title: Some reflections on directed lattice paths

abstract:
  This article analyzes directed lattice paths, when a boundary reflecting or
absorbing condition is added to the classical models. The lattice paths are
characterized by two time-independent sets of rules (also called steps) which
have a privileged direction of increase and are therefore essentially
one-dimensional objects. Depending on the spatial coordinate, one of the two
sets of rules applies, namely one for altitude 0 and one for altitude bigger
than 0. The abscissa y=0 thus acts as a border which either absorbs or reflects
steps. The absorption model corresponds to the model analyzed by Banderier and
Flajolet ("Analytic combinatorics of directed lattice paths"), while the
reflecting model leads to a more complicated situation. We show how the
generating functions are then modified: the kernel method strikes again but
here it unfortunately does not give a nice product formula. This makes the
analysis more challenging, and, in the case of {\L}ukasiewicz walks, we give
the asymptotics for the number of excursions, arches and meanders. Limit laws
for the number of returns to 0 of excursions are given. We also compute the
limit laws of the final altitude of meanders. The full analytic situation is
more complicated than the Banderier-Flajolet model (partly because new
"critical compositions" appear, forcing us to introduce new key quantities,
like the drift at 0), and we quantify to what extent the global drift, and the
drift at 0 play a role in the "universal" behavior of such walks.


title: Colourability and word-representability of near-triangulations

abstract:
  A graph $G = (V,E)$ is word-representable if there is a word $w$ over the
alphabet $V$ such that $x$ and $y$ alternate in $w$ if and only if the edge
$(x, y)$ is in $G$. It is known [6] that all $3$-colourable graphs are
word-representable, while among those with a higher chromatic number some are
word-representable while others are not.
  There has been some recent research on the word-representability of polyomino
triangulations. Akrobotu et al.[1] showed that a triangulation of a convex
polyomino is word-representable if and only if it is $3$-colourable; and Glen
and Kitaev[5] extended this result to the case of a rectangular polyomino
triangulation when a single domino tile is allowed.
  It was shown in [4] that a near-triangulation is $3$-colourable if and only
if it is internally even. This paper provides a much shorter and more elegant
proof of this fact, and also shows that near-triangulations are in fact a
generalization of the polyomino triangulations studied in [1] and [5], and so
we generalize the results of these two papers, and solve all open problems
stated in [5].


title:
Spontaneous breaking of time-reversal symmetry in topological
  superconductors

abstract:
  We study the behavior of spinless fermions in superconducting state, in which
the phases of the superconducting order parameter depend on the direction of
the link. We find that the energy of the superconductor depends on the phase
differences of the superconducting order parameter. The solutions for the
phases corresponding to the energy minimuma, lead to a topological
superconducting state with the nontrivial Chern numbers. We focus our
quantitative analysis on the properties of topological states of
superconductors with different crystalline symmetry and show that the phase
transition in the topological superconducting state is result of spontaneous
breaking of time-reversal symmetry in the superconducting state. The
peculiarities in the chiral gapless edge modes behavior are studied, the Chern
numbers are calculated.


title:
Fog-Aided Wireless Networks for Content Delivery: Fundamental Latency
  Trade-Offs

abstract:
  A fog-aided wireless network architecture is studied in which edge-nodes
(ENs), such as base stations, are connected to a cloud processor via dedicated
fronthaul links, while also being endowed with caches. Cloud processing enables
the centralized implementation of cooperative transmission strategies at the
ENs, albeit at the cost of an increased latency due to fronthaul transfer. In
contrast, the proactive caching of popular content at the ENs allows for the
low-latency delivery of the cached files, but with generally limited
opportunities for cooperative transmission among the ENs. The interplay between
cloud processing and edge caching is addressed from an information-theoretic
viewpoint by investigating the fundamental limits of a high
Signal-to-Noise-Ratio (SNR) metric, termed normalized delivery time (NDT),
which captures the worst-case coding latency for delivering any requested
content to the users. The NDT is defined under the assumptions of either serial
or pipelined fronthaul-edge transmission, and is studied as a function of
fronthaul and cache capacity constraints. Placement and delivery strategies
across both fronthaul and wireless, or edge, segments are proposed with the aim
of minimizing the NDT. Information-theoretic lower bounds on the NDT are also
derived. Achievability arguments and lower bounds are leveraged to characterize
the minimal NDT in a number of important special cases, including systems with
no caching capabilities, as well as to prove that the proposed schemes achieve
optimality within a constant multiplicative factor of 2 for all values of the
problem parameters.


title:
Eco-friendly gas mixtures for Resistive Plate Chambers based on
  Tetrafluoropropene and Helium

abstract:
  Due to the recent restrictions deriving from the application of the Kyoto
protocol, the main components of the gas mixtures presently used in the
Resistive Plate Chambers systems of the LHC experiments will be most probably
phased out of production in the coming years. Identifying possible replacements
with the adequate characteristics requires an intense R&D, which was recently
started, also in collaborations across the various experiments. Possible
candidates have been proposed and are thoroughly investigated. Some tests on
one of the most promising candidate - HFO-1234ze, an allotropic form of
tetrafluoropropane- have already been reported. Here an innovative approach,
based on the use of Helium, to solve the problems related to the too elevate
operating voltage of HFO-1234ze based gas mixtures, is discussed and the
relative first results are shown.


title: Study of the breakdown voltage of SiPMs

abstract:
  The breakdown behaviour of SiPMs (Silicon PhotoMultiplier) with pixel sizes
of 15$\times $15, 25$\times $25, 50$\times $50, and 100$\times $100 $\mu
$m$^2$, manufactured by KETEK, has been investigated. From the current-voltage
characteristics measured with and without illumination by LED light of 470 nm
wavelength, the current-breakdown voltage, $V_I$, and from linear fits of the
voltage dependence of the SiPM gain, measured by recording pulse-area spectra,
the gain-breakdown voltage, $V_G$, have been obtained. The voltage dependence
of the Geiger-breakdown probability was determined from the fraction of zero
photoelectron events with LED illumination. By comparing the results to a model
calculation, the photodetection-breakdown voltage, $V_{PD}$, has been
determined. Within experimental uncertainties, $V_I$ and $V_{PD}$ are equal and
independent of pixel size. For $V_G$, a dependence on pixel size is observed.
The difference $V_I - V_G$ is about 1 V for the SiPM with 15 $\mu $m pixels,
decreases with pixel size and is compatible with zero for the SiPM with 100
$\mu $m pixels.


title: Local Rigidity Of Uniform Lattices

abstract:
  We establish topological local rigidity for uniform lattices in compactly
generated groups, extending the result of Weil from the realm of Lie groups. We
generalize the classical local rigidity theorem of Selberg, Calabi and Weil to
irreducible uniform lattices in $\text{Isom}(X)$ where $X$ is a proper
$\text{CAT}(0)$ space with no Euclidian factors, not isometric to the
hyperbolic plane. We deduce an analog of Wang's finiteness theorem for certain
non-positively curved metric spaces.


title: Theory of magnon motive force in chiral ferromagnets

abstract:
  We predict that magnon motive force can lead to temperature dependent,
nonlinear chiral damping in both conducting and insulating ferromagnets. We
estimate that this damping can significantly influence the motion of skyrmions
and domain walls at finite temperatures. We also find that in systems with low
Gilbert damping moving chiral magnetic textures and resulting magnon motive
forces can induce large spin and energy currents in the transverse direction.


title: Faster Online Matrix-Vector Multiplication

abstract:
  We consider the Online Boolean Matrix-Vector Multiplication (OMV) problem
studied by Henzinger et al. [STOC'15]: given an $n \times n$ Boolean matrix
$M$, we receive $n$ Boolean vectors $v_1,\ldots,v_n$ one at a time, and are
required to output $M v_i$ (over the Boolean semiring) before seeing the vector
$v_{i+1}$, for all $i$. Previous known algorithms for this problem are
combinatorial, running in $O(n^3/\log^2 n)$ time. Henzinger et al. conjecture
there is no $O(n^{3-\varepsilon})$ time algorithm for OMV, for all $\varepsilon
> 0$; their OMV conjecture is shown to imply strong hardness results for many
basic dynamic problems.
  We give a substantially faster method for computing OMV, running in
$n^3/2^{\Omega(\sqrt{\log n})}$ randomized time. In fact, after seeing
$2^{\omega(\sqrt{\log n})}$ vectors, we already achieve
$n^2/2^{\Omega(\sqrt{\log n})}$ amortized time for matrix-vector
multiplication. Our approach gives a way to reduce matrix-vector multiplication
to solving a version of the Orthogonal Vectors problem, which in turn reduces
to "small" algebraic matrix-matrix multiplication. Applications include faster
independent set detection, partial match retrieval, and 2-CNF evaluation.
  We also show how a modification of our method gives a cell probe data
structure for OMV with worst case $O(n^{7/4}/\sqrt{w})$ time per query vector,
where $w$ is the word size. This result rules out an unconditional proof of the
OMV conjecture using purely information-theoretic arguments.


title: A Many Antenna High Rate Wireless System

abstract:
  We describe a TDD MIMO wireless system designed to operate at high bandwidth
and low SNR. Signals are transmitted as a direct sequence. In the uplink
(Multiple Access Channel), signal detection is done by a space-time whitening
filter followed by a matched filter. In the downlink (Broadcast Channel),
precoding is done by the transpose of these filters.
  We further describe an implementation of this system that uses an array of 32
antennas to communicate with 32 single-antenna clients simultaneously on the
same frequencies between 512-608 and 614-698 MHz. At close range, all 32 links
achieve the full PHY data rate, both uplink and downlink, with less than 1\%
Block Error Rate on each link. The total system rate is 3.8 Gb/s. The system
spectral efficiency is 21.7 b/s/Hz for both uplink and downlink.
  We close with some projections to the not-to-distant future.


title: Large-scale dynamics of magnetic helicity

abstract:
  In this paper we investigate the dynamics of magnetic helicity in
magnetohydrodynamic (MHD) turbulent flows focusing at scales larger than the
forcing scale. Our results show a nonlocal inverse cascade of magnetic
helicity, which occurs directly from the forcing scale into the largest scales
of the magnetic field. We also observe that no magnetic helicity and no energy
is transferred to an intermediate range of scales sufficiently smaller than the
container size and larger than the forcing scale. Thus, the statistical
properties of this range of scales, which increases with scale separation, is
shown to be described to a large extent by the zero flux solutions of the
absolute statistical equilibrium theory exhibited by the truncated ideal MHD
equations.


title: Topological Pressure for Locally Compact Metrizable Systems

abstract:
  It is widely known that when $X$ is compact Hausdorff, and when $T: X \to X$
and $f: X \to \mathbb{R}$ are continuous, \begin{equation*} P(T,f) =
\sup_{\text{$\mu$: Radon probability}} \left( h_\mu(T) + \int f\, \mathrm{d}\mu
\right), \end{equation*} where $P(T,f)$ is the "topological pressure" and
$h_\mu(T)$ is the measure theoretic entropy of $T$ with respect to $\mu$. This
result is known as "variational principle". We generalize the concept of
"topological pressure" for the case where $X$ is a separable locally compact
metric space. Our definitions are quite similar to those used in the compact
case. Our main result is the validity of the "variational principle".


title:
Single-Molecule Imaging of Nav1.6 on the Surface of Hippocampal Neurons
  Reveals Somatic Nanoclusters

abstract:
  Voltage-gated sodium (Na$_\mathrm{v}$) channels are responsible for the
depolarizing phase of the action potential in most nerve cells, and
Na$_\mathrm{v}$ channel localization to the axon initial segment is vital to
action potential initiation. Na$_\mathrm{v}$ channels in the soma play a role
in the transfer of axonal output information to the rest of the neuron and in
synaptic plasticity, although little is known about Na$_\mathrm{v}$ channel
localization and dynamics within this neuronal compartment. This study uses
single-particle tracking and photoactivation localization microscopy to analyze
cell-surface Na$_\mathrm{v}$1.6 within the soma of cultured hippocampal
neurons. Mean-square displacement analysis of individual trajectories indicated
that half of the somatic Na$_\mathrm{v}$1.6 channels localized to stable
nanoclusters $\sim$230 nm in diameter. Strikingly, these domains were
stabilized at specific sites on the cell membrane for >30 min, notably via an
ankyrin-independent mechanism, indicating that the means by which
Na$_\mathrm{v}$1.6 nanoclusters are maintained in the soma is biologically
different from axonal localization. Nonclustered Na$_\mathrm{v}$1.6 channels
showed anomalous diffusion, as determined by mean-square-displacement analysis.
High-density single-particle tracking of Na$_\mathrm{v}$ channels labeled with
photoactivatable fluorophores in combination with Bayesian inference analysis
was employed to characterize the surface nanoclusters. A subpopulation of
mobile Na$_\mathrm{v}$1.6 was observed to be transiently trapped in the
nanoclusters. Somatic Na$_\mathrm{v}$1.6 nanoclusters represent a new, to our
knowledge, type of Na$_\mathrm{v}$ channel localization, and are hypothesized
to be sites of localized channel regulation.


title: Generalized emptiness formation probability in the six-vertex model

abstract:
  In the six-vertex model with domain wall boundary conditions, the emptiness
formation probability is the probability that a rectangular region in the top
left corner of the lattice is frozen. We generalize this notion to the case
where the frozen region has the shape of a generic Young diagram. We derive
here a multiple integral representation for this correlation function.


title: A Survey and Evaluation of Data Center Network Topologies

abstract:
  Data centers are becoming increasingly popular for their flexibility and
processing capabilities in the modern computing environment. They are managed
by a single entity (administrator) and allow dynamic resource provisioning,
performance optimization as well as efficient utilization of available
resources. Each data center consists of massive compute, network and storage
resources connected with physical wires. The large scale nature of data centers
requires careful planning of compute, storage, network nodes, interconnection
as well as inter-communication for their effective and efficient operations. In
this paper, we present a comprehensive survey and taxonomy of network
topologies either used in commercial data centers, or proposed by researchers
working in this space. We also compare and evaluate some of those topologies
using mininet as well as gem5 simulator for different traffic patterns, based
on various metrics including throughput, latency and bisection bandwidth.


title: A survival guide for feeble fish

abstract:
  As avid anglers we were always interested in the survival chances of fish in
turbulent oceans. This paper addresses this question mathematically. We show
that a fish with bounded aquatic locomotion speed can reach any point in the
ocean if the fluid velocity is incompressible, bounded, and has small mean
drift.


title: A note on adjusting $R^2$ for using with cross-validation

abstract:
  We show how to adjust the coefficient of determination ($R^2$) when used for
measuring predictive accuracy via leave-one-out cross-validation.


title:
Anisotropic Effects of Oxygen Vacancies on Electrochromic Properties and
  Conductivity of $\gamma$-Monoclinic WO$_3$

abstract:
  Tungsten trioxide (WO$_3$) is a paradigmatic electrochromic material, whose
peculiar optical properties in the presence of oxygen vacancies or intercalated
alkali atoms have been observed and investigated for a long time. In this paper
we propose a rationalization of experiments based on first-principles
calculations of optical and electrical properties of oxygen deficient (reduced)
WO$_3$. Our approach is based on a parameter-free dielectric-dependent hybrid
density functional methodology, used in combination with the charge transition
levels formalism, for studying excitation mechanisms in the presence of
defects. Our results indicate that oxygen vacancies lead to a different physics
in $\gamma$-monoclinic WO$_3$, depending on the orientation of the W-O-W chain
where the vacancy is created, thus evidencing strong anisotropic effects rooted
in the peculiar structural properties of the original nondefective monoclinic
cell. Different types of oxygen vacancies can hence be classified on the basis
of the calculated ground state properties, electronic structure, and
excitation/emission energies, giving a satisfactory explanation to a range of
experimental observations made on oxygen deficient WO$_3$.


title:
The Extremely Low Activity Comet 209P/LINEAR During Its Extraordinary
  Close Approach in 2014

abstract:
  We present results from our observing campaign of Comet 209P/LINEAR during
its exceptionally close approach to Earth during May of 2014, the third
smallest perigee of any comet in two centuries. These circumstances permitted
us to pursue several studies of this intrinsically faint object, including
measurements of gas and dust production rates, searching for coma morphology,
and direct detection of the nucleus to measure its properties. Indeed, we
successfully measured the lowest water production rates of an intact comet in
over 35 years and a corresponding smallest active area, ~0.007 km^2. When
combined with the nucleus size found from radar (Howell et al. 2014), this also
yields the smallest active fraction for any comet, ~0.024%. In all, this
strongly suggests that 209P/LINEAR is on its way to becoming an inert object.
The nucleus was detected but could not easily be disentangled from the inner
coma due to seeing variations and changing spatial scales. Even so, we were
able to measure a double-peaked lightcurve consistent with the shorter of two
viable rotational periods found by Hergenrother (2014). Radial profiles of the
dust coma are quite steep, similar to that observed for some other very anemic
comets and suggestive that vaporizing icy grains are present.


title: Stability results for Gabor frames and the p-order hold models

abstract:
  We prove stability results for a class of Gabor frames in $ L^2(\R)$. We
consider window functions in the Sobolev spaces $H^1_0(\R)$ and B-splines of
order $p\ge 1$. Our results can be used to describe the effect of the timing
jitters in the $p$-order hold models of signal reconstruction.


title:
Search for transient gravitational waves in coincidence with short
  duration radio transients during 2007-2013

abstract:
  We present an archival search for transient gravitational-wave bursts in
coincidence with 27 single pulse triggers from Green Bank Telescope pulsar
surveys, using the LIGO, Virgo and GEO interferometer network. We also discuss
a check for gravitational-wave signals in coincidence with Parkes Fast Radio
Bursts using similar methods. Data analyzed in these searches were collected
between 2007 and 2013. Possible sources of emission of both short-duration
radio signals and transient gravitational-wave emission include starquakes on
neutron stars, binary coalescence of neutron stars, and cosmic string cusps.
While no evidence for gravitational-wave emission in coincidence with these
radio transients was found, the current analysis serves as a prototype for
similar future searches using more sensitive second-generation interferometers.


title: A proof of the peak polynomial positivity conjecture

abstract:
  We say that a permutation $\pi=\pi_1\pi_2\cdots \pi_n \in \mathfrak{S}_n$ has
a peak at index $i$ if $\pi_{i-1} < \pi_i > \pi_{i+1}$. Let $\mathcal{P}(\pi)$
denote the set of indices where $\pi$ has a peak. Given a set $S$ of positive
integers, we define
$\mathcal{P}_S(n)=\{\pi\in\mathfrak{S}_n:\mathcal{P}(\pi)=S\}$. In 2013 Billey,
Burdzy, and Sagan showed that for subsets of positive integers $S$ and
sufficiently large $n$, $| \mathcal{P}_S(n)|=p_S(n)2^{n-|S|-1}$ where $p_S(x)$
is a polynomial depending on $S$. They gave a recursive formula for $p_S(x)$
involving an alternating sum, and they conjectured that the coefficients of
$p_S(x)$ expanded in a binomial coefficient basis centered at $\max(S)$ are all
nonnegative. In this paper we introduce a new recursive formula for
$|\mathcal{P}_S(n)|$ without alternating sums, and we use this recursion to
prove that their conjecture is true.


title:
Electromagnetic fields in the exterior of an oscillating relativistic
  star -- II. Electromagnetic damping

abstract:
  An important issue in the asteroseismology of compact and magnetized stars is
the determination of the dissipation mechanism which is most efficient in
damping the oscillations when these are produced. In a linear regime and for
low-multipolarity modes these mechanisms are confined to either
gravitational-wave or electromagnetic losses. We here consider the latter and
compute the energy losses in the form of Poynting fluxes, Joule heating and
Ohmic dissipation in a relativistic oscillating spherical star with a dipolar
magnetic field in vacuum. While this approach is not particularly realistic for
rapidly rotating stars, it has the advantage that it is fully analytic and that
it provides expressions for the electric and magnetic fields produced by the
most common modes of oscillation both in the vicinity of the star and far away
from it. In this way we revisit and extend to a relativistic context the
classical estimates of McDermott et al. Overall, we find that
general-relativistic corrections lead to electromagnetic damping time-scales
that are at least one order of magnitude smaller than in Newtonian gravity.
Furthermore, with the only exception of $g$ (gravity) modes, we find that $f$
(fundamental), $p$ (pressure), $i$ (interface) and $s$ (shear) modes are
suppressed more efficiently by gravitational losses than by electromagnetic
ones.


title:
Plug-and-Play ADMM for Image Restoration: Fixed Point Convergence and
  Applications

abstract:
  Alternating direction method of multiplier (ADMM) is a widely used algorithm
for solving constrained optimization problems in image restoration. Among many
useful features, one critical feature of the ADMM algorithm is its modular
structure which allows one to plug in any off-the-shelf image denoising
algorithm for a subproblem in the ADMM algorithm. Because of the plug-in
nature, this type of ADMM algorithms is coined the name "Plug-and-Play ADMM".
Plug-and-Play ADMM has demonstrated promising empirical results in a number of
recent papers. However, it is unclear under what conditions and by using what
denoising algorithms would it guarantee convergence. Also, since Plug-and-Play
ADMM uses a specific way to split the variables, it is unclear if fast
implementation can be made for common Gaussian and Poissonian image restoration
problems.
  In this paper, we propose a Plug-and-Play ADMM algorithm with provable fixed
point convergence. We show that for any denoising algorithm satisfying an
asymptotic criteria, called bounded denoisers, Plug-and-Play ADMM converges to
a fixed point under a continuation scheme. We also present fast implementations
for two image restoration problems on super-resolution and single-photon
imaging. We compare Plug-and-Play ADMM with state-of-the-art algorithms in each
problem type, and demonstrate promising experimental results of the algorithm.


title: Minimal braid representatives of quasipositive links

abstract:
  We show that every quasipositive link has a quasipositive minimal braid
representative, partially resolving a question posed by Orevkov. These
quasipositive minimal braids are used to show that the maximal self-linking
number of a quasipositive link is bounded below by the negative of the minimal
braid index, with equality if and only if the link is an unlink. This implies
that the only amphicheiral quasipositive links are the unlinks, answering a
question of Rudolph's.


title: New constraints on interacting dark energy from cosmic chronometers

abstract:
  We use the latest compilation of observational Hubble parameter measurements
estimated with the differential evolution of cosmic chronometers, in
combination with the local value of the Hubble constant recently measured with
2.4% precision, to constrain the cosmological scenario where dark energy
interacts directly with the dark matter sector. To diminish the degeneracy
between the parameters we additionally consider standard probes, such as
Supernovae Type Ia from joint light curves (JLA) sample, Baryon Acoustic
Oscillation distance measurements (BAO), and cosmic microwave background data
from Planck 2015 estimations. Our analysis shows that the direct interaction
between dark energy and dark matter is mildly flavored, while the dark energy
equation-of-state parameter is w < - 1 at 3$\sigma$ confidence level.


title:
Not Just a Black Box: Learning Important Features Through Propagating
  Activation Differences

abstract:
  Note: This paper describes an older version of DeepLIFT. See
https://arxiv.org/abs/1704.02685 for the newer version. Original abstract
follows: The purported "black box" nature of neural networks is a barrier to
adoption in applications where interpretability is essential. Here we present
DeepLIFT (Learning Important FeaTures), an efficient and effective method for
computing importance scores in a neural network. DeepLIFT compares the
activation of each neuron to its 'reference activation' and assigns
contribution scores according to the difference. We apply DeepLIFT to models
trained on natural images and genomic data, and show significant advantages
over gradient-based methods.


title:
Exploring the propagation of relativistic quantum wavepackets in the
  trajectory-based formulation

abstract:
  In the context of nonrelativistic quantum mechanics, Gaussian wavepacket
solutions of the time-dependent Schr\"odinger equation provide useful physical
insight. This is not the case for relativistic quantum mechanics, however, for
which both the Klein-Gordon and Dirac wave equations result in strange and
counterintuitive wavepacket behaviors, even for free-particle Gaussians. These
behaviors include zitterbewegung and other interference effects. As a potential
remedy, this paper explores a new trajectory-based formulation of quantum
mechanics, in which the wavefunction plays no role [Phys. Rev. X, 4, 040002
(2014)]. Quantum states are represented as ensembles of trajectories, whose
mutual interaction is the source of all quantum effects observed in
nature---suggesting a "many interacting worlds" interpretation. It is shown
that the relativistic generalization of the trajectory-based formulation
results in well-behaved free-particle Gaussian wavepacket solutions. In
particular, probability density is positive and well-localized everywhere, and
its spatial integral is conserved over time---in any inertial frame. Finally,
the ensemble-averaged wavepacket motion is along a straight line path through
spacetime. In this manner, the pathologies of the wave-based relativistic
quantum theory, as applied to wavepacket propagation, are avoided.


title:
An O(N) and parallel approach to integral problems by a
  kernel-independent fast multipole method: Application to polarization and
  magnetization of interacting particles

abstract:
  Large classes of materials systems in physics and engineering are governed by
magnetic and electrostatic interactions. Continuum or mesoscale descriptions of
such systems can be cast in terms of integral equations, whose direct
computational evaluation requires O(N^2) operations, where N is the number of
unknowns. Such a scaling, which arises from the many-body nature of the
relevant Green's function, has precluded wide-spread adoption of integral
methods for solution of large-scale scientific and engineering problems. In
this work, a parallel computational approach is presented that relies on using
scalable open source libraries and utilizes a kernel-independent Fast Multipole
Method to evaluate the integrals in O(N) operations, with O(N) memory cost,
thereby substantially improving the scalability and efficiency of computational
integral methods. We demonstrate the accuracy, efficiency, and scalability of
our approach in the contest of two examples. In the first, we solve a boundary
value problem for a ferroelectric/ferromagnetic volume in free space. In the
second, we solve an electrostatic problem involving polarizable dielectric
bodies in an unbounded dielectric medium. The results from these test cases
show that our parallel approach, which is built on a kernel-independent FMM,
can enable highly efficient and accurate simulations and allow for considerable
flexibility in a broad range of applications.

categories: physics.comp-ph cond-mat.mes-hall cond-mat.mtrl-sci cond-mat.soft


title: A duality principle in spin glasses

abstract:
  We prove a duality principle that connects the thermodynamic limits of the
free energies of the Hamiltonians and their squared interactions. Under the
main assumption that the limiting free energy is concave in the squared
temperature parameter, we show that this relation is valid in a large class of
disordered systems. In particular, when applied to mean field spin glasses,
this duality provides an interpretation of the Parisi formula as an inverted
variational principle, establishing a prediction of Guerra.


title:
Negative-Weight Shortest Paths and Unit Capacity Minimum Cost Flow in
  $\tilde{O}(m^{10/7} \log W)$ Time

abstract:
  In this paper, we study a set of combinatorial optimization problems on
weighted graphs: the shortest path problem with negative weights, the weighted
perfect bipartite matching problem, the unit-capacity minimum-cost maximum flow
problem and the weighted perfect bipartite $b$-matching problem under the
assumption that $\Vert b\Vert_1=O(m)$. We show that each one of these four
problems can be solved in $\tilde{O}(m^{10/7}\log W)$ time, where $W$ is the
absolute maximum weight of an edge in the graph, which gives the first in over
25 years polynomial improvement in their sparse-graph time complexity.
  At a high level, our algorithms build on the interior-point method-based
framework developed by Madry (FOCS 2013) for solving unit-capacity maximum flow
problem. We develop a refined way to analyze this framework, as well as provide
new variants of the underlying preconditioning and perturbation techniques.
Consequently, we are able to extend the whole interior-point method-based
approach to make it applicable in the weighted graph regime.


title:
The Complexity of Translationally-Invariant Spin Chains with Low Local
  Dimension

abstract:
  We prove that estimating the ground state energy of a
translationally-invariant, nearest-neighbour Hamiltonian on a 1D spin chain is
QMAEXP-complete, even for systems of low local dimension (roughly 40). This is
an improvement over the best previously-known result by several orders of
magnitude, and it shows that spin-glass-like frustration can occur in
translationally-invariant quantum systems with a local dimension comparable to
the smallest-known non-translationally-invariant systems with similar
behaviour.
  While previous constructions of such systems rely on standard models of
quantum computation, we construct a new model that is particularly well-suited
for encoding quantum computation into the ground state of a
translationally-invariant system. This allows us to shift the proof burden from
optimizing the Hamiltonian encoding a standard computational model to proving
universality of a simple model.
  Previous techniques for encoding quantum computation into the ground state of
a local Hamiltonian allow only a linear sequence of gates, hence only a linear
(or nearly linear) path in the graph of all computational states. We extend
these techniques by allowing significantly more general paths, including
branching and cycles, thus enabling a highly efficient encoding of our
computational model. However, this requires more sophisticated techniques for
analysing the spectrum of the resulting Hamiltonian. To address this, we
introduce a framework of graphs with unitary edge labels. After relating our
Hamiltonian to the Laplacian of such a unitary labelled graph, we analyse its
spectrum by combining matrix analysis and spectral graph theory techniques.


title:
Prescribed scalar curvature plus mean curvature flows in compact
  manifolds with boundary of negative conformal invariant

abstract:
  We employ three different methods to prove the following result on prescribed
scalar curvature plus mean curvature problem: Let $(M^n,g_0)$ be a
$n$-dimensional smooth compact manifold with boundary, where $n \geq 3$, assume
the conformal invariant $Y(M,\partial M)<0$. Given any negative smooth
functions $f$ in $M$ and $h$ on $\partial M$, there exists a unique conformal
metric of $g_0$ such that its scalar curvature equals $f$ and mean curvature
curvature equals $h$. The first two methods are sub-super-solution method and
subcritical approximation, and the third method is a geometric flow. In the
flow approach, assume another conformal invariant $Q(M,\pa M)$ is a negative
real number, for some class of initial data, we prove the short time and long
time existences of the so-called prescribed scalar curvature plus mean
curvature flows, as well as their asymptotic convergence. Via a family of such
flows together with some additional variational arguments, under the flow
assumptions we prove existence and uniqueness of positive minimizers of the
associated energy functional and also the above result by analyzing asymptotic
limits of the flows and the relations among some conformal invariants.


title:
Enhancement of the thermoelectric properties in doped FeSb$_2$ bulk
  crystals

abstract:
  Kondo insulator FeSb$_2$ with large Seebeck coefficient would have potential
in thermoelectric applications in cryogenic temperature range if it had not
been for large thermal conductivity $\kappa$. Here we studied the influence of
different chemical substitutions at Fe and Sb site on thermal conductivity and
thermoelectric effect in high quality single crystals. At $5\%$ of Te doping at
Sb site thermal conductivity is suppressed from $\sim 250$ W/Km in undoped
sample to about 8 W/Km. However, Cr and Co doping at Fe site suppresses thermal
conductivity more slowly than Te doping, and even at 20$\%$ Cr/Co doping the
thermal conductivity remains $\sim 30$ W/Km. The analysis of different
contributions to phonon scattering indicates that the giant suppression of
$\kappa$ with Te is due to the enhanced point defect scattering originating
from the strain field fluctuations. In contrast, Te-doping has small influence
on the correlation effects and then for small Te substitution the large
magnitude of the Seebeck coefficient is still preserved, leading to the
enhanced thermoelectric figure of merit ($ZT\sim 0.05$ at $\sim 100$ K) in
Fe(Sb$_{0.9}$Te$_{0.1}$)$_2$.


title: $E_8$, the most exceptional group

abstract:
  The five exceptional simple Lie algebras over the complex number are included
one within the other as $G_2 \subset F_4 \subset E_6 \subset E_7 \subset E_8$.
The biggest one, $E_8$, is in many ways the most mysterious. This article
surveys what is known about it including many recent results, focusing on the
point of view of Lie algebras and algebraic groups over fields.


title:
On solutions of some of unsolved problems in number theory, specifically
  on the distribution of primes

abstract:
  We solve some famous conjectures on the distribution of primes. These
conjectures are to be listed as Legendre's, Andrica's, Oppermann's, Brocard's,
Cram\'{e}r's, Shanks', and five Smarandache's conjectures. We make use of both
Firoozbakht's conjecture (which recently proved by the author) and Kourbatov's
theorem on the distribution of and gaps between consecutive primes. These
latter conjecture and theorem play an essential role in our methods for proving
these famous conjectures. In order to prove Shanks' conjecture, we make use of
Panaitopol's asymptotic formula for $\pi(x)$ as well.


title:
Stirred, not Clumped: Evolution of Temperature Profiles in the Outskirts
  of Galaxy Clusters

abstract:
  Recent statistical X-ray measurements of the intracluster medium (ICM)
indicate that gas temperature profiles in the outskirts of galaxy clusters
deviate from self-similar evolution. Using a mass-limited sample of galaxy
clusters from cosmological hydrodynamical simulations, we show that the
departure from self-similarity can be explained by non-thermal gas motions
driven by mergers and accretion. Contrary to previous claims, gaseous
substructures only play a minor role in the temperature evolution in cluster
outskirts. A careful choice of halo overdensity definition in self-similar
scaling mitigates these departures. Our work highlights the importance of
non-thermal gas motions in ICM evolution and the use of galaxy clusters as
cosmological probes.


title:
Hard X-ray Luminosity Function of Tidal Disruption Events: First Results
  from MAXI Extragalactic Survey

abstract:
  We derive the first hard X-ray luminosity function (XLF) of stellar tidal
disruption events (TDEs) by supermassive black holes (SMBHs), which gives an
occurrence rate of TDEs per unit volume as a function of peak luminosity and
redshift, utilizing an unbiased sample observed by the Monitor of All-sky X-ray
Image (MAXI). On the basis of the light curves characterized by a power-law
decay with an index of $-5/3$, a systematic search using the MAXI data in the
first 37 months detected four TDEs, all of which have been found in the
literature. To formulate the TDE XLF, we consider the mass function of SMBHs,
that of disrupted stars, the specific TDE rate as a function of SMBH mass, and
the fraction of TDEs with relativistic jets. We perform an unbinned maximum
likelihood fit to the MAXI TDE list and check the consistency with the observed
TDE rate in the ROSAT all sky survey. The results suggest that the intrinsic
fraction of the jet-accompanying events is $0.0007$--$34\%$. We confirm that at
$z \lesssim 1.5$ the contamination by TDEs to the hard X-ray luminosity
functions of active galactic nuclei is not significant and hence that their
contribution to the growth of SMBHs is negligible at the redshifts.


title:
How AGN Jets Heat the Intracluster Medium -- Insights from Hydrodynamic
  Simulations

abstract:
  Feedback from active galactic nuclei (AGN) is believed to prevent
catastrophic cooling in galaxy clusters. However, how the feedback energy is
transformed into heat, and how the AGN jets heat the intracluster medium (ICM)
isotropically, still remain elusive. In this work, we gain insights into the
relative importance of different heating mechanisms using three-dimensional
hydrodynamic simulations including cold gas accretion and momentum-driven jet
feedback, which are the most successful models to date in terms reproducing the
properties of cool cores. We find that there is net heating within two `jet
cones' (within ~30 degrees from the axis of jet precession) where the ICM gains
entropy by shock heating and mixing with the hot thermal gas within bubbles.
Outside the jet cones, the ambient gas is heated by weak shocks, but not enough
to overcome radiative cooling, therefore forming a `reduced' cooling flow.
Consequently, the cluster core is in a process of `gentle circulation' over
billions of years. Within the jet cones, there is significant adiabatic cooling
as the gas is uplifted by buoyantly rising bubbles; outside the cones, energy
is supplied by inflow of already-heated gas from the jet cones as well as
adiabatic compression as the gas moves toward the center. In other words, the
fluid dynamics self-adjusts such that it compensates and transports the heat
provided by the AGN, and hence no fine-tuning of the heating profile of any
process is necessary. Throughout the cluster evolution, turbulent energy is
only at the percent level compared to gas thermal energy, and thus turbulent
heating is not the main source of heating in our simulation.


title: Green-Schwarz superstring on the lattice

abstract:
  We consider possible discretizations for a gauge-fixed Green-Schwarz action
of Type IIB superstring. We use them for measuring the action, from which we
extract the cusp anomalous dimension of planar $\mathcal{N}=4$ SYM as derived
from AdS/CFT, as well as the mass of the two $AdS$ excitations transverse to
the relevant null cusp classical string solution. We perform lattice
simulations employing a Rational Hybrid Monte Carlo (RHMC) algorithm and two
Wilson-like fermion discretizations, one of which preserves the global $SO(6)$
symmetry of the model. We compare our results with the expected behavior at
various values of $g=\frac{\sqrt{\lambda}}{4\pi}$. For both the observables, we
find a good agreement for large $g$, which is the perturbative regime of the
sigma-model. For smaller values of $g$, the expectation value of the action
exhibits a deviation compatible with the presence of quadratic divergences.
After their non-perturbative subtraction the continuum limit can be taken, and
suggests a qualitative agreement with the non-perturbative expectation from
AdS/CFT. Furthermore, we detect a phase in the fermion determinant, whose
origin we explain, that for very small $g$ leads to a sign problem not
treatable via standard reweigthing. The continuum extrapolations of the
observables in the two different discretizations agree within errors, which is
strongly suggesting that they lead to the same continuum limit. Part of the
results discussed here were presented earlier in arXiv:1601.04670.


title: Ultraheavy Element Enrichment in Impulsive Solar Flares

abstract:
  Particle acceleration by cascading Alfven wave turbulence was suggested
(Eichler, 1979b) as being responsible for energetic particle populations in
$^3$He-rich solar flares. In particular, it was noted that the damping of the
turbulence by the tail of the particle distribution in rigidity naturally leads
to dramatic enhancement of pre-accelerated species - as $^3$He is posited to be
- and superheavy elements. The subsequent detection of large enrichment of
ultraheavies, relative to iron, has apparently confirmed this prediction,
lending support to the original idea. It is shown here that this picture could
be somewhat sharpened by progress in understanding the 3-dimensional
geometrical details of cascading Alfven turbulence (Sridhar and Goldreich,
1995). The mechanism may be relevant in other astrophysical environments where
the source of turbulence is non-magnetic, such as clusters of galaxies.


title: Alignments between galaxies, satellite systems and haloes

abstract:
  The spatial distribution of the satellite populations of the Milky Way and
Andromeda are puzzling in that they are nearly perpendicular to the disks of
their central galaxies. To understand the origin of such configurations we
study the alignment of the central galaxy, satellite system and dark matter
halo in the largest of the "Evolution and Assembly of GaLaxies and their
Environments" (EAGLE) simulation. We find that centrals and their satellite
systems tend to be well aligned with their haloes, with a median misalignment
angle of $33^{\circ}$ in both cases. While the centrals are better aligned with
the inner $10$ kpc halo, the satellite systems are better aligned with the
entire halo indicating that satellites preferentially trace the outer halo. The
central - satellite alignment is weak (median misalignment angle of
$52^{\circ}$) and we find that around $20\%$ of systems have a misalignment
angle larger than $78^{\circ}$, which is the value for the Milky Way. The
central - satellite alignment is a consequence of the tendency of both
components to align with the dark matter halo. As a consequence, when the
central is parallel to the satellite system, it also tends to be parallel to
the halo. In contrast, if the central is perpendicular to the satellite system,
as in the case of the Milky Way and Andromeda, then the central - halo
alignment is much weaker. Dispersion-dominated (spheroidal) centrals have a
stronger alignment with both their halo and their satellites than
rotation-dominated (disk) centrals. We also found that the halo, the central
galaxy and the satellite system tend to be aligned with the surrounding
large-scale distribution of matter, with the halo being the better aligned of
the three.


title: A Conformal Fixed-Point Equation for the Effective Average Action

abstract:
  A Legendre transform of the recently discovered conformal fixed-point
equation is constructed, providing an unintegrated equation encoding full
conformal invariance within the framework of the effective average action.


title:
Suppression of the accretion rate in thin discs around binary black
  holes

abstract:
  We present three-dimensional Smoothed Particle Hydrodynamics (SPH)
simulations investigating the dependence of the accretion rate on the disc
thickness around an equal-mass, circular black hole binary system. We find that
for thick/hot discs, with $H/R\gtrsim 0.1$, the binary torque does not prevent
the gas from penetrating the cavity formed in the disc by the binary (in line
with previous investigations). The situation drastically changes for thinner
discs, in this case the mass accretion rate is suppressed, such that only a
fraction (linearly dependent on $H/R$) of the available gas is able to flow
within the cavity and accrete on to the binary. Extrapolating this result to
the cold and thin accretion discs expected around supermassive black hole
binary systems implies that this kind of systems accretes less material than
predicted so far, with consequences not only for the electromagnetic and
gravitational waves emissions during the late inspiral phase but also for the
recoil speed of the black hole formed after binary coalescence, thus
influencing also the evolutionary path both of the binary and of the host
galaxy. Our results, being scale-free, are also applicable to equal mass,
circular binaries of stellar mass black holes, such as the progenitor of the
recently discovered gravitational wave source GW150914.


title:
A Comprehensive Dust Model Applied to the Resolved Beta Pictoris Debris
  Disk from Optical to Radio Wavelengths

abstract:
  We investigate whether varying the dust composition (described by the optical
constants) can solve a persistent problem in debris disk modeling--the
inability to fit the thermal emission without over-predicting the scattered
light. We model five images of the beta Pictoris disk: two in scattered light
from HST/STIS at 0.58 microns and HST/WFC3 at 1.16 microns, and three in
thermal emission from Spitzer/MIPS at 24 microns, Herschel/PACS at 70 microns,
and ALMA at 870 microns. The WFC3 and MIPS data are published here for the
first time. We focus our modeling on the outer part of this disk, consisting of
a parent body ring and a halo of small grains. First, we confirm that a model
using astronomical silicates cannot simultaneously fit the thermal and
scattered light data. Next, we use a simple, generic function for the optical
constants to show that varying the dust composition can improve the fit
substantially. Finally, we model the dust as a mixture of the most plausible
debris constituents: astronomical silicates, water ice, organic refractory
material, and vacuum. We achieve a good fit to all datasets with grains
composed predominantly of silicates and organics, while ice and vacuum are, at
most, present in small amounts. This composition is similar to one derived from
previous work on the HR 4796A disk. Our model also fits the thermal SED,
scattered light colors, and high-resolution mid-IR data from T-ReCS for this
disk. Additionally, we show that sub-blowout grains are a necessary component
of the halo.


title: Orientifolds of Warped Throats from Toric Calabi-Yau Singularities

abstract:
  We study the complex deformations of orientifolds of D3-branes at toric CY
singularities, using their description in terms of dimer diagrams. We describe
orientifold quotients that have fixed lines or fixed points in the dimer, and
characterize the possibilities to deform them in terms of the behaviour of
zig-zag paths under the orientifold symmetry. The resulting models are
holographic duals to warped throats with orientifold planes. Our systematic
construction provides a general class of configurations which includes models
recently appeared in the context of de Sitter uplift by nilpotent goldstino or
dynamical supersymmetry breaking.


title: Matched predictions for the $b\bar{b}H$ cross section at the 13 TeV LHC

abstract:
  We present up-to-date matched predictions for the $b\bar{b}H$ inclusive cross
section at the LHC at $\sqrt{s}=13$ TeV. Using a previously developed method,
our predictions consistently combine the complete NLO contributions that are
present in the 4-flavor scheme calculation, including finite b-quark mass
effects as well as top-loop induced $Y_b Y_t$ interference contributions, with
the resummation of collinear logarithms of $m_b/m_H$ as present in the 5-flavor
scheme calculation up to NNLO. We provide a detailed estimate of the
perturbative uncertainties of the matched result by examining its dependence on
the factorization and renormalization scales, the scale of the Yukawa coupling,
and also the low b-quark matching scale in the PDFs. We motivate the use of a
central renormalization scale of $m_H$/2, which is halfway between the values
typically chosen in the 4-flavor and 5-flavor scheme calculations. We evaluate
the parametric uncertainties due to the PDFs and the b-quark mass, and in
particular discuss how to systematically disentangle the parametric $m_b$
dependence and the unphysical b-quark matching scale dependence. Our best
prediction for the $b\bar{b} H$ production cross section in the Standard Model
at 13 TeV and for $m_H$ = 125 GeV is $\sigma(b\bar b H) = 0.52 \,{\rm pb}\, [1
\pm 9.6\% {\rm (perturbative)}\,{}^{+2.9\%}_{-3.6\%} {\rm (parametric)}]$. We
also provide predictions for a range of Higgs masses $m_H\in [50, 750]$ GeV.
Our method to compute the matched prediction and to evaluate its uncertainty
can be readily applied to other heavy-quark-initiated processes at the LHC.


title: Exploring 21cm - Lyman Alpha emitter synergies for SKA

abstract:
  We study the signatures of reionization and ionizing properties of the early
galaxies in the cross-correlations between the 21cm emission from the spin-flip
transition of neutral hydrogen (HI) and the underlying galaxy population, in
particular a sub-population of galaxies visible as Lyman Alpha Emitters (LAEs).
With both observables simultaneously derived from a $z\simeq6.6$ hydrodynamical
simulation (GADGET-2) snapshot post-processed with a radiative transfer code
(pCRASH) and a dust model, we perform a parameter study and aim to constrain
both the average intergalactic medium (IGM) ionization state ($1-\langle
\chi_{HI} \rangle$) and the reionization topology (outside-in versus
inside-out). We find that in our model LAEs occupy the densest and most-ionized
regions resulting in a very strong anti-correlation between the LAEs and the
21cm emission. A 1000h SKA-LOW1 - Subaru Hyper Suprime Cam experiment can
provide constraints on $\langle \chi_{HI} \rangle$, allowing us to distinguish
between IGM ionization levels of 50%, 25%, 10% and fully ionized at scales
$r<10$ comoving Mpc (assuming foreground avoidance for SKA). Our results
support the inside-out reionization scenario where the densest knots
(under-dense voids) are ionized first (last) for $\langle \chi_{HI} \rangle >=
0.1$. Further, 1000h SKA-LOW1 observations should be able to confirm the
inside-out scenario by detecting a lower 21cm brightness temperature (by about
2-10 mK) in the densest regions ($> 2$ arcminute scales) hosting LAEs compared
to lower-density regions devoid of them.


title: Machine learning phases of matter

abstract:
  Neural networks can be used to identify phases and phase transitions in
condensed matter systems via supervised machine learning. Readily programmable
through modern software libraries, we show that a standard feed-forward neural
network can be trained to detect multiple types of order parameter directly
from raw state configurations sampled with Monte Carlo. In addition, they can
detect highly non-trivial states such as Coulomb phases, and if modified to a
convolutional neural network, topological phases with no conventional order
parameter. We show that this classification occurs within the neural network
without knowledge of the Hamiltonian or even the general locality of
interactions. These results demonstrate the power of machine learning as a
basic research tool in the field of condensed matter and statistical physics.


title: Outflow detection in a 70 $\mu$m dark high-mass core

abstract:
  We present observations towards a high-mass ($\rm >40\,M_{\odot}$), low
luminosity ($\rm <10\,L_{\odot}$) $\rm 70\,\mu$m dark molecular core G 28.34
S-A at 3.4 mm, using the IRAM 30 m telescope and the NOEMA interferometer. We
report the detection of $\rm SiO$ $J=\rm 2\rightarrow1$ line emission, which is
spatially resolved in this source at a linear resolution of $\sim$0.1 pc, while
the 3.4 mm continuum image does not resolve any internal sub-structures. The
SiO emission exhibits two W-E oriented lobes centring on the continuum peak.
Corresponding to the red-shifted and blue-shifted gas with velocities up to
$\rm 40\,km\,s^{-1}$ relative to the quiescent cloud, these lobes clearly
indicate the presence of a strong bipolar outflow from this $\rm 70\,\mu$m dark
core, a source previously considered as one of the best candidates of
"starless" core. Our SiO detection is consistent with ALMA archival data of
$\rm SiO$ $J=\rm 5\rightarrow4$, whose high-velocity blue-shifted gas reveals a
more compact lobe spatially closer to the dust center. This outflow indicates
that the central source may be in an early evolutionary stage of forming a
high-mass protostar. We also find that the low-velocity components (in the
range of $\rm V_{lsr}$$\rm_{-5}^{+3}\,km\,s^{-1}$) have an extended, NW-SE
oriented distribution. Discussing the possible accretion scenarios of the
outflow-powering young stellar object, we argue that the molecular line
emission and the molecular outflows may provide a better indication of the
accretion history when forming young stellar object, than that from a snapshot
observations of the present bolometric luminosity. This is particularly
significant for the cases of episodic accretion, which may occur during the
collapse of the parent molecular core.


title: Superconductivity at very low density: the case of strontium titanate

abstract:
  Doped strontium titanate becomes superconducting at a density as low as n = 5
x 10^17 cm^-3, where the Fermi energy is orders of magnitude smaller than the
longitudinal-optical-phonon frequencies. In this limit the only optical mode
with a frequency which is smaller than the Fermi energy is the plasmon. In
contrast to metals, the interaction strength is weak due to screening by the
crystal, which allows the construction of a controllable theory of plasmon
superconductivity. We show that plasma mediated pairing alone can account for
the observed transition temperatures if the screening by the crystal is reduced
in the slightly doped samples compared with the insulating ones. This mechanism
can also explain the pairing in the two-dimensional superconducting states
observed at surfaces and interfaces with other oxides. We also discuss unique
features of the plasmon mechanism, which appear in the tunneling density of
states above the gap.


title: Time-Varying Sodium Absorption in the Type Ia Supernova 2013gh

abstract:
  Temporal variability of narrow absorption lines in high-resolution spectra of
Type Ia supernovae (SNe Ia) is studied to search for circumstellar matter. Time
series which resolve the profiles of absorption lines such as Na I D or Ca II
H&K are expected to reveal variations due to photoionisation and subsequent
recombination of the gases. The presence, composition, and geometry of
circumstellar matter may hint at the elusive progenitor system of SNe Ia and
could also affect the observed reddening law. To date, there are few known
cases of time-varying Na I D absorption in SNe Ia, all of which occurred during
relatively late phases of the supernova evolution. Photoionisation, however, is
predicted to occur during the early phases of SNe Ia, when the supernova peaks
in the ultraviolet. We therefore attempt to observe early-time absorption-line
variations by obtaining high-resolution spectra of SNe before maximum light. We
have obtained photometry and high-resolution spectroscopy of SNe Ia 2013gh and
iPTF 13dge, to search for absorption- line variations. Furthermore, we study
interstellar absorption features in relation to the observed photometric
colours of the SNe. Results. Both SNe display deep Na I D and Ca II H&K
absorption features. Furthermore, small but significant variations are detected
in a feature of the Na I D profile of SN 2013gh. The variations are consistent
with either geometric effects of rapidly moving or patchy gas clouds or
photoionisation of Na I gas at R \approx 1019 cm from the explosion. Our
analysis indicates that it is necessary to focus on early phases to detect
photoionisation effects of gases in the circumstellar medium of SNe Ia.
Different absorbers such as Na I and Ca II can be used to probe for matter at
different distances from the SNe.


title:
The Intrinsic Eddington Ratio Distribution of Active Galactic Nuclei in
  Star-forming Galaxies from the Sloan Digital Sky Survey

abstract:
  An important question in extragalactic astronomy concerns the distribution of
black hole accretion rates of active galactic nuclei (AGN). Based on
observations at X-ray wavelengths, the observed Eddington ratio distribution
appears as a power law, while optical studies have often yielded a lognormal
distribution. There is increasing evidence that these observed discrepancies
may be due to contamination by star formation and other selection effects.
Using a sample of galaxies from the Sloan Digital Sky Survey Data Release 7, we
test if an intrinsic Eddington ratio distribution that takes the form of a
Schechter function is consistent with previous work that suggests that young
galaxies in optical surveys have an observed lognormal Eddington ratio
distribution. We simulate the optical emission line properties of a population
of galaxies and AGN using a broad instantaneous luminosity distribution
described by a Schechter function near the Eddington limit. This simulated AGN
population is then compared to observed galaxies via the positions on an
emission line excitation diagram and Eddington ratio distributions. We present
an improved method for extracting the AGN distribution using BPT diagnostics
that allows us to probe over one order of magnitude lower in Eddington ratio
counteracting the effects of dilution by star formation. We conclude that for
optically selected AGN in young galaxies, the intrinsic Eddington ratio
distribution is consistent with a possibly universal, broad power law with an
exponential cutoff, as this distribution is observed in old optically selected
galaxies and in X-rays.


title: Searching for GC-like abundance patterns in young massive clusters

abstract:
  Studies during the last decade have revealed that nearly all Globular
Clusters (GCs) host multiple populations (MPs) of stars with a distinctive
chemical patterns in light elements. No evidence of such MPs has been found so
far in lower-mass ($< \sim 10^4$ M$_{\odot}$) open clusters nor in intermediate
age (1-2 Gyr) massive ($> 10^5$ M$_{\odot}$) clusters in the Local Group. Young
massive clusters (YMCs) have masses and densities similar to those expected of
young GCs in the early universe, and their near-infrared (NIR) spectra are
dominated by the light of red super giants (RSGs). The spectra of these stars
may be used to determine the cluster's abundances, even though the individual
stars cannot be spatially resolved from one another. We carry out a
differential analysis between the Al lines of YMC NGC 1705: 1 and field Small
Magellanic Cloud RSGs with similar metallicities. We exclude at high confidence
extreme [Al/Fe] enhancements similar to those observed in GCs like NGC 2808 or
NGC 6752. However, smaller variations cannot be excluded.


title: Privacy and Twitter in Qatar: Traditional Values in the Digital World

abstract:
  We explore the meaning of privacy from the perspective of Qatari nationals as
it manifests in digital environments. Although privacy is an essential and
widely respected value in many cultures, the way in which it is understood and
enacted depends on context. It is especially vital to understand user behaviors
regarding privacy in the digital sphere, where individuals increasingly publish
personal information. Our mixed-methods analysis of 18K Twitter posts that
mention privacy focuses on the face to face and digital contexts in which
privacy is mentioned, and how those contexts lead to varied ideologies
regarding privacy. We find that in the Arab Gulf, the need for privacy is often
supported by Quranic text, advice on how to protect privacy is frequently
discussed, and the use of paternalistic language by men when discussing women
related privacy is common. Above all, privacy is framed as a communal
attribute, including not only the individual, but the behavior of those around
them; it even extends beyond the individual lifespan. We contribute an analysis
and description of these previously unexplored interpretations of privacy,
which play a role in how users navigate social media.


title: Anosov representations and dominated splittings

abstract:
  We provide a link between Anosov representations introduced by Labourie and
dominated splitting of linear cocycles. This allows us to obtain equivalent
characterizations for Anosov representations and to recover recent results due
to Gu\'eritaud-Guichard-Kassel-Wienhard and Kapovich-Leeb-Porti by different
methods. We also give characterizations in terms of multicones and cone-types
inspired in the work of Avila-Bochi-Yoccoz and Bochi-Gourmelon. Finally we
provide a new proof of the higher rank Morse Lemma of Kapovich-Leeb-Porti.


title:
On quasi-isometry invariants associated to the derivation of a Heintze
  group

abstract:
  A a Heintze group is a Lie group of the form $N\rtimes_\alpha \mathbb{R}$,
where $N$ is a simply connected nilpotent Lie group and $\alpha$ is a
derivation of $\mathrm{Lie}(N)$ whose eigenvalues all have positive real parts.
We show that if two purely real Heintze groups equipped with left-invariant
metrics are quasi-isometric, then up to a positive scalar multiple, their
respective derivations have the same characteristic polynomial. Using the same
thecniques, we prove that if we restrict to the class of Heintze groups for
which $N$ is the Heisenberg group, then the Jordan form of $\alpha$, up to
positive scalar multiples, is a quasi-isometry invariant.


title:
Improving Automated Patent Claim Parsing: Dataset, System, and
  Experiments

abstract:
  Off-the-shelf natural language processing software performs poorly when
parsing patent claims owing to their use of irregular language relative to the
corpora built from news articles and the web typically utilized to train this
software. Stopping short of the extensive and expensive process of accumulating
a large enough dataset to completely retrain parsers for patent claims, a
method of adapting existing natural language processing software towards patent
claims via forced part of speech tag correction is proposed. An Amazon
Mechanical Turk collection campaign organized to generate a public corpus to
train such an improved claim parsing system is discussed, identifying lessons
learned during the campaign that can be of use in future NLP dataset collection
campaigns with AMT. Experiments utilizing this corpus and other patent claim
sets measure the parsing performance improvement garnered via the claim parsing
system. Finally, the utility of the improved claim parsing system within other
patent processing applications is demonstrated via experiments showing improved
automated patent subject classification when the new claim parsing system is
utilized to generate the features.


title:
Strong solutions for time-dependent mean field games with non-separable
  Hamiltonians

abstract:
  We prove existence theorems for strong solutions of time-dependent mean field
games with non-separable Hamiltonian. In a recent announcement, we showed
existence of small, strong solutions for mean field games with local coupling.
We first generalize that prior work to allow for non-separable Hamiltonians.
This proof is inspired by the work of Duchon and Robert on the existence of
small-data vortex sheets in incompressible fluid mechanics. Our next existence
result is in the case of weak coupling of the system; that is, we allow the
data to be of arbitrary size, but instead require that the (still possibly
non-separable) Hamiltonian be small in a certain sense. The proof of this
theorem relies upon an appeal to the implicit function theorem.


title: Biobjective Performance Assessment with the COCO Platform

abstract:
  This document details the rationales behind assessing the performance of
numerical black-box optimizers on multi-objective problems within the COCO
platform and in particular on the biobjective test suite bbob-biobj. The
evaluation is based on a hypervolume of all non-dominated solutions in the
archive of candidate solutions and measures the runtime until the hypervolume
value succeeds prescribed target values.


title: Relative entropy and the Pinsker product formula for sofic groups

abstract:
  We continue our study of the outer Pinsker factor for probability
measure-preserving actions of sofic groups. Using the notion of doubly quenched
convergence developed by Austin, we prove that in many cases the outer Pinsker
factor of a product action is the product of the outer Pinsker factors. Our
results are parallel to those of Seward for Rohklin entropy. We use these
Pinsker products formulas to show that for many actions of a sofic group G on X
where X is a compact group and the action is by automorphism, the (measurable)
outer Pinsker factor of the action of G on X is given as a quotient by a
G-invariant, closed, normal subgroup. We use our results to show that if G is
sofic and f in M_{n}(Z(G)) is invertible as a convolution operator, then the
action of G on the Pontryagin dual of \Z(G)^{\oplus n}/\Z(G)^{\oplus n}f has
completely positive measure-theoretic entropy with respect to the Haar measure.
This last application requires our previous work connecting topological entropy
in the presence as defined by Li-Liang to measure-theoretic entropy in the
presence (implicitly defined by Kerr) for actions on compact groups. In
particular, we need our previous formulation of measure-theoretic entropy in
the presence in terms of a given topological model.


title:
Storage-Optimized Data-Atomic Algorithms for Handling Erasures and
  Errors in Distributed Storage Systems

abstract:
  Erasure codes are increasingly being studied in the context of implementing
atomic memory objects in large scale asynchronous distributed storage systems.
When compared with the traditional replication based schemes, erasure codes
have the potential of significantly lowering storage and communication costs
while simultaneously guaranteeing the desired resiliency levels. In this work,
we propose the Storage-Optimized Data-Atomic (SODA) algorithm for implementing
atomic memory objects in the multi-writer multi-reader setting. SODA uses
Maximum Distance Separable (MDS) codes, and is specifically designed to
optimize the total storage cost for a given fault-tolerance requirement. For
tolerating $f$ server crashes in an $n$-server system, SODA uses an $[n, k]$
MDS code with $k=n-f$, and incurs a total storage cost of $\frac{n}{n-f}$. SODA
is designed under the assumption of reliable point-to-point communication
channels. The communication cost of a write and a read operation are
respectively given by $O(f^2)$ and $\frac{n}{n-f}(\delta_w+1)$, where
$\delta_w$ denotes the number of writes that are concurrent with the particular
read. In comparison with the recent CASGC algorithm, which also uses MDS codes,
SODA offers lower storage cost while pays more on the communication cost.
  We also present a modification of SODA, called SODA$_{\text{err}}$, to handle
the case where some of the servers can return erroneous coded elements during a
read operation. Specifically, in order to tolerate $f$ server failures and $e$
error-prone coded elements, the SODA$_{\text{err}}$ algorithm uses an $[n, k]$
MDS code such that $k=n-2e-f$. SODA$_{\text{err}}$ also guarantees liveness and
atomicity, while maintaining an optimized total storage cost of
$\frac{n}{n-f-2e}$.


title: Rank Ordered Autoencoders

abstract:
  A new method for the unsupervised learning of sparse representations using
autoencoders is proposed and implemented by ordering the output of the hidden
units by their activation value and progressively reconstructing the input in
this order. This can be done efficiently in parallel with the use of cumulative
sums and sorting only slightly increasing the computational costs. Minimizing
the difference of this progressive reconstruction with respect to the input can
be seen as minimizing the number of active output units required for the
reconstruction of the input. The model thus learns to reconstruct optimally
using the least number of active output units. This leads to high sparsity
without the need for extra hyperparameters, the amount of sparsity is instead
implicitly learned by minimizing this progressive reconstruction error. Results
of the trained model are given for patches of the CIFAR10 dataset, showing
rapid convergence of features and extremely sparse output activations while
maintaining a minimal reconstruction error and showing extreme robustness to
overfitting. Additionally the reconstruction as function of number of active
units is presented which shows the autoencoder learns a rank order code over
the input where the highest ranked units correspond to the highest decrease in
reconstruction error.


title: Some results on the spectral radii of uniform hypergraphs

abstract:
  Let A(G) be the adjacency tensor (hypermatrix) of uniform hypergraph G. The
maximum modulus of the eigenvalues of A(G) is called the spectral radius of G.
In this paper, the conjecture of Fan et al. in [5] related to compare the
spectral radii of some three uniform hypergraphs is solved. Moreover, some
eigenvalues properties of a kind of uniform hypergraphs are obtained.


title: Measuring gravitational effects on antimatter in space

abstract:
  We propose an experimental test of the gravitational interaction with
antimatter by measuring the branching fraction of the CP~violating decay
$K_\mathrm{L} \to \pi^{+} \pi^{-}$ in space. We show that at the altitude of
the International Space Station, gravitational effects may change the level of
CP~violation such that a 5$\sigma$ discrimination may be obtained by collecting
the $K_\mathrm{L}$ produced by the cosmic proton flux within a few years.


title:
Minimum Power Range Assignment for Symmetric Connectivity in Sensor
  Networks with two Power Levels

abstract:
  This paper examines the problem of assigning a transmission power to every
node of a wireless sensor network. The goal is to minimize the total power
consumption while ensuring that the resulting communication graph is connected.
We focus on a restricted version of this Range Assignment (RA) problem in which
there are two different power levels. We only consider symmetrical transmission
links to allow easy integration with low level wireless protocols that
typically require bidirectional communication between two neighboring nodes. We
introduce a parameterized polynomial time approximation algorithm with a
performance ratio arbitrarily close to $\pi^2/6$. Additionally, we give an
almost linear time approximation algorithm with a tight quality bound of $7/4$.


title:
Phase-Resolved Spectroscopy of Type B Quasi-Periodic Oscillations in GX
  339-4

abstract:
  We present a new spectral-timing technique for phase-resolved spectroscopy
and apply it to the low-frequency Type B quasi-periodic oscillation (QPO) from
the black hole X-ray binary GX 339-4. We show that on the QPO time-scale the
spectrum changes not only in normalisation, but also in spectral shape. Using
several different spectral models which parameterise the blackbody and
power-law components seen in the time-averaged spectrum, we find that both
components are required to vary, although the fractional rms amplitude of
blackbody emission is small, ~1.4 per cent compared to ~25 per cent for the
power-law emission. However the blackbody variation leads the power-law
variation by ~0.3 in relative phase (~110 degrees), giving a significant break
in the Fourier lag-energy spectrum that our phase-resolved spectral models are
able to reproduce. Our results support a geometric interpretation for the QPO
variations where the blackbody variation and its phase relation to the
power-law are explained by quasi-periodic heating of the approaching and
receding sides of the disc by a precessing Comptonising region. The small
amplitude of blackbody variations suggests that the Comptonising region
producing the QPO has a relatively large scale-height, and may be linked to the
base of the jet, as has previously been suggested to explain the binary orbit
inclination-dependence of Type B QPO amplitudes.


title: Generalized Backpropagation Algorithms for Diffraction Tomography

abstract:
  Filtered backpropagation (FBPP) is a well-known technique used for
Diffraction Tomography (DT). For accurate reconstruction of a complex image
using FBPP, full $360^{\circ}$ angular coverage is necessary. However, it has
been shown that using some inherent redundancies in projection data in a
tomographic setup, accurate reconstruction is still possible with $270^{\circ}$
coverage which is called the minimal-scan angle range. This can be done by
applying weighing functions (or filters) on projection data of the object to
eliminate the redundancies and accurately reconstruct the image from this lower
angular coverage. This paper demonstrates procedures to generate many general
classes of these weighing filters. These are all equivalent at $270^{\circ}$
coverage but would perform differently at lower angular coverages and under
presence of noise. This paper does a comparative analysis of different filters
when angular coverage is lower than minimal-scan angle of $270^{\circ}$.
Simulation studies have been done to find optimum weight filters for
sub-minimal angular coverage. The optimum weights can generate images
comparable to a full $360^{\circ}$ coverage FBPP reconstruction. Performance of
these in presence of noise is also analyzed. These algorithms are capable of
reconstructing almost distortionless complex images even at angular coverages
of $200^{\circ}$.


title: DCTNet and PCANet for acoustic signal feature extraction

abstract:
  We introduce the use of DCTNet, an efficient approximation and alternative to
PCANet, for acoustic signal classification. In PCANet, the eigenfunctions of
the local sample covariance matrix (PCA) are used as filterbanks for
convolution and feature extraction. When the eigenfunctions are well
approximated by the Discrete Cosine Transform (DCT) functions, each layer of of
PCANet and DCTNet is essentially a time-frequency representation. We relate
DCTNet to spectral feature representation methods, such as the the short time
Fourier transform (STFT), spectrogram and linear frequency spectral
coefficients (LFSC). Experimental results on whale vocalization data show that
DCTNet improves classification rate, demonstrating DCTNet's applicability to
signal processing problems such as underwater acoustics.


title:
Limit on the Radiative Neutrinoless Double Electron Capture of $^{36}$Ar
  from GERDA Phase I

abstract:
  Neutrinoless double electron capture is a process that, if detected, would
give evidence of lepton number violation and the Majorana nature of neutrinos.
A search for neutrinoless double electron capture of $^{36}$Ar has been
performed with germanium detectors installed in liquid argon using data from
Phase I of the GERmanium Detector Array (GERDA) experiment at the Gran Sasso
Laboratory of INFN, Italy. No signal was observed and an experimental lower
limit on the half-life of the radiative neutrinoless double electron capture of
$^{36}$Ar was established: $T_{1/2} > $ 3.6 $\times$ 10$^{21}$ yr at 90 % C.I.


title: Superconductivity in multiple phases of compressed GeSb2Te4

abstract:
  Here we report the discovery of superconductivity in multiple phases of the
compressed GeSb2Te4 (GST) phase change memory alloy, which has attracted
considerable attention for the last decade due to its unusual physical
properties with many potential applications. Superconductivity is observed
through electrical transport measurements, both for the amorphous (a-GST) and
for the crystalline (c-GST) phases. The superconducting critical temperature,
TC, continuously increases with the applied pressure reaching a maximum Tc =6K
at P=20 GPa for a-GST, whereas the critical temperature of the cubic phase
reaches a maximum Tc =8 K at 30 GPa. This new material system, exhibiting a
superconductor-insulator quantum phase transition (SIT) has an advantage over
disordered metals since it has a continuous control of the crystal structure
and the electronic properties using pressure as an external stimulus, which was
lacking in SIT studies until today.


title: Local symmetry in random graphs

abstract:
  Quite often real-world networks can be thought of as being symmetric, in the
abstract sense that vertices can be found to have similar or equivalent
structural roles. However, traditional measures of symmetry in graphs are based
on their automorphism groups, which do not account for the similarity of local
structures. We introduce the concept of local symmetry, which reflects the
structural equivalence of the vertices' egonets. We study the emergence of
asymmetry in the Erd\H{o}s-R\'enyi random graph model and identify regimes of
both asymptotic local symmetry and asymptotic local asymmetry. We find that
local symmetry persists at least to an average degree of $n^{1/3}$ and local
asymmetry emerges at an average degree not greater than $n^{1/2}$, which are
regimes of much larger average degree than for traditional, global asymmetry.


title: Rational curves on general type hypersurfaces

abstract:
  We develop a technique that allows us to prove results about subvarieties of
general type hypersurfaces. As an application, we use a result of Clemens and
Ran to prove that a very general hypersurface of degree (3n+1)/2 \leq d \leq
2n-3 contains lines but no other rational curves.


title: Adaptive Mesh Booleans

abstract:
  We present a new method for performing Boolean operations on volumes
represented as triangle meshes. In contrast to existing methods which treat
meshes as 3D polyhedra and try to partition the faces at their exact
intersection curves, we treat meshes as adaptive surfaces which can be
arbitrarily refined. Rather than depending on computing precise face
intersections, our approach refines the input meshes in the intersection
regions, then discards intersecting triangles and fills the resulting holes
with high-quality triangles. The original intersection curves are approximated
to a user-definable precision, and our method can identify and preserve creases
and sharp features. Advantages of our approach include the ability to trade
speed for accuracy, support for open meshes, and the ability to incorporate
tolerances to handle cases where large numbers of faces are slightly
inter-penetrating or near-coincident.


title: On the effect of self-steepening in modulation instability

abstract:
  We revisit the problem of modulation instability (MI) in optical fibers,
including higher-order dispersion terms, self-steepening, and Raman response.
We derive expressions for the MI gain and use them to explore the role of
self-steepening towards a high-power limit. We show that, contrary to common
wisdom, there is a pump power level that maximizes the MI gain. Further
increasing the power not only diminishes the gain, but eventually makes it
disappear. We believe these findings to be of special relevance, for instance,
when applied to the generation of supercontinuum in the mid and far infrared
bands. Finally, numerical simulations confirming our analytical results are
presented.


title: Torsion order of smooth projective surfaces

abstract:
  To a smooth projective variety $X$ whose Chow group of $0$-cycles is $\mathbf
Q$-universally trivial one can associate its torsion index $\mathrm{Tor}(X)$,
the smallest multiple of the diagonal appearing in a cycle-theoretic
decomposition \`a la Bloch-Srinivas. We show that $\mathrm{Tor}(X)$ is the
exponent of the torsion in the N\'eron-Severi-group of $X$ when $X$ is a
surface over an algebraically closed field $k$, up to a power of the
exponential characteristic of $k$.


title:
Two-dimensional quantum percolation with binary non-zero hopping
  integrals

abstract:
  In a previous work [Dillon and Nakanishi, Eur.Phys.J B 87, 286 (2014)], we
numerically calculated the transmission coefficient of the two-dimensional
quantum percolation problem and mapped out in detail the three regimes of
localization, i.e., exponentially localized, power-law localized, and
delocalized which had been proposed earlier [Islam and Nakanishi, Phys.Rev. E
77, 061109 (2008)]. We now consider a variation on quantum percolation in which
the hopping integral ($w$) associated with bonds that connect to at least one
diluted site is not zero, but rather a fraction of the hopping integral (V=1)
between non-diluted sites. We study the latter model by calculating quantities
such as the transmission coefficient and the inverse participation ratio and
find the original quantum percolation results to be stable for $w>0$ over a
wide range of energy. In particular, except in the immediate neighborhood of
the band center (where increasing $w$ to just $0.02*V$appears to eliminate
localization effects), increasing $w$ only shifts the boundaries between the 3
regimes but does not eliminate them until $w$ reaches 10%-40% of $V$.


title: Narrow band amplification of light carrying orbital angular momentum

abstract:
  We report on the amplification of an optical vortex beam carrying orbital
angular momentum via induced narrow Raman gain in an ensemble of cold cesium
atoms. A 20\% single-pass Raman gain of a weak vortex signal field is observed
with a spectral width of order of 1 MHz, much smaller than the natural width,
demonstrating that the amplification process preserves the phase structure of
the vortex beam. The gain is observed in the degenerated two-level system
associated with the hyperfine transition $6S_{1/2}(F=3)\leftrightarrow
6P_{3/2}(F^{\prime}=2)$ of cesium. Our experimental observations are explained
with a simple theoretical model based on a three-level $\Lambda$ system
interacting coherently with the weak Laguerre-Gauss field and a strong coupling
field, including an incoherent pumping rate between the two degenerate
ground-states.


title: Cosmicflows-3

abstract:
  The Cosmicflows database of galaxy distances that in the 2nd edition
contained 8,188 entries is now expanded to 17,669 entries. The major additions
are 2,257 distances that we have derived from the correlation between galaxy
rotation and luminosity with photometry at 3.6 microns obtained with Spitzer
Space Telescope and 8,885 distances based on the Fundamental Plane methodology
from the 6dFGS collaboration. There are minor augmentations to the Tip of the
Red Giant Branch and Type Ia supernova compilations. A zero point calibration
of the supernova luminosities give a value for the Hubble Constant of 76.2
+-3.4(r) +-2.7(s) km/s/Mpc. Alternatively, a restriction on the peculiar
velocity monopole term representing global infall/outflow implies H_0 = 75 +-2
km/s/Mpc.


title:
On free decompositions of verbally closed subgroups of free products of
  finite groups

abstract:
  For a subgroup of a free product of finite groups, we obtain necessary
conditions (on its Kurosh decomposition) to be verbally closed.


title:
The negligible photodesorption of methanol ice and the active
  photon-induced desorption of its irradiation products

abstract:
  Methanol is a common component of interstellar and circumstellar ice mantles
and is often used as an evolution indicator in star-forming regions. The
observations of gas-phase methanol in the interiors of dense molecular clouds
at temperatures as low as 10 K suggests that a non-thermal ice desorption must
be active. Ice photodesorption was proposed to explain the abundances of
gas-phase molecules toward the coldest regions. Laboratory experiments were
performed to investigate the potential photodesorption of methanol toward the
coldest regions. Solid methanol was deposited at 8 K and UV-irradiated at
various temperatures starting from 8 K. The irradiation of the ice was
monitored by means of infrared spectroscopy and the molecules in the gas phase
were detected using quadrupole mass spectroscopy. Fully deuterated methanol was
used for confirmation of the results. The photodesorption of methanol to the
gas phase was not observed in the mass spectra at different irradiation
temperatures. We estimate an upper limit of 3x10e-5 molecules per incident
photon. On the other hand, photon-induced desorption of the main photoproducts
was clearly observed. The negligible photodesorption of methanol could be
explained by the ability of UV-photons in the 114 - 180 nm (10.87 - 6.88 eV)
range to dissociate this molecule efficiently. Therefore, the presence of
gas-phase methanol in the absence of thermal desorption remains unexplained. On
the other hand, we find CH_4 to desorb from irradiated methanol ice, which was
not found to desorb in the pure CH_4 ice irradiation experiments.


title: Scarce defects induce anomalous deterministic diffusion

abstract:
  We introduce a simple model of deterministic particles in weakly disordered
media which exhibits a transition from normal to anomalous diffusion. The model
consists of a set of non-interacting overdamped particles moving on a
disordered potential. The disordered potential can be thought as a substrate
having some "defects" scattered along a one-dimensional line. The distance
between two contiguous defects is assumed to have a heavy-tailed distribution
with a given exponent $\alpha$, which means that the defects along the
substrate are scarce if $\alpha$ is small. We prove that this system exhibits a
transition from normal to anomalous diffusion when the distribution exponent
$\alpha$ decreases, i.e., when the defects become scarcer. Thus we identify
three distinct scenarios: a normal diffusive phase for $\alpha>2$, a
superdiffusive phase for $1/2<\alpha\leq 2$, and a subdiffusive phase for
$\alpha \leq 1/2$. We also prove that the particle current is finite for all
the values of $\alpha$, which means that the transport is normal independently
of the diffusion regime (normal, subdiffusive, or superdiffusive). We give
analytical expressions for the effective diffusion coefficient for the normal
diffusive phase and analytical expressions for the diffusion exponent in the
case of anomalous diffusion. We test all these predictions by means of
numerical simulations.


title: Access Control Synthesis for Physical Spaces

abstract:
  Access-control requirements for physical spaces, like office buildings and
airports, are best formulated from a global viewpoint in terms of system-wide
requirements. For example, "there is an authorized path to exit the building
from every room." In contrast, individual access-control components, such as
doors and turnstiles, can only enforce local policies, specifying when the
component may open. In practice, the gap between the system-wide, global
requirements and the many local policies is bridged manually, which is tedious,
error-prone, and scales poorly.
  We propose a framework to automatically synthesize local access control
policies from a set of global requirements for physical spaces. Our framework
consists of an expressive language to specify both global requirements and
physical spaces, and an algorithm for synthesizing local, attribute-based
policies from the global specification. We empirically demonstrate the
framework's effectiveness on three substantial case studies. The studies
demonstrate that access control synthesis is practical even for complex
physical spaces, such as airports, with many interrelated security
requirements.


title: Approximation properties for locally compact quantum groups

abstract:
  This is a survey of some aspects of the subject of approximation properties
for locally compact quantum groups, based on lectures given at the {\it
Topological Quantum Groups} Graduate School, 28 June - 11 July, 2015 in
Bed\l{}ewo, Poland. We begin with a study of the dual notions of amenability
and co-amenability, and then consider weakenings of these properties in the
form of the Haagerup property and weak amenability. For discrete quantum
groups, the interaction between these properties and various operator algebra
approximation properties are investigated. We also study the connection between
central approximation properties for discrete quantum groups and monoidal
equivalence for their compact duals. We finish by discussing the central weak
amenability and central Haagerup property for free quantum groups.


title:
Enhanced spin lifetimes in a two dimensional electron gas in a
  gate-controlled GaAs quantum well

abstract:
  Exciton, trion and electron spin dynamics in a 20 nm wide modulation-doped
GaAs single quantum well are investigated using resonant ultrafast two-color
Kerr rotation spectroscopy. Excitons and trions are selectively detected by
resonant probe pulses while their relative spectral weight is controlled by
adjusting the gate voltage which tunes the carrier density. Tuning the carrier
density markedly influences the spin decay time of the two dimensional electron
gas. The spin decay time can be enhanced by a factor of 3 at an intermediate
carrier concentration in the quantum well, where excitons and trions coexist in
the system. In addition, we explore the capability to tune the g-factor of the
electron gas via the carrier density.


title: Veech surfaces and simple closed curves

abstract:
  We study the SL(2,R)-infimal lengths of simple closed curves on
half-translation surfaces. Our main result is a characterization of Veech
surfaces in terms of these lengths. We also revisit the "no small virtual
triangles" theorem of Smillie and Weiss and establish the following dichotomy:
the virtual triangle area spectrum of a half-translation surface either has a
gap above zero or is dense in a neighborhood of zero. These results make use of
the auxiliary polygon associated to a curve on a half-translation surface, as
introduced by Tang and Webb.


title:
Photoevaporation and close encounters: how the environment around Cygnus
  OB2 affects the evolution of protoplanetary disks

abstract:
  In our Galaxy, star formation occurs in a variety of environments, with a
large fraction of stars formed in clusters hosting massive stars. OB stars have
an important feedback on the evolution of protoplanetary disks around nearby
young stars and likely on the process of planet formation occurring in them.
The nearby massive association Cygnus OB2 is an outstanding laboratory to study
this feedback. It is the closest massive association to our Sun, and hosts
hundreds of massive stars and thousands of low mass members. In this paper, we
analyze the spatial variation of the disk fraction in Cygnus OB2 and we study
its correlation with the local values of Far and Extreme ultraviolet radiation
fields and the local stellar surface density. We present definitive evidence
that disks are more rapidly dissipated in the regions of the association
characterized by intense local UV field and large stellar density. In
particular, the FUV radiation dominates disks dissipation timescales in the
proximity (i.e. within 0.5 pc) of the O stars. In the rest of the association,
EUV photons potentially induce a significant mass loss from the irradiated
disks across the entire association, but the efficiency of this process is
reduced at increasing distances from the massive stars due to absorption by the
intervening intracluster material. We find that disk dissipation due to close
stellar encounters is negligible in Cygnus OB2, and likely to have affected 1%
or fewer of the stellar population. Disk dissipation is instead dominated by
photoevaporation. We also compare our results to what has been found in other
young clusters with different massive populations, concluding that massive
associations like Cygnus OB2 are potentially hostile to protoplanetary disks,
but that the environments where disks can safely evolve in planetary systems
are likely quite common in our Galaxy.


title:
Review: Garbe, Annette. Die partiell konventional, partiell empirisch
  bestimmte Realit\"at physikalischer RaumZeiten. K\"onigshausen & Neumann:
  W\"urzburg 2001, pp. 419, ISBN: 978-3-8260-2080-3

abstract:
  In 2001 the book "Die partiell konventional, partiell empirisch bestimmte
Realit\"at physikalischer RaumZeiten" was published by K\"onigshausen &
Neumann, with a volume of more than 400 pages. It was written by Annette Garbe.
The English translation might be: "The Partial Conventionally, Partial
Empirically Determined Reality of Physical Space-Times." In the following
review it is argued that Garbe's approach comes very close to Michael
Friedman's contemporary defense of the relativized a priori. Whereas Friedman's
analysis of the role of conventional and constitutive principles in the theory
of relativity initiated much discussion in the literature, Garbe's defense of
"partial determination" has been ignored by the scientific community. This is
entirely unjust due to her highly original re-discovery of Ludwig Lange.


title: Adversarial Diversity and Hard Positive Generation

abstract:
  State-of-the-art deep neural networks suffer from a fundamental problem -
they misclassify adversarial examples formed by applying small perturbations to
inputs. In this paper, we present a new psychometric perceptual adversarial
similarity score (PASS) measure for quantifying adversarial images, introduce
the notion of hard positive generation, and use a diverse set of adversarial
perturbations - not just the closest ones - for data augmentation. We introduce
a novel hot/cold approach for adversarial example generation, which provides
multiple possible adversarial perturbations for every single image. The
perturbations generated by our novel approach often correspond to semantically
meaningful image structures, and allow greater flexibility to scale
perturbation-amplitudes, which yields an increased diversity of adversarial
images. We present adversarial images on several network topologies and
datasets, including LeNet on the MNIST dataset, and GoogLeNet and ResidualNet
on the ImageNet dataset. Finally, we demonstrate on LeNet and GoogLeNet that
fine-tuning with a diverse set of hard positives improves the robustness of
these networks compared to training with prior methods of generating
adversarial images.


title:
Non-Gaussian SLAP: Simultaneous Localization and Planning Under
  Non-Gaussian Uncertainty in Static and Dynamic Environments

abstract:
  Simultaneous Localization and Planning (SLAP) under process and measurement
uncertainties is a challenge. It involves solving a stochastic control problem
modeled as a Partially Observed Markov Decision Process (POMDP) in a general
framework. For a convex environment, we propose an optimization-based open-loop
optimal control problem coupled with receding horizon control strategy to plan
for high quality trajectories along which the uncertainty of the state
localization is reduced while the system reaches to a goal state with minimum
control effort. In a static environment with non-convex state constraints, the
optimization is modified by defining barrier functions to obtain collision-free
paths while maintaining the previous goals. By initializing the optimization
with trajectories in different homotopy classes and comparing the resultant
costs, we improve the quality of the solution in the presence of action and
measurement uncertainties. In dynamic environments with time-varying
constraints such as moving obstacles or banned areas, the approach is extended
to find collision-free trajectories. In this paper, the underlying spaces are
continuous, and beliefs are non-Gaussian. Without obstacles, the optimization
is a globally convex problem, while in the presence of obstacles it becomes
locally convex. We demonstrate the performance of the method on different
scenarios.


title: The equivariant Kazhdan-Lusztig polynomial of a matroid

abstract:
  We define the equivariant Kazhdan-Lusztig polynomial of a matroid equipped
with a group of symmetries, generalizing the nonequivariant case. We compute
this invariant for arbitrary uniform matroids and for braid matroids of small
rank.


title: Combinatorial Aspects of the Distribution of Rough Objects

abstract:
  The inverse problem of general rough sets, considered by the present author
in some of her earlier papers, in one of its manifestations is essentially the
question of when an agent's view about crisp and non crisp objects over a set
of objects has a rough evolution. In this research the nature of the problem is
examined from number-theoretic and combinatorial perspectives under very few
assumptions about the nature of data and some necessary conditions are proved.