title:
Light Dark Matter in Superfluid Helium: Detection with Multi-excitation
  Production

abstract:
  We examine in depth a recent proposal to utilize superfluid helium for direct
detection of sub-MeV mass dark matter. For sub-keV recoil energies, nuclear
scattering events in liquid helium primarily deposit energy into long-lived
phonon and roton quasiparticle excitations. If the energy thresholds of the
detector can be reduced to the meV scale, then dark matter as light as ~MeV can
be reached with ordinary nuclear recoils. If, on the other hand, two or more
quasiparticle excitations are directly produced in the dark matter interaction,
the kinematics of the scattering allows sensitivity to dark matter as light as
~keV at the same energy resolution. We present in detail the theoretical
framework for describing excitations in superfluid helium, using it to
calculate the rate for the leading dark matter scattering interaction, where an
off-shell phonon splits into two or more higher-momentum excitations. We
validate our analytic results against the measured and simulated dynamic
response of superfluid helium. Finally, we apply this formalism to the case of
a kinetically mixed hidden photon in the superfluid, both with and without an
external electric field to catalyze the processes.

categories: hep-ph astro-ph.CO hep-ex physics.ins-det


title: ALMA Measurements of Circumstellar Material in the GQ Lup System

abstract:
  We present ALMA observations of the GQ Lup system, a young Sun-like star with
a substellar mass companion in a wide-separation orbit. These observations of
870 $\mu$m continuum and CO J=3-2 line emission with beam size $\sim0.3''$
($\sim45$ AU) resolve the disk of dust and gas surrounding the primary star, GQ
Lup A, and provide deep limits on any circumplanetary disk surrounding the
companion, GQ Lup b. The circumprimary dust disk is compact with a FWHM of
$59\pm12$ AU, while the gas has a larger extent with a characteristic radius of
$46.5\pm1.8$ AU. By forward-modeling the velocity field of the circumprimary
disk based on the CO emission, we constrain the mass of GQ Lup A to be $M_* =
(1.03\pm0.05)*(d/156\text{ pc})$ $M_\odot$, where $d$ is a known distance, and
determine that we view the disk at an inclination angle of
$60.5^\circ\pm0.5^\circ$ and a position angle of $346^\circ \pm1^\circ$. The
$3\sigma$ upper limit on the 870 $\mu$m flux density of any circumplanetary
disk associated with GQ Lup b of $<0.15$ mJy implies an upper limit on the dust
disk mass of $<0.04$ $M_\oplus$ for standard assumptions about optically thin
emission. We discuss proposed mechanisms for the formation of wide-separation
substellar companions given the non-detection of circumplanetary disks around
GQ Lup b and other similar systems.


title: The depletion of water during dispersal of planet-forming disk regions

abstract:
  We present a new velocity-resolved survey of 2.9 $\mu$m spectra of hot H$_2$O
and OH gas emission from protoplanetary disks, obtained with CRIRES at the VLT
($\Delta v \sim$ 3 km s$^{-1}$). With the addition of archival Spitzer-IRS
spectra, this is the most comprehensive spectral dataset of water vapor
emission from disks ever assembled. We provide line fluxes at 2.9-33 $\mu$m
that probe from disk radii of $\sim0.05$ au out to the region across the water
snow line. With a combined dataset for 55 disks, we find a new correlation
between H$_2$O line fluxes and the radius of CO gas emission as measured in
velocity-resolved 4.7 $\mu$m spectra (R$_{\rm co}$), which probes molecular
gaps in inner disks. We find that H$_2$O emission disappears from 2.9 $\mu$m
(hotter water) to 33 $\mu$m (colder water) as R$_{\rm co}$ increases and
expands out to the snow line radius. These results suggest that the infrared
water spectrum is a tracer of inside-out water depletion within the snow line.
It also helps clarifying an unsolved discrepancy between water observations and
models, by finding that disks around stars of M$_{\star}>1.5$ M$_\odot$
generally have inner gaps with depleted molecular gas content. We measure
radial trends in H$_2$O, OH, and CO line fluxes that can be used as benchmarks
for models to study the chemical composition and evolution of planet-forming
disk regions at 0.05-20 au. We propose that JWST spectroscopy of molecular gas
may be used as a probe of inner disk gas depletion, complementary to the larger
gaps and holes detected by direct imaging and by ALMA.


title:
ALMA observations of the nearby AGB star L2 Puppis - I. Mass of the
  central star and detection of a candidate planet

abstract:
  Six billion years from now, while evolving on the asymptotic giant branch
(AGB), the Sun will metamorphose from a red giant into a beautiful planetary
nebula. This spectacular evolution will impact the Solar System planets, but
observational confirmations of the predictions of evolution models are still
elusive as no planet orbiting an AGB star has yet been discovered. The nearby
AGB red giant L2 Puppis (d = 64 pc) is surrounded by an almost edge-on
circumstellar dust disk. We report new observations with ALMA at very high
angular resolution (18 x 15 mas) in band 7 (f ~ 350 GHz) that allow us to
resolve the velocity profile of the molecular disk. We establish that the gas
velocity profile is Keplerian within the central cavity of the dust disk,
allowing us to derive the mass of the central star L2 Pup A, mA = 0.659 +/-
0.011 +/- 0.041 Msun (+/- 6.6%). From evolutionary models, we determine that L2
Pup A had a near-solar main sequence mass, and is therefore a close analog of
the future Sun in 5 to 6 Gyr. The continuum map reveals the presence of a
secondary source (B) at a radius of 2 AU contributing fB/ fA = 1.3 +/- 0.1% of
the flux of the AGB star. L2 Pup B is also detected in CO emission lines at a
radial velocity of vB = 12.2 +/- 1.0 km/s. The close coincidence of the center
of rotation of the gaseous disk with the position of the continuum emission
from the AGB star allows us to constrain the mass of the companion to mB = 12
+/- 16 MJup. L2 Pup B is most likely a planet or low mass brown dwarf with an
orbital period around 5 years. Its continuum brightness and molecular emission
suggest that it may be surrounded by an extended molecular atmosphere or an
accretion disk. L2 Pup therefore emerges as a promising vantage point on the
distant future of our Solar System.


title: Implementing Ideas for Improving Software Citation and Credit

abstract:
  Improving software citation and credit continues to be a topic of interest
across and within many disciplines, with numerous efforts underway. In this
Birds of a Feather (BoF) session, we started with a list of actionable ideas
from last year's BoF and other similar efforts and worked alone or in small
groups to begin implementing them. Work was captured in a common Google
document; the session organizers will disseminate or otherwise put this
information to use in or for the community in collaboration with those who
contributed.


title:
Greybody factors for a nonminimally coupled scalar field in BTZ black
  hole background

abstract:
  In the present work we study the propagation of a probe nonminimally coupled
scalar field in BTZ black hole background. We find analytical expressions for
the reflection coefficient, the absorption cross-section, and the decay rate in
the strong coupling case, where the nonminimal coupling is larger than its
conformal value $\xi_{c}= 1/6$. Our main results are summarized in several
figures, in which we show how the behavior of the aforementioned quantities
depends on the parameters of the theory. Our findings show that i) the
reflection coefficient tends to zero only for a nonminimal coupling $\xi \geq
0.25$, and ii) in the zero angular-momentum case the greybody factor in the low
energy regime tends to a finite constant that generically does not coincide
with the area of the horizon of the black hole. There is, however, a special
case in which this holds.


title:
Compressible flow in front of an axisymmetric blunt object: analytic
  approximation and astrophysical implications

abstract:
  Compressible flows around blunt objects have diverse applications, but
current analytic treatments are inaccurate and limited to narrow parameter
regimes. We show that the gas-dynamic flow in front of an axisymmetric blunt
body is accurately derived analytically using a low order expansion of the
perpendicular gradients in terms of the parallel velocity. This reproduces both
subsonic and supersonic flows measured and simulated for a sphere, including
the transonic regime and the bow shock properties. Some astrophysical
implications are outlined, in particular for planets in the solar wind and for
clumps and bubbles in the intergalactic medium. The bow shock standoff distance
normalized by the obstacle curvature is $\sim 2/(3g)$ in the strong shock
limit, where $g$ is the compression ratio. For a subsonic Mach number $M$
approaching unity, the thickness $\delta$ of an initially weak, draped magnetic
layer is a few times larger than in the incompressible limit, with
amplification $\sim ({1+1.3M^{2.6}})/({3\delta})$.


title:
A halo model for cosmological neutral hydrogen: abundances and
  clustering

abstract:
  We extend the results of previous analyses towards constraining the abundance
and clustering of post-reionization ($z \sim 0-5$) neutral hydrogen (HI)
systems using a halo model framework. We work with a comprehensive HI dataset
including the small-scale clustering, column density and mass function of HI
galaxies at low redshifts, intensity mapping measurements at intermediate
redshifts and the UV/optical observations of Damped Lyman Alpha (DLA) systems
at higher redshifts. We use a Markov Chain Monte Carlo (MCMC) approach to
constrain the parameters of the best-fitting models, both for the HI-halo mass
relation and the HI radial density profile. We find that a radial exponential
profile results in a good fit to the low-redshift HI observations, including
the clustering and the column density distribution. The form of the profile is
also found to match the high-redshift DLA observations, when used in
combination with a three-parameter HI-halo mass relation and a redshift
evolution in the HI concentration. The halo model predictions are in good
agreement with the observed HI surface density profiles of low-redshift
galaxies, and the general trends in the the impact parameter and covering
fraction observations of high-redshift DLAs. We provide convenient tables
summarizing the best-fit halo model predictions.


title:
Host galaxies of luminous z$\sim$0.6 quasars: Major mergers are not
  prevalent at the highest AGN luminosities

abstract:
  Galaxy interactions are thought to be one of the main triggers of Active
Galactic Nuclei (AGN), especially at high luminosities, where the accreted gas
mass during the AGN lifetime is substantial. Evidence for a connection between
mergers and AGN, however, remains mixed. Possible triggering mechanisms remain
particularly poorly understood for luminous AGN, which are thought to require
triggering by major mergers, rather than secular processes. We analyse the host
galaxies of a sample of 20 optically and X-ray selected luminous AGN
(log($L_{bol}$ [erg/s]) $>$ 45) at z $\sim$ 0.6 using HST WFC3 data in the
F160W/H band. 15/20 sources have resolved host galaxies. We create a control
sample of mock AGN by matching the AGN host galaxies to a control sample of
non-AGN galaxies. Visual signs of disturbances are found in about 25% of
sources in both the AGN hosts and control galaxies. Using both visual
classification and quantitative morphology measures, we show that the levels of
disturbance are not enhanced when compared to a matched control sample. We find
no signs that major mergers play a dominant role in triggering AGN at high
luminosities, suggesting that minor mergers and secular processes dominate AGN
triggering up to the highest AGN luminosities. The upper limit on the enhanced
fraction of major mergers is $\leqslant$20%. While major mergers might increase
the incidence of (luminous AGN), they are not the prevalent triggering
mechanism in the population of unobscured AGN.


title:
Dipole anisotropy in cosmic electrons and positrons: inspection on local
  sources

abstract:
  The cosmic electrons and positrons have been measured with unprecedented
statistics up to several hundreds GeV, thus permitting to explore the role that
close single sources can have in shaping the flux at different energies. In the
present analysis, we consider electrons and positrons in cosmic rays to be
produced by spallations of hadron fluxes with the interstellar medium, by a
smooth Supernova Remnant (SNR) population, by all the ATNF catalog pulsars, and
by few discrete, local SNRs. We test several source models on the $e^++e^-$ and
$e^+$ AMS-02 flux data. For the configurations compatible with the data, we
compute the dipole anisotropy in $e^++e^-$, $e^+$, $e^+/e^-$ from single
sources. Our study includes a dedicated analysis to the Vela SNR. We show that
Fermi-LAT present data on dipole anisotropy of $e^++e^-$ start to explore some
of the models for the Vela SNR selected by AMS-02 flux data. We also
investigate how the observed anisotropy could result from a combination of
local sources. Our analysis shows that the search of anisotropy in the lepton
fluxes up to TeV energies can be an interesting tool for the inspection of
properties of close SNRs, complementary to the high precision flux data.


title: Signatures of Dirac cones in a DMRG study of the Kagome Heisenberg model

abstract:
  The antiferromagnetic spin-$1/2$ Heisenberg model on a kagome lattice is one
of the most paradigmatic models in the context of spin liquids, yet the precise
nature of its ground state is not understood. We use large scale density matrix
normalization group simulations (DMRG) on infinitely long cylinders and find
indications for the formation of a gapless Dirac spin liquid. First, we use
adiabatic flux insertion to demonstrate that the spin gap is much smaller than
estimated from previous DMRG simulation. Second, we find that the momentum
dependent excitation spectrum, as extracted from the DMRG transfer matrix,
exhibits Dirac cones that match those of a $\pi$-flux free fermion model (the
parton mean-field ansatz of a $U(1)$ Dirac spin liquid)


title:
Kepler-11 is a Solar Twin: Revising the Masses and Radii of Benchmark
  Planets Via Precise Stellar Characterization

abstract:
  The six planets of the Kepler-11 system are the archetypal example of a
population of surprisingly low-density transiting planets revealed by the
Kepler mission. We have determined the fundamental parameters and chemical
composition of the Kepler-11 host star to unprecedented precision using an
extremely high quality spectrum from Keck-HIRES (R$\simeq$67,000, S/N per
pixel$\simeq$260 at 600 nm). Contrary to previously published results, our
spectroscopic constraints indicate that Kepler-11 is a young main-sequence
solar twin. The revised stellar parameters and new analysis raise the densities
of the Kepler-11 planets by between 20-95% per planet, making them more typical
of the emerging class of "puffy" close-in exoplanets. We obtain photospheric
abundances of 22 elements and find that Kepler-11 has an abundance pattern
similar to that of the Sun with a slightly higher overall metallicity. We
additionally analyze the Kepler lightcurves using a photodynamical model and
discuss the tension between spectroscopic and transit/TTV-based stellar density
estimates.


title:
A new method to reduce the statistical and systematic uncertainty of
  chance coincidence backgrounds measured with waveform digitizers

abstract:
  A new method for measuring chance-coincidence backgrounds during the
collection of coincidence data is presented. The method relies on acquiring
data with near-zero dead time, which is now realistic due to the increasing
deployment of flash electronic-digitizer (waveform digitizer) techniques. An
experiment designed to use this new method is capable of acquiring more
coincidence data, and a much reduced statistical fluctuation of the measured
background. A statistical analysis is presented, and used to derive a figure of
merit for the new method. Factors of four improvement over other analyses are
realistic. The technique is illustrated with preliminary data taken as part of
a program to make new measurements of the prompt fission neutron spectra at Los
Alamos Neutron Science Center. It is expected that the these measurements will
occur in a regime where the maximum figure of merit will be exploited.


title:
Using LSTM recurrent neural networks for monitoring the LHC
  superconducting magnets

abstract:
  The superconducting LHC magnets are coupled with an electronic monitoring
system which records and analyses voltage time series reflecting their
performance. A currently used system is based on a range of preprogrammed
triggers which launches protection procedures when a misbehavior of the magnets
is detected. All the procedures used in the protection equipment were designed
and implemented according to known working scenarios of the system and are
updated and monitored by human operators.
  This paper proposes a novel approach to monitoring and fault protection of
the Large Hadron Collider (LHC) superconducting magnets which employs
state-of-the-art Deep Learning algorithms. Consequently, the authors of the
paper decided to examine the performance of LSTM recurrent neural networks for
modeling of voltage time series of the magnets. In order to address this
challenging task different network architectures and hyper-parameters were used
to achieve the best possible performance of the solution. The regression
results were measured in terms of RMSE for different number of future steps and
history length taken into account for the prediction. The best result of
RMSE=0.00104 was obtained for a network of 128 LSTM cells within the internal
layer and 16 steps history buffer.


title:
On topology optimization of acoustic metamaterial lattices for locally
  resonant bandgaps of flexural waves

abstract:
  Optimized topology of bi-material acoustic metamaterial lattice plates is
studied for maximized locally resonant bandgap of flexural guided waves.
Optimized layout of the two relatively stiff and compliant material phases in
the design domain is explored, free from any restrictions on the topology and
shape of the relevant domains. Multiobjective optimization is performed through
which maximized effective stiffness or minimized overall mass of the bandgap
topology is additionally ensured. Extreme and selected intermediate optimized
topologies of Pareto fronts are presented and their bandgap efficiencies and
effective stiffness are compared. The bi-material constitution of selected
topologies are further altered and modal band structure of resultant
multilateral and porous designs are evaluated. Novel, core-shell like, locally
resonant bandgaps are introduced. It is shown that how the bandgap efficiency
and structural mass and/or stiffness can be optimized through optimized
microstructural design of the matrix and the resonating core domains.


title:
Both Inter- and Intramolecular Coupling of O-H Groups Determine the
  Vibrational Response of the Water/Air Interface

abstract:
  Vibrational coupling is relevant not only for dissipation of excess energy
after chemical reactions but also for elucidating molecular structure and
dynamics. It is particularly important for OH stretch vibrational spectra of
water, for which it is known that in bulk both intra- and intermolecular
coupling alter the intensity and line shape of the spectra. In contrast with
bulk, the unified picture of the inter/intra-molecular coupling of OH groups at
the water-air interface has been lacking. Here, combining sum-frequency
generation experiments and simulation for isotopically diluted water and
alcohols, we unveil effects of inter- and intramolecular coupling on the
vibrational spectra of interfacial water. Our results show that both inter- and
intramolecular coupling contribute to the OH stretch vibrational response of
the neat H2O surface, with intramolecular coupling generating a double-peak
feature, while the intermolecular coupling induces a significant red shift in
the OH stretch response.


title: Shell and explosive hydrogen burning

abstract:
  The nucleosynthesis of light elements, from helium up to silicon, mainly
occurs in Red Giant and Asymptotic Giant Branch stars and Novae. The relative
abundances of the synthesized nuclides critically depend on the rates of the
nuclear processes involved, often through non-trivial reaction chains, combined
with complex mixing mechanisms. In this review, we summarize the contributions
made by LUNA experiments in furthering our understanding of nuclear reaction
rates necessary for modeling nucleosynthesis in AGB stars and Novae explosions.


title: Spikes as regularizers

abstract:
  We present a confidence-based single-layer feed-forward learning algorithm
SPIRAL (Spike Regularized Adaptive Learning) relying on an encoding of
activation spikes. We adaptively update a weight vector relying on confidence
estimates and activation offsets relative to previous activity. We regularize
updates proportionally to item-level confidence and weight-specific support,
loosely inspired by the observation from neurophysiology that high spike rates
are sometimes accompanied by low temporal precision. Our experiments suggest
that the new learning algorithm SPIRAL is more robust and less prone to
overfitting than both the averaged perceptron and AROW.


title:
Mapping and Classifying Molecules from a High-Throughput Structural
  Database

abstract:
  High-throughput computational materials design promises to greatly accelerate
the process of discovering new materials and compounds, and of optimizing their
properties. The large databases of structures and properties that result from
computational searches, as well as the agglomeration of data of heterogeneous
provenance leads to considerable challenges when it comes to navigating the
database, representing its structure at a glance, understanding
structure-property relations, eliminating duplicates and identifying
inconsistencies. Here we present a case study, based on a data set of
conformers of amino acids and dipeptides, of how machine-learning techniques
can help addressing these issues. We will exploit a recently developed strategy
to define a metric between structures, and use it as the basis of both
clustering and dimensionality reduction techniques showing how these can help
reveal structure-property relations, identify outliers and inconsistent
structures, and rationalise how perturbations (e.g. binding of ions to the
molecule) affect the stability of different conformers.

categories: physics.chem-ph cond-mat.mtrl-sci physics.bio-ph physics.data-an


title:
Bifurcation analysis of torsional micromirror actuated by electrostatic
  forces

abstract:
  In this paper, static and dynamic behavior of an electro statically actuated
torsional micro actuator is studied. The micro actuator is composed of a micro
mirror and two torsional beams, which are excited with two electrodes. Unlike
the traditional micro actuators, the electrostatic force exerted to both side
of micro mirror, so the model is exposed to a DC voltage applied from the
ground electrodes. The static governing equation of the torsional micro
actuator is derived and the relation between rotation angle and the driving
voltage is determined. Local and global bifurcation analysis is performed,
considering torsional characteristics of the micro-beams. By solving static
deflection equation, the fixed points of the actuator are obtained. Critical
values of the applied voltage leading to qualitative changes in the micro
actuator behavior through a saddle node or pitchfork bifurcations for different
spatial condition are obtained. Furthermore the effects of different gap and
electrode sizes as well as beam lengths on the dynamic behavior are
investigated. It is shown that increasing the applied voltage leads the
structure to an unstable condition by undergoing to saddle node and pitchfork
bifurcations when the voltages ratio is zero and one, respectively.


title: A stochastic approach to colloidal particle collision/agglomeration

abstract:
  Colloidal particles that experience perfectly elastic collisions can be
modelled using Langevin processes with specular reflection conditions. The
article presents a discretisation scheme and offers a conjecture for the rate
of convergence of the bias produced. Numerically, these conjectures are
confirmed for the specular reflection scheme but also for the absorption
scheme, which models perfect agglomeration.


title:
Geometric Controllability of The Purcell's Swimmer and its Symmetrized
  Cousin

abstract:
  We analyse weak and strong controllability notions for the locomotion of the
3-link Purcell's swimmer, the simplest possible swimmer at low Reynolds number
from a geometric framework. After revisiting a purely kinematic form of the
equations, we apply an extension of Chow's theorem to analyze controllability
in the strong and weak sense. Further, the connection form for the symmetric
version of the Purcell's swimmer is derived, based on which, the
controllability analysis utilizing the Abelian nature of the structure group is
presented. The novelty in our approach is the usage of geometry and the
principal fiber bundle structure of the configuration manifold of the system to
arrive at strong and weak controllability notions.


title:
Inverse Temperature Dependence of Nuclear Quantum Effects in DNA Base
  Pairs

abstract:
  Despite the inherently quantum mechanical nature of hydrogen bonding, it is
unclear how nuclear quantum effects (NQEs) alter the strengths of hydrogen
bonds. With this in mind, we use ab initio path integral molecular dynamics to
determine the absolute contribution of NQEs to the binding in DNA base pair
complexes, arguably the most important hydrogen-bonded systems of all. We find
that depending on the temperature, NQEs can either strengthen or weaken the
binding within the hydrogen-bonded complexes. As a somewhat counterintuitive
consequence, NQEs can have a smaller impact on hydrogen bond strengths at
cryogenic temperatures than at room temperature. We rationalize this in terms
of a competition of NQEs between low-frequency and high-frequency vibrational
modes. Extending this idea, we also propose a simple model to predict the
temperature dependence of NQEs on hydrogen bond strengths in general.


title: Sub 100-ps dynamics of the anomalous Hall effect at THz frequencies

abstract:
  We report about the anomalous Hall effect in 4f 3d metallic alloys measured
using terahertz time-domain spectroscopy. The strength of the observed
terahertz spin-dependent transport phenomenon is in good agreement with
expectations based on electronic transport measurements. Employing this effect,
we succeeded to reveal ultrafast dynamics of the anomalous Hall effect which
accompanies the sub-100 picosecond optically induced magnetization reversal in
a GdFeCo alloy. The experiments demonstrate the ability to control currents at
terahertz frequencies in spintronic devices magnetically and ultrafast.


title:
Compact and versatile laser system for polarization-sensitive stimulated
  Raman spectroscopy

abstract:
  We demonstrate a compact and versatile laser system for stimulated Raman
spectroscopy (SRS). The system is based on a tunable continuous wave (CW) probe
laser combined with a home-built semi-monolithic nanosecond pulsed pump Nd:YVO4
laser at 1064 nm. The CW operation of the probe laser offers narrow linewidth,
low noise and the advantage that temporal synchronization with the pump is not
required. The laser system enables polarization-sensitive stimulated Raman
spectroscopy (PS-SRS) with fast high resolution measurement of the
depolarization ratio by simultaneous detection of Raman scattered light in
orthogonal polarizations, thus providing information about the symmetry of the
Raman-active vibrational modes. Measurements of the depolarization ratios of
the carbon-hydrogen (CH) stretching modes in two different polymer samples in
the spectral range of 2825-3025 cm-1 were performed. Raman spectra are obtained
at a sweep rate of 20 nm/s (84 cm-1/s) with a resolution of 0.65 cm-1. A
normalization method is introduced for the direct comparison of the
simultaneously acquired orthogonal polarized Raman spectra.


title:
Finite Element Modeling of Metasurfaces with Generalized Sheet
  Transition Conditions

abstract:
  A modeling of metasurfaces in the finite element method (FEM) based on
generalized sheet transition conditions (GSTCs) is presented. The
discontinuities in electromagnetic fields across a metasurface as represented
by the GSTC are modeled by assigning nodes to both sides of the metasurface.
The FEM-GSTC formulation in both 1D and 2D domains is derived and implemented.
The method is extended to handle more general bianistroptic metasurfaces. The
formulations are validated by several illustrative examples.


title: Curvatronics with bilayer graphene in an effective $4D$ spacetime

abstract:
  We show that in AB stacked bilayer graphene low energy excitations around the
semimetallic points are described by massless, four dimensional Dirac fermions.
There is an effective reconstruction of the 4 dimensional spacetime, including
in particular the dimension perpendicular to the sheet, that arises dynamically
from the physical graphene sheet and the interactions experienced by the
carriers. The effective spacetime is the Eisenhart-Duval lift of the dynamics
experienced by Galilei invariant L\'evy-Leblond spin $\frac{1}{2}$ particles
near the Dirac points. We find that changing the intrinsic curvature of the
bilayer sheet induces a change in the energy level of the electronic bands,
switching from a conducting regime for negative curvature to an insulating one
when curvature is positive. In particular, curving graphene bilayers allows
opening or closing the energy gap between conduction and valence bands, a key
effect for electronic devices. Thus using curvature as a tunable parameter
opens the way for the beginning of curvatronics in bilayer graphene.


title: Minisuperspace models of discrete systems

abstract:
  A discrete quantum spin system is presented in which several modern methods
of canonical quantum gravity can be tested with promising results. In
particular, features of interacting dynamics are analyzed with an emphasis on
homogeneous configurations and the dynamical building-up and stability of
long-range correlations. Different types of homogeneous minisuperspace models
are introduced for the system, including one based on condensate states, and
shown to capture different aspects of the discrete system. They are evaluated
with effective methods and by means of continuum limits, showing good agreement
with operator calculations whenever the latter are available. As a possibly
quite general result, it is concluded that an analysis of the building-up of
long-range correlations in discrete systems requires non-perturbative solutions
of the dynamical equations. Some questions related to stability can be analyzed
perturbatively, but suggest that matter couplings may be relevant for this
question in the context of quantum cosmology.


title:
Reinforcement Learning through Asynchronous Advantage Actor-Critic on a
  GPU

abstract:
  We introduce a hybrid CPU/GPU version of the Asynchronous Advantage
Actor-Critic (A3C) algorithm, currently the state-of-the-art method in
reinforcement learning for various gaming tasks. We analyze its computational
traits and concentrate on aspects critical to leveraging the GPU's
computational power. We introduce a system of queues and a dynamic scheduling
strategy, potentially helpful for other asynchronous algorithms as well. Our
hybrid CPU/GPU version of A3C, based on TensorFlow, achieves a significant
speed up compared to a CPU implementation; we make it publicly available to
other researchers at https://github.com/NVlabs/GA3C .


title: Field Patterns: A New Mathematical Object

abstract:
  Field patterns occur in space-time microstructures such that a disturbance
propagating along a characteristic line does not evolve into a cascade of
disturbances, but rather concentrates on a pattern of characteristic lines.
This pattern is the field pattern. In one spatial direction plus time, the
field patterns occur when the slope of the characteristics is, in a sense,
commensurate with the space-time microstructure. Field patterns with different
spatial shifts do not generally interact, but rather evolve as if they live in
separate dimensions, as many dimensions as the number of field patterns.
Alternatively one can view a collection as a multicomponent potential, with as
many components as the number of field patterns. Presumably if one added a tiny
nonlinear term to the wave equation one would then see interactions between
these field patterns in the multidimensional space that one can consider them
to live, or between the different field components of the multicomponent
potential if one views them that way. As a result of PT-symmetry many of the
complex eigenvalues of an appropriately defined transfer matrix have unit norm
and hence the corresponding eigenvectors correspond to propagating modes. There
are also modes that blow up exponentially with time.


title:
Why RLC realizations of certain impedances need many more energy storage
  elements than expected

abstract:
  It is a significant and longstanding puzzle that the resistor, inductor,
capacitor (RLC) networks obtained by the established RLC realization procedures
appear highly non-minimal from the perspective of linear systems theory.
Specifically, each of these networks contains significantly more energy storage
elements than the McMillan degree of its impedance, and possesses a non-minimal
state-space representation whose states correspond to the inductor currents and
capacitor voltages. Despite this apparent non-minimality, there have been no
improved algorithms since the 1950s, with the concurrent discovery by Reza,
Pantell, Fialkow and Gerst of a class of networks (the RPFG networks), which
are a slight simplification of the Bott-Duffin networks. Each RPFG network
contains more than twice as many energy storage elements as the McMillan degree
of its impedance, yet it has never been established if all of these energy
storage elements are necessary. In this paper, we present some newly discovered
alternatives to the RPFG networks. We then prove that the RPFG networks, and
these newly discovered networks, contain the least possible number of energy
storage elements for realizing certain positive-real functions. In other words,
all RLC networks which realize certain impedances contain more than twice the
expected number (McMillan degree) of energy storage elements.


title: Flag Descents and Eulerian Polynomials for Wreath Product Quotients

abstract:
  We investigate the $\alpha$-colored Eulerian polynomials and a notion of
descents introduced in a recent paper of Hedmark and show that such polynomials
can be computed as a polynomial encoding descents computed over a quotient of
the wreath product $\mathbb{Z}_\alpha\wr\mathfrak{S}_n$. Moreover, we consider
the flag descent statistic computed over this same quotient and find that the
flag Eulerian polynomial remains palindromic. We prove that the flag descent
polynomial is palindromic over this same quotient by giving a combinatorial
proof that the flag descent statistic is symmetrically distributed over the
collection of colored permutations with fixed last color by way of a new
combinatorial tool, the colored winding number of a colored permutation. We
conclude with some conjectures, observations, and open questions.


title:
Convection onset induced by a density stratification whose unstable part
  is infinitely thin

abstract:
  We consider a vertical cavity composed of two chambers separated by a
retractable thermally insulated thin membrane. The upper and lower chambers are
filled with an incompressible Boussinesq fluid and maintained at temperatures
$T_2$ and $T_1>T_2$, respectively by two separate heaters. Upon retraction of
the membrane, the two fluid masses form an unstably stratified configuration
with cold and heavy fluid overlying a warmer and lighter fluid and separated by
a non-free interface across which there is a jump in the density. The aim of
this paper is to determine the threshold conditions for convection onset and
associated fluid flow patterns induced by this discontinuous density
stratification. We find that the discontinuity of the density profile leads to
the appearance of temperature perturbation iso-contours that have a lens shape
instead of the classical oval shape and that the mixing is confined to near the
location of the density jump with stagnant and isothermal fluid away from the
discontinuity. We derive the flux conditions at the discontinuity interface and
show that it acts like a heat sink for both the lower and upper fluid layers.
Moreover, we put forth the dependence of the stability threshold parameters for
convection onset on the locus of the density discontinuity. The experimental
set-up suggested in the paper can be used to test the predictions of the
present theory.


title: A solution of the maximality problem for one-parameter dynamical systems

abstract:
  We prove a maximality theorem for one-parameter dynamical systems including
multiplier one-parameter dynamical systems. Our main result is new even for
one-parameter actions on commutative multiplier algebras including the algebra
of bounded continuous functions on the set of real numbers acted upon by
translations. The methods we develop and use in our characterization of
maximality include harmonic analysis, topological vector spaces and operator
algebra techniques.


title:
Reply to "Rebuttal of "The multicaloric effect in multiferroic
  materials", [arXiv:1602.04238]"

abstract:
  Vopson first published the multicaloric effect in multiferroics in 2012.
However, a closer examination of the multicaloric effect and its derivation
leads to a contradiction, in which the predicted changes in one of the order
phase at a constant applied field are due to the excitation by the same field.
This apparent paradox has triggered the publication of Rebuttal of The
multicaloric effect in multiferroic materials by Starkov et al. This article is
the response to their rebuttal.


title:
Phase-driven collapse of the Cooper condensate in a nanosized
  superconductor

abstract:
  Superconductivity can be understood in terms of a phase transition from an
uncorrelated electron gas to a condensate of Cooper pairs in which the relative
phases of the constituent electrons are coherent over macroscopic length
scales. The degree of correlation is quantified by a complex-valued order
parameter, whose amplitude is proportional to the strength of the pairing
potential in the condensate. Supercurrent-carrying states are associated with
non-zero values of the spatial gradient of the phase. The pairing potential and
several physical observables of the Cooper condensate can be manipulated by
means of temperature, current bias, dishomogeneities in the chemical
composition or application of a magnetic field. Here we show evidence of
complete suppression of the energy gap in the local density of quasiparticle
states (DOS) of a superconducting nanowire upon establishing a phase difference
equal to pi over a length scale comparable to the superconducting coherence
length. These observations are consistent with a complete collapse of the
pairing potential in the center of the wire, in accordance with theoretical
modeling based on the quasiclassical theory of superconductivity in diffusive
systems. Our spectroscopic data, fully exploring the phase-biased states of the
condensate, highlight the profound effect that extreme phase gradients exert on
the amplitude of the pairing potential. Moreover, the sharp magnetic response
observed near the onset of the superconducting gap collapse regime can be
exploited to realize ultra-low noise magnetic flux detectors.


title: Weak metacirculants of odd prime power order

abstract:
  Metacirculants are a basic and well-studied family of vertex-transitive
graphs, and weak metacirculants are generalizations of them. A graph is called
a weak metacirculant if it has a vertex-transitive metacyclic automorphism
group. This paper is devoted to the study of weak metacirculants with odd prime
power order. We first prove that a weak metacirculant of odd prime power order
is a metacirculant if and only if it has a vertex-transitive split metacyclic
automorphism group. We then prove that for any odd prime $p$ and integer
$\ell\geq 4$, there exist weak metacirculants of order $p^\ell$ which are
Cayley graphs but not Cayley graphs of any metacyclic group; this answers a
question in Li et al. (2013). We construct such graphs explicitly by
introducing a construction which is a generalization of generalized Petersen
graphs. Finally, we determine all smallest possible metacirculants of odd prime
power order which are Cayley graphs but not Cayley graphs of any metacyclic
group.


title:
Deep Clustering and Conventional Networks for Music Separation: Stronger
  Together

abstract:
  Deep clustering is the first method to handle general audio separation
scenarios with multiple sources of the same type and an arbitrary number of
sources, performing impressively in speaker-independent speech separation
tasks. However, little is known about its effectiveness in other challenging
situations such as music source separation. Contrary to conventional networks
that directly estimate the source signals, deep clustering generates an
embedding for each time-frequency bin, and separates sources by clustering the
bins in the embedding space. We show that deep clustering outperforms
conventional networks on a singing voice separation task, in both matched and
mismatched conditions, even though conventional networks have the advantage of
end-to-end training for best signal approximation, presumably because its more
flexible objective engenders better regularization. Since the strengths of deep
clustering and conventional network architectures appear complementary, we
explore combining them in a single hybrid network trained via an approach akin
to multi-task learning. Remarkably, the combination significantly outperforms
either of its components.


title:
Microscopic Mechanism and Kinetics of Ice Formation at Complex
  Interfaces: Zooming in on Kaolinite

abstract:
  Most ice in nature forms thanks to impurities which boost the exceedingly low
nucleation rate of pure supercooled water. However, the microscopic details of
ice nucleation on these substances remain largely unknown. Here, we have
unraveled the molecular mechanism and the kinetics of ice formation on
kaolinite, a clay mineral playing a key role in climate science. We find that
the formation of ice at strong supercooling in the presence of this clay is
twenty orders of magnitude faster than homogeneous freezing. The critical
nucleus is substantially smaller than that found for homogeneous nucleation
and, in contrast to the predictions of classical nucleation theory (CNT), it
has a strong 2D character. Nonetheless, we show that CNT describes correctly
the formation of ice at this complex interface. Kaolinite also promotes the
exclusive nucleation of hexagonal ice, as opposed to homogeneous freezing where
a mixture of cubic and hexagonal polytypes is observed.


title:
Cores of imprimitive symmetric graphs of order a product of two distinct
  primes

abstract:
  A retract of a graph $\Gamma$ is an induced subgraph $\Psi$ of $\Gamma$ such
that there exists a homomorphism from $\Gamma$ to $\Psi$ whose restriction to
$\Psi$ is the identity map. A graph is a core if it has no nontrivial retracts.
In general, the minimal retracts of a graph are cores and are unique up to
isomorphism; they are called the core of the graph. A graph $\Gamma$ is
$G$-symmetric if $G$ is a subgroup of the automorphism group of $\Gamma$ that
is transitive on the vertex set and also transitive on the set of ordered pairs
of adjacent vertices. If in addition the vertex set of $\Gamma$ admits a
nontrivial partition that is preserved by $G$, then $\Gamma$ is an imprimitive
$G$-symmetric graph. In this paper cores of imprimitive symmetric graphs
$\Gamma$ of order a product of two distinct primes are studied. In many cases
the core of $\Gamma$ is determined completely. In other cases it is proved that
either $\Gamma$ is a core or its core is isomorphic to one of two graphs, and
conditions on when each of these possibilities occurs is given.


title: An Observation on Initially $\kappa $-Compact Spaces

abstract:
  In \cite{Chaber}, Chaber has proved that countably compact spaces with a
quasi $G_{\delta }$-diagonal are compact. We prove that initially $\kappa $%
-compact spaces with a quasi $G_{\kappa }$-diagonal are compact, for any
infinite cardinal $\kappa .


title: Twisted Higher Smooth Torsion

abstract:
  In this paper we extend Badzioch's, Dorabiala's, and Williams' definition of
cohomological higher smooth torsion to a twisted cohomological higher torsion
invariant. Additionally, we show that this still satisfies geometric additivity
and transfer, and will also satisfy additivity and transfer for coefficients.


title: Weak Gravity Conjecture and Extremal Black Holes

abstract:
  Motivated by the desire to improve our understanding of the Weak Gravity
Conjecture, we compute the one-loop correction of charged particles to the
geometry and entropy of extremal black holes in 4d. We find that fermion loops
provide evidence for the necessity of the `magnetic' WGC cutoff. Moreover, for
a certain regime of black holes, we find entropy corrections with unusual area
scaling. The corrections are reduced when supersymmetry is present, and
disappear in ${\cal N}=4$ supergravity. We further provide some speculative
arguments that in a theory with only sub-extremal particles, classical
Reissner-Nordstrom black holes actually possess an infinite microcanonical
entropy, though only a finite amount is visible to an external observer.


title:
A Novel Single-Source Surface Integral Method to Compute Scattering from
  Dielectric Objects

abstract:
  Using the traditional surface integral methods, the computation of scattering
from a dielectric object requires two equivalent current densities on the
boundary of the dielectric. In this paper, we present an approach that requires
only a single current density. Our method is based on a surface admittance
operator and is applicable to dielectric bodies of arbitrary shape. The
formulation results in four times lower memory consumption and up to eight
times lower time to solve the linear system than the traditional PMCHWT
formulation. Numerical results demonstrate that the proposed technique is as
accurate as the PMCHWT formulation.


title: Obstructions to lifting abelian subalgebras of corona algebras

abstract:
  Let $A$ be a non-commutative, non-unital $\mathrm{C}^\ast$-algebra. Given a
set of commuting positive elements in the corona algebra $Q(A)$, we study some
obstructions to the existence of a commutative lifting of such set to the
multiplier algebra $M(A)$. Our focus are the obstructions caused by the size of
the collection we want to lift. It is known that no obstacles show up when
lifting a countable family of commuting projections, or of pairwise orthogonal
positive elements. However, this is not the case for larger collections. We
prove in fact that for every primitive, non-unital, $\sigma$-unital
$\mathrm{C}^\ast$-algebra $A$, there exists an uncountable set of pairwise
orthogonal positive elements in $Q(A)$ such that no uncountable subset of it
can be lifted to a set of commuting elements of $M(A)$. Moreover, the positive
elements in $Q(A)$ can be chosen to be projections if $A$ has real rank zero.


title:
Merging symmetry projection methods with coupled cluster theory: Lessons
  from the Lipkin model Hamiltonian

abstract:
  Coupled cluster and symmetry projected Hartree-Fock are two central paradigms
in electronic structure theory. However, they are very different. Single
reference coupled cluster is highly successful for treating weakly correlated
systems, but fails under strong correlation unless one sacrifices good quantum
numbers and works with broken-symmetry wave functions, which is unphysical for
finite systems. Symmetry projection is effective for the treatment of strong
correlation at the mean-field level through multireference non-orthogonal
configuration interaction wavefunctions, but unlike coupled cluster, it is
neither size extensive nor ideal for treating dynamic correlation. We here
examine different scenarios for merging these two dissimilar theories. We carry
out this exercise over the integrable Lipkin model Hamiltonian, which despite
its simplicity, encompasses non-trivial physics for degenerate systems and can
be solved via diagonalization for a very large number of particles. We show how
symmetry projection and coupled cluster doubles individually fail over
different correlation limits, whereas models that merge these two theories are
highly successful over the entire phase diagram. Despite the simplicity of the
Lipkin Hamiltonian, the lessons learned in this work will be useful for
building an ab initio symmetry projected coupled cluster theory that we expect
to be accurate over the weakly and strongly correlated limits, as well as the
recoupling regime.


title: Electron backscattering in a cavity: ballistic and coherent effects

abstract:
  Numerous experimental and theoretical studies have focused on low-dimensional
systems locally perturbed by the biased tip of a scanning force microscope. In
all cases either open or closed weakly gate-tunable nanostructures have been
investigated, such as quantum point contacts, open or closed quantum dots, etc.
We study the behaviour of the conductance of a quantum point contact with a
gradually forming adjacent cavity in series under the influence of a scanning
gate. Here, an initially open quantum point contact system gradually turns into
a closed cavity system. We observe branches and interference fringes known from
quantum point contacts coexisting with irregular conductance fluctuations.
Unlike the branches, the fluctuations cover the entire area of the cavity. In
contrast to previous studies, we observe and investigate branches under the
influence of the confining stadium potential, which is gradually built up. We
find that the branches exist only in the area surrounded by cavity top gates.
As the stadium shrinks, regular fringes originate from tip-induced
constrictions leading to quantized conduction. In addition, we observe arc-like
areas reminiscent of classical electron trajectories in a chaotic cavity. We
also argue that electrons emanating from the quantum point contact spread out
like a fan leaving branch-like regions of enhanced backscattering.


title:
A Deep Proper Motion Catalog Within the Sloan Digital Sky Survey
  Footprint. II. The White Dwarf Luminosity Function

abstract:
  A catalog of 8472 white dwarf (WD) candidates is presented, selected using
reduced proper motions from the deep proper motion catalog of Munn et al. 2014.
Candidates are selected in the magnitude range 16 < r < 21.5 over 980 square
degrees, and 16 < r < 21.3 over an additional 1276 square degrees, within the
Sloan Digital Sky Survey (SDSS) imaging footprint. Distances, bolometric
luminosities, and atmospheric compositions are derived by fitting SDSS ugriz
photometry to pure hydrogen and helium model atmospheres (assuming surface
gravities log g = 8). The disk white dwarf luminosity function (WDLF) is
constructed using a sample of 2839 stars with 5.5 < M_bol < 17, with
statistically significant numbers of stars cooler than the turnover in the
luminosity function. The WDLF for the halo is also constructed, using a sample
of 135 halo WDs with 5 < M_bol < 16. We find space densities of disk and halo
WDs in the solar neighborhood of 5.5 +- 0.1 x 10^-3 pc^-3 and 3.5 +- 0.7 x
10^-5 pc^-3, respectively. We resolve the bump in the disk WDLF due to the
onset of fully convective envelopes in WDs, and see indications of it in the
halo WDLF as well.


title:
Mixing Metaphors: Actors as Channels and Channels as Actors (Extended
  Version)

abstract:
  Channel- and actor-based programming languages are both used in practice, but
the two are often confused. Languages such as Go provide anonymous processes
which communicate using buffers or rendezvous points---known as
channels---while languages such as Erlang provide addressable processes---known
as actors---each with a single incoming message queue. The lack of a common
representation makes it difficult to reason about translations that exist in
the folklore. We define a calculus $\lambda_{\textrm{ch}}$ for typed
asynchronous channels, and a calculus $\lambda_{\textrm{act}}$ for typed
actors. We define translations from $\lambda_{\textrm{act}}$ into
$\lambda_{\textrm{ch}}$ and $\lambda_{\textrm{ch}}$ into
$\lambda_{\textrm{act}}$ and prove that both are type- and
semantics-preserving. We show that our approach accounts for synchronisation
and selective receive in actor systems and discuss future extensions to support
guarded choice and behavioural types.


title:
A Priori Estimation Of Memory Effects In Coarse-Grained Nonlinear
  Systems Using The Mori-Zwanzig Formalism

abstract:
  Reduced Order Models (ROMs) of complex, nonlinear dynamical systems often
require closure, which is the process of representing the contribution of the
unresolved physics on the resolved physics. The Mori-Zwanzig (M-Z) procedure
allows one to write down formally closed evolution equations for the resolved
physics. In these equations, the unclosed terms are recast as a memory integral
involving the past history of the resolved variables, and a "noise" term. While
the M-Z procedure does not directly reduce the complexity of the original
system, these equations can serve as a mathematically consistent starting point
to develop closures based on approximations of the memory. In this scenario, a
priori knowledge of the memory kernel, which is not explicitly known for
nonlinear systems, is of paramount importance to assess the validity of a
memory approximation. Unraveling the memory kernel requires the determination
of the orthogonal dynamics which is a projected high-dimensional partial
differential equation that is not tractable in general. A method to estimate
the memory kernel a priori, using full-order solution snapshots, is proposed.
The main idea is to solve a pseudo orthogonal dynamics equation, that has a
convenient Liouville form, instead of the original one. This ersatz arises from
the assumption that the semi-group of the orthogonal dynamics operator is a
composition operator, akin to semi-groups of Liouville operators, for one
observable. The method is exact in the linear case where the kernel is known
explicitly. Results for under-resolved simulations of the Burgers and
Kuramoto-Sivashinsky equations demonstrate that the proposed technique can
accurately reconstruct the transfer of information between the resolved and
unresolved dynamics through memory, and provide valuable information about the
kernel.


title:
Optimal perturbations for nonlinear systems using graph-based optimal
  transport

abstract:
  We formulate and solve a class of finite-time transport and mixing problems
in the set-oriented framework. The aim is to obtain optimal discrete-time
perturbations in nonlinear dynamical systems to transport a specified initial
measure on the phase space to a final measure in finite time. The measure is
propagated under system dynamics in between the perturbations via the
associated transfer operator. Each perturbation is described by a deterministic
map in the measure space that implements a version of Monge-Kantorovich optimal
transport with quadratic cost. Hence, the optimal solution minimizes a sum of
quadratic costs on phase space transport due to the perturbations applied at
specified times. The action of the transport map is approximated by a
continuous pseudo-time flow on a graph, resulting in a tractable convex
optimization problem. This problem is solved via state-of-the-art solvers to
global optimality. We apply this algorithm to a problem of transport between
measures supported on two disjoint almost-invariant sets in a chaotic fluid
system, and to a finite-time optimal mixing problem by choosing the final
measure to be uniform. In both cases, the optimal perturbations are found to
exploit the phase space structures, such as lobe dynamics, leading to efficient
global transport. As the time-horizon of the problem is increased, the optimal
perturbations become increasingly localized. Hence, by combining the transfer
operator approach with ideas from the theory of optimal mass transportation, we
obtain a discrete-time graph-based algorithm for optimal transport and mixing
in nonlinear systems.


title: Segre's Regularity Bound for Fat Point Schemes

abstract:
  Motivated by questions in interpolation theory and on linear systems of
rational varieties, one is interested in upper bounds for the
Castelnuovo-Mumford regularity of arbitrary subschemes of fat points. An
optimal upper bound, named after Segre, was conjectured by Trung and,
independently, by Fattabi and Lorenzini. It is shown that this conjecture is
true. Furthermore, an alternate regularity bound is established that improves
the Segre bound in some cases. Among the arguments is a new partition result
for matroids.


title: The hydrodynamic limit of beta coalescents that come down from infinity

abstract:
  We quantify the manner in which the beta coalescent $\Pi=\{ \Pi(t), t\geq
0\},$ with parameters $a\in (0, 1),$ $b>0,$ comes down from infinity.
Approximating $\Pi$ by its restriction $\Pi^n$ to $[n]\:= \{1, \ldots, n\},$
the suitably rescaled block counting process $n^{-1}\#\Pi^n(tn^{a-1})$ has a
deterministic limit, $c(t)$, as $n\to\infty.$ An explicit formula for $c(t)$ is
provided in Theorem 1.
  The block size spectrum $(\mathfrak{c}_{1}\Pi^n(t), \ldots,
\mathfrak{c}_{n}\Pi^n(t)),$ where $\mathfrak{c}_{i}\Pi^n(t)$ counts the number
of blocks of size $i$ in $\Pi^n(t),$ captures more refined information about
the coalescent tree corresponding to $\Pi$. Using the corresponding rescaling,
the block size spectrum also converges to a deterministic limit as
$n\to\infty.$ This limit is characterized by a system of ordinary differential
equations whose $i$th solution is a complete Bell polynomial, depending only on
$c(t)$ and $a,$ that we work out explicitly, see Corollary 1.


title:
Hybrid simulation of a parallel collisionless shock in the Large Plasma
  Device

abstract:
  We present two-dimensional hybrid kinetic/magnetohydrodynamic simulations of
planned laser-ablation experiments in the Large Plasma Device (LAPD). Our
results, based on parameters which have been validated in previous experiments,
show that a parallel collisionless shock can begin forming within the available
space. Carbon-debris ions that stream along the magnetic-field direction with a
blow-off speed of four times the Alfven velocity excite strong magnetic
fluctuations, eventually transfering part of their kinetic energy to the
surrounding hydrogen ions. This acceleration and compression of the background
plasma creates a shock front, which satisfies the Rankine-Hugoniot conditions
and can therefore propagate on its own. Furthermore, we analyze the upstream
turbulence and show that it is dominated by the right-hand resonant
instability.


title: A construction of the graphic matroid from the lattice of integer flows

abstract:
  The lattice of integer flows of a graph is known to determine the graph up to
2-isomorphism (work of Su--Wagner and Caporaso--Viviani). In this paper we give
an algorithmic construction of the graphic matroid $\calM(G)$ of a graph $G$,
given its lattice of integer flows $\calF(G)$. The algorithm can then be
applied to compute any other 2-isomorphism invariants (that is, matroid
invariants) of $G$ from $\calF(G)$. Our method is based on a result of Amini
which describes the relationship between the geometry of the Voronoi cell of
$\calF(G)$ and the structure of $G$.


title:
Bounds on Large Extra Dimensions from the Generalized Uncertainty
  Principle

abstract:
  The Generalized Uncertainty Principle (GUP) implies the existence of a
physical minimum length scale $l_m$. In this scenario, black holes must have a
radius larger than $l_m$. They are hotter and evaporate faster than in standard
Hawking thermodynamics. We study the effects of the GUP on black hole
production and decay at the LHC in models with large extra dimensions. Lower
bounds on the fundamental Planck scale and the minimum black hole mass at
formation are determined from black hole production cross section limits by the
CMS Collaboration. The existence of a minimum length generally decreases the
lower bounds on the fundamental Planck scale obtained in the absence of a
minimum length.


title: Understanding Anatomy Classification Through Attentive Response Maps

abstract:
  One of the main challenges for broad adoption of deep learning based models
such as convolutional neural networks (CNN), is the lack of understanding of
their decisions. In many applications, a simpler, less capable model that can
be easily understood is favorable to a black-box model that has superior
performance. In this paper, we present an approach for designing CNNs based on
visualization of the internal activations of the model. We visualize the
model's response through attentive response maps obtained using a fractional
stride convolution technique and compare the results with known imaging
landmarks from the medical literature. We show that sufficiently deep and
capable models can be successfully trained to use the same medical landmarks a
human expert would use. Our approach allows for communicating the model
decision process well, but also offers insight towards detecting biases.


title:
Good characterizations and linear time recognition for 2-probe block
  graphs

abstract:
  Block graphs are graphs in which every block (biconnected component) is a
clique. A graph $G=(V,E)$ is said to be an (unpartitioned) $k$-probe block
graph if there exist $k$ independent sets $N_i\subseteq V$, $1\le i\le k$, such
that the graph $G'$ obtained from $G$ by adding certain edges between vertices
inside the sets $N_i$, $1\le i\le k$, is a block graph; if the independent sets
$N_i$ are given, $G$ is called a partitioned $k$-probe block graph. In this
paper we give good characterizations for $2$-probe block graphs, in both
unpartitioned and partitioned cases. As an algorithmic implication, partitioned
and unpartitioned probe block graphs can be recognized in linear time,
improving a recognition algorithm of cubic time complexity previously obtained
by Chang et al. [Block-graph width, Theoretical Computer Science 412 (2011),
2496--2502].


title: Command of active matter by topological defects and patterns

abstract:
  Self-propelled bacteria are marvels of nature with a potential to power
dynamic materials and microsystems of the future. The challenge is in
commanding their chaotic behavior. By dispersing swimming Bacillus subtilis in
a liquid-crystalline environment with spatially-varying orientation of the
anisotropy axis, we demonstrate control over the distribution of bacteria,
geometry and polarity of their trajectories. Bacteria recognize subtle
differences in liquid crystal deformations, engaging in bipolar swimming in
regions of pure splay and bend but switching to unipolar swimming in mixed
splay-bend regions. They differentiate topological defects, heading towards
defects of positive topological charge and avoiding negative charges.
Sensitivity of bacteria to pre-imposed orientational patterns represents a new
facet of the interplay between hydrodynamics and topology of active matter.


title: XID+ a new prior-based extraction tool for Herschel-SPIRE maps

abstract:
  We present XID+ a new generation of software for prior-based photometry
extraction in the Herschel SPIRE maps. Based on a Bayesian framework, XID+
allows the inclusion of prior information and gives access to the full
posterior probability distribution of fluxes. XID+ is developed within the
Herschel Extragalactic Legacy Project (HELP) and is available at
https://github.com/H-E-L-P/XID_plus.


title:
Convergence Analysis and Numerical Implementation of a Second Order
  Numerical Scheme for the Three-Dimensional Phase Field Crystal Equation

abstract:
  In this paper we analyze and implement a second-order-in-time numerical
scheme for the three-dimensional phase field crystal (PFC) equation. The
numerical scheme was proposed in [46], with the unique solvability and
unconditional energy stability established. However, its convergence analysis
remains open. We present a detailed convergence analysis in this article, in
which the maximum norm estimate of the numerical solution over grid points
plays an essential role. Moreover, we outline the detailed multigrid method to
solve the highly nonlinear numerical scheme over a cubic domain, and various
three-dimensional numerical results are presented, including the numerical
convergence test, complexity test of the multigrid solver and the polycrystal
growth simulation.


title:
Linear stability of the Linet - Tian solution with negative cosmological
  constant

abstract:
  In this paper we analyze the linear stability of the Linet - Tian solution
with negative cosmological constant. In the limit of vanishing cosmological
constant the Linet - Tian metric reduces to a form of the Levi - Civita metric,
and, therefore, it can be considered as a generalization of the former to
include a cosmological constant. The gravitational instability of the Levi -
Civita metric was recently established, and the purpose of this paper is to
investigate what changes result from the introduction of a cosmological
constant. A fundamental difference brought about by a (negative) cosmological
constant is in the structure at infinity. This introduces an added problem in
attempting to define an evolution for the perturbations because the constant
time hypersurfaces are not Cauchy surfaces. In this paper we show that under a
large set of boundary conditions that lead to a unique evolution of the
perturbations, we always find unstable modes, that would generically be present
in the evolution of arbitrary initial data, leading to the conclusion that the
Linet - Tian space times with negative cosmological constant are linearly
unstable under gravitational perturbations.


title: Frobenius split subvarieties pull back in almost all characteristics

abstract:
  Let $X$ and $Y$ be schemes of finite type over $\mathrm{Spec}\ \mathbb{Z}$
and let $\alpha: Y \to X$ be a finite map. We show the following holds for all
sufficiently large primes $p$: If $\phi$ and $\psi$ are any splittings on $X
\times \mathrm{Spec}\ F_p$ and $Y \times \mathrm{Spec}\ F_p$, such that the
restriction of $\alpha$ is compatible with $\phi$ and $\psi$, and $V$ is any
compatibly split subvariety of $(X \times \mathrm{Spec}\ F_p, \phi)$, then the
reduction $\alpha^{-1}(V)^{\mathrm{red}}$ is a compatibly split subvariety of
$(Y \times \mathrm{Spec}\ F_p, \psi)$. This is meant as a tool to aid in
listing the compatibly split subvarieties of various classically split
varieties.


title:
A Gelfand-Graev Formula and Stable Transfer Factors in the Unramidied
  Case for $\text{SL}_\ell(F)$ and $\text{GL}_\ell(F)$, $\ell$ an odd Prime

abstract:
  A result of Gelfand and Graev shows that the supercuspidal representations of
$\text{SL}_2(F)$ for a nonarchimedean local field $F$ are parameterized by
characters of elliptic tori and that by means of a Fourier transform the stable
character data for all such representations may be collected into a single
function. For $G=\text{SL}_\ell(F)$, $\ell$ an odd prime and $F$ a
nonarchimedean local field, we use explicit formulas for supercuspidal
characters to prove a formula analogous to that of Gelfand and Graev for
representations arising from unramified tori. Moreover, this formula is
precisely the stable transfer factor defined by Langlands for the lift of
representations from a maximal elliptic torus $T\subset G$ to $G$. In addition,
we formulate and prove the analogous result for $\text{GL}_\ell(F)$.


title:
Minimizing cyber sickness in head mounted display systems: design
  guidelines and applications

abstract:
  We are experiencing an upcoming trend of using head mounted display systems
in games and serious games, which is likely to become an established practice
in the near future. While these systems provide highly immersive experiences,
many users have been reporting discomfort symptoms, such as nausea, sickness,
and headaches, among others. When using VR for health applications, this is
more critical, since the discomfort may interfere a lot in treatments. In this
work we discuss possible causes of these issues, and present possible solutions
as design guidelines that may mitigate them. In this context, we go deeper
within a dynamic focus solution to reduce discomfort in immersive virtual
environments, when using first-person navigation. This solution applies an
heuristic model of visual attention that works in real time. This work also
discusses a case study (as a first-person spatial shooter demo) that applies
this solution and the proposed design guidelines.


title: Properties of frequentist confidence levels derivatives

abstract:
  In high energy physics, results from searches for new particles or rare
processes are often reported using a modified frequentist approach, known as
$\rm{CL_s}$ method. In this paper, we study the properties of the derivatives
of $\rm{CL_s}$ and $\rm{CL_{s+b}}$ as signal strength estimators if the
confidence levels are interpreted as credible intervals. Our approach allows
obtaining best fit points and $\chi^2$ functions which can be used for
phenomenology studies. In addition, this approach can be used to incorporate
$\rm{CL_s}$ results into Bayesian combinations.


title:
Identification of a monoclinic metallic state in VO2 from a modified
  first-principles approach

abstract:
  Metal-insulator transition underlies many remarkable and technologically
important phenomena in VO2. Even though its monoclinic structure had before
been the reserve of the insulating state, recent experiments have observed an
unexpected monoclinic metallic state. Here we use a modified approach combining
first-principles calculations with orbital-biased potentials to reproduce the
correct stability ordering and electronic structure of different phases of VO2.
We identify a ferromagnetic monoclinic metal that is likely to be the
experimentally observed mysterious metastable state. Furthermore, our
calculations show that an isostructural insulator-metal electronic transition
is followed by the lattice distortion from the monoclinic structure to the
rutile structure. These results not only explain the experimental observations
of the monoclinic metallic state and the decoupled structural and electronic
transitions of VO2, but also provide a understanding for the metal-insulator
transition in other strongly correlated d electron systems.


title:
An efficient method for calculating spatially extended electronic states
  of large systems with a divide-and-conquer approach

abstract:
  We present an efficient post-processing method for calculating the electronic
structure of nanosystems based on the divide-and-conquer approach to density
functional theory (DC-DFT), in which a system is divided into subsystems whose
electronic structure is solved separately. In this post process, the Kohn-Sham
Hamiltonian of the total system is easily derived from the orbitals and orbital
energies of subsystems obtained by DC-DFT without time-consuming and redundant
computation. The resultant orbitals spatially extended over the total system
are described as linear combinations of the orbitals of the subsystems. The
size of the Hamiltonian matrix can be much reduced from that for conventional
calculation, so that our method is fast and applicable to general huge systems
for investigating the nature of electronic states.


title: A Bayesian approach to type-specific conic fitting

abstract:
  A perturbative approach is used to quantify the effect of noise in data
points on fitted parameters in a general homogeneous linear model, and the
results applied to the case of conic sections. There is an optimal choice of
normalisation that minimises bias, and iteration with the correct reweighting
significantly improves statistical reliability. By conditioning on an
appropriate prior, an unbiased type-specific fit can be obtained. Error
estimates for the conic coefficients may also be used to obtain both bias
corrections and confidence intervals for other curve parameters.


title:
A new numerical algorithm for the solutions of hyperbolic partial
  differential equations in $(2+1)$-dimensional space

abstract:
  This paper deals with a construction of new algorithm: the modified
trigonometric cubic B-Spline differential quadrature (MTB-DQM) for space
discretization together with a time integration algorithm" for numerical
computation of the hyperbolic equations. Specially, MTB-DQM has been
implemented for the initial value system of the telegraph equations together
with both Dirichlet and Neumann type boundary conditions. The MTB-DQM is a DQM
based on modified trigonometric cubic B-splines as new base functions. The
problem has been reduced into an amenable system of ordinary differential
equations adopting MTB-DQM. The resulting system of ordinary differential
equations is solved using time integration algorithms. Further, the stability
of MTB-DQM is studied by computing the eigenvalues of the coefficients matrices
for various grid points, which confirmed the stability of MTB-DQM for the
telegraphic equations. The accuracy of the method has been illustrated in terms
of the various discrete error norms for six test problems of the telegraph
equation. A comparison of computed numerical solutions with that obtained by
the other methods has been carried out for various time levels considering
various space sizes


title: Coincidence of algebraic and smooth theta correspondences

abstract:
  An "automatic continuity" question has naturally occurred since Roger Howe
established the local theta correspondence over $\mathbb R$: does the algebraic
version of local theta correspondence over $\mathbb R$ agrees with the smooth
version? We show that the answer is yes, at least when the concerning dual pair
has no quaternionic type I irreducible factor.


title: Content-Centric and Software-Defined Networking with Big Data

abstract:
  Many communities have researched the application of novel network
architectures such as Content-Centric Networking (CCN) and Software-Defined
Networking (SDN) to build the future Internet. Another emerging technology
which is big data analysis has also won lots of attentions from academia to
industry. Many splendid researches have been done on CCN, SDN, and big data,
which all have addressed separately in the traditional literature. In this
paper, we propose a novel network paradigm to jointly consider CCN, SDN, and
big data, and provide the architecture internal data flow, big data processing
and use cases which indicate the benefits and applicability. Simulation results
are exhibited to show the potential benefits relating to the proposed network
paradigm. We refer to this novel paradigm as Data-Driven Networking (DDN).


title:
Polar metals as electrodes to suppress the critical-thickness limit in
  ferroelectric nanocapacitors

abstract:
  Enhancing the performance of nanoscale ferroelectric (FE) field-effect
transistors and FE capacitors for memory devices and logic relies on
miniaturizing the metal electrode/ferroelectric area and reducing the thickness
of the insulator. Although size reductions improve data retention, deliver
lower voltage threshold switching, and increase areal density, they also
degrade the functional electric polarization. There is a critical, nanometer
length $t_\mathrm{FE}^*$ below which the polarization disappears owing to
depolarizing field effects. Here we show how to overcome the critical thickness
limit imposed on ferroelectricity by utilizing electrodes formed from a novel
class of materials known as polar metals. Electronic structure calculations on
symmetric polar-metal electrode/FE capacitor structures demonstrate that
electric polarizations can persist to the sub-nanometer scale with
$t_\mathrm{FE}^*\rightarrow0$ when a component of the polar axis in the
electrode is perpendicular to the electrode/insulator interface. Our results
reveal the importance of interfacial dipolar coherency in sustaining the
polarization, which provides a platform for atomic scale structure-based design
of functions that deteriorate in reduced dimensions.


title:
Inferring Restaurant Styles by Mining Crowd Sourced Photos from
  User-Review Websites

abstract:
  When looking for a restaurant online, user uploaded photos often give people
an immediate and tangible impression about a restaurant. Due to their
informativeness, such user contributed photos are leveraged by restaurant
review websites to provide their users an intuitive and effective search
experience. In this paper, we present a novel approach to inferring restaurant
types or styles (ambiance, dish styles, suitability for different occasions)
from user uploaded photos on user-review websites. To that end, we first
collect a novel restaurant photo dataset associating the user contributed
photos with the restaurant styles from TripAdvior. We then propose a deep
multi-instance multi-label learning (MIML) framework to deal with the unique
problem setting of the restaurant style classification task. We employ a
two-step bootstrap strategy to train a multi-label convolutional neural network
(CNN). The multi-label CNN is then used to compute the confidence scores of
restaurant styles for all the images associated with a restaurant. The computed
confidence scores are further used to train a final binary classifier for each
restaurant style tag. Upon training, the styles of a restaurant can be profiled
by analyzing restaurant photos with the trained multi-label CNN and SVM models.
Experimental evaluation has demonstrated that our crowd sourcing-based approach
can effectively infer the restaurant style when there are a sufficient number
of user uploaded photos for a given restaurant.


title:
Dynamic Resource Allocation in Next Generation Cellular Networks with
  Full-Duplex Self-backhauls

abstract:
  With the dense deployment of small cell networks, low-cost backhaul schemes
for small cell base stations (SBSs) have attracted great attentions.
Self-backhaul using cellular communication technology is considered as a
promising solution. Although some excellent works have been done on
self-backhaul in small cell networks, most of them do not consider the recent
advances of full-duplex (FD) and massive multiple-input and multiple-output
(MIMO) technologies. In this paper, we propose a self-backhaul scheme for small
cell networks by combining FD and massive MIMO technologies. In our proposed
scheme, the macro base station (MBS) is equipped with massive MIMO antennas,
and the SBSs have the FD communication ability. By treating the SBSs as
\textit{special} macro users, we can achieve the simultaneous transmissions of
the access link of users and the backhaul link of SBSs in the same frequency.
Furthermore, considering the existence of inter-tier and intra-tier
interference, we formulate the power allocation problem of the MBS and SBSs as
an optimization problem. Because the formulated power allocation problem is a
non-convex problem, we transform the original problem into a difference of
convex program (DCP) by successive convex approximation method (SCAM) and
variable transformation, and then solve it using a constrained concave convex
procedure (CCCP) based iterative algorithm. Finally, extensive simulations are
conducted with different system configurations to verify the effectiveness of
the proposed scheme.


title: Hilbert's Proof of His Irreducibility Theorem

abstract:
  Hilbert's Irreducibility Theorem is a cornerstone that joins areas of
analysis and number theory. Both the genesis and genius of its proof involved
combining real analysis and combinatorics. We try to expose the motivations
that led Hilbert to this synthesis. Hilbert's famous Cube Lemma supplied fuel
for the proof but without the analytical foundation and framework it would have
been heating empty air. The lemma is said to presage Ramsey Theory but we note
differences in motivation.


title: Testing for unobserved heterogeneous treatment effects

abstract:
  Unobserved heterogeneous treatment effects have been emphasized in recent
policy evaluation literature. In this paper, we extend Lu and White (2014)'s
testing method for unobserved heterogeneous treatment effects by developing
nonparametric tests under the standard exogenous instrumental variable
assumption and allowing for endogenous treatment. Specifically, we propose
Kolmogorov--Smirnov--type statistics that are consistent and simple to
implement. To illustrate, we apply the proposed test method with two empirical
applications: treatment effects of job training program on earnings as well as
the impact of fertility on family income. The null hypotheses, i.e., lack of
unobserved heterogeneous treatment effects, cannot be rejected at a 10%
significance level in the former case, but should be rejected at all usual
significance levels in the latter.


title:
Frustrated Heisenberg Antiferromagnets on Cubic Lattices: Magnetic
  Structures, Exchange Gaps, and Non-Conventional Critical Behaviour

abstract:
  We have studied the Heisenberg antiferromagnets characterized by the magnetic
structures with the periods being two times larger than the lattice period. We
have considered all the types of the Bravais lattices (simple cubic, bcc and
fcc) and divided all these antiferromagnets into 7 classes i.e. 3 plus 4
classes denoted with symbols A and B correspondingly. The order parameter
characterizing the degeneracies of the magnetic structures is an ordinary Neel
vector for A classes and so-called 4-complex for B classes. We have taken into
account the fluctuation corrections for these states within the spin-wave and
large-N expansions ($N$ is the number of spin components). Below the Neel
temperature $T_{\rm{N}}$ quantum and thermal fluctuations lift the degeneracy
making simple one-wave vector collinear structure preferable for all the
classes. A satellite of this effect is opening of the exchange gaps at certain
wave vectors in the spin wave spectrum (there is an analogous effect for the
nonuniform static transverse susceptibility). However, as the temperature
approaches $T_{\rm{N}}$, the exchange gaps are closing. We have calculated the
critical indices $\eta$ and $\nu$ to order of $1/N$ and found that they differ
for A and B classes.


title:
Cross-model convolutional neural network for multiple modality data
  representation

abstract:
  A novel data representation method of convolutional neural net- work (CNN) is
proposed in this paper to represent data of different modalities. We learn a
CNN model for the data of each modality to map the data of differ- ent
modalities to a common space, and regularize the new representations in the
common space by a cross-model relevance matrix. We further impose that the
class label of data points can also be predicted from the CNN representa- tions
in the common space. The learning problem is modeled as a minimiza- tion
problem, which is solved by an augmented Lagrange method (ALM) with updating
rules of Alternating direction method of multipliers (ADMM). The experiments
over benchmark of sequence data of multiple modalities show its advantage.


title: Multi-Scale Saliency Detection using Dictionary Learning

abstract:
  Saliency detection has drawn a lot of attention of researchers in various
fields over the past several years. Saliency is the perceptual quality that
makes an object, person to draw the attention of humans at the very sight.
Salient object detection in an image has been used centrally in many
computational photography and computer vision applications like video
compression, object recognition and classification, object segmentation,
adaptive content delivery, motion detection, content aware resizing, camouflage
images and change blindness images to name a few. We propose a method to detect
saliency in the objects using multimodal dictionary learning which has been
recently used in classification and image fusion. The multimodal dictionary
that we are learning is task driven which gives improved performance over its
counterpart (the one which is not task specific).


title:
Classification of tetravalent $2$-transitive non-normal Cayley graphs of
  finite simple groups

abstract:
  A graph $\Gamma$ is called $(G, s)$-arc-transitive if $G \le
\mathrm{Aut}(\Gamma)$ is transitive on the set of vertices of $\Gamma$ and the
set of $s$-arcs of $\Gamma$, where for an integer $s \ge 1$ an $s$-arc of
$\Gamma$ is a sequence of $s+1$ vertices $(v_0,v_1,\ldots,v_s)$ of $\Gamma$
such that $v_{i-1}$ and $v_i$ are adjacent for $1 \le i \le s$ and $v_{i-1}\ne
v_{i+1}$ for $1 \le i \le s-1$. $\Gamma$ is called 2-transitive if it is
$(\mathrm{Aut}(\Gamma), 2)$-arc-transitive but not $(\mathrm{Aut}(\Gamma),
3)$-arc-transitive. A Cayley graph $\Gamma$ of a group $G$ is called normal if
$G$ is normal in $\mathrm{Aut}(\Gamma)$ and non-normal otherwise. It was proved
by X. G. Fang, C. H. Li and M. Y. Xu that if $\Gamma$ is a tetravalent
2-transitive Cayley graph of a finite simple group $G$, then either $\Gamma$ is
normal or $G$ is one of the groups $\mathrm{PSL}_2(11)$, $M_{11}$, $M_{23}$ and
$A_{11}$. However, it was unknown whether $\Gamma$ is normal when $G$ is one of
these four groups. In the present paper we answer this question by proving that
among these four groups only $M_{11}$ produces connected tetravalent
2-transitive non-normal Cayley graphs. We prove further that there are exactly
two such graphs which are non-isomorphic and both determined in the paper. As a
consequence, the automorphism group of any connected tetravalent 2-transitive
Cayley graph of any finite simple group is determined.


title: Towards a Complete Framework for Virtual Data Center Embedding

abstract:
  Cloud computing is widely adopted by corporate as well as retail customers to
reduce the upfront cost of establishing computing infrastructure. However,
switching to the cloud based services poses a multitude of questions, both for
customers and for data center owners. In this work, we propose an algorithm for
optimal placement of multiple virtual data centers on a physical data center.
Our algorithm has two modes of operation - an online mode and a batch mode.
Coordinated batch and online embedding algorithms are used to maximize resource
usage while fulfilling the QoS demands. Experimental evaluation of our
algorithms show that acceptance rate is high - implying higher profit to
infrastructure provider. Additionaly, we try to keep a check on the number of
VM migrations, which can increase operational cost and thus lead to service
level agreement violations.


title: Local minima in training of neural networks

abstract:
  There has been a lot of recent interest in trying to characterize the error
surface of deep models. This stems from a long standing question. Given that
deep networks are highly nonlinear systems optimized by local gradient methods,
why do they not seem to be affected by bad local minima? It is widely believed
that training of deep models using gradient methods works so well because the
error surface either has no local minima, or if they exist they need to be
close in value to the global minimum. It is known that such results hold under
very strong assumptions which are not satisfied by real models. In this paper
we present examples showing that for such theorem to be true additional
assumptions on the data, initialization schemes and/or the model classes have
to be made. We look at the particular case of finite size datasets. We
demonstrate that in this scenario one can construct counter-examples (datasets
or initialization schemes) when the network does become susceptible to bad
local minima over the weight space.


title:
Understanding the General Feature of Microvariability in ${\it Kepler}$
  Blazar W2R 1926$+$42

abstract:
  We analyze the ${\it Kepler}$ monitoring light curve of a blazar W2R
1926$+$42 to examine features of microvariability by means of the "shot
analysis" technique. We select 195 intra-day, flare-like variations (shots) for
the continuous light curve of Quarter 14 with a duration of 100 d. In the
application of the shot analysis, an averaged profile of variations is assumed
to converge with a universal profile which reflects a physical mechanism
generating the microvariability in a blazar jet, although light-variation
profiles of selected shots show a variety. A mean profile, which is obtained by
aligning the peaks of the 195 shots, is composed of a spiky-shape shot
component at $\pm$0.1 d (with respect to the time of the peak), and two slow
varying components ranging from $-$0.50 d to $-$0.15 d and from 0.10 d to 0.45
d of the peak time. The former spiky feature is well represented by an
exponential rise of 0.043$\pm$0.001 d and an exponential decay of
0.061$\pm$0.002 d. These timescales are consistent with that corresponding to a
break frequency of a power spectrum density calculated from the obtained light
curve. After verification with the Monte-Carlo method, the exponential shape,
but not the observed asymmetry, of the shot component can be explained by noise
variation. The asymmetry is difficult to explain through a geometrical effect
(i.e. changes of the geometry of the emitting region), but is more likely to be
caused by the production and dissipation of high-energy accelerated particles
in the jet. Additionally, durations of the detected shots show a systematic
variation with a dispersion caused by a statistical randomness. A comparison
with the variability of Cygnus X-1 is also briefly discussed.


title:
Actions of trees on semigroups, and an infinitary Gowers--Hales--Jewett
  Ramsey theorem

abstract:
  We introduce the notion of (Ramsey) action of a tree on a (filtered)
semigroup. We then prove in this setting a general result providing a common
generalization of the infinitary Gowers Ramsey theorem for multiple tetris
operations, the infinitary Hales--Jewett theorems (for both located and
nonlocated words), and the Farah--Hindman--McLeod Ramsey theorem for layered
actions on partial semigroups. We also establish a polynomial version of our
main result, recovering the polynomial Milliken--Taylor theorem of
Bergelson--Hindman--Williams as a particular case. We present applications of
our Ramsey-theoretic results to the structure of delta sets in amenable groups.


title:
Asymptotics and monodromy of the algebraic spectrum of quasi-exactly
  solvable sextic oscillator

abstract:
  Below we study theoretically and numerically the asymptotics of the algebraic
part of the spectrum for the quasi-exactly solvable sextic potential, its level
crossing points, and its monodromy in the complex plane of its parameter. We
also discuss connection between the quasi-exactly solvable sextic and the
classical quartic potential.


title: Determining the Veracity of Rumours on Twitter

abstract:
  While social networks can provide an ideal platform for up-to-date
information from individuals across the world, it has also proved to be a place
where rumours fester and accidental or deliberate misinformation often emerges.
In this article, we aim to support the task of making sense from social media
data, and specifically, seek to build an autonomous message-classifier that
filters relevant and trustworthy information from Twitter. For our work, we
collected about 100 million public tweets, including users' past tweets, from
which we identified 72 rumours (41 true, 31 false). We considered over 80
trustworthiness measures including the authors' profile and past behaviour, the
social network connections (graphs), and the content of tweets themselves. We
ran modern machine-learning classifiers over those measures to produce
trustworthiness scores at various time windows from the outbreak of the rumour.
Such time-windows were key as they allowed useful insight into the progression
of the rumours. From our findings, we identified that our model was
significantly more accurate than similar studies in the literature. We also
identified critical attributes of the data that give rise to the
trustworthiness scores assigned. Finally we developed a software demonstration
that provides a visual user interface to allow the user to examine the
analysis.


title: Observational constraints on the generalized $\alpha$ attractor model

abstract:
  We study the generalized $\alpha$ attractor model in the context of the late
time cosmic acceleration. The model interpolates between the scaling freezing
and thawing dark energy models. In the slow roll region, the original potential
is modified whereas the modification ceases in the asymptotic region and the
effective potential behaves as the quadratic one. In our setting, the field
rolls slowly around the present epoch and mimics the scaling behavior in the
future. We obtain observational constraints on the model parameters by using an
integrated data base (SN+Hubble+BAO+CMB).


title:
Existence and uniqueness of $L^p$ solutions to the Boltzmann equation
  with an angle-potential concentrated collision kernel

abstract:
  We solve the Cauchy problem associated to the space homogeneous Boltzmann
equation with an angle-potential singular concentration modeling the collision
kernel, proposed in 2013 by Bobylev and Potapenko. The potential under
consideration ranges from Coulomb to hard spheres cases. However, the
motivation of such a collision kernel is to treat the case of Coulomb
potentials, on which this particular form of collision operator is well
defined. We also show that the scaled angle-potential singular concentration in
a grazing collisions limit makes the Boltzmann operator converge in the sense
of distributions to the Landau operator acting on the Boltzmann solutions.


title:
Conserved charge of a gravity theory with $p$-form gauge fields and its
  property under Kaluza-Klein reduction

abstract:
  In this paper, we investigate the conserved charges of generally
diffeomorphism invariant gravity theories with a wide variety of matter fields,
particularly of the theories with multiple scalar fields and $p$-form
potentials, in the context of the off-shell generalized Abbott-Deser-Tekin
(ADT) formalism. We first construct a new off-shell ADT current that consists
of the terms for the variation of a Killing vector and expressions of the field
equations as well as the Lie derivative of a surface term with respect to the
Killing vector within the framework of generally diffeomorphism invariant
gravity theories involving various matter fields. After deriving the off-shell
ADT potential corresponding to this current, we propose a formula of conserved
charges for these theories. Next, we derive the off-shell ADT potential
associated with the generic Lagrangian that describes a large range of gravity
theories with a number of scalar fields and $p$-form potentials. Finally, the
properties of the off-shell generalized ADT charges for the theory of Einstein
gravity and the gravity theories with a single $p$-form potential are
investigated by performing Kaluza-Klein dimensional reduction along a
compactified direction. The results indicate that the charge contributed by all
the fields in the lower-dimensional theory is equal to that of the
higher-dimensional one at mathematical level with the hypothesis that the
higher-dimensional spacetime allows for the existence of the compactified
dimension. In order to illustrate our calculations, the mass and angular
momentum for the five-dimensional rotating Kaluza-Klein black holes are
explicitly evaluated as an example.


title: Network similarity and statistical analysis of earthquake seismic data

abstract:
  We study the structural similarity of earthquake networks constructed from
seismic catalogs of different geographical regions. A hierarchical clustering
of underlying undirected earthquake networks is shown using Jensen-Shannon
divergence in graph spectra. The directed nature of links indicates that each
earthquake network is strongly connected, which motivates us to study the
directed version statistically. Our statistical analysis of each earthquake
region identifies the hub regions. We calculate the conditional probability of
the forthcoming occurrences of earthquakes in each region. The conditional
probability of each event has been compared with their stationary distribution.

categories: physics.geo-ph cond-mat.dis-nn physics.data-an physics.soc-ph


title: Shapes and singularities in triatic liquid crystal vesicles

abstract:
  Determining the equilibrium configuration and shape of curved two-dimensional
films with (generalized) liquid crystalline (LC) order is a difficult infinite
dimensional problem of direct relevance to the study of generalized
polymersomes, soft matter and the fascinating problem of understanding the
origin and formation of shape (morphogenesis). The symmetry of the free energy
of the LC film being considered and the topology of the surface to be
determined often requires that the equilibrium configuration possesses singular
structures in the form of topological defects such as disclinations for nematic
films. The precise number and type of defect plays a fundamental role in
restricting the space of possible equilibrium shapes. Flexible closed vesicles
with spherical topology and nematic or smectic order, for example, inevitably
possess four elementary strength $+1/2$ disclination defects positioned at the
four vertices of a tetrahedral shell. Here we address the problem of
determining the equilibrium shape of flexible vesicles with generalized LC
order. The order parameter in these cases is an element of $S^1/Z_p$, for any
positive integer $p$. We will focus on the case $p =3$, known as triatic LCs.
We construct the appropriate order parameter for triatics and find the
associated free energy. We then describe the structure of the elementary
defects of strength $+1/3$ in flat space. Finally, we prove that sufficiently
floppy triatic vesicles with the topology of the 2-sphere equilibrate to
octahedral shells with strength $+1/3$ defects at each of the six vertices,
independently of scale.