4,915 research outputs found
Comparison of lunar rocks and meteorites: Implications to histories of the moon and parent meteorite bodies
A number of similarities between lunar and meteoritic rocks are reported and suggest that the comparison is essential for a clear understanding of meteorites as probes of the early history of the solar systems: (1) Monomict and polymict breccias occur in lunar rocks, as well as in achondritic and chondritic meteorites, having resulted from complex and repeated impact processes. (2) Chondrules are present in lunar, as well as in a few achondritic and most chondritic meteorites. It is pointed out that because chondrules may form in several different ways and in different environments, a distinction between the different modes of origin and an estimate of their relative abundance is important if their significance as sources of information on the early history of the solar system is to be clearly understood. (3) Lithic fragments are very useful in attempts to understand the pre- and post-impact history of lunar and meteoritic breccias. They vary from little modified (relative to the apparent original texture), to partly or completely melted and recrystallized lithic fragments
Reexamination of a Bound on the Dirac Neutrino Magnetic Moment from the Supernova Neutrino Luminosity
The neutrino helicity-flip process under the conditions of the supernova core
is reinvestigated. Instead of the uniform ball model for the SN core used in
previous analyses, realistic models for radial distributions and time evolution
of physical parameters in the SN core are considered. A new upper bound on the
Dirac neutrino magnetic moment is obtained from the limit on the supernova core
luminosity for nu_R emission.Comment: 13 pages, LaTeX, 8 EPS figures, submitted to Int. J. Mod. Phys.
The Role of Copper in Hemoglobin Regeneration
During the past few years a considerable amount of investigation has been devoted to the part played by copper in hemoglobin formation. Hart, Steenbock, Waddell, and Elvehjem were the first to show that in nutritional anemia regeneration of hemoglobin does not occur when pure iron salts are administered, but if a small amount of copper as copper sulphate be added along with the iron salt regeneration is very rapid
On the appearance of hyperons in neutron stars
By employing a recently constructed hyperon-nucleon potential the equation of
state of \beta-equilibrated and charge neutral nucleonic matter is calculated.
The hyperon-nucleon potential is a low-momentum potential which is obtained
within a renormalization group framework. Based on the Hartree-Fock
approximation at zero temperature the densities at which hyperons appear in
neutron stars are estimated. For several different bare hyperon-nucleon
potentials and a wide range of nuclear matter parameters it is found that
hyperons in neutron stars are always present. These findings have profound
consequences for the mass and radius of neutron stars.Comment: 12 pages, 12 figures, RevTeX4; summary and conclusions are
strengthened, to appear in PR
Effect of Muons on the Phase Transition in Magnetised Proto-Neutron Star Matter
We study the effect of inclusion of muons and the muon neutrinos on the phase
transition from nuclear to quark matter in a magnetised proto-neutron star and
compare our results with those obtained by us without the muons. We find that
the inclusion of muons changes slightly the nuclear density at which transition
occurs.However the dependence of this transition density on various chemical
potentials, temperature and the magnetic field remains quantitatively the same.Comment: LaTex2e file with four postscript figure
Anisotropic convection in rotating proto-neutron stars
We study the conditions for convective instability in rotating, non-magnetic
proto--neutron stars. The criteria that determine stability of nascent neutron
stars are analogous to the Solberg--Hoiland conditions but including the
presence of lepton gradients. Our results show that, for standard angular
velocity profiles, convectively unstable modes with wave-vectors parallel to
the rotation axis are suppressed by a stable angular momentum profile, while
unstable modes with wave-vectors perpendicular to the axis remain unaltered.
Since the wave-vector is perpendicular to the velocity perturbation, the
directional selection of the unstable modes may result in fluid motions along
the direction of the rotation axis. This occurs in rigidly rotating stars as
well as in the inner core of differentially rotating stars. Our results provide
a natural source of asymmetry for proto--neutron stars with the only
requirement that angular velocities be of the order of the convective
characteristic frequency.Comment: 5 pages, 4 figures, final version to appear in A&
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