text
stringlengths 6
128k
|
|---|
We study the steady creep flow of a perfectly viscoplastic solid reinforced
by fibers with high viscosity contrast. Our study unveils new effects related
to anisotropy and conditioned by the Norton exponent.
|
We show the validity of the Minimal Model Program for threefolds in
characteristic five.
|
The intuitive interaction between the audio and visual modalities is valuable
for cross-modal self-supervised learning. This concept has been demonstrated
for generic audiovisual tasks like video action recognition and acoustic scene
classification. However, self-supervision remains under-explored for
audiovisual speech. We propose a method to learn self-supervised speech
representations from the raw audio waveform. We train a raw audio encoder by
combining audio-only self-supervision (by predicting informative audio
attributes) with visual self-supervision (by generating talking faces from
audio). The visual pretext task drives the audio representations to capture
information related to lip movements. This enriches the audio encoder with
visual information and the encoder can be used for evaluation without the
visual modality. Our method attains competitive performance with respect to
existing self-supervised audio features on established isolated word
classification benchmarks, and significantly outperforms other methods at
learning from fewer labels. Notably, our method also outperforms fully
supervised training, thus providing a strong initialization for speech related
tasks. Our results demonstrate the potential of multimodal self-supervision in
audiovisual speech for learning good audio representations.
|
The ubiquitous presence of machine learning systems in our lives necessitates
research into their vulnerabilities and appropriate countermeasures. In
particular, we investigate the effectiveness of adversarial attacks and
defenses against automatic speech recognition (ASR) systems. We select two ASR
models - a thoroughly studied DeepSpeech model and a more recent Espresso
framework Transformer encoder-decoder model. We investigate two threat models:
a denial-of-service scenario where fast gradient-sign method (FGSM) or weak
projected gradient descent (PGD) attacks are used to degrade the model's word
error rate (WER); and a targeted scenario where a more potent imperceptible
attack forces the system to recognize a specific phrase. We find that the
attack transferability across the investigated ASR systems is limited. To
defend the model, we use two preprocessing defenses: randomized smoothing and
WaveGAN-based vocoder, and find that they significantly improve the model's
adversarial robustness. We show that a WaveGAN vocoder can be a useful
countermeasure to adversarial attacks on ASR systems - even when it is jointly
attacked with the ASR, the target phrases' word error rate is high.
|
In any theory it is unnatural if the observed parameters lie very close to
special values that determine the existence of complex structures necessary for
observers. A naturalness probability, P, is introduced to numerically evaluate
the unnaturalness. If P is small in all known theories, there is an observer
naturalness problem. In addition to the well-known case of the cosmological
constant, we argue that nuclear stability and electroweak symmetry breaking
(EWSB) represent significant observer naturalness problems. The naturalness
probability associated with nuclear stability is conservatively estimated as
P_nuc < 10^{-(3-2)}, and for simple EWSB theories P_EWSB < 10^{-(2-1)}. This
pattern of unnaturalness in three different arenas, cosmology, nuclear physics,
and EWSB, provides evidence for the multiverse. In the nuclear case the problem
is largely solved even with a flat multiverse distribution, and with nontrivial
distributions it is possible to understand both the proximity to neutron
stability and the values of m_e and m_d - m_u in terms of the electromagnetic
contribution to the proton mass. It is reasonable that multiverse distributions
are strong functions of Lagrangian parameters due to their dependence on
various factors. In any EWSB theory, strongly varying distributions typically
lead to a little or large hierarchy, and in certain multiverses the size of the
little hierarchy is enhanced by a loop factor. Since the correct theory of EWSB
is unknown, our estimate for P_EWSB is theoretical. The LHC will determine
P_EWSB more robustly, which may remove or strengthen the observer naturalness
problem of EWSB. For each of the three arenas, the discovery of a natural
theory would eliminate the evidence for the multiverse; but in the absence of
such a theory, the multiverse provides a provisional understanding of the data.
|
Techniques for plan recognition under uncertainty require a stochastic model
of the plan-generation process. We introduce Probabilistic State-Dependent
Grammars (PSDGs) to represent an agent's plan-generation process. The PSDG
language model extends probabilistic context-free grammars (PCFGs) by allowing
production probabilities to depend on an explicit model of the planning agent's
internal and external state. Given a PSDG description of the plan-generation
process, we can then use inference algorithms that exploit the particular
independence properties of the PSDG language to efficiently answer
plan-recognition queries. The combination of the PSDG language model and
inference algorithms extends the range of plan-recognition domains for which
practical probabilistic inference is possible, as illustrated by applications
in traffic monitoring and air combat.
|
The first-generation stars in the $\Lambda$CDM universe are considered to
have formed in dark halos with total masses in the range $\sim
10^{5}-10^{7}M_sun$ at $z \sim 20-50$. These stars expected to be very massive
and in some cases they end their lives as the first supernovae (SNe). We
explore the problem of whether star formation in low mass dark halos (< 10^{7}
M_sun) was triggered or suppressed by the SN feedback from neighboring
star-forming halos. We take into consideration mainly two effects by the SN
shock: one is the evacuation of gas components from the halos and the other is
the promotion of H_2 formation because of the enhanced ionization degree by
shock heating. Combining above effects, we find that the star formation
activities in the neighboring dark matter halos (M < 10^{7} M_sun) are
basically suppressed in case they are located close to the SN center, because
of the gas evacuation effect. The critical distance within which the gas is
blown away falls within the range $\sim 0.3-1.5$kpc depending on the SN energy
and the halo mass. In addition, we find there is very little window in the
parameter space where star formation activities in dark halos are induced or
promoted by neighboring SN.
|
A prototype of LaBr3:Ce in situ gamma-ray spectrometer for marine
environmental monitoring is developed and applied for in situ measurement. A
3-inch LaBr3:Ce scintillator is used in the detector, and a digital pulse
process electronics is chosen as the pulse height analyzer. For this prototype,
the energy response of the spectrometer is linear and the energy resolution of
662keV is 2.6% (much better than NaI). With the measurement of the prototype in
a water tank filled with 137Cs, the detect efficiency for 137Cs is (0.288
0.01)cps/(Bq/L), which is close to the result of Monte Carlo simulation,
0.283cps/(Bq/L). With this measurement, the MDAC for 137Cs in one hour has been
calculated to 0.78Bq/L, better than that of NaI(Tl) in-situ gamma spectrometer,
which is ~1.0Bq/L.
|
We provide a bird's eye view on developments in analyzing the long time,
large crowd behavior of Cucker-Smale alignment dynamics. We consider a class of
(fully-)discrete models, paying particular attention to general alignment
protocols in which agents, with possibly time-dependent masses, are driven by a
large class of heavy-tailed communication kernels. The presence of
time-dependent masses allows, in particular, non-symmetric communication. While
revisiting known results in the literature, we also shed new light of various
aspects on the long time flocking/swarming behavior, driven by the decay of
energy fluctuations and heavy-tailed connectivity. We also discuss the large
crowd dynamics in terms of the hydrodynamic description of Euler alignment
models.
|
We present a numerical study of the one-dimensional BCS-BEC crossover of a
spin-imbalanced Fermi gas. The crossover is described by the Bose-Fermi
resonance model in a real space representation. Our main interest is in the
behavior of the pair correlations, which, in the BCS limit, are of the
Fulde-Ferrell-Larkin-Ovchinnikov type, while in the BEC limit, a superfluid of
diatomic molecules forms that exhibits quasi-condensation at zero momentum. We
use the density matrix renormalization group method to compute the phase
diagram as a function of the detuning of the molecular level and the
polarization. As a main result, we show that FFLO-like correlations disappear
well below full polarization close to the resonance. The critical polarization
depends on both the detuning and the filling.
|
Constraints among test parameters often have substantial effects on the
performance of test case generation for combinatorial interaction testing. This
paper investigates the effectiveness of the use of Binary Decision Diagrams
(BDDs) for constraint handling. BDDs are a data structure used to represent and
manipulate Boolean functions. The core role of a constraint handler is to
perform a check to determine if a partial test case with unspecified parameter
values satisfies the constraints. In the course of generating a test suite,
this check is executed a number of times; thus the efficiency of the check
significantly affects the overall time required for test case generation. In
the paper, we study two different approaches. The first approach performs this
check by computing the logical AND of Boolean functions that represent all
constraint-satisfying full test cases and a given partial test case. The second
approach uses a new technique to construct a BDD that represents all
constraint-satisfying partial test cases. With this BDD, the check can be
performed by simply traversing the BDD from the root to a sink. We developed a
program that incorporates both approaches into IPOG, a well-known test case
generation algorithm. Using this program, we empirically evaluate the
performance of these BDD-based constraint handling approaches using a total of
62 problem instances. In the evaluation, the two approaches are compared with
three different constraint handling approaches, namely, those based on Boolean
satisfiability (SAT) solving, Minimum Forbidden Tuples (MFTs), and Constraint
Satisfiction Problem (CSP) solving. The results of the evaluation show that the
two BDD-based approaches usually outperform the other constraint handling
techniques and that the BDD-based approach using the new technique exhibits
best performance.
|
In this article we conjecture a 4-dimensional characterization of tightness:
a contact structure is tight if and only if a slice-Bennequin inequality holds
for smoothly embedded surfaces in Yx[0,1]. An affirmative answer to our
conjecture would imply an analogue of the Milnor conjecture for torus knots: if
a fibered link L induces a tight contact structure on Y then its fiber surface
maximize Euler characteristic amongst all surfaces in Yx[0,1] with boundary L.
We provide evidence for both conjectures by proving them for contact structures
with non-vanishing Ozsv\'ath-Szab\'o contact invariant. We also show that any
subsurface of a page of an open book inducing a contact structure with
non-trivial invariant maximize "slice" Euler-characteristic for its boundary,
and conjecture that this holds more generally for open books inducing tight
contact structures.
|
We perform in-situ two-cycle thermal cycling and annealing studies for a
transferred CVD-grown monolayer MoS2 on a SiO2/Si substrate, using spatially
resolved micro-Raman and PL spectroscopy. After the thermal cycling and being
annealed at 305 deg C twice, the film morphology and film-substrate bonding are
significantly modified, which together with the removal of polymer residues
cause major changes in the strain and doping distribution over the film, and
thus the optical properties. Before annealing, the strain associated with
ripples in the transferred film dominates the spatial distributions of the PL
peak position and intensity over the film; after annealing, the variation in
film-substrate bonding, affecting both strain and doping, becomes the leading
factor. This work reveals that the film-substrate bonding, and thus the strain
and doping, is unstable under thermal stress, which is important for
understanding the substrate effects on the optical and transport properties of
the 2D material and their impact on device applications.
|
This project aims to produce the next volume of machine-generated poetry, a
complex art form that can be structured and unstructured, and carries depth in
the meaning between the lines. GPoeT-2 is based on fine-tuning a state of the
art natural language model (i.e. GPT-2) to generate limericks, typically
humorous structured poems consisting of five lines with a AABBA rhyming scheme.
With a two-stage generation system utilizing both forward and reverse language
modeling, GPoeT-2 is capable of freely generating limericks in diverse topics
while following the rhyming structure without any seed phrase or a posteriori
constraints.Based on the automated generation process, we explore a wide
variety of evaluation metrics to quantify "good poetry," including syntactical
correctness, lexical diversity, and subject continuity. Finally, we present a
collection of 94 categorized limericks that rank highly on the explored "good
poetry" metrics to provoke human creativity.
|
Intermediate mass black holes (IMBHs, $\sim 10^2-10^5M_{\odot}$) are often
dubbed as the missing link between stellar mass ($\lesssim 10^2M_{\odot}$) and
super-massive ($\gtrsim 10^{5-6} M_{\odot}$) black holes. Observational
signatures of these can result from tidal disruptions of white dwarfs (WDs),
which would otherwise be captured as a whole by super-massive black holes.
Recent observations indicate that IMBHs might be rapidly spinning, while it is
also known that isolated white dwarfs might have large spins, with spin periods
of the order of minutes. Here, we aim to understand the effects of ``coupling''
between black hole and stellar spin, focussing on the tidal disruption of
spinning WDs in the background of spinning IMBHs. Using smoothed particle
hydrodynamics, we perform a suite of numerical simulations of partial tidal
disruptions, where spinning WDs are in eccentric orbits about spinning IMBHs.
We take a hybrid approach, where we integrate the Kerr geodesic equations while
being in a regime where we can treat the internal stellar fluid dynamics in the
Newtonian limit. We observe strong dependence of quantities like the core mass
and the mass differences between tidal tails on such coupled spin effects.
However, observable quantities such as mass fallback rates and gravitational
wave amplitudes show minimal variations with these, in the parameter range that
we consider.
|
The automatic analysis of fine art paintings presents a number of novel
technical challenges to artificial intelligence, computer vision, machine
learning, and knowledge representation quite distinct from those arising in the
analysis of traditional photographs. The most important difference is that many
realist paintings depict stories or episodes in order to convey a lesson,
moral, or meaning. One early step in automatic interpretation and extraction of
meaning in artworks is the identifications of figures (actors). In Christian
art, specifically, one must identify the actors in order to identify the
Biblical episode or story depicted, an important step in understanding the
artwork. We designed an automatic system based on deep convolutional neural
networks and simple knowledge database to identify saints throughout six
centuries of Christian art based in large part upon saints symbols or
attributes. Our work represents initial steps in the broad task of automatic
semantic interpretation of messages and meaning in fine art.
|
Grothendieck and Harder proved that every principal bundle over the
projective line with split reductive structure group (and trivial over the
generic point) can be reduced to a maximal torus. Furthermore, this reduction
is unique modulo automorphisms and the Weyl group. In a series of six
variations on this theme, we prove corresponding results for principal bundles
over the following schemes and stacks: (1) a line modulo the group of nth roots
of unity; (2) a football, that is, an orbifold of genus zero with two marked
points; (3) a gerbe over a football whose structure group is the nth roots of
unity; (4) a chain of lines meeting in nodes; (5) a line modulo an action of a
split torus; and (6) a chain modulo an action of a split torus. We also prove
that the automorphism groups of such bundles are smooth, affine, and connected.
|
The structure constants for Moyal brackets of an infinite basis of functions
on the algebraic manifolds M of pseudo-unitary groups U(N_+,N_-) are provided.
They generalize the Virasoro and W_\infty algebras to higher dimensions. The
connection with volume-preserving diffeomorphisms on M, higher generalized-spin
and tensor operator algebras of U(N_+,N_-) is discussed. These
centrally-extended, infinite-dimensional Lie-algebras provide also the arena
for non-linear integrable field theories in higher dimensions, residual gauge
symmetries of higher-extended objects in the light-cone gauge and C^*-algebras
for tractable non-commutative versions of symmetric curved spaces.
|
This paper introduces the hypervolume maximization with a single solution as
an alternative to the mean loss minimization. The relationship between the two
problems is proved through bounds on the cost function when an optimal solution
to one of the problems is evaluated on the other, with a hyperparameter to
control the similarity between the two problems. This same hyperparameter
allows higher weight to be placed on samples with higher loss when computing
the hypervolume's gradient, whose normalized version can range from the mean
loss to the max loss. An experiment on MNIST with a neural network is used to
validate the theory developed, showing that the hypervolume maximization can
behave similarly to the mean loss minimization and can also provide better
performance, resulting on a 20% reduction of the classification error on the
test set.
|
The origin of the stochastic gravitational wave (GW) background, recently
discovered from pulsar timing array experiments, is still unclear. If this
background is of astrophysical origin, we expect the distribution of GW sources
to follow the one of galaxies. Since galaxies are not perfectly isotropically
distributed at large scales, but follow the cosmological large-scale structure,
this would lead to an intrinsic anisotropy in the distribution of GW sources.
In this work, we develop a formalism to account for this anisotropy, by
considering a Gaussian ensemble of sources in each realization of the universe
and then taking ensemble averages over all such realizations. We find that
large-scale galaxy clustering has no impact on the Hellings-Downs curve,
describing the expectation value of pulsar timing residual correlations.
However, it introduces a new contribution to the variance of the Hellings-Downs
correlation. Hence, due to the anisotropic distribution of sources, the
measurements of pulsar timing residual correlations in our Universe may differ
from the Hellings-Downs curve. This indicates that the variance of the
Hellings-Downs correlation can be utilized as a new cosmological observable
that might help us to unveil the nature of current background observations in
the nHz band.
|
Conventional methods of 3D object generative modeling learn volumetric
predictions using deep networks with 3D convolutional operations, which are
direct analogies to classical 2D ones. However, these methods are
computationally wasteful in attempt to predict 3D shapes, where information is
rich only on the surfaces. In this paper, we propose a novel 3D generative
modeling framework to efficiently generate object shapes in the form of dense
point clouds. We use 2D convolutional operations to predict the 3D structure
from multiple viewpoints and jointly apply geometric reasoning with 2D
projection optimization. We introduce the pseudo-renderer, a differentiable
module to approximate the true rendering operation, to synthesize novel depth
maps for optimization. Experimental results for single-image 3D object
reconstruction tasks show that we outperforms state-of-the-art methods in terms
of shape similarity and prediction density.
|
This paper describes the LIA speaker recognition system developed for the
Speaker Recognition Evaluation (SRE) campaign. Eight sub-systems are developed,
all based on a state-of-the-art approach: i-vector/PLDA which represents the
mainstream technique in text-independent speaker recognition. These sub-systems
differ: on the acoustic feature extraction front-end (MFCC, PLP), at the
i-vector extraction stage (UBM, DNN or two-feats posteriors) and finally on the
data-shifting (IDVC, mean-shifting). The submitted system is a fusion at the
score-level of these eight sub-systems.
|
In recent years, much work in descriptive set theory has been focused on the
Borel complexity of naturally occurring classification problems, in particular,
the study of countable Borel equivalence relations and their structure under
the quasi-order of Borel reducibility. Following the approach of Louveau and
Rosendal for the study of analytic equivalence relations, we study countable
Borel quasi-orders.
In this paper we are concerned with universal countable Borel quasi-orders,
i.e. countable Borel quasi-orders above all other countable Borel quasi-orders
with regard to Borel reducibility. We first establish that there is a universal
countable Borel quasi-order, and then establish that several countable Borel
quasi-orders are universal. An important example is an embeddability relation
on descriptive set theoretic trees.
Our main result states that embeddability of finitely generated groups is a
universal countable Borel quasi-order, answering a question of Louveau and
Rosendal. This immediately implies that biembeddability of finitely generated
groups is a universal countable Borel equivalence relation. The same techniques
are also used to show that embeddability of countable groups is a universal
analytic quasi-order.
Finally, we show that, up to Borel bireducibility, there are continuum-many
distinct countable Borel quasi-orders which symmetrize to a universal countable
Borel equivalence relation.
|
We present the results of a 47-ks Chandra-ACIS observation of the old open
cluster M67. We detected 25 proper-motion cluster members (including ten new
sources) and 12 sources (all new) that we suspect to be members from their
locations close to the main sequence (1 < B-V < 1.7). Of the detected members,
23 are binaries. Among the new sources that are members and probable members
are four spectroscopic binaries with P_orb < 12 d, two contact binaries and two
periodic photometric variables with P_ph < 8.4 d. Their X-rays are likely the
result of coronal activity enhanced by tidally locked rapid rotation. The
X-rays of the new source S997, a blue straggler in a wide eccentric orbit, are
puzzling. Spectral fits show that the X-rays of the brightest sources S1063 (a
binary with a sub-subgiant), S1082 (a triple blue straggler with a close
binary) and S1040 (a circular binary of a giant and a cool white dwarf), are
consistent with coronal emission. We detected a new bright source that must
have brightened at least about ten times since the time of the ROSAT
observations. It is not clear whether its faint blue optical counterpart
belongs to M67. We discuss the possibility that this source is a low-mass X-ray
binary in quiescence, which would be the first of its kind in an open cluster.
In addition to cluster members, we detected about 100 background sources, many
of which we identify with faint objects in the ESO Imaging Survey.
|
We present a generalization of the granocentric model proposed in [Clusel et
al., Nature, 2009, 460, 611615] that is capable of describing the local
fluctuations inside not only polydisperse but also monodisperse packings of
spheres. This minimal model does not take into account the relative particle
positions, yet it captures positional disorder through local stochastic
processes sampled by efficient Monte Carlo methods. The disorder is
characterized by the distributions of local parameters, such as the number of
neighbors and contacts, filled solid angle around a central particle and the
cell volumes. The model predictions are in good agreement with our experimental
data on monodisperse random close packings of PMMA particles. Moreover, the
model can be used to predict the distributions of local fluctuations in any
packing, as long as the average number of neighbors, contacts and the packing
fraction are known. These distributions give a microscopic foundation to the
statistical mechanics framework for jammed matter and allow us to calculate
thermodynamic quantities such as the compactivity in the phase space of
possible jammed configurations.
|
The Ehrenfest dynamics, representing a quantum-classical mean-field type
coupling, is a widely used approximation in quantum molecular dynamics. In this
paper, we propose a time-splitting method for an Ehrenfest dynamics, in the
form of a nonlinearly coupled Schr\"odinger-Liouville system. We prove that our
splitting scheme is stable uniformly with respect to the semiclassical
parameter, and, moreover, that it preserves a discrete semiclassical limit.
Thus one can accurately compute physical observables using time steps induced
only by the classical Liouville equation, i.e., independent of the small
semiclassical parameter - in addition to classical mesh sizes for the Liouville
equation. Numerical examples illustrate the validity of our meshing strategy.
|
We present a semiclassical model for plasmon-enhanced high-harmonic
generation (HHG) in the vicinity of metal nanostructures. We show that both the
inhomogeneity of the enhanced local fields and electron absorption by the metal
surface play an important role in the HHG process and lead to the generation of
even harmonics and to a significantly increased cutoff. For the examples of
silver-coated nanocones and bowtie antennas we predict that the required
intensity reduces by up to three orders of magnitudes and the HHG cutoff
increases by more than a factor of two. The study of the enhanced high-harmonic
generation is connected with a finite-element simulation of the electric field
enhancement due to the excitation of the plasmonic modes.
|
Existing black box search methods have achieved high success rate in
generating adversarial attacks against NLP models. However, such search methods
are inefficient as they do not consider the amount of queries required to
generate adversarial attacks. Also, prior attacks do not maintain a consistent
search space while comparing different search methods. In this paper, we
propose a query efficient attack strategy to generate plausible adversarial
examples on text classification and entailment tasks. Our attack jointly
leverages attention mechanism and locality sensitive hashing (LSH) to reduce
the query count. We demonstrate the efficacy of our approach by comparing our
attack with four baselines across three different search spaces. Further, we
benchmark our results across the same search space used in prior attacks. In
comparison to attacks proposed, on an average, we are able to reduce the query
count by 75% across all datasets and target models. We also demonstrate that
our attack achieves a higher success rate when compared to prior attacks in a
limited query setting.
|
Connecting curves have been shown to organize the rotational structure of
strange attractors in three-dimensional dynamical systems. We extend the
description of connecting curves and their properties to higher dimensions
within the special class of differential dynamical systems. The general
properties of connecting curves are derived and selection rules stated.
Examples are presented to illustrate these properties for dynamical systems of
dimension n=3,4,5.
|
We study the effect of disorder on the dynamics of a transverse domain wall
in ferromagnetic nanostrips, driven either by magnetic fields or spin-polarized
currents, by performing a large ensemble of GPU-accelerated micromagnetic
simulations. Disorder is modeled by including small, randomly distributed
non-magnetic voids in the system. Studying the domain wall velocity as a
function of the applied field and current density reveals fundamental
differences in the domain wall dynamics induced by these two modes of driving:
For the field-driven case, we identify two different domain wall pinning
mechanisms, operating below and above the Walker breakdown, respectively,
whereas for the current-driven case pinning is absent above the Walker
breakdown. Increasing the disorder strength induces a larger Walker breakdown
field and current, and leads to decreased and increased domain wall velocities
at the breakdown field and current, respectively. Furthermore, for adiabatic
spin transfer torque, the intrinsic pinning mechanism is found to be suppressed
by disorder. We explain these findings within the one-dimensional model in
terms of an effective damping parameter $\alpha^*$ increasing with the disorder
strength.
|
We study the dynamical stability of the BTZ black string against fermonic and
gravitational perturbations. The BTZ black string is not always stable against
these perturbations. There exist threshold values for $m^2$ related to the
compactification of the extra dimension for fermonic perturbation, scalar part
of the gravitational perturbation and the tensor perturbation, respectively.
Above the threshold values, perturbations are stable; while below these
thresholds, perturbations can be unstable. We find that this non-trivial
stability behavior qualitatively agrees with that predicted by a
thermodynamical argument, showing that the BTZ black string phase is not the
privileged stable phase.
|
Consider the energy-critical focusing wave equation in odd space dimension
$N\geq 3$. The equation has a nonzero radial stationary solution $W$, which is
unique up to scaling and sign change. In this paper we prove that any radial,
bounded in the energy norm solution of the equation behaves asymptotically as a
sum of modulated $W$s, decoupled by the scaling, and a radiation term.
The proof essentially boils down to the fact that the equation does not have
purely nonradiative multisoliton solutions. The proof overcomes the fundamental
obstruction for the extension of the 3D case (treated in our previous work,
Cambridge Journal of Mathematics 2013, arXiv:1204.0031) by reducing the study
of a multisoliton solution to a finite dimensional system of ordinary
differential equations on the modulation parameters. The key ingredient of the
proof is to show that this system of equations creates some radiation,
contradicting the existence of pure multisolitons.
|
The eccentricity of a vertex $v$ in a graph $G$ is the maximum distance
between $v$ and any other vertex of $G$. The diameter of a graph $G$ is the
maximum eccentricity of a vertex in $G$. The eccentric connectivity index of a
connected graph is the sum over all vertices of the product between
eccentricity and degree. Given two integers $n$ and $D$ with $D\leq n-1$, we
characterize those graphs which have the largest eccentric connectivity index
among all connected graphs of order $n$ and diameter $D$. As a corollary, we
also characterize those graphs which have the largest eccentric connectivity
index among all connected graphs of a given order $n$.
|
The metaverse refers to the merger of technologies for providing a digital
twin of the real world and the underlying connectivity and interactions for the
many kinds of agents within. As this set of technology paradigms - involving
artificial intelligence, mixed reality, the internet-of-things and others -
gains in scale, maturity, and utility there are rapidly emerging design
challenges and new research opportunities. In particular is the metaverse
disconnect problem, the gap in task switching that inevitably occurs when a
user engages with multiple virtual and physical environments simultaneously.
Addressing this gap remains an open issue that affects the user experience and
must be overcome to increase overall utility of the metaverse. This article
presents design frameworks that consider how to address the metaverse as a
hyper-connected meta-environment that connects and expands multiple user
environments, modalities, contexts, and the many objects and relationships
within them. This article contributes to i) a framing of the metaverse as a
social XR-IoT (XRI) concept, ii) design Considerations for XRI metaverse
experiences, iii) a design architecture for social multi-user XRI metaverse
environments, and iv) descriptive exploration of social interaction scenarios
within XRI multi-user metaverses. These contribute a new design framework for
metaverse researchers and creators to consider the coming wave of
interconnected and immersive smart environments.
|
We are interested in the problem of multiagent systems development for risk
detecting and emergency response in an uncertain and partially perceived
environment. The evaluation of the current situation passes by three stages
inside the multiagent system. In a first time, the situation is represented in
a dynamic way. The second step, consists to characterise the situation and
finally, it is compared with other similar known situations. In this paper, we
present an information modelling of an observed environment, that we have
applied on the RoboCupRescue Simulation System. Information coming from the
environment are formatted according to a taxonomy and using semantic features.
The latter are defined thanks to a fine ontology of the domain and are managed
by factual agents that aim to represent dynamically the current situation.
|
Stellar ages are critical building blocks of evolutionary models, but
challenging to measure for low mass main sequence stars. An unexplored solution
in this regime is the application of probabilistic machine learning methods to
gyrochronology, a stellar dating technique that is uniquely well suited for
these stars. While accurate analytical gyrochronological models have proven
challenging to develop, here we apply conditional normalizing flows to
photometric data from open star clusters, and demonstrate that a data-driven
approach can constrain gyrochronological ages with a precision comparable to
other standard techniques. We evaluate the flow results in the context of a
Bayesian framework, and show that our inferred ages recover literature values
well. This work demonstrates the potential of a probabilistic data-driven
solution to widen the applicability of gyrochronological stellar dating.
|
We analyse the high-energy behavior of tree-level graviton Compton amplitudes
for particles of mass m and arbitrary spin, concentrating on a combination of
forward amplitudes that will be unaffected by eventual cross- couplings to
other, higher spins. We first show that for any spin larger than 2, tree-level
unitarity is already violated at energies well below the Planck scale M, if m
<< M. We then restore unitarity to this amplitude up to M by adding non-minimal
couplings that depend on the curvature and its derivatives, and modify the
minimal description - including particle gravitational quadrupole moments - at
scales O(1/m).
|
A recent article reported a comparison study concerning compound-specific
chlorine isotope analysis (CSIA-Cl) of organochlorines using gas
chromatography- isotope ratio mass spectrometry (GC-IRMS) and gas
chromatography-quadrupole mass spectrometry (GC-qMS). Comparable precisions
between the two instruments were achieved and trueness of the analysis results
was confirmed. The CSIA-Cl method using GC-qMS was originally developed by
Sakaguchi-S\"oder et al.and further improved by several relevant studies,and
has been used to evaluate organic contaminant attenuation in the environment.
The essential principle of the method is to calculate the chlorine isotope
ratio (37Cl/35Cl) by using the first pair of neighboring chlorine isotopologues
(two-mass apart) of either the molecular ion or a fragmental ion of a target
analyte, or using all the first isotopologue pairs of all molecular and
fragmental ions. These isotope-ratio calculation schemes using chlorine
isotopologue pair(s) were based on the binomial theorem and the prerequisite
hypothesis that the measured abundances of chlorine isotopologues of individual
analytes were binomially distributed. However, it is not true with the
hypothesis.
|
We introduce a new approach for applying sampling-based sketches to two and
three mode tensors. We illustrate our technique to construct sketches for the
classical problems of $\ell_0$ sampling and producing $\ell_1$ embeddings. In
both settings we achieve sketches that can be applied to a rank one tensor in
$(\mathbb{R}^d)^{\otimes q}$ (for $q=2,3$) in time scaling with $d$ rather than
$d^2$ or $d^3$. Our main idea is a particular sampling construction based on
fast convolution which allows us to quickly compute sums over sufficiently
random subsets of tensor entries.
|
Document-level neural machine translation (NMT) has outperformed
sentence-level NMT on a number of datasets. However, document-level NMT is
still not widely adopted in real-world translation systems mainly due to the
lack of large-scale general-domain training data for document-level NMT. We
examine the effectiveness of using Paracrawl for learning document-level
translation. Paracrawl is a large-scale parallel corpus crawled from the
Internet and contains data from various domains. The official Paracrawl corpus
was released as parallel sentences (extracted from parallel webpages) and
therefore previous works only used Paracrawl for learning sentence-level
translation. In this work, we extract parallel paragraphs from Paracrawl
parallel webpages using automatic sentence alignments and we use the extracted
parallel paragraphs as parallel documents for training document-level
translation models. We show that document-level NMT models trained with only
parallel paragraphs from Paracrawl can be used to translate real documents from
TED, News and Europarl, outperforming sentence-level NMT models. We also
perform a targeted pronoun evaluation and show that document-level models
trained with Paracrawl data can help context-aware pronoun translation.
|
Current-voltage measurements have been made at room temperature on a Si-rich
silicon oxide film deposited via Electron-Cyclotron Resonance Plasma Enhanced
Chemical Vapor Deposition (ECR-PECVD) and annealed at 750 - 1000$ ^\circ$C. The
thickness of oxide between Si quantum dots embedded in the film increases with
the increase of annealing temperature. This leads to the decrease of current
density as the annealing temperature is increased. Assuming the Fowler-Nordheim
tunneling mechanism in large electric fields, we obtain an effective barrier
height $\phi_{eff}$ of $\sim$ 0.7 $\pm$ 0.1 eV for an electron tunnelling
through an oxide layer between Si quantum dots. The Frenkel-Poole effect can
also be used to adequately explain the electrical conduction of the film under
the influence of large electric fields. We suggest that at room temperature Si
quantum dots can be regarded as traps that capture and emit electrons by means
of tunneling.
|
For $N\geq 3$, by the seminal paper of Brezis and V\'eron (Arch. Rational
Mech. Anal. 75(1):1--6, 1980/81), no positive solutions of $-\Delta u+u^q=0$ in
$\mathbb R^N\setminus \{0\}$ exist if $q\geq N/(N-2)$; for $1<q<N/(N-2)$ the
existence and profiles near zero of all positive $C^1(\mathbb R^N\setminus
\{0\})$ solutions are given by Friedman and V\'eron (Arch. Rational Mech. Anal.
96(4):359--387, 1986).
In this paper, for every $q>1$ and $\theta\in \mathbb R$, we prove that the
nonlinear elliptic problem (*) $-\Delta u-\lambda
\,|x|^{-2}\,u+|x|^{\theta}u^q=0$ in $\mathbb R^N\setminus \{0\}$ with $u>0$ has
a $C^1(\mathbb R^N\setminus \{0\})$ solution if and only if
$\lambda>\lambda^*$, where $\lambda^*=\Theta(N-2-\Theta) $ with
$\Theta=(\theta+2)/(q-1)$. We show that (a) if $\lambda>(N-2)^2/4$, then
$U_0(x)=(\lambda-\lambda^*)^{1/(q-1)}|x|^{-\Theta}$ is the only solution of (*)
and (b) if $\lambda^*<\lambda\leq (N-2)^2/4$, then all solutions of (*) are
radially symmetric and their total set is $U_0\cup \{U_{\gamma,q,\lambda}:\
\gamma\in (0,\infty) \}$. We give the precise behavior of $
U_{\gamma,q,\lambda}$ near zero and at infinity, distinguishing between
$1<q<q_{N,\theta}$ and $q>\max\{q_{N,\theta},1\}$, where
$q_{N,\theta}=(N+2\theta+2)/(N-2)$.
In addition, for $\theta\leq -2$ we settle the structure of the set of all
positive solutions of (*) in $\Omega\setminus \{0\}$, subject to
$u|_{\partial\Omega}=0$, where $\Omega$ is a smooth bounded domain containing
zero, complementing the works of C\^{\i}rstea (Mem. Amer. Math. Soc. 227, 2014)
and Wei--Du (J. Differential Equations 262(7):3864--3886, 2017).
|
We present broadly applicable nonperturbative results on the behavior of
eigenvalues and eigenvectors under the addition of self-adjoint operators and
under the multiplication of unitary operators, in finite-dimensional Hilbert
spaces. To this end, we decompose these operations into elementary 1-parameter
processes in which the eigenvalues move similarly to the spheres in Newton's
cradle. As special cases, we recover level repulsion and Cauchy interlacing. We
discuss two examples of applications. Applied to adiabatic quantum computing,
we obtain new tools to relate algorithmic complexity to computational slowdown
through gap narrowing. Applied to information theory, we obtain a
generalization of Shannon sampling theory, the theory that establishes the
equivalence of continuous and discrete representations of information. The new
generalization of Shannon sampling applies to signals of varying information
density and finite length.
|
In order to remove a little of the mysticism surrounding the issue of
strangeness in the nucleon, we present simple, physically transparent estimates
of both the strange magnetic moment and charge radius of the proton. Although
simple, the estimates are in quite good agreement with sophisticated
calculations using the latest input from lattice QCD. We further explore the
possible size of systematic uncertainties associated with charge symmetry
violation (CSV) in the recent precise determination of the strange magnetic
moment of the proton. We find that CSV acts to increase the error estimate by
0.003 \mu_N such that G_M^s = -0.046 +/- 0.022 \mu_N.
|
We report the high strength of magnetoelectric (ME) coupling of trilayered
composites prepared by electro-deposition. The ME coupling of Ni-lead zirconate
titanate (PZT)-Ni trilayered structure was measured ranged from1 kHz to 120
kHz. The trilayered composites exhibit high magnetoelectric voltage coefficient
because of good bonding between piezoelectric and magnetostrictive layers. The
maximum magnetoelectric voltage coefficient can be up to 33 V/cm Oe at the
electromechanical resonance frequency. This magnetoelectric effect shows
promising application in transducers for magnetoelectric energy conversion.
|
We propose constant approximation algorithms for generalizations of the
Flexible Flow Shop (FFS) problem which form a realistic model for
non-preemptive scheduling in MapReduce systems. Our results concern the
minimization of the total weighted completion time of a set of MapReduce jobs
on unrelated processors and improve substantially on the model proposed by
Moseley et al. (SPAA 2011) in two directions. First, we consider each job
consisting of multiple Map and Reduce tasks, as this is the key idea behind
MapReduce computations, and we propose a constant approximation algorithm.
Then, we introduce into our model the crucial cost of data shuffle phase, i.e.,
the cost for the transmission of intermediate data from Map to Reduce tasks. In
fact, we model this phase by an additional set of Shuffle tasks for each job
and we manage to keep the same approximation ratio when they are scheduled on
the same processors with the corresponding Reduce tasks and to provide also a
constant ratio when they are scheduled on different processors. This is the
most general setting of the FFS problem (with a special third stage) for which
a constant approximation ratio is known.
|
We demonstrate that an arbitrary system of screw dislocations in a smectic-A
liquid crystal may be consistently treated within harmonic elasticity theory,
provided that the angles between dislocations are sufficiently small. Using
this theory, we calculate the ground state configuration of the TGB-A phase. We
obtain an estimate of the twist-grain-boundary spacing and screw dislocation
spacing in a boundary in terms of the macroscopic parameters, in reasonable
agreement with experimental results.
|
Software debloating tools seek to improve program security and performance by
removing unnecessary code, called bloat. While many techniques have been
proposed, several barriers to their adoption have emerged. Namely, debloating
tools are highly specialized, making it difficult for adopters to find the
right type of tool for their needs. This is further hindered by a lack of
established metrics and comparative evaluations between tools. To close this
information gap, we surveyed 10 years of debloating literature and several
tools currently under commercial development to taxonomize knowledge about the
debloating ecosystem. We then conducted a broad comparative evaluation of 10
debloating tools to determine their relative strengths and weaknesses. Our
evaluation, conducted on a diverse set of 20 benchmark programs, measures tools
across 12 performance, security, and correctness metrics. Our evaluation
surfaces several concerning findings that contradict the prevailing narrative
in the debloating literature. First, debloating tools lack the maturity
required to be used on real-world software, evidenced by a slim 22% overall
success rate for creating passable debloated versions of medium- and
high-complexity benchmarks. Second, debloating tools struggle to produce sound
and robust programs. Using our novel differential fuzzing tool, DIFFER, we
discovered that only 13% of our debloating attempts produced a sound and robust
debloated program. Finally, our results indicate that debloating tools
typically do not improve the performance or security posture of debloated
programs by a significant degree according to our evaluation metrics. We
believe that our contributions in this paper will help potential adopters
better understand the landscape of tools and will motivate future research and
development of more capable debloating tools.
|
The research on the algorithm of analytic signal has received much attention
for a long time. Takenaka-Malmquist (TM) system was introduced to consider
analytic functions in 1925. If TM system satisfies hyperbolic inseparability
condition, then it is an orthogonal basis. It can form unconditional basis for
Hilbert space $\mathbb{H}^{2}(D)$ and Schauder basis for Banach space
$\mathbb{H}^{p}(D)(1 < p < \infty)$. In characterizing a function space, a
necessary condition is whether the basis is unconditional. But since the
introduction of TM systems in 1925, to the best of our knowledge, no one has
proved the existence of a TM system capable of forming an unconditional basis
for Banach space $\mathbb{H}^{p}(D) (p \neq 2)$. TM system has a simple and
intuitive analytical structure. Hence it is applied also to the learning
algorithms and systematically developed to the reproducing kernel Hilbert
spaces (RKHS). Due to the lack of unconditional basis properties, it cannot be
extended to the reproducing kernel Banach spaces (RKBS) algorithm. But the case
of Banach space plays an important role in machine learning. In this paper, we
prove that two TM systems can form unconditional basis for $\mathbb{H}^{p}(D)
(1<p <\infty)$.
|
We consider NS-NS superstring model with several ``magnetic'' parameters
$b_s$ (s=1, ...,N) associated with twists mixing a compact $S^1$ direction with
angles in $N$ spatial 2-planes of flat 10-dimensional space. It generalizes the
Kaluza-Klein Melvin model which has single parameter $b$. The corresponding
U-dual background is a R-R type IIA solution describing an orthogonal
intersection of $N$ flux 7-branes. Like the Melvin model, the NS-NS string
model with $N$ continuous parameters is explicitly solvable; we present its
perturbative spectrum and torus partition function explicitly for the N=2 case.
For generic $b_s$ (above some critical values) there are tachyons in the $S^1$
winding sector. A remarkable feature of this model is that while in the Melvin
N=1 case all supersymmetry is broken, a fraction of it may be preserved for $N
>1$ by making a special choice of the parameters $b_s$. Such solvable NS-NS
models may be viewed as continuous-parameter analogs of non-compact orbifold
models. They and their U-dual R-R fluxbrane counterparts may have some
``phenomenological'' applications. In particular, in N=3 case one finds a
special 1/4 supersymmetric R-R 3-brane background. Putting Dp-branes in flat
twisted NS-NS backgrounds leads to world-volume gauge theories with reduced
amount of supersymmetry. We also discuss possible ways of evolution of unstable
backgrounds towards stable ones.
|
A graph $G$ is $H$-free, if it contains no $H$ as a subgraph. A graph is said
to be \emph{$H$-minor free}, if it does not contain $H$ as a minor. In recent
years, Nikiforov asked that what is the maximum spectral radius of an $H$-free
graph of order $n$? In this paper, we consider about some
Brualdi-Solheid-Tur\'{a}n type problems on bipartite graphs. In 2015, Zhai, Lin
and Gong proved that if $G$ is a bipartite graph with order $n \geq 2k+2$ and
$\rho(G)\geq \rho(K_{k,n-k})$, then $G$ contains a $C_{2k+2}$ unless $G \cong
K_{k,n-k}$ [Linear Algebra Appl. 471 (2015)]. Firstly, we give a new and more
simple proof for the above theorem. Secondly, we prove that if $G$ is a
bipartite graph with order $n \geq 2k+2$ and $\rho(G)\geq \rho(K_{k,n-k})$,
then $G$ contains all $T_{2k+3}$ unless $G \cong K_{k,n-k}$. Finally, we prove
that among all outerplanar bipartite graphs on $n>344569$ vertices, $K_{1,n-1}$
attains the maximum spectral radius.
|
The EventB2SQL tool translates Event-B models to persistent Java applications
that store the state of the model in a relational database. Most Event-B
assignments are translated directly to SQL database modification statements,
which can then be executed against the database. In this work, we present a
formal semantics for and prove the soundness of the translation of sets of
assignment statements representing the actions of an Event-B event. This allows
the generated code to be used with confidence in its correctness.
|
Encoder layer fusion (EncoderFusion) is a technique to fuse all the encoder
layers (instead of the uppermost layer) for sequence-to-sequence (Seq2Seq)
models, which has proven effective on various NLP tasks. However, it is still
not entirely clear why and when EncoderFusion should work. In this paper, our
main contribution is to take a step further in understanding EncoderFusion.
Many of previous studies believe that the success of EncoderFusion comes from
exploiting surface and syntactic information embedded in lower encoder layers.
Unlike them, we find that the encoder embedding layer is more important than
other intermediate encoder layers. In addition, the uppermost decoder layer
consistently pays more attention to the encoder embedding layer across NLP
tasks. Based on this observation, we propose a simple fusion method,
SurfaceFusion, by fusing only the encoder embedding layer for the softmax
layer. Experimental results show that SurfaceFusion outperforms EncoderFusion
on several NLP benchmarks, including machine translation, text summarization,
and grammatical error correction. It obtains the state-of-the-art performance
on WMT16 Romanian-English and WMT14 English-French translation tasks. Extensive
analyses reveal that SurfaceFusion learns more expressive bilingual word
embeddings by building a closer relationship between relevant source and target
embedding. Source code is freely available at
https://github.com/SunbowLiu/SurfaceFusion.
|
This paper corrects an error in a proof in the original version of the paper
published in 1998 in the Oxford Quarterly. The main theorem remains the same:
The geometric realization of the partially ordered set of proper free factors
in a finitely generated free group of rank $n$ is homotopy equivalent to a
wedge of spheres of dimension $n-2$.
|
The absolute frequency of the 1S0-3P0 clock transition of 87Sr has been
measured to be 429 228 004 229 873.65 (37) Hz using lattice-confined atoms,
where the fractional uncertainty of 8.6x10-16 represents one of the most
accurate measurements of an atomic transition frequency to date. After a
detailed study of systematic effects, which reduced the total systematic
uncertainty of the Sr lattice clock to 1.5x10-16, the clock frequency is
measured against a hydrogen maser which is simultaneously calibrated to the US
primary frequency standard, the NIST Cs fountain clock, NIST-F1. The comparison
is made possible using a femtosecond laser based optical frequency comb to
phase coherently connect the optical and microwave spectral regions and by a
3.5 km fiber transfer scheme to compare the remotely located clock signals.
|
A hysteretic in-plane magnetoresistance develops below the superconducting
transition of LaAlO$_3$/SrTiO$_3$ interfaces for $\left|H_{/\!/}\right|<$ 0.15
T, independently of the carrier density or oxygen annealing. We show that this
hysteresis arises from vortex depinning within a thin superconducting layer, in
which the vortices are created by discrete ferromagnetic dipoles located solely
above the layer. We find no evidence for finite-momentum pairing or bulk
magnetism and hence conclude that ferromagnetism is strictly confined to the
interface, where it competes with superconductivity.
|
We study the triplet-singlet relaxation in two-electron semiconductor quantum
dots. Both single dots and vertically coupled double dots are discussed. In our
work, the electron-electron Coulomb interaction, which plays an important role
in the electronic structure, is included. The spin mixing is caused by
spin-orbit coupling which is the key to the triplet-singlet relaxation. We show
that the selection rule widely used in the literature is incorrect unless near
the crossing/anticrossing point in single quantum dots. The triplet/singlet
relaxation in double quantum dots can be markedly changed by varying barrier
height, inter-dot distance, external magnetic field and dot size.
|
We study the production of right-handed $W_R$ bosons and heavy neutrinos $N$
at a future 100 TeV high energy hadron collider in the context of Left-Right
symmetry, including the effects of $W_L-W_R$ gauge-boson mixing. We estimate
the collider reach for up to 3/ab integrated luminosity using a multi-binned
sensitivity measure. In the Keung-Senjanovi\'c and missing energy channels, the
3$\sigma$ sensitivity extends up to $M_{W_R}=35$ and 37 TeV, respectively. We
further clarify the interplay between the missing energy channel and the
(expected) limits from neutrinoless double beta decay searches, Big Bang
nucleosynthesis and dark matter.
|
We consider condensation of nearly marginal matter tachyons in closed string
field theory and observe that upon restricting to a subspace of states not
containing the ghost dilaton, the on-shell value of the action is proportional
to the shift of the central charge of the matter CFT. This correspondence lets
us find a novel conformal perturbation theory formula for the next-to-leading
order shift of the central charge for a generic theory, which we test on
Zamolodchikov's flow between consecutive minimal models. Upon reintroduction of
the dilaton couplings, it is plausible to have a vanishing value of the
on-shell action.
|
This paper describes work done in collaboration with Andy Cohen. In our
model, ordinary fermions are accompanied by an equal number `terafermions.'
These particles are linked to ordinary quarks and leptons by an unconventional
CP' operation, whose soft breaking in the Higgs mass sector results in their
acquiring large masses. The model leads to no detectable strong CP violating
effects, produces small Dirac masses for neutrinos, and offers a novel
alternative for dark matter as electromagnetically bound systems made of
terafermions.
|
The topic diversity of open-domain videos leads to various vocabularies and
linguistic expressions in describing video contents, and therefore, makes the
video captioning task even more challenging. In this paper, we propose an
unified caption framework, M&M TGM, which mines multimodal topics in
unsupervised fashion from data and guides the caption decoder with these
topics. Compared to pre-defined topics, the mined multimodal topics are more
semantically and visually coherent and can reflect the topic distribution of
videos better. We formulate the topic-aware caption generation as a multi-task
learning problem, in which we add a parallel task, topic prediction, in
addition to the caption task. For the topic prediction task, we use the mined
topics as the teacher to train a student topic prediction model, which learns
to predict the latent topics from multimodal contents of videos. The topic
prediction provides intermediate supervision to the learning process. As for
the caption task, we propose a novel topic-aware decoder to generate more
accurate and detailed video descriptions with the guidance from latent topics.
The entire learning procedure is end-to-end and it optimizes both tasks
simultaneously. The results from extensive experiments conducted on the MSR-VTT
and Youtube2Text datasets demonstrate the effectiveness of our proposed model.
M&M TGM not only outperforms prior state-of-the-art methods on multiple
evaluation metrics and on both benchmark datasets, but also achieves better
generalization ability.
|
We report the realization of nanotube-based quantum dot structures that use
local electrostatic gating to produce individually controllable dots in series
along a nanotube. Electrostatic top-gates produce depletion regions in the
underlying tube; a pair of such depletion regions defines a quantum dot.
Transparencies of tunnel barriers as well as the electrostatic energies, within
single and multiple dots, can be tuned by gate voltages. The approach allows
accurate control over multiple devices on a single tube, and serves as a design
paradigm for nanotube-based electronics and quantum systems.
|
IoT application domains, device diversity and connectivity are rapidly
growing. IoT devices control various functions in smart homes and buildings,
smart cities, and smart factories, making these devices an attractive target
for attackers. On the other hand, the large variability of different
application scenarios and inherent heterogeneity of devices make it very
challenging to reliably detect abnormal IoT device behaviors and distinguish
these from benign behaviors. Existing approaches for detecting attacks are
mostly limited to attacks directly compromising individual IoT devices, or,
require predefined detection policies. They cannot detect attacks that utilize
the control plane of the IoT system to trigger actions in an
unintended/malicious context, e.g., opening a smart lock while the smart home
residents are absent.
In this paper, we tackle this problem and propose ARGUS, the first
self-learning intrusion detection system for detecting contextual attacks on
IoT environments, in which the attacker maliciously invokes IoT device actions
to reach its goals. ARGUS monitors the contextual setting based on the state
and actions of IoT devices in the environment. An unsupervised Deep Neural
Network (DNN) is used for modeling the typical contextual device behavior and
detecting actions taking place in abnormal contextual settings. This
unsupervised approach ensures that ARGUS is not restricted to detecting
previously known attacks but is also able to detect new attacks. We evaluated
ARGUS on heterogeneous real-world smart-home settings and achieve at least an
F1-Score of 99.64% for each setup, with a false positive rate (FPR) of at most
0.03%.
|
We report the observation of a unidirectional magnetoresistance (UMR) that
originates from the nonequilibrium orbital momentum induced by an electric
current in a naturally oxidized Cu/Co bilayer. The orbital-UMR scales with the
torque efficiency due to the orbital Rashba-Edelstein effect upon changing the
Co thickness and temperature, reflecting their common origin. We attribute the
UMR to orbital-dependent electron scattering and orbital-to-spin conversion in
the ferromagnetic layer. In contrast to the spin-current induced UMR, the
magnon contribution to the orbital-UMR is absent in thin Co layers, which we
ascribe to the lack of coupling between low energy magnons and orbital current.
The magnon contribution to the UMR emerges in Co layers thicker than about 5
nm, which is comparable to the orbital-to-spin conversion length. Our results
provide insight into orbital-to-spin momentum transfer processes relevant for
the optimization of spintronic devices based on light metals and orbital
transport.
|
N-site-lattice Hamiltonians H are introduced and perceived as a set of
systematic discrete approximants of a certain PT-symmetric
square-well-potential model with the real spectrum and with a non-Hermiticity
which is localized near the boundaries of the interval. Its strength is
controlled by one, two or three parameters. The problem of the explicit
construction of a nontrivial metric which makes the theory unitary is then
addressed. It is proposed and demonstrated that due to the not too complicated
tridiagonal-matrix form of our input Hamiltonians the computation of the metric
is straightforward and that its matrix elements prove obtainable,
non-numerically, in elementary polynomial forms.
|
Extensive research on automatic fake news detection has been conducted due to
the significant detrimental effects of fake news proliferation. Most existing
approaches rely on a single source of evidence, such as comments or relevant
news, to derive explanatory evidence for decision-making, demonstrating
exceptional performance. However, their single evidence source suffers from two
critical drawbacks: (i) noise abundance, and (ii) resilience deficiency.
Inspired by the natural process of fake news identification, we propose an
Evidence-aware Multi-source Information Fusion (EMIF) network that jointly
leverages user comments and relevant news to make precise decision and excavate
reliable evidence. To accomplish this, we initially construct a co-attention
network to capture general semantic conflicts between comments and original
news. Meanwhile, a divergence selection module is employed to identify the
top-K relevant news articles with content that deviates the most from the
original news, which ensures the acquisition of multiple evidence with higher
objectivity. Finally, we utilize an inconsistency loss function within the
evidence fusion layer to strengthen the consistency of two types of evidence,
both negating the authenticity of the same news. Extensive experiments and
ablation studies on real-world dataset FibVID show the effectiveness of our
proposed model. Notably, EMIF shows remarkable robustness even in scenarios
where a particular source of information is inadequate.
|
We show how various mathematical formalisms, specifically the catastrophe
formalism and group theory, aid in the study of relevant systems in quantum
optics. We describe the phase transition of the Dicke model for a finite number
N of atoms, via 3 different methods, which lead to universal parametric curves
for the expectation value of the first quadrature of the electromagnetic field
and the expectation value of the number operator, as functions of the atomic
relative population. These are valid for all values of the matter-field
coupling parameter, and valid for both the ground and first-excited states.
Using these mathematical tools, the critical value of the atom-field coupling
parameter is found as a function of the number of atoms, from which its
critical exponent is derived.
|
Automatic nuclei segmentation and classification play a vital role in digital
pathology. However, previous works are mostly built on data with limited
diversity and small sizes, making the results questionable or misleading in
actual downstream tasks. In this paper, we aim to build a reliable and robust
method capable of dealing with data from the 'the clinical wild'. Specifically,
we study and design a new method to simultaneously detect, segment, and
classify nuclei from Haematoxylin and Eosin (H&E) stained histopathology data,
and evaluate our approach using the recent largest dataset: PanNuke. We address
the detection and classification of each nuclei as a novel semantic keypoint
estimation problem to determine the center point of each nuclei. Next, the
corresponding class-agnostic masks for nuclei center points are obtained using
dynamic instance segmentation. Meanwhile, we proposed a novel Joint Pyramid
Fusion Module (JPFM) to model the cross-scale dependencies, thus enhancing the
local feature for better nuclei detection and classification. By decoupling two
simultaneous challenging tasks and taking advantage of JPFM, our method can
benefit from class-aware detection and class-agnostic segmentation, thus
leading to a significant performance boost. We demonstrate the superior
performance of our proposed approach for nuclei segmentation and classification
across 19 different tissue types, delivering new benchmark results.
|
A low-energy non-unitary leptonic mixing matrix is a generic effect of some
theories of new physics accounting for neutrino masses. We show how the extra
CP-phases of a general non-unitary matrix allow for sizeable CP-asymmetries in
the $\nu_\mu\to \nu_\tau$ channel. This CP-asymmetries turns out to be an
excellent probe of such new physics.
|
Neural networks are powerful and flexible models that work well for many
difficult learning tasks in image, speech and natural language understanding.
Despite their success, neural networks are still hard to design. In this paper,
we use a recurrent network to generate the model descriptions of neural
networks and train this RNN with reinforcement learning to maximize the
expected accuracy of the generated architectures on a validation set. On the
CIFAR-10 dataset, our method, starting from scratch, can design a novel network
architecture that rivals the best human-invented architecture in terms of test
set accuracy. Our CIFAR-10 model achieves a test error rate of 3.65, which is
0.09 percent better and 1.05x faster than the previous state-of-the-art model
that used a similar architectural scheme. On the Penn Treebank dataset, our
model can compose a novel recurrent cell that outperforms the widely-used LSTM
cell, and other state-of-the-art baselines. Our cell achieves a test set
perplexity of 62.4 on the Penn Treebank, which is 3.6 perplexity better than
the previous state-of-the-art model. The cell can also be transferred to the
character language modeling task on PTB and achieves a state-of-the-art
perplexity of 1.214.
|
AQ Col (EC 05217-3914) is one of the first detected pulsating subdwarf B
(sdB) stars and has been considered to be a single star. Photometric monitoring
of AQ Col reveals a pulsation timing variation with a period of 486 days,
interpreted as time-delay due to reflex motion in a wide-binary formed with an
unseen companion with expected mass larger than 1.05 $M_\odot$. The optical
spectra and color-Magnitude diagram of the system suggested that the companion
is not a main sequence star but a white dwarf or neutron star. The pulsation
timing variation also shows that the system has an eccentricity of 0.424, which
is much larger than any known sdB long period binary system. That might be due
to the existence of another short period companion to the sdB star. Two optical
spectra obtained on 1996 December $5^{\rm th}$ show a radial velocity change of
49.1~km/s in 46.1 minutes, which suggests the hot subdwarf in the wide-binary
is itself a close-binary formed with another unseen white dwarf or neutron star
companion; if further observations show this interpretation to be correct, AQ
Col is an interesting triple system worthy of further study.
|
We present a quasi-analytical solution of a spin-orbital model of KCuF$_{3}$,
using the variational method for Green's functions. By analyzing the spectra
for different partial bosonic compositions as well as the full solution, we
show that hole propagation needs both orbiton and magnon excitations to
develop, but the orbitons dominate the picture. We further elucidate the role
of the different bosons by analyzing the self-energies for simplified models,
establishing that because of the nature of the spin-orbital ground state,
magnons alone do not produce a full quasiparticle band, in contrast to
orbitons. Finally, using the electron-hole transformation between the $e_g$
states of KCuF$_3$ and LaMnO$_3$ we suggest the qualitative scenario for
photoemission experiments in LaMnO$_3$.
|
We have studied the effect of electric field on transport properties of the
prototypical phase separated manganite La5/8-yPryCa3/8MnO3 with y=0.34. Our
results show that the suggested image in which the charge ordered state is
melted by the appliance of an electric current and/or voltage has to be
revised. We were able to explain the observed resistivity drop in terms of an
artifact related to Joule heating and the particular hysteresis that the system
under study display, common to many other phase separated manganites.
|
We present a real-world application that uses a quantum computer.
Specifically, we train a RBM using QA for cybersecurity applications. The
D-Wave 2000Q has been used to implement QA. RBMs are trained on the ISCX data,
which is a benchmark dataset for cybersecurity. For comparison, RBMs are also
trained using CD. CD is a commonly used method for RBM training. Our analysis
of the ISCX data shows that the dataset is imbalanced. We present two different
schemes to balance the training dataset before feeding it to a classifier. The
first scheme is based on the undersampling of benign instances. The imbalanced
training dataset is divided into five sub-datasets that are trained separately.
A majority voting is then performed to get the result. Our results show the
majority vote increases the classification accuracy up from 90.24% to 95.68%,
in the case of CD. For the case of QA, the classification accuracy increases
from 74.14% to 80.04%. In the second scheme, a RBM is used to generate
synthetic data to balance the training dataset. We show that both QA and
CD-trained RBM can be used to generate useful synthetic data. Balanced training
data is used to evaluate several classifiers. Among the classifiers
investigated, K-Nearest Neighbor (KNN) and Neural Network (NN) perform better
than other classifiers. They both show an accuracy of 93%. Our results show a
proof-of-concept that a QA-based RBM can be trained on a 64-bit binary dataset.
The illustrative example suggests the possibility to migrate many practical
classification problems to QA-based techniques. Further, we show that synthetic
data generated from a RBM can be used to balance the original dataset.
|
This paper investigates a time discrete variational model for splines in
Wasserstein spaces to interpolate probability measures. Cubic splines in
Euclidean space are known to minimize the integrated squared acceleration
subject to a set of interpolation constraints. As generalization on the space
of probability measures the integral over the squared acceleration is
considered as a spline energy and regularized by addition of the usual action
functional. Both energies are then discretized in time using local
Wasserstein-2 distances and the generalized Wasserstein barycenter. The
existence of time discrete regularized splines for given interpolation
conditions is established. On the subspace of Gaussian distributions, the
spline interpolation problem is solved explicitly and consistency in the
discrete to continuous limit is shown. The computation of time discrete splines
is implemented numerically, based on entropy regularization and the Sinkhorn
algorithm. A variant of the iPALM method is applied for the minimization of the
fully discrete functional. A variety of numerical examples demonstrate the
robustness of the approach and show striking characteristics of the method. As
a particular application the spline interpolation for synthesized textures is
presented.
|
This paper proposes the User Viewing Flow Modeling (SINGLE) method for the
article recommendation task, which models the user constant preference and
instant interest from user-clicked articles. Specifically, we first employ a
user constant viewing flow modeling method to summarize the user's general
interest to recommend articles. In this case, we utilize Large Language Models
(LLMs) to capture constant user preferences from previously clicked articles,
such as skills and positions. Then we design the user instant viewing flow
modeling method to build interactions between user-clicked article history and
candidate articles. It attentively reads the representations of user-clicked
articles and aims to learn the user's different interest views to match the
candidate article. Our experimental results on the Alibaba Technology
Association (ATA) website show the advantage of SINGLE, achieving a 2.4%
improvement over previous baseline models in the online A/B test. Our further
analyses illustrate that SINGLE has the ability to build a more tailored
recommendation system by mimicking different article viewing behaviors of users
and recommending more appropriate and diverse articles to match user interests.
|
Most population models assume that individuals within a given population are
identical, that is, the fundamental role of variation is ignored. Inhomogeneous
models of populations and communities allow for birth and death rates to vary
among individuals; recently, theorems of existence and asymptotic of solutions
of such models were investigated. Here we develop another approach to modeling
heterogeneous populations by reducing the model to the Cauchy problem for a
special system of ODEs. As a result, the total population size and current
distribution of the vector-parameter can be found in explicit analytical form
or computed effectively. The developed approach is extended to the models of
inhomogeneous communities.
|
We present an alternative method to X-ray surveys for hunting down the
high-redshift type-2 quasar population, using Spitzer and VLA data on the
Spitzer First Look Survey. By demanding objects to be bright at 24 microns but
faint at 3.6 microns, and combining this with a radio criterion, we find 21
type-2 radio-quiet quasar candidates at the epoch at which the quasar activity
peaked. Optical spectroscopy with the WHT confirmed 10 of these objects to be
type-2s with 1.4 < z < 4.2 while the rest are blank. There is no evidence for
contamination in our sample, and we postulate that our 11 blank-spectrum
candidates are obscured by kpc-scale dust as opposed to dust from a torus
around the accretion disk. By carefully modelling our selection criteria, we
conclude that, at high redshift, 50-80 % of the supermassive black hole growth
is obscured by dust.
|
Only a small number of high mass stars (> 30 Mo) have fundamental parameters
(i.e. masses and radii) measured with high enough accuracy from eclipsing
binaries to constrain formation and evolutionary models of massive stars. This
work aims to increase this limited sample, by studying the 4 massive eclipsing
binary candidates discovered by Bonanos in the young massive cluster Westerlund
1. We present new follow-up echelle spectroscopy of these binaries and models
of their light and radial velocity curves. We obtain fundamental parameters
(i.e. masses, radii) for the 8 component stars, finding masses that span a
range of 10-40 Mo, and contributing accurate fundamental parameters for 1
additional very massive star, the 33 Mo component of W13. WR77o is found to
have a ~40 Mo companion, which provides a second dynamical constraint on the
mass of the progenitor of the magnetar known in the cluster. We also use W13 to
estimate the first, direct, eclipsing binary distance to Westerlund 1 and
therefore the magnetar, and find it to be at 3.7 +/- 0.6 kpc. Our results
confirm previous evidence for a high mass for the progenitor of the magnetar.
In addition, the availability of eclipsing binaries with accurate parameters
opens the way for direct, independent, high precision eclipsing binary distance
measurements to Westerlund 1.
|
We have realized an acoustic analog to the Dynamical Casimir effect. The
density of a trapped Bose-Einstein condensate is modulated by changing the trap
stiffness. We observe the creation of correlated excitations with equal and
opposite momenta, and show that for a well defined modulation frequency, the
frequency of the excitations is half that of the trap modulation frequency.
|
The strangeness of the nucleon, <N|ss|N> - <0|ss|0>, is a quantity of
interest for interpreting the results of dark matter detection experiments as
well as for exploring the structure of the nucleon itself. We present a
calculation of this quantity in 2+1 flavor lattice QCD using a range of lattice
spacings and quark masses. The method is based on calculating quark-line
disconnected contributions on the MILC lattice configurations, which include
the effects of dynamical strange quarks. After continuum and chiral
extrapolations, the value is <N|ss|N> - <0|ss|0> = 0.69 +/- 0.07(stat) +/-
0.09(sys) in the msbar(2GeV) regularization.
|
We consider a sample of Galactic classical Cepheids with highly accurate
estimates of their distances taken from Skowron et al., where they were
determined based on the period-luminosity relation. We have refined the
geometric characteristics of two spiral arm segments-the Carina-Sagittarius and
Outer ones. For this purpose, we have selected 269 Cepheids belonging to the
Carina-Sagittarius arm with ages in the range 80-120 Myr. From them we have
estimated the pitch angle of the spiral pattern $i=-11.9\pm0.2^\circ$ and the
position of this arm $a_0=7.32\pm0.05$ kpc for the adopted $R_0=8.1\pm0.1$ kpc.
In the Outer arm we have selected 343 Cepheids with ages in the range 120-300
Myr. From them we have found $i=-11.5\pm0.5^\circ$ and $a_0=12.89\pm0.06$ kpc.
Adhering to the model of a grand-design spiral pattern in the Galaxy with one
pitch angle for all arms, we can conclude that this angle is close to
$-12^\circ$.
|
The degree to which a nucleus can act as a source for coherent pion pairs is
investigated for intermediate-energy heavy-ion collisions. Creation through
both isovector and isoscalar channels is considered. Two experimental signals
are proposed for evidence of two-pion coherent production, two-pion enhancement
and the focusing of outgoing pions along the beam axis.
|
We give an explicit characterization of all minimal value set polynomials in
$\F_q[x]$ whose set of values is a subfield $\F_{q'}$ of $\F_{q}$. We show that
the set of such polynomials, together with the constants of $\F_{q'}$, is an
$\F_{q'}$-vector space of dimension $2^{[\F_{q}:\F_{q'}]}$. Our approach not
only provides the exact number of such polynomials, but also yields a
construction of new examples of minimal value set polynomials for some other
fixed value sets. In the latter case, we also derive a non-trivial lower bound
for the number of such polynomials.
|
We analyze statistical features of the ``optimization landscape'' in a random
version of one of the simplest constrained optimization problems of the
least-square type: finding the best approximation for the solution of an
overcomplete system of $M>N$ linear equations $({\bf a}_k,{\bf x})=b_k, \,
k=1,\ldots,M$ on the $N-$sphere ${\bf x}^2=N$. We treat both the $N-$component
vectors ${\bf a}_k$ and parameters $b_k$ as independent mean zero real Gaussian
random variables. First, we derive the exact expressions for the mean number of
stationary points of the least-square loss function in the framework of the
Kac-Rice approach combined with the Random Matrix Theory for Wishart Ensemble,
and then perform its asymptotic analysis as $N\to \infty$ at a fixed
$\alpha=M/N>1$ in various regimes. In particular, this analysis allows to
extract the Large Deviation Function for the density of the smallest Lagrange
multiplier $\lambda_{min}$ associated with the problem, and in this way to find
its most probable value. This can be further used to predict the asymptotic
minimal value ${\cal E}_{min}$ of the loss function as $N\to \infty$. Finally,
we develop an alternative approach based on the replica trick to conjecture the
form of the Large Deviation function for the density of ${\cal E}_{min}$ at
$N\gg 1$. As a by-product, we find the value of the {\it compatibility
threshold} $\alpha_c$ which is the minimal value of the asymptotic ratio $M/N$
such that the random linear system on the $N-$sphere is typically compatible.
|
A set of coupled non-linear integral equations is derived for a class of
models connected with the quantum group $U_q(\hat g)$ ($g$ simply laced Lie
algebra), which are solvable using the Bethe Ansatz; these equations describe
arbitrary excited states of a system with finite spatial length $L$. They
generalize the Destri-De Vega equation for the Sine-Gordon/massive Thirring
model to affine Toda field theory with imaginary coupling constant. As an
application, the central charge and all the conformal weights of the UV
conformal field theory are extracted in a straightforward manner. The quantum
group truncation for $q$ at a root of unity is discussed in detail; in the UV
limit we recover through this procedure the RCFTs with extended $W(g)$
conformal symmetry.
|
The dynamics of a quantum mechanical particle in a time-independent potential
are found to contain many interesting phenomena. These are direct consequences
of the (typical) existence of more than one time scale governing the problem.
This gives rise to full revivals of initial wavepackets, fractional revivals
(multiple wavepackets appearing at fractions of the revival time) and the
striking quantum carpets. A variety of analytic techniques are used to consider
the interference that gives rise to these phenomena while skirting calculations
involving cross-terms. Novel results include a new theorem on the weighting
coefficients $a_m$ that govern fractional revivals, a demonstration that
$\Psi_{cl}$, the function that governs the distribution and features of these
fractional revivals, really does behave classically, a treatment of the
wavepacket dephasing in the infinite square well by means of the Poisson
summation formula, and a correct analysis of the spatial distribution of
intermode traces. Also, this work presents a coherent treatment of these
phenomena, which before now did not exist.
|
We investigate norms of spectral projectors on thin spherical shells for the
Laplacian on tori. This is closely related to the boundedness of resolvents of
the Laplacian, and to the boundedness of $L^p$ norms of eigenfunctions of the
Laplacian. We formulate a conjecture, and partially prove it.
|
We calculate perturbatively the normalized spatial skewness, $S_3$, and full
three-point correlation function (3PCF), $\zeta$, induced by gravitational
instability of Gaussian primordial fluctuations for a biased tracer-mass
distribution in flat and open cold-dark-matter (CDM) models. We take into
account the dependence on the shape and evolution of the CDM power spectrum,
and allow the bias to be nonlinear and/or evolving in time, using an extension
of Fry's (1996) bias-evolution model. We derive a scale-dependent,
leading-order correction to the standard perturbative expression for $S_3$ in
the case of nonlinear biasing, as defined for the unsmoothed galaxy and
dark-matter fields, and find that this correction becomes large when probing
positive effective power-spectrum indices. This term implies that the inferred
nonlinear-bias parameter, as usually defined in terms of the smoothed density
fields, might depend on the chosen smoothing scale. In general, we find that
the dependence of $S_3$ on the biasing scheme can substantially outweigh that
on the adopted cosmology. We demonstrate that the normalized 3PCF, $Q$, is an
ill-behaved quantity, and instead investigate $Q_V$, the variance-normalized
3PCF. The configuration dependence of $Q_V$ shows similarly strong
sensitivities to the bias scheme as $S_3$, but also exhibits significant
dependence on the form of the CDM power spectrum. Though the degeneracy of
$S_3$ with respect to the cosmological parameters and constant linear- and
nonlinear-bias parameters can be broken by the full configuration dependence of
$Q_V$, neither statistic can distinguish well between evolving and non-evolving
bias scenarios. We show that this can be resolved, in principle, by considering
the redshift dependence of $\zeta$.
|
An analytical solution for light propagation in the post-post-Newtonian
approximation is given for the Schwarzschild metric in harmonic gauge augmented
by PPN and post-linear parameters $\beta$, $\gamma$ and $\epsilon$. The
solutions of both Cauchy and boundary problem are given. The Cauchy problem is
posed using the initial position of the photon $\ve{x}_0 = \ve{x}(t_0)$ and its
propagation direction \ve{\sigma} at minus infinity: $\ve{\sigma} = {1\over c}
\lim\limits_{t \to -\infty}\dot{\ve{x}}(t)$. An analytical expression for the
total light deflection is given. The solutions for $t - t_0$ and $\ve{\sigma}$
are given in terms of boundary conditions $\ve{x}_0 = \ve{x} (t_0)$ and $\ve{x}
= \ve{x}(t)$.
|
Maxwell's first derivation of the equilibrium distribution function for a
dilute gas is generalized in the spirit of the nonextensive q-statistics
proposed by Tsallis. As an application, the q-Doppler broadening of spectral
lines due to the random thermal motion of the radiating atoms is derived.
|
High resolution observations of CO and 13CO 1--0 in the Medusa (NGC4194)
minor merger show the CO/13CO 1--0 intensity ratio (R) increasing from normal
values (5-10) in the outer parts of the galaxy to high (>20) values in the
central, extended starburst region. Ratios >20 are otherwise typical of more
luminous mergers. The Medusa L_FIR/L_CO ratio rivals that of ultraluminous
galaxies (ULIRGs), despite the comparatively modest luminosity, indicating an
exceptionally high star formation efficiency (SFE). We present models of the
high pressure ISM in a ULIRG and the relatively low pressure ISM of the Medusa.
We discuss how these models may explain large R in both types of distributions.
Since the HCN emission is faint towards the Medusa, we suggest that the SFE is
not primarily controlled by the mass fraction of dense (n > 10^4 cm-3) gas, but
is probably strongly dependent on dynamics. The bright HCN emission towards
ULIRGs is not necessarily evidence that the IR emission there is always powered
by starbursts.
|
We study stable W-length in groups, especially for W equal to the n-fold
commutator gamma_n:=[x_1,[x_2, . . . [x_{n-1},x_n]] . . . ]. We prove that in
any perfect group, for any n at least 2 and any element g, the stable
commutator length of g is at least as big as 2^{2-n} times the stable
gamma_n-length of g. We also establish analogues of Bavard duality for words
gamma_n and for beta_2:=[[x,y],[z,w]]. Our proofs make use of geometric
properties of the asymptotic cones of verbal subgroups with respect to
bi-invariant metrics. In particular, we show that for suitable W, these
asymptotic cones contain certain subgroups that are normed vector spaces.
|
Hubble tension is one of the most important problems in cosmology. Although
the local measurements on the Hubble constant with Type Ia supernovae (SNe Ia)
are independent of cosmological models, they suffer the problem of zero-point
calibration of the luminosity distance. The observations of gravitational waves
(GWs) with space-based GW detectors can measure the luminosity distance of the
GW source with high precision. By assuming that massive binary black hole
mergers and SNe Ia occur in the same host galaxy, we study the possibility of
re-calibrating the luminosity distances of SNe Ia by GWs. Then we use
low-redshift re-calibrated SNe Ia to determine the local Hubble constant. We
find that we need at least 7 SNe Ia with their luminosity distances
re-calibrated by GWs to reach a 2\% precision of the local Hubble constant. The
value of the local Hubble constant is free from the problems of zero-point
calibration and model dependence, so the result can shed light on the Hubble
tension.
|
We study the bond percolation game and the site percolation game on the
rooted Galton-Watson tree $T_{\chi}$ with offspring distribution $\chi$. We
obtain the probabilities of win, loss and draw for each player in terms of the
fixed points of functions that involve the probability generating function $G$
of $\chi$, and the parameters $p$ and $q$. Here, $p$ is the probability with
which each edge (respectively vertex) of $T_{\chi}$ is labeled a trap in the
bond (respectively site) percolation game, and $q$ is the probability with
which each edge (respectively vertex) of $T_{\chi}$ is labeled a target in the
bond (respectively site) percolation game. We obtain a necessary and sufficient
condition for the probability of draw to be $0$ in each game, and we examine
how this condition simplifies to yield very precise phase transition results
when $\chi$ is Binomial$(d,\pi)$, Poisson$(\lambda)$, or Negative
Binomial$(r,\pi)$, or when $\chi$ is supported on $\{0,d\}$ for some $d \in
\mathbb{N}$, $d \geqslant 2$. It is fascinating to note that, while all other
specific classes of offspring distributions we consider in this paper exhibit
phase transition phenomena as the parameter-pair $(p,q)$ varies, the
probability that the bond percolation game results in a draw remains $0$ for
all values of $(p,q)$ when $\chi$ is Geometric$(\pi)$, for all $0 < \pi
\leqslant 1$. By establishing a connection between these games and certain
finite state probabilistic tree automata on rooted $d$-regular trees, we obtain
a precise description of the regime (in terms of $p$, $q$ and $d$) in which
these automata exhibit ergodicity or weak spatial mixing.
|
We propose and study a strategic model of hiding in a network, where the
network designer chooses the links and his position in the network facing the
seeker who inspects and disrupts the network. We characterize optimal networks
for the hider, as well as equilibrium hiding and seeking strategies on these
networks. We show that optimal networks are either equivalent to cycles or
variants of a core-periphery networks where every node in the periphery is
connected to a single node in the core.
|
Bremsstrahlung spectra will be strongly distorted due to small lateral beam
sizes at future colliders. That in turn will have large consequences for the
electron and positron beam lifetimes as well as for the luminosity measurements
in the case of electron-hadron colliders. We discuss in detail such
consequences for the Future Circular Collider and Large Hadron electron
Collider cases.
|
In this work we present the mathematical models for single-phase flow in
fractured porous media. An overview of the most common approaches is
considered, which includes continuous fracture models and discrete fracture
models. For the latter, we discuss strategies that are developed in literature
for its numerical solution mainly related to the geometrical relation between
the fractures and porous media grids.
|
We investigate the asymptotic symmetry group of the free SU(N)-Yang-Mills
theory using the Hamiltonian formalism. We closely follow the strategy of
Henneaux and Troessaert who successfully applied the Hamiltonian formalism to
the case of gravity and electrodynamics, thereby deriving the respective
asymptotic symmetry groups of these theories from clear-cut first principles.
These principles include the minimal assumptions that are necessary to ensure
the existence of Hamiltonian structures (phase space, symplectic form,
differentiable Hamiltonian) and, in case of Poincar\'e invariant theories, a
canonical action of the Poincar\'e group. In the first part of the paper we
show how these requirements can be met in the non-abelian SU(N)-Yang-Mills case
by imposing suitable fall-off and parity conditions on the fields. We observe
that these conditions admit neither non-trivial asymptotic symmetries nor
non-zero global charges. In the second part of the paper we discuss possible
gradual relaxations of these conditions by following the same strategy that
Henneaux and Troessaert had employed to remedy a similar situation in the
electromagnetic case. Contrary to our expectation and the findings of Henneaux
and Troessaert for the abelian case, there seems to be no relaxation that meets
the requirements of a Hamiltonian formalism and allows for non-trivial
asymptotic symmetries and charges. Non-trivial asymptotic symmetries and
charges are only possible if either the Poincar\'e group fails to act
canonically or if the formal expression for the symplectic form diverges, i.e.
the form does not exist. This seems to hint at a kind of colour-confinement
built into the classical Hamiltonian formulation of non-abelian gauge theories.
|
While in linear optics the subject of structured light has been a fruitful
field of both theoretical and applied research, its development in the arena of
nonlinear optics has been underexplored. In this paper, we construct
Frozen-Wave-type structured optical beams in Kerr nonlinear media, emphasizing
the self-defocusing case, and use them to guide and control Gaussian optical
beams. The results presented in this study support the expectation that
structured light in nonlinear media can open new venues of theoretical research
and applications, particularly in the realms of light controlling light and for
all-optical photonics.
|
Subsets and Splits