691 research outputs found
Anisotropic Bose-Einstein condensates and completely integrable dynamical systems
A Gaussian ansatz for the wave function of two-dimensional harmonically
trapped anisotropic Bose-Einstein condensates is shown to lead, via a
variational procedure, to a coupled system of two second-order, nonlinear
ordinary differential equations. This dynamical system is shown to be in the
general class of Ermakov systems. Complete integrability of the resulting
Ermakov system is proven. Using the exact solution, collapse of the condensate
is analyzed in detail. Time-dependence of the trapping potential is allowed
Quantum Kinetic Theory III: Quantum kinetic master equation for strongly condensed trapped systems
We extend quantum kinetic theory to deal with a strongly Bose-condensed
atomic vapor in a trap. The method assumes that the majority of the vapor is
not condensed, and acts as a bath of heat and atoms for the condensate. The
condensate is described by the particle number conserving Bogoliubov method
developed by one of the authors. We derive equations which describe the
fluctuations of particle number and phase, and the growth of the Bose-Einstein
condensate. The equilibrium state of the condensate is a mixture of states with
different numbers of particles and quasiparticles. It is not a quantum
superposition of states with different numbers of particles---nevertheless, the
stationary state exhibits the property of off-diagonal long range order, to the
extent that this concept makes sense in a tightly trapped condensate.Comment: 3 figures submitted to Physical Review
Tailoring Anderson localization by disorder correlations in 1D speckle potentials
We study Anderson localization of single particles in continuous, correlated,
one-dimensional disordered potentials. We show that tailored correlations can
completely change the energy-dependence of the localization length. By
considering two suitable models of disorder, we explicitly show that disorder
correlations can lead to a nonmonotonic behavior of the localization length
versus energy. Numerical calculations performed within the transfer-matrix
approach and analytical calculations performed within the phase formalism up to
order three show excellent agreement and demonstrate the effect. We finally
show how the nonmonotonic behavior of the localization length with energy can
be observed using expanding ultracold-atom gases
Ginzburg-Landau functional for nearly antiferromagnetic perfect and disordered Kondo lattices
Interplay between Kondo effect and trends to antiferromagnetic and spin glass
ordering in perfect and disordered bipartite Kondo lattices is considered.
Ginzburg-Landau equation is derived from the microscopic effective action
written in three mode representation (Kondo screening, antiferromagnetic
correlations and spin liquid correlations). The problem of local constraint is
resolved by means of Popov-Fedotov representation for localized spin operators.
It is shown that the Kondo screening enhances the trend to a spin liquid
crossover and suppresses antiferromagnetic ordering in perfect Kondo lattices
and spin glass ordering in doped Kondo lattices. The modified Doniach's diagram
is constructed, and possibilities of going beyond the mean field approximation
are discussed.Comment: 18 pages, RevTeX, 7 EPS figures include
ATLAS Pixel Opto-Electronics
We have developed two radiation-hard ASICs for optical data transmission in
the ATLAS pixel detector at the LHC at CERN: a driver chip for a Vertical
Cavity Surface Emitting Laser (VCSEL) diode for 80 Mbit/s data transmission
from the detector, and a Bi-Phase Mark decoder chip to recover the control data
and 40 MHz clock received optically by a PIN diode. We have successfully
implemented both ASICs in 0.25 micron CMOS technology using enclosed layout
transistors and guard rings for increased radiation hardness. We present
results of the performance of these chips, including irradiation with 24 GeV
protons up to 61 Mrad (2.3 x 10e15 p/cm^2).Comment: 17 pages, 23 figures, submitted to NIM Added references. Added figure
15. Moved sec. IV to sec. I
Gender, HIV Testing and Stigma: The Association of HIV Testing Behaviors and Community-Level and Individual-Level Stigma in Rural South Africa Differ for Men and Women
Stigma remains a significant barrier to HIV testing in South Africa. Despite being a social construct, most HIV-stigma research focuses on individuals; further the intersection of gender, testing and stigma is yet to be fully explored. We examined the relationship between anticipated stigma at individual and community levels and recent testing using a population-based sample (n = 1126) in Mpumalanga, South Africa. We used multi-level regression to estimate the potential effect of reducing community-level stigma on testing uptake using the g-computation algorithm. Men tested less frequently (OR 0.22, 95% CI 0.14–0.33) and reported more anticipated stigma (OR 5.1, 95% CI 2.6–10.1) than women. For men only, testing was higher among those reporting no stigma versus some (OR 1.40, 95% CI 0.97–2.03; p = 0.07). For women only, each percentage point reduction in community-level stigma, the likelihood of testing increased by 3% (p < 0.01). Programming should consider stigma reduction in the context of social norms and gender to tailor activities appropriately
On the Testing of Seismicity Models
Recently a likelihood-based methodology has been developed by the
Collaboratory for the Study of Earthquake Predictability (CSEP) with a view to
testing and ranking seismicity models. We analyze this approach from the
standpoint of possible applications to hazard analysis. We arrive at the
conclusion that model testing can be made more efficient by focusing on some
integral characteristics of the seismicity distribution. This is achieved
either in the likelihood framework but with economical and physically
reasonable coarsening of the phase space or by choosing a suitable measure of
closeness between empirical and model seismicity rate in this space.Comment: To appear at Acta Geophysic
Knowledge dating and knowledge sharing in ad-hoc transient communities
This chapter will focus on the question of what rules and policies are conducive to the emergence of an adequate support infrastructure in the non-formal settings of a Learning Network. Once such an infrastructure is in place, a variety of ways again embedded in rules and policies may be used to guarantee its continued exis-tence. This was the subject of the previous chapter. Here the focus is on the phase of the emergence of social interaction and the formation of an incipient social in-frastructure. It is in this stage that the lone learner makes acquaintance with his or her online peers. More specifically, since learning through the exchange of knowl-edge is the ultimate objective of any Learning Network, we will present guidelines for effective and efficient knowledge dating in Learning Networks; ultimately, this should lead to knowledge sharing. During our discussion, we will introduce the notion of ad-hoc transient communities, temporal online gatherings of people fo-cused on a particular issue, which precisely because of their focus and transience help build a social infrastructure in a Learning Network. Ad-hoc transient com-munities may be seen as a knowledge dating and sharing service, offered in the context of a Learning Network
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