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At least 1,099 records · Page 61

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NASA NTRS1980

I-Xe age and trapped Xe components of the Murray /C-2/ chondrite

A neutron-irradiated bulk sample of the Murray (C-2) carbonaceous chondrite was etched with H2O2 and then divided into colloidal and non-colloidal fractions. The H2O2 treatment removed about 80% of the trapped Xe and greatly increased variations in the Xe-129/Xe-132 ratio measured in stepwise heating. The colloid showed very little excess Xe-129, but the anti-colloid gave a fairly good I-Xe correlation corresponding to formation 3.7 + or - 2.1 m.y. after Bjurbole. Variations in the trapped Xe component were also observed; most notably the 550 C anti-colloid fraction has large deficiencies relative to AVCC at the heavy isotopes.

Niemeyer, S.↗

NASA NTRS1981

Cost effective flat plate photovoltaic modules using light trapping

Work in optical trapping in 'thick films' is described to form a design guide for photovoltaic engineers. A thick optical film can trap light by diffusive reflection and total internal reflection. Light can be propagated reasonably long distances compared with layer thicknesses by this technique. This makes it possible to conduct light from inter-cell and intra-cell areas now not used in photovoltaic modules onto active cell areas.

Bain, C. N.↗

NASA NTRS1981

Timeline Resource Analysis Program (TRAP): User's manual and program document

The Timeline Resource Analysis Program (TRAP), developed for scheduling and timelining problems, is described. Given an activity network, TRAP generates timeline plots, resource histograms, and tabular summaries of the network, schedules, and resource levels. It is written in ANSI FORTRAN for the Honeywell SIGMA 5 computer and operates in the interactive mode using the TEKTRONIX 4014-1 graphics terminal. The input network file may be a standard SIGMA 5 file or one generated using the Interactive Graphics Design System. The timeline plots can be displayed in two orderings: according to the sequence in which the tasks were read on input, and a waterfall sequence in which the tasks are ordered by start time. The input order is especially meaningful when the network consists of several interacting subnetworks. The waterfall sequence is helpful in assessing the project status at any point in time.

Sessler, J. G.↗

NASA NTRS1980

The trapped radiations of Saturn and their absorption by satellites and rings

The Pioneer 11 encounter with Saturn has revealed the existence of a fully developed magnetosphere with high-energy trapped radiation about Saturn. The present paper gives a detailed summary of the energetic charged particle measurements, including the overall characteristics of the trapped electron, proton, and helium radiation, which was found to lie inside 20 Saturn radii from the planet, and the regions extending outward to beyond the planetary bow shocks and into the interplanetary medium.

Simpson, J. A.↗

NASA NTRS1980

Ultrasonic imaging using trapped energy mode Fresnel lens transducers

Trapped-energy focusing transducers operating in the 2-5 MHz range have been fabricated by plating concentric rings of electrodes on a piezoelectric plate. The concentric ring structure acts as a Fresnel lens and can be used to obtain excellent lateral focusing of ultrasonic waves. The trapping is sufficiently strong to permit optimization of electrode spacings to suppress spurious virtual foci and ring sidelobes.

Das, P.↗

NASA NTRS1982

Magnetopause modeling - Flux transfer events and magnetosheath quasi-trapped distributions

Three-dimensional distribution functions for energetic ions are studied numerically in the magnetosphere, through the magnetopause, and in the magnetosheath using a simple one-dimensional quasi-static model and ISEE 1 magnetopause crossing data for November 10, 1977. Quasi-trapped populations in the magnetosheath observed near flux transfer events (FTEs) are investigated, and it is shown that the population in the sheath appears to sandwich the FTE distributions. These quasi-trapped distributions are due to slow, large pitch angle, outward moving particles left behind by the outward rush of the ions more field-aligned at the time the flux was opened. It is found that sheath convective flows can map along the connected flux tube without drastically changing the distribution function, and results suggest that localized tangential fields above the upper limit may exist.

Speiser, T. W.↗

NASA NTRS1982

Plasma shocks and energetic particles in the outer solar system - Trapping and asymmetry observations from Pioneer 10 and Pioneer 11

The April 15 and 28, 1978 solar flares appear to have 0.5-20 MeV protons trapped between a pair of shocks, and the large count rate enhancement observed, along with large ranges of radial distance and longitudinal angles, imply a prolongation of trapping for a period of weeks. The apparent ability of a shock whose plasma signature is faint to confine MeV protons in the outer solar system may have significant implications for cosmic ray studies. Analytical results also imply significant azimuthal asymmetry in plasma and energetic particle behavior, at distances as far as 16 AU from the sun. Combining these observations provides evidence for unexpectedly complex interactions in the outer solar system between energetic particles and solar wind plasma.

Intriligator, D. S.↗

NASA NTRS1983

Trapped particle absorption by the Ring of Jupiter

The interaction of trapped radiation with the ring of Jupiter is investigated. Because it is an identical problem, the rings of Saturn and Uranus are also examined. Data from the Pioneer II encounter, deductions for some of the properties of the rings of Jupiter and Saturn. Over a dozen Jupiter magnetic field models are available in a program that integrates the adiabatic invariants to compute B and L. This program is to label our UCSD Pioneer II encounter data with the most satisfactory of these models. The expected effects of absorbing material on the trapped radiation are studied to obtain the loss rate as a function of ring properties. Analysis of the particle diffusion problem rounds out the theoretical end of the ring absorption problem. Other projects include identification of decay products for energetic particle albedo off the rings and moons of Saturn and a search for flux transfer events at the Jovian magnetopause.

Fillius, W.↗

NASA NTRS1983

Experimental determination of geomagnetically trapped energetic heavy ion fluxes

The observed spatial, directional and spectral characteristics of geomagnetically trapped heavy ions are reviewed. It is found that ions heavier than protons are significantly abundant in the earth's radiation belts, not only at low (ring-current) energies, but also at multi-MeV energies. Observations both at the geomagnetic equator and at low altitudes on the corresponding L-shell show the important roles played by the heavy ions. The heavy ion-to-proton flux ratio can exceed unity when compared at equal total ion energy. This is particularly the case at several MeV energies and in the outer radiation zone. In contrast, comparisons at equal energy per nucleon generally favor protons. The trapped fluxes of helium ions, of carbon, nitrogen and oxygen (CNO) ions, and of ions heavier than fluorine all exhibit high degrees of pitch angle anisotropy. Many of the observed radiation belt particle distribution characteristics are in agreement with first-order (quiet time) theoretical predictions, although some of the finer details await further research.

Spjeldvik, W. N.↗

NASA NTRS1985

Trapped Xe components in etched samples of the Murray (C2) and Murchison (C2) carbonaceous chondrites

Xe isotopic measurements are described. The samples analyzed were bulk chips of the Murray (C2) and Murchison (C2) carbonaceous chondrites that had been freeze-thaw disaggregated, etched with H2O2, and then split into colloidal and noncolloidal fractions using methanol. The etching removed a substantial portion of the trapped Xe and increased variations in measured isotopic ratios compared with bulk sample analyses. The Murray samples appeared to contain a binary mixture of U-Xe and H+L-Xe. The Murchison data concur with the Murray data for the heavy isotopes, but the structure at the light isotopes is obscured by spallation Xe. There is no evidence in these data for the separability of H-Xe and L-Xe. The fact that H2O2 etching removes Xe without prior demineralization supports the view that the carrier of a substantial portion of trapped Xe may reside on grain surfaces.

Jones, C. M.↗

NASA NTRS1985

Trapped particle absorption by the ring of Jupiter

The ring systems of Jupiter and Saturn, and their interaction with the magnetosphere were studied. Opportunities to improve the understanding of the sweeping effect of orbiting material on trapped radiation, and the use of this process to gain insight on both the trapped radiation and the target material are outlined. Within the cosmogony of Hannes Alfven, this mechanism is also the key to understanding the formation of many of the features of the Saturnian rings. A better understanding of the sweeping effect would also help to clarify this process.

Fillius, W.↗

NASA NTRS1986

The case for a Martian origin of the shergottites. II - Trapped and indigenous gas components in EETA 79001 glass

The isotopic composition of N, Ar, Ne, and He, trapped in an uncrushed sample of the antarctic shergottite EETA 79001, was analyzed by subjecting the evacuated sample to stepped heating in the presence of 100 mtorr of oxygen. The isotopic composition of nitrogen (with the delta-N-15 value of greater than 300 percent) and the elemental ratios Ar-36/N-14 and Ar-40/N-14 were covariant along mixing lines passing through the Martian atmospheric composition. The results of this and previous analyses are consistent with a two-component nitrogen system in which about 84 ppb of trapped Martian atmospheric N is mixed in variable proportions with another, more thermally labile N component during stepped heating. The isotopic Ar-36/Ar-38 ratio of the EETA 79001 is different from that of the earth atmosphere by about 25 percent.

Wiens, R. C.↗

NASA NTRS1987

Hydrogen trapping and the interaction of hydrogen with metals

A method has been developed for the determination of trapped hydrogen in metal alloys, involving the determination of mobile hydrogen using the electrochemical method and the determination of total hydrogen with the fusion method, the difference in hydrogen concentrations being due to trapped hydrogen. It has been found that hydrogen enters body-centered cubic structures through the grain bodies rather than through the grain boundaries. Hydrogen also diffuses much more rapidly in body-centered cubic structures on charging than in face-centered cubic structures, the hydrogen distribution being more uniform in nature. The energy necessary to cause hydrogen embrittlement is postulated to arise from the changes in crystal lattice energies brought about through interaction of hydrogen with atoms in the metal lattice. The total energy change is more negative for body-centered cubic structures, believed to be the cause of a greater tendency toward hydrogen embrittlement. Finally, the agreement of hydrogen concentrations obtained at 25 C by the electrochemical method with those obtained by the fusion method are taken as a strong indication of the power and validity of the electrochemical method.

Danford, Merlin D.↗

NASA NTRS1986

Pionener 11 observations of effects of Ganymede and Callisto on Jupiter's trapped radiation

Charged particle data for low-energy protons and electrons from the Pioneer 11 high-latitude flyby of Jupiter in 1974 are reviewed in the light of the Voyager 1 magnetic field model of Connerney et al. (1981). It is found that if the trajectory of Pioneer 11 is mapped to the equatorial plane along the model magnetic field lines, significant features in the time-intensity profiles of trapped protons and electrons, including one microsignaturelike feature, are found to correspond to shells of closed field lines crossed by the orbits of Ganymede and Callisto. It is suggested that these features are signatures of interaction of the trapped particles with Ganymede and Callisto.

Mckibben, R. B.↗

NASA NTRS1987

Numerical simulations of turbulent trapping in the weak beam-plasma instability

Numerical simulations of the weak beam-plasma instability were done in the turbulent regime where small-scale trapping is a dominant feature of the instability, a regime with behavior not predicted by quasi-linear theory. The results of the simulations were compared with those of a specific model of the turbulence, the so-called 'turbulent trapping' model, which gives precise formulas for the particle correlation functions, and predicts a growth rate well enhanced over the quasi-linear value. It was found that the model gives accurate predictions for the correlation functions. On the other hand, while growth rates were enhanced over the quasi-linear values, the enhancements observed are smaller than expected from the quantitative predictions of the model.

Theilhaber, K.↗

NASA NTRS1989

ECRH of trapped electrons in laboratory magnetoplasmas

Heating of plasma electrons by high power millimeter wave fields at cyclotron harmonic resonance is studied. A mirror field is modeled for the local trapping of electrons. It is shown that superthermal electrons can be generated as the consequence of the ECRH of trapped electrons.

Kuo, S. P.↗

NASA NTRS1990

Linear Ion Trap For Atomic Clock

Linear, radio-frequency ion trap increases frequency stability of atomic frequency standard device. Confines ions with less radio-frequency motion than does point ion trap.

Prestage, John D.↗

NASA NTRS1989

Experimental studies of gas trapping in amorphous ice and thermal modelling of comets: Implications for Rosetta

The trapping of mixtures of CO, CH4, N2 and Ar in amorphous water ice was studied experimentally. It is shown that the ice particles could not have been formed at a higher temperature and, subsequently, cool down. Experiments where ice was deposited at elevated temperatures, then cooled down and gas was flowed into the ice, showed that the amount of trapped gas depends only on the highest temperature at which the ice was formed, or resided, prior to cooling and gas flow into it. Consequently, the cometary ice had to be formed at approx. 48 K and the ice is therefore amorphous. The thermal profile of a comet in Halley's orbit was calculated, including the build-up of an insulating dust layer. It was found that an insulating dust layer a few cm thick is enough to choke most of the water emission from the surface. A similar thermal model was calculated for comet P/Temple-1, a candidate for both CRAF and Rosetta (CNSR) missions. The temperature at a depth of 10 m is approx. 160 K for all models considered and, hence, the ice at this depth is crystalline. A crystalline ice layer 40 to 240 m thick was found to overly the gas-laden amorphous ice. Consequently, it should be difficult for the probes of the two comet missions to sample pristine amorphous ice, unless they are aimed at the bottom of an active crater.

Bar-Nun, Akiva↗