424,082 research outputs found
Effect of shape anisotropy on the phase diagram of the Gay-Berne fluid
We have used the density functional theory to study the effect of molecular
elongation on the isotropic-nematic, isotropic-smectic A and nematic-smectic A
phase transitions of a fluid of molecules interacting via the Gay-Berne
intermolecular potential. We have considered a range of length-to-width
parameter in steps of 0.2 at different densities and
temperatures. Pair correlation functions needed as input information in density
functional theory are calculated using the Percus-Yevick integral equation
theory. Within the small range of elongation, the phase diagram shows
significant changes. The fluid at low temperature is found to freeze directly
from isotropic to smectic A phase for all the values of considered by us
on increasing the density while nematic phase stabilizes in between isotropic
and smectic A phases only at high temperatures and densities. Both
isotropic-nematic and nematic-smectic A transition density and pressure are
found to decrease as we increase . The phase diagram obtained is compared
with computer simulation result of the same model potential and is found to be
in good qualitative agreement.Comment: 15 pages, 6 figure
Wolf-Rayet Stars in Starburst Galaxies
Wolf-Rayet stars have been detected in a large number of galaxies
experiencing intense bursts of star formation. All stars initially more massive
than a certain, metallicity-dependent, value are believed to experience the
Wolf-Rayet phase at the end of their evolution, just before collapsing in
supernova explosion. The detection of Wolf-Rayet stars puts therefore important
constraints on the evolutionary status of starbursts, the properties of their
Initial Mass Functions and their star formation regime. In this contribution we
review the properties of galaxies hosting Wolf-Rayet stars, with special
emphasis on the factors that determine their presence and evolution, as well as
their impact on the surrounding medium.Comment: Contribution to the Proceedings of the JENAM 99 conference "The
interplay between massive stars and the ISM", held in Toulouse in September
7-11, 1999. 10 pages, 5 figures. Requires elsart.cls latex macr
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