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1807.02625 | Effects of Elastic Dephasing on Scaling of ultra-small Magnetic Tunnel
Junctions | The study of the effects of scaling on magnetic tunnel junction (MTJ) devices
has become an important topic in the field of spin-based memory devices. Here,
we investigate the effect of elastic dephasing on trilayer and pentalayer MTJ
considered at small transverse cross-sectional areas using the non-equilibrium
Green's function spin transport formalism. We consider the structures with and
without dephasing effects and clearly point out as to how the tunnel
magnetoresistance effect gets affected by dephasing. We attribute the trends
noted by analyzing the transmission spectra and hence the currents across the
devices. Although dephasing affects the TMR values for both devices, we note
that the obtained TMR values are still in a reasonable range that may not
hinder their usability for practical applications.
| cond-mat.mes-hall |
1807.02626 | On masses of the components in SS433 | A huge optical luminosity of the supercritical accretion disc and powerful
stellar wind in the high-mass X-ray binary SS433 make it difficult to reliably
estimate the mass ratio of the binary components from spectroscopic
observations. We analyze different indirect methods of the mass ratio estimate.
We show that with an account of the possible Roche lobe overflow by the optical
star, the analysis of X-ray eclipses in the standard and hard X-ray bands
suggests the estimate $q=M_\mathrm{x}/M_\mathrm{v}\gtrsim 0.3$. We argue that
the double-peak hydrogen Brackett lines in SS433 should form not in the
accretion disc but in a circumbinary envelope, suggesting a total mass of
$M_\mathrm{v}+M_\mathrm{x}\gtrsim 40 M_\odot$. The observed long-term stability
of the orbital period in SS433 $|\dot P_b/P_b|\le 1.793\times
10^{-14}$~s$^{-1}$ over $\sim 28$ year period is used to place an independent
constraint of $q\gtrsim 0.6$ in SS433, confirming its being a Galactic
microquasar hosting a superaccreting black hole.
| astro-ph.HE |
1807.02627 | Regular polygraphs and the Simpson conjecture | We prove Carlos Simpson's "semi-strictification" (or "weak unit") conjecture
in the case of infinity-groupoids. More precisely, we introduce two precise
versions of the conjecture, the "general" and the "regular" conjecture,
involving two different notions of "non-unital categories". The "general"
version involve infinity-categories where absolutely all composition operations
(horizontal, vertical and whiskering) are defined and compatible, the "regular"
version involve infinity-categories where all the composition operations
corresponding to "regular" pasting diagram are defined and compatible. In both
case we construct (weak) model structures on these categories such that fibrant
objects have weak units and weak inverse. We prove the regular version of the
conjecture using the original strategy of Kapranov and Voevodsky, together with
our previous work on polygraphs. The general version cannot be proved by these
methods and is still open. In order to do this we also study some subtle
property of the combinatorics of polygraphs, and we construct a new counting
function for polygraphs, inspired by previous work of Makkai.
| math.CT math.AT |
1807.02628 | Global radial solutions in classical Keller-Segel model of chemotaxis | We consider the simplest parabolic-elliptic model of chemotaxis in the whole
space in several dimensions. Criteria for the existence of radial
global-in-time solutions in terms of suitable Morrey norms are derived.
| math.AP |
1807.02629 | Optimistic mirror descent in saddle-point problems: Going the extra
(gradient) mile | Owing to their connection with generative adversarial networks (GANs),
saddle-point problems have recently attracted considerable interest in machine
learning and beyond. By necessity, most theoretical guarantees revolve around
convex-concave (or even linear) problems; however, making theoretical inroads
towards efficient GAN training depends crucially on moving beyond this classic
framework. To make piecemeal progress along these lines, we analyze the
behavior of mirror descent (MD) in a class of non-monotone problems whose
solutions coincide with those of a naturally associated variational inequality
- a property which we call coherence. We first show that ordinary, "vanilla" MD
converges under a strict version of this condition, but not otherwise; in
particular, it may fail to converge even in bilinear models with a unique
solution. We then show that this deficiency is mitigated by optimism: by taking
an "extra-gradient" step, optimistic mirror descent (OMD) converges in all
coherent problems. Our analysis generalizes and extends the results of
Daskalakis et al. (2018) for optimistic gradient descent (OGD) in bilinear
problems, and makes concrete headway for establishing convergence beyond
convex-concave games. We also provide stochastic analogues of these results,
and we validate our analysis by numerical experiments in a wide array of GAN
models (including Gaussian mixture models, as well as the CelebA and CIFAR-10
datasets).
| cs.LG cs.GT math.OC stat.ML |
1807.02630 | Highly selective chiral discrimination in high harmonic generation by
dynamical symmetry breaking spectroscopy | We propose and numerically demonstrate a new very robust and highly selective
method for femtosecond time-resolved chiral spectroscopy using high harmonic
generation (HHG). The method is based on dynamical symmetry breaking from
chiral media, and relies only on intense electric-dipole transitions, and not
on the interplay of electric and magnetic dipoles. The symmetry breaking
results in the emission of a strong chiral signal in the form of otherwise
'forbidden' harmonics (i.e., that are not emitted from achiral media). The
intensity of these symmetry-forbidden harmonics is directly correlated to the
media's enantiomeric excess, yielding chiral selectivity. On the contrary, the
strength of the 'allowed' harmonics is chiral-independent, hence they can be
used as a reference to provide chiral selectivity from a single measurement,
unlike previous time-resolved schemes that require multiple measurements. We
demonstrate numerically 96% discrimination level from microscopic gas phase
emission, outperforming by far previous time-resolved methods (the selectivity
should be further enhanced when the HHG process is phase matched). We expect
the new method to give rise to precise table-top characterization of chiral
media in the gas-phase, and for highly sensitive time-resolved ultrafast
probing of dynamical chiral processes.
| physics.optics physics.chem-ph |
1807.02631 | Some Insights on Synthesizing Optimal Linear Quadratic Controller Using
Krotov's Sufficiency Conditions | This paper revisits the problem of optimal control law design for linear
systems using the global optimal control framework introduced by Vadim Krotov.
Krotov's approach is based on the idea of total decomposition of the original
optimal control problem (OCP) with respect to time, by an $ad$ $hoc$ choice of
the so-called Krotov's function or solving function, thereby providing
sufficient conditions for the existence of global solution based on another
optimization problem, which is completely equivalent to the original OCP. It is
well known that the solution of this equivalent optimization problem is
obtained using an iterative method. In this paper, we propose suitable Krotov's
functions for linear quadratic OCP and subsequently, show that by imposing
convexity condition on this equivalent optimization problem, there is no need
to compute an iterative solution. We also give some key insights into the
solution procedure of the linear quadratic OCP using the proposed methodology
in contrast to the celebrated Calculus of Variations (CoV) and
Hamilton-Jacobi-Bellman (HJB) equation based approach.
| math.OC cs.SY |
1807.02632 | Representing a Partially Observed Non-Rigid 3D Human Using Eigen-Texture
and Eigen-Deformation | Reconstruction of the shape and motion of humans from RGB-D is a challenging
problem, receiving much attention in recent years. Recent approaches for
full-body reconstruction use a statistic shape model, which is built upon
accurate full-body scans of people in skin-tight clothes, to complete invisible
parts due to occlusion. Such a statistic model may still be fit to an RGB-D
measurement with loose clothes but cannot describe its deformations, such as
clothing wrinkles. Observed surfaces may be reconstructed precisely from actual
measurements, while we have no cues for unobserved surfaces. For full-body
reconstruction with loose clothes, we propose to use lower dimensional
embeddings of texture and deformation referred to as eigen-texturing and
eigen-deformation, to reproduce views of even unobserved surfaces. Provided a
full-body reconstruction from a sequence of partial measurements as 3D meshes,
the texture and deformation of each triangle are then embedded using
eigen-decomposition. Combined with neural-network-based coefficient regression,
our method synthesizes the texture and deformation from arbitrary viewpoints.
We evaluate our method using simulated data and visually demonstrate how our
method works on real data.
| cs.CV |
1807.02633 | Blowing up radial solutions in the minimal Keller-Segel model of
chemotaxis | We consider the simplest parabolic-elliptic model of chemotaxis in the whole
space in several dimensions. Criteria for the blowup of radially symmetric
solutions in terms of suitable Morrey spaces norms are derived.
| math.AP |
1807.02634 | Effective bond-orbital model of III-nitride wurtzite structures based on
modified interaction parameters of zinc-blende structures | A simple theoretical method for deducing the effective bond-orbital model
(EBOM) of III-nitride wurtzite (WZ) semiconductors is presented. In this model,
the interaction parameters for zinc-blende (ZB) structures are used as an
initial guess for WZ structure based on the two-center approximation. The
electronic band structure of III-nitride WZ semiconductors can hence be
produced by utilizing this set of parameters modified to include effects due to
three-center integrals and fitting with first-principles calculations. Details
of the semi-empirical fitting procedure for constructing the EBOM Hamiltonian
for bulk III-nitride WZ semiconductors are presented. The electronic band
structure of bulk AlN, GaN, and InN with WZ structure calculated by EBOM with
modified interaction parameters are shown and compared to the results obtained
from density functional (DFT) theory with meta-generalized gradient
approximation (mGGA). The set of parameters are further optimized by using a
genetic algorithm. In the end, electronic band structures and electron (hole)
effective masses near the zone center calculated by the proposed model with
best fitting parameters are analyzed and compared with the $\mathbf{k}\cdot
\mathbf{p}$ model.
| cond-mat.mtrl-sci |
1807.02635 | Video Prediction with Appearance and Motion Conditions | Video prediction aims to generate realistic future frames by learning dynamic
visual patterns. One fundamental challenge is to deal with future uncertainty:
How should a model behave when there are multiple correct, equally probable
future? We propose an Appearance-Motion Conditional GAN to address this
challenge. We provide appearance and motion information as conditions that
specify how the future may look like, reducing the level of uncertainty. Our
model consists of a generator, two discriminators taking charge of appearance
and motion pathways, and a perceptual ranking module that encourages videos of
similar conditions to look similar. To train our model, we develop a novel
conditioning scheme that consists of different combinations of appearance and
motion conditions. We evaluate our model using facial expression and human
action datasets and report favorable results compared to existing methods.
| cs.CV |
1807.02636 | High energy neutrino beam generation based on crystal optics | The problem of creation of high energy neutrino beams on the basis of modern
and future circular proton accelerators with the help of traditional technology
seems to be expensive and difficult. Because of this, we propose the solution
of this problem based on the usage of focusing bend single crystals. In the
paper we demonstrate the possibilities of acceptance and focusing of a pion
beam with the help of a crystal optical lens system. As an illustration of
these features the calculated neutrino fluxes for energy of circulating proton
beam equal to 6.5 TeV are presented.
| physics.acc-ph hep-ex |
1807.02637 | Recommender system for learning SQL using hints | Today's software industry requires individuals who are proficient in as many
programming languages as possible. Structured query language (SQL), as an
adopted standard, is no exception, as it is the most widely used query language
to retrieve and manipulate data. However, the process of learning SQL turns out
to be challenging. The need for a computer-aided solution to help users learn
SQL and improve their proficiency is vital. In this study, we present a new
approach to help users conceptualize basic building blocks of the language
faster and more efficiently. The adaptive design of the proposed approach aids
users in learning SQL by supporting their own path to the solution and
employing successful previous attempts, while not enforcing the ideal solution
provided by the instructor. Furthermore, we perform an empirical evaluation
with 93 participants and demonstrate that the employment of hints is
successful, being especially beneficial for users with lower prior knowledge.
| cs.AI |
1807.02638 | Dust evolution and satellitesimal formation in circumplanetary disks | It is believed that satellites of giant planets form in circumplanetary
disks. Many of the previous contributions assumed that their formation process
proceeds similarly to rocky planet formation, via accretion of the satellite
seeds, called satellitesimals. However, the satellitesimal formation itself
poses a nontrivial problem as the dust evolution in the circumplanetary disk is
heavily impacted by fast radial drift and thus dust growth to satellitesimals
is hindered. To address this problem, we connected state-of-the-art
hydrodynamical simulations of a circumplanetary disk around a Jupiter-mass
planet with dust growth and drift model in a post-processing step. We found
that there is an efficient pathway to satellitesimal formation if there is a
dust trap forming within the disk. Thanks to the natural existence of an
outward gas flow region in the hydrodynamical simulation, a significant dust
trap arises at the radial distance of 85~R$_{\rm J}$ from the planet, where the
dust-to-gas ratio becomes high enough to trigger streaming instability. The
streaming instability leads to the efficient formation of the satellite seeds.
Because of the constant infall of material from the circumstellar disk and the
very short timescale of dust evolution, the circumplanetary disk acts as a
satellitesimal factory, constantly processing the infalling dust to pebbles
that gather in the dust trap and undergo the streaming instability.
| astro-ph.EP |
1807.02639 | A Precipice Below Which Lies Absurdity? Theories without a Spacetime and
Scientific Understanding | While the relation between visualization and scientific understanding has
been a topic of long-standing discussion, recent developments in physics have
pushed the boundaries of this debate to new and still unexplored realms. For it
is claimed that, in certain theories of quantum gravity, spacetime
'disappears': and this suggests that one may have sensible physical theories in
which spacetime is completely absent. This makes the philosophical question
whether such theories are intelligible, even more pressing. And if such
theories are intelligible, the question then is how they manage to do so. In
this paper, we adapt the contextual theory of scientific understanding,
developed by one of us, to fit the novel challenges posed by physical theories
without spacetime. We construe understanding as a matter of skill rather than
just knowledge. The appeal is thus to understanding, rather than explanation,
because we will be concerned with the tools that scientists have at their
disposal for understanding these theories. Our central thesis is that such
physical theories can provide scientific understanding, and that such
understanding does not require spacetimes of any sort. Our argument consists of
four consecutive steps: (a) We argue, from the general theory of scientific
understanding, that although visualization is an oft-used tool for
understanding, it is not a necessary condition for it; (b) we criticise certain
metaphysical preconceptions which can stand in the way of recognising how
intelligibility without spacetime can be had; (c) we catalogue tools for
rendering theories without a spacetime intelligible; and (d) we give examples
of cases in which understanding is attained without a spacetime, and explain
what kind of understanding these examples provide.
| physics.hist-ph |
1807.02640 | H\"ormander's multiplier theorem for the Dunkl transform | For a normalized root system $R$ in $\mathbb R^N$ and a multiplicity function
$k\geq 0$ let $\mathbf N=N+\sum_{\alpha \in R} k(\alpha)$. Denote by
$dw(\mathbf x)=\prod_{\alpha\in R}|\langle \mathbf
x,\alpha\rangle|^{k(\alpha)}\, d\mathbf x $ the associated measure in $\mathbb
R^N$. Let $\mathcal F$ stands for the Dunkl transform. Given a bounded function
$m$ on $\mathbb R^N$, we prove that if there is $s>\mathbf N$ such that $m$
satisfies the classical H\"ormander condition with the smoothness $s$, then the
multiplier operator $\mathcal T_mf=\mathcal F^{-1}(m\mathcal Ff)$ is of weak
type $(1,1)$, strong type $(p,p)$ for $1<p<\infty$, and bounded on a relevant
Hardy space $H^1$. To this end we study the Dunkl translations and the Dunkl
convolution operators and prove that if $F$ is sufficiently regular, for
example its certain Schwartz class seminorm is finite, then the Dunkl
convolution operator with the function $F$ is bounded on $L^p(dw)$ for $1\leq
p\leq \infty$. We also consider boundedness of maximal operators associated
with the Dunkl convolutions with Schwartz class functions.
| math.FA |
1807.02641 | Quasi-two-body decays $B_{(s)}\to P f_2(1270)\to P\pi\pi$ in the
perturbative QCD approach | In this work, we calculate the $CP$-averaged branching ratios and direct
$CP$-violating asymmetries of the quasi-two-body decays $B_{(s)}\to P
f_2(1270)\to P\pi\pi$ with the two-pion distribution amplitude
$\Phi_{\pi\pi}^{\rm D}$ by using the perturbative QCD factorization approach,
where $P$ represents a light pseudoscalar meson $K, \pi, \eta$ and
$\eta^{\prime}$. The relativistic Breit-Wigner formula for the $D$-wave
resonance $f_2(1270)$ is adopted to parameterize the timelike form factor
$F_{\pi}$, which contains the final state interactions between the pions in the
resonant regions. The consistency of theoretical results with data can be
achieved by determining the Gegenbauer moments of the $D$-wave two-pion
distribution amplitudes. The decay rates for the considered decay modes are
generally in the order of $10^{-9}$ to $ 10^{-6}$. The integrated direct $CP$
asymmetries for the charged modes agree with the {\it BABAR} and Belle
measurements. As a by-product, we extract the branching ratios of $B_{(s)}\to
Pf_2(1270)$ from the corresponding quasi-two-body decay modes, which still need
experimental tests at the ongoing and forthcoming experiments.
| hep-ph hep-ex |
1807.02642 | Properties of 0/1-Matrices of Order n Having Maximum Determinant | We give some necessary conditions for maximality of $0/1$-determinant. Let
${\bf M}$ be a nondegenerate $0/1$-matrix of order $n$. Denote by $\bf A$ the
matrix of order $n+1$ which appears from ${\bf M}$ after adding the $(n+1)$th
row $(0,0,\ldots,0,1)$ and the $(n+1)$th column consisting of $1$'s. Suppose
${\bf A}^{-1}=(l_{ij}),$ then for all $i=1,\ldots,n$ we have $\sum_{j=1}^{n+1}
|l_{ij}|\geq 2.$ Moreover, if $|\det({\bf M})|$ is equal to the maximum value
of a $0/1$-determinant of order $n$, then $\sum_{j=1}^{n+1} |l_{ij}|= 2$ for
all $i=1,\ldots,n$.
Keywords: maximum 0/1-deteminant, simplex, cube, axial diameter
| math.MG math.CO |
1807.02643 | Density Functional Theory (DFT) for atomic nuclei: a simple introduction | The present contribution does not aim at replacing the huge and often
excellent literature on DFT for atomic nuclei, but tries to provide an updated
introduction to this topic. The goal would be, ideally, to help a fresh M.Sc.
or Ph.D. student (or a researcher from other fields) to become acquainted with
some basic concepts, and then move to the specialized textbooks or papers with
some ability for orienteering. We first introduce the basics of DFT, and show
the difference with the "naive" mean-field theory, that is doomed to fail as a
model even in the simple case of uniform nuclear matter. We introduce the
Energy Density Functionals (EDFs) that are used in nuclear structure, with few
examples of their applications. The concepts of symmetry breaking and
restoration are briefly discussed. We also include an introduction to the
time-dependent extension of DFT that, so far, has been implemented essentially
only in the adiabatic approximation and has been applied mainly to the study of
nuclear vibrations. With this material, we hope that any reader is able to deal
with the texts that go deeper into each of the topics, having understood that
DFT is probably the best compromise in nuclear structure theory between
simplicity, accuracy, and broad range of applicability.
| nucl-th cond-mat.other nucl-ex |
1807.02644 | Quantum sensing enhanced by adaptive periodic quantum control | Using a single quantum probe to sense other quantum objects offers distinct
advantages but suffers from some limitations that may degrade the sensing
precision severely, especially when the probe-target coupling is weak. Here we
propose a strategy to improve the sensing precision by using the quantum probe
to engineer the evolution of the target. We consider an exactly solvable model,
in which a qubit is used as the probe to sense the frequency of a harmonic
oscillator. We show that by applying adaptive periodic quantum control on the
qubit, the sensing precision can be enhanced from 1/T scaling with the total
time cost T to 1/T^{2} scaling, thus improving the precision by several orders
of magnitudes. Such improvement can be achieved without any direct access to
the oscillator and the improvement increases with decreasing probe-target
coupling. This provides a useful routine to ultrasensitive quantum sensing of
weakly coupled quantum objects.
| quant-ph |
1807.02645 | Discs and boundary uniqueness for psh functions on almost complex
manifolds | We prove that a totally real manifold (of maximal dimension) is a boundary
uniqueness set for a psh function on an almost complex manifold.
| math.CV |
1807.02646 | Vanishing cohomology on a double cover | In this paper, we prove the irreducibility of the monodromy action on the
anti-invariant part of the vanishing cohomology on a double cover of a very
general element in an ample hypersurface of a complex smooth projective variety
branched at an ample divisor. As an application, we study dominant rational
maps from a double cover of a very general surface $S$ of degree$\geq 7$ in
${\mathbb P}^3$ branched at a very general quadric surface to smooth projective
surfaces $Z$. Our method combines the classification theory of algebraic
surfaces, deformation theory, and Hodge theory.
| math.AG |
1807.02647 | An Image Encryption Algorithm Based on Chaotic Maps and Discrete Linear
Chirp Transform | In this paper, a novel image encryption algorithm, which involves a chaotic
block image scrambling followed by a two-dimensional (2-D) discrete linear
chirp transform, is proposed. The definition of the 2-D discrete linear chirp
transform is introduced and then it is used to construct the basis of the novel
encryption algorithm. Finally, security analysis are performed to show the
quality of the encryption process using different metrics.
| eess.IV cs.CR |
1807.02648 | How game complexity affects the playing behavior of synthetic agents | Agent based simulation of social organizations, via the investigation of
agents' training and learning tactics and strategies, has been inspired by the
ability of humans to learn from social environments which are rich in agents,
interactions and partial or hidden information. Such richness is a source of
complexity that an effective learner has to be able to navigate. This paper
focuses on the investigation of the impact of the environmental complexity on
the game playing-and-learning behavior of synthetic agents. We demonstrate our
approach using two independent turn-based zero-sum games as the basis of
forming social events which are characterized both by competition and
cooperation. The paper's key highlight is that as the complexity of a social
environment changes, an effective player has to adapt its learning and playing
profile to maintain a given performance profile
| cs.AI cs.CC cs.MA |
1807.02649 | The Deformable Mirror Demonstration Mission (DeMi) CubeSat:
optomechanical design validation and laboratory calibration | Coronagraphs on future space telescopes will require precise wavefront
correction to detect Earth-like exoplanets near their host stars. High-actuator
count microelectromechanical system (MEMS) deformable mirrors provide wavefront
control with low size, weight, and power. The Deformable Mirror Demonstration
Mission (DeMi) payload will demonstrate a 140 actuator MEMS deformable mirror
(DM) with \SI{5.5}{\micro\meter} maximum stroke. We present the flight
optomechanical design, lab tests of the flight wavefront sensor and wavefront
reconstructor, and simulations of closed-loop control of wavefront aberrations.
We also present the compact flight DM controller, capable of driving up to 192
actuator channels at 0-250V with 14-bit resolution. Two embedded Raspberry Pi 3
compute modules are used for task management and wavefront reconstruction. The
spacecraft is a 6U CubeSat (30 cm x 20 cm x 10 cm) and launch is planned for
2019.
| astro-ph.IM |
1807.02650 | Weak model categories in classical and constructive mathematics | We introduce a notion of "weak model category" which is a weakening of the
notion of Quillen model category, still sufficient to define a homotopy
category, Quillen adjunctions, Quillen equivalences and most of the usual
construction of categorical homotopy theory. Both left and right semi-model
categories are weak model categories, and the opposite of a weak model category
is again a weak model category. The main advantages of weak model categories is
that they are easier to construct than Quillen model categories. In particular
we give some simple criteria on two weak factorization systems for them to form
a weak model category. The theory is developed in a very weak constructive
framework and we use it to produce, completely constructively (even
predicatively), weak versions of various standard model categories, including
the Kan-Quillen model structure, the variant of the Joyal model structure on
marked simplicial sets, and the Verity model structure for weak complicial
sets. We also construct semi-simplicial versions of all these.
| math.CT math.AT |
1807.02651 | Energy Consumption Optimization in Mobile Communication Networks | This work addresses the challenge of minimizing the energy consumption of a
wireless communication network by joint optimization of the base station
transmit power and the cell activity. A mixed-integer nonlinear optimization
problem is formulated, for which a computationally tractable linear inner
approximation algorithm is provided. The proposed method offers great
flexibility in optimizing the network operation by considering multiple system
parameters jointly, which mitigates a major drawback of existing
state-of-the-art schemes that are mostly based on heuristics. Simulation
results show that the proposed method exhibits high performance in decreasing
the energy consumption, and provides implicit load balancing in difficult high
demand scenarios.
| eess.SP |
1807.02652 | Theoretical investigation on the ferromagnetic two-dimensional scandium
monochloride sheet that has a high Curie temperature and could be exfoliated
from a known material | A two-dimensional scandium monochloride sheet was investigated by using
density functional theory. It could be exfoliated from a known bulk material
with a cleavage energy slightly lower than that of graphene. The sheet has a
ferromagnetic ground state with a Curie temperature of 100 K. Moreover, the
sheet becomes a half-metal under hole doping. The Curie temperature increases
to 250 K with the doping amount of 0.4 per primitive cell, which is close to
the ice point. The two-dimensional scandium monochloride sheet should be a good
candidate for two-dimensional spintronics.
| cond-mat.mtrl-sci |
1807.02653 | When Work Matters: Transforming Classical Network Structures to Graph
CNN | Numerous pattern recognition applications can be formed as learning from
graph-structured data, including social network, protein-interaction network,
the world wide web data, knowledge graph, etc. While convolutional neural
network (CNN) facilitates great advances in gridded image/video understanding
tasks, very limited attention has been devoted to transform these successful
network structures (including Inception net, Residual net, Dense net, etc.) to
establish convolutional networks on graph, due to its irregularity and
complexity geometric topologies (unordered vertices, unfixed number of adjacent
edges/vertices). In this paper, we aim to give a comprehensive analysis of when
work matters by transforming different classical network structures to graph
CNN, particularly in the basic graph recognition problem. Specifically, we
firstly review the general graph CNN methods, especially in its spectral
filtering operation on the irregular graph data. We then introduce the basic
structures of ResNet, Inception and DenseNet into graph CNN and construct these
network structures on graph, named as G_ResNet, G_Inception, G_DenseNet. In
particular, it seeks to help graph CNNs by shedding light on how these
classical network structures work and providing guidelines for choosing
appropriate graph network frameworks. Finally, we comprehensively evaluate the
performance of these different network structures on several public graph
datasets (including social networks and bioinformatic datasets), and
demonstrate how different network structures work on graph CNN in the graph
recognition task.
| cs.LG stat.ML |
1807.02654 | One-shot Texture Segmentation | We introduce one-shot texture segmentation: the task of segmenting an input
image containing multiple textures given a patch of a reference texture. This
task is designed to turn the problem of texture-based perceptual grouping into
an objective benchmark. We show that it is straight-forward to generate large
synthetic data sets for this task from a relatively small number of natural
textures. In particular, this task can be cast as a self-supervised problem
thereby alleviating the need for massive amounts of manually annotated data
necessary for traditional segmentation tasks. In this paper we introduce and
study two concrete data sets: a dense collage of textures (CollTex) and a
cluttered texturized Omniglot data set. We show that a baseline model trained
on these synthesized data is able to generalize to natural images and videos
without further fine-tuning, suggesting that the learned image representations
are useful for higher-level vision tasks.
| cs.CV |
1807.02655 | Congestion fronts of diffusing particles | We study two new models of two particle species invading a surface from
opposite sides. Collisions of particles of different species lead to the
formation of congestion fronts. One of the models implements a reversible
process whereas in the other model the congestion front forms irreversibly. For
both models we find that the congestion fronts are self-affine but with
different roughness exponents. For low densities the system does not congest
and we find a phase transition between a phase of freely moving particles and a
congestion phase.
| cond-mat.stat-mech |
1807.02656 | Review of (anti-)Nuclei Production from High Energy Experiments | An overview of nuclei and anti-nuclei production with results from different
experiments are discussed. The comparison of data with the thermal and
coalescence models is also discussed to understand their production mechanisms
in high energy collisions.
| hep-ex nucl-ex |
1807.02657 | Tournament Based Ranking CNN for the Cataract grading | Solving the classification problem, unbalanced number of dataset among the
classes often causes performance degradation. Especially when some classes
dominate the other classes with its large number of datasets, trained model
shows low performance in identifying the dominated classes. This is common case
when it comes to medical dataset. Because the case with a serious degree is not
quite usual, there are imbalance in number of dataset between severe case and
normal cases of diseases. Also, there is difficulty in precisely identifying
grade of medical data because of vagueness between them. To solve these
problems, we propose new architecture of convolutional neural network named
Tournament based Ranking CNN which shows remarkable performance gain in
identifying dominated classes while trading off very small accuracy loss in
dominating classes. Our Approach complemented problems that occur when method
of Ranking CNN that aggregates outputs of multiple binary neural network models
is applied to medical data. By having tournament structure in aggregating
method and using very deep pretrained binary models, our proposed model
recorded 68.36% of exact match accuracy, while Ranking CNN recorded 53.40%,
pretrained Resnet recorded 56.12% and CNN with linear regression recorded
57.48%. As a result, our proposed method is applied efficiently to cataract
grading which have ordinal labels with imbalanced number of data among classes,
also can be applied further to medical problems which have similar features to
cataract and similar dataset configuration.
| cs.CV |
1807.02658 | Robust and Scalable Differentiable Neural Computer for Question
Answering | Deep learning models are often not easily adaptable to new tasks and require
task-specific adjustments. The differentiable neural computer (DNC), a
memory-augmented neural network, is designed as a general problem solver which
can be used in a wide range of tasks. But in reality, it is hard to apply this
model to new tasks. We analyze the DNC and identify possible improvements
within the application of question answering. This motivates a more robust and
scalable DNC (rsDNC). The objective precondition is to keep the general
character of this model intact while making its application more reliable and
speeding up its required training time. The rsDNC is distinguished by a more
robust training, a slim memory unit and a bidirectional architecture. We not
only achieve new state-of-the-art performance on the bAbI task, but also
minimize the performance variance between different initializations.
Furthermore, we demonstrate the simplified applicability of the rsDNC to new
tasks with passable results on the CNN RC task without adaptions.
| cs.CL cs.LG |
1807.02659 | Quadratic and Cubic Nodal Lines Stabilized by Crystalline Symmetry | In electronic band structures, nodal lines may arise when two (or more) bands
contact and form a one-dimensional manifold of degeneracy in the Brillouin
zone. Around a nodal line, the dispersion for the energy difference between the
bands is typically linear in any plane transverse to the line. Here, we perform
an exhaustive search over all 230 space groups for nodal lines with
higher-order dispersions that can be stabilized by crystalline symmetry in
solid state systems with spin-orbit coupling and time reversal symmetry. We
find that besides conventional linear nodal lines, only lines with quadratic or
cubic dispersions are possible, for which the allowed degeneracy cannot be
larger than two. We derive effective Hamiltonians to characterize the novel
low-energy fermionic excitations for the quadratic and cubic nodal lines, and
explicitly construct minimal lattice models to further demonstrate their
existence. Their signatures can manifest in a variety of physical properties
such as the (joint) density of states, magneto-response, transport behavior,
and topological surface states. Using ab-initio calculations, we also identify
possible material candidates that realize these exotic nodal lines.
| cond-mat.mes-hall cond-mat.mtrl-sci |
1807.02660 | Double carrier transport in electron doped region in black phosphorus
FET | The double carrier transport has been observed in thin film black phosphorus
(BP) field effect transistor (FET) devices in highly electron doped region. BP
thin films with typical thickness of 15 nm were encapsulated by hexagonal boron
nitride (h-BN) thin films to avoid degradation by air exposure. Their Hall
mobility has reached 5300 cm2/Vs and 5400 cm2/Vs at 4.2 K in the hole and
electron doped regions, respectively. The gate voltage dependence of
conductivity exhibits an anomalous shoulder structure in electron doped region.
In addition, at gate voltages above the shoulder, the magnetoresistance changes
to positive, and there appears an additional slow Shubnikov-de Haas
oscillation. These results strongly suggest the appearance of the second
carriers, which originate from the second subband with localized band edge.
| cond-mat.mes-hall |
1807.02661 | Double Bubbles on the Line with Log-convex Density $f$ with $(\log f)'$
Bounded | We extend results of Bongiovanni et al. on double bubbles on the line with
log-convex density to the case where the derivative of the log of the density
is bounded. We show that the tie function between the double interval and the
triple interval still exists but may blow up to infinity in finite time. For
the first time, a density is presented for which the blowup time is positive
and finite.
| math.MG |
1807.02662 | The GeV emission of PSR B1259-63 during its last three periastron
passages observed by Fermi-LAT | PSR B1259-63 is a $\gamma$-ray emitting high mass X-ray binary system, in
which the compact object is a millisecond pulsar. The system has an orbital
period of 1236.7 d and shows peculiar $\gamma$-ray flares when the neutron star
moves out of the stellar disk of the companion star. The $\gamma$-ray flare
events were firstly discovered by using Fermi-LAT around the 2010 periastron
passage, which was repeated for the 2014 and 2017 periastron passages. We
analyze the Fermi-LAT data for all the three periastron passages and found that
in each flare the energy spectrum can be represented well by a simple power
law. The $\gamma$-ray light curves show that in 2010 and 2014 after each
periastron there are two main flares, but in 2017 there are four flares
including one precursor about 10 d after the periastron passage. The first main
flares in 2010 and 2014 are located at around 35 d after the periastron
passage, and the main flare in 2014 is delayed by roughly 1.7 d with respect to
that in 2010. In the 2017 flare, the source shows a precursor about 10 d after
the periastron passage, but the following two flares become weaker and lag
behind those in 2010 by roughly 5 d. The strongest flares in 2017 occurred 58 d
and 70 d after the periastron passage. These results challenge the previous
models.
| astro-ph.HE |
1807.02663 | Fully Spin-Polarized Current in Gated Bilayer Silicene | By applying density functional theory calculations, we predict that the
groundstate of bilayer silicene at certain interlayer distances can be
antiferromagnetic. At small electron or hole doping, it becomes half metallic
under applied out-of-plane electric field, which can be used to produce fully
spin-polarized field-effect-driven current even in the absence of external
magnetic field, ferromagnetic substrates, doped magnetic ions, or spin-orbital
coupling. Our finding points out a new route to overcome the major challenge of
spintronics.
| cond-mat.mtrl-sci |
1807.02664 | A note on topological dimension, Hausdorff measure, and rectifiability | The purpose of this note is to record a consequence, for general metric
spaces, of a recent result of David Bate. We prove the following fact: Let $X$
be a compact metric space of topological dimension $n$. Suppose that the
$n$-dimensional Hausdorff measure of $X$, $\mathcal H^n(X)$, is finite. Suppose
further that the lower n-density of the measure $\mathcal H^n$ is positive,
$\mathcal H^n$-almost everywhere in $X$. Then $X$ contains an $n$-rectifiable
subset of positive $\mathcal H^n$-measure. Moreover, the assumption on the
lower density is unnecessary if one uses recently announced results of
Cs\"ornyei-Jones.
| math.MG math.CA |
1807.02665 | The NOvA Power Distribution System | We describe the power distribution systems and grounding schemes built for
the near and far detectors of the NOvA long-baseline neutrino experiment. They
are used to power the avalanche photodiodes and their thermoelectric coolers,
the front-end boards that read out, digitize and time stamp the signals from
the avalanche photodiodes, and the data concentrator modules used to receive
and format the data from the front-end boards before sending them to a farm of
computers used to build the events. The system powers 344,064 readout channels
in the far detector and 20,192 channels in the near detector.
| physics.ins-det |
1807.02666 | A perturbational duality approach in vector optimization | A perturbational vector duality approach for objective functions $f\colon
X\to \bar{L}^0$ is developed, where $X$ is a Banach space and $\bar{L}^0$ is
the space of extended real valued functions on a measure space, which extends
the perturbational approach from the scalar case. The corresponding strong
duality statement is proved under a closedness type regularity condition.
Optimality conditions and a Moreau-Rockafellar type formula are provided. The
results are specialized for constrained and unconstrained problems. Examples of
integral operators and risk measures are discussed.
| math.OC |
1807.02667 | On the energy equality for the 3D Navier-Stokes equations | In this paper we study the problem of energy conservation for the solutions
of the initial boundary value problem associated to the 3D Navier-Stokes
equations, with Dirichlet boundary conditions. First, we consider Leray-Hopf
weak solutions and we prove some new criteria, involving the gradient of the
velocity. Next, we compare them with the existing literature in scaling
invariant spaces and with the Onsager conjecture. Then, we consider the problem
of energy conservation for very-weak solutions, proving energy equality for
distributional solutions belonging to the so-called Shinbrot class. A possible
explanation of the role of this classical class of solutions, which is not
scaling invariant, is also given.
| math.AP |
1807.02668 | Hair histology as a tool for forensic identification of some domestic
animal species | Animal hair examination at a criminal scene may provide valuable information
in forensic investigations. However, local reference databases for animal hair
identification are rare. In the present study, we provide differential
histological analysis of hair of some domestic animals in Upper Egypt. For this
purpose, guard hair of large ruminants (buffalo, camel and cow), small
ruminants (sheep and goat), equine (horse and donkey) and canine (dog and cat)
were collected and comparative analysis was performed by light microscopy.
Based on the hair cuticle scale pattern, type and diameter of the medulla, and
the pigmentation, characteristic differential features of each animal species
were identified. The cuticle scale pattern was imbricate in all tested animals
except in donkey, in which coronal scales were identified. The cuticle scale
margin type, shape and the distance in between were characteristic for each
animal species. The hair medulla was continuous in most of the tested animal
species with the exception of sheep, in which fragmental medulla was detected.
The diameter of the hair medulla and the margins differ according to the animal
species. Hair shaft pigmentation were not detected in all tested animals with
the exception of camel and buffalo, in which granules and streak-like
pigmentation were detected. In conclusion, the present study provides a
first-step towards preparation of a complete local reference database for
animal hair identification that can be used in forensic investigations.
| q-bio.TO |
1807.02669 | Splashback radius of nonspherical dark matter halos from cosmic density
and velocity fields | We investigate the splashback features of dark-matter halos based on cosmic
density and velocity fields. Besides the density correlation function binned by
the halo orientation angle which was used in the literature, we introduce, for
the first time, the corresponding velocity statistic, alignment momentum
correlation function, to take into account the asphericity of halos. Using
large-volume, high-resolution N-body simulations, we measure the alignment
statistics of density and velocity. On halo scales, $x\sim R_\mathrm{200m} \sim
1Mpc/h$, we detect a sharp steepening in the momentum correlation associated
with the physical halo boundary, or the splashback feature, which is found more
prominent than in the density correlation. We also find that the splashback
radius determined from the density correlation becomes $\sim 3.5\%$ smaller
than that from the momentum correlation, with their correlation coefficient
being 0.605. Moreover, the orientation-dependent splashback feature due to halo
asphericity is measured when the density profile is determined by dark-matter
particles, which can be used as a test of collisional CDM since the halo shape
is predicted to be rounder in such a model.
| astro-ph.CO astro-ph.GA |
1807.02670 | Going from Asymmetric Nuclei to Neutron Stars to Tidal Polarizability in
Gravitational Waves | Among the five-year government-funded World Class University Projects in
Korea, the category-3 program approved at Hanyang University in Seoul led to an
exploratory effort to go from neutron-rich nuclei to dense matter in neutron
stars. The principal results in what transpired in the effort -- and what
followed afterwards -- are described with the focus on the possibly important,
hitherto unexplored, role played in nuclear dynamics of topology and hidden
symmetries of QCD. The potential link to the proton mass problem is pointed
out.
| nucl-th astro-ph.SR hep-ph |
1807.02671 | State-space modeling of intra-seasonal persistence in daily climate
indices: a data-driven approach for seasonal forecasting | Existing methods for diagnosing predictability in climate indices often make
a number of unjustified assumptions about the climate system that can lead to
misleading conclusions. We present a flexible family of state-space models
capable of separating the effects of external forcing on inter-annual time
scales, from long-term trends and decadal variability, short term weather
noise, observational errors and changes in autocorrelation. Standard potential
predictability models only estimate the fraction of the total variance in the
index attributable to external forcing. In addition, our methodology allows us
to partition individual seasonal means into forced, slow, fast and error
components. Changes in the predictable signal within the season can also be
estimated. The model can also be used in forecast mode to assess both intra-
and inter-seasonal predictability.
We apply the proposed methodology to a North Atlantic Oscillation index for
the years 1948-2017. Around 60% of the inter-annual variance in the
December-January-February mean North Atlantic Oscillation is attributable to
external forcing, and 8% to trends on longer time-scales. In some years, the
external forcing remains relatively constant throughout the winter season, in
others it changes during the season. Skillful statistical forecasts of the
December-January-February mean North Atlantic Oscillation are possible from the
end of November onward and predictability extends into March. Statistical
forecasts of the December-January-February mean achieve a correlation with the
observations of 0.48.
| stat.AP |
1807.02672 | Self-sorting of Bi-dispersed Colloidal Particles near Contact Line of an
Evaporating Sessile Droplet | We investigate deposit patterns and associated morphology formed after the
evaporation of an aqueous droplet containing mono- and bi-dispersed colloidal
particles. In particular, the combined effect of substrate heating and particle
diameter is investigated. We employ high-speed visualization, optical
microscopy and scanning electron microscopy to characterize the evaporating
droplets, particle motion, and deposit morphology, respectively. In the context
of mono-dispersed colloidal particles, an inner deposit and a typical ring form
for smaller and larger particles, respectively, on a nonheated surface. At
larger substrate temperature, a thin ring with inner deposit forms, explained
by the self-pinning of the contact line and advection of the particles from the
contact line to the center of the droplet due to Marangoni flow. In the context
of bi-dispersed colloidal particles, self-sorting of the colloidal particles
within the ring occurs at larger substrate temperature. The smaller particles
deposit at the outermost edge as compared to the larger diameter particles and
this preferential deposition in a stagnation region near the contact line is
due to the spatially-varying height of the liquid-gas interface above the
substrate. The sorting occurs at a smaller ratio of the diameter of the smaller
and larger particle. At the larger substrate temperature and a larger ratio,
the particles do not get sorted and mix into each other. Our measurements show
that there exists a critical substrate temperature as well as a diameter ratio
in order to achieve the sorting. We propose regime maps on substrate
temperature-particle diameter and substrate temperature-diameter ratio plane
for mono- and bi-dispersed solutions, respectively.
| physics.flu-dyn cond-mat.soft |
1807.02673 | Analysis of an Evaporating Sessile Droplet on a Non-Wetted Surface | We investigate evaporation of a sessile droplet on a non-wetted surface in
the framework of diffusion-limited and quasi-steady evaporation. We extend
previous models and numerically solve Laplace equation for the diffusion of
liquid vapor in ambient. We propose a unified, simple and accurate expression
of the evaporation mass flux valid for 90^o < theta < 180^o, where theta is the
equilibrium contact angle. In addition, using the derived expression of the
evaporation mass flux, we propose a simple and accurate expression of the
evaporation mass rate for a non-wetted surface, which does not exhibit
singularity at theta = 180^o. Finally, using the scaling analysis, the
expression of the evaporation mass flux is utilized to estimate the direction
and magnitude of the characteristic evaporation-driven flow velocity inside the
droplet on a non-wetted surface. The predicted flow direction is found to be
consistent with the previous measurements.
| physics.flu-dyn cond-mat.soft |
1807.02674 | Liouville theorems and a Schwarz Lemma for holomorphic mappings between
K\"ahler manifolds | We derive some consequences of the Liouville theorem for plurisubharmonic
functions of L.-F. Tam and the author. The first result provides a nonlinear
version of the complex splitting theorem (which splits off a factor of
$\mathbb{C}$ isometrically from the simply-connected K\"ahler manifold with
nonnegative bisectional curvature and a linear growth holomorphic function) of
L.-F. Tam and the author. The second set of results concerns the so-called
$k$-hyperbolicity and its connection with the negativity of the $k$-scalar
curvature (when $k=1$ they are the negativity of holomorphic sectional
curvature and Kobayashi hyperbolicity) introduced recently by F. Zheng and the
author. We lastly prove a new Schwarz Lemma type estimate in terms of {\it only
the holomorphic sectional curvatures of both domain and target manifolds}.
| math.DG |
1807.02675 | High-dimensional dynamics in a single-transistor oscillator containing
Feynman-Sierpinski resonators: effect of fractal depth and irregularity | Fractal structures pervade nature and are receiving increasing engineering
attention towards the realization of broadband resonators and antennas. We show
that fractal resonators can support the emergence of high-dimensional chaotic
dynamics even in the context of an elementary, single-transistor oscillator
circuit. Sierpi\'nski gaskets of variable depth are constructed using discrete
capacitors and inductors, whose values are scaled according to a simple
sequence. It is found that in regular fractals of this kind each iteration
effectively adds a conjugate pole/zero pair, yielding gradually more complex
and broader frequency responses, which can also be implemented as much smaller
Foster equivalent networks. The resonators are instanced in the circuit as
one-port devices, replacing the inductors found in the initial version of the
oscillator. By means of a highly simplified numerical model, it is shown that
increasing the fractal depth elevates the dimension of the chaotic dynamics,
leading to high-order hyperchaos. This result is overall confirmed by SPICE
simulations and experiments, which however also reveal that the non-ideal
behavior of physical components hinders obtaining high-dimensional dynamics.
The issue could be practically mitigated by building the Foster equivalent
networks rather than the verbatim fractals. Furthermore, it is shown that
considerably more complex resonances, and consequently richer dynamics, can be
obtained by rendering the fractal resonators irregular through reshuffling the
inductors, or even by inserting a limited number of focal imperfections. The
present results draw attention to the potential usefulness of fractal
resonators for generating high-dimensional chaotic dynamics, and underline the
importance of irregularities and component non-idealities.
| nlin.CD |
1807.02676 | The mixed quantum Rabi model | The analytical exact solutions to the mixed quantum Rabi model (QRM)
including both one- and two-photon terms are found by using Bogoliubov
operators. Transcendental functions in terms of $4 \times 4$ determinants
responsible for the exact solutions are derived. These so-called $G$-functions
with pole structures can be reduced to the previous ones in the unmixed QRMs.
The zeros of $G$-functions reproduce completely the regular spectra. The
exceptional eigenvalues can also be obtained by another transcendental
function. From the pole structure, we can derive two energy limits when the
two-photon coupling strength tends to the collapse point. All energy levels
only collapse to the lower one, which diverges negatively. The level crossings
in the unmixed QRMs are relaxed to avoided crossings in the present mixed QRM
due to absence of parity symmetry. In the weak two-photon coupling regime, the
mixed QRM is equivalent to an one-photon QRM with an effective positive bias,
suppressed photon frequency and enhanced one-photon coupling, which may pave a
highly efficient and economic way to access the deep-strong one-photon coupling
regime.
| quant-ph |
1807.02677 | Generalized Green functions associated to complex reflection groups | In this paper, we consider the set of r-symbols in a full generality. We
construct Hall-Littlewood functions and Kostka functions associated to those
r-symbols. We also discuss a multi-parameter version of those functions. We
show that there exists a general algorithm of computing multi-parameter Kostka
functions. As an application, we show that the generalized Green functions of
symplectic groups can be described combinatorially in terms of those
(one-parameter) Kostka functions.
| math.RT |
1807.02678 | Three-dimensional quantum Hall effect and metal-insulator transition in
ZrTe5 | Symmetry, dimensionality, and interaction are crucial ingredients for phase
transitions and quantum states of matter. As a prominent example, the integer
quantum Hall effect (QHE) represents a topological phase generally regarded as
characteristic for two-dimensional (2D) electronic systems, and its many
aspects can be understood without invoking electron-electron interaction. The
intriguing possibility of generalizing QHE to three-dimensional (3D) systems
was proposed decades ago, yet it remains elusive experimentally. Here, we
report clear experimental evidence for the 3D QHE observed in bulk ZrTe5
crystals. Owing to the extremely high sample quality, the extreme quantum limit
with only the lowest Landau level occupied can be achieved by an applied
magnetic field as low as 1.5 T. Remarkably, in this regime, we observe a
dissipationless longitudinal resistivity rho_xx=0 accompanied with a
well-developed Hall resistivity plateau rho_xy=(1\pm0.1) h/e^2
(\lambda_(F,z)/2), where \lambda_(F,z) is the Fermi wavelength along the field
direction (z axis). This striking result strongly suggests a Fermi surface
instability driven by the enhanced interaction effects in the extreme quantum
limit. In addition, with further increasing magnetic field, both rho_xx and
rho_xy increase dramatically and display an interesting metal-insulator
transition, representing another magnetic field driven quantum phase
transition. Our findings not only unambiguously reveal a novel quantum state of
matter resulting from an intricate interplay among dimensionality, interaction,
and symmetry breaking, but also provide a promising platform for further
exploration of more exotic quantum phases and transitions in 3D systems.
| cond-mat.mtrl-sci cond-mat.mes-hall |
1807.02679 | Multiple Killing Horizons and Near Horizon Geometries | Near Horizon Geometries with multiply degenerate Killing horizons
$\mathcal{H}$ are considered, and their degenerate Killing vector fields
identified. We prove that they all arise from hypersurface-orthogonal Killing
vectors of any cut of $\mathcal{H}$ with the inherited metric -- cuts are
spacelike co-dimension two submanifolds contained in $\mathcal{H}$. For each of
these Killing vectors on a given cut, there are three different possibilities
for the Near Horizon metric which are presented explicitly. The structure of
the metric for Near Horizon Geometries with multiple Killing horizons of order
$m\geq 3$ is thereby completely determined, and in particular we prove that the
cuts on $\mathcal{H}$ must be warped products with maximally symmetric fibers
(ergo of constant curvature). The question whether multiple degenerate Killing
horizons may lead to inequivalent Near Horizon Geometries by using different
degenerate Killings is addressed, and answered on the negative: all Near
Horizon geometries built from a given multiple degenerate Killing horizon
(using different degenerate Killings) are isometric.
| gr-qc |
1807.02680 | Lyapunov spectrum of nonautonomous linear Young differential equations | We show that a linear Young differential equation generates a topological
two-parameter flow, thus the notions of Lyapunov exponents and Lyapunov
spectrum are well-defined. The spectrum can be computed using the discretized
flow and is independent of the driving path for triangular systems which are
regular in the sense of Lyapunov. In the stochastic setting, the system
generates a stochastic two-parameter flow which satisfies the integrability
condition, hence the Lyapunov exponents are random variables of finite moments.
Finally, we prove a Millionshchikov theorem stating that almost all, in a sense
of an invariant measure, linear nonautonomous Young differential equations are
Lyapunov regular.
| math.DS |
1807.02681 | Realistic estimates of superconducting properties for the cuprates:
reciprocal-space diagrammatic expansion combined with variational approach | We propose a systematic approach to the systems of correlated electrons, the
so-called $\mathbf{k}$-DE-GWF method, based on reciprocal-space
($\mathbf{k}$-resolved) diagrammatic expansion of the variational
Gutzwiller-type wave function for parametrized models of correlated fermions.
The present approach, in contrast to either variational Monte-Carlo (VMC), or
the recently developed real-space diagrammatic expansion of the Gutzwiller-type
wave function (direct-space DE-GWF technique), is applicable directly in the
thermodynamic limit and thus is suitable for describing selected singular
features of the wave-vector-dependent quantities. We employ the
$\mathbf{k}$-DE-GWF method to extract the non-analytic part of the two leading
moments of the fermion spectral-density function across the (two-dimensional)
Brillouin zone for the Hubbard model and away from the half-filling. Those
moments are used to evaluate the nodal quasiparticle velocities and their
spectral weights in the correlated superconducting state. The two velocities
determined in that manner exhibit scaling with the electron concentration
qualitatively different from that obtained earlier for the excited states of
the high-$T_c$ cuprates within the projected quasi-particle ansatz, and the
results are in a very good quantitative agreement with experimental data if
interpreted as those characterizing the spectrum below and above the observed
kink. We provide a detailed discussion of the two gaps and two excitation
branches (two velocities) appearing naturally within our DE-GWF approach. The
two separate sets of characteristics distinguish the renormalized quasiparticle
states very close to the Fermi surface from the deeper correlated-state
properties. Also, an enhancement of the $\mathbf{k}$-dependent magnetic
susceptibility is shown to contain a spin-fluctuation contribution within our
language.
| cond-mat.str-el |
1807.02682 | A Supervised Geometry-Aware Mapping Approach for Classification of
Hyperspectral Images | The lack of proper class discrimination among the Hyperspectral (HS) data
points poses a potential challenge in HS classification. To address this issue,
this paper proposes an optimal geometry-aware transformation for enhancing the
classification accuracy. The underlying idea of this method is to obtain a
linear projection matrix by solving a nonlinear objective function based on the
intrinsic geometrical structure of the data. The objective function is
constructed to quantify the discrimination between the points from dissimilar
classes on the projected data space. Then the obtained projection matrix is
used to linearly map the data to more discriminative space. The effectiveness
of the proposed transformation is illustrated with three benchmark real-world
HS data sets. The experiments reveal that the classification and dimensionality
reduction methods on the projected discriminative space outperform their
counterpart in the original space.
| cs.LG stat.ML |
1807.02683 | Diffusive Molecular Communication in Biological Cylindrical Environment | Diffusive molecular communication (DMC) is one of the most promising
approaches for realizing nano-scale communications in biological environments
for healthcare applications. In this paper, a DMC system in biological
cylindrical environment is considered, inspired by blood vessel structures in
the body. The internal surface of the cylinder boundary is assumed to be
covered by the biological receptors which may irreversibly react with hitting
molecules. Also, information molecules diffusing in the fluid medium are
subject to a degradation reaction and flow. The concentration Green's function
of diffusion in this environment is analytically derived which takes into
account asymmetry in all radial, axial and azimuthal coordinates. Employing
obtained Green's function, information channel between transmitter and
transparent receiver of DMC is characterized. To evaluate the DMC system in the
biological cylinder, a simple on-off keying modulation scheme is adopted and
corresponding error probability is derived. Particle based simulation results
confirm the proposed analysis. Also, the effect of different system parameters
on the concentration Green's function are examined. Our results reveal that the
degradation reaction and the boundary covered by biological receptors may be
utilized to mitigate intersymbol interference and outperform corresponding
error probability.
| cs.IT math.IT |
1807.02684 | VFPred: A Fusion of Signal Processing and Machine Learning techniques in
Detecting Ventricular Fibrillation from ECG Signals | Ventricular Fibrillation (VF), one of the most dangerous arrhythmias, is
responsible for sudden cardiac arrests. Thus, various algorithms have been
developed to predict VF from Electrocardiogram (ECG), which is a binary
classification problem. In the literature, we find a number of algorithms based
on signal processing, where, after some robust mathematical operations the
decision is given based on a predefined threshold over a single value. On the
other hand, some machine learning based algorithms are also reported in the
literature; however, these algorithms merely combine some parameters and make a
prediction using those as features. Both the approaches have their perks and
pitfalls; thus our motivation was to coalesce them to get the best out of the
both worlds. Hence we have developed, VFPred that, in addition to employing a
signal processing pipeline, namely, Empirical Mode Decomposition and Discrete
Time Fourier Transform for useful feature extraction, uses a Support Vector
Machine for efficient classification. VFPred turns out to be a robust algorithm
as it is able to successfully segregate the two classes with equal confidence
(Sensitivity = 99.99%, Specificity = 98.40%) even from a short signal of 5
seconds long, whereas existing works though requires longer signals, flourishes
in one but fails in the other.
| cs.LG eess.SP stat.ML |
1807.02685 | Optimal Satellite Constellation Spare Strategy Using Multi-Echelon
Inventory Control | The recent growing trend to develop large-scale satellite constellations
(i.e., mega-constellation) with low-cost small satellites has brought the need
for an efficient and scalable maintenance strategy decision plan. Traditional
spare strategies for satellite constellations cannot handle these
mega-constellations due to their limited scalability in number of satellites
and/or frequency of failures. In this paper, we propose a novel spare strategy
using an inventory management approach. We consider a set of parking orbits at
a lower altitude than the constellation for spare storage, and model satellite
constellation spare strategy problem using a multi-echelon (s,Q)-type inventory
policy, viewing Earth's ground as a supplier, parking orbits as warehouses, and
in-plane spare stocks as retailers. This inventory model is unique in that the
parking orbits (warehouses) drift away from the orbital planes over time due to
orbital mechanics' effects, and the in-plane spare stocks (retailers) would
receive the resupply from the closest (i.e., minimum waiting time) available
warehouse at the time of delivery. The parking orbits (warehouses) are also
resupplied from the ground (supplier) with stochastic lead time caused by the
order processing and launch opportunities, leveraging the cost saving effects
by launching many satellites in one rocket (i.e., batch launch discount). The
proposed analytical model is validated against simulations using Latin
Hypercube Sampling. Furthermore, based on the proposed model, an optimization
formulation is introduced to identify the optimal spare strategy, comprising
the parking orbits characteristics and all locations policies, to minimize the
maintenance cost of the system given performance requirements. The proposed
model and optimization method are applied to a real-world case study of
satellite mega-constellation to demonstrate their value.
| math.OC cs.CE cs.SY physics.space-ph |
1807.02686 | Topological multiferroic phases in the extended Kane-Mele-Hubbard Model
in the Hofstadter regime | We investigate the new quantum phases on the extended Kane-Mele-Hubbard model
of honeycomb lattice in the Hofstadter regime. In this regime, orbital motion
of the electrons can induce various topological phases with spontaneously
broken symmetries when the spin orbit coupling and electron correlations
coexist. Here, we consider the interaction effects in the Kane-Mele model and
discuss possible phases in the presence of magnetic field at integer fillings
of electrons. In particular, focusing on 2{\pi}/3 magnetic flux per plaquette,
the realization of numerous quantum phases are discussed within the mean field
framework; insulator with coplanar magnetic ordering, ferrimagnetic Chern
insulator with nematic charge order, ferrimagnetic-ferrielectric Chern
insulators etc. Many of these phase transitions are also accompanied with the
change in the topological invariants of the system. Based on our theoretical
study, we propose topological multiferroic phases with a scope of realization
in 2D van-der Waals materials and optical lattice system where the significant
interplay of magnetic field, spin orbit coupling and interactions can be
engineered.
| cond-mat.str-el |
1807.02687 | Amplifying thermal conduction calibre of nanocolloids employing induced
electrophoresis | Electrophoresis has been shown as a novel methodology to enhance heat
conduction capabilities of nanocolloidal dispersions. A thoroughly designed
experimental system has been envisaged to solely probe heat conduction across
nanofluids by specifically eliminating the buoyancy driven convective
component. Electric field is applied across the test specimen in order to
induce electrophoresis in conjunction with the existing thermal gradient. It is
observed that the electrophoretic drift of the nanoparticles acts as an
additional thermal transport drift mechanism over and above the already
existent Brownian diffusion and thermophoresis dominated thermal conduction. A
scaling analysis of the thermophoretic and electrophoretic velocities from
classical Huckel-Smoluchowski formalism is able to mathematically predict the
thermal performance enhancement due to electrophoresis. It is also inferred
that the dielectric characteristics of the particle material is the major
determining component of the electrophoretic amplification of heat transfer.
Influence of surfactants has also been probed into and it is observed that
enhancing the stability via surface charge modulation can in fact enhance the
electrophoretic drift, thereby enhancing heat transfer calibre. Also,
surfactants ensure colloidal stability as well as chemical gradient induced
recirculation, thus ensuring colloidal phase equilibrium and low hysteresis in
spite of the directional drift in presence of electric field forcing. The
findings may have potential implications in enhanced and tunable thermal
management of micro nanoscale devices.
| physics.app-ph cond-mat.mes-hall |
1807.02688 | Stochastic Coupon Probing in Social Networks | In this paper, we study stochastic coupon probing problem in social networks.
Assume there is a social network and a set of coupons. We can offer coupons to
some users adaptively and those users who accept the offer will act as seeds
and influence their friends in the social network. There are two constraints
which are called the inner and outer constraints, respectively. The set of
coupons redeemed by users must satisfy inner constraints, and the set of all
probed users must satisfy outer constraints. One seeks to develop a coupon
probing policy that achieves the maximum influence while satisfying both inner
and outer constraints. Our main result is a constant approximation policy for
the stochastic coupon probing problem for any monotone submodular utility
function.
| cs.SI cs.GT |
1807.02689 | Cellular Controlled Delay TCP (C2TCP) | Cellular networks have special characteristics including highly variable
channels, fast fluctuating capacities, deep per user buffers, self-inflicted
queuing delays, radio uplink/downlink scheduling delays, etc. These
distinguishing properties make the problem of achieving low latency and high
throughput in cellular networks more challenging than in wired networks. That's
why in this environment, TCP and its flavors, which are generally designed for
wired networks, perform poorly.
To cope with these challenges, we present C2TCP, a flexible end-to-end
solution targeting interactive applications requiring high throughput and low
delay in cellular networks. C2TCP stands on top of loss-based TCP and brings it
delay sensitivity without requiring any network state profiling, channel
prediction, or complicated rate adjustment mechanisms. The key idea behind
C2TCP is to absorb dynamics of unpredictable cellular channels by investigating
local minimum delay of packets in a moving time window and react to the
cellular network's capacity changes very fast.
Through extensive trace-based evaluations using traces from five commercial
LTE and 3G networks, we have compared performance of C2TCP with various TCP
variants, and state-of-the-art schemes including BBR, Verus, and Sprout.
Results show that on average, C2TCP outperforms these schemes and achieves
lower average and 95th percentile delay for packets.
| cs.NI |
1807.02690 | Quantum Fisher information matrix for unitary processes: closed relation
for $SU(2)$ | Quantum Fisher information plays a central role in the field of quantum
metrology. In this paper we study the problem of quantum Fisher information of
unitary processes. Associated to each parameter $\theta_i$ of unitary process
$U(\boldsymbol{\theta})$, there exists a unique Hermitian matrix
$M_{\theta_i}=i(U^\dagger\partial_{\theta_i} U)$. Except for some simple cases,
such as when the parameter under estimation is an overall multiplicative factor
in the Hamiltonian, calculation of these matrices is not an easy task to treat
even for estimating a single parameter of qubit systems. Using the Bloch vector
$\boldsymbol{m}_{\theta_i}$, corresponding to each matrix $M_{\theta_i}$, we
find a closed relation for the quantum Fisher information matrix of the $SU(2)$
processes for an arbitrary number of estimation parameters and an arbitrary
initial state. We extend our results and present an explicit relation for each
vector $\boldsymbol{m}_{\theta_i}$ for a general Hamiltonian with arbitrary
parametrization. We illustrate our results by obtaining the quantum Fisher
information matrix of the so-called angle-axis parameters of a general $SU(2)$
process. Using a linear transformation between two different parameter spaces
of a unitary process, we provide a way to move from quantum Fisher information
of a unitary process in a given parametrization to the one of the other
parametrization. Knowing this linear transformation enables one to calculate
the quantum Fisher information of a composite unitary process, i.e. a unitary
process resulted from successive action of some simple unitary processes. We
apply this method for a spin-half system and obtain the quantum Fisher matrix
of the coset parameters in terms of the one of the angle-axis parameters.
| quant-ph |
1807.02691 | Combined limit on the production of a light gauge boson decaying into
$\mu^+\mu^-$ and $\pi^+\pi^-$ | We searched for the $\mu^+\mu^-$ decay of a light vector gauge boson, also
known as dark photon, in the $e^+ e^- \to \mu^+ \mu^- \gamma_{\rm ISR}$ process
by means of the Initial State Radiation (ISR) method. We used 1.93~fb$^{-1}$ of
data collected by the KLOE experiment at the DA$\Phi$NE $\phi$-factory. No
structures have been observed over the irreducible $\mu^+ \mu^-$ background. A
90\% CL limit on the ratio $\varepsilon^2=\alpha^{\prime}/\alpha$ between the
dark coupling constant and the fine structure constant of $ 3\times
10^{-6}-2\times 10^{-7}$ has been set in the dark photon mass region between
519 MeV and 973 MeV. This new limit has been combined with the published result
obtained investigating the hypothesis of the dark photon decaying into hadrons
in $e^+ e^- \to \pi^+ \pi^- \gamma_{\rm ISR}$ events. The combined 90\% CL
limit increases the sensitivity especially in the $\rho-\omega$ interference
region and excludes $\varepsilon^2$ greater than $(13-2)\times 10^{-7}$. For
dark photon masses greater than 600 MeV the combined limit is lower than
8~$\times\, 10^{-7}$ resulting more stringent than present constraints from
other experiments.
| hep-ex |
1807.02692 | Electromagnetic field orientation and dynamics governs advection
characteristics within pendent droplets | The article reports the domineering governing role played by the direction of
electric and magnetic fields on the internal advection pattern and strength
within salt solution pendant droplets. Literature shows that solutal advection
drives circulation cells within salt based droplets. Flow visualization and
velocimetry reveals that the direction of the applied field governs the
enhancement/reduction in circulation velocity and the directionality of
circulation inside the droplet. Further, it is noted that while magnetic fields
augment the circulation velocity, the electric field leads to deterioration of
the same. The concepts of electro andmagnetohydrodynamics are appealed to and a
Stokesian stream function based mathematical model to deduce the field mediated
velocities has been proposed. The model is found to reveal the roles of and
degree of dependence on the governing Hartmann, Stuart, Reynolds and Masuda
numbers. The theoretical predictions are observed to be in good agreement with
experimental average spatio-temporal velocities. The present findings may have
strong implications in microscale electro and/or magnetohydrodynamics.
| physics.flu-dyn physics.app-ph |
1807.02693 | VPKIaaS: A Highly-Available and Dynamically-Scalable Vehicular
Public-Key Infrastructure | The central building block of secure and privacy-preserving Vehicular
Communication (VC) systems is a Vehicular Public-Key Infrastructure (VPKI),
which provides vehicles with multiple anonymized credentials, termed
pseudonyms. These pseudonyms are used to ensure message authenticity and
integrity while preserving vehicle (and thus passenger) privacy. In the light
of emerging large-scale multi-domain VC environments, the efficiency of the
VPKI and, more broadly, its scalability are paramount. In this extended
abstract, we leverage the state-of-the-art VPKI system and enhance its
functionality towards a highly-available and dynamically-scalable design, this
ensures that the system remains operational in the presence of benign failures
or any resource depletion attack, and that it dynamically scales out, or
possibly scales in, according to the requests' arrival rate. Our full-blown
implementation on the Google Cloud Platform shows that deploying a VPKI for a
large-scale scenario can be cost-effective, while efficiently issuing
pseudonyms for the requesters.
| cs.CR |
1807.02694 | Approximate Leave-One-Out for Fast Parameter Tuning in High Dimensions | Consider the following class of learning schemes: $$\hat{\boldsymbol{\beta}}
:= \arg\min_{\boldsymbol{\beta}}\;\sum_{j=1}^n
\ell(\boldsymbol{x}_j^\top\boldsymbol{\beta}; y_j) + \lambda
R(\boldsymbol{\beta}),\qquad\qquad (1) $$ where $\boldsymbol{x}_i \in
\mathbb{R}^p$ and $y_i \in \mathbb{R}$ denote the $i^{\text{th}}$ feature and
response variable respectively. Let $\ell$ and $R$ be the loss function and
regularizer, $\boldsymbol{\beta}$ denote the unknown weights, and $\lambda$ be
a regularization parameter. Finding the optimal choice of $\lambda$ is a
challenging problem in high-dimensional regimes where both $n$ and $p$ are
large. We propose two frameworks to obtain a computationally efficient
approximation ALO of the leave-one-out cross validation (LOOCV) risk for
nonsmooth losses and regularizers. Our two frameworks are based on the primal
and dual formulations of (1). We prove the equivalence of the two approaches
under smoothness conditions. This equivalence enables us to justify the
accuracy of both methods under such conditions. We use our approaches to obtain
a risk estimate for several standard problems, including generalized LASSO,
nuclear norm regularization, and support vector machines. We empirically
demonstrate the effectiveness of our results for non-differentiable cases.
| stat.ML cs.LG |
1807.02695 | The variety of domination games | Domination game [SIAM J.\ Discrete Math.\ 24 (2010) 979--991] and total
domination game [Graphs Combin.\ 31 (2015) 1453--1462] are by now well
established games played on graphs by two players, named Dominator and Staller.
In this paper, Z-domination game, L-domination game, and LL-domination game are
introduced as natural companions of the standard domination games.
Versions of the Continuation Principle are proved for the new games. It is
proved that in each of these games the outcome of the game, which is a
corresponding graph invariant, differs by at most one depending whether
Dominator or Staller starts the game. The hierarchy of the five domination
games is established. The invariants are also bounded with respect to the
(total) domination number and to the order of a graph. Values of the three new
invariants are determined for paths up to a small constant independent from the
length of a path. Several open problems and a conjecture are listed. The latter
asserts that the L-domination game number is not greater than $6/7$ of the
order of a graph.
| math.CO |
1807.02696 | Switching between Limit Cycles in a Model of Running Using Exponentially
Stabilizing Discrete Control Lyapunov Function | This paper considers the problem of switching between two periodic motions,
also known as limit cycles, to create agile running motions. For each limit
cycle, we use a control Lyapunov function to estimate the region of attraction
at the apex of the flight phase. We switch controllers at the apex, only if the
current state of the robot is within the region of attraction of the subsequent
limit cycle. If the intersection between two limit cycles is the null set, then
we construct additional limit cycles till we are able to achieve sufficient
overlap of the region of attraction between sequential limit cycles.
Additionally, we impose an exponential convergence condition on the control
Lyapunov function that allows us to rapidly transition between limit cycles.
Using the approach we demonstrate switching between 5 limit cycles in about 5
steps with the speed changing from 2 m/s to 5 m/s.
| cs.RO |
1807.02697 | Multiloop functional renormalization group for the two-dimensional
Hubbard model: Loop convergence of the response functions | We present a functional renormalization group (fRG) study of the two
dimensional Hubbard model, performed with an algorithmic implementation which
lifts some of the common approximations made in fRG calculations. In
particular, in our fRG flow; (i) we take explicitly into account the momentum
and the frequency dependence of the vertex functions; (ii) we include the
feedback effect of the self-energy; (iii) we implement the recently introduced
multiloop extension which allows us to sum up {\emph{all}} the diagrams of the
parquet approximation with their exact weight. Due to its iterative structure
based on successive one-loop computations, the loop convergence of the fRG
results can be obtained with an affordable numerical effort. In particular,
focusing on the analysis of the physical response functions, we show that the
results become {\emph{independent}} from the chosen cutoff scheme and from the
way the fRG susceptibilities are computed, i.e., either through flowing
couplings to external fields, or through a "post-processing" contraction of the
interaction vertex at the end of the flow. The presented substantial refinement
of fRG-based computation schemes paves a promising route towards future
quantitative fRG analyses of more challenging systems and/or parameter regimes.
| cond-mat.str-el |
1807.02698 | Streamer evolution arrest governed amplified AC breakdown strength of
graphene and CNT colloids | The present article experimentally explores the concept of large improving
the AC dielectric breakdown strength of insulating mineral oils by the addition
of trace amounts of graphene or CNTs to form stable dispersions. The nano-oils
infused with these nanostructures of high electronic conductance indicate
superior AC dielectric behaviour in terms of augmented breakdown strength
compared to the base oils. Experimental observations of two grades of
synthesized graphene and CNT nano-oils show that the nanomaterials not only
improve the average breakdown voltage but also significantly improve the
reliability and survival probabilities of the oils under AC high voltage
stressing. Improvement of the tune of ~ 70-80 % in the AC breakdown voltage of
the oils has been obtained via the present concept. The present study examines
the reliability of such nano-colloids with the help of two parameter Weibull
distribution and the oils show greatly augmented electric field bearing
capacity at both standard survival probability values of 5 % and 63.3 %. The
fundamental mechanism responsible for such observed outcomes is reasoned to be
delayed streamer development and reduced streamer growth rates due to effective
electron scavenging by the nanostructures from the ionized liquid insulator. A
mathematical model based on the principles of electron scavenging is proposed
to quantify the amount of electrons scavenged by the nanostructures. The same
is then employed to predict the enhanced AC breakdown voltage and the
experimental values are found to match well with the model predictions. The
present study can have strong implications in efficient, reliable and safer
operation of real life AC power systems.
| physics.app-ph cond-mat.mes-hall |
1807.02699 | Probing AGN Inner Structure with X-ray Obscured Type 1 AGN | Using the X-ray-selected active galactic nuclei (AGN) from the XMM-XXL north
survey and the SDSS Baryon Oscillation Spectroscopic Survey (BOSS)
spectroscopic follow-up of them, we compare the properties of X-ray unobscured
and obscured broad-line AGN (BLAGN1 and BLAGN2; $N_\textrm{H}$below and above
$10^{21.5}$ cm$^{-2}$), including their X-ray luminosity $L_X$, black hole
mass, Eddington ratio $\lambda_{\textrm{Edd}}$, optical continuum and line
features. We find that BLAGN2 have systematically larger broad line widths and
hence apparently higher (lower) $M_{\textrm{BH}}$ ($\lambda_{\textrm{Edd}}$)
than BLAGN1. We also find that the X-ray obscuration in BLAGN tends to coincide
with optical dust extinction, which is optically thinner than that in
narrow-line AGN (NLAGN) and likely partial-covering to the broad line region.
All the results can be explained in the framework of a multi-component, clumpy
torus model by interpreting BLAGN2 as an intermediate type between BLAGN1 and
NLAGN in terms of an intermediate inclination angle.
| astro-ph.GA |
1807.02700 | Towards Multi-class Object Detection in Unconstrained Remote Sensing
Imagery | Automatic multi-class object detection in remote sensing images in
unconstrained scenarios is of high interest for several applications including
traffic monitoring and disaster management. The huge variation in object scale,
orientation, category, and complex backgrounds, as well as the different camera
sensors pose great challenges for current algorithms. In this work, we propose
a new method consisting of a novel joint image cascade and feature pyramid
network with multi-size convolution kernels to extract multi-scale strong and
weak semantic features. These features are fed into rotation-based region
proposal and region of interest networks to produce object detections. Finally,
rotational non-maximum suppression is applied to remove redundant detections.
During training, we minimize joint horizontal and oriented bounding box loss
functions, as well as a novel loss that enforces oriented boxes to be
rectangular. Our method achieves 68.16% mAP on horizontal and 72.45% mAP on
oriented bounding box detection tasks on the challenging DOTA dataset,
outperforming all published methods by a large margin (+6% and +12% absolute
improvement, respectively). Furthermore, it generalizes to two other datasets,
NWPU VHR-10 and UCAS-AOD, and achieves competitive results with the baselines
even when trained on DOTA. Our method can be deployed in multi-class object
detection applications, regardless of the image and object scales and
orientations, making it a great choice for unconstrained aerial and satellite
imagery.
| cs.CV |
1807.02701 | DeepSource: Point Source Detection using Deep Learning | Point source detection at low signal-to-noise is challenging for astronomical
surveys, particularly in radio interferometry images where the noise is
correlated. Machine learning is a promising solution, allowing the development
of algorithms tailored to specific telescope arrays and science cases. We
present DeepSource - a deep learning solution - that uses convolutional neural
networks to achieve these goals. DeepSource enhances the Signal-to-Noise Ratio
(SNR) of the original map and then uses dynamic blob detection to detect
sources. Trained and tested on two sets of 500 simulated 1 deg x 1 deg MeerKAT
images with a total of 300,000 sources, DeepSource is essentially perfect in
both purity and completeness down to SNR = 4 and outperforms PyBDSF in all
metrics. For uniformly-weighted images it achieves a Purity x Completeness (PC)
score at SNR = 3 of 0.73, compared to 0.31 for the best PyBDSF model. For
natural-weighting we find a smaller improvement of ~40% in the PC score at SNR
= 3. If instead we ask where either of the purity or completeness first drop to
90%, we find that DeepSource reaches this value at SNR = 3.6 compared to the
4.3 of PyBDSF (natural-weighting). A key advantage of DeepSource is that it can
learn to optimally trade off purity and completeness for any science case under
consideration. Our results show that deep learning is a promising approach to
point source detection in astronomical images.
| astro-ph.IM cs.CV cs.LG hep-ph stat.ML |
1807.02702 | Local convergence for permutations and local limits for uniform
$\rho$-avoiding permutations with $|\rho|=3$ | We set up a new notion of local convergence for permutations and we prove a
characterization in terms of proportions of \emph{consecutive} pattern
occurrences. We also characterize random limiting objects for this new topology
introducing a notion of "shift-invariant" property (corresponding to the notion
of unimodularity for random graphs). We then study two models in the framework
of random pattern-avoiding permutations. We compute the local limits of uniform
$\rho$-avoiding permutations, for $|\rho|=3,$ when the size of the permutations
tends to infinity. The core part of the argument is the description of the
asymptotics of the number of consecutive occurrences of any given pattern. For
this result we use bijections between $\rho$-avoiding permutations and rooted
ordered trees, local limit results for Galton--Watson trees, the Second moment
method and singularity analysis.
| math.PR math.CO |
1807.02703 | Vertex and Edge connectivity of the zero divisor graph $\Gamma[\mathbb
{Z}_n]$ | The Zero divisor Graph of a commutative ring $R$, denoted by $\Gamma[R]$, is
a graph whose vertices are non-zero zero divisors of $R$ and two vertices are
adjacent if their product is zero. In this paper we derive the Vertex and Edge
Connectivity of the zero divisor graph $\Gamma[\mathbb{Z}_n]$, for any natural
number $n$ . We also discuss the minimum degree of the zero divisor graph
$\Gamma[\mathbb{Z}_n]$.
| math.RA math.CO |
1807.02704 | Oxygen Potential Transition in Mixed Conducting Oxide Electrolyte | It is generally assumed that oxygen potential in a thin oxide electrolyte
follows a linear distribution between electrodes. Jacobsen and Mogensen have
shown, however, that this is not the case for thin zirconia membranes in solid
oxide electrochemical cells. Here we demonstrate that there is a ubiquitous
oxygen potential transition rooted in the p-type/n-type transition of
electronic conductivity inside mixed conducting oxides, and that the transition
is extremely sensitive to electrode potential and current density. It is also
remarkably sensitive to the conductivity ratio of electrons and holes, as well
as their association with lattice oxygens and vacancies, which tends to
increase the oxygen flow. Direct evidence of a sharp oxygen potential
transition has been found in an equally sharp grain size transition in
electrically loaded zirconia. More broadly speaking, the oxygen potential
transition is akin to a first-order phase transition. Therefore, it will suffer
interface instability, especially in high-current-density devices. These
findings provide new opportunities to understand several disparate observations
in the literature, from microstructural degradation and stress distribution in
solid oxide fuel/electrolyzer cells, to field-assisted sintering, to conducting
filaments in resistance memory, to dendrite formation in electrochemical cells.
| cond-mat.mtrl-sci |
1807.02705 | On the maximum conjecture | We verify the maximum conjecture on the rigidity of totally nondegenerate
model CR manifolds in the following two cases: (i) for all models of CR
dimension one (ii) for the so-called full-models, namely those in which their
associated symbol algebras are free CR. In particular, we discover that in each
arbitrary CR dimension and length >= 3, there exists at least one totally
nondegenerate model, enjoying this conjecture. Our proofs rely upon some recent
results in the Tanaka theory of transitive prolongation of fundamental
algebras.
| math.CV |
1807.02706 | Efficient, Scalable, and Resilient Vehicle-Centric Certificate
Revocation List Distribution in VANETs | In spite of progress in securing Vehicular Communication (VC) systems, there
is no consensus on how to distribute Certificate Revocation Lists (CRLs). The
main challenges lie exactly in (i) crafting an efficient and timely
distribution of CRLs for numerous anonymous credentials, pseudonyms, (ii)
maintaining strong privacy for vehicles prior to revocation events, even with
honest-but-curious system entities, (iii) and catering to computation and
communication constraints of on-board units with intermittent connectivity to
the infrastructure. Relying on peers to distribute the CRLs is a double-edged
sword: abusive peers could "pollute" the process, thus degrading the timely
CRLs distribution. In this paper, we propose a vehicle-centric solution that
addresses all these challenges and thus closes a gap in the literature. Our
scheme radically reduces CRL distribution overhead: each vehicle receives CRLs
corresponding only to its region of operation and its actual trip duration.
Moreover, a "fingerprint" of CRL 'pieces' is attached to a subset of
(verifiable) pseudonyms for fast CRL 'piece' validation (while mitigating
resource depletion attacks abusing the CRL distribution). Our experimental
evaluation shows that our scheme is efficient, scalable, dependable, and
practical: with no more than 25 KB/s of traffic load, the latest CRL can be
delivered to 95% of the vehicles in a region (50x50 KM) within 15s, i.e., more
than 40 times faster than the state-of-the-art. Overall, our scheme is a
comprehensive solution that complements standards and can catalyze the
deployment of secure and privacy-protecting VC systems.
| cs.CR |
1807.02707 | Anomalous quartic gauge couplings and unitarization for the vector boson
scattering process $pp\rightarrow W^+W^+jjX\rightarrow
\ell^+\nu_\ell\ell^+\nu_\ell jjX$ | Weak vector boson scattering (VBS) at the LHC provides an excellent source of
information on the structure of quartic gauge couplings and possible effects of
physics beyond the SM in electroweak symmetry breaking. Parameterizing
deviations from the SM within an effective field theory at tree level, the
dimension-8 operators, which are needed for sufficiently general modeling, lead
to unphysical enhancements of cross sections within the accessible energy range
of the LHC. Preservation of unitarity limits is needed for phenomenological
studies of the $VVjj$ events which signify VBS. Here we develop a numerical
unitarization scheme for the full off-shell VBS processes and apply it to
same-sign $W$ scattering, i.e. processes like $qq\to qqW^+W^+$. The scheme is
implemented within the Monte Carlo program VBFNLO, including leptonic decay of
the weak bosons and NLO QCD corrections. Distributions differentiating between
higher dimensional operators are discussed.
| hep-ph |
1807.02708 | On open flat sets in spaces with bipolar comparison | We show that if a Riemannian manifold satisfies (3,3)-bipolar comparisons and
has an open flat subset then it is flat. The same holds for a version of MTW
where the perpendicularity is dropped.
In particular we get that the (3,3)-bipolar comparison is strictly stronger
than the Alexandrov comparison.
| math.DG |
1807.02709 | HMCF - Hamiltonian Monte Carlo Sampling for Fields - A Python framework
for HMC sampling with NIFTy | HMCF "Hamiltonian Monte Carlo for Fields" is a software add-on for the NIFTy
"Numerical Information Field Theory" framework implementing Hamiltonian Monte
Carlo (HMC) sampling in Python. HMCF as well as NIFTy are designed to address
inference problems in high-dimensional spatially correlated setups such as
image reconstruction. HMCF adds an HMC sampler to NIFTy that automatically
adjusts the many free parameters steering the HMC sampling machinery. A wide
variety of features ensure efficient full-posterior sampling for
high-dimensional inference problems. These features include integration step
size adjustment, evaluation of the mass matrix, convergence diagnostics, higher
order symplectic integration and simultaneous sampling of parameters and
hyperparameters in Bayesian hierarchical models.
| physics.data-an astro-ph.IM physics.comp-ph |
1807.02710 | Improving DNN-based Music Source Separation using Phase Features | Music source separation with deep neural networks typically relies only on
amplitude features. In this paper we show that additional phase features can
improve the separation performance. Using the theoretical relationship between
STFT phase and amplitude, we conjecture that derivatives of the phase are a
good feature representation opposed to the raw phase. We verify this conjecture
experimentally and propose a new DNN architecture which combines amplitude and
phase. This joint approach achieves a better signal-to distortion ratio on the
DSD100 dataset for all instruments compared to a network that uses only
amplitude features. Especially, the bass instrument benefits from the phase
information.
| cs.SD cs.LG eess.AS |
1807.02711 | Capital Regulation under Price Impacts and Dynamic Financial Contagion | We construct a continuous time model for price-mediated contagion
precipitated by a common exogenous stress to the banking book of all firms in
the financial system. In this setting, firms are constrained so as to satisfy a
risk-weight based capital ratio requirement. We use this model to find
analytical bounds on the risk-weights for assets as a function of the market
liquidity. Under these appropriate risk-weights, we find existence and
uniqueness for the joint system of firm behavior and the asset prices. We
further consider an analytical bound on the firm liquidations, which allows us
to construct exact formulas for stress testing the financial system with
deterministic or random stresses. Numerical case studies are provided to
demonstrate various implications of this model and analytical bounds.
| q-fin.MF q-fin.RM |
1807.02712 | The fully frustrated XY model revisited: A new universality class | The two-dimensional ($2d$) fully frustrated Planar Rotator model on a square
lattice has been the subject of a long controversy due to the simultaneous
$Z_2$ and $O(2)$ symmetry existing in the model. The $O(2)$ symmetry being
responsible for the Berezinskii - Kosterlitz - Thouless transition ($BKT$)
while the $Z_2$ drives an Ising-like transition. There are arguments supporting
two possible scenarios, one advocating that the loss of $Ising$ and $BKT$ order
take place at the same temperature $T_{t}$ and the other that the $Z_2$
transition occurs at a higher temperature than the $BKT$ one. In the first case
an immediate consequence is that this model is in a new universality class.
Most of the studies take hand of some order parameter like the stiffness,
Binder's cumulant or magnetization to obtain the transition temperature.
Considering that the transition temperatures are obtained, in general, as an
average over the estimates taken about several of those quantities, it is
difficult to decide if they are describing the same or slightly separate
transitions. In this paper we describe an iterative method based on the
knowledge of the complex zeros of the energy probability distribution to study
the critical behavior of the system. The method is general with advantages over
most conventional techniques since it does not need to identify any order
parameter \emph{a priori}. The critical temperature and exponents can be
obtained with good precision. We apply the method to study the Fully Frustrated
Planar Rotator ($PR$) and the Anisotropic Heisenberg ($XY$) models in two
dimensions. We show that both models are in a new universality class with
$T_{PR}=0.45286(32)$ and $T_{XY}=0.36916(16)$ and the transition exponent
$\nu=0.824(30)$ ($\frac{1}{\nu}=1.22(4)$).
| cond-mat.stat-mech |
1807.02713 | Geometry of Spaces of Orthogonally Additive Polynomials on C(K) | We study the space of orthogonally additive $n$-homogeneous polynomials on
$C(K)$. There are two natural norms on this space. First, there is the usual
supremum norm of uniform convergence on the closed unit ball. As every
orthogonally additive $n$-homogeneous polynomial is regular with respect to the
Banach lattice structure, there is also the regular norm. These norms are
equivalent, but have significantly different geometric properties. We
characterise the extreme points of the unit ball for both norms, with different
results for even and odd degrees. As an application, we prove a Banach-Stone
theorem. We conclude with a classification of the exposed points.
| math.FA |
1807.02714 | Some free boundary problems recast as nonlocal parabolic equations | In this work we demonstrate that a class of some one and two phase free
boundary problems can be recast as nonlocal parabolic equations on a
submanifold. The canonical examples would be one-phase Hele Shaw flow, as well
as its two-phase analog. We also treat nonlinear versions of both one and two
phase problems. In the special class of free boundaries that are graphs over
$\mathbb{R}^d$, we give a precise characterization that shows their motion is
equivalent to that of a solution of a nonlocal (fractional), nonlinear
parabolic equation for functions on $\mathbb{R}^d$. Our main observation is
that the free boundary condition defines a nonlocal operator having what we
call the Global Comparison Property. A consequence of the connection with
nonlocal parabolic equations is that for free boundary problems arising from
translation invariant elliptic operators in the positive and negative phases,
one obtains, in a uniform treatment for all of the problems (one and two
phase), a propagation of modulus of continuity for viscosity solutions of the
free boundary flow.
| math.AP |
1807.02715 | Complexity of Scott Sentences | We give effective versions of some results on Scott sentences. We show that
if $\mathcal{A}$ has a computable $\Pi_\alpha$ Scott sentence, then the orbits
of all tuples are defined by formulas that are computable $\Sigma_\beta$ for
some $\beta <\alpha$. (This is an effective version of a result of
Montalb\'{a}n.) We show that if a countable structure $\mathcal{A}$ has a
computable $\Sigma_\alpha$ Scott sentence and one that is computable
$\Pi_\alpha$, then it has one that is computable $d$-$\Sigma_\beta$ for some
$\beta < \alpha$. (This is an effective version of a result of A. Miller.) We
also give an effective version of a result of D. Miller. Using the
non-effective results of Montalb\'{a}n and A. Miller, we show that a finitely
generated group has a $d$-$\Sigma_2$ Scott sentence iff the orbit of some (or
every) generating tuple is defined by a $\Pi_1$ formula. Using our effective
results, we show that for a computable finitely generated group, there is a
computable $d$-$\Sigma_2$ Scott sentence iff the orbit of some (every)
generating tuple is defined by a computable $\Pi_1$ formula.
| math.LO math.GR |
1807.02716 | A Deep-Learning-Based Geological Parameterization for History Matching
Complex Models | A new low-dimensional parameterization based on principal component analysis
(PCA) and convolutional neural networks (CNN) is developed to represent complex
geological models. The CNN-PCA method is inspired by recent developments in
computer vision using deep learning. CNN-PCA can be viewed as a generalization
of an existing optimization-based PCA (O-PCA) method. Both CNN-PCA and O-PCA
entail post-processing a PCA model to better honor complex geological features.
In CNN-PCA, rather than use a histogram-based regularization as in O-PCA, a new
regularization involving a set of metrics for multipoint statistics is
introduced. The metrics are based on summary statistics of the nonlinear filter
responses of geological models to a pre-trained deep CNN. In addition, in the
CNN-PCA formulation presented here, a convolutional neural network is trained
as an explicit transform function that can post-process PCA models quickly.
CNN-PCA is shown to provide both unconditional and conditional realizations
that honor the geological features present in reference SGeMS geostatistical
realizations for a binary channelized system. Flow statistics obtained through
simulation of random CNN-PCA models closely match results for random SGeMS
models for a demanding case in which O-PCA models lead to significant
discrepancies. Results for history matching are also presented. In this
assessment CNN-PCA is applied with derivative-free optimization, and a subspace
randomized maximum likelihood method is used to provide multiple posterior
models. Data assimilation and significant uncertainty reduction are achieved
for existing wells, and physically reasonable predictions are also obtained for
new wells. Finally, the CNN-PCA method is extended to a more complex
non-stationary bimodal deltaic fan system, and is shown to provide high-quality
realizations for this challenging example.
| stat.ML cs.CV cs.LG physics.geo-ph |
1807.02717 | Two-Dimensional Multiferroic Semiconductors with Coexisting
Ferroelectricity and Ferromagnetism | Low-dimensional multiferroicity, though highly scarce in nature, has
attracted great attention due to both fundamental and technological interests.
Using first-principles density functional theory, we show that ferromagnetism
and ferroelectricity can coexist in monolayer transition metal phosphorus
chalcogenides (TMPCs) - CuMP$_2$X$_6$ (M=Cr, V; X=S, Se). These van der Waals
layered materials represent a class of 2D multiferroic semiconductors that
simultaneously possess ferroelectric and ferromagnetic orders. In these
monolayer materials, Cu atoms spontaneously move away from the center atomic
plane, giving rise to nontrivial electric dipole moment along the plane normal.
In addition, their ferromagnetism originates from indirect exchange interaction
between Cr/V atoms, while their out-of-plane ferroelectricity suggests the
possibility of controlling electric polarization by external vertical electric
field. Monolayer semiconducting TMPCs thus provide a solid-state 2D materials
platform for realizing 2D nanoscale switches and memory devices patterned with
top and bottom electrodes.
| cond-mat.mtrl-sci |
1807.02718 | High-order, Dispersionless "Fast-Hybrid" Wave Equation Solver. Part I:
$\mathcal{O}(1)$ Sampling Cost via Incident-Field Windowing and Recentering | This paper proposes a frequency/time hybrid integral-equation method for the
time dependent wave equation in two and three-dimensional spatial domains.
Relying on Fourier Transformation in time, the method utilizes a fixed
(time-independent) number of frequency-domain integral-equation solutions to
evaluate, with superalgebraically-small errors, time domain solutions for
arbitrarily long times. The approach relies on two main elements, namely, 1) A
smooth time-windowing methodology that enables accurate band-limited
representations for arbitrarily-long time signals, and 2) A novel Fourier
transform approach which, in a time-parallel manner and without causing
spurious periodicity effects, delivers numerically dispersionless
spectrally-accurate solutions. A similar hybrid technique can be obtained on
the basis of Laplace transforms instead of Fourier transforms, but we do not
consider the Laplace-based method in the present contribution. The algorithm
can handle dispersive media, it can tackle complex physical structures, it
enables parallelization in time in a straightforward manner, and it allows for
time leaping---that is, solution sampling at any given time $T$ at
$\mathcal{O}(1)$-bounded sampling cost, for arbitrarily large values of $T$,
and without requirement of evaluation of the solution at intermediate times.
The proposed frequency-time hybridization strategy, which generalizes to any
linear partial differential equation in the time domain for which
frequency-domain solutions can be obtained (including e.g. the time-domain
Maxwell equations), and which is applicable in a wide range of scientific and
engineering contexts, provides significant advantages over other available
alternatives such as volumetric discretization, time-domain integral equations,
and convolution-quadrature approaches.
| math.NA cs.NA physics.comp-ph |
1807.02719 | Nothing But Net: Invading Android User Privacy Using Only Network Access
Patterns | We evaluate the power of simple networks side-channels to violate user
privacy on Android devices. Specifically, we show that, using blackbox network
metadata alone (i.e., traffic statistics such as transmission time and size of
packets) it is possible to infer several elements of a user's location and also
identify their web browsing history (i.e, which sites they visited). We do this
with relatively simple learning and classification methods and basic network
statistics. For most Android phones currently on the market, such process-level
traffic statistics are available for any running process, without any
permissions control and at fine-grained details, although, as we demonstrate,
even device-level statistics are sufficient for some of our attacks. In effect,
it may be possible for any application running on these phones to identify
privacy-revealing elements of a user's location, for example, correlating
travel with places of worship, point-of-care medical establishments, or
political activity.
| cs.CR |
1807.02720 | Competitive electrohydrodynamic and electrosolutal advection arrests
evaporation kinetics of droplets | The present article reports the hitherto unreported phenomenon of arrested
evaporation dynamics in pendent droplets in an electric field ambience. The
evaporation kinetics of pendant droplets of electrically conducting saline
solutions in the presence of a transverse, alternating electric field is
investigated experimentally. It has been observed that while increase of field
strength arrests the evaporation, increment in field frequency has the opposite
effect. The same has been explained on the solvation kinetics of the ions in
the polar water. Theoretical analysis reveals that change in surface tension
and diffusion driven evaporation model cannot predict the arrested or
decelerated evaporation. With the aid of Particle Image Velocimetry,
suppression of internal circulation velocity within the droplet is observed
under electric field stimulus, and this affects the evaporation rate directly.
A mathematical scaling model is proposed to quantify the effects of
electrohydrodynamic circulation, electrothermal and electro-solutal advection
on the evaporation kinetics of the droplet. The analysis encompasses major
governing parameters, viz. the thermal and solutal Marangoni numbers, the
Electrohydrodynamic number, the electro Prandtl and electro Schmidt numbers and
their respective contributions. It has been shown that the electrothermal
Marangoni effect is supressed by the electric field, leading to deteriorated
evaporation rates. Additionally, the electrosolutal Marangoni effect further
supresses the internal advection, which again arrests the evaporation rate by a
larger proportion. Stability analysis reveals that the electric body force
retards the stable internal circulation within such droplets and arrests
advection.
| physics.flu-dyn physics.app-ph |
1807.02721 | Diophantine problems and $p$-adic period mappings | We give an alternative proof of Faltings's theorem (Mordell's conjecture): a
curve of genus at least two over a number field has finitely many rational
points. Our argument utilizes the set-up of Faltings's original proof, but is
in spirit closer to the methods of Chabauty and Kim: we replace the use of
abelian varieties by a more detailed analysis of the variation of $p$-adic
Galois representations in a family of algebraic varieties. The key inputs into
this analysis are the comparison theorems of $p$-adic Hodge theory, and
explicit topological computations of monodromy.
By the same methods we show that, in sufficiently large dimension and degree,
the set of hypersurfaces in projective space, with good reduction away from a
fixed set of primes, is contained in a proper Zariski-closed subset of the
moduli space of all hypersurfaces. This uses in an essential way the
Ax--Schanuel property for period mappings, recently established by Bakker and
Tsimerman.
| math.NT math.AG |
1807.02722 | Wavelength tunable soliton rains in a nanotube-mode locked Tm-doped
fiber laser | We report soliton rains in a tuneable Tm-doped fiber laser mode locked by
carbon nanotubes. We also detect their second- and third-harmonic. We achieve a
tuneability of over 56nm, from 1877 to 1933nm, by introducing a
polarization-maintaining isolator and two in-line polarization controllers.
This makes our system promising as a tuneable filter for ultrafast
spectroscopy.
| physics.optics cond-mat.mes-hall physics.app-ph |
1807.02723 | Machine Learning for Reliable mmWave Systems: Blockage Prediction and
Proactive Handoff | The sensitivity of millimeter wave (mmWave) signals to blockages is a
fundamental challenge for mobile mmWave communication systems. The sudden
blockage of the line-of-sight (LOS) link between the base station and the
mobile user normally leads to disconnecting the communication session, which
highly impacts the system reliability. Further, reconnecting the user to
another LOS base station incurs high beam training overhead and critical
latency problems. In this paper, we leverage machine learning tools and propose
a novel solution for these reliability and latency challenges in mmWave MIMO
systems. In the developed solution, the base stations learn how to predict that
a certain link will experience blockage in the next few time frames using their
past observations of adopted beamforming vectors. This allows the serving base
station to proactively hand-over the user to another base station with a highly
probable LOS link. Simulation results show that the developed deep learning
based strategy successfully predicts blockage/hand-off in close to 95% of the
times. This reduces the probability of communication session disconnection,
which ensures high reliability and low latency in mobile mmWave systems.
| cs.IT eess.SP math.IT |
1807.02724 | Accretion Disk Reverberation Mapping of Active Galactic Nuclei at Wise
Observatory | We have started automatized photometric monitoring of active galactic nuclei
using the 46 cm telescope of the Wise Observatory in Israel. The telescope is
specially equipped with narrow-band filters to perform high-fidelity
photometric reverberation mapping of the accretion disk in V < 17 mag sources
up to z ~ 0.1. Here, we describe the capability and accuracy of the experiment,
and present the first science verification data obtained for the Seyfert 1
galaxy Mrk 279. With sub-diurnal sampling over more than two months, and
typical flux measurement uncertainties of $1\%$, we are able to measure
inter-band time-delays of up to ~2 days across the optical range.
| astro-ph.GA |