3,474 research outputs found
Statistical Ensembles with Fluctuating Extensive Quantities
We suggest an extension of the standard concept of statistical ensembles.
Namely, we introduce a class of ensembles with extensive quantities fluctuating
according to an externally given distribution. As an example the influence of
energy fluctuations on multiplicity fluctuations in limited segments of
momentum space for a classical ultra-relativistic gas is considered.Comment: 4 pages, 2 figure
Multiplicity Fluctuations in Limited Segments of Momentum Space in Statistical Models
Multiplicity fluctuations in limited segments of momentum space are
calculated for a classical pion gas within the statistical model. Results for
the grand canonical, canonical, and micro-canonical ensemble are obtained,
compared and discussed. We demonstrate that even in the large volume limit
correlations between macroscopic subsystems due to energy and momentum
conservation persist. Based on the micro-canonical formulation we make
qualitative predictions for the rapidity and transverse momentum dependence of
multiplicity fluctuations. The resulting effects are of similar magnitude as
the predicted enhancement due to a phase transition from a quark-gluon plasma
to a hadron gas phase, or due to the critical point of strongly interacting
matter, and qualitatively agree with recently published preliminary
multiplicity fluctuation data of the NA49 SPS experiment.Comment: 23 pages, 4 figure
Viscosity in the excluded volume hadron gas model
The shear viscosity in the van der Waals excluded volume
hadron-resonance gas model is considered. For the shear viscosity the result of
the non-relativistic gas of hard-core particles is extended to the mixture of
particles with different masses, but equal values of hard-core radius r. The
relativistic corrections to hadron average momenta in thermal equilibrium are
also taken into account. The ratio of the viscosity to the entropy
density s is studied. It monotonously decreases along the chemical freeze-out
line in nucleus-nucleus collisions with increasing collision energy. As a
function of hard-core radius r, a broad minimum of the ratio near fm is found at high collision energies. For the
charge-neutral system at MeV, a minimum of the ratio is reached for fm. To justify a hydrodynamic approach to
nucleus-nucleus collisions within the hadron phase the restriction from below,
fm, on the hard-core hadron radius should be fulfilled in the
excluded volume hadron-resonance gas.Comment: 12 pages, 3 figure
Particle number fluctuations in nuclear collisions within excluded volume hadron gas model
The multiplicity fluctuations are studied in the van der Waals excluded
volume hadron-resonance gas model. The calculations are done in the grand
canonical ensemble within the Boltzmann statistics approximation. The scaled
variances for positive, negative and all charged hadrons are calculated along
the chemical freeze-out line of nucleus-nucleus collisions at different
collision energies. The multiplicity fluctuations are found to be suppressed in
the van der Waals gas. The numerical calculations are presented for two values
of hard-core hadron radius, fm and 0.5 fm, as well as for the upper
limit of the excluded volume suppression effects.Comment: 19 pages, 4 figure
Preclinical Research into Basic Mechanisms of Radiation-Induced Heart Disease
Radiation-induced heart disease (RIHD) is a potentially severe side effect of radiotherapy of thoracic and chest wall tumors if all or part of the heart was included in the radiation field. RIHD presents clinically several years after irradiation and manifestations include accelerated atherosclerosis, pericardial and myocardial fibrosis, conduction abnormalities, and injury to cardiac valves. There is no method to prevent or reverse these injuries when the heart is exposed to ionizing radiation. This paper presents an overview of recent studies that address the role of microvascular injury, endothelial dysfunction, mast cells, and the renin angiotensin system in animal models of cardiac radiation injury. These insights into the basic mechanisms of RIHD may lead to the identification of targets for intervention in this late radiotherapy side effect
Forward-backward correlations in nucleus-nucleus collisions: baseline contributions from geometrical fluctuations
We discuss the effects of initial collision geometry and centrality bin
definition on correlation and fluctuation observables in nucleus-nucleus
collisions. We focus on the forward-backward correlation coefficient recently
measured by the STAR Collaboration in Au+Au collisions at RHIC. Our study is
carried out within two models: the Glauber Monte Carlo code with a `toy'
wounded nucleon model and the hadron-string dynamics (HSD) transport approach.
We show that strong correlations can arise due to averaging over events in one
centrality bin. We, furthermore, argue that a study of the dependence of
correlations on the centrality bin definition as well as the bin size may
distinguish between these `trivial' correlations and correlations arising from
`new physics'.Comment: 12 pages, 6 figure
Enhanced Anandamide Plasma Levels in Patients with Complex Regional Pain Syndrome following Traumatic Injury: A Preliminary Report
The complex regional pain syndrome (CRPS) is a disabling neuropathic pain condition that may develop following injuries of the extremities. The pathogenesis of this syndrome is not clear; however, it includes complex interactions between the nervous and the immune system resulting in chronic inflammation, pain and trophic changes. This interaction may be mediated by chronic stress which is thought to activate the endogenous cannabinoid (endocannabinoid) system (ECS). We conducted an open, prospective, comparative clinical study to determine plasma level of the endocannabinoid anandamide by high-performance liquid chromatography and a tandem mass spectrometry system in 10 patients with CRPS type I versus 10 age- and sex-matched healthy controls. As compared to healthy controls, CRPS patients showed significantly higher plasma concentrations of anandamide. These results indicate that the peripheral ECS is activated in CRPS. Further studies are warranted to evaluate the role of the ECS in the limitation of inflammation and pain. Copyright (C) 2009 S. Karger AG, Base
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