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arxiv_dataset-103001809.09984 | Dynamic stabilization of plasma instability
physics.plasm-ph physics.flu-dyn
The paper presents a review of dynamic stabilization mechanisms for plasma
instabilities. One of the dynamic stabilization mechanisms for plasma
instability was proposed in the papers [Phys. Plasmas 19, 024503(2012) and
references therein], based on a perturbation phase control. In general,
instabilities emerge from the perturbations of the physical quantity. Normally
the perturbation phase is unknown so that the instability growth rate is
discussed. However, if the perturbation phase is known, the instability growth
can be controlled by a superimposition of perturbations imposed actively: if
the perturbation is introduced by, for example, a driving beam axis oscillation
or so, the perturbation phase can be controlled and the instability growth is
mitigated by the superimposition of the growing perturbations. Based on this
mechanism we present the application results of the dynamic stabilization
mechanism to the Rayleigh-Taylor (R-T) instability and to the filamentation
instability as typical examples in this paper. On the other hand, in the paper
[Comments Plasma Phys. Controlled Fusion 3, 1(1977)] another mechanism was
proposed to stabilize the R-T instability based on the strong oscillation of
acceleration, which was realized by the laser intensity modulation in laser
inertial fusion [Phys. Rev. Lett. 71, 3131(1993)]. In the latter mechanism, the
total acceleration strongly oscillates, so that the additional oscillating
force is added to create a new stable window in the system. Originally the
latter mechanism was proposed by P. L. Kapitza, and it was applied to the
stabilization of an inverted pendulum. In this paper we review the two dynamic
stabilization mechanisms, and present the application results of the former
dynamic stabilization mechanism.
| arxiv topic:physics.plasm-ph physics.flu-dyn |
arxiv_dataset-103011809.10084 | Integral bases and monogenity of pure fields
math.NT
Let $m$ be a square-free integer ($m\neq 0,\pm 1$). We show that the
structure of the integral bases of the fields $K=Q(\sqrt[n]{m})$ are periodic
in $m$. For $3\leq n\leq 9$ we show that the period length is $n^2$. We
explicitly describe the integral bases, and for $n=3,4,5,6,8$ we explicitly
calculate the index forms of $K$. This enables us in many cases to characterize
the monogenity of these fields. Using the explicit form of the index forms
yields a new technic that enables us to derive new results on monogenity and to
get several former results as easy consequences. For $n=4,6,8$ we give an
almost complete characterization of the monogenity of pure fields.
| arxiv topic:math.NT |
arxiv_dataset-103021809.10184 | Dark Mesons at the LHC
hep-ph
A new, strongly-coupled dark sector could be accessible to LHC searches now.
These dark sectors consist of composites formed from constituents that are
charged under the electroweak group and interact with the Higgs, but are
neutral under Standard Model color. In these scenarios, the most promising
target is the dark meson sector, consisting of dark vector-mesons as well as
dark pions. In this paper we study dark meson production and decay at the LHC
in theories that preserve a global SU(2) dark flavor symmetry. Dark pions can
be pair-produced through resonant dark vector meson production, $p
p\to\rho_D\to\pi_D\pi_D$, and decay in one of two distinct ways: gaugephobic,
when $\pi_D\to f\bar{f}'$ generally dominates; or gaugephilic, when $\pi_D\to
W+h,Z+h$ dominates once kinematically open. Unlike QCD, the decay
$\pi^0_D\to\gamma\gamma$ is virtually absent due to the dark flavor symmetry.
We recast a vast set of LHC searches to determine the current constraints on
dark meson production and decay. When $m_{\rho_D}$ is slightly heavier than $2
m_{\pi_D}$ and $\rho_D^{\pm,0}$ kinetically mixes with the weak gauge bosons,
the 8 TeV same-sign lepton search strategy sets the best bound, $m_{\pi_D}>500$
GeV. Yet, when only the $\rho^0_D$ kinetically mixes with hypercharge, we find
the strongest LHC bound is $m_{\pi_D}>130$ GeV, that is only slightly better
than what LEP II achieved. We find the relative insensitivity of LHC searches,
especially at 13 TeV, can be blamed mainly on their penchant for high mass
objects or large MET. Dedicated searches would undoubtedly yield substantially
improved sensitivity. We provide a GitHub page to speed the implementation of
these searches in future LHC analyses. Our findings provide a strong motivation
for model-independent searches of the form $pp\to A\to B+C\to SM\, SM+SM\, SM$
where the theoretical prejudice is for SM to be a t,b,$\tau$ or W,Z,h.
| arxiv topic:hep-ph |
arxiv_dataset-103031809.10284 | When is there a Representer Theorem? Reflexive Banach spaces
math.FA cs.LG stat.ML
We consider a general regularised interpolation problem for learning a
parameter vector from data. The well known representer theorem says that under
certain conditions on the regulariser there exists a solution in the linear
span of the data points. This is at the core of kernel methods in machine
learning as it makes the problem computationally tractable. Most literature
deals only with sufficient conditions for representer theorems in Hilbert
spaces. We prove necessary and sufficient conditions for the existence of
representer theorems in reflexive Banach spaces and illustrate why in a sense
reflexivity is the minimal requirement on the function space. We further show
that if the learning relies on the linear representer theorem, then the
solution is independent of the regulariser and in fact determined by the
function space alone. This in particular shows the value of generalising
Hilbert space learning theory to Banach spaces.
| arxiv topic:math.FA cs.LG stat.ML |
arxiv_dataset-103041809.10384 | First Chern class and birational germs of Kato surfaces
math.DG
We describe some relations between coefficients of irreducible components of
the first Chern class [FP15] and birational germs introduced by Dloussky {Dl16]
for intermediate Kato surfaces.
| arxiv topic:math.DG |
arxiv_dataset-103051809.10484 | Spin wave radiation from vortices in $^3$He-B
cond-mat.supr-con cond-mat.other
We consider a vortex line in the B phase of superfluid $^3$He under uniformly
precessing magnetization. The magnetization exerts torque on the vortex,
causing its order parameter to oscillate. These oscillations generate spin
waves, which is analogous to an oscillating charge generating electromagnetic
radiation. The spin waves carry energy, causing dissipation in the system.
Solving the equations of spin dynamics, we calculate the energy dissipation
caused by spin wave radiation for arbitrary tipping angles of the magnetization
and directions of the magnetic field, and for both vortex types of $^3$He-B.
For the double-core vortex we also consider the anisotropy of the radiation and
the dependence of the dissipation on twisting of the half cores. The radiated
energy is compared with experiments in the mid-temperature range $T \sim 0.5
T_c$. The dependence of the calculated dissipation on several parameters is in
good agreement with the experiments. Combined with numerically calculated
vortex structure, the radiation theory produces the order of magnitude of the
experimental dissipation. The agreement with the experiments indicates that
spin wave radiation is the dominant dissipation mechanism for vortices in
superfluid $^3$He-B in the mid-temperature range.
| arxiv topic:cond-mat.supr-con cond-mat.other |
arxiv_dataset-103061809.10584 | Industrial and Tramp Ship Routing Problems: Closing the Gap for
Real-Scale Instances
cs.DS
Recent studies in maritime logistics have introduced a general ship routing
problem and a benchmark suite based on real shipping segments, considering
pickups and deliveries, cargo selection, ship-dependent starting locations,
travel times and costs, time windows, and incompatibility constraints, among
other features. Together, these characteristics pose considerable challenges
for exact and heuristic methods, and some cases with as few as 18 cargoes
remain unsolved. To face this challenge, we propose an exact branch-and-price
(B&P) algorithm and a hybrid metaheuristic. Our exact method generates
elementary routes, but exploits decremental state-space relaxation to speed up
column generation, heuristic strong branching, as well as advanced
preprocessing and route enumeration techniques. Our metaheuristic is a
sophisticated extension of the unified hybrid genetic search. It exploits a
set-partitioning phase and uses problem-tailored variation operators to
efficiently handle all the problem characteristics. As shown in our
experimental analyses, the B&P optimally solves 239/240 existing instances
within one hour. Scalability experiments on even larger problems demonstrate
that it can optimally solve problems with around 60 ships and 200 cargoes
(i.e., 400 pickup and delivery services) and find optimality gaps below 1.04%
on the largest cases with up to 260 cargoes. The hybrid metaheuristic
outperforms all previous heuristics and produces near-optimal solutions within
minutes. These results are noteworthy, since these instances are comparable in
size with the largest problems routinely solved by shipping companies.
| arxiv topic:cs.DS |
arxiv_dataset-103071809.10684 | Gibbs phenomenon and the emergence of the steady-state in quantum
transport
cond-mat.mes-hall cond-mat.quant-gas quant-ph
Simulations are increasingly employing explicit reservoirs - internal, finite
regions - to drive electronic or particle transport. This naturally occurs in
simulations of transport via ultracold atomic gases. Whether the simulation is
numerical or physical, these approaches rely on the rapid development of the
steady state. We demonstrate that steady state formation is a manifestation of
the Gibbs phenomenon well-known in signal processing and in truncated discrete
Fourier expansions. Each particle separately develops into an individual steady
state due to the spreading of its wave packet in energy. The rise to the steady
state for an individual particle depends on the particle energy - and thus can
be slow - and ringing oscillations appear due to filtering of the response
through the electronic bandwidth. However, the rise to the total steady state -
the one from all particles - is rapid, with timescale $\pi/W$, where $W$ is the
bandwidth. Ringing oscillations are now also filtered through the bias window,
and they decay with a higher power. The Gibbs constant - the overshoot of the
first ring - can appear in the simulation error. These results shed light on
the formation of the steady state and support the practical use of explicit
reservoirs to simulate transport at the nanoscale or using ultracold atomic
lattices.
| arxiv topic:cond-mat.mes-hall cond-mat.quant-gas quant-ph |
arxiv_dataset-103081809.10784 | Adaptive Gaussian process surrogates for Bayesian inference
stat.ML cs.LG
We present an adaptive approach to the construction of Gaussian process
surrogates for Bayesian inference with expensive-to-evaluate forward models.
Our method relies on the fully Bayesian approach to training Gaussian process
models and utilizes the expected improvement idea from Bayesian global
optimization. We adaptively construct training designs by maximizing the
expected improvement in fit of the Gaussian process model to the noisy
observational data. Numerical experiments on model problems with synthetic data
demonstrate the effectiveness of the obtained adaptive designs compared to the
fixed non-adaptive designs in terms of accurate posterior estimation at a
fraction of the cost of inference with forward models.
| arxiv topic:stat.ML cs.LG |
arxiv_dataset-103091809.10884 | A model for system developers to measure the privacy risk of data
cs.CR
In this paper, we propose a model that could be used by system developers to
measure the privacy risk perceived by users when they disclose data into
software systems. We first derive a model to measure the perceived privacy risk
based on existing knowledge and then we test our model through a survey with
151 participants. Our findings revealed that users' perceived privacy risk
monotonically increases with data sensitivity and visibility, and monotonically
decreases with data relevance to the application. Furthermore, how visible data
is in an application by default when the user discloses data had the highest
impact on the perceived privacy risk. This model would enable developers to
measure the users' perceived privacy risk associated with data items, which
would help them to understand how to treat different data within a system
design.
| arxiv topic:cs.CR |
arxiv_dataset-103101809.10984 | An inversion formula for the primitive idempotents of the trivial source
algebra
math.RT
Formulas for the primitive idempotents of the trivial source algebra, in
characteristic zero, have been given by Boltje and Bouc--Th\'{e}venaz. We shall
give another formula for those idempotents, expressing them as linear
combinations of the elements of a canonical basis for the integral ring. The
formula is an inversion formula analogous to the Gluck--Yoshida formula for the
primitive idempotents of the Burnside algebra. It involves all the irreducible
characters of all the normalizers of $p$-subgroups. As a corollary, we shall
show that the linearization map from the monomial Burnside ring has a matrix
whose entries can be expressed in terms of the above Brauer characters and some
reduced Euler characteristics of posets.
| arxiv topic:math.RT |
arxiv_dataset-103111809.11084 | Reuse and Adaptation for Entity Resolution through Transfer Learning
cs.DB cs.LG stat.ML
Entity resolution (ER) is one of the fundamental problems in data
integration, where machine learning (ML) based classifiers often provide the
state-of-the-art results. Considerable human effort goes into feature
engineering and training data creation. In this paper, we investigate a new
problem: Given a dataset D_T for ER with limited or no training data, is it
possible to train a good ML classifier on D_T by reusing and adapting the
training data of dataset D_S from same or related domain? Our major
contributions include (1) a distributed representation based approach to encode
each tuple from diverse datasets into a standard feature space; (2)
identification of common scenarios where the reuse of training data can be
beneficial; and (3) five algorithms for handling each of the aforementioned
scenarios. We have performed comprehensive experiments on 12 datasets from 5
different domains (publications, movies, songs, restaurants, and books). Our
experiments show that our algorithms provide significant benefits such as
providing superior performance for a fixed training data size.
| arxiv topic:cs.DB cs.LG stat.ML |
arxiv_dataset-103121810.00013 | A New High Perihelion Inner Oort Cloud Object: 2015 TG387
astro-ph.EP astro-ph.IM astro-ph.SR
Inner Oort Cloud objects (IOCs) are Trans-Plutonian for their entire orbits.
They are beyond the strong gravitational influences of the known planets yet
close enough to the Sun that outside forces are minimal. Here we report the
discovery of the third known IOC after Sedna and 2012 VP113, called 2015 TG387.
2015 TG387 has a perihelion of $65 \pm 1$ au and semi-major axis of $1170 \pm
70$ au. The longitude of perihelion angle, $\bar{\omega}$, for 2015 TG387 is
between that of Sedna and 2012 VP113, and thus similar to the main group of
clustered extreme trans-Neptunian objects (ETNOs), which may be shepherded into
similar orbital angles by an unknown massive distant planet, called Planet X or
Planet Nine. 2015 TG387's orbit is stable over the age of the solar system from
the known planets and Galactic tide. When including outside stellar encounters
over 4 Gyrs, 2015 TG387's orbit is usually stable, but its dynamical evolution
depends on the stellar encounter scenarios used. Surprisingly, when including a
massive Planet X beyond a few hundred au on an eccentric orbit that is
anti-aligned in longitude of perihelion with most of the known ETNOs, we find
2015 TG387 is typically stable for Planet X orbits that render the other ETNOs
stable as well. Notably, 2015 TG387's argument of perihelion is constrained and
its longitude of perihelion librates about 180 degs from Planet X's longitude
of perihelion, keeping 2015 TG387 anti-aligned with Planet X over the age of
the solar system. We find a power law slope near 3 for the semi-major axis
distribution of IOCs, meaning there are many more high than low semi-major axis
IOCs. There are about 2 million IOCs larger than 40 km, giving a mass of
$10^{22}$ kg. The IOCs inclination distribution is similar to the scattered
disk, with an average inclination of 19 degs.
| arxiv topic:astro-ph.EP astro-ph.IM astro-ph.SR |
arxiv_dataset-103131810.00113 | Predicting the Generalization Gap in Deep Networks with Margin
Distributions
stat.ML cs.LG
As shown in recent research, deep neural networks can perfectly fit randomly
labeled data, but with very poor accuracy on held out data. This phenomenon
indicates that loss functions such as cross-entropy are not a reliable
indicator of generalization. This leads to the crucial question of how
generalization gap should be predicted from the training data and network
parameters. In this paper, we propose such a measure, and conduct extensive
empirical studies on how well it can predict the generalization gap. Our
measure is based on the concept of margin distribution, which are the distances
of training points to the decision boundary. We find that it is necessary to
use margin distributions at multiple layers of a deep network. On the CIFAR-10
and the CIFAR-100 datasets, our proposed measure correlates very strongly with
the generalization gap. In addition, we find the following other factors to be
of importance: normalizing margin values for scale independence, using
characterizations of margin distribution rather than just the margin (closest
distance to decision boundary), and working in log space instead of linear
space (effectively using a product of margins rather than a sum). Our measure
can be easily applied to feedforward deep networks with any architecture and
may point towards new training loss functions that could enable better
generalization.
| arxiv topic:stat.ML cs.LG |
arxiv_dataset-103141810.00213 | Dust-acoustic rogue waves in four component plasmas
physics.plasm-ph
A theoretical investigation has been made on modulational instability (MI)
and dust-acoustic (DA) rogue waves (DARWs) in a four dusty plasma medium
containing inertial negatively charged massive heavy (light) cold (hot) dust
grains as well as super-thermal electrons and non-thermal ions. The reductive
perturbation method is used to derive the nonlinear Schr\"{o}dinger equation,
and two types of modes, namely fast and slow DA modes, have been observed. The
conditions for the MI and the formation of associated DARWs are found to be
significantly modified by the effects of non-thermality of ions ($\alpha$),
super-thermality of electrons ($\kappa$), density-ratio of non-thermal ion to
cold dust ($\mu_i$), and mass-ratio of cold dust to hot dust ($\sigma$), etc.
The implications of our current investigation in space and laboratory plasmas
are briefly discussed.
| arxiv topic:physics.plasm-ph |
arxiv_dataset-103151810.00313 | Finite Horizon Backward Reachability Analysis and Control Synthesis for
Uncertain Nonlinear Systems
cs.SY
We present a method for synthesizing controllers to steer trajectories from
an initial set to a target set on a finite time horizon. The proposed control
synthesis problem is decomposed into two steps. The first step
under-approximates the backward reachable set (BRS) from the target set, using
level sets of storage functions. The storage function is constructed with an
iterative algorithm to maximize the volume of the under-approximated BRS. The
second step obtains a control law by solving a pointwise min-norm optimization
problem using the pre-computed storage function. A closed-form solution of this
min-norm optimization can be computed through the KKT conditions. This control
synthesis framework is then extended to uncertain nonlinear systems with
parametric uncertainties and L_2 disturbances. The computation algorithm for
all cases is derived using sum-of-squares (SOS) programming and the
S-procedure. The proposed method is applied to several robotics and aircraft
examples.
| arxiv topic:cs.SY |
arxiv_dataset-103161810.00413 | Strength conditions, small subalgebras, and Stillman bounds in degree
$\leq 4$
math.AC
In [2], the authors prove Stillman's conjecture in all characteristics and
all degrees by showing that, independent of the algebraically closed field $K$
or the number of variables, $n$ forms of degree at most $d$ in a polynomial
ring $R$ over $K$ are contained in a polynomial subalgebra of $R$ generated by
a regular sequence consisting of at most ${}^\eta\!B(n,d)$ forms of degree at
most $d$: we refer to these informally as "small" subalgebras. Moreover, these
forms can be chosen so that the ideal generated by any subset defines a ring
satisfying the Serre condition R$_\eta$. A critical element in the proof is to
show that there are functions ${}^\eta\!A(n,d)$ with the following property: in
a graded $n$-dimensional $K$-vector subspace $V$ of $R$ spanned by forms of
degree at most $d$, if no nonzero form in $V$ is in an ideal generated by
${}^\eta\!A(n,d)$ forms of strictly lower degree (we call this a {\it strength}
condition), then any homogeneous basis for $V$ is an R$_\eta$ sequence. The
methods of \cite{AH2} are not constructive. In this paper, we use related but
different ideas that emphasize the notion of a {\it key function} to obtain the
functions ${}^\eta\!A(n,d)$ in degrees 2, 3, and 4 (in degree 4 we must
restrict to characteristic not 2, 3). We give bounds in closed form for the key
functions and the ${}^\eta\!A$ functions, and explicit recursions that
determine the functions ${}^\eta\!B$ from the ${}^\eta\!A$ functions. In degree
2, we obtain an explicit value for ${}^\eta\!B(n,2)$ that gives the best known
bound in Stillman's conjecture for quadrics when there is no restriction on
$n$. In particular, for an ideal $I$ generated by $n$ quadrics, the projective
dimension $R/I$ is at most $2^{n+1}(n - 2) + 4$.
| arxiv topic:math.AC |
arxiv_dataset-103171810.00513 | The $\log\log$ growth of channel capacity for nondispersive nonlinear
optical fiber channel in intermediate power range. Extension of the model
cs.IT math.IT
In our previous paper [Phys. Rev. E 95, 062122 (2017)] we considered the
optical channel modelled by the nonlinear Schr\"odinger equation with zero
dispersion and additive Gaussian noise. We found per-sample channel capacity
rof this model. In the present paper we extend per-sample model by introducing
the initial signal dependence on time and the output signal detection
procedure. The proposed model is a closer approximation of the realistic
communication link than the per-sample model where there is no dependence of
the initial signal on time. For the proposed model we found the correlators of
the output signal both analytically and numerically. Using these correlators we
built the conditional probability density function. Then we calculated an
entropy of the output signal, a conditional entropy, and the mutual
information. Maximizing the mutual information we found the optimal input
signal distribution, channel capacity? and their dependence on the shape or the
initial signal in the time domain for the intermediate power range.
| arxiv topic:cs.IT math.IT |
arxiv_dataset-103181810.00613 | An overview of the marine food web in Icelandic waters using Ecopath
with Ecosim
q-bio.PE
Fishing activities have broad impacts that affect, although not exclusively,
the targeted stocks. These impacts affect predators and prey of the harvested
species, as well as the whole ecosystem it inhabits. Ecosystem models can be
used to study the interactions that occur within a system, including those
between different organisms and those between fisheries and targeted species.
Trophic web models like Ecopath with Ecosim (EwE) can handle fishing fleets as
a top predator, with top-down impact on harvested organisms. The aim of this
study was to better understand the Icelandic marine ecosystem and the
interactions within. This was done by constructing an EwE model of Icelandic
waters. The model was run from 1984 to 2013 and was fitted to time series of
biomass estimates, landings data and mean annual temperature. The final model
was chosen by selecting the model with the lowest Akaike information criterion.
A skill assessment was performed using the Pearson's correlation coefficient,
the coefficient of determination, the modelling efficiency and the reliability
index to evaluate the model performance. The model performed satisfactorily
when simulating previously estimated biomass and known landings. Most of the
groups with time series were estimated to have top-down control over their
prey. These are harvested species with direct and/or indirect links to lower
trophic levels and future fishing policies should take this into account. This
model could be used as a tool to investigate how such policies could impact the
marine ecosystem in Icelandic waters.
| arxiv topic:q-bio.PE |
arxiv_dataset-103191810.00713 | Free energy, friction, and mass profiles from short molecular dynamics
trajectories
cond-mat.stat-mech
We address the problem of constructing accurate mathematical models of the
dynamics of molecular systems projected on a collective variable. To this aim
we introduce an algorithm optimizing the parameters of a standard or
generalized Langevin equation until the latter reproduces in a faithful way a
set of molecular dynamics trajectories. In particular, using solvated proline
dipeptide as a test case, we report evidence that ~100 short trajectories
initiated at the top of a high barrier encode all the information needed to
reconstruct free energy, friction, and mass profiles, including non-Markovian
effects. The approach allows accessing the thermodynamics and kinetics of
activated processes in a conceptually direct way, it employs only standard
unbiased molecular dynamics trajectories, and is competitive in computational
cost with respect to existing enhanced sampling methods. Furthermore, the
systematic construction of Langevin models for different choices of collective
variables starting from the same initial data could help in reaction coordinate
optimization.
| arxiv topic:cond-mat.stat-mech |
arxiv_dataset-103201810.00813 | Exact spectral solution of two interacting run-and-tumble particles on a
ring lattice
cond-mat.stat-mech
Exact solutions of interacting random walk models, such as 1D lattice gases,
offer precise insight into the origin of nonequilibrium phenomena. Here, we
study a model of run-and-tumble particles on a ring lattice interacting via
hardcore exclusion. We present the exact solution for one and two particles
using a generating function technique. For two particles, the eigenvectors and
eigenvalues are explicitly expressed using two parameters reminiscent of Bethe
roots, whose numerical values are determined by polynomial equations which we
derive. The spectrum depends in a complicated way on the ratio of direction
reversal rate to lattice jump rate, $\omega$. For both one and two particles,
the spectrum consists of separate real bands for large $\omega$, which mix and
become complex-valued for small $\omega$. At exceptional values of $\omega$,
two or more eigenvalues coalesce such that the Markov matrix is
non-diagonalizable. A consequence of this intricate parameter dependence is the
appearance of dynamical transitions: non-analytic minima in the longest
relaxation times as functions of $\omega$ (for a given lattice size).
Exceptional points are theoretically and experimentally relevant in, e.g., open
quantum systems and multichannel scattering. We propose that the phenomenon
should be a ubiquitous feature of classical nonequilibrium models as well, and
of relevance to physical observables in this context.
| arxiv topic:cond-mat.stat-mech |
arxiv_dataset-103211810.00913 | Artificial Neural Network Approach to the Analytic Continuation Problem
physics.comp-ph cond-mat.str-el
Inverse problems are encountered in many domains of physics, with analytic
continuation of the imaginary Green's function into the real frequency domain
being a particularly important example. However, the analytic continuation
problem is ill defined and currently no analytic transformation for solving it
is known. We present a general framework for building an artificial neural
network (ANN) that solves this task with a supervised learning approach.
Application of the ANN approach to quantum Monte Carlo calculations and
simulated Green's function data demonstrates its high accuracy. By comparing
with the commonly used maximum entropy approach, we show that our method can
reach the same level of accuracy for low-noise input data, while performing
significantly better when the noise strength increases. The computational cost
of the proposed neural network approach is reduced by almost three orders of
magnitude compared to the maximum entropy method
| arxiv topic:physics.comp-ph cond-mat.str-el |
arxiv_dataset-103221810.01013 | AI for Trustworthiness! Credible User Identification on Social Web for
Disaster Response Agencies
cs.SI
Although social media provides a vibrant platform to discuss real-world
events, the quantity of information generated can overwhelm decision making
based on that information. By better understanding who is participating in
information sharing, we can more effectively filter information as the event
unfolds. Fine-grained understanding of credible sources can even help develop a
trusted network of users for specific events or situations. Given the culture
of relying on trusted actors for work practices in the humanitarian and
disaster response domain, we propose to identify potential credible users as
organizational and organizational-affiliated user accounts on social media in
realtime for effective information collection and dissemination. Therefore, we
examine social media using AI and Machine Learning methods during three types
of humanitarian or disaster events and identify key actors responding to social
media conversations as organization (business, group, or institution),
organization-affiliated (individual with an organizational affiliation), and
non-affiliated (individual without organizational affiliation) identities. We
propose a credible user classification approach using a diverse set of social,
activity, and descriptive representation features extracted from user profile
metadata. Our extensive experiments showed a contrasting participation behavior
of the user identities by their content practices, such as the use of higher
authoritative content sharing by organization and organization-affiliated
users. This study provides a direction for designing realtime credible content
analytics systems for humanitarian and disaster response agencies.
| arxiv topic:cs.SI |
arxiv_dataset-103231810.01113 | Superconductivity of $LaH_{10}$ and $LaH_{16}$ polyhydrides
cond-mat.supr-con
We explore high-pressure phase stability and superconductivity of lanthanum
hydrides $LaH_m$ (m=4-11,16). We predict stability of a hitherto unreported
polyhydride $P6/mmm$-$LaH_{16}$ at pressures above 150 GPa; at 200 GPa its
predicted superconducting $T_C$ is 156 K, critical field $\mu_0$$H_C$(0) ~ 35 T
and superconducting gap is up to 35 meV. We revisit superconductivity of the
recently discovered $LaH_{10}$ and find its $T_C$ to be up to 259 K (170 GPa)
from solving the Eliashberg equation and 271 K from solving the gap equation in
SCDFT which also allowed us to compute the Coulomb pseudopotential $\mu^*$ for
$LaH_{10}$ and $LaH_{16}$. Presence of several polymorph modifications of LaH10
may explain the variety in the experimentally measured $T_C$ values for
$LaH_{10}$ [1,2]
| arxiv topic:cond-mat.supr-con |
arxiv_dataset-103241810.01213 | Marginally stable phases in mean-field structural glasses
cond-mat.stat-mech cond-mat.soft
A novel form of amorphous matter characterized by marginal stability was
recently discovered in the mean-field theory of structural glasses. Using this
approach, we provide complete phase diagrams delimiting the location of the
marginally stable glass phase for a large variety of pair interactions and
physical conditions, extensively exploring physical regimes relevant to
granular matter, foams, emulsions, hard and soft colloids, and molecular
glasses. We find that all types of glasses may become marginally stable, but
the extent of the marginally stable phase highly depends on the preparation
protocol. Our results suggest that marginal phases should be observable for
colloidal and non-Brownian particles near jamming, and poorly annealed glasses.
For well-annealed glasses, two distinct marginal phases are predicted. Our
study unifies previous results on marginal stability in mean-field models, and
will be useful to guide numerical simulations and experiments aimed at
detecting marginal stability in finite dimensional amorphous materials.
| arxiv topic:cond-mat.stat-mech cond-mat.soft |
arxiv_dataset-103251810.01313 | An Entropy-Area Law for Neutron Stars Near the Black Hole Threshold
gr-qc astro-ph.HE hep-th
Neutron stars exhibit a set of universal relations independent of their
equation of state that bears semblance to the black hole no hair relations.
Motivated by this, we analytically and numerically explore other relations that
connect neutron star and black hole universality. By analyzing two different
measures, we find that certain rescaled entropies possess a nearly universal
behavior. We also discover that when the compactness of neutron stars
approaches the black hole limit, the rescaled entropy approaches that of a
black hole, and the thermodynamic entropy scales with the stellar surface area
in an ever more universal way.
| arxiv topic:gr-qc astro-ph.HE hep-th |
arxiv_dataset-103261810.01413 | Relative double commutants in coronas of separable C*-algebras
math.OA math.FA
We prove a double commutant theorem for separable subalgebras of a wide class
of corona C*-algebras, largely resolving a problem posed by Pedersen. Double
commutant theorems originated with von Neumann, whose seminal result evolved
into an entire field now called von Neumann algebra theory. Voiculescu later
proved a C*-algebraic double commutant theorem for subalgebras of the Calkin
algebra. We prove a similar result for subalgebras of a much more general class
of so-called corona C*-algebras.
| arxiv topic:math.OA math.FA |
arxiv_dataset-103271810.01513 | Erd\H{o}s-Rado Classes
math.LO
We amalgamate two generalizations of Ramsey's Theorem--Ramsey classes and the
Erd\H{o}s-Rado Theorem--into the notion of a combinatorial Erd\H{o}s-Rado
class. These classes are closely related to Erd\H{o}s-Rado classes, which are
those from which we can build generalized indiscernibles and blueprints in
nonelementary classes, especially Abstract Elementary Classes. We give several
examples and some applications.
| arxiv topic:math.LO |
arxiv_dataset-103281810.01613 | Rational approximations to the zeta function II
math.NT
This note describes continued fraction representations for the rational
approximations to the zeta function recently found by the author. It is
tempting to think that these continued fractions might be analysed using a
souped up version of the Worpitzky argument so as to produce zero-free regions
for the approximations.
| arxiv topic:math.NT |
arxiv_dataset-103291810.01713 | Strongly Resonating Bosons in Hot Nuclei
nucl-ex
When two heavy ions near the Fermi energy collide, a warm and low-density
region can form in which fragments appear. This region is mainly dominated by
proton (p) and alpha particles. In such an environment, the alphas interact
with each other, and especially through strong resonances, form complex systems
such as 8Be and 12C. Our experiments show that in the reactions
70(64)Zn(64Ni)+70(64)Zn(64Ni) at E/A=35 MeV/nucleon levels of 8Be appear around
relative energies Eij=0.092 MeV, 3.03 MeV as well as above 10 MeV and 100 MeV.
For the 3 alpha systems, multi resonance processes give rise to excited levels
of 12C. In particular, the Hoyle state at 7.654 MeV excitation energy shows a
decay component through the ground state of 8Be and also shows components where
two different alpha couples are at relative energies consistent with the ground
state of 8Be at the same time. A component where the three alpha relative
energies are consistent with the ground state of 8Be (i.e., E12=E13=E23=0.092
MeV) is also observed at the 7.458 MeV excitation energy, which was suggested
as an Efimov state.
| arxiv topic:nucl-ex |
arxiv_dataset-103301810.01813 | The AMBRE Project: searching for the closest solar siblings
astro-ph.SR astro-ph.EP astro-ph.GA
Finding solar siblings, that is, stars that formed in the same cluster as the
Sun, will yield information about the conditions at the Sun's birthplace. We
search for solar sibling candidates in AMBRE, the very large spectra database
of solar vicinity stars. Since the ages and chemical abundances of solar
siblings are very similar to those of the Sun, we carried out a chemistry- and
age-based search for solar sibling candidates. We used high-resolution spectra
to derive precise stellar parameters and chemical abundances of the stars. We
used these spectroscopic parameters together with Gaia DR2 astrometric data to
derive stellar isochronal ages. Gaia data were also used to study the
kinematics of the sibling candidates. From the about 17000 stars that are
characterized within the AMBRE project, we first selected 55 stars whose
metallicities are closest to the solar value (-0.1 < [Fe/H] < 0.1 dex). For
these stars we derived precise chemical abundances of several iron-peak, alpha-
and neutron-capture elements, based on which we selected 12 solar sibling
candidates with average abundances and metallicities between -0.03 to 0.03 dex.
Our further selection left us with 4 candidates with stellar ages that are
compatible with the solar age within observational uncertainties. For the 2 of
the hottest candidates, we derived the carbon isotopic ratios, which are
compatible with the solar value. HD186302 is the most precisely characterized
and probably the most probable candidate of our 4 best candidates. Very precise
chemical characterization and age estimation is necessary to identify solar
siblings. We propose that in addition to typical chemical tagging, the study of
isotopic ratios can give further important information about the relation of
sibling candidates with the Sun. Ideally, asteroseismic age determinations of
the candidates could solve the problem of imprecise isochronal ages.
| arxiv topic:astro-ph.SR astro-ph.EP astro-ph.GA |
arxiv_dataset-103311810.01913 | Net-baryon multiplicity distribution consistent with lattice QCD
nucl-th hep-ex hep-ph nucl-ex
We determine the net-baryon multiplicity distribution which reproduces all
cumulants measured so far by lattice QCD. We present the dependence on the
volume and temperature of this distribution. We find that for temperatures and
volumes encountered in heavy ion reactions, the multiplicity distribution is
very close to the Skellam distribution, making the experimental determination
of it rather challenging. We further provide estimates for the statistics
required to measure cumulants of the net-baryon and net-proton distributions.
| arxiv topic:nucl-th hep-ex hep-ph nucl-ex |
arxiv_dataset-103321810.02013 | Probabilistic assessment of the impact of flexible loads under network
tariffs in low voltage distribution networks
cs.SY math.OC
Given the historically static nature of low-voltage networks, distribution
network companies do not possess tools for dealing with an increasingly
variable demand due to the high penetration of distributed energy resources
(DER). Within this context, this paper proposes a probabilistic framework for
tariff design that minimises the impact of DER on network performance,
stabilise network company revenue, and improves the equity of network costs
allocation. To address the issue of the lack of customers' response, we also
show how DER-specific tariffs can be complemented with an automated home energy
management system (HEMS) that reduces peak demand while retaining the desired
comfort level. The proposed framework comprises a nonparametric Bayesian model
which statistically generates synthetic load and PV traces, a hot-water-use
statistical model, a novel HEMS to schedule customers' controllable devices,
and a probabilistic power-flow model. Test cases using both energy- and
demand-based network tariffs show that flat tariffs with a peak demand
component reduce the customers' cost, and alleviate network constraints. This
demonstrates, first, the efficacy of the proposed tool for the development of
tariffs that are beneficial for networks with a high DER penetration, and
second, how customers' HEM systems can be part of the solution.
| arxiv topic:cs.SY math.OC |
arxiv_dataset-103331810.02113 | Improving the Segmentation of Anatomical Structures in Chest Radiographs
using U-Net with an ImageNet Pre-trained Encoder
cs.CV cs.LG
Accurate segmentation of anatomical structures in chest radiographs is
essential for many computer-aided diagnosis tasks. In this paper we investigate
the latest fully-convolutional architectures for the task of multi-class
segmentation of the lungs field, heart and clavicles in a chest radiograph. In
addition, we explore the influence of using different loss functions in the
training process of a neural network for semantic segmentation. We evaluate all
models on a common benchmark of 247 X-ray images from the JSRT database and
ground-truth segmentation masks from the SCR dataset. Our best performing
architecture, is a modified U-Net that benefits from pre-trained encoder
weights. This model outperformed the current state-of-the-art methods tested on
the same benchmark, with Jaccard overlap scores of 96.1% for lung fields, 90.6%
for heart and 85.5% for clavicles.
| arxiv topic:cs.CV cs.LG |
arxiv_dataset-103341810.02213 | Entanglement-enhanced optical gyroscope
quant-ph
Fiber optic gyroscopes (FOG) based on the Sagnac effect are a valuable tool
in sensing and navigation and enable accurate measurements in applications
ranging from spacecraft and aircraft to self-driving vehicles such as
autonomous cars. As with any classical optical sensors, the ultimate
performance of these devices is bounded by the standard quantum limit (SQL).
Quantum-enhanced interferometry allows us to overcome this limit using
non-classical states of light. Here, we report on an entangled-photon gyroscope
that uses path-entangled NOON-states (N=2) to provide phase supersensitivity
beyond the standard-quantum-limit.
| arxiv topic:quant-ph |
arxiv_dataset-103351810.02313 | Effect of intra-channel baseline migration on the measured visibility
and spatial power spectrum
astro-ph.IM
The channel-to-channel migration of radio interferometric baselines for the
same antenna separation causes a flat spectrum source that should have remained
in the zeroth delay (line-of-sight) mode to become centered around a higher
mode - the geometric delay for that particular antenna separation with a spread
(spill-over) of the order of reciprocal bandwidth. While in principle an
errorless gridding interpolation can remove inter-channel migration,
intra-channel baseline migration exists due to the non-zero width (resolution)
of the instrument's spectral channel arising from the finite-period integration
in a DFT cycle. Here for the first time, we analyze this effect and quantify it
using the case of a flat-spectrum point source. We find that the visibility
undergoes an attenuation, the extent of which depends on the auto-correlation
of the window function used for DFT and is more towards the lower-end of the
band. This causes the spill-over of the delay mode to extend beyond the
reciprocal bandwidth order.
| arxiv topic:astro-ph.IM |
arxiv_dataset-103361810.02413 | Dynamical current-current correlation in the two-dimensional parabolic
Dirac system
cond-mat.mes-hall
We theoretically investigate the current-current correlation of the
two-dimensional (2D) parabolic Dirac system in hexogonal lattice. The
analytical expressions of the random phase approximation (RPA) susceptibility,
Ruderman-Kittel-Kasuya-Yosida (RKKY) Hamiltonian, and the diamagnetic orbital
susceptibility in noninteracting case base on the density-density or
current-current correlation function are derived and quantitatively analyzed.
In noninteracting case, the dynamical polarization with- in RPA and spin
transverse susceptibility as well as the RKKY interaction (when close to the
half-filling) are related to the the current-current response in the 2D
parabolic Dirac system. Both the case of anisotropic dispersion and isotropic
dispersion are discussed.
| arxiv topic:cond-mat.mes-hall |
arxiv_dataset-103371810.02513 | Learning To Simulate
cs.LG cs.CV stat.ML
Simulation is a useful tool in situations where training data for machine
learning models is costly to annotate or even hard to acquire. In this work, we
propose a reinforcement learning-based method for automatically adjusting the
parameters of any (non-differentiable) simulator, thereby controlling the
distribution of synthesized data in order to maximize the accuracy of a model
trained on that data. In contrast to prior art that hand-crafts these
simulation parameters or adjusts only parts of the available parameters, our
approach fully controls the simulator with the actual underlying goal of
maximizing accuracy, rather than mimicking the real data distribution or
randomly generating a large volume of data. We find that our approach (i)
quickly converges to the optimal simulation parameters in controlled
experiments and (ii) can indeed discover good sets of parameters for an image
rendering simulator in actual computer vision applications.
| arxiv topic:cs.LG cs.CV stat.ML |
arxiv_dataset-103381810.02613 | Exploring the nuances in the relationship "culture-strategy" for the
business world
econ.GN q-fin.EC
The current article explores interesting, significant and recently identified
nuances in the relationship "culture-strategy". The shared views of leading
scholars at the University of National and World Economy in relation with the
essence, direction, structure, role and hierarchy of "culture-strategy"
relation are defined as a starting point of the analysis. The research emphasis
is directed on recent developments in interpreting the observed realizations of
the aforementioned link among the community of international scholars and
consultants, publishing in selected electronic scientific databases. In this
way a contemporary notion of the nature of "culture-strategy" relationship for
the entities from the world of business is outlined.
| arxiv topic:econ.GN q-fin.EC |
arxiv_dataset-103391810.02713 | Optimizing groups of colluding strong attackers in mobile urban
communication networks with evolutionary algorithms
cs.NE cs.CR cs.NI
In novel forms of the Social Internet of Things, any mobile user within
communication range may help routing messages for another user in the network.
The resulting message delivery rate depends both on the users' mobility
patterns and the message load in the network. This new type of configuration,
however, poses new challenges to security, amongst them, assessing the effect
that a group of colluding malicious participants can have on the global message
delivery rate in such a network is far from trivial. In this work, after
modeling such a question as an optimization problem, we are able to find quite
interesting results by coupling a network simulator with an evolutionary
algorithm. The chosen algorithm is specifically designed to solve problems
whose solutions can be decomposed into parts sharing the same structure. We
demonstrate the effectiveness of the proposed approach on two medium-sized
Delay-Tolerant Networks, realistically simulated in the urban contexts of two
cities with very different route topology: Venice and San Francisco. In all
experiments, our methodology produces attack patterns that greatly lower
network performance with respect to previous studies on the subject, as the
evolutionary core is able to exploit the specific weaknesses of each target
configuration.
| arxiv topic:cs.NE cs.CR cs.NI |
arxiv_dataset-103401810.02813 | A Deep X-Ray Look At Abell 2142 --- Viscosity Constraints From
Kelvin-Helmholtz Eddies, A Displaced Cool Peak That Makes A Warm Core, And A
Possible Plasma Depletion Layer
astro-ph.HE
We analyzed 200 ks of Chandra ACIS observations of the merging galaxy cluster
A2142 to examine its prominent cold fronts in detail. We find that the southern
cold front exhibits well-developed Kelvin-Helmholtz (KH) eddies seen in the sky
plane. Comparing their wavelength and amplitude with those in hydrodynamic
simulations of cold fronts in viscous gas, and estimating the gas tangential
velocity from centripetal acceleration, we constrain the effective viscosity to
be at most 1/5 of Spitzer isotropic viscosity, but consistent with full
Braginskii anisotropic viscosity for magnetized plasma. While the northwestern
front does not show obvious eddies, its shape and the structure of its
brightness profile suggest KH eddies seen in projection. The southern cold
front continues in a spiral to the center of the cluster, ending with another
cold front only 12 kpc from the gas density peak. The cool peak itself is
displaced ~30 kpc from the BCG (the biggest such offset among centrally-peaked
clusters), while the X-ray emission on a larger scale is still centered on the
BCG, indicating that the BCG is at the center of the gravitational potential
and the cool gas is sloshing in it. The specific entropy index of the gas in
the peak ($K\approx49$ keV cm$^2$) makes A2142 a rare "warm core"; apparently
the large displacement of the cool peak by sloshing is the reason. Finally, we
find a subtle narrow, straight channel with a 10% drop in X-ray brightness,
aligned with the southern cold front --- possibly a plasma depletion layer in
projection.
| arxiv topic:astro-ph.HE |
arxiv_dataset-103411810.02913 | Predicting the Sufficient-Statistics Power Spectrum for Galaxy Surveys:
A Recipe for $P_{A*}(k)$
astro-ph.CO
Future galaxy surveys hope to realize significantly tighter constraints on
various cosmological parameters. The higher number densities achieved by these
surveys will allow them to probe the smaller scales affected by non-linear
clustering. However, in these regimes, the standard power spectrum can extract
only a portion of such surveys' cosmological information. In contrast, the
alternate statistic $A^*$ has the potential to double these surveys'
information return, provided one can predict the $A^*$-power spectrum for a
given cosmology. Thus, in this work we provide a prescription for this power
spectrum $P_{A^*}(k)$, finding that the prescription is typically accurate to
about 5 per cent for near-concordance cosmologies. This prescription will thus
allow us to multiply the information gained from surveys such as Euclid and
WFIRST.
| arxiv topic:astro-ph.CO |
arxiv_dataset-103421810.03013 | Orbiting of bacteria around micrometer-sized particles entrapping
shallow tents of fluids
physics.bio-ph cond-mat.soft physics.flu-dyn
Hydrodynamics and confinement dominate bacterial mobility near solid or
air-water boundaries, causing flagellated bacteria to move in circular
trajectories. This phenomenon results from the counter-rotation between the
bacterial body and flagella and lateral drags on them in opposite directions
due to their proximity to the boundaries. Numerous experimental techniques have
been developed to confine and maneuver motile bacteria. Here, we report
observations on Escherichia coli and Enterobacter sp. when they are confined
within a thin layer of water around dispersed micrometer-sized particles
sprinkled over a semi-solid agar gel. In this setting, the flagellated bacteria
orbit around the dispersed particles akin to planetary systems. The liquid
layer is shaped like a shallow tent with its height at the center set by the
seeding particle and the meniscus profile set by the strong surface tension of
water. The tent-shaped constraint and the left handedness of the flagellar
filaments result in exclusively clockwise circular trajectories. The thin fluid
layer is resilient due to a balance between evaporation and reinforcing fluid
pumped out of the agar. The latter is driven by the Laplace pressure caused by
the curved meniscus. This novel mechanism to entrap bacteria within a minimal
volume of fluid is relevant to near surface bacterial accumulation, adhesion,
biofilm growth, development of bio-microdevices, and cleansing hygiene.
| arxiv topic:physics.bio-ph cond-mat.soft physics.flu-dyn |
arxiv_dataset-103431810.03113 | Control of uniflagellar soft robots at low Reynolds number using
buckling instability
cs.RO
In this paper, we analyze the inverse dynamics and control of a
bacteria-inspired uniflagellar robot in a fluid medium at low Reynolds number.
Inspired by the mechanism behind the locomotion of flagellated bacteria, we
consider a robot comprised of a flagellum -- a flexible helical filament --
attached to a spherical head. The flagellum rotates about the head at a
controlled angular velocity and generates a propulsive force that moves the
robot forward. When the angular velocity exceeds a threshold value, the
hydrodynamic force exerted by the fluid can cause the soft flagellum to buckle,
characterized by a dramatic change in shape. In this computational study, a
fluid-structure interaction model that combines Discrete Elastic Rods (DER)
algorithm with Lighthill's Slender Body Theory (LSBT) is employed to simulate
the locomotion and deformation of the robot. We demonstrate that the robot can
follow a prescribed path in three dimensional space by exploiting buckling of
the flagellum. The control scheme involves only a single (binary) scalar input
-- the angular velocity of the flagellum. By triggering the buckling
instability at the right moment, the robot can follow an arbitrary path in
three dimensional space. We also show that the complexity of the dynamics of
the helical filament can be captured using a deep neural network, from which we
identify the input-output functional relationship between the control inputs
and the trajectory of the robot. Furthermore, our study underscores the
potential role of buckling in the locomotion of natural bacteria.
| arxiv topic:cs.RO |
arxiv_dataset-103441810.03213 | Image Completion on CIFAR-10
cs.CV
This project performed image completion on CIFAR-10, a dataset of 60,000
32x32 RGB images, using three different neural network architectures: fully
convolutional networks, convolutional networks with fully connected layers, and
encoder-decoder convolutional networks. The highest performing model was a deep
fully convolutional network, which was able to achieve a mean squared error of
.015 when comparing the original image pixel values with the predicted pixel
values. As well, this network was able to output in-painted images which
appeared real to the human eye.
| arxiv topic:cs.CV |
arxiv_dataset-103451810.03313 | On a Direct Description of Pseudorelativistic Nelson Hamiltonians
math-ph math.MP
Abstract interior-boundary conditions (IBC's) allow for the direct
description of the domain and the action of Hamiltonians for a certain class of
ultraviolet-divergent models in Quantum Field Theory. The method was recently
applied to models where nonrelativistic scalar particles are linearly coupled
to a quantised field, the best known of which is the Nelson model. Since this
approach avoids the use of ultraviolet-cutoffs, there is no need for a
renormalisation procedure. Here, we extend the IBC method to pseudorelativistic
scalar particles that interact with a real bosonic field. We construct the
Hamiltonians for such models via abstract boundary conditions, describing their
action explicitly. In addition, we obtain a detailed characterisation of their
domain and make the connection to renormalisation techniques. As an example, we
apply the method to two relativistic variants of Nelson's model, which have
been renormalised for the first time by J. P. Eckmann and A. D. Sloan in 1970
and 1974, respectively.
| arxiv topic:math-ph math.MP |
arxiv_dataset-103461810.03413 | Random Tug of War games for the ${\mathbf p}$-Laplacian:
${\mathbf{1<p<{\boldsymbol \infty}}}$
math.AP
We propose a new finite difference approximation to the Dirichlet problem for
the homogeneous $\mathbf{p}$-Laplace equation posed on an $N$-dimensional
domain, in connection with the Tug of War games with noise. Our game and the
related mean-value expansion that we develop, superposes the ``deterministic
averages'' ``$\frac{1}{2}(\inf +\sup)$'' taken over balls, with the
``stochastic averages'' ``$\fint$'', taken over $N$-dimensional ellipsoids
whose aspect ratio depends on $N,\mathbf{p}$ and whose orientations span all
directions while determining $\inf / \sup$. We show that the unique solutions
$u_\epsilon$ of the related dynamic programming principle are automatically
continuous for continuous boundary data, and coincide with the well-defined
game values. Our game has thus the min-max property: the order of supremizing
the outcomes over strategies of one player and infimizing over strategies of
their opponent, is immaterial. We further show that domains satisfying the
exterior corkscrew condition are game regular in this context, i.e. the family
$\{u_\epsilon\}_{\epsilon\to 0}$ converges uniformly to the unique viscosity
solution of the Dirichlet problem.
| arxiv topic:math.AP |
arxiv_dataset-103471810.03513 | Time-Message Trade-Offs in Distributed Algorithms
cs.DS
This paper focuses on showing time-message trade-offs in distributed
algorithms for fundamental problems such as leader election, broadcast,
spanning tree (ST), minimum spanning tree (MST), minimum cut, and many graph
verification problems. We consider the synchronous CONGEST distributed
computing model and assume that each node has initial knowledge of itself and
the identifiers of its neighbors - the so-called KT1 model - a well-studied
model that also naturally arises in many applications. Recently, it has been
established that one can obtain (almost) singularly optimal algorithms, i.e.,
algorithms that have simultaneously optimal time and message complexity (up to
polylogarithmic factors), for many fundamental problems in the standard KT0
model (where nodes have only local knowledge of themselves and not their
neighbors). The situation is less clear in the KT1 model. In this paper, we
present several new distributed algorithms in the KT1 model that trade off
between time and message complexity.
Our distributed algorithms are based on a uniform approach which involves
constructing a sparsified spanning subgraph of the original graph - called a
danner - that trades off the number of edges with the diameter of the
sparsifier. In particular, a key ingredient of our approach is a distributed
randomized algorithm that, given a graph G and any delta in [0, 1], with high
probability constructs a danner that has diameter Otilde(D + n^(1 - delta)) and
Otilde(min{m, n^(1 + delta)}) edges in Otilde(n^(1 - delta)) rounds while using
Otilde(min{m, n^(1 + delta)}) messages, where n, m, and D are the number of
nodes, edges, and the diameter of G, respectively. Using our danner
construction, we present a family of distributed randomized algorithms for
various fundamental problems that exhibit a trade-off between message and time
complexity and that improve over previous results.
| arxiv topic:cs.DS |
arxiv_dataset-103481810.03613 | First-Principles Plasma Simulations of Black-Hole Jet Launching
astro-ph.HE gr-qc physics.plasm-ph
Black holes drive powerful plasma jets to relativistic velocities. This
plasma should be collisionless, and self-consistently supplied by pair creation
near the horizon. We present general-relativistic collisionless plasma
simulations of Kerr-black-hole magnetospheres which begin from vacuum, inject
electron-positron pairs based on local unscreened electric fields, and reach
steady states with electromagnetically powered Blandford-Znajek jets and
persistent current sheets. Particles with negative energy-at-infinity are a
general feature, and can contribute significantly to black-hole
rotational-energy extraction in a variant of the Penrose process. The generated
plasma distribution depends on the pair-creation environment, and we describe
two distinct realizations of the force-free electrodynamic solution. This
sensitivity suggests that plasma kinetics will be useful in interpreting future
horizon-resolving submillimeter and infrared observations.
| arxiv topic:astro-ph.HE gr-qc physics.plasm-ph |
arxiv_dataset-103491810.03713 | Gravity safe, electroweak natural axionic solution to strong CP and SUSY
mu problems
hep-ph astro-ph.CO hep-th
Particle physics models with Peccei-Quinn (PQ) symmetry breaking as a
consequence of supersymmetry (SUSY) breaking are attractive in that they solve
the strong CP problem with a SUSY DFSZ-like axion, link the SUSY breaking and
PQ breaking intermediate mass scales and can resolve the SUSY mu problem with a
naturalness-required weak scale mu term whilst soft SUSY breaking terms inhabit
the multi-TeV regime as required by LHC sparticle mass limits and the Higgs
mass measurement. On the negative ledger, models based on global symmetries
suffer a generic gravity spoliation problem. We present a model based on the
discrete R-symmetry Z_{24}^R-- which may emerge from compactification of 10-d
Lorentzian spacetime in string theory-- where the mu term and dangerous proton
decay and R-parity violating operators are either suppressed or forbidden while
a gravity-safe PQ symmetry emerges as an accidental approximate global symmetry
leading to a solution to the strong CP problem and a weak-scale/natural value
for the mu term.
| arxiv topic:hep-ph astro-ph.CO hep-th |
arxiv_dataset-103501810.03813 | Guess Free Maximization of Submodular and Linear Sums
cs.DS
We consider the problem of maximizing the sum of a monotone submodular
function and a linear function subject to a general solvable polytope
constraint. Recently, Sviridenko et al. (2017) described an algorithm for this
problem whose approximation guarantee is optimal in some intuitive and formal
senses. Unfortunately, this algorithm involves a guessing step which makes it
less clean and significantly affects its time complexity. In this work we
describe a clean alternative algorithm that uses a novel weighting technique in
order to avoid the problematic guessing step while keeping the same
approximation guarantee as the algorithm of Sviridenko et al.
| arxiv topic:cs.DS |
arxiv_dataset-103511810.03913 | Analyzing the Noise Robustness of Deep Neural Networks
cs.LG cs.HC stat.ML
Deep neural networks (DNNs) are vulnerable to maliciously generated
adversarial examples. These examples are intentionally designed by making
imperceptible perturbations and often mislead a DNN into making an incorrect
prediction. This phenomenon means that there is significant risk in applying
DNNs to safety-critical applications, such as driverless cars. To address this
issue, we present a visual analytics approach to explain the primary cause of
the wrong predictions introduced by adversarial examples. The key is to analyze
the datapaths of the adversarial examples and compare them with those of the
normal examples. A datapath is a group of critical neurons and their
connections. To this end, we formulate the datapath extraction as a subset
selection problem and approximately solve it based on back-propagation. A
multi-level visualization consisting of a segmented DAG (layer level), an Euler
diagram (feature map level), and a heat map (neuron level), has been designed
to help experts investigate datapaths from the high-level layers to the
detailed neuron activations. Two case studies are conducted that demonstrate
the promise of our approach in support of explaining the working mechanism of
adversarial examples.
| arxiv topic:cs.LG cs.HC stat.ML |
arxiv_dataset-103521810.04013 | Identifying the electron-positron cascade regimes in high-intensity
laser-matter interactions
physics.plasm-ph
Strong-field quantum electrodynamics predicts electron-seeded
electron-positron pair cascades when the electric field in the rest-frame of
the seed electron approaches the Sauter-Schwinger field, i.e. $\eta =
E_{RF}/E_S \sim 1$. Electrons in the focus of next generation multi-PW lasers
are expected to reach this threshold. We identify three distinct cascading
regimes in the interaction of counter-propagating, circularly-polarised laser
pulses with a thin foil by performing a comprehensive scan over the laser
intensity (from $10^{23}$ -- $5\times10^{24}$\ Wcm$^{-2}$) and initial foil
target density (from $10^{26}$ -- $10^{31}$\ m$^{-3}$). For low densities and
intensities the number of pairs grows exponentially. If the intensity and
target density are high enough the number density of created pairs reaches the
relativistically-corrected critical density, the pair plasma efficiently
absorbs the laser energy (through radiation reaction) and the cascade
saturates. If the initial density is too high, such that the initial target is
overdense, the cascade is suppressed by the skin effect. We derive a
semi-analytical model which predicts that dense pair plasmas are endemic
features of these interactions for intensities above $10^{24}$ Wcm$^{-2}$
provided the target's relativistic skin-depth is longer than the laser
wavelength. Further, it shows that pair production is maximised in
near-critical-density targets, providing a guide for near-term experiments.
| arxiv topic:physics.plasm-ph |
arxiv_dataset-103531810.04113 | A study of 3-dimensional shapes of asteroid families with an application
to Eos
astro-ph.EP
In order to fully understand the shapes of asteroids families in the
3-dimensional space of the proper elements $(a_{\rm p}, e_{\rm p}, \sin I_{\rm
p})$ it is necessary to compare observed asteroids with N-body simulations. To
this point, we describe a rigorous yet simple method which allows for a
selection of the observed asteroids, assures the same size-frequency
distribution of synthetic asteroids, accounts for a background population, and
computes a $\chi^2$ metric. We study the Eos family as an example, and we are
able to fully explain its non-isotropic features, including the distribution of
pole latitudes $\beta$. We confirm its age $t = (1.3\pm0.3)\,{\rm Gyr}$; while
this value still scales with the bulk density, it is verified by a Monte-Carlo
collisional model. The method can be applied to other populous families (Flora,
Eunomia, Hygiea , Koronis, Themis, Vesta, etc.).
| arxiv topic:astro-ph.EP |
arxiv_dataset-103541810.04213 | Scalar Asymptotic Charges and Dual Large Gauge Transformations
hep-th
In recent years soft factorization theorems in scattering amplitudes have
been reinterpreted as conservation laws of asymptotic charges. In gauge,
gravity, and higher spin theories the asymptotic charges can be understood as
canonical generators of large gauge symmetries. Such a symmetry interpretation
has been so far missing for scalar soft theorems. We remedy this situation by
treating the massless scalar field in terms of a dual two-form gauge field. We
show that the asymptotic charges associated to the scalar soft theorem can be
understood as generators of large gauge transformations of the dual two-form
field.
The dual picture introduces two new puzzles: the charges have very unexpected
Poisson brackets with the fields, and the monopole term does not always have a
dual gauge transformation interpretation. We find analogs of these two
properties in the Kramers-Wannier duality on a finite lattice, indicating that
the free scalar theory has new edge modes at infinity that canonically commute
with all the bulk degrees of freedom.
| arxiv topic:hep-th |
arxiv_dataset-103551810.04313 | Adding 32-bit Mode to the ACL2 Model of the x86 ISA
cs.LO
The ACL2 model of the x86 Instruction Set Architecture was built for the
64-bit mode of operation of the processor. This paper reports on our work to
extend the model with support for 32-bit mode, recounting the salient aspects
of this activity and identifying the ones that required the most work.
| arxiv topic:cs.LO |
arxiv_dataset-103561810.04413 | Performance analysis and optimization of the JOREK code for many-core
CPUs
cs.PF
This report investigates the performance of the JOREK code on the Intel
Knights Landing and Skylake processor architectures. The OpenMP scaling of the
matrix construction part of the code was analyzed and improved synchronization
methods were implemented. A new switch was implemented to control the number of
threads used for the linear equation solver independently from other parts of
the code. The matrix construction subroutine was vectorized, and the data
locality was also improved. These steps led to a factor of two speedup for the
matrix construction.
| arxiv topic:cs.PF |
arxiv_dataset-103571810.04513 | ET-Lasso: A New Efficient Tuning of Lasso-type Regularization for
High-Dimensional Data
stat.ML cs.LG
The L1 regularization (Lasso) has proven to be a versatile tool to select
relevant features and estimate the model coefficients simultaneously and has
been widely used in many research areas such as genomes studies, finance, and
biomedical imaging. Despite its popularity, it is very challenging to guarantee
the feature selection consistency of Lasso especially when the dimension of the
data is huge. One way to improve the feature selection consistency is to select
an ideal tuning parameter. Traditional tuning criteria mainly focus on
minimizing the estimated prediction error or maximizing the posterior model
probability, such as cross-validation and BIC, which may either be
time-consuming or fail to control the false discovery rate (FDR) when the
number of features is extremely large. The other way is to introduce
pseudo-features to learn the importance of the original ones. Recently, the
Knockoff filter is proposed to control the FDR when performing feature
selection. However, its performance is sensitive to the choice of the expected
FDR threshold. Motivated by these ideas, we propose a new method using
pseudo-features to obtain an ideal tuning parameter. In particular, we present
the Efficient Tuning of Lasso (ET-Lasso) to separate active and inactive
features by adding permuted features as pseudo-features in linear models. The
pseudo-features are constructed to be inactive by nature, which can be used to
obtain a cutoff to select the tuning parameter that separates active and
inactive features. Experimental studies on both simulations and real-world data
applications are provided to show that ET-Lasso can effectively and efficiently
select active features under a wide range of scenarios
| arxiv topic:stat.ML cs.LG |
arxiv_dataset-103581810.04613 | The Standard Model of particle physics with Diracian neutrino sector
physics.gen-ph
The minimally extended standard model of particle physics contains three
right handed or sterile neutrinos, coupled to the active ones by a Dirac mass
matrix and mutually by a Majorana mass matrix. In the pseudo-Dirac case, the
Majorana terms are small and maximal mixing of active and sterile states
occurs, which is generally excluded for solar neutrinos. In a "Diracian" limit,
the physical masses become pairwise degenerate and the neutrinos attain a Dirac
signature. Members of a pair do not oscillate mutually so that their mixing can
be undone, and the standard neutrino model follows as a limit. While two
Majorana phases become physical Dirac phases and three extra mass parameters
occur, a better description of data is offered. Oscillation problems are worked
out in vacuum and in matter. With lepton number -1 assigned to the sterile
neutrinos, the model still violates lepton number conservation and allows very
feeble neutrinoless double beta decay. It supports a sterile neutrino
interpretation of Earth-traversing ultra high energy events detected by ANITA.
| arxiv topic:physics.gen-ph |
arxiv_dataset-103591810.04713 | Fingerprint of the first stars: multi-enriched extremely metal-poor
stars in the TOPoS survey
astro-ph.GA astro-ph.CO astro-ph.SR
Extremely metal poor (EMP) stars in the Milky Way inherited the chemical
composition of the gas out of which they formed. They therefore carry the
chemical fingerprint of the first stars in their spectral lines. It is commonly
assumed that EMP stars form from gas that was enriched by only one progenitor
supernova ('mono-enriched'). However, recent numerical simulations show that
the first stars form in small clusters. Consequently, we expect several
supernovae to contribute to the abundances of an EMP star ('multi-enriched').
We analyse seven recently observed EMP stars from the TOPoS survey by applying
the divergence of the chemical displacement and find that J1035+0641 is
mono-enriched ($p_{mono}=53\%$) and J1507+0051 is multi-enriched
($p_{mono}=4\%$). For the remaining five stars we can not make a distinct
prediction ($p_{mono} \lesssim 50\%$) due to theoretical and observational
uncertainties. Further observations in the near-UV will help to improve our
diagnostic and therefore contribute to constrain the nature of the first stars.
| arxiv topic:astro-ph.GA astro-ph.CO astro-ph.SR |
arxiv_dataset-103601810.04813 | Analogues of the Aoki-Ohno and Le-Murakami relations for finite multiple
zeta values
math.NT
We establish finite analogues of the identities known as the Aoki-Ohno
relation and the Le-Murakami relation in the theory of multiple zeta values. We
use an explicit form of a generating series given by Aoki and Ohno.
| arxiv topic:math.NT |
arxiv_dataset-103611810.04913 | Observation of Dirac-like energy band and unusual spectral line shape in
quasi-one-dimensional superconductor Tl2Mo6Se6
cond-mat.supr-con cond-mat.mes-hall
We have performed high-resolution angle-resolved photoemission spectroscopy
of the quasi-one-dimensional (1D) topological superconductor candidate
Tl2Mo6Se6 consisting of weakly-coupled Mo3Se3 chains. We found a quasi-1D Fermi
surface arising from a Dirac-like energy band, which is associated with the
nonsymmorphic screw symmetry of the chains and predicted to trigger topological
superconductivity. We observed a significant spectral-weight reduction over a
wide energy range, together with a tiny Fermi-edge structure which exhibits a
signature of a superconducting-gap opening below the superconducting-transition
temperature. The observed quasi-1D Dirac-like band and its very small density
of states point to an unconventional nature of superconductivity in Tl2Mo6Se6.
| arxiv topic:cond-mat.supr-con cond-mat.mes-hall |
arxiv_dataset-103621810.05013 | Critically Finite Random Maps of an Interval
math.DS
We consider random multimodal $C^3$ maps with negative Schwarzian derivative,
defined on a finite union of closed intervals in $[0,1]$, onto the interval
$[0,1]$ with the base space $\Omega$ and a base invertible ergodic map
$\theta:\Omega\to\Omega$ preserving a probability measure $m$ on $\Omega$. We
denote the corresponding skew product map by $T$ and call it a critically
finite random map of an interval. We prove that there exists a subset $AA(T)$
of $[0,1]$ with the following properties:
(1) For each $t\in AA(T)$ a $t$-conformal random measure $\nu_t$ exists. We
denote by $\lambda_{t,\nu_t,\omega}$ the corresponding generalized eigenvalues
of the corresponding dual operators $\mathcal{L}_{t,\omega}^*$,
$\omega\in\Omega$.
(2) Given $t\ge 0$ any two $t$-conformal random measures are equivalent.
(3) The expected topological pressure of the parameter $t$:
$$\mathcal{E}P(t):=\int_{\Omega}\log\lambda_{t,\nu,\omega}dm(\omega) $$ is
independent of the choice of a $t$-conformal random measure $\nu$.
(4) The function $$ AA(T)\ni t\longmapsto \mathcal{E}P(t)\in\mathbb R $$ is
monotone decreasing and Lipschitz continuous.
(5) With $b_T$ being defined as the supremum of such parameters $t\in AA(T)$
that $\mathcal{E}P(t)\ge 0$, it holds that $$ \mathcal{E}P(b_T)=0 \ \ \ {\rm
and} \ \ \ [0,b_T]\subset \text{Int}(AA(T)). $$
(6) $\text{HD}(\mathcal{J}_\omega(T))=b_T$ for $m$-a.e $\omega\in\Omega$,
where $\mathcal{J}_\omega(T)$, $\omega\in\Omega$, form the random closed set
generated by the skew product map $T$.
(7) $b_T=1$ if and only if $\bigcup_{\Delta\in \mathcal{G}}\Delta=[0,1]$, and
then $\mathcal{J}_\omega(T)=[0,1]$ for all $\omega\in\Omega$.
| arxiv topic:math.DS |
arxiv_dataset-103631810.05113 | Bounded Invariant Equivalence Relations
math.LO
We study strong types and Galois groups in model theory from a topological
and descriptive-set-theoretical point of view, leaning heavily on topological
dynamical tools. More precisely, we give an abstract (not model theoretic)
treatment of problems related to cardinality and Borel cardinality of strong
types, quotients of definable groups and related objecets, generalising (and
often improving) essentially all hitherto known results in this area. In
particular, we show that under reasonable assumptions, strong type spaces are
"locally" quotients of compact Polish groups. It follows that they are smooth
if and only if they are type-definable, and that a quotient of a type-definable
group by an analytic subgroup is either finite or of cardinality at least
continuum.
| arxiv topic:math.LO |
arxiv_dataset-103641810.05213 | Systematic Study of Accuracy of Wall-Modeled Large Eddy Simulation using
Uncertainty Quantification Techniques
physics.flu-dyn
The predictive accuracy of wall-modeled large eddy simulation is studied by
systematic simulation campaigns of turbulent channel flow. The effect of wall
model, grid resolution and anisotropy, numerical convective scheme and
subgrid-scale modeling is investigated. All of these factors affect the
resulting accuracy, and their action is to a large extent intertwined. The wall
model is of the wall-stress type, and its sensitivity to location of velocity
sampling, as well as law of the wall's parameters is assessed. For efficient
exploration of the model parameter space (anisotropic grid resolution and wall
model parameter values), generalized polynomial chaos expansions are used to
construct metamodels for the responses which are taken to be measures of the
predictive error in quantities of interest (QoIs). The QoIs include the mean
wall shear stress and profiles of the mean velocity, the turbulent kinetic
energy, and the Reynolds shear stress. DNS data is used as reference. Within
the tested framework, a particular second-order accurate CFD code (OpenFOAM),
the results provide ample support for grid and method parameters
recommendations which are proposed in the present paper, and which provide good
results for the QoIs. Notably, good results are obtained with a grid with
isotropic (cubic) hexahedral cells, with $15\, 000$ cells per $\delta^3$, where
$\delta$ is the channel half-height (or thickness of the turbulent boundary
layer). The importance of providing enough numerical dissipation to obtain
accurate QoIs is demonstrated. The main channel flow case investigated is ${\rm
Re}_\tau=5200$, but extension to a wide range of ${\rm Re}$-numbers is
considered. Use of other numerical methods and software would likely modify
these recommendations, at least slightly, but the proposed framework is fully
applicable to investigate this as well.
| arxiv topic:physics.flu-dyn |
arxiv_dataset-103651810.05313 | Xorshift1024*, Xorshift1024+, Xorshift128+ and Xoroshiro128+ Fail
Statistical Tests for Linearity
cs.DS
L'Ecuyer & Simard's Big Crush statistical test suite has revealed statistical
flaws in many popular random number generators including Marsaglia's Xorshift
generators. Vigna recently proposed some 64-bit variations on the Xorshift
scheme that are further scrambled (i.e., Xorshift1024*, Xorshift1024+,
Xorshift128+, Xoroshiro128+). Unlike their unscrambled counterparts, they pass
Big Crush when interleaving blocks of 32 bits for each 64-bit word (most
significant, least significant, most significant, least significant, etc.). We
report that these scrambled generators systematically fail Big
Crush---specifically the linear-complexity and matrix-rank tests that detect
linearity---when taking the 32 lowest-order bits in reverse order from each
64-bit word.
| arxiv topic:cs.DS |
arxiv_dataset-103661810.05413 | Infrared Thermography of Complex 3D Printed Components
physics.app-ph
The possibility of using Infrared Lock-In Thermography (LIT) to estimate the
thickness of a sample was assessed and shown to be accurate up to 1.8mm. LIT is
a technique involving heating samples with halogen lamps with varying intensity
over time. The intensity is defined by sinusoidal functions. LIT was conducted
on samples of varying thickness, gradient, and shape. The Lock-In phase signals
were calculated, and a database was then created with the data obtained and was
used to estimate the thickness based on the original phase signal. A
relationship between gradient and phase signal was also shown based on our
data, contrary to current findings in existing literature.
| arxiv topic:physics.app-ph |
arxiv_dataset-103671810.05513 | Quantum Ekpyrotic mechanism in Fermi-bounce curvaton cosmology
gr-qc hep-th
Within the context of the Fermi-bounce curvaton mechanism, we analyze the
one-loop radiative corrections to the four fermion interaction, generated by
the non-dynamical torsion field in the Einstein-Cartan-Holst-Sciama-Kibble
theory. We show that contributions that arise from the one-loop radiative
corrections modify the energy-momentum tensor, {\it mimicking} an effective
Ekpyrotic fluid contribution. For these reasons, we call this effect {\it
quantum Ekpyrotic} mechanism. This leads to the dynamical washing out of
anisotropic contributions to the energy-momentum tensor, without introducing
any new extra Ekpyrotic fluid. We discuss the stability of the bouncing
mechanism and derive the renormalization group flow of the dimensional coupling
constant $\xi$, checking that any change of its sign takes place towards the
bounce. This enforces the theoretical motivations in favor of the torsion
curvaton bounce cosmology as an alternative candidate to the inflation
paradigm.
| arxiv topic:gr-qc hep-th |
arxiv_dataset-103681810.05613 | Spectral representations of topological groups and near-openly generated
groups
math.GR
Near-openly generated groups are introduced. It is a topological and
multiplicative subclass of $\mathbb R$-factorizable groups. Dense and open
subgroups, quotients and Raikov completion of a near-openly generated group are
near-openly generated. Almost connected pro-Lie groups, lindel\" off almost
metrizable groups and the spaces $C_p(X)$ of all continuous real-valued
functions on a Tychonoff space $X$ with pointwise convergence topology are
near-openly generated.
We provide characterizations of near-openly generated groups using methods of
inverse spectra and topological game theory.
| arxiv topic:math.GR |
arxiv_dataset-103691810.05713 | Improving Generalization of Sequence Encoder-Decoder Networks for
Inverse Imaging of Cardiac Transmembrane Potential
cs.LG stat.ML
Deep learning models have shown state-of-the-art performance in many inverse
reconstruction problems. However, it is not well understood what properties of
the latent representation may improve the generalization ability of the
network. Furthermore, limited models have been presented for inverse
reconstructions over time sequences. In this paper, we study the generalization
ability of a sequence encoder decoder model for solving inverse reconstructions
on time sequences. Our central hypothesis is that the generalization ability of
the network can be improved by 1) constrained stochasticity and 2) global
aggregation of temporal information in the latent space. First, drawing from
analytical learning theory, we theoretically show that a stochastic latent
space will lead to an improved generalization ability. Second, we consider an
LSTM encoder-decoder architecture that compresses a global latent vector from
all last-layer units in the LSTM encoder. This model is compared with
alternative LSTM encoder-decoder architectures, each in deterministic and
stochastic versions. The results demonstrate that the generalization ability of
an inverse reconstruction network can be improved by constrained stochasticity
combined with global aggregation of temporal information in the latent space.
| arxiv topic:cs.LG stat.ML |
arxiv_dataset-103701810.05813 | The absolutely Koszul and Backelin-Roos properties for spaces of
quadrics of small codimension
math.AC
Let $\kk$ be a field, $R$ a standard graded quadratic $\kk$-algebra with
$\dim_{\kk}R_2\le 3$, and let $\ov\kk$ denote an algebraic closure of $\kk$. We
construct a graded surjective Golod homomorphism $\varphi \colon P\to
R\otimes_{\kk}\ov{\kk}$ such that $P$ is a complete intersection of codimension
at most $3$. Furthermore, we show that $R$ is absolutely Koszul (that is, every
finitely generated $R$-module has finite linearity defect) if and only if $R$
is Koszul if and only if $R$ is not a trivial fiber extension of a standard
graded $\kk$-algebra with Hilbert series $(1+2t-2t^3)(1-t)^{-1}$. In
particular, we recover earlier results on the Koszul property of Backelin,
Conca and D'Al\`i.
| arxiv topic:math.AC |
arxiv_dataset-103711810.05913 | Nonequilibrium fluctuations of a driven quantum heat engine via machine
learning
quant-ph cond-mat.stat-mech
We propose a machine learning approach based on artificial neural network to
gain faster insights on the role of geometric contributions to the
nonequilibrium fluctuations of an adiabatically temperature-driven quantum heat
engine coupled to a cavity. Using the artificial neural network we have
explored the interplay between bunched and antibunched photon exchange
statistics for different engine parameters. We report that beyond a pivotal
cavity temperature, the Fano factor oscillates between giant and low values as
a function of phase difference between the driving protocols. We further
observe that the standard thermodynamic uncertainty relation is not valid when
there are finite geometric contributions to the fluctuations, but holds true
for zero phase difference even in presence of coherences.
| arxiv topic:quant-ph cond-mat.stat-mech |
arxiv_dataset-103721810.06013 | Torsional Alfven wave embedded ICME magnetic cloud and corresponding
geomagnetic storm
physics.space-ph
The energy transfer during the interaction of large-scale solar wind
structure and the Earth's magnetosphere is the chronic issue in space-weather
studies. To understand this, researchers widely studied the geomagnetic storms
and sub-storms phenomena. The present understanding suggests that long duration
of southward interplanetary magnetic field component is the most important
parameter for the geomagnetic storm. Such long duration strong southward
magnetic field is often associated with ICMEs, torsional Alfven fluctuations
superposed co-rotating interacting regions (CIRs) and fast solar wind streams.
Torsional Alfven fluctuations embedded CIRs have been known for a long, however
magnetic cloud embedded with such fluctuations are rarely observed. The
presence of Alfven waves in the ICME/MC and influence of these waves on the
storm evolution remains an interesting topic of study. The present work
confirms the torsional Alfven waves in a magnetic cloud associated with a CME
launched on 15th February which impacted the Earth's magnetosphere on February
18, 2011. Further, observations indicate that these waves inject energy into
the magnetosphere during the storm and contribute to the long recovery time of
geomagnetic storms. Our study suggests that presence of torsional Alfven waves
significantly controls the storm dynamics.
| arxiv topic:physics.space-ph |
arxiv_dataset-103731810.06113 | Probing Late-type T dwarf J-H Color Outliers for Signs of Age
astro-ph.SR
We present the results of a Keck/NIRSPEC follow-up survey of thirteen
late-type T dwarfs (T6-T9), twelve of which have unusually red or blue J-H
colors. Previous work suggests that J-H color outliers may represent the
high-gravity, low-metallicity (old) and low-gravity, solar-metallicity (young)
extremes of the late-type T dwarf population. We use medium-resolution Y- and
H-band spectroscopy to probe regions of T dwarf atmospheres that are more
sensitive to gravity and metallicity variations than the J band. We find that
the spectral morphologies of our sample are largely homogeneous, with
peak-normalized, Y- and H-band morphologies consistent with spectral standards.
However, three objects stand out as potentially old, with overluminous Y-band
spectra compared to their respective spectral standards, and a fourth object
stands out as potentially young, with an underluminous Y band. Of these four
objects, three have been previously identified as potential metallicity/gravity
outliers, including the one object in our sample with a normal J-H color. We
fit publicly available atmospheric model grids to our spectra and find that the
best-fit physical parameters vary depending on the model used. As we continue
to probe the characteristics of the late-T population, differences in synthetic
spectra of ~10-20% in the blue wing of the Y band and ~45% at 1.65 microns, for
the same physical parameters, must be reconciled. Further development and
public availability of nonsolar metallicity models is also recommended. Future
progress toward deciphering the impacts of gravity, metallicity, and
variability in the late-type T dwarf population will also require high
signal-to-noise, multiwavelength and multi-epoch photometry and spectroscopy.
| arxiv topic:astro-ph.SR |
arxiv_dataset-103741810.06213 | Dynamic Connected Cooperative Coverage Problem
cs.MA cs.CC
We study the so-called dynamic coverage problem by agents located in some
topological graph. The agents must visit all regions of interest but they also
should stay connected to the base via multi-hop. We prove that the algorithmic
complexity of this planning problem is PSPACE-complete. Furthermore we prove
that the problem becomes NP-complete for bounded plans. We also prove the same
complexities for the reachability problem of some positions. We also prove that
complexities are maintained for a subclass of topological graphs.
| arxiv topic:cs.MA cs.CC |
arxiv_dataset-103751810.06313 | Regret vs. Bandwidth Trade-off for Recommendation Systems
cs.IR cs.LG stat.ML
We consider recommendation systems that need to operate under wireless
bandwidth constraints, measured as number of broadcast transmissions, and
demonstrate a (tight for some instances) tradeoff between regret and bandwidth
for two scenarios: the case of multi-armed bandit with context, and the case
where there is a latent structure in the message space that we can exploit to
reduce the learning phase.
| arxiv topic:cs.IR cs.LG stat.ML |
arxiv_dataset-103761810.06413 | The teacher of the gattini (kittens)
physics.hist-ph hep-ph hep-th
The figure of Raoul Gatto, who died in 2017, is remembered here, with an
illustration of his career and the main results of his research, along with the
personal memories of some of those who worked with him.
| arxiv topic:physics.hist-ph hep-ph hep-th |
arxiv_dataset-103771810.06513 | Diagonal Orbits in a Type A Double Flag Variety of Complexity One
math.AG math.CO math.RT
We continue our study of the inclusion posets of diagonal $SL(n)$-orbit
closures in a product of two partial flag varieties. We prove that, if the
diagonal action is of complexity one, then the poset is isomorphic to one of
the 28 posets that we determine explicitly. Furthermore, our computations show
that the number of diagonal $SL(n)$-orbits in any of these posets is at most 10
for any positive integer $n$. This is in contrast with the complexity 0 case,
where, in some cases, the resulting posets attain arbitrary heights.
| arxiv topic:math.AG math.CO math.RT |
arxiv_dataset-103781810.06613 | Pedestrian Dominance Modeling for Socially-Aware Robot Navigation
cs.RO
We present a Pedestrian Dominance Model (PDM) to identify the dominance
characteristics of pedestrians for robot navigation. Through a perception study
on a simulated dataset of pedestrians, PDM models the perceived dominance
levels of pedestrians with varying motion behaviors corresponding to
trajectory, speed, and personal space. At runtime, we use PDM to identify the
dominance levels of pedestrians to facilitate socially-aware navigation for the
robots. PDM can predict dominance levels from trajectories with ~85% accuracy.
Prior studies in psychology literature indicate that when interacting with
humans, people are more comfortable around people that exhibit complementary
movement behaviors. Our algorithm leverages this by enabling the robots to
exhibit complementing responses to pedestrian dominance. We also present an
application of PDM for generating dominance-based collision-avoidance behaviors
in the navigation of autonomous vehicles among pedestrians. We demonstrate the
benefits of our algorithm for robots navigating among tens of pedestrians in
simulated environments.
| arxiv topic:cs.RO |
arxiv_dataset-103791810.06713 | A Chebyshev-Accelerated Primal-Dual Method for Distributed Optimization
math.OC
We consider a distributed optimization problem over a network of agents
aiming to minimize a global objective function that is the sum of local convex
and composite cost functions. To this end, we propose a distributed
Chebyshev-accelerated primal-dual algorithm to achieve faster ergodic
convergence rates. In standard distributed primal-dual algorithms, the speed of
convergence towards a global optimum (i.e., a saddle point in the corresponding
Lagrangian function) is directly influenced by the eigenvalues of the Laplacian
matrix representing the communication graph. In this paper, we use Chebyshev
matrix polynomials to generate gossip matrices whose spectral properties result
in faster convergence speeds, while allowing for a fully distributed
implementation. As a result, the proposed algorithm requires fewer gradient
updates at the cost of additional rounds of communications between agents. We
illustrate the performance of the proposed algorithm in a distributed signal
recovery problem. Our simulations show how the use of Chebyshev matrix
polynomials can be used to improve the convergence speed of a primal-dual
algorithm over communication networks, especially in networks with poor
spectral properties, by trading local computation by communication rounds.
| arxiv topic:math.OC |
arxiv_dataset-103801810.06813 | A Sharpened Rearrangement Inequality for Convolution on the Sphere
math.CA
One may define a trilinear convolution form on the sphere involving two
functions on the sphere and a monotonic function on the interval $[-1,1]$. A
symmetrization inequality of Baernstein and Taylor states that this form is
maximized when the two functions on the sphere are replaced with their
nondecreasing symmetric rearrangements. In the case of indicator functions, we
show that under natural hypotheses, the symmetric rearrangements are the only
maximizers up to symmetry by establishing a sharpened inequality.
| arxiv topic:math.CA |
arxiv_dataset-103811810.06913 | How to share a cake with a secret agent
cs.MA cs.GT
In this note we study a problem of fair division in the absence of full
information. We give an algorithm which solves the following problem: n $\ge$ 2
persons want to cut a cake into n shares so that each person will get at least
1/n of the cake for his or her own measure, furthermore the preferences of one
person are secret. How can we construct such shares? Our algorithm is a slight
modification of the Even-Paz algorithm and allows to give a connected part to
each agent. Moreover, the number of cuts used during the algorithm is optimal:
O (n log(n)) .
| arxiv topic:cs.MA cs.GT |
arxiv_dataset-103821810.07013 | Impact of Plasma Instability on Constraint of the Intergalactic Magnetic
Field
astro-ph.HE
A relativistic electron-positron pair beam can be produced in the interaction
of TeV photons from a blazar with the extragalactic background light (EBL). The
relativistic $e^{\pm}$ pairs would loss energy through inverse-Compton
scattering (ICS) photons of cosmic microwave background (CMB) or plasma
instabilities. The dominant energy-loss process is under debate. Based on the
assumption that the dominant energy-loss process is ICS, the resulted cascade
GeV radiation is usually used to constrain the intergalactic magnetic field
(IGMF). Here, we include the energy-loss due to plasma oblique instability in
the calculation of cascade gamma-ray flux, and investigate the impact of the
plasma instability on the constraint of IGMF. The up-to-date GeV data and
archival TeV data of the blazar 1ES 0229+200 are used. The results indicate
that even if the oblique instability cooling is dominating over ICS cooling,
the cascade flux could be still used to constrain the IGMF. It is found that
with the ratio between the cooling rates of the oblique instability and the ICS
varying from 0.1, 1 to 10, the lower limit of the IGMF putted by the cascade
flux and the gamma-ray data changes from $8\times10^{-18}\ $G,
$5\times10^{-18}\ $G to $10^{-18}\ $G. If the ratio between the two cooling
rates is 30, the estimate of IGMF based on the cascade flux is invalid.
| arxiv topic:astro-ph.HE |
arxiv_dataset-103831810.07113 | Probing the Gluon Sivers Function through direct photon production at
RHIC
hep-ph
We study the production of prompt-photons at RHIC in the context of a
generalised parton model framework, with a view to obtain information on the
gluon Sivers function (GSF). At RHIC energy ($\sqrt{s}=200$ GeV), the Compton
process, $gq\to\gamma q$ contributes significantly to the production of
direct-photons at midrapidity and dominates it in the negative (backward)
rapdity region. We find that for direct photons, asymmetries of upto 10\% are
allowed by a maximal gluon Sivers function. However, the asymmetry obtained
using existing fits of the GSF available is literature is negligible. We also
estimate the impact that photons produced via fragmentation can have on the
signal and find that their inclusion can dilute the asymmetry by between
10-50\% of the direct-photon value. Finally, using the Colour-Gauge Invariant
generalised parton model (CGI-GPM) approach, we consider the effects of initial
state and final state interactions which can affect the universality of the
Sivers functions in different processes. We find that the inclusion of these
effects leads to the size of the gluon contributions being roughly halved.
However, in the backward region which we are interested in, the sizes of the
quark contributions are suppressed even further, leading to increased dominance
of the gluon contributions.
| arxiv topic:hep-ph |
arxiv_dataset-103841810.07213 | Evidence for the First Extragalactic Hydrogen Recombination Line Maser
in NGC 253
astro-ph.GA
We present the first detection of extragalactic hydrogen recombination line
maser emission in the H26alpha transition toward the inner 13.5 pc nuclear
region of the starburst galaxy NGC 253 using ALMA data. In regions with complex
continuum emission (dust, free-free and synchrotron) we propose to use the
recombination line spectral index, $\alpha_\mathrm{L}$ ($S_\mathrm{L}\cdot
\Delta v \propto \nu^{\alpha_\mathrm{L}}$), between the H30alpha and the
H26alpha lines to study the structure of ultra-compact HII regions and to
identify maser emission ($\alpha_\mathrm{L}> 2.1$) from ionized winds. The
measured values of $\alpha_\mathrm{L}$ ranged from 1.0 to 2.9. The largest
$\alpha_\mathrm{L}$ can only be explained by maser emission. The measured flux
density in the H26$\alpha$ maser in NGC 253 suggests that we are observing
hundreds of stars like MWC349A, a prototypical stellar wind where maser
emission arises from its circumstellar disk. We briefly discuss the implication
of the detection of maser emission in starburst galaxies like NGC 253.
| arxiv topic:astro-ph.GA |
arxiv_dataset-103851810.07313 | Bayesian Time-Resolved Spectroscopy of GRB Pulses
astro-ph.HE
We performed time-resolved spectroscopy on a sample of 38 single pulses from
37 gamma-ray bursts detected by the Fermi/Gamma-ray Burst Monitor during its
first 9 years of mission. For the first time a fully Bayesian approach is
applied. A total of 577 spectra are obtained and their properties studied using
two empirical photon models, namely the cutoff power law and Band model. We
present the obtained parameter distributions, spectral evolution properties,
and parameter relations. We also provide the result files containing this
information for usage in further studies. It is found that the cutoff power law
model is the preferred model, based on the deviance information criterion and
the fact that it consistently provides constrained posterior density maps. In
contrast to previous works, the high-energy power-law index of the Band model,
$\beta$, has in general a lower value for the single pulses in this work. In
particular, we investigate the individual spectrum in each pulse, that has the
largest value of the low-energy spectral indexes, $\alpha$. For these 38
spectra, we find that 60% of the $\alpha$ values are larger than $-2/3$, and
thus incompatible with synchrotron emission.Finally, we find that the parameter
relations show a variety of behaviours. Most noteworthy is the fact that the
relation between $\alpha$ and the energy flux is similar for most of the
pulses, independent of any evolution of the other parameters.
| arxiv topic:astro-ph.HE |
arxiv_dataset-103861810.07413 | Probability Logic: A Model Theoretic Perspective
math.LO
In this paper (propositional) probability logic ($PL$) is investigated from
model theoretic point of view. First of all, the ultraproduct construction is
adapted for $\sigma$-additive probability models, and subsequently when this
class of models is considered it is shown that the compactness property holds
with respect to a fragment of $PL$ called basic probability logic ($BPL$). On
the other hand, when dealing with finitely-additive probability models, one may
extend the compactness property for a larger fragment of probability logic,
namely positive probability logic ($PPL$). We finally prove that while the
L\"owenheim-Skolem number of the class of $\sigma$-additive probability models
is uncountable, it is $\aleph_0$ for the class of finitely additive probability
models.
| arxiv topic:math.LO |
arxiv_dataset-103871810.07513 | Multi-Task Deep Learning for Legal Document Translation, Summarization
and Multi-Label Classification
cs.CL cs.IR cs.LG stat.ML
The digitalization of the legal domain has been ongoing for a couple of
years. In that process, the application of different machine learning (ML)
techniques is crucial. Tasks such as the classification of legal documents or
contract clauses as well as the translation of those are highly relevant. On
the other side, digitized documents are barely accessible in this field,
particularly in Germany. Today, deep learning (DL) is one of the hot topics
with many publications and various applications. Sometimes it provides results
outperforming the human level. Hence this technique may be feasible for the
legal domain as well. However, DL requires thousands of samples to provide
decent results. A potential solution to this problem is multi-task DL to enable
transfer learning. This approach may be able to overcome the data scarcity
problem in the legal domain, specifically for the German language. We applied
the state of the art multi-task model on three tasks: translation,
summarization, and multi-label classification. The experiments were conducted
on legal document corpora utilizing several task combinations as well as
various model parameters. The goal was to find the optimal configuration for
the tasks at hand within the legal domain. The multi-task DL approach
outperformed the state of the art results in all three tasks. This opens a new
direction to integrate DL technology more efficiently in the legal domain.
| arxiv topic:cs.CL cs.IR cs.LG stat.ML |
arxiv_dataset-103881810.07613 | The transformation matrices (distortion, orientation, correspondence),
their continuous forms, and their variants
cond-mat.mtrl-sci
The crystallography of displacive phase transformations can be described with
three types of matrices: the lattice distortion matrix, the orientation
relationship matrix, and the correspondence matrix. The paper gives some
formula to express them in crystallographic bases, orthonormal bases, and
reciprocal bases, and it explains how to use them to deduce the matrices of
inverse transformation. In the case of hard-sphere assumption, a continuous
form of the distortion matrix can be determined, and its derivative is
identified to the velocity gradient used in continuum mechanics. The
distortion, the orientation and the correspondence variants are determined by
coset decomposition with intersection groups that depend on the point groups of
the phases and on the type of transformation matrix. The stretch variants
required in the phenomenological theory of martensitic transformation should be
distinguished from the correspondence variants. The orientation variants and
the correspondence variants are also different; they are defined from the
geometric symmetries and algebraic symmetries, respectively. The concept of
orientation (ir)reversibility during thermal cycling is briefly and partially
treated by generalizing the orientation variants with n-cosets and graphs. Some
simple examples are given to show that there is no general relation between the
numbers of distortion, orientation and correspondence variants, and to
illustrate the concept of orientation variants formed by thermal cycling.
| arxiv topic:cond-mat.mtrl-sci |
arxiv_dataset-103891810.07713 | Large violation of the flavour SU(3) symmetry in $\eta$MAID2018 isobar
model
nucl-th hep-ph nucl-ex
We demonstrate that the explanation of the neutron anomaly around $W\sim
1685$MeV in $\gamma N\to \eta N$ reactions provided by the $\eta$MAID2018
isobar model is based on large violation of the flavour SU(3) symmetry in
hadron interactions. This is yet another example of how conventional
explanation (without invoking exotic narrow nucleon resonance) of the neutron
anomaly metamorphoses into unconventional physics picture of hadron
interactions. A possibility to mend the flavour SU(3) symmetry for some of
resonances in $\eta$MAID model is discussed.
| arxiv topic:nucl-th hep-ph nucl-ex |
arxiv_dataset-103901810.07813 | Controlling error orientation to improve quantum algorithm success rates
quant-ph
The success probability of a quantum algorithm constructed from noisy quantum
gates cannot be accurately predicted from single parameter metrics that compare
noisy and ideal gates. We illustrate this concept by examining a system with
coherent errors and comparing algorithm success rates for different choices of
two-qubit gates that are constructed from composite pulse sequences, where the
residual gate errors are related by a unitary transformation. As a result, all
of the sequences have the same error relative to the ideal gate under any
distance measure that is invariant under unitary transformations. However, the
circuit success can vary dramatically by choosing error orientations that do
not affect the final outcome and error orientations that cancel between
conjugate controlled-nots, as demonstrated here with Clifford circuits,
compiled Toffoli gates, and quantum simulation algorithms. The results point to
the utility of both minimizing the error and optimizing the error direction and
also to the advantages of using multiple control sequences for the same gate
type within a single algorithm.
| arxiv topic:quant-ph |
arxiv_dataset-103911810.07913 | Robust Sparse Reduced Rank Regression in High Dimensions
stat.ML cs.LG
We propose robust sparse reduced rank regression for analyzing large and
complex high-dimensional data with heavy-tailed random noise. The proposed
method is based on a convex relaxation of a rank- and sparsity-constrained
non-convex optimization problem, which is then solved using the alternating
direction method of multipliers algorithm. We establish non-asymptotic
estimation error bounds under both Frobenius and nuclear norms in the
high-dimensional setting. This is a major contribution over existing results in
reduced rank regression, which mainly focus on rank selection and prediction
consistency. Our theoretical results quantify the tradeoff between
heavy-tailedness of the random noise and statistical bias. For random noise
with bounded $(1+\delta)$th moment with $\delta \in (0,1)$, the rate of
convergence is a function of $\delta$, and is slower than the sub-Gaussian-type
deviation bounds; for random noise with bounded second moment, we obtain a rate
of convergence as if sub-Gaussian noise were assumed. Furthermore, the
transition between the two regimes is smooth. We illustrate the performance of
the proposed method via extensive numerical studies and a data application.
| arxiv topic:stat.ML cs.LG |
arxiv_dataset-103921810.08013 | Low-energy Bremsstrahlung photon in relativistic nucleon+nucleon
collisions
nucl-th nucl-ex
We study the production of Bremsstrahlung photon in relativistic
nucleon+nucleon collisions by introducing a deceleration time of
electromagnetic currents. It is found that Bremsstrahlung photon spectrum at
low energy does not depend on the deceleration time but solely on the amount of
reduced electromagnetic current in collision. On the other hand, the photon
spectrum becomes soft with increasing deceleration time. We also find that
Bremsstrahlung photon spectrum in p+n collisions is considerably different from
that in p+p collisions at low energy.
| arxiv topic:nucl-th nucl-ex |
arxiv_dataset-103931810.08113 | Adversarial TableQA: Attention Supervision for Question Answering on
Tables
cs.CL
The task of answering a question given a text passage has shown great
developments on model performance thanks to community efforts in building
useful datasets. Recently, there have been doubts whether such rapid progress
has been based on truly understanding language. The same question has not been
asked in the table question answering (TableQA) task, where we are tasked to
answer a query given a table. We show that existing efforts, of using "answers"
for both evaluation and supervision for TableQA, show deteriorating
performances in adversarial settings of perturbations that do not affect the
answer. This insight naturally motivates to develop new models that understand
question and table more precisely. For this goal, we propose Neural Operator
(NeOp), a multi-layer sequential network with attention supervision to answer
the query given a table. NeOp uses multiple Selective Recurrent Units (SelRUs)
to further help the interpretability of the answers of the model. Experiments
show that the use of operand information to train the model significantly
improves the performance and interpretability of TableQA models. NeOp
outperforms all the previous models by a big margin.
| arxiv topic:cs.CL |
arxiv_dataset-103941810.08213 | Carnegie Supernova Project-II: The Near-infrared Spectroscopy Program
astro-ph.SR
Shifting the focus of Type Ia supernova (SN Ia) cosmology to the
near-infrared (NIR) is a promising way to significantly reduce the systematic
errors, as the strategy minimizes our reliance on the empirical
width-luminosity relation and uncertain dust laws. Observations in the NIR are
also crucial for our understanding of the origins and evolution of these
events, further improving their cosmological utility. Any future experiments in
the rest-frame NIR will require knowledge of the SN Ia NIR spectroscopic
diversity, which is currently based on a small sample of observed spectra.
Along with the accompanying paper, Phillips et al. (2018), we introduce the
Carnegie Supernova Project-II (CSP-II), to follow up nearby SNe Ia in both the
optical and the NIR. In particular, this paper focuses on the CSP-II NIR
spectroscopy program, describing the survey strategy, instrumental setups, data
reduction, sample characteristics, and future analyses on the data set. In
collaboration with the Harvard-Smithsonian Center for Astrophysics (CfA)
Supernova Group, we obtained 661 NIR spectra of 157 SNe Ia. Within this sample,
451 NIR spectra of 90 SNe Ia have corresponding CSP-II follow-up light curves.
Such a sample will allow detailed studies of the NIR spectroscopic properties
of SNe Ia, providing a different perspective on the properties of the unburned
material, radioactive and stable nickel produced, progenitor magnetic fields,
and searches for possible signatures of companion stars.
| arxiv topic:astro-ph.SR |
arxiv_dataset-103951810.08313 | Adaptive Communication Strategies to Achieve the Best Error-Runtime
Trade-off in Local-Update SGD
cs.LG cs.DC stat.ML
Large-scale machine learning training, in particular distributed stochastic
gradient descent, needs to be robust to inherent system variability such as
node straggling and random communication delays. This work considers a
distributed training framework where each worker node is allowed to perform
local model updates and the resulting models are averaged periodically. We
analyze the true speed of error convergence with respect to wall-clock time
(instead of the number of iterations), and analyze how it is affected by the
frequency of averaging. The main contribution is the design of AdaComm, an
adaptive communication strategy that starts with infrequent averaging to save
communication delay and improve convergence speed, and then increases the
communication frequency in order to achieve a low error floor. Rigorous
experiments on training deep neural networks show that AdaComm can take $3
\times$ less time than fully synchronous SGD, and still reach the same final
training loss.
| arxiv topic:cs.LG cs.DC stat.ML |
arxiv_dataset-103961810.08413 | Yukawa Unification with Four Higgs Doublets in Supersymmetric GUT
hep-ph
We discuss the Yukawa coupling unification, a very interesting prediction of
the grand unified theory, in the context of scenarios with more than one pair
of Higgs doublet since the current LHC constraint has become a problem for the
Yukawa unification scenarios with just one pair of Higgs doublet. More than one
pair of Higgs doublets can easily arise in missing partner mechanism which
solves the doublet-triplet splitting problem. In such a scenario, the Yukawa
unification occurs at a medium $\tan\beta$ value, e.g., $\sim$ 30, which
corresponds to much smaller threshold corrections compared to usual large
$\tan\beta$ scenario for $t-b-\tau$ unification in the context of SO(10) and
$b-\tau$ unification in the context of SU(5) models. Further, we show that an
additional Higgs doublet pair lowers the sensitivity of the radiative symmetry
breaking of the electroweak vacuum.
| arxiv topic:hep-ph |
arxiv_dataset-103971810.08513 | Indirect Detection of Extrasolar Planets via Astrometry
astro-ph.EP
Radio wavelength astrometry of stars and other objects has a long and
productive history. The use of that technique to determine whether stars have
planets around them would cover a nearly unique part of the parameter space for
detection of those systems. Namely, astrometric observations are most sensitive
to systems with large planets in moderately wide orbits (a few to ~10 AU),
because it is those systems that produce large reflex motion of the star, in a
short enough measurement period (years to tens of years). In addition,
astrometric observations are most sensitive to systems which are nearly
face-on. Other techniques (radial velocity, or the photometric method of
Kepler) are more sensitive to systems with planets in close orbits (less than
$\sim$1 AU), which are nearly edge-on. We describe here, using the Hipparcos
and Gaia star catalogs, how ngVLA could use this technique on hundreds of
stars, some tens of which are solar analogs, to determine whether these stars
have planets orbiting them.
| arxiv topic:astro-ph.EP |
arxiv_dataset-103981810.08613 | Exact solution for a black hole embedded in a nonstatic dust-filled
universe
gr-qc
An exact solution of the Lema\^{i}tre--Tolman--Bondi class is investigated as
a possible model of the Schwarzschild-like black hole embedded in a non-static
dust-filled universe for the three types of spatial curvature. The solution is
obtained in comoving coordinates by means of the mass function method. It is
shown that the central part of space contains a Schwarzschild-like black hole.
The R-T-structure of the resulting spacetime is built. It is shown that the
solution includes both the Schwarzschild and Friedmann solutions as its natural
limits. The geodesic equations for test particles are analyzed. The particle
observable velocities are found. The trajectories of the test particles are
built from the point of view of both comoving and distant observers. For the
distant observer, the results coincide with the Schwarzschild picture within a
second-order accuracy near the symmetry center.
| arxiv topic:gr-qc |
arxiv_dataset-103991810.08713 | Topological interfaces in Chern-Simons theory and $AdS_3/CFT_2$
hep-th
Recently, topological interfaces between three-dimensional abelian
Chern-Simons theories were constructed. In this note we investigate such
topological interfaces in the context of the $AdS_3/CFT_2$ correspondence. We
show that it is possible to connect the topological interfaces in the bulk
Chern-Simons theory to topological interfaces in the dual CFT on the boundary.
In addition for $[U(1)]^{2N}$ Chern-Simons theory on $AdS_3$, we show that it
is possible to find boundary counter terms which lead to the $N$ conserved
currents in the dual two-dimensional CFT.
| arxiv topic:hep-th |
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