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arxiv_dataset-100001807.02792 | Stable Branched Electron Flow
cond-mat.mes-hall
The pattern of branched electron flow revealed by scanning gate microscopy
shows the distribution of ballistic electron trajectories. The details of the
pattern are determined by the correlated potential of remote dopants with an
amplitude far below the Fermi energy. We find that the pattern persists even if
the electron density is significantly reduced such that the change in Fermi
energy exceeds the background potential amplitude. The branch pattern is robust
against changes in charge carrier density, but not against changes in the
background potential caused by additional illumination of the sample.
| arxiv topic:cond-mat.mes-hall |
arxiv_dataset-100011807.02892 | Automated labeling of bugs and tickets using attention-based mechanisms
in recurrent neural networks
cs.IR cs.LG stat.ML
We explore solutions for automated labeling of content in bug trackers and
customer support systems. In order to do that, we classify content in terms of
several criteria, such as priority or product area. In the first part of the
paper, we provide an overview of existing methods used for text classification.
These methods fall into two categories - the ones that rely on neural networks
and the ones that don't. We evaluate results of several solutions of both
kinds. In the second part of the paper we present our own recurrent neural
network solution based on hierarchical attention paradigm. It consists of
several Hierarchical Attention network blocks with varying Gated Recurrent Unit
cell sizes and a complementary shallow network that goes alongside. Lastly, we
evaluate above-mentioned methods when predicting fields from two datasets -
Arch Linux bug tracker and Chromium bug tracker. Our contributions include a
comprehensive benchmark between a variety of methods on relevant datasets; a
novel solution that outperforms previous generation methods; and two new
datasets that are made public for further research.
| arxiv topic:cs.IR cs.LG stat.ML |
arxiv_dataset-100021807.02992 | Mass modelling of a superthin galaxy, FGC1540
astro-ph.GA
We present high resolution H{\sc i} 21cm Giant Meterwave Radio Telescope
(GMRT) observations of the superthin galaxy FGC1540 with a spatial resolution
of 10$''$ $\times$ 8$''$ and a spectral resolution of 1.73 kms$^{-1}$ and an
rms noise of 0.9 mJy per beam. We obtain its rotation curve as well as
deprojected radial H{\sc i} surface density profile by fitting a 3-dimensional
tilted ring model directly to the H{\sc i} data cubes by using the
publicly-available software, Fully Automated Tirrific (FAT). We also present
the rotation curve of FGC1540 derived from its optical spectroscopy study using
the 6-m BTA telescope of the Special Astrophysical Observatory of the Russian
Academy of Sciences. We use the rotation curve, the H{\sc i} surface density
profile together with Spitzer 3.6 $\mu$m and the SDSS $i$--band data to
construct the mass models for FGC1540. We find that both the Pseudo-isothermal
(PIS), as well as Navarro-Frenk-White (NFW) dark matter (DM) halos, fit the
observed rotation curve equally well. The PIS model indicates a compact dark
matter halo ($R_{\rm C}/R_{\rm D}$ < 2), with the best-fitting core radius
($R_{\rm C}$) approximately half the exponential stellar disc scale length
($R_{\rm D}$), which is in agreement with the mass models of superthin galaxies
studied earlier in the literature. Since the vertical thickness of the galactic
stellar disc is determined by a balance between the net gravitational field and
the velocity dispersion in the vertical direction, the compact dark matter halo
may be primarily responsible in regulating the superthin vertical structure of
the stellar disc in FGC1540 as was found in case of the superthin galaxy
UGC7321.
| arxiv topic:astro-ph.GA |
arxiv_dataset-100031807.03092 | Possible Quantum Paraelectric State in Kitaev Spin Liquid Candidate
H$_{3}$LiIr$_{2}$O$_{6}$
cond-mat.str-el cond-mat.mtrl-sci
A new quantum spin liquid (QSL) candidate material H$_{3}$LiIr$_{2}$O$_{6}$
was synthesized recently and was found not to show any magnetic order or phase
transition down to low temperatures. In this work, we study the quantum
dynamics of the hydrogen ions, i.e., protons, in this material by combining
first-principles calculations and theoretical analysis. We show that each
proton and its adjacent oxygen ions form an electric dipole. The dipole
interactions and the proton tunneling are captured by a transverse-field Ising
model with a quantum disordered paraelectric ground state. The dipole
excitations have an energy gap $\Delta_{\mathrm{d}}\simeq 60$ meV, and can be
probed by the infrared optical spectroscopy and the dielectric response. We
argue that the electric dipole fluctuations renormalize the magnetic
interactions in H$_{3}$LiIr$_{2}$O$_{6}$ and lead to a Kitaev QSL state.
| arxiv topic:cond-mat.str-el cond-mat.mtrl-sci |
arxiv_dataset-100041807.03192 | Thresholded ConvNet Ensembles: Neural Networks for Technical Forecasting
q-fin.CP
Much of modern practice in financial forecasting relies on technicals, an
umbrella term for several heuristics applying visual pattern recognition to
price charts. Despite its ubiquity in financial media, the reliability of its
signals remains a contentious and highly subjective form of 'domain knowledge'.
We investigate the predictive value of patterns in financial time series,
applying machine learning and signal processing techniques to 22 years of US
equity data. By reframing technical analysis as a poorly specified, arbitrarily
preset feature-extractive layer in a deep neural network, we show that better
convolutional filters can be learned directly from the data, and provide visual
representations of the features being identified. We find that an ensemble of
shallow, thresholded CNNs optimised over different resolutions achieves
state-of-the-art performance on this domain, outperforming technical methods
while retaining some of their interpretability.
| arxiv topic:q-fin.CP |
arxiv_dataset-100051807.03292 | Bias Correction For Paid Search In Media Mix Modeling
stat.AP
Evaluating the return on ad spend (ROAS), the causal effect of advertising on
sales, is critical to advertisers for understanding the performance of their
existing marketing strategy as well as how to improve and optimize it. Media
Mix Modeling (MMM) has been used as a convenient analytical tool to address the
problem using observational data. However it is well recognized that MMM
suffers from various fundamental challenges: data collection, model
specification and selection bias due to ad targeting, among others
\citep{chan2017,wolfe2016}.
In this paper, we study the challenge associated with measuring the impact of
search ads in MMM, namely the selection bias due to ad targeting. Using causal
diagrams of the search ad environment, we derive a statistically principled
method for bias correction based on the \textit{back-door} criterion
\citep{pearl2013causality}. We use case studies to show that the method
provides promising results by comparison with results from randomized
experiments. We also report a more complex case study where the advertiser had
spent on more than a dozen media channels but results from a randomized
experiment are not available. Both our theory and empirical studies suggest
that in some common, practical scenarios, one may be able to obtain an
approximately unbiased estimate of search ad ROAS.
| arxiv topic:stat.AP |
arxiv_dataset-100061807.03392 | Evolving Multimodal Robot Behavior via Many Stepping Stones with the
Combinatorial Multi-Objective Evolutionary Algorithm
cs.NE
An important challenge in reinforcement learning, including evolutionary
robotics, is to solve multimodal problems, where agents have to act in
qualitatively different ways depending on the circumstances. Because multimodal
problems are often too difficult to solve directly, it is helpful to take
advantage of staging, where a difficult task is divided into simpler subtasks
that can serve as stepping stones for solving the overall problem.
Unfortunately, choosing an effective ordering for these subtasks is difficult,
and a poor ordering can reduce the speed and performance of the learning
process. Here, we provide a thorough introduction and investigation of the
Combinatorial Multi-Objective Evolutionary Algorithm (CMOEA), which avoids
ordering subtasks by allowing all combinations of subtasks to be explored
simultaneously. We compare CMOEA against two algorithms that can similarly
optimize on multiple subtasks simultaneously: NSGA-II and Lexicase Selection.
The algorithms are tested on a multimodal robotics problem with six subtasks as
well as a maze navigation problem with a hundred subtasks. On these problems,
CMOEA either outperforms or is competitive with the controls. Separately, we
show that adding a linear combination over all objectives can improve the
ability of NSGA-II to solve these multimodal problems. Lastly, we show that, in
contrast to NSGA-II and Lexicase Selection, CMOEA can effectively leverage
secondary objectives to achieve state-of-the-art results on the robotics task.
In general, our experiments suggest that CMOEA is a promising, state-of-the-art
algorithm for solving multimodal problems.
| arxiv topic:cs.NE |
arxiv_dataset-100071807.03492 | The Recommendation System to SNS Community for Tourists by Using
Altruistic Behaviors
cs.MA cs.IR cs.SI
We have already developed the recommendation system of sightseeing
information on SNS by using smartphone based user participatory sensing system.
The system can post the attractive information for tourists to the specified
Facebook page by our developed smartphone application. The users in Facebook,
who are interested in sightseeing, can come flocking through information space
from far and near. However, the activities in the community on SNS are only
supported by the specified people called a hub. We proposed the method of
vitalization of tourist behaviors to give a stimulus to the people. We
developed the simulation system for multi agent system with altruistic
behaviors inspired by the Army Ants. The army ant takes feeding action with
altruistic behaviors to suppress selfish behavior to a common object used by a
plurality of users in common. In this paper, we introduced the altruism
behavior determined by some simulation to vitalize the SNS community. The
efficiency of the revitalization process of the community was investigated by
some experimental simulation results.
| arxiv topic:cs.MA cs.IR cs.SI |
arxiv_dataset-100081807.03592 | Estimating Wealth Distribution: Top Tail and Inequality
stat.AP
This article describes mathematical methods for estimating the top-tail of
the wealth distribution and therefrom the share of total wealth that the
richest $p$ percent hold, which is an intuitive measure of inequality. As the
data base for the top-tail of the wealth distribution is inevitably less
complete than the data for lower wealth, the top-tail distribution is replaced
by a parametric model based on a Pareto distribution. The different methods for
estimating the parameters are compared and new simulations are presented which
favor the maximum-likelihood estimator for the Pareto parameter $\alpha$. New
criteria for the choice of other parameters are presented which have not yet
been discussed in the literature before. The methods are applied to the 2012
data from the ECB Household and Consumption Survey (HFCS) for Germany and the
corresponding rich list from the Manager Magazin. In addition to a presentation
of all formulas, R scripts implementing them are provided by the author.
| arxiv topic:stat.AP |
arxiv_dataset-100091807.03692 | Infrared sensitivity of single jet inclusive production at hadron
colliders
hep-ph hep-ex
Jet production at hadron colliders is a benchmark process to probe the
dynamics of the strong interaction and the structure of the colliding hadrons.
One of the most basic jet production observables is the single jet inclusive
cross section, which is obtained by summing all jets that are observed in an
event. Our recent computation of next-to-next-to-leading order (NNLO) QCD
contributions to single jet inclusive observables uncovered large corrections
in certain kinematical regions, which also resulted in a sizeable ambiguity on
the appropriate choice of renormalization and factorization scales. We now
perform a detailed investigation of the infrared sensitivity of the different
ingredients to the single jet inclusive cross section. We show that the
contribution from the second jet, ordered in transverse momentum $p_{T}$, in
the event is particularly sensitive to higher order effects due to implicit
restrictions on its kinematics. By investigating the second-jet transverse
momentum distribution, we identify large-scale cancellations between different
kinematical event configurations, which are aggravated by certain types of
scale choice. Taking perturbative convergence and stability as selection
criteria enables us to single out the total partonic transverse energy
$\hat{H}_{T}$ and twice the individual jet transverse momentum $2\,p_{T}$ (with
which $\hat{H}_{T}$ coincides in Born kinematics) as the most appropriate
scales in the perturbative description of single jet inclusive production.
| arxiv topic:hep-ph hep-ex |
arxiv_dataset-100101807.03792 | The extended radio jet of an off-nuclear low-mass AGN in NGC 5252
astro-ph.GA
CXO J133815.6+043255 is an ultraluminous X-ray source (ULX) with ultraviolet,
optical, and radio counterparts located 10 kpc away from the nucleus of the
galaxy NGC 5252. Optical spectroscopic studies indicate that the ULX is
kinematically associated with NGC 5252; yet, the compactness of its radio
emission could not rule out the possibility that the ULX is a background
blazar. We present follow-up VLBA radio observations that are able to resolve
the compact radio emission of the ULX into two components, making the blazar
scenario very unlikely. The east component is extended at 4.4 GHz and its
detection also at 7.6 GHz reveals a steep spectral index. The west component is
only detected at 4.4 GHz, is not firmly resolved, and has a flatter spectral
index. Considering that the west component hosts the radio core, we constrain
the black hole mass of the ULX to $10^{3.5} < M_\mathrm{BH} \lesssim 2 \times
10^{6}$ M$_{\odot}$ and its Eddington ratio to $\sim 10^{-3}$. The ULX is thus
most likely powered by an intermediate-mass black hole or low-mass AGN. Our
results constitute the first discovery of a multi-component radio jet in a ULX
and possible intermediate-mass black hole.
| arxiv topic:astro-ph.GA |
arxiv_dataset-100111807.03892 | Characterization of a Canonical Helicopter Hub Wake
physics.flu-dyn
The current study investigates the long-age wake behind rotating helicopter
hub models composed of geometrically simple, canonical bluff body shapes. The
models consisted of a 4-arm rotor mounted on a shaft above a 2-arm (scissor)
rotor with all the rotor arms having a rectangular cross section. The relative
phase between the 2- and 4-arm rotors was either $0\deg$ (in-phase) or $45\deg$
(out-of-phase). The rotors were oriented at zero angle-of-attack and rotated at
30 Hz. Their wakes were measured with particle-image-velocimetry within a water
tunnel at a hub diameter based Reynolds number of $820,000$ and an advance
ratio of $0.2$. Mean profiles, fluctuating profiles and spectral analysis using
time-series analysis as well as dynamic mode decomposition were used to
characterize the wake and identify coherent structures associated with specific
frequency content. The canonical geometry produced coherent structures that
were consistent with previous results using more complex geometries. It was
shown that the dominant structures (2 and 4 times per hub revolution) decay
slowly and were not sensitive to the relative phase between the rotors.
Conversely, the next strongest structure (6 times per hub revolution) was
sensitive to the relative phase with almost no coherence observed for the
in-phase model. This is strong evidence that the 6 per revolution content is a
nonlinear interaction between the 2 and 4 revolution structures. This study
demonstrates that the far wake region is dominated by the main rotor arms wake,
the scissor rotor wake and interactions between these two features.
| arxiv topic:physics.flu-dyn |
arxiv_dataset-100121807.03992 | Real algebraic curves with large finite number of real points
math.AG
We address the problem of the maximal finite number of real points of a real
algebraic curve (of a given degree and, sometimes, genus) in the projective
plane. We improve the known upper and lower bounds and construct close to
optimal curves of small degree. Our upper bound is sharp if the genus is small
as compared to the degree. Some of the results are extended to other real
algebraic surfaces, most notably ruled.
| arxiv topic:math.AG |
arxiv_dataset-100131807.04092 | Explicit Maximal and Minimal Curves of Artin-Schreier Type from
Quadratic Forms
math.AG
In this work we present explicit examples of maximal and minimal curves over
finite fields in odd characteristic. The curves are of Artin-Schreier type and
the construction is closely related to quadratic forms from $\mathbb{F}_{q^n}$
to $\mathbb{F}_q$.
| arxiv topic:math.AG |
arxiv_dataset-100141807.04192 | From Hawkes-type processes to stochastic volatility
math.PR
We introduce a Hawkes-like process and study its scaling limit as the system
becomes increasingly endogenous. We derive functional limit theorems for
intensity and fluctuations. Then, we introduce a high-frequency model for a
price of a liquid traded financial instrument in which the nearly unstable
regime leads to a Heston-type process where the negative correlation between
the noise driving the proce of the instrument and the volatility can be viewed
as a result of high variance of the sell-side order arrivals.
| arxiv topic:math.PR |
arxiv_dataset-100151807.04292 | The Pristine Survey IV: Approaching the Galactic metallicity floor with
the discovery of an ultra metal-poor star
astro-ph.SR astro-ph.GA
The early Universe presented a star formation environment that was almost
devoid of heavy elements. The lowest metallicity stars thus provide a unique
window into the earliest Galactic stages, but are exceedingly rare and
difficult to find. Here we present the discovery of an ultra-metal-poor star,
Pristine_221.8781+9.7844, using narrow-band Ca H&K photometry from the Pristine
survey. Follow-up medium and high-resolution spectroscopy confirms the
ultra-metal-poor nature of Pristine_221.8781+9.7844 ([Fe/H] = -4.66 +/- 0.13 in
1D LTE) with an enhancement of 0.3-0.4 dex in alpha-elements relative to Fe,
and an unusually low carbon abundance. We derive an upper limit of A(C) = 5.6,
well below typical A(C) values for such ultra metal-poor stars. This makes
Pristine_221.8781+9.7844 one of the most metal-poor stars; in fact, it is very
similar to the most metal-poor star known (SDSS J102915+172927). The existence
of a class of ultra metal-poor stars with low(er) carbon abundances suggest
that there must have been several formation channels in the early Universe
through which long-lived, low-mass stars were formed.
| arxiv topic:astro-ph.SR astro-ph.GA |
arxiv_dataset-100161807.04392 | Simulating Motion - Incorporating Spatial Consistency into the NYUSIM
Channel Model
cs.IT eess.SP math.IT
This paper describes an implementation of spatial consistency in the NYUSIM
channel simulation platform. NYUSIM is a millimeter wave (mmWave) channel
simulator that realizes measurement-based channel models based on a wide range
of multipath channel parameters, including realistic multipath time delays and
multipath components that arrive at different 3-D angles in space, and
generates life-like samples of channel impulse responses (CIRs) that
statistically match those measured in the real world. To properly simulate
channel impairments and variations for adaptive antenna algorithms or channel
state feedback, channel models should implement spatial consistency which
ensures correlated channel responses over short time and distance epochs. The
ability to incorporate spatial consistency into channel simulators will be
essential to explore the ability to train and deploy massive multiple-input and
multiple-output (MIMO) and multi-user beamforming in next-generation mobile
communication systems. This paper reviews existing modeling approaches to
spatial consistency, and describes an implementation of spatial consistency in
NYUSIM for when a user is moving in a square area having a side length of 15 m.
The spatial consistency extension will enable NYUSIM to generate realistic
evolutions of temporal and spatial characteristics of the wideband CIRs for
mobile users in motion, or for multiple users who are relatively close to one
another.
| arxiv topic:cs.IT eess.SP math.IT |
arxiv_dataset-100171807.04492 | Dissipation of weakly nonlinear wakefields due to ion motion
physics.plasm-ph physics.acc-ph
In an initially uniform plasma, the lifetime of a weakly nonlinear plasma
wave excited by a short driver is limited by the ion dynamics. The wakefield
contains a slowly varying radial component, which results in a perturbation of
the ion density profile and consequent destruction of the plasma wave. We
suggest a novel method of characterizing the wave lifetime in numerical
simulations quantitatively and study how the lifetime scales with the ion mass.
We also discuss the implications of the limited lifetime on a recently proposed
method of generating high-power terahertz radiation with counterpropagating
wakefields driven by colliding laser pulses.
| arxiv topic:physics.plasm-ph physics.acc-ph |
arxiv_dataset-100181807.04592 | Stellar mass distribution and star formation history of the Galactic
disk revealed by mono-age stellar populations from LAMOST
astro-ph.GA
We present a detailed determination and analysis of 3D stellar mass
distribution of the Galactic disk for mono-age populations using a sample of
0.93 million main-sequence turn-off and subgiant stars from the LAMOST Galactic
Surveys. Our results show (1) all stellar populations younger than 10\,Gyr
exhibit strong disk flaring, which is accompanied with a dumpy vertical density
profile that is best described by a $sech^n$ function with index depending on
both radius and age; (2) Asymmetries and wave-like oscillations are presented
in both the radial and vertical direction, with strength varying with stellar
populations; (3) As a contribution by the Local spiral arm, the mid-plane
stellar mass density at solar radius but 400--800\,pc (3--6$^\circ$) away from
the Sun in the azimuthal direction has a value of
$0.0594\pm0.0008$\,$M_\odot$/pc$^3$, which is 0.0164\,$M_\odot$/pc$^3$ higher
than previous estimates at the solar neighborhood. The result causes doubts on
the current estimate of local dark matter density; (4) The radial distribution
of surface mass density yields a disk scale length evolving from $\sim$4\,kpc
for the young to $\sim$2\,kpc for the old populations. The overall population
exhibits a disk scale length of $2.48\pm0.05$\,kpc, and a total stellar mass of
$3.6(\pm0.1)\times10^{10}$\,$M_\odot$ assuming $R_{\odot}=8.0$\,kpc, and the
value becomes $4.1(\pm0.1)\times10^{10}$\,$M_\odot$ if $R_{\odot}=8.3$\,kpc;
(5) The disk has a peak star formation rate ({\rm SFR}) changing from 6--8\,Gyr
at the inner to 4--6\,Gyr ago at the outer part, indicating an inside-out
assemblage history. The 0--1\,Gyr population yields a recent disk total {\rm
SFR} of $1.96\pm0.12$\,$M_\odot$/yr.
| arxiv topic:astro-ph.GA |
arxiv_dataset-100191807.04692 | Electrodeposition of Ni-P composite coatings: A review
physics.app-ph cond-mat.mtrl-sci
Ni-P coatings produced by electrodeposition have important mechanical,
tribological and electrochemical properties. They can also exhibit catalytic
activity and beneficial magnetic behaviour. With subsequent thermal treatment,
the hardness of such Ni-P coatings can approach or exceed that of hard Cr
coatings. Electrochemical codeposition of homogeneously dispersed second phase
particles within the Ni-P matrix can enhance deposit properties and meet the
challenging demands on modern engineering coatings. A general overview of
research work on the electrodeposition of Ni-P composite coatings containing
included ceramic or solid lubricant particles is provided. Advances in research
into NieP composite layers reinforced by SiC, B4C, WC, Al2O3, SiO2, TiO2, CeO2,
MWCNT, MoS2, WS2, TiN, hexagonal BN, PTFE and their combinations are
considered. Major models proposed for the codeposition of particles, the
influence of bath hydrodynamics and control of operational parameters are
illustrated by examples. Important trends are highlighted and opportunities for
future R & D are summarised.
| arxiv topic:physics.app-ph cond-mat.mtrl-sci |
arxiv_dataset-100201807.04792 | Efficient population transfer via non-ergodic extended states in quantum
spin glass
quant-ph cond-mat.dis-nn cond-mat.stat-mech cond-mat.str-el
We analyze a new computational role of coherent multi-qubit quantum tunneling
that gives rise to bands of non-ergodic extended (NEE) quantum states each
formed by a superposition of a large number of computational states (deep local
minima of the energy landscape) with similar energies. NEE provide a mechanism
for population transfer (PT) between computational states and therefore can
serve as a new quantum subroutine for quantum search, quantum parallel
tempering and reverse annealing optimization algorithms. We study PT in a
quantum n-spin system subject to a transverse field where the energy function
$E(z)$ encodes a classical optimization problem over the set of spin
configurations $z$. Given an initial spin configuration with low energy, PT
protocol searches for other bitstrings at energies within a narrow window
around the initial one. We provide an analytical solution for PT in a simple
yet nontrivial model: $M$ randomly chosen marked bit-strings are assigned
energies $E(z)$ within a narrow strip $[-n -W/2, n + W/2]$, while the rest of
the states are assigned energy 0. We find that the scaling of a typical PT
runtime with n and L is the same as that in the multi-target Grover's quantum
search algorithm, except for a factor that is equal to $\exp(n /(2B^2))$ for
finite transverse field $B\gg1$. Unlike the Hamiltonians used in analog quantum
unstructured search algorithms known so far, the model we consider is
non-integrable and population transfer is not exponentially sensitive in n to
the weight of the driver Hamiltonian. We study numerically the PT subroutine as
a part of quantum parallel tempering algorithm for a number of examples of
binary optimization problems on fully connected graphs.
| arxiv topic:quant-ph cond-mat.dis-nn cond-mat.stat-mech cond-mat.str-el |
arxiv_dataset-100211807.04892 | Computer Analysis of Architecture Using Automatic Image Understanding
cs.CV
In the past few years, computer vision and pattern recognition systems have
been becoming increasingly more powerful, expanding the range of automatic
tasks enabled by machine vision. Here we show that computer analysis of
building images can perform quantitative analysis of architecture, and quantify
similarities between city architectural styles in a quantitative fashion.
Images of buildings from 18 cities and three countries were acquired using
Google StreetView, and were used to train a machine vision system to
automatically identify the location of the imaged building based on the image
visual content. Experimental results show that the automatic computer analysis
can automatically identify the geographical location of the StreetView image.
More importantly, the algorithm was able to group the cities and countries and
provide a phylogeny of the similarities between architectural styles as
captured by StreetView images. These results demonstrate that computer vision
and pattern recognition algorithms can perform the complex cognitive task of
analyzing images of buildings, and can be used to measure and quantify visual
similarities and differences between different styles of architectures. This
experiment provides a new paradigm for studying architecture, based on a
quantitative approach that can enhance the traditional manual observation and
analysis. The source code used for the analysis is open and publicly available.
| arxiv topic:cs.CV |
arxiv_dataset-100221807.04992 | Groups with irreducibly unfaithful subsets for unitary representations
math.GR
Let $G$ be a group. A subset $F \subset G$ is called irreducibly faithful if
there exists an irreducible unitary representation $\pi$ of $G$ such that
$\pi(x) \neq \mathrm{id}$ for all $x \in F \smallsetminus \{e\}$. Otherwise $F$
is called irreducibly unfaithful. Given a positive integer $n$, we say that $G$
has Property $P(n)$ if every subset of size $n$ is irreducibly faithful. Every
group has $P(1)$, by a classical result of Gelfand and Raikov. Walter proved
that every group has $P(2)$. It is easy to see that some groups do not have
$P(3)$.
We provide a complete description of the irreducibly unfaithful subsets of
size $n$ in a countable group $G$ (finite or infinite) with Property $P(n-1)$:
it turns out that such a subset is contained in a finite elementary abelian
normal subgroup of $G$ of a particular kind. We deduce a characterization of
Property $P(n)$ purely in terms of the group structure. It follows that, if a
countable group $G$ has $P(n-1)$ and does not have $P(n)$, then $n$ is the
cardinality of a projective space over a finite field.
A group $G$ has Property $Q(n)$ if, for every subset $F \subset G$ of size at
most $n$, there exists an irreducible unitary representation $\pi$ of $G$ such
that $\pi(x) \ne \pi(y)$ for any distinct $x, y$ in $F$. Every group has
$Q(2)$. For countable groups, it is shown that Property $Q(3)$ is equivalent to
$P(3)$, Property $Q(4)$ to $P(6)$, and Property $Q(5)$ to $P(9)$. For $m, n \ge
4$, the relation between Properties $P(m)$ and $Q(n)$ is closely related to a
well-documented open problem in additive combinatorics.
| arxiv topic:math.GR |
arxiv_dataset-100231807.05092 | IntRepair: Informed Repairing of Integer Overflows
cs.SE
Integer overflows have threatened software applications for decades. Thus, in
this paper, we propose a novel technique to provide automatic repairs of
integer overflows in C source code. Our technique, based on static symbolic
execution, fuses detection, repair generation and validation. This technique is
implemented in a prototype named IntRepair. We applied IntRepair to 2,052C
programs (approx. 1 million lines of code) contained in SAMATE's Juliet test
suite and 50 synthesized programs that range up to 20KLOC. Our experimental
results show that IntRepair is able to effectively detect integer overflows and
successfully repair them, while only increasing the source code (LOC) and
binary (Kb) size by around 1%, respectively. Further, we present the results of
a user study with 30 participants which shows that IntRepair repairs are more
than 10x efficient as compared to manually generated code repairs
| arxiv topic:cs.SE |
arxiv_dataset-100241807.05192 | Base divisors of big and nef line bundles on irreducible symplectic
varieties
math.AG
Under some conditions on the deformation type, which we expect to be
satisfied for arbitrary irreducible symplectic varieties, we describe which big
and nef line bundles on irreducible symplectic varieties have base divisors. In
particular, we show that such base divisors are always irreducible and reduced.
This is applied to understand the behaviour of divisorial base components of
big and nef line bundles under deformations and for K3$^{[n]}$-type and
Kum$^n$-type.
| arxiv topic:math.AG |
arxiv_dataset-100251807.05292 | Neural Networks Regularization Through Representation Learning
cs.LG stat.ML
Neural network models and deep models are one of the leading and state of the
art models in machine learning. Most successful deep neural models are the ones
with many layers which highly increases their number of parameters. Training
such models requires a large number of training samples which is not always
available. One of the fundamental issues in neural networks is overfitting
which is the issue tackled in this thesis. Such problem often occurs when the
training of large models is performed using few training samples. Many
approaches have been proposed to prevent the network from overfitting and
improve its generalization performance such as data augmentation, early
stopping, parameters sharing, unsupervised learning, dropout, batch
normalization, etc.
In this thesis, we tackle the neural network overfitting issue from a
representation learning perspective by considering the situation where few
training samples are available which is the case of many real world
applications. We propose three contributions. The first one presented in
chapter 2 is dedicated to dealing with structured output problems to perform
multivariate regression when the output variable y contains structural
dependencies between its components. The second contribution described in
chapter 3 deals with the classification task where we propose to exploit prior
knowledge about the internal representation of the hidden layers in neural
networks. Our last contribution presented in chapter 4 showed the interest of
transfer learning in applications where only few samples are available. In this
contribution, we provide an automatic system based on such learning scheme with
an application to medical domain. In this application, the task consists in
localizing the third lumbar vertebra in a 3D CT scan. This work has been done
in collaboration with the clinic Rouen Henri Becquerel Center who provided us
with data.
| arxiv topic:cs.LG stat.ML |
arxiv_dataset-100261807.05392 | Interface roughness, carrier localization and wave function overlap in
$c$-plane InGaN/GaN quantum wells: Interplay of well width, alloy
microstructure, structural inhomogeneities and Coulomb effects
cond-mat.mes-hall
In this work we present a detailed analysis of the interplay of Coulomb
effects and different mechanisms that can lead to carrier localization effects
in c-plane InGaN/GaN quantum wells. As mechanisms for carrier localization we
consider here effects introduced by random alloy fluctuations as well as
structural inhomogeneities such as well width fluctuations. Special attention
is paid to the impact of the well width on the results. All calculations have
been carried out in the framework of atomistic tight-binding theory. Our
theoretical investigations show that independent of the here studied well
widths, carrier localization effects due to built-in fields, well width
fluctuations and random alloy fluctuations dominate over Coulomb effects in
terms of charge density redistributions. However, the situation is less clear
cut when the well width fluctuations are absent. For large well width (approx.
> 2.5 nm) charge density redistributions are possible but the electronic and
optical properties are basically dominated by the spatial out-of plane carrier
separation originating from the electrostatic built-in field. The situation
changes for lower well width (< 2.5 nm) where the Coulomb effect can lead to
significant charge density redistributions and thus might compensate a large
fraction of the spatial in-plane wave function separation observed in a
single-particle picture. Given that this in-plane separation has been regarded
as one of the main drivers behind the green gap problem, our calculations
indicate that radiative recombination rates might significantly benefit from a
reduced quantum well barrier interface roughness.
| arxiv topic:cond-mat.mes-hall |
arxiv_dataset-100271807.05492 | Incorporating a soft ordered phase into an amorphous configuration
enhances its uniform plastic deformation under shear
cond-mat.mtrl-sci cond-mat.soft
Amorphous materials of homogeneous structures usually suffer from nonuniform
deformation under shear, which can develop into shear localization and
eventually destructive shear band. One approach to tackle this issue is to
introduce an inhomogeneous structure containing more than one phase, which can
reduce the local nonuniform shear deformation and hinder its percolation
throughout the system. Using thermostated molecular dynamics (MD) simulations,
we compare the deformation behavior between a homogeneous amorphous mixture of
bidisperse disc particles, interacting via an n-6 Lennard-Jones potential of
tunable softness, with an inhomogeneous one containing an evenly-distributed
ordered phase. We change the population ratio of large to small particles to
create a homogeneous or an inhomogeneous mixture, where the softness of a
chosen phase can be manually adjusted by specifying n of the interparticle
potential. Results of applying extensive quasistatic shear on the prepared
mixtures reveal that the inhomogeneous amorphous mixture containing a soft
ordered phase overall deforms more uniformly than the homogeneous one, which
indicates that both the structure inhomogeneity and the inter-phase softness
variance play important roles in enhancing the uniformity of the plastic
deformation under shear.
| arxiv topic:cond-mat.mtrl-sci cond-mat.soft |
arxiv_dataset-100281807.05592 | Pseudo-linear regression identification based on generalized orthonormal
transfer functions: Convergence conditions and bias distribution
cs.SY
In this paper we generalize three identification recursive algorithms
belonging to the pseudo-linear class, by introducing a predictor established on
a generalized orthonormal function basis. Contrary to the existing
identification schemes that use such functions, no constraint on the model
poles is imposed. Not only this predictor parameterization offers the
opportunity to relax the convergence conditions of the associated recursive
schemes, but it entails a modification of the bias distribution linked to the
basis poles. This result is specific to pseudo-linear regression properties,
and cannot be transposed to most of prediction error method algorithms. A
detailed bias distribution is provided, using the concept of equivalent
prediction error, which reveals strong analogies between the three proposed
schemes, corresponding to ARMAX, Output Error and a generalization of ARX
models. That leads to introduce an indicator of the basis poles location effect
on the bias distribution in the frequency domain. As shown by the simulations,
the said basis poles play the role of tuning parameters, allowing to manage the
model fit in the frequency domain, and allowing efficient identification of
fast sampled or stiff discrete-time systems.
| arxiv topic:cs.SY |
arxiv_dataset-100291807.05692 | On SDEs with Lipschitz coefficients, driven by continuous, model-free
martingales
q-fin.MF math.PR
We prove the existence and uniqueness of solutions of SDEs with Lipschitz
coefficients, driven by continuous, model-free martingales. The main tool in
our reasoning is Picard's iterative procedure and a model-free version of the
Burkholder-Davis-Gundy inequality for integrals driven by model-free,
continuous martingales. We work with a new outer measure which assigns zero
value exactly to those properties which are instantly blockable.
| arxiv topic:q-fin.MF math.PR |
arxiv_dataset-100301807.05792 | Existence of Peregrine Solitons in fractional reaction-diffusion
equations
math.AP
In this article, we will analyze the existence of Peregrine type solutions
for the fractional diffusion reaction equation by applying Splitting-type
methods. These functions that have two main characteristics, they are direct
sum of functions of periodic type and functions that tend to zero at infinity.
Global existence results are obtained for each particular characteristic, for
then finally combining both results.
| arxiv topic:math.AP |
arxiv_dataset-100311807.05892 | The Baum--Connes conjecture localised at the unit element of a discrete
group
math.OA math.KT
We construct a Baum--Connes assembly map localised at the unit element of a
discrete group $\Gamma$. This morphism, called $\mu_\tau$, is defined in
$KK$-theory with coefficients in $\mathbb{R}$ by means of the action of the
projection $[\tau]\in KK_{\mathbb{R}}^\Gamma(\mathbb{C},\mathbb{C})$
canonically associated to the group trace of $\Gamma$. We show that the
corresponding $\tau$-Baum--Connes conjecture is weaker then the classical one
but still implies the strong Novikov conjecture. The right hand side of
$\mu_\tau$ is functorial with respect to the group $\Gamma$.
| arxiv topic:math.OA math.KT |
arxiv_dataset-100321807.05992 | Stratification of singular hyperkahler quotients
math.DG math.SG
Hyperkahler quotients by non-free actions are typically highly singular, but
are remarkably still partitioned into smooth hyperkahler manifolds. We show
that these partitions are topological stratifications, in a strong sense. We
also endow the quotients with global Poisson structures which induce the
hyperkahler structures on the strata. Finally, we give a local model which
shows that these quotients are locally isomorphic to linear complex-symplectic
reductions in the GIT sense. These results can be thought of as the hyperkahler
analogues of Sjamaar-Lerman's theorems for symplectic reduction. They are based
on a local normal form for the underlying complex-Hamiltonian manifold, which
may be of independent interest.
| arxiv topic:math.DG math.SG |
arxiv_dataset-100331807.06092 | The Athena X-ray Integral Field Unit
astro-ph.IM astro-ph.CO astro-ph.GA astro-ph.HE
The X-ray Integral Field Unit (X-IFU) is the high resolution X-ray
spectrometer of the ESA Athena X-ray observatory. Over a field of view of 5'
equivalent diameter, it will deliver X-ray spectra from 0.2 to 12 keV with a
spectral resolution of 2.5 eV up to 7 keV on ~5 arcsecond pixels. The X-IFU is
based on a large format array of super-conducting molybdenum-gold Transition
Edge Sensors cooled at about 90 mK, each coupled with an absorber made of gold
and bismuth with a pitch of 249 microns. A cryogenic anti-coincidence detector
located underneath the prime TES array enables the non X-ray background to be
reduced. A bath temperature of about 50 mK is obtained by a series of
mechanical coolers combining 15K Pulse Tubes, 4K and 2K Joule-Thomson coolers
which pre-cool a sub Kelvin cooler made of a 3He sorption cooler coupled with
an Adiabatic Demagnetization Refrigerator. Frequency domain multiplexing
enables to read out 40 pixels in one single channel. A photon interacting with
an absorber leads to a current pulse, amplified by the readout electronics and
whose shape is reconstructed on board to recover its energy with high accuracy.
The defocusing capability offered by the Athena movable mirror assembly enables
the X-IFU to observe the brightest X-ray sources of the sky (up to Crab-like
intensities) by spreading the telescope point spread function over hundreds of
pixels. Thus the X-IFU delivers low pile-up, high throughput (>50%), and
typically 10 eV spectral resolution at 1 Crab intensities, i.e. a factor of 10
or more better than Silicon based X-ray detectors. In this paper, the current
X-IFU baseline is presented, together with an assessment of its anticipated
performance in terms of spectral resolution, background, and count rate
capability. The X-IFU baseline configuration will be subject to a preliminary
requirement review that is scheduled at the end of 2018.
| arxiv topic:astro-ph.IM astro-ph.CO astro-ph.GA astro-ph.HE |
arxiv_dataset-100341807.06192 | Field-induced intermediate phase in $\alpha$-RuCl$_3$: Non-coplanar
order, phase diagram, and proximate spin liquid
cond-mat.str-el
Frustrated magnets with strong spin-orbit coupling promise to host
topological states of matter, with fractionalized excitations and emergent
gauge fields. Kitaev's proposal for a honeycomb-lattice Majorana spin liquid
has triggered an intense search for experimental realizations, with
bond-dependent Ising interaction being the essential building block. A prime
candidate is $\alpha$-RuCl$_3$ whose phase diagram in a magnetic field is,
however, not understood to date. Here we present conclusive experimental
evidence for a novel field-induced ordered phase in $\alpha$-RuCl$_3$,
sandwiched between the zigzag and quantum disordered phases at low and high
fields, respectively. We provide a detailed theoretical study of the relevant
effective spin model which we show to display a field-induced intermediate
phase as well. We fully characterize the intermediate phase within this model,
including its complex spin structure, and pinpoint the parameters relevant to
$\alpha$-RuCl$_3$ based on the experimentally observed critical fields. Most
importantly, our study connects the physics of $\alpha$-RuCl$_3$ to that of the
Kitaev-$\Gamma$ model, which displays a quantum spin liquid phase in zero
field, and hence reveals the spin liquid whose signatures have been detected in
a variety of dynamical probes of $\alpha$-RuCl$_3$.
| arxiv topic:cond-mat.str-el |
arxiv_dataset-100351807.06292 | Generation of tunable ultrashort pulses in the near infrared
physics.optics
A laser source delivering ultrashort pulses (50-100 fs) tunable from 820 nm
to 1200 nm has been developed. It is based on the filtering of a continuum in
the Fourier plane of a zero dispersion line without a phase compensator. We
have also numerically investigated the impact of the residual spectral phase in
order to guarantee ultrashort pulses.
| arxiv topic:physics.optics |
arxiv_dataset-100361807.06392 | Equivalence between nonlinear dynamical systems and urn processes
nlin.CD cond-mat.stat-mech math.DS
An equivalence is shown between a large class of deterministic dynamical
systems and a class of stochastic processes, the balanced urn processes. These
dynamical systems are governed by quasi-polynomial differential systems that
are widely used in mathematical modeling while urn processes are actively
studied in combinatorics and probability theory. The presented equivalence
extends a theorem by Flajolet et al. (Flajolet, Dumas and Puyhaubert Discr.
Math. Theor. Comp. Sc. AG - 2006, DMTCS Proceedings) already establishing an
isomorphism between urn processes and a particular class of differential
systems with monomial vector fields. The present result is based on the fact
that such monomial differential systems are canonical forms for more general
dynamical systems.
| arxiv topic:nlin.CD cond-mat.stat-mech math.DS |
arxiv_dataset-100371807.06492 | Vortex Formation and Survival in Protoplanetary Disks subject to
Vertical Shear Instability
astro-ph.EP
Several protoplanetary disks observed by ALMA show dust concentrations
consistent with particle trapping in giant vortices. The formation and survival
of vortices is of major importance for planet formation, because vortices act
as particle traps and are therefore preferred locations of planetesimal
formation. Recent studies showed that the vertical shear instability (VSI) is
capable of generating turbulence and small vortices in protoplanetary disks
that have the proper radial and vertical stratification and thermally relax on
sufficiently short time scales. But the effect of the azimuthal extend of the
disk is often neglected as the disks azimuth is limited to $\Delta \phi \leq
\pi/2$. We aim to investigate the influence of the azimuthal extent of the disk
on the long-term evolution of a protoplanetary disk and the possibility of
large vortices forming. To this end, we perform 3-dimensional simulations for
up to 1000 local orbits using different values of $\Delta \phi = \pi/2 $ to
$2\pi$ for VSI in disks with a prescribed radial density and temperature
gradient cooling on short timescales. We find the VSI capable of forming large
vortices which can exist at least several hundred orbits in simulations
covering a disk with $\Delta \phi \geq \pi$. This suggests the VSI to be
capable to form vortices or at least to trigger vortex formation via a
secondary instability, e.g. Rossby Wave Instability or Kelvin Helmholtz
Instability.
| arxiv topic:astro-ph.EP |
arxiv_dataset-100381807.06592 | Static Spherically Symmetric solutions in a subclass of Horndeski
theories of gravity
gr-qc
In this paper, we will consider a subclass of models of Horndeski theories of
gravity and we will check for several Static Spherically Symmetric solutions.
We will find a model which admits an exact black hole solution and we will
study its thermodynamics by using the Euclidean Action. We will see that, in
analogy with the case of General Relativity, the integration constant of the
solution can be identified with the mass of the black hole itself. Other
solutions will be discussed, by posing a special attention on the possibility
of reproducing the observed profiles of the rotation curves of galaxies.
| arxiv topic:gr-qc |
arxiv_dataset-100391807.06692 | A characterization of superreflexivity through embeddings of lamplighter
groups
math.FA math.GR math.MG
We prove that finite lamplighter groups
$\{\mathbb{Z}_2\wr\mathbb{Z}_n\}_{n\ge 2}$ with a standard set of generators
embed with uniformly bounded distortions into any non-superreflexive Banach
space, and therefore form a set of test-spaces for superreflexivity. Our proof
is inspired by the well known identification of Cayley graphs of infinite
lamplighter groups with the horocyclic product of trees. We cover
$\mathbb{Z}_2\wr\mathbb{Z}_n$ by three sets with a structure similar to a
horocyclic product of trees, which enables us to construct well-controlled
embeddings.
| arxiv topic:math.FA math.GR math.MG |
arxiv_dataset-100401807.06792 | Unsupervised Online Multitask Learning of Behavioral Sentence Embeddings
cs.CL
Unsupervised learning has been an attractive method for easily deriving
meaningful data representations from vast amounts of unlabeled data. These
representations, or embeddings, often yield superior results in many tasks,
whether used directly or as features in subsequent training stages. However,
the quality of the embeddings is highly dependent on the assumed knowledge in
the unlabeled data and how the system extracts information without supervision.
Domain portability is also very limited in unsupervised learning, often
requiring re-training on other in-domain corpora to achieve robustness. In this
work we present a multitask paradigm for unsupervised contextual learning of
behavioral interactions which addresses unsupervised domain adaption. We
introduce an online multitask objective into unsupervised learning and show
that sentence embeddings generated through this process increases performance
of affective tasks.
| arxiv topic:cs.CL |
arxiv_dataset-100411807.06892 | A unifying approach to constrained and unconstrained optimal reinsurance
q-fin.RM
In this paper, we study two classes of optimal reinsurance models from
perspectives of both insurers and reinsurers by minimizing their convex
combination where the risk is measured by a distortion risk measure and the
premium is given by a distortion premium principle. Firstly, we show that how
optimal reinsurance models for the unconstrained optimization problem and
constrained optimization problems can be formulated in a unified way. Secondly,
we propose a geometric approach to solve optimal reinsurance problems directly.
This paper considers a class of increasing convex ceded loss functions and
derives the explicit solutions of the optimal reinsurance which can be in forms
of quota-share, stop-loss, change-loss, the combination of quota-share and
change-loss or the combination of change-loss and change-loss with different
retentions. Finally, we consider two specific cases: Value at Risk (VaR) and
Tail Value at Risk (TVaR).
| arxiv topic:q-fin.RM |
arxiv_dataset-100421807.06992 | Positive semigroups and perturbations of boundary conditions
math.FA
We present a generation theorem for positive semigroups on an $L^1$ space. It
provides sufficient conditions for the existence of positive and integrable
solutions of initial-boundary value problems. An application to a two-phase
cell cycle model is given.
| arxiv topic:math.FA |
arxiv_dataset-100431807.07092 | Tau invariants for balanced spatial graphs
math.GT
In 2003, Ozsv\'ath and Szab\'o defined the concordance invariant $\tau$ for
knots in oriented 3-manifolds as part of the Heegaard Floer homology package.
In 2011, Sarkar gave a combinatorial definition of $\tau$ for knots in $S^3$
and a combinatorial proof that $\tau$ gives a lower bound for the slice genus
of a knot. Recently, Harvey and O'Donnol defined a relatively bigraded
combinatorial Heegaard Floer homology theory for transverse spatial graphs in
$S^3$ which extends knot Floer homology. We define a $\mathbb{Z}$-filtered
chain complex for balanced spatial graphs whose associated graded chain complex
has homology determined by Harvey and O'Donnol's graph Floer homology. We use
this to show that there is a well-defined $\tau$ invariant for balanced spatial
graphs generalizing the $\tau$ knot concordance invariant. In particular, this
defines a $\tau$ invariant for links in $S^3$. Using techniques similar to
those of Sarkar, we show that our $\tau$ invariant gives an obstruction to a
link being slice.
| arxiv topic:math.GT |
arxiv_dataset-100441807.07192 | Measurement of the angle dependence of magnetostriction in pulsed
magnetic fields using a piezoelectric strain gauge
cond-mat.mtrl-sci physics.ins-det
We present a high resolution method for measuring magnetostriction in
millisecond pulsed magnetic fields at cryogenic temperatures with a sensitivity
of $1.11\times10^{-11}/\sqrt{\rm Hz}$. The sample is bonded to a thin
piezoelectric plate, such that when the sample's length changes, it strains the
piezoelectric and induces a voltage change. This method is more sensitive than
a fiber-Bragg grating method. It measures two axes simultaneously instead of
one. The gauge is small and versatile, functioning in DC and millisecond pulsed
magnetic fields. We demonstrate its use by measuring the magnetostriction of
Ca$_3$Co$_{1.03}$Mn$_{0.97}$O$_6$ single crystals in pulsed magnetic fields. By
comparing our data to new and previously published results from a fiber-Bragg
grating magnetostriction setup, we confirm that this method detects
magnetostriction effects. We also demonstrate the small size and versatility of
this technique by measuring angle dependence with respect to the applied
magnetic field in a rotator probe in 65 T millisecond pulsed magnetic fields.
| arxiv topic:cond-mat.mtrl-sci physics.ins-det |
arxiv_dataset-100451807.07292 | Low Temperature Combustion Synthesis of a Spinel NiCo2O4 Hole Transport
Layer for Perovskite Photovoltaics
physics.app-ph
In the present study, we report the synthesis and characterization of a
low-temperature solution-processable monodispersed nickel cobaltite (NiCo2O4)
nanoparticles via a combustion synthesis using tartaric acid as fuel and
demonstrate its performance as hole transport layer (HTL) for Perovskite Solar
Cells (PVSCs). NiCo2O4 is a p-type semiconductor consisting of environmentally
friendly, abundant elements and higher conductivity compared to NiO. We show
that the combustion synthesis of spinel NiCo2O4 using tartaric acid as fuel can
be used to control the NPs size and provide smooth, compact and homogeneous
functional HTLs processed by blade coating. Study of PVSCs with different
NiCo2O4 thickness as HTL reveal a difference on hole extraction efficiency and
for 15 nm optimized thickness enhanced hole carrier collection is achieved. As
a result, p-i-n structure of PVSCs with 15 nm NiCo2O4 HTLs showed reliable
performance and power conversion efficiency values in the range of 15.5 % with
negligible hysteresis.
| arxiv topic:physics.app-ph |
arxiv_dataset-100461807.07392 | Magnetization nutation induced by surface effects in nanomagnets
cond-mat.mes-hall
We investigate the magnetization dynamics of ferromagnetic nanoparticles in
the atomistic approach taking account of surface anisotropy and the spin
misalignment it causes. We demonstrate that such inhomogeneous spin
configurations induce nutation in the dynamics of the particle's magnetization.
More precisely, in addition to the ordinary precessional motion with frequency
$f_{p}\sim10\,{\rm GHz}$, we find that the dynamics of the net magnetic moment
exhibits two more resonance peaks with frequencies $f_{c}$ and $f_{n}$ which
are higher than the frequency $f_{p} : f_{c}=4\times f_{p}\sim40\,{\rm GHz}$ is
related with the oscillations of the particle's magnetic moment between the
minima of the effective potential induced by weak surface anisotropy. On the
other hand, the much higher frequency $f_{n}\sim1\,{\rm THz}$ is attributed to
the magnetization fluctuations at the atomic level driven by exchange
interaction. We have compared our results on nutation induced by surface
effects with those rendered by the macroscopic approach based on the
Landau-Lifshitz-Gilbert equation augmented by an inertial term (proportional to
the second-order time derivative of the macroscopic moment) with a
phenomenological coefficient. The good agreement between the two models have
allowed us to estimate the latter coefficient in terms of the atomistic
parameters such as the surface anisotropy constant. We have thus proposed a new
origin for the magnetization nutations as being induced by surface effects and
have interpreted the corresponding resonance peaks and their frequencies.
| arxiv topic:cond-mat.mes-hall |
arxiv_dataset-100471807.07492 | Momentum distribution and non-local high order correlation functions of
1D strongly interacting Bose gas
cond-mat.quant-gas
The Lieb-Liniger model is a prototypical integrable model and has been turned
into the benchmark physics in theoretical and numerical investigations of low
dimensional quantum systems.
In this note, we present various methods for calculating local and nonlocal
$M$-particle correlation functions, momentum distribution and static structure
factor. In particular, using the Bethe ansatz wave function of the strong
coupling Lieb-Liniger model, we analytically calculate two-point correlation
function, the large moment tail of momentum distribution and static structure
factor of the model in terms of the fractional statistical parameter $\alpha
=1-2/\gamma$, where $\gamma$ is the dimensionless interaction strength. We also
discuss the Tan's adiabatic relation and other universal relations for the
strongly repulsive Lieb-Liniger model in term of the fractional statistical
parameter.
| arxiv topic:cond-mat.quant-gas |
arxiv_dataset-100481807.07592 | Dielectric Properties and Ion Transport in Layered MoS_{2} Grown by
Vapor-Phase Sulfurization
cond-mat.mtrl-sci physics.app-ph
Electronic and dielectric properties of vapor-phase grown MoS_{2} have been
investigated in metal/MoS_{2}/silicon capacitor structures by
capacitance-voltage and conductancevoltage techniques. Analytical methods
confirm the MoS_{2} layered structure, the presence of interfacial silicon
oxide (SiO_{x}) and the composition of the films. Electrical characteristics in
combination with theoretical considerations quantify the concentration of
electron states at the interface between Si and a 2.5 - 3 nm thick silicon
oxide interlayer between Si and MoS_{2}. Measurements under electric field
stress indicate the existence of mobile ions in MoS_{2} that interact with
interface states. Based on time-offlight secondary ion mass spectrometry, we
propose OH^{-} ions as probable candidates responsible for the observations.
The dielectric constant of the vapor-phase grown MoS_{2} extracted from CV
measurements at 100 KHz is in the range of 2.6 to 2.9. The present study
advances the understanding of defects and interface states in MoS_{2}. It also
indicates opportunities for ion-based plasticity in 2D material devices for
neuromorphic computing applications.
| arxiv topic:cond-mat.mtrl-sci physics.app-ph |
arxiv_dataset-100491807.07692 | A Proposal of a Superconducting Linac in CW Operation for Multi-Purposes
physics.acc-ph
A superconducting (SC) linac is expected to lead to outstanding discoveries
in various scientific fields because its beam current is a few orders of
magnitude larger than in a normal-conducting linac. However, the widespread use
of SC linac is limited by the high construction and operation costs. To resolve
this problem, we propose a continuous wave (CW) operation of a SC linac shared
by electron/positron beams for effective multi-purposes utilization. A high
current positron/electron beam is required for high-energy physics projects
such as linear collider and muon collider while high-current and high-quality
electron beams is expected to realize the next generation X-ray light sources.
As an example, we discuss the injector of the International Linear Collider, an
X-ray free-electron laser and an energy-recovery linac light source. We found a
feasible solution for the proposed multibeam operation despite the high-quality
beam requirements and complicated opertion: control of mixed beams without
pulsed magnets, lower beam loss and heat load in the cavity, high stability of
beam energy, and operation at high average current.
| arxiv topic:physics.acc-ph |
arxiv_dataset-100501807.07792 | Hessenberg varieties, Slodowy slices, and integrable systems
math.AG math.RT math.SG
This work is intended to contextualize and enhance certain well-studied
relationships between Hessenberg varieties and the Toda lattice, thereby
building on the results of Kostant, Peterson, and others. One such relationship
is the fact that every Lagrangian leaf in the Toda lattice is compactified by a
suitable choice of Hessenberg variety. It is then natural to imagine the Toda
lattice as extending to an appropriate union of Hessenberg varieties.
We fix a simply-connected complex semisimple linear algebraic group $G$ and
restrict our attention to a particular family of Hessenberg varieties, a family
that includes the Peterson variety and all Toda leaf compactifications. The
total space of this family, $X(H_0)$, is shown to be a Poisson variety with a
completely integrable system defined in terms of Mishchenko--Fomenko
polynomials. This leads to a natural embedding of completely integrable systems
from the Toda lattice to $X(H_0)$. We also show $X(H_0)$ to have an open dense
symplectic leaf isomorphic to $G/Z \times S_{\text{reg}}$, where $Z$ is the
centre of $G$ and $S_{\text{reg}}$ is a regular Slodowy slice in the Lie
algebra of $G$. This allows us to invoke results about integrable systems on
$G\times S_{\text{reg}}$, as developed by Rayan and the second author. Lastly,
we witness some implications of our work for the geometry of regular Hessenberg
varieties.
| arxiv topic:math.AG math.RT math.SG |
arxiv_dataset-100511807.07892 | Bridging the Gap between Programming Languages and Hardware Weak Memory
Models
cs.PL
We develop a new intermediate weak memory model, IMM, as a way of
modularizing the proofs of correctness of compilation from concurrent
programming languages with weak memory consistency semantics to mainstream
multi-core architectures, such as POWER and ARM. We use IMM to prove the
correctness of compilation from the promising semantics of Kang et al. to POWER
(thereby correcting and improving their result) and ARMv7, as well as to the
recently revised ARMv8 model. Our results are mechanized in Coq, and to the
best of our knowledge, these are the first machine-verified compilation
correctness results for models that are weaker than x86-TSO.
| arxiv topic:cs.PL |
arxiv_dataset-100521807.07992 | On graphs with 2 trivial distance ideals
math.CO math.AC
Distance ideals generalize the Smith normal form of the distance matrix of a
graph. The family of graphs with 2 trivial distance ideals contains the family
of graphs whose distance matrix has at most 2 invariant factors equal to 1.
Here we give an infinite family of forbidden induced subgraphs for the graphs
with 2 trivial distance ideals. These are also related with other well known
graph classes.
| arxiv topic:math.CO math.AC |
arxiv_dataset-100531807.08092 | Auto-electrophoresis in non-Newtonian media: interaction of rheology and
electrocatalytic parameters
physics.flu-dyn cond-mat.soft
Recent findings of possible applications of bio-friendly synthetic
self-phoretic swimmers, have motivated the researchers in investigating the
various motion-generating mechanisms to optimize the operating characteristics
of the same. In this paper we model the auto-electrophoretic motion of a
bimetallic (Au-Pt) spherical swimmer in a non-Newtonian medium. In view of the
fact that many bio-fluids closely follow the generalized Newtonian rheology,
the rheology of the surrounding swimming medium is considered to follow the
Carreau-Yasuda viscosity model. Further to capture the experimentally observed
effects of peroxide concentration and feedback of generated proton
concentration on the surface cation flux, we incorporate a Michaelis-Menten
like surface reaction kinetics. The electrocatalytic efficiency defined as a
ratio between the cost of swimming of an equivalent passively dragged particle
and the input chemical energy via surface reaction, is utilized to assess the
influence of the rheological parameters on the swimmer performance. The results
indicate that the shear thinning and shear thickening nature of the surrounding
fluid causes an enhancement and reduction in swimmer velocity, respectively.
However, an increase in the shear thinning effect does not always guarantee an
efficient operation of the microswimmer. A competition between the particle
velocity and reduction in the drag force on the particle, decides whether the
propulsion efficiency will have a relative augmentation or attenuation with
varying power law index. We further report the existence of maximum efficiency
points for some specific range of Weissenberg number and optimum power law
indices. Moreover the behaviour of such optimum operating conditions strongly
depends on the non-trivial and highly coupled interplay among the rheology and
electrocatalytic parameters.
| arxiv topic:physics.flu-dyn cond-mat.soft |
arxiv_dataset-100541807.08192 | Randomness quantification of coherent detection
quant-ph
Continuous-variable quantum cryptographic systems, including random number
generation and key distribution, are often based on coherent detection. The
essence of the security analysis lies in the randomness quantification.
Previous analyses employ a semi-quantum picture, where the strong local
oscillator limit is assumed. Here, we investigate the randomness of homodyne
detection in a full quantum scenario by accounting for the shot noise in the
local oscillator, which requires us to develop randomness measures in the
infinite-dimensional scenario. Similar to the finite-dimensional case, our
introduced measure of randomness corresponds to the relative entropy of
coherence defined for an infinite-dimensional system. Our results are
applicable to general coherent detection systems, in which the local oscillator
is inevitably of finite power. As an application example, we employ the
analysis method to a practical vacuum-fluctuation quantum random number
generator and explore the limits of generation rate given a continuous-wave
laser.
| arxiv topic:quant-ph |
arxiv_dataset-100551807.08292 | Proof of a Conjecture of Reiner-Tenner-Yong on Barely Set-valued
Tableaux
math.CO
The notion of a barely set-valued semistandard Young tableau was introduced
by Reiner, Tenner and Yong in their study of the probability distribution of
edges in the Young lattice of partitions. Given a partition $\lambda$ and a
positive integer $k$, let ${\mathrm{BSSYT}}(\lambda,k)$ (respectively,
${\mathrm{SYT}}(\lambda,k)$) denote the set of barely set-valued semistandard
Young tableaux (respectively, ordinary semistandard Young tableaux) of shape
$\lambda$ with entries in row $i$ not exceeding $k+i$. In the case when
$\lambda$ is a rectangular staircase partition $\delta_d(b^a)$, Reiner, Tenner
and Yong conjectured that $|{\mathrm{BSSYT}}(\lambda,k)|=
\frac{kab(d-1)}{(a+b)} |{\mathrm{SYT}}(\lambda,k)|$. In this paper, we
establish a connection between barely set-valued tableaux and reverse plane
partitions with designated corners. We show that for any shape $\lambda$, the
expected jaggedness of a subshape of $\lambda$ under the weak probability
distribution can be expressed as $\frac{2|{\mathrm{BSSYT}}(\lambda,k)|}
{k|{\mathrm{SYT}}(\lambda,k)|}$. On the other hand, when $\lambda$ is a
balanced shape with $r$ rows and $c$ columns, Chan, Haddadan, Hopkins and Moci
proved that the expected jaggedness of a subshape in $\lambda$ under the weak
distribution equals $2rc/(r+c)$. Hence, for a balanced shape $\lambda$ with $r$
rows and $c$ columns, we establish the relation that
$|{\mathrm{BSSYT}}(\lambda,k)|=\frac{krc}{(r+c)}|{\mathrm{SYT}}(\lambda,k)|$.
Since a rectangular staircase shape $\delta_d(b^a)$ is a balanced shape, we
confirm the conjecture of Reiner, Tenner and Yong.
| arxiv topic:math.CO |
arxiv_dataset-100561807.08392 | Improving Automatic Skin Lesion Segmentation using Adversarial Learning
based Data Augmentation
cs.CV
Segmentation of skin lesions is considered as an important step in computer
aided diagnosis (CAD) for automated melanoma diagnosis. In recent years,
segmentation methods based on fully convolutional networks (FCN) have achieved
great success in general images. This success is primarily due to the
leveraging of large labelled datasets to learn features that correspond to the
shallow appearance as well as the deep semantics of the images. However, the
dependence on large dataset does not translate well into medical images. To
improve the FCN performance for skin lesion segmentations, researchers
attempted to use specific cost functions or add post-processing algorithms to
refine the coarse boundaries of the FCN results. However, the performance of
these methods is heavily reliant on the tuning of many parameters and
post-processing techniques. In this paper, we leverage the state-of-the-art
image feature learning method of generative adversarial network (GAN) for its
inherent ability to produce consistent and realistic image features by using
deep neural networks and adversarial learning concept. We improve upon GAN such
that skin lesion features can be learned at different level of complexities, in
a controlled manner. The outputs from our method is then augmented to the
existing FCN training data, thus increasing the overall feature diversity. We
evaluated our method on the ISIC 2018 skin lesion segmentation challenge
dataset and showed that it was more accurate and robust when compared to the
existing skin lesion segmentation methods.
| arxiv topic:cs.CV |
arxiv_dataset-100571807.08492 | Digital finite quantum Riemannian geometries
math.DG gr-qc
We study bimodule quantum Riemannian geometries over the field $\Bbb F_2$ of
two elements as the extreme case of a finite-field adaptation of
noncommutative-geometric methods for physics. We classify all parallelisable
such geometries for coordinate algebras up to vector space dimension $n\le 3$,
finding a rich moduli of examples for $n=3$ and top form degree 2, including
many that are not flat. Their coordinate algebras are commutative but their
differentials are not. We also study the quantum Laplacian $\Delta=(\ ,\
)\nabla{\rm d}$ on our models and characterise when it has a massive
eigenvector.
| arxiv topic:math.DG gr-qc |
arxiv_dataset-100581807.08592 | Investigating the Rotational Phase of Stellar Flares on M dwarfs Using
K2 Short Cadence Data
astro-ph.SR
We present an analysis of K2 short cadence data of 34 M dwarfs which have
spectral types in the range M0 - L1. Of these stars, 31 showed flares with a
duration between $\sim$10-90 min. Using distances obtained from Gaia DR2
parallaxes, we determined the energy of the flares to be in the range
$\sim1.2\times10^{29}-6\times10^{34}$ erg. In agreement with previous studies
we find rapidly rotating stars tend to show more flares, with evidence for a
decline in activity in stars with rotation periods longer than $\sim$10 days.
The rotational modulation seen in M dwarf stars is widely considered to result
from a starspot which rotates in and out of view. Flux minimum is therefore the
rotation phase where we view the main starspot close to the stellar disk
center. Surprisingly, having determined the rotational phase of each flare in
our study we find none show any preference for rotational phase. We outline
three scenarios which could account for this unexpected finding. The
relationship between rotation phase and flare rate will be explored further
using data from wide surveys such as NGTS and TESS.
| arxiv topic:astro-ph.SR |
arxiv_dataset-100591807.08692 | Hybrid Diffusion: Spectral-Temporal Graph Filtering for Manifold Ranking
cs.CV
State of the art image retrieval performance is achieved with CNN features
and manifold ranking using a k-NN similarity graph that is pre-computed
off-line. The two most successful existing approaches are temporal filtering,
where manifold ranking amounts to solving a sparse linear system online, and
spectral filtering, where eigen-decomposition of the adjacency matrix is
performed off-line and then manifold ranking amounts to dot-product search
online. The former suffers from expensive queries and the latter from
significant space overhead. Here we introduce a novel, theoretically
well-founded hybrid filtering approach allowing full control of the space-time
trade-off between these two extremes. Experimentally, we verify that our hybrid
method delivers results on par with the state of the art, with lower memory
demands compared to spectral filtering approaches and faster compared to
temporal filtering.
| arxiv topic:cs.CV |
arxiv_dataset-100601807.08792 | PCNNA: A Photonic Convolutional Neural Network Accelerator
cs.ET cs.LG eess.SP
Convolutional Neural Networks (CNN) have been the centerpiece of many
applications including but not limited to computer vision, speech processing,
and Natural Language Processing (NLP). However, the computationally expensive
convolution operations impose many challenges to the performance and
scalability of CNNs. In parallel, photonic systems, which are traditionally
employed for data communication, have enjoyed recent popularity for data
processing due to their high bandwidth, low power consumption, and
reconfigurability. Here we propose a Photonic Convolutional Neural Network
Accelerator (PCNNA) as a proof of concept design to speedup the convolution
operation for CNNs. Our design is based on the recently introduced silicon
photonic microring weight banks, which use broadcast-and-weight protocol to
perform Multiply And Accumulate (MAC) operation and move data through layers of
a neural network. Here, we aim to exploit the synergy between the inherent
parallelism of photonics in the form of Wavelength Division Multiplexing (WDM)
and sparsity of connections between input feature maps and kernels in CNNs.
While our full system design offers up to more than 3 orders of magnitude
speedup in execution time, its optical core potentially offers more than 5
order of magnitude speedup compared to state-of-the-art electronic
counterparts.
| arxiv topic:cs.ET cs.LG eess.SP |
arxiv_dataset-100611807.08892 | On ANITA's sensitivity to long-lived, charged massive particles
astro-ph.HE
We propose that the Antarctic Impulsive Transient Antenna (ANITA) can serve
as a detector for long-lived, charged particles, through its measurement of
extensive air showers from secondary leptons. To test this on an example model,
we simulate the production of staus inside the earth from interactions between
ultra-high energy neutrinos and nuclei. We propose that results of ANITA
searches for upgoing air showers can be interpreted in terms of constraints on
long-lived, charged massive particles (CHAMPs) and consider a supersymmetric
partner of the tau lepton, the stau, as an example of such a particle.
Exploring the parameter space in stau mass and lifetimes, we find that the stau
properties that lead to an observable signal in ANITA are highly energy
dependent. At $10^{18.5}$ eV, we find that the best constraints on the product
of the neutrino flux and the stau production cross section would be placed near
$m_{\tilde{\tau}}=$1 TeV and $\tau_{\tilde{\tau}}=$10 ns. Thus ANITA could be
sensitive to new physics in a region of parameter space that is unconstrained
by experiments at the Large Hadron Collider.
| arxiv topic:astro-ph.HE |
arxiv_dataset-100621807.08992 | Theoretical S1 <- S0 absorption energies of the anionic forms of
oxyluciferin by Variational Monte Carlo and Many Body Green's Function Theory
physics.chem-ph cond-mat.mtrl-sci
The structures of three negatively charged forms (anionic keto-1 and enol-1,
dianonic enol-2) of oxyluciferin (OxyLuc), which are the most probable emitters
responsible for the firefly bioluminescence, have been fully relaxed at the
variational Monte Carlo (VMC) level. Absorption energies of the S1<-S0 vertical
transition have been computed using different levels of theory, such as TDDFT,
CC2 and many body Green's function Theory (MBGFT). The use of MBGFT, by means
of the Bethe-Salpeter (BS) formalism, on VMC structures provides results in
excellent agreement with the value (2.26(8) eV) obtained by action spectroscopy
experiments for the keto-1 form (2.32 eV). To unravel the role of the quality
of the optimized ground state geometry, BS excitation energies have also been
computed on CASSCF geometries, inducing a non negligible blue shift (0.08 and
0.07 eV for keto-1 and enol-1 forms, respectively) with respect to the VMC
ones. Structural effects have been analyzed in terms of over- or
under-correlation along the conjugated bonds of OxyLuc by using different
methods for the ground-state optimization. The relative stability of the S$_1$
state for the keto-1 and enol-1 forms depends on the method chosen for the
excited state calculation, thus representing a fundamental caveat for any
theoretical study on these systems. Finally, Kohn-Sham HOMO and LUMO orbitals
of enol-2 are (nearly) bound only when the dianion is embedded into a solvent
(water and toluene in the present work); excited state calculations are
therefore meaningful only in presence of a dielectric medium which localizes
the electronic density. The combination of VMC for the ground state geometry
and BS formalism for the absorption spectra clearly outperforms standard TDDFT
and quantum chemistry approaches.
| arxiv topic:physics.chem-ph cond-mat.mtrl-sci |
arxiv_dataset-100631807.09092 | On equivariant and motivic slices
math.AT math.AG math.KT
Let $k$ be a field with a real embedding. We compare the motivic slice
filtration of a motivic spectrum over $Spec(k)$ with the $C_2$-equivariant
slice filtration of its equivariant Betti realization, giving conditions under
which realization induces an equivalence between the associated slice towers.
In particular, we show that, up to reindexing, the towers agree for all spectra
obtained from localized quotients of $MGL$ and $MR$, and for motivic Landweber
exact spectra and their realizations. As a consequence, we deduce that
equivariant spectra obtained from localized quotients of $MR$ are even in the
sense of Hill--Meier, and give a computation of the slice spectral sequence
converging to $\pi_{*,*}BP\langle n \rangle/2$ for $1 \le n \le \infty$.
| arxiv topic:math.AT math.AG math.KT |
arxiv_dataset-100641807.09192 | Multicolumn Networks for Face Recognition
cs.CV
The objective of this work is set-based face recognition, i.e. to decide if
two sets of images of a face are of the same person or not. Conventionally, the
set-wise feature descriptor is computed as an average of the descriptors from
individual face images within the set. In this paper, we design a neural
network architecture that learns to aggregate based on both "visual" quality
(resolution, illumination), and "content" quality (relative importance for
discriminative classification). To this end, we propose a Multicolumn Network
(MN) that takes a set of images (the number in the set can vary) as input, and
learns to compute a fix-sized feature descriptor for the entire set. To
encourage high-quality representations, each individual input image is first
weighted by its "visual" quality, determined by a self-quality assessment
module, and followed by a dynamic recalibration based on "content" qualities
relative to the other images within the set. Both of these qualities are learnt
implicitly during training for set-wise classification. Comparing with the
previous state-of-the-art architectures trained with the same dataset
(VGGFace2), our Multicolumn Networks show an improvement of between 2-6% on the
IARPA IJB face recognition benchmarks, and exceed the state of the art for all
methods on these benchmarks.
| arxiv topic:cs.CV |
arxiv_dataset-100651807.09292 | The Warden's de Bruijn Sequence
math.CO
The Warden's Game is a 2-player game, played with a row of coins. One player
(the prisoner) wants to get all coins to show tails; the other player (the
warden) wants to delay that as long as possible. At each turn, one player
transfers the coin on the far right to the far left, and optionally flips that
coin; the prisoner transfers heads, and the warden transfers tails. We will
find the optimal strategies for both players, and we will also analyze some
variations on this game.
| arxiv topic:math.CO |
arxiv_dataset-100661807.09392 | Does a robot path have clearance c?
cs.CG
Most path planning problems among polygonal obstacles ask to find a path that
avoids the obstacles and is optimal with respect to some measure or a
combination of measures, for example an $u$-to-$v$ shortest path of clearance
at least $c$, where $u$ and $v$ are points in the free space and $c$ is a
positive constant. In practical applications, such as emergency
interventions/evacuations and medical treatment planning, a number of
$u$-to-$v$ paths are suggested by experts and the question is whether such
paths satisfy specific requirements, such as a given clearance from the
obstacles. We address the following path query problem: Given a set $S$ of $m$
disjoint simple polygons in the plane, with a total of $n$ vertices, preprocess
them so that for a query consisting of a positive constant $c$ and a simple
polygonal path $\pi$ with $k$ vertices, from a point $u$ to a point $v$ in free
space, where $k$ is much smaller than $n$, one can quickly decide whether $\pi$
has clearance at least $c$ (that is, there is no polygonal obstacle within
distance $c$ of $\pi$). To do so, we show how to solve the following related
problem: Given a set $S$ of $m$ simple polygons in $\Re^{2}$, preprocess $S$
into a data structure so that the polygon in $S$ closest to a query line
segment $s$ can be reported quickly. We present an $O(t \log n)$ time, $O(t)$
space preprocessing, $O((n / \sqrt{t}) \log ^{7/2} n)$ query time solution for
this problem, for any $n ^{1 + \epsilon} \leq t \leq n^{2}$. For a path with
$k$ segments, this results in $O((n k / \sqrt{t}) \log ^{7/2} n)$ query time,
which is a significant improvement over algorithms that can be derived from
existing computational geometry methods when $k$ is small.
| arxiv topic:cs.CG |
arxiv_dataset-100671807.09492 | Highlights of chaos research
nlin.CD
We describe some highlights in the theory of chaos, that started with
Poincare (1899). Generic systems have both ordered and chaotic domains. Chaos
appears mainly near un- stable periodic orbits. Large chaotic domains are due
to resonance overlap. Two recent developments of the theory of chaos, refer (a)
to the analytical formulae (Moser series) in the chaotic domains near unstable
periodic orbits, and (b) quantum chaos, described by the Bohmian theory of
orbits.
| arxiv topic:nlin.CD |
arxiv_dataset-100681807.09592 | Graph Distance from the Topological View of Non-backtracking Cycles
cs.SI physics.data-an physics.soc-ph
Whether comparing networks to each other or to random expectation, measuring
dissimilarity is essential to understanding the complex phenomena under study.
However, determining the structural dissimilarity between networks is an
ill-defined problem, as there is no canonical way to compare two networks.
Indeed, many of the existing approaches for network comparison differ in their
heuristics, efficiency, interpretability, and theoretical soundness. Thus,
having a notion of distance that is built on theoretically robust first
principles and that is interpretable with respect to features ubiquitous in
complex networks would allow for a meaningful comparison between different
networks. Here we introduce a theoretically sound and efficient new measure of
graph distance, based on the "length spectrum" function from algebraic
topology, which compares the structure of two undirected, unweighted graphs by
considering their non-backtracking cycles. We show how this distance relates to
structural features such as presence of hubs and triangles through the behavior
of the eigenvalues of the so-called non-backtracking matrix, and we showcase
its ability to discriminate between networks in both real and synthetic data
sets. By taking a topological interpretation of non-backtracking cycles, this
work presents a novel application of Topological Data Analysis to the study of
complex networks.
| arxiv topic:cs.SI physics.data-an physics.soc-ph |
arxiv_dataset-100691807.09693 | From linear combination of quantum states to Grover's searching
algorithm
quant-ph
Linear combination of unitaries (LCU for short) is one of the most important
techniques in designing quantum algorithms. In this paper, we propose a new
quantum algorithm in three different forms to achieve LCU. Different from
previous algorithms [Childs-linear-system,Clader,Long11], the complexity now
only depends on the number of the unitaries and the precision. So it will play
more important role in the design of quantum algorithms when the number of
unitaries is small, such as quantum iteration algorithms. %Since in iteration
algorithms, $m$ often refers to the iteration steps, which is small if the
iteration algorithms are efficient. Moreover, as an application of the new LCU,
three new quantum algorithms to the searching problem will be proposed, which
will provide us new insights into Grover's searching algorithm. We also show
that the problem of LCU is closely related to the problem of if we can
efficiently implement $U^t$ for $0<t<1$ when $U$ is an efficiently implemented
unitary operator? This problem is not hard to solve. However, it becomes
inefficient when it contains a strict requirement on precision, such as in
Grover's algorithm. Finally, as an application of the new LCU technique, we
will show that the quantum state of any real classical vector can be prepared
efficiently in quantum computer. So this solves the "input problem" in quantum
computer efficiently.
| arxiv topic:quant-ph |
arxiv_dataset-100701807.09794 | De Sitter and Anti-de Sitter branes in self-tuning models
hep-th gr-qc hep-ph
Maximally symmetric curved-brane solutions are studied in dilatonic
braneworld models which realise the self-tuning of the effective
four-dimensional cosmological constant. It is found that no vacua in which the
brane has de Sitter or anti-de Sitter geometry exist, unless one modifies the
near-boundary asymptotics of the bulk fields. In the holographic dual picture,
this corresponds to coupling the UV CFT to a curved metric (possibly with a
defect). Alternatively, the same may be achieved in a flat-space QFT with
suitable variable scalar sources. With these ingredients, it is found that
maximally symmetric, positive and negative curvature solutions with a
stabilised brane position generically exist. The space of such solutions is
studied in two different types of realisations of the self-tuning framework. In
some regimes we observe a large hierarchy between the curvature on the brane
and the boundary UV CFT curvature. This is a dynamical effect due to the
self-stabilisation mechanism. This setup provides an alternative route to
realising de Sitter space in string theory.
| arxiv topic:hep-th gr-qc hep-ph |
arxiv_dataset-100711807.09894 | A fictitious domain approach for a mixed finite element method solving
the two-phase Stokes problem with surface tension forces
math.NA
In this article we study a mixed finite element formulation for solving the
Stokes problem with general surface forces that induce a jump of the normal
trace of the stress tensor, on an interface that splits the domain into two
subdomains. Equality of velocities is assumed at the interface. The interface
conditions are taken into account with multipliers. A suitable Lagrangian
functional is introduced for deriving a weak formulation of the problem. A
specificity of this work is the consideration of the interface with a
fictitious domain approach. The latter is inspired by the XFEM approach in the
sense that cut-off functions are used, but it is simpler to implement since no
enrichment by singular functions is provided. In that context, getting
convergence for the dual variables defined on the interface is non-trivial. For
that purpose, an augmented Lagrangian technique stabilizes the convergence of
the multipliers, which is important because their value would determine the
dynamics of the interface in an unsteady framework. Theoretical analysis is
provided, where we show that a discrete inf-sup condition, independent of the
mesh size, is satisfied for the stabilized formulation. This guarantees optimal
convergence rates, that we observe with numerical tests. The capacity of the
method is demonstrated with robustness tests, and with an unsteady model tested
for deformations of the interface that correspond to ellipsoidal shapes in
dimension 2.
| arxiv topic:math.NA |
arxiv_dataset-100721807.09994 | Torsional chiral magnetic effect due to skyrmion textures in a Weyl
superfluid $^3$He-A
cond-mat.supr-con
We investigate torsional chiral magnetic effect (TCME) induced by
skyrmion-vortex textures in the A phase of the superfluid $^3$He. In $^3$He-A,
Bogoliubov quasiparticles around point nodes behave as Weyl fermions, and the
nodal direction represented by the $\ell$-vector may form a spatially modulated
texture. $\ell$-textures generate a chiral gauge field and a torsion field
directly acting on the chirality of Weyl-Bogoliubov quasiparticles. It has been
clarified by G. E. Volovik [Pi'sma Zh. Eksp. Teor. Fiz. {\bf 43}, 428 (1986)]
that, if the $\ell$-vector is twisted, the chiral gauge field is responsible
for the chiral anomaly, leading to an anomalous current along ${\ell}$. Here we
show that, even for non-twisted $\ell$-vector fields, a torsion arising from
$\ell$-textures brings about contributions to the equilibrium currents of
Weyl-Bogoliubov quasiparticles along ${\rm curl}{\ell}$. This implies that
while the anomalous current appears only for the twisted (Bloch-type) skyrmion
of the $\ell$-vector, the extra mass current due to TCME always exists
regardless of the skyrmion type. Solving the Bogoliubov-de Gennes equation, we
demonstrate that both Bloch-type and N\'{e}el-type skyrmions induce chiral
fermion states with spectral asymmetry, and possess spatially inhomogeneous
structures of Weyl bands in the real coordinate space. Furthermore, we discuss
the contributions of Weyl-Bogoliubov quasiparticles and continuum states to the
mass current density in the vicinity of the topological phase transition. In
the weak coupling limit, continuum states give rise to backflow to the mass
current generated by Weyl-Bogoliubov quasiparticles, which makes a
non-negligible contribution to the orbital angular momentum. As the topological
transition is approached, the mass current density is governed by the
contribution of continuum states.
| arxiv topic:cond-mat.supr-con |
arxiv_dataset-100731807.10094 | Semi-regular Dubuc-Deslauriers wavelet tight frames
math.NA
In this paper, we construct wavelet tight frames with n vanishing moments for
Dubuc-Deslauriers 2npoint semi-regular interpolatory subdivision schemes. Our
motivation for this construction is its practical use for further regularity
analysis of wide classes of semi-regular subdivision. Our constructive tools
are local eigenvalue convergence analysis for semi-regular Dubuc-Deslauriers
subdivision, the Unitary Extension Principle and the generalization of the
Oblique Extension Principle to the irregular setting by Chui, He and
St\"ockler. This group of authors derives suitable approximation of the inverse
Gramian for irregular Bspline subdivision. Our main contribution is the
derivation of the appropriate approximation of the inverse Gramian for the
semi-regular Dubuc-Deslauriers scaling functions ensuring n vanishing moments
of the corresponding framelets.
| arxiv topic:math.NA |
arxiv_dataset-100741807.10194 | Linkage between piecewise constant Mumford-Shah model and ROF model and
its virtue in image segmentation
math.NA cs.CV cs.NA
The piecewise constant Mumford-Shah (PCMS) model and the Rudin-Osher-Fatemi
(ROF) model are two important variational models in image segmentation and
image restoration, respectively. In this paper, we explore a linkage between
these models. We prove that for the two-phase segmentation problem a partial
minimizer of the PCMS model can be obtained by thresholding the minimizer of
the ROF model. A similar linkage is still valid for multiphase segmentation
under specific assumptions. Thus it opens a new segmentation paradigm: image
segmentation can be done via image restoration plus thresholding. This new
paradigm, which circumvents the innate non-convex property of the PCMS model,
therefore improves the segmentation performance in both efficiency (much faster
than state-of-the-art methods based on PCMS model, particularly when the phase
number is high) and effectiveness (producing segmentation results with better
quality) due to the flexibility of the ROF model in tackling degraded images,
such as noisy images, blurry images or images with information loss. As a
by-product of the new paradigm, we derive a novel segmentation method, called
thresholded-ROF (T-ROF) method, to illustrate the virtue of managing image
segmentation through image restoration techniques. The convergence of the T-ROF
method is proved, and elaborate experimental results and comparisons are
presented.
| arxiv topic:math.NA cs.CV cs.NA |
arxiv_dataset-100751807.10294 | Constraining light sterile neutrino mass with the BICEP2/Keck Array 2014
B-mode polarization data
astro-ph.CO hep-ph
We explore the thermal light sterile neutrino situation from cosmological
perspective in the $\Lambda \textrm{CDM} + r_{0.05} + N_{\textrm{eff}} +
m^{\textrm{eff}}_{\textrm{s}}$ model using combinations of latest data sets
available. Here, $r_{0.05}$ is the tensor-to-scalar ratio at the pivot scale of
$k_*=0.05h$ Mpc$^{-1}$, $N_{\textrm{eff}}$ is the effective number of
relativistic species during recombination, and $m^{\textrm{eff}}_{\textrm{s}}$
is the effective mass of the sterile neutrino. Among Cosmic Microwave
Background (CMB) datasets, we use Planck 2015 temperature and low-$l$ ($l <$
30) polarization data and the latest data release on the B-mode polarization up
to and including 2014 from the BICEP2/Keck collaboration (BK14). We also use
the latest BAO data from SDSS-III BOSS DR12, MGS, and 6dFS; and a Gaussian
prior (HST) on the Hubble constant ($H_0 = 73.24 \pm 1.74$ km/sec/Mpc) from
direct measurements. We find that inclusion of BK14 data makes the constraints
on the effective mass of sterile neutrino ($m^{\textrm{eff}}_{\textrm{s}}$)
slightly stronger by preferring higher $\sigma_8$ values. The bound of
$m^{\textrm{eff}}_{\textrm{s}} <$ 0.46 eV (95\% C.L.) is found for the
combination of Planck 2015, BAO and BK14 datasets, whereas the bound is
$m^{\textrm{eff}}_{\textrm{s}} <$ 0.53 eV (95\% C.L.) without the BK14 data.
Our most aggressive bound of $m^{\textrm{eff}}_{\textrm{s}} <$ 0.28 eV (95\%
C.L.) is obtained with Planck 2015, HST and BK14. However, the HST prior also
leads to very high $N_{\textrm{eff}}$ which might be in conflict with bounds
from BBN. Our analysis indicates that fully thermalized sterile neutrinos with
mass $\sim 1$ eV are slightly more disfavoured with the inclusion of BK14 data.
It also seems to make the agreement between Planck 2015 and CFHTLenS (weak
gravitational lensing data) worse due to the higher $\sigma_8$ values (abstract
abridged).
| arxiv topic:astro-ph.CO hep-ph |
arxiv_dataset-100761807.10394 | On the Natural Structure of Amino Acid Patterns in Families of Protein
Sequences
q-bio.BM
All known terrestrial proteins are coded as continuous strings of ~20 amino
acids. The patterns formed by the repetitions of elements in groups of finite
sequences describes the natural architectures of protein families. We present a
method to search for patterns and groupings of patterns in protein sequences
using a mathematically precise definition for 'repetition', an efficient
algorithmic implementation and a robust scoring system with no adjustable
parameters. We show that the sequence patterns can be well-separated into
disjoint classes according to their recurrence in nested structures. The
statistics of pattern occurrences indicate that short repetitions are enough to
account for the differences between natural families and randomized groups by
more than 10 standard deviations, while patterns shorter than 5 residues are
effectively random. A small subset of patterns is sufficient to account for a
robust ''familiarity'' definition of arbitrary sets of sequences.
| arxiv topic:q-bio.BM |
arxiv_dataset-100771807.10494 | DeepLink: A Novel Link Prediction Framework based on Deep Learning
cs.SI cs.LG stat.ML
Recently, link prediction has attracted more attentions from various
disciplines such as computer science, bioinformatics and economics. In this
problem, unknown links between nodes are discovered based on numerous
information such as network topology, profile information and user generated
contents. Most of the previous researchers have focused on the structural
features of the networks. While the recent researches indicate that contextual
information can change the network topology. Although, there are number of
valuable researches which combine structural and content information, but they
face with the scalability issue due to feature engineering. Because, majority
of the extracted features are obtained by a supervised or semi supervised
algorithm. Moreover, the existing features are not general enough to indicate
good performance on different networks with heterogeneous structures. Besides,
most of the previous researches are presented for undirected and unweighted
networks. In this paper, a novel link prediction framework called "DeepLink" is
presented based on deep learning techniques. In contrast to the previous
researches which fail to automatically extract best features for the link
prediction, deep learning reduces the manual feature engineering. In this
framework, both the structural and content information of the nodes are
employed. The framework can use different structural feature vectors, which are
prepared by various link prediction methods. It considers all proximity orders
that are presented in a network during the structural feature learning. We have
evaluated the performance of DeepLink on two real social network datasets
including Telegram and irBlogs. On both datasets, the proposed framework
outperforms several structural and hybrid approaches for link prediction
problem.
| arxiv topic:cs.SI cs.LG stat.ML |
arxiv_dataset-100781807.10594 | Regularity for minimizers of non-autonomous non-quadratic functionals in
the case 1 < p < 2: an a priori estimate
math.AP
We prove an a priori estimate for the second derivatives of local minimizers
of integral functionals of calculus of variation with convex integrand with
respect to the gradient variable, assuming that the function that measures the
oscillation of the integrand with respect to the x variable belongs to a
suitable Sobolev space. The novelty here is that we deal with integrands
satisfying subquadratic growth conditions with respect to gradient variable.
| arxiv topic:math.AP |
arxiv_dataset-100791807.10694 | Scalar multivariate risk measures with a single eligible asset
q-fin.RM
In this paper we present results on scalar risk measures in markets with
transaction costs. Such risk measures are defined as the minimal capital
requirements in the cash asset. First, some results are provided on the dual
representation of such risk measures, with particular emphasis given on the
space of dual variables as (equivalent) martingale measures and prices
consistent with the market model. Then, these dual representations are used to
obtain the main results of this paper on time consistency for scalar risk
measures in markets with frictions. It is well known from the superhedging risk
measure in markets with transaction costs, as in Jouini and Kallal (1995), Roux
and Zastawniak (2016), and Loehne and Rudloff (2014), that the usual scalar
concept of time consistency is too strong and not satisfied. We will show that
a weaker notion of time consistency can be defined, which corresponds to the
usual scalar time consistency but under any fixed consistent pricing process.
We will prove the equivalence of this weaker notion of time consistency and a
certain type of backward recursion with respect to the underlying risk measure
with a fixed consistent pricing process. Several examples are given, with
special emphasis on the superhedging risk measure.
| arxiv topic:q-fin.RM |
arxiv_dataset-100801807.10794 | Phase space mixing in the equatorial plane of a Kerr black hole
gr-qc astro-ph.GA
It is shown that a collisionless, relativistic kinetic gas configuration
propagating in the equatorial plane of a Kerr black hole undergoes a relaxation
process and eventually settles down to a stationary, axisymmetric configuration
surrounding the black hole. The underlying mechanism for this relaxation
process is due to phase space mixing, which implies that although the
one-particle distribution function $f$ satisfying the collisionless Boltzmann
equation which describes the microscopic state of the gas is quasi-periodic in
time, the associated macroscopic observables computed from averages over $f$
possess well-defined limits as time goes to infinity. The final state of the
gas is described by an effective distribution function depending only on
constants of motion which can be predicted from the initial distribution
function.
| arxiv topic:gr-qc astro-ph.GA |
arxiv_dataset-100811807.10894 | A user model for JND-based video quality assessment: theory and
applications
cs.MM
The video quality assessment (VQA) technology has attracted a lot of
attention in recent years due to an increasing demand of video streaming
services. Existing VQA methods are designed to predict video quality in terms
of the mean opinion score (MOS) calibrated by humans in subjective experiments.
However, they cannot predict the satisfied user ratio (SUR) of an aggregated
viewer group. Furthermore, they provide little guidance to video coding
parameter selection, e.g. the Quantization Parameter (QP) of a set of
consecutive frames, in practical video streaming services. To overcome these
shortcomings, the just-noticeable-difference (JND) based VQA methodology has
been proposed as an alternative. It is observed experimentally that the JND
location is a normally distributed random variable. In this work, we explain
this distribution by proposing a user model that takes both subject
variabilities and content variabilities into account. This model is built upon
user's capability to discern the quality difference between video clips encoded
with different QPs. Moreover, it analyzes video content characteristics to
account for inter-content variability. The proposed user model is validated on
the data collected in the VideoSet. It is demonstrated that the model is
flexible to predict SUR distribution of a specific user group.
| arxiv topic:cs.MM |
arxiv_dataset-100821807.10994 | Spin tensor and its role in non-equilibrium thermodynamics
hep-th gr-qc nucl-th
It is shown that the description of a relativistic fluid at local
thermodynamic equilibrium depends on the particular quantum stress-energy
tensor operator chosen, e.g., the canonical or symmetrized Belinfante
stress-energy tensor. We argue that the Belinfante tensor is not appropriate to
describe a relativistic fluid whose macroscopic polarization relaxes slowly to
thermodynamic equilibrium and that a spin tensor, like the canonical spin
tensor, is required. As a consequence, the description of a polarized
relativistic fluid involves an extension of relativistic hydrodynamics
including a new antisymmetric rank-two tensor as a dynamical field. We show
that the canonical and Belinfante tensors lead to different predictions for
measurable quantities such as spectrum and polarization of particles produced
in relativistic heavy-ion collisions.
| arxiv topic:hep-th gr-qc nucl-th |
arxiv_dataset-100831807.11094 | Towards End-to-End Acoustic Localization using Deep Learning: from Audio
Signal to Source Position Coordinates
cs.SD eess.AS
This paper presents a novel approach for indoor acoustic source localization
using microphone arrays and based on a Convolutional Neural Network (CNN). The
proposed solution is, to the best of our knowledge, the first published work in
which the CNN is designed to directly estimate the three dimensional position
of an acoustic source, using the raw audio signal as the input information
avoiding the use of hand crafted audio features. Given the limited amount of
available localization data, we propose in this paper a training strategy based
on two steps. We first train our network using semi-synthetic data, generated
from close talk speech recordings, and where we simulate the time delays and
distortion suffered in the signal that propagates from the source to the array
of microphones. We then fine tune this network using a small amount of real
data. Our experimental results show that this strategy is able to produce
networks that significantly improve existing localization methods based on
\textit{SRP-PHAT} strategies. In addition, our experiments show that our CNN
method exhibits better resistance against varying gender of the speaker and
different window sizes compared with the other methods.
| arxiv topic:cs.SD eess.AS |
arxiv_dataset-100841807.11194 | Product formula for the limits of normalized characters of
Kirillov-Reshetikhin modules
math.QA
The normalized characters of Kirillov-Reshetikhin modules over a quantum
affine algebra have a limit as a formal power series. Mukhin and Young found a
conjectural product formula for this limit, which resembles the Weyl
denominator formula. We prove this formula except for some cases in type $E_8$
by employing an algebraic relation among these limits, which is a variant of
$Q\widetilde{Q}$-relations.
| arxiv topic:math.QA |
arxiv_dataset-100851807.11294 | Benchmarking of Gaussian boson sampling using two-point correlators
quant-ph
Gaussian boson sampling is a promising scheme for demonstrating a quantum
computational advantage using photonic states that are accessible in a
laboratory and, thus, offer scalable sources of quantum light. In this
contribution, we study two-point photon-number correlation functions to gain
insight into the interference of Gaussian states in optical networks. We
investigate the characteristic features of statistical signatures which enable
us to distinguish classical from quantum interference. In contrast to the
typical implementation of boson sampling, we find additional contributions to
the correlators under study which stem from the phase dependence of Gaussian
states and which are not observable when Fock states interfere. Using the first
three moments, we formulate the tools required to experimentally observe
signatures of quantum interference of Gaussian states using two outputs only.
By considering the current architectural limitations in realistic experiments,
we further show that a statistically significant discrimination between quantum
and classical interference is possible even in the presence of loss, noise, and
a finite photon-number resolution. Therefore, we formulate and apply a
theoretical framework to benchmark the quantum features of Gaussian boson
sampling under realistic conditions.
| arxiv topic:quant-ph |
arxiv_dataset-100861807.11394 | Collisional state-changing of OH$^-$ rotations by interaction with Rb
atoms in cold traps
physics.atom-ph physics.chem-ph
We employ an accurate, ab initio potential energy surface (PES) which
describes the electronic interaction energy between the molecular anion OH$^-$
($^1\Sigma^+$) and the neutral rubidium atom Rb ($^2S$), to evaluate the
elastic and inelastic cross sections over a range of energies representative of
the conditions of low-T experiments in MOT traps, when combined with
laser-cooled rubidium gas. The system is considered to be in its vibrational
ground state, while the first four rotational levels are taken to be involved
in the cooling and heating collisional processes that are computed here. The
corresponding cooling and heating rates up to about 35 K are obtained from the
calculations and compared with the recent results in a similar experiments,
where He was the partner atom of the current anion.
| arxiv topic:physics.atom-ph physics.chem-ph |
arxiv_dataset-100871807.11494 | Tabletop experiments for quantum gravity: a user's manual
quant-ph gr-qc hep-th
Recent advances in cooling, control, and measurement of mechanical systems in
the quantum regime have opened the possibility of the first direct observation
of quantum gravity, at scales achievable in experiments. This paper gives a
broad overview of this idea, using some matter-wave and optomechanical systems
to illustrate the predictions of a variety of models of low-energy quantum
gravity. We first review the treatment of perturbatively quantized general
relativity as an effective quantum field theory, and consider the particular
challenges of observing quantum effects in this framework. We then move on to a
variety of alternative models, such as those in which gravity is classical,
emergent, or responsible for a breakdown of quantum mechanics.
| arxiv topic:quant-ph gr-qc hep-th |
arxiv_dataset-100881807.11594 | Zero-free neighborhood around the unit circle for Kac polynomials
math.PR
In this paper, we study how the roots of the so-called Kac polynomial $W_n(z)
= \sum_{k=0}^{n-1} \xi_k z^k$ are concentrating to the unit circle when its
coefficients of $W_n$ are independent and identically distributed
non-degenerate real random variables. It is well-known that the roots of a Kac
polynomial are concentrating around the unit circle as $n\to\infty$ if and only
if $\mathbb{E}[\log( 1+ |\xi_0|)]<\infty$. Under the condition of
$\mathbb{E}[\xi^2_0]<\infty$, we show that there exists an annulus of width
$\mathrm{O}(n^{-2}(\log n)^{-3})$ around the unit circle which is free of roots
with probability $1-\mathrm{O}({(\log n)^{-{1}/{2}}})$. The proof relies on the
so-called small ball probability inequalities and the least common denominator.
| arxiv topic:math.PR |
arxiv_dataset-100891807.11694 | Spectrum concentration in deep residual learning: a free probability
approach
cs.LG stat.ML
We revisit the initialization of deep residual networks (ResNets) by
introducing a novel analytical tool in free probability to the community of
deep learning. This tool deals with non-Hermitian random matrices, rather than
their conventional Hermitian counterparts in the literature. As a consequence,
this new tool enables us to evaluate the singular value spectrum of the
input-output Jacobian of a fully-connected deep ResNet for both linear and
nonlinear cases. With the powerful tool of free probability, we conduct an
asymptotic analysis of the spectrum on the single-layer case, and then extend
this analysis to the multi-layer case of an arbitrary number of layers. In
particular, we propose to rescale the classical random initialization by the
number of residual units, so that the spectrum has the order of $O(1)$, when
compared with the large width and depth of the network. We empirically
demonstrate that the proposed initialization scheme learns at a speed of orders
of magnitudes faster than the classical ones, and thus attests a strong
practical relevance of this investigation.
| arxiv topic:cs.LG stat.ML |
arxiv_dataset-100901807.11794 | Attention is All We Need: Nailing Down Object-centric Attention for
Egocentric Activity Recognition
cs.CV
In this paper we propose an end-to-end trainable deep neural network model
for egocentric activity recognition. Our model is built on the observation that
egocentric activities are highly characterized by the objects and their
locations in the video. Based on this, we develop a spatial attention mechanism
that enables the network to attend to regions containing objects that are
correlated with the activity under consideration. We learn highly specialized
attention maps for each frame using class-specific activations from a CNN
pre-trained for generic image recognition, and use them for spatio-temporal
encoding of the video with a convolutional LSTM. Our model is trained in a
weakly supervised setting using raw video-level activity-class labels.
Nonetheless, on standard egocentric activity benchmarks our model surpasses by
up to +6% points recognition accuracy the currently best performing method that
leverages hand segmentation and object location strong supervision for
training. We visually analyze attention maps generated by the network,
revealing that the network successfully identifies the relevant objects present
in the video frames which may explain the strong recognition performance. We
also discuss an extensive ablation analysis regarding the design choices.
| arxiv topic:cs.CV |
arxiv_dataset-100911807.11894 | Electrostatic Langmuir and SEAWs in spin polarized plasma double layer
physics.plasm-ph
The quantum hydrodynamic model of the electrostatic waves in the two parallel
layers of two dimensional electron gases (2DEGs) is developed. It is considered
for two regimes: classic regime and quantum regime with the separate spin
evolution. Two Langmuir-like waves are found in classic case which have an
interference-like pattern in the frequency dependence on concentration
$\omega^{2}\sim(n_{01}+n_{02}\pm2\sqrt{n_{01}n_{02}})$. They appear instead of
two 2D Langmuir waves in noninteracting 2DEGs. The spectrum of four waves is
found in the quantum regime. Two extra waves are related to the separate spin
evolution and associated to the spin-electron acoustic waves. The influence of
the quantum Bohm potential is considered either.
| arxiv topic:physics.plasm-ph |
arxiv_dataset-100921808.00054 | Modeling Task Effects in Human Reading with Neural Network-based
Attention
cs.CL
Research on human reading has long documented that reading behavior shows
task-specific effects, but it has been challenging to build general models
predicting what reading behavior humans will show in a given task. We introduce
NEAT, a computational model of the allocation of attention in human reading,
based on the hypothesis that human reading optimizes a tradeoff between economy
of attention and success at a task. Our model is implemented using contemporary
neural network modeling techniques, and makes explicit and testable predictions
about how the allocation of attention varies across different tasks. We test
this in an eyetracking study comparing two versions of a reading comprehension
task, finding that our model successfully accounts for reading behavior across
the tasks. Our work thus provides evidence that task effects can be modeled as
optimal adaptation to task demands.
| arxiv topic:cs.CL |
arxiv_dataset-100931808.00154 | Knots Connected by Wide Ribbons
math.GT
A ribbon is, intuitively, a smooth mapping of an annulus $S^1 \times I$ in
3-space having constant width $\varepsilon$. This can be formalized as a triple
$(x,\varepsilon, \mathbf{u})$ where $x$ is smooth curve in 3-space and
$\mathbf{u}$ is a unit vector field based along $x$. In the 1960s and 1970s, G.
Calugareanu, G. H. White, and F. B. Fuller proved relationships between the
geometry and topology of thin ribbons, in particular the "Link = Twist +
Writhe" theorem that has been applied to help understand properties of
double-stranded DNA. Although ribbons of small width have been studied
extensively, it appears that less is known about ribbons of large width whose
images (even via a smooth map) can be singular or self-intersecting.
Suppose $K$ is a smoothly embedded knot in $\mathbb{R}^3$. Given a regular
parameterization $\mathbf{x}(s)$, and a smooth unit vector field
$\mathbf{u}(s)$ based along $K$, we may define a ribbon of width $R$ associated
to $\mathbf{x}$ and $\mathbf{u}$ as the set of all points $\mathbf{x}(s) +
r\mathbf{u}(s)$, $r \in [0,R]$. For large $R$, these wide ribbons typically
have self-intersections. In this paper, we analyze how the knot type of the
outer ribbon edge $\mathbf{x}(s) + R\mathbf{u}(s)$ relates to that of the
original knot $K$.
We show that, generically, there is an eventual limiting knot type of the
outer ribbon edge as $R$ gets arbitrary large. We prove that this eventual knot
type is one of only finitely many possibilities which depend just on the vector
field $\mathbf{u}$. However, the particular knot type within the finite set
depends on the parameterized curves $\mathbf{x}(s)$, $\mathbf{u}(s)$, and their
interactions. Finally, we show how to control the curves and their
parameterizations so that given two knot types $K_1$ and $K_2$, we can find a
smooth ribbon of constant width connecting curves of these two knot types.
| arxiv topic:math.GT |
arxiv_dataset-100941808.00254 | Black holes and topological surgery
math.GT gr-qc
We directly connect topological changes that can occur in mathematical
three-space via surgery, with black hole formation, the formation of wormholes
and new generalizations of these phenomena. This work widens the bridge between
topology and natural sciences and creates a new platform for exploring
geometrical physics.
| arxiv topic:math.GT gr-qc |
arxiv_dataset-100951808.00354 | The KPZ Equation on the Real Line
math.PR math.AP
We prove existence and uniqueness of distributional solutions to the KPZ
equation globally in space and time, with techniques from paracontrolled
analysis. Our main tool for extending the analysis on the torus to the full
space is a comparison result that gives quantitative upper and lower bounds for
the solution. We then extend our analysis to provide a path-by-path
construction of the random directed polymer measure on the real line and we
derive a variational characterisation of the solution to the KPZ equation.
| arxiv topic:math.PR math.AP |
arxiv_dataset-100961808.00454 | A Multiwavelength Look at Galactic Massive Star Forming Regions
astro-ph.GA astro-ph.SR
We present a multiwavelength study of 28 Galactic massive star-forming H II
regions. For 17 of these regions, we present new distance measurements based on
Gaia DR2 parallaxes. By fitting a multicomponent dust, blackbody, and power-law
continuum model to the 3.6 $\mu$m through 10 mm spectral energy distributions,
we find that ${\sim}34$% of Lyman continuum photons emitted by massive stars
are absorbed by dust before contributing to the ionization of H II regions,
while ${\sim}68$% of the stellar bolometric luminosity is absorbed and
reprocessed by dust in the H II regions and surrounding photodissociation
regions. The most luminous, infrared-bright regions that fully sample the upper
stellar initial mass function (ionizing photon rates $N_C \ge 10^{50}~{\rm
s}^{-1}$ and dust-processed $L_{\rm TIR}\ge 10^{6.8}$ L$_{\odot}$) have on
average higher percentages of absorbed Lyman continuum photons ($\sim$51%) and
reprocessed starlight ($\sim$82%) compared to less luminous regions. Luminous H
II regions show lower average PAH fractions than less luminous regions,
implying that the strong radiation fields from early-type massive stars are
efficient at destroying PAH molecules. On average, the monochromatic
luminosities at 8, 24, and 70 $\mu$m combined carry 94% of the dust-reprocessed
$L_{\rm TIR}$. $L_{70}$ captures ${\sim}52$% of $L_{\rm TIR}$, and is therefore
the preferred choice to infer the bolometric luminosity of dusty star-forming
regions. We calibrate SFRs based on $L_{24}$ and $L_{70}$ against the Lyman
continuum photon rates of the massive stars in each region. Standard
extragalactic calibrations of monochromatic SFRs based on population synthesis
models are generally consistent with our values.
| arxiv topic:astro-ph.GA astro-ph.SR |
arxiv_dataset-100971808.00554 | Traj2User: exploiting embeddings for computing similarity of users
mobile behavior
cs.SI cs.DB
Semantic trajectories are high level representations of user movements where
several aspects related to the movement context are represented as
heterogeneous textual labels. With the objective of finding a meaningful
similarity measure for semantically enriched trajectories, we propose
Traj2User, a Word2Vec-inspired method for the generation of a vector
representation of user movements as user embeddings. Traj2User uses simple
representations of trajectories and delegates the definition of the similarity
model to the learning process of the network. Preliminary results show that
Traj2User is able to generate effective user embeddings.
| arxiv topic:cs.SI cs.DB |
arxiv_dataset-100981808.00654 | Cluster-Based Haldane States in Spin-1/2 Cluster Chains
cond-mat.str-el
The Haldane state is a typical quantum and topological state of matter, which
exhibits an edge state corresponding to symmetry-protected topological order in
a one-dimensional integer spin chain. This edge state can be utilized for a
processing unit of quantum computation. Its realization, however, has
difficulties with synthesis of integer spin compounds. In contrast, one-half
spin systems are more designable due to recent progress on intended synthesis
of organic materials, quantum dots, and optical lattices. Here we propose a
concept to design the Haldane state with one-half spins by making use of a
chain composed of one-half spin clusters. If the clusters contains two spins,
the ground state of a chain corresponds to the Affleck--Kennedy--Lieb--Tasaki
state. In the case of an odd number of spins in the clusters, we propose a
concrete procedure to construct a field-induced Haldane state. We illustrate
the procedure with a 5-spin cluster chain.
| arxiv topic:cond-mat.str-el |
arxiv_dataset-100991808.00754 | Quantumness of quantum channels
quant-ph
Quantum coherence is a fundamental aspect of quantum physics and plays a
central role in quantum information science. This essential property of the
quantum states could be fragile under the influence of the quantum operations.
The extent to which quantum coherence is diminished depends both on the channel
and the incoherent basis. Motivated by this, we propose a measure of
nonclassicality of a quantum channel as the average quantum coherence of the
state space after the channel acts on, minimized over all orthonormal basis
sets of the state space. Utilizing the squared $l_1$-norm of coherence for the
qubit channels, the minimization can be treated analytically and the proposed
measure takes a closed form of expression. If we allow the channels to act
locally on a maximally entangled state, the quantum correlation is diminished
making the states more classical. We show that the extent to which quantum
correlation is preserved under local action of the channel cannot exceed the
quantumness of the underlying channel. We further apply our measure to the
quantum teleportation protocol and show that a nonzero quantumness for the
underlying channel provides a necessary condition to overcome the best
classical protocols.
| arxiv topic:quant-ph |
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