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arxiv_dataset-91001711.0299 | On the height of Gross-Schoen cycles in genus three
math.NT math.AG
We show that there exists a sequence of genus three curves defined over the
rationals in which the height of a canonical Gross-Schoen cycle tends to
infinity.
| arxiv topic:math.NT math.AG |
arxiv_dataset-91011711.0309 | Bulk characterization of topological crystalline insulators: stability
under interactions and relations to symmetry enriched U(1) quantum spin
liquids
cond-mat.str-el cond-mat.mes-hall hep-th
Topological crystalline insulators (TCIs) are nontrivial quantum phases of
matter protected by crystalline (and other) symmetries. They are originally
predicted by band theories, so an important question is their stability under
interactions. In this paper, by directly studying the physical bulk properties
of several band-theory-based nontrivial TCIs that are conceptually interesting
and/or experimentally feasible, we show they are stable under interactions.
These TCIs include (1) a weak topological insulator, (2) a TCI with a mirror
symmetry and its time-reversal symmetric generalizations, (3) a doubled
topological insulator with a mirror symmetry, and (4) two TCIs with
symmetry-enforced-gapless surfaces. We describe two complementary methods that
allow us to determine the properties of the magnetic monopoles obtained by
coupling these TCIs to a U(1) gauge field. These methods involve studying
different types of surface states of these TCIs. Applying these methods to our
examples, we find all of them have nontrivial monopoles, which proves their
stability under interactions. Furthermore, we discuss two levels of relations
between these TCIs and symmetry enriched U(1) quantum spin liquids (QSLs).
First, these TCIs are directly related to U(1) QSLs with crystalline
symmetries. Second, there is an interesting correspondence between U(1) QSLs
with crystalline symmetries and U(1) QSLs with internal symmetries. In
particular, the TCIs with symmetry-enforced-gapless surfaces are related to the
"fractional topological paramagnets" introduced in Ref. 1 by Zou et al.
| arxiv topic:cond-mat.str-el cond-mat.mes-hall hep-th |
arxiv_dataset-91021711.0319 | Learning Credible Models
cs.LG stat.ML
In many settings, it is important that a model be capable of providing
reasons for its predictions (i.e., the model must be interpretable). However,
the model's reasoning may not conform with well-established knowledge. In such
cases, while interpretable, the model lacks \textit{credibility}. In this work,
we formally define credibility in the linear setting and focus on techniques
for learning models that are both accurate and credible. In particular, we
propose a regularization penalty, expert yielded estimates (EYE), that
incorporates expert knowledge about well-known relationships among covariates
and the outcome of interest. We give both theoretical and empirical results
comparing our proposed method to several other regularization techniques.
Across a range of settings, experiments on both synthetic and real data show
that models learned using the EYE penalty are significantly more credible than
those learned using other penalties. Applied to a large-scale patient risk
stratification task, our proposed technique results in a model whose top
features overlap significantly with known clinical risk factors, while still
achieving good predictive performance.
| arxiv topic:cs.LG stat.ML |
arxiv_dataset-91031711.0329 | Scalable and fast heterogeneous molecular simulation with predictive
parallelization schemes
physics.comp-ph cond-mat.soft
Multiscale and inhomogeneous molecular systems are challenging topics in the
field of molecular simulation. In particular, modeling biological systems in
the context of multiscale simulations and exploring material properties are
driving a permanent development of new simulation methods and optimization
algorithms. In computational terms, those methods require parallelization
schemes that make a productive use of computational resources for each
simulation and from its genesis. Here, we introduce the heterogeneous domain
decomposition approach which is a combination of an heterogeneity sensitive
spatial domain decomposition with an \textit{a priori} rearrangement of
subdomain-walls. Within this approach, the theoretical modeling and
scaling-laws for the force computation time are proposed and studied as a
function of the number of particles and the spatial resolution ratio. We also
show the new approach capabilities, by comparing it to both static domain
decomposition algorithms and dynamic load balancing schemes. Specifically, two
representative molecular systems have been simulated and compared to the
heterogeneous domain decomposition proposed in this work. These two systems
comprise an adaptive resolution simulation of a biomolecule solvated in water
and a phase separated binary Lennard-Jones fluid.
| arxiv topic:physics.comp-ph cond-mat.soft |
arxiv_dataset-91041711.0339 | Evasion of No-Hair Theorems and Novel Black-Hole Solutions in
Gauss-Bonnet Theories
hep-th gr-qc
We consider a general Einstein-scalar-GB theory with a coupling function
f(\phi). We demonstrate that black-hole solutions appear as a generic feature
of this theory since a regular horizon and an asymptotically-flat solution may
be easily constructed under mild assumptions for f(\phi). We show that the
existing no-hair theorems are easily evaded, and a large number of regular,
black-hole solutions with scalar hair are then presented for a plethora of
coupling functions f(\phi).
| arxiv topic:hep-th gr-qc |
arxiv_dataset-91051711.0349 | Debris Disc Constraints on Planetesimal Formation
astro-ph.EP
Two basic routes for planetesimal formation have been proposed over the last
few decades. One is a classical "slow-growth" scenario. Another one is particle
concentration models, in which small pebbles are concentrated locally and then
collapse gravitationally to form planetesimals. Both types of models make
certain predictions for the size spectrum and internal structure of newly-born
planetesimals. We use these predictions as input to simulate collisional
evolution of debris discs left after the gas dispersal. The debris disc
emission as a function of a system's age computed in these simulations is
compared with several Spitzer and Herschel debris disc surveys around A-type
stars. We confirm that the observed brightness evolution for the majority of
discs can be reproduced by classical models. Further, we find that it is
equally consistent with the size distribution of planetesimals predicted by
particle concentration models - provided the objects are loosely bound "pebble
piles" as these models also predict. Regardless of the assumed planetesimal
formation mechanism, explaining the brightest debris discs in the samples
uncovers a "disc mass problem." To reproduce such discs by collisional
simulations, a total mass of planetesimals of up to ~1000 Earth masses is
required, which exceeds the total mass of solids available in the
protoplanetary progenitors of debris discs. This may indicate that stirring was
delayed in some of the bright discs, that giant impacts occurred recently in
some of them, that some systems may be younger than previously thought, or that
non-collisional processes contribute significantly to the dust production.
| arxiv topic:astro-ph.EP |
arxiv_dataset-91061711.0359 | Fast matrix-free evaluation of discontinuous Galerkin finite element
operators
cs.MS cs.NA math.NA
We present an algorithmic framework for matrix-free evaluation of
discontinuous Galerkin finite element operators based on sum factorization on
quadrilateral and hexahedral meshes. We identify a set of kernels for fast
quadrature on cells and faces targeting a wide class of weak forms originating
from linear and nonlinear partial differential equations. Different algorithms
and data structures for the implementation of operator evaluation are compared
in an in-depth performance analysis. The sum factorization kernels are
optimized by vectorization over several cells and faces and an even-odd
decomposition of the one-dimensional compute kernels. In isolation our
implementation then reaches up to 60\% of arithmetic peak on Intel Haswell and
Broadwell processors and up to 50\% of arithmetic peak on Intel Knights
Landing. The full operator evaluation reaches only about half that throughput
due to memory bandwidth limitations from loading the input and output vectors,
MPI ghost exchange, as well as handling variable coefficients and the geometry.
Our performance analysis shows that the results are often within 10\% of the
available memory bandwidth for the proposed implementation, with the exception
of the Cartesian mesh case where the cost of gather operations and MPI
communication are more substantial.
| arxiv topic:cs.MS cs.NA math.NA |
arxiv_dataset-91071711.0369 | Atomic Interferometric Gravitational-wave Space Observatory (AIGSO)
physics.atom-ph astro-ph.IM gr-qc
We propose a space-borne gravitational-wave detection scheme, called atom
interferometric gravitational-wave space observatory (AIGSO). It is motivated
by the progress in the atomic matter-wave interferometry, which solely utilizes
the standing light waves to split, deflect and recombine the atomic beam. Our
scheme consists of three drag-free satellites orbiting the Earth. The phase
shift of AIGSO is dominated by the Sagnac effect of gravitational-waves, which
is proportional to the area enclosed by the atom interferometer, the frequency
and amplitude of gravitational-waves. The scheme has a strain sensitivity $<
10^{-20}/\sqrt{{\rm Hz}}$ in the 100 mHz-10 Hz frequency range, which fills in
the detection gap between space-based and ground-based laser interferometric
detectors. Thus, our proposed AIGSO can be a good complementary detection
scheme to the space-borne laser interferometric schemes, such as LISA.
Considering the current status of relevant technology readiness, we expect our
AIGSO to be a promising candidate for the future space-based gravitational-wave
detection plan.
| arxiv topic:physics.atom-ph astro-ph.IM gr-qc |
arxiv_dataset-91081711.0379 | The nature of representation in Feynman diagrams
physics.hist-ph
After a brief presentation of Feynman diagrams, we criticizise the idea that
Feynman diagrams can be considered to be pictures or depictions of actual
physical processes. We then show that the best interpretation of the role they
play in quantum field theory and quantum electrodynamics is captured by Hughes'
Denotation, Deduction and Interpretation theory of models (DDI), where models
are to be interpreted as inferential, non-representational devices constructed
in given social contexts by the community of physicists.
| arxiv topic:physics.hist-ph |
arxiv_dataset-91091711.0389 | Interpolation and Extrapolation of Toeplitz Matrices via Optimal Mass
Transport
eess.SP math.ST stat.ME stat.TH
In this work, we propose a novel method for quantifying distances between
Toeplitz structured covariance matrices. By exploiting the spectral
representation of Toeplitz matrices, the proposed distance measure is defined
based on an optimal mass transport problem in the spectral domain. This may
then be interpreted in the covariance domain, suggesting a natural way of
interpolating and extrapolating Toeplitz matrices, such that the positive
semi-definiteness and the Toeplitz structure of these matrices are preserved.
The proposed distance measure is also shown to be contractive with respect to
both additive and multiplicative noise, and thereby allows for a quantification
of the decreased distance between signals when these are corrupted by noise.
Finally, we illustrate how this approach can be used for several applications
in signal processing. In particular, we consider interpolation and
extrapolation of Toeplitz matrices, as well as clustering problems and tracking
of slowly varying stochastic processes.
| arxiv topic:eess.SP math.ST stat.ME stat.TH |
arxiv_dataset-91101711.0399 | Longitudinal Study of Child Face Recognition
cs.CV
We present a longitudinal study of face recognition performance on Children
Longitudinal Face (CLF) dataset containing 3,682 face images of 919 subjects,
in the age group [2, 18] years. Each subject has at least four face images
acquired over a time span of up to six years. Face comparison scores are
obtained from (i) a state-of-the-art COTS matcher (COTS-A), (ii) an open-source
matcher (FaceNet), and (iii) a simple sum fusion of scores obtained from COTS-A
and FaceNet matchers. To improve the performance of the open-source FaceNet
matcher for child face recognition, we were able to fine-tune it on an
independent training set of 3,294 face images of 1,119 children in the age
group [3, 18] years. Multilevel statistical models are fit to genuine
comparison scores from the CLF dataset to determine the decrease in face
recognition accuracy over time. Additionally, we analyze both the verification
and open-set identification accuracies in order to evaluate state-of-the-art
face recognition technology for tracing and identifying children lost at a
young age as victims of child trafficking or abduction.
| arxiv topic:cs.CV |
arxiv_dataset-91111711.0409 | MojiTalk: Generating Emotional Responses at Scale
cs.CL cs.AI
Generating emotional language is a key step towards building empathetic
natural language processing agents. However, a major challenge for this line of
research is the lack of large-scale labeled training data, and previous studies
are limited to only small sets of human annotated sentiment labels.
Additionally, explicitly controlling the emotion and sentiment of generated
text is also difficult. In this paper, we take a more radical approach: we
exploit the idea of leveraging Twitter data that are naturally labeled with
emojis. More specifically, we collect a large corpus of Twitter conversations
that include emojis in the response, and assume the emojis convey the
underlying emotions of the sentence. We then introduce a reinforced conditional
variational encoder approach to train a deep generative model on these
conversations, which allows us to use emojis to control the emotion of the
generated text. Experimentally, we show in our quantitative and qualitative
analyses that the proposed models can successfully generate high-quality
abstractive conversation responses in accordance with designated emotions.
| arxiv topic:cs.CL cs.AI |
arxiv_dataset-91121711.0419 | A Nonthermal Radio Filament Connected to the Galactic Black Hole?
astro-ph.GA
Using the Very Large Array, we have investigated a non-thermal radio filament
(NTF) recently found very near the Galactic black hole and its radio
counterpart, SgrA*. While this NTF -- the Sgr A West Filament (SgrAWF) --
shares many characteristics with the population of NTFs occupying the central
few hundred parsecs of the Galaxy, the SgrAWF has the distinction of having an
orientation and sky location that suggest an intimate physical connection to
SgrA*. We present 3.3 and 5.5 cm images constructed using an innovative
methodology that yields a very high dynamic range, providing an unprecedentedly
clear picture of the SgrAWF. While the physical association of the SgrAWF with
SgrA* is not unambiguous, the images decidedly evoke this interesting
possibility. Assuming that the SgrAWF bears a physical relationship to SgrA*,
we examine the potential implications. One is that SgrA* is a source of
relativistic particles constrained to diffuse along ordered local field lines.
The relativistic particles could also be fed into the local field by a
collimated outflow from SgrA*, perhaps driven by the Poynting flux accompanying
the black hole spin in the presence of a magnetic field threading the event
horizon. Second, we consider the possibility that the SgrAWF is the
manifestation of a low-mass-density cosmic string that has become anchored to
the black hole. The simplest form of these hypotheses would predict that the
filament be bi-directional, whereas the SgrAWF is only seen on one side of
SgrA*, perhaps because of the dynamics of the local medium.
| arxiv topic:astro-ph.GA |
arxiv_dataset-91131711.0429 | Triangulated categories with cluster-tilting subcategories
math.RT
Let $\C$ be a triangulated category with a cluster tilting subcategory $\T$.
We introduce the notion of $\T[1]$-cluster tilting subcategories (also called
ghost cluster tilting subcategories) of $\C$, which are a generalization of
cluster tilting subcategories. We first develop a basic theory on ghost cluster
tilting subcategories. Secondly, we study links between ghost cluster tilting
theory and $\tau$-tilting theory: Inspired by the work of Iyama, J{\o}rgensen
and Yang \cite{ijy}, we introduce the notion of $\tau$-tilting subcategories
and tilting subcategories of $\mod\T$. We show that there exists a bijection
between weak $\T[1]$-cluster tilting subcategories of $\C$ and support
$\tau$-tilting subcategories of $\mod\T$. Moreover, we figure out the
subcategories of $\mod\T$ which correspond to cluster tilting subcategories of
$\C$. This generalizes and improves several results by Adachi-Iyama-Reiten
\cite{AIR}, Beligiannis \cite{Be2}, and Yang-Zhu \cite{YZ}. Finally, we prove
that the definition of ghost cluster tilting objects is equivalent to the
definition of relative cluster tilting objects introduced by the first and the
third author in \cite{YZ}.
| arxiv topic:math.RT |
arxiv_dataset-91141711.0439 | A family of dp-minimal expansions of $(\mathbb{Z};+)$
math.LO
We show that the cyclically ordered-abelian groups expanding $(\mathbb{Z};+)$
contain a continuum-size family of dp-minimal structures such that no two
members define the same subsets of $\mathbb{Z}$.
| arxiv topic:math.LO |
arxiv_dataset-91151711.0449 | Striated Regularity of 2-D inhomogeneous incompressible Navier-Stokes
system with variable viscosity
math.AP
In this paper, we investigate the global existence and uniqueness of strong
solutions to 2D incompressible inhomogeneous Navier-Stokes equations with
viscous coefficient depending on the density and with initial density being
discontinuous across some smooth interface. Compared with the previous results
for the inhomogeneous Navier-Stokes equations with constant viscosity, the main
difficulty here lies in the fact that the $L^1$ in time Lipschitz estimate of
the velocity field can not be obtained by energy method (see \cite{DM17,LZ1,
LZ2} for instance). Motivated by the key idea of Chemin to solve 2-D vortex
patch of ideal fluid (\cite{Chemin91, Chemin93}), namely, striated regularity
can help to get the $L^\infty$ boundedness of the double Riesz transform, we
derive the {\it a priori} $L^1$ in time Lipschitz estimate of the velocity
field under the assumption that the viscous coefficient is close enough to a
positive constant in the bounded function space. As an application, we shall
prove the propagation of $H^3$ regularity of the interface between fluids with
different densities.
| arxiv topic:math.AP |
arxiv_dataset-91161711.0459 | Microwave detection of electron-phonon interactions in a cavity-coupled
double quantum dot
cond-mat.mes-hall quant-ph
Quantum confinement leads to the formation of discrete electronic states in
quantum dots. Here we probe electron-phonon interactions in a suspended InAs
nanowire double quantum dot (DQD) that is electric-dipole coupled to a
microwave cavity. We apply a finite bias across the wire to drive a steady
state population in the DQD excited state, enabling a direct measurement of the
electron-phonon coupling strength at the DQD transition energy. The amplitude
and phase response of the cavity field exhibit features that are periodic in
the DQD energy level detuning due to the phonon modes of the nanowire. The
observed cavity phase shift is consistent with theory that predicts a
renormalization of the cavity center frequency by coupling to phonons.
| arxiv topic:cond-mat.mes-hall quant-ph |
arxiv_dataset-91171711.0469 | Null controllability of linear and semilinear nonlocal heat equations
with integral kernel
math.AP
We consider a linear nonlocal heat equation in a bounded domain
$\Omega\subset\mathbb{R}^d$ with Dirichlet boundary conditions. The
non-locality is given by the presence of an integral kernel. We analyze the
problem of controllability when the control acts on an open subset of the
domain. It is by now known that the system is null-controllable when the kernel
is time-independent and analytic or, in the one-dimensional case, in separated
variables. In this paper, we relax this assumption and we extend the result to
a more general class of kernels. Moreover, we get explicit estimates on the
cost of null-controllability that allow us to extend the result to some
semilinear models.
| arxiv topic:math.AP |
arxiv_dataset-91181711.0479 | Universality and quantum criticality of the one-dimensional spinor Bose
gas
cond-mat.quant-gas cond-mat.stat-mech
We investigate the universal thermodynamics of the two-component
one-dimensional Bose gas with contact interactions in the vicinity of the
quantum critical point separating the vacuum and the ferromagnetic liquid
regime. We find that the quantum critical region belongs to the universality
class of the spin-degenerate impenetrable particle gas which, surprisingly, is
very different from the single-component case and identify its boundaries with
the peaks of the specific heat. In addition, we show that the compressibility
Wilson ratio, which quantifies the relative strength of thermal and quantum
fluctuations, serves as a good discriminator of the quantum regimes near the
quantum critical point. Remarkably, in the Tonks-Girardeau regime the universal
contact develops a pronounced minimum, reflected in a counterintuitive
narrowing of the momentum distribution as we increase the temperature. This
momentum reconstruction, also present at low and intermediate momenta, signals
the transition from the ferromagnetic to the spin-incoherent Luttinger liquid
phase and can be detected in current experiments with ultracold atomic gases in
optical lattices.
| arxiv topic:cond-mat.quant-gas cond-mat.stat-mech |
arxiv_dataset-91191711.0489 | Doping-induced quantum cross-over in Er$_2$Ti$_{2-x}$Sn$_x$O$_7$
cond-mat.str-el
We present the results of the investigation of magnetic properties of the
Er$_2$Ti$_{2-x}$Sn$_x$O$_7$ series. For small doping values the ordering
temperature decreases linearly with $x$ while the moment configuration remains
the same as in the $x = 0$ parent compound. Around $x = 1.7$ doping level we
observe a change in the behavior, where the ordering temperature starts to
increase and new magnetic Bragg peaks appear. For the first time we present
evidence of a long-range order (LRO) in Er$_2$Sn$_2$O$_7$ ($x = 2.0$) below
$T_N = 130$ mK. It is revealed that the moment configuration corresponds to a
Palmer-Chalker type with a value of the magnetic moment significantly
renormalized compared to $x = 0$. We discuss our results in the framework of a
possible quantum phase transition occurring close to $x = 1.7$.
| arxiv topic:cond-mat.str-el |
arxiv_dataset-91201711.0499 | Strong consistency and optimality for generalized estimating equations
with stochastic covariates
math.ST stat.TH
In this article we study the existence and strong consistency of GEE
estimators, when the generalized estimating functions are martingales with
random coefficients. Furthermore, we characterize estimating functions which
are asymptotically optimal.
| arxiv topic:math.ST stat.TH |
arxiv_dataset-91211711.0509 | Efficiency Analysis of ASP Encodings for Sequential Pattern Mining Tasks
cs.AI cs.DB stat.ML
This article presents the use of Answer Set Programming (ASP) to mine
sequential patterns. ASP is a high-level declarative logic programming paradigm
for high level encoding combinatorial and optimization problem solving as well
as knowledge representation and reasoning. Thus, ASP is a good candidate for
implementing pattern mining with background knowledge, which has been a data
mining issue for a long time. We propose encodings of the classical sequential
pattern mining tasks within two representations of embeddings (fill-gaps vs
skip-gaps) and for various kinds of patterns: frequent, constrained and
condensed. We compare the computational performance of these encodings with
each other to get a good insight into the efficiency of ASP encodings. The
results show that the fill-gaps strategy is better on real problems due to
lower memory consumption. Finally, compared to a constraint programming
approach (CPSM), another declarative programming paradigm, our proposal showed
comparable performance.
| arxiv topic:cs.AI cs.DB stat.ML |
arxiv_dataset-91221711.0519 | Restricted power domination and zero forcing problems
math.CO
Power domination in graphs arises from the problem of monitoring an electric
power system by placing as few measurement devices in the system as possible. A
power dominating set of a graph is a set of vertices that observes every vertex
in the graph, following a set of rules for power system monitoring. A practical
problem of interest is to determine the minimum number of additional
measurement devices needed to monitor a power network when the network is
expanded and the existing devices remain in place. In this paper, we study the
problem of finding the smallest power dominating set that contains a given set
of vertices X. We also study the related problem of finding the smallest zero
forcing set that contains a given set of vertices X. The sizes of such sets in
a graph G are respectively called the restricted power domination number and
restricted zero forcing number of G subject to X. We derive several tight
bounds on the restricted power domination and zero forcing numbers of graphs,
and relate them to other graph parameters. We also present exact and
algorithmic results for computing the restricted power domination number,
including integer programs for general graphs and a linear time algorithm for
graphs with bounded treewidth. We also use restricted power domination to
obtain a parallel algorithm for finding minimum power dominating sets in trees.
| arxiv topic:math.CO |
arxiv_dataset-91231711.0529 | Vanishing of local non-Gaussianity in canonical single field inflation
astro-ph.CO gr-qc hep-ph hep-th
We study the production of observable primordial local non-Gaussianity in two
opposite regimes of canonical single field inflation: attractor (standard
single field slow-roll inflation) and non attractor (ultra slow-roll
inflation). In the attractor regime, the standard derivation of the
bispectrum's squeezed limit using co-moving coordinates gives the well known
Maldacena's consistency relation $f_{NL} = 5(1-n_{s})/12$. On the other hand,
in the non-attractor regime, the squeezed limit offers a substantial violation
of this relation given by $f_{NL} = 5/2$. In this work we argue that,
independently of whether inflation is attractor or non-attractor, the size of
the observable primordial local non-Gaussianity is predicted to be
$f_{NL}^{obs} = 0$ (a result that was already understood to hold in the case of
attractor models). To show this, we follow the use of the so-called Conformal
Fermi Coordinates (CFC), recently introduced in the literature. These
coordinates parametrize the local environment of inertial observers in a
perturbed FRW spacetime, allowing one to identify and compute gauge invariant
quantities, such as $n$-point correlation functions. Concretely, we find that
during inflation, after all the modes have exited the horizon, the squeezed
limit of the 3-point correlation function of curvature perturbations vanishes
in the CFC frame, regardless of the inflationary regime. We argue that such a
cancellation should persist after inflation ends.
| arxiv topic:astro-ph.CO gr-qc hep-ph hep-th |
arxiv_dataset-91241711.0539 | Dynamical recovery of SU(2) symmetry in the mass-quenched Hubbard model
cond-mat.str-el
We use non-equilibrium dynamical mean-field theory with iterative
perturbation theory as an impurity solver to study the recovery of $SU(2)$
symmetry in real-time following a hopping integral parameter quench from a
mass-imbalanced to a mass-balanced single-band Hubbard model at half-filling. A
dynamical order parameter $\gamma(t)$ is defined to characterize the evolution
of the system towards $SU(2)$ symmetry. By comparing the momentum dependent
occupation from an equilibrium calculation (with the $SU(2)$ symmetric
Hamiltonian after the quench at an effective temperature) with the data from
our non-equilibrium calculation, we conclude that the $SU(2)$ symmetry
recovered state is a thermalized state. Further evidence from the evolution of
the density of states supports this conclusion. At the same time, we find the
order parameter in the weak Coulomb interaction regime undergoes an approximate
exponential decay. We numerically investigate the interplay of the relevant
parameters (initial temperature, Coulomb interaction strength, initial
mass-imbalance ratio) and their combined effect on the thermalization behavior.
Finally, we study evolution of the order parameter as the hopping parameter is
changed with either a linear ramp or a pulse. Our results can be useful in
strategies to engineer the relaxation behavior of interacting, quantum
many-particle systems.
| arxiv topic:cond-mat.str-el |
arxiv_dataset-91251711.0549 | Measurement of branching fractions of charmless four-body $\Lambda_b^0$
and $\Xi_b^0$ decays
hep-ex
A search for charmless four-body decays of $\Lambda_{b}^{0}$ and
$\Xi_{b}^{0}$ baryons with a proton and three charged mesons (either kaons or
pions) in the final state is performed. The data sample used was recorded in
2011 and 2012 with the LHCb experiment and corresponds to an integrated
luminosity of 3 fb$^{-1}$. Six decay modes are observed, among which
$\Lambda_{b}^{0} \to pK^{-}\pi^{+}\pi^{-}$, $\Lambda_{b}^{0} \to
pK^{-}K^{+}K^{-}$, $\Xi_{b}^{0} \to pK^{-}\pi^{+}\pi^{-}$ and $\Xi_{b}^{0} \to
pK^{-} \pi^{+}K^{-}$ are established for the first time. Their branching
fractions (including the ratio of hadronisation fractions in the case of the
$\Xi_{b}^{0}$ baryon) are determined relative to the $\Lambda_{b}^{0} \to
\Lambda_{c}^{+}\pi^{-}$ decay.
| arxiv topic:hep-ex |
arxiv_dataset-91261711.0559 | Support for the value 5/2 for the spin glass lower critical dimension at
zero magnetic field
cond-mat.dis-nn
We study numerically various properties of the free energy barriers in the
Edwards-Anderson model of spin glasses in the low-temperature region both in
three and four spatial dimensions. In particular, we investigated the
dependence of height of free energy barriers on system size and on the distance
between the initial and final states (i.e. the overlap distance). A related
quantity is the distribution of large local fluctuations of the overlap in
large three-dimensional samples at equilibrium. Our results for both quantities
(barriers and large deviations) are in agreement with the prediction obtained
in the framework of mean field theory. In addition, our result supports
$D_{lc}=2.5$ as the lower critical dimension for the model.
| arxiv topic:cond-mat.dis-nn |
arxiv_dataset-91271711.0569 | Orthogonal foliations on riemannian manifolds
math.DG
In this work, we find an equation that relates the Ricci curvature of a
riemannian manifold $M$ and the second fundamental forms of two orthogonal
foliations of complementary dimensions, $\mathcal{F}$ and $\mathcal{F}^{\bot}$,
defined on $M$. Using this equation, we show a sufficient condition for the
manifold M to be locally a riemannian product of the leaves of $\mathcal{F}$
and $\mathcal{F}^{\bot}$, if one of the foliations is totally umbilical. We
also prove an integral formula for such foliations.
| arxiv topic:math.DG |
arxiv_dataset-91281711.0579 | Rigid Graph Compression: Motif-based rigidity analysis for disordered
fiber networks
cond-mat.dis-nn cond-mat.soft
Using particle-scale models to accurately describe property enhancements and
phase transitions in macroscopic behavior is a major engineering challenge in
composite materials science. To address some of these challenges, we use the
graph theoretic property of rigidity to model me- chanical reinforcement in
composites with stiff rod-like particles. We develop an efficient algorithmic
approach called rigid graph compression (RGC) to describe the transition from
floppy to rigid in disordered fiber networks ('rod-hinge systems'), which form
the reinforcing phase in many composite systems. To establish RGC on a firm
theoretical foundation, we adapt rigidity matroid theory to identify primitive
topological network motifs that serve as rules for composing interacting rigid
par- ticles into larger rigid components. This approach is computationally
efficient and stable, because RGC requires only topological information about
rod interactions (encoded by a sparse unweighted network) rather than
geometrical details such as rod locations or pairwise distances (as required in
rigidity matroid theory). We conduct numerical experiments on simulated
two-dimensional rod-hinge systems to demonstrate that RGC closely approximates
the rigidity percolation threshold for such systems, through comparison with
the pebble game algorithm (which is exact in two dimensions). Importantly,
whereas the pebble game is derived from Laman's condition and is only valid in
two dimensions, the RGC approach naturally extends to higher dimensions.
| arxiv topic:cond-mat.dis-nn cond-mat.soft |
arxiv_dataset-91291711.0589 | Occlusion Aware Unsupervised Learning of Optical Flow
cs.CV
It has been recently shown that a convolutional neural network can learn
optical flow estimation with unsupervised learning. However, the performance of
the unsupervised methods still has a relatively large gap compared to its
supervised counterpart. Occlusion and large motion are some of the major
factors that limit the current unsupervised learning of optical flow methods.
In this work we introduce a new method which models occlusion explicitly and a
new warping way that facilitates the learning of large motion. Our method shows
promising results on Flying Chairs, MPI-Sintel and KITTI benchmark datasets.
Especially on KITTI dataset where abundant unlabeled samples exist, our
unsupervised method outperforms its counterpart trained with supervised
learning.
| arxiv topic:cs.CV |
arxiv_dataset-91301711.0599 | Cholesteric and screw-like nematic phases in systems of helical
particles
cond-mat.soft
Recent numerical simulations of hard helical particle systems unveiled the
existence of a novel chiral nematic phase, termed screw-like, characterised by
the helical organization of the particle C$_2$ symmetry axes round the nematic
director with periodicity equal to the particle pitch. This phase forms at high
density and can follow a less dense uniform nematic phase, with relative
occurrence of the two phases depending on the helix morphology. Since these
numerical simulations were conducted under three-dimensional periodic boundary
conditions, two questions could remain open. Firstly, the real nature of the
lower density nematic phase, expected to be cholesteric. Secondly, the
influence that the latter, once allowed to form, may have on the existence and
stability of the screw-like nematic phase. To address these questions, we have
performed Monte Carlo and molecular dynamics numerical simulations of helical
particle systems confined between two parallel repulsive walls. We have found
that removal of the periodicity constraint along one direction allows a
relatively-long-pitch cholesteric phase to form, in lieu of the uniform nematic
phase, with helical axis perpendicular to the walls while the existence and
stability of the screw-like nematic phase are not appreciably affected by this
change of boundary conditions.
| arxiv topic:cond-mat.soft |
arxiv_dataset-91311711.0609 | Ultrafast Outflow in Tidal Disruption Event ASASSN-14li
astro-ph.HE
At only 90 Mpc, ASASSN-14li is one of the nearest tidal disruption event
(TDE) ever discovered, and because of this, it has been observed by several
observatories at many wavelengths. In this paper, we present new results on
archival XMM-Newton observations, three of which were taken at early times
(within 40 days of the discovery), and three of which were taken at late times,
about one year after the peak. We find that, at early times, in addition to the
~1e5 K blackbody component that dominates the X-ray band, there is evidence for
a broad, P Cygni-like absorption feature at around 0.7 keV in all XMM-Newton
instruments (CCD detectors and grating spectrometers), and that this feature
disappears (or at least diminishes) in the late-time observations. We perform
photoionization modelling with XSTAR and interpret this absorption feature as
blueshifted OVIII, from an ionized outflow with a velocity of 0.2c. As the TDE
transitions from high to low accretion rate, the outflow turns off, thus
explaining the absence of the absorption feature during the late-time
observations.
| arxiv topic:astro-ph.HE |
arxiv_dataset-91321711.0619 | Origin of the orbital and spin orderings in rare-earth titanates
cond-mat.mtrl-sci
Rare-earth titanates RTiO$_3$ are Mott insulators displaying a rich physical
behavior, featuring most notably orbital and spin orders in their ground state.
The origin of their ferromagnetic to antiferromagnetic transition as a function
of the size of the rare-earth however remains debated. Here we show on the
basis of symmetry analysis and first-principles calculations that although
rare-earth titanates are nominally Jahn-Teller active, the Jahn-Teller
distortion is negligible and irrelevant for the description of the ground state
properties. At the same time, we demonstrate that the combination of two
antipolar motions produces an effective Jahn-Teller-like motion which is the
key of the varying spin-orbital orders appearing in titanates. Thus, titanates
are prototypical examples illustrating how a subtle interplay between several
lattice distortions commonly appearing in perovskites can produce orbital
orderings and insulating phases irrespective of proper Jahn-Teller motions.
| arxiv topic:cond-mat.mtrl-sci |
arxiv_dataset-91331711.0629 | Network Geometry and Complexity
cond-mat.dis-nn cond-mat.stat-mech gr-qc physics.soc-ph
Higher order networks are able to characterize data as different as
functional brain networks, protein interaction networks and social networks
beyond the framework of pairwise interactions. Most notably higher order
networks include simplicial complexes formed not only by nodes and links but
also by triangles, tetrahedra, etc. More in general, higher-order networks can
be cell-complexes formed by gluing convex polytopes along their faces.
Interestingly, higher order networks have a natural geometric interpretation
and therefore constitute a natural way to explore the discrete network geometry
of complex networks. Here we investigate the rich interplay between emergent
network geometry of higher order networks and their complexity in the framework
of a non-equilibrium model called Network Geometry with Flavor. This model,
originally proposed for capturing the evolution of simplicial complexes, is
here extended to cell-complexes formed by subsequently gluing different copies
of an arbitrary regular polytope. We reveal the interplay between complexity
and geometry of the higher order networks generated by the model by studying
the emergent community structure and the degree distribution as a function of
the regular polytope forming its building blocks. Additionally we discuss the
underlying hyperbolic nature of the emergent geometry and we relate the
spectral dimension of the higher-order network to the dimension and nature of
its building blocks.
| arxiv topic:cond-mat.dis-nn cond-mat.stat-mech gr-qc physics.soc-ph |
arxiv_dataset-91341711.0639 | Non local branching Brownians with annihilation and free boundary
problems
math.PR math-ph math.AP math.MP
We study a system of branching Brownian motions on $\mathbb R$ with
annihilation: at each branching time a new particle is created and the leftmost
one is deleted. In [7] it has been studied the case of strictly local creations
(the new particle is put exactly at the same position of the branching
particle), in [10] instead the position $y$ of the new particle has a
distribution $p(x,y)dy$, $x$ the position of the branching particle, however
particles in between branching times do not move. In this paper we consider
Brownian motions as in [7] and non local branching as in [10] and prove
convergence in the continuum limit (when the number $N$ of particles diverges)
to a limit density which satisfies a free boundary problem when this has
classical solutions, local in time existence of classical solution has been
proved recently in [13]. We use in the convergence a stronger topology than in
[7] and [10] and have explicit bounds on the rate of convergence.
| arxiv topic:math.PR math-ph math.AP math.MP |
arxiv_dataset-91351711.0649 | Pseudocanalization regime for magnetic dark-field hyperlens
physics.optics cond-mat.mes-hall
Hyperbolic metamaterials (HMMs) are the cornerstone of the hyperlens, which
brings the superresolution effect from the near-field to the far-field zone.
For effective application of the hyperlens it should operate in so-called
canalization regime, when the phase advancement of the propagating fields is
maximally supressed, and thus field broadening is minimized. For conventional
hyperlenses it is relatively straightforward to achieve canalization by tuning
the anisotropic permittivity tensor. However, for a dark-field hyperlens
designed to image weak scatterers by filtering out background radiation
(dark-field regime) this approach is not viable, because design requirements
for such filtering and elimination of phase advancement i.e. canalization, are
mutually exclusive. Here we propose the use of magnetic ($\mu$-positive and
negative) HMMs to achieve phase cancellation at the output equivalent to the
performance of a HMM in the canalized regime. The proposed structure offers
additional flexibility over simple HMMs in tuning light propagation. We show
that in this ``pseudocanalizing'' configuration quality of an image is
comparable to a conventional hyperlens, while the desired filtering of the
incident illumination associated with the dark-field hyperlens is preserved.
| arxiv topic:physics.optics cond-mat.mes-hall |
arxiv_dataset-91361711.0659 | Cosmological abundance of the QCD axion coupled to hidden photons
hep-ph astro-ph.CO hep-th
We study the cosmological evolution of the QCD axion coupled to hidden
photons. For a moderately strong coupling, the motion of the axion field leads
to an explosive production of hidden photons by tachyonic instability. We use
lattice simulations to evaluate the cosmological abundance of the QCD axion. In
doing so, we incorporate the backreaction of the produced hidden photons on the
axion dynamics, which becomes significant in the non-linear regime. We find
that the axion abundance is suppressed by at most ${\cal O}(10^{2})$ for the
decay constant $f_a = 10^{16}$ GeV, compared to the case without the coupling.
For a sufficiently large coupling, the motion of the QCD axion becomes strongly
damped, and as a result, the axion abundance is enhanced. Our results show that
the cosmological upper bound on the axion decay constant can be relaxed by a
few hundred for a certain range of the coupling to hidden photons.
| arxiv topic:hep-ph astro-ph.CO hep-th |
arxiv_dataset-91371711.0669 | Conformal Structure of Massless Scalar Amplitudes Beyond Tree level
hep-th
We show that the one-loop on-shell four-point scattering amplitude of
massless $\phi^4$ scalar field theory in 4D Minkowski space time, when Mellin
transformed to the Celestial sphere at infinity, transforms covariantly under
the global conformal group ($SL(2,C)$) on the sphere. The unitarity of the
four-point scalar amplitudes is recast into this Mellin basis. We show that the
same conformal structure also appears for the two-loop Mellin amplitude.
Finally we comment on some universal structure for all loop four-point Mellin
amplitudes specific to this theory.
| arxiv topic:hep-th |
arxiv_dataset-91381711.0679 | Mitigating Read-disturbance Errors in STT-RAM Caches by Using Data
Compression
cs.AR
Due to its high density and close-to-SRAM read latency, spin transfer torque
RAM (STT-RAM) is considered one of the most-promising emerging memory
technologies for designing large last level caches (LLCs). However, in deep
sub-micron region, STT-RAM shows read-disturbance error (RDE) whereby a read
operation may modify the stored data value and this presents a severe threat to
performance and reliability of STT-RAM caches. In this paper, we present a
technique, named SHIELD, to mitigate RDE in STT-RAM LLCs. SHIELD uses data
compression to reduce number of read operations from STT-RAM blocks to avoid
RDE and also to reduce the number of bits written to cache during both write
and restore operations. Experimental results have shown that SHIELD provides
significant improvement in performance and energy efficiency. SHIELD consumes
smaller energy than two previous RDE-mitigation techniques, namely high-current
restore required read (HCRR, also called restore-after-read) and low-current
long latency read (LCLL) and even an ideal RDE-free STT-RAM cache.
| arxiv topic:cs.AR |
arxiv_dataset-91391711.0689 | One Hundred Years of the Cosmological Constant: from 'Superfluous Stunt'
to Dark Energy
physics.hist-ph astro-ph.CO gr-qc
We present a centennial review of the history of the term known as the
cosmological constant. First introduced to the general theory of relativity by
Einstein in 1917 in order to describe a universe that was assumed to be static,
the term fell from favour in the wake of the discovery of the expanding
universe, only to make a dramatic return in recent times. We consider
historical and philosophical aspects of the cosmological constant over four
main epochs: (i) the use of the term in static cosmologies (both Newtonian and
relativistic); (ii) the marginalization of the term following the discovery of
cosmic expansion; (iii) the use of the term to address specific cosmic puzzles
such as the timespan of expansion, the formation of galaxies and the redshifts
of the quasars; (iv) the re-emergence of the term in today's Lamda-CDM
cosmology. We find that the cosmological constant was never truly banished from
theoretical models of the universe, but was sidelined by astronomers for
reasons of convenience. We also find that the return of the term to the
forefront of modern cosmology did not occur as an abrupt paradigm shift due to
one particular set of observations, but as the result of a number of empirical
advances such as the measurement of present cosmic expansion using the Hubble
Space Telescope, the measurement of past expansion using type SN 1a supernovae
as standard candles, and the measurement of perturbations in the cosmic
microwave background by balloon and satellite. We give a brief overview of
contemporary interpretations of the physics underlying the cosmic constant and
conclude with a synopsis of the famous cosmological constant problem.
| arxiv topic:physics.hist-ph astro-ph.CO gr-qc |
arxiv_dataset-91401711.0699 | Spin-order-induced multiferroicity in LiCuFe2(VO4)3 and disorder effects
in NaCuFe2(VO4)3
cond-mat.mtrl-sci
Mixed spin chain compounds, ACuFe2(VO4)3 (A= Li,Na), reach magnetically
ordered state at TN ~ 11 K (Li) or ~ 9 K (Na) and experience further
transformation of magnetic order at T* ~ 7 K (Li) or ~ 5 K (Na), evidenced in
magnetic susceptibility chi and specific heat Cp measurements. While no anomaly
has been detected in dielectric property of NaCuFe2(VO4)3, the step-like
feature precedes a sharp peak in permittivity epsilon at TN in LiCuFe2(VO4)3.
These data suggest the spin-order-induced ferroelectricity in Li compound and
no such thing in Na compound. On the contrary, the Moessbauer spectroscopy
study suggests similarly wide distribution of hyperfine field in between T* and
TN for both the compounds. The first principles calculations also provide
similar values for magnetic exchange interaction parameters in both compounds.
These observations lead us to conclude on the crucial role of alkali metals
mobility within the channels of the crystal structure needed to be considered
in explaining the improper multiferroicity in one compound and its absence in
other.
| arxiv topic:cond-mat.mtrl-sci |
arxiv_dataset-91411711.0709 | Eigenvector continuation with subspace learning
nucl-th cond-mat.str-el hep-lat hep-ph math.NA
A common challenge faced in quantum physics is finding the extremal
eigenvalues and eigenvectors of a Hamiltonian matrix in a vector space so large
that linear algebra operations on general vectors are not possible. There are
numerous efficient methods developed for this task, but they generally fail
when some control parameter in the Hamiltonian matrix exceeds some threshold
value. In this work we present a new technique called eigenvector continuation
that can extend the reach of these methods. The key insight is that while an
eigenvector resides in a linear space with enormous dimensions, the eigenvector
trajectory generated by smooth changes of the Hamiltonian matrix is well
approximated by a very low-dimensional manifold. We prove this statement using
analytic function theory and propose an algorithm to solve for the extremal
eigenvectors. We benchmark the method using several examples from quantum
many-body theory.
| arxiv topic:nucl-th cond-mat.str-el hep-lat hep-ph math.NA |
arxiv_dataset-91421711.0719 | Block-Cyclic Stochastic Coordinate Descent for Deep Neural Networks
cs.CV
We present a stochastic first-order optimization algorithm, named BCSC, that
adds a cyclic constraint to stochastic block-coordinate descent. It uses
different subsets of the data to update different subsets of the parameters,
thus limiting the detrimental effect of outliers in the training set. Empirical
tests in benchmark datasets show that our algorithm outperforms
state-of-the-art optimization methods in both accuracy as well as convergence
speed. The improvements are consistent across different architectures, and can
be combined with other training techniques and regularization methods.
| arxiv topic:cs.CV |
arxiv_dataset-91431711.0729 | Cosmological dynamics of mimetic gravity
gr-qc hep-th
We present a detailed investigation of the dynamical behavior of mimetic
gravity with a general potential for the mimetic scalar field. Performing a
phase-space and stability analysis, we show that the scenario at hand can
successfully describe the thermal history of the universe, namely the
successive sequence of radiation, matter, and dark-energy eras. Additionally,
at late times the universe can either approach a de Sitter solution, or a
scaling accelerated attractor where the dark-matter and dark-energy density
parameters are of the same order, thus offering an alleviation of the cosmic
coincidence problem. Applying our general analysis to various specific
potential choices, including the power-law and the exponential ones, we show
that mimetic gravity can be brought into good agreement with the observed
behavior of the universe. Moreover, with an inverse square potential we find
that mimetic gravity offers an appealing unified cosmological scenario where
both dark energy and dark matter are characterized by a single scalar field,
and where the cosmic coincidence problem is alleviated.
| arxiv topic:gr-qc hep-th |
arxiv_dataset-91441711.0739 | Distinct multiple fermionic states in a single topological metal
cond-mat.mes-hall cond-mat.mtrl-sci
Among the quantum materials that gained interest recently are the topological
Dirac/Weyl semimetals, where conduction and valence bands touch at points in
reciprocal (k)-space, and the Dirac nodal-line semimetals, where these bands
touch along a line or a loop in k-space. However, the coexistence of multiple
fermion phases in one and the same material has not been verified yet. Using
angle-resolved photoemission spectroscopy (ARPES) and first-principles
electronic structure calculations, we systematically study the metallic
topological quantum material, Hf2Te2P. Our investigations discover various
properties that are rare and never observed in a single Dirac material. We
observe the coexistence of both weak and strong topological surface states in
the same material and interestingly, at the same momentum position. An
one-dimensional Dirac crossing{the Dirac-node arc-along a high-symmetry
direction is revealed by our first-principles calculations and confirmed by our
ARPES measurements. This novel state is associated with the surface bands of a
weak topological insulator protected by in-plane time-reversal invariance.
Ternary compound Hf2Te2P thus emerges as an intriguing platform to study the
coexistence and competition of multi-fermionic states in one material.
| arxiv topic:cond-mat.mes-hall cond-mat.mtrl-sci |
arxiv_dataset-91451711.0749 | Spacetimes dressed with stealth electromagnetic fields
gr-qc hep-th
Stealth field configurations by definition have a vanishing energy-momentum
tensor, thus do not contribute to the gravitational field equations. While only
trivial fields can be stealth in Maxwell's electrodynamics, nontrivial stealth
fields appear in some nonlinear models of electromagnetism. We find the
necessary and sufficient conditions for the electromagnetic fields to be
stealth and analyse which models admit such configurations. Furthermore, we
present some concrete exact solutions, featuring a class of black holes dressed
with the stealth electromagnetic hair, closely related to force-free solutions.
Stealth hair does not alter the generalized Smarr formula, but may contribute
to the Komar charges.
| arxiv topic:gr-qc hep-th |
arxiv_dataset-91461711.0759 | Kinetic energy represented in terms of moments of vorticity and
applications
math-ph math.MP
We study 2d vortex sheets with unbounded support. First we show a version of
the Biot- Savart law related to a class of objects including such vortex
sheets. Next, we give a formula associating the kinetic energy of a very
general class of ows with certain moments of their vorticities. It allows us to
identify a class of vortex sheets of unbounded support being only ?-finite
measures (in particluar including measures \omega such that \omega(R2) =
\infty), but with locally finite kinetic energy. One of such examples are
celebrated Kaden approximations. We study them in details. In particular our
estimates allow us to show that the kinetic energy of Kaden approximations in
the neighbourhood of an origin is dissipated, actually we show that the energy
is pushed out of any ball centered in the origin of the Kaden spiral. The
latter result can be interpreted as an artificial viscosity in the center of a
spiral.
| arxiv topic:math-ph math.MP |
arxiv_dataset-91471711.0769 | Alexandrov's theorem revisited
math.AP math.DG
We show that among sets of finite perimeter balls are the only
volume-constrained critical points of the perimeter functional.
| arxiv topic:math.AP math.DG |
arxiv_dataset-91481711.0779 | Solving Poisson's Equation on the Microsoft HoloLens
cs.GR cs.MS
We present a mixed reality application (HoloFEM) for the Microsoft HoloLens.
The application lets a user define and solve a physical problem governed by
Poisson's equation with the surrounding real world geometry as input data.
Holograms are used to visualise both the problem and the solution. The finite
element method is used to solve Poisson's equation. Solving and visualising
partial differential equations in mixed reality could have potential usage in
areas such as building planning and safety engineering.
| arxiv topic:cs.GR cs.MS |
arxiv_dataset-91491711.0789 | Would You Like to Motivate Software Testers? Ask Them How
cs.SE
Context. Considering the importance of software testing to the development of
high quality and reliable software systems, this paper aims to investigate how
can work-related factors influence the motivation of software testers. Method.
We applied a questionnaire that was developed using a previous theory of
motivation and satisfaction of software engineers to conduct a survey-based
study to explore and understand how professional software testers perceive and
value work-related factors that could influence their motivation at work.
Results. With a sample of 80 software testers we observed that software testers
are strongly motivated by variety of work, creative tasks, recognition for
their work, and activities that allow them to acquire new knowledge, but in
general the social impact of this activity has low influence on their
motivation. Conclusion. This study discusses the difference of opinions among
software testers, regarding work-related factors that could impact their
motivation, which can be relevant for managers and leaders in software
engineering practice.
| arxiv topic:cs.SE |
arxiv_dataset-91501711.0799 | A matrix CFT at multiple large charges
hep-th
We investigate matrix models in three dimensions where the global
$\text{SU}(N)$ symmetry acts via the adjoint map. Analyzing their ground state
which is homogeneous in space and can carry either a unique or multiple fixed
charges, we show the existence of at least two distinct fixed points of the
renormalization group (RG) flow. In particular, the one type of those fixed
points manifests itself via tractable deviations in the large-charge expansion
from the known predictions in the literature. We demonstrate most of the novel
features using mainly the example of the $\text{SU}(4)$ matrix theory to
compute the anomalous dimension of the lowest scalar operator with large global
charge(s).
| arxiv topic:hep-th |
arxiv_dataset-91511711.0809 | Observation of the quantum Hall effect in confined films of the
three-dimensional Dirac semimetal Cd3As2
cond-mat.mes-hall cond-mat.mtrl-sci
The magnetotransport properties of epitaxial films of Cd3As2, a paradigm
three-dimensional Dirac semimetal, are investigated. We show that an energy gap
opens in the bulk electronic states of sufficiently thin films and, at low
temperatures, carriers residing in surface states dominate the electrical
transport. The carriers in these states are sufficiently mobile to give rise to
a quantized Hall effect. The sharp quantization demonstrates surface transport
that is virtually free of parasitic bulk conduction and paves the way for novel
quantum transport studies in this class of topological materials. Our results
also demonstrate that heterostructuring approaches can be used to study and
engineer quantum states in topological semimetals.
| arxiv topic:cond-mat.mes-hall cond-mat.mtrl-sci |
arxiv_dataset-91521711.0819 | Applications of mutations in the derived categories of weighted
projective lines to Lie and quantum algebras
math.RT math.QA
Let $\rm{coh}\mathbb{X}$ be the category of coherent sheaves over a weighted
projective line $\mathbb{X}$ and let $D^b(\rm{coh}\mathbb{X})$ be its bounded
derived category. The present paper focuses on the study of the right and left
mutation functors arising in $D^b(\rm{coh}\mathbb{X})$ attached to certain line
bundles. As applications, we first show that these mutation functors give rise
to simple reflections for the Weyl group of the star shaped quiver $Q$
associated with $\mathbb{X}$. By further dealing with the Ringel--Hall algebra
of $\mathbb{X}$, we show that these functors provide a realization for Tits'
automorphisms of the Kac--Moody algebra $\frak{g}_Q$ associated with $Q$, as
well as for Lusztig's symmetries of the quantum enveloping algebra of ${\frak
g}_Q$.
| arxiv topic:math.RT math.QA |
arxiv_dataset-91531711.0829 | A compact superconducting nanowire memory element operated by nanowire
cryotrons
physics.app-ph
A superconducting loop stores persistent current without any ohmic loss,
making it an ideal platform for energy efficient memories. Conventional
superconducting memories use an architecture based on Josephson junctions (JJs)
and have demonstrated access times less than 10 ps and power dissipation as low
as $10^{-19}$ J. However, their scalability has been slow to develop due to the
challenges in reducing the dimensions of JJs and minimizing the area of the
superconducting loops. In addition to the memory itself, complex readout
circuits require additional JJs and inductors for coupling signals, increasing
the overall area. Here, we have demonstrated a superconducting memory based
solely on lithographic nanowires. The small dimensions of the nanowire ensure
that the device can be fabricated in a dense area in multiple layers, while the
high kinetic inductance makes the loop essentially independent of geometric
inductance, allowing it to be scaled down without sacrificing performance. The
memory is operated by a group of nanowire cryotrons patterned alongside the
storage loop, enabling us to reduce the entire memory cell to 3 {\mu}m $\times
$ 7 {\mu}m in our proof-of-concept device. In this work we present the
operation principles of a superconducting nanowire memory (nMem) and
characterize its bit error rate, speed, and power dissipation.
| arxiv topic:physics.app-ph |
arxiv_dataset-91541711.0839 | Multiplicative Updates for Polynomial Root Finding
math.NA
Let $f(x)=p(x)-q(x)$ be a polynomial with real coefficients whose roots have
nonnegative real part, where $p$ and $q$ are polynomials with nonnegative
coefficients. In this paper, we prove the following: Given an initial point
$x_0 > 0$, the multiplicative update $x_{t+1} = x_t \, p(x_t)/q(x_t)$
($t=0,1,\dots$) monotonically and linearly converges to the largest (resp.
smallest) real roots of $f$ smaller (resp. larger) than $x_0$ if $p(x_0) <
q(x_0)$ (resp. $q(x_0) < p(x_0)$). The motivation to study this algorithm comes
from the multiplicative updates proposed in the literature to solve
optimization problems with nonnegativity constraints; in particular many
variants of nonnegative matrix factorization.
| arxiv topic:math.NA |
arxiv_dataset-91551711.0849 | Learning Deep Representations of Medical Images using Siamese CNNs with
Application to Content-Based Image Retrieval
cs.CV
Deep neural networks have been investigated in learning latent
representations of medical images, yet most of the studies limit their approach
in a single supervised convolutional neural network (CNN), which usually rely
heavily on a large scale annotated dataset for training. To learn image
representations with less supervision involved, we propose a deep Siamese CNN
(SCNN) architecture that can be trained with only binary image pair
information. We evaluated the learned image representations on a task of
content-based medical image retrieval using a publicly available multiclass
diabetic retinopathy fundus image dataset. The experimental results show that
our proposed deep SCNN is comparable to the state-of-the-art single supervised
CNN, and requires much less supervision for training.
| arxiv topic:cs.CV |
arxiv_dataset-91561711.0859 | Contextual-based Image Inpainting: Infer, Match, and Translate
cs.CV
We study the task of image inpainting, which is to fill in the missing region
of an incomplete image with plausible contents. To this end, we propose a
learning-based approach to generate visually coherent completion given a
high-resolution image with missing components. In order to overcome the
difficulty to directly learn the distribution of high-dimensional image data,
we divide the task into inference and translation as two separate steps and
model each step with a deep neural network. We also use simple heuristics to
guide the propagation of local textures from the boundary to the hole. We show
that, by using such techniques, inpainting reduces to the problem of learning
two image-feature translation functions in much smaller space and hence easier
to train. We evaluate our method on several public datasets and show that we
generate results of better visual quality than previous state-of-the-art
methods.
| arxiv topic:cs.CV |
arxiv_dataset-91571711.0869 | Attended End-to-end Architecture for Age Estimation from Facial
Expression Videos
cs.CV cs.MM
The main challenges of age estimation from facial expression videos lie not
only in the modeling of the static facial appearance, but also in the capturing
of the temporal facial dynamics. Traditional techniques to this problem focus
on constructing handcrafted features to explore the discriminative information
contained in facial appearance and dynamics separately. This relies on
sophisticated feature-refinement and framework-design. In this paper, we
present an end-to-end architecture for age estimation, called Spatially-Indexed
Attention Model (SIAM), which is able to simultaneously learn both the
appearance and dynamics of age from raw videos of facial expressions.
Specifically, we employ convolutional neural networks to extract effective
latent appearance representations and feed them into recurrent networks to
model the temporal dynamics. More importantly, we propose to leverage attention
models for salience detection in both the spatial domain for each single image
and the temporal domain for the whole video as well. We design a specific
spatially-indexed attention mechanism among the convolutional layers to extract
the salient facial regions in each individual image, and a temporal attention
layer to assign attention weights to each frame. This two-pronged approach not
only improves the performance by allowing the model to focus on informative
frames and facial areas, but it also offers an interpretable correspondence
between the spatial facial regions as well as temporal frames, and the task of
age estimation. We demonstrate the strong performance of our model in
experiments on a large, gender-balanced database with 400 subjects with ages
spanning from 8 to 76 years. Experiments reveal that our model exhibits
significant superiority over the state-of-the-art methods given sufficient
training data.
| arxiv topic:cs.CV cs.MM |
arxiv_dataset-91581711.0879 | Subalgebra depth and double crossed products
math.RT
In this paper we explore the concept of depth of a ring extension when the
overall algebra factorises as a product of two subalgebras, in particular the
case of finite dimensional Hopf algebras. As a result we generalise the results
by Kadison and Young \cite{HKY} on depth of a Hopf algebra $H$ in its smash
product with a finite dimensional left $H$-module algebra $A$, $A#H$ to the
context of generalised smash products $Q^{*op}#_\psi H$ \cite{Bz1} where $Q$ is
the quotient module coalgebra associated to the extension $R\subseteq H$ of
finite dimensional Hopf algebras \cite{Ka2}\cite{HKY}\cite{H}. Moreover,
following the construction of double crossed products in \cite{Ma} and
\cite{Ma1} we use our result on factorisation algebras to get a general result
on the depth of the extension of a Hopf algebra $H$ in its Drinfel\vtick d
double $D(H)$. $\mathbf{Keywords : }$ Depth, Factorisation Algebra, Smash
Product, Drinfel\vtick d Double, Double Crossed Product, Normal Extension.
$\mathbf{Subject}$ $\mathbf{classification: }$ $20C05$, $20G05$, $16W30$,
$17B37$, $13E10$.
| arxiv topic:math.RT |
arxiv_dataset-91591711.0889 | Forbidden pairs for equality of edge-connectivity and minimum degree
math.CO
Let $\mathcal{H}$ be a class of given graphs. A graph $G$ is said to be
$\mathcal{H}$-free if $G$ contains no induced copies of $H$ for any $H \in
\mathcal{H}$. In this article, we characterize all pairs $\{R,S\}$ of graphs
such that every connected $\{R,S\}$-free graph has the same edge-connectivity
and minimum degree.
| arxiv topic:math.CO |
arxiv_dataset-91601711.0899 | Lorentzian length spaces
math.DG gr-qc math-ph math.MG math.MP
We introduce an analogue of the theory of length spaces into the setting of
Lorentzian geometry and causality theory. The r\^ole of the metric is taken
over by the time separation function, in terms of which all basic notions are
formulated. In this way we recover many fundamental results in greater
generality, while at the same time clarifying the minimal requirements for and
the interdependence of the basic building blocks of the theory. A main focus of
this work is the introduction of synthetic curvature bounds, akin to the theory
of Alexandrov and CAT$(k)$-spaces, based on triangle comparison. Applications
include Lorentzian manifolds with metrics of low regularity, closed cone
structures, and certain approaches to quantum gravity.
| arxiv topic:math.DG gr-qc math-ph math.MG math.MP |
arxiv_dataset-91611711.0909 | Invariance of Weight Distributions in Rectified MLPs
cs.LG stat.ML
An interesting approach to analyzing neural networks that has received
renewed attention is to examine the equivalent kernel of the neural network.
This is based on the fact that a fully connected feedforward network with one
hidden layer, a certain weight distribution, an activation function, and an
infinite number of neurons can be viewed as a mapping into a Hilbert space. We
derive the equivalent kernels of MLPs with ReLU or Leaky ReLU activations for
all rotationally-invariant weight distributions, generalizing a previous result
that required Gaussian weight distributions. Additionally, the Central Limit
Theorem is used to show that for certain activation functions, kernels
corresponding to layers with weight distributions having $0$ mean and finite
absolute third moment are asymptotically universal, and are well approximated
by the kernel corresponding to layers with spherical Gaussian weights. In deep
networks, as depth increases the equivalent kernel approaches a pathological
fixed point, which can be used to argue why training randomly initialized
networks can be difficult. Our results also have implications for weight
initialization.
| arxiv topic:cs.LG stat.ML |
arxiv_dataset-91621711.0919 | Host galaxy properties of mergers of stellar binary black holes and
their implications for advanced LIGO gravitational wave sources
astro-ph.GA
Understanding the host galaxy properties of stellar binary black hole (SBBH)
mergers is important for revealing the origin of the SBBH gravitational-wave
sources detected by advanced LIGO and helpful for identifying their
electromagnetic counterparts. Here we present a comprehensive analysis of the
host galaxy properties of SBBHs by implementing semi-analytical recipes for
SBBH formation and merger into cosmological galaxy formation model. If the time
delay between SBBH formation and merger ranges from $\la$\,Gyr to the Hubble
time, SBBH mergers at redshift $z\la0.3$ occur preferentially in big galaxies
with stellar mass $M_*\ga2\times10^{10}\msun$ and metallicities $Z$ peaking at
$\sim0.6Z_\odot$. However, the host galaxy stellar mass distribution of heavy
SBBH mergers ($M_{\bullet\bullet}\ga50\msun$) is bimodal with one peak at
$\sim10^9\msun$ and the other peak at $\sim2\times10^{10}\msun$. The
contribution fraction from host galaxies with $Z\la0.2Z_\odot$ to heavy mergers
is much larger than that to less heavy mergers. If SBBHs were formed in the
early universe (e.g., $z>6$), their mergers detected at $z\la0.3$ occur
preferentially in even more massive galaxies with $M_*>3\times10^{10}\msun$ and
in galaxies with metallicities mostly $\ga0.2Z_\odot$ and peaking at
$Z\sim0.6Z_\odot$, due to later cosmic assembly and enrichment of their host
galaxies. SBBH mergers at $z\la0.3$ mainly occur in spiral galaxies, but the
fraction of SBBH mergers occur in elliptical galaxies can be significant if
those SBBHs were formed in the early universe; and about two thirds of those
mergers occur in the central galaxies of dark matter halos. We also present
results on the host galaxy properties of SBBH mergers at higher redshift.
| arxiv topic:astro-ph.GA |
arxiv_dataset-91631711.0929 | Increased Prevalence of Bent Lobes for Double-Lobed Radio Galaxies in
Dense Environments
astro-ph.GA astro-ph.CO astro-ph.HE
Double-lobed radio galaxies (DLRGs) often have radio lobes which subtend an
angle of less than 180 degrees, and these bent DLRGs have been shown to
associate preferentially with galaxy clusters and groups. In this study, we
utilize a catalog of DLRGs in SDSS quasars with radio lobes visible in VLA
FIRST 20 cm radio data. We cross-match this catalog against three catalogs of
galaxies over the redshift range $0 < z < 0.70$, obtaining 81 tentative
matches. We visually examine each match and apply a number of selection
criteria, eventually obtaining a sample of 44 securely detected DLRGs which are
paired to a nearby massive galaxy, galaxy group, or galaxy cluster. Most of the
DLRGs identified in this manner are not central galaxies in the systems to
which they are matched. Using this sample, we quantify the projected density of
these matches as a function of projected separation from the central galaxy,
finding a very steep decrease in matches as the impact parameter increases (for
$\Sigma \propto b^{-m}$ we find $m = 2.5^{+0.4}_{-0.3}$) out to $b \sim 2$ Mpc.
In addition, we show that the fraction of DLRGs with bent lobes also decreases
with radius, so that if we exclude DLRGs associated with the central galaxy in
the system the bent fraction is 78\% within 1 Mpc and 56\% within 2 Mpc,
compared to just 29\% in the field; these differences are significant at
$3.6\sigma$ and $2.8\sigma$ respectively. This behavior is consistent with ram
pressure being the mechanism that causes the lobes to bend.
| arxiv topic:astro-ph.GA astro-ph.CO astro-ph.HE |
arxiv_dataset-91641711.0939 | Linear-quadratic McKean-Vlasov stochastic control problems with random
coefficients on finite and infinite horizon, and applications
math.PR math.OC
We propose a simple and original approach for solving linear-quadratic
mean-field stochastic control problems. We study both finite-horizon and
infinite-horizon problems, and allow notably some coefficients to be
stochastic. Our method is based on a suitable extension of the martingale
formulation for verification theorems in control theory. The optimal control
involves the solution to a system of Riccati ordinary differential equations
and to a linear mean-field backward stochastic differential equation, existence
and uniqueness conditions are provided for such a system. Finally, we
illustrate our results through two applications with explicit solutions: the
first one deals with a portfolio liquidation problem with trade crowding, and
the second one considers an economic model of substitutable production goods.
| arxiv topic:math.PR math.OC |
arxiv_dataset-91651711.0949 | Simulating outcomes of interventions using a multipurpose simulation
program based on the Evolutionary Causal Matrices and Markov Chain
stat.AP cs.CE cs.CY cs.SI
Predicting long-term outcomes of interventions is necessary for educational
and social policy-making processes that might widely influence our society for
the long-term. However, performing such predictions based on data from
large-scale experiments might be challenging due to the lack of time and
resources. In order to address this issue, computer simulations based on
Evolutionary Causal Matrices and Markov Chain can be used to predict long-term
outcomes with relatively small-scale lab data. In this paper, we introduce
Python classes implementing a computer simulation model and presented some
pilots implementations demonstrating how the model can be utilized for
predicting outcomes of diverse interventions. We also introduce the
class-structured simulation module both with real experimental data and with
hypothetical data formulated based on social psychological theories. Classes
developed and tested in the present study provide researchers and practitioners
with a feasible and practical method to simulate intervention outcomes
prospectively.
| arxiv topic:stat.AP cs.CE cs.CY cs.SI |
arxiv_dataset-91661711.0959 | Scalable and Efficient Configuration of Time-Division Multiplexed
Resources
cs.DC
Consumer-electronics systems are becoming increasingly complex as the number
of integrated applications is growing. Some of these applications have
real-time requirements, while other non-real-time applications only require
good average performance. For cost-efficient design, contemporary platforms
feature an increasing number of cores that share resources, such as memories
and interconnects. However, resource sharing causes contention that must be
resolved by a resource arbiter, such as Time-Division Multiplexing. A key
challenge is to configure this arbiter to satisfy the bandwidth and latency
requirements of the real-time applications, while maximizing the slack capacity
to improve performance of their non-real-time counterparts. As this
configuration problem is NP-hard, a sophisticated automated configuration
method is required to avoid negatively impacting design time.
The main contributions of this article are: (1) an optimal approach that
takes an existing integer linear programming (ILP) model addressing the problem
and wraps it in a branch-and-price framework to improve scalability. (2) A
faster heuristic algorithm that typically provides near-optimal solutions. (3)
An experimental evaluation that quantitatively compares the branch-and-price
approach to the previously formulated ILP model and the proposed heuristic. (4)
A case study of an HD video and graphics processing system that demonstrates
the practical applicability of the approach.
| arxiv topic:cs.DC |
arxiv_dataset-91671711.0969 | Real-Time Fair Resource Allocation in Distributed Software Defined
Networks
cs.NI
The performance of computer networks relies on how bandwidth is shared among
different flows. Fair resource allocation is a challenging problem particularly
when the flows evolve over time.To address this issue, bandwidth sharing
techniques that quickly react to the traffic fluctuations are of interest,
especially in large scale settings with hundreds of nodes and thousands of
flows. In this context, we propose a distributed algorithm that tackles the
fair resource allocation problem in a distributed SDN control architecture. Our
algorithm continuously generates a sequence of resource allocation solutions
converging to the fair allocation while always remaining feasible, a property
that standard primal-dual decomposition methods often lack. Thanks to the
distribution of all computer intensive operations, we demonstrate that we can
handle large instances in real-time.
| arxiv topic:cs.NI |
arxiv_dataset-91681711.0979 | Particle-in-cell simulations of anomalous transport in a Penning
discharge
physics.plasm-ph
Electrostatic particle-in-cell simulations of a Penning discharge are
performed in order to investigate azimuthally asymmetric, spoke-like structures
previously observed in experiments. Two-dimensional simulations show that for
Penning-discharge conditions, a persistent nonlinear spoke-like structure forms
readily and rotates in the direction of ExB and electron diamagnetic drifts.
The azimuthal velocity is within about a factor of two of the ion acoustic
speed. The spoke frequency follows the experimentally observed scaling with ion
mass, which indicates the importance of ion inertia in spoke formation. The
spoke provides enhanced (anomalous) radial electron transport, and the
effective cross-field conductivity is several times larger than the classical
(collisional) value. The level of anomalous current obtained in the simulations
is in good agreement with the experimental data. The rotating spoke channels
most of the radial current, observable by an edge probe as short pulses.
| arxiv topic:physics.plasm-ph |
arxiv_dataset-91691711.0989 | Prediction and Prevention of Disproportionally Dominant Agents in
Complex Networks
physics.soc-ph cs.SI
We develop an early warning system and subsequent optimal intervention policy
to avoid the formation of disproportional dominance (`winner-takes-all') in
growing complex networks. This is modeled as a system of interacting agents,
whereby the rate at which an agent establishes connections to others is
proportional to its already existing number of connections and its intrinsic
fitness. We derive an exact 4-dimensional phase diagram that separates the
growing system into two regimes: one where the `fit-get-richer' (FGR) and one
where, eventually, the `winner-takes-all' (WTA). By calibrating the system's
parameters with maximum likelihood, its distance from the WTA regime can be
monitored in real time. This is demonstrated by applying the theory to the
eToro social trading platform where users mimic each others trades. If the
system state is within or close to the WTA regime, we show how to efficiently
control the system back into a more stable state along a geodesic path in the
space of fitness distributions. It turns out that the common measure of
penalizing the most dominant agents does not solve sustainably the problem of
drastic inequity. Instead, interventions that first create a critical mass of
high-fitness individuals followed by pushing the relatively low-fitness
individuals upward is the best way to avoid swelling inequity and escalating
fragility.
| arxiv topic:physics.soc-ph cs.SI |
arxiv_dataset-91701711.0999 | Identification of Strong Edges in AMP Chain Graphs
math.CO cs.AI
The essential graph is a distinguished member of a Markov equivalence class
of AMP chain graphs. However, the directed edges in the essential graph are not
necessarily strong or invariant, i.e. they may not be shared by every member of
the equivalence class. Likewise for the undirected edges. In this paper, we
develop a procedure for identifying which edges in an essential graph are
strong. We also show how this makes it possible to bound some causal effects
when the true chain graph is unknown.
| arxiv topic:math.CO cs.AI |
arxiv_dataset-91711711.1009 | Spatio-temporal Modeling of Yellow Taxi Demands in New York City Using
Generalized STAR Models
stat.AP
A highly dynamic urban space in a metropolis such as New York City, the
spatio-temporal variation in demand for transportation, particularly taxis, is
impacted by various factors such as commuting, weather, road work and closures,
disruption in transit services, etc. To understand the user demand for taxis
through space and time, a generalized spatio-temporal autoregressive (STAR)
model is proposed in this study. In order to deal with the high dimensionality
of the model, LASSO-type penalized methods are proposed to tackle the parameter
estimation. The forecasting performance of the proposed models is measured
using the out-of-sample mean squared prediction error (MSPE), and it is found
that the proposed models outperform other alternative models such as vector
autoregressive (VAR) models. The proposed modeling framework has an easily
interpretable parameter structure and practical to be applied by taxi
operators. Efficiency of the proposed model also helps in model estimation in
real-time applications.
| arxiv topic:stat.AP |
arxiv_dataset-91721711.1019 | An Efficient Fog-Assisted Unstable Sensor Detection Scheme with Privacy
Preserved
cs.CR
The Internet of Thing (IoT) has been a hot topic in both research community
and industry. It is anticipated that in future IoT, an enormous number of
sensors will collect the physical information every moment to enable the
control center making better decisions to improve the quality of service (QoS).
However, the sensors maybe faulty and thus generate inaccurate data which would
compromise the decision making. To guarantee the QoS, the system should be able
to detect faulty sensors so as to eliminate the damages of inaccurate data.
Various faulty sensor detection mechanisms have been developed in the context
of wireless sensor network (WSN). Some of them are only fit for WSN while the
others would bring a communication burden to control center. To detect the
faulty sensors for general IoT applications and save the communication resource
at the same time, an efficient faulty sensor detection scheme is proposed in
this paper. The proposed scheme takes advantage of fog computing to save the
computation and communication resource of control center. To preserve the
privacy of sensor data, the Paillier Cryptosystem is adopted in the fog
computing. The batch verification technique is applied to achieve efficient
authentication. The performance analyses are presented to demonstrate that the
proposed detection scheme is able to conserve the communication resource of
control center and achieve a high true positive ratio while maintaining an
acceptable false positive ratio. The scheme could also withstand various
security attacks and preserve data privacy.
| arxiv topic:cs.CR |
arxiv_dataset-91731711.1029 | Scalable and Compact 3D Action Recognition with Approximated RBF Kernel
Machines
cs.CV
Despite the recent deep learning (DL) revolution, kernel machines still
remain powerful methods for action recognition. DL has brought the use of large
datasets and this is typically a problem for kernel approaches, which are not
scaling up efficiently due to kernel Gram matrices. Nevertheless, kernel
methods are still attractive and more generally applicable since they can
equally manage different sizes of the datasets, also in cases where DL
techniques show some limitations. This work investigates these issues by
proposing an explicit approximated representation that, together with a linear
model, is an equivalent, yet scalable, implementation of a kernel machine. Our
approximation is directly inspired by the exact feature map that is induced by
an RBF Gaussian kernel but, unlike the latter, it is finite dimensional and
very compact. We justify the soundness of our idea with a theoretical analysis
which proves the unbiasedness of the approximation, and provides a vanishing
bound for its variance, which is shown to decrease much rapidly than in
alternative methods in the literature. In a broad experimental validation, we
assess the superiority of our approximation in terms of 1) ease and speed of
training, 2) compactness of the model, and 3) improvements with respect to the
state-of-the-art performance.
| arxiv topic:cs.CV |
arxiv_dataset-91741711.1039 | Symmetries of the dynamics and Noether theorem in classical mechanics
physics.class-ph hep-th
The aim of this note is to discuss the relation between one-parameter
continuous symmetries of the dynamics, defined on physical grounds, and
conservation laws. In the Hamiltonian formulation, such symmetries of the
dynamics in general leave the Hamiltonian invariant only up to a total
derivative $ d G(q)/d t$ . In this more general case, the corresponding
formulation of Noether theorem gives that the conservation law displays a sort
of ano\-ma\-ly, the constant of motion being the sum of the canonical generator
of the symmetry transformations plus the generator $G$ of the gauge
transformation $q_i \rightarrow q_i$, $p_i \rightarrow p_i - \partial G/
\partial q_i$.
| arxiv topic:physics.class-ph hep-th |
arxiv_dataset-91751711.1049 | Tensor Modes in Pure Natural Inflation
hep-ph astro-ph.CO hep-lat hep-th
We study tensor modes in pure natural inflation (arXiv:1706.08522), a
recently-proposed inflationary model in which an axionic inflaton couples to
pure Yang-Mills gauge fields. We find that the tensor-to-scalar ratio r is
naturally bounded from below. This bound originates from the finiteness of the
number of metastable branches of vacua in pure Yang-Mills theories. Details of
the model can be probed by future cosmic microwave background experiments and
improved lattice gauge theory calculations of the theta-angle dependence of the
vacuum energy.
| arxiv topic:hep-ph astro-ph.CO hep-lat hep-th |
arxiv_dataset-91761711.1059 | Stellar populations of galaxies in the ALHAMBRA survey up to $z \sim 1$.
II. Stellar content of quiescent galaxies within the dust-corrected stellar
mass$-$colour and the $UVJ$ colour$-$colour diagrams
astro-ph.GA
Our aim is to determine the distribution of stellar population parameters
(extinction, age, metallicity, and star formation rate) of quiescent galaxies
within the rest-frame stellar mass$-$colour and $UVJ$ colour$-$colour diagrams
corrected for extinction up to $z\sim1$. These novel diagrams reduce the
contamination in samples of quiescent galaxies owing to dust-reddened galaxies,
and they provide useful constraints on stellar population parameters. We set
constraints on the stellar population parameters of quiescent galaxies
combining the ALHAMBRA multi-filter photo-spectra with our SED-fitting code
MUFFIT, making use of composite stellar population models. The extinction
obtained by MUFFIT allowed us to remove dusty star-forming (DSF) galaxies from
the sample of red $UVJ$ galaxies. The distributions of stellar population
parameters across these rest-frame diagrams are revealed after the dust
correction and are fitted by the LOESS method to reduce uncertainty effects.
Quiescent galaxy samples defined via classical $UVJ$ diagrams are typically
contaminated by a $\sim20$% fraction of DSF galaxies. A significant part of the
galaxies in the green valley are actually obscured star-forming galaxies
($\sim30-65$%). Consequently, the transition of galaxies from the blue cloud to
the red sequence, and hence the related mechanisms for quenching, seems to be
much more efficient and faster than previously reported. The rest-frame stellar
mass$-$colour and $UVJ$ colour$-$colour diagrams are useful for constraining
the age, metallicity, extinction, and star formation rate of quiescent galaxies
by only their redshift, rest-frame colours, and/or stellar mass. Dust
correction plays an important role in understanding how quiescent galaxies are
distributed in these diagrams and is key to performing a pure selection of
quiescent galaxies via intrinsic colours.
| arxiv topic:astro-ph.GA |
arxiv_dataset-91771711.1069 | Load Forecasting Based Distribution System Network Reconfiguration-A
Distributed Data-Driven Approach
cs.SY
In this paper, a short-term load forecasting approach based network
reconfiguration is proposed in a parallel manner. Specifically, a support
vector regression (SVR) based short-term load forecasting approach is designed
to provide an accurate load prediction and benefit the network reconfiguration.
Because of the nonconvexity of the three-phase balanced optimal power flow, a
second-order cone program (SOCP) based approach is used to relax the optimal
power flow problem. Then, the alternating direction method of multipliers
(ADMM) is used to compute the optimal power flow in distributed manner.
Considering the limited number of the switches and the increasing computation
capability, the proposed network reconfiguration is solved in a parallel way.
The numerical results demonstrate the feasible and effectiveness of the
proposed approach.
| arxiv topic:cs.SY |
arxiv_dataset-91781711.1079 | Thermal contribution to the spin-orbit torque in metallic/ferrimagnetic
systems
cond-mat.mtrl-sci
We report a systematic study of current-induced perpendicular magnetization
switching in W/Co$_{x}$Tb$_{1-x}$/Al thin films with strong perpendicular
magnetic anisotropy. Various Co$_{x}$Tb$_{1-x}$ ferrimagnetic alloys with
different magnetic compensation temperatures are presented. The systems are
characterized using MOKE, SQUID and anomalous Hall resistance at different
cryostat temperature ranging from 10 K to 350 K. The current-switching
experiments are performed in the spin-orbit torque geometry where the current
pulses are injected in plane and the magnetization reversal is detected by
measuring the Hall resistance. The full reversal magnetization has been
observed in all samples. Some experimental results could only be explained by
the strong sample heating effect during the current pulses injection. We have
found that, for a given composition $x$ and switching polarity, the devices
always reach the same temperature $\textit{T}_{switch}(x)$ before switching
independently of the cryostat temperature. $\textit{T}_{switch}$ seems to scale
with the Curie temperature of the Co$_{x}$Tb$_{1-x}$ ferrimagnetic alloys. This
explains the evolution of the critical current (and critical current density)
as a function of the alloy concentration. Future application could take
advantages of this heating effect which allows reducing the in-plane external
field. Unexpected double magnetization switching has been observed when the
heat generated by the current allows crosses the compensation temperature.
| arxiv topic:cond-mat.mtrl-sci |
arxiv_dataset-91791711.1089 | Particle collisions and optical effects in the mining Kerr--Newman
spacetimes
gr-qc
We study ultra-high-energy particle collisions and optical effects in the
extraordinary class of mining braneworld Kerr-Newman (KN) naked singularity
spacetimes, predicting extremely high efficiency of Keplerian accretion, and
compare the results to those related to the other classes of the KN naked
singularity and black hole spacetimes. We demonstrate that in the mining KN
spacetimes the ultra-high centre-of-mass energy occurs for collisions of
particles following the extremely-low-energy stable circular geodesics of the
\uvozovky{mining regime}, colliding with large family of incoming particles,
e.g., those infalling from the marginally stable counter-rotating circular
geodesics. This is qualitatively different situation in comparison to the
standard KN naked singularity or black hole spacetimes where the collisional
ultra-high centre-of-mass energy can be obtained only in the near-extreme
spacetimes. We also show that observers following the stable circular geodesics
of the mining regime can register extremely blue-shifted radiation incoming
from the Universe, and see strongly deformed sky due to highly relativistic
motion along such stable orbits. The strongly blue-shifted radiation could be
thus a significant source of energy for such orbiting observers.
| arxiv topic:gr-qc |
arxiv_dataset-91801711.1099 | Balanced Spanning Caterpillars
math.CO
A $p$-caterpillar is a caterpillar such that every non-leaf vertex is
adjacent to exactly $p$ leaves. We give a tight minimum degree condition for a
graph to have a spanning $p$-caterpillar.
| arxiv topic:math.CO |
arxiv_dataset-91811711.1109 | Rational dilation problems associated with constrained algebras
math.FA math.CV
It is shown that rational dilation fails on broad collection of distinguished
varieties associated to constrained subalgebras of the disk algebra of the form
C + B A(D), where B is a finite Blaschke product with two or more zeros. This
is accomplished in part by finding a minimal set of test functions. In
addition, an Agler-Pick interpolation theorem is given and it is proved that
there exist Kaijser-Varopoulos style examples of non-contractive unital
representations where the generators are contractions.
| arxiv topic:math.FA math.CV |
arxiv_dataset-91821711.1119 | A Multivariate Poisson-Log Normal Mixture Model for Clustering
Transcriptome Sequencing Data
stat.ME q-bio.QM stat.CO
High-dimensional data of discrete and skewed nature is commonly encountered
in high-throughput sequencing studies. Analyzing the network itself or the
interplay between genes in this type of data continues to present many
challenges. As data visualization techniques become cumbersome for higher
dimensions and unconvincing when there is no clear separation between
homogeneous subgroups within the data, cluster analysis provides an intuitive
alternative. The aim of applying mixture model-based clustering in this context
is to discover groups of co-expressed genes, which can shed light on biological
functions and pathways of gene products. A mixture of multivariate Poisson-Log
Normal (MPLN) model is proposed for clustering of high-throughput transcriptome
sequencing data. The MPLN model is able to fit a wide range of correlation and
overdispersion situations, and is ideal for modeling multivariate count data
from RNA sequencing studies. Parameter estimation is carried out via a Markov
chain Monte Carlo expectation-maximization algorithm (MCMC-EM), and information
criteria are used for model selection.
| arxiv topic:stat.ME q-bio.QM stat.CO |
arxiv_dataset-91831711.1129 | Asymptotic Behavior of Colored Jones polynomial and Turaev-Viro
Invariant of figure eight knot
math.GT
In this paper we investigate the asymptotic behavior of the colored Jones
polynomials and the Turaev-Viro invariants for the figure eight knot. More
precisely, we consider the $M$-th colored Jones polynomials evaluated at
$(N+1/2)$-th root of unity with a fixed limiting ratio, $s$, of $M$ and
$(N+1/2)$. We find out the asymptotic expansion formula (AEF) of the colored
Jones polynomials of the figure eight knot with $s$ close to $1$. Nonetheless,
we show that the exponential growth rate of the colored Jones polynomials of
the figure eight knot with $s$ close to $1/2$ is strictly less than those with
$s$ close to $1$. It is known that the Turaev Viro invariant of the figure
eight knot can be expressed in terms of a sum of its colored Jones polynomials.
Our results show that this sum is asymptotically equal to the sum of the terms
with $s$ close to 1. As an application of the asymptotic behavior of the
colored Jones polynomials, we obtain the asymptotic expansion formula for the
Turaev-Viro invariants of the figure eight knot. Finally, we suggest a possible
generalization of our approach so as to relate the AEF for the colored Jones
polynomials and the AEF for the Turaev-Viro invariants for general hyperbolic
knots.
| arxiv topic:math.GT |
arxiv_dataset-91841711.1139 | Semi-Distributed Demand Response Solutions for Smart Homes
cs.NI
The Internet of Things (IoT) paradigm brings an opportunity for advanced
Demand Response (DR) solutions. It enables visibility and control on the
various appliances that may consume, store or generate energy within a home. It
has been shown that a centralized control on the appliances of a set of
households leads to efficient DR mechanisms; unfortunately, such solutions
raise privacy and scalability issues. In this chapter we propose an approach
that deals with these issues. Specifically, we introduce a scalable two-levels
control system where a centralized controller allocates power to each house on
one side and, each household implements a DR local solution on the other side.
A limited feedback to the centralized controller allows to enhance the
performance with little impact on privacy. The solution is proposed for the
general framework of capacity markets.
| arxiv topic:cs.NI |
arxiv_dataset-91851711.1149 | Microscopic theory of cavity-enhanced single-photon emission from
optical two-photon Raman processes
cond-mat.mes-hall
We consider cavity-enhanced single-photon generation from stimulated
two-photon Raman processes in three-level systems. We compare four fundamental
system configurations, one $\Lambda$-, one V- and two ladder ($\Xi$-)
configurations. These can be realized as subsystems of a single quantum dot or
of quantum-dot molecules. For a new microscopic understanding of the Raman
process, we analyze the Heisenberg equation of motion applying the
cluster-expansion scheme. Within this formalism an exact and rigorous
definition of a cavity-enhanced Raman photon via its corresponding Raman
correlation is possible. This definition for example enables us to
systematically investigate the on-demand potential of Raman-transition-based
single-photon sources. The four system arrangements can be divided into two
subclasses, $\Lambda$-type and V-type, which exhibit strongly different
Raman-emission characteristics and Raman-emission probabilities. Moreover, our
approach reveals whether the Raman path generates a single photon or just
induces destructive quantum interference with other excitation paths. Based on
our findings and as a first application, we gain a more detailed understanding
of experimental data from the literature. Our analysis and results are also
transferable to the case of atomic three-level-resonator systems, and can be
extended to more complicated multi-level schemes.
| arxiv topic:cond-mat.mes-hall |
arxiv_dataset-91861712.00001 | Some Physics Notions on Monetary Standard
q-fin.GN physics.soc-ph
Regardless of the gold-standard being considered as outdated, it provides
valuable signs concerning the development of novel monetary standards, better
adjusted to the current macroeconomic environment. By using a point of view of
classical physics, the intent of this work is doing a review of the concept of
monetary standard and show that the energy matrix of an economy together with a
new monetary standard, based on the energy supply capacity, can play an
essential role in the sustainable growth.
| arxiv topic:q-fin.GN physics.soc-ph |
arxiv_dataset-91871712.00101 | A new radiobiology-based HDR brachytherapy treatment planning algorithm
used to investigate the potential for hypofractionation in cervical cancer
physics.med-ph
Most commercially available treatment planning systems for brachytherapy
operate based on physical dose and do not incorporate fractionation or
tissue-specific response. The purpose of this study is to investigate the
potential for hypofractionation in HDR brachytherapy, thereby reducing the
number of implants required. A new treatment planning algorithm was built in
order to optimize based on tissue and fractionation specific parameters.
Different fractionation schemes were considered for 6 patients, and plans were
created using the new algorithm. A baseline fractionation scheme consisting of
5 fractions was compared to hypofractionated plans of 1 to 4 fractions. The
effectiveness of each plan was evaluated using radiobiological criteria taken
from GEC-ESTRO guidelines. The results of this study indicate that an
optimization algorithm based on biological parameters has similar functionality
to traditional planning methods with the additional ability to account for
fractionation effects. Using this algorithm, it was shown that plans consisting
of 3 and 4 fractions have comparable target coverage with equivalent normal
tissue exposure. In some specific cases, further fractionation may present
acceptable target coverage as well.
| arxiv topic:physics.med-ph |
arxiv_dataset-91881712.00201 | A 3D Coarse-to-Fine Framework for Volumetric Medical Image Segmentation
cs.CV
In this paper, we adopt 3D Convolutional Neural Networks to segment
volumetric medical images. Although deep neural networks have been proven to be
very effective on many 2D vision tasks, it is still challenging to apply them
to 3D tasks due to the limited amount of annotated 3D data and limited
computational resources. We propose a novel 3D-based coarse-to-fine framework
to effectively and efficiently tackle these challenges. The proposed 3D-based
framework outperforms the 2D counterpart to a large margin since it can
leverage the rich spatial infor- mation along all three axes. We conduct
experiments on two datasets which include healthy and pathological pancreases
respectively, and achieve the current state-of-the-art in terms of
Dice-S{\o}rensen Coefficient (DSC). On the NIH pancreas segmentation dataset,
we outperform the previous best by an average of over 2%, and the worst case is
improved by 7% to reach almost 70%, which indicates the reliability of our
framework in clinical applications.
| arxiv topic:cs.CV |
arxiv_dataset-91891712.00301 | Towards Time-Limited $\mathcal H_2$-Optimal Model Order Reduction
math.OC
In order to solve partial differential equations numerically and accurately,
a high order spatial discretization is usually needed. Model order reduction
(MOR) techniques are often used to reduce the order of spatially-discretized
systems and hence reduce computational complexity. A particular class of MOR
techniques are $\mathcal H_2$-optimal methods such as the iterative rational
Krylov subspace algorithm (IRKA) and related schemes. However, these methods
are used to obtain good approximations on a infinite time-horizon. Thus, in
this work, our main goal is to discuss MOR schemes for time-limited linear
systems. For this, we propose an alternative time-limited $\mathcal H_2$-norm
and show its connection with the time-limited Gramians. We then provide
first-order optimality conditions for an optimal reduced order model (ROM) with
respect to the time-limited $\mathcal H_2$-norm. Based on these optimality
conditions, we propose an iterative scheme, which, upon convergence, aims at
satisfying these conditions approximately. Then, we analyze how far away the
obtained ROM due to the proposed algorithm is from satisfying the optimality
conditions. We test the efficiency of the proposed iterative scheme using
various numerical examples and illustrate that the newly proposed iterative
method can lead to a better reduced-order compared to the unrestricted IRKA in
the finite time interval of interest.
| arxiv topic:math.OC |
arxiv_dataset-91901712.00401 | On the martingale decompositions of Gundy, Meyer, and Yoeurp in infinite
dimensions
math.PR math.FA
We show that the canonical decomposition (comprising both the Meyer-Yoeurp
and the Yoeurp decompositions) of a general $X$-valued local martingale is
possible if and only if $X$ has the UMD property. More precisely, $X$ is a UMD
Banach space if and only if for any $X$-valued local martingale $M$ there exist
a continuous local martingale $M^c$, a purely discontinuous quasi-left
continuous local martingale $M^q$, and a purely discontinuous local martingale
$M^a$ with accessible jumps such that $M = M^c + M^q + M^a$. The corresponding
weak $L^1$-estimates are provided. Important tools used in the proof are a new
version of Gundy's decomposition of continuous-time martingales and weak
$L^1$-bounds for a certain class of vector-valued continuous-time martingale
transforms.
| arxiv topic:math.PR math.FA |
arxiv_dataset-91911712.00501 | Cryogenic System for the Cryomodule Test Stand at Fermilab
physics.acc-ph
This paper describes the cryogenic system for the Cryomodule Test Stand
(CMTS) at the new Cryomodule Test Facility (CMTF) located at Fermilab. CMTS is
designed for production testing of the 1.3 GHz and 3.9 GHz cryomodules to be
used in the Linac Coherent Light Source II (LCLSII), which is an upgrade to an
existing accelerator at Stanford Linear Accelerator Laboratory (SLAC). This
paper will focus on the cryogenic system that extends from the helium
refrigeration plant to the CMTS cave. Topics covered will include component
design, installation and commissioning progress, and operational plans. The
paper will conclude with a description of the heat load measurement plan.
| arxiv topic:physics.acc-ph |
arxiv_dataset-91921712.00601 | Mirror Symmetry and Modularity
hep-th
This is a review article on mirror symmetry and aspects of it related to the
theory of modular forms. We describe this topic along its historical
development and connect to some more recent results toward the end. The article
is for publication in a special issue of ICCM Notices.
| arxiv topic:hep-th |
arxiv_dataset-91931712.00701 | Test of depending frequencies of the variable Stars of OC: NGC 6866
astro-ph.SR
The search of secondary pulsations is carried out to understand the possible
relations among the known parameters of variables of the cluster, NGC 6866.
These pulsations arise due to the various ongoing physical phenomena of the
variables. Moreover, pulsations of the variables are identified through the
visual inspection of their frequency-amplitude distributions. A total of 18
variables among the 28 known variables are showing the secondary pulsation
modes. Furthermore, these pulsation modes do not occur for PV, EA, EB,
Elliptical and semi-regular. In addition, the field variables seem to be the
red-component-stars (RCS) for the studied cluster. The smoothness of the
frequency-amplitude curves, signal to noise ratio and the significant limits
are play major role for deciding the real peak or frequency values. We are not
rejected those amplitude peak of parabolic patterns, for which, the amplitude
is greater than then significant limit of variables. The weight of pulsation
frequencies is given to be 0.5 for non full cyclic variation but the amplitude
is greater than significant limit. Similarly, our present analysis does not
support the HADS characteristics of previous known HADS stars within stellar
cluster NGC 6866. We are also proposed to new correlation between the secondary
pulsation modes (depending frequencies) and the absolute magnitude of known
variables.
| arxiv topic:astro-ph.SR |
arxiv_dataset-91941712.00801 | Adatom pair distribution up to half coverage: O-Pd(100)
cond-mat.mtrl-sci
The superposition approximation and the Born-Green-Yvon (BGY) equation allows
calculation of pair distributions in thermal equilibrium from pair potentials.
A 2-d variant can be used to derive adatom pair distributions from arbitrary
analytical pair potentials. As practical example substrate mediated elastic
interactions, fitted previously to first principles (FP) calculations, are used
to derive adatom pair distributions of OPd(100). The evaluation method utilizes
the particle-hole symmetry of the pair interaction lattice gas Hamiltonian. The
nonlinear BGY-type integral equation is solved numerically up to half coverage
using power series expansion of coverage. The resulting adatom pair- and
three-body distributions are used to analyze the short-range order of adatoms.
A Monte Carlo (MC) simulation was performed in parallel to compare the current
model with established methods. MC derived pair distributions fit well to those
found with the analytical model, except in the high coverage region. The
Fourier transformed pair correlations are compared with experimental LEED spot
data and provide additional insight. Due to significant attraction the model
predicts formation of 3rd and 4th nearest neighbors (n.n.) at small 3rd n.n.
chains. A long range order of adatoms like a p(2x2) lattice is not found with
the current model but a glassy structure is proposed as also indicated by the
equilibrium Monte Carlo configurations. The glassy structure is assumed to
contain fluctuations explaining broad p(2x2) LEED spots in the 0.25 monolayer
region. The assumptions and limitations of the model towards higher coverages
are discussed and open questions are formulated.
| arxiv topic:cond-mat.mtrl-sci |
arxiv_dataset-91951712.00901 | Torsion in Gauge Theory
gr-qc
The potential conflict between torsion and gauge symmetry in the
Riemann-Cartan curved space-time was noted by Kibble in his 1961 pioneering
paper, and has since been discussed by many authors. Kibble suggested that, to
preserve gauge symmetry, one should forgo the covariant derivative in favor of
the ordinary derivative in the definition of the field strength F_{\mu}{\nu}
for massless gauge theories, while for massive vector fields covariant
derivatives should be adopted. This view was further emphasized by Hehl and
collaborators in their influential 1976 review paper. We address the question
of whether this deviation from normal procedure of forgoing covariant
derivatives in curved spacetime with torsion could give rise to inconsistencies
in the theory, such as the quantum renormalizability of a realistic interacting
theory. We demonstrate in this note the one-loop renormalizability of a
realistic gauge theory of gauge bosons interacting with Dirac spinors, such as
the SU(3) chromodynamics, for the case of a curved Riemann-Cartan spacetime
with totally anti-symmetric torsion. This affirmative confirmation is one step
towards providing justification for the assertion that the flat-space
definition of the gauge field strength should be adopted as the proper
definition.
| arxiv topic:gr-qc |
arxiv_dataset-91961712.01001 | Specifying and Computing Causes for Query Answers in Databases via
Database Repairs and Repair Programs
cs.DB cs.AI cs.LO
A correspondence between database tuples as causes for query answers in
databases and tuple-based repairs of inconsistent databases with respect to
denial constraints has already been established. In this work, answer-set
programs that specify repairs of databases are used as a basis for solving
computational and reasoning problems about causes. Here, causes are also
introduced at the attribute level by appealing to a both null-based and
attribute-based repair semantics. The corresponding repair programs are
presented, and they are used as a basis for computation and reasoning about
attribute-level causes. They are extended to deal with the case of causality
under integrity constraints.
| arxiv topic:cs.DB cs.AI cs.LO |
arxiv_dataset-91971712.01101 | Two null gravitational cones in the theory of GPS-intersatellite
communications between two moving satellites. I. Physical and mathematical
theory of the space-time interval and the geodesic distance on intersecting
null cones
gr-qc
Several space missions such as GRACE, GRAIL, ACES and others rely on
intersatellite communications (ISC) between two satellites at a large distance
one from another. The main goal of the theory is to formulate all the
navigation observables within the General Relativity Theory. The same approach
should be applied also to the intersatellite GPS-communications (in perspective
also between the GPS, GLONASS and Galileo satellite constellations). In this
paper a theoretical approach has been developed for ISC between two satellites
moving on (one-plane) elliptical orbits, based on the introduction of two
gravity null cones with origins at the emitting-signal and receiving-signal
satellites. The two null cones account for the variable distance between the
satellites during their uncorrelated motion.The intersection of the two null
cones defines a distance, which can be found from a differential equation in
full derivatives. This distance is the space-time interval in GRT. Applying
some theorems from higher algebra, it was proved that this space-time distance
can become zero, consequently it can be also negative and positive. But in
order to represent the geodesic distance travelled by the signal, the
space-time interval has to be "compatible" with the Euclidean distance. So this
"compatibility condition", conditionally called "condition for ISC", is the
most important consequence of the theory. The other important consequence is
that the geodesic distance turns out to be the space-time interval, but with
account also of the "condition for ISC". This interpretation enables the strict
mathematical proof that the geodesic distance is greater than the Euclidean
distance - a result, entirely based on the "two null cones approach" and
moreover, without any use of the Shapiro delay formulae. Consistency between
several other newly derived numerical parameters is noted.
| arxiv topic:gr-qc |
arxiv_dataset-91981712.01201 | Charged Obstacles Augment Electrokinetic Energy Conversion Efficiency
physics.flu-dyn
In the present study, we delineate the effect of introducing flow
obstructions on streaming potential and energy conversion efficiency in a
narrow fluidic confinement taking into consideration the wall hydrodynamic
slip, finite ionic size, and local permittivity variation effects. We consider
two types of the geometric pattern of flow obstacle between which regular
pattern turns out to be more effective. It is observed that, implementing
structured flow obstacles of radii greater than 10% of channel height and
charge density ratio (charge density of flow obstacle surface to that of
channel wall) greater than or equal to 9 renders significant enhancement of
power generation efficiency. On the other hand, it is effective to operate at a
charge density ratio~1 for obstacles radii less than or equal to 10% of channel
height. An effective normalized pitch length of magnitude 0.6 or above has to
be maintained in order to obtain optimum energy conversion efficiency. We found
that implementation of charged flow obstacle causes a significant enhancement
of energy conversion efficiency (~18% with regular pattern) comparing to planar
slit channel (~4%) without considering wall hydrodynamic slip and steric
effects. Introducing finite ionic size and wall hydrodynamic slip effect,
pertinent to flows in narrow confinement, leads to further enhancement in
electrokinetic energy conversion efficiency.
| arxiv topic:physics.flu-dyn |
arxiv_dataset-91991712.01301 | Asymptotic properties of random unlabelled block-weighted graphs
math.CO math.PR
We study the asymptotic shape of random unlabelled graphs subject to certain
subcriticality conditions. The graphs are sampled with probability proportional
to a product of Boltzmann weights assigned to their $2$-connected components.
As their number of vertices tends to infinity, we show that they admit the
Brownian tree as Gromov--Hausdorff--Prokhorov scaling limit, and converge in a
strengthened Benjamini--Schramm sense toward an infinite random graph. We also
consider a family of random graphs that are allowed to be disconnected. Here a
giant connected component emerges and the small fragments converge without any
rescaling towards a finite random limit graph.
| arxiv topic:math.CO math.PR |
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