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At least 1,135 records · Page 63
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NASA NTRS1979

Decay of the zincate concentration gradient at an alkaline zinc cathode after charging

The study was carried out by observing the decay of the zincate concentration gradient at a horizontal zinc cathode after charging. This decay was found to approximate first order kinetics as expected from a proposed boundary layer model. The decay half life was shown to be a linear function of the thickness of porous zinc deposit on the cathode indicating a very rapid transport of zincate through porous zinc metal. The rapid transport is attributed to an electrochemical mechanism. The data also indicated a relatively sharp transition between the diffusion and convection transport regions. The diffusion of zincate ion through asbestos submerged in alkaline electrolyte was shown to be comparable with that predicted from the bulk diffusion coefficient of the zincate ion in alkali.

Kautz, H. E.↗
NASA NTRS1979

On the inference of properties of Saturn's Ring E from energetic charged particle observations

The paper demonstrates that information about Saturn's Ring E particle size is potentially obtainable from observations of Saturnian trapped radiation. It is shown that observations of the radial dependence of the intensities, energy spectra, electron-to-proton intensity ratio, and pitch angle distributions of energetic charged particles trapped outside of Ring A can potentially provide information (1) on the existence of Ring E, (2) on the effective size of the particulate matter therein, and (3) on the magnitude of the radial diffusion coefficient for energetic particles. A parametric study of these possibilities is specialized to the characteristics of the University of Iowa detectors on Pioneer 11 which was scheduled to make a close encounter with Saturn in 1979.

Thomsen, M. F.↗
NASA NTRS1980

Saturnian trapped radiation and its absorption by satellites and rings - The first results from Pioneer 11

Preliminary results from Pioneer 11 concerning the acceleration and trapping of charged particles in the magnetic field of Saturn are reported. The identification and measurement of the intensities and spectra of charged particle species was performed by an experiment including four charged particle sensor systems, within 20 Saturn radii of the planet. Increases in the intensity of 0.5- to 1.8-MeV protons within 15 Saturn radii indicate the trapping and acceleration of particles in the dipole field region, while a decrease in proton intensity between seven and four Saturn radii is attributed to absorption by Dione and Enceladus and possibly ring material as well. Proton and electron intensity distributions are found to be axially symmetric within four Saturn radii, indicating a centered dipole aligned with the planetary rotation axis. Trapped radiation absorption at the orbit of Mimas is analyzed to obtain an upper limit of 4 x 10 to the -8th Saturn radii-squared/sec to the inward diffusion coefficient; an absorption-like feature observed at L = 2.5 is attributed to a previously unidentified satellite of diameter less than 200 km and semimajor axis 2.51 Saturn radii. Radiation absorption by the newly discovered F ring was also observed, however beneath the A, B and C rings a low flux of high-energy electrons was detected.

Simpson, J. A.↗
NASA NTRS1980

Thermal diffusion calculations for the ionosphere of Venus

Simplified multicomponent diffusion calculations are made for the ionosphere of Venus. Large differences in temperature between electrons and ions and appreciable temperature gradients that are near those of recent measurements are used. Compositions for which binary thermal diffusion coefficients for ions are the same as multi-ion ones are examined as well as those that are quite different. An attempt to combine binary coefficients to give multi-ions ones has not been particularly successful.

Nakada, M. P.↗
NASA NTRS1980

The effect of injection location on the spectrum of energetic magnetospheric particles

The role of local particle injections and accelerations in determining energetic particle spectra used as an indication of the radial diffusion of trapped magnetospheric particles is assessed. An idealized one-dimensional steady-state model of magnetospheric radial transport in which diffusion is balanced against particle sources and sinks is used to illustrate the effects of particle injection at a point and over a band of radii in which the observation point is immersed in particle spectra. For an injection spectrum uniformly distributed in space and a step function in energy, it is shown that the energy dependence of the measured spectrum is determined not only by adiabatic energization of the input spectrum but by the spatial structure of the injection and the radial dependence of the diffusion coefficient as well. The relevance of the results for observations of particle spectra in the terrestrial and Jovian magnetospheres is also considered

Birmingham, T. J.↗
NASA NTRS1980

Nitric oxide delta band absorption measurements in the lower thermosphere

The first successful measurements of nitric oxide band absorption in the earth's atmosphere have been made by using the high-resolution ultraviolet spectrometers on OSO 8. These measurements were conducted between January and August 1977 and between 30 deg north and south latitudes. The nitric oxide absorption data, at the (1,0) delta band wavelength of 1829.41 A, are numerically inverted to produce nitric oxide density profiles between 85 and 145 km. The major finding of the observations is that for altitudes below 95 km there is more nitric oxide at sunrise than at sunset. A numerical model, incorporating time-dependent ionospheric chemistry and vertical diffusive transport (both eddy and molecular), is used to simulate the OSO 8 nitric oxide profiles. The peak of the model sunset profile lies at 95-km altitude, in agreement with observation, if the vertical component of the eddy diffusion coefficient is 10 million sq cm/s near 100 km.

Massie, S. T.↗
NASA NTRS1980

The vertical distribution of tropospheric ammonia

A one-dimensional tropospheric photochemical model is used to simulate measured profiles of NH3 obtained with the Infrared Heterodyne Radiometer. The relative roles of homogeneous loss, heterogeneous loss, and vertical eddy transport are discussed in terms of selecting parameters which best fit the measurements. The best fit was obtained for a vertical eddy diffusion coefficient of 200,000/sq cm per sec or greater (corresponding to a characteristic vertical transport time in excess of about 35 days), and a characteristic heterogeneous loss time in excess of 10 days. The characteristic homogeneous chemical loss time was found to be about 40 days at the surface and decreased to about 180 days at 10 km, and not very sensitive to model chemical perturbations. Increased ground-level concentrations of NH3 to about 10 ppb, compared to background surface concentrations of about 1 ppb, were measured several weeks after application of ammonium nitrate fertilizer. This suggests that the volatilization of ammonium nitrate fertilizer is rapid, and an important source of NH3. Because of the characteristic times for the loss mechanisms, synoptic time-scale phenomena may play an important role in determining the tropospheric distribution of NH3 concentrations.

Levine, J. S.↗
NASA NTRS1980

Energetics and thermal structure of the middle atmosphere

A study of a large number of temperature measurements in the middle atmosphere shows a much more complex thermal structure of this region than described in the U.S. Standard Atmosphere, 1976. The mesopause height which is generally assumed to be at 80 km varies between 70 and 100 km, often with two minima in temperature at about 70 and 100 km and a maximum between 80-85 km. By solving the energy balance equation and the equations of continuity, the physical significance of the observed thermal structure is discussed in terms of the energetics of the various regions of the middle atmosphere. It is show that the solar UV radiation plays a major role only in the energy budget of the stratosphere and the lower thermosphere. The energetics of the mesosphere is primarily influenced by the dissipation of eddy energy. The temperature in the region is a good indicator of the eddy diffusivity and can be used in deriving the eddy diffusion coefficient.

Chandra, S.↗
NASA NTRS1980

The dynamic F2-layer over Arecibo

The idealized 'servo' model of the ionospheric F2-layer of Rishbeth et al. (1978) is used to simulate the observed behavior of the daytime Fe-peak at Arecibo at sunspot minimum. The meridional pressure-gradient force associated with the meridional neutral-air wind is determined empirically. The local time variation during the day is found to be consistent with the semidiurnal variation given by the MSIS atmospheric model of Hedin et al. (1977). The values of the F2-layer loss and diffusion coefficients needed to match the data are broadly consistent with the MSIS model.

Ganguly, S.↗
NASA NTRS1980

Conditions for acceleration of energetic ions greater than 30 keV associated with the earth's bow shock

A statistical analysis of particles (greater than 30 keV/charge) upstream of the earth's bow shock is conducted and shows that the rate of occurrence of upstream particle events is relative to the angle between the magnetic field and the shock normal at the shock intersection point as well as relative to the angle between the magnetic field and the radial direction (i.e., the sun-earth line). In addition, the occurrence rate of upstream particle events relative to the bow shock connection time of a field line convected with the solar wind is presented for a model bow shock. A linear dependence of the diffusion coefficient on energy per charge is apparent with the value of the mean free path of a 30-keV proton found to be about 4 earth radii, and the free escape boundary to be at about 30 earth radii in front of the bow shock.

Scholer, M.↗
NASA NTRS1980

Float zone experiments

The objectives of this work are: to determine if surface tension-driven convection in float zone experiments may be controlled by means of surface films; and if convection can be controlled, determine whether homogeneous solute distributions will be achieved in float zone solidification and whether accurate measurements of liquid diffusion coefficients may be obtained from float zone solidification experiments. Sn was chosen as a model material because it is a group IV element, chemically similar to Si and Ge and its low melting point and low vapor pressure allow Auger spectroscopy to be employed with liquid samples.

Verhoeven, J.↗
NASA NTRS1980

The energetic charged particle absorption signature of Mimas

In the present paper, the average long-term effect of Saturn's satellite Mimas on the distribution of trapped radiation (macrosignature) is examined, along with a microsignature of satellite absorption, specifically, a brief dip in charged particle intensities observed on the inbound pass of Pioneer 11 as it passed through the orbital range of Mimas. It is hypothesized that it is indeed the shadow of Mimas, in the sense that the observations reveal the effect of this satellite on a distribution of particles which interacted with it in the recent past and then drifted in longitude to the observational location. The hypothesis led to a characterization of the electron energy spectrum in Saturn's inner magnetosphere and to an estimate of the radial diffusion coefficient for such electrons.

Van Allen, J. A.↗
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 NTRS1980

Lyman-alpha observations in the vicinity of Saturn with Copernicus

For the first time, high-resolution Ly-alpha observations of the Saturn vicinity were completed with the Princeton spectrometer on board the Copernicus satellite. They showed that near a minimum solar activity the emissions related to several sources are 250 + or - 50 rayleighs for the interplanetary medium in a near-downwind direction, less than 100 rayleighs for the rings, 200 + or - 100 rayleighs for a torus linked to the Titan orbit, and 1400 + or - 450 rayleighs for the disk of Saturn. These results induce some constraints through the corresponding theoretical evaluations: the B ring as the primary source of the atoms for the ring emissions; an efficient production mechanism for hydrogen atoms in the Titan torus; and a slightly larger eddy diffusion coefficient in the Saturn atmosphere than in the Jupiter atmosphere near solar minimum.

Barker, E.↗
NASA NTRS1981

Transport properties associated with entry into the atmosphere of Titan

In this paper the transport properties in the atmosphere of Titan and at the shock front and the probe surface for non-ablative entry into Titan's atmosphere are calculated, using the kinetic theory of gases. The species N2, H2, CH4, HCN, N, and H contribute to the transport properties under these conditions. The transport properties were calculated by using accurate potential energy curves for each of the thirteen two-body interactions which occur between these species. Results are given for the binary diffusion coefficients, the non-reactive and reactive thermal conductivity, and the viscosity from 1000 K to 8000 K. This information is needed for calculating flowfield properties and surface heating rates. The most important conclusions are that the non-reactive thermal conductivity is much larger behind the shock layer than it is in the ambient atmosphere and that the nonreactive thermal conductivity appears to be nearly constant in the shock layer.

Flori, B.↗
NASA NTRS1980

A physical model of Titan's clouds

A physical model of the formation and growth of aerosols in the atmosphere of Titan has been constructed in light of the observed correlation between variations in Titan's albedo and the sunspot cycle. The model was developed to fit spectral observations of deep methane bands, pressures, temperature distributions, and cloud structure, and is based on a one-dimensional physical-chemical model developed to simulate the earth's stratospheric aerosol layer. Sensitivity tests reveal the model parameters to be relatively insensitive to particle shape but sensitive to particle density, with high particle densities requiring larger aerosol mass production rates to produce compatible clouds. Solution of the aerosol continuity equations for particles of sizes 13 A to about 3 microns indicates the importance of a warm upper atmosphere and a high-altitude mass injection layer, and the production of aerosols at very low aerosol optical depths. Limits are obtained for the chemical production of aerosol mass and the eddy diffusion coefficient, and it is found that an increase in mass input causes a decrease in mean particle size.

Toon, O. B.↗
NASA NTRS1980

Time correlation functions in classical dense fluids

The velocity autocorrelation functions and memory functions of dense classical fluids may be directly obtained from the static radial distribution function g(r) in an approximate way. Following the Mori projection operator formalism, the memory functions may be related to the fluctuating force correlation. At low densities, these functions may be evaluated by following the trajectories of particle pairs in the interatomic potential. At higher densities, the force correlation functions can be evaluated approximately from particle pair trajectories via the potential of the mean force. The results for argon fluids at various densities and temperatures agree satisfactorily with the molecular dynamics and the Enskog values. The decrease of the diffusion coefficient with density is partly due to the nature of g(r) which reflects the stronger clustering of atoms at higher densities.

Tsang, T.↗
NASA NTRS1981

Stratospheric hydroxyl radical concentrations - New limitations suggested by observations of gaseous and particulate sulfur

A one-dimensional aerosol model is employed in investigating the sensitivity of the stratospheric distributions of gaseous sulfur compounds and sulfate aerosol particles to changes in OH and CS2 concentrations, in eddy diffusion coefficients, and in important chemical rate constants. By comparing model predictions with recent observational data for SO2, OCS, and particulates, it is found that, with regard to atmospheric sulfur, CS2 is only a secondary source of sulfur for the stratosphere relative to OCS and that background tropospheric CS2 concentrations by volume are likely to be less than 70 parts per trillion. It is also established that under stratospheric conditions the rate coefficients for the reactions of OH with OCS and CS2 may be substantially smaller than the room temperature laboratory values of Kurylo (1978).

Turco, R. P.↗