.
Compiling and installing DBD::Oracle 1.18 or later on a windows 2000 professional or XP OS for use with Oracle instantClient ver 10.2.0.1 & 10.1.0.5 or Oracle XE requires only a few downloads and a minimal number of environment setting. The procedures below were tested on a clean Windows platform having no Oracle or other development environment installed.
`````` 1) The first part of the process is to download and install the latest version of
Active Perl from http://www.activeperl.com/.
2) Use the PPM application to get the latest version of DBI
4) Download and unzip the Oracle Instant Client (10.2.0.1 or 10.1.0.5) 32 bit from
http://www.oracle.com/technology/tech/oci/instantclient/instantclient.html
You will need all three of these products
i. Instant Client Package - Basic
ii. Instant Client Package - SQL*Plus:
iii. Instant Client Package - SDK:
or
install oracle 10XE http://www.oracle.com/technology/products/database/xe/index.html
5) You will now need the Microsoft Visual C++ toolkit 2003. Unfortunately this product is no longer available from Microsoft.
The file name was VCToolkitSetup.exe and is available at this mirror site http://www.filewatcher.com/m/VCToolkitSetup.exe.32952488.0.0.html at the time of writing.
Microsoft's replacement for this tool kit is Visual C++ 2005 Express Edition and all attempts to compile DBD::Oracle with this product fail. It has been successfully compiled
using a complete edition of Microsoft Visual Studio 2005.
6) You will also need the Windows SDK. Which can be found at
You have the choice to of either to download the entire SDK and install or run an online install from the page.
Both have been tested and proven to work.
7) Next download and install the Microsoft .net framework 1.1 skd from
10) You should at this time attempt to connect to an Oracle database with the version SQL*Plus that
you installed in step 4. If you are unable to connect at this stage then any problems you encounter
later may have nothing to do with DBD::Oracle
11) On the path where you installed Visual C++ find and edit the vcvars32.bat file as follows. You may have to modify
these path values depending where you installed the products on you computer,
i. Add the local path to the windows platform SDK include directory to the Set INCLUDE
Command Line to include the needed files from the Windows SDK.
e.g. "C:\Program Files\Microsoft Platform SDK\Include;"
ii. Add the local path to the .net Vc7 lib directory to the Set LIB command
to include the needed library file from the .Net SKD
e.g. C:\Program Files\Microsoft Visual Studio .NET 2003\Vc7\lib;
iii. Add the local path to the windows platform SDK Lib directory to the Set Lib command
to include the needed library files from the Windows SDK
e.g. C:\Program Files\Microsoft Platform SDK\Lib;
12) Open a Windows Visual C++ command window from the start menu.
13) Add the path to the instant client to the Path command. If you are compiling aginst a 10XE db/client then you can skip steps
12 to 14.
e.g. PATH = C:/Oracle/instantclient;%PATH%
14) Using the "Set" command add "ORACLE_HOME=path to Instant client" to the environment variables.
e.g. Set ORACLE_HOME=C:\Oracle\instantclient
15) Using the "Set" command add "NLS_LANG=.WE8ISO8859P15" to the environment variables. The globalization variable is required,
with this or another compatible value, by Oracle instantclient in order for it to compile correctly.
e.g. Set NLS_LANG=.WE8ISO8859P15
you wish to run the make test files against.
Note: it is not necessary to do this step for the compile and install to work.
However: The self-test programs included with Oracle-DBD will mostly fail.
17) Move to the DBD-Oracle directory in the Visual C++ window DOS prompt and enter the following.
c:\oracle-dbd\>perl Makefile.PL
The Makefile should then run and compile Oracle-dbd without reporting any errors.
18) From this DOS prompt enter the following command
c:\oracle-dbd\>nmake
The Visual C++ make executable will then build you DBD-execuable. There should be no errors at this point.
19) You can test the compile by either entering
c:\oracle-dbd\>nmake test
As long as you have given a valid user name, password and database name in step 15 you will see some results. If it appears to
run but you do not get a connection check the following.
i. User name password and DB Name
ii. Ensure the a valid TNSNAMES.ORA file is in the Instantclient directory
iii. Attempt to log into the version of SQLPLUS that comes with Instantclient.
If you manage to log on use the username password and TNS name with
the Set ORACLE_USERID = and rerun the tests.
iv If you are compiling against 10XE and have skiped steps 12 to 14 try again bu this time carry out these steps
20) You can now install DBD-Oracle into you system by entering the following command from the Visual C++ window dos prompt;
c:\oracle-dbd\>nmake install
21) You should now be able to run DBD-Oracle on you system``````
# 09/30 2006 from asu
DBD::Oracle 1.18a
Linux, Debian unstable ( DBI: 1.52 perl v5.8.8 built for i486-linux-gnu-thread-multi )
Oracle Instant client (10.1.0.5)
The problem is in Makefile.PL. In line 130 the function find_oracle_home is used to guess a value form \$ORACLE_HOME if it is not set explicitely. This value is used in line 138 to setup the environment (regardless which client is used).
in line 1443 (sub get_client_version) sqlplus is used to get the version string, but for the oracle instant client you must not set \$ORACLE_HOME (it will generate an error "SP2-0642: SQL*Plus internal error state 2165, context 4294967295:0:0")
A solution that worked for me was to set local \$ENV{ORACLE_HOME} = ''; in line 1463 immediately before sqlplus is called (but I cannot tell if this fails for full client installations)
11/30/05 -- John Scoles I have confirmed that this Makefile.pl will work for both Oracle InstantClient 10.2.0.1 & 10.1.0.4 using same process the Andy Hassall uses. Starting with a clean OD One needs only to get the latest version of Active Perl 5.8.7 use PPM to get DBI and then install Microsoft Visual C++ toolkit, Windows SDK, and the Microsoft .net framework 1.1. and modify the vcvars32.bat in C++ dir as follows
`````` 1) Add the local path to the windows platform SDK include directory to the
Set INCLUDE Command Line to include the needed files from the Windows SDK.
e.g. "C:\Program Files\Microsoft Platform SDK\Include;"
2) Add the local path to the .net Vc7 lib directory to the Set LIB
command to include the needed library files from the .Net SKD
e.g. C:\Program Files\Microsoft Visual Studio .NET 2003\Vc7\lib;
3) Add the local path to the windows platform SDK Lib directory to the Set Lib
command to include the needed library files from the Windows SDK
e.g. C:\Program Files\Microsoft Platform SDK\Lib;``````
If one happens to have visual studio installed you may not have to download additional MS products.
12/01/05 --- John Scoles Oracle 10XE No big problem here as 10XE seems to use the instantclient as well. Just ensure your NLS_LANG and ORACLE_HOME are set to the same directory that 10XE uses
10/07/05 --John Scoles Andy Hassall kindly added some changes to the Makefile.PL so it will work for the Instant Client 10g on Windows OSs. Below is how he set up his environment and the steps he preformed to get it to compile.
`````` Setting environment for using Microsoft Visual Studio .NET 2003 tools.
(If you have another version of Visual Studio or Visual C++ installed and wish
to use its tools from the command line, run vcvars32.bat for that version.)
C:\Documents and Settings\andyh>d:
D:\>cd cygwin\home\andyh\src\pythian
D:\cygwin\home\andyh\src\pythian>set ORACLE_HOME=d:\lib\instantclient_10_2
D:\cygwin\home\andyh\src\pythian>set NLS_LANG=.WE8ISO8859P15
D:\cygwin\home\andyh\src\pythian>set PATH=d:\lib\instantclient_10_2;D:\Program F
iles\Microsoft Visual Studio .NET 2003\Common7\IDE;D:\Program Files\Microsoft Vi
sual Studio .NET 2003\VC7\BIN;D:\Program Files\Microsoft Visual Studio .NET 2003
\Common7\Tools;D:\Program Files\Microsoft Visual Studio .NET 2003\Common7\Tools\
bin\prerelease;D:\Program Files\Microsoft Visual Studio .NET 2003\Common7\Tools\
bin;D:\Program Files\Microsoft Visual Studio .NET 2003\SDK\v1.1\bin;C:\WINNT\Mic
rosoft.NET\Framework\v1.1.4322;d:\Perl\bin\;C:\WINNT\system32;C:\WINNT;C:\WINNT\
System32\Wbem;D:\Program Files\Microsoft SDK\Bin;D:\Program Files\Microsoft SDK\
Bin\WinNT
D:\cygwin\home\andyh\src\pythian>set ORACLE_USERID=test/test@test102
D:\cygwin\home\andyh\src\pythian>perl Makefile.PL``````
4/27/04 -- Jeff Urlwin
Do not untar this distribution in a directory with spaces. This will not work.
`````` i.e. C:\Program Files\ORacle\DBD Oracle Distribution is bad while
c:\dev\dbd-oracle-1.15 is good ;)``````
9/14/02 -- Michael Chase
Makefile.PL uses Win32::TieRegistry or Win32::Registry to find the current Oracle Home directory if the ORACLE_HOME environment variable is not set. If neither module is installed, you must set ORACLE_HOME before running Makefile.PL. Since the registry location of the current Oracle Home is in different locations in different Oracle versions, it is usually safer to set ORACLE_HOME before running Makefile.PL.
# AUTHORS
• Tim Bunce <[email protected]>
• John Scoles
• Yanick Champoux <[email protected]>
• Martin J. Evans <[email protected]>
|
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|
http://www.chegg.com/homework-help/questions-and-answers/figure-http-imgphotobucketcom-albums-v296-happyfrowns-hw7-1jpg-consider-circuit-shown-figu-q3305830
|
## Circuits
Figure: http://img.photobucket.com/albums/v296/happyfrowns/HW7-1.jpg Consider the circuit shown in the figure. Is = 5A , R = 1 ohm . The switch is opened at t=0. A.) Find v(0+); Answer = 0V B.) Find v(infinity); Answer= 5V
|
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|
https://www.cell.com/neuron/fulltext/S0896-6273(15)00220-2
|
Article| Volume 86, ISSUE 3, P800-812, May 06, 2015
• Top
# Motor Cortex Is Required for Learning but Not for Executing a Motor Skill
Open ArchivePublished:April 16, 2015
## Highlights
• We train rats to execute spatiotemporally precise task-specific motor sequences
• We show that motor cortex is not required for executing the learned skills
• Motor cortex, however, is essential for acquiring the subcortically generated skills
• This suggests that motor cortex “tutors” subcortical motor circuits during skill learning
## Summary
Motor cortex is widely believed to underlie the acquisition and execution of motor skills, but its contributions to these processes are not fully understood. One reason is that studies on motor skills often conflate motor cortex’s established role in dexterous control with roles in learning and producing task-specific motor sequences. To dissociate these aspects, we developed a motor task for rats that trains spatiotemporally precise movement patterns without requirements for dexterity. Remarkably, motor cortex lesions had no discernible effect on the acquired skills, which were expressed in their distinct pre-lesion forms on the very first day of post-lesion training. Motor cortex lesions prior to training, however, rendered rats unable to acquire the stereotyped motor sequences required for the task. These results suggest a remarkable capacity of subcortical motor circuits to execute learned skills and a previously unappreciated role for motor cortex in “tutoring” these circuits during learning.
## Introduction
Motor skills underlie much of what we do, be it playing instruments or sports, signing our names, or tying our shoelaces. Learning a motor skill involves organizing actions into novel sequences that can be executed efficiently and reproducibly to solve a given task (
• Hikosaka O.
• Nakamura K.
• Sakai K.
• Nakahara H.
Central mechanisms of motor skill learning.
,
• Luft A.R.
• Buitrago M.M.
Stages of motor skill learning.
,
• Shmuelof L.
• Krakauer J.W.
• Mazzoni P.
How is a motor skill learned? Change and invariance at the levels of task success and trajectory control.
,
• Willingham D.B.
A neuropsychological theory of motor skill learning.
). When learned, skills are retained long-term (
• Hikosaka O.
• Nakamura K.
• Sakai K.
• Nakahara H.
Central mechanisms of motor skill learning.
,
• Park S.-W.
• Dijkstra T.M.H.
Learning to never forget-time scales and specificity of long-term memory of a motor skill.
,
• Romano J.C.
• Howard Jr., J.H.
• Howard D.V.
One-year retention of general and sequence-specific skills in a probabilistic, serial reaction time task.
), suggesting that they are stored as lasting changes in motor control circuits (
• Dayan E.
• Cohen L.G.
Neuroplasticity subserving motor skill learning.
,
• Ungerleider L.G.
• Doyon J.
• Karni A.
Imaging brain plasticity during motor skill learning.
). However, how the mammalian brain divides the task of learning and executing motor skills across its distributed motor control network is not well understood (Figure 1).
Motor cortex is widely believed to play central roles in both motor skill learning and execution. Its projections to the spinal cord are essential for generating independent joint and digit movements, or “dexterity” broadly defined (
• Alaverdashvili M.
• Whishaw I.Q.
Motor cortex stroke impairs individual digit movement in skilled reaching by the rat.
,
• Lawrence D.G.
• Hopkins D.A.
The development of motor control in the rhesus monkey: evidence concerning the role of corticomotoneuronal connections.
,
• Lawrence D.G.
• Kuypers H.G.
The functional organization of the motor system in the monkey. I. The effects of bilateral pyramidal lesions.
,
• Lemon R.N.
The G. L. Brown Prize Lecture. Cortical control of the primate hand.
,
• Passingham R.E.
• Perry V.H.
• Wilkinson F.
The long-term effects of removal of sensorimotor cortex in infant and adult rhesus monkeys.
,
• Whishaw I.Q.
Loss of the innate cortical engram for action patterns used in skilled reaching and the development of behavioral compensation following motor cortex lesions in the rat.
; Figure 1A). Practice-induced changes in motor cortical control networks (
• Rioult-Pedotti M.S.
• Friedman D.
• Hess G.
• Donoghue J.P.
Strengthening of horizontal cortical connections following skill learning.
,
• Wang L.
• Conner J.M.
• Rickert J.
• Tuszynski M.H.
Structural plasticity within highly specific neuronal populations identifies a unique parcellation of motor learning in the adult brain.
,
• Xu T.
• Yu X.
• Perlik A.J.
• Tobin W.F.
• Zweig J.A.
• Tennant K.
• Jones T.
• Zuo Y.
Rapid formation and selective stabilization of synapses for enduring motor memories.
) can improve the quality and range of movements they can produce (
• Boychuk J.
• Remple M.S.
• Kleim J.A.
Motor training induces experience-specific patterns of plasticity across motor cortex and spinal cord.
,
• Classen J.
• Liepert J.
• Wise S.P.
• Hallett M.
• Cohen L.G.
Rapid plasticity of human cortical movement representation induced by practice.
,
• Kleim J.A.
• Barbay S.
• Nudo R.J.
Functional reorganization of the rat motor cortex following motor skill learning.
), a capacity that helps animals adapt their motor output to difficult control scenarios—an important aspect of many skills.
However, motor cortex is not the only “controller” capable of commandeering spinal circuits for the purpose of generating movements. The phylogenetically older subcortical motor infrastructure is also quite sophisticated in this regard (
• Azim E.
• Jiang J.
• Alstermark B.
• Jessell T.M.
Skilled reaching relies on a V2a propriospinal internal copy circuit.
,
• Barnes C.
Brainstem Control of Spinal Cord Function.
,
• Esposito M.S.
• Capelli P.
• Arber S.
Brainstem nucleus MdV mediates skilled forelimb motor tasks.
,
• Kuypers H.G.J.M.
• Martin G.F.
Descending Pathways to the Spinal Cord.
), as is evident from studies in rodents and primates with motor cortex or corticospinal tract lesions (
• Castro A.J.
The effects of cortical ablations on digital usage in the rat.
,
• Darling W.G.
• Pizzimenti M.A.
• Morecraft R.J.
Functional recovery following motor cortex lesions in non-human primates: experimental implications for human stroke patients.
,
• Lawrence D.G.
• Kuypers H.G.
The functional organization of the motor system in the monkey. I. The effects of bilateral pyramidal lesions.
,
• Passingham R.E.
• Perry V.H.
• Wilkinson F.
The long-term effects of removal of sensorimotor cortex in infant and adult rhesus monkeys.
). Although dexterity is permanently compromised in these animals, other aspects of control survive remarkably intact, consistent with an ability of subcortical controllers to generate a variety of species-typical or “innate” movements and actions (
• Baker S.N.
The primate reticulospinal tract, hand function and functional recovery.
,
• Grillner S.
• Wallén P.
Innate versus learned movements—a false dichotomy? Prog.
,
• Hikosaka O.
Role of Basal Ganglia in Control of Innate Movements, Learned Behavior and Cognition—A Hypothesis.
,
• Honeycutt C.F.
• Kharouta M.
• Perreault E.J.
Evidence for reticulospinal contributions to coordinated finger movements in humans.
,
• Lawrence D.G.
• Kuypers H.G.
The functional organization of the motor system in the monkey. I. The effects of bilateral pyramidal lesions.
,
• Philipp R.
• Hoffmann K.-P.
Arm movements induced by electrical microstimulation in the superior colliculus of the macaque monkey.
,
• Stein P.S.G.
• Grillner S.
• Selverston A.I.
• Stuart D.G.
Neurons, Networks, and Motor Behavior.
; Figure 1A). Disrupting descending brainstem pathways can have far more devastating consequences for baseline motor control than lesions to the corticospinal tract (
• Lawrence D.G.
• Kuypers H.G.
The functional organization of the motor system in the monkey. II. The effects of lesions of the descending brain-stem pathways.
), highlighting the importance of these lower-level controllers.
If subcortical controllers are indeed essential for generating many types of basic movements and action patterns (Figure 1A), how are they engaged during skill learning and execution? Studies on motor skills that focus on facets explicitly requiring cortical control, i.e., dexterity (
• Karni A.
• Meyer G.
• Jezzard P.
• Turner R.
• Ungerleider L.G.
Functional MRI evidence for adult motor cortex plasticity during motor skill learning.
,
• Kleim J.A.
• Barbay S.
• Nudo R.J.
Functional reorganization of the rat motor cortex following motor skill learning.
,
• Poldrack R.A.
• Sabb F.W.
• Foerde K.
• Tom S.M.
• Asarnow R.F.
• Bookheimer S.Y.
• Knowlton B.J.
The neural correlates of motor skill automaticity.
) (Figure 1B), fail to address this question. However, the capacity to sequence and coordinate movements that—in theory at least—can be generated from a pre-established subcortical motor repertoire (
• Shmuelof L.
• Krakauer J.W.
Are we ready for a natural history of motor learning?.
,
• Yin H.H.
• Mulcare S.P.
• Hilário M.R.F.
• Clouse E.
• Holloway T.
• Davis M.I.
• Hansson A.C.
• Lovinger D.M.
• Costa R.M.
Dynamic reorganization of striatal circuits during the acquisition and consolidation of a skill.
) is a fundamental aspect of many motor skills.
Several studies have suggested that innate movement patterns can be quite flexible (
• Berkinblit M.B.
• Feldman A.G.
• Fukson O.I.
Adaptability of innate motor patterns and motor control mechanisms.
,
• Grillner S.
• Wallén P.
Innate versus learned movements—a false dichotomy? Prog.
), leaving open the possibility that new motor behaviors can be formed by adapting subcortically generated motor programs to novel contingencies and demands (
• Berntson G.G.
• Micco D.J.
Organization of brainstem behavioral systems.
,
• Grillner S.
• Wallén P.
Innate versus learned movements—a false dichotomy? Prog.
). But, if so, what are the limits of such plasticity, and what degree of autonomy do lower-level motor circuits have when it comes to executing learned motor skills? Is motor cortex an essential contributor regardless of the control challenges involved, or can subcortical circuits store and produce task-specific motor sequences as long as the components themselves can be generated subcortically (Figures 1B and 1C)?
A related question that cannot be cleanly addressed in tasks requiring dexterity is whether motor cortex has a role in learning that is distinct from its role in control. Motor cortex projects heavily to subcortical circuits (
• Akintunde A.
• Buxton D.F.
Origins and collateralization of corticospinal, corticopontine, corticorubral and corticostriatal tracts: a multiple retrograde fluorescent tracing study.
) and is known to modulate the expression of subcortically generated actions in context-specific ways (
• Drew T.
• Jiang W.
• Kably B.
• Lavoie S.
Role of the motor cortex in the control of visually triggered gait modifications.
,
• Drew T.
• Krouchev N.
Muscle synergies during locomotion in the cat: a model for motor cortex control.
,
• Ioffe M.E.
Pyramidal influences in establishment of new motor coordinations in dogs.
,
• Stoltz S.
• Humm J.L.
• Schallert T.
Cortical injury impairs contralateral forelimb immobility during swimming: a simple test for loss of inhibitory motor control.
). One hypothesis still to be tested is that such modulation, when repeated and consistent, fulfills a “tutoring” function that allows subcortical control networks to acquire, consolidate, and execute new motor sequences (
• Andalman A.S.
• Fee M.S.
A basal ganglia-forebrain circuit in the songbird biases motor output to avoid vocal errors.
,
• Shmuelof L.
• Krakauer J.W.
Are we ready for a natural history of motor learning?.
).
Addressing the above questions and, more generally, the interplay between cortical and subcortical motor circuits during skill learning would benefit from an experimental paradigm that dissociates motor cortex’s role in learning and generating task-specific motor sequences from its role in dexterous control. The rat presents a tractable and well suited model for such a paradigm. It is a good learner, amenable to being trained in complex behavioral tasks (
• Erlich J.C.
• Bialek M.
• Brody C.D.
A cortical substrate for memory-guided orienting in the rat.
,
• Poddar R.
• Kawai R.
• Ölveczky B.P.
A fully automated high-throughput training system for rodents.
,
• Tervo D.G.R.
• Proskurin M.
• Manakov M.
• Kabra M.
• Vollmer A.
• Branson K.
• Karpova A.Y.
Behavioral variability through stochastic choice and its gating by anterior cingulate cortex.
), and capable of generating much of its action repertoire without motor cortex, i.e., subcortically (
• Castro A.J.
The effects of cortical ablations on digital usage in the rat.
). The latter is important because the ideal task for our inquiry is one that, in principle at least, can be solved by sequencing and/or adapting subcortically generated movements and actions (Figure 1C). However, most established motor tasks, even in rats, are designed to interrogate the function and plasticity of cortical controllers (
• Ölveczky B.P.
), making them ill suited for the questions we ask here.
This motivated us to develop a new motor learning paradigm that trains rats to produce complex, spatiotemporally precise, and robustly maintained task-specific motor sequences without explicit requirements for dexterity. By means of motor cortical lesions and high-resolution behavioral analysis, we show that motor cortex is not required for executing the learned skills we train, implying that they can be stored and generated subcortically. Intriguingly, however, we find that motor cortex is essential for learning the very same skills, suggesting that it plays an essential role in guiding plasticity in downstream control circuits during skill learning.
## Results
### A New Motor Skill Learning Paradigm for Rats
To dissociate learning and execution of complex task-specific motor sequences from the cortex-dependent challenge of generating dexterous movements, we developed a motor skill learning paradigm that rewards rats for pressing a lever with their forepaws in a temporally precise sequence—a difficult to learn but not necessarily a dexterous task (Figure 2A; Experimental Procedures). Although the relative timing of the lever-presses was prescribed, the movements that could be used were not, meaning that there were no explicit requirements for dexterity. Force requirements were also modest (<0.1 N to press the lever; Experimental Procedures), making the central challenge of the task to execute temporally precise and reproducible movement sequences.
After learning to press the lever for water, water-restricted animals were rewarded for increasingly precise approximations to the target sequence, which was a sequence of two lever-presses separated by a predefined inter-press interval (IPI). Because rats show a natural proclivity for pressing the lever in fast succession, i.e., within ∼300 ms (Figure S1), we challenged them to overcome this natural tendency and learn new task-specific motor sequences by setting the target to longer IPIs (700 ms, n = 18; Figure 2B). During training, the range of rewarded IPIs was adjusted based on performance to ensure average reward rates around ∼35% (Figure 2C; Experimental Procedures; Supplemental Experimental Procedures). If an IPI was not in the rewarded range, a new trial could only be initiated after 1.2 s without a lever-press. The end goal of training was asymptotically precise performance at the targeted IPI (Figures 2B and 2D; Experimental Procedures; Supplemental Experimental Procedures).
Converging on a behavior that reliably produced a 700-ms IPI took many weeks of training. Rats, on average, required 13,689 ± 5,470 (mean ± SD, n = 18) trials or 35 ± 9 training days to reach “criterion” performance, defined as the mean IPI being within 10% of the target and the coefficient of variation (CV) of the IPI distribution being less than 0.25. The rewarded range was narrowed further until temporal precision reached asymptote (Supplemental Experimental Procedures), which occurred after 17,130 ± 5,228 total trials or 43 ± 10 training days (CV at asymptote, 0.20 ± 0.03; mean IPI, 701 ± 35 ms; Figures 2D and 2E).
Although not essential for reaching criterion performance on the task (Figure S2), all rats also learned to withhold lever-pressing for the prescribed 1.2 s following unrewarded IPIs, making task engagement more efficient. The median time to the next lever-press after unrewarded IPIs exceeded 1.2 s after, on average, 15,526 ± 10,077 trials (n = 18; Experimental Procedures).
### Rats Learn Complex and Stereotyped Movement Patterns
The movement patterns that emerged after weeks of training were highly complex and stereotyped (Movie S1), involving predominantly the forelimbs, although other movements, including hindlimb and whole-body movements, were often incorporated. Many of the motor elements making up the consolidated skills were not directly related to the act of pressing the lever and were perhaps incorporated through trial and error learning as a mechanism for producing the target IPI (700 ms) (
• Killeen P.R.
• Fetterman J.G.
A behavioral theory of timing.
), which was more than double what rats prefer naturally (Figure S1). Thus, rats “solve” what is ostensibly an interval timing task in the motor domain by acquiring spatiotemporally precise movement sequences that produce the prescribed lever-press timing.
To better quantify changes to task-related movement kinematics, we also tracked the forepaws in a subset of rats throughout learning (n = 4) by tattooing them with colored ink and extracting color markers from high-speed (200 frames/s [fps]) movies (Figure 3A; Experimental Procedures; Movie S2). Analysis of the paw trajectories revealed gradual learning-related changes to forelimb movement patterns (Figures 3B and 3C) that were accompanied by reduced trial-to-trial variability (Figure 3D), culminating in precise and individually distinct forepaw trajectories (Figures 3E and 3F). When performance at the target IPI reached asymptote, the underlying kinematics largely stabilized (Figures 3D, 3F, and 3G). Moreover, as with human motor skills (
• Park S.-W.
• Dijkstra T.M.H.
Learning to never forget-time scales and specificity of long-term memory of a motor skill.
,
• Romano J.C.
• Howard Jr., J.H.
• Howard D.V.
One-year retention of general and sequence-specific skills in a probabilistic, serial reaction time task.
), the learned behaviors were maintained even after many days without practice (Figure 3G), suggesting that they had been consolidated into motor control circuitry.
### Motor Cortex Is Not Required for Performing the Learned Skills
To probe whether execution of the complex learned motor sequences requires motor cortex (Figure 4A), we lesioned it after asymptotic performance was reached (n = 11 rats). We initially lesioned motor cortex in the hemisphere contralateral to the paw used for lever-pressing, or, when both paws were used, the paw that pressed the lever first. Induced lesions (>23 mm3 of cortical volume) were similar to those in previous studies, demonstrating motor cortical involvement in skilled reaching tasks requiring dexterity (
• Whishaw I.Q.
Loss of the innate cortical engram for action patterns used in skilled reaching and the development of behavioral compensation following motor cortex lesions in the rat.
,
• Whishaw I.Q.
• O’Connor W.T.
• Dunnett S.B.
The contributions of motor cortex, nigrostriatal dopamine and caudate-putamen to skilled forelimb use in the rat.
), and encompassed both primary and secondary forelimb representations; i.e., the area of cortex that controls the forelimb (
• Bonazzi L.
• Viaro R.
• Lodi E.
• Canto R.
• Bonifazzi C.
• Franchi G.
Complex movement topography and extrinsic space representation in the rat forelimb motor cortex as defined by long-duration intracortical microstimulation.
,
• Neafsey E.J.
• Bold E.L.
• Haas G.
• Hurley-Gius K.M.
• Quirk G.
• Sievert C.F.
• Terreberry R.R.
The organization of the rat motor cortex: a microstimulation mapping study.
; Figure 4B; Figure S3; Experimental Procedures).
As judged by their ability to move around the cage and manipulate food pellets, all lesioned animals were initially impaired on the contralesional side, consistent with prior reports (
• Castro A.J.
The effects of cortical ablations on digital usage in the rat.
). This initially depressed motor activity suggested that subcortical motor circuits were transiently affected by the sudden loss of cortical inputs (
• Seitz R.J.
• Azari N.P.
• Knorr U.
• Binkofski F.
• Herzog H.
• Freund H.J.
The role of diaschisis in stroke recovery.
). By the end of the 10-day recovery period, however, animals were moving around normally, implying that subcortical circuits had recovered to the point of supporting basic motor functions.
If motor cortex is required for storing and executing the learned motor sequences we train, then rats reintroduced to the task after the lesions would be expected to have significant performance deficits and altered movement kinematics. If, on the other hand, the acquired skills are stored subcortically and motor cortical input to the essential control circuits is not essential for generating them, then post-lesion task performance should be much less affected.
Remarkably, when reintroduced into the behavioral apparatus on the 11th day after the lesions, animals performed the task much as they had previously (Figures 4C–4E). Trial-to-trial variability, measured as the CV of the IPI distribution, was increased on the first days of post-lesion training (Figure 4E), consistent with the trend seen after 10-day breaks in unlesioned animals. The mean IPI also showed a trend comparable with what is seen after control breaks. On the first day of post-lesion training, only 1 of 11 rats showed an effect on performance (p < 0.05) above and beyond what could be expected from a 10-day break in intact animals (Experimental Procedures). The affected individual recovered to normal performance levels by the 9th day of training.
The highly stereotyped and individually distinct movement patterns were also largely unaffected by the motor cortex lesions. This becomes strikingly evident when comparing high-speed movies of task performance before and after the lesions (Movie S3). Forepaw trajectories were also similar to pre-lesion already on the very first day of post-lesion training (n = 7; Figures 5A–5C), the only “outlier” being the rat that also showed a significant performance deficit (orange arrow in Figure 5C).
Interestingly, this was the only rat in our cohort to converge on a strategy contingent on precise positioning and movement of the distal digits (Movie S4). That performance and learned kinematics were compromised in this rat following the lesion is consistent with motor cortex being essential for certain types of digit movements (
• Alaverdashvili M.
• Whishaw I.Q.
Motor cortex stroke impairs individual digit movement in skilled reaching by the rat.
,
• Whishaw I.Q.
• Pellis S.M.
• Gorny B.P.
• Pellis V.C.
The impairments in reaching and the movements of compensation in rats with motor cortex lesions: an endpoint, videorecording, and movement notation analysis.
). This rat largely recovered its pre-lesion form after a few days of training, seemingly compensating for the loss of precise digit control (Movie S4). The forepaw trajectories also became more similar to pre-lesion (correlation coefficient going from 0.51 on the first day after lesion to 0.79 on the third day), consistent with the gross structure of the learned motor sequence being stored downstream of motor cortex also in this rat.
To test whether motor cortex in the contralesional hemisphere was integral to the spontaneous recoveries we observed, we lesioned it in a subset of rats (n = 8) after a few additional weeks of training (range, 26–60 days). Following a 10-day recovery period, the now bilaterally motor cortex-lesioned animals still executed the skill similar to pre-lesion (Figures 4C–4E, 5B, and 5C; Movie S5). CV and deviation from target IPI were consistent with having a 10-day break for all but one animal, which transiently sped up the execution of its acquired movement sequence. However, the mean trajectories around the target IPI for this and all other lesioned rats remained similar to pre-lesion (Figures 5B and 5C).
These results show that motor cortex is not obligatory for storing or executing complex learned motor sequences. They further suggest that the function of subcortical motor circuits can be remarkably resilient to the loss of motor cortical input and can even support the execution of certain consolidated motor skills without it.
### Lesioning Motor Cortex prior to Learning the Task
Next we asked whether motor cortex is essential for learning the skills for which it is not, when acquired, a required controller. This gets at whether motor cortex has a role in learning that is distinct from its role in control (
• Willingham D.B.
A neuropsychological theory of motor skill learning.
).
A priori, there are two main possibilities. One is that motor learning is an extension of control (
• Willingham D.B.
A neuropsychological theory of motor skill learning.
) and that circuits sufficient for generating a consolidated skill are also sufficient for learning it. Another possibility is that motor cortical projections to downstream motor circuits “tutor” these phylogenetically older control circuits during learning, allowing them to acquire and produce complex task-specific movement sequences (Figure 6A).
To arbitrate between these possibilities, we lesioned motor cortex bilaterally in untrained rats (n = 11) using the same protocol as for trained animals (Figure 4B; Experimental Procedures). After recovering for 12 ± 4 days (range, 6–21 days), rats were introduced to the task for the first time.
Early in learning, there was little to distinguish lesioned and unlesioned animals in terms of task performance or relevant metrics of motor output (Figures 6B–6H). Across the first 1,000 trials of timed lever-press training (Experimental Procedures), the mean and CV of the IPI distributions were not significantly different for the two cohorts (Figures 6B and 6C). The fraction of IPIs within 10% of the 700-ms target (Figure 6D) and average reward rates (Figure 6E) were also similar, meaning that, during this initial exploratory phase of learning, lesioned rats generated the prescribed lever-press sequence at rates comparable to controls. Motivation for the task, measured as the number of lever-presses in a training session, was similarly unaffected by the lesions (Figure 6F). Furthermore, lesioned rats did not have any deficits in learning the association between the reward tone and the availability of water (Figure 6G). The number of taps outside of the trial context was also similar (Figure 6H). Therefore, exploratory lever-pressing behavior and the capacity to respond to reward—two essential ingredients for the trial and error learning process by which the skills are acquired—were, by our measures, unaffected by motor cortical lesions.
### Skill Learning Is Severely Affected by Motor Cortex Lesions
Even though we found no major deficits in motivation or baseline control to prevent lesioned animals from engaging with the lever and learning from their interactions with it, none of the rats learned the task to criterion (Figures 7A–7D). This was despite being kept in training three times longer than it takes normal animals to master the task (97 ± 23 training days corresponding to 60,029 ± 20,390 trials, n = 11). In terms of precision of motor output (CV of the IPIs), lesioned animals reached asymptotic performance after 27,014 ± 12,178 trials or 53 ± 19 training days (Experimental Procedures), at which point their timing variability (CV of the IPI distribution) was nearly double that of intact animals (0.38 ± 0.06) and only 27% lower than at the start of training (Figure 4C), with none of the animals below 0.25. The mean IPI across the population was also significantly lower than the 700-ms target at this stage of training (601 ± 67 ms), with only 3 of the 11 rats being within 10% of the target IPI (Figure 7B).
Furthermore, although all unlesioned animals learned to withhold lever-pressing for the prescribed 1.2 s after unrewarded IPIs (Figures 7E–7H; Experimental Procedures), only 1 of 11 lesioned animals mastered this aspect of the task within the time frame of training. Lesioned rats instead continued to press the lever prematurely after unrewarded IPIs, showing little affinity for learning the metastructure of the task (Figure 7E). Intriguingly, when normal animals learn the 1.2-s inter-trial delay, this aspect too is robust to motor cortical lesions (Figure S4), providing yet another example of a task-specific behavior that requires motor cortex for learning but not—when acquired—for retention and execution.
To rule out the possibility that the learning deficits we saw in motor cortex-lesioned animals were due to non-specific cortical tissue damage, we induced the same-size lesions 5 mm posterior to motor cortex, targeting parts of sensory and parietal cortices (n = 3 rats). Rats with these extra-motor cortical lesions learned the task and inter-trial delay as well as normal rats (Figure S5), indicating that the severe learning deficits we observed in motor cortex-lesioned animals (Figure 7) were due to the specific loss of motor cortical function.
## Discussion
To probe the role of motor cortex in the acquisition and execution of task-specific motor sequences independently of its established role in dexterous control (Figure 1), we developed a novel motor learning paradigm that trains spatiotemporally precise movement patterns in rats (Figures 2 and 3). Surprisingly, we found that motor cortex is dispensable for executing such non-dexterous skills (Figures 4 and 5), implying that they can be stored and generated in subcortical motor circuits (
• Lashley K.S.
Studies of cerebral function in learning: V. the retention of motor habits after destruction of the so-called motor areas in primates.
,
• Lashley K.S.
In Search of the Engram.
). In contrast, when we lesioned motor cortex prior to training, animals failed to learn the task (Figures 6 and 7), suggesting a role for motor cortex in enabling downstream circuits to learn and execute certain types of motor skills.
### Contrasts with Prior Studies on Motor Skill Execution
At first glance, our results may seem at odds with prior lesion studies implicating motor cortex in skill execution (
• Darling W.G.
• Pizzimenti M.A.
• Morecraft R.J.
Functional recovery following motor cortex lesions in non-human primates: experimental implications for human stroke patients.
,
• Whishaw I.Q.
• O’Connor W.T.
• Dunnett S.B.
The contributions of motor cortex, nigrostriatal dopamine and caudate-putamen to skilled forelimb use in the rat.
,
• Whishaw I.Q.
• Pellis S.M.
• Gorny B.P.
• Pellis V.C.
The impairments in reaching and the movements of compensation in rats with motor cortex lesions: an endpoint, videorecording, and movement notation analysis.
). Importantly, however, many of these studies trained animals to adapt species-typical reaching movements to novel and challenging food retrieving scenarios. Solutions to such tasks typically involve new and dexterous movements that are known to require corticospinal control (
• Bortoff G.A.
• Strick P.L.
Corticospinal terminations in two new-world primates: further evidence that corticomotoneuronal connections provide part of the neural substrate for manual dexterity.
,
• Darling W.G.
• Pizzimenti M.A.
• Morecraft R.J.
Functional recovery following motor cortex lesions in non-human primates: experimental implications for human stroke patients.
,
• Lemon R.N.
Descending pathways in motor control.
).
In contrast, our task was designed to probe the role of motor cortex in learning and executing task-specific motor sequences that, in principle at least, can be built from subcortically generated actions—a complementary dimension of motor skill learning. The central challenge of our task was not to refine the control of specific movements but, rather, to assemble pre-existing movements into novel, stereotyped, and reliably expressed sequences equal to a prescribed task.
That our conclusions relating to motor cortex’s role in skill execution differ from previous studies is not a contradiction but, rather, a reflection of the heterogeneous nature of “motor skill learning” and the fact that different learning and control challenges can rely on different neural circuits and mechanisms (
• Ali F.
• Otchy T.M.
• Pehlevan C.
• Fantana A.L.
• Burak Y.
• Ölveczky B.P.
The basal ganglia is necessary for learning spectral, but not temporal, features of birdsong.
,
• Thorn C.A.
• Atallah H.
• Howe M.
• Graybiel A.M.
Differential dynamics of activity changes in dorsolateral and dorsomedial striatal loops during learning.
).
### Contribution of Subcortical Circuits to Skill Execution
That the learned skills we train are preserved following large bilateral motor cortex lesions suggests a role for subcortical circuits in their storage and execution. Although the cerebellum (
• Ito M.
Cerebellum and Neural Control.
) and basal ganglia (
• Graybiel A.M.
• Aosaki T.
• Flaherty A.W.
• Kimura M.
The basal ganglia and adaptive motor control.
) are known to support many aspects of motor control, their contributions to acquired skills are often presumed to be mediated through interactions with motor cortex (
• Doyon J.
• Bellec P.
• Amsel R.
• Penhune V.
• Monchi O.
• Carrier J.
• Lehéricy S.
• Benali H.
Contributions of the basal ganglia and functionally related brain structures to motor learning.
,
• Hikosaka O.
• Nakamura K.
• Sakai K.
• Nakahara H.
Central mechanisms of motor skill learning.
). Other subcortical motor structures, such as the reticular formation (
• Baker S.N.
The primate reticulospinal tract, hand function and functional recovery.
,
• Esposito M.S.
• Capelli P.
• Arber S.
Brainstem nucleus MdV mediates skilled forelimb motor tasks.
), red nucleus (
• Massion J.
Red nucleus: past and future.
), and superior colliculus (
• Philipp R.
• Hoffmann K.-P.
Arm movements induced by electrical microstimulation in the superior colliculus of the macaque monkey.
), are thought to encode species-specific movements and action patterns or serve as intermediaries for cortical commands (
• Esposito M.S.
• Capelli P.
• Arber S.
Brainstem nucleus MdV mediates skilled forelimb motor tasks.
). Our results expand this view by showing that movements generated by subcortical controllers can be shaped, sequenced, and coordinated during skill learning to yield complex task-specific motor patterns that can be stored and produced independently of motor cortex. The limits of subcortical plasticity and the extent to which lower-level motor circuits can support other forms of complex learned motor behaviors remains to be understood.
### Implications for Understanding Recovery after Motor Cortex Lesions
Functional recovery after motor cortical injury is often attributed to experience-dependent cortical reorganization and plasticity (
• Nudo R.J.
• Plautz E.J.
• Frost S.B.
Role of adaptive plasticity in recovery of function after damage to motor cortex.
,
• Sanes J.N.
• Donoghue J.P.
Plasticity and primary motor cortex.
), a process that hinges on the capacity of unlesioned motor circuits to acquire, through experience, new strategies to compensate for lost functionality (
• Krakauer J.W.
Motor learning: its relevance to stroke recovery and neurorehabilitation.
). Although this may explain some aspects of use-dependent motor recovery, it is not likely to account for the spontaneous and complete recoveries we observed in our task (Figures 4 and 5). This is because the spatiotemporally precise movement patterns we train have no general utility outside the context of our task and are not practiced during the post-lesion recovery period. That the skills, acquired over many weeks of training, were nevertheless expressed in their distinct pre-lesion forms on the very first day of post-lesion training (Figure 5; Movies S3 and S5) suggest that they were consolidated and stored in unlesioned parts of the motor system.
The spontaneous post-lesion recoveries may therefore be better explained by subcortical circuits, including spinal circuits, spontaneously recovering their pre-lesion skill-related activity patterns (
• Seitz R.J.
• Azari N.P.
• Knorr U.
• Binkofski F.
• Herzog H.
• Freund H.J.
The role of diaschisis in stroke recovery.
). The mechanisms that underlie such spontaneous recovery remain to be addressed, but homeostatic regulation of circuit dynamics (
• Golowasch J.
• Casey M.
• Abbott L.F.
• Marder E.
Network stability from activity-dependent regulation of neuronal conductances.
) and augmentation of subcortical inputs to spinal circuits (
• Zaaimi B.
• Edgley S.A.
• Soteropoulos D.S.
• Baker S.N.
Changes in descending motor pathway connectivity after corticospinal tract lesion in macaque monkey.
) are likely candidates.
### Contrasts with Prior Studies on Motor Skill Learning
Previous studies have established the importance of motor cortex for learning and generating new and dexterous movements. Our study was not designed to delve further into this domain of motor control or motor learning. Rather, it was meant to dissociate learning and control processes to investigate whether and how motor cortex contributes to the acquisition of skills that can be built from sequencing and coordinating subcortically generated actions.
We found that rats with motor cortical lesions were unable to learn our sequential lever-pressing task despite having no obvious motor control or motivational deficits that would prevent them from doing so (Figure 6). This inability was surprising, given that rodents can learn to perform skilled reaching tasks even after large motor cortical lesions (
• Gharbawie O.A.
• Whishaw I.Q.
Parallel stages of learning and recovery of skilled reaching after motor cortex stroke: “oppositions” organize normal and compensatory movements.
). The common explanation for such outcomes is that animals compensate for loss of dexterity by adapting their innate reaching movements to the imposed experimental constraints in non-dexterous ways (
• Darling W.G.
• Pizzimenti M.A.
• Morecraft R.J.
Functional recovery following motor cortex lesions in non-human primates: experimental implications for human stroke patients.
,
• Gharbawie O.A.
• Whishaw I.Q.
Parallel stages of learning and recovery of skilled reaching after motor cortex stroke: “oppositions” organize normal and compensatory movements.
,
• Whishaw I.Q.
Loss of the innate cortical engram for action patterns used in skilled reaching and the development of behavioral compensation following motor cortex lesions in the rat.
). But if rats can compensate for such motor deficits and learn to master skilled reaching tasks after motor cortical lesions, then why can they not learn our task, which, after all, does not depend on motor cortex for control?
Although our task differs from skilled reaching in several ways, one distinction that could potentially explain the differential effects of motor cortex lesions is that our task requires learning and consolidating a fairly complex and novel motor sequence with no prior ethological relevance and no clear a priori goal. Skilled reaching, in contrast, involves modifying naturally expressed reaching movements to achieve a clear goal (get food). One hypothesis to be tested is that motor cortex is essential for sequencing movements into new task-specific sequences but less important for modifying the details of existing and habitually expressed behaviors.
### A Tutor Function for Motor Cortex?
Our results suggest that motor cortex functions as a tutor for subcortical motor circuits during learning, helping them acquire and consolidate new motor sequences. The facts that lesioned animals had great difficulty reliably executing longer IPIs (Figures 7B and 7C), persevered with unrewarded motor patterns, and were incapable of withholding lever-pressing after unrewarded IPIs (Figures 7F–7I) are consistent with motor cortex suppressing innate motor tendencies and reflexes (such as rapid tapping; Figure S1) in context-specific ways (
• Ioffe M.E.
Pyramidal influences in establishment of new motor coordinations in dogs.
,
• Stoltz S.
• Humm J.L.
• Schallert T.
Cortical injury impairs contralateral forelimb immobility during swimming: a simple test for loss of inhibitory motor control.
). Our results suggest that such cortical tutoring or modulation can lead, over the course of weeks of training, to the permanent reprogramming of sub-cortical circuits.
The extent to which this explains the essential contributions of motor cortex to the learning process remains to be parsed, and we note that other hypothetical functions of motor cortex, including adaptive shaping of motor variability (
• Chaisanguanthum K.S.
• Shen H.H.
• Sabes P.N.
Motor variability arises from a slow random walk in neural state.
,
• Wu H.G.
• Miyamoto Y.R.
• Gonzalez Castro L.N.
• Ölveczky B.P.
• Smith M.A.
Temporal structure of motor variability is dynamically regulated and predicts motor learning ability.
) and general facilitation of sub-cortical plasticity, could also contribute to its tutor function. But regardless of how motor cortex shapes motor output during skill learning, our results show that the adaptive biases it contributes or enables become incorporated and consolidated in downstream circuits.
Intriguingly, the principle of a cortical brain region tutoring downstream control circuits during complex motor sequence learning has been demonstrated previously in songbirds (
• Andalman A.S.
• Fee M.S.
A basal ganglia-forebrain circuit in the songbird biases motor output to avoid vocal errors.
,
• Bottjer S.W.
• Miesner E.A.
• Arnold A.P.
Forebrain lesions disrupt development but not maintenance of song in passerine birds.
,
• Turner R.S.
• Desmurget M.
Basal ganglia contributions to motor control: a vigorous tutor.
). During vocal learning, the lateral magnocellular nucleus of the anterior nidopallium (LMAN), a cortex-analogous brain area, provides a consistent error-correcting premotor bias that is thought to drive permanent changes in vocal control circuits (
• Andalman A.S.
• Fee M.S.
A basal ganglia-forebrain circuit in the songbird biases motor output to avoid vocal errors.
). LMAN, similarly to motor cortex in our task, is essential for learning the complex motor patterns underlying song but not for executing them when they have been learned and consolidated (
• Bottjer S.W.
• Miesner E.A.
• Arnold A.P.
Forebrain lesions disrupt development but not maintenance of song in passerine birds.
). This suggests that the dissociation between learning and control in neural hardware, and the idea that one motor-related circuit shapes the control policies of another, reflect a general principle of how the brain implements complex motor learning (
• Graybiel A.M.
Habits, rituals, and the evaluative brain.
,
• Turner R.S.
• Desmurget M.
Basal ganglia contributions to motor control: a vigorous tutor.
).
### Evolutionary Implications
Motor cortex is a mammalian addition to the basic vertebrate motor plan that has radically improved the capacity of animals to learn and execute new and dexterous movements (
• Nudo R.J.
• Frost S.
The evolution of motor cortex and motor systems.
). In addition to its unique control function, our results suggest that motor cortex is utilizing phylogenetically older motor controllers to a larger extent than assumed previously. Motor cortex, as the master overseer of the animal’s motor output, has access to contextual, sensory, and planning information from other neocortical areas that may not be independently available to subcortical motor circuits. Using this information to shape the control policies of lower-level motor circuits could be an efficient strategy for influencing and adapting motor output. Rather than reinventing control functionalities already present in the ancestral brain, mammals with a cortex may, instead, have evolved strategies to make better use of these pre-existing and robust control functions (
• Doyle J.C.
• Csete M.
Architecture, constraints, and behavior.
,
• Shmuelof L.
• Krakauer J.W.
Are we ready for a natural history of motor learning?.
).
Therefore, if a task can be solved by assembling individual actions from the animal’s subcortical motor repertoire, then motor cortex could help in sequencing and coordinating those components, expanding the functionality of lower-level motor circuits in the process. When faced with tasks, such as skilled reaching, that cannot be efficiently solved by subcortical control strategies alone, motor cortex could contribute to movement generation directly through its projections to the spinal cord.
If such a division of control is indeed realized, it would imply that many complex motor skills are implemented across cortical and subcortical control networks (
• Drew T.
• Krouchev N.
Muscle synergies during locomotion in the cat: a model for motor cortex control.
). Interestingly, the one outlier rat (Figure 5C; Movie S4) that had difficulty performing the task after motor cortex lesions was also the only one to have adopted a strategy requiring precise digit control, and it was this deficit that seemingly affected its post-lesion performance (Movie S4). Skilled reaching behaviors are compromised in similar ways, with dexterous aspects being affected preferentially (
• Alaverdashvili M.
• Whishaw I.Q.
Motor cortex stroke impairs individual digit movement in skilled reaching by the rat.
), suggesting that the non-dexterous part of the species-typical reaching movements may be stored downstream of motor cortex. If controllers at different levels of the motor hierarchy work in synergy, then synchronizing them will be essential for robust and smooth performance (
• Drew T.
• Krouchev N.
Muscle synergies during locomotion in the cat: a model for motor cortex control.
). How this is implemented in neural circuitry is an intriguing problem that remains to be understood.
In contrast to most studies of motor cortex’s role in skill learning that focus on plasticity in corticospinal controllers, our study was designed to dissociate learning and control processes. Our new paradigm achieved this in a surprisingly clean way, revealing a function of motor cortex in guiding plasticity in downstream control circuits. Although the nature of motor cortex’s interaction with downstream circuits during skill learning still remains to be understood, our new paradigm should provide a powerful means to dissect it.
## Experimental Procedures
### Animals
Experimental subjects were male and female Long Evans rats 3–8-months old at the start of training (Charles River Laboratories). The care and experimental manipulation of the animals were reviewed and approved by the Harvard Institutional Animal Care and Use Committee.
### Behavioral Training
A total of 38 rats were trained in our motor skill learning assay (Figure 2A). Training was done in custom-made behavioral boxes measuring approximately 12” × 12” × 12” (length × width × height). The ventilated boxes were supplied with a lever (14 cm above the floor), a reward spout for water delivery, a loudspeaker for generating the reward tone, and either a high-speed color camera (200 fps, Pike F-032C) or a webcam (30 fps, Agama V-1325R) for monitoring the lever-pressing behavior. The lever was placed behind a protruding slit (∼1.5 cm wide, 5 cm tall, and protruding ∼2 cm into the cage) made of two pieces of cut plastic or glass glued to the wall of the cage. This was done to ensure that the rat pressed the lever with its forepaws and not, for example, with its snout. The force required to press the lever was <0.1 N, and the deflection amplitude threshold required for registering a “press” was ∼3 mm.
Animals were either transferred to the training boxes for ∼1-hr training sessions 5 or 6 times a week (n = 6 rats) or kept in the training boxes for the duration of the experiments and received two 1-hr daily training sessions 7 days a week (n = 32 rats). The fully automated home cage training system that was used for the latter cohort has been described in detail (
• Poddar R.
• Kawai R.
• Ölveczky B.P.
A fully automated high-throughput training system for rodents.
). We have shown previously that the learning rates as well as number of trials performed per day are similar whether animals are trained in home cages or transferred to behavioral boxes for experimental sessions (
• Poddar R.
• Kawai R.
• Ölveczky B.P.
A fully automated high-throughput training system for rodents.
). Therefore, results from rats trained in the different contexts were pooled.
The lever-press sequences were shaped by rewarding water-restricted rats with water for approximations to the desired sequence (700 ms apart for all but two rats, which had targets of 500 and 600 ms, respectively). The predefined and automated training protocol was implemented in custom software (C#) (
• Poddar R.
• Kawai R.
• Ölveczky B.P.
A fully automated high-throughput training system for rodents.
) and is described in the Supplemental Experimental Procedures.
### Kinematic Tracking
#### High-Speed Tracking of Forepaw Movements
To track and quantify the kinematics of the rats’ forepaw movements as a function of learning, we tattooed the paws with colored ink (red and blue) under light anesthesia (1.5% isoflurane in carbogen) in four animals prior to the start of training. Animals were then trained in a behavioral box outfitted with a high-speed camera (200 fps). The box was placed in a lightproof enclosure lit with light-emitting diodes (LEDs) (Rayconn Electronics, catalog no. FLB6 RGB), ensuring constant illumination of the box over the course of training. Video acquisition was triggered on lever-presses, and custom-written software (Matlab) was used to automatically extract the centroid of the colored blob that corresponded to the forepaws (Movie S2) by thresholding the red and blue color channels in the movies (see also “Kinematic Analysis” in the “Data Analysis” section). In practice, it was only possible to continuously track the paw closest to the camera because the other paw was often obscured. For all four animals we tracked, the paw closest to the camera was involved in pressing the lever.
#### Tracking from Webcam Movies
To increase the number of animals in which the effects of 10-day control breaks and motor cortex lesions on paw kinematics could be assessed, we also tracked the paws of animals whose interaction with the lever was captured with the lower frame rate webcams (30 fps). Only a subset of these animals was amenable to paw tracking. The reason for excluding individual rats from tracking were as follows: (1) The camera angle/position prevented us from seeing/tracing either paw (both obscured by the animal’s body, n = 2); (2) inadvertent displacement of the camera during weekly cleaning of the cage preventing us from comparing movie-based paw tracking before and after a given manipulation (n = 1); and (3) for two rats, the plastic protrusion around the lever was opaque (in the other cases they were see-through), therefore obscuring the paw for much of the movement. In one of these cases we were able to instead track a recognizable part of the elbow region of the forelimb, but these data were not pooled with the other subjects because they tracked a different part of the rat’s anatomy. Nevertheless, we present these data in Figure S3 because they show kinematics to be largely preserved, even after a cortical lesion larger than our standard ibotenic acid lesions (Figure 4B).
### Motor Cortex Lesions
Rats received motor cortex lesions either before training (n = 11) or after the behavior reached criterion performance and had asymptoted in terms of CV (n = 20). The lesions in these cohorts were done following the same protocol as described below. Animals were anesthetized with 2% isoflurane in carbogen and placed in a stereotactic apparatus. Craniotomies were made over motor cortex. The location of the bregma was noted, and the lesions were induced relative to the bregma and the midline (Figure 4B). Two of the rats lesioned after asymptotic performance had been reached underwent aspirations of motor cortex as described previously (
• Whishaw I.Q.
Loss of the innate cortical engram for action patterns used in skilled reaching and the development of behavioral compensation following motor cortex lesions in the rat.
). Although the forelimb areas of motor cortex were targeted, in one case, a larger-than-intended area was removed (Figure S3). We initially did aspirations because the collateral impact on downstream circuits is less than that for alternative lesioning methods (
• Glenn M.J.
• Lehmann H.
• Mumby D.G.
• Woodside B.
Differential fos expression following aspiration, electrolytic, or excitotoxic lesions of the perirhinal cortex in rats.
). In our hands, however, aspirations were not as accurate or reproducible in terms of lesion size and location, and we switched to inducing lesions by injecting 1% ibotenic acid, an excitotoxic agent, for the remainder of the rats (i.e., all but the initial two).
The injection sites were at (1.0 mm, 2.0 mm), (3.0 mm, 2.0 mm), and (1.0 mm, 4.0 mm) respectively, where the first coordinate is the anterior distance from the bregma and the second coordinate is the lateral distance from the midline. At each site, 82.8 nl, in increments of 9.2 nl every 10 s, was injected at two depths, 1.5 and 0.75 mm, with respect to the surface, for a total of 165.6 nl per site (Nanoject, WPI). We calibrated the lesions to ensure that they encompassed both the primary and secondary forelimb areas; i.e., the parts of motor cortex that, when electrically stimulated, induce movements of the forelimb (
• Bonazzi L.
• Viaro R.
• Lodi E.
• Canto R.
• Bonifazzi C.
• Franchi G.
Complex movement topography and extrinsic space representation in the rat forelimb motor cortex as defined by long-duration intracortical microstimulation.
,
• Neafsey E.J.
• Bold E.L.
• Haas G.
• Hurley-Gius K.M.
• Quirk G.
• Sievert C.F.
• Terreberry R.R.
The organization of the rat motor cortex: a microstimulation mapping study.
). To ensure that our protocol induced consistent lesions, we lesioned four untrained animals and sacrificed them 3 days post-lesion. We found that our drug injection protocol induced very reproducible lesions (Figure 4B shows the extent of the lesions in these four animals). We used this protocol for all subsequent lesions.
Following surgery and lesions, animals recovered in normal rodent cages for 5 (for the two aspirated rats) or 10 (for the ibotenic acid-lesioned rats) days before resuming behavioral training. We noted that general motor function, i.e., the ability to ambulate normally and to properly use the limb contralateral to the lesioned hemisphere, seemed to recover faster after aspirations than after ibotenic acid lesion, consistent with the excitotoxicity associated with ibotenic acid lesions lasting several days. This was also the main reason for the different recovery periods.
Bilateral motor cortex lesions in untrained rats were done in two stages for 6 of the 11 rats. After one hemisphere had been lesioned, animals recovered for 19–28 (21 ± 3, mean ± SD) days before undergoing lesions to the contralesional hemisphere. Animals then recovered for another 6–21 (11 ± 4) days before starting training. In the remainder of the rats (n = 5), we lesioned motor cortex bilaterally in the same surgery. Because there was no significant difference between one-stage and two-stage lesioned animals in terms of performance or learning, the results from these cohorts were pooled.
At the end of the experiment, animals were euthanized, perfused with 4% paraformaldehyde (PFA), and their brains were harvested for histology to confirm lesion size and location. The brains were sectioned into 100-μm slices and strained with Cresyl Violet. Quantitative assessment of lesion size was done by demarcating the lesions boundaries and then generating a map of the lesion using custom-written software that stitched together the marked slices (Figure 4B).
### Data Analysis
#### Definition of Asymptotic Performance in Terms of Temporal Precision
We first estimated the CV around each trial by calculating the CV over a 500-trial sliding window. We then fit a linear regression to the CV curve every 400 trials using a 2,700-trial window size. Asymptotic performance was defined as the point at which four consecutive linear regression fits had slopes less than 1.5 × 10−5/trial.
#### Calculation of Performance Metrics
For Figures 2 and 7 (learning), the CV was calculated across 100 trials, and the moving average was then low pass-filtered with a 300-trial boxcar filter. The distance from the target was calculated similarly using the absolute deviation from the target as the variable. For Figure 4 (pre/post manipulation), we used the same procedure as for learning but used a smaller moving window (25 trials) and boxcar filter (50 trials).
#### Criterion Performance
Animals were deemed to have reached criterion performance when, for a 3,000-trial sliding window, the CV was less than 0.25 and the mean of the IPI distribution was within 10% of the target.
#### Learning the Prescribed 1.2-s Inter-Trial Delay
According to our definition, the prescribed 1.2-s inter-trial delay was learned when, for a 3,000-trial sliding window, the median time to the next tap was larger than 1.2 s and this was maintained for at least another 3,000 trials. Intervals >5 s or those that occurred after rewarded trials were excluded (but included for the sliding window).
#### Kinematic Analysis of High-Speed Movies
Movie frames were converted to the hue saturation value (HSV) color representations, and, for each animal, a single HSV threshold was determined for isolating the tattooed paw. The threshold was chosen at a value that reliably (>90%) picked out the paw in the video. The location of the paw was defined as the centroid of the pixels above threshold. The trajectories were filtered using a running median filter (window size of 5 frames at 200 fps). All trajectories were aligned to the first lever-press and traced for 1,150 ms, starting 250 ms before the first lever-press. Because some of the paw trajectories were not traced properly, we excluded outliers in our dataset by calculating the principal components (PCs) of the traced trajectories in each session and then using the first three PCs to calculate the Mahalanobis distance for each trajectory. We excluded trajectories beyond the 90% confidence interval of the chi-square distribution (<10% of the tracings were therefore excluded).
#### Pairwise Correlations to Estimate Trial-by-Trial Variability
The trials were pre-selected by IPI (see text). The trial-by-trial variability (Figure 3D) was estimated as the average correlation coefficient of all pairs of trajectories that conformed to the selected IPI range. The correlation coefficient for a given pair was calculated as follows.
The horizontal and vertical paw displacements of the i-th trial (Xi(t) and Yi(t), respectively) were mean-subtracted and concatenated to form one single trajectory vector as follows:
$Ti=[Xi(t)−〈Xi(t)〉Yi(t)−〈Y(t)i〉].$
(Equation 1)
The correlation coefficient of two trials, i and j, was then calculated as
$R(Ti,Tj)=C(Ti,Tj)C(Ti,Ti)C(Tj,Tj),$
(Equation 2)
where C is the covariance.
#### Correlation in the Mean Trajectory across Days and Conditions
The trials were pre-selected by IPI (see text). The mean trajectory of each session was used to calculate the correlation coefficient matrix (Figure 3C). The correlation coefficient across two sessions was calculated with the same equations as above, except here, Xi(t) and Yi(t) were the average paw displacement in a session rather than in an individual trial.
#### Effects of Lesions on Paw Kinematics
To assess whether the effects of the lesions were above and beyond what could be expected from 10-day control breaks, we compared the root-mean-square (RMS) of the IPIs as follows. Let μpre be the mean IPI before a condition (window of 1,000 trials). The RMS before or after a condition was then calculated as follows:
$RMS=1n∑i=1n(ti−μpre)2,$
(Equation 3)
where n = 300 trials immediately preceding or following the condition (lesion/break), and ti the IPI of the i-th trial. To compare across conditions, we calculated the RMS difference as RMSPostRMSPre for each condition. We then performed a z test at the 5% significance level for each animal against the null distribution, which was constructed from the RMS differences across the 10-day control breaks in animals that underwent them.
## Acknowledgments
We thank Ed Soucy and Joel Greenwood for technical assistance, the Harvard University Neurobiology Department and the Neurobiology Imaging Facility for imaging consultation and equipment use, Suraj Krishna-Umang Sheth and Chong Guo for help with data analysis, and Rene Chen for help with the illustration in Figure 2. We thank Armaghan Behlum for assistance with quantifying the extent of the lesions. We are grateful to Joshua Sanes, Timothy Gardner, Jeffrey Markowitz, Jesse Goldberg, Aaron Andalman, Evan Feinberg, Maximilian Joesch, Kenneth Blum, and members of the B.P.Ö. lab for their valuable feedback on the manuscript. This work was supported by a McKnight Scholars Award (to B.P.Ö.) and an NRSA fellowship (to R.K.). A.K.D. is an Ellison Medical Foundation fellow of the Life Sciences Research Foundation.
## Supplemental Information
• Document S1. Supplemental Experimental Procedures and Figures S1–S5
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https://arxiv.org/abs/astro-ph/0511197
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astro-ph
(what is this?)
# Title: Seeing Darkness: the New Cosmology
Abstract: We present some useful ways to visualize the nature of dark energy and the effects of the accelerating expansion on cosmological quantities. Expansion probes such as Type Ia supernovae distances and growth probes such as weak gravitational lensing and the evolution of large scale structure provide powerful tests in complementarity. We present a ladder'' diagram, showing that in addition to dramatic improvements in precision, next generation probes will provide insight through an increasing ability to test assumptions of the cosmological framework, including gravity beyond general relativity.
Comments: plenary talk at TAUP2005; to appear in Journal of Physics; 7 pages Subjects: Astrophysics (astro-ph) Journal reference: J.Phys.Conf.Ser.39:56-62,2006 DOI: 10.1088/1742-6596/39/1/013 Cite as: arXiv:astro-ph/0511197 (or arXiv:astro-ph/0511197v1 for this version)
## Submission history
From: Eric Linder [view email]
[v1] Mon, 7 Nov 2005 21:00:16 GMT (146kb)
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http://www.physicsforums.com/showthread.php?p=2877517
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## Solving for a Surjective Matrix
I saw this in a book as a Proposition but I think it's an error:
Assume that the (n-by-k) matrix, $$A$$, is surjective as a mapping,
$$A:\mathbb{R}^{k}\rightarrow \mathbb{R}^{n}$$.
For any $$y \in \mathbb{R}^{n}$$, consider the optimization problem
$$min_{x \in \mathbb{R}^{k}}\left{||x||^2\right}$$
such that $$Ax = y$$.
Then, the following hold:
(i) The transpose of $$A$$, call it $$A^{T}$$ is injective.
(ii) The matrix $$A^{T}A$$ is invertible.
(iii) etc etc etc....
I have a problem with point (ii), take as an example the (2-by-3) surjective matrix
$$A = \begin{pmatrix} 1 & 0 & 0\\ 0 & 1 & 0 \end{pmatrix}$$
$$A^{T}A$$ in this case is not invertible.
Can anyone confirm that part (ii) of this Proposition is indeed incorrect ?
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I would agree with you that part (ii) of the proposition is incorrect (unless matrices are not acting on vectors from the left). If you look at bijection part http://en.wikipedia.org/wiki/Bijecti...and_surjection it reads: "If g o f is a bijection, then it can only be concluded that f is injective and g is surjective." Working right to left with matrices and composition of functions says if A^{T}A was invertible (i.e. a bijection) then A would be injective and A^{T} would be surjective. Thus something is wrong! P.S. I didn't see the bit where it clearly said the matrices were acting from the left so I would say that it is definitely wrong.
Recognitions:
Quote by lauratyso11n Can anyone confirm that part (ii) of this Proposition is indeed incorrect ?
Yes, you are right. (i) is true but (ii) is false. But (ii) is true if A^TA is replaced by AA^T, so maybe it's a typo? I don't understand what "the optimization problem" has to do with this, or are the other parts of the proposition about this?
## Solving for a Surjective Matrix
Quote by Landau Yes, you are right. (i) is true but (ii) is false. But (ii) is true if A^TA is replaced by AA^T, so maybe it's a typo? I don't understand what "the optimization problem" has to do with this, or are the other parts of the proposition about this?
The full Proposition is as follows:
Assume that the (n-by-k) matrix, $$A$$, is surjective as a mapping,
$$A:\mathbb{R}^{k}\rightarrow \mathbb{R}^{n}$$.
For any $$y \in \mathbb{R}^{n}$$, consider the optimization problem
$$min_{x \in \mathbb{R}^{k}}\left{\left||x|\right|^2\right}$$
such that $$Ax = y$$.
Then, the following hold:
(i) The transpose of $$A$$, call it $$A^{T}$$ is injective.
(ii) The matrix $$A^{T}A$$ is invertible.
(iii) The unique optimal solution of the minimum norm problem is given by
$$(A^TA)^{-1}A^Ty$$
I have a problem with point (ii), take as an example the (2-by-3) surjective matrix
$$A = \begin{pmatrix} 1 & 0 & 0\\ 0 & 1 & 0 \end{pmatrix}$$
$$A^{T}A$$ in this case is not invertible.
Quote by Landau Yes, you are right. (i) is true but (ii) is false. But (ii) is true if A^TA is replaced by AA^T, so maybe it's a typo?
I don't think it's a typo as he uses this result to carry some other analysis further. The crux of it is:
$$\sigma\lambda = \alpha - \bf{r}$$
where $$\sigma \in \mathbb{R}^{n-by-k}$$ is surjective, and $$\lambda \in \mathbb{R}^{k}$$, $$\alpha , \bf{r} \in \mathbb{R}^{n}$$.
How would you solve for $$\lambda$$ ? Isn't is critical that the 'typo' has to be correct to be able to solve for this ?
The author's solution as you might expect is $$\lambda = \left(\sigma^{T}\sigma\right)^{-1}\sigma^{T}\left[\alpha - \bf{r}\right]$$.
So it's either a HUGE mistake on his part or I'm missing something. The author is actually quite insightful, and this error would be quite out of character for him.
BTW, thanks for making the effort to look at the problem. Much appreciated.
Blog Entries: 1 Recognitions: Homework Help Looking at dimension counting with your example, AtA is a 3x3 matrix, which means (AtA)-1 A wouldn't make sense even if the inverse was defined because the sizes of the matrices don't match up. On the other hand A At and A are compatible matrices which suggests that he just put the transpose on the wrong one and carried the error through.
Recognitions:
Quote by lauratyso11n The author's solution as you might expect is $$\lambda = \left(\sigma^{T}\sigma\right)^{-1}\sigma^{T}[\alpha - \bf{r}]$$.
This is correct provided that $\sigma^{T}\sigma$ is invertible, i.e. provided that $\left(\sigma^{T}\sigma\right)^{-1}$ makes sense.
The least square solution of Ax=y satisfies the normal equation:
$$A^TAx=A^Ty.$$
This solution is unique if and only if $A^TA$ is invertible. In this case, it is given by
$$x=(A^TA)^{-1}A^Tb$$, just like the author asserts.
But $A^TA$ is not necessarily invertible, contrary to the proposition. Note that $A^TA:\mathbb{R}^k\to\mathbb{R}^k$ is bijective if and only if its rank equals k. But since $A^TA$ and A always have equal rank, this happens if and only if A has rank k. Since $A:\mathbb{R}^k\to\mathbb{R}^n$ is assumed to be surjective, it has rank n and we must have $k\geq n$. So in fact, $A^TA$ is invertible if and only if k=n! Indeed, in your counter-example k and n are not equal.
Quote by Office_Shredder which means (AtA)-1 A wouldn't make sense even if the inverse was defined because the sizes of the matrices don't match up.
This is not the expression the author uses; it is (AtA)-1 At.
Recognitions: Science Advisor Perhaps you could post a link to the book?
Blog Entries: 1
Recognitions:
Homework Help
Quote by Landau This is not the expression the author uses; it is (AtA)-1 At.
I assumed the * was just referring to matrix multiplication
Recognitions: Science Advisor I assumed * means adjoint, so (in this real case) the transpose. This is also what lauratyso11n writes in post #5 (where A is called sigma).
Quote by Office_Shredder I assumed the * was just referring to matrix multiplication
Quote by Landau I assumed * means adjoint, so (in this real case) the transpose. This is also what lauratyso11n writes in post #5 (where A is called sigma).
SORRYYYYYY, the $$A^*$$ is actually an $$A^T$$. I've corrected it.
The correct statement is that if $$A$$ is surjective then $$A^T$$ is injective and $$AA^T$$ is invertible. The formula for the optimal $$x$$ is $$\hat{x}=A^T(AA^T)^{-1}y$$
Recognitions:
Quote by lauratyso11n The correct statement is that if $$A$$ is surjective then $$A^T$$ is injective and $$AA^T$$ is invertible.
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https://fr.mathworks.com/help/driving/ref/simulation3dcamera.html
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# Simulation 3D Camera
Camera sensor model with lens in 3D simulation environment
• Library:
• UAV Toolbox / Simulation 3D
Automated Driving Toolbox / Simulation 3D
## Description
The Simulation 3D Camera block provides an interface to a camera with a lens in a 3D simulation environment. This environment is rendered using the Unreal Engine® from Epic Games®. The sensor is based on the ideal pinhole camera model, with a lens added to represent a full camera model, including lens distortion. This camera model supports a field of view of up to 150 degrees. For more details, see Algorithms.
If you set Sample time to `-1`, the block uses the sample time specified in the Simulation 3D Scene Configuration block. To use this sensor, you must include a Simulation 3D Scene Configuration block in your model.
The block outputs images captured by the camera during simulation. You can use these images to visualize and verify your driving algorithms. In addition, on the Ground Truth tab, you can select options to output the ground truth data for developing depth estimation and semantic segmentation algorithms. You can also output the location and orientation of the camera in the world coordinate system of the scene. The image shows the block with all ports enabled.
The table summarizes the ports and how to enable them.
PortDescriptionParameter for Enabling PortSample Visualization
Image
Outputs an RGB image captured by the cameran/a
Depth
Outputs a depth map with values from 0 m to 1000 meters
Output depth
Labels
Outputs a semantic segmentation map of label IDs that correspond to objects in the scene
Output semantic segmentation
Location
Outputs the location of the camera in the world coordinate system
Output location (m) and orientation (rad)
n/a
Orientation
Outputs the orientation of the camera in the world coordinate system
Output location (m) and orientation (rad)
n/a
Note
The Simulation 3D Scene Configuration block must execute before the Simulation 3D Camera block. That way, the Unreal Engine 3D visualization environment prepares the data before the Simulation 3D Camera block receives it. To check the block execution order, right-click the blocks and select Properties. On the General tab, confirm these Priority settings:
• Simulation 3D Scene Configuration`0`
• Simulation 3D Camera`1`
## Ports
### Input
expand all
Relative translation of the sensor from its mounting point on the vehicle, in meters, specified as a real-valued 1-by-3 vector of the form [X Y Z].
#### Dependencies
To enable this port, select the Input parameter next to the Relative translation [X, Y, Z] (m) parameter. When you select Input, the Relative translation [X, Y, Z] (m) parameter specifies the initial relative translation and the Translation port specifies the relative translation during simulation. For more details, see Sensor Position Transformation.
Data Types: `single` | `double` | `int8` | `int16` | `int32` | `int64` | `uint8` | `uint16` | `uint32` | `uint64`
Relative rotation of the sensor from its mounting point on the vehicle, in degrees, specified as a real-valued 1-by-3 vector of the form [Roll Pitch Yaw].
#### Dependencies
To enable this port, select the Input parameter next to the Relative rotation [Roll, Pitch, Yaw] (deg) parameter. When you select Input, the Relative translation [Roll, Pitch, Yaw] (deg) parameter specifies the initial relative rotation and the Rotation port specifies the relative rotation during simulation. For more details, see Sensor Position Transformation.
Data Types: `single` | `double` | `int8` | `int16` | `int32` | `int64` | `uint8` | `uint16` | `uint32` | `uint64`
### Output
expand all
3D output camera image, returned as an m-by-n-by-3 array of RGB triplet values. m is the vertical resolution of the image, and n is the horizontal resolution of the image.
Data Types: `int8` | `uint8`
Object depth for each pixel in the image, output as an m-by-n array. m is the vertical resolution of the image, and n is the horizontal resolution of the image. Depth is in the range from 0 to 1000 meters.
#### Dependencies
To enable this port, on the Ground Truth tab, select Output depth.
Data Types: `double`
Label identifier for each pixel in the image, output as an m-by-n array. m is the vertical resolution of the image, and n is the horizontal resolution of the image.
The table shows the object IDs used in the default scenes that are selectable from the Simulation 3D Scene Configuration block. If you are using a custom scene, in the Unreal® Editor, you can assign new object types to unused IDs. For more details, see Apply Labels to Unreal Scene Elements for Semantic Segmentation and Object Detection. If a scene contains an object that does not have an assigned ID, that object is assigned an ID of `0`. The detection of lane markings is not supported.
IDType
`0`
None/default
`1`
Building
`2`
Not used
`3`
Other
`4`
Not used
`5`
Pole
`6`
Lane Markings
`7`
`8`
Sidewalk
`9`
Vegetation
`10`
Vehicle
`11`
Not used
`12`
Generic traffic sign
`13`
Stop sign
`14`
Yield sign
`15`
Speed limit sign
`16`
Weight limit sign
`17-18`
Not used
`19`
Left and right arrow warning sign
`20`
Left chevron warning sign
`21`
Right chevron warning sign
`22`
Not used
`23`
Right one-way sign
`24`
Not used
`25`
School bus only sign
`26-38`
Not used
`39`
Crosswalk sign
`40`
Not used
`41`
Traffic signal
`42`
Curve right warning sign
`43`
Curve left warning sign
`44`
Up right arrow warning sign
`45-47`
Not used
`48`
`49`
Street sign
`50`
`51`
Fire hydrant
`52`
Exit sign
`53`
Bike lane sign
`54-56`
Not used
`57`
Sky
`58`
Curb
`59`
Flyover ramp
`60`
`61-66`
Not used
`67`
Deer
`68-70`
Not used
`71`
`72`
Motorcycle
`73-255`
Not used
#### Dependencies
To enable this port, on the Ground Truth tab, select Output semantic segmentation.
Data Types: `uint8`
Sensor location along the X-axis, Y-axis, and Z-axis of the scene. The Location values are in the world coordinates of the scene. In this coordinate system, the Z-axis points up from the ground. Units are in meters.
#### Dependencies
To enable this port, on the Ground Truth tab, select Output location (m) and orientation (rad).
Data Types: `double`
Roll, pitch, and yaw sensor orientation about the X-axis, Y-axis, and Z-axis of the scene. The Orientation values are in the world coordinates of the scene. These values are positive in the clockwise direction when looking in the positive directions of these axes. Units are in radians.
#### Dependencies
To enable this port, on the Ground Truth tab, select Output location (m) and orientation (rad).
Data Types: `double`
## Parameters
expand all
### Mounting
Unique sensor identifier, specified as a positive integer. In a multisensor system, the sensor identifier distinguishes between sensors. When you add a new sensor block to your model, the Sensor identifier of that block is N + 1. N is the highest Sensor identifier value among existing sensor blocks in the model.
Example: `2`
Name of the parent to which the sensor is mounted, specified as ```Scene Origin``` or as the name of a vehicle in your model. The vehicle names that you can select correspond to the Name parameters of the simulation 3D vehicle blocks in your model. If you select ```Scene Origin```, the block places a sensor at the scene origin.
Example: `SimulinkVehicle1`
Sensor mounting location.
• When Parent name is ```Scene Origin```, the block mounts the sensor to the origin of the scene. You can set the Mounting location to `Origin` only. During simulation, the sensor remains stationary.
• When Parent name is the name of a vehicle (for example, `SimulinkVehicle1`) the block mounts the sensor to one of the predefined mounting locations described in the table. During simulation, the sensor travels with the vehicle.
Vehicle Mounting LocationDescriptionOrientation Relative to Vehicle Origin [Roll, Pitch, Yaw] (deg)
`Origin`
Forward-facing sensor mounted to the vehicle origin, which is on the ground, at the geometric center of the vehicle
[0, 0, 0]
`Front bumper`
Forward-facing sensor mounted to the front bumper
[0, 0, 0]
`Rear bumper`
Backward-facing sensor mounted to the rear bumper
[0, 0, 180]
`Right mirror`
Downward-facing sensor mounted to the right side-view mirror
[0, –90, 0]
`Left mirror`
Downward-facing sensor mounted to the left side-view mirror
[0, –90, 0]
`Rearview mirror`
Forward-facing sensor mounted to the rearview mirror, inside the vehicle
[0, 0, 0]
`Hood center`
Forward-facing sensor mounted to the center of the hood
[0, 0, 0]
`Roof center`
Forward-facing sensor mounted to the center of the roof
[0, 0, 0]
Roll, pitch, and yaw are clockwise-positive when looking in the positive direction of the X-axis, Y-axis, and Z-axis, respectively. When looking at a vehicle from the top down, the yaw angle (that is, the orientation angle) is counterclockwise-positive, because you are looking in the negative direction of the axis.
The (X, Y, Z) mounting location of the sensor relative to the vehicle depends on the vehicle type. To specify the vehicle type, use the Type parameter of the Simulation 3D Vehicle with Ground Following block to which you are mounting the sensor. To obtain the (X, Y, Z) mounting locations for a vehicle type, see the reference page for that vehicle.
To determine the location of the sensor in world coordinates, open the sensor block. Then, on the Ground Truth tab, select Output location (m) and orientation (rad) and inspect the data from the Location output port.
Select this parameter to specify an offset from the mounting location by using the Relative translation [X, Y, Z] (m) and Relative rotation [Roll, Pitch, Yaw] (deg) parameters.
Translation offset relative to the mounting location of the sensor, specified as a real-valued 1-by-3 vector of the form [X, Y, Z]. Units are in meters.
If you mount the sensor to a vehicle by setting Parent name to the name of that vehicle, then X, Y, and Z are in the vehicle coordinate system, where:
• The X-axis points forward from the vehicle.
• The Y-axis points to the left of the vehicle, as viewed when looking in the forward direction of the vehicle.
• The Z-axis points up.
The origin is the mounting location specified in the Mounting location parameter. This origin is different from the vehicle origin, which is the geometric center of the vehicle.
If you mount the sensor to the scene origin by setting Parent name to `Scene Origin`, then X, Y, and Z are in the world coordinates of the scene.
For more details about the vehicle and world coordinate systems, see Coordinate Systems for Unreal Engine Simulation in Automated Driving Toolbox.
Example: `[0,0,0.01]`
#### Adjust Relative Translation During Simulation
To adjust the relative translation of the sensor during simulation, enable the Translation input port by selecting the Input parameter next to the Relative translation [X, Y, Z] (m) parameter. When you enable the Translation port, the Relative translation [X, Y, Z] (m) parameter specifies the initial relative translation of the sensor and the Translation port specifies the relative translation of the sensor during simulation. For more details about the relative translation and rotation of this sensor, see Sensor Position Transformation.
#### Dependencies
To enable this parameter, select .
Rotational offset relative to the mounting location of the sensor, specified as a real-valued 1-by-3 vector of the form [Roll, Pitch, Yaw] . Roll, pitch, and yaw are the angles of rotation about the X-, Y-, and Z-axes, respectively. Units are in degrees.
If you mount the sensor to a vehicle by setting Parent name to the name of that vehicle, then X, Y, and Z are in the vehicle coordinate system, where:
• The X-axis points forward from the vehicle.
• The Y-axis points to the left of the vehicle, as viewed when looking in the forward direction of the vehicle.
• The Z-axis points up.
• Roll, pitch, and yaw are clockwise-positive when looking in the forward direction of the X-axis, Y-axis, and Z-axis, respectively. If you view a scene from a 2D top-down perspective, then the yaw angle (also called the orientation angle) is counterclockwise-positive because you are viewing the scene in the negative direction of the Z-axis.
The origin is the mounting location specified in the Mounting location parameter. This origin is different from the vehicle origin, which is the geometric center of the vehicle.
If you mount the sensor to the scene origin by setting Parent name to `Scene Origin`, then X, Y, and Z are in the world coordinates of the scene.
For more details about the vehicle and world coordinate systems, see Coordinate Systems for Unreal Engine Simulation in Automated Driving Toolbox.
Example: `[0,0,10]`
#### Adjust Relative Rotation During Simulation
To adjust the relative rotation of the sensor during simulation, enable the Rotation input port by selecting the Input parameter next to the Relative rotation [Roll, Pitch, Yaw] (deg) parameter. When you enable the Rotation port, the Relative rotation [Roll, Pitch, Yaw] (deg) parameter specifies the initial relative rotation of the sensor and the Rotation port specifies the relative rotation of the sensor during simulation. For more details about the relative translation and rotation of this sensor, see Sensor Position Transformation.
#### Dependencies
To enable this parameter, select .
Sample time of the block in seconds, specified as a positive scalar. The 3D simulation environment frame rate is the inverse of the sample time.
If you set the sample time to `-1`, the block inherits its sample time from the Simulation 3D Scene Configuration block.
### Parameters
These intrinsic camera parameters are equivalent to the properties of a `cameraIntrinsics` object. To obtain the intrinsic parameters for your camera, use the Camera Calibrator app.
For details about the camera calibration process, see Using the Single Camera Calibrator App and What Is Camera Calibration?.
Specify the focal length of the camera as a 1-by-2 positive integer vector of the form [fx, fy]. Units are in pixels.
fx = F × sx
fy = F × sy
where:
• F is the focal length in world units, typically millimeters.
• [sx, sy] are the number of pixels per world unit in the x and y direction, respectively.
This parameter is equivalent to the `FocalLength` property of a `cameraIntrinsics` object.
Specify the optical center of the camera as a 1-by-2 positive integer vector of the form [cx,cy]. Units are in pixels.
This parameter is equivalent to the `PrincipalPoint` property of a `cameraIntrinsics` object.
Specify the image size produced by the camera as a 1-by-2 positive integer vector of the form [mrows,ncols]. Units are in pixels.
This parameter is equivalent to the `ImageSize` property of a `cameraIntrinsics` object.
Specify the radial distortion coefficients as a real-valued 2-element, 3-element, or 6-element vector. Radial distortion is the displacement of image points along radial lines extending from the principal point.
• As image points move away from the principal point (positive radial displacement), image magnification decreases and a pincushion-shaped distortion occurs on the image.
• As image points move toward the principal point (negative radial displacement), image magnification increases and a barrel-shaped distortion occurs on the image.
The camera sensor calculates the (xd,yd) radial-distorted location of a point using a two-coefficient, three-coefficient, or six-coefficient formula. This table shows the various formulas, where:
• (x,y) = undistorted pixel locations
• k1,k2,k3,k4,k5,k6 = radial distortion coefficients of the lens
• r2 = x2 + y2
Coefficients Formula Description `[k1, k2]` xd = x(1 + k1r2 + k2r4) yd = y(1 + k1r2 + k2r4) This model is equivalent to the two-coefficient model used by the `RadialDistortion` property of a `cameraIntrinsics` object. `[k1, k2, k3]` xd = x(1 + k1r2 + k2r4 + k3r6) yd = y(1 + k1r2 + k2r4 + k3r6) This model is equivalent to the three-coefficient model used by the `RadialDistortion` property of a `cameraIntrinsics` object. `[k1, k2, k3, k4, k5, k6]` $\begin{array}{l}{x}_{\text{d}}=x×\frac{1+{k}_{1}{r}^{2}+\text{}{k}_{2}{r}^{4}+{k}_{3}{r}^{6}}{1+{k}_{4}{r}^{2}+{k}_{5}{r}^{4}+{k}_{6}{r}^{6}}\\ {y}_{\text{d}}=y×\frac{1+{k}_{1}{r}^{2}+\text{}{k}_{2}{r}^{4}+{k}_{3}{r}^{6}}{1+{k}_{4}{r}^{2}+{k}_{5}{r}^{4}+{k}_{6}{r}^{6}}\end{array}$ The six-coefficient model is based on the OpenCV radial distortion model.NoteThe Camera Calibrator app does not support this model. To calibrate a camera using this model, see Camera Calibration and 3D Reconstruction in the OpenCV documentation.
Specify the tangential distortion coefficients as a real-valued 2-element vector. Tangential distortion occurs when the lens and the image plane are not parallel.
The camera sensor calculates the tangential distorted location of a point, (xd, yd), using this formula:
xd = x + [2p1xy + p2 × (r2 + 2x2)]
yd = y + [p1 × (r2 + 2y2) + 2p2xy]
where:
• x, y = undistorted pixel locations
• p1, p2 = tangential distortion coefficients of the lens
• r2 = x2 + y2
The undistorted pixel locations appear in normalized image coordinates, with the origin at the optical center. The coordinates are expressed in world units.
This parameter is equivalent to the `TangentialDistortion` property of a `cameraIntrinsics` object.
Specify the skew angle of the camera axes as a nonnegative real-valued scalar. If the X-axis and Y-axis are exactly perpendicular, then the skew must be `0`. Units are dimensionless.
This parameter is equivalent to the `Skew` property of a `cameraIntrinsics` object.
### Ground Truth
Select this parameter to output a depth map at the Depth port.
Select this parameter to output a semantic segmentation map of label IDs at the Labels port.
Select this parameter to output the location and orientation of the sensor at the Location and Orientation ports, respectively.
expand all
## References
[1] Bouguet, J. Y. Camera Calibration Toolbox for Matlab. http://www.vision.caltech.edu/bouguetj/calib_doc
[2] Zhang, Z. "A Flexible New Technique for Camera Calibration." IEEE Transactions on Pattern Analysis and Machine Intelligence. Vol. 22, No. 11, 2000, pp. 1330–1334.
[3] Heikkila, J., and O. Silven. “A Four-step Camera Calibration Procedure with Implicit Image Correction.” IEEE International Conference on Computer Vision and Pattern Recognition. 1997.
## Version History
Introduced in R2019b
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https://economics.stackexchange.com/questions/33298/can-you-take-the-moving-average-of-quarterly-data-of-an-explanatory-variable-in
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# Can you take the moving average of quarterly data of an explanatory variable in a regression to smoothen noise and get more accurate coefficients?
I'm trying to use acceleration of quarterly data on household debt (the difference in the difference in debt) in a regression on unemployment (only concerned with correlation) but quarterly data is much noisier than annual data, which may weaken the correlation. I was wondering if transforming the already differenced (twice) data as a moving average would change my coefficients at all and if they would be more accurate. Is this a common technique in econometrics?
## 2 Answers
Let's say $$D_t$$ is the stock of debt at time $$t$$.
The first difference is $$D_t - D_{t-1}$$.
The second difference is $$(D_t - D_{t-1}) - (D_{t-1}-D_{t-2}) = D_t - 2D_{t-1} + D_{t-2}$$.
The [4-period] moving average is then given by
\begin{align*} &= \frac 1 4 (D_t-2D_{t-1}+D_{t-2}+D_{t-1}-2D_{t-2}+D_{t-3}\\ &\qquad+D_{t-2}-2D_{t-3}+D_{t-4}+D_{t-3}-2D_{t-4}+D_{t-5})\\ &= \frac 1 4 (D_t - D_{t-1} - D_{t-4} + D_{t-5})\\ &= \frac 1 4 ((D_t - D_{t-4}) - (D_{t-1} - D_{t-5})) \end{align*}
Which would be the yearly increase in the stock of debt this period compared to the same thing a quarter ago. Only you could tell if this is what you want in your regression. Something to consider is only to use the first difference: $$D_t - D_{t-4}$$.
The word "noise" implies that there is error in the measurement of household debt, but there is no good reason to believe this is so. In fact, I argue that a finer time period would give you more detail, and a more accurate measurement of the correlation between two variables. You don't want to find a moving average because that throws away valuable variation in the data.
What you should be more concerned about is which lag is most correlated with the current unemployment rate, and you can find those coefficients by including multiple degrees of lag in the multivariate regression.
Overall, no, it is not a common technique in econometrics. Don't do it. Rather use the standard errors to determine how accurate your estimates are.
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https://blogs.ams.org/visualinsight/2014/01/01/pentagon-hexagon-decagon-identity/
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Pentagon-Hexagon-Decagon Identity
Icosahedron Illustrating Pentagon-Hexagon-Decagon Identity – Greg Egan
Suppose we inscribe a regular pentagon, a regular decagon, and a regular hexagon in circles of the same radius. If we denote the respective edge lengths of these polygons by $P$, $D$ and $H$, then these lengths satisfy the identity
$$P^2=D^2+H^2$$
This means that the edges of a pentagon, decagon and hexagon of identical radii can fit together to form a right triangle!
Euclid stated this beautiful but mysterious identity as Proposition 10 of Book XIII of the Elements. This is the last book of the Elements, the one which deals with properties of the Platonic solids. He used Proposition 10 as part of his construction of the regular icosahedron in Proposition 13.
This has led some historians to suggest that the pentagon-decagon-hexagon identity was first discovered in the course of research on the icosahedron. The idea is this. If you hold an icosahedron so that one vertex is on top and one is on bottom, you’ll see that its vertices are arranged in 4 horizontal layers. From top to bottom, these are:
• 1 vertex on top
• 5 vertices forming a pentagon: the "upper pentagon"
• 5 vertices forming a pentagon: the "lower pentagon"
• 1 vertex on bottom
Pick a vertex from the upper pentagon: call this $A$. Pick a vertex as close as possible from the lower pentagon: call this $B$. $A$ is not directly above $B$. Drop a vertical line down from $A$ until it hits the horizontal plane on which $B$ lies. Call the resulting point $C$:
It is easy to check that $ABC$ is a right triangle. If we apply the Pythagorean theorem to this triangle we get the equation
$$P^2=D^2+H^2$$
But to see this, we need to check that:
• the length $AB$ equals the edge of a pentagon inscribed in a circle;
• the length $AC$ equals the edge of a hexagon inscribed in a circle;
• the length $BC$ equals the edge of a decagon inscribed in a circle.
Different circles, but of the same radius! What’s this radius? The five vertices of the lower pentagon lie on the circle shown in blue. This circle has the right radius.
Using this idea, it’s easy to see that the length $AB$ equals the edge of a pentagon inscribed in a circle. It’s also easy to see that $BC$ equals the edge of a decagon inscribed in a circle of the same radius. The hard part is showing that $AC$ equals the edge of a hexagon inscribed in a circle of the same radius… or in other words, the radius of that circle! (The hexagon appears to be a red herring.)
To prove this, it suffices to show the following marvelous fact: the distance between the "upper pentagon" and the "lower pentagon" equals the radius of the circle containing the vertices of the upper pentagon!
Can you prove this?
In Ian Mueller’s book Philosophy of Mathematics and Deductive Structure in Euclid’s Elements, he suggested various ideas the Greeks could have had about this. Today’s image shows one. Let’s look at it again:
The trick is to construct a new right triangle $AB’C’$. Here $B’$ is the top vertex, and $C’$ is where a line going straight down from $B’$ hits the plane containing the upper pentagon.
Remember, we’re trying to show the distance between the upper pentagon and lower pentagon
equals the radius of the circle containing the vertices of the upper pentagon.
But that’s equivalent to showing that $AC’$ is congruent to $AC$.
To do this, it suffices to show that the right triangles $ABC$ and $AB’C’$ are congruent! Can you do it?
In the references to Mueller’s book, he says the historians Dijksterhuis (in 1929) and Neuenschwander (in 1975) claimed this is “intuitively evident”. He also notes that Eva Sachs, in her book Die Fünf Platonischen Körper, suggested an accurately drawn figure could let someone guess that the distance between the two pentagons equals the radius of either one. But that’s not a proof.
You can see a proof due to Greg Egan here:
• Pentagon-hexagon-decagon identity: Proof using the icosahedron, nLab.
Egan put some other proofs of the pentagon-hexagon-decagon identity here:
Also see:
• John Baez, This Week’s Finds in Mathematical Physics, Week 283, and discussion on the n-Category Café.
• Eva Sachs, Die Fünf Platonischen Körper, zur Geschichte der Mathematik und der Elementenlehre Platons und der Pythagoreer, Berlin, Weidmann, 1917, pp. 102–104. See page 102–103 here and page 104 here.
• Ian Mueller, Philosophy of Mathematics and Deductive Structure in Euclid’s Elements, MIT Press, Cambridge Massachusetts, 1981, pp. 257–258 and references therein.
Of course, we can prove also prove the pentagon-hexagon-decagon identity using algebra. Start with a unit circle. If we inscribe a regular hexagon in it, then clearly
$$H = 1$$
So we just need to compute $P$ and $D$. If we think of the unit circle as living in the complex plane, then the solutions of
$$z^5 = 1$$
are the corners of a regular pentagon. So let’s solve this equation. We’ve got
$$0 = z^5 – 1 = (z – 1)(z^4 + z^3 + z^2 + z + 1)$$
so ignoring the dull solution $z = 1$, we must solve
$$z^4 + z^3 + z^2 + z + 1 = 0$$
This says that the center of mass of the pentagon’s corners lies right in the middle of the pentagon.
Now, quartic equations can always be solved using radicals, but it’s a lot of work. Luckily, we can solve this one by repeatedly using the quadratic equation! And that’s why the Greeks could construct the regular pentagon using a ruler and compass.
The trick is to rewrite our equation like this:
$$z^2 + z + 1 + z^{-1} + z^{-2} = 0$$
and then like this:
$$(z + z^{-1})^2 \, + \,(z + z^{-1}) \, -\, 1 = 0$$
If we write
$$z + z^{-1} = x$$
our equation becomes
$$x^2 + x \; – 1 = 0$$
Solving this, we get two solutions. One of them is the golden ratio
$$x = \phi = \frac{\sqrt{5} -1}{2} \approx 0.6180339\dots$$
Next we need to solve
$$z + z^{-1} = \phi$$
$$z^2 – \phi z + 1 = 0$$
with two conjugate solutions, one being
$$z = \frac{\phi + \sqrt{\phi^2 – 4}}{2}$$
This is a fifth root of unity in the first quadrant of the complex plane, so we know
$$z = \exp(2 \pi i/5) = \cos(2\pi/5) + i \sin(2\pi/5)$$
So, we’re getting
$$\cos(2\pi/5) = \phi/ 2$$
A fact we should have learned in high school, but probably never did! Now we’re ready to compute $P$, the length of the side of a pentagon inscribed in the unit circle:
$$P^2 = |1 – z|^2 = (1 – \cos (2\pi/5))^2 + \sin^2 (2\pi/5) = 2 – 2 \cos (2\pi/5) = 2 \; – \phi$$
Next let’s compute $D$, the length of the side of a decagon inscribed in the unit circle! We can mimic the last stage of the above calculation, but with an angle half as big:
$$D^2 = 2 – 2 \cos(\pi/5)$$
To go further, we can use the half-angle formula:
$$\cos(\pi/5) = \sqrt{\frac{1 + \cos (2\pi/5)}{2}} = \sqrt{\frac{1}{2} + \frac{\phi}{4}}$$
This gives
$$D^2 = 2 \; – \sqrt{2 + \phi}$$
But we can simplify this a bit more. As any lover of the golden ratio should know,
$$2 + \phi \approx 2.6180339\dots$$
is the square of
$$1 + \phi \approx 1.6180339\dots$$
So we really have
$$D^2 = 1 – \phi$$
And now we’re done! We see that the pentagon-hexagon-decagon identity
$$P^2=D^2+H^2$$
simply says:
$$2 – \phi = 1 + (1 – \phi)$$
Visual Insight is a place to share striking images that help explain advanced topics in mathematics. I’m always looking for truly beautiful images, so if you know about one, please drop a comment here and let me know!
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http://eprints.lancs.ac.uk/63488/
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# Identifying the curvaton within MSSM
Allahverdi, Rouzbeh and Enqvist, Kari and Jokinen, Asko and Mazumdar, Anupam (2006) Identifying the curvaton within MSSM. Journal of Cosmology and Astroparticle Physics, 2006 (10). ISSN 1475-7516
Full text not available from this repository.
## Abstract
We consider inflaton couplings to MSSM flat directions and the thermalization of the inflaton decay products, taking into account gauge symmetry breaking due to flat direction condensates. We then search for a suitable curvaton candidate among the flat directions, requiring an early thermally induced start for the flat direction oscillations to facilitate the necessary curvaton energy density dominance. We demonstrate that the supersymmetry breaking $A$-term is crucial for achieving a successful curvaton scenario. Among the many possible candidates, we identify the ${\bf u_1dd}$ flat direction as a viable MSSM curvaton.
Item Type: Article Journal of Cosmology and Astroparticle Physics 9 pages. Discussion on the evaporation of condensate added, final version published in JCAP inflation ; physics of the early universe Faculty of Science and Technology > Physics 63488 ep_importer_pure 19 Apr 2013 10:05 Yes Published 21 Nov 2017 18:30 http://eprints.lancs.ac.uk/id/eprint/63488
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http://aas.org/archives/BAAS/v25n4/aas183/abs/S10002.html
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Statistical Results from the First Caltech--Jodrell Bank VLBI Survey
Session 100 -- AGN: Unified Picture
Oral presentation, Friday, January 14, 2:15-3:45, Crystal Forum Room (Crystal City Marriott)
## [100.02] Statistical Results from the First Caltech--Jodrell Bank VLBI Survey
In the Pearson--Readhead (PR) and Caltech--Jodrell (CJ1) surveys we have made milliarcsecond-resolution images at $\lambda6$ and $\lambda18$~cm of the cores of 127 radio sources from a complete sample of 200 objects with total $\lambda6$~cm flux density $\ge 0.7$~Jy. This large sample is suitable for a variety of statistical studies, including the following.\par (1)~The distribution of $\Delta$PA, the difference in position angle between parsec-scale and kiloparsec-scale structure, is bimodal with peaks at $0^\circ$ and $90^\circ$, confirming the result found in a smaller subsample by Pearson and Readhead. We discuss the differences in properties of the two types of object, and interpret the distribution in terms of relativistic beaming of helical jets (cf.~Conway \& Murphy 1993, ApJ, 411, 89).\par (2)~We present the $\theta$--$z$ (angular size--redshift) diagram for this sample, and compare it with the results of Kellermann (1993, Nature, 361, 134) which showed evidence for a deceleration parameter $q_0=0.5$. In contrast to Kellermann, we find that the the angular displacement between the unresolved nucleus and the 2\% contour in the jet does not depend on redshift in the way expected for a standard measuring rod, and that most parsec-scale jets have a self-similar, scale-free structure that cannot be used for cosmological inferences.
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http://wiki.zcubes.com/Manuals/calci/MATRIXSCALARDIVIDE
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# Manuals/calci/MATRIXSCALARDIVIDE
MATRIXSCALARDIVIDE (a,afactor)
• is any matrix.
• is any constant value.
## Description
• This function is dividing the scalar value with the given matrix.
• In , is any matrix.
• Suppose when we are dividing two matrices,the order of the matrices to be considered.
• But while dividing with a scalar order of matrix is not considered.
• Normally we could not do the matrix division directly.
• To divide a matrix by a scalar which is a single number,that simply divide each element in the matrix by this number.
• So all the entries in the given matrix are divide by the scalar value.
## Examples
1. MATRIXSCALARDIVIDE([[6,7,8],[10,12,-22],[7,17,23]],2)
3 3.5 4 5 6 -11 3.5 8.5 11.5
2. MATRIXSCALARDIVIDE([[1,2,3,4],[7,8,-9,10],[11,12,-13.56,14],[10,12,17,18],[21,22,23,24]],6.4)
0.15625 0.3125 0.46875 0.625 1.09375 1.25 -1.40625 1.5625 1.71875 1.875 -2.11875 2.1875 1.5625 1.875 2.65625 2.8125 3.28125 3.4375 3.59375 3.75
## Related Videos
Scalar Multiplication
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http://annals.math.princeton.edu/articles/10911
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# A structure theorem for actions of semisimple Lie groups
### Abstract
We consider a connected semisimple Lie group $G$ with finite center, an admissible probability measure $\mu$ on $G$, and an ergodic $(G,\mu)$-space $(X,\nu)$. We first note (Lemma 0.1) that $(X,\nu)$ has a unique maximal projective factor of the form $(G/Q,\nu_0)$, where $Q$ is a parabolic subgroup of $G$, and then prove:
1. Theorem 1. If every noncompact simple factor of $G$ has real rank at least two, then the maximal projective factor is nontrivial, unless $\nu$ is a $G$-invariant measure.
2. Theorem 2. For any $G$ of real rank at least two, if the action has positive entropy and fails to have nontrivial projective factor, then $(X,\nu)$ has an equivariant factor space with the same properties, on which $G$ acts via a real-rank-one factor group.
3. Theorem 3. Write $\nu = \nu_0\ast \lambda$, where $\lambda$ is a $P$-invariant measure, $P = MSV$ a minimal parabolic subgroup [F2], [NZ1]. If the entropy $h_\mu(G/P,\nu_0)$ is finite, and every nontrivial element of $S$ is ergodic on $(X,\lambda)$ (or just a well chosen finite set, Theorem 9.1), then ($X,\nu)$ is a measure-preserving extension of its maximal projective factor.
4. The foregoing results are best possible (see Section 11, in particular Theorem 11.4).
We also give some corollaries and applications of the main results. These include an entropy characterization of amenable actions, an explicit entropy criterion for the invariance of $\nu$, and construction of a projective factor for an action of a lattice in $G$ on a compact metric space.
Amos Nevo
Robert J. Zimmer
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https://brilliant.org/problems/fractions-sum-to-1/
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# Fractions sum to 1?
Find number of solutions in positive integers of the following equation,
$$\large \dfrac{1}{a}+\dfrac{1}{b}+\dfrac{1}{c} +\dfrac{1}{d} =1$$ with $$a\le b\le c \le d$$.
×
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http://math.stackexchange.com/users/117727/mattecapu?tab=activity
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mattecapu
Reputation
314
Top tag
Next privilege 500 Rep.
Access review queues
Apr 13 revised Is basis change ever useful in practical linear algebra? title/tags improvement Apr 13 suggested approved edit on Is basis change ever useful in practical linear algebra? Apr 13 revised Would an infinite random sequence of real numbers contain repetitions? title improvement Apr 13 comment Would an infinite random sequence of real numbers contain repetitions? infinite like countably infinite? uncountably infinite? which uncountable infinite then? Apr 13 suggested approved edit on Would an infinite random sequence of real numbers contain repetitions? Apr 6 comment Are Euclidean domains exactly the ones which we can define “mod” on? Actually the congruence relation can be defined on a lot of algebraic structures, for the quotient group $G / H$ (where $H \leq G$) is exactly the quotient set of the congruence relation $a mod b \iff ab^{-1} \in H$ Mar 9 awarded Yearling Mar 9 revised Explain why the following conjecture for $f(x)=[x]+(x-[x])^{[x]}$ is not correct? corrected typo Mar 9 comment Explain why the following conjecture for $f(x)=[x]+(x-[x])^{[x]}$ is not correct? What did you try to (dis)prove them? Mar 9 suggested approved edit on Explain why the following conjecture for $f(x)=[x]+(x-[x])^{[x]}$ is not correct? Mar 9 comment Linear dependent or independent Change your question to that and add what you've tried Mar 9 suggested rejected edit on Number of ways of shuffling cards such that $i^{th}$ card is not in the $i^{th}$ position Mar 9 comment Linear dependent or independent Welcome to math.SE: since you are new, I wanted to let you know a few things about the site. In order to get the best possible answers, it is helpful if you say in what context you encountered the problem, and what your thoughts on it are; this will prevent people from telling you things you already know, and help them give their answers at the right level. Mar 9 awarded Citizen Patrol Mar 9 answered Is it possible to define a monotonically increasing sequence on $\mathbb Z$ in such a way that the sequence is $\ldots,-3, -2, -1, 0, 1, 2, 3,\ldots$ Mar 9 comment Formula for the square root of a number? This algorithm provides an approximation, you should address this in your answer Feb 5 awarded Enthusiast Jan 22 comment $H,K$ be subgroups of a group $G$ such that $G$ is isomorphic with $H \times K$ ; then is $H$ normal in $G$ ? @DanielFischer you're right, I didn't see it Jan 21 answered $H,K$ be subgroups of a group $G$ such that $G$ is isomorphic with $H \times K$ ; then is $H$ normal in $G$ ? Jan 20 revised What's wrong with this use of Taylor's expansions? added 1 character in body
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http://mathoverflow.net/questions/141150/2-class-group-of-a-quadratic-imaginary-extension/141153
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# 2-class group of a quadratic imaginary extension
Let $p\equiv 5 [8]$ be a prime number, and consider $K=\mathbb{Q}(\sqrt{-p})$.
I would like to check that the $2$-Sylow subgroup of the class group $C_K$ has order $2$ (I'm pretty sure it's true).
Apparently, this can be done using genus theory, but I don't know anything about it or class field theory , really.
I know that $M=\mathbb{Q}(i,\sqrt{p})$ is the genus field of $K$. Knowing this, using the few results I found in the literature, I can show that, if $K'/K$ is an unramified abelian extension of degree $4$, then $K'/\mathbb{Q}$ is Galois, with Galois group the quaternionic group $\mathbb{H}_8$, and I'm stuck...
If someone knows how to prove this, I would be happy to read a proof.
Greg
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Greg,---In the edit to my answer I should have said that a generator of one of the 2 ideals is a square root of r(a+bi), while that of the other is a square root of r(a-bi). Anyway, does my answer solve your follow-up question to your satisfaction? I think I've kept the use of class-field theory to a minimum. – paul Monsky Sep 9 '13 at 13:14
Here's a simple argument using Hilbert's theorem 90. No doubt it's the same as Will's (deleted) argument couched in quadratic form language, and I suppose it's the same as the Frohlich -Taylor argument as well.
First one shows that the 2-torsion in the class group has order 2 and is generated by the prime P of norm 2. For suppose I lies in an order 2 ideal class C. Then the fractional ideal I/I(bar) is principal on some alpha, and the norm of alpha can only be 1. Using Hilbert's theorem 90, one finds an ideal J in the class of C with J=J(bar). Since only 2 and p ramify, and the prime over p is principal, we can assume J is P or (1). Since aa+pbb isn't 2, the result follows.
It remains to show that P isn't equivalent to the square of any ideal. Suppose on the contrary that we have (beta)=P*(Q^2). Taking norms we get aa+pbb=2(non-zero square), We may assume a and b are in Z and are odd. Then the left-hand side is 6 mod 8, a contradiction.
EDIT: Here's an idea for handling your follow-up question in a reasonably elementary way, giving an explicit generator of your ideal lying over p, without heavy class-field-theory artillery. Let K be Q(root(-p)).
Lemma 1__There is no unramified degree 2 extension of K other than K(i).
For let K(root(alpha) be such an extension. Then (alpha) is the square of an ideal. So from what we know, this ideal is principal or P*(principal), and alpha is in the group generated by -1,2 and the squares. The rest is easy.
Lemma 2__There is no degree 4 cyclic unramified extension of K.
For Let D(L) and D(K) be the groups of fractional ideals of L and K. The first inequality of class field theory (whose proof, using the Herbrand quotient is elementary; no ideles required) tells us that the quotient of D(K) by the subgroup generated by the principal fractional ideals and the norms of elements of D(L) has order at least 4. It follows that C/C^4 has order at least 4, where C is the ideal class group of K. But we know that C^4=C^2,and that C/C^2 has order 2.
Corollary__There is no unramified degree 2 extension L of K(i).
For in this case, L/K would be of degree 4 and solvable, and the smallest Galois extension of K containing L would contain a degree 4 unramified abelian extension of K, contradicting Lemmas 1 and 2.
Now write p as a^2+b^2 with b even, and let r be the fundamental unit in Z[(1+root(p))/2]. Then it should be possible to show that the extension of K(i) obtained by adjoining a square root of r(a+bi) is unramified. So by the corollary r(a+bi) has a square root in K(i), and this square root is what you're looking for.
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Of course Hilbert's theorem 90 in this situation is a triviality, and in some sense goes back to Gauss. – paul Monsky Sep 3 '13 at 21:09
Thanks! Very nice. Now, I'd like to ask another thing, which is related. I'd like to prove that the class group of M=Q(i,p√) has no element of order 2, in an elementary way. I know how to prove that M has no unramified 2-extension; properties of Hilbert class field then implies the result. However, I wonder if there is an elementary way to see this, in the spirit of the previous answer. My ultimate goal is to prove that the ideals lying above p are principal in an elementary way. Since the square of these ideals are principal, I would be done. – GreginGre Sep 4 '13 at 11:13
Is this true when p=37? I don't think that either root(37) or(6+root(37))(root(37)) is a norm from the ring of integers in Q(i,root(37)). – paul Monsky Sep 4 '13 at 13:09
The element $\alpha=(-3+4i)+(1-i)\dfrac{1+\sqrt{37}}{2}$ is an algebraic integer with absolute norm $37$. In fact, its norm over $\mathbb{Q}(i)$ is $-6+i$. – GreginGre Sep 4 '13 at 14:12
Proof of the fact that $M$ has no unramified $2$-extension: let $G$ be the Galois group of the the maximal unramified $2$-extension of $K$. The previous result shows that $G^{ab}$ has order $2$. A classical result of group theory says that $G$ has order $2$ in this case. So the maximal unramified $2$-extension of $K$ has degree $2$ over $K$. So, this is $M$, since $M/K$ is unramified. In particular, $M$ has no unramified $2$-extensions. So $C_M$ is odd. But the square of an ideal $\mathcal{P}$ above $p$ is principal (generated by a prime divisor of $p$ in $\mathbb{Z}[i]$) and we are done. – GreginGre Sep 4 '13 at 14:22
The result is contained in Theorem 41 of Fröhlich-Taylor: Algebraic number theory. See also Theorem 39 in that book.
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Thanks! I had a look to Fröhlich-Taylor . The proof seems quite involded. I thought this would be easier to show, using elementary arguments. At least, the result is true :-) – GreginGre Sep 3 '13 at 19:51
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https://www.physicsforums.com/threads/circularly-polarized-plane-wave-and-electron.248281/
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# Circularly-polarized plane wave and electron
1. Aug 3, 2008
### fizzle
Can a classical circularly-polarized plane electromagnetic wave, that's bounded in time, transfer net energy/momentum to an electron?
2. Aug 3, 2008
### cesiumfrog
So you're excluding Compton scattering..
A point charge in a circularly polarized wave will be driven around, by the direction of the local field, in a little circle (so some energy must be transferred at least temporarily). And since it is accelerated into such motion, the point charge must radiate its own EM wave. This is very similar to the way light interacts with a medium; in one direction the little EM wave will slightly cancel (and retard) the driving wave, and in the opposite direction this little EM wave can be thought of as reflection of the driving wave. By global argument, the electron must be pushed forward (tracing a slackening helix) to complement the reflected component of the wave momentum.
Last edited: Aug 3, 2008
3. Aug 3, 2008
### Andy Resnick
Are you asking if electromagnetic radiation can transfer (angular) momentum to a free particle? Circularly polarized light incident on a linearly birefringent object will transfer angular momentum to the object.
Or are you asking if the electromagnetic field can drive angular momentum transitions for a bound electron? Yes- but circularly polarized light will not transfer angular momentum. Instead, so-called optical vortices are associated with orbital angular momentum- circular polarization states are associated with spin transitions. However, the literature is a little unclear (to me) if an optical vortex is formally identical to the angular momentum operator.
4. Aug 3, 2008
### fizzle
I need to be more specific! I'm talking about a single free electron initially at rest and a single CP plane wave in a completely classical world.
The CP wave forces the electron in a helical path in the direction the CP wave is travelling, while under the influence of the wave. I'm interested in the end result where the CP wave's amplitude increases from zero to some max value then decreases back to zero. When I do a simple computer simulation of this the result is no net transfer of energy/momentum to the electron. It always returns to rest when the CP wave's amplitude is a Gaussian.
Last edited: Aug 3, 2008
5. Aug 3, 2008
### cesiumfrog
By "bounded" (Gaussian) you must mean a (half-) wave "pulse"?
I used global argument because the mechanism is not obvious. There have been published papers on the topic of how a transverse wave on a string can transfer longitudinal momentum (that case can be answered with Pythagorean longitudinal stretching of the string). It is well known that a mirror recoils from a light pulse, but the mechanism is obscure since ideal mirrors have no longitudinal extent and since the EM fields appear perfectly transverse.
I suspect your simulation would have to be extremely precise (this is a small effect) and take into account the finite extent of the charge as well as its self-interaction. There is no effect if the driving field is static or if the field of the charge itself is insignificant. There is reasonable basis against treating the electron as a point particle in such context as this. By the way, did you have a specific reference mentioning the effect?
Last edited: Aug 3, 2008
6. Aug 3, 2008
### fizzle
This is all standard electromagnetic theory so there's no need to get into self-interaction, etc. The E field in the CP wave drives the electron in a circle and that circular motion results in v x B forcing the electron in the direction of the wave's motion. The non-zero amplitude could be hundreds, thousands, millions, etc. of cycles of the wave.
Why am I asking this question? Because it would have significant implications in any classical description of Compton Scattering. It means that an electron would never get "ejected" from the target block simply because it interacted with an incident CP wave. The electron must interact with something else (eg. an atom, another electron, etc.) while interacting with the incident CP wave in order to retain any energy. This would explain one of the problems in a classical description of Compton Scattering => the speed of the electron required to produce the correct angular-dependence of the scattered radiation due to the relativistic Doppler Effect is much less than the speed of an ejected electron. When I calculate the orbital component of the electron's velocity when interacting with a CP wave (when the electron has effectively absorbed a "photon" of energy), I find that the orbital speed is equal to the maximum possible ejection velocity.
I think this gives a much more complete classical description of the Compton Effect, including the seemingly random electron ejection direction. Basically, the incident CP sets the electron on its helical path where it then has to interact with a third party to retain any energy.
7. Aug 3, 2008
### cesiumfrog
I had forgotten to consider the magnetic field, thank you.
(FWIW, self-interaction is relevant to some problems in a completely classical world, such as the inertia of a charged object/"electron".) Why did your simulation fail?
8. Aug 4, 2008
### Andy Resnick
I don't follow you here. Why do you think a circularly polarized plane wave will "force the (free) electron (to move) in a helical path"? Under what conditions?
A circularly polarized beam incident onto a conductor should generate synchotron radiation, if your idea is correct.
9. Aug 4, 2008
### fizzle
Standard em theory. The electric field forces the electron to travel in a circle while v x B forces the electron to move in the direction of travel of the wave. The overall result is a helical path. This is all well known.
A CP wave incident on a conductor results in a reflected CP wave.
10. Aug 4, 2008
### Andy Resnick
Not to me.... can you provide a reference?
Erm, yes... but if the conduction electrons are induced to move in little circles, as you claim is well-known, they are undergoing an acceleration, which produces a field. Has anyone measured or detected this field?
11. Aug 4, 2008
### fizzle
Reference? This is very old stuff. I guess you could look up Thomson Scattering and then not ignore v x B. More modern references are in papers on laser acceleration.
The field radiated by electrons is responsible for the reflection off a conductor. You measure and see it all the time. How do you think a mirror works? The electric field in the incident em wave causes the electrons to accelerate and emit a wave whose electric field is the inverse of that in the incident wave. You typically ignore qv x B in the incident wave because it's force is neglible compared to qE.
I'm interested in the regime where v x B is not neglible => very high field strengths in the incident wave.
12. Aug 4, 2008
### Andy Resnick
Oh- plasmas. I don't know much about them. From what I just read, an interesting experiment would be to use dusty plasmas- the particle size is larger, so the optical wavelength would be larger as well- one could probably use visible light and track individual particles.
I don't know the relevant literature- maybe someone has already done it.
13. Aug 4, 2008
### cesiumfrog
Why are you specifically interested in circularly polarised light?
Why are you so interested in describing Compton scattering classically (whereas it seems like evidence for the quantisation of light)?
Are you trying to describe bound electrons as classical charged particles orbiting a nucleus? If so, how do you explain that they do not radiate and fall in?
Do you agree that a free electron exposed to (circularly polarised) light, with a finite envelope, will indeed experience a net transfer of energy and momentum (rather than being restored to its original velocity)? Do you have any contrary evidence/argument?
Why do you say (classically) that an electron would need to interact with some other object in order to "be ejected" by (sufficiently intense) light?
Since you did mention the photon, could you clarify what you mean by "classical description"?
14. Aug 5, 2008
### fizzle
I'm interested in CP waves because they're the easiest to analyze.
I'm interested in a classical description of Compton Scattering because I want to see how far I can get with it. Does it provide any physical insight into quantum theory? Where does it go wrong? In the abstract of his 1925 paper, "A Quantum Theory of the Scattering of X-Rays by Light Elements", Compton explicitly states that the angular-dependence of the wavelength shift can be explained by classical theory if you assume an electron moving in the direction of propagation (the "drift velocity").
I'm not trying to describe bound electrons, just the most simple electromagnetic interaction possible: a single free electron and a single plane wave.
I do not agree that a free electron will receive net energy/momentum from a bounded CP em wave. By "net" I mean that the energy/momentum of the free electron will be the same before and after the CP wave has passed it by. Here's a paper by McDonald with more details and references:
http://www.hep.princeton.edu/~mcdonald/accel/dressing.pdf
I say that a free electron, initially at rest, must interact with a third party in order to be "ejected" (aka. gain net energy/momentum) from a bounded CP wave ... otherwise it would have returned to rest after the wave had passed by. It will be displaced by the wave but will not net any energy/momentum.
By "classical description" I mean classical electromagnetic theory plus special relativity.
I've done the full analysis for Compton's original experiment (incident photon of 17.49 KeV) and the results are as follows:
1) An electron reaching Compton's drift velocity, where the angular-dependence of scattered em radiation matches his experiment with an incident wavelength of 7.09 x 10^-11m, is moving with the wave at 3.31% of the speed of light.
2) The electron's orbital component, remember that it's under the influence of a circularly-polarized incident wave, is 25.3% of the speed of light. Its orbital radius is 2.95 x 10^-12 m.
3) The electric field in the incident CP wave has to be 1.18 x 10^16 V/m.
#3 is the killer here. That's an extraordinarily high electric field strength. Furthermore, the electric field energy varies as the cube of the frequency -- a "Compton Catastrophe", if you will.
Just for laughs, I plugged in some other interesting numbers to see what fell out of the equations:
a) For an electron absorbing a photon of energy equal to an electron's rest mass (511 KeV), the drift velocity is exactly 50% of the speed of light. I was surprised by this initially but it makes sense when you look at it from a momentum viewpoint.
b) For an electron absorbing a photon of energy required for pair production (1.022 KeV), the drift velocity is equal to 66.67% of the speed of light, as expected after seeing (a). However, an interesting number falls out of the equations: the electron's orbital radius is equal to its Compton Wavelength (3.86 x 10^-13 m).
A final observation from the analysis is the value of the recoil electron's velocity. In Compton Scattering, the recoil/ejected electron's velocity is a certain value that depends on the recoil angle, which Compton calculated assuming a billiard ball-like interaction between a photon and an electron. For the most part, this ejection velocity is much higher than the drift velocity in the classical analysis. However, there is a one distinct match with the classical analysis: the maximum value of the ejected electron's velocity is equal to the orbital velocity in the classical analysis.
The bottom line of this exercise is that classical em theory can offer an explanation of Compton Scattering. It requires ultra-high field strengths and adds in the requirement of an interaction with a third party (which, interestingly enough, adds randomness/probability to the process).
15. Aug 5, 2008
### cesiumfrog
We agreed that the free electron will be longitudinally accelerated (in a "slackening helix") for the duration of the external pulse; by what mechanism do you propose it will be decelerated after the pulse?
Do you concede that the electron will scatter part of the EM wave? That the EM wave must therefore end up with less momentum in its original direction? Would not the principle of momentum conservation then be violated if the responsible electron finished up with the same momentum as it started with?
(I found the paper you cited to be unclear, incomplete and non-refereed, but I'll look into its Kibble reference...)
16. Aug 5, 2008
### fizzle
The electron isn't decelerated after the pulse, it's decelerated as the pulse's amplitude decreases. Anyway, I figured it out. You have to think in terms of unstable versus stable states between the electron's velocity and the incident wave. Initially, the electron is at rest and inertia keeps it from instantly adjusting its velocity to the incident wave. The wave's E and B fields "lead" the electron's velocity. This accelerates the electron orbitally and longitudinally, and is an unstable state.
Eventually, the electron's velocity becomes perfectly in phase with the wave's E and B fields, where E is perpendicular to the velocity and B is parallel. With E perpendicular to v, there's no orbital acceleration and since B is parallel to v, there's no more longitudinal acceleration. This is a stable state and I imagine with more analysis you'd find that any small deviations around this state would lead back to it.
Finally, when the amplitude of the incident wave begins to decrease, E and B in the wave begin to "lag" the electron's velocity because of inertia. E has a small component in the opposite direction of v and that reduces the orbital speed. Correspondingly, B is no longer perfectly parallel to v so v x B results in longitudinal deceleration.
What's interesting is that the time derivative of the magnitude of E and B is critical here. Obviously, you think about the spatial and temporal derivatives in em theory all the time but here the time derivative of the magnitude is the most important part.
No concession necessary. The scattering is an integral part of the whole process and carries away the energy and momentum removed from the incident plane wave. Be careful when accounting for energy and momentum in classical em fields!
Doubt McDonald's analysis at your own peril. Better yet, derive the results yourself (as I did before finding his). He is correct.
17. Aug 6, 2008
### cesiumfrog
That is incorrect, but after reading Kibble I understand what you are trying to articulate. Since the acceleration corresponds with the peaks of E, the simple harmonic motion of the charge must have velocity lagging by a quarter of a cycle (where a=E=0), which coincides upon the zero of B. Since the slope of the wave envelope can drive the charge velocity to lag by just slightly more/less than a quarter cycle (i.e., no longer exactly centred upon B=0), the net Lorentz force provides longitudinal acceleration then deceleration.
This basic derivation neglects back-reaction of any wave produced (read: back-scattered) by the charge. In this toy-context energy-momentum is conserved, and Kibble writes that the electron will no longer be returned to rest if it "scatters a photon".
18. Aug 6, 2008
### fizzle
No, it is correct. Do you have a link to Kibble's paper? It sounds like you (and he?) are referring to a linearly-polarized incident wave. I'm talking about a circularly-polarized incident wave, where |E| never goes to zero in a cycle. In that case, the electron reaches a stable state where its tangential velocity is perpendicular to E and parallel to B. I call this being perfectly in phase with the wave. If the wave's amplitude decreases a bit, the wave "lags" behind a bit because the electron is moving too fast. This lag results in E having a small component in the opposite direction of the electron's velocity. This is what slows the electron's orbital speed. Simultaneously, the lag causes B to be slightly non-parallel to the electron's velocity and results in a force that decelerates it's longitudinal speed.
Note that the electron is not "scattering a photon" when it cycles from rest to interacting to rest again. As best as I can tell, that would be equivalent to the electron absorbing then re-emitting a photon unchanged. What's called "scattering a photon" happens when the electron interacts with a third party while interacting with the incident wave and doesn't return to rest. This causes a discontinuity in the electron's radiated em wave. If this paragraph appears to be vague and "hand waving", that's because it is! I reduced it to the most simple case possible. I don't know what happens when the incident wave has different polarizations. Circular is the easiest and produces the strongest effect since the longitudinal acceleration is the greatest.
19. Aug 6, 2008
### cesiumfrog
I linked Kibble's paper in post #15, but it's properly cited inside your own reference. For the stable state I do understand broadly saying "the electron is in phase with the wave" but note that the velocity lags E by 90 degrees (and may be perfectly in phase or exactly out of phase with B depending on polarisation chirality). Sorry if, earlier, my only describing one transverse component (independent of polarisation) caused confusion.
I agree that, if the electron does not scatter any of the external wave, the electron will be longitudinally accelerated as the wave increases in intensity then decelerated back to its initial momentum as the wave decays past. (I hadn't previously been aware of this mechanism, which applies a net longitudinal force whenever the orbit of the charge is mismatched to the intensity of the wave.)
However, consider the neglected (synchrotron) radiation produced by the rapid transverse acceleration of the electron. Obviously (since the position of the charge is 180 degrees out of phase with the applied E field) this radiation will be 180 degrees out of phase from the wave (hence the component propagating in the same direction will destructively interfere with the energy of the original wave) and we can call it a reflection (or continuous classical scattering) of part of the original wave, off from the electron.
Since part of the wave is scattered, the wave momentum decreases. But the emission of radiation has a back-reaction (e.g., the Abram-Lorentz force) which will damp the transverse motion of the electron. This will maintain such a mismatch (between the external wave and the transverse orbit of the charge) as to re-invoke the earlier mechanism to also maintain a longitudinal acceleration (even now that the intensity of the incident wave is constant). However, when the incident wave intensity finally decreases away, the amount of associated longitudinal deceleration will be no more than before (despite extra intervening acceleration) therefore the free electron will ultimately retain some momentum from the wave (just as was required by global conservation of momentum to balance for the reflected part of the wave).
Last edited: Aug 6, 2008
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https://www.quizover.com/course/section/results-optimizing-transient-finger-damping-on-a-driven-by-openstax
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# 10.4 Optimizing transient finger damping on a driven string (Page 2/2)
Page 2 / 2
${u}_{xx}\approx \frac{u\left(x+dx,t\right)-2u\left(x,t\right)+u\left(x-dx,t\right)}{d{x}^{2}}$
These approximations may be substituted into our original partial differential equation in order to solve for $u\left(x,t\right)$ .
The second finite difference method used to solve the wave equation is the trapezoidal approximation method, where we have the system of equations
${\left(\begin{array}{c}u\\ {u}_{t}\end{array}\right)}_{t}=\left(\begin{array}{cc}0& I\\ {\partial }_{xx}& -c\left(t\right)\delta \left(x-{x}_{c}\right)\end{array}\right)\left(\begin{array}{c}u\\ {u}_{t}\end{array}\right)+\left(\begin{array}{c}0\\ b\left(t\right)\delta \left(x-{x}_{b}\right)\end{array}\right)$
which we will denote as
${V}^{\text{'}}\left(t\right)=A\left(t\right)V\left(t\right)+B\left(t\right)$
where $I$ represents the identity matrix. The ${\partial }_{xx}$ operator is a tridiagonal matrix with -2 along the diagonal and ones along the superdiagonal and subdiagonal. The approximating integral equation
${\int }_{\left(j-1\right)dt}^{jdt}{V}^{\text{'}}\left(t\right)\phantom{\rule{0.166667em}{0ex}}dt={\int }_{\left(j-1\right)dt}^{jdt}\left(A\left(t\right)V\left(t\right)+B\left(t\right)\right)\phantom{\rule{0.166667em}{0ex}}dt$
is solved to reveal a solution for $u\left(jdt\right)$ . The trapezoidal integration method turns out to be the more accurate of the two solution methods, since its error is less than the error of the forward Euler method. Real values for the string's tension, density, and length were used to evaluate the solution for the trapezoidal method, but gave us unintelligible results when used for the forward Euler method. Both methods were used to evaluate the solution using arbitrary values.
## Optimization
With all the preliminary work established, we can move on to the optimization problem. We investigated two objective functions for optimization. The first objective function considered was the following
$J\left(c\left(t\right)\right)={\int }_{0}^{\ell }{\left(u\left(x,T;c\left(t\right)\right)-{u}_{0}\left(x,T\right)\right)}^{2}dx.$
Here a suitable time $T$ is preordained. It is legitimate to do this since damping should not affect the periodic details of the waveform. The $u\left(x,T\right)$ is solved with the given $c\left(t\right)$ and fitted to ${u}_{0}\left(x,T\right)=sin\left(\frac{4\pi x}{\ell }\right)$ . We parameterize
$c\left(t\right)={e}^{-{c}_{1}t}-{e}^{-{c}_{2}t}$
which acts at one point on the string with a shape similar to the following.
It is important also that ${c}_{1}<{c}_{2}$ to guarantee the above shape. Our control problem then, is to
$\begin{array}{cccc}& \underset{{c}_{1},{c}_{2}}{min}\hfill & \hfill \phantom{\rule{1.em}{0ex}}& {\int }_{0}^{\ell }{\left(u\left(x,T;c\left(t\right)\right)-{u}_{0}\left(x,T\right)\right)}^{2}dx\hfill \end{array}$
subject to $u\left(x,T;c\left(t\right)\right)$ solving our wave equation with the same initial and boundary conditions. There is a scaling issue since $u\left(x,T\right)$ is small (on the order of ${10}^{-5}$ ) at times. To correct this we scale our target ${u}_{0}$ so that the two waveforms are comparable before we run the optimization. Normalizing $u$ instead, would be cumbersome since the maximum amplitude depends on time. To expedite the optimizer, we supply the gradient of our objective
$\nabla J\left(c\left(t\right)\right)=\left(\frac{\partial J\left(c\left(t\right)\right)}{\partial {c}_{1}},\frac{\partial J\left(c\left(t\right)\right)}{\partial {c}_{2}}\right).$
The equations for the partial derivatives are as follows.
$\frac{\partial J\left(c\left(t\right)\right)}{\partial {c}_{1}}=2{\int }_{0}^{\ell }\left(u\left(x,T;c\left(t\right)\right)-{u}_{0}\left(x,T\right)\right)\left(\frac{\partial u\left(x,T,c\left(t\right)\right)}{\partial {c}_{1}}\right)dx,$
$\frac{\partial J\left(c\left(t\right)\right)}{\partial {c}_{2}}=2{\int }_{0}^{\ell }\left(u\left(x,T;c\left(t\right)\right)-{u}_{0}\left(x,T\right)\right)\left(\frac{\partial u\left(x,T,c\left(t\right)\right)}{\partial {c}_{2}}\right)dx$
The inner partial derivatives will be approximated by the same finite difference method we used above.
One of the main difficulties with this objective function is that it requires a $T$ to be found beforehand and thus we can only optimize with respect to our spacial dimension. Optimizing over both space and time would rid us of needing to find a good $T$ but complicates our objective function and retards our optimizer. Another concern with this objective is that it takes into account the sign of the target waveform, but whether the waveform is $sin\left(x\right)$ or $-sin\left(x\right)$ is no matter to the musician. Along the same lines we have the scaling difficulty. Another objective function we have explored is the following energy minimization problem. We note that $u\left(x,t\right)$ can be represented as a combination of sinusoids. For a given $T$ we have
$u\left(x,T\right)=\sum _{n=1}^{N}{u}_{n}sin\left(\frac{2n\pi x}{\ell }\right).$
Here each ${u}_{n}$ represents the nth Fourier coefficient that corresponds to the expression of the nth mode in the total wave. Since we are interested in expressing only the fourth mode, our optimization problem will try to minimize all other modes
$\begin{array}{cccc}& \underset{{c}_{1},{c}_{2}}{min}\hfill & \hfill \phantom{\rule{1.em}{0ex}}& \phantom{\rule{4pt}{0ex}}F\left(c\left(t\right)\right)={\int }_{0}^{{T}_{fin}}\left(\sum _{n=1,n\ne 4}^{10},\left[{\left({\int }_{0}^{\ell },\left(u\left(x,t;c\left(t\right)\right)sin,\left(\frac{n\pi x}{\ell }\right),d,x\right)}^{2}\right]\right)dt\hfill \end{array}$
subject to our wave equation with the same conditions. We decide on clearing up the first ten modes (except the fourth) to ensure that we are left with a waveform closest to our target. Like before we supply the gradient.
$\frac{\partial F\left(c\left(t\right)\right)}{\partial {c}_{1}}=2{\int }_{0}^{{T}_{fin}}\left(\sum _{n=1,n\ne 4}^{10},{\int }_{0}^{\ell },\left(u\left(x,t;c\left(t\right)\right)sin,\left(\frac{n\pi x}{\ell }\right),\frac{\partial u\left(x,t,c\left(t\right)\right)}{\partial {c}_{1}},d,x\right)dt,$
$\frac{\partial F\left(c\left(t\right)\right)}{\partial {c}_{2}}=2{\int }_{0}^{{T}_{fin}}\left(\sum _{n=1,n\ne 4}^{10},{\int }_{0}^{\ell },\left(u\left(x,t;c\left(t\right)\right)sin,\left(\frac{n\pi x}{\ell }\right),\frac{\partial u\left(x,t,c\left(t\right)\right)}{\partial {c}_{2}},d,x\right)dt.$
This objective function solves the sign and amplitude problems of the first. Additionally we are now optimizing over time so we need not specify a $T$ . One may wish to reset the bounds of the time integral through a different interval.
## Results
This is the result of our optimizer given a certain driving force $b\left(t\right)$ using our first objective function.
This is the result of our optimizer at a certain time using the energy minimization objective. Since we optimized over space and time, we express this as a three dimensional plot.
For the energy minimization objective function using multiple dampings, we have this result.
Comparatively, the values of the objective function for single and multiple dampings are on the same order of magnitude, with the value for the single dampings being slightly smaller. Therefore the optimization process for a single damping is more effective, but not by much.
## Acknowledgments
We would like to give a big thanks to Dr. Steve Cox for his guidance and support throughout the course of the project. This paper describes work completed with the support of the NSF.
## Appendix
All of the codes used in this project are available on our website at
http://www.owlnet.rice.edu/ mlg6/strings/.
## References
1. Bamerger, A., J. Rauch and M. Taylor. A model for harmonics on stringed instruments . Arch. Rational Mech. Anal. 79(1982) 267-290.
2. Cheney, E. W., and David Kincaid. Numerical Mathematics and Computing . Pacific Grove, CA: Brooks/Cole Pub., 1994. Print.
3. Cox, S., and Antoine Hernot. Eliciting Harmonics on Strings . ESAIM: COCV 14(2008) 657-677.
4. Fletcher, Neville H., and Thomas D. Rossing. The Physics of Musical Instruments . New York: Springer-Verlag, 1991. Print.
5. Knobel, Roger. An Introduction to the Mathematical Theory of Waves . Providence, RI: American Mathematical Society, 2000. Print.
6. Rayleigh, John William Strutt, and Robert Bruce Lindsay. The Theory of Sound . New York: Dover, 1945. Print.
do you think it's worthwhile in the long term to study the effects and possibilities of nanotechnology on viral treatment?
absolutely yes
Daniel
how to know photocatalytic properties of tio2 nanoparticles...what to do now
it is a goid question and i want to know the answer as well
Maciej
Abigail
Do somebody tell me a best nano engineering book for beginners?
what is fullerene does it is used to make bukky balls
are you nano engineer ?
s.
fullerene is a bucky ball aka Carbon 60 molecule. It was name by the architect Fuller. He design the geodesic dome. it resembles a soccer ball.
Tarell
what is the actual application of fullerenes nowadays?
Damian
That is a great question Damian. best way to answer that question is to Google it. there are hundreds of applications for buck minister fullerenes, from medical to aerospace. you can also find plenty of research papers that will give you great detail on the potential applications of fullerenes.
Tarell
what is the Synthesis, properties,and applications of carbon nano chemistry
Mostly, they use nano carbon for electronics and for materials to be strengthened.
Virgil
is Bucky paper clear?
CYNTHIA
so some one know about replacing silicon atom with phosphorous in semiconductors device?
Yeah, it is a pain to say the least. You basically have to heat the substarte up to around 1000 degrees celcius then pass phosphene gas over top of it, which is explosive and toxic by the way, under very low pressure.
Harper
Do you know which machine is used to that process?
s.
how to fabricate graphene ink ?
for screen printed electrodes ?
SUYASH
What is lattice structure?
of graphene you mean?
Ebrahim
or in general
Ebrahim
in general
s.
Graphene has a hexagonal structure
tahir
On having this app for quite a bit time, Haven't realised there's a chat room in it.
Cied
what is biological synthesis of nanoparticles
what's the easiest and fastest way to the synthesize AgNP?
China
Cied
types of nano material
I start with an easy one. carbon nanotubes woven into a long filament like a string
Porter
many many of nanotubes
Porter
what is the k.e before it land
Yasmin
what is the function of carbon nanotubes?
Cesar
I'm interested in nanotube
Uday
what is nanomaterials and their applications of sensors.
what is nano technology
what is system testing?
preparation of nanomaterial
Yes, Nanotechnology has a very fast field of applications and their is always something new to do with it...
what is system testing
what is the application of nanotechnology?
Stotaw
In this morden time nanotechnology used in many field . 1-Electronics-manufacturad IC ,RAM,MRAM,solar panel etc 2-Helth and Medical-Nanomedicine,Drug Dilivery for cancer treatment etc 3- Atomobile -MEMS, Coating on car etc. and may other field for details you can check at Google
Azam
anybody can imagine what will be happen after 100 years from now in nano tech world
Prasenjit
after 100 year this will be not nanotechnology maybe this technology name will be change . maybe aftet 100 year . we work on electron lable practically about its properties and behaviour by the different instruments
Azam
name doesn't matter , whatever it will be change... I'm taking about effect on circumstances of the microscopic world
Prasenjit
how hard could it be to apply nanotechnology against viral infections such HIV or Ebola?
Damian
silver nanoparticles could handle the job?
Damian
not now but maybe in future only AgNP maybe any other nanomaterials
Azam
Hello
Uday
I'm interested in Nanotube
Uday
this technology will not going on for the long time , so I'm thinking about femtotechnology 10^-15
Prasenjit
how did you get the value of 2000N.What calculations are needed to arrive at it
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https://www.gradesaver.com/textbooks/math/algebra/algebra-2-1st-edition/chapter-10-counting-methods-and-probability-10-5-find-probabilities-of-independent-and-dependent-events-10-5-exercises-skill-practice-page-722/30
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## Algebra 2 (1st Edition)
a) In this case the events are independent: $\frac{4}{52}\frac{4}{52}\frac{4}{52}=\frac{1}{2197}$ b) In this case the events are not independent: the first one has probability $\frac{4}{52}$; the second one has probability $\frac{4}{51}$; and the third one has probability $\frac{4}{50}$. Thus the probability is: $\frac{4}{52}\frac{4}{51}\frac{4}{50}=\frac{8}{16575}$
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https://blog.theleapjournal.org/2008/10/few-currency-crises-coming-together.html
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## Monday, October 27, 2008
### A few currency crises coming together?
So far, the global financial crisis was largely about financial firms and markets in the first world. This was a novel experience; it had never happened before. Now it might morph into a few currency crises hitting pegged exchange rates. This is an old movie; we have seen this many times before and we know a lot about it.
Speculative attacks on pegged exchange rates appear to be in the offing. The market is carefully analysing all countries with pegged exchange rates, looking at the possibility of large devaluations when the central bank runs out of reserves. Countries which have interfered with exchange rate devaluation are in focus now. Thankfully, by and large, India is not one of these.
A key mistake that is being made in thinking about these problems is that many countries hold reserves that are "large enough". As an example, writing in Financial Times, Charles Clover reports:
After two months of crisis, meanwhile, Russias currency reserves have dropped from $597bn in August to$515bn on October 17, partly as a result of defending the rouble. Capital flight is running at $12bn-$16bn a week. The Moscow interbank lending rate hit 22 per cent last week before settling back to 17 per cent, by far its highest level this decade, reflecting the scale of the stress in the banking system. Domestic banks are seeing depositors confidence evaporate four retail banks have experienced runs and been sold off in a hurry.
This month, the central bank instituted the first measures designed to prevent a speculative attack on the rouble when it banned currency swaps. But analysts are starting to ask how long the authorities can stand as substitute for the cut-off foreign investment and seized-up credit markets. They have enough reserves to last a year at this rate, maybe 18 months, says an economist at a Moscow bank.
This economist at a Moscow bank' is not reckoning with the incredibly nonlinear behaviour of the system when a speculative attack comes together. Once a speculative attack starts, reserves can essentially vanish in no time. Linear extrapolation is a poor guide to the outlook for reserves.
Exchange rate flexibility is now highly desirable. If countries try to hang on to exchange rate targets (e.g. RBI was a bit squeamish about breaching INR 50 per dollar) then this could cause a lot of damage. In this environment, it's easy to get into a speculative attack. In contrast, exchange rate flexibility has a lot to offer. Countries that allow bad news to result in a sharp depreciation of the currency (and a sharp drop in asset prices) benefit from the lack of a perception of a one-way bet. A currency that has dropped in response to market forces (without interference by a government) has a good chance of going up the next day: there is no one-way bet in taking capital out of the country.
Holding "large" reserves is not a very good deal. In peacetime, they are not required, and in wartime, they are useless.
From an Indian point of view, as the Aziz, Patnaik, Shah paper has emphasised, there is a case for RBI using dollars to solve the dollar liquidity problems of Indian firms. The outer limit for the quantity of dollars that might get used in this fashion is $50 billion (partly because the London money market is showing some halting signs of life). There is no case for RBI to have any kind of exchange rate target. If RBI embarks on trading on the market in order to influence the exchange rate, this would be imprudent. From a trader's point of view, the consequences of this are simple. Look for countries where there is exchange rate rigidity, where the central bank has sold reserves in doing market manipulation, and short those currencies / stock market indexes. In doing this, be careful to not mis-interpret a decline in reserves expressed in USD. If a clutch of countries experiences speculative attacks, and then large devaluations take place, this would add to the negative outlook for the world economy, for we know that in the aftermath of a currency crisis, it takes a year or three for the country to put itself together. Hopefully, these countries will come back to life with better monetary policy frameworks, so in the long run, this will turn out to have been for the better. But in the short run, this could be quite painful. #### 7 comments: 1. I enjoy reading your blog regularly, and I can easily say I don't know nearly as much as you about everything regarding$, economics, and probably math.
But here is my question:
What if the RBI simultaneously did two things, at least temporarily, which I know you are very much against.
Continue the dollar peg while increasing opacity as to the RBI's intervention (I don't know if its possible to hide intervention).
Wouldn't this prevent one way bets while maintaining a stable currency.
Patel
2. Which peg's are under attack?? because there are not that many around these days, owing to the crisis that occurred during the 90's. Unless you know you can defend your peg very few governments opt for it as exchange rate policy and they certainly haven't been introducing them in any large numbers.
There are a few if not many managed exchange rates, but peg's are few and far between these days and the ones that are around are very robust. Look at the Hong Kong dollar which did more than survive during the Asian Crisis, they managed to burn speculators outright with intervention.
By Your own reckoning Russia has half a trillion in reserves, it can fend off speculators by simply sneezing, and in the current environment you find me a hedge fund that is not openly licking its wounds and hasn't haemorrhaged or is not in desperate need of cash. I am sure people would love to take a speculative positions on the devaluation of a currency, and hope that such positions would force a devaluation so they can profit, but the fact of the matter very few people have that ability in this current environment to run positions like that, certainly not large enough in size, that any economy worth doing it too could not defend itself.
The Dollar continues to rally and currencies continues to fall against it as a flight to supposed quality continues to occur. That is why we see the movements we see, not because the market has taken a view that a currency seems to be weak and a peg cannot be defended.
I see no speculative attacks on anyone's currency, no one has the muscle right now to do that as much as they might like too. There may be a few shorts or even many I don't dispute that as some people will be enjoying momentum but employing leverage right now, try borrowing for a start, very difficult and people are in the midst of reducing their risk not increasing it.
3. Sharat,
I feel oddly squeamish naming countries because that's part of how these things get out of hand.
You don't need hedge funds to get speculative attacks that work. Speculative attacks have been a part of our experience well before hedge funds came along. Yes, leverage in the hands of modern players has helped. But it's by no means the big thing. The most important sources of breakdown of East Asian exchange rate regimes in 1997 were locals.
The word peg' is used a bit differently from the way you seem to assume. Perhaps part of our difference of perception is nomenclature.
I feel quite confident that Russia is not safe with their hoard of reserves. The protection that big numbers for reserves yield is much more limited than generally meets the eye. I wonder what's the implied pdf of the ruble exchange rate right now.
4. Anonymous,
There are no real secrets. RBI staff have friends and they have friends and all you gain from the non-transparency is a non-level playing field in the world of information.
The checks and balances of democracy work less when there is opacity. E.g. if Thailand in 1997 had more transparency, the mistakes they made on forward trades would not have been made. Similarly, I believe that it was the broad intellectual consensus in India that stopped RBI from dogmatically buying dollars in 1997. So there are deeper costs from doing things in darkness.
5. Hi Ajay,
Thanks for coming back to me. I have to say a peg, in the strictest sense of the word is exactly what the name suggests, a peg to a particular currency, usually the dollar at a particular value or very very narrow band, using a currency board system to maintain that very narrow band. Peg's allow zero flexibility on the part of the government who use them and monetary policy is determined by the country whose currency is being pegged to.
These days the more favoured approach by governments in exchange rate policy and what you refer to is a managed float where the currency trades against an opaque basket of currencies and is allowed much more freedom to move which means countries can determine their own interest rate policy. Though India does prefer to benchmark against the dollar for whatever reason.
I have to be pedantic I cannot allow liberal use of the term peg to describe a managed exchange rate for two good reasons. They are very different things, and more importantly, I grew up in Hong Kong and lived there for over 30 years, and the currency that was in my pocket during that entire time had a value that was pegged to the US$using the currency board system. To use the term to describe a managed float is faux pas. Forgive me, I do not wish to sound arrogant in the slightest, but if someone used the term hills to describe the Himalayas we as Indians would have to correct them and say they are mountains. I have to respectfully disagree with you however, for hedge funds or any institution to take positions in a market particularly the currency markets, and again I say this after having worked on trading floor right next to the prime brokerage desk during the Asian financial crisis. Leverage is required. These funds without leverage are puny. look at Citadel which is facing difficulty right now, one of the most successfully managed hedge funds ever, with$15 Billion under management, its a minuscule amount of money. If they want returns then they need to lever up, otherwise they cannot return the 30% per annum that they were doing the previous 5 years
I have to disagree with your view on reserves as well, they can be very potent weapons and a means of defence. I was there the day the Hong Kong government intervened to fend off speculators and bought US$30 Billion worth of equity over a two day period. Not only did currency speculators who were shorting dollar and the index cave they got badly burned and to date I have never seen so much frenzy on the floor. You are right, a concerted attack by a market that lasts weeks or months cannot be defended against no matter how much you have in reserves, but a short one where speculators do not have the wherewithal to take the pain on immediate losses can, and I have seen it work with my own eyes as it happened and even participated in it. Honestly speaking with the way asset markets are selling off right now investors are trying to stem their own haemorrhage, there isn't a manager out there looking at running a speculative position other than an unleveraged short perhaps at best and no one has the ability to lever up, and I respectfully disagree again, if you want a decent return on a position you need some degree of leverage, which is simply not feasible right now. In fact the term leverage right now is a dirty word and nobody wants to hear it. 6. You might want a short read of my stuff. I don't get to be as wonkish as you are allowed to be, the luxury of a personal blog means you can write when you want and about exactly what you want about and I envy that, but about once a week or so I write something of interest to me personally http://www.money-india.com/news/finance-news/the-future-for-india-remains-bright-3102/ 7. Ajay can you pls help to understand drop in australian dollar??? Thanks Manish Please note: Comments are moderated. Only civilised conversation is permitted on this blog. Criticism is perfectly okay; uncivilised language is not. We delete any comment which is spam, has personal attacks against anyone, or uses foul language. We delete any comment which does not contribute to the intellectual discussion about the blog article in question. LaTeX mathematics works. This means that if you want to say$10 you have to say \\$10.
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http://proceedings.mlr.press/v75/el-alaoui18a.html
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# Detection limits in the high-dimensional spiked rectangular model
Ahmed El Alaoui, Michael I. Jordan
Proceedings of the 31st Conference On Learning Theory, PMLR 75:410-438, 2018.
#### Abstract
We study the problem of detecting the presence of a single unknown spike in a rectangular data matrix, in a high-dimensional regime where the spike has fixed strength and the aspect ratio of the matrix converges to a finite limit. This setup includes Johnstone’s spiked covariance model. We analyze the likelihood ratio of the spiked model against an “all noise" null model of reference, and show it has asymptotically Gaussian fluctuations in a region below—but in general not up to—the so-called BBP threshold from random matrix theory. Our result parallels earlier findings of Onatski et al. (2013) and Johnstone-Onatski (2015) for spherical spikes. We present a probabilistic approach capable of treating generic product priors. In particular, sparsity in the spike is allowed. Our approach operates through the principle of the cavity method from spin-glass theory. The question of the maximal parameter region where asymptotic normality is expected to hold is left open. This region, not necessarily given by BBP, is shaped by the prior in a non-trivial way. We conjecture that this is the entire paramagnetic phase of an associated spin-glass model, and is defined by the vanishing of the replica-symmetric solution of Lesieur et al. (2015).
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https://cstheory.stackexchange.com/questions/40478/examples-of-algorithms-and-proofs-that-seem-correct-but-arent
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# Examples of algorithms and proofs that seem correct, but aren't
In my intro to programming course, we're learning about the Initialization-Maintenance-Termination method of proving an algorithm does what we expect it to. But we've only had to prove that an algorithm already known to be correct, is correct. We've never been asked to show that an algorithm isn't correct.
Are there any classic examples of algorithms that look correct, but aren't? I am looking for cases where the Initialization-Maintenance-Termination approach catches something that first-glance intuition doesn't.
• Possibly of interest: cs.stackexchange.com/q/29475/755 – D.W. Mar 29 '18 at 19:53
• Upvoting because I think that this is a very important pedagogical question. It is slightly out of scope for cstheory, but I don't know a better platform for it, and there are many algorithms instructors in the cstheory community. Most algorithm-design courses expose students only to correct, existing algorithms and to problems that are easily solvable using known techniques. This reinforces the impression, so attractive to students, that one can safely trust one's intuitive feeling that a seemingly plausible algorithm is right. A good algorithm-design course should do the opposite! – Neal Young Mar 31 '18 at 2:14
• I would love to have a collection like this. – Chandra Chekuri Mar 31 '18 at 11:28
2D local maximum
input: 2-dimensional $n \times n$ array $A$
output: a local maximum -- a pair $(i,j)$ such that $A[i,j]$ has no neighboring cell in the array that contains a strictly larger value.
(The neighboring cells are those among $A[i, j+1], A[i, j-1], A[i-1, j], A[i+1, j]$ that are present in the array.) So, for example, if $A$ is
$$\begin{array}{cccc} 0&1&3&\mathbf{4}\\ \mathbf{3}&2&\mathbf{3}&1\\ 2&\mathbf{5}&0&1\\ \mathbf{4}&0&1&\mathbf{3}\end{array}$$
then each bolded cell is a local maximum. Every non-empty array has at least one local maximum.
Algorithm. There is an $O(n^2)$-time algorithm: just check each cell. Here's an idea for a faster, recursive algorithm.
Given $A$, define cross $X$ to consist of the cells in the middle column, and the cells in the middle row. First check each cell in $X$ to see if the cell is a local maximum in $A$. If so, return such a cell. Otherwise, let $(i, j)$ be a cell in $X$ with maximum value. Since $(i, j)$ is not a local maximum, it must have a neighboring cell $(i', j')$ with larger value.
Partition $A \setminus X$ (the array $A$, minus the cells in $X$) into four quadrants -- the upper left, upper right, lower left, and lower right quadrants -- in the natural way. The neighboring cell $(i', j')$ with larger value must be in one of those quadrants. Call that quadrant $A'$.
Lemma. Quadrant $A'$ contains a local maximum of $A$.
Proof. Consider starting at the cell $(i', j')$. If it is not a local maximum, move to a neighbor with a larger value. This can be repeated until arriving at a cell that is a local maximum. That final cell has to be in $A'$, because $A'$ is bounded on all sides by cells whose values are smaller than the value of cell $(i', j')$. This proves the lemma. $\diamond$
The algorithm calls itself recursively on the $\frac{n}{2}\times\frac{n}{2}$ sub-array $A'$ to find a local maximum $(i, j)$ there, then returns that cell.
The running time $T(n)$ for an $n\times n$ matrix satisfies $T(n) = T(n/2) + O(n)$, so $T(n) = O(n)$.
Thus, we have proven the following theorem:
Theorem. There is an $O(n)$-time algorithm for finding a local-maximum in an $n\times n$ array.
Or have we?
• At first reading, the only mistake I spotted was the recurrence solution. Is that the only mistake? – Radu GRIGore Mar 31 '18 at 8:08
• The recurrence is correct. The algorithm is not! – Neal Young Mar 31 '18 at 11:08
• Ah, yes, I made a dumb mistake with the recurrence. I see the problem: the maximum you prove exists is not (necessarily) what you find. And what you find ignores the X. – Radu GRIGore Mar 31 '18 at 11:19
• Here's an example: $$\begin{pmatrix}2&1&4&3&3&0&0\\1&0&1&2&3&0&0\\0&{\color{red}1}&0&2&3&0&0\\2&2&2&2&2&2&2\\3&3&3&2&3&3&3\\0&0&3&2&3&0&0\\0&0&3&2&3&0&0\end{pmatrix}$$ – Radu GRIGore Mar 31 '18 at 11:42
• @Marin, what is missing is a proof that a local maximum of $A'$ is also a local maximum of $A$, because it's not true. (I somehow like my initial wording, but it is not precise, and it is not clear. But, it may aid intuition.) – Radu GRIGore Apr 4 '18 at 5:11
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https://scaron.info/publications/rss-2015.html
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# Leveraging Cone Double Description for Multi-contact Stability of Humanoids with Applications to Statics and Dynamics
Stéphane Caron, Quang-Cuong Pham and Yoshihiko Nakamura. RSS 2015, Roma, Italy, July 2015.
## Abstract
We build on previous works advocating the use of the Gravito-Inertial Wrench Cone (GIWC) as a general contact stability criterion (a "ZMP for non-coplanar contacts"). We show how to compute this wrench cone from the friction cones of contact forces by using an intermediate representation, the surface contact wrench cone, which is the minimal representation of contact stability for each surface contact. The observation that the GIWC needs to be computed only once per stance leads to particularly efficient algorithms, as we illustrate in two important problems for humanoids : "testing robust static equilibrium" and "time-optimal path parameterization". We show, through theoretical analysis and in physical simulations, that our method is more general and/or outperforms existing ones.
## BibTeX
@inproceedings{caron2015rss,
title = {Leveraging Cone Double Description for Multi-contact Stability of Humanoids with Applications to Statics and Dynamics},
author = {Caron, St{\'e}phane and Pham, Quang-Cuong and Nakamura, Yoshihiko},
booktitle = {Robotics: Science and System},
year = {2015},
month = jul,
}
## Discussion
In your previous work, you provided an analytical formula for the contact wrench cone. Why don't you use it in this paper?
Unfortunately the analytical formula of the contact wrench cone is only known (yet) for a single contact. In multi-contact, the best call so far is to use numerical algorithms such as the double description method.
According to Figure 2, you use the double-description method to compute the span matrix $$V_{surf}$$ at each contact. Is this necessary?
It is not, as we later found out: local span matrices are straightforward to compute, as detailed for instance in the introduction of this paper. The only point where the double description remains necessary so far is for computing the gravito-inertial face matrix $$U_{stance}.$$
What is the link between the matrix $$U_{stance}$$ in this paper and the matrices $$A_O$$ or $$A_G$$ used in your 3D-COM pattern generator?
In this paper, the gravito-inertial wrench coordinates $$w_{GI} = (f_{GI}, \tau_{GI})$$ are taken at the origin $$O$$ of the world frame. Using proper notations, we should have written $$w^{gi}_O$$ to acknowledge this reference point. (We apologize for the non-standard notations.) Our later works uses the net contact wrench, i.e. the sum of all contact wrenches applied to the robot, which yields the opposite of the gravito-inertial one: $$w^{c}_O = -w^{gi}_O.$$ Therefore, the face matrices are opposed as well: $$U_{stance} = -A_O.$$
Given an $$n \times m$$ matrix $$V,$$ is it the case that its dual (face or H-representation) matrix $$U = V^F$$ has shape $$m \times n?$$
It is not always the case, as you can see in Table I of the paper. In single support, redundant inequalities simplify and the $$6 \times 16$$ span matrix of the wrench cone has a $$16 \times 6$$ face dual. However, in double-support the dual of the $$6 \times 32$$ span matrix typically has more than 100 rows.
The cdd library gives me the error "Numerical inconsistency is found. Use the GMP exact arithmetic." What can I do?
It may happen that your problem is "doable" but you ended up hitting some near-singular configuration. In such cases, a simple hack is to perturb the input (contact locations, or coordinates where the CWC is taken) by some epsilon.
Another cause of numerical instabilities are vectors that are "almost" rational, for instance with coordinates such as 0.4 + 1e-12. Rounding up coordinates to a sound number of decimals can filter out those.
If none of the above apply, you can try with rational rather than floating point numbers. In that case, I'd advise using PPL or its Python wrapper pyparma rather than cdd.
What about calling the Canonicalize() function in cdd to remove redundant rays from the input V-description?
In my experience this extra step only make matters worse (with regards to numerical-inconsistency errors), so I would advise against doing it. Also, note that, even if your input V-description is irreducible, cdd may output you a non-minimal H-description.
Numerical instabilities seem to happen more often in stances with more contacts. Why?
Unfortunately I have only an intuition here: making more contacts implies a resultant polyhedron with more faces, i.e. with more rays in the V-description and more hyperplanes in the H-one. This increases the risk of "tricky" faces (of very small area) in the output polyhedron, especially if some of your input rays are nearly aligned. My guess is that these make the double-description fail when it tries to cut (c.f. Fukuda's paper on the algorithm) by an "almost meaningless" hyperplane.
One footnote of the paper mentions Dirac fields. Are you referring here to the Dirac delta function and its higher dimensional versions?
Yes, in this case we refer to the Dirac delta function, that is to say, a distribution that concentrates forces at the vertices of the contact area. You will find a bit more discussion on this point, along with a proof of the corresponding proposition, at the end of Section III of this study of surface contacts.
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https://lqp2.org/node/1189
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# Applications of local gauge covariance: Anomalies and QED in external potentials
DPG Spring Conference
Jochen Zahn on March 19, 2015
TalkDPG.pdf
The framework of locally covariant field theory proved extremely fruitful for QFT on curved space-times. It can be straightforwardly generalized to more general non trivial background fields, in particular gauge connections. I will present two applications of this framework. The first is an elementary computation of the chiral anomalies, directly on Lorentzian space-times. The second is QED in external potentials, where I compare the locally covariant definition of the current to other definitions and consider it in concrete cases.
Related papers:
Locally covariant chiral fermions and anomalies
The current density in quantum electrodynamics in external potentials
The current density in quantum electrodynamics in time-dependent external potentials and the Schwinger effect
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http://www.gap-system.org/Manuals/pkg/Toric-1.9.4/doc/chap3.html
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Goto Chapter: Top 1 2 3 4 Bib Ind
### 3 Affine toric varieties
This chapter concerns toric commands which deal with the coordinate rings of affine toric varieties U_σ.
#### 3.1 Ideals defining affine toric varieties
##### 3.1-1 EmbeddingAffineToricVariety
‣ EmbeddingAffineToricVariety( L ) ( function )
Input: L is a list generating a cone (as in DualSemigroupGenerators).
Output: the toroidal embedding of X=Spec(I), where I is the ideal of the affine toric variety (given as a list of multinomials).
gap> phi:=EmbeddingAffineToricVariety([[1,0],[3,4]]);
[ x_2, x_1, x_1^2/x_4, x_1^3/x_4^2, x_1^4/x_4^3 ]
gap> L:=[[1,0,0],[1,1,0],[1,1,1],[1,0,1]];;
gap> phi:=EmbeddingAffineToricVariety(L);
[ x_3, x_2, x_1/x_5, x_1/x_6 ]
Goto Chapter: Top 1 2 3 4 Bib Ind
generated by GAPDoc2HTML
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https://akhbarnama.com/allama-iqbal-express-train-schedule-daily-timings-6513.html
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# Allama Iqbal Express Train Schedule & Daily timings
Allama Iqbal Express is the train that runs daily between Karachi and Sialkot, joining the two business cities together. The train was launched in 1940 and it is one of the oldest trains of Pakistan. Allama Iqbal Express train was known as Shaheen Express before 1985. In 1998 it was redirected through Lahore and Wazirabad and later in 2004 it was redirected through Lahore and Narowal. The name of the train was laid after great philosopher and poet Dr. Muhammad Iqbal who belonged to Sialkot. The train travels a distance of 1,362 kilometers daily.
Allama Iqbal Express train has 15 economy coaches, 1 power van and 1 luggage coach for passengers. It completely runs on Diesel Traction. The train claims to cover the distance from Karachi to Sialkot in 25 hours and 5 minutes. It is one of the economy class trains that are especially designed to facilitate the passengers and provide standard facilities at economical price. It is one of the trains that are still running successfully after a long time since its establishment in 1940.
Allama Iqbal Express train departs from Karachi 9 up and reaches Sialkot 10 down via Lahore. The train departs at 14:00 daily and stops at Drigh Road at 14:15, Kotri at 16:04, Hyderabad Junction at 16:20, Tando Adam Junction at 17:12, Nawabshah Junction at 17:55, Mahrabpur Junction at 19:33, Rohri Junction at 21:05 and stays there till 21:30, Ghotki at 22:15, Sadikabad at 23:43, Rahim Yar Khan at 00:10, Khanpur junction at 00:55, Bahawalpur at 02:37, Dunyapur at 03:44, Jahania at 04:30, Khanewal Junction at 05:05, Sahiwal at 07:12, Okara at 07:40, Pattoki at 08:21, Kot Radha Kishn at 08:46, Riwind Junction at 09:12, Kot Lakhpat at 9:53, Lahore Junction at 10:30 and stays there till 11:00, Shahdara Bagh Junction at 11:14 Narang at 12:01, Baddomalhi at 12:32, Narowal Junction at 13:20, Kila Sobha Singh at 13:47, Pasrur at 14:09, Chawinda at 14:29 and reaches Sialkot Junction at 15:15.
For kids and mature person ticket and fare charges you can contact Pakistan railway contact number at +92-21-99201116, 99201117
1. rehman May 16, 2016
2. rehman May 16, 2016
3. malik zahid July 25, 2016
• Muhammad sabir July 9, 2017
4. ghulamnabi August 23, 2016
5. armjee January 3, 2017
6. sharafat ali February 27, 2017
7. sidra March 10, 2017
8. Abulrasheed October 29, 2017
9. zara December 14, 2017
• zara December 14, 2017
• Umerfarooq December 19, 2017
10. Muhammd Rauf July 11, 2018
11. MUhammd rauf July 11, 2018
12. Muhammad rauf July 11, 2018
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http://www.wowinterface.com/downloads/search.php?usrcmnts=111776
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File: Combuctor02-08-11 Error 4.0.6 Posted By: xythian I get a Combuctor error with 4.0.6. The error happens on every login and prevents any items from being displayed in my Combuctor bag. ---------------- Date: 2011-02-08 12:05:53 ID: 1 Error occured in: Global Count: 1 Message: ..\AddOns\Combuctor\item.lua line 408: bad argument #2 to 'format' (string expected, got nil)...
File: Pawn12-18-10 I'll watch the behavior more closel... Posted By: xythian I'll watch the behavior more closely over the next day or so and report back.
File: Pawn12-18-10 Quest Integration: Coin Reward and Disabled Armor Classes Posted By: xythian First, I love Pawn. That just has to be said. Second, I noticed a weird quirk in Pawn yesterday after I went through and disabled all non-plate armor classes for the stat scales for my DK. The Pawn Quest advisor also ignores any items for which the armor class is disabled, even if they are the highest gold reward for a quest with...
File: DDR - DocsDebugRunes09-01-10 Enable/Config Posted By: xythian How do you enable or config DDR? It doesn't load automatically for me. I tried guessing commands and poked around in the lua but it didn't get me anywhere. Edit: This is on the Cataclysm beta.
File: AVR04-02-10 Originally posted by Olog Do you... Posted By: xythian Originally posted by Olog Do you remember what you were doing just before you got that? I could only think of one way to get that error and it is to toggle the hide all option and then go to scene editor. Was it something like that? Oy, I wish I could remember in more detail exactly what I was doing. I was playing around with t...
File: AVR04-01-10 Error after first edit Posted By: xythian My first attempt at making a scene worked, I was able to create and save several meshes. However, my 2nd attempt produced an error which now repeats every time I try to use the editing tool. Reloading the UI doesn't make the error go away. Date: 2010-04-01 13:45:57 ID: 1 Error occured in: Global Count: 861 Message: ..\AddOns...
File: Pawn02-25-10 Re: Re: Can't click on scales, Pawn 1.3 Posted By: xythian Originally posted by VgerAN I had one other person report this during the beta, but I wasn't able to reproduce it. Do you have any other related mods running, or do you get any errors? Right now I don't have much of anything to go on. It is now working as expected. I too have no idea what caused the earlier issue. No errors w...
File: Pawn02-25-10 Can't click on scales, Pawn 1.3 Posted By: xythian Anybody else not able to click on Pawn scales in 1.3? I have 4 custom scales but can not select them (or any other scales). The scale at the top of the list is selected by default and I can't choose any others.
File: Elitist Group01-07-10 Tooltips clash with EquipCompare Posted By: xythian I noticed that the tooltips in EG that show gem/enchant information tend to clash with EquipCompare. When I mouse over an item in EG, EquipCompare activates and shows my companion item to the one in EG. EG then puts its tooltip "under" the EquipCompare addon. Any ideas on how to suppress or alter the tooltips in some way that the...
File: Quick Auctions 311-25-09 Originally posted by Kazragore Er... Posted By: xythian Originally posted by Kazragore Error after posting auctions: 3x QuickAuctions\modules\manage.lua:343: bad argument #4 to 'format' (number expected, got nil) QuickAuctions\modules\manage.lua:343: in function PostItems' QuickAuctions\modules\manage.lua:372: in function ?' CallbackHandler-1.0-5 (Ace3):146: in function <...Ons...
File: Quick Auctions 310-05-09 I receive the following error when... Posted By: xythian I receive the following error when I click on the "Status" button in the latest QA2. Date: 2009-10-05 09:19:16 ID: 1 Error occured in: Global Count: 1 Message: ..\AddOns\QuickAuctions\QuickAuctions.lua line 114: attempt to index local 'scrollBar' (a nil value) Debug: (tail call): ? QuickAuctions\QuickAuctions.lua:...
File: BankStack09-25-09 I think I've fixed the issue (at le... Posted By: xythian I think I've fixed the issue (at least for me) with Bank Stack ignoring profession bags. You want to edit the "IsSpecialtyBag" function in core.lua to look like the following. function core.IsSpecialtyBag(bagid) if safe or is_guild_bank_bag(bagid) then return false end local invslot = ContainerIDToInventoryID(bagid) if...
File: BankStack09-24-09 I too am having problems with BankS... Posted By: xythian I too am having problems with BankStack working with inscription bags. If I try to fill my inscription bags from the bank, it will only fill the backpack slot and then stops. The inscription bags are untouched. Note: I am only trying to move glyphs into these bags. It's not an item-bag conflict. I've poked around the Bank Stack...
08-25-09 Originally posted by toumei64 Rig... Posted By: xythian Originally posted by toumei64 Rigged it up so that it works. I'm no expert or anything http://wow.tatsumaru.org/DynamicPerformance.zip You sir are a saint. DP works again!
File: AuctionLite05-26-09 Excellent addon and a fine replacem... Posted By: xythian Excellent addon and a fine replacement for the super bloated Auctioneer. However, like many others, I have a feature request/question. Yes, I realize the irony of praising for lean programming and then requesting features. :) The only feature of auctioneer that I can not seem to replicate in Auction Lite is the ability to scan for...
File: Caith UI05-25-09 How do I move the player debuff fra... Posted By: xythian How do I move the player debuff frame? I poked around in the rbuff.lua doc, but I don't see coords just for the debuff frame. I'm not talking about the pitbull debuffs for targets, but my player debuffs. I tweaked the buff frame via buffalo and now my buffs clip the debuffs and I want to move the debuffs down a little to compensate.
File: Caith UI05-22-09 Thanks for the help! Working wit... Posted By: xythian Thanks for the help! Working with Buffalo rather than rBuff has made the changes possible.
File: Caith UI05-22-09 Originally posted by BoeserO Hi C... Posted By: xythian Originally posted by BoeserO Hi Caith, absolutely wonderful UI. Thank you! One Question, the buff icons are too big for my resolution, but scaling of rBuff doesn't work for me. I edited the .lua to BuffFrame:SetScale(0.7) TemporaryEnchantFrame:SetScale(0.7) but nothing happens. Changing the values in any way does exact...
File: LoggerHead04-20-09 Ulduar Support Posted By: xythian Ulduar support is mostly built in to the addon already. If you play around with the LibTourist and LibBabble lua files you'll see Ulduar stuff commented out. I enabled Ulduar support in the version you can d/l below. It's only good for 10 downloads so share the love if you can. http://rapidshare.com/files/223616162/LoggerHead_U...
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http://mathoverflow.net/questions/32032/on-a-theorem-of-jacobson/32067
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# On a theorem of Jacobson
In a comment to an answer to a MO question, in which Bill Dubuque mentioned Jacobson's theorem stating that a ring in which $X^n=X$ is an identity is commutative (theorem which has shown up on MO quite a bit recently, e.g. here), Pierre-Yves Gaillard observed that there is a more general theorem in which $n$ is allowed to be different for each element of the ring, so that in fact we can rephrase the theorem as saying that the set $S=\{X^n-X:n>1\}\subset\mathbb Z[X]$ has the following property:
If $A$ is a ring such that for every $a\in A$ there is an $f\in S$ such that $f(a)=0$, then $A$ is commutative.
Of course, $S\cup (-S)$ also has this property, and even if we construct $S'$ from $S\cup(-S)$ by closing it under the operation of taking divisors in $\mathbb Z[X]$, it also has the same property. Pierre-Yves then asked:
Is $S'$ maximal for this property?
So, is it?
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@Litt, I guess you are taking minimal in cardinality. But minimal in what sense, such that it implies commutative? x^2-x=0 is enough. Notice that putting more elements in the set doesn't necessarily make things better to get the commutativity because then some a's can satisfy equations from S and some others satisfy the new equations. (or all satisfy the new equations). – Mlazhinka Shung Gronzalez LeWy Jul 15 '10 at 16:56
Dear Mariano: Thanks for mentioning this question. I think one should ask if $S\cup(-S)$ [and not $S$] is maximal for the property in question. – Pierre-Yves Gaillard Jul 15 '10 at 16:57
$S$ isn't remotely maximal, as far as I can see. For example any divisor of $X^n-X$ for any $n$ can be added to it, as if $P(X)=0$ for $P$ some divisor of $X^n-X$ then $X^n-X=0$. Moreover, if you have a ring in which every element other than the number 9 satisfies $X^n=X$ for some $n$, then 9 will also satisfy this, because $3^n=3$ implies $9^n=9$. So you can also add $X-9$ to $S$. And so on and so on... – Kevin Buzzard Jul 15 '10 at 18:17
@Pierre: can you prove that your set works before we start worrying about whether it's maximal? I only added $X-9$, I didn't add all $X-n$ simultaneously. But my gut instinct is that, if your set is OK, it won't be maximal because there are still plenty of other stupid tricks you can try (square of a linear factor etc). Note however that if someone comes up with an enlargement and then someone else says "OK then is this enlarged set maximal" we could be here all year! – Kevin Buzzard Jul 15 '10 at 19:23
It still might be true though! I certainly don't know a counterexample (as you probably guessed---because if I did I would have played it instantly!). I am not optimistic about finding a "nice" maximal set though. I think the first thing to do is to read the proof and to see what's really going on, and to go from there. – Kevin Buzzard Jul 15 '10 at 20:38
Herstein proved that $S$ can be enlarged to the set of all $a^2 p(a) - a$ with $p$ a polynomial (with integer coefficients).
EDIT. Herstein's set may be maximal. The set can't contain any polynomials whose vanishing would be consistent with the ring containing (nonzero) nilpotent elements, so nothing in $S$ can be divisible by $a^2$. The lower degree terms are also highly constrained by the condition that if there is $p$-torsion then no $p^2$-torsion.
I think I found the reference: Herstein, I. N. The structure of a certain class of rings. Amer. J. Math. 75, (1953). 864-871. --- Herstein even proves this: If, for every $a$ a ring $R$, there exists a polynomial $p_a(t)$ (with integral coefficients) such that $a^2p_a(a)-a$ is central, then $R$ is commutative. – Pierre-Yves Gaillard Jul 15 '10 at 22:56
Yes, I should have explained that the full result only requires central rather than zero, but the latter is enough to answer the question. I never proved the full Jacobson theorem but I did work out the $f(x) = x^n - x$ problem some time ago (using the universal ring generated by the required relations) and if I remember correctly, the key conditions are that $f(x)=x$ mod $p$ and the form of $f$ rules out nilpotent elements. These two conditions easily force a direct sum decomposition into finite fields and this concludes the proof. Herstein apparently showed this is enough in general. – T.. Jul 15 '10 at 23:07
I hope the following is correct. Let $A$ be the set of $f(X)\in\mathbb Z[X]$ with constant term $\pm1$, let $XA$ be the set of the $Xf(X)$, $f(X)$ in $A$. Let $R$ be a ring and $C$ its center. Herstein's Theorem says that if for any $r$ in $R$ there is an $f(X)$ in $XA$ such that $f(r)$ is in $C$, then $R=C$. It implies trivially the following. Put $B:=\{X-n\ |\ n\in\mathbb Z\}$. If for any $r$ in $R$ there is an $f(X)$ in $XA\cup A$ such that $f(r)=0$, then $R=C$. If for any $r$ in $R$ there is an $f(X)$ in $XA\cup B$ such that $f(r)$ is in $C$, then $R=C$. – Pierre-Yves Gaillard Jul 16 '10 at 5:41
@T.: Herstein's set isn't maximal because you can add $X-1$. – Kevin Buzzard Jul 16 '10 at 5:43
If you allow the zero ring as a ring, yes. But the $\pm X-n$ and the ones from A in Pierre-Yves' comment seem to be all you can add to Herstein's set. – T. 2 mins ago – T.. Jul 16 '10 at 6:47
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http://math.stackexchange.com/questions/38480/how-much-does-symbolic-integration-mean-to-mathematics
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# How much does symbolic integration mean to mathematics?
(Before reading, I apologize for my poor English ability.)
I have enjoyed calculating some symbolic integrals as a hobby, and this has been one of the main source of my interest towards the vast world of mathematics. For instance, the integral below $$\int_0^{\frac{\pi}{2}} \arctan (1 - \sin^2 x \; \cos^2 x) \,\mathrm dx = \pi \left( \frac{\pi}{4} - \arctan \sqrt{\frac{\sqrt{2} - 1}{2}} \right).$$ is what I succeeded in calculating today.
But recently, as I learn advanced fields, it seems to me that symbolic integration is of no use for most fields in mathematics. For example, in analysis where the integration first stems from, now people seem to be interested only in performing numerical integration. One integrates in order to find an evolution of a compact hypersurface governed by mean curvature flow, to calculate a probabilistic outcome described by Ito integral, or something like that. Then numerical calculation will be quite adequate for those problems. But it seems that few people are interested in finding an exact value for a symbolic integral.
So this is my question: Is it true that problems related to symbolic integration have lost their attraction nowadays? Is there no such field that seriously deals with symbolic calculation (including integration, summation) anymore?
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Manipulationally, an analytic (closed) form would be terribly convenient, in the sense that we know so much about (special) functions and the identities they satisfy that we would like to be able to exploit that whole body of knowledge for the integral at hand. For numerical work, a closed form may or may not be the best thing to have, depending on the circumstances. – Ｊ. Ｍ. May 11 '11 at 15:29
If you broaden the question, allowing multiparameter (in)definite integrals and sums, then the question is not about only (transcendental) constants but, more generally, about the utility of closed form functions solving differential / difference equations, i.e. special functions. Do you intend to ask only about special constants or, more generally, special functions? – Bill Dubuque May 11 '11 at 15:52
@J.M. : Thanks for your comment. But if you won't mind, can you be a little more specific? – sos440 May 11 '11 at 15:56
@Bill Dubuque : Oh, that's my point. I am also interested in special functions. – sos440 May 11 '11 at 15:57
Since you find symbolic integration interesting, you may find useful the references I mention in this answer: math.stackexchange.com/questions/37088/integration-doubt/… – Andres Caicedo May 12 '11 at 16:39
I think it would be appropriate at this point to quote Forman Acton:
...at a more difficult but less pernicious level we have the inefficiencies engendered by exact analytic integrations where a sensible approximation would give a simpler and more effective algorithm. Thus
\begin{align*}\int_0^{0.3}\sin^8\theta\,\mathrm d\theta&=\left[\left(-\frac18\cos\,\theta\right)\left(\sin^4\theta+\frac76\sin^2\theta+\frac{35}{24}\right)\sin^3\theta+\frac{105}{384}\left(\theta-\sin\,2\theta\right)\right]_0^{0.3}\\ &=(-0.119417)(0.007627+0.101887+1.458333)(0.0258085)+0.004341\\ &=-0.0048320+0.0048341=0.0000021\end{align*}
manages to compute a very small result as the difference between two much larger numbers. The crudest approximation for $\sin\,\theta$ will give
$$\int_0^{0.3}\theta^8\,\mathrm d\theta=\frac19\left[\theta^9\right]_0^{0.3}=0.00000219$$
with considerably more potential accuracy and much less trouble. If several more figures are needed, a second term of the series may be kept.
In a similar vein, if not too many figures are required, the quadrature
$$\int_{0.45}^{0.55}\frac{\mathrm dx}{1+x^2}=\left[\tan^{-1}x\right]_{0.45}^{0.55}=0.502843-0.422854=0.079989\approx 0.0800$$
causes the computer to spend a lot of time evaluating two arctangents to get a result that would have been more expediently calculated as the product of the range of integration ($0.1$) by the value of the integrand at the midpoint ($0.8$). The expenditure of times for the two calculations is roughly ten to one. For more accurate quadrature, Simpson's rule would still be more efficient than the arctangent evaluations, nor would it lose a significant figure by subtraction. The student that worships at the altars of Classical Mathematics should really be warned that his rites frequently have quite oblique connections with the external world.
It may very well be that choosing the closed form approach would still end up with you having to (implicitly) perform a quadrature anyway; for instance, one efficient method for numerically evaluating the zeroth-order Bessel function of the first kind $J_0(x)$ uses the trapezoidal rule!
On the other hand, there are also situations where the closed form might be better for computational purposes. The usual examples are the complete elliptic integrals $K(m)$ and $E(m)$; both are more efficiently computed via the arithmetic-geometric mean than by using a numerical quadrature method.
But, as I said in the comments, for manipulational work, possessing a closed form for your integral is powerful stuff; there is a whole body of results that are now conveniently at your disposal once you have a closed form at hand. Think of it as "standing on the shoulders of giants".
In short, again, "it depends on the situation and the terrain".
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+1 for retyping Acton into $\TeX$. – lhf May 11 '11 at 17:29
For the original problem, things are similar. After realizing that $1-\sin^2 x\, \cos^2 x = [7+\cos(4x)]/8$, i.e., $7/8$ plus something oscillating, one is tempted to replace the integrand by $\arctan(7/8)$. Then one gets $\pi \arctan(7/8)/2 \approx 1.129$ for the integral which coincides with the exact expression $1.126$ up to $3\times 10^{-3}$. I don't know how much time the OP spend for his answer, but Pareto's principle seems to apply. – Fabian May 11 '11 at 20:36
Thanks to everyone, especially J.M., for giving insightful answers. It's really convincing that distinction between numerical one and symbolic one is subject not to a particular classification of research area, but rather to a situation. – sos440 May 12 '11 at 10:24
@sos440: You're very much welcome. :) Don't let my answer deter you from the fun you seem to have in teasing out analytic solutions; what I'm merely saying is that in real-world applications, one must eventually develop a "feel" for choosing the "right tool for the job". – Ｊ. Ｍ. May 12 '11 at 10:28
I don't think your point of view is the right one. To compute an integral analytically and to compute an integral numerically are different things. A numerical analysis professor of mine once said that, in applications (engineering, physics...) it is often more convenient to directly evaluate integrals by numerical means, even if they are integrable analytically! For example, suppose that you need
$$\int_{0}^{\frac{\pi}{2}} \arctan (1 - \sin^2 x \; \cos^2 x) \,\mathrm dx$$
meters of conducting wire. You make a phone call to the wire factory and ask for what? For $\pi \left( \frac{\pi}{4} - \arctan \sqrt{\frac{\sqrt{2} - 1}{2}} \right)$ meters of wire? More realistically you will ask for something like $1.13$ meters of wire.
To obtain this number $1.13$ you performed an approximation over the non-rational quantity $\pi \left( \frac{\pi}{4} - \arctan \sqrt{\frac{\sqrt{2} - 1}{2}} \right)$. In doing so you wasted information. It would have been more convenient (and, maybe, even more accurate) to perform this approximation on the first integral directly, that is, to evaluate it numerically.
Of course this does not render analytical methods useless. You could have a family of integrals depending on a parameter, for example. Numerical methods tell you nothing here. You could run across an integral in the middle of a proof, and need its exact value for theoretical purposes. The possibilities are countless.
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Also, if you don't need that much accuracy (which is often in applications), even the simple-minded methods like trapezoidal or Simpson's might end up being faster to compute with than having to use a special routine for some exotic transcendental. – Ｊ. Ｍ. May 11 '11 at 16:04
In short, if I may borrow the usual piece of military wisdom: "it depends on the situation and the terrain". – Ｊ. Ｍ. May 11 '11 at 16:12
Surely you mean something like 1.126 instead of 1.49... Also I'm curious if it is sure or just very likely that this number is not rational, as you state. – Myself May 12 '11 at 2:58
@Myself: Oh yes, sorry about that, I must have done some mistake in typing that number into Maple. Regarding the irrationality of $\pi \left( \frac{\pi}{4} - \arctan \sqrt{\frac{\sqrt{2} - 1}{2}} \right)$, I haven't checked it. Looks like a safe bet, though... Don't you agree? – Giuseppe Negro May 12 '11 at 17:26
Yes, I completely agree. But for all I know these things are typically hard to prove, so I thought perhaps I had missed something. – Myself May 12 '11 at 17:33
If you're talking about practical engineering applications, then really only numerical approximations are used (and studied in computer science as 'numerical analysis' or more recently 'scientific computing').
As to an academic mathematical field nowadays that deals with symbolic integration, first some perspective. Newton/Leibniz invented integral calculus in ...hm...late 1600's and was popularized (as much as you can say that) in the 1700's. Some basic symbolic integration even occurred (without that name and system) before then. So let's just say there's been at least 300 years of work there.
Also, there's more to inverting derivatives than just integrals. Solving systems of partial differential equations seem to be the big thing (both numerically and symbolically) for almost as long as simple single variable integrals.
That said, there is a small academic group of people working in 'symbolic computation' (with their own journals), and one subarea is symbolic integration. There are proofs of impossibility (i.e. proving that given certain restrictions there is no 'closed form' for a particular integral), and there are algorithms for computing integrals given other certain restrictions (the Risch algorithm). The latter are often implemented in computer algebra packages (Mathematica, Maple, etc.).
There is surely room for solving particular integrals (in the AMM there don't seem to be many integrals though in the Problems section) and for finding patterns. I'd look at those journals to see what particular interest there is for integrals.
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Back in the day, SIAM Reviews used to maintain a "problems column" where people submitted various requests for simple proofs, and yes, integrals/sums/whatever to evaluate. With the computing environments now, I suppose there is now less reason to submit those sorts of problems. – Ｊ. Ｍ. May 11 '11 at 17:25
@J.M.: It's been a longstanding (15 years?) challenge by Doron Zeilberger that he (and his computer) can solve automatically any summation sent in to the AMM Problems section. Surely there are summations (and integrals) that are people-solvable and currently not computer-solvable, but as the technology progresses, these will be harder for people to come by. – Mitch May 11 '11 at 17:44
I would also note that it may very well be that the symbolic output of current computing environments may be less than optimal, and some further human massaging may be needed. For instance, Mathematica sucks at producing optimal elliptic integral expressions... – Ｊ. Ｍ. May 12 '11 at 1:24
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https://fysugusybyjavuk.steinrenovationanddesigngroup.com/further-measurements-of-steady-and-oscillatory-pressures-on-a-rectangular-wing-book-26114xt.php
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Last edited by Fegar
Sunday, July 26, 2020 | History
2 edition of Further measurements of steady and oscillatory pressures on a rectangular wing found in the catalog.
Further measurements of steady and oscillatory pressures on a rectangular wing
D. G. Mabey
# Further measurements of steady and oscillatory pressures on a rectangular wing
## by D. G. Mabey
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ID Numbers Statement by D. G. Mabey, B. L. Welsh, C. R. Pyne. Series Technical report -- 92003 Contributions Welsh, B. L., Pyne, C. R., Defence Research Agency. Aerospace Division. Open Library OL17234130M
Supercritical wing design using numerical optimization and comparisons with experimentto improve C cruise performance. Analysis of interfering lifting surfaces in steady, oscillatory and transient incompressible flows. E. SUCIU and; L. MORINO Pressure and velocity measurements in a three dimensional wall jethigh lift V. The present measurements confirm the earlier measurement by Güven. The well- known drop in drag coefficient in the critical Reynolds regime (2 × 10 5 measurements also confirm the vortex shedding frequencies of a smooth cylinder, as found by.
Chapter 2 • Pressure Distribution in a Fluid 73 For the linear law to be accurate, the 2nd term in parentheses must be much less than unity. If the starting point is not at z = 0, then replace z by δz: Denver, Colorado, has an average altitude of ft. On a U.S. standard day, pres-sure gage A reads 83 kPa and gage B reads kPa. pressure at the new soil surface is kN/m3 × m ⇒ u = kPa The effective stress at the sand surface is zero. Particle size analysis and soil filters Q A sieve analysis on a sample of initial total mass g gave the following results: Sieve size, mm
Chapter 5 Measurement of Atmospheric Pressure Definition and Units Definition The atmospheric pressure is the force exerted by the weight of the Earth's atmosphere, expressed per unit area in a given horizontal cross-section. Thus, the atmospheric pressure is equal to the weight of a vertical column of air above the Earth's surface. American Institute of Aeronautics and Astronautics Sunrise Valley Drive, Suite Reston, VA
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### Further measurements of steady and oscillatory pressures on a rectangular wing by D. G. Mabey Download PDF EPUB FB2
Measurements in Low-speed Flow of Unsteady Pressure Distributions on a Rectangular Wing with an Oscillating Control Surface By D. DRANE Structures Department, R.A.E., Farnborough Reports and Memoranda No. * October, Summary.
of the wing. Thus, pressures corresponding to a 'suction' surface were measured with the wing at positive incidence.
Pressures corresponding to a 'pressure' surface were obtained in separate experiments with the wing mounted at a negative incidence. Instrumentation for Oscillatory Pressure Measurements. Worked Example shows the same trend: at contact (D = 0) the entropic solvation pressure would have been simply −kT/σ 3 ≈ 3 × 10 7 N m −2 ( atm), whereas the van der Waals contact pressure for A = 6 × 10 −22 J would have been A/σ 2 ≈ 3 × 10 6 N m −2, which is a factor of 10 smaller.
Both steady and oscillatory force Based Control from Surface Pressure Measurements. stall flow around a rectangular low-aspect-ratio wing. Steady actuation is used to examine effective. Cambridge Core - Fluid Dynamics and Solid Mechanics - Flow Measurement Handbook - by Roger C. BakerCited by: The use of sweep-frequency excitation for rapid measurement of time-dependent pressures on wind-tunnel models is examined.
Results obtained from two different wind-tunnels covering the Mach number range from toand a wide range of flow conditions, are compared with measurements made using the slower, traditional method of discrete-frequency excitation.
The wing was built in a standard rectangular configuration and featured an interchangeable plate on the tip to test the effect of the wing slots (feathers that project from the tips) and to see if.
Fluid Mechanics Frank White 5th Ed - ID:5ca11de. Fluid Mechanics McGraw-Hill Series in Mechanical Engineering CONSULTING EDITORS Jack P. Holman, Southern Methodist Univ. AFD Acoustic/Fluid Dynamic Phenomena I • Monday, 17 June • hrs.
Figure 4. Static and Total Pressure Measurements Within a Dynamic Fluid System Figure 5. Types of Pressure Probes When measuring dynamic system pressures, care must be taken to ensure accuracy. For static pressure measurements, the pressure tap location should be chosen so that the measurement is not influenced by the fluid flow.
Typically, taps. Measurement of oscillatory pressures on interfering surfaces is a preferable but, admittedly, more difficult alternative. Experimental measurements of oscillatory air loads (lift and moment) on two interacting lifting surfaces in tandem have been presented by Destuynder (Part II, AGARD ).
Test your knowledge on all of Review of Oscillations. Perfect prep for Review of Oscillations quizzes and tests you might have in school. For a trailing, or tip, vortex like this one (the vane is essentially a very short wing), the pressure outside the vortex flow is atmospheric. Thus the pressure in the core is below atmospheric pressure.
As air from upstream flows into the vortex core, the pressure and the temperature drop (see the discussion of isentropic relations in Chapter. A similar analysis of other oscillatory system – a simple (mathematical) pendulum – leads to the following formula for the oscillation period: $T = 2\pi \sqrt {\frac{L}{g}},$ where $$L$$ is the length of the pendulum, $$g$$ is the acceleration of gravity.
In the case of a compound or physical pendulum, the period of oscillation is given by. Under closed-loop conditions, the oscillator was able to maintain a mechanical test load at both positive and negative mean pressures during oscillatory excitations from to Hz. Chapter 1: MEASUREMENT 1. The SI standard of time is based on: A.
the daily rotation of the earth B. the frequency of light emitted by Kr86 C. the yearly revolution of the earth about the sun D. a precision pendulum clock E. none of these Ans: E 2. A nanosecond is: A. s B.
10−9 s C. 10−10 s D. 10−10 s E. 10−12 Ans: B 3. The SI. Velocity measurements were taken, using a Particle Image Velocimetry system, around the tip and in the near wake of a rectangular wing, which was equipped with several blowing slots.
Pressure measurements and particle image velocimetry measurements were conducted to investigate the formation of leading-edge vortices for oscillatory blowing, compared with completely stalled.
The rectangular planform semispan wing was vertically mounted in the wind tunnel. The wing profile was defined by the V airfoil sec- tion. The wing semispan was m (excluding the tips) and the chord was m.
The aspect ratio based on the semispan, without the tips, was Inclusion of Active Flow Control (AFC) into Computational Fluid Dynamics (CFD) simulations is usually highly time-consuming and requires extensive computational resources and effort.
In principle, the flow inside of the fluidic AFC actuators should be incorporated into the problem under consideration. However, for many applications, the internal actuator flow is not crucial, and only its.
Nikolaos D. Katopodes, in Free-Surface Flow, Periodic Flow Motion – The Strouhal Number. The Strouhal number represents the ratio of inertial forces due to the local acceleration of the flow to the inertial forces due to the convective acceleration.
Depending on the time scale of the problem, this ratio may be of order unity, and therefore its importance is not obvious.1 Physics Lecture 12 Oscillations – II SJ 7th Ed.: ChapRead only & • Recap: SHM using phasors (uniform circular motion) • Ph i l d l lPhysical pendulum example • Damped harmonic oscillations • Forced oscillations and resonance.
• Resonance examples and discussion – music – structural and mechanical engineering – waves • Sample problems.hydrostatic pressure to the dilation that it produces.
Where -p is the hydrostatic pressure, and β is the compressibility. Many useful relationships may be derived between the elastic constants E, G, v, K. For example, if we add up the three equations (). β σ 1 = ∆ − .
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https://planetmath.org/boundsfore
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# bounds for e
If $n$ and $m$ are positive integers and $n>m$, we have the following inequality:
$\left(1+{1\over n}\right)^{n}<{n\over n+1}\left(1+{1\over m}\right)^{m+1}$
Taking the limit as $n\to\infty$, we obtain an upper bound for $e$. Combining this with the fact that the $(1+1/n)^{n}$ is an increasing sequence, we have the following bounds for $e$:
$\left(1+{1\over m}\right)^{m}
This can be used to show that $e$ is not an integer – if we take $m=5$, we obtain $2.48832, for instance.
Title bounds for e BoundsForE 2013-03-22 15:48:48 2013-03-22 15:48:48 rspuzio (6075) rspuzio (6075) 7 rspuzio (6075) Theorem msc 33B99
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|
https://www.intmath.com/blog/environment/man-so-thoughtlessly-destroyed-350
|
# Man so thoughtlessly destroyed
By Murray Bourne, 30 Jul 2006
This is an interesting quote from Theodore Roosevelt, US president from 1901 to 1909.
We of an older generation can get along with what we have, though with growing hardship; but in your full manhood and womanhood you will want what nature once so bountifully supplied and man so thoughtlessly destroyed; and because of that want you will reproach us, not for what we have used, but for what we have wasted...So any nation which in its youth lives only for the day, reaps without sowing, and consumes without husbanding, must expect the penalty of the prodigal whose labor could with difficulty find him the bare means of life.
~Theodore Roosevelt (Arbor Day message to the school children of the United States, April 1907)
Roosevelt was way before his time in the conservation movement:
"It seems time for the country to take account of its natural resources and to enquire how long they are likely to last."
~ 1908 Conference of Governors
See more in Wikipedia: Roosevelt the Conservationist.
Be the first to comment below.
### Comment Preview
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To enter math, you can can either:
1. Use simple calculator-like input in the following format (surround your math in backticks, or qq on tablet or phone):
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NOTE: You can mix both types of math entry in your comment.
|
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|
https://tex.stackexchange.com/questions/511369/how-can-i-put-a-table-and-a-graph-figure-next-to-each-other-with-separate-capt
|
# How can I put a table and a graph (figure) next to each other with separate captions for each?
I am trying to get this table on the left of my page with the graph which is below on the right. They both have their own captions. I've heard of \minipage and \floatrow but I am not sure of the best way to go about it.
\documentclass[a4paper,10pt]{article}
\usepackage{tabularx} % extra features for tabular environment
\usepackage{amsmath} % improve math presentation
\usepackage{graphicx} % takes care of graphic including machinery
\usepackage[margin=0.75in,a4paper]{geometry} % decreases margins
\usepackage{cite} % takes care of citations
\usepackage[final]{hyperref} % adds hyper links inside the generated pdf file
\usepackage{floatrow}
\hypersetup{
colorlinks=true, % false: boxed links; true: colored links
linkcolor=blue, % color of internal links
citecolor=blue, % color of links to bibliography
filecolor=magenta, % color of file links
urlcolor=blue
}
%++++++++++++++++++++++++++++++++++++++++
\begin{document}
\begin{figure}
\centering
\label{fig:graphmeasurements}
\includegraphics[width=0.7\columnwidth]{graphmeasurements}
\caption{
% spaces are big no-no withing labels
% things like fig: are optional in the label but it helps
% to orient yourself when you have multiple figures,
% equations and tables
Graph of all measurements taken during the experiment.
}
\end{figure}
\begin{table}
\begin{center}
\caption{Current readings for first dip.}
\label{tbl:dip1} % spaces are big no-no withing labels
\begin{tabular}{| c | c |}
\hline
\multicolumn{1}{|c|}{Potential (V)} & \multicolumn{1}{c|}{Current (nA)} \\
\hline
8.25 & 0.5000\\
8.55 & 0.4950\\
8.77 & 0.4900\\
9.02 & 0.4900\\
9.25 & 0.5100\\
9.50 & 0.5200\\
9.75 & 0.5800\\
9.99 & 0.6000\\
\hline
\end{tabular}
\end{center}
\end{table}
\begin{figure}
\centering
\label{fig:dip1}
\includegraphics[width=0.4\columnwidth]{dip1}
\caption{
% spaces are big no-no withing labels
% things like fig: are optional in the label but it helps
% to orient yourself when you have multiple figures,
% equations and tables
Graph of all measurements taken during the experiment.
}
\end{figure}
\begin{table}
\begin{center}
\caption{Current readings for second dip.}
\label{tbl:dip1} % spaces are big no-no withing labels
\begin{tabular}{| c | c |}
\hline
\multicolumn{1}{|c|}{Potential (V)} & \multicolumn{1}{c|}{Current (nA)} \\
\hline
13.00 & 1.1300\\
13.24 & 1.1000\\
13.48 & 1.0000\\
13.75 & 0.8500\\
14.01 & 0.9000\\
14.25 & 1.0500\\
14.51 & 1.0750\\
14.74 & 1.1500\\
\hline
\end{tabular}
\end{center}
\end{table}
\begin{figure}
\centering
\label{fig:dip2}
\includegraphics[width=0.4\columnwidth]{dip2}
\caption{
% spaces are big no-no withing labels
% things like fig: are optional in the label but it helps
% to orient yourself when you have multiple figures,
% equations and tables
Graph of all measurements taken during the experiment.
}
\end{figure}
\begin{table}
\begin{center}
\caption{Current readings for third dip.}
\label{tbl:dip1} % spaces are big no-no withing labels
\begin{tabular}{| c | c |}
\hline
\multicolumn{1}{|c|}{Potential (V)} & \multicolumn{1}{c|}{Current (nA)} \\
\hline
18.50 & 2.1000\\
18.75 & 2.0000\\
19.00 & 1.9000\\
19.26 & 1.8000\\
19.50 & 1.8000\\
19.75 & 1.9000\\
19.99 & 2.0000\\
20.27 & 2.1000\\
20.48 & 2.2500\\
20.75 & 2.5000\\
\hline
\end{tabular}
\end{center}
\end{table}
\begin{figure}
\centering
\label{fig:dip3}
\includegraphics[width=0.4\columnwidth]{dip3}
\caption{
% spaces are big no-no withing labels
% things like fig: are optional in the label but it helps
% to orient yourself when you have multiple figures,
% equations and tables
Graph of all measurements taken during the experiment.
}
\end{figure}
\begin{table}
\begin{center}
\caption{Current readings for fourth dip.}
\label{tbl:dip1} % spaces are big no-no withing labels
\begin{tabular}{| c | c |}
\hline
\multicolumn{1}{|c|}{Potential (V)} & \multicolumn{1}{c|}{Current (nA)} \\
\hline
23.52 & 3.2000\\
23.84 & 2.9500\\
24.07 & 2.7500\\
24.29 & 2.7000\\
24.51 & 2.6500\\
24.76 & 2.7000\\
24.99 & 2.7000\\
25.26 & 3.0000\\
25.50 & 3.1000\\
25.76 & 3.3500\\
\hline
\end{tabular}
\end{center}
\end{table}
\begin{figure}
\centering
\label{fig:dip4}
\includegraphics[width=0.4\columnwidth]{dip4}
\caption{
% spaces are big no-no withing labels
% things like fig: are optional in the label but it helps
% to orient yourself when you have multiple figures,
% equations and tables
Graph of all measurements taken during the experiment.
}
\end{figure}
\end{document}
• Welcome to TeX.SE! Please extend your code snippet to complete small document which we can compile as it is. Please clarify, what you like to have. Question title is contradictory to text in the question. – Zarko Oct 8 at 2:23
• – John Kormylo Oct 8 at 13:31
## 1 Answer
According to your question title I gues that you look for something like this:
(red lines indicate text area borders)
Do I'm right?
Edit: I reduce your document to MWE (Minimal Working Example) in which I consider from its preamble only packages which are relevant to your problem and only one example of a combination table/image. By it is produced above image.
As you can see, table andpPicture are in the same float table for picture caption is used captionof{figure}{<caption text>} which is numbered as figure. Picture is vertically centered by use option valign=c determined in the package adjustbox.
\documentclass[a4paper,10pt]{article}
\usepackage[margin=0.75in]{geometry} % decreases margins
\usepackage{tabularx} % extra features for tabular environment
\usepackage{caption} % new
\usepackage[export]{adjustbox}% it also load "graphicx"
% needed for "valign=c" option
%---------------- show page layout. don't use in a real document!
\usepackage{showframe}
\renewcommand\ShowFrameLinethickness{0.15pt}
\renewcommand*\ShowFrameColor{\color{red}}
%---------------------------------------------------------------%
\begin{document}
\documentclass[a4paper,10pt]{article}
\usepackage[margin=0.75in]{geometry} % decreases margins
\usepackage{tabularx} % extra features for tabular environment
\usepackage{caption} % new
\usepackage[export]{adjustbox}% it also load "graphicx"
%---------------- show page layout. don't use in a real document!
\usepackage{showframe}
\renewcommand\ShowFrameLinethickness{0.15pt}
\renewcommand*\ShowFrameColor{\color{red}}
%---------------------------------------------------------------%
\begin{document}
\begin{table}[ht]
\centering
\begin{tabularx}{\linewidth}{*{2}{>{\centering\arraybackslash}X}}
\begin{tabular}{| c | c |}
\hline
Potential (V) & Current (nA) \\
\hline
8.25 & 0.5000\\
8.55 & 0.4950\\
8.77 & 0.4900\\
9.02 & 0.4900\\
9.25 & 0.5100\\
9.50 & 0.5200\\
9.75 & 0.5800\\
9.99 & 0.6000\\
\hline
\end{tabular}
& \includegraphics[width=\linewidth,valign=c]{example-image-duck} \\
%
\caption{Current readings for first dip.}
\label{tbl:dip1}
& \captionof{figure}{Graph of the first current trough.}
\label{fig:dip1}
\end{tabularx}
\end{table}
\end{document}
• @Schrödinger'scat, more extended comment ... ok, i will ad some code :-) – Zarko Oct 8 at 3:14
• Yes that is exactly what I am after!! How did you do this? – Lachlan Southam Oct 8 at 3:14
• I just add some code, however, for it completion you need first to extend your code sniped to small complete document (we need to see relevant part of your document). – Zarko Oct 8 at 3:20
• Is that code better for you? – Lachlan Southam Oct 8 at 3:50
• @LachlanSoutham, not only for me but for all members of site :-). See edited answer. Now it contain complete MWE. – Zarko Oct 8 at 4:07
|
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|
https://indico.cern.ch/event/292366/
|
Workshop on the determination of centrality in pA collisions at the LHC
February 14, 2014
CERN
Europe/Zurich timezone
The analysis of pPb collisions allows for the study of cold nuclear effects in order to establish a baseline for the interpretation of heavy ion results. Nuclear modification factors in minimum bias pPb collisions with respect to the pp reference have been measured at LHC for a large variety of probes ranging from inclusive hadrons to heavy flavors and jets. To measure the centrality dependence of these observables, the binary scaling factors (Ncoll) between pp and p-Pb have to be determined for each centrality class. Since the pA@LHC workshop organized in June 2012 in front of the first pPb data taking at the LHC, it has become clear that due to the looser correlation between centrality estimators and Ncoll, centrality determination in pPb is a delicate task. Kinematic biases on the centrality dependent observables can not be excluded and need special attention. Two recent conferences, IS2013 and Hard Probes 2013, had discussion sessions on centrality determination in p(d)A collisions as part of their program demonstrating the importance of this topic. These discussions have not yet come to a conclusion. The procedures developped by the LHC experiments are quite different, while first preliminary results on centrality dependent nuclear modification factors have already been presented. The aim of this Workshop is to start a more formal discussion, to be carried on by the studies of this inter-experiments Working Group, with the goal of formulating a common approach to the definition, determination and use of centrality in pA events.
Working Group conveners:
ALICE: Andreas Morsch (chair)
ATLAS: Brian Cole and Dennis Perepelitsa
CMS: Shengquan Tuo
LHCb: Michael Schmelling and Burkhard Schmidt
|
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|
https://economics.stackexchange.com/questions/41661/question-on-general-equilibrium-how-to-write-offer-curves
|
# Question on General Equilibrium: how to write offer curves?
QUESTION:
Consider simple two-person, two-good economy in which agents’ utility functions are given by
$$U_1(x_{11}, x_{21}) = min\{x_{11}, x_{21}\}$$, and $$U_2(x_{12}, x_{22}) = min\{4x_{12}, x_{22}\}$$.
Endowments are w1 =(30,0) and w2 =(0,20).
If neither agents can have negative consumption of either good, what is Walrasian equilibrium?
SOLUTION:
With Leontiev preferences, the indifference curves of both agents are right-angles. For agent 1 their vertices lie on the line $$x_{11} = x_{21}$$, whereas, for agent 2, they lie on the line $$x_{22} = 4x_{12}$$. These lines are respective offer curves of both agents when both prices are strictly positive. For the case when one of the prices is zero, we have following offer curves:
————
$$OC_1(P_1, P_2)=$$
if $$(P_1, P_2) \in$$ {0} $$\times R_+$$ then $$OC_1(P_1, P_2)= \{(x_{11}, w_{21}): x_{11} > w_{21} \}$$,
if $$(P_1, P_2) \in$$ $$R_+ \times$$ {0} then $$OC_1(P_1, P_2)= \{(w_{11}, x_{21}) : x_{21} > w_{11} \}$$,
$$OC_2(P_1, P_2)=$$
if $$(P_1, P_2) \in$$ {0} $$\times R_+$$ then $$OC_2(P_1, P_2)= \{(x_{11}, w_{21}) : x_{11} > (1/4) w_{21} \}$$,
if $$(P_1, P_2) \in$$ $$R_+ \times$$ {0} then $$OC_2(P_1, P_2)= \{(w_{11}, x_{21}) : x_{21} > 4 w_{11} \}$$,
my question is how to write this offer curve? I don't ask to solve this question. I dont understand the point where the offer curves are written. Especially I find to be difficult to write the OC2 for the second consumer. I mean writing OC_2 is especially difficult for me. If you show how to write offer curves, I will really glad. Thank you.
$$EO_2BO_1$$ is 2's offer curve and $$EO_1A$$ is 1's offer curve. Set of competitive equilibrium allocations is given by the intersection of the two offer curves that is the set of allocations on the line segment $$O_1B$$.
|
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|
http://math.stackexchange.com/questions/411066/typo-in-crandall-and-pomerance-pp-121
|
Typo in Crandall and Pomerance pp. 121
In Crandall and Pomerance "Prime Numbers: A Computational Perspective" Second Ed., pp. 121 just before Eq. (3.1) it says: "The number of steps in the sieve of Eratosthenes is proportional to $\sum_{p\leq N} N/p$, where $p$ runs over primes."
However, in the sieve of Eratosthenes one only sieves with primes $p \leq \sqrt{N}$, so I would say the sum should be $\sum_{p\leq \sqrt{N}} N/p$. Now, except for a constant term, the sum turns out to be the same in the two cases, so for the purposes of the complexity estimate in the book, it makes no difference. Nevertheless, I'd say this constitutes a typo.
|
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|
https://tex.stackexchange.com/questions/490577/creating-diagrams-on-latex
|
# Creating diagrams on LaTeX
I am trying to recreate the diagram shown in the picture below using LaTeX.
For reference, I would like to be able to include an image/picture at the top of the diagram (in the picture you'll see my attempt at drawing a car and a tree). Then I want to be able to show a line connecting it to a {word}. And lastly, I'd like to connect that word to other words that are circled around. If possible, I would like to be able to link other diagrams to the words from the original diagram with simply lines, as shown in the picture below.
I would appreciate it if anyone could help me create a diagram like this, thanks!
You can include graphics in TikZ pictures and forest trees. So just replace example-image-a by an image of a car and example-image-b by an image of a tree.
\documentclass[tikz,border=3.14mm]{standalone}
\usepackage{forest}
\usetikzlibrary{shapes.geometric,positioning}
\tikzset{elli/.style={ellipse,draw}}
\begin{document}
\begin{forest}
for tree={l sep+=1em,where level=2{elli}{}}
[{\includegraphics[width=1.5cm]{example-image-a}},alias=car
[{\{word\}},alias=wordL
[word,alias=elli1]
[word,alias=elli2]
[word,alias=elli3]
[word,alias=elli4]
]
]
\node[right=2em of elli4,elli] (elliR) {word};
\node (wordR) at (elliR|-wordL) {{\{word\}}};
\node (tree) at (elliR|-car) {\includegraphics[width=1.5cm]{example-image-b}};
\draw (tree) -- (wordR) foreach \X in {3,4,R}
{(wordR) -- (elli\X)};
\end{forest}
\end{document}
And just for fun: drawing the car and the tree with TikZ.
\documentclass[border=3.14mm]{standalone}
\usepackage{forest}
\usepackage{tikzducks}
\usetikzlibrary{shapes.geometric,positioning}
\usetikzlibrary{decorations.pathmorphing,shapes}
\tikzset{elli/.style={ellipse,draw}}
\newsavebox\Car
\newsavebox\Tree
\begin{document}
\begin{lrbox}{\Car}
\begin{tikzpicture} see https://tex.stackexchange.com/users/101651/carlatex
\fill (-4.7,-0.8) arc(180:0:1.7 and 1.1) --cycle;
\fill (1.3,-0.8) arc(180:0:1.7 and 1.1) --cycle;
% right front wheel
\fill (-3.3,-0.1) circle (1.5cm);
% left front wheel
\shade[inner color=black,outer color=black!70] (-3,-0.7) circle (1.5cm);
\fill[black!20!white] (-3,-0.7) circle (0.8cm);
\foreach \X in {0,30,...,330} {\fill[black] (-3,-0.7) +({\X-5}:0.6) circle (1pt);}
% back wheel
\fill (2.7,-0.1) circle (1.5cm);
% back wheel left
\shade[inner color=black,outer color=black!70] (3,-0.7) circle (1.5cm);
\fill[black!20!white] (3,-0.7) circle (0.8cm);
\foreach \X in {0,30,...,330} {\fill[black] (3,-0.7) +({\X+11}:0.6) circle (1pt);}
% seat
\fill[top color=red,bottom color=red!20!black] (2.9,2.2) arc(0:360:3 and 0.3);
% driver
\begin{scope}[xshift=-2.3cm,yshift=1cm,scale=1.5]
\duck[squareglasses=blue!50!black,longhair=black];
\end{scope}
% right light
\shade[bottom color=red,top color=red!30] (-4.35,1) arc(-90:90:0.3 and 0.4) |-
cycle;
\shade[bottom color=yellow!30,top color=white] (-4.45,1) arc(-90:270:0.1 and
0.4);
% body
\shade[bottom color=red,top color=red!30] (-4.7,-0.8) arc(180:0:1.7) -- (-1.3,-0.8) -- (1.3,-0.8) arc(180:0:1.7)
-- (4.9,-0.8) arc(0:90:2 and 3)
arc(0:-180:3 and 0.3)
-- (-2.9,2.2) arc(90:180:2 and 3) -- cycle;
\shade[bottom color=red,top color=red!30] (-4.7,-0.8) arc(180:0:1.7 and 1.1) arc(0:180:1.7 and 1.8);
\shade[bottom color=red,top color=red!30] (1.3,-0.8) arc(180:0:1.7 and 1.1) arc(0:180:1.7 and 1.8);
% door
\draw[very thin] (1.1,1.9) to[out=-90,in=80] (1,-0.6) -- (-1,-0.6)
to[out=110,in=-90] (-1.1,1.9);
\node[blue,font=\sffamily\Huge] at (0,0.8) {\LaTeX};
% left light
\shade[bottom color=red,top color=red!30] (-4.4,0.8) arc(-90:90:0.3 and 0.4) |-
cycle;
\shade[bottom color=yellow!30,top color=white] (-4.4,0.8) arc(-90:270:0.1 and
0.4);
% windshield
(-3.2,2.2) arc(180:130:3 and 0.3) arc(180:150:2.5 and 4)
arc(130:180:3 and 0.3) -- cycle;
(-3.2,2.2) arc(180:230:3 and 0.3) arc(180:150:2.5 and 4)
arc(230:180:3 and 0.3) -- cycle;
\end{tikzpicture}
\end{lrbox}%
\begin{lrbox}{\Tree}
\begin{tikzpicture}[treetop/.style = {% from https://tex.stackexchange.com/a/101113/121799
decoration={random steps, segment length=0.4mm},
decorate
},
trunk/.style = {
decoration={random steps, segment length=2mm, amplitude=0.2mm},
decorate
}]
\foreach \w/\f in {0.3/30,0.2/50,0.1/70} {
\fill [brown!\f!black, trunk] (0,0) ++(-\w/2,0) rectangle +(\w,-3);
}
\foreach \n/\f in {1.4/40,1.2/50,1/60,0.8/70,0.6/80,0.4/90} {
\fill [green!\f!black, treetop] ellipse (\n/1.5 and \n);
}
\end{tikzpicture}
\end{lrbox}%
\begin{forest}
for tree={l sep+=1em,where level=2{elli}{}}
[{\usebox\Car},scale=0.2,alias=car
[{\{word\}},alias=wordL
[word,alias=elli1]
[word,alias=elli2]
[word,alias=elli3]
[word,alias=elli4]
]
]
\node[right=2em of elli4,elli] (elliR) {word};
\node (wordR) at (elliR|-wordL) {{\{word\}}};
\node[xscale=0.4,yscale=0.25] (tree) at (elliR|-car) {\usebox\Tree};
\draw (tree) -- (wordR) foreach \X in {3,4,R}
{(wordR) -- (elli\X)};
\end{forest}
\end{document}
No worries, this is an electric car, so the tree should be fine, and it is safe to use forest.
• The car is really pretty! :):):) – CarLaTeX May 13 at 7:29
• This is exactly what I was looking for, thanks! – Ernesto May 13 at 8:46
|
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|
https://www.atmos-chem-phys.net/18/3469/2018/acp-18-3469-2018.html
|
Journal cover Journal topic
Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
Journal topic
• IF 5.668
• IF 5-year
6.201
• CiteScore
6.13
• SNIP 1.633
• IPP 5.91
• SJR 2.938
• Scimago H
index 174
• h5-index 87
# Abstracted/indexed
Abstracted/indexed
Atmos. Chem. Phys., 18, 3469–3483, 2018
https://doi.org/10.5194/acp-18-3469-2018
Atmos. Chem. Phys., 18, 3469–3483, 2018
https://doi.org/10.5194/acp-18-3469-2018
Research article 08 Mar 2018
Research article | 08 Mar 2018
# Implications of potential future grand solar minimum for ozone layer and climate
Pavle Arsenovic1, Eugene Rozanov1,2, Julien Anet3, Andrea Stenke1, Werner Schmutz2, and Thomas Peter1 Pavle Arsenovic et al.
• 1Institute for Atmospheric and Climate Science, ETH, Zürich, Switzerland
• 2Physikalisch-Meteorologisches Observatorium Davos/World Radiation Center, Davos, Switzerland
• 3Zürich University of Applied Sciences, Winterthur, Switzerland
Abstract. Continued anthropogenic greenhouse gas (GHG) emissions are expected to cause further global warming throughout the 21st century. Understanding the role of natural forcings and their influence on global warming is thus of great interest. Here we investigate the impact of a recently proposed 21st century grand solar minimum on atmospheric chemistry and climate using the SOCOL3-MPIOM chemistry–climate model with an interactive ocean element. We examine five model simulations for the period 2000–2199, following the greenhouse gas concentration scenario RCP4.5 and a range of different solar forcings. The reference simulation is forced by perpetual repetition of solar cycle 23 until the year 2199. This reference is compared with grand solar minimum simulations, assuming a strong decline in solar activity of 3.5 and 6.5 W m−2, respectively, that last either until 2199 or recover in the 22nd century. Decreased solar activity by 6.5 W m−2 is found to yield up to a doubling of the GHG-induced stratospheric and mesospheric cooling. Under the grand solar minimum scenario, tropospheric temperatures are also projected to decrease compared to the reference. On the global scale a reduced solar forcing compensates for at most 15 % of the expected greenhouse warming at the end of the 21st and around 25 % at the end of the 22nd century. The regional effects are predicted to be significant, in particular in northern high-latitude winter. In the stratosphere, the reduction of around 15 % of incoming ultraviolet radiation leads to a decrease in ozone production by up to 8 %, which overcompensates for the anticipated ozone increase due to reduced stratospheric temperatures and an acceleration of the Brewer–Dobson circulation. This, in turn, leads to a delay in total ozone column recovery from anthropogenic halogen-induced depletion, with a global ozone recovery to the pre-ozone hole values happening only upon completion of the grand solar minimum.
|
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|
https://kullabs.com/classes/subjects/units/lessons/notes/note-detail/2328
|
Simple Interest | kullabs.com
## Note on Simple Interest
• Note
• Things to remember
• Exercise
• Quiz
Interest is a profit of an investment. There are many ways to calculate the interest. The quick method of calculating the interest charge on a loan is called simple interest. The sum of money invested is called the principal which is denoted by 'P'. The money earned by the principal is called the interest (I) and is earned at a rate known as the interest rate (R).
Example
Let us consider an investment on simple interest terms of Rs 200 invested for 2 years at 15% per annum ( p.a). Each year the investor will receive interest equal to 15% of the principal. Interest received at the end of the first year = 15% of Rs 200 = $$\frac{15}{100}$$x 200 = Rs.30
Similarly, interest received at the end of the second year = Rs 30.
The total interest ( I ), received = Rs 30 + Rs 30 = Rs 60
The investor also gets the principal of Rs 200 back at the end of the second year.
In the above example, interest ( I ) = 15 % of Rs 200 x 2
Interest ( I ) = 15 % of Rs 200 x 2
= $$\frac{15}{100}$$x 200 x 2
Replace, $$\frac{15}{100}$$ by R, Rs 200 by P and 2 by T
I = R x P xT
Thus, I = PTR
Hence, if Rs P is invested at the rate of R% per annum for T years, then the interest, Rs I, earned is given by I = PTR
Also, P = $$\frac{I}{TR}$$, T = $$\frac{I}{PR}$$ and R = $$\frac{I}{PT}$$
The sum of principal and interest is called amount ( A )
Thus, A = P + I
A = P +PTR
A = P (1 + TR )
So, P = $$\frac{A}{1+TR}$$
Examples
1. Sabina borrowed Rs 2,000 for 2 years at 10% interest rate. How much interest will she pay at simple interest?
Solution:
Principal (P) = Rs.2,000
Rate (R) = 10% = $$\frac{10}{100}$$ p.a
Time (T) = 2 years
We have,
Simple interest (I) = P × T × R
= Rs.2000 × 2 × $$\frac{10}{100}$$
= Rs.400
$$\therefore$$ Sabina will pay Rs.400 as interest.
2. Tripti borrowed Rs 10,000 at a rate of 15 % p.a. for 6 months. How much simple interest did she pay?
Principal (P) =Rs 10,000
Rate (R) = 15 % p.a. = $$\frac{15}{100}$$ p.a
Time (T) = 6 months =$$\frac{6}{12}$$years
W e have,
Simple Interest (I) = P × T × R
= Rs.10,000 ×$$\frac{6}{12}$$ ×$$\frac{15}{100}$$
= Rs.750
$$\therefore$$ Tripti paid Rs.750 as interest.
• Simple interest is a quick method of calculating the interest charge on a loan.
• Simple interest is determined by multiplying the interest rate by the principal by the number of periods.
• The sum of money invested is called the principal which is denoted by ' P '.
• The money earned by the principal is called the interest (I) and is earned at a rate known as the interest rate (R).
.
### Very Short Questions
Solution,
Given information,
Principal amount (P)= Rs 76,00
Time (T) = 3 years
Interest (I) = Rs 1,254
Rate (R) =?
Formula, R = $$\frac{I×100}{PT}$$
(R) = $$\frac{1254×100}{7600×3}$$
= 5.5%
Solution:
Given information,
Time (T) = 7 years
Interest (I) =Rs 4200
Rate (R) = 6%
Principal (P) = ?
Formula, P= $$\frac{I×100}{TR}$$
∴ (P) = $$\frac{4200×100}{7×6}$$
= $$\frac{420000}{42}$$
= Rs 10,000
∴ She has to Rs 10,000 now.
Solution:
Given inforamtion,
Principal (P) = Rs 3,000
Rate (R) = 5% = $$\frac{5}{100}$$ p.a
We have,
Simple Interest (I) =P× T× R
= Rs 3,000× 4× $$\frac{5}{100}$$
=Rs 600
Hence , She will pay Rs 600 at simple interest.
Solution:
Given information,
Principal(P) = Rs 12,000
Rate (R) = 18% = $$\frac{18}{100}$$ p.a
Time (T) = 9 Months = $$\frac{9}{12}$$ years
We have,
Simple Interest (I) = P× T× R
= Rs 12,000× $$\frac{18}{100}$$× $$\frac{9}{12}$$
= Rs 1,620
So, Suzu paid Rs 1,620 in interest.
Solution:
Given information,
Principal (P) = Rs 3000
Since, we are doubling Rs 3000, we made an additional Rs 3000 on this investment, which is the interest.
So, Interest (I) = Rs 3000
Rate (R)= 20% = $$\frac{20}{100}$$ p.a
We have,
Time (T) = $$\frac{3000}{3000 \times \frac{20}{100}}$$
= $$\frac{100}{20}$$
Hence, It takes 5 years to double the amount.
Solution:
Given information,
Time (T) = 2 Years
Simple Interest (I) = Rs 100
Rate (R) = 8% =$$\frac{8}{100}$$
We have,
P = $$\frac{I}{T×R}$$
= $$\frac{100}{2\times\frac{8}{100}}$$
= $$\frac{10000}{16}$$
= 625
Hence, principal is Rs 625
Solution:
Given information,
Principal (P) =Rs 100
Interest (I) =Rs 200
Time (T) = 3 years
We have,
R = $$\frac{I}{P×T}$$
= $$\frac{200}{100×3}$$
= $$\frac{200}{300}$$
= 66%
Hence, The interest rate is 66%
Solution:
Given Information,
Rate (R) =2%
Time (T) = 3 years
Interest (I)= Rs 120
Principal (P) = ?
We know ,
P =$$\frac{I×100}{T×R}$$
= Rs $$\frac{120×100}{T×R}$$
= Rs 2000
∴ Rs 2000 amount should be invested.
Solution:
Given information,
Principal (P) = Rs 1500
Time (T) = 4 years
Interest (I) = Rs 200
Rate (R) =?
We know,
Interest Rate (R) = $$\frac{I×100}{P×T}$$
= $$\frac{I×100}{1500×4}$$
=$$\frac{50}{15}$$
=$$\frac{10}{3}$$%
= 3 $$\frac{1}{3}$$ %
∴ Interest Rate (R) = 3 $$\frac{1}{3}$$ %
Solution:
Given information,
Principal(P)= Rs 7,200
Time (T) = 5 Years
Interest(I) = Rs 1080
Interest Rate(R) = ?
We know,
R = $$\frac{I\times100}{PT}$$
= $$\frac{1080\times100}{7100\times5}$$
Hence, Interest Rate(R) = 3%
0%
4Years
7 Years
9 Years
5 Years
9%
7%
8%
11%
Rs 70
Rs 50
Rs 60
Rs40
Rs 18.38
Rs 25
Rs 20
Rs 27
Rs 15,000
Rs 16,000
Rs 12,000
Rs 10,000
Rs 55
Rs 45
Rs 60
Rs 50
5%
6%
7%
10%
Rs 1500
Rs 1170
Rs 1200
Rs 1000
Rs 200
Rs 325
Rs 350
Rs 205
Rs 40,000
Rs 45,000
Rs 30,000
Rs 35,000
Rs 55,000
Rs 50,000
Rs 65,000
Rs 60,500
Rs 1250
Rs 1500
Rs 1000
Rs 1200
Rs 55
Rs 45
Rs 50
Rs 40
8 Years
5 Years
7 Years
11 Years
Rs 65,000
Rs 55,500
Rs 60,000
Rs 50,000
• ## You scored /15
Forum Time Replies Report
Plz do this?
##### Drishya
Find the rate of interest if Rs 4000 amounts to Rs 6000 in 2 years
|
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|
http://math.stackexchange.com/users/54929/lee-dae-seok
|
# Lee Dae Seok
less info
reputation
4
bio website location age member for 1 year, 3 months seen Feb 20 '13 at 6:28 profile views 13
3 Consider a function $f(x) = x^4+x^3+x^2+x+1$, where x is an integer, $x\gt 1$. What will be the remainder when $f(x^5)$ is divided by $f(x)$? 3 Prove $n^\frac{1+2}{\sqrt{\log n}} = O(n \log n)$ 2 Cyclic group of order $4$ and Klein four-group are not isomorphic.
# 151 Reputation
+25 $G$ is a finite group and $G_1$,$G_2$ are subgroup that $G_1 \cap G_2=\{1\}$, then $|G_1|.|G_2| \big| |G|$? +45 Prove $n^\frac{1+2}{\sqrt{\log n}} = O(n \log n)$ +30 Consider a function $f(x) = x^4+x^3+x^2+x+1$, where x is an integer, $x\gt 1$. What will be the remainder when $f(x^5)$ is divided by $f(x)$? +5 Is there any manifold that is not a subspace of a finite dimensional euclidean space?
# 3 Questions
5 $G$ is a finite group and $G_1$,$G_2$ are subgroup that $G_1 \cap G_2=\{1\}$, then $|G_1|.|G_2| \big| |G|$? 3 Is there any manifold that is not a subspace of a finite dimensional euclidean space? 3 Is this a transcendental number?
# 8 Tags
3 algebra-precalculus 0 transcendental-numbers 3 calculus 0 finite-groups 3 asymptotics 0 group-theory 2 abstract-algebra 0 manifolds
# 1 Account
Mathematics 151 rep 4
|
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|
https://photo.stackexchange.com/questions/16401/how-to-delete-jpg-files-but-only-if-the-matching-raw-file-exists
|
# How to delete JPG files, but only if the matching RAW file exists?
My early (Canon G2) photos are all JPG, but when I got my Nikon D90 I initially shot in JPG, then switched to RAW+JPG, and now I would like to switch to RAW only.
I have literally thousands of photos on my HDD. The photos are in sub-directories (by date) under a single directory called Import.
I am about to import all these photos into Lightroom 3.0, however, I would like to delete all the JPG files, but only where there is already a corresponding RAW file (ie. I no longer want to keep JPG and RAW versions of the same file).
If I can do this easily within Lightroom (after importing everything, including the duplicate JPG files) that would be great. It would also be OK if there were an easy way to do this before importing the files (but hopefully this wouldn't involve having to visit every directory looking for filenames with both JPG and NEF extensions).
Does anybody know of a way to do this (in Lightroom, or with some tool/script in Windows)?
• Do all of your jpg files and RAW files have at a minimum the same string(other characters could be added to either)? Eg IMG_1234_portrait_picture.jpg & IMG_1234.CR2. – dpollitt Oct 15 '11 at 3:28
• I think that all of my JPG/NEF pairs have exactly the same filename (except for the extension). – seanmc Oct 15 '11 at 3:29
• I will vote to move this to Stack Overflow, where you should get an answer within minutes =) – anon Oct 15 '11 at 15:17
• @anon: How exactly does this belong on StackOverflow? This is most definitely an on-topic question here, as it deals with image management and photo editing tools. Outside of a tangential reference to script...this has nothing to do with programming. – jrista Oct 15 '11 at 17:04
• I'm voting to close this question as off-topic because this isn't really about photography, it is about managing files that just happen to be photographs. The question and answer would be the same if the two types of files in question were any other types of files that could be translated from one form to another, such as .doc and .pdf files, etc. – xiota Aug 31 '18 at 4:51
On Windows, go to the folder, and run this in a command prompt:
for /f "delims==" %r in ('dir /b *.nef') do del "%~dpr%~nr.jpg" 2> nul
Basically, it goes through the current folder, runs through the NEF files, and deletes the JPG if present. It ignores any errors if the JPG is not there.
If you want subfolders, include /s in the dir command.
• Perfect, thanks! Of course before I ran it the first time, I changed "del" to "echo". Then I ran "help for" to understand what it was doing. It's obviously been a long time since I've looked at command prompt scripting, because I had no idea that the "for" command had so many options. – seanmc Oct 16 '11 at 20:14
• No problem! As I was testing, I also used "echo" =) To see more output, remove the "2> nul." I'd been meaning to do something like this for my own NEF/JPG files, and this was the perfect opportunity. – anon Oct 17 '11 at 2:14
• Fantastic. Cleaning up and old raw+jpeg folder structure made easy with one neat cmd :) – HenningK Apr 5 '20 at 11:20
Here is a modified version of Tomy's Python script. Differences:
• multiple raw extensions allowed
• remove jpg only if the pairs are in the same folder (avoid accidental removal of a jpg named like a raw file in an other folder)
• case insensitive
#!/usr/bin/env python
# Script: remove_jpg_if_raw_exists.py
#
# Description: This script looks in all sub directories for
# pairs of JPG and RAW files.
# For each pair found the JPG is moved to a
# Otherwise JPG is kept.
#
# Author: Thomas Dahlmann
# Modified by: Renaud Boitouzet
import os
import shutil
# define your file extensions here, case is ignored.
# multiple raw extensions allowed, single jpg extension only
raw_extensions = (".Dng", ".cR2", ".nef", ".crw")
jpg_extension = ".jPg"
# define waste basket directory here. Include trainling slash or backslash.
# Windows : waste_dir = "C:\path\to\waste\"
waste_dir = "/Users/marvin/Pictures/waste/"
##### do not modify below ##########
# find files
def locate(folder, extensions):
'''Locate files in directory with given extensions'''
for filename in os.listdir(folder):
if filename.endswith(extensions):
yield os.path.join(folder, filename)
if not os.path.exists(waste_dir):
os.makedirs(waste_dir)
# Make search case insensitive
raw_ext = tuple(map(str.lower,raw_extensions)) + tuple(map(str.upper,raw_extensions))
jpg_ext = (jpg_extension.lower(), jpg_extension.upper())
root=os.curdir
#find subdirectories
for path, dirs, files in os.walk(os.path.abspath(root)):
print path
raw_hash = {}
for raw in locate(path, raw_ext):
base_name = os.path.basename(raw)
base_name = os.path.splitext(base_name)[0]
raw_hash[base_name] = True
# find pairs and move jpgs of pairs to waste basket
for jpg in locate(path, jpg_ext):
base_name = os.path.basename(jpg)
base_name = os.path.splitext(base_name)[0]
if base_name in raw_hash:
jpg_base_name_with_ext = base_name + jpg_extension
new_jpg = waste_dir + jpg_base_name_with_ext
print "%s: %s = %s => %s" % (path, base_name, jpg, waste_dir)
if os.path.exists(new_jpg):
os.remove(jpg)
else:
shutil.move(jpg, new_jpg)
• great script. I will use it because it has many good failovers. However you should add this line #!/usr/bin/env python to the beginning. Otherwise I had strange ImageMagick errors (seems my mac open .py files with ImageMagick) – therealmarv Apr 2 '15 at 5:48
• Just FYI: it also seems it does not work when the files are really named .jPg. It also does not work when files are on external disk and waste directory e.g. in /home dir. – therealmarv Apr 2 '15 at 5:55
• some corrections: gist.github.com/therealmarv/ec603bd4a91d51092a18 – therealmarv Apr 2 '15 at 6:02
• @therealmarv: actually what's happening with ImageMagick is that the script is being opened in the shell, not ImageMagick, but "import" is the name of an ImageMagick tool. – Max Sep 2 '16 at 8:50
Here's a Python script that moves JPG files when no corresponding RAW file exists. Useful on Mac OS X!
import os
import shutil
raw_ext = '.CR2'
jpg_ext = '.JPG'
destination = '/Users/JohnSmith/Desktop/jpgs/'
for filename in os.listdir('.'):
(shortname, extension) = os.path.splitext(filename)
if extension == raw_ext:
if os.path.isfile(shortname + jpg_ext):
print 'Moving ' + shortname + jpg_ext + '...'
shutil.move(shortname + jpg_ext, destination)
• Create an empty Library
• From the Lightroom main menu, choose Edit > Preferences (Windows) or Lightroom > Preferences (Mac OS).
• In the General preferences unselect "Treat JPEG Files Next To Raw Files As Separate Photos"
• This should be the default.
• Import all of your files (you can select search subfolders), telling it to move to a new location
• The JPG files that have RAW files will be left in the original location for you to remove
As I understand it, the thumbnail in lightroom might say RAW+JPG, but the JPG isn't actually stored or accessible in any way.
You can also write a pretty simple batch script with any programming language.
I like the bash script for OS X (by T.Toivonen), but I have noticed there are a few issues.
• It did not like my directory names, which contain spaces. That required a bit different handling of the find command.
• The original script only works for lowercase extensions. I have slightly improved that part of the script to account for extensions that are in uppercase as well. Note, that it only accepts DNG+JPG or dng+jpg pairs, and it will ignore any combinations such as DNG+jpg or DnG+JpG.
• The original solution proposed only one wastedir location, whereas my fix allows a subdirectory to be created on each directory branch as it travels though. You define a name of the directory before the loop.
• I like to see what's going on, especially when mv or rm commands are used ;)
For the sake of the space I am showing only the last part of the script, from setting a basedir, wastedir and the loop.
[...]
#Now set it as a basedir
BASEDIR=$arg WASTEDIR=duplicates find "$BASEDIR" -iname '*.dng' -print0 | while read -d $'\0' filename do filepath="${filename%/*}"
basename="${filename##*/}" prefix="${basename%%.*}"
suffix=${filename##*.} if [[ "$suffix" =~ [A-Z] ]]; then rsuffix="JPG"; else rsuffix="jpg"; fi
if [ -e "$filepath/$prefix.$rsuffix" ]; then let counter="$counter+1"
if (( $isSetE==1 )); then echo "FOUND:$filepath/$prefix.$rsuffix"
fi
if (( $isSetM==1 )); then echo "Moving$filepath/$prefix.$rsuffix to $filepath/$WASTEDIR"
if [ ! -d "$filepath/$WASTEDIR" ]; then mkdir "$filepath/$WASTEDIR"; fi
mv "$filepath/$prefix.$rsuffix" "$filepath/$WASTEDIR" fi if (($isSetD==1 )); then
echo "Removing duplicate $filepath/$prefix.$rsuffix" rm "$filepath/$prefix.$rsuffix"
fi
fi
done
• The question was tagged "windows" so you could do with saying how this could be made to work in a typical Windows system. I run Cygwin, for example (and I plan to have a better look at this answer when I'm on desktop, to change the behavior a bit) – Chris H Apr 10 '17 at 7:10
Here is a solution for bash (Linux or Mac OS X). On Windows, you can install Cygwin to get a copy of bash.
keep=$(ls | grep -v ps | grep -A1 JPG | grep NEF) for i in$keep ; do
mv $i$i.keep
done
ls | egrep -v '(JPG|keep)' | xargs rm -f
change=$(ls | grep keep | sed 's/.keep//g') for i in$change ; do
mv $i.keep$i
done
Here is another bash version using find (Linux). As with Ben Pingilley's answer, you can install Cygwin to get bash on Windows.
#!/bin/bash
read -p "please enter file suffix for raw format (e.g ORF, NEF, CR2): " suffix
find . -type f -iname "*.${suffix}" | \ while read line do lowercase=$(echo "$line" | sed "s/${suffix}/jpg/gi")
uppercase=$(echo "$line" | sed "s/${suffix}/JPG/gi") if [ -f "${lowercase}" ]
then
rm -v "${lowercase}" elif [ -f "${uppercase}" ]
then
rm -v "${uppercase}" else echo "${line}: no jpg present"
fi
done
Here's my take on this issue. A lot of good ideas came from earlier scripts mentioned here.
This is a bash script for OS X. It looks for files that exist with same base filename and dng+jpg extensions. If a jpg is found with an exactly same name as dng, then that filename is displayed (-e), file is moved (-m) or deleted (-d).
It will go through subfolders, so you could use it for your entire catalog or just parts of it.
For other raw file extensions just substitute *.dng in the script with your preferred extension.
Warning: You could have two different images with same name, but different extension. Those are inevitable casualties of this script.
Here's how to use the script:
Usage: dng-jpg.sh [-m <path>] [-d <path>] [-e <path>] [-h]
-m: for move (moves files to <path>/duplicates)
-d: for delete (deletes duplicate files)
-e: for echo (lists duplicate files)
-h: for help
Basic usage would work like this:
$./dng-jpg.sh -e /Volumes/photo/DNG/2015 That would echo all filenames of jpg files that match the criteria of having both dng and jpg file with same name. Result would look like something like this: Echo selected with path: /Volumes/photo/DNG/2015 /Volumes/photo/DNG/2015/03/18/2015-03-18_02-11-17.jpg /Volumes/photo/DNG/2015/06/01/2015-06-01_05-10-50.jpg /Volumes/photo/DNG/2015/06/01/2015-06-01_05-10-56.jpg /Volumes/photo/DNG/2015/06/01/2015-06-01_05-11-39.jpg /Volumes/photo/DNG/2015/06/01/2015-06-01_05-11-54.jpg /Volumes/photo/DNG/2015/06/01/2015-06-01_05-12-26.jpg /Volumes/photo/DNG/2015/06/01/2015-06-01_05-12-43.jpg /Volumes/photo/DNG/2015/06/01/2015-06-01_05-13-21.jpg /Volumes/photo/DNG/2015/06/01/2015-06-01_05-13-56.jpg 9 files found. Now if I want to delete the files I would just switch the -e to -d: $ ./dng-jpg.sh -d /Volumes/photo/DNG/2015
Or if I'd like to move the files to /duplicates I'd execute it with -m.
$./dng-jpg.sh -m /Volumes/photo/DNG/2015 Now the duplicate jpg files would be in /Volumes/photo/DNG/2015/duplicates Here's the script: dng-jpg.sh #!/bin/bash # Init variables isSetM=0 isSetD=0 isSetE=0 isSetCount=0 counter=0 #Display usage info usage() { cat <<EOF Usage: dng-jpg.sh [-m <path>] [-d <path>] [-e <path>] [-h] -m: for move (moves files to <path>/duplicates) -d: for delete (deletes duplicate files) -e: for echo (lists duplicate files) -h: for help EOF exit 1 } #Check for parameters while getopts ":m:d:e:h" opt; do case${opt} in
m)
isSetM=1
let isSetCount="$isSetCount+1" arg=${OPTARG}
echo "Move selected with path:" $arg ;; d) isSetD=1 let isSetCount="$isSetCount+1"
arg=${OPTARG} echo "Delete selected with path:"$arg
;;
e)
isSetE=1
let isSetCount="$isSetCount+1" arg=${OPTARG}
echo "Echo selected with path:" $arg ;; h) let isSetCount="$isSetCount+1"
usage
;;
\?)
echo "Invalid option: -$OPTARG" >&2 usage ;; :) echo "Option -$OPTARG requires a directory argument." >&2
usage
;;
*)
usage
;;
esac
done
# If no parameters, show usage help and exit
if test -z "$1"; then usage fi # If multiple parameters (not counting -a), show usage help and exit if (($isSetCount > 1)); then
usage
fi
#Verify directory
if [ ! -d "$arg" ]; then echo "$arg is not a path to a directory." >&2
usage
fi
#Now set it as a basedir
BASEDIR=$arg WASTEDIR="$BASEDIR/duplicates/"
if (( $isSetM==1 )); then mkdir$WASTEDIR
fi
for filename in $(find$BASEDIR -name '*.dng' -exec echo {} \; | sort); do
prefix=${filename%.dng} if [ -e "$prefix.jpg" ]; then
let counter="$counter+1" if (($isSetE==1 )); then
echo "$prefix.jpg" fi if (($isSetM==1 )); then
mv $prefix.jpg$WASTEDIR
fi
if (( $isSetD==1 )); then rm$prefix.jpg
fi
fi
done
echo "$counter files found." Here’s a bash script for Mac OS X. It may work on Linux with some changes. #!/bin/bash read -p "Delete JPEGs when DNG exists? Ctrl-C to cancel. [Enter] to continue: " for FILE in *.dng; do JPG_FILE=$(echo "$FILE" | sed "s/dng/jpg/g") rmtrash "${JPG_FILE}" 1>/dev/null
done
rmtrash is a utility that moves files to the Trash, instead of deleting them outright. You can get it from MacPorts thus:
sudo port install rmtrash
If you’d like to avoid that, just replace rmtrash in the script with rm, which will immediately delete the JPG files.
I wrote the following Python script. Compared with ttaveira's script, it does some extra work.
• Looks in sub-directories.
• Creates destination waste directory.
• Removes files that already exist in waste directory to avoid move errors.
# Script: remove_jpg_if_raw_exists.py
#
# Description: This script looks in all sub directories for
# pairs of JPG and RAW files.
# For each pair found the JPG is moved to a
# Otherwise JPG is kept.
#
# Author: Thomas Dahlmann
import os, fnmatch
# define your file extensions here, case is ignored
raw_extension = "nef"
jpg_extension = "jpg"
# define waste basket directory here
##### do not modify below ##########
# recursive find files
def locate(pattern, root=os.curdir):
'''Locate all files matching supplied filename pattern
in and below root directory.'''
for path, dirs, files in os.walk(os.path.abspath(root)):
for filename in fnmatch.filter(files, pattern):
yield os.path.join(path, filename)
# get base names from raw's
raw_hash = {}
for raw in locate("*." + raw_extension):
base_name = os.path.basename(raw)
base_name = os.path.splitext(base_name)[0]
raw_hash[base_name] = True
if not os.path.exists(waste_dir):
os.makedirs(waste_dir)
# find pairs and move jpgs of pairs to waste basket
for jpg in locate("*." + jpg_extension):
base_name = os.path.basename(jpg)
base_name = os.path.splitext(base_name)[0]
if base_name in raw_hash:
jpg_base_name_with_ext = base_name + "." + jpg_extension
new_jpg = waste_dir + "\\" + jpg_base_name_with_ext
print "%s => %s" % (jpg, waste_dir)
if os.path.exists(new_jpg):
os.remove(jpg)
else:
os.rename(jpg, new_jpg)
• Hi and welcome to Photo.SE. How is your answer different from ttaveira's answer? – Saaru Lindestøkke Apr 8 '14 at 14:56
• The script does some extra work: also looks in all sub-directories, creates destination waste directory for jpg's if it does no exist and it does remove a jpg instead of moving if it if it already exists in waste directory (avoids moving errors) – Tomy Apr 30 '14 at 15:58
Working on Mac OS X, I was missing a sanity check for "same content" in the previous answers. I had duplicate names for different pictures because I had forgotten to enable the image counter in my camera. Here's my version, which checks the EXIF information for same capture time:
You need to run
sudo port install rmtrash exiv2
before you can use the following command. It was written to compare JPG with NEF files from my Nikon D90. Adjust the file extensions according to your needs.
find . -name \*.NEF |sed s/\.NEF/.JPG/g | xargs find 2>/dev/null | \
xargs perl -e 'foreach(@ARGV) {my $jpg=$_;my $nef=s/\.JPG/.NEF/r; my$tjpg = exiv2 -g Exif.Photo.DateTimeOriginal -pt $jpg; my$nef=s/\.JPG/.NEF/r; my $tnef = exiv2 -g Exif.Photo.DateTimeOriginal -pt$nef; if($tjpg eq$tnef) {print "\$jpg\n"}}' | \
xargs rmtrash
without the sanity check, the whole thing would become a very short one liner:
find . -name \*.NEF |sed s/\.NEF/.JPG/g | xargs find 2>/dev/null | xargs rmtrash
|
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|
https://sc2math.wordpress.com/2010/10/30/mining-speed-measurement-methods/
|
## Mining Speed Measurement Methods
Today I’m going to discuss how I measured the mining speed in my previous post, because I didn’t use a stopwatch like some others have. No, no, these results are far to important to be tainted by human hand eye coordination errors. What I did, as usual, was to utilize the map editor. The map editor will allow functions to be triggered when orders are given, such as those given to SCV’s. Here’s a picture of the map I used:
In this map each of the SCV’s is adjacent to a point, which allows me to assign each of the SCV’s to its own varible, which ultimately makes it possible for me to track which SCV’s are doing what. The mineral node in the green the circle is the node that I ordered them to mine from. So after I order the SCV’s to mine, the game will naturally order the SCV’s back and forth from the command center and the mineral patch. The map I created has a function that gets triggered every time an SCV uses its harvest ability. When triggered, the function records which SCV caused the trigger, what “stage” the SCV is in, and the current mineral count and game time.
The actual event I used in my trigger was “Unit Uses Ability”, and the “Harvest” ability has many stages such as “Approach Resource”, “Wait at Resource”, and “Harvest”. In my previous experiment, I dumped data to a list box in the UI. This experiment lead to a lot more data, and so I wanted a way to write the data to a file. It turns out that it is entirely possibly to do that using “Bank” functionality of the map editor. Data stored in the bank is written to file after a custom game is saved and closed. I used the bank to store the data from each event as as comma separated value (csv) row, which was stored as big string in the bank. After the games is saved I opened the bank file, which on my computer was in “C:\Users\Sean\Documents\StarCraft II\Banks”. The bank files are stored in XML format, so I just had to get rid of all that formatting, and afterwards I was able to load the data in Excel. The rest just consisted of finding a fair way to choose a beginning and starting event in that data, calculating the differences in minerals and time, and dividing the two:
$\text{Mining Rate } = \frac{\text{Number of Minerals Mined}}{\text{Duration of Mining}}$
I still have the map if anyone wants to inspect/and/or use it. Email [email protected], which I occasionally check.
Also, it was pointed out in a comment, that someone else has done some more testing on the mining speed issue, and I highly recommend checking this post out from the Team Liquid forums if you are interested in the topic: http://www.teamliquid.net/forum/viewmessage.php?topic_id=140055
This entry was posted in Experiment Methods and tagged , , , , . Bookmark the permalink.
### 1 Response to Mining Speed Measurement Methods
1. pat says:
ah, now i understand y u were using the scvs to measure the faster game time
|
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|
https://lavelle.chem.ucla.edu/forum/viewtopic.php?p=108081
|
## Exam
$c=\lambda v$
Nick Bazett 1F
Posts: 32
Joined: Fri Sep 28, 2018 12:15 am
### Exam
What is the best study method to succeed in Chem 14A?
Kristen Kim 2K
Posts: 70
Joined: Fri Sep 28, 2018 12:16 am
### Re: Exam
I think doing the practice problems are the most helpful since you're practicing how to solve questions that might essentially be asking the same question but just with a completely different wording. Also, I would think that really taking time to understand the concepts rather than memorizing them would be more efficient, because in the end, you're being tested on applying those concepts to questions you've never seen. But these are just my speculations since I'm pretty much in the same boat as you are
kateminden
Posts: 63
Joined: Fri Sep 28, 2018 12:24 am
### Re: Exam
I'm not sure exactly what the best way to study is, but I've also just been doing the practice problems. I'm making sure that I know how to do each different type of problem. I might also use the audio-visual focus-topics to review material covered in class.
EllerySchlingmann1E
Posts: 76
Joined: Fri Sep 28, 2018 12:24 am
### Re: Exam
I think doing all of the homework problems as well as the audio-visual modules is the way to go, because the syllabus said that homework would sometimes be used for tests. Furthermore, the questions in the assessments for the modules were developed by Dr. Lavelle so they may give some sense of what the question will be like. *The only caveat with the modules is they are multiple choice and the tests aren't.
Ashley Kim
Posts: 62
Joined: Fri Sep 28, 2018 12:19 am
Been upvoted: 1 time
### Re: Exam
Solving all the problems (both in the modules and in the textbook) is a good way to prepare for the test. Mark the ones you got wrong, and then resolve the wrong ones to understand the concepts.
charlotte_jacobs_4I
Posts: 63
Joined: Fri Sep 28, 2018 12:29 am
### Re: Exam
The way I have been looking at it is first reviewing the problems that we did in our discussions. Those seem to have many important features. Next I am going to watch the audio videos and take notes. The pre and post assessments i am going to use to gauge my understanding of the concepts and then add on with additional homework problems in the needed areas. With that said i may still do all of the homework problems just in case.
Saachi_Kotia_4E
Posts: 68
Joined: Fri Sep 28, 2018 12:23 am
### Re: Exam
So far, I have just been repeating problems from the textbook in order to see what areas I'm weak in. I personally didn't like the audio visual modules because the answers were multiple choice, which isn't what we're going to have on the test. I will also do more problems from the book that aren't assigned and I might look up some practice problems online.
Lauren Huang 1H
Posts: 60
Joined: Fri Sep 28, 2018 12:16 am
### Re: Exam
You can also go to the TAs office hours or UA peer learning sessions.
|
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|
https://worldwidescience.org/topicpages/e/electron+laser+based.html
|
Sample records for electron laser based
1. Beam manipulation for compact laser wakefield accelerator based free-electron lasers
National Research Council Canada - National Science Library
Loulergue, A; Labat, M; Evain, C; Benabderrahmane, C; Malka, Victor; Couprie, M E
2015-01-01
.... After the success of FELs based on conventional acceleration using radio-frequency cavities, an important challenge is the development of FELs based on electron bunching accelerated by a laser wakefield accelerator (LWFA...
2. A laser printing based approach for printed electronics
Science.gov (United States)
Zhang, T.; Hu, M.; Liu, Y.; Guo, Q.; Wang, X.; Zhang, W.; Lau, W.; Yang, J.
2016-03-01
Here we report a study of printing of electronics using an office use laser printer. The proposed method eliminates those critical disadvantages of solvent-based printing techniques by taking the advantages of electroless deposition and laser printing. The synthesized toner acts as a catalyst for the electroless copper deposition as well as an adhesion-promoting buffer layer between the substrate and deposited copper. The easy metallization of printed patterns and strong metal-substrate adhesion make it an especially effective method for massive production of flexible printed circuits. The proposed process is a high throughput, low cost, efficient, and environmentally benign method for flexible electronics manufacturing.
3. Laser-Based Electron Acceleration Experiment in KERI/APRI-GIST
CERN Document Server
Kim, Guang-Hoon; Hafz, Nasr; Ko Do Kyeong; Lee Jong Min; Suk, Hyyong; Yu, T J
2005-01-01
Laser-based acceleration of charged particles has been of interest since laser wakefield produces very strong longitudinal electrical field to accelerate electrons upto relativistic energy. Recently, 20TW Ti:sapphire laser system, with pulse width of 30 fs and energy pf 600 mJ, was installed in APRI-GIST. The laser pulse is focused onto a gas jet to produce plasma and accelerate electrons in the scheme of self-modulated laser wakefield acceleration. Details of laser system and diagnostic results of electron beam will be discussed
4. Generation of electron beams from a laser-based advanced accelerator at Shanghai Jiao Tong University
CERN Document Server
Elsied, Ahmed M M; Li, Song; Mirzaie, Mohammad; Sokollik, Thomas; Zhang, Jie
2014-01-01
At Shanghai Jiao Tong University, we have established a research laboratory for advanced acceleration research based on high-power lasers and plasma technologies. In a primary experiment based on the laser wakefield acceleration (LWFA) scheme, multi-hundred MeV electron beams having a reasonable quality are generated using 20-40 TW, 30 femtosecond laser pulses interacting independently with helium, neon, nitrogen and argon gas jet targets. The laser-plasma interaction conditions are optimized for stabilizing the electron beam generation from each type of gas. The electron beam pointing angle stability and divergence angle as well as the energy spectra from each gas jet are measured and compared.
5. Free-electron lasers
CERN Document Server
Schmüser, P
2006-01-01
The synchrotron radiation of relativistic electrons in undulator magnets and the low-gain Free-Electron Laser (FEL) are discussed in some detail. The highgain FEL based on the principle of Self Amplified Spontaneous Emission is treated on a qualitative level.
6. Lasers in Electronic Warfare
Science.gov (United States)
Manke, Gerald C.
2014-10-01
The use of lasers for Electronic Warfare applications will be discussed and reviewed. Specific examples of deployed EW systems which include lasers will be presented along with a discussion of their most salient features.
7. Proposed method for internal electron therapy based on high-intensity laser acceleration
Science.gov (United States)
Tepper, Michal; Barkai, Uri; Gannot, Israel
2015-05-01
Radiotherapy is one of the main methods to treat cancer. However, due to the propagation pattern of high-energy photons in tissue and their inability to discriminate between healthy and malignant tissues, healthy tissues may also be damaged, causing undesired side effects. A possible method for internal electron therapy, based on laser acceleration of electrons inside the patient's body, is suggested. In this method, an optical waveguide, optimized for high intensities, is used to transmit the laser radiation and accelerate electrons toward the tumor. The radiation profile can be manipulated in order to create a patient-specific radiation treatment profile by changing the laser characteristics. The propagation pattern of electrons in tissues minimizes the side effects caused to healthy tissues. A simulation was developed to demonstrate the use of this method, calculating the trajectories of the accelerated electron as a function of laser properties. The simulation was validated by comparison to theory, showing a good fit for laser intensities of up to 2×1020 (W/cm2), and was then used to calculate suggested treatment profiles for two tumor test cases (with and without penetration to the tumor). The results show that treatment profiles can be designed to cover tumor area with minimal damage to adjacent tissues.
8. Imaging of Endogenous Metabolites of Plant Leaves by Mass Spectrometry Based on Laser Activated Electron Tunneling.
Science.gov (United States)
Huang, Lulu; Tang, Xuemei; Zhang, Wenyang; Jiang, Ruowei; Chen, Disong; Zhang, Juan; Zhong, Hongying
2016-04-07
A new mass spectrometric imaging approach based on laser activated electron tunneling (LAET) was described and applied to analysis of endogenous metabolites of plant leaves. LAET is an electron-directed soft ionization technique. Compressed thin films of semiconductor nanoparticles of bismuth cobalt zinc oxide were placed on the sample plate for proof-of-principle demonstration because they can not only absorb ultraviolet laser but also have high electron mobility. Upon laser irradiation, electrons are excited from valence bands to conduction bands. With appropriate kinetic energies, photoexcited electrons can tunnel away from the barrier and eventually be captured by charge deficient atoms present in neutral molecules. Resultant unpaired electron subsequently initiates specific chemical bond cleavage and generates ions that can be detected in negative ion mode of the mass spectrometer. LAET avoids the co-crystallization process of routinely used organic matrix materials with analyzes in MALDI (matrix assisted-laser desorption ionization) analysis. Thus uneven distribution of crystals with different sizes and shapes as well as background peaks in the low mass range resulting from matrix molecules is eliminated. Advantages of LAET imaging technique include not only improved spatial resolution but also photoelectron capture dissociation which produces predictable fragment ions.
9. High-brightness electron beam evolution following laser-based cleaning of a photocathode
Directory of Open Access Journals (Sweden)
F. Zhou
2012-09-01
Full Text Available Laser-based techniques have been widely used for cleaning metal photocathodes to increase quantum efficiency (QE. However, the impact of laser cleaning on cathode uniformity and thereby on electron beam quality are less understood. We are evaluating whether this technique can be applied to revive photocathodes used for high-brightness electron sources in advanced x-ray free-electron laser (FEL facilities, such as the Linac Coherent Light Source (LCLS at the SLAC National Accelerator Laboratory. The laser-based cleaning was applied to two separate areas of the current LCLS photocathode on July 4 and July 26, 2011, respectively. The QE was increased by 8–10 times upon the laser cleaning. Since the cleaning, routine operation has exhibited a slow evolution of the QE improvement and comparatively rapid improvement of transverse emittance, with a factor of 3 QE enhancement over five months, and a significant emittance improvement over the initial 2–3 weeks following the cleaning. Currently, the QE of the LCLS photocathode is holding constant at about 1.2×10^{-4}, with a normalized injector emittance of about 0.3 μm for a 150-pC bunch charge. With the proper procedures, the laser-cleaning technique appears to be a viable tool to revive the LCLS photocathode. We present observations and analyses for the QE and emittance evolution in time following the laser-based cleaning of the LCLS photocathode, and comparison to the previous studies, the measured thermal emittance versus the QE and comparison to the theoretical model.
10. Higher-order mode-based cavity misalignment measurements at the free-electron laser FLASH
Science.gov (United States)
Hellert, Thorsten; Baboi, Nicoleta; Shi, Liangliang
2017-12-01
At the Free-Electron Laser in Hamburg (FLASH) and the European X-Ray Free-Electron Laser, superconducting TeV-energy superconducting linear accelerator (TESLA)-type cavities are used for the acceleration of electron bunches, generating intense free-electron laser (FEL) beams. A long rf pulse structure allows one to accelerate long bunch trains, which considerably increases the efficiency of the machine. However, intrabunch-train variations of rf parameters and misalignments of rf structures induce significant trajectory variations that may decrease the FEL performance. The accelerating cavities are housed inside cryomodules, which restricts the ability for direct alignment measurements. In order to determine the transverse cavity position, we use a method based on beam-excited dipole modes in the cavities. We have developed an efficient measurement and signal processing routine and present its application to multiple accelerating modules at FLASH. The measured rms cavity offset agrees with the specification of the TESLA modules. For the first time, the tilt of a TESLA cavity inside a cryomodule is measured. The preliminary result agrees well with the ratio between the offset and angle dependence of the dipole mode which we calculated with eigenmode simulations.
11. Frequency mixing in accelerator based sources and application to tunable seeded free-electron lasers
Directory of Open Access Journals (Sweden)
C. Evain
2014-12-01
Full Text Available In this article we address the problem of tunability of seeded free-electron lasers (FELs, working typically in the domain of the vacuum ultraviolet. The seeding of FELs with an external laser permits us to obtain FEL pulses with both good longitudinal coherence and good stability properties (contrary to an amplification starting from noise. However, with a fixed external laser wavelength, only amplification at harmonics of this wavelength is possible. If full tunability is wanted, it is necessary to have a tunable external source; but this type of source has much less power, hence it is much harder to reach high harmonics numbers. Here we propose the so-called frequency mixing scheme (from its analogy with the similar process in nonlinear optics, based on two laser/electron interactions. Numerical and analytic studies show that it permits to increase significantly the tunability at short wavelengths using a low-energy tunable source. Numerical simulations are made with the parameters of FERMI-FEL 1, the first seeded FEL for user operation.
12. Nanofocusing of hard X-ray free electron laser pulses using diamond based Fresnel zone plates
Science.gov (United States)
David, C.; Gorelick, S.; Rutishauser, S.; Krzywinski, J.; Vila-Comamala, J.; Guzenko, V. A.; Bunk, O.; Färm, E.; Ritala, M.; Cammarata, M.; Fritz, D. M.; Barrett, R.; Samoylova, L.; Grünert, J.; Sinn, H.
2011-08-01
A growing number of X-ray sources based on the free-electron laser (XFEL) principle are presently under construction or have recently started operation. The intense, ultrashort pulses of these sources will enable new insights in many different fields of science. A key problem is to provide x-ray optical elements capable of collecting the largest possible fraction of the radiation and to focus into the smallest possible focus. As a key step towards this goal, we demonstrate here the first nanofocusing of hard XFEL pulses. We developed diamond based Fresnel zone plates capable of withstanding the full beam of the world's most powerful x-ray laser. Using an imprint technique, we measured the focal spot size, which was limited to 320 nm FWHM by the spectral band width of the source. A peak power density in the focal spot of 4×1017 W/cm2 was obtained at 70 fs pulse length.
13. Free standing diamond-like carbon thin films by PLD for laser based electrons/protons acceleration
Energy Technology Data Exchange (ETDEWEB)
Thema, F.T.; Beukes, P.; Ngom, B.D. [UNESCO Africa Chair in Nanosciences-Nanotechnology, College of Graduate Studies, University of South Africa, Muckleneuk Ridge, PO Box 392, Pretoria (South Africa); Nanosciences African Network (NANOAFNET), iThemba LABS-National Research Foundation, 1 Old Faure Road, Somerset West, 7129, PO Box722, Western Cape Province (South Africa); Manikandan, E., E-mail: [email protected] [UNESCO Africa Chair in Nanosciences-Nanotechnology, College of Graduate Studies, University of South Africa, Muckleneuk Ridge, PO Box 392, Pretoria (South Africa); Nanosciences African Network (NANOAFNET), iThemba LABS-National Research Foundation, 1 Old Faure Road, Somerset West, 7129, PO Box722, Western Cape Province (South Africa); Central Research Laboratory, Sree Balaji Medical College & Hospital (SBMCH), Chrompet, Bharath University, Chennai, 600044 (India); Maaza, M., E-mail: [email protected] [UNESCO Africa Chair in Nanosciences-Nanotechnology, College of Graduate Studies, University of South Africa, Muckleneuk Ridge, PO Box 392, Pretoria (South Africa); Nanosciences African Network (NANOAFNET), iThemba LABS-National Research Foundation, 1 Old Faure Road, Somerset West, 7129, PO Box722, Western Cape Province (South Africa)
2015-11-05
This study we reports for the first time on the synthesis and optical characteristics of free standing diamond-like carbon (DLC) deposited by pulsed laser deposition (PLD) onto graphene buffer layers for ultrahigh intensity laser based electron/proton acceleration applications. The fingerprint techniques of micro-Raman, UV–VIS–NIR and the IR spectroscopic investigations indicate that the suitability of such free standing DLC thin-films within the laser window and long wave infrared (LWIR) spectral range and hence their appropriateness for the targeted applications. - Highlights: • We report for the first time synthesis of free standing diamond-like carbon. • Pulsed laser deposition onto graphene buffer layers. • Fingerprint techniques of micro-Raman, UV–VIS–NIR and the IR spectroscopic investigations. • Ultrahigh intensity laser based electron/proton acceleration applications. • This material's suitable for the laser window and long wave infrared (LWIR) spectral range.
14. Low-emittance thermionic-gun-based injector for a compact free-electron laser
Science.gov (United States)
Asaka, Takao; Ego, Hiroyasu; Hanaki, Hirohumi; Hara, Toru; Hasegawa, Taichi; Hasegawa, Teruaki; Inagaki, Takahiro; Kobayashi, Toshiaki; Kondo, Chikara; Maesaka, Hirokazu; Matsubara, Shinichi; Matsui, Sakuo; Ohshima, Takashi; Otake, Yuji; Sakurai, Tatsuyuki; Suzuki, Shinsuke; Tajiri, Yasuyuki; Tanaka, Shinichiro; Togawa, Kazuaki; Tanaka, Hitoshi
2017-08-01
A low-emittance thermionic-gun-based injector was developed for the x-ray free-electron laser (XFEL) facility known as the SPring-8 angstrom compact free-electron laser (SACLA). The thermionic-gun-based system has the advantages of maintainability, reliability, and stability over a photocathode radio-frequency (rf) gun because of its robust thermionic cathode. The basic performance of the injector prototype was confirmed at the SPring-8 compact self-amplified spontaneous emission source (SCSS) test accelerator, where stable FEL generation in an extreme ultraviolet wavelength range was demonstrated. The essential XFEL innovation is the achievement of a constant beam peak current of 3-4 kA, which is 10 times higher than that generated by the SCSS test accelerator, while maintaining a normalized-slice emittance below 1 mm mrad. Thus, the following five modifications were applied to the SACLA injector: (i) a nonlinear energy chirp correction; (ii) the optimization of the rf acceleration frequency; (iii) rf system stabilization; (iv) nondestructive beam monitoring; and (v) a geomagnetic field correction. The SACLA injector successfully achieved the target beam performance, which shows that a thermionic-gun-based injector is applicable to an XFEL accelerator system. This paper gives an overview of the SACLA injector and describes the physical and technical details, together with the electron beam performance obtained in the beam commissioning.
15. Low-emittance thermionic-gun-based injector for a compact free-electron laser
Directory of Open Access Journals (Sweden)
Takao Asaka
2017-08-01
Full Text Available A low-emittance thermionic-gun-based injector was developed for the x-ray free-electron laser (XFEL facility known as the SPring-8 angstrom compact free-electron laser (SACLA. The thermionic-gun-based system has the advantages of maintainability, reliability, and stability over a photocathode radio-frequency (rf gun because of its robust thermionic cathode. The basic performance of the injector prototype was confirmed at the SPring-8 compact self-amplified spontaneous emission source (SCSS test accelerator, where stable FEL generation in an extreme ultraviolet wavelength range was demonstrated. The essential XFEL innovation is the achievement of a constant beam peak current of 3–4 kA, which is 10 times higher than that generated by the SCSS test accelerator, while maintaining a normalized-slice emittance below 1 mm mrad. Thus, the following five modifications were applied to the SACLA injector: (i a nonlinear energy chirp correction; (ii the optimization of the rf acceleration frequency; (iii rf system stabilization; (iv nondestructive beam monitoring; and (v a geomagnetic field correction. The SACLA injector successfully achieved the target beam performance, which shows that a thermionic-gun-based injector is applicable to an XFEL accelerator system. This paper gives an overview of the SACLA injector and describes the physical and technical details, together with the electron beam performance obtained in the beam commissioning.
16. Welding of Mo-Based Alloy Using Electron Beam and Laser-GTAW Hybrid Welding Techniques
Science.gov (United States)
Chatterjee, Anjan; Kumar, Santosh; Tewari, Raghvendra; Dey, Gautam Kumar
2016-03-01
In the current study, welding of TZM (molybdenum-based alloy) plates in square-butt configuration was carried out using electron beam and laser-GTAW hybrid power sources. Microstructures of weld joint containing three zones—parent metal, heat-affected zone, and fusion zone—were clearly identified when examined through optical and scanning electron microscopy. The weld joints were found to be sound with very wide fusion and heat-affected zones. The microstructure of the fusion zone was coarse-grained. as-solidified microstructure, while the microstructure of heat-affected zone was the recrystallized microstructure with reduction in grain size as distance from the fusion line increased. Microhardness profile using Vickers hardness tester was obtained across the weld region, and the tensile properties of the weld joints were evaluated by performing room temperature tensile test and fracture was examined using scanning electron microscope. Joint coefficient of the weld joints were ~40 to 45 pct of that of the parent metals with nonmeasurable tensile ductility with predominantly transgranular mode of fracture indicating weakness along the grain boundary. Detailed orientation imaging and transmission electron microscopy were carried out to understand the most dominating factor in introducing weld joint brittleness.
17. IRIDE: Interdisciplinary research infrastructure based on dual electron linacs and lasers
Energy Technology Data Exchange (ETDEWEB)
Ferrario, M., E-mail: [email protected] [INFN-LNF (Italy); Alesini, D. [INFN-LNF (Italy); Alessandroni, M. [RMP Srl (Italy); Anania, M.P. [INFN-LNF (Italy); Andreas, S. [DESY, Hamburg (Germany); Angelone, M. [ENEA, Frascati (Italy); Arcovito, A. [Univ. Cattolica del Sacro Cuore - Roma (Italy); Arnesano, F. [Univ. di Bari (Italy); Artioli, M. [ENEA, Frascati (Italy); Avaldi, L. [CNR, Area Ric. di Roma 1 (Italy); Babusci, D. [INFN-LNF (Italy); Bacci, A. [INFN and Univ. di Milano (Italy); Balerna, A.; Bartalucci, S.; Bedogni, R.; Bellaveglia, M. [INFN-LNF (Italy); Bencivenga, F. [Sincrotrone Trieste (Italy); Benfatto, M. [INFN-LNF (Italy); Biedron, S. [Colorado Univ. (United States); Bocci, V. [INFN and Univ. di Roma, La Sapienza (Italy); and others
2014-03-11
This paper describes the scientific aims and potentials as well as the preliminary technical design of IRIDE, an innovative tool for multi-disciplinary investigations in a wide field of scientific, technological and industrial applications. IRIDE will be a high intensity “particles factory”, based on a combination of high duty cycle radio-frequency superconducting electron linacs and of high energy lasers. Conceived to provide unique research possibilities for particle physics, for condensed matter physics, chemistry and material science, for structural biology and industrial applications, IRIDE will open completely new research possibilities and advance our knowledge in many branches of science and technology. IRIDE is also supposed to be realized in subsequent stages of development depending on the assigned priorities.
18. Transverse effects in the production of x rays with a free-electron laser based on an optical undulator
Directory of Open Access Journals (Sweden)
A. Bacci
2006-06-01
Full Text Available The interaction between high-brilliance electron beams and counterpropagating laser pulses produces x rays via Thomson backscattering. If the laser source is long and intense enough, the electrons of the beam can bunch on the scale of the emitted x-ray wavelength and a regime of collective effects can establish. In this case of dominating collective effects, the FEL instability can develop and the system behaves like a free-electron laser based on an optical undulator. Coherent x rays can be irradiated, with a bandwidth very much thinner than that of the corresponding incoherent emission. The emittance of the electron beam and the distribution nonuniformity of the laser energy are the principal quantities that limit the growth of the x-ray signal. In this work we analyze with a 3D code the transverse effects in the emission produced by a relativistic electron beam when it is under the action of an optical laser pulse and the x-ray spectra obtained. The scalings typical of the optical wiggler, characterized by very short gain lengths and overall time durations of the process, make possible considerable emission also in violation of the Pellegrini criterion for static wigglers. A generalized form of this criterion is validated on the basis of the numerical evidence.
19. Extremely intense laser-based electron acceleration in a plasma channel
Science.gov (United States)
Vranic, Marija; Fonseca, Ricardo A.; Silva, Luis O.
2018-03-01
Laser pulses of extreme intensities (I> {10}22 {{W}} {{cm}}-2) are about to become available in the laboratory. The prepulse of such a laser can induce a plasma expansion that generates a low-density channel in near-critical gas jets. We present a study of channel formation and subsequent direct laser acceleration of electrons within the pre-formed channel. Radiation reaction affects the acceleration in several ways. It first interferes with the motion of the return current on the channel walls. In addition, it reduces the radial expelling efficiency of the transverse ponderomotive force, leading to the radiative trapping of particles near the channel axis. These particles then interact with the peak laser intensity and can attain multi-GeV energies.
20. Chemical imaging of latent fingerprints by mass spectrometry based on laser activated electron tunneling.
Science.gov (United States)
Tang, Xuemei; Huang, Lulu; Zhang, Wenyang; Zhong, Hongying
2015-03-03
Identification of endogenous and exogenous chemicals contained in latent fingerprints is important for forensic science in order to acquire evidence of criminal identities and contacts with specific chemicals. Mass spectrometry has emerged as a powerful technique for such applications without any derivatization or fluorescent tags. Among these techniques, MALDI (Matrix Assisted Laser Desorption Ionization) provides small beam size but has interferences with MALDI matrix materials, which cause ion suppressions as well as limited spatial resolution resulting from uneven distribution of MALDI matrix crystals with different sizes. LAET (Laser Activated Electron Tunneling) described in this work offers capabilities for chemical imaging through electron-directed soft ionization. A special film of semiconductors has been designed for collection of fingerprints. Nanoparticles of bismuth cobalt zinc oxide were compressed on a conductive metal substrate (Al or Cu sticky tape) under 10 MPa pressure. Resultant uniform thin films provide tight and shining surfaces on which fingers are impressed. Irradiation of ultraviolet laser pulses (355 nm) on the thin film instantly generates photoelectrons that can be captured by adsorbed organic molecules and subsequently cause electron-directed ionization and fragmentation. Imaging of latent fingerprints is achieved by visualization of the spatial distribution of these molecular ions and structural information-rich fragment ions. Atomic electron emission together with finely tuned laser beam size improve spatial resolution. With the LAET technique, imaging analysis not only can identify physical shapes but also reveal endogenous metabolites present in females and males, detect contacts with prohibited substances, and resolve overlapped latent fingerprints.
1. En Route: next-generation laser-plasma-based electron accelerators; En Route: Elektronenbeschleuniger der naechsten Generation auf Laser-Plasma-Basis
Energy Technology Data Exchange (ETDEWEB)
Hidding, Bernhard
2008-05-15
Accelerating electrons to relativistic energies is of fundamental interest, especially in particle physics. Today's accelerator technology, however, is limited by the maximum electric fields which can be created. This thesis presents results on various mechanisms aiming at exploiting the fields in focussed laser pulses and plasma waves for electron acceleration, which can be orders of magnitude higher than with conventional accelerators. With relativistic, underdense laser-plasma-interaction, quasimonoenergetic electron bunches with energies up to {approx}50 MeV and normalized emittances of the order of 5mmmrad have been generated. This was achieved by focussing the {approx}80 fs, 1 J pulses of the JETI-laser at the FSU Jena to intensities of several 10{sup 19}W=cm{sup 2} into gas jets. The experimental observations could be explained via 'bubble acceleration', which is based on self-injection and acceleration of electrons in a highly nonlinear breaking plasma wave. For the rst time, this bubble acceleration was achieved explicitly in the self-modulated laser wakefield regime (SMLWFA). This quasimonoenergetic SMLWFA-regime stands out by relaxing dramatically the requirements on the driving laser pulse necessary to trigger bubble acceleration. This is due to self-modulation of the laser pulse in high-density gas jets, leading to ultrashort laser pulse fragments capable of initiating bubble acceleration. Electron bunches with durations laser pulse fragment can be powerful enough to drive a bubble. Distinct double peaks have been observed in the electron spectra, indicating that two quasimonoenergetic electron bunches separated by only few tens of fs have formed. This is backed up by PIC-Simulations (Particle-in-Cell). These results underline the feasibility of the construction of small table
2. Rf Feedback free electron laser
Science.gov (United States)
Brau, Charles A.; Swenson, Donald A.; Boyd, Jr., Thomas J.
1981-01-01
A free electron laser system and electron beam system for a free electron laser which use rf feedback to enhance efficiency. Rf energy is extracted from an electron beam by decelerating cavities and returned to accelerating cavities using rf returns such as rf waveguides, rf feedthroughs, etc. This rf energy is added to rf klystron energy to lower the required input energy and thereby enhance energy efficiency of the system.
3. Electron beam test of key elements of the laser-based calibration system for the muon g - 2 experiment
Energy Technology Data Exchange (ETDEWEB)
Anastasi, A.; Basti, A.; Bedeschi, F.; Bartolini, M.; Cantatore, G.; Cauz, D.; Corradi, G.; Dabagov, S.; Di Sciascio, G.; Di Stefano, R.; Driutti, A.; Escalante, O.; Ferrari, C.; Fienberg, A. T.; Fioretti, A.; Gabbanini, C.; Gioiosa, A.; Hampai, D.; Hertzog, D. W.; Iacovacci, M.; Karuza, M.; Kaspar, J.; Liedl, A.; Lusiani, A.; Marignetti, F.; Mastroianni, S.; Moricciani, D.; Pauletta, G.; Piacentino, G. M.; Raha, N.; Rossi, E.; Santi, L.; Venanzoni, G.
2017-01-01
We report the test of many of the key elements of the laser-based calibration system for muon g - 2 experiment E989 at Fermilab. The test was performed at the Laboratori Nazionali di Frascati's Beam Test Facility using a 450 MeV electron beam impinging on a small subset of the final g - 2 lead-fluoride crystal calorimeter system. The calibration system was configured as planned for the E989 experiment and uses the same type of laser and most of the final optical elements. We show results regarding the calorimeter's response calibration, the maximum equivalent electron energy which can be provided by the laser and the stability of the calibration system components.
4. Interaction of relativistic electrons with an intense laser pulse: High-order harmonic generation based on Thomson scattering
Energy Technology Data Exchange (ETDEWEB)
Hack, Szabolcs [ELI-ALPS, ELI-HU Non-Profit Ltd., Dugonics tér 13, H-6720 Szeged (Hungary); Department of Theoretical Physics, University of Szeged, Tisza L. krt. 84-86, H-6720 Szeged (Hungary); Varró, Sándor [ELI-ALPS, ELI-HU Non-Profit Ltd., Dugonics tér 13, H-6720 Szeged (Hungary); Wigner Research Center for Physics, SZFI, PO Box 49, H-1525 Budapest (Hungary); Czirják, Attila [ELI-ALPS, ELI-HU Non-Profit Ltd., Dugonics tér 13, H-6720 Szeged (Hungary); Department of Theoretical Physics, University of Szeged, Tisza L. krt. 84-86, H-6720 Szeged (Hungary)
2016-02-15
We investigate nonlinear Thomson scattering as a source of high-order harmonic radiation with the potential to enable attosecond light pulse generation. We present a new analytic solution of the electron’s relativistic equations of motion in the case of a short laser pulse with a sine-squared envelope. Based on the single electron emission, we compute and analyze the radiated amplitude and phase spectrum for a realistic electron bunch, with special attention to the correct initial values. These results show that the radiation spectrum of an electron bunch in head-on collision with a sufficiently strong laser pulse of sine-squared envelope has a smooth frequency dependence to allow for the synthesis of attosecond light pulses.
5. Femtosecond laser high-efficiency drilling of high-aspect-ratio microholes based on free-electron-density adjustments.
Science.gov (United States)
Jiang, Lan; Fang, Juqiang; Cao, Qiang; Zhang, Kaihu; Wang, Peng; Yu, Yanwu; Huang, Qiang; Lu, Yongfeng
2014-11-01
We studied the micromachining of high-aspect-ratio holes in poly(methylmethacrylate) using a visible double-pulse femtosecond laser based on free-electron-density adjustments. Hole depth and aspect ratio increased simultaneously upon decreasing the wavelength in the visible-light zone. When the pulse energy reached a high level, the free-electron density was adjusted by using a double-pulse laser, which induced fewer free electrons, a lower reflectivity plasma plume, and more pulse energy deposition in the solid bottom. Thus, the aspect ratio of the hole was improved considerably. At a moderate pulse energy level, a 1.3-1.4 times enhancement of both the ablation depth and the aspect ratio was observed when the double-pulse delay was set between 100 and 300 fs, probably due to an enhanced photon-electron coupling effect through adjusting the free-electron density. At a lower pulse energy level, this effect also induced the generation of a submicrometer string. In addition, the ablation rate was improved significantly by using visible double pulses.
6. Toward all-carbon electronics: fabrication of graphene-based flexible electronic circuits and memory cards using maskless laser direct writing.
Science.gov (United States)
Liang, Jiajie; Chen, Yongsheng; Xu, Yanfei; Liu, Zhibo; Zhang, Long; Zhao, Xin; Zhang, Xiaoliang; Tian, Jianguo; Huang, Yi; Ma, Yanfeng; Li, Feifei
2010-11-01
Owing to its extraordinary electronic property, chemical stability, and unique two-dimensional nanostructure, graphene is being considered as an ideal material for the highly expected all-carbon-based micro/nanoscale electronics. Herein, we present a simple yet versatile approach to constructing all-carbon micro/nanoelectronics using solution-processing graphene films directly. From these graphene films, various graphene-based microcosmic patterns and structures have been fabricated using maskless computer-controlled laser cutting. Furthermore, a complete system involving a prototype of a flexible write-once-read-many-times memory card and a fast data-reading system has been demonstrated, with infinite data retention time and high reliability. These results indicate that graphene could be the ideal material for fabricating the highly demanded all-carbon and flexible devices and electronics using the simple and efficient roll-to-roll printing process when combined with maskless direct data writing.
7. Ultrashort laser pulse driven inverse free electron laser accelerator experiment
Directory of Open Access Journals (Sweden)
J. T. Moody
2016-02-01
Full Text Available In this paper we discuss the ultrashort pulse high gradient inverse free electron laser accelerator experiment carried out at the Lawrence Livermore National Laboratory which demonstrated gradients exceeding 200 MV/m using a 4 TW 100 fs long 800 nm Ti:Sa laser pulse. Due to the short laser and electron pulse lengths, synchronization was determined to be one of the main challenges in this experiment. This made necessary the implementation of a single-shot, nondestructive, electro-optic sampling based diagnostics to enable time-stamping of each laser accelerator shot with <100 fs accuracy. The results of this experiment are expected to pave the way towards the development of future GeV-class IFEL accelerators.
8. Development of a Silicon Based Electron Beam Transmission Window for Use in a KrF Excimer Laser System
CERN Document Server
Gentile, C A; Hartfield, J W; Hawryluk, R J; Hegeler, F; Heitzenroeder, P J; Jun, C H; Ku, L P; Lamarche, P H; Myers, M C; Parker, J J; Parsells, R F; Payen, M; Raftopoulos, S; Sethian, J D
2002-01-01
The Princeton Plasma Physics Laboratory (PPPL), in collaboration with the Naval Research Laboratory (NRL), is currently investigating various novel materials (single crystal silicon, , and ) for use as electron-beam transmission windows in a KrF excimer laser system. The primary function of the window is to isolate the active medium (excimer gas) from the excitation mechanism (field-emission diodes). Chosen window geometry must accommodate electron energy transfer greater than 80% (750 keV), while maintaining structural integrity during mechanical load (1.3 to 2.0 atm base pressure differential, approximate 0.5 atm cyclic pressure amplitude, 5 Hz repetition rate) and thermal load across the entire hibachi area (approximate 0.9 W centre dot cm superscript ''-2''). In addition, the window must be chemically resistant to attack by fluorine free-radicals (hydrofluoric acid, secondary). In accordance with these structural, functional, and operational parameters, a 22.4 mm square silicon prototype window, coated w...
9. Single-shot method for measuring femtosecond bunch length in linac-based free-electron lasers
Directory of Open Access Journals (Sweden)
Z. Huang
2010-09-01
Full Text Available There is growing interest in the generation and characterization of femtosecond and subfemtosecond pulses from linac-based free-electron lasers (FELs. In this report, following the method of Ricci and Smith [Phys. Rev. ST Accel. Beams 3, 032801 (2000PRABFM1098-440210.1103/PhysRevSTAB.3.032801], we investigate the measurement of the longitudinal bunch profile of an ultrashort electron bunch produced by these FELs. We show that this method can be applied in a straightforward manner at x-ray FEL facilities such as the Linac Coherent Light Source by slightly adjusting the second bunch compressor followed by running the bunch on an rf zero-crossing phase of the final linac. We find that the linac wakefield strongly perturbs the measurement, and through analysis show that it can be compensated in a simple way. We demonstrate the effectiveness of this method and wakefield compensation through numerical simulations, including effects of coherent synchrotron radiation and longitudinal space charge. When used in conjunction with a high-resolution electron spectrometer, this method potentially reveals the temporal profile of the electron beam down to the femtosecond and subfemotsecond scale.
10. Sub-picosecond timing fluctuation suppression in laser-based atmospheric transfer of microwave signal using electronic phase compensation
Science.gov (United States)
Chen, Shijun; Sun, Fuyu; Bai, Qingsong; Chen, Dawei; Chen, Qiang; Hou, Dong
2017-10-01
We demonstrated a timing fluctuation suppression in outdoor laser-based atmospheric radio-frequency transfer over a 110 m one-way free-space link using an electronic phase compensation technique. Timing fluctuations and Allan Deviation are both measured to characterize the instability of transferred frequency incurred during the transfer process. With transferring a 1 GHz microwave signal over a timing fluctuation suppressed transmission link, the total root-mean-square (rms) timing fluctuation was measured to be 920 femtoseconds in 5000 s, with fractional frequency instability on the order of 1 × 10-12 at 1 s, and order of 2 × 10-16 at 1000 s. This atmospheric frequency transfer scheme with the timing fluctuation suppression technique can be used to fast build an atomic clock-based frequency free-space transmission link since its stability is superior to a commercial Cs and Rb clock.
11. Free Electron Laser Synthesis of Functional Coatings
Science.gov (United States)
Schaaf, Peter; Höche, Daniel
Functional and smart surfaces and coatings play an increasingly decisive role in the applicability and performance of modern materials. From an industrial point of view, there is a great interest with respect to friction, wear, corrosion, and further properties. Many methods have been developed for the improvement of the respective surface and material properties. Traditionally, these treatments range from simple PVD and CVD processes to complicated plasma and hybrid methods. Recently, it has been established that short laser pulses of high energy can induce a direct laser synthesis of functional coatings if the material's surface is irradiated in a reactive atmosphere. The process is based on a complicated combination of laser plasma - gas - material surface interactions. Tests for steel, aluminum, magnesium, titanium, and silicon in nitrogen, methane, and hydrogen atmospheres have been carried out successfully; with these materials, interesting coatings can be produced by direct laser synthesis, for example, AlN and SiC. Various laser types can be used for this purpose: Excimer, Nd:YAG, CO2 Laser, and even the free electron laser (FEL).
12. Matching-based fresh-slice method for generating two-color x-ray free-electron lasers
Directory of Open Access Journals (Sweden)
Weilun Qin
2017-09-01
Full Text Available Two-color high intensity x-ray free-electron lasers (FELs provide powerful tools for probing ultrafast dynamic systems. A novel concept of realizing fresh-slice two-color lasing through slice-dependent transverse mismatch has been proposed by one of the authors [Y. Chao, SLAC Report No. SLAC-PUB-16935, 2016]. In this paper we present a feasible example following this concept based on the Linac Coherent Light Source parameters. Time-dependent mismatch along the bunch is generated by a passive dechirper module and controlled by downstream matching sections, enabling FEL lasing at different wavelength with a split undulator configuration. Simulations for soft x-ray FELs show that tens of gigawatts pulses with femtosecond duration can be generated.
13. Matching-based fresh-slice method for generating two-color x-ray free-electron lasers
Science.gov (United States)
Qin, Weilun; Ding, Yuantao; Lutman, Alberto A.; Chao, Yu-Chiu
2017-09-01
Two-color high intensity x-ray free-electron lasers (FELs) provide powerful tools for probing ultrafast dynamic systems. A novel concept of realizing fresh-slice two-color lasing through slice-dependent transverse mismatch has been proposed by one of the authors [Y. Chao, SLAC Report No. SLAC-PUB-16935, 2016]. In this paper we present a feasible example following this concept based on the Linac Coherent Light Source parameters. Time-dependent mismatch along the bunch is generated by a passive dechirper module and controlled by downstream matching sections, enabling FEL lasing at different wavelength with a split undulator configuration. Simulations for soft x-ray FELs show that tens of gigawatts pulses with femtosecond duration can be generated.
14. Goniometer-based femtosecond crystallography with X-ray free electron lasers.
Science.gov (United States)
Cohen, Aina E; Soltis, S Michael; González, Ana; Aguila, Laura; Alonso-Mori, Roberto; Barnes, Christopher O; Baxter, Elizabeth L; Brehmer, Winnie; Brewster, Aaron S; Brunger, Axel T; Calero, Guillermo; Chang, Joseph F; Chollet, Matthieu; Ehrensberger, Paul; Eriksson, Thomas L; Feng, Yiping; Hattne, Johan; Hedman, Britt; Hollenbeck, Michael; Holton, James M; Keable, Stephen; Kobilka, Brian K; Kovaleva, Elena G; Kruse, Andrew C; Lemke, Henrik T; Lin, Guowu; Lyubimov, Artem Y; Manglik, Aashish; Mathews, Irimpan I; McPhillips, Scott E; Nelson, Silke; Peters, John W; Sauter, Nicholas K; Smith, Clyde A; Song, Jinhu; Stevenson, Hilary P; Tsai, Yingssu; Uervirojnangkoorn, Monarin; Vinetsky, Vladimir; Wakatsuki, Soichi; Weis, William I; Zadvornyy, Oleg A; Zeldin, Oliver B; Zhu, Diling; Hodgson, Keith O
2014-12-02
The emerging method of femtosecond crystallography (FX) may extend the diffraction resolution accessible from small radiation-sensitive crystals and provides a means to determine catalytically accurate structures of acutely radiation-sensitive metalloenzymes. Automated goniometer-based instrumentation developed for use at the Linac Coherent Light Source enabled efficient and flexible FX experiments to be performed on a variety of sample types. In the case of rod-shaped Cpl hydrogenase crystals, only five crystals and about 30 min of beam time were used to obtain the 125 still diffraction patterns used to produce a 1.6-Å resolution electron density map. For smaller crystals, high-density grids were used to increase sample throughput; 930 myoglobin crystals mounted at random orientation inside 32 grids were exposed, demonstrating the utility of this approach. Screening results from cryocooled crystals of β2-adrenoreceptor and an RNA polymerase II complex indicate the potential to extend the diffraction resolution obtainable from very radiation-sensitive samples beyond that possible with undulator-based synchrotron sources.
15. A monolithic relativistic electron beam source based on a dielectric laser accelerator structure
Energy Technology Data Exchange (ETDEWEB)
McNeur, Josh; Carranza, Nestor; Travish, Gil; Yin Hairong; Yoder, Rodney [UCLA Dept. of Physics and Astronomy, Los Angeles, CA 90095 (United States); College of Physical Electronics, University of Electronic Science and Technology of China, Chengdu, Sichuan, 610054 (China); Manhattanville College, Physics Dept., 2900 Purchase St., Purchase, NY 10577 (United States)
2012-12-21
Work towards a monolithic device capable of producing relativistic particle beams within a cubic-centimeter is detailed. We will discuss the Micro-Accelerator Platform (MAP), an optical laser powered dielectric accelerator as the main building block of this chip-scale source along with a field enhanced emitter and a region for sub-relativistic acceleration.
16. A bremsstrahlung gamma-ray source based on stable ionization injection of electrons into a laser wakefield accelerator
Energy Technology Data Exchange (ETDEWEB)
Döpp, A., E-mail: [email protected] [LOA, ENSTA ParisTech, CNRS, École polytechnique, Université Paris-Saclay, 828 bd des Maréchaux, 91762 Palaiseau Cedex (France); Centro de Laseres Pulsados, Parque Cientfico, 37185 Villamayor, Salamanca (Spain); Guillaume, E.; Thaury, C.; Lifschitz, A. [LOA, ENSTA ParisTech, CNRS, École polytechnique, Université Paris-Saclay, 828 bd des Maréchaux, 91762 Palaiseau Cedex (France); Sylla, F. [SourceLAB SAS, 86 rue de Paris, 91400 Orsay (France); Goddet, J-P.; Tafzi, A.; Iaquanello, G.; Lefrou, T.; Rousseau, P. [LOA, ENSTA ParisTech, CNRS, École polytechnique, Université Paris-Saclay, 828 bd des Maréchaux, 91762 Palaiseau Cedex (France); Conejero, E.; Ruiz, C. [Departamento de Física Aplicada, Universidad de Salamanca, Plaza de laMerced s/n, 37008 Salamanca (Spain); Ta Phuoc, K.; Malka, V. [LOA, ENSTA ParisTech, CNRS, École polytechnique, Université Paris-Saclay, 828 bd des Maréchaux, 91762 Palaiseau Cedex (France)
2016-09-11
Laser wakefield acceleration permits the generation of ultra-short, high-brightness relativistic electron beams on a millimeter scale. While those features are of interest for many applications, the source remains constraint by the poor stability of the electron injection process. Here we present results on injection and acceleration of electrons in pure nitrogen and argon. We observe stable, continuous ionization-induced injection of electrons into the wakefield for laser powers exceeding a threshold of 7 TW. The beam charge scales approximately with the laser energy and is limited by beam loading. For 40 TW laser pulses we measure a maximum charge of almost 1 nC per shot, originating mostly from electrons of less than 10 MeV energy. The relatively low energy, the high charge and its stability make this source well-suited for applications such as non-destructive testing. Hence, we demonstrate the production of energetic radiation via bremsstrahlung conversion at 1 Hz repetition rate. In accordance with GEANT4 Monte-Carlo simulations, we measure a γ-ray source size of less than 100 μm for a 0.5 mm tantalum converter placed at 2 mm from the accelerator exit. Furthermore we present radiographs of image quality indicators.
17. Widely tunable opto-electronic oscillator based on a dual frequency laser
Science.gov (United States)
Maxin, J.; Saleh, K.; Pillet, G.; Morvan, L.; Llopis, O.; Dolfi, D.
2013-03-01
We present the stabilization of the beatnote of an Er,Yb:glass Dual Frequency Laser at 1.53 μm with optical fiber delay lines. Instead of standard optoelectronics oscillators, this architecture does not need RF filter and offers a wide tunability from 2.5 to 5.5 GHz. Thank to a fine analysis of the laser RIN to phase noise conversion in the photodiodes, the expected RF-amplifiers noise limit is reached with a phase noise power spectral density of -25 dBc/Hz at 10 Hz (respectively -110 dBc/Hz at 10 kHz) from the carrier over the whole tuning range. Implementation of a double fiber coil architecture improves the oscillator spectral purity: the phase noise reaches a level of -35 dBc/Hz at 10 Hz (respectively -112 dBc/Hz respectively 10 kHz) from the carrier.
18. Optimizing chirped laser pulse parameters for electron acceleration in vacuum
Energy Technology Data Exchange (ETDEWEB)
Akhyani, Mina; Jahangiri, Fazel; Niknam, Ali Reza; Massudi, Reza, E-mail: [email protected] [Laser and Plasma Research Institute, Shahid Beheshti University, Tehran 1983969411 (Iran, Islamic Republic of)
2015-11-14
Electron dynamics in the field of a chirped linearly polarized laser pulse is investigated. Variations of electron energy gain versus chirp parameter, time duration, and initial phase of laser pulse are studied. Based on maximizing laser pulse asymmetry, a numerical optimization procedure is presented, which leads to the elimination of rapid fluctuations of gain versus the chirp parameter. Instead, a smooth variation is observed that considerably reduces the accuracy required for experimentally adjusting the chirp parameter.
19. Optimization and control of electron beams from laser wakefield accelerations using asymmetric laser pulses
Science.gov (United States)
Gopal, K.; Gupta, D. N.
2017-10-01
Optimization and control of electron beam quality in laser wakefield acceleration are explored by using a temporally asymmetric laser pulse of the sharp rising front portion. The temporally asymmetric laser pulse imparts stronger ponderomotive force on the ambient plasma electrons. The stronger ponderomotive force associated with the asymmetric pulse significantly affects the injection of electrons into the wakefield and consequently the quality of the injected bunch in terms of injected charge, mean energy, and emittance. Based on particle-in-cell simulations, we report to generate a monoenergetic electron beam with reduced emittance and enhanced charge in laser wakefield acceleration using an asymmetric pulse of duration 30 fs.
20. Vanderbilt free electron laser project in biomedical and materials research
Science.gov (United States)
Haglund, Richard F.; Tolk, N. H.
1988-06-01
The Medical Free Electron Laser Program was awarded to develop, construct and operate a free-electron laser facility dedicated to biomedical and materials studies, with particular emphases on: fundamental studies of absorption and localization of electromagnetic energy on and near material surfaces, especially through electronic and other selective, non-statistical processes; non-thermal photon-materials interactions (e.g., electronic bond-breaking or vibrational energy transfer) in physical and biological materials as well as in long-wavelength biopolymer dynamics; development of FEL-based methods to study drug action and to characterize biomolecular properties and metabolic processes in biomembranes; clinical applications in otolaryngology, neurosurgery, ophthalmology and radiology stressing the use of the laser for selective laser-tissue, laser-cellular and laser-molecule interactions in both therapeutic and diagnostic modalities.
1. Development of a far infrared free electron laser based on compact microtron
Energy Technology Data Exchange (ETDEWEB)
Lee, Jong Min; Lee, Byung Cheol; Kim, Sun Kook; Jeong, Young Uk; Cho, Sung Oh
1998-11-01
As a result of the cooperative research between KAERI and BINP, a FIR FEL having tunable range of output wavelength from 30 {mu}m to 50 {mu}m. The peak power is 10kW at maximum. The micropulse width is 10 ps and the macropulse width is 5 {mu}s. The repetition rate of micropulses is 2.8 GHz and that of macropulses is 1 - 10 Hz. In addition to the FIR FEL system, many key technologies of high power FELs have been developed. Among them are there electron accelerator technology, design and optimization of electron beamline, design of undulator, measurement of magnetic field of undulators, high-voltage technology, optical cavity, etc.. (author). 10 refs., 11 tabs., 48figs.
2. Power Beaming, Orbital Debris Removal, and Other Space Applications of a Ground Based Free Electron Laser
Science.gov (United States)
2010-03-01
considerable biological damage, but the collisions involved can generate neutrons and even gamma radiation in some cases. Therefore, the beam dump...at energies low enough so that neutrons are not produced. 20 B. FEL RESONANCE CONDITION For optimum energy exchange between the electrons and...surfaces to mitigate the risk of damage from collisions with them [48]. 97 Figure 40, Figure 41, and Figure 42 display an instantaneous “ snap -shot” of
NARCIS (Netherlands)
van Oerle, Bartholomeus Mathias; van Oerle, B.M.
1997-01-01
In a free electron laser, coherent radiation is generated by letting an electron beam propagate through an alternating magnetic field. The magnetic field is created by a linear array of magnets, which is called an undulator or a wiggler. The wavelength of the laser radiation depends on the amplitude
4. Laser electron collider within a micro-channel
Science.gov (United States)
Ji, Liangliang
2017-10-01
We propose a laser-electron collider based on a laser-driven micro-channel-plate target. In this unique geometry, electrons accelerated within the channel can collide head-on with the laser reflected from a foil attached onto the rear target surface. The simple scheme allows for efficient generation of gamma-photons and most importantly, the observing of radiation-reaction effect for the first time. It resolves the aligning and time synchronization challenges for laser-electron colliding scenarios involving two light/electron beams. We predict that a single 5PW laser is sufficient to make radiation-reaction effect measurable. A principle-of-proof experiment was conducted at a currently available 200TW laser system. The superior acceleration of electrons with the novel micro-channel structure was confirmed, showing enhanced electron cut-off energies and slope temperatures compared to ordinary flat interfaces. The results set forth the basis for radiation-reaction measurement from laser-electron colliding in upcoming multi-petawatt laser systems.
5. Time-resolved electron spectrum diagnostics for a free-electron laser
NARCIS (Netherlands)
Gillespie, W. A.; MacLeod, A. M.; Martin, P. F.; van der Meer, A. F. G.; van Amersfoort, P. W.
1996-01-01
Time-resolved electron-beam diagnostics have been developed for use with free-electron lasers (FELs) and associated electron sources, based on the techniques of secondary electron emission and optical transition radiation (OTR). The 32-channel OTR detector forms part of a high-resolution (0.18%)
6. [Comparison of adaptation and microstructure of titanium upper complete denture base fabricated by selecting laser melting and electron beam melting].
Science.gov (United States)
Ye, Y; Xiong, Y Y; Zhu, J R; Sun, J
2017-06-09
Objective: To fabricate Ti alloy frameworks for a maxillary complete denture with three-dimensional printing (3DP) technique, such as selective laser melting (SLM) and electron beam melting (EBM), and to evaluate the microstructure of these frameworks and their adaptation to the die stone models. Methods: Thirty pairs of edentulous casts were divided into 3 groups randomly and equally. In each group, one of the three techniques (SLM, EBM, conventional technique) was used to fabricate Ti alloy frameworks. The base-cast sets were transversally sectioned into 3 sections at the distal of canines, mesial of first molars, and the posterior palatal zone. The gap between the metal base and cast was measured in the 3 sections. Stereoscopic microscope was used to measure the gap. Three pieces of specimens of 5 mm diameter were fabricated with Ti alloy by SLM, EBM and the traditional casting technology (as mentioned above). Scanning electron microscope (SEM) was used to evaluate the differences of microstructure among these specimens. Results: The gaps between the metal base and cast were (99.4±17.0), (98.2±26.1), and (99.6± 16.1) μm in conventional method; (99.4 ± 22.8), (83.1 ± 19.3), and (103.3 ± 13.8) μm in SLM technique; (248.3±70.3), (279.1±71.9), and (189.1±31.6) μm in EBM technique. There was no statistical difference in the value of gaps between SLM Ti alloy and conventional method Ti alloy group (P>0.05). There was statistical difference among EBM Ti alloy, conventional method Ti alloy and SLM Ti alloy group (P<0.05). The SLM Ti alloy showed more uniform and compact microstructure than the cast Ti alloy and EBM Ti alloy did. Conclusions: SLM technique showed initial feasibility to manufacture the dental base of complete denture. The mechanical properties and microstructure of the denture frameworks prepared by SLM indicate that these dentures are appropriate for clinical use. EBM technique is inadequate to make a complete denture now.
7. Biological applications of ultraviolet free-electron lasers
Energy Technology Data Exchange (ETDEWEB)
Sutherland, J.C.
1997-10-01
This review examines the possibilities for biological research using the three ultraviolet free-electron lasers that are nearing operational status in the US. The projected operating characteristics of major interest in biological research of the free-electron lasers at Brookhaven National Laboratory, the Thomas Jefferson National Accelerator Facility, and Duke University are presented. Experimental applications in the areas of far- and vacuum ultraviolet photophysics and photochemistry, structural biology, environmental photobiology, and medical research are discussed and the prospects for advances in these areas, based upon the characteristics of the new ultraviolet free-electron lasers, are evaluated.
8. Free electron laser and superconductivity
CERN Document Server
Iwata, A
2003-01-01
The lasing of the first free-electron laser (FEL) in the world was successfully carried out in 1977, so the history of FELs as a light source is not so long. But FELs are now utilized for research in many scientific and engineering fields owing to such characteristics as tunability of the wavelength, and short pulse and high peak power, which is difficult utilizing a common light source. Research for industrial applications has also been carried out in some fields, such as life sciences, semiconductors, nano-scale measurement, and others. The task for the industrial use of FEL is the realization of high energy efficiency and high optical power. As a means of promoting realization, the combining of an FEL and superconducting linac is now under development in order to overcome the thermal limitations of normal-conducting linacs. Further, since tuning the wavelength is carried out by changing the magnetic density of the undulator, which is now induced by moving part of the stack of permanent magnets, there is un...
9. Theoretical study of free electron laser physics
Energy Technology Data Exchange (ETDEWEB)
Yoo, Jae Gwon; Cho, Sung Oh; Jeong, Young Uk; Kim, Sun Kook; Lee, Byung Cheol; Cha, Byung Heon; Lee, Jong Min [Korea Atomic Energy Research Institute, Taejeon (Korea)
2000-04-01
A theoretical study of free electron laser physics is presented in this report. In particular, an analysis is given of the free electron laser with a linearly polarized magnetic wiggler. We describe the basic electron dynamics and gain mechanism in a free electron laser by solving the one-body classical Lorentz force equations in the presence of a periodic magnetic field and a plane electromagnetic wave. Phase space paths for electrons analogously related to those of a simple pendulum are used to describe the laser gain and saturation, and the evolution of the electron beam energy and position distributions. We present an analysis of the single-mode problem and a self-consistent nonlinear treatment of the finite transverse dimensional effects associated with the free electron laser in a steady state. Results computed by applying an external D.C. electric field to the system are discussed for investigating efficiency enhancement of the free electron lasers. Finally optical guiding effect in small signal regime is described to investigate the possibility of amplifying radiation fields in very long wigglers for large gain and high extraction efficiency. 14 refs., 45 figs. (Author)
10. Proceedings of the Laser Issues for Electron RF Photoinjectors Workshop
CERN Document Server
Bolton, P
2003-01-01
The Linac Coherent Light Source (LCLS) proposed for SLAC is a SASE FEL designed to generate high brightness, coherent, ultrashort x-ray pulses. The injector of choice is the RF photoinjector, which is capable of producing suitably low emittance electron beams. It is well established that the performance of the SASE FEL depends critically on properties of the electron beam generated by the injector and therefore on the injector laser beam parameters. This workshop was established specifically to provide a forum for discussion of photoinjector laser systems. Laser design requirements and technical challenges common to RF photoinjectors were highlighted and some solutions were explored. This included not only details of laser systems but also those of laser-based diagnostics envisioned for monitoring ultrashort electron microbunches on a single shot basis. Sixty-one registrants representing twenty-three institutions from Italy, Germany, Japan and the United States attended. The program listing shows that the twe...
11. Laser-electron Compton interaction in plasma channels
Energy Technology Data Exchange (ETDEWEB)
Pogorelsky, I.V.; Ben-Zvi, I. [Brookhaven National Lab., Upton, NY (United States); Hirose, T. [Tokyo Metropolitan Univ. (Japan). Physics Dept.
1998-10-01
A concept of high intensity femtosecond laser synchrotron source (LSS) is based on Compton backscattering of focused electron and laser beams. The short Rayleigh length of the focused laser beam limits the length of interaction to a few picoseconds. However, the technology of the high repetition rate high-average power picosecond lasers required for high put through LSS applications is not developed yet. Another problem associated with the picosecond laser pulses is undesirable nonlinear effects occurring when the laser photons are concentrated in a short time interval. To avoid the nonlinear Compton scattering, the laser beam has to be split, and the required hard radiation flux is accumulated over a number of consecutive interactions that complicates the LSS design. In order to relieve the technological constraints and achieve a practically feasible high-power laser synchrotron source, the authors propose to confine the laser-electron interaction region in the extended plasma channel. This approach permits to use nanosecond laser pulses instead of the picosecond pulses. That helps to avoid the nonlinear Compton scattering regime and allows to utilize already existing technology of the high-repetition rate TEA CO{sub 2} lasers operating at the atmospheric pressure. They demonstrate the advantages of the channeled LSS approach by the example of the prospective polarized positron source for Japan Linear Collider.
12. Resonant Laser Incisions: Molecular Targets Using the Free Electron Laser
Science.gov (United States)
Reinisch, Lou; Bryant, Grady; Ossoff, Robert H.
1996-03-01
Laser ablation of tissue for medical incisions is normally concerned with the energy absorption and the subsequent vaporization of intracellular water. Using Fourier transform infrared spectroscopy, we have identified specific non-water resonances within tissues. Then, using the Vanderbilt Free Electron Laser (wavelength tunable from 2 to 10 microns) and our Computer Assisted Surgical Techniques program (to standardize the laser delivery), we have targeted specific molecular resonances for laser incisions and tissue removal. Using both acute and chronic studies, we can map out the resonant action spectrum to improve surgical outcomes. We have modeled these ablation mechanisms and working to establish the link between these ablation mechanisms and wound healing. This work has been supported, in part, by a grant from the Department of Defense, Medical Free Electron Laser Program, ONR Grant #N000149411023.
13. Rationalizing the photophysical properties of BODIPY laser dyes via aromaticity and electron-donor-based structural perturbations
Energy Technology Data Exchange (ETDEWEB)
Waddell, Paul G.; Liu, Xiaogang; Zhao, Teng; Cole, Jacqueline M.
2015-05-01
The absorption and fluorescence properties of six boron dipyrromethene (BODIPY) laser dyes with simple non-aromatic substituents are rationalized by relating them to observable structural perturbations within the molecules of the dyes. An empirical relationship involving the structure and the optical properties is derived using a combination of single-crystal X-ray diffraction data, quantum chemical calculations and electronic constants: i.e. the tendency of the pyrrole bond lengths towards aromaticity and the UV-vis absorption and fluorescence wavelengths correlating with the electron-donor properties of the substituents. The effect of molecular conformation on the solid-state optical properties of the dyes is also discussed. The findings in this study also demonstrate the usefulness and limitations of using crystal structure data to develop structure-property relationships in this class of optical materials, contributing to the growing effort to design optoelectronic materials with tunable properties via molecular engineering.
14. Single-pulse femtosecond laser Bessel beams drilling of high-aspect-ratio microholes based on electron dynamics control
Science.gov (United States)
Zhao, Weiwei; Li, Xiaowei; Xia, Bo; Yan, Xueliang; Han, Weina; Lu, Yongfeng; Jiang, Lan
2014-11-01
Microholes drilling has attracted extensive research efforts for its broad applications in photonics, microfluidics, optical fibers and many other fields. A femtosecond (fs) laser is a promising tool for high-precision materials processing with reduced recast/microcracks and minimized heat affected zones. But there remain many challenges in hole drilling using conventional fs laser with Gaussian beams, such as low aspect ratio and taper effects. We report small-diameter and high-aspect-ratio microholes with taper free drilling in PMMA (polymethyl methacrylate) using single-pulse fs laser Bessel beams. Axicon is used to transform Gaussian beams into Bessel beams, which then irradiate in the sample by a telescope consisting of plano-convex lens and microscope objective. Using this technique, we enhance the aspect ratio of microholes by 55 times as compared with Gaussian beams. We attribute this high aspect ratio and high quality microholes formation to the unique spatial intensity distribution and propagation stability of Bessel beams, which can effectively adjust the transient localized electron density distribution leading to a long and uniform localized-interacted zone. By using the optimized pulse energy and focal depth position, the microholes diameter ranges between 1.4-2.1 μm and the aspect ratio can exceed 460. This efficient technique is of great potentials for fabrication of microphotonics devices and microfluidics.
15. Status of and Future Plans for the CERN Linac4 Emittance Meter based on Laser Electron-detachment and a Diamond Strip-detector
CERN Document Server
Bravin, E; Raich, U; Roncarolo, F; Zocca, F; Gibson, S; Kruchinin, KO; Bosco, A; Boorman, G; Griesmayer, E
2014-01-01
LINAC4 has started its staged commissioning at CERN. After completion it will accelerate high brightness H- beams to 160 MeV. To measure the transverse profile and emittance of the beam, a non-destructive method based on electron photo detachment is proposed, using a pulsed, fibre-coupled laser to strip electrons from the H- ions. The laser can be focused and scanned through the H- beam, acting like a conventional slit. A downstream dipole separates the neutral H0 beamlet, created by the laser interaction, from the main H- beam, so that it can be measured by a diamond stripdetector. Combining the H0 beamlet profiles with the laser position allows the transverse emittance to be reconstructed. A prototype of this instrument was tested while commissioning the LINAC4 at 3 and 12 MeV. In this paper we shall describe the experimental setup, challenges and results of the measurements, and also address the characteristics and performance of the diamond strip-detector subsystem. In addition, the proposal for a permane...
16. Direct longitudinal laser acceleration of electrons in free space
Directory of Open Access Journals (Sweden)
Sergio Carbajo
2016-02-01
Full Text Available Compact laser-driven accelerators are pursued heavily worldwide because they make novel methods and tools invented at national laboratories widely accessible in science, health, security, and technology [V. Malka et al., Principles and applications of compact laser-plasma accelerators, Nat. Phys. 4, 447 (2008]. Current leading laser-based accelerator technologies [S. P. D. Mangles et al., Monoenergetic beams of relativistic electrons from intense laser-plasma interactions, Nature (London 431, 535 (2004; T. Toncian et al., Ultrafast laser-driven microlens to focus and energy-select mega-electron volt protons, Science 312, 410 (2006; S. Tokita et al. Single-shot ultrafast electron diffraction with a laser-accelerated sub-MeV electron pulse, Appl. Phys. Lett. 95, 111911 (2009] rely on a medium to assist the light to particle energy transfer. The medium imposes material limitations or may introduce inhomogeneous fields [J. R. Dwyer et al., Femtosecond electron diffraction: “Making the molecular movie,”, Phil. Trans. R. Soc. A 364, 741 (2006]. The advent of few cycle ultraintense radially polarized lasers [S. Carbajo et al., Efficient generation of ultraintense few-cycle radially polarized laser pulses, Opt. Lett. 39, 2487 (2014] has ushered in a novel accelerator concept [L. J. Wong and F. X. Kärtner, Direct acceleration of an electron in infinite vacuum by a pulsed radially polarized laser beam, Opt. Express 18, 25035 (2010; F. Pierre-Louis et al. Direct-field electron acceleration with ultrafast radially polarized laser beams: Scaling laws and optimization, J. Phys. B 43, 025401 (2010; Y. I. Salamin, Electron acceleration from rest in vacuum by an axicon Gaussian laser beam, Phys. Rev. A 73, 043402 (2006; C. Varin and M. Piché, Relativistic attosecond electron pulses from a free-space laser-acceleration scheme, Phys. Rev. E 74, 045602 (2006; A. Sell and F. X. Kärtner, Attosecond electron bunches accelerated and
17. Intrinsic normalized emittance growth in laser-driven electron accelerators
Directory of Open Access Journals (Sweden)
M. Migliorati
2013-01-01
Full Text Available Laser-based electron sources are attracting strong interest from the conventional accelerator community due to their unique characteristics in terms of high initial energy, low emittance, and significant beam current. Extremely strong electric fields (up to hundreds of GV/m generated in the plasma allow accelerating gradients much higher than in conventional accelerators and set the basis for achieving very high final energies in a compact space. Generating laser-driven high-energy electron beam lines therefore represents an attractive challenge for novel particle accelerators. In this paper we show that laser-driven electrons generated by the nowadays consolidated TW laser systems, when leaving the interaction region, are subject to a very strong, normalized emittance worsening which makes them quickly unusable for any beam transport. Furthermore, due to their intrinsic beam characteristics, controlling and capturing the full beam current can only be achieved improving the source parameters.
18. Experimental and theoretical studies of picosecond laser interactions with electronic materials-laser ablation
Energy Technology Data Exchange (ETDEWEB)
Mao, Samuel S. [Univ. of California, Berkeley, CA (United States)
2000-05-01
Lasers having picosecond and shorter pulse duration are receiving much attention due to their capabilities for direct-write micromachining on many materials with minimal substrate damage. Substantial progress has been made in the understanding of laser ablation processes, particularly the creation of plasmas that often shield the target and reduce the material processing efficiency at nanosecond time scales. However, a considerable challenge that still remains is the understanding of the underlying mechanisms during picosecond laser interactions with electronic solids. In this work we first study picosecond laser-induced electron emission from semiconductor surfaces. A theoretical model was set up based on carrier transport inside the semiconductor material during picosecond laser-semiconductor interactions. We demonstrate that nonequilibrium carrier dynamics plays a significant role for picosecond, as well as short nanosecond, laser induced electron emission from semiconductors. Photoelectric effect is found to be responsible for electron emission at low incident laser fluences, whereas thermionic emission is dominant at higher fluences. We have also performed experimental and theoretical studies on the formation and subsequent evolution of plasmas during laser-metal interactions at the picosecond time scale. Using picosecond time-resolved shadowgrams ahd interferograms, a novel type of plasma is observed, which has an electron density on the order of 1020cm-3.The origin of this picosecond plasma is attributed to gas breakdown, which is caused by laser-induced electron emission fi-om the target surface. After the laser pulse is completed, the longitudinal expansion of the plasma is suppressed. This suppression is found to result from an electric field above the target that prevents, after laser irradiation, fbrther movement of the electrons inside the plasma. Measurements of lateral plasma expansion indicate that the picosecond plasma may absorb
19. Undulators and free-electron lasers
CERN Document Server
Luchini, P
1990-01-01
This book is a reference text for all those working in free-electron laser research as well as being a learning aid for physicists and graduate students who wish an introduction to this field. Only a basic understanding of relativistic mechanics and electromagnetism is presupposed. After an overview of early developments and general principles of operation, the different models that can be used to describe free-electron lasers are presented, organized according to their range of applicability. The relevent conceptual and mathematical constructs are built up from first principles with attention to obtaining the practically important results in a simple but rigorous way. Interaction of the undulator with the driving electron accelerator and the laser cavity and design of undulator magnets are treated and an overview is given of some typical experiments.
20. Measurement of the relaxation time of hot electrons in laser-solid interaction at relativistic laser intensities
Energy Technology Data Exchange (ETDEWEB)
Chen, H; Shepherd, R; Chung, H K; Dyer, G; Faenov, A; Fournier, K B; Hansen, S B; Hunter, J; Kemp, A; Pikuz, T; Ping, Y; Widmann, K; Wilks, S C; Beiersdorfer, P
2006-08-22
The authors have measured the relaxation time of hot electrons in short pulse laser-solid interactions using a picosecond time-resolved x-ray spectrometer and a time-integrated electron spectrometer. Employing laser intensities of 10{sup 17}, 10{sup 18}, and 10{sup 19} W/cm{sup 2}, they find increased laser coupling to hot electrons as the laser intensity becomes relativistic and thermalization of hot electrons at timescales on the order of 10 ps at all laser intensities. They propose a simple model based on collisional coupling and plasma expansion to describe the rapid relaxation of hot electrons. The agreement between the resulting K{sub {alpha}} time-history from this model with the experiments is best at highest laser intensity and less satisfactory at the two lower laser intensities.
1. Precision laser processing for micro electronics and fiber optic manufacturing
Science.gov (United States)
Webb, Andrew; Osborne, Mike; Foster-Turner, Gideon; Dinkel, Duane W.
2008-02-01
The application of laser based materials processing for precision micro scale manufacturing in the electronics and fiber optic industry is becoming increasingly widespread and accepted. This presentation will review latest laser technologies available and discuss the issues to be considered in choosing the most appropriate laser and processing parameters. High repetition rate, short duration pulsed lasers have improved rapidly in recent years in terms of both performance and reliability enabling flexible, cost effective processing of many material types including metal, silicon, plastic, ceramic and glass. Demonstrating the relevance of laser micromachining, application examples where laser processing is in use for production will be presented, including miniaturization of surface mount capacitors by applying a laser technique for demetalization of tracks in the capacitor manufacturing process and high quality laser machining of fiber optics including stripping, cleaving and lensing, resulting in optical quality finishes without the need for traditional polishing. Applications include telecoms, biomedical and sensing. OpTek Systems was formed in 2000 and provide fully integrated systems and sub contract services for laser processes. They are headquartered in the UK and are establishing a presence in North America through a laser processing facility in South Carolina and sales office in the North East.
2. Quantum aspects of the free electron laser
Energy Technology Data Exchange (ETDEWEB)
Gaiba, R.
2007-03-15
We study the role of Quantum Mechanics in the physics of Free Electron Lasers. While the Free Electron Laser (FEL) is usually treated as a classical device, we review the advantages of a quantum formulation of the FEL. We then show the existence of a regime of operation of the FEL that can only be described using Quantum Mechanics: if the dimensionless quantum parameter anti {rho} is smaller than 1, then in the 1-dimensional approximation the Hamiltonian that describes the FEL becomes equivalent to the Hamiltonian of a two-level system coupled to a radiation field. We give analytical and numerical solutions for the photon statistics of a Free Electron Laser operating in the quantum regime under various approximations. Since in the quantum regime the momentum of the electrons is discrete, we give a description of the electrons in phase space by introducing the Discrete Wigner Function. We then drop the assumption of a mono-energetic electron beam and describe the general case of a initial electron energy spread G({gamma}). Numerical analysis shows that the FEL quantum regime is observed only when the width of the initial momentum distribution is smaller than the momentum of the emitted photons. Both the analytical results in the linear approximation and the numerical simulations show that only the electrons close to a certain resonant energy start to emit photons. This generates the so-called Hole-burning effect in the electrons energy distribution, as it can be seen in the simulations we provide. Finally, we present a brief discussion about a fundamental uncertainty relation that ties the electron energy spread and the electron bunching. (orig.)
3. Rippled beam free electron Laser Amplifier
Energy Technology Data Exchange (ETDEWEB)
Carlsten, Bruce E.
1998-04-21
A free electron laser amplifier provides a scalloping annular electron beam that interacts with the axial electric field of a T{sub 0n} mode. A waveguide defines an axial centerline and . A solenoid arranged about the waveguide produces an axial constant magnetic field within the waveguide. An electron beam source outputs a annular electron beam that interacts with the axial magnetic field to have an equilibrium radius and a ripple radius component having a variable radius with a ripple period along the axial centerline. An rf source outputs an axial electric field that propagates within the waveguide coaxial with the electron beam and has a radial mode that interacts at the electron beam at the equilibrium radius component of the electron beam.
4. Short wavelength free electron lasers in 1998
OpenAIRE
Colson, W.B.
1999-01-01
A table is presented that describes the characteristics of 58 short wavelength free electron lasers, operating and proposed, around the world. The author is grateful for support of this work by the Naval Postgraduate School and the Directed Energy Weapons Group, SPAWAR, U.S. Navy.
5. Applications for Energy Recovering Free Electron Lasers
Energy Technology Data Exchange (ETDEWEB)
George Neil
2007-08-01
The availability of high-power, high-brilliance sources of tunable photons from energy-recovered Free Electron Lasers is opening up whole new fields of application of accelerators in industry. This talk will review some of the ideas that are already being put into production, and some of the newer ideas that are still under development.
6. Plasma wave undulator for laser-accelerated electrons
CERN Document Server
Corde, S; 10.1063/1.3569827
2011-01-01
Laser-plasma accelerators have become compact sources of ultrashort electron bunches at energies up to the gigaelectronvolt range thanks to the remarkable progress made over the past decade. A direct application of these electron bunches is the production of short pulse x-ray radiation sources. In this letter, we study a fully optically driven x-ray source based on the combination of a laser-plasma accelerator and a plasma wave undulator. The longitudinal electric field of a laser-generated plasma wave is used to wiggle electrons transversally. The period of this plasma undulator being equal to the plasma wavelength, tunable photon energies in the 10 keV range can be achieved with electron energies in the 100-200 MeV range. Considering a 10s TW class femtosecond laser system, undulators with a strength parameter K~0.5 and with about ten periods can be combined with a laser-plasma accelerator, resulting in several 10^-2 emitted x-ray photons per electron.
7. Performance of the thermionic RF gun injector for the linac-based IR free electron laser at the FEL-SUT
CERN Document Server
Oda, F; Kawai, M; Koike, H; Sobajima, M
2001-01-01
Kawasaki Heavy Industries, Ltd. (KHI) has developed a linac-based compact IR free electron laser device and has installed it in the FEL-SUT (IR FEL Research Center of Science University of Tokyo). The FEL device adopts a combination of a multi-cell RF gun with a thermionic cathode and an alpha-magnet as an injector. The fundamental design of this RF gun is the pi/2 mode standing wave structure. It has two accelerating cells and a coupling cell located on the beam axis, a so-called 'on axis coupled structure' (OCS). Characteristics of momentum distribution and micropulse bunch length of the electron beam are compared with beam dynamics simulation results in this paper. We succeeded in obtaining sufficient peak current for FEL lasing with this injector, and the first lasing was achieved on 6 July 2000.
8. A Submillimeter Free Electron Laser
Science.gov (United States)
1985-09-30
radiation fields sinale- etage M design and b) the uv-visible- generated by a single electron have an angar ir region using a two- etage M device...the UCSB M -dill be tested as a two- etage device. The range of wavelength that will be covered with this mode of operation is from the vacuum
9. Free electron lasers for transmission of energy in space
Science.gov (United States)
Segall, S. B.; Hiddleston, H. R.; Catella, G. C.
1981-01-01
A one-dimensional resonant-particle model of a free electron laser (FEL) is used to calculate laser gain and conversion efficiency of electron energy to photon energy. The optical beam profile for a resonant optical cavity is included in the model as an axial variation of laser intensity. The electron beam profile is matched to the optical beam profile and modeled as an axial variation of current density. Effective energy spread due to beam emittance is included. Accelerators appropriate for a space-based FEL oscillator are reviewed. Constraints on the concentric optical resonator and on systems required for space operation are described. An example is given of a space-based FEL that would produce 1.7 MW of average output power at 0.5 micrometer wavelength with over 50% conversion efficiency of electrical energy to laser energy. It would utilize a 10 m-long amplifier centered in a 200 m-long optical cavity. A 3-amp, 65 meV electrostatic accelerator would provide the electron beam and recover the beam after it passes through the amplifier. Three to five shuttle flights would be needed to place the laser in orbit.
10. Nonlinear optics with coherent free electron lasers
Science.gov (United States)
Bencivenga, F.; Capotondi, F.; Mincigrucci, R.; Cucini, R.; Manfredda, M.; Pedersoli, E.; Principi, E.; Simoncig, A.; Masciovecchio, C.
2016-12-01
We interpreted the recent construction of free electron laser (FELs) facilities worldwide as an unprecedented opportunity to bring concepts and methods from the scientific community working with optical lasers into the domain of x-ray science. This motivated our efforts towards the realization of FEL-based wave-mixing applications. In this article we present new extreme ultraviolet transient grating (X-TG) data from vitreous SiO2, collected using two crossed FEL pulses (photon frequency 38 eV) to generate the X-TG and a phase matched optical probing pulse (photon frequency 3.1 eV). This experiment extends our previous investigation, which was carried out on a nominally identical sample using a different FEL photon frequency (45 eV) to excite the X-TG. The present data are featured by a peak intensity of the X-TG signal substantially larger than that previously reported and by slower modulations of the X-TG signal at positive delays. These differences could be ascribed to the different FEL photon energy used in the two experiments or to differences in the sample properties. A systematic X-TG study on the same sample as a function of the FEL wavelength is needed to draw a consistent conclusion. We also discuss how the advances in the performance of the FELs, in terms of generation of fully coherent photon pulses and multi-color FEL emission, may push the development of original experimental strategies to study matter at the femtosecond-nanometer time-length scales, with the unique option of element and chemical state specificity. This would allow the development of advanced experimental tools based on wave-mixing processes, which may have a tremendous impact in the study of a large array of phenomena, ranging from nano-dynamics in complex materials to charge and energy transfer processes.
11. Electron Impact of Laser Media.
Science.gov (United States)
1980-08-14
60 10 first Porn approximation. E trx tiqy oFVI 0.4" 0. \\\\ ... * 94 D. E. Golden and N. C Stepb together with the calculations of Baluja and McDowell...monochromator and are detected by a RCA C31034A-02 ported coincidence measurements between energy aria- photomultiplier tube (PMT) cooled to -20 ’C. The pho...The recent R-matrix calculation of Fon Conventional tube lenses focus the electron beam et al.14 is in fair agreement with the small-angle onto the
12. Desorption by Femtosecond Laser Pulses : An Electron-Hole Effect?
OpenAIRE
D. M., NEWNS; T. F., HEINZ; J. A., MISEWICH; IBM Research Division, T. J. Watson Research Center; IBM Research Division, T. J. Watson Research Center; IBM Research Division, T. J. Watson Research Center
1992-01-01
Desorption of molecules from metal surfaces induced by femtosecond visible laser pulses has been reported. Since the lattice temperature rise is insufficient to explain desorption, an electronic mechanism is clearly responsible. It is shown that a theory based on direct coupling between the center-of-mass degree of freedom of the adsorbate and the electron-hole excitations of the substrate provides a satisfactory explanation of the various experimental findings.
13. Physics of Laser-driven plasma-based acceleration
Energy Technology Data Exchange (ETDEWEB)
Esarey, Eric; Schroeder, Carl B.
2003-06-30
The physics of plasma-based accelerators driven by short-pulse lasers is reviewed. This includes the laser wake-field accelerator, the plasma beat wave accelerator, the self-modulated laser wake-field accelerator, and plasma waves driven by multiple laser pulses. The properties of linear and nonlinear plasma waves are discussed, as well as electron acceleration in plasma waves. Methods for injecting and trapping plasma electrons in plasma waves are also discussed. Limits to the electron energy gain are summarized, including laser pulse direction, electron dephasing, laser pulse energy depletion, as well as beam loading limitations. The basic physics of laser pulse evolution in underdense plasmas is also reviewed. This includes the propagation, self-focusing, and guiding of laser pulses in uniform plasmas and plasmas with preformed density channels. Instabilities relevant to intense short-pulse laser-plasma interactions, such as Raman, self-modulation, and hose instabilities, are discussed. Recent experimental results are summarized.
Science.gov (United States)
Dorschner, Terry A.; Lambert, Larry Q.; Smith, Irl W.; Harris, Clarke E.
1999-05-01
The recent development of optical phased arrays (OPAs) enables practical, electronically programmable, control of laser beams for laser radar and other advanced optical sensors. OPAs are the direct analog of microwave phased array antennas; they are electronically programmable optical elements that control the phase distribution on an optical aperture in order to control beam direction and shape. Operating principles and construction of OPAs are briefly described and current and potential performance capabilities are summarized. An OPA supports spatial-domain beam control such as agile or continuous scanning patterns, adaptive electronic focus control, and far-field beam shape control, as well as the generation of multiple beams from a single input beam (pattern generation, or fanout). OPAs also support time-domain beam control, including precision time delay or positioning of short pulses, pulse compression and expansion, and the generation of dense pulse bursts from a single pulse. All of these functions are software controllable, which enables mission-flexible and mission-adaptive optical systems, including so-called 'smart' optical systems with autonomous alignment and calibration capabilities. These and other electronically programmable capabilities are discussed. As a concrete example of an advanced sensor enabled by the OPA, the potential for an adaptable-format, high-resolution, multi-beam laser radar with no moving parts is discussed.
15. Polarization in free electron lasers
Energy Technology Data Exchange (ETDEWEB)
Papadichev, V.A. [Lebedev Physical Institute, Moscow (Russian Federation)
1995-12-31
Polarization of electromagnetic radiation is required very often in numerous scientific and industrial applications: studying of crystals, molecules and intermolecular interaction high-temperature superconductivity, semiconductors and their transitions, polymers and liquid crystals. Using polarized radiation allows to obtain important data (otherwise inaccessible) in astrophysics, meteorology and oceanology. It is promising in chemistry and biology for selective influence on definite parts of molecules in chain synthesis reactions, precise control of various processes at cell and subcell levels, genetic engineering etc. Though polarization methods are well elaborated in optics, they can fail in far-infrared, vacuum-ultraviolet and X-ray regions because of lack of suitable non-absorbing materials and damaging of optical elements at high specific power levels. Therefore, it is of some interest to analyse polarization of untreated FEL radiation obtained with various types of undulators, with and without axial magnetic field. The polarization is studied using solutions for electron orbits in various cases: plane or helical undulator with or without axial magnetic field, two plane undulators, a combination of right- and left-handed helical undulators with equal periods, but different field amplitudes. Some examples of how a desired polarization (elliptical circular or linear) can be obtained or changed quickly, which is necessary in many experiments, are given.
16. Bunch decompression for laser-plasma driven free-electron laser demonstration schemes
Directory of Open Access Journals (Sweden)
T. Seggebrock
2013-07-01
Full Text Available X-ray free-electron lasers (FELs require a very high electron beam quality in terms of emittance and energy spread. Since 2004 high quality electrons produced by laser-wakefield accelerators have been demonstrated, but the electron quality up to now did not allow the operation of a compact x-ray FEL using these electrons. Maier et al. [Phys. Rev. X 2, 031019 (2012PRXHAE2160-330810.1103/PhysRevX.2.031019] suggested a concept for a proof-of-principle experiment allowing FEL operation in the vacuum ultraviolet range based on an optimized undulator and bunch decompression using electron bunches from a laser-plasma accelerator as currently available. In this paper we discuss in more detail how a chicane can be used as a bunch stretcher instead of a bunch compressor to allow the operation of a laser-wakefield accelerator driven FEL using currently available electrons. A scaling characterizing the impact of bunch decompression on the gain length is derived and the feasibility of the concept is tested numerically in a demanding scenario.
17. Chaos in free electron laser oscillators
Energy Technology Data Exchange (ETDEWEB)
Bruni, C. [Univ Paris 11, LAL, UMR 8607, F-91898 Orsay, (France); Bachelard, R.; Couprie, M.E. [Synchrotron SOLEIL, F-91192 Gif Sur Yvette, (France); Garzella, D. [CEA DSM DRECAM SPAM, F-91191 Gif Sur Yvette, (France); Orlandi, G.L. [CR Frascati FIM FISACC, ENEA, I-00044 Frascati, (Italy)
2009-07-01
The chaotic nature of a storage-ring free electron laser (FEL) is investigated. The derivation of a low embedding dimension for the dynamics allows the low-dimensionality of this complex system to be observed, whereas its unpredictability is demonstrated, in some ranges of parameters, by a positive Lyapounov exponent. The route to chaos is then explored by tuning a single control parameter, and a period-doubling cascade is evidenced, as well as intermittence. (authors)
18. Inverse free electron laser accelerator for advanced light sources
Directory of Open Access Journals (Sweden)
J. P. Duris
2012-06-01
Full Text Available We discuss the inverse free electron laser (IFEL scheme as a compact high gradient accelerator solution for driving advanced light sources such as a soft x-ray free electron laser amplifier or an inverse Compton scattering based gamma-ray source. In particular, we present a series of new developments aimed at improving the design of future IFEL accelerators. These include a new procedure to optimize the choice of the undulator tapering, a new concept for prebunching which greatly improves the fraction of trapped particles and the final energy spread, and a self-consistent study of beam loading effects which leads to an energy-efficient high laser-to-beam power conversion.
19. Radiation-Reaction Trapping of Electrons in Extreme Laser Fields
CERN Document Server
Ji, L L; Kostyukov, I Yu; Shen, B F; Akli, K
2014-01-01
proposed analysis shows that the threshold of laser field amplitude for RRT is approximately the cubic root of laser wavelength over classical electron radius. Because of the pinching effect of the trapped electron bunch, the required laser intensity for RRT can be further reduced.
20. SIMCON 3.0 eight channel FPGA-based cavity simulator and controller for VUV free-electron laser
Science.gov (United States)
Pozniak, Krzysztof T.; Czarski, Tomasz; Koprek, Waldemar; Romaniuk, Ryszard S.
2006-10-01
The work describes integrated system of hardware controller and simulator of superconductive cavity. The controller was realized on FPGA chip Xilinx-VirtexII-V4000. The solution uses DSP EMBEDDED BOARD positioned on a LLRF Modular Control Platform. The algorithm was realized in VHDL using hardware multiplication components existing in VirtexII series of chips. There was obtained implementation of a device working in real-time according to the control condition demands of LLRF system for TESLA superconductive cavities. The system is predicted as a developmental stage for FLASH accelerator and FEL laser and next for XFEL. The paper describes in detail functional layer, parameter programming, control basics for particular blocks, monitoring of real-time processes. There are presented results of system usage for control of the module ACC1 of FLASH laser.
1. Intensity dependence of electron gas kinetics in a laser corona
Directory of Open Access Journals (Sweden)
Mašek Martin
2013-11-01
Full Text Available In various experimental situations relevant to the laser fusion, such as plasma near the light entrance holes of hohlraum in the indirect drive experiments or more recently in the shock ignition direct drive a relatively long underdense plasma of corona type is encountered, which is subject to an intense nanosecond laser beam. The plasma is only weakly collisional and thus in the electron phase space a complicated kinetic evolution is going on, which is taking the electron gas fairly far from the thermal equilibrium and contributes to its unstable behaviour. These phenomena impede the absorption and thermalization of the incoming laser energy, create groups of fast electrons and also may lead to a non-linear reflection of the heating laser beam. One of the key processes leading to the electron acceleration is the stimulated Raman scattering (SRS in its non-linear phase. The SRS in the presence of electron-ion collisions requires a certain threshold intensity above which the mentioned non-dissipative phenomena can occur and develop to the stage, where they may become unpleasant for the fusion experiments. To assess this intensity limit a computational model has been developed based on the Vlasov-Maxwell kinetics describing such a plasma in 1D geometry. At a relatively high intensity of 1016 W/cm2 a number of non-linear phenomena are predicted by the code such as a saturation of Landau damping, which is then translated in an unfavourable time dependence of the reflected light intensity and formation of accelerated electron groups due to the electron trapping. The purpose of the present contribution is to map the intensity dependence of this non-linear development with the aim of assessing its weight in fusion relevant situations.
2. Laser-based additive manufacturing of metals
CSIR Research Space (South Africa)
Kumar, S
2010-11-01
Full Text Available For making metallic products through Additive Manufacturing (AM) processes, laser-based systems play very significant roles. Laser-based processes such as Selective Laser Melting (SLM) and Laser Engineered Net Shaping (LENS) are dominating processes...
3. Kinetic theory of free electron lasers
Energy Technology Data Exchange (ETDEWEB)
Hafizi, B. [Naval Research Lab., Washington, DC (United States); Roberson, C.W. [Office of Naval Research, Arlington, VA (United States)
1995-12-31
We have developed a relativistic kinetic theory of free electron lasers (FELs). The growth rate, efficiency, filling factor and radius of curvature of the radiation wave fronts are determined. We have used the theory to examine the effects of beam compression on growth rate. The theory has been extended to include self field effects on FEL operation. These effects are particularly important in compact, low voltage FELs. The surprising result is that the self field contribution to the beam quality is opposite to the emittance contribution. Hence self fields can improve beam quality, particularly in compact, low voltage FELs.
4. Externally Controlled Injection of Electrons by a Laser Pulse in a Laser Wakefield Electron Accelerator
CERN Document Server
Chen Szu Yuan; Chen Wei Ting; Chien, Ting-Yei; Lee, Chau-Hwang; Lin, Jiunn-Yuan; Wang, Jyhpyng
2005-01-01
Spatially and temporally localized injection of electrons is a key element for development of plasma-wave electron accelerator. Here we report the demonstration of two different schemes for electron injection in a self-modulated laser wakefield accelerator (SM-LWFA) by using a laser pulse. In the first scheme, by implementing a copropagating laser prepulse with proper timing, we are able to control the growth of Raman forward scattering and the production of accelerated electrons. We found that the stimulated Raman backward scattering of the prepulse plays the essential role of injecting hot electrons into the fast plasma wave driven by the pump pulse. In the second scheme, by using a transient density ramp we achieve self-injection of electrons in a SM-LWFA with spatial localization. The transient density ramp is produced by a prepulse propagating transversely to drill a density depression channel via ionization and expansion. The same mechanism of injection with comparable efficiency is also demonstrated wi...
5. Manipulation and electron-oscillation-measurement of laser accelerated electron beams
Energy Technology Data Exchange (ETDEWEB)
Kotaki, H; Hayashi, Y; Kawase, K; Mori, M; Kando, M; Homma, T; Koga, J K; Daido, H; Bulanov, S V, E-mail: [email protected] [Advanced Photon Research Center, Japan Atomic Energy Agency, 8-1-7, Umemidai, Kizugawa, Kyoto (Japan)
2011-01-15
Monoenergetic electron beams have been generated in the self-injection scheme of laser acceleration. In applications of these laser accelerated electron beams, stable and controllable electron beams are necessary. A stable electron beam is generated in the self-injection scheme by using a nitrogen gas jet target. We found the profile of the electron beam was manipulated by rotating the laser polarization. The electron beam is in the first bucket of the wake wave. In the energy space, transverse oscillation is observed when the laser pulse has S-polarization. The direction of the electron beam is controlled by the gas jet position.
6. High flux, narrow bandwidth compton light sources via extended laser-electron interactions
Science.gov (United States)
Barty, V P
2015-01-13
New configurations of lasers and electron beams efficiently and robustly produce high flux beams of bright, tunable, polarized quasi-monoenergetic x-rays and gamma-rays via laser-Compton scattering. Specifically, the use of long-duration, pulsed lasers and closely-spaced, low-charge and low emittance bunches of electron beams increase the spectral flux of the Compton-scattered x-rays and gamma rays, increase efficiency of the laser-electron interaction and significantly reduce the overall complexity of Compton based light sources.
7. Airborne Tactical Free-Electron Laser
Energy Technology Data Exchange (ETDEWEB)
Whitney, Roy; Neil, George
2007-02-01
The goal of 100 kilowatts (kW) of directed energy from an airborne tactical platform has proved challenging due to the size and weight of most of the options that have been considered. However, recent advances in Free-Electron Lasers appear to offer a solution along with significant tactical advantages: a nearly unlimited magazine, time structures for periods from milliseconds to hours, radar like functionality, and the choice of the wavelength of light that best meets mission requirements. For an Airborne Tactical Free-Electron Laser (ATFEL) on a platforms such as a Lockheed C-130J-30 and airships, the two most challenging requirements, weight and size, can be met by generating the light at a higher harmonic, aggressively managing magnet weights, managing cryogenic heat loads using recent SRF R&D results, and using FEL super compact design concepts that greatly reduce the number of components. The initial R&D roadmap for achieving an ATFEL is provided in this paper. Performing this R&D is expected to further reduce the weight, size and power requirements for the FELs the Navy is currently developing for shipboard applications, as well as providing performance enhancements for the strategic airborne MW class FELs. The 100 kW ATFEL with its tactical advantages may prove sufficiently attractive for early advancement in the queue of deployed FELs.
8. Femtosecond laser ablation of gold interdigitated electrodes for electronic tongues
Science.gov (United States)
Manzoli, Alexandra; de Almeida, Gustavo F. B.; Filho, José A.; Mattoso, Luiz H. C.; Riul, Antonio; Mendonca, Cleber R.; Correa, Daniel S.
2015-06-01
Electronic tongue (e-tongue) sensors based on impedance spectroscopy have emerged as a potential technology to evaluate the quality and chemical composition of food, beverages, and pharmaceuticals. E-tongues usually employ transducers based on metal interdigitated electrodes (IDEs) coated with a thin layer of an active material, which is capable of interacting chemically with several types of analytes. IDEs are usually produced by photolithographic methods, which are time-consuming and costly, therefore, new fabrication technologies are required to make it more affordable. Here, we employed femtosecond laser ablation with pulse duration of 50 fs to microfabricate gold IDEs having finger width from 2.3 μm up to 3.2 μm. The parameters used in the laser ablation technique, such as light intensity, scan speed and beam spot size have been optimized to achieve uniform IDEs, which were characterized by optical and scanning electron microscopy. The electrical properties of gold IDEs fabricated by laser ablation were evaluated by impedance spectroscopy, and compared to those produced by conventional photolithography. The results show that femtosecond laser ablation is a promising alternative to conventional photolithography for fabricating metal IDEs for e-tongue systems.
9. Laser-driven electron beam and radiation sources for basic, medical and industrial sciences
Science.gov (United States)
NAKAJIMA, Kazuhisa
2015-01-01
To date active research on laser-driven plasma-based accelerators have achieved great progress on production of high-energy, high-quality electron and photon beams in a compact scale. Such laser plasma accelerators have been envisaged bringing a wide range of applications in basic, medical and industrial sciences. Here inheriting the groundbreaker’s review article on “Laser Acceleration and its future” [Toshiki Tajima, (2010)],1) we would like to review recent progress of producing such electron beams due to relativistic laser-plasma interactions followed by laser wakefield acceleration and lead to the scaling formulas that are useful to design laser plasma accelerators with controllability of beam energy and charge. Lastly specific examples of such laser-driven electron/photon beam sources are illustrated. PMID:26062737
10. Fast-electron-relaxation measurement for laser-solid interaction at relativistic laser intensities.
Science.gov (United States)
Chen, H; Shepherd, R; Chung, H K; Kemp, A; Hansen, S B; Wilks, S C; Ping, Y; Widmann, K; Fournier, K B; Dyer, G; Faenov, A; Pikuz, T; Beiersdorfer, P
2007-11-01
We present measurements of the fast-electron-relaxation time in short-pulse (0.5 ps) laser-solid interactions for laser intensities of 10(17), 10(18), and 10(19) Wcm2, using a picosecond time-resolved x-ray spectrometer and a time-integrated electron spectrometer. We find that the laser coupling to hot electrons increases as the laser intensity becomes relativistic, and that the thermalization of fast electrons occurs over time scales on the order of 10 ps at all laser intensities. The experimental data are analyzed using a combination of models that include Kalpha generation, collisional coupling, and plasma expansion.
11. The influence of quaternary electron blocking layer on the performance characteristics of intracavity-contacted oxide-confined InGaN-based vertical cavity surface emitting lasers
Science.gov (United States)
Goharrizi, A. Zandi; Alahyarizadeh, Gh.; Hassan, Z.; Hassan, H. Abu
2015-11-01
The effect of electron blocking layer (EBL) on the performance characteristics of InGaN-based vertical cavity surface emitting lasers (VCSELs) was numerically investigated using an integrated system engineering technical computer aided design (ISE TCAD) simulation program. Simulation results indicated that the performance characteristics of InGaN quantum well VCSEL were improved by the ternary Al0.17Ga0.83N EBL. Better performance was also obtained when Al0.17Ga0.83N EBL was replaced by a polarization-matched Al0.275In0.115Ga0.61N EBL having the same energy bandgap. The quaternary EBL enhances the output power and differential quantum efficiency (DQE) as well as reduces the threshold current compared with the ternary EBL. Enhancement in the value of the optical intensity was also observed in the VCSEL structure with quaternary EBL. Furthermore, the effect of Al composition of AlInGaN EBL on the performance of InGaN-based VCSEL structure that uses the quaternary AlInGaN EBL was studied. In mole fraction was 0.115, Al mole fraction changed from 0.260 to 0.290 by step 0.005, and optimum performance was achieved in 0.275 Al mole fraction of AlInGaN EBL.
12. Compact beam transport system for free-electron lasers driven by a laser plasma accelerator
Directory of Open Access Journals (Sweden)
Tao Liu
2017-02-01
Full Text Available Utilizing laser-driven plasma accelerators (LPAs as a high-quality electron beam source is a promising approach to significantly downsize the x-ray free-electron laser (XFEL facility. A multi-GeV LPA beam can be generated in several-centimeter acceleration distance, with a high peak current and a low transverse emittance, which will considerably benefit a compact FEL design. However, the large initial angular divergence and energy spread make it challenging to transport the beam and realize FEL radiation. In this paper, a novel design of beam transport system is proposed to maintain the superior features of the LPA beam and a transverse gradient undulator (TGU is also adopted as an effective energy spread compensator to generate high-brilliance FEL radiation. Theoretical analysis and numerical simulations are presented based on a demonstration experiment with an electron energy of 380 MeV and a radiation wavelength of 30 nm.
13. Quantum regime of free electron lasers starting from noise
National Research Council Canada - National Science Library
Bonifacio, R; Piovella, N; Robb, G. R. M; Schiavi, A
2006-01-01
.... In the first part, we neglect the radiation propagation and we formulate a quantum linear theory of the N-particle free-electron laser Hamiltonian model, quantizing both the radiation field and the electron motion...
14. Short Rayleigh length free electron lasers
Directory of Open Access Journals (Sweden)
W. B. Colson
2006-03-01
Full Text Available Conventional free electron laser (FEL oscillators minimize the optical mode volume around the electron beam in the undulator by making the resonator Rayleigh length about one third to one half of the undulator length. This maximizes gain and beam-mode coupling. In compact configurations of high-power infrared FELs or moderate power UV FELs, the resulting optical intensity can damage the resonator mirrors. To increase the spot size and thereby reduce the optical intensity at the mirrors below the damage threshold, a shorter Rayleigh length can be used, but the FEL interaction is significantly altered. We model this interaction using a coordinate system that expands with the rapidly diffracting optical mode from the ends of the undulator to the mirrors. Simulations show that the interaction of the strongly focused optical mode with a narrow electron beam inside the undulator distorts the optical wave front so it is no longer in the fundamental Gaussian mode. The simulations are used to study how mode distortion affects the single-pass gain in weak fields, and the steady-state extraction in strong fields.
15. Electron bunch timing with femtosecond precision in a superconducting free-electron laser.
Science.gov (United States)
Löhl, F; Arsov, V; Felber, M; Hacker, K; Jalmuzna, W; Lorbeer, B; Ludwig, F; Matthiesen, K-H; Schlarb, H; Schmidt, B; Schmüser, P; Schulz, S; Szewinski, J; Winter, A; Zemella, J
2010-04-09
High-gain free-electron lasers (FELs) are capable of generating femtosecond x-ray pulses with peak brilliances many orders of magnitude higher than at other existing x-ray sources. In order to fully exploit the opportunities offered by these femtosecond light pulses in time-resolved experiments, an unprecedented synchronization accuracy is required. In this Letter, we distributed the pulse train of a mode-locked fiber laser with femtosecond stability to different locations in the linear accelerator of the soft x-ray FEL FLASH. A novel electro-optic detection scheme was applied to measure the electron bunch arrival time with an as yet unrivaled precision of 6 fs (rms). With two beam-based feedback systems we succeeded in stabilizing both the arrival time and the electron bunch compression process within two magnetic chicanes, yielding a significant reduction of the FEL pulse energy jitter.
16. CERN's web application updates for electron and laser beam technologies
CERN Document Server
Sigas, Christos
2017-01-01
This report describes the modifications at CERN's web application for electron and laser beam technologies. There are updates at both the front and the back end of the application. New electron and laser machines were added and also old machines were updated. There is also a new feature for printing needed information.
17. Role of Direct Laser Acceleration of Electrons in a Laser Wakefield Accelerator with Ionization Injection.
Science.gov (United States)
Shaw, J L; Lemos, N; Amorim, L D; Vafaei-Najafabadi, N; Marsh, K A; Tsung, F S; Mori, W B; Joshi, C
2017-02-10
We show the first experimental demonstration that electrons being accelerated in a laser wakefield accelerator operating in the forced or blowout regimes gain significant energy from both the direct laser acceleration (DLA) and the laser wakefield acceleration mechanisms. Supporting full-scale 3D particle-in-cell simulations elucidate the role of the DLA of electrons in a laser wakefield accelerator when ionization injection of electrons is employed. An explanation is given for how electrons can maintain the DLA resonance condition in a laser wakefield accelerator despite the evolving properties of both the drive laser and the electrons. The produced electron beams exhibit characteristic features that are indicative of DLA as an additional acceleration mechanism.
18. High quality electron bunch generation with CO2-laser-plasma interaction
Science.gov (United States)
Zhang, Lingang; Shen, Baifei; Xu, Jiancai; Ji, Liangliang; Zhang, Xiaomei; Wang, Wenpeng; Zhao, Xueyan; Yi, Longqing; Yu, Yahong; Shi, Yin; Xu, Tongjun; Xu, Zhizhan
2015-02-01
CO2 laser-driven electron acceleration in low-density plasma is demonstrated using particle-in-cell simulation. An intense CO2 laser pulse of long wavelength excites a wake bubble that has a large elongated volume for accelerating a large number of electrons before reaching the charge saturation limit. A transversely injected laser pulse is used to induce and control the electron injection. It is found that an electron bunch with total charge up to 10 nC and absolute energy spread less than 16 MeV can be obtained. As a result, the charge per energy interval of the bunch reaches up to 0.6 nC/MeV. Intense CO2-laser based electron acceleration can provide a new direction for generating highly charged electron bunches with low energy spread, which is of much current interest, especially for table-top X-ray generation.
19. All-optical time-resolved measurement of laser energy modulation in a relativistic electron beam
Directory of Open Access Journals (Sweden)
D. Xiang
2011-11-01
Full Text Available We propose and demonstrate an all-optical method to measure laser energy modulation in a relativistic electron beam. In this scheme the time-dependent energy modulation generated from the electron-laser interaction in an undulator is converted into time-dependent density modulation with a chicane, which is measured to infer the laser energy modulation. The method, in principle, is capable of simultaneously providing information on femtosecond time scale and 10^{-5} energy scale not accessible with conventional methods. We anticipate that this method may have wide applications in many laser-based advanced beam manipulation techniques.
20. Electronic properties of asymmetrical quantum dots dressed by laser field
Energy Technology Data Exchange (ETDEWEB)
Kibis, O.V. [Department of Applied and Theoretical Physics, Novosibirsk State Technical University, Karl Marx Avenue 20, 630092 Novosibirsk (Russian Federation); Slepyan, G.Ya.; Maksimenko, S.A. [Institute for Nuclear Problems, Belarus State University, Bobruyskaya St. 11, 220050 Minsk (Belarus); Hoffmann, A. [Institut fuer Festkoerperphysik, Technische Universitaet Berlin, Hardenbergstrasse 36, 10623 Berlin (Germany)
2012-05-15
In the present paper, we demonstrate theoretically that the strong non-resonant interaction between asymmetrical quantum dots (QDs) and a laser field results in harmonic oscillations of their band gap. It is shown that such oscillations change the spectrum of elementary electron excitations in QDs: in the absence of the laser pumping there is only one resonant electron frequency, but QDs dressed by the laser field have a set of electron resonant frequencies. One expects that this modification of elementary electron excitations in QDs can be observable in optical experiments. (Copyright copyright 2012 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)
1. Scaling the Yield of Laser-Driven Electron-Positron Jets to Laboratory Astrophysical Applications
Science.gov (United States)
Chen, Hui; Fiuza, F.; Link, A.; Hazi, A.; Hill, M.; Hoarty, D.; James, S.; Kerr, S.; Meyerhofer, D. D.; Myatt, J.; Park, J.; Sentoku, Y.; Williams, G. J.
2015-05-01
We report new experimental results obtained on three different laser facilities that show directed laser-driven relativistic electron-positron jets with up to 30 times larger yields than previously obtained and a quadratic (˜EL2 ) dependence of the positron yield on the laser energy. This favorable scaling stems from a combination of higher energy electrons due to increased laser intensity and the recirculation of MeV electrons in the mm-thick target. Based on this scaling, first principles simulations predict the possibility of using such electron-positron jets, produced at upcoming high-energy laser facilities, to probe the physics of relativistic collisionless shocks in the laboratory.
2. Two-pulse laser control of nuclear and electronic motion
DEFF Research Database (Denmark)
Grønager, Michael; Henriksen, Niels Engholm
1997-01-01
We discuss an explicitly time-dependent two-pulse laser scheme for controlling where nuclei and electrons are going in unimolecular reactions. We focus on electronic motion and show, with HD+ as an example, that one can find non-stationary states where the electron (with some probability) oscilla......We discuss an explicitly time-dependent two-pulse laser scheme for controlling where nuclei and electrons are going in unimolecular reactions. We focus on electronic motion and show, with HD+ as an example, that one can find non-stationary states where the electron (with some probability...
3. High energy gain electron beam acceleration by 100TW laser
Energy Technology Data Exchange (ETDEWEB)
Kotaki, Hideyuki; Kando, Masaki; Kondo, Shuji; Hosokai, Tomonao; Kanazawa, Shuhei; Yokoyama, Takashi; Matoba, Toru; Nakajima, Kazuhisa [Japan Atomic Energy Research Inst., Kizu, Kyoto (Japan). Kansai Research Establishment
2001-10-01
A laser wakefield acceleration experiment using a 100TW laser is planed at JAERI-Kansai. High quality and short pulse electron beams are necessary to accelerate the electron beam by the laser. Electron beam - laser synchronization is also necessary. A microtron with a photocathode rf-gun was prepared as a high quality electron injector. The quantum efficiency (QE) of the photocathode of 2x10{sup -5} was obtained. A charge of 100pC from the microtron was measured. The emittance and pulse width of the electron beam was 6{pi} mm-mrad and 10ps, respectively. In order to produce a short pulse electron beam, and to synchronize between the electron beam and the laser pulse, an inverse free electron laser (IFEL) is planned. One of problems of LWFA is the short acceleration length. In order to overcome the problem, a Z-pinch plasma waveguide will be prepared as a laser wakefield acceleration tube for 1 GeV acceleration. (author)
4. Development of a high power free-electron laser
Energy Technology Data Exchange (ETDEWEB)
Lee, Jong Min; Lee, Byung Chul; Kim, Sun Kook; Jung, Yung Wook; Cho, Sung Oh [Korea Atomic Energy Research Institute, Taejon (Korea, Republic of)
1995-01-01
A millimeter-wave free electron laser (FEL) driven by a recirculating electrostatic accelerator has been developed. The wavelength of the FEL is tunable in the range of 3 - 12 mm by tuning the energy of the electron beam. The output power is estimated to be 1 kW. The electrostatic accelerator is composed of high-current electron gun, acceleration tube, high-voltage generator, high-voltage terminal, deceleration tube, electron collator, and vacuum pumps. Two types of LaB{sub 6}-based thermionic electron guns (triode gun and diode gun) and their power supplies have been developed. The voltage of the guns is 30 kV and the output current is - 2 A. A beam-focusing planar undulator and a permanent-magnet helical undulator have been developed and 3D trajectories of electron beam in the undulators have been calculated to find optimal input condition of electron beam. 135 figs, 15 pix, 17 tabs, 98 refs. (Author).
5. Laser Assisted Free-Free Transition in Electron - Atom Collision
Science.gov (United States)
Sinha, C.; Bhatia, A. K.
2011-01-01
Free-free transition is studied for electron-Hydrogen atom system in ground state at very low incident energies in presence of an external homogeneous, monochromatic and linearly polarized laser field. The incident electron is considered to be dressed by the laser in a non perturbative manner by choosing the Volkov solutions in both the channels. The space part of the scattering wave function for the electron is solved numerically by taking into account the effect of electron exchange, short range as well as of the long range interactions. Laser assisted differential as well as elastic total cross sections are calculated for single photon absorption/emission in the soft photon limit, the laser intensity being much less than the atomic field intensity. A strong suppression is noted in the laser assisted cross sections as compared to the field free situations. Significant difference is noted in the singlet and the triplet cross sections.
6. Identification of Nodal Kink in Electron-Doped (Nd1.85Ce0.15CuO4 Superconductor from Laser-Based Angle-Resolved Photoemission Spectroscopy
Directory of Open Access Journals (Sweden)
Zhou X. J.
2012-03-01
Full Text Available High-resolution laser-based angle-resolved photoemission measurements have been carried out on the electron-doped (Nd1.85Ce0.15CuO4 high temperature superconductor. We have revealed a clear kink at ~60 meV in the dispersion along the (0,0–(π,π nodal direction, accompanied by a peak-dip-hump feature in the photoemission spectra. This indicates that the nodal electrons are coupled to collective excitations (bosons in electron-doped superconductors, with the phonons as the most likely candidate of the boson. This finding has established a universality of nodal electron coupling in both hole- and electron-doped high temperature cuprate superconductors.
7. Pulse Duration of Seeded Free-Electron Lasers
Science.gov (United States)
Finetti, Paola; Höppner, Hauke; Allaria, Enrico; Callegari, Carlo; Capotondi, Flavio; Cinquegrana, Paolo; Coreno, Marcello; Cucini, Riccardo; Danailov, Miltcho B.; Demidovich, Alexander; De Ninno, Giovanni; Di Fraia, Michele; Feifel, Raimund; Ferrari, Eugenio; Fröhlich, Lars; Gauthier, David; Golz, Torsten; Grazioli, Cesare; Kai, Yun; Kurdi, Gabor; Mahne, Nicola; Manfredda, Michele; Medvedev, Nikita; Nikolov, Ivaylo P.; Pedersoli, Emanuele; Penco, Giuseppe; Plekan, Oksana; Prandolini, Mark J.; Prince, Kevin C.; Raimondi, Lorenzo; Rebernik, Primoz; Riedel, Robert; Roussel, Eleonore; Sigalotti, Paolo; Squibb, Richard; Stojanovic, Nikola; Stranges, Stefano; Svetina, Cristian; Tanikawa, Takanori; Teubner, Ulrich; Tkachenko, Victor; Toleikis, Sven; Zangrando, Marco; Ziaja, Beata; Tavella, Franz; Giannessi, Luca
2017-04-01
The pulse duration, and, more generally, the temporal intensity profile of free-electron laser (FEL) pulses, is of utmost importance for exploring the new perspectives offered by FELs; it is a nontrivial experimental parameter that needs to be characterized. We measured the pulse shape of an extreme ultraviolet externally seeded FEL operating in high-gain harmonic generation mode. Two different methods based on the cross-correlation of the FEL pulses with an external optical laser were used. The two methods, one capable of single-shot performance, may both be implemented as online diagnostics in FEL facilities. The measurements were carried out at the seeded FEL facility FERMI. The FEL temporal pulse characteristics were measured and studied in a range of FEL wavelengths and machine settings, and they were compared to the predictions of a theoretical model. The measurements allowed a direct observation of the pulse lengthening and splitting at saturation, in agreement with the proposed theory.
8. Laser-modified electron scattering from a slowly ionising atom
Science.gov (United States)
Fiordilino, E.; Mittleman, M. H.
1983-01-01
When an electron scatters from an atom in the presence of a laser field which is resonant with an atomic transition, off-shell effects enter into the cross section. These only become significant at higher laser intensities where the atom may also be ionised by the laser. Cross-sections are obtained for electron-atom scattering in which these off-shell effects appear and in which the slow ionisation of the atom by the laser is included. Experiments are suggested in which simplifications can occur and which still retain these 'exotic' effects.
9. Laser-pumped coherent x-ray free-electron laser
Directory of Open Access Journals (Sweden)
P. Sprangle
2009-05-01
Full Text Available In a laser-pumped x-ray free-electron laser (FEL an intense laser field replaces the magnetic wiggler field of a conventional FEL. Depending on the intensity and quality of both the electron beam and pump laser, the Thomson backscattered radiation can be coherently amplified. In a conventional FEL the generation of x rays requires electron beam energies in the multi-GeV range. In a laser-pumped x-ray FEL, electron beam energies in the multi-MeV range would be sufficient. To generate coherent x rays with this mechanism a number of physics and technology issues must be addressed. Foremost among these are the stringent requirements placed on the electron beam quality and brightness as well as on the pump laser. The seed radiation for the laser-pumped FEL is the laser-induced spontaneous radiation. The evolution of incoherent radiation into coherent radiation as well as the power gain lengths associated with the coherent x rays are analyzed and discussed. There is excellent agreement between our analytical results and GENESIS simulations for the radiated power, gain length, conversion efficiency, linewidth, and saturation length. These issues, as well as others, necessary to achieve coherent amplified x rays in a laser-pumped FEL are discussed. While a coherent x-ray source would have a number of attractive features, the requirements placed on both the electron beam and pump laser are extremely challenging.
10. Application of CO2 laser for electronic components soldering
Science.gov (United States)
Mascorro-Pantoja, J.; Soto-Bernal, J. J.; Nieto-Pérez, M.; Gonzalez-Mota, R.; Rosales-Candelas, I.
2011-10-01
Laser provides a high controllable and localized spot for soldering joint formation and this is a valuable tool in Sn/Pb Soldering process on electronic industry, in recent years, laser beam welding has become an emerging welding technique, the use of laser in welding area is a high efficiency method. A 60 Watts CO2 continuous laser was used on this study, during welding experimental results indicated the laser could significantly improve speed and weld quality. In this work, the welding interactions of CO2 laser with Sn/Pb wire have been investigated in details through varying the energy ratios of laser. And at the same time, the effect of distance from laser spot to material.
11. Electron acceleration via high contrast laser interacting with submicron clusters
Energy Technology Data Exchange (ETDEWEB)
Zhang Lu; Chen Liming; Wang Weiming; Yan Wenchao; Yuan Dawei; Mao Jingyi; Wang Zhaohua; Liu Cheng; Shen Zhongwei; Li Yutong; Dong Quanli; Lu Xin; Ma Jinglong; Wei Zhiyi [Beijing National Laboratory of Condensed Matter Physics, Institute of Physics, CAS, Beijing 100080 (China); Faenov, Anatoly; Pikuz, Tatiana [Joint Institute for High Temperature of the Russian Academy of Sciences, Izhorskaya 13/19, Moscow 127412 (Russian Federation); Quantum Beams Science Directorate, JAEA, Kizugawa, Kyoto (Japan); Li Dazhang [Beijing National Laboratory of Condensed Matter Physics, Institute of Physics, CAS, Beijing 100080 (China); Institute of High Energy Physics, CAS, Beijing 100049 (China); Sheng Zhengming [Department of Physics, Shanghai Jiao Tong University, Shanghai 200240 (China); Zhang Jie [Beijing National Laboratory of Condensed Matter Physics, Institute of Physics, CAS, Beijing 100080 (China); Department of Physics, Shanghai Jiao Tong University, Shanghai 200240 (China)
2012-01-02
We experimentally investigated electron acceleration from submicron size argon clusters-gas target irradiated by a 100 fs, 10 TW laser pulses having a high-contrast. Electron beams are observed in the longitudinal and transverse directions to the laser propagation. The measured energy of the longitudinal electron reaches 600 MeV and the charge of the electron beam in the transverse direction is more than 3 nC. A two-dimensional particle-in-cell simulation of the interaction has been performed and it shows an enhancement of electron charge by using the cluster-gas target.
12. Laser-assisted electron diffraction for femtosecond molecular imaging
Energy Technology Data Exchange (ETDEWEB)
Morimoto, Yuya; Kanya, Reika [Department of Chemistry, School of Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033 (Japan); Yamanouchi, Kaoru, E-mail: [email protected] [Department of Chemistry, School of Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033 (Japan); NANOQUINE, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033 (Japan)
2014-02-14
We report the observation of laser-assisted electron diffraction (LAED) through the collision of 1 keV electrons with gas-phase CCl{sub 4} molecules in a femtosecond near-infrared laser field. In the angular distribution of the scattered electrons with the energy shifts of ±ℏω, we observed clear diffraction patterns which reflect the geometrical structure of the molecules at the moment of laser irradiation. Our results demonstrate that ultrafast nuclear dynamics of molecules can be probed by LAED with the high temporal (<10 fs) and spatial (∼0.01 Å) resolutions.
13. Ultraviolet laser transverse profile shaping for improving x-ray free electron laser performance
Directory of Open Access Journals (Sweden)
S. Li
2017-08-01
Full Text Available The photocathode rf gun is one of the most critical components in x-ray free electron lasers. The drive laser strikes the photocathode surface, which emits electrons with properties that depend on the shape of the drive laser. Most free electron lasers use photocathodes with work function in the ultraviolet, a wavelength where direct laser manipulation becomes challenging. In this paper, we present a novel application of a digital micromirror device (DMD for the 253 nm drive laser at the Linear Coherent Light Source. Laser profile shaping is accomplished through an iterative algorithm that takes into account shaping error and efficiency. Next, we use laser shaping to control the X-ray laser output via an online optimizer, which shows improvement in FEL pulse energy. Lastly, as a preparation for electron beam shaping, we use the DMD to measure the photocathode quantum efficiency across cathode surface with an averaged laser rms spot size of 59 μm. Our experiments demonstrate promising outlook of using DMD to shape ultraviolet lasers for photocathode rf guns with various applications.
14. Ultraviolet laser transverse profile shaping for improving x-ray free electron laser performance
Science.gov (United States)
Li, S.; Alverson, S.; Bohler, D.; Egger, A.; Fry, A.; Gilevich, S.; Huang, Z.; Miahnahri, A.; Ratner, D.; Robinson, J.; Zhou, F.
2017-08-01
The photocathode rf gun is one of the most critical components in x-ray free electron lasers. The drive laser strikes the photocathode surface, which emits electrons with properties that depend on the shape of the drive laser. Most free electron lasers use photocathodes with work function in the ultraviolet, a wavelength where direct laser manipulation becomes challenging. In this paper, we present a novel application of a digital micromirror device (DMD) for the 253 nm drive laser at the Linear Coherent Light Source. Laser profile shaping is accomplished through an iterative algorithm that takes into account shaping error and efficiency. Next, we use laser shaping to control the X-ray laser output via an online optimizer, which shows improvement in FEL pulse energy. Lastly, as a preparation for electron beam shaping, we use the DMD to measure the photocathode quantum efficiency across cathode surface with an averaged laser rms spot size of 59 μ m . Our experiments demonstrate promising outlook of using DMD to shape ultraviolet lasers for photocathode rf guns with various applications.
15. Large-Scale Production of Carbon Nanotubes Using the Jefferson Lab Free Electron Laser
Science.gov (United States)
Holloway, Brian C.
2003-01-01
We report on our interdisciplinary program to use the Free Electron Laser (FEL) at the Thomas Jefferson National Accelerator Facility (J-Lab) for high-volume pulsed laser vaporization synthesis of carbon nanotubes. Based in part on the funding of from this project, a novel nanotube production system was designed, tested, and patented. Using this new system nanotube production rates over 100 times faster than conventional laser systems were achieved. Analysis of the material produced shows that it is of as high a quality as the standard laser-based materials.
16. Generating ultrarelativistic attosecond electron bunches with laser wakefield accelerators
NARCIS (Netherlands)
Luttikhof, M.J.H.; Khachatryan, A.G.; van Goor, F.A.; Boller, Klaus J.
2010-01-01
Femtosecond electron bunches with ultrarelativistic energies were recently generated by laser wakefield accelerators. Here we predict that laser wakefield acceleration can generate even attosecond bunches, due to a strong chirp of the betatron frequency. We show how the bunch duration scales with
17. Anti-Ship Missile Defense and the Free Electron Laser
National Research Council Canada - National Science Library
Herbert, Paul
1998-01-01
In order to improve ship self-defense against sea-skimming missiles, several concepts, such as the free electron laser, high-power microwaves, and the Phalanx gun system are reviewed and evaluated in this thesis...
18. Characterization and control of femtosecond electron and X-ray beams at free-electron lasers
Energy Technology Data Exchange (ETDEWEB)
Behrens, Christopher
2012-11-15
X-ray free-electron lasers (FELs) open up new frontiers in photon science, and in order to take full advantage of these unique accelerator-based light sources, the characterization and control of the femtosecond electron and X-ray beams is essential. Within this cumulative thesis, recent results achieved within the active research field of femtosecond electron and X-ray beams at FELs are reported.The basic principles of X-ray FELs are described, and concepts of longitudinal electron beam diagnostics with femtosecond accuracy are covered. Experimental results obtained with a transverse deflecting structure (TDS) and spectroscopy of coherent terahertz radiation are presented, and the suppression of coherent optical radiation effects, required for diagnostics utilizing a TDS, is demonstrated. Control of the longitudinal phase space by using multiple radio frequencies for longitudinal electron beam tailoring is presented, and a new technique of reversible electron beam heating with two TDSs is described. For the characterization of femtosecond X-ray pulses, a novel method based on dedicated longitudinal phase space diagnostics for electron beams is introduced, and recent measurements with a streaking technique using external terahertz fields are presented.
19. Introduction to free electron lasers (1/3)
CERN Multimedia
CERN. Geneva
2002-01-01
The Free-electron laser (FEL) is a source of coherent electromagnetic radiation based on a relativistic electron beam. First operated 25 years ago, the FEL has now reached a stage of maturity for operation in the infra-red region of the spectrum and several facilities provide intense FEL radiation beams for research covering a wide range of disciplines. Several projects both underway and proposed aim at pushing the minimum wavelength from its present limit around 100 nm progressively down to the 1 Angstrom region where the X-ray FEL would open up many new and exciting research possibilities. Other developments aim at increasing power levels to the 10's of kW level. In this series of lectures we give an introduction to the basic principles of FELs and their different modes of operation, and summarise their applications and current state of development.
20. Introduction to free electron lasers (2/3)
CERN Multimedia
CERN. Geneva
2002-01-01
The Free-electron laser (FEL) is a source of coherent electromagnetic radiation based on a relativistic electron beam. First operated 25 years ago, the FEL has now reached a stage of maturity for operation in the infra-red region of the spectrum and several facilities provide intense FEL radiation beams for research covering a wide range of disciplines. Several projects both underway and proposed aim at pushing the minimum wavelength from its present limit around 100 nm progressively down to the 1 Angstrom region where the X-ray FEL would open up many new and exciting research possibilities. Other developments aim at increasing power levels to the 10's of kW level. In this series of lectures we give an introduction to the basic principles of FELs and their different modes of operation, and summarise their applications and current state of development.
1. Introduction to free electron lasers (3/3)
CERN Multimedia
CERN. Geneva
2002-01-01
The Free-electron laser (FEL) is a source of coherent electromagnetic radiation based on a relativistic electron beam. First operated 25 years ago, the FEL has now reached a stage of maturity for operation in the infra-red region of the spectrum and several facilities provide intense FEL radiation beams for research covering a wide range of disciplines. Several projects both underway and proposed aim at pushing the minimum wavelength from its present limit around 100 nm progressively down to the 1 Angstrom region where the X-ray FEL would open up many new and exciting research possibilities. Other developments aim at increasing power levels to the 10's of kW level. In this series of lectures we give an introduction to the basic principles of FELs and their different modes of operation, and summarise their applications and current state of development.
2. Čerenkov free-electron laser with side walls
Energy Technology Data Exchange (ETDEWEB)
Kalkal, Yashvir, E-mail: [email protected] [Homi Bhabha National Institute, Mumbai 400094 (India); Accelerator and Beam Physics Laboratory, Raja Ramanna Centre for Advanced Technology, Indore 452013 (India); Kumar, Vinit [Homi Bhabha National Institute, Mumbai 400094 (India); Accelerator and Beam Physics Laboratory, Raja Ramanna Centre for Advanced Technology, Indore 452013 (India)
2016-08-11
In this paper, we have proposed a Čerenkov free-electron laser (CFEL) with metallic side walls, which are used to confine an electromagnetic surface mode supported by a thin dielectric slab placed on top of a conducting surface. This leads to an enhancement in coupling between the optical mode and the co-propagating electron beam, and consequently, performance of the CFEL is improved. We set up coupled Maxwell–Lorentz equations for the system, in analogy with an undulator based conventional FEL, and obtain formulas for the small-signal gain and growth rate. It is shown that small signal gain and growth rate in this configuration are larger compared to the configuration without the side walls. In the nonlinear regime, we solve the coupled Maxwell–Lorentz equations numerically and study the saturation behaviour of the system. It is found that the Čerenkov FEL with side walls saturates quickly, and produces powerful coherent terahertz radiation.
3. High quality electron bunch generation with CO2-laser plasma accelerator
CERN Document Server
Zhang, L G; Xu, J C; Ji, L L; Zhang, X M; Wang, W P; Zhao, X Y; Yi, L Q; Yu, Y H; Shi, Y; Xu, T J; Xu, Z Z
2014-01-01
CO2 laser-driven electron acceleration is demonstrated with particle-in-cell simulation in low-density plasma. An intense CO2 laser pulse with long wavelength excites wakefield. The bubble behind it has a broad space to sustain a large amount of electrons before reaching its charge saturation limit. A transversely propagating inject pulse is used to induce and control the ambient electron injection. The accelerated electron bunch with total charge up to 10 nC and the average charge per energy interval of more than 0.6 nC/MeV are obtained. Plasma-based electron acceleration driven by intense CO2 laser provides a new potential way to generate high-charge electron bunch with low energy spread, which has broad applications, especially for X-ray generation by table-top FEL and bremsstrahlung.
4. Second harmonic generation in Te crystal using free electron laser
CERN Document Server
Yamauchi, T; Minehara, E J
2002-01-01
The second harmonic generation signal converted from the fundamental wavelength of 22 mu m of a free electron laser was observed for the first time using a birefringent Te crystal. The experimental conversion efficiency of Te crystal for second harmonic generation is 0.53%, which is equivalent to the theoretical value within a factor of 2. The Te crystal has been incorporated into an autocorrelator system to measure the micro-pulse width of infrared free electron laser successfully. (author)
5. Electron Dynamics in Nanostructures in Strong Laser Fields
Energy Technology Data Exchange (ETDEWEB)
Kling, Matthias
2014-09-11
The goal of our research was to gain deeper insight into the collective electron dynamics in nanosystems in strong, ultrashort laser fields. The laser field strengths will be strong enough to extract and accelerate electrons from the nanoparticles and to transiently modify the materials electronic properties. We aimed to observe, with sub-cycle resolution reaching the attosecond time domain, how collective electronic excitations in nanoparticles are formed, how the strong field influences the optical and electrical properties of the nanomaterial, and how the excitations in the presence of strong fields decay.
6. Radiation from laser accelerated electron bunches: Coherent terahertz and femtosecond X-rays
Energy Technology Data Exchange (ETDEWEB)
Leemans, W.P.; Esarey, E.; van Tilborg, J.; Michel, P.A.; Schroeder, C.B.; Toth, Cs.; Geddes, C.G.R.; Shadwick, B.A.
2004-10-01
Electron beam based radiation sources provide electromagnetic radiation for countless applications. The properties of the radiation are primarily determined by the properties of the electron beam. Compact laser driven accelerators are being developed that can provide ultra-short electron bunches (femtosecond duration) with relativistic energies reaching towards a GeV. The electron bunches are produced when an intense laser interacts with a dense plasma and excites a large amplitude plasma density modulation (wakefield) that can trap background electrons and accelerate them to high energies. The short pulse nature of the accelerated bunches and high particle energy offer the possibility of generating radiation from one compact source that ranges from coherent terahertz to gamma rays. The intrinsic synchronization to a laser pulse and unique character of the radiation offers a wide range of possibilities for scientific applications. Two particular radiation source regimes are discussed: Coherent terahertz emission and x-ray emission based on betatron oscillations and Thomson scattering.
7. Controlled injection and acceleration of electrons in plasma wakefields by colliding laser pulses.
Science.gov (United States)
Faure, J; Rechatin, C; Norlin, A; Lifschitz, A; Glinec, Y; Malka, V
2006-12-07
In laser-plasma-based accelerators, an intense laser pulse drives a large electric field (the wakefield) which accelerates particles to high energies in distances much shorter than in conventional accelerators. These high acceleration gradients, of a few hundreds of gigavolts per metre, hold the promise of compact high-energy particle accelerators. Recently, several experiments have shown that laser-plasma accelerators can produce high-quality electron beams, with quasi-monoenergetic energy distributions at the 100 MeV level. However, these beams do not have the stability and reproducibility that are required for applications. This is because the mechanism responsible for injecting electrons into the wakefield is based on highly nonlinear phenomena, and is therefore hard to control. Here we demonstrate that the injection and subsequent acceleration of electrons can be controlled by using a second laser pulse. The collision of the two laser pulses provides a pre-acceleration stage which provokes the injection of electrons into the wakefield. The experimental results show that the electron beams obtained in this manner are collimated (5 mrad divergence), monoenergetic (with energy spread electron bunch durations shorter than 10 fs. We anticipate that this stable and compact electron source will have a strong impact on applications requiring short bunches, such as the femtolysis of water, or high stability, such as radiotherapy with high-energy electrons or radiography for materials science.
8. Electron Beam Charge Diagnostics for Laser Plasma Accelerators
Energy Technology Data Exchange (ETDEWEB)
Nakamura, Kei; Gonsalves, Anthony; Lin, Chen; Smith, Alan; Rodgers, David; Donahue, Rich; Byrne, Warren; Leemans, Wim
2011-06-27
A comprehensive study of charge diagnostics is conducted to verify their validity for measuring electron beams produced by laser plasma accelerators (LPAs). First, a scintillating screen (Lanex) was extensively studied using subnanosecond electron beams from the Advanced Light Source booster synchrotron, at the Lawrence Berkeley National Laboratory. The Lanex was cross calibrated with an integrating current transformer (ICT) for up to the electron energy of 1.5 GeV, and the linear response of the screen was confirmed for charge density and intensity up to 160 pC/mm{sup 2} and 0.4 pC/(ps mm{sup 2}), respectively. After the radio-frequency accelerator based cross calibration, a series of measurements was conducted using electron beams from an LPA. Cross calibrations were carried out using an activation-based measurement that is immune to electromagnetic pulse noise, ICT, and Lanex. The diagnostics agreed within {+-}8%, showing that they all can provide accurate charge measurements for LPAs.
9. Free-electron laser emission architecture impact on EUV lithography
Science.gov (United States)
Hosler, Erik R.; Wood, Obert R.; Barletta, William A.
2017-03-01
Laser-produced plasma (LPP) EUV sources have demonstrated approximately 125 W at customer sites, establishing confidence in EUV lithography as a viable manufacturing technology. However, beyond the 7 nm technology node existing scanner/source technology must enable higher-NA imaging systems (requiring increased resist dose and providing half-field exposures) and/or EUV multi-patterning (requiring increased wafer throughput proportional to the number of exposure passes. Both development paths will require a substantial increase in EUV source power to maintain the economic viability of the technology, creating an opportunity for free-electron laser (FEL) EUV sources. FEL-based EUV sources offer an economic, high-power/single-source alternative to LPP EUV sources. Should free-electron lasers become the preferred next generation EUV source, the choice of FEL emission architecture will greatly affect its operational stability and overall capability. A near-term industrialized FEL is expected to utilize one of the following three existing emission architectures: (1) selfamplified spontaneous emission (SASE), (2) regenerative amplification (RAFEL), or (3) self-seeding (SS-FEL). Model accelerator parameters are put forward to evaluate the impact of emission architecture on FEL output. Then, variations in the parameter space are applied to assess the potential impact to lithography operations, thereby establishing component sensitivity. The operating range of various accelerator components is discussed based on current accelerator performance demonstrated at various scientific user facilities. Finally, comparison of the performance between the model accelerator parameters and the variation in parameter space provides a means to evaluate the potential emission architectures. A scorecard is presented to facilitate this evaluation and provide a framework for future FEL design and enablement for EUV lithography applications.
10. Staged electron laser accelerator (STELLA) experiment at brookhaven ATF
Energy Technology Data Exchange (ETDEWEB)
Pogorelsky, I.V.; Steenbergen, A. van; Gallardo, J.C. [Brookhaven National Lab., Upton, NY (United States)] [and others
1998-03-01
The STELLA experiment is being prepared at the BNL Accelerator Test Facility (STF). The goal of the experiment is to demonstrate quasi-monochromatic inverse Cherenkov acceleration (ICA) of electrons bunched to the laser wavelength period. Microbunches on the order of 2 {mu}m in length separated by 10.6 {mu}m will be produced using an inverse free electron laser (IFEL) accelerator driven by a CO{sub 2} laser. The design and simulations for two phases of this experiment including demonstration of 10 MeV and 100 MeV acceleration are presented. (author)
11. Biomolecular imaging and electronic damage using X-ray free-electron lasers
CERN Document Server
Quiney, Harry M
2010-01-01
Proposals to determine biomolecular structures from diffraction experiments using femtosecond X-ray free-electron laser (XFEL) pulses involve a conflict between the incident brightness required to achieve diffraction-limited atomic resolution and the electronic and structural damage induced by the illumination. Here we show that previous estimates of the conditions under which biomolecular structures may be obtained in this manner are unduly restrictive, because they are based on a coherent diffraction model that is not appropriate to the proposed interaction conditions. A more detailed imaging model derived from optical coherence theory and quantum electrodynamics is shown to be far more tolerant of electronic damage. The nuclear density is employed as the principal descriptor of molecular structure. The foundations of the approach may also be used to characterize electrodynamical processes by performing scattering experiments on complex molecules of known structure.
12. Staged concept of laser-plasma acceleration toward multi-GeV electron beams
Directory of Open Access Journals (Sweden)
Victor Malka
2006-09-01
Full Text Available The concepts of the laser-plasma based accelerator and injector are discussed here. The recent tests done at LOA as well as design studies of high-quality GeV electron beam production with low energy spread (1% are presented. These laser-produced particle beams have a number of interesting properties and could lend themselves to applications in many fields, including medicine (radiotherapy, chemistry (radiolysis, and accelerator physics. They could be used as a source for the production of γ ray beams for nondestructive material inspection by radiography, or for future compact X-free electron laser machines.
13. Laser-driven dielectric electron accelerator for radiobiology researches
Science.gov (United States)
Koyama, Kazuyoshi; Matsumura, Yosuke; Uesaka, Mitsuru; Yoshida, Mitsuhiro; Natsui, Takuya; Aimierding, Aimidula
2013-05-01
In order to estimate the health risk associated with a low dose radiation, the fundamental process of the radiation effects in a living cell must be understood. It is desired that an electron bunch or photon pulse precisely knock a cell nucleus and DNA. The required electron energy and electronic charge of the bunch are several tens keV to 1 MeV and 0.1 fC to 1 fC, respectively. The smaller beam size than micron is better for the precise observation. Since the laser-driven dielectric electron accelerator seems to suite for the compact micro-beam source, a phase-modulation-masked-type laser-driven dielectric accelerator was studied. Although the preliminary analysis made a conclusion that a grating period and an electron speed must satisfy the matching condition of LG/λ = v/c, a deformation of a wavefront in a pillar of the grating relaxed the matching condition and enabled the slow electron to be accelerated. The simulation results by using the free FDTD code, Meep, showed that the low energy electron of 20 keV felt the acceleration field strength of 20 MV/m and gradually felt higher field as the speed was increased. Finally the ultra relativistic electron felt the field strength of 600 MV/m. The Meep code also showed that a length of the accelerator to get energy of 1 MeV was 3.8 mm, the required laser power and energy were 11 GW and 350 mJ, respectively. Restrictions on the laser was eased by adopting sequential laser pulses. If the accelerator is illuminated by sequential N pulses, the pulse power, pulse width and the pulse energy are reduced to 1/N, 1/N and 1/N2, respectively. The required laser power per pulse is estimated to be 2.2 GW when ten pairs of sequential laser pulse is irradiated.
14. Atomic electron correlations in intense laser fields
Energy Technology Data Exchange (ETDEWEB)
DiMauro, L.F.; Sheehy, B.; Walker, B. [Brookhaven National Lab., Upton, NY (United States); Agostini, P.A. [SPAM, Gif Sur Yvette (France). Centre dEtudes de Saclay; Kulander, K.C. [Lawrence Livermore National Lab., CA (United States)
1998-11-01
This talk examines two distinct cases in strong optical fields where electron correlation plays an important role in the dynamics. In the first example, strong coupling in a two-electron-like system is manifested as an intensity-dependent splitting in the ionized electron energy distribution. This two-electron phenomenon (dubbed continuum-continuum Autler-Townes effect) is analogous to a strongly coupled two-level, one-electron atom but raises some intriguing questions regarding the exact nature of electron-electron correlation. The second case examines the evidence for two-electron ionization in the strong-field tunneling limit. Although their ability to describe the one-electron dynamics has obtained a quantitative level of understanding, a description of the two (multiple) electron ionization remains unclear.
15. Paper based electronics platform
KAUST Repository
2017-07-20
A flexible and non-functionalized low cost paper-based electronic system platform fabricated from common paper, such as paper based sensors, and methods of producing paper based sensors, and methods of sensing using the paper based sensors are provided. A method of producing a paper based sensor can include the steps of: a) providing a conventional paper product to serve as a substrate for the sensor or as an active material for the sensor or both, the paper product not further treated or functionalized; and b) applying a sensing element to the paper substrate, the sensing element selected from the group consisting of a conductive material, the conductive material providing contacts and interconnects, sensitive material film that exhibits sensitivity to pH levels, a compressible and/or porous material disposed between a pair of opposed conductive elements, or a combination of two of more said sensing elements. The method of sensing can further include measuring, using the sensing element, a change in resistance, a change in voltage, a change in current, a change in capacitance, or a combination of any two or more thereof.
16. High Efficiency Electron-Laser Interactions in Tapered Helical Undulators
Science.gov (United States)
Duris, Joseph Patrick
Efficient coupling of relativistic electron beams with high power radiation lies at the heart of advanced accelerator and light source research and development. The inverse free electron laser is a stable accelerator capable of harnessing very high intensity laser electric fields to efficiently transfer large powers from lasers to electron beams. In this dissertation, we first present the theoretical framework to describe the interaction, and then apply our improved understanding of the IFEL to the design and numerical study of meter-long, GeV IFELs for compact light sources. The central experimental work of the dissertation is the UCLA BNL helical inverse free electron laser experiment at the Accelerator Test Facility in Brookhaven National Laboratory which used a strongly tapered 54cm long, helical, permanent magnet undulator and a several hundred GW CO2 laser to accelerate electrons from 52 to 106MeV, setting new records for inverse free electron laser energy gain (54MeV) and average accelerating gradient (100MeV/m). The undulator design and fabrication as well as experimental diagnostics are presented. In order to improve the stability and quality of the accelerated electron beam, we redesigned the undulator for a slightly reduced output energy by modifying the magnet gap throughout the undulator, and we used this modified undulator to demonstrated capture of >25% of the injected beam without prebunching. In the study of heavily loaded GeV inverse free electron lasers, we show that a majority of the power may be transferred from a laser to the accelerated electron beam. Reversing the process to decelerate high power electron beams, a mechanism we refer to as tapering enhanced stimulated superradiant amplification, offers a clear path to high power light sources. We present studies of radiation production for a wide range of wavelengths (10mum, 13nm, and 0.3nm) using this method and discuss the design for a deceleration experiment using the same undulator used
17. Modeling and multidimensional optimization of a tapered free electron laser
Directory of Open Access Journals (Sweden)
Y. Jiao
2012-05-01
Full Text Available Energy extraction efficiency of a free electron laser (FEL can be greatly increased using a tapered undulator and self-seeding. However, the extraction rate is limited by various effects that eventually lead to saturation of the peak intensity and power. To better understand these effects, we develop a model extending the Kroll-Morton-Rosenbluth, one-dimensional theory to include the physics of diffraction, optical guiding, and radially resolved particle trapping. The predictions of the model agree well with that of the GENESIS single-frequency numerical simulations. In particular, we discuss the evolution of the electron-radiation interaction along the tapered undulator and show that the decreasing of refractive guiding is the major cause of the efficiency reduction, particle detrapping, and then saturation of the radiation power. With this understanding, we develop a multidimensional optimization scheme based on GENESIS simulations to increase the energy extraction efficiency via an improved taper profile and variation in electron beam radius. We present optimization results for hard x-ray tapered FELs, and the dependence of the maximum extractable radiation power on various parameters of the initial electron beam, radiation field, and the undulator system. We also study the effect of the sideband growth in a tapered FEL. Such growth induces increased particle detrapping and thus decreased refractive guiding that together strongly limit the overall energy extraction efficiency.
18. A microtron accelerator for a free electron laser
NARCIS (Netherlands)
Botman, J.I.M.; Delhez, J.L.; Webers, G.A.; Hagedoorn, H.L.; Kleeven, W.J.G.M.; Timmermans, J.C.M.; Ernst, G.J.; Verschuur, Jeroen W.J.; Witteman, W.J.; Haselhoff, E.H.; Haselhoff, E.H.
1991-01-01
A racetrack microtron as a source for a free electron laser is being constructed. It will accelerate electrons up to 25 MeV to provide 10 ¿m radiation in a hybrid undulator with a periodicity distance of 25 mm. The aim is to accelerate 100 A bunches of 30 ps pulse length at 81.25 MHz. This frequency
19. Electron bunch injection at an angle into a laser wakefield
NARCIS (Netherlands)
Luttikhof, M.J.H.; Khachatryan, A.G.; van Goor, F.A.; Boller, Klaus J.; Mora, P.
2009-01-01
External injection of electron bunches longer than the plasma wavelength in a laser wakefield accelerator can lead to the generation of femtosecond ultra relativistic bunches with a couple of percent energy spread. Extensive study has been done on external electron bunch (e.g., one generated by a
20. Enhanced electron yield from a laser-plasma accelerator using high-Z gas jet targets
CERN Document Server
Mirzaie, Mohammad; Li, Song; Sokollik, Thomas; He, Fei; Cheng, Ya; Sheng, Zhengming; Zhang, Jie
2014-01-01
An investigation of the multi-hundred MeV electron beam yield (charge) form helium, nitrogen, neon and argon gas jet plasmas in a laser-plasma wakefield acceleration experiment was carried out. The charge measurement has been made via imaging the electron beam intensity profile on a fluorescent screen into a 14-bit charge coupled device (CCD) which was cross-calibrated with nondestructive electronics-based method. Within given laser and plasma parameters, we found that laser-driven low Z- gas jet targets generate high-quality and well-collimated electron beams with reasonable yields at the level of 10-100 pC. On the other hand, filamentary electron beams which were observed from high-Z gas jets at higher densities reached much higher yield. Evidences for cluster formation were clearly observed in high-Z gases, especially in the argon gas jet target where we received the highest yield of ~ 3 nC
1. Theory and Simulation of an Inverse Free Electron Laser Experiment
Science.gov (United States)
Guo, S. K.; Bhattacharjee, A.; Fang, J. M.; Marshall, T. C.
1996-11-01
An experimental demonstration of the acceleration of electrons using a high power CO2 laser in an inverse free electron laser (IFEL) is underway at the Brookhaven National Laboratory. This experiment has generated data, which we are attempting to simulate. Included in our studies are such effects as: a low-loss metallic waveguide with a dielectric coating on the walls; multi-mode coupling due to self-consistent interaction between the electrons and the optical wave; space charge (which is significant at lower laser power); energy-spread of the electrons; arbitrary wiggler field profile; and slippage. Two types of wiggler profile have been considered: a linear taper of the period, and a step-taper of the period (the period is ~ 3cm, the field is ~ 1T, and the wiggler length is 47cm). The energy increment of the electrons ( ~ 1-2%) is analyzed in detail as a function of laser power, wiggler parameters, and the initial beam energy (40MeV). For laser power ~ 0.5GW, the predictions of the simulations are in good accord with experimental results. A matter currently under study is the discrepancy between theory and observations for the electron energy distribution observed at the end of the IFEL. This work is supported by the Department of Energy.
2. Enhanced Laser-to-Electron Energy Conversion Efficiency using Micro-Plasma Waveguide (MPW) Targets
Science.gov (United States)
Nasir, Derek; Snyder, Joseph; Ji, Liang; George, Kevin; Willis, Christopher; Cochran, Ginevra; Zingale, Anthony; Daskalova, Rebecca; Schumacher, Doug; van Woerkom, Linn
2017-10-01
We present experiments from the Scarlet laser facility and 3D Particle in Cell (PIC) simulations detailing the improved hot electron spectrum of MPW targets over flat targets. We observe an increase in the electron cutoff energy by a factor of 3 and a 10x enhancement of the total signal of electrons above 5MeV. From PIC simulations, we see strong transverse electric fields extract electron bunches from the MPW walls with the laser period, which are then accelerated by the usual vxB force. In addition, quasi-static longitudinal electric fields arise and are observed to increase the acceleration length of electrons along the tube walls. In this way, the micro-engineered structures provide a geometry more conducive to efficient direct laser acceleration and offer a new dimension in target design. We present evidence that by varying the structure's geometry we can alter the laser plasma interactions with applications in high field science, laser based proton therapy and relativistic nonlinear optics. In particular, the relationship between the MPW tube and laser-electron dephasing length is examined. AFOSR #FA9550-14-1-0085; NNSA #DE-NA0003107; DOE #DE-SC0012333.
3. Electron heating by intense short-pulse lasers propagating through near-critical plasmas
Science.gov (United States)
Debayle, A.; Mollica, F.; Vauzour, B.; Wan, Y.; Flacco, A.; Malka, V.; Davoine, X.; Gremillet, L.
2017-12-01
We investigate the electron heating induced by a relativistic-intensity laser pulse propagating through a near-critical plasma. Using particle-in-cell simulations, we show that a specific interaction regime sets in when, due to the energy depletion caused by the plasma wakefield, the laser front profile has steepened to the point of having a length scale close to the laser wavelength. Wave breaking and phase mixing have then occurred, giving rise to a relativistically hot electron population following the laser pulse. This hot electron flow is dense enough to neutralize the cold bulk electrons during their backward acceleration by the wakefield. This neutralization mechanism delays, but does not prevent the breaking of the wakefield: the resulting phase mixing converts the large kinetic energy of the backward-flowing electrons into thermal energy greatly exceeding the conventional ponderomotive scaling at laser intensities > {10}21 {{{W}}{cm}}-2 and gas densities around 10% of the critical density. We develop a semi-numerical model, based on the Akhiezer–Polovin equations, which correctly reproduces the particle-in-cell-predicted electron thermal energies over a broad parameter range. Given this good agreement, we propose a criterion for full laser absorption that includes field-induced ionization. Finally, we show that our predictions still hold in a two-dimensional geometry using a realistic gas profile.
4. Nonlinear model for thermal effects in free-electron lasers
OpenAIRE
Peter, Eduardo Alcides; Endler, Antônio; Rizzato, Felipe Barbedo
2014-01-01
In the present work, we extend results of a previous paper [Peter et al., Phys. Plasmas 20, 12 3104 (2013)] and develop a semi-analytical model to account for thermal effects on the nonlinear dynamics of the electron beam in free-electron lasers. We relax the condition of a cold electron beam but still use the concept of compressibility, now associated with a warm beam model, to evaluate the time scale for saturation and the peak laser intensity in high-gain regimes. Although vanishing compre...
5. Longitudinal Coherence Preservation and Chirp Evolution in a High Gain Laser Seeded Free Electron Laser Amplifier
Energy Technology Data Exchange (ETDEWEB)
Murphy, J.B.; /BNL, NSLS; Wu, Juhao; /SLAC; Wang, X.J.; Watanabe, T.; /BNL, NSLS
2006-06-07
In this letter we examine the start-up of a high gain free electron laser in which a frequency-chirped coherent seed laser pulse interacts with a relativistic electron beam. A Green function formalism is used to evaluate the initial value problem. We have fully characterized the startup and evolution through the exponential growth regime. We obtain explicit expressions for the pulse duration, bandwidth and chirp of the amplified light and show that the FEL light remains fully longitudinally coherent.
6. Femtosecond laser electronic excitation tagging for aerodynamic and thermodynamic measurements
Science.gov (United States)
Calvert, Nathan David
This thesis presents applications of Femtosecond Laser Electronic Excitation Tagging (FLEET) to a variety of aerodynamic and thermodynamic measurements. FLEET tagged line characteristics such as intensity, width and spectral features are investigated in various flow conditions (pressure, temperature, velocity, steadiness, etc.) and environments (gas composition) for both temporally and spatially instantaneous and averaged data. Special attention is drawn to the nature of first and second positive systems of molecular nitrogen and the ramifications on FLEET measurements. Existing laser-based diagnostic techniques are summarized and FLEET is directly compared with Particle Image Velocimetry (PIV) in various low speed flows. Multidimensional velocity, acceleration, vorticity and other flow parameters are extracted in supersonic free jets and within an enclosed in-draft tunnel test section. Probability distribution functions of the mean and standard deviation of critical flow parameters are unveiled by utilizing a Bayesian statistical framework wherein likelihood functions are established from prior and posterior distributions. Advanced image processing techniques based on fuzzy logic are applied to single-shot FLEET images with low signal-to-noise ratio to improve image quality and reduce uncertainty in data processing algorithms. Lastly, FLEET second positive and first negative emission are considered at a wide range of pressures to correct for changes in select rovibrational peak magnitude and shape due to density from which bulk gas temperature may be extracted.
7. Compact two-beam push-pull free electron laser
Science.gov (United States)
Hutton, Andrew [Yorktown, VA
2009-03-03
An ultra-compact free electron laser comprising a pair of opposed superconducting cavities that produce identical electron beams moving in opposite directions such that each set of superconducting cavities accelerates one electron beam and decelerates the other electron beam. Such an arrangement, allows the energy used to accelerate one beam to be recovered and used again to accelerate the second beam, thus, each electron beam is decelerated by a different structure than that which accelerated it so that energy exchange rather than recovery is achieved resulting in a more compact and highly efficient apparatus.
8. Functional Laser Trimming of Automotive Electronics
OpenAIRE
Chris Davison; Junji Mitobe
1981-01-01
This paper discusses the use of laser trim systems for the trimming of automotive hybrids. Being high volume parts these devices are best trimmed in two stages; first, a passive trim of the resistor substrate and secondly, a functional trim. The requirements for such a functional trim are such as to demand a fully integrated system.
9. High-flux electron beams from laser wakefield accelerators driven by petawatt lasers
Science.gov (United States)
Zeng, Ming; Tesileanu, Ovidiu
2017-07-01
Laser wakefield accelerators (LWFAs) are considered to be one of the most competitive next-generation accelerator candidates. In this paper, we will study the potential high-flux electron beam production of an LWFA driven by petawatt-level laser pulses. In our three-dimensional particle-in-cell simulations, an optimal set of parameters gives ˜ 40 {nC} of charge with 2 {PW} laser power, thus ˜ 400 {kA} of instantaneous current if we assume the electron beam duration is 100 fs. This high flux and its secondary radiation are widely applicable in nuclear and QED physics, industrial imaging, medical and biological studies.
10. Spatial Control of Laser Wakefield Accelerated Electron Beams
Science.gov (United States)
Maksimchuk, A.; Behm, K.; Zhao, T.; Joglekar, A. S.; Hussein, A.; Nees, J.; Thomas, A. G. R.; Krushelnick, K.; Elle, J.; Lucero, A.; Samarin, G. M.; Sarry, G.; Warwick, J.
2017-10-01
The laser wakefield experiments to study and control spatial properties of electron beams were performed using HERCULES laser at the University of Michigan at power of 100 TW. In the first experiment multi-electron beam generation was demonstrated using co-propagating, parallel laser beams with a π-phase shift mirror and showing that interaction between the wakefields can cause injection to occur for plasma and laser parameters in which a single wakefield displays no significant injection. In the second experiment a magnetic triplet quadrupole system was used to refocus and stabilize electron beams at the distance of 60 cm from the interaction region. This produced a 10-fold increase in remote gamma-ray activation of 63Cu using a lead converter. In the third experiment measurements of un-trapped electrons with high transverse momentum produce a 500 mrad (FWHM) ring. This ring is formed by electrons that receive a forward momentum boost by traversing behind the bubble and its size is inversely proportional to the plasma density. The characterization of divergence and charge of this electron ring may reveal information about the wakefield structure and trapping potential. Supported by U.S. Department of Energy and the National Nuclear Security Administration and Air Force Office of Scientific Research.
11. Dimuon production by laser-wakefield accelerated electrons
Directory of Open Access Journals (Sweden)
A. I. Titov
2009-11-01
Full Text Available We analyze μ^{+}μ^{-} pair production generated by high-energy electrons emerging from a laser-wakefield accelerator. The μ^{+}μ^{-} pairs are created in a solid thick high-Z target, following the electron accelerating plasma region. Numerical estimates are presented for 1 to 10 GeV electron beams which are expected to be reliable in the nearest future. Reactions induced by the secondary bremsstrahlung photons dominate the dimuon production. According to our estimates, a 20 pC electron bunch with energy of 1 (10 GeV may create about 100 (5000 muon pairs. The produced μ^{±} can be used in studying various aspects of muon-related physics in tabletop installations. This may be considered as an important step towards the investigation of more complicated elementary processes induced by laser-driven electrons.
12. Verification of a characterization method of the laser-induced selective activation based on industrial lasers
DEFF Research Database (Denmark)
Zhang, Yang; Hansen, Hans Nørgaard; Tang, Peter T.
2013-01-01
In this article, laser-induced selective activation (LISA) for subsequent autocatalytic copper plating is performed by several types of industrial scale lasers, including a Nd:YAG laser, a UV laser, a fiber laser, a green laser, and a short pulsed laser. Based on analysis of all the laser-machine...
13. Biomedical Studies with the Free Electron Laser
Science.gov (United States)
1989-05-15
Liaw L-H. and &,rns NMW%, Retinal References effects of the frequencý -doubled 15 3- m AG laser Histo- pathological comnparison with argon laser...much mare speaficaiIy locaiznd. (A-fl) X 630- Vol. S.90 No. 5. May 4. 1988 - 4D~~i .i ’’.A. ’A G. ii KieS R6,. -ft ’i 1’a’e- M-.r~.r ~c ji’N ot ýanccr...CHE-4o M-L Biological and biophysical properties of -,hc pntrialocyaninc-s. V. Photodynamic therapy of E.Mt-h mammary tu- tumor localizing component
14. Laser-initiated explosive electron emission from flat germanium crystals
Energy Technology Data Exchange (ETDEWEB)
Porshyn, V., E-mail: [email protected]; Mingels, S.; Lützenkirchen-Hecht, D.; Müller, G. [Faculty of Mathematics and Natural Sciences, Physics Department, University of Wuppertal, Wuppertal 42119 (Germany)
2016-07-28
Flat Sb-doped germanium (100) crystals were investigated in the triode configuration under pulsed tunable laser illumination (pulse duration t{sub laser} = 3.5 ns and photon energy hν = 0.54–5.90 eV) and under DC voltages <10{sup 4} V. Large bunch charges up to ∼1 μC were extracted from the cathodes for laser pulses >1 MW/cm{sup 2} corresponding to a high quantum efficiency up to 3.3% and cathode currents up to 417 A. This laser-induced explosive electron emission (EEE) from Ge was characterized by its voltage-, laser power- and hν-sensitivity. The analysis of the macroscopic surface damage caused by the EEE is included as well. Moreover, we have carried out first direct measurements of electron energy distributions produced during the EEE from the Ge samples. The measured electron spectra hint for electron excitations to the vacuum level of the bulk and emission from the plasma plume with an average kinetic energy of ∼0.8 eV.
Science.gov (United States)
1984-04-01
and 1,,) call be obtained quickly from F(.)) by dividing out the detector response P(W). If 1,(/) is modeled the inverse bunch length can be estimated...If a single harmonic of the comb spectrum of l(.’) is examined the change in the amplitude will be inversely proportional to the bunch-length change...obtained while operating the SRFEL as an amplier to an externa ’ laser [8,)]. All of the measurements presented here were obtained with svnchronous
16. Electron acceleration using laser produced plasmas
CERN Multimedia
CERN. Geneva; Landua, Rolf
2005-01-01
Low density plasmas have long been of interest as a potential medium for particle acceleration since relativistic plasma waves are capable of supporting electric fields greater than 100 GeV/m. The physics of particle acceleration using plasmas will be reviewed, and new results will be discussed which have demonstrated that relatively narrow energy spread (<3%) beams having energies greater than 100 MeV can be produced from femtosecond laser plasma interactions. Future experiments and potential applications will also be discussed.
17. Short Rayleigh Range Free Electron Laser Amplifiers
CERN Document Server
Yu, L H; Murphy, J B; Rose, J; Shaftan, T V; Wang, X J; Watanabe, T
2005-01-01
An important requirement for a high average power laser system is a manageable power density on the first optical element. One possibility to achieve this is a single pass amplifier which generates a short Rayleigh range (SRL) light beam. We present design parameters and calculated performances for several SRL configurations. These include a simulation of the optically guided (pinched) MW class FEL [1], the scalloped beam FEL amplifier [2] and high gain TOK amplifiers we propose to explore at our SDL facility.
18. Ultraviolet Free Electron Laser Facility preliminary design report
Energy Technology Data Exchange (ETDEWEB)
Ben-Zvi, I. [ed.
1993-02-01
This document, the Preliminary Design Report (PDR) for the Brookhaven Ultraviolet Free Electron Laser (UV FEL) facility, describes all the elements of a facility proposed to meet the needs of a research community which requires ultraviolet sources not currently available as laboratory based lasers. Further, for these experiments, the requisite properties are not extant in either the existing second or upcoming third generation synchrotron light sources. This document is the result of our effort at BNL to identify potential users, determine the requirements of their experiments, and to design a facility which can not only satisfy the existing need, but have adequate flexibility for possible future extensions as need dictates and as evolving technology allows. The PDR is comprised of three volumes. In this, the first volume, background for the development of the proposal is given, including descriptions of the UV FEL facility, and representative examples of the science it was designed to perform. Discussion of the limitations and potential directions for growth are also included. A detailed description of the facility design is then provided, which addresses the accelerator, optical, and experimental systems. Information regarding the conventional construction for the facility is contained in an addendum to volume one (IA).
19. Laser and electron beam processing of silicon and gallium arsenide
Energy Technology Data Exchange (ETDEWEB)
Narayan, J.
1979-10-01
Laser (photon) and electron beams provide a controlled source of heat by which surface layers of silicon and gallium arsenide can be rapidly melted and cooled with rates exceeding 10/sup 80/C/sec. The melting process has been used to remove displacement damage in ion implanted Si and GaAs, to remove dislocations, loops and precipitates in silicon and to study impurity segregation and solubility limits. The mechanisms associated with various phenomena will be examined. The possible impact of laser and electron beam processing on device technology, particularly with respect to solar cells is discussed.
20. Search for electron EDM with laser cooled radioactive atom
Science.gov (United States)
Inoue, T.; Arikawa, H.; Ezure, S.; Harada, K.; Hayamizu, T.; Ishikawa, T.; Itoh, M.; Kato, T.; Kawamura, H.; Nataraj, H. S.; Sato, T.; Aoki, T.; Furukawa, T.; Hatakeyama, A.; Hatanaka, K.; Imai, K.; Murakami, T.; Shimizu, Y.; Wakasa, T.; Yoshida, H. P.; Sakemi, Y.
2013-05-01
The permanent electric dipole moment (EDM) of the elementary particle has the sensitivity to the CP violation in the theories beyond the standard model (SM). The search for the EDM constitutes the stringent test to discriminate between the SM and beyond it. We plan to perform the electron EDM search by using the laser cooled francium (Fr) atom which has the largest enhancement factor of the electron EDM in the alkali atoms. In this paper, the present status of the laser cooled Fr factory that is being constructed at Cyclotron and Radioisotope Center (CYRIC), Tohoku University are reported.
1. Control Chaotic Diffusion in a Single Pass Free Electron Laser
CERN Document Server
Antoniazzi, A
2005-01-01
We apply an innovative strategy to control chaotic diffusion in conservative systems to the case of a single pass Free Electron Laser. The core of our approach is a small apt modification of the system which channels chaos by building barriers to diffusion. By confining the electrons in phase space and limiting the oscillations of the dense core, we aim at stabilizing the laser intensity. Calculations are perfomed within the framework of a simplified Hamiltonian picture. Further extensions and future experimental applications are also discussed.
2. A "slingshot" laser-driven acceleration mechanism of plasma electrons
CERN Document Server
Fiore, Gaetano; Fedele, Renato
2016-01-01
We briefly report on the recently proposed [G. Fiore, R. Fedele, U. de Angelis, Phys. Plasmas 21 (2014), 113105], [G. Fiore, S. De Nicola, arXiv:1509.04656] electron acceleration mechanism named "slingshot effect": under suitable conditions the impact of an ultra-short and ultra-intense laser pulse against the surface of a low-density plasma is expected to cause the expulsion of a bunch of superficial electrons with high energy in the direction opposite to that of the pulse propagation; this is due to the interplay of the huge ponderomotive force, huge longitudinal field arising from charge separation, and the finite size of the laser spot.
3. Supersonic micro-jets and their application to few-cycle laser-driven electron acceleration
Energy Technology Data Exchange (ETDEWEB)
Schmid, Karl
2009-07-23
This thesis covers the few-cycle laser-driven acceleration of electrons in a laser-generated plasma. The laser system employed in this work is a new development based on optical parametric chirped pulse amplification and is the only multi-TW few-cycle laser in the world. In the experiment, the laser beam is focused onto a supersonic helium gas jet which leads to the formation of a plasma channel. The laser pulse, having an intensity of 10{sup 19} W/cm{sup 2} propagates through the plasma with an electron density of 2 x 10{sup 19} cm{sup -3} and forms via a highly nonlinear interaction a strongly anharmonic plasma wave. The amplitude of the wave is so large that the wave breaks, thereby injecting electrons from the background plasma into the accelerating phase. The energy transfer from the laser pulse to the plasma is so strong that the maximum propagation distance is limited to the 100 m range. Therefore, gas jets specifically tuned to these requirements have to be employed. The properties of microscopic supersonic gas jets are thoroughly analyzed in this work. Based on numeric flow simulation, this study encompasses several extensive parameter studies that illuminate all relevant features of supersonic flows in microscopic gas nozzles. This allowed the optimized design of de Laval nozzles with exit diameters ranging from 150 {mu}m to 3 mm. The employment of these nozzles in the experiment greatly improved the electron beam quality. After these optimizations, the laser-driven electron accelerator now yields monoenergetic electron pulses with energies up to 50 MeV and charges between one and ten pC. The electron beam has a typical divergence of 5 mrad and comprises an energy spectrum that is virtually free from low energetic background. The electron pulse duration could not yet be determined experimentally but simulations point towards values in the range of 1 fs. The acceleration gradient is estimated from simulation and experiment to be approximately 0.5 TV/m. The
4. Short electron bunches generated by perpendicularly crossing laser pulses
Science.gov (United States)
Horný, Vojtěch; Petržílka, Václav; Klimo, Ondřej; Krůs, Miroslav
2017-10-01
Optical injection of electrons into a laser wakefield accelerator by a low intensity orthogonally colliding laser pulse is investigated using 2D particle-in-cell simulations. The collision of the main laser pulse driving the plasma wave in the cavitated regime and the low intensity injection pulse affects the trajectories of electrons in the crossing region. As a consequence, some electrons are ejected into the front part of the bubble, and these electrons are subsequently trapped in the rear part of the bubble. The injected and accelerated electron bunch reaches a peak energy of 630 MeV after 8 ps of acceleration being as short as 7.0 fs and is quasimonoenergetic with a low energy spread of 20 MeV (3.8%), having a charge of several dozens of pC and a relatively large emittance of 2.27 π . mm . mrad. Two main injection mechanisms—crossing beatwave injection and injection by laser field preacceleration—were identified.
5. Plasma Channel Diagnostic Based on Laser Centroid Oscillations
Energy Technology Data Exchange (ETDEWEB)
Gonsalves, Anthony; Nakamura, Kei; Lin, Chen; Osterhoff, Jens; Shiraishi, Satomi; Schroeder, Carl; Geddes, Cameron; Toth, Csaba; Esarey, Eric; Leemans, Wim
2010-09-09
A technique has been developed for measuring the properties of discharge-based plasma channels by monitoring the centroid location of a laser beam exiting the channel as a function of input alignment offset between the laser and the channel. The centroid position of low-intensity (<10{sup 14}Wcm{sup -2}) laser pulses focused at the input of a hydrogen-filled capillary discharge waveguide was scanned and the exit positions recorded to determine the channel shape and depth with an accuracy of a few %. In addition, accurate alignment of the laser beam through the plasma channel can be provided by minimizing laser centroid motion at the channel exit as the channel depth is scanned either by scanning the plasma density or the discharge timing. The improvement in alignment accuracy provided by this technique will be crucial for minimizing electron beam pointing errors in laser plasma accelerators.
6. Laser manufacturing for transparent, flexible and stretchable electronics (Conference Presentation)
Science.gov (United States)
Wang, Shutong; Yu, Yongchao; Feng, Guoying; Hu, Anming
2017-02-01
We investigated the interaction between femotsecond laser and polyimide with a high repetition femtosecond fiber laser and a precisely motorized 3D stage. We have found that high repetition femtosecond laser pulse train can effectively fabricate double-layer electrical conductive tracks inside a polyimide (PI) sheets by a single-time irradiation. This interaction comprised multi-photon absorption, dissociation of polymer molecules and the thermal accumulation. The experiment unveiled that dual-layer carbonization was a consequence of an inside micro-lens formed instantly as laser was just focused into the inside of polyimide. This micro-lens further focused the subsequent laser pulse to carbonize the polymer through multi-photon excitation, bond breaking and graphite layer reformation and eventually form the second electronic conductive layer. The second conductive layer was generated below the focal point. With the laser irradiating is kept at the same height, the top layer at the focused plane continued to absorb laser energy then carbonized into the conductive layer. We called the process as a kind of self-focusing phenomenon. We study the focus effect of inside microlenses under different laser powers and irradiation times. The gap of double electronic tracks embedded in the polyimide matrix can be adjusted with the laser processing parameters. When the gap is more than 30 micrometer, two conductive layers are electrically insulating. While the gap is smaller than 10 micrometer, two conductive layers are electrically connected. Various applications, such as, supercapacitors, capacitive sensors and the field effect transistors were investigated in the flexible PI sheets using this 3D double-layer electrical conductive architecture.
7. Electron Acceleration By The Use Of Segmented Cylindrical Electrodes In An Inverse Free Electron Laser
Directory of Open Access Journals (Sweden)
M. Nikrah
2015-08-01
Full Text Available Abstract- In this paper we expend a theory of high gradient laser excited electron accelerator by the use of an inverse free-electron laser IFEL but with using new structure and design. The wiggler used in our scheme that is to say Paul wiggler is obtainedby segmented cylindrical electrodes with applied oscillatory voltagesVosc tover 90-degrees segments. The inverse free-electron laser interaction can be demonstrated by the equations that govern the electron motion in the composed fields of both laser pulse and Paul wiggler field. A numerical research of electron energy and electron trajectories has been made using fourth order Runge-Kutta method. The results show that the electron gains the maximum energy at a short distance for high wiggler amplitude intensities a0w. In addition it is discovered that the electron energy gains various peaks for different initial axial velocities. It is seen that aappropriate small initial axial velocity of e-beam produces remarkably high energy gain. According to the transverse limitation of the electron beam in a Paul wiggler there is no applied axial guide magnetic field in this devise.
8. Simulation of relativistically colliding laser-generated electron flows
CERN Document Server
Yang, Xiaohu; Sarri, Gianluca; Borghesi, Marco
2012-01-01
The plasma dynamics resulting from the simultaneous impact, of two equal, ultra-intense laser pulses, in two spatially separated spots, onto a dense target is studied via particle-in-cell (PIC) simulations. The simulations show that electrons accelerated to relativistic speeds, cross the target and exit at its rear surface. Most energetic electrons are bound to the rear surface by the ambipolar electric field and expand along it. Their current is closed by a return current in the target, and this current configuration generates strong surface magnetic fields. The two electron sheaths collide at the midplane between the laser impact points. The magnetic repulsion between the counter-streaming electron beams separates them along the surface normal direction, before they can thermalize through other beam instabilities. This magnetic repulsion is also the driving mechanism for the beam-Weibel (filamentation) instability, which is thought to be responsible for magnetic field growth close to the internal shocks of ...
9. Nonlinear electron emission in ultrashort laser pulses and rescattering suppression
Science.gov (United States)
Mikhin, E. A.; Preobrazhenskii, M. A.; Golovinski, P. A.
2017-11-01
The process of nonlinear electron emission from a metal surface under the action of femtosecond laser pulse with moderate intensity ~1011 W/cm2 is considered. One-dimensional model is formulated, taking into account the advantage of the p-polarized light in the nonlinear emission. The time dependent Schrödinger equation with fixed equilibrium boundary conditions is solved in the half-space using the Laplace transform technique. The energy spectrum of emitted electrons is presented, including analysis of dependence on the laser pulse parameters. In the framework of classical mechanics, the impact of additional dc electric field on the rescattering of emitted electron on the metal surface is investigated. The model reproduces the fiches of electron energy distribution and can be used at arbitrary Keldysh parameters.
10. Electron bow-wave injection of electrons in laser-driven bubble acceleration.
Science.gov (United States)
Ma, Y Y; Kawata, S; Yu, T P; Gu, Y Q; Sheng, Z M; Yu, M Y; Zhuo, H B; Liu, H J; Yin, Y; Takahashi, K; Xie, X Y; Liu, J X; Tian, C L; Shao, F Q
2012-04-01
An electron injection regime in laser wake-field acceleration, namely electron bow-wave injection, is investigated by two- and three-dimensional particle-in-cell simulation as well as analytical model. In this regime electrons in the intense electron bow wave behind the first bubble catch up with the bubble tail and are trapped by the bubble finally, resulting in considerable enhancement of the total trapped electron number. For example, with the increase of the laser intensity from 2 × 10(19) to 1 × 10(20) W/cm(2), the electron trapping changes from normal self-injection to bow-wave injection and the trapped electron number is enhanced by two orders of magnitude. An analytical model is proposed to explain the numerical observation.
11. Emittance Measurements from a Laser Driven Electron Injector
Energy Technology Data Exchange (ETDEWEB)
Reis, David A
2003-07-28
The Gun Test Facility (GTF) at the Stanford Linear Accelerator Center was constructed to develop an appropriate electron beam suitable for driving a short wavelength free electron laser (FEL) such as the proposed Linac Coherent Light Source (LCLS). For operation at a wavelength of 1.5 {angstrom}, the LCLS requires an electron injector that can produce an electron beam with approximately 1 {pi} mm-mrad normalized rms emittance with at least 1 nC of charge in a 10 ps or shorter bunch. The GTF consists of a photocathode rf gun, emittance-compensation solenoid, 3 m linear accelerator (linac), drive laser, and diagnostics to measure the beam. The rf gun is a symmetrized 1.6 cell, s-band high gradient, room temperature, photocathode structure. Simulations show that this gun when driven by a temporally and spatially shaped drive laser, appropriately focused with the solenoid, and further accelerated in linac can produce a beam that meets the LCLS requirements. This thesis describes the initial characterization of the laser and electron beam at the GTF. A convolved measurement of the relative timing between the laser and the rf phase in the gun shows that the jitter is less than 2.5 ps rms. Emittance measurements of the electron beam at 35 MeV are reported as a function of the (Gaussian) pulse length and transverse profile of the laser as well as the charge of the electron beam at constant phase and gradient in both the gun and linac. At 1 nC the emittance was found to be {approx} 13 {pi} mm-mrad for 5 ps and 8 ps long laser pulses. At 0.5 nC the measured emittance decreased approximately 20% in the 5 ps case and 40% in the 8 ps case. These measurements are between 40-80% higher than simulations for similar experimental conditions. In addition, the thermal emittance of the electron beam was measured to be 0.5 {pi} mm-mrad.
12. Short energetic electron bunches from laser wakefield accelerator with orthogonally polarized perpendicularly crossed laser pulses
Science.gov (United States)
Horný, Vojtěch; Petržílka, Václav; Klimo, Ondřej; Krůs, Miroslav
2017-05-01
Electron acceleration with optical injection by a perpendicularly propagating and orthogonally polarized low intensity laser pulse into a nonlinear plasma wave driven by a short intense laser pulse was explored by particle- in-cell simulations. The scheme presented here provides an energetic electron bunch in the first ion cavity with a low energy spread. The electron bunch short and compact, with the mean energy about 400 MeV and a low energy spread about 10 MeV in time of 6 ps of acceleration. The injected charge is several tens of pC for the low intensity of the injection pulse. Initial positions of electrons forming the energetic bunch are shown and then these electrons are followed during the simulation in order to understand the injection process and determine electron bunch properties.
13. Quantum/classical mode evolution in free electron laser oscillators
Science.gov (United States)
Bosco, P.; Colson, W. B.; Freedman, R. A.
1983-01-01
The problem of oscillator evolution and mode competition in free electron lasers is studied. Relativistic quantum field theory is used to calculate electron wave functions, the angular distribution of spontaneous emission, and the transition rates for stimulated emission and absorption in each mode. The photon rate equation for the weakfield regime is presented. This rate equation is applied to oscillator evolution with a conventional undulator, a two-stage optical klystron, and a tapered undulator. The effects of noise are briefly discussed.
14. Laser-based coatings removal
Energy Technology Data Exchange (ETDEWEB)
Freiwald, J.G.; Freiwald, D.A. [F2 Associates, Inc., Albuquerque, NM (United States)
1995-10-01
Over the years as building and equipment surfaces became contaminated with low levels of uranium or plutonium dust, coats of paint were applied to stabilize the contaminants in place. Most of the earlier paint used was lead-based paint. More recently, various non-lead-based paints, such as two-part epoxy, are used. For D&D (decontamination and decommissioning), it is desirable to remove the paints or other coatings rather than having to tear down and dispose of the entire building. This report describes the use of pulse-repetetion laser systems for the removal of paints and coatings.
15. Microlens Array Laser Transverse Shaping Technique for Photoemission Electron Source
Energy Technology Data Exchange (ETDEWEB)
Halavanau, A. [Northern Illinois Univ., DeKalb, IL (United States); Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States); Ha, G. [Argonne National Lab. (ANL), Argonne, IL (United States); Pohang Univ. of Science and Technology (POSTECH) (Korea, Republic of); Qiang, G. [Argonne National Lab. (ANL), Argonne, IL (United States); Tsinghua Univ., Beijing (China); Gai, W. [Argonne National Lab. (ANL), Argonne, IL (United States); Power, J. [Argonne National Lab. (ANL), Argonne, IL (United States); Piot, P. [Northern Illinois Univ., DeKalb, IL (United States); Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States); Wisniewski, E. [Argonne National Lab. (ANL), Argonne, IL (United States); Edstrom, D. [Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States); Ruan, J. [Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States); Santucci, J. [Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States)
2016-09-06
A common issue encountered in photoemission electron sources used in electron accelerators is distortion of the laser spot due to non ideal conditions at all stages of the amplification. Such a laser spot at the cathode may produce asymmetric charged beams that will result in degradation of the beam quality due to space charge at early stages of acceleration and fail to optimally utilize the cathode surface. In this note we study the possibility of using microlens arrays to dramatically improve the transverse uniformity of the drive laser pulse on UV photocathodes at both Fermilab Accelerator Science \\& Technology (FAST) facility and Argonne Wakefield Accelerator (AWA). In particular, we discuss the experimental characterization of the homogeneity and periodic patterned formation at the photocathode. Finally, we compare the experimental results with the paraxial analysis, ray tracing and wavefront propagation software.
16. Nonlinear Optics with a Free-Electron Laser
NARCIS (Netherlands)
Eliel, E. R.; van der Ham, E. W. M.; Vrehen, Q. H. F.; Barmentlo, M.; Thooft, G. W.; van der Meer, A. F. G.; van Amersfoort, P. W.
1994-01-01
We report on an experiment on spectroscopic infrared-visible Sum-Frequency Generation (SFG) with a Free-Electron Laser (FEL) as the IR-source. The SFG spectrum of gallium phosphide has been investigated in detail in an experiment covering the unsurpassed spectral range from 20 to 32 mum. This
17. Mechanisms for the production of harmonics in free electron lasers
NARCIS (Netherlands)
Elgin, J.N.; Penman, C.
1991-01-01
Harmonics in the radiation of a free electron laser are useful for extending the range of tuning, may originate in spontaneous or parametric processes, and can take part in stimulated emission or amplification. These mechanisms exhibit interesting analogies with those of nonlinear optics. Apart from
18. Modeling paraxial wave propagation in free-electron laser oscillators
NARCIS (Netherlands)
Karssenberg, J.G.; van der Slot, Petrus J.M.; Volokhine, I.; Verschuur, Jeroen W.J.; Boller, Klaus J.
2006-01-01
Modeling free-electron laser (FEL) oscillators requires calculation of both the light-beam interaction within the undulator and the light propagation outside the undulator. We have developed a paraxial optical propagation code that can be combined with various existing models of gain media, for
19. Accuracy of laser measurements improved by pulse autocorrelator electronic system
Science.gov (United States)
Campanella, S. J.
1967-01-01
Pulse autocorrelator electronic system discriminates between the dispersion effect of a disturbed laser signal and background noise by detecting multipath arrivals of Gaussian-shaped signal pulses. The autocorrelation function is time-dependent and can be determined by integrating the product of a received pulse and its delayed replicas.
20. Laguerre-Gaussian Modes in the Free Electron Laser
Science.gov (United States)
2007-06-01
www.fel.duke.edu, 20 March 2007. [6] W.B. Colson, C. Pellegrini and A. Renieri, Free Electron Laser Handbook, Volume 6, Chapter 5, North-Holland...California 6. Professor Peter Crooker Naval Postgraduate School Monterey, California 7. Chairman, Physics Department Naval Postgraduate School Monterey, California 8. Air Attache Embassy of Greece Washington, DC
1. Measurements of plasma temperature and electron density in laser ...
Abstract. Plasma produced by a 355 nm pulsed Nd:YAG laser with a pulse duration of 6 ns focussed onto a copper solid sample in air at atmospheric pressure is studied spectroscopically. The temperature and electron density characterizing the plasma are measured by time-resolved spectroscopy of neutral atom and ion ...
2. Femtosecond electron-bunch dynamics in laser wakefields and vacuum
NARCIS (Netherlands)
Khachatryan, A.G.; Irman, A.; van Goor, F.A.; Boller, Klaus J.
2007-01-01
Recent advances in laser wakefield acceleration demonstrated the generation of extremely short (with a duration of a few femtoseconds) relativistic electron bunches with relatively low (of the order of couple of percent) energy spread. In this article we study the dynamics of such bunches in drift
3. Electron yield enhancement in a laser wakefield accelerator driven by asymmetric laser pulses
Energy Technology Data Exchange (ETDEWEB)
Leemans, W.P.; Catravas, P.; Esarey, E.; Geddes, C.G.R.; Toth, C.; Trines, R.; Schroeder, C.B.; Shadwick, B.A.; van Tilborg, J.; Faure, J.
2002-08-01
The effect of asymmetric laser pulses on electron yield from a laser wakefield accelerator has been experimentally studied using > 10{sup 19} cm{sup -3} plasmas and a 10 TW, > 45 fs, Ti:Al{sub 2}O{sub 3} laser. Laser pulse shape was controlled through non-linear chirp with a grating pair compressor. Pulses (76 fs FWHM) with a steep rise and positive chirp were found to significantly enhance the electron yield compared to pulses with a gentle rise and negative chirp. Theory and simulation show that fast rising pulses can generate larger amplitude wakes that seed the growth of the self-modulation instability and that frequency chirp is of minimal importance for the experimental parameters.
4. Strongly directed electron emission in non-sequential double ionization of Ne by intense laser pulses
Energy Technology Data Exchange (ETDEWEB)
Moshammer, R [Max-Planck-Institut fuer Kernphysik, Saupfercheckweg 1, D-67119 Heidelberg (Germany); Ullrich, J [Max-Planck-Institut fuer Kernphysik, Saupfercheckweg 1, D-67119 Heidelberg (Germany); Feuerstein, B [Max-Planck-Institut fuer Kernphysik, Saupfercheckweg 1, D-67119 Heidelberg (Germany); Fischer, D [Max-Planck-Institut fuer Kernphysik, Saupfercheckweg 1, D-67119 Heidelberg (Germany); Dorn, A [Max-Planck-Institut fuer Kernphysik, Saupfercheckweg 1, D-67119 Heidelberg (Germany); Schroeter, C D [Max-Planck-Institut fuer Kernphysik, Saupfercheckweg 1, D-67119 Heidelberg (Germany); Lopez-Urrutia, J R Crespo [Max-Planck-Institut fuer Kernphysik, Saupfercheckweg 1, D-67119 Heidelberg (Germany); Hoehr, C [Max-Planck-Institut fuer Kernphysik, Saupfercheckweg 1, D-67119 Heidelberg (Germany); Rottke, H [Max-Born-Institut, Max-Born-Strasse 2a, D-12489 Berlin (Germany); Trump, C [Max-Born-Institut, Max-Born-Strasse 2a, D-12489 Berlin (Germany); Wittmann, M [Max-Born-Institut, Max-Born-Strasse 2a, D-12489 Berlin (Germany); Korn, G [Max-Born-Institut, Max-Born-Strasse 2a, D-12489 Berlin (Germany); Hoffmann, K [Max-Born-Institut, Max-Born-Strasse 2a, D-12489 Berlin (Germany); Sandner, W [Max-Born-Institut, Max-Born-Strasse 2a, D-12489 Berlin (Germany)
2003-03-28
Double ionization of Ne by 25 fs, 1.0 PW cm{sup -2} laser pulses has been explored in a kinematically complete experiment using a 'reaction microscope'. Electrons are found to be emitted into a narrow cone along the laser polarization ({epsilon}), much more confined than for single ionization, with a broad maximum in their energy distribution along {epsilon}. Correlated momentum spectra show both electrons being ejected into the same hemisphere, in sharp contrast to predictions based on field-free (e, 2e) recollision dynamics, but in overall agreement with recent semiclassical calculations for He. (letter to the editor)
5. Free Electron Laser Research in Europe.
Science.gov (United States)
1983-03-03
given the time Transactions in Nuclear Science). required to lower the undulator after stable operation has been <ummary achieved, the actual current...C.N.E.N. engaged in nuclear physics. The Centre di Frascati FEL experimental project underC.P. 65 the leadership of Renieri was C.P. 5 Rfunded by the...injection); modification to injection from Instituto Nazionale di Fisica within the cavity (Kapitza Nuclere injection) has increased the electron beam
6. Laser-induced electron diffraction for dynamic imaging of molecules
Science.gov (United States)
Lin, Chii-Dong
2017-04-01
Electron diffraction is the well-established tool for probing the structure of gas-phase molecules near the equilibrium geometry. To study chemical dynamics ultrashort electron pulses below a few tens of femtoseconds are needed. Laser-induced electron diffraction (LIED) is a method where molecules can be probed with femtosecond temporal resolution and sub-angstrom spatial resolution. In LIED, molecules are exposed to an intense femtosecond laser pulse. The electrons that have been previously removed by the laser field can be driven back later to rescatter with the parent molecular ion. Using diffraction images from large-angle backscattered events, sub-angstrom spatial resolution can be achieved with tens to hundreds eV electrons. Recent LIED experimental results showing bond breaking in molecules will be illustrated. Practical issues related to the retrieval of diffraction images from LIED on aligned molecules and possibilities of real-time imaging of dissociating molecules using LIED will be presented. US Department of Energy. This work is performed in collaboration with Anh Thu Le (Kansas State University) and the experimental group of Jens Biegert (ICFO, Barcelona).
7. Energy Spread Reduction of Electron Beams Produced via Laser Wake
Energy Technology Data Exchange (ETDEWEB)
Pollock, Bradley Bolt [Univ. of California, San Diego, CA (United States)
2012-01-01
Laser wakefield acceleration of electrons holds great promise for producing ultra-compact stages of GeV scale, high quality electron beams for applications such as x-ray free electron lasers and high energy colliders. Ultra-high intensity laser pulses can be self-guided by relativistic plasma waves over tens of vacuum diffraction lengths, to give >1 GeV energy in cm-scale low density plasma using ionization-induced injection to inject charge into the wake at low densities. This thesis describes a series of experiments which investigates the physics of LWFA in the self-guided blowout regime. Beginning with high density gas jet experiments the scaling of the LWFA-produced electron beam energy with plasma electron density is found to be in excellent agreement with both phenomenological theory and with 3-D PIC simulations. It is also determined that self-trapping of background electrons into the wake exhibits a threshold as a function of the electron density, and at the densities required to produce electron beams with energies exceeding 1 GeV a different mechanism is required to trap charge into low density wakes. By introducing small concentrations of high-Z gas to the nominal He background the ionization-induced injection mechanism is enabled. Electron trapping is observed at densities as low as 1.3 x 1018 cm-3 in a gas cell target, and 1.45 GeV electrons are demonstrated for the first time from LWFA. This is currently the highest electron energy ever produced from LWFA. The ionization-induced trapping mechanism is also shown to generate quasi-continuous electron beam energies, which is undesirable for accelerator applications. By limiting the region over which ionization-induced trapping occurs, the energy spread of the electron beams can be controlled. The development of a novel two-stage gas cell target provides the capability to tailor the gas composition in the longitudinal direction, and confine the trapping process to occur only in a
Science.gov (United States)
Wang, Mingchang; Xu, Zhizhan; Yu, Jinhui; Lee, Byung Cheol; Lee, Jongmin
2000-10-01
A compact beam source produced by pseudospark discharge for free electron lasers is developed. An impedance match between a Marx generator and a pseudospark discharge chamber is analyzed, the impedance characteristic curve for the pseudospark discharge chamber is measured for the first time. The configuration of the new device is described, it has a length of one meter; the original pulse line accelerator has total length of 6 meters. A voltage of 300 kV, a current of 4 kA for the compact device is measured. The electron beam has a diameter of 1.5 mm and has self-pinch effect. The beam has a brightness of 10^12 A/(m rad)^2, as same as a brightness from photo-cathode. The compact beam source can be used for free electron lasers and high power switch.
9. Relativistic electron acceleration by mJ-class kHz lasers normally incident on liquid targets.
Science.gov (United States)
Feister, Scott; Austin, Drake R; Morrison, John T; Frische, Kyle D; Orban, Chris; Ngirmang, Gregory; Handler, Abraham; Smith, Joseph R H; Schillaci, Mark; LaVerne, Jay A; Chowdhury, Enam A; Freeman, R R; Roquemore, W M
2017-08-07
We report observation of kHz-pulsed-laser-accelerated electron energies up to 3 MeV in the -klaser (backward) direction from a 3 mJ laser interacting at normal incidence with a solid density, flowing-liquid target. The electrons/MeV/s.r. >1 MeV recorded here using a mJ-class laser exceeds or equals that of prior super-ponderomotive electron studies employing lasers at lower repetition-rates and oblique incidence. Focal intensity of the 40-fs-duration laser is 1.5 · 1018 W cm-2, corresponding to only ∼80 keV electron ponderomotive energy. Varying laser intensity confirms electron energies in the laser-reflection direction well above what might be expected from ponderomotive scaling in normal-incidence laser-target geometry. This direct, normal-incidence energy spectrum measurement is made possible by modifying the final focusing off-axis-paraboloid (OAP) mirror with a central hole that allows electrons to pass, and restoring laser intensity through adaptive optics. A Lanex-based, optics-free high-acquisition rate (>100 Hz) magnetic electron-spectrometer was developed for this study to enable shot-to-shot statistical analysis and real-time feedback, which was leveraged in finding optimal pre-plasma conditions. 3D Particle-in-cell simulations of the interaction show qualitative super-ponderomotive spectral agreement with experiment. The demonstration of a high-repetition-rate, high-flux source containing >MeV electrons from a few-mJ, 40 fs laser and a simple liquid target encourages development of future ≥kHz-repetition, fs-duration electron-beam applications.
10. Investigation of electron heating in laser-plasma interaction
Directory of Open Access Journals (Sweden)
A Parvazian
2013-03-01
Full Text Available In this paper, stimulated Raman scattering (SRS and electron heating in laser plasma propagating along the plasma fusion is investigated by particle-in cell simulation. Applying an external magnetic field to plasma, production of whistler waves and electron heating associated with whistler waves in the direction perpendicular to external magnetic field was observed in this simulation. The plasma waves with low phase velocities, generated in backward-SRS and dominateing initially in time and space, accelerated the backward electrons by trapping them. Then these electrons promoted to higher energies by the forward-SRS plasma waves with high phase velocities. This tow-stage electron acceleration is more efficient due to the coexistence of these two instabilities.
11. Dielectric laser acceleration of non-relativistic electrons at a photonic structure
Energy Technology Data Exchange (ETDEWEB)
Breuer, John
2013-08-29
This thesis reports on the observation of dielectric laser acceleration of non-relativistic electrons via the inverse Smith-Purcell effect in the optical regime. Evanescent modes in the vicinity of a periodic grating structure can travel at the same velocity as the electrons along the grating surface. A longitudinal electric field component is used to continuously impart momentum onto the electrons. This is only possible in the near-field of a suitable photonic structure, which means that the electron beam has to pass the structure within about one wavelength. In our experiment we exploit the third spatial harmonic of a single fused silica grating excited by laser pulses derived from a Titanium:sapphire oscillator and accelerate non-relativistic 28 keV electrons. We measure a maximum energy gain of 280 eV, corresponding to an acceleration gradient of 25 MeV/m, already comparable with state-of-the-art radio-frequency linear accelerators. To experience this acceleration gradient the electrons approach the grating closer than 100 nm. We present the theory behind grating-based particle acceleration and discuss simulation results of dielectric laser acceleration in the near-field of photonic grating structures, which is excited by near-infrared laser light. Our measurements show excellent agreement with our simulation results and therefore confirm the direct acceleration with the light field. We further discuss the acceleration inside double grating structures, dephasing effects of non-relativistic electrons as well as the space charge effect, which can limit the attainable peak currents of these novel accelerator structures. The photonic structures described in this work can be readily concatenated and therefore represent a scalable realization of dielectric laser acceleration. Furthermore, our structures are directly compatible with the microstructures used for the acceleration of relativistic electrons demonstrated in parallel to this work by our collaborators in
12. Measurements of electron-induced neutrons as a tool for determination of electron temperature of fast electrons in the task of optimization laser-produced plasma ions acceleration.
Science.gov (United States)
Sakaki, H; Nishiuchi, M; Maeda, S; Sagisaka, A; Pirozhkov, A S; Pikuz, T; Faenov, A; Ogura, K; Fukami, T; Matsukawa, K; Kanasaki, M; Fukuda, Y; Yogo, A; Esirkepov, T; Kiriyama, H; Shimomura, T; Nakai, Y; Tanoue, M; Torimoto, K; Okamoto, M; Sato, T; Niita, K; Tamura, J; Nishio, K; Sako, H; Yamauchi, T; Watanabe, Y; Bulanov, S; Kondo, K
2014-02-01
High intensity laser-plasma interaction has attracted considerable interest for a number of years. The laser-plasma interaction is accompanied by generation of various charged particle beams, such as high-energy proton and ions with high charge to mass ratio (Q/M; same as multi-charged ions). Results of simultaneous novel measurements of electron-induced photonuclear neutrons (photoneutron), which are a diagnostic of the laser-plasma interaction, are proposed to use for optimization of the laser-plasma ion generation. The proposed method is demonstrated by the laser irradiation with the intensity of 1 × 10(21) W/cm(2) on the metal foil target. The photoneutrons are measured by using NE213 liquid scintillation detectors. Heavy-ion signal is registered with the CR-39 track detector simultaneously. The measured signals of the electron-induced photoneutrons are well reproduced by using the Particle and Heavy Ion Transport code System. The results obtained provide useful approach for analyzing the various laser based ion beams.
13. Relativistic electron mirrors from high intensity laser nanofoil interactions
Energy Technology Data Exchange (ETDEWEB)
Kiefer, Daniel
2012-12-21
The reflection of a laser pulse from a mirror moving close to the speed of light could in principle create an X-ray pulse with unprecedented high brightness owing to the increase in photon energy and accompanying temporal compression by a factor of 4γ{sup 2}, where γ is the Lorentz factor of the mirror. While this scheme is theoretically intriguingly simple and was first discussed by A. Einstein more than a century ago, the generation of a relativistic structure which acts as a mirror is demanding in many different aspects. Recently, the interaction of a high intensity laser pulse with a nanometer thin foil has raised great interest as it promises the creation of a dense, attosecond short, relativistic electron bunch capable of forming a mirror structure that scatters counter-propagating light coherently and shifts its frequency to higher photon energies. However, so far, this novel concept has been discussed only in theoretical studies using highly idealized interaction parameters. This thesis investigates the generation of a relativistic electron mirror from a nanometer foil with current state-of-the-art high intensity laser pulses and demonstrates for the first time the reflection from those structures in an experiment. To achieve this result, the electron acceleration from high intensity laser nanometer foil interactions was studied in a series of experiments using three inherently different high power laser systems and free-standing foils as thin as 3nm. A drastic increase in the electron energies was observed when reducing the target thickness from the micrometer to the nanometer scale. Quasi-monoenergetic electron beams were measured for the first time from ultrathin (≤5nm) foils, reaching energies up to ∝35MeV. The acceleration process was studied in simulations well-adapted to the experiments, indicating the transition from plasma to free electron dynamics as the target thickness is reduced to the few nanometer range. The experience gained from those
14. 10-fs-level synchronization of photocathode laser with RF-oscillator for ultrafast electron and X-ray sources
Science.gov (United States)
Yang, Heewon; Han, Byungheon; Shin, Junho; Hou, Dong; Chung, Hayun; Baek, In Hyung; Jeong, Young Uk; Kim, Jungwon
2017-01-01
Ultrafast electron-based coherent radiation sources, such as free-electron lasers (FELs), ultrafast electron diffraction (UED) and Thomson-scattering sources, are becoming more important sources in today’s ultrafast science. Photocathode laser is an indispensable common subsystem in these sources that generates ultrafast electron pulses. To fully exploit the potentials of these sources, especially for pump-probe experiments, it is important to achieve high-precision synchronization between the photocathode laser and radio-frequency (RF) sources that manipulate electron pulses. So far, most of precision laser-RF synchronization has been achieved by using specially designed low-noise Er-fibre lasers at telecommunication wavelength. Here we show a modular method that achieves long-term (>1 day) stable 10-fs-level synchronization between a commercial 79.33-MHz Ti:sapphire laser oscillator and an S-band (2.856-GHz) RF oscillator. This is an important first step toward a photocathode laser-based femtosecond RF timing and synchronization system that is suitable for various small- to mid-scale ultrafast X-ray and electron sources.
15. submitter Parametric study of transport beam lines for electron beams accelerated by laser-plasma interaction
CERN Document Server
Scisciò, M; Migliorati, M; Mostacci, A; Palumbo, L; Papaphilippou, Y; Antici, P
2016-01-01
In the last decade, laser-plasma acceleration of high-energy electrons has attracted strong attention in different fields. Electrons with maximum energies in the GeV range can be laser-accelerated within a few cm using multi-hundreds terawatt (TW) lasers, yielding to very high beam currents at the source (electron bunches with up to tens-hundreds of pC in a few fs). While initially the challenge was to increase the maximum achievable electron energy, today strong effort is put in the control and usability of these laser-generated beams that still lack of some features in order to be used for applications where currently conventional, radio-frequency (RF) based, electron beam lines represent the most common and efficient solution. Several improvements have been suggested for this purpose, some of them acting directly on the plasma source, some using beam shaping tools located downstream. Concerning the latter, several studies have suggested the use of conventional accelerator magnetic devices (such as quadrupo...
16. Transverse Laser Beam Shaping in High Brightness Electron Gun at ATF
CERN Document Server
Roychowdhury, S
2005-01-01
The brightness of electron beams from a photo injector is influenced by the transverse and longitudinal distribution of the laser beam illuminating the cathode. Previous studies at Brookhaven Accelerator Test Facility have shown that formation of an ideal e-beam with lowest transverse emittance requires uniform circular distribution of the emitted electrons. The use of the uniformly distributed power of the laser beam may not lead to that of the emitted electrons because of the non-uniform quantum efficiency. A proper shaping of the laser beam can compensate for this non-uniformity. In this paper we describe the use of digital light processing (DLP) technique based on digital mirror device (DMD) for spatial modulation of the laser beam, for measurements of the quantum efficiency map, and for creating the desirable e-beam density profiles. A DMD is aμelectronic mechanical system (MEMS) comprising of millions of highly reflectiveμmirrors controlled by underlying electronics. We present exper...
17. Dynamics of electron injection in a laser-wakefield accelerator
Science.gov (United States)
Xu, J.; Buck, A.; Chou, S.-W.; Schmid, K.; Shen, B.; Tajima, T.; Kaluza, M. C.; Veisz, L.
2017-08-01
The detailed temporal evolution of the laser-wakefield acceleration process with controlled injection, producing reproducible high-quality electron bunches, has been investigated. The localized injection of electrons into the wakefield has been realized in a simple way—called shock-front injection—utilizing a sharp drop in plasma density. Both experimental and numerical results reveal the electron injection and acceleration process as well as the electron bunch's temporal properties. The possibility to visualize the plasma wave gives invaluable spatially resolved information about the local background electron density, which in turn allows for an efficient suppression of electron self-injection before the controlled process of injection at the sharp density jump. Upper limits for the electron bunch duration of 6.6 fs FWHM, or 2.8 fs (r.m.s.) were found. These results indicate that shock-front injection not only provides stable and tunable, but also few-femtosecond short electron pulses for applications such as ultrashort radiation sources, time-resolved electron diffraction or for the seeding of further acceleration stages.
18. STUDIES OF A FREE ELECTRON LASER DRIVEN BY A LASER-PLASMA ACCELERATOR
Energy Technology Data Exchange (ETDEWEB)
Montgomery, A.; Schroeder, C.; Fawley, W.
2008-01-01
A free electron laser (FEL) uses an undulator, a set of alternating magnets producing a periodic magnetic fi eld, to stimulate emission of coherent radiation from a relativistic electron beam. The Lasers, Optical Accelerator Systems Integrated Studies (LOASIS) group at Lawrence Berkeley National Laboratory (LBNL) will use an innovative laserplasma wakefi eld accelerator to produce an electron beam to drive a proposed FEL. In order to optimize the FEL performance, the dependence on electron beam and undulator parameters must be understood. Numerical modeling of the FEL using the simulation code GINGER predicts the experimental results for given input parameters. Among the parameters studied were electron beam energy spread, emittance, and mismatch with the undulator focusing. Vacuum-chamber wakefi elds were also simulated to study their effect on FEL performance. Energy spread was found to be the most infl uential factor, with output FEL radiation power sharply decreasing for relative energy spreads greater than 0.33%. Vacuum chamber wakefi elds and beam mismatch had little effect on the simulated LOASIS FEL at the currents considered. This study concludes that continued improvement of the laser-plasma wakefi eld accelerator electron beam will allow the LOASIS FEL to operate in an optimal regime, producing high-quality XUV and x-ray pulses.
Energy Technology Data Exchange (ETDEWEB)
White, Thomas A., E-mail: [email protected]; Barty, Anton; Stellato, Francesco [DESY, Notkestrasse 85, 22607 Hamburg (Germany); Holton, James M. [University of California, San Francisco, CA 94158 (United States); Lawrence Berkeley National Laboratory, Berkeley, CA 94720 (United States); Kirian, Richard A. [DESY, Notkestrasse 85, 22607 Hamburg (Germany); Arizona State University, Tempe, AZ 85287 (United States); Zatsepin, Nadia A. [Arizona State University, Tempe, AZ 85287 (United States); Chapman, Henry N. [DESY, Notkestrasse 85, 22607 Hamburg (Germany); University of Hamburg, Luruper Chaussee 149, 22761 Hamburg (Germany)
2013-07-01
A processing pipeline for diffraction data acquired using the ‘serial crystallography’ methodology with a free-electron laser source is described with reference to the crystallographic analysis suite CrystFEL and the pre-processing program Cheetah. A processing pipeline for diffraction data acquired using the ‘serial crystallography’ methodology with a free-electron laser source is described with reference to the crystallographic analysis suite CrystFEL and the pre-processing program Cheetah. A detailed analysis of the nature and impact of indexing ambiguities is presented. Simulations of the Monte Carlo integration scheme, which accounts for the partially recorded nature of the diffraction intensities, are presented and show that the integration of partial reflections could be made to converge more quickly if the bandwidth of the X-rays were to be increased by a small amount or if a slight convergence angle were introduced into the incident beam.
20. Electron dynamics in RF sources with a laser controlled emission
CERN Document Server
Khodak, I V; Metrochenko, V V
2001-01-01
Photoemission radiofrequency (RF) electron sources are sources of electron beams with extremely high brightness. Beam bunching processes in such devices are well studied in case when laser pulse duration is much lower of rf oscillation period.At the same time photoemission RF guns have some merits when operating in 'long-pulse' mode. In this case the laser pulse duration is much higher of rf oscillation period but much lower of rise time of oscillations in a gun cavity. Beam parameters at the gun output are compared for photoemission and thermoemission cathode applications. The paper presents results of a beam dynamics simulation in such guns with different resonance structures. Questions connected with defining of the current pulse peak value that can be obtained in such guns are discussed.
1. Injection of electrons by colliding laser pulses in a laser wakefield accelerator
CERN Document Server
Hansson, Martin; Ekerfelt, Henrik; Persson, Anna; Lundh, Olle
2016-01-01
To improve the stability and reproducibility of laser wakefield accelerators and to allow for future applications, controlling the injection of electrons is of great importance. This allows us to control the amount of charge in the beams of accelerated electrons and final energy of the electrons. Results are presented from a recent experiment on controlled injection using the scheme of colliding pulses and performed using the Lund multi-terawatt laser. Each laser pulse is split into two parts close to the interaction point. The main pulse is focused on a 2 mm diameter gas jet to drive a nonlinear plasma wave below threshold for self-trapping. The second pulse, containing only a fraction of the total laser energy, is focused to collide with the main pulse in the gas jet under an angle of 150°. Beams of accelerated electrons with low divergence and small energy spread are produced using this set-up. Control over the amount of accelerated charge is achieved by rotating the plane of polarization of the second p...
2. Electron beam, laser beam and plasma arc welding studies
Science.gov (United States)
Banas, C. M.
1974-01-01
This program was undertaken as an initial step in establishing an evaluation framework which would permit a priori selection of advanced welding processes for specific applications. To this end, a direct comparison of laser beam, electron beam and arc welding of Ti-6Al-4V alloy was undertaken. Ti-6Al-4V was selected for use in view of its established welding characteristics and its importance in aerospace applications.
3. Super-Radiant Free Electron Laser Measurement and Detection
Science.gov (United States)
2013-09-01
Pyrometers Pyrometers measure the energy from electromagnetic radiation by the change in temperature due to the absorption of light in the detector. The...dependence of the resistivity of a certain material to measure the absorption of electromagnetic radiation . Like pyrometers , they are used for...relativistic electron bunches and a periodic magnetic field to generate coherent radiation . These types of lasers are of interest to the Navy because
4. Optical synchronization of a free-electron laser with femtosecond precision
Energy Technology Data Exchange (ETDEWEB)
Loehl, F.
2009-09-15
High-gain free-electron lasers (FELs) are capable of generating sub-10 fs long light pulses. In order to take full advantage of these extremely short light pulses in time-resolved experiments, synchronization with a so far unprecedented timing accuracy is required. Within this thesis, an optical synchronization system providing sub-10 fs stability has been developed and was implemented at the ultra-violet and soft X-ray free-electron laser FLASH at DESY, Hamburg. The system uses a mode-locked laser as a timing reference. The laser pulses are distributed via length stabilized optical fiber-links to the remote locations. A key feature of the system is a bunch arrival-time monitor detecting the electron bunch arrival-time with an unrivaled resolution of 6 fs. A feedback system based on the arrival-time monitor was established, improving the arrival-time fluctuations from 200 fs in the unstabilized case to 25 fs with active feedback. In order to achieve the high peak current of several thousand amperes required for the FEL process, the electron bunches are longitudinally compressed in two magnetic chicanes. A second feedback system was developed stabilizing the bunch compression process based on measurements of diffraction radiation. The combination of both feedback systems improves the stability of the FEL radiation significantly. (orig.)
5. Free Electron Lasers with Slowly Varying Beam and Undulator Parameters
CERN Document Server
Huang, Zhirong
2005-01-01
The performance of a free electron lasers (FEL) is affected when the electron beam energy varies alone the undulator as would be caused by vacuum pipe wakefields and/or when the undulator strength parameter is tapered in the small signal regime until FEL saturation. In this paper, we present a self-consistent theory of FELs with slowly-varying beam and undulator parameters. A general method is developed to apply the WKB approximation to the beam-radiation system by employing the adjoint eigenvector that is orthogonal to the eigenfunctions of the coupled Maxwell-Vlasov equations. This method may be useful for other slowly varying processes in beam dynamics.
6. Ultrafast Diagnostics for Electron Beams from Laser Plasma Accelerators
Energy Technology Data Exchange (ETDEWEB)
Matlis, N. H.; Bakeman, M.; Geddes, C. G. R.; Gonsalves, T.; Lin, C.; Nakamura, K.; Osterhoff, J.; Plateau, G. R.; Schroeder, C. B.; Shiraishi, S.; Sokollik, T.; van Tilborg, J.; Toth, Cs.; Leemans, W. P.
2010-06-01
We present an overview of diagnostic techniques for measuring key parameters of electron bunches from Laser Plasma Accelerators (LPAs). The diagnostics presented here were chosen because they highlight the unique advantages (e.g., diverse forms of electromagnetic emission) and difficulties (e.g., shot-to-shot variability) associated with LPAs. Non destructiveness and high resolution (in space and time and energy) are key attributes that enable the formation of a comprehensive suite of simultaneous diagnostics which are necessary for the full characterization of the ultrashort, but highly-variable electron bunches from LPAs.
7. Electron Rephasing in a Laser-Wakefield Accelerator.
Science.gov (United States)
Guillaume, E; Döpp, A; Thaury, C; Ta Phuoc, K; Lifschitz, A; Grittani, G; Goddet, J-P; Tafzi, A; Chou, S W; Veisz, L; Malka, V
2015-10-09
An important limit for energy gain in laser-plasma wakefield accelerators is the dephasing length, after which the electron beam reaches the decelerating region of the wakefield and starts to decelerate. Here, we propose to manipulate the phase of the electron beam in the wakefield, in order to bring the beam back into the accelerating region, hence increasing the final beam energy. This rephasing is operated by placing an upward density step in the beam path. In a first experiment, we demonstrate the principle of this technique using a large energy spread electron beam. Then, we show that it can be used to increase the energy of monoenergetic electron beams by more than 50%.
8. Mobility of Electron in DNA Crystals by Laser Radiation
Science.gov (United States)
Zhang, Kaixi; Zhao, Qingxun; Cui, Zhiyun; Zhang, Ping; Dong, Lifang
1996-01-01
The mobility of electrons in laser radiated DNA is closed to the energy transfer and energy migration of a biological molecule. Arrhenius has studied the conductivity of the electrons in a biological molecule. But his result is far from the experimental result and meanwhile the relation between some parameters in his theory and the micro-quantities in DNA is not very clear. In this paper, we propose a new phonon model of electron mobility in DNA and use Lippman-Schwinger equation and S-matrix theory to study the mobility of electrons in DNA crystal. The result is relatively close to the experiment result and some parameters in Arrhenius theory are explained in our work.
9. Patterning and electronic tuning of laser scribed graphene for flexible all-carbon devices.
Science.gov (United States)
Strong, Veronica; Dubin, Sergey; El-Kady, Maher F; Lech, Andrew; Wang, Yue; Weiller, Bruce H; Kaner, Richard B
2012-02-28
Engineering a low-cost graphene-based electronic device has proven difficult to accomplish via a single-step fabrication process. Here we introduce a facile, inexpensive, solid-state method for generating, patterning, and electronic tuning of graphene-based materials. Laser scribed graphene (LSG) is shown to be successfully produced and selectively patterned from the direct laser irradiation of graphite oxide films under ambient conditions. Circuits and complex designs are directly patterned onto various flexible substrates without masks, templates, post-processing, transferring techniques, or metal catalysts. In addition, by varying the laser intensity and laser irradiation treatments, the electrical properties of LSG can be precisely tuned over 5 orders of magnitude of conductivity, a feature that has proven difficult with other methods. This inexpensive method for generating LSG on thin flexible substrates provides a mode for fabricating a low-cost graphene-based NO(2) gas sensor and enables its use as a heterogeneous scaffold for the selective growth of Pt nanoparticles. The LSG also shows exceptional electrochemical activity that surpasses other carbon-based electrodes in electron charge transfer rate as demonstrated using a ferro-/ferricyanide redox couple.
Energy Technology Data Exchange (ETDEWEB)
Lee, Jong Min; Lee, Byung Cheol; Kim, Sun Kook; Jeong, Young Uk; Cho, Sung Oh
2000-10-01
As a result of the cooperative research between the KAERI and Peking University, the key technologies of superconducting acceleration cavity and photoelectron gun have been developed for the application to high power free electron lasers. A 1.5-GHz, 1-cell superconducting RF cavity has been designed and fabricated by using pure Nb sheets. The unloaded Q values of the fabricated superconducting cavity has been measured to be 2x10{sup 9} at 2.5K, and 8x10{sup 9} at 1.8K. The maximum acceleration gradient achieved was 12 MeV/m at 2.5K, and 20MV/m at 1.8 K. A cryostat for the 1-cell superconducting cavity has been designed. As a source of electron beam, a DC photocathode electron gun has been designed and fabricated, which is composed of a photocathode evaporation chamber and a 100-keV acceleration chamber. The efficiency of the Cs2Te photocathode is 3% nominally at room temperature, 10% at 290 deg C. The superconducting photoelectron gun system developed has been estimated to be a good source of high-brightness electron beam for high-power free electron lasers.
11. Laser-ion acceleration via anomalous electron heating
CERN Document Server
Yogo, A; Iwata, N; Tosaki, S; Morace, A; Arikawa, Y; Fujioka, S; Nishimura, H; Sagisaka, A; Johzaki, T; Matsuo, K; Kamitsukasa, N; Kojima, S; Nagatomo, H; Nakai, M; Shiraga, H; Murakami, M; Tokita, S; Kawanaka, J; Miyanaga, N; Yamanoi, K; Norimatsu, T; Sakagami, H; Bulanov, S V; Kondo, K; Azechi, H
2016-01-01
Using a kilojoule class laser, we demonstrate for the first time that high-contrast picosecond pulses are advantageous for ion acceleration. We show that a laser pulse with optimum duration and a large focal spot accelerates electrons beyond the ponderomotive energy. This anomalous electron heating enables efficient ion acceleration reaching 52 MeV at an intensity of 1.2X10^19 Wcm^-2. The proton energy observed agrees quantitatively with a one-dimensional plasma expansion model newly developed by taking the anomalous heating effect into account. The heating process is confirmed by both measurements with an electron spectrometer and a one-dimensional particle-in-cell simulation. By extending the pulse duration to 6 ps, 5% energy conversion efficiency to protons (50 J out of 1 kJ laser energy) is achieved with an intensity of 10^18-Wcm^-2. The present results are quite encouraging for realizing ion-driven fast ignition and novel ion beamlines.
12. Laser Spot Detection Based on Reaction Diffusion
Directory of Open Access Journals (Sweden)
Alejandro Vázquez-Otero
2016-03-01
Full Text Available Center-location of a laser spot is a problem of interest when the laser is used for processing and performing measurements. Measurement quality depends on correctly determining the location of the laser spot. Hence, improving and proposing algorithms for the correct location of the spots are fundamental issues in laser-based measurements. In this paper we introduce a Reaction Diffusion (RD system as the main computational framework for robustly finding laser spot centers. The method presented is compared with a conventional approach for locating laser spots, and the experimental results indicate that RD-based computation generates reliable and precise solutions. These results confirm the flexibility of the new computational paradigm based on RD systems for addressing problems that can be reduced to a set of geometric operations.
13. A robust fibre laser system for electro-optic electron bunch profile measurements at FLASH
Energy Technology Data Exchange (ETDEWEB)
Wissmann, Laurens-Georg
2012-08-15
For the electro-optic measurement of electron bunch profiles at FLASH a robust ytterbium doped fibre laser (YDFL) system has been developed consisting of a laser oscillator and a two-staged amplifier. The oscillator is designed to meet the specifications of high reliability and low noise operation. The amplifier makes use of tailored nonlinearity to enhance the spectral bandwidth of the output laser pulses. Active repetition rate control enables sub-picosecond synchronisation of the laser to the accelerator reference RF. Using a two-stage gating scheme the output pulse train repetition rate is adopted to the accelerator repetition rate. An experimental site used for electro-optic electron bunch diagnostics has been redesigned to support single-shot bunch profile measurements based on spectral decoding. An existing bunch profile monitor with a similar laser system was upgraded and electro-optic bunch profile measurements were conducted, allowing for a comparison with measurements done with other longitudinal electron bunch diagnostics and with former measurements.
14. Exact and variational calculations of eigenmodes for three-dimensional free electron laser interaction with a warm electron beam
Energy Technology Data Exchange (ETDEWEB)
Xie, M. [Lawrence Berkeley Lab., CA (United States)
1995-12-31
I present an exact calculation of free-electron-laser (FEL) eigenmodes (fundamental as well as higher order modes) in the exponential-gain regime. These eigenmodes specify transverse profiles and exponential growth rates of the laser field, and they are self-consistent solutions of the coupled Maxwell-Vlasov equations describing the FEL interaction taking into account the effects due to energy spread, emittance and betatron oscillations of the electron beam, and diffraction and guiding of the laser field. The unperturbed electron distribution is assumed to be of Gaussian shape in four dimensional transverse phase space and in the energy variable, but uniform in longitudinal coordinate. The focusing of the electron beam is assumed to be matched to the natural wiggler focusing in both transverse planes. With these assumptions the eigenvalue problem can be reduced to a numerically manageable integral equation and solved exactly with a kernel iteration method. An approximate, but more efficient solution of the integral equation is also obtained for the fundamental mode by a variational technique, which is shown to agree well with the exact results. Furthermore, I present a handy formula, obtained from interpolating the numerical results, for a quick calculation of FEL exponential growth rate. Comparisons with simulation code TDA will also be presented. Application of these solutions to the design and multi-dimensional parameter space optimization for an X-ray free electron laser driven by SLAC linac will be demonstrated. In addition, a rigorous analysis of transverse mode degeneracy and hence the transverse coherence of the X-ray FEL will be presented based on the exact solutions of the higher order guided modes.
15. Electron beam optics and trajectory control in the Fermi free electron laser delivery system
Directory of Open Access Journals (Sweden)
S. Di Mitri
2012-01-01
Full Text Available Electron beam optics (particle betatron motion and trajectory (centroid secular motion in the FERMI@Elettra free electron laser (FEL are modeled and experimentally controlled by means of the elegant particle tracking code. This powerful tool, well known to the accelerator community, is here for the first time fully integrated into the Tango-server based high level software of an FEL facility, thus ensuring optimal charge transport efficiency and superposition of the beam Twiss parameters to the design optics. The software environment, the experimental results collected during the commissioning of FERMI@Elettra, and the comparison with the model are described. As a result, a matching of the beam optics to the design values is accomplished and quantified in terms of the betatron mismatch parameter with relative accuracy down to the 10^{-3} level. The beam optics control allows accurate energy spread measurements with sub-keV accuracy in dedicated dispersive lines. Trajectory correction and feedback is achieved to a 5 μm level with the implementation of theoretical response matrices. In place of the empirical ones, they speed up the process of trajectory control when the machine optics is changed, avoid particle losses that may occur during the on-line computation of experimental matrices, and confirm a good agreement of the experimental magnetic lattice with the model.
16. Sub-picosecond snapshots of fast electrons from high intensity laser-matter interactions.
Science.gov (United States)
Pompili, R; Anania, M P; Bisesto, F; Botton, M; Castellano, M; Chiadroni, E; Cianchi, A; Curcio, A; Ferrario, M; Galletti, M; Henis, Z; Petrarca, M; Schleifer, E; Zigler, A
2016-12-26
The interaction of a high-intensity short-pulse laser with thin solid targets produces electron jets that escape the target and positively charge it, leading to the formation of the electrostatic potential that in turn governs the ion acceleration. The typical timescale of such phenomena is on the sub-picosecond level. Here we show, for the first time, temporally-resolved measurements of the first released electrons that escaped from the target, so-called fast electrons. Their total charge, energy and temporal profile are provided by means of a diagnostics based on Electro-Optical Sampling with temporal resolution below 100 fs.
17. Continuous point-like high-temperature laser discharge produced by terahertz free electron laser
Directory of Open Access Journals (Sweden)
V. V. Kubarev
2017-09-01
Full Text Available A continuous point-like laser discharge of record high temperature has been produced in argon at atmospheric pressure with focusing of the radiation of the Novosibirsk terahertz free electron laser (NovoFEL. According to spectral measurements, the temperature in the center of the millimeter-sized plasma sphere was 28000 K at a plasma density of 1.5×1017 cm-3 and an average NovoFEL power of 200 W at a wavelength of 130 μm (2.3 THz.
18. Satellite-based laser windsounder
Energy Technology Data Exchange (ETDEWEB)
Schultz, J.F.; Czuchlewski, S.J.; Quick, C.R. [and others
1997-08-01
This is the final report of a one-year, Laboratory-Directed Research and Development (LDRD) project at the Los Alamos National Laboratory (LANL). The projects primary objective is to determine the technical feasibility of using satellite-based laser wind sensing systems for detailed study of winds, aerosols, and particulates around and downstream of suspected proliferation facilities. Extensive interactions with the relevant operational organization resulted in enthusiastic support and useful guidance with respect to measurement requirements and priorities. Four candidate wind sensing techniques were evaluated, and the incoherent Doppler technique was selected. A small satellite concept design study was completed to identify the technical issues inherent in a proof-of-concept small satellite mission. Use of a Mach-Zehnder interferometer instead of a Fabry-Perot would significantly simplify the optical train and could reduce weight, and possibly power, requirements with no loss of performance. A breadboard Mach-Zehnder interferometer-based system has been built to verify these predictions. Detailed plans were made for resolving other issues through construction and testing of a ground-based lidar system in collaboration with the University of Wisconsin, and through numerical lidar wind data assimilation studies.
19. Quantum regime of free electron lasers starting from noise
Directory of Open Access Journals (Sweden)
R. Bonifacio
2006-09-01
Full Text Available We investigate the quantum regime of a high-gain free-electron laser starting from noise. In the first part, we neglect the radiation propagation and we formulate a quantum linear theory of the N-particle free-electron laser Hamiltonian model, quantizing both the radiation field and the electron motion. Quantum effects such as frequency shift, line narrowing, quantum limitation for bunching and energy spread, and minimum uncertainty states are described. Using a second-quantization formalism, we demonstrate quantum entanglement between the recoiling electrons and the radiation field. In the second part, we describe the field classically but we include propagation effects (i.e. slippage and we demonstrate the novel regime of quantum SASE with high temporal coherence and discrete spectrum. Furthermore, we describe “quantum purification” of SASE: the classical chaotic spiking behavior disappears and the spectrum becomes a series of discrete very narrow lines which correspond to transitions between discrete momentum eigenstates (which originate high temporal coherence.
20. Comparative study of electron and laser beam surface alloying
Science.gov (United States)
Valkov, Stefan Ts.; Petrov, Peter, Iv.; Lazarova, Rumiana L.
2016-01-01
High intensity energy fluxes, such as electron beams and laser beams are widely used for surface alloying of metals and alloys. These technologies are able to cause the formation of the so called melt pool where the alloying elements interact each other. It is known that the homogenization of the surface alloy can be explained by intense Marangoni convection, caused by the high temperature gradient in the melt pool. The convection is inversely to the speed of the specimen motion during the alloying process and therefore, the choice of low alloying velocity will reflect on more homogeneous structure of the obtained alloy. In this study, a comparison of the structure and properties of electron and laser beam surface alloying of aluminium with niobium was conducted. The phase composition of the alloyed layers was determined by XRD (X-ray diffraction) with CuKα radiation. The microstructure was studied by SEM (Scanning Electron Microscopy). Chemical analysis was carried out using an EDX electron probe microanalyser. The microhardness of the obtained samples is also measured and compared with respect to the technology of the formation of each surface alloy.
1. High average current electron guns for high-power free electron lasers
Directory of Open Access Journals (Sweden)
Phillip Sprangle
2011-02-01
Full Text Available High average power free-electron lasers (FELs require high average current electron injectors capable of generating high quality, short duration electron bunches with a repetition rate equal to the frequency of the rf linac. In this paper we propose, analyze, and simulate an rf-gated, gridded thermionic electron gun for use in high average power FELs. Thermionic cathodes can provide the necessary high current, have long lifetimes, and require modest vacuums. In the proposed configuration the rf-gated grid is modulated at the fundamental and 3rd harmonic of the linac frequency. The addition of the 3rd harmonic on the grid results in shorter electron bunches. In this configuration, every rf bucket of the linac accelerating field contains an electron bunch. Particle-in-cell simulations indicate that this approach can provide the necessary charge per bunch, bunch duration, longitudinal and transverse emittance, and repetition rate for high average power FELs operating in the IR regime.
2. Femtosecond laser-induced damage threshold of electron beam deposited dielectrics for 1-m class optics
Science.gov (United States)
Hervy, Adrien; Gallais, Laurent; Chériaux, Gilles; Mouricaud, Daniel
2017-01-01
In order to transport multi-petawatt (PW) femtosecond laser beams with large spectral bandwidth, specific mirrors have to be designed and manufactured. We report on an experimental study of the laser-damage resistance and other optical properties of coating materials deposited in a 1-m class coating chamber. The study is conducted on single-layer coatings deposited by electron beam evaporation at 500 fs. Based on the experience of large optics for nanosecond applications, hafnia and silica are particularly investigated. However, in the case of sub-15 fs, the spectral specifications for PW beam transport mirrors cannot be reached by classical high laser-resistant quarter-wave SiO2/HfO2 stacks. Therefore, we investigate the laser resistance of different dielectrics of interest deposited with electron-beam processes: Al2O3, Y2O3, Sc2O3, HfO2, Ta2O5, TiO2. The influence of multiple pulse irradiations and environmental conditions, such as vacuum and temperature, is studied. With the investigation of multilayer stacks, we also show that there is no difference in behavior when a film is studied as a single layer or embedded in a stack. Based on these results, we were able to optimize high reflective (>99.5%), broadband (300 nm) and high laser-induced damage threshold (2.5 J/cm2) mirrors for PW applications.
3. Extremely short relativistic-electron-bunch generation in the laser wakefield via novel bunch injection scheme
NARCIS (Netherlands)
Khachatryan, A.G.; van Goor, F.A.; Boller, Klaus J.; Reitsma, A.J.W.; Jaroszynski, D.A.
2004-01-01
Recently a new electron-bunch injection scheme for the laser wakefield accelerator has been proposed [JETP Lett. 74, 371 (2001); Phys. Rev. E 65, 046504 (2002)]. In this scheme, a low energy electron bunch, sent in a plasma channel just before a high-intensity laser pulse, is trapped in the laser
4. Infrared free electron laser enhanced transdermal drug delivery
Science.gov (United States)
Awazu, Kunio; Uchizono, Takeyuki; Suzuki, Sachiko; Yoshikawa, Kazushi
2005-08-01
It is necessary to control enhancement of transdermal drug delivery with non-invasive. The present study was investigated to assess the effectivity of enhancing the drug delivery by irradiating 6-μm region mid infrared free electron laser (MIR-FEL). The enhancement of transdermal drug (lidocaine) delivery of the samples (hairless mouse skin) irradiated with lasers was examined for flux (μg/cm2/h) and total penetration amount (μg/cm2) of lidocaine by High performance Liquid Chromatography (HPLC). The flux and total amount penatration date was enhanced 200-300 fold faster than the control date by the laser irradiation. FEL irradiating had the stratum corneum, and had the less thermal damage in epidermis. The effect of 6-μm region MIR-FEL has the enhancement of transdermal drug delivery without removing the stratum corneum because it has the less thermal damage. It leads to enhancement drug delivery system with non-invasive laser treatment.
5. Electron optical injection with head-on and countercrossing colliding laser pulses.
Science.gov (United States)
Kotaki, H; Daito, I; Kando, M; Hayashi, Y; Kawase, K; Kameshima, T; Fukuda, Y; Homma, T; Ma, J; Chen, L-M; Esirkepov, T Zh; Pirozhkov, A S; Koga, J K; Faenov, A; Pikuz, T; Kiriyama, H; Okada, H; Shimomura, T; Nakai, Y; Tanoue, M; Sasao, H; Wakai, D; Matsuura, H; Kondo, S; Kanazawa, S; Sugiyama, A; Daido, H; Bulanov, S V
2009-11-06
A high stability electron bunch is generated by laser wakefield acceleration with the help of a colliding laser pulse. The wakefield is generated by a laser pulse; the second laser pulse collides with the first pulse at 180 degrees and at 135 degrees realizing optical injection of an electron bunch. The electron bunch has high stability and high reproducibility compared with single pulse electron generation. In the case of 180 degrees collision, special measures have been taken to prevent damage. In the case of 135 degrees collision, since the second pulse is countercrossing, it cannot damage the laser system.
6. Electron acceleration by laser fields in a gas. Final report
Energy Technology Data Exchange (ETDEWEB)
Fontana, J.R.
1997-08-01
The purpose of the project is an investigation of topics related to the high-energy acceleration of electrons by means of suitably shaped laser beams in an inert gaseous medium. By slowing down the phase velocity of the fields by its index of refraction, the gas allows a cumulative interaction with the electrons resulting in net acceleration and also focusing. The objectives of the work reported here were twofold: (1) to participate as a consultant in the design and analysis of demonstration experiments performed at the Brookhaven National Laboratory by STI Optronics, a Belleview, WA company, under a separate DOE funded contract; (2) to perform further analytic and design work on the laser acceleration scheme originally proposed and explore a possible extension of the method to acceleration in vacuum using the same field configuration and analogous interaction process as with a gas. This report thus comprises an account of both activities. Section 2 is an overview of the various laser acceleration methods that have been proposed, in order to provide a framework to the work reported. Section 3 contains a list of meetings attended by the Principal Investigator to present his work and interact with research community colleagues and STI staff, and a list of publications containing work he co-authored or was acknowledged for. Section 4 summarizes the work performed by STI to which he contributed. Section 5 consists of the technical reports the Principal Investigator wrote describing his independent theoretical work elaborating and extending the scope of the original project.
7. Femtosecond electron-bunch dynamics in laser wakefields and vacuum
Directory of Open Access Journals (Sweden)
A. G. Khachatryan
2007-12-01
Full Text Available Recent advances in laser wakefield acceleration demonstrated the generation of extremely short (with a duration of a few femtoseconds relativistic electron bunches with relatively low (of the order of couple of percent energy spread. In this article we study the dynamics of such bunches in drift space (vacuum and in channel-guided laser wakefields. Analytical solutions were found for the transverse coordinate of an electron and for the bunch envelope in the wakefield in the case of arbitrary change in the energy. Our results show strong bunch dynamics already on a millimeter scale propagation distance both in plasma and in vacuum. When the bunch propagates in vacuum, its transverse sizes grow considerably; the same is observed for the normalized bunch emittance that worsens the focusability of the bunch. A scheme of two-stage laser wakefield accelerator with small drift space between the stages is proposed. It is found that fast longitudinal betatron phase mixing occurs in a femtosecond bunch when it propagates along the wakefield axis. When bunch propagates off axis, strong bunch decoherence and fast emittance degradation due to the finite bunch length was observed.
8. Conceptual design of industrial free electron laser using superconducting accelerator
Energy Technology Data Exchange (ETDEWEB)
Saldin, E.L.; Schneidmiller, E.A.; Ulyanov, Yu.N. [Automatic Systems Corporation, Samara (Russian Federation)] [and others
1995-12-31
Paper presents conceptual design of free electron laser (FEL) complex for industrial applications. The FEL complex consists of three. FEL oscillators with the optical output spanning the infrared (IR) and ultraviolet (UV) wave-lengths ({lambda} = 0.3...20 {mu}m) and with the average output power 10 - 20 kW. The driving beam for the FELs is produced by a superconducting accelerator. The electron beam is transported to the FELs via three beam lines (125 MeV and 2 x 250 MeV). Peculiar feature of the proposed complex is a high efficiency of the. FEL oscillators, up to 20 %. This becomes possible due to the use of quasi-continuous electron beam and the use of the time-dependent undulator tapering.
9. Two electron response to an intense x-ray free electron laser pulse
Energy Technology Data Exchange (ETDEWEB)
Moore, L R; Parker, J S; Meharg, K J; Armstrong, G S J; Taylor, K T, E-mail: [email protected] [DAMTP, David Bates Building, Queen' s University Belfast, Belfast, BT7 1NN (United Kingdom)
2009-11-01
New x-ray free electron lasers (FELs) promise an ultra-fast ultra-intense regime in which new physical phenomena, such as double core hole formation in at atom, should become directly observable. Ahead of x-ray FEL experiments, an initial key task is to theoretically explore such fundamental laser-atom interactions and processes. To study the response of a two-electron positive ion to an intense x-ray FEL pulse, our theoretical approach is a direct numerical integration, incorporating non-dipole Hamiltonian terms, of the full six-dimensional time-dependent Schroedinger equation. We present probabilities of double K-shell ionization in the two-electron positive ions Ne{sup 8+} and Ar{sup 16+} exposed to x-ray FEL pulses with frequencies in the range 50 au to 300 au and intensities in the range 10{sup 17} to 10{sup 22} W/cm{sup 2}.
10. Design study of Thomson Laser-Electron X-ray Generator (LEX) for Millisecond Angiography
Science.gov (United States)
Artyukov, I. A.; Bessonov, E. G.; Feshchenko, R. M.; Gorbunkov, M. V.; Maslova, Yu Ya; Popov, N. L.; Dyachkov, N. V.; Postnov, A. A.; Vinogradov, S. L.; Vinogradov, A. V.
2017-01-01
In this concept study a laser-electron X-ray generator (LEX) is considered for the medical imaging of the inner vessel structure. It is demonstrated that the modern lasers and linear electron accelerators are suitable for the design of the new generation of angiography medical equipment combining higher spatial and time resolution with the reduced patient dose. Angiography setup based on LEXG can make use of different contrast media (iodine, gadolinium) working on absorption edge due to the narrow tuneable spectrum which is not possible with conventional X-ray tubes. In the present study all estimations are made for iodine-based contrast agents. The conclusion is that modern technologies allow practical implementation of LEX for angiography based on multibunch linear accelerator and photon storage device.
11. Acceleration of electrons using an inverse free electron laser auto- accelerator
Energy Technology Data Exchange (ETDEWEB)
Wernick, I.K.; Marshall, T.C.
1992-07-01
We present data from our study of a device known as the inverse free electron laser. First, numerical simulations were performed to optimize the design parameters for an experiment that accelerates electrons in the presence of an undulator by stimulated absorption of radiation. The Columbia free electron laser (FEL) was configured as an auto-accelerator (IFELA) system; high power (MW's) FEL radiation at {approximately}1.65 mm is developed along the first section of an undulator inside a quasi-optical resonator. The electron beam then traverses a second section of undulator where a fraction of the electrons is accelerated by stimulated absorption of the 1.65 mm wavelength power developed in the first undulator section. The second undulator section has very low gain and does not generate power on its own. We have found that as much as 60% of the power generated in the first section can be absorbed in the second section, providing that the initial electron energy is chosen correctly with respect to the parameters chosen for the first and second undulators. An electron momentum spectrometer is used to monitor the distribution of electron energies as the electrons exit the IFELA. We have found; using our experimental parameters, that roughly 10% of the electrons are accelerated to energies as high as 1100 keV, in accordance with predictions from the numerical model. The appearance of high energy electrons is correlated with the abrupt absorption of millimeter power. The autoaccelerator configuration is used because there is no intense source of coherent power at the 1.65 mm design wavelength other than the FEL.
12. Acceleration of electrons using an inverse free electron laser auto- accelerator
Energy Technology Data Exchange (ETDEWEB)
Wernick, Iddo K. [Columbia Univ., New York, NY (United States); Marshall, Thomas C. [Columbia Univ., New York, NY (United States)
1992-07-01
We present data from our study of a device known as the inverse free electron laser. First, numerical simulations were performed to optimize the design parameters for an experiment that accelerates electrons in the presence of an undulator by stimulated absorption of radiation. The Columbia free electron laser (FEL) was configured as an auto-accelerator (IFELA) system; high power (MWs) FEL radiation at ~1.65 mm is developed along the first section of an undulator inside a quasi-optical resonator. The electron beam then traverses a second section of undulator where a fraction of the electrons is accelerated by stimulated absorption of the 1.65 mm wavelength power developed in the first undulator section. The second undulator section has very low gain and does not generate power on its own. We have found that as much as 60% of the power generated in the first section can be absorbed in the second section, providing that the initial electron energy is chosen correctly with respect to the parameters chosen for the first and second undulators. An electron momentum spectrometer is used to monitor the distribution of electron energies as the electrons exit the IFELA. We have found; using our experimental parameters, that roughly 10% of the electrons are accelerated to energies as high as 1100 keV, in accordance with predictions from the numerical model. The appearance of high energy electrons is correlated with the abrupt absorption of millimeter power. The autoaccelerator configuration is used because there is no intense source of coherent power at the 1.65 mm design wavelength other than the FEL.
13. Short Wavelength Seeding through Compression for Fee Electron Lasers
Energy Technology Data Exchange (ETDEWEB)
Qiang, Ji
2010-03-29
In this paper, we propose a seeding scheme that compresses an initial laser modulation in the longitudinal phase space of an electron beam by using two opposite sign bunch compressors and two opposite sign energy chirpers. This scheme could potentially reduce the initial modulation wavelength by a factor of C and increase the energy modulation amplitude by a factor of C , where Cis the compression factor of the first bunch compressor. Using two lasers as energy chirpers, such a modulation compression scheme can generate kilo-Ampershort wavelength current modulation with significant bunching factor from an initial a few tens Amper current. This compression scheme can also be used togenerate a prebunched single atto-second short wavelength current modulation and prebunched two color, two atto-second modulations.
14. Gain of a Smith-Purcell free-electron laser
Directory of Open Access Journals (Sweden)
H. L. Andrews
2004-07-01
Full Text Available A formula is derived for the small-signal gain of a Smith-Purcell free-electron laser. The theory describes the electron beam as a moving plasma dielectric, and assumes that the electron beam interacts with an evanescent mode traveling along the surface of a periodic waveguide with a rectangular profile. The phase velocity of the evanescent wave is synchronous with the electron velocity, but the group velocity is actually negative. The electron beam amplifies the evanescent wave, which does not itself radiate. According to this picture, the radiation observed emanating from the grating is Smith-Purcell radiation enhanced by the bunching of the electrons due to the interaction with the evanescent mode. There will also be radiation from the part of the evanescent mode that is outcoupled from the ends of the grating. This radiation appears at a lower frequency than the Smith-Purcell radiation. The new results explain both the gain and the radiation observed in the experiments of Urata and Walsh, and the cube-root current dependence of the gain inferred by Bakhtyari, Walsh, and Brownell.
15. Electron acceleration by a radially polarized laser pulse during ionization of low density gases
Directory of Open Access Journals (Sweden)
Kunwar Pal Singh
2011-03-01
Full Text Available The acceleration of electrons by a radially polarized intense laser pulse has been studied. The axial electric field of the laser is responsible for electron acceleration. The axial electric field increases with decreasing laser spot size; however, the laser pulse gets defocused sooner for smaller values and the electrons do not experience high electric field for long, reducing the energy they can reach. The electron remains confined in the electric field of the laser for longer and the electron energy peaks for the normalized laser spot size nearly equal to the normalized laser intensity parameter. Electron energy peaks for initial laser phase ϕ_{0}=π due to accelerating laser phase and decreases with transverse initial position of the electrons. The energy and angle of the emittance spectrum of the electrons generated during ionization of krypton and argon at low densities have been obtained and a right choice of laser parameters has been suggested to obtain high energy quasimonoenergetic collimated electron beams. It has been found that argon is more suitable than krypton to obtain high energy electron beams due to higher ionization potential of inner shells for the former.
16. Applications of laser wakefield accelerator-based light sources
Science.gov (United States)
Albert, Félicie; Thomas, Alec G. R.
2016-11-01
Laser-wakefield accelerators (LWFAs) were proposed more than three decades ago, and while they promise to deliver compact, high energy particle accelerators, they will also provide the scientific community with novel light sources. In a LWFA, where an intense laser pulse focused onto a plasma forms an electromagnetic wave in its wake, electrons can be trapped and are now routinely accelerated to GeV energies. From terahertz radiation to gamma-rays, this article reviews light sources from relativistic electrons produced by LWFAs, and discusses their potential applications. Betatron motion, Compton scattering and undulators respectively produce x-rays or gamma-rays by oscillating relativistic electrons in the wakefield behind the laser pulse, a counter-propagating laser field, or a magnetic undulator. Other LWFA-based light sources include bremsstrahlung and terahertz radiation. We first evaluate the performance of each of these light sources, and compare them with more conventional approaches, including radio frequency accelerators or other laser-driven sources. We have then identified applications, which we discuss in details, in a broad range of fields: medical and biological applications, military, defense and industrial applications, and condensed matter and high energy density science.
17. Ultrafast supercontinuum fiber-laser based pump-probe scanning magneto-optical Kerr effect microscope for the investigation of electron spin dynamics in semiconductors at cryogenic temperatures with picosecond time and micrometer spatial resolution.
Science.gov (United States)
Henn, T; Kiessling, T; Ossau, W; Molenkamp, L W; Biermann, K; Santos, P V
2013-12-01
We describe a two-color pump-probe scanning magneto-optical Kerr effect microscope which we have developed to investigate electron spin phenomena in semiconductors at cryogenic temperatures with picosecond time and micrometer spatial resolution. The key innovation of our microscope is the usage of an ultrafast "white light" supercontinuum fiber-laser source which provides access to the whole visible and near-infrared spectral range. Our Kerr microscope allows for the independent selection of the excitation and detection energy while avoiding the necessity to synchronize the pulse trains of two separate picosecond laser systems. The ability to independently tune the pump and probe wavelength enables the investigation of the influence of excitation energy on the optically induced electron spin dynamics in semiconductors. We demonstrate picosecond real-space imaging of the diffusive expansion of optically excited electron spin packets in a (110) GaAs quantum well sample to illustrate the capabilities of the instrument.
18. Controlling electron-electron correlation in frustrated double ionization of triatomic molecules with orthogonally polarized two-color laser fields
Science.gov (United States)
Chen, A.; Kling, M. F.; Emmanouilidou, A.
2017-09-01
We demonstrate the control of electron-electron correlation in frustrated double ionization (FDI) of the two-electron triatomic molecule D3 + when driven by two orthogonally polarized two-color laser fields. We employ a three-dimensional semiclassical model that fully accounts for the electron and nuclear motion in strong fields. We analyze the FDI probability and the distribution of the momentum of the escaping electron along the polarization direction of the longer wavelength and more intense laser field. These observables, when considered in conjunction, bear clear signatures of the prevalence or absence of electron-electron correlation in FDI, depending on the time delay between the two laser pulses. We find that D3 + is a better candidate than H2 for demonstrating also experimentally that electron-electron correlation indeed underlies FDI.
19. Upgrade of laser and electron beam welding database
CERN Document Server
Furman, Magdalena
2014-01-01
The main purpose of this project was to fix existing issues and update the existing database holding parameters of laser-beam and electron-beam welding machines. Moreover, the database had to be extended to hold the data for the new machines that arrived recently at the workshop. As a solution - the database had to be migrated to Oracle framework, the new user interface (using APEX) had to be designed and implemented with the integration with the CERN web services (EDMS, Phonebook, JMT, CDD and EDH).
20. Review of x-ray free-electron laser theory
Directory of Open Access Journals (Sweden)
Zhirong Huang
2007-03-01
Full Text Available High-gain free-electron lasers (FELs are being developed as extremely bright sources for a next-generation x-ray facility. In this paper, we review the basic theory of the start-up, the exponential growth, and the saturation of the high-gain process, emphasizing the self-amplified spontaneous emission. The radiation characteristics of an x-ray FEL, including its transverse coherence, temporal characteristics, and harmonic content, are discussed. FEL performance in the presence of machine errors and undulator wakefields is examined. Various enhancement schemes through seeding and beam manipulations are summarized.
1. Electron scattering by laser-excited barium atoms
Science.gov (United States)
Register, D. F.; Trajmar, S.; Jensen, S. W.; Poe, R. T.
1978-01-01
Inelastic and superelastic scattering of 30- and 100-eV electrons by laser-excited 6s 6p 1P and subsequent cascade-populated 6s 6p 3P, 6s 5d 1D, and 6s 5d 3D Ba atoms have been observed. Absolute differential cross sections for the singlet and relative scattering intensities for the triplet species have been determined in the 5 to 20 deg angular region. Under the present conditions excitations dominate over deexcitations.
2. Plasma channel diagnostic based on laser centroid oscillations
Energy Technology Data Exchange (ETDEWEB)
Gonsalves, A. J.; Nakamura, K.; Lin, C.; Osterhoff, J.; Shiraishi, S.; Schroeder, C. B.; Geddes, C. G. R.; Tóth, Cs.; Esarey, E.; Leemans, W. P.
2010-05-01
A technique has been developed for measuring the properties of discharge-based plasma channels by monitoring the centroid location of a laser beam exiting the channel as a function of input alignment offset between the laser and the channel. Experiments were performed using low-intensity (<1014 Wcm-2) laser pulses focused onto the entrance of a hydrogen-filled capillary discharge waveguide. Scanning the laser centroid position at the input of the channel and recording the exit position allows determination of the channel depth with an accuracy of a few percent, measurement of the transverse channel shape, and inference of the matched spot size. In addition, accurate alignment of the laser beam through the plasma channel is provided by minimizing laser centroid motion at the channel exit as the channel depth is scanned either by scanning the plasma density or the discharge timing. The improvement in alignment accuracy provided by this technique will be crucial for minimizing electron beam pointing errors in laser plasma accelerators.
3. Three-dimensional simulation of laser–plasma-based electron ...
Abstract. A sequential three-dimensional (3D) particle-in-cell simulation code PICPSI-3D with a user friendly graphical user interface (GUI) has been developed and used to study the interaction of plasma with ultrahigh intensity laser radiation. A case study of laser–plasma-based electron acceleration has been carried out ...
4. Three-dimensional simulation of laser–plasma-based electron ...
A sequential three-dimensional (3D) particle-in-cell simulation code PICPSI-3D with a user friendly graphical user interface (GUI) has been developed and used to study the interaction of plasma with ultrahigh intensity laser radiation. A case study of laser–plasma-based electron acceleration has been carried out to assess ...
5. Optical control of hard X-ray polarization by electron injection in a laser wakefield accelerator
Science.gov (United States)
Schnell, Michael; Sävert, Alexander; Uschmann, Ingo; Reuter, Maria; Nicolai, Maria; Kämpfer, Tino; Landgraf, Björn; Jäckel, Oliver; Jansen, Oliver; Pukhov, Alexander; Kaluza, Malte Christoph; Spielmann, Christian
2013-01-01
Laser-plasma particle accelerators could provide more compact sources of high-energy radiation than conventional accelerators. Moreover, because they deliver radiation in femtosecond pulses, they could improve the time resolution of X-ray absorption techniques. Here we show that we can measure and control the polarization of ultra-short, broad-band keV photon pulses emitted from a laser-plasma-based betatron source. The electron trajectories and hence the polarization of the emitted X-rays are experimentally controlled by the pulse-front tilt of the driving laser pulses. Particle-in-cell simulations show that an asymmetric plasma wave can be driven by a tilted pulse front and a non-symmetric intensity distribution of the focal spot. Both lead to a notable off-axis electron injection followed by collective electron–betatron oscillations. We expect that our method for an all-optical steering is not only useful for plasma-based X-ray sources but also has significance for future laser-based particle accelerators. PMID:24026068
6. Dynamic molecular structure retrieval from low-energy laser-induced electron diffraction spectra
Science.gov (United States)
Vu, Dinh-Duy T.; Phan, Ngoc-Loan T.; Hoang, Van-Hung; Le, Van-Hoang
2017-12-01
A recently developed quantitative rescattering theory showed that a laser-free elastic cross section can be separated from laser-induced electron diffraction (LIED) spectra. Based upon this idea, Blaga et al investigated the possibility of reconstructing molecular structure from LIED spectra (2012 Nature 483 7388). In the above study, an independent atoms model (IAM) was used to interpret high-energy electron–molecule collisions induced by a mid-infrared laser. Our research aims to extend the application range of this structural retrieval method to low-energy spectra induced by more common near-infrared laser sources. The IAM is insufficient in this case, so we switch to a more comprehensive model—the multiple scattering (MS) theory. From the original version concerning only neutral targets, we upgrade the model so that it is compatible with electron–ion collisions at low energy. With available LIED experiment data of CO2 and O2, the upgraded MS is shown to be greatly effective as a tool for molecular imaging from spectra induced by a near-infrared laser. The captured image is at about 2 fs after the ionization, shorter than the period 4–6 fs by using the mid-infrared laser in Blaga’s experiment.
7. Longitudinal space charge assisted echo seeding of a free-electron laser with laser-spoiler noise suppression
Directory of Open Access Journals (Sweden)
Kirsten Hacker
2014-09-01
Full Text Available Seed lasers are employed to improve the temporal coherence of free-electron laser (FEL light. However, when these seed pulses are short relative to the particle bunch, the noisy, temporally incoherent radiation from the unseeded electrons can overwhelm the coherent, seeded radiation. In this paper, a technique to seed a particle bunch with an external laser is presented in which a new mechanism to improve the contrast between coherent and incoherent free electron laser radiation is employed together with a novel, simplified echo-seeding method. The concept relies on a combination of longitudinal space charge wakes and an echo-seeding technique to make a short, coherent pulse of FEL light together with noise background suppression. Several different simulation codes are used to illustrate the concept with conditions at the soft x-ray free-electron laser in Hamburg, FLASH.
8. A Low-Energy-Spread Rf Accelerator for a Far-Infrared Free-Electron Laser
NARCIS (Netherlands)
van der Geer, C. A. J.; Bakker, R. J.; van der Meer, A. F. G.; van Amersfoort, P. W.; Gillespie, W. A.; Saxon, G.; Poole, M. W.
1993-01-01
A high electron current and a small energy spread are essential for the operation of a free electron laser (FEL). In this paper we discuss the design and performance of the accelerator for FELIX, the free electron laser for infrared experiments. The system consists of a thermionic gun, a prebuncher,
9. Direct acceleration of electrons by a CO2 laser in a curved plasma waveguide
OpenAIRE
Yi, Longqing; Pukhov, Alexander; Shen, Baifei
2016-01-01
Laser plasma interaction with micro-engineered targets at relativistic intensities has been greatly promoted by recent progress in the high contrast lasers and the manufacture of advanced micro- and nano-structures. This opens new possibilities for the physics of laser-matter interaction. Here we propose a novel approach that leverages the advantages of high-pressure CO$_{2}$ laser, laser-waveguide interaction, as well as micro-engineered plasma structure to accelerate electrons to peak energ...
10. Microscopic study on lasing characteristics of the UVSOR storage ring free electron laser
Energy Technology Data Exchange (ETDEWEB)
Hama, H. [Institute for Molecular Science, Okazaki (Japan)]|[Graduate Univ. for Advanced Stuides, Okazaki (Japan); Yamazaki, J.; Kinoshita, T. [Institute for Molecular Science, Okazaki (Japan)] [and others
1995-12-31
Characteristics of storage ring free electron laser (SRFEL) at a short wavelength region (UV and visible) has been studied at the UVSOR facility, Institute for Molecular Science. We have measured the laser power evolution by using a biplanar photodiode, and the micro-macro temporal structure of both the laser and the electron bunch with a dualsweep streak camera. The saturated energy of the laser micropulse in the gain-switching (Q-switching) mode has been measured as a function of the ring current. We have not observed a limitation of the output power yet within the beam current can be stored. We have analyzed the saturated micropulse energy based on a model of gain reduction due to the bunch-heating. The bunch-heating process seems to be very complicate. We derived time dependent gain variations from the shape of macropulse and the bunch length. Those two gain variations are almost consistent with each other but slightly different in detail. The gain may be not only simply reduced by the energy spread but also affected by the phase space rotation due to synchrotron oscillation of the electron bunch. As reported in previous issue, the lasing macropulse consists of a couple of micropulses that are simultaneously evolved. From high resolution two-dimensional spectra taken by the dual-sweep streak camera, we noticed considerable internal substructures of the laser micropulse in both the time distribution and the spectral shape. There are a couple of peaks separated with almost same distance in a optical bunch. Such substructure does not seem to result from statistical fluctuations of laser seeds. Although the origin of the substructure of macropulse is not dear at the present, we are going to discuss about SRFEL properties.
11. Simulated electronic heterodyne recording and processing of pulsed-laser holograms
Science.gov (United States)
Decker, A. J.
1979-01-01
The electronic recording of pulsed-laser holograms is proposed. The polarization sensitivity of each resolution element of the detector is controlled independently to add an arbitrary phase to the image waves. This method which can be used to simulate heterodyne recording and to process three-dimensional optical images, is based on a similar method for heterodyne recording and processing of continuous-wave holograms.
12. Diode Laser Based LIF Diagnostics for Argon and Helium Plasmas.
Science.gov (United States)
Stolzenberg, E.; Boivin, R. F.; Compton, C.; Hardin, R.; Keesee, A.; Kline, J. L.; Scime, E. E.
2002-11-01
A diode laser based Laser Induced Fluorescence (LIF) diagnostic that uses an inexpensive diode laser system is presented. The same diode laser is used to pump Ar II and He I transitions to obtain the ion and the neutral temperature of the respective species. The 1 MHz bandwidth diode laser has a Littrow external cavity with a mode-hop free tuning range up to 15 GHz and with a total power output of about 10 mWatt. The wavelength is measured by a wavemeter and frequent monitoring prevent wavelength drift. For the argon ion population, the laser tuned at 668.61 nm, is used to pump the 3d4F7/2 Ar II metastable level to the 4p4D5/2 excited level. The fluorescence radiation between the 4p4D5/2 and the 4s4P3/2 levels (442.6 nm) is monitored by a photomultiplier detector. For neutral helium, the laser is tuned at 667.82 nm to pump a fraction of the electron population from the 21P state to the 31D upper level. Although the 21P level is not a metastable state, the close proximity of 21S metastable level makes this new He I LIF possible in collisional plasmas. Some electrons of this 31D level undergo collisional excitation transfer (optically allowed transition) to the 31P. In turn, this state decay to the metastable 21S by emitting 501.6 nm fluorescence photons. The new LIF diagnostic has been developed at West Virginia University (WVU) and tested on the Hot hELIcon eXperiment (HELIX) plasma device. Ion and neutral temperatures obtained using this new LIF diagnostic are presented and compared to previous measurements performed with a more expensive and elaborate ring dye laser system.
13. Electronically Excited C2 from Laser Photodissociated C60
Science.gov (United States)
Arepalli, Sivaram; Scott, Carl D.; Nikolaev, Pavel; Smalley, Richard E.
1999-01-01
Spectral and transient emission measurements are made of radiation from products of laser excitation of buckminsterfullerene (C60) vapor diluted in argon at 973 K. The principal radiation is from the Swan band system of C2 and, at early times, also from a black body continuum. The C2 radiation is observed only when C60 is excited by green (532 nm) and not with IR (1064 nm) laser radiation at energy densities of about 1.5 J/square cm. Transient measurements indicate that there are two characteristic periods of decay of radiation. The first period, lasting about 2 micro seconds, has a characteristic decay time of about 0.3 micro seconds. The second period, lasting at least 50 micro seconds, has a characteristic decay time of about 5 micro seconds. These characteristic times are thought to be associated with cooling of C60 molecules or nanosized carbon particles during the early period; and with electronically excited C2 that is a decomposition product of laser excited C60, C58, ... molecules during the later period.
14. Generating Periodic Terahertz Structures in a Relativistic Electron Beam through Frequency Down-Conversion of Optical Lasers
Energy Technology Data Exchange (ETDEWEB)
Dunning, Michael
2012-07-19
We report generation of density modulation at terahertz (THz) frequencies in a relativistic electron beam through laser modulation of the beam longitudinal phase space. We show that by modulating the energy distribution of the beam with two lasers, density modulation at the difference frequency of the two lasers can be generated after the beam passes through a chicane. In this experiment, density modulation around 10 THz was generated by down-converting the frequencies of an 800 nm laser and a 1550 nm laser. The central frequency of the density modulation can be tuned by varying the laser wavelengths, beam energy chirp, or momentum compaction of the chicane. This technique can be applied to accelerator-based light sources for generation of coherent THz radiation and marks a significant advance toward tunable narrow-band THz sources.
15. Design of sub-Angstrom compact free-electron laser source
Science.gov (United States)
Bonifacio, Rodolfo; Fares, Hesham; Ferrario, Massimo; McNeil, Brian W. J.; Robb, Gordon, R. M.
2017-01-01
In this paper, we propose for first time practical parameters to construct a compact sub-Angstrom Free Electron Laser (FEL) based on Compton backscattering. Our recipe is based on using picocoulomb electron bunch, enabling very low emittance and ultracold electron beam. We assume the FEL is operating in a quantum regime of Self Amplified Spontaneous Emission (SASE). The fundamental quantum feature is a significantly narrower spectrum of the emitted radiation relative to classical SASE. The quantum regime of the SASE FEL is reached when the momentum spread of the electron beam is smaller than the photon recoil momentum. Following the formulae describing SASE FEL operation, realistic designs for quantum FEL experiments are proposed. We discuss the practical constraints that influence the experimental parameters. Numerical simulations of power spectra and intensities are presented and attractive radiation characteristics such as high flux, narrow linewidth, and short pulse structure are demonstrated.
16. Fiber-Based Ultraviolet Laser System Project
Data.gov (United States)
National Aeronautics and Space Administration — The purpose of this program is to develop a compact and efficient ultraviolet laser system for use in space-based uv-Raman instruments. The basis for this system...
17. Numerical Simulations of X-Ray Free Electron Lasers (XFEL)
KAUST Repository
Antonelli, Paolo
2014-11-04
We study a nonlinear Schrödinger equation which arises as an effective single particle model in X-ray free electron lasers (XFEL). This equation appears as a first principles model for the beam-matter interactions that would take place in an XFEL molecular imaging experiment in [A. Fratalocchi and G. Ruocco, Phys. Rev. Lett., 106 (2011), 105504]. Since XFEL are more powerful by several orders of magnitude than more conventional lasers, the systematic investigation of many of the standard assumptions and approximations has attracted increased attention. In this model the electrons move under a rapidly oscillating electromagnetic field, and the convergence of the problem to an effective time-averaged one is examined. We use an operator splitting pseudospectral method to investigate numerically the behavior of the model versus that of its time-averaged version in complex situations, namely the energy subcritical/mass supercritical case and in the presence of a periodic lattice. We find the time-averaged model to be an effective approximation, even close to blowup, for fast enough oscillations of the external field. This work extends previous analytical results for simpler cases [P. Antonelli, A. Athanassoulis, H. Hajaiej, and P. Markowich, Arch. Ration. Mech. Anal., 211 (2014), pp. 711--732].
18. A Novel Diagnostics of Ultrashort Electron Bunches Based on Detection of Coherent Radiation from Bunched Electron Beam in an Undulator
CERN Document Server
Saldin, Evgeny L; Yurkov, Mikhail V
2004-01-01
We propose a new method for measurements of the longitudinal profile of 100 femtosecond electron bunches for X-ray Free Electron Lasers (XFELs). The method is based on detection of coherent undulator radiation produced by modulated electron beam. Seed optical quantum laser is used to produce exact optical replica of ultrashort electron bunches. The replica is generated in apparatus which consists of an input undulator (energy modulator), and output undulator (radiator) separated by a dispersion section. The radiation in the output undulator is excited by the electron bunch modulated at the optical wavelength and rapidly reaches a hundred-MW-level power. We then use the now-standard method of ultrashort laser pulse-shape measurement, a tandem combination of autocorrelator and spectrum (FROG -- frequency resolved optical gating) providing real-time single-shot measurements of the electron bunch structure. The big advantage of proposed technique is that it can be used to determine the slice energy spread and emi...
19. Effects of beam quality in a free-electron laser oscillator with two electron beams
Science.gov (United States)
Nam, Soon-Kwon
2017-11-01
We have studied the electron beam quality in a free-electron laser (FEL) oscillator by using two electron beams of different harmonically related energies in the FEL facility, which is operated in the infrared and far-infrared regions. The electron beam quality, such as emittance, energy spread, and higher-order modes were studied using an extended three-dimensional (3D) FEL code for two electron beams that we have developed. The variations in the radiation amplitude of the electron beam's emittances, and energy spread were also calculated for a tapered wiggler for the multiparticle and multi-pass number using a new 3D code. The evolution of the radiation field intensity for higher-order modes of the wiggler with beam emittance and energy spread was studied for the two-electron beam's FEL performance. We found that the radiation intensity was degraded due to the energy spread and the emittance of the electron beam. We minimized the degradation of the radiation intensity by optimizing the tapered wiggler for the coupled two-beam FEL oscillator.
20. Field Emitter Arrays for a Free Electron Laser Application
CERN Document Server
Shing-Bruce-Li, Kevin; Ganter, Romain; Gobrecht, Jens; Raguin, Jean Yves; Rivkin, Leonid; Wrulich, Albin F
2004-01-01
The development of a new electron gun with the lowest possible emittance would help reducing the total length and cost of a free electron laser. Field emitter arrays (FEAs) are an attractive technology for electron sources of ultra high brightness. Indeed, several thousands of microscopic tips can be deposited on a 1 mm diameter area. Electrons are then extracted by applying voltage to a first grid layer close to the tip apexes, the so called gate layer, and focused by a second grid layer one micrometer above the tips. The typical aperture diameter of the gate and the focusing layer is in the range of one micrometer. One challenge for such cathodes is to produce peak currents in the ampere range since the usual applications of FEAs require less than milliampere. Encouraging peak current performances have been obtained by applying voltage pulses at low frequency between gate and tips. In this paper we report on different tip materials available on the market: diamond FEAs from Extreme Devices Inc., ZrC single ...
1. Influence of non-collisional laser heating on the electron dynamics in dielectric materials
CERN Document Server
Barilleau, L; Chimier, B; Geoffroy, G; Tikhonchuk, V
2016-01-01
The electron dynamics in dielectric materials induced by intense femtosecond laser pulses is theoretically addressed. The laser driven temporal evolution of the energy distribution of electrons in the conduction band is described by a kinetic Boltzmann equation. In addition to the collisional processes for energy transfer such as electron-phonon-photon and electron-electron interactions, a non-collisional process for photon absorption in the conduction band is included. It relies on direct transitions between sub-bands of the conduction band through multiphoton absorption. This mechanism is shown to significantly contribute to the laser heating of conduction electrons for large enough laser intensities. It also increases the time required for the electron distribution to reach the equilibrium state as described by the Fermi-Dirac statistics. Quantitative results are provided for quartz irradiated by a femtosecond laser pulse with a wavelength of 800 nm and for intensities in the range of tens of TW/cm$^2$, lo...
2. Direct acceleration of electrons by a CO2 laser in a curved plasma waveguide
CERN Document Server
Yi, Longqing; Shen, Baifei
2016-01-01
Laser plasma interaction with micro-engineered targets at relativistic intensities has been greatly promoted by recent progress in the high contrast lasers and the manufacture of advanced micro- and nano-structures. This opens new possibilities for the physics of laser-matter interaction. Here we propose a novel approach that leverages the advantages of high-pressure CO 2 laser, laser-waveguide interaction, as well as micro-engineered plasma structure to accelerate electrons to peak energy greater than 1 GeV with narrow slice energy spread (~1%) and high overall efficiency. The acceleration gradient is 26 GV/m for a 1.3 TW CO2 laser system. The micro-bunching of a long electron beam leads to the generation of a chain of ultrashort electron bunches with the duration roughly equal to half-laser-cycle. These results open a way for developing a compact and economic electron source for diverse applications.
3. Direct acceleration of electrons by a CO$_{2}$ laser in a curved plasma waveguide
CERN Document Server
Yi, Longqing; Shen, Baifei
2016-01-01
Laser plasma interaction with micro-engineered targets at relativistic intensities has been greatly promoted by recent progress in the high contrast lasers and the manufacture of advanced micro- and nano-structures. This opens new possibilities for the physics of laser-matter interaction. Here we propose a novel approach that leverages the advantages of high-pressure CO$_{2}$ laser, laser-waveguide interaction, as well as micro-engineered plasma structure to accelerate electrons to peak energy greater than 1 GeV with narrow slice energy spread ($\\sim1\\%$) and high overall efficiency. The acceleration gradient is 26 GV/m for a 1.3 TW CO$_{2}$ laser system. The micro-bunching of a long electron beam leads to the generation of a chain of ultrashort electron bunches with the duration roughly equal to half-laser-cycle. These results open a way for developing a compact and economic electron source for diverse applications.
4. Semiconductor-based, large-area, flexible, electronic devices
Science.gov (United States)
Goyal, Amit [Knoxville, TN
2011-03-15
Novel articles and methods to fabricate the same resulting in flexible, large-area, triaxially textured, single-crystal or single-crystal-like, semiconductor-based, electronic devices are disclosed. Potential applications of resulting articles are in areas of photovoltaic devices, flat-panel displays, thermophotovoltaic devices, ferroelectric devices, light emitting diode devices, computer hard disc drive devices, magnetoresistance based devices, photoluminescence based devices, non-volatile memory devices, dielectric devices, thermoelectric devices and quantum dot laser devices.
5. Laser generated nanoparticles based photovoltaics.
Science.gov (United States)
Petridis, C; Savva, K; Kymakis, E; Stratakis, E
2017-03-01
The exploitation of nanoparticles (NP), synthesized via laser ablation in liquids, in photovoltaic devices is reviewed. In particular, the impact of NPs' incorporation into various building blocks within the solar cell architecture on the photovoltaic performance and stability is presented and analysed for the current state of the art photovoltaic technologies. Copyright © 2016. Published by Elsevier Inc.
6. A High-Average-Power Free Electron Laser for Microfabrication and Surface Applications
Science.gov (United States)
Dylla, H. F.; Benson, S.; Bisognano, J.; Bohn, C. L.; Cardman, L.; Engwall, D.; Fugitt, J.; Jordan, K.; Kehne, D.; Li, Z.;
1995-01-01
CEBAF has developed a comprehensive conceptual design of an industrial user facility based on a kilowatt ultraviolet (UV) (160-1000 mm) and infrared (IR) (2-25 micron) free electron laser (FEL) driven by a recirculating, energy recovering 200 MeV superconducting radio frequency (SRF) accelerator. FEL users, CEBAF's partners in the Lase Processing Consortium, including AT&T, DuPont, IBM, Northrop Grumman, 3M, and Xerox, are developing applications such as metal, ceramic, and electronic material micro-fabrication and polymer and metal surface processing, with the overall effort leading to later scale-up to industrial systems at 50-100 kW. Representative applications are described. The proposed high-average-power FEL overcomes limitations of conventional laser sources in available power, cost-effectiveness, tunability, and pulse structure.
7. Energy Technology Data Exchange (ETDEWEB)
Nuhn, H
2004-01-09
The intensity of X-ray sources has increased at a rapid rate since the late 1960s by 10 orders of magnitude and more through the use of synchrotron radiation produced by bending magnets, wigglers and undulators. Three generations of radiation sources have been identified depending on amplitude and quality of the radiation provided. While user facilities of the third generation were being constructed a new concept of radiation generating devices was being developed that offers an even larger increase in peak and average brightness than had been achieved till then. The new concept of the X-ray Free Electron Laser based on the principle of Self-Amplified Spontaneous Emission will be the basis of fourth generation X-ray source user facilities of this century. The paper will start with a brief history of the development of x-ray sources, discuss some of the differences between storage ring and free electron laser based approaches, and close with an update of the present development of x-ray free electron laser user facilities.
8. A novel approach to electron data background treatment in an online wide-angle spectrometer for laser-accelerated ion and electron bunches
Science.gov (United States)
Lindner, F. H.; Bin, J. H.; Englbrecht, F.; Haffa, D.; Bolton, P. R.; Gao, Y.; Hartmann, J.; Hilz, P.; Kreuzer, C.; Ostermayr, T. M.; Rösch, T. F.; Speicher, M.; Parodi, K.; Thirolf, P. G.; Schreiber, J.
2018-01-01
Laser-based ion acceleration is driven by electrical fields emerging when target electrons absorb laser energy and consecutively leave the target material. A direct correlation between these electrons and the accelerated ions is thus to be expected and predicted by theoretical models. We report on a modified wide-angle spectrometer, allowing the simultaneous characterization of angularly resolved energy distributions of both ions and electrons. Equipped with online pixel detectors, the RadEye1 detectors, the investigation of this correlation gets attainable on a single shot basis. In addition to first insights, we present a novel approach for reliably extracting the primary electron energy distribution from the interfering secondary radiation background. This proves vitally important for quantitative extraction of average electron energies (temperatures) and emitted total charge.
9. Above-Threshold Ionization and Laser-Induced Electron Diffraction in Diatomic Molecules
CERN Document Server
Suárez, N; Ciappina, M F; Wolter, B; Biegert, J; Lewenstein, M
2016-01-01
Strong field photoemission and electron recollision provide a viable route to extract electronic and nuclear dynamics from molecular targets with attosecond temporal resolution. However, since an {\\em ab-initio} treatment of even the simplest diatomic systems is beyond today's capabilities approximate qualitative descriptions are warranted. In this paper, we develop such a theoretical approach to model the photoelectrons resulting from intense laser-molecule interaction. We present a general theory for symmetric diatomic molecules in the single active electron approximation that, amongst other capabilities, allows adjusting both the internuclear separation and molecular potential in a direct and simple way. More importantly we derive an analytic approximate solution of the time dependent Schr\\"odinger equation (TDSE), based on a generalized strong field approximation (SFA) version. Using that approach we obtain expressions for electrons emitted transition amplitudes from two different molecular centres, and a...
10. Multistate optical memory based on serially interconnected lasers
NARCIS (Netherlands)
Zhang, S.; Owens, D.; Liu, Y.S.; Hill, M. T.; Lenstra, D.; Tzanakaki, A.; Khoe, G.D.; Dorren, H.J.S.
2005-01-01
A multistate optical memory based on serially inter-connected lasers is presented. We show that only one of the lasers can lase at a time, thus, the state of the optical memory is determined by the wavelength of the dominant laser. The light from the dominant laser suppresses its neighboring lasers
11. Material Processing Opportunites Utilizing a Free Electron Laser
Science.gov (United States)
Todd, Alan
1996-11-01
Many properties of photocathode-driven Free Electron Lasers (FEL) are extremely attractive for material processing applications. These include: 1) broad-band tunability across the IR and UV spectra which permits wavelength optimization, depth deposition control and utilization of resonance phenomena; 2) picosecond pulse structure with continuous nanosecond spacing for optimum deposition efficiency and minimal collateral damage; 3) high peak and average radiated power for economic processing in quantity; and 4) high brightness for spatially defined energy deposition and intense energy density in small spots. We discuss five areas: polymer, metal and electronic material processing, micromachining and defense applications; where IR or UV material processing will find application if the economics is favorable. Specific examples in the IR and UV, such as surface texturing of polymers for improved look and feel, and anti-microbial food packaging films, which have been demonstrated using UV excimer lamps and lasers, will be given. Unfortunately, although the process utility is readily proven, the power levels and costs of lamps and lasers do not scale to production margins. However, from these examples, application specific cost targets ranging from 0.1=A2/kJ to 10=A2/kJ of delivered radiation at power levels from 10 kW to 500 kW, have been developed and are used to define strawman FEL processing systems. Since =46EL radiation energy extraction from the generating electron beam is typically a few percent, at these high average power levels, economic considerations dictate the use of a superconducting RF accelerator with energy recovery to minimize cavity and beam dump power loss. Such a 1 kW IR FEL, funded by the US Navy, is presently under construction at the Thomas Jefferson National Accelerator Facility. This dual-use device, scheduled to generate first light in late 1997, will test both the viability of high-power FELs for shipboard self-defense against cruise
12. Design and simulation of laser wakefield acceleration with external electron bunch injection in front of the laser pulse
NARCIS (Netherlands)
Irman, A.; Luttikhof, M.J.H.; Khachatryan, A.G.; van Goor, F.A.; Verschuur, Jeroen W.J.; Bastiaens, Hubertus M.J.; Boller, Klaus J.
2007-01-01
In this article we present a theoretical investigation on an experimental design of a laser wakefield accelerator in which electron bunches from a photocathode radio frequency linac are injected into a capillary discharge plasma channel just in front of a few tens of terawatt drive laser pulse. The
13. Design and experimental tests of free electron laser wire scanners
Directory of Open Access Journals (Sweden)
G. L. Orlandi
2016-09-01
Full Text Available SwissFEL is a x-rays free electron laser (FEL driven by a 5.8 GeV linac under construction at Paul Scherrer Institut. In SwissFEL, wire scanners (WSCs will be complementary to view-screens for emittance measurements and routinely used to monitor the transverse profile of the electron beam during FEL operations. The SwissFEL WSC is composed of an in-vacuum beam-probe—motorized by a stepper motor—and an out-vacuum pick-up of the wire signal. The mechanical stability of the WSC in-vacuum hardware has been characterized on a test bench. In particular, the motor induced vibrations of the wire have been measured and mapped for different motor speeds. Electron-beam tests of the entire WSC setup together with different wire materials have been carried out at the 250 MeV SwissFEL Injector Test Facility (SITF, Paul Scherrer Institut, CH and at FERMI (Elettra-Sincrotrone Trieste, Italy. In particular, a comparative study of the relative measurement accuracy and the radiation-dose release of Al(99∶Si(1 and tungsten (W wires has been carried out. On the basis of the outcome of the bench and electron-beam tests, the SwissFEL WSC can be qualified as a high resolution and machine-saving diagnostic tool in consideration of the mechanical stability of the scanning wire at the micrometer level and the choice of the wire material ensuring a drastic reduction of the radiation-dose release with respect to conventional metallic wires. The main aspects of the design, laboratory characterization and electron beam tests of the SwissFEL WSCs are presented.
14. Design and experimental tests of free electron laser wire scanners
Science.gov (United States)
Orlandi, G. L.; Heimgartner, P.; Ischebeck, R.; Loch, C. Ozkan; Trovati, S.; Valitutti, P.; Schlott, V.; Ferianis, M.; Penco, G.
2016-09-01
SwissFEL is a x-rays free electron laser (FEL) driven by a 5.8 GeV linac under construction at Paul Scherrer Institut. In SwissFEL, wire scanners (WSCs) will be complementary to view-screens for emittance measurements and routinely used to monitor the transverse profile of the electron beam during FEL operations. The SwissFEL WSC is composed of an in-vacuum beam-probe—motorized by a stepper motor—and an out-vacuum pick-up of the wire signal. The mechanical stability of the WSC in-vacuum hardware has been characterized on a test bench. In particular, the motor induced vibrations of the wire have been measured and mapped for different motor speeds. Electron-beam tests of the entire WSC setup together with different wire materials have been carried out at the 250 MeV SwissFEL Injector Test Facility (SITF, Paul Scherrer Institut, CH) and at FERMI (Elettra-Sincrotrone Trieste, Italy). In particular, a comparative study of the relative measurement accuracy and the radiation-dose release of Al (99 )∶Si (1 ) and tungsten (W) wires has been carried out. On the basis of the outcome of the bench and electron-beam tests, the SwissFEL WSC can be qualified as a high resolution and machine-saving diagnostic tool in consideration of the mechanical stability of the scanning wire at the micrometer level and the choice of the wire material ensuring a drastic reduction of the radiation-dose release with respect to conventional metallic wires. The main aspects of the design, laboratory characterization and electron beam tests of the SwissFEL WSCs are presented.
15. Electronic tuning of integrated blue-violet GaN tunable coupled-cavity laser
NARCIS (Netherlands)
Guziy, O.; Grzanka, S.; Leszczynski, M.; Perlin, P.; Schemmann, M.; Salemink, H.W.M.
2012-01-01
We demonstrate an integrated tunable coupled-cavity InGaN/GaN laser with the emission wavelength centered on 409 nm. The electronic tuning range was 1.6 nm and threshold currents were 650 mA per cavity for 8.7-?m-wide laser ridges. Multimode laser emission with an average full width at half maximum
16. Laser-based agriculture system
KAUST Repository
Ooi, Boon S.
2016-03-31
A system and method are provided for indoor agriculture using at least one growth chamber illuminated by laser light. In an example embodiment of the agriculture system, a growth chamber is provided having one or more walls defining an interior portion of the growth chamber. The agriculture system may include a removable tray disposed within the interior portion of the growth chamber. The agriculture system also includes a light source, which may be disposed outside the growth chamber. The one or more walls may include at least one aperture. The light source is configured to illuminate at least a part of the interior portion of the growth chamber. In embodiments in which the light source is disposed outside the growth chamber, the light source is configured to transmit the laser light to the interior portion of the growth chamber via the at least one aperture.
17. High energy gain of trapped electrons in a tapered, diffraction-dominated inverse-free-electron laser.
Science.gov (United States)
Musumeci, P; Tochitsky, S Ya; Boucher, S; Clayton, C E; Doyuran, A; England, R J; Joshi, C; Pellegrini, C; Ralph, J E; Rosenzweig, J B; Sung, C; Tolmachev, S; Travish, G; Varfolomeev, A A; Varfolomeev, A A; Yarovoi, T; Yoder, R B
2005-04-22
Energy gain of trapped electrons in excess of 20 MeV has been demonstrated in an inverse-free-electron-laser (IFEL) accelerator experiment. A 14.5 MeV electron beam is copropagated with a 400 GW CO2 laser beam in a 50 cm long undulator strongly tapered in period and field amplitude. The Rayleigh range of the laser, approximately 1.8 cm, is much shorter than the undulator length yielding a diffraction-dominated interaction. Experimental results on the dependence of the acceleration on injection energy, laser focus position, and laser power are discussed. Simulations, in good agreement with the experimental data, show that most of the energy gain occurs in the first half of the undulator at a gradient of 70 MeV/m and that the structure in the measured energy spectrum arises because of higher harmonic IFEL interaction in the second half of the undulator.
18. High Energy Gain of Trapped Electrons in a Tapered, Diffraction-Dominated Inverse-Free-Electron Laser
Science.gov (United States)
Musumeci, P.; Tochitsky, S. Ya.; Boucher, S.; Clayton, C. E.; Doyuran, A.; England, R. J.; Joshi, C.; Pellegrini, C.; Ralph, J. E.; Rosenzweig, J. B.; Sung, C.; Tolmachev, S.; Travish, G.; Varfolomeev, A. A.; Varfolomeev, A. A.; Yarovoi, T.; Yoder, R. B.
2005-04-01
Energy gain of trapped electrons in excess of 20 MeV has been demonstrated in an inverse-free-electron-laser (IFEL) accelerator experiment. A 14.5 MeV electron beam is copropagated with a 400 GW CO2 laser beam in a 50 cm long undulator strongly tapered in period and field amplitude. The Rayleigh range of the laser, ˜1.8 cm, is much shorter than the undulator length yielding a diffraction-dominated interaction. Experimental results on the dependence of the acceleration on injection energy, laser focus position, and laser power are discussed. Simulations, in good agreement with the experimental data, show that most of the energy gain occurs in the first half of the undulator at a gradient of 70 MeV/m and that the structure in the measured energy spectrum arises because of higher harmonic IFEL interaction in the second half of the undulator.
19. Graphite oxide based targets applied in laser matter interaction
Science.gov (United States)
Cutroneo, Mariapompea; Torrisi, Lorenzo; Badziak, Jan; Rosinski, Marcin; Havranek, Vladimir; Mackova, Anna; Malinsky, Petr; Sofer, Zdenek; Luxa, Jan; Cannavò, Antonino; Lorincik, Jan
2018-01-01
In the present work, we propose the production of a hybrid graphene based material suitable to be laser irradiated with the aim to produce quasi-monoenergetic proton beams using a femtosecond laser system. The unique lattice structure of the irradiated solid thin target can affect the inside electron propagation, their outgoing from the rear side of a thin foil, and subsequently the plasma ion acceleration. The produced targets, have been characterized in composition, roughness and structure and for completeness irradiated. The yield and energy of the ions emitted from the laser-generated plasma have been monitored and the emission of proton stream profile exhibited an acceleration of the order of several MeVs/charge state.
20. Graphite oxide based targets applied in laser matter interaction
Directory of Open Access Journals (Sweden)
Cutroneo Mariapompea
2018-01-01
Full Text Available In the present work, we propose the production of a hybrid graphene based material suitable to be laser irradiated with the aim to produce quasi-monoenergetic proton beams using a femtosecond laser system. The unique lattice structure of the irradiated solid thin target can affect the inside electron propagation, their outgoing from the rear side of a thin foil, and subsequently the plasma ion acceleration. The produced targets, have been characterized in composition, roughness and structure and for completeness irradiated. The yield and energy of the ions emitted from the laser-generated plasma have been monitored and the emission of proton stream profile exhibited an acceleration of the order of several MeVs/charge state.
1. Imaging charge and energy transfer in molecules using free-electron lasers
Science.gov (United States)
Rudenko, Artem
2014-05-01
Charge and energy transfer reactions drive numerous important processes in physics, chemistry and biology, with applications ranging from X-ray astrophysics to artificial photosynthesis and molecular electronics. Experimentally, the central goal in studies of transfer phenomena is to trace the spatial localization of charge at a given time. Because of their element and site sensitivity, ultrafast X-rays provide a promising tool to address this goal. In this talk I will discuss several experiments where free-electron lasers were employed to study charge and energy transfer dynamics in fragmenting molecules. In a first example, we used intense, 70 femtosecond 1.5 keV pulses from the Linac Coherent Light Source (LCLS) to study distance dependence of electron transfer in laser-dissociated methyl iodide molecules. Inducing well-localized positive charge on the heavy iodine atom, we observe signature of electron transition from the separated methyl group up to the distances of 35 atomic units. In a complementary experiment, we studied charge exchange between two partners in a dissociating molecular iodine employing a pump-probe arrangement with two identical 90 eV pulses from the Free-Electron LASer in Hamburg (FLASH). In both cases, the effective spatial range of the electron transfer can be reasonably described by a classical over-the-barrier model developed for ion-atom collisions. Finally, I will discuss a time-resolved measurement on non-local relaxation mechanism based on a long-range energy transfer, the so-called interatomic Coulombic decay. This work was supported by Chemical Sciences, Geosciences, and Biosciences Division, Office of Basic Energy Sciences, Office of Science, US Department of Energy and by the Kansas NSF First Award'' program.
2. Modal analysis of a seeded free-electron laser
Directory of Open Access Journals (Sweden)
Sven Ackermann
2013-10-01
Full Text Available It has been shown that the direct seeding can enhance the performance of a free-electron laser (FEL in terms of its spectral, temporal, and coherence properties and reduces fluctuations in FEL output energy and arrival-time jitter. The properties of the used seed photon pulse are of high importance. In this paper, we describe the influence of the M^{2} onto the achievable power contrast between the direct seeded and the unseeded FEL radiation. The results of these studies are compared with the data from the high harmonic generation direct seeding experiment “sFLASH” in Hamburg, Germany. A method to measure M^{2} from a single transverse intensity distribution of the high harmonics beam at waist is discussed.
3. Microstructural features and mechanical properties of a cobalt-based laser coating
NARCIS (Netherlands)
Mol van Otterloo, J.L.de; de Hosson, J.T.M.
Electron microscopy, mechanical hardness measurements and pin-on-disc wear experiments were carried out on a laser-coated cobalt based Stellite alloy. It was found that with optimum laser parameters a poreless coating with a hardness of 11.3 GPa can be attained. The mechanical properties of the
4. Surface engineering with lasers : An application to co-base materials
NARCIS (Netherlands)
DeHosson, JTM; VanOtterloo, LD; Sudarshan, TS; Khor, KA; Jeandin, M
1997-01-01
Electron microscopy, mechanical hardness measurements and wear experiments were carried out on laser coated cobalt based Stellite alloys. It was found that with optimum laser parameters, a poreless coating with a hardness of 11.3 GPa can be attained. Detailed analysis indicates that solid solution
5. Using the X-ray free-electron laser to drive a photo-pumped helium-like neon X-ray laser at 23 nm
Science.gov (United States)
Nilsen, Joseph; Scott, Howard A.
2011-03-01
Nearly four decades ago resonantly photo-pumped laser schemes based on hydrogen-like and helium-like ions were proposed for producing X-ray lasers. These schemes have yet to be demonstrated because of the difficulty of finding a strong pump line with an adequate resonance to pump the laser transition. With the construction of the X-ray free-electron laser (X-FEL) at the SLAC Linac Coherent Light Source (LCLS) researchers now have a very bright tunable X-ray laser source that can be used to replace the pump line in previously proposed laser schemes and allow one to study the physics and feasibility of photo-pumped laser schemes. In this paper we model the sodium-pumped neon X-ray laser scheme that was proposed and studied many years ago by replacing the Na He-α pump line at 1127 eV with the X-FEL. Using the X-FEL to photo-ionize Ne down to He-like Ne and then photo-pump the He-γ line we predict gains greater than 400 cm -1 on the 4f - 3d transition at 23.1 nm in He-like Ne. The 4d - 3p line at 23.16 nm and the 4p - 3s line at 22.27 nm are also predicted to lase strongly.
6. Novel Single-Shot Diagnostics for Electrons from Laser-Plasma Interaction at SPARC_LAB
Directory of Open Access Journals (Sweden)
Fabrizio Bisesto
2017-10-01
Full Text Available Nowadays, plasma wakefield acceleration is the most promising acceleration technique for compact and cheap accelerators, needed in several fields, e.g., novel compact light sources for industrial and medical applications. Indeed, the high electric field available in plasma structures (>100 GV/m allows for accelerating electrons at the GeV energy scale in a few centimeters. Nevertheless, this approach still suffers from shot-to-shot instabilities, mostly related to experimental parameter fluctuations, e.g., laser intensity and plasma density. Therefore, single shot diagnostics are crucial in order to properly understand the acceleration mechanism. In this regard, at the SPARC_LAB Test Facility, we have developed two diagnostic tools to investigate properties of electrons coming from high intensity laser–matter interaction: one relying on Electro Optical Sampling (EOS for the measurement of the temporal profile of the electric field carried by fast electrons generated by a high intensity laser hitting a solid target, the other one based on Optical Transition Radiation (OTR for single shot measurements of the transverse emittance. In this work, the basic principles of both diagnostics will be presented as well as the experimental results achieved by means of the SPARC high brightness photo-injector and the high power laser FLAME.
7. Enhanced acceleration of injected electrons in a laser-beat-wave-induced plasma channel.
Science.gov (United States)
Tochitsky, S Ya; Narang, R; Filip, C V; Musumeci, P; Clayton, C E; Yoder, R B; Marsh, K A; Rosenzweig, J B; Pellegrini, C; Joshi, C
2004-03-05
Enhanced energy gain of externally injected electrons by a approximately 3 cm long, high-gradient relativistic plasma wave (RPW) is demonstrated. Using a CO2 laser beat wave of duration longer than the ion motion time across the laser spot size, a laser self-guiding process is initiated in a plasma channel. Guiding compensates for ionization-induced defocusing (IID) creating a longer plasma, which extends the interaction length between electrons and the RPW. In contrast to a maximum energy gain of 10 MeV when IID is dominant, the electrons gain up to 38 MeV energy in a laser-beat-wave-induced plasma channel.
8. Generation of Homogeneous and Patterned Electron Beams using a Microlens Array Laser-Shaping Technique
Energy Technology Data Exchange (ETDEWEB)
Halavanau, Aliaksei [NICADD, DeKalb; Edstrom, Dean [Fermilab; Gai, Wei [Argonne, HEP; Ha, Gwanghui [Argonne, HEP; Piot, Philippe [NICADD, DeKalb; Power, John [Argonne, HEP; Qiang, Gao [Unlisted, CN; Ruan, Jinhao [Fermilab; Santucci, James [Fermilab; Wisniewski, Eric [Argonne, HEP
2016-06-01
In photocathodes the achievable electron-beam parameters are controlled by the laser used to trigger the photoemission process. Non-ideal laser distribution hampers the final beam quality. Laser inhomogeneities, for instance, can be "amplified" by space-charge force and result in fragmented electron beams. To overcome this limitation laser shaping methods are routinely employed. In the present paper we demonstrate the use of simple microlens arrays to dramatically improve the transverse uniformity. We also show that this arrangement can be used to produce transversely-patterned electron beams. Our experiments are carried out at the Argonne Wakefield Accelerator facility.
9. First-principles electron dynamics control simulation of diamond under femtosecond laser pulse train irradiation.
Science.gov (United States)
Wang, Cong; Jiang, Lan; Wang, Feng; Li, Xin; Yuan, Yanping; Xiao, Hai; Tsai, Hai-Lung; Lu, Yongfeng
2012-07-11
A real-time and real-space time-dependent density functional is applied to simulate the nonlinear electron-photon interactions during shaped femtosecond laser pulse train ablation of diamond. Effects of the key pulse train parameters such as the pulse separation, spatial/temporal pulse energy distribution and pulse number per train on the electron excitation and energy absorption are discussed. The calculations show that photon-electron interactions and transient localized electron dynamics can be controlled including photon absorption, electron excitation, electron density, and free electron distribution by the ultrafast laser pulse train.
10. Extension of the Free-Electron Laser-Amplifier Code Tda to Resonator Configurations
NARCIS (Netherlands)
Faatz, B.; Best, R. W. B.; Oepts, D.; van Amersfoort, P. W.; Tran, T. M.
1993-01-01
The investigation of many interesting, complex phenomena in a free-electron laser (FEL) requires the use of numerical computer codes. In this paper we describe the extension of one such code (TDA), which in its original form could only be used to study free-electron laser amplifiers, to include
11. Relativistic laser hosing instability suppression and electron acceleration in a preformed plasma channel
Science.gov (United States)
Huang, T. W.; Zhou, C. T.; Zhang, H.; Wu, S. Z.; Qiao, B.; He, X. T.; Ruan, S. C.
2017-04-01
The hosing processes of a relativistic laser pulse, electron acceleration, and betatron radiation in a parabolic plasma channel are investigated in the direct laser acceleration regime. It is shown that the laser hosing instability would result in the generation of a randomly directed off-axis electron beam and radiation source with a large divergence angle. While employing a preformed parabolic plasma channel, the restoring force provided by the plasma channel would correct the perturbed laser wave front and thus suppress the hosing instability. As a result, the accelerated electron beam and the emitted photons are well guided and concentrated along the channel axis. The employment of a proper plasma density channel can stably guide the relativistically intense laser pulse and greatly improve the properties of the electron beam and radiation source. This scheme is of great interest for the generation of high quality electron beams and radiation sources.
12. Experimental investigations on the influence of the photocathode laser pulse parameters on the electron bunch quality in an RF-photoelectron source
Energy Technology Data Exchange (ETDEWEB)
Haenel, Marc
2010-07-15
Free Electron Lasers based on the SASE principle like the European XFEL require electron bunches having peak currents of several kiloamperes as well as very low transverse emittance. While high peak currents can be generated using longitudinal bunch compression techniques, the transverse emittance must have values as low as 1mmmrad already at the source. The development of electron sources fulfilling these demanding specifications is the goal of the Photo Injector Test Facility (PITZ) in DESY, Zeuthen site. The key component of a photoinjector is the electron gun cavity where the electrons bunches are generated and immediately accelerated. The extraction of the electrons is based on the photoelectric effect of the cathode which requires a laser system having special capabilities. In the first part of the thesis, measurements are presented which were performed to investigate whether the laser and the laser transport system fulfill these requirements. The second part of the thesis is dedicated to simulations as well as experimental studies on the impact of the temporal and spatial parameters of the laser pulses on the electron bunch quality. This influence is possible because the response time of the Cs{sub 2}Te photocathode is short compared to the laser pulse duration. Based on these investigations, suggestions for improvements are given and tolerances for the laser pulse properties are defined. (orig.)
13. The History of X-ray Free-Electron Lasers
Energy Technology Data Exchange (ETDEWEB)
Pellegrini, C.; /UCLA /SLAC
2012-06-28
The successful lasing at the SLAC National Accelerator Laboratory of the Linear Coherent Light Source (LCLS), the first X-ray free-electron laser (X-ray FEL), in the wavelength range 1.5 to 15 {angstrom}, pulse duration of 60 to few femtoseconds, number of coherent photons per pulse from 10{sup 13} to 10{sup 11}, is a landmark event in the development of coherent electromagnetic radiation sources. Until now electrons traversing an undulator magnet in a synchrotron radiation storage ring provided the best X-ray sources. The LCLS has set a new standard, with a peak X-ray brightness higher by ten orders of magnitudes and pulse duration shorter by three orders of magnitudes. LCLS opens a new window in the exploration of matter at the atomic and molecular scales of length and time. Taking a motion picture of chemical processes in a few femtoseconds or less, unraveling the structure and dynamics of complex molecular systems, like proteins, are some of the exciting experiments made possible by LCLS and the other X-ray FELs now being built in Europe and Asia. In this paper, we describe the history of the many theoretical, experimental and technological discoveries and innovations, starting from the 1960s and 1970s, leading to the development of LCLS.
14. X-ray free electron laser: opportunities for drug discovery.
Science.gov (United States)
Cheng, Robert K Y; Abela, Rafael; Hennig, Michael
2017-11-08
Past decades have shown the impact of structural information derived from complexes of drug candidates with their protein targets to facilitate the discovery of safe and effective medicines. Despite recent developments in single particle cryo-electron microscopy, X-ray crystallography has been the main method to derive structural information. The unique properties of X-ray free electron laser (XFEL) with unmet peak brilliance and beam focus allow X-ray diffraction data recording and successful structure determination from smaller and weaker diffracting crystals shortening timelines in crystal optimization. To further capitalize on the XFEL advantage, innovations in crystal sample delivery for the X-ray experiment, data collection and processing methods are required. This development was a key contributor to serial crystallography allowing structure determination at room temperature yielding physiologically more relevant structures. Adding the time resolution provided by the femtosecond X-ray pulse will enable monitoring and capturing of dynamic processes of ligand binding and associated conformational changes with great impact to the design of candidate drug compounds. © 2017 The Author(s). Published by Portland Press Limited on behalf of the Biochemical Society.
15. Influence of plasma density on the generation of 100's MeV electrons via Direct Laser Acceleration
Science.gov (United States)
Hussein, Amina; Batson, T.; Arefiev, A. V.; Chen, H.; Craxton, R. S.; Davies, A.; Froula, D. H.; Haberberger, D.; Jansen, O.; Krushelnick, K.; Nilson, P. M.; Theobald, W.; Wang, T.; Williams, G. J.; Willingale, L.
2017-10-01
The role of plasma density and quasi-static fields in the acceleration of electrons to many times the ponderomotive energies (exceeding 400 MeV) by high-energy, picosecond duration laser pulses via Direct Laser Acceleration (DLA) from underdense CH plasma was investigated. Experiments using the OMEGA EP laser facility and two-dimensional particle-in-cell simulations using the EPOCH code were performed. The existence of an optimal plasma density for the generation of high-energy, low-divergence electron beams is demonstrated. The role of quasi-static channel fields on electron energy enhancement, beam pointing and divergence elucidate the mechanisms and action of DLA at different plasma densities. This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-FOA-0001109.
16. Energy modulation of nonrelativistic electrons with a CO2 laser using a metal microslit
OpenAIRE
Jongsuck, Bae; Ryo, Ishikawa; Sumio, Okuyama; Takashi, Miyajima; Taiji, Akizuki; Tatsuya, Okamoto; Koji, Mizuno
2000-01-01
A metal microslit has been used as an interaction circuit between a CO2 laser beam and nonrelativistic free electrons. Evanescent waves which are induced on the slit by illumination of the laser light modulate the energy of electrons passing close to the surface of the slit. The electron-energy change of more than ±5 eV for the 80 keV electron beam has been observed using the 7 kW laser beam at the wavelength of 10.6 μm.
17. Energy modulation of nonrelativistic electrons with a CO2 laser using a metal microslit
Science.gov (United States)
Bae, Jongsuck; Ishikawa, Ryo; Okuyama, Sumio; Miyajima, Takashi; Akizuki, Taiji; Okamoto, Tatsuya; Mizuno, Koji
2000-04-01
A metal microslit has been used as an interaction circuit between a CO2 laser beam and nonrelativistic free electrons. Evanescent waves which are induced on the slit by illumination of the laser light modulate the energy of electrons passing close to the surface of the slit. The electron-energy change of more than ±5 eV for the 80 keV electron beam has been observed using the 7 kW laser beam at the wavelength of 10.6 μm.
18. Studies of harmonic generation in free electron lasers
Energy Technology Data Exchange (ETDEWEB)
Goldammer, K.
2007-11-12
Nonlinear harmonic generation is one of the most interesting aspects of Free Electron Lasers under study today. It provides for coherent, high intensity radiation at higher harmonics of the FEL resonant frequency. The sources, numerical simulation and applications of harmonic radiation in cascaded High Gain Harmonic Generation FELs were the subject of this thesis. Harmonic emission in FELs originates from harmonic microbunching of the particles and the particular electron trajectory during FEL interaction. Numerical FEL simulation codes model these analytical equations and predict the performance of Free Electron Lasers with good accuracy. This thesis has relied heavily upon the FEL simulation code Genesis 1.3 which has been upgraded in the framework of this thesis to compute harmonic generation in a self-consistent manner. Tests against analytical predictions suggest that the harmonic power levels as well as harmonic gain lengths are simulated correctly. A benchmark with the FEL simulation code GINGER yields excellent agreement of the harmonic saturation length and saturation power. The new version of the simulation code Genesis was also tested against measurements from the VUV-FEL FLASH at DESY. The spectral power distributions of fundamental and third harmonic radiation were recorded at 25.9 nm and 8.6 nm, respectively. The relative bandwidths (FWHM) were in the range of 2 % for both the fundamental as well as the third harmonic, which was accurately reproduced by time-dependent simulations with Genesis. The new code was also used to propose and evaluate a new design for the BESSY Soft X-Ray FEL, a cascaded High Gain Harmonic Generation FEL proposed by BESSY in Berlin. The original design for the BESSY High Energy FEL line requires four HGHG stages to convert the initial seed laser wavelength of 297.5 nm down to 1.24 nm. A new scheme is proposed that makes use of fifth harmonic radiation from the first stage and reduces the number of HGHG stages to three. It
19. Observation of two-dimensional longitudinal-transverse correlations in an electron beam by laser-electron interactions
Directory of Open Access Journals (Sweden)
G. Angelova
2008-07-01
Full Text Available During the preparatory work for the optical-replica synthesizer experiment in the free-electron laser FLASH at DESY, we were able to superimpose a short, approximately 200 fs long pulse from a frequency-doubled mode-locked erbium laser with titanium-sapphire amplifier and an approximately 20 ps long electron bunch in an undulator. This induces an energy modulation in a longitudinal slice of the electron bunch. A magnetic chicane downstream of the undulator converts the energy modulation into a density modulation within the slice that causes the emission of coherent optical transition radiation from a silver-coated silicon screen. Varying the relative timing between electron and laser, we use a camera to record two-dimensional images of the slices as a function of the longitudinal position within the electron bunch.
20. High efficiency, multiterawatt x-ray free electron lasers
Directory of Open Access Journals (Sweden)
C. Emma
2016-02-01
Full Text Available In this paper we present undulator magnet tapering methods for obtaining high efficiency and multiterawatt peak powers in x-ray free electron lasers (XFELs, a key requirement for enabling 3D atomic resolution single molecule imaging and nonlinear x-ray science. The peak power and efficiency of tapered XFELs is sensitive to time dependent effects, like synchrotron sideband growth. To analyze this dependence in detail we perform a comparative numerical optimization for the undulator magnetic field tapering profile including and intentionally disabling these effects. We show that the solution for the magnetic field taper profile obtained from time independent optimization does not yield the highest extraction efficiency when time dependent effects are included. Our comparative optimization is performed for a novel undulator designed specifically to obtain TW power x-ray pulses in the shortest distance: superconducting, helical, with short period and built-in strong focusing. This design reduces the length of the breaks between modules, decreasing diffraction effects, and allows using a stronger transverse electron focusing. Both effects reduce the gain length and the overall undulator length. We determine that after a fully time dependent optimization of a 100 m long Linac coherent light source-like XFEL we can obtain a maximum efficiency of 7%, corresponding to 3.7 TW peak radiation power. Possible methods to suppress the synchrotron sidebands, and further enhance the FEL peak power, up to about 6 TW by increasing the seed power and reducing the electron beam energy spread, are also discussed.
1. Tailoring laser wakefield accelerated electron beams. An experimental study on the influence of experimental conditions on electron beam parameters
Energy Technology Data Exchange (ETDEWEB)
Couperus, Jurjen P.; Koehler, Alexander; Zarini, Omid; Huebl, Axel; Schramm, Ulrich [Institute of Radiation Physics, Helmholtz-Zentrum Dresden-Rossendorf (Germany); Technische Universitaet Dresden (Germany); Jochmann, Axel; Debus, Alexander; Irman, Arie [Institute of Radiation Physics, Helmholtz-Zentrum Dresden-Rossendorf (Germany)
2016-07-01
Laser wakefield acceleration (LWFA) has emerged as a promising concept for the next generation of high energy electron accelerators. In LFWA a high intensity ultrashort laser pulse drives plasma density waves, inducing a high accelerating field gradient in the order of GV/m. To create stable reproducible electron beams, tailoring of experimental parameters like gas density, laser energy and laser pulse duration is required. In this talk we present an overview of our experimental studies with the DRACO (3 J on target, 30 fs) laser on ultrasonic gas-jet targets (He and He-N{sub 2} mixtures). We discuss the influence of experimental parameters on beam parameters like beam charge, shot-to-shot stability and energy distribution, both in the self-injecting bubble regime as well as in the ionisation injection regime.
2. Nanoscale Electron Bunching in Laser-Triggered Ionization Injection in Plasma Accelerators.
Science.gov (United States)
Xu, X L; Pai, C-H; Zhang, C J; Li, F; Wan, Y; Wu, Y P; Hua, J F; Lu, W; An, W; Yu, P; Joshi, C; Mori, W B
2016-07-15
Ionization injection is attractive as a controllable injection scheme for generating high quality electron beams using plasma-based wakefield acceleration. Because of the phase-dependent tunneling ionization rate and the trapping dynamics within a nonlinear wake, the discrete injection of electrons within the wake is nonlinearly mapped to a discrete final phase space structure of the beam at the location where the electrons are trapped. This phenomenon is theoretically analyzed and examined by three-dimensional particle-in-cell simulations which show that three-dimensional effects limit the wave number of the modulation to between >2k_{0} and about 5k_{0}, where k_{0} is the wave number of the injection laser. Such a nanoscale bunched beam can be diagnosed by and used to generate coherent transition radiation and may find use in generating high-power ultraviolet radiation upon passage through a resonant undulator.
3. Nano-scale electron bunching in laser-triggered ionization injection in plasma accelerators
CERN Document Server
Xu, X L; Li, F; Wan, Y; Wu, Y P; Hua, J F; Pai, C -H; Lu, W; An, W; Yu, P; Mori, W B; Joshi, C
2015-01-01
Ionization injection is attractive as a controllable injection scheme for generating high quality electron beams using plasma-based wakefield acceleration. Due to the phase dependent tunneling ionization rate and the trapping dynamics within a nonlinear wake, the discrete injection of electrons within the wake is nonlinearly mapped to discrete final phase space structure of the beam at the location where the electrons are trapped. This phenomenon is theoretically analyzed and examined by three-dimensional particle-in-cell simulations which show that three dimensional effects limit the wave number of the modulation to between $> 2k_0$ and about $5k_0$, where $k_0$ is the wavenumber of the injection laser. Such a nano-scale bunched beam can be diagnosed through coherent transition radiation upon its exit from the plasma and may find use in generating high-power ultraviolet radiation upon passage through a resonant undulator.
4. Electron-atom potential scattering assisted by a bichromatic elliptically polarized laser field
Science.gov (United States)
Korajac, Arman; Habibović, Dino; Čerkić, Aner; Busuladžić, Mustafa; Milošević, Dejan B.
2017-10-01
Electron-atom potential scattering assisted by a bichromatic (two-component) elliptically polarized laser field is analyzed in the frame of the S-matrix theory. The second Born approximation is applied in the expansion of the S-matrix element. The first term in the expansion corresponds to the single scattering, while the second term in the expansion corresponds to the double scattering of electrons on atomic targets. The double scattering is possible in the presence of a laser field. The electron that has scattered on an atomic target may be driven back by the laser field and scatter again on the same atom. The double-scattered electrons may have considerably higher energies than those that scattered only once. We have investigated the dependence of the energy spectrum on various laser-field and incident electron parameters. The calculated electron energy spectra show the plateau-like structures with abrupt cutoffs. These cutoffs are explained by a classical analysis.
5. A CW normal-conductive RF gun for free electron laser and energy recovery linac applications
Energy Technology Data Exchange (ETDEWEB)
Baptiste, Kenneth; Corlett, John; Kwiatkowski, Slawomir; Lidia, Steven; Qiang, Ji; Sannibale, Fernando; Sonnad, Kiran; Staples, John; Virostek, Steven; Wells, Russell
2008-10-08
Currently proposed energy recovery linac and high average power free electron laser projects require electron beam sources that can generate up to {approx} 1 nC bunch charges with less than 1 mmmrad normalized emittance at high repetition rates (greater than {approx} 1 MHz). Proposed sources are based around either high voltage DC or microwave RF guns, each with its particular set of technological limits and system complications. We propose an approach for a gun fully based on mature RF and mechanical technology that greatly diminishes many of such complications. The concepts for such a source as well as the present RF and mechanical design are described. Simulations that demonstrate the beam quality preservation and transport capability of an injector scheme based on such a gun are also presented.
6. Impact properties and hardening behavior of laser and electron-beam welds of V-4Cr-4Ti
Energy Technology Data Exchange (ETDEWEB)
Chung, H.M.; Strain, R.V.; Tsai, H.C.; Park, J.H.; Smith, D.L. [Argonne National Lab., IL (United States)
1996-10-01
The authors are conducting a program to develop an optimal laser welding procedure that can be applied to large-scale fusion-reactor structural components to be fabricated from vanadium-base alloys. Results of initial investigation of mechanical properties and hardening behavior of laser and electron-beam (EB) welds of the production-scale heat of V-4Cr-4Ti (500-kg Heat 832665) in as-welded and postwelding heat-treated (PWHT) conditions are presented in this paper. The laser weld was produced in air using a 6-kW continuous CO{sub 2} laser at a welding speed of {approx}45 mm/s. Microhardness of the laser welds was somewhat higher than that of the base metal, which was annealed at a nominal temperature of {approx}1050{degrees}C for 2 h in the factory. In spite of the moderate hardening, ductile-brittle transition temperatures (DBTTs) of the initial laser ({approx}80{degrees}C) and EB ({approx}30{degrees}C) welds were significantly higher than that of the base metal ({approx}{minus}170{degrees}C). However, excellent impact properties, with DBTT < {minus}80{degrees}C and similar to those of the base metal, could be restored in both the laser and EB welds by postwelding annealing at 1000{degrees}C for 1 h in vacuum.
7. Vehicle based laser range finding in crops.
Science.gov (United States)
Ehlert, Detlef; Adamek, Rolf; Horn, Hans-Juergen
2009-01-01
Laser rangefinders and laser scanners are widely used for industrial purposes and for remote sensing. In agriculture information about crop parameters like volume, height, and density can support the optimisation of production processes. In scientific papers the measurement of these parameters by low cost laser rangefinders with one echo has been presented for short ranges. Because the cross section area of the beam increases with the measuring range, it can be expected that laser rangefinders will have a reduced measuring accuracy in small sized crops and when measuring far distances. These problems are caused by target areas smaller than the beam and by the beam striking the edges of crop objects. Lab tests under defined conditions and a real field test were performed to assess the measuring properties under such difficult conditions of a chosen low cost sensor. Based on lab tests it was shown that the accuracy was reduced, but the successful use of the sensor under field conditions demonstrated the potential to meet the demands for agricultural applications, Insights resulting from investigations made in the paper contribute to facilitating the choice or the development of laser rangefinder sensors for vehicle based measurement of crop parameters for optimisation of production processes.
8. In situ TEM Raman spectroscopy and laser-based materials modification
Energy Technology Data Exchange (ETDEWEB)
Allen, F.I., E-mail: [email protected] [Department of Materials Science and Engineering, University of California, Berkeley, CA 94720 (United States); National Center for Electron Microscopy, Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley, CA 94720 (United States); Kim, E. [Department of Mechanical Engineering, University of California, Berkeley, CA 94720 (United States); Andresen, N.C. [Engineering Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720 (United States); Grigoropoulos, C.P. [Department of Mechanical Engineering, University of California, Berkeley, CA 94720 (United States); Minor, A.M., E-mail: [email protected] [Department of Materials Science and Engineering, University of California, Berkeley, CA 94720 (United States); National Center for Electron Microscopy, Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley, CA 94720 (United States)
2017-07-15
We present a modular assembly that enables both in situ Raman spectroscopy and laser-based materials processing to be performed in a transmission electron microscope. The system comprises a lensed Raman probe mounted inside the microscope column in the specimen plane and a custom specimen holder with a vacuum feedthrough for a tapered optical fiber. The Raman probe incorporates both excitation and collection optics, and localized laser processing is performed using pulsed laser light delivered to the specimen via the tapered optical fiber. Precise positioning of the fiber is achieved using a nanomanipulation stage in combination with simultaneous electron-beam imaging of the tip-to-sample distance. Materials modification is monitored in real time by transmission electron microscopy. First results obtained using the assembly are presented for in situ pulsed laser ablation of MoS{sub 2} combined with Raman spectroscopy, complimented by electron-beam diffraction and electron energy-loss spectroscopy. - Highlights: • Raman spectroscopy and laser-based materials processing in a TEM are demonstrated. • A lensed Raman probe is mounted in the sample chamber for close approach. • Localized laser processing is achieved using a tapered optical fiber. • Raman spectroscopy and pulsed laser ablation of MoS{sub 2} are performed in situ.
9. Laser Cladding of Ultra-Thin Nickel-Based Superalloy Sheets.
Science.gov (United States)
Gabriel, Tobias; Rommel, Daniel; Scherm, Florian; Gorywoda, Marek; Glatzel, Uwe
2017-03-10
Laser cladding is a well-established process to apply coatings on metals. However, on substrates considerably thinner than 1 mm it is only rarely described in the literature. In this work 200 µm thin sheets of nickel-based superalloy 718 are coated with a powder of a cobalt-based alloy, Co-28Cr-9W-1.5Si, by laser cladding. The process window is very narrow, therefore, a precisely controlled Yb fiber laser was used. To minimize the input of energy into the substrate, lines were deposited by setting single overlapping points. In a design of experiments (DoE) study, the process parameters of laser power, laser spot area, step size, exposure time, and solidification time were varied and optimized by examining the clad width, weld penetration, and alloying depth. The microstructure of the samples was investigated by optical microscope (OM) and scanning electron microscopy (SEM), combined with electron backscatter diffraction (EBSD) and energy dispersive X-ray spectroscopy (EDX). Similarly to laser cladding of thicker substrates, the laser power shows the highest influence on the resulting clad. With a higher laser power, the clad width and alloying depth increase, and with a larger laser spot area the weld penetration decreases. If the process parameters are controlled precisely, laser cladding of such thin sheets is manageable.
10. Laser Cladding of Ultra-Thin Nickel-Based Superalloy Sheets
Directory of Open Access Journals (Sweden)
Tobias Gabriel
2017-03-01
Full Text Available Laser cladding is a well-established process to apply coatings on metals. However, on substrates considerably thinner than 1 mm it is only rarely described in the literature. In this work 200 µm thin sheets of nickel-based superalloy 718 are coated with a powder of a cobalt-based alloy, Co–28Cr–9W–1.5Si, by laser cladding. The process window is very narrow, therefore, a precisely controlled Yb fiber laser was used. To minimize the input of energy into the substrate, lines were deposited by setting single overlapping points. In a design of experiments (DoE study, the process parameters of laser power, laser spot area, step size, exposure time, and solidification time were varied and optimized by examining the clad width, weld penetration, and alloying depth. The microstructure of the samples was investigated by optical microscope (OM and scanning electron microscopy (SEM, combined with electron backscatter diffraction (EBSD and energy dispersive X-ray spectroscopy (EDX. Similarly to laser cladding of thicker substrates, the laser power shows the highest influence on the resulting clad. With a higher laser power, the clad width and alloying depth increase, and with a larger laser spot area the weld penetration decreases. If the process parameters are controlled precisely, laser cladding of such thin sheets is manageable.
11. Accurate Alignment of Plasma Channels Based on Laser Centroid Oscillations
Energy Technology Data Exchange (ETDEWEB)
Gonsalves, Anthony; Nakamura, Kei; Lin, Chen; Osterhoff, Jens; Shiraishi, Satomi; Schroeder, Carl; Geddes, Cameron; Toth, Csaba; Esarey, Eric; Leemans, Wim
2011-03-23
A technique has been developed to accurately align a laser beam through a plasma channel by minimizing the shift in laser centroid and angle at the channel outptut. If only the shift in centroid or angle is measured, then accurate alignment is provided by minimizing laser centroid motion at the channel exit as the channel properties are scanned. The improvement in alignment accuracy provided by this technique is important for minimizing electron beam pointing errors in laser plasma accelerators.
12. Electron Backscatter Diffraction Analysis of Inconel 718 Parts Fabricated by Selective Laser Melting Additive Manufacturing
Science.gov (United States)
Wang, Xiaoqing; Chou, Kevin
2017-02-01
In this study, the crystallographic texture of an Inconel 718 part fabricated by selective laser melting was investigated. The front surface (X-Z plane) microstructure is characterized by the columnar grains growing along the build direction, and the width of columnar grains is in the range of about 75-150 µm, with the bottom layers having narrower grains as a result of a higher cooling rate. In addition to equiaxed grains, the top surface (X-Y plane) has a feature of patch patterns resulting from the laser scanning strategy. Based on the electron backscatter diffraction results, there appears only weak crystallographic texture in both the X-Z plane and the X-Y plane of the part. From the grain boundary map, the microstructures are composed of high-angle boundaries with a larger fraction of subgrain boundaries.
13. Impact of laser wavelength on the emission of electrons and ions from thin gold films during femtosecond laser ablation
Science.gov (United States)
Haustrup, N.; O'Connor, G. M.
2014-05-01
This experimental study supports computational evidence that the excitation of d-band electrons have a significant impact on the material response of gold to an ultrashort laser pulse. A voltage biased Langmuir probe was used to detect the electron and positive ion emission from a 20 nm thick Au film at 343 nm, 515 nm and 1030 nm laser wavelengths. The laser wavelengths used provided photon energies above and below the interband transition threshold (ITT) for d-band excitation in gold (1.9 eV). Variations in optical properties of the Au film at different laser wavelengths were accounted for to ensure that comparisons were made at equal values of absorbed fluences. Data showed a significantly higher number of electrons emitted over a longer period when the energy of the incident photons exceeded the ITT. The electronic current generated at the probe indicated that the first electrons detected were primarily emitted via multiphoton photoemission. Electrons were also detected at later times when the photon energy exceeded the ITT and this was attributed to thermionic emission. The current generated from the positive ion emission was significantly lower than for electron emission, but indicated the formation of a plasma at a threshold fluence that increases with decreasing photon energy.
14. Influence of laser frequency noise on scanning Fabry-Perot interferometer based laser Doppler velocimetry
DEFF Research Database (Denmark)
Rodrigo, Peter John; Pedersen, Christian
2014-01-01
n this work, we study the performance of a scanning Fabry-Perot interferometer based laser Doppler velocimeter (sFPILDV) and compare two candidate 1.5 um single-frequency laser sources for the system – a fiber laser (FL) and a semiconductor laser (SL). We describe a straightforward calibration...... procedure for the sFPI-LDV and investigate the effect of different degrees of laser frequency noise between the FL and the SL on the velocimeter’s performance...
15. Ultra-High-Contrast Laser Acceleration of Relativistic Electrons in Solid Targets
Energy Technology Data Exchange (ETDEWEB)
Higginson, Drew Pitney [Univ. of California, San Diego, CA (United States)
2013-01-01
The cone-guided fast ignition approach to Inertial Con nement Fusion requires laser-accelerated relativistic electrons to deposit kilojoules of energy within an imploded fuel core to initiate fusion burn. One obstacle to coupling electron energy into the core is the ablation of material, known as preplasma, by laser energy proceeding nanoseconds prior to the main pulse. This causes the laser-absorption surface to be pushed back hundreds of microns from the initial target surface; thus increasing the distance that electrons must travel to reach the imploded core. Previous experiments have shown an order of magnitude decrease in coupling into surrogate targets when intentionally increasing the amount of preplasma. Additionally, for electrons to deposit energy within the core, they should have kinetic energies on the order of a few MeV, as less energetic electrons will be stopped prior to the core and more energetic electrons will pass through the core without depositing much energy. Thus a quantitative understanding of the electron energy spectrum and how it responds to varied laser parameters is paramount for fast ignition. For the rst time, this dissertation quantitatively investigates the acceleration of electrons using an ultra-high-contrast laser. Ultra-high-contrast lasers reduce the laser energy that reaches the target prior to the main pulse; drastically reducing the amount of preplasma. Experiments were performed in a cone-wire geometry relevant to fast ignition. These experiments irradiated the inner-tip of a Au cone with the laser and observed electrons that passed through a Cu wire attached to the outer-tip of the cone. The total emission of K x-rays is used as a diagnostic to infer the electron energy coupled into the wire. Imaging the x-ray emission allowed an e ective path-length of electrons within the wire to be determined, which constrained the electron energy spectrum. Experiments were carried out on the ultra-high-contrast Trident laser at Los
16. Self-amplified coherent spontaneous emission in a free electron laser with “quiet” bunches
Directory of Open Access Journals (Sweden)
V. A. Goryashko
2013-03-01
Full Text Available For a planar free electron laser (FEL configuration we study self-amplified coherent spontaneous emission driven by a gradient of the bunch current in the presence of different levels of noise in bunches. The longitudinal granularity of the electron bunch density originating from shot noise is maintained throughout the analysis. For the FEL model with the SwissFEL injector bunch parameters, we calculate the probability density distribution of the maximum power of the radiation pulses for different levels of shot noise. It turns out that the temporal coherence quickly increases as the noise level reduces. We also show that the FEL based on coherent spontaneous emission produces almost Fourier transform limited pulses. The analysis indicates that the time-bandwidth product is mainly determined by the bunch length and the interaction distance in an undulator. Calculations of the FEL characteristics for different rise times of the front of the current pulse are performed, and it is found that a reduced level of the power fluctuations is preserved for the bunch current pulse with a front duration up to several FEL wavelengths. We also propose a novel scheme that permits the formation of electron bunches with a reduced level of noise and a high gradient of the current at the bunch tail to enhance coherent spontaneous emission. The presented scheme uses effects of noise reduction and controlled microbunching instability and consists of a laser heater, a bunch compressor, and a shot noise suppression section. We show that shot noise reduction by 2 orders of magnitude in electron bunches produced by the SwissFEL injector can be achieved in a compact noise suppression section. The noise factor and microbunching gain of the overall proposed scheme with and without laser heater are estimated.
17. Femtosecond X-ray Absorption Spectroscopy at a Hard X-ray Free Electron Laser
DEFF Research Database (Denmark)
Lemke, Henrik T.; Bressler, Christian; Chen, Lin X.
2013-01-01
X-ray free electron lasers (XFELs) deliver short (hard X-rays, making them excellent sources for time-resolved studies. Here we show that, despite the inherent instabilities of current (SASE based) XFELs, they can be used for measuring high......-quality X-ray absorption data and we report femtosecond time-resolved X-ray absorption near-edge spectroscopy (XANES) measurements of a spin-crossover system, iron(II) tris(2,2'-bipyridine) in water. The data indicate that the low-spin to high-spin transition can be modeled by single-exponential kinetics...
18. Intense ultrashort pulse generation using the JAERI far-infrared free electron laser
CERN Document Server
Nagai, R; Nishimori, N; Kikuzawa, N; Sawamura, M; Minehara, E J
2002-01-01
An intense ultrashort optical pulse has been quasi-continuously generated using a superconducting RF linac-based free-electron laser at a wavelength of 22.5 mu m. The pulse shape and width are measured by second-order optical autocorrelation with a birefringent Te crystal. At synchronism of the optical resonator, the pulse shape is a smooth single pulse with an FWHM width of 255 fs and energy of 74 mu J. A train of subpulses is developed by increasing the desynchronism of the optical resonator. The measured results are in good agreement with numerical simulation.
19. Variational Approach for Coupled Backward and Forward Wave Excitation in Free-Electron Lasers
CERN Document Server
Yahalom, A; Pinhasi, Y
2005-01-01
In a recent paper [1] we have described a novel variational formulation for the propagation and generation of radiation in wave-guides. The formulation is based on the representation of all the involved quantities in the frequency domain and the decomposition of field and currents in terms of the wave-guide transversal Eigen function. In this work we present the utilization of this formalism to the derivation of a numerical scheme that is used to study the build up of radiation in free electron lasers in the linear approximation.
20. Femtosecond Fiber Lasers Based on Dissipative Processes for Nonlinear Microscopy
Science.gov (United States)
Wise, Frank W.
2012-01-01
Recent progress in the development of femtosecond-pulse fiber lasers with parameters appropriate for nonlinear microscopy is reviewed. Pulse-shaping in lasers with only normal-dispersion components is briefly described, and the performance of the resulting lasers is summarized. Fiber lasers based on the formation of dissipative solitons now offer performance competitive with that of solid-state lasers, but with the benefits of the fiber medium. Lasers based on self-similar pulse evolution in the gain section of a laser also offer a combination of short pulse duration and high pulse energy that will be attractive for applications in nonlinear bioimaging. PMID:23869163
1. Capturing Structural Dynamics in Crystalline Silicon Using Chirped Electrons from a Laser Wakefield Accelerator.
Science.gov (United States)
He, Z-H; Beaurepaire, B; Nees, J A; Gallé, G; Scott, S A; Pérez, J R Sánchez; Lagally, M G; Krushelnick, K; Thomas, A G R; Faure, J
2016-11-08
Recent progress in laser wakefield acceleration has led to the emergence of a new generation of electron and X-ray sources that may have enormous benefits for ultrafast science. These novel sources promise to become indispensable tools for the investigation of structural dynamics on the femtosecond time scale, with spatial resolution on the atomic scale. Here, we demonstrate the use of laser-wakefield-accelerated electron bunches for time-resolved electron diffraction measurements of the structural dynamics of single-crystal silicon nano-membranes pumped by an ultrafast laser pulse. In our proof-of-concept study, we resolve the silicon lattice dynamics on a picosecond time scale by deflecting the momentum-time correlated electrons in the diffraction peaks with a static magnetic field to obtain the time-dependent diffraction efficiency. Further improvements may lead to femtosecond temporal resolution, with negligible pump-probe jitter being possible with future laser-wakefield-accelerator ultrafast-electron-diffraction schemes.
2. Reduction of secondary electron yield for E-cloud mitigation by laser ablation surface engineering
Energy Technology Data Exchange (ETDEWEB)
Valizadeh, R., E-mail: [email protected] [ASTeC, STFC Daresbury Laboratory, Warrington WA4 4AD (United Kingdom); Malyshev, O.B. [ASTeC, STFC Daresbury Laboratory, Warrington WA4 4AD (United Kingdom); Wang, S. [ASTeC, STFC Daresbury Laboratory, Warrington WA4 4AD (United Kingdom); Department of Physics, Loughborough University, Loughborough LE11 3TU (United Kingdom); Sian, T. [ASTeC, STFC Daresbury Laboratory, Warrington WA4 4AD (United Kingdom); The Photon Science Institute, The University of Manchester, Manchester M13 9PL (United Kingdom); Cropper, M.D. [Department of Physics, Loughborough University, Loughborough LE11 3TU (United Kingdom); Sykes, N. [Micronanics Ltd., Didcot, Oxon OX11 0QX (United Kingdom)
2017-05-15
Highlights: • SEY below 1 can be achieved with Laser ablation surface engineering. • SEY <1 surface can be produced with different types of nanosecond lasers. • Both microstructure (groves) and nano-structures are playing a role in reducing SEY. - Abstract: Developing a surface with low Secondary Electron Yield (SEY) is one of the main ways of mitigating electron cloud and beam-induced electron multipacting in high-energy charged particle accelerators. In our previous publications, a low SEY < 0.9 for as-received metal surfaces modified by a nanosecond pulsed laser was reported. In this paper, the SEY of laser-treated blackened copper has been investigated as a function of different laser irradiation parameters. We explore and study the influence of micro- and nano-structures induced by laser surface treatment in air of copper samples as a function of various laser irradiation parameters such as peak power, laser wavelength (λ = 355 nm and 1064 nm), number of pulses per point (scan speed and repetition rate) and fluence, on the SEY. The surface chemical composition was determined by x-ray photoelectron spectroscopy (XPS) which revealed that heating resulted in diffusion of oxygen into the bulk and induced the transformation of CuO to sub-stoichiometric oxide. The surface topography was examined with high resolution scanning electron microscopy (HRSEM) which showed that the laser-treated surfaces are dominated by microstructure grooves and nanostructure features.
3. Time-resolved measurements with streaked diffraction patterns from electrons generated in laser plasma wakefield
Science.gov (United States)
He, Zhaohan; Nees, John; Hou, Bixue; Krushelnick, Karl; Thomas, Alec; Beaurepaire, Benoît; Malka, Victor; Faure, Jérôme
2013-10-01
Femtosecond bunches of electrons with relativistic to ultra-relativistic energies can be robustly produced in laser plasma wakefield accelerators (LWFA). Scaling the electron energy down to sub-relativistic and MeV level using a millijoule laser system will make such electron source a promising candidate for ultrafast electron diffraction (UED) applications due to the intrinsic short bunch duration and perfect synchronization with the optical pump. Recent results of electron diffraction from a single crystal gold foil, using LWFA electrons driven by 8-mJ, 35-fs laser pulses at 500 Hz, will be presented. The accelerated electrons were collimated with a solenoid magnetic lens. By applying a small-angle tilt to the magnetic lens, the diffraction pattern can be streaked such that the temporal evolution is separated spatially on the detector screen after propagation. The observable time window and achievable temporal resolution are studied in pump-probe measurements of photo-induced heating on the gold foil.
4. LIPSS Free-Electron Laser Searches for Dark Matter
Energy Technology Data Exchange (ETDEWEB)
Afanaciev, Andrei; Beard, Kevin; Biallas, George; Boyce, James R; Minarni, M; Ramdon, R; Robinson, Taylor; Shinn, Michelle D
2011-09-01
A variety of Dark Matter particle candidates have been hypothesized by physics Beyond the Standard Model (BSM) in the very light (10{sup -6} - 10{sup -3} eV) range. In the past decade several international groups have conducted laboratory experiments designed to either produce such particles or extend the boundaries in parameter space. The LIght Pseudo-scalar and Scalar Search (LIPSS) Collaboration, using the 'Light Shining through a Wall' (LSW) technique, passes the high average power photon beam from Jefferson Lab's Free-Electron Laser through a magnetic field upstream from a mirror and optical beam dump. Light Neutral Bosons (LNBs), generated by coupling of photons with the magnetic field, pass through the mirror ('the Wall') into an identical magnetic field where they revert to detectable photons by the same coupling process. While no evidence of LNBs was evident, new scalar coupling boundaries were established. New constraints were also determined for hypothetical para-photons and for millicharged fermions. We will describe our experimental setup and results for LNBs, para-photons, and milli-charged fermions. Plans for chameleon particle searches are underway.
5. Extreme-Ultraviolet Vortices from a Free-Electron Laser
Directory of Open Access Journals (Sweden)
Primož Rebernik Ribič
2017-08-01
Full Text Available Extreme-ultraviolet vortices may be exploited to steer the magnetic properties of nanoparticles, increase the resolution in microscopy, and gain insight into local symmetry and chirality of a material; they might even be used to increase the bandwidth in long-distance space communications. However, in contrast to the generation of vortex beams in the infrared and visible spectral regions, production of intense, extreme-ultraviolet and x-ray optical vortices still remains a challenge. Here, we present an in-situ and an ex-situ technique for generating intense, femtosecond, coherent optical vortices at a free-electron laser in the extreme ultraviolet. The first method takes advantage of nonlinear harmonic generation in a helical undulator, producing vortex beams at the second harmonic without the need for additional optical elements, while the latter one relies on the use of a spiral zone plate to generate a focused, micron-size optical vortex with a peak intensity approaching 10^{14} W/cm^{2}, paving the way to nonlinear optical experiments with vortex beams at short wavelengths.
6. Extreme-Ultraviolet Vortices from a Free-Electron Laser
Science.gov (United States)
Rebernik Ribič, Primož; Rösner, Benedikt; Gauthier, David; Allaria, Enrico; Döring, Florian; Foglia, Laura; Giannessi, Luca; Mahne, Nicola; Manfredda, Michele; Masciovecchio, Claudio; Mincigrucci, Riccardo; Mirian, Najmeh; Principi, Emiliano; Roussel, Eléonore; Simoncig, Alberto; Spampinati, Simone; David, Christian; De Ninno, Giovanni
2017-07-01
Extreme-ultraviolet vortices may be exploited to steer the magnetic properties of nanoparticles, increase the resolution in microscopy, and gain insight into local symmetry and chirality of a material; they might even be used to increase the bandwidth in long-distance space communications. However, in contrast to the generation of vortex beams in the infrared and visible spectral regions, production of intense, extreme-ultraviolet and x-ray optical vortices still remains a challenge. Here, we present an in-situ and an ex-situ technique for generating intense, femtosecond, coherent optical vortices at a free-electron laser in the extreme ultraviolet. The first method takes advantage of nonlinear harmonic generation in a helical undulator, producing vortex beams at the second harmonic without the need for additional optical elements, while the latter one relies on the use of a spiral zone plate to generate a focused, micron-size optical vortex with a peak intensity approaching 1014 W /cm2 , paving the way to nonlinear optical experiments with vortex beams at short wavelengths.
7. Free Electron Laser Pulse Control by Acousto Optic Modulators
CERN Document Server
Kanai, T; Yoshihashi-Suzuki, S
2005-01-01
Free Electron Laser (FEL) at Osaka University can be continuously varied in the range of 5.0-20.0 μm. A FEL has a double pulse structure. The structure consists of a train of macropulses of the pulse width 15 μs, and each macropulse contains a train of 330 micropulses of the pulse width 5 ps. The tunability and short pulse afford new medical applications such as investigation of protein dynamics and ablation of soft tissues. Precise control of micropulse train is very important for medical applications using FEL because macropulse with long pulse duration sometimes leads to undesirable thermal effects. FEL pulse control system using an acousto optic modulators (AOM) was developed in order to investigate of non-thermal effect between the FEL and tissue. This system provide a very good efficiency (~60 %) and a fast switching speed (>200 ns). A phosphorylated protein was irradiated with FEL that controlled the pulse. These result confirmed that the thermal effect is controlled by pulse durat...
8. Laser-Compton scattering from a 20 MeV electron beam
CERN Document Server
Chouffani, K; Harmon, F; Jones, J; Lancaster, G
2002-01-01
Laser-Compton scattering (LCS) experiments were carried out at the Idaho Accelerator Center. A 20 MeV electron beam was brought to a head-on collision with a 100 MW 7 ns Nd:YAG laser. We observed clear narrow LCS X-ray spectral peaks resulting from the interaction of the electron beam with the two Nd:YAG laser photon lines of 1064 and 532 nm. The LCS X-ray energy lines and widths were measured as a function of the electron beam energy and energy spread, respectively. The results recorded showed good agreement with the predicted values.
9. Acceleration of electrons by high intensity laser radiation in a magnetic field
OpenAIRE
Melikian, Robert
2013-01-01
We consider the acceleration of electrons in vacuum by means of the circularly-polirized electromagnetic wave, propagating along a magnetic field. We show that the electron energy growth, when using ultra-short and ultra-intense laser pulses (10 ps, 10^{18} Bm/cm^2, CO_{2} laser) in the presence of a magnetic field, may reach up to the value 2,1 Gev. The growth of the electron energy is shown to increase proportionally with the increase of the laser intensity and the initial energy of the ele...
10. High-Flux Femtosecond X-Ray Emission from Controlled Generation of Annular Electron Beams in a Laser Wakefield Accelerator.
Science.gov (United States)
Zhao, T Z; Behm, K; Dong, C F; Davoine, X; Kalmykov, S Y; Petrov, V; Chvykov, V; Cummings, P; Hou, B; Maksimchuk, A; Nees, J A; Yanovsky, V; Thomas, A G R; Krushelnick, K
2016-08-26
Annular quasimonoenergetic electron beams with a mean energy in the range 200-400 MeV and charge on the order of several picocoulombs were generated in a laser wakefield accelerator and subsequently accelerated using a plasma afterburner in a two-stage gas cell. Generation of these beams is associated with injection occurring on the density down ramp between the stages. This well-localized injection produces a bunch of electrons performing coherent betatron oscillations in the wakefield, resulting in a significant increase in the x-ray yield. Annular electron distributions are detected in 40% of shots under optimal conditions. Simultaneous control of the pulse duration and frequency chirp enables optimization of both the energy and the energy spread of the annular beam and boosts the radiant energy per unit charge by almost an order of magnitude. These well-defined annular distributions of electrons are a promising source of high-brightness laser plasma-based x rays.
11. Commercialization plan laser-based decoating systems
Energy Technology Data Exchange (ETDEWEB)
Freiwald, J.; Freiwald, D.A.
1998-01-01
F2 Associates Inc. (F2) is a small, high-technology firm focused on developing and commercializing environmentally friendly laser ablation systems for industrial-rate removal of surface coatings from metals, concrete, and delicate substrates such as composites. F2 has a contract with the US Department of Energy Federal Energy Technology Center (FETC) to develop and test a laser-based technology for removing contaminated paint and other contaminants from concrete and metal surfaces. Task 4.1 in Phase 2 of the Statement of Work for this DOE contract requires that F2 document its plans for commercializing and marketing the stationary laser ablation system. This document shall include a discussion of prospects for commercial customers and partners and may require periodic update to reflect changing strategy. This document shall be submitted to the DOE for review. This report is being prepared and submitted in fulfillment of that requirement. This report describes the laser-based technology for cleaning and coatings removal, the types of laser-based systems that have been developed by F2 based on this technology, and the various markets that are emerging for this technology. F2s commercialization and marketing plans are described, including how F2s organization is structured to meet the needs of technology commercialization, F2s strategy and marketing approach, and the necessary steps to receive certification for removing paint from aircraft and DOE certification for D and D applications. The future use of the equipment built for the DOE contract is also discussed.
12. Enhancement of electron energy to the multi-GeV regime by a dual-stage laser-wakefield accelerator pumped by petawatt laser pulses.
Science.gov (United States)
Kim, Hyung Taek; Pae, Ki Hong; Cha, Hyuk Jin; Kim, I Jong; Yu, Tae Jun; Sung, Jae Hee; Lee, Seong Ku; Jeong, Tae Moon; Lee, Jongmin
2013-10-18
Laser-wakefield acceleration offers the promise of a compact electron accelerator for generating a multi-GeV electron beam using the huge field gradient induced by an intense laser pulse, compared to conventional rf accelerators. However, the energy and quality of the electron beam from the laser-wakefield accelerator have been limited by the power of the driving laser pulses and interaction properties in the target medium. Recent progress in laser technology has resulted in the realization of a petawatt (PW) femtosecond laser, which offers new capabilities for research on laser-wakefield acceleration. Here, we present a significant increase in laser-driven electron energy to the multi-GeV level by utilizing a 30-fs, 1-PW laser system. In particular, a dual-stage laser-wakefield acceleration scheme (injector and accelerator scheme) was applied to boost electron energies to over 3 GeV with a single PW laser pulse. Three-dimensional particle-in-cell simulations corroborate the multi-GeV electron generation from the dual-stage laser-wakefield accelerator driven by PW laser pulses.
13. Low emittance electron beam generation from a laser wakefield accelerator using two laser pulses with different wavelengths
Directory of Open Access Journals (Sweden)
X. L. Xu
2014-06-01
Full Text Available Ionization injection triggered by short wavelength laser pulses inside a nonlinear wakefield driven by a longer wavelength laser is examined via multidimensional particle-in-cell simulations. We find that very bright electron beams can be generated through this two-color scheme in either collinear propagating or transverse colliding geometry. For a fixed laser intensity I, lasers with longer/shorter wavelength λ have larger/smaller ponderomotive potential (∝Iλ^{2}. The two-color scheme utilizes this property to separate the injection process from the wakefield excitation process. Very strong wakes can be generated at relatively low laser intensities by using a longer wavelength laser driver (e.g., a 10 μm CO_{2} laser due to its very large ponderomotive potential. On the other hand, a short wavelength laser can produce electrons with very small residual momenta (p_{⊥}∼a_{0}∼sqrt[I]λ inside the wake, leading to electron beams with very small normalized emittances (tens of nm. Using particle-in-cell simulations we show that a ∼10 fs electron beam with ∼4 pC of charge and a normalized emittance of ∼50 nm can be generated by combining a 10 μm driving laser with a 400 nm injection laser, which is an improvement of more than 1 order of magnitude compared to the typical results obtained when a single wavelength laser is used for both the wake formation and ionization injection. With the transverse colliding geometry, simulations show that similarly low emittance and much lower slice energy spread (∼30 keV, comparing with the typical value of few MeV in the longitudinal injection scheme can be simultaneously obtained for electron beams with a few pC charge. Such low slice energy spread may have significant advantages in applications relevant to future coherent light sources driven by plasma accelerators.
14. Slippage effect on energy modulation in seeded free-electron lasers with frequency chirped seed laser pulses
Directory of Open Access Journals (Sweden)
Chao Feng
2013-06-01
Full Text Available Free-electron lasers (FELs seeded with external lasers hold great promise for generating high power radiation with nearly transform-limited bandwidth in the soft x-ray region. However, it has been pointed out that the initial seed laser phase error will be amplified by the frequency up-conversion process, which may degrade the quality of the output radiation produced by a harmonic generation scheme. In this paper, theoretical and simulation studies on frequency chirp amplification in seeded FEL schemes with slippage effect taken into account are presented. It is found that the seed laser imperfection experienced by the electron beam can be significantly smoothed by the slippage effect in the modulator when the slippage length is comparable to the seed laser pulse length. This smoothing effect allows one to preserve the excellent temporal coherence of seeded FELs in the presence of large frequency chirp in the seed laser. Our studies show that the tolerance on frequency chirp in the seed laser for generating nearly transform-limited soft x-ray pulses in seeded FELs is much looser than previously thought and fully coherent radiation at nanometer wavelength may be reached with current technologies.
15. Laser-assisted electron scattering in strong-field ionization of dense water vapor by ultrashort laser pulses
Science.gov (United States)
Wilke, M.; Al-Obaidi, R.; Moguilevski, A.; Kothe, A.; Engel, N.; Metje, J.; Kiyan, I. Yu; Aziz, E. F.
2014-08-01
We report on strong-field ionization of dense water gas in a short infrared laser pulse. By employing a unique combination of photoelectron spectroscopy with a liquid micro-jet technique, we observe how the character of electron emission at high kinetic energies changes with the increase of the medium density. This change is associated with the process of laser-assisted electron scattering (LAES) on neighboring particles, which becomes a dominant mechanism of hot electron emission at higher medium densities. The manifestation of this mechanism is found to require densities that are orders of magnitude lower than those considered for heating the laser-generated plasmas via the LAES process. The experimental results are supported by simulations of the LAES yield with the use of the Kroll-Watson theory.
16. Innovative single-shot diagnostics for electrons from laser wakefield acceleration at FLAME
Science.gov (United States)
Bisesto, F. G.; Anania, M. P.; Cianchi, A.; Chiadroni, E.; Curcio, A.; Ferrario, M.; Pompili, R.; Zigler, A.
2017-07-01
Plasma wakefield acceleration is the most promising acceleration technique known nowadays, able to provide very high accelerating fields (> 100 GV/m), enabling acceleration of electrons to GeV energy in few centimeters. Here we present all the plasma related activities currently underway at SPARC_LAB exploiting the high power laser FLAME. In particular, we will give an overview of the single shot diagnostics employed: Electro Optic Sampling (EOS) for temporal measurement and Optical Transition Radiation (OTR) for an innovative one shot emittance measurements. In detail, the EOS technique has been employed to measure for the first time the longitudinal profile of electric field of fast electrons escaping from a solid target, driving the ions and protons acceleration, and to study the impact of using different target shapes. Moreover, a novel scheme for one shot emittance measurements based on OTR, developed and tested at SPARC_LAB LINAC, used in an experiment on electrons from laser wakefield acceleration still undergoing, will be shown.
17. Study of electron kinetics in nitrogen plasma induced by CO2 laser radiation
Science.gov (United States)
Nassef, O. Aied; Gamal, Yosr E. E.-D.
2017-12-01
In the present work, a numerical modeling is performed to study the electron kinetics in nitrogen plasma induced by CO2 laser radiation operating at wavelength 9.621 μm, and pulse duration of 60 ns corresponding to the measurements carried out by Camacho et al. (J Phys B At Mol Opt Phys 40:4573, 2007). In this experiment, the breakdown threshold intensity is determined for molecular nitrogen over a pressure range 301-760 torr. A previously developed electron cascade model (Evans and Gamal in J Phys D Appl Phys 13:1447, 1980) is modified and applied. This model is based on numerical solution of a time-dependent energy equation and a set of rate equations that describe the time variation of the formed excited states population. The effect of breakdown mechanism is decided through the calculations of the threshold intensity as a function of gas pressure considering the various physical processes that might take place during the interaction. The individual effect of each loss process on the electron energy distribution function and its parameters is studied. This study is performed at the lowest and highest values of the experimentally tested gas pressure range namely; 301 and 760 torr. The obtained results clarified the exact contribution of each loss process to the breakdown of nitrogen induced by CO2 laser radiation.
18. Study of electron kinetics in nitrogen plasma induced by CO2 laser radiation
Science.gov (United States)
Nassef, O. Aied; Gamal, Yosr E. E.-D.
2017-06-01
In the present work, a numerical modeling is performed to study the electron kinetics in nitrogen plasma induced by CO2 laser radiation operating at wavelength 9.621 μm, and pulse duration of 60 ns corresponding to the measurements carried out by Camacho et al. (J Phys B At Mol Opt Phys 40:4573, 2007). In this experiment, the breakdown threshold intensity is determined for molecular nitrogen over a pressure range 301-760 torr. A previously developed electron cascade model (Evans and Gamal in J Phys D Appl Phys 13:1447, 1980) is modified and applied. This model is based on numerical solution of a time-dependent energy equation and a set of rate equations that describe the time variation of the formed excited states population. The effect of breakdown mechanism is decided through the calculations of the threshold intensity as a function of gas pressure considering the various physical processes that might take place during the interaction. The individual effect of each loss process on the electron energy distribution function and its parameters is studied. This study is performed at the lowest and highest values of the experimentally tested gas pressure range namely; 301 and 760 torr. The obtained results clarified the exact contribution of each loss process to the breakdown of nitrogen induced by CO2 laser radiation.
19. Testing relativity again, laser, laser, laser, laser
NARCIS (Netherlands)
Einstein, A.
2015-01-01
laser, laser, laser, laser, laser, laser, laser, laser, laser, laser, laser, laser, laser, laser, laser, laser, laser, laser, laser, laser, laser, laser, laser, laser, laser, laser, laser, laser, laser, laser, laser, laser, laser, laser, laser, laser, laser, laser, laser, laser, laser, laser, laser,
20. Electron kinetics dependence on gas pressure in laser-induced oxygen plasma experiment: Theoretical analysis
Science.gov (United States)
Gamal, Yosr E. E.-D.; Abdellatif, Galila
2017-08-01
A study is performed to investigate the dependency of threshold intensity on gas pressure observed in the measurements of the breakdown of molecular oxygen that carried out by Phuoc (2000) [1]. In this experiment, the breakdown was induced by 532 nm laser radiation of pulse width 5.5 ns and spot size of 8.5 μm, in oxygen over a wide pressure range (190-3000 Torr). The analysis aimed to explore the electron kinetic reliance on gas pressure for the separate contribution of each of the gain and loss processes encountered in this study. The investigation is based on an electron cascade model applied previously in Gamal and Omar (2001) [2] and Gaabour et al. (2013) [3]. This model solves numerically a differential equation designates the time evolution of the electron energy distribution, and a set of rate equations that describe the change of excited states population. The numerical examination of the electron energy distribution function and its parameters revealed that photo-ionization of the excited molecules plays a significant role in enhancing the electron density growth rate over the whole tested gas pressure range. This process is off set by diffusion of electrons out of the focal volume in the low-pressure regime. At atmospheric pressure electron, collisional processes dominate and act mainly to populate the excited states. Hence photo-ionization becomes efficient and compete with the encountered loss processes (electron diffusion, vibrational excitation of the ground state molecules as well as two body attachments). At high pressures ( 3000 Torr) three body attachments are found to be the primary cause of losses which deplete the electron density and hence results in the slow decrease of the threshold intensity.
1. High-quality stable electron beams from laser wakefield acceleration in high density plasma
Directory of Open Access Journals (Sweden)
B. S. Rao
2014-01-01
Full Text Available High-quality, stable electron beams are produced from self-injected laser wakefield acceleration using the interaction of moderate 3 TW, 45 fs duration Ti:sapphire laser pulses with high density (>5×10^{19} cm^{−3} helium gas jet plasma. The electron beam has virtually background-free quasimonoenergetic distribution with energy 35.6_{−2.5}^{+3.9} MeV, charge 3.8_{−1.2}^{+2.8} pC, divergence and pointing variation ∼10 mrad. The stable and high quality of the electron beam opens an easy way for applications of the laser wakefield accelerator in the future, particularly due to the widespread availability of sub-10 TW class lasers with a number of laser plasma laboratories around the world.
2. Characterizing and Optimizing Photocathode Laser Distributions for Ultra-low Emittance Electron Beam Operations
Energy Technology Data Exchange (ETDEWEB)
Zhou, F. [SLAC National Accelerator Lab., Menlo Park, CA (United States); Bohler, D. [SLAC National Accelerator Lab., Menlo Park, CA (United States); Ding, Y. [SLAC National Accelerator Lab., Menlo Park, CA (United States); Gilevich, S. [SLAC National Accelerator Lab., Menlo Park, CA (United States); Huang, Z. [SLAC National Accelerator Lab., Menlo Park, CA (United States); Loos, H. [SLAC National Accelerator Lab., Menlo Park, CA (United States); Ratner, D. [SLAC National Accelerator Lab., Menlo Park, CA (United States); Vetter, S. [SLAC National Accelerator Lab., Menlo Park, CA (United States)
2015-12-07
Photocathode RF gun has been widely used for generation of high-brightness electron beams for many different applications. We found that the drive laser distributions in such RF guns play important roles in minimizing the electron beam emittance. Characterizing the laser distributions with measurable parameters and optimizing beam emittance versus the laser distribution parameters in both spatial and temporal directions are highly desired for high-brightness electron beam operation. In this paper, we report systematic measurements and simulations of emittance dependence on the measurable parameters represented for spatial and temporal laser distributions at the photocathode RF gun systems of Linac Coherent Light Source. The tolerable parameter ranges for photocathode drive laser distributions in both directions are presented for ultra-low emittance beam operations.
3. Laser-wakefield acceleration of electron beams in a low density plasma channel
Directory of Open Access Journals (Sweden)
T. P. A. Ibbotson
2010-03-01
Full Text Available The generation of quasimonoenergetic electron beams, with energies greater than 500 MeV, in a laser-plasma accelerator driven by 2.5 J, 80 fs laser pulses guided in a low density plasma channel, is investigated. The laser energy required to achieve electron injection is found to depend strongly on the quality of the input laser focal spot. Simulations show that, although the matched spot size of the plasma channel is greater than the self-focused spot size, the channel assists relativistic self-focusing and enables electron injection to occur at lower plasma densities and laser powers than would be possible without a waveguide.
4. Initial source of microbunching instability studies in a free electron laser injector
Energy Technology Data Exchange (ETDEWEB)
Seletskiy, S.; Hidaka, Y; Murphy, J.B.; Podobedov, B.; Qian, H.; Shen, Y.; Wang, X.J.; Yang, X
2011-11-16
We present the first experimental studies of the initial source of electron beam microbunching instability in a free electron laser (FEL) injector. By utilizing for the studies a transform-limited laser pulse at the photocathode, we eliminated laser-induced microbunching at the National Synchrotron Light Source Source Development Laboratory (SDL). The detailed measurements of the resulting electron beam led us to conclude that, at SDL, microbunching arising from shot noise is not amplified to any significant level, thereby allowing us to set an upper limit on the initial modulation depth of microbunching arising from shot noise. Our analysis demonstrated that the only significant source of microbunching instability under normal operational conditions at SDL is the longitudinal modulation of the photocathode laser pulse. Our work shows that assuring a longitudinally smoothed photocathode laser pulse allows mitigating microbunching instability at a typical FEL injector with a moderate microbunching gain.
5. Initial source of microbunching instability studies in a free electron laser injector
Directory of Open Access Journals (Sweden)
S. Seletskiy
2011-11-01
Full Text Available We present the first experimental studies of the initial source of electron beam microbunching instability in a free electron laser (FEL injector. By utilizing for the studies a transform-limited laser pulse at the photocathode, we eliminated laser-induced microbunching at the National Synchrotron Light Source Source Development Laboratory (SDL. The detailed measurements of the resulting electron beam led us to conclude that, at SDL, microbunching arising from shot noise is not amplified to any significant level, thereby allowing us to set an upper limit on the initial modulation depth of microbunching arising from shot noise. Our analysis demonstrated that the only significant source of microbunching instability under normal operational conditions at SDL is the longitudinal modulation of the photocathode laser pulse. Our work shows that assuring a longitudinally smoothed photocathode laser pulse allows mitigating microbunching instability at a typical FEL injector with a moderate microbunching gain.
6. Generation of attosecond electron bunches in a laser-plasma accelerator using a plasma density upramp
Energy Technology Data Exchange (ETDEWEB)
Weikum, M.K., E-mail: [email protected] [Deutsches Elektronensynchrotron (DESY), Bdg. 30b, Notkestr. 85, 22607 Hamburg (Germany); Department of Physics, University of Strathclyde, G4 0NG Glasgow (United Kingdom); Li, F.Y. [Department of Physics, University of Strathclyde, G4 0NG Glasgow (United Kingdom); Assmann, R.W. [Deutsches Elektronensynchrotron (DESY), Bdg. 30b, Notkestr. 85, 22607 Hamburg (Germany); Sheng, Z.M. [Department of Physics, University of Strathclyde, G4 0NG Glasgow (United Kingdom); Laboratory for Laser Plasmas and Department of Physics and Astronomy, Shanghai Jiao Tong University, Shanghai 200240 (China); Jaroszynski, D. [Department of Physics, University of Strathclyde, G4 0NG Glasgow (United Kingdom)
2016-09-01
Attosecond electron bunches and attosecond radiation pulses enable the study of ultrafast dynamics of matter in an unprecedented regime. In this paper, the suitability for the experimental realization of a novel scheme producing sub-femtosecond duration electron bunches from laser-wakefield acceleration in plasma with self-injection in a plasma upramp profile has been investigated. While it has previously been predicted that this requires laser power above a few hundred terawatts typically, here we show that the scheme can be extended with reduced driving laser powers down to tens of terawatts, generating accelerated electron pulses with minimum length of around 166 attoseconds and picocoulombs charge. Using particle-in-cell simulations and theoretical models, the evolution of the accelerated electron bunch within the plasma as well as simple scalings of the bunch properties with initial laser and plasma parameters are presented. - Highlights: • LWFA with an upramp density profile can trap and accelerate sub-fs electron beams. • A reduction of the necessary threshold laser intensity by a factor 4 is presented. • Electron properties are tuned by varying initial laser and plasma parameters. • Simulations predict electron bunch lengths below 200 attoseconds with pC charge. • Strong bunch evolution effects and a large energy spread still need to be improved.
7. Electron Generation and Transport in Intense Relativistic Laser-Plasma Interactions Relevant to Fast Ignition ICF
Energy Technology Data Exchange (ETDEWEB)
Ma, Tammy Yee Wing [Univ. of California, San Diego, CA (United States)
2010-01-01
The reentrant cone approach to Fast Ignition, an advanced Inertial Confinement Fusion scheme, remains one of the most attractive because of the potential to efficiently collect and guide the laser light into the cone tip and direct energetic electrons into the high density core of the fuel. However, in the presence of a preformed plasma, the laser energy is largely absorbed before it can reach the cone tip. Full scale fast ignition laser systems are envisioned to have prepulses ranging between 100 mJ to 1 J. A few of the imperative issues facing fast ignition, then, are the conversion efficiency with which the laser light is converted to hot electrons, the subsequent transport characteristics of those electrons, and requirements for maximum allowable prepulse this may put on the laser system. This dissertation examines the laser-to-fast electron conversion efficiency scaling with prepulse for cone-guided fast ignition. Work in developing an extreme ultraviolet imager diagnostic for the temperature measurements of electron-heated targets, as well as the validation of the use of a thin wire for simultaneous determination of electron number density and electron temperature will be discussed.
8. Monolithic Ge-on-Si lasers for large-scale electronic-photonic integration
Science.gov (United States)
Liu, Jifeng; Kimerling, Lionel C.; Michel, Jurgen
2012-09-01
A silicon-based monolithic laser source has long been envisioned as a key enabling component for large-scale electronic-photonic integration in future generations of high-performance computation and communication systems. In this paper we present a comprehensive review on the development of monolithic Ge-on-Si lasers for this application. Starting with a historical review of light emission from the direct gap transition of Ge dating back to the 1960s, we focus on the rapid progress in band-engineered Ge-on-Si lasers in the past five years after a nearly 30-year gap in this research field. Ge has become an interesting candidate for active devices in Si photonics in the past decade due to its pseudo-direct gap behavior and compatibility with Si complementary metal oxide semiconductor (CMOS) processing. In 2007, we proposed combing tensile strain with n-type doping to compensate the energy difference between the direct and indirect band gap of Ge, thereby achieving net optical gain for CMOS-compatible diode lasers. Here we systematically present theoretical modeling, material growth methods, spontaneous emission, optical gain, and lasing under optical and electrical pumping from band-engineered Ge-on-Si, culminated by recently demonstrated electrically pumped Ge-on-Si lasers with >1 mW output in the communication wavelength window of 1500-1700 nm. The broad gain spectrum enables on-chip wavelength division multiplexing. A unique feature of band-engineered pseudo-direct gap Ge light emitters is that the emission intensity increases with temperature, exactly opposite to conventional direct gap semiconductor light-emitting devices. This extraordinary thermal anti-quenching behavior greatly facilitates monolithic integration on Si microchips where temperatures can reach up to 80 °C during operation. The same band-engineering approach can be extended to other pseudo-direct gap semiconductors, allowing us to achieve efficient light emission at wavelengths previously
9. THz cavities and injectors for compact electron acceleration using laser-driven THz sources
Directory of Open Access Journals (Sweden)
Moein Fakhari
2017-04-01
Full Text Available We present a design methodology for developing ultrasmall electron injectors and accelerators based on cascaded cavities excited by short multicycle THz pulses obtained from laser-driven THz generation schemes. Based on the developed concept for optimal coupling of the THz pulse, a THz electron injector and two accelerating stages are designed. The designed electron gun consists of a four cell cavity operating at 300 GHz and a door-knob waveguide to coaxial coupler. Moreover, special designs are proposed to mitigate the problem of thermal heat flow and induced mechanical stress to achieve a stable device. We demonstrated a gun based on cascaded cavities that is powered by only 1.1 mJ of THz energy in 300 cycles to accelerate electron bunches up to 250 keV. An additional two linac sections can be added with five and four cell cavities both operating at 300 GHz boosting the bunch energy up to 1.2 MeV using a 4-mJ THz pulse.
10. Developing laser ablation in an electron cyclotron resonance ion source for actinide detection with AMS
Energy Technology Data Exchange (ETDEWEB)
Bauder, W. [Argonne National Laboratory, Physics Division, 9600 S. Cass Ave, Lemont, IL 60439 (United States); University of Notre Dame, Nuclear Science Laboratory, 124 Nieuwland Science Hall, Notre Dame, IN 46556 (United States); Pardo, R.C.; Kondev, F.G.; Kondrashev, S.; Nair, C.; Nusair, O. [Argonne National Laboratory, Physics Division, 9600 S. Cass Ave, Lemont, IL 60439 (United States); Palchan, T. [Hebrew University, Racah Institute of Physics, Jerusalem 91904 (Israel); Scott, R.; Seweryniak, D.; Vondrasek, R. [Argonne National Laboratory, Physics Division, 9600 S. Cass Ave, Lemont, IL 60439 (United States); Collon, P. [University of Notre Dame, Nuclear Science Laboratory, 124 Nieuwland Science Hall, Notre Dame, IN 46556 (United States); Paul, M. [Hebrew University, Racah Institute of Physics, Jerusalem 91904 (Israel)
2015-10-15
A laser ablation material injection system has been developed at the ATLAS electron cyclotron resonance (ECR) ion source for use in accelerator mass spectrometry experiments. Beam production with laser ablation initially suffered from instabilities due to fluctuations in laser energy and cratering on the sample surface by the laser. However, these instabilities were rectified by applying feedback correction for the laser energy and rastering the laser across the sample surface. An initial experiment successfully produced and accelerated low intensity actinide beams with up to 1000 counts per second. With continued development, laser ablation shows promise as an alternative material injection scheme for ECR ion sources and may help substantially reduce cross talk in the source.
11. All-electronic suppression of mode hopping noise in diode lasers
DEFF Research Database (Denmark)
Bager, L.
1990-01-01
A simple all-electronic stabilization scheme is presented for suppression of external-cavity mode-hopping noise in diode lasers. This excess noise is generated when the laser is subjected to optical feedback and may degrade the overall performance of optical systems including sensors. Suppression...
12. Generation of ultra-short relativistic-electron-bunch by a laser wakefield
NARCIS (Netherlands)
Khachatryan, A.G.; Boller, Klaus J.; van Goor, F.A.
2003-01-01
The possibility of the generation of an ultra-short (about one micron long) relativistic (up to a few GeVs) electron-bunch in a moderately nonlinear laser wakefield excited in an underdense plasma by an intense laser pulse is investigated. The ultra-short bunch is formed by trapping, effective
13. Hermite-Gaussian Modes and Mirror Distortions in the Free Electron Laser
Science.gov (United States)
2006-06-01
Pellegrini W. B. Colson and A. Renieri, editors. Free Electron Laser Handbook. North-Holland Physics, 1990. [19] W. Silfvast. Laser Fundamentals...Professor Joseph Blau Naval Postgraduate School Monterey, CA 14. Professor Peter Crooker Naval Postgraduate School Monterey, CA 15. Professor Wayne Roberge
14. Tuning laser produced electron-positron jets for lab-astrophysics experiment
Energy Technology Data Exchange (ETDEWEB)
Chen, Hui [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Fiuza, F. [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Hazi, A. [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Kemp, A. [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Link, A. [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Pollock, B. [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Marley, E. [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Nagel, S. R. [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Park, J. [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Schneider, M. [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Shepherd, R. [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Tommasini, R. [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Wilks, S. C. [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Williams, G. J. [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Barnak, D. [Univ. of Rochester, NY (United States). Lab. for Laser Energetics (LLE); Chang, P-Y. [Univ. of Rochester, NY (United States). Lab. for Laser Energetics (LLE); Fiksel, G. [Univ. of Rochester, NY (United States). Lab. for Laser Energetics (LLE); Glebov, V. [Univ. of Rochester, NY (United States). Lab. for Laser Energetics (LLE); Meyerhofer, D. D. [Univ. of Rochester, NY (United States). Lab. for Laser Energetics (LLE); Myatt, J. F. [Univ. of Rochester, NY (United States). Lab. for Laser Energetics (LLE); Stoeckel, C. [Univ. of Rochester, NY (United States). Lab. for Laser Energetics (LLE); Nakai, M. [Osaka Univ. (Japan). ILE; Arikawa, Y. [Osaka Univ. (Japan). ILE; Azechi, H. [Osaka Univ. (Japan). ILE; Fujioka, S. [Osaka Univ. (Japan). ILE; Hosoda, H. [Osaka Univ. (Japan). ILE; Kojima, S. [Osaka Univ. (Japan). ILE; Miyanga, N. [Osaka Univ. (Japan). ILE; Morita, T. [Osaka Univ. (Japan). ILE; Moritaka, T. [Osaka Univ. (Japan). ILE; Nagai, T. [Osaka Univ. (Japan). ILE; Namimoto, T. [Osaka Univ. (Japan). ILE; Nishimura, H. [Osaka Univ. (Japan). ILE; Ozaki, T. [Osaka Univ. (Japan). ILE; Sakawa, Y. [Osaka Univ. (Japan). ILE; Takabe, H. [Osaka Univ. (Japan). ILE; Zhang, Z. [Osaka Univ. (Japan). ILE
2015-02-23
This paper reviews the experiments on the laser produced electron-positron jets using large laser facilities worldwide. The goal of the experiments was to optimize the parameter of the pair jets for their potential applications in laboratory-astrophysical experiment. Results on tuning the pair jet’s energy, number, emittance and magnetic collimation will be presented.
15. Present status and future outlook of selective metallization for electronics industry by laser irradiation to metal nanoparticles
Science.gov (United States)
Watanabe, Akira
2015-03-01
Recently an alternative to conventional methods based on vacuum processes such as evaporation or sputtering is desired to reduce the energy consumption and the environmental impact. Printed electronics has been developed as a one of the candidates, which is based on wet processes using soluble functional materials such as organic semiconductors, inorganic nanomaterials, organic-inorganic hybrids, and so on. Although inkjet printing has been studied widely as a core technology of printed electronics, the limitation of resolution is around 20 micrometer. The combination of the inkjet printing with other selective metallization process is necessary because the resolution of several micrometers is required in some optical and electrical devices. The laser processing has emerged as an attractive technique in microelectronics because of the fascinating features such as high resolution, high degree of flexibility to control the resolution and size of the micro-patterns, high speed, and a little environmental pollution. In this paper, the present status and future outlook of selective metallization for interconnection and the formation of transparent conductive film based on the laser processing using metal nanoparticles were reported. The laser beam irradiation to metal nanoparticles causes the fast and efficient sintering by plasmon resonance of metal nanoparticle, where the absorbed energy is confined in a nanoparticle and the nanoparticle acts as a nano-heater. The laser irradiation to metal nanoparticles was applied to the laser direct writing of metal wiring and micropatterns using silver and copper nanoparticles.
16. Space-charge effects in ultrahigh current electron bunches generated by laser-plasma accelerators
National Research Council Canada - National Science Library
Grüner, F. J; Schroeder, C. B; Maier, A. R; Becker, S; Mikhailova, J. M
2009-01-01
...) generated in laser-plasma accelerators. At low electron energies such peak currents are expected to cause space-charge effects such as bunch expansion and induced energy variations along the bunch, potentially hindering the FEL process...
17. Electron Raman scattering in a double quantum well tuned by an external nonresonant intense laser field
Science.gov (United States)
Tiutiunnyk, A.; Mora-Ramos, M. E.; Morales, A. L.; Duque, C. M.; Restrepo, R. L.; Ungan, F.; Martínez-Orozco, J. C.; Kasapoglu, E.; Duque, C. A.
2017-02-01
In this work we shall present a study of inelastic light scattering involving inter-subband electron transitions in coupled GaAs-(Ga,Al)As quantum wells. Calculations include the electron related Raman differential cross section and Raman gain. The effects of an external nonresonant intense laser field are used in order to tune these output properties. The confined electron states will be described by means of a diagonalization procedure within the effective mass and parabolic band approximations. It is shown that the application of the intense laser field can produce values of the intersubband electron Raman gain above 400 cm-1. The system proposed here is an alternative choice for the development of AlxGa1-xAs semiconductor laser diodes that can be tuned via an external nonresonant intense laser field.
18. Radiobiological Effectiveness of Ultrashort Laser-Driven Electron Bunches: Micronucleus Frequency, Telomere Shortening and Cell Viability.
Science.gov (United States)
Andreassi, Maria Grazia; Borghini, Andrea; Pulignani, Silvia; Baffigi, Federica; Fulgentini, Lorenzo; Koester, Petra; Cresci, Monica; Vecoli, Cecilia; Lamia, Debora; Russo, Giorgio; Panetta, Daniele; Tripodi, Maria; Gizzi, Leonida A; Labate, Luca
2016-09-01
19. Free electron lasers and other advanced sources of light: Scientific research opportunities
Science.gov (United States)
1994-09-01
The free electron laser uses a beam of relativistic electrons passing through a periodic, transverse magnetic field to produce coherent radiation. The advantages of these devices are: A resonance condition that involves the energy of the electron beam, the strength of the magnetic field, and the periodicity of the magnet determines the wavelength of the radiation. Because one medium, the electrons, provides the gain in all spectral regions, adjusting either the beam energy or the field strength tunes the wavelength easily and rapidly over a wide range. Waste energy leaves the medium as kinetic energy of the electrons at nearly the speed of light. Moreover, the lasting medium consists only of electrons in a vacuum, and it does not have the material damage or thermal lensing problems associated with ordinary lasers. Therefore, free electron lasers can achieve very high peak powers. The main disadvantages of the free electron laser are its size and cost. Because the free electron laser requires an electron accelerator with its associated shielding, it has not been a device that could be placed in an individual investigator's laboratory and be operated and maintained by graduate students whose primary expertise is in other areas of science. Because free electron lasers are currently used only in central facilities, their use in scientific research involves both the cost of the device, and the cost and inconvenience of maintaining a facility. Unlike synchrotrons, free electron lasers serve one user, or at most a few users, at any one time. The required electron beam energy increases with decreasing wavelength, and the cost and size of the accelerator as well as the cost and size of the magnetic structure increase with decreasing wavelength. In addition to energy requirements, the electron beam must meet other requirements for emittance, energy spread, and peak current that become more stringent at shorter wavelengths. The shortest wavelength reached by existing free
20. Rotational coherence as an alternative to coincidence techniques at x-ray free electron lasers
Science.gov (United States)
Coffee, Ryan; Hegazy, Kareem; Hartmann, Nick; Walter, Peter; Osipov, Timur; Lindahl, Anton; Helml, Wolfram; Ilchen, Markus; Galler, Andreas; Liu, Jia; Buck, Jens; Shevchuk, Ivan; Viefhaus, Jens; Hartmann, Gregor; Knie, Andre; Demekhin, Philipp; Inhester, Ludger; Li, Zheng; Ziaja-Motyka, Beata; Medvedev, Nikita; Bostedt, Christoph; Guillemin, Renaud; Simon, Marc; Novella-Piancastelli, Maria; Miron, Catalin; LCLS-AMOI0314 Team
2017-04-01
We demonstrate an alternative approach to coincidence particle detection, based on impulsive rotational Raman excitation, for molecular frame measurements at x-ray FELs. A train of 8 infrared laser pulses induces the lab-frame observable coherence. At a field-free alignment revival, we register the angle-resolved laboratory frame Auger and photo-electron spectral feature variations with the tumbling molecular body frame. The time and angle dependence of the electron emission patterns that constrain theory are amenable to large numbers of interactions per pulse and, more importantly, has no axial recoil requirement for kinematic reconstruction. We see this as a method to bypass experimental challenges at XFELs by accepting The Linac Coherent Light Source (LCLS) is supported by the U.S. DoE-BES Contract No. DE-AC02-76SF0051.
1. Optical Sideband Generation: a Longitudinal Electron Beam Diagnostic Beyond the Laser Bandwidth Resolution Limit
Energy Technology Data Exchange (ETDEWEB)
Lawrence Berkeley National Laboratory; Tilborg, J. van; Matlis, N. H.; Plateau, G. R.; Leemans, W. P.
2010-06-01
Electro-optic sampling (EOS) is widely used as a technique to measure THz-domain electric field pulses such asthe self-fields of femtosecond electron beams. We present an EOS-based approach for single-shot spectral measurement that excels in simplicity (compatible with fiber integration) and bandwidth coverage (overcomes the laser bandwidth limitation), allowing few-fs electron beams or single-cycle THz pulses to be characterized with conventional picosecond probes. It is shown that the EOS-induced optical sidebands on the narrow-bandwidth optical probe are spectrally-shifted replicas of the THz pulse. An experimental demonstration on a 0-3 THz source is presented.
2. Single-Molecule Imaging with X-Ray Free-Electron Lasers: Dream or Reality?
KAUST Repository
Fratalocchi, Andrea
2011-03-09
X-ray free-electron lasers (XFEL) are revolutionary photon sources, whose ultrashort, brilliant pulses are expected to allow single-molecule diffraction experiments providing structural information on the atomic length scale of nonperiodic objects. This ultimate goal, however, is currently hampered by several challenging questions basically concerning sample damage, Coulomb explosion, and the role of nonlinearity. By employing an original ab initio approach, we address these issues showing that XFEL-based single-molecule imaging will be only possible with a few-hundred long attosecond pulses, due to significant radiation damage and the formation of preferred multisoliton clusters which reshape the overall electronic density of the molecular system at the femtosecond scale.
3. Innovative single-shot diagnostics for electrons accelerated through laser-plasma interaction at FLAME
Science.gov (United States)
Bisesto, F. G.; Anania, M. P.; Chiadroni, E.; Cianchi, A.; Costa, G.; Curcio, A.; Ferrario, M.; Galletti, M.; Pompili, R.; Schleifer, E.; Zigler, A.
2017-05-01
Plasma wakefield acceleration is the most promising acceleration technique known nowadays, able to provide very high accelerating fields (> 100 GV/m), enabling acceleration of electrons to GeV energy in few centimeters. Here we present all the plasma related activities currently underway at SPARC LAB exploiting the high power laser FLAME. In particular, we will give an overview of the single shot diagnostics employed: Electro Optic Sampling (EOS) for temporal measurement and optical transition radiation (OTR) for an innovative one shot emittance measurements. In detail, the EOS technique has been employed to measure for the first time the longitudinal profile of electric field of fast electrons escaping from a solid target, driving the ions and protons acceleration, and to study the impact of using different target shapes. Moreover, a novel scheme for one shot emittance measurements based on OTR, developed and tested at SPARC LAB LINAC, will be shown.
4. Electron Acceleration by Beating of Two Intense Cross-Focused Hollow Gaussian Laser Beams in Plasma
Science.gov (United States)
Mahmoud, Saleh T.; Gauniyal, Rakhi; Ahmad, Nafis; Rawat, Priyanka; Purohit, Gunjan
2018-01-01
This paper presents propagation of two cross-focused intense hollow Gaussian laser beams (HGBs) in collisionless plasma and its effect on the generation of electron plasma wave (EPW) and electron acceleration process, when relativistic and ponderomotive nonlinearities are simultaneously operative. Nonlinear differential equations have been set up for beamwidth of laser beams, power of generated EPW, and energy gain by electrons using WKB and paraxial approximations. Numerical simulations have been carried out to investigate the effect of typical laser-plasma parameters on the focusing of laser beams in plasmas and further its effect on power of excited EPW and acceleration of electrons. It is observed that focusing of two laser beams in plasma increases for higher order of hollow Gaussian beams, which significantly enhanced the power of generated EPW and energy gain. The amplitude of EPW and energy gain by electrons is found to enhance with an increase in the intensity of laser beams and plasma density. This study will be useful to plasma beat wave accelerator and in other applications requiring multiple laser beams. Supported by United Arab Emirates University for Financial under Grant No. UPAR (2014)-31S164
5. High energy electron and ion generation from thin target using ultra short table top laser
Energy Technology Data Exchange (ETDEWEB)
Nemoto, K.; Oishi, Y.; Fujii, T.; Nayuki, T.; Takizawa, Y. [Central Research Institute of Electric Power Industry, Tokyo (Japan); Sekiya, T; Okano, Y.; Hironaka, Y.; Nakamura, K. G.; Horioka, K.; Kondo, K. [Materials and Structures Laboratory, Toyko Institute of Technology, Tokyo (Japan)
2003-07-01
The influence of laser pulse duration on energetic electrons and protons generation was investigated using a Ti:sapphire laser. Energetic electrons with the temperature of 350 keV were produced by the irradiation of 90 mJ and 50 fs pulse onto a 30 {mu} m copper tape target. For ions, when laser pulse was changed by varying grating distance in the pulse compressor with keeping laser energy at constant value, the maximum proton energy was not changed so much in the region where laser pulse duration was between 55 fs and 400 fs and laser intensity was order of 10{sup 18} W/ cm{sup 2}. The maximum proton energy seems to more depend on the laser energy density on the target than laser intensity. When we evaluate the performance of ion acceleration using the value of E{sub p-max}/U{sub p} (the maximum proton energy normalized by the ponderomotive potential of the laser field), it increasing along with increasing of laser pulse duration.
6. Pulsed gas lasers based on electric transitions of diatomic molecules
Energy Technology Data Exchange (ETDEWEB)
Kaslin, V.M.; Petrash, G.G.
1975-01-01
A detailed experimental study was carried out on the most important laser systems based on electron-oscillatory-rotational transitions of diatomic molecules. A study was made of the following transitions: in the N/sub 2/ molecule the C/sup 3/P/sub u/-B/sup 3/P/sub g/ (second positive band system) and the B/sup 3/P/sub g/-A/sup 3/..sigma../sub u//sup +/ (first positive band system) transitions; in the CO molecule the transition B/sup 1/..sigma../sup +/-A/sup 1/P (band system of Angstrom); in the H/sub 2/ molecule the transition 2sE/sup 1/..sigma../sub g//sup +/-2psigmab/sup 1/..sigma../sub u//sup +/. It is shown that in all these systems a single mechanism is responsible for the inverse population. It is based on excitation of the working levels by direct electron shock from the ground state of the molecules. The distribution of excitation and amplification among the bands is determined by the Frank-Cordon principle. The energy and temporal characteristics of light generation in tubes of equal diameter is unambiguously defined by the parameter E/N, where E is the tension of the electric field in the discharge tube, and N is the density of the working gas. It was found that cooling the active substance in these lasers leads to a sharp increase of the amplification coefficient. This feature made it possible to obtain record radiation output in most of these lasers, to observe modes of high emission in the lasers, to observe a variation of intensities in the molecular spectra, and to realize more than 180 new lines of light generation.
7. Experimental search for the electron electric dipole moment with laser cooled francium atoms
Science.gov (United States)
Inoue, T.; Ando, S.; Aoki, T.; Arikawa, H.; Ezure, S.; Harada, K.; Hayamizu, T.; Ishikawa, T.; Itoh, M.; Kato, K.; Kawamura, H.; Uchiyama, A.; Aoki, T.; Asahi, K.; Furukawa, T.; Hatakeyama, A.; Hatanaka, K.; Imai, K.; Murakami, T.; Nataraj, H. S.; Sato, T.; Shimizu, Y.; Wakasa, T.; Yoshida, H. P.; Yoshimi, A.; Sakemi, Y.
2015-04-01
A laser cooled heavy atom is one of the candidates to search for the permanent electric dipole moment (EDM) of the electron due to the enhancement mechanism and its long coherence time. The laser cooled francium (Fr) factory has been constructed to perform the electron EDM search at the Cyclotron and Radioisotope Center, Tohoku University. The present status of Fr production and the EDM measurement system is presented.
8. Experimental search for the electron electric dipole moment with laser cooled francium atoms
Energy Technology Data Exchange (ETDEWEB)
Inoue, T., E-mail: [email protected] [Tohoku University, Frontier Research Institute of Interdisciplinary Sciences (Japan); Ando, S.; Aoki, T.; Arikawa, H.; Ezure, S.; Harada, K.; Hayamizu, T.; Ishikawa, T.; Itoh, M.; Kato, K.; Kawamura, H.; Uchiyama, A. [Tohoku University, Cyclotron and Radioisotope Center (Japan); Aoki, T. [University of Tokyo, Graduate School of Arts and Sciences (Japan); Asahi, K. [Tokyo Institute of Technology, Department of Physics (Japan); Furukawa, T. [Tokyo Metropolitan University, Department of Physics (Japan); Hatakeyama, A. [Tokyo University of Agriculture and Technology, Department of Applied Physics (Japan); Hatanaka, K. [Osaka University, Research Center for Nuclear Physics (Japan); Imai, K. [Advanced Science Research Center, Japan Atomic Energy Agency (Japan); Murakami, T. [Kyoto University, Department of Physics (Japan); Nataraj, H. S. [Indian Institute of Technology Roorkee (India); and others
2015-04-15
A laser cooled heavy atom is one of the candidates to search for the permanent electric dipole moment (EDM) of the electron due to the enhancement mechanism and its long coherence time. The laser cooled francium (Fr) factory has been constructed to perform the electron EDM search at the Cyclotron and Radioisotope Center, Tohoku University. The present status of Fr production and the EDM measurement system is presented.
9. Target Surface Area Effects on Hot Electron Dynamics from High Intensity Laser-Plasma Interactions
Science.gov (United States)
2016-08-19
sheath field confinement on electron dynamics. X-ray emission due to energetic electrons was imaged using a aK imaging crystal. Electronswere observed to...laser conversion efficiency into particle andfield energy. Previous efforts tominimize this effect have primarily focused on small, isolated targets...leading to enhanced fields [12] improved conversion efficiency [13] and enhanced proton energies [14]with laser pulse durations of hundreds of fs
10. Nonlinear theory of short-wavelength free-electron lasers
Science.gov (United States)
Freund, H. P.
1995-11-01
The nonlinear evolution of free-electron laser (FEL) amplifiers is studied for infrared and shorter wavelengths. The configuration of interest consists in the propagation of an energetic electron beam through a drift tube in the presence of a periodic wiggler magnetic field with planar symmetry. A three-dimensional formulation is derived in which the electromagnetic field is represented as an expansion of Gaussian optical modes. Since the wiggler model is characterized by planar symmetry, the Gauss-Hermite modes are used for this purpose. A set of nonlinear differential equations is derived for the evolution of the amplitude and phase of each mode, and they are solved simultaneously in conjunction with the three-dimensional Lorentz force equations for an ensemble of electrons in the presence of the magneto-static wiggler, self-electric and self-magnetic fields due to the charge and current distributions of the beam, and the electromagnetic fields. It is important to note that no wiggler average is used in the integration of the electron trajectories. This permits the self-consistent modeling of effects associated with (1) the injection of the beam into the wiggler, (2) emittance growth due to inhomogeneities in the wiggler and radiation fields as well as due to the self-fields, (3) the effect of wiggler imperfections, and (4) betatron oscillations. The optical guiding of the radiation field is implicitly included in the formulation. This approach has important practical advantages in analyzing FELs, since it is necessary only to characterize the beam upon injection into the wiggler, and the subsequent evolution is treated self-consistently. Numerical simulations are performed for two examples corresponding to an infrared FEL at wavelengths near 3.5 μm, and an x-ray FEL operating in the neighborhood of 1.4 Å wavelengths corresponding to the proposed linear coherent light source (LCLS) at the Stanford Linear Accelerator Center. Results for both cases indicate that
11. High energy electron beams from a laser wakefield acceleration with a long gas jet
Science.gov (United States)
Kim, Jaehoon; Hwangbo, Yong Hun; Lee, Shin-Yeong
2017-09-01
A long gas jet was used as a gas target for laser wake field acceleration to increase the energy and quality of the electron beam. When the plasma density was 7 × 1018 cm-3, quasi monoenergetic electron beams with a maximum energy of 152 MeV, a beam divergence 3 mrad, and a pointing stability 4 mrad were generated with a 5 mm long gas jet. The maximum energy was close to the theoretical limit predicted from the bubble model. This means that the length of the plasma was sufficiently long to accelerate the electron to the dephasing length after the electrons were self-injected by self-focusing. As the plasma density increased, the dephasing length decreased and the electron energy decreased. The continuous injection with higher density plasmas generated highly diverging beams. As the laser power increased, a number of electron beams with different propagation directions were generated. As shown by the measured shadowgram, the laser was divided into several filaments and each filament accelerated electron beam having different directions. The electron beam generated at this time decreased as the laser energy decreased due the division of the laser into different directions.
12. Laser-sub-cycle two-dimensional electron momentum mapping using orthogonal two-color fields
CERN Document Server
Zhang, Li; Roither, Stefan; Kartashov, Daniil; Wang, YanLan; Wang, ChuanLiang; Schöffler, Markus; Shafir, Dror; Corkum, Paul; Baltuška, Andrius; Ivanov, Igor; Kheifets, Anatoli; Liu, XiaoJun; Staudte, André; Kitzler, Markus
2014-01-01
The two-dimensional sub-cycle-time to electron momentum mapping provided by orthogonal two-color laser fields is applied to photoelectron spectroscopy. Using neon as the example we gain experimental access to the dynamics of emitted electron wave packets in electron momenta spectra measured by coincidence momentum imaging. We demonstrate the opportunities provided by this time-to-momentum mapping by investigating the influence of the parent ion on the emitted electrons on laser-sub-cycle times. It is found that depending on their sub-cycle birth time the trajectories of photoelectrons are affected differently by the ion's Coulomb field.
13. Plasma scale-length effects on electron energy spectra in high-irradiance laser plasmas.
Science.gov (United States)
Culfa, O; Tallents, G J; Rossall, A K; Wagenaars, E; Ridgers, C P; Murphy, C D; Dance, R J; Gray, R J; McKenna, P; Brown, C D R; James, S F; Hoarty, D J; Booth, N; Robinson, A P L; Lancaster, K L; Pikuz, S A; Faenov, A Ya; Kampfer, T; Schulze, K S; Uschmann, I; Woolsey, N C
2016-04-01
An analysis of an electron spectrometer used to characterize fast electrons generated by ultraintense (10^{20}Wcm^{-2}) laser interaction with a preformed plasma of scale length measured by shadowgraphy is presented. The effects of fringing magnetic fields on the electron spectral measurements and the accuracy of density scale-length measurements are evaluated. 2D EPOCH PIC code simulations are found to be in agreement with measurements of the electron energy spectra showing that laser filamentation in plasma preformed by a prepulse is important with longer plasma scale lengths (>8 μm).
14. Heating of solid target in electron refluxing dominated regime with ultra-intense laser
Science.gov (United States)
Nakatsutsumi, M.; Kodama, R.; Aglitskiy, Y.; Akli, K. U.; Batani, D.; Baton, S. D.; Beg, F. N.; Benuzzi-Mounaix, A.; Chen, S. N.; Clark, D.; Davies, J. R.; Freeman, R. R.; Fuchs, J.; Green, J. S.; Gregory, C. D.; Guillou, P.; Habara, H.; Heathcote, R.; Hey, D. S.; Highbarger, K.; Jaanimagi, P.; Key, M. H.; Koenig, M.; Krushelnick, K.; Lancaster, K. L.; Loupias, B.; Ma, T.; Macphee, A.; Mackinonn, A. J.; Mima, K.; Morace, A.; Nakamura, H.; Norryes, P. A.; Piazza, D.; Rousseaux, C.; Stephans, R. B.; Storm, M.; Tampo, M.; Theobald, W.; Woerkom, L. V.; Weber, R. L.; Wei, M. S.; Woolsey, N. C.
2008-05-01
Propagation of electron beams generated in laser-plasma interactions is strongly influenced by self-induced electrostatic fields at target-vacuum interfaces, resulting the refluxing of electrons. We confirmed the refluxing and propagation of electrons with three different kinds of target configurations; thin-wide foil, thin-narrow foil, and long-wire geometry. Enhancement of target heating, effective guiding and collimation of high density MeV electrons were observed.
15. Evolution of MEMS scanning mirrors for laser projection in compact consumer electronics
Science.gov (United States)
Tauscher, Jason; Davis, Wyatt O.; Brown, Dean; Ellis, Matt; Ma, Yunfei; Sherwood, Michael E.; Bowman, David; Helsel, Mark P.; Lee, Sung; Coy, John Wyatt
2010-02-01
The applicability of MOEMS scanning mirrors towards the creation of "flying spot" scanned laser displays is well established. The extension of this concept towards compact embedded pico-projectors has required an evolution of scanners and packaging to accommodate the needs of the consumer electronics space. This paper describes the progression of the biaxial MOEMS scanning mirrors developed by Microvision over recent years. Various aspects of the individual designs are compared. Early devices used a combination of magnetic quasistatic actuation and resonant electrostatic operation in an evacuated atmosphere to create a projection engine for retinal scanned displays. Subsequent designs realized the elimination of both the high voltage electrostatic drive and the vacuum package, and a simplification of the actuation scheme through proprietary technical advances. Additional advances have doubled the scan angle capability and greatly miniaturized the MOEMS component while not incurring significant increase in power consumption, making it an excellent fit for the consumer pico-projector application. The simplicity of the scanned laser-based pico-projector optical design enables high resolution and a large effective image size in a thin projection engine, all of which become critical both to the viability of the technology and adoption by consumers. Microvision's first scanned laser pico-projector is built around a MOEMS scanning mirror capable of projecting 16:9 aspect ratio, WVGA display within a 6.6 mm high package. Further evolution on this path promises continued improvement in resolution, size, and power.
16. Laser Opto-Electronic Correlator for Robotic Vision Automated Pattern Recognition
Science.gov (United States)
Marzwell, Neville
1995-01-01
A compact laser opto-electronic correlator for pattern recognition has been designed, fabricated, and tested. Specifically it is a translation sensitivity adjustable compact optical correlator (TSACOC) utilizing convergent laser beams for the holographic filter. Its properties and performance, including the location of the correlation peak and the effects of lateral and longitudinal displacements for both filters and input images, are systematically analyzed based on the nonparaxial approximation for the reference beam. The theoretical analyses have been verified in experiments. In applying the TSACOC to important practical problems including fingerprint identification, we have found that the tolerance of the system to the input lateral displacement can be conveniently increased by changing a geometric factor of the system. The system can be compactly packaged using the miniature laser diode sources and can be used in space by the National Aeronautics and Space Administration (NASA) and ground commercial applications which include robotic vision, and industrial inspection of automated quality control operations. The personnel of Standard International will work closely with the Jet Propulsion Laboratory (JPL) to transfer the technology to the commercial market. Prototype systems will be fabricated to test the market and perfect the product. Large production will follow after successful results are achieved.
17. Soft x-ray free-electron laser induced damage to inorganic scintillators
Czech Academy of Sciences Publication Activity Database
Burian, Tomáš; Hájková, Věra; Chalupský, Jaromír; Vyšín, Luděk; Boháček, Pavel; Přeček, Martin; Wild, J.; Özkan, C.; Coppola, N.; Farahani, S.D.; Schulz, J.; Sinn, H.; Tschentscher, T.; Gaudin, J.; Bajt, S.; Tiedtke, K.; Toleikis, S.; Chapman, H.N.; Loch, R.A.; Jurek, M.; Sobierajski, R.; Krzywinski, J.; Moeller, S.; Harmand, M.; Galasso, G.; Nagasono, M.; Saskl, K.; Sovák, P.; Juha, Libor
2015-01-01
Roč. 5, č. 2 (2015), 254-264 ISSN 2159-3930 R&D Projects: GA ČR(CZ) GAP108/11/1312; GA MŠk EE2.3.30.0057 Grant - others:OP VK 4 POSTDOK(XE) CZ.1.07/2.3.00/30.0057 Institutional support: RVO:68378271 Keywords : fluorescent and luminescent materials * laser damage * free-electron lasers * soft x-rays * laser materials processing Subject RIV: BH - Optics, Masers, Lasers Impact factor: 2.657, year: 2015
18. Laser sources for polarized electron beams in cw and pulsed accelerators
CERN Document Server
Hatziefremidis, A; Fraser, D; Avramopoulos, H
1999-01-01
We report the characterization of a high power, high repetition rate, mode-locked laser system to be used in continuous wave and pulsed electron accelerators for the generation of polarized electron beams. The system comprises of an external cavity diode laser and a harmonically mode-locked Ti:Sapphire oscillator and it can provide up to 3.4 W average power, with a corresponding pulse energy exceeding 1 nJ at 2856 MHz repetition rate. The system is tunable between 770-785 and 815-835 nm with two sets of diodes for the external cavity diode laser. (author)
19. Electron density and temperature measurements in a laser produced carbon plasma
Energy Technology Data Exchange (ETDEWEB)
Harilal, S.S.; Bindhu, C.V.; Issac, R.C.; Nampoori, V.P.; Vallabhan, C.P. [Laser Division, International School of Photonics, Cochin University of Science Technology, Cochin 682 022 (India)
1997-09-01
Plasma generated by fundamental radiation from a Nd:YAG laser focused onto a graphite target is studied spectroscopically. Measured line profiles of several ionic species were used to infer electron temperature and density at several sections located in front of the target surface. Line intensities of successive ionization states of carbon were used for electron temperature calculations. Stark broadened profiles of singly ionized species have been utilized for electron density measurements. Electron density as well as electron temperature were studied as functions of laser irradiance and time elapsed after the incidence of laser pulse. The validity of the assumption of local thermodynamic equilibrium is discussed in light of the results obtained. {copyright} {ital 1997 American Institute of Physics.}
20. Aerosol Imaging with a Soft X-ray Free Electron Laser
Energy Technology Data Exchange (ETDEWEB)
Bogan, Michael J.; /SLAC /LLNL, Livermore; Boutet, Sebastien; /SLAC; Chapman, Henry N.; /DESY /Hamburg U.; Marchesini, Stefano; /LBL, Berkeley; Barty, Anton; Benner, W.Henry /LLNL, Livermore; Rohner, Urs; /LLNL, Livermore /TOFWERK AG; Frank, Matthias; Hau-Riege, Stefan P.; /LLNL, Livermore; Bajt, Sasa; /DESY; Woods, Bruce; /LLNL, Livermore; Seibert, M.M.; Iwan, Bianca; Timneanu, Nicusor; Hajdu, Janos; /Uppsala U.; Schulz, Joachim; /DESY
2011-08-22
Lasers have long played a critical role in the advancement of aerosol science. A new regime of ultrafast laser technology has recently be realized, the world's first soft xray free electron laser. The Free electron LASer in Hamburg, FLASH, user facility produces a steady source of 10 femtosecond pulses of 7-32 nm x-rays with 10{sub 12} photons per pulse. The high brightness, short wavelength, and high repetition rate (>500 pulses per second) of this laser offers unique capabilities for aerosol characterization. Here we use FLASH to perform the highest resolution imaging of single PM2.5 aerosol particles in flight to date. We resolve to 35 nm the morphology of fibrous and aggregated spherical carbonaceous nanoparticles that existed for less than two milliseconds in vacuum. Our result opens the possibility for high spatialand time-resolved single particle aerosol dynamics studies, filling a critical technological need in aerosol science.
1. Laser-plasma-based linear collider using hollow plasma channels
Energy Technology Data Exchange (ETDEWEB)
Schroeder, C.B., E-mail: [email protected]; Benedetti, C.; Esarey, E.; Leemans, W.P.
2016-09-01
A linear electron–positron collider based on laser-plasma accelerators using hollow plasma channels is considered. Laser propagation and energy depletion in the hollow channel is discussed, as well as the overall efficiency of the laser-plasma accelerator. Example parameters are presented for a 1-TeV and 3-TeV center-of-mass collider based on laser-plasma accelerators.
2. Planar Laser-Based QEPAS Trace Gas Sensor
OpenAIRE
Yufei Ma; Ying He; Cheng Chen; Xin Yu; Jingbo Zhang; Jiangbo Peng; Rui Sun; Tittel, Frank K.
2016-01-01
A novel quartz enhanced photoacoustic spectroscopy (QEPAS) trace gas detection scheme is reported in this paper. A cylindrical lens was employed for near-infrared laser focusing. The laser beam was shaped as a planar line laser between the gap of the quartz tuning fork (QTF) prongs. Compared with a spherical lens-based QEPAS sensor, the cylindrical lens-based QEPAS sensor has the advantages of easier laser beam alignment and a reduction of stringent stability requirements. Therefore, the repo...
3. Free-Free Transitions in the Presence of Laser Fields at Very Low Incident Electron Energy
Science.gov (United States)
Bhatia, A. K.; Sinha, Chandana
2010-01-01
We study the free-free transition in electron-hydrogenic systems in ground state in presence of an external laser field at very loud incident energies. The laser field is treated classically while the collision dynamics is treated quantum mechanically. The laser field is chosen to be monochromatic, linearly polarized and homogeneous. The incident electron is considered to be dressed by the laser in a nonperturbative manner by choosing a Volkov wave function for it. The scattering weave function for the electron is solved numerically by taking into account the effect of the electron exchange, short-range as well as of the long-range interactions to get the S and P wave phase shifts while for the higher angular momentum phase shifts the exchange approximation has only been considered. We calculate the laser assisted differential cross sections (LADCS) for the aforesaid free-free transition process for single photon absorption/emission. The laser intensity is chosen to be much less than the atomic field intensity. A strong suppression is noted in the LADCS as compared to the field free (FF) cross sections. Unlike the FF ones, the LADCS exhibit some oscillations having a distinct maximum at a low value of the scattering angle depending on the laser parameters as well as on the incident energies.
4. Direct acceleration of electrons by a CO2 laser in a curved plasma waveguide
Science.gov (United States)
Yi, Longqing; Pukhov, Alexander; Shen, Baifei
2016-06-01
Laser plasma interaction with micro-engineered targets at relativistic intensities has been greatly promoted by recent progress in the high contrast lasers and the manufacture of advanced micro- and nano-structures. This opens new possibilities for the physics of laser-matter interaction. Here we propose a novel approach that leverages the advantages of high-pressure CO2 laser, laser-waveguide interaction, as well as micro-engineered plasma structure to accelerate electrons to peak energy greater than 1 GeV with narrow slice energy spread (~1%) and high overall efficiency. The acceleration gradient is 26 GV/m for a 1.3 TW CO2 laser system. The micro-bunching of a long electron beam leads to the generation of a chain of ultrashort electron bunches with the duration roughly equal to half-laser-cycle. These results open a way for developing a compact and economic electron source for diverse applications.
5. CTS and CZTS for solar cells made by pulsed laser deposition and pulsed electron deposition
DEFF Research Database (Denmark)
Ettlinger, Rebecca Bolt
This thesis concerns the deposition of thin films for solar cells using pulsed laser deposition (PLD) and pulsed electron deposition (PED). The aim was to deposit copper tin sulfide (CTS) and zinc sulfide (ZnS) by pulsed laser deposition to learn about these materials in relation to copper zinc tin......, which make them promising alternatives to the commercially successful solar cell material copper indium gallium diselenide (CIGS). Complementing our group's work on pulsed laser deposition of CZTS, we collaborated with IMEM-CNR in Parma, Italy, to deposit CZTS by pulsed electron deposition for the first...... of using pulsed electron deposition was to make CZTS at a low processing temperature, avoiding the 570 °C annealing step used for our pulsed laser deposited solar cells. Preliminary solar cells had an efficiency of 0.2 % with a 300 °C deposition step without annealing. Further process control is needed...
6. Relativistic Electron Acceleration with Ultrashort Mid-IR Laser Pulses
Science.gov (United States)
Feder, Linus; Woodbury, Daniel; Shumakova, Valentina; Gollner, Claudia; Miao, Bo; Schwartz, Robert; Pugžlys, Audrius; Baltuška, Andrius; Milchberg, Howard
2017-10-01
We report the first results of laser plasma wakefield acceleration driven by ultrashort mid-infrared laser pulses (λ = 3.9 μm , pulsewidth 100 fs, energy width, as well as trends in the accelerated beam profiles, charge and energy spectra which are supported by 3D particle-in-cell simulations. These results extend earlier work with sub-TW self-modulated laser wakefield acceleration using near IR drivers to the Mid-IR, and enable us to capture time-resolved images of relativistic self-focusing of the laser pulse. This work supported by DOE (DESC0010706TDD, DESC0015516); AFOSR(FA95501310044, FA95501610121); NSF(PHY1535519); DHS.
7. Nonadiabaticity of electron-tunneling-ionization processes in elliptical strong laser fields
Science.gov (United States)
Cai, Jun; Chen, Yan-jun; Xia, Qin-zhi; Ye, Di-fa; Liu, Jie; Fu, Li-bin
2017-09-01
We theoretically investigate the electron-tunneling process for a helium atom irradiated by an elliptical strong laser field. The momentum distribution for an electron ionized during the cycle when the laser intensity reaches its maximum is captured, such that we can ignore the interference between the wave packets ionized in different laser cycles and precisely determine the center of the momentum distribution. The quantum mechanical prediction of the center position is further compared to the semiclassical single-trajectory simulation as well as the experimental data. We find that the electron momentums along the minor axis of the laser polarization show good agreement with the nonadiabatic semiclassical calculation for a wide range of laser intensities, indicating the existence of a nonzero lateral momentum when the electron exits the barrier. On the other hand, the offset angles obtained by our quantum mechanical approach for different laser intensities are larger than the nonadiabatic semiclassical results, indicating the importance of the quantum effects during the electron's under-the-barrier dynamics.
8. Laser-assisted electron capture and emission in slow proton-hydrogen collisions.
Science.gov (United States)
Niederhausen, Thomas; Feuerstein, Bernold; Thumm, Uwe
2004-03-01
We investigate the effects of a strong laser field on the dynamics of ion-atom collisions by solving the time-dependent Schrödinger equation (TDSE) on a numerical grid for a 2D (reduced dimensionality) and a full 3D model of the scattering system. In the 2D model the electron system is confined to the two dimensions of the scattering plane, which also includes the laser electric field vector. This allows us to study the influence of the laser intensity and polarization (linear, circular, elliptic) on the capture and ionization probabilities for a large number of collision and laser parameters. After intergrating over impact parameters of the classical projectile trajectory and after averagering over the relative phase between the laser electric field and the collision, we find for intensities above 10^13 W/cm^2 noticeable laser electric field effects and circular dichroism in the capture probability.
9. High-quality electron beams from a helical inverse free-electron laser accelerator
National Research Council Canada - National Science Library
Duris, J; Musumeci, P; Babzien, M; Fedurin, M; Kusche, K; Li, R K; Moody, J; Pogorelsky, I; Polyanskiy, M; Rosenzweig, J B; Sakai, Y; Swinson, C; Threlkeld, E; Williams, O; Yakimenko, V
2014-01-01
.... By using an undulator magnetic field in combination with a laser, GeV m(-1) gradients may be sustained over metre-scale distances using laser intensities several orders of magnitude less than those used in laser wake-field accelerators...
10. Modeling distributed feedback GaAs-based lasers in dentistry
Science.gov (United States)
Shih, Meng-Mu
2012-01-01
Distributed-feedback gallium-arsenide-based lasers with metal-gratings can generate stable wavelength at 980nm for applications in dentistry. This model uses the periodic optical waveguide method to calculate the coupling coefficient, which is a key parameter of laser performance. This model shows how the optical, geometrical, and material parameters depending on each other and how they affect the coupling coefficients in the laser waveguides. Numerical results compare the coupling coefficients of 980 nm lasers with those of 810 nm lasers. The modeling processes, including results, discussions, and physical interpretations, help to design and analyze lasers for more clinical and research applications in dentistry.
11. A comparison of the physics of Gas Tungsten Arc Welding (GTAW), Electron Beam Welding (EBW), and Laser Beam Welding (LBW)
Science.gov (United States)
Nunes, A. C., Jr.
1985-01-01
The physics governing the applicability and limitations of gas tungsten arc (GTA), electron beam (EB), and laser beam (LB) welding are compared. An appendix on the selection of laser welding systems is included.
12. Influence of laser induced hot electrons on the threshold for shock ignition of fusion reactions
Energy Technology Data Exchange (ETDEWEB)
Colaïtis, A.; Ribeyre, X.; Le Bel, E.; Duchateau, G.; Nicolaï, Ph.; Tikhonchuk, V. [Centre Lasers Intenses et Applications, Université de Bordeaux - CNRS - CEA, UMR 5107,351 Cours de la Libération, 33400 Talence (France)
2016-07-15
The effects of Hot Electrons (HEs) generated by the nonlinear Laser-Plasma Interaction (LPI) on the dynamics of Shock Ignition Inertial Confinement Fusion targets are investigated. The coupling between the laser beam, plasma dynamics and hot electron generation and propagation is described with a radiative hydrodynamics code using an inline model based on Paraxial Complex Geometrical Optics [Colaïtis et al., Phys. Rev. E 92, 041101 (2015)]. Two targets are considered: the pure-DT HiPER target and a CH-DT design with baseline spike powers of the order of 200–300 TW. In both cases, accounting for the LPI-generated HEs leads to non-igniting targets when using the baseline spike powers. While HEs are found to increase the ignitor shock pressure, they also preheat the bulk of the imploding shell, notably causing its expansion and contamination of the hotspot with the dense shell material before the time of shock convergence. The associated increase in hotspot mass (i) increases the ignitor shock pressure required to ignite the fusion reactions and (ii) significantly increases the power losses through Bremsstrahlung X-ray radiation, thus rapidly cooling the hotspot. These effects are less prominent for the CH-DT target where the plastic ablator shields the lower energy LPI-HE spectrum. Simulations using higher laser spike powers of 500 TW suggest that the CH-DT capsule marginally ignites, with an ignition window width significantly smaller than without LPI-HEs, and with three quarters of the baseline target yield. The latter effect arises from the relation between the shock launching time and the shell areal density, which becomes relevant in presence of a LPI-HE preheating.
13. Theory and computation of few-electron atoms in intense laser fields
CERN Document Server
Moore, L
2001-01-01
experimental peak laser intensity measurement. At 780 nm preliminary results of a comparable calculation of double-ionization are given. In anticipation of a high intensity, high frequency radiation source becoming available in Germany by 2003, a calculation at 14 nm has also been performed. Momentum distributions have revealed the new process of double-electron above threshold ionization. In this process both electrons absorb excess photons during double-ionization. The study of the helium atom-exposed to an intense laser field forms the topic of this thesis. In the context of laser-atom interactions, a laser is said to be intense if the force it exerts on an electron in an atomic orbital is comparable to the force experienced by that electron due to the binding atomic potential. The electronic response of the helium atom to an intense laser field is governed by the interactions of the two electrons between themselves, with the nucleus and with the field. The problem therefore is the fundamental three-body p...
14. Modeling laser-driven electron acceleration using WARP with Fourier decomposition
Science.gov (United States)
Lee, P.; Audet, T. L.; Lehe, R.; Vay, J.-L.; Maynard, G.; Cros, B.
2016-09-01
WARP is used with the recent implementation of the Fourier decomposition algorithm to model laser-driven electron acceleration in plasmas. Simulations were carried out to analyze the experimental results obtained on ionization-induced injection in a gas cell. The simulated results are in good agreement with the experimental ones, confirming the ability of the code to take into account the physics of electron injection and reduce calculation time. We present a detailed analysis of the laser propagation, the plasma wave generation and the electron beam dynamics.
15. Tuning the electron energy by controlling the density perturbation position in laser plasma accelerators
CERN Document Server
Brijesh, P; Phuoc, K T; Corde, S; Lambert, G; Malka, V; Mangles, S P D; Bloom, M; Kneip, S
2012-01-01
A density perturbation produced in an underdense plasma was used to improve the quality of electron bunches produced in the laser-plasma wakefield acceleration scheme. Quasi-monoenergetic electrons were generated by controlled injection in the longitudinal density gradients of the density perturbation. By tuning the position of the density perturbation along the laser propagation axis, a fine control of the electron energy from a mean value of 60 MeV to 120 MeV has been demonstrated with a relative energy-spread of 15 +/- 3.6%, divergence of 4 +/- 0.8 mrad and charge of 6 +/- 1.8 pC.
16. Parametric waves excitation in relativistic laser-plasma interactions for electron acceleration
Science.gov (United States)
Shulyapov, S. A.; Ivanov, K. A.; Tsymbalov, I. N.; Krestovskih, D. A.; Savel'ev, A. B.; Ksenofontov, P. A.; Brantov, A. V.; Bychenkov, V. Yu
2015-11-01
Plasma created by femtosecond laser pulse of high intensity can be used as the brilliant source of high energy electrons, ions and x- or γ-rays. In most cases, laser pulses with high contrast are used for particle acceleration. But, it has been shown, that changing parameters of pre-plasma layer on the surface of the target can significantly increase electron energies. In this work we present the results of the experimental and numerical studies of the abnormally hot electron generation mechanisms in the case of long scale pre-plasma layer subcritical density.
17. R&D for a Soft X-Ray Free Electron Laser Facility
Energy Technology Data Exchange (ETDEWEB)
Corlett, John; Attwood, David; Byrd, John; Denes, Peter; Falcone, Roger; Heimann, Phil; Leemans, Wim; Padmore, Howard; Prestemon, Soren; Sannibale, Fernando; Schlueter, Ross; Schroeder, Carl; Staples, John; Venturini, Marco; Warwick, Tony; Wells, Russell; Wilcox, Russell; Zholent, Alexander; Adolphsen, Chris; Arthur, John; Bergmann, Uwe; Cai, Yunhai; Colby, Eric; Dowell, David; Emma, Paul; Fox, John; Frisch, Josef; Galayda, John; Hettel, Robert; Huang, Zhirong; Phinney, Nan; Rabedeau, Tom; Raubenheimer, Tor; Reis, David; Schmerge, John; Stohr, Joachim; Stupakov, Gennady; White, Bill; Xiang, Dao
2009-06-08
Several recent reports have identified the scientific requirements for a future soft x-ray light source, and a high-repetition-rate free-electron laser (FEL) facility that is responsive to these requirements is now on the horizon. R&D in some critical areas is needed, however, to demonstrate technical performance, thus reducing technical risks and construction costs. Such a facility most likely will be based on a CW superconducting linear accelerator with beam supplied by a high-brightness, high-repetition-rate photocathode electron gun operating in CW mode, and on an array of FELs to which the accelerated beam is distributed, each operating at high repetition rate and with even pulse spacing. Dependent on experimental requirements, the individual FELs can be configured for either self-amplified spontaneous emission (SASE), seeded, or oscillator mode of operation, including the use of high-gain harmonic generation (HGHG), echo-enhanced harmonic generation (EEHG), harmonic cascade, or other configurations. In this White Paper we identify the overall accelerator R&D needs, and highlight the most important pre-construction R&D tasks required to value-engineer the design configuration and deliverables for such a facility. In Section 1.4 we identify the comprehensive R&D ultimately needed. We identify below the highest-priority requirements for understanding machine performance and reduce risk and costs at this pre-conceptual design stage. Details of implementing the required tasks will be the subject of future evaluation. Our highest-priority R&D program is the injector, which must be capable of delivering a beam with bunches up to a nanocoulomb at MHz repetition rate and with normalized emittance {le} 1 mm {center_dot} mrad. This will require integrated accelerating structure, cathode, and laser systems development. Cathode materials will impact the choice of laser technology in wavelength and energy per pulse, as well as vacuum requirements in the accelerating
18. Demonstration of electron beam focusing by a laser-plasma lens
CERN Document Server
Thaury, Cédric; Döpp, Andreas; Lehe, Remi; Lifschitz, Agustin; Phuoc, Kim Ta; Gautier, Julien; Goddet, Jean-Philippe; Tafzi, Amar; Flacco, Alessandro; Tissandier, Fabien; Sebban, Stéphane; Rousse, Antoine; Malka, Victor
2014-01-01
Laser-plasma technology promises a drastic reduction of the size of high energy electron accelerators. It could make free electron lasers available to a broad scientific community, and push further the limits of electron accelerators for high energy physics. Furthermore the unique femtosecond nature of the source makes it a promising tool for the study of ultra-fast phenomena. However, applications are hindered by the lack of suitable lens to transport this kind of high-current electron beams, mainly due to their divergence. Here we show that this issue can be solved by using a laser-plasma lens, in which the field gradients are five order of magnitude larger than in conventional optics. We demonstrate a reduction of the divergence by nearly a factor of three, which should allow for an efficient coupling of the beam with a conventional beam transport line.
19. High gain harmonic generation free electron lasers enhanced by pseudoenergy bands
Directory of Open Access Journals (Sweden)
Takashi Tanaka
2017-08-01
Full Text Available We propose a new scheme for high gain harmonic generation free electron lasers (HGHG FELs, which is seeded by a pair of intersecting laser beams to interact with an electron beam in a modulator undulator located in a dispersive section. The interference of the laser beams gives rise to a two-dimensional modulation in the energy-time phase space because of a strong correlation between the electron energy and the position in the direction of dispersion. This eventually forms pseudoenergy bands in the electron beam, which result in efficient harmonic generation in HGHG FELs in a similar manner to the well-known scheme using the echo effects. The advantage of the proposed scheme is that the beam quality is less deteriorated than in other existing schemes.
20. Energy enhancer for mask based laser materials processing
DEFF Research Database (Denmark)
Bastue, Jens; Olsen, Flemmming Ove
1996-01-01
A device capable of drastically improving the energy efficiency of present mask based laser materials processing systems is presented. Good accordance between experiments and simulations for a TEA-CO2 laser system designed for laser marking has been demonstrated. The energy efficiency may...
1. Constraints on photon pulse duration from longitudinal electron beam diagnostics at a soft x-ray free-electron laser
Directory of Open Access Journals (Sweden)
C. Behrens
2012-03-01
Full Text Available The successful operation of x-ray free-electron lasers (FELs, like the Linac Coherent Light Source or the Free-Electron Laser in Hamburg (FLASH, makes unprecedented research on matter at atomic length and ultrafast time scales possible. However, in order to take advantage of these unique light sources and to meet the strict requirements of many experiments in photon science, FEL photon pulse durations need to be known and tunable. This can be achieved by controlling the FEL driving electron beams, and high-resolution longitudinal electron beam diagnostics can be utilized to provide constraints on the expected FEL photon pulse durations. In this paper, we present comparative measurements of soft x-ray pulse durations and electron bunch lengths at FLASH. The soft x-ray pulse durations were measured by FEL radiation pulse energy statistics and compared to electron bunch lengths determined by frequency-domain spectroscopy of coherent transition radiation in the terahertz range and time-domain longitudinal phase space measurements. The experimental results, theoretical considerations, and simulations show that high-resolution longitudinal electron beam diagnostics provide reasonable constraints on the expected FEL photon pulse durations. In addition, we demonstrated the generation of soft x-ray pulses with durations below 50 fs (FWHM after the implementation of the new uniform electron bunch compression scheme used at FLASH.
2. A table-top x-ray FEL based on a laser wakefield accelerator-undulator system
Energy Technology Data Exchange (ETDEWEB)
Nakajima, K.; Kawakubo, T.; Nakanishi, H. [National Lab. for High Energy Physics, Ibaraki-ken (Japan)] [and others
1995-12-31
Ultrahigh-gradient electron acceleration has been confirmed owing to the laser wakefield acceleration mechanism driven by an intense short laser wakefield acceleration mechanism driven by an intense short laser pulse in an underdense plasma. The laser wakefield acceleration makes it possible to build a compact electron linac capable of producing an ultra-short bunched electron beam. While the accelerator is attributed to longitudinal wakefields, transverse wakefields simultaneously generated by a short laser pulse can serve as a plasma undulator with a very short wavelength equal to a half of the plasma wavelength. We propose a new FEL concept for X-rays based on a laser wakefield accelerator-undulator system driven by intense short laser pulses delivered from table-top terawatt lasers. The system is composed of the accelerator stage and the undulator stage in a table-top size. A low energy electron beam is accelerated an bunched into microbunches due to laser wakefields in the accelerator stage. A micro-bunched beam travelling to the opposite direction of driving laser pulses produces coherent X-ray radiation in the undulator stage. A practical configuration and its analyses are presented.
3. Ultrafast electronic dynamics in laser-excited crystalline bismuth
Directory of Open Access Journals (Sweden)
Chekalin S.
2013-03-01
Full Text Available Femtosecond spectroscopy was applied to capture complex dynamics of non equilibrium electrons in bismuth. Data analysis reveals significant wavevector dependence of electron-hole and electron-phonon coupling strength along the Γ-T direction of the Brillouin zone
4. Plasma-optical spatiotemporal diagnostics and alignment for electron and laser beams
Science.gov (United States)
Heinemann, Thomas; Knetsch, Alexander; Beaton, Andrew; Delinikolas, Panagiotis; Habib, Fahim; Manahan, Grace; Scherkl, Paul; Ullmann, Daniel; Sutherland, Andrew; Karger, Oliver; Rosenzweig, James; Hidding, Bernhard
2017-10-01
The steadily increasing demand for compact accelerator-driven light sources imposes new challenges for generating compact, high-quality electron beams and concomitant μm-scale, fs-scale diagnostics. During the E210 experimental campaign at FACET (SLAC), we have amended state-of-the-art electro-optical sampling timing diagnostics and optical transition radiation spatial diagnostics with novel plasma-based techniques. By harnessing the ultrasensitive plasma response to intersecting laser and electron beams, we have developed novel diagnostic techniques which potentially enable spatiotemporal alignment with sub-fs and sub- μm accuracy. Furthermore, the diagnostics can be realized in a simple and robust layout; they are based on measuring the time-integrated plasma recombination light from tunnel ionization as well as electron impact ionization. They thus map ultrashort and small dynamics onto much longer and larger scales, such that the main diagnostic element is a simple imaging device. These techniques, the underlying physics and their potentially far-reaching impact will be presented and discussed.
5. Operational Radiation Protection in Synchrotron Light and Free Electron Laser Facilities
Energy Technology Data Exchange (ETDEWEB)
Liu, James C.; Rokni, Sayed H.; /SLAC; Vylet, Vaclav; /Jefferson Lab
2009-12-11
The 3rd generation synchrotron radiation (SR) facilities are storage ring based facilities with many insertion devices and photon beamlines, and have low injection beam power (< few tens of watts), but extremely high stored beam power ({approx} 1 GW). The 4th generation x-ray free electron laser (FEL) facilities are based on an electron Linac with a long undulator and have high injection beam power (a few kW). Due to its electron and photon beam characteristics and modes of operation, storage ring and photon beamlines have unique safety aspects, which are the main subjects of this paper. The shielding design limits, operational modes, and beam losses are first reviewed. Shielding analysis (source terms and methodologies) and interlocked safety systems for storage ring and photon beamlines (including SR and gas bremsstrahlung) are described. Specific safety issues for storage ring top-off injection operation and FEL facilities are discussed. The operational safety program, e.g., operation authorization, commissioning, training, and radiation measurements, for SR facilities is also presented.
6. Experimental Characterization Of The Saturating, Near Infrared, Self-amplified Spontaneous Emission Free Electron Laser Analysis Of Radiation Properties And Electron Beam Dynamics
CERN Document Server
Murokh, A
2002-01-01
In this work, the main results of the VISA experiment (Visible to Infrared SASE Amplifier) are presented and analyzed. The purpose of the experiment was to build a state-of-the-art single pass self-amplified spontaneous emission (SASE) free electron laser (FEL) based on a high brightness electron beam, and characterize its operation, including saturation, in the near infrared spectral region. This experiment was hosted by Accelerator Test Facility (ATF) at Brookhaven National Laboratory, which is a users facility that provides high brightness relativistic electron beams generated with the photoinjector. During the experiment, SASE FEL performance was studied in two regimes: a long bunch, lower gain operation; and a short bunch high gain regime. The transition between the two conditions was possible due to a novel bunch compression mechanism, which was discovered in the course of the experiment. This compression allowed the variation of peak current in the electron beam before it was launched into the 4-m VISA...
7. Recent results in mirror based high power laser cutting
DEFF Research Database (Denmark)
Olsen, Flemming Ove; Nielsen, Jakob Skov; Elvang, Mads
2004-01-01
In this paper, recent results in high power laser cutting, obtained in reseach and development projects are presented. Two types of mirror based focussing systems for laser cutting have been developed and applied in laser cutting studies on CO2-lasers up to 12 kW. In shipyard environment cutting...... speed increase relative to state-of-the-art cutting of over 100 % has been achieved....
8. A Shuttle based laser system for space communication
Science.gov (United States)
Fitzmaurice, Michael W.; Bruno, Ronald C.
1988-01-01
A key element of NASA-Goddard's plan for future laser space communications is the Space Shuttle-based Laser Technology Experiments Facility (LTEF), which will be designed to communicate with a cooperative laser system under development for the Advanced Communication Technology Satellite (ACTS) and will conduct a comprehensive set of acquisition, tracking, and communication experiments. Attention is presently given to the challenges faced by designers in achieving LTEF acquisition of the ACTS downlink beacon laser.
9. Three electron beams from a laser-plasma wakefield accelerator and the energy apportioning question.
Science.gov (United States)
Yang, X; Brunetti, E; Gil, D Reboredo; Welsh, G H; Li, F Y; Cipiccia, S; Ersfeld, B; Grant, D W; Grant, P A; Islam, M R; Tooley, M P; Vieux, G; Wiggins, S M; Sheng, Z M; Jaroszynski, D A
2017-03-10
Laser-wakefield accelerators are compact devices capable of delivering ultra-short electron bunches with pC-level charge and MeV-GeV energy by exploiting the ultra-high electric fields arising from the interaction of intense laser pulses with plasma. We show experimentally and through numerical simulations that a high-energy electron beam is produced simultaneously with two stable lower-energy beams that are ejected in oblique and counter-propagating directions, typically carrying off 5-10% of the initial laser energy. A MeV, 10s nC oblique beam is ejected in a 30°-60° hollow cone, which is filled with more energetic electrons determined by the injection dynamics. A nC-level, 100s keV backward-directed beam is mainly produced at the leading edge of the plasma column. We discuss the apportioning of absorbed laser energy amongst the three beams. Knowledge of the distribution of laser energy and electron beam charge, which determine the overall efficiency, is important for various applications of laser-wakefield accelerators, including the development of staged high-energy accelerators.
10. Beam dynamics analysis of femtosecond microbunches produced by the staged electron laser acceleration experiment
Directory of Open Access Journals (Sweden)
F. Zhou
2003-05-01
Full Text Available Preservation of the femtosecond (fs microbunches, created during laser acceleration, is a crucial step to enable staging of the laser acceleration process. This paper focuses on the optimization of the beam dynamics of fs microbunches transported through the staged electron laser acceleration (STELLA-II experiment being carried out at the Brookhaven National Laboratory Accelerator Test Facility. STELLA-II consists of an inverse free electron laser (IFEL untapered undulator, which acts as an electron beam energy modulator; a magnetic chicane, which acts as a buncher; a second IFEL tapered undulator, which acts as an accelerator; and a dipole, which serves as an energy spectrometer. When the energy-modulated macrobunch traverses through the chicane and a short drift space, microbunches of order fs in duration (i.e., ∼3 fs FWHM are formed. The 3-fs microbunches are accelerated by interacting with a high-power CO_{2} laser beam in the following tapered undulator. These extremely short microbunches may experience significant space charge and coherent synchrotron radiation effects when traversing the STELLA-II transport line. These effects are analyzed and the safe operating conditions are determined. With less than 0.5-pC microbunch charge, both microbunch debunching and emittance growth are negligible, and the energy-spread increase is less than 5%. These results are also useful for the laser electron acceleration project at SLAC and in possible future programs where the fs microbunches are employed for other purposes.
11. Three electron beams from a laser-plasma wakefield accelerator and the energy apportioning question
Science.gov (United States)
Yang, X.; Brunetti, E.; Gil, D. Reboredo; Welsh, G. H.; Li, F. Y.; Cipiccia, S.; Ersfeld, B.; Grant, D. W.; Grant, P. A.; Islam, M. R.; Tooley, M. P.; Vieux, G.; Wiggins, S. M.; Sheng, Z. M.; Jaroszynski, D. A.
2017-01-01
Laser-wakefield accelerators are compact devices capable of delivering ultra-short electron bunches with pC-level charge and MeV-GeV energy by exploiting the ultra-high electric fields arising from the interaction of intense laser pulses with plasma. We show experimentally and through numerical simulations that a high-energy electron beam is produced simultaneously with two stable lower-energy beams that are ejected in oblique and counter-propagating directions, typically carrying off 5–10% of the initial laser energy. A MeV, 10s nC oblique beam is ejected in a 30°–60° hollow cone, which is filled with more energetic electrons determined by the injection dynamics. A nC-level, 100s keV backward-directed beam is mainly produced at the leading edge of the plasma column. We discuss the apportioning of absorbed laser energy amongst the three beams. Knowledge of the distribution of laser energy and electron beam charge, which determine the overall efficiency, is important for various applications of laser-wakefield accelerators, including the development of staged high-energy accelerators. PMID:28281679
12. Three electron beams from a laser-plasma wakefield accelerator and the energy apportioning question
CERN Document Server
Yang, X; Reboredo Gil, David; Welsh, Gregor H; Li, Y.F; Cipiccia, Silvia; Ersfeld, Bernhard; Grant, D. W; Grant, P. A; Islam, Muhammad; Tooley, M.B; Vieux, Gregory; Wiggins, Sally; Sheng, Zheng-Ming; Jaroszynski, Dino
2017-01-01
Laser-wakefield accelerators are compact devices capable of delivering ultra-short electron bunches with pC-level charge and MeV-GeV energy by exploiting the ultra-high electric fields arising from the interaction of intense laser pulses with plasma. We show experimentally and through numerical simulations that a high-energy electron beam is produced simultaneously with two stable lowerenergy beams that are ejected in oblique and counter-propagating directions, typically carrying off 5–10% of the initial laser energy. A MeV, 10s nC oblique beam is ejected in a 30°–60° hollow cone, which is filled with more energetic electrons determined by the injection dynamics. A nC-level, 100s keV backward-directed beam is mainly produced at the leading edge of the plasma column. We discuss the apportioning of absorbed laser energy amongst the three beams. Knowledge of the distribution of laser energy and electron beam charge, which determine the overall efficiency, is important for various applications of laser-wake...
13. Modified stimulated Raman scattering of a laser induced by trapped electrons in a plasma
Science.gov (United States)
Baliyan, Sweta; Rafat, Mohd.; Ahmad, Nafis; Sajal, Vivek
2017-10-01
The plasma wave, generated in stimulated Raman scattering process by an intense laser in the plasmas, traps a significant number of electrons in its potential energy minima. These electrons travel with the phase velocity of plasma wave and oscillate with bounce frequency. When the bounce frequency of electrons becomes equal to the growth rate of Raman process, resonance takes place. Now, Raman scattering gets modified by parametrically exciting a trapped electron mode and an electromagnetic sideband. The ponderomotive force due to the pump and sideband drives the plasma wave, whereas the density perturbation due to the trapped electron mode couples with the oscillating velocity of electrons due to the laser to produce a nonlinear current, driving the sideband.
14. Scanning electron microscopy comparison of the cleaning efficacy of a root canal system by Nd:YAG laser and rotary instruments.
Science.gov (United States)
Samiei, Mohammad; Pakdel, Seyyed Mahdi Vahid; Rikhtegaran, Sahand; Shakoei, Sahar; Ebrahimpour, Delaram; Taghavi, Pedram
2014-08-01
This study evaluated the cleaning efficacy of a root canal system by Nd:YAG laser and rotary instruments. Sixty single-rooted human teeth were divided into four experimental groups (n=15). In the first group the teeth were prepared with a step-back technique using conventional K-files. In the second and third groups, tooth preparation was carried out using Nd:YAG laser and rotary NiTi instruments, respectively. Teeth in the fourth group were prepared by combined laser and rotary methods. The smear layer remaining on canal walls was then assessed by scanning electron microscopy in the coronal, middle, and apical portions. The comparison of smear layer removal efficacy between groups was carried out by Kruskal-Wallis and Mann-Whitney U tests. The mean grades of smear layer removal in rotary-laser, rotary, laser and step-back techniques were 1.34 ± 0.18, 2.2 ± 0.28, 1.91 ± 0.25, and 2.42 ± 0.19, respectively. On the whole, differences between rotary-laser and rotary groups, step-back, and the three other techniques (rotary, laser, and rotary-laser) were significant at p=0.034. Based on the findings of this study, the cleaning efficacy of rotary, laser, and rotary-laser techniques were better than the step-back technique and the combined laser and rotary technique was the most efficient method.
15. Detecting Molecular Properties by Various Laser-Based Techniques
Energy Technology Data Exchange (ETDEWEB)
Hsin, Tse-Ming [Iowa State Univ., Ames, IA (United States)
2007-01-01
Four different laser-based techniques were applied to study physical and chemical characteristics of biomolecules and dye molecules. These techniques are liole burning spectroscopy, single molecule spectroscopy, time-resolved coherent anti-Stokes Raman spectroscopy and laser-induced fluorescence microscopy. Results from hole burning and single molecule spectroscopy suggested that two antenna states (C708 & C714) of photosystem I from cyanobacterium Synechocystis PCC 6803 are connected by effective energy transfer and the corresponding energy transfer time is ~6 ps. In addition, results from hole burning spectroscopy indicated that the chlorophyll dimer of the C714 state has a large distribution of the dimer geometry. Direct observation of vibrational peaks and evolution of coumarin 153 in the electronic excited state was demonstrated by using the fs/ps CARS, a variation of time-resolved coherent anti-Stokes Raman spectroscopy. In three different solvents, methanol, acetonitrile, and butanol, a vibration peak related to the stretch of the carbonyl group exhibits different relaxation dynamics. Laser-induced fluorescence microscopy, along with the biomimetic containers-liposomes, allows the measurement of the enzymatic activity of individual alkaline phosphatase from bovine intestinal mucosa without potential interferences from glass surfaces. The result showed a wide distribution of the enzyme reactivity. Protein structural variation is one of the major reasons that are responsible for this highly heterogeneous behavior.
16. Autocorrelation measurement of fast electron pulses emitted through the interaction of femtosecond laser pulses with a solid target.
Science.gov (United States)
Inoue, Shunsuke; Tokita, Shigeki; Otani, Kazuto; Hashida, Masaki; Hata, Masayasu; Sakagami, Hitoshi; Taguchi, Toshihiro; Sakabe, Shuji
2012-11-02
We report the first direct measurement of the emission duration of laser-accelerated fast electrons from the surface of a solid target irradiated by a high-intensity femtosecond laser pulse. The emission duration is determined by autocorrelation measurement using the Coulomb repulsive forces that act on two equivalent electron pulses. The emission duration depends on the laser pulse duration for laser pulses of 200-690 fs. Numerical modeling of three-dimensional charged particle dynamics indicates that the emission duration of fast electrons is almost equal to the duration of the laser pulse.
17. Free Electron Laser For Siberian Centre For Photochemical Research The Control System For The Magnet Power Supplies
CERN Document Server
Velikanov, Yu M; Evtushenko, Yu A; Kayran, D A; Kozak, V R; Kuper, E A; Medvedev, L E; Medvedko, A S; Oreshkov, A D; Petrov, S P; Serednyakov, S I; Tararyshkin, S V; Veremeenko, V F; Vinokurov, N A; Zagorodnikov, E I
2004-01-01
A control system for the magnetic system of the free electron laser (FEL) is described. The characteristics and structure of the power supply system are presented. The control system is based on embedded intelligent controllers with the CAN-BUS interfaced. The control software structure and capabilities are described. A possibility of connection of the control software to the integrated control system using the Epics Channel Access protocol is also discussed.
18. Automatic electronic-controlled mode locking self-start in fibre lasers with non-linear polarisation evolution.
Science.gov (United States)
Radnatarov, Daba; Khripunov, Sergey; Kobtsev, Sergey; Ivanenko, Aleksey; Kukarin, Sergey
2013-09-09
The present work demonstrates a fibre-laser system with automatic electronic-controlled triggering of dissipative soliton generation mode. Passive mode locking based on the effect of non-linear polarisation evolution has been achieved through a polarisation controller containing a single low-voltage liquid crystal plate whose optimal wave delay was determined from analysis of inter-mode beat spectrum of the output radiation.
19. Investigation of Plasma Processes in Electronic Transition Lasers
Science.gov (United States)
1985-05-30
Electrical insulator FIG. 1. Illustraiionof heated HgBr(fi|/HgBr, laser discharge cell. 1057 AppI Phys. Lett. 37(12), 15 December1980 003-6951/80/241057... insulated from each other by shielded alumina spacers and, when assembled into the collision chamber, constituted an enclosure from which the loss...nors typically used in rare-gas fluoride lasers. Formation of XeCl(5) by way ofXeCPjyHCl reactions is slightly endo- thermic at 300 °K,’ reflecting the
20. Numerical calculations of the electron beam emittance for laser acceleration experiments
Science.gov (United States)
Balascuta, Septimiu
2017-06-01
At the E6 experimental area at ELI-NP, two 10 PW Laser (pump and probe) pulses, with their directions making an 135° angle, will be used for the study of the radiation reaction, non-linear Thomson scattering, electron beam cooling and other QED phenomena in the relativistic regime. The pump 10 PW Laser beam focused in a gas-jet will generate a plasma wakefield that accelerate electrons by self-injection. The probe 10PW Laser pulse has to be synchronized and focused on the electron bunch. In order to maximize the flux of gamma rays produced in this collision, for a given Laser field intensity, the transversal area of the electron beam at the collision point has to be smaller than the focus of the probe pulse. This work presents the calculation of electron beam emittance and angular divergence, versus the distance traveled by electron bunch in vacuum. A configuration of dipole permanent magnets is proposed for the study of energy distribution of electrons and positrons.
1. Electron-molecule scattering in a strong laser field: Two-center interference effects
Science.gov (United States)
Dakić, J.; Habibović, D.; Čerkić, A.; Busuladžić, M.; Milošević, D. B.
2017-10-01
Laser-assisted scattering of electrons on diatomic molecules is considered using the S -matrix theory within the second Born approximation. The first term of the expansion in powers of the scattering potential corresponds to the direct or single laser-assisted scattering of electrons on molecular targets, while the second term of this expansion corresponds to the laser-assisted rescattering or double scattering. The rescattered electrons may have considerably higher energies in the final state than those that scattered only once. For multicenter polyatomic molecules scattering and rescattering may happen at any center and in any order. All these cases contribute to the scattering amplitude and the interference of different contributions leads to an increase or a decrease of the differential cross section in particular electron energy regions. For diatomic molecules there are two such contributions for single scattering and four contributions for double scattering. Analyzing the spectra of the scattered electrons, we find two interesting effects. For certain molecular orientations, the plateaus in the electron energy spectrum, characteristic of laser-assisted electron-atom scattering, are replaced by a sequence of gradually declining maxima, caused by the two-center interference effects. The second effect is the appearance of symmetric U -shaped structures in the angle-resolved energy spectra, which are described very well by the analytical formulas we provide.
2. Laser-based detection of chemical contraband
Science.gov (United States)
Clemmer, Robert G.; Kelly, James F.; Martin, Steven W.; Mong, Gary M.; Sharpe, Steven W.
1997-02-01
The goal of our work is tow fold; 1) develop a portable and rapid laser based air sampler for detection of specific chemical contraband and 2) compile a spectral data base in both the near- and mid-IR of sufficiently high quality to be useful for gas phase spectroscopic identification of chemical contraband. During the synthesis or 'cooking' of many illicit chemical substances, relatively high concentrations of volatile solvents, chemical precursors and byproducts are unavoidably released to the atmosphere. In some instances, the final product may have sufficient vapor pressure to be detectable in the surrounding air. The detection of a single high-value effluent or the simultaneous detection of two or more low-value effluents can be used as reliable indicators of a nearby clandestine cooking operation. The designation of high- versus low-value effluent reflects both the commercial availability and legitimate usage of a specific chemical. This paper will describe PNNL's progress and efforts towards the development of a portable laser based air sampling system for the detection of clandestine manufacturing of methamphetamine. Although our current efforts ar focused on methamphetamine, we see no fundamental limitations on detection of other forms of chemical contraband manufacturing. This also includes the synthesis of certain classes of chemical weapons that have recently been deployed by terrorist groups.
3. Dynamics of electron acceleration in laser-driven wakefields. Acceleration limits and asymmetric plasma waves
Energy Technology Data Exchange (ETDEWEB)
Popp, Antonia
2011-12-16
The experiments presented in this thesis study several aspects of electron acceleration in a laser-driven plasma wave. High-intensity lasers can efficiently drive a plasma wave that sustains electric fields on the order of 100 GV/m. Electrons that are trapped in this plasma wave can be accelerated to GeV-scale energies. As the accelerating fields in this scheme are 3-4 orders of magnitude higher than in conventional radio-frequency accelerators, the necessary acceleration distance can be reduced by the same factor, turning laser-wakefield acceleration (LWFA) into a promising compact, and potentially cheaper, alternative. However, laser-accelerated electron bunches have not yet reached the parameter standards of conventional accelerators. This work will help to gain better insight into the acceleration process and to optimize the electron bunch properties. The 25 fs, 1.8 J-pulses of the ATLAS laser at the Max-Planck-Institute of Quantum Optics were focused into a steady-state flow gas cell. This very reproducible and turbulence-free gas target allows for stable acceleration of electron bunches. Thus the sensitivity of electron parameters to subtle changes of the experimental setup could be determined with meaningful statistics. At optimized experimental parameters, electron bunches of {approx}50 pC total charge were accelerated to energies up to 450 MeV with a divergence of {approx}2 mrad FWHM. As, in a new design of the gas cell, its length can be varied from 2 to 14 mm, the electron bunch energy could be evaluated after different acceleration distances, at two different electron densities. From this evolution important acceleration parameters could be extracted. At an electron density of 6.43. 10{sup 18} cm{sup -3} the maximum electric field strength in the plasma wave was determined to be {approx}160 GV/m. The length after which the relativistic electrons outrun the accelerating phase of the electric field and are decelerated again, the so-called dephasing length
4. A laser triggered electron source for pulsed radiolysis
CERN Document Server
Monard, H; Le Duff, J; Garvey, Terence; Mouton, B; Rodier, J; Thiery, Y; Gaillard, M
1999-01-01
We present the design of a photo-injector based accelerator for pulsed radiolysis applications. This machine is destined to meet the needs of the physical chemistry community at the Universite de Paris XI. A 4 MeV Energy electron pulse of a few picoseconds duration and with a charge in the range of 1 to 10 nC is produced from a Cs/sub 2 /Te photocathode. The photocathode is placed in the half energy spread cell of a 1-1/2 cell, 3 GHz RF gun, whose design is based on the gun used for the drive beam of the CERN CLIC Test facility. A 4 cell "booster" cavity is then used to accelerate the beam to an energy of 9 MeV. The transport system consists of a quadrupole triplet downsteam of the booster, two rectangular, 30 degree bend, dipoles with a pair of quadrupoles between them and a second triplet downstream of the second dipole. Energy dependent path length effects in the two dipoles allow the possibility of magnetic bunch compression depending on the phase-energy correlation of the bunch exiting the booster cavity...
5. Detailed characterization of electron sources yielding first demonstration of European X-ray Free-Electron Laser beam quality
Directory of Open Access Journals (Sweden)
F. Stephan
2010-02-01
Full Text Available The photoinjector test facility at DESY, Zeuthen site (PITZ, was built to develop and optimize photoelectron sources for superconducting linacs for high-brilliance, short-wavelength free-electron laser (FEL applications like the free-electron laser in Hamburg (FLASH and the European x-ray free-electron laser (XFEL. In this paper, the detailed characterization of two laser-driven rf guns with different operating conditions is described. One experimental optimization of the beam parameters was performed at an accelerating gradient of about 43 MV/m at the photocathode and the other at about 60 MV/m. In both cases, electron beams with very high phase-space density have been demonstrated at a bunch charge of 1 nC and are compared with corresponding simulations. The rf gun optimized for the lower gradient has surpassed all the FLASH requirements on beam quality and rf parameters (gradient, rf pulse length, repetition rate and serves as a spare gun for this facility. The rf gun studied with increased accelerating gradient at the cathode produced beams with even higher brightness, yielding the first demonstration of the beam quality required for driving the European XFEL: The geometric mean of the normalized projected rms emittance in the two transverse directions was measured to be 1.26±0.13 mm mrad for a 1-nC electron bunch. When a 10% charge cut is applied excluding electrons from those phase-space regions where the measured phase-space density is below a certain level and which are not expected to contribute to the lasing process, the normalized projected rms emittance is about 0.9 mm mrad.
6. Selective Two-Photon Absorptive Resonance Femtosecond-Laser Electronic-Excitation Tagging (STARFLEET) Velocimetry in Flow and Combustion Diagnostics
Science.gov (United States)
Jiang, Naibo; Halls, Benjamin R.; Stauffer, Hans U.; Roy, Sukesh; Danehy, Paul M.; Gord, James R.
2016-01-01
Selective Two-Photon Absorptive Resonance Femtosecond-Laser Electronic-Excitation Tagging (STARFLEET), a non-seeded ultrafast-laser-based velocimetry technique, is demonstrated in reactive and non-reactive flows. STARFLEET is pumped via a two-photon resonance in N2 using 202.25-nm 100-fs light. STARFLEET greatly reduces the per-pulse energy required (30 µJ/pulse) to generate the signature FLEET emission compared to the conventional FLEET technique (1.1 mJ/pulse). This reduction in laser energy results in less energy deposited in the flow, which allows for reduced flow perturbations (reactive and non-reactive), increased thermometric accuracy, and less severe damage to materials. Velocity measurements conducted in a free jet of N2 and in a premixed flame show good agreement with theoretical velocities and further demonstrate the significantly less-intrusive nature of STARFLEET.
7. A mirrorless photonic free-electron laser oscillator
NARCIS (Netherlands)
van der Slot, P.J.M.; Strooisma, A.; Denis, T.; Boller, Klaus J.
2017-01-01
Photonic crystals have been used to provide fundamental control over the interaction between light and matter, including stimulated emission. For example, in Bloch-mode lasers, the photonic crystal provides field enhancement through reduced group velocity and offers larger mode volumes through
8. A Cerenkov free electron laser with high peak power
NARCIS (Netherlands)
van der Slot, Petrus J.M.; Couperus, J.; Witteman, W.J.; Lebedev, A.N.; Krastelev, E.G.; Agafonov, A.V.; Voronin, V.S.; Krasnopolsky, V.A.
1995-01-01
A Cherenkov FEL can be a suitable source for radiation from the millimeter wavelength region down to the far infrared. With only a few different dielectric materials the laser can range from 6 mm down to ¿ 600 ¿m. Nonlinear theory shows, for an amplifier configuration, power levels of about 100 kW
9. Beam Diagnostics for Laser Undulator Based on Compton Backward Scattering
CERN Document Server
Kuroda, R
2005-01-01
A compact soft X-ray source is required in various research fields such as material and biological science. The laser undulator based on Compton backward scattering has been developed as a compact soft X-ray source for the biological observation at Waseda University. It is performed in a water window region (250eV - 500 eV) using the interaction between 1047 nm Nd:YLF laser (10ps FWHM) and about 5 MeV high quality electron beam (10ps FWHM) generated from rf gun system. The range of X-ray energy in the water window region has K-shell absorption edges of Oxygen, Carbon and Nitrogen, which mainly constitute of living body. Since the absorption coefficient of water is much smaller than the protein's coefficient in this range, a dehydration of the specimens is not necessary. To generate the soft X-ray pulse stably, the electron beam diagnostics have been developed such as the emittance measurement using double slit scan technique, the bunch length measurement using two frequency analysis technique. In this confere...
10. Intense γ ray generated by refocusing laser pulse on wakefield accelerated electrons
Science.gov (United States)
Feng, Jie; Wang, Jinguang; Li, Yifei; Zhu, Changqing; Li, Minghua; He, Yuhang; Li, Dazhang; Wang, Weimin; Chen, Liming
2017-09-01
Ultrafast x/γ ray emission from the combination of laser wake-field acceleration and plasma mirror has been investigated as a promising Thomson scattering source. However, the photon energy and yield of radiation are limited to the intensity of reflected laser pulses. We use the 2D particle in cell simulation to demonstrate that a 75TW driven laser pulse can be refocused on the accelerated electron bunches through a hemispherical plasma mirror with a small f number of 0.25. The energetic electrons with the maximum energy about 350 MeV collide with the reflected laser pulse of a0 = 3.82 at the focal spot, producing high order multi-photon Thomson scattering, and resulting in the scattering spectrum which extends up to 21.2 MeV. Such a high energy γ ray source could be applied to photonuclear reaction and materials science.
11. Plasma mirror implementation on LFEX laser for ion and fast electron fast ignition
Science.gov (United States)
Morace, A.; Kojima, S.; Arikawa, Y.; Fujioka, S.; Yogo, A.; Tosaki, S.; Sakata, S.; Abe, Y.; Lee, S. H.; Matsuo, K.; Sagisaka, A.; Kondo, K.; Pirozhkov, A. S.; Norimatsu, T.; Jitsuno, T.; Miyanaga, N.; Shiraga, H.; Nakai, M.; Nishimura, H.; Azechi, H.
2017-12-01
In this work we report the successful implementation of plasma mirror (PM) technology on an LFEX laser facility at the Institute of Laser Engineering, Osaka University. The LFEX laser pulse was successfully refocused at the target chamber center (TCC) by means of a spherical plasma mirror, resulting in 5 × 1018 W cm-2 laser intensity, with 45% reflectivity at a laser flux of about 90 J cm-2 on the PM. Experimental results show stable focusing and pointing of the LFEX pulse after PM refocusing. The contrast improvement was demonstrated by both cooler fast electron slope temperature distribution as well as by the ability to shoot sub-µm plastic foils obtaining proton beams with maximum energy exceeding 20 MeV. Experimental results are qualitatively reproduced by 2D particle in cell simulations.
12. Plasma optical modulation for lasers based on the plasma induced by femtosecond pulses.
Science.gov (United States)
Tan, Chao; Fu, Xiquan; Hu, Yonghua; Deng, Yangbao; Shi, Xiaohui; Zhan, Shiping; Xi, Zaifang
2017-06-26
We present a theoretical and experimental study of plasma optical modulation for probe lasers based on the plasma induced by pump pulses. This concept relies on two co-propagating laser pulses in carbon disulfide, where a drive laser pulse first excites plasma channels while a following carrier laser pulse is modulated by the plasma. The modulation on the probe beam can be conveniently adjusted through electron density, plasma width, propagation distance of plasma, the power of pump lasers, or the pump beam's profile. The experimental results and theoretical solutions are very consistent, which fully illustrates that this method for plasma optical modulation is reasonable. This pump-probe method is also a potential measurement technique for inferring the on-axis plasma density shape.
13. Advancement of High Power Quasi-CW Laser Diode Arrays For Space-based Laser Instruments
Science.gov (United States)
Amzajerdian, Farzin; Meadows, Byron L.; Baker, nathaniel R.; Baggott, Renee S.; Singh, Upendra N.; Kavaya, Michael J.
2004-01-01
Space-based laser and lidar instruments play an important role in NASA s plans for meeting its objectives in both Earth Science and Space Exploration areas. Almost all the lidar instrument concepts being considered by NASA scientist utilize moderate to high power diode-pumped solid state lasers as their transmitter source. Perhaps the most critical component of any solid state laser system is its pump laser diode array which essentially dictates instrument efficiency, reliability and lifetime. For this reason, premature failures and rapid degradation of high power laser diode arrays that have been experienced by laser system designers are of major concern to NASA. This work addresses these reliability and lifetime issues by attempting to eliminate the causes of failures and developing methods for screening laser diode arrays and qualifying them for operation in space.
14. Determination of the electron affinity of astatine and polonium by laser photodetachment
CERN Multimedia
We propose to conduct the first electron affinity (EA) measurements of the two elements astatine (At) and polonium (Po). Collinear photo-detachment spectroscopy will allow us to measure these quantities with an uncertainty limited only by the spectral line width of the laser. We plan to use negative ion beams of the two radioactive elements At and Po, which are only accessible on-line and at ISOLDE. The feasibility of our proposed method and the functionality of the experimental setup have been demonstrated at ISOLDE in off-line tests by the clear observation of the photo-detachment threshold for stable iodine. This proposal is based on our Letter of Intent I-148.
15. Undulator beamline optimization with integrated chicanes for X-ray free-electron-laser facilities.
Science.gov (United States)
Prat, Eduard; Calvi, Marco; Ganter, Romain; Reiche, Sven; Schietinger, Thomas; Schmidt, Thomas
2016-07-01
An optimization of the undulator layout of X-ray free-electron-laser (FEL) facilities based on placing small chicanes between the undulator modules is presented. The installation of magnetic chicanes offers the following benefits with respect to state-of-the-art FEL facilities: reduction of the required undulator length to achieve FEL saturation, improvement of the longitudinal coherence of the FEL pulses, and the ability to produce shorter FEL pulses with higher power levels. Numerical simulations performed for the soft X-ray beamline of the SwissFEL facility show that optimizing the advantages of the layout requires shorter undulator modules than the standard ones. This proposal allows a very compact undulator beamline that produces fully coherent FEL pulses and it makes possible new kinds of experiments that require very short and high-power FEL pulses.
16. Time-dependent density-functional theory simulation for electron-ion dynamics in molecules under intense laser pulses.
Science.gov (United States)
Kawashita, Y; Nakatsukasa, T; Yabana, K
2009-02-11
We have developed a simulation method to describe three-dimensional dynamics of electrons and ions in a molecule based on the time-dependent density-functional theory. We solve the time-dependent Kohn-Sham equation for electrons employing the real-space and real-time method, while the ion dynamics are described in classical mechanics by the Ehrenfest method. For an efficient calculation in massively parallel computers, the code is parallelized dividing the spatial grid points. We apply the method to the Coulomb explosion of the H(2)S molecule under an intense and ultrashort laser pulse and investigate the mechanism of the process.
17. Analytic description of elastic electron-atom scattering in an elliptically polarized laser field
Science.gov (United States)
Flegel, A. V.; Frolov, M. V.; Manakov, N. L.; Starace, Anthony F.; Zheltukhin, A. N.
2013-01-01
An analytic description of laser-assisted electron-atom scattering (LAES) in an elliptically polarized field is presented using time-dependent effective range (TDER) theory to treat both electron-laser and electron-atom interactions nonperturbatively. Closed-form formulas describing plateau features in LAES spectra are derived quantum mechanically in the low-frequency limit. These formulas provide an analytic explanation for key features of the LAES differential cross section. For the low-energy region of the LAES spectrum, our result generalizes the Kroll-Watson formula to the case of elliptic polarization. For the high-energy (rescattering) plateau in the LAES spectrum, our result generalizes prior results for a linearly polarized field valid for the high-energy end of the rescattering plateau [Flegel , J. Phys. BJPAPEH0953-407510.1088/0953-4075/42/24/241002 42, 241002 (2009)] and confirms the factorization of the LAES cross section into three factors: two field-free elastic electron-atom scattering cross sections (with laser-modified momenta) and a laser field-dependent factor (insensitive to the scattering potential) describing the laser-driven motion of the electron in the elliptically polarized field. We present also approximate analytic expressions for the exact TDER LAES amplitude that are valid over the entire rescattering plateau and reduce to the three-factor form in the plateau cutoff region. The theory is illustrated for the cases of e-H scattering in a CO2-laser field and e-F scattering in a midinfrared laser field of wavelength λ=3.5μm, for which the analytic results are shown to be in good agreement with exact numerical TDER results.
18. Heat-Flux Measurements in Laser-Produced Plasmas Using Thomson Scattering from Electron Plasma Waves
Science.gov (United States)
Henchen, R. J.; Goncharov, V. N.; Cao, D.; Katz, J.; Froula, D. H.; Rozmus, W.
2017-10-01
An experiment was designed to measure heat flux in coronal plasmas using collective Thomson scattering. Adjustments to the electron distribution function resulting from heat flux affect the shape of the collective Thomson scattering features through wave-particle resonance. The amplitude of the Spitzer-Härm electron distribution function correction term (f1) was varied to match the data and determines the value of the heat flux. Independent measurements of temperature and density obtained from Thomson scattering were used to infer the classical heat flux (q = - κ∇Te) . Time-resolved Thomson-scattering data were obtained at five locations in the corona along the target normal in a blowoff plasma formed from a planar Al target with 1.5 kJ of 351-nm laser light in a 2-ns square pulse. The flux measured through the Thomson-scattering spectra is a factor of 5 less than the κ∇Te measurements. The lack of collisions of heat-carrying electrons suggests a nonlocal model is needed to accurately describe the heat flux. This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0001944.
19. Laser-Driven Very High Energy Electron/Photon Beam Radiation Therapy in Conjunction with a Robotic System
Directory of Open Access Journals (Sweden)
Kazuhisa Nakajima
2014-12-01
Full Text Available We present a new external-beam radiation therapy system using very-high-energy (VHE electron/photon beams generated by a centimeter-scale laser plasma accelerator built in a robotic system. Most types of external-beam radiation therapy are delivered using a machine called a medical linear accelerator driven by radio frequency (RF power amplifiers, producing electron beams with an energy range of 6–20 MeV, in conjunction with modern radiation therapy technologies for effective shaping of three-dimensional dose distributions and spatially accurate dose delivery with imaging verification. However, the limited penetration depth and low quality of the transverse penumbra at such electron beams delivered from the present RF linear accelerators prevent the implementation of advanced modalities in current cancer treatments. These drawbacks can be overcome if the electron energy is increased to above 50 MeV. To overcome the disadvantages of the present RF-based medical accelerators, harnessing recent advancement of laser-driven plasma accelerators capable of producing 1-GeV electron beams in a 1-cm gas cell, we propose a new embodiment of the external-beam radiation therapy robotic system delivering very high-energy electron/photon beams with an energy of 50–250 MeV; it is more compact, less expensive, and has a simpler operation and higher performance in comparison with the current radiation therapy system.
20. Temporal characterization of ultrashort linearly chirped electron bunches generated from a laser wakefield accelerator
Directory of Open Access Journals (Sweden)
C. J. Zhang
2016-06-01
Full Text Available A new method for diagnosing the temporal characteristics of ultrashort electron bunches with linear energy chirp generated from a laser wakefield accelerator is described. When the ionization-injected bunch interacts with the back of the drive laser, it is deflected and stretched along the direction of the electric field of the laser. Upon exiting the plasma, if the bunch goes through a narrow slit in front of the dipole magnet that disperses the electrons in the plane of the laser polarization, it can form a series of bunchlets that have different energies but are separated by half a laser wavelength. Since only the electrons that are undeflected by the laser go through the slit, the energy spectrum of the bunch is modulated. By analyzing the modulated energy spectrum, the shots where the bunch has a linear energy chirp can be recognized. Consequently, the energy chirp and beam current profile of those bunches can be reconstructed. This method is demonstrated through particle-in-cell simulations and experiment.
1. Vehicle Based Laser Range Finding in Crops
OpenAIRE
Hans-Juergen Horn; Rolf Adamek; Detlef Ehlert
2009-01-01
Laser rangefinders and laser scanners are widely used for industrial purposes and for remote sensing. In agriculture information about crop parameters like volume, height, and density can support the optimisation of production processes. In scientific papers the measurement of these parameters by low cost laser rangefinders with one echo has been presented for short ranges. Because the cross section area of the beam increases with the measuring range, it can be expected that laser rangefinder...
2. Obtaining attosecond x-ray pulses using a self-amplified spontaneous emission free electron laser
Directory of Open Access Journals (Sweden)
A. A. Zholents
2005-05-01
Full Text Available We describe a technique for the generation of a solitary attosecond x-ray pulse in a free-electron laser (FEL, via a process of self-amplified spontaneous emission. In this method, electrons experience an energy modulation upon interacting with laser pulses having a duration of a few cycles within single-period wiggler magnets. Two consecutive modulation sections, followed by compression in a dispersive section, are used to obtain a single, subfemtosecond spike in the electron peak current. This region of the electron beam experiences an enhanced growth rate for FEL amplification. After propagation through a long undulator, this current spike emits a ∼250 attosecond x-ray pulse whose intensity dominates the x-ray emission from the rest of the electron bunch.
3. Energetic electron-bunch generation in a phase-locked longitudinal laser electric field.
Science.gov (United States)
Xiao, K D; Huang, T W; Ju, L B; Li, R; Yang, S L; Yang, Y C; Wu, S Z; Zhang, H; Qiao, B; Ruan, S C; Zhou, C T; He, X T
2016-04-01
Energetic electron acceleration processes in a plasma hollow tube irradiated by an ultraintense laser pulse are investigated. It is found that the longitudinal component of the laser field is much enhanced when a linear polarized Gaussian laser pulse propagates through the plasma tube. This longitudinal field is of π/2 phase shift relative to the transverse electric field and has a π phase interval between its upper and lower parts. The electrons in the plasma tube are first pulled out by the transverse electric field and then trapped by the longitudinal electric field. The trapped electrons can further be accelerated to higher energy in the presence of the longitudinal electric field. This acceleration mechanism is clearly illustrated by both particle-in-cell simulations and single particle modelings.
4. Electron injection and emittance control by transverse colliding pulses in a laser-plasma accelerator
Directory of Open Access Journals (Sweden)
M. Chen
2014-05-01
Full Text Available A method to inject electron beams with controllable transverse emittances in a laser-plasma accelerators is proposed and analyzed. It uses two colliding laser pulses that propagate transversely to the plasma wave. For colliding pulses with equal frequencies, a beam with very low emittance is generated when the collision is close to the density peak of the plasma wave. Electrons near the axis are accelerated longitudinally by the ponderomotive force of the colliding pulses, accelerated transversely by the beat wave, and subsequently injected into the second bucket of the wake. Ionization is used to increase the transverse injection area and the final trapped charge. Simulations show that the transverse emittance can be less than the 0.1 mm mrad level, which is important for many applications. For colliding laser pulses with different frequencies, the beat wave can produce asymmetric injection, which can enhance betatron radiation generated by the electron beam.
5. Short period, high field cryogenic undulator for extreme performance x-ray free electron lasers
Directory of Open Access Journals (Sweden)
F. H. O’Shea
2010-07-01
Full Text Available Short period, high field undulators can enable short wavelength free electron lasers (FELs at low beam energy, with decreased gain length, thus allowing much more compact and less costly FEL systems. We describe an ongoing initiative to develop such an undulator based on an approach that utilizes novel cryogenic materials. While this effort was begun in the context of extending the photon energy regime of a laser-plasma accelerator based electron source, we consider here implications of its application to sub-fs scenarios in which more conventional injectors are employed. The use of such low-charge, ultrashort beams, which has recently been proposed as a method of obtaining single-spike performance in x-ray FELs, is seen in simulation to give unprecedented beam brightness. This brightness, when considered in tandem with short wavelength, high field undulators, enables extremely high performance FELs. Two examples discussed in this paper illustrate this point well. The first is the use of the SPARX injector at 2.1 GeV with 1 pC of charge to give 8 GW peak power in a single spike at 6.5 Å with a photon beam peak brightness greater than 10^{35} photons/(s mm^{2} mrad^{2} 0.1% BW, which will also reach LCLS wavelengths on the 5th harmonic. The second is the exploitation of the LCLS injector with 0.25 pC, 150 as pulses to lase at 1.5 Å using only 4.5 GeV energy; beyond this possibility, we present start-to-end simulations of lasing at unprecedented short wavelength, 0.15 Å, using 13.65 GeV LCLS design energy.
6. Specular Reflectivity and Hot-Electron Generation in High-Contrast Relativistic Laser-Plasma Interactions
Energy Technology Data Exchange (ETDEWEB)
Kemp, Gregory Elijah [The Ohio State Univ., Columbus, OH (United States)
2013-01-01
Ultra-intense laser (> 1018 W/cm2) interactions with matter are capable of producing relativistic electrons which have a variety of applications in state-of-the-art scientific and medical research conducted at universities and national laboratories across the world. Control of various aspects of these hot-electron distributions is highly desired to optimize a particular outcome. Hot-electron generation in low-contrast interactions, where significant amounts of under-dense pre-plasma are present, can be plagued by highly non-linear relativistic laser-plasma instabilities and quasi-static magnetic field generation, often resulting in less than desirable and predictable electron source characteristics. High-contrast interactions offer more controlled interactions but often at the cost of overall lower coupling and increased sensitivity to initial target conditions. An experiment studying the differences in hot-electron generation between high and low-contrast pulse interactions with solid density targets was performed on the Titan laser platform at the Jupiter Laser Facility at Lawrence Livermore National Laboratory in Livermore, CA. To date, these hot-electrons generated in the laboratory are not directly observable at the source of the interaction. Instead, indirect studies are performed using state-of-the-art simulations, constrained by the various experimental measurements. These measurements, more-often-than-not, rely on secondary processes generated by the transport of these electrons through the solid density materials which can susceptible to a variety instabilities and target material/geometry effects. Although often neglected in these types of studies, the specularly reflected light can provide invaluable insight as it is directly influenced by the interaction. In this thesis, I address the use of (personally obtained) experimental specular reflectivity measurements to indirectly study hot-electron generation in the context of high-contrast, relativistic
7. Solar-pumped electronic-to-vibrational energy transfer lasers
Science.gov (United States)
Harries, W. L.; Wilson, J. W.
1981-01-01
The possibility of using solar-pumped lasers as solar energy converters is examined. The absorbing media considered are halogens or halogen compounds, which are dissociated to yield excited atoms, which then hand over energy to a molecular lasing medium. Estimates of the temperature effects for a Br2-CO2-He system with He as the cooling gas are given. High temperatures can cause the lower energy levels of the CO2 laser transition to be filled. The inverted populations are calculated and lasing should be possible. However, the efficiency is less than 0.001. Examination of other halogen-molecular lasant combinations (where the rate coefficients are known) indicate efficiencies in all cases of less than 0.005.
8. Extremely short relativistic-electron-bunch generation in the laser wakefield via novel bunch injection scheme
Directory of Open Access Journals (Sweden)
A. G. Khachatryan
2004-12-01
Full Text Available Recently a new electron-bunch injection scheme for the laser wakefield accelerator has been proposed [JETP Lett. 74, 371 (2001JTPLA20021-364010.1134/1.1427124; Phys. Rev. E 65, 046504 (2002PLEEE81063-651X10.1103/PhysRevE.65.046504]. In this scheme, a low energy electron bunch, sent in a plasma channel just before a high-intensity laser pulse, is trapped in the laser wakefield, considerably compressed and accelerated to an ultrarelativistic energy. In this paper we show the possibility of the generation of an extremely short (on the order of 1 μm long or a few femtoseconds in duration relativistic-electron-bunch by this mechanism. The initial electron bunch, which can be generated, for example, by a laser-driven photocathode rf gun, should have an energy of a few hundred keVs to a few MeVs, a duration in the picosecond range or less and a relatively low concentration. The trapping conditions and parameters of an accelerated bunch are investigated. The laser pulse dynamics as well as a possible experimental setup for the demonstration of the injection scheme are also considered.
9. Space-charge effects in ultrahigh current electron bunches generated by laser-plasma accelerators
Directory of Open Access Journals (Sweden)
F. J. Grüner
2009-02-01
Full Text Available Recent advances in laser-plasma accelerators, including the generation of GeV-scale electron bunches, enable applications such as driving a compact free-electron laser (FEL. Significant reduction in size of the FEL is facilitated by the expected ultrahigh peak beam currents (10–100 kA generated in laser-plasma accelerators. At low electron energies such peak currents are expected to cause space-charge effects such as bunch expansion and induced energy variations along the bunch, potentially hindering the FEL process. In this paper we discuss a self-consistent approach to modeling space-charge effects for the regime of laser-plasma-accelerated ultracompact electron bunches at low or moderate energies. Analytical treatments are considered as well as point-to-point particle simulations, including the beam transport from the laser-plasma accelerator through focusing devices and the undulator. In contradiction to non-self-consistent analyses (i.e., neglecting bunch evolution, which predict a linearly growing energy chirp, we have found the energy chirp reaches a maximum and decreases thereafter. The impact of the space-charge induced chirp on FEL performance is discussed and possible solutions are presented.
10. Effects of the precursor electron bunch on quasi-phase matched direct laser acceleration
Science.gov (United States)
Lin, M.-W.; Hsieh, C.-Y.; Liu, Y.-L.; Chen, S.-H.; Jovanovic, I.
2016-12-01
Direct laser acceleration (DLA) of electrons can be achieved by utilizing the axial field of a well-guided, radially polarized laser pulse in a density-modulated plasma waveguide. When a laser pulse of a few terawatt (TW) peak power is applied, however, the laser ponderomotive force perturbs plasma electrons to concentrate in the center, such that the generated electrostatic fields can significantly defocus the externally injected electron witness bunch and considerably deteriorate the acceleration efficiency. To improve the performance of DLA, a leading electron bunch, which acts as a precursor, can be introduced in DLA to effectively confine the witness bunch. Three-dimensional particle-in-cell simulations have been conducted to demonstrate that the transverse properties of the witness bunch can be significantly improved when a precursor bunch is used. Selected bunch transverse sizes, bunch charges, and axial separation from the witness bunch have been assigned to the precursor in a series of DLA simulations. Since a favorable ion-focusing force is provided by the precursor, the transverse properties of witness bunch can be maintained when a relatively high-power (˜2 TW) laser pulse is used in DLA, and an improved overall acceleration efficiency can be achieved.
11. Analysis of data transmission technique based on pulsed laser
Science.gov (United States)
Drozd, T.; Zygmunt, M.; Knysak, P.; Wojtanowski, J.
2012-03-01
Pulsed lasers are used mainly in lidar systems as sources of short and highly energetic light pulses. In data transmission systems continuous wave lasers are typically applied, however it is also possible to use pulsed lasers in such systems. Such approach seems to be especially reasonable for devices where a pulsed laser is applied anyway and executes another function (rangefinding). The article discusses a data transmission concept based on a pulsed laser technology. Advantages and limits of such a transmission method are described. Influence of individual transmission elements on the effective data transmission speed is analysed.
12. Laser Direct Write micro-fabrication of large area electronics on flexible substrates
Energy Technology Data Exchange (ETDEWEB)
Zacharatos, F.; Makrygianni, M. [National Technical University of Athens, Physics Department, Zografou Campus, 15780 (Greece); Geremia, R.; Biver, E.; Karnakis, D. [Oxford Lasers Ltd, Unit 8 Moorbrook Park, Oxfordshire OX11 7HP (United Kingdom); Leyder, S.; Puerto, D.; Delaporte, P. [Aix-Marseille University, CNRS, LP3 – UMR 7341, 13288 Marseille Cedex 9 (France); Zergioti, I., E-mail: [email protected] [National Technical University of Athens, Physics Department, Zografou Campus, 15780 (Greece)
2016-06-30
Highlights: • Laser Direct Writing of metallic patterns with a minimum feature size of 1 μm. • Selective Laser Ablation of 50 nm thick metal films on flexible substrates. • Selective Laser sintering resulting in an electrical resistivity of 9 μΩ cm. • Laser fabrication of interdigitated electrodes for sensor applications. - Abstract: To date, Laser Direct Write (LDW) techniques, such as Laser Induced Forward Transfer (LIFT), selective laser ablation and selective laser sintering of metal nanoparticle (NP) ink layers are receiving growing attention for the printing of uniform and well-defined conductive patterns with resolution down to 10 μm. For flexible substrates in particular, selective laser sintering of such NP patterns has been widely applied, as a low temperature and high resolution process compatible with large area electronics. In this work, LDW of silver NP inks has been carried out on polyethylene-terephthalate (PET), polyethylene-naphthalate (PEN) and polyimide (PI) substrates to achieve low electrical resistivity electrodes. In more detail, high speed short pulsed (picosecond and nanosecond) lasers with repetition rates up to 1 MHz were used to print (LIFT) metal NP inks. We thus achieved uniform and continuous patterns with a minimum feature size of 1 μm and a total footprint larger than 1 cm{sup 2}. Next, the printed patterns were laser sintered with ns pulses at 532 nm over a wide laser fluence window, resulting in an electrical resistivity of 10 μΩ cm. We carried out spatial beam shaping experiments to achieve a top-hat laser intensity profile and employed selective laser ablation of thin films (thickness on the order of 100 nm) to produce silver micro-electrodes with a resolution on the order of 10 μm and a low line edge roughness. Laser sintering was combined with laser ablation to constitute a fully autonomous micro-patterning technique of metallic micro-features, with a 10 μm resolution and geometrical characteristics tuned for
13. Ultrafast electron diffraction from non-equilibrium phonons in femtosecond laser heated Au films
Energy Technology Data Exchange (ETDEWEB)
Chase, T. [Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, California 94025 (United States); Department of Applied Physics, Stanford University, Stanford, California 94305 (United States); Trigo, M.; Reid, A. H.; Dürr, H. A. [Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, California 94025 (United States); Li, R.; Vecchione, T.; Shen, X.; Weathersby, S.; Coffee, R.; Hartmann, N.; Wang, X. J. [SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, California 94025 (United States); Reis, D. A. [Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, California 94025 (United States); Department of Applied Physics, Stanford University, Stanford, California 94305 (United States); PULSE Institute, SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, California 94025 (United States)
2016-01-25
We use ultrafast electron diffraction to detect the temporal evolution of non-equilibrium phonons in femtosecond laser-excited ultrathin single-crystalline gold films. From the time-dependence of the Debye-Waller factor, we extract a 4.7 ps time-constant for the increase in mean-square atomic displacements. The observed increase in the diffuse scattering intensity demonstrates that the energy transfer from laser-heated electrons to phonon modes near the X and K points in the Au fcc Brillouin zone proceeds with timescales of 2.3 and 2.9 ps, respectively, faster than the Debye-Waller average mean-square displacement.
14. A “slingshot” laser-driven acceleration mechanism of plasma electrons
Energy Technology Data Exchange (ETDEWEB)
Fiore, Gaetano, E-mail: [email protected] [Dip. di Matematica e Applicazioni, Università “Federico II”, Complesso Universitario M. S. Angelo, Via Cintia, 80126 Napoli (Italy); INFN, Sezione di Napoli, Complesso Universitario M. S. Angelo, Via Cintia, 80126 Napoli (Italy); De Nicola, Sergio [SPIN-CNR, Complesso Universitario M. S. Angelo, Via Cintia, 80126 Napoli (Italy); INFN, Sezione di Napoli, Complesso Universitario M. S. Angelo, Via Cintia, 80126 Napoli (Italy)
2016-09-01
We briefly report on the recently proposed Fiore et al. [1] and Fiore and De Nicola [2] electron acceleration mechanism named “slingshot effect”: under suitable conditions the impact of an ultra-short and ultra-intense laser pulse against the surface of a low-density plasma is expected to cause the expulsion of a bunch of superficial electrons with high energy in the direction opposite to that of the pulse propagation; this is due to the interplay of the huge ponderomotive force, huge longitudinal field arising from charge separation, and the finite size of the laser spot.
15. Effects of front-surface target structures on properties of relativistic laser-plasma electrons.
Science.gov (United States)
Jiang, S; Krygier, A G; Schumacher, D W; Akli, K U; Freeman, R R
2014-01-01
We report the results of a study of the role of prescribed geometrical structures on the front of a target in determining the energy and spatial distribution of relativistic laser-plasma electrons. Our three-dimensional particle-in-cell simulation studies apply to short-pulse, high-intensity laser pulses, and indicate that a judicious choice of target front-surface geometry provides the realistic possibility of greatly enhancing the yield of high-energy electrons while simultaneously confining the emission to narrow (<5°) angular cones.
16. Submillimeter-resolution radiography of shielded structures with laser-accelerated electron beams
OpenAIRE
Vidya Ramanathan; Sudeep Banerjee; Nathan Powers; Nathaniel Cunningham; Nathan A. Chandler-Smith; Kun Zhao; Kevin Brown; Donald Umstadter; Shaun Clarke; Sara Pozzi; James Beene; Vane, C R; David Schultz
2010-01-01
We investigate the use of energetic electron beams for high-resolution radiography of flaws embedded in thick solid objects. A bright, monoenergetic electron beam (with energy >100 MeV) was generated by the process of laser-wakefield acceleration through the interaction of 50-TW, 30-fs laser pulses with a supersonic helium jet. The high energy, low divergence, and small source size of these beams make them ideal for high-resolution radiographic studies of cracks or voids embedded in dense ma...
17. Submillimeter-resolution radiography of shielded structures with laser-accelerated electron beams
Directory of Open Access Journals (Sweden)
Vidya Ramanathan
2010-10-01
Full Text Available We investigate the use of energetic electron beams for high-resolution radiography of flaws embedded in thick solid objects. A bright, monoenergetic electron beam (with energy >100 MeV was generated by the process of laser-wakefield acceleration through the interaction of 50-TW, 30-fs laser pulses with a supersonic helium jet. The high energy, low divergence, and small source size of these beams make them ideal for high-resolution radiographic studies of cracks or voids embedded in dense materials that are placed at a large distance from the source. We report radiographic imaging of steel with submillimeter resolution.
18. Submillimeter-Resolution Radiography of Shielded Structures with Laser-Accelerated Electron Beams
Energy Technology Data Exchange (ETDEWEB)
Ramanathan, Vidya [University of Nebraska, Lincoln; Banerjee, Sudeep [University of Nebraska, Lincoln; Powell, Nathan [University of Nebraska, Lincoln; Cummingham, N. J. [University of Nebraska, Lincoln; Chandler-Smith, Nate [University of Nebraska, Lincoln; Zhao, Kun [University of Nebraska, Lincoln; Brown, Kevin [University of Nebraska, Lincoln; Umstadter, Donald [University of Nebraska, Lincoln; Clarke, Shaun [University of Michigan; Pozzi, Sara [University of Michigan; Beene, James R [ORNL; Vane, C Randy [ORNL; Schultz, David Robert [ORNL
2010-10-01
We investigate the use of energetic electron beams for high-resolution radiography of flaws embedded in thick solid objects. A bright, monoenergetic electron beam (with energy >100 MeV) was generated by the process of laser-wakefield acceleration through the interaction of 50-TW, 30-fs laser pulses with a supersonic helium jet. The high energy, low divergence, and small source size of these beams make them ideal for high-resolution radiographic studies of cracks or voids embedded in dense materials that are placed at a large distance from the source. We report radiographic imaging of steel with submillimeter resolution.
19. Projection imaging with directional electron and proton beams emitted from an ultrashort intense laser-driven thin foil target
Science.gov (United States)
Nishiuchi, M.; Choi, I. W.; Daido, H.; Nakamura, T.; Pirozhkov, A. S.; Yogo, A.; Ogura, K.; Sagisaka, A.; Orimo, S.; Daito, I.; Bulanov, S. V.; Sung, J. H.; Lee, S. K.; Yu, T. J.; Jeong, T. M.; Kim, I. J.; Kim, C. M.; Kang, S. W.; Pae, K. H.; Oishi, Y.; Lee, J.
2015-02-01
Projection images of a metal mesh produced by directional MeV electron beam together with directional proton beam, emitted simultaneously from a thin foil target irradiated by an ultrashort intense laser, are recorded on an imaging plate for the electron imaging and on a CR-39 nuclear track detector for the proton imaging. The directional electron beam means the portion of the electron beam which is emitted along the same direction (i.e., target normal direction) as the proton beam. The mesh patterns are projected to each detector by the electron beam and the proton beam originated from tiny virtual sources of ~20 µm and ~10 µm diameters, respectively. Based on the observed quality and magnification of the projection images, we estimate sizes and locations of the virtual sources for both beams and characterize their directionalities. To carry out physical interpretation of the directional electron beam qualitatively, we perform 2D particle-in-cell simulation which reproduces a directional escaping electron component, together with a non-directional dragged-back electron component, the latter mainly contributes to building a sheath electric field for proton acceleration. The experimental and simulation results reveal various possible applications of the simultaneous, synchronized electron and proton sources to radiography and pump-probe measurements with temporal resolution of ~ps and spatial resolution of a few tens of µm.
20. Cleaning space debris with a space-based laser system
Directory of Open Access Journals (Sweden)
Shen Shuangyan
2014-08-01
Full Text Available High-energy pulsed laser radiation may be the most feasible means to mitigate the threat of collision of a space station or other valuable space assets with orbital debris in the size range of 1–10 cm. Under laser irradiation, part of the debris material is ablated and provides an impulse to the debris particle. Proper direction of the impulse vector either deflects the object trajectory or forces the debris on a trajectory through the upper atmosphere, where it burns up. Most research concentrates on ground-based laser systems but pays little attention to space-based laser systems. There are drawbacks of a ground-based laser system in cleaning space debris. Therefore the placement of a laser system in space is proposed and investigated. Under assumed conditions, the elimination process of space debris is analyzed. Several factors such as laser repetition frequency, relative movement between the laser and debris, and inclination of debris particles which may exercise influence to the elimination effects are discussed. A project of a space-based laser system is proposed according to the numerical results of a computer study. The proposed laser system can eliminate debris of 1–10 cm and succeed in protecting a space station.
1. Proposed Physics Experiments for Laser-Driven Electron Linear Acceleration in a Dielectric Loaded Vacuum, Final Report
Energy Technology Data Exchange (ETDEWEB)
Byer, Robert L. [Stanford Univ., CA (United States). Dept. of Applied Physics. Edward L. Ginzton Lab.
2016-07-08
This final report summarizes the last three years of research on the development of advanced linear electron accelerators that utilize dielectric wave-guide vacuum channels pumped by high energy laser fields to accelerate beams of electrons.
2. Key techniques for space-based solar pumped semiconductor lasers
Science.gov (United States)
He, Yang; Xiong, Sheng-jun; Liu, Xiao-long; Han, Wei-hua
2014-12-01
In space, the absence of atmospheric turbulence, absorption, dispersion and aerosol factors on laser transmission. Therefore, space-based laser has important values in satellite communication, satellite attitude controlling, space debris clearing, and long distance energy transmission, etc. On the other hand, solar energy is a kind of clean and renewable resources, the average intensity of solar irradiation on the earth is 1353W/m2, and it is even higher in space. Therefore, the space-based solar pumped lasers has attracted much research in recent years, most research focuses on solar pumped solid state lasers and solar pumped fiber lasers. The two lasing principle is based on stimulated emission of the rare earth ions such as Nd, Yb, Cr. The rare earth ions absorb light only in narrow bands. This leads to inefficient absorption of the broad-band solar spectrum, and increases the system heating load, which make the system solar to laser power conversion efficiency very low. As a solar pumped semiconductor lasers could absorb all photons with energy greater than the bandgap. Thus, solar pumped semiconductor lasers could have considerably higher efficiencies than other solar pumped lasers. Besides, solar pumped semiconductor lasers has smaller volume chip, simpler structure and better heat dissipation, it can be mounted on a small satellite platform, can compose satellite array, which can greatly improve the output power of the system, and have flexible character. This paper summarizes the research progress of space-based solar pumped semiconductor lasers, analyses of the key technologies based on several application areas, including the processing of semiconductor chip, the design of small and efficient solar condenser, and the cooling system of lasers, etc. We conclude that the solar pumped vertical cavity surface-emitting semiconductor lasers will have a wide application prospects in the space.
3. Formation of plasmonic colloidal silver for flexible and printed electronics using laser ablation
Energy Technology Data Exchange (ETDEWEB)
Kassavetis, S., E-mail: [email protected] [University of Ioannina, Department of Materials Science and Engineering, 45110 Ioannina (Greece); Kaziannis, S. [University of Ioannina, Department of Physics, 45110 Ioannina (Greece); Pliatsikas, N. [University of Ioannina, Department of Materials Science and Engineering, 45110 Ioannina (Greece); Aristotle University of Thessaloniki, Department of Physics, 54124 Thessaloniki (Greece); Avgeropoulos, A.; Karantzalis, A.E. [University of Ioannina, Department of Materials Science and Engineering, 45110 Ioannina (Greece); Kosmidis, C. [University of Ioannina, Department of Physics, 45110 Ioannina (Greece); Lidorikis, E. [University of Ioannina, Department of Materials Science and Engineering, 45110 Ioannina (Greece); Patsalas, P. [Aristotle University of Thessaloniki, Department of Physics, 54124 Thessaloniki (Greece)
2015-05-01
Highlights: • Silver plasmonic colloidal in organic solvents by ps laser ablation process. • Ag NPs that meet size requirements of the printed organic electronics technology. • Ag NPs size refinement by secondary process using the 355 nm beam of a ns laser. - Abstract: Laser ablation (LA) in liquids has been used for the development of various nanoparticles (NPs); among them, Ag NPs in aqueous solutions (usually produced by nanosecond (ns) LA) have attracted exceptional interest due to its strong plasmonic response. In this work, we present a comprehensive study of the LA of Ag in water, chloroform and toluene, with and without PVP, using a picosecond (ps) Nd:YAG laser and we consider a wide range of LA parameters such as the laser wavelength (1064, 532, 355 nm), the pulse energy (0.3–17 mJ) and the number of pulses. In addition, we consider the use of a secondary nanosecond laser beam for the refinement of the NPs size distribution. The optical properties of the NPs were evaluated by in situ optical transmittance measurements in the UV–vis spectral ranges. The morphology of the NPs and the formation of aggregates were investigated by Scanning Electron Microscopy and High-Resolution Transmission Electron Microscopy. The ps LA process resulted in the development of bigger Ag NPs, compared to the ns LA, compatible with the size requirements of the printed organic electronics technology. The optimum conditions for the ps LA of Ag in organic solvents include the use of the 355 nm beam at low pulse energy (<1 mJ); these conditions rendered isolated Ag nanoparticles manifesting strong and well defined surface plasmon resonance peak. The use of the secondary ns laser beam was proven to be able to refine the nanoparticles to intermediate size between those produced by the single ns or ps LA.
4. Compact 13.5-nm free-electron laser for extreme ultraviolet lithography
Directory of Open Access Journals (Sweden)
Y. Socol
2011-04-01
Full Text Available Optical lithography has been actively used over the past decades to produce more and more dense integrated circuits. To keep with the pace of the miniaturization, light of shorter and shorter wavelength was used with time. The capabilities of the present 193-nm UV photolithography were expanded time after time, but it is now believed that further progress will require deployment of extreme ultraviolet (EUV lithography based on the use of 13.5-nm radiation. However, presently no light source exists with sufficient average power to enable high-volume manufacturing. We report here the results of a study that shows the feasibility of a free-electron laser EUV source driven by a multiturn superconducting energy-recovery linac (ERL. The proposed 40×20 m^{2} facility, using MW-scale consumption from the power grid, is estimated to provide about 5 kW of average EUV power. We elaborate the self-amplified spontaneous emission (SASE option, which is presently technically feasible. A regenerative-amplifier option is also discussed. The proposed design is based on a short-period (2–3 cm undulator. The corresponding electron beam energy is about 0.5–1.0 GeV. The proposed accelerator consists of a photoinjector, a booster, and a multiturn ERL.
5. Net electron energy gain induced by superluminal phase velocity and subluminal group velocity of a laser in a plasma channel
Science.gov (United States)
Cheng, Li-Hong; Yao, Zheng-Wei; Zhang, Xiao-Bo; Xue, Ju-Kui
2017-08-01
We examine electron dynamics induced by laser-plasma interaction in a two-dimensional plasma channel, taking into action the laser phase velocity as well as the group velocity. The coupled effects of phase velocity, group velocity, and plasma channel on electron dynamics are discussed in detail. The superluminal phase velocity and the corresponding subluminal group velocity of the laser result in rich and complex electron dynamics, which are depicted in the plane of the phase velocity and plasma charge density. For weak superluminosity of the phase velocity, the effects of the phase velocity and the group velocity can be neglected. For moderate superluminosity of the phase velocity, a cross-over region can exist, where the highly energetic electron could be found and the net energy gain is several times greater than the energy gain in vacuum. For strong superluminosity of the phase velocity, the dephasing rate increases and thus limits the electron energy gain from the laser. However, the asymmetric laser pulse, attributed by the superluminal phase velocity and the subluminal group velocity, results in the electron getting adjustable net energy gain from the laser. The electron oscillations are no longer limited by the charge density threshold and the electron can always get net energy from the laser. These electron dynamics can also be modified by adjusting the polarization of the laser.
6. On the Production of Flat Electron Bunches for Laser Wake Field Acceleration
Energy Technology Data Exchange (ETDEWEB)
Kando, M.; Fukuda, Y.; Kotaki, H.; Koga, J.; Bulanov, S.V.; Tajima, T.; /JAERI, Kyoto; Chao, A.; Pitthan, R.; /SLAC; Schuler, K.-P.; /DESY; Zhidkov, A.G.; /CRIEPI, Tokyo; Nemoto, K.; /CRIEPI, Tokyo
2006-06-27
We suggest a novel method for injection of electrons into the acceleration phase of particle accelerators, producing low emittance beams appropriate even for the demanding high energy Linear Collider specifications. In this paper we work out the injection into the acceleration phase of the wake field in a plasma behind a high intensity laser pulse, taking advantage of the laser polarization and focusing. With the aid of catastrophe theory we categorize the injection dynamics. The scheme uses the structurally stable regime of transverse wake wave breaking, when electron trajectory self-intersection leads to the formation of a flat electron bunch. As shown in three-dimensional particle-in-cell simulations of the interaction of a laser pulse in a line-focus with an underdense plasma, the electrons, injected via the transverse wake wave breaking and accelerated by the wake wave, perform betatron oscillations with different amplitudes and frequencies along the two transverse coordinates. The polarization and focusing geometry lead to a way to produce relativistic electron bunches with asymmetric emittance (flat beam). An approach for generating flat laser accelerated ion beams is briefly discussed.
7. Microstresses and microstructure in thick cobalt-based laser deposited coatings
NARCIS (Netherlands)
de Oliveira, U.; Ocelik, V.; De Hosson, J. Th. M.
2007-01-01
Microstresses in a thick laser clad Co-based coating on steel substrate were investigated with 3D X-ray microscopy using an intense synchrotron microfocused beam. The microstructure was examined with tight microscopy and field emission scanning electron microscopy equipped with X-ray energy
8. Characterization of fast photoelectron packets in weak and strong laser fields in ultrafast electron microscopy.
Science.gov (United States)
Plemmons, Dayne A; Tae Park, Sang; Zewail, Ahmed H; Flannigan, David J
2014-11-01
The development of ultrafast electron microscopy (UEM) and variants thereof (e.g., photon-induced near-field electron microscopy, PINEM) has made it possible to image atomic-scale dynamics on the femtosecond timescale. Accessing the femtosecond regime with UEM currently relies on the generation of photoelectrons with an ultrafast laser pulse and operation in a stroboscopic pump-probe fashion. With this approach, temporal resolution is limited mainly by the durations of the pump laser pulse and probe electron packet. The ability to accurately determine the duration of the electron packets, and thus the instrument response function, is critically important for interpretation of dynamics occurring near the temporal resolution limit, in addition to quantifying the effects of the imaging mode. Here, we describe a technique for in situ characterization of ultrashort electron packets that makes use of coupling with photons in the evanescent near-field of the specimen. We show that within the weakly-interacting (i.e., low laser fluence) regime, the zero-loss peak temporal cross-section is precisely the convolution of electron packet and photon pulse profiles. Beyond this regime, we outline the effects of non-linear processes and show that temporal cross-sections of high-order peaks explicitly reveal the electron packet profile, while use of the zero-loss peak becomes increasingly unreliable. Copyright © 2014 Elsevier B.V. All rights reserved.
9. Proton beam shaped by “particle lens” formed by laser-driven hot electrons
Energy Technology Data Exchange (ETDEWEB)
Zhai, S. H.; Shen, B. F., E-mail: [email protected], E-mail: [email protected], E-mail: [email protected]; Wang, W. P., E-mail: [email protected], E-mail: [email protected], E-mail: [email protected]; Zhang, H.; Zhang, L. G.; Huang, S.; Xu, Z. Z. [State Key Laboratory of High Field Laser Physics, Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, Shanghai 201800 (China); University of Chinese Academy of Sciences, Beijing 100049 (China); He, S. K.; Lu, F.; Zhang, F. Q.; Deng, Z. G.; Dong, K. G.; Wang, S. Y.; Zhou, K. N.; Xie, N.; Wang, X. D.; Liu, H. J.; Zhao, Z. Q.; Gu, Y. Q., E-mail: [email protected], E-mail: [email protected], E-mail: [email protected]; Zhang, B. H. [Science and Technology on Plasma Physics Laboratory, Laser Fusion Research Center, China Academy of Engineering Physics, Mianyang 621900 (China)
2016-05-23
Two-dimensional tailoring of a proton beam is realized by a “particle lens” in our experiment. A large quantity of electrons, generated by an intense femtosecond laser irradiating a polymer target, produces an electric field strong enough to change the trajectory and distribution of energetic protons flying through the electron area. The experiment shows that a strip pattern of the proton beam appears when hot electrons initially converge inside the plastic plate. Then the shape of the proton beam changes to a “fountain-like” pattern when these hot electrons diffuse after propagating a distance.
10. Instantaneous nonvertical electronic transitions with shaped femtosecond laser pulses: Is it possible?
DEFF Research Database (Denmark)
Henriksen, Niels Engholm; Møller, Klaus Braagaard
2003-01-01
electronic state. Now, applying pulse shaping via the modulation of the phases of each spectral component of an ultrashort pulse, it is tempting to ask whether it is also possible to induce instantaneous nonvertical transitions to bound electronic states, provided that the phases of each spectral component......In molecular electronic transitions, a vertical transition can be induced by an ultrashort laser pulse. That is, a replica of the initial nuclear state-times the transition dipole moment of the electronic transition-can be created instantaneously (on the time scale of nuclear motion) in the excited...
11. Demonstration of electron acceleration in a laser-driven dielectric microstructure
Science.gov (United States)
Peralta, E. A.; Soong, K.; England, R. J.; Colby, E. R.; Wu, Z.; Montazeri, B.; McGuinness, C.; McNeur, J.; Leedle, K. J.; Walz, D.; Sozer, E. B.; Cowan, B.; Schwartz, B.; Travish, G.; Byer, R. L.
2013-11-01
12. Laser-based sensor for detection of hazardous gases in the air using waveguide CO2 laser.
Science.gov (United States)
Gondal, Mohammed A; Bakhtiari, Imran A; Dastageer, Abdul K
2007-06-01
A spectrometer based on the principle of photoacoustic spectroscopy has been developed recently at our laboratory for the detection of hazardous gases such as O3, C2H4, SO2, NO2 and SF6. In most of our earlier works, we employed a mechanical chopper to modulate the laser beam and this chopper modulation has the crucial disadvantage of instability in the chopper frequency. Even a minor shift of about 1 Hz in the modulation frequency could significantly reduce the photoacoustic signal by an order of magnitude at the acoustic resonant mode of the photoacoustic cell. To overcome this problem, we developed a photoacoustic spectrometer where a wave guided CW CO2 laser beam is modulated electronically with the external frequency generator. Our preliminary results show that the electronic modulation of CO2 laser beam improved the sensitivity of our spectrometer by a factor of 6. The parametric dependence of photoacoustic signal on laser power, modulation frequency and trace gas concentration, was investigated and the comparison between the two modulation techniques is presented in this paper for detection of trace gases such as C2H4.
13. New concept of waveguide for inverse free electron laser accelerator
CERN Document Server
Zakowicz, W Z
2000-01-01
A segmented waveguide formed by a periodic system of pairs of wedge prisms with a gap between them is proposed. The prisms are made of single-crystal sapphire for which the refraction index nu<1 for CO sub 2 laser radiation (lambda=10.6 mu m). The attenuation of 0.1 db/m can be estimated for a 5 mm diameter radiation beam for which the Rayleigh distance is approximately 1 m. The gap between adjacent prisms can be useful in FEL-like applications.
14. Tunable Laser Plasma Accelerator based on Longitudinal Density Tailoring
Energy Technology Data Exchange (ETDEWEB)
Gonsalves, Anthony; Nakamura, Kei; Lin, Chen; Panasenko, Dmitriy; Shiraishi, Satomi; Sokollik, Thomas; Benedetti, Carlo; Schroeder, Carl; Geddes, Cameron; Tilborg, Jeroen van; Osterhoff, Jens; Esarey, Eric; Toth, Csaba; Leemans, Wim
2011-07-15
Laser plasma accelerators have produced high-quality electron beams with GeV energies from cm-scale devices and are being investigated as hyperspectral fs light sources producing THz to {gamma}-ray radiation and as drivers for future high-energy colliders. These applications require a high degree of stability, beam quality and tunability. Here we report on a technique to inject electrons into the accelerating field of a laser-driven plasma wave and coupling of this injector to a lower-density, separately tunable plasma for further acceleration. The technique relies on a single laser pulse powering a plasma structure with a tailored longitudinal density profile, to produce beams that can be tuned in the range of 100-400 MeV with percent-level stability, using laser pulses of less than 40 TW. The resulting device is a simple stand-alone accelerator or the front end for a multistage higher-energy accelerator.
15. External magnetic field effect on the growth rate of a plasma-loaded free-electron laser
Science.gov (United States)
Esmaeildoost, N.; Jafari, S.; Abbasi, E.
2016-06-01
In order to extend the production of intense coherent radiation to angstrom wavelengths, a laser wave is employed as a laser wiggler which propagates through a magnetized plasma channel. The plasma-loaded laser wigglers increase the ability of laser guidance and electron bunching process compared to the counterpropagating laser wigglers in vacuum. The presence of the plasma medium can make it possible to propagate the laser wiggler and the electron beam parallel to each other so that the focusing of the pulse will be saved. In addition, employing an external guide magnetic field can confine both the ambient plasma and the transverse motions of the electron beam, therefore, improving the free-electron lasers' efficiency, properly. Electron trajectories have been obtained by solving the steady state equations of motion for a single particle and the fourth-order Runge-Kutta method has been used to simulate the electron orbits. To study the growth rate of a laser-pumped free-electron laser in the presence of a plasma medium, perturbation analysis has been performed to combine the momentum transfer, continuity, and wave equations, respectively. Numerical calculations indicate that by increasing the guide magnetic field frequency, the growth rate for group I orbits increases, while for group II and III orbits decreases.
16. A tunable electron beam source using trapping of electrons in a density down-ramp in laser wakefield acceleration.
Science.gov (United States)
Ekerfelt, Henrik; Hansson, Martin; Gallardo González, Isabel; Davoine, Xavier; Lundh, Olle
2017-09-25
One challenge in the development of laser wakefield accelerators is to demonstrate sufficient control and reproducibility of the parameters of the generated bunches of accelerated electrons. Here we report on a numerical study, where we demonstrate that trapping using density down-ramps allows for tuning of several electron bunch parameters by varying the properties of the density down-ramp. We show that the electron bunch length is determined by the difference in density before and after the ramp. Furthermore, the transverse emittance of the bunch is controlled by the steepness of the ramp. Finally, the amount of trapped charge depends both on the density difference and on the steepness of the ramp. We emphasize that both parameters of the density ramp are feasible to vary experimentally. We therefore conclude that this tunable electron accelerator makes it suitable for a wide range of applications, from those requiring short pulse length and low emittance, such as the free-electron lasers, to those requiring high-charge, large-emittance bunches to maximize betatron X-ray generation.
17. Ultrashort laser pulse-induced anti-Stokes photoluminescence of hot electrons in gold nanorods
Science.gov (United States)
Sitnikov, D. S.; Yurkevich, A. A.; Kotelev, M. S.; Ziangirova, M.; Chefonov, O. V.; Ilina, I. V.; Vinokurov, V. A.; Muradov, A. V.; Itzkan, I.; Agranat, M. B.; Perelman, L. T.
2014-07-01
We report observing anti-Stokes broadband radiation induced in gold nanorods by ultrashort laser pulses. The radiation is in the visible spectral range along with the second harmonic peak. Unlike conventional photoluminescence of metal nanoparticles, the energy of the excitation photons is smaller than the gap between the top of the d band and the Fermi level. Because the gold nanorods are irradiated with a pulse whose time is shorter than the electron-phonon equilibration time in gold, the energy is absorbed by s/p band electrons, creating a temperature difference between the electrons and the lattice, as described by the two-temperature model. Therefore, we identify the origin of the observed radiation as the recombination of hot conduction electrons with the d band holes created by the same ultrashort laser pulse.
18. On the way to stabilized laser-driven GeV electrons
Energy Technology Data Exchange (ETDEWEB)
Chou, Shao-wei; Weineisen, Tobias; Fuchs, Matthias; Popp, Antonia; Major, Zsuzsanna; Weingartner, Raphael; Ahmad, Izhar; Schmid, Karl; Marx, Benjamin; Krausz, Ferenc; Gruener, Florian; Karsch, Stefan [Max-Planck Institute of Quantum Optics, Munich (Germany); Ludwig-Maximilians University, Munich (Germany); Osterhoff, Jens [LOASIS Program, Lawrence Livermore National Laboratory, Livermore (United States); Schroeder, Hartmut; Haas, Harald [Max-Planck Institute of Quantum Optics, Munich (Germany); Rowlands-Rees, Tom; Hooker, Simon [University of Oxford, Oxford (United Kingdom)
2010-07-01
Laser-driven-wakefield electron accelerators have shown electron beams with energies of up to 1 GeV from a centimeter-scale plasma accelerator. In order to achieve higher electron energies, these acceleration distances need to be increased. This can be realized with a discharge capillary. However, a discharge typically introduces instabilities on both pointing and energy of the generated electrons. In order to improve the stability, we demonstrate a preliminary test of a modified discharge which includes a pre-pulse circuit before the firing of the main pulse. We also show gas density shaping by a laser- machined nozzle which should be able to make a more precise injection in the capillary accelerator thus reducing the energy instability.
19. Spin dynamics in Kapitza-Dirac scattering of electrons from bichromatic laser fields
CERN Document Server
Dellweg, Matthias M; Müller, Carsten
2016-01-01
Kapitza-Dirac scattering of nonrelativistic electrons from counterpropagating bichromatic laser waves of linear polarization i s studied. The focus lies on the electronic spin dynamics in the Bragg regime when the laser fields possess a frequency ratio of two. To this end, the time-dependent Pauli equation is solved numerically, both in coordinate space and momentum space. Our numerical results are corroborated by analytical derivations. We demonstrate that, for certain incident electron momenta, the scattering crucially relies on the electron spin which undergo es characteristic Rabi-like oscillations. A parameter regime is identified where the Rabi oscillations reach maximum amplitude. We also briefly discuss spin-dependent Kapitza-Dirac scattering of protons.
20. Microstructural stability of wrought, laser and electron beam glazed NARloy-Z alloy at elevated temperatures
Energy Technology Data Exchange (ETDEWEB)
Singh, J.; Jerman, G.; Bhat, B.; Poorman, R.
1993-11-01
Microstructure of wrought, laser, and electron-beam glazed NARloy-Z(Cu-3 wt.% Ag-0.5 wt.% Zr) was investigated for thermal stability at elevated temperatures (539 to 760 C (1,100 to 1,400 F)) up to 94 h. Optical and scanning electron microscopy and electron probe microanalysis were employed for studying microstructural evolution and kinetics of precipitation. Grain boundary precipitation and precipitate free zones (PFZ`s) were observed in the wrought alloy after exposing to temperatures above 605 C (1,120 F). The fine-grained microstructure observed in the laser and electron-beam glazed NARloy-Z was much more stable at elevated temperatures. Microstructural changes correlated well with hardness measurements.
1. Few-femtosecond time-resolved measurements of X-ray free-electron lasers.
Science.gov (United States)
Behrens, C; Decker, F-J; Ding, Y; Dolgashev, V A; Frisch, J; Huang, Z; Krejcik, P; Loos, H; Lutman, A; Maxwell, T J; Turner, J; Wang, J; Wang, M-H; Welch, J; Wu, J
2014-04-30
X-ray free-electron lasers, with pulse durations ranging from a few to several hundred femtoseconds, are uniquely suited for studying atomic, molecular, chemical and biological systems. Characterizing the temporal profiles of these femtosecond X-ray pulses that vary from shot to shot is not only challenging but also important for data interpretation. Here we report the time-resolved measurements of X-ray free-electron lasers by using an X-band radiofrequency transverse deflector at the Linac Coherent Light Source. We demonstrate this method to be a simple, non-invasive technique with a large dynamic range for single-shot electron and X-ray temporal characterization. A resolution of less than 1 fs root mean square has been achieved for soft X-ray pulses. The lasing evolution along the undulator has been studied with the electron trapping being observed as the X-ray peak power approaches 100 GW.
2. Quantized form factor shift in the presence of free electron laser radiation
CERN Document Server
Fratini, F; Hayrapetyan, A G; Jänkälä, K; Amaro, P; Santos, J P
2015-01-01
In electron scattering, the target form factors contribute significantly to the diffraction pattern and carry information on the target electromagnetic charge distribution. Here we show that the presence of electromagnetic radiation, as intense as currently available in Free Electron Lasers, shifts the dependence of the target form factors by a quantity that depends on the number of photons absorbed or emitted by the electron as well as on the parameters of the electromagnetic radiation. As example, we show the impact of intense ultraviolet and soft X-ray radiation on elastic electron scattering by Ne-like Argon ion and by Xenon atom. We find that the shift brought by the radiation to the form factor is in the order of some percent. Our results may open up a new avenue to explore matter with the assistance of laser.
3. Investigation of the Electron Acceleration by a High-Power Laser and a Density-Tapered Mixed-Gas Cell
Science.gov (United States)
Kim, Jinju; Phung, Vanessa L. J.; Kim, Minseok; Hur, Min-Sup; Suk, Hyyong
2017-10-01
Plasma-based accelerators can generate about 1000 times stronger acceleration field compared with RF-based conventional accelerators, which can be done by high power laser and plasma. There are many issues in this research and one of them is development of a good plasma source for higher electron beam energy. For this purpose, we are investigating a special type of plasma source, which is a density-tapered gas cell with a mixed-gas for easy injection. By this type of special gas cell, we expect higher electron beam energies with easy injection in the wakefield. In this poster, some experimental results for electron beam generation with the density-tapered mixed-gas cell are presented. In addition to the experimental results, CFD (Computational-Fluid-Dynamics) and PIC (Particle-In-Cell) simulation results are also presented for comparison studies.
4. High brightness laser source based on polarization coupling of two diode lasers with asymmetric feedback
DEFF Research Database (Denmark)
Thestrup, B.; Chi, M.; Sass, B.
2003-01-01
In this letter, we show that polarization coupling and asymmetric diode-laser feedback can be used to combine two diode-laser beams with low spatial coherence into a single beam with high spatial coherence. The coupled laser source is based on two similar laser systems each consisting of a 1 mumx......200 mum broad area laser diode applied with a specially designed feedback circuit. When operating at two times threshold, 50% of the freely running system output power is obtained in a single beam with an M-2 beam quality factor of 1.6+/-0.1, whereas the M-2 values of the two freely running diode...... lasers are 29+/-1 and 34+/-1, respectively. (C) 2003 American Institute of Physics....
5. Self-generated magnetic fields and electron transport in laser driven hohlraums
Science.gov (United States)
Edwards, John; Alley, Ed; Hammer, Jim; Town, Richard; Haines, Malcolm
2002-11-01
It is well known that magnetic fields can be generated during the interaction of an intense laser beam with solid targets. The principle source of magnetic field from Ohm's law is the familiar grad(T)xgrad(n) term, which results in Megagauss fields for laser intensities typical of inertial fusion and other high energy density experiments. In a hohlraum the main consequence of this is to increase the electron temperature by x2 near the laser entrance holes because of reduced thermal conduction in the cross-field (axial) direction. Despite the "localizing" effect of the magnetic field on the electrons, it appears that the diffusion approximation for electron heat flow breaks down, with the departure becoming progressively worse as the laser power is increased. The results of Lasnex simulations are used to illustrate these effects for laser powers ranging from 10TW to 500TW which cover conditions from Nova to NIF. Potential knock on consequences for inertial fusion are discussed. -This work was performed under the auspices of the U.S. Department of Energy by the University of California, Lawrence Livermore National Laboratory under contract No. W-7405-Eng-48.
6. Non-Maxwellian electron distributions resulting from direct laser acceleration in near-critical plasmas
Directory of Open Access Journals (Sweden)
T. Toncian
2016-01-01
Full Text Available The irradiation of few-nm-thick targets by a finite-contrast high-intensity short-pulse laser results in a strong pre-expansion of these targets at the arrival time of the main pulse. The targets decompress to near and lower than critical densities with plasmas extending over few micrometers, i.e. multiple wavelengths. The interaction of the main pulse with such a highly localized but inhomogeneous target leads to the generation of a short channel and further self-focusing of the laser beam. Experiments at the Glass Hybrid OPCPA Scaled Test-bed (GHOST laser system at University of Texas, Austin using such targets measured non-Maxwellian, peaked electron distribution with large bunch charge and high electron density in the laser propagation direction. These results are reproduced in 2D PIC simulations using the EPOCH code, identifying direct laser acceleration (DLA [1] as the responsible mechanism. This is the first time that DLA has been observed to produce peaked spectra as opposed to broad, Maxwellian spectra observed in earlier experiments [2]. This high-density electrons have potential applications as injector beams for a further wakefield acceleration stage as well as for pump-probe applications.
7. Focusing effects in laser-electron Thomson scattering
Directory of Open Access Journals (Sweden)
Chris Harvey
2016-09-01
Full Text Available We study the effects of laser pulse focusing on the spectral properties of Thomson scattered radiation. Modeling the laser as a paraxial beam we find that, in all but the most extreme cases of focusing, the temporal envelope has a much bigger effect on the spectrum than the focusing itself. For the case of ultrashort pulses, where the paraxial model is no longer valid, we adopt a subcycle vector beam description of the field. It is found that the emission harmonics are blue shifted and broaden out in frequency space as the pulse becomes shorter. Additionally the carrier envelope phase becomes important, resulting in an angular asymmetry in the spectrum. We then use the same model to study the effects of focusing beyond the limit where the paraxial expansion is valid. It is found that fields focussed to subwavelength spot sizes produce spectra that are qualitatively similar to those from subcycle pulses due to the shortening of the pulse with focusing. Finally, we study high-intensity fields and find that, in general, the focusing makes negligible difference to the spectra in the regime of radiation reaction.
8. Focussing effects in laser-electron Thomson scattering
CERN Document Server
Harvey, C; Holkundkar, A R
2016-01-01
We study the effects of laser pulse focussing on the spectral properties of Thomson scattered radiation. Modelling the laser as a paraxial beam we find that, in all but the most extreme cases of focussing, the temporal envelope has a much bigger effect on the spectrum than the focussing itself. For the case of ultra-short pulses where the paraxial model is no longer valid, we adopt a sub-cycle vector beam description of the field. It is found that the emission harmonics are blue shifted and broaden out in frequency space as the pulse becomes shorter. Additionally the carrier envelope phase becomes important, resulting in an angular asymmetry in the spectrum. We then use the same model to study the effects of focussing beyond the limit where the paraxial expansion is valid. It is found that fields focussed to sub-wavelength spot sizes produce spectra that are qualitatively similar to those from sub-cycle pulses due to the shortening of the pulse with focussing. Finally, we study high-intensity fields and find ...
9. Theory and simulation of an inverse free-electron laser experiment
Science.gov (United States)
Gou, S. K.; Bhattacharjee, A.; Fang, J.-M.; Marshall, T. C.
1997-03-01
An experimental demonstration of the acceleration of electrons using a high-power CO2 laser interacting with a relativistic electron beam moving along a wiggler has been carried out at the Accelerator Test Facility of the Brookhaven National Laboratory [Phys. Rev. Lett. 77, 2690 (1996)]. The data generated by this inverse free-electron-laser (IFEL) experiment are studied by means of theory and simulation. Included in the simulations are such effects as: a low-loss metallic waveguide with a dielectric coating on the walls; multi-mode coupling due to self-consistent interaction between the electrons and the optical wave; space charge; energy spread of the electrons; and arbitrary wiggler-field profile. Two types of wiggler profile are considered: a linear taper of the period, and a step-taper of the period. (The period of the wiggler is ˜3 cm, its magnetic field is ˜1 T, and the wiggler length is 0.47 m.) The energy increment of the electrons (˜1-2%) is analyzed in detail as a function of laser power, wiggler parameters, and the initial beam energy (˜40 MeV). At a laser power level ˜0.5 Gw, the simulation results on energy gain are in reasonable agreement with the experimental results. Preliminary results on the electron energy distribution at the end of the IFEL are presented. Whereas the experiment produces a near-monotone distribution of electron energies with the peak shifted to higher energy, the simulation shows a more structured and non-monotonic distribution at the end of the wiggler. Effects that may help reconcile these differences are considered.
10. Ultrasensitive photoacoustic sensor based on quantum cascade laser spectroscopy.
Science.gov (United States)
Kumar, Deepak; Gautam, Surya; Kumar, Subodh; Gupta, Saurabh; Srivastava, Hari B; Thakur, Surya N; Sharma, Ramesh C
2017-04-05
The paper focuses on development of ultra-sonic detection system based on laser photoacoustic spectroscopic technique and processing of signal for detection of very low quantity chemicals, explosive materials, and mixtures of these hazardous molecules. The detection system has been developed for the first time with specially designed one side open photo-acoustic cell having high quality factor. Explosive and Hazardous materials like RDX, DNT, PETN, Gun Powder, TATP (Tri acetone tri-peroxide) and their simulants like Acetone were detected in 7 to 9μm wavelength band. Lock in amplifier electronic instrument was used for the detection of hazardous chemicals and mixture of explosives in very low quantity. Detection limit of the photoacoustic ultrasonic sensor was also carried out of powder, liquid and adsorbed on surfaces. Copyright © 2016. Published by Elsevier B.V.
11. Ultrasensitive photoacoustic sensor based on quantum cascade laser spectroscopy
Science.gov (United States)
Kumar, Deepak; Gautam, Surya; Kumar, Subodh; Gupta, Saurabh; Srivastava, Hari B.; Thakur, Surya N.; Sharma, Ramesh C.
2017-04-01
The paper focuses on development of ultra-sonic detection system based on laser photoacoustic spectroscopic technique and processing of signal for detection of very low quantity chemicals, explosive materials, and mixtures of these hazardous molecules. The detection system has been developed for the first time with specially designed one side open photo-acoustic cell having high quality factor. Explosive and Hazardous materials like RDX, DNT, PETN, Gun Powder, TATP (Tri acetone tri-peroxide) and their simulants like Acetone were detected in 7 to 9 μm wavelength band. Lock in amplifier electronic instrument was used for the detection of hazardous chemicals and mixture of explosives in very low quantity. Detection limit of the photoacoustic ultrasonic sensor was also carried out of powder, liquid and adsorbed on surfaces.
12. Planar Laser-Based QEPAS Trace Gas Sensor
Directory of Open Access Journals (Sweden)
Yufei Ma
2016-06-01
Full Text Available A novel quartz enhanced photoacoustic spectroscopy (QEPAS trace gas detection scheme is reported in this paper. A cylindrical lens was employed for near-infrared laser focusing. The laser beam was shaped as a planar line laser between the gap of the quartz tuning fork (QTF prongs. Compared with a spherical lens-based QEPAS sensor, the cylindrical lens-based QEPAS sensor has the advantages of easier laser beam alignment and a reduction of stringent stability requirements. Therefore, the reported approach is useful in long-term and continuous sensor operation.
13. Planar Laser-Based QEPAS Trace Gas Sensor.
Science.gov (United States)
Ma, Yufei; He, Ying; Chen, Cheng; Yu, Xin; Zhang, Jingbo; Peng, Jiangbo; Sun, Rui; Tittel, Frank K
2016-06-28
A novel quartz enhanced photoacoustic spectroscopy (QEPAS) trace gas detection scheme is reported in this paper. A cylindrical lens was employed for near-infrared laser focusing. The laser beam was shaped as a planar line laser between the gap of the quartz tuning fork (QTF) prongs. Compared with a spherical lens-based QEPAS sensor, the cylindrical lens-based QEPAS sensor has the advantages of easier laser beam alignment and a reduction of stringent stability requirements. Therefore, the reported approach is useful in long-term and continuous sensor operation.
14. Transverse Dynamics and Energy Tuning of Fast Electrons Generated in Sub-Relativistic Intensity Laser Pulse Interaction with Plasmas
OpenAIRE
Mori, M.; Kando, M.; Daito, I.; Kotaki, H.; Hayashi, Y.; Yamazaki, A.; Ogura, K.; Sagisaka, A.; Koga, J.; Nakajima, K.; Daido, H.; Bulanov, S. V.; Kimura, T.
2006-01-01
The regimes of quasi-mono-energetic electron beam generation were experimentally studied in the sub-relativistic intensity laser plasma interaction. The observed electron acceleration regime is unfolded with two-dimensional-particle-in-cell simulations of laser-wakefield generation in the self-modulation regime.
15. Transverse dynamics and energy tuning of fast electrons generated in sub-relativistic intensity laser pulse interaction with plasmas
Energy Technology Data Exchange (ETDEWEB)
2006-07-31
The regimes of quasi-monoenergetic electron beam generation were experimentally studied in the sub-relativistic intensity laser plasma interaction. The observed electron acceleration regime is unfolded with two-dimensional-particle-in-cell simulations of laser-wakefield generation in the self-modulation regime.
16. Laser-Based Lighting: Experimental Analysis and Perspectives
Directory of Open Access Journals (Sweden)
Nicola Trivellin
2017-10-01
Full Text Available This paper presents an extensive analysis of the operating principles, theoretical background, advantages and limitations of laser-based lighting systems. In the first part of the paper we discuss the main advantages and issues of laser-based lighting, and present a comparison with conventional LED-lighting technology. In the second part of the paper, we present original experimental data on the stability and reliability of phosphor layers for laser lighting, based on high light-intensity and high-temperature degradation tests. In the third part of the paper (for the first time we present a detailed comparison between three different solutions for laser lighting, based on (i transmissive phosphor layers; (ii a reflective/angled phosphor layer; and (iii a parabolic reflector, by discussing the advantages and drawbacks of each approach. The results presented within this paper can be used as a guideline for the development of advanced lighting systems based on laser diodes.
17. Integration and test of high-speed transmitter electronics for free-space laser communications
Science.gov (United States)
Soni, Nitin J.; Lizanich, Paul J.
1994-01-01
The NASA Lewis Research Center in Cleveland, Ohio, has developed the electronics for a free-space, direct-detection laser communications system demonstration. Under the High-Speed Laser Integrated Terminal Electronics (Hi-LITE) Project, NASA Lewis has built a prototype full-duplex, dual-channel electronics transmitter and receiver operating at 325 megabit S per second (Mbps) per channel and using quaternary pulse-position modulation (QPPM). This paper describes the integration and testing of the transmitter portion for future application in free-space, direct-detection laser communications. A companion paper reviews the receiver portion of the prototype electronics. Minor modifications to the transmitter were made since the initial report on the entire system, and this paper addresses them. The digital electronics are implemented in gallium arsenide integrated circuits mounted on prototype boards. The fabrication and implementation issues related to these high-speed devices are discussed. The transmitter's test results are documented, and its functionality is verified by exercising all modes of operation. Various testing issues pertaining to high-speed circuits are addressed. A description of the transmitter electronics packaging concludes the paper.
18. Hot electron production in laser solid interactions with a controlled pre-pulse
Energy Technology Data Exchange (ETDEWEB)
Culfa, O.; Tallents, G. J.; Wagenaars, E.; Ridgers, C. P.; Dance, R. J.; Rossall, A. K.; Woolsey, N. C. [York Plasma Institute, Department of Physics, The University of York, York YO10 5DD (United Kingdom); Gray, R. J.; McKenna, P. [Department of Physics, SUPA, University of Strathclyde, Glasgow G4 0NG (United Kingdom); Brown, C. D. R.; James, S. F.; Hoarty, D. J. [AWE, Aldermaston, Reading, Berkshire RG7 4PR (United Kingdom); Booth, N.; Robinson, A. P. L. [CLF, STFC Rutherford Appleton Laboratory, Didcot, Oxfordshire OX11 0QX (United Kingdom); Lancaster, K. L. [York Plasma Institute, Department of Physics, The University of York, York YO10 5DD (United Kingdom); CLF, STFC Rutherford Appleton Laboratory, Didcot, Oxfordshire OX11 0QX (United Kingdom); Pikuz, S. A. [Joint Institute for High Temperatures, Russian Academy of Sciences, Moscow 125412 (Russian Federation); Faenov, A. Ya. [Joint Institute for High Temperatures, Russian Academy of Sciences, Moscow 125412 (Russian Federation); Quantum Beam Science Directorate, Japan Atomic Energy Agency, Kizugawa, Kyoto 619-0215 (Japan); Kampfer, T.; Schulze, K. S.; Uschmann, I. [Friedrich Schiller University of Jena, D-07743 Jena (Germany)
2014-04-15
Hot electron generation plays an important role in the fast ignition approach to inertial confinement fusion (ICF) and other applications with ultra-intense lasers. Hot electrons of temperature up to 10–20 MeV have been produced by high contrast picosecond duration laser pulses focussed to intensities of ∼10{sup 20} W cm{sup −2} with a deliberate pre-pulse on solid targets using the Vulcan Petawatt Laser facility. We present measurements of the number and temperature of hot electrons obtained using an electron spectrometer. The results are correlated to the density scale length of the plasma produced by a controlled pre-pulse measured using an optical probe diagnostic. 1D simulations predict electron temperature variations with plasma density scale length in agreement with the experiment at shorter plasma scale lengths (<7.5μm), but with the experimental temperatures (13–17 MeV) dropping below the simulation values (20–25 MeV) at longer scale lengths. The experimental results show that longer interaction plasmas produced by pre-pulses enable significantly greater number of hot electrons to be produced.
19. The Effect of Background Pressure on Electron Acceleration from Ultra-Intense Laser-Matter Interactions
Science.gov (United States)
Le, Manh; Ngirmang, Gregory; Orban, Chris; Morrison, John; Chowdhury, Enam; Roquemore, William
2017-10-01
We present two-dimensional particle-in-cell (PIC) simulations that investigate the role of background pressure on the acceleration of electrons from ultra intense laser interaction at normal incidence with liquid density ethylene glycol targets. The interaction was simulated at ten different pressures varying from 7.8 mTorr to 26 Torr. We calculated conversion efficiencies from the simulation results and plotted the efficiencies with respect to the background pressure. The results revealed that the laser to > 100 keV electron conversion efficiency remained flat around 0.35% from 7.8 mTorr to 1.2 Torr and increased exponentially from 1.2 Torr onward to about 1.47% at 26 Torr. Increasing the background pressure clearly has a dramatic effect on the acceleration of electrons from the target. We explain how electrostatic effects, in particular the neutralization of the target by the background plasma, allows electrons to escape more easily and that this effect is strengthened with higher densities. This work could facilitate the design of future experiments in increasing laser to electron conversion efficiency and generating substantial bursts of electrons with relativistic energies. This research is supported by the Air Force Office of Scientific Research under LRIR Project 17RQCOR504 under the management of Dr. Riq Parra and Dr. Jean-Luc Cambier. Support was also provided by the DOD HPCMP Internship Program.
20. Enhanced single-stage laser-driven electron acceleration by self-controlled ionization injection.
Science.gov (United States)
Li, Song; Hafz, Nasr A M; Mirzaie, Mohammad; Sokollik, Thomas; Zeng, Ming; Chen, Min; Sheng, Zhengming; Zhang, Jie
2014-12-01
We report on overall enhancement of a single-stage laser wakefield acceleration (LWFA) using the ionization injection in a mixture of 0.3% nitrogen gas in 99.7% helium gas. Upon the interaction of 30-TW, 30-fs laser pulses with a gas jet of the above gas mixture, >300 MeV electron beams were generated at a helium plasma densities of 3.3-8.5 × 10(18) cm(-3). Compared with the uncontrolled electron self-injection in pure helium gas jet, the ionization injection process due to the presence of ultra-low nitrogen concentrations appears to be self-controlled; it has led to the generation of electron beams with higher energies, higher charge, lower density threshold for trapping, and a narrower energy spread without dark current (low energy electrons) or multiple bunches. It is foreseen that further optimization of such a scheme is expected to bring the electron beam energy-spread down to 1%, making them suitable for driving ultra-compact free-electron lasers.
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http://www.sisef.it/iforest/contents/?id=ifor3312-013
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## Wildfire and harvesting effects on carbon dynamics in an oak-pine mixed forest
iForest - Biogeosciences and Forestry, Volume 13, Issue 5, Pages 435-440 (2020)
doi: https://doi.org/10.3832/ifor3312-013
Research Articles
CO2 emission to the atmosphere is the main cause of global warming. The impacts of land-use changes for agriculture and urbanisation, deforestation, and fire disturbance are attributed to the increase in CO2 emissions. Soil respiration, largely due to microbial activity, is one of the CO2 sources being released to the atmosphere. In this regard, several soil parameters related with carbon cycle, including organic matter, total N, C/N ratio, CO2 efflux, microbial biomass C (Cmic), the Cmic/Corg ratio, the metabolic quotient qCO2, and β-D glucosidase activity, were determined in a burned (harvested, H; non-harvested, NH), and its adjacent unburned (UB), mixed oak-pine forest to estimate the effects of burning and removal of residual woods. The Cmic increased gradually with burning and harvesting after Month 9, and sharp increases were observed in all areas, likely due to the abundant rainfall after Month 12. CO2 efflux decreased in the burned areas at Months 4 and 6; however, this reversed in Month 9. In spite of non-significant differences, we detected higher CO2 efflux values in the unburned areas compared to the burned ones, probably as a result of the drought effect observed in the burned areas up to Months 9 and 12 due to the increased soil heat. There was no significant difference between the H and NH burned areas, while both areas were different from the unburned areas in all soil parameters, except CO2 efflux and qCO2. The harvesting effect was not significant compared to the fire effect with regard to the considered soil variables, likely due to the management and protection of the burned area which allowed a fast vegetation recover. The abundance of the microbial biomass was independent of the changes in CO2 efflux and showed a negative correlation with β-D glucosidase activity. This might be related to the variation in substrate quality, microbial composition and abundance after burning and harvesting.
# Introduction
The increase in C stocks in forest ecosystems depends on the preservation of C in tree biomass and soil against degradation. Wildfire and harvesting both affect the soil organic carbon storage by combusting organic matter, volatilization, changing soil structure, vegetation canopy, microclimatic conditions, erosion, litter layer composition, microbial population and their activity, and decomposition ([49], [29], [35], [42], [33], [1]). Fire may accelerate the decomposition of organic matter (OM), promoting CO2 emission. Logging and removal of burned trees increase the CO2 emissions (about 120 gr C m-2 in burned pine forests) and reduce the renovation capacity of Mediterranean ecosystems after the wildfire ([46]). On the other hand, though no significant effect on total ecosystem carbon stocks was observed, a decrease was seen in carbon stored in snags and down woody material after the salvage logging in burned sub-boreal jack pine forests ([10]) The soil microflora contributes to soil C storage, soil respiration and ecosystem productivity, despite representing only a small portion of the soil ([6]). Microbial biomass C (Cmic) has been suggested as an indicator of changes in the soil ([6]) as a consequence of forest management ([5], [41], [40]). Fire may alter the microbial abundance both directly by killing microbes soil surface due to heating and indirectly by modifying the community composition and environmental conditions ([13], [20], [56]). Additionally, harvesting may affect these conditions by compacting the soil and causing increases in runoff rates and erosion ([36], [15]). Decreases were found in microbial biomass carbon after harvest (18%), burn (74%), and burn-salvage (53%) treatments ([49]).
The metabolic quotient (qCO2), which is the microbial respiration/microbial biomass C ratio, decreases with increasing the quality of substrate, and increases under unfavourable conditions ([3], [54], [6], [32]). Microbial parameters, including Cmic, qCO2 and qC, have been used in several studies ([37]) in order to understand the impacts of soil management or disturbance.
Soil microorganisms apply different strategies to use available C, such as biotic (e.g., release of extracellular enzymes) and abiotic (e.g., redox and metal complexation) mechanisms ([22]). β-D glucosidase which takes part in the degradation of cellulose, decreased in burned soils, as reported by Hernandez et al. ([21]), but little is known about the harvesting effect of burned residues on this enzyme activity.
The purpose of this study was to understand the relationship between the C dynamics and the microbial activity after a wildfire, and after harvesting of the residues, by using several microbial parameters, including CO2 evolution, Cmic, qCO2, and β-D glucosidase enzyme activity. It was hypothesized that burning alters the microbial activity related to C dynamics, and harvesting contributes to these changes.
# Materials and methods
## Study area and soil sampling
We conducted this study in a mixed pine (Pinus nigra Arnld. subsp. pallasiana Lamb.) and oak (Quercus pubescens Wild.) forest in Safranbolu, Turkey (41° 16′ 11″ N, 32° 37′ 41″ E) following a wildfire occurred on the 9th and 10th of October, 2011. The fire was caused by a picnic fire, and affected an area of 5 hectares. Fire severity was estimated based on the litter consumption ([44]) and whether the ashes whiten or not ([29]). The severity of the fire ranged from low to medium due to black ash and bare soil surface dominated the majority of the site. Additionally, this determination also complies with the criteria of Ryan & Noste ([44]) modified from Ryan ([45]) and Turner et al. ([52]) ([30]). We did not measure the percentage of vegetatition cover, but based on our observation the understory was mainly composed of Phillyrea latifolia L., Cistus creticus L., Juniperus oxycedrus L., Colutea cilicica Boiss. & Balansa, and Rubus sp. The annual rainfall was between 630 and 650 mm in the region during the study period. The elevation of the area was 720-760 m a.s.l., and the slope 30-45%. The soil with typical A-C horizons belongs to the order intrazonal and suborder calsimorfic and was classified as a rendzina, according to FAO/UNESCO ([25], [50]). The main characteristics of the soils in the study area are given in Tab. 1. The area was covered with residues, consisting of twigs, for the protection of the soil and the new generation. In several parts of the burnt area the residual trees were removed (harvested).
Tab. 1 - Main soil characteristics in the study area. (EC): Electrical conductivity.
- Variable Profile horizons
Ah C1 C2 C3
Physical analysis Depth (cm) 0-2 2-36 36-46 46-83
Total weight (g) 1614.48 1946.15 1740.84 2080.9
Gravel weight (g) 211.48 389.51 377.71 546.70
Gravel volume (ml) 87.50 158.33 155.00 240.00
Sand (%) 29.41 37.07 36.97 42.36
Silt (%) 29.63 26.95 21.47 26.42
Clay (%) 40.97 35.99 41.56 31.22
Soil texture Silty clay loam Silty clay loam Clay loam Clay loam
Chemical analysis pH 1:2.5 7.2 7.5 7.6 7.7
Total lime (%) 2.915 14.84 28.09 24.11
Organic Matter, OM (%) 6.88 1.65 1.07 0.87
Total Nitrogen, Nt (%) 0.39 0.09 0.06 0.04
P2O5 (mg kg-1) 9.73 16.8 11.2 9.05
EC (×103, mS cm-1) 0.70 0.59 0.41 0.71
Soil sampling was conducted in Months 4, 6, 9, 12 and 24 after the fire. We selected 22 plots (10 × 10 m2) including eight burned-non harvested (NH), eight burned-harvested (H) and three adjacent, unburned areas for each species. Three soil samples per plot were collected at depths of 0-7.5 cm, following removal of the surface residues, including oak leaves and pine needles. We collected the samples from low- and medium-severity burned areas in order to achieve homogeneity. Soil samples were transferred to the laboratory, sieved through a 2-mm mesh and stored at +4 °C.
## Laboratory analyses
The CO2 evolution was determined according to the method of Isermeyer ([24]), modified by Alef ([2]). Following incubation of the samples with NaOH traps for 24 hours at 25 °C in sealed containers, the remaining NaOH was titrated with HCl after adding BaCl2 solution and phenolphthalein. The CO2 flux was calculated from the amount of consumption of HCl through titration given by the following formula (eqn. 1):
$$CO_2 (mg)/SW/t= \frac{(V_0-V) \cdot 1.1}{dwt}$$
where SW is the amount of soil dry weight, t is the incubation time, V0 is the HCl used for titration, V is the HCl used for soil sample, dwt is the dry weight of 1 g moist soil, and 1.1 is the conversion factor (i.e., 1 ml 0.05 M NaOH equals 1.1 mg CO2).
The Cmic was determined according to the chloroform extraction method described by Vance et al. ([53]). Half of each sample was fumigated with CHCl3 and then incubated at 25 °C for 24 h. The fumigated and non-fumigated samples were extracted using 0.5 M K2SO4 at a soil/extract ratio of 1:4, and then kept at -20 °C until they were analysed using a TOC-L® analyser (Shimadzu Corp., Kyoto, Japan). The Cmic was calculated following Wu et al. ([55]) using the following equation (eqn. 2):
$$Biomass \;C = 2.22 \cdot Ec$$
where Ec is the difference between the amount of Corg extracted from the fumigated and non-fumigated soils.
The qCO2 (metabolic quotient) is a specific respiration rate of CO2 C evolved per unit of Cmic, which is calculated from CO2 evolution and Cmic C.
The β-D glucosidase activity was measured according to the method of Naseby & Lynch ([38]). A 1.5 g aliquot of soil was extracted using an acetate buffer at pH 5.5, agitated on an orbital rotary shaker with a slope angle of 60° to the horizontal for 1 h, and then centrifuged at 4000 rpm for 15 min. Following incubation at 37 °C for 24 h with buffered substrate p-nitrophenyl-β-D glucoside, 1 ml NaOHCO3 was added to the extracts, which were then quantified at 400 nm in a spectrophotometer.
## Statistical analyses
Differences between the burned (H and NH) and unburned soil samples were determined by ANOVA for each period and in total. Data was transformed when it was not normally distributed as log (1+ √qCO2), or alternatively a non-parametric test (Mann-Whitney U) was used. Correlations between the parameters were estimated. All statistical analyses were performed using the software SPSS® v. 21 (IBM, Armonk, NY, USA).
# Results
We observed significant differences in most of the soil samples in terms of burning, while the harvested and non-harvested samples were similar for most of the variables analysed. A significant decrease was determined in Corg in burned samples but the results were relatively higher in burned-H samples. No difference in total nitrogen (Nt) was found between the unburned and burned soils but the Month 9. The C/N ratios were slightly different in favor of the unburned samples (p = 0.05 - Fig. 1a, Tab. 2). There was no significant difference in CO2 evolution (p = 0.956); however, the maximum values were observed in the unburned soils, and the minimum values were found in the burned-NH soils (Tab. 2). The Cmic values were different at Month 12 (p = 0.036) while it was comparatively high in the burned areas at all months (Fig. 1b, Tab. 2). We observed significant differences (p = 0.029) in Cmic/Corg at Month 12 similarly (Fig. 1c, Tab. 2). An increase in the total amount of Cmic in all areas was observed through the time, but the increase was higher in the burned areas between Months 12 and 24.
Fig. 1 - (a) C/N ratio, (b) Cmic values, (c) Cmic/Corg ratio, (d) β-D glucosidase activity, and (e) qCO2 ratios in burned (H: harvested; NH: non-harvested) and unburned areas.
Tab. 2 - Means (± standard error) of the soil parameters analysed for different periods after fire (Month) and level of disturbance (Dist). Different letters indicate significant differences (p<0.05) between unburned (UB), burned non-harvested (B-NH) and burned harvested (B-H) areas. (OM): organic matter (%); (Nt): total nitrogen; (Cmic): microbial carbon (µg C g-1); (Corg): organic carbon; (β-DG): β-D glucosidase (mg pNP h-1 g-1); (N): sample size.
Month Dist OM
(%)
Nt
(%)
C/N
ratio
CO2 efflux
(mg CO2
g-1 h-1)
Cmic
(µg C g-1)
Cmic/Corg
ratio
qCO2
(mg CO2 g-1
Cmic h-1)
β-DG
(mg pNP
h-1 g-1)
N
4 UB 6.09 ± 1.48 a 0.26 ± 0.07 a 14 ± 1 b 19.81 ± 6.11 a 3760 ± 2239 a 0.07 ± 0.04 a 7.12 ± 5.23 b 1.49 ± 0.32 a 6
B-NH 5.49 ± 1.72 a 0.27 ± 0.09 a 12 ± 1 a 13.45 ± 2.88 a 3862 ± 1200 a 0.07 ± 0.02 a 3.84 ± 1.52 a 1.22 ± 0.97 a 8
B-H 6.50 ± 1.60 a 0.29 ± 0.09 a 13 ± 2 ab 14.36 ± 9.89 a 4251 ± 1489 a 0.07 ± 0.02 a 3.18 ± 0.96 a 1.12 ± 0.84 a 8
Total 6.02 ± 1.60 0.28 ± 0.08 13 ± 1 15.51 ± 7.19 3976 ± 1568 0.07 ± 0.02 4.50 ± 3.22 1.26 ± 0.77 22
6 UB 6.57 ± 1.22 b 0.25 ± 0.08 a 17 ± 8 a 8.88 ± 2.15 b 3703 ± 2533 a 0.05 ± 0.03 a 4.60 ± 4.45 a 3.08 ± 3.32 a 6
B-NH 4.14 ± 0.84 a 0.19 ± 0.04 a 13 ± 4 a 5.52 ± 1.06 a 3555 ± 1777 a 0.09 ± 0.04 a 1.91 ± 1.05 a 1.84 ± 1.94 a 8
B-H 5.15 ± 2.18 ab 0.24 ± 0.06 a 12 ± 3 a 6.53 ± 2.20 ab 4393 ± 3056 a 0.10 ± 0.07 a 1.95 ± 0.85 a 1.17 ± 0.85 a 8
Total 5.17 ± 1.77 0.23 ± 0.06 14 ± 5 6.80 ± 2.23 3900 ± 2417 0.08 ± 0.05 2.66 ± 2.61 1.93 ± 2.17 22
9 UB 8.37 ± 3.16 b 0.43 ± 0.17 b 11 ± 0 a 1.96 ± 0.93 a 3276 ± 1872 a 0.04 ± 0.01 a 0.73 ± 0.41 a 3.01 ± 1.36 b 6
B-NH 5.37 ± 1.40 a 0.27 ± 0.07 a 11 ± 0 a 3.70 ± 1.58 a 3357 ± 1428 a 0.06 ± 0.02 a 1.40 ± 1.10 a 1.22 ± 1.06 ab 8
B-H 5.73 ± 2.55 ab 0.29 ± 0.13 ab 11 ± 0 a 3.25 ± 2.03 a 3522 ± 1590 a 0.07 ± 0.04 a 1.09 ± 0.82 a 1.05 ± 0.64 a 8
Total 6.32 ± 2.62 0.32 ± 0.14 11 ± 0 3.06 ± 1.71 3395 ± 1539 0.06 ± 0.03 1.11 ± 0.86 1.65 ± 1.30 22
12 UB 6.18 ± 1.11 a 0.24 ± 0.05 a 15 ± 2 a 4.21 ± 1.30 a 3575 ± 7880 a 0.06 ± 0.02 a 1.23 ± 0.51 a 1.40 ± 0.36 a 6
B-NH 4.40 ± 1.99 a 0.19 ± 0.06 a 14 ± 5 a 6.95 ± 2.56 a 4415 ± 1023 ab 0.12 ± 0.06 b 1.66 ± 0.66 a 1.29 ± 1.34 a 8
B-H 4.88 ± 1.28 a 0.22 ± 0.06 a 13 ± 3 a 6.59 ± 2.86 a 5009 ± 1359 b 0.11 ± 0.03 ab 1.42 ± 0.75 a 1.49 ± 1.19 a 8
Total 5.06 ± 1.64 0.21 ± 0.06 14 ± 4 6.07 ± 2.59 4402 ± 1203 0.10 ± 0.05 1.45 ± 0.65 1.39 ± 1.05 22
24 UB 4.52 ± 2.08 a 0.21 ± 0.12 a 13 ± 2 a 9.47 ± 2.57 a 14417 ± 15842 a 0.43 ± 0.52 a 1.24 ± 0.87 a 0.42 ± 0.24 a 6
B-NH 3.57 ± 1.43 a 0.16 ± 0.05 a 13 ± 3 a 8.86 ± 1.92 a 20805 ± 20733 a 0.88 ± 1.07 a 1.36 ± 1.25 a 0.21 ± 0.17 a 8
B-H 4.00 ± 0.84 a 0.21 ± 0.05 a 11 ± 3 a 9.13 ± 1.99 a 30156 ± 28705 a 0.83 ± 0.82 a 1.24 ± 1.39 a 0.22 ± 0.15 a 8
Total 3.99 ± 1.45 0.19 ± 0.08 12 ± 3 9.12 ± 2.04 22463 ± 22799 0.74 ± 0.84 1.29 ± 1.16 0.27 ± 0.20 22
Total UB 6.35 ± 2.21 b 0.28 ± 0.13 a 14 ± 4 b 8.87 ± 6.93 a 5746 ± 8088 a 0.13 ± 0.26 a 2.98 ± 3.84 a 1.88 ± 1.83 b 30
B-NH 4.59 ± 1.62 a 0.22 ± 0.08 a 13 ± 3 a 7.69 ± 3.93 a 7199 ± 11231 b 0.24 ± 0.56 b 2.03 ± 1.44 a 1.16 ± 1.29 a 40
B-H 5.25 ± 1.90 a 0.25 ± 0.09 a 12 ± 2 a 7.97 ± 5.95 a 9466 ± 16148 b 0.23 ± 0.46 b 1.78 ± 1.20 a 1.01 ± 0.88 a 40
Total 5.31 ± 2.01 0.25 ± 0.1 13 ± 3 8.11 ± 5.58 7627 ± 12574 0.21 ± 0.46 2.20 ± 2.33 1.30 ± 1.38 110
Significant differences were observed between the burned and unburned areas (p = 0.023) in favor of unburned areas in regard to β-D glucosidase enzyme activity (Fig. 1d, Tab. 2). The qCO2 values did not vary significantly with burning (p = 0.786) except for Month 4 (Fig. 1e, Tab. 2).
There were significant differences between the different periods, in terms of the soil properties, with p < 0.05 for C/N and β-D glucosidase, and p < 0.001 for the others. The interaction effect of period and burning for qCO2 was significant (p < 0.05), while it was unclear for CO2 evolution (p = 0.052).
Cmic and Cmic/Corg were well correlated with each other, while negative relations between Corg, TN, qCO2 and β-D glucosidase were recorded (Tab. 3).
Tab. 3 - Correlation coefficients among the analyzed soil parameters (n=110). (Nt): total nitrogen; (Cmic): microbial carbon; (Corg): organic carbon; (β-DG): β-D glucosidase; (*): p<0.05; (**): p<0.001; (ns): non-significant.
- Corg Nt C/N CO2 efflux Cmic Cmic/Corg qCO2 β-DG
Corg 1 0.873** 0.207* 0.128 ns -0.277** -0.384** 0.135 ns 0.181 ns
Nt - 1 -0.274** 0.078 ns -0.266** -0.341** 0.106 ns 0.143 ns
C/N - - 1 0.055 ns -0.001 ns -0.076 ns 0.000 ns 0.097 ns
CO2 efflux - - - 1 0.046 ns 0.011 ns 0.592** -0.154 ns
Cmic - - - - 1 0.925** -0.298** -0.241*
Cmic/Corg - - - - - 1 -0.274** -0.241*
qCO2 - - - - - - 1 -0.024 ns
β-DG - - - - - - - 1
# Discussion
Although the Corg, C/N, Cmic, Cmic/Corg and β-D glucosidase values were different between the burned and unburned plots, there were no significant differences between the H (burned, harvested) and NH (burned, non-harvested) areas, in terms of the soil parameters.
Organic carbon content decreases as a result of fire as observed in this study, and changes may occur in organic matter fractions. As a matter of fact, loss of Corg and Nt has been reported due to the fire severity reaching 220-460 °C ([16], [12]). Similarly, the lower levels of OM were significant at Month 6 and 9 according to our results. Relatively high OM content in burned-harvested samples was likely due to mixing of the forest floor with the mineral soil during harvesting ([42]). Nt content in burned samples were low as well as non-significant in general. Higher Nt concentration was observed at Month 9 likely due to the warmer conditions in more moist unburned samples ([26], [27], [57]). Slight changes in C/N ratio may be related with the formation of new recalcitrant N and volatisation of C compounds, as suggested by previous studies conducted in burned pine forests ([43], [18]).
A general increase in Cmic was probably due to the increase in the concentration of oxidisable C and nutrients in burned soils as previously reported ([18], [17]); immediate increases have been found in soils after fire ([51], [14]). Likely because of the relatively late sampling in our study, we did not detect significant changes in the above variables in burned (especially burned and harvested) areas in Month 4 and Month 6. Bárcenas-Moreno et al. ([9]) categorised the process of microbial recovery after a wildfire as initial depletion of microorganisms in soil and the proliferation of fast-growing bacteria after a few months due to rapid and short increase of available nutrients. Cmic increase was reported after 8 months in a burned pine (Pinus halepensis) and oak (Quercus coccifera) mixed forest by Bárcenas-Moreno et al. ([9]) which was maintained for the rest of their study and reversed after 32 months. We assessed a significant decrease at Month 12 and non-significant decrease at Month 24 in Cmic values of the unburned areas, in comparison with those at Months 4 and 6. An increase in the total amount of Cmic was observed in all areas, more in the burned areas, likely due to the higher amount of rainfall between Months 12 and 24.
We found a negative correlation between Cmic and qCO2 that is inconsistent with the results from previous studies ([54], [8]), whereas a positive correlation between Cmic and CO2 evolution was detected. A high qCO2 indicates the need for restoring the C demand as a result of the microbial biomass depending on the renewal of C lost through respiration ([4], [8]). After a low-intensity prescribed fire in a Picea abies forest, basal respiration diminished while there was a disproportionate decrease in Cmic ([41]), which clearly led to higher values of qCO2 in the burned areas compared to unburned ones ([11]). This indicator predicts soil fertility ([3], [54], [6], [32], [7]). The lower levels of qCO2 in the burned soils in the first and second sampling dates indicate an improvement in soil conditions for the new vegetation due to the warmer soils in burned areas. Similar values in the burned and unburned areas after Month 9 may have resulted from vegetation succession ([23]).
β-D glucosidase enzyme activity plays an important role in energy availability in the soil, as it is directly related to the labile C content and its ability to stabilise the soil organic matter independently of seasonal variability ([34]). Our results indicate that this enzyme activity decreased with burning up to the last sampling date, two years after the wildfire, and was significantly different among H, NH, and UB plots at Month 9. The decrease in enzyme activity related with the lack of C entry to the system via plant inputs of Corg and Nt ([47], [48]) is consistent with our results. There was a negative correlation between enzyme activity and Cmic. The decrease in enzyme activity compared to Cmic likely resulted from the enzymes being retained in the stabilised fraction of the soil rather than that part associated with the viable microbial population ([31]).
Decomposition increased due to harvesting, possibly resulting in changes to the C budget ([39]). The harvesting of burned tree residues did not affect the measured soil parameters significantly in this study, probably because of the sensitive protection precautions used after the wildfire (such as covering the soil surface with residual brushwood material) and the rapid regeneration of forest ([19], [18]), which is characteristic of oak forests.
# Conclusions
Fire affected the microbial biomass likely due to changes in the substrate quality, microbial composition, and abundance. However, this increase was not significant one year after burning. The correlation between qCO2 and β-D glucosidase activity showed that the former might be a more coherent indicator of microbial functionality than Cmic and CO2 evolution. In fact, enzymes might be independent of microbial proliferation, as it can attach to dead cells or cellular fragments instead of viable microorganisms.
The decrease in qCO2 after burning at low severity may indicate to the forest managers that the soil has relatively ideal conditions, simplifying the preparation of the area for new vegetation. The harvesting of burned trees in post-fire areas provides many advantages, in terms of economic benefits or protection of the forest against pests. Proper precautions for the soil, such as covering it after the fire with residues, comprising branches and small, felled burned trees, may be advantageous by allowing soil and nutrient loss to be avoided.
# Acknowledgements
This study was supported by the General Directorate of Forestry of Turkey. All the analyses were conducted at the Research Institute for Forest Soil and Ecology in the context of project ESK-11 (6300)/2011-2015. Part of the data for some of the soil characteristics were used in the publication Kaptanoglu & Namli ([28]), for different periods and in a different context. We would like to thank Aydin Çömez, Oguz Can Turgay, Münevver Arslan, and Kürsad Özkan for their comments.
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#### Authors’ Affiliation
(1)
Aliye Sepken Kaptanoglu 0000-0001-6535-5257
General Directorate of Forestry, Research Institute for Forest Soil and Ecology, 26160 Eskisehir (Turkey)
(2)
Ayten Namli 0000-0003-1913-2751
Ankara University, Soil Science Department, Ankara (Turkey)
#### Corresponding author
Aliye Sepken Kaptanoglu
[email protected]
#### Citation
Kaptanoglu AS, Namli A (2020). Wildfire and harvesting effects on carbon dynamics in an oak-pine mixed forest. iForest 13: 435-440. - doi: 10.3832/ifor3312-013
Davide Ascoli
#### Paper history
Accepted: Jul 08, 2020
First online: Sep 16, 2020
Publication Date: Oct 31, 2020
Publication Time: 2.33 months
© SISEF - The Italian Society of Silviculture and Forest Ecology 2020
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{"extraction_info": {"found_math": true, "script_math_tex": 0, "script_math_asciimath": 0, "math_annotations": 0, "math_alttext": 0, "mathml": 0, "mathjax_tag": 0, "mathjax_inline_tex": 0, "mathjax_display_tex": 0, "mathjax_asciimath": 0, "img_math": 0, "codecogs_latex": 0, "wp_latex": 0, "mimetex.cgi": 0, "/images/math/codecogs": 0, "mathtex.cgi": 0, "katex": 0, "math-container": 0, "wp-katex-eq": 0, "align": 0, "equation": 2, "x-ck12": 0, "texerror": 0, "math_score": 0.5413986444473267, "perplexity": 15042.021238630094}, "config": {"markdown_headings": true, "markdown_code": true, "boilerplate_config": {"ratio_threshold": 0.18, "absolute_threshold": 20, "end_threshold": 15, "enable": true}, "remove_buttons": true, "remove_image_figures": true, "remove_link_clusters": true, "table_config": {"min_rows": 2, "min_cols": 3, "format": "plain"}, "remove_chinese": true, "remove_edit_buttons": true, "extract_latex": true}, "warc_path": "s3://commoncrawl/crawl-data/CC-MAIN-2021-43/segments/1634323588246.79/warc/CC-MAIN-20211028003812-20211028033812-00537.warc.gz"}
|
https://infoscience.epfl.ch/record/129103
|
## A lower bound for the rank of $J_0(q)$
Published in:
Acta arithmetica, 94, 4, 303-343
Year:
2000
Keywords:
Laboratories:
|
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|
https://languagelog.ldc.upenn.edu/nll/?p=30539
|
## American freedoms
It's probably not an accident that yesterday's inaugural address, compared to the previous half-century or so, has the highest frequency of the morpheme america (= America, American, Americans) and the lowest frequency of the morpheme freedom (= freedom, freedoms):
Following a suggestion from Jason Stanley in the comments, I've added counts for the morpheme liberty (= liberty, liberties), which makes the point even more strongly:
The numbers (with morpheme counts translated to frequencies per million words — and I know that this means I'm giving too many significant digits…):
WHO AMERICA FREEDOM FREEDOM+LIBERTY
Kennedy1961 5117 2924 3655
Johnson1965 6614 1323 5291
Nixon1969 4684 937 937
Nixon1973 12644 2199 2199
Carter1977 4062 3249 4874
Reagan1981 6528 3264 4488
Reagan1985 8099 5399 5785
Bush1989 4717 2573 3002
Clinton1993 20497 1863 2484
Clinton1997 14279 921 1842
Bush2001 12484 3121 3745
Bush2005 14395 12956 20154
Obama2009 6227 1245 2076
Obama2013 8941 3294 5647
Trump2017 23368 687 687
I should point out that the underlying single-document counts are small — thus Trump used "freedoms" once in 1455 words, while G.W. Bush used "freedom" 27 times in 2084 words. The data comes from the transcripts at The American Presidency Project.
1. ### Theophylact said,
January 21, 2017 @ 1:02 pm
America First!; freedom, last.
2. ### Jonathan Gress-Wright said,
January 21, 2017 @ 1:54 pm
Next step is to establish correlation between a president's use of the word "freedom" and his actual protection of our constitutional liberties.
[(myl) My hypothesis, in contrast, would be that word counts in major speeches tell us about PR themes, and therefore predict results only to the extent that (for example) Wheaties correlates with championships or MacDonalds with getting a break today.
Consistent with his word choices — or rather with Steve Bannon and Stephen Miller's word choices — nationalism is certainly a central theme of Donald Trump's campaign; civil liberties, not so much. What this means about his record on civil liberties as compared to G.W. Bush's — or his record on national prestige as compared to Obama's — remains to be seen.]
3. ### Jon W said,
January 21, 2017 @ 2:22 pm
But, natch, civil liberties were not a major theme of GW Bush's campaign either. Rather, "freedom" was the thing that the terrorists hated us for.
[(myl) True enough — but W maintained the ideology that the fight was about ideas, not just about them vs. us.]
4. ### Jonathan Gress-Wright said,
January 21, 2017 @ 3:52 pm
Interesting that Clinton seems to come in second for nationalist rhetoric, at least going by frequency of "America".
5. ### Jason Stanley said,
January 21, 2017 @ 7:01 pm
Thanks for this. You scooped an article David Beaver and I were writing – we did this work this morning but we were going to enclose it in an article for public consumption to explain the significance. Can you do me a huge favor and also factor in the cognates for "freedom", like "liberty"? By only focusing on "freedom" and "freedoms" you are in fact diminishing the problem. Trump didn't use "liberty" once and you need to count both "freedom" and "liberty" to see how extreme it is (excuse me if you already did this). Now to package this in a way that someone other than professional linguists see this…it's a really really vital point and cannot be buried.
[(myl) The raw counts for total words and for forms of freedom (= freedom, freedoms) and liberty (= liberty, liberties):
WORDS AMERICA FREEDOM LIBERTY
Kennedy1961 1368 7 4 1
Johnson1965 1512 10 2 6
Nixon1969 2135 10 2 0
Nixon1973 1819 23 4 0
Carter1977 1231 5 4 2
Reagan1981 2451 16 8 3
Reagan1985 2593 21 14 1
Bush1989 2332 11 6 1
Clinton1993 1610 33 3 1
Clinton1997 2171 31 2 2
Bush2001 1602 20 5 1
Bush2005 2084 30 27 15
Obama2009 2409 15 3 2
Obama2013 2125 19 7 5
Trump2017 1455 34 1 0
Adding the Freedom+Liberty counts and re-graphing:
]
6. ### J.W. Brewer said,
January 21, 2017 @ 7:57 pm
I assume you thought that Pres. Ford's remarks on the occasion of assuming office under unusual circumstances in Aug. '74 shouldn't be included because they weren't really an example of the same genre, due to those unusual circumstances? Which seems fair except it makes one curious about the scoring. (He didn't say "carnage," but that speech did introduce the striking NP "long national nightmare.")
7. ### J.W. Brewer said,
January 21, 2017 @ 8:10 pm
It also appears that the "new words" search the Post was doing is doing just a straight/dumb identification of wordforms. It's not doing lemmas (e.g. that "subsidized" is new doesn't mean no prior president said "subsidize" or "subsidizing") or closely-related words (maybe some prior incumbent said "subsidy"?) and certainly not concepts. If "bleed" is new, there's a rather famous phrase in Lincoln's second inaugural that uses a closely-related word ("until every drop of blood drawn with the lash shall be paid by another drawn with the sword") and indeed that phrase is part of a passage that could fairly be described as a meditation on "carnage."
8. ### Joseph F Foster said,
January 22, 2017 @ 8:31 am
One comment on a phrase in Jasaon Stanley's comment above:
Can you do me a huge favor and also factor in the cognates for "freedom", like "liberty"?
Since this is a Linguistics / Language site, I point out that freedom and liberty are not "cognates". They may be near synonyms which I believe was the term wanted. English free and German frei are cognates — words descended directly each from *Proto-Germanic, neither borrowed from the other.
9. ### Jason Stanley said,
January 22, 2017 @ 9:31 am
Thank you for doing this work! Much appreciated.
10. ### Rose Eneri said,
January 22, 2017 @ 10:01 am
The inauguration speech word-count chart within Jason Stanely's comment is really interesting. Kennedy's is the 2nd shortest, but probably the only one that can be quoted. Johnson's frequent use of "liberty" reflects the fear of Communism being played-out in Vietnam.
What exactly did Carter say?!
Reagan's frequent use of "freedom" in his 2nd speech reflects his efforts to bring down the Berlin wall and all that entailed. Clinton's 2 speeches are amazingly similar, both with heavy use of "America." GWB's second speech reflects the threat to America's freedoms and liberties posed by terrorism. Trump's highest use of "America" reflects his platform to put America first.
|
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|
http://mathhelpforum.com/geometry/12988-help-plz.html
|
# Math Help - help plz
1. ## help plz
May someone help me solve this problem.
In a circle whose diameter is 20 inches, a chord is 6 inches from the center. What is the length of the chord?
I do not understand this problem.
Thank you for the help.
2. Originally Posted by JayJay1206
May someone help me solve this problem.
In a circle whose diameter is 20 inches, a chord is 6 inches from the center. What is the length of the chord?
...
Hello, JayJay,
I've attached an image of the situation:
length of chord = 2s
Use the Pythagoran theorem:
r² = s² + 6² with r = 10'' because r is the half diameter:
100 = s² + 36 ===> s² = 64 ===> s = 8''
Therefore the length of the chord is 16''
EB
Attached Thumbnails
|
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|
https://tug.org/pipermail/tex-live/2016-July/039102.html
|
# [tex-live] Erors rebuilding format after updating TexLive 2016 with tlmgr
Benoît RIVET benoit.rivet at free.fr
Sat Jul 23 21:40:06 CEST 2016
```I have errors rebuilding format after updating TexLive 2016 with the TexLive Utility program on Mac OS X. I have quite a few failure messages, such as :
> (/usr/local/texlive/2016/texmf-dist/tex/generic/hyph-utf8/patterns/tex/hyph-ka.tex
> ! Undefined control sequence.
> \utfthreeuniglyph ... \expandafter {\the \numexpr
> ...
> ...
> ...
> (That makes 100 errors please try again)
> fmtutil [ERROR]: running `pdftex -ini -jobname=mllatex -progname=mllatex -translate-file=cp227.tcx -mltex mllatex.ini
> fmtutil [ERROR]: return error due to options --strict
> fmtutil [INFO]: Disabled formats: 17
> fmtutil [INFO]: Not selected formats: 51
> fmtutil [INFO]: Failed to build: 1 (pdftex/mllatex)
> fmtutil [INFO]: Total formats: 69
> fmtutil [INFO]: exiting with status 1
This happens for several formats : for example I read in the logs :
> fmtutil [INFO]: Failed to build: 1 (xetex/cont-en)
> fmtutil [INFO]: Failed to build: 1 (pdftex/jadetex)
> fmtutil [INFO]: Failed to build: 1 (pdftex/mllatex)
> fmtutil [INFO]: Failed to build: 1 (pdftex/pdfxmltex)
> fmtutil [INFO]: Failed to build: 1 (pdftex/pdfjadetex)
> fmtutil [INFO]: Failed to build: 1 (pdftex/xmltex)
These errors have proven harmless for me, since I only use lualatex and pdflatex; both of which seem to work without problem despite the above mentioned errors.
I reinstalled MacTex 2016 from scratch, and the same errors happens when trying to update with TexLive Utility. However, I spotted in the logs the following message :
> fmtutil: fmtutil is using the following fmtutil.cnf files (in precedence order):
> fmtutil: /usr/local/texlive/texmf-local/web2c/fmtutil.cnf
> fmtutil: /usr/local/texlive/2016/texmf-dist/web2c/fmtutil.cnf
which make me wonder whether the texmf-local/web2c/files may be conflicting with TexLive 2016 : they seem to have been created 9 years ago (2007) and never changed since (with the exception of updmap.cfg). I assume I can safely remove all the files in texmf-local.web2c (keeping only updmap.cfg) and let tlmgr rebuild the formats when needed.
This bug may of course be specific to Mac OS X (and/or due to the fact that I’ve been using TexLive for more than 9 years), but since it is my understanding that TexLive Utility is only a nice gui built on top of tlmgr on MacOS X, I guess that this may be relevant in other contexts as well. I must add that I do not remember stumbling upon a similar bug since I am using the TexLive Utillity (eg since 2008…).
I wish to thank all the people working hard to provide us this wonderful piece of software which I’m using on a daily basis and which has always proven reliable and to all the people on this list who have always been very helpful,
Benoît RIVET
PS: I could not find the mllatex log (and other .log files) corresponding to the unsuccessful format rebuild; however, I’ve been able to reconstruct these log file from ~/Library/Application Support/Tex Live Utility/Log Messages.plist (which is an xml file logging every step of every action made with Tex Live Utility). This is available on https://www.dropbox.com/s/9wcqxltnkmsiq4s/TexLiveUtility.log?dl=0
```
|
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|
http://mathhelpforum.com/advanced-statistics/189837-can-i-improve-accuracy-method-print.html
|
# Can I improve the accuracy of this method?
• Oct 8th 2011, 09:55 AM
davidwhite
Can I improve the accuracy of this method?
I hope it is OK to post here - I am a total non-expert with only basic maths ability, but with what I think is a tricky problem to solve. I hope someone here may be able to help.
I need to estimate the value of X (unknown) when I know only the value for Y. To do this I have a list of other occurrences of X and Y, and I have to determining any pattern in the correlation of X to Y. Although X and Y are not totally random, there is no definite or consistent correlation other than there is a tendency for the value of X to be larger if Y is larger. The best that can be hoped for is as accurate a guess as possible. Here is an example:
1. X = 380 Y = 320
2. X = 840 Y = 5500
3. X = 5176 Y = 499
4. X = 5315 Y = 1074
5. X = 6484 Y = 140
6. X = 7244 Y = 5002
7. X = 10950 Y = 1104
8. X = 11040 Y = 279
9. X = 16791 Y = 3001
10. X = 17096 Y = 2788
11. X = 20700 Y = 9194
12. X = 169901 Y = 20886
13. X = 178322 Y = 94437
14. X = 184739 Y = 1198
15. X = 525257 Y = 29129
X = ? if Y = 1198
X = ? if Y = 8062
X = ? if Y = 31419
As a non-expert, at the moment my best guess at the Xs involves the following process: I divide X by Y for all known values, in the example above this gives results ranging from 0.15 (No.2) to 154.21 (No. 14). I then find the median value across the sample set, in the example above this is 6.13 (represented by No. 10). I then apply this value to Y in the case of unknown X, so in this case I would estimate the 3 unknown Xs to be 7346 and 49420 and 192599.
I have two questions.
a) My simple method gets within +-50% in 60% of cases (the actual data sets are larger than the small example above, with anything from 50 to 500 known X and Ys). Is there a more advanced approach that would give more accurate estimates?
b) If I have to use a formula for estimating 100 unknown X's, and my goal is to get, say, 75% of my estimates to within, say, +-50%. As all values are positive, the most my result can be in error on the negative side is close to -100%, but my method can easily give errors on the positive side in excess of +100%, +200%, even 1,000%. So the scope for positive error is unlimited while the scope for negative error is limited to -100%. Can this fact be harnessed to improve the statistical accuracy and get more results within my target tolerance range?
For practical purposes any suggestions or solutions ideally need to be executable on Excel.
Thank you in advance for your patience with this problem and any help.
• Oct 8th 2011, 08:57 PM
CaptainBlack
Re: Can I improve the accuracy of this method?
Quote:
Originally Posted by davidwhite
I hope it is OK to post here - I am a total non-expert with only basic maths ability, but with what I think is a tricky problem to solve. I hope someone here may be able to help.
I need to estimate the value of X (unknown) when I know only the value for Y. To do this I have a list of other occurrences of X and Y, and I have to determining any pattern in the correlation of X to Y. Although X and Y are not totally random, there is no definite or consistent correlation other than there is a tendency for the value of X to be larger if Y is larger. The best that can be hoped for is as accurate a guess as possible. Here is an example:
1. X = 380 Y = 320
2. X = 840 Y = 5500
3. X = 5176 Y = 499
4. X = 5315 Y = 1074
5. X = 6484 Y = 140
6. X = 7244 Y = 5002
7. X = 10950 Y = 1104
8. X = 11040 Y = 279
9. X = 16791 Y = 3001
10. X = 17096 Y = 2788
11. X = 20700 Y = 9194
12. X = 169901 Y = 20886
13. X = 178322 Y = 94437
14. X = 184739 Y = 1198
15. X = 525257 Y = 29129
X = ? if Y = 1198
X = ? if Y = 8062
X = ? if Y = 31419
As a non-expert, at the moment my best guess at the Xs involves the following process: I divide X by Y for all known values, in the example above this gives results ranging from 0.15 (No.2) to 154.21 (No. 14). I then find the median value across the sample set, in the example above this is 6.13 (represented by No. 10). I then apply this value to Y in the case of unknown X, so in this case I would estimate the 3 unknown Xs to be 7346 and 49420 and 192599.
I have two questions.
a) My simple method gets within +-50% in 60% of cases (the actual data sets are larger than the small example above, with anything from 50 to 500 known X and Ys). Is there a more advanced approach that would give more accurate estimates?
b) If I have to use a formula for estimating 100 unknown X's, and my goal is to get, say, 75% of my estimates to within, say, +-50%. As all values are positive, the most my result can be in error on the negative side is close to -100%, but my method can easily give errors on the positive side in excess of +100%, +200%, even 1,000%. So the scope for positive error is unlimited while the scope for negative error is limited to -100%. Can this fact be harnessed to improve the statistical accuracy and get more results within my target tolerance range?
For practical purposes any suggestions or solutions ideally need to be executable on Excel.
Thank you in advance for your patience with this problem and any help.
We would need to know more about the process producing these numbers, and would need to see a lot more data to offer any meaningful opinion.
CB
• Oct 9th 2011, 01:02 AM
davidwhite
1 Attachment(s)
Re: Can I improve the accuracy of this method?
The X and Y values are asset types, and I can have data sets where, for example, I have 500 records in a data set. For 200 records both X and Y values may be known, for the remaining 300 records only Y is known. I'm trying to establish the most accurate method of estimating X in these cases.
I know there is no consistent relationship between the two values, but there is a tendency / probability (I use these terms as a layperson) for both to increase in size. I notice that X does not always increase with Y, so I suspect part of the problem may involve quantifying the probability for X and Y to both increase, as well as calculating the most probable proportion of one value to the other. Or maybe the approach required is totally different?
I have attached a larger data set of several hundred records as requested.
• Oct 14th 2011, 04:40 AM
CaptainBlack
Re: Can I improve the accuracy of this method?
Quote:
Originally Posted by davidwhite
The X and Y values are asset types, and I can have data sets where, for example, I have 500 records in a data set. For 200 records both X and Y values may be known, for the remaining 300 records only Y is known. I'm trying to establish the most accurate method of estimating X in these cases.
I know there is no consistent relationship between the two values, but there is a tendency / probability (I use these terms as a layperson) for both to increase in size. I notice that X does not always increase with Y, so I suspect part of the problem may involve quantifying the probability for X and Y to both increase, as well as calculating the most probable proportion of one value to the other. Or maybe the approach required is totally different?
I have attached a larger data set of several hundred records as requested.
Look at a log-log plot of this data.
CB
• Oct 14th 2011, 08:11 AM
davidwhite
1 Attachment(s)
Re: Can I improve the accuracy of this method?
I've produced a log-log of the example data set where X and Y values are both known. I have attached the log-log graph generated in Excel using base 10 (Excel default, it can be changed). It produces two Y axis, which is no doubt correct. I'm sure this is the approach and I can see that there is a clustering which appears to hint at potential order. But I have no idea how to use this data to produce an Excel formula which I can then apply to future known Y values to estimate unknown X values.
I understand there is a degree of 'figure it out yourself' appropriate for students of maths but I'm not - not even a CSE in maths 30 years ago! If this forum isn't the right place for non-mathematicians to get help can you point me in the right direction? Thanks.
• Oct 14th 2011, 08:50 AM
CaptainBlack
Re: Can I improve the accuracy of this method?
Quote:
Originally Posted by davidwhite
I've produced a log-log of the example data set where X and Y values are both known. I have attached the log-log graph generated in Excel using base 10 (Excel default, it can be changed). It produces two Y axis, which is no doubt correct. I'm sure this is the approach and I can see that there is a clustering which appears to hint at potential order. But I have no idea how to use this data to produce an Excel formula which I can then apply to future known Y values to estimate unknown X values.
I understand there is a degree of 'figure it out yourself' appropriate for students of maths but I'm not - not even a CSE in maths 30 years ago! If this forum isn't the right place for non-mathematicians to get help can you point me in the right direction? Thanks.
The problem with a non-educational problem that may be used commercially is the MHF cannot do anything that might result in us being liable in any way for losses financial or otherwise of the advice.
But a linear realationship in a log-log plot implies a relationship of the form:
$Y=k X^{\alpha}$
where $k$ and $\alpha$ are constants.
CB
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https://ipc.susu.ru/210-2.html?problem=165
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Èìÿ: Ïàðîëü: Âõîä Çàðåãèñòðèðîâàòüñÿ Âîññòàíîâèòü ïàðîëü
28/09/2022 07:20:41
# Ðàáî÷åå ìåñòî ó÷àñòíèêà
## Çàäà÷è
165. Beer Land
Îãðàíè÷åíèÿ: âðåìÿ – 2s/4s, ïàìÿòü – 32MiB Ââîä: input.txt èëè ñòàíäàðòíûé ââîä Âûâîä: output.txt èëè ñòàíäàðòíûé âûâîä
Ïîñëàòü ðåøåíèå Blockly Ïîñûëêè Òåìû Ãäå Îáñóäèòü (0)
King ACM 2002 received some clear ground and some money through inheritance. Terms of the will and testament require the heir to build n towns. He was also required to build the least quantity of two-way roads between the towns such that one could travel from any town to any other town even if one road was closed under repair. Carefully, all such roads must be constructed as geometrically straight lines. Further, the condition that a traveller be able to get from one town to another (even with one road closed) needs to be satisfied by traversing the roads as straight lines in their entirety – not stopping partway along one road to switch to another. Because of rich soil in those lands, the future inhabitants of the place have decided to produce beer. On the crossroads (a crossroad is merey the intersection of two or more roads) the king plans to build beer stands (one stand per a crossroad). So, if three or four (or twenty) roads intersect in a single point, theres still only one appropriate place for a beer stand. The King must choose locations for the towns and the roads. You need to advise him so that he builds as many beer stands as possible.
Input
The first line of input contains the number of test cases. For each case there is a line containing a single integer n (1\ ≤\ n\ ≤\ 32767). This represents the number of towns to be built.
Output
For each n, print a line containing the maximum number of beer stands possible to build.
Sample Input
3
3
4
5
Sample Output
0
1
5
Source: ACM ICPC SEERC, 2002
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http://mathhelpforum.com/discrete-math/9927-simple-word-problem-sets-venn.html
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# Math Help - Simple Word Problem Sets, Venn
1. ## Simple Word Problem Sets, Venn
I'm sure this is a super easy problem, but I've been out of school for five years and didn't take much math my first time since I received a B.A. So I just need a little help getting a jumpstart back into it. I've worked this problem over and over just can't get it to go. Thanks for your help.
Assume that 170 surveys are completed. Of those surveyed, 88 responded positively to effectiveness, 93 responded positively to side effects, and 80 responded positively to cost. Also, 47 responded positively to both effectiveness and side effects, 37 to effectiveness and cost, 47 to side effects and cost, and 20 to none of the items. How many responded to all three?
2. Originally Posted by Tainted1
I'm sure this is a super easy problem, but I've been out of school for five years and didn't take much math my first time since I received a B.A. So I just need a little help getting a jumpstart back into it. I've worked this problem over and over just can't get it to go. Thanks for your help.
Assume that 170 surveys are completed. Of those surveyed, 88 responded positively to effectiveness, 93 responded positively to side effects, and 80 responded positively to cost. Also, 47 responded positively to both effectiveness and side effects, 37 to effectiveness and cost, 47 to side effects and cost, and 20 to none of the items. How many responded to all three?
Of these:
150-88-93-80+47+37+47=20
responded to all three (this is an example of the inclusion/exclusion principle)
We start with the number of surveys with response subtract the numbers
of repsonses to each question, but now we have removed those that
responded to more than one question multiple times - twice for those that
answered exactly two questions and three times for those that responded
to all three.
So adding back in the numbers that responded to each pair of questions
we have removed those who answered exactly two questions, and left
one count in for each person who responded to all three.
RonL
3. Here's the diagram.
170-88-93-80+47+47+37-20=20
4. Hello, Tainted1!
No, this is not an easy problem . . . even with Venn diagrams.
170 surveys are completed. .Of those surveyed, their positive responses were:
88 to Effectiveness
93 to Side effects
80 to Cost
47 to Effectiveness and Side effects
37 to Effectiveness and Cost
47 to Side effects and Cost
20 to none of the items.
How many responded to all three?
There is a formula for the number of elements in the union of three sets.
$n(E \cup S \cup C) \;=\;n(E) + n(S) + n(C) - n(E\cap S) - n(S\cap C)$ $- n(E\cap C) + n(E \cap S \cap C)$
Of the 170 surveys, 20 responded to none of the three.
. . Then there are $150$ who responded to at least one.
The formula becomes: . $150 \:=\:88 + 93 + 80 - 47 - 37 - 47 + n(E \cap S \cap C)$
Therefore: . $n(E \cap S \cap C) \:=\:20$
5. ## Thank You
Thank you everyone. It is much clearer now. Math isn't my best subject so I'm sure I'll be back.
Thanks again.
T
|
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|
http://math.tutornext.com/geometry/area-of-equilateral-triangle.html
|
# Area of Equilateral Triangle
Sub Topics
The triangle is a polygon with the least number of sides. This fact that the triangle encloses a well defined plane region made it possible to find the perimeter enclosing and the area enclosed using formulas.
Measurement problems on plane figures mainly involve perimeter and area. The two formulas for a general scalene triangle are
Perimeter of a triangle = a + b + c
where a, b and c are the lengths of the sides of the triangle.
Area of a triangle = $\frac{1}{2}$.bh
Where 'b' the base is the length of a side and 'h' the corresponding height.
## Area of Equilateral Triangle Formula
Now substituting this value of h in the formula for the area of the triangle
2s = a + b + c
Area = $\sqrt{}$s(s - a)(s - b)(s - c)
Area of a triangle =$\frac{1}{2}$.bh
Area of an equilateral triangle of side ‘a’ = $\frac{\sqrt{3a^2}}{4}$
## How to Find the Area of an Equilateral Triangle
Below you could see how to find the area of an equilateral triangle
## Perimeter of an Equilateral Triangle
An equilateral triangle is a triangle with three congruent sides. This attribute simplifies the formulas for perimeter and area further.
Since the three sides are of equal lengths in an equilateral triangle, a = b = c.
Perimeter of equilateral triangle = 3a
Where a is the length of the side.
## Height of Equilateral Triangle
The equiangular property of an equilateral triangle enables the h to be written in terms of the base.
In the equilateral triangle each side is of length a units, and each angle measures 60o. CD is the altitude drawn to side ABApplying Pythagorean theorem for the right triangle ADC, h2+$(\frac{a}{2})^2$=a2→h2+$\frac{a^2}{4}$=a2 h2+$\frac{3a^2}{4}$→h = $\frac{\sqrt{3}}{2}$ Height of an equilateral triangle of side 'a' = $\frac{\sqrt{3a}}{2}$
|
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https://nersc.gitlab.io/filesystems/unix-file-permissions/
|
# Unix File Permissions¶
## Brief Overview¶
Every file (and directory) has an owner, an associated Unix group, and a set of permission flags that specify separate read, write, and execute permissions for the "user" (owner), "group", and "other". Group permissions apply to all users who belong to the group associated with the file. "Other" is also sometimes known as "world" permissions, and applies to all users who can login to the system. The command ls -l displays the permissions and associated group for any file. Here is an example of the output of this command:
drwx------ 2 elvis elvis 2048 Jun 12 2012 private
-rw------- 2 elvis elvis 1327 Apr 9 2012 try.f90
-rwx------ 2 elvis elvis 12040 Apr 9 2012 a.out
drwxr-x--- 2 elvis bigsci 2048 Oct 17 2011 share
drwxr-xr-x 3 elvis bigsci 2048 Nov 13 2011 public
From left to right, the fields above represent:
1. set of ten permission flags
2. link count (irrelevant to this topic)
3. owner
4. associated group
5. size
6. date of last modification
7. name of file
The permission flags from left to right are:
Position Meaning
1 "d" if a directory, "-" if a normal file
2, 3, 4 read, write, execute permission for user (owner) of file
5, 6, 7 read, write, execute permission for group
8, 9, 10 read, write, execute permission for other (world)
and have the following meanings:
Value Meaning
- Flag is not set.
w File is writable. For directories, files may be created or removed.
x File is executable. For directories, files may be listed.
s Set group ID (sgid). For directories, files created therein will be associated with the same group as the directory, rather than default group of the user. Subdirectories created therein will not only have the same group, but will also inherit the sgid setting.
These definitions can be used to interpret the example output of ls -l presented above:
drwx------ 2 elvis elvis 2048 Jun 12 2012 private
This is a directory named "private", owned by user elvis and associated with Unix group elvis. The directory has read, write, and execute permissions for the owner, and no permissions for any other user.
-rw------- 2 elvis elvis 1327 Apr 9 2012 try.f90
This is a normal file named "try.f90", owned by user elvis and associated with group elvis. It is readable and writable by the owner, but is not accessible to any other user.
-rwx------ 2 elvis elvis 12040 Apr 9 2012 a.out
This is a normal file named "a.out", owned by user elvis and associated with group elvis. It is executable, as well as readable and writable, for the owner only.
drwxr-x--- 2 elvis bigsci 2048 Oct 17 2011 share
This is a directory named "share", owned by user elvis and associated with group bigsci. The owner can read and write the directory; all members of the file group bigsci can list the contents of the directory. Presumably, this directory would contain files that also have "group read" permissions.
drwxr-xr-x 3 elvis bigsci 2048 Nov 13 2011 public
This is a directory named "public", owned by user elvis and associated with group bigsci. The owner can read and write the directory; all other users can only read the contents of the directory. A directory such as this would most likely contain files that have "world read" permissions.
## Useful File Permission Commands¶
When a file is created, the permission flags are set according to the file mode creation mask, which can be set using the umask command. The file mode creation mask (sometimes referred to as "the umask") is a three-digit octal value whose nine bits correspond to fields 2-10 of the permission flags. The resulting permissions are calculated via the bitwise AND of the unary complement of the argument (using bitwise NOT) and the default permissions specified by the shell (typically 666 for files and 777 for directories). Common useful values are:
umask value File Permissions Directory Permissions
002 -rw-rw-r-- drwxrwxr-x
007 -rw-rw---- drwxrwx---
022 -rw-r--r-- drwxr-xr-x
027 -rw-r----- drwxr-x---
077 -rw------- drwx------
Note that at NERSC, a default umask of 007 is set in .bash_profile. This is read after .bashrc, so setting umask in your .bashrc won't work, you will need to set it in your .bash_profile.
### chmod¶
The chmod ("change mode") command is used to change the permission flags on existing files. It can be applied recursively using the -R option. It can be invoked with either octal values representing the permission flags, or with symbolic representations of the flags. The octal values have the following meaning:
Octal Digit Binary Representation (rwx) Permission
0 000 none
1 001 execute only
2 010 write only
3 011 write and execute
7 111 read, write, and execute (full permissions)
Here is an example of chmod using octal values:
nersc$umask 0077 nersc$ touch foo
nersc$ls -l foo -rw------- 1 elvis elvis 0 Nov 19 14:49 foo nersc$ chmod 755 foo
nersc$ls -l foo -rwxr-xr-x 1 elvis elvis 0 Nov 19 14:49 foo In the above example, the umask for user elvis results in a file that is read-write for the user, with no other permissions. The chmod command specifies read-write-execute permissions for the user, and read-execute permissions for group and other. Here is the format of the chmod command when using symbolic values: chmod [-R] [classes][operator][modes] file ... The classes determine to which combination of user/group/other the operation will apply, the operator specifies whether permissions are being added or removed, and the modes specify the permissions to be added or removed. Classes are formed by combining one or more of the following letters: Letter Class Description u user Owner of the file g group Users who are members of the file's group o other Users who are not the owner of the file or members of the file's group a all All of the above (equivalent to "ugo") The following operators are supported: Operator Description + Add the specified modes to the specified classes. - Remove the specified modes from the specified classes. = The specified modes are made the exact modes for the specified classes. The modes specify which permissions are to be added to or removed from the specified classes. There are three primary values which correspond to the basic permissions, and two less frequently-used values that are useful in specific circumstances: Mode Name Description r read Read a file or list a directory's contents. w write Write to a file or directory. x execute Execute a file or traverse a directory. X "special" execute This is a slightly more restrictive version of "x". It applies execute permissions to directories in all cases, and to files only if at least one execute permission bit is already set. It is typically used with the "+" operator and the -R option, to give group and/or other access to a large directory tree, without setting execute permissions on normal (non-executable) files (e.g., text files). For example, chmod -R go+rx bigdir would set read and execute permissions on every file (including text files) and directory in the bigdir directory, recursively, for group and other. The command chmod -R go+rX bigdir would set read and execute permissions on every directory, and would set group and other read and execute permissions on files that were already executable by the owner. s setgid or sgid This setting is typically applied to directories. If set, any file created in that directory will be associated with the directory's group, rather than with the default file group of the owner. This is useful in setting up directories where many users share access. This setting is sometimes referred to as the "sticky bit", although that phrase has a historical meaning unrelated to this context. Sets of class/operator/mode may separated by commas. Using the above definitions, the previous (octal notation) example can be done symbolically: nersc$ umask
0077
nersc$touch foo nersc$ ls -l foo
-rw------- 1 elvis elvis 0 Nov 19 14:49 foo
nersc$chmod u+x,go+rx foo nersc$ ls -l foo
-rwxr-xr-x 1 elvis elvis 0 Nov 19 14:49 foo
## Unix File Groups¶
Unix file groups provide a means to control access to shared data on disk and tape.
### Overview of Unix Groups¶
Every user on a Unix system is a member of one or more Unix groups, including their primary or default group. Every file (or directory) on the system has an owner and an associated group. When a user creates a file, the file's associated group will be the user's default group. The user (owner) has the ability to change the associated group to any of the groups to which the user belongs. Unix groups can be defined that allow users to share data with other users who belong to the same group.
### Unix Groups at NERSC¶
Group names are limited to eight characters. A user's default group is the same as their username. NERSC users usually belong to several other groups, including groups associated with specific research projects. For example, consider a NERSC user named "elvis", who is working with the "Big Science" research project. This project has an allocation on NERSC's MPP systems, controlled by the repository (repo) "bigsci". Associated with this the repo is the Unix group "bigsci". The user (elvis) would then be a member of two file groups, elvis and bigsci. Because a NERSC user can be a member of more than one research project, such a user would be a member of more than one repo-associated Unix groups.
NERSC PIs, PI Proxies, and Project Managers can manage group membership within Iris. Continuing with the example above, if user elvis wants to collaborate with another user "jimi", but does not want other members of bigsci to be able to see the data, the PI for Big Science could create a new group (for example, "ejdata", for elvis and jimi's data). The PI would then add elvis and jimi to the ejdata group. Those two users could then use "group permissions" on directories and files to share data with one another. Currently, PIs who wish to create a new Unix group should contact NERSC Consulting.
### Useful Unix Group Commands¶
Command Description
groups username List group membership
id username List group membership
ls -l List group associated with file or directory
chgrp Change group associated with file or directory
newgrp Create new shell with different default group
sg Execute command with different default group
NERSC also provides the make-dir-group-writable script, to open up permissions for one or more files or directories to a group:
make-dir-group-writable -g groupname /path/to/dir1 /path/to/file2 ...
|
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|
http://mathhelpforum.com/advanced-algebra/1297-word-problem-help.html
|
# Math Help - Word Problem help
1. ## Word Problem help
A cashier has only one dollar, five dollar and ten dollar bills in her cash drawer. she has 3 times as many fives as tens and has 5 times as many ones as fives. if she has a total of $440 in the drawer, set up and solve an equation to find the number of each kind of bill in the drawer. thank you. 2. Originally Posted by erickalittle I've been working on this for about 20 min. and cannot figure it out. please help. A cashier has only one dollar, five dollar and ten dollar bills in her cash drawer. she has 3 times as many fives as tens and has 5 times as many ones as fives. if she has a total of$440 in the drawer, set up and solve an equation to find the number of each kind of bill in the drawer.
|
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|
http://physics.stackexchange.com/questions/28948/positive-permutation-tensor?answertab=oldest
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# Positive Permutation Tensor
I have seen that one can make an operator with $$L^i=\epsilon^{ijk}x_{j}\partial_{k}$$ But what if I want to make instead items that are sums, instead of differences. For instance $$\mathcal{L}^z=x\partial_y +y\partial_x$$ Is there an object like $|\epsilon_{ijk}|$ that has only 1s (no -1s)?
Thanks,
-
The short answer is No. The difference between the right $\epsilon_{abc}$ that changes the sign under transpositions – the antisymmetric one – and the wrong $\epsilon_{abc}$ that doesn't – yours – is that the right one is invariant under rotations while yours is not. The right epsilon tensor is a privileged invariant tensor; yours is just a random tensor, a random collection of components.
One may demonstrate it in this way. The $\epsilon$ symbol is a set of coefficients that may be used to construct a single quantity – scalar $Q$ – out of three vectors $S,T,U$: $$Q = \sum_{a,b,c=1}^3 \epsilon_{abc} S_a T_b U_c$$ If you think about it, $Q=(S\times T)\cdot U$ which is the inner product of a vector and a cross product of two other vectors. Its value is given purely geometrically; it doesn't depend on the coordinates.
This $Q$ may also be interpreted as the determinant of a matrix with vectors $S,T,U$ as its rows (or columns).
If you replaced the mixed-sign $\epsilon$ tensor by the "purely positive ones", the determinant would change to the sum over permutations without the sign and it wouldn't be rotationally invariant. Consequently, all objects constructed out of your version of $\epsilon$ would depend on the choice of the coordinates.
For example, consider $S=e_x$, $T=e_y$, $U=e_z$, unit vectors in the direction of the axes. You get $Q=1$. But you may also rotate $S,T,U$ by 90 degrees around the $z$-axis. Then you will have $S=e_y$, $T=-e_x$, $U=e_z$. The $Q$ constructed out of these vectors will still give $Q=1$ but yours would change to $Q=-1$ so it isn't rotationally symmetric.
All tensors that are symmetric under rotations are polynomials in $\epsilon_{abc}$ and $\delta_{ab}$.
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http://www.dummies.com/how-to/content/realworld-signals-and-systems-case-solving-the-dac.html
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The zero-order-hold (ZOH), which is inherent in many digital-to-analog converters (DACs), holds the analog output constant between samples. The action of the ZOH introduces frequency droop, a roll off of the effective DAC frequency response on the frequency interval zero to one-half the sampling rate fs, in reconstructing y(t) from y[n]. Two possible responses are to
• Apply an inverse sinc function shaping filter in the continuous-time domain.
• Correct for the droop before the signal emerges from the DAC.
The system block diagram is shown here.
Imagine that a senior engineer asks you to investigate the effectiveness of the simple infinite impulse response (IIR) and finite impulse response (FIR) digital filters as a way to mitigate ZOH frequency droop. You need to verify just how well these filters really work. The filter system functions are
To solve this problem, you need to use the frequency-domain relationship from the discrete- to continuous-time domains. The relationship, relative to the notation of the figure, is
You can assume that the analog reconstruction filter removes signal spectra beyond fs/2.
The frequency response of interest turns out to be the cascade of
Follow these steps to justify this outcome:
1. Let
From the convolution theorem for frequency spectra in the discrete-time domain, get
2. Use the discrete to continuous spectra relationship to discover that the output side of the DAC is
3. Use the convolution theorem for frequency spectra in the continuous-time domain to push the DAC output spectra through the ZOH filter:
The cascade result is now established.
To view the equivalent frequency response for this problem in the discrete-time domain, you just need to change variables according to the sampling theory:
Rearranging the variables in the cascade result viewed from the discrete-time domain perspective is
The ZOH frequency response is
Putting the pieces together and considering only the magnitude response reveals this equation:
To verify the performance, evaluate the sinc function and the FIR responses by using the SciPy signal.freqz() function approach of the frequency domain recipe. Check out the results in the following figure.
```In [393]: w = linspace(0,pi,400)
In [394]: H_ZOH_T = sinc(w/(2*pi))
In [395]: w,H_FIR = signal.freqz(array([-1, 18,-1])/16.,1,w)
In [396]: w,H_IIR = signal.freqz([-9/8.],[1, 1/8.],w)
In [402]: plot(w/(2*pi),20*log10(abs(H_ZOH_T)))
In [403]: # other plot cammand lines similar
In [412]: plot(w/(2*pi),20*log10(abs(H_FIR)*abs(H_ZOH_T)))```
These results are quite impressive for such simple correction filters. The goal is to get flatness that’s near 0 dB from 0 to π rad/sample (0 to 0.5 normalized). The response is flat to within 0.5 dB out to 0.4 rad/sample for the IIR filter; it’s a little worse for the FIR filter.
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http://tex.stackexchange.com/questions/151939/angles-in-chemfig
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# Angles in Chemfig
I want to draw this formula using chemfig:
This is what I've got so far:
\chemfig{Cu^+(-[:180]N**6(-**6(------)--(-OOC-)---))(-[1]N)(-[5]N)(-[7]N)}
I don't get the angle from N to Cu+ right. I tried to rotate parts of the formula, but there is always at least one angle that does not fit.
Any idea?
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Welcome to TeX.SX! – strpeter Dec 31 '13 at 15:34
Yes, I have an idea:
\documentclass{article}
\usepackage{chemfig}
\begin{document}
\definesubmol\cc{**6(---!\ff-!\ee--)}
\definesubmol\dd{**6(-!\ee--!\ff---)}
\definesubmol\ee{**6(-----)}
\definesubmol\ff[(-^{-}OOC)]{(-COO^{-})}
\chemfig{Cu^+(-[1]N([0,.5]!\cc))(-[3]N([:180,.5]!\dd))(-[5]N([:180,.5]!\cc))(-[7]N([:0,.5]!\dd))}
\end{document}
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The following code is similar to what unbonpetit wrote. The term .5 in [0,.5] and [180,.5] is chosen such that the aromatic cycles do not get too big.
\documentclass{standalone}
\usepackage{chemfig}
\begin{document}
\chemfig{Cu^+
(-[:+ 45]N([0,.5]**6(---(-COO^{-})-**6(------)--)))
(-[:+135]N([180,.5]**6(-**6(------)--(-^{-}OOC)---)))
(-[:+225]N([180,.5]**6(---(-^{-}OOC)-**6(------)--)))
(-[:+315]N([0,.5]**6(-**6(------)--(-COO^{-})---)))}
\end{document}
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@unbonpetit: I don't see the point... – strpeter Dec 31 '13 at 16:28
It is not exactly the same since your inner ring has 6 bonds instead of 5. Moreover, your code is not more or less explicit than mine, even after several edits. – unbonpetit Dec 31 '13 at 16:29
I must admit that the term "explicit" is misleading. – strpeter Dec 31 '13 at 16:37
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