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arxiv_dataset-94001802.0046 | OSSOS: X. How to use a Survey Simulator: Statistical Testing of
Dynamical Models Against the Real Kuiper Belt
astro-ph.EP
All surveys include observational biases, which makes it impossible to
directly compare properties of discovered trans-Neptunian Objects (TNOs) with
dynamical models. However, by carefully keeping track of survey pointings on
the sky, detection limits, tracking fractions, and rate cuts, the biases from a
survey can be modelled in Survey Simulator software. A Survey Simulator takes
an intrinsic orbital model (from, for example, the output of a dynamical Kuiper
belt emplacement simulation) and applies the survey biases, so that the biased
simulated objects can be directly compared with real discoveries. This
methodology has been used with great success in the Outer Solar System Origins
Survey (OSSOS) and its predecessor surveys. In this chapter, we give four
examples of ways to use the OSSOS Survey Simulator to gain knowledge about the
true structure of the Kuiper Belt. We demonstrate how to statistically compare
different dynamical model outputs with real TNO discoveries, how to quantify
detection biases within a TNO population, how to measure intrinsic population
sizes, and how to use upper limits from non-detections. We hope this will
provide a framework for dynamical modellers to statistically test the validity
of their models.
| arxiv topic:astro-ph.EP |
arxiv_dataset-94011802.0056 | Interpretable Deep Convolutional Neural Networks via Meta-learning
cs.LG cs.AI stat.ML
Model interpretability is a requirement in many applications in which crucial
decisions are made by users relying on a model's outputs. The recent movement
for "algorithmic fairness" also stipulates explainability, and therefore
interpretability of learning models. And yet the most successful contemporary
Machine Learning approaches, the Deep Neural Networks, produce models that are
highly non-interpretable. We attempt to address this challenge by proposing a
technique called CNN-INTE to interpret deep Convolutional Neural Networks (CNN)
via meta-learning. In this work, we interpret a specific hidden layer of the
deep CNN model on the MNIST image dataset. We use a clustering algorithm in a
two-level structure to find the meta-level training data and Random Forest as
base learning algorithms to generate the meta-level test data. The
interpretation results are displayed visually via diagrams, which clearly
indicates how a specific test instance is classified. Our method achieves
global interpretation for all the test instances without sacrificing the
accuracy obtained by the original deep CNN model. This means our model is
faithful to the deep CNN model, which leads to reliable interpretations.
| arxiv topic:cs.LG cs.AI stat.ML |
arxiv_dataset-94021802.0066 | Investigation of modified ATLAS pixel implantations after irradiation
with neutrons
physics.ins-det
The innermost part of the tracking detector of the ATLAS experiment consists
mainly of planar n$^+$-in-n silicon pixel sensors. During the phase-0 upgrade,
the Insertable B-Layer (IBL) was installed closest to the beam pipe. Its pixels
are arranged with a pitch of $250\,\mu$m$\,\times\,50\,\mu$m with a rectangular
shaped n$^+$ implantation. Based on this design modified pixel designs have
been developed in Dortmund.
Six of these new pixel designs are arranged in structures of ten columns and
were placed beside structures with the standard design on one sensor. Because
of a special guard ring design, each structure can be powered and investigated
separately. Several of these sensors were bump bonded to FE-I4 read-out chips.
One of these modules was irradiated with reactor neutrons up to a fluence of $5
\times 10^{15} \, n_{\text{eq}}\text{cm}^{-2}$.
This contribution presents important sensor characteristics, charge
collection determined with radioactive sources and hit efficiency measurements,
performed in laboratory and test beam, of this irradiated device. It is shown
that the new modified designs perform similar or better than the IBL standard
design in terms of charge collection and tracking efficiency, at the cost of a
slightly increased leakage current.
| arxiv topic:physics.ins-det |
arxiv_dataset-94031802.0076 | Image Quality in High-resolution and High-cadence Solar Imaging
astro-ph.SR
Broad-band imaging and even imaging with a moderate bandpass (about 1 nm)
provides a "photon-rich" environment, where frame selection ("lucky imaging")
becomes a helpful tool in image restoration allowing us to perform a
cost-benefit analysis on how to design observing sequences for high-spatial
resolution imaging in combination with real-time correction provided by an
adaptive optics (AO) system. This study presents high-cadence (160 Hz) G-band
and blue continuum image sequences obtained with the High-resolution Fast
Imager (HiFI) at the 1.5-meter GREGOR solar telescope, where the speckle
masking technique is used to restore images with nearly diffraction-limited
resolution. HiFI employs two synchronized large-format and high-cadence sCMOS
detectors. The Median Filter Gradient Similarity (MFGS) image quality metric is
applied, among others, to AO-corrected image sequences of a pore and a small
sunspot observed on 2017 June 4 and 5. A small region-of-interest, which was
selected for fast imaging performance, covered these contrast-rich features and
their neighborhood, which were part of active region NOAA 12661. Modifications
of the MFGS algorithm uncover the field- and structure-dependency of this image
quality metric. However, MFGS still remains a good choice for determining image
quality without a priori knowledge, which is an important characteristic when
classifying the huge number of high-resolution images contained in data
archives. In addition, this investigation demonstrates that a fast cadence and
millisecond exposure times are still insufficient to reach the coherence time
of daytime seeing. Nonetheless, the analysis shows that data acquisition rates
exceeding 50 Hz are required to capture a substantial fraction of the best
seeing moments, significantly boosting the performance of post-facto image
restoration.
| arxiv topic:astro-ph.SR |
arxiv_dataset-94041802.0086 | The Black Hole Accretion Code: adaptive mesh refinement and constrained
transport
gr-qc
With the forthcoming VLBI images of Sgr A* and M87, simulations of accretion
flows onto black holes acquire a special importance to aid with the
interpretation of the observations and to test the predictions of different
accretion scenarios, including those coming from alternative theories of
gravity. The Black Hole Accretion Code (BHAC) is a new multidimensional
general-relativistic magnetohydrondynamics (GRMHD) module for the MPI-AMRVAC
framework. It exploits its adaptive mesh refinement techniques (AMR) to solve
the equations of ideal magnetohydrodynamics in arbitrary curved spacetimes with
a significant speedup and saving in computational cost. In a previous work,
this was shown using a Generalized Lagrange Multiplier (GLM) to enforce the
solenoidal constraint of the magnetic field. While GLM is fully compatible with
MPI-AMRVAC's AMR infrastructure, we found that simulations were sensible to the
divergence control technique employed, resulting in an improved behavior for
those using Constrained Transport (CT). However, cell-centered CT is
incompatible with AMR, and several modifications were required to make AMR
compatible with staggered CT. We present here preliminary results of these new
additions, which achieved machine precision fulfillment of the solenoidal
constraint and a significant speedup in a problem close to the intended
scientific application.
| arxiv topic:gr-qc |
arxiv_dataset-94051802.0096 | Injective Hulls In a Locally Finite Topos
math.CT
We show that in a locally finite topos, every object has an essential
extension that is injective, and that this extension is unique up to
isomorphism.
The construction was motivated by work on Bewl, a software project for doing
topos-theoretic calculations.
| arxiv topic:math.CT |
arxiv_dataset-94061802.0106 | Magnetotransport in Layered Dirac Fermion System Coupled with Magnetic
Moments
cond-mat.str-el
We theoretically investigate the magnetotransport of Dirac fermions coupled
with localized moments to understand the physical properties of the Dirac
material EuMnBi$_2$. Using an interlayer hopping form, which simplifies the
complicated interaction between the layers of Dirac fermions and the layers of
magnetic moments in EuMnBi$_2$, the theory reproduces most of the features
observed in this system. The hysteresis observed in EuMnBi$_2$ can be caused by
the valley splitting that is induced by the spin-orbit coupling and the
external magnetic field with the molecular field created by localized moments.
Our theory suggests that the magnetotransport in EuMnBi$_2$ is due to the
interplay among Dirac fermions, localized moments, and spin-orbit coupling.
| arxiv topic:cond-mat.str-el |
arxiv_dataset-94071802.0116 | Characterizing the astrophysical S-factor for $^{12}$C+$^{12}$C with
wave-packet dynamics
nucl-th
A quantitative study of the astrophysically important sub-barrier fusion of
$^{12}$C+$^{12}$C is presented. Low-energy collisions are described in the
body-fixed reference frame using wave-packet dynamics within a nuclear
molecular picture. A collective Hamiltonian drives the time propagation of the
wave-packet through the collective potential-energy landscape. The fusion
imaginary potential for specific dinuclear configurations is crucial for
understanding the appearance of resonances in the fusion cross section. The
theoretical sub-barrier fusion cross sections explain some observed resonant
structures in the astrophysical S-factor. These cross sections monotonically
decline towards stellar energies. The structures in the data that are not
explained are possibly due to cluster effects in the nuclear molecule, which
are to be included in the present approach.
| arxiv topic:nucl-th |
arxiv_dataset-94081802.0126 | q-Analogues of two "divergent" Ramanujan-type supercongruences
math.NT math.CO
Guillera and Zudilin proved three "divergent" Ramanujan-type supercongruences
by means of the Wilf-Zeilberger algorithmic technique. In this paper, we prove
$q$-analogues of two of them via the $q$-WZ method. Additionally, we give
$q$-analogues of two related congruence of Sun, one is confirmed and the other
is conjectural.
| arxiv topic:math.NT math.CO |
arxiv_dataset-94091802.0136 | ORLA/OLAA: Orthogonal Coexistence of LAA and WiFi in Unlicensed Spectrum
cs.NI
Future mobile networks will exploit unlicensed spectrum to boost capacity and
meet growing user demands cost-effectively. The 3GPP has recently defined a
Licensed-Assisted Access (LAA) scheme to enable global Unlicensed LTE (U-LTE)
deployment, aiming at ($i$) ensuring fair coexistence with incumbent WiFi
networks, i.e., impacting on their performance no more than another WiFi
device, and ($ii$) achieving superior airtime efficiency as compared to WiFi.
In this paper we show the standardized LAA fails to simultaneously fulfill
these objectives, and design an alternative orthogonal (collision-free)
listen-before-talk coexistence paradigm that provides a substantial improvement
in performance, yet imposes no penalty on existing WiFi networks. We derive two
LAA optimal transmission policies, ORLA and OLAA, that maximize LAA throughput
in both asynchronous and synchronous (i.e., with alignment to licensed anchor
frame boundaries) modes of operation, respectively. We present a comprehensive
performance evaluation through which we demonstrate that, when aggregating
packets, IEEE 802.11ac WiFi can be more efficient than 3GPP LAA, whereas our
proposals can attain 100% higher throughput, without harming WiFi. We further
show that long U-LTE frames incur up to 92% throughput losses on WiFi when
using 3GPP LAA, whilst ORLA/OLAA sustain $>$200% gains at no cost, even in the
presence of non-saturated WiFi and/or in multi-rate scenarios.
| arxiv topic:cs.NI |
arxiv_dataset-94101802.0146 | Diamagnetism of 2D-Fermions in the Strong Nonhomogeneous Static Magnetic
Field $( {\bf B} =B( 0, 0, 1/cosh^{2}( \frac{x-x_{0} }{ \delta })))$ : gas
magnetization, ... and gas compressibility
cond-mat.mes-hall quant-ph
We study diamagnetism of a gas of fermions moving in a nonhomogeneous
magnetic field $( {\bf B} =B( 0, 0, 1/cosh^{2}( \frac{x-x_{0} }{ \delta })))$
The gas magnetization, the static magnetic susceptibility, the chemical
potential and the gas compressibility are discussed and compared with the
uniform field case. General need to study dynamics of electrons in different
types of magnetic fields follows from a large number of experimental situations
in which its understanding enables physicists to obtain new information.
| arxiv topic:cond-mat.mes-hall quant-ph |
arxiv_dataset-94111802.0156 | Fractional De Giorgi classes and applications to nonlocal regularity
theory
math.AP
We present some recent results obtained by the author on the regularity of
solutions to nonlocal variational problems. In particular, we review the notion
of fractional De Giorgi class, explain its role in nonlocal regularity theory,
and propose some open questions in the subject.
| arxiv topic:math.AP |
arxiv_dataset-94121802.0166 | Significant efficiency enhancement in thin film solar cells using laser
beam-induced graphene transparent conductive electrodes
physics.app-ph physics.optics
Thin film solar cells have been attractive for decades in advanced green
technology platforms due to its possibilities to be integrated with buildings
and on-chip applications. However, the bottleneck issues involved to consider
the current solar cells as a major electricity source includes the lower
efficiencies and cost-effectiveness. We numerically demonstrate the concept of
the absorption enhancement in thin-film amorphous silicon solar cells using the
laser beam-induced graphene material based on the insensitive polarization
space-filling fractal design as transparent conductive electrodes. With the
optimization of parameters such as thickness, width, and period of fractals, an
enhancement of photocurrent generation of solar cells by a factor of 24.5% is
achieved compared to reference solar cell with a traditional ITO.
| arxiv topic:physics.app-ph physics.optics |
arxiv_dataset-94131802.0176 | Motion and collision of particles in rotating linear dilaton black hole
gr-qc hep-th
We study the motion of particles in the background of a four-dimensional
linear dilaton black hole. We solve analytically the equations of motion of the
test particles and we describe their motion. We show that the dilaton black
hole acts as a particle accelerator by analyzing the energy in the center of
mass (CM) frame of two colliding particles in the vicinity of its horizon. In
particular we find that there is a critical value of the angular momentum,
which depends on the string coupling, and a particle with this critical angular
momentum can reach the inner horizon with an arbitrarily high CM energy. This
is known as the Ba\~nados, Silk and West (BSW) process. We also show that the
motion and collisions of particles have a similar behavior to the
three-dimensional BTZ black hole. In fact, the photons can plunge into the
horizon or escape to infinity, and they can not be deflected, while for massive
particles there are no confined orbits of first kind, like planetary or
circular orbits.
| arxiv topic:gr-qc hep-th |
arxiv_dataset-94141802.0186 | Effect of differential cross section in Breit-Wheeler pair beaming
physics.plasm-ph astro-ph.HE
The pair beaming in the Breit-Wheeler (BW) process is investigated. We
examine the effect of the BW differential cross section on pair angular and
energy distributions. Although, this study is relevant for laser induced
intense gamma-ray source collisions experiments, we apply the pair beaming in
astrophysical context, in particular for Active Galactic Nuclei (AGN).
| arxiv topic:physics.plasm-ph astro-ph.HE |
arxiv_dataset-94151802.0196 | The performances of R GPU implementations of the GMRES method
cs.DC
Although the performance of commodity computers has improved drastically with
the introduction of multicore processors and GPU computing, the standard R
distribution is still based on single-threaded model of computation, using only
a small fraction of the computational power available now for most desktops and
laptops. Modern statistical software packages rely on high performance
implementations of the linear algebra routines there are at the core of several
important leading edge statistical methods. In this paper we present a GPU
implementation of the GMRES iterative method for solving linear systems. We
compare the performance of this implementation with a pure single threaded
version of the CPU. We also investigate the performance of our implementation
using different GPU packages available now for R such as gmatrix, gputools or
gpuR which are based on CUDA or OpenCL frameworks.
| arxiv topic:cs.DC |
arxiv_dataset-94161802.0206 | A study of two dwarf irregular galaxies with asymmetrical star formation
distributions
astro-ph.GA
Two dwarf irregular galaxies DDO 187 and NGC 3738 exhibit a striking pattern
of star formation: intense star formation is taking place in a large region
occupying roughly half of the inner part of the optical galaxy. We use data on
the HI distribution and kinematics and stellar images and colors to examine the
properties of the environment in the high star formation rate (HSF) halves of
the galaxies in comparison with the low star formation rate (LSF) halves. We
find that the pressure and gas density are higher on the HSF sides by 30-70%.
In addition we find in both galaxies that the HI velocity fields exhibit
significant deviations from ordered rotation and there are large regions of
high velocity dispersion and multiple velocity components in the gas beyond the
inner regions of the galaxies. The conditions in the HSF regions are likely the
result of large-scale external processes affecting the internal environment of
the galaxies and enabling the current star formation there.
| arxiv topic:astro-ph.GA |
arxiv_dataset-94171802.0216 | Quantum Spectral Curve of $\gamma$-twisted ${\cal N}=4$ SYM theory and
fishnet CFT
hep-th
We review the quantum spectral curve (QSC) formalism for anomalous dimensions
of planar ${\cal\ N}=4$ SYM, including its $\gamma$-deformation. Leaving aside
its derivation, we concentrate on formulation of the "final product" in its
most general form: a minimal set of assumptions about the algebraic structure
and the analyticity of the $Q$-system -- the full system of Baxter
$Q$-functions of the underlying integrable model. The algebraic structure of
the $Q$-system is entirely based on (super)symmetry of the model and is
efficiently described by Wronskian formulas for $Q$-functions organized into
the Hasse diagram. When supplemented with analyticity conditions on
$Q$-functions, it fixes completely the set of physical solutions for spectrum
of an integrable model. First we demonstrate the spectral equations on the
example of $gl(N)$ and $gl(K|M)$ Heisenberg (super)spin chains. Supersymmetry
$gl(K|M)$ occurs as a "rotation" of the Hasse diagram for a $gl(K+M)$ system.
This picture helps us to construct the QSC formalism for spectrum of
AdS$_5$/CFT$_4$-duality, with more complicated analyticity constraints on
$Q$-functions which involve an infinitely branching Riemann surface and a set
of Riemann-Hilbert conditions. As an example of application of QSC, we consider
a special double scaling limit of $\gamma$-twisted ${\cal\ N}=4$ SYM, combining
weak coupling and strong imaginary twist. This leads to a new type of
non-unitary CFT dominated by particular integrable, and often computable, 4D
fishnet Feynman graphs. For the simplest of such models -- the bi-scalar theory
-- the QSC degenerates into the $Q$-system for integrable non-compact
Heisenberg spin chain with conformal, $SU(2,2)$ symmetry. We apply the QSC for
derivation of Baxter equation and the quantization condition for particular,
"wheel" fishnet graphs, and review numerical and analytic results for them.
| arxiv topic:hep-th |
arxiv_dataset-94181802.0226 | Second order backward SDE with random terminal time
math.PR math.OC
Backward stochastic differential equations extend the martingale
representation theorem to the nonlinear setting. This can be seen as
path-dependent counterpart of the extension from the heat equation to fully
nonlinear parabolic equations in the Markov setting. This paper extends such a
nonlinear representation to the context where the random variable of interest
is measurable with respect to the information at a finite stopping time. We
provide a complete wellposedness theory which covers the semilinear case
(backward SDE), the semilinear case with obstacle (reflected backward SDE), and
the fully nonlinear case (second order backward SDE).
| arxiv topic:math.PR math.OC |
arxiv_dataset-94191802.0236 | Cyber-Physical Architecture Assisted by Programmable Networking
cs.CR cs.SY
Cyber-physical technologies are prone to attacks, in addition to faults and
failures. The issue of protecting cyber-physical systems should be tackled by
jointly addressing security at both cyber and physical domains, in order to
promptly detect and mitigate cyber-physical threats. Towards this end, this
letter proposes a new architecture combining control-theoretic solutions
together with programmable networking techniques to jointly handle crucial
threats to cyber-physical systems. The architecture paves the way for new
interesting techniques, research directions, and challenges which we discuss in
our work.
| arxiv topic:cs.CR cs.SY |
arxiv_dataset-94201802.0246 | Upscaling Singular Sources in Weighted Sobolev Spaces by Sub-Grid
Corrections
math.NA
In this paper, we develop a numerical multiscale method to solve elliptic
boundary value problems with heterogeneous diffusion coefficients and with
singular source terms. When the diffusion coefficient is heterogeneous, this
adds to the computational costs, and this difficulty is compounded by a
singular source term. For singular source terms, the solution does not belong
to the Sobolev space $H^1$, but to the space $W^{1,p}$ for some $p<2$. Hence,
the problem may be reformulated in a distance-weighted Sobolev space. Using
this formulation, we develop a method to upscale the multiscale coefficient
near the singular sources by incorporating corrections into the coarse-grid.
Using a sub-grid correction method, we correct the basis functions in a
distance-weighted Sobolev space and show that these corrections can be
truncated to design a computationally efficient scheme with optimal convergence
rates. Due to the nature of the formulation in weighted spaces, the variational
form must be posed on the cross product of complementary spaces. Thus, two such
sub-grid corrections must be computed, one for each multiscale space of the
cross product. A key ingredient of this method is the use of
quasi-interpolation operators to construct the fine scale spaces. Therefore, we
develop a weighted projective quasi-interpolation that can be used for a
general class of Muckenhoupt weight functions. We verify the optimal
convergence of the method in some numerical examples with singular point
sources and line fractures, and with oscillatory and heterogeneous diffusion
coefficients.
| arxiv topic:math.NA |
arxiv_dataset-94211802.0256 | Cubic Preferences and the Character Admissibility Problem
math.CO
In multiple-question referendum elections, the separability problem occurs
when a voter's preferences on some questions or proposals depend on the
predicted outcomes of others. The notion of separability formalizes the study
of interdependence in multidimensional preferences, and the character
admissibility problem deals with the construction of voter preferences with
given separability structures. In this paper, we develop a graph theoretic
approach to the character admissibilty problem, using Hamiltonian paths to
generate voter preferences. We apply this method specifically to the hypercube
graph, defining the class of cubic preferences. We then explore how the
algebraic structure of the group of symmetries of the hypercube impacts the
separability structures exhibited by cubic preferences. We prove that the
characters of cubic preferences satisfy set theoretic properties distinct from
those produced by previous methods, and we define two functions to construct
cubic preferences. Our results have potential applications to experimental work
involving election simulation.
| arxiv topic:math.CO |
arxiv_dataset-94221802.0266 | Deletable edges in 3-connected graphs and their applications
math.CO
Let $G$ and $H$ be simple 3-connected graphs such that $G$ has an $H$-minor.
An edge $e$ in $G$ is called {\it $H$-deletable} if $G\backslash e$ is
3-connected and has an $H$-minor. The main result in this paper establishes
that, if $G$ has no $H$-deletable edges, then there exists a sequence of simple
3-connected graphs $G_0, \dots , G_k$ with no $H$-deletable edges such that
$G_0\cong H$, $G_k= G$, and for $1 \le i \le k$ one of three possibilities
holds: $G_{i-1}= G_i/f$; $G_{i-1}=G_i/f \backslash e$ where $e$ and $f$ are
incident to a degree 3 vertex in $G_i$; or $G_{i-1}=G_i-w$ where $w$ is a
degree $3$ vertex in $G_i$. Several applications are given including a graph
theoretic proof of the matroid theory result known as the Strong Splitter
Theorem, a short new proof of Dirac's characterization of 3-connected graphs
with no minor isomorphic to the prism graph, and an extension of a result by
Halin that bounds the number of edges in a minimally 3-connected graph. Halin
proved that if $G$ is a minimally $3$-connected graph on $n\ge 8$ vertices,
then $|E(G)|\le 3n-9$ and equality holds if and only if $G\cong K_{3, n-3}$. We
give a different proof of Halin's result and extend it by identifying the
minimally 3-connected infinite family of graphs with $|E(G)|=3n-10$.
| arxiv topic:math.CO |
arxiv_dataset-94231802.0276 | Tuning Streamed Applications on Intel Xeon Phi: A Machine Learning Based
Approach
cs.PF
Many-core accelerators, as represented by the XeonPhi coprocessors and
GPGPUs, allow software to exploit spatial and temporal sharing of computing
resources to improve the overall system performance. To unlock this performance
potential requires software to effectively partition the hardware resource to
maximize the overlap between hostdevice communication and accelerator
computation, and to match the granularity of task parallelism to the resource
partition. However, determining the right resource partition and task
parallelism on a per program, per dataset basis is challenging. This is because
the number of possible solutions is huge, and the benefit of choosing the right
solution may be large, but mistakes can seriously hurt the performance. In this
paper, we present an automatic approach to determine the hardware resource
partition and the task granularity for any given application, targeting the
Intel XeonPhi architecture. Instead of hand-crafting the heuristic for which
the process will have to repeat for each hardware generation, we employ machine
learning techniques to automatically learn it. We achieve this by first
learning a predictive model offline using training programs; we then use the
learned model to predict the resource partition and task granularity for any
unseen programs at runtime. We apply our approach to 23 representative parallel
applications and evaluate it on a CPU-XeonPhi mixed heterogenous many-core
platform. Our approach achieves, on average, a 1.6x (upto 5.6x) speedup, which
translates to 94.5% of the performance delivered by a theoretically perfect
predictor.
| arxiv topic:cs.PF |
arxiv_dataset-94241802.0286 | Mean field model of a game for power
physics.soc-ph
Our aim is to model a game for power as a dynamical process, where an excess
of power possessed by a player allows him to gain even more power. Such a
positive feedback is often termed as the Matthew effect. Analytical and
numerical methods allow to identify a set of fixed points of the model
dynamics. The positions of the unstable fixed points give an insight on the
basins of attraction of the stable fixed points. The results are interpreted in
terms of modeling of coercive power.
| arxiv topic:physics.soc-ph |
arxiv_dataset-94251802.0296 | Singular values of large non-central random matrices
math.PR
We study largest singular values of large random matrices, each with mean of
a fixed rank $K$. Our main result is a limit theorem as the number of rows and
columns approach infinity, while their ratio approaches a positive constant. It
provides a decomposition of the largest $K$ singular values into the
deterministic rate of growth, random centered fluctuations given as explicit
linear combinations of the entries of the matrix, and a term negligible in
probability. We use this representation to establish asymptotic normality of
the largest singular values for random matrices with means that have block
structure. We also deduce asymptotic normality for the largest eigenvalues of
the normalized covariance matrix arising in a model of population genetics.
| arxiv topic:math.PR |
arxiv_dataset-94261802.0306 | Simulations of Galactic polarized synchrotron emission for Epoch of
Reionization observations
astro-ph.CO
The detection of the redshifted cosmological $21$~cm line signal requires the
removal of the Galactic and extragalactic foreground emission, which is orders
of magnitude brighter anywhere in the sky. Foreground cleaning methods
currently used are efficient in removing spectrally smooth components. However,
they struggle in the presence of not spectrally smooth contamination that is,
therefore, potentially the most dangerous one. An example of this is the
polarized synchrotron emission, which is Faraday rotated by the interstellar
medium and leaks into total intensity due to instrumental imperfections. In
this work we present new full-sky simulations of this polarized synchrotron
emission in the $50-200$~MHz range, obtained from the observed properties of
diffuse polarized emission at low frequencies. The simulated polarized maps are
made publicly available, aiming to provide more realistic templates to simulate
the effect of instrumental leakage and the effectiveness of foreground
separation techniques.
| arxiv topic:astro-ph.CO |
arxiv_dataset-94271802.0316 | Distributed Spanner Approximation
cs.DS cs.DC
We address the fundamental network design problem of constructing approximate
minimum spanners. Our contributions are for the distributed setting, providing
both algorithmic and hardness results.
Our main hardness result shows that an $\alpha$-approximation for the minimum
directed $k$-spanner problem for $k \geq 5$ requires $\Omega(n
/\sqrt{\alpha}\log{n})$ rounds using deterministic algorithms or
$\Omega(\sqrt{n }/\sqrt{\alpha}\log{n})$ rounds using randomized ones, in the
CONGEST model of distributed computing. Combined with the constant-round
$O(n^{\epsilon})$-approximation algorithm in the LOCAL model of [Barenboim,
Elkin and Gavoille, 2016], as well as a polylog-round
$(1+\epsilon)$-approximation algorithm in the LOCAL model that we show here,
our lower bounds for the CONGEST model imply a strict separation between the
LOCAL and CONGEST models. Notably, to the best of our knowledge, this is the
first separation between these models for a local approximation problem.
Similarly, a separation between the directed and undirected cases is implied.
We also prove a nearly-linear lower bound for the minimum weighted $k$-spanner
problem for $k \geq 4$, and we show lower bounds for the weighted 2-spanner
problem.
On the algorithmic side, apart from the aforementioned
$(1+\epsilon)$-approximation algorithm for minimum $k$-spanners, our main
contribution is a new distributed construction of minimum 2-spanners that uses
only polynomial local computations. Our algorithm has a guaranteed
approximation ratio of $O(\log(m/n))$ for a graph with $n$ vertices and $m$
edges, which matches the best known ratio for polynomial time sequential
algorithms [Kortsarz and Peleg, 1994], and is tight if we restrict ourselves to
polynomial local computations. Our approach allows us to extend our algorithm
to work also for the directed, weighted, and client-server variants of the
problem.
| arxiv topic:cs.DS cs.DC |
arxiv_dataset-94281802.0326 | The MUCHFUSS photometric campaign
astro-ph.SR
Hot subdwarfs (sdO/Bs) are the helium-burning cores of red giants, which lost
almost all of their hydrogen envelopes. This mass loss is often triggered by
common envelope interactions with close stellar or even substellar companions.
Cool companions like late-type stars or brown dwarfs are detectable via
characteristic light curve variations like reflection effects and often also
eclipses. To search for such objects we obtained multi-band light curves of 26
close sdO/B binary candidates from the MUCHFUSS project with the BUSCA
instrument. We discovered a new eclipsing reflection effect system
($P=0.168938$~d) with a low-mass M dwarf companion ($0.116 M_{\rm \odot}$).
Three more reflection effect binaries found in the course of the campaign were
already published, two of them are eclipsing systems, in one system only
showing the reflection effect but no eclipses the sdB primary is found to be
pulsating. Amongst the targets without reflection effect a new long-period sdB
pulsator was discovered and irregular light variations were found in two sdO
stars. The found light variations allowed us to constrain the fraction of
reflection effect binaries and the substellar companion fraction around sdB
stars. The minimum fraction of reflection effect systems amongst the close sdB
binaries might be greater than 15\% and the fraction of close substellar
companions in sdB binaries might be as high as $8.0\%$. This would result in a
close substellar companion fraction to sdB stars of about 3\%. This fraction is
much higher than the fraction of brown dwarfs around possible progenitor
systems, which are solar-type stars with substellar companions around 1 AU, as
well as close binary white dwarfs with brown dwarf companions. This might be a
hint that common envelope interactions with substellar objects are
preferentially followed by a hot subdwarf phase.
| arxiv topic:astro-ph.SR |
arxiv_dataset-94291802.0336 | Information Planning for Text Data
stat.ML cs.LG
Information planning enables faster learning with fewer training examples. It
is particularly applicable when training examples are costly to obtain. This
work examines the advantages of information planning for text data by focusing
on three supervised models: Naive Bayes, supervised LDA and deep neural
networks. We show that planning based on entropy and mutual information
outperforms random selection baseline and therefore accelerates learning.
| arxiv topic:stat.ML cs.LG |
arxiv_dataset-94301802.0346 | Electrochemical and mechanical behaviors of dissimilar friction stir
welding between 5086 and 6061 aluminum alloy
cond-mat.mtrl-sci physics.chem-ph
The electrochemical behavior and mechanical properties of friction stir
welded AA5086 and AA6061 Al alloys were investigated. Micro-hardness
measurements and tensile tests showed that the heat-affected zone (HAZ) in
AA6061 had minimum hardness value (i.e., 88 HV) and served as failure site in
the dissimilar weld. Corrosion testing revealed that the minimum value of Icorr
appeared in the HAZ 5086 (0.54 uA/cm2) and HAZ 5086 was most resistant to
corrosion. The AA 5086 side of the weld showed better corrosion resistance than
the AA 6061 side.
| arxiv topic:cond-mat.mtrl-sci physics.chem-ph |
arxiv_dataset-94311802.0356 | The Importance of Norm Regularization in Linear Graph Embedding:
Theoretical Analysis and Empirical Demonstration
cs.LG
Learning distributed representations for nodes in graphs is a crucial
primitive in network analysis with a wide spectrum of applications. Linear
graph embedding methods learn such representations by optimizing the likelihood
of both positive and negative edges while constraining the dimension of the
embedding vectors. We argue that the generalization performance of these
methods is not due to the dimensionality constraint as commonly believed, but
rather the small norm of embedding vectors. Both theoretical and empirical
evidence are provided to support this argument: (a) we prove that the
generalization error of these methods can be bounded by limiting the norm of
vectors, regardless of the embedding dimension; (b) we show that the
generalization performance of linear graph embedding methods is correlated with
the norm of embedding vectors, which is small due to the early stopping of SGD
and the vanishing gradients. We performed extensive experiments to validate our
analysis and showcased the importance of proper norm regularization in
practice.
| arxiv topic:cs.LG |
arxiv_dataset-94321802.0366 | Tuning emission energy and fine structure splitting in quantum dots
emitting in the telecom O-band
cond-mat.mes-hall quant-ph
We report on optical investigations of MOVPE-grown InGaAs/GaAs quantum dots
emitting at the telecom O-band that were integrated onto uniaxial piezoelectric
actuators. This promising technique, which does not degrade the optical quality
or performances of the quantum emitters, enables us to tune the quantum dot
emission wavelengths and their fine-structure splitting. By spectrally
analyzing the emitted light with respect to its polarization, we are able to
demonstrate the cancelation of the fine structure splitting within the
experimental resolution limit. This work represents an important step towards
the high-yield generation of entangled photon pairs at telecommunication
wavelength, together with the capability to precisely tune the emission to
target wavelengths.
| arxiv topic:cond-mat.mes-hall quant-ph |
arxiv_dataset-94331802.0376 | Distributed Evaluation of Subgraph Queries Using Worstcase Optimal
LowMemory Dataflows
cs.DC cs.DB
We study the problem of finding and monitoring fixed-size subgraphs in a
continually changing large-scale graph. We present the first approach that (i)
performs worst-case optimal computation and communication, (ii) maintains a
total memory footprint linear in the number of input edges, and (iii) scales
down per-worker computation, communication, and memory requirements linearly as
the number of workers increases, even on adversarially skewed inputs.
Our approach is based on worst-case optimal join algorithms, recast as a
data-parallel dataflow computation. We describe the general algorithm and
modifications that make it robust to skewed data, prove theoretical bounds on
its resource requirements in the massively parallel computing model, and
implement and evaluate it on graphs containing as many as 64 billion edges. The
underlying algorithm and ideas generalize from finding and monitoring subgraphs
to the more general problem of computing and maintaining relational equi-joins
over dynamic relations.
| arxiv topic:cs.DC cs.DB |
arxiv_dataset-94341802.0386 | Discovery of switchable weak topological insulator state in
quasi-one-dimensional bismuth iodide
cond-mat.mtrl-sci
The major breakthroughs in the understanding of topological materials over
the past decade were all triggered by the discovery of the Z$_2$ topological
insulator (TI). In three dimensions (3D), the TI is classified as either
"strong" or "weak", and experimental confirmations of the strong topological
insulator (STI) rapidly followed the theoretical predictions. In contrast, the
weak topological insulator has so far eluded experimental verification, since
the topological surface states emerge only on particular side surfaces which
are typically undetectable in real 3D crystals. Here we provide experimental
evidence for the WTI state in a bismuth iodide, $\beta$-Bi4I4. Significantly,
the crystal has naturally cleavable top and side planes both stacked via
van-der-Waals forces, which have long been desirable for the experimental
realization of the WTI state. As a definitive signature of it, we find quasi-1D
Dirac TSS at the side-surface (100) while the top-surface (001) is
topologically dark. Furthermore, a crystal transition from the $\beta$- to
$\alpha$-phase drives a topological phase transition from a nontrivial WTI to
the trivial insulator around room temperature. This topological phase, viewed
as quantum spin Hall (QSH) insulators stacked three-dimensionally, and
excellent functionality with on/off switching will lay a foundation for new
technology benefiting from highly directional spin-currents with large density
protected against backscattering.
| arxiv topic:cond-mat.mtrl-sci |
arxiv_dataset-94351802.0396 | Large deviations for the maximum of a branching random walk
math.PR
We consider real-valued branching random walks and prove a large deviation
result for the position of the rightmost particle. The position of the
rightmost particle is the maximum of a collection of a random number of
dependent random walks. We characterise the rate function as the solution of a
variational problem. We consider the same random number of independent random
walks, and show that the maximum of the branching random walk is dominated by
the maximum of the independent random walks. For the maximum of independent
random walks, we derive a large deviation principle as well. It turns out that
the rate functions for upper large deviations coincide, but in general the rate
functions for lower large deviations do not.
| arxiv topic:math.PR |
arxiv_dataset-94361802.0406 | Notable Characteristics Search through Knowledge Graphs
cs.DB
Query answering routinely employs knowledge graphs to assist the user in the
search process. Given a knowledge graph that represents entities and
relationships among them, one aims at complementing the search with intuitive
but effective mechanisms. In particular, we focus on the comparison of two or
more entities and the detection of unexpected, surprising properties, called
notable characteristics. Such characteristics provide intuitive explanations of
the peculiarities of the selected entities with respect to similar entities. We
propose a solid probabilistic approach that first retrieves entity nodes
similar to the query nodes provided by the user, and then exploits
distributional properties to understand whether a certain attribute is
interesting or not. Our preliminary experiments demonstrate the solidity of our
approach and show that we are able to discover notable characteristics that are
indeed interesting and relevant for the user.
| arxiv topic:cs.DB |
arxiv_dataset-94371802.0416 | Inflationary predictions of double-well, Coleman-Weinberg, and hilltop
potentials with non-minimal coupling
astro-ph.CO hep-ph
We discuss how the non-minimal coupling $\xi\phi^2R$ between the inflaton and
the Ricci scalar affects the predictions of single field inflation models where
the inflaton has a non-zero vacuum expectation value (VEV) $v$ after inflation.
We show that, for inflaton values both above the VEV and below the VEV during
inflation, under certain conditions the inflationary predictions become
approximately the same as the predictions of the Starobinsky model. We then
analyze inflation with double-well and Coleman-Weinberg potentials in detail,
displaying the regions in the $v$-$\xi$ plane for which the spectral index
$n_s$ and the tensor-to-scalar ratio $r$ values are compatible with the current
observations. $r$ is always larger than 0.002 in these regions. Finally, we
consider the effect of $\xi$ on small field inflation (hilltop) potentials.
| arxiv topic:astro-ph.CO hep-ph |
arxiv_dataset-94381802.0426 | Potentialities of the future technical improvements in the search of
rare nuclear decays by bolometers
physics.ins-det nucl-ex
Bolometers are cryogenic calorimeters which feature excellent energy
resolution, low energy threshold, high detection efficiency, flexibility in
choice of materials, particle identification capability if operated as hybrid
devices. After thirty years of rapid progresses, they represent nowadays a
leading technology in several fields: particle and nuclear physics, X-ray
astrophysics, cosmology. However, further and substantial developments are
required to increase the sensitivity to the levels envisioned by future
researches. A review of the challenges to be addressed and potentialities of
bolometers in the search for rare nuclear decays is given, with particular
emphasis to the neutrinoless double beta decay physics case.
| arxiv topic:physics.ins-det nucl-ex |
arxiv_dataset-94391802.0436 | The consequences of a nearby supernova on the early Solar System
astro-ph.SR astro-ph.EP
If the Sun was born in a relatively compact open cluster, it is quite likely
that a massive (10MSun) star was nearby when it exploded in a supernova. The
repercussions of a supernova can be rather profound, and the current Solar
System may still bear the memory of this traumatic event. The truncation of the
Kuiper belt and the tilt of the ecliptic plane with respect to the Sun's
rotation axis could be such signatures. We simulated the effect of a nearby
supernova on the young Solar System using the Astronomical Multipurpose
Software Environment. Our calculations are realized in two subsequent steps in
which we study the effect of the supernova irradiation on the circumstellar
disk and the effect of the impact of the nuclear blast-wave which arrives a few
decades later. We find that the blastwave of our adopted supernova exploding at
a distance of $0.15$--$0.40$\,pc and at an angle of $35^\circ$--$65^\circ$ with
respect to the angular-momentum axis of the circumsolar disk would induce a
misalignment between the Sun's equator and its disk to $5^\circ.6\pm1^\circ.2$,
consistent with the current value. The blast of a supernova truncates the disk
at a radius between $42$ and $55$\,au, which is consistent with the current
edge of the Kuiper belt. For the most favored parameters, the irradiation by
the supernova as well as the blast wave heat the majority of the disk to $\sim
1200$\,K, which is sufficiently hot to melt chondrules in the circumstellar
disk. The majority of planetary system may have been affected by a nearby
supernova, some of its repercussions, such as truncation and tilting of the
disk, may still be visible in their current planetary system's topology. The
amount of material from the supernova blast wave that is accreted by the
circumstellar disk is too small by several orders of magnitude to explain the
current abundance of the short live radionuclide $^{26}$Al.
| arxiv topic:astro-ph.SR astro-ph.EP |
arxiv_dataset-94401802.0446 | Parameterized Bilinear Matrix Inequality Techniques in ${\cal
H}_{\infty}$ Fuzzy PID Control Design
cs.SY
Proportional-integral-derivative (PID) structured controller is the most
popular class of industrial control but still could not be appropriately
exploited in fuzzy systems. To gain the practicability and tractability of
fuzzy systems, this paper develops a parameterized bilinear matrix inequality
characterization for the ${\cal H}_{\infty}$ fuzzy PID control design, which is
then relaxed into a bilinear matrix inequality optimization problem of
nonconvex optimization. Several computational procedures are then developed for
its solution. The merit of the developed algorithms is shown through the
benchmark examples.
| arxiv topic:cs.SY |
arxiv_dataset-94411802.0456 | Massive, wide binaries as tracers of massive star formation
astro-ph.GA astro-ph.SR
Massive stars can be found in wide (hundreds to thousands AU) binaries with
other massive stars. We use $N$-body simulations to show that any bound cluster
should always have approximately one massive wide binary: one will probably
form if none are present initially; and probably only one will survive if more
than one are present initially. Therefore any region that contains many massive
wide binaries must have been composed of many individual subregions.
Observations of Cyg OB2 show that the massive wide binary fraction is at least
a half (38/74) which suggests that Cyg OB2 had at least 30 distinct massive
star formation sites. This is further evidence that Cyg OB2 has always been a
large, low-density association. That Cyg OB2 has a normal high-mass IMF for its
total mass suggests that however massive stars form they 'randomly sample' the
IMF (as the massive stars did not 'know' about each other).
| arxiv topic:astro-ph.GA astro-ph.SR |
arxiv_dataset-94421802.0466 | Implanting germanium into graphene
cond-mat.mtrl-sci
Incorporating heteroatoms into the graphene lattice may be used to tailor its
electronic, mechanical and chemical properties. Direct substitutions have thus
far been limited to incidental Si impurities and P, N and B dopants introduced
using low-energy ion implantation. We present here the heaviest impurity to
date, namely $^{74}$Ge$^+$ ions implanted into monolayer graphene. Although
sample contamination remains an issue, atomic resolution scanning transmission
electron microscopy imaging and quantitative image simulations show that Ge can
either directly substitute single atoms, bonding to three carbon neighbors in a
buckled out-of-plane configuration, or occupy an in-plane position in a
divacancy. First principles molecular dynamics provides further atomistic
insight into the implantation process, revealing a strong chemical effect that
enables implantation below the graphene displacement threshold energy. Our
results show that heavy atoms can be implanted into the graphene lattice,
pointing a way towards advanced applications such as single-atom catalysis with
graphene as the template.
| arxiv topic:cond-mat.mtrl-sci |
arxiv_dataset-94431802.0476 | Perfect fluid Lagrangian and its cosmological implications in theories
of gravity with nonminimally coupled matter fields
gr-qc astro-ph.CO hep-ph hep-th
In this paper we show that the on-shell Lagrangian of a perfect fluid depends
on microscopic properties of the fluid, giving specific examples of perfect
fluids with different on-shell Lagrangians but with the same energy-momentum
tensor. We demonstrate that if the fluid is constituted by localized
concentrations of energy with fixed rest mass and structure (solitons) then the
average on-shell Lagrangian of a perfect fluid is given by ${\mathcal L}_m=T$,
where $T$ is the trace of the energy-momentum tensor. We show that our results
have profound implications for theories of gravity where the matter Lagrangian
appears explicitly in the equations of motion of the gravitational and matter
fields, potentially leading to observable deviations from a nearly perfect
cosmic microwave background black body spectrum: $n$-type spectral distortions,
affecting the normalization of the spectral energy density. Finally, we put
stringent constraints on $f(R,{\mathcal L}_m)$ theories of gravity using the
COBE-FIRAS measurement of the spectral radiance of the cosmic microwave
background.
| arxiv topic:gr-qc astro-ph.CO hep-ph hep-th |
arxiv_dataset-94441802.0486 | Lagrange stability of semilinear differential-algebraic equations and
application to nonlinear electrical circuits
math.DS math.FA math.SP
We study a semilinear differential-algebraic equation (DAE) with the focus on
the Lagrange stability (instability). The conditions for the existence and
uniqueness of global solutions (a solution exists on an infinite interval) of
the Cauchy problem, as well as conditions of the boundedness of the global
solutions, are obtained. Furthermore, the obtained conditions for the Lagrange
stability of the semilinear DAE guarantee that every its solution is global and
bounded, and, in contrast to theorems on the Lyapunov stability, allow to prove
the existence and uniqueness of global solutions regardless of the presence and
the number of equilibrium points. We also obtain the conditions of the
existence and uniqueness of solutions with a finite escape time (a solution
exists on a finite interval and is unbounded, i.e., is Lagrange unstable) for
the Cauchy problem. We do not use constraints of a global Lipschitz condition
type, that allows to use the work results efficiently in practical
applications. The mathematical model of a radio engineering filter with
nonlinear elements is studied as an application. The numerical analysis of the
model verifies the results of theoretical investigations.
| arxiv topic:math.DS math.FA math.SP |
arxiv_dataset-94451802.0496 | Vertex nomination: The canonical sampling and the extended spectral
nomination schemes
stat.ML
Suppose that one particular block in a stochastic block model is of interest,
but block labels are only observed for a few of the vertices in the network.
Utilizing a graph realized from the model and the observed block labels, the
vertex nomination task is to order the vertices with unobserved block labels
into a ranked nomination list with the goal of having an abundance of
interesting vertices near the top of the list. There are vertex nomination
schemes in the literature, including the optimally precise canonical nomination
scheme~$\mathcal{L}^C$ and the consistent spectral partitioning nomination
scheme~$\mathcal{L}^P$. While the canonical nomination scheme $\mathcal{L}^C$
is provably optimally precise, it is computationally intractable, being
impractical to implement even on modestly sized graphs. With this in mind, an
approximation of the canonical scheme---denoted the {\it canonical sampling
nomination scheme} $\mathcal{L}^{CS}$---is introduced; $\mathcal{L}^{CS}$
relies on a scalable, Markov chain Monte Carlo-based approximation of
$\mathcal{L}^{C}$, and converges to $\mathcal{L}^{C}$ as the amount of sampling
goes to infinity. The spectral partitioning nomination scheme is also extended
to the {\it extended spectral partitioning nomination scheme},
$\mathcal{L}^{EP}$, which introduces a novel semisupervised clustering
framework to improve upon the precision of $\mathcal{L}^P$. Real-data and
simulation experiments are employed to illustrate the precision of these vertex
nomination schemes, as well as their empirical computational complexity.
Keywords: vertex nomination, Markov chain Monte Carlo, spectral partitioning,
Mclust MSC[2010]: 60J22, 65C40, 62H30, 62H25
| arxiv topic:stat.ML |
arxiv_dataset-94461802.0506 | Kondo behavior and metamagnetic phase transition in a heavy fermion
compound CeBi2
cond-mat.str-el cond-mat.mtrl-sci
Heavy fermions represent an archetypal example of strongly correlated
electron systems which, due to entanglement among different interactions, often
exhibit exotic and fascinating physics involving Kondo screening, magnetism and
unconventional superconductivity. Here we report a comprehensive study on the
transport and thermodynamic properties of a cerium-based heavy fermion compound
CeBi$_2$ which undergoes an anti-ferromagnetic transition at $T_N$ $\sim$ 3.3
K. Its high temperature paramagnetic state is characterized by an enhanced heat
capacity with Sommerfeld coefficient $\gamma$ over 200 mJ/molK$^2$. The
magnetization in the magnetically ordered state features a metamagnetic
transition. Remarkably, a large negative magnetoresistance associated with the
magnetism was observed in a wide temperature and field-angle range.
Collectively, CeBi$_2$ may serve as an intriguing system to study the interplay
between $f$ electrons and the itinerant Fermi sea.
| arxiv topic:cond-mat.str-el cond-mat.mtrl-sci |
arxiv_dataset-94471802.0516 | Cognitive Deficit of Deep Learning in Numerosity
cs.CV
Subitizing, or the sense of small natural numbers, is an innate cognitive
function of humans and primates; it responds to visual stimuli prior to the
development of any symbolic skills, language or arithmetic. Given successes of
deep learning (DL) in tasks of visual intelligence and given the primitivity of
number sense, a tantalizing question is whether DL can comprehend numbers and
perform subitizing. But somewhat disappointingly, extensive experiments of the
type of cognitive psychology demonstrate that the examples-driven black box DL
cannot see through superficial variations in visual representations and distill
the abstract notion of natural number, a task that children perform with high
accuracy and confidence. The failure is apparently due to the learning method
not the CNN computational machinery itself. A recurrent neural network capable
of subitizing does exist, which we construct by encoding a mechanism of
mathematical morphology into the CNN convolutional kernels. Also, we
investigate, using subitizing as a test bed, the ways to aid the black box DL
by cognitive priors derived from human insight. Our findings are mixed and
interesting, pointing to both cognitive deficit of pure DL, and some measured
successes of boosting DL by predetermined cognitive implements. This case study
of DL in cognitive computing is meaningful for visual numerosity represents a
minimum level of human intelligence.
| arxiv topic:cs.CV |
arxiv_dataset-94481802.0526 | Permutation polynomials over $\mathbb{F}_{q^2}$ from rational functions
math.CO math.NT
Let $\mu_{q+1}$ denote the set of $(q+1)$-th roots of unity in
$\mathbb{F}_{q^2 }$. We construct permutation polynomials over
$\mathbb{F}_{q^2}$ by using rational functions of any degree that induce
bijections either on $\mu_{q+1}$ or between $\mu_{q+1}$ and $\mathbb{F}_q \cup
\{\infty\}$. In particular, we generalize results from Zieve.
| arxiv topic:math.CO math.NT |
arxiv_dataset-94491802.0536 | Radial transport and plasma heating in Jupiter's magnetodisc
physics.space-ph
The ion temperature of the magnetosphere of Jupiter derived from Galileo PLS
data was observed to increase by about an order of magnitude from 10 to 40
Jupiter radii. This suggests the presence of heating sources that counteract
the adiabatic cooling effect of expanding plasma. There have been different
attempts of explaining this phenomena, including a magnetohydrodynamic (MHD)
turbulent heating model which is based on flux tube diffusion [Saur, Astrophys.
J. Lett., 602, L137, 2004]. We explore an alternate turbulent heating model
based on advection, similar to models commonly used in solar wind heating.
Based on spectral analysis of Galileo magnetometer (MAG) data, we find that
observed MHD turbulence could potentially provide the required heating to
explain some of the increase in plasma temperature. This indicates that
advection is a more appropriate way to describe radial transport of plasma in
the jovian magnetosphere beyond 10 Jupiter radii.
| arxiv topic:physics.space-ph |
arxiv_dataset-94501802.0546 | Shape invariance and equivalence relations for pseudowronskians of
Laguerre and Jacobi polynomials
math.CA math-ph math.MP nlin.SI
In a previous paper we derived equivalence relations for pseudo-Wronskian
determinants of Hermite polynomials. In this paper we obtain the analogous
result for Laguerre and Jacobi polynomials. The equivalence formulas are richer
in this case since rational Darboux transformations can be defined for four
families of seed functions, as opposed to only two families in the Hermite
case. The pseudo-Wronskian determinants of Laguerre and Jacobi type will thus
depend on two Maya diagrams, while Hermite pseudo-Wronskians depend on just one
Maya diagram. We show that these equivalence relations can be interpreted as
the general transcription of shape invariance and specific discrete symmetries
acting on the parameters of the isotonic oscillator and Darboux-Poschl-Teller
potential.
| arxiv topic:math.CA math-ph math.MP nlin.SI |
arxiv_dataset-94511802.0556 | Extension of the unit normal vector field from a hypersurface
math.DG
It is important in many applications to be able to extend the (outer) unit
normal vector field from a hypersurface to its neighborhood in such a way that
the result is a unit gradient field. The aim of the paper is to provide an
elementary proof of the existence and uniqueness of such an extension.
| arxiv topic:math.DG |
arxiv_dataset-94521802.0566 | Fidelity based Measurement Induced Nonlocality over two-sided
measurements
quant-ph
In this paper, we introduce quantum fidelity based measurement induced
nonlocality for the bipartite state over two-sided von Neumann projective
measurements. While all the properties of this quantity are reflected from that
of one-sided measurement, the latter one is shown to set an upper bound for
arbitrary bipartite state. As an illustration, we have studied the nonlocality
of Bell diagonal state.
| arxiv topic:quant-ph |
arxiv_dataset-94531802.0576 | The mid-infrared properties and gas content of active galaxies over
large look-back times
astro-ph.GA
Upon an expansion of all of the searches for redshifted HI 21-cm absorption
(0.0021 < z 5.19), we update recent results regarding the detection of 21-cm in
the non-local Universe. Specifically, we confirm that photo-ionisation of the
gas is the mostly likely cause of the low detection rate at high redshift, in
addition to finding that at z < 0.1 there may also be a decrease in the
detection rate, which we suggest is due to the dilution of the absorption
strength by 21-cm emission. By assuming that associated and intervening
absorbers have similar cosmological mass densities, we find evidence that the
spin temperature of the gas evolves with redshift, consistent with heating by
ultra-violet photons. From the near--infrared (3.4, 4.6 and 12 micron) colours,
we see that radio galaxies become more quasar-like in their activity with
increasing redshift. We also find that the non-detection of 21-cm absorption at
high redshift is not likely to be due to the selection of gas-poor ellipticals,
in addition to a strong correlation between the ionising photon rate and the
[3.4] - [4.6] colour, indicating that the UV photons arise from AGN activity.
Like previous studies, we find a correlation between the detection of 21-cm
absorption and the [4.6] - [12] colour, which is a tracer of star-forming
activity. However, this only applies at the lowest redshifts (z < 0.1), the
range considered by the other studies.
| arxiv topic:astro-ph.GA |
arxiv_dataset-94541802.0586 | On the maximal number of real embeddings of spatial minimally rigid
graphs
math.AG math.CO
The number of embeddings of minimally rigid graphs in $\mathbb{R}^D$ is (by
definition) finite, modulo rigid transformations, for every generic choice of
edge lengths. Even though various approaches have been proposed to compute it,
the gap between upper and lower bounds is still enormous. Specific values and
its asymptotic behavior are major and fascinating open problems in rigidity
theory. Our work considers the maximal number of real embeddings of minimally
rigid graphs in $\mathbb{R}^3$. We modify a commonly used parametric
semi-algebraic formulation that exploits the Cayley-Menger determinant to
minimize the {\em a priori} number of complex embeddings, where the parameters
correspond to edge lengths. To cope with the huge dimension of the parameter
space and find specializations of the parameters that maximize the number of
real embeddings, we introduce a method based on coupler curves that makes the
sampling feasible for spatial minimally rigid graphs.
Our methodology results in the first full classification of the number of
real embeddings of graphs with 7 vertices in $\mathbb{R}^3$, which was the
smallest open case. Building on this and certain 8-vertex graphs, we improve
the previously known general lower bound on the maximum number of real
embeddings in $\mathbb{R}^3$.
| arxiv topic:math.AG math.CO |
arxiv_dataset-94551802.0596 | Study of Knowledge-Aided Iterative Detection and Decoding for Multiuser
MIMO Systems
cs.IT math.IT
In this work, we consider the problem of reduced latency of low-density
parity-check (LDPC) codes with iterative detection and decoding (IDD) receiver
in multiuser multiple-antenna systems. The proposed knowledge-aided IDD
(KA-IDD) system employs a minimum mean-square error detector with refined
iterative processing and a reweighted belief propagation (BP) decoding
algorithm. We present reweighted BP decoding algorithms, which exploit the
knowledge of short cycles in the graph structure and reweighting factors
derived from the expansion of hypergraphs. Simulation results show that the
proposed KA-IDD scheme and algorithms outperform prior art and require a
reduced number of decoding iterations.
| arxiv topic:cs.IT math.IT |
arxiv_dataset-94561802.0606 | Any-k: Anytime Top-k Tree Pattern Retrieval in Labeled Graphs
cs.SI cs.DB cs.DS
Many problems in areas as diverse as recommendation systems, social network
analysis, semantic search, and distributed root cause analysis can be modeled
as pattern search on labeled graphs (also called "heterogeneous information
networks" or HINs). Given a large graph and a query pattern with node and edge
label constraints, a fundamental challenge is to nd the top-k matches ac-
cording to a ranking function over edge and node weights. For users, it is di
cult to select value k . We therefore propose the novel notion of an any-k
ranking algorithm: for a given time budget, re- turn as many of the top-ranked
results as possible. Then, given additional time, produce the next lower-ranked
results quickly as well. It can be stopped anytime, but may have to continues
until all results are returned. This paper focuses on acyclic patterns over
arbitrary labeled graphs. We are interested in practical algorithms that
effectively exploit (1) properties of heterogeneous networks, in particular
selective constraints on labels, and (2) that the users often explore only a
fraction of the top-ranked results. Our solution, KARPET, carefully integrates
aggressive pruning that leverages the acyclic nature of the query, and
incremental guided search. It enables us to prove strong non-trivial time and
space guarantees, which is generally considered very hard for this type of
graph search problem. Through experimental studies we show that KARPET achieves
running times in the order of milliseconds for tree patterns on large networks
with millions of nodes and edges.
| arxiv topic:cs.SI cs.DB cs.DS |
arxiv_dataset-94571802.0616 | Effect of $\alpha$-particle irradiation on a NdFeAs(O,F) thin film
cond-mat.supr-con cond-mat.mtrl-sci physics.app-ph
The effect of $\alpha$-particle irradiation on a NdFeAs(O,F) thin film has
been investigated to determine how the introduction of defects affects basic
superconducting properties, including the critical temperature $T_c$ and the
upper critical field $H_{c2}$, and properties more of interest for
applications, like the critical current density $J_c$ and the related pinning
landscape. The irradiation-induced suppression of the film $T_c$ is
significantly smaller than on a similarly damaged single crystal. Moreover
$H_{c2}$ behaves differently, depending on the field orientation: for H//c the
$H_{c2}$ slope monotonically increases with increasing disorder, whereas for
H//ab it remains constant at low dose and it increases only when the sample is
highly disordered. This suggests that a much higher damage level is necessary
to drive the NdFeAs(O,F) thin film into the dirty limit. Despite the increase
in the low temperature $H_{c2}$, the effects on the $J_c$(H//c) performances
are moderate in the measured temperature and field ranges, with a shifting of
the pinning force maximum from 4.5 T to 6 T after an irradiation of
$2\times10^{15} cm^{-2}$. On the contrary, $J_c$(H//ab) is always suppressed.
The analysis demonstrates that irradiation does introduce point defects acting
as pinning centres proportionally to the irradiation fluence but also
suppresses the effectiveness of c-axis correlated pinning present in the
pristine sample. We estimate that significant performance improvements may be
possible at high field or at temperatures below 10 K. The suppression of the
$J_c$(H//ab) performance is not related to a decrease of the $J_c$ anisotropy
as found in other superconductors. Instead it is due to the presence of point
defects that decrease the efficiency of the ab-plane intrinsic pinning typical
of materials with a layered structure.
| arxiv topic:cond-mat.supr-con cond-mat.mtrl-sci physics.app-ph |
arxiv_dataset-94581802.0626 | A Collaborative Computer Aided Diagnosis (C-CAD) System with
Eye-Tracking, Sparse Attentional Model, and Deep Learning
cs.CV cs.AI cs.LG
There are at least two categories of errors in radiology screening that can
lead to suboptimal diagnostic decisions and interventions:(i)human fallibility
and (ii)complexity of visual search. Computer aided diagnostic (CAD) tools are
developed to help radiologists to compensate for some of these errors. However,
despite their significant improvements over conventional screening strategies,
most CAD systems do not go beyond their use as second opinion tools due to
producing a high number of false positives, which human interpreters need to
correct. In parallel with efforts in computerized analysis of radiology scans,
several researchers have examined behaviors of radiologists while screening
medical images to better understand how and why they miss tumors, how they
interact with the information in an image, and how they search for unknown
pathology in the images. Eye-tracking tools have been instrumental in exploring
answers to these fundamental questions. In this paper, we aim to develop a
paradigm shift CAD system, called collaborative CAD (C-CAD), that unifies both
of the above mentioned research lines: CAD and eye-tracking. We design an
eye-tracking interface providing radiologists with a real radiology reading
room experience. Then, we propose a novel algorithm that unifies eye-tracking
data and a CAD system. Specifically, we present a new graph based clustering
and sparsification algorithm to transform eye-tracking data (gaze) into a
signal model to interpret gaze patterns quantitatively and qualitatively. The
proposed C-CAD collaborates with radiologists via eye-tracking technology and
helps them to improve diagnostic decisions. The C-CAD learns radiologists'
search efficiency by processing their gaze patterns. To do this, the C-CAD uses
a deep learning algorithm in a newly designed multi-task learning platform to
segment and diagnose cancers simultaneously.
| arxiv topic:cs.CV cs.AI cs.LG |
arxiv_dataset-94591802.0636 | Anomaly Detection using One-Class Neural Networks
cs.LG cs.NE stat.ML
We propose a one-class neural network (OC-NN) model to detect anomalies in
complex data sets. OC-NN combines the ability of deep networks to extract a
progressively rich representation of data with the one-class objective of
creating a tight envelope around normal data. The OC-NN approach breaks new
ground for the following crucial reason: data representation in the hidden
layer is driven by the OC-NN objective and is thus customized for anomaly
detection. This is a departure from other approaches which use a hybrid
approach of learning deep features using an autoencoder and then feeding the
features into a separate anomaly detection method like one-class SVM (OC-SVM).
The hybrid OC-SVM approach is sub-optimal because it is unable to influence
representational learning in the hidden layers. A comprehensive set of
experiments demonstrate that on complex data sets (like CIFAR and GTSRB), OC-NN
performs on par with state-of-the-art methods and outperformed conventional
shallow methods in some scenarios.
| arxiv topic:cs.LG cs.NE stat.ML |
arxiv_dataset-94601802.0646 | Embedding distance graphs in finite field vector spaces
math.CO math.CA math.NT
We show that large subsets of vector spaces over finite fields determine
certain point configurations with prescribed distance structure. More
specifically, we consider the complete graph with vertices as the points of $A
\subseteq \mathbf{F}_q^d$ and edges assigned the algebraic distance between
pairs of vertices. We prove nontrivial results on locating specified subgraphs
of maximum vertex degree at most $t$ in dimensions $d \geq 2t$.
| arxiv topic:math.CO math.CA math.NT |
arxiv_dataset-94611802.0656 | An implementation of the maximum-caliber principle by replica-averaged
time-resolved restrained simulations
q-bio.BM cond-mat.stat-mech
Inferential methods can be used to integrate experimental informations and
molecular simulations. The maximum entropy principle provides a framework for
using equilibrium experimental data and it has been shown that replica-averaged
simulations, restrained using a static potential, are a practical and powerful
implementation of such principle. Here we show that replica-averaged
simulations restrained using a time-dependent potential are equivalent to the
principle of maximum caliber, the dynamic version of the principle of maximum
entropy, and thus may allow to integrate time-resolved data in molecular
dynamics simulations. We provide an analytical proof of the equivalence as well
as a computational validation making use of simple models and synthetic data.
Some limitations and possible solutions are also discussed.
| arxiv topic:q-bio.BM cond-mat.stat-mech |
arxiv_dataset-94621802.0666 | Linear Equations with Ordered Data
cs.LO
Following a recently considered generalization of linear equations to
unordered data vectors, we perform a further generalization to ordered data
vectors. These generalized equations naturally appear in the analysis of vector
addition systems (or Petri nets) extended with ordered data. We show that
nonnegative-integer solvability of linear equations is computationally
equivalent (up to an exponential blowup) with the reachability problem for
(plain) vector addition systems. This high complexity is surprising, and
contrasts with NP-completeness for unordered data vectors. Also surprisingly,
we achieve polynomial time complexity of the solvability problem when the
nonnegative-integer restriction on solutions is dropped.
| arxiv topic:cs.LO |
arxiv_dataset-94631802.0676 | One-dimensional System Arising in Stochastic Gradient Descent
math.PR
We consider SDEs of the form $dX_t = |f(X_t)|/t^{\gamma} dt+1/t^{\gamma}
dB_t$, where $f(x)$ behaves comparably to $|x|^k$ in a neighborhood of the
origin, for $k\in [1,\infty)$. We show that there exists a threshold value
$:=\tilde{\gamma}$ for $\gamma$, depending on $k$, such that when $\gamma \in
(1/2, \tilde{\gamma})$ then $\mathbb{P}(X_n\rightarrow 0) = 0$, and for the
rest of the permissible values $\mathbb{P}(X_n\rightarrow 0)>0$. The previous
results extend for discrete processes that satisfy $X_{n+1}-X_n =
f(X_n)/n^\gamma +Y_n/n^\gamma$. Here, $Y_{n+1}$ are martingale differences that
are a.s. bounded.
This result shows that for a function $F$, whose second derivative at
degenerate saddle points is of polynomial order, it is always possible to
escape saddle points via the iteration $X_{n+1}-X_n =F'(X_n)/n^\gamma
+Y_n/n^\gamma$ for a suitable choice of $\gamma$.
| arxiv topic:math.PR |
arxiv_dataset-94641802.0686 | The momentum budget of clustered supernova feedback in a 3D, magnetised
medium
astro-ph.GA
While the evolution of superbubbles driven by clustered supernovae has been
studied by numerous authors, the resulting radial momentum yield is uncertain
by as much as an order of magnitude depending on the computational methods and
assumed properties of the surrounding interstellar medium (ISM). In this work,
we study the origin of these discrepancies, and seek to determine the correct
momentum budget for a homogeneous ISM. We carry out 3D hydrodynamic (HD) and
magnetohydrodynamic (MHD) simulations of clustered supernova explosions, using
a Lagrangian method and checking for convergence with respect to resolution. We
find that the terminal momentum of a shell driven by clustered supernovae is
dictated primarily by the mixing rate across the contact discontinuity between
the hot and cold phases, and that this energy mixing rate is dominated by
numerical diffusion even at the highest resolution we can complete, 0.03
$M_\odot$. Magnetic fields also reduce the mixing rate, so that MHD simulations
produce higher momentum yields than HD ones at equal resolution. As a result,
we obtain only a lower limit on the momentum yield from clustered supernovae.
Combining this with our previous 1D results, which provide an upper limit
because they allow almost no mixing across the contact discontinuity, we
conclude that the momentum yield per supernova from clustered supernovae in a
homogeneous ISM is bounded between $2\times 10^5$ and $3\times 10^6$ $M_\odot$
km s$^{-1}$. A converged value for the simple homogeneous ISM remains elusive.
| arxiv topic:astro-ph.GA |
arxiv_dataset-94651802.0696 | Agile Amulet: Real-Time Salient Object Detection with Contextual
Attention
cs.CV
This paper proposes an Agile Aggregating Multi-Level feaTure framework (Agile
Amulet) for salient object detection. The Agile Amulet builds on previous works
to predict saliency maps using multi-level convolutional features. Compared to
previous works, Agile Amulet employs some key innovations to improve training
and testing speed while also increase prediction accuracy. More specifically,
we first introduce a contextual attention module that can rapidly highlight
most salient objects or regions with contextual pyramids. Thus, it effectively
guides the learning of low-layer convolutional features and tells the backbone
network where to look. The contextual attention module is a fully convolutional
mechanism that simultaneously learns complementary features and predicts
saliency scores at each pixel. In addition, we propose a novel method to
aggregate multi-level deep convolutional features. As a result, we are able to
use the integrated side-output features of pre-trained convolutional networks
alone, which significantly reduces the model parameters leading to a model size
of 67 MB, about half of Amulet. Compared to other deep learning based saliency
methods, Agile Amulet is of much lighter-weight, runs faster (30 fps in
real-time) and achieves higher performance on seven public benchmarks in terms
of both quantitative and qualitative evaluation.
| arxiv topic:cs.CV |
arxiv_dataset-94661802.0706 | CATTmew: Defeating Software-only Physical Kernel Isolation
cs.CR
All the state-of-the-art rowhammer attacks can break the MMU-enforced
inter-domain isolation because the physical memory owned by each domain is
adjacent to each other. To mitigate these attacks, physical domain isolation,
introduced by CATT, physically separates each domain by dividing the physical
memory into multiple partitions and keeping each partition occupied by only one
domain. CATT implemented physical kernel isolation as the first generic and
practical software-only defense to protect kernel from being rowhammered as
kernel is one of the most appealing targets.
In this paper, we develop a novel exploit that could effectively defeat the
physical kernel isolation and gain both root and kernel privileges. Our exploit
can work without exhausting the page cache or the system memory, or relying on
the information of the virtual-to-physical address mapping. The exploit is
motivated by our key observation that the modern OSes have double-owned kernel
buffers (e.g., video buffers and SCSI Generic buffers) owned concurrently by
the kernel and user domains. The existence of such buffers invalidates the
physical kernel isolation and makes the rowhammer-based attack possible again.
Existing conspicuous rowhammer attacks achieving the root/kernel privilege
escalation exhaust the page cache or even the whole system memory. Instead, we
propose a new technique, named memory ambush. It is able to place the
hammerable double-owned kernel buffers physically adjacent to the target
objects (e.g., page tables) with only a small amount of memory. As a result,
our exploit is stealthier and has fewer memory footprints. We also replace the
inefficient rowhammer algorithm that blindly picks up addresses to hammer with
an efficient one. Our algorithm selects suitable addresses based on an existing
timing channel.
| arxiv topic:cs.CR |
arxiv_dataset-94671802.0716 | Performance analysis of a novel hybrid FSO / RF communication system
eess.SP
In this paper, a novel dual-hop relay-assisted hybrid Free Space Optical /
Radio Frequency (FSO / RF) communication system is presented. In this structure
an access point connects users within the building to the Base Station via a
hybrid parallel FSO / RF link, this link is proposed firstly. Parallel
combination of FSO and RF links and use of an access point, will increase
capacity, reliability and data rate of the system. It is the first time that
the effect of number of users on the performance of a dual-hop relay-assisted
hybrid parallel FSO / RF system is investigated. FSO link is considered in
Gamma-Gamma atmospheric turbulence with the effect of pointing error and RF
link is considered in Rayleigh fading. For the first time, closed-form
expressions are derived for Bit Error Rate (BER) and Outage Probability (P_out)
of the proposed system. Derived expressions are verified through MATLAB
simulations. It is shown that the performance of the proposed system is almost
independent of atmospheric turbulence intensity, thereby when atmospheric
turbulence strengthens, low power consumption is required for maintenance of
the system performance. Hence the proposed structure is particularly suitable
for mobile communication systems in which a small mobile battery supplies
transmitter power. Also the proposed system performance of the system is
preferable even at low signal to noise ratio (SNR). Therefore, proposed
structure significantly reduces power consumption while maintaining performance
of the system.
| arxiv topic:eess.SP |
arxiv_dataset-94681802.0726 | Deep Learning Classification in Asteroseismology Using an Improved
Neural Network: Results on 15000 Kepler Red Giants and Applications to K2 and
TESS Data
astro-ph.IM astro-ph.SR
Deep learning in the form of 1D convolutional neural networks have previously
been shown to be capable of efficiently classifying the evolutionary state of
oscillating red giants into red giant branch stars and helium-core burning
stars by recognizing visual features in their asteroseismic frequency spectra.
We elaborate further on the deep learning method by developing an improved
convolutional neural network classifier. To make our method useful for current
and future space missions such as K2, TESS and PLATO, we train classifiers that
are able to classify the evolutionary states of lower frequency resolution
spectra expected from these missions. Additionally, we provide new
classifications for 8633 Kepler red giants, out of which 426 have previously
not been classified using asteroseismology. This brings the total to 14983
Kepler red giants classified with our new neural network. We also verify that
our classifiers are remarkably robust to suboptimal data, including low
signal-to-noise and incorrect training truth labels.
| arxiv topic:astro-ph.IM astro-ph.SR |
arxiv_dataset-94691802.0736 | Comparison of the Magnetic properties of Mn3Fe2Si3O12 as a crystalline
garnet and as a glass
cond-mat.mtrl-sci
The crystalline garnet Mn3Fe2Si3O12 and an amorphous phase of the same
nominal composition are synthesized at high pressure. The magnetic properties
of the two forms are reported. Both phases order antiferromagnetically. The
crystalline phase exhibits a Curie-Weiss theta of -47.2 K, with a sharp
ordering transition at 12 K. The glassy phase exhibits a larger
antiferromagnetic Curie-Weiss theta, of -83.0 K, with a broad ordering
transition observed at 2.5 K. Both phases can be classified as magnetically
frustrated, although the amorphous phase shows a much higher degree of
frustration. The amorphous phase exhibits spin-glass behavior and is determined
to have an actual composition of Mn3Fe2Si3O13.
| arxiv topic:cond-mat.mtrl-sci |
arxiv_dataset-94701802.0746 | Learning Image Conditioned Label Space for Multilabel Classification
cs.CV
This work addresses the task of multilabel image classification. Inspired by
the great success from deep convolutional neural networks (CNNs) for
single-label visual-semantic embedding, we exploit extending these models for
multilabel images. Specifically, we propose an image-dependent ranking model,
which returns a ranked list of labels according to its relevance to the input
image. In contrast to conventional CNN models that learn an image
representation (i.e. the image embedding vector), the developed model learns a
mapping (i.e. a transformation matrix) from an image in an attempt to
differentiate between its relevant and irrelevant labels. Despite the
conceptual simplicity of our approach, experimental results on a public
benchmark dataset demonstrate that the proposed model achieves state-of-the-art
performance while using fewer training images than other multilabel
classification methods.
| arxiv topic:cs.CV |
arxiv_dataset-94711802.0756 | Critical yield numbers and limiting yield surfaces of particle arrays
settling in a Bingham fluid
math.OC
We consider the flow of multiple particles in a Bingham fluid in an
anti-plane shear flow configuration. The limiting situation in which the
internal and applied forces balance and the fluid and particles stop flowing,
that is, when the flow settles, is formulated as finding the optimal ratio
between the total variation functional and a linear functional. The minimal
value for this quotient is referred to as the critical yield number or, in
analogy to Rayleigh quotients, generalized eigenvalue. This minimum value can
in general only be attained by discontinuous, hence not physical, velocities.
However, we prove that these generalized eigenfunctions, whose jumps we refer
to as limiting yield surfaces, appear as rescaled limits of the physical
velocities. Then, we show the existence of geometrically simple minimizers.
Furthermore, a numerical method for the minimization is then considered. It is
based on a nonlinear finite difference discretization, whose consistency is
proven, and a standard primal-dual descent scheme. Finally, numerical examples
show a variety of geometric solutions exhibiting the properties discussed in
the theoretical sections.
| arxiv topic:math.OC |
arxiv_dataset-94721802.0766 | Cosmological screening and the phantom braneworld model
gr-qc astro-ph.CO
The scalar and vector cosmological perturbations at all length scales of our
Universe are studied in the framework of the phantom braneworld model. The
model is characterized by the parameter $\Omega_M\equiv M^3/2m^2H_0$, with $M$
and $m$ the 5- and 4-dimensional Planck scales, respectively, and $H_0$ the
Hubble parameter today, while $\Omega_M\rightarrow 0$ recovers the $\Lambda\rm
CDM$ model. Ignoring the backreaction due to the peculiar velocities and also
the bulk cosmological constant, allows the explicit computation of the
gravitational potentials, $\Phi$ and $\Psi$. They exhibit exponentially
decreasing screening behaviour characterized by a screening length which is a
function of the quasidensity parameter $ \Omega_M$.
| arxiv topic:gr-qc astro-ph.CO |
arxiv_dataset-94731802.0776 | Decompositions of Bernstein-Sato polynomials and slices
math.RT
Let $G$ be a linearly reductive group acting on a vector space $V$, and $f$ a
(semi-)invariant polynomial on $V$. In this paper we study systematically
decompositions of the Bernstein-Sato polynomial of $f$ in parallel with some
representation-theoretic properties of the action of $G$ on $V$. We provide a
technique based on a multiplicity one property, that we use to compute the
Bernstein-Sato polynomials of several classical invariants in an elementary
fashion. Furthermore, we derive a "slice method" which shows that the
decomposition of $V$ as a representation of $G$ can induce a decomposition of
the Bernstein-Sato polynomial of $f$ into a product of two Bernstein-Sato
polynomials - that of an ideal and that of a semi-invariant of smaller degree.
Using the slice method, we compute Bernstein-Sato polynomials for a large class
of semi-invariants of quivers.
| arxiv topic:math.RT |
arxiv_dataset-94741802.0786 | Neural Predictive Coding using Convolutional Neural Networks towards
Unsupervised Learning of Speaker Characteristics
cs.SD cs.CL eess.AS
Learning speaker-specific features is vital in many applications like speaker
recognition, diarization and speech recognition. This paper provides a novel
approach, we term Neural Predictive Coding (NPC), to learn speaker-specific
characteristics in a completely unsupervised manner from large amounts of
unlabeled training data that even contain many non-speech events and
multi-speaker audio streams. The NPC framework exploits the proposed short-term
active-speaker stationarity hypothesis which assumes two temporally-close short
speech segments belong to the same speaker, and thus a common representation
that can encode the commonalities of both the segments, should capture the
vocal characteristics of that speaker. We train a convolutional deep siamese
network to produce "speaker embeddings" by learning to separate `same' vs
`different' speaker pairs which are generated from an unlabeled data of audio
streams. Two sets of experiments are done in different scenarios to evaluate
the strength of NPC embeddings and compare with state-of-the-art in-domain
supervised methods. First, two speaker identification experiments with
different context lengths are performed in a scenario with comparatively
limited within-speaker channel variability. NPC embeddings are found to perform
the best at short duration experiment, and they provide complementary
information to i-vectors for full utterance experiments. Second, a large scale
speaker verification task having a wide range of within-speaker channel
variability is adopted as an upper-bound experiment where comparisons are drawn
with in-domain supervised methods.
| arxiv topic:cs.SD cs.CL eess.AS |
arxiv_dataset-94751802.0796 | Electric quadrupole and magnetic dipole coupling in plasmonic
nanoparticle arrays
physics.optics
Collective resonances in plasmonic nanoparticle arrays with electric dipole
moment oriented along the lattice wave propagation are theoretically
investigated. The role of electric quadrupole (EQ) and magnetic dipole (MD)
moments of gold nanoparticles in the resonant features of the arrays is
analyzed. We perform both semi-analytical calculations of coupled multipole
equations and rigorous numerical simulations varying contributions of the
electric and magnetic multipoles by changing particle size and shape (spheres
and disks). The arrays in homogeneous and non-homogeneous environments are
considered. We find that even very weak non-resonant EQ and MD moments of a
single particle are significantly enhanced in the periodic lattice at the
wavelength of collective (lattice) resonance excitation. Importantly, we show
that in the infinite arrays, the EQ and MD moments of nanoparticles are coupled
and affect each other resonant contributions. We also demonstrate that at the
lattice-resonance wavelength, the enhanced EQ and MD moments have contributions
to reflection comparable to the dipole one resulting in a significant decrease
of reflection and providing the satisfaction of the generalized Kerker
condition for reflection suppression.
| arxiv topic:physics.optics |
arxiv_dataset-94761802.0806 | Shadows of spherically symmetric black holes and naked singularities
astro-ph.HE gr-qc hep-th
We compare shadows cast by Schwarzschild black holes with those produced by
two classes of naked singularities that result from gravitational collapse of
spherically symmetric matter. The latter models consist of an interior naked
singularity spacetime restricted to radii $r\leq R_b$, matched to Schwarzschild
spacetime outside the boundary radius $R_b$. While a black hole always has a
photon sphere and always casts a shadow, we find that the naked singularity
models have photon spheres only if a certain parameter $M_0$ that characterizes
these models satisfies $M_0\geq 2/3$, or equivalently, if $R_b\leq 3M$, where
$M$ is the total mass of the object. Such models do produce shadows. However,
models with $M_0<2/3$ (or $R_b>3M$) have no photon sphere and do not produce a
shadow. Instead, they produce an interesting `full-moon' image. These results
imply that the presence of a shadow does not by itself prove that a compact
object is necessarily a black hole. The object could be a naked singularity
with $M_0\geq 2/3$, and we will need other observational clues to distinguish
the two possibilities. On the other hand, the presence of a full-moon image
would certainly rule out a black hole and might suggest a naked singularity
with $M_0<2/3$. It would be worthwhile to generalize the present study, which
is restricted to spherically symmetric models, to rotating black holes and
naked singularities.
| arxiv topic:astro-ph.HE gr-qc hep-th |
arxiv_dataset-94771802.0816 | Quantum Walk in Momentum Space with a Bose-Einstein Condensate
quant-ph cond-mat.quant-gas physics.atom-ph
We present a discrete-time, one-dimensional quantum walk based on the
entanglement between the momentum of ultracold rubidium atoms (the walk space)
and two internal atomic states (the "coin" degree of freedom). Our scheme is
highly flexible and can provide a platform for a wide range of applications
such as quantum search algorithms, the observation of topological phases, and
the realization of walks with higher dimensionality. Along with the
investigation of the quantum-to-classical transition, we demonstrate the
distinctive features of a quantum walk and contrast them to those of its
classical counterpart. Also, by manipulating either the walk or coin operator,
we show how the walk dynamics can be steered or even reversed.
| arxiv topic:quant-ph cond-mat.quant-gas physics.atom-ph |
arxiv_dataset-94781802.0826 | Signature of Planetary Mergers on Stellar Spins
astro-ph.SR astro-ph.EP
One of the predictions of high eccentricity planetary migration is that many
planets will end up plunging into their host stars. We investigate the
consequence of planetary mergers on their stellar hosts' spin-period. Energy
and angular momentum conservation yield that a planet consumption by a star
will spin-up the star. We find that our calculations align with the observed
bifurcation in the stellar spin-period in young clusters. For example, after a
Sun-like star has eaten a Jupiter-mass planet it will spin up by ~60% (i.e.,
spin-period is reduced by ~60%), causing an apparent gap in the stellar spin
period, between stars that consumed a planet and those that did not. The
spun-up star will later spin down due to magnetic braking, consistent with the
disappearance of this bifurcation in clusters (>300Myr). The agreement between
the calculations presented here, and the observed spin-period color diagram of
stars in young clusters provides circumstantial evidence that planetary
accretion onto their host stars is a generic feature of planetary-system
evolution.
| arxiv topic:astro-ph.SR astro-ph.EP |
arxiv_dataset-94791802.0836 | Discrete parabolic groups in ${\rm PSL}(3, \Bbb{C})$
math.DS
We study and classify the purely parabolic discrete subgroups of
$PSL(3,\Bbb{C})$. This includes all discrete subgroups of the Heisenberg group
${\rm Heis}(3,\Bbb{C})$. While for $PSL(2,\Bbb{C})$ every purely parabolic
subgroup is Abelian and acts on $\Bbb{P}^1_\Bbb{C}$ with limit set a single
point, the case of $PSL(3,\Bbb{C})$ is far more subtle and intriguing. We show
that there are five families of purely parabolic discrete groups in
$PSL(3,\Bbb{C})$, and some of these actually split into subfamilies. We
classify all these by means of their limit set and the control group. We use
first the Lie-Kolchin Theorem and Borel's fixed point theorem to show that all
purely parabolic discrete groups in $PSL(3,\Bbb{C})$ are virtually
triangularizable. Then we prove that purely parabolic groups in
$PSL(3,\Bbb{C})$ are virtually solvable and polycyclic, hence finitely
presented. We then prove a slight generalization of the Lie-Kolchin Theorem for
these groups: they are either virtually unipotent or else Abelian of rank 2 and
of a very special type. All the virtually unipotent ones turn out to be
conjugate to subgroups of the Heisenberg group ${\rm Heis}(3,\Bbb{C})$. We
classify these using the obstructor dimension introduced by Bestvina, Kapovich
and Kleiner. We find that their Kulkarni limit set is either a projective line,
a cone of lines with base a circle or else the whole $\Bbb{P}^2_\Bbb{C}$. We
determine the relation with the Conze-Guivarc'h limit set of the action on the
dual projective space $\check{\Bbb{P}}^2_\Bbb{C}$ and we show that in all cases
the Kulkarni region of discontinuity is the largest open set where the group
acts properly discontinuously.
| arxiv topic:math.DS |
arxiv_dataset-94801802.0846 | The envelope of the power spectra of over a thousand \delta Scuti stars.
The $\bar{T}_{eff}$-$\nu_{max}$ scaling relation
astro-ph.SR
CoRoT and Kepler high-precision photometric data allowed the detection and
characterization of the oscillation parameters in stars other than the Sun.
Moreover, thanks to the scaling relations, it is possible to estimate masses
and radii for thousands of solar-type oscillating stars. Recently, a \Delta\nu
- \rho relation has been found for \delta Scuti stars. Now, analyzing several
hundreds of this kind of stars observed with CoRoT and Kepler, we present an
empiric relation between their frequency at maximum power of their oscillation
spectra and their effective temperature. Such a relation can be explained with
the help of the \kappa-mechanism and the observed dispersion of the residuals
is compatible with they being caused by the gravity-darkening effect.
| arxiv topic:astro-ph.SR |
arxiv_dataset-94811802.0856 | Teaching students about informatics and astronomy using real data for
detection of asteroids
astro-ph.IM
In this paper we approach the astronomy teaching process for the students in
computer sciences through the controlled investigation method on real
astronomical data, using data reduction and quality control of the astrometry
of near-Earth asteroids. The method used the data collected on the Isaac Newton
Telescope (INT) located at the ORM observatory on the island of La Palma in the
Spanish Canary Islands and was successfully tested on a group of students in
the second-year of study.
| arxiv topic:astro-ph.IM |
arxiv_dataset-94821802.0866 | A Semantic Framework for the Security Analysis of Ethereum smart
contracts
cs.CR
Smart contracts are programs running on cryptocurrency (e.g., Ethereum)
blockchains, whose popularity stem from the possibility to perform financial
transactions, such as payments and auctions, in a distributed environment
without need for any trusted third party. Given their financial nature, bugs or
vulnerabilities in these programs may lead to catastrophic consequences, as
witnessed by recent attacks. Unfortunately, programming smart contracts is a
delicate task that requires strong expertise: Ethereum smart contracts are
written in Solidity, a dedicated language resembling JavaScript, and shipped
over the blockchain in the EVM bytecode format. In order to rigorously verify
the security of smart contracts, it is of paramount importance to formalize
their semantics as well as the security properties of interest, in particular
at the level of the bytecode being executed.
In this paper, we present the first complete small-step semantics of EVM
bytecode, which we formalize in the F* proof assistant, obtaining executable
code that we successfully validate against the official Ethereum test suite.
Furthermore, we formally define for the first time a number of central security
properties for smart contracts, such as call integrity, atomicity, and
independence from miner controlled parameters. This formalization relies on a
combination of hyper- and safety properties. Along this work, we identified
various mistakes and imprecisions in existing semantics and verification tools
for Ethereum smart contracts, thereby demonstrating once more the importance of
rigorous semantic foundations for the design of security verification
techniques.
| arxiv topic:cs.CR |
arxiv_dataset-94831802.0876 | Sensitivity and Generalization in Neural Networks: an Empirical Study
stat.ML cs.AI cs.LG cs.NE
In practice it is often found that large over-parameterized neural networks
generalize better than their smaller counterparts, an observation that appears
to conflict with classical notions of function complexity, which typically
favor smaller models. In this work, we investigate this tension between
complexity and generalization through an extensive empirical exploration of two
natural metrics of complexity related to sensitivity to input perturbations.
Our experiments survey thousands of models with various fully-connected
architectures, optimizers, and other hyper-parameters, as well as four
different image classification datasets.
We find that trained neural networks are more robust to input perturbations
in the vicinity of the training data manifold, as measured by the norm of the
input-output Jacobian of the network, and that it correlates well with
generalization. We further establish that factors associated with poor
generalization $-$ such as full-batch training or using random labels $-$
correspond to lower robustness, while factors associated with good
generalization $-$ such as data augmentation and ReLU non-linearities $-$ give
rise to more robust functions. Finally, we demonstrate how the input-output
Jacobian norm can be predictive of generalization at the level of individual
test points.
| arxiv topic:stat.ML cs.AI cs.LG cs.NE |
arxiv_dataset-94841802.0886 | Cohomologies of coherent sheaves and massless spectra in F-theory
hep-th
In this PhD thesis we investigate the significance of Chow groups for zero
mode counting and anomaly cancellation in F-theory vacua.
The major part of this thesis focuses on zero mode counting. We explain that
elements of Chow group describe a subset of gauge backgrounds and give rise to
a line bundle on each matter curve. The sheaf cohomologies of these line
bundles are found to encode the chiral and anti-chiral localised zero modes in
this compactification. Therefore, it is of prime interest to compute these
sheaf cohomologies. Unfortunately, the line bundles in question are in general
non-pullback line bundles. In particular, this is the case for the hypercharge
flux employed in F-theory models of grand unified theories (GUTs).
Consequently, existing methods, such as the cohomCalg-algorithm, cannot be
applied. In collaboration with the mathematician Mohamed Barakat, we have
therefore implemented algorithms which determine the sheaf cohomologies of all
coherent sheaves on toric varieties. These algorithms are provided by the
gap-package SheafCohomologiesOnToricVarieties which extends the homalg-project
of Mohamed Barakat. We exemplify these algorithms in explicit (toy-)models of
F-theory GUTs.
As a spin-off of this analysis, we proved that in an entire class of F-theory
vacua, the matter surface fluxes satisfy a number of relations in the Chow
ring, which we related to anomaly cancellation. Based on this evidence we
conjecture that the well-known anomaly cancellation conditions in F-theory -
typically phrased as intersections in the cohomology ring - can be extended
even to relations in the Chow ring.
| arxiv topic:hep-th |
arxiv_dataset-94851802.0896 | Bonnet: An Open-Source Training and Deployment Framework for Semantic
Segmentation in Robotics using CNNs
cs.RO cs.CV
The ability to interpret a scene is an important capability for a robot that
is supposed to interact with its environment. The knowledge of what is in front
of the robot is, for example, relevant for navigation, manipulation, or
planning. Semantic segmentation labels each pixel of an image with a class
label and thus provides a detailed semantic annotation of the surroundings to
the robot. Convolutional neural networks (CNNs) are popular methods for
addressing this type of problem. The available software for training and the
integration of CNNs for real robots, however, is quite fragmented and often
difficult to use for non-experts, despite the availability of several
high-quality open-source frameworks for neural network implementation and
training. In this paper, we propose a tool called Bonnet, which addresses this
fragmentation problem by building a higher abstraction that is specific for the
semantic segmentation task. It provides a modular approach to simplify the
training of a semantic segmentation CNN independently of the used dataset and
the intended task. Furthermore, we also address the deployment on a real
robotic platform. Thus, we do not propose a new CNN approach in this paper.
Instead, we provide a stable and easy-to-use tool to make this technology more
approachable in the context of autonomous systems. In this sense, we aim at
closing a gap between computer vision research and its use in robotics
research. We provide an open-source codebase for training and deployment. The
training interface is implemented in Python using TensorFlow and the deployment
interface provides a C++ library that can be easily integrated in an existing
robotics codebase, a ROS node, and two standalone applications for label
prediction in images and videos.
| arxiv topic:cs.RO cs.CV |
arxiv_dataset-94861802.0906 | On higher direct images of convergent isocrystals
math.AG math.NT
Let k be a perfect field of characteristic p>0 and W the ring of Witt vectors
of k. In this article, we give a new proof of the Frobenius descent for
convergent isocrystals on a variety over k relative to W. This proof allows us
to deduce an analogue of the de Rham complexes comparaison theorem of Berthelot
without assuming a lifting of the Frobenius morphism. As an application, we
prove a version of Berthelot's conjecture on the preservation of convergent
isocrystals under the higher direct image by a smooth proper morphism of
k-varieties.
| arxiv topic:math.AG math.NT |
arxiv_dataset-94871802.0916 | Splitting Fermi Surfaces and Heavy Electronic States in
Non-Centrosymmetric U3Ni3Sn4
cond-mat.str-el
We report the single-crystal growth of the non-centrosymmetric paramagnet
U3Ni3Sn4 by the Bridgman method and the Fermi surface properties detected by de
Haas-van Alphen (dHvA) experiments. We have also investigated single-crystal
U3Ni3Sn4 by single-crystal X-ray diffraction, magnetization, electrical
resistivity, and heat capacity measurements. The angular dependence of the dHvA
frequencies reveals many closed Fermi surfaces, which are nearly spherical in
topology. The experimental results are in good agreement with local density
approximation (LDA) band structure calculations based on the 5f-itinerant
model. The band structure calculation predicts many Fermi surfaces, mostly with
spherical shape, derived from 12 bands crossing the Fermi energy. To our
knowledge, the splitting of Fermi surfaces due to the non-centrosymmetric
crystal in 5f-electron systems is experimentally detected for the first time.
The temperature dependence of the dHvA amplitude reveals a large cyclotron
effective mass of up to 35m0, indicating the heavy electronic state of U3Ni3Sn4
due to the proximity of the quantum critical point. From the field dependence
of the dHvA amplitude, a mean free path of conduction electrons of up to 1950A
is detected, reflecting the good quality of the grown crystal. The small
splitting energy related to the antisymmetric spin-orbit interaction is most
likely due to the large cyclotron effective mass.
| arxiv topic:cond-mat.str-el |
arxiv_dataset-94881802.0926 | Stimulated scattering instability in a relativistic plasma
physics.plasm-ph
We study the stimulated scattering instabilities of an intense linearly
polarized electromagnetic wave (EMW) in a relativistic plasma with degenerate
electrons. Starting from a relativistic hydrodynamic model and the Maxwell's
equations, we derive coupled nonlinear equations for low-frequency electron and
ion plasma oscillations that are driven by the EMW's ponderomotive force. The
nonlinear dispersion relations are then obtained from the coupled nonlinear
equations which reveal stimulated Raman scattering (SRS), stimulated Brillouin
scattering (SBS), and modulational instabilities (MIs) of EMWs. It is shown
that the thermal pressure of ions and the relativistic degenerate pressure of
electrons significantly modify the characteristics of SRS, SBS, and MIs.
| arxiv topic:physics.plasm-ph |
arxiv_dataset-94891802.0936 | A surge of light at the birth of a supernova
astro-ph.HE astro-ph.SR
It is difficult to establish the properties of massive stars that explode as
supernovae. The electromagnetic emission during the first minutes to hours
after the emergence of the shock from the stellar surface conveys important
information about the final evolution and structure of the exploding star.
However, the unpredictable nature of supernova events hinders the detection of
this brief initial phase. Here we report the serendipitous discovery of a newly
born, normal type IIb supernova (SN 2016gkg), which reveals a rapid brightening
at optical wavelengths of about 40 magnitudes per day. The very frequent
sampling of the observations allowed us to study in detail the outermost
structure of the progenitor of the supernova and the physics of the emergence
of the shock. We develop hydrodynamical models of the explosion that naturally
account for the complete evolution of the supernova over distinct phases
regulated by different physical processes. This result suggests that it is
appropriate to decouple the treatment of the shock propagation from the unknown
mechanism that triggers the explosion.
| arxiv topic:astro-ph.HE astro-ph.SR |
arxiv_dataset-94901802.0946 | On the type Ia supernovae 2007on and 2011iv: Evidence for
Chandrasekhar-mass explosions at the faint end of the luminosity-width
relationship
astro-ph.HE
Radiative transfer models of two transitional type Ia supernova (SNe Ia) have
been produced using the abundance stratification technique. These two objects
--designated SN 2007on and SN 2011iv-- both exploded in the same galaxy, NGC
1404, which allows for a direct comparison. SN 2007on synthesised 0.25
$M_{\odot}$ of $^{56}$Ni and was less luminous than SN 2011iv, which produced
0.31 $M_{\odot}$ of $^{56}$Ni. SN 2007on had a lower central density
($\rho_{c}$) and higher explosion energy ($E_{\rm kin}$ $\sim
1.3\pm$0.3$\times10^{51}$erg) than SN 2011iv, and it produced less nuclear
statistical equilibrium (NSE) elements (0.06 $M_{\odot}$). Whereas, SN 2011iv
had a larger $\rho_{c}$, which increased the electron capture rate in the
lowest velocity regions, and produced 0.35 $M_{\odot}$ of stable NSE elements.
SN 2011iv had an explosion energy of $E_{\rm kin}$ $\sim 0.9
\pm$0.2$\times10^{51}$erg. Both objects had an ejecta mass consistent with the
Chandrasekhar mass (Ch-mass), and their observational properties are well
described by predictions from delayed-detonation explosion models. Within this
framework, comparison to the sub-luminous SN 1986G indicates SN 2011iv and SN
1986G have different transition densities ($\rho_{tr}$) but similar $\rho_{c}$.
Whereas, SN 1986G and SN 2007on had a similar $\rho_{tr}$ but different
$\rho_{c}$. Finally, we examine the colour-stretch parameter $s_{BV}$ vs.
$L_{max}$ relation and determine that the bulk of SNe Ia (including the
sub-luminous ones) are consistent with Ch-mass delayed-detonation explosions,
where the main parameter driving the diversity is $\rho_{tr}$. We also find
$\rho_{c}$ to be driving the second order scatter observed at the faint end of
the luminosity-width relationship.
| arxiv topic:astro-ph.HE |
arxiv_dataset-94911802.0956 | Evolution of the Stellar Mass--Metallicity Relation - I: Galaxies in the
z~0.4 Cluster Cl0024
astro-ph.GA
We present the stellar mass-stellar metallicity relationship (MZR) in the
Cl0024+1654 galaxy cluster at z~0.4 using full spectrum stellar population
synthesis modeling of individual quiescent galaxies. The lower limit of our
stellar mass range is $M_*=10^{9.7}M_\odot$, the lowest galaxy mass at which
individual stellar metallicity has been measured beyond the local universe. We
report a detection of an evolution of the stellar MZR with observed redshift at
$0.037\pm0.007$ dex per Gyr, consistent with the predictions from
hydrodynamical simulations. Additionally, we find that the evolution of the
stellar MZR with observed redshift can be explained by an evolution of the
stellar MZR with their formation time, i.e., when the single stellar population
(SSP)-equivalent ages of galaxies are taken into account. This behavior is
consistent with stars forming out of gas that also has an MZR with a
normalization that decreases with redshift. Lastly, we find that over the
observed mass range, the MZR can be described by a linear function with a
shallow slope, ($[Fe/H] \propto (0.16 \pm 0.03) \log M_*$). The slope suggests
that galaxy feedback, in terms of mass-loading factor, might be
mass-independent over the observed mass and redshift range.
| arxiv topic:astro-ph.GA |
arxiv_dataset-94921802.0966 | Computational Red Teaming in a Sudoku Solving Context: Neural Network
Based Skill Representation and Acquisition
cs.LG cs.NE
In this paper we provide an insight into the skill representation, where
skill representation is seen as an essential part of the skill assessment stage
in the Computational Red Teaming process. Skill representation is demonstrated
in the context of Sudoku puzzle, for which the real human skills used in Sudoku
solving, along with their acquisition, are represented computationally in a
cognitively plausible manner, by using feed-forward neural networks with
back-propagation, and supervised learning. The neural network based skills are
then coupled with a hard-coded constraint propagation computational Sudoku
solver, in which the solving sequence is kept hard-coded, and the skills are
represented through neural networks. The paper demonstrates that the modified
solver can achieve different levels of proficiency, depending on the amount of
skills acquired through the neural networks. Results are encouraging for
developing more complex skill and skill acquisition models usable in general
frameworks related to the skill assessment aspect of Computational Red Teaming.
| arxiv topic:cs.LG cs.NE |
arxiv_dataset-94931802.0976 | Kac polynomials and Lie algebras associated to quivers and curves
math.RT math.AG
A survey of the theory of Kac polynomials for quivers and for curves. In
particular, we describe the representation-theoretic meaning of Kac polynomials
in terms of Hall algebras, and the geometric meaning of Kac polynomials in
relation to the geometry of moduli spaces of representations of quivers or
vector bundles on smooth projective curves. We end with some heuristics
concerning a family of infinite-dimensional $\mathbb{Z}^2$-graded Lie algebras
attached to curves of a fixed genus (over a finite field), whose 'Cartan datum'
encodes the dimension of the spaces of absolutely cuspidal functions.
| arxiv topic:math.RT math.AG |
arxiv_dataset-94941802.0986 | CCP: Conflicts Check Protocol for Bitcoin Block Security
cs.CR
In this work, we present our early stage results on a Conflicts Check
Protocol (CCP) that enables preventing potential attacks on bitcoin system.
Based on the observation and discovery of a common symptom that many attacks
may generate, CCP refines the current bitcoin systems by proposing a novel
arbitration mechanism that is capable to determine the approval or abandon of
certain transactions involved in confliction. This work examines the security
issue of bitcoin from a new perspective, which may extend to a larger scope of
attack analysis and prevention
| arxiv topic:cs.CR |
arxiv_dataset-94951802.0996 | Challenges of identifying putative planetary-origin meteorites composed
of non-igneous material
astro-ph.EP
This concept article discusses the challenges of identifying planetary-origin
meteorites of non-igneous composition, primarily of sedimentary origin,
distinct from SNC meteorites. The paper reviews evidence on putative
sedimentary-origin meteorites and potential parent bodies for sedimentary
meteorites. Authors conclude that the list of candidate parent bodies for
sedimentary meteorites includes, but is not limited by the Earth, Mars,
Enceladus, Ganymede, Europa, and hypothetical planets that could exist between
orbits of Mars and Jupiter in the past. Authors argue that extraterrestrial
origin and a parent body for meteoritic sedimentary rocks may be identified
based on the entire body of evidence which is not limited solely by tests of
oxygen and noble gas isotopes whose signatures may undergo terrestrial
contamination and may exhibit significant heterogeneity within the Solar system
and within the parent cosmic bodies. Observed fall of a cosmic body, evidence
of hypervelocity fall, signs of impact in target, and the presence of fusion
crust, melting, and/or shock deformation features in the fragments should be
considered as priority signs of meteoritic origin.
| arxiv topic:astro-ph.EP |
arxiv_dataset-94961802.1006 | Detuning the Honeycomb of $\alpha$-RuCl$_{3}$: Pressure-Dependent
Optical Studies Reveal Broken Symmetry
cond-mat.str-el
The honeycomb Mott insulator $\alpha$-RuCl$_3$ loses its low-temperature
magnetic order by pressure. We report clear evidence for a dimerized structure
at $P>1$ GPa and observe the breakdown of the relativistic $j_{\rm eff}$
picture in this regime strongly affecting the electronic properties. A
pressure-induced Kitaev quantum spin liquid cannot occur in this broken
symmetry state. We shed light on the new phase by broad-band infrared
spectroscopy of the low-temperature properties of $\alpha$-RuCl$_{3}$ and ab
initio density functional theory calculations, both under hydrostatic pressure.
| arxiv topic:cond-mat.str-el |
arxiv_dataset-94971802.1016 | Manifestations of the onset of chaos in condensed matter and complex
systems
cond-mat.stat-mech nlin.CD physics.soc-ph
We review the occurrence of the patterns of the onset of chaos in
low-dimensional nonlinear dissipative systems in leading topics of condensed
matter physics and complex systems of various disciplines. We consider the
dynamics associated with the attractors at period-doubling accumulation points
and at tangent bifurcations to describe features of glassy dynamics, critical
fluctuations and localization transitions. We recall that trajectories
pertaining to the routes to chaos form families of time series that are readily
transformed into networks via the Horizontal Visibility algorithm, and this in
turn facilitates establish connections between entropy and Renormalization
Group properties. We discretize the replicator equation of game theory to
observe the onset of chaos in familiar social dilemmas, and also to mimic the
evolution of high-dimensional ecological models. We describe an analytical
framework of nonlinear mappings that reproduce rank distributions of large
classes of data (including Zipf's law). We extend the discussion to point out a
common circumstance of drastic contraction of configuration space driven by the
attractors of these mappings. We mention the relation of generalized entropy
expressions with the dynamics along and at the period doubling, intermittency
and quasi-periodic routes to chaos. Finally, we refer to additional natural
phenomena in complex systems where these conditions may manifest.
| arxiv topic:cond-mat.stat-mech nlin.CD physics.soc-ph |
arxiv_dataset-94981802.1026 | High-entropy ceramic thin films; A case study on transition metal
diborides
cond-mat.mtrl-sci
High-entropy materials often outperform their lower-entropy relatives in
various aspects, such as thermal stability and fracture toughness. While there
are extensive research activities in the field of high-entropy alloys,
comparably little is performed for high-entropy ceramics, and especially for
high-entropy diborides. Here we show, that not only the hardness of ZrB2 layers
can be improved from 43.2 to 45.8 to 47.2 GPa through the formation of solid
solution ternary diborides (Zr0.61Ti0.39B2) and high-entropy diborides
(Zr0.23Ti0.20Hf0.19V0.14Ta0.24B2), respectively, but especially their thermal
stability against structural rearrangements and decomposition towards the
constituting binary diborides.
| arxiv topic:cond-mat.mtrl-sci |
arxiv_dataset-94991802.1036 | Casimir-Polder Potential of a Driven Atom
quant-ph
We investigate theoretically the Casimir-Polder potential of an atom which is
driven by a laser field close to a surface. This problem is addressed in the
framework of macroscopic quantum electrodynamics using the Green's tensor
formalism and we distinguish between two different approaches, a perturbative
ansatz and a method based on Bloch equations. We apply our results to a
concrete example, namely an atom close to a perfectly conducting mirror, and
create a scenario where the tunable Casimir-Polder potential becomes similar to
the respective potential of an undriven atom due to fluctuating field modes.
Whereas the perturbative approach is restricted to large detunings, the ansatz
based on Bloch equations is exact and yields an expression for the potential
which does not exceed 1/2 of the undriven Casimir-Polder potential.
| arxiv topic:quant-ph |
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