1,813 research outputs found
Numerical Simulations and Analysis of Thermally Excited Waves in Plasma Crystals
A numerical model for a 2D-monolayer plasma crystal was established using the
Box_tree code. Box_tree is a Barnes_Hut tree code which has proven effective in
modeling systems composed of large numbers of particles. Thermally excited
waves in this plasma crystal were numerically simulated and dispersion
relations for both the longitudinal and transverse wave modes were found. These
were compared with the dispersion relations extrapolated from experiment as
well as a theory based on harmonic approximation. The results were found to
agree with theoretical dispersion relations under different wave propagation
directions with different particle charges and over a range of 0.9<k<5.Comment: 7 pages, Presented at COSPAR '0
Transformation of stimulus correlations by the retina
Redundancies and correlations in the responses of sensory neurons seem to
waste neural resources but can carry cues about structured stimuli and may help
the brain to correct for response errors. To assess how the retina negotiates
this tradeoff, we measured simultaneous responses from populations of ganglion
cells presented with natural and artificial stimuli that varied greatly in
correlation structure. We found that pairwise correlations in the retinal
output remained similar across stimuli with widely different spatio-temporal
correlations including white noise and natural movies. Meanwhile, purely
spatial correlations tended to increase correlations in the retinal response.
Responding to more correlated stimuli, ganglion cells had faster temporal
kernels and tended to have stronger surrounds. These properties of individual
cells, along with gain changes that opposed changes in effective contrast at
the ganglion cell input, largely explained the similarity of pairwise
correlations across stimuli where receptive field measurements were possible.Comment: author list corrected in metadat
Dispersion Relations for Thermally Excited Waves in Plasma Crystals
Thermally excited waves in a Plasma crystal were numerically simulated using
a Box_Tree code. The code is a Barnes_Hut tree code proven effective in
modeling systems composed of large numbers of particles. Interaction between
individual particles was assumed to conform to a Yukawa potential. Particle
charge, mass, density, Debye length and output data intervals are all
adjustable parameters in the code. Employing a Fourier transform on the output
data, dispersion relations for both longitudinal and transverse wave modes were
determined. These were compared with the dispersion relations obtained from
experiment as well as a theory based on a harmonic approximation to the
potential. They were found to agree over a range of 0.9<k<5, where k is the
shielding parameter, defined by the ratio between interparticle distance a and
dust Debye length lD. This is an improvement over experimental data as current
experiments can only verify the theory up to k = 1.5.Comment: 8 pages, Presented at COSPAR '0
Extrakontext- und Applikationslogik in Anwendungssystemen zur UnterstĂŒtzung virtueller Gemeinschaften
Die Analyse von Anwendungssystemen in kommerziellen nformationssystemen - vor allem im Bereich interaktiver Online-Systeme - erfordert hĂ€ufig die Modellierung von Strukturen, die erst bei der Nutzung des fertigen Softwareproduktes, nicht aber in der Software selbst, zum Tragen kommen. Es existieren Gesichtspunkte, die mit Hilfe der meisten gĂ€ngigen Modellierungsmethoden nicht oder nur unzureichend erfaĂt werden können und hier unter der Bezeichnung âExtrakontext-Logikâ diskutiert werden. Am Beispiel der Modellierung eines Anwendungssystems zur UnterstĂŒtzung virtueller Gemeinschaften (Virtual Community Engine) auf der Ebene von Kontextdiagrammen werden AusprĂ€gungen der Extrakontext-Logik exemplarisch dargestellt. Ferner thematisiert der Beitrag untemehmensstrategisch-organisatorische Strukturen als Parameter der Extrakontext-Logik und bietet ein ErklĂ€rungsmodell an, das die ZusammenhĂ€nge zwischen Strategie und Analysemodellen von Anwendungssystemen mit Hilfe von Mustern verdeutlicht
Dynamics of a Dust Crystal with Two Different Size Dust Species
A self-consistent three-dimensional model for a complex (dusty) plasma is
used to study the effects of multiple-sized dust grains in a dust crystal. In
addition to the interparticle forces, which interact through a Yukawa
potential, the model includes the effects of gravity, the variation of the
sheath potential above the powered electrode, and a radial confining potential.
Simulations studied various ratios of a mix of 6.5- and 8.9-micron monodisperse
particles and compared their correlation functions, electric potential energy
of the crystal formations, and the dispersion relations for in-plane and
out-of-plane dust lattice wave (DLW) modes for two different sheath
thicknesses. In the 7 mm sheath, the particles formed two layers in the
vertical direction by size, and acted as a two-layer crystal with weak
correlation between the layers. In the 3 mm sheath, the particles formed an
essentially monolayer crystal; however the crystal dynamics showed some
characteristics of a bilayer crystal
CD4 memory T cells divide poorly in response to antigen because of their cytokine profile
Immunological memory is a hallmark of adaptive immunity, and understanding T cell memory will be central to the development of effective cell-mediated vaccines. The characteristics and functions of CD4 memory cells have not been well defined. Here we demonstrate that the increased size of the secondary response is solely a consequence of the increased antigen-specific precursor frequency within the memory pool. Memory cells proliferated less than primary responding cells, even within the same host. By analyzing the entry of primary and memory cells into the cell cycle, we found that the two populations proliferated similarly until day 5; after this time, fewer of the reactivated memory cells proliferated. At this time, fewer of the reactivated memory cells made IL-2 than primary responding cells, but more made IFNÎł. Both these factors affected the low proliferation of the memory cells, because either exogenous IL-2 or inhibition of IFNÎł increased the proliferation of the memory cells
Short-term salivary acetaldehyde increase due to direct exposure to alcoholic beverages as an additional cancer risk factor beyond ethanol metabolism
<p>Abstract</p> <p>Background</p> <p>An increasing body of evidence now implicates acetaldehyde as a major underlying factor for the carcinogenicity of alcoholic beverages and especially for oesophageal and oral cancer. Acetaldehyde associated with alcohol consumption is regarded as 'carcinogenic to humans' (IARC Group 1), with sufficient evidence available for the oesophagus, head and neck as sites of carcinogenicity. At present, research into the mechanistic aspects of acetaldehyde-related oral cancer has been focused on salivary acetaldehyde that is formed either from ethanol metabolism in the epithelia or from microbial oxidation of ethanol by the oral microflora. This study was conducted to evaluate the role of the acetaldehyde that is found as a component of alcoholic beverages as an additional factor in the aetiology of oral cancer.</p> <p>Methods</p> <p>Salivary acetaldehyde levels were determined in the context of sensory analysis of different alcoholic beverages (beer, cider, wine, sherry, vodka, calvados, grape marc spirit, tequila, cherry spirit), without swallowing, to exclude systemic ethanol metabolism.</p> <p>Results</p> <p>The rinsing of the mouth for 30 seconds with an alcoholic beverage is able to increase salivary acetaldehyde above levels previously judged to be carcinogenic in vitro, with levels up to 1000 ÎŒM in cases of beverages with extreme acetaldehyde content. In general, the highest salivary acetaldehyde concentration was found in all cases in the saliva 30 sec after using the beverages (average 353 ÎŒM). The average concentration then decreased at the 2-min (156 ÎŒM), 5-min (76 ÎŒM) and 10-min (40 ÎŒM) sampling points. The salivary acetaldehyde concentration depends primarily on the direct ingestion of acetaldehyde contained in the beverages at the 30-sec sampling, while the influence of the metabolic formation from ethanol becomes the major factor at the 2-min sampling point.</p> <p>Conclusions</p> <p>This study offers a plausible mechanism to explain the increased risk for oral cancer associated with high acetaldehyde concentrations in certain beverages.</p
Genetic polymorphisms of manganese-superoxide dismutase and glutathione-S-transferase in chronic alcoholic pancreatitis
Chronic alcohol consumption is a major risk factor for the development of chronic pancreatitis. However, chronic pancreatitis occurs only in a minority of heavy drinkers. This variability may be due to yet unidentified genetic factors. Several enzymes involved in the degradation of reactive oxidants and xenobiotics, such as glutathione-S-transferase P1 (GSTP1) and manganese-superoxide dismutase (MnSOD) reveal functional polymorphisms that affect the antioxidative capacity and may therefore modulate the development of chronic pancreatitis and long-term complications like endocrine and exocrine pancreatic insufficiency. Two functional polymorphisms of the MnSOD and the GSTP1 gene were assessed by polymerase chain reaction and restriction fragment length polymorphism in 165 patients with chronic alcoholic pancreatitis, 140 alcoholics without evidence of pancreatic disease and 160 healthy control subjects. The distribution of GSTP1 and MnSOD genotypes were in Hardy-Weinberg equilibrium in the total cohort. Genotype and allele frequencies for both genes were not statistically different between the three groups. Although genotype MnSOD Ala/Val was seemingly associated with the presence of exocrine pancreatic insufficiency, this subgroup was too small and the association statistically underpowered. None of the tested genotypes affected the development of endocrine pancreatic insufficiency. Polymorphisms of MnSOD and GSTP1 are not associated with chronic alcoholic pancreatitis. The present data emphasize the need for stringently designed candidate gene association studies with well-characterized cases and controls and sufficient statistical power to exclude chance observation
- âŠ