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Despite decades of effort, the timing and duration of He II reionization, as
well as its morphology and the properties of the quasars believed to drive it,
are still not well constrained. In this paper we present a new method to study
both He II reionization and quasars via the thermal proximity effect -- the
photoelectric heating of the intergalactic medium around quasars when their
hard radiation doubly ionizes helium. We post-process a SPH simulation with 1D
radiative calculations, and study how the thermal proximity effect depends on
the amount of singly ionized helium, $x_{\rm HeII,0}$, which prevailed in the
IGM before the quasar turned on, and the characteristic lifetime $t_{\rm Q}$
for which quasars shine. We find that the amplitude of the temperature boost in
the quasar environment depends on $x_{\rm HeII,0}$, with a characteristic value
of $\Delta T \simeq 10^4\,{\rm K}$ for an initially singly ionized IGM ($x_{\rm
HeII,0} = 1.0$), whereas the size of the thermal proximity zone is sensitive to
quasar lifetime $t_{\rm Q}$, with typical sizes of ~100 cMpc for luminous
quasars shining for $t_{\rm Q}=10^8$ yr. This temperature boost is manifest as
a change in the thermal broadening of H I absorption lines near the quasar. We
introduce a new method based on measuring the Ly$\alpha$ forest power spectrum
as a function of distance from the quasar, and conduct Bayesian MCMC analysis
to demonstrate that the thermal proximity effect should be easily detectable.
For a mock dataset of 50 quasars at z~4, we predict that one can measure
$x_{\rm HeII,0}$ to a precision $\approx 0.04$, and $t_{\rm Q}$ to a precision
of $\approx 0.1$ dex. By applying our formalism to existing high-resolution
Ly$\alpha$ forest spectra of quasars at $3.1 \lesssim z \lesssim 5.0$, one
should be able to detect the thermal proximity effect, and reconstruct the full
reionization history of He II.
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We investigate the motion of a hard cylinder rolling down a soft inclined
plane. The cylinder is subjected to a viscous drag force and stochastic
fluctuations due to the surrounding medium. In a wide range of parameters we
observe bistability of the rolling velocity. In dependence on the parameters,
increasing noise level may lead to increasing or decreasing average velocity of
the cylinder. The approximative analytical theory agrees with numerical
results.
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The spectrum of gluons in the presence of a static quark-antiquark pair is
studied using Monte Carlo simulations on anisotropic space-time lattices. For
very small quark-antiquark separations R, the level orderings and approximate
degeneracies disagree with the expectations from an effective string theory. As
the quark-antiquark separation R increases, a dramatic rearrangement of the
energies occurs, and above 2 fm, all of the levels studied show behavior
consistent with an effective string description. The energy spacings are nearly
pi/R, but a tantalizing fine structure remains. In addition to 4-dimensional
SU(3) gauge theory, results from 3-dimensional SU(2) and compact U(1) gauge
theories are also presented.
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We seek an appropriate definition for a Shimura curve of Hodge type in
positive characteristics via characterizing curves in positive characteristics
which are reduction of Shimura curve over $\mathbb{C}$. In this paper, we study
the liftablity of a curve in the moduli space of principally polarized abelian
varieties over $k, \text{char} k=p$. We show that in the generic ordinary case,
some tensor decomposition of the isocrystal associated to the family imply that
this curve can be lifted to a Shimura curve.
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In an earlier paper the authors proved that limits of convergent graph
sequences can be described by various structures, including certain 2-variable
real functions called graphons, random graph models satisfying certain
consistency conditions, and normalized, multiplicative and reflection positive
graph parameters. In this paper we show that each of these structures has a
related, relaxed version, which are also equivalent. Using this, we describe a
further structure equivalent to graph limits, namely probability measures on
countable graphs that are ergodic with respect to the group of permutations of
the nodes.
As an application, we prove an analogue of the Positivstellensatz for graphs:
We show that every linear inequality between subgraph densities that holds
asymptotically for all graphs has a formal proof in the following sense: it can
be approximated arbitrarily well by another valid inequality that is a "sum of
squares" in the algebra of partially labeled graphs.
|
We present an active learning architecture that allows a robot to actively
learn which data collection strategy is most efficient for acquiring motor
skills to achieve multiple outcomes, and generalise over its experience to
achieve new outcomes. The robot explores its environment both via interactive
learning and goal-babbling. It learns at the same time when, who and what to
actively imitate from several available teachers, and learns when not to use
social guidance but use active goal-oriented self-exploration. This is
formalised in the framework of life-long strategic learning. The proposed
architecture, called Socially Guided Intrinsic Motivation with Active Choice of
Teacher and Strategy (SGIM-ACTS), relies on hierarchical active decisions of
what and how to learn driven by empirical evaluation of learning progress for
each learning strategy. We illustrate with an experiment where a simulated
robot learns to control its arm for realising two kinds of different outcomes.
It has to choose actively and hierarchically at each learning episode: 1) what
to learn: which outcome is most interesting to select as a goal to focus on for
goal-directed exploration; 2) how to learn: which data collection strategy to
use among self-exploration, mimicry and emulation; 3) once he has decided when
and what to imitate by choosing mimicry or emulation, then he has to choose who
to imitate, from a set of different teachers. We show that SGIM-ACTS learns
significantly more efficiently than using single learning strategies, and
coherently selects the best strategy with respect to the chosen outcome, taking
advantage of the available teachers (with different levels of skills).
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Previously observed non-Arrhenius behavior in fast ion conducting glasses
[\textit{Phys.\ Rev.\ Lett.}\ \textbf{76}, 70 (1996)] occurs at temperatures
near the glass transition temperature, $T_{g}$, and is attributed to changes in
the ion mobility due to ion trapping mechanisms that diminish the conductivity
and result in a decreasing conductivity with increasing temperature. It is
intuitive that disorder in glass will also result in a distribution of the
activation energies (DAE) for ion conduction, which should increase the
conductivity with increasing temperature, yet this has not been identified in
the literature. In this paper, a series of high precision ionic conductivity
measurements are reported for $0.5{Na}_{2}{S}+0.5[x{GeS}_{2}+(1-x){PS}_{5/2}]$
glasses with compositions ranging from $0 \leq x \leq 1$. The impact of the
cation site disorder on the activation energy is identified and explained using
a DAE model. The absence of the non-Arrhenius behavior in other glasses is
explained and it is predicted which glasses are expected to accentuate the DAE
effect on the ionic conductivity.
|
The rate of long-duration gamma ray bursts (GRBs) has been identified as a
potential proxy for the star formation rate (SFR) across redshift, but the
exact relationship depends on GRB progenitor models (single versus binary). The
single-progenitor collapsar model accounts for the preference towards
low-metallicity GRB progenitors, but is in apparent tension with some
high-metallicity GRB host galaxy measurements. As a possible solution, we
consider the scenario where high-metallicity GRB hosts harbour low metallicity
regions in which GRB progenitors form. For this, we use the IllustrisTNG
cosmological hydrodynamical simulation to investigate the internal metallicity
distribution of GRB hosts, implementing in post-processing different GRB
formation models. Predictions (GRB rate, host metallicities and stellar masses)
are compared to the high-completeness GRB legacy surveys BAT6 and SHOALS and a
sample of high-redshift GRB-DLA metallicities, allowing us to compute their
relative likelihoods. When the internal metallicity distribution of galaxies is
ignored, the best-fitting model requires a metallicity-independent channel, as
previously proposed by Trenti, Perna & Jimenez. However, when the internal
metallicity distribution is considered, a basic metallicity bias model with a
cutoff at $Z_{max}=0.35Z_\odot$ is the best fitting one. Current data are
insufficient to discriminate among more detailed metallicity bias models, such
as weak metallicity dependence of massive binaries vs stronger metallicity bias
of collapsars. An increased sample of objects, and direct measurements of host
stellar masses at redshift $z>2$ would allow to further constrain the origin of
long GRBs.
|
The hedgehog Skyrme model on three-sphere admits very rich spectrum of
solitonic solutions which can be encompassed by a strikingly simple scheme. The
main result of this paper is the statement of the tripartite structure of
solutions of the model and the discovery in what configurations these solutions
appear. The model contains features of more complicated models in General
Relativity and as such can give insight into them.
|
We performed numerical experiments on a two-dimensional driven lattice gas,
which constitutes a simple stochastic nonequilibrium many-body model. In this
model, focusing on the behavior along the direction transverse to the external
driving force, we numerically measure transport coefficients and dynamical
fluctuations outside the linear response regime far from equilibrium. Using
these quantities, we find the validity of the Einstein relation, the Green-Kubo
relation and the fluctuation-response relation.
|
This paper proposes a unified framework for the effective rate analysis over
arbitrary correlated and not necessarily identical multiple inputs single
output (MISO) fading channels, which uses moment generating function (MGF)
based approach and H transform representation. The proposed framework has the
potential to simplify the cumbersome analysis procedure compared to the
probability density function (PDF) based approach. Moreover, the effective
rates over two specific fading scenarios are investigated, namely independent
but not necessarily identical distributed (i.n.i.d.) MISO hyper Fox's H fading
channels and arbitrary correlated generalized K fading channels. The exact
analytical representations for these two scenarios are also presented. By
substituting corresponding parameters, the effective rates in various practical
fading scenarios, such as Rayleigh, Nakagami-m, Weibull/Gamma and generalized K
fading channels, are readily available. In addition, asymptotic approximations
are provided for the proposed H transform and MGF based approach as well as for
the effective rate over i.n.i.d. MISO hyper Fox's H fading channels.
Simulations under various fading scenarios are also presented, which support
the validity of the proposed method.
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The mid-infrared (mid-IR) is a strategically important band for numerous
applications ranging from night vision to biochemical sensing. Unlike visible
or near-infrared optical parts which are commonplace and economically available
off-the-shelf, mid-IR optics often requires exotic materials or complicated
processing, which accounts for their high cost and inferior quality compared to
their visible or near-infrared counterparts. Here we theoretically analyzed and
experimentally realized a Huygens metasurface platform capable of fulfilling a
diverse cross-section of optical functions in the mid-IR. The meta-optical
elements were constructed using high-index chalcogenide films deposited on
fluoride substrates:the choices of wide-band transparent materials allow the
design to be scaled across a broad infrared spectrum. Capitalizing on a novel
two-component Huygens' meta-atom design, the meta-optical devices feature an
ultra-thin profile ($\lambda_0/8$ in thickness, where $\lambda_0$ is the
free-space wavelength) and measured optical efficiencies up to 75% in
transmissive mode, both of which represent major improvements over
state-of-the-art. We have also demonstrated, for the first time, mid-IR
transmissive meta-lenses with diffraction-limited focusing and imaging
performance. The projected size, weight and power advantages, coupled with the
manufacturing scalability leveraging standard microfabrication technologies,
make the Huygens meta-optical devices promising for next-generation mid-IR
system applications.
|
Geodesic contraction in vector-valued differential equations is readily
verified by linearized operators which are uniformly negative-definite in the
Riemannian metric. In the infinite-dimensional setting, however, such analysis
is generally restricted to norm-contracting systems. We develop a
generalization of geodesic contraction rates to Banach spaces using a
smoothly-weighted semi-inner product structure on tangent spaces. We show that
negative contraction rates in bijectively weighted spaces imply asymptotic
norm-contraction, and apply recent results on asymptotic contractions in Banach
spaces to establish the existence of fixed points. We show that contraction in
surjectively weighted spaces verify non-equilibrium asymptotic properties, such
as convergence to finite- and infinite-dimensional subspaces, submanifolds,
limit cycles, and phase-locking phenomena. We use contraction rates in weighted
Sobolev spaces to establish existence and continuous data dependence in
nonlinear PDEs, and pose a method for constructing weak solutions using
vanishing one-sided Lipschitz approximations. We discuss applications to
control and order reduction of PDEs.
|
Gravitational lensing deflects light. A single lens deflector can only shear
images, but cannot induce rotations. Multiple lens planes can induce rotations.
Such rotations can be observed in quadruply imaged sources, and can be used to
distinguish between two proposed solutions of the flux anomaly problem:
substructures in lensing galaxies vs large scale structure. We predict the
expected amount of rotation due to large scale structure in strong lensing
systems, and show how this effect can be measured using ~ mas VLBI astrometry
of quadruple lenses with extended source structures. The magnitude of rotation
is around one degree. The biggest theoretical uncertainty is the power spectrum
of dark matter on very small scales. This procedure can potentially be turned
around to measure the dark matter power spectrum on very small scales. We list
the predicted RMS rotation angles for several quadruple lenses with known lens
and source redshifts.
|
Cyclotron resonance (CR) is considered one of the fundamental phenomena in
conducting systems. In this paper, we study CR in a gated two-dimensional (2D)
electron system (ES). Namely, we analyze the absorption of electromagnetic
radiation incident normal to the gated 2DES, where a standard dielectric
substrate separates the 2D electron sheet and the metallic steering electrode
("gate"); the whole system is placed in the perpendicular magnetic field. Our
analysis reveals the redshift of the absorption peak frequency compared to the
electron cyclotron frequency. The redshift appears in low-frequency regime,
when the resonant frequency is much less than the frequency of Fabry-Perot
modes in natural resonator "2D electron sheet - substrate - gate". Moreover, we
find this shift to be dependent on the electron density of 2DES. Therefore, it
can be controlled by varying the gate voltage. We predict that the shift can be
large in realistic gated or back-gated 2DESs. The obtained controllability of
CR in gated 2DES opens the door for exploring new physics and applications of
this phenomenon.
|
Considering a generalization of the Gibbons-Hawking-York covariant boundary
action that depends on both the extrinsic and the intrinsic geometry of the
boundary, we derive boundary conditions for the cosmological background and
tensor perturbations in a closed universe with space-like boundaries. We also
give a general method to reconstruct the covariant boundary action starting
from a given set of boundary conditions for the cosmological background. These
results may be of special relevance in the context of the path-integral
formulation of quantum cosmology, where boundary terms contain essential
physical information of the system.
|
Nested matroids were introduced by Crapo in 1965 and have appeared frequently
in the literature since then. A flat of a matroid $M$ is Hamiltonian if it has
a spanning circuit. A matroid $M$ is nested if and only if its Hamiltonian
flats form a chain under inclusion; $M$ is laminar if and only if, for every
$1$-element independent set $X$, the Hamiltonian flats of $M$ containing $X$
form a chain under inclusion. We generalize these notions to define the classes
of $k$-closure-laminar and $k$-laminar matroids. This paper focuses on
structural properties of these classes noting that, while the second class is
always minor-closed, the first is if and only if $k \le 3$. The main results
are excluded-minor characterizations for the classes of 2-laminar and
2-closure-laminar matroids.
|
The aim of this paper is to investigate the intersection problem between two
linear sets in the projective line over a finite field. In particular, we
analyze the intersection between two clubs with eventually different maximum
fields of linearity. Also, we analyze the intersection between the linear set
defined by the polynomial $\alpha x^{q^k}+\beta x$ and other linear sets having
the same rank; this family contains the linear set of pseudoregulus type
defined by $x^q$. The strategy relies on the study of certain algebraic curves
whose rational points describe the intersection of the two linear sets. Among
other geometric and algebraic tools, function field theory and the Hasse-Weil
bound play a crucial role. As an application, we give asymptotic results on
semifields of BEL-rank two.
|
Accurate stellar parameters and precise elemental abundances are vital pieces
to correctly characterize discovered planetary systems, better understand
planet formation, and trace galactic chemical evolution. We have performed a
uniform spectroscopic analysis for 1127 stars, yielding accurate gravity,
temperature, and projected rotational velocity in addition to precise
abundances for 15 elements (C, N, O, Na, Mg, Al, Si, Ca, Ti, V, Cr, Mn, Fe, Ni,
and Y). Most of the stars in this sample are Kepler Objects of Interest,
observed by the California-Kepler Survey (CKS) and include 1,003 stars hosting
1,562 confirmed planets. This catalog extends the uniform analysis of our
previous catalog, bringing the total of homogeneously analyzed stars to almost
2,700 F, G, and K dwarfs. To ensure consistency between the catalogs, we
performed an analysis of our ability to recover parameters as a function of S/N
ratio and present individual uncertainties as well as functions to calculate
uncertainties for parameters derived from lower S/N ratio spectra. With the
updated parameters, we used isochrone fitting to derived new radii, masses and
ages for the stars. Finally, we look at the Mg/Si ratios of super-Earth and
sub-Neptune hosts to test whether differences in initial composition might lead
to differences in planet radius. We find no differences in the Mg/Si
distribution as a function of planet radius.
|
The mass distribution of the Galactic disk is constructed from the terminal
velocity curve and the mass discrepancy-acceleration relation. Mass models
numerically quantifying the detailed surface density profiles are tabulated.
For $R_0 = 8$ kpc, the models have stellar mass $5 < M_* < 6 \times 10^{10}$
M$_{\odot}$, scale length $2.0 \le R_d \le 2.9$ kpc, LSR circular velocity $222
\le \Theta_0 \le 233$ km s$^{-1}$, and solar circle stellar surface density $34
\le \Sigma_d(R_0) \le 61$ M$_{\odot}$ pc$^{-2}$. The present inter-arm location
of the solar neighborhood may have a somewhat lower stellar surface density
than average for the solar circle. The Milky Way appears to be a normal spiral
galaxy that obeys scaling relations like the Tully-Fisher relation, the
size-mass relation, and the disk maximality-surface brightness relation. The
stellar disk is maximal, and the spiral arms are massive. The bumps and wiggles
in the terminal velocity curve correspond to known spiral features (e.g., the
Centaurus Arm is a $\sim 50\%$ overdensity). The rotation curve switches
between positive and negative over scales of hundreds of parsecs. The rms
amplitude $\langle$$|$$dV/dR$$|^2$$\rangle$$^{1/2} \approx 14$ km s$^{-1}$
kpc$^{-1}$, implying that commonly neglected terms in the Jeans equations may
be non-negligible. The spherically averaged local dark matter density is
$\rho_{0,DM} \approx 0.009$ M$_{\odot}$ pc$^{-3}$ (0.3 GeV cm$^{-3}$).
Adiabatic compression of the dark matter halo may help reconcile the Milky Way
with the $c$-$V_{200}$ relation expected in $\Lambda$CDM while also helping to
mitigate the too big to fail problem, but it remains difficult to reconcile the
inner bulge/bar dominated region with a cuspy halo. We note that NGC 3521 is a
near twin to the Milky Way, having a similar luminosity, scale length, and
rotation curve.
|
Ferroelectrics offer a promising materials platform to realize
energy-efficient non-volatile memory technology with the FeFET-based
implementations being one of the most area-efficient ferroelectric memory
architectures. However, the FeFET operation entails a fundamental trade-off
between the read and the program operations. To overcome this trade-off, we
propose in this work, a novel device, Mott-FeFET, that aims to replace the
Silicon channel of the FeFET with VO2- a material that exhibits an electrically
driven insulator-metal phase transition. The Mott-FeFET design, which
demonstrates a (ferroelectric) polarization-dependent threshold voltage,
enables the read current distinguishability (i.e., the ratio of current sensed
when the Mott-FeFET is in state 1 and 0, respectively) to be independent of the
program voltage. This enables the device to be programmed at low voltages
without affecting the ability to sense/read the state of the device. Our work
provides a pathway to realize low-voltage and energy-efficient non-volatile
memory solutions.
|
In this paper, we study damped Langevin stochastic differential equations
with singular velocity fields. We prove the strong well-posedness of such
equations. Moreover, by combining the technique of Lyapunov functions with
Krylov's estimate, we also establish the exponential ergodicity for the unique
strong solution.
|
Current large language models (LLMs) primarily utilize next-token prediction
method for inference, which significantly impedes their processing speed. In
this paper, we introduce a novel inference methodology termed next-sentence
prediction, aimed at enhancing the inference efficiency of LLMs. We present
Sentence Variational Autoencoder (SentenceVAE), a tiny model consisting of a
Sentence Encoder and a Sentence Decoder. The Sentence Encoder can effectively
condense the information within a sentence into a singular token, while the
Sentence Decoder can reconstruct this compressed token back into sentence. By
integrating SentenceVAE into the input and output layers of LLMs, we develop
Sentence-level LLMs (SLLMs) that employ a sentence-by-sentence inference
method. In addition, the SentenceVAE module of SLLMS can maintain the integrity
of the original semantic content by segmenting the context into sentences,
thereby improving accuracy while boosting inference speed. Moreover, compared
to previous LLMs, SLLMs process fewer tokens over equivalent context length,
significantly reducing memory demands for self-attention computation and
facilitating the handling of longer context. Extensive experiments on Wanjuan
dataset have reveal that the proposed method can accelerate inference speed by
204~365%, reduce perplexity (PPL) to 46~75% of its original metric, and
decrease memory overhead by 86~91% for the equivalent context length, compared
to the token-by-token method.
|
A single neuron receives an extensive array of synaptic inputs through its
dendrites, raising the fundamental question of how these inputs undergo
integration and summation, culminating in the initiation of spikes in the soma.
Experimental and computational investigations have revealed various modes of
integration operations that include linear, superlinear, and sublinear
summation. Interestingly, distinct neuron types exhibit diverse patterns of
dendritic integration contingent upon the spatial distribution of dendrites.
The functional implications of these specific integration modalities remain
largely unexplored. In this study, we employ the Purkinje cell as a model
system to investigate these intricate questions. Our findings reveal that
Purkinje cells (PCs) generally exhibit sublinear summation across their
expansive dendrites. The degree of sublinearity is dynamically modulated by
both spatial and temporal input. Strong sublinearity necessitates that the
synaptic distribution in PCs be globally scattered sensitive, whereas weak
sublinearity facilitates the generation of complex firing patterns in PCs.
Leveraging dendritic branches characterized by strong sublinearity as
computational units, we demonstrate that a neuron can adeptly address the
feature-binding problem. Collectively, these results offer a systematic
perspective on the functional role of dendritic sublinearity, providing
inspiration for a broader understanding of dendritic integration across various
neuronal types.
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We introduce a simple algorithm, True Asymptotic Natural Gradient
Optimization (TANGO), that converges to a true natural gradient descent in the
limit of small learning rates, without explicit Fisher matrix estimation.
For quadratic models the algorithm is also an instance of averaged stochastic
gradient, where the parameter is a moving average of a "fast", constant-rate
gradient descent. TANGO appears as a particular de-linearization of averaged
SGD, and is sometimes quite different on non-quadratic models. This further
connects averaged SGD and natural gradient, both of which are arguably optimal
asymptotically.
In large dimension, small learning rates will be required to approximate the
natural gradient well. Still, this shows it is possible to get arbitrarily
close to exact natural gradient descent with a lightweight algorithm.
|
The ability to create high-quality 3D faces from a single image has become
increasingly important with wide applications in video conferencing, AR/VR, and
advanced video editing in movie industries. In this paper, we propose Face
Diffusion NeRF (FaceDNeRF), a new generative method to reconstruct high-quality
Face NeRFs from single images, complete with semantic editing and relighting
capabilities. FaceDNeRF utilizes high-resolution 3D GAN inversion and expertly
trained 2D latent-diffusion model, allowing users to manipulate and construct
Face NeRFs in zero-shot learning without the need for explicit 3D data. With
carefully designed illumination and identity preserving loss, as well as
multi-modal pre-training, FaceDNeRF offers users unparalleled control over the
editing process enabling them to create and edit face NeRFs using just
single-view images, text prompts, and explicit target lighting. The advanced
features of FaceDNeRF have been designed to produce more impressive results
than existing 2D editing approaches that rely on 2D segmentation maps for
editable attributes. Experiments show that our FaceDNeRF achieves exceptionally
realistic results and unprecedented flexibility in editing compared with
state-of-the-art 3D face reconstruction and editing methods. Our code will be
available at https://github.com/BillyXYB/FaceDNeRF.
|
We obtain a sharp local well-posedness result for the Gradient
Nonlinear Wave Equation on a nonsmooth curved background. In the process we
introduce variable coefficient versions of Bourgain's $X^{s,b}$ spaces, and use
a trilinear multiscale wave packet decomposition in order to prove a key
trilinear estimate.
|
I present results and highlight aspects of halo EFT to loosely bound systems
composed of nucleons and alpha particles, with emphasis on Coulomb
interactions.
|
The structural, magnetic, and electronic properties of
NdFe$_{0.5}$Mn$_{0.5}$O$_3$ have been studied in detail using bulk
magnetization, neutron/x-ray diffraction and first principles density
functional theory calculations. The material crystallizes in the orthorhombic
$Pbnm$ structure, where both Mn and Fe occupy the same crystallographic site
($4b$).
Mn/Fe sublattice of the compound orders in to a G-type antiferromagnetic
phase close to 250\,K where the magnetic structure belongs to ${\Gamma}_{1}$
irreducible representation with spins aligned along the crystallographic $b$
direction. This is unconventional in the sense that most of the orthoferrites
and orthochromites order in the ${\Gamma}_{4}$ representation below the
N\'{e}el temperature.This magnetic structure then undergoes a complete spin
reorientation transition with temperature in the range 75\,K$\gtrsim$ T
$\gtrsim$ 25\,K where the magnetic structure exists as a sum of two irreducible
representations (${\Gamma}_{1}$+${\Gamma}_{2}$) as seen from neutron
diffraction measurements. At 6\,K, the magnetic structure belongs entirely to
${\Gamma}_{2}$ representation with spins aligned antiferromagnetically along
the crystallographic $c$ direction having a small ferromagnetic component
($F_x$). The unusual spin reorientation and correlation between magnetic ground
state and electronic structure have been investigated using first principles
calculations within GGA+U and GGA+U+SO formalisms.
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Homogeneous binary function products are often encountered in the
sub-universes modeled by databases, from genealogical trees to sports, from
education to healthcare, etc. Their properties must be discovered and enforced
by the software applications managing such data to guarantee plausibility. The
(Elementary) Mathematical Data Model provides 18 dyadic-type homogeneous binary
function product constraint types. MatBase, an intelligent data and knowledge
base management system prototype, allows database designers to simply declare
them by only clicking corresponding checkboxes and automatically generates code
for enforcing them. This paper describes the algorithms that MatBase uses for
enforcing all these 18 homogeneous binary function product constraint types,
which may also be used by developers not having access to MatBase.
|
Accurate parameter estimation of gravitational waves from coalescing compact
binary sources is a key requirement for gravitational-wave astronomy.
Evaluating the posterior probability density function of the binary's
parameters (component masses, sky location, distance, etc.) requires computing
millions of waveforms. The computational expense of parameter estimation is
dominated by waveform generation and scales linearly with the waveform
computational cost. Previous work showed that gravitational waveforms from
non-spinning compact binary sources are amenable to a truncated singular value
decomposition, which allows them to be reconstructed via interpolation at fixed
computational cost. However, the accuracy requirement for parameter estimation
is typically higher than for searches, so it is crucial to ascertain that
interpolation does not lead to significant errors. Here we provide a proof of
principle to show that interpolated waveforms can be used to recover posterior
probability density functions with negligible loss in accuracy with respect to
non-interpolated waveforms. This technique has the potential to significantly
increase the efficiency of parameter estimation.
|
The recent discovery of pure boron nanotubes raises questions about their
detailed atomic structure. Previous simulations predicted tubular structures
with smooth or puckered surfaces. Here, we present some novel results based on
ab initio simulations of bundled single-wall zigzag boron nanotubes (ropes).
Besides the known smooth and puckered modifications, we found new forms that
are radially constricted, and which seem to be energetically superior to the
known isomers. Furthermore, those structures might be interpreted as
intermediate states between ideal tubular phases and the known bulk phases
based on boron icosahedra.
|
An alternating electric field, applied to a quantum dot, couples to the
electron spin via the spin-orbit interaction. We analyze different types of
spin-orbit coupling known in the literature and find two efficient mechanisms
of spin control in quantum dots. The linear in momentum Dresselhaus and Rashba
spin-orbit couplings give rise to a fully transverse effective magnetic field
in the presence of a Zeeman splitting at lowest order in the spin-orbit
interaction. The cubic in momentum Dresselhaus terms are efficient in a quantum
dot with non-harmonic confining potential and give rise to a spin-electric
coupling proportional to the orbital magnetic field. We derive an effective
spin Hamiltonian, which can be used to implement spin manipulation on a
timescale of $10 {\rm ns}$ with the current experimental setups.
|
In this work, we investigate the near horizon and asymptotic symmetries of
static and rotating hairy$-$AdS black hole in the framework of general minimal
massive gravity. We obtain energy, angular momentum and entropy of the
solutions. Then we show that our results for these quantities are consistent
with the first law of black hole thermodynamics. By considering the near
horizon geometry of black hole, we find near horizon conserved charges and
their algebra. By writing the algebra of conserved charges in terms of Fourier
modes we have obtained the conserved charges in terms of zero modes.
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We give a "second generation" exposition of the slope filtration theorem for
modules with Frobenius action over the Robba ring, providing a number of
simplifications in the arguments. Some of these are inspired by parallel work
of Hartl and Pink, which points out some analogies with the formalism of stable
vector bundles.
|
This article consists of two parts. The first section presents the highlights
on the goals of neutrino physics, status of the current neutrino experiments
and future directions and program. The second section describes the theme,
program and research efforts for the TEXONO Collaboration among scientists from
Taiwan and China.
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We present a deterministic distributed algorithm to compute all-pairs
shortest paths(APSP) in an edge-weighted directed or undirected graph. Our
algorithm runs in $\tilde{O}(n^{3/2})$ rounds in the Congest model, where $n$
is the number of nodes in the graph. This is the first $o(n^2)$ rounds
deterministic distributed algorithm for the weighted APSP problem. Our
algorithm is fairly simple and incorporates a deterministic distributed
algorithm we develop for computing a `blocker set' \cite{King99}, which has
been used earlier in sequential dynamic computation of APSP.
|
We consider the iterated function systems (IFSs) that consist of three
general similitudes in the plane with centres at three non-collinear points,
and with a common contraction factor $\la\in(0,1)$.
As is well known, for $\la=1/2$ the invariant set, $\S_\la$, is a fractal
called the Sierpi\'nski sieve, and for $\la<1/2$ it is also a fractal. Our goal
is to study $\S_\la$ for this IFS for $1/2<\la<2/3$, i.e., when there are
"overlaps" in $\S_\la$ as well as "holes". In this introductory paper we show
that despite the overlaps (i.e., the Open Set Condition breaking down
completely), the attractor can still be a totally self-similar fractal,
although this happens only for a very special family of algebraic $\la$'s
(so-called "multinacci numbers"). We evaluate $\dim_H(\S_\la)$ for these
special values by showing that $\S_\la$ is essentially the attractor for an
infinite IFS which does satisfy the Open Set Condition. We also show that the
set of points in the attractor with a unique ``address'' is self-similar, and
compute its dimension.
For ``non-multinacci'' values of $\la$ we show that if $\la$ is close to 2/3,
then $\S_\la$ has a nonempty interior and that if $\la<1/\sqrt{3}$ then \S_\la$
has zero Lebesgue measure. Finally we discuss higher-dimensional analogues of
the model in question.
|
Two classes of stringy instanton effects, stronger than standard field theory
instantons, are identified in the heterotic string theory. These contributions
are established using type IIA/heterotic and type I/heterotic dualities. They
provide examples for the heterotic case of the effects predicted by Shenker
based on the large-order behavior of perturbation theory. The corrections
vanish as the radius of the compactification goes to infinity. For appropriate
amplitudes, they are computable worldsheet or worldline instanton effects on
the dual side. Some potential applications are discussed.
|
The mechanical properties and microstructural evolution of a medium-entropy
alloy Co$_{17.5}$Cr$_{12.5}$Fe$_{55}$Ni$_{10}$Mo$_{5}$ (at%) in a low
temperature range (including the record low temperatures region down to 0.5 K)
were investigated. It has been established that low-temperature plastic
deformation initiates martensitic phase transformations in this alloy, and the
values of the dynamic modulus of elasticity correlate with the degree of phase
transformations.
|
We prove in this paper that the weighted volume of the set of integral
transportation matrices between two integral histograms r and c of equal sum is
a positive definite kernel of r and c when the set of considered weights forms
a positive definite matrix. The computation of this quantity, despite being the
subject of a significant research effort in algebraic statistics, remains an
intractable challenge for histograms of even modest dimensions. We propose an
alternative kernel which, rather than considering all matrices of the
transportation polytope, only focuses on a sub-sample of its vertices known as
its Northwestern corner solutions. The resulting kernel is positive definite
and can be computed with a number of operations O(R^2d) that grows linearly in
the complexity of the dimension d, where R^2, the total amount of sampled
vertices, is a parameter that controls the complexity of the kernel.
|
High-resolution location ("heartbeat") data of transit fleet vehicles is a
relatively new data source for many transit agencies. On its surface, the
heartbeat data can provide a wealth of information about all operational
details of a recorded transit vehicle trip, from its location trajectory to its
speed and acceleration profiles. Previous studies have mainly focused on
decomposing the total trip travel time into different components by vehicle
state and then extracting measures of delays to draw conclusions on the
performance of a transit route. This study delves into the task of
reconstructing a complete, continuous and smooth transit vehicle trajectory
from the heartbeat data that allows for the extraction of operational
information of a bus at any point in time into its trip. Using only the
latitude, longitude, and timestamp fields of the heartbeat data, the authors
demonstrate that a continuous, smooth, and monotonic vehicle trajectory can be
reconstructed using local regression in combination with monotonic cubic spline
interpolation. The resultant trajectory can be used to evaluate transit
performance and identify locations of bus delay near infrastructure such as
traffic signals, pedestrian crossings, and bus stops.
|
We review recent progress made in quantum information processing (QIP) which
can be applied in the simulation of quantum systems and chemical phenomena. The
review is focused on quantum algorithms which are useful for quantum simulation
of chemistry and advances in nuclear magnetic resonance (NMR) and electron spin
resonance (ESR) QIP. Discussions also include a number of recent experiments
demonstrating the current capabilities of the NMR QIP for quantum simulation
and prospects for spin-based implementations of QIP.
|
We use the density matrix renormalization group method(DMRG) and the infinite
time evolved block decimation method(iTEBD) to investigate the ground states of
the spin-orbit coupled Fermi gas in a one dimensional optical lattice with a
transverse magnetic field. We discover that the system with attractive
interaction can have a polarized insulator(PI), a superconducting phase(SC), a
Luther-Emery(LE) phase and a band insulator(BI) phase as we vary the chemical
potential and the strength of magnetic field. We find that spin-orbit coupling
induces a triplet pairing order at zero momentum with the same critical
exponent as that of the singlet pairing one in both the SC and the LE phase. In
contrast to the FFLO phase found in the spin imbalanced system without
spin-orbit coupling, pairings at finite momentum in these two phases have a
larger exponent hence do not dictate the long range behavior. We also find good
agreements of the dominant correlations between numerical results and the
prediction from the bosonization method. The presence of Majorana fermions is
tested. However, unlike results from the mean field study, we do not find
positive evidence of Majorana fermions in our system.
|
We compare the domain of the assembly map in algebraic K-theory with respect
to the family of finite subgroups with the domain of the assembly map with
respect to the family of virtually cyclic subgroups and prove that the former
is a direct summand of the later.
|
In this paper, we propose a general meshless structure-preserving Galerkin
method for solving dissipative PDEs on surfaces. By posing the PDE in the
variational formulation and simulating the solution in the finite-dimensional
approximation space spanned by (local) Lagrange functions generated with
positive definite kernels, we obtain a semi-discrete Galerkin equation that
inherits the energy dissipation property. The fully-discrete
structure-preserving scheme is derived with the average vector field method. We
provide a convergence analysis of the proposed method for the Allen-Cahn
equation. The numerical experiments also verify the theoretical analysis
including the convergence order and structure-preserving properties.
|
Despite numerous experimental and theoretical studies devoted to the oxygen
evolution reaction, the mechanism of the OER on transition metal oxides remains
controversial. This is in part owed to the ambiguity of electrochemical
parameters of the mechanism such as the Tafel slope and reaction orders. We
took the most commonly assumed adsorbate mechanism and calculated the Tafel
slopes and reaction orders with respect to pH based on microkinetic analysis.
We demonstrate that number of possible Tafel slopes strongly depends on a
number of preceding steps and surface coverage. Furthermore, the Tafel slope
becomes pH dependent when the coverage of intermediates changes with pH. These
insights complicate the identification of a rate-limiting step by a single
Tafel slope at a single pH. Yet, simulations of reaction orders complementary
to Tafel slopes can solve some ambiguities to distinguish between possible
rate-limiting steps. The most insightful information can be obtained from the
low overpotential region of the Tafel plot. The simulations in this work
provide clear guidelines to experimentalists for the identification of the
limiting steps in the adsorbate mechanism using the observed values of the
Tafel slope and reaction order in pH-dependent studies.
|
Various new brain-computer interface technologies or neuroscience
applications require decoding stimulus-following neural responses to natural
stimuli such as speech and video from, e.g., electroencephalography (EEG)
signals. In this context, generalized canonical correlation analysis (GCCA) is
often used as a group analysis technique, which allows the extraction of
correlated signal components from the neural activity of multiple subjects
attending to the same stimulus. GCCA can be used to improve the signal-to-noise
ratio of the stimulus-following neural responses relative to all other
irrelevant (non-)neural activity, or to quantify the correlated neural activity
across multiple subjects in a group-wise coherence metric. However, the
traditional GCCA technique is stimulus-unaware: no information about the
stimulus is used to estimate the correlated components from the neural data of
several subjects. Therefore, the GCCA technique might fail to extract relevant
correlated signal components in practical situations where the amount of
information is limited, for example, because of a limited amount of training
data or group size. This motivates a new stimulus-informed GCCA (SI-GCCA)
framework that allows taking the stimulus into account to extract the
correlated components. We show that SI-GCCA outperforms GCCA in various
practical settings, for both auditory and visual stimuli. Moreover, we showcase
how SI-GCCA can be used to steer the estimation of the components towards the
stimulus. As such, SI-GCCA substantially improves upon GCCA for various
purposes, ranging from preprocessing to quantifying attention.
|
We present a new contribution of the R-parity violating supersymmetry (SUSY)
to neutrinoless double beta decay via the pion exchange between decaying
neutrons. The pion coupling to the final state electrons is induced by the
R-parity violating SUSY interactions. We have found this pion-exchange
mechanism to dominate over the conventional two-nucleon one. The latter
corresponds to direct interaction between quarks from two decaying neutrons
without any light hadronic mediator like pion. The constraints on the certain
R-parity violating SUSY parameters are extracted from the current experimental
neutrinoless double beta decay half-life limit. These constraints are
significantly stronger than those previously known or expected from the ongoing
accelerator experiments.
|
When humans perform contact-rich manipulation tasks, customized tools are
often necessary to simplify the task. For instance, we use various utensils for
handling food, such as knives, forks and spoons. Similarly, robots may benefit
from specialized tools that enable them to more easily complete a variety of
tasks. We present an end-to-end framework to automatically learn tool
morphology for contact-rich manipulation tasks by leveraging differentiable
physics simulators. Previous work relied on manually constructed priors
requiring detailed specification of a 3D object model, grasp pose and task
description to facilitate the search or optimization process. Our approach only
requires defining the objective with respect to task performance and enables
learning a robust morphology through randomizing variations of the task. We
make this optimization tractable by casting it as a continual learning problem.
We demonstrate the effectiveness of our method for designing new tools in
several scenarios, such as winding ropes, flipping a box and pushing peas onto
a scoop in simulation. Additionally, experiments with real robots show that the
tool shapes discovered by our method help them succeed in these scenarios.
|
The temporal evolution of mechanical energy and spatially-averaged crack
speed are both monitored in slowly fracturing artificial rocks. Both signals
display an irregular burst-like dynamics, with power-law distributed
fluctuations spanning a broad range of scales. Yet, the elastic power released
at each time step is proportional to the global velocity all along the process,
which enables defining a material-constant fracture energy. We characterize the
intermittent dynamics by computing the burst statistics. This latter displays
the scale-free features signature of crackling dynamics, in qualitative but not
quantitative agreement with the depinning interface models derived for fracture
problems. The possible sources of discrepancies are pointed out and discussed.
|
We state a conjecture on the stability of Betti diagrams of powers of
monomial ideals.
|
In the realm of 3D computer vision, parametric models have emerged as a
ground-breaking methodology for the creation of realistic and expressive 3D
avatars. Traditionally, they rely on Principal Component Analysis (PCA), given
its ability to decompose data to an orthonormal space that maximally captures
shape variations. However, due to the orthogonality constraints and the global
nature of PCA's decomposition, these models struggle to perform localized and
disentangled editing of 3D shapes, which severely affects their use in
applications requiring fine control such as face sculpting. In this paper, we
leverage diffusion models to enable diverse and fully localized edits on 3D
meshes, while completely preserving the un-edited regions. We propose an
effective diffusion masking training strategy that, by design, facilitates
localized manipulation of any shape region, without being limited to predefined
regions or to sparse sets of predefined control vertices. Following our
framework, a user can explicitly set their manipulation region of choice and
define an arbitrary set of vertices as handles to edit a 3D mesh. Compared to
the current state-of-the-art our method leads to more interpretable shape
manipulations than methods relying on latent code state, greater localization
and generation diversity while offering faster inference than optimization
based approaches. Project page: https://rolpotamias.github.io/Shapefusion/
|
The study of transcription remains one of the centerpieces of modern biology
with implications in settings from development to metabolism to evolution to
disease. Precision measurements using a host of different techniques including
fluorescence and sequencing readouts have raised the bar for what it means to
quantitatively understand transcriptional regulation. In particular our
understanding of the simplest genetic circuit is sufficiently refined both
experimentally and theoretically that it has become possible to carefully
discriminate between different conceptual pictures of how this regulatory
system works. This regulatory motif, originally posited by Jacob and Monod in
the 1960s, consists of a single transcriptional repressor binding to a promoter
site and inhibiting transcription. In this paper, we show how seven distinct
models of this so-called simple-repression motif, based both on equilibrium and
kinetic thinking, can be used to derive the predicted levels of gene expression
and shed light on the often surprising past success of the equilbrium models.
These different models are then invoked to confront a variety of different data
on mean, variance and full gene expression distributions, illustrating the
extent to which such models can and cannot be distinguished, and suggesting a
two-state model with a distribution of burst sizes as the most potent of the
seven for describing the simple-repression motif.
|
We investigate the effect of an applied uniaxial strain on the ferromagnetic
instability due to long- range Coulomb interaction between Dirac fermions in
graphene. In case of undeformed graphene the ferromagnetic exchange instability
occurs at sufficiently strong interaction within the Hartree- Fock
approximation. In this work we show that using the same theoretical framework
but with an additional applied uniaxial strain, the transition can occur for
much weaker interaction, within the range in suspended graphene. We also study
the consequence of strain on the formation of localized magnetic states on
adatoms in graphene. We systematically analyze the interplay between the
anisotropic (strain- induced) nature of the Dirac fermions in graphene, on-
site Hubbard interaction at the impurity and the hybridization between the
graphene and impurity electrons. The polarization of the electrons in the
localized orbital is numerically calculated within the mean- field self-
consistent scheme. We obtain complete phase diagram containing non- magnetic as
well as magnetic regions and our results can find prospective application in
the field of carbon- based spintronics.
|
We present an HST STIS spectrum of the HeII Gunn-Peterson effect towards
HE2347-4342. Compared to the previous HST GHRS data obtained by Reimers et al.
(1997), the STIS spectrum has a much improved resolution. The 2-D detector also
allows us to better characterize the sky and dark background. We confirm the
presence of two spectral ranges of much reduced opacity, the opacity gaps, and
provide improved lower limits on the HeII G-P opacity in the high opacity
regions. We use the STIS spectrum together with a Keck--HIRES spectrum covering
the corresponding HI Lya forest to calculate a 1-D map of the softness S of the
ionization radiation along the line of sight towards HE 2347-4342, where S is
the ratio of the HI to HeII photoionization rates. We find that S is generally
large but presents important variations, from S ~ 30 in the opacity gaps to a 1
sigma lower limit of 2300 at z~2.86, in a region which shows an extremely low
HI opacity over a 6.5 A range. We note that a large S naturally accounts for
most of the large SiIV to CIV ratios seen in other quasar absorption line
spectra. We present a simple model that reproduces the shape of the opacity
gaps in absence of large individual absorption lines. We extend the model
described in Heap et al. (2000) to account for the presence of sources close to
the line of sight of the background quasar. As an alternative to the delayed
reionization model suggested by Reimers et al. (1997), we propose that the
large softness observed at z~2.86 is due to the presence of bright soft sources
close to the line of sight, i.e. for which the ratio between the number of HI
to HeII ionizing photons reaching the IGM is large. We discuss these two models
and suggest ways to discriminate between them.
|
This work deals with the problem of uplink communication and localization in
an integrated sensing and communication system, where users are in the near
field (NF) of antenna aperture due to the use of high carrier frequency and
large antenna arrays at base stations. We formulate joint NF signal detection
and localization as a problem of recovering signals with a sparse pattern. To
solve the problem, we develop a message passing based sparse Bayesian learning
(SBL) algorithm, where multiple unitary approximate message passing
(UAMP)-based sparse signal estimators work jointly to recover the sparse
signals with low complexity. Simulation results demonstrate the effectiveness
of the proposed method.
|
We explore the possibility that a new physics interaction can provide an
explanation for the knee just above $10^6$ GeV in the cosmic ray spectrum. We
model the new physics modifications to the total proton-proton cross section
with an incoherent term that allows for missing energy above the scale of new
physics. We add the constraint that the new physics must also be consistent
with published $pp$ cross section measurements, using cosmic ray observations,
an order of magnitude and more above the knee. We find that the rise in cross
section required at energies above the knee is radical. The increase in cross
section suggests that it may be more appropriate to treat the scattering
process in the black disc limit at such high energies. In this case there may
be no clean separation between the standard model and new physics contributions
to the total cross section. We model the missing energy in this limit and find
a good fit to the Tibet III cosmic ray flux data. We comment on testing the new
physics proposal for the cosmic ray knee at the Large Hadron Collider.
|
We present a novel, reflection-aware method for 3D sound localization in
indoor environments. Unlike prior approaches, which are mainly based on
continuous sound signals from a stationary source, our formulation is designed
to localize the position instantaneously from signals within a single frame. We
consider direct sound and indirect sound signals that reach the microphones
after reflecting off surfaces such as ceilings or walls. We then generate and
trace direct and reflected acoustic paths using inverse acoustic ray tracing
and utilize these paths with Monte Carlo localization to estimate a 3D sound
source position. We have implemented our method on a robot with a cube-shaped
microphone array and tested it against different settings with continuous and
intermittent sound signals with a stationary or a mobile source. Across
different settings, our approach can localize the sound with an average
distance error of 0.8m tested in a room of 7m by 7m area with 3m height,
including a mobile and non-line-of-sight sound source. We also reveal that the
modeling of indirect rays increases the localization accuracy by 40% compared
to only using direct acoustic rays.
|
In this paper we solve several reverse isoperimetric problems in the class of
$\lambda$-convex bodies, i.e., convex bodies whose curvature at each point of
their boundary is bounded below by some $\lambda > 0$.
We give an affirmative answer in $\mathbb{R}^3$ to a conjecture due to
Borisenko which states that the $\lambda$-convex lens, i.e., the intersection
of two balls of radius $1/\lambda$, is the unique minimizer of volume among all
$\lambda$-convex bodies of given surface area.
Also, we prove a reverse inradius inequality: in model spaces of constant
curvature and arbitrary dimension, we show that the $\lambda$-convex lens
(properly defined in non-zero curvature spaces) has the smallest inscribed ball
among all $\lambda$-convex bodies of given surface area. This solves a
conjecture due to Bezdek on minimal inradius of isoperimetric ball-polyhedra in
$\mathbb{R}^n$.
|
We present the cationic impurity assisted band offset phenomena in NixCd1-xO
(x= 0, 0.02, 0.05, 0.1, 0.2, 0.4, 0.8, 1) thin films and further discussed in
the light of orbital hybridization modification. Compositional and structural
studies revealed that cationic substitution of Cd2+ by Ni2+ ions leads to a
monotonic shift in (220) diffraction peak, indicating the suppression of
lattice distortion while evolution of local strain with increasing Ni
concentration mainly associated to the mismatch in electro-negativity of Cd2+
and Ni2+ ion. In fact, Fermi level pinning towards conduction band minima takes
place with increasing Ni concentration at the cost of electronically
compensated oxygen vacancies, resulting modification in the distribution of
carrier concentration which eventually affects the band edge effective mass of
conduction band electrons and further endorses band gap renormalization.
Besides that, the appearance of longitudinal optical (LO) mode at 477 cm-1 as
manifested by Raman spectroscopy also indicate the active involvement of
electron-phonon scattering whereas modification in local coordination
environment particularly anti-crossing interaction in conjunction with presence
of satellite features and shake-up states with Ni doping is confirmed by X-ray
absorption near-edge and X-ray photoelectron spectroscopy studies. These
results manifest the gradual reduction of orbital hybridization with Ni
incorporation, leading to decrement in the band edge effective mass of
electron. Finally, molecular dynamics simulation reflects 13% reduction in
lattice parameter for NiO thin film as compared to undoped one while projected
density of states calculation further supports the experimental observation of
reduced orbital hybridization with increasing Ni concentration.
|
Infections from parasitic nematodes (or roundworms) contribute to a
significant disease burden and productivity losses for humans and livestock.
The limited number of anthelmintics (or antinematode drugs) available today to
treat these infections are rapidly losing their efficacy as multidrug
resistance in parasites becomes a global health challenge. We propose an
engineering approach to discover an anthelmintic drug combination that is more
potent at killing wild-type Caenorhabditis elegans worms than four individual
drugs. In the experiment, freely swimming single worms are enclosed in
microfluidic drug environments to assess the centroid velocity and track
curvature of worm movements. After analyzing the behavioral data in every
iteration, the feedback system control (FSC) scheme is used to predict new drug
combinations to test. Through a differential evolutionary search, the winning
drug combination is reached that produces minimal centroid velocity and high
track curvature, while requiring each drug in less than their EC50
concentrations. The FSC approach is model-less and does not need any
information on the drug pharmacology, signaling pathways, or animal biology.
Toward combating multidrug resistance, the method presented here is applicable
to the discovery of new potent combinations of available anthelmintics on C.
elegans, parasitic nematodes, and other small model organisms.
|
The development of molecular signatures for the prediction of time-to-event
outcomes is a methodologically challenging task in bioinformatics and
biostatistics. Although there are numerous approaches for the derivation of
marker combinations and their evaluation, the underlying methodology often
suffers from the problem that different optimization criteria are mixed during
the feature selection, estimation and evaluation steps. This might result in
marker combinations that are only suboptimal regarding the evaluation criterion
of interest. To address this issue, we propose a unified framework to derive
and evaluate biomarker combinations. Our approach is based on the concordance
index for time-to-event data, which is a non-parametric measure to quantify the
discrimatory power of a prediction rule. Specifically, we propose a
component-wise boosting algorithm that results in linear biomarker combinations
that are optimal with respect to a smoothed version of the concordance index.
We investigate the performance of our algorithm in a large-scale simulation
study and in two molecular data sets for the prediction of survival in breast
cancer patients. Our numerical results show that the new approach is not only
methodologically sound but can also lead to a higher discriminatory power than
traditional approaches for the derivation of gene signatures.
|
Non-classical electron diffusion in crossed-field, low-temperature plasmas is
measured experimentally. Laser-induced fluorescence and Thomson scattering are
used to determine the inverse Hall parameter, a metric for cross-field
transport, in a Hall ion source. The measured diffusion is found to depart from
fluid model results at the peak electric field, remaining constant instead of
exhibiting a sharp transport barrier. The implications of this result are
discussed in terms of the current understanding of non-classical diffusion in
low-temperature plasmas.
|
We study a few basic photon- and lepton-initiated processes at the LHC which
can be computed using the recently developed photon and lepton parton
densities. First, we consider the production of a massive scalar particle
initiated by lepton-antilepton annihilation and photon-photon fusion as
representative examples of searches of exotic particles. Then we study
lepton-lepton scattering, since this Standard-Model process may be observable
at the LHC. We examine these processes at leading and next-to-leading order
and, using the POWHEG method, we match our calculations to parton shower
programs that implement the required lepton or photon initial-states. We assess
the typical size of cross-sections and their uncertainties and discuss the
preferred choices for the factorization scale. These processes can also be
computed starting directly from the lepto-production hadronic tensor, leading
to a result where some collinear-enhanced QED corrections are missing, but all
strong corrections are included. Thus, we are in the unique position to perform
a comparison of results obtained via the factorization approach to a
calculation that does not have strong corrections. This is particularly
relevant in the case of lepton-scattering, that is more abundant at lower
energies where it is affected by larger strong corrections. We thus compute
this process also with the hadronic-tensor method, and compare the results with
those obtained with POWHEG. Finally, for some lepton-lepton scattering
processes, we compare the size of the signal to the main quark-induced
background, which is double Drell-Yan production, and outline a preliminary
search strategy to enhance the signal to background ratio.
|
The vacuum expectation value of the evolution operator for a general class of
Hamiltonians used in quantum field theory and statistical physics and which
include unstable particles is considered. An exact formula which describes the
large time behavior of the evolution operator is proved.
|
Several extended supersymmetric models, motivated by either grand
unification, or by neutrino mass generation, predict light doubly charged
higgsinos. We study the production of a single doubly charged higgsino and its
decay channels at the International Linear Collider (ILC) operating in the e-e-
mode. We analyze the production cross section for e-e- -->
tilde{Delta}^{--}_{L,R} chi^0_1 as a function of different kinematic variables,
followed by the decay, through several channels, of the doubly charged higgsino
into a final state of two leptons plus missing energy. We include the standard
model background and discuss how kinematic cuts could be used effectively to
limit this background. Single production of these exotics could provide a
spectacular signal for a new underlying symmetry and for physics beyond the
minimal supersymmetric standard model.
|
I discuss our current understanding of parton distributions. I begin with the
underlying theoretical framework, and the way in which different data sets
constrain different partons, highlighting recent developments. The methods of
examining the uncertainties on the distributions and those physical quantities
dependent on them is analysed. Finally I look at the evidence that additional
theoretical corrections beyond NLO perturbative QCD may be necessary, what type
of corrections are indicated and the impact these may have on the
uncertainties.
|
This document is a reply to arXiv:1810.11506. In that document, D\"onmez and
Ba\v{z}ant raise a number of criticism on the hypotheses Critical Shear Crack
Theory (CSCT). The aspects criticized have however been largely discussed in
previous works of the CSCT, proving the validity of the theory. This document
compiles such previous knowledge as a reply to the authors of the report.
|
The theory of $F$-manifolds, and more generally, manifolds endowed with
commutative and associative multiplication of their tangent fields, was
discovered and formalised in various models of quantum field theory involving
algebraic and analytic geometry, at least since 1990's.
The focus of this paper consists in the demonstration that various spaces of
probability distributions defined and studied at least since 1960's also carry
natural structures of $F$-manifolds.
This fact remained somewhat hidden in various domains of the vast territory
of models of information storing and transmission that are briefly surveyed
here.
|
In this paper, we study the solvability of a Cauchy- Dirichlet problem for
nonlinear parabolic equation with non standard growths and nonlocal terms. We
show the existence of weak solutions of the considered problem under more
general conditions. In addition, we obtain some results on the behavior of the
solution when the problem is homogeneous.
|
We study the motion of a solid particle immersed in a Newtonian fluid and
confined between two parallel elastic membranes possessing shear and bending
rigidity. The hydrodynamic mobility depends on the frequency of the particle
motion due to the elastic energy stored in the membrane. Unlike the
single-membrane case, a coupling between shearing and bending exists. The
commonly used approximation of superposing two single-membrane contributions is
found to give reasonable results only for motions in the parallel, but not in
the perpendicular direction. We also compute analytically the membrane
deformation resulting from the motion of the particle, showing that the
presence of the second membrane reduces deformation. Using the
fluctuation-dissipation theorem we compute the Brownian motion of the particle,
finding a long-lasting subdiffusive regime at intermediate time scales. We
finally assess the accuracy of the employed point-particle approximation via
boundary-integral simulations for a truly extended particle. They are found to
be in excellent agreement with the analytical predictions.
|
The compositional dependence of thermal expansion behaviour in 19 different
perovskite-like metal-organic frameworks (MOFs) of composition [AI][MII(HCOO)3]
(A = alkylammonium cation; M = octahedrally-coordinated divalent metal) is
studied using variable-temperature X-ray powder diffraction measurements. While
all systems show essentially the same type of thermomechanical
response-irrespective of their particular structural details-the magnitude of
this response is shown to be a function of AI and MII cation radii, as well as
the molecular anisotropy of AI. Flexibility is maximised for large MII and
small AI, while the shape of AI has implications for the direction of framework
hingeing.
|
The recently proposed Hysteretic Optimization (HO) procedure is applied to
the 1D Ising spin chain with long range interactions. To study its
effectiveness, the quality of ground state energies found as a function of the
distance dependence exponent, $\sigma$, is assessed. It is found that the
transition from an infinite-range to a long-range interaction at $\sigma=0.5$
is accompanied by a sharp decrease in the performance . The transition is
signaled by a change in the scaling behavior of the average avalanche size
observed during the hysteresis process. This indicates that HO requires the
system to be infinite-range, with a high degree of interconnectivity between
variables leading to large avalanches, in order to function properly. An
analysis of the way auto-correlations evolve during the optimization procedure
confirm that the search of phase space is less efficient, with the system
becoming effectively stuck in suboptimal configurations much earlier. These
observations explain the poor performance that HO obtained for the
Edwards-Anderson spin glass on finite-dimensional lattices, and suggest that
its usefulness might be limited in many combinatorial optimization problems.
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We analyzed Chandra observations of three gravitational lenses, SBS0909+523,
FBQS0951+2635, and B1152+199, to measure the differential X-ray absorption and
the dust-to-gas ratio of the lens galaxies. We successfully detected the
differential X-ray absorption in SBS0909+523 and B1152+199, and failed to
detect it in FBQS0951+2635 due to the dramatic drop in its flux from the ROSAT
epoch. These measurements significantly increase the sample of dust-to-gas
ratio measurements in cosmologically-distant, normal galaxies. Using the larger
sample, we obtain an average dust-to-gas ratio of E(B-V)/NH = (1.5\pm0.5)e-22
mag cm^2/atoms with an estimated intrinsic dispersion in the ratio of \simeq
40%. This average dust-to-gas ratio is consistent with our previous
measurement, and the average Galactic value of 1.7e-22 mag cm^2/atoms and the
estimated intrinsic dispersion is also consistent with the 30% observed in the
Galaxy. A larger sample size is still needed to improve the measurements and to
begin studying the evolution in the ratio with cosmic time. We also detected
X-ray microlensing in SBS0909+523 and significant X-ray variability in
FBQS0951+2635.
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Polarized emission from aligned dust is a crucial tool for studies of
magnetism in the ISM and a troublesome contaminant for studies of CMB
polarization. In each case, an understanding of the significance of the
polarization signal requires well-calibrated physical models of dust grains.
Despite decades of progress in theory and observation, polarized dust models
remain largely underconstrained. During its 2012 flight, the balloon-borne
telescope BLASTPol obtained simultaneous broad-band polarimetric maps of a
translucent molecular cloud at 250, 350, and 500 microns. Combining these data
with polarimetry from the Planck 850 micron band, we have produced a
submillimeter polarization spectrum for a cloud of this type for the first
time. We find the polarization degree to be largely constant across the four
bands. This result introduces a new observable with the potential to place
strong empirical constraints on ISM dust polarization models in a previously
inaccessible density regime. Comparing with models by Draine and Fraisse
(2009), our result disfavors two of their models for which all polarization
arises due only to aligned silicate grains. By creating simple models for
polarized emission in a translucent cloud, we verify that extinction within the
cloud should have only a small effect on the polarization spectrum shape
compared to the diffuse ISM. Thus we expect the measured polarization spectrum
to be a valid check on diffuse ISM dust models. The general flatness of the
observed polarization spectrum suggests a challenge to models where temperature
and alignment degree are strongly correlated across major dust components.
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The performance of a molecular motor, characterized by its power output and
energy efficiency, is investigated in the motor design space spanned by the
stepping rate function and the motor-track interaction potential. Analytic
results and simulations show that a gating mechanism that restricts forward
stepping in a narrow window in configuration space is needed for generating
high power at physiologically relevant loads. By deriving general
thermodynamics laws for nonequilibrium motors, we find that the maximum torque
(force) at stall is less than its theoretical limit for any realistic
motor-track interactions due to speed fluctuations. Our study reveals a
tradeoff for the motor- track interaction: while a strong interaction generates
a high power output for forward steps, it also leads to a higher probability of
wasteful spontaneous back steps. Our analysis and simulations show that this
tradeoff sets a fundamental limit to the maximum motor efficiency in the
presence of spontaneous back steps, i.e., loose-coupling. Balancing this
tradeoff leads to an optimal design of the motor-track interaction for
achieving a maximum efficiency close to 1 for realistic motors that are not
perfectly coupled with the energy source.Comparison with existing data and
suggestions for future experiments are discussed.
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Estimating a vector $\mathbf{x}$ from noisy linear measurements
$\mathbf{Ax}+\mathbf{w}$ often requires use of prior knowledge or structural
constraints on $\mathbf{x}$ for accurate reconstruction. Several recent works
have considered combining linear least-squares estimation with a generic or
"plug-in" denoiser function that can be designed in a modular manner based on
the prior knowledge about $\mathbf{x}$. While these methods have shown
excellent performance, it has been difficult to obtain rigorous performance
guarantees. This work considers plug-in denoising combined with the
recently-developed Vector Approximate Message Passing (VAMP) algorithm, which
is itself derived via Expectation Propagation techniques. It shown that the
mean squared error of this "plug-and-play" VAMP can be exactly predicted for
high-dimensional right-rotationally invariant random $\mathbf{A}$ and Lipschitz
denoisers. The method is demonstrated on applications in image recovery and
parametric bilinear estimation.
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Self-assembling novel ordered structures with nanoparticles has recently
received much attention. Here we use computer simulations to study a
two-dimensional model system characterized by a simple isotropic interaction
that could be realized with building blocks on the nanoscale. We find that the
particles arrange themselves into hexagonal superstructures of twin boundaries
whose superlattice vector can be tuned reversibly by changing the temperature.
Thermodynamic stability is confirmed by calculating the free energy with a
combination of thermodynamic integration and the Frenkel-Ladd method. Different
contributions to the free energy difference are discussed.
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We introduce the notion of integrable modules over $\imath$quantum groups
(a.k.a. quantum symmetric pair coideal subalgebras). After determining a
presentation of such modules, we prove that each integrable module over a
quantum group is integrable when restricted to an $\imath$quantum group. As an
application, we show that the space of matrix coefficients of all simple
integrable modules over an $\imath$quantum group of finite type with specific
parameters coincides with Bao-Song's coordinate ring of the $\imath$quantum
group.
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Planets are like children with each one being unique and special. A better
understanding of their collective properties requires a deeper understanding of
each planet. Here we add the transit and eclipse spectra of hot Jupiter
WASP-74b into the ever growing dataset of exoplanet atmosphere spectral
library. With six transits and three eclipses using the Hubble Space Telescope
(HST) and Spitzer Space Telescope (\textit{Spitzer}), we present the most
complete and precise atmospheric spectra of WASP-74b. We found no evidence for
TiO/VO nor super-Rayleigh scattering reported in previous studies. The transit
shows a muted water feature with strong Rayleigh scattering extending into the
infrared. The eclipse shows a featureless blackbody-like WFC3/G141 spectrum and
a weak methane absorption feature in the Spitzer 3.6 $\mu m$ band. Future James
Webb Space Telescope (JWST) follow up observations are needed to confirm these
results.
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We introduce \underline{F}actor-\underline{A}ugmented \underline{Ma}trix
\underline{R}egression (FAMAR) to address the growing applications of
matrix-variate data and their associated challenges, particularly with
high-dimensionality and covariate correlations. FAMAR encompasses two key
algorithms. The first is a novel non-iterative approach that efficiently
estimates the factors and loadings of the matrix factor model, utilizing
techniques of pre-training, diverse projection, and block-wise averaging. The
second algorithm offers an accelerated solution for penalized matrix factor
regression. Both algorithms are supported by established statistical and
numerical convergence properties. Empirical evaluations, conducted on synthetic
and real economics datasets, demonstrate FAMAR's superiority in terms of
accuracy, interpretability, and computational speed. Our application to
economic data showcases how matrix factors can be incorporated to predict the
GDPs of the countries of interest, and the influence of these factors on the
GDPs.
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In this work, we analyze the implications of graviton to photon conversion in
the presence of large scale magnetic fields. We consider the magnetic fields
associated with galaxy clusters, filaments in the large scale structure, as
well as primordial magnetic fields. {We analyze the interaction of these
magnetic fields with an exogenous high-frequency gravitational wave (HFGW)
background which may exist in the Universe. We show that, in the presence of
the magnetic fields, a sufficiently strong HFGW background would lead to an
observable signature in the frequency spectrum of the Cosmic Microwave
Background (CMB).} The sensitivity of current day CMB experiments allows to
place significant constraints on the strength of HFGW background,
$\Omega_{GW}\lesssim1$. These limits are about 25 orders of magnitude stronger
{than currently existing direct constraints} in this frequency region.
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Semantic segmentation remains a computationally intensive algorithm for
embedded deployment even with the rapid growth of computation power. Thus
efficient network design is a critical aspect especially for applications like
automated driving which requires real-time performance. Recently, there has
been a lot of research on designing efficient encoders that are mostly task
agnostic. Unlike image classification and bounding box object detection tasks,
decoders are computationally expensive as well for semantic segmentation task.
In this work, we focus on efficient design of the segmentation decoder and
assume that an efficient encoder is already designed to provide shared features
for a multi-task learning system. We design a novel efficient non-bottleneck
layer and a family of decoders which fit into a small run-time budget using
VGG10 as efficient encoder. We demonstrate in our dataset that experimentation
with various design choices led to an improvement of 10\% from a baseline
performance.
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The physics of systems that cannot be described by a Hermitian Hamiltonian,
has been attracting a great deal of attention in recent years, motivated by
their nontrivial responses and by a plethora of applications for sensing,
lasing, energy transfer/harvesting, topology and quantum networks.
Electromagnetics is an inherently non-Hermitian research area because all
materials are lossy, loss and gain distributions can be controlled with various
mechanisms, and the underlying systems are open to radiation. Therefore, the
recent developments in non-Hermitian physics offer exciting opportunities for a
broad range of basic research and engineering applications relevant to the
antennas and propagation community. In this work, we offer a tutorial geared at
introducing the unusual electromagnetic phenomena emerging in non-Hermitian
systems, with particular emphasis on a sub-class of these systems that obey
parity-time (PT) symmetry. We discuss the basic concepts behind this topic and
explore their implications for various phenomena. We first discuss the basic
features of P, T and PT operators applied to electromagnetic and quantum
mechanical phenomena. We then discuss the exotic response of PT-symmetric
electromagnetic structures and their opportunities, with particular attention
to singularities, known as exceptional points, emerging in these systems, and
their unusual scattering response.
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A variety of real-world applications rely on far future information to make
decisions, thus calling for efficient and accurate long sequence multivariate
time series forecasting. While recent attention-based forecasting models show
strong abilities in capturing long-term dependencies, they still suffer from
two key limitations. First, canonical self attention has a quadratic complexity
w.r.t. the input time series length, thus falling short in efficiency. Second,
different variables' time series often have distinct temporal dynamics, which
existing studies fail to capture, as they use the same model parameter space,
e.g., projection matrices, for all variables' time series, thus falling short
in accuracy. To ensure high efficiency and accuracy, we propose Triformer, a
triangular, variable-specific attention. (i) Linear complexity: we introduce a
novel patch attention with linear complexity. When stacking multiple layers of
the patch attentions, a triangular structure is proposed such that the layer
sizes shrink exponentially, thus maintaining linear complexity. (ii)
Variable-specific parameters: we propose a light-weight method to enable
distinct sets of model parameters for different variables' time series to
enhance accuracy without compromising efficiency and memory usage. Strong
empirical evidence on four datasets from multiple domains justifies our design
choices, and it demonstrates that Triformer outperforms state-of-the-art
methods w.r.t. both accuracy and efficiency. This is an extended version of
"Triformer: Triangular, Variable-Specific Attentions for Long Sequence
Multivariate Time Series Forecasting", to appear in IJCAI 2022 [Cirstea et al.,
2022a], including additional experimental results.
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"Changing-look" active galactic nuclei (CL-AGNs) are a newly-discovered class
of AGNs that show the appearance (or disappearance) of broad emission lines
within a short time scale (months to years) and are often associated with the
dramatic change of their continuum emissions. They provide us an unprecedented
chance to directly investigate the host galaxy properties with minimal
contamination from the luminous central engine during the "turn-off" state,
which is difficult for normal luminous AGNs. In this work, for the first time,
we systematically characterize the stellar populations and star formation
histories (SFHs) of host galaxies for 26 turn-off CL-AGNs using the stellar
population synthesis code STARLIGHT. We find that the stellar populations of
CL-AGNs are similar to that of normal AGNs, excepts that the intermediate
stellar populations contribute more fraction. We estimate their stellar
velocity dispersions ($\rm \sigma_{\star}$) and black hole masses ($\rm
M_{BH,vir}$) and find that CL-AGNs also follow the overall $\rm
M_{BH}-\sigma_{\star}$ relationship. We also confirm the previous claim that
CL-AGNs tend to be biased towards lower Eddington ratio, and their extreme
variabilities are more likely due to the intrinsic changes of accretion rates.
In addition, CL-AGNs with recent star formations (SF) tend to have higher
Eddington ratio. Compared with previous studies, our analysis suggests that
there may be a correlation between the CL-AGN host galaxy properties and their
CL phenomena.
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High density direct currents (DC) are used to drive flux quanta via the
Lorentz force towards a highly ordered "free flux flow" (FFF) dynamic state,
made possible by the weak-pinning environment of high-quality, single-crystal
samples of two low-Tc superconducting compounds, V3Si and LuNi2B2C. We report
the effect of the magnetic field-dependent fluxon core size on flux flow
resistivity rho_f. Much progress has been made in minimizing the technical
challenges associated with the use of high currents. Attainment of a FFF phase
is indicated by the saturation at highest currents of flux-flow dissipation
levels that are well below the normal state resistance and have field-dependent
values. The field dependence of the corresponding rho_f is shown to be
consistent with a prediction based on a model for the decrease of flux core
size at higher fields in weak-coupling BCS s-wave materials.
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We present the properties of the ensemble variability $V$ for nearly 5000
near-infrared (NIR) AGNs selected from the catalog of Quasars and Active
Galactic Nuclei (13th Ed.) and the SDSS-DR7 quasar catalog. From 2MASS, DENIS,
and UKIDSS/LAS point source catalogs, we extract 2MASS-DENIS and 2MASS-UKIDSS
counterparts for cataloged AGNs by catalog cross-identification. We further
select variable AGNs based on an optimal criterion for selecting the variable
sources. The sample objects are divided into subsets according to whether NIR
light originates by optical or NIR emission in the rest frame; and we examine
the correlations of the ensemble variability with the rest-frame wavelength,
redshift, luminosity, and rest-frame time lag. In addition, we also examine the
correlations of variability amplitude with optical variability, radio
intensity, and radio-to-optical flux ratio. The rest-frame optical variability
of our samples shows known negative correlations with luminosity and positive
correlations with rest-frame time lag (i.e., the structure function, SF).
However, no well-known negative correlation exists between the rest wavelength
and optical variability. This inconsistency might be due to a biased sampling
of high-redshift AGNs. NIR variability in the rest frame is anticorrelated with
the rest wavelength, which is consistent with previous suggestions. However,
correlations of NIR variability with luminosity and rest-frame time lag are the
opposite of these correlations of the optical variability; that is, the NIR
variability is positively correlated with luminosity but negatively correlated
with the rest-frame time lag. Because these trends are qualitatively consistent
with the properties of radio-loud quasars reported by some previous studies,
most of our sample objects are probably radio-loud quasars. Finally, we also
discuss the negative correlations seen in the NIR SFs.
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We study the feasibility of short finite impulse response (FIR) synthesis for
perfect reconstruction (PR) in generic FIR filter banks. Among all PR synthesis
banks, we focus on the one with the minimum filter length. For filter banks
with oversampling factors of at least two, we provide prescriptions for the
shortest filter length of the synthesis bank that would guarantee PR almost
surely. The prescribed length is as short or shorter than the analysis filters
and has an approximate inverse relationship with the oversampling factor. Our
results are in form of necessary and sufficient statements that hold
generically, hence only fail for elaborately-designed nongeneric examples. We
provide extensive numerical verification of the theoretical results and
demonstrate that the gap between the derived filter length prescriptions and
the true minimum is small. The results have potential applications in synthesis
FB design problems, where the analysis bank is given, and for analysis of
fundamental limitations in blind signals reconstruction from data collected by
unknown subsampled multi-channel systems.
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We observe intensity oscillations along coronal fan loops associated with the
active region AR 11428. The intensity oscillations were triggered by blast
waves which were generated due to X-class flares in the distant active region
AR 11429. To characterise the nature of oscillations, we created time-distance
maps along the fan loops and noted that the intensity oscillations at two ends
of the loops were out of phase. As we move along the fan loop, the amplitude of
the oscillations first decreased and then increased. The out-of-phase nature
together with the amplitude variation along the loop implies that these
oscillations are very likely to be standing waves. The period of the
oscillations are estimated to be $\sim$27 min, damping time to be $\sim$45 min
and phase velocity projected in the plane of sky $\sim$ 65-83 km s$^{-1}$. The
projected phase speeds were in the range of acoustic speed of coronal plasma at
about 0.6 MK which further indicates that these are slow waves. To best of our
knowledge, this is the first report on the existence of the standing slow waves
in non-flaring fan loops.
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Bismuth donors ion-implanted in $^{28}$Si and $^\text{nat}$Si are studied
using magnetic resonance spectroscopy based on spin dependent recombination.
The hyperfine clock transition, at which the linewidth is significantly
narrowed, is observed for the bismuth donors. The experimental results are
modeled quantitatively by molecular orbital theory for a coupled pair
consisting of a bismuth donor and a spin dependent recombination readout
center, including the effect of hyperfine and Zeeman interactions.
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We place observational constraints on a dark energy (DE) model in which a
quintessence scalar field $\phi$ is coupled to dark matter (DM) through
momentum and energy exchanges.The momentum transfer is weighed by an
interaction between the field derivative and DM four velocity with a coupling
constant $\beta$, whereas the energy exchange is characterized by an
exponential scalar-field coupling to the DM density with a coupling constant
$Q$. A positive coupling $\beta$ leads to the suppression for the growth of DM
density perturbations at low redshifts, whose property offers a possibility for
resolving the $\sigma_8$ tension problem. A negative coupling $Q$ gives rise to
a $\phi$-matter-dominated epoch, whose presence can reduce the sound horizon
around the Cosmic Microwave Background (CMB) decoupling epoch. Using the data
of Planck 2018, 12-th Sloan Digital Sky Survey, Phantheon supernovae samples,
and 1-year dark energy survey, we find that the two couplings are constrained
to be $\beta=0.332^{+1.246}_{-0.237}$ and $Q =-0.0312^{+0.0312}_{-0.0085}$ at
68\,\% confidence level (CL). Thus, there is an interesting observational
signature of the momentum exchange ($\beta \neq 0$) between DE and DM, with a
peak of the probability distribution of the energy transfer coupling at $Q<0$.
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We present a versatile density functional approach (DFT) for calculating the
depletion potential in general fluid mixtures. In contrast to brute force DFT,
our approach requires only the equilibrium density profile of the small
particles {\em before} the big (test) particle is inserted. For a big particle
near a planar wall or a cylinder or another fixed big particle the relevant
density profiles are functions of a single variable, which avoids the numerical
complications inherent in brute force DFT. We implement our approach for
additive hard-sphere mixtures. By investigating the depletion potential for
high size asymmetries we assess the regime of validity of the well-known
Derjaguin approximation for hard-sphere mixtures and argue that this fails. We
provide an accurate parametrization of the depletion potential in hard-sphere
fluids which should be useful for effective Hamiltonian studies of phase
behavior and colloid structure.
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The current status of our Chandra and XMM-Newton project on high-redshift
(z>4) quasars is briefly reviewed. We report the main results obtained in the
last few years for the detected quasars, along with a few (~10%) intriguing
cases where no detection has been obtained with Chandra snapshot observations.
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The Bogomolny decompositions (Bogomolny equations) for the gauged baby Skyrme
models: restricted and full one, in (2+0)-dimensions, are derived, for some
general classes of the potentials. The conditions, which must be satisfied by
the potentials, for each of these mentioned models, are also derived.
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Position embeddings, encoding the positional relationships among tokens in
text sequences, make great contributions to modeling local context features in
Transformer-based pre-trained language models. However, in Extractive Question
Answering, position embeddings trained with instances of varied context lengths
may not perform well as we expect. Since the embeddings of rear positions are
updated fewer times than the front position embeddings, the rear ones may not
be properly trained. In this paper, we propose a simple but effective strategy,
Random Padding, without any modifications to architectures of existing
pre-trained language models. We adjust the token order of input sequences when
fine-tuning, to balance the number of updating times of every position
embedding. Experiments show that Random Padding can significantly improve model
performance on the instances whose answers are located at rear positions,
especially when models are trained on short contexts but evaluated on long
contexts. Our code and data will be released for future research.
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We argue that the factorizable $c\bar c$ long- and short-distance
contributions to the $B\to K^*\gamma$ amplitude vanish, separately, if defined
in a gauge-invariant way. Therefore, the $c\bar c$ states contribute to the
radiative decay only through the non-factorizable soft-gluon exchanges.
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We study the topological heterotic ring in (0,2) Landau-Ginzburg models
without a (2,2) locus. The ring elements correspond to elements of the Koszul
cohomology groups associated to a zero-dimensional ideal in a polynomial ring,
and the computation of half-twisted genus zero correlators reduces to a map
from the first non-trivial Koszul cohomology group to complex numbers. This map
is a generalization of the local Grothendieck residue. The results may be
applied to computations of Yukawa couplings in a heterotic compactification at
a Landau-Ginzburg point.
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The directed flow of inclusive, transported and non-transported (including
produced) protons, as well as antiprotons, has been studied in the framework of
Ultra-Relativistic Quantum Molecular Dynamics approach (UrQMD model) for Au+Au
collisions at\surdsNN =7.7, 11.5, 19.6, 27, 39, 62.4 and 200 GeV. The rapidity,
centrality and energy dependence of directed flow for various proton groups are
presented. It is found that the integrated directed flow decreases
monotonically as a function of collision energy for\surdsNN =11.5 GeV and
beyond. However, the sign-change of directed flow of inclusive protons, seen in
experimental data as a function of centrality and collision energy, can be
explained by the competing effect of directed flow between transported and
non-transported protons. Similarly the difference in directed flow between
protons and antiprotons can be explained. Our study offers a conventional
explanation on the cause of the v1 sign-change other than the antiflow
component of protons alone which is argued to be linked to a phase transition.
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