512 research outputs found
Promising effects of oxytocin on social and food-related behaviour in young children with Prader-Willi syndrome: A randomized, double-blind, controlled crossover trial
Background: Prader-Willi syndrome (PWS) is known for hyperphagia with impaired satiety and a specific behavioural phenotype with stubbornness, temper tantrums, manipulative and controlling behaviour and obsessive
Order parameter model for unstable multilane traffic flow
We discuss a phenomenological approach to the description of unstable vehicle
motion on multilane highways that explains in a simple way the observed
sequence of the phase transitions "free flow -> synchronized motion -> jam" as
well as the hysteresis in the transition "free flow synchronized motion".
We introduce a new variable called order parameter that accounts for possible
correlations in the vehicle motion at different lanes. So, it is principally
due to the "many-body" effects in the car interaction, which enables us to
regard it as an additional independent state variable of traffic flow. Basing
on the latest experimental data (cond-mat/9905216) we assume that these
correlations are due to a small group of "fast" drivers. Taking into account
the general properties of the driver behavior we write the governing equation
for the order parameter. In this context we analyze the instability of
homogeneous traffic flow manifesting itself in both of the mentioned above
phase transitions where, in addition, the transition "synchronized motion ->
jam" also exhibits a similar hysteresis. Besides, the jam is characterized by
the vehicle flows at different lanes being independent of one another. We
specify a certain simplified model in order to study the general features of
the car cluster self-formation under the phase transition "free flow
synchronized motion". In particular, we show that the main local parameters of
the developed cluster are determined by the state characteristics of vehicle
motion only.Comment: REVTeX 3.1, 10 pages with 10 PostScript figure
Combined effect of coherent Z exchange and the hyperfine interaction in atomic PNC
The nuclear spin-dependent parity nonconserving (PNC) interaction arising
from a combination of the hyperfine interaction and the coherent,
spin-independent, PNC interaction from Z exchange is evaluated using many-body
perturbation theory. For the 6s-7s transition in 133Cs, we obtain a result that
is about 40% smaller than that found previously by Bouchiat and Piketty [Phys.
Lett. B 269, 195 (1991)]. Applying this result to 133Cs, leads to an increase
in the experimental value of nuclear anapole moment and exacerbates differences
between constraints on PNC meson coupling constants obtained from the Cs
anapole moment and those obtained from other nuclear parity violating
experiments. Nuclear spin-dependent PNC dipole matrix elements, including
contributions from the combined weak-hyperfine interaction, are also given for
the 7s-8s transition in 211Fr and for transitions between ground-state
hyperfine levels in K, Rb, Cs, Ba+, Au, Tl, Fr, and Ra+.Comment: Revtex4 preprint 19 pages 4 table
Probing Orientifold Behavior Near NS Branes
The effect of NS 5 branes on an orientifold is studied. The orientifold is
allowed to pass through a pile of k NS branes forming a regularized CHS
geometry. Its effect on open strings in its vicinity is used to study the
change in the orientifold charge induced by the NS branes.Comment: Important references added, 30 pages, 8 figure
D-branes on a Deformation of SU(2)
We discuss D-branes on a line of conformal field theories connected by an
exact marginal deformation. The line contains an SU(2) WZW model and two
mutually T-dual SU(2)/U(1) cosets times a free boson. We find the D-branes
preserving a U(1) isometry, an F-flux quantization condition and conformal
invariance. Away from the SU(2) point a U(1) times U(1) symmetry is broken to
U(1) times Z_k, i.e. continuous rotations of branes are accompanied by
rotations along the branes. Requiring decoupling of the cosets from the free
boson at the endpoints of the deformation breaks the continuous rotation of
branes to Z_k. At the SU(2) point the full U(1) times U(1) symmetry is
restored. This suggests the occurrence of phase transitions for branes at
angles in the coset model, at a semiclassical level. We also discuss briefly
the orientifold planes along the deformation line.Comment: 19 pages, latex, 5 figures, references adde
Matrix dynamics of fuzzy spheres
We study the dynamics of fuzzy two-spheres in a matrix model which represents
string theory in the presence of RR flux. We analyze the stability of known
static solutions of such a theory which contain commuting matrices and SU(2)
representations. We find that irreducible as well as reducible representations
are stable. Since the latter are of higher energy, this stability poses a
puzzle. We resolve this puzzle by noting that reducible representations have
marginal directions corresponding to non-spherical deformations. We obtain new
static solutions by turning on these marginal deformations. These solutions now
have instability or tachyonic directions. We discuss condensation of these
tachyons which correspond to classical trajectories interpolating from
multiple, small fuzzy spheres to a single, large sphere. We briefly discuss
spatially independent configurations of a D3/D5 system described by the same
matrix model which now possesses a supergravity dual.Comment: 26 pages, 3 figures, uses JHEP.cls; (v2) references adde
On Deterministic Sketching and Streaming for Sparse Recovery and Norm Estimation
We study classic streaming and sparse recovery problems using deterministic
linear sketches, including l1/l1 and linf/l1 sparse recovery problems (the
latter also being known as l1-heavy hitters), norm estimation, and approximate
inner product. We focus on devising a fixed matrix A in R^{m x n} and a
deterministic recovery/estimation procedure which work for all possible input
vectors simultaneously. Our results improve upon existing work, the following
being our main contributions:
* A proof that linf/l1 sparse recovery and inner product estimation are
equivalent, and that incoherent matrices can be used to solve both problems.
Our upper bound for the number of measurements is m=O(eps^{-2}*min{log n, (log
n / log(1/eps))^2}). We can also obtain fast sketching and recovery algorithms
by making use of the Fast Johnson-Lindenstrauss transform. Both our running
times and number of measurements improve upon previous work. We can also obtain
better error guarantees than previous work in terms of a smaller tail of the
input vector.
* A new lower bound for the number of linear measurements required to solve
l1/l1 sparse recovery. We show Omega(k/eps^2 + klog(n/k)/eps) measurements are
required to recover an x' with |x - x'|_1 <= (1+eps)|x_{tail(k)}|_1, where
x_{tail(k)} is x projected onto all but its largest k coordinates in magnitude.
* A tight bound of m = Theta(eps^{-2}log(eps^2 n)) on the number of
measurements required to solve deterministic norm estimation, i.e., to recover
|x|_2 +/- eps|x|_1.
For all the problems we study, tight bounds are already known for the
randomized complexity from previous work, except in the case of l1/l1 sparse
recovery, where a nearly tight bound is known. Our work thus aims to study the
deterministic complexities of these problems
Fermi Surfaces of Diborides: MgB2 and ZrB2
We provide a comparison of accurate full potential band calculations of the
Fermi surfaces areas and masses of MgB2 and ZrB2 with the de Haas-van Alphen
date of Yelland et al. and Tanaka et al., respectively. The discrepancies in
areas in MgB2 can be removed by a shift of sigma-bands downward with respect to
pi-bands by 0.24 eV. Comparison of effective masses lead to orbit averaged
electron-phonon coupling constants lambda(sigma)=1.3 (both orbits),
lambda(pi)=0.5. The required band shifts, which we interpret as an exchange
attraction for sigma states beyond local density band theory, reduces the
number of holes from 0.15 to 0.11 holes per cell. This makes the occurrence of
superconductivity in MgB2 a somewhat closer call than previously recognized,
and increases the likelihood that additional holes can lead to an increased Tc.Comment: 7 pages including 4 figure
Schottky barrier heights at polar metal/semiconductor interfaces
Using a first-principle pseudopotential approach, we have investigated the
Schottky barrier heights of abrupt Al/Ge, Al/GaAs, Al/AlAs, and Al/ZnSe (100)
junctions, and their dependence on the semiconductor chemical composition and
surface termination. A model based on linear-response theory is developed,
which provides a simple, yet accurate description of the barrier-height
variations with the chemical composition of the semiconductor. The larger
barrier values found for the anion- than for the cation-terminated surfaces are
explained in terms of the screened charge of the polar semiconductor surface
and its image charge at the metal surface. Atomic scale computations show how
the classical image charge concept, valid for charges placed at large distances
from the metal, extends to distances shorter than the decay length of the
metal-induced-gap states.Comment: REVTeX 4, 11 pages, 6 EPS figure
Pre - Inflationary Clues from String Theory ?
"Brane supersymmetry breaking" occurs in String Theory when the only
available combinations of D-branes and orientifolds are not mutually BPS and
yet do not introduce tree-level tachyon instabilities. It is characterized by
the emergence of a steep exponential potential, and thus by the absence of
maximally symmetric vacua. The corresponding low-energy supergravity admits
intriguing spatially-flat cosmological solutions where a scalar field is forced
to climb up toward the steep potential after an initial singularity, and
additional milder terms can inject an inflationary phase during the ensuing
descent. We show that, in the resulting power spectra of scalar perturbations,
an infrared suppression is typically followed by a pre-inflationary peak that
reflects the end of the climbing phase and can lie well apart from the
approximately scale invariant profile. A first look at WMAP9 raw data shows
that, while the chi^2 fits for the low-l CMB angular power spectrum are clearly
compatible with an almost scale invariant behavior, they display nonetheless an
eye-catching preference for this type of setting within a perturbative string
regime.Comment: 34 pages, LaTeX, 16 eps figures. Relative displacement in fig. 14 and
some typos corrected, references and acknowledgments updated. To appear in
JCA
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