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New approach to p-adic and adelic strings, which takes into account that not
only world sheet but also Minkowski space-time and string momenta can be p-adic
and adelic, is formulated. p-Adic and adelic string amplitudes are considered
within Feynman's path integral formalism. The adelic Veneziano amplitude is
calculated. Some discreteness of string momenta is obtained. Also, adelic
coupling constant is equal to unity.
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In previous works, we proposed a method to characterize jointly
self-similarity and anisotropy properties of a large class of self--similar
Gaussian random fields. We provide here a mathematical analysis of our
approach, proving that the sharpest way of measuring smoothness is related to
these anisotropies and thus to the geometry of these fields.
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Treating Coulomb scattering of two free electrons in a stationary approach,
we explore the momentum and spin entanglement created by the interaction. We
show that a particular discretisation provides an estimate of the von Neumann
entropy of the one-electron reduced density matrix from the experimentally
accessible Shannon entropy. For spinless distinguishable electrons the entropy
is sizeable at low energies, indicating strong momentum entanglement, and drops
to almost zero at energies of the order of 10 keV when the azimutal degree of
freedom is integrated out, i.e. practically no entanglement and almost pure
one-electron states. If spin is taken into account, the entropy for electrons
with antiparallel spins should be larger than in the parallel-spin case, since
it embodies both momentum and spin entanglement. Surprisingly, this difference,
as well as the deviation from the spin-less case, is extremely small for the
complete scattering state. Strong spin entanglement can however be obtained by
post-selecting states at scattering angle pi/2.
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It was recently discovered that fractional quantum Hall (FQH) states can be
classified by the way ground state wave functions go to zero when electrons are
brought close together. Quasiparticles in the FQH states can be classified in a
similar way, by the pattern of zeros that result when electrons are brought
close to the quasiparticles. In this paper we combine the pattern-of-zero
approach and the conformal-field-theory (CFT) approach to calculate the
topological properties of quasiparticles. We discuss how the quasiparticles in
FQH states naturally form representations of a magnetic translation algebra,
with members of a representation differing from each other by Abelian
quasiparticles. We find that this structure dramatically simplifies topological
properties of the quasiparticles, such as their fusion rules, charges, and
scaling dimensions, and has consequences for the ground state degeneracy of FQH
states on higher genus surfaces. We find constraints on the pattern of zeros of
quasiparticles that can fuse together, which allow us to obtain the fusion
rules of quasiparticles from their pattern of zeros, at least in the case of
the (generalized and composite) parafermion states. We also calculate from CFT
the number of quasiparticle types in the generalized and composite parafermion
states, which confirm the result obtained previously through a completely
different approach.
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Heckenberger introduced the Weyl groupoid of a finite-dimensional Nichols
algebra of diagonal type. We replace the matrix of its braiding by a higher
tensor and present a construction which yields further Weyl groupoids. Abelian
cohomology theory gives evidence for the existence of a higher braiding
associated to such a tensor.
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High-speed visible imaging of sub-microsecond electric explosion of wires at
the low specific energy deposition threshold reveals three distinct modes of
wire failure as capacitor charge voltage and energy deposition are increased.
For 100 micron diameter gold-plated tungsten wires of 2 cm length, deposited
energies of 1.9 eV/atom produces a liquid column that undergoes hydrodynamic
breakup into droplets with radii of order of wire diameter on timescales of 200
microseconds. Instability growth, column breakup, and droplet coalescence
follow classic Rayleigh-Plateau predictions for instability of fluid column.
Above 3.2 eV/atom of deposited energy, wires are seen to abruptly transition to
an expanding mixture of micron scale liquid-droplets and vapor within one frame
(less than 3.33 microseconds), which has been termed phase explosion in
literature. Between these two limits, at 2.5 eV/atom of deposited energy, wire
radius is unchanged for the first 10 microseconds before the onset of a rapid
expansion and disintegration that resembles homogeneous nucleation of
mechanically unstable bubbles. Thermodynamic calculations are presented that
separate cases by temperature obtained during heating: below boiling point,
near boiling point, and exceeding boiling point.
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Magnetic and orbital structures in KCuF$_{3}$ are revisited by the cluster
self-consistent field approach developed recently. We clearly showed that due
to the inherent frustration, the ground state of the system with the
superexchange and Jahn-Teller phonon-mediated orbital couplings is highly
degenerate without broken symmetry; the orthorhombic crystalline field
splitting arising from static Jahn-Teller distortion stabilizes the orbital
ordering, about 42% in the $x^{2}-y^{2}$ orbit and 58% in the $3z^{2}-r^{2}$
orbit in sublattices. The magnetic moment of Cu is considerably reduced to
0.49$\mu_{B}$, and the magnetic coupling strengths are highly anisotropic,
J$_{c}$/J$_{ab}$ $\approx$ 26. These results are in agreement with the
experiments, implying that as an orbital selector, the crystalline field plays
an essential role in stabilizing the ground state of KCuF$_{3}$. The 1s-3d
resonant X-ray scattering amplitudes in KCuF$_{3}$ with the {\it type-a} and
{\it type-d} structures are also presented.
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When planning for autonomous driving, it is crucial to consider essential
traffic elements such as lanes, intersections, traffic regulations, and dynamic
agents. However, they are often overlooked by the traditional end-to-end
planning methods, likely leading to inefficiencies and non-compliance with
traffic regulations. In this work, we endeavor to integrate the perception of
these elements into the planning task. To this end, we propose Perception Helps
Planning (PHP), a novel framework that reconciles lane-level planning with
perception. This integration ensures that planning is inherently aligned with
traffic constraints, thus facilitating safe and efficient driving.
Specifically, PHP focuses on both edges of a lane for planning and perception
purposes, taking into consideration the 3D positions of both lane edges and
attributes for lane intersections, lane directions, lane occupancy, and
planning. In the algorithmic design, the process begins with the transformer
encoding multi-camera images to extract the above features and predicting
lane-level perception results. Next, the hierarchical feature early fusion
module refines the features for predicting planning attributes. Finally, the
double-edge interpreter utilizes a late-fusion process specifically designed to
integrate lane-level perception and planning information, culminating in the
generation of vehicle control signals. Experiments on three Carla benchmarks
show significant improvements in driving score of 27.20%, 33.47%, and 15.54%
over existing algorithms, respectively, achieving the state-of-the-art
performance, with the system operating up to 22.57 FPS.
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In a recent paper, McMullen showed an inequality between the Thurston norm
and the Alexander norm of a 3-manifold. This generalizes the well-known fact
that twice the genus of a knot is bounded from below by the degree of the
Alexander polynomial.
We extend the Bennequin inequality for links to an inequality for all points
of the Thurston norm, if the manifold is a link complement. We compare these
two inequalities on two classes of closed braids.
In an additional section we discuss a conjectured inequality due to Morton
for certain points of the Thurston norm. We prove Morton's conjecture for
closed 3-braids.
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The 21-card trick is a way of dealing cards in order to predict the card
selected by a volunteer. We give a mathematical explanation of why the
well-known 21-card trick works using a simple linear discrete function. The
function has a stable fixed point which corresponds to the position where the
selected card reaches at the end of the trick. We then generalize the 21(7 x
3)-card trick to a p x q - card trick where p and q are odd integers greater
than or equal to three, determine the fixed point and prove that it is also
stable.
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We study orbital and physical properties of Trojan asteroids of Jupiter. We
try to discern all families previously discussed in literature, but we conclude
there is only one significant family among Trojans, namely the cluster around
asteroid (3548) Eurybates. It is the only cluster, which has all of the
following characteristics: (i) it is clearly concentrated in the proper-element
space; (ii) size-frequency distribution is different from background asteroids;
(iii) we have a reasonable collisional/dynamical model of the family.
Henceforth, we can consider it as a real collisional family.
We also report a discovery of a possible family around the asteroid (4709)
Ennomos, composed mostly of small asteroids. The asteroid (4709) Ennomos is
known to have a very high albedo $p_V \simeq 0.15$, which may be related to a
hypothetical cratering event which exposed ice (Fern\'andez et al. 2003). The
relation between the collisional family and the exposed surface of the parent
body is a unique opportunity to study the physics of cratering events. However,
more data are needed to confirm the existence of this family and its
relationship with Ennomos.
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Operators with zero dimensional spectral measures appear naturally in the
theory of ergodic Schr\"odinger operators. We develop the concept of a complete
family of Hausdorff measure functions in order to analyze and distinguish
between these measures with any desired precision. We prove that the dimension
of spectral measures of half-line operators with positive upper Lyapunov
exponent are at most logarithmic for every possible boundary phase. We show
that this is sharp by constructing an explicit operator whose spectral measure
obtains this dimension. We also extend and improve some basic results from the
theory of rank one perturbations and quantum dynamics to encompass generalized
Hausdorff dimensions.
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We present a method of directly obtaining the parity of a Gaussian state of
light without recourse to photon-number counting. The scheme uses only a simple
balanced homodyne technique, and intensity correlation. Thus interferometric
schemes utilizing coherent or squeezed light, and parity detection may be
practically implemented for an arbitrary photon flux. Specifically we
investigate a two-mode, squeezed-light, Mach-Zehnder interferometer and show
how the parity of the output state may be obtained. We also show that the
detection may be described independent of the parity operator, and that this
"parity-by-proxy" measurement has the same signal as traditional parity.
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We analyze the Farey spin chain, a one dimensional spin system with effective
interaction decaying like the squared inverse distance. Using a polymer model
technique, we show that when the temperature is decreased below the (single)
critical temperature T_c=1/2, the magnetization jumps from zero to one.
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We give a necessary and sufficient condition for the orientability of a
locally standard 2-torus manifold with a fixed point which generalizes previous
results of Nakayama-Nishimura in 2005 and Soprunova-Sottile in 2013. We
construct manifolds with boundary where the boundary is a disjoint union of
locally standard 2-torus manifolds. We discuss equivariant oriented cobordism
class of locally standard 2-torus manifolds.
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We study the possibility of testing some generic properties of Brane-World
scenarios at the LHC. In particular, we pay attention to KK-graviton and branon
production. Both signals can be dominant depending on the value of the brane
tension. We analyze the differences between these two signatures. Finally, we
use recent data in the single photon channel from the ATLAS collaboration to
constraint the parameter space of both phenomenologies.
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We demonstrate how an evolutionary algorithm can be extended with a
curriculum learning process that selects automatically the environmental
conditions in which the evolving agents are evaluated. The environmental
conditions are selected so to adjust the level of difficulty to the ability
level of the current evolving agents and so to challenge the weaknesses of the
evolving agents. The method does not require domain knowledge and does not
introduce additional hyperparameters. The results collected on two benchmark
problems, that require to solve a task in significantly varying environmental
conditions, demonstrate that the method proposed outperforms conventional
algorithms and generates solutions that are robust to variations
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We consider a general two Higgs doublet model which can simultaneously solve
discrepancies in neutral B meson decay ($b\to s\ell \overline \ell$
distribution) and charged B meson decay ($b\to c\tau\overline\nu$) with a
charged Higgs. The model contains two additional neutral scalars at the same
mass scale and predicts distinctive signals at the LHC. Based on the recent
same-sign top search by the ATLAS collaboration, we found the constraint on the
scalar mass spectrum. To probe the remaining mass window, we propose a novel
$cg\to t\tau\overline\tau$ process at the LHC.
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We conduct binary population synthesis to investigate the formation of
wind-fed high-mass X-ray binaries containing black holes (BH-HMXBs). We evolve
multiple populations of high-mass binary stars and consider BH-HMXB formation
rates, masses, spins and separations. We find that systems similar to Cygnus
X-1 likely form after stable Case A mass transfer (MT) from the main sequence
progenitors of black holes, provided such MT is characterised by low accretion
efficiency, $\beta \lesssim 0.1$, with modest orbital angular momentum losses
from the non-accreted material. Additionally, efficient BH-HMXB formation
relies on a new simple treatment for Case A MT that allows donors to retain
larger core masses compared to traditional rapid population-synthesis
assumptions. At solar metallicity, our Preferred model yields $\mathcal{O}(1)$
observable BH-HMXBs in the Galaxy today, consistent with observations. In this
simulation, $8\%$ of BH-HMXBs go on to merge as binary black holes or neutron
star-black hole binaries within a Hubble time; however, none of the merging
binaries have BH-HMXB progenitors with properties similar to Cygnus X-1. With
our preferred settings for core mass growth, mass transfer efficiency and
angular momentum loss, accounting for an evolving metallicity, and integrating
over the metallicity-specific star formation history of the Universe, we find
that BH-HMXBs may have contributed $\approx2$--$5$ BBH merger signals to
detections reported in the third gravitational-wave transient catalogue of the
LIGO-Virgo-KAGRA Collaboration. We also suggest MT efficiency should be higher
during stable Case B MT than during Case A MT.
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Fully localised patterns involving cellular hexagons or squares have been
found experimentally and numerically in various continuum models. However,
there is currently no mathematical theory for the emergence of these localised
cellular patterns from a quiescent state. A key issue is that standard
techniques for one-dimensional patterns have proven insufficient for
understanding localisation in higher dimensions. In this work, we present a
comprehensive approach to this problem by using techniques developed in the
study of axisymmetric patterns. Our analysis covers localised patterns equipped
with a wide range of dihedral symmetries, avoiding a restriction to solutions
on a predetermined lattice. The context in this paper is a theory for the
emergence of such patterns near a Turing instability for a general class of
planar reaction-diffusion equations. Posing the reaction-diffusion system in
polar coordinates, we carry out a finite-mode Fourier decomposition in the
angular variable to yield a large system of coupled radial ordinary
differential equations. We then utilise various radial spatial dynamics
methods, such as invariant manifolds, rescaling charts, and normal form
analysis, leading to an algebraic matching condition for localised patterns to
exist in the finite-mode reduction. This algebraic matching condition is
nontrivial, which we solve via a combination of by-hand calculations and
Gr\"obner bases from polynomial algebra to reveal the existence of a plethora
of localised dihedral patterns. These results capture the essence of the
emergent localised hexagonal patterns witnessed in experiments. Moreover, we
combine computer-assisted analysis and a Newton-Kantorovich procedure to prove
the existence of localised patches with 6m-fold symmetry for arbitrarily large
Fourier decompositions. This includes the localised hexagon patches that have
been elusive to analytical treatment.
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Several adaptations of Transformers models have been developed in various
domains since its breakthrough in Natural Language Processing (NLP). This trend
has spread into the field of Music Information Retrieval (MIR), including
studies processing music data. However, the practice of leveraging NLP tools
for symbolic music data is not novel in MIR. Music has been frequently compared
to language, as they share several similarities, including sequential
representations of text and music. These analogies are also reflected through
similar tasks in MIR and NLP. This survey reviews NLP methods applied to
symbolic music generation and information retrieval studies following two axes.
We first propose an overview of representations of symbolic music adapted from
natural language sequential representations. Such representations are designed
by considering the specificities of symbolic music. These representations are
then processed by models. Such models, possibly originally developed for text
and adapted for symbolic music, are trained on various tasks. We describe these
models, in particular deep learning models, through different prisms,
highlighting music-specialized mechanisms. We finally present a discussion
surrounding the effective use of NLP tools for symbolic music data. This
includes technical issues regarding NLP methods and fundamental differences
between text and music, which may open several doors for further research into
more effectively adapting NLP tools to symbolic MIR.
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We present a combined neutron diffraction and high field muon spin rotation
($\mu$SR) study of the magnetically ordered and superconducting phases of the
high-temperature superconductor La$_{1.94}$Sr$_{0.06}$CuO$_{4+y}$ ($T_{\rm c} =
37.5(2)$~K) in a magnetic field applied perpendicular to the CuO$_2$ planes. We
observe a linear field-dependence of the intensity of the neutron diffraction
peak that reflects the modulated antiferromagnetic stripe order. The magnetic
volume fraction extracted from $\mu$SR data likewise increases linearly with
applied magnetic field. The combination of these two observations allows us to
unambiguously conclude that stripe-ordered regions grow in an applied field,
whereas the stripe-ordered magnetic moment itself is field-independent. This
contrasts with earlier suggestions that the field-induced neutron diffraction
intensity in La-based cuprates is due to an increase in the ordered moment. We
discuss a microscopic picture that is capable of reconciling these conflicting
viewpoints.
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We compute the Hausdorff dimension of the set of $\psi$-exactly approximable
vectors, in the simultaneous case, in dimension strictly larger than $2$ and
for approximating functions $\psi$ with order at infinity less than or equal to
$-2$. Our method relies on the analogous result in dimension $1$, proved by
Yann Bugeaud and Carlos Moreira, and a version of Jarn\'ik's Theorem on fibres.
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In this paper, we describe sufficient conditions when block-diagonal
solutions to Lyapunov and $\mathcal{H}_{\infty}$ Riccati inequalities exist. In
order to derive our results, we define a new type of comparison systems, which
are positive and are computed using the state-space matrices of the original
(possibly nonpositive) systems. Computing the comparison system involves only
the calculation of $\mathcal{H}_{\infty}$ norms of its subsystems. We show that
the stability of this comparison system implies the existence of block-diagonal
solutions to Lyapunov and Riccati inequalities. Furthermore, our proof is
constructive and the overall framework allows the computation of block-diagonal
solutions to these matrix inequalities with linear algebra and linear
programming. Numerical examples illustrate our theoretical results.
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Heavy ion collisions pose interesting challenges to quantum chromodynamics,
because they probe the parton structure of the incoming nuclei at very small
longitudinal momentum fractions. Combined with the large size of nuclei, this
may lead to the phenomenon of gluon saturation. The Color Glass Condensate is
an effective QCD description that aims to cope with such a situation. In this
talk, I show how one may study heavy ion collisions in this framework.
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An unprecedented number of new cancer targets are in development, and most
are being developed in combination therapies. Early oncology development is
strategically challenged in choosing the best combinations to move forward to
late stage development. The most common early endpoints to be assessed in such
decision-making include objective response rate, duration of response and tumor
size change. In this paper, using independent-drug-action and
Bliss-drug-independence concepts as a foundation, we introduce simple models to
predict combination therapy efficacy for duration of response and tumor size
change. These models complement previous publications using the independent
action models (Palmer 2017, Schmidt 2020) to predict progression-free survival
and objective response rate and serve as new predictive models to understand
drug combinations for early endpoints. The models can be applied to predict the
combination treatment effect for early endpoints given monotherapy data, or to
estimate the possible effect of one monotherapy in the combination if data are
available from the combination therapy and the other monotherapy. Such
quantitative work facilitates efficient oncology drug development.
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Certain physical aspects of quantum error correction are discussed for a
quantum computer (n-qubit register) in contact with a decohering environment.
Under rather plausible assumptions upon the form of the computer-environment
interaction, the efficiency of a general correcting procedure is evaluated as a
function of the spontaneous-decay duration and the rank of errors covered by
the procedure. It is proved that the probability of errors can be made
arbitrarily small by enhancing the correction method, provided the decohering
interaction is represented by a bounded operator.
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We show that the quantum disk, i.e. the quantum space corresponding to the
Toeplitz C*-algebra does not admit any compact quantum group structure. We
prove that if such a structure existed the resulting compact quantum group
would simultaneously be of Kac type and not of Kac type. The main tools used in
the solution come from the theory of type I locally compact quantum groups, but
also from the theory of operators on Hilbert spaces.
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In this work we argue that the power and effectiveness of the Bohrian
approach to quantum mechanics is essentially grounded on an inconsistent form
of anti-realist realism which supports not only the uncritical tolerance -- in
physics -- towards the "standard" account of the theory of quanta but also --
in philosophy -- to the mad reproduction of mythical (inconsistent and vague)
narratives -- known as "interpretations". We will discuss the existence of --
what John Archibald Wheeler named -- "smoky dragons" not only within the
standard formulation of the theory but also within the many interpretations
that have been -- later on -- introduced by philosophers and philosophically
inclined physicists. After analyzing the role of smoky dragons within both
contemporary physics and philosophy of physics we will propose a general
procedure grounded on a series of necessary theoretical conditions for
producing meaningful physical concepts that -- hopefully -- could be used as
tools and weapons to capture and defeat these beautiful and powerful mythical
creatures.
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Many optimization problems can be naturally represented as (hyper) graphs,
where vertices correspond to variables and edges to tasks, whose cost depends
on the values of the adjacent variables. Capitalizing on the structure of the
graph, suitable dynamic programming strategies can select certain orders of
evaluation of the variables which guarantee to reach both an optimal solution
and a minimal size of the tables computed in the optimization process. In this
paper we introduce a simple algebraic specification with parallel composition
and restriction whose terms up to structural axioms are the graphs mentioned
above. In addition, free (unrestricted) vertices are labelled with variables,
and the specification includes operations of name permutation with finite
support. We show a correspondence between the well-known tree decompositions of
graphs and our terms. If an axiom of scope extension is dropped, several
(hierarchical) terms actually correspond to the same graph. A suitable
graphical structure can be found, corresponding to every hierarchical term.
Evaluating such a graphical structure in some target algebra yields a dynamic
programming strategy. If the target algebra satisfies the scope extension
axiom, then the result does not depend on the particular structure, but only on
the original graph. We apply our approach to the parking optimization problem
developed in the ASCENS e-mobility case study, in collaboration with
Volkswagen. Dynamic programming evaluations are particularly interesting for
autonomic systems, where actual behavior often consists of propagating local
knowledge to obtain global knowledge and getting it back for local decisions.
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Many recent works have explored using WiFi-based sensing to improve SLAM,
robot manipulation, or exploration. Moreover, widespread availability makes
WiFi the most advantageous RF signal to leverage. But WiFi sensors lack an
accurate, tractable, and versatile toolbox, which hinders their widespread
adoption with robot's sensor stacks.
We develop WiROS to address this immediate need, furnishing many WiFi-related
measurements as easy-to-consume ROS topics. Specifically, WiROS is a
plug-and-play WiFi sensing toolbox providing access to coarse-grained WiFi
signal strength (RSSI), fine-grained WiFi channel state information (CSI), and
other MAC-layer information (device address, packet id's or frequency-channel
information). Additionally, WiROS open-sources state-of-art algorithms to
calibrate and process WiFi measurements to furnish accurate bearing information
for received WiFi signals. The open-sourced repository is:
https://github.com/ucsdwcsng/WiROS
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We present a detailed analysis of the intrinsic scatter in the integrated SZ
effect - cluster mass (Y-M) relation, using semi-analytic and simulated cluster
samples. Specifically, we investigate the impact on the Y-M relation of energy
feedback, variations in the host halo concentration and substructure
populations, and projection effects due to unresolved clusters along the line
of sight (the SZ background). Furthermore, we investigate at what radius (or
overdensity) one should measure the integrated SZE and define cluster mass so
as to achieve the tightest possible scaling. We find that the measure of Y with
the least scatter is always obtained within a smaller radius than that at which
the mass is defined; e.g. for M_{200} (M_{500}) the scatter is least for
Y_{500} (Y_{1100}). The inclusion of energy feedback in the gas model
significantly increases the intrinsic scatter in the Y-M relation due to larger
variations in the gas mass fraction compared to models without feedback. We
also find that variations in halo concentration for clusters of a given mass
may partly explain why the integrated SZE provides a better mass proxy than the
central decrement. Substructure is found to account for approximately 20% of
the observed scatter in the Y-M relation. Above M_{200} = 2x10^{14} h^{-1}
msun, the SZ background does not significantly effect cluster mass
measurements; below this mass, variations in the background signal reduce the
optimal angular radius within which one should measure Y to achieve the
tightest scaling with M_{200}.
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An association scheme is called amorphic if every possible fusion of
relations gives rise to a fusion scheme. We call a pair of relations fusing if
fusing that pair gives rise to a fusion scheme. We define the fusing-relations
graph on the set of relations, where a pair forms an edge if it fuses. We show
that if the fusing-relations graph is connected but not a path, then the
association scheme is amorphic. As a side result, we show that an association
scheme in which at most one relation is not strongly regular of (negative)
Latin square type, is amorphic.
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Monochromatic coherent light traversing a disordered photonic medium evolves
into a random field whose statistics are dictated by the disorder level. Here
we demonstrate experimentally that light statistics can be deterministically
tuned in certain disordered lattices, even when the disorder level is held
fixed, by controllably breaking the excitation symmetry of the lattice modes.
We exploit a lattice endowed with disorder-immune chiral symmetry in which the
eigenmodes come in skew-symmetric pairs. If a single lattice site is excited, a
"photonic thermalization gap" emerges: the realm of sub-thermal light
statistics is inaccessible regardless of the disorder level. However, by
exciting two sites with a variable relative phase, as in a traditional two-path
interferometer, the chiral symmetry is judiciously broken and interferometric
control over the light statistics is exercised, spanning sub-thermal and
super-thermal regimes. These results may help develop novel incoherent lighting
sources from coherent lasers.
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We present a new family of exchangeable stochastic processes, the Functional
Neural Processes (FNPs). FNPs model distributions over functions by learning a
graph of dependencies on top of latent representations of the points in the
given dataset. In doing so, they define a Bayesian model without explicitly
positing a prior distribution over latent global parameters; they instead adopt
priors over the relational structure of the given dataset, a task that is much
simpler. We show how we can learn such models from data, demonstrate that they
are scalable to large datasets through mini-batch optimization and describe how
we can make predictions for new points via their posterior predictive
distribution. We experimentally evaluate FNPs on the tasks of toy regression
and image classification and show that, when compared to baselines that employ
global latent parameters, they offer both competitive predictions as well as
more robust uncertainty estimates.
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A pilot survey was sent to chairs of 14 doctoral math departments asking for
three types of data: (1) category on job-placements for research post-docs
leaving their department in three recent years; (2) category of jobs from which
their new faculty hires came in two recent years and two years a decade
earlier; and (3) preparation for future careers offered by their department to
their research post-docs. Eleven departments submitted data on post-docs. Of
the 162 departing post-docs for whom data was supplied, 25% obtained
tenure-track jobs in doctoral departments; 22% took another post-doc; and 18%
were reported as "unknown/other". The remaining 35% were evenly divided among
tenure-track in non-doctoral departments, full-time non-tenure-track, academic
outside the US, and business-industry-government. Eight departments gave
complete responses to (2): From the early 2000's to the early 2010's tenure
track hiring increased by about 35% (from 18 to 25). The changes across this
period as strikingly larger for other ranks: 233%(from 21 to 70) for research
post-docs and 211% (from 18 to 56)full-time non-tenure-track doctoral teaching
faculty. In section (3), all departments reported observing post-docs' teaching
and providing feedback. However, relatively few provided explicit preparation
for teaching or guidance for communicating with audiences other than research
specialists.
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The concept of complementarity, originally defined for non-commuting
observables of quantum systems with states of non-vanishing dispersion, is
extended to classical dynamical systems with a partitioned phase space.
Interpreting partitions in terms of ensembles of epistemic states (symbols)
with corresponding classical observables, it is shown that such observables are
complementary to each other with respect to particular partitions unless those
partitions are generating. This explains why symbolic descriptions based on an
\emph{ad hoc} partition of an underlying phase space description should
generally be expected to be incompatible. Related approaches with different
background and different objectives are discussed.
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A recently suggested modified BCS (MBCS) model has been studied at finite
temperature. We show that this approach does not allow the existence of the
normal (non-superfluid) phase at any finite temperature. Other MBCS predictions
such as a negative pairing gap, pairing induced by heating in closed-shell
nuclei, and ``superfluid -- super-superfluid'' phase transition are discussed
also. The MBCS model is tested by comparing with exact solutions for the picket
fence model. Here, severe violation of the internal symmetry of the problem is
detected. The MBCS equations are found to be inconsistent. The limit of the
MBCS applicability has been determined to be far below the ``superfluid --
normal'' phase transition of the conventional FT-BCS, where the model performs
worse than the FT-BCS.
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We derive masses of the central super-massive black hole (SMBH) and accretion
rates for 154 type1 AGN belonging to a well-defined X-ray-selected sample, the
XMM-Newton Serendipitous Sample (XBS). To this end, we use the most recent
"single-epoch" relations, based on Hbeta and MgII2798A emission lines, to
derive the SMBH masses. We then use the bolometric luminosities, computed on
the basis of an SED-fitting procedure, to calculate the accretion rates, both
absolute and normalized to the Eddington luminosity (Eddington ratio). The
selected AGNs cover a range of masses from 10^7 to 10^10 Msun with a peak
around 8x10^8 Msun and a range of accretion rates from 0.01 to ~50 Msun/year
(assuming an efficiency of 0.1), with a peak at ~1 Msun/year. The values of
Eddington ratio range from 0.001 to ~0.5 and peak at 0.1.
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Change captioning aims to succinctly describe the semantic change between a
pair of similar images, while being immune to distractors (illumination and
viewpoint changes). Under these distractors, unchanged objects often appear
pseudo changes about location and scale, and certain objects might overlap
others, resulting in perturbational and discrimination-degraded features
between two images. However, most existing methods directly capture the
difference between them, which risk obtaining error-prone difference features.
In this paper, we propose a distractors-immune representation learning network
that correlates the corresponding channels of two image representations and
decorrelates different ones in a self-supervised manner, thus attaining a pair
of stable image representations under distractors. Then, the model can better
interact them to capture the reliable difference features for caption
generation. To yield words based on the most related difference features, we
further design a cross-modal contrastive regularization, which regularizes the
cross-modal alignment by maximizing the contrastive alignment between the
attended difference features and generated words. Extensive experiments show
that our method outperforms the state-of-the-art methods on four public
datasets. The code is available at https://github.com/tuyunbin/DIRL.
|
For a torus knot K, we bound the crosscap number c(K) in terms of the genus
g(K) and crossing number n(K): c(K) \leq [(g(K)+9)/6] and c(K) \leq [(n(K) +
16)/12]. The (6n-2,3) torus knots show that these bounds are sharp.
|
The largest underground neutrino observatory, Super-Kamiokande, located near
Kamioka, Japan has been collecting data since April 1996. It is located at a
depth of roughly 2.7 kmwe in a zinc mine under a mountain, and has an effective
area for detecting entering-stopping and through-going muons of about $1238
m^2$ for muons of $>1.7 GeV$. These events are collected at a rate of 1.5 per
day from the lower hemisphere of arrival directions, with 2.5 muons per second
in the downgoing direction.
We report preliminary results from 229 live days analyzed so far with respect
to zenith angle variation of the upcoming muons. These results do not yet have
enough statistical weight to discriminate between the favored hypothesis for
muon neutrino oscillations and no-oscillations. We report on the search for
astrophysical sources of neutrinos and high energy neutrino fluxes from the sun
and earth center, as might arise from WIMP annihilations. None are found. We
also present a topographical map of the overburden made from the downgoing
muons. The detector is performing well, and with several years of data we
should be able to make significant progress in this area.
|
The need for wireless communication has driven the communication systems to
high performance. However, the main bottleneck that affects the communication
capability is the Fast Fourier Transform (FFT), which is the core of most
modulators. This study presents an on-chip implementation of pipeline
digit-slicing multiplier-less butterfly for FFT structure. The approach is
taken, in order to reduce computation complexity in the butterfly,
digit-slicing multiplier-less single constant technique was utilized in the
critical path of Radix-2 Decimation In Time (DIT) FFT structure. The proposed
design focused on the trade-off between the speed and active silicon area for
the chip implementation. The new architecture was investigated and simulated
with MATLAB software. The Verilog HDL code in Xilinx ISE environment was
derived to describe the FFT Butterfly functionality and was downloaded to
Virtex II FPGA board. Consequently, the Virtex-II FG456 Proto board was used to
implement and test the design on the real hardware. As a result, from the
findings, the synthesis report indicates the maximum clock frequency of 549.75
MHz with the total equivalent gate count of 31,159 is a marked and significant
improvement over Radix 2 FFT butterfly. In comparison with the conventional
butterfly architecture, the design that can only run at a maximum clock
frequency of 198.987 MHz and the conventional multiplier can only run at a
maximum clock frequency of 220.160 MHz, the proposed system exhibits better
results. The resulting maximum clock frequency increases by about 276.28% for
the FFT butterfly and about 277.06% for the multiplier. It can be concluded
that on-chip implementation of pipeline digit-slicing multiplier-less butterfly
for FFT structure is an enabler in solving problems that affect communications
capability in FFT and possesses huge potentials for future related works and
research areas.
|
Graph neural networks (GNNs) are the predominant approach for graph-based
machine learning. While neural networks have shown great performance at
learning useful representations, they are often criticized for their limited
high-level reasoning abilities. In this work, we present Graph Reasoning
Networks (GRNs), a novel approach to combine the strengths of fixed and learned
graph representations and a reasoning module based on a differentiable
satisfiability solver. While results on real-world datasets show comparable
performance to GNN, experiments on synthetic datasets demonstrate the potential
of the newly proposed method.
|
We recently demonstrated that the superconductor-to-insulator transition
induced by ionic liquid gating of the high temperature superconductor YBa2Cu3O7
(YBCO) is accompanied by a deoxygenation of the sample [Perez-Munoz et al.,
PNAS 114, 215 (2017)]. DFT calculations helped establish that the pronounced
changes in the spectral features of the Cu K-edge absorption spectra measured
in situ during the gating experiment arise from a decrease of the Cu
coordination within the CuO chains. In this work, we provide a detailed
analysis of the electronic structure origin of the changes in the spectra
resulting from three different types of doping: i) the formation of oxygen
vacancies within the CuO chains, ii) the formation of oxygen vacancies within
the CuO2 planes and iii) the electrostatic doping. For each case, three
stoichiometries are studied and compared to the stoichiometric YBa2Cu3O7, i.e
YBa2Cu3O6.75, YBa2Cu3O6.50 and YBa2Cu3O6.25. Computed vacancy formation
energies further support the chain-vacancy mechanism. In the case of doping by
vacancies within the chains, we study the effect of oxygen ordering on the
spectral features and we clarify the connection between the polarization of the
x-rays and this doping mechanism. Finally, the inclusion of the Hubbard U
correction on the computed spectra for antiferromagnetic YBa2Cu3O6.25 is
discussed.
|
We present an updated analysis of radial velocity data of the HD 82943
planetary system based on 10 years of measurements obtained with the Keck
telescope. Previous studies have shown that the HD 82943 system has two planets
that are likely in 2:1 mean-motion resonance (MMR), with the orbital periods
about 220 and 440 days (Lee et al. 2006). However, alternative fits that are
qualitatively different have also been suggested, with two planets in a 1:1
resonance (Gozdziewski & Konacki 2006) or three planets in a Laplace 4:2:1
resonance (Beauge et al. 2008). Here we use \c{hi}2 minimization combined with
parameter grid search to investigate the orbital parameters and dynamical
states of the qualitatively different types of fits, and we compare the results
to those obtained with the differential evolution Markov chain Monte Carlo
method. Our results support the coplanar 2:1 MMR configuration for the HD 82943
system, and show no evidence for either the 1:1 or 3-planet Laplace resonance
fits. The inclination of the system with respect to the sky plane is well
constrained at about 20(+4.9 -5.5) degree, and the system contains two planets
with masses of about 4.78 MJ and 4.80 MJ (where MJ is the mass of Jupiter) and
orbital periods of about 219 and 442 days for the inner and outer planet,
respectively. The best fit is dynamically stable with both eccentricity-type
resonant angles {\theta}1 and {\theta}2 librating around 0 degree.
|
We present our best estimates of the uncertainties due to heavy particle
threshold corrections on the unification scale $M_U$, intermediate scale $M_I$
and coupling constant Alpha_U in the minimal non-supersymmetric SO(10) models.
Using these , we update the predictions for proton life-time in these models.
|
This paper concerns estimates of the lifespan of solutions to the semilinear
damped wave equation. We give upper estimates of the lifespan for the
semilinear damped wave equation with variable coefficients in all space
dimensions.
|
Cosmology based on large scale peculiar velocity preferes volume weighted
velocity statistics. However, measuring the volume weighted velocity statistics
from inhomogeneously distributed galaxies (simulation particles/halos) suffer
from an inevitable and significant sampling artifact. We study this sampling
artifact in the velocity power spectrum measured by the nearest-particle (NP)
velocity assignment method(Zheng et al. 2013, PRD). We derive the analytical
expression of leading and higher order terms. We find that the sampling
artifact suppresses the $z=0$ E-mode velocity power spectrum by $\sim 10\%$ at
$k=0.1h/$Mpc , for samples with number density $10^{-3}({\rm Mpc}/h)^{-3}$.
This suppression becomes larger for larger $k$ and for sparser samples. We
argue that, this source of systematic errors in peculiar velocity cosmology,
albeit severe, can be self-calibrated in the framework of our theoretical
modelling. We also work out the sampling artifact in the density-velocity cross
power spectrum measurement. More robust evaluation of related statistics
through simulations will be presented in a companion paper (Zheng, Zhang &
Jing, 2015, PRD). We also argue that similar sampling artifact exists in other
velocity assignment methods and hence must be carefully corrected to avoid
systematic bias in peculiar velocity cosmology.
|
Bacterial microcompartments are large, roughly icosahedral shells that
assemble around enzymes and reactants involved in certain metabolic pathways in
bacteria. Motivated by microcompartment assembly, we use coarse-grained
computational and theoretical modeling to study the factors that control the
size and morphology of a protein shell assembling around hundreds to thousands
of molecules. We perform dynamical simulations of shell assembly in the
presence and absence of cargo over a range of interaction strengths, subunit
and cargo stoichiometries, and the shell spontaneous curvature. Depending on
these parameters, we find that the presence of a cargo can either increase or
decrease the size of a shell relative to its intrinsic spontaneous curvature,
as seen in recent experiments. These features are controlled by a balance of
kinetic and thermodynamic effects, and the shell size is assembly pathway
dependent. We discuss implications of these results for synthetic biology
efforts to target new enzymes to microcompartment interiors.
|
In this paper we characterize primitive branched coverings with minimal
defect over the projective plane with respect to the properties decomposable
and indecomposable. This minimality is achieved when the covering surface is
also the projective plane, which corresponds to the last case to be solved. As
a consequence, we have extended the family of realisations of branched
coverings on the projective plane and established a type of generalisation of
results on primitive permutation groups.
|
User-generated cinematic creations are gaining popularity as our daily
entertainment, yet it is a challenge to master cinematography for producing
immersive contents. Many existing automatic methods focus on roughly
controlling predefined shot types or movement patterns, which struggle to
engage viewers with the circumstances of the actor. Real-world cinematographic
rules show that directors can create immersion by comprehensively synchronizing
the camera with the actor. Inspired by this strategy, we propose a deep camera
control framework that enables actor-camera synchronization in three aspects,
considering frame aesthetics, spatial action, and emotional status in the 3D
virtual stage. Following rule-of-thirds, our framework first modifies the
initial camera placement to position the actor aesthetically. This adjustment
is facilitated by a self-supervised adjustor that analyzes frame composition
via camera projection. We then design a GAN model that can adversarially
synthesize fine-grained camera movement based on the physical action and
psychological state of the actor, using an encoder-decoder generator to map
kinematics and emotional variables into camera trajectories. Moreover, we
incorporate a regularizer to align the generated stylistic variances with
specific emotional categories and intensities. The experimental results show
that our proposed method yields immersive cinematic videos of high quality,
both quantitatively and qualitatively. Live examples can be found in the
supplementary video.
|
Previously published observations of 60 externally-polluted white dwarfs show
that none of the stars have accreted from intact refractory-dominated parent
bodies composed mainly of Al, Ca and O, although planetesimals with such a
distinctive composition have been predicted to form. We propose that such
remarkable objects are not detected, by themselves, because, unless they are
scattered outward from their initial orbit, they are engulfed and destroyed
during the star's Asymptotic Giant Branch evolution. As-yet, there is at most
only weak evidence supporting a scenario where the composition of any
extrasolar minor planet can be explained by blending of an outwardly scattered
refractory-dominated planetesimal with an ambient asteroid.
|
I discuss the theoretical motivations for R-parity violation, review the
experimental bounds and outline the main changes in collider phenomenology
compared to conserved R-parity. I briefly comment on the effects of R-parity
violation on cosmology.
|
The Scanning Quantum Cryogenic Atom Microscope (SQCRAMscope) is a quantum
sensor in which a quasi-1D quantum gas images electromagnetic fields emitted
from a nearby sample. We report improvements to the microscope. Cryogen usage
is reduced by replacing the liquid cryostat with a closed-cycle system and
modified cold finger, and cryogenic cooling is enhanced by adding a radiation
shield. The minimum accessible sample temperature is reduced from 35 K to 5.8 K
while maintaining low sample vibrations. A new sample mount is easier to
exchange, and quantum gas preparation is streamlined.
|
We probe the principle of complementarity by performing a double-slit
experiment based on entangled photons created by spontaneous parametric
down-conversion from a pump mode in a TEM01-mode. Our setup brings out the need
for a careful selection of the signal-idler photon pairs for our study of
visibility and distinguishability. Indeed, when the signal photons interfering
at the double-slit belong to this double-hump mode we obtain almost perfect
visibility of the interference fringes and no "which-slit" information is
available. However, when we break the symmetry between the two maxima of the
mode by detecting the entangled idler photon, the paths through the slits
become distinguishable and the visibility vanishes. It is the mode function of
the photons selected by the detection system which decides if interference, or
"which-slit" information is accessible in the experiment.
|
While the majority of approaches to the characterization of complex networks
has relied on measurements considering only the immediate neighborhood of each
network node, valuable information about the network topological properties can
be obtained by considering further neighborhoods. The current work discusses on
how the concepts of hierarchical node degree and hierarchical clustering
coefficient (introduced in cond-mat/0408076), complemented by new hierarchical
measurements, can be used in order to obtain a powerful set of topological
features of complex networks. The interpretation of such measurements is
discussed, including an analytical study of the hierarchical node degree for
random networks, and the potential of the suggested measurements for the
characterization of complex networks is illustrated with respect to simulations
of random, scale-free and regular network models as well as real data
(airports, proteins and word associations). The enhanced characterization of
the connectivity provided by the set of hierarchical measurements also allows
the use of agglomerative clustering methods in order to obtain taxonomies of
relationships between nodes in a network, a possibility which is also
illustrated in the current article.
|
Predicting camera-space hand meshes from single RGB images is crucial for
enabling realistic hand interactions in 3D virtual and augmented worlds.
Previous work typically divided the task into two stages: given a cropped image
of the hand, predict meshes in relative coordinates, followed by lifting these
predictions into camera space in a separate and independent stage, often
resulting in the loss of valuable contextual and scale information. To prevent
the loss of these cues, we propose unifying these two stages into an end-to-end
solution that addresses the 2D-3D correspondence problem. This solution enables
back-propagation from camera space outputs to the rest of the network through a
new differentiable global positioning module. We also introduce an image
rectification step that harmonizes both the training dataset and the input
image as if they were acquired with the same camera, helping to alleviate the
inherent scale-depth ambiguity of the problem. We validate the effectiveness of
our framework in evaluations against several baselines and state-of-the-art
approaches across three public benchmarks.
|
A report on the works hep-th/9411050, q-alg/9412017, q-alg/9503013,
q-alg/9506011 and a joint work with R.Bezrukavnikov.
|
A diffusion auction is a market to sell commodities over a social network,
where the challenge is to incentivize existing buyers to invite their neighbors
in the network to join the market. Existing mechanisms have been designed to
solve the challenge in various settings, aiming at desirable properties such as
non-deficiency, incentive compatibility and social welfare maximization. Since
the mechanisms are employed in dynamic networks with ever-changing structures,
buyers could easily generate fake nodes in the network to manipulate the
mechanisms for their own benefits, which is commonly known as the Sybil attack.
We observe that strategic agents may gain an unfair advantage in existing
mechanisms through such attacks. To resist this potential attack, we propose
two diffusion auction mechanisms, the Sybil tax mechanism (STM) and the Sybil
cluster mechanism (SCM), to achieve both Sybil-proofness and incentive
compatibility in the single-item setting. Our proposal provides the first
mechanisms to protect the interests of buyers against Sybil attacks with a mild
sacrifice of social welfare and revenue.
|
Heteroskedasticity is a statistical anomaly that describes differing
variances of error terms in a time series dataset. The presence of
heteroskedasticity in data imposes serious challenges for forecasting models
and many statistical tests are not valid in the presence of heteroskedasticity.
Heteroskedasticity of the data affects the relation between the predictor
variable and the outcome, which leads to false positive and false negative
decisions in the hypothesis testing. Available approaches to study
heteroskedasticity thus far adopt the strategy of accommodating
heteroskedasticity in the time series and consider it an inevitable source of
noise. In these existing approaches, two forecasting models are prepared for
normal and heteroskedastic scenarios and a statistical test is to determine
whether or not the data is heteroskedastic.
This work-in-progress research introduces a quantifying measurement for
heteroskedasticity. The idea behind the proposed metric is the fact that a
heteroskedastic time series features a uniformly distributed local variances.
The proposed measurement is obtained by calculating the local variances using
linear time invariant filters. A probability density function of the calculated
local variances is then derived and compared to a uniform distribution of
theoretical ultimate heteroskedasticity using statistical divergence
measurements. The results demonstrated on synthetic datasets shows a strong
correlation between the proposed metric and number of variances locally
estimated in a heteroskedastic time series.
|
We present an efficient Monte Carlo framework for perturbative calculations
of infinite nuclear matter based on chiral two-, three-, and four-nucleon
interactions. The method enables the incorporation of all many-body
contributions in a straightforward and transparent way, and makes it possible
to extract systematic uncertainty estimates by performing order-by-order
calculations in the chiral expansion as well as the many-body expansion. The
versatility of this new framework is demonstrated by applying it to chiral
low-momentum interactions, exhibiting a very good many-body convergence up to
fourth order. Following these benchmarks, we explore new chiral interactions up
to next-to-next-to-next-to-leading order (N$^3$LO). Remarkably, simultaneous
fits to the triton and to saturation properties can be achieved, while all
three-nucleon low-energy couplings remain natural. The theoretical
uncertainties of nuclear matter are significantly reduced when going from
next-to-next-to-leading order to N$^3$LO.
|
The primary goal in the study of entanglement as a resource theory is to find
conditions that determine when one quantum state can or cannot be transformed
into another via local operations and classical communication. This is
typically done through entanglement monotones or conversion witnesses. Such
quantities cannot be computed for arbitrary quantum states in general, but it
is useful to consider classes of symmetric states for which closed-form
expressions can be found. In this paper, we show how to compute the convex roof
of any entanglement monotone for all Werner states. The convex roofs of the
well-known Vidal monotones are computed for all isotropic states, and we show
how this method can generalize to other entanglement measures and other types
of symmetries as well. We also present necessary and sufficient conditions that
determine when a pure bipartite state can be deterministically converted into a
Werner state or an isotropic state.
|
EIT waves are a wavelike phenomenon propagating outward from the coronal mass
ejection (CME) source region, with expanding dimmings following behind. We
present a spectroscopic study of an EIT wave/dimming event observed by
Hinode/EIS. Although the identification of the wave front is somewhat affected
by the pre-existing loop structures, the expanding dimming is well defined. We
investigate the line intensity, width, and Doppler velocity for 4 EUV lines. In
addition to the significant blue shift implying plasma outflows in the dimming
region as revealed in previous studies, we find that the widths of all the 4
spectral lines increase at the outer edge of the dimmings. We illustrate that
this feature can be well explained by the field line stretching model, which
claims that EIT waves are apparently moving brightenings that are generated by
the successive stretching of the closed field lines.
|
We have investigated the electronic and magnetic response of a single Fe atom
and a pair of interacting Fe atoms placed in patterned dehydrogenated channels
in graphane within the framework of density functional theory. We have
considered two channels: "armchair" and "zigzag" channels. Fully relaxed
calculations have been carried out for three different channel widths. Our
calculations reveal that the response to the magnetic impurities is very
different for these two channels. We have also shown that one can stabilize
magnetic impurities (Fe in the present case) along the channels of bare carbon
atoms, giving rise to a magnetic insulator or a spin gapless semiconductor. Our
calculations with spin-orbit coupling shows a large in-plane magnetic
anisotropy energy for the case of the armchair channel. The magnetic exchange
coupling between two Fe atoms placed in the semiconducting channel with an
armchair edge is very weakly ferromagnetic whereas a fairly strong
ferromagnetic coupling is observed for reasonable separations between Fe atoms
in the zigzag-edged metallic channel with the coupling mediated by the bare
carbon atoms. The possibility of realizing an ultrathin device with interesting
magnetic properties is discussed.
|
We introduce an interatomic potential for hexagonal boron nitride (hBN) based
on the Gaussian approximation potential (GAP) machine learning methodology. The
potential is based on a training set of configurations collected from density
functional theory (DFT) simulations and is capable of treating bulk and
multilayer hBN as well as nanotubes of arbitrary chirality. The developed force
field faithfully reproduces the potential energy surface predicted by DFT while
improving the efficiency by several orders of magnitude. We test our potential
by comparing formation energies, geometrical properties, phonon dispersion
spectra and mechanical properties with respect to benchmark DFT calculations
and experiments. In addition, we use our model and a recently developed
graphene-GAP to analyse and compare thermally and mechanically induced rippling
in large scale two-dimensional (2D) hBN and graphene. Both materials show
almost identical scaling behaviour with an exponent of $\eta \approx 0.85$ for
the height fluctuations agreeing well with the theory of flexible membranes.
Based on its lower resistance to bending, however, hBN experiences slightly
larger out-of-plane deviations both at zero and finite applied external strain.
Upon compression a phase transition from incoherent ripple motion to
soliton-ripples is observed for both materials. Our potential is freely
available online at [http://www.libatoms.org].
|
Diffuse emission is produced in energetic cosmic ray (CR) interactions,
mainly protons and electrons, with the interstellar gas and radiation field and
contains the information about particle spectra in distant regions of the
Galaxy. It may also contain information about exotic processes such as dark
matter annihilation, black hole evaporation etc. A model of the diffuse
emission is important for determination of the source positions and spectra.
Calculation of the Galactic diffuse continuum gamma-ray emission requires a
model for CR propagation as the first step. Such a model is based on theory of
particle transport in the interstellar medium as well as on many kinds of data
provided by different experiments in Astrophysics and Particle and Nuclear
Physics. Such data include: secondary particle and isotopic production cross
sections, total interaction nuclear cross sections and lifetimes of radioactive
species, gas mass calibrations and gas distribution in the Galaxy (H_2, H I, H
II), interstellar radiation field, CR source distribution and particle spectra
at the sources, magnetic field, energy losses, gamma-ray and synchrotron
production mechanisms, and many other issues. We are continuously improving the
GALPROP model and the code to keep up with a flow of new data. Improvement in
any field may affect the Galactic diffuse continuum gamma-ray emission model
used as a background model by the GLAST LAT instrument. Here we report about
the latest improvements of the GALPROP and the diffuse emission model.
|
Using the results of arXiv:0804.0009, where all timelike supersymmetric
backgrounds of N=2, D=4 matter-coupled supergravity with Fayet-Iliopoulos
gauging were classified, we construct genuine nut-charged BPS black holes in
AdS_4 with nonconstant moduli. The calculations are exemplified for the
SU(1,1)/U(1) model with prepotential F=-iX^0X^1. The resulting supersymmetric
black holes have a hyperbolic horizon and carry two electric, two magnetic and
one nut charge, which are however not all independent, but are given in terms
of three free parameters. We find that turning on a nut charge lifts the flat
directions in the effective black hole potential, such that the horizon values
of the scalars are completely fixed by the charges. We also oxidize the
solutions to eleven dimensions, and find that they generalize the geometry
found in hep-th/0105250 corresponding to membranes wrapping holomorphic curves
in a Calabi-Yau five-fold. Finally, a class of nut-charged Nernst branes is
constructed as well, but these have curvature singularities at the horizon.
|
Diffuse cluster radio sources, in the form of radio halos and relics, reveal
the presence of cosmic rays and magnetic fields in the intracluster medium
(ICM). These cosmic rays are thought to be (re-)accelerated through ICM
turbulence and shock waves generated by cluster merger events. Here we
characterize the presence of diffuse radio emission in known galaxy clusters in
the HETDEX Spring Field, covering 424 deg$^2$. For this, we developed a method
to extract individual targets from LOFAR observations processed with the LoTSS
DDF-pipeline. This procedure enables improved calibration and joint imaging and
deconvolution of multiple pointings of selected targets. The calibration
strategy can also be used for LOFAR Low-Band Antenna (LBA) and
international-baseline observations.
The fraction of Planck PSZ2 clusters with any diffuse radio emission
apparently associated with the ICM is $73\pm17\%$. We detect a total of 10
radio halos and 12 candidate halos in the HETDEX Spring Field. Five clusters
host radio relics. The fraction of radio halos in Planck PSZ2 clusters is
$31\pm11\%$, and $62\pm15\%$ when including the candidate radio halos. Based on
these numbers, we expect that there will be at least $183 \pm 65$ radio halos
found in the LoTSS survey in PSZ2 clusters, in agreement with predictions. The
integrated flux densities for the radio halos were computed by fitting
exponential models to the radio images. From these flux densities, we determine
the cluster mass (M$_{500}$) and Compton Y parameter (Y$_{500}$) 150 MHz radio
power (P$_{\rm{150 MHz}}$) scaling relations for Planck PSZ2-detected radio
halos. We find that the slopes of these relations are steeper than those
determined from the 1.4 GHz radio powers. However, considering the
uncertainties this is not a statistically significant result.
|
We provide the theoretical basis of calorimetry for a class of active
particles subject to thermal noise. Simulating AC-calorimetry, we numerically
evaluate the heat capacity of run-and-tumble particles in double-well and in
periodic potentials, and of systems with a flashing potential. Low-temperature
Schottky-like peaks show the role of activity and indicate shape transitions,
while regimes of negative heat capacity appear at higher propulsion speeds.
From there, a significant increase in heat capacities of active systems may be
inferred at low temperatures, as well as the possibility of diagnostic tools
for the activity of self-motile artificial or biomimetic systems based on heat
capacity measurements.
|
Answering a question of Benjamini, we present an isometry-invariant random
partition of the Euclidean space $\mathbb{R}^d$, $d\geq 3$, into infinite
connected indistinguishable pieces, such that the adjacency graph defined on
the pieces is the 3-regular infinite tree. Along the way, it is proved that any
finitely generated one-ended amenable Cayley graph can be represented in
$\mathbb{R}^d$ as an isometry-invariant random partition of $\mathbb{R}^d$ to
bounded polyhedra, and also as an isometry-invariant random partition of
$\mathbb{R}^d$ to indistinguishable pieces. A new technique is developed to
prove indistinguishability for certain constructions, connecting this notion to
factor of iid's.
|
Coherently manipulating Rydberg atoms in mesoscopic systems has proven
challenging due to the unwanted population of nearby Rydberg levels by
black-body radiation. Recently, there have been some efforts towards
understanding these effects using states with a low principal quantum number
that only have resonant dipole-dipole interactions. We perform experiments that
exhibit black-body-induced dipole-dipole interactions for a state that also has
a significant van der Waals interaction. Using an enhanced rate-equation model
that captures some of the long-range properties of the dipolar interaction, we
show that the initial degree of Rydberg excitation is dominated by the van der
Waals interaction, while the observed linewidth at later times is dominated by
the dipole-dipole interaction. We also point out some prospects for quantum
simulation.
|
The last decade has witnessed an experimental revolution in data science and
machine learning, epitomised by deep learning methods. Indeed, many
high-dimensional learning tasks previously thought to be beyond reach -- such
as computer vision, playing Go, or protein folding -- are in fact feasible with
appropriate computational scale. Remarkably, the essence of deep learning is
built from two simple algorithmic principles: first, the notion of
representation or feature learning, whereby adapted, often hierarchical,
features capture the appropriate notion of regularity for each task, and
second, learning by local gradient-descent type methods, typically implemented
as backpropagation.
While learning generic functions in high dimensions is a cursed estimation
problem, most tasks of interest are not generic, and come with essential
pre-defined regularities arising from the underlying low-dimensionality and
structure of the physical world. This text is concerned with exposing these
regularities through unified geometric principles that can be applied
throughout a wide spectrum of applications.
Such a 'geometric unification' endeavour, in the spirit of Felix Klein's
Erlangen Program, serves a dual purpose: on one hand, it provides a common
mathematical framework to study the most successful neural network
architectures, such as CNNs, RNNs, GNNs, and Transformers. On the other hand,
it gives a constructive procedure to incorporate prior physical knowledge into
neural architectures and provide principled way to build future architectures
yet to be invented.
|
West African Pidgin English is a language that is significantly spoken in
West Africa, consisting of at least 75 million speakers. Nevertheless, proper
machine translation systems and relevant NLP datasets for pidgin English are
virtually absent. In this work, we develop techniques targeted at bridging the
gap between Pidgin English and English in the context of natural language
generation. %As a proof of concept, we explore the proposed techniques in the
area of data-to-text generation. By building upon the previously released
monolingual Pidgin English text and parallel English data-to-text corpus, we
hope to build a system that can automatically generate Pidgin English
descriptions from structured data. We first train a data-to-English text
generation system, before employing techniques in unsupervised neural machine
translation and self-training to establish the Pidgin-to-English cross-lingual
alignment. The human evaluation performed on the generated Pidgin texts shows
that, though still far from being practically usable, the pivoting +
self-training technique improves both Pidgin text fluency and relevance.
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The large majority of the research performed on stance detection has been
focused on developing more or less sophisticated text classification systems,
even when many benchmarks are based on social network data such as Twitter.
This paper aims to take on the stance detection task by placing the emphasis
not so much on the text itself but on the interaction data available on social
networks. More specifically, we propose a new method to leverage social
information such as friends and retweets by generating relational embeddings,
namely, dense vector representations of interaction pairs. Our method can be
applied to any language and target without any manual tuning. Our experiments
on seven publicly available datasets and four different languages show that
combining our relational embeddings with textual methods helps to substantially
improve performance, obtaining best results for six out of seven evaluation
settings, outperforming strong baselines based on large pre-trained language
models.
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The rate constants required to model the OH$^+$ observations in different
regions of the interstellar medium have been determined using state of the art
quantum methods.
First, state-to-state rate constants for the H$_2(v=0,J=0,1)$+ O$^+$($^4S$)
$\rightarrow$ H + OH$^+(X ^3\Sigma^-, v', N)$ reaction have been obtained using
a quantum wave packet method. The calculations have been compared with
time-independent results to asses the accuracy of reaction probabilities at
collision energies of about 1 meV. The good agreement between the simulations
and the existing experimental cross sections in the $0.01-$1 eV energy range
shows the quality of the results.
The calculated state-to-state rate constants have been fitted to an
analytical form. Second, the Einstein coefficients of OH$^+$ have been obtained
for all astronomically significant ro-vibrational bands involving the
$X^3\Sigma^-$ and/or $A^3\Pi$ electronic states.
For this purpose the potential energy curves and electric dipole transition
moments for seven electronic states of OH$^+$ are calculated with {\it ab
initio} methods at the highest level and including spin-orbit terms, and the
rovibrational levels have been calculated including the empirical spin-rotation
and spin-spin terms. Third, the state-to-state rate constants for inelastic
collisions between He and OH$^+(X ^3\Sigma^-)$ have been calculated using a
time-independent close coupling method on a new potential energy surface. All
these rates have been implemented in detailed chemical and radiative transfer
models. Applications of these models to various astronomical sources show that
inelastic collisions dominate the excitation of the rotational levels of
OH$^+$. In the models considered the excitation resulting from the chemical
formation of OH$^+$ increases the line fluxes by about 10 % or less depending
on the density of the gas.
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The problem of differentiating a function with bounded second derivative in
the presence of bounded measurement noise is considered in both continuous-time
and sampled-data settings. Fundamental performance limitations of causal
differentiators, in terms of the smallest achievable worst-case differentiation
error, are shown. A robust exact differentiator is then constructed via the
adaptation of a single parameter of a linear differentiator. It is demonstrated
that the resulting differentiator exhibits a combination of properties that
outperforms existing continuous-time differentiators: it is robust with respect
to noise, it instantaneously converges to the exact derivative in the absence
of noise, and it attains the smallest possible -- hence optimal -- upper bound
on its differentiation error under noisy measurements. For sample-based
differentiators, the concept of quasi-exactness is introduced to classify
differentiators that achieve the lowest possible worst-case error based on
sampled measurements in the absence of noise. A straightforward sample-based
implementation of the proposed linear adaptive continuous-time differentiator
is shown to achieve quasi-exactness after a single sampling step as well as a
theoretically optimal differentiation error bound that, in addition, converges
to the continuous-time optimal one as the sampling period becomes arbitrarily
small. A numerical simulation illustrates the presented formal results.
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The phase structure of QCD-like gauge theories with fermions in various
representations is an interesting but generally analytically intractable
problem. One way to ensure weak coupling is to define the theory in a small
finite volume, in this case S^3 x S^1. Genuine phase transitions can then occur
in the large N theory. Here, we use this technique to investigate SU(N) gauge
theory with a number N_f of massive adjoint-valued Majorana fermions having
non-thermal boundary conditions around S^1. For N_f =1 we find a line of
transitions that separate the weak-coupling analogues of the confined and
de-confined phases for which the density of eigenvalues of the Wilson line
transform from the uniform distribution to a gapped distribution. However, the
situation for N_f >1 is much richer and a series of weak-coupling analogues of
partially-confined phases appear which leave unbroken a Z_p subgroup of the
centre symmetry. In these Z_p phases the eigenvalue density has p gaps and they
are separated from the confining phase and from one-another by first order
phase transitions. We show that for small enough mR (the mass of the fermions
times the radius of the S^3) only the confined phase exists. The large N phase
diagram is consistent with the finite N result and with other approaches based
on R^3 x S^1 calculations and lattice simulations.
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We investigate, through the density-matrix renormalization group and the
Lanczos technique, the possibility of a two-leg Kondo ladder present an
incommensurate orbital order. Our results indicate a staggered short-range
orbital order at half-filling. Away from half-filling our data are consistent
with an incommensurate quasi-long-range orbital order. We also observed that an
interaction between the localized spins enhances the rung-rung current
correlations.
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In this paper, a novel conserved Lorentz covariant tensor, termed the
helicity tensor, is introduced in Maxwell theory. The conservation of the
helicity tensor expresses the conservation laws contained in the helicity
array, introduced by Cameron et al., including helicity, spin, and the
spin-flux or infra-zilch. The Lorentz covariance of the helicity tensor is in
contrast to previous formulations of the helicity hierarchy of conservation
laws, which required the non-Lorentz covariant transverse gauge. The helicity
tensor is shown to arise as a Noether current for a variational symmetry of a
duality-symmetric Lagrangian for Maxwell theory. This symmetry transformation
generalizes the duality symmetry and includes the symmetry underlying the
conservation of the spin part of the angular momentum.
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Atomistic simulations based on the first-principles of quantum mechanics are
reaching unprecedented length scales. This progress is due to the growth in
computational power allied with the development of new methodologies that allow
the treatment of electrons and nuclei as quantum particles. In the realm of
materials science, where the quest for desirable emergent properties relies
increasingly on soft weakly-bonded materials, such methods have become
indispensable. In this perspective, an overview of simulation methods that are
applicable for large system sizes and that can capture the quantum nature of
electrons and nuclei in the adiabatic approximation is given. In addition, the
remaining challenges are discussed, especially regarding the inclusion of
nuclear quantum effects (NQE) beyond a harmonic or perturbative treatment, the
impact of NQE on electronic properties of weakly-bonded systems, and how
different first-principles potential energy surfaces can change the impact of
NQE on the atomic structure and dynamics of weakly bonded systems.
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Harmonic numbers have been studied since antiquity, while hyperharmonic
numbers were intoduced by Conway and Guy in 1996. The degenerate harmonic
numbers and degenerate hyperharmonic numbers are their respective degenerate
versions. The aim of this paper is to further investigate some properties,
recurrence relations and identities involving the degenerate harmonic and
degenerate hyperharmonic numbers in connection with degenerate Stirling numbers
of the first kind, degenerate Daehee numbers and degenerate derangements.
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Rhombic cell analysis as outlined in the first paper of the present series is
applied to samples of varying depths and liming luminosities of the IRAS/PSCz
Catalogue. Numerical indices are introduced to summarize essential information.
Because of the discrete nature of the anlaysis and of the space distribution of
galaxies, the indices for a given sample must be regarded as each having an
irreducible scatter. Despite the scatter, the mean indices show remarkable
variations across the samples. The underlying factor for the variations is
shown to be the limiting luminosity rather than the sampling depth. As samples
of more and more luminous galaxies are considered over a range of some 2
magnitudes (a factor of some 50 in space density), the morpholgy of the filled
and empty regions the galaxies define degrades steadily towards insignificance,
and the degrading is faster for the filled than the empty region.
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In the propositional setting, the marginal problem is to find a
(maximum-entropy) distribution that has some given marginals. We study this
problem in a relational setting and make the following contributions. First, we
compare two different notions of relational marginals. Second, we show a
duality between the resulting relational marginal problems and the maximum
likelihood estimation of the parameters of relational models, which generalizes
a well-known duality from the propositional setting. Third, by exploiting the
relational marginal formulation, we present a statistically sound method to
learn the parameters of relational models that will be applied in settings
where the number of constants differs between the training and test data.
Furthermore, based on a relational generalization of marginal polytopes, we
characterize cases where the standard estimators based on feature's number of
true groundings needs to be adjusted and we quantitatively characterize the
consequences of these adjustments. Fourth, we prove bounds on expected errors
of the estimated parameters, which allows us to lower-bound, among other
things, the effective sample size of relational training data.
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We investigate the scattered palindromic subwords in a finite word. We start
by characterizing the words with the least number of scattered palindromic
subwords. Then, we give an upper bound for the total number of palindromic
subwords in a word of length $n$ in terms of Fibonacci number $F_n$ by proving
that at most $F_n$ new scattered palindromic subwords can be created on the
concatenation of a letter to a word of length $n-1$. We propose a conjecture on
the maximum number of scattered palindromic subwords in a word of length $n$
with $q$ distinct letters. We support the conjecture by showing its validity
for words where $q\geq \frac{n}{2}$.
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Minimal Supersymmetric Standard Model with gauge mediated supersymmetry
breaking has all the necessary ingredients for a successful sub-eV Hubble scale
inflation $H_{\rm inf} \sim 10^{-3}-10^{-1}$ eV. The model generates the right
amplitude for scalar density perturbations and a spectral tilt within the
range, $0.90 \leq n_s \leq 1$. The reheat temperature is $T_{\rm R} \ls 10$
TeV, which strongly prefers electroweak baryogenesis and creates the right
abundance of gravitinos with a mass $m_{3/2} \gs 100$ keV to be the dark
matter.
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We perform a semiclassical analysis for the planar Schr\"odinger-Poisson
system
\[
\cases{
-\varepsilon^{2} \Delta\psi+V(x)\psi= E(x) \psi \quad \text{in
$\mathbb{R}^2$},\cr
-\Delta E= |\psi|^{2} \quad \text{in $\mathbb{R}^2$}, \cr
} \tag{$SP_\varepsilon$}
\] where $\varepsilon$ is a positive parameter corresponding to the Planck
constant and $V$ is a bounded external potential. We detect solution pairs
$(u_\varepsilon, E_\varepsilon)$ of the system $(SP_\varepsilon)$ as~$\ge
\rightarrow 0$.
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Alpha and cluster decays are analyzed for heavy nuclei located above
$^{208}$Pb on the chart of nuclides: $^{216-220}$Rn and $^{220-224}$Ra, that
are also candidates for observing the $2 \alpha$ decay mode. A microscopic
theoretical approach based on relativistic Energy Density Functionals (EDF), is
used to compute axially-symmetric deformation energy surfaces as functions of
quadrupole, octupole and hexadecupole collective coordinates. Dynamical
least-action paths for specific decay modes are calculated on the corresponding
potential energy surfaces. The effective collective inertia is determined using
the perturbative cranking approximation, and zero-point and rotational energy
corrections are included in the model. The predicted half-lives for
$\alpha$-decay are within one order of magnitude of the experimental values. In
the case of single $\alpha$ emission, the nuclei considered in the present
study exhibit least-action paths that differ significantly up to the scission
point. The differences in alpha-decay lifetimes are not only driven by Q
values, but also by variances of the least-action paths prior to scission. In
contrast, the $2 \alpha$ decay mode presents very similar paths from
equilibrium to scission, and the differences in lifetimes are mainly driven by
the corresponding Q values. The predicted $^{14}$C cluster decay half-lives are
within three orders of magnitudes of the empirical values, and point to a much
more complex pattern compared to the alpha-decay mode.
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The orbit-sum method is an algebraic version of the reflection-principle that
was introduced by Bousquet-M\'{e}lou and Mishna to solve functional equations
that arise in the enumeration of lattice walks with small steps restricted to
$\mathbb{N}^2$. Its extension to walks with large steps was started by Bostan,
Bousquet-M\'{e}lou and Melczer. We continue it here, making use of the
primitive element theorem, Gr\"{o}bner bases and the shape lemma, and the
Newton-Puiseux algorithm.
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Borrowing constraints are a key component of modern international
macroeconomic models. The analysis of Emerging Markets (EM) economies generally
assumes collateral borrowing constraints, i.e., firms access to debt is
constrained by the value of their collateralized assets. Using credit registry
data from Argentina for the period 1998-2020 we show that less than 15% of
firms debt is based on the value of collateralized assets, with the remaining
85% based on firms cash flows. Exploiting central bank regulations over banks
capital requirements and credit policies we argue that the most prevalent
borrowing constraints is defined in terms of the ratio of their interest
payments to a measure of their present and past cash flows, akin to the
interest coverage borrowing constraint studied by the corporate finance
literature. Lastly, we argue that EMs exhibit a greater share of interest
sensitive borrowing constraints than the US and other Advanced Economies. From
a structural point of view, we show that in an otherwise standard small open
economy DSGE model, an interest coverage borrowing constraints leads to
significantly stronger amplification of foreign interest rate shocks compared
to the standard collateral constraint. This greater amplification provides a
solution to the Spillover Puzzle of US monetary policy rates by which EMs
experience greater negative effects than Advanced Economies after a US interest
rate hike. In terms of policy implications, this greater amplification leads to
managed exchange rate policy being more costly in the presence of an interest
coverage constraint, given their greater interest rate sensitivity, compared to
the standard collateral borrowing constraint.
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We present four-dimensional ab initio potential energy surfaces for the three
spin states of the NH-NH complex. The potentials are partially based on the
work of Dhont et al. [J. Chem. Phys. 123, 184302 (2005)]. The surface for the
quintet state is obtained at the RCCSD(T)/aug-cc-pVTZ level of theory and the
energy diferences with the singlet and triplet states are calculated at the
CASPTn/aug-cc-pVTZ (n = 2; 3) level of theory. The ab initio potentials are
fitted to coupled spherical harmonics in the angular coordinates, and the long
range is further expanded as a power series in 1/R. The RCCSD(T) potential is
corrected for a size-consistency error prior to fitting. The long-range
coeficients obtained from the fit are found to be in good agreement with
perturbation theory calculations.
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Modeling and synthesizing low-light raw noise is a fundamental problem for
computational photography and image processing applications. Although most
recent works have adopted physics-based models to synthesize noise, the
signal-independent noise in low-light conditions is far more complicated and
varies dramatically across camera sensors, which is beyond the description of
these models. To address this issue, we introduce a new perspective to
synthesize the signal-independent noise by a generative model. Specifically, we
synthesize the signal-dependent and signal-independent noise in a physics- and
learning-based manner, respectively. In this way, our method can be considered
as a general model, that is, it can simultaneously learn different noise
characteristics for different ISO levels and generalize to various sensors.
Subsequently, we present an effective multi-scale discriminator termed Fourier
transformer discriminator (FTD) to distinguish the noise distribution
accurately. Additionally, we collect a new low-light raw denoising (LRD)
dataset for training and benchmarking. Qualitative validation shows that the
noise generated by our proposed noise model can be highly similar to the real
noise in terms of distribution. Furthermore, extensive denoising experiments
demonstrate that our method performs favorably against state-of-the-art methods
on different sensors.
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Recent advances on 3D object detection heavily rely on how the 3D data are
represented, \emph{i.e.}, voxel-based or point-based representation. Many
existing high performance 3D detectors are point-based because this structure
can better retain precise point positions. Nevertheless, point-level features
lead to high computation overheads due to unordered storage. In contrast, the
voxel-based structure is better suited for feature extraction but often yields
lower accuracy because the input data are divided into grids. In this paper, we
take a slightly different viewpoint -- we find that precise positioning of raw
points is not essential for high performance 3D object detection and that the
coarse voxel granularity can also offer sufficient detection accuracy. Bearing
this view in mind, we devise a simple but effective voxel-based framework,
named Voxel R-CNN. By taking full advantage of voxel features in a two stage
approach, our method achieves comparable detection accuracy with
state-of-the-art point-based models, but at a fraction of the computation cost.
Voxel R-CNN consists of a 3D backbone network, a 2D bird-eye-view (BEV) Region
Proposal Network and a detect head. A voxel RoI pooling is devised to extract
RoI features directly from voxel features for further refinement. Extensive
experiments are conducted on the widely used KITTI Dataset and the more recent
Waymo Open Dataset. Our results show that compared to existing voxel-based
methods, Voxel R-CNN delivers a higher detection accuracy while maintaining a
real-time frame processing rate, \emph{i.e}., at a speed of 25 FPS on an NVIDIA
RTX 2080 Ti GPU. The code is available at
\url{https://github.com/djiajunustc/Voxel-R-CNN}.
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The theory of locally anisotropic superspaces (supersymmetric generalizations
of various types of Kaluza--Klein, Lagrange and Finsler spaces) is laid down.
In this framework we perform the analysis of construction of the supervector
bundles provided with nonlinear and distinguished connections and metric
structures. Two models of locally anisotropic supergravity are proposed and
studied in details.
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We present a multiple time step algorithm for hybrid path integral Monte
Carlo simulations involving rigid linear rotors. We show how to calculate the
quantum torques needed in the simulation from the rotational density matrix,
for which we develop an approximate expression suitable in the case of
heteronuclear molecules.
We use this method to study the effect of rotational quantization on the
quantum sieving properties of carbon nanotubes, with particular emphasis to the
para-T2/para-H2 selectivity at 20 K. We show how to treat classically only some
of the degrees of freedom of the hydrogen molecule and we find that in the
limit of zero pressure the quantized nature of the rotational degrees of
freedom greatly influence the selectivity, especially in the case of the (3,6)
nanotube, which is the narrowest tube that we have studied.
We also use path integral Monte Carlo simulations to calculate adsorption
isotherms of different hydrogen isotopes in the interior of carbon nanotubes
and the corresponding selectivity at finite pressures. It is found that the
selectivity increases with respect to the zero pressure value and tends to a
constant value at saturation. We use a simplified effective harmonic oscillator
model to discuss the origin of this behavior.
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We show that in the presence of U(1) noncommutative gauge interaction the
noncommutative tachyonic system exhibits solitonic solutions for finite value
of the noncommutativity parameter.
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This paper has been withdrawn by the authors.
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We examine the stability issue in the inverse problem of determining a scalar
potential appearing in the stationary Schr{\"o}dinger equation in a bounded
domain, from a partial elliptic Dirichlet-to-Neumann map. Namely, the Dirichlet
data is imposed on the shadowed face of the boundary of the domain and the
Neumann data is measured on its illuminated face. We establish a log log
stability estimate for the L2-norm (resp. the H minus 1-norm) of bounded (resp.
L2) potentials whose difference is lying in any Sobolev space of order positive
order.
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We present the abundance analysis of 97 nearby metal-poor (-3.3<[Fe/H]<-0.5)
stars having kinematics characteristics of the Milky Way (MW) thick disk,
inner, and outer stellar halos. The high-resolution, high-signal-to-noise
optical spectra for the sample stars have been obtained with the High
Dispersion Spectrograph mounted on the Subaru Telescope. Abundances of Fe, Mg,
Si, Ca and Ti have been derived using a one-dimensional LTE abundance analysis
code with Kurucz NEWODF model atmospheres. By assigning membership of the
sample stars to the thick disk, inner or outer halo components based on their
orbital parameters, we examine abundance ratios as a function of [Fe/H] and
kinematics for the three subsamples in wide metallicity and orbital parameter
ranges.
We show that, in the metallicity range of -1.5<[Fe/H]<= -0.5, the thick disk
stars show constantly high mean [Mg/Fe] and [Si/Fe] ratios with small scatter.
In contrast, the inner, and the outer halo stars show lower mean values of
these abundance ratios with larger scatter. The [Mg/Fe], [Si/Fe] and [Ca/Fe]
for the inner and the outer halo stars also show weak decreasing trends with
[Fe/H] in the range [Fe/H]$>-2$. These results favor the scenarios that the MW
thick disk formed through rapid chemical enrichment primarily through Type II
supernovae of massive stars, while the stellar halo has formed at least in part
via accretion of progenitor stellar systems having been chemically enriched
with different timescales.
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High-performance thermoelectric oxides could offer a great energy solution
for integrated and embedded applications in sensing and electronics industries.
Oxides, however, often suffer from low Seebeck coefficient when compared with
other classes of thermoelectric materials. In search of high-performance
thermoelectric oxides, we present a comprehensive density functional
investigation, based on GGA$+U$ formalism, surveying the 3d and 4d
transition-metal-containing ferrites of the spinel structure. Consequently, we
predict MnFe$_2$O$_4$ and RhFe$_2$O$_4$ have Seebeck coefficients of $\sim \pm
600$ $\mu$V K$^{-1}$ at near room temperature, achieved by light hole and
electron doping. Furthermore, CrFe$_2$O$_4$ and MoFe$_2$O$_4$ have even higher
ambient Seebeck coefficients at $\sim \pm 700$ $\mu$V K$^{-1}$. In the latter
compounds, the Seebeck coefficient is approximately a flat function of
temperature up to $\sim 700$ K, offering a tremendous operational convenience.
Additionally, MoFe$_2$O$_4$ doped with $10^{19}$ holes/cm$^3$ has a calculated
thermoelectric power factor of $689.81$ $\mu$W K$^{-2}$ m$^{-1}$ at $300$ K,
and $455.67$ $\mu$W K$^{-2}$ m$^{-1}$ at $600$ K. The thermoelectric properties
predicted here can bring these thermoelectric oxides to applications at lower
temperatures traditionally fulfilled by more toxic and otherwise burdensome
materials.
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