text
stringlengths 6
128k
|
|---|
In this perspective, we discuss how one can initiate, image, and disentangle
the ultrafast elementary steps of thermal-energy chemical dynamics, building
upon advances in technology and scientific insight. We propose that
combinations of ultrashort mid-infrared laser pulses, controlled molecular
species in the gas phase, and forefront imaging techniques allow to unravel the
elementary steps of general-chemistry reaction processes in real time. We
detail, for prototypical first reaction systems, experimental methods enabling
these investigations, how to sufficiently prepare and promote gas-phase samples
to thermal-energy reactive states with contemporary ultrashort mid-infrared
laser systems, and how to image the initiated ultrafast chemical dynamics. The
results of such experiments will clearly further our understanding of
general-chemistry reaction dynamics.
|
Diffusion models have been extensively utilized in AI-generated content
(AIGC) in recent years, thanks to the superior generation capabilities.
Combining with semantic communications, diffusion models are used for tasks
such as denoising, data reconstruction, and content generation. However,
existing diffusion-based generative models do not consider the stringent
bandwidth limitation, which limits its application in wireless communication.
This paper introduces a diffusion-driven semantic communication framework with
advanced VAE-based compression for bandwidth-constrained generative model. Our
designed architecture utilizes the diffusion model, where the signal
transmission process through the wireless channel acts as the forward process
in diffusion. To reduce bandwidth requirements, we incorporate a downsampling
module and a paired upsampling module based on a variational auto-encoder with
reparameterization at the receiver to ensure that the recovered features
conform to the Gaussian distribution. Furthermore, we derive the loss function
for our proposed system and evaluate its performance through comprehensive
experiments. Our experimental results demonstrate significant improvements in
pixel-level metrics such as peak signal to noise ratio (PSNR) and semantic
metrics like learned perceptual image patch similarity (LPIPS). These
enhancements are more profound regarding the compression rates and SNR compared
to deep joint source-channel coding (DJSCC).
|
In this paper, we present CCEdit, a versatile generative video editing
framework based on diffusion models. Our approach employs a novel trident
network structure that separates structure and appearance control, ensuring
precise and creative editing capabilities. Utilizing the foundational
ControlNet architecture, we maintain the structural integrity of the video
during editing. The incorporation of an additional appearance branch enables
users to exert fine-grained control over the edited key frame. These two side
branches seamlessly integrate into the main branch, which is constructed upon
existing text-to-image (T2I) generation models, through learnable temporal
layers. The versatility of our framework is demonstrated through a diverse
range of choices in both structure representations and personalized T2I models,
as well as the option to provide the edited key frame. To facilitate
comprehensive evaluation, we introduce the BalanceCC benchmark dataset,
comprising 100 videos and 4 target prompts for each video. Our extensive user
studies compare CCEdit with eight state-of-the-art video editing methods. The
outcomes demonstrate CCEdit's substantial superiority over all other methods.
|
We analyse transverse oscillations of a coronal loop excited by continuous
monoperiodic motions of the loop footpoint at different frequencies in the
presence of gravity. Using the MPI-AMRVAC code, we perform three-dimensional
numerical magnetohydrodynamic simulations, considering the loop as a magnetic
flux tube filled in with denser, hotter, and gravitationally stratified plasma.
We show the resonant response of the loop to its external excitation and
analyse the development of the Kelvin-Helmholtz instability at different
heights. We also study the spatial distribution of plasma heating due to
transverse oscillations along the loop. The positions of the maximum heating
are in total agreement with those for the intensity of the Kelvin-Helmholtz
instability, and correspond to the standing wave anti-nodes in the resonant
cases. The initial temperature configuration and plasma mixing effect appear to
play a significant role in plasma heating by transverse footpoint motions. In
particular, the development of the Kelvin-Helmholtz instability in a hotter
loop results in the enhancement of the mean plasma temperature in the domain.
|
Challenges related to development, deployment, and maintenance of reusable
software for science are becoming a growing concern. Many scientists' research
increasingly depends on the quality and availability of software upon which
their works are built. To highlight some of these issues and share experiences,
the First Workshop on Sustainable Software for Science: Practice and
Experiences (WSSSPE1) was held in November 2013 in conjunction with the SC13
Conference. The workshop featured keynote presentations and a large number (54)
of solicited extended abstracts that were grouped into three themes and
presented via panels. A set of collaborative notes of the presentations and
discussion was taken during the workshop.
Unique perspectives were captured about issues such as comprehensive
documentation, development and deployment practices, software licenses and
career paths for developers. Attribution systems that account for evidence of
software contribution and impact were also discussed. These include mechanisms
such as Digital Object Identifiers, publication of "software papers", and the
use of online systems, for example source code repositories like GitHub.
This paper summarizes the issues and shared experiences that were discussed,
including cross-cutting issues and use cases. It joins a nascent literature
seeking to understand what drives software work in science, and how it is
impacted by the reward systems of science. These incentives can determine the
extent to which developers are motivated to build software for the long-term,
for the use of others, and whether to work collaboratively or separately. It
also explores community building, leadership, and dynamics in relation to
successful scientific software.
|
We introduce a new technique for isolating components on the spectral side of
the trace formula. By applying it to the Jacquet--Rallis relative trace
formula, we complete the proof of the global Gan--Gross--Prasad conjecture and
its refinement Ichino--Ikeda conjecture for
$\mathrm{U}(n)\times\mathrm{U}(n+1)$ in the stable case.
|
We consider $u(t,x)=(u_1(t,x),\cdots,u_d(t,x))$ the solution to a system of
non-linear stochastic heat equations in spatial dimension one driven by a
$d$-dimensional space-time white noise. We prove that, when $d\leq 3$, the
local time $L(\xi,t)$ of $\{u(t,x)\,,\;t\in[0,T]\}$ exists and $L(\bullet,t) $
belongs a.s. to the Sobolev space $ H^{\alpha}(\mathbb{R}^d)$ for
$\alpha<\frac{4-d}{2}$, and when $d\geq 4$, the local time does not exist. We
also show joint continuity and establish H\"{o}lder conditions for the local
time of $\{u(t,x)\,,\;t\in[0,T]\}$. These results are then used to investigate
the irregularity of the coordinate functions of $\{u(t,x)\,,\;t\in[0,T]\}$.
Comparing to similar results obtained for the linear stochastic heat equation
(i.e., the solution is Gaussian), we believe that our results are sharp.
Finally, we get a sharp estimate for the partial derivatives of the joint
density of $(u(t_1,x)-u(t_0,x),\cdots,u(t_n,x)-u(t_{n-1},x))$, which is a new
result and of independent interest.
|
We prove that for a given operator in the Standard Model (SM) with baryon
number B and lepton number L, that the operator's dimension is even (odd) if
(B-L)/2 is even (odd). Consequently, this establishes the veracity of
statements that were long observed or expected to be true, but not proven,
e.g., operators with B-L=0 are of even dimension, B-L must be an even number,
etc. These results remain true even if the SM is augmented by any number of
right-handed neutrinos with L=1.
|
Cool stars on the main sequence generate X-rays from coronal activity,
powered by a convective dynamo. With increasing temperature, the convective
envelope becomes smaller and X-ray emission fainter. We present Chandra/HRC-I
observations of four single stars with early A spectral types. Only the coolest
star of this sample, $\tau^3$ Eri ($T_\mathrm{eff}\approx8\,,000$ K), is
detected with $\log(L_X/L_\mathrm{bol})=-7.6$ while the three hotter stars
($T_\mathrm{eff}\geq8\,,000$ K), namely $\delta$ Leo, $\beta$ Leo, and $\iota$
Cen, remain undetected with upper limits $\log(L_X/L_\mathrm{bol})<-8.4$. The
drop in X-ray emission thus occurs in a narrow range of effective temperatures
around $\sim 8100$ K and matches the drop of activity in the C III and O VI
transition region lines.
|
In this paper, the design and the characterization of a novel interrogator
based on integrated Fourier transform (FT) spectroscopy is presented. To the
best of our knowledge, this is the first integrated FT spectrometer used for
the interrogation of photonic sensors. It consists of a planar spatial
heterodyne spectrometer, which is implemented using an array of Mach-Zehnder
interferometers (MZIs) with different optical path differences. Each MZI
employs a 3$\times$3 multi-mode interferometer, allowing the retrieval of the
complex Fourier coefficients. We derive a system of non-linear equations whose
solution, which is obtained numerically from Newton's method, gives the
modulation of the sensor's resonances as a function of time. By taking one of
the sensors as a reference, to which no external excitation is applied and its
temperature is kept constant, about 92$\%$ of the thermal induced phase drift
of the integrated MZIs has been compensated. The minimum modulation amplitude
that is obtained experimentally is 400 fm, which is more than two orders of
magnitude smaller than the FT spectrometer resolution.
|
Let $K$ be an algebraically closed field of characteristic zero and let $R =
K[X_1,\ldots,X_n]$. Let $I$ be an ideal in $R$. Let $A_n(K)$ be the $n^{th}$
Weyl algebra over $K$. By a result of Lyubeznik, the local cohomology modules
$H^i_I(R)$ are holonomic $A_n(K)$-modules for each $i \geq 0$. In this paper we
compute the Euler characteristic of De-Rahm cohomology of $H^{\htt P}_P(R)$ for
certain classes of prime ideals $P$ in $R$.
|
A trade-off between the precision of an arbitrary current and the
dissipation, known as the thermodynamic uncertainty relation, has been
investigated for various Markovian systems. Here, we study the thermodynamic
uncertainty relation for underdamped Langevin dynamics. By employing
information inequalities, we prove that, for such systems, the relative
fluctuation of a current at a steady state is constrained by both the entropy
production and the average dynamical activity. We find that, unlike what is the
case for overdamped dynamics, the dynamical activity plays an important role in
the bound. We illustrate our results with two systems, a single-well potential
system and a periodically driven Brownian particle model, and numerically
verify the inequalities.
|
Fast Abstracts are short presentations of work in progress or opinion pieces
and aim to serve as a rapid and flexible mechanism to (i) Report on current
work that may or may not be complete; (ii) Introduce new ideas to the
community; (iii) State positions on controversial issues or open problems.
On the other hand, the goal of the Student Forum is to encourage students to
attend EDCC and present their work, exchange ideas with researchers and
practitioners, and get early feedback on their research efforts.
|
Multiquantum vortices in dilute atomic Bose-Einstein condensates confined in
long cigar-shaped traps are known to be both energetically and dynamically
unstable. They tend to split into single-quantum vortices even in the ultralow
temperature limit with vanishingly weak dissipation, which has also been
confirmed in the recent experiments [Y. Shin et al., Phys. Rev. Lett. 93,
160406 (2004)] utilizing the so-called topological phase engineering method to
create multiquantum vortices. We study the stability properties of multiquantum
vortices in different trap geometries by solving the Bogoliubov excitation
spectra for such states. We find that there are regions in the trap asymmetry
and condensate interaction strength plane in which the splitting instability of
multiquantum vortices is suppressed, and hence they are dynamically stable. For
example, the doubly quantized vortex can be made dynamically stable even in
spherical traps within a wide range of interaction strength values. We expect
that this suppression of vortex-splitting instability can be experimentally
verified.
|
This paper introduces the notion of objection-based causal networks which
resemble probabilistic causal networks except that they are quantified using
objections. An objection is a logical sentence and denotes a condition under
which a, causal dependency does not exist. Objection-based causal networks
enjoy almost all the properties that make probabilistic causal networks
popular, with the added advantage that objections are, arguably more intuitive
than probabilities.
|
Let $A$ be a CQG Hopf $*$-algebra, i.e. a Hopf $*$-algebra with a positive
invariant state. Given a unital right coideal $*$-subalgebra $B$ of $A$, we
provide conditions for the existence of a quasi-invariant integral on the
stabilizer coideal $B^{\perp}$ inside the dual discrete multiplier Hopf
$*$-algebra of $A$. Given such a quasi-invariant integral, we show how it can
be extended to a quasi-invariant integral on the Drinfeld double coideal. We
moreover show that the representation theory of the Drinfeld double coideal has
a monoidal structure. As an application, we determine the quasi-invariant
integral for the coideal $*$-algebra $U_q(\mathfrak{sl}(2,\mathbb{R}))$
constructed from the Podle\'{s} spheres.
|
Let k be an algebraically closed field of characteristic 0. We conclude the
classification of finite dimensional pointed Hopf algebras whose group of
group-likes is S_4. We also describe all pointed Hopf algebras over S_5 whose
infinitesimal braiding is associated to the rack of transpositions.
|
It is well known that every modular form~$f$ on a discrete subgroup
$\Gamma\leqslant \textrm{SL}(2, \mathbb R)$ satisfies a third-order nonlinear
ODE that expresses algebraic dependence of the functions~$f$, $f'$, $f''$
and~$f'''$. These ODEs are automatically invariant under the Lie group
$\textrm{SL}(2, \mathbb R)$, which acts on the solution spaces thereof with an
open orbit (and the discrete stabiliser~$\Gamma$ of a generic solution).
Similarly, every modular form satisfies a fourth-order nonlinear ODE that is
invariant under the Lie group $\textrm{GL}(2, \mathbb R)$ acting on its
solution space with an open orbit. ODEs for modular forms can be compactly
expressed in terms of the differential invariants of these actions. The
invariant forms of both ODEs define plane algebraic curves naturally associated
with every modular form; the corresponding ODEs can be seen as modular
parametrisations of the associated curves.
After reviewing examples of nonlinear ODEs satisfied by classical modular
forms (such as Eisenstein series, modular forms on congruence subgroups of
level two and three, theta constants, and some newforms of weight two), we
generalise these results to Jacobi forms; these satisfy involutive third-order
PDE systems that are invariant under the Lie group $\textrm{SL}(2, \mathbb
R)\ltimes H$ where $H$ is the Heisenberg group.
|
A Rota--Baxter operator is an algebraic abstraction of integration, which is
the typical example of a weight zero Rota-Baxter operator. We show that
studying the modules over the polynomial Rota--Baxter algebra $(k[x],P)$ is
equivalent to studying the modules over the Jordan plane, and we generalize the
direct decomposability results for the $(k[x],P)$-modules in [Iy] from
algebraically closed fields of characteristic zero to fields of characteristic
zero. Furthermore, we provide a classification of Rota--Baxter modules up to
isomorphism based on indecomposable $k[x]$-modules.
|
We study cumulants of the chiral order parameter as function of beam energy
as a possible signal for the presence of a critical end point and first-order
phase transition in the QCD phase diagram. We model the expansion of a
heavy-ion collision by a fluid dynamic expansion coupled to the explicit
propagation of the chiral order parameter sigma via a Langevin equation. We
evolve the medium until a parametrized freeze-out condition is met where we
calculate event-by-event fluctuations and cumulants of sigma which are expected
to follow the trend of net-proton number cumulants. We emphasize the role of a
nonequilibrium first-order phase transition: The presence of an unstable phase
causes the well-known bending of the trajectories in the space of temperature
and baryochemical potential. For these cases at lower beam energies, the system
crosses the freeze-out line more than once, allowing us to calculate a range of
cumulants for each initial condition which are overall enhanced for the second
hit of the freeze-out line. We thus find not only the critical end point but
also the phase transition of the underlying model clearly reflected in the
cumulants. The impact of volume fluctuations is demonstrated to play a
measurable role for fluid dynamical evolutions that last significantly long.
|
Given a function $f$ from the set $[N]$ to a $d$-dimensional integer grid, we
consider data structures that allow efficient orthogonal range searching
queries in the image of $f$, without explicitly storing it.
We show that, if $f$ is of the form $[N]\to [2^{w}]^d$ for some
$w=\mathrm{polylog} (N)$ and is computable in constant time, then, for any
$0<\alpha <1$, we can obtain a data structure using $\tilde {O}(N^{1-\alpha /
3})$ words of space such that, for a given $d$-dimensional axis-aligned box
$B$, we can search for some $x\in [N]$ such that $f(x) \in B$ in time
$\tilde{O}(N^{\alpha})$.
This result is obtained simply by combining integer range searching with the
Fiat-Naor function inversion scheme, which was already used in data-structure
problems previously.
We further obtain
- data structures for range counting and reporting, predecessor, selection,
ranking queries, and combinations thereof, on the set $f([N])$,
- data structures for preimage size and preimage selection queries for a
given value of $f$, and
- data structures for selection and ranking queries on geometric quantities
computed from tuples of points in $d$-space.
These results unify and generalize previously known results on 3SUM-indexing
and string searching, and are widely applicable as a black box to a variety of
problems.
In particular, we give a data structure for a generalized version of gapped
string indexing, and show how to preprocess a set of points on an integer grid
in order to efficiently compute (in sublinear time), for points contained in a
given axis-aligned box, their Theil-Sen estimator, the $k$th largest area
triangle, or the induced hyperplane that is the $k$th furthest from the origin.
|
We present the form of the Dirac quantisation condition for the p-form
charges carried by p-brane solutions of supergravity theories. This condition
agrees precisely with the conditions obtained in lower dimensions, as is
necessary for consistency with Kaluza-klein dimensional reduction. These
considerations also determine the charge lattice of BPS soliton states, which
proves to be a universal modulus-independent lattice when the charges are
defined to be the canonical charges corresponding to the quantum supergravity
symmetry groups.
|
A recent study of ultra-compact dwarf galaxies (UCDs) in the Virgo cluster
revealed that some of them show faint envelopes and have measured mass-to-light
ratios of 5 and larger, which can not be explained by simple population
synthesis models. It is believed that this proves that some of the UCDs must
possess a dark matter halo and may therefore be stripped nuclei of dwarf
ellipticals rather than merged star cluster complexes. Using an efficient
N-body method we investigate if a close passage of a UCD through the central
region of the host galaxy is able to enhance the measured mass-to-light ratio
by tidal forces leaving the satellite slightly out of virial equilibrium and
thereby leading to an overestimation of its virial mass. We find this to be
possible and discuss the general problem of measuring dynamical masses for
objects that are probably interacting with their hosts.
|
We propose a configuration of D-branes welded by analogous orbifold operation
to be responsible for the enhancement of $SO(2N)$ gauge symmetry in type II
string compactified on the $D_n$-type singular limit of K3. Evidences are
discussed from the $D_n$-type ALE and D-manifold point of view. A subtlety
regarding the ability of seeing the enhanced $SO(2N)$ gauge symmetry
perturbatively is briefly addressed.
|
We define a natural concept of duality for the h-Hopf algebroids introduced
by Etingof and Varchenko. We prove that the special case of the trigonometric
SL(2) dynamical quantum group is self-dual, and may therefore be viewed as a
deformation both of the function algebra F(SL(2)) and of the enveloping algebra
U(sl(2)). Matrix elements of the self-duality in the Peter-Weyl basis are
6j-symbols; this leads to a new algebraic interpretation of the hexagon
identity or quantum dynamical Yang-Baxter equation for quantum and classical
6j-symbols.
|
This article is the first in a series of three papers, whose scope is to give
new proofs to the well known theorems of Calder\'{o}n, Coifman, McIntosh and
Meyer. Here we treat the case of the first commutator and some of its
generalizations.
|
Probabilistic image registration methods estimate the posterior distribution
of transformation. The conventional way of interpreting the transformation
posterior is to use the mode as the most likely transformation and assign its
corresponding intensity to the registered voxel. Meanwhile, summary statistics
of the posterior are employed to evaluate the registration uncertainty, that is
the trustworthiness of the registered image. Despite the wide acceptance, this
convention has never been justified. In this paper, based on illustrative
examples, we question the correctness and usefulness of conventional methods.
In order to faithfully translate the transformation posterior, we propose to
encode the variability of values into a novel data type called ensemble fields.
Ensemble fields can serve as a complement to the registered image and a
foundation for developing advanced methods to characterize the uncertainty in
registration-based tasks. We demonstrate the potential of ensemble fields by
pilot examples
|
In recent years, there has been an explosive growth in multimodal learning.
Image captioning, a classical multimodal task, has demonstrated promising
applications and attracted extensive research attention. However, recent
studies have shown that image caption models are vulnerable to some security
threats such as backdoor attacks. Existing backdoor attacks against image
captioning typically pair a trigger either with a predefined sentence or a
single word as the targeted output, yet they are unrelated to the image
content, making them easily noticeable as anomalies by humans. In this paper,
we present a novel method to craft targeted backdoor attacks against image
caption models, which are designed to be stealthier than prior attacks.
Specifically, our method first learns a special trigger by leveraging universal
perturbation techniques for object detection, then places the learned trigger
in the center of some specific source object and modifies the corresponding
object name in the output caption to a predefined target name. During the
prediction phase, the caption produced by the backdoored model for input images
with the trigger can accurately convey the semantic information of the rest of
the whole image, while incorrectly recognizing the source object as the
predefined target. Extensive experiments demonstrate that our approach can
achieve a high attack success rate while having a negligible impact on model
clean performance. In addition, we show our method is stealthy in that the
produced backdoor samples are indistinguishable from clean samples in both
image and text domains, which can successfully bypass existing backdoor
defenses, highlighting the need for better defensive mechanisms against such
stealthy backdoor attacks.
|
In this paper we reconsider recently derived bounds on $MeV$ tau neutrinos,
taking into account previously unaccounted for effects. We find that, assuming
that the neutrino life-time is longer than $O(100~sec)$, the constraint
$N_{eff}<3.6$ rules out $\nu_{\tau}$ masses in the range
$0.5~(MeV)<m_{\nu_\tau}<35~(MeV)$ for Majorana neutrinos and
$0.74~(MeV)<m_{\nu_\tau}<35~(MeV)$ for Dirac neutrinos. Given that the present
laboratory bound is 35 MeV, our results lower the present bound to $0.5$ and
$0.74$ for Majorana and Dirac neutrinos respectively.
|
The idea of unifying quarks and leptons in a gauge symmetry is very
appealing. However, such an unification gives rise to leptoquark type gauge
bosons for which current collider limits push their masses well beyond the TeV
scale. We present a model in the framework of extra dimensions which breaks
such quark-lepton unification symmetry via compactification at the TeV scale.
These color triplet leptoquark gauge bosons, as well as the new quarks present
in the model, can be produced at the LHC with distinctive final state
signatures. These final state signals include high p_T multi-jets and
multi-leptons with missing energy, monojets with missing energy, as well as the
heavy charged particles passing through the detectors, which we also discuss
briefly. The model also has a neutral Standard Model singlet heavy lepton which
is stable, and can be a possible candidate for the dark matter.
|
GuessWhat?! is a two-player visual dialog guessing game where player A asks a
sequence of yes/no questions (Questioner) and makes a final guess (Guesser)
about a target object in an image, based on answers from player B (Oracle).
Based on this dialog history between the Questioner and the Oracle, a Guesser
makes a final guess of the target object. Previous baseline Oracle model
encodes no visual information in the model, and it cannot fully understand
complex questions about color, shape, relationships and so on. Most existing
work for Guesser encode the dialog history as a whole and train the Guesser
models from scratch on the GuessWhat?! dataset. This is problematic since
language encoder tend to forget long-term history and the GuessWhat?! data is
sparse in terms of learning visual grounding of objects. Previous work for
Questioner introduces state tracking mechanism into the model, but it is
learned as a soft intermediates without any prior vision-linguistic insights.
To bridge these gaps, in this paper we propose Vilbert-based Oracle, Guesser
and Questioner, which are all built on top of pretrained vision-linguistic
model, Vilbert. We introduce two-way background/target fusion mechanism into
Vilbert-Oracle to account for both intra and inter-object questions. We propose
a unified framework for Vilbert-Guesser and Vilbert-Questioner, where
state-estimator is introduced to best utilize Vilbert's power on single-turn
referring expression comprehension. Experimental results show that our proposed
models outperform state-of-the-art models significantly by 7%, 10%, 12% for
Oracle, Guesser and End-to-End Questioner respectively.
|
We analyse the internal structure and dynamics of cosmic-web filaments that
connect massive high-$z$ haloes. Our analysis is based on a high-resolution
AREPO cosmological simulation zooming-in on a volume encompassing three ${\rm
Mpc}$-scale filaments feeding three massive haloes of $\sim
10^{12}\,\text{M}_\odot$ at $z \sim 4$, embedded in a large-scale sheet. Each
filament is surrounded by a cylindrical accretion shock of radius $r_{\rm
shock} \sim 50 \,{\rm kpc}$. The post-shock gas is in virial equilibrium with
the potential well set by an isothermal dark-matter filament. The filament
line-mass is $\sim 9\times 10^8\,\text{M}_\odot\,{\rm kpc}^{-1}$, the gas
fraction within $r_{\rm shock}$ is the universal baryon fraction, and the
virial temperature is $\sim 7\times 10^5 {\rm K}$. In the outer ''thermal'' (T)
zone, $r \geq 0.65 \, r_{\rm shock}$, inward gravity and ram-pressure forces
are over-balanced by outwards thermal pressure forces, decelerating the
inflowing gas expanding the shock outward. In the intermediate ''vortex'' (V)
zone, $0.25 \leq r/ r_{\rm shock} \leq 0.65$, the velocity field is dominated
by a quadrupolar vortex structure due to offset inflow along the sheet through
the post-shock gas. The outwards force is dominated by centrifugal forces
associated with these vortices, with additional contributions from global
rotation and thermal pressure. The shear and turbulent forces associated with
the vortices act inward. The inner ''stream'' (S) zone, $r < 0.25 \, r_{\rm
shock}$, is a dense isothermal core, $T\sim 3 \times 10^4 \, {\rm K}$ and
$n_{\rm H}\sim 0.01 \,{\rm cm^{-3}}$, defining the cold streams that feed
galaxies. The core is formed by an isobaric cooling flow and is associated with
a decrease in outwards forces, though it exhibits both inflows and outflows.
[abridged]
|
Over the past 20 years, Kenya's demand for petroleum products has
proliferated. This is mainly because this particular commodity is used in many
sectors of the country's economy. Exchange rates are impacted by constantly
shifting prices, which also impact Kenya's industrial output of commodities.
The cost of other items produced and even the expansion of the economy is
significantly impacted by any change in the price of petroleum products.
Therefore, accurate petroleum price forecasting is critical for devising
policies that are suitable to curb fuel-related shocks. Data mining techniques
are the tools used to find valuable patterns in data. Data mining techniques
used in petroleum price prediction, including artificial neural networks
(ANNs), support vector machines (SVMs), and intelligent optimization techniques
like the genetic algorithm (GA), have grown increasingly popular. This study
provides a comprehensive review of the existing data mining techniques for
making predictions on petroleum prices. The data mining techniques are
classified into regression models, deep neural network models, fuzzy sets and
logic, and hybrid models. A detailed discussion of how these models are
developed and the accuracy of the models is provided.
|
Sixth generation systems are expected to face new security challenges, while
opening up new frontiers towards context awareness in the wireless edge. The
workhorse behind this projected technological leap will be a whole new set of
sensing capabilities predicted for 6G devices, in addition to the ability to
achieve high precision localization. The combination of these enhanced traits
can give rise to a new breed of context-aware security protocols, following the
quality of security (QoSec) paradigm. In this framework, physical layer
security solutions emerge as competitive candidates for low complexity,
low-delay and low-footprint, adaptive, flexible and context aware security
schemes, leveraging the physical layer of the communications in genuinely
cross-layer protocols, for the first time.
|
The Somos 5 sequences are a family of sequences defined by a fifth order
bilinear recurrence relation with constant coefficients. For particular choices
of coefficients and initial data, integer sequences arise. By making the
connection with a second order nonlinear mapping with a first integral, we
prove that the two subsequences of odd/even index terms each satisfy a Somos 4
(fourth order) recurrence. This leads directly to the explicit solution of the
initial value problem for the Somos 5 sequences in terms of the Weierstrass
sigma function for an associated elliptic curve.
|
We propose a modification of a recently introduced generalized translation
operator, by including a $q$-exponential factor, which implies in the
definition of a Hermitian deformed linear momentum operator $\hat{p}_q$, and
its canonically conjugate deformed position operator $\hat{x}_q$. A canonical
transformation leads the Hamiltonian of a position-dependent mass particle to
another Hamiltonian of a particle with constant mass in a conservative force
field of a deformed phase space. The equation of motion for the classical phase
space may be expressed in terms of the generalized dual $q$-derivative. A
position-dependent mass confined in an infinite square potential well is shown
as an instance. Uncertainty and correspondence principles are analyzed.
|
We propose a generalization of the Chern-Simon (CS) Lagrangian which is
invariant under the SIM(2) transformations but not under the full Lorentz
group. We study the effect of such a term on radiation propagating over
cosmological distances. We find that the dominant effect of this term is to
produce circular polarization as radiation propagates through space. We use the
circular polarization data from distant radio sources in order to impose a
limit on this term.
|
We estimate the $L^{p}$ norms of the discrepancy between the volume and the
number of integer points in $r\Omega-x$, a dilated by a factor $r$ and
translated by a vector $x$ of a convex body $\Omega$ in $\mathbb{R}^{d}$ with
smooth boundary with strictly positive curvature, \[ \left\{
{\displaystyle\int_{\mathbb R}}{\displaystyle\int_{\mathbb{T}^{d}}}\left\vert
\sum_{k\in\mathbb{Z}^{d}}\chi _{r\Omega-x}(k)-r^{d}\left\vert \Omega\right\vert
\right\vert ^{p}dxd\mu(r-R) \right\} ^{1/p}, \] where $\mu$ is a Borel measure
compactly supported on the positive real axis and $R\to+\infty$.
|
In this paper, we analyze the upper critical field of four MgB2 thin films,
with different resistivity (between 5 to 50 mWcm) and critical temperature
(between 29.5 to 38.8 K), measured up to 28 Tesla. In the perpendicular
direction the critical fields vary from 13 to 24 T and we can estimate 42-57 T
range in other direction. We observe linear temperature dependence even at low
temperatures without saturation, in contrast to BCS theory. Considering the
multiband nature of the superconductivity in MgB2, we conclude that two
different scattering mechanisms influence separately resistivity and critical
field. In this framework, resistivity values have been calculated from Hc2(T)
curves and compared with the measured ones.
|
We study biwarped product submanifolds which are special cases of multiply
warped product submanifolds in K\"{a}hler manifolds. We observe the
non-existence of such submanifolds under some circumstances. We show that there
exists a non-trivial biwarped product submanifold of a certain type by giving
an illustrate example. We also give a necessary and sufficient condition for
such submanifolds to be locally trivial. Moreover, we establish an inequality
for the squared norm of the second fundamental form in terms of the warping
functions for such submanifolds. The equality case is also discussed.
|
This paper discusses the relationship between memoized top-down recognizers
and chart parsers. It presents a version of memoization suitable for
continuation-passing style programs. When applied to a simple formalization of
a top-down recognizer it yields a terminating parser.
|
We aim to determine the production rates of several parent and product
volatiles and the 12C/13C isotopic carbon ratio in the long-period comet C/2004
Q2 (Machholz), which is likely to originate from the Oort Cloud. The line
emission from several molecules in the coma was measured with high
signal-to-noise ratio in January 2005 at heliocentric distance of 1.2 AU by
means of high-resolution spectroscopic observations using the Submillimeter
Telescope (SMT). We have obtained production rates of several volatiles (CH3OH,
HCN, H13CN, HNC, H2CO, CO and CS) by comparing the observed and simulated
line-integrated intensities. Furthermore, multiline observations of the CH3OH
(7-6) series allow us to estimate the rotational temperature using the rotation
diagram technique. We find that the CH3OH population distribution of the levels
sampled by these lines can be described by a rotational temperature of 40 \pm 3
K. Derived mixing ratios relative to hydrogen cyanide are
CO/CH3OH/H2CO/CS/HNC/H13CN/HCN = 30.9/24.6/4.8/0.57/0.031/0.013/1 assuming a
pointing offset of 8" due to the uncertain ephemeris at the time of the
observations and the telescope pointing error. The measured relative molecular
abundances in C/2004 Q2 (Machholz) are between low- to typical values of those
obtained in Oort Cloud comets, suggesting that it has visited the inner solar
system previously and undergone thermal processing. The HNC/HCN abundance ratio
of ~3.1% is comparable to that found in other comets, accounting for the
dependence on the heliocentric distance, and could possibly be explained by
ion-molecule chemical processes in the low-temperature atmosphere. From a
tentative H13CN detection, the measured value of 97 \pm 30 for the H12CN/H13CN
isotopologue pair is consistent with a telluric value.
|
A key aim in biology and psychology is to identify fundamental principles
underpinning the behavior of animals, including humans. Analyses of human
language and the behavior of a range of non-human animal species have provided
evidence for a common pattern underlying diverse behavioral phenomena: words
follow Zipf's law of brevity (the tendency of more frequently used words to be
shorter), and conformity to this general pattern has been seen in the behavior
of a number of other animals. It has been argued that the presence of this law
is a sign of efficient coding in the information theoretic sense. However, no
strong direct connection has been demonstrated between the law and compression,
the information theoretic principle of minimizing the expected length of a
code. Here we show that minimizing the expected code length implies that the
length of a word cannot increase as its frequency increases. Furthermore, we
show that the mean code length or duration is significantly small in human
language, and also in the behavior of other species in all cases where
agreement with the law of brevity has been found. We argue that compression is
a general principle of animal behavior, that reflects selection for efficiency
of coding.
|
This paper studies the second moment boundedness of solutions of linear
stochastic delay differential equations. First, we give a framework, for
general $\mathrm{N}$-dimensional linear stochastic differential equations with
a single discrete delay, of calculating the characteristic function for the
second moment boundedness. Next, we apply the proposed framework to a special
case of a type of 2-dimensional equation that the stochastic terms are
decoupled. For the 2-dimensional equation, we obtain the characteristic
function explicitly given by equation coefficients, the characteristic function
gives sufficient conditions for the second moment to be bounded or unbounded.
|
We demonstrate a fiber-integrated quantum optical circulator that is operated
by a single atom and that relies on the chiral interaction between emitters and
transversally confined light. Like its counterparts in classical optics, our
circulator exhibits an inherent asymmetry between light propagation in the
forward and the backward direction. However, rather than a magnetic field or a
temporal modulation, it is the internal quantum state of the atom that controls
the operation direction of the circulator. This working principle is compatible
with preparing the circulator in a coherent superposition of its operational
states. Such a quantum circulator may thus become a key element for routing and
processing quantum information in scalable integrated optical circuits.
Moreover, it features a strongly nonlinear response at the single-photon level,
thereby enabling, e.g., photon number-dependent routing and novel quantum
simulation protocols.
|
Let $(R,\mathfrak{m})$ be a Noetherian local ring of dimension $d > 0$. Let
$I_\bullet = \{I_n\}_{n \in \mathbb{N}}$ be a graded family of
$\mathfrak{m}$-primary ideals in $R$. We examine how far off from a polynomial
can the length function $\ell_R(R/I_n)$ be asymptotically. More specifically,
we show that there exists a constant $\gamma > 0$ such that for all $n \ge 0$,
$$\ell_R(R/I_{n+1}) - \ell_R(R/I_n) < \gamma n^{d-1}.$$
|
A core issue with learning to optimize neural networks has been the lack of
generalization to real world problems. To address this, we describe a system
designed from a generalization-first perspective, learning to update optimizer
hyperparameters instead of model parameters directly using novel features,
actions, and a reward function. This system outperforms Adam at all neural
network tasks including on modalities not seen during training. We achieve 2x
speedups on ImageNet, and a 2.5x speedup on a language modeling task using over
5 orders of magnitude more compute than the training tasks.
|
Do we know if a short selling ban or a Tobin Tax result in more stable asset
prices? Or do they in fact make things worse? Just like medicine regulatory
measures in financial markets aim at improving an already complex system. And
just like medicine these interventions can cause side effects which are even
harder to assess when taking the interplay with other measures into account. In
this paper an agent based stock market model is built that tries to find
answers to the questions above. In a stepwise procedure regulatory measures are
introduced and their implications on market liquidity and stability examined.
Particularly, the effects of (i) a ban of short selling (ii) a mandatory risk
limit, i.e. a Value-at-Risk limit, (iii) an introduction of a Tobin Tax, i.e.
transaction tax on trading, and (iv) any arbitrary combination of the measures
are observed and discussed. The model is set up to incorporate non-linear
feedback effects of leverage and liquidity constraints leading to fire sales
and escape dynamics. In its unregulated version the model outcome is capable of
reproducing stylised facts of asset returns like fat tails and clustered
volatility. Introducing regulatory measures shows that only a mandatory risk
limit is beneficial from every perspective, while a short selling ban - though
reducing volatility - increases tail risk. The contrary holds true for a Tobin
Tax: it reduces the occurrence of crashes but increases volatility.
Furthermore, the interplay of measures is not negligible: measures block each
other and a well chosen combination can mitigate unforeseen side effects.
Concerning the Tobin Tax the findings indicate that an overdose can do severe
harm.
|
We investigate efficiency of a gauge-covariant neural network and an
approximation of the Jacobian in optimizing the complexified integration path
toward evading the sign problem in lattice field theories. For the construction
of the complexified integration path, we employ the path optimization method.
The $2$-dimensional $\text{U}(1)$ gauge theory with the complex gauge coupling
constant is used as a laboratory to evaluate the efficiency. It is found that
the gauge-covariant neural network, which is composed of the Stout-like
smearing, can enhance the average phase factor, as the gauge-invariant input
does. For the approximation of the Jacobian, we test the most drastic case in
which we perfectly drop the Jacobian during the learning process. It reduces
the numerical cost of the Jacobian calculation from ${\cal O}(N^3)$ to ${\cal
O}(1)$, where $N$ means the number of degrees of freedom of the theory. The
path optimization using this Jacobian approximation still enhances the average
phase factor at expense of a slight increase of the statistical error.
|
We report on van der Waals epitaxial growth, materials characterization and
magnetotransport experiments in crystalline nanosheets of Bismuth
Telluro-Sulfide (BTS). Highly layered, good-quality crystalline nanosheets of
BTS are obtained on SiO$_2$ and muscovite mica. Weak-antilocalization (WAL),
electron-electron interaction-driven insulating ground state and universal
conductance fluctuations are observed in magnetotransport experiments on BTS
devices. Temperature, thickness and magnetic field dependence of the transport
data indicate the presence of two-dimensional surface states along with bulk
conduction, in agreement with theoretical models. An extended-WAL model is
proposed and utilized in conjunction with a two-channel conduction model to
analyze the data, revealing a surface component and evidence of multiple
conducting channels. A facile growth method and detailed magnetotransport
results indicating BTS as an alternative topological insulator material system
are presented.
|
We have performed a deep Chandra observation of Galactic Type Ia supernova
remnant G299.2-2.9. Here we report the initial results from our imaging and
spectral analysis. The observed abundance ratios of the central ejecta are in
good agreement with those predicted by delayed-detonation Type Ia supernovae
models. We reveal inhomogeneous spatial and spectral structures of metal-rich
ejecta in G299.2-2.9. The Fe/Si abundance ratio in the northern part of the
central ejecta is higher than that in the southern part. An elongation of
ejecta material extends out to the western outermost boundary of the remnant.
In this western elongation, both the Si and Fe are enriched with a similar
abundance ratio to that in the southern part of the central nebula. These
structured distributions of metal-rich ejecta material suggest that this Type
Ia supernova might have undergone a significantly asymmetric explosion and/or
has been expanding into a structured medium.
|
To study the variability of the 523 B and Be stars observed in the Magellanic
clouds with the VLT-FLAMES, we cross-matched the stars of our sample with the
photometric database MACHO, which provides for each star an 8 years lightcurve.
We searched for long, medium, and short-term periodicity and found the
eclipsing binaries in our sample. For these stars, combining, spectroscopy and
photometry, we were able to provide information on several systems of stars
(systemic velocities, ratios of masses, etc). We also present the ratios of
B-binaries to B-non binaries in the LMC/SMC in comparison with the MW. Note
that this ratio is also an important issue to understand the mechanism of
star-formation at low metallicity. We also found the first multiperiodic B and
Be stars in the SMC, in particular the first SMC Beta Cep and SPB, while,
according to the models, pulsations were not foreseen in low metallicity
environments, i.e. typically in the SMC. Our results show that the instability
strips are shifted towards higher temperatures in comparison with the Milky
Way' strips of pulsating B-type stars. By the fact that we found more pulsating
Be stars than pulsating B stars in the SMC, it seems that the fast rotation
favours the presence of pulsations. However, the ratio of pulsating B-type
stars to "non"-pulsating B-type stars at low metallicity is lower than at high
metallicity.
|
We describe a fully broadband approach for electron spin resonance (ESR)
experiments where it is possible to not only tune the magnetic field but also
the frequency continuously over wide ranges. Here a metallic coplanar
transmission line acts as compact and versatile microwave probe that can easily
be implemented in different cryogenic setups. We perform ESR measurements at
frequencies between 0.1 and 67 GHz and at temperatures between 50 mK and room
temperature. Three different types of samples (Cr3+ ions in ruby, organic
radicals of the nitronyl-nitroxide family, and the doped semiconductor Si:P)
represent different possible fields of application for the technique. We
demonstrate that an extremely large phase space in temperature, magnetic field,
and frequency for ESR measurements, substantially exceeding the range of
conventional ESR setups, is accessible with metallic coplanar lines.
|
In this work, we analysed new LOw Frequency ARray observations of the mini
halo in the cluster RBS797, together with archival Very Large Array
observations and the recent Chandra results. This cluster is known to host a
powerful active galactic nucleus (AGN) at its centre, with two pairs of jets
propagating in orthogonal directions. Recent X-ray observations have detected
three pairs of shock fronts, connected with the activity of the central AGN.
Our aim is to investigate the connection between the mini halo emission and the
activity of the central source. We find that the diffuse radio emission is
elongated in different directions at 144 MHz (east-west) with respect to 1.4
GHz (north-south), tracing the orientation of the two pairs of jets. The mini
halo emission is characterised by an average spectral index $\alpha=-1.02\pm
0.05$. The spectral index profile of the mini halo shows a gradual flattening
from the centre to the periphery. Such a trend is unique among the mini halos
studied to date, and resembles the spectral index trend typical of particles
re-accelerated by shocks. However, the estimated contribution to the radio
brightness profile coming from shock re-acceleration is found to be
insufficient to account for the radial brightness profile of the mini halo. We
propose three scenarios that could explain the observed trend: (i) the
AGN-driven shocks are propagating onto an already existing mini halo,
re-energising the electrons. We estimate that the polarisation induced by the
shocks could be detected at 6 GHz and above; (ii) we could be witnessing
turbulent re-acceleration in a high magnetic field cluster; and (iii) the mini
halo could have a hadronic origin, in which the particles are injected by
Future observations in polarisation would be fundamental to understand the role
of shocks and the magnetic field.
|
The solving degree of a system of multivariate polynomial equations provides
an upper bound for the complexity of computing the solutions of the system via
Groebner bases methods. In this paper, we consider polynomial systems that are
obtained via Weil restriction of scalars. The latter is an arithmetic
construction which, given a finite Galois field extension $k\hookrightarrow K$,
associates to a system $\mathcal{F}$ defined over $K$ a system
$\mathrm{Weil}(\mathcal{F})$ defined over $k$, in such a way that the solutions
of $\mathcal{F}$ over $K$ and those of $\mathrm{Weil}(\mathcal{F})$ over $k$
are in natural bijection. In this paper, we find upper bounds for the
complexity of solving a polynomial system $\mathrm{Weil}(\mathcal{F})$ obtained
via Weil restriction in terms of algebraic invariants of the system
$\mathcal{F}$.
|
The raw coronagraphic performance of current high-contrast imaging
instruments is limited by the presence of a quasi-static speckle (QSS)
background, resulting from instrumental non-common path errors (NCPEs). Rapid
development of efficient speckle subtraction techniques in data reduction has
enabled final contrasts of up to 10-6 to be obtained, however it remains
preferable to eliminate the underlying NCPEs at the source. In this work we
introduce the coronagraphic Modal Wavefront Sensor (cMWS), a new wavefront
sensor suitable for real-time NCPE correction. This pupil-plane optic combines
the apodizing phase plate coronagraph with a holographic modal wavefront
sensor, to provide simultaneous coronagraphic imaging and focal-plane wavefront
sensing using the science point spread function. We first characterise the
baseline performance of the cMWS via idealised closed-loop simulations, showing
that the sensor successfully recovers diffraction-limited coronagraph
performance over an effective dynamic range of +/-2.5 radians root-mean-square
(RMS) wavefront error within 2-10 iterations. We then present the results of
initial on-sky testing at the William Herschel Telescope, and demonstrate that
the sensor is able to retrieve injected wavefront aberrations to an accuracy of
10nm RMS under realistic seeing conditions. We also find that the cMWS is
capable of real-time broadband measurement of atmospheric wavefront variance at
a cadence of 50Hz across an uncorrected telescope sub-aperture. When combined
with a suitable closed-loop adaptive optics system, the cMWS holds the
potential to deliver an improvement in raw contrast of up to two orders of
magnitude over the uncorrected QSS floor. Such a sensor would be eminently
suitable for the direct imaging and spectroscopy of exoplanets with both
existing and future instruments, including EPICS and METIS for the E-ELT.
|
We develop and calibrate a realistic model flame for hydrodynamical
simulations of deflagrations in white dwarf (Type Ia) supernovae. Our flame
model builds on the advection-diffusion-reaction model of Khokhlov and includes
electron screening and Coulomb corrections to the equation of state in a
self-consistent way. We calibrate this model flame--its energetics and
timescales for energy release and neutronization--with self-heating reaction
network calculations that include both these Coulomb effects and up-to-date
weak interactions. The burned material evolves post-flame due to both weak
interactions and hydrodynamic changes in density and temperature. We develop a
scheme to follow the evolution, including neutronization, of the NSE state
subsequent to the passage of the flame front. As a result, our model flame is
suitable for deflagration simulations over a wide range of initial central
densities and can track the temperature and electron fraction of the burned
material through the explosion and into the expansion of the ejecta.
|
In 2007 Lam and Pylyavskyy found a combinatorial formula for the dual stable
Grothendieck polynomials, which are the dual basis of the stable Grothendieck
polynomials with respect to the Hall inner product. In 2016 Galashin, Grinberg,
and Liu introduced refined dual stable Grothendieck polynomials by putting
additional sequence of parameters in the combinatorial formula of Lam and
Pylyavskyy. Grinberg conjectured a Jacobi--Trudi type formula for refined dual
stable Grothendieck polynomials. In this paper this conjecture is proved by
using bijections of Lam and Pylyavskyy.
|
We develop a new perspective on research conducted through visualization
design study that emphasizes design as a method of inquiry and the broad range
of knowledge-contributions achieved through it as multiple, subjective, and
socially constructed. From this interpretivist position we explore the nature
of visualization design study and develop six criteria for rigor. We propose
that rigor is established and judged according to the extent to which
visualization design study research and its reporting are INFORMED, REFLEXIVE,
ABUNDANT, PLAUSIBLE, RESONANT, and TRANSPARENT. This perspective and the
criteria were constructed through a four-year engagement with the discourse
around rigor and the nature of knowledge in social science, information
systems, and design. We suggest methods from cognate disciplines that can
support visualization researchers in meeting these criteria during the
planning, execution, and reporting of design study. Through a series of
deliberately provocative questions, we explore implications of this new
perspective for design study research in visualization, concluding that as a
discipline, visualization is not yet well positioned to embrace, nurture, and
fully benefit from a rigorous, interpretivist approach to design study. The
perspective and criteria we present are intended to stimulate dialogue and
debate around the nature of visualization design study and the broader
underpinnings of the discipline.
|
A finite or infinite matrix $A$ with rational entries (and only finitely many
non-zero entries in each row) is called image partition regular if, whenever
the natural numbers are finitely coloured, there is a vector $x$, with entries
in the natural numbers, such that $Ax$ is monochromatic. Many of the classical
results of Ramsey theory are naturally stated in terms of image partition
regularity.
Our aim in this paper is to investigate maximality questions for image
partition regular matrices. When is it possible to add rows on to $A$ and
remain image partition regular? When can one add rows but `nothing new is
produced'? What about adding rows and also new variables? We prove some results
about extensions of the most interesting infinite systems, and make several
conjectures.
Perhaps our most surprising positive result is a compatibility result for
Milliken-Taylor systems, stating that (in many cases) one may adjoin one
Milliken-Taylor system to a translate of another and remain image partition
regular. This is in contrast to earlier results, which had suggested a strong
inconsistency between different Milliken-Taylor systems. Our main tools for
this are some algebraic properties of the $\beta N$, the Stone-Cech
compactification of the natural numbers.
|
We construct geometric examples of pseudomanifolds that satisfy the Witt
condition for intersection homology Poincare duality with respect to certain
fields but not others. We also compute the bordism theory of $K$-Witt spaces
for an arbitrary field $K$, extending results of Siegel for $K=Q$.
|
The typical transverse momentum of a quark in the proton is a basic property
of any QCD based model of nucleon structure. However, calculations in
phenomenological models typically give rather small values of transverse
momenta, which are difficult to reconcile with the larger values observed in
high energy experiments such as Drell-Yan reactions and Semi-inclusive deep
inelastic scattering. In this letter we calculate the leading twist transverse
momentum dependent distribution functions (TMDs) using a generalization of the
Adelaide group's relativistic formalism that has previously given good fits to
the parton distributions. This enables us to examine the $k_{T}$ dependence of
the TMDs in detail, and determine typical widths of these distributions. These
are found to be significantly larger than those of previous calculations. We
then use TMD factorization in order to evolve these distributions up to
experimental scales where we can compare with data on $\langle k_{T} \rangle$
and $\langle k^{2}_{T} \rangle$. Our distributions agree well with this data.
|
To achieve a smooth and safe guiding of a drone formation by a human
operator, we propose a novel interaction strategy for a human-swarm
communication which combines impedance control and vibrotactile feedback. The
presented approach takes into account the human hand velocity and changes the
formation shape and dynamics accordingly using impedance interlinks simulated
between quadrotors, which helps to achieve a natural swarm behavior. Several
tactile patterns representing static and dynamic parameters of the swarm are
proposed. The user feels the state of the swarm at the fingertips and receives
valuable information to improve the controllability of the complex formation. A
user study revealed the patterns with high recognition rates. A flight
experiment demonstrated the possibility to accurately navigate the formation in
a cluttered environment using only tactile feedback. Subjects stated that
tactile sensation allows guiding the drone formation through obstacles and
makes the human-swarm communication more interactive. The proposed technology
can potentially have a strong impact on the human-swarm interaction, providing
a higher level of awareness during the swarm navigation.
|
Using methods of effective field theory, we show that after resummation of
Sudakov logarithms the spectral densities of interacting quark and gluon fields
in ordinary quantum field theories such as QCD are virtually indistinguishable
from those of "unparticles" of a hypothetical conformal sector coupled to the
Standard Model, recently studied by Georgi. Unparticles are therefore less
exotic that originally thought. Models in which a hidden sector weakly coupled
to the Standard Model contains a QCD-like theory, which confines at some scale
much below the characteristic energy of a given process, can give rise to
signatures closely resembling those from unparticles.
|
Smart and agile drones are fast becoming ubiquitous at the edge of the cloud.
The usage of these drones are constrained by their limited power and compute
capability. In this paper, we present a Transfer Learning (TL) based approach
to reduce on-board computation required to train a deep neural network for
autonomous navigation via Deep Reinforcement Learning for a target algorithmic
performance. A library of 3D realistic meta-environments is manually designed
using Unreal Gaming Engine and the network is trained end-to-end. These trained
meta-weights are then used as initializers to the network in a test environment
and fine-tuned for the last few fully connected layers. Variation in drone
dynamics and environmental characteristics is carried out to show robustness of
the approach. Using NVIDIA GPU profiler it was shown that the energy
consumption and training latency is reduced by 3.7x and 1.8x respectively
without significant degradation in the performance in terms of average distance
traveled before crash i.e. Mean Safe Flight (MSF). The approach is also tested
on a real environment using DJI Tello drone and similar results were reported.
|
We give sharp conditions for global in time existence of gradient flow
solutions to a Cahn-Hilliard-type equation, with backwards second order
degenerate diffusion, in any dimension and for general initial data. Our
equation is the 2-Wasserstein gradient flow of a free energy with two competing
effects: the Dirichlet energy and the power-law internal energy. Homogeneity of
the functionals reveals critical regimes that we analyse. Sharp conditions for
global in time solutions, constructed via the minimising movement scheme, also
known as JKO scheme, are obtained. Furthermore, we study a system of two
Cahn-Hilliard-type equations exhibiting an analogous gradient flow structure.
|
In this paper, we consider the problem of visual scanning mechanism
underpinning sensorimotor tasks, such as walking and driving, in dynamic
environments. We exploit eye tracking data for offering two new cognitive
effort measures in visual scanning behavior of virtual driving. By utilizing
the retinal flow induced by fixation, two novel measures of cognitive effort
are proposed through the importance of grids in the viewing plane and the
concept of information quantity, respectively. Psychophysical studies are
conducted to reveal the effectiveness of the two proposed measures. Both these
two cognitive effort measures have shown their significant correlation with
pupil size change. Our results suggest that the quantitative exploitation of
eye tracking data provides an effective approach for the evaluation of
sensorimotor activities.
|
A limit variety is a variety that is minimal with respect to being
non-finitely based. The two limit varieties of Marcel Jackson are the only
known examples of limit varieties of aperiodic monoids. Our previous work had
shown that there exists a limit subvariety of aperiodic monoids that is
different from Marcel Jackson's limit varieties. In this paper, we introduce a
new limit variety of aperiodic monoids.
|
We initiate the study of property testing problems concerning relations
between permutations. In such problems, the input is a tuple
$(\sigma_1,\dotsc,\sigma_d)$ of permutations on $\{1,\dotsc,n\}$, and one
wishes to determine whether this tuple satisfies a certain system of relations
$E$, or is far from every tuple that satisfies $E$. If this computational
problem can be solved by querying only a small number of entries of the given
permutations, we say that $E$ is testable. For example, when $d=2$ and $E$
consists of the single relation $\mathsf{XY=YX}$, this corresponds to testing
whether $\sigma_1\sigma_2=\sigma_2\sigma_1$, where $\sigma_1\sigma_2$ and
$\sigma_2\sigma_1$ denote composition of permutations.
We define a collection of graphs, naturally associated with the system $E$,
that encodes all the information relevant to the testability of $E$. We then
prove two theorems that provide criteria for testability and non-testability in
terms of expansion properties of these graphs. By virtue of a deep connection
with group theory, both theorems are applicable to wide classes of systems of
relations.
In addition, we formulate the well-studied group-theoretic notion of
stability in permutations as a special case of the testability notion above,
interpret all previous works on stability as testability results, survey
previous results on stability from a computational perspective, and describe
many directions for future research on stability and testability.
|
We found an active state lasting for ~200 d in the AM CVn star NSV 1440 in
2022. During this state, the object reached a magnitude of 16.5, 2.0-2.5 mag
above quiescence, and showed a number of superposed normal outbursts. Such an
active state was probably brought either by an enhanced mass-transfer from the
secondary or increased quiescent viscosity of the accretion disk. These
possibilities are expected to be distinguished by an observation of the
interval to the next superoutburst. We also found that the brightness and the
course toward the end of the event were similar to the post-superoutburst
fading tail in 2021. The mechanism producing the 2022 active state and
post-superoutburst fading tails in AM CVn stars may be the same, and the
present finding is expected to clarify the nature of these still poorly
understood fading tails in AM CVn stars, and potentially of the corresponding
phenomenon in hydrogen-rich WZ Sge stars. We also note that the faint, long
"superoutbursts" in long-period AM CVn stars claimed in the past were not true
outbursts powered by disk instability, but were more likely phenomena similar
to the 2022 active state in NSV 1440.
|
In this paper we study the area minimizing problem in some kinds of conformal
cones. This concept is a generalization of the cones in Eulcidean spaces and
the cylinders in product manifolds. We define a non-closed-minimal (NCM)
condition for bounded domains. Under this assumption and other necessary
conditions we establish the existence of bounded minimal graphs in mean convex
conformal cones. Moreover those minimal graphs are the solutions to
corresponding area minizing problems. We can solve the area minimizing problem
in non-mean convex translating conformal cones if these cones are contained in
a larger mean convex conformal cones with the NCM assumption. We give examples
to illustrate that this assumption can not be removed for our main results.
|
Using the method of renormalization group, we improve the two-loop effective
potential of the massive $\phi^4$ theory to obtain the next-next-to-leading
logarithm correction in the $\bar{MS}$ scheme. Our result well reproduces the
next-next-to-leading logarithm parts of the ordinary loop expansion result
known up to the four-loop order.
|
Chiral perturbation theory is nowadays a well-established approach to
incorporate the chiral constraints from QCD. Nevertheless, for systems
involving one baryon, the power counting which dictates the chiral order of
observables is not as simple and consensual as in the purely mesonic case. The
heavy baryon approach, which relies on a non-relativistic expansion around the
limit of infinitely heavy baryon, recovers the usual power counting but
destroys some analytic properties of the scattering amplitude. Some years ago,
Becher and Leutwyler proposed a Lorentz-invariant formulation of chiral
perturbation theory that maintains the required analytic properties, but at the
expense of a less intuitive power counting.
Aware of the shortcomings of the heavy baryon formalism, the S\~ao Paulo
group derived the two-pion exchange component of the nucleon-nucleon potential
in line with the works of Becher and Leutwyler. A striking result was that the
long distance properties of the potential is determined by the specific low
energy region of the pion-nucleon scattering amplitude where the heavy baryon
expansion fails. In this talk I will discuss the origin of such failure and how
it reflects in the asymptotics of the nucleon-nucleon interaction. Some results
for phase shifts and deuteron properties will be shown, followed by a
comparison with the heavy baryon predictions.
|
We show that the minimization problem of any non-convex and non-lower
semi-continuous function on a compact convex subset of a locally convex real
topological vector space can be studied via an associated convex and lower
semi-continuous function $\Gamma \left( h\right) $. This observation uses the
notion of $\Gamma $-regularization as a key ingredient. As an application we
obtain, on any locally convex real space, a generalization of the Lanford
III-Robinson theorem which has only been proven for separable real Banach
spaces. The latter is a characterization of subdifferentials of convex
continuous functions.
|
Context. RW Aur A is a classical T Tauri star (CTTS) with an unusually rich
emission line spectrum. In 2014 the star faded by ~ 3 magnitudes in the V band
and went into a long-lasting minimum. In 2010 the star suffered from a similar
fading, although less deep. These events in RW Aur A are very unusual among the
CTTS, and have been attributed to occultations by passing dust clouds. Aims. We
want to find out if any spectral changes took place after the last fading of RW
Aur A with the intention to gather more information on the occulting body and
the cause of the phenomenon. Methods. We collected spectra of the two
components of RW Aur. Photometry was made before and during the minimum.
Results. The overall spectral signatures reflecting emission from accretion
flows from disk to star did not change after the fading. However, blue-shifted
absorption components related to the stellar wind had increased in strength in
certain resonance lines, and the profiles and strengths, but not fluxes, of
forbidden lines had become drastically different. Conclusions. The extinction
through the obscuring cloud is grey indicating the presence of large dust
grains. At the same time, there are no traces of related absorbing gas. The
cloud occults the star and the interior part of the stellar wind, but not the
wind/jet further out. The dimming in 2014 was not accompanied by changes in the
accretion flows at the stellar surface. There is evidence that the structure
and velocity pattern of the stellar wind did change significantly. The dimmings
could be related to passing condensations in a tidally disrupted disk, as
proposed earlier, but we also speculate that large dust grains have been
stirred up from the inclined disk into the line-of-sight through the
interaction with an enhanced wind.
|
Achieving quantum-level control over electromagnetic waves, magnetisation
dynamics, vibrations and heat is invaluable for many practical application and
possible by exploiting the strong radiation-matter coupling. Most of the modern
strong microwave photon-magnon coupling developments rely on the integration of
metal-based microwave resonators with a magnetic material. However, it has
recently been realised that all-dielectric resonators made of or containing
magneto-insulating materials can operate as a standalone strongly-coupled
system characterised by low dissipation losses and strong local microwave field
enhancement. Here, after a brief overview of recent developments in the field,
I discuss examples of such dielectric resonant systems and demonstrate their
ability to operate as multiresonant antennas for light, microwaves, magnons,
sound, vibrations and heat. This multiphysics behaviour opens up novel
opportunities for the realisation of multiresonant coupling such as, for
example, photon-magnon-phonon coupling. I also propose several novel systems in
which strong photon-magnon coupling in dielectric antennas and similar
structures is expected to extend the capability of existing devices or may
provide an entirely new functionality. Examples of such systems include novel
magnetofluidic devices, high-power microwave power generators, and hybrid
devices exploiting the unique properties of electrical solitons.
|
Elliptic operators on stratified manifolds with any finite number of strata
are considered. Under certain assumptions on the symbols of operators, we
obtain index formulas, which express index as a sum of indices of elliptic
operators on the strata.
|
To understand the origin of the magnetic fields in massive stars as well as
their impact on stellar internal structure, evolution, and circumstellar
environment, within the MiMeS project, we searched for magnetic objects among a
large sample of massive stars, and build a sub-sample for in-depth follow-up
studies required to test the models and theories of fossil field origins,
magnetic wind confinement and magnetospheric properties, and magnetic star
evolution.
We obtained high-resolution spectropolarimetric observations of a large
number of OB stars thanks to three large programs that have been allocated on
the high-resolution spectropolarimeters ESPaDOnS, Narval, and the polarimetric
module HARPSpol of the HARPS spectrograph. We report here on the methods and
first analysis of the HARPSpol magnetic detections. We identified the magnetic
stars using a multi-line analysis technique. Then, when possible, we monitored
the new discoveries to derive their rotation periods, which are critical for
follow-up and magnetic mapping studies. We also performed a first-look analysis
of their spectra and identified obvious spectral anomalies (e.g., abundance
peculiarities, Halpha emission), which are also of interest for future studies.
In this paper, we focus on eight of the 11 stars in which we discovered or
confirmed a magnetic field from the HARPSpol LP sample (the remaining three
were published in a previous paper). Seven of the stars were detected in
early-type Bp stars, while the last star was detected in the Ap companion of a
normal early B-type star. We report obvious spectral and multiplicity
properties, as well as our measurements of their longitudinal field strengths,
and their rotation periods when we are able to derive them. We also discuss the
presence or absence of Halpha emission with respect to the theory of
centrifugally-supported magnetospheres. (Abriged)
|
A cylindrical GEM detector is under development, to serve as an upgraded
inner tracker at the BESIII spectrometer. It will consist of three layers of
cylindrically-shaped triple GEMs surrounding the interaction point. The
experiment is taking data at the e+e- collider BEPCII in Beijing (China) and
the GEM tracker will be installed in 2018. Tests on the performances of triple
GEMs in strong magnetic field have been run by means of the muon beam available
in the H4 line of SPS (CERN) with both planar chambers and the first
cylindrical prototype. Efficiencies and resolutions have been evaluated using
different gains, gas mixtures, with and without magnetic field. The obtained
efficiency is 97-98% on single coordinate view, in many operational
arrangements. The spatial resolution for planar GEMs has been evaluated with
two different algorithms for the position determination: the charge centroid
and the micro time projection chamber (mu-TPC) methods. The two modes are
complementary and are able to cope with the asymmetry of the electron avalanche
when running in magnetic field, and with non-orthogonal incident tracks. With
the charge centroid, a resolution lower than 100 micron has been reached
without magnetic field and lower than 200 micron with a magnetic field up to 1
T. The mu-TPC mode showed to be able to improve those results. In the first
beam test with the cylindrical prototype, the detector had a very good
stability under different voltage configurations and particle intensities. The
resolution evaluation is in progress.
|
We re-analyze the Cepheid data used to infer the value of $H_0$ by
calibrating SnIa. We do not enforce a universal value of the empirical Cepheid
calibration parameters $R_W$ (Cepheid Wesenheit color-luminosity parameter) and
$M_H^{W}$ (Cepheid Wesenheit H-band absolute magnitude). Instead, we allow for
variation of either of these parameters for each individual galaxy. We also
consider the case where these parameters have two universal values: one for low
galactic distances $D<D_c$ and one for high galactic distances $D>D_c$ where
$D_c$ is a critical transition distance. We find hints for a $3\sigma$ level
mismatch between the low and high galactic distance parameter values. We then
use AIC and BIC criteria to compare and rank the following types of models:
Base models: Universal values for $R_W$ and $M_H^{W}$ (no parameter variation),
I Individual fitted galactic $R_W$ with a universal fitted $M_H^{W}$, II
Universal fixed $R_W$ with individual fitted galactic $M_H^{W}$, III Universal
fitted $R_W$ with individual fitted galactic $M_H^{W}$, IV Two universal fitted
$R_W$ (near and far) with one universal fitted $M_H^{W}$, V Universal fitted
$R_W$ with two universal fitted $M_H^{W}$ (near and far), VI Two universal
fitted $R_W$ with two universal fitted $M_H^{W}$ (near and far). We find that
the AIC and BIC criteria consistently favor model IV instead of the commonly
used Base model where no variation is allowed for the Cepheid empirical
parameters. The best fit value of the SnIa absolute magnitude $M_B$ and of
$H_0$ implied by the favored model IV is consistent with the inverse distance
ladder calibration based on the CMB sound horizon $H_0=67.4\pm
0.5\,km\,s^{-1}\,Mpc^{-1}$. Thus in the context of the favored model IV the
Hubble crisis is not present. This model may imply the presence of a
fundamental physics transition taking place at a time more recent than
$100\,Myrs$ ago.
|
In this note, we provide a simple derivation of expressions for the
restricted partition function and its polynomial part. Our proof relies on
elementary algebra on rational functions and a lemma that expresses the
polynomial part as an average of the partition function.
|
We propose a new file format named "H5MD" for storing molecular simulation
data, such as trajectories of particle positions and velocities, along with
thermodynamic observables that are monitored during the course of the
simulation. H5MD files are HDF5 (Hierarchical Data Format) files with a
specific hierarchy and naming scheme. Thus, H5MD inherits many benefits of
HDF5, e.g., structured layout of multi-dimensional datasets, data compression,
fast and parallel I/O, and portability across many programming languages and
hardware platforms. H5MD files are self-contained and foster the
reproducibility of scientific data and the interchange of data between
researchers using different simulation programs and analysis software. In
addition, the H5MD specification can serve for other kinds of data (e.g.
experimental data) and is extensible to supplemental data, or may be part of an
enclosing file structure.
|
We compute the R-matrix which intertwines two dimensional evaluation
representations with Drinfeld comultiplication for U_q(\widehat{sl}_2). This
R-matrix contains terms proportional to the delta-function. We construct the
algebra A(R) generated by the elements of the matrices L^\pm(z) with relations
determined by R. In the category of highest weight representations, there is a
Hopf algebra isomorphism between A(R) and an extension
\overline{U}_q(\widehat{sl}_2)} of Drinfeld's algebra.
|
Building on a specific formalization of analogical relationships of the form
"A relates to B as C relates to D", we establish a connection between two
important subfields of artificial intelligence, namely analogical reasoning and
kernel-based machine learning. More specifically, we show that so-called
analogical proportions are closely connected to kernel functions on pairs of
objects. Based on this result, we introduce the analogy kernel, which can be
seen as a measure of how strongly four objects are in analogical relationship.
As an application, we consider the problem of object ranking in the realm of
preference learning, for which we develop a new method based on support vector
machines trained with the analogy kernel. Our first experimental results for
data sets from different domains (sports, education, tourism, etc.) are
promising and suggest that our approach is competitive to state-of-the-art
algorithms in terms of predictive accuracy.
|
We are concerned with the inviscid limit of the Navier-Stokes equations to
the Euler equations for compressible fluids in $\mathbb{R}^3$. Motivated by the
Kolmogorov hypothesis (1941) for incompressible flow, we introduce a
Kolmogorov-type hypothesis for barotropic flows, in which the density and the
sonic speed normally vary significantly. We then observe that the compressible
Kolmogorov-type hypothesis implies the uniform boundedness of some fractional
derivatives of the weighted velocity and sonic speed in the space variables in
$L^2$, which is independent of the viscosity coefficient $\mu>0$. It is shown
that this key observation yields the equicontinuity in both space and time of
the density in $L^\gamma$ and the momentum in $L^2$, as well as the uniform
bound of the density in $L^{q_1}$ and the velocity in $L^{q_2}$ independent of
$\mu>0$, for some fixed $q_1 >\gamma$ and $q_2 >2$, where $\gamma>1$ is the
adiabatic exponent. These results lead to the strong convergence of solutions
of the Navier-Stokes equations to a solution of the Euler equations for
barotropic fluids in $\mathbb{R}^3$. Not only do we offer a framework for
mathematical existence theories, but also we offer a framework for the
interpretation of numerical solutions through the identification of a function
space in which convergence should take place, with the bounds that are
independent of $\mu>0$, that is in the high Reynolds number limit.
|
We apply a new method of determination of the size of the broad emission-line
region (BLR) in active galactic nuclei. This method relates the radius of the
broad-line region of AGN to the soft X-ray luminosity and spectral index.
Comparing the BLR distances calculated from our photoionization scaling model
to the BLR distances determined by reverberation mapping shows that the scaling
law agrees with the $R\sim L^{1/2}$ empirical relation. We investigate a
complimentary method of estimating the BLR distance - based on the Keplerian
broadening of the emission lines and the central mass estimated from X-ray
variability.
|
We demonstrate how the zitterbewegung charge oscillations can be detected
through a charge conductance measurement in a three-terminal junction. By
tuning the spin-orbit interaction strength or an external magnetic field the
zitterbewegung period can be modulated, translating into complementary
conductance oscillations in the two outgoing leads of the junction. The
proposed experimental setup is within the reach of demonstrated technology and
material parameters, and enables the observation of the so far elusive
zitterbewegung phenomenon.
|
We investigated the possibility of construction the homogeneous and isotropic
cosmological solutions in Weyl geometry. We derived the self-consistency
condition which ensures the conformal invariance of the complete set of
equations of motion. There is the special gauge in choosing the conformal
factor when the Weyl vector equals zero. In this gauge we found new vacuum
cosmological solutions absent in General Relativity. Also, we found new
solution in Weyl geometry for the radiation dominated universe with the
cosmological term, corresponding to the constant curvature scalar in our
special gauge. Possible relation of our results to the understanding both dark
matter and dark energy is discussed.
|
Bethe's view-point on the global energy problems is presented. Bethe claimed
that the nuclear power is a necessity in future. Nuclear energetic must be
based on breeder reactors. Bethe considered the non-proliferation of nuclear
weapons as the main problem of long-range future of nuclear energetics. The
solution of this problem he saw in heavy water moderated thermal breeders,
using uranium-233, uranium-238 and thorium as a fuel.
|
Software vulnerabilities, caused by unintentional flaws in source code, are a
primary root cause of cyberattacks. Static analysis of source code has been
widely used to detect these unintentional defects introduced by software
developers. Large Language Models (LLMs) have demonstrated human-like
conversational abilities due to their capacity to capture complex patterns in
sequential data, such as natural languages. In this paper, we harness LLMs'
capabilities to analyze source code and detect known vulnerabilities. To ensure
the proposed vulnerability detection method is universal across multiple
programming languages, we convert source code to LLVM IR and train LLMs on
these intermediate representations. We conduct extensive experiments on various
LLM architectures and compare their accuracy. Our comprehensive experiments on
real-world and synthetic codes from NVD and SARD demonstrate high accuracy in
identifying source code vulnerabilities.
|
The Sloan Digital Sky Survey has identified a total of 212 cataclysmic
variables, most of which are fainter than 18th magnitude. This is the deepest
and most populous homogeneous sample of cataclysmic variables to date, and we
are undertaking a project to characterise this population. We have found that
the SDSS sample is dominated by a great ``silent majority'' of old and faint
CVs. We detect, for the first time, a population spike at the minimum period of
80 minutes which has been predicted by theoretical studies for over a decade.
|
In contrast to the abundant research focusing on large-scale models, the
progress in lightweight semantic segmentation appears to be advancing at a
comparatively slower pace. However, existing compact methods often suffer from
limited feature representation capability due to the shallowness of their
networks. In this paper, we propose a novel lightweight segmentation
architecture, called Multi-scale Feature Propagation Network (MFPNet), to
address the dilemma. Specifically, we design a robust Encoder-Decoder structure
featuring symmetrical residual blocks that consist of flexible bottleneck
residual modules (BRMs) to explore deep and rich muti-scale semantic context.
Furthermore, taking benefit from their capacity to model latent long-range
contextual relationships, we leverage Graph Convolutional Networks (GCNs) to
facilitate multi-scale feature propagation between the BRM blocks. When
evaluated on benchmark datasets, our proposed approach shows superior
segmentation results.
|
Waring's classical problem deals with expressing every natural number as a
sum of g(k) k-th powers. Recently there has been considerable interest in
similar questions for nonabelian groups, and simple groups in particular. Here
the k-th power word is replaced by an arbitrary nontrivial group word w, and
the goal is to express group elements as short products of values of w.
We give a best possible and somewhat surprising solution for this Waring type
problem for various finite simple groups, showing that a product of length two
suffices to express all elements. We also show that the set of values of w is
very large, improving various results obtained previously.
Along the way we also obtain new results of independent interest on character
values and class squares in symmetric groups.
Our methods involve algebraic geometry, representation theory, probabilistic
arguments, as well as three prime theorems from additive number theory
(approximating Goldbach's Conjecture).
|
A new fabrication process is developed for growing Bi2Se3 topological
insulators in the form of nanowires/nanobelts and ultra-thin films. It consists
of two consecutive procedures: first Bi2Se3 nanowires/nanobelts are deposited
by standard catalyst free vapour-solid deposition on different substrates
positioned inside a quartz tube. Then, the Bi2Se3, stuck on the inner surface
of the quartz tube, is re-evaporated and deposited in the form of ultra-thin
films on new substrates at temperature below 100 {\deg}C, which is of relevance
for flexible electronic applications. The method is new, quick, very
inexpensive, easy to control and allows obtaining films with different
thickness down to one quintuple layer (QL) during the same procedure. The
composition and the crystal structure of both the nanowires/nanobelts and the
thin films is analysed by different optical, electronic and structural
techniques. For the films, scanning tunnelling spectroscopy shows that the
Fermi level is positioned in the middle of the energy bandgap as a consequence
of the achieved correct stoichiometry. Ultra-thin films, with thickness in the
range 1-10 QLs deposited on n-doped Si substrates, show good rectified
properties suitable for their use as photodetectors in the ultra
violet-visible-near infrared wavelength range
|
Ti3SiC2 is a potential structural material for nuclear reactor applications.
However, He irradiation effects in this material are not well understood,
especially at high temperatures. Here, we compare the effects of He irradiation
in Ti3SiC2 at room temperature (RT) and at 750 {\deg}C. Irradiation at 750
{\deg}C was found to lead to extremely elongated He bubbles that are
concentrated in the nano-laminate layers of Ti3SiC2, whereas the overall
crystal structure of the material remained intact. In contrast, at RT, the
layered structure was significantly damaged and highly disordered after
irradiation. Our study reveals that at elevated temperatures, the unique
structure of Ti3SiC2 can accommodate large amounts of He atoms in the
nano-laminate layer, without compromising the structural stability of the
material. The structure and the mechanical tests results show that the
irradiation induced swelling and hardening at 750 {\deg}C are much smaller than
those at RT. These results indicate that Ti3SiC2 has an excellent resistance to
accumulation of radiation-induced He impurities and that it has a considerable
tolerance to irradiation-induced degradation of mechanical properties at high
temperatures.
|
An unified scheme for describing both spin and orbital motion in
symmetry-breaking chiral quark model is suggested. The analytic results of the
spin and orbital angular momenta carried by different quark flavors in the
nucleon are given. The quark spin reduction due to spin-flip in the chiral
splitting processes is compensated by the increase of the orbital angular
momentum carried by the quarks and antiquarks. The sum of both spin and orbital
angular momenta in the nucleon is 1/2, if the gluons and other degrees of
freedom are neglected. The same conclusion holds for other octet and decuplet
baryons. Possible modification and application are briefly discussed.
|
We present an analysis of the distribution of structural properties for Milky
Way-mass halos in the Millennium-II Simulation (MS-II). This simulation of
structure formation within the standard LCDM cosmology contains thousands of
Milky Way-mass halos and has sufficient resolution to properly resolve many
subhalos per host. It thus provides a major improvement in the statistical
power available to explore the distribution of internal structure for halos of
this mass. In addition, the MS-II contains lower resolution versions of the
Aquarius Project halos, allowing us to compare our results to simulations of
six halos at a much higher resolution. We study the distributions of mass
assembly histories, of subhalo mass functions and accretion times, and of
merger and stripping histories for subhalos capable of impacting disks at the
centers of halos. We show that subhalo abundances are not well-described by
Poisson statistics at low mass, but rather are dominated by intrinsic scatter.
Using the masses of subhalos at infall and the abundance-matching assumption,
there is less than a 10% chance that a Milky Way halo with M_vir =10^12 M_sun
will host two galaxies as bright as the Magellanic Clouds. This probability
rises to ~25% for a halo with M_vir=2.5 x 10^12 M_sun. The statistics relevant
for disk heating are very sensitive to the mass range that is considered
relevant. Mergers with infall mass : redshift zero virial mass greater than
1:30 could well impact a central galactic disk and are a near inevitability
since z=2, whereas only half of all halos have had a merger with infall mass :
redshift zero virial mass greater than 1:10 over this same period.
|
We consider spacelike graphs $\Gamma_f$ of simple products $(M\times N,
g\times -h)$ where $(M,g)$ and $(N,h)$ are Riemannian manifolds and $f:M\to N$
is a smooth map. Under the condition of the Cheeger constant of $M$ to be zero
and some condition on the second fundamental form at infinity, we conclude that
if $\Gamma_f \subset M\times N$ has parallel mean curvature $H$ then $H=0$.
This holds trivially if $M$ is closed. If $M$ is the $m$-hyperbolic space then
for any constant $c$, we describe a explicit foliation of $H^m\times R$ by
hypersurfaces with constant mean curvature $c$.
|
Flash flooding is a significant societal problem, but related precipitation
forecasts are often poor. To address this, one can try to use output from
convection-parametrising (global) ensembles, post-processed to forecast at
point-scale, or convection-resolving limited area ensembles. In this study, we
combine both. First, we apply the "ecPoint-rainfall" post-processing to the
ECMWF global ensemble. Then, we use 2.2km COSMO LAM ensemble output (centred on
Italy), and also post-process it using a scale-selective neighbourhood approach
to compensate for insufficient members. The two components then undergo
lead-time-weighted blending, to create the final probabilistic 6h rainfall
forecasts. Product creation for forecasters constituted the "Italy Flash Flood
use case" within the EU-funded MISTRAL project and it will be a real-time
open-access product.
One year of verification shows that ecPoint is the most skilful ensemble
product. The post-processed COSMO ensemble adds most value to summer convective
events in the evening, when the global model has an underprediction bias. In
two heavy rainfall case studies we observed underestimation of the largest
point totals in the raw ECMWF ensemble, and overestimation in the raw COSMO
ensemble. However, ecPoint increase the value and highlighted best the most
affected areas, whilst post-processing of COSMO diminished extremes by
eradicating unreliable detail. The final merged products looked best from a
user perspective and seemed to be the most skilful of all. Although our LAM
post-processing does not implicitly include bias correction (a topic for
further work) our study nonetheless provides a unique blueprint for
successfully combining ensemble rainfall forecasts from global and LAM systems
around the world. It also has important implications for forecast products as
global ensembles move ever closer to having convection-permitting resolution.
|
Kirby and Thompson introduced a length of a trisection. They also defined the
length of a 4-manifold as the minimum of length among all lengths of trisection
of a 4-manifold. In this paper, we consider trisections whose Kirby-Thompson
length is 2. Kirby and Thompson conjectured that length 2 trisection is a
trisection of 4-manifold with length 0. We shall prove this conjecture in this
paper.
|
Subsets and Splits