18,636 research outputs found
Investigation of critical slowing down in a bistable S-SEED
A simulation of S-SEED switching based upon experimental data is developed that includes the effect of critical slowing down. The simulation's accuracy is demonstrated by close agreement with the results from experimental S-SEED switching. The simulation is subsequently used to understand how the phenomenon of critical slowing down applies to switching of an S-SEED and how the effect on photonic analog-to-digital (A/D) converter performance may be minimized.B. A. Clare, K. A. Corbett, K. J. Grant, P. B. Atanackovic, W. Marwood and J. Munc
Summary of the electromagnetic compatibility evaluation of the proposed satellite power system
The effects of the proposed solar power satellite (SPS) operations on electronic equipment and systems by fundamental, harmonic, and intermodulation component emissions from the orbital station; and the fundamental, harmonic, and structural intermodulation emissions from the rectenna site were evaluated. The coupling and affects interactions affecting a wide spectrum of electronic equipment are considered. The primary EMC tasking areas are each discussed separately
Laser velocimeter for simultaneous two-dimensional velocity measurements
Laser velocimeter provides simultaneous orthogonal measurements in manner which minimizes many problems attending prior systems, and allows spatial traversing of flowfield in order to obtain velocity profiles. Velocimeter permits rapid interrogation of unsteady flows where area of interest is of the order of one meter in extent and flow does not vary appreciably over time of about one second
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
Description of the Immature Stages of Trioza uniqua (Caldwell) (Homoptera: Psyllidae)
The taxonomic position of Trioza uniqua (Caldwell) and its evolutionary affinities with the genera Kuwayama and Trioza are reviewed. Detailed descriptions of the five nymphal instars are given
Parasites Associated with the Leucaena Psyllid, Heteropsylla cubana Crawford, in Hawaii
Four species of parasitoid Hymenoptera have been reared from the Leucaena psyllid, Heteropsylla cubana Crawford, in Hawaii. In addition to the purposely introduced primary parasite Psyllaephagus yaseeni Noyes (Encyrtidae), three species of hyperparasites have been reared. These are a pteromalid, Pachyneuron siphonophorae (Ashmead), and two encyrtids, Syrphophagus aphidivorus (Mayr) and Syrphophagus sp. A key to parasitoids reared from H. cubana in Hawaii is presented
Origin and emergence of entrepreneurship as a research field
This paper seeks to map out the emergence and evolution of entrepreneurship as an independent field in the social science literature from the early 1990s to 2009. Our analysis indicates that entrepreneurship has grown steadily during the 1990s but has truly emerged as a legitimate academic discipline in the latter part of the 2000s. The field has been dominated by researchers from Anglo-Saxon countries over the past 20 years, with particularly strong representations from the US, UK, and Canada. The results from our structural analysis, which is based on a core document approach, point to five large knowledge clusters and further 16 sub-clusters. We characterize the clusters from their cognitive structure and assess the strength of the relationships between these clusters. In addition, a list of most cited articles is presented and discussed
Phantom energy traversable wormholes
It has been suggested that a possible candidate for the present accelerated
expansion of the Universe is ''phantom energy''. The latter possesses an
equation of state of the form , consequently violating
the null energy condition. As this is the fundamental ingredient to sustain
traversable wormholes, this cosmic fluid presents us with a natural scenario
for the existence of these exotic geometries. Due to the fact of the
accelerating Universe, macroscopic wormholes could naturally be grown from the
submicroscopic constructions that originally pervaded the quantum foam. One
could also imagine an advanced civilization mining the cosmic fluid for phantom
energy necessary to construct and sustain a traversable wormhole.
In this context, we investigate the physical properties and characteristics
of traversable wormholes constructed using the equation of state , with . We analyze specific wormhole geometries, considering
asymptotically flat spacetimes and imposing an isotropic pressure. We also
construct a thin shell around the interior wormhole solution, by imposing the
phantom energy equation of state on the surface stresses. Using the ''volume
integral quantifier'' we verify that it is theoretically possible to construct
these geometries with vanishing amounts of averaged null energy condition
violating phantom energy. Specific wormhole dimensions and the traversal
velocity and time are also deduced from the traversability conditions for a
particular wormhole geometry. These phantom energy traversable wormholes have
far-reaching physical and cosmological implications. For instance, an advanced
civilization may use these geometries to induce closed timelike curves,
consequently violating causality.Comment: 9 pages, Revtex4. V2: Considerable comments and references added, no
physics changes, now 10 pages. Accepted for publication in Physical Review
SSM/I Rainfall Volume Correlated with Deepening Rate in Extratropical Cyclones
With the emergence of reasonably robust, physically based rain rate algorithms designed for the Special Sensor Microwave/Imager (SSM/I), a unique opportunity exists to directly observe a physical component which can contribute to or be a signature of cyclone deepening (latent heat release). The emphasis of the research in this paper is to seek systematic differences in rain rate observed by the SSM/I, using the algorithm of Petty in cases of explosive and nonexplosive cyclone deepening
Advanced high temperature static strain sensor development
An examination was made into various techniques to be used to measure static strain in gas turbine liners at temperatures up to 1150 K (1600 F). The methods evaluated included thin film and wire resistive devices, optical fibers, surface acoustic waves, the laser speckle technique with a heterodyne readout, optical surface image and reflective approaches and capacitive devices. A preliminary experimental program to develop a thin film capacitive device was dropped because calculations showed that it would be too sensitive to thermal gradients. In a final evaluation program, the laser speckle technique appeared to work well up to 1150 K when it was used through a relatively stagnant air path. The surface guided acoustic wave approach appeared to be interesting but to require too much development effort for the funds available. Efforts to develop a FeCrAl resistive strain gage system were only partially successful and this part of the effort was finally reduced to a characterization study of the properties of the 25 micron diameter FeCrAl (Kanthal A-1) wire. It was concluded that this particular alloy was not suitable for use as the resistive element in a strain gage above about 1000 K
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