title: Spatial distribution of stars and brown dwarfs in sigma Orionis

abstract:
  I have re-visited the spatial distribution of stars and high-mass brown
dwarfs in the sigma Orionis cluster (~3 Ma, ~360 pc). The input was a catalogue
of 340 cluster members and candidates at separations less than 30 arcmin to
sigma Ori AB. Of them, 70 % have features of extreme youth. I fitted the
normalised cumulative number of objects counting from the cluster centre to
several power-law, exponential and King radial distributions. The cluster seems
to have two components: a dense core that extends from the centre to r ~ 20
arcmin and a rarified halo at larger separations. The radial distribution in
the core follows a power-law proportional to r^1, which corresponds to a volume
density proportional to r^(-2). This is consistent with the collapse of an
isothermal spherical molecular cloud. The stars more massive than 3.7 Msol
concentrate, however, towards the cluster centre, where there is also an
apparent deficit of very low-mass objects (M < 0.16 Msol). Last, I demonstrated
through Monte Carlo simulations that the cluster is azimuthally asymmetric,
with a filamentary overdensity of objects that runs from the cluster centre to
the Horsehead Nebula.


title: Complexified Path Integrals and the Phases of Quantum Field Theory

abstract:
  The path integral by which quantum field theories are defined is a particular
solution of a set of functional differential equations arising from the
Schwinger action principle. In fact these equations have a multitude of
additional solutions which are described by integrals over a complexified path.
We discuss properties of the additional solutions which, although generally
disregarded, may be physical with known examples including spontaneous symmetry
breaking and theta vacua. We show that a consideration of the full set of
solutions yields a description of phase transitions in quantum field theories
which complements the usual description in terms of the accumulation of
Lee-Yang zeroes. In particular we argue that non-analyticity due to the
accumulation of Lee-Yang zeros is related to Stokes phenomena and the collapse
of the solution set in various limits including but not restricted to, the
thermodynamic limit. A precise demonstration of this relation is given in terms
of a zero dimensional model. Finally, for zero dimensional polynomial actions,
we prove that Borel resummation of perturbative expansions, with several
choices of singularity avoiding contours in the complex Borel plane, yield
inequivalent solutions of the action principle equations.


title: Gauge-Dependence of Green's Functions in QCD and QED

abstract:
  When all Green's functions are known in a given gauge we may raise a question
of whether it is possible or not to derive the corresponding ones in a
different gauge. The answer is negative in QCD but affirmative in QED provided
that we confine ourselves to the covariant gauge characterized by a gauge
parameter $\alpha$. We shall discuss the physical significance of this
conclusion.


title: Minimization of convex functionals over frame operators

abstract:
  We present results about minimization of convex functionals defined over a
finite set of vectors in a finite dimensional Hilbert space, that extend
several known results for the Benedetto-Fickus frame potential. Our approach
depends on majorization techniques. We also consider some perturbation
problems, where a positive perturbation of the frame operator of a set of
vectors is realized as the frame operator of a set of vectors which is close to
the original one.


title: Calculation of surface tension via area sampling

abstract:
  We examine the performance of several molecular simulation techniques aimed
at evaluation of the surface tension through its thermodynamic definition. For
all methods explored, the surface tension is calculated by approximating the
change in Helmholtz free energy associated with a change in interfacial area
through simulation of a liquid slab at constant particle number, volume, and
temperature. The methods explored fall within three general classes:
free-energy perturbation, the Bennett acceptance-ratio scheme, and the expanded
ensemble technique. Calculations are performed for both the truncated
Lennard-Jones and square-well fluids at select temperatures spaced along their
respective liquid-vapor saturation lines. Overall, we find that Bennett and
expanded ensemble approaches provide the best combination of accuracy and
precision. All of the methods, when applied using sufficiently small area
perturbation, generate equivalent results for the Lennard-Jones fluid. However,
single-stage free-energy-perturbation methods and the closely related test-area
technique recently introduced by Gloor et al. [J. Chem. Phys. 123, 134703
(2005)], generate surface tension values for the square-well fluid that are not
consistent with those obtained from the more robust expanded ensemble and
Bennett approaches, regardless of the size of the area perturbation.
Single-stage perturbation methods fail also for the Lennard-Jones system when
applied using large area perturbations. Here an analysis of phase-space overlap
produces a quantitative explanation of the observed inaccuracy, and shows that
the satisfactory results obtained in these cases from the test-area method
arise from a cancellation of errors that cannot be expected in general.


title: Three loop MSbar renormalization of QED in the 't~Hooft-Veltman gauge

abstract:
  Quantum electrodynamics (QED) fixed in the 't~Hooft-Veltman gauge is
renormalized to three loops in the MSbar scheme. The beta-functions and
anomalous dimensions are computed as functions of the usual QED coupling and
the additional coupling, xi, which is introduced as part of the nonlinear gauge
fixing condition. Similar to the maximal abelian gauge of quantum
chromodynamics, the renormalization of the gauge parameter is singular.


title:
Coulomb distortion effects in quasi-elastic (e,e') scattering on heavy
  nuclei

abstract:
  The influence of the Coulomb distortion for quasi-elastic (e,e') scattering
on highly charged nuclei is investigated in distorted wave Born approximation
for electrons. The Dirac equation is solved numerically in order to obtain
exact electron continuum states in the electrostatic field generated by the
charge distribution of an atomic nucleus. Different approximate models are used
to describe the nucleon current in order to show that, at high electron
energies and energy-momentum transfer, the influence of Coulomb distortions on
(e,e') cross sections can be reliably described by the effective momentum
approximation, irrespective of details concerning the description of the
nuclear current.


title: Algorithmically detecting the bridge number of hyperbolic knots

abstract:
  We exhibit an algorithm to determine the bridge number of a hyperbolic knot
in the 3-sphere. The proof uses adaptations of almost normal surface theory for
compact surfaces with boundary in ideally triangulated knot exteriors.


title: Preparing for N_f=2 simulations at small lattice spacings

abstract:
  We discuss some large effects of dynamical fermions. One is a cutoff effect,
others concern the contribution of multi-pion states to correlation functions
and are expected to survive the continuum limit. We then turn to the
preparation for simulations at small lattice spacings which we are planning
down to around a=0.04fm in order to understand the size of O(a^2)-effects of
the standard O(a)-improved theory. The dependence of the lattice spacing on the
bare coupling is determined through the Schr"odinger functional renormalized
coupling.


title: Photo-gating Carbon Nanotube Transistors

abstract:
  Optoelectronic measurements of carbon nanotube transistors have shown a wide
variety of sensitivites to the incident light. Direct photocurrent processes
compete with a number of extrinsic mechanisms. Here we show that visible light
absorption in the silicon substrate generates a photovoltage that can
electrically gate the nanotube device. The photocurrent induced by the changing
gate voltage can be significantly larger than that due to direct electron-hole
pair generation in the nanotube. The dominance of photogating in these devices
is confirmed by the power and position dependence of the resulting
photocurrent. The power dependence is strongly non-linear and photocurrents are
measured through the device even when the laser illuminates up to 1~mm from the
nanotube.


title:
Quantum Monte Carlo calculations of electroweak transition matrix
  elements in A = 6,7 nuclei

abstract:
  Green's function Monte Carlo calculations of magnetic dipole, electric
quadrupole, Fermi, and Gamow-Teller transition matrix elements are reported for
A=6,7 nuclei. The matrix elements are extrapolated from mixed estimates that
bracket the relevant electroweak operator between variational Monte Carlo and
GFMC propagated wave functions. Because they are off-diagonal terms, two mixed
estimates are required for each transition, with a VMC initial (final) state
paired with a GFMC final (initial) state. The realistic Argonne v18 two-nucleon
and Illinois-2 three-nucleon interactions are used to generate the nuclear
states. In most cases we find good agreement with experimental data.


title: Collisional Energy Loss of a Fast Muon in a Hot QED Plasma

abstract:
  We calculate the collisional energy loss of a muon of high energy $E$ in a
hot QED plasma beyond logarithmic accuracy, i.e., we determine the constant
terms of order O(1) in $-dE/dx \propto \ln{E}+ O(1)$. Considering first the
$t$-channel contribution to $-dE/dx$, we show that the terms $\sim O(1)$ are
sensitive to the full kinematic region for the momentum exchange $q$ in elastic
scattering, including large values $q \sim O(E)$. We thus redress a previous
calculation by Braaten and Thoma, which assumed $q << E$ and could not find the
correct constant (in the large $E$ limit). The relevance of 'very hard'
momentum transfers then requires, for consistency, that $s$ and $u$-channel
contributions from Compton scattering must be included, bringing a second
modification to the Braaten-Thoma result. Most importantly, Compton scattering
yields an additional large logarithm in $-dE/dx$. Our results might have
implications in the QCD case of parton collisional energy loss in a quark gluon
plasma.


title:
Production of a pion in association with a high-Q2 dilepton pair in
  antiproton-proton annihilation at GSI-FAIR

abstract:
  We evaluate the cross section for anti-p p -> l+ l- pi0 in the forward
direction and for large lepton pair invariant mass. In this kinematical region,
the leading-twist amplitude factorises into a short-distance matrix element,
long-distance dominated antiproton Distribution Amplitudes and proton to pion
Transition Distribution Amplitudes (TDA). Using a modelling inspired from the
chiral limit for these TDAs, we obtain a first estimate of this cross section,
thus demonstrating that this process can be measured at GSI-FAIR.


title: Top Hypercharge

abstract:
  We propose a top hypercharge model with gauge symmetry SU(3)_C x SU(2)_L x
U(1)_1 x U(1)_2 where the first two families of the Standard Model (SM)
fermions are charged under U(1)_1 while the third family is charged under
U(1)_2. The U(1)_1 x U(1)_2 gauge symmetry is broken down to the U(1)_Y gauge
symmetry, when a SM singlet Higgs field acquires a vacuum expectation value. We
consider the electroweak constraints, and compare the fit to experimental
observables to that of the SM. We study the quark CKM mixing between the first
two families and the third family, the neutrino masses and mixing, the flavour
changing neutral current effects in meson mixing and decays, the Z' discovery
potential at the Large Hadron Collider, the dark matter with a gauged Z_2
symmetry, and the Higgs boson masses.


title: Generic mixed columnar-plaquette phases in Rokhsar-Kivelson models

abstract:
  We revisit the phase diagram of Rokhsar-Kivelson models, which are used in
fields such as superconductivity, frustrated magnetism, cold bosons, and the
physics of Josephson junction arrays. From an extended height effective theory,
we show that one of two simple generic phase diagrams contains a mixed phase
that interpolates continuously between columnar and plaquette states. For the
square lattice quantum dimer model we present evidence from exact
diagonalization and Green's function Monte Carlo techniques that this scenario
is realised, by combining an analysis of the excitation gaps of different
symmetry sectors with information on plaquette structure factors. This presents
a natural framework for resolving the disagreement between previous studies.


title: Note on graviton MHV amplitudes

abstract:
  Two new formulas which express n-graviton MHV tree amplitudes in terms of
sums of squares of n-gluon amplitudes are discussed. The first formula is
derived from recursion relations. The second formula, simpler because it
involves fewer permutations, is obtained from the variant of the Berends,
Giele, Kuijf formula given in Arxiv:0707.1035.


title:
Flavor Evolution of the Neutronization Neutrino Burst from an O-Ne-Mg
  Core-Collapse Supernova

abstract:
  We present results of 3-neutrino flavor evolution simulations for the
neutronization burst from an O-Ne-Mg core-collapse supernova. We find that
nonlinear neutrino self-coupling engineers a single spectral feature of
stepwise conversion in the inverted neutrino mass hierarchy case and in the
normal mass hierarchy case, a superposition of two such features corresponding
to the vacuum neutrino mass-squared differences associated with solar and
atmospheric neutrino oscillations. These neutrino spectral features offer a
unique potential probe of the conditions in the supernova environment and may
allow us to distinguish between O-Ne-Mg and Fe core-collapse supernovae.


title:
Coupling Lattice Boltzmann with Atomistic Dynamics for the multiscale
  simulation of nano-biological flows

abstract:
  We describe a recent multiscale approach based on the concurrent coupling of
constrained molecular dynamics for long biomolecules with a mesoscopic lattice
Boltzmann treatment of solvent hydrodynamics. The multiscale approach is based
on a simple scheme of exchange of space-time information between the atomistic
and mesoscopic scales and is capable of describing self-consistent hydrodynamic
effects on molecular motion at a computational cost which scales linearly with
both solute size and solvent volume. For an application of our multiscale
method, we consider the much studied problem of biopolymer translocation
through nanopores: we find that the method reproduces with remarkable accuracy
the statistical scaling behavior of the translocation process and provides
valuable insight into the cooperative aspects of biopolymer and hydrodynamic
motion.


title: Generic canonical form of pairs of matrices with zeros

abstract:
  We consider a family of pairs of m-by-p and m-by-q matrices, in which some
entries are required to be zero and the others are arbitrary, with respect to
transformations (A,B)--> (SAR,SBL) with nonsingular S, R, L. We prove that
almost all of these pairs reduce to the same pair (C, D) from this family,
except for pairs whose arbitrary entries are zeros of a certain polynomial. The
polynomial and the pair (C D) are constructed by a combinatorial method based
on properties of a certain graph.


title: Gravity model in the Korean highway

abstract:
  We investigate the traffic flows of the Korean highway system, which contains
both public and private transportation information. We find that the traffic
flow T(ij) between city i and j forms a gravity model, the metaphor of physical
gravity as described in Newton's law of gravity, P(i)P(j)/r(ij)^2, where P(i)
represents the population of city i and r(ij) the distance between cities i and
j. It is also shown that the highway network has a heavy tail even though the
road network is a rather uniform and homogeneous one. Compared to the highway
network, air and public ground transportation establish inhomogeneous systems
and have power-law behaviors.


title: On Convergence Properties of Shannon Entropy

abstract:
  Convergence properties of Shannon Entropy are studied. In the differential
setting, it is shown that weak convergence of probability measures, or
convergence in distribution, is not enough for convergence of the associated
differential entropies. A general result for the desired differential entropy
convergence is provided, taking into account both compactly and uncompactly
supported densities. Convergence of differential entropy is also characterized
in terms of the Kullback-Liebler discriminant for densities with fairly general
supports, and it is shown that convergence in variation of probability measures
guarantees such convergence under an appropriate boundedness condition on the
densities involved. Results for the discrete setting are also provided,
allowing for infinitely supported probability measures, by taking advantage of
the equivalence between weak convergence and convergence in variation in this
setting.


title:
Riemannian groupoids and solitons for three-dimensional homogeneous
  Ricci and cross curvature flows

abstract:
  In this paper we investigate the behavior of three-dimensional homogeneous
solutions of the cross curvature flow using Riemannian groupoids. The
Riemannian groupoid technique, introduced by John Lott, allows us to
investigate the long term behavior of collapsing solutions of the flow,
producing soliton solutions in the limit. We also review Lott's results on the
long term behavior of three-dimensional homogeneous solutions of Ricci flow,
demonstrating the coordinates we choose and reviewing the groupoid technique.
We find cross curvature soliton metrics on Sol and Nil, and show that the cross
curvature flow of SL(2,R) limits to Sol.


title:
New results on particle acceleration in the Centaurus A jet and
  counterjet from a deep Chandra observation

abstract:
  We present new deep Chandra observations of the Centaurus A jet, with a
combined on-source exposure time of 719 ks. These data allow detailed X-ray
spectral measurements to be made along the jet out to its disappearance at 4.5
kpc from the nucleus. We distinguish several regimes of high-energy particle
acceleration: while the inner part of the jet is dominated by knots and has
properties consistent with local particle acceleration at shocks, the particle
acceleration in the outer 3.4 kpc of the jet is likely to be dominated by an
unknown distributed acceleration mechanism. In addition to several compact
counterjet features we detect probable extended emission from a counterjet out
to 2.0 kpc from the nucleus, and argue that this implies that the diffuse
acceleration process operates in the counterjet as well. A preliminary search
for X-ray variability finds no jet knots with dramatic flux density variations,
unlike the situation seen in M87.


title: Miniversal deformations of chains of linear mappings

abstract:
  V.I. Arnold [Russian Math. Surveys, 26 (no. 2), 1971, pp. 29-43] gave a
miniversal deformation of matrices of linear operators; that is, a simple
canonical form, to which not only a given square matrix A, but also the family
of all matrices close to A, can be reduced by similarity transformations
smoothly depending on the entries of matrices. We study miniversal deformations
of quiver representations and obtain a miniversal deformation of matrices of
chains of linear mappings.


title: The 3He + 4He --> 7Be Astrophysical S-factor

abstract:
  We present precision measurements of the 3He + 4He --> 7Be reaction in the
range ECM = 0.33 to 1.23 MeV using a small gas cell and detection of both
prompt gamma rays and 7Be activity. Our prompt and activity measurements are in
good agreement within an experimental uncertainty of several percent. We find
S(0) = 0.595 +/- 0.018 keV b from fits of the Kajino theory to our data. We
compare our results with published measurements, and we discuss the
consequences for Big Bang Nucleosynthesis and for solar neutrino flux
calculations.


title:
On the Relationship between Mutual Information and Minimum Mean-Square
  Errors in Stochastic Dynamical Systems

abstract:
  We consider a general stochastic input-output dynamical system with output
evolving in time as the solution to a functional coefficients, It\^{o}'s
stochastic differential equation, excited by an input process. This general
class of stochastic systems encompasses not only the classical communication
channel models, but also a wide variety of engineering systems appearing
through a whole range of applications. For this general setting we find
analogous of known relationships linking input-output mutual information and
minimum mean causal and non-causal square errors, previously established in the
context of additive Gaussian noise communication channels. Relationships are
not only established in terms of time-averaged quantities, but also their
time-instantaneous, dynamical counterparts are presented. The problem of
appropriately introducing in this general framework a signal-to-noise ratio
notion expressed through a signal-to-noise ratio parameter is also taken into
account, identifying conditions for a proper and meaningful interpretation.


title: Normal holomorphic curves from parabolic regions to projective spaces

abstract:
  A holomorphic map from the complex line to a complex projective space is
called normal (a. k. a. Brody curve) if it is uniformly continuous from the
Euclidean metric to the Fubini--Study metric. The paper contains a survey of
known results about such maps, as well as some new theorems.


title: The Relativistic framework of Positioning systems

abstract:
  Emission relativistic coordinates are a class of spacetime coordinates
defined and generated by four emitters (satellites, pulsars) broadcasting their
proper time by radio signals. They are the main ingredient of the simplest
conceivable relativistic positioning system. The emission coordinates are
independent of any observer. Receiving directly the proper time at emission of
four satellites, any user or observer can measure the values of the emission
coordinates, from which he/she can obtain his trajectory and hence, in
particular, his position. Moreover, if and only if the four satellites also
broadcast to the users the proper times they are receiving by cross-link
autonavigation from the other emitters, the positioning system is called
autolocated or autonomous. In an autolocated positioning system the
trajectories of the satellites of the constellation can also be known by the
users and they can also obtain the metric of the spacetime (the gravitational
field) on the constellation.
  The study of autolocated relativistic positioning systems has been initiated
by Coll and coll. several years ago and it has been aimed for developing an
exact fully relativistic theory of positioning systems and gravimetry, based on
the framework and concepts of General Relativity. This exact relativistic
framework is the alternative to considering post-newtonian relativistic
corrections in a classical Newtonian framework, which is the customary approach
yet now used in GPS and GLONASS.


title: Renewal-type Limit Theorem for the Gauss Map and Continued Fractions

abstract:
  In this paper we prove the following renewal-type limit theorem. Given an
irrational $\alpha$ in (0,1) and R>0, let $q_{n_R}$ be the first denominator of
the convergents of $\alpha$ which exceeds R. The main result in the paper is
that the ratio $q_{n_R}/R$ has a limiting distribution as R tends to infinity.
The existence of the limiting distribution uses mixing of a special flow over
the natural extension of the Gauss map.


title:
Comment on "Similarity analysis in magnetohydrodynamics: effects of Hall
  and ion-slip currents on free convection flow and mass transfer of a gas past
  a semi-infinite vertical plate," A.A. Megahed, S.R. Komy, A.A. Afify

abstract:
  Comment on Similarity analysis in magnetohydrodynamics:effects of Hall and
ion-slip currents on free convection flow and mass transfer of a gas past a
semi-infinite vertical plate, A.A. Megahed, S.R. Komy, A.A. Afify [Acta
Mechanica 151, 185-194 (2001)]
  In the above paper is investigated the boundary layer flow of an electrically
conducting fluid over a vertical, stationary plate placed in a calm fluid. The
effects of Hall and ion-slip currents are taken into account. The boundary
layer equations are transformed into ordinary ones using a scaling group of
transformations and subsequently are solved numerically. However, there are two
fundamental errors in the above paper which are presented below.


title:
Small scale behavior of the physical conditions and the abundance
  discrepancy in the Orion nebula

abstract:
  We present results of long-slit spectroscopy in several positions of the
Orion nebula. Our goal is to study the spatial distribution of a large number
of nebular quantities, including line fluxes, physical conditions and ionic
abundances at a spatial resolution of about 1". We find that protoplanetary
disks (proplyds) show prominent spikes of T([N II]) probably produced by
collisional deexcitation due to the high electron densities found in these
objects. Herbig-Haro objects show also relatively high T([N II]) but probably
produced by local heating due to shocks. We also find that the spatial
distribution of pure recombination O II and [O III] lines is fairly similar, in
contrast to that observed in planetary nebulae. The abundance discrepancy
factor (ADF) of O^{++} remains rather constant along the slit positions, except
in some particular small areas of the nebula where this quantity reaches
somewhat higher values, in particular at the location of the most conspicuous
Herbig-Haro objects: HH 202, HH 203, and HH 204. There is also an apparent
slight increase of the ADF in the inner 40" around theta^1 Ori C. We find a
negative radial gradient of T([O III]) and T([N II]) in the nebula based on the
projected distance from theta^1 Ori C. We explore the behavior of the ADF of
O^{++} with respect to other nebular quantities, finding that it seems to
increase very slightly with the electron temperature. Finally, we estimate the
value of the mean-square electron temperature fluctuation, the so-called t^2
parameter. Our results indicate that the hypothetical thermal inhomogeneities
--if they exist-- should be smaller than our spatial resolution element.


title:
Propagation-based x-ray phase-contrast imaging with broad focus
  conventional x-ray sources

abstract:
  A propagation-based x-ray phase-contrast imaging (PBI) setup using a
conventional x-ray source (LFF Cu target) is presented. A virtual x-ray source
of 40 x 50 $\mu$$m^2$ was created by using, horizontally, a $6^o$ take-off
angle (with the x-ray tube working in the line focus geometry) and, vertically,
a 50 $\mu$m slit . The sample was set 12 $m$ from the source. Propagation-based
x-ray phase-contrast (PB) image and conventional radiography (CR) of a
polypropylene tube were acquired. Edge enhanced effects and a crack, not
detected in CR, were clearly seen in the PB image. Contrast, visibility of the
object edges and signal to noise ratio of the acquired images were exploited.
The results show that PB images can be acquired by using normal focus (macro
focus) conventional x-ray sources. This apparatus can be used as an standard
phase-contrast imaging setup to analyze different kind of samples with large
field of view (75 x 75 $mm^2$), discarding the use of translators for sample
and detector.


title:
A Limit Theorem for Birkoff sums of non-integrable functions over
  rotations

abstract:
  We consider Birkhoff sums of functions with a singularity of type 1/x over
rotations and prove the following limit theorem. Let $S_N= S_N(\alpha,x)$ be
the N^th non-renormalized Birkhoff sum, where $x in [0,1)$ is the initial
point, $\alpha\in [0,1)$ is the rotation number and $(\alpha, x)$ are uniformly
distributed. We prove that $S_N/N$ has a joint limiting distribution in
$(\alpha,x)$ as N tends to infinity. As a corollary, we get the existence of a
limiting distribution for certain trigonometric sums.


title: On Groups with a Supercomplemented Subgroup

abstract:
  Groups, in which every subgroup containing some fixed primary cyclic subgroup
has a complement, are investigated.


title: Medium dependence of asphaltene agglomeration inhibitor efficiency

abstract:
  Applying chemical additives (molecule inhibitors or dispersants) is one of
the common ways to control asphaltene agglomeration and precipitation. However,
it is not clear why at some conditions the synthetic flocculation inhibitors as
well as resins not only do not inhibit the asphaltene agglomeration,, they may
also promote it, and why the increasing of the additive concentration may lead
to the diminishing of their efficacy. To clarify this issue, in the present
work we have performed a set of vapor preassure osmometry experiments
investigating the asphaltene agglomeration inhibition by commercial and new
inhibitor molecules in toluene and o-diclorobenzene. Monte Carlo computer
modeling has been applied to interpret some unexpected trends of molar mass of
the Puerto Ceiba asphaltene clusters at different concentrations of inhibitor,
assuming that inhibitors efficiency is directly related to their adsorption on
the surface of asphaltene or its complexes. It has been found that a
self-assembly of inhibitor molecules, induced by relative lyophilic or
lyophobic interactions, may be a reason of the inhibitor efficacy declining.


title:
Limiting jump conditions for Josephson junctions in Ginzburg-Landau
  theory

abstract:
  We consider a superconducting/normal/superconducting Josephson junction
modeled through the Ginzburg-Landau theory. When the normal material is
sufficiently thin and the applied magnetic field is below the critical field of
vortex nucleation, we prove to leading order that jump boundary conditions of
the type predicted by de Gennes are satisfied across the junction.


title: A viability criterion for modified gravity with an extra force

abstract:
  A recently proposed theory of modified gravity with an explicit ``anomalous''
coupling of the Ricci curvature to matter is discussed, and an inequality is
derived which expresses a necessary and sufficient condition to avoid the
notorius Dolgov-Kawasaki instability.


title:
Relationship between EIT Post Eruption Arcades, Coronal Mass Ejections,
  Coronal Neutral Line and Magnetic Clouds

abstract:
  There is observational evidence that the elongation of an Earth directed
coronal mass ejection (CME) may indicate the orientation of the underlying
erupting flux rope. In this study, we compare orientations of CMEs, MCs,
eruption arcades and coronal neutral line (CNL). We report on good correlations
between i) the directions of the axial field in EIT arcades and the elongations
of halo CMEs and ii) the tilt of the CNL and MC axis orientations. We found
that majority of the eruptions that had EIT arcades, CMEs and MCs similarly
oriented also had the CNL co-aligned with them. To the contrary, those events
that showed no agreement between orientations of the EIT arcades, CMEs and MCs,
had their MCs aligned with the coronal neutral line. We speculate that the axis
of the ejecta may be rotated in such a way that it is locally aligns itself
with the heliospheric current sheet.


title:
Old stellar counter-rotating components in early-type galaxies from
  elliptical-spiral mergers

abstract:
  We investigate, by means of numerical simulations, the possibility of forming
counter-rotating old stellar components by major mergers between an elliptical
and a spiral galaxy. We show that counter-rotation can appear both in
dissipative and dissipationless retrograde mergers, and it is mostly associated
to the presence of a disk component, which preserves part of its initial spin.
In turn, the external regions of the two interacting galaxies acquire part of
the orbital angular momentum, due to the action of tidal forces exerted on each
galaxy by the companion.


title: Transition Distribution Amplitudes for gamma* gamma collisions

abstract:
  We study the exclusive production of pi-pi and rho-pi in hard gamma* gamma
scattering in the forward kinematical region where the virtuality of one photon
provides us with a hard scale in the process. The newly introduced concept of
Transition Distribution Amplitudes (TDA) is used to perform a QCD calculation
of these reactions thanks to two simple models for TDAs. The sizable cross
sections for rho-pi and pi-pi production may be tested at intense
electron-positron colliders such as CLEO and B factories (Belle and BaBar).


title: On freely indecomposable measures

abstract:
  We show that a probability measure is not a nontrivial free additive
convolution if it puts no mass in an interval whose endpoints are atoms. The
analogous results for free multiplicative convolutions are proved as well. The
proofs use analytic subordination.


title: Type IIA/M-theory Moduli fixing in a Class of Orientifold Models

abstract:
  We present the study of type II A flux vacua and their M-theory duals for
compactification on a class of Calabi-Yau orientifolds. The Kaehler potential
is derived from toroidal compactifications and the superpotential contains a
contribution from non-Abelian gauge degrees of freedoms. We obtain complete
stabilisation of the moduli. We found one supersymmetric minimum and several
non supersymmetric ones. Consistency of the analysis constrains the parameters
of the models in a finite region containing a finite, although very large,
number of flux vacua. From the M-theory side, we found some differences in the
distributions of the physical quantities with respect to the M-theory ensemble
studied by Acharya et al. In particular, it is easier to find small
supersymmetry breaking scale.


title: The Fossil Phase in the Life of a Galaxy Group

abstract:
  We investigate the origin and evolution of fossil groups in a concordance
LCDM cosmological simulation. We consider haloes with masses between
$(1-5)\times10^{13} \hMsun$ and study the physical mechanisms that lead to the
formation of the large gap in magnitude between the brightest and the second
most bright group member, which is typical for these fossil systems. Fossil
groups are found to have high dark matter concentrations, which we can relate
to their early formation time. The large magnitude-gaps arise after the groups
have build up half of their final mass, due to merging of massive group
members. We show that the existence of fossil systems is primarily driven by
the relatively early infall of massive satellites, and that we do not find a
strong environmental dependence for these systems. In addition, we find
tentative evidence for fossil group satellites falling in on orbits with
typically lower angular momentum, which might lead to a more efficient merger
onto the host. We find a population of groups at higher redshifts that go
through a ``fossil phase'': a stage where they show a large magnitude-gap,
which is terminated by renewed infall from their environment.


title: On isogenous principally polarized abelian surfaces

abstract:
  We study a relationship between two genus 2 curves whose jacobians are
isogenous with kernel equal to a maximal isotropic subspace of p-torsion points
with respect to the Weil pairing. For p = 3 we find an explicit relationship
between the set of Weierstrass points of the two curves extending the classical
results of F. Richelot (1837) and G. Humbert (1901) in the case p = 2.


title: Kaluza-Klein relics from warped reheating

abstract:
  It has been suggested that after brane-antibrane inflation in a
Klebanov-Strassler (KS) warped throat, metastable Kaluza-Klein (KK) excitations
can be formed due to nearly-conserved angular momenta along isometric
directions in the throat. If sufficiently long-lived, these relics could
conflict with big bang nucleosynthesis or baryogenesis by dominating the energy
density of the universe. We make a detailed estimate of the decay rate of such
relics using the low energy effective action of type IIB string theory
compactified on the throat geometry, with attention to powers of the warp
factor. We find that it is necessary to turn on SUSY-breaking deformations of
the KS background in order to ensure that the most dangerous relics will decay
fast enough. The decay rate is found to be much larger than the naive guess
based on the dimension of the operators which break the angular isometries of
the throat. For an inflationary warp factor of order $w\sim 10^{-4}$, we obtain
the bound $M_{3/2} \gsim 10^9$ GeV on the scale of SUSY breaking to avoid
cosmological problems from the relics, which is satisfied in the KKLT
construction assumed to stabilize the compactification. Given the requirement
that the relics decay before nucleosynthesis or baryogenesis, we place bounds
on the mass of the relic as a function of the warp factor in the throat for
more general warped backgrounds.


title: Massive Quark-Gluon Scattering Amplitudes at Tree Level

abstract:
  Results for four-, five-, and six-parton tree amplitudes for massive
quark-antiquark scattering with gluons are calculated using the recursion
relations of Britto, Cachazo, Feng, and Witten. The required diagrams are
generated using shifts of the momenta of a pair of massless legs to complex
values. Checks verifying the calculations are described, and a simple formula
for the shifted spinors of an internal gluon is presented.


title: Fault-tolerant quantum computation against biased noise

abstract:
  We formulate a scheme for fault-tolerant quantum computation that works
effectively against highly biased noise, where dephasing is far stronger than
all other types of noise. In our scheme, the fundamental operations performed
by the quantum computer are single-qubit preparations, single-qubit
measurements, and conditional-phase (CPHASE) gates, where the noise in the
CPHASE gates is biased. We show that the accuracy threshold for quantum
computation can be improved by exploiting this noise asymmetry; e.g., if
dephasing dominates all other types of noise in the CPHASE gates by four orders
of magnitude, we find a rigorous lower bound on the accuracy threshold higher
by a factor of five than for the case of unbiased noise.


title: Enhanced Non-Gaussianity from Excited Initial States

abstract:
  We use the techniques of effective field theory in an expanding universe to
examine the effect of choosing an excited inflationary initial state built over
the Bunch-Davies state on the CMB bi-spectrum. We find that even for Hadamard
states, there are unexpected enhancements in the bi-spectrum for certain
configurations in momentum space due to interactions of modes in the early
stages of inflation. These enhancements can be parametrically larger than the
standard ones and are potentially observable in current and future data. These
initial state effects have a characteristic signature in $l$-space which
distinguishes them from the usual contributions, with the enhancement being
most pronounced for configurations corresponding to flattened triangles for
which two momenta are collinear.


title: Testing Reionization with Gamma Ray Burst Absorption Spectra

abstract:
  We propose to study cosmic reionization using absorption line spectra of
high-redshift Gamma Ray Burst (GRB) afterglows. We show that the statistics of
the dark portions (gaps) in GRB absorption spectra represent exquisite tools to
discriminate among different reionization models. We then compute the
probability to find the largest gap in a given width range [Wmax, Wmax + dW] at
a flux threshold Fth for burst afterglows at redshifts 6.3 < z < 6.7. We show
that different reionization scenarios populate the (Wmax, Fth) plane in a very
different way, allowing to distinguish among different reionization histories.
We provide here useful plots that allow a very simple and direct comparison
between observations and model results. Finally, we apply our methods to GRB
050904 detected at z = 6.29. We show that the observation of this burst
strongly favors reionization models which predict a highly ionized
intergalactic medium at z~6, with an estimated mean neutral hydrogen fraction
xHI = 6.4 \pm 0.3 \times 10^-5 along the line of sight towards GRB 050904.


title: Balanced metrics and noncommutative Kaehler geometry

abstract:
  In this paper we show how Einstein metrics are naturally described using the
quantization of the algebra of functions on a Kahler manifold M. In this setup
one interprets M as the phase space itself, equipped with the Poisson brackets
inherited from the Kahler 2-form. We compare the geometric quantization
framework with several deformation quantization approaches. We find that the
balanced metrics appear naturally as a result of setting the vacuum energy to
be the constant function on the moduli space of semiclassical vacua. In the
classical limit these metrics become Kahler-Einstein (when M admits such
metrics). Finally, we sketch several applications of this formalism, such as
explicit constructions of special Lagrangian submanifolds in compact Calabi-Yau
manifolds.


title: Unique continuation results for Ricci curvature and applications

abstract:
  Unique continuation results are proved for metrics with prescribed Ricci
curvature in the setting of bounded metrics on compact manifolds with boundary,
and in the setting of complete, conformally compact metrics. Related to this
issue, an isometry extension property is proved: continuous groups of
isometries at conformal infinity extend into the bulk of any complete
conformally compact Einstein metric. Relations of this property with the
invariance of the Gauss-Codazzi constraint equations under deformations are
also discussed.


title: Strain-induced insulator state in La_0.7Sr_0.3CoO_3

abstract:
  We report on the observation of a strain-induced insulator state in
ferromagnetic La_0.7Sr_0.3CoO_3 films. Tensile strain above 1% is found to
enhance the resistivity by several orders of magnitude. Reversible strain of
0.15% applied using a piezoelectric substrate triggers huge resistance
modulations, including a change by a factor of 10 in the paramagnetic regime at
300 K. However, below the ferromagnetic ordering temperature, the magnetization
data indicate weak dependence on strain for the spin state of the Co ions. We
interpret the changes observed in the transport properties in terms of a
strain-induced splitting of the Co e_g levels and reduced double exchange,
combined with a percolation-type conduction in an electronic cluster state.


title: Common Markets, Strong Currencies & the Collective Welfare

abstract:
  The so called "globalization" process (i.e. the inexorable integration of
markets, currencies, nation-states, technologies and the intensification of
consciousness of the world as a whole) has a behavior exactly equivalent to a
system that is tending to a maximum entropy state. This globalization process
obeys a collective welfare principle in where the maximum payoff is given by
the equilibrium of the system and its stability by the maximization of the
welfare of the collective besides the individual welfare. This let us predict
the apparition of big common markets and strong common currencies. They will
reach the "equilibrium" by decreasing its number until they reach a state
characterized by only one common currency and only one big common community
around the world.


title: Scaling Laws for NanoFET Sensors

abstract:
  The sensitive conductance change of semiconductor nanowires and carbon
nanotubes in response to binding of charged molecules provide a novel sensing
modality which is generally denoted as nanoFET sensors. In this paper, we study
the scaling laws of nanoplate FET sensors by simplifying nanoplates as random
resistor networks with molecular receptors sitting on lattice sites.
Nanowire/tube FETs are included as the limiting cases where the device width
goes small. Computer simulations show that the field effect strength exerted by
the binding molecules has significant impact on the scaling behaviors. When the
field effect strength is small, nanoFETs have little size and shape dependence.
In contrast, when the field-effect strength becomes stronger, there exists a
lower detection threshold for charge accumulation FETs and an upper detection
threshold for charge depletion FET sensors. At these thresholds, the nanoFET
devices undergo a transition between low and large sensitivities. These
thresholds may set the detection limits of nanoFET sensors, while could be
eliminated by designing devices with very short source-drain distance and large
width.


title:
Correspondence between Andreev reflection and Klein tunneling in bipolar
  graphene

abstract:
  Andreev reflection at a superconductor and Klein tunneling through an n-p
junction in graphene are two processes that couple electrons to holes -- the
former through the superconducting pair potential Delta and the latter through
the electrostatic potential U. We derive that the energy spectra in the two
systems are identical, at low energies E<<Delta and for an antisymmetric
potential profile U(-x,y)=-U(x,y). This correspondence implies that bipolar
junctions in graphene may have zero density of states at the Fermi level and
carry a current in equilibrium, analogously to superconducting Josephson
junctions. It also implies that nonelectronic systems with the same band
structure as graphene, such as honeycomb-lattice photonic crystals, can exhibit
pseudo-superconducting behavior.


title: EVLA Observations of OH Masers in ON 1

abstract:
  This Letter reports on initial Expanded Very Large Array (EVLA) observations
of the 6035 MHz masers in ON 1. The EVLA data are of good quality, lending
confidence in the new receiver system. Nineteen maser features, including six
Zeeman pairs, are detected. The overall distribution of 6035 MHz OH masers is
similar to that of the 1665 MHz OH masers. The spatial resolution is sufficient
to unambiguously determine that the magnetic field is strong (~ -10 mG) at the
location of the blueshifted masers in the north, consistent with Zeeman
splitting detected in 13441 MHz OH masers in the same velocity range. Left and
right circularly polarized ground-state features dominate in different regions
in the north of the source, which may be due to a combination of magnetic field
and velocity gradients. The combined distribution of all OH masers toward the
south is suggestive of a shock structure of the sort previously seen in W3(OH).


title:
The star formation histories of early-type galaxies: insights from the
  rest-frame ultra-violet

abstract:
  Our current understanding of the star formation histories of early-type
galaxies is reviewed, in the context of recent observational studies of their
ultra-violet (UV) properties. Combination of UV and optical spectro-photometric
data indicates that the bulk of the stellar mass in the early-type population
forms at high redshift (z > 2), typically over short timescales (< 1 Gyr).
Nevertheless, early-types of all luminosities form stars over the lifetime of
the Universe, with most luminous (-23 < M(V) < -21) systems forming 10-15% of
their stellar mass after z = 1 (with a scatter to higher value), while their
less luminous (M(V) > -21) counterparts form 30-60% of their mass in the same
redshift range. The large scatter in the (rest-frame) UV colours in the
redshift range 0 < z < 0.7 indicates widespread low-level star formation in the
early-type population over the last 8 billion years. The mass fraction of young
(< 1 Gyr old) stars in luminous early-type galaxies varies between 1% and 6% at
z~0 and is in the range 5-13% at z~0.7. The intensity of recent star formation
and the bulk of the UV colour distribution is consistent with what might be
expected from minor mergers (mass ratios < 1:6) in an LCDM cosmology.


title: On Braid Excitations in Quantum Gravity

abstract:
  We propose a new notation for the states in some models of quantum gravity,
namely 4-valent spin networks embedded in a topological three manifold. With
the help of this notation, equivalence moves, namely translations and
rotations, can be defined, which relate the projections of diffeomorphic
embeddings of a spin network. Certain types of topological structures, viz
3-strand braids as local excitations of embedded spin networks, are defined and
classified by means of the equivalence moves. This paper formulates a
mathematical approach to the further research of particle-like excitations in
quantum gravity.


title: Semi--vector spaces and units of measurement

abstract:
  This paper is aimed at introducing an algebraic model for physical scales and
units of measurement. This goal is achieved by means of the concept of
``positive space'' and its rational powers. Positive spaces are 1-dimensional
``semi-vector spaces'' without the zero vector. A direct approach to this
subject might be sufficient. On the other hand, a broader mathematical
understanding requires the notions of sesqui- and semi-tensor products between
semi-vector spaces and vector spaces. So, the paper is devoted to an original
contribution to the algebraic theory of semi-vector spaces, to the algebraic
analysis of positive spaces and, eventually, to the algebraic model of physical
scales and units of measurement in terms of positive spaces.


title:
An exact solution to the temperature equation in a column of ice and
  bedrock

abstract:
  We construct a solution of a pure conduction problem in ice and bedrock. This
solution is suitable for, and is used in this paper for, verifying a numerical
scheme for conservation of energy. This exact solution forms one of a suite of
verification tests for PISM (Parallel Ice Sheet Model;
https://gna.org/projects/pism/).


title:
Renormalization group flow of quartic perturbations in graphene: Strong
  coupling and large-N limits

abstract:
  We explore the renormalization group flow of quartic perturbations in the
low-energy theory of graphene, in the strong Coulomb coupling and large-N
limits, where N is the number of fermion flavors. We compute the anomalous
dimensions of the quartic couplings u up to next-to-leading order in 1/N and
find both relevant and irrelevant directions in the space of quartic couplings.
We discuss possible phase diagrams and relevance for the physics of graphene.


title: Elliptic nets and elliptic curves

abstract:
  An elliptic divisibility sequence is an integer recurrence sequence
associated to an elliptic curve over the rationals together with a rational
point on that curve. In this paper we present a higher-dimensional analogue
over arbitrary base fields. Suppose E is an elliptic curve over a field K, and
P_1, ..., P_n are points on E defined over K. To this information we associate
an n-dimensional array of values in K satisfying a nonlinear recurrence
relation. Arrays satisfying this relation are called elliptic nets. We
demonstrate an explicit bijection between the set of elliptic nets and the set
of elliptic curves with specified points. We also obtain
Laurentness/integrality results for elliptic nets.


title:
Monitoring noise-resonant effects in cancer growth influenced by
  external fluctuations and periodic treatment

abstract:
  In the paper we investigate a mathematical model describing the growth of
tumor in the presence of immune response of a host organism. The dynamics of
tumor and immune cells is based on the generic Michaelis-Menten kinetics
depicting interaction and competition between the tumor and the immune system.
The appropriate phenomenological equation modeling cell-mediated immune
surveillance against cancer is of the predator-prey form and exhibits
bistability within a given choice of the immune response-related parameters.
Under the influence of weak external fluctuations, the model may be analyzed in
terms of a stochastic differential equation bearing the form of an overdamped
Langevin-like dynamics in the external quasi-potential represented by a double
well. We analyze properties of the system within the range of parameters for
which the potential wells are of the same depth and when the additional
perturbation, modeling a periodic treatment, is insufficient to overcome the
barrier height and to cause cancer extinction. In this case the presence of a
small amount of noise can positively enhance the treatment, driving the system
to a state of tumor extinction. On the other hand, however, the same noise can
give rise to return effects up to a stochastic resonance behavior. This
observation provides a quantitative analysis of mechanisms responsible for
optimization of periodic tumor therapy in the presence of spontaneous external
noise. Studying the behavior of the extinction time as a function of the
treatment frequency, we have also found the typical resonant activation effect:
For a certain frequency of the treatment, there exists a minimum extinction
time.


title: New Model Atmospheres: Testing the Solar Spectrum in the UV

abstract:
  We present preliminary results on the calculation of synthetic spectra
obtained with the stellar model atmospheres developed by Cardona, Crivellari,
and Simonneau. These new models have been used as input within the SYNTHE
series of codes developed by Kurucz. As a first step we have tested if SYNTHE
is able to handle these models which go down to log tau(Ross)= -13. We have
successfully calculated a synthetic solar spectrum in the wavelength region
2000--4500 A at high resolution (R=522,000). Within this initial test we have
found that layers at optical depths with log tau(Ross) < -7 significantly
affect the mid-UV properties of a synthetic spectrum computed from a solar
model. We anticipate that these new extended models will be a valuable tool for
the analysis of UV stellar light arising from the outermost layers of the
atmospheres.


title:
The non-existence of certain mod 2 Galois representations of some small
  quadratic fields

abstract:
  For a few quadratic fields, the non-existence is proved of continuous
irreducible mod 2 Galois representations of degree 2 unramified outside 2.


title: Measurements in the L\'{e}vy quantum walk

abstract:
  We study the quantum walk subjected to measurements with a L\'evy
waiting-time distribution. We find that the system has a sub-ballistic behavior
instead of a diffusive one. We obtain an analytical expression for the exponent
of the power law of the variance as a function of the characteristic parameter
of the L\'evy distribution.


title: Unification with and without Supersymmetry: Adjoint SU(5)

abstract:
  I present two new renormalizable grand unified theories where the neutrino
masses are generated through the type I and type III seesaw mechanisms. These
theories can be considered as the simplest (SUSY) renormalizable grand unified
theories based on the SU(5) gauge symmetry. Several phenomenological and
cosmological aspects of these proposals are discussed.


title:
Effects of the disconnected flavor singlet corrections on the hyperfine
  splitting in charmonium

abstract:
  Experimentally the charmonium hyperfine splitting is
$M_{J/\psi}-M_{\eta_c}=117$ MeV and current lattice results are generally below
this value. The difference could be due to the effects of the disconnected
flavor singlet diagrams which have not been included in these calculations.
Previous attempts to determine the disconnected flavor singlet corrections have
led just to rough estimates in the range of $\pm 20$ MeV. We present
preliminary results for these corrections calculated on fine ($a\approx 0.09$
fm) Asqtad 2+1 flavor lattices provided by the MILC Collaboration.


title:
Dedekind-Carlitz Polynomials as Lattice-Point Enumerators in Rational
  Polyhedra

abstract:
  We study higher-dimensional analogs of the Dedekind-Carlitz polynomials
c(u,v;a,b) := sum_{k=1..b-1} u^[ka/b] v^(k-1), where u and v are indeterminates
and a and b are positive integers. Carlitz proved that these polynomials
satisfy the reciprocity law (v-1) c(u,v;a,b) + (u-1) c(v,u;b,a) = u^(a-1)
v^(b-1) - 1, from which one easily deduces many classical reciprocity theorems
for the Dedekind sum and its generalizations. We illustrate that
Dedekind-Carlitz polynomials appear naturally in generating functions of
rational cones and use this fact to give geometric proofs of the Carlitz
reciprocity law and various extensions of it. Our approach gives rise to new
reciprocity theorems and computational complexity results for Dedekind-Carlitz
polynomials, a characterization of Dedekind-Carlitz polynomials in terms of
generating functions of lattice points in triangles, and a multivariate
generalization of the Mordell-Pommersheim theorem on the appearance of Dedekind
sums in Ehrhart polynomials of 3-dimensional lattice polytopes.


title: Traces of heat operators on Riemannian foliations

abstract:
  We consider the basic heat operator on functions on a Riemannian foliation of
a compact, Riemannian manifold, and we show that the trace of this operator has
a particular short time asymptotic expansion. The coefficients in this
expansion are obtainable from local transverse geometric invariants - functions
computable by analyzing the manifold in an arbitrarily small neighborhood of a
leaf closure. Using this expansion, we prove some results about the spectrum of
the basic Laplacian, such as the analogue of Weyl's asymptotic formula. Also,
we explicitly calculate the first two nontrivial coefficients of the expansion
for special cases such as codimension two foliations and foliations with
regular closure.


title: The MIMOME Channel

abstract:
  The MIMOME channel is a Gaussian wiretap channel in which the sender,
receiver, and eavesdropper all have multiple antennas. We characterize the
secrecy capacity as the saddle-value of a minimax problem. Among other
implications, our result establishes that a Gaussian distribution maximizes the
secrecy capacity characterization of Csisz{\'a}r and K{\"o}rner when applied to
the MIMOME channel. We also determine a necessary and sufficient condition for
the secrecy capacity to be zero. Large antenna array analysis of this condition
reveals several useful insights into the conditions under which secure
communication is possible.


title: Magnetar Driven Bubbles and the Origin of Collimated Outflows from GRBs

abstract:
  We model the interaction between the wind from a newly formed rapidly
rotating magnetar and the surrounding progenitor. In the first few seconds
after core collapse the magnetar inflates a bubble of plasma and magnetic
fields behind the supernova shock, which expands asymmetrically because of the
pinching effect of the toroidal magnetic field, as in PWNe, even if the host
star is spherically symmetric. The degree of asymmetry depends on the ratio of
the magnetic energy to the total energy in the bubble. We assume that the wind
by newly formed magnetars inflating these bubbles is more magnetized than for
PWNe. We show that for a magnetic to total power supplied by the central
magnetar $\sim 0.1$ the bubble expands relatively spherically while for values
greater than 0.3, most of the pressure in the bubble is exerted close to the
rotation axis, driving a collimated outflow out through the host star. This can
account for the collimation inferred from observations of long-duration
gamma-ray bursts (GRBs). Given that the wind magnetization increases in time,
we thus suggest that the magnetar-driven bubble initially expands relatively
spherically (enhancing the energy of the associated supernova) while at late
times it becomes progressivelymore collimated (producing the GRB). Similar
processes may operate in more modestly rotating neutron stars to produce
asymmetric supernovae and lower energy transients such as X-ray flashes.


title: Unveiling GRB hard X-ray afterglow emission with Simbol-X

abstract:
  Despite the enormous progress occurred in the last 10 years, the Gamma-Ray
Bursts (GRB) phenomenon is still far to be fully understood. One of the most
important open issues that have still to be settled is the afterglow emission
above 10 keV, which is almost completely unexplored. This is due to the lack of
sensitive enough detectors operating in this energy band. The only detection,
by the BeppoSAX/PDS instrument (15-200 keV), of hard X-ray emission from a GRB
(the very bright GRB 990123), combined with optical and radio observations,
seriously challenged the standard scenario in which the dominant mechanism is
synchrotron radiation produced in the shock of a ultra-relativistic fireball
with the ISM, showing the need of a substantial revision of present models. In
this respect, thanks to its unprecedented sensitivity in the 10-80 keV energy
band, Simbol-X, through follow-up observations of bright GRBs detected and
localized by GRB dedicated experiments that will fly in the >2010 time frame,
will provide an important breakthrough in the GRB field.


title: The Galois action on character tables

abstract:
  A geometric interpretation and generalisation for the Galois action on finite
group character tables is sketched. The generalisation is a Galois action on
the space Map_G(G^n,\bar{Q})/S_n for each finite G, where G acts by
simultaneous conjugation on the n-tuples G^n and the symmetric group S_n
permutes the components.


title: Conformal field theory and mapping class groups

abstract:
  Rational conformal field theories produce a tower of finite-dimensional
representations of surface mapping class groups, acting on the conformal blocks
of the theory. We review this formalism. We show that many recent mathematical
developments can be fit into the first 2 floors of this tower. We also review
what is known in higher genus.


title: QCD thermodynamics with 2+1 flavors at nonzero chemical potential

abstract:
  We present results for the QCD equation of state, quark densities and
susceptibilities at nonzero chemical potential, using 2+1 flavor asqtad
ensembles with $N_t=4$. The ensembles lie on a trajectory of constant physics
for which $m_{ud}\approx0.1m_s$. The calculation is performed using the Taylor
expansion method with terms up to sixth order in $\mu/T$.


title: Resonance Related Spiral Substructure in a Galactic Gaseous Disk

abstract:
  We use high resolution 2D hydrodynamic simulations to study the formation of
spiral substructure in the gaseous disk of a galaxy. The obtained gaseous
response is driven by a self-consistent non-axisymmetric potential obtained
from an imposed spiral mass distribution. We highlight the importance of
ultraharmonic resonances in generating these features. The temporal evolution
of the system is followed with the parallel ZEUS-MP code, and we follow the
steepening of perturbations induced by the spiral potential until large-scale
shocks emerge. These shocks exhibit bifurcations that protrude from the gaseous
arms and continue to steepen until new shocks are formed. When the contribution
from the spiral potential relative to the axisymmetric background is increased
from our default value, spurs protrude from the main arms after several
revolutions of the gaseous disk. Such spurs overlap on top of the
aforementioned shocks. These results support the hypothesis that a complicated
gaseous response can coexist with an orderly spiral potential term, in the
sense that the underlying background potential can be smooth yet drive a
gaseous response that is far more spatially complex.


title: Polyexponentials

abstract:
  We discuss a special function (polyexponential) that extends the natural
exponential function and also the exponential integral. The basic properties of
the polyexponential are listed and some applications are given. In particular,
it is shown that certain Mellin integrals can be evaluated in terms of
polyexponentials. The polyexponential is related to the exponential
polynomials, the Riemann zeta function, the Dirichlet eta function and the
Lerch Transcendent.


title: Dynamics and robustness of familiarity memory

abstract:
  When one is presented with an item or a face, one can sometimes have a sense
of recognition without being able to recall where or when one has encountered
it before. This sense of recognition is known as familiarity. Following
previous computational models of familiarity memory we investigate the
dynamical properties of familiarity discrimination, and contrast two different
familiarity discriminators: one based on the energy of the neural network, and
the other based on the time derivative of the energy. We show how the
familiarity signal decays after a stimulus is presented, and examine the
robustness of the familiarity discriminator in the presence of random
fluctuations in neural activity. For both discriminators we establish, via a
combined method of signal-to-noise ratio and mean field analysis, how the
maximum number of successfully discriminated stimuli depends on the noise
level.


title: Spin Anisotropy in ZnCu_3(OH)_6Cl_2

abstract:
  The spin anisotropic exchange interaction is suggested to contribute
significantly to the abnormal upturn of the magnetic susceptibility in the
ZnCu$_3$(OH)$_6$Cl$_2$. The saturation of the magnetic susceptibility below 300
mK observed in the muon spin resonance ($\mu$SR) experiment is the quantum
effect of the spin flipping process.


title: Effects of kinked linear defects on planar flux line arrays

abstract:
  In the hard core limit, interacting vortices in planar type II
superconductors can be modeled as non-interacting one dimensional fermions
propagating in imaginary time. We use this analogy to derive analytical
expressions for the probability density and imaginary current of vortex lines
interacting with an isolated bent line defect and to understand the pinning
properties of such systems. When there is an abrupt change of the direction of
the pinning defect, we find a sinusoidal modulation of the vortex density in
directions both parallel and perpendicular to the defect.


title:
Multi-User Diversity vs. Accurate Channel Feedback for MIMO Broadcast
  Channels

abstract:
  A multiple transmit antenna, single receive antenna (per receiver) downlink
channel with limited channel feedback is considered. Given a constraint on the
total system-wide channel feedback, the following question is considered: is it
preferable to get low-rate feedback from a large number of receivers or to
receive high-rate/high-quality feedback from a smaller number of (randomly
selected) receivers? Acquiring feedback from many users allows multi-user
diversity to be exploited, while high-rate feedback allows for very precise
selection of beamforming directions. It is shown that systems in which a
limited number of users feedback high-rate channel information significantly
outperform low-rate/many user systems. While capacity increases only double
logarithmically with the number of users, the marginal benefit of channel
feedback is very significant up to the point where the CSI is essentially
perfect.


title: Search for Rare b-hadron Decays at CDF

abstract:
  We report on searches for B^0_s to \mu^+ \mu^-, B^0_d to \mu^+ \mu^- decays
and b to s \mu^+\mu^- transitions in exclusive decays of B mesons.
  Using 2 fb^{-1} of data collected by the CDF II detector we find upper limits
on the branching fractions B(B^0_s to \mu^+ \mu^-) < 5.8 x 10^{-8} and B(B^0_d
to \mu^+ \mu^-) < 1.8 x 10^{-8} at 95% confidence level.
  Using 924 pb^{-1} of data we measure the branching fractions B(B^+ to \mu^+
\mu^- K^+) = (0.60 \pm 0.15 \pm 0.04) x 10^{-6}, B(B^0_d to \mu^+ \mu^- K^{*0})
= (0.82 \pm 0.31 \pm 0.10) x 10^{-6} and the limit B(B^0_s to \mu^+ \mu^-
phi)/B(B^0_s to J/\psi\phi) < 2.61(2.30) x 10^{-3} at 95(90)% confidence level.


title: Binary Black Hole Coalescence

abstract:
  The two-body problem in general relativity is reviewed, focusing on the final
stages of the coalescence of the black holes as uncovered by recent successes
in numerical solution of the field equations.


title: Resonant ratcheting of a Bose-Einstein condensate

abstract:
  We study the rectification process of interacting quantum particles in a
periodic potential exposed to the action of an external ac driving. The
breaking of spatio-temporal symmetries leads to directed motion already in the
absence of interactions. A hallmark of quantum ratcheting is the appearance of
resonant enhancement of the current (Europhys. Lett. 79 (2007) 10007 and Phys.
Rev. A 75 (2007) 063424). Here we study the fate of these resonances within a
Gross-Pitaevskii equation which describes a mean field interaction between many
particles. We find, that the resonance is i) not destroyed by interactions, ii)
shifting its location with increasing interaction strength. We trace the
Floquet states of the linear equations into the nonlinear domain, and show that
the resonance gives rise to an instability and thus to the appearance of new
nonlinear Floquet states, whose transport properties differ strongly as
compared to the case of noninteracting particles.


title: A possible disk mechanism for the 23d QPO in Mkn~501

abstract:
  Optically thin two-temperature accretion flows may be thermally and viscously
stable, but acoustically unstable. Here we propose that the O-mode instability
of a cooling-dominated optically thin two-temperature inner disk may explain
the 23-day quasi-periodic oscillation (QPO) period observed in the TeV and
X-ray light curves of Mkn~501 during its 1997 high state. In our model the
relativistic jet electrons Compton upscatter the disk soft X-ray photons to TeV
energies, so that the instability-driven X-ray periodicity will lead to a
corresponding quasi-periodicity in the TeV light curve and produce correlated
variability. We analyse the dependence of the instability-driven
quasi-periodicity on the mass (M) of the central black hole, the accretion rate
($\rm{\dot{M}}$) and the viscous parameter ($\alpha$) of the inner disk. We
show that in the case of Mkn~501 the first two parameters are constrained by
various observational results, so that for the instability occurring within a
two-temperature disk where $\alpha=0.05-1.0$, the quasi-period is expected to
lie within the range of 8 to 100 days, as indeed the case. In particular, for
the observed 23-day QPO period our model implies a viscosity coefficient
$\alpha \leq 0.28$, a sub-Eddington accretion rate $\dot{M} \simeq 0.02
\dot{M}_{\rm Edd}$ and a transition radius to the outer standard disk of $r_0
\sim 60 r_g$, and predicts a period variation $\delta P/P \sim 0.23$ due to the
motion of the instability region.


title:
Modulated phases in magnetic models frustrated by long-range
  interactions

abstract:
  We study an Ising model in one dimension with short range ferromagnetic and
long range (power law) antiferromagnetic interactions. We show that the zero
temperature phase diagram in a (longitudinal) field H involves a sequence of up
and down domains whose size varies continuously with H, between -H_c and H_c
which represent the edge of the ferromagnetic up and down phases. The
implications of long range interaction in many body systems are discussed.


title:
Marginal Deformations as Lower Dimensional D-brane Solutions in Open
  String Field theory

abstract:
  By direct calculation we showed that a finite analytic solution for marginal
deformation of open string field theory, by a matter primary operator with
singular OPE, can be obtained to all orders in the deformation parameter. In
particular, we obtained solutions that describe lower dimensional D-branes and
our results agree with the results obtained when the same problem is treated in
the world-sheet conformal field theory language.


title: Dimension Reduction for the Hyperbolic Space

abstract:
  A dimension reduction for the hyperbolic space is established. When points
are far apart an embedding with bounded distortion into the hyperbolic plane is
achieved.


title: Decoherence rates for Galilean covariant dynamics

abstract:
  We introduce a measure of decoherence for a class of density operators. For
Gaussian density operators in dimension one it coincides with an index used by
Morikawa (1990). Spatial decoherence rates are derived for three large classes
of the Galilean covariant quantum semigroups introduced by Holevo. We also
characterize the relaxation to a Gaussian state for these dynamics and give a
theorem for the convergence of the Wigner function to the probability
distribution of the classical analog of the process.


title:
GHASP : an H alpha kinematic survey of spiral and irregular galaxies. V.
  Dark matter distribution in 36 nearby spiral galaxies

abstract:
  The results obtained from a study of the mass distribution of 36 spiral
galaxies are presented. The galaxies were observed using Fabry-Perot
interferometry as part of the GHASP survey. The main aim of obtaining high
resolution H alpha 2D velocity fields is to define more accurately the rising
part of the rotation curves which should allow to better constrain the
parameters of the mass distribution. The H alpha velocities were combined with
low resolution HI data from the literature, when available. Combining the
kinematical data with photometric data, mass models were derived from these
rotation curves using two different functional forms for the halo: an
isothermal sphere and an NFW profile. For the galaxies already modeled by other
authors, the results tend to agree. Our results point at the existence of a
constant density core in the center of the dark matter halos rather than a
cuspy core, whatever the type of the galaxy from Sab to Im. This extends to all
types the result already obtained by other authors studying dwarf and LSB
galaxies but would necessitate a larger sample of galaxies to conclude more
strongly. Whatever model is used (ISO or NFW), small core radius halos have
higher central densities, again for all morphological types. We confirm
different halo scaling laws, such as the correlations between the core radius
and the central density of the halo with the absolute magnitude of a galaxy:
low luminosity galaxies have small core radius and high central density. We
find that the product of the central density with the core radius of the dark
matter halo is nearly constant, whatever the model and whatever the absolute
magnitude of the galaxy. This suggests that the halo surface density is
independent from the galaxy type.


title:
On the Limiting Empirical Measure of the sum of rank one matrices with
  log-concave distribution

abstract:
  We consider $n\times n$ real symmetric and hermitian random matrices
$H_{n,m}$ equals the sum of a non-random matrix $H_{n}^{(0)}$ matrix and the
sum of $m$ rank-one matrices determined by $m$ i.i.d. isotropic random vectors
with log-concave probability law and i.i.d. random amplitudes $\{\tau_{\alpha
}\}_{\alpha =1}^{m}$. This is a generalization of the case of vectors uniformly
distributed over the unit sphere, studied in [Marchenko-Pastur (1967)]. We
prove that if $n\to \infty, m\to \infty, m/n\to c\in \lbrack 0,\infty)$ and
that the empirical eigenvalue measure of $H_{n}^{(0)}$ converges weakly, then
the empirical eigenvalue measure of $H_{n,m}$ converges in probability to a
non-random limit, found in [Marchenko-Pastur (1967)].


title:
The asymptotic Tian-Yau-Zelditch expansion on Riemann surfaces with
  Constant Curvature

abstract:
  Let $M$ be a regular Riemann surface with a metric which has constant scalar
curvature $\rho$. We give the asymptotic expansion of the sum of the square
norm of the sections of the pluricanonical bundles $K_{M}^{m}$. That is,
\[\sum_{i=0}^{d_{m}-1}\|S_{i}(x_{0})\|_{h_{m}}^{2} \sim m(1+\frac{\rho}{2
m})+O(e^{-\frac{(\log m)^{2}}{8}}),\] where $\{S_{0},...,S_{d_{m}-1}\}$ is an
orthonormal basis for $H^{0}(M, K_{M}^{m})$ for sufficiently large $m$.


title:
Two-step Quantum Key Distribution Schemes Using Polarization and
  Frequency Doubly Entangled Photons

abstract:
  A two-step quantum key distribution protocol using frequency and polarization
doubly entangled photons is proposed. In this protocol, information is encoded
by a unitary operation on each of the two doubly entangled photons and sent
from Alice to Bob in two steps. State measurement device is designed. The
security of the communication is analyzed.


title:
Derivation of asymptotic two-dimensional time-dependent equations for
  ocean wave propagation

abstract:
  A general method for the derivation of asymptotic nonlinear shallow water and
deep water models is presented. Starting from a general dimensionless version
of the water-wave equations, we reduce the problem to a system of two equations
on the surface elevation and the velocity potential at the free surface. These
equations involve a Dirichlet-Neumann operator and we show that all the
asymptotic models can be recovered by a simple asymptotic expansion of this
operator, in function of the shallowness parameter (shallow water limit) or the
steepness parameter (deep water limit). Based on this method, a new
two-dimensional fully dispersive model for small wave steepness is also
derived, which extends to uneven bottom the approach developed by Matsuno
\cite{matsuno3} and Choi \cite{choi}. This model is still valid in shallow
water but with less precision than what can be achieved with Green-Naghdi
model, when fully nonlinear waves are considered. The combination, or the
coupling, of the new fully dispersive equations with the fully nonlinear
shallow water Green-Naghdi equations represents a relevant model for describing
ocean wave propagation from deep to shallow waters.


title: On the Kirchheim-Magnani counterexample to metric differentiability

abstract:
  In this short note we give an interpretation of the Kirchheim-Magnani
counterexample to metric differentiability in terms of dilatation structures.


title:
Strong cosmic censorship for T^2-symmetric spacetimes with cosmological
  constant and matter

abstract:
  We address the issue of strong cosmic censorship for T^2-symmetric spacetimes
with positive cosmological constant. In the case of collisionless matter, we
complete the proof of the C^2 formulation of the conjecture for this class of
spacetimes. In the vacuum case, we prove that the conjecture holds for the
special cases where the area element of the group orbits does not vanish on the
past boundary of the maximal Cauchy development.


title:
NGC 346 in The Small Magellanic Cloud. IV. Triggered Star Formation in
  the HII Region N66

abstract:
  Stellar feedback, expanding HII regions, wind-blown bubbles, and supernovae
are thought to be important triggering mechanisms of star formation. Stellar
associations, being hosts of significant numbers of early-type stars, are the
loci where these mechanisms act. In this part of our photometric study of the
star-forming region NGC346/N66 in the Small Magellanic Cloud, we present
evidence based on previous and recent detailed studies, that it hosts at least
two different events of triggered star formation and we reveal the complexity
of its recent star formation history. In our earlier studies of this region
(Papers I, III) we find that besides the central part of N66, where the bright
OB stellar content of the association NGC346 is concentrated, an arc-like
nebular feature, north of the association, hosts recent star formation. This
feature is characterized by a high concentration of emission-line stars and
Young Stellar Objects, as well as embedded sources seen as IR-emission peaks
that coincide with young compact clusters of low-mass pre-main sequence stars.
All these objects indicate that the northern arc of N66 encompasses the most
current star formation event in the region. We present evidence that this star
formation is the product of a different mechanism than that in the general area
of the association, and that it is triggered by a wind-driven expanding HII
region (or bubble) blown by a massive supernova progenitor, and possibly other
bright stars, a few Myr ago. We propose a scenario according to which this
mechanism triggered star formation away from the bar of N66, while in the bar
of N66 star formation is introduced by the photo-ionizing OB stars of the
association itself.


title:
Exact Numerical Study of Pair Formation with Imbalanced Fermion
  Populations

abstract:
  We present an exact Quantum Monte Carlo study of the attractive 1-dimensional
Hubbard model with imbalanced fermion population. The pair-pair correlation
function, which decays monotonically in the absence of polarization P, develops
oscillations when P is nonzero, characteristic of
Fulde-Ferrell-Larkin-Ovchinnikov phase. The pair momentum distribution peaks at
a momentum equal to the difference in the Fermi momenta. At strong coupling,
the minority and majority momentum distributions are shown to be deformed,
reflecting the presence of the other species, and its Fermi surface. The FFLO
oscillations survive the presence of a confining potential, and the local
polarization at the trap center exhibits a marked dip, similar to that observed
experimentally.


title:
On the Newman sum over multiples of a prime with a primitive or
  semiprimitive root 2

abstract:
  We obtain a simple relations for the Newman sum over multiples of a prime
with a primitive or semiprimitive root 2. We consider the case of p=17 as well.


title: Studies on the Lorenz model

abstract:
  We study the Lorenz model from the viewpoint of its accessible singularities
and local index.


title: Quantum Monte Carlo Study of a Dynamic Hubbard Model

abstract:
  The `dynamic' Hubbard Hamiltonian describes interacting fermions on a lattice
whose on-site repulsion is modulated by a coupling to a fluctuating bosonic
field. We investigate one such model, introduced by Hirsch, using the
determinant Quantum Monte Carlo method. Our key result is that the extended
s-wave pairing vertex, repulsive in the usual static Hubbard model, becomes
attractive as the coupling to the fluctuating Bose field increases. The sign
problem prevents us from exploring a low enough temperature to see if a
superconducting transition occurs. We also observe a stabilization of
antiferromagnetic correlations and the Mott gap near half-filling, and a near
linear behavior of the energy as a function of particle density which indicates
a tendency toward phase separation.


title: Does Sex Induce a Phase Transition?

abstract:
  We discovered a dynamic phase transition induced by sexual reproduction. The
dynamics is a pure Darwinian rule with both fundamental ingredients to drive
evolution: 1) random mutations and crossings which act in the sense of
increasing the entropy (or diversity); and 2) selection which acts in the
opposite sense by limiting the entropy explosion. Selection wins this
competition if mutations performed at birth are few enough. By slowly
increasing the average number m of mutations, however, the population suddenly
undergoes a mutational degradation precisely at a transition point mc. Above
this point, the "bad" alleles spread over the genetic pool of the population,
overcoming the selection pressure. Individuals become selectively alike, and
evolution stops. Only below this point, m < mc, evolutionary life is possible.
  The finite-size-scaling behaviour of this transition is exhibited for large
enough "chromosome" lengths L. One important and surprising observation is the
L-independence of the transition curves, for large L. They are also independent
on the population size. Another is that mc is near unity, i.e. life cannot be
stable with much more than one mutation per diploid genome, independent of the
chromosome length, in agreement with reality. One possible consequence is that
an eventual evolutionary jump towards larger L enabling the storage of more
genetic information would demand an improved DNA copying machinery in order to
keep the same total number of mutations per offspring.


title:
Nodal solutions to quasilinear elliptic equations on compact Riemannian
  manifolds

abstract:
  We show the existence of nodal solutions to perturbed quasilinear elliptic
equations with critical Sobolev exponent on compact Riemannian manifolds. A
nonexistence result is also given.


title:
The Fractal Density Structure in Supersonic Isothermal Turbulence:
  Solenoidal versus Compressive Energy Injection

abstract:
  In a systematic study, we compare the density statistics in high resolution
numerical experiments of supersonic isothermal turbulence, driven by the
usually adopted solenoidal (divergence-free) forcing and by compressive
(curl-free) forcing. We find that for the same rms Mach number, compressive
forcing produces much stronger density enhancements and larger voids compared
to solenoidal forcing. Consequently, the Fourier spectra of density
fluctuations are significantly steeper. This result is confirmed using the
Delta-variance analysis, which yields power-law exponents beta~3.4 for
compressive forcing and beta~2.8 for solenoidal forcing. We obtain fractal
dimension estimates from the density spectra and Delta-variance scaling, and by
using the box counting, mass size and perimeter area methods applied to the
volumetric data, projections and slices of our turbulent density fields. Our
results suggest that compressive forcing yields fractal dimensions
significantly smaller compared to solenoidal forcing. However, the actual
values depend sensitively on the adopted method, with the most reliable
estimates based on the Delta-variance, or equivalently, on Fourier spectra.
Using these methods, we obtain D~2.3 for compressive and D~2.6 for solenoidal
forcing, which is within the range of fractal dimension estimates inferred from
observations (D~2.0-2.7). The velocity dispersion to size relations for both
solenoidal and compressive forcing obtained from velocity spectra follow a
power law with exponents in the range 0.4-0.5, in good agreement with previous
studies.


title: Complementary self-similarity

abstract:
  A few aspects of self-similarity related to complementary components of
closed subsets of R^n are briefly discussed.


title: Blow-up rate for a semi-linear accretive wave equation

abstract:
  In this paper we consider the semi-linear wave equation: $u_{tt}-\Delta
u=u_t|u_t|^{p-1}$ in $\mathbb{R}^N$. We provide an associated energy. With this
energy we give the blow-up rate for blowing up solutions in the case of bounded
below energy.


title: Smeared BTZ Black Hole from Space Noncommutativity

abstract:
  We study a novel phenomena of smearing of black hole horizons from the effect
of space noncommutativity. We present an explicit example in $AdS_3$ space,
using the Chern-Simons formulation of gravity. This produces a smeared BTZ
black hole which goes beyond the classical spacetime unexpectedly and there is
{\it no} reality problem in our approach with the gauge group $U(1,1) \times
U(1,1)$. The horizons are smeared, due to a splitting of the Killing horizon
and the apparent horizon, and there is a metric signature change to Euclidean
in the smeared region. The inner boundary of the smeared region acts as a
trapped surface for timelike particles but the outer as a classical barrier for
ingoing particles. The lightlike signals can escape from or reach the smeared
region in a {\it finite} time, which indicates that {\it the black hole is not
so dark, even classically.} In addition, it is remarked that the Hawking
temperature can {\it not} be defined by the regularity in the Euclidean
geometry except in the non-rotating case, and the origin can be smeared by a
{\it new} (apparent) horizon.


title:
The influence of the structure imperfectness of a crystalline undulator
  on the emission spectrum

abstract:
  We study the influence of an imperfect structure of a crystalline undulator
on the spectrum of the undulator radiation. The main attention is paid to the
undulators in which the periodic bending in the bulk appears as a result of a
regular (periodic) surface deformations. We demonstrate that this method of
preparation of a crystalline undulator inevitably leads to a variation of the
bending amplitude over the crystal thickness and to the presence of the
subharmonics with smaller bending period. Both of these features noticeably
influence the monochromatic pattern of the undulator radiation.


title:
Boltzmann distribution of free energies in a finite-connectivity
  spin-glass system and the cavity approach

abstract:
  At sufficiently low temperatures, the configurational phase space of a large
spin-glass system breaks into many separated domains, each of which is referred
to as a macroscopic state. The system is able to visit all spin configurations
of the same macroscopic state, while it can not spontaneously jump between two
different macroscopic states. Ergodicity of the whole configurational phase
space of the system, however, can be recovered if a temperature-annealing
process is repeated an infinite number of times. In a heating-annealing cycle,
the environmental temperature is first elevated to a high level and then
decreased extremely slowly until a final low temperature $T$ is reached.
Different macroscopic states may be reached in different rounds of the
annealing experiment; while the probability of finding the system in
macroscopic state $\alpha$ decreases exponentially with the free energy
$F_\alpha(T)$ of this state. For finite-connectivity spin glass systems, we use
this free energy Boltzmann distribution to formulate the cavity approach of
M{\'{e}}zard and Parisi [Eur. Phys. J. B {\bf 20}, 217 (2001)] in a slightly
different form. For the $\pm J$ spin-glass model on a random regular graph of
degree K=6, the predictions of the present work agree with earlier simulational
and theoretical results.


title:
Distribution of equilibrium free energies in a thermodynamic system with
  broken ergodicity

abstract:
  At low temperatures the configurational phase space of a macroscopic complex
system (e.g., a spin-glass) of $N\sim 10^{23}$ interacting particles may split
into an exponential number $\Omega_s \sim \exp({\rm const} \times N)$ of
ergodic sub-spaces (thermodynamic states). Previous theoretical studies assumed
that the equilibrium collective behavior of such a system is determined by its
ground thermodynamic states of the minimal free-energy density, and that the
equilibrium free energies follow the distribution of exponential decay. Here we
show that these assumptions are not necessarily valid. For some complex
systems, the equilibrium free-energy values may follow a Gaussian distribution
within an intermediate temperature range, and consequently their equilibrium
properties are contributed by {\em excited} thermodynamic states. This work
will help improving our understanding of the equilibrium statistical mechanics
of spin-glasses and other complex systems.


title: Matrices Totally Positive Relative to a Tree

abstract:
  It is known that for a totally positive (TP) matrix, the eigenvalues are
positive and distinct and the eigenvector associated with the smallest
eigenvalue is totally nonzero and has an alternating sign pattern. Here, a
certain weakening of the TP hypothesis is shown to yield a similar conclusion.


title: Faster than Light Quantum Communication

abstract:
  Faster than light communication might be possible using the collapse of the
quantum wave-function without any accompanying paradoxes.


title: Measurement of the Tau Lepton Polarisation at LEP2

abstract:
  A first measurement of the average polarisation P_tau of tau leptons produced
in e+e- annihilation at energies significantly above the Z resonance is
presented. The polarisation is determined from the kinematic spectra of tau
hadronic decays. The measured value P_tau = -0.164 +/- 0.125 is consistent with
the Standard Model prediction for the mean LEP energy of 197 GeV.


title: Consequence of doping in spatiotemporal rock-paper-scissors games

abstract:
  What determines species diversity is dramatic concern in science. Here we
report the effect of doping on diversity in spatiotemporal rock-paper-scissors
(RPS) games, which can be observed directly in ecological, biological and
social systems in nature. Doping means that there exists some buffer patches
which do not involve the main procession of the conflicts but occupied the game
space. Quantitative lattices simulation finds that (1) decrease of extinction
possibility is exponential dependent on the increase of doping rate, (2) the
possibility of the conflict is independent of doping rate at well mix evolution
beginning, and is buffered by doping in long time coexistence procession.
Practical meaning of doping are discussed. To demonstrate the importance of
doping, we present one practical example for microbial laboratory efficient
operation and one theoretical example for human-environment co-existence system
better understanding. It suggests that, for diversity, doping can not be
neglected.


title: A problem of enumeration of two-color bracelets with several variations

abstract:
  We consider the problem of enumeration of incongruent two-color bracelets of
$n$ beads, $k$ of which are black, and study several natural variations of this
problem. We also give recursion formulas for enumeration of $t$-color
bracelets, $t\geq3.


title:
Study of the Exclusive Initial-State-Radiation Production of the DDbar
  System

abstract:
  A search for charmonium and other new states is performed in a study of
exclusive initial-state-radiation production of D Dbar events from
electron-positron annihilations at a center-of-mass energy of 10.58 GeV. The
data sample corresponds to an integrated luminosity of 384 fb-1 and was
recorded by the BABAR experiment at the PEP-II storage ring. The D Dbar mass
spectrum shows clear evidence of the psi(3770) plus other structures near 3.9,
4.1, and 4.4 GeV/c^2. No evidence for Y(4260) -> D Dbar is observed, leading to
an upper limit of B(Y(4260) -> D Dbar)/B(Y(4260) -> J/psi pi+ pi-) < 1.0 at 90
% confidence level.


title:
The average kinetic energy density of Cooper pairs above T_c in
  YBa_2Cu_3O_{7-x}}, Bi_2Sr_2CaCu_2O_{8+\delta}, and Nb}

abstract:
  We have obtained isofield curves for the square root of the average kinetic
energy density of the superconducting state for three single crystals of
underdoped YBa_2Cu_3O_{7-x}, an optimally doped single crystal of
Bi_2Sr_2CaCu_2O_{8+\delta}, and Nb. These curves, determined from isofield
magnetization versus temperature measurements and the virial theorem of
superconductivity, probe the order parameter amplitude near the upper critical
field. The striking differences between the Nb and the high-T_c curves clearly
indicate for the latter cases the presence of a unique superconducting
condensate below and above T_c.


title:
Generalized parton distributions from domain wall valence quarks and
  staggered sea quarks

abstract:
  Moments of the generalized parton distributions of the nucleon, calculated
with a mixed action of domain wall valence quarks and asqtad staggered sea
quarks, are presented for pion masses extending down to 359 MeV. Results for
the moments of the unpolarized, helicity, and transversity distributions are
given and compared to the available experimental measurements. Additionally, a
selection of the generalized form factors are shown and the implications for
the spin decomposition and transverse structure of the nucleon are discussed.
Particular emphasis is placed on understanding systematic errors in the lattice
calculation and exploring a variety of chiral extrapolations.


title: Nanosecond electro-optical switching with a repetition rate above 20MHz

abstract:
  We describe an electro-optical switch based on a commercial electro-optic
modulator (modified for high-speed operation) and a 340V pulser having a rise
time of 2.2ns (at 250V). It can produce arbitrary pulse patterns with an
average repetition rate beyond 20MHz. It uses a grounded-grid triode driven by
transmitting power transistors. We discuss variations that enable analog
operation, use the step-recovery effect in bipolar transistors, or offer other
combinations of output voltage, size, and cost.


title: Dynamic Models of Learning and Education Measurement

abstract:
  Pre-post testing is a commonly used method in physics education community for
evaluating students' achievement and or the effectiveness of teaching through a
specific period of instruction. A popular method to analyze pre-post testing
results is the normalized gain first brought to the physics education community
in wide use by R.R. Hake. This paper presents a measurement based probabilistic
model of the dynamic process of learning that explains the experimentally
observed features of the normalized gain. In Hake's study with thousands of
students' pre-post testing results, he observed that on average 48 courses
employing "interactive engagement" types of instruction achieved average
normalized gains about two standard deviations greater than did 14 courses
subjected to traditional instruction. For all courses the average normalized
gains had a very low correlation +0.02 with average pretest scores. This
feature of the normalized gain has allowed researchers to investigate the
effectiveness of instruction using data collected from classes with widely
different average pretest scores. However, the question of why the average
normalized gain has this feature and to what extent this feature is generally
present is not well understood. In addition, there have been debates as to what
the normalized gain actually measures, and concerns that it lacks a probability
framework that undergirds psychometric methods such as Item Response Theory
(IRT). The present model leads to an explanation of the observed features of
the normalized gain, connects to other models such as IRT, and shows that the
normalized gain does have a probability framework but one different from that
emphasized by IRT.


title: Emergent Symmetry and Dimensional Reduction at a Quantum Critical Point

abstract:
  We show that the spatial dimensionality of the quantum critical point
associated with Bose--Einstein condensation at T=0 is reduced when the
underlying lattice comprises a set of layers coupled by a frustrating
interaction. For this purpose, we use an heuristic mean field approach that is
complemented and justified by a more rigorous renormalization group analysis.
Due to the presence of an emergent symmetry, i.e. a symmetry of the ground
state that is absent in the underlying Hamiltonian, a three--dimensional
interacting Bose system undergoes a chemical potential tuned quantum phase
transition that is strictly two dimensional. Our theoretical predictions for
the critical temperature as a function of the chemical potential correspond
very well with recent measurements in BaCuSi$_{2}$O$_{6}$.


title: Entropy of Stars, Black Holes and Dark Energy

abstract:
  When a star collapses to form a black hole, its entropy increases
considerably, for a solar mass black hole, there is a factor of 1019 increase
in entropy. This corresponds to a tremendous loss of information as only the
total mass, angular momentum or electric charge (if any) of the matter going
inside the horizon can be measured by an outside observer. Information about
all other characteristics of the matter becomes irrelevant.