title: On equivariant Chern-Weil forms and determinant lines

abstract:
  A strong from of invariance under a group G is manifested in a family over
the classifying space BG. We advocate a differential-geometric avatar of BG
when G is a Lie group. Applied to G-equivariant connections on smooth principal
or vector bundles, the equivariance-->families principle converts the
G-equivariant extensions of curvature and Chern-Weil forms to the standard
nonequivariant versions. An application of this technique yields the moment map
of the determinant line of a G-equivariant Dirac operator, which in turn sheds
light on some anomaly formulas in quantum field theory.


title:
The effect of anisotropy on the absorption spectrum and the density of
  states of two-dimensional Frenkel exciton systems with Gaussian diagonal
  disorder

abstract:
  On the optical absorption and the density of states of Frenkel exciton
systems on square, rectangular, and triangular lattices with nearest-neighbor
interactions and a Gaussian distribution of transition frequencies. The
analysis is based on an elliptic integral approach that gives results over the
entire spectrum. It is found that the absorption is weakly affected by the
anisotropy in contrast to the density of states where the effects can be much
stronger. The results for the square lattice are in good agreement with the
finite array calculations of Schreiber and Toyozawa. Our findings suggest that
the coherent potential approximation can be useful in interpreting the optical
properties of two-dimensional systems with dominant nearest-neighbor
interactions and Gaussian diagonal disorder where the optically excited states
are Frenkel excitons.


title: Absolute real root separation

abstract:
  While the separation (the minimal nonzero distance) between roots of a
polynomial is a classical topic, its absolute counterpart (the minimal nonzero
distance between their absolute values) does not seem to have been studied
much. We present the general context and give tight bounds for the case of real
roots.


title:
Quasi Normal Modes and P-V Criticallity for scalar perturbations in a
  class of dRGT massive gravity around Black Holes

abstract:
  We investigate black holes in a class of dRGT massive gravity for their quasi
normal modes (QNMs) for neutral and charged ones using Improved Asymptotic
Iteration Method (Improved AIM) and their thermodynamic behavior. The QNMs are
studied for different values of the massive parameter m_g for both neutral and
charged dRGT black holes under a massless scalar perturbation. As m_g
increases, the magnitude of the quasi normal frequencies are found to be
increasing. The results are also compared with the Schwarzchild de Sitter (SdS)
case. P-V criticallity of the aforesaid black hoels under massles scalar
perturbation in the de Sitter space are also studied in this paper. It is found
that the thermodynamic behavior of a neutral black hole shows no physically
feasible phase transition while a charged black hole shows a definite phase
transition.


title:
Charged-particle distributions at low transverse momentum in
  $\sqrt{s}$=13 TeV pp interactions measured with the ATLAS detector at the LHC

abstract:
  Measurements of distributions of charged particles produced in proton-proton
collisions with a centre-of-mass energy of 13 TeV are presented. The data were
recorded by the ATLAS detector at the LHC and correspond to an integrated
luminosity of 151 $\mu$b$^{-1}$. The particles are required to have a
transverse momentum greater than 100 MeV and an absolute pseudorapidity less
than 2.5. The charged-particle multiplicity, its dependence on transverse
momentum and pseudorapidity and the dependence of the mean transverse momentum
on multiplicity are measured in events containing at least two charged
particles satisfying the above kinematic criteria. The results are corrected
for detector effects and compared to the predictions from several Monte Carlo
event generators.


title: A Comprehensive Census of Nearby Infrared Excess Stars

abstract:
  The conclusion of the WISE mission presents an opportune time to summarize
the history of using excess emission in the infrared as a tracer of
circumstellar material and exploit all available data for future missions such
as JWST. We have compiled a catalog of infrared excess stars from peer-reviewed
articles and perform an extensive search for new infrared excess stars by
cross-correlating the Tycho-2 and AllWISE catalogs. We define a significance of
excess in four spectral type divisions and select stars showing greater than
either 3$\sigma$ or 5$\sigma$ significance of excess in the mid- and
far-infrared. Through procedures including SED fitting and various image
analyses, each potential excess source was rigorously vetted to eliminate
false-positives. The infrared excess stars from the literature and the new
stars found through the Tycho-2 and AllWISE cross-correlation produced nearly
500 `Prime' infrared excess stars and $\geq$1200 `Reserved' stars. The main
catalog of infrared excess stars are nearby, bright, and either demonstrate
excess in more than one passband or have infrared spectroscopy confirming the
infrared excess. This study identifies stars that display a spectral energy
distribution suggestive of a secondary or post-protoplanetary generation of
dust and they are ideal targets for future optical and infrared imaging
observations. The final catalogs of stars summarizes the past work using
infrared excess to detect dust disks and with the most extensive compilation of
infrared excess stars ($\sim$ 1750) to date, we investigate various
relationships among stellar and disk parameters.


title: Enhanced spin-orbit coupling in core/shell nanowires

abstract:
  The spin-orbit coupling (SOC) in semiconductors is strongly influenced by
structural asymmetries, as prominently observed in bulk crystal structures that
lack inversion symmetry. Here, we study an additional effect on the SOC: the
asymmetry induced by the large interface area between a nanowire core and its
surrounding shell. Our experiments on purely wurtzite GaAs/AlGaAs core/shell
nanowires demonstrate optical spin injection into a single free-standing
nanowire and determine the effective electron g-factor of the hexagonal GaAs
wurtzite phase. The spin relaxation is highly anisotropic in time-resolved
micro-photoluminescence measurements on single nanowires, showing a significant
increase of spin relaxation in external magnetic fields. This behavior is
counterintuitive compared to bulk wurtzite crystals. We present a model for the
observed electron spin dynamics highlighting the dominant role of the
interface-induced SOC in these core/shell nanowires. This enhanced SOC may
represent an interesting tuning parameter for the implementation of
spin-orbitronic concepts in semiconductor-based structures.


title:
Adjoint-based Sensitivity Analysis for High-Energy Density Radiaitive
  Transfer using Flux-Limited Diffusion

abstract:
  Uncertainty quantification and sensitivity analyses are a vital component for
predictive modeling in the sciences and engineering. The adjoint approach to
sensitivity analysis requires solving a primary system of equations and a
mathematically related set of adjoint equations. The information contained in
the equations can be combined to produce sensitivity information in a
computationally efficient manner. In this work, sensitivity analyses are
performed on systems described by flux-limited radiative diffusion using the
adjoint approach. The sensitivities computed are shown to agree with standard
perturbation theory, and can be obtained in significantly less computational
time.


title: Bifurcation Analysis of a Stochastically Driven Limit Cycle

abstract:
  We establish the existence of a bifurcation from an attractive random
equilibrium to shear-induced chaos for a stochastically driven limit cycle,
indicated by a change of sign of the first Lyapunov exponent. This addresses an
open problem posed by Kevin Lin and Lai-Sang Young, extending results by
Qiudong Wang and Lai-Sang Young on periodically kicked limit cycles to the
stochastic context.


title: Swift J174540.7-290015: a new accreting binary in the Galactic Center

abstract:
  We report on the identification of the new Galactic Center (GC) transient
Swift J174540.7-290015 as a likely low mass X-ray binary (LMXB) located at only
16 arcsec from Sgr A*. This transient was detected on 2016 February 6th during
the Swift GC monitoring, and it showed long-term spectral variations compatible
with a hard to soft state transition. We observed the field with XMM-Newton on
February 26th for 35 ks, detecting the source in the soft state, characterised
by a low level of variability and a soft X-ray thermal spectrum with a high
energy tail (detected by INTEGRAL up to ~50 keV), typical of either accreting
neutron stars or black holes. We observed: i) a high column density of neutral
absorbing material, suggesting that Swift J174540.7-290015 is located near or
beyond the GC and; ii) a sub-Solar Iron abundance, therefore we argue that Iron
is depleted into dust grains. The lack of detection of FeK absorption lines,
eclipses or dipping suggests that the accretion disc is observed at a low
inclination angle. Radio (VLA) observations did not detect any radio
counterpart to Swift J174540.7-290015. No evidence for X-ray or radio
periodicity is found. The location of the transient was observed also in the
near-IR with GROND at MPG/ESO La Silla 2.2m telescope and VLT/NaCo pre- and
post-outburst. Within the Chandra error region we find multiple objects that
display no significant variations.


title:
A partitioned shift-without-invert algorithm to improve parallel
  eigensolution efficiency in real-space electronic transport

abstract:
  We present an eigenspectrum partitioning scheme without inversion for the
recently described real-space electronic transport code, TRANSEC. The primary
advantage of TRANSEC is its highly parallel algorithm, which enables studying
conductance in large systems. The present scheme adds a new source of
parallelization, significantly enhancing TRANSEC's parallel scalability,
especially for systems with many electrons. In principle, partitioning could
enable super-linear parallel speedup, as we demonstrate in calculations within
TRANSEC. In practical cases, we report better than five-fold improvement in CPU
time and similar improvements in wall time, compared to previously-published
large calculations. Importantly, the suggested scheme is relatively simple to
implement. It can be useful for general large Hermitian or weakly non-Hermitian
eigenvalue problems, whenever relatively accurate inversion via direct or
iterative linear solvers is impractical.

categories: physics.comp-ph cond-mat.mes-hall cs.CE cs.PF


title: The Complexity of Computing all Subfields of an Algebraic Number Field

abstract:
  For a finite separable field extension K/k, all subfields can be obtained by
intersecting so-called principal subfields of K/k. In this work we present a
way to quickly compute these intersections. If the number of subfields is high,
then this leads to faster run times and an improved complexity.


title:
On Valid Optimal Assignment Kernels and Applications to Graph
  Classification

abstract:
  The success of kernel methods has initiated the design of novel positive
semidefinite functions, in particular for structured data. A leading design
paradigm for this is the convolution kernel, which decomposes structured
objects into their parts and sums over all pairs of parts. Assignment kernels,
in contrast, are obtained from an optimal bijection between parts, which can
provide a more valid notion of similarity. In general however, optimal
assignments yield indefinite functions, which complicates their use in kernel
methods. We characterize a class of base kernels used to compare parts that
guarantees positive semidefinite optimal assignment kernels. These base kernels
give rise to hierarchies from which the optimal assignment kernels are computed
in linear time by histogram intersection. We apply these results by developing
the Weisfeiler-Lehman optimal assignment kernel for graphs. It provides high
classification accuracy on widely-used benchmark data sets improving over the
original Weisfeiler-Lehman kernel.


title:
Transport in a gravity dual with a varying gravitational coupling
  constant

abstract:
  We study asymptotically AdS Brans-Dicke (BD) backgrounds, where the Ricci
tensor R is coupled to a scalar in the radial dimension, as effective models of
metals with a varying coupling constant. We show that, for translational
invariant backgrounds, the regular part of the dc conductivity $\sigma_Q$
deviates from the universal result of Einstein-Maxwell-Dilaton (EMD) models.
However, the shear viscosity to entropy ratio saturates the
Kovtun-Son-Starinets (KSS) bound. Similar results apply to more general f(R)
gravity models. In four bulk dimensions we study momentum relaxation induced by
gravitational and electromagnetic axion-dependent couplings. For sufficiently
strong momentum dissipation induced by the former, a recently proposed bound on
the dc conductivity $\sigma$ is violated for any finite electromagnetic axion
coupling. Interestingly, in more than four bulk dimensions, the dc conductivity
for strong momentum relaxation decreases with temperature in the low
temperature limit. In line with other gravity backgrounds with momentum
relaxation, the shear viscosity to entropy ratio is always lower than the KSS
bound. The numerical computation of the optical conductivity reveals a linear
growth with the frequency in the limit of low temperature, low frequency and
large momentum relaxation. We have also shown that the module and argument of
the optical conductivity for intermediate frequencies are not consistent with
cuprates experimental results, even assuming several channel of momentum
relaxation.


title: Relativistic jet feedback in high-redshift galaxies I: Dynamics

abstract:
  We present the results of three dimensional relativistic hydrodynamic
simulations of interaction of AGN jets with a dense turbulent two-phase
interstellar medium, which would be typical of high redshift galaxies. We
describe the effect of the jet on the evolution of the density of the turbulent
ISM. The jet driven energy bubble affects the gas to distances up to several
kiloparsecs from the injection region. The shocks resulting from such
interactions create a multi-phase ISM and radial outflows. One of the striking
result of this work is that low power jets (P_jet < 10^{43} erg/s) although
less efficient in accelerating clouds, are trapped in the ISM for a longer time
and hence affect the ISM over a larger volume. Jets of higher power drill
through with relative ease. Although the relativistic jets launch strong
outflows, there is little net mass ejection to very large distances, supporting
a galactic fountain scenario for local feedback.


title:
Constraining the escape fraction of ionizing photons from HII regions
  within NGC 300: A concept paper

abstract:
  Using broadband photometry from the Hubble Space Telescope in combination
with Very Large Telescope narrowband Halpha observations of the nearby spiral
galaxy NGC 300, we explore a method for estimating the escape fractions of
hydrogen-ionizing photons from HII regions within this galaxy. Our goal in this
concept study is to evaluate the spectral types of the most massive stars using
the broadband data and estimating their ionizing photon output with the help of
stellar atmosphere models. A comparison with the Halpha flux that gives the
amount of ionized gas in the HII region provides a measure of the escape
fraction of ionizing photons from that region. We performed some tests with a
number of synthetic young clusters with varying parameters to assess the
reliability of the method. However, we found that the derived stellar spectral
types and consequently the expected ionizing photon luminosity of a region is
highly uncertain. The tests also show that on one hand we tended to
overestimate the integrated photon output of a region for young ages and low
numbers of stars, and on the other hand we mostly underestimated the combined
ionizing luminosity for a large stellar number and older cluster ages. We
conclude that the proposed method of using stellar broadband photometry to
infer the leakage of ionizing photons from HII regions is highly uncertain and
dominated by the errors of the resulting stellar spectral types. Therefore this
method is not suitable. Stellar spectra are needed to reliably determine the
stellar types and escape fractions. Studies to this end have been carried out
for the Magellanic Clouds.


title:
Microscopic derivation of the one qubit Kraus operators for amplitude
  and phase damping

abstract:
  This article presents microscopic derivation of the Kraus operators for (the
generalized) amplitude and phase damping process. Derivation is based on the
recently developed method [Andersson et al, J. Mod.Opt. 54, 1695 (2007)] which
concerns finite dimensional systems (e.g. qubit). The form of these operators
is usually estimated without insight into the microscopic details of the
dynamics. The behavior of the qubit dynamics is simulated and depicted via
Bloch sphere change.


title: Photoionization models of the CALIFA HII regions. I. Hybrid models

abstract:
  Photoionization models of HII regions require as input a description of the
ionizing SED and of the gas distribution, in terms of ionization parameter U
and chemical abundances (e.g. O/H and N/O). A strong degeneracy exists between
the hardness of the SED and U, which in turn leads to high uncertainties in the
determination of the other parameters, including abundances. One way to resolve
the degeneracy is to fix one of the parameters using additional information.
  For each of the ~ 20000 sources of the CALIFA HII regions catalog, a grid of
photoionization models is computed assuming the ionizing SED being described by
the underlying stellar population obtained from spectral synthesis modeling.
The ionizing SED is then defined as the sum of various stellar bursts of
different ages and metallicities. This solves the degeneracy between the shape
of the ionizing SED and U. The nebular metallicity (associated to O/H) is
defined using the classical strong line method O3N2 (which gives to our models
the status of "hybrids"). The remaining free parameters are the abundance ratio
N/O and the ionization parameter U, which are determined by looking for the
model fitting [NII]/Ha and [OIII]/Hb. The models are also selected to fit
[OII]/Hb. This process leads to a set of ~ 3200 models that reproduce
simultaneously the three observations.
  We find that the regions associated to young stellar bursts suffer leaking of
the ionizing photons, the proportion of escaping photons having a median of
80\%. The set of photoionization models satisfactorily reproduces the electron
temperature derived from the [OIII]4363/5007 line ratio. We determine new
relations between the ionization parameter U and the [OII]/[OIII] or
[SII]/[SIII] line ratios. New relations between N/O and O/H and between U and
O/H are also determined.
  All the models are publicly available on the 3MdB database.


title: Singularities in FLRW Spacetimes

abstract:
  We point out that past-incompleteness of geodesics in FLRW spacetimes does
not necessarily imply that these spacetimes start from a singularity. Namely,
if a test particle that follows such a trajectory has a non-vanishing velocity,
its energy was super-Planckian at some time in the past if it kept following
that geodesic. That indicates a breakdown of the particle's description, which
is why we should not consider those trajectories for the definition of an
initial singularity. When one only considers test particles that do not have
this breakdown of their trajectory, it turns out that the only singular FLRW
spacetimes are the ones that have a scale parameter that vanishes at some
initial time.


title: Tripartite Unions

abstract:
  This note provides conditions under which the union of three well-founded
binary relations is also well-founded.


title:
First principles Kinetic-Collective thermal conductivity of
  semiconductors

abstract:
  A fully predictive Kinetic Collective Model using first principles phonon
spectra and relaxation times is presented. Thermal conductivity values obtained
for Si, Ge, C (diamond) and GaAs in a wide range of sizes and temperatures have
good agreement with experimental data without the use of any fitting parameter.
This validation of the model open the door to discuss how the precise
combination of kinetic and collective contributions to heat transport could
provide a useful framework to interpret recent complex experiments displaying
non-Fourier behavior.


title: Redundancy of multiset topological spaces

abstract:
  In this paper, we prove the redundancies of multiset topologies. It is shown
that there is a complement preserving isomorphism between
$(P^\star(U),\sqsubseteq)$ and $(\mathcal{P}(X\times\mathbb{N}),\subseteq)$. It
therefore follows that multiset topologies are superfluous and unnecessary in
the theoretical view point.


title:
Using Neural Generative Models to Release Synthetic Twitter Corpora with
  Reduced Stylometric Identifiability of Users

abstract:
  We present a method for generating synthetic versions of Twitter data using
neural generative models. The goal is protecting individuals in the source data
from stylometric re-identification attacks while still releasing data that
carries research value. Specifically, we generate tweet corpora that maintain
user-level word distributions by augmenting the neural language models with
user-specific components. We compare our approach to two standard text data
protection methods: redaction and iterative translation. We evaluate the three
methods on measures of risk and utility. We define risk following the
stylometric models of re-identification, and we define utility based on two
general word distribution measures and two common text analysis research tasks.
We find that neural models are able to significantly lower risk over previous
methods with little cost to utility. We also demonstrate that the neural models
allow data providers to actively control the risk-utility trade-off through
model tuning parameters. This work presents promising results for a new tool
addressing the problem of privacy for free text and sharing social media data
in a way that respects privacy and is ethically responsible.


title:
Search for exotic spin-dependent interactions with a spin-exchange
  relaxation-free magnetometer

abstract:
  We propose a novel experimental approach to explore exotic spin-dependent
interactions using a spin-exchange relaxation-free (SERF) magnetometer, the
most sensitive non-cryogenic magnetic-field sensor. This approach studies the
interactions between optically polarized electron spins located inside a vapor
cell of the SERF magnetometer and unpolarized or polarized particles of
external solid-state objects. The coupling of spin-dependent interactions to
the polarized electron spins of the magnetometer induces the tilt of the
electron spins, which can be detected with high sensitivity by a probe laser
beam similarly as an external magnetic field. We estimate that by moving
unpolarized or polarized objects next to the SERF Rb vapor cell, the
experimental limit to the spin-dependent interactions can be significantly
improved over existing experiments, and new limits on the coupling strengths
can be set in the interaction range below 0.01 m.


title:
Bounding stationary averages of polynomial diffusions via semidefinite
  programming

abstract:
  We introduce an algorithm based on semidefinite programming that yields
increasing (resp. decreasing) sequences of lower (resp. upper) bounds on
polynomial stationary averages of diffusions with polynomial drift vector and
diffusion coefficients. The bounds are obtained by optimising an objective,
determined by the stationary average of interest, over the set of real vectors
defined by certain linear equalities and semidefinite inequalities which are
satisfied by the moments of any stationary measure of the diffusion. We
exemplify the use of the approach through several applications: a Bayesian
inference problem; the computation of Lyapunov exponents of linear ordinary
differential equations perturbed by multiplicative white noise; and a
reliability problem from structural mechanics. Additionally, we prove that the
bounds converge to the infimum and supremum of the set of stationary averages
for certain SDEs associated with the computation of the Lyapunov exponents, and
we provide numerical evidence of convergence in more general settings.


title: A gap theorem of four-dimensional gradient shrinking solitons

abstract:
  In this paper, we will prove a gap theorem for four-dimensional gradient
shrinking soliton. More precisely, we will show that any complete
four-dimensional gradient shrinking soliton with nonnegative and bounded Ricci
curvature, satisfying a pinched Weyl curvature, either is flat, or $\lambda_1 +
\lambda_2\ge c_0 R>0$ everywhere for some $c_0\approx 0.29167$, where
$\{\lambda_i\}$ are the two least eigenvalues of Ricci curvature. Furthermore,
we will show that $\lambda_1 + \lambda_2\ge \frac 13R>0$ under a better pinched
Weyl tensor assumption. We point out that the lower bound $\frac 13R$ is sharp.


title:
Modelling the angle-dependent magnetoresistance oscillations of Fermi
  surfaces with hexagonal symmetry

abstract:
  By solving the Boltzmann transport equation we investigate theoretically the
general form of oscillations in the resistivity caused by varying the direction
of an applied magnetic field for the case of quasi-two dimensional systems on
hexagonal lattices. The presence of the angular magnetoresistance oscillations
can be used to map out the topology of the Fermi surface and we study how this
effect varies as a function of the degree of interplane warping as well as a
function of the degree of isotropic scattering. We find that the angular
dependent effect due to in-plane rotation follows the symmetry imposed by the
lattice whereas for inter-plane rotation the degree of warping dictates the
dominant features observed in simulations. Our calculations make predictions
for specific angle-dependent magnetotransport signatures in magnetic fields
expected for quasi-two dimensional hexagonal compounds similar to PdCoO2 and
PtCoO2.


title: Coupling of Particle Filters

abstract:
  Particle filters provide Monte Carlo approximations of intractable quantities
such as point-wise evaluations of the likelihood in state space models. In many
scenarios, the interest lies in the comparison of these quantities as some
parameter or input varies. To facilitate such comparisons, we introduce and
study methods to couple two particle filters in such a way that the correlation
between the two underlying particle systems is increased. The motivation stems
from the classic variance reduction technique of positively correlating two
estimators. The key challenge in constructing such a coupling stems from the
discontinuity of the resampling step of the particle filter. As our first
contribution, we consider coupled resampling algorithms. Within bootstrap
particle filters, they improve the precision of finite-difference estimators of
the score vector and boost the performance of particle marginal
Metropolis--Hastings algorithms for parameter inference. The second
contribution arises from the use of these coupled resampling schemes within
conditional particle filters, allowing for unbiased estimators of smoothing
functionals. The result is a new smoothing strategy that operates by averaging
a number of independent and unbiased estimators, which allows for 1)
straightforward parallelization and 2) the construction of accurate error
estimates. Neither of the above is possible with existing particle smoothers.


title:
Four-dimensional Einstein manifolds with sectional curvature bounded
  from above

abstract:
  Given an Einstein structure with positive scalar curvature on a
four-dimensional Riemannian manifolds, that is $Ric=\lambda g$ for some
positive constant $\lambda$. For convenience, the Ricci curvature is always
normalized to $Ric=1$. A basic problem is to classify four-dimensional Einstein
manifolds with positive or nonnegative curvature and $Ric=1$. In this paper, we
firstly show that if the sectional curvature satisfies $K\le M_1=
\frac{\sqrt{3}}2\approx 0.866025$, then the sectional curvature will be
nonnegative. Next, we prove a family of rigidity theorems of Einstein
four-manifolds with nonnegative sectional curvature, and satisfies
$K_{ik}+sK_{ij}\ge K_s = \frac{1 + \sqrt{2}}3 - \frac{\sqrt{4+2\sqrt{2}}}4 +
\frac{2-\sqrt{2}}6 s$ for every orthonormal basis $\{e_i\}$ with $K_{ik}\ge
K_{ij}$, where $s$ is any nonnegative constant. Indeed, we will show that these
Einstein manifolds must be isometric either $S^4$, $RP^4$ or $CP^2$ with
standard metrics. As a corollary, we give a rigidity result of Einstein
four-manifolds with $Ric=1$, and the sectional curvature satisfies $K \le M_2 =
\frac {2-\sqrt{2}}6 + \frac{\sqrt{4+2\sqrt{2}}}4 \approx 0.750912$.


title:
Boundary behaviour of Weil-Petersson and fiber metrics for Riemann
  moduli spaces

abstract:
  The Weil-Petersson and Takhtajan-Zograf metrics on the Riemann moduli spaces
of complex structures for an $n$-fold punctured oriented surface of genus $g,$
in the stable range $g+2n>2,$ are shown here to have complete asymptotic
expansions in terms of Fenchel-Nielsen coordinates at the exceptional divisors
of the Knudsen-Deligne-Mumford compactification. This is accomplished by
finding a full expansion for the hyperbolic metrics on the fibers of the
universal curve as they approach the complete metrics on the nodal curves above
the exceptional divisors and then using a push-forward theorem for conormal
densities. This refines a two-term expansion due to Obitsu-Wolpert for the
conformal factor relative to the model plumbing metric which in turn refined
the bound obtained by Masur. A similar expansion for the Ricci metric is also
obtained.


title:
Heat kernel asymptotics on sub-Riemannian manifolds with symmetries and
  applications to the bi-Heisenberg group

abstract:
  By adapting a technique of Molchanov, we obtain the heat kernel asymptotics
at the sub-Riemannian cut locus, when the cut points are reached by an
$r$-dimensional parametric family of optimal geodesics. We apply these results
to the bi-Heisenberg group, that is, a nilpotent left-invariant
sub-Rieman\-nian structure on $\mathbb{R}^{5}$ depending on two real parameters
$\alpha_{1}$ and $\alpha_{2}$. We develop some results about its geodesics and
heat kernel associated to its sub-Laplacian and we illuminate some interesting
geometric and analytic features appearing when one compares the isotropic
($\alpha_{1}=\alpha_{2}$) and the non-isotropic cases ($\alpha_{1}\neq
\alpha_{2}$). In particular, we give the exact structure of the cut locus, and
we get the complete small-time asymptotics for its heat kernel.


title: Robust Ensemble Clustering Using Probability Trajectories

abstract:
  Although many successful ensemble clustering approaches have been developed
in recent years, there are still two limitations to most of the existing
approaches. First, they mostly overlook the issue of uncertain links, which may
mislead the overall consensus process. Second, they generally lack the ability
to incorporate global information to refine the local links. To address these
two limitations, in this paper, we propose a novel ensemble clustering approach
based on sparse graph representation and probability trajectory analysis. In
particular, we present the elite neighbor selection strategy to identify the
uncertain links by locally adaptive thresholds and build a sparse graph with a
small number of probably reliable links. We argue that a small number of
probably reliable links can lead to significantly better consensus results than
using all graph links regardless of their reliability. The random walk process
driven by a new transition probability matrix is utilized to explore the global
information in the graph. We derive a novel and dense similarity measure from
the sparse graph by analyzing the probability trajectories of the random
walkers, based on which two consensus functions are further proposed.
Experimental results on multiple real-world datasets demonstrate the
effectiveness and efficiency of our approach.


title:
Exploiting Multi-typed Treebanks for Parsing with Deep Multi-task
  Learning

abstract:
  Various treebanks have been released for dependency parsing. Despite that
treebanks may belong to different languages or have different annotation
schemes, they contain syntactic knowledge that is potential to benefit each
other. This paper presents an universal framework for exploiting these
multi-typed treebanks to improve parsing with deep multi-task learning. We
consider two kinds of treebanks as source: the multilingual universal treebanks
and the monolingual heterogeneous treebanks. Multiple treebanks are trained
jointly and interacted with multi-level parameter sharing. Experiments on
several benchmark datasets in various languages demonstrate that our approach
can make effective use of arbitrary source treebanks to improve target parsing
models.


title:
Spectral descriptors for bulk metallic glasses based on the
  thermodynamics of competing crystalline phases

abstract:
  Metallic glasses have attracted considerable interest in recent years due to
their unique combination of superb properties and processability. Predicting
bulk metallic glass formers from known parameters remains a challenge and the
search for new systems is still performed by trial and error. It has been
speculated that some sort of "confusion" during crystallization of the
crystalline phases competing with glass formation could play a key role. Here,
we propose a heuristic descriptor quantifying confusion and demonstrate its
validity by detailed experiments on two well-known glass forming alloy systems.
With the insight provided by these results, we develop a robust model for
predicting glass formation ability based on the spectral decomposition of
geometrical and energetic features of crystalline phases calculated ab-initio
in the AFLOW high throughput framework. Our findings indicate that the
formation of metallic glass phases could be a much more common phenomenon than
currently estimated, with more than 17% of binary alloy systems being potential
glass formers. Our approach is capable of pinpointing favorable compositions,
overcoming a major bottleneck hindering the discovery of new materials. Hence,
it is demonstrated that smart descriptors, based solely on the energetics and
structure of competing crystalline phases calculated from first-principles and
available in online databases, others the sought-after key for accelerated
discovery of novel metallic glasses.


title:
Reduced basis isogeometric mortar approximations for eigenvalue problems
  in vibroacoustics

abstract:
  We simulate the vibration of a violin bridge in a multi-query context using
reduced basis techniques. The mathematical model is based on an eigenvalue
problem for the orthotropic linear elasticity equation. In addition to the nine
material parameters, a geometrical thickness parameter is considered. This
parameter enters as a 10th material parameter into the system by a mapping onto
a parameter independent reference domain. The detailed simulation is carried
out by isogeometric mortar methods. Weakly coupled patch-wise tensorial
structured isogeometric elements are of special interest for complex geometries
with piecewise smooth but curvilinear boundaries. To obtain locality in the
detailed system, we use the saddle point approach and do not apply static
condensation techniques. However within the reduced basis context, it is
natural to eliminate the Lagrange multiplier and formulate a reduced eigenvalue
problem for a symmetric positive definite matrix. The selection of the
snapshots is controlled by a multi-query greedy strategy taking into account an
error indicator allowing for multiple eigenvalues.


title: Dense Associative Memory for Pattern Recognition

abstract:
  A model of associative memory is studied, which stores and reliably retrieves
many more patterns than the number of neurons in the network. We propose a
simple duality between this dense associative memory and neural networks
commonly used in deep learning. On the associative memory side of this duality,
a family of models that smoothly interpolates between two limiting cases can be
constructed. One limit is referred to as the feature-matching mode of pattern
recognition, and the other one as the prototype regime. On the deep learning
side of the duality, this family corresponds to feedforward neural networks
with one hidden layer and various activation functions, which transmit the
activities of the visible neurons to the hidden layer. This family of
activation functions includes logistics, rectified linear units, and rectified
polynomials of higher degrees. The proposed duality makes it possible to apply
energy-based intuition from associative memory to analyze computational
properties of neural networks with unusual activation functions - the higher
rectified polynomials which until now have not been used in deep learning. The
utility of the dense memories is illustrated for two test cases: the logical
gate XOR and the recognition of handwritten digits from the MNIST data set.

categories: cs.NE cond-mat.dis-nn cs.LG q-bio.NC stat.ML


title:
Origin of central abundances in the hot intra-cluster medium - I.
  Individual and average abundance ratios from XMM-Newton EPIC

abstract:
  The hot intra-cluster medium (ICM) is rich in metals, which are synthesized
by supernovae (SNe) explosions and accumulate over time into the deep
gravitational potential well of clusters of galaxies. Since most of the
elements visible in X-rays are formed by type Ia (SNIa) and/or core-collapse
(SNcc) supernovae, measuring their abundances gives us direct information on
the nucleosynthesis products of billions of SNe since the epoch of the star
formation peak (z ~ 2-3). In this study, we use the EPIC and RGS instruments
onboard XMM-Newton to measure the abundances of 9 elements (O, Ne, Mg, Si, S,
Ar, Ca, Fe and Ni) from a sample of 44 nearby cool-core galaxy clusters,
groups, and elliptical galaxies. We find that the Fe abundance shows a large
scatter (~20-40%) over the sample, within 0.2$r_{500}$ and, especially,
0.05$r_{500}$. Unlike the absolute Fe abundance, the abundance ratios (X/Fe)
are quite uniform over the considered temperature range (~0.6-8 keV), and with
a limited scatter. In addition to a unprecedented treatment of systematic
uncertainties, we provide the most accurate abundance ratios measured so far in
the ICM, including Cr/Fe and Mn/Fe that we firmly detect (>4{\sigma} with MOS
and pn independently). We find that Cr/Fe, Mn/Fe and Ni/Fe, differ
significantly from the proto-solar values. However, the large uncertainties in
the proto-solar abundances prevent us from making a robust comparison between
the local and the intra-cluster chemical enrichments. We also note that,
interestingly, and despite the large net exposure time (~4.5 Ms) of our
dataset, no line emission feature is seen around ~3.5 keV.


title:
Generalizing the Convolution Operator to extend CNNs to Irregular
  Domains

abstract:
  Convolutional Neural Networks (CNNs) have become the state-of-the-art in
supervised learning vision tasks. Their convolutional filters are of paramount
importance for they allow to learn patterns while disregarding their locations
in input images. When facing highly irregular domains, generalized
convolutional operators based on an underlying graph structure have been
proposed. However, these operators do not exactly match standard ones on grid
graphs, and introduce unwanted additional invariance (e.g. with regards to
rotations). We propose a novel approach to generalize CNNs to irregular domains
using weight sharing and graph-based operators. Using experiments, we show that
these models resemble CNNs on regular domains and offer better performance than
multilayer perceptrons on distorded ones.


title: How Deep is the Feature Analysis underlying Rapid Visual Categorization?

abstract:
  Rapid categorization paradigms have a long history in experimental
psychology: Characterized by short presentation times and speedy behavioral
responses, these tasks highlight the efficiency with which our visual system
processes natural object categories. Previous studies have shown that
feed-forward hierarchical models of the visual cortex provide a good fit to
human visual decisions. At the same time, recent work in computer vision has
demonstrated significant gains in object recognition accuracy with increasingly
deep hierarchical architectures. But it is unclear how well these models
account for human visual decisions and what they may reveal about the
underlying brain processes.
  We have conducted a large-scale psychophysics study to assess the correlation
between computational models and human participants on a rapid animal vs.
non-animal categorization task. We considered visual representations of varying
complexity by analyzing the output of different stages of processing in three
state-of-the-art deep networks. We found that recognition accuracy increases
with higher stages of visual processing (higher level stages indeed
outperforming human participants on the same task) but that human decisions
agree best with predictions from intermediate stages.
  Overall, these results suggest that human participants may rely on visual
features of intermediate complexity and that the complexity of visual
representations afforded by modern deep network models may exceed those used by
human participants during rapid categorization.


title: Regularity inheritance in pseudorandom graphs

abstract:
  Advancing the sparse regularity method, we prove one-sided and two-sided
regularity inheritance lemmas for subgraphs of bijumbled graphs, improving on
results of Conlon, Fox and Zhao [Adv. Math. 256 (2014), 206--290]. These
inheritance lemmas also imply improved $H$-counting lemmas for subgraphs of
bijumbled graphs, for some $H$.


title:
Leveraging Evolution Dynamics to Generate Benchmark Complex Networks
  with Community Structures

abstract:
  The past decade has seen tremendous growth in the field of Complex Social
Networks. Several network generation models have been extensively studied to
develop an understanding of how real world networks evolve over time. Two
important applications of these models are to study the evolution dynamics and
processes that shape a network, and to generate benchmark networks with known
community structures. Research has been conducted in both these directions,
relatively independent of the other. This creates a disjunct between real world
networks and the networks generated as benchmarks to study community detection
algorithms.
  In this paper, we propose to study both these application areas together. We
introduce a network generation model which is based on evolution dynamics of
real world networks and, it can generate networks with community structures
that can be used as benchmark graphs. We study the behaviour of different
community detection algorithms based on the proposed model and compare it with
other models to generate benchmark graphs. Results suggest that the proposed
model can generate networks which are not only structurally similar to real
world networks but can be used to generate networks with varying community
sizes and topologies.


title:
Superconductivity in FeSe thin films driven by the interplay between
  nematic fluctuations and spin-orbit coupling

abstract:
  The origin of the high-temperature superconducting state observed in FeSe
thin films, whose phase diagram displays no sign of magnetic order, remains a
hotly debated topic. Here we investigate whether fluctuations arising due to
the proximity to a nematic phase, which is observed in the phase diagram of
this material, can promote superconductivity. We find that nematic fluctuations
alone promote a highly degenerate pairing state, in which both $s$-wave and
$d$-wave symmetries are equally favored, and $T_{c}$ is consequently
suppressed. However, the presence of a sizable spin-orbit coupling or inversion
symmetry-breaking at the film interface lifts this harmful degeneracy and
selects the $s$-wave state, in agreement with recent experimental proposals.
The resulting gap function displays a weak anisotropy, which agrees with
experiments in monolayer FeSe and intercalated Li$_{1-x}$(OH)$_{x}$FeSe.


title: The Standard Complex and the 3-dimensional Poincar\'e Conjecture

abstract:
  We develop a method for constructing standard complexes which turns easy the
calculation of their algebraic invariants and, as well, the precise evaluation
of whether these complexes are embeddable or not in a 3-manifold. This method
applies to all familiar spines of 3-manifolds and, in particular, to the Bing
house with two rooms and the classical standard spine of the Poincar\'e sphere.
Finally, we exhibit a compact, connected standard complex which is embeddable
into an orientable 3-manifold, its fundamental group is $Z_{2}$ and it contains
a Klein bottle. This standard complex is the spine of a reducible 3-manifold
$M^3$, sum of a Seifert fiber space with a fake solid torus, whose universal
covering space $W^3$ is a closed and simply connected 3-manifold that cannot be
homeomorphic to $S^{3}$.


title: Generic case completeness

abstract:
  In this note we introduce a notion of a generically (strongly generically)
NP-complete problem and show that the randomized bounded version of the halting
problem is strongly generically NP-complete.


title: Tapered amplifier laser with frequency-shifted feedback

abstract:
  We present a frequency-shifted feedback (FSF) laser based on a tapered
amplifier. The laser operates as a coherent broadband source with up to 370GHz
spectral width and 2.3us coherence time. If the FSF laser is seeded by a
continuous-wave laser a frequency comb spanning the output spectrum appears in
addition to the broadband emission. The laser has an output power of 280mW and
a center wavelength of 780nm. The ease and flexibility of use of tapered
amplifiers makes our FSF laser attractive for a wide range of applications,
especially in metrology.


title:
Semimetallic "Electride Bands" Derived from Interlayer Electrons in
  Quasi-Two-Dimensional Electride Y$_2$C

abstract:
  Two-dimensional (2D) electrides are a new concept material in which anionic
electrons are confined in the interlayer space between positively charged
layers. We have performed angle-resolved photoemission spectroscopy
measurements on Y$_2$C, which is a possible 2D electride, in order to verify
the formation of 2D electride states in Y$_2$C. We clearly observe the
existence of semimetallic "electride bands" near the Fermi level, as predicted
by ${ab}$ ${initio}$ calculations, conclusively demonstrating that Y$_2$C is a
quasi-2D electride with electride bands derived from interlayer anionic
electrons.


title: Infant directed speech is consistent with teaching

abstract:
  Infant-directed speech (IDS) has distinctive properties that differ from
adult-directed speech (ADS). Why it has these properties -- and whether they
are intended to facilitate language learning -- is matter of contention. We
argue that much of this disagreement stems from lack of a formal, guiding
theory of how phonetic categories should best be taught to infant-like
learners. In the absence of such a theory, researchers have relied on
intuitions about learning to guide the argument. We use a formal theory of
teaching, validated through experiments in other domains, as the basis for a
detailed analysis of whether IDS is well-designed for teaching phonetic
categories. Using the theory, we generate ideal data for teaching phonetic
categories in English. We qualitatively compare the simulated teaching data
with human IDS, finding that the teaching data exhibit many features of IDS,
including some that have been taken as evidence IDS is not for teaching. The
simulated data reveal potential pitfalls for experimentalists exploring the
role of IDS in language learning. Focusing on different formants and phoneme
sets leads to different conclusions, and the benefit of the teaching data to
learners is not apparent until a sufficient number of examples have been
provided. Finally, we investigate transfer of IDS to learning ADS. The teaching
data improves classification of ADS data, but only for the learner they were
generated to teach; not universally across all classes of learner. This
research offers a theoretically-grounded framework that empowers
experimentalists to systematically evaluate whether IDS is for teaching.


title:
A Markov Chain Approach for Defining the Fundamental Efficiency Limits
  of Classical and Bifacial Multi-junction Tandem Solar Cells

abstract:
  Bifacial tandem cells promise to reduce three fundamental losses
(above-bandgap, below bandgap, and the uncollected light between panels)
inherent in classical single junction PV systems. The successive filtering of
light through the bandgap cascade, and requirement of current continuity make
optimization of tandem cells difficult, accessible only to numerical solution
through computer modeling. The challenge is even more complicated for bifacial
design. In this paper, we use an elegantly simple Markov chain approach to show
that the essential physics of optimization is intuitively obvious, and deeply
insightful results can obtained analytically with a few lines of algebra. This
powerful approach reproduces, as special cases, all the known results of
traditional/bifacial tandem cells, and highlights the asymptotic efficiency
gain of these technologies.


title: Axodraw Version 2

abstract:
  We present version two of the Latex graphical style file Axodraw. It has a
number of new drawing primitives and many extra options, and it can now work
with \program{pdflatex} to directly produce output in PDF file format (but with
the aid of an auxiliary program).


title: Reinforcement Learning for Semantic Segmentation in Indoor Scenes

abstract:
  Future advancements in robot autonomy and sophistication of robotics tasks
rest on robust, efficient, and task-dependent semantic understanding of the
environment. Semantic segmentation is the problem of simultaneous segmentation
and categorization of a partition of sensory data. The majority of current
approaches tackle this using multi-class segmentation and labeling in a
Conditional Random Field (CRF) framework or by generating multiple object
hypotheses and combining them sequentially. In practical settings, the subset
of semantic labels that are needed depend on the task and particular scene and
labelling every single pixel is not always necessary. We pursue these
observations in developing a more modular and flexible approach to multi-class
parsing of RGBD data based on learning strategies for combining independent
binary object-vs-background segmentations in place of the usual monolithic
multi-label CRF approach. Parameters for the independent binary segmentation
models can be learned very efficiently, and the combination strategy---learned
using reinforcement learning---can be set independently and can vary over
different tasks and environments. Accuracy is comparable to state-of-art
methods on a subset of the NYU-V2 dataset of indoor scenes, while providing
additional flexibility and modularity.


title:
An estimate of the second moment of a sampling of the Riemann zeta
  function on the critical line

abstract:
  We investigate the second moment of a random sampling $\zeta(1/2+iX_t)$ of
the Riemann zeta function on the critical line. Our main result states that if
$X_t$ is an increasing random sampling with gamma distribution, then for all
sufficiently large $t$, \[\mathbb{E} |\zeta(1/2+iX_t)|^2 = \log t +
O(\sqrt{\log t}\log\log t).\]


title: Min-Max Regret Problems with Ellipsoidal Uncertainty Sets

abstract:
  We consider robust counterparts of uncertain combinatorial optimization
problems, where the difference to the best possible solution over all scenarios
is to be minimized. Such minmax regret problems are typically harder to solve
than their nominal, non-robust counterparts. While current literature almost
exclusively focuses on simple uncertainty sets that are either finite or
hyperboxes, we consider problems with more flexible and realistic ellipsoidal
uncertainty sets. We present complexity results for the unconstrained
combinatorial optimization problem and for the shortest path problem. To solve
such problems, two types of cuts are introduced, and compared in a
computational experiment.


title: A New Overview of Secular Period Changes of RR Lyrae stars inM5

abstract:
  Secular period variations, $\beta=\dot{P}$, in 76 RR Lyrae stars in the
globular cluster M5 are analysed using our most recent CCD $V$ photometry and
the historical photometric database available in the literature since 1889.
This provides a time baseline of up to 118 years for these variables. The
analysis was performed using two independent approaches: first, the classical
$O-C$ behaviour of the time of maximum light, and second, via a grid
$(P,\beta)$, where the solution producing the minimum scatter in the phased
light curve is chosen. The results of the two methods agree satisfactorily.
This allowed a new interpretation of the nature of the period changes in many
RR Lyrae stars in M5. It is found that in $96\%$ of the stars studied no
irregular or stochastic variations need to be claimed, but that $66\%$ of the
population shows steady period increases or decreases, and that $34\%$ of the
periods seem to have been stable over the last century.
  The lack of systematic positive or negative period variations in RR Lyrae
stars in other globular clusters is addressed, and the paradigm of period
changes being a consequence of stellar evolution is discussed in terms of
chemical variations near the stellar core and of multiple stellar populations.
In M5 we found a small positive average value of $\beta$ and a small surplus of
RRab stars with a period increase. Nevertheless, in M5 we have been able to
isolate a group of likely evolved stars that systematically show positive, and
in some cases large, period change rates.


title: On maximal stable quotients of definable groups in NIP theories

abstract:
  For G a group definable in an NIP theory we prove that there is a smallest
type-definable subgroup H of G such that the quotient G/H is stable. This
generalizes the existence of G^00, the smallest type-definable subgroup of G of
bounded index.


title: Peter Hall's work on high-dimensional data and classification

abstract:
  In this article, I summarise Peter Hall's contributions to high-dimensional
data, including their geometric representations and variable selection methods
based on ranking. I also discuss his work on classification problems,
concluding with some personal reflections on my own interactions with him.


title:
On the properties of compact groups identified in different photometric
  bands

abstract:
  Historically, compact group catalogues vary not only in their identification
algorithms and selection functions, but also in their photometric bands.
Differences between compact group catalogues have been reported. However, it is
difficult to assess the impact of the photometric band in these differences
given the variety of identification algorithms. We used the mock lightcone
built by Henriques et al. (2012) to identify and compare compact groups in
three different photometric bands: $K$, $r$, and $u$. We applied the same
selection functions in the three bands, and found that compact groups in the
u-band look the smallest in projection, the difference between the two
brightest galaxies is the largest in the K-band, while compact groups in the
r-band present the lowest compactness. We also investigated the differences
between samples when galaxies are selected only in one particular band (pure
compact groups) and those that exist regardless the band in which galaxies were
observed (common compact groups). We found that the differences between the
total samples are magnified, but also some others arise: pure-r compact groups
are the largest in projection; pure-u compact groups have the brightest first
ranked galaxies, and the most similar two first ranked galaxies; pure-K compact
groups have the highest compactness and the most different two first ranked
galaxies; and common compact groups show the largest percentage of physically
dense groups. Therefore, without a careful selection and identification of the
samples, the characteristic features of group properties in a particular
photometric band could be overshadowed.


title: Non-Markovianity and memory of the initial state

abstract:
  We explore in a rigorous manner the intuitive connection between the
non-Markovianity of the evolution of an open quantum system and the performance
of the system as a quantum memory. Using the paradigmatic case of a two-level
open quantum system coupled to a bosonic bath, we compute the recovery
fidelity, which measures the best possible performance of the system to store a
qubit of information. We deduce that this quantity is connected, but not
uniquely determined, by the non-Markovianity, for which we adopt the BLP
measure proposed in \cite{breuer2009}. We illustrate our findings with explicit
calculations for the case of a structured environment.


title:
Spin-glass phase transition and behavior of nonlinear susceptibility in
  the Sherrington-Kirkpatrick model with random fields

abstract:
  The behavior of the nonlinear susceptibility $\chi_3$ and its relation to the
spin-glass transition temperature $T_f$, in the presence of random fields, are
investigated. To accomplish this task, the Sherrington-Kirkpatrick model is
studied through the replica formalism, within a one-step
replica-symmetry-breaking procedure. In addition, the dependence of the
Almeida-Thouless eigenvalue $\lambda_{\rm AT}$ (replicon) on the random fields
is analyzed. Particularly, in absence of random fields, the temperature $T_f$
can be traced by a divergence in the spin-glass susceptibility $\chi_{\rm SG}$,
which presents a term inversely proportional to the replicon $\lambda_{\rm
AT}$. As a result of a relation between $\chi_{\rm SG}$ and $\chi_3$, the
latter also presents a divergence at $T_f$, which comes as a direct consequence
of $\lambda_{\rm AT}=0$ at $T_f$. However, our results show that, in the
presence of random fields, $\chi_3$ presents a rounded maximum at a temperature
$T^{*}$, which does not coincide with the spin-glass transition temperature
$T_f$ (i.e., $T^* > T_f$ for a given applied random field). Thus, the maximum
value of $\chi_3$ at $T^*$ reflects the effects of the random fields in the
paramagnetic phase, instead of the non-trivial ergodicity breaking associated
with the spin-glass phase transition. It is also shown that $\chi_3$ still
maintains a dependence on the replicon $\lambda_{\rm AT}$, although in a more
complicated way, as compared with the case without random fields. These results
are discussed in view of recent observations in the LiHo$_x$Y$_{1-x}$F$_4$
compound.


title: Multidomain Skyrmion Lattice State in Cu$_2$OSeO$_3$

abstract:
  Magnetic skyrmions in chiral magnets are nanoscale, topologically-protected
magnetization swirls that are promising candidates for spintronics memory
carriers. Therefore, observing and manipulating the skyrmion state on the
surface level of the materials are of great importance for future applications.
Here, we report a controlled way of creating a multidomain skyrmion state near
the surface of a Cu$_{2}$OSeO$_{3}$ single crystal, observed by soft resonant
elastic x-ray scattering. This technique is an ideal tool to probe the magnetic
order at the $L_{3}$ edge of $3d$ metal compounds giving a depth sensitivity of
${\sim}50$ nm. The single-domain sixfold-symmetric skyrmion lattice can be
broken up into domains overcoming the propagation directions imposed by the
cubic anisotropy by applying the magnetic field in directions deviating from
the major cubic axes. Our findings open the door to a new way to manipulate and
engineer the skyrmion state locally on the surface, or on the level of
individual skyrmions, which will enable applications in the future.


title:
A parabolic Triebel-Lizorkin space estimate for the fractional Laplacian
  operator

abstract:
  In this paper we prove a parabolic Triebel-Lizorkin space estimate for the
operator given by \[T^{\alpha}f(t,x) = \int_0^t \int_{{\mathbb R}^d}
P^{\alpha}(t-s,x-y)f(s,y) dyds,\] where the kernel is \[P^{\alpha}(t,x) =
\int_{{\mathbb R}^d} e^{2\pi ix\cdot\xi} e^{-t|\xi|^\alpha} d\xi.\] The
operator $T^{\alpha}$ maps from $L^{p}F_{s}^{p,q}$ to
$L^{p}F_{s+\alpha/p}^{p,q}$ continuously. It has an application to a class of
stochastic integro-differential equations of the type $du =
-(-\Delta)^{\alpha/2} u dt + f dX_t$.


title: Quanta of Geometry and Unification

abstract:
  This is a tribute to Abdus Salam's memory whose insight and creative thinking
set for me a role model to follow. In this contribution I show that the simple
requirement of volume quantization in space-time (with Euclidean signature)
uniquely determines the geometry to be that of a noncommutative space whose
finite part is based on an algebra that leads to Pati-Salam grand unified
models. The Standard Model corresponds to a special case where a mathematical
constraint (order one condition) is satisfied. This provides evidence that
Salam was a visionary who was generations ahead of his time.


title: Distributed stochastic optimization via matrix exponential learning

abstract:
  In this paper, we investigate a distributed learning scheme for a broad class
of stochastic optimization problems and games that arise in signal processing
and wireless communications. The proposed algorithm relies on the method of
matrix exponential learning (MXL) and only requires locally computable gradient
observations that are possibly imperfect and/or obsolete. To analyze it, we
introduce the notion of a stable Nash equilibrium and we show that the
algorithm is globally convergent to such equilibria - or locally convergent
when an equilibrium is only locally stable. We also derive an explicit linear
bound for the algorithm's convergence speed, which remains valid under
measurement errors and uncertainty of arbitrarily high variance. To validate
our theoretical analysis, we test the algorithm in realistic
multi-carrier/multiple-antenna wireless scenarios where several users seek to
maximize their energy efficiency. Our results show that learning allows users
to attain a net increase between 100% and 500% in energy efficiency, even under
very high uncertainty.


title: On Chari-Loktev bases for local Weyl modules in type $A$

abstract:
  This paper is a study of the bases introduced by Chari-Loktev for local Weyl
modules of the current algebra associated to a special linear Lie algebra.
Partition overlaid patterns, POPs for short---whose introduction is one of the
aims of this paper---form convenient parametrizing sets of these bases. They
play a role analogous to that played by (Gelfand-Tsetlin) patterns in the
representation theory of the special linear Lie algebra.
  The notion of a POP leads naturally to the notion of area of a pattern. We
observe that there is a unique pattern of maximal area among all those with a
given bounding sequence and given weight. We give a combinatorial proof of this
and discuss its representation theoretic relevance.
  We then state a conjecture about the "stability", i.e., compatibility in the
long range, of Chari-Loktev bases with respect to inclusions of local Weyl
modules. In order to state the conjecture, we establish a certain bijection
between colored partitions and POPs, which may be of interest in itself.


title: Transverse spin and transverse momentum in scattering of plane waves

abstract:
  We study the near field to the far field evolution of spin angular momentum
(SAM) density and the Poynting vector of the scattered waves from spherical
scatterers. The results show that at the near field, the SAM density and the
Poynting vector are dominated by their transverse components. While the former
(transverse SAM) is independent of the helicity of the incident circular
polarization state, the latter (transverse Poynting vector) depends upon the
polarization state. It is further demonstrated that the magnitudes and the
spatial extent of the transverse SAM and the transverse momentum components can
be controllably enhanced by exploiting the interference of the transverse
electric and transverse magnetic scattering modes.


title: Homogeneity degree of some symmetric products

abstract:
  For a metric continuum $X$, we consider the $n^{\tiny\textrm{th}}$-symmetric
product $F_{n}(X)$ defined as the hyperspace of all nonempty subsets of $X$
with at most $n$ points. The homogeneity degree $hd(X)$ of a continuum $X$ is
the number of orbits for the action of the group of homeomorphisms of $X$ onto
itself. In this paper we determine $hd(F_{n}(X))$ for every manifold without
boundary and $n\in \mathbb{N}$. We also compute $hd(F_{n}[0,1])$ for all $n\in
\mathbb{N}$.


title:
Resonant Elastic X-ray Scattering from the Skyrmion Lattice in
  Cu$_{2}$OSeO$_{3}$

abstract:
  We report the study of the skyrmion state near the surface of Cu$_2$OSeO$_3$
using soft resonant elastic x-ray scattering (REXS) at the Cu $L_3$ edge.
Within the lateral sampling area of $200 \times 200$ $\mu$m$^2$, we found a
long-range-ordered skyrmion lattice phase as well as the formation of skyrmion
domains via the multiple splitting of the diffraction spots. In a recent REXS
study of the skyrmion phase of Cu$_2$OSeO$_3$ [Phys. Rev. Lett. 112, 167202
(2014)], Langner et al. reported the observation of the unexpected existence of
two distinct skyrmion sublattices that arise from inequivalent Cu sites, and
that the rotation and superposition of the two periodic structures leads to a
moir\'{e} pattern. However, we find no energy splitting of the Cu peak in x-ray
absorption measurements and, instead, discuss alternative origins of the peak
splitting. In particular, we find that for magnetic field directions deviating
from the major cubic axes, a multidomain skyrmion lattice state is obtained,
which consistently explains the splitting of the magnetic spots into two - and
more - peaks.


title:
A Flexible Phase Retrieval Framework for Flux-limited Coherent X-Ray
  Imaging

abstract:
  Coherent X-ray diffraction imaging (CXDI) experiments are intrinsically
limited by shot noise, a lack of prior knowledge about the sample's support,
and missing measurements due to the experimental geometry. We propose a
flexible, iterative phase retrieval framework that allows for accurate modeling
of Gaussian or Poissonian noise statistics, modified support updates,
regularization of reconstructed signals, and handling of missing data in the
observations. The proposed method is efficiently solved using alternating
direction method of multipliers (ADMM) and is demonstrated to consistently
outperform state-of-the-art algorithms for low-photon phase retrieval from CXDI
experiments, both for simulated diffraction patterns and for experimental
measurements.


title:
The Desktop Muon Detector: A simple, physics-motivated machine- and
  electronics-shop project for university students

abstract:
  This paper describes an undergraduate-level physics project that incorporates
various aspects of machine- and electronics-shop technical development. The
desktop muon detector is a self-contained apparatus that employs plastic
scintillator as a detection medium and a silicon photomultiplier for light
collection. These detectors can be used in conjunction with the provided
software to make interesting physics measurements. The total cost of each
counter is approximately $100.


title:
Measurement of the profiles of disorder-induced localized resonances in
  photonic crystal waveguides by local tuning

abstract:
  Near the band edge of photonic crystal waveguides, localized modes appear due
to disorder. We demonstrate a new method to elucidate spatial profile of the
localized modes in such systems using precise local tuning. Using deconvolution
with the known thermal profile, the spatial profile of a localized mode with
quality factor ($Q$) $>10^5$ is successfully reconstructed with a resolution of
$2.5 \ \mu $m.


title:
Quantum dynamics of wave packets in a nonstationary parabolic potential
  and the Kramers escape rate theory

abstract:
  At sufficiently low temperatures, the reaction rates in solids are controlled
by quantum rather than by thermal fluctuations. We solve the Schr\"odinger
equation for a Gaussian wave packet in a nonstation-ary harmonic oscillator and
derive simple analytical expressions for the increase of its mean energy with
time induced by the time-periodic modulation. Applying these expressions to the
modified Kra-mers theory, we demonstrate a strong increase of the rate of
escape out of a potential well under the time-periodic driving, when the
driving frequency of the well position equals its eigenfrequency, or when the
driving frequency of the well width exceeds its eigenfrequency by a factor of
~2. Such re-gimes can be realized near localized anharmonic vibrations (LAVs),
in which the amplitude of atomic oscillations greatly exceeds that of harmonic
oscillations (phonons) that determine the system tem-perature. LAVs can be
excited either thermally or by external triggering, which can result in strong
catalytic effects due to amplification of the Kramers rate


title: On the Complexity and Decidability of Some Problems Involving Shuffle

abstract:
  The complexity and decidability of various decision problems involving the
shuffle operation are studied. The following three problems are all shown to be
$NP$-complete: given a nondeterministic finite automaton (NFA) $M$, and two
words $u$ and $v$, is $L(M)$ not a subset of $u$ shuffled with $v$, is $u$
shuffled with $v$ not a subset of $L(M)$, and is $L(M)$ not equal to $u$
shuffled with $v$? It is also shown that there is a polynomial-time algorithm
to determine, for $NFA$s $M_1, M_2$ and a deterministic pushdown automaton
$M_3$, whether $L(M_1)$ shuffled with $L(M_2)$ is a subset of $L(M_3)$. The
same is true when $M_1, M_2,M_3$ are one-way nondeterministic
$l$-reversal-bounded $k$-counter machines, with $M_3$ being deterministic.
Other decidability and complexity results are presented for testing whether
given languages $L_1, L_2$ and $R$ from various languages families satisfy
$L_1$ shuffled with $L_2$ is a subset of $R$, and $R$ is a subset of $L_1$
shuffled with $L_2$. Several closure results on shuffle are also shown.


title: Simple and Honest Confidence Intervals in Nonparametric Regression

abstract:
  We consider the problem of constructing honest confidence intervals (CIs) for
a scalar parameter of interest, such as the regression discontinuity parameter,
in nonparametric regression based on kernel or local polynomial estimators. To
ensure that our CIs are honest, we use critical values that take into account
the possible bias of the estimator upon which the CIs are based. We show that
this approach leads to CIs that are more efficient than conventional CIs that
achieve coverage by undersmoothing or subtracting an estimate of the bias. We
give sharp efficiency bounds of using different kernels, and derive the optimal
bandwidth for constructing honest CIs. We show that using the bandwidth that
minimizes the maximum mean-squared error results in CIs that are nearly
efficient and that in this case, the critical value depends only on the rate of
convergence. For the common case in which the rate of convergence is
$n^{-2/5}$, the appropriate critical value for 95% CIs is 2.18, rather than the
usual 1.96 critical value. We illustrate our results in a Monte Carlo analysis
and an empirical application.


title:
Recent X-Recent X-ray observations of the symbiotic star AG Peg: do they
  signify Colliding Stellar Winds?

abstract:
  We present an analysis of recent X-ray observations of the symbiotic star AG
Peg. The X-ray emission of AG Peg as observed with Swift in 2015 shows
considerable variability on time scale of days as variability on shorter time
scales might be present as well. Analysis of the X-ray spectra obtained in 2013
and 2015 confirms that AG Peg is an X-ray source of class $\beta$ of the X-ray
sources amongst the symbiotic stars. The X-ray emission of AG Peg as observed
with ROSAT (1993 June) might well originate from colliding stellar winds (CSW)
in binary system. On the other hand, the characteristics of the X-ray emission
of AG Peg in 2013 and 2015 (Swift) are hard to accommodate in the framework of
the CSW picture. Analysis of the light curves in 2015 shows that the power
spectrum of the X-ray variability in AG Peg resembles that of the flicker noise
(or flickering) being typical for accretion processes in astronomical objects.
This is a sign that CSWs did not play a key role for the X-ray emission from AG
Peg in 2013-2015 and a different mechanism (probably accretion) is also getting
into play.


title: When Does a Boltzmannian Equilibrium Exist?

abstract:
  The received wisdom in statistical mechanics is that isolated systems, when
left to themselves, approach equilibrium. But under what circumstances does an
equilibrium state exist and an approach to equilibrium take place? In this
paper we address these questions from the vantage point of the long-run
fraction of time definition of Boltzmannian equilibrium that we developed in
two recent papers (Werndl and Frigg 2015a, 2015b). After a short summary of
Boltzmannian statistical mechanics and our definition of equilibrium, we state
an existence theorem which provides general criteria for the existence of an
equilibrium state. We first illustrate how the theorem works with a toy
example, which allows us to illustrate the various elements of the theorem in a
simple setting. After commenting on the ergodic programme, we discuss
equilibria in a number of different gas systems: the ideal gas, the dilute gas,
the Kac gas, the stadium gas, the mushroom gas and the multi-mushroom gas. In
the conclusion we briefly summarise the main points and highlight open
questions.

categories: cond-mat.stat-mech math-ph math.DS math.MP stat.OT


title:
Topological defects at octahedral tilting plethora in bi-layered
  perovskites

abstract:
  Oxygen octahedral distortions including tilts/rotations, deformations and
off-centering in (layered) perovskites play the key role in their numerous
functional properties. At the polar-centrosymmetric phase boundary in
bi-layered perovskite Ca3-xSrxTi2O7 with x~1, we found the presence of abundant
topological Z8 vortex-antivortex pairs, associated with four oxygen octahedral
tilts at domains and another four different oxygen octahedral tilts at domain
boundaries. Our discovery opens a new revenue to unveil topological defects
associated with various types of oxygen octahedral distortions.


title: Matching and Independence Complexes Related to Small Grids

abstract:
  The topology of the matching complex for the $2\times n$ grid graph is
mysterious. We describe a discrete Morse matching for a family of independence
complexes $\mathrm{Ind}(\Delta_n^m)$ that include these matching complexes.
Using this matching, we determine the dimensions of the chain spaces for the
resulting Morse complexes and derive bounds on the location of non-trivial
homology groups for certain $\mathrm{Ind}(\Delta_n^m)$. Further, we determine
the Euler characteristic of $\mathrm{Ind}(\Delta_n^m)$ and prove that several
homology groups of $\mathrm{Ind}(\Delta_n^m)$ are non-zero.


title: On the Lusternik-Schnirelmann category of a simplicial map

abstract:
  In this paper, we study the Lusternik-Schnirelmann category of a simplicial
map between simplicial complexes, generalizing the simplicial category of a
complex to that of a map. Several properties of this new invariant are shown,
including its relevance to products and fibrations. We relate this category of
a map to the classical Lusternik-Schnirelmann category of a map between finite
topological spaces. Finally, we show how the simplicial category of a map may
be used to define and study a simplicial version of the essential category
weight of J. Strom.


title: The complexity of reverse engineering problems for conjunctive queries

abstract:
  Reverse engineering problems for conjunctive queries (CQs), such as query by
example (QBE) or definability, take a set of user examples and convert them
into an explanatory CQ. Despite their importance, the complexity of these
problems is prohibitively high (coNEXPTIME-complete). We isolate their two main
sources of complexity and propose relaxations of them that reduce the
complexity while having meaningful theoretical interpretations. The first
relaxation is based on the idea of using existential pebble games for
approximating homomorphism tests. We show that this characterizes
QBE/definability for CQs up to treewidth $k$, while reducing the complexity to
EXPTIME. As a side result, we obtain that the complexity of the
QBE/definability problems for CQs of treewidth $k$ is EXPTIME-complete for each
$k \geq 1$. The second relaxation is based on the idea of "desynchronizing"
direct products, which characterizes QBE/definability for unions of CQs and
reduces the complexity to coNP. The combination of these two relaxations yields
tractability for QBE and characterizes it in terms of unions of CQs of
treewidth at most $k$. We also study the complexity of these problems for
conjunctive regular path queries over graph databases, showing them to be no
more difficult than for CQs.


title:
The ISLAndS project II: The Lifetime Star Formation Histories of Six
  Andromeda dSphs

abstract:
  The Initial Star formation and Lifetimes of Andromeda Satellites (ISLAndS)
project uses Hubble Space Telescope imaging to study a representative sample of
six Andromeda dSph satellite companion galaxies. The main goal of the program
is to determine whether the star formation histories (SFHs) of the Andromeda
dSph satellites demonstrate significant statistical differences from those of
the Milky Way, which may be attributable to the different properties of their
local environments. Our observations reach the oldest main sequence turn-offs,
allowing a time resolution at the oldest ages of ~ 1 Gyr, which is comparable
to the best achievable resolution in the MW satellites. We find that the six
dSphs present a variety of SFHs that are not strictly correlated with
luminosity or present distance from M31. Specifically, we find a significant
range in quenching times (lookback times from 9 to 6 Gyr), but with all
quenching times more than ~ 6 Gyr ago. In agreement with observations of Milky
Way companions of similar mass, there is no evidence of complete quenching of
star formation by the cosmic UV background responsible for reionization, but
the possibility of a degree of quenching at reionization cannot be ruled out.
We do not find significant differences between the SFHs of the three members of
the vast, thin plane of satellites and the three off-plane dSphs. The primary
difference between the SFHs of the ISLAndS dSphs and Milky Way dSph companions
of similar luminosities and host distances is the absence of very late
quenching (< 5 Gyr ago) dSphs in the ISLAndS sample. Thus, models that can
reproduce satellite populations with and without late quenching satellites will
be of extreme interest.


title: Gravitational scaling in Beijing Subway Network

abstract:
  Recently, with the availability of various traffic datasets, human mobility
has been studied in different contexts. Researchers attempt to understand the
collective behaviors of human movement with respect to the spatio-temporal
distribution in traffic dynamics, from which a gravitational scaling law
characterizing the relation between the traffic flow, population and distance
has been found. However, most studies focus on the integrated properties of
gravitational scaling, neglecting its dynamical evolution during different
hours of a day. Investigating the hourly traffic flow data of Beijing subway
network, based on the hop-count distance of passengers, we find that the
scaling exponent of the gravitational law is smaller in Beijing subway system
compared to that reported in Seoul subway system. This means that traffic
demand in Beijing is much stronger and less sensitive to the travel distance.
Furthermore, we analyzed the temporal evolution of the scaling exponents in
weekdays and weekends. Our findings may help to understand and improve the
traffic congestion control in different subway systems.


title:
Deep VLA observations of nearby star forming regions I: Barnard 59 and
  Lupus

abstract:
  Barnard 59 and Lupus 1 are two nearby star-forming regions visible from the
southern hemisphere. In this manuscript, we present deep ($\sigma$ $\lesssim$
15 $ \mu$Jy) radio observations ($\nu$ = 6 GHz; $\lambda$ = 5 cm) of these
regions, and report the detection of a total of 114 sources. Thirteen of these
sources are associated with known young stellar objects, nine in Barnard 59 and
four in Lupus 1. The properties of the radio emission (spectral index and, in
some cases, polarization) suggest a thermal origin for most young stellar
objects. Only for two sources (Sz~65 and Sz~67) are there indications for a
possible non-thermal origin; more observations will be needed to ascertain the
exact nature of the radio emission in these sources. The remaining radio
detections do not have counterparts at other wavelengths, and the number of
sources detected per unit solid angle is in agreement with extragalactic number
counts. This suggests that all radio sources not associated with known young
stellar objects are background extragalactic sources.


title:
An improved analysis of GW150914 using a fully spin-precessing waveform
  model

abstract:
  This paper presents updated estimates of source parameters for GW150914, a
binary black-hole coalescence event detected by the Laser Interferometer
Gravitational-wave Observatory (LIGO) on September 14, 2015 [1]. Reference
presented parameter estimation [2] of the source using a 13-dimensional,
phenomenological precessing-spin model (precessing IMRPhenom) and a
11-dimensional nonprecessing effective-one-body (EOB) model calibrated to
numerical-relativity simulations, which forces spin alignment (nonprecessing
EOBNR). Here we present new results that include a 15-dimensional
precessing-spin waveform model (precessing EOBNR) developed within the EOB
formalism. We find good agreement with the parameters estimated previously [2],
and we quote updated component masses of $35^{+5}_{-3}\mathrm{M}_\odot$ and
$30^{+3}_{-4}\mathrm{M}_\odot$ (where errors correspond to 90% symmetric
credible intervals). We also present slightly tighter constraints on the
dimensionless spin magnitudes of the two black holes, with a primary spin
estimate $0.65$ and a secondary spin estimate $0.75$ at 90% probability.
Reference [2] estimated the systematic parameter-extraction errors due to
waveform-model uncertainty by combining the posterior probability densities of
precessing IMRPhenom and nonprecessing EOBNR. Here we find that the two
precessing-spin models are in closer agreement, suggesting that these
systematic errors are smaller than previously quoted.


title: Metallicity in Ultra-Thin Oxygen-Deficient SrTiO$_3$ Thin Films

abstract:
  We report on the observation of metallic behavior in thin films of
oxygen-deficient SrTiO$_3$ - down to 9 unit cells - when coherently strained on
(001) SrTiO$_3$ or DyScO$_3$-buffered (001) SrTiO$_3$ substrates. These films
have carrier concentrations of up to 2$\times10^{22}$ cm$^{-3}$ and mobilities
of up to 19,000 cm$^2$/V-s at 2 K. There exists a non-conducting layer in our
SrTiO$_{3-\delta}$ films that is larger in films with lower carrier
concentrations. This non-conducting layer can be attributed to a surface
depletion layer due to a Fermi level pinning potential. The depletion width,
transport, and structural properties are not greatly affected by the insertion
of a DyScO$_3$ buffer between the SrTiO$_3$ film and SrTiO$_3$ substrate.


title: Sharp Fundamental Gap Estimate on Convex Domains of Sphere

abstract:
  In their celebrated work, B. Andrews and J. Clutterbuck proved the
fundamental gap (the difference between the first two eigenvalues) conjecture
for convex domains in the Euclidean space and conjectured similar results holds
for spaces with constant sectional curvature. We prove the conjecture for the
sphere. Namely when $D$, the diameter of a convex domain in the unit $S^n$
sphere, is $\le \frac{\pi}{2}$, the gap is greater than the gap of the
corresponding $1$-dim sphere model. We also prove the gap is $\ge
3\frac{\pi^2}{D^2}$ when $n \ge 3$, giving a sharp bound. As in
Andrews-Clutterbuck's proof of the fundamental gap, the key is to prove a super
log-concavity of the first eigenfunction.


title: Discrete solitons in infinite reduced words

abstract:
  We consider a discrete dynamical system where the roles of the states and the
carrier are played by translations in an affine Weyl group of type $A$. The
Coxeter generators are enriched by parameters, and the interactions with the
carrier are realized using Lusztig's braid move $(a,b,c) \mapsto (bc/(a+c),
a+c, ab/(a+c))$. We use wiring diagrams on a cylinder to interpret chamber
variables as $\tau$-functions. This allows us to realize our systems as
reductions of the Hirota bilinear difference equation and thus obtain
$N$-soliton solutions.


title: A distance exponent for Liouville quantum gravity

abstract:
  Let $\gamma \in (0,2)$ and let $h$ be the random distribution on $\mathbb C$
which describes a $\gamma$-Liouville quantum gravity (LQG) cone. Also let
$\kappa = 16/\gamma^2 >4$ and let $\eta$ be a whole-plane space-filling
SLE$_\kappa$ curve sampled independent from $h$ and parametrized by
$\gamma$-quantum mass with respect to $h$. We study a family $\{\mathcal
G^\epsilon\}_{\epsilon>0}$ of planar maps associated with $(h, \eta)$ called
the \textit{LQG structure graphs} (a.k.a.\ \textit{mated-CRT maps}) which we
conjecture converge in probability in the scaling limit with respect to the
Gromov-Hausdorff topology to a random metric space associated with
$\gamma$-LQG.
  In particular, $\mathcal G^\epsilon$ is the graph whose vertex set is
$\epsilon \mathbb Z$, with two such vertices $x_1,x_2\in \epsilon \mathbb Z$
connected by an edge if and only if the corresponding curve segments
$\eta([x_1-\epsilon , x_1])$ and $\eta([x_2-\epsilon,x_2])$ share a non-trivial
boundary arc. Due to the peanosphere description of SLE-decorated LQG due to
Duplantier, Miller, and Sheffield (2014), the graph $\mathcal G^\epsilon$ can
equivalently be expressed as an explicit functional of a correlated
two-dimensional Brownian motion, so can be studied without any reference to SLE
or LQG.
  We prove non-trivial upper and lower bounds for the cardinality of a
graph-distance ball of radius $n$ in $\mathcal G^\epsilon$ which are consistent
with the prediction of Watabiki (1993) for the Hausdorff dimension of LQG.
Using subadditivity arguments, we also prove that there is an exponent $\chi >
0$ for which the expected graph distance between generic points in the subgraph
of $\mathcal G^\epsilon$ corresponding to the segment $\eta([0,1])$ is of order
$\epsilon^{-\chi + o_\epsilon(1)}$, and this distance is extremely unlikely to
be larger than $\epsilon^{-\chi + o_\epsilon(1)}$.


title: Self-gravitating fluid solutions of Shape Dynamics

abstract:
  Shape Dynamics is a 3D conformally invariant theory of gravity which
possesses a large set of solutions in common with General Relativity. When
looked closely, these solutions are found to behave in surprising ways, so in
order to probe the fitness of Shape Dynamics as a viable alternative to General
Relativity one must find and understand increasingly more complex, less
symmetrical exact solutions, on which to base perturbative studies and
numerical analyses in order to compare them with data. Spherically symmetric
exact solutions have been studied, but only in a static vacuum setup. In this
work we construct a class of time-dependent exact solutions of Shape Dynamics
from first principles, representing a central inhomogeneity in an evolving
cosmological environment. By assuming only a perfect fluid source in a
spherically symmetric geometry we show that this fully dynamic non-vacuum
solution satisfies in all generality the Hamiltonian structure of Shape
Dynamics. The simplest choice of solutions is shown to be a member of the
McVittie family.


title:
Preconditioned Iterative Solves in Model Reduction of Second Order
  Linear Dynamical Systems

abstract:
  Recently a new algorithm for model reduction of second order linear dynamical
systems with proportional damping, the Adaptive Iterative Rational Global
Arnoldi (AIRGA) algorithm, has been proposed. The main computational cost of
the AIRGA algorithm is in solving a sequence of linear systems. These linear
systems do change only slightly from one iteration step to the next. Here we
focus on efficiently solving these systems by iterative methods and the choice
of an appropriate preconditioner. We propose the use of relevant iterative
algorithm and the Sparse Approximate Inverse (SPAI) preconditioner. A technique
to cheaply update the SPAI preconditioner in each iteration step of the model
order reduction process is given. Moreover, it is shown that under certain
conditions the AIRGA algorithm is stable with respect to the error introduced
by iterative methods. Our theory is illustrated by experiments. It is
demonstrated that SPAI preconditioned Conjugate Gradient (CG) works well for
model reduction of a one dimensional beam model with AIRGA algorithm. Moreover,
the computation time of preconditioner with update is on an average 2/3 rd of
the computation time of preconditioner without update. With average timings
running into hours for very large systems, such savings are substantial.


title: Recent results from T2K

abstract:
  The T2K long-baseline neutrino oscillation experiment has produced the first
observation of $\nu_{e}$ appearance and the most precise measurement of the
mixing angle $\theta_{23}$ from $6.57 \times 10^{20}$ protons-on-target (POT)
of neutrino beam data. We present here the results of T2K antineutrino
oscillation analyses searching for $\bar{\nu}_{e}$ appearance and measuring the
dominant oscillation parameters for $\bar{\nu}_{\mu}$ disappearance, including
the results from the T2K near detector fit. Using $4.01 \times 10^{20}$ POT of
antineutrino beam data T2K measured $\sin^{2}(\bar{\theta}_{23}) =
0.45^{+0.29}_{-0.12}$ and $|\Delta \bar{m}^{2}_{32}| = 2.51\pm0.28 \times
10^{-3} (eV^{2})$, consistent with previous existing $\nu_{\mu}$ and
$\bar{\nu}_{\mu}$ disappearance measurements. From the same dataset 3
$\bar{\nu}_{e}$ candidate events were selected at the far detector, which did
not provide evidence either for or against the $\bar{\nu}_{e}$ appearance
hypothesis.


title:
World Financial 2014-2016 Market Bubbles: Oil Negative - US Dollar
  Positive

abstract:
  Based on the Log-Periodic Power Law (LPPL) methodology, with the universal
preferred scaling factor $\lambda \approx 2$, the negative bubble on the oil
market in 2014-2016 has been detected. Over the same period a positive bubble
on the so called commodity currencies expressed in terms of the US dollar
appears to take place with the oscillation pattern which largely is mirror
reflected relative to oil price oscillation pattern. This documents recent
strong anti-correlation between the dynamics of the oil price and of the USD. A
related forecast made at the time of FENS 2015 conference (beginning of
November) turned out to be quite satisfactory. These findings provide also
further indication that such a log-periodically accelerating down-trend signals
termination of the corresponding decreases.


title: Learning Stylometric Representations for Authorship Analysis

abstract:
  Authorship analysis (AA) is the study of unveiling the hidden properties of
authors from a body of exponentially exploding textual data. It extracts an
author's identity and sociolinguistic characteristics based on the reflected
writing styles in the text. It is an essential process for various areas, such
as cybercrime investigation, psycholinguistics, political socialization, etc.
However, most of the previous techniques critically depend on the manual
feature engineering process. Consequently, the choice of feature set has been
shown to be scenario- or dataset-dependent. In this paper, to mimic the human
sentence composition process using a neural network approach, we propose to
incorporate different categories of linguistic features into distributed
representation of words in order to learn simultaneously the writing style
representations based on unlabeled texts for authorship analysis. In
particular, the proposed models allow topical, lexical, syntactical, and
character-level feature vectors of each document to be extracted as
stylometrics. We evaluate the performance of our approach on the problems of
authorship characterization and authorship verification with the Twitter,
novel, and essay datasets. The experiments suggest that our proposed text
representation outperforms the bag-of-lexical-n-grams, Latent Dirichlet
Allocation, Latent Semantic Analysis, PVDM, PVDBOW, and word2vec
representations.


title: Energy Losses of Magnetic Monopoles in Aluminum, Iron and Copper

abstract:
  The Energy Losses and Ranges of magnetic monopoles with magnetic charges
$1g_{D}$, $2g_{D}$, $3g_{D}$, $6g_{D}$ and $9g_{D}$ in Aluminum, Iron and in
Copper are computed, in the different regimes of velocities. The Restricted
Energy Losses of monopoles with magnetic charges $1g_{D}$, $2g_{D}$ and
$3g_{D}$ in Nuclear Track Detector is also given.


title:
Error analysis of staggered finite difference finite volume schemes on
  unstructured meshes

abstract:
  This work combines the consistency in lower-order differential operators with
external approximations of functional spaces to obtain error estimates for
finite difference finite volume schemes on unstructured non-uniform meshes.
This combined approach is first applied to the one-dimensional elliptic
boundary value problem on non-uniform meshes, and a first-order convergence
rate is obtained, which agrees with the results previously reported. The
approach is also applied to the staggered MAC scheme for the two-dimensional
incompressible Stokes problem on unstructured meshes. A first-order convergence
rate is obtained, which improves over a previously reported result in that it
also holds on unstructured meshes. For both problems considered in this work,
the convergence rate is one order higher on meshes satisfying special
requirements.


title:
Higher Regularity of the Free Boundary in the Obstacle Problem for the
  Fractional Laplacian

abstract:
  We prove a higher regularity result for the free boundary in the obstacle
problem for the fractional Laplacian via a higher order boundary Harnack
inequality.


title: Constraining Curvatonic Reheating

abstract:
  We derive the first systematic observational constraints on reheating in
models of inflation where an additional light scalar field contributes to
primordial density perturbations and affects the expansion history during
reheating. This encompasses the original curvaton model but also covers a
larger class of scenarios. We find that, compared to the single-field case,
lower values of the energy density at the end of inflation and of the reheating
temperature are preferred when an additional scalar field is introduced. For
instance, if inflation is driven by a quartic potential, which is one of the
most favoured models when a light scalar field is added, the upper bound
$T_{\mathrm{reh}}<5\times 10^{4}\,\mathrm{GeV}$ on the reheating temperature
$T_{\mathrm{reh}}$ is derived, and the implications of this value on
post-inflationary physics are discussed. The information gained about reheating
is also quantified and it is found that it remains modest in plateau inflation
(though still larger than in the single-field version of the model) but can
become substantial in quartic inflation. The role played by the vev of the
additional scalar field at the end of inflation is highlighted, and opens
interesting possibilities for exploring stochastic inflation effects that could
determine its distribution.


title:
In-situ real-space imaging of crystal surface reconstruction dynamics
  via electron microscopy

abstract:
  Crystal surfaces are sensitive to the surrounding environment, where atoms
left with broken bonds reconstruct to minimize surface energy. In many cases,
the surface can exhibit chemical properties unique from the bulk. These
differences are important as they control reactions and mediate thin film
growth. This is particularly true for complex oxides where certain terminating
crystal planes are polar and have a net dipole moment. For polar terminations,
reconstruction of atoms on the surface is the central mechanism to avoid the so
called polar catastrophe. This adds to the complexity of the reconstruction
where charge polarization and stoichiometry govern the final surface in
addition to standard thermodynamic parameters such as temperature and partial
pressure. Here we present direct, in-situ determination of polar SrTiO3 (110)
surfaces at temperatures up to 900 C using cross-sectional aberration corrected
scanning transmission electron microscopy (STEM). Under these conditions, we
observe the coexistence of various surface structures that change as a function
of temperature. As the specimen temperature is lowered, the reconstructed
surface evolves due to thermal mismatch with the substrate. Periodic defects,
similar to dislocations, are found in these surface structures and act to
relieve stress due to mismatch. Combining STEM observations and electron
spectroscopy with density functional theory, we find a combination of lattice
misfit and charge compensation for stabilization. Beyond the characterization
of these complex reconstructions, we have developed a general framework that
opens a new pathway to simultaneously investigate the surface and near surface
regions of single crystals as a function of environment.