26,807 research outputs found
Self lensing effects for compact stars and their mass-radius relation
During the last couple of years astronomers and astrophysicists have been
debating on the fact whether the so called `strange stars' - stars made up of
strange quark matter, have been discovered with the candidates like SAX
J1808.4-3658, 4U 1728-34, RX J1856.5-3754, etc. The main contention has been
the estimation of radius of the star for an assumed mass of ~ 1.4 M_sun and to
see whether the point overlaps with the graphs for the neutron star equation of
state or whether it goes to the region of stars made of strange matter equation
of state. Using the well established formulae from general relativity for the
gravitational redshift and the `lensing effect' due to bending of photon
trajectories, we, in this letter, relate the parameters M and R with the
observable parameters, the redshift z and the radiation radius R_\infty, thus
constraining both M and R for specific ranges, without any other arbitrariness.
With the required inputs from observations, one ought to incorporate the
effects of self lensing of the compact stars which has been otherwise ignored
in all of the estimations done so far. Nonetheless, these effect of self
lensing makes a marked difference and constraints on the M-R relation.Comment: 7 pages, 1 figure, accepted for publication in Mod. Phys. Lett.
Growth of solid hcp \^4He off the melting curve
We report studies of the growth of solid hcp \4he at pressures higher than
the bulk freezing pressure using a cell design that allows us to inject atoms
into the solid. Near the melting curve during injection we observe random
events during which the pressure recorded in the cell drops abruptly. These
events are accompanied by transient increases in the temperature of the cell.
We discuss these transients and conclude that they represent the solidification
of meta-stable liquid regions and the associated relief of strain in the local
solid. We also observe that further from the melting curve the transients are
no longer recorded, but that we can continue to add atoms to the solid,
increasing its density at fixed volume. We document these changes in density
with respect to changes in the chemical potential as a function of temperature
and discuss these in the context of recent theoretical work.Comment: 7 pages, 8 figure
Radio Observations of Super Star Clusters in Dwarf Starburst Galaxies
We present new radio continuum observations of two dwarf starburst galaxies,
NGC3125 and NGC5408, with observations at 4.80GHz (6cm) and 8.64GHz (3cm),
taken with the Australia Telescope Compact Array (ATCA). Both galaxies show a
complex radio morphology with several emission regions, mostly coincident with
massive young star clusters. The radio spectral indices of these regions are
negative (with alpha ~ -0.5 - -0.7), indicating that the radio emission is
dominated by synchrotron emission associated with supernova activity from the
starburst. One emission region in NGC5408 has a flatter index (alpha ~ -0.1)
indicative of optically thin free-free emission, which could indicate it is a
younger cluster. Consequently, in these galaxies we do not see regions with the
characteristic positive spectral index indicative of optically obscured
star-formation regions, as seen in other dwarf starbursts such as Hen 2-10.Comment: Accepted for publication in MNRA
Mass flow through solid 4He induced by the fountain effect
Using an apparatus that allows superfluid liquid 4He to be in contact with
hcp solid \4he at pressures greater than the bulk melting pressure of the
solid, we have performed experiments that show evidence for 4He mass flux
through the solid and the likely presence of superfluid inside the solid. We
present results that show that a thermomechanical equilibrium in quantitative
agreement with the fountain effect exists between two liquid reservoirs
connected to each other through two superfluid-filled Vycor rods in series with
a chamber filled with solid 4He. We use the thermomechanical effect to induce
flow through the solid and measure the flow rate. On cooling, mass flux appears
near T = 600 mK and rises smoothly as the temperature is lowered. Near T = 75
mK a sharp drop in the flux is present. The flux increases as the temperature
is reduced below 75 mK. We comment on possible causes of this flux minimum.Comment: 20 pages, 22 figures, 7 table
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Larval fish in the vicinity of aquaculture intakes
Texas Parks and Wildlife Department has recently proposed that all facilities pumping water from Texas estuaries be fitted with 0.5 mm screening to prevent larval fish mortality at these facilities. Data on larval fish distributions in Texas estuaries is quite limited (Holt et al. 1990). This report presents the results of a pilot study to examine the impact on larval fishes and shrimps of pumping water into mariculture facilities at three sites on the central and southern Texas Coast. The primary objective of this study was to determine the species composition, density and size structure of ichthyoplankton populations in the vicinity of the intake structures of the three mariculture facilities during their spring and fall pumping seasons. A secondary objective was to determine what organisms were actually being pumped through the system.Final report for contract IAC(90-91)111.5Prepared for Texas A&M Sea Grant, Texas General Land OfficeFebruary 1991Marine Scienc
Feeder Cattle Costs and Returns 1955-1956
Livestock Production/Industries,
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