title: D-branes in Supersymmetric Backgrounds

abstract:
  In this Ph. D. Thesis we concentrate on the study of the extension of the
AdS/CFT correspondence to theories with less supersymmetry. In particular, we
search for the possibility of adding supersymmetric D-branes in type IIB
supergravity solutions which are dual to N=1 supersymmetric gauge theories in
four dimensions. In the probe approximation we perform a systematic analysis of
the possible supersymmetric D-brane configurations in backgrounds dual to N=1
superconformal field theories, firstly in the AdS_5xY^{p,q} solutions and then
in their generalisation to the AdS_5xL^{a,b,c} backgrounds. Some checks of the
correspondence between D-brane configurations and chiral operators of the dual
gauge theory are performed. We also analyse the possible supersymmetric
D5-brane configurations dual to defects (of codimension one and two) in N=1 SYM
theory in the framework of the Maldacena-Nunez solution. Beyond the probe
approximation, we develop techniques in order to take into account the
backreaction undergone by the type IIB supergravity solutions (dual to N=1
superconformal field theories and their extensions to cascading theories) due
to the addition of a number of flavour branes of the same order as the number
of colour branes which generate the unflavour background. The dual
interpretation of those flavour branes is given in terms of dynamical fields
transforming in the fundamental representation of the gauge group. Several
gauge theories features are matched, like beta functions, anomalies and the
duality cascade which describes the RG flow of the cascading field theories.


title:
On widening the angular existence domain for Dyakonov surface waves
  using the Pockels effect

abstract:
  The propagation of Dyakonov surface waves (DSWs) at the planar interface
between an isotropic material and a linear electro-optic birefringent material
can be dynamically controlled using the Pockels effect. The range of directions
for DSW propagation has been previously found to be rather narrow. By careful
choice of various parameters, this range of directions can be increased by more
than an order of magnitude.


title: Flexible Quasi-Three-Dimensional Terahertz Metamaterials

abstract:
  We characterize planar electric terahertz metamaterials fabricated on thin,
flexible substrates using terahertz time-domain spectroscopy.
Quasi-three-dimensional metamaterials are formed by stacking multiple
metamaterial layers. Transmission measurements reveal resonant band-stop
behavior that becomes stronger with an increasing number of layers. Extracted
metamaterial dielectric functions are shown to be independent of the number of
layers, validating the effective medium approximation. Limitations of this
approximation are discussed.


title: Search Space Contraction in Canonical Labeling of Graphs

abstract:
  The individualization-refinement paradigm for computing a canonical labeling
and the automorphism group of a graph is investigated. A new algorithmic design
aimed at reducing the size of the associated search space is introduced, and a
new tool, named "Traces", is presented, together with experimental results and
comparisons with existing software, such as McKay's "nauty". It is shown that
the approach presented here leads to a huge reduction in the search space,
thereby making computation feasible for several classes of graphs which are
hard for all the main canonical labeling tools in the literature.


title: On the deformation chirality of real cubic fourfolds

abstract:
  According to our previous results, the conjugacy class of the involution
induced by the complex conjugation in the homology of a real non-singular cubic
fourfold determines the fourfold up to projective equivalence and deformation.
Here, we show how to eliminate the projective equivalence and to obtain a pure
deformation classification, that is how to respond to the chirality question:
which cubics are not deformation equivalent to their image under a mirror
reflection. We provide an arithmetical criterion of chirality, in terms of the
eigen-sublattices of the complex conjugation involution in homology, and show
how this criterion can be effectively applied taking as examples $M$-cubics
(that is those for which the real locus has the richest topology) and
$(M-1)$-cubics (the next case with respect to complexity of the real locus). It
happens that there is one chiral class of $M$-cubics and three chiral classes
of $(M-1)$-cubics, contrary to two achiral classes of $M$-cubics and three
achiral classes of $(M-1)$-cubics.


title:
Eternal solutions and heteroclinic orbits of a semilinear parabolic
  equation

abstract:
  This dissertation describes the space of heteroclinic orbits for a class of
semilinear parabolic equations, focusing primarily on the case where the
nonlinearity is a second degree polynomial with variable coefficients. Along
the way, a new and elementary proof of existence and uniqueness of solutions is
given. Heteroclinic orbits are shown to be characterized by a particular
functional being finite. A novel asymptotic-numeric matching scheme is used to
uncover delicate bifurcation behavior in the equilibria. The exact nature of
this bifurcation behavior leads to a demonstration that the equilibria are
degenerate critical points in the sense of Morse. Finally, the space of
heteroclinic orbits is shown to have a cell complex structure, which is finite
dimensional when the number of equilibria is finite.


title:
Minor-Embedding in Adiabatic Quantum Computation: I. The Parameter
  Setting Problem

abstract:
  We show that the NP-hard quadratic unconstrained binary optimization (QUBO)
problem on a graph $G$ can be solved using an adiabatic quantum computer that
implements an Ising spin-1/2 Hamiltonian, by reduction through minor-embedding
of $G$ in the quantum hardware graph $U$. There are two components to this
reduction: embedding and parameter setting. The embedding problem is to find a
minor-embedding $G^{emb}$ of a graph $G$ in $U$, which is a subgraph of $U$
such that $G$ can be obtained from $G^{emb}$ by contracting edges. The
parameter setting problem is to determine the corresponding parameters, qubit
biases and coupler strengths, of the embedded Ising Hamiltonian. In this paper,
we focus on the parameter setting problem. As an example, we demonstrate the
embedded Ising Hamiltonian for solving the maximum independent set (MIS)
problem via adiabatic quantum computation (AQC) using an Ising spin-1/2 system.
We close by discussing several related algorithmic problems that need to be
investigated in order to facilitate the design of adiabatic algorithms and AQC
architectures.


title: SimDialog: A visual game dialog editor

abstract:
  SimDialog is a visual editor for dialog in computer games. This paper
presents the design of SimDialog, illustrating how script writers and
non-programmers can easily create dialog for video games with complex branching
structures and dynamic response characteristics. The system creates dialog as a
directed graph. This allows for play using the dialog with a state-based cause
and effect system that controls selection of non-player character responses and
can provide a basic scoring mechanism for games.


title:
Localization and interaction of indirect excitons in GaAs coupled
  quantum wells

abstract:
  We introduced an elevated trap technique and exploited it for lowering the
effective temperature of indirect excitons. We observed narrow
photoluminescence lines which correspond to the emission of individual states
of indirect excitons in a disorder potential. We studied the effect of
exciton-exciton interaction on the localized and delocalized exciton states and
found that the homogeneous line broadening increases with density and dominates
the linewidth at high densities.


title: Relaxation processes in a disordered Luttinger liquid

abstract:
  The Luttinger liquid model, which describes interacting electrons in a
single-channel quantum wire, is completely integrable in the absence of
disorder and as such does not exhibit any relaxation to equilibrium. We
consider relaxation processes induced by inelastic electron-electron
interactions in a disordered Luttinger liquid, focusing on the equilibration
rate and its essential differences from the electron-electron scattering rate
as well as the rate of phase relaxation. In the first part of the paper, we
review the basic concepts in the disordered Luttinger liquid at equilibrium.
These include the elastic renormalization, dephasing, and interference-induced
localization. In the second part, we formulate a conceptually important
framework for systematically studying the nonequilibrium properties of the
strongly correlated (non-Fermi) Luttinger liquid. We derive a coupled set of
kinetic equations for the fermionic and bosonic distribution functions that
describe the evolution of the nonequilibrium Luttinger liquid. Remarkably, the
energy equilibration rate in the conducting disordered quantum wire (at
sufficiently high temperature, when the localization effects are suppressed by
dephasing) is shown to be of the order of the rate of elastic scattering off
disorder, independent of the interaction constant and temperature.


title: Asymmetric embedding in brane cosmology

abstract:
  We derive a system of cosmological equations for a braneworld with induced
curvature which is a junction between several bulk spaces. The permutation
symmetry of the bulk spaces is not imposed, and the values of the fundamental
constants, and even the signatures of the extra dimension, may be different on
different sides of the brane. We then consider the usual partial case of two
asymmetric bulk spaces and derive an exact closed system of scalar equations on
the brane. We apply this result to the cosmological evolution on such a brane
and describe its various partial cases.


title:
Substochastic semigroups and densities of piecewise deterministic Markov
  processes

abstract:
  Necessary and sufficient conditions are given for a substochastic semigroup
on $L^1$ obtained through the Kato--Voigt perturbation theorem to be either
stochastic or strongly stable. We show how such semigroups are related to
piecewise deterministic Markov process, provide a probabilistic interpretation
of our results, and apply them to fragmentation equations.


title:
Static $\bar Q Q$ Potentials and the Magnetic Component of QCD Plasma
  near $T_c$

abstract:
  Static quark-anti-quark potential encodes important information on the
chromodynamical interaction between color charges, and recent lattice results
show its very nontrivial behavior near the deconfinement temperature $T_c$. In
this paper we study such potential in the framework of the ``magnetic
scenario'' for the near Tc QCD plasma, and particularly focus on the linear
part (as quantified by its slope, the tension) in the potential as well as the
strong splitting between the free energy and internal energy. By using an
analytic ``ellipsoidal bag'' model, we will quantitatively relate the free
energy tension to the magnetic condensate density and relate the internal
energy tension to the thermal monopole density. By converting the lattice
results for static potential into density for thermal monopoles we find the
density to be very large around Tc and indicate at quantum coherence, in good
agreement with direct lattice calculation of such density. A few important
consequences for heavy ion collisions phenomenology will also be discussed.


title:
Comment on "New method for studying neutrino mixing and mass
  differences"

abstract:
  It has been suggested that the temporal oscillations in the rate of decay of
Pr ions reported in the GSI K-capture experiment arise from interference
between different values of the momentum of the Pr ions. It is shown here that
any such interference cannot contribute to the decay rate of those ions.


title: Square-Difference-Free Sets of Size Omega(n^{0.7334...})

abstract:
  A set A is square-difference free (henceforth SDF) if there do not exist
x,y\in A, x\ne y, such that |x-y| is a square. Let sdf(n) be the size of the
largest SDF subset of {1,...,n}. Ruzsa has shown that sdf(n) = \Omega(n^{0.5(1+
\log_{65} 7)}) = \Omega(n^{0.733077...}) We improve on the lower bound by
showing sdf(n) = \Omega(n^{0.5(1+ \log_{205} 12)})= \Omega(n^{.7443...}) As a
corollary we obtain a new lower bound on the quadratic van der Waerden numbers.


title: Azimuthal correlations of forward dijets in d+Au collisions at RHIC

abstract:
  Measuring correlations between forward dijets in deuteron-gold collisions at
RHIC will further test the Color Glass Condensate (CGC) picture of the nuclear
wavefunction at small-x, which successfully predicted the suppressed production
of high-p_T particles at forward rapidities in d+Au collisions: R_dA<1. I
present predictions for the correlation in azimuthal angle between forward
dijets in the CGC framework, with both multiple scatterings and non-linear QCD
evolution at small-x taken into account.


title:
An analog of the Furstenberg-Katznelson-Weiss theorem on triangles in
  sets of positive density in finite field geometries

abstract:
  We prove that if the cardinality of a subset of the 2-dimensional vector
space over a finite field with $q$ elements is $\ge \rho q^2$, with
$\frac{1}{\sqrt{q}}<<\rho \leq 1$, then it contains an isometric copy of $\ge
c\rho q^3$ triangles.


title:
Origin of Intense Magnetic Fields Near Black Holes Due to Non-Minimal
  Gravitational-Electromagnetic Coupling

abstract:
  The origin of magnetic fields in astrophysical objects is a challenging
problem in astrophysics. Throughout the years, many scientists have suggested
that non-minimal gravitational-electromagnetic coupling (NMGEC) could be the
origin of the ubiquitous astrophysical magnetic fields. We investigate the
possible origin of intense magnetic fields $\sim 10^{15}-10^{16}$ by NMGEC near
rotating neutron stars and black holes, connected with magnetars, quasars, and
gamma-ray bursts. Whereas these intense magnetic fields are difficult to
explain astrophysically, we find that they are easily explained by NMGEC.


title: Monotony in Service Orchestrations

abstract:
  Web Service orchestrations are compositions of different Web Services to form
a new service. The services called during the orchestration guarantee a given
performance to the orchestrater, usually in the form of contracts. These
contracts can be used by the orchestrater to deduce the contract it can offer
to its own clients, by performing contract composition. An implicit assumption
in contract based QoS management is: "the better the component services
perform, the better the orchestration's performance will be". Thus, contract
based QoS management for Web services orchestrations implicitly assumes
monotony. In some orchestrations, however, monotony can be violated, i.e., the
performance of the orchestration improves when the performance of a component
service degrades. This is highly undesirable since it can render the process of
contract composition inconsistent. In this paper we define monotony for
orchestrations modelled by Colored Occurrence Nets (CO-nets) and we
characterize the classes of monotonic orchestrations. We show that few
orchestrations are indeed monotonic, mostly since latency can be traded for
quality of data. We also propose a sound refinement of monotony, called
conditional monotony, which forbids this kind of cheating and show that
conditional monotony is widely satisfied by orchestrations. This finding leads
to reconsidering the way SLAs should be formulated.


title:
Non-unitary deviation from the tri-bimaximal lepton mixing and its
  implications on neutrino oscillations

abstract:
  We propose a new pattern of the neutrino mixing matrix which can be
parametrized as the product of an arbitrary Hermitian matrix and the well-known
tri-bimaximal mixing matrix. In this scenario, nontrivial values of the
smallest neutrino mixing angle \theta_13 and the CP-violating phases entirely
arise from the non-unitary corrections. We present a complete set of series
expansion formulas for neutrino oscillation probabilities both in vacuum and in
matter of constant density. We do a numerical analysis to show the non-unitary
effects on neutrino oscillations. The possibility of determining small
non-unitary perturbations and CP-violating phases is discussed by measuring
neutrino oscillation probabilities and constructing "deformed unitarity
triangles". Some brief comments on the non-unitary neutrino mixing matrix in
the type-II seesaw models are also given.


title: A Quadratic Loss Multi-Class SVM

abstract:
  Using a support vector machine requires to set two types of hyperparameters:
the soft margin parameter C and the parameters of the kernel. To perform this
model selection task, the method of choice is cross-validation. Its
leave-one-out variant is known to produce an estimator of the generalization
error which is almost unbiased. Its major drawback rests in its time
requirement. To overcome this difficulty, several upper bounds on the
leave-one-out error of the pattern recognition SVM have been derived. Among
those bounds, the most popular one is probably the radius-margin bound. It
applies to the hard margin pattern recognition SVM, and by extension to the
2-norm SVM. In this report, we introduce a quadratic loss M-SVM, the M-SVM^2,
as a direct extension of the 2-norm SVM to the multi-class case. For this
machine, a generalized radius-margin bound is then established.


title:
The Size Function of Galaxy Disks out to z ~ 1 from the
  Canada-France-Hawaii-Telescope Legacy Survey

abstract:
  The formation and growth of galaxy disks over cosmic time is crucial to our
understanding of galaxy formation. Despite steady improvements in the size and
quality of disk samples over the last decade, many aspects of galaxy disk
evolution remain unclear. Using two square degrees of deep, wide-field i'-band
imaging from the Canada-France-Hawaii Telescope Legacy Survey, we compute size
functions for 6000 disks from z=0.2 to z=1 and explore luminosity and number
density evolution scenarios with an emphasis on the importance of selection
effects on the interpretation of the data. We also compute the size function of
a very large sample of disks from the Sloan Digital Sky Survey to use as a
local (z ~ 0.1) comparison. CFHTLS size functions computed with the same fixed
luminosity-size selection window at all redshifts exhibit evolution that
appears to be best modelled by a pure number density evolution. The z = 0.3
size function is an excellent match to the z = 0.9 one if disks at the highest
redshift are a factor of 2.5 more abundant than in the local universe. The SDSS
size function would also match the z = 0.9 CFHTLS size function very well with
a similar change in number density. On the other hand, the CFHTLS size
functions computed with a varying luminosity-size selection window with
redshift remain constant if the selection window is shifted by 1.0$-$1.5 mag
towards fainter magnitudes with decreasing redshift. There is a weak dependence
on disk scale length with smaller ($h \lesssim $ 4 kpc) disks requiring more
luminosity evolution than larger ones. Given that changes in number density are
primarily due to mergers and that current estimates of merger rates below z = 1
are low, luminosity evolution appears to be a more plausible scenario to
explain the observations.


title: Satellite Ecology: The Dearth of Environment Dependence

abstract:
  Using the Sloan Digital Sky Survey (SDSS) galaxy group catalogue of Yang et
al. (2007), we study the average colour and average concentration of satellite
galaxies as function of (i) their stellar mass, (ii) their group mass, and
(iii) their group-centric radius. We find that the colours and concentrations
of satellite galaxies are (almost) completely determined by their stellar mass.
In particular, at fixed stellar mass, the average colours and concentrations of
satellite galaxies are independent of either halo mass or halo-centric radius.
We find clear evidence for mass segregation of satellite galaxies in haloes of
all masses, and argue that this explains why satellites at smaller halo-centric
radii are somewhat redder and somewhat more concentrated. In addition, the weak
colour and concentration dependence of satellite galaxies on halo mass is
simply a reflection of the fact that more massive haloes host, on average, more
massive satellites. Combining these results with the fact that satellite
galaxies are, on average, redder and somewhat more concentrated than central
galaxies of the same stellar mass, the following picture emerges: galaxies
become redder and somewhat more concentrated once they fall into a bigger halo
(i.e., once they become a satellite galaxy). This is a clear manifestation of
environment dependence. However, there is no indication that the magnitude of
the transformation (or its timescale) depends on environment; a galaxy
undergoes a transition when it becomes a satellite, but it does not matter
whether it becomes a satellite of a small (Milky Way sized) halo, or of a
massive cluster. We discuss the implication of this `dearth' of environment
dependence for the physical processes responsible for transforming satellite
galaxies.


title:
Phase diagram of chiral and diquark condensates at finite temperature
  and density in the 2-dimensional Gross Neveu model

abstract:
  We construct the phase diagram of the chiral and diquark condensates at
finite temperature and density in the 1+1 dimensional (2D) two flavor massless
Gross Neveu model. The resultant phase diagram shows (I) the chiral condensed
phase at low temperature and density, (II) the diquark condensed phase at low
temperature and high density, and (III) the chiral and diquark coexisting phase
at low temperature and intermediate density. This phase structure is also seen
in the 3D Gross Neveu model and the 4D Nambu Jona-Lasinio (NJL) model. Thus the
phase diagrams of the chiral and diquark condensates in the NJL-type models do
not change qualitatively in 2D, 3D and 4D.


title:
The DEEP2 Galaxy Redshift Survey: Environments of Poststarburst Galaxies
  at z~0.1 and z~0.8

abstract:
  Postststarburst (K+A) galaxies are candidates for galaxies in transition from
a star-forming phase to a passively-evolving phase. We have spectroscopically
identified large samples of K+A galaxies both in the SDSS at z~0.1 and in the
DEEP2 survey at z~0.8, using a robust selection method based on a cut in Hbeta
emission rather than the more problematic [OII] 3727. Based on measurements of
the overdensity of galaxies around each object, we find that K+A galaxies
brighter than 0.4L*_B at low-z have a similar, statistically indistinguishable
environment distribution as blue galaxies, preferring underdense environments,
but dramatically different from that of red galaxies. However, at higher-z, the
environment distribution of K+A galaxies is more similar to red galaxies than
to blue galaxies. We conclude that the quenching of star formation and the
build-up of the red sequence through the K+A phase is happening in relatively
overdense environments at z~1 but in relatively underdense environments at z~0.
Although the relative environments where quenching occurs are decreasing with
time, the corresponding absolute environment may have stayed the same along
with the quenching mechanisms, because the mean absolute environments of all
galaxies has to grow with time. In addition, we do not find any significant
dependence on luminosity in the environment distribution of K+As. The existence
of a large K+A population in the field at both redshifts indicates that
cluster-specific mechanisms cannot be the dominant route by which these
galaxies are formed. We also demonstrates that studying K+A-environment
relations by measuring the K+A fraction in different environments is highly
non-robust. Statistical comparisons of the overall environment distributions of
different populations are much better behaved.


title: Automorphisms of the truth-table degrees are fixed on some cone

abstract:
  Let Dtt denote the set of truth-table degrees. A bijection p from Dtt to Dtt
is an automorphism if for all truth-table degrees x and y we have x <=tt y if
and only if p(x) <=tt p(y). We say an automorphism p is fixed on some cone if
there is a degree b such that for all x >=tt b we have p(x) = x. We first prove
that for every 2-generic real X we have X' is not tt below X + 0'. We next
prove that for every real X >=tt 0' there is a real Y such that Y + 0' =tt Y'
=tt X. Finally, we use this to demonstrate that every automorphism of the
truth-table degrees is fixed on some cone.


title: Campedelli surfaces with fundamental group of order 8

abstract:
  We prove that an etale cover Y of degree 8 of a Campedelli surface S is a
complete intersection of four quadrics in P^6, obtaining as a consequence that
Y is the universal cover of S, the covering group G=Gal(Y/S)is the topological
fundamental group of S and that G cannot be the dihedral group of order 8. This
paper patches up an incomplete manuscript of the third author.


title: Superpolynomial speedups based on almost any quantum circuit

abstract:
  The first separation between quantum polynomial time and classical
bounded-error polynomial time was due to Bernstein and Vazirani in 1993. They
first showed a O(1) vs. Omega(n) quantum-classical oracle separation based on
the quantum Hadamard transform, and then showed how to amplify this into a
n^{O(1)} time quantum algorithm and a n^{Omega(log n)} classical query lower
bound.
  We generalize both aspects of this speedup. We show that a wide class of
unitary circuits (which we call dispersing circuits) can be used in place of
Hadamards to obtain a O(1) vs. Omega(n) separation. The class of dispersing
circuits includes all quantum Fourier transforms (including over nonabelian
groups) as well as nearly all sufficiently long random circuits. Second, we
give a general method for amplifying quantum-classical separations that allows
us to achieve a n^{O(1)} vs. n^{Omega(log n)} separation from any dispersing
circuit.


title: Spectral distribution of Be/X-ray binaries in the Small Magellanic Cloud

abstract:
  The spectral distributions of Be/X-ray binaries in the Large Magellanic Cloud
and Galaxy have been shown to differ significantly from the distribution of
isolated Be stars in the Galaxy. Population synthesis models can explain this
difference in spectral distributions through substantial angular momentum loss
from the binary system. In this work we explore the spectral distribution of
Be/X-ray binaries in the Small Magellanic Cloud (SMC) using high
signal-to-noise spectroscopy of a sample of 37 optical counterparts to known
X-ray pulsars. Our results show that the spectral distribution of Be/X-ray
binaries in the SMC is consistent with that of the Galaxy, despite the lower
metallicity environment of the SMC. This may indicate that, although the
metallicity of the SMC is conducive to the formation of a large number of
HMXBs, the spectral distribution of these systems is likely to be most strongly
influenced by angular momentum losses during binary evolution, which are not
particularly dependent on the local metallicity.


title: Observation of Unusual Mass Transport in Solid hcp 4He

abstract:
  Solid 4He has been created off the melting curve by growth at nearly constant
mass via the "blocked capillary" technique and growth from the 4He superfluid
at constant temperature. The experimental apparatus allows injection of 4He
atoms from superfluid directly into the solid. Evidence for the superfluid-like
transport of mass through a sample cell filled with hcp solid 4He off the
melting curve is found. This mass flux depends on temperature and pressure.


title: Towards the theory of Benney equations

abstract:
  Particular solutions of the Benney equations are constructed. Their
properties are discussed.


title:
NSR measures on hyperelliptic locus and non-renormalization of
  1,2,3-point functions

abstract:
  We demonstrate (under a modest assumption) that the sums over spin-structures
of the simplest combinations of fermionic correlators (Szego kernels) and
DHP/CDG/Grushevsky NSR measures vanish at least on the hyperelliptic loci in
the moduli space of Riemann surfaces -- despite the violation of the theta_e^4
hypothesis at g>2. This provides an additional important support to validity of
these measures and is also a step towards a proof of the non-renormalization
theorems in the NSR approach.


title:
Joint Physical Layer Coding and Network Coding for Bi-Directional
  Relaying

abstract:
  We consider the problem of two transmitters wishing to exchange information
through a relay in the middle. The channels between the transmitters and the
relay are assumed to be synchronized, average power constrained additive white
Gaussian noise channels with a real input with signal-to-noise ratio (SNR) of
snr. An upper bound on the capacity is 1/2 log(1+ snr) bits per transmitter per
use of the medium-access phase and broadcast phase of the bi-directional relay
channel. We show that using lattice codes and lattice decoding, we can obtain a
rate of 1/2 log(0.5 + snr) bits per transmitter, which is essentially optimal
at high SNRs. The main idea is to decode the sum of the codewords modulo a
lattice at the relay followed by a broadcast phase which performs Slepian-Wolf
coding with structured codes. For asymptotically low SNR's, jointly decoding
the two transmissions at the relay (MAC channel) is shown to be optimal. We
also show that if the two transmitters use identical lattices with minimum
angle decoding, we can achieve the same rate of 1/2 log(0.5 + snr). The
proposed scheme can be thought of as a joint physical layer, network layer code
which outperforms other recently proposed analog network coding schemes.


title:
Photoinduced electrification of solids. IV. Space charge effects
  assessed

abstract:
  Our recent arXiv preprints have described the experimental evidence for the
universal occurrence of short circuit photocurrents on illumination of solid
state surfaces by strongly absorbed light. A likely mechanism has been proposed
based on the photodesorption of surface ions to the surrounding atmosphere.
Analyses have been made of observed oscilloscope tracings of short circuit
photo voltages in terms of the linear rate theory in fair concomitance. Space
charge effects having been left unaccounted for, we now propose an approach to
them in the diffusion-free approximation.


title: Two simple families of exact inhomogeneous stiff cosmologies

abstract:
  Two families of exact simple solutions of Einstein field equations for
inhomogeneous stiff cosmologies are presented. The method to obtain the
solutions is based on the introduction of auxiliary functions in order to cast
the Einstein equations in such a way that can be explicitly integrated. Now,
despite of the equations are mathematically equivalent to the equations
obtained when the source of matter is a scalar field, is worth to mention that
the source that we consider is not a scalar field but a perfect fluid with the
stiff equation of state. The obtained solutions are expressed in terms of
simple functions of the used coordinates and two families of particular
solutions are considered. The geometrical and kinematical properties of the
solutions are then analyzed and the parameters are restricted in order to have
a physically acceptable behavior. The two particular solutions are of the
Petrov type I, the first one being regular everywhere whereas the second one
presents a big-bang singularity. Now, for a particular value of one of the
parameters, the second particular solution is a vacuum solution of the Bianchi
I type that reduces to the Kasner solution.


title:
An Ultra-High Stability, Low-Noise Laser Current Driver with Digital
  Control

abstract:
  We present a low-noise, high modulation-bandwidth design for a laser current
driver with excellent long term stability. The driver improves upon the
commonly-used Hall-Libbrecht design. The current driver can be operated
remotely by way of a micro-processing unit, which controls the current set
point digitally. This allows precise repeatability and improved accuracy and
stability. It also allows the driver to be placed near the laser for reduced
noise and for lower phase lag when using the modulation input. We present the
theory of operation for our driver in detail, and give a thorough
characterization of its stability, noise, set point accuracy and repeatability,
temperature dependence, transient response, and modulation bandwidth.


title: 3--symmetric and 3--decomposable drawings of $K_n$ (extended version)

abstract:
  Even the most superficial glance at the vast majority of crossing-minimal
geometric drawings of $K_n$ reveals two hard-to-miss features. First, all such
drawings appear to be 3-fold symmetric (or simply {\em 3-symmetric}) . And
second, they all are {\em 3-decomposable}, that is, there is a triangle $T$
enclosing the drawing, and a balanced partition $A, B, C$ of the underlying set
of points $P$, such that the orthogonal projections of $P$ onto the sides of
$T$ show $A$ between $B$ and $C$ on one side, $B$ between $A$ and $C$ on
another side, and $C$ between $A$ and $B$ on the third side. In fact, we
conjecture that all optimal drawings are 3-decomposable, and that there are
3-symmetric optimal constructions for all $n$ multiple of 3. In this paper, we
show that any 3-decomposable geometric drawing of $K_n$ has at least
$0.380029\binom{n}{4}+\Theta(n^3)$ crossings. On the other hand, we produce
3-symmetric and 3-decomposable drawings that improve the {\em general} upper
bound for the rectilinear crossing number of $K_n$ to
$0.380488\binom{n}{4}+\Theta(n^3)$. We also give explicit 3-symmetric and
3-decomposable constructions for $n<100$ that are at least as good as those
previously known.


title:
Mapping Hydrogen in the Galaxy, Galactic Halo, and Local Group with
  ALFA: The GALFA-HI Survey Starting with TOGS

abstract:
  Radio observations of gas in the Milky Way and Local Group are vital for
understanding how galaxies function as systems. The unique sensitivity of
Arecibo's 305m dish, coupled with the 7-beam Arecibo L-Band Feed Array (ALFA),
provides an unparalleled tool for investigating the full range of interstellar
phenomena traced by the HI 21cm line. The GALFA (Galactic ALFA) HI Survey is
mapping the entire Arecibo sky over a velocity range of -700 to +700 km/s with
0.2 km/s velocity channels and an angular resolution of 3.4 arcminutes. We
present highlights from the TOGS (Turn on GALFA Survey) portion of GALFA-HI,
which is covering thousands of square degrees in commensal drift scan
observations with the ALFALFA and AGES extragalactic ALFA surveys. This work is
supported in part by the National Astronomy and Ionosphere Center, operated by
Cornell University under cooperative agreement with the National Science
Foundation.


title:
Importance of Granular Structure in the Initial Conditions for the
  Elliptic Flow

abstract:
  We show effects of granular structure of the initial conditions (IC) of
hydrodynamic description of high-energy nucleus-nucleus collisions on some
observables, especially on the elliptic-flow parameter v2. Such a structure
enhances production of isotropically distributed high-pT particles, making v2
smaller there. Also, it reduces v2 in the forward and backward regions where
the global matter density is smaller, so where such effects become more
efficacious.


title:
Radius Destabilization in Five Dimensional Orbifolds Due to an Enhanced
  Casimir Effect

abstract:
  One of the challenges in connecting higher dimensional theories to cosmology
is stabilization of the moduli fields. We investigate the role of a Lorentz
violating vector field in the context of stabilization. Specifically, we
compute the one loop Casimir energy in Randall-Sundrum 5-dimensional
(non-supersymmetric) S^1/ Z_2 orbifolds resulting from the interaction of a
real scalar field with periodic boundary conditions with a Lorentz violating
vector field. We find that the result is an enhanced attractive Casimir force.
Hence, for stability, positive contributions to the Casimir force from branes
and additional fields would be required to counter the destabilizing,
attractive effect of Lorentz violating fields.


title: On the breakup of air bubbles in Hele-Shaw cell

abstract:
  We study the problem of breakup of an air bubble in a Hele-Shaw cell. In
particular, we propose some sufficient conditions of breakup of the bubble, and
ways to find the contraction points of its parts. We also study regulated
contraction of a pair of bubbles (in which the rates of air extraction from the
bubbles is controlled), and study various asymptotic questions (such as the
asymptotics of contraction of a bubble to a degenerate critical point, and
asymptotics of contraction of a small bubble in presence of a big bubble).


title: Low-Mass Star Forming Cores in the GF9 Filament

abstract:
  We carried out an unbiased mapping survey of dense molecular cloud cores
traced by the NH3 (1,1) and (2,2) inversion lines in the GF9 filament which
contains an extremely young low-mass protostar GF9-2 (Furuya et al. 2006, ApJ,
653, 1369). The survey was conducted using the Nobeyama 45m telescope over a
region of ~1.5 deg with an angular resolution of 73". The large-scale map
revealed that the filament contains at least 7 dense cores, as well as 3
possible ones, located at regular intervals of ~0.9 pc. Our analysis shows that
these cores have kinetic temperatures of $\lesssim$ 10 K and LTE-masses of 1.8
-- 8.2 Msun, making them typical sites of low-mass star formation. All the
identified cores are likely to be gravitationally unstable because their
LTE-masses are larger than their virial masses. Since the LTE-masses and
separations of the cores are consistent with the Jeans masses and lengths,
respectively, for the low-density ambient gas, we argue that the identified
cores have formed via the gravitational fragmentation of the natal filamentary
cloud.


title: Straight Skeletons of Three-Dimensional Polyhedra

abstract:
  This paper studies the straight skeleton of polyhedra in three dimensions. We
first address voxel-based polyhedra (polycubes), formed as the union of a
collection of cubical (axis-aligned) voxels. We analyze the ways in which the
skeleton may intersect each voxel of the polyhedron, and show that the skeleton
may be constructed by a simple voxel-sweeping algorithm taking constant time
per voxel. In addition, we describe a more complex algorithm for straight
skeletons of voxel-based polyhedra, which takes time proportional to the area
of the surfaces of the straight skeleton rather than the volume of the
polyhedron. We also consider more general polyhedra with axis-parallel edges
and faces, and show that any n-vertex polyhedron of this type has a straight
skeleton with O(n^2) features. We provide algorithms for constructing the
straight skeleton, with running time O(min(n^2 log n, k log^{O(1)} n)) where k
is the output complexity. Next, we discuss the straight skeleton of a general
nonconvex polyhedron. We show that it has an ambiguity issue, and suggest a
consistent method to resolve it. We prove that the straight skeleton of a
general polyhedron has a superquadratic complexity in the worst case. Finally,
we report on an implementation of a simple algorithm for the general case.


title: Two-Component Nonlinear Schrodinger Models with a Double-Well Potential

abstract:
  We introduce a model motivated by studies of Bose-Einstein condensates (BECs)
trapped in double-well potentials. We assume that a mixture of two hyperfine
states of the same atomic species is loaded in such a trap.The analysis is
focused on symmetry-breaking bifurcations in the system, starting at the linear
limit and gradually increasing the nonlinearity. Depending on values of the
chemical potentials of the two species, we find numerous states, as well as
symmetry-breaking bifurcations, in addition to those known in the
single-component setting. These branches, which include all relevant stationary
solutions of the problem, are predicted analytically by means of a two-mode
approximation, and confirmed numerically. For unstable branches, outcomes of
the instability development are explored in direct simulations.


title:
Absence of low-temperature dependence of the decay of 7Be and 198Au in
  metallic hosts

abstract:
  The electron-capture (EC) decay rate of 7Be in metallic Cu host and the
beta-decay rate of 198Au in the host alloy Al-Au have been measured
simultaneously at several temperatures, ranging from 0.350 K to 293 K. No
difference of the half-life of 198Au between 12.5 K and 293 K is observed to a
precision of 0.1%. By utilizing the special characteristics of our
double-source assembly, possible geometrical effects that influence the
individual rates could be eliminated. The ratio of 7Be to 198Au activity thus
obtained also remains constant for this temperatures range to the experimental
precision of 0.15(0.16)%. The resulting null temperature dependence is
discussed in terms of the inadequacy of the often-used Debye-Huckel model for
such measurements.


title: Optimized Schwarz preconditioning for SEM based magnetohydrodynamics

abstract:
  A recent theoretical result on optimized Schwarz algorithms demonstrated at
the algebraic level enables the modification of an existing Schwarz procedure
to its optimized counterpart. In this work, it is shown how to modify a
bilinear FEM based Schwarz preconditioning strategy originally presented in
[Fischer, JCP 133:84 1997] to its optimized version. The latter is employed to
precondition the pseudo--Laplacian operator arising from the spectral element
discretization of the magnetohydrodynamic equations in Elsasser form.


title:
Using photoemission spectroscopy to probe a strongly interacting Fermi
  gas

abstract:
  Ultracold atom gases provide model systems in which many-body quantum physics
phenomena can be studied. Recent experiments on Fermi gases have realized a
phase transition to a Fermi superfluid state with strong interparticle
interactions. This system is a realization of the BCS-BEC crossover connecting
the physics of BCS superconductivity and that of Bose-Einstein condensation
(BEC). While many aspects of this system have been investigated, it has not yet
been possible to measure the single-particle excitation spectrum, which is a
fundamental property directly predicted by many-body theories. Here we show
that the single-particle spectral function of the strongly interacting Fermi
gas at T ~ Tc is dramatically altered in a way that is consistent with a large
pairing gap. We use photoemission spectroscopy to directly probe the elementary
excitations and energy dispersion in the Fermi gas of atoms. In these
photoemission experiments, an rf photon ejects an atom from our strongly
interacting system via a spin-flip transition to a weakly interacting state. We
measure the occupied single-particle density of states for an ultracold Fermi
gas of 40-potassium atoms at the cusp of the BCS-BEC crossover and on the BEC
side of the crossover, and compare these results to that for a nearly ideal
Fermi gas. Our results probe the many-body physics in a way that could be
compared to data for high-Tc superconductors. This new measurement technique
for ultracold atom gases, like photoemission spectroscopy for electronic
materials, directly probes low energy excitations and thus can reveal
excitation gaps and/or pseudogaps. Furthermore, this technique can provide an
analog to angle-resolved photoemission spectroscopy (ARPES) for probing
anisotropic systems, such as atoms in optical lattice potentials.


title:
Optimal Estimation of Several Linear Parameters in the Presence of
  Lorentzian Thermal Noise

abstract:
  In a previous article we developed an approach to the optimal (minimum
variance, unbiased) statistical estimation technique for the equilibrium
displacement of a damped, harmonic oscillator in the presence of thermal noise.
Here, we expand that work to include the optimal estimation of several linear
parameters from a continuous time series. We show that working in the basis of
the thermal driving force both simplifies the calculations and provides
additional insight to why various approximate (not optimal) estimation
techniques perform as they do. To illustrate this point, we compare the
variance in the optimal estimator that we derive for thermal noise with those
of two approximate methods which, like the optimal estimator, suppress the
contribution to the variance that would come from the irrelevant, resonant
motion of the oscillator. We discuss how these methods fare when the dominant
noise process is either white displacement noise or noise with power spectral
density that is inversely proportional to the frequency ($1/f$ noise). We also
construct, in the basis of the driving force, an estimator that performs well
for a mixture of white noise and thermal noise. To find the optimal
multi-parameter estimators for thermal noise, we derive and illustrate a
generalization of traditional matrix methods for parameter estimation that can
accommodate continuous data. We discuss how this approach may help refine the
design of experiments as they allow an exact, quantitative comparison of the
precision of estimated parameters under various data acquisition and data
analysis strategies.


title: Tunable transmission and harmonic generation in nonlinear metamaterials

abstract:
  We study the properties of a tunable nonlinear metamaterial operating at
microwave frequencies. We fabricate the nonlinear metamaterial composed of
double split-ring resonators and wires where a varactor diode is introduced
into each resonator so that the magnetic resonance can be tuned dynamically by
varying the input power. We show that at higher powers the transmission of the
metamaterial becomes power dependent, and we demonstrate experimentally
power-dependent transmission properties and selective generation of higher
harmonics.


title: How to simulate a quantum computer using negative probabilities

abstract:
  The concept of negative probabilities can be used to decompose the
interaction of two qubits mediated by a quantum controlled-NOT into three
operations that require only classical interactions (that is, local operations
and classical communication) between the qubits. For a single gate, the
probabilities of the three operations are 1, 1, and -1. This decomposition can
be applied in a probabilistic simulation of quantum computation by randomly
choosing one of the three operations for each gate and assigning a negative
statistical weight to the outcomes of sequences with an odd number of negative
probability operations. The exponential speed-up of a quantum computer can then
be evaluated in terms of the increase in the number of sequences needed to
simulate a single operation of the quantum circuit.


title:
Introduction of an Elementary Method to Express $\zeta(2n+1)$ in Terms
  of $\zeta(2k)$ with $k\geq 1$

abstract:
  In this note we give the most elementary method (as far as we know) to
express $\zeta(2n+1)$ in terms of $\{\zeta(2k)|k\geq 1\}$. The method is based
on only some elementary works by Leonhard Euler, so it is very instructive to
non-experts or students.


title:
Final Results from the KTeV Experiment on the Decay KL -> pi0 gamma
  gamma

abstract:
  We report on a new measurement of the branching ratio B(KL->pi0 gamma
gamma)using the KTeV detector. We reconstruct 1982 events with an estimated
background of 608, that results in B(KL -> pi0 gamma gamma) = (1.29 +/-
0.03(stat) +/- 0.05(syst)) x 10**-6. We also measure the parameter, aV, which
characterizes the strength of vector meson exchange terms in this decay. We
find aV = -0.31 +/- 0.05(stat) +/- 0.07(syst). These results utilize the full
KTeV data set collected from 1997 to 2000 and supersede earlier KTeV
measurements of the branching ratio and aV.


title:
Efficient polarization entanglement purification based on parametric
  down-conversion sources with cross-Kerr nonlinearity

abstract:
  We present a way for entanglement purification based on two parametric
down-conversion (PDC) sources with cross-Kerr nonlinearities. It is comprised
of two processes. The first one is a primary entanglement purification protocol
for PDC sources with nondestructive quantum nondemolition (QND) detectors by
transferring the spatial entanglement of photon pairs to their polarization. In
this time, the QND detectors act as the role of controlled-not (CNot) gates.
Also they can distinguish the photon number of the spatial modes, which
provides a good way for the next process to purify the entanglement of the
photon pairs kept more. In the second process for entanglement purification,
new QND detectors are designed to act as the role of CNot gates. This protocol
has the advantage of high yield and it requires neither CNot gates based on
linear optical elements nor sophisticated single-photon detectors, which makes
it more convenient in practical applications.


title: Bifurcating Transport of Glassy Matter Within Annular Micropores

abstract:
  Glassy matter, as subjected to high shear rates, exhibit shear thinning :
i.e., the viscosity diminishes with increasing shear rate. Meanwhile one
prominent difference between the transport in micropores and that in macroscale
is the (relatively) larger roughness observed inside micropores. As the pore
size decreases, the surface-to-volume ratio increases and therefore, surface
roughness will greatly affect the transport in micropores. By treating the
glass as a shear-thinning matter and using the rate-dependent model together
with the boundary perturbation method, we can analytically obtain the transport
results up to the second order.


title: Diversity Order Gain with Noisy Feedback in Multiple Access Channels

abstract:
  In this paper, we study the effect of feedback channel noise on the
diversity-multiplexing tradeoff in multiuser MIMO systems using quantized
feedback, where each user has m transmit antennas and the base-station receiver
has n antennas. We derive an achievable tradeoff and use it to show that in
SNR-symmetric channels, a single bit of imperfect feedback is sufficient to
double the maximum diversity order to 2mn compared to when there is no feedback
(maximum is mn at multiplexing gain of zero). Further, additional feedback bits
do not increase this maximum diversity order beyond 2mn. Finally, the above
diversity order gain of mn over non-feedback systems can also be achieved for
higher multiplexing gains, albeit requiring more than one bit of feedback.


title: Conductance Quantization in Graphene Nanoribbons

abstract:
  We report the experimental observation of conductance quantization in
graphene nanoribbons, where 1D transport subbands are formed due to the lateral
quantum confinement. We show that this quantization in graphene nanoribbons can
be observed at temperatures as high as 80 K and channel lengths as long as 1.7
$\mu$m. The observed quantization is in agreement with that predicted by
theoretical calculations.


title:
More on Meta-Stable Brane Configurations by Dualizing the Multiple Gauge
  Groups

abstract:
  We reexamine the N=1 supersymmetric gauge theories with product gauge groups
by adding the mass terms and the quartic terms for the flavors: two gauge group
theory with fundamentals, bifundamentals and adjoints, three gauge group theory
with fundamentals and bifundamentals, and their orientifold 4-plane
generalizations. By moving the branes appropriately, we obtain the
corresponding dual gauge theories. By analyzing the dual superpotentials, we
present the type IIA nonsupersymmetric meta-stable brane configurations.


title:
OMCat: Catalogue of Serendipitous Sources Detected with the XMM-Newton
  Optical Monitor

abstract:
  The Optical Monitor Catalogue of serendipitous sources (OMCat) contains
entries for every source detected in the publicly available XMM-Newton Optical
Monitor (OM) images taken in either the imaging or ``fast'' modes. Since the OM
is coaligned and records data simultaneously with the X-ray telescopes on
XMM-Newton, it typically produces images in one or more near-UV/optical bands
for every pointing of the observatory. As of the beginning of 2006, the public
archive had covered roughly 0.5% of the sky in 2950 fields.
  The OMCat is not dominated by sources previously undetected at other
wavelengths; the bulk of objects have optical counterparts. However, the OMCat
can be used to extend optical or X-ray spectral energy distributions for known
objects into the ultraviolet, to study at higher angular resolution objects
detected with GALEX, or to find high-Galactic-latitude objects of interest for
UV spectroscopy.


title:
The effect of Galactic foreground subtraction on redshifted 21-cm
  observations of quasar HII regions

abstract:
  We assess the impact of Galactic synchrotron foreground removal on the
observation of high-redshift quasar HII regions in redshifted 21-cm emission.
We consider the case where a quasar is observed in an intergalactic medium
(IGM) whose ionisation structure evolves slowly relative to the light crossing
time of the HII region, as well as the case where the evolution is rapid. The
latter case is expected towards the end of the reionisation era where the
highest redshift luminous quasars will be observed. In the absence of
foregrounds the fraction of neutral hydrogen in the IGM could be measured
directly from the contrast between the HII region and surrounding IGM. However,
we find that foreground removal lowers the observed contrast between the HII
region and the IGM. This indicates that measurement of the neutral fraction
would require modelling to correct for this systematic effect. On the other
hand, foreground removal does not modify the most prominent features of the
21-cm maps. Using a simple algorithm we demonstrate that measurements of the
size and shape of observed HII regions will not be affected by continuum
foreground removal. Moreover, measurements of these quantities will not be
adversely affected by the presence of a rapidly evolving IGM.


title:
Superradiant Raman scattering in an ultracold Bose gas at finite
  temperature

abstract:
  We study superradiant Raman scattering from an ultra-cold, but finite
temperature Bose gas in a harmonic trap. Numerical simulations indicate the
existence of distinct timescales associated with the decoherence of the
condensed versus thermal fractions, and the concomitant preferred scattering
from atoms in low lying trap states in the regime where superradiance takes
place on a timescale comparable to an inverse trap frequency. As a consequence
the scattered atoms experience a modest reduction in temperature as compared to
the unscattered atoms.


title: Quantum computation and the evaluation of tensor networks

abstract:
  We present a quantum algorithm that additively approximates the value of a
tensor network to a certain scale. When combined with existing results, this
provides a complete problem for quantum computation. The result is a simple new
way of looking at quantum computation in which unitary gates are replaced by
tensors and time is replaced by the order in which the tensor-network is
"swallowed". We use this result to derive new quantum algorithms that
approximate the partition function of a variety of classical statistical
mechanics models, including the Potts model.


title:
Spin Ordering in LaOFeAs and Its Suppression in Superconductor
  LaO0.89F0.11FeAs Probed by M\"ossbauer Spectroscopy

abstract:
  The 57Fe M\"ossbauer spectroscopy was applied to an iron-based layered
superconductor LaO0.89F0.11FeAs with a transition temperature of 26 K and its
parent material LaOFeAs. Throughout the temperature range from 4.2 to 298 K, a
singlet spectrum with no magnetic splitting was observed as a main component of
each M\"ossbauer spectrum of the F-doped superconductor. No additional internal
magnetic field was observed for the spectrum measured at 4.2 K under a magnetic
field of 7 T. On the other hand, the parent LaOFeAs shows a magnetic transition
at around 140 K, and this temperature is slightly lower than that of a
structural phase transition from tetragonal to orthorhombic phase, which
accompanies the resistivity anomaly at around 150 K. The magnetic moment is
estimated to be ~0.35 $\mu$B/Fe at 4.2 K in the orthorhombic phase, and the
spin disorder remains in the magnetic ordered state even at 4.2 K. The fact
that no magnetic transition in LaO0.89F0.11FeAs was observed even at 4.2 K
under 7 T implies a strong spin fluctuation above Tc or small magnetic moment
in this system. Therefore, the present results show that the F-doping
effectively suppresses the magnetic and structural transitions in the parent
material and the suppression leads to emergence of superconductivity in this
system.


title:
A new series of compact minitwistor spaces and Moishezon twistor spaces
  over them

abstract:
  In recent papers math.DG/0701278 and arXiv:0705.0060, we gave explicit
description of some new Moishezon twistor spaces. In this paper, developing the
method in the papers much further, we explicitly give projective models of a
number of new Moishezon twistor spaces, as conic bundles over some rational
surfaces (called minitwistor spaces). These include the twistor spaces studied
in the papers as very special cases.
  Our source of the result is a series of self-dual metrics with torus action
constructed by D. Joyce. Actually, for arbitrary Joyce metrics and
U(1)-subgroups of the torus which fixes a torus-invariant 2-sphere, we first
determine the associated minitwistor spaces in explicit forms. Next by
analyzing the meromorphic maps from the twistor spaces to the minitwistor
spaces, we realize projective models of the twistor spaces of all Joyce
metrics, as conic bundles over the minitwistor spaces. Then we prove that for
any one of these minitwistor spaces, there exist Moishezon twistor spaces with
only C*-action whose quotient space is the given minitwistor space. This result
generates numerous Moishezon twistor spaces which cannot be found in the
literature (including the author's papers), in quite explicit form.


title: Multistability in nonlinear left-handed transmission lines

abstract:
  Employing a nonlinear left-handed transmission line as a model system, we
demonstrate experimentally the multi-stability phenomena predicted
theoretically for microstructured left-handed metamaterials with a nonlinear
response. We show that the bistability is associated with the period doubling
which at higher power may result in chaotic dynamics of the transmission line.


title:
Energy Extraction from a Rotating Black Hole by Magnetic Reconnection in
  Ergosphere

abstract:
  We investigate mechanisms of energy extraction from a rotating black hole in
terms of negative energy-at-infinity. In addition to the Penrose process
through particle fission, the Blandford-Znajek mechanism by magnetic tension,
and the magnetohydrodynamic Penrose process, we examine energy extraction from
a black hole caused by magnetic reconnection in the ergosphere. The
reconnection redistributes the angular momentum efficiently to yield the
negative energy-atinfinity. We derive a condition for the process to operate in
a simple situation, where the plasma is incompressible and the magnetic energy
is converted completely to the plasma kinetic energy locally. Astrophysical
situations of magnetic reconnection around the black holes are also discussed.


title: Affine Deligne-Lusztig varieties in affine flag varieties

abstract:
  This paper studies affine Deligne-Lusztig varieties in the affine flag
manifold of a split group. Among other things, it proves emptiness for certain
of these varieties, relates some of them to those for Levi subgroups, extends
previous conjectures concerning their dimensions, and generalizes the superset
method.


title: Projective models of the twistor spaces of Joyce metrics

abstract:
  We provide a simple algebraic construction of the twistor spaces of arbitrary
Joyce's self-dual metrics on the 4-manifold H^2 x T^2 that extend smoothly to
nCP^2, the connected sum of complex projective planes. Indeed, we explicitly
realize projective models of the twistor spaces of arbitrary Joyce metrics on
nCP^2 in a CP^4-bundle over CP^1, and show that they contain the twistor spaces
of H^2 x T^2 as dense non-Zariski open subsets. In particular, we see that the
last non-compact twistor spaces can be realized in rank-4 vector bundles over
CP^1 by quite simple defining equations.


title: Divergence-free Nonrenormalizable Models

abstract:
  A natural procedure is introduced to replace the traditional, perturbatively
generated counter terms to yield a formulation of covariant, self-interacting,
nonrenormalizable scalar quantum field theories that has the added virtue of
exhibiting a divergence-free perturbation analysis. To achieve this desirable
goal it is necessary to reexamine the meaning of the free theory about which
such a perturbation takes place.


title: A Discrete Construction for Gaussian Markov Processes

abstract:
  In the L\'evy construction of Brownian motion, a Haar-derived basis of
functions is used to form a finite-dimensional process $W^{N}$ and to define
the Wiener process as the almost sure path-wise limit of $W^{N}$ when $N$ tends
to infinity. We generalize such a construction to the class of centered
Gaussian Markov processes $X$ which can be written $X_{t} = g(t) \cdot
\int_{0}^{t} f(t) dW_{t}$ with $f$ and $g$ being continuous functions. We build
the finite-dimensional process $X^{N}$ so that it gives an exact representation
of the conditional expectation of $X$ with respect to the filtration generated
by ${\lbrace X_{k/2^{N}}\rbrace}$ for $0 \leq k \leq 2^{N}$. Moreover, we prove
that the process $X^{N}$ converges in distribution toward $X$.


title: Random Matrices in 2D, Laplacian Growth and Operator Theory

abstract:
  Since it was first applied to the study of nuclear interactions by Wigner and
Dyson, almost 60 years ago, Random Matrix Theory (RMT) has developed into a
field of its own within applied mathematics, and is now essential to many parts
of theoretical physics, from condensed matter to high energy. The fundamental
results obtained so far rely mostly on the theory of random matrices in one
dimension (the dimensionality of the spectrum, or equilibrium probability
density). In the last few years, this theory has been extended to the case
where the spectrum is two-dimensional, or even fractal, with dimensions between
1 and 2. In this article, we review these recent developments and indicate some
physical problems where the theory can be applied.

categories: nlin.SI cond-mat.mes-hall cond-mat.soft math-ph math.MP nlin.PS


title: On the k-pairs problem

abstract:
  We consider network coding rates for directed and undirected $k$-pairs
networks. For directed networks, meagerness is known to be an upper bound on
network coding rates. We show that network coding rate can be $\Theta(|V|)$
multiplicative factor smaller than meagerness. For the undirected case, we show
some progress in the direction of the $k$-pairs conjecture.


title: Communicating the sum of sources over a network

abstract:
  We consider a network (that is capable of network coding) with a set of
sources and terminals, where each terminal is interested in recovering the sum
of the sources. Considering directed acyclic graphs with unit capacity edges
and independent, unit-entropy sources, we show the rate region when (a) there
are two sources and $n$ terminals, and (b) $n$ sources and two terminals. In
these cases as long as there exists at least one path from each source to each
terminal we demonstrate that there exists a valid assignment of coding vectors
to the edges such that the terminals can recover the sum of the sources.


title: On a variance for twins of $k-$free numbers in arithmetic progressions

abstract:
  In this paper, we give a new upper bound of Barban-Davenport-Halberstam type
for twins of $k-$free numbers in arithmetic progressions.


title:
Particle Filtering for Large Dimensional State Spaces with Multimodal
  Observation Likelihoods

abstract:
  We study efficient importance sampling techniques for particle filtering (PF)
when either (a) the observation likelihood (OL) is frequently multimodal or
heavy-tailed, or (b) the state space dimension is large or both. When the OL is
multimodal, but the state transition pdf (STP) is narrow enough, the optimal
importance density is usually unimodal. Under this assumption, many techniques
have been proposed. But when the STP is broad, this assumption does not hold.
We study how existing techniques can be generalized to situations where the
optimal importance density is multimodal, but is unimodal conditioned on a part
of the state vector. Sufficient conditions to test for the unimodality of this
conditional posterior are derived. The number of particles, N, to accurately
track using a PF increases with state space dimension, thus making any regular
PF impractical for large dimensional tracking problems. We propose a solution
that partially addresses this problem. An important class of large dimensional
problems with multimodal OL is tracking spatially varying physical quantities
such as temperature or pressure in a large area using a network of sensors
which may be nonlinear and/or may have non-negligible failure probabilities.


title:
Alternating Direction Implicit Method for Two-Dimensional Fokker-Planck
  Equation of Dense Spherical Stellar Systems

abstract:
  The Fokker-Planck (FP) model is one of the commonly used methods for studies
of the dynamical evolution of dense spherical stellar systems such as globular
clusters and galactic nuclei. The FP model is numerically stable in most cases,
but we find that it encounters numerical difficulties rather often when the
effects of tidal shocks are included in two-dimensional (energy and angular
momentum space) version of the FP model or when the initial condition is
extreme (e.g., a very large cluster mass and a small cluster radius). To avoid
such a problem, we have developed a new integration scheme for a
two-dimensional FP equation by adopting an Alternating Direction Implicit (ADI)
method given in the Douglas-Rachford split form. We find that our ADI method
reduces the computing time by a factor of ~2 compared to the fully implicit
method, and resolves problems of numerical instability.


title:
Formation of hydrogen peroxide and water from the reaction of cold
  hydrogen atoms with solid oxygen at 10K

abstract:
  The reactions of cold H atoms with solid O2 molecules were investigated at 10
K. The formation of H2O2 and H2O has been confirmed by in-situ infrared
spectroscopy. We found that the reaction proceeds very efficiently and obtained
the effective reaction rates. This is the first clear experimental evidence of
the formation of water molecules under conditions mimicking those found in cold
interstellar molecular clouds. Based on the experimental results, we discuss
the reaction mechanism and astrophysical implications.


title: Quantile tomography: using quantiles with multivariate data

abstract:
  The use of quantiles to obtain insights about multivariate data is addressed.
It is argued that incisive insights can be obtained by considering directional
quantiles, the quantiles of projections. Directional quantile envelopes are
proposed as a way to condense this kind of information; it is demonstrated that
they are essentially halfspace (Tukey) depth levels sets, coinciding for
elliptic distributions (in particular multivariate normal) with density
contours. Relevant questions concerning their indexing, the possibility of the
reverse retrieval of directional quantile information, invariance with respect
to affine transformations, and approximation/asymptotic properties are studied.
It is argued that the analysis in terms of directional quantiles and their
envelopes offers a straightforward probabilistic interpretation and thus
conveys a concrete quantitative meaning; the directional definition can be
adapted to elaborate frameworks, like estimation of extreme quantiles and
directional quantile regression, the regression of depth contours on
covariates. The latter facilitates the construction of multivariate growth
charts---the question that motivated all the development.


title: Indirect quantum control for finite-dimensional coupled systems

abstract:
  We present a new analysis on the quantum control for a quantum system coupled
to a quantum probe. This analysis is based on the coherent control for the
quantum system and a hyperthesis that the probe can be prepared in specified
initial states. The results show that a quantum system can be manipulated by
probe state-dependent coherent control. In this sense, the present analysis
provides a new control scheme which combines the coherent control and state
preparation technology.


title:
Dynamical evolution of the mass function and radial profile of the
  Galactic globular cluster system

abstract:
  Evolution of the mass function (MF) and radial distribution (RD) of the
Galactic globular cluster (GC) system is calculated using an advanced and a
realistic Fokker-Planck (FP) model that considers dynamical friction,
disc/bulge shocks and eccentric cluster orbits. We perform hundreds of FP
calculations with different initial cluster conditions, and then search a
wide-parameter space for the best-fitting initial GC MF and RD that evolves
into the observed present-day Galactic GC MF and RD. By allowing both MF and RD
of the initial GC system to vary, which is attempted for the first time in the
present Letter, we find that our best-fitting models have a higher peak mass
for a lognormal initial MF and a higher cut-off mass for a power-law initial MF
than previous estimates, but our initial total masses in GCs, M_{T,i} =
1.5-1.8x10^8 Msun, are comparable to previous results. Significant findings
include that our best-fitting lognormal MF shifts downward by 0.35 dex during
the period of 13 Gyr, and that our power-law initial MF models well-fit the
observed MF and RD only when the initial MF is truncated at >~10^5 Msun. We
also find that our results are insensitive to the initial distribution of orbit
eccentricity and inclination, but are rather sensitive to the initial
concentration of the clusters and to how the initial tidal radius is defined.
If the clusters are assumed to be formed at the apocentre while filling the
tidal radius there, M_{T,i} can be as high as 6.9x10^8 Msun, which amounts to
~75 per cent of the current mass in the stellar halo.


title: Populating the Galaxy with pulsars I: stellar & binary evolution

abstract:
  The computation of theoretical pulsar populations has been a major component
of pulsar studies since the 1970s. However, the majority of pulsar population
synthesis has only regarded isolated pulsar evolution. Those that have examined
pulsar evolution within binary systems tend to either treat binary evolution
poorly or evolve the pulsar population in an ad-hoc manner. Thus no complete
and direct comparison with observations of the pulsar population within the
Galactic disk has been possible to date. Described here is the first component
of what will be a complete synthetic pulsar population survey code. This
component is used to evolve both isolated and binary pulsars. Synthetic
observational surveys can then be performed on this population for a variety of
radio telescopes. The final tool used for completing this work will be a code
comprised of three components: stellar/binary evolution, Galactic kinematics
and survey selection effects. Results provided here support the need for
further (apparent) pulsar magnetic field decay during accretion, while they
conversely suggest the need for a re-evaluation of the assumed \textit{typical}
MSP formation process. Results also focus on reproducing the observed
$P\dot{P}$ diagram for Galactic pulsars and how this precludes short timescales
for standard pulsar exponential magnetic field decay. Finally, comparisons of
bulk pulsar population characteristics are made to observations displaying the
predictive power of this code, while we also show that under standard binary
evolutionary assumption binary pulsars may accrete much mass.


title: Pion weak decay constant at finite density from the instanton vacuum

abstract:
  We investigate the pion weak decay constant (F_pi) and pion mass (m_pi) at
finite density within the framework of the nonlocal chiral quark model from the
instanton vacuum with the finite quark-number chemical potential (mu) taken
into account. We mainly focus on the Nambu-Goldstone phase below the critical
value of the chemical potential mu_c ~ 320 MeV, which is determined
consistently within the present framework. The breakdown of Lorentz invariance
at finite density being considered, the time (F^t_pi) and space (F^s_pi)
components are computed separately, and the corresponding results turn out to
be: F^t_pi = 82.96 MeV and F^s_pi = 80.29 MeV at mu_c, respectively. Using the
in-medium Gell-Mann-Oakes-Renner (GOR) relation, we show that the pion mass
increases by about 15% at mu_c.


title: Reddening Behaviors of Galaxies in the SDSS Photometric System

abstract:
  We analyze the behaviors of reddening vectors in the SDSS photometric system
for galaxies of different morphologies, ages, and redshifts. As seen in other
photometric systems, the dependence of reddening on the spectral energy
distribution (SED) and the nonlinearity of reddening are likewise
non-negligible for the SDSS system if extinction is significant (~> 1 mag).
These behaviors are most significant for the g filter, which has the largest
bandwidth-to-central wavelength ratio among SDSS filters. The SDSS colors
involving adjacent filters show greater SED-dependence and nonlinearity. A
procedure for calculating the correct amount of extinction from an observed
color excess is provided. The relative extinctions between (i.e., the
extinction law for) SDSS filters given by Schlegel et al., which were
calculated with an older version of filter response functions, would
underestimate the amount of extinction in most cases by ~5 to 10 % (maximum ~20
%). We recommend A/A_{5500} values of 1.574, 1.191, 0.876, 0.671 & 0.486 for
the u, g, r, i, & z filters, respectively, as a representative extinction law
for the SDSS galaxies with a small extinction (i.e., for cases where the
nonlinearity and SED-dependence of the reddening is not important). The
dependence of reddening on redshift at low extinction is the largest for colors
involving the g filter as well, which is due to the Balmer break.


title: Incidence of high-amplitude delta Scuti type variable stars

abstract:
  An order-of-magnitude estimate for the incidence of high-amplitude delta
Scuti-type variable stars (HADS) in the delta Scuti area of the H-R diagram is
calculated. Using a model for the stellar distribution in the Milky Way, we
calculate the number of stars that are expected to fall in the delta Scuti area
of the H-R diagram within the magnitude range and sky coverage of the ROTSE
Survey for Variables I (RSV1). The incidence of the HADS phenomenon is then
obtained by comparing the number of stars calculated by the model and the
actual, observed number of HADS in the RSV1. We find that ~0.3 % of the stars
that lie in the delta Scuti area of the H-R diagram within the RSV1
observational limits exhibit the HADS phenomenon. This number is much lower
than the incidence of the low-amplitude delta Scuti stars (LADS), ~>1/3,
implying that the HADS phenomenon takes place in a very small fraction of stars
and/or its duration is very short, compared to the LADS.


title: Anisotropic drop morphologies on corrugated surfaces

abstract:
  The spreading of liquid drops on surfaces corrugated with micron-scale
parallel grooves is studied both experimentally and numerically. Because of the
surface patterning, the typical final drop shape is no longer spherical. The
elongation direction can be either parallel or perpendicular to the direction
of the grooves, depending on the initial drop conditions. We interpret this
result as a consequence of both the anisotropy of the contact line movement
over the surface and the difference in the motion of the advancing and receding
contact lines. Parallel to the grooves, we find little hysteresis due to the
surface patterning and that the average contact angle approximately conforms to
Wenzel's law as long as the drop radius is much larger than the typical length
scale of the grooves. Perpendicular to the grooves, the contact line can be
pinned at the edges of the ridges leading to large contact angle hysteresis.


title: Hadronic dissipative effects on transverse dynamics at RHIC

abstract:
  We simulate the dynamics of Au+Au collisions at the Relativistic Heavy Ion
Collider (RHIC) with a hybrid model that treats the quark-gluon plasma
macroscopically as an ideal fluid, but models the hadron resonance gas
microscopically using a hadronic cascade. We find that much of the
mass-ordering pattern for v_2(p_T) observed at RHIC is generated during the
hadronic stage due to build-up of additional radial flow. We also find that the
mass-ordering pattern is violated for phi meson due to small interaction cross
section in the hadron resonance gas.


title: Communication Requirements for Generating Correlated Random Variables

abstract:
  Two familiar notions of correlation are rediscovered as extreme operating
points for simulating a discrete memoryless channel, in which a channel output
is generated based only on a description of the channel input. Wyner's "common
information" coincides with the minimum description rate needed. However, when
common randomness independent of the input is available, the necessary
description rate reduces to Shannon's mutual information. This work
characterizes the optimal tradeoff between the amount of common randomness used
and the required rate of description.


title:
Study of low energy Si$_5^-$ and Cs$^-$ implantation induced
  amorphization effects in Si(100)

abstract:
  The damage growth and surface modifications in Si(100), induced by 25 keV
Si$_5^-$ cluster ions, as a function of fluence, $\phi$, has been studied using
atomic force microscopy (AFM) and channeling Rutherford backscattering
spectrometry (CRBS). CRBS results indicate a nonlinear growth in damage from
which it has been possible to get a threshold fluence, $\phi_0$, for
amorphization as $2.5\times 10^{13}$ ions-cm$^{-2}$. For $\phi$ below $\phi_0$,
a growth in damage as well as surface roughness has been observed. At a $\phi$
of $1\times 10^{14}$ ions-cm$^{-2}$, damage saturation coupled with a much
reduced surface roughness has been found. In this case a power spectrum
analysis of AFM data showed a significant drop, in spectral density, as
compared to the same obtained for a fluence, $\phi < \phi_0$. This drop,
together with damage saturation, can be correlated with a transition to a
stress relaxed amorphous phase. Irradiation with similar mass Cs$^-$ ions, at
the same energy and fluence, has been found to result in a reduced accumulation
of defects in the near surface region leading to reduced surface features.


title: A bijective enumeration of labeled trees with given indegree sequence

abstract:
  For a labeled tree on the vertex set $\set{1,2,\ldots,n}$, the local
direction of each edge $(i\,j)$ is from $i$ to $j$ if $i<j$. For a rooted tree,
there is also a natural global direction of edges towards the root. The number
of edges pointing to a vertex is called its indegree. Thus the local (resp.
global) indegree sequence $\lambda = 1^{e_1}2^{e_2} \ldots$ of a tree on the
vertex set $\set{1,2,\ldots,n}$ is a partition of $n-1$. We construct a
bijection from (unrooted) trees to rooted trees such that the local indegree
sequence of a (unrooted) tree equals the global indegree sequence of the
corresponding rooted tree. Combining with a Pr\"ufer-like code for rooted
labeled trees, we obtain a bijective proof of a recent conjecture by Cotterill
and also solve two open problems proposed by Du and Yin. We also prove a
$q$-multisum binomial coefficient identity which confirms another conjecture of
Cotterill in a very special case.


title: Formulations of the Einstein equations for numerical simulations

abstract:
  We review recent efforts to re-formulate the Einstein equations for fully
relativistic numerical simulations. In order to complete a long-term and
accurate simulations of binary compact objects, people seek a robust set of
equations against the violation of constraints. Many trials have revealed that
mathematically equivalent sets of evolution equations show different numerical
stability in free evolution schemes. In this article, we overview the efforts
of the community, categorizing them into three directions: (1) modifications of
the standard Arnowitt-Deser-Misner equations initiated by the Kyoto group (the
so-called Baumgarte-Shapiro-Shibata-Nakamura equations), (2) rewriting the
evolution equations in a hyperbolic form, and (3) construction of an
"asymptotically constrained" system. We then introduce our series of works that
tries to explain these evolution behaviors in a unified way using eigenvalue
analysis of the constraint propagation equations. The modifications of (or
adjustments to) the evolution equations change the character of constraint
propagation, and several particular adjustments using constraints are expected
to damp the constraint-violating modes. We show several set of adjusted
ADM/BSSN equations, together with their numerical demonstrations.


title: Multiparticle Entanglement in the Lipkin-Meshkov-Glick Model

abstract:
  The multiparticle entanglement in the Lipkin-Meshkov-Glick model has been
discussed extensively in this paper. Measured by the global entanglement and
its generalization, our calculation shows that the multiparticle entanglement
can faithfully detect quantum phase transitions. For an antiferromagnetic case
the multiparticle entanglement reaches the maximum at the transition point,
whereas for ferromagnetic coupling, two different behaviors of multiparticle
entanglement can be identified, dependent on the anisotropic parameter in the
coupling.


title: Density Evolution in the New Modified Chaplygin Gas Model

abstract:
  In this paper, we have considered new modified Chaplygin gas (NMCG) model
which interpolates between radiation at early stage and $\Lambda$CDM at late
stage. This model is regarded as a unification of dark energy and dark matter
(with general form of matter). We have derived the density parameters from the
equation of motion for the interaction between dark energy and dark matter.
Also we have studied the evolution of the various components of density
parameters.


title: Non-commutative A-G mean inequality

abstract:
  In this paper we consider non-commutative analogue for the
arithmeticgeometric mean inequality $$a^{r}b^{1-r}+(r-1)b\geq ra$$ for two
positive numbers $a,b$ and $r> 1$. We show that under some assumptions the
non-commutative analogue for $a^{r}b^{1-r}$ which satisfies this inequality is
unique and equal to $r$-mean. The case $0<r<1$ is also considered. In
particular, we give a new characterization of the geometric mean.


title:
Periodicity Search of Possible X-ray Counterparts to Radio-quiet
  Gamma-ray Pulsar Candidates

abstract:
  Periodicity search in gamma-ray data is usually difficult because of the
small number of detected photons. A periodicity in the timing signal at other
energy bands from the counterpart to the gamma-ray source may help to establish
the periodicity in the gamma-ray emission and strengthen the identification of
the source in different energy bands. It may, however, still be difficult to
find the period directly from X-ray data because of limited exposure. We
developed a procedure, by cross-checking two X-ray data sets, to find candidate
periods for X-ray sources which are possible counterparts to gamma-ray pulsar
candidates. Here we report the results of this method obtained with all the
currently available X-ray data of 8 X-ray sources. Some tempting periodicity
features were found. Those candidate periods can serve as the target periods
for future search when new data become available so that a blind search with a
huge number of trials can be avoided.


title:
Compressible Fluids: the discontinuity of the vorticity vector on a
  shock wave in thermodynamical variables

abstract:
  The discontinuity of the vorticity is written as a function of the vector T
grad s, (where T is the temperature and s the specific entropy). The expression
is obtained thanks to potential equations and independently of the mass
conservation and the equation of momentum balance.


title:
A nonparametric estimator of the spectral density of a continuous-time
  Gaussian process observed at random times

abstract:
  In numerous applications data are observed at random times and an estimated
graph of the spectral density may be relevant for characterizing and explaining
phenomena. By using a wavelet analysis, one derives a nonparametric estimator
of the spectral density of a Gaussian process with stationary increments (or a
stationary Gaussian process) from the observation of one path at random
discrete times. For every positive frequency, this estimator is proved to
satisfy a central limit theorem with a convergence rate depending on the
roughness of the process and the moment of random durations between successive
observations. In the case of stationary Gaussian processes, one can compare
this estimator with estimators based on the empirical periodogram. Both
estimators reach the same optimal rate of convergence, but the estimator based
on wavelet analysis converges for a different class of random times. Simulation
examples and application to biological data are also provided.


title:
Existence results for quasilinear elliptic boundary value problems via
  topological methods

abstract:
  In this paper, existence and localization results of $C^1$-solutions to
elliptic Dirichlet boundary value problems are established. The approach is
based on the nonlinear alternative of Leray-Schauder.


title:
Can the Hagedorn Phase Transition be explained from Matrix Model for
  Strings?

abstract:
  The partition function of BFSS matrix model is studied for two different
classical backgrounds upto 1-loop level. One of the backgrounds correspond to a
membrane wrapped around a compact direction and another to a localized cluster
of $D0$-branes. It is shown there exist phase transitions between these two
configurations - but only in presence of an IR cut-off. The low temperature
phase corresponds to a string (wrapped membrane) phase and so we call this the
Hagedorn phase transition. While the presence of an IR cut-off seemingly is
only required for perturbative analysis to be valid, the physical necessity of
such a cut-off can be seen in the dual supergravity side. It has been argued
from entropy considerations that a finite size horizon must develop even in an
extremal configuration of D0-branes, from higher derivative $O(g_s)$
corrections to supergravity. It can then be shown that the Hagedorn like
transition exists in supergravity also. Interestingly the perturbative analysis
also shows a second phase transition back to a string phase. This is also
reminiscent of the Gregory-Laflamme instability.


title: Motional dispersions and ratchet effect in inertial systems

abstract:
  We obtain ratchet effect in inertial structureless systems in symmetric
periodic potentials where the asymmetry comes from the nonuniform friction
offered by the medium and driven by symmetric periodic forces. In the adiabatic
limit the calculations are done by extending the matrix continued fraction
method and also by numerically solving the appropriate Langevin equation. For
finite frequency field drive the ratchet effect is obtained only numerically.
In the transient time scales the system shows dispersionless behaviour as
reported earlier when a constant force is applied. In the periodic drive case
the dispersion behaviour is more complex. In this brief communication we report
some of the results of our work


title:
Improved ring potential of QED at finite temperature and in the presence
  of weak and strong magnetic field

abstract:
  Using the general structure of the vacuum polarization tensor
$\Pi_{\mu\nu}(k_{0},\mathbf{k})$ in the infrared (IR) limit, $k_{0}\to 0$, the
ring contribution to QED effective potential at finite temperature and non-zero
magnetic field is determined beyond the static limit, $(k_{0}\to
0,\mathbf{k}\to \mathbf{0})$. The resulting ring potential is then studied in
weak and strong magnetic field limit. In the limit of weak magnetic field, at
high temperature and for $\alpha\to 0$, the improved ring potential consists of
a term proportional to $T^{4}\alpha^{5/2}$, in addition to the expected
$T^{4}\alpha^{3/2}$ term arising from the static limit. Here, $\alpha$ is the
fine structure constant. In the limit of strong magnetic field, where QED
dynamics is dominated by the lowest Landau level (LLL), the ring potential
includes a novel term consisting of dilogarithmic function
$(eB){Li}_{2}(-\frac{2\alpha}{\pi}\frac{eB}{m^{2}})$. Using the ring improved
(one-loop) effective potential including the one-loop effective potential and
ring potential in the IR limit, the dynamical chiral symmetry breaking of QED
is studied at finite temperature and in the presence of strong magnetic field.
The gap equation, the dynamical mass and the critical temperature of QED in the
regime of LLL dominance are determined in the improved IR as well as in the
static limit. For a given value of magnetic field, the improved ring potential
is shown to be more efficient in decreasing the critical temperature arising
from one-loop effective potential.


title:
A Fast Way to Compute Functional Determinants of Radially Symmetric
  Partial Differential Operators in General Dimensions

abstract:
  Recently the partial wave cutoff method was developed as a new calculational
scheme for a functional determinant of quantum field theory in radial
backgrounds. For the contribution given by an infinite sum of large partial
waves, we derive explicitly radial WKB series in the angular momentum cutoff
for $d=2,3,4$ and 5 ($d$ is the spacetime dimension), which has uniform
validity irrespectively of any specific values assumed for other parameters.
Utilizing this series, precision evaluation of the renormalized functional
determinant is possible with a relatively small number of low partial wave
contributions determined separately. We illustrate the power of this scheme in
numerically exact evaluation of the prefactor (expressed as a functional
determinant) in the case of the false vacuum decay of 4D scalar field theory.


title: Acoustic cloaking theory

abstract:
  An acoustic cloak envelopes an object so that sound incident from all
directions passes through and around the cloak as though the object were not
present. A theory of acoustic cloaking is developed using the transformation or
change-of-variables method for mapping the cloaked region to a point with
vanishing scattering strength. We show that the acoustical parameters in the
cloak must be anisotropic: either the mass density or the mechanical stiffness
or both. If the stiffness is isotropic, corresponding to a fluid with a single
bulk modulus, then the inertial density must be infinite at the inner surface
of the cloak. This requires an infinitely massive cloak. We show that perfect
cloaking can be achieved with finite mass through the use of anisotropic
stiffness. The generic class of anisotropic material required is known as a
pentamode material. If the transformation deformation gradient is symmetric
then the pentamode material parameters are explicit, otherwise its properties
depend on a stress like tensor which satisfies a static equilibrium equation.
For a given transformation mapping the material composition of the cloak is not
uniquely defined, but the phase and wave speeds of the pseudo-acoustic waves in
the cloak are unique. Examples are given from 2D and 3D.


title:
K* production in Cu+Cu and Au+Au collisions at sqrt(s_{NN}) = 62.4 GeV
  and 200 GeV in STAR

abstract:
  We report the measurements of $p_T$ spectra of $K^*$ up to intermediate $p_T$
region in mid-rapidity through its hadronic decay channel using the STAR
detector in Au+Au and Cu+Cu collisions at $\sqrt{s_{\mathrm{NN}}}$= 62.4 GeV
and 200 GeV. Particle ratios such as $K^{*}/K$ and $K^{*}/\phi$ is used to
understand the rescattering and regeneration effect on $K^{*}$ production in
the hadronic medium. The $K^*$ $v_{2}$ measurement using a high statistics
Au+Au 200 GeV dataset and nuclear modification factor measurement supports the
quark coalescence model of particle production in the intermediate $p_T$ range.


title: Graph braid groups and right-angled Artin groups

abstract:
  We give a necessary and sufficient condition for a graph to have a
right-angled Artin group as its braid group for braid index $\ge 5$. In order
to have the necessity part, graphs are organized into small classes so that one
of homological or cohomological characteristics of right-angled Artin groups
can be applied. Finally we show that a given graph is planar iff the first
homology of its 2-braid group is torsion-free and leave the corresponding
statement for $n$-braid groups as a conjecture along with few other conjectures
about graphs whose braid groups of index $\le 4$ are right-angled Artin groups.


title:
Random walks, arrangements, cell complexes, greedoids, and
  self-organizing libraries

abstract:
  The starting point is the known fact that some much-studied random walks on
permutations, such as the Tsetlin library, arise from walks on real hyperplane
arrangements. This paper explores similar walks on complex hyperplane
arrangements. This is achieved by involving certain cell complexes naturally
associated with the arrangement. In a particular case this leads to walks on
libraries with several shelves.
  We also show that interval greedoids give rise to random walks belonging to
the same general family. Members of this family of Markov chains, based on
certain semigroups, have the property that all eigenvalues of the transition
matrices are non-negative real and given by a simple combinatorial formula.
  Background material needed for understanding the walks is reviewed in rather
great detail.


title: Predicting the species abundance distribution using a model food web

abstract:
  A large number of models of the species abundance distribution (SAD) have
been proposed, many of which are generically similar to the log-normal
distribution, from which they are often indistinguishable when describing a
given data set. Ecological data sets are necessarily incomplete samples of an
ecosystem, subject to statistical noise, and cannot readily be combined to
yield a closer approximation to the underlying distribution. In this paper we
use empirical data obtained from an ecosystem model to study the predicted SAD
in detail, resolving features which can distinguish between models but which
are poorly seen in field data. We find that the power-law normal distribution
is superior to both the log-normal and logit-normal distributions, and that the
data can improve on even this at the high-population cut-off.


title: Particle acceleration in the driven relativistic reconnection

abstract:
  We study the compression driven magnetic reconnection in the relativistic
electron-positron plasma. Making use of a 2.5D particle-in-cell code, we
simulated compression of a magnetized plasma layer containing a current sheet
within it. We found that the particle spectrum within the reconnecting sheet
becomes non-thermal; it could be approximated by a power-law distribution with
an index of -1 and an exponential cutoff.


title: Erosion of a granular bed driven by laminar fluid flow

abstract:
  Motivated by examples of erosive incision of channels in sand, we investigate
the motion of individual grains in a granular bed driven by a laminar fluid to
give us new insights into the relationship between hydrodynamic stress and
surface granular flow. A closed cell of rectangular cross-section is partially
filled with glass beads and a constant fluid flux $Q$ flows through the cell.
The refractive indices of the fluid and the glass beads are matched and the
cell is illuminated with a laser sheet, allowing us to image individual beads.
The bed erodes to a rest height $h_r$ which depends on $Q$. The Shields
threshold criterion assumes that the non-dimensional ratio $\theta$ of the
viscous stress on the bed to the hydrostatic pressure difference across a grain
is sufficient to predict the granular flux. Furthermore, the Shields criterion
states that the granular flux is non-zero only for $\theta >\theta_c$. We find
that the Shields criterion describes the observed relationship $h_r \propto
Q^{1/2}$ when the bed height is offset by approximately half a grain diameter.
Introducing this offset in the estimation of $\theta$ yields a collapse of the
measured Einstein number $q^*$ to a power-law function of $\theta - \theta_c$
with exponent $1.75 \pm 0.25$. The dynamics of the bed height relaxation are
well described by the power law relationship between the granular flux and the
bed stress.


title: Universe Detectors for Sybil Defense in Ad Hoc Wireless Networks

abstract:
  The Sybil attack in unknown port networks such as wireless is not considered
tractable. A wireless node is not capable of independently differentiating the
universe of real nodes from the universe of arbitrary non-existent fictitious
nodes created by the attacker. Similar to failure detectors, we propose to use
universe detectors to help nodes determine which universe is real. In this
paper, we (i) define several variants of the neighborhood discovery problem
under Sybil attack (ii) propose a set of matching universe detectors (iii)
demonstrate the necessity of additional topological constraints for the
problems to be solvable: node density and communication range; (iv) present
SAND -- an algorithm that solves these problems with the help of appropriate
universe detectors, this solution demonstrates that the proposed universe
detectors are the weakest detectors possible for each problem.