text
stringlengths 6
128k
|
|---|
Generative Adversarial Networks have become a core technique in Machine
Learning to generate unknown distributions from data samples. They have been
used in a wide range of context without paying much attention to the possible
theoretical limitations of those models. Indeed, because of the universal
approximation properties of Neural Networks, it is a general assumption that
GANs can generate any probability distribution. Recently, people began to
question this assumption and this article is in line with this thinking. We
provide a new result based on Extreme Value Theory showing that GANs can't
generate heavy tailed distributions. The full proof of this result is given.
|
The right to access is a great tool provided by the GDPR to empower data
subjects with their data. However, it needs to be implemented properly
otherwise it could turn subject access requests against the subjects privacy.
Indeed, recent works have shown that it is possible to abuse the right to
access using impersonation attacks. We propose to extend those impersonation
attacks by considering that the adversary has an access to governmental
resources. In this case, the adversary can forge official documents or exploit
copy of them. Our attack affects more people than one may expect. To defeat the
attacks from this kind of adversary, several solutions are available like
multi-factors or proof of aliveness. Our attacks highlight the need for strong
procedures to authenticate subject access requests.
|
5G millimeter wave (mmWave) signals have inherent geometric connections to
the propagation channel and the propagation environment. Thus, they can be used
to jointly localize the receiver and map the propagation environment, which is
termed as simultaneous localization and mapping (SLAM). One of the most
important tasks in the 5G SLAM is to deal with the nonlinearity of the
measurement model. To solve this problem, existing 5G SLAM approaches rely on
sigma-point or extended Kalman filters, linearizing the measurement function
with respect to the prior probability density function (PDF). In this paper, we
study the linearization of the measurement function with respect to the
posterior PDF, and implement the iterated posterior linearization filter into
the Poisson multi-Bernoulli SLAM filter. Simulation results demonstrate the
accuracy and precision improvements of the resulting SLAM filter.
|
The goal of text generation is to make machines express in human language. It
is one of the most important yet challenging tasks in natural language
processing (NLP). Since 2014, various neural encoder-decoder models pioneered
by Seq2Seq have been proposed to achieve the goal by learning to map input text
to output text. However, the input text alone often provides limited knowledge
to generate the desired output, so the performance of text generation is still
far from satisfaction in many real-world scenarios. To address this issue,
researchers have considered incorporating various forms of knowledge beyond the
input text into the generation models. This research direction is known as
knowledge-enhanced text generation. In this survey, we present a comprehensive
review of the research on knowledge enhanced text generation over the past five
years. The main content includes two parts: (i) general methods and
architectures for integrating knowledge into text generation; (ii) specific
techniques and applications according to different forms of knowledge data.
This survey can have broad audiences, researchers and practitioners, in
academia and industry.
|
Most visual recognition methods implicitly assume the data distribution
remains unchanged from training to testing. However, in practice domain shift
often exists, where real-world factors such as lighting and sensor type change
between train and test, and classifiers do not generalise from source to target
domains. It is impractical to train separate models for all possible situations
because collecting and labelling the data is expensive. Domain adaptation
algorithms aim to ameliorate domain shift, allowing a model trained on a source
to perform well on a different target domain. However, even for the setting of
unsupervised domain adaptation, where the target domain is unlabelled,
collecting data for every possible target domain is still costly. In this
paper, we propose a new domain adaptation method that has no need to access
either data or labels of the target domain when it can be described by a
parametrised vector and there exits several related source domains within the
same parametric space. It greatly reduces the burden of data collection and
annotation, and our experiments show some promising results.
|
In this current technological world, the application of machine learning is
becoming ubiquitous. Incorporating machine learning algorithms on extremely
low-power and inexpensive embedded devices at the edge level is now possible
due to the combination of the Internet of Things (IoT) and edge computing. To
estimate an outcome, traditional machine learning demands vast amounts of
resources. The TinyML concept for embedded machine learning attempts to push
such diversity from usual high-end approaches to low-end applications. TinyML
is a rapidly expanding interdisciplinary topic at the convergence of machine
learning, software, and hardware centered on deploying deep neural network
models on embedded (micro-controller-driven) systems. TinyML will pave the way
for novel edge-level services and applications that survive on distributed edge
inferring and independent decision-making rather than server computation. In
this paper, we explore TinyML's methodology, how TinyML can benefit a few
specific industrial fields, its obstacles, and its future scope.
|
The non-equilibrium structural and dynamical properties of a flexible polymer
tethered to a reflecting wall and subject to oscillatory linear flow are
studied by numerical simulations. Polymer is confined in two dimensions and is
modeled as a bead-spring chain immersed in a fluid described by the Brownian
multiparticle collision dynamics. At high strain, the polymer is stretched
along the flow direction following the applied flow, then recoils at flow
inversion before flipping and elongate again. When strain is reduced, it may
happen that the chain recoils without flipping when the applied shear changes
sign. Conformations are analyzed and compared to stiff polymers revealing more
compact patterns at low strains and less stretched configurations at high
strain. The dynamics is investigated by looking at the center-of-mass motion
which shows a frequency doubling along the direction normal to the external
flow. The center-of-mass correlation function is characterized by smaller
amplitudes when reducing bending rigidity.
|
Simulation is pivotal in evaluating the performance of autonomous driving
systems due to the advantages of high efficiency and low cost compared to
on-road testing. Bridging the gap between simulation and the real world
requires realistic agent behaviors. However, the existing works have the
following shortcomings in achieving this goal: (1) log replay offers realistic
scenarios but often leads to collisions due to the absence of dynamic
interactions, and (2) both heuristic-based and data-based solutions, which are
parameterized and trained on real-world datasets, encourage interactions but
often deviate from real-world data over long horizons. In this work, we propose
LitSim, a long-term interactive simulation approach that maximizes realism by
minimizing the interventions in the log. Specifically, our approach primarily
uses log replay to ensure realism and intervenes only when necessary to prevent
potential conflicts. We then encourage interactions among the agents and
resolve the conflicts, thereby reducing the risk of unrealistic behaviors. We
train and validate our model on the real-world dataset NGSIM, and the
experimental results demonstrate that LitSim outperforms the currently popular
approaches in terms of realism and reactivity.
|
Marine debris is an important issue for environmental protection, but current
methods for locating marine debris are yet limited. In order to achieve higher
efficiency and wider applicability in the localization of Marine debris, this
study tries to combine the instance segmentation of YOLOv7 with different
attention mechanisms and explores the best model. By utilizing a labelled
dataset consisting of satellite images containing ocean debris, we examined
three attentional models including lightweight coordinate attention, CBAM
(combining spatial and channel focus), and bottleneck transformer (based on
self-attention). Box detection assessment revealed that CBAM achieved the best
outcome (F1 score of 77%) compared to coordinate attention (F1 score of 71%)
and YOLOv7/bottleneck transformer (both F1 scores around 66%). Mask evaluation
showed CBAM again leading with an F1 score of 73%, whereas coordinate attention
and YOLOv7 had comparable performances (around F1 score of 68%/69%) and
bottleneck transformer lagged behind at F1 score of 56%. These findings suggest
that CBAM offers optimal suitability for detecting marine debris. However, it
should be noted that the bottleneck transformer detected some areas missed by
manual annotation and displayed better mask precision for larger debris pieces,
signifying potentially superior practical performance.
|
This technique report introduces TexSmart, a text understanding system that
supports fine-grained named entity recognition (NER) and enhanced semantic
analysis functionalities. Compared to most previous publicly available text
understanding systems and tools, TexSmart holds some unique features. First,
the NER function of TexSmart supports over 1,000 entity types, while most other
public tools typically support several to (at most) dozens of entity types.
Second, TexSmart introduces new semantic analysis functions like semantic
expansion and deep semantic representation, that are absent in most previous
systems. Third, a spectrum of algorithms (from very fast algorithms to those
that are relatively slow but more accurate) are implemented for one function in
TexSmart, to fulfill the requirements of different academic and industrial
applications. The adoption of unsupervised or weakly-supervised algorithms is
especially emphasized, with the goal of easily updating our models to include
fresh data with less human annotation efforts.
The main contents of this report include major functions of TexSmart,
algorithms for achieving these functions, how to use the TexSmart toolkit and
Web APIs, and evaluation results of some key algorithms.
|
Large-angle Coulomb collisions lead to an avalanching generation of runaway
electrons in a plasma. We present the first fully conservative large-angle
collision operator, derived from the relativistic Boltzmann operator. The
relation to previous models for large-angle collisions is investigated, and
their validity assessed. We present a form of the generalized collision
operator which is suitable for implementation in a numerical kinetic-equation
solver, and demonstrate the effect on the runaway-electron growth rate. Finally
we consider the reverse avalanche effect, where runaways are slowed down by
large-angle collisions, and show that the choice of operator is important if
the electric field is close to the avalanche threshold.
|
We study the production, in Deep Inelastic Scattering at high energy, of a
quark-gluon dijet induced by $t$-channel quark exchange with the target, which
goes beyond the eikonal approximation. Throughout this study we follow the
Color Glass Condensate approach, keep full dependence on the quark mass and
consider the target to be unpolarized. We focus on the correlation limit in
which the produced jets fly almost back-to-back and find a factorized
expression for the cross section, for both longitudinal and transverse photons,
involving the unpolarized quark transverse momentum dependent distribution.
Quark-gluon dijets can be distinguished from other types of dijets at least in
the heavy quark case, thanks to heavy flavor tagging. In that case, the
dominant background is expected to come from the eikonal production of a
quark-antiquark-gluon system. We propose experimental cuts to suppress that
background contribution, making the process of quark-gluon dijet production in
Deep Inelastic Scattering a new method to probe the quark transverse momentum
dependent distribution at the Electron Ion Collider.
|
In this letter, we propose two power allocation schemes based on the
statistical channel state information (CSI) and instantaneous s->r CSI at
transmitters respectively for a 2-N-2 cooperative multicast system with
non-regenerative network coding.Then the isolated precoder and the distributed
precoder are respectively applied to the schemes to further improve the system
performance by achieving the full diversity gain. Finally, we demonstrate that
joint instantaneous s->r CSI based power allocation and distributed precoder
design achieve the best performance.
|
We consider a branching random walk (BRW) taking its values in the
$\mathtt{b}$-ary rooted tree $\mathbb W_{ \mathtt{b}}$ (i.e. the set of finite
words written in the alphabet $\{ 1, \ldots, \mathtt{b} \}$, with $\mathtt{b}\!
\geq \! 2$). The BRW is indexed by a critical Galton--Watson tree conditioned
to have $n$ vertices; its offspring distribution is aperiodic and is in the
domain of attraction of a $\gamma$-stable law, $\gamma \in (1, 2]$. The jumps
of the BRW are those of a nearest-neighbour null-recurrent random walk on
$\mathbb W_{ \mathtt{b}}$ (reflection at the root of $\mathbb W_{ \mathtt{b}}$
and otherwise: probability $1/2$ to move closer to the root of $\mathbb W_{
\mathtt{b}}$ and probability $1/(2\mathtt{b})$ to move away from it to one of
the $\mathtt{b}$ sites above). We denote by $\mathcal R_{\mathtt{b}} (n)$ the
range of the BRW in $\mathbb W_{ \mathtt{b}}$ which is the set of all sites in
$\mathbb W_{\mathtt{b}}$ visited by the BRW. We first prove a law of large
numbers for $\# \mathcal R_{\mathtt{b}} (n)$ and we also prove that if we equip
$\mathcal R_{\mathtt{b}} (n)$ (which is a random subtree of $\mathbb
W_{\mathtt{b}}$) with its graph-distance $d_{\mathtt{gr}}$, then there exists a
scaling sequence $(a_n)_{n\in \mathbb N}$ satisfying $a_n \! \rightarrow \!
\infty$ such that the metric space $(\mathcal R_{\mathtt{b}} (n),
a_n^{-1}d_{\mathtt{gr}})$, equipped with its normalised empirical measure,
converges to the reflected Brownian cactus with $\gamma$-stable branching
mechanism: namely, a random compact real tree that is a variant of the Brownian
cactus introduced by N. Curien, J-F. Le Gall and G. Miermont.
|
We find that the nonperturbative physics of the standard-model Higgs
Lagrangian provides a dark matter candidate, "dormant skyrmion in the standard
model", the same type of the skyrmion, a soliton, as in the hadron physics. It
is stabilized by another nonperturbative object in the standard model, the
dynamical gauge boson of the hidden local symmetry, which is also an analogue
of the rho meson.
|
Spinning black holes create electromagnetic storms when immersed in ambient
magnetic fields, illuminating the otherwise epically dark terrain. In an
electromagnetic extension of the Penrose process, tremendous energy can be
extracted, boosting the energy of radiating particles far more efficiently than
the mechanical Penrose process. We locate the regions from which energy can be
mined and demonstrate explicitly that they are no longer restricted to the
ergosphere. We also show that there can be toroidal regions that trap negative
energy particles in orbit around the black hole. We find that the effective
charge coupling between the black hole and the super-radiant particles
decreases as energy is extracted, much like the spin of a black hole decreases
in the mechanical analogue. While the effective coupling decreases, the actual
charge of the black hole increases in magnitude reaching the
energetically-favored Wald value, at which point energy extraction is impeded.
We demonstrate the array of orbits for products from the electromagnetic
Penrose process.
|
We investigate the symmetry property and the stability of dibaryons
containing two strange quarks and one heavy flavor with $I=\frac{1}{2}$. We
construct the wave function of the dibaryon in two ways. First, we directly
construct the color and spin state of the dibaryon starting from the four
possible SU(3) flavor state. Second, we consider the states composed of five
light quarks, and then construct the wave function of the dibaryon by adding
one heavy quark. The stability of the dibaryon against the strong decay into
two baryons is discussed by using variational method in a constituent quark
model with confining and hyperfine potential. We find that for all
configurations with S=0,1,2, the ground states of the dibaryons are the sum of
two baryons, and there are no compact bound state that is stable against the
strong decay.
|
The use of electric fields for signalling and control in liquids is
widespread, spanning bioelectric activity in cells to electrical manipulation
of microstructures in lab-on-a-chip devices. However, an appropriate tool to
resolve the spatio-temporal distribution of electric fields over a large
dynamic range has yet to be developed. Here we present a label-free method to
image local electric fields in real time and under ambient conditions. Our
technique combines the unique gate-variable optical transitions of graphene
with a critically coupled planar waveguide platform that enables highly
sensitive detection of local electric fields with a voltage sensitivity of a
few microvolts, a spatial resolution of tens of micrometres and a frequency
response over tens of kilohertz. Our imaging platform enables parallel
detection of electric fields over a large field of view and can be tailored to
broad applications spanning lab-on-a-chip device engineering to analysis of
bioelectric phenomena.
|
Segmentation of organs of interest in 3D medical images is necessary for
accurate diagnosis and longitudinal studies. Though recent advances using deep
learning have shown success for many segmentation tasks, large datasets are
required for high performance and the annotation process is both time consuming
and labor intensive. In this paper, we propose a 3D few shot segmentation
framework for accurate organ segmentation using limited training samples of the
target organ annotation. To achieve this, a U-Net like network is designed to
predict segmentation by learning the relationship between 2D slices of support
data and a query image, including a bidirectional gated recurrent unit (GRU)
that learns consistency of encoded features between adjacent slices. Also, we
introduce a transfer learning method to adapt the characteristics of the target
image and organ by updating the model before testing with arbitrary support and
query data sampled from the support data. We evaluate our proposed model using
three 3D CT datasets with annotations of different organs. Our model yielded
significantly improved performance over state-of-the-art few shot segmentation
models and was comparable to a fully supervised model trained with more target
training data.
|
We discuss CP violation in supersymmetric theories and show that CP phenomena
can act as a probe of their origins, i.e., compactification and spontaneous
supersymmetry breaking. CP violation as a probe of the flavor structure of
supersymmetric theories is also discussed. A brief overview is given of several
low energy phenomena where CP phases can produce new effects. These include
important CP effects in processes involving sparticles and CP mixing effects in
the neutral Higgs boson system. We also discuss the possibility of violations
of scaling in the electric dipole moments (EDMs) due to the presence of
nonuniversalities and show that with inclusion of nonuniversalities the muon
EDM could be up to 1-2 orders of magnitude larger than implied by scaling and
within reach of the next generation of experiments. Thus the EDMs are an
important probe of the flavor structure of supersymmetric theories.
|
The 2.5 sigma discrepancy between theory and experiment observed in the
difference A_CP(B^- --> pi^0 K^-)-A_CP(Bbar^0 --> pi^+ K^-) can be explained by
a new electroweak penguin amplitude. Motivated by this result, we analyse the
purely isospin-violating decays B_s --> phi rho^0 and B_s --> phi pi^0, which
are dominated by electroweak penguins, and show that in presence of a new
electroweak penguin amplitude their branching ratio can be enhanced by up to an
order of magnitude, without violating any constraints from other hadronic B
decays. This makes them very interesting modes for LHCb and future B factories.
We perform both a model-independent analysis and a study within realistic New
Physics models such as a modified-Z^0-penguin scenario, a model with an
additional Z' boson and the MSSM. In the latter cases the new amplitude can be
correlated with other flavour phenomena, such as semileptonic B decays and
B_s-Bbar_s mixing, which impose stringent constraints on the enhancement of the
two B_s decays. In particular we find that, contrary to claims in the
literature, electroweak penguins in the MSSM can reduce the discrepancy in the
B --> pi K modes only marginally. As byproducts we update the SM predictions to
Br(Bbar_s --> phi pi^0)=1.6^{+1.1}_{-0.3}*10^{-7} and Br(Bbar_s --> phi
rho^0)=4.4^{+2.7}_{-0.7}*10^{-7} and perform a state-of-the-art analysis of B
--> pi K amplitudes in QCD factorisation.
|
We study the relationship between functional inequalities for a Markov kernel
on a metric space $X$ and inequalities of transportation distances on the space
of probability measures $\mathcal{P}(X)$. Extending results of Luise and
Savar\'e on Hellinger--Kantorovich contraction inequalities for the particular
case of the heat semigroup on an $RCD(K,\infty)$ metric space, we show that
more generally, such contraction inequalities are equivalent to reverse
Poincar\'e inequalities. We also adapt the "dynamic dual" formulation of the
Hellinger--Kantorovich distance to define a new family of divergences on
$\mathcal{P}(X)$ which generalize the R\'enyi divergence, and we show that
contraction inequalities for these divergences are equivalent to the reverse
logarithmic Sobolev and Wang Harnack inequalities. We discuss applications
including results on the convergence of Markov processes to equilibrium, and on
quasi-invariance of heat kernel measures in finite and infinite-dimensional
groups.
|
Large Language Models (LLMs) still face challenges in tasks requiring
understanding implicit instructions and applying common-sense knowledge. In
such scenarios, LLMs may require multiple attempts to achieve human-level
performance, potentially leading to inaccurate responses or inferences in
practical environments, affecting their long-term consistency and behavior.
This paper introduces the Internal Time-Consciousness Machine (ITCM), a
computational consciousness structure to simulate the process of human
consciousness. We further propose the ITCM-based Agent (ITCMA), which supports
action generation and reasoning in open-world settings, and can independently
complete tasks. ITCMA enhances LLMs' ability to understand implicit
instructions and apply common-sense knowledge by considering agents'
interaction and reasoning with the environment. Evaluations in the Alfworld
environment show that trained ITCMA outperforms the state-of-the-art (SOTA) by
9% on the seen set. Even untrained ITCMA achieves a 96% task completion rate on
the seen set, 5% higher than SOTA, indicating its superiority over traditional
intelligent agents in utility and generalization. In real-world tasks with
quadruped robots, the untrained ITCMA achieves an 85% task completion rate,
which is close to its performance in the unseen set, demonstrating its
comparable utility and universality in real-world settings.
|
This paper presents design of a Maximum Power Point Tracking (MPPT) circuit
and its functionality for tuning the maximum power transfer from an energy
harvester (EH) unit. Simple and practical Perturb and Observe algorithm is
investigated and implemented. We describe the circuit functionality and the
improvements that have been introduced to the original algorithm. The proposed
MPPT design is divided into three main blocks. The output signal is being
generated by the PWM or PFM block. The tracking speed has been enhanced by
implementing a variable step size in the Tracking Block. Finally, the overall
power consumption of the MPPT circuit itself is controlled by the Power
Management Block, which manages delivering the clock signal to the rest of the
circuit. The RTL code of the proposed MPPT has been described in Verilog, then
has been synthesized and placed-and-routed in a general purpose 130nm CMOS
technology.
|
A thermodynamically consistent model for soft deformable viscoelastic magnets
is formulated in actual space (Eulerian) coordinates. The possibility of a
ferro-paramagnetic-type (or ferri-antiferromagnetic) transition exploiting
Landau phase transition theory as well as mechanical melting or solidification
is considered, being motivated and applicable to paleomagnetism (involving both
thermo- and isothermal and viscous remanent magnetization) in rocks in Earth's
crust and to rock-magma transition. The temperature-dependent Jeffreys rheology
in the deviatoric part combined with the Kelvin-Voigt rheology in the spherical
(volumetric) part is used. The energy balance and the entropy imbalance behind
the model are demonstrated, and its analysis is performed by time
discretization, proving existence of weak solutions.
|
We describe the LoopInvGen tool for generating loop invariants that can
provably guarantee correctness of a program with respect to a given
specification. LoopInvGen is an efficient implementation of the inference
technique originally proposed in our earlier work on PIE
(https://doi.org/10.1145/2908080.2908099).
In contrast to existing techniques, LoopInvGen is not restricted to a fixed
set of features -- atomic predicates that are composed together to build
complex loop invariants. Instead, we start with no initial features, and use
program synthesis techniques to grow the set on demand. This not only enables a
less onerous and more expressive approach, but also appears to be significantly
faster than the existing tools over the SyGuS-COMP 2018 benchmarks from the INV
track.
|
The first on-sky results obtained by CANARY, the Multi-Object Adaptive Optics
(MOAO) demonstrator, are analysed. The data were recorded at the William
Herschel Telescope, at the end of September 2010. We describe the command and
calibrations algorithms used during the run and present the observing
conditions. The processed data are MOAO-loop engaged or disengaged slope
buffers, comprising the synchronised measurements of the four Natural Guide
Stars (NGS) wavefront sensors running in parallel, and near Infra-Red (IR)
images. We describe the method we use to establish the error budget of CANARY.
We are able to evaluate the to- mographic and the open loop errors, having
median values around 216 nm and 110 nm respectively. In addition, we identify
an unexpected residual quasi-static field aberration term of mean value 110 nm.
We present the detailed error budget analysed for three sets of data for three
different asterisms. We compare the experimental budgets with the numerically
simulated ones and demonstrate a good agreement. We find also a good agreement
between the computed error budget from the slope buffers and the measured
Strehl ratio on the IR images, ranging between 10% and 20% at 1 530 nm. These
results make us confident in our ability to establish the error budget of
future MOAO instruments.
|
Perspective taking, which allows people to imagine another's thinking and
goals, is known to be an effective method for promoting prosocial behaviors in
human-computer interactions. However, most of the previous studies have focused
on simulating human-human interactions in the real world by offering
participants experiences related to various moral tasks through the use of
human-like virtual agents. In this study, we investigated whether taking the
perspective of a different robot in a robot-altruistic task would influence the
social behaviors of participants in a dictator game. Our findings showed that
participants who watched the help-receiver view exhibited more altruistic
behaviors toward a robot than those who watched the help-provider view. We also
found that, after watching robots from two different viewpoints in the task,
participants did not change their behavior toward another participant.
|
We develop a technique for generating multi-photon nonclassical states via
interference between coherent and Fock states using quantum catalysis. By
modulating the coherent field strength, the number of catalyst photons and the
ratio of the beam splitter upon which they interfere, a wide range of
nonclassical phenomena can be created, including squeezing of up to 1.25 dB,
anti- and super-bunched photon statistics and states exhibiting over 90%
fidelity to displaced coherent superposition states. We perform quantum
catalysis experimentally, showing tunability into the nonclassical regime. Our
protocol is not limited by weak nonlinearities that underlie most known
strategies of preparing multi-photon nonclassical states. Successive iterations
of this protocol can lead to direct control over the weights of higher-order
terms in the Fock basis, paving the way towards conditional preparation of
"designer" multi-photon states for applications in quantum computation,
communication and metrology.
|
Photo-induced charge separation in transition metal dichalcogenide
heterobilayers is being explored for moir\'e excitons, spin-valley
polarization, and quantum phases of excitons/electrons. While different
momentum spaces may be critically involved in charge separation dynamics,
little is known directly from experiments. Here we determine momentum-resolved
electron dynamics in the WS2/MoS2 heterobilayer using time and angle resolved
photoemission spectroscopy (TR-ARPES). Upon photoexcitation in the K valleys,
we detect electrons in M/2, M, and Q valleys/points on time scales as short as
~70 fs, followed by dynamic equilibration in K and Q valleys in ~400 fs. The
interlayer charge transfer is accompanied by momentum-specific band
renormalization. These findings reveal the essential role of phonon scattering,
the coexistence of direct and indirect interlayer excitons, and constraints on
spin-valley polarization.
|
We here present, the ElasTool package, an automated toolkit for calculating
the second-order elastic constants (SOECs) of any two- (2D) and
three-dimensional (3D) crystal systems. It can utilize three kinds of
strain-matrix sets, the high-efficiency strain-matrix sets (OHESS), the
universal linear-independent coupling strains (ULICS) and the
all-single-element strain-matrix sets (ASESS) to calculate the SOECs
automatically. In an automatic manner, ElasTool can deal with both zero- and
high-temperature elastic constants. The theoretical background and
computational method of elastic constants, the package structure, the
installation and run, the input/output files, the controlling parameters, and
two representative examples of ElasTool are described detailedly. ElasTool is
useful for either the exploration of materials' elastic properties or
high-throughput new materials design. ElasTool is also available at our
website: www.matdesign.cn.
|
We study R\'enyi entropies for geometries with Lifshitz scaling and
hyperscaling violation. We calculate them for specific values of the Lifshitz
parameter, and analyze the dual spectrum of the ground state. In the large
$d-\theta$ limit they show that the ground state is unique in specific
parameter ranges. We also calculate the R\'enyi entropies perturbatively around
$n=1$, and derive constraints using the R\'enyi entropy inequalities, which
correspond to the thermodynamic stability of the black holes.
|
Algorithmic bias is a major issue in machine learning models in educational
contexts. However, it has not yet been studied thoroughly in Asian learning
contexts, and only limited work has considered algorithmic bias based on
regional (sub-national) background. As a step towards addressing this gap, this
paper examines the population of 5,986 students at a large university in the
Philippines, investigating algorithmic bias based on students' regional
background. The university used the Canvas learning management system (LMS) in
its online courses across a broad range of domains. Over the period of three
semesters, we collected 48.7 million log records of the students' activity in
Canvas. We used these logs to train binary classification models that predict
student grades from the LMS activity. The best-performing model reached AUC of
0.75 and weighted F1-score of 0.79. Subsequently, we examined the data for bias
based on students' region. Evaluation using three metrics: AUC, weighted
F1-score, and MADD showed consistent results across all demographic groups.
Thus, no unfairness was observed against a particular student group in the
grade predictions.
|
The t2g quasi-particle spectra of Na_0.3CoO_2 are calculated within the
dynamical mean field theory. It is shown that as a result of dynamical Coulomb
correlations charge is transfered from the nearly filled e_g' subbands to the
a_1g band, thereby reducing orbital polarization among Co t2g states. Dynamical
correlations therefore stabilize the small e_g' Fermi surface pockets, in
contrast to angle-resolved photoemission data, which do not reveal these
pockets.
|
In the covariant cosmological perturbation theory, a 1+3 decomposition
ensures that all variables in the frame-independent equations are covariant,
gauge-invariant and have clear physical interpretations. We develop this
formalism in the case of Brans-Dicke gravity, and apply this method to the
calculation of cosmic microwave background (CMB) anisotropy and large scale
structures (LSS). We modify the publicly available Boltzmann code CAMB to
calculate numerically the evolution of the background and adiabatic
perturbations, and obtain the temperature and polarization spectra of the
Brans-Dicke theory for both scalar and tensor mode, the tensor mode result for
the Brans-Dicke gravity are obtained numerically for the first time. We first
present our theoretical formalism in detail, then explicitly describe the
techniques used in modifying the CAMB code. These techniques are also very
useful to other gravity models. Next we compare the CMB and LSS spectra in
Brans-Dicke theory with those in the standard general relativity theory. At
last, we investigate the ISW effect and the CMB lensing effect in the
Brans-Dicke theory. Constraints on Brans-Dicke model with current observational
data is presented in a companion paper (paper II).
|
In this work thin films of the La1-xSrxCoO3 (0.05 < x < 0.26) compound were
grown, employing the so-called spray pyrolysis process. The as-grown thin films
exhibit polycrystalline microstructure, with uniform grain size distribution,
and observable porosity. Regarding their electrical transport properties, the
produced thin films show semiconducting-like behavior, regardless the Sr doping
level, which is most likely due to both the oxygen deficiencies and the grainy
nature of the films. Furthermore, room temperature current-voltage (I-V)
measurements reveal stable resistance switching behavior, which is well
explained in terms of space-charge limited conduction mechanism. The presented
experimental results provide essential evidence regarding the engagement of low
cost, industrial-scale methods of growing perovskite transition metal oxide
thin films, for potential applications in random access memory devices.
|
(Write-up of a talk at the Bialowieza meeting, July 2007.)
Gelfand and Kolmogorov in 1939 proved that a compact Hausdorff topological
space $X$ can be canonically embedded into the infinite-dimensional vector
space $C(X)^* $, the dual space of the algebra of continuous functions $C(X)$
as an "algebraic variety" specified by an infinite system of quadratic
equations.
Buchstaber and Rees have recently extended this to all symmetric powers
$\Sym^n(X)$ using their notion of the Frobenius $n$-homomorphisms.
We give a simplification and a further extension of this theory, which is
based, rather unexpectedly, on results from super linear lgebra.
|
Domain adaptation for sensor-based activity learning is of utmost importance
in remote health monitoring research. However, many domain adaptation
algorithms suffer with failure to operate adaptation in presence of target
domain heterogeneity (which is always present in reality) and presence of
multiple inhabitants dramatically hinders their generalizability producing
unsatisfactory results for semi-supervised and unseen activity learning tasks.
We propose \emph{AEDA}, a novel deep auto-encoder-based model to enable
semi-supervised domain adaptation in the existence of target domain
heterogeneity and how to incorporate it to empower heterogeneity to any
homogeneous deep domain adaptation architecture for cross-domain activity
learning. Experimental evaluation on 18 different heterogeneous and
multi-inhabitants use-cases of 8 different domains created from 2 publicly
available human activity datasets (wearable and ambient smart homes) shows that
\emph{AEDA} outperforms (max. 12.8\% and 8.9\% improvements for ambient smart
home and wearables) over existing domain adaptation techniques for both seen
and unseen activity learning in a heterogeneous setting.
|
We develop the superspace geometry of N-extended conformal supergravity in
three space-time dimensions. General off-shell supergravity-matter couplings
are constructed in the cases N=1,2,3,4.
|
We study the most general cosmological model with real scalar field which is
minimally coupled to gravity. Our calculations are based on
Friedmann-Lemaitre-Robertson-Walker (FLRW) background metric. Field equations
consist of three differential equations. We switch independent variable from
time to scale factor by change of variable $\dot{a}/a=H(a)$. Thus a new set of
differential equations are analytically solvable with known methods. We
formulate Hubble function, the scalar field, potential and energy density when
one of them is given in the most general form. $a(t)$ can be explicitly found
as long as methods of integration techniques are available. We investigate the
dynamics of the universe at early times as well as at late times in light of
these formulas. We find mathematical machinery which turns on and turns off
early accelerated expansion. On the other hand late time accelerated expansion
is explained by cosmic domain walls. We have compared our results with recent
observations of type Ia supernovae by considering the Hubble tension and
absolute magnitude tension. Eighty-nine percent of present universe may consist
of domain walls while rest is matter.
|
We report the $\gamma$-ray detection of a young radio galaxy, PKS 1718$-$649,
belonging to the class of Compact Symmetric Objects (CSOs), with the Large Area
Telescope (LAT) on board the {\it Fermi} satellite. The third {\it Fermi}
Gamma-ray LAT catalog (3FGL) includes an unassociated $\gamma$-ray source, 3FGL
J1728.0$-$6446, located close to PKS 1718$-$649. Using the latest Pass 8
calibration, we confirm that the best fit $1 \sigma$ position of the
$\gamma$-ray source is compatible with the radio location of PKS 1718$-$649.
Cross-matching of the $\gamma$-ray source position with the positions of blazar
sources from several catalogs yields negative results. Thus, we conclude that
PKS 1718$-$649 is the most likely counterpart to the unassociated LAT source.
We obtain a detection test statistics TS$\sim 36$ ($>$5$\sigma$) with a best
fit photon spectral index $\Gamma=$2.9$\pm$0.3 and a 0.1-100 GeV photon flux
density $F_{\rm 0.1-100GeV}=$(11.5$\pm$0.3)$\times{\rm 10^{-9}}$ ph cm$^{-2}$
s$^{-1}$. We argue that the linear size ($\sim$2 pc), the kinematic age
($\sim$100 years), and the source distance ($z=0.014$) make PKS 1718$-$649 an
ideal candidate for $\gamma$-ray detection in the framework of the model
proposing that the most compact and the youngest CSOs can efficiently produce
GeV radiation via inverse-Compton scattering of the ambient photon fields by
the radio lobe non-thermal electrons. Thus, our detection of the source in
$\gamma$-rays establishes young radio galaxies as a distinct class of
extragalactic high-energy emitters, and yields an unique insight on the
physical conditions in compact radio lobes interacting with the interstellar
medium of the host galaxy.
|
We study the rank of the random $n\times m$ 0/1 matrix ${\bf A}_{n,m;k}$
where each column is chosen independently from the set $\Omega_{n,k}$ of 0/1
vectors with exactly $k$ 1's. Here 0/1 are the elements of the field $GF_2$. We
obtain an asymptotically correct estimate for the rank in terms of $c,n,k$,
assuming that $m=cn$.
In addition, we assign i.i.d. $U[0,1]$ weights $X_{{\bf c}},{\bf
c}\in\Omega_{n,k}$ and let the weight of a set of columns $C$ be
$X(C)=\sum_{{\bf c}\in C}X_{{\bf c}}$. Let a basis be a set of
$n-1_{k\text{even}}$ linearly independent columns. We obtain an asymptotically
correct estimate for the minimum weight of a basis. This generalises the
well-known result for $k=2$ viz. that the expected length of a minimum weight
spanning tree tends to $\zeta(3)$.
|
It is shown that the fluctuation in the temperature of the cosmic microwave
background in any direction may be evaluated as an integral involving scalar
and dipole form factors, which incorporate all relevant information about
acoustic oscillations before the time of last scattering. A companion paper
gives asymptotic expressions for the multipole coefficient $C_\ell$ in terms of
these form factors. Explicit expressions are given here for the form factors in
a simplified hydrodynamic model for the evolution of perturbations.
|
In this article, I provide significant mathematical evidence in support of
the existence of short-time approximations of any polynomial order for the
computation of density matrices of physical systems described by arbitrarily
smooth and bounded from below potentials. While for Theorem 2, which is
``experimental'', I only provide a ``physicist's'' proof, I believe the present
development is mathematically sound. As a verification, I explicitly construct
two short-time approximations to the density matrix having convergence orders 3
and 4, respectively. Furthermore, in the Appendix, I derive the convergence
constant for the trapezoidal Trotter path integral technique. The convergence
orders and constants are then verified by numerical simulations. While the two
short-time approximations constructed are of sure interest to physicists and
chemists involved in Monte Carlo path integral simulations, the present article
is also aimed at the mathematical community, who might find the results
interesting and worth exploring. I conclude the paper by discussing the
implications of the present findings with respect to the solvability of the
dynamical sign problem appearing in real-time Feynman path integral
simulations.
|
We consider symplectic cohomology twisted by sphere bundles, which can be
viewed as an analogue of local systems. Using the associated Gysin exact
sequence, we prove the uniqueness of part of the ring structure on cohomology
of fillings for those asymptotically dynamically convex manifolds with
vanishing property considered in [30,31]. In particular, for simply connected
$4n+1$ dimensional flexible fillable contact $Y$, we show that real cohomology
$H^*(W)$ is unique as a ring for any Liouville filling $W$ of $Y$ as long as
$c_1(W)=0$. Uniqueness of real homotopy type of Liouville fillings is also
obtained for a class of flexibly fillable contact manifolds.
|
As quantum technology advances and the size of quantum computers grow, it
becomes increasingly important to understand the extent of quality in the
devices. As large-scale entanglement is a quantum resource crucial for
achieving quantum advantage, the challenge in its generation makes it a
valuable benchmark for measuring the performance of universal quantum devices.
In this work, we study entanglement in Greenberger-Horne-Zeilinger (GHZ) and
graph states prepared on the range of IBM Quantum devices. We generate GHZ
states and investigate their coherence times with respect to state size and
dynamical decoupling techniques. A GHZ fidelity of $0.519 \pm 0.014$ is
measured on a 32-qubit GHZ state, certifying its genuine multipartite
entanglement (GME). We show a substantial improvement in GHZ decoherence rates
for a 7-qubit GHZ state after implementing dynamical decoupling, and observe a
linear trend in the decoherence rate of $\alpha=(7.13N+5.54)10^{-3} \mu s^{-1}$
for up to $N=15$ qubits, confirming the absence of superdecoherence.
Additionally, we prepare and characterise fully bipartite entangled native
graph states on 22 IBM Quantum devices with qubit counts as high as 414 qubits,
all active qubits of the 433-qubit Osprey device. Analysis of the decay of
2-qubit entanglement within the prepared states shows suppression of coherent
noise signals with the implementation of dynamical decoupling techniques.
Additionally, we observe that the entanglement in some qubit pairs oscillates
over time, which is likely caused by residual ZZ-interactions. Characterising
entanglement in native graph states, along with detecting entanglement
oscillations, can be an effective approach to low-level device benchmarking
that encapsulates 2-qubit error rates along with additional sources of noise,
with possible applications to quantum circuit compilation.
|
For the rational quantum Calogero systems of type $A_1{\oplus}A_2$, $AD_3$
and $BC_3$, we explicitly present complete sets of independent conserved
charges and their nonlinear algebras. Using intertwining (or shift) operators,
we include the extra `odd' charges appearing for integral couplings. Formulae
for the energy eigenstates are used to tabulate the low-level wave functions.
|
Using the high-resolution HR-DEMNUni simulations, we computed neutrino
profiles within virialized dark matter haloes. These new high-resolution
simulations allowed us to revisit fitting formulas proposed in the literature
and provided updated fitting parameters that extend to less massive haloes and
lower neutrino masses than previously in the literature, in accordance with new
cosmological limits. The trend we observe for low neutrino masses is that, for
dark matter halo masses below $\sim 4\times10^{14}$$h^{-1}M_\odot$, the
presence of the core becomes weaker and the profile over the whole radius is
closer to a simple power law. We also characterized the neutrino density
profile dependence on the solid angle within clustered structures: a
forward-backward asymmetry larger than 10% was found when comparing the density
profiles from neutrinos along the direction of motion of cold dark matter
particles within the same halo. In addition, we looked for neutrino wakes
around halo centres produced by the peculiar motion of the halo itself. Our
results suggest that the wakes effect is observable in haloes with masses
greater than $3\times10^{14}$ $h^{-1}M_\odot$ where a mean displacement of
$0.06$\hmpc was found.
|
The problem of diffraction of a waveguide mode by a thin Neumann screen is
considered. The incident mode is assumed to have frequency close to the
cut-off. The problem is reduced to a propagation problem on a branched surface
and then is considered in the parabolic approximation. Using the embedding
formula approach, the reflection and transmission coefficients are expressed
through the directivities of the edge Green's function of the propagation
problem. The asymptotics of the directivities of the edge Green's functions are
constructed for the case of small gaps between the screen and the walls of the
waveguide. As the result, the reflection and transmission coefficients are
found. The validity of known asymptotics of these coefficients is studied.
|
In this paper we shall analyze the $f(\mathcal{G})$ gravity phase space, in
the case that the corresponding dynamical system is autonomous. In order to
make the dynamical system autonomous, we shall appropriately choose the
independent variables, and we shall analyze the evolution of the variables
numerically, emphasizing on the inflationary attractors. As we demonstrate, the
dynamical system has only one de Sitter fixed point, which is unstable, with
the instability being traced in one of the independent variables. This result
holds true both in the presence and in the absence of matter and radiation
perfect fluids. We argue that this instability could loosely be viewed as an
indication of graceful exit in the $f(\mathcal{G})$ theory of gravity.
|
Internet traffic exhibits self-similarity and long-range dependence (LRD) on
various time scales. A well studied issue is the estimation of statistical
parameters characterizing traffic self-similarity and LRD, such as the Hurst
parameter H. In this paper, we propose to adapt the Modified Allan Variance
(MAVAR), a time-domain quantity originally conceived to discriminate fractional
noise in frequency stability measurement, to estimate the Hurst parameter of
LRD traffic traces and, more generally, to identify fractional noise components
in network traffic. This novel method is validated by comparison to one of the
best techniques for analyzing self-similar and LRD traffic: the logscale
diagram based on wavelet analysis. Both methods are applied to pseudo-random
LRD data series, generated with assigned values of H. The superior spectral
sensitivity of MAVAR achieves outstanding accuracy in estimating H, even better
than the logscale method. The behaviour of MAVAR with most common deterministic
signals that yield nonstationarity in data under analysis is also studied.
Finally, both techniques are applied to a real IP traffic trace, providing a
sound example of the usefulness of MAVAR also in traffic characterization, to
complement other established techniques as the logscale method.
|
We consider time discretization methods for abstract parabolic problems with
inhomogeneous linear constraints. Prototype examples that fit into the general
framework are the heat equation with inhomogeneous (time dependent) Dirichlet
boundary conditions and the time dependent Stokes equation with an
inhomogeneous divergence constraint. Two common ways of treating such linear
constraints, namely explicit or implicit (via Lagrange multipliers) are
studied. These different treatments lead to different variational formulations
of the parabolic problem. For these formulations we introduce a modification of
the standard discontinuous Galerkin (DG) time discretization method in which an
appropriate projection is used in the discretization of the constraint. For
these discretizations (optimal) error bounds, including superconvergence
results, are derived. Discretization error bounds for the Lagrange multiplier
are presented. Results of experiments confirm the theoretically predicted
optimal convergence rates and show that without the modification the (standard)
DG method has sub-optimal convergence behavior.
|
Quasimodules for vertex algebras are generalizations of modules for vertex
algebras. These new objects arise from a generalization of locality for fields.
Quasimodules tie together module theory and twisted module theory, and both
twisted and untwisted modules feature Poincare-Birkhoff-Witt-like spanning
sets. This paper generalizes these spanning set results to quasimodules for
certain Mobius vertex algebras. In particular this paper presents two spanning
sets, one featuring a difference-zero ordering restriction on modes and another
featuring a difference-one condition.
|
Goltz and Reisig generalised Petri's concept of processes of one-safe Petri
nets to general nets where places carry multiple tokens. BD-processes are
equivalence classes of Goltz-Reisig processes connected through the swapping
transformation of Best and Devillers; they can be considered as an alternative
representation of runs of nets. Here we present an order respecting bijection
between the BD-processes and the FS-processes of a countable net, the latter
being defined -- in an analogous way -- as equivalence classes of firing
sequences. Using this, we show that a countable net without binary conflicts
has a (unique) largest BD-process.
|
The Search for Extra-terrestrial Intelligence (SETI) using radio telescopes
is an area of research that is now more than 50 years old. Thus far, both
targeted and wide-area surveys have yet to detect artificial signals from
intelligent civilisations. In this paper, I argue that the incidence of
co-existing intelligent and communicating civilisations is probably small in
the Milky Way. While this makes successful SETI searches a very difficult
pursuit indeed, the huge impact of even a single detection requires us to
continue the search. A substantial increase in the overall performance of radio
telescopes (and in particular future wide-field instruments such as the Square
Kilometre Array, SKA), provide renewed optimism in the field. Evidence for this
is already to be seen in the success of SETI researchers in acquiring
observations on some of the world's most sensitive radio telescope facilities
via open, peer-reviewed processes. The increasing interest in the dynamic radio
sky, and our ability to detect new and rapid transient phenomena such as Fast
Radio Bursts (FRB) is also greatly encouraging. While the nature of FRBs is not
yet fully understood, I argue they are unlikely to be the signature of distant
extra-terrestrial civilisations. As astronomers face a data avalanche on all
sides, advances made in related areas such as advanced Big Data analytics, and
cognitive computing are crucial to enable serendipitous discoveries to be made.
In any case, as the era of the SKA fast approaches, the prospects of a SETI
detection have never have been better.
|
We present and study models of adversarial online learning where the feedback
observed by the learner is noisy, and the feedback is either full information
feedback or bandit feedback. Specifically, we consider binary losses xored with
the noise, which is a Bernoulli random variable. We consider both a constant
noise rate and a variable noise rate. Our main results are tight regret bounds
for learning with noise in the adversarial online learning model.
|
Singular points of a fingerprint image are special locations having high
curvature properties. They can play a pivotal role in fingerprint normalization
and reliable feature extraction. Accurate and efficient extraction of a
singular point plays a major role in successful fingerprint recognition and
indexing. In this paper, a novel deep learning based architecture is proposed
for one shot (end-to-end) singular point detection from an input fingerprint
image. The model consists of a Macro-Localization Network and a
Micro-Regression Network along with three stacked hourglass as a bottleneck.
The proposed model has been tested on three databases viz. FVC2002 DB1_A,
FVC2002 DB2_A and FPL30K and has been found to achieve true detection rate of
98.75%, 97.5% and 92.72% respectively, which is better than any other
state-of-the-art technique.
|
We consider neutrino Minimal extension of the Standard Model ($\nu$MSM),
which by introducing only three sterile neutrinos in sub electroweak region can
explain active neutrino oscillations (via seesaw type I mechanism), baryon
asymmetry of the Universe (leptogenesis via oscillations) and dark matter
phenomena (with keV-scale sterile neutrino forming dark matter). We estimate
sterile neutrino virtual contributions to various lepton flavor and lepton
number violating processes. The contributions are too small, giving no chance
for indirect searches to compete with direct measurements in exploring
$\nu$MSM.
|
Approximately 30-40% of all baryons in the present day universe reside in a
warm-hot intergalactic medium (WHIM), with temperatures between 10^5<T<10^7 K.
This is a generic prediction from six hydrodynamic simulations of currently
favored structure formation models having a wide variety of numerical methods,
input physics, volumes, and spatial resolutions. Most of these warm-hot baryons
reside in diffuse large-scale structures with a median overdensity around
10-30, not in virialized objects such as galaxy groups or galactic halos. The
evolution of the WHIM is primarily driven by shock heating from gravitational
perturbations breaking on mildly nonlinear, non-equilibrium structures such as
filaments. Supernova feedback energy and radiative cooling play lesser roles in
its evolution. WHIM gas is consistent with observations of the 0.25 keV X-ray
background without being significantly heated by non-gravitational processes
because the emitting gas is very diffuse. Our results confirm and extend
previous work by Cen & Ostriker and Dave' et al.
|
We investigate black holes in a class of dRGT massive gravity for their quasi
normal modes (QNMs) for neutral and charged ones using Improved Asymptotic
Iteration Method (Improved AIM) and their thermodynamic behavior. The QNMs are
studied for different values of the massive parameter m_g for both neutral and
charged dRGT black holes under a massless scalar perturbation. As m_g
increases, the magnitude of the quasi normal frequencies are found to be
increasing. The results are also compared with the Schwarzchild de Sitter (SdS)
case. P-V criticallity of the aforesaid black hoels under massles scalar
perturbation in the de Sitter space are also studied in this paper. It is found
that the thermodynamic behavior of a neutral black hole shows no physically
feasible phase transition while a charged black hole shows a definite phase
transition.
|
We consider how the quasinormal spectrum for the conformal wave operator on
the static patch of de Sitter changes in response to the addition of a small
potential. Since the quasinormal modes and co-modes are explicitly known, we
are able to give explicit formulae for the instantaneous rate of change of each
frequency in terms of the perturbing potential. We verify these exact
computations numerically using a novel technique extending the spectral
hyperboloidal approach of Jaramillo et al. (2021). We propose a definition for
a family of pseudospectra that we show capture the instability properties of
the quasinormal frequencies.
|
We study distributions of differences of unscaled Riemann zeta zeros,
$\gamma-\gamma^{'}$, at large distances. We show, that independently of the
height, a subset of finite number of successive zeros knows the locations of
lower level zeros. The information contained in the subset of zeros is
inversely proportional to $ln(\gamma/(2\pi))$, where $\gamma$ is the average
zeta of the subset. Because the mean difference of the zeros also decreases as
inversely proportional to $ln(\gamma/(2\pi))$, each equally long segment of the
line $\Re(z)=1/2$ contains equal amount of information. The distributions of
differences are skewed towards the nearest zeta zero, or at least, in the case
of very nearby zeros, the skewness always decreases when zeta zero is crossed
in increasing direction. We also show that the variance of distributions has
local maximum or, at least, a turning point at every zeta zero, i.e., local
minimum of the second derivative of the variance. In addition, it seems that
the higher the zeros the more compactly the distributions of the differences
are located in the skewness-kurtosis -plane. The flexibility of the Johnson
distribution allows us to fit the distributions nicely, despite of the values
of skewness and kurtosis of the distributions.
|
We propose a scheme for realizing quantum controlled phase gates with two
nonidentical quantum dots trapped in two coupled photonic crystal cavities and
driven by classical laser fields under the condition of non-small hopping
limit. During the gate operation, neither the quantum dots are excited, while
the system can acquire different phases conditional upon the different states
of the quantum dots. Along with single-qubit operations, a two-qubit controlled
phase gate can be achieved.
|
In the last years there have been several new constructions of surfaces of
general type with $p_g=0$, and important progress on their classification. The
present paper presents the status of the art on surfaces of general type with
$p_g=0$, and gives an updated list of the existing surfaces, in the case where
$K^2= 1,...,7$. It also focuses on certain important aspects of this
classification.
|
We present a perturbative result for the temporal evolution of the fidelity
of the quantum kicked rotor, i.e. the overlap of the same initial state evolved
with two slightly different kicking strengths, for kicking periods close to a
principal quantum resonance. Based on a pendulum approximation we describe the
fidelity for rotational orbits in the pseudo-classical phase space of a
corresponding classical map. Our results are compared to numerical simulations
indicating the range of applicability of our analytical approximation.
|
We present phase-resolved spectroscopy of AM Herculis obtained with the
HST/GHRS when the system was in a high state. The ultraviolet light curve shows
a quasi-sinusoidal modulation, which can be explained by a hot spot on the
rotating white dwarf. The broad Lalpha absorption expected for photospheric
radiation of a moderately hot white dwarf is largely filled in with emission.
The UV/FUV spectrum of AM Her in high state can be quantitatively understood by
a two-component model consisting of the unheated white dwarf plus a
blackbody-like radiating hot spot. A kinematic study of the strong UV emission
lines using Doppler tomography is presented. The characteristics of the low
ionization species lines and the SiIV doublet can be explained within the
classical picture, as broad emission from the accretion stream and narrow
emission from the heated hemisphere of the secondary. However, we find that the
narrow emission of the NV doublet originates from material of low velocity
dispersion located somewhere between L_1 and the centre of mass. The high
signal-to-noise spectra contain a multitude of interstellar absorption lines
but no metal absorption lines from the white dwarf photosphere.
|
Let $E$ be an elliptic curve over a finite field $\mathbb{F}_q$ where $q$ is
a prime power. The Schoof--Elkies--Atkin (SEA) algorithm is a standard method
for counting the number of $\mathbb{F}_q$-points on $E$. The asymptotic
complexity of the SEA algorithm depends on the distribution of the so-called
Elkies primes.
Assuming GRH, we prove that the least Elkies prime is bounded by $(2\log
4q+4)^2$ when $q\geq 10^9$. This is the first such explicit bound in the
literature. Previously, Satoh and Galbraith established an upper bound of
$O((\log q)^{2+\varepsilon})$.
Let $N_E(X)$ denote the number of Elkies primes less than $X$. Assuming GRH,
we also show $$
N_E(X)=\frac{\pi(X)}{2}+O\left(\frac{\sqrt{X}(\log qX)^2}{\log X}\right)\,.
$$
|
We consider transport through a non-Hermitian conductor connected to a pair
of Hermitian leads and analyze the underlying non-Hermitian scattering problem.
In a typical non-Hermitian system, such as a Hatano--Nelson-type asymmetric
hopping model, the continuity of probability and probability current is broken
at a local level. As a result, the notion of transmission and reflection
probabilities becomes ill-defined. Instead of these probabilities, we introduce
the injection rate $R_{\rm I}=1-|{\cal R}|^2$ and the transmission rate $R_{\rm
T}=|{\cal T}|^2$ as relevant physical quantities, where ${\cal T}$ and ${\cal
R}$ are the transmission and reflection amplitudes, respectively. In a generic
non-Hermitian case, $R_{\rm I}$ and $R_{\rm T}$ have independent information.
We provide a modified continuity equation in terms of incoming and outgoing
currents, from which we derive a global probability conservation law that
relates $R_{\rm I}$ and $R_{\rm T}$. We have tested the usefulness of our
probability conservation law in the interpretation of numerical results for
non-Hermitian localization and delocalization phenomena.
|
For a Dirac operator $D_{\bar{g}}$ over a spin compact Riemannian manifold
with boundary $(\bar{X},\bar{g})$, we give a natural construction of the
Calder\'on projector and of the associated Bergman projector on the space of
harmonic spinors on $\bar{X}$, and we analyze their Schwartz kernels. Our
approach is based on the conformal covariance of $D_{\bar{g}}$ and the
scattering theory for the Dirac operator associated to the complete conformal
metric $g=\bar{g}/\rho^2$ where $\rho$ is a smooth function on $\bar{X}$ which
equals the distance to the boundary near $\partial\bar{X}$. We show that $({\rm
Id}+\tilde{S}(0))/2$ is the orthogonal Calder\'on projector, where
$\tilde{S}(\lambda)$ is the holomorphic family in $\{\Re(\lambda)\geq 0\}$ of
normalized scattering operators constructed in our previous work, which are
classical pseudo-differential of order $2\lambda$. Finally we construct natural
conformally covariant odd powers of the Dirac operator on any spin manifold.
|
We report on suppression of long-range wakefields in CLIC accelerating
structures. Strong detuning and moderate damping is employed. In these initial
design studies we focus on the CLIC_G structure and enforce a moderate Q of 300
and 500. We maintain a dipole bandwidth of approximately 1 GHz as specified
from breakdown constraints in a modified structure, CLIC_DDS. The circuit
model, which facilitates a rapid design of manifolds slot-coupled to the main
accelerating cells, is described.
|
Intrinsic topological superconducting materials are exotic and vital to
develop the next-generation topological superconducting devices, topological
quantum calculations, and quantum information technologies. Here, we predict
the topological and nodal superconductivity of MS (M = Nb and Ta)
transition-metal sulfides by using the density functional theory for
superconductors combining with the symmetry indicators. We reveal their
higher-order topology nature with an index of Z4 = 2. These materials have a
higher Tc than the Nb or Ta metal superconductors due to their flat-band and
strong electron-phonon coupling nature. Electron doping and lighter isotopes
can effectively enhance the Tc. Our findings show that the MS (M = Nb and Ta)
systems can be new platforms to study exotic physics in the higher-order
topological superconductors, and provide a theoretical support to utilize them
as the topological superconducting devices in the field of advanced topological
quantum calculations and information technologies.
|
We prove a weak rate of convergence of a fully discrete scheme for stochastic
Cahn--Hilliard equation with additive noise, where the spectral Galerkin method
is used in space and the backward Euler method is used in time. Compared with
the Allen--Cahn type stochastic partial differential equation, the error
analysis here is much more sophisticated due to the presence of the unbounded
operator in front of the nonlinear term. To address such issues, a novel and
direct approach has been exploited which does not rely on a Kolmogorov equation
but on the integration by parts formula from Malliavin calculus. To the best of
our knowledge, the rates of weak convergence are revealed in the stochastic
Cahn--Hilliard equation setting for the first time.
|
We present a novel large-context end-to-end automatic speech recognition
(E2E-ASR) model and its effective training method based on knowledge
distillation. Common E2E-ASR models have mainly focused on utterance-level
processing in which each utterance is independently transcribed. On the other
hand, large-context E2E-ASR models, which take into account long-range
sequential contexts beyond utterance boundaries, well handle a sequence of
utterances such as discourses and conversations. However, the transformer
architecture, which has recently achieved state-of-the-art ASR performance
among utterance-level ASR systems, has not yet been introduced into the
large-context ASR systems. We can expect that the transformer architecture can
be leveraged for effectively capturing not only input speech contexts but also
long-range sequential contexts beyond utterance boundaries. Therefore, this
paper proposes a hierarchical transformer-based large-context E2E-ASR model
that combines the transformer architecture with hierarchical encoder-decoder
based large-context modeling. In addition, in order to enable the proposed
model to use long-range sequential contexts, we also propose a large-context
knowledge distillation that distills the knowledge from a pre-trained
large-context language model in the training phase. We evaluate the
effectiveness of the proposed model and proposed training method on Japanese
discourse ASR tasks.
|
Support teams of high-performance computing (HPC) systems often find
themselves between a rock and a hard place: on one hand, they understandably
administrate these large systems in a conservative way, but on the other hand,
they try to satisfy their users by deploying up-to-date tool chains as well as
libraries and scientific software. HPC system users often have no guarantee
that they will be able to reproduce results at a later point in time, even on
the same system-software may have been upgraded, removed, or recompiled under
their feet, and they have little hope of being able to reproduce the same
software environment elsewhere. We present GNU Guix and the functional package
management paradigm and show how it can improve reproducibility and sharing
among researchers with representative use cases.
|
Real-time tweets can provide useful information on evolving events and
situations. Geotagged tweets are especially useful, as they indicate the
location of origin and provide geographic context. However, only a small
portion of tweets are geotagged, limiting their use for situational awareness.
In this paper, we adapt, improve, and evaluate a state-of-the-art deep learning
model for city-level geolocation prediction, and integrate it with a visual
analytics system tailored for real-time situational awareness. We provide
computational evaluations to demonstrate the superiority and utility of our
geolocation prediction model within an interactive system.
|
While convergence behaviour archetypes can explain behaviour of individuals
who actively converge on and participate in crises, less is known about
individuals who converge on an event and choose to remain passive i.e.
"bystanders". Bystanders are important, because of their proximity to an event
and their function as an "eye-witness". To investigate the role of bystanders
in crisis communications we analysed Twitter communication generated from the
2016 Munich Shooting event. Our findings revealed the impassive convergence
behaviour archetype could influence an event as a passive and rational
"eye-witness", by gathering and sharing information close to where the event is
occurring.
|
In this paper, we consider a Newtonian system whose relativistic counterpart
describes a superimposed halo with a black hole. Our aim is to determine how
the quadrupole and octupole moments affect the nature of the motion of a test
particle, moving in the close vicinity of the black hole. The different types
of trajectories for the test particle are mainly classified as bounded,
collisional, and escaping, by using modern color-coded basin diagrams.
Moreover, an additional analysis is carried out for distinguishing between the
different types of bounded motion (regular, sticky, and chaotic). Our results
strongly indicate that the multipole moments, along with the total orbital
energy, highly affect the final state of the test particle, while at the same
time the basin geometry of the phase space tends to be highly dominated by
collision and escape orbits.
|
We describe here a structured system for distributed mechanism design
appropriate for both Intranet and Internet applications. In our approach the
players dynamically form a network in which they know neither their neighbours
nor the size of the network and interact to jointly take decisions. The only
assumption concerning the underlying communication layer is that for each pair
of processes there is a path of neighbours connecting them. This allows us to
deal with arbitrary network topologies.
We also discuss the implementation of this system which consists of a
sequence of layers. The lower layers deal with the operations that implement
the basic primitives of distributed computing, namely low level communication
and distributed termination, while the upper layers use these primitives to
implement high level communication among players, including broadcasting and
multicasting, and distributed decision making.
This yields a highly flexible distributed system whose specific applications
are realized as instances of its top layer. This design is implemented in Java.
The system supports at various levels fault-tolerance and includes a
provision for distributed policing the purpose of which is to exclude
`dishonest' players. Also, it can be used for repeated creation of dynamically
formed networks of players interested in a joint decision making implemented by
means of a tax-based mechanism. We illustrate its flexibility by discussing a
number of implemented examples.
|
The single $\beta$ decay of $^{96}$Zr to the ground state of $^{96}$Nb is
spin forbidden and poses a great experimental challenge. The $\beta$ decay of
$^{96}$Zr can be studied via coincident detection of de-exciting gamma rays in
$^{96}$Mo, which is the end product of $^{96}$Nb $\beta$ decay. Simulations are
done with four HPGe detector setup (~33% relative efficiency each) to optimize
the source configuration. The results suggest that ~70g of 50% enriched
$^{96}$Zr will yield sensitivity comparable to the reported results.
|
We analyze the problem of the Nielsen-Olesen unstable modes in the $SU(2)$
lattice gauge theory by means of a recently introduced gauge-invariant
effective action. We perform numerical simulations in the case of a constant
Abelian chromomagnetic field. We find that for lattice sizes above a certain
critical length the density of effective action shows a behaviour compatible
with the presence of the unstable modes.
|
Any quantum algorithm can be implemented by an adaptive sequence of single
node measurements on an entangled cluster of qubits in a square lattice
topology. Photons are a promising candidate for encoding qubits but assembling
a photonic entangled cluster with linear optical elements relies on
probabilistic operations. Given a supply of $n$-photon-entangled microclusters,
using a linear optical circuit and photon detectors, one can assemble a random
entangled state of photons that can be subsequently "renormalized" into a
logical cluster for universal quantum computing. In this paper, we prove that
there is a fundamental tradeoff between $n$ and the minimum success probability
$\lambda_c^{(n)}$ that each two-photon linear-optical fusion operation must
have, in order to guarantee that the resulting state can be renormalized:
$\lambda_c^{(n)} \ge 1/(n-1)$. We present a new way of formulating this problem
where $\lambda_c^{(n)}$ is the bond percolation threshold of a logical graph
and provide explicit constructions to produce a percolated cluster using $n=3$
photon microclusters (GHZ states) as the initial resource. We settle a
heretofore open question by showing that a renormalizable cluster can be
created with $3$-photon microclusters over a 2D graph without feedforward,
which makes the scheme extremely attractive for an integrated-photonic
realization. We also provide lattice constructions, which show that $0.5 \le
\lambda_c^{(3)} \le 0.5898$, improving on a recent result of $\lambda_c^{(3)}
\le 0.625$. Finally, we discuss how losses affect the bounds on the threshold,
using loss models inspired by a recently-proposed method to produce photonic
microclusters using quantum dot emitters.
|
While the increasing number of Vantage Points (VPs) in RIPE RIS and
RouteViews
improves our understanding of the Internet, the quadratically increasing
volume of collected data poses a challenge to the scientific and operational
use of the data. The design and implementation of BGP and BGP data
collection systems lead to data archives with enormous redundancy, as
there is substantial overlap in announced routes across many different VPs.
Researchers thus often resort to arbitrary sampling of the data,
which we demonstrate
comes at a cost to the accuracy and coverage of previous works. The continued
growth of the Internet, and of these collection systems, exacerbates
this cost. The community needs a better approach to managing
and using these data archives.
We propose MVP, a system that
scores VPs according to their level of redundancy with other VPs,
allowing more informed sampling of these data archives.
Our challenge is that the degree of redundancy between two updates depends
on how we define redundancy, which in turn depends on
the analysis objective. Our key contribution is
a general framework and associated algorithms to assess
redundancy between VP observations.
We quantify the benefit of our approach for four canonical BGP routing
analyses: AS relationship inference, AS rank computation, hijack detection, and
routing detour detection. MVP improves the coverage or accuracy (or both) of
all these analyses while processing the same volume of data.
|
Recently, formalism has been derived for studying electroweak transition
amplitudes for three-body systems both in infinite and finite volumes. The
formalism provides exact relations that the infinite-volume amplitudes must
satisfy, as well as a relationship between physical amplitudes and
finite-volume matrix elements, which can be constrained from lattice QCD
calculations. This formalism poses additional challenges when compared with the
analogous well-studied two-body equivalent one, including the necessary step of
solving integral equations of singular functions. In this work, we provide some
non-trivial analytical and numerical tests on the aforementioned formalism. In
particular, we consider a case where the three-particle system can have
three-body bound states as well as bound states in the two-body subsystem. For
kinematics below the three-body threshold, we demonstrate that the scattering
amplitudes satisfy unitarity. We also check that for these kinematics the
finite-volume matrix elements are accurately described by the formalism for
two-body systems up to exponentially suppressed corrections. Finally, we verify
that in the case of the three-body bound state, the finite-volume matrix
element is equal to the infinite-volume coupling of the bound state, up to
exponentially suppressed errors.
|
Dialogue summarization task involves summarizing long conversations while
preserving the most salient information. Real-life dialogues often involve
naturally occurring variations (e.g., repetitions, hesitations) and existing
dialogue summarization models suffer from performance drop on such
conversations. In this study, we systematically investigate the impact of such
variations on state-of-the-art dialogue summarization models using publicly
available datasets. To simulate real-life variations, we introduce two types of
perturbations: utterance-level perturbations that modify individual utterances
with errors and language variations, and dialogue-level perturbations that add
non-informative exchanges (e.g., repetitions, greetings). We conduct our
analysis along three dimensions of robustness: consistency, saliency, and
faithfulness, which capture different aspects of the summarization model's
performance. We find that both fine-tuned and instruction-tuned models are
affected by input variations, with the latter being more susceptible,
particularly to dialogue-level perturbations. We also validate our findings via
human evaluation. Finally, we investigate if the robustness of fine-tuned
models can be improved by training them with a fraction of perturbed data and
observe that this approach is insufficient to address robustness challenges
with current models and thus warrants a more thorough investigation to identify
better solutions. Overall, our work highlights robustness challenges in
dialogue summarization and provides insights for future research.
|
The recent analysis of De la Torre, Daleo and Garcia-Mata of the reply of
Bohr to the famous clock-in-the-box challenge of Einstein is criticized.
|
In this work we are interested in effectively solving the quasi-static,
linear Biot model for poromechanics. We consider the fixed-stress splitting
scheme, which is a popular method for iteratively solving Biot's equations. It
is well-known that the convergence of the method is strongly dependent on the
applied stabilization/tuning parameter. In this work, we propose a new approach
to optimize this parameter. We show theoretically that it depends also on the
fluid flow properties and not only on the mechanics properties and the coupling
coefficient. The type of analysis presented in this paper is not restricted to
a particular spatial discretization. We only require it to be inf-sup stable.
The convergence proof applies also to low-compressible or incompressible fluids
and low-permeable porous media. Illustrative numerical examples, including
random initial data, random boundary conditions or random source terms and a
well-known benchmark problem, i.e. Mandel's problem are performed. The results
are in good agreement with the theoretical findings. Furthermore, we show
numerically that there is a connection between the inf-sup stability of
discretizations and the performance of the fixed-stress splitting scheme.
|
We revisit the challenging problem of finding an efficient Monte Carlo (MC)
algorithm solving the constrained evolution equations for the initial-state QCD
radiation. The type of the parton (quark, gluon) and the energy fraction x of
the parton exiting emission chain (entering hard process) are predefined, i.e.
constrained throughout the evolution. Such a constraint is mandatory for any
realistic MC for the initial state QCD parton shower. We add one important
condition: the MC algorithm must not require the a priori knowledge of the full
numerical exact solutions of the evolution equations, as is the case in the
popular ``Markovian MC for backward evolution''. Our aim is to find at least
one solution of this problem that would function in practice. Finding such a
solution seems to be definitely within the reach of the currently available
computer CPUs and the sophistication of the modern MC techniques. We describe
in this work the first example of an efficient solution of this kind. Its
numerical implementation is still restricted to the pure gluon-strahlung. As
expected, it is not in the class of the so-called Markovian MCs. For this
reason we refer to it as belonging to a class of non-Markovian MCs. We show
that numerical results of our new MC algorithm agree very well (to 0.2%) with
the results of the other MC program of our own (unconstrained Markovian) and
another non-MC program QCDnum16. This provides a proof of the existence of the
new class of MC techniques, to be exploited in the precision perturbative QCD
calculations for the Large Hadron Collider.
|
In this paper, we explore the interior dynamics of neutral and charged black
holes in $f(R)$ gravity. We transform $f(R)$ gravity from the Jordan frame into
the Einstein frame and simulate scalar collapses in flat, Schwarzschild, and
Reissner-Nordstr\"om geometries. In simulating scalar collapses in
Schwarzschild and Reissner-Nordstr\"om geometries, Kruskal and Kruskal-like
coordinates are used, respectively, with the presence of $f'$ and a physical
scalar field being taken into account. The dynamics in the vicinities of the
central singularity of a Schwarzschild black hole and of the inner horizon of a
Reissner-Nordstr\"om black hole is examined. Approximate analytic solutions for
different types of collapses are partially obtained. The scalar degree of
freedom $\phi$, transformed from $f'$, plays a similar role as a physical
scalar field in general relativity. Regarding the physical scalar field in
$f(R)$ case, when $d\phi/dt$ is negative (positive), the physical scalar field
is suppressed (magnified) by $\phi$, where $t$ is the coordinate time. For dark
energy $f(R)$ gravity, inside black holes, gravity can easily push $f'$ to $1$.
Consequently, the Ricci scalar $R$ becomes singular, and the numerical
simulation breaks down. This singularity problem can be avoided by adding an
$R^2$ term to the original $f(R)$ function, in which case an infinite Ricci
scalar is pushed to regions where $f'$ is also infinite. On the other hand, in
collapse for this combined model, a black hole, including a central
singularity, can be formed. Moreover, under certain initial conditions, $f'$
and $R$ can be pushed to infinity as the central singularity is approached.
Therefore, the classical singularity problem, which is present in general
relativity, remains in collapse for this combined model.
|
We consider the finite horizon continuous reinforcement learning problem. Our
contribution is three-fold. First,we give a tractable algorithm based on
optimistic value iteration for the problem. Next,we give a lower bound on
regret of order $\Omega(T^{2/3})$ for any algorithm discretizes the state
space, improving the previous regret bound of $\Omega(T^{1/2})$ of Ortner and
Ryabko \cite{contrl} for the same problem. Next,under the assumption that the
rewards and transitions are H\"{o}lder Continuous we show that the upper bound
on the discretization error is $const.Ln^{-\alpha}T$. Finally,we give some
simple experiments to validate our propositions.
|
Charge density waves are thought to be common in two-dimensional electron
systems in quantizing magnetic fields. Such phases are formed by the
quasiparticles of the topmost occupied Landau level when it is partially
filled. One class of charge density wave phases can be described as electron
solids. In weak magnetic fields (at high Landau levels) solids with many
particles per unit cell - bubble phases - predominate. In strong magnetic
fields (at the lowest Landau level) only crystals with one particle per unit
cell - Wigner crystals - can form. Experimental identification of these phases
is facilitated by the fact that even a weak disorder influences their dc and ac
magnetotransport in a very specific way. In the ac domain, a range of
frequencies appears where the electromagnetic response is dominated by
magnetophonon collective modes. The effect of disorder is to localize the
collective modes and to create an inhomogeneously broadened absorption line,
the pinning mode. In recent microwave experiments pinning modes have been
discovered both at the lowest and at high Landau levels. We present the theory
of the pinning mode for a classical two-dimensional electron crystal
collectively pinned by weak impurities. We show that long-range Coulomb
interaction causes a dramatic line narrowing, in qualitative agreement with the
experiments.
|
We investigate the collider signatures of heavy, long-lived, neutral
particles that decay to charged particles plus missing energy. Specifically, we
focus on the case of a neutralino NLSP decaying to Z and gravitino within the
context of General Gauge Mediation. We show that a combination of searches
using the inner detector and the muon spectrometer yields a wide range of
potential early LHC discoveries for NLSP lifetimes ranging from 10^(-1)-10^5
mm. We further show that events from Z(l+l-) can be used for detailed kinematic
reconstruction, leading to accurate determinations of the neutralino mass and
lifetime. In particular, we examine the prospects for detailed event study at
ATLAS using the ECAL (making use of its timing and pointing capabilities)
together with the TRT, or using the muon spectrometer alone. Finally, we also
demonstrate that there is a region in parameter space where the Tevatron could
potentially discover new physics in the delayed Z(l+l-)+MET channel. While our
discussion centers on gauge mediation, many of the results apply to any
scenario with a long-lived neutral particle decaying to charged particles.
|
Braided Thompson's groups are finitely presented groups introduced by Brin
and Dehornoy which contain the ordinary braid groups $B_n$, the finitary braid
group $B_{\infty}$ and Thompson's group $F$ as subgroups. We describe some of
the metric properties of braided Thompson's groups and give upper and lower
bounds for word length in terms of the number of strands and the number of
crossings in the diagrams used to represent elements.
|
Linearizability is a standard correctness criterion for concurrent
algorithms, typically proved by establishing the algorithms' linearization
points. However, relying on linearization points leads to proofs that are
implementation-dependent, and thus hinder abstraction and reuse. In this paper
we show that one can develop more declarative proofs by foregoing linearization
points and instead relying on a technique of axiomatization of visibility
relations. While visibility relations have been considered before, ours is the
first study where the challenge is to formalize the helping nature of the
algorithms. In particular, we show that by axiomatizing the properties of
separation between events that contain bunches of help requests, we can extract
what is common for high-level understanding of several descriptor-based helping
algorithms of Harris et al. (RDCSS, MCAS, and optimizations), and produce novel
proofs of their linearizability that share significant components.
|
General relativity predicts the existence of closed timelike curves (CTCs),
along which an object could travel to its own past. A consequence of CTCs is
the failure of determinism, even for classical systems: one initial condition
can result in multiple evolutions. Here we introduce a new quantum formulation
of a classic example, where a billiard ball can travel along two possible
trajectories: one unperturbed and one, along a CTC, where it collides with its
past self. Our model includes a vacuum state, allowing the ball to be present
or absent on each trajectory, and a clock, which provides an operational way to
distinguish the trajectories. We apply the two foremost quantum theories of
CTCs to our model: Deutsch's model (D-CTCs) and postselected teleportation
(P-CTCs). We find that D-CTCs reproduce the classical solution multiplicity in
the form of a mixed state, while P-CTCs predict an equal superposition of the
two trajectories, supporting a conjecture by Friedman et al. [Phys. Rev. D 42,
1915 (1990)].
|
We study an integrable spin chain with an alternating array of spins S=1/2, 1
in external magnetic fields using the Bethe ansatz exact solution. The
calculated magnetization possesses a cusp structure at a critical magnetic
field H=H_{C}, at which the specific heat shows a divergence property. We also
calculate finite-size corrections to the energy spectrum, and obtain the
critical exponents of correlation functions with the use of conformal field
theory (CFT). Low-energy properties of the model are described by two c=1 U(1)
CFTs in H<H_{C} and one c=1 U(1) CFT in H>H_{C}.
|
We develop further the implementation and analysis of Kac boundary conditions
in the general logarithmic minimal models ${\cal LM}(p,p')$ with $1\le p<p'$
and $p,p'$ coprime. Working in a strip geometry, we consider the $(r,s)$
boundary conditions, which are organized into infinitely extended Kac tables
labeled by $r,s=1,2,3,...$. They are conjugate to Virasoro Kac representations
with conformal dimensions $\Delta_{r,s}$ given by the usual Kac formula. On a
finite strip of width $N$, built from a square lattice, the associated
integrable boundary conditions are constructed by acting on the vacuum $(1,1)$
boundary with an $s$-type seam of width $s-1$ columns and an $r$-type seam of
width $\rho-1$ columns. The $r$-type seam contains an arbitrary boundary field
$\xi$. The usual fusion construction of the $r$-type seam relies on the
existence of Wenzl-Jones projectors restricting its application to
$r\le\rho<p'$. This limitation was recently removed by Pearce, Rasmussen and
Villani who further conjectured that the conformal boundary conditions labeled
by $r$ are realized, in particular, for $\rho=\rho(r)=\lfloor
\frac{rp'}{p}\rfloor$. In this paper, we confirm this conjecture by performing
extensive numerics on the commuting double row transfer matrices and their
associated quantum Hamiltonian chains. Letting $[x]$ denote the fractional
part, we fix the boundary field to the specialized values $\xi=\frac{\pi}{2}$
if $[\frac{\rho}{p'}]=0$ and $\xi=[\frac{\rho p}{p'}]\frac{\pi}{2}$ otherwise.
For these boundary conditions, we obtain the Kac conformal weights
$\Delta_{r,s}$ by numerically extrapolating the finite-size corrections to the
lowest eigenvalue of the quantum Hamiltonians out to sizes $N\le 32-\rho-s$.
Additionally, by solving local inversion relations, we obtain general analytic
expressions for the boundary free energies allowing for more accurate estimates
of the conformal data.
|
Feedback from active galactic nuclei (AGN) is widely considered to be the
main driver in regulating the growth of massive galaxies through heating or
driving gas out of the galaxy, preventing further increase in stellar mass.
Observational proof for this scenario has, however, been scarce. We have
assembled a sample of 132 radio-quiet type-2 and red AGN at 0.1<z<1. We measure
the kinematics of the AGN-ionized gas, the host galaxies' stellar masses and
star formation rates and investigate the relationships between AGN
luminosities, specific star formation rates (sSFR) and outflow strengths W90 --
the 90\% velocity width of the [OIII]5007 line power and a proxy for the
AGN-driven outflow speed. Outflow strength is independent of sSFR for AGN
selected on their mid-IR luminosity, in agreement with previous work
demonstrating that star formation is not sufficient to produce the observed
ionized gas outflows which have to be powered by AGN activity. More
importantly, we find a negative correlation between W90 and sSFR in the AGN
hosts with the highest SFRs, i.e., with the highest gas content, where
presumably the coupling of the AGN-driven wind to the gas is strongest. This
implies that AGN with strong outflow signatures are hosted in galaxies that are
more `quenched' than galaxies with weaker outflow signatures. Despite the
galaxies' high SFRs, we demonstrate that the outflows are not star-formation
driven but indeed due to AGN-powering. This observation is consistent with the
AGN having a net suppression, `negative' impact, through feedback on the
galaxies' star formation history.
|
Quantum illumination can utilize entangled light to detect the
low-reflectivity target that is hidden in a bright thermal background. This
technique is applied to the detection of an object in the curved spacetime of
the Earth, in order to explore how the curvature of spacetime affects quantum
illumination. It is found that the spatial quantum illumination with entangled
state transmitter outperforms that with coherent-state transmitter in the
near-Earth curved spacetime. Moreover, either the quantum illumination system
or the coherent-state system is employed, and gravity can enhance the spacetime
target detection by reducing the thermal signal at the receiver. Besides, our
model in principle can be applied to microwave quantum illumination and thus
provides, to some degree, a theoretical foundation for the upcoming spatial
quantum radar technologies.
|
A diffusion-limited aggregation process, in which clusters coalesce by means
of 3-particle reaction, A+A+A->A, is investigated. In one dimension we give a
heuristic argument that predicts logarithmic corrections to the mean-field
asymptotic behavior for the concentration of clusters of mass $m$ at time $t$,
$c(m,t)~m^{-1/2}(log(t)/t)^{3/4}$, for $1 << m << \sqrt{t/log(t)}$. The total
concentration of clusters, $c(t)$, decays as $c(t)~\sqrt{log(t)/t}$ at $t -->
\infty$. We also investigate the problem with a localized steady source of
monomers and find that the steady-state concentration $c(r)$ scales as
$r^{-1}(log(r))^{1/2}$, $r^{-1}$, and $r^{-1}(log(r))^{-1/2}$, respectively,
for the spatial dimension $d$ equal to 1, 2, and 3. The total number of
clusters, $N(t)$, grows with time as $(log(t))^{3/2}$, $t^{1/2}$, and
$t(log(t))^{-1/2}$ for $d$ = 1, 2, and 3. Furthermore, in three dimensions we
obtain an asymptotic solution for the steady state cluster-mass distribution:
$c(m,r) \sim r^{-1}(log(r))^{-1}\Phi(z)$, with the scaling function
$\Phi(z)=z^{-1/2}\exp(-z)$ and the scaling variable $z ~ m/\sqrt{log(r)}$.
|
We propose an inverse reinforcement learning (IRL) approach using Deep
Q-Networks to extract the rewards in problems with large state spaces. We
evaluate the performance of this approach in a simulation-based autonomous
driving scenario. Our results resemble the intuitive relation between the
reward function and readings of distance sensors mounted at different poses on
the car. We also show that, after a few learning rounds, our simulated agent
generates collision-free motions and performs human-like lane change behaviour.
|
Subsets and Splits
Filtered Text Samples
Retrieves 100 samples of text containing the specific phrase "You are a helpful assistant", providing limited insight into the dataset.
Helpful Assistant Text Samples
Returns a limited set of rows containing the phrase 'helpful assistant' in the text, providing basic filtering of relevant entries.