title:
Equilibrium of disordered systems : constructing the appropriate valleys
  in each sample via strong disorder renormalization in configuration space

abstract:
  To describe the equilibrium properties of disordered systems and the possible
emergence of various 'phases' at low temperature, we adopt here the 'broken
ergodicity' point of view advocated in particular by Palmer [Adv. Phys. 31, 669
(1982)] : the aim is then to construct the valleys of configurations that
become separated by diverging barriers and to study their relative weights, as
well as their internal properties. To characterize the slow non-equilibrium
dynamics of disordered systems, we have recently introduced in [C. Monthus and
T. Garel, J. Phys. A 41, 255002 (2008) and arxiv:0804.1847] a strong disorder
renormalization procedure in configuration space, based on the iterative
elimination of the smallest barrier remaining in the system. In the present
paper, we show how this renormalization procedure allows to construct the
longest-lived valleys in each disordered sample, and to obtain their
free-energies, energies and entropies. This explicit RG formulation is very
general since it can be defined for any master equation, and it gives new
insights into the main ingredients of the droplet scaling picture. As an
application, we have followed numerically the RG flow for the case of a
directed polymer in a two-dimensional random medium to obtain histograms of the
free-energy, entropy and energy differences between the two longest-lived
valleys in each sample.


title: HNNLO: a MC program for Higgs boson production at hadron colliders

abstract:
  We consider Higgs boson production through gluon--gluon fusion in hadron
collisions. We present a numerical program that computes the cross section up
to NNLO in QCD perturbation theory. The program allows the user to apply
arbitrary cuts on the momenta of the partons and of the photons or leptons that
are produced in the final state. We present selected numerical results at the
Tevatron and the LHC.


title: Test beam Characterizations of 3D Silicon Pixel detectors

abstract:
  3D silicon detectors are characterized by cylindrical electrodes
perpendicular to the surface and penetrating into the bulk material in contrast
to standard Si detectors with planar electrodes on its top and bottom. This
geometry renders them particularly interesting to be used in environments where
standard silicon detectors have limitations, such as for example the radiation
environment expected in an LHC upgrade. For the first time, several 3D sensors
were assembled as hybrid pixel detectors using the ATLAS-pixel front-end chip
and readout electronics. Devices with different electrode configurations have
been characterized in a 100 GeV pion beam at the CERN SPS. Here we report
results on unirradiated devices with three 3D electrodes per 50 x 400 um2 pixel
area. Full charge collection is obtained already with comparatively low bias
voltages around 10 V. Spatial resolution with binary readout is obtained as
expected from the cell dimensions. Efficiencies of 95.9% +- 0.1 % for tracks
parallel to the electrodes and of 99.9% +- 0.1 % at 15 degrees are measured.
The homogeneity of the efficiency over the pixel area and charge sharing are
characterized.


title:
Slow passage through parametric resonance for a weakly nonlinear
  dispersive wave

abstract:
  A solution of the nonlinear Klein-Gordon equation perturbed by a parametric
driver is studied. The frequency of the parametric perturbation varies slowly
and passes through a resonant value. It yields a change in a solution. We
obtain a connection formula for the asymptotic solution before and after the
resonance.


title:
The softening phenomenon due to the curvature effect: in the case of
  extremely short intrinsic emission

abstract:
  The curvature effect is explored in the case of extremely short intrinsic
emission. Assuming a $\delta$ function emission we get formulas that get rid of
the impacts from the intrinsic emission duration, which are applicable to any
forms of continuum. The formulas predict that the same form of spectrum could
be observed at different times, with the peak energy of the spectrum shifting
from higher energy bands to lower bands following $E_{peak}\propto t^{-1}$.
When the emission is early enough the light curve in the form $f_{\nu
}(t)t^{2}$ will possess exactly the intrinsic spectral form, for which the
temporal power law index and the spectral power law index will be related by
$\alpha =2+\beta $. The analysis shows that there do exist a temporal steep
decay phase and a spectral softening which occur simultaneously, and both are
caused by the shifting of the Band function spectrum. According to the
analysis, we predict that the softening due to the curvature effect will appear
at different frequencies; it occurs earlier for higher frequencies and later
for lower frequencies; the maximum spectral index time follows the
$t_{b,max}\propto \nu^{-1}$ law. We also find: the softening duration would be
linearly correlated with the maximum spectral index time; the observed
$\beta_{min}$ and $\beta_{max}$ are determined by the low and high energy
indexes of the observed Band function spectrum. We propose to check the
curvature effect with the $\log f_{\nu}(t)t^{3}$ vs. $log t$ curve which would
be in agreement with the $\log \nu f_{\nu}$ vs. $log \nu$ curve. Applying this
to GRB 060614 shows that the peak energy of its observed spectrum is expected
to pass through the observation band at $\sim $175 s.


title: New Mechanics of Spinal Injury

abstract:
  The prediction and prevention of spinal injury is an important aspect of
preventive health science. The spine, or vertebral column, represents a chain
of 26 movable vertebral bodies, joint together by transversal viscoelastic
intervertebral discs and longitudinal elastic tendons. This paper proposes a
new locally-coupled loading-rate hypothesis}, which states that the main cause
of both soft- and hard-tissue spinal injury is a localized Euclidean jolt, or
SE(3)-jolt, an impulsive loading that strikes a localized spine in several
coupled degrees-of-freedom simultaneously. To show this, based on the
previously defined covariant force law, we formulate the coupled Newton-Euler
dynamics of the local spinal motions and derive from it the corresponding
coupled SE(3)-jolt dynamics. The SE(3)-jolt is the main cause of two basic
forms of spinal injury: (i) hard-tissue injury of local translational
dislocations; and (ii) soft-tissue injury of local rotational disclinations.
Both the spinal dislocations and disclinations, as caused by the SE(3)-jolt,
are described using the Cosserat multipolar viscoelastic continuum model.
  Keywords: localized spinal injury, coupled loading-rate hypothesis, coupled
Newton-Euler dynamics, Euclidean jolt dynamics, spinal dislocations and
disclinations


title: Heavy Flavor in the sQGP

abstract:
  We attempt a unified treatment of heavy quarkonia and heavy-quark diffusion
in the Quark-Gluon Plasma. Our approach is based on finite-temperature
T-matrices with interaction potentials estimated from the heavy-quark internal
energy computed in thermal lattice QCD (lQCD). In the charmonium sector S-wave
bound states (J/\psi, \eta_c) survive up to temperatures of ~2 T_c, not
inconsistent with constraints from euclidean correlation functions in lQCD. In
the open-heavy flavor sector, the T-matrix interaction reduces heavy-quark
diffusion substantially, leading to fair agreement with single-electron spectra
at RHIC and suggestive for a small viscosity-to-entropy ratio close to T_c.


title: Interaction-induced harmonic frequency mixing in quantum dots

abstract:
  We show that harmonic frequency mixing in quantum dots coupled to two leads
under the influence of time-dependent voltages of different frequency is
dominated by interaction effects. This offers a unique and direct spectroscopic
tool to access correlations, and holds promise for efficient frequency mixing
in nano-devices. Explicit results are provided for an Anderson dot and for a
molecular level with phonon-mediated interactions.


title:
PACIAE Model Predictions for Pb+Pb Collisions at LHC Compared to the
  Au+Au Collisions at RHIC

abstract:
  The parton and hadron cascade model PACIAE is used to simulate the 0-6,
15-25, and 35-45 % most central Au+Au collisions at \sqrt{s_{NN}}=19.6, 62.4,
130, and 200 GeV and the 0-10 % most central Pb+Pb collisions at
\sqrt{s_{NN}}=5500 GeV. The calculated charged multiplicity and the charged
particle transverse momentum distribution, pseudorapidity distribution, and
extended longitudinal scaling for Au+Au collisions well agree with the
corresponding PHOBOS data. Thus the above observables calculated for Pb+Pb
collisions would be a reliable prediction.


title: Constant Flux Relation for diffusion limited cluster-cluster aggregation

abstract:
  In a non-equilibrium system, a Constant Flux Relation (CFR) expresses the
fact that a constant flux of a conserved quantity exactly determines the
scaling of the particular correlation function linked to the flux of that
conserved quantity. This is true regardless of whether mean--field theory is
applicable or not. We focus on cluster--cluster aggregation and discuss the
consequences of mass conservation for the steady state of aggregation models
with a monomer source in the diffusion-limited regime. We derive the CFR for
the flux-carrying correlation function for binary aggregation with a general
scale-invariant kernel and show that this exponent is unique. It is independent
of both the dimension and of the details of the spatial transport mechanism, a
property which is very atypical in the diffusion-limited regime. We then
discuss in detail the ``locality criterion'' which must be satisfied in order
for the CFR scaling to be realisable. Locality may be checked explicitly for
the mean-field Smoluchowski equation. We show that if it is satisfied at the
mean-field level, it remains true over some finite range as one perturbatively
decreases the dimension of the system below the critical dimension, $d_c=2$,
entering the fluctuation-dominated regime. We turn to numerical simulations to
verify locality for a range of systems in one dimension which are, presumably,
beyond the perturbative regime. Finally, we illustrate how the CFR scaling may
break down as a result of a violation of locality or as a result of finite size
effects and discuss the extent to which the results apply to higher order
aggregation processes.


title:
Accurate determination of crystal structures based on averaged local
  bond order parameters

abstract:
  Local bond order parameters based on spherical harmonics, also known as
Steinhardt order parameters, are often used to determine crystal structures in
molecular simulations. Here we propose a modification of this method in which
the complex bond order vectors are averaged over the first neighbor shell of a
given particle and the particle itself. As demonstrated using soft particle
systems, this averaging procedure considerably improves the accuracy with which
different crystal structures can be distinguished.


title:
Unexpectedly wide reversible vortex region in $\beta$-pyrochlore
  RbOs$_{2}$O$_{6}$

abstract:
  We study the extent of the reversible region in the vortex phase diagram of
recently available RbOs$_2$O$_6$ single crystals \cite{Rogacki08a} by means of
bulk magnetization measurements. We found that the irreversible magnetic
response sets in at a field $H_{\rm irr}(T) \sim 0.3 H_{\rm c2}(T)$ for $0.5
\lesssim T/T_{\rm c} \lesssim 0.8$, yielding a reversible vortex region that is
uncommonly wide in comparison with typical low-$T_{\rm c}$ materials. The
relevance of thermal fluctuations is limited since we estimate a Ginzburg
number $G_{\rm i} = 5 \times 10^{-7}$. However, the relevance of quenched
disorder is unconventionally low since the critical-current density ratio at
low fields and temperatures is of the order of that found in high-T$_{\rm
c}$'s. We therefore conclude that an intrinsically low bulk pinning magnitude
favors the existence of an unexpectedly wide reversible vortex region that
seems to be generic to $\beta$-pyrochlores.


title: H.E.S.S. upper limits for Kepler's supernova remnant

abstract:
  Observations of Kepler's supernova remnant (G4.5+6.8) with the H.E.S.S.
telescope array in 2004 and 2005 with a total live time of 13 h are presented.
Stereoscopic imaging of Cherenkov radiation from extensive air showers is used
to reconstruct the energy and direction of the incident gamma rays. No evidence
for a very high energy (VHE: >100 GeV) gamma-ray signal from the direction of
the remnant is found. An upper limit (99% confidence level) on the energy flux
in the range 230 GeV - 12.8 TeV of 8.6 x 10^{-13} erg cm^{-2} s^{-1} is
obtained. In the context of an existing theoretical model for the remnant, the
lack of a detectable gamma-ray flux implies a distance of at least 6.4 kpc. A
corresponding upper limit for the density of the ambient matter of 0.7 cm^{-3}
is derived. With this distance limit, and assuming a spectral index Gamma = 2,
the total energy in accelerated protons is limited to E_p < 8.6 x 10^{49} erg.
In the synchrotron/inverse Compton framework, extrapolating the power law
measured by RXTE between 10 and 20 keV down in energy, the predicted gamma-ray
flux from inverse Compton scattering is below the measured upper limit for
magnetic field values greater than 52 muG.


title: Thermodynamics of Born-Infeld Black Holes

abstract:
  We discuss the horizon structure for Born-Infeld black holes, in the context
of Einstein-Born-Infeld gravity. We show that the entropy function formalism
agrees with a direct calculation of the entropy. With the entropy function
formalism we also obtain the entropy when an axion-dilaton system as well as
gravitational derivative corrections are included.


title: Kekule-distortion-induced Exciton instability in graphene

abstract:
  Effects of a Kekule distortion on exciton instability in single-layer
graphene are discussed. In the framework of quantum electrodynamics the mass of
the electron generated dynamically is worked out using a Schwinger-Dyson
equation. For homogeneous lattice distortion it is shown that the generated
mass is independent of the amplitude of the lattice distortion at the one-loop
approximation. Formation of excitons induced by the homogeneous Kekule
distortion could appear only through direct dependence of the lattice
distortion.


title:
Variation of the light-like particle energy and its critical curve
  equations

abstract:
  We consider variation of energy of the light-like particle in Riemann
space-time, find lagrangian, canonical momenta and forces. Equations of the
critical curve are obtained by the nonzero energy integral variation in
accordance with principles of the calculus of variations in mechanics. This
method is shown to not lead to violation of conformity of varied curve to the
null path in contradistinction of the interval variation. Though found
equations are differ from standard form of geodesics equations, for the
Schwarzschild space-time their solutions coincide with each other to within
parameter of differentiation.


title: Cyclic orders on the quantum grassmannian

abstract:
  The quantum grassmannian is known to be a graded quantum algebra with a
straightening law when the poset of generating quantum minors is endowed with
the standard partial ordering. In this paper it is shown that this result
remains true when the ordering is subjected to cyclic shifts. The method
involves proving that noncommutative dehomogenisation is possible at any
consecutive quantum minor.


title:
Low-temperature density matrix renormalization group using regulated
  polynomial expansion

abstract:
  We propose a density matrix renormalization group (DMRG) technique at finite
temperatures. As is the case of the ground state DMRG, we use a single-target
state that is calculated by making use of a regulated polynomial expansion.
Both static and dynamical quantities are obtained after a random-sampling and
averaging procedure. We apply this technique to the one-dimensional Hubbard
model at half filling and find that this gives excellent results at low
temperatures.


title: All-order results for soft and collinear gluons

abstract:
  I briefly review some general features and some recent developments
concerning the resummation of long-distance singularities in QCD and in more
general non-abelian gauge theories. I emphasize the field-theoretical tools of
the trade, and focus mostly on the exponentiation of infrared and collinear
divergences in amplitudes, which underlies the resummation of large logarithms
in the corresponding cross sections. I then describe some recent results
concerning the conformal limit, notably the case of N = 4 superymmetric
Yang-Mills theory


title:
Emission lines of Fe X in active region spectra obtained with the Solar
  Extreme-ultraviolet Research Telescope and Spectrograph

abstract:
  Fully relativistic calculations of radiative rates and electron impact
excitation cross sections for Fe X are used to derive theoretical emission-line
ratios involving transitions in the 174-366 A wavelength range. A comparison of
these with solar active region observations obtained during the 1989 and 1995
flights of the Solar Extreme-ultraviolet Research Telescope and Spectrograph
(SERTS) reveals generally very good agreement between theory and experiment.
Several Fe X emission features are detected for the first time in SERTS
spectra, while the transition at 195.32 A is identified for the first time (to
our knowledge) in an astronomical source. The most useful Fe X electron density
diagnostic line ratios are assessed to be 175.27/174.53 and 175.27/177.24,
which both involve lines close in wavelength and free from blends, vary by
factors of 13 between Ne = 1E8 and 1E13 cm-3, and yet show little temperature
sensitivity. Should these lines not be available, then the 257.25/345.74 ratio
may be employed to determine Ne, although this requires an accurate evaluation
of the instrument intensity calibration over a relatively large wavelength
range. However, if the weak 324.73 A line of Fe X is reliably detected, the use
of 324.73/345.74 or 257.25/324.73 is recommended over 257.25/345.74.


title:
Fibr\'es vectoriels de rang deux sur $\P^2$ provenant d'un rev\^etement
  double

abstract:
  Since Schwarzenberger and his celebrated paper called "Vector bundles on the
projective plane" we know that any rank two vector bundle on $\P^2$ is a direct
image of a line bundle on a double covering of the plane. This theorem suggests
to study the rank two vector bundles according to the branch curve of the
covering which they come from. Thus, in the first part we prove that, given a
double covering ramified over an irreducible curve $C_{2r}$ with degree $2r$,
the jumping lines of fixed order (order depending on $r$ and on the parity of
the rank two vector bundle) of the direct images vector bundles are necessarely
$r$-tangent to $C_{2r}$. In the second part we concentrate on the case $r=2$.
Then we give a list of vector bundles for which the jumping lines are exactly
the bitangent lines to the branch quartic.


title: Spontaneous symmetry breaking in Loop Quantum Gravity

abstract:
  In this paper we investigate the question how spontaneous symmetry breaking
works in the framework of Loop Quantum Gravity and we compare it to the results
obtained in the case of the Proca field, where we were able to quantise the
theory in Loop Quantum Gravity without introducing a Higgs field. We obtained
that the Hamiltonian of the two systems are very similar, the only difference
is an extra scalar field in the case of spontaneous symmetry breaking. This
field can be identified as the field that carries the mass of the vector field.
In the quantum regime this becomes a well defined operator, which turns out to
be a self adjoint operator with continuous spectrum. To calculate the spectrum
we used a new representation in the case of the scalar fields, which in
addition enabled us to rewrite the constraint equations to a finite system of
linear partial differential equations. This made it possible to solve part of
the constraints explicitly.


title: Quarkyonic matter in lattice QCD at strong coupling

abstract:
  We study the phase diagram of quark matter at finite temperature and density
in the strong coupling lattice QCD with one species of unrooted staggered
fermions including finite coupling ($1/g^2$) effects for color SU($N_c$). We
find that we may have partially chiral restored medium density matter at
$N_c=3$, which would correspond to the quarkyonic matter suggested at large
$N_c$.


title: The Role of Conformal Symmetry in the Jackiw-Pi Model

abstract:
  The Jackiw-Pi model in 2+1 dimensions is a non-relativistic conformal field
theory of charged particles with point-like self-interaction. For specific
values of the interaction strengths the classical theory possesses vortex and
multi-vortex solutions, which are all degenerate in energy. We compute the full
set of first-order perturbative quantum corrections. Only the coupling constant
g^2 requires renormalization; the fields and electric charge e are not
renormalized. It is shown that in general the conformal symmetries are broken
by an anomalous contribution to the conservation law, proportional to the
beta-function. However, the beta-function vanishes upon restricting the
coupling constants to values g^2 = +/- e^2, which includes the case in which
vortex solutions exist. Therefore the existence of vortices also guarantees the
preservation of the conformal symmetries.


title:
Quark contribution to r-mode instabilities for several phases of
  deconfined quark matter

abstract:
  R-mode instabilities lead to specific signatures in the evolution of rotating
pulsars, and may provide a unique signature which can identify the phase of
matter that exists in the interiors of such objects.
  The contributions of quarks' bulk and shear viscosities to the dissipation of
r-mode instabilities are studied. It is shown that (contrary to earlier works)
the quark contribution is \emph{not} fully suppressed in the presence of fully
gapped color-superconducting phase due to the fact that the bulk viscosity is a
resonance effect between the density oscillation on one side, and the
interaction rates that try to restore $\beta$-equilibrium during these
oscillations on the other. This will have an effect on the structure of the
r-mode instability window and will affect the angular momentum evolution of
pulsars.


title: Electromagnetic Form Factors of Hadrons in Quantum Field Theories

abstract:
  In this talk, recent results are presented of calculations of electromagnetic
form factors of hadrons in the framework of two quantum field theories (QFT),
(a) Dual-Large $N_c$ QCD (Dual-$QCD_\infty$) for the pion, proton, and
$\Delta(1236)$, and (b) the Kroll-Lee-Zumino (KLZ) fully renormalizable Abelian
QFT for the pion form factor. Both theories provide a QFT platform to improve
on naive (tree-level) Vector Meson Dominance (VMD). Dual-$QCD_\infty$ provides
a tree-level improvement by incorporating an infinite number of zero-width
resonances, which can be subsequently shifted from the real axis to account for
the time-like behaviour of the form factors. The renormalizable KLZ model
provides a QFT improvement of VMD in the framework of perturbation theory. Due
to the relative mildness of the $\rho\pi\pi$ coupling, and the size of loop
suppression factors, the perturbative expansion is well defined in spite of
this being a strong coupling theory. Both approaches lead to considerable
improvements of VMD predictions for electromagnetic form factors, in excellent
agreement with data.


title:
Supersymmetric seesaw type II: CERN LHC and lepton flavour violating
  phenomenology

abstract:
  We study the supersymmetric version of the type-II seesaw mechanism assuming
minimal supergravity boundary conditions. We calculate branching ratios for
lepton flavour violating (LFV) scalar tau decays, potentially observable at the
LHC, as well as LFV decays at low energy, such as $l_i \to l_j + \gamma$ and
compare their sensitivity to the unknown seesaw parameters. In the minimal case
of only one triplet coupling to the standard model lepton doublets, ratios of
LFV branching ratios can be related unambigously to neutrino oscillation
parameters. We also discuss how measurements of soft SUSY breaking parameters
at the LHC can be used to indirectly extract information of the seesaw scale.


title: Quantum algorithms for shifted subset problems

abstract:
  We consider a recently proposed generalisation of the abelian hidden subgroup
problem: the shifted subset problem. The problem is to determine a subset S of
some abelian group, given access to quantum states of the form |S+x>, for some
unknown shift x. We give quantum algorithms to find Hamming spheres and other
subsets of the boolean cube {0,1}^n. The algorithms have time complexity
polynomial in n and give rise to exponential separations from classical
computation.


title:
Proper acceleration, geometric tachyon and dynamics of a fundamental
  string near D$p$ branes

abstract:
  We present a detailed analysis of our recent observation that the origin of
the geometric tachyon, which arises when a D$p$-brane propagates in the
vicinity of a stack of coincident NS5-branes, is due to the proper acceleration
generated by the background dilaton field. We show that when a fundamental
string (F-string), described by the Nambu-Goto action, is moving in the
background of a stack of coincident D$p$-branes, the geometric tachyon mode can
also appear since the overall conformal mode of the induced metric for the
string can act as a source for proper acceleration. We also studied the
detailed dynamics of the F-string as well as the instability by mapping the
Nambu-Goto action of the F-string to the tachyon effective action of the
non-BPS D-string. We qualitatively argue that the condensation of the geometric
tachyon is responsible for the (F,D$p$) bound state formation.


title:
Building a Nest at Tree Level: Classical Metastability and Non-Trivial
  Vacuum Structure in Supersymmetric Field Theories

abstract:
  It is becoming increasingly clear that metastable vacua may play a prominent
role in supersymmetry-breaking. To date, however, this idea has been realized
only in models where non-perturbative dynamics complicates the analysis of
metastability. In this paper, we present a simple construction in which
metastable vacua occur classically, i.e., at tree-level, and in which
supersymmetry-breaking is sourced by both D-terms and F-terms. All relevant
dynamics is perturbative, and hence calculations of vacuum energies and
lifetimes can be performed explicitly. Moreover, we find that our construction
can even give rise to multiple non-supersymmetric vacua which are degenerate.
The non-trivial vacuum structure of such models therefore suggests that they
can provide a rich arena for future studies of vacuum metastability in
supersymmetric field theories. Our results may also have important consequences
for Z' phenomenology and the string landscape.


title: Ab initio GW many-body effects in graphene

abstract:
  We present an {\it ab initio} many-body GW calculation of the self-energy,
the quasiparticle band plot and the spectral functions in free-standing undoped
graphene. With respect to other approaches, we numerically take into account
the full ionic and electronic structure of real graphene and we introduce
electron-electron interaction and correlation effects from first principles.
Both non-hermitian and also dynamical components of the self-energy are fully
taken into account. With respect to DFT-LDA, the Fermi velocity is
substantially renormalized and raised by a 17%, in better agreement with
magnetotransport experiments. Furthermore, close to the Dirac point the linear
dispersion is modified by the presence of a kink, as observed in ARPES
experiments. Our calculations show that the kink is due to low-energy $\pi \to
\pi^*$ single-particle excitations and to the $\pi$ plasmon. Finally, the GW
self-energy does not open the band gap.


title:
Approximation of Holder continuous homeomorphisms by piecewise affine
  homeomorphisms

abstract:
  This paper is concerned with the problem of approximating a homeomorphism by
piecewise affine homeomorphisms. The main result is as follows: every
homeomorphism from a planar domain with a polygonal boundary to R^2 that is
globally Holder continuous of exponent \alpha, and whose inverse is also
globally Holder continuous of exponent \alpha can be approximated in the Holder
norm of exponent \beta by piecewise affine homeomorphisms, for some \beta that
only depends on \alpha. The proof is constructive. We adapt the proof of
simplicial approximation in the supremum norm, and measure the side lengths and
angles of the triangulation over which the approximating homeomorphism is
piecewise affine. The approximation in the supremum norm, and a control on the
minimum angle and on the ratio between the maximum and minimum side lengths of
the triangulation suffice to obtain approximation in the Holder norm.


title: The coordinate-free approach to spherical harmonics

abstract:
  We present in a unified and self-contained manner the coordinate-free
approach to spherical harmonics initiated in the mid 19th century by James
Clerk Maxwell, William Thomson and Peter Guthrie Tait. We stress the
pedagogical advantages of this approach which leads in a natural way to many
physically relevant results that students find often difficult to work out
using spherical coordinates and associated Legendre functions. It is shown how
most physically relevant results of the theory of spherical harmonics - such as
recursion relations, Legendre's addition theorem,surface harmonics expansions,
the method of images, multipolar charge distributions, partial wave expansions,
Hobson's integral theorem, rotation matrix and Gaunt's integrals - can be
efficiently derived in a coordinate free fashion from a few basic elements of
the theory of solid and surface harmonics discussed in the paper.


title: Binding Isotherms and Cooperative Effects for Metal-DNA Complexes

abstract:
  The stoichiometric binding constants of Nickel(II), Cobalt(II),
Manganese(II), Silver(I), Zinc(II) ions with DNA, from Spirulina platensis were
determined from their binding isotherms by equilibrium dialysis and atomic
absorption spectroscopy. It was shown, that the nature of these ions
interaction with DNA, from S .platensis is different. For Cobalt(II), Zinc(II)
ions were observed cooperative effects and existence of two different types of
the binding sites. Nickel(II)_, Silver(I) -DNA complexes shows independent and
identical binding sites and Manganese(II)_ negative cooperative interaction.
The logarithm of binding constants for Cobalt (II)_, Nickel (II)_, Manganese
(II)_, Zinc (II)_, Silver (I) - DNA, from S. platensis in 3 mM Na(I) are 5.11;
5.18; 4.77; 5.05; 5.42; respectively. The linear correlation of logarithm of
binding constants (for complexes of metal-DNA from S. platensis) and the
covalent index of Pauling are observed.


title: Dynamical properties of a large young disk galaxy at z=2.03

abstract:
  Context. The study of high redshift Tully-Fisher relations (TFRs) is limited
by the use of long slit spectrographs, rest frame B band and star formation
selected galaxies. Aims. We try to circumvent these issues by using integral
field spectroscopy (SINFONI), by studying the rest frame K band and stellar
mass TFR, and by selecting targets without a bias to strongly star forming
galaxies. In this paper, we demonstrate our methods on our best case. This
galaxy, F257, at z=2.03, was selecte from a sample of candidate high redshift
large disk galaxies in the Hubble Deep Field South that were selected with
photometric and morphological criteria. Methods. We used SINFONI at the VLT to
obtain an integral field spectrum of the Halpha line and hence a velocity field
and rotation curve. We also use UBVIJHK+IRAC band photometry to determine a
stellar photometric mass. Results. We find that F257 is indistinguishable from
local late type galaxies in many respects: it has a regular velocity field,
increasing velocity disperion towards its center, its rotation curve flattens
at 1-2 disk scale lengths, it has the same specific angular momentum as local
disks, its properties are consistent with the local K band TFR. Although mainly
rotationally supported, its gas component is dynamically heated with respect to
local galaxies (V/sigma_z ~ 4) and it is offset from the local stellar mass TFR
at the 2sigma level. But, this offset depends on the SED modeling parameters.
In particular, for a 2-component star formation history (SFH), F257 is in
agreement with the local stellar mass TFR. F257 is then a nearly (~75%) maximum
disk. The dynamical properties of F257 are more like those of local galaxies
than those of any other galaxy at similar redshift observed to date. However,
the gas-to-stellar mass ratio is unusally large: 2.5.


title: Matching gauge theory and string theory in a decoupling limit of AdS/CFT

abstract:
  We identify a regime of the AdS/CFT correspondence in which we can
quantitatively match N=4 super Yang-Mills (SYM) for small 't Hooft coupling
with weakly coupled type IIB string theory on AdS_5 x S^5. We approach this
regime by taking the same decoupling limit on both sides of the correspondence.
On the gauge theory side only the states in the SU(2) sector survive, and in
the planar limit the Hamiltonian is given by the XXX_{1/2} Heisenberg spin
chain. On the string theory side we show that the decoupling limit corresponds
to a non-relativistic limit. In this limit some of the bosonic modes and all of
the fermionic modes of the string become infinitely heavy and decouple. We
first take the decoupling limit of the string sigma-model classically. This
enables us to identify a semi-classical regime with semi-classical string
states even though we are in a regime corresponding to small 't Hooft coupling.
We furthermore analyze the quantum corrections that enter in taking the limit.
  From this we infer that gauge theory and string theory match, both in terms
of the action and the spectrum, for the leading part and the first correction
away from the semi-classical regime. Finally we consider the implications for
the hitherto unexplained matching of the one-loop contribution to the energy of
certain gauge theory and string theory states, and we explain how our results
give a firm basis for the matching of the Hagedorn temperature in
hep-th/0608115.


title: Nonparametric adaptive estimation for pure jump L\'evy processes

abstract:
  This paper is concerned with nonparametric estimation of the L\'evy density
of a pure jump L\'evy process. The sample path is observed at $n$ discrete
instants with fixed sampling interval. We construct a collection of estimators
obtained by deconvolution methods and deduced from appropriate estimators of
the characteristic function and its first derivative. We obtain a bound for the
${\mathbb L}^2$-risk, under general assumptions on the model. Then we propose a
penalty function that allows to build an adaptive estimator. The risk bound for
the adaptive estimator is obtained under additional assumptions on the L\'evy
density. Examples of models fitting in our framework are described and rates of
convergence of the estimator are discussed.


title:
Intermediate-mass fragments from fission and multifragmentation in the
  spallation of 136Xe

abstract:
  A correlation between the production and kinematic properties of the
fragments issued of fission and multifragmentation is established in the study
of the reaction 136Xe+hydrogen at 1 GeV per nucleon, measured in inverse
kinematics at the FRagment Separator (GSI, Darmstadt). Such observables are
analysed in a comprehensive study, selected as a function of the decay mode,
and related to the isotopic properties of the fragments in the
intermediate-mass region. Valuable information can be deduced on the
characteristics of the heaviest product in the reaction, which has been
considered a fundamental observable for tagging the thermodynamic properties of
finite nuclear systems.


title: Downfolded Self-Energy of Many-Electron Systems

abstract:
  Starting from the full many-body Hamiltonian of interacting electrons the
effective self-energy acting on electrons residing in a subspace of the full
Hilbert space is derived. This subspace may correspond to, for example,
partially filled narrow bands, which often characterize strongly correlated
materials. The formalism delivers naturally the frequency-dependent effective
interaction (the Hubbard U) and provides a general framework for constructing
theoretical models based on the Green function language. It also furnishes a
general scheme for first-principles calculations of complex systems in which
the main correlation effects are concentrated on a small subspace of the full
Hilbert space.


title: Subleading contributions to the width of the D_{s0}*(2317)

abstract:
  We construct the effective chiral Lagrangian involving the
  D--mesons and Goldstone bosons at next-to-leading order taking into account
strong as well as electromagnetic interactions. This allows us to disentangle
-- to leading order in isospin violation -- the electromagnetic and the strong
contribution to the D--meson mass differences. In addition, we also apply the
interaction to the decay D_{s0}^*(2317)-> D_s pi0 under the assumption that the
D_{s0}^*(2317) is a hadronic molecule. We find (180+-110) keV for the decay
width $\Gamma (D_{s0}^*(2317)-> D_s pi0) -- consistent with currently existing
experimental constraints as well as previous theoretical investigations. The
result provides further evidence that this decay width can serve as a criterion
for testing the nature of the D_{s0}^*(2317).


title:
Identical chaotic synchronization and bidirectional message transmission
  in incoherently coupled semiconductor laser diodes

abstract:
  A chaos-based communication scheme allowing simultaneous bidirectional
message transmission (Opt. Lett. 32, 403, 2007) is investigated numerically.
Incoherent feedback and coupling case is analyzed, which is expected in real
long-distance optical communication systems. It is shown that identical
synchronization of chaotic laser waveforms and bidirectional message
transmission are possible as in the coherent coupling case. However, the
chaotic regime at incoherent feedback and coupling is quite different. It is
regular destabilized relaxation oscillations with the chaotic envelope. Such
dynamics leads to restriction of the transmitting signal bit rate by a portion
of relaxation oscillations frequency.


title:
Entanglement entropy in gauge theories and the holographic principle for
  electric strings

abstract:
  We consider quantum entanglement between gauge fields in some region of space
A and its complement B. It is argued that the Hilbert space of physical states
of gauge theories cannot be decomposed into a direct product of Hilbert spaces
of states localized in A and B. The reason is that elementary excitations in
gauge theories - electric strings - are associated with closed loops rather
than points in space, and there are closed loops which belong both to A and B.
Direct product structure and hence the reduction procedure with respect to the
fields in B can only be defined if the Hilbert space of physical states is
extended by including the states of electric strings which can open on the
boundary of A. The positions of string endpoints on this boundary are the
additional degrees of freedom which also contribute to the entanglement
entropy. We explicitly demonstrate this for the three-dimensional Z2 lattice
gauge theory both numerically and using a simple trial ground state wave
function. The entanglement entropy appears to be saturated almost completely by
the entropy of string endpoints, thus reminding of a ``holographic principle''
in quantum gravity and AdS/CFT correspondence.


title: Low frequency estimates for long range perturbations in divergence form

abstract:
  We prove low frequency estimates for the boundary values of the resolvent of
long range perturbations of the flat Laplacian in divergence form.


title:
Comparison of Scatchard and Klotz methods for Metal(II) -DNA complexes
  in the case two type of binding

abstract:
  It was shown, that modified Scatchard plots and Klotz properties of graphical
representations of two classes of binding sites could be used to determine
binding constants of metal ion to DNA. More realistic picture is obtained by
Scatchard plots.


title:
Well-posedness of the spatially homogeneous Landau equation for soft
  potentials

abstract:
  We consider the spatially homogeneous Landau equation of kinetic theory, and
provide a differential inequality for the Wasserstein distance with quadratic
cost between two solutions. We deduce some well-posedness results. The main
difficulty is that this equation presents a singularity for small relative
velocities. Our uniqueness result is the first one in the important case of
soft potentials. Furthermore, it is almost optimal for a class of moderately
soft potentials, that is for a moderate singularity. Indeed, in such a case,
our result applies for initial conditions with finite mass, energy, and
entropy. For the other moderatley soft potentials, we assume additionnally some
moment conditions on the initial data. For very soft potentials, we obtain only
a local (in time) well-posedness result, under some integrability conditions.
Our proof is probabilistic, and uses a stochastic version of the Landau
equation, in the spirit of Tanaka.


title: Chow motives without projectivity

abstract:
  In paper 0704.4003, Bondarko recently defined the notion of weight structure,
and proved that the category $\DgM$ of geometrical motives over a perfect field
k, as defined and studied by Voevodsky, Suslin and Friedlander, is canonically
equipped with such a structure. Building on this result, and under a condition
on the weights avoided by the boundary motive, we describe a method to
construct intrinsically in $\DgM$ a motivic version of interior cohomology of
smooth, but possibly non-projective schemes. In a sequel to this work, this
method will be applied to Shimura varieties.


title: Astrophysical implications of hypothetical stable TeV-scale black holes

abstract:
  We analyze macroscopic effects of TeV-scale black holes, such as could
possibly be produced at the LHC, in what is regarded as an extremely
hypothetical scenario in which they are stable and, if trapped inside Earth,
begin to accrete matter. We examine a wide variety of TeV-scale gravity
scenarios, basing the resulting accretion models on first-principles, basic,
and well-tested physical laws. These scenarios fall into two classes, depending
on whether accretion could have any macroscopic effect on the Earth at times
shorter than the Sun's natural lifetime. We argue that cases with such effect
at shorter times than the solar lifetime are ruled out, since in these
scenarios black holes produced by cosmic rays impinging on much denser white
dwarfs and neutron stars would then catalyze their decay on timescales
incompatible with their known lifetimes. We also comment on relevant lifetimes
for astronomical objects that capture primordial black holes. In short, this
study finds no basis for concerns that TeV-scale black holes from the LHC could
pose a risk to Earth on time scales shorter than the Earth's natural lifetime.
Indeed, conservative arguments based on detailed calculations and the
best-available scientific knowledge, including solid astronomical data,
conclude, from multiple perspectives, that there is no risk of any significance
whatsoever from such black holes.


title: Curvature Perturbation from Supersymmetric Flat Directions

abstract:
  We show that a contribution to the total curvature perturbation may be due to
the presence of flat directions in supersymmetric models. It is generated at
the first os- cillation of the flat direction condensate when the latter
relaxes to the minimum of its potential after the end of inflation. We also
point out that, if the contribution to the total curvature perturbation from
supersymmetric flat direction is the dominant one, then a significant level of
non-Gaussianity in the cosmological perturbation is also naturally expected.


title: Polarimetric imaging of interacting pairs

abstract:
  We present optical polarization maps of a sample of four interacting pairs at
different phases of encounter, from nearly unperturbed galaxies to on-going
mergers. Only the pair RR 24 shows a linear polarization pattern which extends
in both galaxies for several kiloparsecs. The more perturbed member, RR 24b, is
lineraly polarized up to the level of ~3%. No polarization is measured in the
strongly perturbed late-type pair members of RR 23 and RR 99. Also, in the
central part of the double nuclei shell galaxy ESO 2400100 there is no
significant polarization. We use the ionized gas velocity field of RR 24 to
interpret its linear polarization structure. In RR 24a the quite regular gas
kinematics reflect the unperturbed spiral-like polarization structure. In RR
24b a strong velocity gradient in ionized gas could be associated with the
polarization structure. We suggest that the large-scale magnetic field of the
RR 24 pair members still plays a role in shaping the polarization pattern.


title:
SSPMJ1102-3431 brown dwarf characterization from accurate proper motion
  and trigonometric parallax

abstract:
  In 2005, Scholz and collaborators (Scholz et al. 2005) discovered, in a
proper motion survey, a young brown dwarf SSSPMJ1102-3431(SSSPMJ1102) of
spectral type M8.5, probable member of the TW Hydrae Association (TWA) and
possible companion of the T Tauri star TW Hya. The physical characterization of
SSSPMJ1102 was based on the hypothesis that it forms a binary system with TW
Hya. The recent discovery of a probable giant planet inside the TW Hya
protoplanetary disk with a very short-period (Setiawan et al. 2008) and a disk
around SSSPMJ1102 (Riaz and Gizis 2008) make it especially interesting and
important to measure well the physical parameters of SSSPMJ1102. Trigonometric
parallax and proper motion measurements of SSSPMJ1102 are necessary to test for
TWA membership and, thus, to determine the mass and age of this young brown
dwarf and the possibility that it forms a wide binary system with TW Hya. Two
years of regular observations at the ESO NTT/SUSI2 telescope, have enabled us
to determine the trigonometric parallax and proper motion of SSSPMJ1102. Our
parallax and proper motion determination allow us to precisely describe the
physical properties of this low mass object and to confirm its TWA membership.
Our results are not incompatible with the hypothesis that SSSPMJ1102 is a
binary companion of the star TW Hya.


title:
Charge instabilities and electron-phonon interaction in the
  Hubbard-Holstein model

abstract:
  We consider the Hubbard-Holstein model in the adiabatic limit to investigate
the effects of electron-electron interactions on the electron-phonon coupling.
To this aim we compute at any momentum and filling the static charge
susceptibility of the Hubbard model within the Gutzwiller approximation and we
find that electron-electron correlations effectively screen the electron
coupling to the lattice. This screening is more effective at large momenta and,
as a consequence, the charge-density wave phase due to the usual Peierls
instability of the Fermi surface momenta is replaced by a phase-separation
instability when the correlations are sizable.


title:
Automated supervised classification of variable stars II. Application to
  the OGLE database

abstract:
  We aim to extend and test the classifiers presented in a previous work
against an independent dataset. We complement the assessment of the validity of
the classifiers by applying them to the set of OGLE light curves treated as
variable objects of unknown class. The results are compared to published
classification results based on the so-called extractor methods.Two
complementary analyses are carried out in parallel. In both cases, the original
time series of OGLE observations of the Galactic bulge and Magellanic Clouds
are processed in order to identify and characterize the frequency components.
In the first approach, the classifiers are applied to the data and the results
analyzed in terms of systematic errors and differences between the definition
samples in the training set and in the extractor rules. In the second approach,
the original classifiers are extended with colour information and, again,
applied to OGLE light curves. We have constructed a classification system that
can process huge amounts of time series in negligible time and provide reliable
samples of the main variability classes. We have evaluated its strengths and
weaknesses and provide potential users of the classifier with a detailed
description of its characteristics to aid in the interpretation of
classification results. Finally, we apply the classifiers to obtain object
samples of classes not previously studied in the OGLE database and analyse the
results. We pay specific attention to the B-stars in the samples, as their
pulsations are strongly dependent on metallicity.


title:
Dissipative dynamics of a biased qubit coupled to a harmonic oscillator:
  Analytical results beyond the rotating wave approximation

abstract:
  We study the dissipative dynamics of a biased two-level system (TLS) coupled
to a harmonic oscillator (HO), the latter interacting with an Ohmic
environment. Using Van-Vleck perturbation theory and going to second order in
the coupling between TLS and HO, we show how the Hamiltonian of the TLS-HO
system can be diagonalized analytically. Our model represents an improvement to
the usually used Jaynes-Cummings Hamiltonian as an initial rotating wave
approximation is avoided. By assuming a weak coupling to the thermal bath,
analytical expressions for the time evolution of the populations of the TLS are
found: the population is characterized by a multiplicity of damped oscillations
together with a complex relaxation dynamics towards thermal equilibrium. The
long time evolution is characterized by a single relaxation rate, which is
largest at resonance and whose expression can be given in closed analytic form.


title:
Comparison of the atmosphere above the South Pole, Dome C and Dome A:
  first attempt

abstract:
  The atmospheric properties above three sites (Dome C, Dome A and the South
Pole) on the Internal Antarctic Plateau are investigated for astronomical
applications using the monthly median of the analyses from ECMWF (the European
Centre for Medium-Range Weather Forecasts). Radiosoundings extended on a yearly
time scale at the South Pole and Dome C are used to quantify the reliability of
the ECMWF analyses in the free atmosphere as well as in the boundary and
surface layers, and to characterize the median wind speed in the first 100 m
above the two sites. Thermodynamic instability properties in the free
atmosphere above the three sites are quantified with monthly median values of
the Richardson number. We find that the probability to trigger thermodynamic
instabilities above 100 m is smaller on the Internal Antarctic Plateau than on
mid-latitude sites. In spite of the generally more stable atmospheric
conditions of the Antarctic sites compared to mid-latitude sites, Dome C shows
worse thermodynamic instability conditions than those predicted above the South
Pole and Dome A above 100 m. A rank of the Antarctic sites done with respect to
the strength of the wind speed in the free atmosphere (ECMWF analyses) as well
as the wind shear in the surface layer (radiosoundings) is presented.


title: Geometric Engineering 5d Black Holes with Rod Diagrams

abstract:
  Static solutions of 5-dimensional gravity with two spatial Killing vectors
are characterized by their rod structures. In this note we describe how the
orbifold singularities and the topologies of the horizons and asymptotic
regions can be determined from the corresponding rod diagrams. As an example we
introduce the black lens, a static 5-dimensional black hole with a horizon of
lens space topology which is asymptotically Minkowski space. The solution is
novel in that the asymptotic Minkowski space is not quotiented. However it
suffers from a naked singularity. While the conical and orbifold singularities
have been removed, two spherical curvature singularities remain. These
singularities do not contribute to the ADM mass, and the thermodynamics of the
black lens is well behaved, although its entropy is lower than that of a
Tangherlini black hole of the same mass.


title:
Eighth-Order Vacuum-Polarization Function Formed by Two
  Light-by-Light-Scattering Diagrams and its Contribution to the Tenth-Order
  Electron g-2

abstract:
  We have evaluated the contribution to the anomalous magnetic moment of the
electron from six tenth-order Feynman diagrams which contain eighth-order
vacuum-polarization function formed by two light-by-light scattering diagrams
connected by three photons. The integrals are constructed by two different
methods. In the first method the subtractive counter terms are used to deal
with ultraviolet (UV) singularities together with the requirement of
gauge-invariance. In the second method, the Ward-Takahashi identity is applied
to the light-by-light scattering amplitudes to eliminate UV singularities.
Numerical evaluation confirms that the two methods are consistent with each
other within their numerical uncertainties. Combining the two results
statistically and adding small contribution from the muons and/or tau leptons,
we obtain $ 0.000 399 9 (18) (\alpha/\pi)^5$. We also evaluated the
contribution to the muon $g-2$ from the same set of diagrams and found $ -1.263
44 (14) (\alpha/\pi)^5$.


title: On Type IIA Penrose Limit and N=6 Chern-Simons Theories

abstract:
  Recently, Aharony, Bergman, Jafferis and Maldacena proposed that the N=6
Chern-Simons gauge theories are holographically dual to the M-theory
backgrounds with multiple M2-branes on orbifolds C^4/Z_k. When k is large, they
have the type IIA string description. In this paper we analyze the Penrose
limit of this IIA background and express the string spectrum as the conformal
dimensions of operators in the gauge theories. For BPS operators, we can
confirm the agreements between the IIA string on plane waves and the gauge
theories. We point out that there exist BMN-like operators in the gauge
theories, though their holographic interpretation does not seem to be simple.
Also we analyze the weak coupling limit of this theory and show that the
Hagedorn/deconfinement transition occurs as expected.


title:
Log-concavity and q-Log-convexity Conjectures on the Longest Increasing
  Subsequences of Permutations

abstract:
  Let $P_{n,k}$ be the number of permutations $\pi$ on [n]={1, 2,..., n} such
that the length of the longest increasing subsequences of $\pi$ equals k, and
let $M_{2n, k}$ be the number of matchings on [2n] with crossing number k.
Define $P_n(x)= \sum_k P_{n,k}x^k$ and $M_{2n}(x)=\sum_{k} M_{2n,k}x^k$. We
propose some conjectures on the log-concavity and q-log-convexity of the
polynomials $P_n(x)$ and $M_{2n}(x)$. We also introduce the notions of
$\infty$-q-log-convexity and $\infty$-q-log-concavity, and the notion of higher
order log-concavity with respect to $\infty$-q-log-convex or
$\infty$-q-log-concavity. A conjecture on the $\infty$-q-log-convexity of the
Boros-Moll polynomials is presented. It seems that $M_{2n}(x)$ are log-concave
of any order with respect to $\infty$-q-log-convexity.


title: On special geometry of the moduli space of string vacua with fluxes

abstract:
  In this paper we construct a special geometry over the moduli space of type
II string vacua with both NS and RR fluxes turning on. Depending on what fluxes
are turning on we divide into three cases of moduli space of generalized
structures. They are respectively generalized Calabi-Yau structures,
generalized Calabi-Yau metric structures and ${\cal N} =1$ generalized string
vacua. It is found that the $d d^{\cal J}$ lemma can be established for all
three cases. With the help of the $d d^{\cal J}$ lemma we identify the moduli
space locally as a subspace of $d_{H}$ cohomologies. This leads naturally to
the special geometry of the moduli space. It has a flat symplectic structure
and a K$\ddot{\rm a}$hler metric with the Hitchin functional (modified if RR
fluxes are included) the K$\ddot{\rm a}$hler potential. Our work is based on
previous works of Hitchin and recent works of Gra$\tilde{\rm
n}$a-Louis-Waldram, Goto, Gualtieri, Yi Li and Tomasiello. The special geometry
is useful in flux compactifications of type II string theories.


title:
Cold gas in the Intra Cluster Medium: implications for flow dynamics and
  powering optical nebulae

abstract:
  We show that the mechanical energy injection rate generated as the
intra-cluster medium (ICM) flows around cold clouds may be sufficient to power
the optical and near infra-red emission of nebulae observed in the central
regions of a sample of seven galaxy clusters. The energy injection rate is
extremely sensitive to the velocity difference between the ICM and cold clouds,
which may help to explain why optical and infra-red luminosity is often larger
than expected in systems containing AGNs. We also find that mass recycling is
likely to be important for the dynamics of the ICM. This effect will be
strongest in the central regions of clusters where there is more than enough
cold gas for its evaporation to contribute significantly to the density of the
hot phase.


title:
Creation and detection of a mesoscopic gas in a non-local quantum
  superposition

abstract:
  We investigate the scattering of a quantum matter wave soliton on a barrier
in a one dimensional geometry and we show that it can lead to mesoscopic
Schr\"odinger cat states, where the atomic gas is in a coherent superposition
of being in the half-space to the left of the barrier and being in the
half-space to the right of the barrier. We propose an interferometric method to
reveal the coherent nature of this superposition and we discuss in details the
experimental feasibility.


title: Dirac's Equation in Different Numerical Rings

abstract:
  Dirac's equations are formulated in a consistent way by using only elements
from each of R, C, and H. In H, the quaternions, the symmetry resulting from a
"single" conjugation (i, j, or k) results in three conserved currents -
possibly associated with "color." The role that the numerical field plays is
discussed and speculated on.


title:
A solution of linearized Einstein field equations in vacuum used for the
  detection of the stochastic background of gravitational waves

abstract:
  A solution of linearized Einstein field equations in vacuum is given and
discussed. First it is shown that, computing from our particular metric the
linearized connections, the linearized Riemann tensor and the linearized Ricci
tensor, the linearized Ricci tensor results equal to zero. Then the effect on
test masses of our solution, which is a gravitational wave, is discussed. In
our solution test masses have an apparent motion in the direction of
propagation of the wave, while in the transverse direction they appear at rest.
In this way it is possible to think that gravitational waves would be
longitudinal waves, but, from careful investigation of this solution, it is
shown that the tidal forces associated with gravitational waves act along the
directions orthogonal to the direction of propagation of waves. The computation
is first made in the long wavelengths approximation (wavelength much larger
than the linear distances between test masses), then the analysis is
generalized to all gravitational waves.
  In the last sections of this paper it is shown that the frequency dependent
angular pattern of interferometers can be obtained from our solution and the
total signal seen from an interferometer for the stochastic background of
gravitational waves is computed.


title:
Pressure-induced phase transition to a novel spin state in striped
  nickelates

abstract:
  We analyze pressure effects on stripe states within a selfconsistent
Hartree-Fock calculation for a model of a striped nickelates. The results show
a transition induced by high pressure and predict possible new spin states. We
describe characteristics in the phonon excitations at the predicted transition,
based on a real-space random phase approximation.


title: Heterogeneous credit portfolios and the dynamics of the aggregate losses

abstract:
  We study the impact of contagion in a network of firms facing credit risk. We
describe an intensity based model where the homogeneity assumption is broken by
introducing a random environment that makes it possible to take into account
the idiosyncratic characteristics of the firms. We shall see that our model
goes behind the identification of groups of firms that can be considered
basically exchangeable. Despite this heterogeneity assumption our model has the
advantage of being totally tractable. The aim is to quantify the losses that a
bank may suffer in a large credit portfolio. Relying on a large deviation
principle on the trajectory space of the process, we state a suitable law of
large number and a central limit theorem useful to study large portfolio
losses. Simulation results are provided as well as applications to portfolio
loss distribution analysis.


title:
Time-dependent photoionization of azulene: Competition between
  ionization and relaxation in highly excited states

abstract:
  Pump-probe photoionization has been used to map the relaxation processes
taking place from highly vibrationally excited levels of the S2 state of
azulene, populated directly or via internal conversion from the S4 state.
Photoelectron spectra obtained by 1+2[prime] two-color time-resolved
photoelectron imaging are invariant (apart from in intensity) to the pump-probe
time delay and to the pump wavelength. This reveals a photoionization process
which is driven by an unstable electronic state (e.g., doubly excited state)
lying below the ionization potential. This state is postulated to be populated
by a probe transition from S2 and to rapidly relax via an Auger-like process
onto highly vibrationally excited Rydberg states. This accounts for the time
invariance of the photoelectron spectrum. The intensity of the photoelectron
spectrum is proportional to the population in S2. An exponential energy gap law
is used to describe the internal conversion rate from S2 to S0. The vibronic
coupling strength is found to be larger than 60$\pm$5 $\mu$eV.


title:
Time-dependent photoionization of azulene: Optically induced anisotropy
  on the femtosecond scale

abstract:
  We measure the photoionization cross-section of vibrationally excited levels
in the S2 state of azulene by femtosecond pump-probe spectroscopy. At the
wavelengths studied (349-265 nm in the pump) the transient signals exhibit two
distinct and well-defined behaviours: (i) Short-term (on the order of a
picosecond) polarization dependent transients and (ii) longer (10 ps - 1 ns)
time-scale decays. This letter focuses on the short time transient. In contrast
to an earlier study by Diau et al.22 [J. Chem. Phys. 110 (1999) 9785.] we
unambiguously assign the fast initial decay signal to rotational dephasing of
the initial alignment created by the pump transition.


title:
Ionization in a frozen Rydberg gas with attractive or repulsive
  potentials

abstract:
  We report clear evidence of the role of dipole-dipole interaction in Penning
ionization of Rydberg atoms, leading to the formation of an ultracold plasma.
Penning ionization of np Rydberg Cesium atoms is prevented for states with in n
< 42, which correspond to a repulsive potential, but it does not occur for n
larger than 42, corresponding to an attractive potential. Blackbody radiation
is mostly responsible for the background and initial ionization, although
ion-Rydberg collisions and population transfer due to limited superradiance may
have to be considered.


title:
Calculating Effective Diffusivities in the Limit of Vanishing Molecular
  Diffusion

abstract:
  In this paper we study the problem of the numerical calculation (by Monte
Carlo Methods) of the effective diffusivity for a particle moving in a periodic
divergent-free velocity filed, in the limit of vanishing molecular diffusion.
In this limit traditional numerical methods typically fail, since they do not
represent accurately the geometry of the underlying deterministic dynamics. We
propose a stochastic splitting method that takes into account the volume
preserving property of the equations motion in the absence of noise, and when
inertial effects can be neglected. An extension of the method is then proposed
for the cases where the noise has a non trivial time-correlation structure and
when inertial effects cannot be neglected. Modified equations are used to
perform backward error analysis. The new stochastic geometric integrators are
shown to outperform standard Euler-based integrators. Various asymptotic limits
of physical interest are investigated by means of numerical experiments, using
the new integrators.


title: N in turn-off stars of NGC 6397 and NGC 6752

abstract:
  We measure the nitrogen abundance in 5 Turn Off(TO) stars of the Globular
Clusters NGC 6397 and NGC 6752, and compare the cluster abundances with those
of field stars of comparable metallicity. We determine the nitrogen abundance
from the band head system at 3360 \AA, using spectra of resolution R=45000
obtained with the UVES spectrograph on the VLT. We apply the same method
previously used on field stars, to allow a direct comparison of the results.
Nitrogen is found to have the same abundance in two of the NGC 6397 stars, in
spite of a difference of one order of magnitude in oxygen abundance between
them. In a third star of NGC 6397 the value is slightly lower, but compatible
with the other two, within the uncertainties. All the stars in NGC 6397 are
N-rich with respect to field objects of similar metallicity. The two stars in
NGC 6752 show a difference in nitrogen abundance by over one order of
magnitude. The same stars differ in the abundances of other elements such as
Na, O and Li, only by a factor 3-4. The behaviour of N is different in the two
clusters: no variation is observed NGC 6397, while a large variation is
observed in NGC 6752. This is consistent with a picture in which the stars in
NGC 6752 have been formed by a mixture of ``pristine'' material and material
which has been processed by an early generation of stars, referred to as
``polluters''. The N abundances here reported will help to constrain the
properties of the polluters. In the case of NGC 6397 a simple pollution history
is probably not viable, since the observed variations in O abundances are not
accompanied by corresponding variations in N or Li.


title:
The second physical moment of the heavy quark vector correlator at
  O(alpha_s^3)

abstract:
  The second moment of the heavy quark vector correlator at O(alpha_s^3) is
presented. The implications of this result on recent determinations of the
charm and bottom quark mass are discussed.


title: Theory of magnetization plateaux in the Shastry-Sutherland model

abstract:
  Using perturbative continuous unitary transformations, we determine the
long-range interactions between triplets in the Shastry-Sutherland model, and
we show that an unexpected structure develops at low magnetization with
plateaux progressively appearing at 2/9, 1/6, 1/9 and 2/15 upon increasing the
inter-dimer coupling. A critical comparison with previous approaches is
included. Implications for the compound SrCu$_2$(BO$_3$)$_2$ are also
discussed: we reproduce the magnetization profile around localized triplets
revealed by NMR, we predict the presence of a 1/6 plateau, and we suggest that
residual interactions beyond the Shastry-Sutherland model are responsible for
the other plateaux below 1/3.


title:
Comparison of the pressure dependences of Tc in the trivalent d-electron
  superconductors

abstract:
  Whereas dhcp La superconducts at ambient pressure with Tc = 5 K, the other
trivalent d-electron metals Sc, Y, and Lu only superconduct if high pressures
are applied. Earlier measurements of the pressure dependence of Tc for Sc and
Lu metal are here extended to much higher pressures. Whereas Tc for Lu
increases monotonically with pressure to 12.4 K at 174 GPa (1.74 Mbar). Tc for
Sc reaches 19.6 K at 107 GPa, the 2nd highest value observed for any elemental
superconductor. At higher pressures a phase transition occurs whereupon Tc
drops to 8.31 K at 111 GPa. The Tc(P) dependences for Sc and Lu are compared to
those of Y and La. An interesting correlation is pointed out between the value
of Tc and the fractional free volume available to the conduction electrons
outside the ion cores, a quantity which is directly related to the number of d
electrons in the conduction band.


title: The Attractor and the Quantum States

abstract:
  The dissipative dynamics anticipated in the proof of 't Hooft's existence
theorem -- "For any quantum system there exists at least one deterministic
model that reproduces all its dynamics after prequantization" -- is constructed
here explicitly. We propose a generalization of Liouville's classical phase
space equation, incorporating dissipation and diffusion, and demonstrate that
it describes the emergence of quantum states and their dynamics in the
Schroedinger picture. Asymptotically, there is a stable ground state and two
decoupled sets of degrees of freedom, which transform into each other under the
energy-parity symmetry of Kaplan and Sundrum. They recover the familiar Hilbert
space and its dual. Expectations of observables are shown to agree with the
Born rule, which is not imposed a priori. This attractor mechanism is
applicable in the presence of interactions, to few-body or field theories in
particular.


title:
Decay estimates for variable coefficient wave equations in exterior
  domains

abstract:
  In this article we consider variable coefficient, time dependent wave
equations in exterior domains. We prove localized energy estimates if the
domain is star-shaped and global in time Strichartz estimates if the domain is
strictly convex.


title:
The Airy_1 process is not the limit of the largest eigenvalue in GOE
  matrix diffusion

abstract:
  Using a systematic approach to evaluate Fredholm determinants numerically, we
provide convincing evidence that the Airy_1-process, arising as a limit law in
stochastic surface growth, is not the limit law for the evolution of the
largest eigenvalue in GOE matrix diffusion.


title: N-th root

abstract:
  The quaternion equation X^n=A is solved for any integer number n > 1. A is a
given quaternion with komplex numbers as its elements. We use the isomorphism
between quaternions and (4,4)-matrices to solve this equation.


title: Overpseudoprimes, Mersenne Numbers and Wieferich primes

abstract:
  We introduce a new class of pseudoprimes-so called "overpseudoprimes" which
is a special subclass of super-Poulet pseudoprimes. Denoting via h(n) the
multiplicative order of 2 modulo n, we show that odd number n is
overpseudoprime iff value of h(n) is invariant of all divisors d>1 of n. In
particular, we prove that all composite Mersenne numbers 2^p-1,where p is
prime, and squares of Wieferich primes are overpseudoprimes. We give also a
generalization of the results on arbitrary base a>1 and prove that every
overpseudoprime is strong pseudoprime of the same base.


title:
Meeting the Cool Neighbors X: Ultracool dwarfs from the 2MASS All-Sky
  Data Release

abstract:
  Using data from the 2MASS All-Sky Point Source Catalogue, we have extended
our census of nearby ultracool dwarfs to cover the full celestial sphere above
Galactic latitute 15 degrees. Starting with an initial catalogue of 2,139,484
sources, we have winnowed the sample to 467 candidate late-type M or L dwarfs
within 20 parsecs of the Sun. Fifty-four of those sources already have
spectroscopic observations confirming them as late-type dwarfs. We present
optical spectroscopy of 376 of the remaining 413 sources, and identify 44 as
ultracool dwarfs with spectroscopic distances less than 20 parsecs. Twenty-five
of the 37 sources that lack optical data have near-infrared spectroscopy.
Combining the present sample with our previous results and data from the
literature, we catalogue 94 L dwarf systems within 20 parsecs. We discuss the
distribution of activity, as measured by H-alpha emission, in this
volume-limited sample. We have coupled the present ultracool catalogue with
data for stars in the northern 8-parsec sample and recent (incomplete)
statistics for T dwarfs to provide a snapshot of the current 20-parsec census
as a function of spectral type.


title: Review of the Safety of LHC Collisions

abstract:
  The safety of collisions at the Large Hadron Collider (LHC) was studied in
2003 by the LHC Safety Study Group, who concluded that they presented no
danger. Here we review their 2003 analysis in light of additional experimental
results and theoretical understanding, which enable us to confirm, update and
extend the conclusions of the LHC Safety Study Group. The LHC reproduces in the
laboratory, under controlled conditions, collisions at centre-of-mass energies
less than those reached in the atmosphere by some of the cosmic rays that have
been bombarding the Earth for billions of years. We recall the rates for the
collisions of cosmic rays with the Earth, Sun, neutron stars, white dwarfs and
other astronomical bodies at energies higher than the LHC. The stability of
astronomical bodies indicates that such collisions cannot be dangerous.
Specifically, we study the possible production at the LHC of hypothetical
objects such as vacuum bubbles, magnetic monopoles, microscopic black holes and
strangelets, and find no associated risks. Any microscopic black holes produced
at the LHC are expected to decay by Hawking radiation before they reach the
detector walls. If some microscopic black holes were stable, those produced by
cosmic rays would be stopped inside the Earth or other astronomical bodies. The
stability of astronomical bodies constrains strongly the possible rate of
accretion by any such microscopic black holes, so that they present no
conceivable danger. In the case of strangelets, the good agreement of
measurements of particle production at RHIC with simple thermodynamic models
constrains severely the production of strangelets in heavy-ion collisions at
the LHC, which also present no danger.


title: f(R) Gravity and Chameleon Theories

abstract:
  We analyse f(R) modifications of Einstein's gravity as dark energy models in
the light of their connection with chameleon theories. Formulated as
scalar-tensor theories, the f(R) theories imply the existence of a strong
coupling of the scalar field to matter. This would violate all experimental
gravitational tests on deviations from Newton's law. Fortunately, the existence
of a matter dependent mass and a thin shell effect allows one to alleviate
these constraints. The thin shell condition also implies strong restrictions on
the cosmological dynamics of the f(R) theories. As a consequence, we find that
the equation of state of dark energy is constrained to be extremely close to -1
in the recent past. We also examine the potential effects of f(R) theories in
the context of the Eot-wash experiments. We show that the requirement of a thin
shell for the test bodies is not enough to guarantee a null result on
deviations from Newton's law. As long as dark energy accounts for a sizeable
fraction of the total energy density of the Universe, the constraints which we
deduce also forbid any measurable deviation of the dark energy equation of
state from -1. All in all, we find that both cosmological and laboratory tests
imply that f(R) models are almost coincident with a Lambda-CDM model at the
background level.


title:
Tunneling conductance in Superconductor/Ferromagnet junctions: a self
  consistent approach

abstract:
  We evaluate the tunneling conductance of clean Ferromomagnet/Superconductor
junctions via a fully self-consistent numerical solution of the microscopic
Bogoliubov-DeGennes equations. We present results for a relevant range of
values of the Fermi wavevector mismatch (FWM), the spin polarization, and the
interfacial scattering strength. For nonzero spin polarization, the conductance
curves vary nonmonotonically with FWM. The FWM dependence of the
self-consistent results is stronger than that previously found in
non-self-consistent calculations, since, in the self-consistent case, the
effective scattering potential near the interface depends on the FWM. The
dependence on interfacial scattering is monotonic. These results confirm that
it is impossible to characterize both the the FWM and the interfacial
scattering by a single effective parameter and that analysis of experimental
data via the use of such one-parameter models is unreliable.


title: Global existence for the MHD system in critical spaces

abstract:
  In this article, we show that the magneto-hydrodynamic system (MHD) in $\R^N$
with variable density, variable viscosity and variable conductivity has a local
weak solution in the Besov space $\dot
B^{\frac{N}{p_1}}_{p_1,1}(\R^N)\times\dot B^{\frac{N}{p_2}-1}_{p_2,1}(\R^N)
\times\dot B^{\frac{N}{p_2}-1}_{p_2,1}(\R^N)$ for all $1<p_2<+\infty$ and some
$1<p_1\leq\frac{2N}{3}$ if the initial density approaches a positive constant.
Moreover, this solution is unique if we impose the restrictive condition
$1<p_2\leq2N$. We prove also that the constructed solution exist globally in
time if the initial data are small enough. In particular, this allows us to
work in the frame of Besov space with negative regularity indices and this fact
is particularly important when the initial data are strong oscillating.


title: Some comments on the possible causes of climate change

abstract:
  Climate change is an important current issue and there is much debate about
the causes and effects. This article examines the changes in our climate,
comparing the recent changes with those in the past. There have been changes in
temperature, resulting in an average global rise over the last 300 years, as
well as widespread melting of snow and ice, and rising global average sea
level. There are many theories for the causes of the recent change in the
climate, including some natural and some human influenced. The most widely
believed cause of the climate change is increasing levels of Greenhouse gases
in the atmosphere and as the atmosphere plays an important role in making our
planet inhabitable, it is important to understand it in order to protect it.
However, there are other theories for the cause of climate change, the Sun and
cosmic rays, for example, are felt by some to have a significant role to play.
There is also well-established evidence that the three Milankovitch cycles
change the amount and alter the distribution of sunlight over the Earth,
heating and cooling it. There are many influences on our planet and they all
have differing levels of impact. The purpose of this article is to review the
present overall position and urge open, reasoned discussion of the problem.


title:
Evidence of thin-film precursors formation in hydrokinetic and atomistic
  simulations of nano-channel capillary filling

abstract:
  We present hydrokinetic Lattice Boltzmann and Molecular Dynamics simulations
of capillary filling of high-wetting fluids in nano-channels, which provide
clear evidence of the formation of thin precursor films, moving ahead of the
main capillary front. The dynamics of the precursor films is found to obey the
Lucas-Washburn law as the main capillary front, z2(t) proportional to t,
although with a larger prefactor, which we find to take the same value for both
geometries under inspection. Both hydrokinetic and Molecular Dynamics
approaches indicate a precursor film thickness of the order of one tenth of the
capillary diameter. The quantitative agreement between the hydrokinetic and
atomistic methods indicates that the formation and propagation of thin
precursors can be handled at a mesoscopic/hydrokinetic level, thereby opening
the possibility of using hydrokinetic methods to space-time scales and complex
geometries of direct experimental relevance.


title: Decay widths of lowest massive Regge excitations of open strings

abstract:
  With the advent of the LHC there is widespread interest in the discovery
potential for physics beyond the standard model. In TeV-scale open string
theory, the new physics can be manifest in the excitation and decay of new
resonant structures, corresponding to Regge recurrences of standard model
particles. An essential input for the prediction of invariant mass spectra of
the decay products (which could serve to identify the resonance as a string
excitation) are the partial and total widths of the decay products. We present
a parameter-free calculation of these widths for the first Regge recurrence of
the SU(3) gluon octet, of the U(1) gauge boson which accompanies gluons in
D-brane constructions, and of the quark triplet.


title: Norm Varieties and the Chain Lemma (after Markus Rost)

abstract:
  The goal of this paper is to present proofs of two results of Markus Rost:
the Chain Lemma and the Norm Principle. These are the final steps needed to
complete the publishable verification of the Bloch-Kato conjecture, that the
norm residue maps are isomorphisms between Milnor K-theory $K_n^M(k)/p$ and
etale cohomology $H^n(k,\mu_p^n)$ for every prime p, every n and every field k
containing 1/p.
  Our proofs of these two results are based on Rost's 1998 preprints, his web
site and Rost's lectures at the Institute for Advanced Study in 1999-2000 and
2005.


title:
M\'etodos de Multiresoluci\'on y su Aplicaci\'on a un Modelo de
  Ingenier\'ia

abstract:
  The main objective of this dissertation is to present an adaptation of some
finite volume methods used in the resolution of problems arising in
sedimentation processes of flocculated suspensions (or sedimentation with
compression).
  This adaptation is based on the utilization of multiresolution techniques,
originally designed to reduce the computational cost incurred in solving using
high resolution schemes in the numerical solution of hyperbolic systems of
conservation laws.


title:
Impurity bands and the character of the electronic states in
  ferromagnetic GaMnAs layers

abstract:
  The interplay between disorder and spin polarization in a GaMnAs thin layer
results into spin-polarized impurity hole bands. A figure of merit is defined
to label the hole state as being extended or localized. The calculation leads
to a phase diagram determining the metallic or non-metallic character of the
sample. It is shown that samples with the highest figures of merit have a ratio
between the extended hole density and the Mn concentration near 0.2, in
agreement with the ratio of 0.1-0.25 known to occur among samples produced with
the highest Curie temperatures. Both the non-metal-to-metal and the
metal-to-non-metal transitions experimentally observed in the ferromagnetic
regime are obtained, as the Mn concentration increases. An explanation is given
for the occurrence of a maximal Curie temperature in ferromagnetic GaMnAs
samples.


title:
Existence, multiplicity and stability of endemic states for an
  age-structured S-I epidemic model

abstract:
  We study an S--I type epidemic model in an age-structured population, with
mortality due to the disease. A threshold quantity is found that controls the
stability of the disease-free equilibrium and guarantees the existence of an
endemic equilibrium. We obtain conditions on the age-dependence of the
susceptibility to infection that imply the uniqueness of the endemic
equilibrium. An example with two endemic equilibria is shown. Finally, we
analyse numerically how the stability of the endemic equilibrium is affected by
extra-mortality and by the possible periodicities induced by the demographic
age-structure.


title: Multiresolution Schemes and its Application to Sedimentation Models

abstract:
  A numerical method is presented to obtain approximate solutions to problems
arising from sedimentation models. These processes are widely utilized in
minery for recovering water from suspensions coming out of flotation processes.
The main idea is to apply a multiresolution method to the existing schemes
developed by B\"urger et al. [2, 3, 4] and to observe the good performance of
the multiresolution strategy when applied to these kind of problems. We obtain
high rates of memory compression without affecting the quality of the solution.


title:
Destruction of Neel order and appearance of superconductivity in
  electron-doped cuprates by oxygen annealing process

abstract:
  We use thermodynamic and neutron scattering measurements to study the effect
of oxygen annealing on the superconductivity and magnetism in
Pr$_{0.88}$LaCe$_{0.12}$CuO$_{4-\delta}$. Although the transition temperature
$T_c$ measured by susceptibility and superconducting coherence length increase
smoothly with gradual oxygen removal from the annealing process, bulk
superconductivity, marked by a specific heat anomaly at $T_c$ and the presence
of a neutron magnetic resonance, only appears abruptly when $T_c$ is close to
the largest value. These results suggest that the effect of oxygen annealing
must be first determined in order to establish a Ce-doping dependence of
antiferromagnetism and superconductivity phase diagram for electron-doped
copper oxides.


title: Towards establishing the spin of warped gravitons

abstract:
  We study the possibility of experimental verification of the spin=2 nature of
the Kaluza-Klein (KK) graviton which is predicted to exist in the
extra-dimensional Randal-Sundrum (RS) warped models. The couplings of these
gravitons to the particles located on or near the TeV brane is the strongest as
the overlap integral of their profiles in the extra-dimension is large. Among
them are unphysical Higgses ($W^{\pm}_L$ and $Z_L$) and KK excitations of the
Standard Model (SM) gauge bosons. We consider the possibility to confirm the
spin-2 nature of the first KK mode of the warped graviton ($G_1$) based on the
angular distribution of the Z bozon in the graviton rest frame in the gg$\to
G_1 \to W^{KK} (Z^{KK}) W (Z)\to WWZ$, gg$\to G_1\to ZZ$ and gg$\to G_1 \to
Z^{KK} Z\to ZZH$ decay channels. Using Wigner D-matrix properties, we derive
the relationship between the graviton spin, signal angular distribution peak
value, and other theoretically calculable quantities. We then study the LHC
signals for these decay modes and find that with 1000 fb$^{-1}$ of data, spin
of the RS graviton up to $\sim$ 2 TeV may be confirmed in the $pp \to W^{KK}
(Z^{KK}) W (Z) \to WWZ \to$ 3 leptons + jet + $\slashed{E}_T$ and $pp \to ZZ
\to$ 4 leptons decay modes.


title: Toeplitz Corona Theorems for the Polydisk and the Unit Ball

abstract:
  The main purpose of this paper is to extend and refine some work of
Agler-McCarthy and Amar concerning the Corona problem for the polydisk and the
unit ball in $\mathbb{C}^n$.


title: Fast nuclear spin hyperpolarization of phosphorus in silicon

abstract:
  We experimentally demonstrate a method for obtaining nuclear spin
hyperpolarization, that is, polarization significantly in excess of that
expected for a thermal equilibrium. By exploiting a modified Overhauser
process, we obtain more than 68% nuclear anti-polarization of phosphorus donors
in silicon. This polarization is reached with a time constant of ~150 seconds,
at a temperature of 1.37 K and a magnetic field of 8.5 T. The ability to obtain
such large polarizations is discussed with regards to its significance for
quantum information processing and magnetic resonance imaging.


title:
Minimal supporting subtrees for the free energy of polymers on
  disordered trees

abstract:
  We consider a model of directed polymers on a regular tree with a disorder
given by independent, identically distributed weights attached to the vertices.
For suitable weight distributions this model undergoes a phase transition with
respect to its localization behaviour. We show that, for high temperatures, the
free energy is supported by a random tree of positive exponential growth rate,
which is strictly smaller than that of the full tree. The growth rate of the
minimal supporting subtree is decreasing to zero as the temperature decreases
to the critical value. At the critical value and all lower temperatures, a
single polymer suffices to support the free energy. Our proofs rely on elegant
martingale methods adapted from the theory of branching random walks.


title: Long spin coherence in silicon with an electrical spin trap readout

abstract:
  Pulsed electrically-detected magnetic resonance of phosphorous (31P) in bulk
crystalline silicon at very high magnetic fields (B > 8.5 T) and low
temperatures (T = 2.8 K) is presented. We find that the spin-dependent capture
and reemission of highly polarized (>95%) conduction electrons by equally
highly polarized 31P donor electrons introduces less decoherence than other
mechanisms for spin-to-charge conversion. This allows the electrical detection
of spin coherence times in excess of 100 microseconds: 50 times longer than the
previous maximum for electrically-detected spin readout experiments.


title: Effective Hamiltonian for FeAs based superconductors

abstract:
  The recently discovered FeAs-based superconductors show intriguing behavior
and unusual dynamics of electrons and holes which occupy the Fe $d$-orbitals
and As $4s$ and $4p$ orbitals. Starting from the atomic limit, we carry out a
strong coupling expansion to derive an effective hamiltonian that describes the
electron and hole behavior. The hopping and the hybridization parameters
between the Fe $d$ and As $s$ and $p$-orbitals are obtained by fitting the
results of our density-functional-theory calculations to a tight-binding model
with nearest-neighbor interactions and a minimal orbital basis. We find that
the effective hamiltonian, in the strong on-site Coulomb repulsion limit,
operates on three distinct sub-spaces coupled through Hund's rule. The three
sub-spaces describe different components (or subsystems): (a) one spanned by
the $d_{x^2-y^2}$ Fe orbital; (b) one spanned by the degenerate atomic Fe
orbitals $d_{xz}$ and $d_{yz}$; and (c) one spanned by the atomic Fe orbitals
$d_{xy}$ and $d_{z^2}$. Each of these Hamiltonians is an extended t-t'-J-J'
model and is characterized by different coupling constants and filling factors.
For the case of the undoped material the second subspace alone prefers a ground
state characterized by a spin-density-wave order similar to that observed in
recent experimental studies, while the other two subspaces prefer an
antiferromagnetic order. We argue that the observed spin-density-wave order
minimizes the ground state energy of the total hamiltonian.


title: Boolean 2-designs and the embedding of a 2-design in a group

abstract:
  We try to embed a t-design in a finite commutative group in such a way that
the sum of the k points of a block is zero. We can compute the number of blocks
of the boolean 2-design having all the non zero vectors of $(Z_2)^n$ as the set
of points and the k-subsets of elements the sum of which is zero as blocks.


title:
The Role of the Radial Orbit Instability in Dark Matter Halo Formation
  and Structure

abstract:
  For a decade, N-body simulations have revealed a nearly universal dark matter
density profile, which appears to be robust to changes in the overall density
of the universe and the underlying power spectrum. Despite its universality,
the physical origin of this profile has not yet been well understood.
Semi--analytic models by Barnes et al. (2005) have suggested that the density
structure of dark matter halos is determined by the onset of the radial orbit
instability (ROI). We have tested this hypothesis using N-body simulations of
collapsing dark matter halos with a variety of initial conditions. For
dynamically cold initial conditions, the resulting halo structures are triaxial
in shape, due to the mild aspect of the instability. We examine how variations
in initial velocity dispersion affect the onset of the instability, and find
that an isotropic velocity dispersion can suppress the ROI entirely, while a
purely radial dispersion does not. The quantity sigma^2/vc^2 is a criterion for
instability, where regions with sigma^2/vc^2 <~1 become triaxial due to the ROI
or other perturbations. We also find that the radial orbit instability sets a
scale length at which the velocity dispersion changes rapidly from isotropic to
radially anisotropic. This scale length is proportional to the radius at which
the density profile changes shape, as is the case in the semi--analytic models;
however, the coefficient of proportionality is different by a factor of ~2.5.
We conclude that the radial orbit instability is likely to be a key physical
mechanism responsible for the nearly universal profiles of simulated dark
matter halos.


title: Polarized Bremsstrahlung in the Equivalent Photon Method

abstract:
  An economic technique for calculation of polarized bremsstrahlung process is
proposed, assuming typical atomic momentum transfer $q\ll m$. The adopted
approach is based on the natural reduction of the matrix element to the form
$V^{\alpha}\gamma^{\alpha}+A_{5}\gamma ^{5}$. Polarization distribution in the
fully differential cross-section is analyzed. It is found that at a given
momentum transfer to the atom polarization in the plane of small radiation
angles is oriented along circles passing through two common points. It is shown
that with angular selection of radiated photons carried out, even with momentum
transfers to the atom being integrated over, for particular radiation angles
polarization may stay as high as 100%. Without angular selection of photons,
only by control of the recoil, it is impossible to gain radiation polarization
above 50%.


title:
Resistive jet simulations extending radially self-similar
  magnetohydrodynamic models

abstract:
  Numerical simulations with self-similar initial and boundary conditions
provide a link between theoretical and numerical investigations of jet
dynamics. We perform axisymmetric resistive magnetohydrodynamic (MHD)
simulations for a generalised solution of the Blandford & Payne type, and
compare them with the corresponding analytical and numerical ideal-MHD
solutions. We disentangle the effects of the numerical and physical
diffusivity. The latter could occur in outflows above an accretion disk, being
transferred from the underlying disk into the disk corona by MHD turbulence
(anomalous turbulent diffusivity), or as a result of ambipolar diffusion in
partially ionized flows. We conclude that while the classical magnetic Reynolds
number $R_{\rm m}$ measures the importance of resistive effects in the
induction equation, a new introduced number, $\rbeta=(\beta/2)R_{\rm m}$ with
$\beta$ the plasma beta, measures the importance of the resistive effects in
the energy equation. Thus, in magnetised jets with $\beta<2$, when $\rbeta \la
1$ resistive effects are non-negligible and affect mostly the energy equation.
The presented simulations indeed show that for a range of magnetic
diffusivities corresponding to $\rbeta \ga 1$ the flow remains close to the
ideal-MHD self-similar solution.


title:
Quantum and Randomized Lower Bounds for Local Search on
  Vertex-Transitive Graphs

abstract:
  We study the problem of \emph{local search} on a graph. Given a real-valued
black-box function f on the graph's vertices, this is the problem of
determining a local minimum of f--a vertex v for which f(v) is no more than f
evaluated at any of v's neighbors. In 1983, Aldous gave the first strong lower
bounds for the problem, showing that any randomized algorithm requires
$\Omega(2^{n/2 - o(1)})$ queries to determine a local minima on the
n-dimensional hypercube. The next major step forward was not until 2004 when
Aaronson, introducing a new method for query complexity bounds, both
strengthened this lower bound to $\Omega(2^{n/2}/n^2)$ and gave an analogous
lower bound on the quantum query complexity. While these bounds are very
strong, they are known only for narrow families of graphs (hypercubes and
grids). We show how to generalize Aaronson's techniques in order to give
randomized (and quantum) lower bounds on the query complexity of local search
for the family of vertex-transitive graphs. In particular, we show that for any
vertex-transitive graph G of N vertices and diameter d, the randomized and
quantum query complexities for local search on G are $\Omega(N^{1/2}/d\log N)$
and $\Omega(N^{1/4}/\sqrt{d\log N})$, respectively.


title: Linear aggregation beyond isodesmic symmetry

abstract:
  Exactly solvable models of linear aggregation have been known since Ising's
seminal one-dimensional model. This model is defined by a unique
nearest-neighbour bond strength that is independent of the length of the
cluster; known as isodesmic symmetry. Linear aggregation in real systems has
often been associated with broken isodesmic symmetry. Here we show that
important examples can be mapped to a class of one-dimensional models that are
also exactly solvable.