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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 793 records · Page 44
All sourcesNASA NTRSDOE OSTI
NASA NTRS1979

Monitoring of thickness changes of the continental ice sheets by satellite altimetry

Radar altimeter measurements from the GEOS 3 satellite are being utilized to define the topography of the southern Greenland ice sheet between latitudes 60 deg N and 65 deg N. The resultant elevations have been correlated with two geoceiver sites on the ice surface; the agreement is within a few meters. The internal repeatability of the altimeter-derived elevations has been assessed at the crossovers of the satellite ground tracks; the observed agreements vary from 0.07 to 3.10 m, intervening times being 1 day and 674 days, respectively. Improved knowledge of the temporal changes in the topographic expression of the continental ice sheets, via satellite altimetry, will significantly add to the understanding of glaciological and climatological processes.

Brooks, R. L.↗
NASA NTRS1979

ISEE 1 and 2 particle observations of outer plasma sheet boundary

Observations of particle structures by a medium-energy particle experiment on the ISEE 1 and 2 spacecraft at a distance of about 20 earth radii in the geomagnetic tail are presented. Comparison of these data with plasma data indicates the existence of a layer of energetic electrons and ions just outside the plasma sheet. The region outside the plasma sheet in the high-latitude lobe is permeated with low-intensity low-energy (about 1.5 KeV) ions. These particle structures have velocities of a few kilometers per second to at least about 60 km/s. Large-scale motions are observed with onset and recovery of substorms. The dimensions of the particle structures are estimated to range from about 200 to 10,000 km at 20 earth radii. The particle structures are dependent upon the energy as well as the species of the particles.

Parks, G. K.↗
NASA NTRS1979

Free oscillations in a climate model with ice-sheet dynamics

A study of stable periodic solutions to a simple nonlinear model of the ocean-atmosphere-ice system is presented. The model has two dependent variables: ocean-atmosphere temperature and latitudinal extent of the ice cover. No explicit dependence on latitude is considered in the model. Hence all variables depend only on time and the model consists of a coupled set of nonlinear ordinary differential equations. The globally averaged ocean-atmosphere temperature in the model is governed by the radiation balance. The reflectivity to incoming solar radiation, i.e., the planetary albedo, includes separate contributions from sea ice and from continental ice sheets. The major physical mechanisms active in the model are (1) albedo-temperature feedback, (2) continental ice-sheet dynamics and (3) precipitation-rate variations. The model has three-equilibrium solutions, two of which are linearly unstable, while one is linearly stable. For some choices of parameters, the stability picture changes and sustained, finite-amplitude oscillations obtain around the previously stable equilibrium solution. The physical interpretation of these oscillations points to the possibility of internal mechanisms playing a role in glaciation cycles.

Kallen, E.↗
NASA NTRS1980

A statistical determination of the shape and position of the geomagnetic neutral sheet

Using 2.5-minute average field values from Imp 6, 7, and 8 magnetic field measurements, the standard magnetotail neutral sheet (MNS) model is examined. The best representation for the MNS is found to be an arched surface which crosses the solar magnetospheric equatorial plane on the flanks of the tail about 18 earth radii (ER) from the tail axis; the surface is anchored to the geomagnetic dipole at a hinging distance of 10.5 ER. In addition, the shape and position of the neutral sheet (NS) do not vary significantly with distance down the tail, but the NS is anchored somewhat closer to the earth during disturbed geomagnetic conditions.

Fairfield, D. H.↗
NASA NTRS1980

Observation of the plasma boundary layer at lunar distances - Direct injection of plasma into the plasma sheet

The paper presents observational evidence from the Apollo suprathermal ion detector experiments that the injection of magnetosheath particles at the low-latitude magnetopause operates at lunar distances as well. An interface between the magnetosheath and the plasma sheet, termed the plasma sheet boundary layer (PSBL), is identified and believed to be the extension of the magnetospheric boundary layer (also called the plasma boundary layer) observed on the dayside. Using measurements of the PSBL's thickness, magnetic field, and plasma velocity the average electric potential drop across the PSBL is estimated at 4.2 kV and compared with the potential drop which is needed to insure that the magnetopause is an equipotential for a closed magnetosphere. It was concluded though that the magnetosphere is open since this drop is much larger than 4.2 kV.

Sanders, G. D.↗
NASA NTRS1981

Current sheet model

The model of a rectenna based on the current sheet equivalency of a large planar array is described. The model is mathematically characterized by expression for the fraction of the incident plane wave that is reflected from the sheet. The model is conceptually justified for normal incidence by comparing it to the waveguide model in which evanescent modes, present as beyond and cutoff, correspond to the near field components which become negligible at any significant distance from the antenna array.

Source record↗
NASA NTRS1980

Transmitted sound field due to an impulsive line acoustic source bounded by a plate followed by a vortex sheet

The propagation of sound due to a line acoustic source in the moving stream across a semiinfinite vortex sheet which trails from a rigid plate is examined in a linear theory for the subsonic case. A solution for the transmitted sound field is obtained with the aid of multiple integral transforms and the Wiener-Hopf technique for both the steady state (time harmonic) and initial value (impulsive source) situations. The contour of inverse transform and hence the decomposition of the functions are determined through causality and radiation conditions. The solution obtained satisfies causality and the full Kutta conditions. The transmitted sound field is composed of two waves in both the stady state and initial value problems. One is the wave scattered from the edge of the plate which is associated with the bow wave and the instability wave. These waves exist in the downstream sectors. The other is the wave transmitted through the vortex sheet which is also associated with the instability wave. Regional divisions of the transmitted sound field are identified.

Miura, T.↗
NASA NTRS1980

Statics of the nightside Jovian plasma sheet

Data are analyzed from the low energy charged particle (LECP) and magnetic field (MAG) experiments on the Voyager 2 spacecraft that demonstrate that the configuration of the Jovian plasma sheet at distances of about .80 to about 120 Jupiter radii is determined by ions (protons and heavier nuclei) of energies greater than approximately 30 keV. The energy densities of these ions are sufficient to provide the diamagnetic depressions in the magnetic field strengths observed as the spacecraft crossed the Jovian plasma sheet. The particle bulk direction of motion is predominantly across the local magnetic field, consistent with that expected from corotation of the planetary magnetic field.

Lanzerotti, L. J.↗
NASA NTRS1980

On the tearing mode in quasi-neutral sheets

The paper examines the stability of the tearing mode in a quasi-neutral sheet which contains electron pitch angle scattering wave turbulence (or collisions). It is found that the pitch angle scattering dissipation destabilizes the tearing mode and that the tearing growth rate is proportional to the pitch angle diffusion coefficient. The results are discussed with reference to theories of the plasma sheet.

Coroniti, F. V.↗
NASA NTRS1981

Nonlinear evolution of the sheet pinch

An incompressible, dissipative numerical code of the spectral type is used to follow the nonlinear evolution of a magnetohydrodynamic sheet pinch in two spatial dimensions. The evolution involves considerable turbulent activity in the electric current field, with the excited spatial scales ranging from the size of the containing volume down to the dissipation lengths of the magnetic and velocity fields. Strong current filamentation near magnetic X-points is observed, as is 'jetting', or expulsion of magnetofluid from the vicinity of the X-point parallel to the current sheet.

Matthaeus, W. H.↗
NASA NTRS1980

Low-cost conversion of polycrystalline silicon into sheet by HEM and FAST

The conversion of polycrystalline silicon to sheet form (the wafers produced are 10 cm x 10 cm cross section with minimum surface damage) by the Heat Exchanger Method (HEM) and multi-wire Fixed Abrasive Slicing Technique (FAST), as a means of reducing the cost of solar arrays for adaptation of photovoltaic technology for terrestrial applications, is given. A schematic of a HEM furnace, which includes a silica crucible, and developments in the HEM process are presented. A new machine for slicing with wire was designed and fabricated. The high-speed slicer has been used to slice 19 wafers per cm from 10 cm diameter crystals. Both HEM and FAST are low-cost processes and they have the potential of giving one of the lowest add-on costs ($6.24 and $6.48 per square meter of sheet respectively, with the combination add-on cost of $14.87 per square meter) of this conversion.

Khattak, C. P.↗
NASA NTRS1981

Relationship between energetic particles and plasmas in the distant plasma sheet

Measurements of ions from three different instruments on the IMP-7 and 8 spacecraft are combined to yield the differential energy spectra of ions over the entire energy range of 100 eV to 4 MeV in the earth's distant (30 to 40 earth radii) plasma sheet. These spectra, obtained during times of relatively small bulk flow velocities, span the intensity range from 10 to the -5th to 10 to the 5th per sq cm-sec-sr-keV, varying smoothly over the entire energy range both when the plasma is cold (about 1 keV) and hot (about 9 keV). Overall, the shape of the spectrum resembles a Maxwellian but with a high energy (not less than 50 keV) tail described well by a power law. The high energy tail is displaced in a parallel fashion to higher or lower intensities when the plasma is hot or cold, respectively. It is found that the energetic particle populations in the plasma sheet appear to be directly related to the mean thermal energies of the corresponding plasmas.

Sarris, E. T.↗
NASA NTRS1981

Earthward transport of energetic protons in the earth's plasma sheet

An analysis is made to assess the transport of energetic protons (0.29-0.50 MeV) at downstream distances of 30-45 earth radii in the earth's plasma sheet surveyed by the IMP 7 and IMP 8 spacecraft. It is found that there is a net earthward transport of these particles, although tailward streaming is observed as frequently as earthward streaming. The averaged flux is 200 per sq cm s in this energy range and the total flux over the plasma sheet region is 4 x 10 to the 22nd per s. It is suggested that this net earthward flux of energetic protons may contribute to the population of the outer radiation belt.

Lui, A. T. Y.↗
NASA NTRS1981

A class of analytic solutions for the thermally balanced magnetostatic prominence sheet

A theoretical study is presented for the nonlinear interplay between magnetostatic equilibrium and energy balance in a Kippenhahn-Schlueter type solar prominence sheet. A class of theoretical models is presented, expressed in closed analytic forms, thus facilitating the direct illustration of the nonlinear physical properties. The model couples the equilibrium between magnetic field, plasma pressure, and weight on the one hand, with the balance between a rho-squared T radiative loss, a rho wave heating (where rho equals plasma density, and T equals plasma temperature), and thermal conduction channeled along magnetic field lines on the other. The steady solutions are divided into three classes, and are characterized by the total wave heating in the prominence sheet which is greater than, equal to, or less than the total radiative loss. The compaction of the plasma along the field lines, under its own weight, and the energy transport effects determine which of the three basic behaviors obtains in a particular situation. A discussion is presented of the implications of the steady solutions for the formation of prominences.

Low, B. C.↗
NASA NTRS1981

Rapid solution casting under vacuum of very thick sheets of a segmented polyurethane elastomer

A technique has been developed for rapidly casting from solution under vacuum smooth, bubble-free, clear-white and uniformly thick (about 0.20 cm) sheets of a segmented polyurethane elastomer. The casting is carried out from dimethylformamide solutions inside temperature-controlled air-circulated ovens in order to minimize the establishment of thermal gradients throughout the casting solution. The technique produces quality sheets in 9 days, compared with 40-45 days for an inferior film produced in open pans.

Cuddihy, E. F.↗
NASA NTRS1980

Thermomechanical processing of Haynes alloy No. 188 sheet to improve creep strength

A study has been carried out with the objective of improving the low-strain creep strength of thin gauge (0.38 mm) sheet of Haynes alloy No. 188, a candidate material for the heat shields of advanced reentry and hypersonic vehicles. It is found that significant improvements in the low-strain creep strength are obtained in sheets with a strong recrystallized texture produced by a thermomechanical treatment. The optimum results are achieved after 80% final coldwork followed by a 10-min anneal at 1505 K.

Klarstrom, D. L.↗
NASA NTRS1983

Silicon Sheet Quality is Improved By Meniscus Control

Better quality silicon crystals for solar cells are possible with instrument that monitors position of meniscus as sheet of solid silicon is drawn from melt. Using information on meniscus height, instrument generates feedback signal to control melt temperature. Automatic control ensures more uniform silicon sheets.

Yates, D. A.↗