4,192 research outputs found
Propulsion systems dispersion analysis and optimum propellant management
Propulsion systems dispersion analysis and propellant optimization method for Apollo subsystem
Oscillating scalar-field dark matter in supergravity
We show that an oscillating scalar field in supergravity of mass of the order
of TeV with a nonzero vacuum expectation value ( GeV) can
be a candidate of cold dark matter (CDM). To avoid the gravitino problem, we
need a low reheating temperature after the primordial inflation. Then, the
energy density of the oscillating scalar field satisfies all the requirements
for CDM at present in the universe.Comment: LaTeX JHEP-format, to appear in JHE
Non-Gaussianity analysis of GW background made by short-duration burst signals
We study an observational method to analyze non-Gaussianity of a
gravitational wave (GW) background made by superposition of weak burst signals.
The proposed method is based on fourth-order correlations of data from four
detectors, and might be useful to discriminate the origin of a GW background.
With a formulation newly developed to discuss geometrical aspects of the
correlations, it is found that the method provides us with linear combinations
of two interesting parameters, I_2 and V_2 defined by the Stokes parameters of
individual GW burst signals. We also evaluate sensitivities of specific
detector networks to these parameters.Comment: 18 pages, to appear in PR
Apollo cryogenic integrated systems program
The integrated systems program is capable of simulating both nominal and anomalous operation of the Apollo cryogenics storage system (CSS). Two versions of the program exist; one for the Apollo 14 configuration and the other for J Type Mission configurations. The program consists of two mathematical models which are dynamically coupled. A model of the CSS components and lines determines the oxygen and hydrogen flowrate from each storage tank given the tank pressures and temperatures, and the electrical power subsystem and environmental control subsystem flow demands. Temperatures and pressures throughout the components and lines are also determined. A model of the CSS tankage determines the pressure and temperatures in the tanks given the flowrate from each tank and the thermal environment. The model accounts for tank stretch and includes simplified oxygen tank heater and stratification routines. The program is currently operational on the Univac 1108 computer
Hiding cosmic strings in supergravity D-term inflation
The influence of higher-order terms in the K\"{a}hler potential of the
supergravity D-term inflation model on the density perturbation is studied. We
show that these terms can make the inflaton potential flatter, which lowers the
energy scale of inflation under the COBE/WMAP normalization. As a result, the
mass per unit length of cosmic strings, which are produced at the end of
inflation, can be reduced to a harmless but detectable level without
introducing a tiny Yukawa coupling. Our scenario can naturally be implemented
in models with a low cut-off as in Type I or Type IIB orientifold models.Comment: 15 pages, 4 figure
Gravitational Wave Background from Neutrino-Driven Gamma-Ray Bursts
We discuss the gravitational wave background (GWB) from a cosmological
population of gamma-ray bursts (GRBs). Among various emission mechanisms for
the gravitational waves (GWs), we pay a particular attention to the vast
anisotropic neutrino emissions from the accretion disk around the black hole
formed after the so-called failed supernova explosions. The produced GWs by
such mechanism are known as burst with memory, which could dominate over the
low-frequency regime below \sim 10Hz. To estimate their amplitudes, we derive
general analytic formulae for gravitational waveform from the axisymmetric
jets. Based on the formulae, we first quantify the spectrum of GWs from a
single GRB. Then, summing up its cosmological population, we find that the
resultant value of the density parameter becomes roughly \Omega_{GW} \approx
10^{-20} over the wide-band of the low-frequency region, f\sim 10^{-4}-10^1Hz.
The amplitude of GWB is sufficiently smaller than the primordial GWBs
originated from an inflationary epoch and far below the detection limit.Comment: 6 pages, 4 figures, accepted for publication in MNRA
Unbinding Transition Induced by Osmotic Pressure in Relation to Unilamellar Vesicle Formation
Small-angle X-ray scattering and phase-contrast microscopy experiments were
performed to investigate the effect of the osmotic pressure on vesicle
formation in a dioleoylphosphatidylcholine (DOPC)/water/NaI system.
Multi-lamellar vesicles were formed when a pure lipid film was hydrated with an
aqueous solution of NaI. On the other hand, uni-lamellar vesicles (ULVs) were
formed when a lipid film mixed with an enough amount of NaI was hydrated. To
confirm the effect of the osmotic pressure due to NaI, a free-energy
calculation was performed. This result showed that the osmotic pressure induced
an unbinding transition on the hydration process, which resulted in ULV
formation
Prospects for direct detection of circular polarization of gravitational-wave background
We discussed prospects for directly detecting circular polarization signal of
gravitational wave background. We found it is generally difficult to probe the
monopole mode of the signal due to broad directivity of gravitational wave
detectors. But the dipole (l=1) and octupole (l=3) modes of the signal can be
measured in a simple manner by combining outputs of two unaligned detectors,
and we can dig them deeply under confusion and detector noises. Around f~0.1mHz
LISA will provide ideal data streams to detect these anisotropic components
whose magnitudes are as small as ~1 percent of the detector noise level in
terms of the non-dimensional energy density \Omega_{GW}(f).Comment: 5 pages, 1 figure, PRL in pres
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