67,946 research outputs found
Manufacture and evaluation of Li/BCX DD cells
This project is divided into four main tasks: cell manufacture, acceptance, and lot certification of cells, performance testing of cells, and abuse testing of cells. Lithium/bromine chloride in thionyl chloride (Li/BCX) 149 DD cells (PN 3B2085-XA) were built according to the provisions of Electrochem Industries Quality Plan 17096. Acceptance and lot certification testing was performed according to NASA JSC Document EP5-83-025, Revision B. Acceptance testing included open circuit and load voltage check, visual examination, size and weight measurements, and high temperature exposure. Lot certification tests were performed for capacity performance and for performance under conditions of thermal and electrical abuse. These tests included 149 C exposure, capacity discharge, fuse check, high temperature exposure, high rate discharge, short circuit, vibration, and overdischarge testing. A quantity of 200 cells was delivered to Johnson Space Center for life test evaluation. A parametric evaluation of the capacity discharge of Li/BCX DD cells was performed over a variety of temperatures and discharge rates. This testing served to map the performance capability of the cell. Tests were also performed over a variety of electrical and thermal abuse conditions. Abuse tests included short circuit, charging, overdischarge, high temperature exposure, shock, and vibration
Two-temperature coronal flow above a thin disk
We extended the disk corona model (Meyer & Meyer-Hofmeister 1994; Meyer, Liu,
& Meyer-Hofmeister 2000a) to the inner region of galactic nuclei by including
different temperatures in ions and electrons as well as Compton cooling. We
found that the mass evaporation rate and hence the fraction of accretion energy
released in the corona depend strongly on the rate of incoming mass flow from
outer edge of the disk, a larger rate leading to more Compton cooling, less
efficient evaporation and a weaker corona. We also found a strong dependence on
the viscosity, higher viscosity leading to an enhanced mass flow in the corona
and therefore more evaporation of gas from the disk below. If we take accretion
rates in units of the Eddington rate our results become independent on the mass
of the central black hole. The model predicts weaker contributions to the hard
X-rays for objects with higher accretion rate like narrow-line Seyfert 1
galaxies (NLS1s), in agreement with observations. For luminous active galactic
nuclei (AGN) strong Compton cooling in the innermost corona is so efficient
that a large amount of additional heating is required to maintain the corona
above the thin disk.Comment: 17 pages, 6 figures. ApJ accepte
Properties of Intercalated 2H-NbSe2, 4Hb-TaS2 and 1T-TaS2
The layered compounds 2H-NbSe, 24Hb-TaS, 2and 1T-TaS2 have been intercalated with organic molecules; and the resulting crystal structure, heat capacity, conductivity, and superconductivity have been studied. The coordination in the disulfide layers was found to be unchanged in the product phase. Resistance minima appear and the superconducting transition temperature is reduced in the NbSe2 complex. Conversely, superconductivity is induced in the 4Hb-TaS2 complex. Corresponding evidence of a large change of the density of states, negative for 2H-NbSe2 and positive for 4Hb-TaS2, was also observed upon intercalation. The transport properties of all the intercalation complexes show a pronounced dependence upon the coordination of the transition metal
Competing interactions in two dimensional Coulomb systems: Surface charge heterogeneities in co-assembled cationic-anionic incompatible mixtures
A binary mixture of oppositely charged components confined to a plane such as
cationic and anionic lipid bilayers may exhibit local segregation. The relative
strength of the net short range interactions, which favors macroscopic
segregation, and the long range electrostatic interactions, which favors
mixing, determines the length scale of the finite size or microphase
segregation. The free energy of the system can be examined analytically in two
separate regimes, when considering small density fluctuations at high
temperatures, and when considering the periodic ordering of the system at low
temperatures (F. J. Solis and M. Olvera de la Cruz, J. Chem. Phys. 122, 054905
(2000)). A simple Molecular Dynamics simulation of oppositely charged monomers,
interacting with a short range Lennard Jones potential and confined to a two
dimensional plane, is examined at different strengths of short and long range
interactions. The system exhibits well-defined domains that can be
characterized by their periodic length-scale as well as the orientational
ordering of their interfaces. By adding salt, the ordering of the domains
disappears and the mixture macroscopically phase segregates in agreement with
analytical predictions.Comment: 8 pages, 5 figures, accepted for publication in J. Chem. Phys, Figure
1 include
Searching for gas giant planets on Solar System scales - A NACO/APP L'-band survey of A- and F-type Main Sequence stars
We report the results of a direct imaging survey of A- and F-type main
sequence stars searching for giant planets. A/F stars are often the targets of
surveys, as they are thought to have more massive giant planets relative to
solar-type stars. However, most imaging is only sensitive to orbital
separations 30 AU, where it has been demonstrated that giant planets are
rare. In this survey, we take advantage of the high-contrast capabilities of
the Apodizing Phase Plate coronagraph on NACO at the Very Large Telescope.
Combined with optimized principal component analysis post-processing, we are
sensitive to planetary-mass companions (2 to 12 ) at Solar System
scales (30 AU). We obtained data on 13 stars in L'-band and detected one
new companion as part of this survey: an M dwarf companion around HD
984. We re-detect low-mass companions around HD 12894 and HD 20385, both
reported shortly after the completion of this survey. We use Monte Carlo
simulations to determine new constraints on the low-mass (80 )
companion frequency, as a function of mass and separation. Assuming solar-type
planet mass and separation distributions, normalized to the planet frequency
appropriate for A-stars, and the observed companion mass-ratio distribution for
stellar companions extrapolated to planetary masses, we derive a truncation
radius for the planetary mass companion surface density of 135 AU at 95%
confidence.Comment: Accepted for publication in MNRAS, 8 pages, 4 figure
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