216 research outputs found
Superluminal pions in a hadronic fluid
We study the propagation of pions at finite temperature and finite chemical
potential in the framework of the linear sigma model with 2 quark flavors and
colors. The velocity of massless pions in general differs from that of
light. One-loop calculations show that in the chiral symmetry broken phase
pions, under certain conditions, propagate faster than light.Comment: 8 pages, 3 figures included. Considerably revised, discussions
expanded, one figure added, typos corrected, results unchanged. To be
published in Phys. Rev.
Mayfly ecological traits in a European karst spring: species, microhabitats and life histories
Despite the recent increase in the number of mayfly studies in karst freshwater habitats, their biology and ecology in springs are still poorly characterized. Therefore, we studied mayfly assemblages in a European karst rheocrene spring at five microhabitats monthly over a one-year period. Three species were recorded: Baetis alpinus (Pictet, 1843), Baetis rhodani (Pictet, 1843) and Rhithrogena braaschi (Jacob, 1974). The latter species represents a new record for the fauna of Bosnia and Herzegovina. All three species inhabited all studied microhabitats but with varying abundance. Individual species were associated with a specific substrate type and/or water velocity and/or water depth. The grazer/scraper Rh. braaschi was most common at microhabitats with inorganic substrate (cobbles, mixture of pebbles and sand), moderate water velocity and higher water depth. The rheophilic grazer/scraper and gatherer/collector B. alpinus was most common at microhabitats with mosses and highest water velocity. The grazer/scraper and gatherer/collector B. rhodani was recorded at all microhabitats, yet due to its preference for moderate water velocity, the highest number of individuals were collected from cobbles. We recorded movements of mayfly nymphs among the available microhabitats during their life cycles, due likely to their dietary requirements and search for suitable refugia. Baetis alpinus has a bivoltine, B. rhodani polyvoltine and Rh. braaschi univoltine life cycle with a long emergence period. The results presented here contribute to the knowledge of spring and mayfly ecology
Quenched QCD at finite density
Simulations of quenched at relatively small but {\it nonzero} chemical
potential on lattices indicate that the nucleon
screening mass decreases linearly as increases predicting a critical
chemical potential of one third the nucleon mass, , by extrapolation.
The meson spectrum does not change as increases over the same range, from
zero to . Past studies of quenched lattice QCD have suggested that
there is phase transition at . We provide alternative
explanations for these results, and find a number of technical reasons why
standard lattice simulation techniques suffer from greatly enhanced
fluctuations and finite size effects for ranging from to
. We find evidence for such problems in our simulations, and suggest
that they can be surmounted by improved measurement techniques.Comment: 23 pages, Revte
Generalized Chaplygin Gas Model: Dark Energy - Dark Matter Unification and CMBR Constraints
The generalized Chaplygin gas (GCG) model allows for an unified description
of the recent accelerated expansion of the Universe and the evolution of energy
density perturbations. This dark energy - dark matter unification is achieved
through an exotic background fluid whose equation of state is given by , where is a positive constant and .
Stringent constraints on the model parameters can be obtained from recent WMAP
and BOOMERanG bounds on the locations of the first few peaks and troughs of the
Cosmic Microwave Background Radiation (CMBR) power spectrum as well as SNe Ia
data.Comment: 9 pages, 2 figures; essay selected for an honorable mention by the
Gravity Research Foundation, 200
Self-gravitating clouds of generalized Chaplygin and modified anti-Chaplygin Gases
The Chaplygin gas has been proposed as a possible dark energy, dark matter
candidate. As a working fluid in a Friedmann-Robertson-Walker universe, it
exhibits early behavior reminiscent of dark matter, but at later times is more
akin to a cosmological constant. In any such universe, however, one can expect
local perturbations to form. Here we obtain the general equations for a
self-gravitating relativistic Chaplygin gas. We solve these equations and
obtain the mass-radius relationship for such structures, showing that only in
the phantom regime is the mass-radius relationship large enough to be a serious
candidate for highly compact massive objects at the galaxy core. In addition,
we study the cosmology of a modified anti-Chaplygin gas. A self-gravitating
cloud of this matter is an exact solution to Einstein's equations.Comment: 16 page
Focal laryngeal dystonia: diagnostics, therapeutics and novelties in neurophysiologic research
Aim of study: To present and discuss diagnostic procedures, therapeutic options and novelties in
neurophysiological research of laryngeal dystonia (LD), a rare movement disorder with an unknown cause
affecting the intrinsic muscles of the larynx. Material and methods: 1) Literature overview of the on the
standard guidelines in the diagnostics and treatment of LD; 2) The use of transcranial magnetic stimulation
(TMS) in the neurophysiologic research of LD by investigation of cortical silent period (cSP) reflecting the
intracortical inhibitory process mediated by GABAA and GABAB receptors; 3) The use of navigated TMS in
mapping the laryngeal motor cortex by investigating the duration of cortical silent period in two LD cases,
abductor and adductor LD type. Results: The study presents standard diagnostic, treatment of LD disorder, and
results of investigation by groups from School of Medicine, University of Minnesota, Minneapolis, MN, USA
and School of Medicine, University of Split, Croatia on the duration of cSP in vocal and cricothyroid muscles
in LD patients and healthy control subjects. The research groups presented norms for cSP duration in vocal
and cricothyroid muscle in healthy subjects and pointed to the altered (shortened) duration of the cSP in LD
patients (adductor type). Conclusion: The cSP measure might be useful neurophysiologic biomarker for
understanding the LD disorder. In LD, the cortical activation during phonation may not be efficiently or
effectively associated with inhibitory processes, leading to muscular dysfunction. Promising techniques such
as TMS might bring new light to the diagnosis and treatment of LD disorder
Optimization of walnut oil production
Walnut is recognized worldwide as a functional health food. In the walnut oil production it is very important to find an appropriate method to recover the oil from seeds. Walnut oil in this study was obtained by pressing the seeds followed by extraction with supercritical CO2. The effects of pressing temperature (70, 85, 100 Ā°C), frequency (20, 30, 40 Hz) and nozzle size (8, 10, 12 mm) in pressing experiments on oil recovery and oil temperature were monitored. The optimal calculated pressing condition within the experimental range of the variables studied was determined. In obtained walnut oil the following parameters were analyzed: peroxide value, free fatty acids, insoluble impurities, moisture content, iodine value, saponification value, p-anisidine value and Totox value. The residual oil from pressed cake obtained at optimal conditions was extracted with CO2 with a goal to extract tocopherols residue from walnut after applied screw press process. Content of tocopherols in walnut oil obtained by pressing and oil extracted by supercritical CO2 were compared
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