18,143 research outputs found
Nickel-cadmium cell life test
Over 6,9000 Low Earth Orbit cycles were accumulated at 30% Depth of Discharge on twelve INTELSAT-design nickel-hydrogen cells. Physical equipment and cells are described. Performance characteristics are seen to be uniform. Further testing is planned to seek a failure mode, and also to investigate the effects of a new additive for nickel-hydrogen cells. Initial results indicate improved performance at higher temperatures and diminished swelling of positive nickel plates
Carbon dioxide and water exchange rates by a wheat crop in NASA's biomass production chamber: Results from an 86-day study (January to April 1989)
Gas exchange measurements were taken for a 20 sq m wheat stand grown from seed to harvest in NASA's Biomass Production Chamber. Respiration of the wheat stand caused the CO2 concentrations to rise an average of 440 ppm during the 4-h dark period each day, or 7.2 umol/sq m/sec. Dark period respiration was sensitive to temperature changes and could be increased 70 to 75 percent by raising the temperature from 16 C to 24 C. Stand photosynthesis (measured from the rate of CO2 drawdown immediately after the lights came on each day) peaked at 27 umol/sq m/sec at 25 days after planting and averaged 15 umol/sq m/sec throughout the study. By combining the average light period photosynthesis and average dark period respiration, a net of 860 g or 470 liters of CO2 were fixed per day. Stand photosynthetic rates showed a linear increase with increasing irradiance (750 umol/sq m/sec PPF the highest level tested), with an average light compensation point after day 30 of 190 umol/sq m/sec. Stand photosynthesis decreased slightly when CO2 levels were decreased from 2200 to 800 ppm, but dropped sharply when CO2 was decreased below 700 to 800 ppm. Water production from stand transpiration peaked at 120 L/day near 25 days and averaged about 90 L/day, or 4.5 L/sq m/day throughout the study
Supernova Asymmetries
All core collapse supernovae are strongly aspherical. The "Bochum event,"
with velocity components displaced symmetrically about the principal H
line, strongly suggests that SN 1987A was a bi-polar rather than a uni-polar
explosion. While there is a general tendency to display a single prominant axis
in images and spectropolarimetry, there is also growing evidence for frequent
departures from axisymmetry. There are various mechanisms that might contribute
to large scale departures from spherical symmetry: jet-induced processes, the
spherical shock accretion instability (SASI) and associated phenomena, and
non-axisymmetric instabilities (NAXI). The MRI gives inevitable production of
large toroidal magnetic fields. In sum: no without B. The role of
magnetic fields, non-axisymmetric instabilities, and of the de-leptonization
phase are discussed.Comment: 8 pages, 3 figures, to be published in the proceedings of the
conference "Supernova 1987A: 20 Years After" Aspen, 200
Photon-propagation model with random background field: Length scales and Cherenkov limits
We present improved experimental bounds on typical length scales of a
photon-propagation model with a frozen (time-independent) random background
field, which could result from anomalous effects of a static, multiply
connected spacetime foam.Comment: 6 pages with revtex4; v3: final versio
Space Time Foam: a ground state candidate for Quantum Gravity
A model of space-time foam, made by wormholes is considered. The Casimir
energy leading to such a model is computed by means of the phase shift method
which is in agreement with the variational approach used in Refs.[9-14]. The
collection of Schwarzschild and Reissner-Nordstr\"{o}m wormholes are separately
considered to represent the foam. The Casimir energy shows that the
Reissner-Nordstr\"{o}m wormholes cannot be used to represent the foam.Comment: 6 pages.RevTeX with package epsf and two eps figures. To be submitted
to the proceedings of the 4th Workshop of `Mysteries, Puzzles And Paradoxes
In Quantum Mechanics' Gargnano (Italy), 27 August-1 September 200
Launch vehicle wind and turbulence response by nonstationary statistical methods
Nonstationary adjoint algorithm for determining launch vehicle flight loads due to winds and turbulenc
Scenarios for optimizing potato productivity in a lunar CELSS
The use of controlled ecological life support system (CELSS) in the development and growth of large-scale bases on the Moon will reduce the expense of supplying life support materials from Earth. Such systems would use plants to produce food and oxygen, remove carbon dioxide, and recycle water and minerals. In a lunar CELSS, several factors are likely to be limiting to plant productivity, including the availability of growing area, electrical power, and lamp/ballast weight for lighting systems. Several management scenarios are outlined in this discussion for the production of potatoes based on their response to irradiance, photoperiod, and carbon dioxide concentration. Management scenarios that use 12-hr photoperiods, high carbon dioxide concentrations, and movable lamp banks to alternately irradiate halves of the growing area appear to be the most efficient in terms of growing area, electrical power, and lamp weights. However, the optimal scenario will be dependent upon the relative 'costs' of each factor
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