title: Optical vortex coronagraphs on ground-based telescopes

abstract:
  The optical vortex coronagraph is potentially a remarkably effective device,
at least for an ideal unobstructed telescope. Most ground-based telescopes
however suffer from central obscuration and also have to operate through the
aberrations of the turbulent atmosphere. This note analyzes the performance of
the optical vortex in these circumstances and compares to some other designs,
showing that it performs similarly in this situation. There is a large class of
coronagraphs of this general type, and choosing between them in particular
applications depends on details of performance at small off-axis distances and
uniformity of response in the focal plane. Issues of manufacturability to the
necessary tolerances are also likely to be important.


title: Generalised thermostatistics using hyperensembles

abstract:
  The hyperensembles, introduced by Crooks in a context of non-equilibrium
statistical physics, are considered here as a tool for systems in equilibrium.
Simple examples like the ideal gas, the mean-field model, and the Ising
interaction on small square lattices, are worked out to illustrate the
concepts.


title: Transition Phenomena Induced by Internal Noise and Quasi-absorbing State

abstract:
  We study a simple chemical reaction system and effects of the internal noise.
The chemical reaction system causes the same transition phenomenon discussed by
Togashi and Kaneko [Phys. Rev. Lett. 86 (2001) 2459; J. Phys. Soc. Jpn. 72
(2003) 62]. By using the simpler model than Togashi-Kaneko's one, we discuss
the transition phenomenon by means of a random walk model and an effective
model. The discussion makes it clear that quasi-absorbing states, which are
produced by the change of the strength of the internal noise, play an important
role in the transition phenomenon. Stabilizing the quasi-absorbing states
causes bifurcation of the peaks in the stationary probability distribution
discontinuously.


title:
The solution of the Minkowski problem for closed surfaces in Riemannian
  space

abstract:
  Author of this article created for the first time the method for finding
solutions of the Minkowski problem for closed surfaces in Riemannian space.


title:
The effect of partonic wind on charm quark correlations in high-energy
  nuclear collisions

abstract:
  In high-energy collisions, massive heavy quarks are produced back-to-back
initially and they are sensitive to early dynamical conditions. The strong
collective partonic wind from the fast expanding quark-gluon plasma created in
high-energy nuclear collisions modifies the correlation pattern significantly.
As a result, the angular correlation function for D$\bar{\rm D}$ pairs is
suppressed at the angle $\Delta\phi=\pi$. While the hot and dense medium in
collisions at RHIC ($\sqrt{s_{NN}}=200$ GeV) can only smear the initial
back-to-back D$\bar {\rm D}$ correlation, a clear and strong near side
D$\bar{\rm D}$ correlation is expected at LHC ($\sqrt{s_{NN}}=5500$ GeV).


title:
The Christoffel problem and two analogs of the Minkowski problem in
  Riemannian space

abstract:
  Author finds the solutions of the Christoffel problem for open and closed
surfaces in Riemannian space. The Christoffel problem is reduced to the problem
of construction the continuous G-deformations preserving the sum of principal
radii of curvature for every point of surface in Riemannian space.
G-deformation transfers every normal vector of surface in parallel along the
path of the translation for each point of surface. The following analogs of the
Minkowski problem for open and closed surfaces in Riemannian space are being
considered in this article: 1) the problem of construction the surface with
prescribed mean curvature and condition of G-deformation; 2) the problem of
construction the deformations preserving the area of each arbitrary region of
surface and condition of G-deformation.


title: An empirical behavioral model of liquidity and volatility

abstract:
  We develop a behavioral model for liquidity and volatility based on empirical
regularities in trading order flow in the London Stock Exchange. This can be
viewed as a very simple agent based model in which all components of the model
are validated against real data. Our empirical studies of order flow uncover
several interesting regularities in the way trading orders are placed and
cancelled. The resulting simple model of order flow is used to simulate price
formation under a continuous double auction, and the statistical properties of
the resulting simulated sequence of prices are compared to those of real data.
The model is constructed using one stock (AZN) and tested on 24 other stocks.
For low volatility, small tick size stocks (called Group I) the predictions are
very good, but for stocks outside Group I they are not good. For Group I, the
model predicts the correct magnitude and functional form of the distribution of
the volatility and the bid-ask spread, without adjusting any parameters based
on prices. This suggests that at least for Group I stocks, the volatility and
heavy tails of prices are related to market microstructure effects, and
supports the hypothesis that, at least on short time scales, the large
fluctuations of absolute returns are well described by a power law with an
exponent that varies from stock to stock.


title: The Lunar Cherenkov Technique: From Parkes Onwards

abstract:
  The lunar Cherenkov technique, which aims to detect the coherent Cherenkov
radiation produced when UHE particles interact in the lunar regolith, was first
attempted with the Parkes radio-telescope in 1995, though the theory was not
sufficiently developed at this time to calculate a limit on the UHE neutrino
flux from the non-observation. Since then, the technique has evolved to include
experiments utilising lower frequencies, wider bandwidths, and entire arrays of
antenna. We develop a simulation to analyse the full range of experiments, and
calculate the UHE neutrino flux limit from the Parkes experiment, including the
directional dependence. Our results suggest a methodology for planning future
observations, and demonstrate how to utilise all available information on the
nature of radio pulses from the Moon for the detection of UHE particles.


title:
Integral equation for gauge invariant quark two-point Green's function
  in QCD

abstract:
  Gauge invariant quark two-point Green's functions defined with path-ordered
gluon field phase factors along skew-polygonal lines joining the quark to the
antiquark are considered. Functional relations between Green's functions with
different numbers of path segments are established. An integral equation is
obtained for the Green's function defined with a phase factor along a single
straight line. The equation implicates an infinite series of two-point Green's
functions, having an increasing number of path segments; the related kernels
involve Wilson loops with contours corresponding to the skew-polygonal lines of
the accompanying Green's function and with functional derivatives along the
sides of the contours. The series can be viewed as an expansion in terms of the
global number of the functional derivatives of the Wilson loops. The
lowest-order kernel, which involves a Wilson loop with two functional
derivatives, provides the framework for an approximate resolution of the
equation.


title:
Trotter Derivation of Algorithms for Brownian and Dissipative Particle
  Dynamics

abstract:
  This paper focuses on the temporal discretization of the Langevin dynamics,
and on different resulting numerical integration schemes. Using a method based
on the exponentiation of time dependent operators, we carefully derive a
numerical scheme for the Langevin dynamics, that we found equivalent to the
proposal of Ermak, and not simply to the stochastic version of the
velocity-Verlet algorithm. However, we checked on numerical simulations that
both algorithms give similar results, and share the same ``weak order two''
accuracy. We then apply the same strategy to derive and test two numerical
schemes for the dissipative particle dynamics (DPD). The first one of them was
found to compare well, in terms of speed and accuracy, with the best currently
available algorithms.


title: Induced gravity and entanglement entropy of 2D black holes

abstract:
  Using the fact that 2D Newton constant is wholly induced by a conformal field
theory, we derive a formula for the entanglement entropy of the anti-de Sitter
black hole in two spacetime dimensions. The leading term in the large black
hole mass expansion of our formula reproduces exactly the Bekenstein-Hawking
entropy S_{BH}, whereas the subleading term behaves as ln S_{BH}. This
subleading term has the universal form typical for the entanglement entropy of
physical systems described by effective conformal fields theories (e.g.
one-dimensional statistical models at the critical point).


title: Magnetic Ordering of Nuclear Spins in an Interacting 2D Electron Gas

abstract:
  We investigate the magnetic behavior of nuclear spins embedded in a 2D
interacting electron gas using a Kondo lattice model description. We derive an
effective magnetic Hamiltonian for the nuclear spins which is of the RKKY type
and where the interactions between the nuclear spins are strongly modified by
the electron-electron interactions. We show that the nuclear magnetic ordering
at finite temperature relies on the (anomalous) behavior of the 2D static
electron spin susceptibility, and thus provides a connection between
low-dimensional magnetism and non-analyticities in interacting 2D electron
systems. Using various perturbative and non-perturbative approximation schemes
in order to establish the general shape of the electron spin susceptibility as
function of its wave vector, we show that the nuclear spins locally order
ferromagnetically, and that this ordering can become global in certain regimes
of interest. We demonstrate that the associated Curie temperature for the
nuclear system increases with the electron-electron interactions up to the
millikelvin range.


title: Of mice and men: Sparse statistical modeling in cardiovascular genomics

abstract:
  In high-throughput genomics, large-scale designed experiments are becoming
common, and analysis approaches based on highly multivariate regression and
anova concepts are key tools. Shrinkage models of one form or another can
provide comprehensive approaches to the problems of simultaneous inference that
involve implicit multiple comparisons over the many, many parameters
representing effects of design factors and covariates. We use such approaches
here in a study of cardiovascular genomics. The primary experimental context
concerns a carefully designed, and rich, gene expression study focused on
gene-environment interactions, with the goals of identifying genes implicated
in connection with disease states and known risk factors, and in generating
expression signatures as proxies for such risk factors. A coupled exploratory
analysis investigates cross-species extrapolation of gene expression
signatures--how these mouse-model signatures translate to humans. The latter
involves exploration of sparse latent factor analysis of human observational
data and of how it relates to projected risk signatures derived in the animal
models. The study also highlights a range of applied statistical and genomic
data analysis issues, including model specification, computational questions
and model-based correction of experimental artifacts in DNA microarray data.


title:
Constraining Dark Matter hypothesis through Diffuse Source observations
  with the GLAST-LAT detector

abstract:
  The Gamma-Ray Large Area Space Telescope (GLAST), scheduled to be launched in
Fall 2007, is a next generation high energy gamma-ray observatory. The Large
Area Telescope (LAT) instrument on-board GLAST with a wide field of view ($>$ 2
sr), large effective area and 20 MeV to $>$300 GeV energy range, will provide
excellent opportunity for future Dark Matter studies. We present an overview of
the GLAST Dark Matter and New Physics Working Group efforts in the study of the
LAT capability to detect a gamma-ray flux coming from WIMP pair annihilations
in diffuse astrophysical sources. Particular attention will be given to
extragalactic diffuse gamma-ray radiation and line searches from annihilation
into gamma-gamma and/or gamma-Z final states.


title:
Covariant anomaly and Hawking radiation from the modified black hole in
  the rainbow gravity theory

abstract:
  Recently, Banerjee and Kulkarni (R. Banerjee, S. Kulkarni, arXiv:0707.2449
[hep-th]) suggested that it is conceptually clean and economical to use only
the covariant anomaly to derive Hawking radiation from a black hole. Based upon
this simplified formalism, we apply the covariant anomaly cancellation method
to investigate Hawking radiation from a modified Schwarzschild black hole in
the theory of rainbow gravity. Hawking temperature of the gravity's rainbow
black hole is derived from the energy-momentum flux by requiring it to cancel
the covariant gravitational anomaly at the horizon. We stress that this
temperature is exactly the same as that calculated by the method of cancelling
the consistent anomaly.


title: Gravitational waves from 3D MHD core collapse simulations

abstract:
  We present the gravitational wave analysis from rotating (model s15g) and
nearly non-rotating (model s15h) 3D MHD core collapse supernova simulations at
bounce and the first couple of ten milliseconds afterwards. The simulations are
launched from 15M_{\odot} progenitor models stemming from stellar evolution
calculations. Gravity is implemented by a spherically symmetric effective
general relativistic potential. The input physics uses the Lattimer-Swesty
equation of state for hot, dense matter and a neutrino parametrisation scheme
that is accurate until the first few ms after bounce. The 3D simulations allow
us to study features already known from 2D simulations as well as
nonaxisymmetric effects. In agreement with recent results we find only type I
gravitational wave signals at core bounce. In the later stage of the
simulations, one of our models (s15g) shows nonaxisymmetric gravitational wave
emission caused by a low T/|W| dynamical instability, while the other model
radiates gravitational waves due to a convective instability in the
protoneutron star. The total energy released in gravitational waves within the
considered time intervals is 1.52\times10^{-7}M_{\odot} (s15g) and
4.72\times10^{-10}M_{\odot} (s15h). Both core collapse simulations indicate
that corresponding events in our Galaxy would be detectable either by the LIGO
or Advanced LIGO detector.


title:
Quantitative optical and near-infrared spectroscopy of molecular
  hydrogen towards HH91A

abstract:
  Integral-field spectroscopy of molecular hydrogen in the optical wavelength
region and complementary long-slit near-infrared spectroscopy are presented
towards HH91A.The detection of some 200 H_2 lines arising from ro-vibrational
levels up to v'=8 ranging between 7700A and 2.3 microns is reported. The
emission arises from thermally excited gas where the bulk of the material is at
2750 K and where 1% is at 6000 K. The total column density of shocked gas is
N(H_2) = 10^{18} cm^{-2}. Non-thermal excitation scenarios such as
UV-fluorescence do not contribute to the excitation of H_2 towards HH91A. The
emission is explained in terms of a slow non-dissociative J-shock which
propagates into a low-density medium which has been swept-up by previous
episodes of outflows which have occurred in the evolved HH90/91 complex.


title: Untangling a Planar Graph

abstract:
  A straight-line drawing $\delta$ of a planar graph $G$ need not be plane, but
can be made so by \emph{untangling} it, that is, by moving some of the vertices
of $G$. Let shift$(G,\delta)$ denote the minimum number of vertices that need
to be moved to untangle $\delta$. We show that shift$(G,\delta)$ is NP-hard to
compute and to approximate. Our hardness results extend to a version of
\textsc{1BendPointSetEmbeddability}, a well-known graph-drawing problem.
  Further we define fix$(G,\delta)=n-shift(G,\delta)$ to be the maximum number
of vertices of a planar $n$-vertex graph $G$ that can be fixed when untangling
$\delta$. We give an algorithm that fixes at least $\sqrt{((\log n)-1)/\log
\log n}$ vertices when untangling a drawing of an $n$-vertex graph $G$. If $G$
is outerplanar, the same algorithm fixes at least $\sqrt{n/2}$ vertices. On the
other hand we construct, for arbitrarily large $n$, an $n$-vertex planar graph
$G$ and a drawing $\delta_G$ of $G$ with fix$(G,\delta_G) \le \sqrt{n-2}+1$ and
an $n$-vertex outerplanar graph $H$ and a drawing $\delta_H$ of $H$ with
fix$(H,\delta_H) \le 2 \sqrt{n-1}+1$. Thus our algorithm is asymptotically
worst-case optimal for outerplanar graphs.


title: Quark motional effects on the interquark potential in baryons

abstract:
  We study the heavy-heavy-light quark ($QQq$) system in a non-relativistic
potential model, and investigate the quark motional effect on the
inter-two-quark potential in baryons. We adopt the Hamiltonian with the static
three-quark potential which is obtained by the first-principle calculation of
lattice QCD, rather than the two-body force in ordinary quark models. Using the
renormalization-group inspired variational method in discretized space, we
calculate the ground-state energy of $QQq$ systems and the light-quark spatial
distribution. We find that the effective string tension between the two heavy
quarks is reduced compared to the static three-quark case. This reduction of
the effective string tension originates from the geometrical difference between
the inter-quark distance and the flux-tube length, and is conjectured to be a
general property for baryons.


title: Improving the consensus performance via predictive mechanisms

abstract:
  Considering some predictive mechanisms, we show that ultrafast
average-consensus can be achieved in networks of interconnected agents. More
specifically, by predicting the dynamics of the network several steps ahead and
using this information in the design of the consensus protocol of each agent,
drastic improvements can be achieved in terms of the speed of consensus
convergence, without changing the topology of the network. Moreover, using
these predictive mechanisms, the range of sampling periods leading to consensus
convergence is greatly expanded compared with the routine consensus protocol.
This study provides a mathematical basis for the idea that some predictive
mechanisms exist in widely-spread biological swarms, flocks, and networks. From
the industrial engineering point of view, inclusion of an efficient predictive
mechanism allows for a significant increase in the speed of consensus
convergence and also a reduction of the communication energy required to
achieve a predefined consensus performance.


title: \alpha_S from LEP

abstract:
  Recent results on measurements of the strong coupling $\alpha_S$ from LEP are
reported. These include analyses of the 4-jet rate using the Durham or
Cambridge algorithm, of hadronic $Z^0$ decays with hard final state photon
radiation, of scaling violations of the fragmentation function, of the
longitudinal cross section, of the $Z^0$ lineshape and of hadronic $\tau$
lepton decays.


title:
Dark Matter & Dark Energy from a single scalar field: CMB spectrum and
  matter transfer function

abstract:
  The dual axion model (DAM), yielding bot DM and DE form a PQ-like scalar
field solving the strong CP problem, is known to allow a fair fit of CMB data.
Recently, however, it was shown that its transfer function exhibits significant
anomalies, causing difficulties to fit deep galaxy sample data. Here we show
how DAM can be modified to agree with the latter data set. The modification
follows the pattern suggested to reconcile any PQ-like approach with gravity.
Modified DAM allows precise predictions which can be testable against future
CMB and/or deep sample data.


title: Pairings on Jacobians of Hyperelliptic Curves

abstract:
  Consider the jacobian of a hyperelliptic genus two curve defined over a
finite field. Under certain restrictions on the endomorphism ring of the
jacobian we give an explicit description all non-degenerate, bilinear,
anti-symmetric and Galois-invariant pairings on the jacobian. From this
description it follows that no such pairing can be computed more efficiently
than the Weil pairing.
  To establish this result, we need an explicit description of the
representation of the Frobenius endomorphism on the l-torsion subgroup of the
jacobian. This description is given. In particular, we show that if the
characteristic polynomial of the Frobenius endomorphism splits into linear
factors modulo l, then the Frobenius is diagonalizable.
  Finally, under the restriction that the Frobenius element is an element of a
certain subring of the endomorphism ring, we prove that if the characteristic
polynomial of the Frobenius endomorphism splits into linear factors modulo l,
then the embedding degree and the total embedding degree of the jacobian with
respect to l are the same number.


title: Representations of orbifold groupoids

abstract:
  Orbifold groupoids have been recently widely used to represent both effective
and ineffective orbifolds. We show that every orbifold groupoid can be
faithfully represented on a continuous family of finite dimensional Hilbert
spaces. As a consequence we obtain the result that every orbifold groupoid is
Morita equivalent to the translation groupoid of an action of a bundle of
compact topological groups.


title: Star Formation in Bulges from GALEX

abstract:
  Early-type galaxies, considered as large bulges, have been found to have had
a much-more-than-boring star formation history in recent years by the UV
satellite GALEX. The most massive bulges, brightest cluster galaxies, appear to
be relatively free of young stars. But smaller bulges, normal ellipticals and
lenticulars, often show unambiguous sign of recent star formation in their UV
flux. The fraction of such UV-bright bulges in the volume-limited sample climbs
up to the staggering 30%. The bulges of spirals follow similar trends but a
larger fraction showing signs of current and recent star formation. The
implication on the bulge formation and evolution is discussed.


title: Effective Generation of Subjectively Random Binary Sequences

abstract:
  We present an algorithm for effectively generating binary sequences which
would be rated by people as highly likely to have been generated by a random
process, such as flipping a fair coin.


title:
The intrinsic degree of freedom for quasiparticle in thermodynamics with
  medium effects

abstract:
  The thermodynamics with medium effects expressed by the temperature- and
density-dependent effective mass of quasiparticle is studied. Series
difficulties and many wrangles in references due to the extraordinary parameter
dependence are addressed. A new independent intrinsic degree of freedom of
quasiparticle $m^*$ in the equation of reversible process is introduced to
clear the ambiguity. We prove all results are self-consistent.


title:
Harmonic oscillator chains as Wigner Quantum Systems: periodic and fixed
  wall boundary conditions in gl(1|n) solutions

abstract:
  We describe a quantum system consisting of a one-dimensional linear chain of
n identical harmonic oscillators coupled by a nearest neighbor interaction. Two
boundary conditions are taken into account: periodic boundary conditions (where
the nth oscillator is coupled back to the first oscillator) and fixed wall
boundary conditions (where the first oscillator and the $n$th oscillator are
coupled to a fixed wall). The two systems are characterized by their
Hamiltonian. For their quantization, we treat these systems as Wigner Quantum
Systems (WQS), allowing more solutions than just the canonical quantization
solution. In this WQS approach, one is led to certain algebraic relations for
operators (which are linear combinations of position and momentum operators)
that should satisfy triple relations involving commutators and
anti-commutators. These triple relations have a solution in terms of the Lie
superalgebra gl(1|n). We study a particular class of gl(1|n) representations
V(p), the so-called ladder representations. For these representations, we
determine the spectrum of the Hamiltonian and of the position operators (for
both types of boundary conditions). Furthermore, we compute the eigenvectors of
the position operators in terms of stationary states. This leads to explicit
expressions for position probabilities of the n oscillators in the chain. An
analysis of the plots of such position probability distributions gives rise to
some interesting observations. In particular, the physical behavior of the
system as a WQS is very much in agreement with what one would expect from the
classical case, except that all physical quantities (energy, position and
momentum of each oscillator) have a finite spectrum.


title:
The Nature of the Ultraluminous Oxygen-Rich Supernova Remnant in NGC
  4449

abstract:
  Optical images and spectra, both ground based and taken by Hubble Space
Telescope (HST), of the young, luminous O-rich supernova remnant in the
irregular galaxy NGC 4449 are presented. HST images of the remnant and its
local region were obtained with the ACS/WFC using filters F435W, F555W, F814W
(B, V, and I, respectively), F502N ([O III]), F658N (Halpha + [N II]), F660N
([N II]), and F550M (line-free continuum). These images show an unresolved
remnant (FWHM < 0.05 arcsec) located within a rich cluster of OB stars which
itself is enclosed by a nearly complete interstellar shell seen best in Halpha
+ [N II] emission approximately 8'' x 6'' (150 pc x 110 pc) in size. The
remnant and its associated OB cluster are isolated from two large nearby H II
regions. The ACS [O III] image shows the remnant may be partially surrounded by
a clumpy ring of emission approximately 1'' (~20 pc) in diameter. Recent
ground-based spectra of the remnant reveal (1) the emergence of broad,
blueshifted emission lines of [S II] 6716, 6731, [Ar III] 7136, and [Ca II]
7291, 7324 which were not observed in spectra taken in 1978 -- 1980; (2) faint
emission at 6540 -- 6605 A centered about Halpha and [N II] 6548, 6583 with an
expansion velocity of 500 +/- 100 km/s; and (3) excess emission around 4600 --
4700 A suggestive of a Wolf-Rayet population in the remnant's star cluster. We
use these new data to re-interpret the origin of the remnant's prolonged and
bright luminosity and propose that the remnant is strongly interacting with
dense, circumstellar wind loss material from a ~20 Msolar progenitor star.


title:
Bell-state preparation for electron spins in a semiconductor double
  quantum dot

abstract:
  A robust scheme for state preparation and state trapping for the spins of two
electrons in a semiconductor double quantum dot is presented. The system is
modeled by two spins coupled to two independent bosonic reservoirs. Decoherence
effects due to this environment are minimized by application of optimized
control fields which make the target state to the ground state of the isolated
driven spin system. We show that stable spin entanglement with respect to pure
dephasing is possible. Specifically, we demonstrate state trapping in a
maximally entangled state (Bell state) in the presence of decoherence.


title: The Formation of Slow-Massive-Wide Jets

abstract:
  I propose a model for the formation of slow-massive-wide (SMW) jets by
accretion disks around compact objects. This study is motivated by claims for
the existence of SMW jets in some astrophysical objects such as in planetary
nebulae (PNs) and in some active galactic nuclei in galaxies and in cooling
flow clusters. In this model the energy still comes from accretion onto a
compact object. The accretion disk launches two opposite jets with velocity of
the order of the escape velocity from the accreting object and with mass
outflow rate of ~1-20% of the accretion rate as in most popular models for jet
launching; in the present model these are termed fast-first-stage (FFS) jets.
However, the FFS jets encounter surrounding gas that originates in the mass
accretion process, and are terminated by strong shocks close to their origin.
Two hot bubbles are formed. These bubbles accelerate the surrounding gas to
form two SMW jets that are more massive and slower than the FFS jets. There are
two conditions for this mechanism to work. Firstly, the surrounding gas should
be massive enough to block the free expansion of the FFS jets. Most efficiently
this condition is achieved when the surrounding gas is replenished. Secondly,
the radiative energy losses must be small.


title: Nahm's equations and free-boundary problems

abstract:
  This paper is a discussion of relations between some free-boundary problems
and infinite dimensional Lie groups; particularly a version of Nahm's equations
for the group of Hamiltonian diffeomorphisms in two dimensions.


title: Some remarks about Cauchy integrals and fractal sets

abstract:
  Some aspects of Cauchy integrals on sets with dimension larger than 1 are
briefly discussed.


title: A canonical Frobenius structure

abstract:
  We show that it makes sense to speak of THE Frobenius manifold attached to a
convenient and nondegenerate Laurent polynomial


title: X-rays profiles in symmetric and asymmetric supernova remnants

abstract:
  The non-thermal X-rays from the SN 1006 NE rim present characteristic scale
lengths that are interpreted in the context of diffusion of a relativistic
electron. The adopted theoretical framework is the mathematical diffusion in
3D, 1D and 1D with drift as well as the Monte Carlo random walk in 1D with
drift. The asymmetric random walk with diffusion from a plane can explain the
scale widths of 0.04 pc upstream and 0.2 pc downstream in the non thermal
intensity of X-ray emission in SN 1006. A mathematical image of the non thermal
X-flux from an supernova remnant as well as profiles function of the distance
from the center can be simulated. This model provides a reasonable description
of both the limbs and the central region of SN 1006. A new method to deduce the
magnetic field in supernova remnant is suggested.


title:
Finite-dimensional modules for the polynomial ring in one variable as a
  vertex algebra

abstract:
  A commutative associative algebra $A$ over ${\mathbb C}$ with a derivation is
one of the simplest examples of a vertex algebra. However, the differences
between the modules for $A$ as a vertex algebra and the modules for $A$ as an
associative algebra are not well understood.
  In this paper, I give the classification of finite-dimensional indecomposable
untwisted or twisted modules for the polynomial ring in one variable over
${\mathbb C}$ as a vertex algebra.


title: Crossed ratchet effects for magnetic domain wall motion

abstract:
  We study both experimentally and theoretically the driven motion of domain
walls in extended amorphous magnetic films patterned with a periodic array of
asymmetric holes. We find two crossed ratchet effects of opposite sign that
change the preferred sense for domain wall propagation, depending on whether a
flat or a kinked wall is moving. By solving numerically a simple $\phi^4$-model
we show that the essential physical ingredients for this effect are quite
generic and could be realized in other experimental systems involving elastic
interfaces moving in multidimensional ratchet potentials.


title: A complex environment around Cir X-1

abstract:
  We present the results of an archival 54 ks long Chandra observation of the
peculiar source Cir X--1 during the phase passage 0.223-0.261. A comparative
analysis of X-ray spectra, selected at different flux levels of the source,
allows us to distinguish between a very hard state, at a low countrate, and a
brighter, softer, highly absorbed spectrum during episodes of flaring activity,
when the unabsorbed source luminosity is about three times the value in the
hard state. The spectrum of the hard state clearly shows emission lines of
highly ionized elements, while, during the flaring state, the spectrum also
shows strong resonant absorption lines. The most intense and interesting
feature in this latter state is present in the Fe K alpha region: a very
broadened absorption line at energies ~ 6.5 keV that could result from a
smeared blending of resonant absorption lines of moderately ionized iron ions
(Fe XX - Fe XXIV). We also observe strong resonant absorption lines of Fe XXV
and Fe XXVI, together with a smeared absorption edge above 7 keV. We argue that
the emitting region during the quiescent/hard state is constituted of a purely
photo-ionized medium, possibly present above an accretion disk, or of a
photo-ionized plasma present in a beamed outflow. During the flaring states the
source undergoes enhanced turbulent accretion that modifies both the accretion
geometry and the optical depth of the gas surrounding the primary X-ray source.


title: Including heavy flavour production in PDF fits

abstract:
  AT HERA heavy quarks may contribute up to 30% of the structure function
$F_2$. The introduction of heavy quarks requires an extension of the DGLAP
formalism. The effect of using different heavy flavour number schemes, and
different approaches to the running of $\alpha_s$, are compared using the ZEUS
PDF fit formalism. The potential of including charm data in the fit is
explored, using $D^*$ double differential cross-sections rather than the
inclusive quantity $F_2^{c\bar{c}}$.


title: The Atomic hypothesis: Physical consequences

abstract:
  The hypothesis that matter is made of some ultimate and indivisible objects,
together the restricted relativity principle, establishes a constraint on the
kind of variables we are allowed to use for the variational description of
elementary particles. We consider that the atomic hypothesis not only states
the indivisibility of elementary particles, but also that these ultimate
objects, if not annihilated, cannot be modified by any interaction so that all
allowed states of an elementary particle are only kinematical modifications of
any one of them. Terefore, an elementary particle cannot have excited states.
In this way, the kinematical group of spacetime symmetries not only defines the
symmetries of the system, but also the variables in terms of which the
mathematical description of the elementary particles can be expressed in either
the classical or the quantum mechanical description. When considering the
interaction of two Dirac particles, the atomic hypothesis restricts the
interaction Lagrangian to a kind of minimal coupling interaction.


title:
Diamagnetism around the Meissner transition in a homogeneous cuprate
  single crystal

abstract:
  The in-plane diamagnetism around the Meissner transition was measured in a
Tl$_2$Ba$_2$Ca$_2$Cu$_3$O$_{10}$ single crystal of high chemical and structural
quality, which minimizes the inhomogeneity and disorder rounding effects on the
magnetization. When analyzed quantitatively and consistently above and below
the transition in terms of the Ginzburg-Landau (GL) approach with fluctuations
of Cooper pairs and vortices, these data provide a further confirmation that
the observed Meissner transition is a conventional GL superconducting
transition in a homogeneous layered superconductor.


title: Gradings on $o(8,\mathbb C)$

abstract:
  This is a matricial description of all the fine group gradings on the
exceptional Lie algebra $o(8,\mathbb C)$. There are fourteen.


title: On generically stable types in dependent theories

abstract:
  We develop the theory of generically stable types, independence relation
based on nonforking and stable weight in the context of dependent (NIP)
theories.


title:
Structure-Dependent Fluorescence Efficiencies of Individual
  Single-Walled Carbon Nanotubes

abstract:
  Single-nanotube photometry was used to measure the product of absorption
cross-section and fluorescence quantum yield for 12 (n,m) structural species of
semiconducting SWNTs in aqueous SDBS suspension. These products ranged from 1.7
to 4.5 x 10(-19) cm2/C atom, generally increasing with optical band gap as
described by the energy gap law. The findings suggest fluorescent quantum
yields of ~8% for the brightest, (10,2) species and introduce the empirical
calibration factors needed to deduce quantitative (n,m) distributions from bulk
fluorimetric intensities.


title: Convective and non-convective mixing in AGB stars

abstract:
  We review the current state of modeling convective mixing in AGB stars. The
focus is on results obtained through multi-dimensional hydrodynamic simulations
of AGB convection, both in the envelope and the unstable He-shell. Using two
different codes and a wide range of resolutions and modeling assumptions we
find that mixing across convective boundaries is significant for He-shell flash
convection. We present a preliminary quantitative analysis of this convectively
induced extra mixing, based on a sub-set of our simulations. Other non-standard
mixing will be discussed briefly.


title: The host galaxy of GRB031203: a new spectroscopic study

abstract:
  The host galaxy of the long-duration gamma-ray burst (GRB) 031203 (HG031203)
offers a precious opportunity to study in detail the environment of a nearby
GRB. The aim is to better characterize this galaxy and analyse the possible
evolution with time of the spectroscopic quantities we derive. We analyse
HG031203 using a set of optical spectra acquired with the ESO-VLT and Keck
telescope. We compare the metallicity, luminosity and star formation properties
of this galaxy and of the other supernova-long gamma-ray burst hosts in the
local universe (z<0.2) against the KPNO International Spectroscopic Survey.
HG031203 is a metal poor, actively star forming galaxy (star formation rate of
12.9+/-2.2 {M_{sun} yr^-1) at z=0.1054. From the emission-line analysis we
derive an intrinsic reddening E_{HG}(B-V)\approx 0.4. This parameter doesn't
show a compelling evidence of evolution at a month time-scale. We find an
interstellar medium temperature of 12500 K and an electronic density of
N_{e}=160 cm^-3. After investigating for possible Wolf-Rayet emission features
in our spectra, we consider dubious the classification of HG031203 as a
Wolf-Rayet galaxy. Long gamma-ray burst (LGRB) and supernova hosts in the local
universe (z<0.2) show, on average, specific star formation rates higher than
ordinary star forming galaxy at the same redshift. On the other hand, we find
that half of the hosts follows the metallicity-luminosity relation found for
star-burst galaxies; HG031203 is a clear outlier, with its really low
metallicity (12+\log{{O/H}}=8.12+/-0.04).


title: No de Sitter invariant vacuum in massive gravity theory with ghost

abstract:
  In this letter we point out that the massive gravity theory with a graviton
ghost mode in de Sitter background cannot possess a de Sitter invariant vacuum
state. In order to avoid a negative norm state, we must associate the creation
operator of the ghost mode with a negative-energy mode function instead of a
positive-energy one as the mode function. Namely, we have to adopt a different
procedure of quantization for a ghost. When a theory has a symmetry mixing a
ghost mode with ordinary non-ghost modes, the choice of a ghost mode is not
unique. However, quantization of a ghost is impossible without specifying a
choice of ghost mode, which breaks the symmetry. For this reason, the vacuum
state cannot respect the symmetry. In the massive gravity theory with a
graviton ghost mode in de Sitter background, the ghost is the helicity-0 mode
of the graviton. This ghost mode is mixed with the other helicity graviton
modes under the action of de Sitter symmetry. Therefore, there is no de Sitter
invariant vacuum in such models. This leads to an interesting possibility that
non-covariant cutoff of the low energy effective theory may naturally arise. As
a result, the instability due to the pair production of a ghost and normal
non-ghost particles gets much milder and that the model may escape from being
rejected.


title: Confinement encoded in Landau gauge gluon and ghost propagators

abstract:
  An introduction is given into current lattice investigations of the
non-perturbative gluon and ghost propagators, in the light of the
Gribov-Zwanziger and Kugo-Ojima scenarios of confinement, in the context of
results obtained from the non-perturbative Dyson-Schwinger approach in the
continuum and in connection with the vortex mechanism of confinement.


title:
Lane-formation vs. cluster-formation in two dimensional square-shoulder
  systems: A genetic algorithm approach

abstract:
  Introducing genetic algorithms as a reliable and efficient tool to find
ordered equilibrium structures, we predict minimum energy configurations of the
square shoulder system for different values of corona width $\lambda$. Varying
systematically the pressure for different values of $\lambda$ we obtain
complete sequences of minimum energy configurations which provide a deeper
understanding of the system's strategies to arrange particles in an
energetically optimized fashion, leading to the competing self-assembly
scenarios of cluster-formation vs. lane-formation.


title: Can very massive stars avoid Pair-instability Supernovae?

abstract:
  Very massive primordial stars ($140 M_{\odot} < M < 260 M_{\odot}$) are
supposed to end their lives as pair-instability supernovae. Such an event can
be traced by a typical chemical signature in low metallicity stars, but at the
present time, this signature is lacking in the extremely metal-poor stars we
are able to observe. Does it mean that those very massive objects did not form,
contrarily to the primordial star formation scenarios? Could they avoid this
tragical fate?
  We explore the effects of rotation, anisotropic mass loss and magnetic fields
on the core size of a very massive Population III model, in order to check if
its mass is sufficiently modified to prevent the pair instability.
  We obtain that a Population III model of $150 M_{\odot}$ with
$\upsilon/\upsilon_{\rm crit}=0.56$ computed with the inclusion of wind
anisotropy and Tayler-Spruit dynamo avoids the pair instability explosion.


title:
Enhancement of polarization in a spin-orbit coupling quantum wire with a
  constriction

abstract:
  We investigate the enhancement of spin polarization in a quantum wire in the
presence of a constriction and a spin-orbit coupling segment. It is shown that
the spin-filtering effect is significantly heightened in comparison with the
configuration without the constriction. It is understood in the studies that
the constriction structure plays a critical role in enhancing the spin
filtering by means of confining the incident electrons to occupy one channel
only while the outgoing electrons occupy two channels. The enhancement of
spin-filtering has also been analyzed within the perturbation theory. Because
the spin polarization arises mainly from the scattering between the
constriction and the segment with spin-orbit coupling, the sub-band mixing
induced by spin-orbit interaction in the scattering process and the
interferences result in higher spin-filtering effect.


title:
Capacity constraints and the inevitability of mediators in adword
  auctions

abstract:
  One natural constraint in the sponsored search advertising framework arises
from the fact that there is a limit on the number of available slots,
especially for the popular keywords, and as a result, a significant pool of
advertisers are left out. We study the emergence of diversification in the
adword market triggered by such capacity constraints in the sense that new
market mechanisms, as well as, new for-profit agents are likely to emerge to
combat or to make profit from the opportunities created by shortages in
ad-space inventory. We propose a model where the additional capacity is
provided by for-profit agents (or, mediators), who compete for slots in the
original auction, draw traffic, and run their own sub-auctions. The quality of
the additional capacity provided by a mediator is measured by its {\it fitness}
factor. We compute revenues and payoffs for all the different parties at a {\it
symmetric Nash equilibrium} (SNE) when the mediator-based model is operated by
a mechanism currently being used by Google and Yahoo!, and then compare these
numbers with those obtained at a corresponding SNE for the same mechanism, but
without any mediators involved in the auctions. Such calculations allow us to
determine the value of the additional capacity. Our results show that the
revenue of the auctioneer, as well as the social value (i.e. efficiency),
always increase when mediators are involved; moreover even the payoffs of {\em
all} the bidders will increase if the mediator has a high enough fitness. Thus,
our analysis indicates that there are significant opportunities for
diversification in the internet economy and we should expect it to continue to
develop richer structure, with room for different types of agents and
mechanisms to coexist.


title: Kaehlerian reduction in steps

abstract:
  We study Hamiltonian actions of compact Lie groups K on Kaehler manifolds
which extend to a holomorphic action of the complexified group K^C. For a
closed normal subgroup L of K we show that the Kaehlerian reduction with
respect to L is a stratified Hamiltonian Kaehler K^C/L^C-space whose Kaehlerian
reduction with respect to K/L is naturally isomorphic to the Kaehlerian
reduction of the original manifold with respect to K.


title:
Establishing the Uniqueness of the Connection between SdS_5 and
  Conformally Invariant Relativistic Systems: A Group/Field Theoretical
  Approach

abstract:
  Adopting as working assumption that the conformal group O(4,2) of Minkowski
space, being the largest symmetry group which respects its light cone
structure, is the appropriate global symmetry underlying the description of
relativistic systems, it is shown that AdS$_5$ uniquely emerges as the space on
the boundary of which a corresponding relativistic field system should be
accommodated. The basic mathematical tools employed for establishing this
result are (a) Cartan's theory of spinors and (b) group contraction methods.
Extending our considerations to supersymmetry it is demostrated how an $N$=1
SUSY YM field system can emerge as a broken version of an $N$=4 SUSY YM field
system. An especially important feature of the presentation is the `unearthing'
of seminal, independent from each other, works of I. Segal and of S. Fubini
which give a purely field theoretical perspective on the intimate relation
between conformally invariant relativistic field theories and AdS$_5$
including, in particular, the warping phenomenon.


title: Modular intersection cohomology complexes on flag varieties

abstract:
  We present a combinatorial procedure (based on the W-graph of the Coxeter
group) which shows that the characters of many intersection cohomology
complexes on low rank complex flag varieties with coefficients in an arbitrary
field are given by Kazhdan-Lusztig basis elements. Our procedure exploits the
existence and uniqueness of parity sheaves. In particular we are able to show
that the characters of all intersection cohomology complexes with coefficients
in a field on the flag variety of type A_n for n < 7 are given by
Kazhdan-Lusztig basis elements. By results of Soergel, this implies a part of
Lusztig's conjecture for SL(n) with n \le 7. We also give examples where our
techniques fail.
  In the appendix by Tom Braden examples are given of intersection cohomology
complexes on the flag varities for SL(8) and SO(8) which have torsion in their
stalks or costalks.


title: Three regularization models of the Navier-Stokes equations

abstract:
  We determine how the differences in the treatment of the subfilter-scale
physics affect the properties of the flow for three closely related
regularizations of Navier-Stokes. The consequences on the applicability of the
regularizations as SGS models are also shown by examining their effects on
superfilter-scale properties. Numerical solutions of the Clark-alpha model are
compared to two previously employed regularizations, LANS-alpha and Leray-alpha
(at Re ~ 3300, Taylor Re ~ 790) and to a DNS. We derive the Karman-Howarth
equation for both the Clark-alpha and Leray-alpha models. We confirm one of two
possible scalings resulting from this equation for Clark as well as its
associated k^(-1) energy spectrum. At sub-filter scales, Clark-alpha possesses
similar total dissipation and characteristic time to reach a statistical
turbulent steady-state as Navier-Stokes, but exhibits greater intermittency. As
a SGS model, Clark reproduces the energy spectrum and intermittency properties
of the DNS. For the Leray model, increasing the filter width decreases the
nonlinearity and the effective Re is substantially decreased. Even for the
smallest value of alpha studied, Leray-alpha was inadequate as a SGS model. The
LANS energy spectrum k^1, consistent with its so-called "rigid bodies,"
precludes a reproduction of the large-scale energy spectrum of the DNS at high
Re while achieving a large reduction in resolution. However, that this same
feature reduces its intermittency compared to Clark-alpha (which shares a
similar Karman-Howarth equation). Clark is found to be the best approximation
for reproducing the total dissipation rate and the energy spectrum at scales
larger than alpha, whereas high-order intermittency properties for larger
values of alpha are best reproduced by LANS-alpha.


title:
Resolving the complex structure of the dust torus in the active nucleus
  of the Circinus galaxy

abstract:
  To test the dust torus model for active galactic nuclei directly, we study
the extent and morphology of the nuclear dust distribution in the Circinus
galaxy using high resolution interferometric observations in the mid-infrared
with the MIDI instrument at the Very Large Telescope Interferometer. We find
that the dust distribution in the nucleus of Circinus can be explained by two
components, a dense and warm disk-like component of 0.4 pc size and a slightly
cooler, geometrically thick torus component with a size of 2.0 pc. The disk
component is oriented perpendicular to the ionisation cone and outflow and
seems to show the silicate feature at 10 micron in emission. It coincides with
a nuclear maser disk in orientation and size. From the energy needed to heat
the dust, we infer a luminosity of the accretion disk corresponding to 20% of
the Eddington luminosity of the nuclear black hole. We find that the
interferometric data are inconsistent with a simple, smooth and axisymmetric
dust emission. The irregular behaviour of the visibilities and the shallow
decrease of the dust temperature with radius provide strong evidence for a
clumpy or filamentary dust structure. We see no evidence for dust reprocessing,
as the silicate absorption profile is consistent with that of standard galactic
dust. We argue that the collimation of the ionising radiation must originate in
the geometrically thick torus component. Our findings confirm the presence of a
geometrically thick, torus-like dust distribution in the nucleus of Circinus,
as required in unified schemes of Seyfert galaxies. Several aspects of our data
require that this torus is irregular, or "clumpy".


title: $\eta'$ production in proton-proton collisions far from the threshold

abstract:
  I discuss exclusive production of the $\eta'$ meson in the $pp \to p\eta'p$
reaction far from the threshold. The contribution of diffractive component as
well as that for $\gamma^* \gamma^* \to \eta'$ fusion are calculated. In the
first case the formalism of unintegrated gluon distribution functions (UGDF) is
used. The distributions in the Feynman $x_F$ (or rapidity), transferred
four-momenta squared between initial and final protons ($t_1$, $t_2$) and
azimuthal angle difference between outgoing protons ($\Phi$) are calculated.
The deviations from the $\sin^2(\Phi)$ dependence predicted by one-step
vector-vector-pseudoscalar coupling are quantified and discussed. The results
are compared with the results of the WA102 collaboration at CERN. Most of the
models of UGDF from the literature give too small cross section as compared to
the WA102 data and predict angular distribution in relative azimuthal angle
strongly asymmetric with respect to $\pi/2$ in disagreement with the WA102
data. This points to a different mechanism at the WA102 energy. Predictions for
RHIC, Tevatron and LHC are given.


title: Relativistic dynamical friction in a collisional fluid

abstract:
  The dynamical friction force experienced by a body moving at relativistic
speed in a gaseous medium is examined. This force, which arises due to the
gravitational interaction of the body with its own gravitationally-induced
wake, is calculated for straight-line and circular motion, generalizing
previous results by several authors. Possible applications to the study of
extreme mass-ratio inspirals around strongly-accreting supermassive black holes
are suggested.


title:
Non-critically squeezed light via spontaneous rotational symmetry
  breaking

abstract:
  We theoretically address squeezed light generation through the spontaneous
breaking of the rotational invariance occuring in a type I degenerate optical
parametric oscillator (DOPO) pumped above threshold. We show that a DOPO with
spherical mirrors, in which the signal and idler fields correspond to first
order Laguerre-Gauss modes, produces a perfectly squeezed vacuum with the shape
of a Hermite-Gauss mode, within the linearized theory. This occurs at any
pumping level above threshold, hence the phenomenon is non-critical.
Imperfections of the rotational symmetry, due e.g. to cavity anisotropy, are
shown to have a small impact, hence the result is not singular.


title:
On the discrete spectrum of spin-orbit Hamiltonians with singular
  interactions

abstract:
  We give a variational proof of the existence of infinitely many bound states
below the continuous spectrum for spin-orbit Hamiltonians (including the Rashba
and Dresselhaus cases) perturbed by measure potentials thus extending the
results of J.Bruening, V.Geyler, K.Pankrashkin: J. Phys. A 40 (2007)
F113--F117.


title: Thermal Evolution of Strange Stars

abstract:
  We investigated the thermal evolution of rotating strange stars with the
deconfinement heating due to magnetic braking. We consider the stars consisting
of either normal quark matter or color-flavor-locked phase. Combining
deconfinement heating with magnetic field decay, we find that the thermal
evolution curves are identical to pulsar data.


title:
Energetic radiation and the sulfur chemistry of protostellar envelopes:
  Submillimeter interferometry of AFGL 2591

abstract:
  CONTEXT: The chemistry in the inner few thousand AU of accreting envelopes
around young stellar objects is predicted to vary greatly with far-UV and X-ray
irradiation by the central star. Aim We search for molecular tracers of
high-energy irradiation by the protostar in the hot inner envelope. METHODS:
The Submillimeter Array (SMA) has observed the high-mass star forming region
AFGL 2591 in lines of CS, SO, HCN, HCN(v2=1), and HC15N with 0.6" resolution at
350 GHz probing radial scales of 600-3500 AU for an assumed distance of 1 kpc.
The SMA observations are compared with the predictions of a chemical model
fitted to previous single-dish observations. RESULTS: The CS and SO main peaks
are extended in space at the FWHM level, as predicted in the model assuming
protostellar X-rays. However, the main peak sizes are found smaller than
modeled by nearly a factor of 2. On the other hand, the lines of CS, HCN, and
HC15N, but not SO and HCN(v2=1), show pedestal emissions at radii of about 3500
AU that are not predicted. All lines except SO show a secondary peak within the
approaching outflow cone. A dip or null in the visibilities caused by a sharp
decrease in abundance with increasing radius is not observed in CS and only
tentatively in SO. CONCLUSIONS: The emission of protostellar X-rays is
supported by the good fit of the modeled SO and CS amplitude visibilities
including an extended main peak in CS. The broad pedestals can be interpreted
by far-UV irradiation in a spherically non-symmetric geometry, possibly
comprising outflow walls on scales of 3500 -- 7000 AU. The extended CS and SO
main peaks suggest sulfur evaporation near the 100 K temperature radius.


title:
Heart - Shaped Nuclei: Condensation of Rotational Aligned Octupole
  Phonons

abstract:
  The strong octupole correlations in the mass region $A\approx 226$ are
interpreted as rotation-induced condensation of octupole phonons having their
angular momentum aligned with the rotational axis. Discrete phonon energy and
parity conservation generate oscillations of the energy difference between the
lowest rotational bands with positive and negative parity. Anharmonicities tend
to synchronize the the rotation of the condensate and the quadrupole shape of
the nucleus forming a rotating heart shape.


title:
Mobility promotes and jeopardizes biodiversity in rock-paper-scissors
  games

abstract:
  Biodiversity is essential to the viability of ecological systems. Species
diversity in ecosystems is promoted by cyclic, non-hierarchical interactions
among competing populations. Such non-transitive relations lead to an evolution
with central features represented by the `rock-paper-scissors' game, where rock
crushes scissors, scissors cut paper, and paper wraps rock. In combination with
spatial dispersal of static populations, this type of competition results in
the stable coexistence of all species and the long-term maintenance of
biodiversity. However, population mobility is a central feature of real
ecosystems: animals migrate, bacteria run and tumble. Here, we observe a
critical influence of mobility on species diversity. When mobility exceeds a
certain value, biodiversity is jeopardized and lost. In contrast, below this
critical threshold all subpopulations coexist and an entanglement of travelling
spiral waves forms in the course of temporal evolution. We establish that this
phenomenon is robust, it does not depend on the details of cyclic competition
or spatial environment. These findings have important implications for
maintenance and evolution of ecological systems and are relevant for the
formation and propagation of patterns in excitable media, such as chemical
kinetics or epidemic outbreaks.


title: Inferring Neuronal Network Connectivity using Time-constrained Episodes

abstract:
  Discovering frequent episodes in event sequences is an interesting data
mining task. In this paper, we argue that this framework is very effective for
analyzing multi-neuronal spike train data. Analyzing spike train data is an
important problem in neuroscience though there are no data mining approaches
reported for this. Motivated by this application, we introduce different
temporal constraints on the occurrences of episodes. We present algorithms for
discovering frequent episodes under temporal constraints. Through simulations,
we show that our method is very effective for analyzing spike train data for
unearthing underlying connectivity patterns.


title: Complex-space singularities of 2D Euler flow in Lagrangian coordinates

abstract:
  We show that, for two-dimensional space-periodic incompressible flow, the
solution can be evaluated numerically in Lagrangian coordinates with the same
accuracy achieved in standard Eulerian spectral methods. This allows the
determination of complex-space Lagrangian singularities. Lagrangian
singularities are found to be closer to the real domain than Eulerian
singularities and seem to correspond to fluid particles which escape to
(complex) infinity by the current time. Various mathematical conjectures
regarding Eulerian/Lagrangian singularities are presented.


title:
The influence of out-of-plane disorder on the formation of pseudogap and
  Fermi arc in Bi2Sr2-xRxCuOy (R=La and Eu)

abstract:
  We found that the length of the Fermi arc decreases with increasing
out-of-plane disorder by performing angle resolved photoemission spectroscopy
(ARPES) measurements in the superconducting state of optimally doped R=La and
Eu samples of Bi2Sr2−xRxCuOy. Since out-of-plane disorder stabilizes the
antinodal pseudogap as was shown in our previous study of the normal state, the
present results indicate that this antinodal pseudogap persists into the
superconducting state and decreases the Fermi arc length. We think that the
shrinkage of the Fermi arc reduces the superfluid density, which explains the
large suppression of the superconducting transition temperature when
out-of-plane disorder is increased.


title:
Scanning the Landscape of Flux Compactifications: Vacuum Structure and
  Soft Supersymmetry Breaking

abstract:
  We scan the landscape of flux compactifications for the Calabi-Yau manifold
$\mathbb{P}^4_{[1,1,1,6,9]}$ with two K\" ahler moduli by varying the value of
the flux superpotential $W_0$ over a large range of values. We do not include
uplift terms. We find a rich phase structure of AdS and dS vacua. Starting with
$W_0\sim 1$ we reproduce the exponentially large volume scenario, but as $W_0$
is reduced new classes of minima appear. One of them corresponds to the
supersymmetric KKLT vacuum while the other is a new, deeper non-supersymmetric
minimum. We study how the bare cosmological constant and the soft supersymmetry
breaking parameters for matter on D7 branes depend on $W_0$, for these classes
of minima. We discuss potential applications of our results.


title: Large-eddy simulation of the flow in a lid-driven cubical cavity

abstract:
  Large-eddy simulations of the turbulent flow in a lid-driven cubical cavity
have been carried out at a Reynolds number of 12000 using spectral element
methods. Two distinct subgrid-scales models, namely a dynamic Smagorinsky model
and a dynamic mixed model, have been both implemented and used to perform
long-lasting simulations required by the relevant time scales of the flow. All
filtering levels make use of explicit filters applied in the physical space (on
an element-by-element approach) and spectral (modal) spaces. The two
subgrid-scales models are validated and compared to available experimental and
numerical reference results, showing very good agreement. Specific features of
lid-driven cavity flow in the turbulent regime, such as inhomogeneity of
turbulence, turbulence production near the downstream corner eddy, small-scales
localization and helical properties are investigated and discussed in the
large-eddy simulation framework. Time histories of quantities such as the total
energy, total turbulent kinetic energy or helicity exhibit different evolutions
but only after a relatively long transient period. However, the average values
remain extremely close.


title: Brief encounter networks

abstract:
  Many complex human and natural phenomena can usefully be represented as
networks describing the relationships between individuals. While these
relationships are typically intermittent, previous research has used network
representations that aggregate the relationships at discrete intervals.
However, such an aggregation discards important temporal information, thus
inhibiting our understanding of the networks dynamic behaviour and evolution.
We have recorded patterns of human urban encounter using Bluetooth technology
thus retaining the temporal properties of this network. Here we show how this
temporal information influences the structural properties of the network. We
show that the temporal properties of human urban encounter are scale-free,
leading to an overwhelming proportion of brief encounters between individuals.
While previous research has shown preferential attachment to result in
scale-free connectivity in aggregated network data, we found that scale-free
connectivity results from the temporal properties of the network. In addition,
we show that brief encounters act as weak social ties in the diffusion of
non-expiring information, yet persistent encounters provide the means for
sustaining time-expiring information through a network.


title: Diffractive production of quarkonia

abstract:
  I discuss two selected examples of diffractive production of quarkonia: $p p
\to p \eta' p$ and $p p \to p J/\psi p$. In the first case I consider
diffractive pQCD approach and $\gamma \gamma$ fusion, in the second case the
amplitude is linked to the amplitude of the process for $J/\psi$
photoproduction at HERA. Absorption effects are discussed briefly for the
second reaction.


title: Anomalous finite-size effects in the Battle of the Sexes

abstract:
  The Battle of the Sexes describes asymmetric conflicts in mating behavior of
males and females. Males can be philanderer or faithful, while females are
either fast or coy, leading to a cyclic dynamics. The adjusted replicator
equation predicts stable coexistence of all four strategies. In this situation,
we consider the effects of fluctuations stemming from a finite population size.
We show that they unavoidably lead to extinction of two strategies in the
population. However, the typical time until extinction occurs strongly prolongs
with increasing system size. In the meantime, a quasi-stationary probability
distribution forms that is anomalously flat in the vicinity of the coexistence
state. This behavior originates in a vanishing linear deterministic drift near
the fixed point. We provide numerical data as well as an analytical approach to
the mean extinction time and the quasi-stationary probability distribution.


title: Imaging Electron Wave Functions Inside Open Quantum Rings

abstract:
  Combining Scanning Gate Microscopy (SGM) experiments and simulations, we
demonstrate low temperature imaging of electron probability density
$|\Psi|^{2}(x,y)$ in embedded mesoscopic quantum rings (QRs). The tip-induced
conductance modulations share the same temperature dependence as the
Aharonov-Bohm effect, indicating that they originate from electron wavefunction
interferences. Simulations of both $|\Psi|^{2}(x,y)$ and SGM conductance maps
reproduce the main experimental observations and link fringes in SGM images to
$|\Psi|^{2}(x,y)$.


title:
Importance of constraining the dense matter Equation of State in pulsar
  astrophysics

abstract:
  We study the dependence of the surface magnetic fields of radio pulsars on
the choice of Equations of State, pulsar masses and the values of the angle
between the magnetic axis and the spin axis of the pulsars within simple dipole
model. We show that the values of the surface magnetic field can be even order
of magnitude different from its canonical values. This difference will effect
any magnetosphere related model to explain observational features of radio
pulsars and magnetars. We find a significant difference of the value of the
surface magnetic field from the commonly quoted value for the faster member of
the double pulsar system, i.e. PSR J0737-3039A as here both the mass of the
pulsar and the angle between the magnetic axis and the spin axis are known. Our
study reveals the importance of constraining the dense matter Equations of
State in pulsar astrophysics as well as hints an alternative way to constrain
these by independent determination of the pulsar magnetic field.


title:
Nuclear Chemical and Mechanical Instability and the Liquid-Gas Phase
  Transition in Nuclei

abstract:
  The thermodynamic properties of nuclei are studied in a mean field model
using a Skryme interaction. Properties of two component systems are
investigated over the complete range of proton fraction from a system of pure
neutrons to a system of only protons. Besides volume, symmetry, and Coulomb
effects we also include momentum or velocity dependent forces. Applications of
the results developed are then given which include nuclear mechanical and
chemical instability and an associated liquid/gas phase transition in two
component systems. The velocity dependence leads to further changes in the
coexistence curve and nuclear mechanical and chemical instability curves.


title:
Quantum phase transitions and thermodynamics of quantum antiferromagnets
  with competing interactions

abstract:
  We study the isotropic Heisenberg chain with nearest and next-nearest
neighbour interactions. The ground state phase diagram is constructed in
dependence on the additonal interactions and an external magnetic field. The
thermodynamics is studied by use of finite sets of non-linear integral
equations resulting from integrabiliy. The equations are solved numerically and
analytically in suitable limiting cases. We find second and first order
transition lines. The exponents of the low temperature asymptotics at the phase
transitions are determined.


title: $\eta \to 3 \pi$ at Two Loops In Chiral Perturbation Theory

abstract:
  We calculate the decay $\eta\to3\pi$ at next-to-next-to-leading order or
order $p^6$ in Chiral Perturbation Theory. The corrections are somewhat larger
than was indicated by dispersive estimates. We present numerical results for
the Dalitz plot parameters, the ratio $r$ of the neutral to charged decay and
the total decay rate. In addition we derive an inequality between the slope
parameters of the charged and neutral decay. The experimental charged decay
rate leads to central values for the isospin breaking quantities $R=42.2$ and
$Q=23.2$.


title: ATLAS silicon module assembly and qualification tests at IFIC Valencia

abstract:
  ATLAS experiment, designed to probe the interactions of particles emerging
out of proton proton collisions at energies of up to 14 TeV, will assume
operation at the Large Hadron Collider (LHC) at CERN in 2007. This paper
discusses the assembly and the quality control tests of forward detector
modules for the ATLAS silicon microstrip detector assembled at the Instituto de
Fisica Corpuscular (IFIC) in Valencia. The construction and testing procedures
are outlined and the laboratory equipment is briefly described. Emphasis is
given on the module quality achieved in terms of mechanical and electrical
stability.


title: Valuations and dynamic convex risk measures

abstract:
  This paper approaches the definition and properties of dynamic convex risk
measures through the notion of a family of concave valuation operators
satisfying certain simple and credible axioms. Exploring these in the simplest
context of a finite time set and finite sample space, we find natural
risk-transfer and time-consistency properties for a firm seeking to spread its
risk across a group of subsidiaries.


title:
Parameterization of the Angular Distribution of Gamma Rays Produced by
  p-p Interaction in Astronomical Environment

abstract:
  We present the angular distribution of gamma rays produced by proton-proton
interactions in parameterized formulae to facilitate calculations in
astrophysical environments. The parameterization is derived from Monte Carlo
simulations of the up-to-date proton-proton interaction model by Kamae et al.
(2005) and its extension by Kamae et al. (2006). This model includes the
logarithmically rising inelastic cross section, the diffraction dissociation
process and Feynman scaling violation. The extension adds two baryon resonance
contributions: one representing the Delta(1232) and the other representing
multiple resonances around 1600 MeV/c^2. We demonstrate the use of the formulae
by calculating the predicted gamma-ray spectrum for two different cases: the
first is a pencil beam of protons following a power law and the second is a
fanned proton jet with a Gaussian intensity profile impinging on the
surrounding material. In both cases we find that the predicted gamma-ray
spectrum to be dependent on the viewing angle.


title: On the magnetic fields generated by experimental dynamos

abstract:
  We review the results obtained by three successful fluid dynamo experiments
and discuss what has been learnt from them about the effect of turbulence on
the dynamo threshold and saturation. We then discuss several questions that are
still open and propose experiments that could be performed to answer some of
them.


title: Flavors and Phases in Unparticle Physics

abstract:
  Inspired by the recent Georgi's unparticle proposal, we study the flavor
structures of the standard model (SM) particles when they couple to
unparticles. At a very high energy scale, we introduce $\BZ$ charges for the SM
particles, which are universal for each generation and allow $\BZ$ fields to
distinguish flavor generations. At the $\Lambda_{\UP}$ scale, $\BZ$ operators
and charges are matched onto unparticle operators and charges, respectively. In
this scenario, we find that tree flavor changing neutral currents (FCNCs) can
be induced by the rediagonalizations of the SM fermions. As an illustration, we
employ the Fritzsch ansatz to the SM fermion mass matrices and we find that the
FCNC effects could be simplified to be associated with the mass ratios denoted
by $\sqrt{m_{i}m_{j}/m^2_{3}}$, where $m_3$ is the mass of the heaviest
particle in each type of fermion generations and $i, j$ are the flavor indices.
In addition, we show that there is no new CP violating phase beside the unique
one in the CKM matrix. We use $\bar B_{q}\to \ell^{+} \ell^{-}$ as examples to
display the new FCNC effects. In particular, we demonstrate that the direct CP
asymmetries in the decays can be $O(10%)$ due to the peculiar CP conserving
phase in the unparticle propagator.


title: The hierarchical build-up of bulges in CDM

abstract:
  We investigate the hierarchical build-up of stars in bulges within the
standard $\Lambda$-cold dark matter scenario. By separating the population into
stars born during starbursts that accompany the formation of spheroids in major
mergers ({\it starburst} component), and stars that are previously formed in
discs of progenitor galaxies ({\it quiescent} component) and added to the
spheroid by dynamical interaction. Our results are summarised as follows:
bulges that form early have larger starburst fraction and hence should be
smaller than their counter parts that form later. The quiescent fraction in
bulges is an increasing function of bulge mass, becoming constant at
$M_{\rm{q}}/M_{\rm{bul}} \sim 0.8$, mainly due to the infall of satellite
galaxies that contribute disc stars to the bulge. Minor mergers are an order of
magnitude more frequent than major mergers and must play a significant role in
the evolution of bulges. Above the critical mass $M_{\rm{c}}\sim 3 \times
10^{10}$ M$_{\odot}$ most of the stars in the universe are in spheroids, which
at high redshift are exclusively elliptical galaxies and at low redshifts
partly bulges. Due to the enhanced evolution of galaxies ending up in high
density environments, the starburst fraction and the surface mass densities of
bulges below $M_{\rm{c}}$ should be enhanced with respect to field galaxies.
Dissipation during the formation of massive bulges in present day early-type
spirals is less important than for the formation of present day elliptical
galaxies of the same mass thereby explaining the possible difference in
phase-space densities between spiral galaxies and elliptical galaxies.


title: Interqubit coupling mediated by a high-excitation-energy quantum object

abstract:
  We consider a system composed of two qubits and a high-excitation-energy
quantum object used to mediate coupling between the qubits. We treat the entire
system quantum mechanically and analyze the properties of the eigenvalues and
eigenstates of the total Hamiltonian. After reproducing well-known results
concerning the leading term in the mediated coupling, we obtain an expression
for the residual coupling between the qubits in the off state. We also analyze
the entanglement between the three objects, i.e. the two qubits and the
coupler, in the eigenstates of the total Hamiltonian. Although we focus on the
application of our results to the recently realized parametric-coupling scheme
with two qubits, we also discuss extensions of our results to
harmonic-oscillator couplers, couplers that are near resonance with the qubits
and multi-qubit systems. In particular, we find that certain errors that are
absent for a two-qubit system arise when dealing with multi-qubit systems.


title:
Large deviation for return times in open sets for axiom A
  diffeomorphisms

abstract:
  For axiom A diffeomorphisms and equilibrium state, we prove a Large deviation
result for the sequence of successive return times into a fixed open set, under
some assumption on the boundary. Our result relies on and extends the work by
Chazottes and Leplaideur who where considering cylinder sets of a Markov
partition.


title: Percolation sur le syst\`eme \`a trois points

abstract:
  The three dot system is an action by homeomorphisms of $\mathbb Z^2$ on a
compact space, which invariant measures are supposed to satisfy rigidity
properties analoguous to the ones of invariant measures of angle doubling and
tripling on the circle. For such measures, we establish a dichotomy which is
related to percolation properties.


title: Analyse harmonique sur le graphe de Pascal

abstract:
  We prove a spectral decomposition theorem for a well-known self-similar
graph, for some finite graphs which are quotients of this graph and for a
compactification of it.


title: Scalar Emission in the Bulk in a Rotating Black Hole Background

abstract:
  We study the emission of scalars into the bulk from a higher-dimensional
rotating black hole. We obtain an analytic solution to the field equation by
employing matching techniques on expressions valid in the near-horizon and
far-field regimes. Both analytic and numerical results for the absorption
probability, in the low-energy and low-angular momentum limit, are derived and
found to be in excellent agreement. We also compute the energy emission rate,
and show that the brane-to-bulk ratio of the energy emission rates for scalar
fields remains always larger than unity in the aforementioned regime.


title:
The Poisson bracket compatible with the classical reflection equation
  algebra

abstract:
  We introduce a family of compatible Poisson brackets on the space of $2\times
2$ polynomial matrices, which contains the reflection equation algebra bracket.
Then we use it to derive a multi-Hamiltonian structure for a set of integrable
systems that includes the $XXX$ Heisenberg magnet with boundary conditions, the
generalized Toda lattices and the Kowalevski top.


title: The sharp $A_p$ constant for weights in a reverse-H\"older class

abstract:
  In a recent paper V. Vasyunin presented a proof of the reverse H\"older
inequality with sharp constants for the weights satisfying the usual
Muckenhoupt condition. In this paper we present the inverse, that is, we use
the Bellman function technique to find the sharp $A_p$ constants for weights in
a reverse-H\"older class on an interval; we also find the sharp constants for
the higher-integrability result of Gehring.
  Additionally, we find bounds for the $A_p$ constants of
reverse-H\"older-class weights defined on rectangles and on cubes in n
dimensions.


title: Neutrino Interactions with Nuclei

abstract:
  We investigate neutrino-nucleus collisions at intermediate energies
incorporating quasi-elastic scattering and the excitation of 13 resonances as
elementary processes, taking into account medium effects such as Fermi motion,
Pauli blocking, mean-field potentials and in-medium spectral functions. A
coupled-channel treatment of final state interactions is achieved with the
GiBUU transport model. Results for inclusive reactions, neutrino- and
electron-induced, as well as for pion production and nucleon knockout are
presented.


title:
Instanton effects in N=1 brane models and the Kahler metric of twisted
  matter

abstract:
  We consider locally consistent systems of magnetized D9 branes on an
orbifolded six-torus which support N=1 gauge theories. In such realizations,
the matter multiplets arise from "twisted" strings connecting different stacks
of branes. The introduction of Euclidean 5 branes (E5) wrapped on the
six-dimensional compact space leads to instanton effects. For instance, if the
system is engineered so as to yield SQCD, a single E5 brane may account for the
ADS/TVY superpotential. We discuss the subtle interplay that exists between the
annuli diagrams with an E5 boundary and the holomorphicity properties of the
effective low-energy action of the N=1 theory. The consistency of this picture
allows to obtain information on the Kahler metric of the chiral matter
multiplets arising from twisted strings.


title:
Mesh update techniques for free-surface flow solvers using spectral
  element method

abstract:
  This paper presents a novel mesh-update technique for unsteady free-surface
Newtonian flows using spectral element method and relying on the arbitrary
Lagrangian--Eulerian kinematic description for moving the grid. Selected
results showing compatibility of this mesh-update technique with spectral
element method are given.


title: Decay of the Mixed States

abstract:
  We study the classical escape from local minima for 2d multi-well Hamiltonian
systems, realizing the mixed state. We show that escape from such local minima
has a diversity of principally new features, representing an interesting topic
for conceptual understanding of chaotic dynamics and applications.


title: Homotopy theoretic models of identity types

abstract:
  This paper presents a novel connection between homotopical algebra and
mathematical logic. It is shown that a form of intensional type theory is valid
in any Quillen model category, generalizing the Hofmann-Streicher groupoid
model of Martin-Loef type theory.


title:
First-order phase transitions in two-dimensional off-lattice liquid
  crystals

abstract:
  We consider an off-lattice liquid crystal pair potential in strictly two
dimensions. The potential is purely repulsive and short-ranged. Nevertheless,
by means of a single parameter in the potential, the system is shown to undergo
a first-order phase transition. The transition is studied using mean-field
density functional theory, and shown to be of the isotropic-to-nematic kind. In
addition, the theory predicts a large density gap between the two coexisting
phases. The first-order nature of the transition is confirmed using computer
simulation and finite-size scaling. Also presented is an analysis of the
interface between the coexisting domains, including estimates of the line
tension, as well as an investigation of anchoring effects.


title:
Large-eddy simulation of the lid-driven cubic cavity flow by the
  spectral element method

abstract:
  This paper presents the large-eddy simulation of the lid-driven cubic cavity
flow by the spectral element method (SEM) using the dynamic model. Two spectral
filtering techniques suitable for these simulations have been implemented.
Numerical results for Reynolds number $\text{Re}=12'000$ are showing very good
agreement with other experimental and DNS results found in the literature.


title: Femtosecond Photoionization of Atoms under Noise

abstract:
  We investigate the effect of incoherent perturbations on atomic
photoionization due to a femtosecond mid-infrared laser pulse by solving the
time-dependent stochastic Schr\"odinger equation. For a weak laser pulse which
causes almost no ionization, an addition of a Gaussian white noise to the pulse
leads to a significantly enhanced ionization probability. Tuning the noise
level, a stochastic resonance-like curve is observed showing the existence of
an optimum noise for a given laser pulse. Besides studying the sensitivity of
the obtained enhancement curve on the pulse parameters, such as the pulse
duration and peak amplitude, we suggest that experimentally realizable
broadband chaotic light can also be used instead of the white noise to observe
similar features. The underlying enhancement mechanism is analyzed in the
frequency-domain by computing a frequency-resolved atomic gain profile, as well
as in the time-domain by controlling the relative delay between the action of
the laser pulse and noise.


title: Asymptotic analysis of the Bell polynomials by the ray method

abstract:
  We analyze the Bell polynomials $B_{n}(x)$ asymptotically as $n\to\infty$. We
obtain asymptotic approximations from the differential-difference equation
which they satisfy, using a discrete version of the ray method. We give some
examples showing the accuracy of our formulas.


title: Neutrino Mass, Dark Energy, and the Linear Growth Factor

abstract:
  We study the degeneracies between neutrino mass and dark energy as they
manifest themselves in cosmological observations. In contradiction to a popular
formula in the literature, the suppression of the matter power spectrum caused
by massive neutrinos is not just a function of the ratio of neutrino to total
mass densities f_nu=Omega_nu/Omega_m, but also each of the densities
independently. We also present a fitting formula for the logarithmic growth
factor of perturbations in a flat universe, f(z, k;f_nu,w,Omega_DE)=
(1-A(k)*Omega_DE*f_nu+B(k)*f_nu^2-C(k)*f_nu^3)*Omega_m(z)^alpha, where alpha
depends on the dark energy equation of state parameter w. We then discuss
cosmological probes where the f factor directly appears: peculiar velocities,
redshift distortion and the Intergrated Sachs-Wolfe effect. We also modify the
approximation of Eisenstein & Hu (1999) for the power spectrum of fluctuations
in the presence of massive neutrinos and provide a revised code
(http://www.star.ucl.ac.uk/~lahav/nu_matter_power.f)


title: Tidal waves as yrast states in transitional nuclei

abstract:
  The yrast states of transitional nuclei are described as quadrupole waves
running over the nuclear surface, which we call tidal waves. In contrast to a
rotor, which generates angular momentum by increasing the angular velocity at
approximately constant deformation, a tidal wave generates angular momentum by
increasing the deformation at approximately constant angular velocity. The
properties of the tidal waves are calculated by means of the cranking model in
a microscopic way. The calculated energies and E2 transition probabilities of
the yrast states in the transitional nuclides with $Z$= 44, 46, 48 and $N=56,
58, ..., 66$ reproduce the experiment in detail. The nonlinear response of the
nucleonic orbitals results in a strong coupling between shape and single
particle degrees of freedom.


title:
Exclusive J/psi and Upsilon hadroproduction as a probe of the QCD
  Odderon

abstract:
  We study the exclusive production of J/psi or Upsilon in pp and bar pp
collisions, where the meson emerges from the pomeron--odderon and the
pomeron--photon fusion. We estimate the cross sections for these processes for
the kinematical conditions of the Tevatron and of the LHC.


title: Magnetic fields in massive star forming regions

abstract:
  We present the largest sample of high-mass star-forming regions observed
using submillimetre imaging polarimetry. The data were taken using SCUBA in
conjunction with the polarimeter on the JCMT in Hawaii. In total, 16 star
forming regions were observed, although some of these contain multiple cores.
The polarimetry implies a variety of magnetic field morphologies, with some
very ordered fields. We see a decrease in polarisation percentage for 7 of the
cores. The magnetic field strengths estimated for 14 of the cores, using the
corrected CF method, range from <0.1 mG to almost 6 mG. These magnetic fields
are weaker on these large scales when compared to previous Zeeman measurements
from maser emission, implying the role of the magnetic field in star formation
increases in importance on smaller scales. Analysis of the alignment of the
mean field direction and the outflow directions reveal no relation for the
whole sample, although direct comparison of the polarimetry maps suggests good
alignment (to at least one outflow direction per source) in 7 out of the 15
sources with outflows.


title: D-branes in T-fold conformal field theory

abstract:
  We investigate boundary dynamics of orbifold conformal field theory involving
T-duality twists. Such models typically appear in contexts of non-geometric
string compactifications that are called monodrofolds or T-folds in recent
literature. We use the framework of boundary conformal field theory to analyse
the models from a microscopic world-sheet perspective. In these backgrounds
there are two kinds of D-branes that are analogous to bulk and fractional
branes in standard orbifold models. The bulk D-branes in T-folds allow
intuitive geometrical interpretations and are consistent with the classical
analysis based on the doubled torus formalism. The fractional branes, on the
other hand, are `non-geometric' at any point in the moduli space and their
geometric counterparts seem to be missing in the doubled torus analysis. We
compute cylinder amplitudes between the bulk and fractional branes, and find
that the lightest modes of the open string spectra show intriguing non-linear
dependence on the moduli (location of the brane or value of the Wilson line),
suggesting that the physics of T-folds, when D-branes are involved, could
deviate from geometric backgrounds even at low energies. We also extend our
analysis to the models with SU(2) WZW fibre at arbitrary levels.


title:
Networks of Polynomial Pieces with Application to the Analysis of Point
  Clouds and Images

abstract:
  We consider Holder smoothness classes of surfaces for which we construct
piecewise polynomial approximation networks, which are graphs with polynomial
pieces as nodes and edges between polynomial pieces that are in `good
continuation' of each other. Little known to the community, a similar
construction was used by Kolmogorov and Tikhomirov in their proof of their
celebrated entropy results for Holder classes.
  We show how to use such networks in the context of detecting geometric
objects buried in noise to approximate the scan statistic, yielding an
optimization problem akin to the Traveling Salesman. In the same context, we
describe an alternative approach based on computing the longest path in the
network after appropriate thresholding.
  For the special case of curves, we also formalize the notion of `good
continuation' between beamlets in any dimension, obtaining more economical
piecewise linear approximation networks for curves.
  We include some numerical experiments illustrating the use of the beamlet
network in characterizing the filamentarity content of 3D datasets, and show
that even a rudimentary notion of good continuity may bring substantial
improvement.


title: Spectrum Sensing in Wideband OFDM Cognitive Radios

abstract:
  In this paper, detection of the primary user (PU) signal in an orthogonal
frequency division multiplexing (OFDM) based cognitive radio (CR) system is
addressed. According to the prior knowledge of the PU signal known to the
detector, three detection algorithms based on the Neyman-Pearson philosophy are
proposed. In the first case, a Gaussian PU signal with completely known
probability density function (PDF) except for its received power is considered.
The frequency band that the PU signal resides is also assumed known. Detection
is performed individually at each OFDM sub-carrier possibly interfered by the
PU signal, and the results are then combined to form a final decision. In the
second case, the sub-carriers that the PU signal resides are known.
Observations from all possibly interfered sub-carriers are considered jointly
to exploit the fact that the presence of a PU signal interferers all of them
simultaneously. In the last case, it is assumed no PU signal prior knowledge is
available. The detection is involved with a search of the interfered band. The
proposed detector is able to detect an abrupt power change when tracing along
the frequency axis.


title: Mixing of shear Alfven wave packets

abstract:
  The propagation of shear Alfven wave packets in inhomogeneous magnetic
fields, at the origin of their distortion, regardless of the occurrence of
non-linear coupling, is considered. It is shown that the distortion mechanism
can be regarded as mixing process and hence, standard "phase mixing"
corresponds to the effect of an "Alfvenic" shear flow while enhanced
dissipation at a magnetic X-point corresponds to mixing by an "Alfvenic" strain
flow. The evolution of the global wave field is supposed to result from the
dynamics of a superposition of wave packets and a kinetic equation for the wave
energy is obtained following this eikonal (WKB) description. Since shear Alfven
wave packets experience continuous shearing/straining while transported by an
inhomogeneous Alfvenic flow $\mathbf{V}_{A}$, their mixing process, in physical
space, is also a cascade of wave energy in k-space. The wave energy spectrum
resulting from this linear mechanism of energy transfer is determined for the
special case of waves propagating along chaotic magnetic field lines, the
analog of a chaotic mixing process. The latter follows a $k^{-1}$ power-law, in
the energy conserving range in $k$ space.


title: No resonant tunneling in standard scalar quantum field theory

abstract:
  We investigate the nature of resonant tunneling in Quantum Field Theory.
Following the pioneering work of Banks, Bender and Wu, we describe quantum
field theory in terms of infinite dimensional quantum mechanics and utilize the
``Most probable escape path'' (MPEP) as the class of paths which dominate the
path integral in the classically forbidden region. Considering a 1+1
dimensional field theory example we show that there are five conditions that
any associated bound state in the classically allowed region must satisfy if
resonant tunnelling is to occur, and we then proceed to show that it is
impossible to satisfy all five conditions simultaneously.


title:
Discovery of multiple Lorentzian components in the X-ray timing
  properties of the Narrow Line Seyfert 1 Ark 564

abstract:
  We present a power spectral analysis of a 100 ksec XMM-Newton observation of
the narrow line Seyfert 1 galaxy Ark~564. When combined with earlier RXTE and
ASCA observations, these data produce a power spectrum covering seven decades
of frequency which is well described by a power law with two very clear breaks.
This shape is unlike the power spectra of almost all other AGN observed so far,
which have only one detected break, and resemble Galactic binary systems in a
soft state. The power spectrum can also be well described by the sum of two
Lorentzian-shaped components, the one at higher frequencies having a hard
spectrum, similar to those seen in Galactic binary systems. Previously we have
demonstrated that the lag of the hard band variations relative to the soft band
in Ark 564 is dependent on variability time-scale, as seen in Galactic binary
sources. Here we show that the time-scale dependence of the lags can be
described well using the same two-Lorentzian model which describes the power
spectrum, assuming that each Lorentzian component has a distinct time lag. Thus
all X-ray timing evidence points strongly to two discrete, localised, regions
as the origin of most of the variability. Similar behaviour is seen in Galactic
X-ray binary systems in most states other than the soft state, i.e. in the
low-hard and intermediate/very high states. Given the very high accretion rate
of Ark 564 the closest analogy is with the very high (intermediate) state
rather than the low-hard state. We therefore strengthen the comparison between
AGN and Galactic binary sources beyond previous studies by extending it to the
previously poorly studied very high accretion rate regime.


title:
Violation of the Luttinger sum rule within the Hubbard model on a
  triangular lattice

abstract:
  The frequency-moment expansion method is developed to analyze the validity of
the Luttinger sum rule within the Mott-Hubbard insulator, as represented by the
generalized Hubbard model at half filling and large $U$. For the particular
case of the Hubbard model with nearest-neighbor hopping on a triangular lattice
lacking the particle-hole symmetry results reveal substantial violation of the
sum rule.


title: A search for electron cyclotron maser emission from compact binaries

abstract:
  Unipolar induction (UI) is a fundamental physical process, which occurs when
a conducting body transverses a magnetic field. It has been suggested that UI
is operating in RX J0806+15 and RX J1914+24, which are believed to be
ultra-compact binaries with orbital periods of 5.4 min and 9.6 min
respectively. The UI model predicts that those two sources may be electron
cyclotron maser sources at radio wavelengths. Other systems in which UI has
been predicted to occur are short period extra-solar terrestrial planets with
conducting cores. If UI is present, circularly polarised radio emission is
predicted to be emitted. We have searched for this predicted radio emission
from short period binaries using the VLA and ATCA. In one epoch we find
evidence for a radio source, coincident in position with the optical position
of RX J0806+15. Although we cannot completely exclude that this is a chance
alignment between the position of RX J0806+15 and an artifact in the data
reduction process, the fact that it was detected at a significance level of 5.8
sigma and found to be transient, suggests that it is more likely that RX
J0806+15 is a transient radio source. We find an upper limit on the degree of
circular polarisation to be ~50%. The inferred brightness temperature exceeds
10^18 K, which is too high for any known incoherent process, but is consistent
with maser emission and UI being the driving mechanism. We did not detect radio
emission from ES Cet, RX J1914+24 or Gliese 876.


title:
How far can you go ? Surprises and pitfalls in three-flavour chiral
  extrapolations

abstract:
  The presence of strange sea quark pairs may have a significant impact of the
pattern of chiral symmetry breaking : in particular large differences can occur
between the chiral limits of two and three massless flavours (i.e., whether
$m_s$ is kept at its physical value or sent to zero). We recall some
indications of such a scenario in QCD, in relation with the peculiar dynamics
of the scalar sector. We explain how this could affect the convergence of
three-flavour chiral series, commonly used to extrapolate the results of
lattice simulations. Finally, we indicate how lattice simulations with three
dynamical flavours could unveil such an effect through the quark-mass
dependence of light meson masses and decay constants.