1,703 research outputs found
Exact Baryon, Strangeness and Charge Conservation in Hadronic Gas Models
Relativistic heavy ion collisions are studied assuming that particles can be
described by a hadron gas in thermal and chemical equilibrium. The exact
conservation of baryon number, strangeness and charge are explicitly taken into
account. For heavy ions the effect arising from the neutron surplus becomes
important and leads to a substantial increase in e.g. the ratio.
A method is developed which is very well suited for the study of small systems.Comment: 5 pages, 5 Postscript figure
First upper limit analysis and results from LIGO science data: stochastic background
I describe analysis of correlations in the outputs of the three LIGO
interferometers from LIGO's first science run, held over 17 days in August and
September of 2002, and the resulting upper limit set on a stochastic background
of gravitational waves. By searching for cross-correlations between the LIGO
detectors in Livingston, LA and Hanford, WA, we are able to set a 90%
confidence level upper limit of h_{100}^2 Omega_0 < 23 +/- 4.6.Comment: 7 pages; 1 eps figures; proceeding from 2003 Edoardo Amaldi Meeting
on Gravitational Wave
Method of Monte Carlo grid for data analysis
This paper presents an analysis procedure for experimental data using
theoretical functions generated by Monte Carlo. Applying the classical
chi-square fitting procedure for some multiparameter systems is extremely
difficult due to a lack of an analytical expression for the theoretical
functions describing the system. The proposed algorithm is based on the least
square method using a grid of Monte Carlo generated functions each
corresponding to definite values of the minimization parameters. It is used for
the E742 experiment (TRIUMF, Vancouver, Canada) data analysis with the aim to
extract muonic atom scattering parameters on solid hydrogen.Comment: 16 pages, 10 figures, submitted to NI
The Snowball Stratosphere
According to the Snowball Earth hypothesis, Earth has experienced periods of
low-latitude glaciation in its deep past. Prior studies have used general
circulation models (GCMs) to examine the effects such an extreme climate state
might have on the structure and dynamics of Earth's troposphere, but the
behavior of the stratosphere has not been studied in detail. Understanding the
snowball stratosphere is important for developing an accurate account of the
Earth's radiative and chemical properties during these episodes. Here we
conduct the first analysis of the stratospheric circulation of the Snowball
Earth using ECHAM6 general circulation model simulations. In order to
understand the factors contributing to the stratospheric circulation, we extend
the Statistical Transformed Eulerian Mean framework. We find that the
stratosphere during a snowball with prescribed modern ozone levels exhibits a
weaker meridional overturning circulation, reduced wave activity, stronger
zonal jets, and is extremely cold relative to modern conditions. Notably, the
snowball stratosphere displays no sudden stratospheric warmings. Without ozone,
the stratosphere displays slightly weaker circulation, a complete lack of polar
vortex, and even colder temperatures. We also explicitly quantify for the first
time the cross-tropopause mass exchange rate and stratospheric mixing
efficiency during the snowball and show that our values do not change the
constraints on CO inferred from geochemical proxies during the Marinoan
glaciation (635 Ma), unless the O concentration during the snowball
was orders of magnitude less than the CO concentration.Comment: 28 pages, 11 figures, submitted to JGR-Atmosphere
Neurotrophin and Trk expression by cells of the human lamina cribrosa following oxygen-glucose deprivation
BACKGROUND: Ischemia within the optic nerve head (ONH) may contribute to retinal ganglion cell (RGC) loss in primary open angle glaucoma (POAG). Ischemia has been reported to increase neurotrophin and high affinity Trk receptor expression by CNS neurons and glial cells. We have previously demonstrated neurotrophin and Trk expression within the lamina cribrosa (LC) region of the ONH. To determine if ischemia alters neurotrophin and Trk protein expression in cells from the human LC, cultured LC cells and ONH astrocytes were exposed to 48 hours of oxygen-glucose deprivation (OGD). Also cells were exposed to 48 hours of OGD followed by 24 hours of recovery in normal growth conditions. Cell number, neurotrophin and Trk receptor protein expression, neurotrophin secretion, and Trk receptor activation were examined. RESULTS: Cell number was estimated using an assay for cell metabolism following 24, 48 and 72 hours of OGD. A statistically significant decrease in LC and ONH astrocyte cell number did not occur until 72 hours of OGD, therefore cellular protein and conditioned media were collected at 48 hours OGD. Protein expression of NGF, BDNF and NT-3 by LC cells and ONH astrocytes increased following OGD, as did NGF secretion. Recovery from OGD increased BDNF protein expression in LC cells. In ONH astrocytes, recovery from OGD increased NGF protein expression, and decreased BDNF secretion. Trk A expression and activation in LC cells was increased following OGD while expression and activation of all other Trk receptors was decreased. A similar increase in Trk A expression and activation was observed in ONH astrocytes following recovery from OGD. CONCLUSIONS: In vitro conditions that mimic ischemia increase the expression and secretion of neurotrophins by cells from the ONH. Increased Trk A expression and activation in LC cells following OGD and in ONH astrocytes following recovery from OGD suggest autocrine/paracrine neurotrophin signaling could be a response to ONH ischemia in POAG. Also, the increase in NGF, BDNF and NT-3 protein expression and NGF secretion following OGD also suggest LC cells and ONH astrocytes may be a paracrine source of neurotrophins for RGCs
Astrometric observations of Saturn's satellites from McDonald Observatory, 1972
Observations of Saturn's satellites were reduced by means of secondary reference stars obtained by reduction of Palomar Sky Survey (PSS) plates. This involved the use of 39 SAO stars and plate overlap technique to determine the coordinates of 59 fainter stars in the satellite field. Fourteen plate constants were determined for each of the two PSS plates. Comparison of two plate measurement and reduction techniques on the satellite measurements demonstrate the existence of a serious background gradient effect and the utility of microdensitometry to eliminate this error source in positional determinations of close satellites
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