title: Regular Representations of Time-Frequency Groups

abstract:
  In this paper, we study the Plancherel measure of a class of non-connected
nilpotent groups which is of special interest in Gabor theory. Let $G$ be a
time-frequency group. More precisely, that is $G=\left\langle
T_{k},M_{l}:k\in\mathbb{Z}^{d},l\in B\mathbb{Z}^{d}\right\rangle ,$ $T_{k}$,
$M_{l}$ are translations and modulations operators acting in
$L^{2}(\mathbb{R}^{d}),$ and $B$ is a non-singular matrix. We compute the
Plancherel measure of the left regular representation of $G\ $which is denoted
by $L.$ The action of $G$ on $L^{2}(\mathbb{R}^{d})$ induces a representation
which we call a Gabor representation. Motivated by the admissibility of this
representation, we compute the decomposition of $L$ into direct integral of
irreducible representations by providing a precise description of the unitary
dual and its Plancherel measure. As a result, we generalize Hartmut F\"uhr's
results which are only obtained for the restricted case where $d=1$,
$B=1/L,L\in\mathbb{Z}$ and $L>1.$ Even in the case where $G$ is not type I, we
are able to obtain a decomposition of the left regular representation of $G$
into a direct integral decomposition of irreducible representations when $d=1$.
Some interesting applications to Gabor theory are given as well. For example,
when $B$ is an integral matrix, we are able to obtain a direct integral
decomposition of the Gabor representation of $G.$


title: Uniqueness of Conformal Ricci Flow using Energy Methods

abstract:
  We analyze an energy functional associated to Conformal Ricci Flow along
closed manifolds with constant negative scalar curvature. Given initial
conditions we use this functional to demonstrate the uniqueness of both the
metric and the pressure function along Conformal Ricci Flow.


title: Top Quark Polarization and the Search for New Physics

abstract:
  Forward-backward asymmetries $A_{FB}^t$ and $A_{FB}^\ell$ are observed in the
top quark $t$ rapidity distribution and in the rapidity distribution of charged
leptons $\ell$ from top quark decay at the Tevatron proton-antiproton collider,
and a charge asymmetry $A_C$ is seen in proton-proton collisions at the Large
Hadron Collider (LHC). In this presentation, I summarize research my
collaborators and I have done on the interpretation and implications of the
Tevatron asymmetries and provide expectations for $A_C$ at the LHC. The two
asymmetries $A_{FB}^t$ and $A_{FB}^\ell$ are connected through the $(V-A)$ spin
correlation between the charged lepton and the top quark with different
polarization states. The ratio of the two asymmetries provides independent
insight into the physics interpretation of the top quark asymmetry. A new
physics model which produces more right-handed than left-handed top quarks
appears to be indicated by the present Tevatron data, but an improvement in
precision is desirable.


title: A Note on Probabilistic Models over Strings: the Linear Algebra Approach

abstract:
  Probabilistic models over strings have played a key role in developing
methods allowing indels to be treated as phylogenetically informative events.
There is an extensive literature on using automata and transducers on
phylogenies to do inference on these probabilistic models, in which an
important theoretical question in the field is the complexity of computing the
normalization of a class of string-valued graphical models. This question has
been investigated using tools from combinatorics, dynamic programming, and
graph theory, and has practical applications in Bayesian phylogenetics. In this
work, we revisit this theoretical question from a different point of view,
based on linear algebra. The main contribution is a new proof of a known result
on the complexity of inference on TKF91, a well-known probabilistic model over
strings. Our proof uses a different approach based on classical linear algebra
results, and is in some cases easier to extend to other models. The proving
method also has consequences on the implementation and complexity of inference
algorithms.


title: Nested Recursions, Simultaneous Parameters and Tree Superpositions

abstract:
  We apply a tree-based methodology to solve new, very broadly defined families
of nested recursions of the general form R(n)=sum_{i=1}^k R(n-a_i-sum_{j=1}^p
R(n-b_{ij})), where a_i are integers, b_{ij} are natural numbers, and k,p are
natural numbers that we use to denote "arity" and "order," respectively, and
with some specified initial conditions. The key idea of the tree-based solution
method is to associate such recursions with infinite labelled trees in a
natural way so that the solution to the recursions solves a counting question
relating to the corresponding trees. We characterize certain recursion families
within R(n) by introducing "simultaneous parameters" that appear both within
the recursion itself and that also specify structural properties of the
corresponding tree. First, we extend and unify recently discovered results
concerning two families of arity k=2, order p=1 recursions. Next, we
investigate the solution of nested recursion families by taking linear
combinations of solution sequence frequencies for simpler nested recursions,
which correspond to superpositions of the associated trees; this leads us to
identify and solve two new recursion families for arity k=2 and general order
p. Finally, we extend these results to general arity k>2. We conclude with
several related open problems.


title:
Quasi-two-dimensional non-collinear magnetism in the Mott insulator
  Sr$_2$F$_2$Fe$_2$OS$_2$

abstract:
  The magnetism of Sr$_2$F$_2$Fe$_2$OS$_2$ was examined through neutron powder
diffraction and thermodynamic and transport measurements. Quasi-two-dimensional
magnetic order develops below $T_N$ = 106(2) K with an in-plane correlation
length exceeding 310 \AA\ and an out-of-plane correlation length of just 17(3)
\AA. The data are consistent with a two-k structure with $k_1$ = (1/2, 0, 1/2)
and $k_2$ = (0, 1/2, 1/2) and an ordered moment of 3.3(1) $\mu_B$ oriented
along the in-plane components of k. This structure is composed of orthogonal
AFM chains intersecting at super-exchange mediating O sites. Density Functional
Theory (DFT) also points to this structure and a narrower Fe 3d band than for
the iron pnictides from which electronic correlations produce a Mott insulator.


title:
Charged Nielsen-Olesen vortices from a Generalized Abelian
  Chern-Simons-Higgs Theory

abstract:
  We consider a generalization of abelian Chern-Simons-Higgs model by
introducing a nonstandard kinetic term. In particular we show that the
Bogomolnyi equations of the abelian Higgs theory may be obtained, being its
solutions Nielsen-Olesen vortices with electric charge. In addition we study
the self-duality equations for a generalized non-relativistic
Maxwell-Chern-Simons model.


title:
The effects of nutrient chemotaxis on bacterial aggregation patterns
  with non-linear degenerate cross diffusion

abstract:
  This paper introduces a reaction-diffusion-chemotaxis model for bacterial
aggregation patterns on the surface of thin agar plates. It is based on the
non-linear degenerate cross diffusion model proposed by Kawasaki et al. (J. of
Theor. Biol. 188(2) 1997) and it includes a suitable nutrient chemotactic term
compatible with such type of diffusion. High resolution numerical simulations
using Graphic Processing Units (GPUs) of the new model are presented, showing
that the chemotactic term enhances the velocity of propagation of the colony
envelope for dense-branching morphologies. In addition, the chemotaxis seems to
stabilize the formation of branches in the soft-agar, low-nutrient regime. An
asymptotic estimation predicts the growth velocity of the colony envelope as a
function of both the nutrient concentration and the chemotactic sensitivity.
For fixed nutrient concentrations, the growth velocity is an increasing
function of the chemotactic sensitivity.


title: Zonal Flow as Pattern Formation

abstract:
  Zonal flows are well known to arise spontaneously out of turbulence. We show
that for statistically averaged equations of the stochastically forced
generalized Hasegawa-Mima model, steady-state zonal flows and inhomogeneous
turbulence fit into the framework of pattern formation. There are many
implications. First, the wavelength of the zonal flows is not unique. Indeed,
in an idealized, infinite system, any wavelength within a certain continuous
band corresponds to a solution. Second, of these wavelengths, only those within
a smaller subband are linearly stable. Unstable wavelengths must evolve to
reach a stable wavelength; this process manifests as merging jets.

categories: physics.ao-ph nlin.PS physics.flu-dyn physics.plasm-ph


title:
A comparison study of CORSIKA and COSMOS simulations for extensive air
  showers

abstract:
  Cosmic rays with energy exceeding ~ 10^{18} eV are referred to as ultra-high
energy cosmic rays (UHECRs). Monte Carlo codes for extensive air shower (EAS)
simulate the development of EASs initiated by UHECRs in the Earth's atmosphere.
Experiments to detect UHECRs utilize EAS simulations to estimate their energy,
arrival direction, and composition. In this paper, we compare EAS simulations
with two different codes, CORSIKA and COSMOS, presenting quantities including
the longitudinal distribution of particles, depth of shower maximum, kinetic
energy distribution of particle at the ground, and energy deposited to the air.
We then discuss implications of our results to UHECR experiments.


title:
Capacity Region Bounds and Resource Allocation for Two-Way OFDM Relay
  Channels

abstract:
  In this paper, we consider two-way orthogonal frequency division multiplexing
(OFDM) relay channels, where the direct link between the two terminal nodes is
too weak to be used for data transmission. The widely known per-subcarrier
decode-and-forward (DF) relay strategy, treats each subcarrier as a separate
channel, and performs independent channel coding over each subcarrier. We show
that this per-subcarrier DF relay strategy is only a suboptimal DF relay
strategy, and present a multi-subcarrier DF relay strategy which utilizes
cross-subcarrier channel coding to achieve a larger rate region. We then
propose an optimal resource allocation algorithm to characterize the achievable
rate region of the multi-subcarrier DF relay strategy. The computational
complexity of this algorithm is much smaller than that of standard Lagrangian
duality optimization algorithms. We further analyze the asymptotic performance
of two-way relay strategies including the above two DF relay strategies and an
amplify-and-forward (AF) relay strategy. The analysis shows that the
multi-subcarrier DF relay strategy tends to achieve the capacity region of the
two-way OFDM relay channels in the low signal-to-noise ratio (SNR) regime,
while the AF relay strategy tends to achieve the multiplexing gain region of
the two-way OFDM relay channels in the high SNR regime. Numerical results are
provided to justify all the analytical results and the efficacy of the proposed
optimal resource allocation algorithm.


title: Some identities involving associated sequences of special polynomials

abstract:
  In this paper, we study some properties of associated sequences of special
polynomials. From the properties of associated sequences of polynomials, we
derive some interesting identities of special polynomials.


title:
Heteroscedastic Conditional Ordinal Random Fields for Pain Intensity
  Estimation from Facial Images

abstract:
  We propose a novel method for automatic pain intensity estimation from facial
images based on the framework of kernel Conditional Ordinal Random Fields
(KCORF). We extend this framework to account for heteroscedasticity on the
output labels(i.e., pain intensity scores) and introduce a novel dynamic
features, dynamic ranks, that impose temporal ordinal constraints on the static
ranks (i.e., intensity scores). Our experimental results show that the proposed
approach outperforms state-of-the art methods for sequence classification with
ordinal data and other ordinal regression models. The approach performs
significantly better than other models in terms of Intra-Class Correlation
measure, which is the most accepted evaluation measure in the tasks of facial
behaviour intensity estimation.


title:
Tensor hypercontraction: A universal technique for the resolution of
  matrix elements of local, finite-range $N$-body potentials in many-body
  quantum problems

abstract:
  Configuration-space matrix elements of N-body potentials arise naturally and
ubiquitously in the Ritz-Galerkin solution of many-body quantum problems. For
the common specialization of local, finite-range potentials, we develop the
eXact Tensor HyperContraction (X-THC) method, which provides a quantized
renormalization of the coordinate-space form of the N-body potential, allowing
for a highly separable tensor factorization of the configuration-space matrix
elements. This representation allows for substantial computational savings in
chemical, atomic, and nuclear physics simulations, particularly with respect to
difficult "exchange-like" contractions.


title: Security in Wireless Sensor Networks

abstract:
  Wireless sensor networks have attracted a lot of interest over the last
decade in wireless and mobile computing research community. Applications of
these networks are numerous and growing, which range from indoor deployment
scenarios in the home and office to outdoor deployment in adversary's territory
in a tactical battleground. However, due to distributed nature and their
deployment in remote areas, these networks are vulnerable to numerous security
threats that can adversely affect their performance. This chapter provides a
comprehensive discussion on the state of the art in security technologies for
wireless sensor networks. It identifies various possible attacks at different
layers of the communication protocol stack in a typical sensor network and
their possible countermeasures. A brief discussion on the future direction of
research in WSN security is also included.


title: Femtosecond x rays from laser-plasma accelerators

abstract:
  Relativistic interaction of short-pulse lasers with underdense plasmas has
recently led to the emergence of a novel generation of femtosecond x-ray
sources. Based on radiation from electrons accelerated in plasma, these sources
have the common properties to be compact and to deliver collimated, incoherent
and femtosecond radiation. In this article we review, within a unified
formalism, the betatron radiation of trapped and accelerated electrons in the
so-called bubble regime, the synchrotron radiation of laser-accelerated
electrons in usual meter-scale undulators, the nonlinear Thomson scattering
from relativistic electrons oscillating in an intense laser field, and the
Thomson backscattered radiation of a laser beam by laser-accelerated electrons.
The underlying physics is presented using ideal models, the relevant parameters
are defined, and analytical expressions providing the features of the sources
are given. Numerical simulations and a summary of recent experimental results
on the different mechanisms are also presented. Each section ends with the
foreseen development of each scheme. Finally, one of the most promising
applications of laser-plasma accelerators is discussed: the realization of a
compact free-electron laser in the x-ray range of the spectrum. In the
conclusion, the relevant parameters characterizing each sources are summarized.
Considering typical laser-plasma interaction parameters obtained with currently
available lasers, examples of the source features are given. The sources are
then compared to each other in order to define their field of applications.


title:
Direct Gravitational Imaging of Intermediate Mass Black Holes in
  Extragalactic Halos

abstract:
  A galaxy halo may contain a large number of intermediate mass black holes
(IMBHs) with masses in the range of 10^{2-6} solar mass. We propose to directly
detect these IMBHs by observing multiply imaged QSO-galaxy or galaxy-galaxy
strong lens systems in the submillimeter bands with high angular resolution.
The silhouette of an IMBH in the lensing galaxy halo would appear as either a
monopole-like or a dipole-like variation at the scale of the Einstein radius
against the Einstein ring of the dust-emitting region surrounding the QSO. We
use a particle tagging technique to dynamically populate a Milky Way-sized dark
matter halo with black holes, and show that the surface mass density and number
density of IMBHs have power-law dependences on the distance from the center of
the host halo if smoothed on a scale of ~ 1 kpc. Most of the black holes
orbiting close to the center are freely roaming as they have lost their dark
matter hosts during infall due to tidal stripping. Next generation
submillimeter telescopes with high angular resolution (< 0.3 mas) will be
capable of directly mapping such off-nuclear freely roaming IMBHs with a mass
of ~ 10^6 solar mass in a lensing galaxy that harbours a O(10^9) solar mass
supermassive black hole in its nucleus.


title:
Enhanced mixing of partial waves near threshold for heavy meson pairs
  and properties of $Z_b(10610)$ and $Z_b(10650)$ resonances

abstract:
  The mixing of $S-D$ partial waves for the heavy meson pairs in the decays
$\Upsilon(5S) \to [B^* \bar B+ {\rm c.c.}] \pi$ and $\Upsilon(5S) \to B^* \bar
B^* \pi$ is considered. It is argued that this mixing, enhanced by the heavy
meson mass, is calculable as dominated by a rescattering through pion exchange
if the production of the heavy mesons is dominated by $S$-wave `molecular'
resonances $Z_b(10610)$ and $Z_b(10650)$. The effect of the mixing grows with
the c.m. energy $E$ in each channel over the threshold, and may reach $10 \div
20$% in the rate at the upper end of applicability of the discussed approach,
$E \sim 15 $MeV. It is also argued that the mixing is likely to reach maximum
at energy approximately equal to the mass gap between the thresholds.


title: Secrecy without one-way functions

abstract:
  We show that some problems in information security can be solved without
using one-way functions. The latter are usually regarded as a central concept
of cryptography, but the very existence of one-way functions depends on
difficult conjectures in complexity theory, most notably on the notorious "$P
\ne NP$" conjecture.
  In this paper, we suggest protocols for secure computation of the sum,
product, and some other functions, without using any one-way functions. A new
input that we offer here is that, in contrast with other proposals, we conceal
"intermediate results" of a computation. For example, when we compute the sum
of $k$ numbers, only the final result is known to the parties; partial sums are
not known to anybody. Other applications of our method include voting/rating
over insecure channels and a rather elegant and efficient solution of Yao's
"millionaires' problem".
  Then, while it is fairly obvious that a secure (bit) commitment between two
parties is impossible without a one-way function, we show that it is possible
if the number of parties is at least 3. We also show how our (bit) commitment
scheme for 3 parties can be used to arrange an unconditionally secure (bit)
commitment between just two parties if they use a "dummy" (e.g., a computer) as
the third party. We explain how our concept of a "dummy" is different from a
well-known concept of a "trusted third party".
  We also suggest a protocol, without using a one-way function, for "mental
poker", i.e., a fair card dealing (and playing) over distance. We also propose
a secret sharing scheme where an advantage over Shamir's and other known secret
sharing schemes is that nobody, including the dealer, ends up knowing the
shares owned by any particular player.
  It should be mentioned that computational cost of our protocols is negligible
to the point that all of them can be executed without a computer.


title:
Improved Approximation Algorithms for Computing k Disjoint Paths Subject
  to Two Constraints

abstract:
  For a given graph $G$ with positive integral cost and delay on edges,
distinct vertices $s$ and $t$, cost bound $C\in Z^{+}$ and delay bound $D\in
Z^{+}$, the $k$ bi-constraint path ($k$BCP) problem is to compute $k$ disjoint
$st$-paths subject to $C$ and $D$. This problem is known NP-hard, even when
$k=1$ \cite{garey1979computers}. This paper first gives a simple approximation
algorithm with factor-$(2,2)$, i.e. the algorithm computes a solution with
delay and cost bounded by $2*D$ and $2*C$ respectively. Later, a novel improved
approximation algorithm with ratio
$(1+\beta,\,\max\{2,\,1+\ln\frac{1}{\beta}\})$ is developed by constructing
interesting auxiliary graphs and employing the cycle cancellation method. As a
consequence, we can obtain a factor-$(1.369,\,2)$ approximation algorithm by
setting $1+\ln\frac{1}{\beta}=2$ and a factor-$(1.567,\,1.567)$ algorithm by
setting $1+\beta=1+\ln\frac{1}{\beta}$. Besides, by setting $\beta=0$, an
approximation algorithm with ratio $(1,\, O(\ln n))$, i.e. an algorithm with
only a single factor ratio $O(\ln n)$ on cost, can be immediately obtained. To
the best of our knowledge, this is the first non-trivial approximation
algorithm for the $k$BCP problem that strictly obeys the delay constraint.


title:
Validity of single-channel model for a spin-orbit coupled atomic Fermi
  gas near Feshbach resonances

abstract:
  We theoretically investigate a Rashba spin-orbit coupled Fermi gas near
Feshbach resonances, by using mean-field theory and a two-channel model that
takes into account explicitly Feshbach molecules in the close channel. In the
absence of spin-orbit coupling, when the channel coupling $g$ between the
closed and open channels is strong, it is widely accepted that the two-channel
model is equivalent to a single-channel model that excludes Feshbach molecules.
This is the so-called broad resonance limit, which is well-satisfied by
ultracold atomic Fermi gases of $^{6}$Li atoms and $^{40}$K atoms in current
experiments. Here, with Rashba spin-orbit coupling we find that the condition
for equivalence becomes much more stringent. As a result, the single-channel
model may already be insufficient to describe properly an atomic Fermi gas of
$^{40}$K atoms at a moderate spin-orbit coupling. We determine a characteristic
channel coupling strength $g_{c}$ as a function of the spin-orbit coupling
strength, above which the single-channel and two-channel models are
approximately equivalent. We also find that for narrow resonance with small
channel coupling, the pairing gap and molecular fraction is strongly suppressed
by SO coupling. Our results can be readily tested in $^{40}$K atoms by using
optical molecular spectroscopy.


title:
The microarcsecond structure of an AGN jet via interstellar
  scintillation

abstract:
  We describe a new tool for studying the structure and physical
characteristics of ultracompact AGN jets and their surroundings with
microarcsecond precision. This tool is based on the frequency dependence of the
light curves observed for intra-day variable radio sources, where the
variability is caused by interstellar scintillation. We apply this method to
PKS1257-326 to resolve the core-shift as a function of frequency on scales well
below ~12 microarcseconds. We find that the frequency dependence of the
position of the scintillating component is r \propto \nu^{-0.1 \pm 0.24} (99%
confidence interval) and the frequency dependence of the size of the
scintillating component is d \propto \nu^{-0.64 \pm 0.006}. Together, these
results imply that the jet opening angle increases with distance along the jet:
d \propto r^{n_d}$ with n_d > 1.8. We show that the flaring of the jet, and
flat frequency dependence of the core position is broadly consistent with a
model in which the jet is hydrostatically confined and traversing a steep
pressure gradient in the confining medium with p \propto r^{-n_p} and n_p > 7.
Such steep pressure gradients have previously been suggested based on VLBI
studies of the frequency dependent core shifts in AGN.


title: Finite Gap Jacobi Matrices: A Review

abstract: A review of Finite Gap Jacobi Matrices.


title: How Computers Work: Computational Thinking for Everyone

abstract:
  What would you teach if you had only one course to help students grasp the
essence of computation and perhaps inspire a few of them to make computing a
subject of further study? Assume they have the standard college prep
background. This would include basic algebra, but not necessarily more advanced
mathematics. They would have written a few term papers, but would not have
written computer programs. They could surf and twitter, but could not
exclusive-or and nand. What about computers would interest them or help them
place their experience in context? This paper provides one possible answer to
this question by discussing a course that has completed its second iteration.
Grounded in classical logic, elucidated in digital circuits and computer
software, it expands into areas such as CPU components and massive databases.
The course has succeeded in garnering the enthusiastic attention of students
with a broad range of interests, exercising their problem solving skills, and
introducing them to computational thinking.


title:
Connecting the Dots: Computer Systems Education using a Functional
  Hardware Description Language

abstract:
  A functional hardware description language enables students to gain a working
understanding of computer systems, and to see how the levels of abstraction fit
together. By simulating circuits, digital design becomes a living topic, like
programming, and not just a set of inert facts to memorise. Experiences gained
from more than 20 years of teaching computer systems via functional programming
are discussed.


title: Mathematics Is Imprecise

abstract:
  We commonly think of mathematics as bringing precision to application
domains, but its relationship with computer science is more complex. This
experience report on the use of Racket and Haskell to teach a required first
university CS course to students with very good mathematical skills focusses on
the ways that programming forces one to get the details right, with consequent
benefits in the mathematical domain. Conversely, imprecision in mathematical
abstractions and notation can work to the benefit of beginning programmers, if
handled carefully.


title:
Forty hours of declarative programming: Teaching Prolog at the Junior
  College Utrecht

abstract:
  This paper documents our experience using declarative languages to give
secondary school students a first taste of Computer Science. The course aims to
teach students a bit about programming in Prolog, but also exposes them to
important Computer Science concepts, such as unification or searching
strategies. Using Haskell's Snap Framework in combination with our own
NanoProlog library, we have developed a web application to teach this course.


title: Stability for the inverse resonance problem for the CMV operator

abstract:
  For the class of unitary CMV operators with super-exponentially decaying
Verblunsky coefficients we give a new proof of the inverse resonance problem of
reconstructing the operator from its resonances - the zeros of the Jost
function. We establish a stability result for the inverse resonance problem
that shows continuous dependence of the operator coefficients on the location
of the resonances.


title: Cluster algebras and singular supports of perverse sheaves

abstract:
  We propose an approach to Geiss-Leclerc-Schroer's conjecture on the cluster
algebra structure on the coordinate ring of a unipotent subgroup and the dual
canonical base. It is based on singular supports of perverse sheaves on the
space of representations of a quiver, which give the canonical base.


title:
Approaches for enumerating permutations with a prescribed number of
  occurrences of patterns

abstract:
  In recent work, Zeilberger and the author used a functional equations
approach for enumerating permutations with r occurrences of the pattern 12...k.
In particular, the approach yielded a polynomial-time enumeration algorithm for
any fixed nonnegative r. We extend that approach to patterns of the form
12...(k-2)(k)(k-1) by deriving analogous functional equations and using them to
develop similar algorithms that enumerate permutations with r occurrences of
the pattern. We also generalize those techniques to handle patterns of the form
23...k1 and derive analogous functional equations and enumeration algorithms.
Finally, we show how the functional equations and algorithms can be modified to
track inversions as well as handle multiple patterns simultaneously. This paper
is accompanied by Maple packages that implement the algorithms described.


title:
Crossover from Growing to Stationary Interfaces in the
  Kardar-Parisi-Zhang Class

abstract:
  This Letter reports on how the interfaces in the (1+1)-dimensional
Kardar-Parisi-Zhang (KPZ) class undergo, in the course of time, a transition
from the flat, growing regime to the stationary one. Simulations of the
polynuclear growth model and experiments on turbulent liquid crystal reveal
universal functions of the KPZ class governing this transition, which connect
the distribution and correlation functions for the growing and stationary
regimes. This in particular shows how interfaces realized in experiments and
simulations actually approach the stationary regime, which is never attained
unless a stationary interface is artificially given as an initial condition.


title:
Precise simulation of the initial-state QCD activity associated with
  $Z$-boson production in hadron collisions

abstract:
  The $\phi_{\eta}^{*}$ distribution of the $Z/\gamma^{*} \rightarrow
\ell^{+}\ell^{-}$ production in hadron collisions is simulated using a
leading-order event generator, GR@PPA. The initial-state parton shower, which
simulates the multiple QCD-radiation effects in the initial state, plays the
dominant role in this simulation. The simulation in the default setting agrees
with the high-statistics measurement by ATLAS at LHC with the precision at the
level of 5%. The observed systematic deviation, which can be attributed to the
effects of ignored higher-order contributions, can be reduced by adjusting the
arbitrary energy scales in the simulation. The agreement at the level of 1% can
be achieved over a very wide range without introducing any modification in the
implemented naive leading-logarithmic parton shower.


title: Improved Asymptotic Key Rate of the B92 Protocol

abstract:
  We analyze the asymptotic key rate of the single photon B92 protocol by using
Renner's security analysis given in 2005. The new analysis shows that the B92
protocol can securely generate key at 6.5% depolarizing rate, while the
previous analyses cannot guarantee the secure key generation at 4.2%
depolarizing rate.


title: Oxidation of D=3 cosets and Bonnor dualities in $D\leq 6$

abstract:
  Bonnor's map in General Relativity is duality between (dimensionally reduced)
vacuum gravity and static truncation of electro-vacuum theory. It was used as a
tool to generate an exact solution of electro-vacuum from some vacuum solution.
It can be expected that similar dualities will be useful for solution
generation in higher-dimensional theories too. Here we study such maps within a
class of theories in dimensions $D\leq 6$ using oxidation of D=3 cosets and
consistent truncation of the corresponding theories. Our class includes those
theories whose D=3 symmetries are subgroups of $G=O(5,4)$. It contains
six-dimensional minimal supergravity, five-dimensional minimal and $U(1)^3$
supergravities and a number of four-dimensional theories which attracted
attention recently in the search of exact solutions. We give explicit
reduction/truncation formulas relating different theories in dimensions $D=4,
5, 6$ in terms of metrics and matter fields and discuss various alternative
duality chains between them.


title:
A Precise Calculation of Delayed Coincidence Selection Efficiency and
  Accidental Coincidence Rate

abstract:
  A model is proposed to address issues on the precise background evaluation
due to the complex data structure defined by the delayed coincidence method,
which is widely used in reactor electron-antineutrino oscillation experiments.
In this model, the effects from the muon veto, uncorrelated random background,
coincident signal and background are all studied with the analytical solutions,
simplifying the estimation of the systematic uncertainties of signal efficiency
and accidental background rate determined by the unstable single rate. The
result of calculation is validated numerically with a number of simulation
studies and is also applied and validated in the recent Daya Bay
hydrogen-capture based oscillation measurement.


title: Exponential Ratio Type Estimators In Stratified Random Sampling

abstract:
  Kadilar and Cingi (2003) have introduced a family of estimators using
auxiliary information in stratified random sampling. In this paper, we propose
the ratio estimator for the estimation of population mean in the stratified
random sampling by using the estimators in Bahl and Tuteja (1991) and Kadilar
and Cingi (2003). Obtaining the mean square error (MSE) equations of the
proposed estimators, we find theoretical conditions that the proposed
estimators are more efficient than the other estimators. These theoretical
findings are supported by a numerical example.


title:
Categorical models of computation: partially traced categories and
  presheaf models of quantum computation

abstract:
  This dissertation has two main parts. The first part deals with questions
relating to Haghverdi and Scott's notion of partially traced categories. The
main result is a representation theorem for such categories: we prove that
every partially traced category can be faithfully embedded in a totally traced
category. Also conversely, every monoidal subcategory of a totally traced
category is partially traced, so this characterizes the partially traced
categories completely. The main technique we use is based on Freyd's
paracategories, along with a partial version of Joyal, Street, and Verity's Int
construction. Along the way, we discuss some new examples of partially traced
categories, mostly arising in the context of quantum computation.
  The second part deals with the construction of categorical models of
higher-order quantum computation. We construct a concrete semantic model of
Selinger and Valiron's quantum lambda calculus, which has been an open problem
until now. We do this by considering presheaf categories over appropriate base
categories arising from first-order quantum computation. The main technical
ingredients are Day's convolution theory and Kelly and Freyd's notion of
continuity of functors. We first give an abstract description of the properties
required of the base categories for the model construction to work; then
exhibit a specific example of base categories satisfying these properties.


title: Piecewise Linear Multilayer Perceptrons and Dropout

abstract:
  We propose a new type of hidden layer for a multilayer perceptron, and
demonstrate that it obtains the best reported performance for an MLP on the
MNIST dataset.


title:
An interpretation of the Sigma-2 fragment of classical Analysis in
  System T

abstract:
  We show that it is possible to define a realizability interpretation for the
$\Sigma_2$-fragment of classical Analysis using G\"odel's System T only. This
supplements a previous result of Schwichtenberg regarding bar recursion at
types 0 and 1 by showing how to avoid using bar recursion altogether. Our
result is proved via a conservative extension of System T with an operator for
composable continuations from the theory of programming languages due to Danvy
and Filinski. The fragment of Analysis is therefore essentially constructive,
even in presence of the full Axiom of Choice schema: Weak Church's Rule holds
of it in spite of the fact that it is strong enough to refute the formal
arithmetical version of Church's Thesis.


title:
A detailed X-ray investigation of {\zeta} Puppis III. A spectral
  analysis of the whole RGS spectrum

abstract:
  Context. Zeta Pup is the X-ray brightest O-type star of the sky. This object
was regularly observed with the RGS instrument aboard XMM-Newton for
calibration purposes, leading to an unprecedented set of high-quality spectra.
Aims. We have previously reduced and extracted this data set and combined it
into the most detailed high-resolution X-ray spectrum of any early-type star so
far. Here we present the analysis of this spectrum accounting for the presence
of structures in the stellar wind. Methods. For this purpose, we use our new
modeling tool that allows fitting the entire spectrum with a multi-temperature
plasma. We illustrate the impact of a proper treatment of the radial dependence
of the X-ray opacity of the cool wind on the best-fit radial distribution of
the temperature of the X-ray plasma. Results. The best fit of the RGS spectrum
of Zeta Pup is obtained assuming no porosity. Four plasma components at
temperatures between 0.10 and 0.69 keV are needed to adequately represent the
observed spectrum. Whilst the hardest emission is concentrated between ~3 and 4
R*, the softer emission starts already at 1.5 R* and extends to the outer
regions of the wind. Conclusions. The inferred radial distribution of the
plasma temperatures agrees rather well with theoretical expectations. The mass-
loss rate and CNO abundances corresponding to our best-fit model also agree
quite well with the results of recent studies of Zeta Pup in the UV and optical
domain.


title:
Cryptanalysis and improvement of two certificateless three-party
  authenticated key agreement protocols

abstract:
  Recently, two certificateless three-party authenticated key agreement
protocols were proposed, and both protocols were claimed they can meet the
desirable security properties including forward security, key compromise
impersonation resistance and so on. Through cryptanalysis, we show that one
neither meets forward security and key compromise impersonation resistance nor
resists an attack by an adversary who knows all users' secret values, and the
other cannot resist key compromise impersonation attack. Finally, we propose
improved protocols to make up two original protocols' security weaknesses,
respectively. Further security analysis shows that our improved protocols can
remove such security weaknesses.


title: Correlators of massive string states with conserved currents

abstract:
  We calculate correlation functions of the R-current or the stress-energy
tensor T_{\mu\nu} with two non-protected operators dual to generic massive
string states with rotation in S^5, in the context of the AdS/CFT
correspondence. Field theory Ward identities make predictions about the
all-loop behaviour of these correlators. In particular, they restrict the
fusion coefficient to be proportional to the R-charge of the operators or to
their dimension, respectively, with certain coefficients of proportionality. We
reproduce these predictions, at strong coupling, using string theory.
Furthermore, we point out that the recently observed strong coupling
factorisation of 4-point correlators is consistent with conformal symmetry and
puts constraints on the strong coupling expressions of 4-point correlators
involving R-currents or the stress-energy tensor.


title:
Characteristics of Intronic and Intergenic Human miRNAs and Features of
  their Interaction with mRNA

abstract:
  Regulatory relationships of 686 intronic miRNA and 784 intergenic miRNAs with
mRNAs of 51 intronic miRNA coding genes were established. Interaction features
of studied miRNAs with 5'UTR, CDS and 3'UTR of mRNA of each gene were revealed.
Functional regions of mRNA were shown to be significantly heterogenous
according to the number of binding sites of miRNA and to the location density
of these sites.


title: Geometric algebra and M-theory compactifications

abstract:
  We show how supersymmetry conditions for flux compactifications of
supergravity and string theory can be described in terms of a flat subalgebra
of the Kahler-Atiyah algebra of the compactification space, a description which
has wide-ranging applications. As a motivating example, we consider the most
general M-theory compactifications on eight-manifolds down to AdS3 spaces which
preserve N=2 supersymmetry in 3 dimensions. We also give a brief sketch of the
lift of such equations to the cone over the compactification space and of the
geometric algebra approach to `constrained generalized Killing pinors', which
forms the technical and conceptual core of our investigation.


title:
Global phase and minimum time of quantum Fourier transform for qudits
  represented by quadrupole nuclei

abstract:
  We demonstrate the relation between a global phase of the quantum gate and
the layout of energy levels of its effective Hamiltonian required for
implementing the gate for minimum time. By an example of the quantum Fourier
transform gate for a qudit represented by a quadrupole nucleus with the spin I
= 1, the effective Hamiltonians and minimum implementation times for different
global phases are found. Using numerical optimal control methods, the problem
of the global phase in searching for the optimal pulse shape is considered in
detail for the quantum Fourier transform gate at I = 1, 3/2, 2, and 5/2. It is
shown that at the constrained control time the gradient algorithms can converge
to the solutions corresponding to different global phases or the same global
phase with different minimum times of the gate implementation.


title: Minimax Filtering via Relations between Information and Estimation

abstract:
  We investigate the problem of continuous-time causal estimation under a
minimax criterion. Let $X^T = \{X_t,0\leq t\leq T\}$ be governed by the
probability law $P_{\theta}$ from a class of possible laws indexed by $\theta
\in \Lambda$, and $Y^T$ be the noise corrupted observations of $X^T$ available
to the estimator. We characterize the estimator minimizing the worst case
regret, where regret is the difference between the causal estimation loss of
the estimator and that of the optimum estimator.
  One of the main contributions of this paper is characterizing the minimax
estimator, showing that it is in fact a Bayesian estimator. We then relate
minimax regret to the channel capacity when the channel is either Gaussian or
Poisson. In this case, we characterize the minimax regret and the minimax
estimator more explicitly. If we further assume that the uncertainty set
consists of deterministic signals, the worst case regret is exactly equal to
the corresponding channel capacity, namely the maximal mutual information
attainable across the channel among all possible distributions on the
uncertainty set of signals. The corresponding minimax estimator is the Bayesian
estimator assuming the capacity-achieving prior. Using this relation, we also
show that the capacity achieving prior coincides with the least favorable
input. Moreover, we show that this minimax estimator is not only minimizing the
worst case regret but also essentially minimizing regret for "most" of the
other sources in the uncertainty set.
  We present a couple of examples for the construction of an minimax filter via
an approximation of the associated capacity achieving distribution.


title:
Actively switchable non-degenerate polarization entangled photon pair
  distribution in a dense wave-division multiplexing

abstract:
  We have realized experimentally a non-degenerate polarization-entangled
photon pair distribution in a commercial telecom dense wave-division
multiplexing device (DWDM) with 8 channels. A promising point of this work is
that the entangled photon pair is obtained via spontaneously parametric down
conversion in a single type-II periodically poled KTiOPO4 crystal without usual
post-selection. Another promising advantage is that we can actively control and
switch the distribution of the photon pair between different channel pairs in
DWDM at will. There is no crosstalk between the different channel pair because
of a limited emission bandwidth of the source. High raw visibility of greater
than 90% in Bell-type interference measurement in each channel pair and the
CHSH inequality S parameter of 2.63+/-0.08 prove high entanglement of our
source. Our work is helpful for building quantum communication networks.


title: Nonlinearly-enhanced energy transport in many dimensional quantum chaos

abstract:
  By employing a nonlinear quantum kicked rotor model, we investigate the
transport of energy in multidimensional quantum chaos. Parallel numerical
simulations and analytic theory demonstrate that the interplay between
nonlinearity and Anderson localization establishes a perfectly classical
correspondence in the system, neglecting any quantum time reversal. The
resulting dynamics exhibits a nonlinearly-induced, enhanced transport of energy
through soliton wave particles.


title:
Double Electromagnetically Induced Transparency and Narrowing of Probe
  Absorption in a Ring Cavity with Nanomechanical Mirrors

abstract:
  We study the effect of a strong coupling field on the absorptive property of
a ring cavity with two mirrors oscillating at slightly different frequencies to
a weak probe field. We observe double electromagnetically induced transparency
windows separated by an absorption peak at line center in the output probe
field under the action of a strong coupling field. We find that increasing
driving power can broaden the two transparency windows, which results in
narrowing of the central absorption peak. At high driving power, the linewidth
of the sharp central absorption peak is approximately equal to the mechanical
linewidth. We show the normal mode splitting in both the output probe field and
the generated Stokes field. We also find that the suppression of the four-wave
mixing process can be achieved on resonance.


title: Bitwise operations related to a combinatorial problem on binary matrices

abstract:
  Some techniques for the use of bitwise operations are described in the
article. As an example, an open problem of isomorphism-free generations of
combinatorial objects is discussed. An equivalence relation on the set of
square binary matrices having the same number of units in each row and each
column is defined. Each binary matrix is represented using ordered n-tuples of
natural numbers. It is shown how by using the bitwise operations can be
implemented an algorithm that gets canonical representatives which are extremal
elements of equivalence classes relative to a double order on the set of
considered objects.


title: The Resolved Asteroid Program - Size, shape, and pole of (52) Europa

abstract:
  With the adaptive optics (AO) system on the 10 m Keck-II telescope, we
acquired a high quality set of 84 images at 14 epochs of asteroid (52) Europa
on 2005 January 20. The epochs covered its rotation period and, by following
its changing shape and orientation on the plane of sky, we obtained its
triaxial ellipsoid dimensions and spin pole location. An independent
determination from images at three epochs obtained in 2007 is in good agreement
with these results. By combining these two data sets, along with a single epoch
data set obtained in 2003, we have derived a global fit for (52) Europa of
diameters (379x330x249) +/- (16x8x10) km, yielding a volume-equivalent
spherical-diameter of 315 +/- 7 km, and a rotational pole within 7 deg of [RA;
Dec] = [257,+12] in an Equatorial J2000 reference frame (ECJ2000: 255,+35).
Using the average of all mass determinations available forEuropa, we derive a
density of 1.5 +/- 0.4, typical of C-type asteroids. Comparing our images with
the shape model of Michalowski et al. (A&A 416, 2004), derived from optical
lightcurves, illustrates excellent agreement, although several edge features
visible in the images are not rendered by the model. We therefore derived a
complete 3-D description of Europa's shape using the KOALA algorithm by
combining our imaging epochs with 4 stellar occultations and 49 lightcurves. We
use this 3-D shape model to assess these departures from ellipsoidal shape.
Flat facets (possible giant craters) appear to be less distinct on (52) Europa
than on other C-types that have been imaged in detail. We show that fewer giant
craters, or smaller craters, is consistent with its expected impact history.
Overall, asteroid (52) Europa is still well modeled as a smooth triaxial
ellipsoid with dimensions constrained by observations obtained over several
apparitions.


title:
Fundamental solutions of the Knizhnik-Zamolodchikov equation of one
  variable and the Riemann-Hilbert problem

abstract:
  In this article, we derive multiple polylogarithms from multiple zeta values
by using a recursive Riemann-Hilbert problem of additive type. Furthermore we
show that this Riemann-Hilbert problem is regarded as an inverse problem for
the connection problem of the KZ equation of one variable, so that the
fundamental solutions to the equation are derived from the Drinfel'd associator
by using a Riemann-Hilbert problem of multiplicative type. These results say
that the duality relation for the Drinfel'd associator can be interpreted as
the solvability condition for this inverse problem.


title:
High-temperature expansion of the one-loop free energy of a scalar field
  on a curved background

abstract:
  The complete form of the high-temperature expansion of the one-loop
contribution to the free energy of a scalar field on a stationary gravitational
background is derived. The explicit expressions for the divergent and finite
parts of the high-temperature expansion in a three-dimensional space without
boundaries are obtained. These formulas generalize the known one for the
stationary spacetime. In particular, we confirm that for a massless conformal
scalar field the leading correction to the Planck law proportional to the
temperature squared turns out to be nonzero due to non-static nature of the
metric. The explicit expression for the so-called energy-time anomaly is found.
The interrelation between this anomaly and the conformal (trace) anomaly is
established. The natural simplest Lagrangian for the "Killing vector field" is
given.


title:
On a generalization of Abelian equivalence and complexity of infinite
  words

abstract:
  In this paper we introduce and study a family of complexity functions of
infinite words indexed by $k \in \ints ^+ \cup {+\infty}.$ Let $k \in \ints ^+
\cup {+\infty}$ and $A$ be a finite non-empty set. Two finite words $u$ and $v$
in $A^*$ are said to be $k$-Abelian equivalent if for all $x\in A^*$ of length
less than or equal to $k,$ the number of occurrences of $x$ in $u$ is equal to
the number of occurrences of $x$ in $v.$ This defines a family of equivalence
relations $\thicksim_k$ on $A^*,$ bridging the gap between the usual notion of
Abelian equivalence (when $k=1$) and equality (when $k=+\infty).$ We show that
the number of $k$-Abelian equivalence classes of words of length $n$ grows
polynomially, although the degree is exponential in $k.$ Given an infinite word
$\omega \in A^\nats,$ we consider the associated complexity function $\mathcal
{P}^{(k)}_\omega :\nats \rightarrow \nats$ which counts the number of
$k$-Abelian equivalence classes of factors of $\omega$ of length $n.$ We show
that the complexity function $\mathcal {P}^{(k)}$ is intimately linked with
periodicity. More precisely we define an auxiliary function $q^k: \nats
\rightarrow \nats$ and show that if $\mathcal {P}^{(k)}_{\omega}(n)<q^k(n)$ for
some $k \in \ints ^+ \cup {+\infty}$ and $n\geq 0,$ the $\omega$ is ultimately
periodic. Moreover if $\omega$ is aperiodic, then $\mathcal
{P}^{(k)}_{\omega}(n)=q^k(n)$ if and only if $\omega$ is Sturmian. We also
study $k$-Abelian complexity in connection with repetitions in words. Using
Szemer\'edi's theorem, we show that if $\omega$ has bounded $k$-Abelian
complexity, then for every $D\subset \nats$ with positive upper density and for
every positive integer $N,$ there exists a $k$-Abelian $N$ power occurring in
$\omega$ at some position $j\in D.$


title: The hexagon equations for dilogarithms and the Riemann-Hilbert problem

abstract:
  In this article we present the hexagon equations for dilogarithms which come
from the analytic continuation of the dilogarithm $\mathrm{Li}_2(z)$ to
${\mathbf P}^1 \setminus {0,1,\infty}$. The hexagon equations are equivalent to
the coboundary relations for a certain 1-cocycle of holomorphic functions on
${\mathbf P}^1$, and are solved by the Riemann-Hilbert problem of additive
type. They uniquely characterize the dilogarithm under the normalization
condition.


title:
Revisiting eight-manifold flux compactifications of M-theory using
  geometric algebra techniques

abstract:
  Motivated by open problems in F-theory, we reconsider warped
compactifications of M theory on 8-manifolds to AdS3 spaces in the presence of
a non-trivial field strength of the M-theory 3-form, studying the most general
conditions under which such backgrounds preserve N=2 supersymmetry in three
dimensions. In contrast with previous studies, we allow for the most general
pair of Majorana generalized Killing pinors on the internal 8-manifold, without
imposing any chirality conditions on those pinors. We also show how such pinors
can be lifted to the 9-dimensional metric cone over the compactification
8-manifold. We describe the translation of the generalized Killing pinor
equations for such backgrounds to a system of differential and algebraic
constraints on certain form-valued pinor bilinears and develop techniques
through which such equations can be analyzed efficiently.


title: Broadcasting Algorithm with Per-neighbor Queues

abstract:
  Broadcasting systems such as P2P streaming systems represent important
network applications that support up to millions of online users. An efficient
broadcasting mechanism is at the core of the system design. Despite substantial
efforts on developing efficient broadcasting algorithms, the following
important question remains open: How to achieve the maximum broadcast rate in a
distributed manner with each user maintaining information queues only for its
direct neighbors? In this work, we first derive an innovative formulation of
the problem over acyclic overlay networks with arbitrary underlay capacity
constraints. Then, based on the formulation, we develop a distributed algorithm
to achieve the maximum broadcast rate and every user only maintains one queue
per-neighbor. Due to its lightweight nature, our algorithm scales very well
with the network size and remains robust against high system dynamics. Finally,
by conducting simulations we validate the optimality of our algorithm under
different network capacity models. Simulation results further indicate that the
convergence time of our algorithm grows linearly with the network size, which
suggests an interesting direction for future investigation.


title: Balanced Sparsest Generator Matrices for MDS Codes

abstract:
  We show that given $n$ and $k$, for $q$ sufficiently large, there always
exists an $[n, k]_q$ MDS code that has a generator matrix $G$ satisfying the
following two conditions: (C1) Sparsest: each row of $G$ has Hamming weight $n
- k + 1$; (C2) Balanced: Hamming weights of the columns of $G$ differ from each
other by at most one.


title: Constrained Source Coding with Side Information

abstract:
  The source-coding problem with side information at the decoder is studied
subject to a constraint that the encoder---to whom the side information is
unavailable---be able to compute the decoder's reconstruction sequence to
within some distortion. For discrete memoryless sources and finite
single-letter distortion measures, an expression is given for the minimal
description rate as a function of the joint law of the source and side
information and of the allowed distortions at the encoder and at the decoder.
The minimal description rate is also computed for a memoryless Gaussian source
with squared-error distortion measures. A solution is also provided to a more
general problem where there are more than two distortion constraints and each
distortion function may be a function of three arguments: the source symbol,
the encoder's reconstruction symbol, and the decoder's reconstruction symbol.


title: On the Concept of Law in Physics

abstract:
  I discuss the main features of the concept of law in physics. Fundamental
laws from Newtonian mechanics to general relativity are reviewed. I end with an
outlook on the new form of laws in the emerging theory of quantum gravity.


title: The exponential parameterization of the quark mixing matrix

abstract:
  We comment on the exponential parameterization of the quark mixing matrix, by
stressing that it naturally incorporates the Cabibbo structure and the
hierarchical features of the Wolfenstein form. We extend our results to the
neutrino mixing and introduce an exponential generator of the tribimaximal
matrix.


title: Active Learning on Trees and Graphs

abstract:
  We investigate the problem of active learning on a given tree whose nodes are
assigned binary labels in an adversarial way. Inspired by recent results by
Guillory and Bilmes, we characterize (up to constant factors) the optimal
placement of queries so to minimize the mistakes made on the non-queried nodes.
Our query selection algorithm is extremely efficient, and the optimal number of
mistakes on the non-queried nodes is achieved by a simple and efficient mincut
classifier. Through a simple modification of the query selection algorithm we
also show optimality (up to constant factors) with respect to the trade-off
between number of queries and number of mistakes on non-queried nodes. By using
spanning trees, our algorithms can be efficiently applied to general graphs,
although the problem of finding optimal and efficient active learning
algorithms for general graphs remains open. Towards this end, we provide a
lower bound on the number of mistakes made on arbitrary graphs by any active
learning algorithm using a number of queries which is up to a constant fraction
of the graph size.


title: Abelian maximal pattern complexity of words

abstract:
  In this paper we study the maximal pattern complexity of infinite words up to
Abelian equivalence. We compute a lower bound for the Abelian maximal pattern
complexity of infinite words which are both recurrent and aperiodic by
projection. We show that in the case of binary words, the bound is actually
achieved and gives a characterization of recurrent aperiodic words.


title:
Transitive actions of locally compact groups on locally contractible
  spaces

abstract:
  Suppose that $X=G/K$ is the quotient of a locally compact group by a closed
subgroup. If $X$ is locally contractible and connected, we prove that $X$ is a
manifold. If the $G$-action is faithful, then $G$ is a Lie group.


title: Central sets generated by uniformly recurrent words

abstract:
  A subset $A$ of $\nats$ is called an IP-set if $A$ contains all finite sums
of distinct terms of some infinite sequence $(x_n)_{n\in \nats} $ of natural
numbers. Central sets, first introduced by Furstenberg using notions from
topological dynamics, constitute a special class of IP-sets possessing rich
combinatorial properties: Each central set contains arbitrarily long arithmetic
progressions, and solutions to all partition regular systems of homogeneous
linear equations. In this paper we investigate central sets in the framework of
combinatorics on words. Using various families of uniformly recurrent words,
including Sturmian words, the Thue-Morse word and fixed points of weak mixing
substitutions, we generate an assortment of central sets which reflect the rich
combinatorial structure of the underlying words. The results in this paper rely
on interactions between different areas of mathematics, some of which had not
previously been directly linked. They include the general theory of
combinatorics on words, abstract numeration systems, and the beautiful theory,
developed by Hindman, Strauss and others, linking IP-sets and central sets to
the algebraic/topological properties of the Stone-\v{C}ech compactification of
$\nats .$


title:
Rational matrix solutions to the Leech equation: The Ball-Trent approach
  revisited

abstract:
  Using spectral factorization techniques, a method is given by which rational
matrix solutions to the Leech equation with rational matrix data can be
computed explicitly. This method is based on an approach by J.A. Ball and T.T.
Trent, and generalizes techniques from recent work of T.T. Trent for the case
of polynomial matrix data.


title:
On deforming a sector of a circular cylindrical tube into an intact
  tube: existence, uniqueness, and stability

abstract:
  Within the context of finite deformation elasticity theory the problem of
deforming an open sector of a thick-walled circular cylindrical tube into a
complete circular cylindrical tube is analyzed. The analysis provides a means
of estimating the radial and circumferential residual stress present in an
intact tube, which is a problem of particular concern in dealing with the
mechanical response of arteries. The initial sector is assumed to be unstressed
and the stress distribution resulting from the closure of the sector is then
calculated in the absence of loads on the cylindrical surfaces. Conditions on
the form of the elastic strain-energy function required for existence and
uniqueness of the deformed configuration are then examined. Finally, stability
of the resulting finite deformation is analyzed using the theory of incremental
deformations superimposed on the finite deformation, implemented in terms of
the Stroh formulation. The main results are that convexity of the strain energy
as a function of a certain deformation variable ensures existence and
uniqueness of the residually-stressed intact tube, and that bifurcation can
occur in the closing of thick, widely opened sectors, depending on the values
of geometrical and physical parameters. The results are illustrated for
particular choices of these parameters, based on data available in the
biomechanics literature.


title: On additive properties of sets defined by the Thue-Morse word

abstract:
  In this paper we study some additive properties of subsets of the set $\nats$
of positive integers: A subset $A$ of $\nats$ is called {\it $k$-summable}
(where $k\in\ben$) if $A$ contains $\textstyle \big{\sum_{n\in F}x_n | \emp\neq
F\subseteq {1,2,...,k\} \big}$ for some $k$-term sequence of natural numbers
$x_1<x_2 < ... < x_k$. We say $A \subseteq \nats$ is finite FS-big if $A$ is
$k$-summable for each positive integer $k$. We say is $A \subseteq \nats$ is
infinite FS-big if for each positive integer $k,$ $A$ contains ${\sum_{n\in
F}x_n | \emp\neq F\subseteq \nats and #F\leq k}$ for some infinite sequence of
natural numbers $x_1<x_2 < ... $. We say $A\subseteq \nats $ is an IP-set if
$A$ contains ${\sum_{n\in F}x_n | \emp\neq F\subseteq \nats and #F<\infty}$ for
some infinite sequence of natural numbers $x_1<x_2 < ... $. By the Finite Sums
Theorem [5], the collection of all IP-sets is partition regular, i.e., if $A$
is an IP-set then for any finite partition of $A$, one cell of the partition is
an IP-set. Here we prove that the collection of all finite FS-big sets is also
partition regular. Let $\TM =011010011001011010... $ denote the Thue-Morse word
fixed by the morphism $0\mapsto 01$ and $1\mapsto 10$. For each factor $u$ of
$\TM$ we consider the set $\TM\big|_u\subseteq \nats$ of all occurrences of $u$
in $\TM$. In this note we characterize the sets $\TM\big|_u$ in terms of the
additive properties defined above. Using the Thue-Morse word we show that the
collection of all infinite FS-big sets is not partition regular.


title:
Unique continuation property and local asymptotics of solutions to
  fractional elliptic equations

abstract:
  Asymptotics of solutions to fractional elliptic equations with Hardy type
potentials is studied in this paper. By using an Almgren type monotonicity
formula, separation of variables, and blow-up arguments, we describe the exact
behavior near the singularity of solutions to linear and semilinear fractional
elliptic equations with a homogeneous singular potential related to the
fractional Hardy inequality. As a consequence we obtain unique continuation
properties for fractional elliptic equations.


title: Blackbody excess in persistent Be pulsars

abstract:
  We report on the main results obtained thanks to an observation campaign,
performed with XMM-Newton, of four persistent, low-luminosity (Lx ~ 10^34
erg/s) and long-period (P > 200 s) Be accreting pulsars. We found that all
sources considered here are characterized by a spectral excess that can be
described with a blackbody component of high temperature (kT > 1 keV) and small
area (R < 0.5 km). We show that: 1) this feature is a common property of
several low-luminosity X-ray binaries; 2) for most sources the blackbody
parameters (radius and temperature) are within a narrow range of values; 3) it
can be interpreted as emission from the NS polar caps.


title: Partitioning Graph Databases - A Quantitative Evaluation

abstract:
  Electronic data is growing at increasing rates, in both size and
connectivity: the increasing presence of, and interest in, relationships
between data. An example is the Twitter social network graph. Due to this
growth demand is increasing for technologies that can process such data.
Currently relational databases are the predominant technology, but they are
poorly suited to processing connected data as they are optimized for
index-intensive operations. Conversely, graph databases are optimized for graph
computation. They link records by direct references, avoiding index lookups,
and enabling retrieval of adjacent elements in constant time, regardless of
graph size. However, as data volume increases these databases outgrow the
resources of one computer and data partitioning becomes necessary. We evaluate
the viability of using graph partitioning algorithms to partition graph
databases. A prototype partitioned database was developed. Three partitioning
algorithms explored and one implemented. Three graph datasets were used: two
real and one synthetically generated. These were partitioned in various ways
and the impact on database performance measured. We defined one synthetic
access pattern per dataset and executed each on the partitioned datasets.
Evaluation took place in a simulation environment, ensuring repeatability and
allowing measurement of metrics like network traffic and load balance. Results
show that compared to random partitioning the partitioning algorithm reduced
traffic by 40-90%. Executing the algorithm intermittently during usage
maintained partition quality, while requiring only 1% the computation of
initial partitioning. Strong correlations were found between theoretic quality
metrics and generated network traffic under non-uniform access patterns.


title: On a conjecture of Rudin on squares in Arithmetic Progressions

abstract:
  Let Q(N;q,a) denotes the number of squares in the arithmetic progression
qn+a, for n=0, 1,...,N-1, and let Q(N) be the maximum of Q(N;q,a) over all
non-trivial arithmetic progressions qn + a. Rudin's conjecture asserts that
Q(N)=O(Sqrt(N)), and in its stronger form that Q(N)=Q(N;24,1) if N=> 6. We
prove the conjecture above for 6<=N<=52. We even prove that the arithmetic
progression 24n+1 is the only one, up to equivalence, that contains Q(N)
squares for the values of N such that Q(N) increases, for 7<=N<=52 (hence, for
N=8,13,16,23,27,36,41 and 52). This allow us to assert, what we have called
Super-Strong Rudin's Conjecture: let be N=GP_k+1=> 8 for some integer k, where
GP_k is the k-th generalized pentagonal number, then Q(N)=Q(N;q,a) with
gcd(q,a) squarefree and q> 0 if and only if (q,a)=(24,1).


title:
Classification of invariant AHS--structures on semisimple locally
  symmetric spaces

abstract:
  In this article, we discuss which semisimple locally symmetric spaces admit
an AHS--structure invariant to local symmetries. We classify them for all types
of AHS--structures and determine possible equivalence classes of such
AHS--structures.


title:
Stripe disorder and dynamics in the hole-doped antiferromagnetic
  insulator La5/3Sr1/3CoO4

abstract:
  We report on an investigation into the dynamics of the stripe phase of
La5/3Sr1/3CoO4, a material recently shown to have an hour-glass magnetic
excitation spectrum. A combination of magnetic susceptibility, muon-spin
relaxation and nuclear magnetic resonance measurements strongly suggest that
the physics is determined by a disordered configuration of charge and spin
stripes whose frustrated magnetic degrees of freedom are strongly dynamic at
high temperature and which freeze out in a glassy manner as the temperature is
lowered. Our results broadly confirm a recent theoretical prediction, but show
that the charge quenching remains incomplete well below the charge ordering
temperature and reveal, in detail, the manner in which the magnetic degrees of
freedom are frozen.


title: Crossed products for interactions and graph algebras

abstract:
  We consider Exel's interaction $(V,H)$ over a unital $C^*$-algebra $A$, such
that $V(A)$ and $H(A)$ are hereditary subalgebras of $A$. For the associated
crossed product, we obtain a uniqueness theorem, ideal lattice description,
simplicity criterion and a version of Pimsner-Voiculescu exact sequence. These
results cover the case of crossed products by endomorphisms with hereditary
ranges and complementary kernels. As model examples of interactions not coming
from endomorphisms we introduce and study in detail interactions arising from
finite graphs.
  The interaction $(V,H)$ associated to a graph $E$ acts on the core $F_E$ of
the graph algebra $C^*(E)$. By describing a partial homeomorphism of
$\widehat{F}_E$ dual to $(V,H)$ we find Cuntz-Krieger uniqueness theorem,
criteria for gauge-invariance of all ideals and simplicity of $C^*(E)$ as
results concerning reversible noncommutative dynamics. We also provide a new
approach to calculation of $K$-theory of $C^*(E)$ using only an induced partial
automorphism of $K_0(F_E)$ and the six-term exact sequence.


title:
Incompressible limit of the non-isentropic ideal magnetohydrodynamic
  equations

abstract:
  We study the incompressible limit of the compressible non-isentropic ideal
magnetohydrodynamic equations with general initial data in the whole space
$\mathbb{R}^d$ ($d=2,3$). We first establish the existence of classic solutions
on a time interval independent of the Mach number. Then, by deriving uniform a
priori estimates, we obtain the convergence of the solution to that of the
incompressible magnetohydrodynamic equations as the Mach number tends to zero.


title:
Spontaneous emission enhancement from polymer-embedded colloidal PbS
  nanocrystals into Si-based photonics at telecom wavelengths

abstract:
  We experimentally demonstrate the coupling of optically excited PbS
nanocrystal (NC) photoluminescence (PL) into Si-based ring resonators and
waveguides at 300K. The PbS NCs are dissolved into Novolak polymer at various
concentrations and applied by drop-casting. The coupling mechanism and the
spontaneous emission enhancement are experimentally investigated and compared
to theoretical predictions. Quality (Q) factors of 2500 were obtained in
emission and transmission for wavelengths centered around 1.45{\mu}m. PL
intensity shows a linear dependence on the excitation power and no degradation
of the Q factors. Devices with stable optical properties are obtained by this
versatile technique.


title: Stochastic bias in multi-dimensional excursion set approaches

abstract:
  We describe a simple fully analytic model of the excursion set approach
associated with two Gaussian random walks: the first walk represents the
initial overdensity around a protohalo, and the second is a crude way of
allowing for other factors which might influence halo formation. This model is
richer than that based on a single walk, because it yields a distribution of
heights at first crossing. We provide explicit expressions for the
unconditional first crossing distribution which is usually used to model the
halo mass function, the progenitor distributions, and the conditional
distributions from which correlations with environment are usually estimated.
These latter exhibit perhaps the simplest form of what is often called nonlocal
bias, and which we prefer to call stochastic bias, since the new bias effects
arise from `hidden-variables' other than density, but these may still be
defined locally. We provide explicit expressions for these new bias factors. We
also provide formulae for the distribution of heights at first crossing in the
unconditional and conditional cases. In contrast to the first crossing
distribution, these are exact, even for moving barriers, and for walks with
correlated steps. The conditional distributions yield predictions for the
distribution of halo concentrations at fixed mass and formation redshift. They
also exhibit assembly bias like effects, even when the steps in the walks
themselves are uncorrelated. Finally, we show how the predictions are modified
if we add the requirement that halos form around peaks: these depend on whether
the peaks constraint is applied to a combination of the overdensity and the
other variable, or to the overdensity alone. Our results demonstrate the power
of requiring models to reproduce not just halo counts but the distribution of
overdensities at fixed protohalo mass as well.


title:
A Bayesian Non-Parametric Approach to Asymmetric Dynamic Conditional
  Correlation Model With Application to Portfolio Selection

abstract:
  We propose a Bayesian non-parametric approach for modeling the distribution
of multiple returns. In particular, we use an asymmetric dynamic conditional
correlation (ADCC) model to estimate the time-varying correlations of financial
returns where the individual volatilities are driven by GJR-GARCH models. The
ADCC-GJR-GARCH model takes into consideration the asymmetries in individual
assets' volatilities, as well as in the correlations. The errors are modeled
using a Dirichlet location-scale mixture of multivariate Gaussian distributions
allowing for a great flexibility in the return distribution in terms of
skewness and kurtosis. Model estimation and prediction are developed using MCMC
methods based on slice sampling techniques. We carry out a simulation study to
illustrate the flexibility of the proposed approach. We find that the proposed
DPM model is able to adapt to several frequently used distribution models and
also accurately estimates the posterior distribution of the volatilities of the
returns, without assuming any underlying distribution. Finally, we present a
financial application using Apple and NASDAQ Industrial index data to solve a
portfolio allocation problem. We find that imposing a restrictive parametric
distribution can result into underestimation of the portfolio variance, whereas
DPM model is able to overcome this problem.


title: No Conformal Anomaly in Unimodular Gravity

abstract:
  The conformal invariance of unimodular gravity survives quantum corrections,
even in the presence of conformal matter. Unimodular gravity can actually be
understood as a certain truncation of the full Einstein-Hilbert theory, where
in the Einstein frame the metric tensor enjoys unit determinant. Our result is
compatible with the idea that the corresponding restriction in the functional
integral is consistent as well.


title:
The expected value of the squared euclidean cophenetic metric under the
  Yule and the uniform models

abstract:
  The cophenetic metrics $d_{\varphi,p}$, for $p\in {0}\cup[1,\infty[$, are a
recent addition to the kit of available distances for the comparison of
phylogenetic trees. Based on a fifty years old idea of Sokal and Rohlf, these
metrics compare phylogenetic trees on a same set of taxa by encoding them by
means of their vectors of cophenetic values of pairs of taxa and depths of
single taxa, and then computing the $L^p$ norm of the difference of the
corresponding vectors. In this paper we compute the expected value of the
square of $d_{\varphi,2}$ on the space of fully resolved rooted phylogenetic
trees with $n$ leaves, under the Yule and the uniform probability
distributions.


title: Parametric Estimation of Handoff

abstract:
  The efficiency of wireless technology depends upon the seamless connectivity
to the user at anywhere any time.Heterogeneous wireless networks are an
integration of different networks with diversified technologies. The most
essential requirement for Seamless vertical handover is that the received
signal strength should always be healthy. Mobile device enabled with multiple
wireless technologies makes it possible to maintain seamless connectivity in
highly dynamic environment.Since the available bandwidth is limited and the
number of users is growing rapidly, it is a real challenge to maintain the
received signal strength in a healthy stage.In this work, the proposed, cost
effective parametric estimation for vertical handover shows that the received
signal strength maintains a healthy level by considering the novel concept.


title:
Critical velocity, vortex shedding and drag in a unitary Fermi
  superfluid

abstract:
  We study the real-time motion of a microscopic object in a cold Fermi gas at
unitary conditions by using an extended Thomas-Fermi density functional
approach. We find that spontaneous creation of singly quantized
vortex-antivortex pairs occurs as a critical velocity is exceeded, which leads
to a drag between the moving object and the Fermi gas. The resulting force is
linear in the velocity for subsonic motion and becomes quadratic for supersonic
motion.


title:
Statistical and polarization properties of giant pulses of the
  millisecond pulsar B1937+21

abstract:
  We have studied the statistical and polarization properties of giant pulses
(GPs) emitted by the millisecond pulsar B1937+21, with high sensitivity and
time resolution. The observations were made in June 2005 with the 100-m Robert
C. Byrd Green Bank Telescope at S-band (2052-2116 MHz) using the Mk5A VLBI
recording system, with formal time resolution of 16 ns. The total observing
time was about 4.5 hours; the rate of detection of GPs was about 130 per hour
at the average longitudes of the main pulse (MPGPs) and 60 per hour at the
interpulse (IPGPs). While the average profile shows well-defined polarization
behavior, with regular evolution of the linear polarization position angle
(PA), GPs exhibit random properties, occasionally having high linear or
circular polarization. Neither MPGPs nor IPGPs show a preferred PA. The
cumulative probability distribution (CPD) of GP pulse energy was constructed
down to the level where GPs merge with regular pulses and noise. For both MPGPs
and IPGPs, the CPD follows a power law with a break, the power index changing
from -2.4 at high energy to -1.6 for low energy. Pulse smearing due to
scattering masks the intrinsic shape and duration of the detected GPs. The
smearing time varied during the observing session within a range of a few
hundred nanoseconds. The measured polarization and statistical properties of
GPs impose strong constraints on physical models of GPs. Some of these
properties support a model in which GPs are generated by the electric discharge
caused by magnetic reconnection of field lines connecting the opposite magnetic
poles of a neutron star.


title:
Einstein-Cartan gravity, Asymptotic Safety, and the running Immirzi
  parameter

abstract:
  In this paper we analyze the functional renormalization group flow of quantum
gravity on the Einstein-Cartan theory space. The latter consists of all action
functionals depending on the spin connection and the vielbein field (co-frame)
which are invariant under both spacetime diffeomorphisms and local frame
rotations. In the first part of the paper we develop a general methodology and
corresponding calculational tools which can be used to analyze the flow
equation for the pertinent effective average action for any truncation of this
theory space. In the second part we apply it to a specific three-dimensional
truncated theory space which is parametrized by Newton's constant, the
cosmological constant, and the Immirzi parameter. A comprehensive analysis of
their scale dependences is performed, and the possibility of defining an
asymptotically safe theory on this hitherto unexplored theory space is
investigated. In principle Asymptotic Safety of metric gravity (at least at the
level of the effective average action) is neither necessary nor sufficient for
Asymptotic Safety on the Einstein-Cartan theory space which might accommodate
different "universality classes" of microscopic quantum gravity theories.
Nevertheless, we do find evidence for the existence of at least one
non-Gaussian renormalization group fixed point which seems suitable for the
Asymptotic Safety construction in a setting where the spin connection and the
vielbein are the fundamental field variables.


title:
Secret Key Agreement Using Conferencing in State- Dependent Multiple
  Access Channels with An Eavesdropper

abstract:
  In this paper, the problem of secret key agreement in state-dependent
multiple access channels with an eavesdropper is studied. For this model, the
channel state information is non-causally available at the transmitters;
furthermore, a legitimate receiver observes a degraded version of the channel
state information. The transmitters can partially cooperate with each other
using a conferencing link with a limited rate. In addition, a backward public
channel is assumed between the terminals. The problem of secret key sharing
consists of two rounds. In the first round, the transmitters wish to share a
common key with the legitimate receiver. Lower and upper bounds on the common
key capacity are established. In a special case, the capacity of the common key
is obtained. In the second round, the legitimate receiver agrees on two
independent private keys with the corresponding transmitters using the public
channel. Inner and outer bounds on the private key capacity region are
characterized. In a special case, the inner bound coincides with the outer
bound. We provide some examples to illustrate our results.


title: Optimal Shortcuts to Adiabaticity for a Quantum Piston

abstract:
  In this paper we use optimal control to design minimum-time adiabatic-like
paths for the expansion of a quantum piston. Under realistic experimental
constraints, we calculate the minimum expansion time and compare it with that
obtained from a state of the art inverse engineering method. We use this result
to rederive the known upper bound for the cooling rate of a refrigerator, which
provides a quantitative description for the unattainability of absolute zero,
the third law of thermodynamics. We finally point out the relation of the
present work to the fast adiabatic-like expansion of an accordion optical
lattice, a system which can be used to magnify the initial quantum state
(quantum microscope).


title: Black hole complementarity and firewall in two dimensions

abstract:
  In connection with black hole complementarity, we study the possibility of
the duplication of information in the RST model which is an exactly soluble
quantized model in two dimensions. We find that the duplication of information
can be observed without resort to assuming an excessively large number of
scalar fields. If we introduce a firewall, then we can circumvent this problem;
however, the firewall should be outside the event horizon.


title: The Tree Width of Separation Logic with Recursive Definitions

abstract:
  Separation Logic is a widely used formalism for describing dynamically
allocated linked data structures, such as lists, trees, etc. The decidability
status of various fragments of the logic constitutes a long standing open
problem. Current results report on techniques to decide satisfiability and
validity of entailments for Separation Logic(s) over lists (possibly with
data). In this paper we establish a more general decidability result. We prove
that any Separation Logic formula using rather general recursively defined
predicates is decidable for satisfiability, and moreover, entailments between
such formulae are decidable for validity. These predicates are general enough
to define (doubly-) linked lists, trees, and structures more general than
trees, such as trees whose leaves are chained in a list. The decidability
proofs are by reduction to decidability of Monadic Second Order Logic on graphs
with bounded tree width.


title: Riemannian geodesics of semi Riemannian warped metrics

abstract:
  Let $(M_1,g_1)$ and $(M_2,g_2)$ be two $C^\infty$--differentiable connected,
complete Riemannian manifolds, $k:M_1\to\mathbb R$ a $C^\infty$--differentiable
function, having $0<k_0<k(x)\leq K_0$, for any $x\in M_1$ and $g:=g_1-kg_2$ the
semi Riemannian metric on the product manifold $M:=M_1\times M_2$. We associate
to $g$ a suitable family of Riemannian metrics $G_r+g_2$, with $r>-K_0^{-1}$,
on $M$ and we call Riemannian geodesics of $g$ the geodesics of $g$ which are
geodesics of a metric of the previous family, via a suitable reparametrization.
Among the properties of these geodesics, we quote: For any $z_0=(x_0,y_0)\in M$
and for any $y_1\in M_2$ there exists a subset $A$ of $M_1$, such that all the
geodesics of $g$ joining $z_0$ with a point $(x_1,y_1)$, with $x_1\in A$, are
Riemannian. The Riemannian geodesics of $g$ determine a "partial" property of
geodesic connection on $M$. Finally, we determine two new classes of semi
Riemannian metrics (one of which includes some FLRM-metrics), geodesically
connected by Riemannian geodesics of $g$.


title:
Malliavin calculus approach to statistical inference for Levy driven
  SDE's

abstract:
  By means of the Malliavin calculus, integral representations for the
likelihood function and for the derivative of the log-likelihood function are
given for a model based on discrete time observations of the solution to
equation dX_t=a_\theta(X_t)dt + dZ_t with a tempered \alpha-stable process Z.
Using these representations, regularity of the statistical experiment and the
Cramer-Rao inequality are proved.


title: Key agreement over a 3-receiver broadcast channel

abstract:
  In this paper, we consider the problem of secret key agreement in
state-dependent 3-receiver broadcast channels. In the proposed model, there are
two legitimate receivers, an eavesdropper and a transmitter where the channel
state information is non-causally available at the transmitter. We consider two
setups. In the first setup, the transmitter tries to agree on a common key with
the legitimate receivers while keeping it concealed from the eavesdropper.
Simultaneously, the transmitter agrees on a private key with each of the
legitimate receivers that needs to be kept secret from the other legitimate
receiver and the eavesdropper. For this setup, we derive inner and outer bounds
on the secret key capacity region. In the second setup, we assume that a
backward public channel is available among the receivers and the transmitter.
Each legitimate receiver wishes to share a private key with the transmitter.
For this setup, an inner bound on the private key capacity region is found.
Furthermore, the capacity region of the secret key in the state-dependent
wiretap channel can be deduced from our inner and outer bounds.


title: Interactions between para-quaternionic and Grassmannian geometry

abstract:
  Almost para-quaternionic structures on smooth manifolds of dimension $2n$ are
equivalent to almost Grassmannian structures of type $(2,n)$. We remind the
equivalence and exhibit some interrelations between subjects that were
previously studied independently from the para-quaternionic and the
Grassmannian point of view. In particular, we relate the respective
normalization conditions, distinguished curves and twistor constructions.


title:
On the number of zeros of linear combinations of independent
  characteristic polynomials of random unitary matrices

abstract:
  We show that almost all the zeros of any finite linear combination of
independent characteristic polynomials of random unitary matrices lie on the
unit circle. This result is the random matrix analogue of an earlier result by
Bombieri and Hejhal on the distribution of zeros of linear combinations of
$L$-functions, thus providing further evidence for the conjectured links
between the value distribution of the characteristic polynomial of random
unitary matrices and the value distribution of $L$-functions on the critical
line.


title:
Impact of Torsion Space-Time on $t\bar{t}$ observables at Hadron
  Colliders

abstract:
  Starting from the effective torsion space-time model, we study its effects on
the top pair production cross section at hadron colliders. We also study the
effect of this model on top pair asymmetries at the Tevatron and the LHC. We
find that torsion space-time can explain forward-backward asymmetry according
to measured anomaly at Tevatron. We find an allowed region in the parameters
space which can satisfy simultaneously all $t\bar{t}$ observables measured at
Tevatron and LHC.


title:
High-frequency response of GaN in moderate electric and magnetic fields:
  Interplay between cyclotron and optical phonon transient time resonances

abstract:
  We have studied the high-frequency properties of the non-equilibrium electron
gas in GaN samples subjected to electric and magnetic fields. Spectra of the
complex tensor of the dynamical mobility have been calculated for THz frequency
range. For the compensated GaN and low temperatures, in the intervals of
electric fields of the few $kV/cm$ and magnetic fields of the few $T$ the
existence of the cyclotron and optical phonon transit-time resonances has been
identified. We have shown that interplay of two resonances gives rise to
specific spectra of THz transmission and absorption (or gain). We suggest that
experimental investigation of these effects will facilitate elaboration of
field controlled devices for THz optoelectronics.


title: A real open book not fillable by a real Lefschetz fibration

abstract:
  A real 3- or 4-manifold has by definition an orientation preserving smooth
involution acting on it. We consider Lefschetz fibrations of 4-dimensional
manifolds-with-boundary and open book decompositions on their boundary in the
existence of a real structure. We prove that there is a real open book which
cannot be filled by a real Lefschetz fibration, although it is filled by
non-real Lefschetz fibrations.


title:
Limit-cycle-based control of the myogenic wingbeat rhythm in the fruit
  fly Drosophila

abstract:
  In many animals, rhythmic motor activity is governed by neural limit cycle
oscillations under the control of sensory feedback. In the fruit fly Drosophila
melanogaster, the wingbeat rhythm is generated myogenically by
stretch-activated muscles and hence independently from direct neural input. In
this study, we explored if generation and cycle-by-cycle control of
Drosophila's wingbeat are functionally separated, or if the steering muscles
instead couple into the myogenic rhythm as a weak forcing of a limit cycle
oscillator. We behaviourally tested tethered flying flies for characteristic
properties of limit cycle oscillators. To this end, we mechanically stimulated
the fly's gyroscopic organs, the halteres, and determined the phase
relationship between the wing motion and stimulus. The flies synchronized with
the stimulus for specific ranges of stimulus amplitude and frequency, revealing
the characteristic Arnold tongues of a forced limit cycle oscillator. Rapid
periodic modulation of the wingbeat frequency prior to locking demonstrates the
involvement of the fast steering muscles in the observed control of the
wingbeat frequency. We propose that the mechanical forcing of a myogenic limit
cycle oscillator permits flies to avoid the comparatively slow control based on
a neural central pattern generator.


title: Perfect graphs: a survey

abstract:
  Perfect graphs were defined by Claude Berge in the 1960s. They are important
objects for graph theory, linear programming and combinatorial optimization.
Claude Berge made a conjecture about them, that was proved by Chudnovsky,
Robertson, Seymour and Thomas in 2002, and is now called the strong perfect
graph theorem. This is a survey about perfect graphs, mostly focused on the
strong perfect graph theorem.


title:
Studies of FemIrn nano clusters using Density Functional Theory
  Techniques

abstract:
  The structure, binding energy, magnetic moments and electronic structure of
FemIrn clusters are investigated using state of the art density functional
theory techniques. Fully unconstrained structural relaxations are undertaken by
considering all possible non equivalent cluster structures. The optimized
clusters are all compact, indicating a clear tendency to maximize the number of
nearest neighbour Fe-Ir pairs. The binding energy shows an increment with
cluster size. All the clusters preserve ferromagnetic order after optimization.
The average magnetic moment generally shows an increase with Fe concentration.
The spin polarized density of states is largely dominated by the contribution
of d orbitals. An important enhancement of the local Fe moments in an Ir rich
environment is observed due to the charge transfer between Fe and Ir. On the
other hand, the Ir moments are already large in the pure Ir clusters and does
not show significant enhancement with Fe doping. The HOMO-LUMO gaps show a
general reduction with alloying, indicating more metallicity for the doped
clusters than the pure ones.


title: Two-pion excited state contribution to pseudo-scalar correlators

abstract:
  We study multi-particle state contributions to the QCD two-point functions of
pseudo-scalar quark bilinears in a finite spatial volume. For sufficiently
small quark masses one expects three-meson states with two additional pions at
rest to have the lowest total energy after the ground state. Using chiral
perturbation theory, we find the amplitude of this state to be too small to be
seen in present-day lattice simulations. We speculate that curvature in the
effective mass plot extracted from the pseudo-scalar density two-point function
instead corresponds to a genuine resonance, the \pi(1300).


title: Scattering of Graphene plasmons by defects in the graphene sheet

abstract:
  A theoretical study is presented on the scattering of graphene surface
plasmons by defects in the graphene sheet they propagate in. These defects can
be either natural (as domain boundaries, ripples and cracks, among others) or
induced by an external gate. The scattering is shown to be governed by an
integral equation, derived from a plane wave expansion of the fields, which in
general must be solved numerically but it provides useful analytical results
for small defects. Two main cases are considered: smooth variations of the
graphene conductivity (characterized by a Gaussian conductivity profile) and
sharp variations (represented by islands with different conductivity). In
general, reflection largely dominates over radiation out of the graphene sheet.
However, in the case of sharply defined conductivity islands there are some
values of island size and frequency where the reflectance vanishes and,
correspondingly, the radiation out of plane is the main scattering process. For
smooth defects, the reflectance spectra present a single maximum at the
condition $k_p a \approx \sqrt{2}$, where $k_p$ is the GSP wavevector and $a$
the spatial width of the defect. In contrast, the reflectance spectra of sharp
defects present periodic oscillations with period $k_p' a$, where $k_p'$ is the
GSP wavelength inside the defect. Finally, the case of cracks (gaps in the
graphene conductivity) is considered, showing that the reflectance is
practically unity for gap widths larger than one tenth of the GSP wavelength.


title:
The Effects of radial inflow of gas and galactic fountains on the
  chemical evolution of M31

abstract:
  Galactic fountains and radial gas flows are very important ingredients in
modeling the chemical evolution of galactic disks. Our aim here is to study the
effects of galactic fountains and radial gas flows in the chemical evolution of
the disk of M31. We adopt a ballistic method to study the effects of galactic
fountains on the chemical enrichment of the M31 disk. We find that the landing
coordinate for the fountains in M31 is no more than 1 kpc from the starting
point, thus producing negligible effect on the chemical evolution of the disk.
We find that the delay time in the enrichment process due to fountains is no
longer than 100 Myr and this timescale also produces negligible effects on the
results. Then, we compute the chemical evolution of the M31 disk with radial
gas flows produced by the infall of extragalactic material and fountains. We
find that a moderate inside-out formation of the disk coupled with radial flows
of variable speed can very well reproduce the observed gradient. We discuss
also the effects of other parameters such a threshold in the gas density for
star formation and an efficiency of star formation varying with the galactic
radius. We conclude that the most important physical processes in creating disk
gradients are the inside-out formation and the radial gas flows. More data on
abundance gradients both locally and at high redshift are necessary to confirm
this conclusion.


title: A Rational and Efficient Algorithm for View Revision in Databases

abstract:
  The dynamics of belief and knowledge is one of the major components of any
autonomous system that should be able to incorporate new pieces of information.
In this paper, we argue that to apply rationality result of belief dynamics
theory to various practical problems, it should be generalized in two respects:
first of all, it should allow a certain part of belief to be declared as
immutable; and second, the belief state need not be deductively closed. Such a
generalization of belief dynamics, referred to as base dynamics, is presented,
along with the concept of a generalized revision algorithm for Horn knowledge
bases. We show that Horn knowledge base dynamics has interesting connection
with kernel change and abduction. Finally, we also show that both variants are
rational in the sense that they satisfy certain rationality postulates stemming
from philosophical works on belief dynamics.