14,993 research outputs found
New Pacific Records of Juvenile Albacore Thunnus alalunga (Bonnaterre) from Stomach Contents
Because the albacore, Thunnus alalunga
(Bonnaterre), is commercially one of the more
valuable species of tuna , a great deal of effort
has been expended in investigating its biology.
Although much has been learned in recent years
about the albacore, its age and growth, movements
and migrations (Otsu, 1960; Clemens,
1961; Otsu and Uchida, 1963), many facets of
the biology of this species still need to be studied.
As part of the Albacore Ecology Program,
staff members of the Bureau of Commercial
Fisheries Biological Laboratory, Honolulu, Hawaii,
have been studying the early life history
of albacore in order to fill the gaps in our
knowledge
A search for x-ray counterparts of gamma-ray bursts with the ROSAT PSPC
We search for faint X-ray bursts with duration 10--300 seconds in the ROSAT
PSPC pointed observations with a total exposure of 1.6e7 seconds. We do not
detect any events shorter than ~100s, i.e. those that could be related to the
classic gamma-ray bursts. At the same time, we detect a number of long flares
with durations of several hundred seconds. Most, but not all, of the long
flares are associated with stars. If even a small number of those long flares,
that cannot identified with stars, are X-ray afterglows of GRB, the number of
X-ray afterglows greatly exceeds the number of BATSE GRB. This would imply that
the beaming factor of gamma-rays from the burst should be >100. The
non-detection of any short bursts in our data constrains the GRB counts at the
fluences 1--2.5 orders of magnitude below the BATSE limit. The constrained
burst counts are consistent with the extrapolation of the BATSE log N - log S
relation. Finally, our results do not confirm a reality of short X-ray flashes
found in the Einstein IPC data by Gotthelf, Hamilton and Helfand.Comment: Accepted to ApJ Letters. 4 pages with 3 figures, LaTeX2
Ag and N acceptors in ZnO: ab initio study of acceptor pairing, doping efficiency, and the role of hydrogen
Efficiency of ZnO doping with Ag and N shallow acceptors, which substitute
respectively cations and anions, was investigated. First principles
calculations indicate a strong tendency towards formation of nearest neighbor
Ag-N pairs and N-Ag-N triangles. Binding of acceptors stems from the formation
of quasi-molecular bonds between dopants, and has a universal character in
semiconductors. The pairing increases energy levels of impurities, and thus
lowers doping efficiency. In the presence of donors, pairing is weaker or even
forbidden. However, hydrogen has a tendency to form clusters with Ag and N,
which favors the Ag-N aggregation and lowers the acceptor levels of such
complexes.Comment: 10 pages, 4 figure
Polaronic behavior of undoped high-Tc cuprates
We present angle-resolved photoemission spectroscopy (ARPES) data on undoped
La2CuO4, indicating polaronic coupling between bosons and charge carriers.
Using a shell model, we calculate the electron-phonon coupling and find that it
is strong enough to give polarons. We develop an efficient method for
calculating ARPES spectra in undoped systems. Using the calculated couplings,
we find the width of the phonon side band in good agreement with experiment. We
analyze reasons for the observed dependence of the width on the binding energy.Comment: 4 pages, RevTeX, 5 eps figures, more material available at
http://www.fkf.mpg.de/andersen/phonons
Resonant Cyclotron Radiation Transfer Model Fits to Spectra from Gamma-Ray Burst GRB870303
We demonstrate that models of resonant cyclotron radiation transfer in a
strong field (i.e. cyclotron scattering) can account for spectral lines seen at
two epochs, denoted S1 and S2, in the Ginga data for GRB870303. Using a
generalized version of the Monte Carlo code of Wang et al. (1988,1989b), we
model line formation by injecting continuum photons into a static
plane-parallel slab of electrons threaded by a strong neutron star magnetic
field (~ 10^12 G) which may be oriented at an arbitrary angle relative to the
slab normal. We examine two source geometries, which we denote "1-0" and "1-1,"
with the numbers representing the relative electron column densities above and
below the continuum photon source plane. We compare azimuthally symmetric
models, i.e. models in which the magnetic field is parallel to the slab normal,
with models having more general magnetic field orientations. If the bursting
source has a simple dipole field, these two model classes represent line
formation at the magnetic pole, or elsewhere on the stellar surface. We find
that the data of S1 and S2, considered individually, are consistent with both
geometries, and with all magnetic field orientations, with the exception that
the S1 data clearly favor line formation away from a polar cap in the 1-1
geometry, with the best-fit model placing the line-forming region at the
magnetic equator. Within both geometries, fits to the combined (S1+S2) data
marginally favor models which feature equatorial line formation, and in which
the observer's orientation with respect to the slab changes between the two
epochs. We interpret this change as being due to neutron star rotation, and we
place limits on the rotation period.Comment: LaTeX2e (aastex.cls included); 45 pages text, 17 figures (on 21
pages); accepted by ApJ (to be published 1 Nov 1999, v. 525
The Formation and Fragmentation of Disks around Primordial Protostars
The very first stars to form in the Universe heralded an end to the cosmic
dark ages and introduced new physical processes that shaped early cosmic
evolution. Until now, it was thought that these stars lived short, solitary
lives, with only one extremely massive star, or possibly a very wide binary
system, forming in each dark matter minihalo. Here we describe numerical
simulations that show that these stars were, to the contrary, often members of
tight multiple systems. Our results show that the disks that formed around the
first young stars were unstable to gravitational fragmentation, possibly
producing small binary and higher-order systems that had separations as small
as the distance between the Earth and the Sun.Comment: This manuscript has been accepted for publication in Science. This
version has not undergone final editing. Please refer to the complete version
of record at http://www.sciencemag.org
r-modes in Relativistic Superfluid Stars
We discuss the modal properties of the -modes of relativistic superfluid
neutron stars, taking account of the entrainment effects between superfluids.
In this paper, the neutron stars are assumed to be filled with neutron and
proton superfluids and the strength of the entrainment effects between the
superfluids are represented by a single parameter . We find that the
basic properties of the -modes in a relativistic superfluid star are very
similar to those found for a Newtonian superfluid star. The -modes of a
relativistic superfluid star are split into two families, ordinary fluid-like
-modes (-mode) and superfluid-like -modes (-mode). The two
superfluids counter-move for the -modes, while they co-move for the
-modes. For the -modes, the quantity is
almost independent of the entrainment parameter , where and
are the azimuthal wave number and the oscillation frequency observed by an
inertial observer at spatial infinity, respectively. For the -modes, on
the other hand, almost linearly increases with increasing . It
is also found that the radiation driven instability due to the -modes is
much weaker than that of the -modes because the matter current associated
with the axial parity perturbations almost completely vanishes.Comment: 14 pages, 4 figures. To appear in Physical Review
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