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arxiv_dataset-79001611.04553 | Nonlinear Modal Decoupling of Multi-Oscillator Systems with Applications
to Power Systems
cs.SY
Many natural and manmade dynamical systems that are modeled as large
nonlinear multi-oscillator systems like power systems are hard to analyze. For
such a system, we propose a nonlinear modal decoupling (NMD) approach inversely
constructing as many decoupled nonlinear oscillators as the system oscillation
modes so that individual decoupled oscillators can easily be analyzed to infer
dynamics and stability of the original system. The NMD follows a similar idea
to the normal form except that we eliminate inter-modal terms but allow
intra-modal terms of desired nonlinearities in decoupled systems, so decoupled
systems can flexibly be shaped into desired forms of nonlinear oscillators. The
NMD is then applied to power systems towards two types of nonlinear
oscillators, i.e. the single-machine-infinite-bus (SMIB) systems and a proposed
non-SMIB oscillator. Numerical studies on a 3-machine 9-bus system and New
England 10-machine 39-bus system show that (i) decoupled oscillators keep a
majority of the original system modal nonlinearities and the NMD provides a
bigger validity region than the normal form, and (ii) decoupled non-SMIB
oscillators may keep more authentic dynamics of the original system than
decoupled SMIB systems.
| arxiv topic:cs.SY |
arxiv_dataset-79011611.04653 | Event Detection and Localization in Distribution Grids with Phasor
Measurement Units
cs.SY math.OC
The recent introduction of synchrophasor technology into power distribution
systems has given impetus to various monitoring, diagnostic, and control
applications, such as system identification and event detection, which are
crucial for restoring service, preventing outages, and managing equipment
health. Drawing on the existing framework for inferring topology and
admittances of a power network from voltage and current phasor measurements,
this paper proposes an online algorithm for event detection and localization in
unbalanced three-phase distribution systems. Using a convex relaxation and a
matrix partitioning technique, the proposed algorithm is capable of identifying
topology changes and attributing them to specific categories of events. The
performance of this algorithm is evaluated on a standard test distribution
feeder with synthesized loads, and it is shown that a tripped line can be
detected and localized in an accurate and timely fashion, highlighting its
potential for real-world applications.
| arxiv topic:cs.SY math.OC |
arxiv_dataset-79021611.04753 | Non-archimedean gauge seminorms
math.AG
This paper is intended to provide foundations to the theory of Witt-type
topological group and ring functors defined on a category of topological
algebras, and, in presence of Banach norms, to show how to topologically deal
with them. It is logically the first of a series of papers in preparation on
the use of Barsotti-Witt constructions to obtain Scholze's tilting equivalence
uniformly with respect to the perfectoid field K of characteristic 0 lifting a
particular perfectoid field F of characteristic p>0.
The paper is basically self-contained and may have an independent interest
especially for specialists of topological algebra and non-archimedean
functional analysis: this accounts for its independent submission. We indicate
a new viewpoint in the theory of non-archimedean Banach algebras, based on a
higher-dimensional generalization of the notion of gauge-seminorm as explained
in P. Schneider "Non-archimedean Functional Analysis" Springer 2002
| arxiv topic:math.AG |
arxiv_dataset-79031611.04853 | On the Coded Caching Delivery Design over Wireless Networks
cs.IT math.IT
Coded caching scheme is a promising technique to migrate the network burden
in peak hours, which attains more prominent gains than the uncoded caching. The
coded caching scheme can be classified into two types, namely, the centralized
and the decentralized scheme, according to whether the placement procedures are
carefully designed or operated at random. However, most of the previous
analysis assumes that the connected links between server and users are
error-free. In this paper, we explore the coded caching based delivery design
in wireless networks, where all the connected wireless links are different. For
both centralized and decentralized cases, we proposed two delivery schemes,
namely, the orthogonal delivery scheme and the concurrent delivery scheme. We
focus on the transmission time slots spent on satisfying the system requests,
and prove that for both the centralized and the decentralized cases, the
concurrent delivery always outperforms orthogonal delivery scheme. Furthermore,
for the orthogonal delivery scheme, we derive the gap in terms of transmission
time between the decentralized and centralized case, which is essentially no
more than 1.5.
| arxiv topic:cs.IT math.IT |
arxiv_dataset-79041611.04953 | End-to-End Neural Sentence Ordering Using Pointer Network
cs.CL
Sentence ordering is one of important tasks in NLP. Previous works mainly
focused on improving its performance by using pair-wise strategy. However, it
is nontrivial for pair-wise models to incorporate the contextual sentence
information. In addition, error prorogation could be introduced by using the
pipeline strategy in pair-wise models. In this paper, we propose an end-to-end
neural approach to address the sentence ordering problem, which uses the
pointer network (Ptr-Net) to alleviate the error propagation problem and
utilize the whole contextual information. Experimental results show the
effectiveness of the proposed model. Source codes and dataset of this paper are
available.
| arxiv topic:cs.CL |
arxiv_dataset-79051611.05053 | Learning Detailed Face Reconstruction from a Single Image
cs.CV
Reconstructing the detailed geometric structure of a face from a given image
is a key to many computer vision and graphics applications, such as motion
capture and reenactment. The reconstruction task is challenging as human faces
vary extensively when considering expressions, poses, textures, and intrinsic
geometries. While many approaches tackle this complexity by using additional
data to reconstruct the face of a single subject, extracting facial surface
from a single image remains a difficult problem. As a result, single-image
based methods can usually provide only a rough estimate of the facial geometry.
In contrast, we propose to leverage the power of convolutional neural networks
to produce a highly detailed face reconstruction from a single image. For this
purpose, we introduce an end-to-end CNN framework which derives the shape in a
coarse-to-fine fashion. The proposed architecture is composed of two main
blocks, a network that recovers the coarse facial geometry (CoarseNet),
followed by a CNN that refines the facial features of that geometry (FineNet).
The proposed networks are connected by a novel layer which renders a depth
image given a mesh in 3D. Unlike object recognition and detection problems,
there are no suitable datasets for training CNNs to perform face geometry
reconstruction. Therefore, our training regime begins with a supervised phase,
based on synthetic images, followed by an unsupervised phase that uses only
unconstrained facial images. The accuracy and robustness of the proposed model
is demonstrated by both qualitative and quantitative evaluation tests.
| arxiv topic:cs.CV |
arxiv_dataset-79061611.05153 | Central charges of T-dual branes for toric varieties
math.AG math-ph math.MP math.SG
Given any equivariant coherent sheaf $\mathcal L$ on a compact semi-positive
toric orbifold $\mathcal X$, its SYZ T-dual mirror dual is a Lagrangian brane
in the Landau-Ginzburg mirror. We prove the oscillatory integral of the
equivariant superpotential in the Landau Ginzburg mirror over this Lagrangian
brane is the genus-zero $1$-descendant Gromov-Witten potential with a
Gamma-type class of $\mathcal L$ inserted.
| arxiv topic:math.AG math-ph math.MP math.SG |
arxiv_dataset-79071611.05253 | Strict upper and lower bounds for quantities of interest in static
response sensitivity analysis
math.NA cs.NA
In this paper, a goal-oriented error estimation technique for static response
sensitivity analysis is proposed based on the constitutive relation error (CRE)
estimation for finite element analysis (FEA). Strict upper and lower bounds of
various quantities of interest (QoI) that are associated with the response
sensitivity derivative fields are acquired. Numerical results are presented to
assess the strict bounding properties of the proposed technique.
| arxiv topic:math.NA cs.NA |
arxiv_dataset-79081611.05353 | Context Awareness in Next Generation of Mobile Core Networks
cs.NI
Context awareness is an important enabler for next generation of Mobile Core
Networks (MCN). However there exist a number of challenges in this regard. For
example how to develop a framework which 1) is able to generate context richer
than what is available today; 2) allows reusability of context across the
network; 3) provides a mechanism for exposing context to third parties; and 4)
can bring together "big data" for mobile core network optimization. In this
work, we introduce a context awareness framework addressing the aforementioned
challenges but also taking into account the 3GPP standardization activities
related to context awareness in MCN. Within this framework we propose Context
Generation and Handling Function (CGHF) which generates rich context by
processing information from various sources and then handles its distribution
through an efficient publish subscribe mechanism. In addition we provide
examples where context can be used to optimize control plane decision making.
While the focus of this work is on the use of context for MCN, we still believe
such context can be also used by applications (at the edge as well as in data
centers) and third party services to improve their operations and providing new
unforeseen services.
| arxiv topic:cs.NI |
arxiv_dataset-79091611.05453 | Signatures of Earth-scattering in the direct detection of Dark Matter
hep-ph astro-ph.CO
Direct detection experiments search for the interactions of Dark Matter (DM)
particles with nuclei in terrestrial detectors. But if these interactions are
sufficiently strong, DM particles may scatter in the Earth, affecting their
distribution in the lab. We present a new analytic calculation of this
`Earth-scattering' effect in the regime where DM particles scatter at most once
before reaching the detector. We perform the calculation self-consistently,
taking into account not only those particles which are scattered away from the
detector, but also those particles which are deflected towards the detector.
Taking into account a realistic model of the Earth and allowing for a range of
DM-nucleon interactions, we present the EarthShadow code, which we make
publicly available, for calculating the DM velocity distribution after
Earth-scattering. Focusing on low-mass DM, we find that Earth-scattering
reduces the direct detection rate at certain detector locations while
increasing the rate in others. The Earth's rotation induces a daily modulation
in the rate, which we find to be highly sensitive to the detector latitude and
to the form of the DM-nucleon interaction. These distinctive signatures would
allow us to unambiguously detect DM and perhaps even identify its interactions
in regions of the parameter space within the reach of current and future
experiments.
| arxiv topic:hep-ph astro-ph.CO |
arxiv_dataset-79101611.05553 | Tunable Photonic Radiofrequency Filter with An Ultra-high Out-Of-Band
Rejection
physics.optics
As radiofrequency filtering plays a vital role in electromagnetic devices and
systems, recently photonic techniques have been intensively studied to
implement radiofrequency filters to harness wide frequency coverage, large
instantaneous bandwidth, low frequency-dependent loss, flexible tunability and
strong immunity to electromagnetic interference. However, one crucial challenge
facing the photonic radiofrequency filter (PRF) is the less impressive
out-of-band rejection. Here, to the best of our knowledge, we demonstrate a
tunable PRF with a record out-of-band rejection of 80 dB, which is 3 dB higher
than the maximum value (~77 dB) reported so far, when incorporating highly
selective polarization control and large narrow-band amplification enabled by
stimulated Brillouin scattering effect. In particular, this record rejection is
arduous to be achieved for a narrow passband (e.g., a few megahertz) and a high
finesse in a PRF. Moreover, the proposed PRF is an active one capable of
providing negligible insertion loss and even signal gain. Tunable central
frequency ranging from 2.1 to 6.1 GHz is also demonstrated. The proposed PRF
will provide an ultra-high noise or clutter suppression for harsh
electromagnetic scenarios, particularly when room-temperature implementation
and remote distribution are needed.
| arxiv topic:physics.optics |
arxiv_dataset-79111611.05653 | Iterative Channel Estimation Using LSE and Sparse Message Passing for
MmWave MIMO Systems
cs.IT math.IT
We propose an iterative channel estimation algorithm based on the Least
Square Estimation (LSE) and Sparse Message Passing (SMP) algorithm for the
Millimeter Wave (mmWave) MIMO systems. The channel coefficients of the mmWave
MIMO are approximately modeled as a Bernoulli-Gaussian distribution and the
channel matrix is sparse with only a few non-zero entries. By leveraging the
advantage of sparseness, we propose an algorithm that iteratively detects the
exact locations and values of non-zero entries of the sparse channel matrix. At
each iteration, the locations are detected by the SMP, and values are estimated
with the LSE. We also analyze the Cram\'er-Rao Lower Bound (CLRB), and show
that the proposed algorithm is a minimum variance unbiased estimator under the
assumption that we have the partial priori knowledge of the channel.
Furthermore, we employ the Gaussian approximation for message densities under
density evolution to simplify the analysis of the algorithm, which provides a
simple method to predict the performance of the proposed algorithm. Numerical
experiments show that the proposed algorithm has much better performance than
the existing sparse estimators, especially when the channel is sparse. In
addition, our proposed algorithm converges to the CRLB of the genie-aided
estimation of sparse channels with only five turbo iterations.
| arxiv topic:cs.IT math.IT |
arxiv_dataset-79121611.05753 | Maximizing a Submodular Function with Viability Constraints
cs.DS
We study the problem of maximizing a monotone submodular function with
viability constraints. This problem originates from computational biology,
where we are given a phylogenetic tree over a set of species and a directed
graph, the so-called food web, encoding viability constraints between these
species. These food webs usually have constant {depth}. The goal is to select a
subset of $k$ species that satisfies the viability constraints and has maximal
phylogenetic diversity. As this problem is known to be NP-hard, we investigate
approximation algorithms. We present the first constant factor approximation
algorithm if the depth is constant. Its approximation ratio is
$(1-\frac{1}{\sqrt{e}})$. This algorithm not only applies to phylogenetic trees
with viability constraints but for arbitrary monotone submodular set functions
with viability constraints. Second, we show that there is no
$(1-1/e+\epsilon)$-approximation algorithm for our problem setting (even for
additive functions) and that there is no approximation algorithm for a slight
extension of this setting.
| arxiv topic:cs.DS |
arxiv_dataset-79131611.05853 | Bubble nucleation and growth in very strong cosmological phase
transitions
astro-ph.CO
Strongly first-order phase transitions, i.e., those with a large order
parameter, are characterized by a considerable supercooling and high velocities
of phase transition fronts. A very strong phase transition may have important
cosmological consequences due to the departures from equilibrium caused in the
plasma. In general, there is a limit to the strength, since the metastability
of the old phase may prevent the transition to complete. Near this limit, the
bubble nucleation rate achieves a maximum and thus departs from the widely
assumed behavior in which it grows exponentially with time. We study the
dynamics of this kind of phase transitions. We show that in some cases a
gaussian approximation for the nucleation rate is more suitable, and in such a
case we solve analytically the evolution of the phase transition. We compare
the gaussian and exponential approximations with realistic cases and we
determine their ranges of validity. We also discuss the implications for cosmic
remnants such as gravitational waves.
| arxiv topic:astro-ph.CO |
arxiv_dataset-79141611.05953 | Lossy DC Power Flow
math.OC
The DC Power Flow approximation has been widely used for decades in both
industry and academia due to its computational speed and simplicity, but
suffers from inaccuracy, in part due to the assumption of a lossless network.
Here we present a natural extension of the DC Power Flow to lossy networks. Our
approach is based on reformulating the lossy active power flow equations into a
novel fixed-point equation, and iterating this fixed-point mapping to generate
a sequence of improving estimates for the active power flow solution. Each
iteration requires the solution of a standard DC Power Flow problem with a
modified vector of power injections. The first iteration returns the standard
DC Power Flow, and one or two additional iterations yields a one or two
order-of-magnitude improvement in accuracy. For radial networks, we give
explicit conditions on the power flow data which guarantee (i) that the active
power flow equations possess a unique solution, and (ii) that our iteration
converges exponentially and monotonically to this solution. For meshed
networks, we extensively test our results via standard power flow cases.
| arxiv topic:math.OC |
arxiv_dataset-79151611.06053 | Focal adhesion kinase - the reversible molecular mechanosensor
q-bio.SC cond-mat.soft physics.bio-ph
Sensors are the first element of the pathways that control the response of
cells to their environment. After chemical, the next most important cue is
mechanical, and protein complexes that produce or enable a chemical signal in
response to a mechanical stimulus are called mechanosensors. There is a sharp
distinction between sensing an external force or pressure/tension applied to
the cell, and sensing the mechanical stiffness of the environment. We call the
first mechanosensitivity of the 1st kind, and the latter mechanosensitivity of
the 2nd kind. There are two variants of protein complexes that act as
mechanosensors of the 2nd kind: producing either a one-off or a reversible
action. The latent complex of TGF-$\beta$ is an example of the one-off action:
on the release of active TGF-$\beta$ signal, the complex is discarded and needs
to be replaced. In contrast, focal adhesion kinase (FAK) in a complex with
integrin is a reversible mechanosensor, which initiates the chemical signal in
its active phosphorylated conformation, but can spontaneously return to its
closed folded conformation. Here we study the physical mechanism of the
reversible mechanosensor of the 2nd kind, using FAK as a practical example. We
find how the rates of conformation changes depend on the substrate stiffness
and the pulling force applied from the cell cytoskeleton. The results compare
well with the phenotype observations of cells on different substrates.
| arxiv topic:q-bio.SC cond-mat.soft physics.bio-ph |
arxiv_dataset-79161611.06153 | Propagating spin-wave normal modes: A dynamic matrix approach using
plane-wave demagnetizating tensors
cond-mat.mes-hall
We present a finite-difference micromagnetic approach for determining the
normal modes of spin-waves propagating in extended magnetic films and strips,
which is based on the linearized Landau-Lifshitz equation and uses the dynamic
matrix method. The model takes into account both short range exchange
interactions and long range dipole-dipole interactions. The latter are
accounted for through plane-wave dynamic demagnetization factors, which depend
not only on the geometry and relative positions of the magnetic cells, as usual
demagnetization factors do, but also on the wave vector of the propagating
waves. Such a numerical model is most relevant when the spin-wave medium is
spatially inhomogeneous perpendicular to the direction of propagation, either
in its magnetic properties or in its equilibrium magnetic configuration. We
illustrate this point by studying surface spin-waves in magnetic bilayer films
and spin-waves channelized along magnetic domain walls in perpendicularly
magnetized strips. In both cases, dynamic dipolar interactions produce
non-reciprocity effects, where counter-propagative spin-waves have different
frequencies.
| arxiv topic:cond-mat.mes-hall |
arxiv_dataset-79171611.06253 | Finite Element Modeling of Metasurfaces with Generalized Sheet
Transition Conditions
physics.class-ph
A modeling of metasurfaces in the finite element method (FEM) based on
generalized sheet transition conditions (GSTCs) is presented. The
discontinuities in electromagnetic fields across a metasurface as represented
by the GSTC are modeled by assigning nodes to both sides of the metasurface.
The FEM-GSTC formulation in both 1D and 2D domains is derived and implemented.
The method is extended to handle more general bianistroptic metasurfaces. The
formulations are validated by several illustrative examples.
| arxiv topic:physics.class-ph |
arxiv_dataset-79181611.06353 | Cone distribution functions and quantiles for multivariate random
variables
math.ST stat.TH
Set-valued quantiles for multivariate distributions with respect to a general
convex cone are introduced which are based on a family of (univariate)
distribution functions rather than on the joint distribution function. It is
shown that these quantiles enjoy basically all the properties of univariate
quantile functions. Relationships to families of univariate quantile functions
and to depth functions are discussed. Finally, a corresponding Value at Risk
for multivariate random variables as well as stochastic orders are introduced
via the set-valued approach.
| arxiv topic:math.ST stat.TH |
arxiv_dataset-79191611.06453 | Fast Video Classification via Adaptive Cascading of Deep Models
cs.CV cs.LG cs.NE
Recent advances have enabled "oracle" classifiers that can classify across
many classes and input distributions with high accuracy without retraining.
However, these classifiers are relatively heavyweight, so that applying them to
classify video is costly. We show that day-to-day video exhibits highly skewed
class distributions over the short term, and that these distributions can be
classified by much simpler models. We formulate the problem of detecting the
short-term skews online and exploiting models based on it as a new sequential
decision making problem dubbed the Online Bandit Problem, and present a new
algorithm to solve it. When applied to recognizing faces in TV shows and
movies, we realize end-to-end classification speedups of 2.4-7.8x/2.6-11.2x (on
GPU/CPU) relative to a state-of-the-art convolutional neural network, at
competitive accuracy.
| arxiv topic:cs.CV cs.LG cs.NE |
arxiv_dataset-79201611.06553 | Spin-Dependent Weakly-Interacting-Massive-Particle--Nucleon Cross
Section Limits from First Data of PandaX-II Experiment
hep-ex astro-ph.CO hep-ph
New constraints are presented on the spin-dependent WIMP-nucleon interaction
from the PandaX-II experiment, using a data set corresponding to a total
exposure of 3.3$\times10^4$ kg-days. Assuming a standard axial-vector
spin-dependent WIMP interaction with $^{129}$Xe and $^{131}$Xe nuclei, the most
stringent upper limits on WIMP-neutron cross sections for WIMPs with masses
above 10 GeV/c$^{2}$ are set in all dark matter direct detection experiments.
The minimum upper limit of $4.1\times 10^{-41}$ cm$^2$ at 90\% confidence level
is obtained for a WIMP mass of 40 GeV/c$^{2}$. This represents more than a
factor of two improvement on the best available limits at this and higher
masses. These improved cross-section limits provide more stringent constraints
on the effective WIMP-proton and WIMP-neutron couplings.
| arxiv topic:hep-ex astro-ph.CO hep-ph |
arxiv_dataset-79211611.06653 | SIMEX estimation for single-index model with covariate measurement error
stat.ME
In this paper, we consider the single-index measurement error model with
mismeasured covariates in the nonparametric part. To solve the problem, we
develop a simulation-extrapolation (SIMEX) algorithm based on the local linear
smoother and the estimating equation. For the proposed SIMEX estimation, it is
not needed to assume the distribution of the unobserved covariate. We transform
the boundary of a unit ball in $\mathbb{R}^p$ to the interior of a unit ball in
$\mathbb{R}^{p-1}$ by using the constraint $\|\beta\|=1$. The proposed SIMEX
estimator of the index parameter is shown to be asymptotically normal under
some regularity conditions. We also derive the asymptotic bias and variance of
the estimator of the unknown link function. Finally, the performance of the
proposed method is examined by simulation studies and is illustrated by a real
data example.
| arxiv topic:stat.ME |
arxiv_dataset-79221611.06753 | Shrinkage estimation of covariance matrix for portfolio choice with high
frequency data
math.ST stat.AP stat.TH
This paper examines the usefulness of high frequency data in estimating the
covariance matrix for portfolio choice when the portfolio size is large. A
computationally convenient nonlinear shrinkage estimator for the integrated
covariance (ICV) matrix of financial assets is developed in two steps. The
eigenvectors of the ICV are first constructed from a designed time variation
adjusted realized covariance matrix of noise-free log-returns of relatively low
frequency data. Then the regularized eigenvalues of the ICV are estimated by
quasi-maximum likelihood based on high frequency data. The estimator is always
positive definite and its inverse is the estimator of the inverse of ICV. It
minimizes the limit of the out-of-sample variance of portfolio returns within
the class of rotation-equivalent estimators. It works when the number of
underlying assets is larger than the number of time series observations in each
asset and when the asset price follows a general stochastic process. Our
theoretical results are derived under the assumption that the number of assets
(p) and the sample size (n) satisfy p/n \to y >0 as n goes to infty . The
advantages of our proposed estimator are demonstrated using real data.
| arxiv topic:math.ST stat.AP stat.TH |
arxiv_dataset-79231611.06853 | Symbolic Iterative Solution of Boundary Value Problems for Partial
Differential Equations
math.GM
In this article we introduce a simple straightforward and powerful method
involving symbolic manipulation, Picard iteration, and auxiliary variables for
approximating solutions of partial differential boundary value problems. The
method is easy to implement, computationally efficient, and it is highly
accurate. The output of the method is a function that approximates the exact
solution.
| arxiv topic:math.GM |
arxiv_dataset-79241611.06953 | Associative Adversarial Networks
cs.LG cs.AI
We propose a higher-level associative memory for learning adversarial
networks. Generative adversarial network (GAN) framework has a discriminator
and a generator network. The generator (G) maps white noise (z) to data samples
while the discriminator (D) maps data samples to a single scalar. To do so, G
learns how to map from high-level representation space to data space, and D
learns to do the opposite. We argue that higher-level representation spaces
need not necessarily follow a uniform probability distribution. In this work,
we use Restricted Boltzmann Machines (RBMs) as a higher-level associative
memory and learn the probability distribution for the high-level features
generated by D. The associative memory samples its underlying probability
distribution and G learns how to map these samples to data space. The proposed
associative adversarial networks (AANs) are generative models in the
higher-levels of the learning, and use adversarial non-stochastic models D and
G for learning the mapping between data and higher-level representation spaces.
Experiments show the potential of the proposed networks.
| arxiv topic:cs.LG cs.AI |
arxiv_dataset-79251611.07053 | Second-order transport, quasinormal modes and zero-viscosity limit in
the Gauss-Bonnet holographic fluid
hep-th cond-mat.str-el gr-qc nucl-th
Gauss-Bonnet holographic fluid is a useful theoretical laboratory to study
the effects of curvature-squared terms in the dual gravity action on transport
coefficients, quasinormal spectra and the analytic structure of thermal
correlators at strong coupling. To understand the behavior and possible
pathologies of the Gauss-Bonnet fluid in $3+1$ dimensions, we compute
(analytically and non-perturbatively in the Gauss-Bonnet coupling) its
second-order transport coefficients, the retarded two- and three-point
correlation functions of the energy-momentum tensor in the hydrodynamic regime
as well as the relevant quasinormal spectrum. The Haack-Yarom universal
relation among the second-order transport coefficients is violated at second
order in the Gauss-Bonnet coupling. In the zero-viscosity limit, the
holographic fluid still produces entropy, while the momentum diffusion and the
sound attenuation are suppressed at all orders in the hydrodynamic expansion.
By adding higher-derivative electromagnetic field terms to the action, we also
compute corrections to charge diffusion and identify the non-perturbative
parameter regime in which the charge diffusion constant vanishes.
| arxiv topic:hep-th cond-mat.str-el gr-qc nucl-th |
arxiv_dataset-79261611.07153 | Dramatic change of photoexcited quasiparticle relaxation dynamics across
Yb valence state transition in YbInCu$_4$
cond-mat.str-el
YbInCu$_4$ undergoes a first order structural phase transition near $T_v$=40
K associated with an abrupt change of Yb valence state. We perform ultrafast
pump-probe measurement on YbInCu$_4$ and find that the expected heavy fermion
properties arising from the \emph{c-f} hybridization exist only in a limited
temperature range above $T_v$. Below $T_v$, the compound behaves like a normal
metal though a prominent hybridization energy gap is still present in infrared
measurement. We elaborate that those seemingly controversial phenomena could be
well explained by assuming that the Fermi level suddenly shifts up and becomes
far away from the flat \emph{f}-electron band as well as the indirect
hybridization energy gap in the mixed valence state below $T_v$.
| arxiv topic:cond-mat.str-el |
arxiv_dataset-79271611.07253 | On Wigner-Ville Spectra and the Unicity of Time-Varying Quantile-Based
Spectral Densities
math.ST stat.TH
The unicity of the time-varying quantile-based spectrum proposed in Birr et
al. (2016) is established via an asymptotic representation result involving
Wigner-Ville spectra.
| arxiv topic:math.ST stat.TH |
arxiv_dataset-79281611.07353 | Multi-mirror imaging optics for low-loss transport of divergent neutron
beams and tailored wavelength spectra
physics.ins-det hep-ex nucl-ex
A neutron optical transport system is proposed which comprises nested short
elliptical mirrors located halfway between two common focal points M and M'. It
images cold neutrons from a diverging beam or a source with finite size at M by
single reflections onto a spot of similar size at M'. Direct view onto the
neutron source is blocked by a central absorber with little impact on the
transported solid angle. Geometric neutron losses due to source size can be
kept small using modern supermirrors and distances M-M' of a few tens of
metres. Very short flat mirrors can be used in practical implementations.
Transport with a minimum of reflections remedies losses due to multiple
reflections that are common in long elliptical neutron guides. Moreover,
well-defined reflection angles lead to new possibilities for enhancing the
spectral quality of primary beams, such as clear-cut discrimination of short
neutron wavelengths or beam monochromation using bandpass supermirrors.
Multi-mirror imaging systems may thus complement or even replace ordinary
neutron guides, in particular at the European Spallation Source.
| arxiv topic:physics.ins-det hep-ex nucl-ex |
arxiv_dataset-79291611.07453 | On distortion of normal subgroups
math.GR
We examine distortion of finitely generated normal subgroups. We show a
connection between subgroup distortion and group divergence. We suggest a
method computing the distortion of normal subgroups by decomposing the whole
group into smaller subgroups. We apply our work to compute the distortion of
normal subgroups of graph of groups and normal subgroups of right-angled Artin
groups that induce infinite cyclic quotient groups. We construct normal
subgroups of $\CAT(0)$ groups introduced by Macura and introduce a collection
of normal subgroups of right-angled Artin groups. These groups provide a rich
source to study the connection between subgroup distortion and group divergence
on $\CAT(0)$ groups.
| arxiv topic:math.GR |
arxiv_dataset-79301611.07553 | Uncertainty product of an out-of-equilibrium Bose-Einstein condensate
cond-mat.quant-gas quant-ph
The variance and uncertainty product of the position and momentum
many-particle operators of structureless bosons interacting by a long-range
inter-particle interaction and trapped in a single-well potential are
investigated. In the first example, of an out-of-equilibrium interaction-quench
scenario, it is found that, despite the system being fully condensed, already
when a fraction of a particle is depleted differences with respect to the
mean-field quantities emerge. In the second example, of the pathway from
condensation to fragmentation of the ground state, we find out that, although
the cloud's density broadens while the system's fragments, the position
variance actually decreases, the momentum variance increases, and the
uncertainty product is not a monotonous function but has a maximum. Implication
are briefly discussed.
| arxiv topic:cond-mat.quant-gas quant-ph |
arxiv_dataset-79311611.07653 | Thermal X-ray emission from massive, fast rotating, highly magnetized
white dwarfs
astro-ph.HE astro-ph.SR
There is solid observational evidence on the existence of massive, $M\sim
1~M_\odot$, highly magnetized white dwarfs (WDs) with surface magnetic fields
up to $B\sim 10^9$ G. We show that, if in addition to these features, the star
is fast rotating, it can become a rotation-powered pulsar-like WD and emit
detectable high-energy radiation. We infer the values of the structure
parameters (mass, radius, moment of inertia), magnetic field, rotation period
and spin-down rates of a WD pulsar death-line. We show that WDs above the
death-line emit blackbody radiation in the soft X-ray band via the magnetic
polar cap heating by back flowing pair-created particle bombardment and discuss
as an example the X-ray emission of soft gamma-repeaters and anomalous X-ray
pulsars within the WD model.
| arxiv topic:astro-ph.HE astro-ph.SR |
arxiv_dataset-79321611.07753 | Synthesizing invariants by solving solvable loops
cs.LO
When proving invariance properties of a program, we face two problems. The
first problem is related to the necessity of proving tautologies of considered
assertion language, whereas the second manifests in the need of finding
sufficiently strong invariants. This paper focuses on the second problem and
describes a new method for the automatic generation of loop invariants that
handles polynomial and non deterministic assignments. This technique is based
on the eigenvector generation for a given linear transformation and on the
polynomial optimization problem, which we implemented in the open-source tool
Pilat.
| arxiv topic:cs.LO |
arxiv_dataset-79331611.07853 | Vector-valued multibang control of differential equations
math.OC
We consider a class of (ill-posed) optimal control problems in which a
distributed vector-valued control is enforced to pointwise take values in a
finite set $\mathcal{M}\subset\mathbb{R}^m$. After convex relaxation, one
obtains a well-posed optimization problem, which still promotes control values
in $\mathcal{M}$. We state the corresponding well-posedness and stability
analysis and exemplify the results for two specific cases of quite general
interest, optimal control of the Bloch equation and optimal control of an
elastic deformation. We finally formulate a semismooth Newton method to
numerically solve a regularized version of the optimal control problem and
illustrate the behavior of the approach for our example cases.
| arxiv topic:math.OC |
arxiv_dataset-79341611.07953 | Three-dimensional isolated quotient singularities in even characteristic
math.AG
This paper is a complement to the work of the second author on modular
quotient singularities in odd characteristic (see arXiv:1210.8006). Here we
prove that if $V$ is a three-dimensional vector space over a field of
characteristic $2$ and $G<GL(V)$ is a finite subgroup generated by
pseudoreflections and possessing a $2$-dimensional invariant subspace $W$ such
that the restriction of $G$ to $W$ is isomorphic to the group
$SL_{2}(\mathbb{F}_{2^n})$, then the quotient $V/G$ is non-singular. This,
together with earlier known results on modular quotient singularities, implies
first that a theorem of Kemper and Malle on irreducible groups generated by
pseudoreflections generalizes to reducible groups in dimension three, and,
second, that the classification of three-dimensional isolated singularities
which are quotients of a vector space by a linear finite group reduces to
Vincent's classification of non-modular isolated quotient singularities.
| arxiv topic:math.AG |
arxiv_dataset-79351611.08053 | Computational Power of Symmetry-Protected Topological Phases
quant-ph
We consider ground states of quantum spin chains with symmetry-protected
topological (SPT) order as resources for measurement-based quantum computation
(MBQC). We show that, for a wide range of SPT phases, the computational power
of ground states is uniform throughout each phase. This computational power,
defined as the Lie group of executable gates in MBQC, is determined by the same
algebraic information that labels the SPT phase itself. We prove that these Lie
groups always contain a full set of single-qubit gates, thereby affirming the
long-standing conjecture that general SPT phases can serve as computationally
useful phases of matter.
| arxiv topic:quant-ph |
arxiv_dataset-79361611.08153 | Magnetic behavior of Ni substituted LiCoO2, magnetization and electron
paramagnetic resonance studies
cond-mat.mtrl-sci
Single phase Ni substituted LiCo1-xNixO2 solid solutions with x < 0.15 have
been synthesized to study the effect of substitution on the magnetic behavior.
Two different techniques, magnetic susceptibility and electron paramagnetic
resonance, EPR which provide information in two different time windows have
been used. The solid solutions have been found to be single phase with large
grains conforming to R-3m rhombohedral structure. The lattice parameters c and
a increase with increasing Ni substitution but with a nearly constant c/a ratio
of about 4.99 in all the cases indicating that the CoO6 and LiO6 octahedra do
not undergo any Jahn-Teller distortions. The room temperature EPR absorption
spectra clearly shows a peak in all the compounds at a field of 314 mT
corresponding to a g-factor of 2.14. The peak width however is found to be a
strong function of Ni substitution; increasing with increasing Ni from 3.6 mT
to 6.5 mT for x = 0.08. The magnetization increases with decreasing temperature
in all the compounds, a paramagnetic behavior, unlike Li-deficient compounds
which show a Pauli paramagnetic susceptibility. Also, the magnetization
exhibits thermal irreversibility which vanishes at large magnetic fields in all
the compounds. The unsubstituted compound has discontinuities at 200 K and 50 K
corresponding to magnetic transitions which disappear on substitution with 2 %
Ni for Co. The effective magnetic moment is found to increase from 0.32 Bohr
magnetons to 0.66 Bohr magnetons on increasing the substitution to 0.15. The
unique feature however is that all the compounds exhibit a clear magnetic
hysteresis at room temperature with a finite coercivity. The coercivity
increases from 31 Oe to 168 Oe for x = 0.04 and then decreases on further
increasing of x. A deconvolution of the hysteresis loops clearly shows an
increasing paramagnetic component with substitution.
| arxiv topic:cond-mat.mtrl-sci |
arxiv_dataset-79371611.08253 | A geometric proof of L\"uck's vanishing theorem for the first
$L^2$-Betti number of the total space of a fibration
math.AT
A significant theorem of L\"uck says that the first $L^2$-Betti number of the
total space of a fibration vanishes under some conditions on the fundamental
groups. The proof is based on constructions on chain complexes. In the present
paper, we translate the proof into the world of CW-complexes to make it more
accessible.
| arxiv topic:math.AT |
arxiv_dataset-79381611.08353 | An In Vitro Nematic Model for Proliferating Cell Cultures
physics.bio-ph
Confluent populations of elongated cells give rise to ordered patterns seen
in nematic phase liquid crystals. We correlate cell elongation and
intercellular distance with intercellular alignment using an amorphous spin
glass model. We compare in vitro time-lapse imaging with Monte Carlo simulation
results by framing a novel hard ellipses model in terms of Boltzmann
statistics. Furthermore, we find a statistically distinct alignment energy at
quasi-steady state among fibroblasts, smooth muscle cells, and pluripotent cell
populations when cultured in vitro. These findings have important implications
in both non-invasive clinical screening of the stem cell differentiation
process and in relating shape parameters to coupling in active crystal systems
such as nematic cell monolayers.
| arxiv topic:physics.bio-ph |
arxiv_dataset-79391611.08453 | Confinement effects on the nuclear spin isomer conversion of H$_2$O
physics.chem-ph
The mechanism for interconversion between the nuclear spin isomers (NSI) of
H$_2$O remains shrouded in uncertainties. The temperature dependence displayed
by NSI interconversion rates for H$_2$O isolated in an Argon matrix provides
evidence that confinement effects are responsible for the dramatic increase in
their kinetics with respect to the gas phase, providing new pathways for
o-H$_2$O $\leftrightarrow$ p-H$_2$O conversion in endohedral compounds. This
reveals intramolecular aspects of the interconversion mechanism which may
improve methodologies for the separation and storage of NSI en route to
applications in nuclear magnetic resonance spectroscopy and imaging. It may
also improve astronomers' ability to use their relative abundance in the
interstellar medium as proxies, thereby providing a valuable "astronomical
clock".
| arxiv topic:physics.chem-ph |
arxiv_dataset-79401611.08553 | A moving mesh finite difference method for non-monotone solutions of
non-equilibrium equations in porous media
physics.comp-ph
An adaptive moving mesh finite difference method is presented to solve two
types of equations with dynamic capillary pressure term in porous media. One is
the non-equilibrium Richards Equation and the other is the modified
Buckley-Leverett equation. The governing equations are discretized with an
adaptive moving mesh finite difference method in the space direction and an
implicit-explicit method in the time direction. In order to obtain high quality
meshes, an adaptive time-dependent monitor function with directional control is
applied to redistribute the mesh grid in every time step, and a diffusive
mechanism is used to smooth the monitor function. The behaviors of the central
difference flux, the standard local Lax-Friedrich flux and the local
Lax-Friedrich flux with reconstruction are investigated by solving a 1D
modified Buckley-Leverett equation. With the moving mesh technique, good mesh
quality and high numerical accuracy are obtained. A collection of
one-dimensional and two-dimensional numerical experiments is presented to
demonstrate the accuracy and effectiveness of the proposed method.
| arxiv topic:physics.comp-ph |
arxiv_dataset-79411611.08653 | Nb/InAs nanowire proximity junctions from Josephson to quantum dot
regimes
cond-mat.mes-hall
The superconducting proximity effect is probed experimentally in Josephson
junctions fabricated with InAs nanowires contacted by Nb leads. Contact
transparencies $t \sim 0.7$ are observed. The electronic phase coherence length
at low temperatures exceeds the channel length. However, the elastic scattering
length is a few times shorter than the channel length. Electrical measurements
reveal two regimes of quantum transport: (i) the Josephson regime,
characterized by a dissipationless current up to $\sim 100$ nA, and (ii) the
quantum dot regime, characterized by the formation of Andreev Bound States
(ABS) associated with spontaneous quantum dots inside the nanowire channel. In
regime (i), the behaviour of the critical current $I_c$ versus an axial
magnetic field $B_{||}$ shows an unexpected modulation and persistence to
fields $>2$ T. In the quantum dot regime, the ABS are modelled as the
current-biased solutions of an Anderson-type model. The applicability of
devices in both transport regimes to Majorana fermion experiments is discussed.
| arxiv topic:cond-mat.mes-hall |
arxiv_dataset-79421611.08753 | Midgap states and band gap modification in defective graphene/h-BN
heterostructures
cond-mat.mtrl-sci cond-mat.mes-hall
The role of defects in van der Waals heterostructures made of graphene and
hexagonal boron nitride (h-BN) is studied by a combination of ab initio and
model calculations. Despite the weak van der Waals interaction between layers,
defects residing in h-BN, such as carbon impurities and antisite defects,
reveal a hybridization with graphene p$_{\rm z}$ states, leading to midgap
state formation. The induced midgap states modify the transport properties of
graphene and can be reproduced by means of a simple effective tight-binding
model. In contrast to carbon defects, it is found that oxygen defects do not
strongly hybridize with graphene's low-energy states. Instead, oxygen
drastically modifies the band gap of graphene, which emerges in a commensurate
stacking on h-BN lattices.
| arxiv topic:cond-mat.mtrl-sci cond-mat.mes-hall |
arxiv_dataset-79431611.08853 | A Low Complexity Detection Algorithm for SCMA
cs.IT math.IT
Sparse code multiple access (SCMA) is a new multiple access technique which
supports massive connectivity. Compared with the current Long Term Evolution
(LTE) system, it enables the overloading of active users on limited orthogonal
resources and thus meets the requirement of the fifth generation (5G) wireless
networks. However, the computation complexity of existing detection algorithms
increases exponentially with $d_f$ (the degree of the resource nodes). Although
the codebooks are designed to have low density, the detection still takes
considerable time. The parameter $d_f$ must be designed to be very small, which
largely limits the choice of codebooks. In this paper, a new detection
algorithm is proposed by discretizing the probability distribution functions
(PDFs) in the layer nodes (variable nodes). Given $M$ as the size of one
codebook, the detection complexity of each resource node (function node) is
reduced from $O(d_f M^{d_f})$ to $O(d_f^3 \ln (d_f))$. Its detection accuracy
can quickly approach that of the previous detection algorithms with the
decrease of sampling interval in discretization.
| arxiv topic:cs.IT math.IT |
arxiv_dataset-79441611.08953 | Note on a Paper by Ooguri and Vafa
hep-th
In a recent paper, Ooguri and Vafa [arXiv:1610.04564] argued that a mild
extension of the Weak Gravity conjecture\cite{weakgrav} led to the conclusion
that the only models of quantum gravity in AdS space with "radius large
compared to the string scale" were models with exact AdS-SUSY. This note
clarifies certain obscure parts of their argument by reinterpreting it as a
statement about brane configurations in flat space. In that context the
statement is that stable non-supersymmetric configurations of branes are
characterized by charges in the torsion subgroup of K-theory and their only
long range fields are gravitational and scalar. The field equations do not have
large radius near horizon AdS solutions. Instead the horizons are Schwarzschild
black branes. This leads us to conjecture that for $d \leq 11$ the K theory
charges are bounded by a small integer, and there can be no large gravitational
back reaction in the near horizon limit, for stable configurations. Unbounded
values of these discrete charges would violate the Covariant Entropy Bound. We
discuss a counterexample to the conjecture in $AdS_3$. We find similar
counterexamples in higher dimensional AdS spaces, but argue that none of them
lead to SUSY violating models of quantum gravity in Minkowski space.
| arxiv topic:hep-th |
arxiv_dataset-79451611.09053 | Bidirectional Multirate Reconstruction for Temporal Modeling in Videos
cs.CV
Despite the recent success of neural networks in image feature learning, a
major problem in the video domain is the lack of sufficient labeled data for
learning to model temporal information. In this paper, we propose an
unsupervised temporal modeling method that learns from untrimmed videos. The
speed of motion varies constantly, e.g., a man may run quickly or slowly. We
therefore train a Multirate Visual Recurrent Model (MVRM) by encoding frames of
a clip with different intervals. This learning process makes the learned model
more capable of dealing with motion speed variance. Given a clip sampled from a
video, we use its past and future neighboring clips as the temporal context,
and reconstruct the two temporal transitions, i.e., present$\rightarrow$past
transition and present$\rightarrow$future transition, reflecting the temporal
information in different views. The proposed method exploits the two
transitions simultaneously by incorporating a bidirectional reconstruction
which consists of a backward reconstruction and a forward reconstruction. We
apply the proposed method to two challenging video tasks, i.e., complex event
detection and video captioning, in which it achieves state-of-the-art
performance. Notably, our method generates the best single feature for event
detection with a relative improvement of 10.4% on the MEDTest-13 dataset and
achieves the best performance in video captioning across all evaluation metrics
on the YouTube2Text dataset.
| arxiv topic:cs.CV |
arxiv_dataset-79461611.09153 | On the Eigenvalues of the ADER-WENO Galerkin Predictor
physics.comp-ph math.NA
ADER-WENO methods have proved extremely useful in obtaining arbitrarily
high-order solutions to problems involving hyperbolic systems of PDEs. For
example, it has been demonstrated that for the same computational cost as a
Runge-Kutta scheme of a certain order, one can obtain an ADER scheme of one
higher order of accuracy. Additionally, Runge-Kutta schemes suffer from the
presence of Butcher barriers, limiting the order of temporal accuracy that one
can comfortably achieve. There are no such limitations present in ADER-WENO
schemes.
The cumbersome analytical derivation of the temporal derivatives of the
solution required by the original ADER formulation has been replaced by the use
of a cell-wise local Galerkin predictor. The predictor can take either a
discontinuous or a continuous form. The Galerkin predictor is a high-order
polynomial reconstruction of the data in both space and time, found as the root
of a non-linear system.
It has been conjectured that the eigenvalues of certain matrices appearing in
these non-linear systems are always zero, leading to desirable system
properties for certain classes of PDEs. It is proved here that this is in deed
the case for any number of spatial dimensions and any desired order of
accuracy, for both the discontinuous and continuous Galerkin variants. This
result is independent of the choice of reconstruction basis polynomials.
| arxiv topic:physics.comp-ph math.NA |
arxiv_dataset-79471611.09253 | Amplitude analysis of $D^{0} \rightarrow \pi^{+} \pi^{-} \pi^{+}
\pi^{-}$ decays using CLEO-c data
hep-ex
The resonant substructure of the decay $D^{0} \rightarrow \pi^{+} \pi^{-}
\pi^{+} \pi^{-}$ is studied by performing a full five-dimensional amplitude
analysis. Preliminary results based on data collected by the CLEO-c detector
are presented. This is the largest dataset of $D^{0} \rightarrow \pi^{+}
\pi^{-} \pi^{+} \pi^{-}$ decays analysed in this way to-date. The two most
significant contributions are $D^{0} \rightarrow a_{1}(1260)^{+} \pi^{-}$ and
$D^{0} \rightarrow \rho(770)^{0}\rho(770)^{0}$. The line shape, mass and width
of the $a_{1}(1260)$ resonance are determined, and model-independent studies of
the line shapes of several resonant contributions are preformed.
| arxiv topic:hep-ex |
arxiv_dataset-79481611.09353 | Observational and Physical Classification of Supernovae
astro-ph.HE
This chapter describes the current classification scheme of supernovae (SNe).
This scheme has evolved over many decades and now includes numerous SN Types
and sub-types. Many of these are universally recognized, while there are
controversies regarding the definitions, membership and even the names of some
sub-classes; we will try to review here the commonly-used nomenclature, noting
the main variants when possible. SN Types are defined according to
observational properties; mostly visible-light spectra near maximum light, as
well as according to their photometric properties. However, a long-term goal of
SN classification is to associate observationally-defined classes with specific
physical explosive phenomena. We show here that this aspiration is now finally
coming to fruition, and we establish the SN classification scheme upon direct
observational evidence connecting SN groups with specific progenitor stars.
Observationally, the broad class of Type II SNe contains objects showing strong
spectroscopic signatures of hydrogen, while objects lacking such signatures are
of Type I, which is further divided to numerous subclasses. Recently a class of
super-luminous SNe (SLSNe, typically 10 times more luminous than standard
events) has been identified, and it is discussed. We end this chapter by
briefly describing a proposed alternative classification scheme that is
inspired by the stellar classification system. This system presents our
emerging physical understanding of SN explosions, while clearly separating
robust observational properties from physical inferences that can be debated.
This new system is quantitative, and naturally deals with events distributed
along a continuum, rather than being strictly divided into discrete classes.
Thus, it may be more suitable to the coming era where SN numbers will quickly
expand from a few thousands to millions of events.
| arxiv topic:astro-ph.HE |
arxiv_dataset-79491611.09453 | Time-dependent current into and through multilevel parallel quantum dots
in a photon cavity
cond-mat.mes-hall
We analyze theoretically the charging current into, and the transport current
through, a nanoscale two-dimensional electron system with two parallel quantum
dots embedded in a short wire placed in a photon cavity. A plunger gate is used
to place specific many-body states of the interacting system in the bias window
defined by the external leads. We show how the transport phenomena active in
the many-level complex central system strongly depend on the gate voltage. We
identify a resonant transport through the central system as the two spin
components of the one-electron ground state are in the bias window. This
resonant transport through the lowest energy electron states seems to a large
extent independent of the detuned photon field when judged from the transport
current. This could be expected in the small bias regime, but an observation of
the occupancy of the states of the system reveals that this picture is not
entirely true. The current does not reflect slower photon-active internal
transitions bringing the system into the steady state. The number of initially
present photons determines when the system reaches the real steady state. With
two-electron states in the bias window we observe a more complex situation with
intermediate radiative and nonradiative relaxation channels leading to a steady
state with a weak nonresonant current caused by inelastic tunneling through the
two-electron ground state of the system. The presence of the radiative channels
makes this phenomena dependent on the number of photons initially in the
cavity.
| arxiv topic:cond-mat.mes-hall |
arxiv_dataset-79501611.09553 | Galactic Chemical Evolution
astro-ph.GA
We analyze the evolution of oxygen abundance radial gradients resulting from
our chemical evolution models calculated with different prescriptions for the
star formation rate (SFR) and for the gas infall rate, in order to assess their
respective roles in shaping gradients. We also compare with cosmological
simulations and confront all with recent observational datasets, in particular
with abundances inferred from planetary nebulae. We demonstrate the critical
importance in isolating the specific radial range over which a gradient is
measured, in order for their temporal evolution to be useful indicators of disk
growth with redshift.
| arxiv topic:astro-ph.GA |
arxiv_dataset-79511611.09653 | Gauge fermions with flat bands and anomalous transport via chiral modes
from breaking gauge symmetry
cond-mat.mes-hall hep-th
The dispersionless longitudinal photon in Maxwell theory is thought of as a
redundant degree of freedom due to the gauge symmetry. We find that when there
exist exactly flat bands with zero energy in a condensed matter system, the
fermion field may locally transform as a gauge field and the system possesses a
gauge symmetry. As the longitudinal photon, the redundant degrees of freedom
from the flat bands must be gauged away from the physical states. As an
example, we study spinless fermions on a generalized Lieb lattice in three
dimensions. The flat band of the longitudinal fermion induces a gauge symmetry.
An external magnetic field breaks this gauge symmetry and emerges a bunch of
non-topologically chiral modes. Combining these emergent chiral modes with the
chiral anomaly mode which is of an opposite chirality, rich anomalous electric
transport phenomena exhibit and are expected to be observed in
Pd$_3$Bi$_2$S$_2$ and Ag$_3$Se$_2$Au.
| arxiv topic:cond-mat.mes-hall hep-th |
arxiv_dataset-79521611.09753 | The Atacama Cosmology Telescope: Two-Season ACTPol Lensing Power
Spectrum
astro-ph.CO
We report a measurement of the power spectrum of cosmic microwave background
(CMB) lensing from two seasons of Atacama Cosmology Telescope Polarimeter
(ACTPol) CMB data. The CMB lensing power spectrum is extracted from both
temperature and polarization data using quadratic estimators. We obtain results
that are consistent with the expectation from the best-fit Planck LCDM model
over a range of multipoles L=80-2100, with an amplitude of lensing A_lens =
1.06 +/- 0.15 (stat.) +/- 0.06 (sys.) relative to Planck. Our measurement of
the CMB lensing power spectrum gives sigma_8 Omega_m^0.25 = 0.643 +/- 0.054;
including baryon acoustic oscillation scale data, we constrain the amplitude of
density fluctuations to be sigma_8 = 0.831 +/- 0.053. We also update
constraints on the neutrino mass sum. We verify our lensing measurement with a
number of null tests and systematic checks, finding no evidence of significant
systematic errors. This measurement relies on a small fraction of the ACTPol
data already taken; more precise lensing results can therefore be expected from
the full ACTPol dataset.
| arxiv topic:astro-ph.CO |
arxiv_dataset-79531611.09853 | Magnetic field evolution in tidal disruption events
astro-ph.HE
When a star gets tidally disrupted by a supermassive black hole, its magnetic
field is expected to pervade its debris. In this paper, we study this process
via smoothed particle magnetohydrodynamical simulations of the disruption and
early debris evolution including the stellar magnetic field. As the gas
stretches into a stream, we show that the magnetic field evolution is strongly
dependent on its orientation with respect to the stretching direction. In
particular, an alignment of the field lines with the direction of stretching
induces an increase of the magnetic energy. For disruptions happening well
within the tidal radius, the star compression causes the magnetic field
strength to sharply increase by an order of magnitude at the time of pericentre
passage. If the disruption is partial, we find evidence for a dynamo process
occurring inside the surviving core due to the formation of vortices. This
causes an amplification of the magnetic field strength by a factor of $\sim
10$. However, this value represents a lower limit since it increases with
numerical resolution. For an initial field strength of 1 G, the magnetic field
never becomes dynamically important. Instead, the disruption of a star with a
strong 1 MG magnetic field produces a debris stream within which magnetic
pressure becomes similar to gas pressure a few tens of hours after disruption.
If the remnant of one or multiple partial disruptions is eventually fully
disrupted, its magnetic field could be large enough to magnetically power the
relativistic jet detected from Swift J1644+57. Magnetized streams could also be
significantly thickened by magnetic pressure when it overcomes the confining
effect of self-gravity.
| arxiv topic:astro-ph.HE |
arxiv_dataset-79541611.09953 | "Orphan" $\gamma$-ray Flares and Stationary Sheaths of Blazar Jets
astro-ph.HE
Blazars exhibit flares across the entire electromagnetic spectrum. Many
$\gamma$-ray flares are highly correlated with flares detected at longer
wavelengths; however, a small subset appears to occur in isolation, with little
or no correlated variability at longer wavelengths. These "orphan" $\gamma$-ray
flares challenge current models of blazar variability, most of which are unable
to reproduce this type of behavior. Macdonald et al. have developed the Ring of
Fire model to explain the origin of orphan $\gamma$-ray flares from within
blazar jets. In this model, electrons contained within a blob of plasma moving
relativistically along the spine of the jet inverse-Compton scatter synchrotron
photons emanating off of a ring of shocked sheath plasma that enshrouds the jet
spine. As the blob propagates through the ring, the scattering of the ring
photons by the blob electrons creates an orphan $\gamma$-ray flare. This model
was successfully applied to modeling a prominent orphan $\gamma$-ray flare
observed in the blazar PKS 1510$-$089. To further support the plausibility of
this model, Macdonald et al. presented a stacked radio map of PKS 1510$-$089
containing the polarimetric signature of a sheath of plasma surrounding the
spine of the jet. In this paper, we extend our modeling and stacking techniques
to a larger sample of blazars: 3C 273, 4C 71$.$01, 3C 279, 1055$+$018, CTA 102,
and 3C 345, the majority of which have exhibited orphan $\gamma$-ray flares. We
find that the model can successfully reproduce these flares, while our stacked
maps reveal the existence of jet sheaths within these blazars.
| arxiv topic:astro-ph.HE |
arxiv_dataset-79551611.10053 | Using Temporal and Semantic Developer-Level Information to Predict
Maintenance Activity Profiles
cs.SE
Predictive models for software projects' characteristics have been
traditionally based on project-level metrics, employing only little
developer-level information, or none at all. In this work we suggest novel
metrics that capture temporal and semantic developer-level information
collected on a per developer basis. To address the scalability challenges
involved in computing these metrics for each and every developer for a large
number of source code repositories, we have built a designated repository
mining platform. This platform was used to create a metrics dataset based on
processing nearly 1000 highly popular open source GitHub repositories,
consisting of 147 million LOC, and maintained by 30,000 developers. The
computed metrics were then employed to predict the corrective, perfective, and
adaptive maintenance activity profiles identified in previous works. Our
results show both strong correlation and promising predictive power with
R-squared values of 0.83, 0.64, and 0.75. We also show how these results may
help project managers to detect anomalies in the development process and to
build better development teams. In addition, the platform we built has the
potential to yield further predictive models leveraging developer-level metrics
at scale.
| arxiv topic:cs.SE |
arxiv_dataset-79561611.10153 | Tautological rings on Jacobian varieties of curves with automorphisms
math.AG
Let $J$ be the Jacobian of a smooth projective complex curve $C$ which admits
non-trivial automorphisms, and let $A(J)$ be the ring of algebraic cycles on
$J$ with rational coefficients modulo algebraic equivalence. We present new
tautological rings in $A(J)$ which extend in a natural way the tautological
ring studied by Beauville (Compos Math 140(3):683-688, 2004). We then show
there exist tautological rings induced on special complementary abelian
subvarieties of $J$.
| arxiv topic:math.AG |
arxiv_dataset-79571611.10253 | Learning Radio Resource Management in 5G Networks: Framework,
Opportunities and Challenges
cs.NI cs.IT math.IT math.OC
In the fifth generation (5G) of mobile broadband systems, Radio Resources
Management (RRM) will reach unprecedented levels of complexity. To cope with
the ever more sophisticated RRM functionalities and with the growing variety of
scenarios, while carrying out the prompt decisions required in 5G, this
manuscript presents a lean 5G RRM architecture that capitalizes on recent
advances in the field of machine learning in combination with the large amount
of data readily available in the network from measurements and system
observations. The architecture relies on a single general-purpose learning
framework conceived for RRM directly using the data gathered in the network.
The complexity of RRM is shifted to the design of the framework, whilst the RRM
algorithms derived from this framework are executed in a computationally
efficient distributed manner at the radio access nodes. The potential of this
approach is verified in a pair of pertinent scenarios and future directions on
applications of machine learning to RRM are discussed.
| arxiv topic:cs.NI cs.IT math.IT math.OC |
arxiv_dataset-79581611.10353 | Minimization of errors in narrowband laser phase noise measurements
based on reference measurement channels
physics.ins-det physics.data-an physics.optics
We propose a novel scheme for laser phase noise measurements with minimized
sensitivity to external fluctuations including interferometer vibration,
temperature instability, other low-frequency noise, and relative intensity
noise. In order to minimize the effect of these external fluctuations, we
employ simultaneous measurement of two spectrally separated channels in the
scheme. We present an algorithm for selection of the desired signal to extract
the phase noise. Experimental results demonstrate potential of the suggested
scheme for a wide range of technological applications.
| arxiv topic:physics.ins-det physics.data-an physics.optics |
arxiv_dataset-79591612.00091 | A homogeneous distance catalogue for Galactic RV Tauri objects
astro-ph.SR
A subset of Post-AGB (PAGB) objects are the highly luminous RV Tauri
variables that show similarities to Type-II Cepheids. By using a sample of
known RV Tauri stars from the Magellanic Clouds we are able to determine period
luminosity relationships (PLRs) in various bands that have been used to
determine the luminosities of their Galactic counterparts. We have gathered all
available photometry in order to generate an SED for each object and determine
the total integrated flux. This total flux combined with a calculated or
inferred intrinsic luminosity leads to a distance (Vickers et al. 2015). This
distance catalogue has allowed us to begin to constrain the physical parameters
of this poorly understood evolutionary phase and to determine links between
these physical characteristics as a function of their stellar population.
| arxiv topic:astro-ph.SR |
arxiv_dataset-79601612.00191 | Infinite algebraic subgroups of the real Cremona group
math.AG
We give the classification of the maximal infinite algebraic subgroups of the
real Cremona group of the plane up to conjugacy and present a parametrisation
space of each conjugacy class. Moreover, we show that the real plane Cremona
group is not generated by a countable union of its infinite algebraic
subgroups.
| arxiv topic:math.AG |
arxiv_dataset-79611612.00291 | Aggressive Quadrotor Flight through Narrow Gaps with Onboard Sensing and
Computing using Active Vision
cs.RO
We address one of the main challenges towards autonomous quadrotor flight in
complex environments, which is flight through narrow gaps. While previous works
relied on off-board localization systems or on accurate prior knowledge of the
gap position and orientation, we rely solely on onboard sensing and computing
and estimate the full state by fusing gap detection from a single onboard
camera with an IMU. This problem is challenging for two reasons: (i) the
quadrotor pose uncertainty with respect to the gap increases quadratically with
the distance from the gap; (ii) the quadrotor has to actively control its
orientation towards the gap to enable state estimation (i.e., active vision).
We solve this problem by generating a trajectory that considers geometric,
dynamic, and perception constraints: during the approach maneuver, the
quadrotor always faces the gap to allow state estimation, while respecting the
vehicle dynamics; during the traverse through the gap, the distance of the
quadrotor to the edges of the gap is maximized. Furthermore, we replan the
trajectory during its execution to cope with the varying uncertainty of the
state estimate. We successfully evaluate and demonstrate the proposed approach
in many real experiments. To the best of our knowledge, this is the first work
that addresses and achieves autonomous, aggressive flight through narrow gaps
using only onboard sensing and computing and without prior knowledge of the
pose of the gap.
| arxiv topic:cs.RO |
arxiv_dataset-79621612.00391 | Recovering the spacetime metric from a holographic dual
hep-th gr-qc
We review our recent proposal to use certain spatial cross-sections of the
boundary at infinity -- light-cone cuts -- to recover the conformal metric in
the bulk. We discuss some extensions of this work, including how to obtain the
conformal metric near the horizon of a collapsing black hole. We also show how
to obtain the conformal factor under certain conditions.
| arxiv topic:hep-th gr-qc |
arxiv_dataset-79631612.00491 | Gas Accretion and Giant Lyman-alpha Nebulae
astro-ph.GA astro-ph.CO
Several decades of observations and discoveries have shown that high-redshift
AGN and massive galaxies are often surrounded by giant Lyman-alpha nebulae
extending in some cases up to 500 kpc in size. In this review, I discuss the
properties of the such nebulae discovered at z>2 and their connection with gas
flows in and around the galaxies and their halos. In particular, I show how
current observations are used to constrain the physical properties and origin
of the emitting gas in terms of the Lyman-alpha photon production processes and
kinematical signatures. These studies suggest that recombination radiation is
the most viable scenario to explain the observed Lyman-alpha luminosities and
Surface Brightness for the large majority of the nebulae and imply that a
significant amount of dense, ionized and cold clumps should be present within
and around the halos of massive galaxies. Spectroscopic studies suggest that,
among the giant Lyman-alpha nebulae, the one associated with radio-loud AGN
should have kinematics dominated by strong, ionized outflows within at least
the inner 30-50 kpc. Radio-quiet nebulae instead present more quiescent
kinematics compatible with stationary situation and, in some cases, suggestive
of rotating structures. However, definitive evidences for accretion onto
galaxies of the gas associated with the giant Lyman-alpha emission are not
unambiguously detected yet. Deep surveys currently ongoing using other bright,
non-resonant lines such as Hydrogen H-alpha and HeII1640 will be crucial to
search for clearer signatures of cosmological gas accretion onto galaxies and
AGN.
| arxiv topic:astro-ph.GA astro-ph.CO |
arxiv_dataset-79641612.00591 | The Effect of Galactic Feedback on Gas Accretion and Wind Recycling
astro-ph.GA
In the absence of galactic winds, the rate at which gas accretes onto
galaxies is determined by the gravitational potential and by radiative cooling.
However, outflows driven by supernovae and active galactic nuclei not only
eject gas from galaxies, but also prevent gas from accreting in the first
place. Furthermore, gas previously ejected from a galaxy can re-accrete onto
(the same or a different) galaxy. Because this gas has a high metallicity, its
cooling rate is relatively high, which will increase its chances to re-accrete.
This complex interplay between gas inflows and outflows is discussed in this
chapter. Wind recycling is found to be an important process that fuels galaxies
at late times and the recycled gas has different properties than gas accreting
for the first time. Quantitative conclusions, however, vary between studies,
because the amount of wind recycling is dependent on the details of the
feedback model. We discuss these differences, known caveats, and ways to make
progress in understanding how galaxies are fed at low redshift.
| arxiv topic:astro-ph.GA |
arxiv_dataset-79651612.00691 | The quark propagator in QCD and $G_2$ QCD
hep-ph
QCD-like theories provide testing grounds for truncations of functional
equations at non-zero density, since comparisons with lattice results are
possible due to the absence of the sign problem. As a first step towards such a
comparison, we determine for QCD and $G_2$ QCD the chiral and
confinement/deconfinement transitions from the quark propagator Dyson-Schwinger
equation at zero chemical potential by calculating the chiral and dual chiral
condensates, respectively.
| arxiv topic:hep-ph |
arxiv_dataset-79661612.00791 | Kondo correlations formation and the local magnetic moment dynamics in
the Anderson model
cond-mat.mes-hall
We investigated the typical time scales of the Kondo correlations formation
for the single-state Anderson model, when coupling to the reservoir is switched
on at the initial time moment. The influence of the Kondo effect appearance on
the system non-stationary characteristics was analyzed and discussed.
| arxiv topic:cond-mat.mes-hall |
arxiv_dataset-79671612.00891 | Parameter Compression of Recurrent Neural Networks and Degradation of
Short-term Memory
cs.CV cs.LG cs.NE
The significant computational costs of deploying neural networks in
large-scale or resource constrained environments, such as data centers and
mobile devices, has spurred interest in model compression, which can achieve a
reduction in both arithmetic operations and storage memory. Several techniques
have been proposed for reducing or compressing the parameters for feed-forward
and convolutional neural networks, but less is understood about the effect of
parameter compression on recurrent neural networks (RNN). In particular, the
extent to which the recurrent parameters can be compressed and the impact on
short-term memory performance, is not well understood. In this paper, we study
the effect of complexity reduction, through singular value decomposition rank
reduction, on RNN and minimal gated recurrent unit (MGRU) networks for several
tasks. We show that considerable rank reduction is possible when compressing
recurrent weights, even without fine tuning. Furthermore, we propose a
perturbation model for the effect of general perturbations, such as a
compression, on the recurrent parameters of RNNs. The model is tested against a
noiseless memorization experiment that elucidates the short-term memory
performance. In this way, we demonstrate that the effect of compression of
recurrent parameters is dependent on the degree of temporal coherence present
in the data and task. This work can guide on-the-fly RNN compression for novel
environments or tasks, and provides insight for applying RNN compression in
low-power devices, such as hearing aids.
| arxiv topic:cs.CV cs.LG cs.NE |
arxiv_dataset-79681612.00991 | Ensembles of Generative Adversarial Networks
cs.CV
Ensembles are a popular way to improve results of discriminative CNNs. The
combination of several networks trained starting from different initializations
improves results significantly. In this paper we investigate the usage of
ensembles of GANs. The specific nature of GANs opens up several new ways to
construct ensembles. The first one is based on the fact that in the minimax
game which is played to optimize the GAN objective the generator network keeps
on changing even after the network can be considered optimal. As such ensembles
of GANs can be constructed based on the same network initialization but just
taking models which have different amount of iterations. These so-called self
ensembles are much faster to train than traditional ensembles. The second
method, called cascade GANs, redirects part of the training data which is badly
modeled by the first GAN to another GAN. In experiments on the CIFAR10 dataset
we show that ensembles of GANs obtain model probability distributions which
better model the data distribution. In addition, we show that these improved
results can be obtained at little additional computational cost.
| arxiv topic:cs.CV |
arxiv_dataset-79691612.01091 | A new rule for almost-certain termination of probabilistic- and demonic
programs
cs.LO
Extending our own and others' earlier approaches to reasoning about
termination of probabilistic programs, we propose and prove a new rule for
termination with probability one, also known as "almost-certain termination".
The rule uses both (non-strict) super martingales and guarantees of progress,
together, and it seems to cover significant cases that earlier methods do not.
In particular, it suffices for termination of the unbounded symmetric random
walk in both one- and two dimensions: for the first, we give a proof; for the
second, we use a theorem of Foster to argue that a proof exists.
Non-determinism (i.e. demonic choice) is supported; but we do currently
restrict to discrete distributions.
| arxiv topic:cs.LO |
arxiv_dataset-79701612.01191 | The study of massive stars with 50 Msun initial mass at different
evolutionary stages
astro-ph.SR
We will present results of studies of several massive stars at different
evolutionary stages, but with similar values of the initial mass: O-supergiants
belonging to association Cyg OB2, unique LBV/post-LBV - Romano's star and two
Wolf-Rayet stars - WR156 and FSZ35. All these stars have similar initial mass
of about 50 Msun. It allows us to consider them a single star at different
moments of life, and it gives an opportunity to track changes in the physical
parameters (such as effective temperature, luminosity, mass loss rate, wind
velocity) and chemical abundances during the life of a massive star. It is
important to test the current evolution theories of such objects.
| arxiv topic:astro-ph.SR |
arxiv_dataset-79711612.01291 | Models for the assessment of treatment improvement: the ideal and the
feasible
stat.ME
Comparisons of different treatments or production processes are the goals of
a significant fraction of applied research. Unsurprisingly, two-sample problems
play a main role in Statistics through natural questions such as `Is the the
new treatment significantly better than the old?'. However, this is only
partially answered by some of the usual statistical tools for this task. More
importantly, often practitioners are not aware of the real meaning behind these
statistical procedures. We analyze these troubles from the point of view of the
order between distributions, the stochastic order, showing evidence of the
limitations of the usual approaches, paying special attention to the classical
comparison of means under the normal model. We discuss the unfeasibility of
statistically proving stochastic dominance, but show that it is possible,
instead, to gather statistical evidence to conclude that slightly relaxed
versions of stochastic dominance hold.
| arxiv topic:stat.ME |
arxiv_dataset-79721612.01391 | Asymptotics for moments of certain cotangent sums for arbitrary
exponents
math.CA
In this paper we extend a result on the asymptotics of moments of certain
cotangent sums associated to the Estermann and Riemann zeta functions
established in a previous paper for integer exponents to arbitrary positive
real exponents.
| arxiv topic:math.CA |
arxiv_dataset-79731612.01491 | Enabling Bio-Plausible Multi-level STDP using CMOS Neurons with
Dendrites and Bistable RRAMs
cs.ET cs.NE
Large-scale integration of emerging nanoscale non-volatile memory devices,
e.g. resistive random-access memory (RRAM), can enable a new generation of
neuromorphic computers that can solve a wide range of machine learning
problems. Such hybrid CMOS-RRAM neuromorphic architectures will result in
several orders of magnitude reduction in energy consumption at a very small
form factor, and herald autonomous learning machines capable of self-adapting
to their environment. However, the progress in this area has been impeded from
the realization that the actual memory devices fall well short of their
expected behavior. In this work, we discuss the challenges associated with
these memory devices and their use in neuromorphic computing circuits, and
propose pathways to overcome these limitations by introducing 'dendritic
learning'.
| arxiv topic:cs.ET cs.NE |
arxiv_dataset-79741612.01591 | Neutrino oscillations in dense matter
hep-ph
We propose a modification of the electroweak theory, where the fermions with
the same electroweak quantum numbers are combined in multiplets and are treated
as different quantum states of a single particle. The developed approach
enables one to calculate the probabilities of the processes taking place in the
detector at long distances from the particle source. Calculations of
higher-order processes including the computation of the contributions due to
radiative corrections can be performed in the framework of the perturbation
theory using the regular diagram technique. As a result, we obtain the analog
to the Dirac--Schwinger equation of quantum electrodynamics describing neutrino
oscillations and its spin rotation in dense matter.
| arxiv topic:hep-ph |
arxiv_dataset-79751612.01691 | Fleet Size and Mix Split-Delivery Vehicle Routing
cs.AI
In the classic Vehicle Routing Problem (VRP) a fleet of of vehicles has to
visit a set of customers while minimising the operations' costs. We study a
rich variant of the VRP featuring split deliveries, an heterogeneous fleet, and
vehicle-commodity incompatibility constraints. Our goal is twofold: define the
cheapest routing and the most adequate fleet.
To do so, we split the problem into two interdependent components: a fleet
design component and a routing component. First, we define two Mixed Integer
Programming (MIP) formulations for each component. Then we discuss several
improvements in the form of valid cuts and symmetry breaking constraints.
The main contribution of this paper is a comparison of the four resulting
models for this Rich VRP. We highlight their strengths and weaknesses with
extensive experiments.
Finally, we explore a lightweight integration with Constraint Programming
(CP). We use a fast CP model which gives good solutions and use the solution to
warm-start our models.
| arxiv topic:cs.AI |
arxiv_dataset-79761612.01791 | Method for estimating cycle lengths from multidimensional time series:
Test cases and application to a massive "in silico" dataset
astro-ph.SR astro-ph.IM stat.AP
Many real world systems exhibit cyclic behavior that is, for example, due to
the nearly harmonic oscillations being perturbed by the strong fluctuations
present in the regime of significant non-linearities. For the investigation of
such sys- tems special techniques relaxing the assumption to periodicity are
required. In this paper, we present the generalization of one of such
techniques, namely the D2 phase dispersion statistic, to multidimensional
datasets, especially suited for the analysis of the outputs from
three-dimensional numerical simulations of the full magnetohydrodynamic
equations. We present the motivation and need for the usage of such a method
with simple test cases, and present an application to a solar-like semi-global
numerical dynamo simulation covering nearly 150 magnetic cycles.
| arxiv topic:astro-ph.SR astro-ph.IM stat.AP |
arxiv_dataset-79771612.01891 | Controlled growth of CH$_3$NH$_3$PbI$_3$ nanowires in arrays of open
nanofluidic channels
cond-mat.mes-hall
Spatial positioning of nanocrystal building blocks on a solid surface is a
prerequisite for assembling individual nanoparticles into functional devices.
Here, we report on the graphoepitaxial liquid-solid growth of nanowires of the
photovoltaic compound CH$_3$NH$_3$PbI$_3$ in open nanofluidic channels. The
guided growth, visualized in real-time with a simple optical microscope,
undergoes through a metastable solvatomorph formation in polar aprotic
solvents. The presently discovered crystallization leads to the fabrication of
mm2-sized surfaces composed of perovskite nanowires having controlled sizes,
cross-sectional shapes, aspect ratios and orientation which have not been
achieved thus far by other deposition methods. The automation of this general
strategy paves the way towards fabrication of wafer-scale perovskite nanowire
thin films well-suited for various optoelectronic devices, e.g. solar cells,
lasers, light-emitting diodes and photodetectors.
| arxiv topic:cond-mat.mes-hall |
arxiv_dataset-79781612.01991 | Diverse Sampling for Self-Supervised Learning of Semantic Segmentation
cs.CV
We propose an approach for learning category-level semantic segmentation
purely from image-level classification tags indicating presence of categories.
It exploits localization cues that emerge from training classification-tasked
convolutional networks, to drive a "self-supervision" process that
automatically labels a sparse, diverse training set of points likely to belong
to classes of interest. Our approach has almost no hyperparameters, is modular,
and allows for very fast training of segmentation in less than 3 minutes. It
obtains competitive results on the VOC 2012 segmentation benchmark. More,
significantly the modularity and fast training of our framework allows new
classes to efficiently added for inference.
| arxiv topic:cs.CV |
arxiv_dataset-79791612.02091 | Coherent back and forward scattering peaks in the quantum kicked rotor
cond-mat.quant-gas
We propose and analyze an experimental scheme using the quantum kicked rotor
to observe the newly-predicted coherent forward scattering peak together with
its long-known twin brother, the coherent backscattering peak. Contrary to
coherent backscattering, which arises already under weak-localization
conditions, coherent forward scattering is only triggered by Anderson or strong
localization. So far, coherent forward scattering has not been observed in
conservative systems with elastic scattering by spatial disorder. We propose to
turn to the quantum kicked rotor, which has a long and succesful history as an
accurate experimental platform to observe dynamical localization, i.e.,
Anderson localization in momentum space. We analyze the coherent forward
scattering effect for the quantum kicked rotor by extensive numerical
simulations, both in the orthogonal and unitary class of disordered quantum
systems, and show that an experimental realization involving phase-space
rotation techniques is within reach of state-of-the-art cold-atom experiments.
| arxiv topic:cond-mat.quant-gas |
arxiv_dataset-79801612.02191 | Biphoton states in correlated turbulence
quant-ph physics.optics
The effect of turbulence on a pair of photons propagating together through
the same medium is analyzed. The behavior is compared to the case where these
photons propagate separately through different turbulent media. The analysis is
done with a multiple phase screen approach, by deriving and solving an
infinitesimal propagation equation. We apply these results to the case where
the initial photons are entangled in their spatial degrees of freedom with the
aid of spontaneous parametric down-conversion. It is found that for this input
state, the decay of entanglement in correlated media under the weak
scintillation approximation is quicker than in uncorrelated media. Beyond the
weak scintillation approximation, the entanglement in correlated media decays
slower when it is close to zero --- approaching zero asymptotically as a
function of scintillation strength. This is contrary to the case in
uncorrelated media where entanglement becomes zero at a finite scintillation
strength.
| arxiv topic:quant-ph physics.optics |
arxiv_dataset-79811612.02291 | Renormalization for singular-potential scattering
quant-ph hep-th math-ph math.MP
In the calculation of quantum-mechanical singular-potential scattering, one
encounters divergence. We suggest three renormalization schemes, dimensional
renormalization, analytic continuation approach, and minimal-subtraction scheme
to remove the divergence.
| arxiv topic:quant-ph hep-th math-ph math.MP |
arxiv_dataset-79821612.02391 | Semi-Supervised linear regression
math.ST stat.TH
We study a regression problem where for some part of the data we observe both
the label variable ($Y$) and the predictors (${\bf X}$), while for other part
of the data only the predictors are given. Such a problem arises, for example,
when observations of the label variable are costly and may require a skilled
human agent. When the conditional expectation $E[Y | {\bf X}]$ is not exactly
linear, one can consider the best linear approximation to the conditional
expectation, which can be estimated consistently by the least squares estimates
(LSE). The latter depends only on the labeled data. We suggest improved
alternative estimates to the LSE that use also the unlabeled data. Our
estimation method can be easily implemented and has simply described asymptotic
properties.The new estimates asymptotically dominate the usual standard
procedures under certain non-linearity condition of $E[Y | {\bf X}]$;
otherwise, they are asymptotically equivalent.The performance of the new
estimator for small sample size is investigated in an extensive simulation
study. A real data example of inferring homeless population is used to
illustrate the new methodology.
| arxiv topic:math.ST stat.TH |
arxiv_dataset-79831612.02491 | Rethinking the Experiment
q-bio.OT
The crisis in the reproducibility of experiments invites a re-evaluation of
methods of inquiry and validation procedures. The text challenges current
assumptions of knowledge acquisition and introduces G-complexity for defining
decidable vs. non-decidable knowledge domains. A "second Cartesian revolution,"
informed by and in awareness of anticipatory processes, should result in
scientific methods that transcend determinism and reductionism. Physics and
physics-based disciplines convincingly ascertained themselves by adequately
describing the non-living. A complementary perspective should account for the
specific causality characteristic of life by integrating past, present, and
future. Knowledge about anticipatory processes facilitates attainment of this
goal. Society cannot afford the dead-end street of reductionism. Science,
itself an expression of anticipatory activity, makes possible in our days
alternative understandings of reality and its dynamics.
| arxiv topic:q-bio.OT |
arxiv_dataset-79841612.02591 | The Auslander-Reiten duality via morphisms determined by objects
math.RT
Given an exact category $\mathcal{C}$, we denote by $\mathcal{C}_l$ the
smallest additive subcategory containing injectives and indecomposable objects
which appear as the first term of an almost split conflation. We prove that a
deflation is right determined by some object if and only if its intrinsic
kernel lies in $\mathcal{C}_l$. We give characterizations for $\mathcal{C}$
having Auslander-Reiten duality.
| arxiv topic:math.RT |
arxiv_dataset-79851612.02691 | Exotic Dual of Type II Double Field Theory
hep-th
We perform an exotic dualization of the Ramond-Ramond fields in type II
double field theory, in which they are encoded in a Majorana-Weyl spinor of
O(D,D). Starting from a first-order master action, the dual theory in terms of
a tensor-spinor of O(D,D) is determined. This tensor-spinor is subject to an
exotic version of the (self-)duality constraint needed for a democratic
formulation. We show that in components, reducing O(D,D) to GL(D), one obtains
the expected exotically dual theory in terms of mixed Young tableaux fields. To
this end, we generalize exotic dualizations to self-dual fields, such as the
4-form in type IIB string theory.
| arxiv topic:hep-th |
arxiv_dataset-79861612.02791 | Unitary Correlation Sets
math.OA
The unitary correlation sets defined by the first author in conjunction with
tensor products of $\mathcal{U}_{nc}(n)$ are further studied. We show that
Connes' embedding problem is equivalent to deciding whether or not two smaller
versions of the unitary correlation sets are equal. Moreover, we obtain the
result that Connes' embedding problem is equivalent to deciding whether or not
two cross norms on $M_n \otimes M_n$ are equal for all $n \geq 2$.
| arxiv topic:math.OA |
arxiv_dataset-79871612.02891 | Theoretical Origin of CP violation in the FCNC-free 2HDM and Its
Extensions to the Standard Model and 3HDM
hep-ph
In this manuscript, a general FCNC-free and CP-violating pattern of
quark-mass matrices in the 2HDM derived in our previous investigations is
revised. This revised pattern is to be diagonalized analytically with no
symmetries imposed. The unitary transformation matrices thus derived depend on
only two parameters in each quark type and subsequently lead to a CKM matrix
which depends on at most four parameters. The fitting of theoretically derived
CKM elements and their corresponding empirical values are as good as ${\bf
O}(10^{-2})$ at tree-level. In a phenomenological way which imposes several
fine-tuning parameters into the CKM matrix suitably, the fitting is further
improved to ${\bf O}(10^{-4})$. After the derivation, we find this hypothesis
also applies to the Standard Model and even a model with three Higgs doublets.
This will be a big progress in the derivation of a theoretical origin of CP
violation.
| arxiv topic:hep-ph |
arxiv_dataset-79881612.02991 | Weak Galactic Halo--Fornax dSph Connection from RR Lyrae Stars
astro-ph.GA
For the first time accurate pulsation properties of the ancient variable
stars of the Fornax dwarf spheroidal galaxy (dSph) are discussed in the broad
context of galaxy formation and evolution. Homogeneous multi-band $BVI$ optical
photometry of spanning {\it twenty} years has allowed us to identify and
characterize more than 1400 RR Lyrae stars (RRLs) in this galaxy. Roughly 70\%
are new discoveries. We investigate the period-amplitude distribution and find
that Fornax shows a lack of High Amplitude (A$_V\gsim$0.75 mag) Short Period
fundamental-mode RRLs (P$\lsim$0.48 d, HASPs). These objects occur in stellar
populations more metal-rich than [Fe/H]$\sim$-1.5 and they are common in the
Galactic halo (Halo) and in globulars. This evidence suggests that old (age
older than 10 Gyr) Fornax stars are relatively metal-poor.
A detailed statistical analysis of the role of the present-day Fornax dSph in
reproducing the Halo period distribution shows that it can account for only a
few to 20\% of the Halo when combined with RRLs in massive dwarf galaxies
(Sagittarius dSph, Large Magellanic Cloud). This finding indicates that
Fornax-like systems played a minor role in building up the Halo when compared
with massive dwarfs. We also discuss the occurrence of HASPs in connection with
the luminosity and the early chemical composition of nearby dwarf galaxies. We
find that, independently of their individual star formation histories, bright
(M$_V\lsim$-13.5 mag) galaxies have HASPs, whereas faint ones (M$_V\gsim$-11
mag) do not. Interestingly enough, Fornax belongs to a luminosity range
(--11$<$M$_V<$--13.5 mag) in which the occurrence of HASPs appears to be
correlated with the early star formation and chemical enrichment of the host
galaxy.
| arxiv topic:astro-ph.GA |
arxiv_dataset-79891612.03091 | Characterization of the inner disk around HD 141569 A from Keck/NIRC2
L-band vortex coronagraphy
astro-ph.SR astro-ph.EP astro-ph.IM
HD 141569 A is a pre-main sequence B9.5 Ve star surrounded by a prominent and
complex circumstellar disk, likely still in a transition stage from
protoplanetary to debris disk phase. Here, we present a new image of the third
inner disk component of HD 141569 A made in the L' band (3.8 micron) during the
commissioning of the vector vortex coronagraph recently installed in the
near-infrared imager and spectrograph NIRC2 behind the W.M. Keck Observatory
Keck II adaptive optics system. We used reference point spread function
subtraction, which reveals the innermost disk component from the inner working
distance of $\simeq 23$ AU and up to $\simeq 70$ AU. The spatial scale of our
detection roughly corresponds to the optical and near-infrared scattered light,
thermal Q, N and 8.6 micron PAH emission reported earlier. We also see an
outward progression in dust location from the L'-band to the H-band (VLT/SPHERE
image) to the visible (HST/STIS image), likely indicative of dust blowout. The
warm disk component is nested deep inside the two outer belts imaged by HST
NICMOS in 1999 (respectively at 406 and 245 AU). We fit our new L'-band image
and spectral energy distribution of HD 141569 A with the radiative transfer
code MCFOST. Our best-fit models favor pure olivine grains, and are consistent
with the composition of the outer belts. While our image shows a putative
very-faint point-like clump or source embedded in the inner disk, we did not
detect any true companion within the gap between the inner disk and the first
outer ring, at a sensitivity of a few Jupiter masses.
| arxiv topic:astro-ph.SR astro-ph.EP astro-ph.IM |
arxiv_dataset-79901612.03191 | Multiparty testing preorders
cs.LO
Variants of the must testing approach have been successfully applied in
service oriented computing for analysing the compliance between (contracts
exposed by) clients and servers or, more generally, between two peers. It has
however been argued that multiparty scenarios call for more permissive notions
of compliance because partners usually do not have full coordination
capabilities. We propose two new testing preorders, which are obtained by
restricting the set of potential observers. For the first preorder, called
uncoordinated, we allow only sets of parallel observers that use different
parts of the interface of a given service and have no possibility of
intercommunication. For the second preorder, that we call individualistic, we
instead rely on parallel observers that perceive as silent all the actions that
are not in the interface of interest. We have that the uncoordinated preorder
is coarser than the classical must testing preorder and finer than the
individualistic one. We also provide a characterisation in terms of decorated
traces for both preorders: the uncoordinated preorder is defined in terms of
must-sets and Mazurkiewicz traces while the individualistic one is described in
terms of classes of filtered traces that only contain designated visible
actions and must-sets.
| arxiv topic:cs.LO |
arxiv_dataset-79911612.03291 | $\tau^-\to\eta^{(\prime)}\pi^-\nu_\tau \gamma$ decays as backgrounds in
the search for second class currents
hep-ph hep-ex
Observation of $\tau^-\to\eta^{(\prime)}\pi^-\nu_\tau $ decays at Belle-II
would indicate either a manifestation of isospin symmetry breaking or genuine
second class currents (SCC) effects. The corresponding radiative
$\tau^-\to\eta^{(\prime)}\pi^-\nu_\tau \gamma$ decay channels are not
suppressed by $G$-parity considerations and may represent a serious background
in searches of SCC in the former. We compute the observables associated to
these radiative decays using Resonance Chiral Lagrangians and conclude that
vetoing photons with $E_\gamma>100$ MeV should get rid of this background in
the Belle-II environment searching for the $\tau^-\to\eta \pi^-\nu_\tau $
channel. Similar considerations hold inconclusive for decays involving the
$\eta^\prime$ given the theory uncertainties in the prediction of the
$\tau^-\to\eta^\prime\pi^-\nu_\tau$ branching ratio. Still, additional
kinematics-based cuts should be able to suppress this background in the
$\eta^\prime$ case to a negligible level.
| arxiv topic:hep-ph hep-ex |
arxiv_dataset-79921612.03391 | Massive Neutral Gas Outflow in Reddened Quasar SDSS J072910.34+333634.3
astro-ph.GA
SDSS J072910.34+333634.3 is a reddened quasar at z=0.96. The archivel
Keck/ESI spectrum and our new P200/TripleSpec spectrum reveal an absorption
line system in He I*, Ca II H\&K and Na ID. The absorption line system has a
width of $\sim$600 km/s and a blueshift velocity of $\sim$800 km/s relative to
the core of narrow emission lines, indicating an outflow. Using the Ca II
doublet, we determined that the outflowing gas covers $\sim$70\% of the
continuum. On the other hand, the HST/ACS image which taken in rest-frame 4130
\AA\ show that the fraction of the quasar emission in ESI aperture was $<$40\%.
We thus conclude that the absorbing gas covers a significant fraction of
extended starlight emission, and the best-estimated fraction of $\sim$50\%
yields a lower limit of the crosssectional area of the outflowing gas to be
$>$8 kpc$^2$. The strong Na\&Ca absorption suggests that the absorbing gas is
thick and mostly neutral, which is also supported by dust extinction
$A_V\sim3$. Using the best-estimated hydrogen column density
$N_H\sim3\times10^{22}$ cm$^{-2}$, the total mass of the outflowing gas is
$>3\times10^9 M_\odot$. The outflow is likely to be driven by AGN because of
the $\sim$800 km/s blueshift velocity, suggesting SDSS J072910.34+333634.3 is
undergoing one of the most violent AGN feedback we have seen. In the future,
one can find more such massive neutral gas outflows in other reddened quasars
using similar method, and this can shed new light on the study of AGN feedback.
| arxiv topic:astro-ph.GA |
arxiv_dataset-79931612.03491 | A counterexample to the easy direction of the geometric Gersten
conjecture
math.GR
For finitely generated groups H and G, equipped with word metrics, a
translation-like action of H on G is a free action such that each element of H
acts by a map which has finite distance from the identity map in the uniform
metric. For example, if H is a subgroup of G, then right translation by
elements of H yields a translation-like action of H on G. Whyte asked whether a
group with no translation-like action by a Baumslag-Solitar group must be
hyperbolic, where the free abelian group of rank 2 is understood to be a
Baumslag-Solitar group. We show that the converse of this conjecture is false,
and in particular the fundamental group of a closed hyperbolic 3-manifold
admits a translation-like action by the free abelian group of rank 2.
| arxiv topic:math.GR |
arxiv_dataset-79941612.03591 | Physical Contact between the +20 km/s Cloud and the Galactic
Circumnuclear Disk
astro-ph.GA
This paper reports the discovery of evidence for physical contact between the
Galactic circumnuclear disk (CND) and an exterior giant molecular cloud. The
central 10 pc of our Galaxy has been imaged in the HCN J=1-0, HCO+ J=1-0, CS
J=2-1, H13CN J=1-0, SiO J=2-1, SO N_J=2_3-1_2, and HC3N J=11-10 lines using the
Nobeyama Radio Observatory 45 m radio telescope. Based on our examination of
the position-velocity maps of several high-density probe lines, we have found
that an emission "bridge" may be connecting the +20 km/s cloud (M-0.13-0.08)
and the negative-longitude extension of the CND. Analyses of line intensity
ratios imply that the chemical property of the bridge is located between the
+20 km/s cloud and the CND. We introduce a new interpretation that a part of
the CND may be colliding with the 20 km/s cloud and the collision may be
responsible for the formation of the bridge. Such collisional events could
promote mass accretion onto the CND or into the inner ionized cavity, which may
be further tested by proper motion studies.
| arxiv topic:astro-ph.GA |
arxiv_dataset-79951612.03691 | Characterizing the path-independent property of the Girsanov density for
degenerated stochastic differential equations
math.PR
In this paper, we derive a characterization theorem for the path-independent
property of the density of the Girsanov transformation for {\it degenerated}
stochastic differential equations (SDEs), extending the characterization
theorem of \cite{twwy} for the non-degenerated SDEs. We further extends our
consideration to non-Lipschitz SDEs with jumps and with degenerated diffusion
coefficients, which generalizes the corresponding characterization theorem
established in \cite{hqwu}.
| arxiv topic:math.PR |
arxiv_dataset-79961612.03791 | Neural Machine Translation by Minimising the Bayes-risk with Respect to
Syntactic Translation Lattices
cs.CL
We present a novel scheme to combine neural machine translation (NMT) with
traditional statistical machine translation (SMT). Our approach borrows ideas
from linearised lattice minimum Bayes-risk decoding for SMT. The NMT score is
combined with the Bayes-risk of the translation according the SMT lattice. This
makes our approach much more flexible than $n$-best list or lattice rescoring
as the neural decoder is not restricted to the SMT search space. We show an
efficient and simple way to integrate risk estimation into the NMT decoder
which is suitable for word-level as well as subword-unit-level NMT. We test our
method on English-German and Japanese-English and report significant gains over
lattice rescoring on several data sets for both single and ensembled NMT. The
MBR decoder produces entirely new hypotheses far beyond simply rescoring the
SMT search space or fixing UNKs in the NMT output.
| arxiv topic:cs.CL |
arxiv_dataset-79971612.03891 | Loops in AdS from Conformal Field Theory
hep-th
We propose and demonstrate a new use for conformal field theory (CFT)
crossing equations in the context of AdS/CFT: the computation of loop
amplitudes in AdS, dual to non-planar correlators in holographic CFTs. Loops in
AdS are largely unexplored, mostly due to technical difficulties in direct
calculations. We revisit this problem, and the dual $1/N$ expansion of CFTs, in
two independent ways. The first is to show how to explicitly solve the crossing
equations to the first subleading order in $1/N^2$, given a leading order
solution. This is done as a systematic expansion in inverse powers of the spin,
to all orders. These expansions can be resummed, leading to the CFT data for
finite values of the spin. Our second approach involves Mellin space. We show
how the polar part of the four-point, loop-level Mellin amplitudes can be fully
reconstructed from the leading-order data. The anomalous dimensions computed
with both methods agree. In the case of $\phi^4$ theory in AdS, our crossing
solution reproduces a previous computation of the one-loop bubble diagram. We
can go further, deriving part of the four-point function in $\phi^3+\phi^4$
theory in AdS which had never been computed. In the process, we show how to
analytically derive anomalous dimensions from Mellin amplitudes with an
infinite series of poles, and discuss applications to more complicated cases
such as the ${\cal N}=4$ super-Yang-Mills theory.
| arxiv topic:hep-th |
arxiv_dataset-79981612.03991 | Performance Improvements of Probabilistic Transcript-adapted ASR with
Recurrent Neural Network and Language-specific Constraints
cs.CL
Mismatched transcriptions have been proposed as a mean to acquire
probabilistic transcriptions from non-native speakers of a language.Prior work
has demonstrated the value of these transcriptions by successfully adapting
cross-lingual ASR systems for different tar-get languages. In this work, we
describe two techniques to refine these probabilistic transcriptions: a
noisy-channel model of non-native phone misperception is trained using a
recurrent neural net-work, and decoded using minimally-resourced
language-dependent pronunciation constraints. Both innovations improve quality
of the transcript, and both innovations reduce phone error rate of a
trainedASR, by 7% and 9% respectively
| arxiv topic:cs.CL |
arxiv_dataset-79991612.04091 | Identifiability issues of age-period and age-period-cohort models of the
Lee-Carter type
stat.AP
The predominant way of modelling mortality rates is the Lee-Carter model and
its many extensions. The Lee-Carter model and its many extensions use a latent
process to forecast. These models are estimated using a two-step procedure that
causes an inconsistent view on the latent variable. This paper considers
identifiability issues of these models from a perspective that acknowledges the
latent variable as a stochastic process from the beginning. We call this
perspective the plug-in age-period or plug-in age-period-cohort model. Defining
a parameter vector that includes the underlying parameters of this process
rather than its realisations, we investigate whether the expected values and
covariances of the plug-in Lee-Carter models are identifiable. It will be seen,
for example, that even if in both steps of the estimation procedure we have
identifiability in a certain sense it does not necessarily carry over to the
plug-in models.
| arxiv topic:stat.AP |
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