title:
Vlasov-Poisson simulations of electrostatic parametric instability for
  localized Langmuir wave packets in the solar wind

abstract:
  Recent observation of large amplitude Langmuir waveforms during a Type III
event in the solar wind have been interpreted as the signature of the
electrostatic decay of beam-driven Langmuir waves. This mechanism is thought to
be a first step to explain the generation of solar Type III radio emission. The
threshold for this parametric instability in typical solar wind condition is
investigated here by means of 1D-1V Vlasov-Poisson simulations. We show that
the amplitude of the observed Langmuir beat-like waveforms is of the order of
the effective threshold computed from the full kinetic simulations. The
expected level of associated ion acoustic density fluctuations have also been
computed for comparison with observations.

categories: astro-ph.SR astro-ph.EP physics.plasm-ph physics.space-ph


title: Saturation of gluon density and soft p-p collisions at LHC

abstract:
  We calculate the unintegrated gluon distribution at low intrinsic transverse
momenta and its parameters are found from the best description of the SPS and
LHC data on the $pp$ collision in the soft kinematical region. It allows us to
study the saturation of the gluon density at low $Q^2$ more carefully and find
the saturation scale.


title: Least-action filtering

abstract:
  This paper presents an approach to estimating a hidden process in a
continuous-time setting, where the hidden process is a diffusion. The approach
is simply to minimize the negative log-likelihood of the hidden path, where the
likelihood is expressed relative to Wiener measure. This negative
log-likelihood is the action integral of the path, which we minimize by
calculus of variations. We then perform an asymptotic maximum-likelihood
analysis to understand better how the actual path is distributed around the
least-action path; it turns out that the actual path can be expressed
(approximately) as the sum of the least-action path and a zero-mean Gaussian
process which can be specified quite explicitly. Numerical solution of the ODEs
which arise from the calculus of variations is often feasible, but is
complicated by the shooting nature of the problem, and the possibility that we
have found a local but not global minimum. We analyze the situations when this
happens, and provide effective numerical methods for studying this. We also
show how the methodology works in a situation where the hidden positive
diffusion acts as the random intensity of a point process which is observed;
here too it is possible to estimate the hidden process.


title: Colour-independent partition functions in coloured vertex models

abstract:
  We study lattice configurations related to S_n, the scalar product of an
off-shell state and an on-shell state in rational A_n integrable vertex models,
n = {1, 2}. The lattice lines are colourless and oriented. The state variables
are n conserved colours that flow along the line orientations, but do not
necessarily cover every bond in the lattice.
  Choosing boundary conditions such that the positions where the colours flow
into the lattice are fixed, and where they flow out are summed over, we show
that the partition functions of these configurations, with these boundary
conditions, are n-independent. Our results extend to trigonometric A_n models,
and to all n.
  This n-independence explains, in vertex-model terms, results from recent
studies of S_2 [1, 2]. Namely, 1. S_2 which depends on two sets of Bethe roots,
b_1 and b_2, and cannot (as far as we know) be expressed in single determinant
form, degenerates in the limit b_1 -> infinity, and/or b_2 -> infinity, into a
product of determinants, 2. Each of the latter determinants is an A_1
vertex-model partition function.


title: International collaboration clusters in Africa

abstract:
  Recent discussion about the increase in international research collaboration
suggests a comprehensive global network centred around a group of core
countries and driven by generic socio-economic factors where the global system
influences all national and institutional outcomes. In counterpoint, we
demonstrate that the collaboration pattern for countries in Africa is far from
universal. Instead, it exhibits layers of internal clusters and external links
that are explained not by monotypic global influences but by regional geography
and, perhaps even more strongly, by history, culture and language. Analysis of
these bottom-up, subjective, human factors is required in order to provide the
fuller explanation useful for policy and management purposes.


title: See the Tree Through the Lines: The Shazoo Algorithm -- Full Version --

abstract:
  Predicting the nodes of a given graph is a fascinating theoretical problem
with applications in several domains. Since graph sparsification via spanning
trees retains enough information while making the task much easier, trees are
an important special case of this problem. Although it is known how to predict
the nodes of an unweighted tree in a nearly optimal way, in the weighted case a
fully satisfactory algorithm is not available yet. We fill this hole and
introduce an efficient node predictor, Shazoo, which is nearly optimal on any
weighted tree. Moreover, we show that Shazoo can be viewed as a common
nontrivial generalization of both previous approaches for unweighted trees and
weighted lines. Experiments on real-world datasets confirm that Shazoo performs
well in that it fully exploits the structure of the input tree, and gets very
close to (and sometimes better than) less scalable energy minimization methods.


title:
Conformal coupling associated with the Noether symmetry and its
  connection with the $\Lambda$CDM dynamics

abstract:
  The aim of the present work is to investigate a non-minimally coupled scalar
field model through the Noether symmetry approach, with the radiation, matter
and cosmological constant eras being analyzed. The Noether symmetry condition
allows a conformal coupling and by means of a change of coordinates in the
configuration space the field equations can be reduced to a single equation,
which is of the form of the Friedmann equation for the $\Lambda$CDM model. In
this way, it is formally shown that the dynamical system can furnish solutions
with the same form as those of the $\Lambda$CDM model, although the theory here
considered is physically different from the former. The conserved quantity
associated with the Noether symmetry can be related to the kinetic term of the
scalar field and could constrain the possible deviations of the model from the
$\Lambda$CDM picture. Observational constraints on the variation of the
gravitational constant can be imposed on the model through the initial
condition of the scalar field.


title:
Nonseparable spaceability and strong algebrability of sets of continuous
  singular functions

abstract:
  Let CBV denote the Banach algebra of all continuous real-valued functions of
bounded variation, defined in [0,1]. We show that the set of strongly singular
functions in CBV is nonseparably spaceable. We also prove that certain families
of singular functions constitute strongly c-algebrable sets. The argument is
based on a new general criterion of strong c-algebrability.


title:
Cosmological models with spinor and scalar fields by Noether symmetry
  approach

abstract:
  General cosmological models with spinor and scalar fields playing the role of
gravitational sources are analyzed. The Noether symmetry approach is taken as a
criterion to constrain the undefined potentials and couplings of the generic
actions. For all the found Noether symmetries the corresponding dynamical
systems can be analytically integrated. The obtained cosmological solutions
describe the early and late Universe as expected by basing on the known eras of
the Universe.


title: Josephson vortex coupled to a flux qubit

abstract:
  Experiments towards realizing a readout of superconducting qubits by using
ballistic Josephson vortices are reported. We measured the microwave radiation
induced by a fluxon moving in an annular Josephson junction. By coupling a flux
qubit as a current dipole to the annular junction, we detect periodic
variations of the fluxon's oscillation frequency versus magnetic flux through
the qubit. We found that the scattering of a fluxon on a current dipole can
lead to the acceleration of a fluxon regardless of a dipole polarity. We use
the perturbation theory and numerical simulations of the perturbed sine-Gordon
equation to analyze our results.


title:
Relaxation of N-body systems with additive r^-{\alpha} interparticle
  forces

abstract:
  In Newtonian gravity the final states of cold dissipationless collapses are
characterized by several structural and dynamical properties remarkably similar
to those of observed elliptical galaxies. Are these properties a peculiarity of
the Newtonian force or a more general feature of long-range forces? We study
this problem by means of $N-$body simulations of dissipationless collapse of
systems of particles interacting via additive $r^{-\alpha}$ forces. We find
that most of the results holding in Newtonian gravity are also valid for
$\alpha\neq2$. In particular the end products are triaxial and never flatter
than an E7 system, their surface density profiles are well described by the
S\'ersic law, the global density slope-anisotropy inequality is obeyed, the
differential energy distribution is an exponential over a large range of
energies (for $\alpha\geq1$), and the pseudo phase-space density is a power law
of radius. In addition, we show that the process of virialization takes longer
(in units of the system's dynamical time) for decreasing values of $\alpha$,
and becomes infinite for $\alpha=-1$ (the harmonic oscillator). This is in
agreement with the results of deep-MOND collapses (qualitatively corresponding
to $\alpha=1$) and it is due to the fact the force becomes more and more
similar to the $\alpha=-1$ case, where as well known no relaxation can happen
and the system oscillates forever.


title:
On the maximum orders of elements of finite almost simple groups and
  primitive permutation groups

abstract:
  We determine upper bounds for the maximum order of an element of a finite
almost simple group with socle T in terms of the minimum index m(T) of a
maximal subgroup of T: for T not an alternating group we prove that, with
finitely many exceptions, the maximum element order is at most m(T). Moreover,
apart from an explicit list of groups, the bound can be reduced to m(T)/4.
These results are applied to determine all primitive permutation groups on a
set of size n that contain permutations of order greater than or equal to n/4.


title: The Higgs Mass as a Signature of Heavy SUSY

abstract:
  We compute the mass of the Higgs particle in a scheme in which SUSY is broken
at a large scale M_{SS} well above the electroweak scale M_{EW}. Below M_{SS}
one assumes one is just left with the SM with a fine-tuned Higgs potential.
Under standard unification assumptions one can compute the mass of the Higgs
particle as a function of the SUSY breaking scale M_{SS}. For M_{SS} > 10^{10}
GeV one obtains m_H=126 \pm 3 GeV, consistent with CMS and ATLAS results. For
lower values of M_{SS} the values of the Higgs mass tend to those of a
fine-tuned MSSM with m_H < 130 GeV. These results support the idea that the
measured value of the Higgs mass at LHC may be considered as indirect evidence
for the existence of SUSY at some (not necessarily low) mass scale.


title: On singular equivalences of Morita type

abstract:
  Stable equivalences of Morita type preserve many interesting properties and
is proved to be the appropriate concept to study for equivalences between
stable categories. Recently the singularity category attained much attraction
and Xiao-Wu Chen and Long-Gang Sun gave an appropriate definition of singular
equivalence of Morita type. We shall show that under some conditions singular
equivalences of Morita type have some biadjoint functor properties and preserve
positive degree Hochschild homology.


title:
Lieb-Thirring type inequalities for non self-adjoint perturbations of
  magnetic Schr\"odinger operators

abstract:
  Let $H := H_{0} + V$ and $H_{\perp} := H_{0,\perp} + V$ be respectively
perturbations of the free Schr\"odinger operators $H_{0}$ on
$L^{2}\big(\mathbb{R}^{2d+1}\big)$ and $H_{0,\perp}$ on
$L^{2}\big(\mathbb{R}^{2d}\big)$, $d \geq 1$ with constant magnetic field of
strength $b>0$, and $V$ is a complex relatively compact perturbation. We prove
Lieb-Thirring type inequalities for the discrete spectrum of $H$ and
$H_{\perp}$. In particular, these estimates give $a\, priori$ information on
the distribution of the discrete eigenvalues around the Landau levels of the
operator, and describe how fast sequences of eigenvalues converge.


title:
The $\Gamma$-limit for singularly perturbed functionals of Perona-Malik
  type in arbitrary dimension

abstract:
  In this paper we generalize to arbitrary dimensions a one-dimensional
equicoerciveness and $\Gamma$-convergence result for a second derivative
perturbation of Perona-Malik type functionals. Our proof relies on a new
density result in the space of special functions of bounded variation with
vanishing diffuse gradient part. This provides a direction of investigation to
derive approximation for functionals with discontinuities penalized with a
"cohesive" energy, that is, whose cost depends on the actual opening of the
discontinuity.


title: Depth of some special monomial ideals

abstract:
  Let $I\supsetneq J$ be two squarefree monomial ideals of a polynomial algebra
over a field. Suppose that $I$ is generated by one squarefree monomial of
degree $ d>0$, and other squarefree monomials of degrees $\geq d+1$. If the
Stanley depth of $I/J$ is $\leq d+1$ then almost always the usual depth of
$I/J$ is $\leq d+1$ too.


title:
On the Existence of Frames of Some Extremal Odd Unimodular Lattices and
  Self-Dual Zk-Codes

abstract:
  For some extremal (optimal) odd unimodular lattices L in dimensions
n=12,16,20,32,36,40 and 44, we determine all positive integers k such that L
contains a k-frame. This result yields the existence of an extremal Type I
Zk-code of lengths 12,16,20,32,36,40 and 44 and a near-extremal Type I Zk-code
of length 28 for positive integers k with only a few exceptions.


title: On Existence of Regular Jacobi Structures

abstract:
  We prove $h$-principle for locally conformal symplectic foliations and
contact foliations on open manifolds. We interpret the result on $h$ principle
of contact foliations in terms of the regular Jacobi structures.


title:
Long Term Variability of O VII Line Intensity toward the Lockman Hole
  Observed with Suzaku from 2006 to 2011

abstract:
  Long-term time variabilities of the OVII (0.57 keV) emission in the soft
X-ray diffuse background were studied using six Suzaku annual observations of
blank sky towards the Lockman Hole made from 2006 to 2011. After time intervals
in which the emission was enhanced on time scales of a few tens of ks were
removed, the O VII intensity was found to be constant from 2006 to 2009 within
the 90% statistical errors. The intensity in 2010 and 2011 was higher by 2-3 LU
(photons/s/cm/sr) than the earlier values. The most plausible origin of the
fast variable component is Solar wind charge exchange (SWCX). The intensity
increase is not positively correlated with the proton flux at the L1 point.
Since all the observations were made in the same season of a year, the
variation cannot be explained by parallax of the SWCX induced X-ray emission
from the Heliosphere. We consider that it is related to the geometrical change
of slow and fast solar wind structures associated with the 11 year solar
activity. The observed variation was compared with that expected from the SWCX
induced X-ray emission model.


title: Singularity of Full Scaling Limits of Planar Nearcritical Percolation

abstract:
  We consider full scaling limits of planar nearcritical percolation in the
Quad-Crossing-Topology introduced by Schramm and Smirnov. We show that two
nearcritical scaling limits with different parameters are singular with respect
to each other. The results hold for percolation models on rather general
lattices, including bond percolation on the square lattice and site percolation
on the triangular lattice.


title:
Boundary Behavior of Subelliptic Parabolic Equations on Time-Dependent
  Domains

abstract:
  In this paper we study the boundary behavior of solutions of a
divergence-form subelliptic heat equation in a time-varying domain \Omega in
R^{n+1}, structured on a set of vector fields X = (X_1, ... X_m) with smooth
coefficients satisfying H\"ormander's finite rank condition. Assuming that
\Omega is an X-NTA domain, we first prove a Dahlberg type estimate comparing
the X-caloric measure of \Omega and the Green function of the subelliptic heat
operator. We then prove a backward Harnack inequality, the doubling property
for the X-caloric measure of \Omega, the H\"older continuity at the boundary
for quotients of solutions of H, and a Fatou theorem.


title:
"Seed+Expand": A validated methodology for creating high quality
  publication oeuvres of individual researchers

abstract:
  The study of science at the individual micro-level frequently requires the
disambiguation of author names. The creation of author's publication oeuvres
involves matching the list of unique author names to names used in publication
databases. Despite recent progress in the development of unique author
identifiers, e.g., ORCID, VIVO, or DAI, author disambiguation remains a key
problem when it comes to large-scale bibliometric analysis using data from
multiple databases. This study introduces and validates a new methodology
called seed+expand for semi-automatic bibliographic data collection for a given
set of individual authors. Specifically, we identify the oeuvre of a set of
Dutch full professors during the period 1980-2011. In particular, we combine
author records from the National Research Information System (NARCIS) with
publication records from the Web of Science. Starting with an initial list of
8,378 names, we identify "seed publications" for each author using five
different approaches. Subsequently, we "expand" the set of publication in three
different approaches. The different approaches are compared and resulting
oeuvres are evaluated on precision and recall using a "gold standard" dataset
of authors for which verified publications in the period 2001-2010 are
available.


title:
SuGra on G2 Structure Backgrounds that Asymptote to AdS4 and Holographic
  Duals of Confining 2+1d Gauge Theories with N=1 SUSY

abstract:
  In this work the solution generated by performing a U-duality on a
deformation of the Maldacena-Nastase solution is studied. This is a solution of
type-IIA with a metric that is asymptotically AdS4 and supports a G2 structure.
It is believed to be dual to a 2+1d, N=1 gauge theory similar to the baryonic
branch of Klebanov-Strassler with an additional intermediate scale. An improved
radial coordinate is used allowing the derivation of UV series solutions to the
BPS equation that persist to all orders. A study of the properties of the dual
field theory is performed which includes an operator analysis, Wilson loops and
a proposal for gauge couplings. The gauge theory dual appears to be a confining
Chern-Simons quiver with gauge couplings that become constant at high energies.


title: Random matrix ensembles: Wang-Landau algorithm for spectral densities

abstract:
  We propose a method based on the Wang-Landau algorithm to numerically
generate the spectral densities of random matrix ensembles. The method employs
Dyson's log-gas formalism for random matrix eigenvalues and also enables one to
simultaneously investigate the thermodynamic properties. This approach is a
powerful alternative to the conventionally used Monte Carlo simulations based
on the Boltzmann sampling, and is ideally suited for investigating
beta-ensembles.


title:
A perturbative model for predicting the high-Reynolds-number behaviour
  of the streamwise travelling waves technique in turbulent drag reduction

abstract:
  The background of this work is the problem of reducing the aerodynamic
turbulent friction drag, which is an important source of energy waste in
innumerable technological fields. We develop a theoretical framework aimed at
predicting the behaviour of existing drag reduction techniques when used at the
large values of Re which are typical of applications. We focus on one recently
proposed and very promising technique, which consists in creating at the wall
streamwise-travelling waves of spanwise velocity. A perturbation analysis of
the Navier-Stokes equations that govern the fluid motion is carried out, for
the simplest wall-bounded flow geometry, i.e. the plane channel flow. The
streamwise base flow is perturbed by the spanwise time-varying base flow
induced by the travelling waves. An asymptotic expansion is then carried out
with respect to the velocity amplitude of the travelling wave. The analysis,
although based on several assumptions, leads to predictions of drag reduction
that agree well with the measurements available in literature and mostly
computed through DNS of the full Navier-Stokes equations. New DNS data are
produced on purpose in this work to validate our method further. The method is
then applied to predict the drag-reducing performance of the
streamwise-travelling waves at increasing Re, where comparison data are not
available. The current belief, based on a Re-range of about one decade only
above the transitional value, that drag reduction obtained at low Re is deemed
to decrease as Re is increased is fully confirmed by our results. From a
quantitative standpoint, however, our outlook based on several decades of
increase in Re is much less pessimistic than other existing estimates, and
motivates further, more accurate studies on the present subject.


title: Rashba plasmon polaritons in semiconductor heterostructures

abstract:
  We propose a concept of surface plasmon-polariton amplification in the
structure comprising interface between dielectric, metal and asymmetric quantum
well. Due to the Rashba spin-orbit interaction, mimina of dispersion relation
for electrons in conduction band are shifted with respect to the maximum of
dispersion dependence for holes in $\Gamma$-point. When energy and momentum
intervals between extrema in dispersion relations of electrons and holes match
dispersion relation of plasmons, indirect radiative transition can amplify the
plasmons; excitation of leaky modes is forbidden due to the selection rules.
Efficiency of the indirect radiative transition is calculated and design of the
structure is analysed.


title:
Josephson junction on one edge of a two dimensional topological
  insulator affected by magnetic impurity

abstract:
  Current-phase relation in a Josephson junction formed by putting two s-wave
superconductors on the same edge of a two dimensional topological insulator is
investigated. We consider the case that the junction length is finite and
magnetic impurity exists. The similarity and difference with conventional
Josephson junction is discussed. The current is calculated in the semiconductor
picture. Both the $2\pi$- and $4\pi$-period current-phase relations
($I_{2\pi}(\phi), I_{4\pi}(\phi)$) are studied. There is a sharp jump at
$\phi=\pi$ and $\phi=2\pi$ for $I_{2\pi}$ and $I_{4\pi}$ respectively in the
clean junction. For $I_{2\pi}$, the sharp jump is robust against impurity
strength and distribution. However for $I_{4\pi}$, the impurity makes the jump
at $\phi=2\pi$ smooth. The critical (maximum) current of $I_{2\pi}$ is given
and we find it will be increased by asymmetrical distribution of impurity.


title: The Status of Glueballs

abstract:
  Calculations within QCD (lattice and sum rules) find the lightest glueball to
be a scalar and with mass in the range of about 1000-1700 MeV. Several
phenomenological investigations are discussed which aim at the identification
of the scalar meson nonets of lowest mass and the super-numerous states if any.
Results on the flavour structure of the light scalars f0(500), f0(980) and
f0(1500) are presented; the evidence for f0(1370) is scrutinized. A significant
surplus of leading clusters of neutral charge in gluon jets is found at LEP in
comparison with MCs, possibly a direct signal for glueball production; further
studies with more energetic jets at LHC are suggested. As a powerful tool in
the identification of the scalar nonets or other multiplets, along with signals
from glueballs we propose the exploration of symmetry relations for decay rates
of C=+1 heavy quark states like chi-c or chi-b. Results from chi-c decays are
discussed; they are not in support of a tetra-quark substructure of f0(980). A
minimal scenario for scalar quarkonium - glueball spectroscopy is presented.


title: Instanton Bound States in ABJM Theory

abstract:
  The partition function of the ABJM theory receives non-perturbative
corrections due to instanton effects. We study these non-perturbative
corrections, including bound states of worldsheet instantons and membrane
instantons, in the Fermi-gas approach. We require that the total
non-perturbative correction should be always finite for arbitrary Chern-Simons
level. This finiteness is realized quite non-trivially because each bound state
contribution naively diverges at some levels. The poles of each contribution
should be canceled out in total. We use this pole cancellation mechanism to
find unknown bound state corrections from known ones. We conjecture a general
expression of the bound state contribution. Summing up all the bound state
contributions, we find that the effect of bound states is simply incorporated
into the worldsheet instanton correction by a redefinition of the chemical
potential in the Fermi-gas system. Analytic expressions of the 3- and
4-membrane instanton corrections are also proposed.


title: Searching for Neutrino Radio Flashes from the Moon with LOFAR

abstract:
  Ultra-high-energy neutrinos and cosmic rays produce short radio flashes
through the Askaryan effect when they impact on the Moon. Earthbound radio
telescopes can search the Lunar surface for these signals. A new generation of
low- frequency, digital radio arrays, spearheaded by LOFAR, will allow for
searches with unprecedented sensitivity. In the first stage of the NuMoon
project, low-frequency observations were carried out with the Westerbork
Synthesis Radio Telescope, leading to the most stringent limit on the cosmic
neutrino flux above 10$^{23}$ eV. With LOFAR we will be able to reach a
sensitivity of over an order of magnitude better and to decrease the threshold
energy.


title: Maximum Fidelity

abstract:
  The most fundamental problem in statistics is the inference of an unknown
probability distribution from a finite number of samples. For a specific
observed data set, answers to the following questions would be desirable: (1)
Estimation: Which candidate distribution provides the best fit to the observed
data?, (2) Goodness-of-fit: How concordant is this distribution with the
observed data?, and (3) Uncertainty: How concordant are other candidate
distributions with the observed data? A simple unified approach for univariate
data that addresses these traditionally distinct statistical notions is
presented called "maximum fidelity". Maximum fidelity is a strict frequentist
approach that is fundamentally based on model concordance with the observed
data. The fidelity statistic is a general information measure based on the
coordinate-independent cumulative distribution and critical yet previously
neglected symmetry considerations. An approximation for the null distribution
of the fidelity allows its direct conversion to absolute model concordance (p
value). Fidelity maximization allows identification of the most concordant
model distribution, generating a method for parameter estimation, with
neighboring, less concordant distributions providing the "uncertainty" in this
estimate. Maximum fidelity provides an optimal approach for parameter
estimation (superior to maximum likelihood) and a generally optimal approach
for goodness-of-fit assessment of arbitrary models applied to univariate data.
Extensions to binary data, binned data, multidimensional data, and classical
parametric and nonparametric statistical tests are described. Maximum fidelity
provides a philosophically consistent, robust, and seemingly optimal foundation
for statistical inference. All findings are presented in an elementary way to
be immediately accessible to all researchers utilizing statistical analysis.


title: Which is faster: Bowtie2GP > Bowtie > Bowtie2 > BWA

abstract:
  We have recently used genetic programming to automatically generate an
improved version of Langmead's DNA read alignment tool Bowtie2 Sect.5.3
RN/12/09. We find it runs more than four times faster than the Bioinformatics
sequencing tool (BWA) currently used with short next generation paired end DNA
sequences by the Cancer Institute, takes less memory and yet finds similar
matches in the human genome.


title: A Supersonic Ping Pong Gun

abstract:
  The Ping Pong gun or Ping Pong bazooka has been a popular and compelling tool
for physics education. However, the design necessarily means the ball emerges
at subsonic speed. The design has been modified to include a pressure chamber
and a convergent-divergent nozzle, similar to the design of some supersonic
wind tunnels. This modification results in supersonic speeds. The current
design has achieved a launch speed of 406 m/sec, about Mach 1.23.


title: Structure of neutron stars in R-squared gravity

abstract:
  The effects implied for the structure of compact objects by the modification
of General Relativity produced by the generalization of the Lagrangian density
to the form f(R)=R+\alpha R^2, where R is the Ricci curvature scalar, have been
recently explored. It seems likely that this squared-gravity may allow heavier
Neutron Stars (NSs) than GR. In addition, these objects can be useful to
constrain free parameters of modified-gravity theories. The differences between
alternative gravity theories is enhanced in the strong gravitational regime. In
this regime, because of the complexity of the field equations, perturbative
methods become a good choice to treat the problem. Following previous works in
the field, we performed a numerical integration of the structure equations that
describe NSs in f(R)-gravity, recovering their mass-radius relations, but
focusing on particular features that arise from this approach in the profiles
of the NS interior.
  We show that these profiles run in correlation with the second-order
derivative of the analytic approximation to the Equation of State (EoS), which
leads to regions where the enclosed mass decreases with the radius in a
counter-intuitive way. We reproduce all computations with a simple polytropic
EoS to separate zeroth-order modified gravity effects.


title: Toroidal Seifert fibered surgeries on alternating knots

abstract:
  We give a complete classification of toroidal Seifert fibered surgeries on
alternating knots. Precisely, we show that if an alternating knot admits a
toroidal Seifert fibered surgery, then the knot is either the trefoil knot and
the surgery slope is zero, or the connected sum of a (2,p)-torus knot and a
(2,q)-torus knot and the surgery slope is 2(p+q) with |p|, |q| at least three.


title: Evolution of single-particle states beyond $^{132}$Sn

abstract:
  We have performed shell-model calculations for the two one valence-neutron
isotones $^{135}$Te and $^{137}$Xe and the two one valence-proton isotopes
$^{135,137}$Sb. The main aim of our study has been to investigate the evolution
of single-particle states with increasing nucleon number. To this end, we have
focused attention on the spectroscopic factors and the effective
single-particle energies. In our calculations, we have employed a realistic
low-momentum two-body effective interaction derived from the CD-Bonn
nucleon-nucleon potential that has already proved quite successful in
describing the spectroscopic properties of nuclei in the $^{132}$Sn region.
Comparison shows that our results reproduce very well the available
experimental data. This gives confidence in the evolution of the
single-particle states 4 figures predicted by the present study.


title: Spectral instability of some non-selfadjoint anharmonic oscillators

abstract:
  The purpose of this Note is to highlight the spectral instability of some
non-selfadjoint differential operators, by studying the growth rate of the
norms of the spectral projections $\Pi_n$ associated with their eigenvalues.
More precisely, we are concerned with the complex Airy operator and even
anharmonic oscillator. We get asymptotic expansions for the norm of the
spectral projections associated with the large eigenvalues, extending the
results of Davies and Davies-Kuijlaars.


title:
Unproceedings of the Fourth .Astronomy Conference (.Astronomy 4),
  Heidelberg, Germany, July 9-11 2012

abstract:
  The goal of the .Astronomy conference series is to bring together
astronomers, educators, developers and others interested in using the Internet
as a medium for astronomy. Attendance at the event is limited to approximately
50 participants, and days are split into mornings of scheduled talks, followed
by 'unconference' afternoons, where sessions are defined by participants during
the course of the event. Participants in unconference sessions are discouraged
from formal presentations, with discussion, workshop-style formats or informal
practical tutorials encouraged. The conference also designates one day as a
'hack day', in which attendees collaborate in groups on day-long projects for
presentation the following morning. These hacks are often a way of
concentrating effort, learning new skills, and exploring ideas in a practical
fashion. The emphasis on informal, focused interaction makes recording
proceedings more difficult than for a normal meeting. While the first
.Astronomy conference is preserved formally in a book, more recent iterations
are not documented. We therefore, in the spirit of .Astronomy, report
'unproceedings' from .Astronomy 4, which was held in Heidelberg in July 2012.


title: Duality rotations in supersymmetric nonlinear electrodynamics revisited

abstract:
  We revisit the U(1) duality-invariant nonlinear models for N=1 and N=2 vector
multiplets coupled to off-shell supergravities. For such theories we develop
new formulations which make use of auxiliary chiral superfields (spinor in the
N=1 case and scalar for N=2) and are characterized by the remarkable property
that U(1) duality invariance is equivalent to the manifest U(1) invariance of
the self-interaction. Our construction is inspired by the non-supersymmetric
approach that was proposed by Ivanov and Zupnik a decade ago and recently
re-discovered in the form of twisted self-duality.


title:
Hemispherical power asymmetries in the WMAP 7-year low-resolution
  temperature and polarization maps

abstract:
  We test the hemispherical power asymmetry of the WMAP 7-year low-resolution
temperature and polarization maps. We consider two natural estimators for such
an asymmetry and exploit our implementation of an optimal angular power
spectrum estimator for all the six CMB spectra. By scanning the whole sky
through a sample of 24 directions, we search for asymmetries in the power
spectra of the two hemispheres, comparing the results with Monte Carlo
simulations drawn from the WMAP 7-year best-fit model. Our analysis extends
previous results to the polarization sector. The level of asymmetry on the ILC
temperature map is found to be compatible with previous results, whereas no
significant asymmetry on the polarized spectra is detected. Moreover, we show
that our results are only weakly affected by the a posteriori choice of the
maximum multipole considered for the analysis. We also forecast the capability
to detect dipole modulation by our methodology at Planck sensitivity.


title:
Revisiting the angular momentum growth of protostructures evolved from
  non-Gaussian initial conditions

abstract:
  I adopt a formalism previously developed by Catelan and Theuns (CT) in order
to estimate the impact of primordial non-Gaussianity on the quasi-linear spin
growth of cold dark matter protostructures. A variety of bispectrum shapes are
considered, spanning the currently most popular early Universe models for the
occurrence of non-Gaussian density fluctuations. In their original work, CT
considered several other shapes, and suggested that only for one of those does
the impact of non-Gaussianity seem to be perturbatively tractable. For that
model, and on galactic scales, the next-to-linear non-Gaussian contribution to
the angular momentum variance has an upper limit of $\sim 10%$ with respect to
the linear one. I find that all the new models considered in this work can also
be seemingly described via perturbation theory. Considering current bounds on
$f_\mathrm{NL}$ for inflationary non-Gaussianity leads to the quasi-linear
contribution being $\sim 10-20%$ of the linear one. This result motivates the
systematic study of higher-order non-Gaussian corrections, in order to attain a
comprehensive picture of how structure gravitational dynamics descends from the
physics of the primordial Universe.


title: From Two-Way to One-Way Finite State Transducers

abstract:
  Any two-way finite state automaton is equivalent to some one-way finite state
automaton. This well-known result, shown by Rabin and Scott and independently
by Shepherdson, states that two-way finite state automata (even
non-deterministic) characterize the class of regular languages. It is also
known that this result does not extend to finite string transductions:
(deterministic) two-way finite state transducers strictly extend the expressive
power of (functional) one-way transducers. In particular deterministic two-way
transducers capture exactly the class of MSO-transductions of finite strings.
In this paper, we address the following definability problem: given a function
defined by a two-way finite state transducer, is it definable by a one-way
finite state transducer? By extending Rabin and Scott's proof to transductions,
we show that this problem is decidable. Our procedure builds a one-way
transducer, which is equivalent to the two-way transducer, whenever one exists.


title: Multiwavelength observations of TANAMI sources

abstract:
  The TANAMI VLBI program is monitoring a sample of 84 Active Galactic Nuclei
of the Southern Sky at 8.4 and 22 GHz. The combination of VLBI and
multiwavelength data allows us to study changes in the spectral energy
distributions, as well as changes in the structure of the inner jets and to
search correlations between both. We present initial results of the
multiwavelength analysis of a sub-sample of the TANAMI sources, combining our
radio data with simultaneous X-ray and optical/UV observations from Swift and
XMM-Newton, and gamma-ray data from Fermi, focusing on the broadband spectral
energy distributions as well as variability in different wavebands.


title:
Coarse-graining complex dynamics: Continuous Time Random Walks vs.
  Record Dynamics

abstract:
  Continuous Time Random Walks (CTRW) are widely used to coarse-grain the
evolution of systems jumping from a metastable sub-set of their configuration
space, or trap, to another via rare intermittent events. The multi-scaled
behavior typical of complex dynamics is provided by a fat-tailed distribution
of the waiting time between consecutive jumps. We first argue that CTRW are
inadequate to describe macroscopic relaxation processes for three reasons:
macroscopic variables are not self-averaging, memory effects require an
all-knowing observer,and different mechanisms whereby the jumps affect
macroscopic variables all produce identical long time relaxation behaviors.
Hence, CTRW shed no light on the link between microscopic and macroscopic
dynamics. We then highlight how a more recent approach, Record Dynamics (RD)
provides a viable alternative, based on a very different set of physical ideas:
while CTRW make use of a renewal process involving identical traps of infinite
size, RD embodies a dynamical entrenchment into a hierarchy of traps which are
finite in size and possess different degrees of meta-stability. We show in
particular how RD produces the stretched exponential, power-law and logarithmic
relaxation behaviors ubiquitous in complex dynamics, together with the
sub-diffusive time dependence of the Mean Square Displacement characteristic of
single particles moving in a complex environment.


title:
The puzzling merging cluster Abell 1914: new insights from the
  kinematics of member galaxies

abstract:
  We analyze the dynamical state of Abell 1914, a merging cluster hosting a
radio halo, quite unusual for its structure. Our study considers spectroscopic
data for 119 galaxies obtained with the Italian Telescopio Nazionale Galileo.
We select 89 cluster members from spatial and velocity distributions. We also
use photometry Canada-France-Hawaii Telescope archives. We compute the mean
cluster redshift, <z>=0.168, and the velocity dispersion which shows a high
value, sigma_v=1210_{-110}^{+125} km/s. From the 2D analysis we find that Abell
1914 has a NE-SW elongated structure with two galaxy clumps, that mostly merge
in the plane of the sky. Our best, but very uncertain estimate of the velocity
dispersion of the main system is sigma_v~1000 km/s. We estimate a virial mass
M_sys=1.4--2.6 10^{15} h_{70}^{-1} Msun for the whole system. We study the
merger through a simple two-body model and find that data are consistent with a
bound, outgoing substructure observed just after the core crossing. By studying
the 2D distribution of the red galaxies, photometrically selected, we show that
Abell 1914 is contained in a rich large scale structure, with two close
companion galaxy systems, known to be at z~0.17. The system at SW supports the
idea that the cluster is accreting groups from a filament aligned in the NE-SW
direction, while that at NW suggests a second direction of the accretion NW-SE.
We conclude that Abell 1914 well fits among typical clusters with radio halos.
We argue that the unusual radio emission is connected to the complex cluster
accretion and suggest that Abell 1914 resembles the well-known nearby merging
cluster Abell 754 for its particular observed phenomenology.


title:
Models of Social Groups in Blogosphere Based on Information about
  Comment Addressees and Sentiments

abstract:
  This work concerns the analysis of number, sizes and other characteristics of
groups identified in the blogosphere using a set of models identifying social
relations. These models differ regarding identification of social relations,
influenced by methods of classifying the addressee of the comments (they are
either the post author or the author of a comment on which this comment is
directly addressing) and by a sentiment calculated for comments considering the
statistics of words present and connotation. The state of a selected blog
portal was analyzed in sequential, partly overlapping time intervals. Groups in
each interval were identified using a version of the CPM algorithm, on the
basis of them, stable groups, existing for at least a minimal assumed duration
of time, were identified.


title:
A scientific case for future X-ray Astronomy: Galaxy Clusters at high
  redshifts

abstract:
  Clusters of galaxies at high redshift (z>1) are vitally important to
understand the evolution of the large scale structure of the Universe, the
processes shaping galaxy populations and the cycle of the cosmic baryons, and
to constrain cosmological parameters. After 13 years of operation of the
Chandra and XMM-Newton satellites, the discovery and characterization of
distant X-ray clusters is proceeding at a slow pace, due to the low solid angle
covered so far, and the time-expensive observations needed to physically
characterize their intracluster medium (ICM). At present, we know that at z>1
many massive clusters are fully virialized, their ICM is already enriched with
metals, strong cool cores are already in place, and significant star formation
is ongoing in their most massive galaxies, at least at z>1.4. Clearly, the
assembly of a large and well characterized sample of high-z X-ray clusters is a
major goal for the future. We argue that the only means to achieve this is a
survey-optimized X-ray mission capable of offering large solid angle, high
sensitivity, good spectral coverage, low background and angular resolution as
good as 5 arcsec.


title: GRB 080407: an ultra-long burst discovered by the IPN

abstract:
  We present observations of the extremely long GRB 080704 obtained with the
instruments of the Interplanetary Network (IPN). The observations reveal two
distinct emission episodes, separated by a ~1500 s long period of quiescence.
The total burst duration is about 2100 s. We compare the temporal and spectral
characteristics of this burst with those obtained for other ultra-long GRBs and
discuss these characteristics in the context of different models.


title: Radiative decays of charmonia on the lattice

abstract:
  We present the results of our lattice QCD study of the hadronic matrix
elements relevant to the physical radiative J/psi -> eta_c gamma and hc ->
eta_c gamma decays. From computations with Nf=2 dynamical quark in twisted mass
QCD at four lattice spacings, we were able to take the continuum limit and
obtained Gamma(J/psi -> eta_c gamma) = 2.64(11) keV and Gamma(hc -> eta_c
gamma) = 0.72(5) MeV. We also computed the the hyperfine splitting and found
that it does not depend from the sea quark mass and we obtain Delta = m_J/psi -
m_eta_c = 112(4) MeV.


title: Higher derivative effects for 4d AdS gravity

abstract:
  Motivated by holography, we explore higher derivative corrections to
four-dimensional Anti-de Sitter (AdS) gravity. We point out that in such a
theory the variational problem is generically not well-posed given only a
boundary condition for the metric. However, when one evaluates the higher
derivative terms perturbatively on a leading order Einstein solution, the
equations of motion are always second order and therefore the variational
problem indeed requires only a boundary condition for the metric. The equations
of motion required to compute the spectrum around the corrected background are
still generically higher order, with the additional boundary conditions being
associated with new operators in the dual conformal field theory. We discuss
which higher derivative curvature invariants are expected to arise in the
four-dimensional action from a top-down perspective and compute the corrections
to planar AdS black holes and to the spectrum around AdS in various cases.
Requiring that the dual theory is unitary strongly constrains the higher
derivative terms in the action, as the operators associated with the extra
boundary conditions generically have complex conformal dimensions and
non-positive norms.


title:
Exact model categories, approximation theory, and cohomology of
  quasi-coherent sheaves

abstract:
  Our aim is to give a fairly complete account on the construction of
compatible model structures on exact categories and symmetric monoidal exact
categories, in some cases generalizing previously known results. We describe
the close connection of this theory to approximation theory and cotorsion
pairs. We also discuss the motivating applications with the emphasis on
constructing monoidal model structures for the derived category of
quasi-coherent sheaves of modules over a scheme.


title: On the rational Picard group of the moduli space of higher spin curves

abstract:
  We refine the notion of higher spin curves defined in terms of line bundles
by Caporaso, Cornalba and Casagrande by adding the data of coherent nets of
roots introduced by Jarvis in terms of torsion-free sheaves and we describe the
boundary part of their moduli space. We provide then a presentation of the
rational Picard group of this moduli space.


title:
Different roles of Zn$^{2+}$ and Li$^{+}$ impurities in the CuO$_2$
  plane in undoped cuprate compounds

abstract:
  A planar Mott insulator with easy plane N\'eel order can be mapped onto a
Gutzwiller-projected spin Hall state. The in-plane substitution of Zn$^{2+}$
and Li$^{+}$ for Cu$^{2+}$ brings zero modes around the spin vacancy. The
Gutzwiller projection precludes single particle excitations, however, preserves
the zero modes which have a local spin moment for Zn$^{2+}$ and a local charged
hole for Li$^{+}$, respectively. While the local spin moment for Zn$^{2+}$ is
screened by the long-range spin correlations, the active charge degree of
freedom for Li$^{+}$ impurity twists the spin background with long ranged
disturbances. This proposal explains the very different roles of the Zn$^{2+}$
and Li$^{+}$ impurities on the magnetic perturbations in the CuO$_2$ plane in
the undoped cuprate compounds.


title:
The Regularity problem for second order elliptic operators with
  complex-valued bounded measurable coefficients

abstract:
  The present paper establishes a certain duality between the Dirichlet and
Regularity problems for elliptic operators with $t$-independent complex bounded
measurable coefficients ($t$ being the transversal direction to the boundary).
To be precise, we show that the Dirichlet boundary value problem is solvable in
$L^{p'}$, subject to the square function and non-tangential maximal function
estimates, if and only if the corresponding Regularity problem is solvable in
$L^p$. Moreover, the solutions admit layer potential representations.
  In particular, we prove that for any elliptic operator with $t$-independent
real (possibly non-symmetric) coefficients there exists a $p>1$ such that the
Regularity problem is well-posed in $L^p$.


title:
Studying the Interplay of Strong and Electromagnetic Forces in Heavy Ion
  Collisions with NICA

abstract:
  In the following we stress the advantages of the NICA research programme in
the context of studying the spectator-induced electromagnetic phenomena present
in proton-nucleus and heavy ion collisions. We point at the specific interest
of using these phenomena as a new, independent source of information on the
space-time evolution of the reaction and of the non-perturbative process of
particle production. We propose an extended series of measurements of
well-defined observables to be performed in different types of nuclear
reactions and in the whole range of collision energies available to NICA. We
expect these measurements to bring very valuable new insight into the mechanism
of non-perturbative strong interactions, complementary to the studies made at
the SPS at CERN, RHIC at BNL, and the LHC.


title: Two questions on polynomial decomposition

abstract:
  Given a univariate polynomial f(x) over a ring R, we examine when we can
write f(x) as g(h(x)) where g and h are polynomials of degree at least 2. We
answer two questions of Gusic regarding when the existence of such g and h over
an extension of R implies the existence of such g and h over R. We also pose
two new questions along these lines.


title: Skeletons and superscars

abstract:
  Semiclassical wave functions in billiards based on the Maslov-Fedoriuk
approach are constructed. They are defined on classical constructions called
skeletons which are the billiards generalization of the Arnold tori. Skeletons
in the rational polygon billiards considered in the phase space can be closed
with a definite genus or can be open being a cylinder-like or Moebius-like
bands. The skeleton formulation is applied to calculate semiclassical wave
functions and the corresponding energy spectra for the integrable and
pseudointegrable billiards as well as in the limiting forms in some cases of
chaotic ones. The superscars of Bogomolny and Schmit are shown to be simply
singular semiclassical solutions of the eigenvalue problem in the billiards
well built on the singular skeletons in the billiards with flat boundaries in
both the integrable and the pseudointegrable billiards as well as in the
chaotic cases of such billiards.


title:
Vortex dynamics for the two dimensional non homogeneous Gross-Pitaevskii
  equation

abstract:
  We derive the asymptotical dynamical law for Ginzburg-Landau vortices in an
inhomogeneous background density under the Schr\"odinger dynamics, when the
Ginzburg-Landau parameter goes to zero. New ingredients involve across the
cores lower bound estimates and approximations.


title:
Effect of partial ionization on wave propagation in solar magnetic flux
  tubes

abstract:
  Observations show that waves are ubiquitous in the solar atmosphere and may
play an important role for plasma heating. The study of waves in the solar
corona is usually based on linear ideal magnetohydrodynamics (MHD) for a fully
ionized plasma. However, the plasma in the photosphere and the chromosphere is
only partially ionized. Here we investigate theoretically the impact of partial
ionization on MHD wave propagation in cylindrical flux tubes in the two-fluid
model. We derive the general dispersion relation that takes into account the
effects of neutral-ion collisions and the neutral gas pressure. We take the
neutral-ion collision frequency as an arbitrary parameter. Particular results
for transverse kink modes and slow magnetoacoustic modes are shown. We find
that the wave frequencies only depend on the properties of the ionized fluid
when the neutral-ion collision frequency is much lower that the wave frequency.
For high collision frequencies realistic of the solar atmosphere ions and
neutrals behave as a single fluid with an effective density corresponding to
the sum of densities of both fluids and an effective sound velocity computed as
the average of the sound velocities of ions and neutrals. The MHD wave
frequencies are modified accordingly. The neutral gas pressure can be neglected
when studying transverse kink waves but it has to be taken into account for a
consistent description of slow magnetoacoustic waves. The MHD waves are damped
due to neutral-ion collisions. The damping is most efficient when the wave
frequency and the collision frequency are of the same order of magnitude. For
high collision frequencies slow magnetoacoustic waves are more efficiently
damped than transverse kink waves. In addition, we find the presence of
cut-offs for certain combinations of parameters that cause the waves to become
non-propagating.


title:
Mapping spin coherence of a single rare-earth ion in a crystal onto a
  single photon polarization state

abstract:
  We report on optical detection of a single photostable Ce3+ ion in an yttrium
aluminium garnet (YAG) crystal and on its magneto-optical properties at room
temperature. The quantum state of an electron spin of the emitting level of
cerium ion in YAG can be initialized by circularly polarized laser pulse.
Furthermore, its quantum state can be read out by observing temporal behaviour
of circularly polarized fluorescence of the ion. This implies direct mapping of
the spin quantum state of Ce3+ ion onto the polarization state of the emitted
photon and represents one-way quantum interface between a single spin and a
single photon.


title: Improved Hardness of Approximating Chromatic Number

abstract:
  We prove that for sufficiently large K, it is NP-hard to color K-colorable
graphs with less than 2^{K^{1/3}} colors. This improves the previous result of
K versus K^{O(log K)} in Khot [14].


title:
The decays of on-shell and off-shell polarized gauge bosons into massive
  quark pairs at NLO QCD

abstract:
  We discuss the polar angle decay distribution in the decay of on-shell and
off-shell polarized (W,Z) gauge bosons into massive quark pairs. In particular
for the off-shell decays in $H \to (W,Z) + (W^\ast,Z^\ast) (\to q_1\bar q_2)$
it is important to keep the masses of the charm and bottom quarks at their
finite values since the scale of the problem is not set by $m_{W,Z}^2$ but by
the off-shellness of the gauge boson which varies in the range $(m_1+m_2)^2 \le
q^2 \le (m_H-m_{W,Z})^2$.


title:
Many-body problem in Kaluza-Klein models: theory and observational
  consequences

abstract:
  We consider a system of gravitating bodies in Kaluza-Klein models with
toroidal compactification of extra dimensions. To simulate the astrophysical
objects (e.g., our Sun and pulsars) with the energy density much greater than
the pressure, we suppose that these bodies are pressureless in the external/our
space. At the same time, they may have nonzero parameters \omega_{(\bar\alpha
-3)} \, (\bar\alpha =4,...,D) of the equations of state in the extra
dimensions. We construct the Lagrange function of this many-body system for any
value of \Sigma =\sum_{\bar\alpha} \omega_{(\bar\alpha -3)}. Moreover, the
gravitational tests (PPN parameters, perihelion/periastron advance) require
negligible deviation from the latent soliton value \Sigma =-(D-3)/2. However,
the presence of pressure/tension in the internal space results necessarily in
the smearing of the gravitating masses over the internal space and in the
absence of the KK modes. This looks very unnatural from the point of quantum
physics.


title: The two-dimensional 4-state Potts model in a magnetic field

abstract:
  We present a solution of the non-linear renormalization group equations
leading to the dominant and subdominant singular behaviours of physical
quantities (free energy density, correlation length, internal energy, specific
heat, magnetization, susceptibility and magnetocaloric coefficient) at the
critical temperature in a non- vanishing magnetic field. The solutions i) lead
to exact cancellation of logarithmic corrections in universal amplitude ratios
and ii) prove recently proposed relations among logarithmic exponents.


title: Properties of the Least Squares Temporal Difference learning algorithm

abstract:
  This paper presents four different ways of looking at the well-known Least
Squares Temporal Differences (LSTD) algorithm for computing the value function
of a Markov Reward Process, each of them leading to different insights: the
operator-theory approach via the Galerkin method, the statistical approach via
instrumental variables, the linear dynamical system view as well as the limit
of the TD iteration. We also give a geometric view of the algorithm as an
oblique projection. Furthermore, there is an extensive comparison of the
optimization problem solved by LSTD as compared to Bellman Residual
Minimization (BRM). We then review several schemes for the regularization of
the LSTD solution. We then proceed to treat the modification of LSTD for the
case of episodic Markov Reward Processes.


title: Motives of graph hypersurfaces with torus operations

abstract:
  We investigate graph hypersurfaces and study conditions under which graph
hypersurfaces admit algebraic torus operations. This leads in principle to a
computation of graph motives using the theorem of Bialynicki-Birula, provided
one knows the fixed point loci in a resolution of singularities.


title:
Bifurcations and Competing Coherent Structures in the Cubic-Quintic
  Ginzburg-Landau Equation I: Plane Wave (CW) Solutions

abstract:
  Singularity Theory is used to comprehensively investigate the bifurcations of
the steady-states of the traveling wave ODEs of the cubic-quintic
Ginzburg-Landau equation (CGLE). These correspond to plane waves of the PDE. In
addition to the most general situation, we also derive the degeneracy
conditions on the eight coefficients of the CGLE under which the equation for
the steady states assumes each of the possible quartic (the quartic fold and an
unnamed form), cubic (the pitchfork and the winged cusp), and quadratic (four
possible cases) normal forms for singularities of codimension up to three.
Since the actual governing equations are employed, all results are globally
valid, and not just of local applicability. In each case, the recognition
problem for the unfolded singularity is treated. The transition varieties, i.e.
the hysteresis, isola, and double limit curves are presented for each normal
form. For both the most general case, as well as for various combinations of
coefficients relevant to the particular cases, the bifurcations curves are
mapped out in the various regions of parameter space delimited by these
varieties. The multiplicities and interactions of the plane wave solutions are
then comprehensively deduced from the bifurcation plots in each regime, and
include features such as regimes of hysteresis among co-existing states,
domains featuring more than one interval of hysteresis, and isola behavior
featuring dynamics unrelated to the primary solution branch in limited ranges
of parameter space.


title: Aerodynamic Stability of Satellites in Elliptic Low Earth Orbits

abstract:
  Topical observations of the thermosphere at altitudes below $200 \, km$ are
of great benefit in advancing the understanding of the global distribution of
mass, composition, and dynamical responses to geomagnetic forcing, and momentum
transfer via waves. The perceived risks associated with such low altitude and
short duration orbits has prohibited the launch of Discovery-class missions.
Miniaturization of instruments such as mass spectrometers and advances in the
nano-satellite technology, associated with relatively low cost of
nano-satellite manufacturing and operation, open an avenue for performing low
altitude missions. The time dependent coefficients of a second order
non-homogeneous ODE which describes the motion have a double periodic shape.
Hence, they will be approximated using Jacobi elliptic functions. Through a
change of variables the original ODE will be converted into Hill's ODE for
stability analysis using Floquet theory. We are interested in how changes in
the coefficients of the ODE affect the stability of the solution. The expected
result will be an allowable range of parameters for which the motion is
dynamically stable. A possible extension of the application is a computational
tool for the rapid evaluation of the stability of entry or re-entry vehicles in
rarefied flow regimes and of satellites flying in relatively low orbits.


title:
A Laboratory Search for a Long-Range T-odd, P-odd Interaction from
  Axion-Like Particles using Dual Species Nuclear Magnetic Resonance with
  Polarized Xe-129 and Xe-131 Gas

abstract:
  We place new limits on potential T- and P- violating monopole-dipole
interactions between unpolarized nucleons and neutrons using dual species
magnetic resonance in polarzed Xe gas. Free-induction decay transients with
relaxation times ~20 s allow high precision measurements of the NMR
frequencies, whose ratios cancel magnetic fluctuations. The new limits on the
product gsgp improve on previous laboratory work by 2 orders of magnitude.


title:
Shell-model half-lives for r-process waiting point nuclei including
  first-forbidden contributions

abstract:
  We have performed large-scale shell-model calculations of the half-lives and
neutron-branching probabilities of the r-process waiting point nuclei at the
magic neutron numbers N=50, 82, and 126. The calculations include contributions
from allowed Gamow-Teller and first-forbidden transitions. We find good
agreement with the measured half-lives for the N=50 nuclei with charge numbers
Z=28-32 and for the N=82 nuclei 129Ag and 130Cd. The contribution of forbidden
transitions reduce the half-lives of the N=126 waiting point nuclei
significantly, while they have only a small effect on the half-lives of the
N=50 and 82 r-process nuclei.


title:
Feedback-induced stationary localized patterns in networks of
  diffusively coupled bistable elements

abstract:
  Effects of feedbacks on self-organization phenomena in networks of
diffusively coupled bistable elements are investigated. For regular trees, an
approximate analytical theory for localized stationary patterns under
application of global feedbacks is constructed. Using it, properties of such
patterns in different parts of the parameter space are discussed. Numerical
investigations are performed for large random Erd\"os-R\'enyi and scale-free
networks. In both kinds of systems, localized stationary activation patterns
have been observed. The active nodes in such a pattern form a subnetwork, whose
size decreases as the feedback intensity is increased. For strong feedbacks,
active subnetworks are organized as trees. Additionally, local feedbacks
affecting only the nodes with high degrees (i.e. hubs) or the periphery nodes
are considered.


title:
Solving and refining novel thin film phases using Cu X-ray radiation:
  the epitaxy-induced CuMnAs tetragonal phase

abstract:
  We present a combined experimental and computational method which enables the
precise determination of the atomic positions in a thin film using CuK{\alpha}
radiation, only. The capabilities of this technique surpass simple structure
refinement and allow solving unknown phases stabilized by substrate-induced
stress. We derive the appropriate corrections to transform the measured
integrated intensities into structure factors. Data collection was performed
entirely on routinely available laboratory diffractometers (CuK{\alpha}
radiation); the subsequent analysis was carried out by single-crystal direct
methods ({\delta} recycling procedure) followed by the least-squares refinement
of the structural parameters of the unit cell content. We selected an epitaxial
thin film of CuMnAs grown on top of a GaAs substrate, which formed a crystal
structure with tetragonal symmetry, differing from the bulk material which is
orthorhombic. Here we demonstrate the new tetragonal form of epitaxial CuMnAs
grown on GaAs substrate and present consistent high-resolution scanning
transmission electron microscopy and stoichiometry analyses.


title:
Analytic classification of families of linear differential systems
  unfolding a resonant irregular singularity

abstract:
  We give a complete classification of analytic equivalence of germs of
parametric families of systems of complex linear differential equations
unfolding a generic resonant singularity of Poincare rank 1 in dimension $n =
2$ whose leading matrix is a Jordan bloc. The moduli space of analytic
equivalence classes is described in terms of a tuple of formal invariants and a
single analytic invariant obtained from the trace of monodromy, and analytic
normal forms are given. We also explain the underlying phenomena of confluence
of two simple singularities and of a turning point, the associated Stokes
geometry, and the change of order of Borel summability of formal solutions in
dependence on a complex parameter.


title: Majorization relations and entanglement generation in a beam splitter

abstract:
  We prove that a beam splitter, one of the most common optical components,
fulfills several classes of majorization relations, which govern the amount of
quantum entanglement that it can generate. First, we show that the state
resulting from k photons impinging on a beam splitter majorizes the
corresponding state with any larger photon number k'>k, implying that the
entanglement monotonically grows with k. Then, we examine parametric
infinitesimal majorization relations as a function of the beam-splitter
transmittance, and find that there exists a parameter region where majorization
is again fulfilled, implying a monotonic increase of entanglement by moving
towards a balanced beam splitter. We also identify regions with a majorization
default, where the output states become incomparable. In this latter situation,
we find examples where catalysis may nevertheless be used in order to recover
majorization. The catalyst states can be as simple as a path-entangled
single-photon state or a two-mode vacuum squeezed state.


title:
Disentangling the entangled: Observations and analysis of the triple
  non-coeval protostellar system VLA1623

abstract:
  Commonplace at every evolutionary stage, Multiple Protostellar Systems (MPSs)
are thought to be formed through fragmentation, but it is unclear when and how.
The youngest MPSs, which have not yet undergone much evolution, provide
important constraints to this question. It is then of interest to disentangle
early stage MPSs. In this letter we present the results of our work on VLA1623
using our observations and archival data from the Submillimeter Array (SMA).
Our continuum and line observations trace VLA1623's components, outflow and
envelope, revealing unexpected characteristics. We construct the SED for each
component using the results of our work and data from literature, as well as
derive physical parameters from continuum and perform a simple kinematical
analysis of the circumstellar material. Our results show VLA1623 to be a triple
non-coeval system composed of VLA1623A, B & W, with each source driving its own
outflow and unevenly distributed circumstellar material. From the SED, physical
parameters and IR emission we conclude that VLA1623A & W are Class 0 and I
protostars, respectively, and together drive the bulk of the observed outflow.
Furthermore, we find two surprising results, first the presence of a rotating
disk-like structure about VLA1623A with indications of pure Keplerian rotation,
which, if real, would make it one of the first evidence of Keplerian disk
structures around Class 0 protostars. Second, we find VLA1623B to be a bonafide
extremely young protostellar object between the starless core and Class 0
stages.


title: The quasi-Poisson Goldman formula

abstract:
  We prove a quasi-Poisson bracket formula for the space of representations of
the fundamental groupoid of a surface with boundary, which generalizes
Goldman's Poisson bracket formula. We also deduce a similar formula for
quasi-Poisson cross-sections.


title:
Post-Newtonian expansion of a rigidly rotating disc of dust with a
  constant specific charge

abstract:
  We present an algorithm for obtaining the post-Newtonian expansion of the
asymptotically flat solution to the Einstein-Maxwell equations describing a
rigidly rotating disc of dust with a constant specific charge. Explicit
analytic expressions are calculated up to the eighth order. The results are
used for a physical discussion of the extreme relativistic limiting cases. We
identify strong evidence for a transition to an extreme Kerr-Newman black hole.


title: Galactic Disc Rotation: Analytic models and asymptotic results

abstract:
  This paper outlines an exact analytic model for self-gravitating thin disc
galaxies with flat rotation curves. It is shown that thin discs of matter alone
can support perfectly flat rotation curves under Newtonian gravity, without
needing extended halos or modified gravity. The method allows disc density to
be inferred from polynomial approximations to the rotation curve. Several
expository models are presented. The model also shows the link between flat
rotation curves and "exponential" discs. It is also shown that reconstructed
discs inherently posses vast mass "hinterlands" in their outer regions, that
can contain the majority of their total mass. Some implications for the problem
of missing mass are discussed.


title:
Some dual conditions for global weak sharp minimality of nonconvex
  functions

abstract:
  Weak sharp minimality is a notion emerged in optimization, whose utility is
largeley recognized in the convergence analysis of algorithms for solving
extremum problems as well as in the study of the perturbation behaviour of such
problems. In the present paper some dual constructions of nonsmooth analysis,
mainly related to quasidifferential calculus and its recent developments, are
employed in formulating sufficient conditions for global weak sharp minimality.
They extend to nonconvex functions a condition, which is known to be valid in
the convex case. A feature distinguishing the results here proposed is that
they avoid to assume the Asplund property on the underlying space.


title: The Dirichlet problem for higher order equations in composition form

abstract:
  The present paper commences the study of higher order differential equations
in composition form. Specifically, we consider the equation Lu=\Div
B^*\nabla(a\Div A\nabla u)=0, where A and B are elliptic matrices with
complex-valued bounded measurable coefficients and a is an accretive function.
Elliptic operators of this type naturally arise, for instance, via a pull-back
of the bilaplacian \Delta^2 from a Lipschitz domain to the upper half-space.
More generally, this form is preserved under a Lipschitz change of variables,
contrary to the case of divergence-form fourth order differential equations. We
establish well-posedness of the Dirichlet problem for the equation Lu=0, with
boundary data in L^2, and with optimal estimates in terms of nontangential
maximal functions and square functions.


title: BCS-BEC crossover in a quasi-two-dimensional Fermi gas

abstract:
  We consider a two-component gas of fermionic atoms confined to a
quasi-two-dimensional (quasi-2D) geometry by a harmonic trapping potential in
the transverse direction. We construct a mean field theory of the BCS-BEC
crossover at zero temperature that allows us to extrapolate to an infinite
number of transverse harmonic oscillator levels. In the extreme BEC limit,
where the confinement length exceeds the dimer size, we recover 3D dimers
confined to 2D with weak repulsive interactions. However, even when the
interactions are weak and the Fermi energy is less than the confinement
frequency, we find that the higher transverse levels can substantially modify
fermion pairing. We argue that recent experiments on pairing in quasi-2D Fermi
gases [Y. Zhang et al., Phys. Rev. Lett. 108, 235302 (2012)] have already
observed the effects of higher transverse levels.


title:
Structural, magnetic, and nanoscale switching properties of BiFeO3 thin
  films grown by pulsed electron deposition

abstract:
  We report the epitaxial growth of BiFeO3 by pulsed electron deposition and
the resulting crystal quality, magnetic and nanoscale switching properties.
X-ray diffraction shows high quality single phase, epitaxial (001) oriented
films grown on SrTiO3 (001) substrates. Both field and temperature dependent
magnetic properties reveal an antiferromagnetic behavior of the films. For the
film with a SrRuO3 bottom electrode, an exchange-enhancement effect between
antiferromagnetic BiFeO3 and ferromagnetic SrRuO3 was observed at low
temperature. The piezoelectric force microscopy and switching spectroscopy
measurements demonstrate the local domain switching process and suggest that
the BiFeO3 films are high quality ferroelectrics.


title: Well-posedness of the plasma-vacuum interface problem

abstract:
  We consider the free boundary problem for the plasma-vacuum interface in
ideal compressible magnetohydrodynamics (MHD). In the plasma region the flow is
governed by the usual compressible MHD equations, while in the vacuum region we
consider the pre-Maxwell dynamics for the magnetic field. At the
free-interface, driven by the plasma velocity, the total pressure is continuous
and the magnetic field on both sides is tangent to the boundary. The
plasma-vacuum system is not isolated from the outside world, because of a given
surface current on the fixed boundary that forces oscillations.
  Under a suitable stability condition satisfied at each point of the initial
interface, stating that the magnetic fields on either side of the interface are
not collinear, we show the existence and uniqueness of the solution to the
nonlinear plasma-vacuum interface problem in suitable anisotropic Sobolev
spaces. The proof is based on the results proved in the companion paper
arXiv:1112.3101, about the well-posedness of the homogeneous linearized problem
and the proof of a basic a priori energy estimate. The proof of the resolution
of the nonlinear problem given in the present paper follows from the analysis
of the elliptic system for the vacuum magnetic field, a suitable tame estimate
in Sobolev spaces for the full linearized equations, and a Nash-Moser
iteration.


title: On close-in magnetized star-planet interactions

abstract:
  We present 2D magnetohydrodynamic simulations performed with the PLUTO code
to model magnetized star-planet interactions. We study two simple scenarios of
magnetized star-planet interactions: the unipolar and dipolar interactions.
Despite the simplified hypotheses we consider in the model, the qualitative
behavior of the interactions is very well recovered. These encouraging results
promote further developments of the model to obtain predictions on the effect
and the physical manifestation of magnetized star--close-in planet
interactions.


title:
On the potential of the Cherenkov Telescope Array for the study of
  cosmic-ray diffusion in molecular clouds

abstract:
  Molecular clouds act as primary targets for cosmic-ray interactions and are
expected to shine in gamma-rays as a by-product of these interactions. Indeed
several detected gamma-ray sources both in HE and VHE gamma-rays (HE: 100 MeV <
E < 100 GeV; VHE: E > 100 GeV) have been directly or indirectly associated with
molecular clouds. Information on the local diffusion coefficient and the
cosmic-ray population can be inferred from the observed gamma-ray signals. In
this work we explore the capability of the forthcoming Cherenkov Telescope
Array Observatory (CTA) to provide such measurements. We investigate the
expected emission from clouds hosting an accelerator, surveying the parameter
space for different modes of acceleration, age of the source, cloud density
profile, and cosmic-ray diffusion coefficient. We present some of the most
interesting cases for CTA regarding this science topic. The simulated gamma-ray
fluxes depend strongly on the input parameters. In several cases, we find that
it will be possible to constrain both the properties of the accelerator and the
propagation mode of cosmic rays in the cloud from CTA data alone.


title: Quantum resistance standard accuracy close to the zero-dissipation state

abstract:
  We report on a comparison of four GaAs/AlGaAs-based quantum resistance
standards using an original technique adapted from the well-known Wheatstone
bridge. This work shows that the quantized Hall resistance at Landau level
filling factor $\nu=2$ can be reproducible with a relative uncertainty of
$32\times 10^{-12}$ in the dissipationless limit of the quantum Hall effect
regime. In the presence of a very small dissipation characterized by a mean
macroscopic longitudinal resistivity $\bar{R_{xx}(B)}$ of a few $\mu\Omega$,
the discrepancy $\Delta R_{\mathrm{H}}(B)$ measured on the Hall plateau between
quantum Hall resistors turns out to follow the so-called resistivity rule
$\bar{R_{xx}(B)}=\alpha B\times d(\Delta R_{\mathrm{H}}(B))/dB$. While the
dissipation increases with the measurement current value, the coefficient
$\alpha$ stays constant in the range investigated ($40-120 \mathrm{\mu A}$).
This result enlightens the impact of the dissipation emergence in the
two-dimensional electron gas on the Hall resistance quantization, which is of
major interest for the resistance metrology. The quantum Hall effect is used to
realize a universal resistance standard only linked to the electron charge
\emph{e} and the Planck's constant \emph{h} and it is known to play a central
role in the upcoming revised \emph{Syst\`eme International} of units. There are
therefore fundamental and practical benefits in testing the reproducibility
property of the quantum Hall effect with better and better accuracy.


title:
A versatile variable field module for field and angular dependent
  scanning probe microscopy measurements

abstract:
  We demonstrate a versatile variable field module (VFM) with capability of
both field and angular dependent measurements up to 1800 Oe for scanning probe
system. The magnetic field strength is changed by adjusting the distance
between a rare earth magnet and the probe tip and is monitored in-situ by a
built-in Hall sensor. Rotating the magnet allows the field vector to change
from the horizontal to vertical direction and makes it possible to do angular
dependent measurements. The capability of the VFM system is demonstrated by
degaussing a floppy disk media with increasing magnetic field. Angular
dependent measurements clearly show the evolution of magnetic domain
structures, with a completely reversible magnetic force microscopy phase
contrast observed when the magnetic field is rotated by 180{\deg}. A further
demonstration of out-of-plane and in-plane magnetic switching of CoFe2O4
pillars in CoFe2O4-BiFeO3 nanocomposites was presented and discussed.


title:
Hubble parameter measurement constraints on the cosmological
  deceleration-acceleration transition redshift

abstract:
  We compile a list of 28 independent measurements of the Hubble parameter
between redshifts 0.07 < z < 2.3 and use this to place constraints on model
parameters of constant and time-evolving dark energy cosmologies. These H(z)
measurements by themselves require a currently accelerating cosmological
expansion at about, or better than, 3-sigma confidence. The mean and standard
deviation of the 6 best-fit model deceleration-acceleration transition
redshifts (for the 3 cosmological models and 2 Hubble constant priors we
consider) is $z_{\rm da} = 0.74 \pm 0.05$, in good agreement with the recent
Busca et al. (2012) determination of $z_{\rm da} = 0.82 \pm 0.08$ based on 11
H(z) measurements between redshifts 0.2 < z < 2.3, almost entirely from
BAO-like data.


title: Remarks on a parameter estimation for von Mises--Fisher distributions

abstract:
  We point out an error in the proof of the main result of the paper of Tanabe
et al. (2007) concerning a parameter estimation for von Mises--Fisher
distributions, we correct the proof of the main result and we present a short
alternative proof.


title: Density Functional approach to Nonlinear Rheology

abstract:
  We present a density functional based closure of the pair Smoluchowski
equation for Brownian particles under shear flow. Given an equilibrium free
energy functional as input the theory provides first-principles predictions for
the flow-distorted pair correlation function and associated rheological
quantities over a wide range of volume fractions and flow rates. Taking
two-dimensional hard-disks under shear flow as an illustrative model we
calculate the pair correlation function, viscosity and normal stress difference
under both steady and start-up shear.


title: Super Morita Theory

abstract:
  We develop the basics of Morita theory for super rings. As an application, we
produce a more explicit super Morita equivalence in the case of super Azumaya
algebras.


title: Ding projective dimension of complexes

abstract:
  In this paper, we define and study a notion of Ding projective dimension for
complexes of left modules over associative rings. In particular, we consider
the class of homologically bounded below complexes of left R-modules, and show
that Ding projective dimension has a nice functorial description.


title: Gordian adjacency for torus knots

abstract:
  A knot K is called Gordian adjacent to a knot L if there exists an unknotting
sequence for L containing K. We provide a sufficient condition for Gordian
adjacency of torus knots via the study of knots in the thickened torus. We also
completely describe Gordian adjacency for torus knots of index 2 and 3 using
Levine-Tristram signatures as obstructions to Gordian adjacency. Finally,
Gordian adjacency for torus knots is compared to the notion of adjacency for
plane curve singularities.


title:
Higher-Order Nonlinear Schrodinger equation with derivative non-Kerr
  nonlinear terms: A model for sub-10fs pulse propagation

abstract:
  We analytically solved the higher-order nonlinear Schrodinger (HNLS) equation
with non-Kerr nonlinearity under some parametric conditions and investigated
explicitly bright and dark solitary wave solutions. Periodic wave solutions are
also presented. The functional form of the bright and dark solitons presented
are different from fundamental known sech(.) and tanh(.) respectively. We have
estimated theoretically the size of the derivative non-Kerr nonlinear
coefficients of the HNLS equation that agreed the reality of the waveguide made
of highly nonlinear optical materials, could be used as the model parameters
for sub-10fs pulse propagation.


title: Bouncing Model in Brane World Theory

abstract:
  We examine the nonlinear dynamics of a closed Friedmann-Robertson-Walker
universe in the framework of Brane World formalism with a timelike extra
dimension. In this scenario, the Friedmann equations contain additional terms
arising from the bulk-brane interaction which provide a concrete model for
nonsingular bounces in the early phase of the Universe. We construct a
nonsingular cosmological scenario sourced with dust, radiation and a
cosmological constant. The structure of the phase space shows a nonsingular
orbit with two accelerated phases, separated by a smooth transition
corresponding to a decelerated expansion. Given observational parameters we
connect such phases to a primordial accelerated phase, a soft transition to
Friedmann (where the classical regime is valid), and a graceful exit to a de
Sitter accelerated phase.


title:
Formation and upper critical fields of the two distinct A15 phases in
  the subelements of Powder-In-Tube Nb3Sn wires

abstract:
  It is well known that the A15 layer in the subelements of a Powder-In-Tube
(PIT) Nb3Sn wire exhibits two different grain morphologies: a region with fine
grains (~200 nm in size) representing about 60% of the total A15 area and one
with large grains (1-2 {\mu}m in size). By means of high field specific heat
and magnetization measurements we have shown that these two A15 phases
correspond to two distinctly different Tc distributions, the large grains
region exhibiting a higher Tc and a lower Bc2, the fine grains region a lower
Tc and a higher Bc2. We report here the values of the superconducting
parameters (Tc, Bc2) of the two A15 phases, as determined from an original
model to fit the experimental Tc distribution. After a prolonged reaction
treatment (625{\deg}C/320h), an increase of the fine grain region was observed
at the expenses of the large grain region, the Bc2(0K) value of the former
being raised from 28.8 to 31.7 T. These changes explain the marked increase of
Jc to 2'700 A/cm2 at 4.2K/12T, the highest value measured so far in PIT wires.


title: Trapped Atoms in One-Dimensional Photonic Crystals

abstract:
  We describe one-dimensional photonic crystals that support a guided mode
suitable for atom trapping within a unit cell, as well as a second probe mode
with strong atom-photon interactions. A new hybrid trap is analyzed that
combines optical and Casimir-Polder forces to form stable traps for neutral
atoms in dielectric nanostructures. By suitable design of the band structure,
the atomic spontaneous emission rate into the probe mode can exceed the rate
into all other modes by more than tenfold. The unprecedented single-atom
reflectivity $r_0 \gtrsim 0.9$ for the guided probe field should enable diverse
investigations of photon-mediated interactions for 1D atom chains and cavity
QED.


title: Drainage in a model stratified porous medium

abstract:
  We show that when a non-wetting fluid drains a stratified porous medium at
sufficiently small capillary numbers Ca, it flows only through the coarsest
stratum of the medium; by contrast, above a threshold Ca, the non-wetting fluid
is also forced laterally, into part of the adjacent, finer strata. The spatial
extent of this partial invasion increases with Ca. We quantitatively understand
this behavior by balancing the stratum-scale viscous pressure driving the flow
with the capillary pressure required to invade individual pores. Because
geological formations are frequently stratified, we anticipate that our results
will be relevant to a number of important applications, including understanding
oil migration, preventing groundwater contamination, and sub-surface CO$_{2}$
storage.


title: Modularity spectra, eigen-subspaces, and structure of weighted graphs

abstract:
  The role of the normalized modularity matrix in finding homogeneous cuts will
be presented. We also discuss the testability of the structural eigenvalues and
that of the subspace spanned by the corresponding eigenvectors of this matrix.
In the presence of a spectral gap between the k-1 largest absolute value
eigenvalues and the remainder of the spectrum, this in turn implies the
testability of the sum of the inner variances of the k clusters that are
obtained by applying the k-means algorithm for the appropriately chosen vertex
representatives.


title: Landen inequalities for special functions

abstract:
  In this paper our aim is to present some Landen inequalities for Gaussian
hypergeometric functions, confluent hypergeometric functions, generalized
Bessel functions and for general power series. Our main results complement and
generalize some known results in the literature.


title:
Model-based discrete relaxation process representation of band-limited
  power-law attenuation

abstract:
  Frequency-dependent acoustical loss due to a multitude of physical mechanisms
is commonly modeled by multiple relaxations. For discrete relaxation
distributions, such models correspond with causal wave equations of
integer-order temporal derivatives. It has also been shown that certain
continuous distributions may give causal wave equations with fractional-order
temporal derivatives. This paper demonstrates analytically that if the
wave-frequency {\omega} satisfies \Omega_L << {\omega} << \Omega_H, a
continuous relaxation distribution populating only {\Omega} belongs to
[\Omega_L,\Omega_H] gives the same effective wave equation as for a fully
populated distribution. This insight sparks the main contribution: the
elaboration of a method to determine discrete relaxation parameters intended
for mimicking a desired attenuation behavior for band-limited waves. In
particular, power-law attenuation is discussed as motivated by its prevalence
in complex media, e.g. biological tissue. A Mittag-Leffler function related
distribution of relaxation mechanisms has previously been shown to be related
to the fractional Zener wave equation of three power-law attenuation regimes.
Because these regimes correspond to power-law regimes in the relaxation
distribution, the idea is to sample the distribution's compressibility
contributions evenly in logarithmic frequency while appropriately taking the
stepsize into account. This work thence claims to provide a model-based
approach to determination of discrete relaxation parameters intended to
adequately model attenuation power-laws.


title:
Evidence of d-wave Superconductivity in K_(1-x)Na_xFe_2As_2 (x = 0, 0.1)
  Single Crystals from Low-Temperature Specific Heat Measurements

abstract:
  From the measurement and analysis of the specific heat of high-quality
K_(1-x)Na_xFe_2As_2 single crystals we establish the presence of large T^2
contributions with coefficients alpha_sc ~ 30 mJ/mol K^3 at low-T for both x=0
and 0.1. Together with the observed square root field behavior of the specific
heat in the superconducting state both findings evidence d-wave
superconductivity on almost all Fermi surface sheets with an average gap
amplitude of Delta_0 in the range of 0.4 - 0.8 meV. The derived Delta_0 and the
observed T_c agree well with the values calculated within the Eliashberg
theory, adopting a spin-fluctuation mediated pairing in the intermediate
coupling regime.


title: Extremality Properties for the Basic Polarization Transformations

abstract:
  We study the extremality of the BEC and the BSC for Gallager's reliability
function $E_0$ evaluated under the uniform input distribution for binary input
DMCs from the aspect of channel polarization. In particular, we show that
amongst all B-DMCs of a given $E_0(\rho)$ value, for a fixed $\rho \geq 0$, the
BEC and BSC are extremal in the evolution of $E_0$ under the one-step
polarization transformations.


title: SVD, discrepancy, and regular structure of contingency tables

abstract:
  We will use the factors obtained by correspondence analysis to find
biclustering of a contingency table such that the row-column cluster pairs are
regular, i.e., they have small discrepancy. In our main theorem, the constant
of the so-called volume-regularity is related to the SVD of the normalized
contingency table. Our result is applicable to two-way cuts when both the rows
and columns are divided into the same number of clusters, thus extending partly
the result of Butler estimating the discrepancy of a contingency table by the
second largest singular value of the normalized table (one-cluster, rectangular
case), and partly a former result of the author for estimating the constant of
volume-regularity by the structural eigenvalues and the distances of the
corresponding eigen-subspaces of the normalized modularity matrix of an
edge-weighted graph (several clusters, symmetric case).


title:
Fermat Surface and Group Theory in Symmetry of Rapidity Family in Chiral
  Potts Model

abstract:
  The present paper discusses various mathematical aspects about the rapidity
symmetry in chiral Potts model (CPM) in the context of algebraic geometry and
group theory . We re-analyze the symmetry group of a rapidity curve in
$N$-state CPM, explore the universal group structure for all $N$, and further
enlarge it to modular symmetries of the complete rapidity family in CPM. As
will be shown in the article that all rapidity curves in $N$-state CPM
constitute a Fermat hypersurface in $\PZ^3$ of degree 2N as the natural
generalization of the Fermat K3 elliptic surface $(N=2)$, we conduct a thorough
algebraic geometry study about the rapidity fibration of Fermat surface and its
reduced hyperelliptic fibration via techniques in algebraic surface theory.
Symmetries of rapidity family in CPM and hyperelliptic family in
$\tau^{(2)}$-model are exhibited through the geometrical representation of the
universal structural group in mathematics.

categories: math.AG cond-mat.stat-mech hep-th math-ph math.MP


title:
Nonperturbative semiclassical stability of de Sitter spacetime for small
  metric deviations

abstract:
  We consider the linearized semiclassical Einstein equations for small
deviations around de Sitter spacetime including the vacuum polarization effects
of conformal fields. Employing the method of order reduction, we find the exact
solutions for general metric perturbations (of scalar, vector and tensor type).
Our exact (nonperturbative) solutions show clearly that in this case de Sitter
is stable with respect to small metric deviations and a late-time attractor.
Furthermore, they also reveal a breakdown of perturbative solutions for a
sufficiently long evolution inside the horizon. Our results are valid for any
conformal theory, even self-interacting ones with arbitrarily strong coupling.


title: On the Possibility of Medium-Energy Compact X-ray Free-Electron Laser

abstract:
  The problem of X-ray Free-Electron Laser operating on self-amplified
spontaneous emission in irregular microundulator is considered. The case when
the spectrum width of spontaneous radiation is conditioned by the spatial
distribution of sources creating the undulating field is considered. In this
case gain function of the stimulated radiation is dozens of times higher than
that of the conventional undulators. We propose a model of irregular
microundulator, which can be used to construct a drastically cheap and compact
X-ray free-electron laser operating on medium energy electron bunch.


title: A Coloring Problem for Sturmian and Episturmian Words

abstract:
  We consider the following open question in the spirit of Ramsey theory: Given
an aperiodic infinite word $w$, does there exist a finite coloring of its
factors such that no factorization of $w$ is monochromatic? We show that such a
coloring always exists whenever $w$ is a Sturmian word or a standard
episturmian word.


title: The rise of a tensor instability in Eddington-inspired gravity

abstract:
  In this work an extension to Eddington's gravitational action is analyzed. We
consider the tensor perturbations of a FLRW space-time in the Eddington regime
in where the tensor mode is linearly unstable deep and the resulting
modifications to Einstein regime are quite strong.


title:
An asteroseismic study of the Southern $\beta$ Cephei star \astrobj{ALS
  3721}

abstract:
  We present the results of a new investigation aimed to identify the
pulsational characteristics of the Southern $\beta$ Cephei star ALS 3721.
Spectroscopic and multicolour photometric data were acquired at the South
African Astronomical Observatory (SAAO), South Africa in 2011. Frequency
analysis showed that the oscillations of ALS 3721 could be attributed to the
two main frequencies with higher significance. Stellar parameters and projected
rotational velocity obtained by the spectra were also used to perform
photometric mode identification. In order to determine spherical harmonic
degrees ($l$), a principal method was followed by comparing the observed light
amplitude ratios in different passbands with those computed from non--adiabatic
pulsation models. In general case, therefore, the spherical harmonic degrees
corresponding of the frequencies were found in the expected $\beta$ Cephei
range.


title:
General method for the security analysis in a quantum direct
  communication protocol

abstract:
  We introduce a general approach for the analysis of a quantum direct
communication protocol. The method is based on the investigation of the
superoperator acting on a joint system of the communicating parties and the
eavesdropper. The introduced method is more versatile than the approaches used
so far as it permits to incorporate different noise models in a unified way.
Moreover, it make use of a well grounded theory of quantum discrimination for
the purpose of estimating the eavesdropper's information gain.