16,469 research outputs found
Determining solar abundances using helioseismology
The recent downward revision of solar photospheric abundances of Oxygen and
other heavy elements has resulted in serious discrepancies between solar models
and solar structure as determined through helioseismology. In this work we
investigate the possibility of determining the solar heavy-element abundance
without reference to spectroscopy by using helioseismic data. Using the
dimensionless sound-speed derivative in the solar convection zone, we find that
the heavy element abundance, Z, of 0.0172 +/- 0.002, which is closer to the
older, higher value of the abundances.Comment: To appear in Ap
The thermal conductivity of steam in the zero density limit as a function of temperature
An equation for the thermal conductivity of steam at pressures of 1 atmosphere and below is presented. Sources of the experimental data and the actual data used in the analysis are presented. Also included is low density data below 100 C
Analysis of temperature effects near mode I cracks in glassy polymers
A previous isothermal study has shown that the toughness of glassy polymers is governed by the competition between shear yielding and crazing. The present work aims at investigating loading rates for which thermal effects need to be accounted for. The influence of the heat coming from the viscoplastic shear yielding and from crazing on their competition and on the toughness is examined. Crazing is shown to be the dominant heat source, and the dependence of the craze properties on temperature appears to be key in controlling the toughness of the material.
Causality Implies Inflationary Back-Reaction
There is a widespread belief among inflationary cosmologists that a local
observer cannot sense super-horizon gravitons. The argument goes that a local
observer would subsume super-horizon gravitons into a redefinition of his
coordinate system. We show that adopting this view for pure gravity on de
Sitter background leads to time variation in the Hubble parameter measured by a
local observer. It also leads to a violation of the gravitational field
equation because that equation is obeyed by the full metric,
rather than the one which has been cleansed of super-horizon modes.Comment: 20 pages, 2 figures, uses LaTeX2e, version 2 slightly revised for
publicatio
Modified Bethe-Weizsacker mass formula with isotonic shift and new driplines
Nuclear masses are calculated using the modified Bethe-Weizsacker mass
formula in which the isotonic shifts have been incorporated. The results are
compared with the improved liquid drop model with isotonic shift. Mass excesses
predicted by this method compares well with the microscopic-macroscopic model
while being much more simple. The neutron and proton drip lines have been
predicted using this modified Bethe-Weizsacker mass formula with isotonic
shifts.Comment: 9 pages including 2 figure
The relation between and for solar-like oscillations
Establishing relations between global stellar parameters and asteroseismic
quantities can help improve our understanding of stellar astrophysics and
facilitate the interpretation of observations. We present an observed relation
between the large frequency separation, , and the frequency of
maximum power, . We find that is proportional to
, allowing prediction of to about 15 per cent
given . Our result is further supported by established scaling
relations for and and by extended stellar model
calculations, which confirm that can be estimated using this
relation for basically any star showing solar-like oscillations in the
investigated range (0.5<M/Msol<4.0).Comment: 5 pages, 8 figures, Letter accepted by MNRA
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