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In this paper we explain how the notion of ''weak Dirichlet process'' is the
suitable generalization of the one of semimartingale with jumps. For such a
process we provide a unique decomposition which is new also for
semimartingales: in particular we introduce ''characteristics'' for weak
Dirichlet processes. We also introduce a weak concept (in law) of finite
quadratic variation. We investigate a set of new useful chain rules and we
discuss a general framework of (possibly path-dependent with jumps) martingale
problems with a set of examples of SDEs with jumps driven by a distributional
drift.
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One of the main features of superfluids is the presence of topological
defects with quantised circulation. These objects are known as quantum vortices
and exhibit a hydrodynamic behaviour. Nowadays, particles are the main
experimental tool used to visualise quantum vortices and to study their
dynamics. We use a self-consistent model based on the three-dimensional
Gross-Pitaevskii (GP) equation to explore theoretically and numerically the
attractive interaction between particles and quantised vortices at very low
temperature. Particles are described as localised potentials depleting the
superfluid and following Newtonian dynamics. We are able to derive analytically
a reduced central-force model that only depends on the classical degrees of
freedom of the particle. Such model is found to be consistent with the GP
simulations. We then generalised the model to include deformations of the
vortex filament. The resulting long-range mutual interaction qualitatively
reproduces the observed generation of a cusp on the vortex filament during the
particle approach. Moreover, we show that particles can excite Kelvin waves on
the vortex filament through a resonance mechanism even if they are still far
from it.
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It is usually assumed that the inflationary fluctuations start from the
Bunch-Davies (BD) vacuum and the $i\varepsilon$ prescription is used when
interactions are calculated. We show that those assumptions can be verified
explicitly by calculating the loop corrections to the inflationary two-point
and three-point correlation functions. Those loop corrections can be resumed to
exponential factors, which suppress non-BD coefficients and behave as the
$i\varepsilon$ factor for the case of the BD initial condition. A new technique
of loop chain diagram resummation is developed for this purpose. For the non-BD
initial conditions which is setup at finite time and has not fully decayed,
explicit correction to the two-point and three-point correlation functions are
calculated. Especially, non-Gaussianity in the folded limit is regularized due
to the interactions.
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The physics of strongly correlated quantum particles within a flat band was
originally explored as a route to itinerant ferromagnetism and, indeed, a
celebrated theorem by Lieb rigorously establishes that the ground state of the
repulsive Hubbard model on a bipartite lattice with unequal number of sites in
each sublattice must have nonzero spin S at half-filling. Recently, there has
been interest in Lieb geometries due to the possibility of novel topological
insulator, nematic, and Bose-Einstein condensed (BEC) phases. In this paper, we
extend the understanding of the attractive Hubbard model on the Lieb lattice by
using Determinant Quantum Monte Carlo to study real space charge and pair
correlation functions not addressed by the Lieb theorems.
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The newly developed "strongly constrained and appropriately normed" (SCAN)
meta-generalized-gradient approximation (meta-GGA) can generally improve over
the non-empirical Perdew-Burke-Ernzerhof (PBE) GGA not only for strong chemical
bonding, but also for the intermediate-range van der Waals (vdW) interaction.
However, the long-range vdW interaction is still missing. To remedy this, we
propose here pairing SCAN with the non-local correlation part from the rVV10
vdW density functional, with only two empirical parameters. The resulting
SCAN+rVV10 yields excellent geometric and energetic results not only for
molecular systems, but also for solids and layered-structure materials, as well
as the adsorption of benzene on coinage metal surfaces. Especially, SCAN+rVV10
outperforms all current methods with comparable computational efficiencies,
accurately reproducing the three most fundamental parameters---the inter-layer
binding energies, inter-, and intra-layer lattice constants---for 28
layered-structure materials. Hence, we have achieved with SCAN+rVV10 a
promising vdW density functional for general geometries, with minimal
empiricism.
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The advent of Transformers marked a significant breakthrough in sequence
modelling, providing a highly performant architecture capable of leveraging GPU
parallelism. However, Transformers are computationally expensive at inference
time, limiting their applications, particularly in low-resource settings (e.g.,
mobile and embedded devices). Addressing this, we (1) begin by showing that
attention can be viewed as a special Recurrent Neural Network (RNN) with the
ability to compute its \textit{many-to-one} RNN output efficiently. We then (2)
show that popular attention-based models such as Transformers can be viewed as
RNN variants. However, unlike traditional RNNs (e.g., LSTMs), these models
cannot be updated efficiently with new tokens, an important property in
sequence modelling. Tackling this, we (3) introduce a new efficient method of
computing attention's \textit{many-to-many} RNN output based on the parallel
prefix scan algorithm. Building on the new attention formulation, we (4)
introduce \textbf{Aaren}, an attention-based module that can not only (i) be
trained in parallel (like Transformers) but also (ii) be updated efficiently
with new tokens, requiring only constant memory for inferences (like
traditional RNNs). Empirically, we show Aarens achieve comparable performance
to Transformers on $38$ datasets spread across four popular sequential problem
settings: reinforcement learning, event forecasting, time series
classification, and time series forecasting tasks while being more time and
memory-efficient.
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The spin dynamics of the ferromagnetic Kondo lattice CeRuPO is investigated
by Electron Spin Resonance (ESR) at microwave frequencies of 1, 9.4, and
34~GHz. The measured resonance can be ascribed to a rarely observed bulk Ce3+
resonance in a metallic Ce compound and can be followed below the ferromagnetic
transition temperature Tc=14 K. At T>Tc the interplay between the RKKY-exchange
interaction and the crystal electric field anisotropy determines the ESR
parameters. Near Tc the spin relaxation rate is influenced by the critical
fluctuations of the order parameter.
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As the complexity of quantum systems such as quantum bit arrays increases,
efforts to automate expensive tuning are increasingly worthwhile. We
investigate machine learning based tuning of gate arrays using the CMA-ES
algorithm for the case study of Majorana wires with strong disorder. We find
that the algorithm is able to efficiently improve the topological signatures,
learn intrinsic disorder profiles, and completely eliminate disorder effects.
For example, with only 20 gates, it is possible to fully recover Majorana zero
modes destroyed by disorder by optimizing gate voltages.
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We introduce a scheme for constructing partly occupied, maximally localized
Wannier functions (WFs) for both molecular and periodic systems. Compared to
the traditional occupied WFs the partly occupied WFs posses improved symmetry
and localization properties achieved through a bonding-antibonding closing
procedure. We demonstrate the equivalence between bonding-antibonding closure
and the minimization of the average spread of the WFs in the case of a benzene
molecule and a linear chain of Pt atoms. The general applicability of the
method is demonstrated through the calculation of WFs for a metallic system
with an impurity: a Pt wire with a hydrogen molecular bridge.
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We study the prospects of detecting continuous gravitational waves (CGWs)
from spinning neutron stars (NSs), gravitationally lensed by the galactic
supermassive black hole. Assuming various astrophysically motivated spatial
distributions of galactic NSs, we find that CGW signals from a few ($\sim 0-6$)
neutron stars should be strongly lensed. Lensing will produce two copies of the
signal (with time delays of seconds to minutes) that will interfere with each
other. The relative motion of the NS with respect to the lensing optical axis
will change the interference pattern, which will help us to identify a lensed
signal. Accounting for the magnifications and time delays of the lensed
signals, we investigate their detectability by ground-based detectors.
Modelling the spin distribution of NSs based on that of known pulsars and
assuming an ellipticity of $\epsilon = 10^{-7}$, lensed CGWs are unlikely to be
detectable by LIGO and Virgo in realistic searches involving
$\mathcal{O}(10^{12})$ templates. However, third generation detectors have a
$\sim 2-51\%$ probability of detecting at least one lensed CGW signal. For an
ellipticity of $\epsilon = 10^{-8}$, the detection probability reduces to $\sim
0-18 \, \% $. Though rare, such an observation will enable interesting probes
of the supermassive black hole and its environment.
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In this article we are describing a new algorithm for detecting and
validating partial horizontal gene transfers (HGT). The presented algorithm is
based on a sliding window procedure which analyzes fragments of the given
multiple sequence alignment. A bootstrap procedure incorporated in our method
can be used to estimate the support of each inferred partial HGT. The new
algorithm can be also applied to confirm or discard complete (i.e.,
traditional) horizontal gene transfers detected by any HGT inferring algorithm.
While working on a full-genome scale, the introduced algorithm can be used to
assess the level of mosaicism of the whole species genomes as well as the rates
of complete and partial HGT underlying the evolution of the considered set of
species.
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We show that if $n\geq 1$, $\Omega\subset \mathbb R^{n+1}$ is a connected
domain with porous boundary, and $E\subset \partial\Omega$ is a set of finite
and positive Hausdorff $H^{n}$-measure upon which the harmonic measure $\omega$
is absolutely continuous with respect to $H^{n}$, then $\omega|_E$ is
concentrated on an $n$-rectifiable set.
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Matrix representations of the Maxwell equations are well-known. However, all
these representations lack an exactness or/and are given in terms of a {\em
pair} of matrix equations. We present a matrix representation of the Maxwell
equation in presence of sources in a medium with varying permittivity and
permeability. It is shown that such a representation necessarily requires $8
\times 8$ matrices and an explicit representation for them is presented.
|
High-throughput ab-initio calculations, cluster expansion techniques and
thermodynamic modeling have been synergistically combined to characterize the
binodal and the spinodal decompositions features in the pseudo-binary lead
chalcogenides PbSe-PbTe, PbS-PbTe, and PbS-PbSe. While our results agree with
the available experimental data, our consolute temperatures substantially
improve with respect to previous computational modeling. The computed phase
diagrams corroborate that the formation of spinodal nanostructures causes low
thermal conductivities in these alloys. The presented approach, making a
rational use of online quantum repositories, can be extended to study
thermodynamical and kinetic properties of materials of technological interest.
|
We report on the current-induced magnetization switching of a three-terminal
perpendicular magnetic tunnel junction by spin-orbit torque and the read-out
using the tunnelling magnetoresistance (TMR) effect. The device is composed of
a perpendicular Ta/FeCoB/MgO/FeCoB stack on top of a Ta current line. The
magnetization of the bottom FeCoB layer can be switched reproducibly by the
injection of current pulses with density $5\times10^{11}$ A/m$^2$ in the Ta
layer in the presence of an in-plane bias magnetic field, leading to the
full-scale change of the TMR signal. Our work demonstrates the proof of concept
of a perpendicular spin-orbit torque magnetic memory cell.
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We develop two N=2 superfield formulations of free equations of motion for
the joint model of all D=4 massless higher-superspin fields in generating form.
The explicit Osp(2|4) supersymmetry is achieved without exploiting the harmonic
superspace, and with adding no auxiliary component fields to those of N=1
superfields. The formulations are developed in two different Osp(2|4)
homogeneous superspaces which have a structure of a fibre bundle over the
standard D=4 AdS superspace, with dimensions (7|4) and (7|8). The N=2 covariant
derivatives in these spaces are expressed in terms of N=1 ones which gives
simple rules for component analysis.
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Introductory lectures on the Kraichnan model of passive advection
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Emerging trends in smartphones, online maps, social media, and the resulting
geo-located data, provide opportunities to collect traces of people's
socio-economical activities in a much more granular and direct fashion,
triggering a revolution in empirical research. These vast mobile data offer new
perspectives and approaches for measurements of economic dynamics and are
broadening the research fields of social science and economics. In this paper,
we explore the potential of using mobile big data for measuring economic
activities of China. Firstly, We build indices for gauging employment and
consumer trends based on billions of geo-positioning data. Secondly, we advance
the estimation of store offline foot traffic via location search data derived
from Baidu Maps, which is then applied to predict revenues of Apple in China
and detect box-office fraud accurately. Thirdly, we construct consumption
indicators to track the trends of various industries in service sector, which
are verified by several existing indicators. To the best of our knowledge, we
are the first to measure the second largest economy by mining such
unprecedentedly large scale and fine granular spatial-temporal data. Our
research provides new approaches and insights on measuring economic activities.
|
We present the analysis of the muon events with all muon multiplicities
collected during 21804 hours of operation of the first LVD tower. The measured
angular distribution of muon intensity has been converted to the `depth --
vertical intensity' relation in the depth range from 3 to 12 km w.e.. The
analysis of this relation allowed to derive the power index, $\gamma$, of the
primary all-nucleon spectrum: $\gamma=2.78 \pm 0.05$. The `depth -- vertical
intensity' relation has been converted to standard rock and the comparison with
the data of other experiments has been done. We present also the derived
vertical muon spectrum at sea level.
|
For the first time, baryon-antibaryon photoproduction in the reaction $\gamma
p \to \Lambda \bar{\Lambda} p$ has been observed at photon energies from
threshold near 4.9 GeV to 11.6 GeV. The measurements are in progress with the
GlueX spectrometer in Hall D at Jefferson Lab. We describe here the apparatus
and methods used to make these measurements and outline the physics goals of
the work. Some of the newly-seen reaction phenomenology is presented.
|
To date publish of a giant social network jointly from different parties is
an easier collaborative approach. Agencies and researchers who collect such
social network data often have a compelling interest in allowing others to
analyze the data. In many cases the data describes relationships that are
private and sharing the data in full can result in unacceptable disclosures.
Thus, preserving privacy without revealing sensitive information in the social
network is a serious concern. Recent developments for preserving privacy using
anonymization techniques are focused on relational data only. Preserving
privacy in social networks against neighborhood attacks is an initiation which
uses the definition of privacy called k-anonymity. k-anonymous social network
still may leak privacy under the cases of homogeneity and background knowledge
attacks. To overcome, we find a place to use a new practical and efficient
definition of privacy called ldiversity. In this paper, we take a step further
on preserving privacy in collaborative social network data with algorithms and
analyze the effect on the utility of the data for social network analysis.
|
We provide groupoid models for Toeplitz and Cuntz-Krieger algebras of
topological higher-rank graphs. Extending the groupoid models used in the
theory of graph algebras and topological dynamical systems to our setting, we
prove results on essential freeness and amenability of the groupoids which
capture the existing theory, and extend results involving group crossed
products of graph algebras.
|
Compression schemes have been extensively used in Federated Learning (FL) to
reduce the communication cost of distributed learning. While most approaches
rely on a bounded variance assumption of the noise produced by the compressor,
this paper investigates the use of compression and aggregation schemes that
produce a specific error distribution, e.g., Gaussian or Laplace, on the
aggregated data. We present and analyze different aggregation schemes based on
layered quantizers achieving exact error distribution. We provide different
methods to leverage the proposed compression schemes to obtain
compression-for-free in differential privacy applications. Our general
compression methods can recover and improve standard FL schemes with Gaussian
perturbations such as Langevin dynamics and randomized smoothing.
|
We report the first laboratory and interstellar detection of the alpha-cyano
vinyl radical (H2CCCN). This species was produced in the laboratory by an
electric discharge of a gas mixture of vinyl cyanide, CH2CHCN, and Ne, and its
rotational spectrum was characterized using a Balle-Flygare narrowband-type
Fourier-transform microwave spectrometer operating in the frequency region of
8-40 GHz. The observed spectrum shows a complex structure due to tunneling
splittings between two torsional sublevels of the ground vibronic state, 0+ and
0-, derived from a large-amplitude inversion motion. In addition, the presence
of two equivalent hydrogen nuclei makes necessary to discern between ortho- and
para-H2CCCN. A least squares analysis reproduces the observed transition
frequencies with a standard deviation of ca. 3 kHz. Using the laboratory
predictions, this radical is detected in the cold dark cloud TMC-1 using the
Yebes 40m telescope and the QUIJOTE line survey. The 404-303 and 505-404
rotational transitions, composed of several hyperfine components, were observed
in the 31.0-50.4 GHz range. Adopting a rotational temperature of 6K we derive a
column density of (1.4+/-0.2)e11 cm-2 and (1.1+/-0.2)e11 cm-2 for ortho-H2CCCN
and para-H2CCCN, respectively. The reactions C + CH3CN, and perhaps also N +
CH2CCH, emerge as the most likely routes to H2CCCN in TMC-1.
|
Odometry forms an important component of many manned and autonomous systems.
In the rail industry in particular, having precise and robust odometry is
crucial for the correct operation of the Automatic Train Protection systems
that ensure the safety of high-speed trains in operation around the world. Two
problems commonly encountered in such odometry systems are miscalibration of
the wheel encoders and slippage of the wheels under acceleration and braking,
resulting in incorrect velocity estimates. This paper introduces an odometry
system that addresses these problems. It comprises of an Extended Kalman Filter
that tracks the calibration of the wheel encoders as state variables, and a
measurement pre-processing stage called Sensor Consensus Analysis (SCA) that
scales the uncertainty of a measurement based on how consistent it is with the
measurements from the other sensors. SCA uses the statistical z-test to
determine when an individual measurement is inconsistent with the other
measurements, and scales the uncertainty until the z-test passes. This system
is demonstrated on data from German Intercity-Express high-speed trains and it
is shown to successfully deal with errors due to miscalibration and wheel slip.
|
A common problem in various applications is the additive decomposition of the
output of a function with respect to its input variables. Functions with binary
arguments can be axiomatically decomposed by the famous Shapley value. For the
decomposition of functions with real arguments, a popular method is the
pointwise application of the Shapley value on the domain. However, this
pointwise application largely ignores the overall structure of functions. In
this paper, axioms are developed which fully preserve functional structures and
lead to unique decompositions for all Borel measurable functions.
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Simple models are constructed for "acceleressence" dark energy: the latent
heat of a phase transition occurring in a hidden sector governed by the seesaw
mass scale v^2/M_Pl, where v is the electroweak scale and M_Pl the
gravitational mass scale. In our models, the seesaw scale is stabilized by
supersymmetry, implying that the LHC must discover superpartners with a
spectrum that reflects a low scale of fundamental supersymmetry breaking.
Newtonian gravity may be modified by effects arising from the exchange of
fields in the acceleressence sector whose Compton wavelengths are typically of
order the millimeter scale. There are two classes of models. In the first class
the universe is presently in a metastable vacuum and will continue to inflate
until tunneling processes eventually induce a first order transition. In the
simplest such model, the range of the new force is bounded to be larger than 25
microns in the absence of fine-tuning of parameters, and for couplings of order
unity it is expected to be \approx 100 microns. In the second class of models
thermal effects maintain the present vacuum energy of the universe, but on
further cooling, the universe will "soon" smoothly relax to a matter dominated
era. In this case, the range of the new force is also expected to be of order
the millimeter scale or larger, although its strength is uncertain. A firm
prediction of this class of models is the existence of additional energy
density in radiation at the eV era, which can potentially be probed in
precision measurements of the cosmic microwave background. An interesting
possibility is that the transition towards a matter dominated era has occurred
in the very recent past, with the consequence that the universe is currently
decelerating.
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Graph coloring is one of the most famous computational problems with
applications in a wide range of areas such as planning and scheduling, resource
allocation, and pattern matching. So far coloring problems are mostly studied
on static graphs, which often stand in stark contrast to practice where data is
inherently dynamic and subject to discrete changes over time. A temporal graph
is a graph whose edges are assigned a set of integer time labels, indicating at
which discrete time steps the edge is active. In this paper we present a
natural temporal extension of the classical graph coloring problem. Given a
temporal graph and a natural number $\Delta$, we ask for a coloring sequence
for each vertex such that (i) in every sliding time window of $\Delta$
consecutive time steps, in which an edge is active, this edge is properly
colored (i.e. its endpoints are assigned two different colors) at least once
during that time window, and (ii) the total number of different colors is
minimized. This sliding window temporal coloring problem abstractly captures
many realistic graph coloring scenarios in which the underlying network changes
over time, such as dynamically assigning communication channels to moving
agents. We present a thorough investigation of the computational complexity of
this temporal coloring problem. More specifically, we prove strong
computational hardness results, complemented by efficient exact and
approximation algorithms. Some of our algorithms are linear-time
fixed-parameter tractable with respect to appropriate parameters, while others
are asymptotically almost optimal under the Exponential Time Hypothesis (ETH).
|
We describe a combined halo model to constrain the distribution of neutral
hydrogen (HI) in the post-reionization universe. We combine constraints from
the various probes of HI at different redshifts: the low-redshift 21-cm
emission line surveys, intensity mapping experiments at intermediate redshifts,
and the Damped Lyman-Alpha (DLA) observations at higher redshifts. We use a
Markov Chain Monte Carlo (MCMC) approach to combine the observations and place
constraints on the free parameters in the model. Our best-fit model involves a
relation between neutral hydrogen mass $M_{\rm HI}$ and halo mass $M$ with a
non-unit slope, and an upper and a lower cutoff. We find that the model fits
all the observables but leads to an underprediction of the bias parameter of
DLAs at $z \sim 2.3$. We also find indications of a possible tension between
the HI column density distribution and the mass function of HI-selected
galaxies at $z\sim 0$. We provide the central values of the parameters of the
best-fit model so derived. We also provide a fitting form for the derived
evolution of the concentration parameter of HI in dark matter haloes, and
discuss the implications for the redshift evolution of the HI-halo mass
relation.
|
The Meridional Overturning Circulation (MOC) is a system of surface and deep
currents encompassing all ocean basins, crucial to the Earth's climate.
Detecting potential climatic changes in the MOC first requires a careful
characterisation of its inherent variability. Key components of the MOC are the
Atlantic MOC (AMOC) and the Antarctic Circumpolar Current (ACC). The role of
boundary properties in determining the AMOC and ACC is investigated, as a
function of cross-sectional coordinate and depth, using a hierarchy of general
circulation models. The AMOC is decomposed as the sum of near-surface Ekman,
depth-independent bottom velocity and eastern and western boundary density
components. The decomposition proves a useful low-dimensional characterisation
of the full 3-D overturning circulation. The estimated total basin-wide AMOC
overturning streamfunction, reconstructed using only boundary information, is
in good agreement with direct calculations of the overturning using meridional
velocities. The time-mean maximum overturning streamfunction is relatively
constant with latitude, despite its underlying boundary contributions varying
considerably, especially in the northern hemisphere. Applying a similar
decomposition diagnostic to the ACC provides insight into the differences
between model simulations, revealing spatial resolution dependence of ACC
transport through the Drake Passage. All models exhibit a weak ACC compared to
observations. Density maps along sloping ocean boundaries are produced,
incorporating the western and eastern Atlantic boundaries and the Antarctic
coastline. Isopycnals are flat over long portions of eastern ocean boundaries,
and slope linearly on western boundaries. Results of this thesis serve to
indicate the importance of boundary information in characterising the AMOC and
the ACC, and the relative simplicity of along-sloping-boundary density
structure.
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In this work a comparison between different galaxy luminosity function
estimators by means of Monte-Carlo simulations is presented. The simulations
show that the C- method of Lynden-Bell (1971) and the STY method derived by
Sandage, Tammann & Yahil (1979) are the best estimators to measure the shape of
the luminosity function. The simulations also show that the STY estimator has a
bias such that the faint-end slope is underestimated for steeper inclinations
of the Schechter Function, and that this bias becomes quite severe when the
sample contains only a few hundred objects. Overall, the C- is the most robust
estimator, being less affected by different values of the faint end slope of
the Schechter parameterization and sample size. The simulations are also used
to compare different estimators of the luminosity function normalization. They
demonstrate that most methods bias the recovered mean density towards values
which are about 20% lower than the input value.
|
Optical Character Recognition (OCR), the task of extracting textual
information from scanned documents is a vital and broadly used technology for
digitizing and indexing physical documents. Existing technologies perform well
for clean documents, but when the document is visually degraded, or when there
are non-textual elements, OCR quality can be greatly impacted, specifically due
to erroneous detections. In this paper we present an improved detection network
with a masking system to improve the quality of OCR performed on documents. By
filtering non-textual elements from the image we can utilize document-level OCR
to incorporate contextual information to improve OCR results. We perform a
unified evaluation on a publicly available dataset demonstrating the usefulness
and broad applicability of our method. Additionally, we present and make
publicly available our synthetic dataset with a unique hard-negative component
specifically tuned to improve detection results, and evaluate the benefits that
can be gained from its usage
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In this note we analyse the relation between the triple-pomeron and
Good-Walker formalisms for diffractive excitation in DIS and hadronic
collisions. In both approaches gap events are interpreted as the shadow of
absorption into inelastic channels. We here argue that the two formalisms are
just different views of the same phenomenon. We first demonstrate how this
relation works in a simple toy model, and then show how the relevant features
of the toy model are also realized in real perturbative QCD.
|
Detecting and analyzing various defect types in semiconductor materials is an
important prerequisite for understanding the underlying mechanisms as well as
tailoring the production processes. Analysis of microscopy images that reveal
defects typically requires image analysis tasks such as segmentation and object
detection. With the permanently increasing amount of data that is produced by
experiments, handling these tasks manually becomes more and more impossible. In
this work, we combine various image analysis and data mining techniques for
creating a robust and accurate, automated image analysis pipeline. This allows
for extracting the type and position of all defects in a microscopy image of a
KOH-etched 4H-SiC wafer that was stitched together from approximately 40,000
individual images.
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Mixtures of polarised fermions of two different masses can form weakly-bound
clusters, such as dimers and trimers, that are universally described by the
scattering length between the heavy and light fermions. We use the resonating
group method to investigate the low-energy scattering processes involving
dimers or trimers. The method reproduces approximately the known particle-dimer
and dimer-dimer scattering lengths. We use it to estimate the trimer-trimer
scattering length, which is presently unknown, and find it to be positive.
|
Fontanari et al introduced [Phys. Rev. Lett. 91, 218101 (2003)] a model for
studying the Muller's ratchet phenomenon in growing asexual populations. They
studied two situations, either including or not a death probability for each
newborn, but were able to find analytical (recursive) expressions only in the
no-decay case. In this paper a branching process formalism is used to find
recorrence equations that generalize the analytical results of the original
paper besides confirming the interesting effects their simulations revealed.
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Few-shot Named Entity Recognition (NER) exploits only a handful of
annotations to identify and classify named entity mentions. Prototypical
network shows superior performance on few-shot NER. However, existing
prototypical methods fail to differentiate rich semantics in other-class words,
which will aggravate overfitting under few shot scenario. To address the issue,
we propose a novel model, Mining Undefined Classes from Other-class (MUCO),
that can automatically induce different undefined classes from the other class
to improve few-shot NER. With these extra-labeled undefined classes, our method
will improve the discriminative ability of NER classifier and enhance the
understanding of predefined classes with stand-by semantic knowledge.
Experimental results demonstrate that our model outperforms five
state-of-the-art models in both 1-shot and 5-shots settings on four NER
benchmarks. We will release the code upon acceptance. The source code is
released on https: //github.com/shuaiwa16/OtherClassNER.git.
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Collective plasmon excitations in solids that result from the process of
photoemission are an important area of fundamental research. In this study, we
identify a significant number ($n$) of multiple bulk plasmons ($n\omega_p$) in
the hard x-ray photoelectron spectra of the core levels and valence bands (VBs)
of two well-known, nearly free electron metals, aluminum (Al) and magnesium
(Mg). On the basis of earlier theoretical works, we estimate the contributions
of extrinsic, intrinsic, and interference processes to the intensities of 1$s$
to 2$s$ core level plasmons. The intrinsic contribution diminishes from 22% for
1$\omega_p$, to 4.4% for 2$\omega_p$, and becomes negligible thereafter (0.5%
for 3$\omega_p$). The extrinsic and intrinsic plasmon contributions do not vary
significantly across a broad range of photoelectron kinetic energies, and also
between the two metals (Al and Mg). The interference contribution varies from
negative to zero as $n$ increases. An asymmetric line shape is observed for the
bulk plasmons, which is most pronounced for 1$\omega_p$. Signature of the
surface plasmon is detected in normal emission, and it exhibits a significantly
increased intensity in the grazing emission. The VB spectra of Al and Mg, which
are dominated by $s$-like states, exhibit excellent agreement with the
calculated VB based on density functional theory. The VB exhibits four multiple
bulk plasmon peaks in the loss region, which are influenced by an intrinsic
process in addition to the extrinsic process. On a completely oxidized aluminum
surface, the relative intensity of the Al metal bulk plasmon remains nearly
unaltered, while the surface plasmon is completely attenuated.
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We reconstruct dark energy properties from two complementary supernova
datasets -- the newly released Gold+HST sample and SNLS. The results obtained
are consistent with standard $\Lambda$CDM model within $2\sigma$ error bars
although the Gold+HST data favour evolving dark energy slightly more than SNLS.
Using complementary data from baryon acoustic oscillations and the cosmic
microwave background to constrain dark energy, we find that our results in this
case are strongly dependent on the present value of the matter density
$\Omega_m$. Consequently, no firm conclusions regarding constancy or
variability of dark energy density can be drawn from these data alone unless
the value of $\Omega_m$ is known to an accuracy of a few percent. However,
possible variability is significantly restricted if this data is used in
conjunction with supernova data.
|
A central issue in the design of tokamaks or stellarators is the coils that
produce the external magnetic fields. The freedom that remains unstudied in the
design of coils is enormous. This freedom could be quickly studied
computationally at low cost with high reliability. In particular, the space
between toroidal field or modular coils that block access to the plasma chamber
could be increased by a large factor. This paper explains how this could be
done using the concept of current-potential patches that was developed in Todd
Elder's thesis.
|
We present a scheme for symmetric multiparty quantum state sharing of an
arbitrary $m$-qubit state with $m$ Greenberger-Horne-Zeilinger states following
some ideas from the controlled teleportation [Phys. Rev. A \textbf{72}, 02338
(2005)]. The sender Alice performs $m$ Bell-state measurements on her $2m$
particles and the controllers need only to take some single-photon product
measurements on their photons independently, not Bell-state measurements, which
makes this scheme more convenient than the latter. Also it does not require the
parties to perform a controlled-NOT gate on the photons for reconstructing the
unknown $m$-qubit state and it is an optimal one as its efficiency for qubits
approaches the maximal value.
|
We study multiple zeta values (MZVs) from the viewpoint of zeta-functions
associated with the root systems which we have studied in our previous papers.
In fact, the $r$-ple zeta-functions of Euler-Zagier type can be regarded as the
zeta-function associated with a certain sub-root system of type $C_r$. Hence,
by the action of the Weyl group, we can find new aspects of MZVs which imply
that the well-known formula for MZVs given by Hoffman and Zagier coincides with
Witten's volume formula associated with the above sub-root system of type
$C_r$. Also, from this observation, we can prove some new formulas which
especially include the parity results of double and triple zeta values. As
another important application, we give certain refinement of restricted sum
formulas, which gives restricted sum formulas among MZVs of an arbitrary depth
$r$ which were previously known only in the cases of depth $2,3,4$.
Furthermore, considering a sub-root system of type $B_r$ analogously, we can
give relevant analogues of the Hoffman-Zagier formula, parity results and
restricted sum formulas.
|
Presence-only records may provide data on the distributions of rare species,
but commonly suffer from large, unknown biases due to their typically haphazard
collection schemes. Presence-absence or count data collected in systematic,
planned surveys are more reliable but typically less abundant.
We proposed a probabilistic model to allow for joint analysis of
presence-only and survey data to exploit their complementary strengths. Our
method pools presence-only and presence-absence data for many species and
maximizes a joint likelihood, simultaneously estimating and adjusting for the
sampling bias affecting the presence-only data. By assuming that the sampling
bias is the same for all species, we can borrow strength across species to
efficiently estimate the bias and improve our inference from presence-only
data.
We evaluate our model's performance on data for 36 eucalypt species in
southeastern Australia. We find that presence-only records exhibit a strong
sampling bias toward the coast and toward Sydney, the largest city. Our
data-pooling technique substantially improves the out-of-sample predictive
performance of our model when the amount of available presence-absence data for
a given species is scarce.
If we have only presence-only data and no presence-absence data for a given
species, but both types of data for several other species that suffer from the
same spatial sampling bias, then our method can obtain an unbiased estimate of
the first species' geographic range.
|
Relativistic Riemannian superfluid hydrodynamics used in general relativity
to investigate superfluids in pulsars is extended to non-Riemannian background
spacetime endowed with Cartan torsion. From the Gross-Pitaeviskii (GP) it is
shown that in the weak field Cartan torsion approximation, the torsion vector
is orthogonal to the superfluid plane wave velocity. Torsion vector is also
shown to be aligned along the vortex direction in the superfluid. The
background torsion is shown to induce rotation on the fluid as happens with the
acoustic torsion in the analogue non-Riemannian non-relativistic superfluid
models. The torsion part of the current would be connected to the normal part
of the superfluid velocity while the Riemannian part of the velocity would be
connected to the superfluid velocity itself. Magnus effect and the rotation of
the superfluid are analysed. Since the Kalb-Ramond field is easily associated
with torsion our method seems to be equivalent to the vortex-cosmic string
relativistic superfluid method developed by Carter and Langlois to investigate
rotating neutron stars.
|
We present a semi-parametric approach to photographic image synthesis from
semantic layouts. The approach combines the complementary strengths of
parametric and nonparametric techniques. The nonparametric component is a
memory bank of image segments constructed from a training set of images. Given
a novel semantic layout at test time, the memory bank is used to retrieve
photographic references that are provided as source material to a deep network.
The synthesis is performed by a deep network that draws on the provided
photographic material. Experiments on multiple semantic segmentation datasets
show that the presented approach yields considerably more realistic images than
recent purely parametric techniques. The results are shown in the supplementary
video at https://youtu.be/U4Q98lenGLQ
|
Some aspects of light-like compactifications of superstring theory and their
implications for the matrix model of M-theory are discussed.
|
We provide a generalization of the Lie algebra of conformal Killing vector
fields to conformal Killing-Yano forms. A new Lie bracket for conformal
Killing-Yano forms that corresponds to slightly modified Schouten-Nijenhuis
bracket of differential forms is proposed. We show that conformal Killing-Yano
forms satisfy a graded Lie algebra in constant curvature manifolds. It is also
proven that normal conformal Killing-Yano forms in Einstein manifolds also
satisfy a graded Lie algebra. The constructed graded Lie algebras reduce to the
graded Lie algebra of Killing-Yano forms and the Lie algebras of conformal
Killing and Killing vector fields in special cases.
|
We study the applicability of composite fermion theory to electrons in
two-dimensional parabolically-confined quantum dots in a strong perpendicular
magnetic field in the limit of low Zeeman energy. The non-interacting composite
fermion spectrum correctly specifies the primary features of this system.
Additional features are relatively small, indicating that the residual
interaction between the composite fermions is weak. \footnote{Published in
Phys. Rev. B {\bf 52}, 2798 (1995).}
|
The present article analyses the impact on cosmology, in particular on the
evolution of cosmological perturbations, of the existence of extra-dimensions.
The model considered here is that of a five-dimensional Anti-de Sitter
spacetime where ordinary matter is confined to a brane-universe. The
homogeneous cosmology is recalled. The equations governing the evolution of
cosmological perturbations are presented in the most transparent way: they are
rewritten in a form very close to the equations of standard cosmology with two
types of corrections: a. corrections due to the unconventional evolution of the
homogeneous solution, which change the background-dependent coefficients of the
equations; b. corrections due to the curvature along the fifth dimension, which
act as source terms in the evolution equations.
|
Determining the poverty levels of various regions throughout the world is
crucial in identifying interventions for poverty reduction initiatives and
directing resources fairly. However, reliable data on global economic
livelihoods is hard to come by, especially for areas in the developing world,
hampering efforts to both deploy services and monitor/evaluate progress. This
is largely due to the fact that this data is obtained from traditional
door-to-door surveys, which are time consuming and expensive. Overhead
satellite imagery contain characteristics that make it possible to estimate the
region's poverty level. In this work, I develop deep learning computer vision
methods that can predict a region's poverty level from an overhead satellite
image. I experiment with both daytime and nighttime imagery. Furthermore,
because data limitations are often the barrier to entry in poverty prediction
from satellite imagery, I explore the impact that data quantity and data
augmentation have on the representational power and overall accuracy of the
networks. Lastly, to evaluate the robustness of the networks, I evaluate them
on data from continents that were absent in the development set.
|
We present Paper II of the Eccentric Debris Disc Morphologies series to
explore the effects that significant free and forced eccentricities have on
high-resolution millimetre-wavelength observations of debris discs, motivated
by recent ALMA images of HD53143's disc. In this work, we explore the effects
of free eccentricity, and by varying disc fractional widths and observational
resolutions, show for a range of narrow eccentric discs, orbital overlaps
result in dust emission distributions that have either one or two radial peaks
at apocentre and/or pericentre. The narrowest discs contain two radial peaks,
whereas the broadest discs contain just one radial peak. For fixed
eccentricities, as fractional disc widths are increased, we show that these
peaks merge first at apocentre (producing apocentre glow), and then at
pericentre (producing pericentre glow). Our work thus demonstrates that
apocentre/pericentre glows in models with constant free and forced
eccentricities can be both width and resolution dependent at millimetre
wavelengths, challenging the classical assertion that apocentre/pericentre
glows are purely wavelength dependent. We discuss future high-resolution
observations that can distinguish between competing interpretations of
underlying debris disc eccentricity distributions.
|
We discuss an extension of the scalar auxiliary variable approach, which was
originally introduced by Shen et al. ([Shen, Xu, Yang, J. Comput. Phys., 2018])
for the discretization of deterministic gradient flows. By introducing an
additional scalar auxiliary variable, this approach allows to derive a linear
scheme, while still maintaining unconditional stability. Our extension augments
the approximation of the evolution of this scalar auxiliary variable with
higher order terms, which enables its application to stochastic partial
differential equations. Using the stochastic Allen--Cahn equation as a
prototype for nonlinear stochastic partial differential equations with
multiplicative noise, we propose an unconditionally energy stable, linear,
fully discrete finite element scheme based on our augmented scalar auxiliary
variable method. Recovering a discrete version of the energy estimate and
establishing Nikolskii estimates with respect to time, we are able to prove
convergence of discrete solutions towards pathwise unique martingale solutions
by applying Jakubowski's generalization of Skorokhod's theorem. A
generalization of the Gy\"ongy--Krylov characterization of convergence in
probability to quasi-Polish spaces finally provides convergence of fully
discrete solutions towards strong solutions of the stochastic Allen--Cahn
equation. Finally, we present numerical simulations underlining the
practicality of the scheme and the importance of the introduced augmentation
terms.
|
We present analytical results for the $O(\alpha _s ^2)$ contributions to the
functions $\eta _A$ and $\eta _V$ which parameterize QCD corrections to
semileptonic $b \to c$ transitions at zero recoil. Previously obtained
approximate results are confirmed. The methods of computing the relevant
two-loop diagrams with two mass scales are discussed in some detail.
|
The newly discovered topological Dirac semimetals host the possibilities of
various topological phase transitions through the control of spin-orbit
coupling as well as symmetries and dimensionalities. Here, we report a
magnetotransport study of high-mobility (Cd1-xZnx)3As2 films, where the
topological Dirac semimetal phase can be turned into a trivial insulator via
chemical substitution. By high-field measurements with a Hall-bar geometry,
magnetoresistance components ascribed to the chiral charge pumping have been
distinguished from other extrinsic effects. The negative magnetoresistance
exhibits a clear suppression upon Zn doping, reflecting decreasing Berry
curvature of the band structure as the topological phase transition is induced
by reducing the spin-orbit coupling.
|
Given a graph $G=(V,E)$ on $n$ vertices and an assignment of colours to its
edges, a set of edges $S \subseteq E$ is said to be rainbow if edges from $S$
have pairwise different colours assigned to them. In this paper, we investigate
rainbow spanning trees in randomly coloured random $G_{k-out}$ graphs.
|
In this article, we adapted five recent SSL methods to the task of audio
classification. The first two methods, namely Deep Co-Training (DCT) and Mean
Teacher (MT), involve two collaborative neural networks. The three other
algorithms, called MixMatch (MM), ReMixMatch (RMM), and FixMatch (FM), are
single-model methods that rely primarily on data augmentation strategies. Using
the Wide-ResNet-28-2 architecture in all our experiments, 10% of labeled data
and the remaining 90% as unlabeled data for training, we first compare the
error rates of the five methods on three standard benchmark audio datasets:
Environmental Sound Classification (ESC-10), UrbanSound8K (UBS8K), and Google
Speech Commands (GSC). In all but one cases, MM, RMM, and FM outperformed MT
and DCT significantly, MM and RMM being the best methods in most experiments.
On UBS8K and GSC, MM achieved 18.02% and 3.25% error rate (ER), respectively,
outperforming models trained with 100% of the available labeled data, which
reached 23.29% and 4.94%, respectively. RMM achieved the best results on ESC-10
(12.00% ER), followed by FM which reached 13.33%. Second, we explored adding
the mixup augmentation, used in MM and RMM, to DCT, MT, and FM. In almost all
cases, mixup brought consistent gains. For instance, on GSC, FM reached 4.44%
and 3.31% ER without and with mixup. Our PyTorch code will be made available
upon paper acceptance at https:// github. com/ Labbe ti/ SSLH.
|
We consider an $\varepsilon$-periodic ($\varepsilon\to 0$) tubular structure,
modelled as a magnetic Laplacian on a metric graph, which is periodic along a
single axis. We show that the corresponding Hamiltonian admits norm-resolvent
convergence to an ODE on $\mathbb{R}$ which is fourth order at a discrete set
of values of the magnetic potential (\emph{critical points}) and second-order
generically. In a vicinity of critical points we establish a mixed-order
asymptotics. The rate of convergence is also estimated. This represents a
physically viable model of a phase transition as the strength of the (constant)
magnetic field increases.
|
Falling oil revenues and rapid urbanization are putting a strain on the
budgets of oil producing nations which often subsidize domestic fuel
consumption. A direct way to decrease the impact of subsidies is to reduce fuel
consumption by reducing congestion and car trips. While fuel consumption models
have started to incorporate data sources from ubiquitous sensing devices, the
opportunity is to develop comprehensive models at urban scale leveraging
sources such as Global Positioning System (GPS) data and Call Detail Records.
We combine these big data sets in a novel method to model fuel consumption
within a city and estimate how it may change due to different scenarios. To do
so we calibrate a fuel consumption model for use on any car fleet fuel economy
distribution and apply it in Riyadh, Saudi Arabia. The model proposed, based on
speed profiles, is then used to test the effects on fuel consumption of
reducing flow, both randomly and by targeting the most fuel inefficient trips
in the city. The estimates considerably improve baseline methods based on
average speeds, showing the benefits of the information added by the GPS data
fusion. The presented method can be adapted to also measure emissions. The
results constitute a clear application of data analysis tools to help decision
makers compare policies aimed at achieving economic and environmental goals.
|
We determine a class of ringed space X, for which the category of locally
free sheaves of bounded rank is equivalent to the category of finitely
generated projective A(X)-modules, where A(X) denote the ring of global
sections of X. The well-known Serre-Swan theorems for affine schemes,
differentiable manifolds, Stein spaces, etc., are then derived.
|
We present in detail a calculation of the next-to-leading order QCD
corrections to the process $e^+e^-\to 3$ jets with massive quarks. To isolate
the soft and collinear divergencies of the four parton matrix elements, we
modify the phase space slicing method to account for masses. Our computation
allows for the prediction of oriented three jet events involving heavy quarks,
both on and off the Z resonance, and of any event shape variable which is
dominated by three jet configurations. We show next-to-leading order results
for the three jet fraction, the differential two jet rate, and for the thrust
distribution at various c.m. energies.
|
We benchmark contemporary action recognition models (TSN, TRN, and TSM) on
the recently introduced EPIC-Kitchens dataset and release pretrained models on
GitHub (https://github.com/epic-kitchens/action-models) for others to build
upon. In contrast to popular action recognition datasets like Kinetics,
Something-Something, UCF101, and HMDB51, EPIC-Kitchens is shot from an
egocentric perspective and captures daily actions in-situ. In this report, we
aim to understand how well these models can tackle the challenges present in
this dataset, such as its long tail class distribution, unseen environment test
set, and multiple tasks (verb, noun and, action classification). We discuss the
models' shortcomings and avenues for future research.
|
Numerical simulations of vesicle suspensions are performed in two dimensions
to study their dynamical and rheological properties. An hybrid method is
adopted, which combines a mesoscopic approach for the solvent with a
curvature-elasticity model for the membrane. Shear flow is induced by two
counter-sliding parallel walls, which generate a linear flow profile. The flow
behavior is studied for various vesicle concentrations and viscosity ratios
between the internal and the external fluid. Both the intrinsic viscosity and
the thickness of depletion layers near the walls are found to increase with
increasing viscosity ratio.
|
Many factors influence speech yielding different renditions of a given
sentence. Generative models, such as variational autoencoders (VAEs), capture
this variability and allow multiple renditions of the same sentence via
sampling. The degree of prosodic variability depends heavily on the prior that
is used when sampling. In this paper, we propose a novel method to compute an
informative prior for the VAE latent space of a neural text-to-speech (TTS)
system. By doing so, we aim to sample with more prosodic variability, while
gaining controllability over the latent space's structure.
By using as prior the posterior distribution of a secondary VAE, which we
condition on a speaker vector, we can sample from the primary VAE taking
explicitly the conditioning into account and resulting in samples from a
specific region of the latent space for each condition (i.e. speaker). A formal
preference test demonstrates significant preference of the proposed approach
over standard Conditional VAE. We also provide visualisations of the latent
space where well-separated condition-specific clusters appear, as well as
ablation studies to better understand the behaviour of the system.
|
We review some recent progress on applications of Cluster Expansions. We
focus on a system of classical particles living in a continuous medium and
interacting via a stable and tempered pair potential. We review the cluster
expansion in both the canonical and the grand canonical ensemble and compute
thermodynamic quantities such as the pressure, the free energy as well as
various correlation functions. We derive the equation of state either by
performing inversion of the density-activity series or directly in the
canonical ensemble. Further applications to the liquid state expansions and the
relevant closures are discussed, in particular their convergence in the gas
regime.
|
The radio-wavelength detection of extensive air showers (EAS) initiated by
cosmic-ray interactions in the Earth's atmosphere is a promising technique for
investigating the origin of these particles and the physics of their
interactions. The Low Frequency Array (LOFAR) and the Owens Valley Long
Wavelength Array (OVRO-LWA) have both demonstrated that the dense cores of low
frequency radio telescope arrays yield detailed information on the radiation
ground pattern, which can be used to reconstruct key EAS properties and infer
the primary cosmic-ray composition. Here, we demonstrate a new observation mode
of the Murchison Widefield Array (MWA), tailored to the observation of the
sub-microsecond coherent bursts of radiation produced by EAS. We first show how
an aggregate 30.72 MHz bandwidth (3072x 10 kHz frequency channels) recorded at
0.1 ms resolution with the MWA's voltage capture system (VCS) can be
synthesised back to the full bandwidth Nyquist resolution of 16.3 ns. This
process, which involves `inverting' two sets of polyphase filterbanks, retains
90.5% of the signal-to-noise of a cosmic ray signal. We then demonstrate the
timing and positional accuracy of this mode by resolving the location of a
calibrator pulse to within 5 m. Finally, preliminary observations show that the
rate of nanosecond radio-frequency interference (RFI) events is 0.1 Hz, much
lower than that found at the sites of other radio telescopes that study cosmic
rays. We conclude that the identification of cosmic rays at the MWA, and hence
with the low-frequency component of the Square Kilometre Array, is feasible
with minimal loss of efficiency due to RFI.
|
MoTe2 is a paradigmatic van der Waals layered semimetal with two
energetically close electronic phases, the topologically trivial 1Tprime and
the low-temperature Td type-II Weyl semimetal phase. The ability to manipulate
this phase transition, perhaps towards occurring near room temperature, would
open new avenues for harnessing the full potential of Weyl semimetals for
high-efficiency electronic and spintronic applications. Here, we show that
potassium dosing on 1Tprime-MoTe2 induces a Lifshitz transition by a
combination of angle-resolved photoemission spectroscopy, scanning tunneling
microscopy, x-ray spectroscopy and density functional theory. While the
electronic structure shifts rigidly for small concentrations of K, MoTe2
undergoes significant band structure renormalization for larger concentrations.
Our results demonstrate that the origin of this electronic structure change
stems from alkali metal intercalation. We show that these profound changes are
caused by effectively decoupling the 2D sheets, bringing K-intercalated
1Tprime-MoTe2 to the quasi-2D limit, but do not cause a topological phase
transition.
|
We consider the problem of explaining the decisions of deep neural networks
for image recognition in terms of human-recognizable visual concepts. In
particular, given a test set of images, we aim to explain each classification
in terms of a small number of image regions, or activation maps, which have
been associated with semantic concepts by a human annotator. This allows for
generating summary views of the typical reasons for classifications, which can
help build trust in a classifier and/or identify example types for which the
classifier may not be trusted. For this purpose, we developed a user interface
for "interactive naming," which allows a human annotator to manually cluster
significant activation maps in a test set into meaningful groups called "visual
concepts". The main contribution of this paper is a systematic study of the
visual concepts produced by five human annotators using the interactive naming
interface. In particular, we consider the adequacy of the concepts for
explaining the classification of test-set images, correspondence of the
concepts to activations of individual neurons, and the inter-annotator
agreement of visual concepts. We find that a large fraction of the activation
maps have recognizable visual concepts, and that there is significant agreement
between the different annotators about their denotations. Our work is an
exploratory study of the interplay between machine learning and human
recognition mediated by visualizations of the results of learning.
|
We review various theoretical methods for measuring dark matter properties at
the Large Hadron Collider.
|
We report on the first analysis of AstroSat observation of the Z-source GX 5-
1 on February 26-27, 2017. The hardness-intensity plot reveals that the source
traced out the horizontal and normal branches. The 0.8-20 keV spectra from
simultaneous SXT and LAXPC data at different locations of the
hardness-intensity plot can be well described by a disk emission and a thermal
Comptonized component. The ratio of the disk flux to the total i.e. the disk
flux ratio increases monotonically along the horizontal to the normal one.
Thus, the difference between the normal and horizontal branches is that in the
normal branch, the disk dominates the flux while in the horizontal one it is
the Comptonized component which dominates. The disk flux scales with the inner
disk temperature as T_{in}^{5.5} and not as T_{in}{4} suggesting that either
the inner radii changes dramatically or that the disk is irradiated by the
thermal component changing its hardness factor. The power spectra reveal a
Quasi Periodic Oscillation whose frequency changes from \sim 30 Hz to 50 Hz.
The frequency is found to correlate well with the disk flux ratio. In the 3-20
keV LAXPC band the r.m.s of the QPO increases with energy (r.m.s \prop E0.8),
while the harder X-ray seems to lag the soft ones with a time-delay of a
milliseconds. The results suggest that the spectral properties of the source
are characterized by the disk flux ratio and that the QPO has its origin in the
corona producing the thermal Comptonized component.
|
The electroproduction of J/psi and psi(2S) mesons is studied in elastic,
quasi-elastic and inclusive reactions for four momentum transfers 2 < Q^2 < 80
GeV^2 and photon-proton centre of mass energies 25 < W < 180 GeV. The data were
taken with the H1 detector at the electron proton collider HERA in the years
1995 to 1997. The total virtual photon-proton cross section for elastic J/psi
production is measured as a function of Q^2 and W. The dependence of the
production rates on the square of the momentum transfer from the proton (t) is
extracted. Decay angular distributions are analysed and the ratio of the
longitudinal and transverse cross sections is derived. The ratio of the cross
sections for quasi-elastic psi(2S) and J/psi meson production is measured as a
function of Q^2. The results are discussed in terms of theoretical models based
upon perturbative QCD. Differential cross sections for inclusive and inelastic
production of J/psi mesons are determined and predictions within two
theoretical frameworks are compared with the data, the non-relativistic QCD
factorization approach including colour octet and colour singlet contributions,
and the model of Soft Colour Interactions.
|
We provide the last missing piece of the complete non-perturbative
description of the low energy effective action emerging from Calabi-Yau
compactifications of type II string theory --- NS5-brane instanton corrections
to the hypermultiplet moduli space $M_H$. We find them using S-duality symmetry
of the type IIB formulation. The result is encoded in a set of holomorphic
functions on the twistor space of $M_H$ and includes all orders of the
instanton expansion.
|
Face clustering plays an essential role in exploiting massive unlabeled face
data. Recently, graph-based face clustering methods are getting popular for
their satisfying performances. However, they usually suffer from excessive
memory consumption especially on large-scale graphs, and rely on empirical
thresholds to determine the connectivities between samples in inference, which
restricts their applications in various real-world scenes. To address such
problems, in this paper, we explore face clustering from the pairwise angle.
Specifically, we formulate the face clustering task as a pairwise relationship
classification task, avoiding the memory-consuming learning on large-scale
graphs. The classifier can directly determine the relationship between samples
and is enhanced by taking advantage of the contextual information. Moreover, to
further facilitate the efficiency of our method, we propose a rank-weighted
density to guide the selection of pairs sent to the classifier. Experimental
results demonstrate that our method achieves state-of-the-art performances on
several public clustering benchmarks at the fastest speed and shows a great
advantage in comparison with graph-based clustering methods on memory
consumption.
|
Quantum trajectories describe the stochastic evolution of an open quantum
system conditioned on continuous monitoring of its output, such as by an ideal
photodetector. In practice an experimenter has access to an output filtered
through various electronic devices, rather than the microscopic states of the
detector. This introduces several imperfections into the measurement process,
of which only inefficiency has previously been incorporated into quantum
trajectory theory. However, all electronic devices have finite bandwidths, and
the consequent delay in conveying the output signal to the observer implies
that the evolution of the conditional state of the quantum system must be
non-Markovian. We present a general method of describing this evolution and
apply it to avalanche photodiodes (APDs) and to photoreceivers. We include the
effects of efficiency, dead time, bandwidth, electronic noise, and dark counts.
The essential idea is to treat the quantum system and classical detector
jointly, and to average over the latter to obtain the conditional quantum
state.
The significance of our theory is that quantum trajectories for realistic
detection are necessary for sophisticated approaches to quantum feedback, and
our approach could be applied in many areas of physics.
|
Consider a graph with a rotation system, namely, for every vertex, a circular
ordering of the incident edges. Given such a graph, an angle cover maps every
vertex to a pair of consecutive edges in the ordering -- an angle -- such that
each edge participates in at least one such pair. We show that any graph of
maximum degree 4 admits an angle cover, give a poly-time algorithm for deciding
if a graph with no degree-3 vertices has an angle-cover, and prove that, given
a graph of maximum degree 5, it is NP-hard to decide whether it admits an angle
cover. We also consider extensions of the angle cover problem where every
vertex selects a fixed number $a>1$ of angles or where an angle consists of
more than two consecutive edges. We show an application of angle covers to the
problem of deciding if the 2-blowup of a planar graph has isomorphic thickness
2.
|
The Smoothed Particles Hydrodynamics (SPH) is a particle-based, meshfree,
Lagrangian method used to simulate multidimensional fluids with arbitrary
geometries, most commonly employed in astrophysics, cosmology, and
computational fluid-dynamics (CFD). It is expected that these
computationally-demanding numerical simulations will significantly benefit from
the up-and-coming Exascale computing infrastructures, that will perform 10 18
FLOP/s. In this work, we review the status of a novel SPH-EXA mini-app, which
is the result of an interdisciplinary co-design project between the fields of
astrophysics, fluid dynamics and computer science, whose goal is to enable SPH
simulations to run on Exascale systems. The SPH-EXA mini-app merges the main
characteristics of three state-of-the-art parent SPH codes (namely ChaNGa,
SPH-flow, SPHYNX) with state-of-the-art (parallel) programming, optimization,
and parallelization methods. The proposed SPH-EXA mini-app is a C++14
lightweight and flexible header-only code with no external software
dependencies. Parallelism is expressed via multiple programming models, which
can be chosen at compilation time with or without accelerator support, for a
hybrid process+thread+accelerator configuration. Strong and weak-scaling
experiments on a production supercomputer show that the SPH-EXA mini-app can be
efficiently executed with up 267 million particles and up to 65 billion
particles in total on 2,048 hybrid CPU-GPU nodes.
|
We propose a method to account for model error due to unresolved scales in
the context of the ensemble transform Kalman filter (ETKF). The approach
extends to this class of algorithms the deterministic model error formulation
recently explored for variational schemes and extended Kalman filter. The model
error statistic required in the analysis update is estimated using historical
reanalysis increments and a suitable model error evolution law. Two different
versions of the method are described; a time-constant model error treatment
where the same model error statistical description is time-invariant, and a
time-varying treatment where the assumed model error statistics is randomly
sampled at each analysis step. We compare both methods with the standard method
of dealing with model error through inflation and localization, and illustrate
our results with numerical simulations on a low order nonlinear system
exhibiting chaotic dynamics. The results show that the filter skill is
significantly improved through the proposed model error treatments, and that
both methods require far less parameter tuning than the standard approach.
Furthermore, the proposed approach is simple to implement within a pre-existing
ensemble based scheme. The general implications for the use of the proposed
approach in the framework of square-root filters such as the ETKF are also
discussed.
|
We numerically investigate density perturbations generated in the smooth
hybrid new inflation model, a kind of double inflation model that is designed
to reproduce the running spectral index suggested by the WMAP results. We
confirm that this model provides the running spectral index within 1sigma range
of the three year WMAP result. In addition, we find a sharp and strong peak on
the spectrum of primordial curvature perturbation at small scales. This
originates from amplification of fluctuation in the first inflaton fields due
to parametric resonance, which takes place in the oscillatory phase between two
inflationary regime. Formation probability of primordial black holes (PBHs) is
discussed as a consequence of such peak.
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In this note we focus on three independent problems on Okounkov bodies for
projective varieties. The main goal is to present a geometric version of the
classical Fujita Approximation Theorem, a Jow-type theorem and a cardinality
formulae for Minkowski bases on a certain class of smooth projective surfaces.
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Over the last decade, simultaneous wireless information and power transfer
(SWIPT) has become a practical and promising solution for connecting and
recharging battery-limited devices, thanks to significant advances in low-power
electronics technology and wireless communications techniques. To realize the
promised potentials, advanced resource allocation design plays a decisive role
in revealing, understanding, and exploiting the intrinsic rate-energy tradeoff
capitalizing on the dual use of radio frequency (RF) signals for wireless
charging and communication. In this paper, we provide a comprehensive tutorial
overview of SWIPT from the perspective of resource allocation design. The
fundamental concepts, system architectures, and RF energy harvesting (EH)
models are introduced. In particular, three commonly adopted EH models, namely
the linear EH model, the nonlinear saturation EH model, and the nonlinear
circuit-based EH model are characterized and discussed. Then, for a typical
wireless system setup, we establish a generalized resource allocation design
framework which subsumes conventional resource allocation design problems as
special cases. Subsequently, we elaborate on relevant tools from optimization
theory and exploit them for solving representative resource allocation design
problems for SWIPT systems with and without perfect channel state information
(CSI) available at the transmitter, respectively. The associated technical
challenges and insights are also highlighted. Furthermore, we discuss several
promising and exciting future research directions for resource allocation
design for SWIPT systems intertwined with cutting-edge communication
technologies, such as intelligent reflecting surfaces, unmanned aerial
vehicles, mobile edge computing, federated learning, and machine learning.
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The frequency shift of light in the gravitational field generated by a
rotating body is investigated. We consider the scenario in which both the light
source and the observer are in motion. The frequency shift is calculated up to
the second-order post-Minkowskian approximation via two different methods and
the same result is achieved. The higher-order effects of the gravitational
source's rotation on the frequency shift is obtained. Especially, when both the
light source and the observer are located in the asymptotically flat region, an
elegant formula is obtained, which can be easily used in the astronomical
observations to determine the rotating gravitational source's mass and angular
momentum.
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The first author in recent work with D. Gay developed the notion of a Morse
structure on an open book as a tool for studying closed contact 3-manifolds. We
extend the notion of Morse structure to extendable partial open books in order
to study contact 3-manifolds with convex boundary.
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We introduce a lattice model of interacting spins and bosons that leads to
Luttinger-liquid physics, and allows for quantitative tests of the theory of
bosonization by means of trapped-ion or superconducting-circuit experiments. By
using a variational bosonization ansatz, we calculate the power-law decay of
spin and boson correlation functions, and study their dependence on a single
tunable parameter, namely a bosonic driving. For small drivings,
Matrix-Product-States (MPS) numerical methods are shown to be efficient and
validate our ansatz. Conversely, even static MPS become inefficient for
large-driving regimes, such that the experiment can potentially outperform
classical numerics, achieving one of the goals of quantum simulations.
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Providing secure communications over the physical layer with the objective of
achieving perfect secrecy without requiring a secret key has been receiving
growing attention within the past decade. The vast majority of the existing
studies in the area of physical layer security focus exclusively on the
scenarios where the channel inputs are Gaussian distributed. However, in
practice, the signals employed for transmission are drawn from discrete signal
constellations such as phase shift keying and quadrature amplitude modulation.
Hence, understanding the impact of the finite-alphabet input constraints and
designing secure transmission schemes under this assumption is a mandatory step
towards a practical implementation of physical layer security. With this
motivation, this article reviews recent developments on physical layer security
with finite-alphabet inputs. We explore transmit signal design algorithms for
single-antenna as well as multi-antenna wiretap channels under different
assumptions on the channel state information at the transmitter. Moreover, we
present a review of the recent results on secure transmission with discrete
signaling for various scenarios including multi-carrier transmission systems,
broadcast channels with confidential messages, cognitive multiple access and
relay networks. Throughout the article, we stress the important behavioral
differences of discrete versus Gaussian inputs in the context of the physical
layer security. We also present an overview of practical code construction over
Gaussian and fading wiretap channels, and we discuss some open problems and
directions for future research.
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We have performed transverse-field muon spin relaxation (TF-$\mu$SR)
measurements on ambient-pressure-grown polycrystalline
$\mathrm{LaO_{0.5}F_{0.5}BiS_{2}}$. From these measurements, no signature of
magnetic order is found down to 25 mK. The value of the magnetic penetration
depth extrapolated to 0 K is 0.89 (5) $\mu$m. The temperature dependence of
superconducting penetration depth is best described by either a multigap s +
s-wave model with $\Delta_{1}$ = 0.947 (7) meV and $\Delta_{2}$ = 0.22 (4) meV
or the ansiotropic s-wave model with $\Delta(0)$ = 0.776 meV and anisotropic
gap amplitude ratio $\Delta_{min}/\Delta_{max}$ = 0.34. Comparisons with other
potentially multigap $\mathrm{BiS_{2}}$-based superconductors are discussed. We
find that these $\mathrm{BiS_{2}}$-based superconductors, including
$\mathrm{Bi_{4}O_{4}S_3}$ and the high-pressure synthesized
$\mathrm{LaO_{0.5}F_{0.5}BiS_{2}}$, generally conform to the Uemura relation.
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Autonomous driving is a complex task which requires advanced decision making
and control algorithms. Understanding the rationale behind the autonomous
vehicles' decision is crucial to ensure their safe and effective operation on
highway driving. This study presents a novel approach, HighwayLLM, which
harnesses the reasoning capabilities of large language models (LLMs) to predict
the future waypoints for ego-vehicle's navigation. Our approach also utilizes a
pre-trained Reinforcement Learning (RL) model to serve as a high-level planner,
making decisions on appropriate meta-level actions. The HighwayLLM combines the
output from the RL model and the current state information to make safe,
collision-free, and explainable predictions for the next states, thereby
constructing a trajectory for the ego-vehicle. Subsequently, a PID-based
controller guides the vehicle to the waypoints predicted by the LLM agent. This
integration of LLM with RL and PID enhances the decision-making process and
provides interpretability for highway autonomous driving.
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Existence of shear horizontal (SH) surface waves in 2D-periodic phononic
crystals with an asymmetric depth-dependent profile is theoretically reported.
Examples of dispersion spectra with band gaps for subsonic and supersonic SH
surface waves are demonstrated. The link between the effective (quasistatic)
speeds of the SH bulk and surface waves is established. Calculation and
analysis is based on the integral form of projector on the subspace of
evanescent modes which means no need for their explicit finding. This new
method can be extended to the vector waves and the 3D case.
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In this paper we develope a categorical theory of relations and use this
formulation to define the notion of quantization for relations. Categories of
relations are defined in the context of symmetric monoidal categories. They are
shown to be symmetric monoidal categories in their own right and are found to
be isomorphic to certain categories of $A-A$ bicomodules. Properties of
relations are defined in terms of the symmetric monoidal structure. Equivalence
relations are shown to be commutative monoids in the category of relations.
Quantization in our view is a property of functors between monoidal categories.
This notion of quantization induce a deformation of all algebraic structures in
the category, in particular the ones defining properties of relations like
transitivity and symmetry.
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We study the generation and evolution of entanglement between two qubits
coupled through one-dimensional waveguide modes. By using a complete quantum
electrodynamical formalism we go beyond the Markovian approximation. The
diagonalization of the hamiltonian is carried out, and a set of quasi-localized
eigenstates is found. We show that when the qubit-waveguide coupling is
increased, the Markov approximation is not anymore valid, and the generation of
entanglement is worsened.
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We solve numerically the Boltzmann equation in the early universe in the
presence of a constant electric field and find the electrical conductivity
$\sigma$ in the range $1\MeV\lsim T\lsim M_W$. The main contribution to
$\sigma$ is shown to be due to leptonic interactions. For $T\lsim 100\MeV$ we
find $\sigma\simeq 0.76T$ while at $T\simeq M_W$ we obtain $\sigma\simeq 6.7T$
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Nonlinear couplings between photons and electrons in new materials give rise
to a wealth of interesting nonlinear phenomena. This includes frequency mixing,
optical rectification or nonlinear current generation, which are of particular
interest for generating radiation in spectral regions that are difficult to
access, such as the terahertz gap. Owing to its specific linear dispersion and
high electron mobility at room temperature, graphene is particularly attractive
for realizing strong nonlinear effects. However, since graphene is a
centrosymmetric material, second-order nonlinearities a priori cancel, which
imposes to rely on less attractive third-order nonlinearities. It was
nevertheless recently demonstrated that dc-second-order nonlinear currents as
well as ultrafast ac-currents can be generated in graphene under optical
excitation. The asymmetry is introduced by the excitation at oblique incidence,
resulting in the transfer of photon momentum to the electron system, known as
the photon drag effect. Here, we show broadband coherent terahertz emission,
ranging from about 0.1-4 THz, in epitaxial graphene under femtosecond optical
excitation, induced by a dynamical photon drag current. We demonstrate that, in
contrast to most optical processes in graphene, the next-nearest-neighbor
couplings as well as the distinct electron-hole dynamics are of paramount
importance in this effect. Our results indicate that dynamical photon drag
effect can provide emission up to 60 THz opening new routes for the generation
of ultra-broadband terahertz pulses at room temperature.
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This paper presents an extension of the recently introduced planewave density
interpolation (PWDI) method to the electric field integral equation (EFIE)
formulation of problems of scattering and radiation by perfect electric
conducting (PEC) objects. Relying on Kirchhoff integral formula and local
interpolation of surface current densities that regularize the kernel
singularities, the PWDI method enables off- and on-surface EFIE operators to be
re-expressed in terms of integrands that are globally bounded (or even more
regular) over the whole domain of integration, regardless of the magnitude of
the distance between target and source points. Surface integrals resulting from
the application of the method-of-moments (MoM) using Rao-Wilton-Glisson (RWG)
basis functions, can then be directly and easily evaluated by means of
elementary quadrature rules irrespective of the singularity location. The
proposed technique can be applied to simple and composite surfaces comprising
two or more simply-connected overlapping components. The use of composite
surfaces can significantly simplify the geometric treatment of complex
structures, as the PWDI method enables the use of separate non-conformal meshes
for the discretization of each of the surface components that make up the
composite surface. A variety of examples, including multi-scale and intricate
structures, demonstrate the effectiveness of the proposed methodology.
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In this work we have studied the scattering of scalar field around an
extended black hole in F(R) gravity using WKB method. We have obtained the wave
function in different regions such as near the horizon region, away from
horizon and far away from horizon and the absorption cross section are
calculated. We find that the absorption cross section is inversely proportional
to the cube of Hawking temperature. We have also evaluated the Hawking
temperature of the black hole via tunneling method.
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Let $X$ be a smooth compact complex surface with the canonical divisor $K_X$
ample and let $\Theta_X$ be its holomorphic tangent bundle. Bridgeland
stability conditions are used to study the space $H^1 (\Theta_X)$ of
infinitesimal deformations of complex structures of $X$ and its relation to the
geometry/topology of $X$. The main observation is that for $X$ with $H^1
(\Theta_X)$ nonzero and the Chern numbers $(c_2 (X), K^2_X)$ subject to $$
\tau_X :=2ch_2 (\Theta_X)=K^2_X -2c_2(X) >0 $$ the object $\Theta_X [1]$ of the
derived category of bounded complexes of coherent sheaves on $X$ is Bridgeland
unstable in a certain part of the space of Bridgeland stability conditions. The
Harder-Narasimhan filtrations of $\Theta_X [1]$ for those stability conditions
are expected to provide new insights into geometry of surfaces of general type
and the study of their moduli. The paper provides a certain body of evidence
that this is indeed the case.
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We describe the origins of recurrence relations between field theory
amplitudes in terms of the construction of Feynman diagrams. In application we
derive recurrence relations for the amplitudes of QED which hold to all loop
orders and for all combinations of external particles. These results may also
be derived from the Schwinger-Dyson equations.
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We theoretically investigate photonic time-crystalline behaviour initiated by
optical excitation above the electronic gap of the excitonic insulator
candidate $\rm{Ta_2 Ni Se_5}$. We show that after electron photoexcitation,
electron-phonon coupling leads to an unconventional squeezed phonon state,
characterised by periodic oscillations of phonon fluctuations. Squeezing
oscillations lead to photonic time crystalline behaviour. The key signature of
the photonic time crystalline behaviour is THz amplification of reflectivity in
a narrow frequency band. The theory is supported by experimental results on
$\rm{Ta_2 Ni Se_5}$ where photoexcitation with short pulses leads to enhanced
terahertz reflectivity with the predicted features. We explain the key
mechanism leading to THz amplification in terms of a simplified Hamiltonian
whose validity is supported by ab-initio DFT calculations. Our theory suggests
that the pumped $\rm{Ta_2 Ni Se_5}$ is a gain medium, demonstrating that
squeezed phonon noise may be used to create THz amplifiers in THz communication
applications.
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Reliable offroad autonomy requires low-latency, high-accuracy state estimates
of pose as well as velocity, which remain viable throughout environments with
sub-optimal operating conditions for the utilized perception modalities. As
state estimation remains a single point of failure system in the majority of
aspiring autonomous systems, failing to address the environmental degradation
the perception sensors could potentially experience given the operating
conditions, can be a mission-critical shortcoming. In this work, a method for
integration of radar velocity information in a LiDAR-inertial odometry solution
is proposed, enabling consistent estimation performance even with degraded
LiDAR-inertial odometry. The proposed method utilizes the direct
velocity-measuring capabilities of an Frequency Modulated Continuous Wave
(FMCW) radar sensor to enhance the LiDAR-inertial smoother solution onboard the
vehicle through integration of the forward velocity measurement into the
graph-based smoother. This leads to increased robustness in the overall
estimation solution, even in the absence of LiDAR data. This method was
validated by hardware experiments conducted onboard an all-terrain vehicle
traveling at high speed, ~12 m/s, in demanding offroad environments.
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This paper proposes FREEtree, a tree-based method for high dimensional
longitudinal data with correlated features. Popular machine learning
approaches, like Random Forests, commonly used for variable selection do not
perform well when there are correlated features and do not account for data
observed over time. FREEtree deals with longitudinal data by using a piecewise
random effects model. It also exploits the network structure of the features by
first clustering them using weighted correlation network analysis, namely
WGCNA. It then conducts a screening step within each cluster of features and a
selection step among the surviving features, that provides a relatively
unbiased way to select features. By using dominant principle components as
regression variables at each leaf and the original features as splitting
variables at splitting nodes, FREEtree maintains its interpretability and
improves its computational efficiency. The simulation results show that
FREEtree outperforms other tree-based methods in terms of prediction accuracy,
feature selection accuracy, as well as the ability to recover the underlying
structure.
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One of the primary goals of nuclear physics is to understand the force
between nucleons, which is a necessary step for understanding the structure of
nuclei and how nuclei interact with each other. Rutherford discovered the
atomic nucleus in 1911, and the large body of knowledge about the nuclear force
since acquired was derived from studies made on nucleons or nuclei. Although
antinuclei up to antihelium-4 have been discovered and their masses measured,
we have no direct knowledge of the nuclear force between antinucleons. Here, we
study antiproton pair correlations among data taken by the STAR experiment at
the Relativistic Heavy Ion Collider and show that the force between two
antiprotons is attractive. In addition, we report two key parameters that
characterize the corresponding strong interaction: namely, the scattering
length (f0) and effective range (d0). As direct information on the interaction
between two antiprotons, one of the simplest systems of antinucleons, our
result provides a fundamental ingredient for understanding the structure of
more complex antinuclei and their properties.
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We extend two rigorous results of Aizenman, Lebowitz, and Ruelle in their
pioneering paper of 1987 on the Sherrington-Kirkpatrick spin-glass model
without external magnetic field to the quantum case with a "transverse field"
of strength $b$. More precisely, if the Gaussian disorder is weak in the sense
that its standard deviation $v>0$ is smaller than the temperature $1/\beta$,
then the (random) free energy almost surely equals the annealed free energy in
the macroscopic limit and there is no spin-glass phase for any $b/v\geq0$. The
macroscopic annealed free energy (times $\beta$) turns out to be non-trivial
and given, for any $\beta v>0$, by the global minimum of a certain functional
of square-integrable functions on the unit square according to a Varadhan
large-deviation principle. For $\beta v<1$ we determine this minimum up to the
order $(\beta v)^4$ with the Taylor coefficients explicitly given as functions
of $\beta b$ and with a remainder not exceeding $(\beta v)^6/16$. As a
by-product we prove that the so-called static approximation to the minimization
problem yields the wrong $\beta b$-dependence even to lowest order. Our main
tool for dealing with the non-commutativity of the spin-operator components is
a probabilistic representation of the Boltzmann-Gibbs operator by a Feynman-Kac
(path-integral) formula based on an independent collection of Poisson processes
in the positive half-line with common rate $\beta b$. Its essence dates back to
Kac in 1956, but the formula was published only in 1989 by Gaveau and Schulman.
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In this paper, we study several aspects of solitary wave solutions of the
rotation Benjamin-Ono equation. By solving a minimization problem on the line,
we construct a family of even travelling waves $\psi_{c,\gamma}$. We also study
the strong convergence of this family and we establish the uniqueness of
$\psi_{c,\gamma}$ for $\gamma$ small enough. Note that this improves the
results in [5] where the stability of the set of ground states is proven.
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