title: Logarithmic speed-up of relaxation in A-B annihilation with exclusion

abstract:
  We show that the decay of the density of active particles in the reaction
$A+B \rightarrow 0$ in one dimension, with exclusion interaction, results in
logarithmic corrections to the expected power law decay, when the starting
initial condition (i.c.) is periodic. It is well-known that the late-time
density of surviving particles goes as $t^{-1/4}$ with random initial
conditions, and as $t^{-1/2}$ with alternating initial conditions
($ABABAB$...). We show that the decay for periodic i.c.s made of longer blocks
($A^{n}B^{n}A^{n}B^{n}$...) do not show a pure power-law decay when $n$ is
even. By means of first-passage Monte Carlo simulations, and a mapping to a
q-state coarsening model which can be solved in the Independent Interval
Approximation (IIA), we show that the late-time decay of the density of
surviving particles goes as $t^{-1/2}(\log{(t)})^{-1}$ for $n$ even, but as
$t^{-1/2}$ when $n$ is odd. We relate this kinetic symmetry breaking in the
Glauber Ising model. We also see a very slow crossover from a
$t^{-1/2}(\log{(t)})^{-1}$ regime to eventual $t^{-1/2}$ behaviour for i.c.s
made of mixtures of odd- and even-length blocks.


title: Robust Mean-Variance Hedging via G-Expectation

abstract:
  In this paper we study mean-variance hedging under the G-expectation
framework. Our analysis is carried out by exploiting the G-martingale
representation theorem and the related probabilistic tools, in a contin- uous
financial market with two assets, where the discounted risky one is modeled as
a symmetric G-martingale. By tackling progressively larger classes of
contingent claims, we are able to explicitly compute the optimal strategy under
general assumptions on the form of the contingent claim.


title: Power Beaming Leakage Radiation as a SETI Observable

abstract:
  The most observable leakage radiation from an advanced civilization may well
be from the use of power beaming to transfer energy and accelerate spacecraft.
Applications suggested for power beaming involve launching spacecraft to orbit,
raising satellites to a higher orbit, and interplanetary concepts involving
space-to-space transfers of cargo or passengers. We also quantify beam-driven
launch to the outer solar system, interstellar precursors and ultimately
starships. We estimate the principal observable parameters of power beaming
leakage. Extraterrestrial civilizations would know their power beams could be
observed, and so could put a message on the power beam and broadcast it for our
receipt at little additional energy or cost. By observing leakage from power
beams we may find a message embedded on the beam. Recent observations of the
anomalous star KIC8462852 by the Allen Telescope Array set some limits on
extraterrestrial power beaming in that system. We show that most power beaming
applications commensurate with those suggested for our solar system would be
detectable if using the frequency range monitored by the ATA, and so the lack
of detection is a meaningful, if modest, constraint on extraterrestrial power
beaming in that system. Until more extensive observations are made, the limited
observation time and frequency coverage are not sufficiently broad in frequency
and duration to produce firm conclusions. Such beams would be visible over
large interstellar distances. This implies a new approach to the SETI search:
Instead of focusing on narrowband beacon transmissions generated by another
civilization, look for more powerful beams with much wider bandwidth. This
requires a new approach for their discovery by telescopes on Earth. Further
studies of power beaming applications should be done, which could broaden the
parameter space of observable features we have discussed here.


title:
A Statistical Framework for Utilization of Simultaneous Pupil Plane and
  Focal Plane Telemetry for Exoplanet Imaging, Part II: The Science Camera
  Image as a Function of the Wavefront Sensor Field

abstract:
  In an effort to transcend the limitations of differential imaging of
exoplanets in the era of extremely large telescopes (ELTs), the first paper in
this series established a rigorous, fully polarimetric framework for
determining the science camera (SC) image given a turbulent wavefront and
unknown aberrations in multiple planes the optical system. This article builds
on the structure developed in Paper I in order to rigorously express the
polarimetric SC image in terms of the field impinging on the wavefront sensor
(WFS), thereby providing a direct connection between the measurements made in
both subsystems. This formulation allows the SC image to be written as a
function of the WFS measurements, including the following unknown quantities
which can, in principle, be estimated via statistical inference: the non-common
path aberration (NCPA), WFS gain errors, aberrations downstream of the
beamsplitter, and the planetary image. It is demonstrated that WFS bias error
is mathematically equivalent to NCPA. Thus, with the ability to treat WFS bias
and gains, the method should not be overly sensitive to WFS calibration
problems. Importantly, this formulation includes stochastic processes that
represent noisy measurement of the SC image, noisy WFS measurements, and
high-frequency components of the wavefront to which the WFS is insensitive. It
is shown that wavefront error due to noise in the WFS measurements has a
convenient semi-analytical representation in terms of the WFS measurement
operator's singular functions. Further, the first and second order statistics
of these processes are specified, thereby setting the stage for the application
of statistical inference methods to be describe in later papers in this series.


title: Metric methods for heteroclinic connections

abstract:
  We consider the problem $\min\int_{\mathbb{R}}
\frac{1}{2}|\dot{\gamma}|^2+W(\gamma)\mathop{}\mathopen{}\mathrm{d} t $ among
curves connecting two given wells of $W\geq 0$ and we reduce it, following a
standard method, to a geodesic problem of the form $\min\int_0^1
K(\gamma)|\dot{\gamma}|\mathop{}\mathopen{}\mathrm{d} t$ with $K=\sqrt{2W}$. We
then prove existence of curves minimizing this new action just by proving that
the distance induced by $K$ is proper (i.e. its closed balls are compact). The
assumptions on $W$ are minimal, and the method seems robust enough to be
applied in the future to some PDE problems.


title:
Selected List of Low Energy Beam Transport Facilities for Light-Ion,
  High-Intensity Accelerators

abstract:
  This paper presents a list of Low Energy Beam Transport (LEBT) facilities for
light-ion, high-intensity accelerators. It was put together to facilitate
comparisons with the PXIE LEBT design choices. A short discussion regarding the
importance of the beam perveance in the choice of the transport scheme follows.


title: Do co-jumps impact correlations in currency markets?

abstract:
  We quantify how co-jumps impact correlations in currency markets. To
disentangle the continuous part of quadratic covariation from co-jumps, and
study the influence of co-jumps on correlations, we propose a new wavelet-based
estimator. The proposed estimation framework is able to localize the co-jumps
very precisely through wavelet coefficients and identify statistically
significant co-jumps. Empirical findings reveal the different behaviors of
co-jumps during Asian, European and U.S. trading sessions. Importantly, we
document that co-jumps significantly influence correlation in currency markets.


title:
Simple formalism for efficient derivatives and multi-determinant
  expansions in quantum Monte Carlo

abstract:
  We present a simple and general formalism to compute efficiently the
derivatives of a multi-determinant Jastrow-Slater wave function, the local
energy, the interatomic forces, and similar quantities needed in quantum Monte
Carlo. Through a straightforward manipulation of matrices evaluated on the
occupied and virtual orbitals, we obtain an efficiency equivalent to
algorithmic differentiation in the computation of the interatomic forces and
the optimization of the orbital paramaters. Furthermore, for a large
multi-determinant expansion, the significant computational gain recently
reported for the calculation of the wave function is here improved and extended
to all local properties in both all-electron and pseudopotential calculations.


title:
Anderson polymer in a fractional Brownian environment: asymptotic
  behavior of the partition function

abstract:
  We consider the Anderson polymer partition function $$
u(t):=\mathbb{E}^X\Bigl[e^{\int_0^t \mathrm{d}B^{X(s)}_s}\Bigr]\,, $$ where
$\{B^{x}_t\,;\, t\geq0\}_{x\in\mathbb{Z}^d}$ is a family of independent
fractional Brownian motions all with Hurst parameter $H\in(0,1)$, and
$\{X(t)\}_{t\in \mathbb{R}^{\geq 0}}$ is a continuous-time simple symmetric
random walk on $\mathbb{Z}^d$ with jump rate $\kappa$ and started from the
origin. $\mathbb{E}^X$ is the expectation with respect to this random walk.
  We prove that when $H\leq 1/2$, the function $u(t)$ almost surely grows
asymptotically like $e^{l t}$, where $l>0$ is a deterministic number. More
precisely, we show that as $t$ approaches $+\infty$, the expression
$\{\frac{1}{t}\log u(t)\}_{t\in \mathbb{R}^{>0}}$ converges both almost surely
and in the $\mathcal{L}^1$ sense to some deterministic number $l>0$.
  For $H>1/2$, we first show that $\lim_{t\rightarrow \infty} \frac{1}{t}\log
u(t)$ exists both almost surely and in the $\mathcal{L}^1$ sense, and equals a
strictly positive deterministic number (possibly $+\infty$); hence almost
surely $u(t)$ grows asymptotically at least like $e^{a t}$ for some
deterministic constant $a>0$. On the other hand, we also show that almost
surely and in the $\mathcal{L}^1$ sense, $\limsup_{t\rightarrow \infty}
\frac{1}{t\sqrt{\log t}}\log u(t)$ is a deterministic finite real number
(possibly zero), hence proving that almost surely $u(t)$ grows asymptotically
at most like $e^{b t\sqrt{\log t}}$ for some deterministic positive constant
$b$.
  Finally, for $H>1/2$ when $\mathbb{Z}^d$ is replaced by a circle endowed with
a H\"older continuous covariance function, we show that $\limsup_{t\rightarrow
\infty} \frac{1}{t}\log u(t)$ is a finite deterministic positive number, hence
proving that almost surely $u(t)$ grows asymptotically at most like $e^{c t}$
for some deterministic positive constant $c$.


title: Anisotropic tensor calculus

abstract:
  We introduce the anisotropic tensor calculus, which is a way of handling with
tensors that depend on the direction remaining always in the same class. This
means that the derivative of an anisotropic tensor is a tensor of the same
type. As an application, we show how to define derivations using anisotropic
linear connections in a manifold. In particular, we show that the Chern
connection of a Finsler metric can be interpreted as the Levi-Civita connection
and we introduce the anisotropic curvature tensor. We also relate the concept
of anisotropic connection with the classical concept of linear connections in
the vertical bundle. Furthermore, we also introduce the concept of anisotropic
Lie derivative.


title: Time to move on?

abstract:
  Cosmology and particle physics have long been dominated by theoretical
paradigms: Einstein's general theory of relativity in cosmology and the
Standard Model of particle physics. The time may have come for paradigm shifts.
Does cosmological inflation require a modification of Einstein's gravity? Have
experiments at the LHC discovered a new particle beyond the Standard Model? It
is premature to answer these questions, but we theorists can dream about the
possibilities.


title:
Cluster automorphisms and the marked exchange graphs of
  skew-symmetrizable cluster algebras

abstract:
  Cluster automorphisms have been shown to have links to the mapping class
groups of surfaces, maximal green sequences and to exchange graph automorphisms
for skew-symmetric cluster algebras. In this paper we aim to generalise these
results to the skew-symmetrizable case by introducing a marking on the exchange
graph. Many skew-symmetrizable matrices unfold to skew-symmetric matrices and
we consider how cluster automorphisms behave under this unfolding with
applications to coverings of orbifolds by surfaces.


title:
One-loop renormalisation of the NMSSM in SloopS : 1. the
  neutralino-chargino and sfermion sectors

abstract:
  We have completed the one-loop renormalisation of the Next-to-Minimal
Supersymmetric Standard Model (NMSSM) allowing for and comparing between
different renormalisation schemes. A special attention is paid to on-shell
schemes. We study a variety of these schemes based on alternative choices of
the physical input parameters. In this paper we present our approach to the
renormalisation of the NMSSM and report on our results for the
neutralino-chargino and sfermion sectors. We will borrow some results from our
study of the Higgs sector whose full discussion is left for a separate
publication. We have implemented the set up for all the sectors of the NMSSM
within \sloops, a code for the automatic computation of one-loop corrections
initially developed for the standard model and the MSSM. Among the many
applications that allows the code, we present here the one-loop corrections to
neutralino masses and to partial widths of neutralinos and charginos into final
states with one gauge boson. One-loop electroweak and QCD corrections to the
partial widths of third generation sfermions into a fermion and a chargino or a
neutralino are also computed.


title: A Gr\"uss type operator inequality

abstract:
  In [P. Renaud, "A matrix formulation of Gr\"uss inequality", Linear Algebra
Appl. 335 (2001), 95--100] it was proved an operator inequality involving the
usual trace functional. In this article, we give a refinement of such result
and we answer positively the Renaud's open problem.


title:
Simulated Annealing Approach to the Temperature-Emissivity Separation
  Problem in Thermal Remote Sensing Part One: Mathematical Background

abstract:
  The method of simulated annealing is adapted to the temperature-emissivity
separation (TES) problem. A patch of surface at the bottom of the atmosphere is
assumed to be a greybody emitter with spectral emissivity $\epsilon(k)$
describable by a mixture of spectral endmembers. We prove that a simulated
annealing search conducted according to a suitable schedule converges to a
solution maximizing the $\textit{A-Posteriori}$ probability that spectral
radiance detected at the top of the atmosphere originates from a patch with
stipulated $T$ and $\epsilon(k)$. Any such solution will be nonunique. The
average of a large number of simulated annealing solutions, however, converges
almost surely to a unique Maximum A-Posteriori solution for $T$ and
$\epsilon(k)$. The limitation to a stipulated set of endmember emissivities may
be relaxed by allowing the number of endmembers to grow without bound, and to
be generic continuous functions of wavenumber with bounded first derivatives
with respect to wavenumber.


title:
Fluctuation analysis of high frequency electric power load in the Czech
  Republic

abstract:
  We analyze the electric power load in the Czech Republic (CR) which exhibits
a seasonality as well as other oscillations typical for European countries.
Moreover, we detect 1/f noise property of electrical power load with extra
additional peaks that allows to separate it into a deterministic and stochastic
part. We then focus on the analysis of the stochastic part using improved
Multi-fractal Detrended Fluctuation Analysis method (MFDFA) to investigate
power load datasets with a minute resolution. Extracting the noise part of the
signal by using Fourier transform allows us to apply this method to obtain the
fluctuation function and to estimate the generalized Hurst exponent together
with the correlated Hurst exponent, its improvement for the non-Gaussian
datasets. The results exhibit a strong presence of persistent behaviour and the
dataset is characterized by a non-Gaussian skewed distribution. There are also
indications for the presence of the probability distribution that has heavier
tail than the Gaussian distribution.


title:
Some notes on the Kodama state, maximal symmetry, and the isolated
  horizon boundary condition

abstract:
  We recall some well and some less known results about the Kodama state and
the related $\theta$ ambiguity in defining canonical variables. Based on them,
we make some comments highlighting that the Kodama state for real connection
variables can be given a precise meaning and that it implements a vacuum peaked
on a (in a suitable sense) maximally symmetric geometry. We also highlight the
similarity of this construction with the isolated horizon boundary condition $F
\propto \Sigma$ and stress that it is, in agreement with earlier work,
inadequate to define the notion of a quantum horizon.


title: An Arctangent Law

abstract:
  Let $M_r$ be the maximum value of an one-dimensional Brownian motion on the
(time) interval $[0, r]$. We derive an explicit formula for the distribution of
the time required (after $r$) for the Brownian motion to exceed $M_r$.


title:
Strong screening effects on resonant nuclear reaction $^{23}$Mg
  $(p,\gamma)$ $^{24}$Al in the surface of magnetars

abstract:
  Based on the theory of relativistic superstrong magnetic fields(SMFs), by
using the method of the Thomas-Fermi-Dirac approximations, we investigate the
problem of strong electron screening(SES) in SMFs, and the influence of SES on
the nuclear reaction of $^{23}$Mg $(p, \gamma)$$^{24}$Al. Our calculations show
that the nuclear reaction will be markedly effected by the SES in SMFs in the
surface of magnetars. Our calculated screening rates can increase two orders of
magnitude due to SES in SMFs.


title: de Sitter Spacetime as a Natural Superconductor

abstract:
  Motivated by the studies done on magnetically induced superconduc- tivity on
QCD vaccum we propose that de Sitter spacetime is a natural superconductor.
This is due to the occurrence of spinor condensation. We provide a framework
for joining the curvature of spacetime with super- conductor processes. We
demonstrate that for a critical value of de Sitter radius unstable tachyon
modes exist showing the existence of a supercon- ducting phase


title:
Magnetism, superconductivity, and spontaneous orbital order in
  iron-based superconductors: who comes first and why?

abstract:
  Magnetism and nematic order are the two non-superconducting orders observed
in iron-based superconductors. To elucidate the interplay between them and
ultimately unveil the pairing mechanism, several models have been investigated.
In models with quenched orbital degrees of freedom, magnetic fluctuations
promote stripe magnetism which induces orbital order. In models with quenched
spin degrees of freedom, charge fluctuations promote spontaneous orbital order
which induces stripe magnetism. Here we develop an unbiased approach, in which
we treat magnetic and orbital fluctuations on equal footing. Key to our
approach is the inclusion of the orbital character of the low-energy electronic
states into renormalization group analysis. Our results show that in systems
with large Fermi energies, such as BaFe2As2, LaFeAsO, and NaFeAs, orbital order
is induced by stripe magnetism. However, in systems with small Fermi energies,
such as FeSe, the system develops a spontaneous orbital order, while magnetic
order does not develop. Our results provide a unifying description of different
iron-based materials.


title: Reflectors and globalizations of partial actions of groups

abstract:
  Given a partial action $\theta$ of a group on a set with an algebraic
structure, we construct a reflector of $\theta$ in the corresponding
subcategory of global actions and study the question when this reflector is a
globalization. In particular, if $\theta$ is a partial action on an algebra
from a variety ${\sf V}$, then we show that the problem reduces to the
embeddability of certain generalized amalgam of ${\sf V}$-algebras associated
with $\theta$. As an application, we describe globalizable partial actions on
semigroups, whose domains are ideals.


title:
White Holes as the Asymptotic Limit of Evaporating Primordial Black
  Holes

abstract:
  This paper examines the interaction of an intense fermion field with all of
the particle species of an attometer primordial black hole's (PBH)'s high
energy Hawking radiation spectrum. By extrapolating to Planck-sized PBH's, it
is shown that, although Planck-sized PBH's closely simulate the zero absorption
requirement of white holes, the absorption probability is not truly zero, and
therefore, thermodynamically, Planck-sized PBH's are not true white holes.


title:
Stationarity breaking in coupled physical systems revealed by recurrence
  analysis

abstract:
  In this letter we explore how recurrence quantifier, the determinism
($\Delta$), can reveal stationarity breaking and coupling between physical
systems. We demonstrate that it is possible to detect small variations in a
dynamical system based only on temporal signal displayed by another system
coupled to it. To introduce basic ideas, we consider a well known dynamical
system composed of two master-slave coupled Lorenz oscillators. We start
evidencing that due to the sensitivity of $\Delta$ computed from temporal time
series of slave oscillator, its is possible to detect the stationary breaking
imposed in the master oscillator. As a second example, the method is carried
out in a real physiological data acquired from accelerometer sensors
($\mathrm{A_{cc}}$) and used to detect micro arousal phenomenology (described
by a sharp burst in $\mathrm{A_{cc}}$ signal) during sleep periods in mice.
Moreover, we show for the first time that making use of recurrence quantifier
it is possible to infer a coupling between electric signals from hippocampus
and "locomotor brain areas" of mice, based only on non invasive data from
$\mathrm{A_{cc}}$. Our results suggest new possibilities of analysis of coupled
systems making use of accessible time series. Our second example supports an
interpretation of an internal coupling detectable as a stationarity breaking in
$\mathrm{A_{cc}}$ that occurs some seconds before micro arousal processes
during sleep periods in rodents, contributing to the idea that micro arousals
are elements of sleep taking part in the regulation of sleep process. Such a
characterization of micro arousals can improve our knowledge about sleep
fostering tools of sleep diagnose and pharmacology research for mammals in
general.


title: Cybernetic Interpretation of the Riemann Zeta Function

abstract:
  This paper uses cybernetic approach to study behavior of the Riemann zeta
function. It is based on the elementary cybernetic concepts like feedback,
transfer functions, time delays, PI (Proportional--Integral) controllers or
FOPDT (First Order Plus Dead Time) models, respectively. An unusual dynamic
interpretation of the Riemann zeta function is obtained.


title:
Subatomic mechanism of the oscillatory magnetoresistance in
  superconductors

abstract:
  In the recent experiments the unusual oscillatory magnetoresistance in
superconductors was discovered with a periodicity essentially independent on
magnetic field direction and even material parameters. The nearly universal
period points to a subatomic mechanism of the phenomenon. This mechanism is
related to formation inside samples of subatomically thin ($10^{-11}cm$)
threads in the form of rings of the interatomic radius. Electron states of
rings go over into conduction electrons which carry the same spin imbalance in
energy as rings. The imbalance occurs due to spin interaction with the orbital
momentum of the ring. The conductivity near $T_c$ is determined by fluctuating
Cooper pairs consisting of electrons with shifted energies. Due to different
angular momenta of rings these energies periodically depend on magnetic field
resulting in the observed oscillatory magnetoresistance. Calculated universal
positions of peaks $(n+1/2)\Delta H$ ($\Delta H\simeq 0.18T$ and $n=0,1,2...$)
on the $R(H)$ curve are in a good agreement with experiments.


title:
PAMELA's measurements of geomagnetic cutoff variations during the 14
  December 2006 storm

abstract:
  Data from the Payload for Antimatter Matter Exploration and Light-nuclei
Astrophysics (PAMELA) satellite experiment were used to measure the geomagnetic
cutoff for high-energy (>80 MeV) protons during the 14 December 2006
geomagnetic storm. The variations of the cutoff latitude as a function of
rigidity were studied on relatively short timescales, corresponding to
spacecraft orbital periods (94 min). Estimated cutoff values were compared with
those obtained by means of a trajectory tracing approach based on a dynamical
empirical modeling of the Earth's magnetosphere. We found significant
variations in the cutoff latitude, with a maximum suppression of about 7 deg at
lowest rigidities during the main phase of the storm. The observed reduction in
the geomagnetic shielding and its temporal evolution were related to the
changes in the magnetospheric configuration, investigating the role of
interplanetary magnetic field, solar wind and geomagnetic parameters. PAMELA's
results represent the first direct measurement of geomagnetic cutoffs for
protons with kinetic energies in the sub-GeV and GeV region.


title:
HeSP: a simulation framework for solving the task
  scheduling-partitioning problem on heterogeneous architectures

abstract:
  In this paper we describe HeSP, a complete simulation framework to study a
general task scheduling-partitioning problem on heterogeneous architectures,
which treats recursive task partitioning and scheduling decisions on equal
footing. Considering recursive partitioning as an additional degree of freedom,
tasks can be dynamically partitioned or merged at runtime for each available
processor type, exposing additional or reduced degrees of parallelism as
needed. Our simulations reveal that, for a specific class of dense linear
algebra algorithms taken as a driving example, simultaneous decisions on task
scheduling and partitioning yield significant performance gains on two
different heterogeneous platforms: a highly heterogeneous CPU-GPU system and a
low-power asymmetric big.LITTLE ARM platform. The insights extracted from the
framework can be further applied to actual runtime task schedulers in order to
improve performance on current or future architectures and for different
task-parallel codes.


title: Multihead Multitrack Detection with Reduced-State Sequence Estimation

abstract:
  To achieve ultra-high storage capacity, the data tracks are squeezed more and
more on the magnetic recording disks, causing severe intertrack interference
(ITI). The multihead multitrack (MHMT) detector is proposed to better combat
ITI. Such a detector, however, has prohibitive implementation complexity. In
this paper we propose to use the reduced-state sequence estimation (RSSE)
algorithm to significantly reduce the complexity, and render MHMT practical. We
first consider a commonly used symmetric two-head two-track (2H2T) channel
model. The effective distance between two input symbols is redefined. It
provides a better distance measure and naturally leads to an unbalanced set
partition tree. Different trellis configurations are obtained based on the
desired performance/complexity tradeoff. Simulation results show that the
reduced MHMT detector can achieve near maximum-likelihood (ML) performance with
a small fraction of the original number of trellis states. Error event analysis
is given to explain the behavior of RSSE algorithm on 2H2T channel. Search
results of dominant RSSE error events for different channel targets are
presented. We also study an asymmetric 2H2T system. The simulation results and
error event analysis show that RSSE is applicable to the asymmetric channel.


title: An Infinite Family of Links with Critical Bridge Spheres

abstract:
  A closed, orientable, splitting surface in an oriented $3$-manifold is a
topologically minimal surface of index $n$ if its associated disk complex is
$(n-2)$-connected but not $(n-1)$-connected. A critical surface is a
topologically minimal surface of index $2$. In this paper, we use an equivalent
combinatorial definition of critical surfaces to construct the first known
critical bridge spheres for nontrivial links.


title:
Multihead Multitrack Detection with ITI Estimation in Next Generation
  Magnetic Recording System

abstract:
  Multitrack detection with array-head reading is a promising technique
proposed for next generation magnetic storage systems. The multihead multitrack
(MHMT) system is characterized by intersymbol interference (ISI) in the
downtrack direction and intertrack interference (ITI) in the crosstrack
direction. Constructing the trellis of a MHMT maximum likelihood (ML) detector
requires knowledge of the ITI, which is generally unknown at the receiver. In
addition, to retain efficiency, the ML detector requires a static estimate of
the ITI, whose true value may in reality vary. In this paper we propose a
modified ML detector on the $n$-head, $n$-track ($n$H$n$T) channel which could
efficiently track the change of ITI, and adapt to new estimates. The trellis
used in the proposed detector is shown to be independent of the ITI level. A
gain loop structure is used to estimate the ITI. Simulation results show that
the proposed detector offers a performance advantage in settings where
complexity constraints limit the traditional ML detector to use a static ITI
estimate.


title: Bilinear quark operator renormalization at generalized symmetric point

abstract:
  We compute Green's functions with a bilinear quark operator inserted at
non-zero momentum for a generalized momentum configuration to two loops. These
are required to assist lattice gauge theory measurements of the same quantity
in matching to the high energy behaviour. The flavour non-singlet operators
considered are the scalar, vector and tensor currents as well as the second
moment of the twist-2 Wilson operator used in deep inelastic scattering for the
measurement of nucleon structure functions.


title:
Endomorphisms of Cuboidal Hamming Graphs, Latin Hypercuboids of Class
  $r$, and Mixed MDS Codes

abstract:
  In this paper we investigate the existence of singular endomorphisms of the
cuboidal Hamming graph $H(n_1,...,n_d,S)$ over the set $\left[ n_1\right]\times
\left[ n_2\right]\times \cdots \times \left[ n_d\right]$, where $\left[
n\right]=\{1,...,n\}$, which is a generalisation of the well-known (cubic)
Hamming graph over $\left[ n\right]^{d}$. Two vertices in $H$ are adjacent, if
their Hamming distance lies in the set $S$. In this paper $S=\{1,...,r\}$, for
some integer $1\leq r\leq d-1$, and we first show that the singular
endomorphisms of minimal rank ( which is the size of their image) of
$H(n,...,n,S)$ correspond to Latin hypercubes of class $r$ (those were
originally defined by Kishen (1950)). Then we generalise those hypercubes to
Latin hypercuboids of class $r$. We discuss the existence of these objects,
provide constructions and count Latin hypercuboids for small parameters. In the
last part, we extend the natural connection between Latin hypercubes of class
$r$ and MDS codes to Latin hypercuboids of class $r$ leading to the definition
of MDS codes for mixed codes (mixed MDS codes), that is for codes over
hypercuboids. Here, we demonstrate the interdependence between graph
endomorphisms, Latin hypercuboids and mixed MDS codes.


title:
Overview of the software architecture and data flow for the J-PET
  tomography device

abstract:
  Modern TOF-PET scanner systems require high-speed computing resources for
efficient data processing, monitoring and image reconstruction. In this article
we present the data flow and software architecture for the novel TOF-PET
scanner developed by the J-PET collaboration. We discuss the data acquisition
system, reconstruction framework and image reconstruction software. Also, the
concept of computing outside hospitals in the remote centers such as \'Swierk
Computing Centre in Poland is presented.


title:
Scaling laws in earthquake occurrence: Disorder, viscosity, and finite
  size effects in Olami-Feder-Christensen models

abstract:
  The relation between seismic moment and fractured area is crucial to
earthquake hazard analysis. Experimental catalogs show multiple scaling
behaviors, with some controversy concerning the exponent value in the large
earthquake regime. Here, we show that the original Olami, Feder, and
Christensen model does not capture experimental findings. Taking into account
heterogeneous friction, the visco elastic nature of faults together with
finite-size effects, we are able to reproduce the different scaling regimes of
field observations. We provide an explanation for the origin of the two
crossovers between scaling regimes, which are shown to be controlled both by
the geometry and the bulk dynamics.


title:
Atomically flat reconstructed rutile TiO2(001) surfaces for oxide film
  growth

abstract:
  The availability of low-index rutile TiO2 single crystal substrates with
atomically flat surfaces is essential for enabling epitaxial growth of rutile
transition metal oxide films. The high surface energy of the rutile (001)
surface often leads to surface faceting, which precludes the sputter and
annealing treatment commonly used for the preparation of clean and atomically
flat TiO2(110) substrate surfaces. In this work, we reveal that stable and
atomically flat rutile TiO2(001) surfaces can be prepared with an atomically
ordered reconstructed surface already during a furnace annealing treatment in
air. We tentatively ascribe this result to the decrease in surface energy
associated with the surface reconstruction, which removes the driving force for
faceting. Despite the narrow temperature window where this morphology can
initially be formed, we demonstrate that it persists in homoepitaxial growth of
TiO2(001) thin films. The stabilization of surface reconstructions that prevent
faceting of high-surface-energy crystal faces may offer a promising avenue
towards the realization of a wider range of high quality epitaxial transition
metal oxide heterostructures.


title: Crafting zero-bias one-way transport of charge and spin

abstract:
  We explore the electronic structure and transport properties of a metal on
top of a (weakly coupled) two-dimensional topological insulator. Unlike the
widely studied junctions between topological non-trivial materials, the systems
studied here allow for a unique bandstructure and transport steering. First,
states on the topological insulator layer may coexist with the gapless bulk
and, second, the edge states on one edge can be selectively switched-off,
thereby leading to nearly perfect directional transport of charge and spin even
in the zero bias limit. We illustrate these phenomena for Bernal stacked
bilayer graphene with Haldane or intrinsic spin-orbit terms and a perpendicular
bias voltage. This opens a path for realizing directed transport in materials
such as van der Waals heterostructures, monolayer and ultrathin topological
insulators.


title: Optimal Currents on Arbitrarily Shaped Surfaces

abstract:
  An optimization problem has been formulated to find a resonant current
extremizing various antenna parameters. The method is presented on, but not
limited to, particular cases of gain $G$, quality factor $Q$, gain to quality
factor ratio $G/Q$, and radiation efficiency $\eta$ of canonical shapes with
conduction losses explicitly included. The Rao-Wilton-Glisson basis
representation is used to simplify the underlying algebra while still allowing
surface current regions of arbitrary shape to be treated. By switching to
another basis generated by a specific eigenvalue problem, it is finally shown
that the optimal current can, in principle, be found as a combination of a few
eigenmodes. The presented method constitutes a general framework in which the
antenna parameters, expressed as bilinear forms, can automatically be
extremized.


title:
Joint Transmit and Receive Beamforming for Multi-Relay MIMO-OFDMA
  Cellular Networks

abstract:
  A novel transmission protocol is conceived for a multi-user, multi-relay,
multiple-input--multiple-output orthogonal frequency-division multiple-access
(MIMO-OFDMA) cellular network based on joint transmit and receive beamforming.
More specifically, the network's MIMO channels are mathematically decomposed
into several effective multiple-input--single-output (MISO) channels, which are
spatially multiplexed for transmission. For the sake of improving the
attainable capacity, these MISO channels are grouped using a pair of novel
grouping algorithms, which are then evaluated in terms of their performance
versus complexity trade-off\footnote{This paper concisely focuses on the
transmission protocol proposed in our previous work [1]. For more details,
please refer to [1].}.


title:
Central limit theorems for functionals of large sample covariance matrix
  and mean vector in matrix-variate location mixture of normal distributions

abstract:
  In this paper we consider the asymptotic distributions of functionals of the
sample covariance matrix and the sample mean vector obtained under the
assumption that the matrix of observations has a matrix-variate location
mixture of normal distributions. The central limit theorem is derived for the
product of the sample covariance matrix and the sample mean vector. Moreover,
we consider the product of the inverse sample covariance matrix and the mean
vector for which the central limit theorem is established as well. All results
are obtained under the large-dimensional asymptotic regime where the dimension
$p$ and the sample size $n$ approach to infinity such that $p/n\to c\in[0 ,
+\infty)$ when the sample covariance matrix does not need to be invertible and
$p/n\to c\in [0, 1)$ otherwise.


title: Eigen-Epistasis for detecting Gene-Gene interactions

abstract:
  A large amount of research has been devoted to the detection and
investigation of epistatic interactions in genome-wide association studies
(GWASs). Most of the literature focuses on low-order interactions between
single-nucleotide polymorphisms (SNPs) with significant main effects.In this
paper we propose an original approach for detecting epistasis at the gene
level, without systematically filtering on significant genes. We first compute
interaction variables for each gene pair by finding its Eigen-Epistasis
component, defined as the linear combination of Gene SNPs having the highest
correlation with the phenotype. The selection of significant effects is done
using a penalized regression method based on Group Lasso controlling the False
Discovery Rate.The method is tested against two recent alternative proposals
from the literature using synthetic data, and shows good performances in
different settings. We demonstrate the power of our approach by detecting new
gene-gene interactions on three genome-wide association studies.


title:
Combined effects in nonlinear problems arising in the study of
  anisotropic continuous media

abstract:
  The paper deals with the study of a Lane-Emden-Fowler equation with Dirichlet
boundary condition and variable potential functions. The analysis developed in
this paper combines monotonicity methods with variational arguments. Remark
(April 21, 2020): Our results were later studied also by D.-P. Covei,
Quasilinear problems with the competition between convex and concave
nonlinearities and variable potentials, Internat. J. Math. 24:1 (2013), art.
1350005), arXiv:1104.4626v1.


title: Novel quark smearing for hadrons with high momenta in lattice QCD

abstract:
  Hadrons in lattice QCD are usually created employing smeared interpolators.
We introduce a new quark smearing that allows us to maintain small statistical
errors and good overlaps of hadronic wavefunctions with the respective ground
states, also at high spatial momenta. The method is successfully tested for the
pion and the nucleon at a pion mass $m_{\pi}\approx 295$ MeV and momenta as
high as 2.8 GeV. We compare the results obtained to dispersion relations and
suggest further optimizations.


title: A High-Quality Speech and Audio Codec With Less Than 10 ms Delay

abstract:
  With increasing quality requirements for multimedia communications, audio
codecs must maintain both high quality and low delay. Typically, audio codecs
offer either low delay or high quality, but rarely both. We propose a codec
that simultaneously addresses both these requirements, with a delay of only 8.7
ms at 44.1 kHz. It uses gain-shape algebraic vector quantisation in the
frequency domain with time-domain pitch prediction. We demonstrate that the
proposed codec operating at 48 kbit/s and 64 kbit/s out-performs both G.722.1C
and MP3 and has quality comparable to AAC-LD, despite having less than one
fourth of the algorithmic delay of these codecs.


title:
Persistent Asymmetric Structure of Sagittarius A* on Event Horizon
  Scales

abstract:
  The Galactic Center black hole Sagittarius A* (Sgr A*) is a prime observing
target for the Event Horizon Telescope (EHT), which can resolve the 1.3 mm
emission from this source on angular scales comparable to that of the general
relativistic shadow. Previous EHT observations have used visibility amplitudes
to infer the morphology of the millimeter-wavelength emission. Potentially much
richer source information is contained in the phases. We report on 1.3 mm phase
information on Sgr A* obtained with the EHT on a total of 13 observing nights
over 4 years. Closure phases, the sum of visibility phases along a closed
triangle of interferometer baselines, are used because they are robust against
phase corruptions introduced by instrumentation and the rapidly variable
atmosphere. The median closure phase on a triangle including telescopes in
California, Hawaii, and Arizona is nonzero. This result conclusively
demonstrates that the millimeter emission is asymmetric on scales of a few
Schwarzschild radii and can be used to break 180-degree rotational ambiguities
inherent from amplitude data alone. The stability of the sign of the closure
phase over most observing nights indicates persistent asymmetry in the image of
Sgr A* that is not obscured by refraction due to interstellar electrons along
the line of sight.


title: Persistent search in confined domains: a velocity-jump process model

abstract:
  We analyze velocity-jump process models of persistent search for a single
target on a bounded domain. The searcher proceeds along ballistic trajectories
and is absorbed upon collision with the target boundary. When reaching the
domain boundary, the searcher chooses a random direction for its new
trajectory. For circular domains and targets, we can approximate the mean first
passage time (MFPT) using a Markov chain approximation of the search process.
Our analysis and numerical simulations reveal that the time to find the target
decreases for targets closer to the domain boundary. When there is a small
probability of direction-switching within the domain, we find the time to find
the target decreases slightly with the turning probability. We also extend our
exit time analysis to the case of partitioned domains, where there is a single
target within one of multiple disjoint subdomains. Given an average time of
transition between domains $\langle T \rangle$, we find that the optimal rate
of transition that minimizes the time to find the target obeys $\beta_{{\rm
min}} \propto 1/ \sqrt{\langle T \rangle}$.


title:
Modeling the afterglow of the possible Fermi-GBM event associated with
  GW150914

abstract:
  We model the possible afterglow of the Fermi GBM event associated with LIGO
detection GW150914, under the assumption that the gamma-ray are produced by a
short GRB-like relativistic outflow. We model GW150914-GBM as both a weak,
on-axis short GRB and normal short GRB seen far off axis. Given the large
uncertainty in the position of GW150914, we determine that the best chance of
finding the afterglow is with ASKAP or possibly the MWA, with the flux from an
off-axis short GRB reaching 0.2 - 4 mJy (0.12 - 16 mJy) at 150 MHz (863.5 MHz)
by 1 - 12 months after the initial event. At low frequencies, the source would
evolve from a hard to soft spectrum over several months. The radio afterglow
would be detectable for several months to years after it peaks, meaning the
afterglow may still be detectable and increasing in brightness NOW (mid-July
2016). With a localization from the MWA or ASKAP, the afterglow would be
detectable at higher radio frequencies with the ATCA and in X-rays with Chandra
or XMM.


title:
Extreme robustness of scaling in sample space reducing processes
  explains Zipf's law in diffusion on directed networks

abstract:
  It has been shown recently that a specific class of path-dependent stochastic
processes, which reduce their sample space as they unfold, lead to exact
scaling laws in frequency and rank distributions. Such Sample Space Reducing
processes (SSRP) offer an alternative new mechanism to understand the emergence
of scaling in countless processes. The corresponding power law exponents were
shown to be related to noise levels in the process. Here we show that the
emergence of scaling is not limited to the simplest SSRPs, but holds for a huge
domain of stochastic processes that are characterized by non-uniform prior
distributions. We demonstrate mathematically that in the absence of noise the
scaling exponents converge to $-1$ (Zipf's law) for almost all prior
distributions. As a consequence it becomes possible to fully understand
targeted diffusion on weighted directed networks and its associated scaling
laws law in node visit distributions. The presence of cycles can be properly
interpreted as playing the same role as noise in SSRPs and, accordingly,
determine the scaling exponents. The result that Zipf's law emerges as a
generic feature of diffusion on networks, regardless of its details, and that
the exponent of visiting times is related to the amount of cycles in a network
could be relevant for a series of applications in traffic-, transport- and
supply chain management.


title: On the Use of Deep Learning for Blind Image Quality Assessment

abstract:
  In this work we investigate the use of deep learning for distortion-generic
blind image quality assessment. We report on different design choices, ranging
from the use of features extracted from pre-trained Convolutional Neural
Networks (CNNs) as a generic image description, to the use of features
extracted from a CNN fine-tuned for the image quality task. Our best proposal,
named DeepBIQ, estimates the image quality by average pooling the scores
predicted on multiple sub-regions of the original image. The score of each
sub-region is computed using a Support Vector Regression (SVR) machine taking
as input features extracted using a CNN fine-tuned for category-based image
quality assessment. Experimental results on the LIVE In the Wild Image Quality
Challenge Database and on the LIVE Image Quality Assessment Database show that
DeepBIQ outperforms the state-of-the-art methods compared, having a Linear
Correlation Coefficient (LCC) with human subjective scores of almost 0.91 and
0.98 respectively. Furthermore, in most of the cases, the quality score
predictions of DeepBIQ are closer to the average observer than those of a
generic human observer.


title:
Light cone dynamics in excitonic states of two-component Bose and Fermi
  gases

abstract:
  We consider the non-equilibrium dynamics of two-component one dimensional
quantum gases in the limit of extreme population imbalance where the minority
species has but a single particle. We consider the situation where the gas is
prepared in a state with a single spatially localized exciton: the single
particle of the minority species is spatially localized while the density of
the majority species in the vicinity of the minority particle sees a
depression. Remarkably, we are able to consider cases where the gas contains on
the order of $N=100$ particles, comparable to that studied in experiments on
cold atomic gases. We are able to do by exploiting the integrability of the gas
together with the observation that the excitonic state can be constructed
through a simple superposition of exact eigenstates of the gas. The number of
states in this superposition, rather than being exponentially large in the
number of particles, scales linearly with $N$.
  We study the evolution of such spatially localized states in both strongly
interacting Bose and Fermi gases. The behavior of the light cones when the
interaction strength and density of the gas is varied can be understood from
exact results for the spin excitation spectrum in these systems. We argue that
the light cone in both cases exhibits scaling collapse. However unique to the
Bose gas, we show that the presence of gapped finite-momentum roton-like
excitations provide the Bose gas dynamics with secondary light cones.


title:
Heart and diamond Fermi arcs in Pd and Pt oxide topological Dirac
  semimetals

abstract:
  Topological Dirac semimetals (DSMs) exhibit nodal points through which energy
bands disperse linearly in three-dimensional (3D) momentum space, a 3D analogue
of graphene. The first experimentally confirmed DSMs with a pair of Dirac
points (DPs), Na$_{3}$Bi and Cd$_{3}$As$_{2}$, show topological surface Fermi
arc states and exotic magneto-transport properties, boosting the interest in
the search for stable and nontoxic DSM materials. Here, based on the {\it
ab-initio} band structure calculations we predict a family of palladium and
platinum oxides as robust 3D DSMs. The novel topological properties of these
compounds are distinct from all other previously reported DSMs, they are
rendered by the multiple number of DPs in the compounds. We show that along
three unit axes of the cubic lattice there exist three pairs of DPs, which are
linked by Fermi arcs on the surface. The Fermi arcs display a Lifshitz
transition from a heart- to a diamond-shape upon varying the chemical
potential. Corresponding oxides are already available as high-quality single
crystals, which is an excellent precondition for the verification of our
prediction by photoemission and magneto-transport experiments. Our findings not
only predict a number of much robust 3D DSM candidates but also extend DSMs to
transition metal oxides, a versatile family of materials, which opens the door
to investigate the interplay between DSMs and electronic correlations that is
not possible in the previously discovered DSM materials.


title:
A hyper-K\"ahler compactification of the Intermediate Jacobian fibration
  associated to a cubic fourfold

abstract:
  For a general cubic fourfold, it was observed by Donagi and Markman that the
relative intermediate Jacobian fibration associated to the family of its
hyperplane sections carries a natural holomorphic symplectic form making the
fibration Lagrangian. In this paper, we obtain a smooth projective
compactification of the intermediate Jacobian fibration giving a
ten-dimensional compact hyper-K\"ahler manifold, which we then show to be
deformation equivalent to the exceptional example of O'Grady. This proves a
conjecture by Markushevich.


title: Doppelg\"angers: Bijections of Plane Partitions

abstract:
  We say two posets are "doppelg\"angers" if they have the same number of
$P$-partitions of each height $k$. We give a uniform framework for bijective
proofs that posets are doppelg\"angers by synthesizing $K$-theoretic Schubert
calculus techniques of H. Thomas and A. Yong with M. Haiman's rectification
bijection and an observation of R. Proctor. Geometrically, these bijections
reflect the rational equivalence of certain subvarieties of minuscule flag
manifolds. As a special case, we provide the first bijective proof of a 1983
theorem of R. Proctor---that plane partitions of height $k$ in a rectangle are
equinumerous with plane partitions of height $k$ in a trapezoid.


title:
Backhaul Traffic Balancing and Dynamic Content-Centric Clustering for
  the Downlink of Fog Radio Access Network

abstract:
  Recently, an evolution of the Cloud Radio Access Network (C-RAN) has been
proposed, named as Fog Radio Access Network (F-RAN). Compared to C-RAN, the
Radio Units (RUs) in F-CAN are equipped with local caches, which can store some
frequently requested files. In the downlink, users requesting the same file
form a multicast group, and are cooperatively served by a cluster of RUs. The
requested file is either available locally in the cache of this cluster or
fetched from the Central Processor (CP) via backhauls. Thus caching some
frequently requested files can greatly reduce the burden on backhaul links.
Whether a specific RU should be involved in a cluster to serve a multicast
group depends on its backhaul capacity, requested files, cached files and the
channel. Therefore it is subject to optimization. In this paper we investigate
the joint design of multicast beamforming, dynamic clustering and backhaul
traffic balancing. Beamforming and clustering are jointly optimized in order to
minimize the power consumed, while QoS of each user is to be met and the
traffic on each backhaul link is balanced according to its capacity.


title:
Whither probabilistic security management for real-time operation of
  power systems ?

abstract:
  This paper investigates the stakes of introducing probabilistic approaches
for the management of power system's security. In real-time operation, the aim
is to arbitrate in a rational way between preventive and corrective control,
while taking into account i) the prior probabilities of contingencies, ii) the
possible failure modes of corrective control actions, iii) the socio-economic
consequences of service interruptions. This work is a first step towards the
construction of a globally coherent decision making framework for security
management from long-term system expansion, via mid-term asset management,
towards short-term operation planning and real-time operation.


title: Capillary levelling of free-standing liquid nanofilms

abstract:
  We report on the capillary-driven levelling of a topographical perturbation
at the surface of a free-standing liquid nanofilm. The width of a stepped
surface profile is found to evolve as the square root of time. The hydrodynamic
model is in excellent agreement with the experimental data. In addition to
exhibiting an analogy with diffusive processes, this novel system serves as a
precise nanoprobe for the rheology of liquids at interfaces in a configuration
that avoids substrate effects.

categories: cond-mat.soft cond-mat.mes-hall cond-mat.mtrl-sci physics.chem-ph physics.flu-dyn


title: The Fourth Generation Quark and the 750 GeV Diphoton Excess

abstract:
  Recently, the CMS and ATLAS collaborations have reported a diphoton peak at
750 GeV in the RunII of LHC at 13 TeV. We assume that the heavy fourth
generation quark doublet $z,~y$ with $380 $GeV mass, and the width of $z,t$ is
much less $b$ quark. Then we show that the contributions of the $(z \bar z+y
\bar y)/\sqrt{2}$ bound state $\eta_{zy}(1S)$ to the diphoton measurements
through $\sigma (pp\to \eta_{zy}(1s)\to \gamma \gamma) $ are $
5.6^{+5.6}_{-2.8} {\rm fb}$ at $\sqrt S=13$ TeV. They are constant with the 750
GeV diphoton excess measured by the CMS ant ATLAS collaborations.


title:
Robust Covariance Estimation under Imperfect Constraints using an
  Expected Likelihood Approach

abstract:
  We address the problem of structured covariance matrix estimation for radar
space-time adaptive processing (STAP). A priori knowledge of the interference
environment has been exploited in many previous works to enable accurate
estimators even when training is not generous. Specifically, recent work has
shown that employing practical constraints such as the rank of clutter subspace
and the condition number of disturbance covariance leads to powerful estimators
that have closed form solutions. While rank and the condition number are very
effective constraints, often practical non-idealities makes it difficult for
them to be known precisely using physical models. Therefore, we propose a
robust covariance estimation method for radar STAP via an expected likelihood
(EL) approach. We analyze covariance estimation algorithms under three cases of
imperfect constraints: 1) a rank constraint, 2) both rank and noise power
constraints, and 3) condition number constraint. In each case, we formulate
precise constraint determination as an optimization problem using the EL
criterion. For each of the three cases, we derive new analytical results which
allow for computationally efficient, practical ways of setting these
constraints. In particular, we prove formally that both the rank and condition
number as determined by the EL criterion are unique. Through experimental
results from a simulation model and the KASSPER data set, we show the estimator
with optimal constraints obtained by the EL approach outperforms state of the
art alternatives.


title:
Alpha-CIR Model with Branching Processes in Sovereign Interest Rate
  Modelling

abstract:
  We introduce a class of interest rate models, called the $\alpha$-CIR model,
which gives a natural extension of the standard CIR model by adopting the
$\alpha$-stable L{\'e}vy process and preserving the branching property. This
model allows to describe in a unified and parsimonious way several recent
observations on the sovereign bond market such as the persistency of low
interest rate together with the presence of large jumps at local extent. We
emphasize on a general integral representation of the model by using random
fields, with which we establish the link to the CBI processes and the affine
models. Finally we analyze the jump behaviors and in particular the large
jumps, and we provide numerical illustrations.


title: On metric graphs with prescribed gonality

abstract:
  We prove that in the moduli space of genus-g metric graphs the locus of
graphs with gonality at most d has the classical dimension min{3g-3,2g+2d-5}.
This follows from a careful parameter count to establish the upper bound and a
construction of sufficiently many graphs with gonality at most d to establish
the lower bound. Here, gonality is the minimal degree of a non-degenerate
harmonic map to a tree that satisfies the Riemann-Hurwitz condition everywhere.
Along the way, we establish a convenient combinatorial datum capturing such
harmonic maps to trees.


title: Swift/XRT view on S5 0716+714 during a flare

abstract:
  The blazar S5 0716+714 has been monitored in its flaring state between 2015
January 19 and February 22 with Swift/XRT. During this period an exceptional
flux level was observed in the X-ray range as well as in the other wavelengths,
e.g. optical, near infrared and very high energy $\gamma$ rays. Here, we report
X-ray observations of S5 0716+714 carried out during the outburst. The observed
X-ray spectra, well described with broken power-law model, disentangle both
synchrotron and inverse Compton components. The break energy shifts towards
higher energies with increasing flux, revealing the dominance of synchrotron
radiation in the X-ray spectrum observed. We also report spectrum softening
with increasing flux. During the recent flare, significant temporal intranight
variability is observed in the X-ray range.


title: On a class of parametric $(p,2)$-equations

abstract:
  We consider parametric equations driven by the sum of a $p$-Laplacian and a
Laplace operator (the so-called $(p,2)$-equations). We study the existence and
multiplicity of solutions when the parameter $\lambda>0$ is near the principal
eigenvalue $\hat{\lambda}_1(p)>0$ of $(-\Delta_p,W^{1,p}_{0}(\Omega))$. We
prove multiplicity results with precise sign information when the near
resonance occurs from above and from below of $\hat{\lambda}_1(p)>0$.


title: A Small Deformation of a Simple Theory

abstract:
  We study an interesting relevant deformation of the simplest interacting N=2
SCFT---the original Argyres-Douglas (AD) theory. We argue that, although this
deformation is not strictly speaking Banks-Zaks like (certain operator
dimensions change macroscopically), there are senses in which it constitutes a
mild deformation of the parent AD theory: the exact change in the "a" anomaly
is small and is essentially saturated at one loop. Moreover, contributions from
IR operators that have a simple description in the UV theory reproduce a
particular limit of the IR index to a remarkably high order. These results lead
us to conclude that the IR theory is an interacting N=1 SCFT with particularly
small "a" and "c" central charges and that this theory sheds some interesting
light on the spectrum of its AD parent.


title:
Fault and Byzantine Tolerant Self-stabilizing Mobile Robots Gathering -
  Feasibility Study -

abstract:
  Gathering is a fundamental coordination problem in cooperative mobile
robotics. In short, given a set of robots with arbitrary initial locations and
no initial agreement on a global coordinate system, gathering requires that all
robots, following their algorithm, reach the exact same but not predetermined
location. Gathering is particularly challenging in networks where robots are
oblivious (i.e., stateless) and direct communication is replaced by
observations on their respective locations. Interestingly any algorithm that
solves gathering with oblivious robots is inherently self-stabilizing if no
specific assumption is made on the initial distribution of the robots. In this
paper, we significantly extend the studies of de-terministic gathering
feasibility under different assumptions This manuscript considerably extends
preliminary results presented as an extended abstract at the DISC 2006
conference [7]. The current version is under review at Distributed Computing
Journal since February 2012 (in a previous form) and since 2014 in the current
form. The most important results have been also presented in MAC 2010 organized
in Ottawa from August 15th to 17th 2010 related to synchrony and faults (crash
and Byzantine). Unlike prior work, we consider a larger set of scheduling
strategies, such as bounded schedulers. In addition, we extend our study to the
feasibility of probabilistic self-stabilizing gathering in both fault-free and
fault-prone environments.


title:
A Polynomial-Time Algorithm for Reachability in Branching VASS in
  Dimension One

abstract:
  Branching VASS (BVASS) generalise vector addition systems with states by
allowing for special branching transitions that can non-deterministically
distribute a counter value between two control states. A run of a BVASS
consequently becomes a tree, and reachability is to decide whether a given
configuration is the root of a reachability tree. This paper shows
P-completeness of reachability in BVASS in dimension one, the first
decidability result for reachability in a subclass of BVASS known so far.
Moreover, we show that coverability and boundedness in BVASS in dimension one
are P-complete as well.


title:
Energy-Efficient Resource Allocation Optimization for Multimedia
  Heterogeneous Cloud Radio Access Networks

abstract:
  The heterogeneous cloud radio access network (H-CRAN) is a promising paradigm
which incorporates the cloud computing into heterogeneous networks (HetNets),
thereby taking full advantage of cloud radio access networks (C-RANs) and
HetNets. Characterizing the cooperative beamforming with fronthaul capacity and
queue stability constraints is critical for multimedia applications to
improving energy efficiency (EE) in H-CRANs. An energy-efficient optimization
objective function with individual fronthaul capacity and inter-tier
interference constraints is presented in this paper for queue-aware multimedia
H-CRANs. To solve this non-convex objective function, a stochastic optimization
problem is reformulated by introducing the general Lyapunov optimization
framework. Under the Lyapunov framework, this optimization problem is
equivalent to an optimal network-wide cooperative beamformer design algorithm
with instantaneous power, average power and inter-tier interference
constraints, which can be regarded as the weighted sum EE maximization problem
and solved by a generalized weighted minimum mean square error approach. The
mathematical analysis and simulation results demonstrate that a tradeoff
between EE and queuing delay can be achieved, and this tradeoff strictly
depends on the fronthaul constraint.


title:
Continuous Monitoring of A/B Tests without Pain: Optional Stopping in
  Bayesian Testing

abstract:
  A/B testing is one of the most successful applications of statistical theory
in modern Internet age. One problem of Null Hypothesis Statistical Testing
(NHST), the backbone of A/B testing methodology, is that experimenters are not
allowed to continuously monitor the result and make decision in real time. Many
people see this restriction as a setback against the trend in the technology
toward real time data analytics. Recently, Bayesian Hypothesis Testing, which
intuitively is more suitable for real time decision making, attracted growing
interest as an alternative to NHST. While corrections of NHST for the
continuous monitoring setting are well established in the existing literature
and known in A/B testing community, the debate over the issue of whether
continuous monitoring is a proper practice in Bayesian testing exists among
both academic researchers and general practitioners. In this paper, we formally
prove the validity of Bayesian testing with continuous monitoring when proper
stopping rules are used, and illustrate the theoretical results with concrete
simulation illustrations. We point out common bad practices where stopping
rules are not proper and also compare our methodology to NHST corrections.
General guidelines for researchers and practitioners are also provided.


title: Confinement-Induced Resonances in Ultracold Atom-Ion Systems

abstract:
  We investigate confinement-induced resonances in a system composed by a
tightly trapped ion and a moving atom in a waveguide. We determine the
conditions for the appearance of such resonances in a broad region -- from the
"long-wavelength" limit to the opposite case when the typical length scale of
the atom-ion polarisation potential essentially exceeds the transverse
waveguide width. We find considerable dependence of the resonance position on
the atomic mass which, however, disappears in the "long-wavelength and
zero-energy" limit, where the known result for the confined atom-atom
scattering is reproduced. We also derive an analytic and a semi-analytic
formula for the resonance position in the "long-wavelength and zero-energy"
limit and we investigate numerically how the position of the resonance is
affected by a finite atomic colliding energy. Our results, which can be
investigated experimentally in the near future, could be used to determine the
atom-ion scattering length, the temperature of the atomic ensemble in the
presence of an ion impurity, and to control the atom-phonon coupling in a
linear ion crystal in interaction with a quasi one dimensional atomic quantum
gas.


title:
Differentiated latency in data center networks with erasure coded files
  through traffic engineering

abstract:
  This paper proposes an algorithm to minimize weighted service latency for
different classes of tenants (or service classes) in a data center network
where erasure-coded files are stored on distributed disks/racks and access
requests are scattered across the network. Due to limited bandwidth available
at both top-of-the-rack and aggregation switches and tenants in different
service classes need differentiated services, network bandwidth must be
apportioned among different intra- and inter-rack data flows for different
service classes in line with their traffic statistics. We formulate this
problem as weighted queuing and employ a class of probabilistic request
scheduling policies to derive a closed-form upper-bound of service latency for
erasure-coded storage with arbitrary file access patterns and service time
distributions. The result enables us to propose a joint weighted latency (over
different service classes) optimization over three entangled "control knobs":
the bandwidth allocation at top-of-the-rack and aggregation switches for
different service classes, dynamic scheduling of file requests, and the
placement of encoded file chunks (i.e., data locality). The joint optimization
is shown to be a mixed-integer problem. We develop an iterative algorithm which
decouples and solves the joint optimization as 3 sub-problems, which are either
convex or solvable via bipartite matching in polynomial time. The proposed
algorithm is prototyped in an open-source, distributed file system, {\em
Tahoe}, and evaluated on a cloud testbed with 16 separate physical hosts in an
Openstack cluster using 48-port Cisco Catalyst switches. Experiments validate
our theoretical latency analysis and show significant latency reduction for
diverse file access patterns. The results provide valuable insights on
designing low-latency data center networks with erasure coded storage.


title:
Ground state of the U2Mo compound: Physical properties of the
  Omega-phase

abstract:
  Using ab initio calculations, unexpected structural instability was recently
found in the ground state of the U$_2$Mo compound. Instead of the unstable
$I4/mmm$ structure, in this work the $P6/mmm$ ($\# 191$) space group, usually
called $\Omega$-phase, is proposed as the fundamental state. Electronic and
elastic properties are studied in this work in order to characterize the
physical properties of the new ground state. The stability of the
$\Omega$-phase is studied by means of its elastic constants calculation and
phonon dispersion spectrum. Analysis of isotropic indices shows that the new
phase is a ductile material with a minimal degree of anisotropy, suggesting
that U$_2$Mo in the $P6/mmm$ structure is an elastic isotropic material.
Analysis of charge density, density of electronic states (DOS) and the
character of the bands revealed a high level of hybridization between
$d$-molybdenum electronic states and $d$- and $f$-uranium ones.


title: The Multi-Dimensional Character of Core-Collapse Supernovae

abstract:
  Core-collapse supernovae, the culmination of massive stellar evolution, are
spectacular astronomical events and the principle actors in the story of our
elemental origins. Our understanding of these events, while still incomplete,
centers around a neutrino-driven central engine that is highly hydrodynamically
unstable. Increasingly sophisticated simulations reveal a shock that stalls for
hundreds of milliseconds before reviving. Though brought back to life by
neutrino heating, the development of the supernova explosion is inextricably
linked to multi-dimensional fluid flows. In this paper, the outcomes of
three-dimensional simulations that include sophisticated nuclear physics and
spectral neutrino transport are juxtaposed to learn about the nature of the
three dimensional fluid flow that shapes the explosion. Comparison is also made
between the results of simulations in spherical symmetry from several groups,
to give ourselves confidence in the understanding derived from this
juxtaposition.


title:
Binary Black Hole Merger Rates Inferred from Luminosity Function of
  Ultra-Luminous X-ray Sources

abstract:
  The Advanced Laser Interferometer Gravitational-Wave Observatory (aLIGO) has
detected direct signals of gravitational waves (GWs) from GW150914. The event
was a merger of binary black holes whose masses are $36^{+5}_{-4}M_{\odot}$ and
$29^{+4}_{-4}M_{\odot}$. Such binary systems are expected to be directly
evolved from stellar binary systems or formed by dynamical interactions of
black holes in dense stellar environments. Here we derive the binary black hole
merger rate based on the nearby ultra-luminous X-ray source (ULX) luminosity
function (LF) under the assumption that binary black holes evolve through X-ray
emitting phases. We obtain the binary black hole merger rate as $5.8 ({t}_{\rm
ULX}/{0.1 \ \rm Myr})^{-1} \lambda^{-0.6} \exp{(-0.30\lambda)} \ {\rm Gpc^{-3}\
yr^{-1}}$, where $t_{\rm ULX}$ is the typical duration of the ULX phase and
$\lambda$ is the Eddington ratio in luminosity. This is coincident with the
event rate inferred from the detection of GW150914 as well as the predictions
based on binary population synthesis models. Although we are currently unable
to constrain the Eddington ratio of ULXs in luminosity due to the uncertainties
of our models and measured binary black hole merger event rates, further X-ray
and GW data will allow us to narrow down the range of the Eddington ratios of
ULXs. We also find the cumulative merger rate for the mass range of
$5M_\odot\le M_{\rm BH}\le100M_\odot$ inferred from the ULX LF is consistent
with that estimated by the aLIGO collaboration considering various
astrophysical conditions such as the mass function of black holes.


title: Repetition-Free Derivability from a Regular Grammar is NP-Hard

abstract:
  We prove the NP-hardness of the problem whether a given word can be derived
from a given regular grammar without repeated occurrence of any nonterminal.


title: Packet Error Rate Performance of IEEE802.11g under Bluetooth Interface

abstract:
  This study approaches the issues concerning the coexistence of the IEEE
802.11g wireless networks and the adhoc Bluetooth networks that operate within
the same 2.4 GHz band. The performance of 802.11g is evaluated by simulating
the PER (Packet Error Rate) parameter and coverage area. The simulation
experiments are based on the worst case scenario presumption, which entails the
transmission of HV1 packet which HV1 link requires transmission on 100% of the
Bluetooth (BT) time slots using the maximum hop rate of 1600 hops per sec. The
paper suggests a practical approach to mitigate the interference using symbol
erasures technique through the assessment of the PER parameter at various Eb/No
values. The results show that the symbol erasures can effectively mitigate the
interference and enhance the performance of the 802.11g.


title: Equiangular tight frames from hyperovals

abstract:
  An equiangular tight frame (ETF) is a set of equal norm vectors in a
Euclidean space whose coherence is as small as possible, equaling the Welch
bound. Also known as Welch-bound-equality sequences, such frames arise in
various applications, such as waveform design, quantum information theory,
compressed sensing and algebraic coding theory. ETFs seem to be rare, and only
a few methods of constructing them are known. In this paper, we present a new
infinite family of complex ETFs that arises from hyperovals in finite
projective planes. In particular, we give the first ever construction of a
complex ETF of 76 vectors in a space of dimension 19. Recently, a
computer-assisted approach was used to show that real ETFs of this size do not
exist, resolving a longstanding open problem in this field. Our construction is
a modification of a previously known technique for constructing ETFs from
balanced incomplete block designs.


title:
Molecular-level tuning of cellular autonomy controls the collective
  behaviors of cell populations

abstract:
  A rigorous understanding of how multicellular behaviors arise from the
actions of single cells requires quantitative frameworks that bridge the gap
between genetic circuits, the arrangement of cells in space, and
population-level behaviors. Here, we provide such a framework for a ubiquitous
class of multicellular systems - namely, "secrete-and-sense cells" that
communicate by secreting and sensing a signaling molecule. By using formal,
mathematical arguments and introducing the concept of a phenotype diagram, we
show how these cells tune their degrees of autonomous and collective behavior
to realize distinct single-cell and population-level phenotypes; these
phenomena have biological analogs, such as quorum sensing or paracrine
signaling. We also define the "entropy of population," a measurement of the
number of arrangements that a population of cells can assume, and demonstrate
how a decrease in the entropy of population accompanies the formation of
ordered spatial patterns. Our conceptual framework ties together diverse
systems, including tissues and microbes, with common principles.

categories: q-bio.MN nlin.CG nlin.PS physics.bio-ph q-bio.CB


title:
Key Economic and Environmental Perspectives on Sustainability in the ICT
  Sector

abstract:
  Telecommunication networks have become as critical to the 21st century
development as were railways, roads and canals, to the 19th Century
developments and is now seen as enabler to a more sustained business,
environment and society as a whole. Still fascinating has been and is the
exponential rate of growth in this industry. This is one sector where the next
revolution is always just around the corner whether known or unknown. The
telecoms industry is categorized by high rates of innovation in a rapidly
changing technological environment. This in turn is associated with an immense
range of sustainability concerns and challenges for the Telecoms service
providers, the service users and the whole industry and its far reaching
influence on other industries. This paper discusses three key aspects of such
challenges namely; the question of sustainable power/energy supply for the
industry when the change is resulting in increasing energy and operational
cost, the exploitation of technologies advancement for sustainability and their
business and environmental benefits.


title: Lower bounds for moments of global scores of pairwise Markov chains

abstract:
  Let $X_1,X_2,\ldots$ and $Y_1,Y_2,\ldots$ be two random sequences so that
every random variable takes values in a finite set $\mathbb{A}$. We consider a
global similarity score $L_n:=L(X_1,\ldots,X_n;Y_1,\ldots,Y_n)$ that measures
the homology (relatedness) of words $(X_1,\ldots,X_n)$ and $(Y_1,\ldots,Y_n)$.
A typical example of such score is the length of the longest common
subsequence. We study the order of central absolute moment $E|L_n-EL_n|^r$ in
the case where two-dimensional process $(X_1,Y_1),(X_2,Y_2),\ldots$ is a Markov
chain on $\mathbb{A}\times \mathbb{A}$. This is a very general model involving
independent Markov chains, hidden Markov models, Markov switching models and
many more. Our main result establishes a general condition that guarantees that
$E|L_n-EL_n|^r\asymp n^{r\over 2}$. We also perform simulations indicating the
validity of the condition.


title:
Lexis: An Optimization Framework for Discovering the Hierarchical
  Structure of Sequential Data

abstract:
  Data represented as strings abounds in biology, linguistics, document mining,
web search and many other fields. Such data often have a hierarchical
structure, either because they were artificially designed and composed in a
hierarchical manner or because there is an underlying evolutionary process that
creates repeatedly more complex strings from simpler substrings. We propose a
framework, referred to as "Lexis", that produces an optimized hierarchical
representation of a given set of "target" strings. The resulting hierarchy,
"Lexis-DAG", shows how to construct each target through the concatenation of
intermediate substrings, minimizing the total number of such concatenations or
DAG edges. The Lexis optimization problem is related to the smallest grammar
problem. After we prove its NP-Hardness for two cost formulations, we propose
an efficient greedy algorithm for the construction of Lexis-DAGs. We also
consider the problem of identifying the set of intermediate nodes (substrings)
that collectively form the "core" of a Lexis-DAG, which is important in the
analysis of Lexis-DAGs. We show that the Lexis framework can be applied in
diverse applications such as optimized synthesis of DNA fragments in genomic
libraries, hierarchical structure discovery in protein sequences,
dictionary-based text compression, and feature extraction from a set of
documents.


title: Present Status of Single Pion Production in Neutrino-Nucleus Reactions

abstract:
  Some of the recent progress in the physics of pion production induced by
neutrinos on nucleons and nuclei is reviewed from a theoretical perspective.
The importance of Watson's theorem to reconcile ANL and BNL data with the
off-diagonal Goldberger-Treiman relation for the $\Delta(1232)$ is discussed.
The disagreement between MiniBooNE data and theoretical calculations is
presented in the light of the new MINERvA data. The coherent pion production
data on $^{12}$C obtained by MINERvA are also compared to different microscopic
and PCAC models.


title:
Robust Kernel (Cross-) Covariance Operators in Reproducing Kernel
  Hilbert Space toward Kernel Methods

abstract:
  To the best of our knowledge, there are no general well-founded robust
methods for statistical unsupervised learning. Most of the unsupervised methods
explicitly or implicitly depend on the kernel covariance operator (kernel CO)
or kernel cross-covariance operator (kernel CCO). They are sensitive to
contaminated data, even when using bounded positive definite kernels. First, we
propose robust kernel covariance operator (robust kernel CO) and robust kernel
crosscovariance operator (robust kernel CCO) based on a generalized loss
function instead of the quadratic loss function. Second, we propose influence
function of classical kernel canonical correlation analysis (classical kernel
CCA). Third, using this influence function, we propose a visualization method
to detect influential observations from two sets of data. Finally, we propose a
method based on robust kernel CO and robust kernel CCO, called robust kernel
CCA, which is designed for contaminated data and less sensitive to noise than
classical kernel CCA. The principles we describe also apply to many kernel
methods which must deal with the issue of kernel CO or kernel CCO. Experiments
on synthesized and imaging genetics analysis demonstrate that the proposed
visualization and robust kernel CCA can be applied effectively to both ideal
data and contaminated data. The robust methods show the superior performance
over the state-of-the-art methods.


title: Anomalous Parity-Time Symmetry Transition away from an Exceptional Point

abstract:
  Parity-time (PT) symmetric systems have two distinguished phases, e.g., one
with real energy eigenvalues and the other with complex conjugate eigenvalues.
To enter one phase from the other, it is believed that the system must pass
through an exceptional point, which is a non-Hermitian degenerate point with
coalesced eigenvalues and eigenvectors. In this letter we reveal an anomalous
PT transition that takes place away from an exceptional point in a nonlinear
system: as the nonlinearity increases, the original linear system evolves along
two distinct PT-symmetric trajectories, each of which can have an exceptional
point. However, the two trajectories collide and vanish away from these
exceptional points, after which the system is left with a PT-broken phase. We
first illustrate this phenomenon using a coupled mode theory and then exemplify
it using paraxial wave propagation in a transverse periodic potential.


title:
A high-dimensional CLT in $\mathcal{W}_2$ distance with near optimal
  convergence rate

abstract:
  Let $X_1, \ldots , X_n$ be i.i.d. random vectors in $\mathbb{R}^d$ with
$\|X_1\| \le \beta$. Then, we show that $\frac{1}{\sqrt{n}}(X_1 + \ldots +
X_n)$ converges to a Gaussian in quadratic transportation (also known as
"Kantorovich" or "Wasserstein") distance at a rate of $O\left( \frac{\sqrt{d}
\beta \log n}{\sqrt{n}} \right)$, improving a result of Valiant and Valiant.
The main feature of our theorem is that the rate of convergence is within $\log
n$ of optimal for $n, d \rightarrow \infty$.


title: A Note on Time Measurements in LAMMPS

abstract:
  We examine the issue of assessing the efficiency of components of a parallel
program at the example of the MD package LAMMPS. In particular, we look at how
LAMMPS deals with the issue and explain why the approach adopted might lead to
inaccurate conclusions. The misleading nature of this approach is subsequently
verified experimentally with a case study. Afterwards, we demonstrate how one
should correctly determine the efficiency of the components and show what
changes to the code base of LAMMPS are necessary in order to get the correct
behavior.

categories: cond-mat.mtrl-sci cs.CE physics.chem-ph physics.comp-ph


title:
A nodal domain theorem and a higher-order Cheeger inequality for the
  graph $p$-Laplacian

abstract:
  We consider the nonlinear graph $p$-Laplacian and its set of eigenvalues and
associated eigenfunctions of this operator defined by a variational principle.
We prove a nodal domain theorem for the graph $p$-Laplacian for any $p\geq 1$.
While for $p>1$ the bounds on the number of weak and strong nodal domains are
the same as for the linear graph Laplacian ($p=2$), the behavior changes for
$p=1$. We show that the bounds are tight for $p\geq 1$ as the bounds are
attained by the eigenfunctions of the graph $p$-Laplacian on two graphs.
Finally, using the properties of the nodal domains, we prove a higher-order
Cheeger inequality for the graph $p$-Laplacian for $p>1$. If the eigenfunction
associated to the $k$-th variational eigenvalue of the graph $p$-Laplacian has
exactly $k$ strong nodal domains, then the higher order Cheeger inequality
becomes tight as $p\rightarrow 1$.


title: Multi-layer Representation Learning for Medical Concepts

abstract:
  Learning efficient representations for concepts has been proven to be an
important basis for many applications such as machine translation or document
classification. Proper representations of medical concepts such as diagnosis,
medication, procedure codes and visits will have broad applications in
healthcare analytics. However, in Electronic Health Records (EHR) the visit
sequences of patients include multiple concepts (diagnosis, procedure, and
medication codes) per visit. This structure provides two types of relational
information, namely sequential order of visits and co-occurrence of the codes
within each visit. In this work, we propose Med2Vec, which not only learns
distributed representations for both medical codes and visits from a large EHR
dataset with over 3 million visits, but also allows us to interpret the learned
representations confirmed positively by clinical experts. In the experiments,
Med2Vec displays significant improvement in key medical applications compared
to popular baselines such as Skip-gram, GloVe and stacked autoencoder, while
providing clinically meaningful interpretation.


title: Aspects of Symmetry, Topology and Anomalies in Quantum Matter

abstract:
  In this thesis, we explore the aspects of symmetry, topology and anomalies in
quantum matter with entanglement from both condensed matter and high energy
theory viewpoints. The focus of our research is on the gapped many-body quantum
systems including symmetry-protected topological states and topologically
ordered states. Chapter 1. Introduction. Chapter 2. Geometric phase,
wavefunction overlap, spacetime path integral and topological invariants.
Chapter 3. Aspects of Symmetry. Chapter 4. Aspects of Topology. Chapter 5.
Aspects of Anomalies. Chapter 6. Quantum Statistics and Spacetime Surgery.
Chapter 7. Conclusion: Finale and A New View of Emergence-Reductionism. (Thesis
supervisor: Prof. Xiao-Gang Wen)

categories: cond-mat.str-el hep-th math-ph math.MP quant-ph


title:
From Spin Noise to Systematics: Stochastic Processes in the First
  International Pulsar Timing Array Data Release

abstract:
  We analyse the stochastic properties of the 49 pulsars that comprise the
first International Pulsar Timing Array (IPTA) data release. We use Bayesian
methodology, performing model selection to determine the optimal description of
the stochastic signals present in each pulsar. In addition to spin-noise and
dispersion-measure (DM) variations, these models can include timing noise
unique to a single observing system, or frequency band. We show the improved
radio-frequency coverage and presence of overlapping data from different
observing systems in the IPTA data set enables us to separate both system and
band-dependent effects with much greater efficacy than in the individual PTA
data sets. For example, we show that PSR J1643$-$1224 has, in addition to DM
variations, significant band-dependent noise that is coherent between PTAs
which we interpret as coming from time-variable scattering or refraction in the
ionised interstellar medium. Failing to model these different contributions
appropriately can dramatically alter the astrophysical interpretation of the
stochastic signals observed in the residuals. In some cases, the spectral
exponent of the spin noise signal can vary from 1.6 to 4 depending upon the
model, which has direct implications for the long-term sensitivity of the
pulsar to a stochastic gravitational-wave (GW) background. By using a more
appropriate model, however, we can greatly improve a pulsar's sensitivity to
GWs. For example, including system and band-dependent signals in the PSR
J0437$-$4715 data set improves the upper limit on a fiducial GW background by
$\sim 60\%$ compared to a model that includes DM variations and spin-noise
only.

categories: astro-ph.IM astro-ph.HE astro-ph.SR gr-qc


title: A note on a bijection for Schr\"oder permutations

abstract:
  There is a bijection from Schroder paths to {4132, 4231}-avoiding
permutations due to Bandlow, Egge, and Killpatrick that sends "area" to
"inversion number". Here we give a concise description of this bijection.


title:
A landmark-based algorithm for automatic pattern recognition and
  abnormality detection

abstract:
  We study a class of mathematical and statistical algorithms with the aim of
establishing a computer-based framework for fast and reliable automatic
abnormality detection on landmark represented image templates. Under this
framework, we apply a landmark-based algorithm for finding a group average as
an estimator that is said to best represent the common features of the group in
study. This algorithm extracts information of momentum at each landmark through
the process of template matching. If ever converges, the proposed algorithm
produces a local coordinate system for each member of the observing group, in
terms of the residual momentum. We use a Bayesian approach on the collected
residual momentum representations for making inference. For illustration, we
apply this framework to a small database of brain images for detecting
structure abnormality. The brain structure changes identified by our framework
are highly consistent with studies in the literature.


title:
Gravitational wave astrophysics, data analysis and multimessenger
  astronomy

abstract:
  This paper reviews gravitational wave sources and their detection. One of the
most exciting potential sources of gravitational waves are coalescing binary
black hole systems. They can occur on all mass scales and be formed in numerous
ways, many of which are not understood. They are generally invisible in
electromagnetic waves, and they provide opportunities for deep investigation of
Einstein's general theory of relativity. Sect. 1 of this paper considers ways
that binary black holes can be created in the universe, and includes the
prediction that binary black hole coalescence events are likely to be the first
gravitational wave sources to be detected. The next parts of this paper address
the detection of chirp waveforms from coalescence events in noisy data. Such
analysis is computationally intensive. Sect. 2 reviews a new and powerful
method of signal detection based on the GPU-implemented summed parallel
infinite impulse response filters. Such filters are intrinsically real time
alorithms, that can be used to rapidly detect and localise signals. Sect. 3 of
the paper reviews the use of GPU processors for rapid searching for
gravitational wave bursts that can arise from black hole births and
coalescences. In sect. 4 the use of GPU processors to enable fast efficient
statistical significance testing of gravitational wave event candidates is
reviewed. Sect. 5 of this paper addresses the method of multimessenger
astronomy where the discovery of electromagnetic counterparts of gravitational
wave events can be used to identify sources, understand their nature and obtain
much greater science outcomes from each identified event.


title: Aleksandrov projection problem for convex lattice sets

abstract:
  Let $K$ and $L$ be origin-symmetric convex integer polytopes in
$\mathbb{R}^n$. We study a discrete analogue of the Aleksandrov projection
problem. If for every $u\in \mathbb{Z}^n$, the sets $(K\cap
\mathbb{Z}^n)|u^\perp$ and $(L\cap \mathbb{Z}^n)|u^\perp$ have the same number
of points, is then $K=L$? We give a positive answer to this problem in
$\mathbb{Z}^2$ under an additional hypothesis that $(2K\cap
\mathbb{Z}^2)|u^\perp$ and $(2L\cap \mathbb{Z}^2)|u^\perp$ have the same number
of points.


title:
Conserved Charges and First Law of Thermodynamics for Kerr-de Sitter
  Black Holes

abstract:
  Recently, a general method for calculating conserved charges for (black hole)
solutions to generally covariant gravitational theories, in any dimensions and
with arbitrary asymptotic behaviors has been introduced. Equipped with this
method, which can be dubbed as "solution phase space method," we calculate mass
and angular momentum for the Kerr-dS black holes. Furthermore, for any choice
of horizons, associated entropy and the first law of thermodynamics are
derived. Interestingly, according to insensitivity of the analysis to the
chosen cosmological constant, the analysis unifies the thermodynamics of
rotating stationary black holes in 4 (and other) dimensions with either AdS,
flat or dS asymptotics. We extend the analysis to include electric charge, i.e.
to the Kerr-Newman-dS black holes.


title: Physics of Core-Collapse Supernovae in Three Dimensions: a Sneak Preview

abstract:
  Nonspherical mass motions are a generic feature of core-collapse supernovae,
and hydrodynamic instabilities play a crucial role for the explosion mechanism.
First successful neutrino-driven explosions could be obtained with
self-consistent, first-principle simulations in three spatial dimensions (3D).
But 3D models tend to be less prone to explosion than corresponding
axisymmetric (2D) ones. This has been explained by 3D turbulence leading to
energy cascading from large to small spatial scales, inversely to the 2D case,
thus disfavoring the growth of buoyant plumes on the largest scales. Unless the
inertia to explode simply reflects a lack of sufficient resolution in relevant
regions, it suggests that some important aspect may still be missing for robust
and sufficiently energetic neutrino-powered explosions. Such deficits could be
associated with progenitor properties like rotation, magnetic fields or
pre-collapse perturbations, or with microphysics that could lead to an
enhancement of neutrino heating behind the shock. 3D simulations have also
revealed new phenomena that are not present in 2D, for example spiral modes of
the standing accretion shock instability (SASI) and a stunning dipolar
lepton-emission self-sustained asymmetry (LESA). Both impose time- and
direction-dependent variations on the detectable neutrino signal. The
understanding of these effects and of their consequences is still in its
infancy.


title: Topological Number of Edge States

abstract:
  We show that the edge states of the four-dimensional class A system can have
topological charges, which are characterized by Abelian/non-Abelian monopoles.
The edge topological charges are a new feature of relations among theories with
different dimensions. From this novel viewpoint, we provide a non-Abelian
analogue of the TKNN number as an edge topological charge, which is defined by
an SU(2) 't Hooft-Polyakov BPS monopole through an equivalence to Nahm
construction. Furthermore, putting a constant magnetic field yields an edge
monopole in a non-commutative momentum space, where D-brane methods in string
theory facilitate study of edge fermions.


title:
$\mu$-Distortions or Running: A Guaranteed Discovery from CMB
  Spectrometry

abstract:
  We discuss the implications of a PIXIE-like experiment, which would measure
$\mu$-type spectral distortions of the CMB at a level of
$\sigma_{\mu}=(1/n)\times 10^{-8}$, with $n\geq1$ representing an improved
sensitivity (e.g. $n=10$ corresponds to PRISM). Using Planck data and
considering the six-parameter $\Lambda$CDM model, we compute the posterior for
$\mu_8\equiv\mu\times 10^{8}$ and find $\mu_8=1.57^{+0.11}_{-0.13}$
($68\%\,\mathrm{CL}$). This becomes $\mu_{8} = 1.28^{+0.30}_{-0.52}$
($68\%\,\mathrm{CL}$) when the running $\alpha_\mathrm{s}$ of the spectral
index is included. We point out that a sensitivity of about $3\times$ PIXIE
implies a guaranteed discovery: $\mu$-distortion is detected or
$\alpha_\mathrm{s}\geq 0$ is excluded (both at $95\%\,\mathrm{CL}$ or higher).
This threshold sensitivity sets a clear benchmark for CMB spectrometry. For a
combined analysis of PIXIE and current Planck data, we discuss the improvement
on measurements of the tilt $n_\mathrm{s}$ and the running $\alpha_\mathrm{s}$
and the dependence on the choice of the pivot. A fiducial running of
$\alpha_\mathrm{s}=-0.01$ (close to the Planck best-fit) leads to a detection
of negative running at $2\sigma$ for $5\times$ PIXIE. A fiducial running of
$\alpha_\mathrm{s}=-0.02$, still compatible with Planck, requires $3\times$
PIXIE to rule out $\alpha_\mathrm{s} = 0$ (at $95\%\,\mathrm{CL}$). We propose
a convenient and compact visualization of the improving constraints on the
tilt, running and tensor-to-scalar ratio.