10,829 research outputs found
Probing strongly interacting atomic gases with energetic atoms
We investigate properties of an energetic atom propagating through strongly
interacting atomic gases. The operator product expansion is used to
systematically compute a quasiparticle energy and its scattering rate both in a
spin-1/2 Fermi gas and in a spinless Bose gas. Reasonable agreement with recent
quantum Monte Carlo simulations even at a relatively small momentum k/kF>1.5
indicates that our large-momentum expansions are valid in a wide range of
momentum. We also study a differential scattering rate when a probe atom is
shot into atomic gases. Because the number density and current density of the
target atomic gas contribute to the forward scattering only, its contact
density (measure of short-range pair correlation) gives the leading
contribution to the backward scattering. Therefore, such an experiment can be
used to measure the contact density and thus provides a new local probe of
strongly interacting atomic gases.Comment: 35 pages, 11 figures; (v4) published with the new titl
Socio-economic status over the life-course and depressive symptoms in men and women in Eastern Europe
Objective: Research into social inequalities in depression has studied western populations but data from non-western countries are sparse. In this paper, we investigate the extent of social inequalities in depression in Eastern Europe, the relative importance of social position at different points of the life-course, and whether social patterning of depression differs between men and women.Method: A cross-sectional study examined 12,053 men and 13,582 women in Russia, Poland and the Czech Republic. Depressive symptoms (16 or above on the CESD-20) were examined in relation to socio-economic circumstances at three phases of the life-course: childhood (household amenities and father's education); own education; current circumstances (financial difficulties and possession of household items).Results: Pronounced social differences in depression exist in men and women throughout Eastern Europe. Depression was largely influenced by current circumstances rather than by early life or education, with effects stronger in Poland and Russia. Odds ratios in men for current disadvantage were 3.16 [95% CI: 2.57-3.89], 3.16 [2.74-3.64] and 2.17 [1.80-2.63] in Russia, Poland and the Czech Republic respectively. Social variables did not explain the female excess in depression, which varied from 2.91 [2.58-3.27] in Russia to 1.90 [1.74-2.08] in Poland. Men were more affected by adult disadvantage than women, leading to narrower sex differentials in the presence of disadvantage.Limitations: Cross-sectional data with recall of childhood conditions were used.Conclusion: Current social circumstances are the strongest influence on increased depressive symptoms in countries which have recently experienced social changes. (C) 2007 Elsevier B.V. All rights reserved
Breaking of ergodicity and long relaxation times in systems with long-range interactions
The thermodynamic and dynamical properties of an Ising model with both short
range and long range, mean field like, interactions are studied within the
microcanonical ensemble. It is found that the relaxation time of
thermodynamically unstable states diverges logarithmically with system size.
This is in contrast with the case of short range interactions where this time
is finite. Moreover, at sufficiently low energies, gaps in the magnetization
interval may develop to which no microscopic configuration corresponds. As a
result, in local microcanonical dynamics the system cannot move across the gap,
leading to breaking of ergodicity even in finite systems. These are general
features of systems with long range interactions and are expected to be valid
even when the interaction is slowly decaying with distance.Comment: 4 pages, 5 figure
The burden of sickle cell disease in Cape Town
Background. South Africa has a low incidence of sickle cell disease (SCD). However, its demographics are changing because of immigration from sub-Saharan African countries where SCD is prevalent.Objectives. We aimed to determine the frequency of SCD presenting to the Haematology/Oncology Service at Red Cross War Memorial Children’s Hospital in Cape Town and to measure the associated disease burden.Methods. This was a retrospective cross-sectional study of patients first attending the Haematology Service between January 2001 and June 2010.Results. A total of 58 SCD patients were indentified, with an annual frequency that increased over the study period by 300 -400%. Up to 93.1% (n=54) were originally from other African countries, mainly the Democratic Republic of Congo (62.1%, n=36). One patient had sickle D-Punjab genotype, and all the other patients had the homozygous sickle cell anaemia genotype (Hb SS). Their haematological parameters  demonstrated a normocytic anaemia with high white cell counts. The mean number of clinic visits per patient per year was 22.2 (range 0 - 64), and the mean number of hospital admissions per patient per year was 1.2 (range 0 - 5). All the patients were on antibiotic prophylaxis. The majorityhad at least one blood transfusion (65.5%, n=38), and a significantproportion required intravenous analgesia on admission (29.3%, n=17) and hydroxyurea treatment (36.2%, n=21).Conclusions. Over the past 10 years the frequency of SCD has increased considerably, imposing a significant burden and new challenges to the health services in Cape Town
Direct path from microscopic mechanics to Debye shielding, Landau damping, and wave-particle interaction
The derivation of Debye shielding and Landau damping from the -body
description of plasmas is performed directly by using Newton's second law for
the -body system. This is done in a few steps with elementary calculations
using standard tools of calculus, and no probabilistic setting. Unexpectedly,
Debye shielding is encountered together with Landau damping. This approach is
shown to be justified in the one-dimensional case when the number of particles
in a Debye sphere becomes large. The theory is extended to accommodate a
correct description of trapping and chaos due to Langmuir waves. Shielding and
collisional transport are found to be two related aspects of the repulsive
deflections of electrons, in such a way that each particle is shielded by all
other ones while keeping in uninterrupted motion.Comment: arXiv admin note: substantial text overlap with arXiv:1310.3096,
arXiv:1210.154
- …