title:
Computing the smallest fixed point of order-preserving nonexpansive
  mappings arising in positive stochastic games and static analysis of programs

abstract:
  The problem of computing the smallest fixed point of an order-preserving map
arises in the study of zero-sum positive stochastic games. It also arises in
static analysis of programs by abstract interpretation. In this context, the
discount rate may be negative. We characterize the minimality of a fixed point
in terms of the nonlinear spectral radius of a certain semidifferential. We
apply this characterization to design a policy iteration algorithm, which
applies to the case of finite state and action spaces. The algorithm returns a
locally minimal fixed point, which turns out to be globally minimal when the
discount rate is nonnegative.


title:
Dependence of geosynchrotron radio emission on the energy and depth of
  maximum of cosmic ray showers

abstract:
  Based on CORSIKA and REAS2 simulations, we investigate the dependence of
geosynchrotron radio emission from extensive air showers on the energy of the
primary cosmic ray and the depth of the shower maximum. It is found that at a
characteristic lateral distance, the amplitude of the bandpass-filtered radio
signal is directly proportional to the energy deposited in the atmosphere by
the electromagnetic cascade, with an RMS uncertainty due to shower-to-shower
fluctuations of less than 3%. In addition, the ratio of this radio amplitude
and that at a larger lateral distance is directly related to the atmospheric
depth of the shower maximum, with an RMS uncertainty of ~15-20 g cm-2. By
measuring these quantities, geosynchrotron radio emission from cosmic ray air
showers can be used to infer the energy of the primary particle and the depth
of the air shower maximum on a shower-to-shower basis.


title:
The p/pi ratio pT-dependence in the RHIC range od baryo-chemical
  potential

abstract:
  The BRAHMS measurement of proton-to-pion ratios in Au+Au and p+p collisions
at 62.4 and 200 GeV is presented as a function of transverse momentum and
collision centrality within the pseudorapidity range 0 < eta < 3.2. The p/pi
ratio measured for Au+Au system at 62.4 GeV, eta = 3.2 reaches astounding value
of 8-10 at pT >= 1.5 GeV/c. For these energy and pseudorapidity interval no
centrality dependency of p/pi ratio is observed. The baryon-to-meson ratio of
nucleus-nucleus data are consistent with results obtained for p+p interactions.


title: Breaking the chain

abstract:
  We consider the motion of a Brownian particle in $\mathbb{R}$, moving between
a particle fixed at the origin and another moving deterministically away at
slow speed $\epsilon>0$. The middle particle interacts with its neighbours via
a potential of finite range $b>0$, with a unique minimum at $a>0$, where
$b<2a$. We say that the chain of particles breaks on the left- or right-hand
side when the middle particle is greater than a distance $b$ from its left or
right neighbour, respectively. We study the asymptotic location of the first
break of the chain in the limit of small noise, in the case where $\epsilon =
\epsilon(\sigma)$ and $\sigma>0$ is the noise intensity.


title:
Overcoming non-Markovian dephasing in single photon sources through
  post-selection

abstract:
  We study the effects of realistic dephasing environments on a pair of
solid-state single-photon sources in the context of the Hong-Ou-Mandel dip. By
means of solutions for the Markovian or exact non-Markovian dephasing dynamics
of the sources, we show that the resulting loss of visibility depends crucially
on the timing of photon detection events. Our results demonstrate that the
effective visibility can be improved via temporal post-selection, and also that
time-resolved interference can be a useful probe of the interaction between the
emitter and its host environment.


title: Implications of Einstein-Weyl Causality on Quantum Mechanics

abstract:
  A fundamental physical principle that has consequences for the topology of
space-time is the principle of Einstein-Weyl causality. We show here that this
may have implications on quantum mechanics, as well. Borchers and Sen have
rigorously investigated the mathematical implications of Einstein-Weyl
causality and shown the denumerable space-time Q^2 would be implied. They then
imbedded this space in a non-denumerable space but were left with important
philosophical paradoxes regarding the nature of the physical real line E, e.g.,
whether E = R, the real line of mathematics. Alternatively, their initial
result could suggest a constructible foundation. We have pursued such a program
and find it indeed provides a dense, denumerable space-time and, moreover, an
interesting connection with quantum mechanics.


title:
Cooling of the crust in the neutron star low-mass X-ray binary MXB
  1659-29

abstract:
  In quasi-persistent neutron star transients, long outbursts cause the neutron
star crust to be heated out of thermal equilibrium with the rest of the star.
During quiescence, the crust then cools back down. Such crustal cooling has
been observed in two quasi-persistent sources: KS 1731-260 and MXB 1659-29.
Here we present an additional Chandra observation of MXB 1659-29 in quiescence,
which extends the baseline of monitoring to 6.6 yr after the end of the
outburst. This new observation strongly suggests that the crust has thermally
relaxed, with the temperature remaining consistent over 1000 days. Fitting the
temperature cooling curve with an exponential plus constant model we determine
an e-folding timescale of 465 +/- 25 days, with the crust cooling to a constant
surface temperature of kT = 54 +/- 2 eV (assuming D=10 kpc). From this, we
infer a core temperature in the range 3.5E7-8.3E7 K (assuming D=10 kpc), with
the uncertainty due to the surface composition. Importantly, we tested two
neutron star atmosphere models as well as a blackbody model, and found that the
thermal relaxation time of the crust is independent of the chosen model and the
assumed distance.


title: Instantaneous interaction in massive gravity

abstract:
  In general relativity, the instantaneous contributions to the gravitational
potentials cancel each other in observable, leaving the theory free of physical
instantaneous interactions. In models where these subtle cancellations are
spoiled by the presence of fields that break Lorentz invariance, physical
instantaneous interactions are possible. Such interactions are studied for a
model of Lorentz- violating massive gravity.


title:
Tangential interpolation in weighted vector-valued H^p spaces, with
  applications

abstract:
  In this paper, norm estimates are obtained for the problem of minimal-norm
tangential interpolation by vector-valued analytic functions in weighted H^p
spaces, expressed in terms of the Carleson constants of related scalar
measures. Applications are given to the notion of p-controllability properties
of linear semigroup systems and controllability by functions in certain Sobolev
spaces.


title:
Towards a Unified Understanding of Jet Quenching and Elliptic Flow
  within Perturbative QCD Parton Transport

abstract:
  The gluonic contribution to the nuclear modification factor R_AA is
investigated for central Au + Au collisions at sqrt(s) = 200 GeV employing a
perturbative QCD-based parton cascade including radiative processes. A flat
quenching pattern is found up to transverse momenta of 30 GeV which is slightly
smaller compared with results from the Gyulassy-Levai-Vitev formalism. We
demonstrate that the present microscopic transport description provides
challenging means of investigating both jet-quenching and a strong buildup of
elliptic flow in terms of the same standard perturbative QCD interactions.


title: The 2006-2008 Oil Bubble and Beyond

abstract:
  We present an analysis of oil prices in US$ and in other major currencies
that diagnoses unsustainable faster-than-exponential behavior. This supports
the hypothesis that the recent oil price run-up has been amplified by
speculative behavior of the type found during a bubble-like expansion. We also
attempt to unravel the information hidden in the oil supply-demand data
reported by two leading agencies, the US Energy Information Administration
(EIA) and the International Energy Agency (IEA). We suggest that the found
increasing discrepancy between the EIA and IEA figures provides a measure of
the estimation errors. Rather than a clear transition to a supply restricted
regime, we interpret the discrepancy between the IEA and EIA as a signature of
uncertainty, and there is no better fuel than uncertainty to promote
speculation!


title: Supertropical algebra

abstract:
  We develop the algebraic polynomial theory for "supertropical algebra," as
initiated earlier over the real numbers by the first author. The main
innovation there was the introduction of "ghost elements," which also play the
key role in our structure theory. Here, we work somewhat more generally over an
ordered monoid, and develop a theory which contains the analogs of several
basic theorems of classical commutative algebra. This structure enables one to
develop a Zariski-type algebraic geometric approach to tropical geometry,
viewing tropical varieties as sets of roots of (supertropical) polynomials,
leading to an analog of the Hilbert Nullstellensatz. Particular attention is
paid to factorization of polynomials. In one indeterminate, any polynomial can
be factored into linear and quadratic factors, and unique factorization holds
in a certain sense. On the other hand, the failure of unique factorization in
several indeterminates is explained by geometric phenomena described in the
paper.


title: Optimal quantum tomography for states, measurements, and transformations

abstract:
  We present the first complete optimization of quantum tomography, for states,
POVMs, and various classes of transformations, for arbitrary prior ensemble and
arbitrary representation, giving corresponding feasible experimental schemes.


title: Asymptotics of posteriors for binary branching processes

abstract:
  We compute the posterior distributions of the initial population and
parameter of binary branching processes, in the limit of a large number of
generations. We compare this Bayesian procedure with a more na\"ive one, based
on hitting times of some random walks. In both cases, central limit theorems
are available, with explicit variances.


title: Bloch vectors for qudits

abstract:
  We present three different matrix bases that can be used to decompose density
matrices of $d$--dimensional quantum systems, so-called qudits: the
\emph{generalized Gell-Mann matrix basis}, the \emph{polarization operator
basis}, and the \emph{Weyl operator basis}. Such a decomposition can be
identified with a vector --the Bloch vector, i.e. a generalization of the well
known qubit case-- and is a convenient expression for comparison with
measurable quantities and for explicit calculations avoiding the handling of
large matrices. We present a new method to decompose density matrices via
so--called standard matrices, consider the important case of an isotropic
two--qudit state and decompose it according to each basis. In case of qutrits
we show a representation of an entanglement witness in terms of expectation
values of spin 1 measurements, which is appropriate for an experimental
realization.


title: Completions, Reversals, and Duality for Tropical Varieties

abstract:
  The algebraic foundation of tropical polynomial algebra provides the
framework for the geometric construction of the supplement and the reversal of
tropical varieties, thereby inducing a duality of reduced tropical varieties;
for classes of tropical hypersurfaces the corresponding point symmetry is
obtained for their Newton polytopes and lattice polytopes.


title: A fresh look at some questions surrounding black holes

abstract:
  The modern notion of a black hole singularity is considered with reference to
the Schwarzschild solution to Einstein's field equations of general relativity.
A brief derivation of both the original and the modern line elements is given.
The argument is put forward that the singularity occurring within the
Schwarzschild line element that has been associated with the radius of the
black hole event horizon is, in fact, merely a mathematical occurrence and does
not exist physically. The real aim here, however, is to attempt to open up the
whole problem, draw some conclusions, but finally to urge everyone to consider
the points raised with no preconceived opinions and then come to their own
final conclusion.


title:
Evolution of Fermi surface and normal-state gap in chemically
  substituted cuprates Bi$_{2}$Sr$_{2-x}$Bi$_{x}$CuO$_{6+\delta}$

abstract:
  We have performed a systematic angle-resolved photoemission study of
chemically substituted cuprates Bi$_{2}$Sr$_{2-x}$Bi$_{x}$CuO$_{6+\delta}$. We
observed that the Fermi surface area shrinks linearly with Bi substitution
content $x$, reflecting the electron doping nature of this chemical
substitution. In addition, the spectral linewidth broadens rapidly with
increasing $x$, and becomes completely incoherent at the
superconducting-insulating boundary. The d-wave-like normal-state gap observed
in the lightly underdoped region gradually evolves into a large soft gap, which
suppresses antinodal spectral weight linearly in both the excitation energy and
temperature. Combining with the bulk resistivity data obtained on the same
samples, we establish the emergence of the Coulomb gap behavior in the very
underdoped regime. Our results reveal the dual roles, doping and disorder, of
off-plane chemical substitutions in high-$T_c$ cuprates and elucidate the
nature of the quantum electronic states due to strong correlation and disorder.


title: Supertropical matrix algebra

abstract:
  The objective of this paper is to develop a general algebraic theory of
supertropical matrix algebra, extending [11]. Our main results are as follows:
  * The tropical determinant (i.e., permanent) is multiplicative when all the
determinants involved are tangible.
  * There exists an adjoint matrix $\adj{A}$ such that the matrix $A \adj{A}$
behaves much like the identity matrix (times $|A|$).
  * Every matrix $A$ is a supertropical root of its Hamilton-Cayley polynomial
$f_A$. If these roots are distinct, then $A$ is conjugate (in a certain
supertropical sense) to a diagonal matrix.
  * The tropical determinant of a matrix $A$ is a ghost iff the rows of $A$ are
tropically dependent, iff the columns of $A$ are tropically dependent.
  * Every root of $f_A$ is a "supertropical" eigenvalue of $A$ (appropriately
defined), and has a tangible supertropical eigenvector.


title: Feynman graphs, rooted trees, and Ringel-Hall algebras

abstract:
  We construct symmetric monoidal categories $\LRF, \FD$ of rooted forests and
Feynman graphs. These categories closely resemble finitary abelian categories,
and in particular, the notion of Ringel-Hall algebra applies. The Ringel-Hall
Hopf algebras of $\LRF, \FD$, $\HH_{\LRF}, \HH_{\FD}$ are dual to the
corresponding Connes-Kreimer Hopf algebras on rooted trees and Feynman graphs.
We thus obtain an interpretation of the Connes-Kreimer Lie algebras on rooted
trees and Feynman graphs as Ringel-Hall Lie algebras.


title: Incompressible flow in porous media with fractional diffusion

abstract:
  In this paper we study the heat transfer with a general fractional diffusion
term of an incompressible fluid in a porous medium governed by Darcy's law. We
show formation of singularities with infinite energy and for finite energy we
obtain existence and uniqueness results of strong solutions for the
sub-critical and critical cases. We prove global existence of weak solutions
for different cases. Moreover, we obtain the decay of the solution in $L^p$,
for any $p\geq2$, and the asymptotic behavior is shown. Finally, we prove the
existence of an attractor in a weak sense and, for the sub-critical dissipative
case with $\alpha\in (1,2]$, we obtain the existence of the global attractor
for the solutions in the space $H^s$ for any $s > (N/2)+1-\alpha$.


title:
Some remarks on the coherent-state variational approach to nonlinear
  boson models

abstract:
  The mean-field pictures based on the standard time-dependent variational
approach have widely been used in the study of nonlinear many-boson systems
such as the Bose-Hubbard model. The mean-field schemes relevant to
Gutzwiller-like trial states $|F>$, number-preserving states $|\xi >$ and
Glauber-like trial states $|Z>$ are compared to evidence the specific
properties of such schemes. After deriving the Hamiltonian picture relevant to
$|Z>$ from that based on $|F>$, the latter is shown to exhibit a Poisson
algebra equipped with a Weyl-Heisenberg subalgebra which preludes to the
$|Z>$-based picture. Then states $|Z>$ are shown to be a superposition of $\cal
N$-boson states $|\xi>$ and the similarities/differences of the $|Z>$-based and
$|\xi>$-based pictures are discussed. Finally, after proving that the simple,
symmetric state $|\xi>$ indeed corresponds to a SU(M) coherent state, a dual
version of states $|Z>$ and $|\xi>$ in terms of momentum-mode operators is
discussed together with some applications.

categories: math-ph cond-mat.other cond-mat.stat-mech math.MP


title:
Photometry and spectroscopy of GRB 060526: A detailed study of the
  afterglow and host galaxy of a z=3.2 gamma-ray burst

abstract:
  Aims: With this paper we want to investigate the highly variable afterglow
light curve and environment of gamma-ray burst (GRB) 060526 at $z=3.221$.
Methods: We present one of the largest photometric datasets ever obtained for a
GRB afterglow, consisting of multi-color photometric data from the ultraviolet
to the near infrared. The data set contains 412 data points in total to which
we add additional data from the literature. Furthermore, we present
low-resolution high signal-to-noise spectra of the afterglow. The afterglow
light curve is modeled with both an analytical model using broken power law
fits and with a broad-band numerical model which includes energy injections.
The absorption lines detected in the spectra are used to derive column
densities using a multi-ion single-component curve-of-growth analysis from
which we derive the metallicity of the host of GRB 060526. Results: The
temporal behaviour of the afterglow follows a double broken power law with
breaks at $t=0.090\pm0.005$ and $t=2.401\pm0.061$ days. It shows deviations
from the smooth set of power laws that can be modeled by additional energy
injections from the central engine, although some significant microvariability
remains. The broadband spectral-energy distribution of the afterglow shows no
significant extinction along the line of sight. The metallicity derived from
\ion{S}{II} and \ion{Fe}{II} of [S/H] = --0.57 $\pm$0.25 and [Fe/H] =
--1.09$\pm$0.24 is relatively high for a galaxy at that redshift but comparable
to the metallicity of other GRB hosts at similar redshifts. At the position of
the afterglow, no host is detected to F775W(AB) = 28.5 mag with the HST,
implying an absolute magnitude of the host M(1500 \AA{})$>$--18.3 mag which is
fainter than most long-duration hosts, although the GRB may be associated with
a faint galaxy at a distance of 11 kpc.


title:
Analytic structure of the four-wave mixing model in photorefractive
  materials

abstract:
  In order to later find explicit analytic solutions, we investigate the
singularity structure of a fundamental model of nonlinear optics, the four-wave
mixing model in one space variable z. This structure is quite similar, and this
is not a surprise, to that of the cubic complex Ginzburg-Landau equation. The
main result is that, in order to be single valued, time-dependent solutions
should depend on the space-time coordinates through the reduced variable
xi=\sqrt{z} exp(-t / tau), in which tau is the relaxation time.


title:
Global Fits of the Large Volume String Scenario to WMAP5 and Other
  Indirect Constraints Using Markov Chain Monte Carlo

abstract:
  We present global fits to the Large Volume Scenario (LVS) of string models
using current indirect data. We use WMAP5 constraints on dark matter relic
density, b-physics and electroweak observables as well as direct search
constraints. Such data can be adequately fit by LVS, with the best-fit point
for mu>0 having chi^2=13.6 for 8 degrees of freedom. The resulting constraints
on parameter space are robust in that they do not depend much upon the prior,
or upon whether one uses Bayesian or frequentist interpretations of the data.
Sparticle masses are constrained to be well below the 1 TeV level, predicting
early SUSY discovery at the LHC. We devise a method of quantifying which are
the most important constraints. We find that the LEP2 Higgs mass constraint,
the relic density of dark matter and the anomalous magnetic moment of the muon
affect the fits to the strongest degree.


title:
A classification of periodic time-dependent generalized harmonic
  oscillators using a Hamiltonian action of the Schr\"odinger-Virasoro group

abstract:
  In the wake of a preceding article \cite{RogUnt06} introducing the
Schr\"odinger-Virasoro group, we study its affine action on a space of
$(1+1)$-dimensional Schr\"odinger operators with time- and space-dependent
potential $V$ periodic in time. We focus on the subspace corresponding to
potentials that are at most quadratic in the space coordinate, which is in some
sense the natural quantization of the space of Hill (Sturm-Liouville) operators
on the one-dimensional torus. The orbits in this subspace have finite
codimension, and their classification by studying the stabilizers can be
obtained by extending Kirillov's results on the orbits of the space of Hill
operators under the Virasoro group. We then explain the connection to the
theory of Ermakov-Lewis invariants for time-dependent harmonic oscillators.
These exact adiabatic invariants behave covariantly under the action of the
Schr\"odinger-Virasoro group, which allows a natural classification of the
orbits in terms of a monodromy operator on $L^2(\R)$ which is closely related
to the monodromy matrix for the corresponding Hill operator.


title: Intricate dynamics of a deterministic walk confined in a strip

abstract:
  We study the dynamics of a deterministic walk confined in a narrow
two-dimensional space randomly filled with point-like targets. At each step,
the walker visits the nearest target not previously visited. Complex dynamics
is observed at some intermediate values of the domain width, when, while
drifting, the walk performs long intermittent backward excursions. As the width
is increased, evidence of a transition from ballistic motion to a weakly
non-ergodic regime is shown, characterized by sudden inversions of the drift
velocity with a probability slowly decaying with time, as $1/t$ at leading
order. Excursion durations, first-passage times and the dynamics of unvisited
targets follow power-law distributions. For parameter values below this scaling
regime, precursory patterns in the form of "wild" outliers are observed, in
close relation with the presence of log-oscillations in the probability
distributions. We discuss the connections between this model and several
evolving biological systems.


title: Is the ground state of Yang-Mills theory Coulombic?

abstract:
  We study trial states modelling the heavy quark-antiquark ground state in
SU(2) Yang-Mills theory. A state describing the flux tube between quarks as a
thin string of glue is found to be a poor description of the continuum ground
state; the infinitesimal thickness of the string leads to UV artifacts which
suppress the overlap with the ground state. Contrastingly, a state which
surrounds the quarks with non-abelian Coulomb fields is found to have a good
overlap with the ground state for all charge separations. In fact, the overlap
increases as the lattice regulator is removed. This opens up the possibility
that the Coulomb state is the true ground state in the continuum limit.


title: Four-free groups and hyperbolic geometry

abstract:
  We give new information about the geometry of closed, orientable hyperbolic
3-manifolds with 4-free fundamental group. As an application we show that such
a manifold has volume greater than 3.44. This is in turn used to show that if M
is a closed orientable hyperbolic 3-manifold such that vol M < 3.44, then
H_1(M;Z/2Z) has dimension at most 7.


title:
Optical polarimetry toward the Pipe nebula: Revealing the importance of
  the magnetic field

abstract:
  Magnetic fields are proposed to play an important role in the formation and
support of self-gravitating clouds and the formation and evolution of
protostars in such clouds. We use R-band linear polarimetry collected for about
12000 stars in 46 fields with lines of sight toward the Pipe nebula to
investigate the properties of the polarization across this dark cloud complex.
Mean polarization vectors show that the magnetic field is locally perpendicular
to the large filamentary structure of the Pipe nebula (the `stem'), indicating
that the global collapse may have been driven by ambipolar diffusion. The
polarization properties clearly change along the Pipe nebula. The northwestern
end of the nebula (B59 region) is found to have a low degree of polarization
and high dispersion in polarization position angle, while at the other extreme
of the cloud (the `bowl') we found mean degrees of polarization as high as
$\approx$15% and a low dispersion in polarization position angle. The plane of
the sky magnetic field strength was estimated to vary from about 17 $\mu$G in
the B59 region to about 65 $\mu$G in the bowl. We propose that three distinct
regions exist, which may be related to different evolutionary states of the
cloud; this idea is supported by both the polarization properties across the
Pipe and the estimated mass-to-flux ratio that varies between approximately
super-critical toward the B59 region and sub-critical inside the bowl. The
three regions that we identify are: the B59 region, which is currently forming
stars; the stem, which appears to be at an earlier stage of star formation
where material has been through a collapsing phase but not yet given birth to
stars; and the bowl, which represents the earliest stage of the cloud in which
the collapsing phase and cloud fragmentation has already started.


title: Heavy-Ion Physics with CMS

abstract:
  This article presents a brief overview of the CMS experiment capabilities to
study the hot and dense matter created in relativistic heavy-ion collisions.
The CERN Large Hadron Collider will provide collisions of Pb nuclei at 5.5 TeV
per nucleon. The CMS heavy ion group has developed a plethora of physics
analyses addressing many important aspects of heavy-ion physics in preparation
for a competitive and successful program.


title: Composite dark matter from a model with composite Higgs boson

abstract:
  In a previous paper \cite{Khlopov:2007ic}, we showed how the minimal walking
technicolor model (WTC) can provide a composite dark matter candidate, by
forming bound states between a -2 electrically charged techniparticle and a
$^4He^{++}$. We studied the properties of these \emph{techni-O-helium} $tOHe$
"atoms", which behave as warmer dark matter rather than cold. In this paper we
extend our work on several different aspects. We study the possibility of a
mixed scenario where both $tOHe$ and bound states between +2 and -2
electrically charged techniparticles coexist in the dark matter density. We
argue that these newly proposed bound states solely made of techniparticles,
although they behave as Weakly Interacting Massive Particles (WIMPs), due to
their large elastic cross section with nuclei, can only account for a small
percentage of the dark matter density. Therefore we conclude that within the
minimal WTC, composite dark matter should be mostly composed of $tOHe$.
Moreover in this paper, we put cosmological bounds in the masses of the
techniparticles, if they compose the dark matter density. Finally we propose
within this setup, a possible explanation of the discrepancy between the
DAMA/NaI and DAMA/LIBRA findings and the negative results of CDMS and other
direct dark matter searches that imply nuclear recoil measurement, which should
accompany ionization.


title: Note on bipartite graph tilings

abstract:
  Let s<t be two fixed positive integers. We study what are the minimum degree
conditions for a bipartite graph G, with both color classes of size n=k(s+t),
which ensure that G has a K_{s,t}-factor. Exact result for large n is given.
Our result extends the work of Zhao, who determined the minimum degree
threshold which guarantees that a bipartite graph has a K_{s,s}-factor.


title: V-T Theory of Self Dynamic Response in a Monatomic Liquid

abstract:
  A new theoretical model for self dynamic response is developed using
Vibration-Transit (V-T) theory, and is applied to liquid sodium at all
wavevectors q from the hydrodynamic regime to the free particle limit. In this
theory the zeroth-order Hamiltonian describes the vibrational motion in a
single random valley harmonically extended to infinity. This Hamiltonian is
tractable, is evaluated a priori for monatomic liquids, and the same
Hamiltonian (the same set of eigenvalues and eigenvectors) is used for
equilibrium and nonequlibrium theory. Here, for the self intermediate
scattering function Fself(q,t) we find the vibrational contribution is in near
perfect agreement with molecular dynamics (MD) through short and intermediate
times, at all q. This is direct confirmation that normal mode vibrational
correlations are present in the motion of the liquid state. The primary transit
effect is diffusive motion of the vibrational equilibrium positions, as the
liquid transits rapidly among random valleys. This motion is modeled as a
standard random walk, and the resulting theoretical Fself(q,t) is in excellent
agreement with MD results at all q and t. In the limit for q to infinity, the
theory automatically exhibits the correct approach to the free-particle limit.
Also in the limit for q to zero, the hydrodynamic limit emerges as well. In
contrast to the benchmark theories of generalized hydrodynamics and mode
coupling, the present theory is near a priori, while achieving modestly better
accuracy. Therefore, in our view, it constitutes an improvement over the
traditional theories.


title:
Viable models of traversable wormholes supported by small amounts of
  exotic matter

abstract:
  Wormholes allowed by the general theory of relativity that are simultaneously
traversable by humanoid travelers are subject to severe constraints from
quantum field theory, particularly the so-called quantum inequalities, here
slightly extended. Moreover, self-collapse of such wormholes can only be
prevented by the use of "exotic matter," which, being rather problematical,
should be used in only minimal quantities. However, making the layer of exotic
matter arbitrarily thin leads to other problems, such as the need for extreme
fine-tuning. This paper discusses a class of wormhole geometries that strike a
balance between reducing the proper distance across the exotic region and the
degree of fine-tuning required to achieve this reduction. Surprisingly, the
degree of fine-tuning appears to be a generic feature of the type of wormhole
discussed. No particular restriction is placed on the throat size, even though
the proper thickness of the exotic region can indeed be quite small. Various
traversability criteria are shown to be met.


title: Evolution of massive protostars: the IRAS 18151-1208 region

abstract:
  The study of physical and chemical properties of massive protostars is
critical to better understand the evolutionary sequence which leads to the
formation of high-mass stars. IRAS 18151-1208 is a nearby massive region (d =
3kpc, L ~ 20000 Lsun) which splits into three cores: MM1, MM2 and MM3
(separated by 1'-2'). We aim at (1) studying the physical and chemical
properties of the individual MM1, MM2 and MM3 cores; (2) deriving their
evolutionary stages; (3) using these results to improve our view of the
evolutionary sequence of massive cores. The region was observed in the CS,
C34S, H2CO, HCO+, H13CO+, and N2H+ lines at mm wavelengths with the IRAM 30m
and Mopra telescopes. We use 1D and 2D modeling of the dust continuum to derive
the density and temperature distributions, which are then used in the RATRAN
code to model the lines and constrain the abundances of the observed species.
All the lines were detected in MM1 and MM2. MM3 shows weaker emission, or even
is undetected in HCO+ and all isotopic species. MM2 is driving a newly
discovered CO outflow and hosts a mid-IR-quiet massive protostar. The abundance
of CS is significantly larger in MM1 than in MM2, but smaller than in a
reference massive protostar such as AFGL2591. In contrast the N2H+ abundance
decreases from MM2 to MM1, and is larger than in AFGL2591. Both MM1 and MM2
host an early phase massive protostar, but MM2 (and mid-IR-quiet sources in
general) is younger and more dominated by the host protostar than MM1
(mid-IR-bright). The MM3 core is probably in a pre-stellar phase. We find that
the N2H+/C34S ratio varies systematically with age in the massive protostars
for which the data are available. It can be used to identify young massive
protostars.


title:
Creating ultracold molecules by collisions with ultracold rare gas atoms
  in an optical trap

abstract:
  We study collisions of para-H$_2$ with five rare gas atomic species (He, Ne,
Ar, Kr and Xe) over the range from 1 K to 1 $\mu$ K and evaluate the
feasibility of sympathetic cooling H$_2$ with ultracold ground state rare gas
atoms co-trapped within a deep optical trap. Collision cross-sections over this
large temperature range show that all of these species could be used to cool
H$_2$ to ultracold temperatures and that argon and helium are the most
promising species for future experiments.


title: Universal Kounterterms in Lovelock AdS gravity

abstract:
  We show the universal form of the boundary term (Kounterterm series) which
regularizes the Euclidean action and background-independent definition of
conserved quantities for any Lovelock gravity theory with AdS asymptotics
(including Einstein-Hilbert and Einstein-Gauss-Bonnet). We discuss on the
connection of this procedure to the existence of topological invariants and
Chern-Simons forms in the corresponding dimensions.


title: Absolute Total np and pp Cross Section Determinations

abstract:
  Absolute total cross sections for np and pp scattering below 1000 MeV are
determined based on partial-wave analyses of NN scattering data. These cross
sections are compared with most recent ENDF/B and JENDL data files, and the
Nijmegen partial-wave analysis. Systematic deviations from the ENDF/B and JENDL
evaluations are found to exist in the low-energy region.


title: Belief Propagation and Beyond for Particle Tracking

abstract:
  We describe a novel approach to statistical learning from particles tracked
while moving in a random environment. The problem consists in inferring
properties of the environment from recorded snapshots. We consider here the
case of a fluid seeded with identical passive particles that diffuse and are
advected by a flow. Our approach rests on efficient algorithms to estimate the
weighted number of possible matchings among particles in two consecutive
snapshots, the partition function of the underlying graphical model. The
partition function is then maximized over the model parameters, namely
diffusivity and velocity gradient. A Belief Propagation (BP) scheme is the
backbone of our algorithm, providing accurate results for the flow parameters
we want to learn. The BP estimate is additionally improved by incorporating
Loop Series (LS) contributions. For the weighted matching problem, LS is
compactly expressed as a Cauchy integral, accurately estimated by a saddle
point approximation. Numerical experiments show that the quality of our
improved BP algorithm is comparable to the one of a fully polynomial randomized
approximation scheme, based on the Markov Chain Monte Carlo (MCMC) method,
while the BP-based scheme is substantially faster than the MCMC scheme.

categories: cs.IT cond-mat.stat-mech cs.AI cs.LG math.IT physics.flu-dyn


title:
PSR J1856+0245: Arecibo Discovery of a Young, Energetic Pulsar
  Coincident with the TeV Gamma-ray Source HESS J1857+026

abstract:
  We present the discovery of the Vela-like radio pulsar J1856+0245 in the
Arecibo PALFA survey. PSR J1856+0245 has a spin period of 81ms, a
characteristic age of 21kyr, and a spin-down luminosity Edot = 4.6 x 10^36
ergs/s. It is positionally coincident with the TeV gamma-ray source HESS
J1857+026, which has no other known counterparts. Young, energetic pulsars
create wind nebulae, and more than a dozen pulsar wind nebulae have been
associated with very-high-energy (100GeV-100TeV) gamma-ray sources discovered
with the HESS telescope. The gamma-ray emission seen from HESS J1857+026 is
potentially produced by a pulsar wind nebula powered by PSR J1856+0245; faint
X-ray emission detected by ASCA at the pulsar's position supports this
hypothesis. The inferred gamma-ray efficiency is epsilon_gamma = L_gamma/Edot =
3.1% (1-10TeV, for a distance of 9kpc), comparable to that observed in similar
associations.


title:
Stability of persistent currents in a Bose-Einstein condensate confined
  in a toroidal trap

abstract:
  Motivated by recent experiments in Bose-Einstein condensed atoms that have
been confined in toroidal traps, we examine the stability of persistent
currents in such systems. We investigate the extent that the stability of these
currents may be tunable, and the possible difficulties in their creation and
detection.


title: Top quark mass measurements at the Tevatron

abstract:
  The mass of the top quark has been measured at Fermilab using the Tevatron
ppbar collider to a precision of less than 1%. I discuss the individual
measurements that go into this result and its impact on our understanding of
the standard model of the electroweak interactions.


title: Ground State Energy of Extended Hubbard Model by self-consistent RPA

abstract:
  Using the SCRPA, we study the intersite interaction effect on the dynamics of
N electrons system. We have considered an extended Hubbard model including
intrasite and intersite interactions, and we have applied this model to a
system of two neighbouring atoms containing a free electron. The application of
SCRPA to this model allows us to study the intersite interaction effect on the
ground state and the excitation energies of system. We show that the repulsive
interaction between the electrons of the neighbouring atoms is the origin of an
supplementary conductivity of the system.

categories: cond-mat.str-el cond-mat.stat-mech cond-mat.supr-con hep-th math-ph math.MP


title: Opinion polarization in the Receipt-Accept-Sample model

abstract:
  The Zaller theory of opinion formation is reformulated with one free
parameter $\mu$, which measures the largest possible ideological distance which
can be made by a citizen in one mental step. Our numerical results show the
transient effects: {\it i)} the political awareness, measured by the number of
received messages, increases with time first exponentially, later linearly;
{\it ii)} for small $\mu$ correlations are present between previously and newly
received messages; {\it iii)} these correlation lead to a hyperdiffusion effect
in the space of attitudes of messages. Citizens with small $\mu$ are more prone
to extremal opinions.


title: Fast domain wall motion in nanostripes with out-of-plane fields

abstract:
  Controlling domain wall motion is important due to the impact on the
viability of proposed nanowire devices. One hurdle is slow domain wall speed
when driven by fields greater than the Walker field, due to nucleation of
vortices in the wall. We present simulation results detailing the dynamics of
these vortices; including the nucleation and subsequent fast ejection of the
vortex core leading to fast domain wall speeds. The ejection is due to the
reversal of the core moments by an out-of-plane field. The technique can be
used to produce domain walls of known orientation independent of the initial
state.


title: Global solution to the Cauchy problem on a universe fireworks model

abstract:
  We prove existence and uniqueness of the global solution to the Cauchy
problem on a universe fireworks model with finite total mass at the initial
state when the ratio of the mass surviving the explosion, the probability of
the explosion of fragments and the probability function of the velocity change
of a surviving particle satisfy the corresponding physical conditions. Although
the nonrelativistic Boltzmann-like equation modeling the universe fireworks is
mathematically easy, this paper leads rather theoretically to an understanding
of how to construct contractive mappings in a Banach space for the proof of the
existence and uniqueness by means of methods taken from the famous work by
DiPerna & Lions about the Boltzmann equation. We also show both the regularity
and the time-asymptotic behavior of solution to the Cauchy problem.


title:
Electromagnons in multiferroic RMn2O5 compounds and their microscopic
  origin

abstract:
  We summarize the existing experimental data on electromagnons in multiferroic
RMn2O5 compounds, where R denotes a rare earth ion, Y or Bi, and discuss a
realistic microscopic model of these materials based on assumption that the
microscopic mechanism of magnetically-induced ferroelectricity and
electromagnon absorption relies entirely on the isotropic Heisenberg exchange
and magnetostrictive coupling of spins to a polar lattice mode and does not
involve relativistic effects. This model explains many magnetic and optical
properties of RMn2O5 manganites, such as the spin re-orientation transition,
magnetically-induced polarisation, appearance of the electromagnon peak in the
non-collinear spin state and the polarisation of light for which this peak is
observed. We compare experimental and theoretical results on electromagnons in
RMn2O5 and RMnO3 compounds.


title: Colliders and Cosmology

abstract:
  Dark matter in variations of constrained minimal supersymmetric standard
models will be discussed. Particular attention will be given to the comparison
between accelerator and direct detection constraints.


title: Superconductivity in hole-doped (Sr$_{1-x}$K$_x$)Fe$_2$As$_2$

abstract:
  A series of layered (Sr$_{1-x}$K$_x$)Fe$_2$As$_2$ compounds with nominal x=0
to 0.40 are synthesized by solid state reaction method. Similar to other parent
compounds of iron-based pnictide superconductors, the pure SrFe$_2$As$_2$ shows
a strong resistivity anomaly near 210 K, which was ascribed to the
spin-density-wave instability. The anomaly temperature is much higher than
those observed in LaOFeAs and BaFe$_2$As$_2$, the two prototype parent
compounds with ZrCuSiAs- and ThCr$_2$Si$_2$-type structures. K-doping strongly
suppresses this anomaly and induces superconductivity. Like in the case of
K-doped BaFe$_2$As$_2$, sharp superconducting transitions at T$_c\sim$38 K was
observed. We performed the Hall coefficient measurement, and confirmed that the
dominant carriers are hole-type. The carrier density is enhanced by a factor of
3 in comparison to F-doped LaOFeAs superconductor.


title: Paperfolding sequences, paperfolding curves and local isomorphism

abstract:
  For each integer n, an n-folding curve is obtained by folding n times a strip
of paper in two, possibly up or down, and unfolding it with right angles.
Generalizing the usual notion of infinite folding curve, we define complete
folding curves as the curves without endpoint which are unions of increasing
sequences of n-folding curves for n integer. We prove that there exists a
standard way to extend any complete folding curve into a covering of the plane
by disjoint such curves, which satisfies the local isomorphism property
introduced to investigate aperiodic tiling systems. This covering contains at
most six curves.


title: Universal dephasing in a chiral 1D interacting fermion system

abstract:
  We consider dephasing by interactions in a one-dimensional chiral fermion
system (e.g. a Quantum Hall edge state). For finite-range interactions, we
calculate the spatial decay of the Green's function at fixed energy, which sets
the contrast in a Mach-Zehnder interferometer. Using a physically transparent
semiclassical ansatz, we find a power-law decay of the coherence at high
energies and zero temperature (T=0), with a universal asymptotic exponent of 1,
independent of the interaction strength. We obtain the dephasing rate at T>0
and the fluctuation spectrum acting on an electron.


title: Pre-torsors and Galois comodules over mixed distributive laws

abstract:
  We study comodule functors for comonads arising from mixed distributive laws.
Their Galois property is reformulated in terms of a (so-called) regular arrow
in Street's bicategory of comonads. Between categories possessing equalizers,
we introduce the notion of a regular adjunction. An equivalence is proven
between the category of pre-torsors over two regular adjunctions $(N_A,R_A)$
and $(N_B,R_B)$ on one hand, and the category of regular comonad arrows
$(R_A,\xi)$ from some equalizer preserving comonad ${\mathbb C}$ to $N_BR_B$ on
the other. This generalizes a known relationship between pre-torsors over equal
commutative rings and Galois objects of coalgebras.Developing a bi-Galois
theory of comonads, we show that a pre-torsor over regular adjunctions
determines also a second (equalizer preserving) comonad ${\mathbb D}$ and a
co-regular comonad arrow from ${\mathbb D}$ to $N_A R_A$, such that the
comodule categories of ${\mathbb C}$ and ${\mathbb D}$ are equivalent.


title: Painlev\'e VI equations with algebraic solutions and family of curves

abstract:
  In families of Painlev\'e VI differential equations having common algebraic
solutions we classify all the members which come from geometry, i.e. the
corresponding linear differential equations which are Picard-Fuchs associated
to families of algebraic varieties. In our case, we have one family with zero
dimensional fibers and all others are families of curves. We use the
classification of families of elliptic curves with four singular fibers done by
Herfurtner in 1992 and generalize the results of Doran in 2001 and Ben Hamed
and Gavrilov in 2005.


title: On the number of extreme measures with fixed marginals

abstract:
  In this paper we give an improved upper bound, as compared to the one given
in [3] for the number of extreme points of the convex set of all G-invariant
probability measures on X*Y with given marginals of full support.


title: Performance of LDPC Codes Under Faulty Iterative Decoding

abstract:
  Departing from traditional communication theory where decoding algorithms are
assumed to perform without error, a system where noise perturbs both
computational devices and communication channels is considered here. This paper
studies limits in processing noisy signals with noisy circuits by investigating
the effect of noise on standard iterative decoders for low-density parity-check
codes. Concentration of decoding performance around its average is shown to
hold when noise is introduced into message-passing and local computation.
Density evolution equations for simple faulty iterative decoders are derived.
In one model, computing nonlinear estimation thresholds shows that performance
degrades smoothly as decoder noise increases, but arbitrarily small probability
of error is not achievable. Probability of error may be driven to zero in
another system model; the decoding threshold again decreases smoothly with
decoder noise. As an application of the methods developed, an achievability
result for reliable memory systems constructed from unreliable components is
provided.


title:
The experimental lifetime alpha-quantization of the 36 metastable
  elementary particle lifetimes

abstract:
  The fine structure constant alpha ~ 1/137 appears as a lifetime scaling
factor for the 36 metastable (t > 10^-21 sec) elementary particles -- 34
hadrons and the mu and tau leptons. The hadrons divide into 24 long-lived
unpaired-quark (UQ) and 3 short-lived paired-quark (PQ) ground states (the
lowest-mass states for each u, d, s, c, b quark flavor combination), plus 7
excited states. The lifetime ratios include six factors of alpha, six factors
of alpha^4, and one factor of alpha^3 (the leptons). This experimental lifetime
alpha-quantization has seven salient features, where (1)-(3) show powers of
alpha and (4)-(7) show smaller scaling effects): (1) A low-mass (m < 1 Gev)
particle alpha-chain of linked alpha and alpha^4 lifetime ratios that extends
from the neutron to the eta' meson and spans 11 powers of alpha. (2) Four
unpaired-quark lifetime clusters (UQ)(pi, s, b, c) that contain 23 ground
states which are sorted by the quark priorities c > b > s. (3) Four
paired-quark clusters (PQ)(pi, s, b, c), and four alpha^4 pairing gaps between
the fast PQ decays (which conserve flavor) and the slow UQ decays (which do
not). (4) IR integer-ratio scaling inside UQ clusters, with integer lifetime
ratios of 2, 3, or 4. (5) RP random perturbations that produce ~10% deviations
from exact IR scaling. (6) Hadronic BC-scaling, which reflects the empirical BC
= t(b)/t(c) ~ 3 lifetime ratios that occur between unpaired b-quark states and
corresponding unpaired c-quark states. (7) Leptonic BC-scaling, shown in the
lifetime equation (t(tau) x BC) / t(mu) = alpha^3, which is accurate to 2% for
BC = 3.0, and which utilizes an alpha^3 scaling factor. The UQ and PQ lifetime
clusters clearly reflect their u, d, s, c, b quark substructures


title: Variational approach to vortex penetration and vortex interaction

abstract:
  A variational calculation for vortex penetration is presented. Variational
trial functions for the Meissner state are combined with variational functions
for a vortex near the surface. The latter is based on Clem's trial solutions
for a vortex in bulk, which were adapted to include surface effects through
consideration of an image vortex. Three variational parameters are considered,
corresponding to the effective coherence length of the vortex, the effective
penetration length for the Meissner currents, and the value of the order
parameter at the surface. The results show that the last two variational
parameters are independent of vortex position. Explicit calculations are
presented for several $\kappa$ values. The energy barrier for vortex
penetration is shown to be in good agreement with full numerical calculations
of the Ginzburg--Landau equations. We consider the variation of the magnetic
flux carried by a vortex as it gets inside the superconductor and agreement
with known experimental and theoretical results is obtained. The model was
extended to calculate the force between two vortices, and the results show that
the force goes to zero as the pair comes close to the surface. This result can
be of interest for the study of the melting of the vortex lattice and for
vortices confined in mesoscopic superconductors. The variational approach can
be very helpful for intermediate $\kappa$ values when numerical calculations
become computationally demanding because it provides manageable expressions for
all physically relevant quantities.


title:
N=6 superconformal Chern-Simons-matter theories, M2-branes and their
  gravity duals

abstract:
  We construct three dimensional Chern-Simons-matter theories with gauge groups
U(N)xU(N) and SU(N)xSU(N) which have explicit N=6 superconformal symmetry.
Using brane constructions we argue that the U(N)xU(N) theory at level k
describes the low energy limit of N M2-branes probing a C^4/Z_k singularity. At
large N the theory is then dual to M theory on AdS_4xS^7/Z_k. The theory also
has a 't Hooft limit (of large N with a fixed ratio N/k) which is dual to type
IIA string theory on AdS_4xCP^3. For k=1 the theory is conjectured to describe
N M2-branes in flat space, although our construction realizes explicitly only
six of the eight supersymmetries. We give some evidence for this conjecture,
which is similar to the evidence for mirror symmetry in d=3 gauge theories.
When the gauge group is SU(2)xSU(2) our theory has extra symmetries and becomes
identical to the Bagger-Lambert theory.


title: Nonequilibrium critical dynamics of the three-dimensional gauge glass

abstract:
  We study the non-equilibrium aging behavior of the gauge glass model in three
dimensions at the critical temperature. We perform Monte Carlo simulations with
a Metropolis update, and correlation and response functions are calculated for
different waiting times. We obtain a multiplicative aging scaling of the
correlation and response functions, calculating the aging exponent $b$ and the
nonequilibrium autocorrelation decay exponent $\lambda_c/z_c$. We also analyze
the fluctuation-dissipation relationship at the critical temperature, obtaining
the critical fluctuation-dissipation ratio $X_\infty$. By comparing our results
with the aging scaling reported previously for a model of interacting flux
lines in the vortex glass regime, we found that the exponents for both models
are very different.


title: Quantum-Fluctuation-Driven Coherent Spin Dynamics in Small Condensates

abstract:
  We have studied quantum spin dynamics of small condensates of cold sodium
atoms. For a condensate initially prepared in a mean field ground state, we
show that coherent spin dynamics are {\em purely} driven by quantum
fluctuations of collective spin coordinates and can be tuned by quadratic
Zeeman coupling and magnetization. These dynamics in small condensates can be
probed in a high-finesse optical cavity where temporal behaviors of excitation
spectra of a coupled condensate-photon system reveal the time evolution of
populations of atoms at different hyperfine spin states.


title:
GEMINI near-infrared spectroscopic observations of young massive stars
  embedded in molecular clouds

abstract:
  K-band spectra of young stellar candidates in four southern hemisphere
clusters have been obtained with the near-infrared spectrograph GNIRS in Gemini
South. The clusters are associated with IRAS sources that have colours
characteristic of ultracompact HII regions. Spectral types were obtained by
comparison of the observed spectra with those of a NIR library; the results
include the spectral classification of nine massive stars and seven objects
confirmed as background late-type stars. Two of the studied sources have K-band
spectra compatible with those characteristic of very hot stars, as inferred
from the presence of Civ, Niii, and Nv emission lines at 2.078 micron, 2.116
micron, and 2.100 micron respectively. One of them, I16177 IRS1, has a K-band
spectrum similar to that of Cyg OB2 7, an O3If* supergiant star. The nebular
K-band spectrum of the associated UC Hii region shows the s-process [Kriii] and
[Seiv] high excitation emission lines, previously identified only in planetary
nebula. One young stellar object (YSO) was found in each cluster, associated
with either the main IRAS source or a nearby resolved MSX component, confirming
the results obtained from previous NIR photometric surveys. The distances to
the stars were derived from their spectral types and previously determined JHK
magnitudes; they agree well with the values obtained from the kinematic method,
except in the case of IRAS15408-5356, for which the spectroscopic distance is
about a factor two smaller than the kinematic value.


title: Star formation histories from multi-band photometry: A new approach

abstract:
  A new method of determining galaxy star-formation histories (SFHs) is
presented. Using the method, the feasibility of recovering SFHs with multi-band
photometry is investigated. The method divides a galaxy's history into discrete
time intervals and reconstructs the average rate of star formation in each
interval. This directly gives the total stellar mass. A simple linear inversion
solves the problem of finding the most likely discretised SFH for a given set
of galaxy parameters. It is shown how formulating the method within a Bayesian
framework lets the data simultaneously select the optimal regularisation
strength and the most appropriate number of discrete time intervals for the
reconstructed SFH. The method is demonstrated by applying it to mono-metallic
synthetic photometric catalogues created with different input SFHs, assessing
how the accuracy of the recovered SFHs and stellar masses depend on the
photometric passband set, signal-to-noise and redshift. The results show that
reconstruction of SFHs using multi-band photometry is possible, being able to
distinguish an early burst of star formation from a late one, provided an
appropriate passband set is used. Although the resolution of the recovered SFHs
is on average inferior compared to what can be achieved with spectroscopic
data, the multi-band approach can process a significantly larger number of
galaxies per unit exposure time.


title:
A kinetic approach to cosmic ray induced streaming instability at
  supernova shocks

abstract:
  We show that a purely kinetic approach to the excitation of waves by cosmic
rays in the vicinity of a shock front leads to predict the appearance of a
non-alfv\'enic fastly growing mode which has the same dispersion relation as
that previously found by \cite{bell04} by treating the plasma in the MHD
approximation. The kinetic approach allows us to investigate the dependence of
the dispersion relation of these waves on the microphysics of the current which
compensates the cosmic ray flow. We also show that a resonant and a
non-resonant mode may appear at the same time and one of the two may become
dominant on the other depending on the conditions in the acceleration region.
We discuss the role of the unstable modes for magnetic field amplification and
particle acceleration in supernova remnants at different stages of the remnant
evolution.


title:
Quantitative and empirical demonstration of the Matthew effect in a
  study of career longevity

abstract:
  The Matthew effect refers to the adage written some two-thousand years ago in
the Gospel of St. Matthew: "For to all those who have, more will be given."
Even two millennia later, this idiom is used by sociologists to qualitatively
describe the dynamics of individual progress and the interplay between status
and reward. Quantitative studies of professional careers are traditionally
limited by the difficulty in measuring progress and the lack of data on
individual careers. However, in some professions, there are well-defined
metrics that quantify career longevity, success, and prowess, which together
contribute to the overall success rating for an individual employee. Here we
demonstrate testable evidence of the age-old Matthew "rich get richer" effect,
wherein the longevity and past success of an individual lead to a cumulative
advantage in further developing his/her career. We develop an exactly solvable
stochastic career progress model that quantitatively incorporates the Matthew
effect, and validate our model predictions for several competitive professions.
We test our model on the careers of 400,000 scientists using data from six
high-impact journals, and further confirm our findings by testing the model on
the careers of more than 20,000 athletes in four sports leagues. Our model
highlights the importance of early career development, showing that many
careers are stunted by the relative disadvantage associated with inexperience.


title: Influence of quenched jets on di-hadron correlations

abstract:
  A simple jet absorption model is used to study the influence of hadron pairs
produced by quenched jets, on di-hadron angular correlations at intermediate
transverse momentum ($p_T$). We demonstrate that such pairs can dominate both
the yield and the shape of angular correlations, and may account for the
similar properties between the near-side "ridge" and the away-side
"double-humped" structure seen in recent data. These hadron pairs also show
azimuthal anisotropy which is sensitive to the emission angle of hadrons
relative to that of the jet. Measurement of this anisotropy may provide a
constraint for elucidating the production mechanism for near- and away-side
hadron pairs at intermediate $p_T$.


title: Adiabatic expansion, early x-ray data and the central engine in GRBs

abstract:
  The Swift satellite early x-ray data shows a very steep decay in most of the
Gamma-Ray Bursts light curves. This decay is either produced by the rapidly
declining continuation of the central engine activity or by some left-over
radiation starting right after the central engine shuts off. The latter
scenario consists of the emission from an "ember" that cools via adiabatic
expansion and, if the jet angle is larger than the inverse of the source
Lorentz factor, the large angle emission. In this work, we calculate the
temporal and spectral properties of the emission from such a cooling ember,
providing a new treatment for the micro-physics of the adiabatic expansion. We
use the adiabatic invariance of p_{\perp}^2/B (p_{\perp} is the component of
the electrons' momentum normal to the magnetic field, B) to calculate the
electrons' Lorentz factor during the adiabatic expansion; the electron momentum
becomes more and more aligned with the local magnetic field as the expansion
develops. We compare the theoretical expectations of the adiabatic expansion
(and the large angle emission) with the current observations of the early x-ray
data and find that only about 20% of our sample of 107 bursts is potentially
consistent with this model. This leads us to believe that, for most bursts, the
central engine does not turn off completely during the steep decay of the x-ray
light curve; therefore, this phase is produced by the continued rapidly
declining activity of the central engine.


title:
First Observation of Exclusive chi_cJ Decays to Two Charged and Two
  Neutral Hadrons

abstract:
  We study exclusive chi_c0, chi_c1 and chi_c2 decays to four-hadron final
states involving two charged and two neutral mesons: pi^+pi^-pi^0pi^0,
K^+K^-pi^0pi^0, pppi^0pi^0, K^+K^-etapi^0, and K^+-pi^-+K^0pi^0o. The chi_c
states are produced in radiative decays of 3.08 million psi-prime resonance
decays and observed in the CLEO detector. We also measure the largest
substructure contributions to the modes pi^+pi^-pi^0pi^0 and K^+-pi^-+K^0pi^0.


title: Polarization Charge Distribution in Gapped Graphene

abstract:
  We study the distribution of vacuum polarization charge induced by a Coulomb
impurity in massive graphene. By analytically computing the polarization
function, we show that the charge density is distributed in space in a
non-trivial fashion, and on a characteristic length-scale set by the effective
Compton wavelength. The density crosses over from a logarithmic behavior below
this scale, to a power law variation above it. Our results in the continuum
limit are confirmed by explicit diagonalization of the corresponding
tight-binding model on a finite-size lattice. Electron-electron interaction
effects are also discussed.


title:
Detection of period variations in extrasolar transiting planet
  OGLE-TR-111b

abstract:
  Two consecutive transits of planetary companion OGLE-TR-111b were observed in
the I band. Combining these observations with data from the literature, we find
that the timing of the transits cannot be explained by a constant period, and
that the observed variations cannot be originated by the presence of a
satellite. However, a perturbing planet with the mass of the Earth in an
exterior orbit could explain the observations if the orbit of OGLE-TR-111b is
eccentric. We also show that the eccentricity needed to explain the
observations is not ruled out by the radial velocity data found in the
literature.


title: Minimal Flavor Protection: A New Flavor Paradigm in Warped Models

abstract:
  We propose a new flavor paradigm for models with warped extra dimensions. The
idea is to impose the minimal amount of flavor protection to make warped models
compatible with all current flavor and electroweak precision constraints. We
discuss a particular realization of this minimal flavor protection in the quark
sector, by means of a flavor symmetry acting on the right handed down sector.
Hierarchical quark masses and mixing angles are naturally reproduced through
wave function localization, and flavor violating processes are predicted, in
the absence of large brane kinetic terms for the right handed down quarks,
below but not too far from current experimental limits in several channels.
With this new flavor pattern, models with warped extra dimensions can be
accessible through direct production of new resonances at the LHC and also
through precision flavor experiments.


title: Improving Classical Authentication with Quantum Communication

abstract:
  We propose a quantum-enhanced protocol to authenticate classical messages,
with improved security with respect to the classical scheme introduced by
Brassard in 1983. In that protocol, the shared key is the seed of a
pseudo-random generator (PRG) and a hash function is used to create the
authentication tag of a public message. We show that a quantum encoding of
secret bits offers more security than the classical XOR function introduced by
Brassard. Furthermore, we establish the relationship between the bias of a PRG
and the amount of information about the key that the attacker can retrieve from
a block of authenticated messages. Finally, we prove that quantum resources can
improve both the secrecy of the key generated by the PRG and the secrecy of the
tag obtained with a hidden hash function.


title: Avoiding spurious breaks in binned luminosity functions

abstract:
  We show that using either the method of Page & Carrera or the well-known
$1/V_a$ method to construct the binned luminosity function (LF) of a flux
limited sample of Active Galactic Nuclei (AGN) can produce an artificial
flattening (or steepening in the case of negative evolution) of the binned LF
for bins intersected by the flux cutoff of the sample. This effect is more
pronounced for samples with steep and strongly evolving parent LFs but is still
present even for non-evolving LFs. As a result of this distortion of the true
LF, fitting a model LF to binned data may lead to errors in the estimation of
the parameters and may even prompt the erroneous use of broken power law
functions. We compute the expected positions of apparent breaks in the binned
LF. We show that these spurious breaks in the binned LFs can be avoided if the
binning is done in the flux--redshift plane instead of the typically used
luminosity--redshift plane. Binning in the flux--redshift plane can be used in
conjunction with the binning in the luminosity--redshift plane to test for real
breaks in the binned LFs and to identify the features that are the result of
binning biases. We illustrate this effect for most typical forms of luminosity
dependence and redshift evolution and show how the proposed method helps
address this problem. We also apply this method to the MOJAVE AGN sample and
show that it eliminates an apparent break in the binned LF.


title: Crystal Structure Studies of Human Dental Apatite as a Function of Age

abstract:
  Studies of the average crystal structure properties of human dental apatite
as a function of the tooth-age in the range of 5-87 years are reported. The
crystallinity of the dental hydroxyapatite decreases with the tooth-age. The
a-lattice constant that is associated with the carbonate content in carbonate
apatite decreases with the tooth-age in a systematic way, whereas the c-lattice
constant does not change significantly. Thermogravimetric measurements
demonstrate an increase of the carbonate content with the tooth-age. FTIR
spectroscopy reveals both, B and A-type carbonate substitutions with the B-type
greater than the A-type substitution by a factor up to ~5. An increase of the
carbonate content as a function of the tooth-age can be deduced from the ratio
of the v2 CO3 to the v1 PO4 IR modes.


title: The Theory of Relativity - Galileo's Child

abstract:
  We determine the Lorentz transformations and the kinematic content and
dynamical framework of special relativity as purely an extension of Galileo's
thoughts. No reference to light is ever required: The theories of relativity
are logically independent of any properties of light. The thoughts of Galileo
are fully realized in a system of Lorentz transformations with a parameter
1/c^2, some undetermined, universal constant of nature; and are realizable in
no other. Isotropy of space plays a deep and pivotal role in all of this, since
here three-dimensional space appears at first blush, and persists until the
conclusion: Relativity can never correctly be fully developed in just one
spatial dimension.


title: Strong Conformal Dynamics at the LHC and on the Lattice

abstract:
  Conformal technicolor is a paradigm for new physics at LHC that may solve the
problems of strong electroweak symmetry breaking for quark masses and precision
electroweak data. We give explicit examples of conformal technicolor theories
based on a QCD-like sector. We suggest a practical method to test the conformal
dynamics of these theories on the lattice.


title: Monotone loop models and rational resonance

abstract:
  Let $T_{n,m}=\mathbb Z_n\times\mathbb Z_m$, and define a random mapping
$\phi\colon T_{n,m}\to T_{n,m}$ by $\phi(x,y)=(x+1,y)$ or $(x,y+1)$
independently over $x$ and $y$ and with equal probability. We study the orbit
structure of such ``quenched random walks'' $\phi$ in the limit $m,n\to\infty$,
and show how it depends sensitively on the ratio $m/n$. For $m/n$ near a
rational $p/q$, we show that there are likely to be on the order of $\sqrt{n}$
cycles, each of length O(n), whereas for $m/n$ far from any rational with small
denominator, there are a bounded number of cycles, and for typical $m/n$ each
cycle has length on the order of $n^{4/3}$.


title:
Influence of Anharmonic Effects on the Zero-point Vacancy Concentration
  in Solid 4He

abstract:
  We conduct a theoretical study in which we determine the zero-point vacancy
concentration in solid 4He at T=0 K. To this end, we employ the
quantum-classical isomorphism, by which the quantum-mechanical probability
density function of a system composed of bosons at T=0K can be interpreted in
terms of a Boltzmann factor of a classical system at finite temperature. By
using this classical isomorph we apply the methods of classical statistical
mechanics to compute the vacancy formation free energy and the vacancy
concentration in the associated quantum system at T=0. In this context, we
focus specifically on the role of anharmonic effects that are expected to be
non-negligible due to the significant zero-point motion. For this purpose, we
compute the formation free energies using both the harmonic approximation (HA)
as well as reversible-work (RW) method, in which all anharmonic effects are
taken into account. The results suggest that anharmonic effects indeed play a
significant role, lowering the classical formation free energy by ~25% and
increasing the zero-point vacancy concentration by more than an order of
magnitude compared to the HA.


title: Consistent cosmological modifications to the Einstein equations

abstract:
  General Relativity (GR) is a phenomenologically successful theory that rests
on firm foundations, but has not been tested on cosmological scales. The advent
of dark energy (and possibly even the requirement of cold dark matter), has
increased the need for testing modifications to GR, as the inference of such
otherwise undetected fluids, depends crucially on the theory of gravity. In
this work I outline a general scheme for constructing consistent and covariant
modifications to the Einstein equations. This framework is such that there is a
clear connection between the modification and the underlying field content that
produces it. I conclude by a simple metric based modification of the
fluctuation equations for which the background is exact Lambda-CDM and present
its impact on observations of the cosmic microwave background radiation.


title: Charmonium Production at High $p_t$ at RHIC

abstract:
  We calculate transverse-momentum ($p_t$) spectra and elliptic flow of
$J/\psi$'s in $Au$-$Au$ and $Cu$-$Cu$ collisions at RHIC. We employ an earlier
constructed 2-component approach for direct and regenerated charmonia which is
fairly consistent with the centrality dependence of inclusive $J/\psi$ yields
at SPS and RHIC. Discrepancies with high-$p_t$ data in $Cu$-$Cu$ collisions are
addressed by implementing effects of a finite formation time and an estimate of
$B$ meson feeddown, which largely resolve the problem. The sensitivity of the
spectra to the Cronin effect and different in-medium dissociation rates is
studied. The predicted elliptic flow in semicentral $Au$-$Au$ collisions is
rather small, $\sim$2-3%.


title:
Electroweak Corrections using Effective Field Theory: Applications to
  the LHC

abstract:
  Electroweak Sudakov logarithms at high energy, of the form alpha/sin^2
theta_W^n log^m s/M_{Z,W}^2, are summed using effective theory (EFT) methods.
The exponentiation of Sudakov logarithms and factorization is discussed in the
EFT formalism. Radiative corrections are computed to scattering processes in
the standard model involving an arbitrary number of external particles. The
computations include non-zero particle masses such as the t-quark mass,
electroweak mixing effects which lead to unequal W and Z masses and a massless
photon, and Higgs corrections proportional to the top quark Yukawa coupling.
The structure of the radiative corrections, and which terms are summed by the
EFT renormalization group is discussed in detail. The omitted terms are smaller
than 1%. We give numerical results for the corrections to dijet production,
dilepton production, t-\bar t production, and squark pair production. The
purely electroweak corrections are significant -- about 15% at 1 TeV,
increasing to 30% at 5 TeV, and they change both the scattering rate and
angular distribution. The QCD corrections (which are well-known) are also
computed with the EFT. They are much larger -- about a factor of four at 1 TeV,
increasing to a factor of thirty at 5 TeV. Mass effects are also significant;
the q \bar q -> t \bar t rate is enchanced relative to the light-quark
production rate by 40%.


title:
Scaling relations in the collapse of elastic icosadeltahedral shells
  under uniform external pressure

abstract:
  We discuss collapse of icosadeltahedral shells subjected to uniform external
pressure. We demonstrate that there is a universal collapse pressure curve. The
parameter that uniquely determines the collapse pressure is shown to be the
Foppl-von Karman number of the non-pressurized shells. Numerical results are
interpreted in terms of buckling instabilities of spheres and cylinders under
hydrostatic pressure.


title: Degenerate and star colorings of graphs on surfaces

abstract:
  We study the degenerate, the star and the degenerate star chromatic numbers
and their relation to the genus of graphs. As a tool we prove the following
strengthening of a result of Fertin et al.: If $G$ is a graph of maximum degree
$\Delta$, then $G$ admits a degenerate star coloring using $O(\Delta^{3/2})$
colors. We use this result to prove that every graph of genus $g$ admits a
degenerate star coloring with $O(g^{3/5})$ colors. It is also shown that these
results are sharp up to a logarithmic factor.


title: Noether-Lefschetz theorem with base locus

abstract:
  We compute the class groups of very general normal surfaces in complex
projective three-space containing an arbitrary base locus $Z$, thereby
extending the classic Noether-Lefschetz theorem (the case when $Z$ is empty).
Our method is an adaptation of Griffiths and Harris' degeneration proof,
simplified by a cohomology and base change argument. We give applications to
computing Picard groups, which generalize several known results.


title: Progress Towards Understanding Quarkonia at PHENIX

abstract:
  Quarkonia (J/psi, psi', chi_C, Upsilon) production provides a sensitive probe
of gluon distributions and their modification in nuclei; and is a leading probe
of the hot-dense (deconfined) matter created in high-energy collisions of heavy
ions. We will discuss the physics of quarkonia production in the context of
recent p+p measurements at PHENIX. We next discuss Cold-Nuclear Matter (CNM)
effects as seen in our measurements in $d+Au$ collisions - both for intrinsic
physics such as gluon saturation and final-state dissociation, and as a
baseline for studies in nucleus-nucleus collisions. Then we review the latest
nucleus-nucleus results in the light of the expected CNM effects, and discuss
two leading scenarios for the observed suppression patterns. Finally we show
the latest data from PHENIX, including new d+Au data from the 2007-2008 run;
and then look into the future.


title: Ekpyrotic and Cyclic Cosmology

abstract:
  Ekpyrotic and cyclic cosmologies provide theories of the very early and of
the very late universe. In these models, the big bang is described as a
collision of branes - and thus the big bang is not the beginning of time.
Before the big bang, there is an ekpyrotic phase with equation of state w=P/rho
>> 1 (where P is the average pressure and rho the average energy density)
during which the universe slowly contracts. This phase resolves the standard
cosmological puzzles and generates a nearly scale-invariant spectrum of
cosmological perturbations containing a significant non-gaussian component. At
the same time it produces small-amplitude gravitational waves with a blue
spectrum. The dark energy dominating the present-day cosmological evolution is
reinterpreted as a small attractive force between our brane and a parallel one.
This force eventually induces a new ekpyrotic phase and a new brane collision,
leading to the idea of a cyclic universe. This review discusses the detailed
properties of these models, their embedding in M-theory and their viability,
with an emphasis on open issues and observational signatures.


title: ICT, Community Memory and Technological Appropriation

abstract:
  The core mission of universities and higher education institutions is to make
public the results of their work and to preserve the collective memory of the
institution. This includes the effective use of information and communication
technologies (ICT) to systematically compile academic and research achievements
as well as disseminate effectively this accumulated knowledge to society at
large. Current efforts in Latin America and Venezuela in particular, are
limited but provide some valuable insights to pave the road to this important
goal. The institutional repository of Universidad de Los Andes (ULA) in
Venezuela (www.saber.ula.ve) is such an example of ICT usage to store, manage
and disseminate digital material produced by our University. In this paper we
elaborate on the overall process of promoting a culture of content creation,
publishing and preservation within ULA.


title: O-segments on topological measure spaces

abstract:
  Let $X$ be a topological space and $\mu$ be a nonatomic finite measure on a
$\sigma$-algebra $\Sigma$ containing the Borel $\sigma$-algebra of $X$. We say
$\mu$ is weakly outer regular, if for every $A \in \Sigma$ and $\epsilon>0$,
there exists an open set $O$ such that $\mu(A \backslash O)=0$ and $\mu(O
\backslash A)<\epsilon$. The main result of this paper is to show that if $f,g
\in L^1(X,\Sigma, \mu)$ with $\int_X f d\mu=\int_X g d\mu=1$, then there exists
an increasing family of open sets $u(t)$, $t\in [0,1]$, such that
$u(0)=\emptyset$, $u(1)=X$, and $\int_{u(t)} f d\mu=\int_{u(t)} g d\mu=t$ for
all $t\in [0,1]$. We also study a similar problem for a finite collection of
integrable functions on general finite and $\sigma$-finite nonatomic measure
spaces.


title:
Simulational study for the crossover in the generalized contact process
  with diffusion

abstract:
  In a recent work, Dantas and Stilck studied a model that generalizes the
contact process model with diffusion. Our approach, based on the supercritical
expansion, showed that for a weak diffusion regime the crossover exponent
between the directed percolation and compact directed percolation universality
classes was $\phi\approx 2$. However this approach did not work for reduced
diffusion rates higher than $D\approx 0.3$, where $0\leq D\leq 1$ and D=1
corresponds to an infinite diffusion rate. Thus, in the present work we
estimate this crossover exponent for higher diffusion rates using a numerical
simulation approach.


title:
Real time particle production in QED and QCD from strong fields and the
  Back-Reaction problem

abstract:
  We review the history of analytical approaches to particle production from
external strong fields in QED and QCD, and numerical studies of the back
reaction problem for the electric field in QED. We discuss the formulation of
the backreaction problem for the chromoelectric field in QCD both in leading
and next to leading order in flavor large-N QCD.


title: Scaling of the atmosphere of self-avoiding walks

abstract:
  The number of free sites next to the end of a self-avoiding walk is known as
the atmosphere. The average atmosphere can be related to the number of
configurations. Here we study the distribution of atmospheres as a function of
length and how the number of walks of fixed atmosphere scale. Certain bounds on
these numbers can be proved. We use Monte Carlo estimates to verify our
conjectures. Of particular interest are walks that have zero atmosphere, which
are known as trapped. We demonstrate that these walks scale in the same way as
the full set of self-avoiding walks, barring an overall constant factor.

categories: cond-mat.stat-mech math-ph math.CO math.MP


title:
Determining role of Krein signature for 3D Arnold tongues of oscillatory
  dynamos

abstract:
  Using a homotopic family of boundary eigenvalue problems for the mean-field
$\alpha^2$-dynamo with helical turbulence parameter
$\alpha(r)=\alpha_0+\gamma\Delta\alpha(r)$ and homotopy parameter $\beta \in
[0,1]$, we show that the underlying network of diabolical points for Dirichlet
(idealized, $\beta=0$) boundary conditions substantially determines the
choreography of eigenvalues and thus the character of the dynamo instability
for Robin (physically realistic, $\beta=1$) boundary conditions. In the
$(\alpha_0,\beta,\gamma)-$space the Arnold tongues of oscillatory solutions at
$\beta=1$ end up at the diabolical points for $\beta=0$. In the vicinity of the
diabolical points the space orientation of the 3D tongues, which are cones in
first-order approximation, is determined by the Krein signature of the modes
involved in the diabolical crossings at the apexes of the cones. The Krein
space induced geometry of the resonance zones explains the subtleties in
finding $\alpha$-profiles leading to spectral exceptional points, which are
important ingredients in recent theories of polarity reversals of the
geomagnetic field.

categories: math-ph astro-ph math.DS math.MP physics.geo-ph


title: $L$-valley electron $g$ factor in bulk GaAs and AlAs

abstract:
  We study the Land\'e $g$-factor of conduction electrons in the $L$-valley of
bulk GaAs and AlAs by using a three-band $\mathbf{k}\cdot\mathbf{p}$ model
together with the tight-binding model. We find that the $L$-valley $g$-factor
is highly anisotropic, and can be characterized by two components, $g_{\perp}$
and $g_{\|}$. $g_{\perp}$ is close to the free electron Land\'e factor but
$g_{\|}$ is strongly affected by the remote bands. The contribution from remote
bands on $g_{\|}$ depends on how the remote bands are treated. However, when
the magnetic field is in the Voigt configuration, which is widely used in the
experiments, different models give almost identical $g$-factor.


title:
Magnetic Moment Generation from non-minimal couplings in a scenario with
  Lorentz-Symmetry Violation

abstract:
  This paper deals with situations that illustrate how the violation of Lorentz
symmetry in the gauge sector may contribute to magnetic moment generation of
massive neutral particles with spin-1/2 and spin-1. The procedure we adopt here
is based on Relativistic Quantum Mechanics. We work out the non-relativistic
regime that follows from the wave equation corresponding to a certain particle
coupled to an external electromagnetic field and a background that accounts for
the Lorentz symmetry violation, and we read thereby the magnetic dipole moment
operator for the particle under consideration.We keep track of the parameters
that govern the non-minimal electromagnetic coupling and the breaking of
Lorentz symmetry in the expressions we get for the magnetic moments in the
different cases we contemplate. Our claim is that the tiny magnetic dipole
moment of truly elementary neutral particles might signal Lorentz symmetry
violation.


title: Study of Bc -> BP,BV Decays with QCD Factorization

abstract:
  The Bc -> BP,BV decays are studied with the QCD factorization approach (where
P and V denote pseudoscalar and vector mesons, respectively). Considering the
contributions of both current-current and penguin operators, the amplitudes of
branching ratios are estimated at the leading approximation. We find that the
contributions of the penguin operators are very small due to the serious
suppression by the CKM elements. The most promising decay modes are Bc -> Bs
Pi, Bs rho, which might be easily detected at hadron colliders.


title:
Geometric decompositions and local bases for spaces of finite element
  differential forms

abstract:
  We study the two primary families of spaces of finite element differential
forms with respect to a simplicial mesh in any number of space dimensions.
These spaces are generalizations of the classical finite element spaces for
vector fields, frequently referred to as Raviart-Thomas, Brezzi-Douglas-Marini,
and Nedelec spaces. In the present paper, we derive geometric decompositions of
these spaces which lead directly to explicit local bases for them, generalizing
the Bernstein basis for ordinary Lagrange finite elements. The approach applies
to both families of finite element spaces, for arbitrary polynomial degree,
arbitrary order of the differential forms, and an arbitrary simplicial
triangulation in any number of space dimensions. A prominent role in the
construction is played by the notion of a consistent family of extension
operators, which expresses in an abstract framework a sufficient condition for
deriving a geometric decomposition of a finite element space leading to a local
basis.


title: Understanding individual human mobility patterns

abstract:
  Despite their importance for urban planning, traffic forecasting, and the
spread of biological and mobile viruses, our understanding of the basic laws
governing human motion remains limited thanks to the lack of tools to monitor
the time resolved location of individuals. Here we study the trajectory of
100,000 anonymized mobile phone users whose position is tracked for a six month
period. We find that in contrast with the random trajectories predicted by the
prevailing Levy flight and random walk models, human trajectories show a high
degree of temporal and spatial regularity, each individual being characterized
by a time independent characteristic length scale and a significant probability
to return to a few highly frequented locations. After correcting for
differences in travel distances and the inherent anisotropy of each trajectory,
the individual travel patterns collapse into a single spatial probability
distribution, indicating that despite the diversity of their travel history,
humans follow simple reproducible patterns. This inherent similarity in travel
patterns could impact all phenomena driven by human mobility, from epidemic
prevention to emergency response, urban planning and agent based modeling.

categories: physics.soc-ph cond-mat.stat-mech cs.CY physics.bio-ph


title: General framework for quantum search algorithms

abstract:
  Grover's quantum search algorithm drives a quantum computer from a prepared
initial state to a desired final state by using selective transformations of
these states. Here, we analyze a framework when one of the selective
trasformations is replaced by a more general unitary transformation. Our
framework encapsulates several previous generalizations of the Grover's
algorithm. We show that the general quantum search algorithm can be improved by
controlling the transformations through an ancilla qubit. As a special case of
this improvement, we get a faster quantum algorithm for the two-dimensional
spatial search.


title: Self-similar planar graphs as models for complex networks

abstract:
  In this paper we introduce a family of planar, modular and self-similar
graphs which have small-world and scale-free properties. The main parameters of
this family are comparable to those of networks associated to complex systems,
and therefore the graphs are of interest as mathematical models for these
systems. As the clustering coefficient of the graphs is zero, this family is an
explicit construction that does not match the usual characterization of
hierarchical modular networks, namely that vertices have clustering values
inversely proportional to their degrees.


title: Laboratory study of differential rotation in a convective rotating layer

abstract:
  The evolution of a large-scale azimuthal velocity field in a rotating
cylindrical layer of fluid with meridional convective circulation was studied
experimentally. Two cases were considered: direct circulation provided by a rim
heater at the periphery and indirect circulation provided by a central heater.
The detailed 3D structure of the mean large-scale velocity field is
reconstructed using the PIV technique. Due to the action of the Coriolis force
the meridional flow results in differential rotation. Differential rotation is
characterized by the mean values of radial and vertical gradients of azimuthal
velocity. Strong negative mean radial gradient which grows with the Grasshoff
number is provided by direct circulation. In the case of indirect circulation a
pronounced negative gradient arises at moderate Grashoff number. The behavior
of the mean vertical gradient is quite different: a positive vertical gradient
grows logarithmically with Grasshoff number under direct circulation, whereas a
weak negative gradient characterizes the indirect circulation. This difference
follows from the structure of the flow -- the direct circulation provides a
large cyclonic area localized above the anticyclonic flow, while indirect
circulation leads to a strong separation of these two areas in the radial
direction (the central part is occupied by the cyclonic flow and the periphery
by the anticyclonic flow). Meridional circulation leads to substantial
variation of the integral angular momentum. Direct circulation results in the
growth of the integral angular momentum and indirect circulation causes it to
decrease. At the same heating power, the increase of angular momentum at direct
circulation is much stronger than its decrease at indirect circulation.


title: Chandra Reveals Twin X-ray Jets in the Powerful FR-II Radio Galaxy 3C353

abstract:
  We report X-ray imaging of the powerful FR-II radio galaxy 3C353 using the
Chandra X-ray Observatory. 3C353's two 4"-wide and 2'-long jets allow us to
study in detail the internal structure of the large-scale relativistic outflows
at both radio and X-ray photon energies with the sub-arcsecond spatial
resolution. In a 90 ks Chandra observation, we have detected X-ray emission
from most radio structures in 3C353, including the nucleus, the jet and the
counterjet, the terminal jet regions (hotspots), and one radio lobe. We show
that the detection of the X-ray emission associated with the radio knots and
counterknots puts several crucial constraints on the X-ray emission mechanisms
in powerful large-scale jets of quasars and FR-II sources. In particular, we
show that this detection is inconsistent with the inverse-Compton model
proposed in the literature, and instead implies a synchrotron origin of the
X-ray jet photons. We also find that the width of the X-ray counterjet is
possibly narrower than that measured in radio bands, that the radio-to-X-ray
flux ratio decreases systematically downstream along the jets, and that there
are substantial (kpc-scale) offsets between the positions of the X-ray and
radio intensity maxima within each knot, whose magnitudes increase away from
the nucleus. We discuss all these findings in the wider context of the physics
of extragalactic jets, proposing some particular though not definitive
solutions or interpretations for each problem.


title: Dirac structures, nonholonomic systems and reduction

abstract:
  The reduction of nonholonomic systems is formulated in terms of Dirac
reduction. An optimal reduction method for a class of nonholonomic systems is
formulated. Several examples are studied in detail.


title: Size-dependent magnetization fluctuations in NiO nanoparticles

abstract:
  The finite size and surface roughness effects on the magnetization of NiO
nanoparticles is investigated. A large magnetic moment arises for an
antiferromagnetic nanoparticle due to these effects. The magnetic moment
without the surface roughness has a non-monotonic and oscillatory dependence on
$R$, the size of the particles, with the amplitude of the fluctuations varying
linearly with $R$. The geometry of the particle also matters a lot in the
calculation of the net magnetic moment. An oblate spheroid shape particle shows
an increase in net magnetic moment by increasing oblateness of the particle.
However, the magnetic moment values thus calculated are very small compared to
the experimental values for various sizes, indicating that the bulk
antiferromagnetic structure may not hold near the surface. We incorporate the
surface roughness in two different ways; an ordered surface with surface spins
inside a surface roughness shell aligned due to an internal field, and a
disordered surface with randomly oriented spins inside surface roughness shell.
Taking a variational approach we find that the core interaction strength is
modified for nontrivial values of $\Delta$ which is a signature of
multi-sublattice ordering for nanoparticles. The surface roughness scale
$\Delta $ is also showing size dependent fluctuations, with an envelope decay
$\Delta\sim R^{-1/5}$. The net magnetic moment values calculated using
spheroidal shape and ordered surface are close to the experimental values for
different sizes.


title:
Semigroup inequalities, stochastic domination, Hardy's inequality, and
  strong ergodicity

abstract:
  There is a mathematical error in the first version of this paper. A new
corrected version will be posted when the error is fixed, possibly with a
modified title.


title:
Can a Plantar Pressure-Based Tongue-Placed Electrotactile Biofeedback
  Improve Postural Control Under Altered Vestibular and Neck Proprioceptive
  Conditions?

abstract:
  We investigated the effects of a plantar pressure-based tongue-placed
electrotactile biofeedback on postural control during quiet standing under
normal and altered vestibular and neck proprioceptive conditions. To achieve
this goal, fourteen young healthy adults were asked to stand upright as
immobile as possible with their eyes closed in two Neutral and Extended head
postures and two conditions of No-biofeedback and Biofeedback. The underlying
principle of the biofeedback consisted of providing supplementary information
related to foot sole pressure distribution through a wireless embedded
tongue-placed tactile output device. Centre of foot pressure (CoP)
displacements were recorded using a plantar pressure data acquisition system.
Results showed that (1) the Extended head posture yielded increased CoP
displacements relative to the Neutral head posture in the No-biofeedback
condition, with a greater effect along the anteroposterior than mediolateral
axis, whereas (2) no significant difference between the two Neutral and
Extended head postures was observed in the Biofeedback condition. The present
findings suggested that the availability of the plantar pressure-based
tongue-placed electrotactile biofeedback allowed the subjects to suppress the
destabilizing effect induced by the disruption of vestibular and neck
proprioceptive inputs associated with the head extended posture. These results
are discussed according to the sensory re-weighting hypothesis, whereby the
central nervous system would dynamically and selectively adjust the relative
contributions of sensory inputs (i.e., the sensory weights) to maintain upright
stance depending on the sensory contexts and the neuromuscular constraints
acting on the subject.


title: Superconductivity in single crystals of LaFePO

abstract:
  Single crystals of the compound LaFePO were prepared using a flux growth
technique at high temperatures. Electrical resistivity measurements reveal
metallic behavior and a resistive transition to the superconducting state at a
critical temperature T_c ~ 6.6 K. Magnetization measurements also show the
onset of superconductivity near 6 K. In contrast, specific heat measurements
manifest no discontinuity at T_c. These results lend support to the conclusion
that the superconductivity is associated with oxygen vacancies that alter the
carrier concentration in a small fraction of the sample, although
superconductivity characterized by an unusually small gap value can not be
ruled-out. Under applied magnetic fields, T_c is suppressed anisotropically for
fields perpendicular and parallel to the ab-plane, suggesting that the
crystalline anisotropy strongly influences the superconducting state.
Preliminary high-pressure measurements show that T_c passes through a maximum
of nearly 14 K at ~ 110 kbar, demonstrating that significantly higher T_c
values may be achieved in the phosphorus-based oxypnictides.


title:
Pseudo-radial solutions of semi-linear elliptic equations on symmetric
  domains

abstract:
  In this paper we investigate existence and characterization of non-radial
pseudo-radial (or separable) solutions of some semi-linear elliptic equations
on symmetric 2-dimensional domains. The problem reduces to the phase plane
analysis of a dynamical system. In particular, we give a full description of
the set of pseudo-radial solutions of equations of the form $\Delta u = \pm
a^2(|x|) u|u|^{q-1}$, with $q>0$, $q\neq 1$. We also study such equations over
spherical or hyperbolic symmetric domains.