title:
Generalized Virial Theorem and Pressure Relation for a strongly
  correlated Fermi gas

abstract:
  For a two-component Fermi gas in the unitarity limit (ie, with infinite
scattering length), there is a well-known virial theorem, first shown by J. E.
Thomas et al, Phys. Rev. Lett. 95, 120402 (2005). A few people rederived this
result, and extended it to few-body systems, but their results are all
restricted to the unitarity limit. Here I show that there is a generalized
virial theorem for FINITE scattering lengths. I also generalize an exact result
concerning the pressure, first shown in cond-mat/0508320, to the case of
imbalanced populations.


title: Leading coefficients and cellular bases of Hecke algebras

abstract:
  Let $\bH$ be the generic Iwahori--Hecke algebra associated with a finite
Coxeter group $W$. Recently, we have shown that $\bH$ admits a natural cellular
basis in the sense of Graham--Lehrer, provided that $W$ is a Weyl group and all
parameters of $\bH$ are equal. The construction involves some data arising from
the Kazhdan--Lusztig basis $\{\bC_w\}$ of $\bH$ and Lusztig's asymptotic ring
$\bJ$. This article attemps to study $\bJ$ and its representation theory from a
new point of view. We show that $\bJ$ can be obtained in an entirely different
fashion from the generic representations of $\bH$, without any reference to
$\{\bC_w\}$. Then we can extend the construction of the cellular basis to the
case where $W$ is not crystallographic. Furthermore, if $\bH$ is a
multi-parameter algebra, we will see that there always exists at least one
cellular structure on $\bH$. Finally, one may also hope that the new
construction of $\bJ$ can be extended to Hecke algebras associated to complex
reflection groups.


title: Cylindrical equilibrium shapes of fluid membranes

abstract:
  Within the framework of the well-known curvature models, a fluid lipid
bilayer membrane is regarded as a surface embedded in the three-dimensional
Euclidean space whose equilibrium shapes are described in terms of its mean and
Gaussian curvatures by the so-called membrane shape equation. In the present
paper, all solutions to this equation determining cylindrical membrane shapes
are found and presented, together with the expressions for the corresponding
position vectors, in explicit analytic form. The necessary and sufficient
conditions for such a surface to be closed are derived and several sufficient
conditions for its directrix to be simple or self-intersecting are given.


title: Modeling interaction of trading volume in financial dynamics

abstract:
  A dynamic herding model with interactions of trading volumes is introduced.
At time $t$, an agent trades with a probability, which depends on the ratio of
the total trading volume at time $t-1$ to its own trading volume at its last
trade. The price return is determined by the volume imbalance and number of
trades. The model successfully reproduces the power-law distributions of the
trading volume, number of trades and price return, and their relations.
Moreover, the generated time series are long-range correlated. We demonstrate
that the results are rather robust, and do not depend on the particular form of
the trading probability.


title: Knapsack cryptosystems built on NP-hard instance

abstract:
  We construct three public key knapsack cryptosystems. Standard knapsack
cryptosystems hide easy instances of the knapsack problem and have been broken.
The systems considered in the article face this problem: They hide a random
(possibly hard) instance of the knapsack problem. We provide both complexity
results (size of the key, time needed to encypher/decypher...) and experimental
results. Security results are given for the second cryptosystem (the fastest
one and the one with the shortest key). Probabilistic polynomial reductions
show that finding the private key is as difficult as factorizing a product of
two primes. We also consider heuristic attacks. First, the density of the
cryptosystem can be chosen arbitrarily close to one, discarding low density
attacks. Finally, we consider explicit heuristic attacks based on the LLL
algorithm and we prove that with respect to these attacks, the public key is as
secure as a random key.


title: Ground State Properties of a Tonks-Girardeau Gas in a Split Trap

abstract:
  We determine the exact many-body properties of a bosonic Tonks-Girardeau gas
confined in a harmonic potential with a tunable $\delta$-function barrier at
the trap center. This is done by calculating the reduced single particle
density matrix, the pair-distribution function, and momentum distribution of
the gas as a function of barrier strength and particle number. With increasing
barrier height we find that the ground state occupation in a diagonal basis
diverges from the $\sqrt N$ behavior that is expected for the case of a simple
harmonic trap. In fact, the scaling of the occupation number depends on whether
one has an even or odd number of particles. Since this quantity is a measure of
the coherence of our sample we show how the odd-even effect manifests itself in
both the momentum distribution of the Bose gas and interference fringe
visibility during free temporal evolution.


title: A simple adaptive estimator of the integrated square of a density

abstract:
  Given an i.i.d. sample $X_1,...,X_n$ with common bounded density $f_0$
belonging to a Sobolev space of order $\alpha$ over the real line, estimation
of the quadratic functional $\int_{\mathbb{R}}f_0^2(x) \mathrm{d}x$ is
considered. It is shown that the simplest kernel-based plug-in estimator
\[\frac{2}{n(n-1)h_n}\sum_{1\leq i<j\leq n}K\biggl(\frac{X_i-X_j}{h_n}\biggr)\]
is asymptotically efficient if $\alpha>1/4$ and rate-optimal if $\alpha\le1/4$.
A data-driven rule to choose the bandwidth $h_n$ is then proposed, which does
not depend on prior knowledge of $\alpha$, so that the corresponding estimator
is rate-adaptive for $\alpha \leq1/4$ and asymptotically efficient if
$\alpha>1/4$.


title: Asymptotic analysis of $k$-noncrossing matchings

abstract:
  In this paper we study $k$-noncrossing matchings. A $k$-noncrossing matching
is a labeled graph with vertex set $\{1,...,2n\}$ arranged in increasing order
in a horizontal line and vertex-degree 1. The $n$ arcs are drawn in the upper
halfplane subject to the condition that there exist no $k$ arcs that mutually
intersect. We derive: (a) for arbitrary $k$, an asymptotic approximation of the
exponential generating function of $k$-noncrossing matchings $F_k(z)$. (b) the
asymptotic formula for the number of $k$-noncrossing matchings $f_{k}(n) \sim
c_k n^{-((k-1)^2+(k-1)/2)} (2(k-1))^{2n}$ for some $c_k>0$.


title: The Universal Cardinal Ordering of Fixed Points

abstract:
  We present the theorem which determines, by a permutation, the cardinal
ordering of fixed points for any orbit of a period doubling cascade. The
inverse permutation generates the orbit and the symbolic sequence of the orbit
is obtained as a corollary. The problem present in the symbolic sequences is
solved. There, repeated symbols appear, for example, the R (right), which
cannot be distinguished among them as it is not known which R is the rightmost
of them all. Therefore, there is a lack of information about the dynamical
system. Interestingly enough, it is important to point that this theorem needs
no previous information about any other orbit.


title:
Zinc adaptation and resistance to cadmium toxicity in mammalian cells.
  Molecular insight by proteomic analysis

abstract:
  To identify proteins involved in cellular adaptive responses to zinc, a
comparative proteome analysis between a previously developed high zinc- and
cadmium- resistant human epithelial cell line (HZR) and the parental HeLa cells
has been carried out. Differentially produced proteins included co-chaperones,
proteins associated with oxido-reductase activities, and ubiquitin. Biochemical
pathways to which these proteins belong were probed for their involvement in
the resistance of both cell lines against cadmium toxicity. Among endoplasmic
reticulum stressors, thapsigargin sensitized HZR cells, but not HeLa cells, to
cadmium toxicity more acutely than tunicamycin, implying that these cells
heavily relied on proper intracellular calcium distribution. The similar
sensitivity of both HeLa and HZR cells to inhibitors of the proteasome, such as
MG-132 or lactacystin, excluded improved proteasome activity as a mechanism
associated with zinc adaptation of HZR cells. The enzyme
4-hydroxyphenylpyruvate dioxygenase was overproduced in HZR cells as compared
to HeLa cells. It transforms 4-hydroxyphenylpyruvate to homogentisate in the
second step of tyrosine catabolism. Inhibition of 4-hydroxyphenylpyruvate
dioxygenase decreased the resistance of HZR cells against cadmium, but not that
of HeLa cells, suggesting that adaptation to zinc overload and increased
4-hydroxyphenylpyruvate removal are linked in HZR cells


title: Low-temperature properties of the dilute dipolar magnet LiHo_xY_(1-x)F_4

abstract:
  We analyze recent experiments on the dilute rare-earth compound
LiHo_xY_(1-x)F_4 in the context of an effective Ising dipolar model. Using a
Monte Carlo method we calculate the low-temperature behavior of the specific
heat and linear susceptibility, and compare our results to measurements. In our
model the susceptibility follows a Curie-Weiss law at high temperature, chi ~
1/(T-T_cw), with a Curie-Weiss temperature that scales with dilution, T_cw ~ x,
consistent with early experiments. We also find that the peak in the specific
heat scales linearly with dilution, C_max(T) ~ x, in disagreement with recent
experiments. Experimental studies do not reach a consensus on the functional
form of these quantities, and in particular we do not see reported scalings of
the form chi ~ T^-0.75 and chi ~ exp(-T/T_0). Furthermore we calculate the
ground state magnetization as a function of dilution, and re-examine the phase
diagram around the critical dilution x_c=0.24(3). We find that the spin glass
susceptibility for the Ising model does not diverge below x_c, while recent
experiments give strong evidence for a stable spin-glass phase in
LiHo_0.167Y_0.833F_4.


title: Lindenmayer systems and primes

abstract:
  We study the surprising discrepancy between the number of primes
corresponding, respectively, to the two letters of an infinite word engendered
by one of the simplest Lindenmayer systems. We formulate a conjecture
concerning the rate of growth of this discrepancy, which seems to tend to e for
every two sufficiently high consecutive even rank iterates of the Lindenmayer
system.


title: Girard couples of quantales

abstract:
  We introduce the concept of a Girard couple, which consists of two (not
necessarily unital) quantales linked by a strong form of duality. The two basic
examples of Girard couples arise in the study of endomorphism quantales and of
the spectra of operator algebras. We construct, for an arbitrary sup-lattice
$S$, a Girard quantale whose right-sided part is isomorphic to $S$.


title:
Finite frequency noise of a superconductor/ferromagnet quantum point
  contact

abstract:
  We have calculated the finite-frequency current noise of a
superconductor-ferromagnet quantum point contact (SF QPC). This signal is
qualitatively affected by the spin-dependence of interfacial phase shifts
(SDIPS) acquired by electrons upon reflection on the QPC. For a weakly
transparent QPC, noise steps appear at frequencies or voltages determined
directly by the SDIPS. These steps can occur at experimentally accessible
temperatures and frequencies. Finite frequency noise is thus a promising tool
to characterize the scattering properties of a SF QPC.


title: The Geometric Bogomolov Conjecture for Small Genus Curves

abstract:
  The Bogomolov Conjecture is a finiteness statement about algebraic points of
small height on a smooth complete curve defined over a global field. We verify
an effective form of the Bogomolov Conjecture for all curves of genus at most 4
defined over a function field of characteristic zero. We recover the known
result for genus 2 curves and in many cases improve upon the known bound for
genus 3 curves. For many curves of genus 4 with bad reduction, the conjecture
was previously unproved.


title: First-principles approach to lattice-mediated magnetoelectric effects

abstract:
  We present a first-principles scheme for the computation of the
magnetoelectric response of magnetic insulators. The method focuses on the
lattice-mediated part of the magnetic response to an electric field, which we
argue can be expected to be the dominant contribution in materials displaying a
strong magnetoelectric coupling. We apply our method to Cr2O3, a relatively
simple and experimentally well studied magnetoelectric compound.


title:
Explicit integration of one problem of motion of the generalized
  Kowalevski top

abstract:
  In the problem of motion of the Kowalevski top in a double force field the
4-dimensional invariant submanifold of the phase space was pointed out by
M.P.Kharlamov (Mekh. Tverd. Tela, 32, 2002). We show that the equations of
motion on this manifold can be separated by the appropriate change of
variables, the new variables s1, s2 being elliptic functions of time. The
natural phase variables (components of the angular velocity and the direction
vectors of the forces with respect to the movable basis) are expressed via s1,
s2 explicitly in elementary algebraic functions.


title: Untangling planar graphs from a specified vertex position - Hard cases

abstract:
  Given a planar graph $G$, we consider drawings of $G$ in the plane where
edges are represented by straight line segments (which possibly intersect).
Such a drawing is specified by an injective embedding $\pi$ of the vertex set
of $G$ into the plane. We prove that a wheel graph $W_n$ admits a drawing $\pi$
such that, if one wants to eliminate edge crossings by shifting vertices to new
positions in the plane, then at most $(2+o(1))\sqrt n$ of all $n$ vertices can
stay fixed. Moreover, such a drawing $\pi$ exists even if it is presupposed
that the vertices occupy any prescribed set of points in the plane. Similar
questions are discussed for other families of planar graphs.


title: Speedy sound and cosmic structure

abstract:
  If the speed of sound were vastly larger in the early Universe a near
scale-invariant spectrum of density fluctuations could have been produced even
if the Universe did not submit to conventional solutions to the horizon
problem. We examine how the mechanism works, presenting full mathematical
solutions and their heuristics. We then discuss several concrete models based
on scalar fields and hydrodynamical matter which realize this mechanism, but
stress that the proposed mechanism is more fundamental and general.


title: L\'{e}vy-based growth models

abstract:
  In the present paper, we give a condensed review, for the nonspecialist
reader, of a new modelling framework for spatio-temporal processes, based on
L\'{e}vy theory. We show the potential of the approach in stochastic geometry
and spatial statistics by studying L\'{e}vy-based growth modelling of planar
objects. The growth models considered are spatio-temporal stochastic processes
on the circle. As a by product, flexible new models for space--time covariance
functions on the circle are provided. An application of the L\'{e}vy-based
growth models to tumour growth is discussed.


title:
Energy-momentum tensor of a Casimir apparatus in a weak gravitational
  field: scalar case

abstract:
  Recent work in the literature had evaluated the energy-momentum tensor of a
Casimir apparatus in a weak gravitational field, for an electromagnetic field
subject to perfect conductor boundary conditions on parallel plates. The
Casimir apparatus was then predicted to experience a tiny push in the upwards
direction, and the regularized energy-momentum tensor was found to have a trace
anomaly. The latter, unexpected property made it compelling to assess what
happens in a simpler case. For this purpose, the present paper studies a free,
real massless scalar field subject to homogeneous Dirichlet conditions on the
parallel plates. Working to first order in the constant gravity acceleration,
the resulting regularized and renormalized energy-momentum tensor is found to
be covariantly conserved, while the trace anomaly vanishes if the massless
scalar field is conformally coupled to gravity. Conformal coupling also ensures
a finite Casimir energy and finite values of the pressure upon parallel plates.


title: xPerm: fast index canonicalization for tensor computer algebra

abstract:
  We present a very fast implementation of the Butler-Portugal algorithm for
index canonicalization with respect to permutation symmetries. It is called
xPerm, and has been written as a combination of a Mathematica package and a C
subroutine. The latter performs the most demanding parts of the computations
and can be linked from any other program or computer algebra system. We
demonstrate with tests and timings the effectively polynomial performance of
the Butler-Portugal algorithm with respect to the number of indices, though we
also show a case in which it is exponential. Our implementation handles generic
tensorial expressions with several dozen indices in hundredths of a second, or
one hundred indices in a few seconds, clearly outperforming all other current
canonicalizers. The code has been already under intensive testing for several
years and has been essential in recent investigations in large-scale tensor
computer algebra.


title:
The solar photospheric abundance of europium. Results from CO5BOLD 3-D
  hydrodynamical model atmospheres

abstract:
  Context. Europium is an almost pure r-process element, which may be useful as
a reference in nucleocosmochronology. Aims. To determine the photospheric solar
abundance using CO5BOLD 3-D hydrodynamical model atmospheres. Methods.
Disc-centre and integrated-flux observed solar spectra are used. The europium
abundance is derived from the equivalent width measurements. As a reference 1D
model atmospheres have been used, in addition. Results. The europium
photospheric solar abundance is 0.52 +- 0.02 in agreement with previous
determinations. We also determine the photospheric isotopic fraction of Eu(151)
to be 49 % +- 2.3 % from the intensity spectra and 50% +-2.3 from the flux
spectra. This compares well to the the meteoritic isotopic fraction 47.8%. We
explore the 3D corrections also for dwarfs and sub-giants in the temperature
range ~5000 K to ~6500 K and solar and 1/10--solar metallicities and find them
to be negligible for all the models investigated. Conclusions. Our photospheric
Eu abundance is in good agreement with previous determinations based on 1D
models. This is in line with our conclusion that 3D effects for this element
are negligible in the case of the Sun.


title: An upper bound for the number of perfect matchings in graphs

abstract:
  We give an upper bound on the number of perfect matchings in an undirected
simple graph $G$ with an even number of vertices, in terms of the degrees of
all the vertices in $G$. This bound is sharp if $G$ is a union of complete
bipartite graphs. This bound is a generalization of the upper bound on the
number of perfect matchings in bipartite graphs on $n+n$ vertices given by the
Bregman-Minc inequality for the permanents of $(0,1)$ matrices.


title: Symmetry Coefficients of Semilinear Partial Differential Equations

abstract:
  We show that for any semilinear partial differential equation of order m, the
infinitesimals of the independent variables depend only on the independent
variables and, if m>1 and the equation is also linear in its derivatives of
order m-1 of the dependent variable, then the infinitesimal of the dependent
variable is at most linear on the dependent variable. Many examples of
important partial differential equations in Analysis, Geometry and Mathematical
- Physics are given in order to enlighten the main result.


title:
Mass loss from late-type WN stars and its Z-dependence: very massive
  stars approaching the Eddington limit

abstract:
  The mass loss from Wolf-Rayet (WR) stars is of fundamental importance for the
final fate of massive stars and their chemical yields. Its Z-dependence is
discussed in relation to the formation of long-duration Gamma Ray Bursts (GRBs)
and the yields from early stellar generations. However, the mechanism of
formation of WR-type stellar winds is still under debate. We present the first
fully self-consistent atmosphere/wind models for late-type WN stars. We
investigate the mechanisms leading to their strong mass loss, and examine the
dependence on stellar parameters, in particular on the metallicity Z. We
identify WNL stars as very massive stars close to the Eddington limit,
potentially still in the phase of central H-burning. Due to their high L/M
ratios, these stars develop optically thick, radiatively driven winds. These
winds show qualitatively different properties than the thin winds of OB stars.
The resultant mass loss depends strongly on Z, but also on the Eddington
factor, and the stellar temperature. We combine our results in a parametrized
mass loss recipe for WNL stars. According to our present model computations,
stars close to the Eddington limit tend to form strong WR-type winds, even at
very low Z. Our models thus predict an efficient mass loss mechanism for low
metallicity stars. For extremely metal-poor stars, we find that the
self-enrichment with primary nitrogen can drive WR-type mass loss. These first
WN stars might play an important role in the enrichment of the early ISM with
freshly produced nitrogen.


title:
On the stability of spherically symmetric spacetimes in metric f(R)
  gravity

abstract:
  We consider stability properties of spherically symmetric spacetimes of stars
in metric f(R) gravity. We stress that these not only depend on the particular
model, but also on the specific physical configuration. Typically
configurations giving the desired $\gamma_{\rm PPN} \approx 1$ are strongly
constrained, while those corresponding to $\gamma_{\rm PPN} \approx 1/2$ are
less affected. Furthermore, even when the former are found strictly stable in
time, the domain of acceptable static spherical solutions typically shrinks to
a point in the phase space. Unless a physical reason to prefer such a
particular configuration can be found, this poses a naturalness problem for the
currently known metric f(R) models for accelerating expansion of the Universe.


title: Selection from a stable box

abstract:
  Let $\{X_j\}$ be independent, identically distributed random variables. It is
well known that the functional CUSUM statistic and its randomly permuted
version both converge weakly to a Brownian bridge if second moments exist.
Surprisingly, an infinite-variance counterpart does not hold true. In the
present paper, we let $\{X_j\}$ be in the domain of attraction of a strictly
$\alpha$-stable law, $\alpha\in(0,2)$. While the functional CUSUM statistics
itself converges to an $\alpha$-stable bridge and so does the permuted version,
provided both the $\{X_j\}$ and the permutation are random, the situation turns
out to be more delicate if a realization of the $\{X_j\}$ is fixed and
randomness is restricted to the permutation. Here, the conditional distribution
function of the permuted CUSUM statistics converges in probability to a random
and nondegenerate limit.


title: Robust single-parameter quantized charge pumping

abstract:
  This paper investigates a scheme for quantized charge pumping based on
single-parameter modulation. The device was realized in an AlGaAs-GaAs gated
nanowire. We find a remarkable robustness of the quantized regime against
variations in the driving signal, which increases with applied rf power. This
feature together with its simple configuration makes this device a potential
module for a scalable source of quantized current.


title:
New experimental limit on Pauli Exclusion Principle violation by
  electrons (the VIP experiment)

abstract:
  The Pauli Exclusion Principle is one of the basic principles of modern
physics and is at the very basis of our understanding of matter: thus it is
fundamental importance to test the limits of its validity. Here we present the
VIP (Violation of the Pauli Exclusion Principle) experiment, where we search
for anomalous X-rays emitted by copper atoms in a conductor: any detection of
these anomalous X-rays would mark a Pauli-forbidden transition. ] VIP is
currently taking data at the Gran Sasso underground laboratories, and its
scientific goal is to improve by at least four orders of magnitude the previous
limit on the probability of Pauli violating transitions, bringing it into the
10**-29 - 10**-30 region. First experimental results, together with future
plans, are presented.


title:
Properties of the ultraviolet flux of type Ia supernovae: an analysis
  with synthetic spectra of SN 2001ep and SN 2001eh

abstract:
  The spectral properties of type Ia supernovae in the ultraviolet (UV) are
investigated using the early-time spectra of SN 2001ep and SN 2001eh obtained
using the Hubble Space Telescope (HST). A series of spectral models is computed
with a Monte Carlo spectral synthesis code, and the dependence of the UV flux
on the elemental abundances and the density gradient in the outer layers of the
ejecta is tested. A large fraction of the UV flux is formed by reverse
fluorescence scattering of photons from red to blue wavelengths. This process,
combined with ionization shifts due to enhanced line blocking, can lead to a
stronger UV flux as the iron-group abundance in the outer layers is increased,
contrary to previous claims.


title: Cluster formation in the Fermi system with long-range interaction

abstract:
  Based on statistical approach we described possible formation of spatially
inhomogeneous distribution in the system of interacting Fermi particles by
long-rage forces, and we demonstrated nonperturbative calculation of the
partition function in this case. It was shown, that particles interacting with
an attractive $1/r$ potential form clusters. Cluster is equilibrium structure,
if we suppose that average energy of interaction of two particles is much less
than their average kinetic energy $kT$. The analogy between self-gravitation
gas and plasma was shown. The dynamics of cluster formation was considered with
help hydrodynamical and statistical approaches, and time of relaxation to
equilibrium state was found.


title:
XMM-Newton observations of Zeta Orionis (O9.7 Ib): A Collisional
  Ionization Equilibrium model

abstract:
  We present XMM-Newton observations of the O supergiant Zeta Orionis (O9.7
Ib). The spectra are rich in emission lines over a wide range of ionization
stages. The RGS-spectra show for the first time lines of low ion stages such as
C VI, N VI, N VII, and O VII. The line profiles are symmetric and rather broad
(FWHM approximately 1500 km/s) and show only a slight blue shift. With the
XMM-epic spectrometer several high ions are detected in this star for the first
time including Ar XVII and S XV. Simultaneous multi-temperature fits and
DEM-modeling were applied to the RGS and EPIC spectra to obtain emission
measures, elemental abundances and plasma temperatures. The calculations show
temperatures in the range of about 0.07-0.6 keV. According to the derived
models the intrinsic source X-ray luminosity at a distance of 251 pc
Lx=1.37(.03) times 10^{32} ergs/s, in the energy range 0.3-10 keV. In the best
multi-temperature model fit, the abundances of C, N, O, and Fe are near their
solar values, while the abundances of Ne, Mg, and Si appear somewhat enhanced.
The sensitivity of the He-like forbidden and intercombination lines to Zeta
Ori's strong radiation field is used to derive the radial distances at which
lines are formed. Values of 34 R-star for N VI, 12.5 R-star for O VII, 4.8
R-star for Ne IX, and 3.9 R-star for Mg XI are obtained.


title:
A Method for Solving Cyclic Block Penta-diagonal Systems of Linear
  Equations

abstract:
  A method for solving cyclic block three-diagonal systems of equations is
generalized for solving a block cyclic penta-diagonal system of equations.
Introducing a special form of two new variables the original system is split
into three block pentagonal systems, which can be solved by the known methods.
As such method belongs to class of direct methods without pivoting.
Implementation of the algorithm is discussed in some details and the numerical
examples are present.


title: Vandermonde Frequency Division Multiplexing for Cognitive Radio

abstract:
  We consider a cognitive radio scenario where a primary and a secondary user
wish to communicate with their corresponding receivers simultaneously over
frequency selective channels. Under realistic assumptions that the secondary
transmitter has no side information about the primary's message and each
transmitter knows only its local channels, we propose a Vandermonde precoder
that cancels the interference from the secondary user by exploiting the
redundancy of a cyclic prefix. Our numerical examples show that VFDM, with an
appropriate design of the input covariance, enables the secondary user to
achieve a considerable rate while generating zero interference to the primary
user.


title: Improved Study of the Antiprotonic Helium Hyperfine Structure

abstract:
  We report the initial results from a systematic study of the hyperfine (HF)
structure of antiprotonic helium (n,l) = (37,~35) carried out at the Antiproton
Decelerator (AD) at CERN. We performed a laser-microwave-laser resonance
spectroscopy using a continuous wave (cw) pulse-amplified laser system and
microwave cavity to measure the HF transition frequencies. Improvements in the
spectral linewidth and stability of our laser system have increased the
precision of these measurements by a factor of five and reduced the line width
by a factor of three compared to our previous results. A comparison of the
experimentally measured transition frequencies with three body QED calculations
can be used to determine the antiproton spin magnetic moment, leading towards a
test of CPT invariance.


title:
Searching for links between magnetic fields and stellar evolution III.
  Measurement of magnetic fields in open cluster Ap stars with ESPaDOnS

abstract:
  We are carrying out a survey of magnetic fields in Ap stars in open clusters
in order to obtain the first sample of magnetic upper main sequence stars with
precisely known ages. These data will constrain theories of field evolution in
these stars. Using the new spectropolarimeter ESPaDOnS at CFHT, we have
obtained 44 measurements of the mean longitudinal fields of 23 B6 - A2 stars
that have been identified as possible Ap stars and that are possible members of
open clusters, with a median uncertainty of about 45 G. Of these stars, 10 have
definite field detections. Nine stars of our sample are found not to be
magnetic Ap stars. The ESPaDOnS data contain a large amount of useful
information not readily obtained from lower resolution spectropolarimetry. With
the new observations we are able to expand the available data on fields of
low-mass, relatively evolved Ap stars, and identify more robustly which
observed stars are actually magnetic Ap stars and cluster members. Re-analysis
of the enlarged data set of cluster Ap stars indicates that such stars with
masses in the range of 2 -- 5 \mo show RMS fields larger than about 1 kG only
when they are near the ZAMS. The time scale on which these large fields
disappear varies strongly with mass, ranging from about 250 Myr for stars of 2
- 3 solar mass to 15 Myr for stars of 4 - 5 solar mass. Our data are consistent
either with emergent flux conservation for most (but not all) Ap stars, or with
modest decline in flux with age.


title:
The 3-dimensional random walk with applications to overstretched DNA and
  the protein titin

abstract:
  We study the three-dimensional persistent random walk with drift. Then we
develop a thermodynamic model that is based on this random walk without
assuming the Boltzmann-Gibbs form for the equilibrium distribution. The
simplicity of the model allows us to perform all calculations in closed form.
We show that, despite its simplicity, the model can be used to describe
different polymer stretching experiments. We study the reversible
overstretching transition of DNA and the static force-extension relation of the
protein titin.


title: Statistical analysis of self-similar conservative fragmentation chains

abstract:
  We explore statistical inference in self-similar conservative fragmentation
chains when only approximate observations of the sizes of the fragments below a
given threshold are available. This framework, introduced by Bertoin and
Martinez [Adv. Appl. Probab. 37 (2005) 553--570], is motivated by mineral
crushing in the mining industry. The underlying object that can be identified
from the data is the step distribution of the random walk associated with a
randomly tagged fragment that evolves along the genealogical tree
representation of the fragmentation process. We compute upper and lower rates
of estimation in a parametric framework and show that in the nonparametric
case, the difficulty of the estimation is comparable to ill-posed linear
inverse problems of order 1 in signal denoising.


title:
Quasi-static and dynamic order-disorder transition in presence of strong
  pinning

abstract:
  We present the results of an experimental study of vortex dynamics in
non-twinned $YBa_2Cu_3O_{6,87}$ crystal. It is found that critical currents
$J_c$ and $J_{c,dyn}$, which correspond to the pinning force in the thermal
creep and flux flow mode, respectively, non-monotonically vary with the
magnetic field. However, the minimum in the $J_{c,dyn}(H)$ dependence is
observed in higher fields, compared with the minimum position $H_{OD}$ in the
$J_c(H)$ dependence. Considering that the field $H_{OD}$ corresponds to the
static order-disorder transition, this difference is explained by partial
dynamic ordering of the vortex solid. It is concluded that finite transverse
barriers guarantee finite density of transverse displacements of vortex lines
$u_t\simeq c_La_0$ suitable for preservation of the disordered state of the
moving vortex solid.


title: Multiple Quantum Well AlGaAs Nanowires

abstract:
  This letter reports on the growth, structure and luminescent properties of
individual multiple quantum well (MQW) AlGaAs nanowires (NWs). The composition
modulations (MQWs) are obtained by alternating the elemental flux of Al and Ga
during the molecular beam epitaxy growth of the AlGaAs wire on GaAs (111)B
substrates. Transmission electron microscopy and energy dispersive X-ray
spectroscopy performed on individual NWs are consistent with a configuration
composed of conical segments stacked along the NW axis. Micro-photoluminescence
measurements and confocal microscopy showed enhanced light emission from the
MQW NWs as compared to non-segmented NWs due to carrier confinement and
sidewall passivation.


title:
Separation of variables and integral manifolds in one problem of motion
  of generalized Kowalevski top

abstract:
  In the phase space of the integrable Hamiltonian system with three degrees of
freedom used to describe the motion of a Kowalevski-type top in a double
constant force field, we point out the four-dimensional invariant manifold. It
is shown that this manifold consists of critical motions generating a smooth
sheet of the bifurcation diagram, and the induced dynamic system is Hamiltonian
with certain subset of points of degeneration of the symplectic structure. We
find the transformation separating variables in this system. As a result, the
solutions can be represented in terms of elliptic functions of time. The
corresponding phase topology is completely described.


title: Herwig++ Physics and Manual

abstract:
  In this paper we describe Herwig++ version 2.3, a general-purpose Monte Carlo
event generator for the simulation of hard lepton-lepton, lepton-hadron and
hadron-hadron collisions. A number of important hard scattering processes are
available, together with an interface via the Les Houches Accord to specialized
matrix element generators for additional processes. The simulation of Beyond
the Standard Model (BSM) physics includes a range of models and allows new
models to be added by encoding the Feynman rules of the model. The
parton-shower approach is used to simulate initial- and final-state QCD
radiation, including colour coherence effects, with special emphasis on the
correct description of radiation from heavy particles. The underlying event is
simulated using an eikonal multiple parton-parton scattering model. The
formation of hadrons from the quarks and gluons produced in the parton shower
is described using the cluster hadronization model. Hadron decays are simulated
using matrix elements, where possible including spin correlations and off-shell
effects.


title: Condensation of Classical Nonlinear Waves in a Two-Component System

abstract:
  We study the formation of large-scale coherent structures (a condensate) for
a system of two weakly interacting classical waves. Using the coupled
defocusing nonlinear Schr\"odinger (NLS) equations as a representative model,
we focus on condensation in the phase mixing regime. We employ weak turbulence
theory to provide a complete thermodynamic description of the classical
condensation process. We show that the temperature and the condensate mass
fractions are fully determined by the total number of particles in each
component and the initial total energy. Moreover, we find that, at higher
energies, condensation can occur in only one component. The theory presented
provides excellent agreement with results of numerical simulations obtained by
directly integrating the dynamical model.


title: On deriving p-mode parameters for inclined solar-like stars

abstract:
  Thanks to their high quality, new and upcoming asteroseismic observations -
with CoRoT, Kepler, and from the ground... - can benefit from the experience
gained with helioseismology. We focus in this paper on solar-like oscillations,
for which the inclination of the rotation axis is unknown. We present a
theoretical study of the errors of p-mode parameters determined by means of a
maximum-likelihood estimator, and we also analyze correlations and biases. We
have used different, complementary approaches: we have performed either
semi-analytical computation of the Hessian matrix, fitting of single mean
profiles, or Monte Carlo simulations. We give first analytical approximations
for the errors of frequency, inclination and rotational splitting. The
determination of the inclination is very challenging for the common case of
slow rotators (like the Sun), making difficult the determination of a reliable
rotational splitting. Moreover, due to the numerous correlations, biases - more
or less significant - can appear in the determination of various parameters in
the case of bad inclination fittings, especially when a locking at 90 degrees
occurs. This issue concerning inclination locking is also discussed.
Nevertheless, the central frequency and some derived parameters such as the
total power of the mode are free of such biases.


title: Neutron-Neutron Correlations in the Dissociation of Halo Nuclei

abstract:
  Studies attempting to probe the spatial configuration of the valence neutrons
in two-neutron halo nuclei using the technique of intensity interferometry are
described. Following a brief review of the method and its application to
earlier measurements of the breakup of 6He, 11Li and 14Be, the results of the
analysis of a high statistics data set for 6He are presented. The limitations
of the technique, including the assumption of incoherent emission in the
breakup and the sensitivity to the continuum states populated in the
dissociation rather than the ground state, are discussed.


title: Off resonance background effects in e+e- -> t anti-t H

abstract:
  The top quark Yukawa coupling to the intermediate mass Higgs boson can be
determined in the reaction e+e- -> t anti-t H that, after taking into account
decays, will be detected at the International Linear Collider through reactions
with 8 particles in the final state. Such 2 -> 8 reactions receive
contributions from tens thousands of Feynman diagrams, already in the lowest
order of Standard Model, most of which comprise background to resonant
associated production and decay of the top quark pair and Higgs boson. We
illustrate the background effects by comparing cross sections of three
reactions, which represent different detection channels of e+e- -> t anti-t H,
calculated with the complete sets of the lowest order Feynman diagrams with the
corresponding signal cross sections calculated with the diagrams of associated
production and decay of off mass shell top quark pair and Higgs boson only. The
comparison that is performed with different selections of cuts shows that the
background effects are sizeable, but they can be reduced by appropriate choice
of cuts.


title:
Matrix genetics, part 1: permutations of positions in triplets and
  symmetries of genetic matrices

abstract:
  The Kronecker family of the genetic matrices is investigated, which is based
on the genetic matrix [C T; A G], where C, T, A, G are the letters of the
genetic alphabet. The matrix [C T; A G] in the second Kronecker power is the
(4*4)-matrix of 16 duplets. The matrix [C T; A G] in the third Kronecker power
is the (8*8)-matrix of 64 triplets. It is significant that peculiarities of the
degeneracy of the genetic code are reflected in the symmetrical black-and-white
mosaic of these genetic matrices. The article represents interesting
mathematical properties of these mosaic matrices, which are connected with
positional permutations inside duplets and triplets; with projector operators;
with unitary matrices and cyclic groups, etc. Fractal genetic nets are proposed
as a new effective tool to study long nucleotide sequences. Some results about
revealing new symmetry principles of long nucleotide sequences are described.


title:
Probing the Effective Number of Neutrino Species with Cosmic Microwave
  Background

abstract:
  We discuss how much we can probe the effective number of neutrino species
N_nu with cosmic microwave background alone. Using the data of WMAP, ACBAR, CBI
and BOOMERANG experiments, we obtain a constraint on the effective number of
neutrino species as 0.96< N_nu <7.94 at 95% C.L. for a power-law LCDM flat
universe model. The limit is improved to be 1.39 < N_nu < 6.38 at 95% C.L. if
we assume that the baryon density, N_nu and the helium abundance are related by
the big bang nucleosynthesis theory. We also provide a forecast for the PLANCK
experiment using a Markov chain Monte Carlo approach. In addition to
constraining N_nu, we investigate how the big bang nucleosynthesis relation
affects the estimation for these parameters and other cosmological parameters.


title: Locality of dynamics in general harmonic quantum systems

abstract:
  The Lieb-Robinson theorem states that locality is approximately preserved in
the dynamics of quantum lattice systems. Whenever one has finite-dimensional
constituents, observables evolving in time under a local Hamiltonian will
essentially grow linearly in their support, up to exponentially suppressed
corrections. In this work, we formulate Lieb-Robinson bounds for general
harmonic systems on general lattices, for which the constituents are
infinite-dimensional, as systems representing discrete versions of free fields
or the harmonic approximation to the Bose-Hubbard model. We consider both local
interactions as well as infinite-ranged interactions, showing how corrections
to locality are inherited from the locality of the Hamiltonian: Local
interactions result in stronger than exponentially suppressed corrections,
while non-local algebraic interactions result in algebraic suppression. We
derive bounds for canonical operators, Weyl operators and outline
generalization to arbitrary operators. As an example, we discuss the
Klein-Gordon field, and see how the approximate locality in the lattice model
becomes the exact causality in the field limit. We discuss the applicability of
these results to quenched lattice systems far from equilibrium, and the
dynamics of quantum phase transitions.


title:
Optical circuits based on Polariton Neurons in Semiconductor
  Microcavities

abstract:
  By exploiting the polarization multistability of polaritons, we show that
polarized signals can be conducted in the plane of a semiconductor microcavity
along controlled channels or "neurons". Furthermore due to the interaction of
polaritons with opposite spins it is possible to realize binary logic gates
operating on the polarization degree of freedom. Multiple gates can be
integrated together to form an optical circuit contained in a single
semiconductor microcavity.


title: Sagbi Bases of Cox-Nagata Rings

abstract:
  We degenerate Cox-Nagata rings to toric algebras by means of sagbi bases
induced by configurations over the rational function field. For del Pezzo
surfaces, this degeneration implies the Batyrev-Popov conjecture that these
rings are presented by ideals of quadrics. For the blow-up of projective
n-space at n+3 points, sagbi bases of Cox-Nagata rings establish a link between
the Verlinde formula and phylogenetic algebraic geometry, and we use this to
answer questions due to D'Cruz-Iarobbino and Buczynska-Wisniewski. Inspired by
the zonotopal algebras of Holtz and Ron, our study emphasizes explicit
computations, and offers a new approach to Hilbert functions of fat points.


title: Bifurcation diagrams of the Kowalevski top in two constant fields

abstract:
  The Kowalevski top in two constant fields is known as the unique profound
example of an integrable Hamiltonian system with three degrees of freedom not
reducible to a family of systems in fewer dimensions. As the first approach to
topological analysis of this system we find the critical set of the integral
map; this set consists of the trajectories with number of frequencies less than
three. We obtain the equations of the bifurcation diagram in R^3. A
correspondence to the Appelrot classes in the classical Kowalevski problem is
established. The admissible regions for the values of the first integrals are
found in the form of some inequalities of general character and boundary
conditions for the induced diagrams on energy levels.


title: Unconventional quasiparticle lifetime in undoped graphene

abstract:
  We address the question of how small can the quasiparticle decay rate be at
low energies in undoped graphene, where kinematical constraints are known to
prevent the decay into particle-hole excitations. For this purpose, we study
the renormalization of the phonon dispersion by many-body effects, which turns
out to be very strong in the case of the out-of-plane phonons at the K point of
the spectrum. We show that these evolve into a branch of very soft modes that
provide the relevant channel for quasiparticle decay, at energies below the
scale of the optical phonon modes. In this regime, we find that the decay rate
is proportional to the cube of the quasiparticle energy. This implies that a
crossover should be observed in transport properties from the linear dependence
characteristic of the high-energy regime to the much slower decay rate due to
the soft phonon modes.


title: AdS/CFT Duality for Non-Anticommutative Supersymmetric Gauge Theory

abstract:
  We construct type IIB supergravity duals of non-anticommutative deformed N =
4 SU(N) gauge theories. We consider in particular deformations preserving N =
(1,0) and N = (1/2,0) supersymmetry. Such theories can be realised on N
D3-branes in specific self-dual 5-form backgrounds. We show that the required
5-form field strengths can be produced by configurations of intersecting
D3-branes and we are then able to construct the supergravity solutions in the
near-horizon limit. We consider some consequences of this duality, in
particular showing that the gravity duals predict that the dimensions of a
subset of BPS operators are not modified by the deformation.


title:
The broad-band XMM-Newton and INTEGRAL spectra of bright type 1 Seyfert
  galaxies

abstract:
  The 0.5-150 keV broad-band spectra of a sample of nine bright type 1 Seyfert
galaxies are analyzed here. These sources have been discovered/detected by
INTEGRAL and subsequently observed with XMM--Newton for the first time with
high sensitivity below 10 keV. The sample, although small, is representative of
the population of type 1 AGN which are now being observed above 20 keV. The
intrinsic continuum has been modeled using three different parameterizations: a
power-law model, an exponential cut-off power-law and an exponential cut-off
power-law with a Compton reflection component. In each model the presence of
intrinsic absorption, a soft component and emission line reprocessing features
has also been tested. A simple power-law model is a statistically good
description of most of the spectra presented here; an FeK line, fully and/or
partial covering absorption and a soft spectral component are detected in the
majority of the sample sources. The average photon index (< Gamma > = 1.7 $\pm$
0.2) is consistent, within errors, with the canonical spectral slope often
observed in AGN although the photon index distribution peaks in our case at
flat Gamma (~ 1.5) values. For four sources, we find a significantly improved
fit when the power-law is exponentially cut-off at an energy which is
constrained to be below ~ 150 keV. The Compton reflection parameter could be
estimated in only two objects of the sample and in both cases is found to be R
> 1.


title:
Admissibility and Controllability of diagonal Volterra equations with
  scalar inputs

abstract:
  This article studies Volterra evolution equations from the point of view of
control theory, in the case that the generator of the underlying semigroup has
a Riesz basis of eigenvectors. Conditions for admissibility of the system's
control operator are given in terms of the Carleson embedding properties of
certain discrete measures. Moreover, exact and null controllability are
expressed in terms of a new interpolation question for analytic functions,
providing a generalization of results known to hold for the standard Cauchy
problem. The results are illustrated by examples involving heat conduction with
memory.


title: Asymptotic link invariants for ergodic vector fields

abstract:
  We study the asymptotics of a family of link invariants on the orbits of a
smooth volume-preserving ergodic vector field on a compact domain of the
3-space. These invariants, called linear saddle invariants, include many
concordance invariants and generate an infinite-dimensional vector space of
link invariants. In contrast, the vector space of asymptotic linear saddle
invariants is 1-dimensional, generated by the asymptotic signature. We also
relate the asymptotic slice genus to the asymptotic signature.


title:
Polarized emission of GaN/AlN quantum dots : single dot spectroscopy and
  symmetry-based theory

abstract:
  We report micro-photoluminescence studies of single GaN/AlN quantum dots
grown along the (0001) crystal axis by molecular beam epitaxy on Si(111)
substrates. The emission lines exhibit a linear polarization along the growth
plane, but with varying magnitudes of the polarization degree and with
principal polarization axes that do not necessarily correspond to
crystallographic directions. Moreover, we could not observe any splitting of
polarized emission lines, at least within the spectral resolution of our setup
(1 meV). We propose a model based on the joint effects of electron-hole
exchange interaction and in-plane anisotropy of strain and/or quantum dot
shape, in order to explain the quantitative differences between our
observations and those previously reported on, e.g. CdTe- or InAs-based quantum
dots.


title: Series of Reciprocal Powers of k-almost Primes

abstract:
  Sums over inverse s-th powers of semiprimes and k-almost primes are
transformed into sums over products of powers of ordinary prime zeta functions.
Multinomial coefficients known from the cycle decomposition of permutation
groups play the role of expansion coefficients. Founded on a known convergence
acceleration for the ordinary prime zeta functions, the sums and first
derivatives are tabulated with high precision for indices k=2,...,6 and integer
powers s=2,...,8.


title: Heavy Quark Diffusion as a Probe of the Quark-Gluon Plasma

abstract:
  We report on recent research on the properties of elementary particle matter
governed by the strong force at high temperatures, where QCD predicts hadrons
to dissolve into the Quark-Gluon Plasma (QGP). After a short introduction to
the basic elements of QCD in the vacuum, most notably quark confinement and
mass generation, we discuss how these phenomena relate to phase changes in
strongly interacting matter at high temperature. We briefly review the main
experimental findings at the Relativistic Heavy Ion Collider (RHIC) which
provide strong evidence that a QGP has been produced, with unprecedentedly
small viscosity and large opacity. We discuss how heavy quarks (charm and
bottom) can be utilized to quantitatively probe the transport properties of a
strongly coupled QGP (sQGP). The large heavy-quark (HQ) mass allows to set up a
Brownian motion approach, which can serve to evaluate different approaches for
HQ interactions in the sQGP. The implementation of lattice QCD based HQ
potentials generates pre-hadronic resonance structures in HQ scattering in the
medium, leading to large interaction rates and small diffusion coefficients.
The resonance correlations are strongest close to the critical temperature
(T_c), suggesting an intimate connection to the hadronization of the QGP. The
implementation of HQ transport into Langevin simulations of an expanding QGP
fireball at RHIC enables quantitative comparisons with experiment. The
extracted HQ diffusion coefficients are employed for schematic estimates of the
shear viscosity, corroborating the notion of a strongly-coupled QGP in the
vicinity of T_c.


title: Radiative heat transfer between metallic nanoparticles

abstract:
  In this letter, we study the radiative heat transfer between two
nanoparticles in the near field and in the far field. We find that the heat
transfer is dominated by the electric dipole-dipole interaction for dielectric
particles and by the magnetic dipole-dipole interaction for metallic
nanoparticles. We introduce polarizabilities formulas valid for arbitrary
values of the skin depth. While the heat transfer mechanism is different for
metallic and dielectric nanoparticles, we show that the distance dependence is
the same. However, the dependence of the heat flux on the particle radius is
different.


title:
Convergence dynamics of 2-dimensional isotropic and anisotropic
  Bak-Sneppen models

abstract:
  The conventional Hamming distance measurement captures only the short-time
dynamics of the displacement between the uncorrelated random configurations.
The minimum difference technique introduced by Tirnakli and Lyra [Int. J. Mod.
Phys. C 14, 805 (2003)] is used to study the short-time and long-time dynamics
of the two distinct random configurations of the isotropic and anisotropic
Bak-Sneppen models on a square lattice. Similar to 1-dimensional case, the time
evolution of the displacement is intermittent. The scaling behavior of the jump
activity rate and waiting time distribution reveal the absence of typical
spatial-temporal scales in the mechanism of displacement jumps used to quantify
the convergence dynamics.


title:
A Numerical Approach to the Estimation of the Solutions of some
  Variational Problems with Convexity Costraints

abstract:
  We present an algorithm to approximate the solutions to variational problems
where set of admissible functions consists of convex functions. The main
motivator behind this numerical method is estimating solutions to Adverse
Selection problems within a Principal-Agent framework. Problems such as product
lines design, optimal taxation, structured derivatives design, etc. can be
studied through the scope of these models. We develop a method to estimate
their optimal pricing schedules.


title: Spherically symmetric cosmology: resource paper

abstract:
  We use the 1+3 frame formalism to write down the evolution equations for
spherically symmetric models as a well-posed system of first order PDEs in two
variables, suitable for numerical and qualitative analysis.


title: On the ruin problem in the renewal risk processes perturbed by diffusion

abstract:
  In this paper, we consider the perturbed renewal risk process. Systems of
integro-differential equations for the Gerber-Shiu functions at ruin caused by
a claim and oscillation are established, respectively. The explicit Laplase
transforms of Gerber-Shiu functions are obtained, while the closed form
expressions for the Gerber-Shiu functions are derived when the claim amount
distribution is from the rational family. Finally, we present numerical
examples intended to illustrate the main results.


title: Entropy maximization in the force network ensemble for granular solids

abstract:
  A long-standing issue in the area of granular media is the tail of the force
distribution, in particular whether this is exponential, Gaussian, or even some
other form. Here we resolve the issue for the case of the force network
ensemble in two dimensions. We demonstrate that conservation of the total area
of a reciprocal tiling, a direct consequence of local force balance, is crucial
for predicting the local stress distribution. Maximizing entropy while
conserving the tiling area and total pressure leads to a distribution of local
pressures with a generically Gaussian tail that is in excellent agreement with
numerics, both with and without friction and for two different contact
networks.


title: Uniform partitions of frames of exponentials into Riesz sequences

abstract:
  The Feichtinger Conjecture, if true, would have as a corollary that for each
set $E\subset \T$ and $\Lambda \subset \Z$, there is a partition
$\Lambda_1,...,\Lambda_N$ of $\Z$ such that for each $1\le i \le N$,
$\{\exp(2\pi i x\lambda): \lambda \in \Lambda_i\}$ is a Riesz sequence. In this
paper, sufficient conditions on sets $E\subset \T$ and $\Lambda\subset \R$ are
given so that $\{\exp(2\pi i x\lambda) 1_E: \lambda \in \Lambda\}$ can be
uniformly partitioned into Riesz sequences.


title: Quantum computing, phase estimation and applications

abstract:
  In this thesis, attention is paid to small experimental testbed applications
with respect to the quantum phase estimation algorithm, the core approach for
finding energy eigenvalues. An iterative scheme for quantum phase estimation
(IPEA) is derived from the Kitaev phase estimation, a study of robustness of
the IPEA utilized as a few-qubit testbed application is performed, and an
improved protocol for phase reference alignment is presented. Additionally, a
short overview of quantum cryptography is given, with a particular focus on
quantum steganography and authentication.


title:
The Multi-Dimensional Hardy Uncertainty Principle and its Interpretation
  in Terms of the Wigner Distribution; Relation With the Notion of Symplectic
  Capacity

abstract:
  We extend Hardy's uncertainty principle for a square integrable function and
its Fourier transform to the multidimensional case using a symplectic
diagonalization. We use this extension to show that Hardy's uncertainty
principle is equivalent to a statement on the Wigner distribution of the
function. We give a geometric interpretation of our results in terms of the
notion of symplectic capacity of an ellipsoid. Furthermore, we show that
Hardy's uncertainty principle is valid for a general Lagrangian frame of the
phase space. Finally, we discuss an extension of Hardy's theorem for the Wigner
distribution for exponentials with convex exponents.


title:
A new measurement of the structure functions $P_{LL}-P_{TT}/epsilon$ and
  $P_{LT}$ in virtual Compton scattering at $Q^2=$ 0.33 (GeV/c)$^2$

abstract:
  The cross section of the $ep \to e' p' \gamma$ reaction has been measured at
$Q^2 = 0.33$ (GeV/c)$^2$. The experiment was performed using the electron beam
of the MAMI accelerator and the standard detector setup of the A1
Collaboration. The cross section is analyzed using the low-energy theorem for
virtual Compton scattering, yielding a new determination of the two structure
functions $P_LL}-P_{TT}/epsilon$ and $P_{LT}$ which are linear combinations of
the generalized polarizabilities of the proton. We find somewhat larger values
than in the previous investigation at the same $Q^2$. This difference, however,
is purely due to our more refined analysis of the data. The results tend to
confirm the non-trivial $Q^2$-evolution of the generalized polarizabilities and
call for more measurements in the low-$Q^2$ region ($\le$ 1 (GeV/c)$^2$).


title:
Tilted anisotropic Dirac cones in quinoid-type graphene and
  alpha-(BEDT-TTF)_2I_3

abstract:
  We investigate a generalized two-dimensional Weyl Hamiltonian, which may
describe the low-energy properties of mechanically deformed graphene and of the
organic compound alpha-(BEDT-TTF)_2I_3 under pressure. The associated
dispersion has generically the form of tilted anisotropic Dirac cones. The tilt
arises due to next-nearest-neighbor hopping when the Dirac points, where the
valence band touches the conduction band, do not coincide with crystallographic
high-symmetry points within the first Brillouin zone. Within a semiclassical
treatment, we describe the formation of Landau levels in a strong magnetic
field, the relativistic form of which is reminiscent to that of graphene, with
a renormalized Fermi velocity due to the tilt of the Dirac cones. These
relativistic Landau levels, experimentally accessible via spectroscopy or even
a quantum Hall effect measurement, may be used as a direct experimental
verification of Dirac cones in alpha-(BEDT-TTF)_2I_3.


title: Quaternions, octonions and Bell-type inequalities

abstract:
  Multipartite Bell-type inequalities are derived for general systems. They
involve up to eight observables with arbitrary spectra on each site. These
inequalities are closely related to the algebras of quaternions and octonions.


title:
Bound States in Time-Dependent Quantum Transport: Oscillations and
  Memory Effects in Current and Density

abstract:
  The presence of bound states in a nanoscale electronic system attached to two
biased, macroscopic electrodes is shown to give rise to persistent,
non-decaying, localized current oscillations which can be much larger than the
steady part of the current. The amplitude of these oscillations depends on the
entire history of the applied potential. The bound-state contribution to the
{\em static} density is history-dependent as well. Moreover, the time-dependent
formulation leads to a natural definition of the bound-state occupations out of
equilibrium.


title:
Effective one body approach to the dynamics of two spinning black holes
  with next-to-leading order spin-orbit coupling

abstract:
  Using a recent, novel Hamiltonian formulation of the gravitational
interaction of spinning binaries, we extend the Effective One Body (EOB)
description of the dynamics of two spinning black holes to next-to-leading
order (NLO) in the spin-orbit interaction. The spin-dependent EOB Hamiltonian
is constructed from four main ingredients: (i) a transformation between the
``effective'' Hamiltonian and the ``real'' one, (ii) a generalized effective
Hamilton-Jacobi equation involving higher powers of the momenta, (iii) a
Kerr-type effective metric (with Pad\'e-resummed coefficients) which depends on
the choice of some basic ``effective spin vector'' $\bf{S}_{\rm eff}$, and
which is deformed by comparable-mass effects, and (iv) an additional effective
spin-orbit interaction term involving another spin vector $\bsigma$. As a first
application of the new, NLO spin-dependent EOB Hamiltonian, we compute the
binding energy of circular orbits (for parallel spins) as a function of the
orbital frequency, and of the spin parameters. We also study the
characteristics of the last stable circular orbit: binding energy, orbital
frequency, and the corresponding dimensionless spin parameter $\hat{a}_{\rm
LSO}\equiv c J_{\rm LSO}/\boldsymbol(G(H_{\rm LSO}/c^2)^2\boldsymbol)$. We find
that the inclusion of NLO spin-orbit terms has a significant ``moderating''
effect on the dynamical characteristics of the circular orbits for large and
parallel spins.


title:
Anisotropic Heisenberg model on hierarchical lattices with aperiodic
  interactions: a renormalization-group approach

abstract:
  Using a real-space renormalization-group approximation, we study the
anisotropic quantum Heisenberg model on hierarchical lattices, with
interactions following aperiodic sequences. Three different sequences are
considered, with relevant and irrelevant fluctuations, according to the
Luck-Harris criterion. The phase diagram is discussed as a function of the
anisotropy parameter $\Delta$ (such that $\Delta=0$ and $\Delta=1$ correspond
to the isotropic Heisenberg and Ising models, respectively). We find three
different types of phase diagrams, with general characteristics: the isotropic
Heisenberg plane is always an invariant one (as expected by symmetry arguments)
and the critical behavior of the anisotropic Heisenberg model is governed by
fixed points on the Ising-model plane. Our results for the isotropic Heisenberg
model show that the relevance or irrelevance of aperiodic models, when compared
to their uniform counterpart, is as predicted by the Harris-Luck criterion. A
low-temperature renormalization-group procedure was applied to the
\textit{classical} isotropic Heisenberg model in two-dimensional hierarchical
lattices: the relevance criterion is obtained, again in accordance with the
Harris-Luck criterion.


title:
Siegel modular forms of genus 2 and level 2: cohomological computations
  and conjectures

abstract:
  We study the cohomology of certain local systems on moduli spaces of
principally polarized abelian surfaces with a level 2 structure. The trace of
Frobenius on the alternating sum of the \'etale cohomology groups of these
local systems can be calculated by counting the number of pointed curves of
genus 2 with a prescribed number of Weierstrass points over the given finite
field. This cohomology is intimately related to vector-valued Siegel modular
forms. The corresponding scheme in level 1 was carried out in [FvdG]. Here we
extend this to level 2 where new phenomena appear.
  We determine the contribution of the Eisenstein cohomology together with its
S_6-action for the full level 2 structure and on the basis of our computations
we make precise conjectures on the endoscopic contribution. We also make a
prediction about the existence of a vector-valued analogue of the
Saito-Kurokawa lift. Assuming these conjectures that are based on ample
numerical evidence, we obtain the traces of the Hecke-operators T(p) for p < 41
on the remaining spaces of `genuine' Siegel modular forms. We present a number
of examples of 1-dimensional spaces of eigenforms where these traces coincide
with the Hecke eigenvalues. We hope that the experts on lifting and on
endoscopy will be able to prove our conjectures.


title: The Aspen--Amsterdam Void Finder Comparison Project

abstract:
  Despite a history that dates back at least a quarter of a century studies of
voids in the large--scale structure of the Universe are bedevilled by a major
problem: there exist a large number of quite different void--finding
algorithms, a fact that has so far got in the way of groups comparing their
results without worrying about whether such a comparison in fact makes sense.
Because of the recent increased interest in voids, both in very large galaxy
surveys and in detailed simulations of cosmic structure formation, this
situation is very unfortunate. We here present the first systematic comparison
study of thirteen different void finders constructed using particles, haloes,
and semi--analytical model galaxies extracted from a subvolume of the
Millennium simulation. The study includes many groups that have studied voids
over the past decade. We show their results and discuss their differences and
agreements. As it turns out, the basic results of the various methods agree
very well with each other in that they all locate a major void near the centre
of our volume. Voids have very underdense centres, reaching below 10 percent of
the mean cosmic density. In addition, those void finders that allow for void
galaxies show that those galaxies follow similar trends. For example, the
overdensity of void galaxies brighter than $m_B = -20 $ is found to be smaller
than about -0.8 by all our void finding algorithms.


title: Nonrational conformal field theory

abstract:
  We discuss the problem to develop a mathematical theory of a certain class of
nonrational conformal field theories (CFT) which contain the unitary CFT. A
variant of the concept of a modular functor is proposed that appears to be
suitable for such CFT.


title: Perihelion precession for modified Newtonian gravity

abstract:
  We calculate the perihelion precession delta for nearly circular orbits in a
central potential V(r). Differently from other approaches to this problem, we
do not assume that the potential is close to the Newtonian one. The main idea
in the deduction is to apply the underlying symmetries of the system to show
that delta must be a function of r V''(r)/V'(r), and to use the transformation
behaviour of delta in a rotating system of reference. This is equivalent to
say, that the effective potential can be written in a one-parameter set of
possibilities as sum of centrifugal potential and potential of the central
force. We get a universal formula for delta. It has to be read as follows: a
circular orbit at this value r exists and is stable if and only if this delta
is a well-defined real; and if this is the case, then the angular difference
from one perihelion to the next one for nearly circular orbits at this r is
exactly 2 pi + delta. Then we show how to apply this result to examples of
recent interest like modified Newtonian gravity and linearized fourth-order
gravity. In the second part of the paper, we generalize this universal formula
to static spherically symmetric space-times. For the Schwarzschild black hole
with mass parameter m > 0 it leads to a surprisingly unknown formula. It
represents a strict result and is applicable for all values r > 6m and is in
good agreement with the fact that stable circular orbits exist for r > 6m only.


title:
Protecting coherence in Optimal Control Theory: State dependent
  constraint approach

abstract:
  Optimal control theory is developed for the task of obtaining a primary
objective in a subspace of the Hilbert space while avoiding other subspaces of
the Hilbert space. The primary objective can be a state-to-state transition or
a unitary transformation. A new optimization functional is introduced which
leads to monotonic convergence of the algorithm. This approach becomes
necessary for molecular systems subject to processes implying loss of coherence
such as predissociation or ionization. In these subspaces controllability is
hampered or even completely lost. Avoiding the lossy channels is achieved via a
functional constraint which depends on the state of the system at each instant
in time. We outline the resulting new algorithm, discuss its convergence
properties and demonstrate its functionality for the example of a
state-to-state transition and of a unitary transformation for a model of cold
Rb2.


title:
The Polychronakos-Frahm spin chain of BC_N type and Berry-Tabor's
  conjecture

abstract:
  We compute the partition function of the su(m) Polychronakos-Frahm spin chain
of BC_N type by means of the freezing trick. We use this partition function to
study several statistical properties of the spectrum, which turn out to be
analogous to those of other spin chains of Haldane-Shastry type. In particular,
we find that when the number of particles is sufficiently large the level
density follows a Gaussian distribution with great accuracy. We also show that
the distribution of (normalized) spacings between consecutive levels is of
neither Poisson nor Wigner type, but is qualitatively similar to that of the
original Haldane-Shastry spin chain. This suggests that spin chains of
Haldane-Shastry type are exceptional integrable models, since they do not
satisfy a well-known conjecture of Berry and Tabor according to which the
spacings distribution of a generic integrable system should be Poissonian. We
derive a simple analytic expression for the cumulative spacings distribution of
the BC_N-type Polychronakos-Frahm chain using only a few essential properties
of its spectrum, like the Gaussian character of the level density and the fact
the energy levels are equally spaced. This expression is in excellent agreement
with the numerical data and, moreover, there is strong evidence that it can
also be applied to the Haldane-Shastry and the Polychronakos-Frahm spin chains.


title:
The nonlinear bending-torsion theory for curved rods as Gamma-limit of
  three-dimensional elasticity

abstract:
  The problem of the rigorous derivation of one-dimensional models for
nonlinearly elastic curved beams is studied in a variational setting.
Considering different scalings of the three-dimensional energy and passing to
the limit as the diameter of the beam goes to zero, a nonlinear model for
strings and a bending-torsion theory for rods are deduced.


title: What Can We Learn Privately?

abstract:
  Learning problems form an important category of computational tasks that
generalizes many of the computations researchers apply to large real-life data
sets. We ask: what concept classes can be learned privately, namely, by an
algorithm whose output does not depend too heavily on any one input or specific
training example? More precisely, we investigate learning algorithms that
satisfy differential privacy, a notion that provides strong confidentiality
guarantees in contexts where aggregate information is released about a database
containing sensitive information about individuals. We demonstrate that,
ignoring computational constraints, it is possible to privately agnostically
learn any concept class using a sample size approximately logarithmic in the
cardinality of the concept class. Therefore, almost anything learnable is
learnable privately: specifically, if a concept class is learnable by a
(non-private) algorithm with polynomial sample complexity and output size, then
it can be learned privately using a polynomial number of samples. We also
present a computationally efficient private PAC learner for the class of parity
functions. Local (or randomized response) algorithms are a practical class of
private algorithms that have received extensive investigation. We provide a
precise characterization of local private learning algorithms. We show that a
concept class is learnable by a local algorithm if and only if it is learnable
in the statistical query (SQ) model. Finally, we present a separation between
the power of interactive and noninteractive local learning algorithms.


title: Robust Smoothed Analysis of a Condition Number for Linear Programming

abstract:
  We perform a smoothed analysis of the GCC-condition number C(A) of the linear
programming feasibility problem \exists x\in\R^{m+1} Ax < 0. Suppose that
\bar{A} is any matrix with rows \bar{a_i} of euclidean norm 1 and,
independently for all i, let a_i be a random perturbation of \bar{a_i}
following the uniform distribution in the spherical disk in S^m of angular
radius \arcsin\sigma and centered at \bar{a_i}. We prove that E(\ln C(A)) =
O(mn / \sigma). A similar result was shown for Renegar's condition number and
Gaussian perturbations by Dunagan, Spielman, and Teng [arXiv:cs.DS/0302011].
Our result is robust in the sense that it easily extends to radially symmetric
probability distributions supported on a spherical disk of radius
\arcsin\sigma, whose density may even have a singularity at the center of the
perturbation. Our proofs combine ideas from a recent paper of B\"urgisser,
Cucker, and Lotz (Math. Comp. 77, No. 263, 2008) with techniques of Dunagan et
al.


title:
On the Second-Order Correlation Function of the Characteristic
  Polynomial of a Hermitian Wigner Matrix

abstract:
  We consider the asymptotics of the second-order correlation function of the
characteristic polynomial of a random matrix. We show that the known result for
a random matrix from the Gaussian Unitary Ensemble essentially continues to
hold for a general Hermitian Wigner matrix. Our proofs rely on an explicit
formula for the exponential generating function of the second-order correlation
function of the characteristic polynomial.


title:
Asymptotic models for curved rods derived from nonlinear elasticity by
  Gamma-convergence

abstract:
  We study the problem of the rigorous derivation of one-dimensional models for
a thin curved beam starting from three-dimensional nonlinear elasticity. We
describe the limiting models obtained for different scalings of the energy. In
particular, we prove that the limit functional corresponding to higher scalings
coincides with the one derived by dimension reduction starting from linearized
elasticity. Finally we also address the case of thin elastic rings.


title:
Nodal Gap in Fe-Based Layered Superconductor LaO_0.9F_{0.1-delta}FeAs
  Probed by Specific Heat Measurements

abstract:
  We report the specific heat measurements on the newly discovered Fe-based
layered superconductor LaO_0.9F_{0.1-delta}FeAs with the onset transition
temperature T_c \approx 28 K. A nonlinear magnetic field dependence of the
electronic specific heat coefficient gamma(H) has been found in the low
temperature limit, which is consistent with the prediction for a nodal
superconductor. The maximum gap value Delta_0 \approx 3.4$\pm$0.5 meV was
derived by analyzing gamma(H) based on the d-wave model. We also detected the
electronic specific heat difference between 9 T and 0 T in wide temperature
region, a specific heat anomaly can be clearly observed near T_c. The Debye
temperature of our sample was determined to be about 315.7 K. Our results
suggest an unconventional mechanism for this new superconductor.


title: Graph Sparsification by Effective Resistances

abstract:
  We present a nearly-linear time algorithm that produces high-quality
sparsifiers of weighted graphs. Given as input a weighted graph $G=(V,E,w)$ and
a parameter $\epsilon>0$, we produce a weighted subgraph
$H=(V,\tilde{E},\tilde{w})$ of $G$ such that $|\tilde{E}|=O(n\log
n/\epsilon^2)$ and for all vectors $x\in\R^V$ $(1-\epsilon)\sum_{uv\in
E}(x(u)-x(v))^2w_{uv}\le \sum_{uv\in\tilde{E}}(x(u)-x(v))^2\tilde{w}_{uv} \le
(1+\epsilon)\sum_{uv\in E}(x(u)-x(v))^2w_{uv}. (*)$
  This improves upon the sparsifiers constructed by Spielman and Teng, which
had $O(n\log^c n)$ edges for some large constant $c$, and upon those of
Bencz\'ur and Karger, which only satisfied (*) for $x\in\{0,1\}^V$.
  A key ingredient in our algorithm is a subroutine of independent interest: a
nearly-linear time algorithm that builds a data structure from which we can
query the approximate effective resistance between any two vertices in a graph
in $O(\log n)$ time.


title: Scaling breakdown in flow fluctuations on complex networks

abstract:
  We propose a model of random diffusion to investigate flow fluctuations in
complex networks. We derive an analytical law showing that the dependence of
fluctuations with the mean traffic in a network is ruled by the delicate
interplay of three factors, respectively of dynamical, topological and
statistical nature. In particular, we demonstrate that the existence of a
power-law scaling characterizing the flow fluctuations at every node in the
network can not be claimed for. We show the validity of this scaling breakdown
under quite general topological and dynamical situations by means of different
traffic algorithms and by analyzing real data.


title:
Damage as Gamma-limit of microfractures in anti-plane linearized
  elasticity

abstract:
  A homogenization result is given for a material having brittle inclusions
arranged in a periodic structure. According to the relation between the
softness parameter and the size of the microstructure, three different limit
models are deduced via Gamma-convergence. In particular, damage is obtained as
limit of periodically distributed microfractures.


title:
On the Second-Order Correlation Function of the Characteristic
  Polynomial of a Real Symmetric Wigner Matrix

abstract:
  We consider the asymptotic behaviour of the second-order correlation function
of the characteristic polynomial of a real symmetric random matrix. Our main
result is that the existing result for a random matrix from the Gaussian
Orthogonal Ensemble essentially continues to hold for a general real symmetric
Wigner matrix.


title: The Optimal Inhomogeneity for Superconductivity: Finite Size Studies

abstract:
  We report the results of exact diagonalization studies of Hubbard models on a
$4\times 4$ square lattice with periodic boundary conditions and various
degrees and patterns of inhomogeneity, which are represented by inequivalent
hopping integrals $t$ and $t^{\prime}$. We focus primarily on two patterns, the
checkerboard and the striped cases, for a large range of values of the on-site
repulsion $U$ and doped hole concentration, $x$. We present evidence that
superconductivity is strongest for $U$ of order the bandwidth, and intermediate
inhomogeneity, $0 <t^\prime< t$. The maximum value of the ``pair-binding
energy'' we have found with purely repulsive interactions is $\Delta_{pb} =
0.32t$ for the checkerboard Hubbard model with $U=8t$ and $t^\prime = 0.5t$.
Moreover, for near optimal values, our results are insensitive to changes in
boundary conditions, suggesting that the correlation length is sufficiently
short that finite size effects are already unimportant.


title:
Variational method study of the spin-1 Ising model with biaxial
  crystal-field anisotropy

abstract:
  The phase diagram of the spin-1 Ising model in the presence of a biaxial
crystal-field anisotropy is studied within the framework of a variational
approach, based on the Bogolyubov inequality for the free energy. We have
investigated the effects of a transverse crystal-field $D_{y}$ on the phase
diagram in the $T-D_{x}$ plane. Results obtained by using effective-field
theory (EFT) on the honeycomb (% $z=3$), square ($z=4$) and simple cubic
($z=6$) lattices ($z$ is the coordination number) show only continuous phase
transitions, while the variational approach presents first-order and continuous
phase transitions for $D_{y}=0$% . We have also used the EFT for larger values
of $z$ and we observe the presence of tricritical points in the phase diagrams,
for $z\geq 7$, in accordance with the variational approach results.


title:
Unitarity Constraint upon Kinematical Analyses of the GSI Time-Modulated
  Radioactive Decay Experiment

abstract:
  It is tempting to try to explain the reported time-modulated decay rate in
the GSI experiment by arguing that the matrix element for decay at any time
results in an interference between two slightly different momentum values in
the parent ion beam. I show here that a unitarity theorem of quantum mechanics
rules out a wide class of such explanations.


title: Dynamical coupled channel approach to omega meson production

abstract:
  The dynamical coupled channel approach is applied to study the
$\omega$--meson production induced by pions and photons scattering from the
proton. The parameters of the model are fixed in a two-channel (\on,\pn)
calculation for the non-resonant and resonant contributions to the $T$ matrix
by fitting the available unpolarized differential cross section data. The
polarized photon beam asymmetry is predicted and compared to existing data.


title:
Spectrum of the Laplacian in a narrow curved strip with combined
  Dirichlet and Neumann boundary conditions

abstract:
  We consider the Laplacian in a domain squeezed between two parallel curves in
the plane, subject to Dirichlet boundary conditions on one of the curves and
Neumann boundary conditions on the other. We derive two-term asymptotics for
eigenvalues in the limit when the distance between the curves tends to zero.
The asymptotics are uniform and local in the sense that the coefficients depend
only on the extremal points where the ratio of the curvature radii of the
Neumann boundary to the Dirichlet one is the biggest. We also show that the
asymptotics can be obtained from a form of norm-resolvent convergence which
takes into account the width-dependence of the domain of definition of the
operators involved.


title: Formation of simple organic molecules in inner T Tauri disks

abstract:
  We present time dependent chemical models for a dense and warm O-rich gas
exposed to a strong far ultraviolet field aiming at exploring the formation of
simple organic molecules in the inner regions of protoplanetary disks around T
Tauri stars. An up-to-date chemical network is used to compute the evolution of
molecular abundances. Reactions of H2 with small organic radicals such as C2
and C2H, which are not included in current astrochemical databases, overcome
their moderate activation energies at warm temperatures and become very
important for the gas phase synthesis of C-bearing molecules. The
photodissociation of CO and release of C triggers the formation of simple
organic species such as C2H2, HCN, and CH4. In timescales between 1 and 10,000
years, depending on the density and FUV field, a steady state is reached in the
model in which molecules are continuously photodissociated but also formed,
mainly through gas phase chemical reactions involving H2. The application of
the model to the upper layers of inner protoplanetary disks predicts large gas
phase abundances of C2H2 and HCN. The implied vertical column densities are as
large as several 10^(16) cm^(-2) in the very inner disk (< 1 AU), in good
agreement with the recent infrared observations of warm C2H2 and HCN in the
inner regions of IRS 46 and GV Tau disks. We also compare our results with
previous chemical models studying the photoprocessing in the outer disk
regions, and find that the gas phase chemical composition in the upper layers
of the inner terrestrial zone (a few AU) is predicted to be substantially
different from that in the upper layers of the outer disk (> 50 AU).


title: Planetary-Scale Views on an Instant-Messaging Network

abstract:
  We present a study of anonymized data capturing a month of high-level
communication activities within the whole of the Microsoft Messenger
instant-messaging system. We examine characteristics and patterns that emerge
from the collective dynamics of large numbers of people, rather than the
actions and characteristics of individuals. The dataset contains summary
properties of 30 billion conversations among 240 million people. From the data,
we construct a communication graph with 180 million nodes and 1.3 billion
undirected edges, creating the largest social network constructed and analyzed
to date. We report on multiple aspects of the dataset and synthesized graph. We
find that the graph is well-connected and robust to node removal. We
investigate on a planetary-scale the oft-cited report that people are separated
by ``six degrees of separation'' and find that the average path length among
Messenger users is 6.6. We also find that people tend to communicate more with
each other when they have similar age, language, and location, and that
cross-gender conversations are both more frequent and of longer duration than
conversations with the same gender.


title: A Smooth, Inductively Coupled Ring Trap for Atoms

abstract:
  We propose and numerically investigate a scalable ring trap for cold atoms
that surmounts problems of roughness of the potential and end--effects of trap
wires. A stable trapping potential is formed about an electrically isolated,
conducting loop in an ac magnetic field by time averaging the superposition of
the external and induced magnetic fields. We investigate the use of additional
fields to eliminate Majorana spin flip losses and to create novel trapping
geometries. The possibility of micro--fabrication of these ring traps offers
the prospect of developing Sagnac atom interferometry in atom--chip devices.


title:
Fermi surface and van Hove singularities in the itinerant metamagnet
  Sr3Ru2O7

abstract:
  The low-energy electronic structure of the itinerant metamagnet Sr3Ru2O7 is
investigated by angle resolved photoemission and density functional
calculations. We find well-defined quasiparticle bands with resolution limited
line widths and Fermi velocities up to an order of magnitude lower than in
single layer Sr2RuO4. The complete topography, the cyclotron masses and the
orbital character of the Fermi surface are determined, in agreement with bulk
sensitive de Haas - van Alphen measurements. An analysis of the dxy band
dispersion reveals a complex density of states including van Hove singularities
(vHs) near the Fermi level; a situation which is favorable for magnetic
instabilities.


title:
Asymptotic solution of the Schrodinger equation for the elliptic wire in
  the magnetic field

abstract:
  The asymptotic solution of the Schrodinger equation with non-separable
variables is obtained for a particle confined to an infinite elliptic cylinder
potential well under applied uniform longitudinal magnetic field. Using
standard-problem method, dimension quantized eigenvalues have been calculated
when the magnetic length is large enough in comparison with the half of the
distance between the boundary ellipse focuses. In semi-classical approximation,
the confined electron (hole) states are divided into the Boundary States (BS),
Ring States (RS), Hyperbolic Caustic States (HCS), and Harmonic Oscillator
States (HOS). For large angular momentum quantum numbers and small radial
quantum numbers, the BS and RS are grouped into the Whispering Gallery mode.
They associate with particles moving along the wire cross section boundary. The
motion is limited from the wire core by the elliptic caustic. Consisting of the
HCS and HOS, the Jumping Ball modes correspond to the states of particle moving
along a wire diameter when the angular momentum quantum number is much less
than the radial quantum number. In this case, the motion is restricted by the
hyperbolic caustics and two boundary ellipse arcs. For excited hole states in
Bi wire, the energy spectrum and space probability distribution are analyzed.


title:
$A_n^{(1)}$ affine Toda field theories with integrable boundary
  conditions revisited

abstract:
  Generic classically integrable boundary conditions for the $A_{n}^{(1)}$
affine Toda field theories (ATFT) are investigated. The present analysis rests
primarily on the underlying algebra, defined by the classical version of the
reflection equation. We use as a prototype example the first non-trivial model
of the hierarchy i.e. the $A_2^{(1)}$ ATFT, however our results may be
generalized for any $A_{n}^{(1)}$ ($n>1$). We assume here two distinct types of
boundary conditions called some times soliton preserving (SP), and soliton
non-preserving (SNP) associated to two distinct algebras, i.e. the reflection
algebra and the ($q$) twisted Yangian respectively. The boundary local
integrals of motion are then systematically extracted from the asymptotic
expansion of the associated transfer matrix. In the case of SNP boundary
conditions we recover previously known results. The other type of boundary
conditions (SP), associated to the reflection algebra, are novel in this
context and lead to a different set of conserved quantities that depend on free
boundary parameters. It also turns out that the number of local integrals of
motion for SP boundary conditions is `double' compared to those of the SNP
case.


title:
Physics from scratch. Letter on M. Tegmark's ``The Mathematical
  Universe''

abstract:
  In a recent article, M. Tegmark poses the hypothesis that our known universe
is a ``baggage free'' mathematical structure among many other possible ones,
which also correspond to other physical universes --Mathematical Universe
Hypothesis, MUH. Naturally, questions arise, such as how to obtain the physical
properties of our world from the mathematical structure, or how many
possibilities exist for a Universe minimally similar to ours.
  In this letter we present some results which can be regarded as a
strengthening of MUH, as they give some hints on the derivation of spacetime in
current physics from a baggage free mathematical structure.
  Concretely, we argue that the set of mathematical structures which can be
interpreted as a description of a spacetime is drastically reduced, if one
admits some natural postulates on minimal symmetry. Furthermore, the apparently
very particular form of classical Galilei-Newton and relativistic spacetimes,
is not arbitrary and cannot be regarded as ``two possibilities among
arbitrarily many others''. In fact, such theories are determined by a single
mathematical structure which only permits four possible types of spacetimes.
Finally, we show how the minimal postulates on symmetry can be endowed with a
simple physical interpretation, i.e., they acquire ``baggage'' in a natural
way.


title:
Effect of Inversion Symmetry on Incommensurate Order in Multiferroic
  RMn2O5, R=rare earth

abstract:
  Starting from the irreducible representations of the group of the wave vector
we construct the spin wave functions consistent with inversion symmetry,
neglected in the usual representation analysis. We obtain the relation between
the basis functions of different members of the star of the wave vector. We
introduce order parameters and determine their transformation properties under
the operations of the space group of the paramagnetic crystal. The results are
applied to construct terms in the magnetoelectric interaction which are
quadratic and quartic in the magnetic order parameters. The higher order
magnetoelectric interactions can in principle induce components of the
spontaneous polarization which are not allowed by the lowest order
magnetoelectric interaction. We also obtain the relation between the spin wave
functions of the incommensurate phase and those of the commensurate phase which
lead to analogous relations between the order parameters of these two phases.


title: Fixed-node diffusion Monte Carlo study of the structures of m-benzyne

abstract:
  Diffusion Monte Carlo (DMC) calculations are performed on the monocyclic and
bicyclic forms of m-benzyne, which are the equilibrium structures at the
CCSD(T) and CCSD levels of coupled cluster theory. We employed
multi-configuration self-consistent field trial wave functions which are
constructed from a carefully selected 8-electrons-in-8-orbitals complete active
space [CAS(8,8)], with CSF coefficients that are reoptimized in the presence of
a Jastrow factor. The DMC calculations show that the monocyclic structure is
lower in energy than the bicyclic structure by 1.9(2) kcal/mole, in excellent
agreement with the best coupled cluster results.


title:
Abundances determination of A, Am and F stars in the Pleiades and Coma
  Berenices clusters

abstract:
  Abundances of 18 chemical elements have been derived for 27 A/Am and 16 F
stars members of the Pleiades and Coma Berenices open clusters. We have
specifically computed, with the Montr\'eal code, a series of evolutionary
models for two A stars members of these two clusters. None of the models
reproduces entirely the overall shape of the abundances patterns. The inclusion
of competing processes such as rotational mixing in the radiative zones of
these stars seems necessary to improve the agreement between observed and
predicted abundances patterns.


title: Crack growth by surface diffusion in viscoelastic media

abstract:
  We discuss steady state crack growth in the spirit of a free boundary
problem. It turns out that mode I and mode III situations are very different
from each other: In particular, mode III exhibits a pronounced transition
towards unstable crack growth at higher driving forces, and the behavior close
to the Griffith point is determined entirely through crack surface dissipation,
whereas in mode I the fracture energy is renormalized due to a remaining finite
viscous dissipation. Intermediate mixed-mode scenarios allow steady state crack
growth with higher velocities, leading to the conjecture that mode I cracks can
be unstable with respect to a rotation of the crack front line.


title: Magneto-gyrotropic effects in semiconductor quantum wells (review)

abstract:
  Magneto-gyrotropic photogalvanic effects in quantum wells are reviewed. We
discuss experimental data, results of phenomenological analysis and microscopic
models of these effects. The current flow is driven by spin-dependent
scattering in low-dimensional structures gyrotropic media resulted in asymmetry
of photoexcitation and relaxation processes. Several applications of the
effects are also considered.


title:
Observation and Modeling of the Solar-Cycle Variation of the Meridional
  Flow

abstract:
  We present independent observations of the solar-cycle variation of flows
near the solar surface and at a depth of about 60 Mm, in the latitude range
$\pm45^\circ$. We show that the time-varying components of the meridional flow
at these two depths have opposite sign, while the time-varying components of
the zonal flow are in phase. This is in agreement with previous results. We
then investigate whether the observations are consistent with a theoretical
model of solar-cycle dependent meridional circulation based on a flux-transport
dynamo combined with a geostrophic flow caused by increased radiative loss in
the active region belt (the only existing quantitative model). We find that the
model and the data are in qualitative agreement, although the amplitude of the
solar-cycle variation of the meridional flow at 60 Mm is underestimated by the
model.


title: O(\alpha_s^2) corrections to semileptonic decay b \to c l \bar \nu_l

abstract:
  We compute the next-to-next-to-leading order (NNLO) QCD corrections to b \to
c l \bar \nu_l decay rate at a fully differential level. Arbitrary cuts on
kinematic variables of the decay products can be imposed. Our computation can
be used to study the NNLO QCD corrections to the total decay rate as well as to
the lepton energy, hadronic invariant mass and hadronic energy moments and to
incorporate those corrections into global fits of inclusive semileptonic
B-decays.