5,636 research outputs found
Interference detection and correction applied to incoherent-scatter radar power spectrum measurement
A median filter based interference detection and correction technique is evaluated and the method applied to the Arecibo incoherent scatter radar D-region ionospheric power spectrum is discussed. The method can be extended to other kinds of data when the statistics involved in the process are still valid
The r-Process in Neutrino-Driven Winds from Nascent, "Compact" Neutron Stars of Core-Collapse Supernovae
We present calculations of r-process nucleosynthesis in neutrino-driven winds
from the nascent neutron stars of core-collapse supernovae. A full dynamical
reaction network for both the alpha-rich freezeout and the subsequent r-process
is employed. The physical properties of the neutrino-heated ejecta are deduced
from a general relativistic model in which spherical symmetry and steady flow
are assumed. Our results suggest that proto-neutron stars with a large
compaction ratio provide the most robust physical conditions for the r-process.
The third peak of the r-process is well reproduced in the winds from these
``compact'' proto-neutron stars even for a moderate entropy, \sim 100-200 N_A
k, and a neutrino luminosity as high as \sim 10^{52} ergs s^{-1}. This is due
to the short dynamical timescale of material in the wind. As a result, the
overproduction of nuclei with A \lesssim 120 is diminished (although some
overproduction of nuclei with A \approx 90 is still evident). The abundances of
the r-process elements per event is significantly higher than in previous
studies. The total-integrated nucleosynthesis yields are in good agreement with
the solar r-process abundance pattern. Our results have confirmed that the
neutrino-driven wind scenario is still a promising site in which to form the
solar r-process abundances. However, our best results seem to imply both a
rather soft neutron-star equation of state and a massive proto-neutron star
which is difficult to achieve with standard core-collapse models. We propose
that the most favorable conditions perhaps require that a massive supernova
progenitor forms a massive proto-neutron star by accretion after a failed
initial neutrino burst.Comment: 12 pages, 6 figures, accepted for publication in the Astrophysical
Journa
Revised Relativistic Hydrodynamical Model for Neutron-Star Binaries
We report on numerical results from a revised hydrodynamic simulation of
binary neutron-star orbits near merger. We find that the correction recently
identified by Flanagan significantly reduces but does not eliminate the
neutron-star compression effect. Although results of the revised simulations
show that the compression is reduced for a given total orbital angular
momentum, the inner most stable circular orbit moves to closer separation
distances. At these closer orbits significant compression and even collapse is
still possible prior to merger for a sufficiently soft EOS. The reduced
compression in the corrected simulation is consistent with other recent studies
of rigid irrotational binaries in quasiequilibrium in which the compression
effect is observed to be small. Another significant effect of this correction
is that the derived binary orbital frequencies are now in closer agreement with
post-Newtonian expectations.Comment: Submitted to Phys. Rev.
Measurements of Static and Total Pressure Throughout the Transonic Speed Range as Obtained from an Airspeed Head Mounted on a Freely Falling Body
No abstract availabl
Fully quantum mechanical dynamic analysis of single-photon transport in a single-mode waveguide coupled to a traveling-wave resonator
We analyze the dynamics of single photon transport in a single-mode waveguide
coupled to a micro-optical resonator using a fully quantum mechanical model. We
examine the propagation of a single-photon Gaussian packet through the system
under various coupling conditions. We review the theory of single photon
transport phenomena as applied to the system and we develop a discussion on the
numerical technique we used to solve for dynamical behavior of the quantized
field. To demonstrate our method and to establish robust single photon results,
we study the process of adiabatically lowering or raising the energy of a
single photon trapped in an optical resonator under active tuning of the
resonator. We show that our fully quantum mechanical approach reproduces the
semi-classical result in the appropriate limit and that the adiabatic invariant
has the same form in each case. Finally, we explore the trapping of a single
photon in a system of dynamically tuned, coupled optical cavities.Comment: 24 pages, 10 figure
Binary Induced Neutron-Star Compression, Heating, and Collapse
We analyze several aspects of the recently noted neutron star collapse
instability in close binary systems. We utilize (3+1) dimensional and spherical
numerical general relativistic hydrodynamics to study the origin, evolution,
and parametric sensitivity of this instability. We derive the modified
conditions of hydrostatic equilibrium for the stars in the curved space of
quasi-static orbits. We examine the sensitivity of the instability to the
neutron star mass and equation of state. We also estimate limits to the
possible interior heating and associated neutrino luminosity which could be
generated as the stars gradually compress prior to collapse. We show that the
radiative loss in neutrinos from this heating could exceed the power radiated
in gravity waves for several hours prior to collapse. The possibility that the
radiation neutrinos could produce gamma-ray (or other electromagnetic) burst
phenomena is also discussed.Comment: 17 pages, 7 figure
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