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NASA NTRS1975

Elemental composition and size distribution of particulates in Cleveland, Ohio

Measurements were made of the elemental particle size distribution at five contrasting urban environments with different source-type distributions in Cleveland, Ohio. Air quality conditions ranged from normal to air pollution alert levels. A parallel network of high-volume cascade impactors (5-state) were used for simultaneous sampling on glass fiber surfaces for mass determinations and on Whatman-41 surfaces for elemental analysis by neutron activation for 25 elements. The elemental data are assessed in terms of distribution functions and interrelationships and are compared between locations as a function of resultant wind direction in an attempt to relate the findings to sources.

King, R. B.↗

NASA NTRS1976

A study of turbulent flow between parallel plates by a statistical method

Turbulent Couette flow between parallel plates was studied from a statistical mechanics approach utilizing a model equation, similar to the Boltzmann equation of kinetic theory, which was proposed by Lundgren from the velocity distribution of fluid elements. Solutions to this equation are obtained numerically, employing the discrete ordinate method and finite differences. Two types of boundary conditions on the distribution function are considered, and the results of the calculations are compared to available experimental data. The research establishes that Lundgren's equation provides a very good description of turbulence for the flow situation considered and that it offers an analytical tool for further study of more complex turbulent flows. The present work also indicates that modelling of the boundary conditions is an area where further study is required.

Srinivasan, R.↗

NASA NTRS1975

Wave theory of turbulence in compressible media

An acoustical theory of turbulence was developed to aid in the study of the generation of sound in turbulent flows. The statistical framework adopted is a quantum-like wave dynamical formulation in terms of complex distribution functions. This formulation results in nonlinear diffusion-type transport equations for the probability densities of the five modes of wave propagation: two vorticity modes, one entropy mode, and two acoustic modes. This system of nonlinear equations is closed and complete. The technique of analysis was chosen such that direct applications to practical problems can be obtained with relative ease.

Kentzer, C. P.↗

NASA NTRS1976

Digital processing of satellite imagery application to jungle areas of Peru

The author has identified the following significant results. The use of clustering methods permits the development of relatively fast classification algorithms that could be implemented in an inexpensive computer system with limited amount of memory. Analysis of CCTs using these techniques can provide a great deal of detail permitting the use of the maximum resolution of LANDSAT imagery. Potential cases were detected in which the use of other techniques for classification using a Gaussian approximation for the distribution functions can be used with advantage. For jungle areas, channels 5 and 7 can provide enough information to delineate drainage patterns, swamp and wet areas, and make a reasonable broad classification of forest types.

Pomalaza, J. C.↗

NASA NTRS1975

Experimental observation of the ion-ion beam instability in a cylindrical geometry

The ion-ion beam instability is investigated in a cylindrical geometry. In the presence of a cylindrically symmetric ion beam a coherent ion-ion beam instability is observed for a well-defined range of beam velocity. This instability gives rise to cylindrical standing waves whose frequency depends upon beam velocity. The beam distribution function is measured to be a ring in velocity space. The dispersion relation appropriate for the cylindrical standing waves is solved numerically and is shown to be in good agreement with the experimentally observed instability.

Romesser, T.↗

NASA NTRS1975

A grid of model atmospheres for metal-deficient giant stars. I

A grid of flux-constant model atmospheres for stars with effective temperatures between 3750 and 6000 K, log g between 0.75 and 3.0, and (A/H) between -3.0 and 0.0 has been constructed. The line absorption is approximated by opacity distribution functions. Metal lines and molecular lines, including those from the infrared bands of CO and CN, are taken into account. The variation of the structure of the models with metal abundance and microturbulence parameter is found to be quite regular and not very drastic. The surface cooling produced by CO is important for all the models with a maximum temperature of 5000 K, while CN mainly causes a backwarming effect but is not very important for solar CNO abundances. The effects of convection, estimated by using the mixing-length approximation, are important only for the coldest models. The models compare very well with models from overlapping regions of other grids. A solar model consistent with the grid models is found to agree satisfactorily with empirical solar model atmospheres. The careful use of scaled solar models for stars with (A/H) approximately equal to zero is justified.

Gustafsson, B.↗

NASA NTRS1975

On the alleged collisional origin of the Kirkwood Gaps

This paper examines two proposed mechanisms whereby asteroidal collisions and close approaches may have given rise to the Kirkwood Gaps. The first hypothesis is that asteroids in near-resonant orbits have markedly increased collision probabilities and so are preferentially destroyed, or suffer decay in population density, within the resonance zones. A simple order-of-magnitude analysis shows that this hypothesis is untenable since it leads to conclusions which are either unrealistic or not in accord with present understanding of asteroidal physics. The second hypothesis is the Brouwer-Jefferys theory that collisions would smooth an asteroidal distribution function, as a function of Jacobi constant, thus forming resonance gaps. This hypothesis is examined by direct numerical integration of 50 asteroid orbits near the 2:1 resonance, with collisions simulated by random variables. No tendency to form a gap was observed.

Heppenheimer, T. A.↗

NASA NTRS1975

Elemental composition and size distribution of particulates in Cleveland, Ohio

Measurements have been made of the elemental particle size distribution at five contrasting urban environments with different source-type distributions in Cleveland, Ohio. Air quality conditions ranged from normal to air pollution alert levels. A parallel network of high-volume cascade impactors (5-stage) were used for simultaneous sampling on glass fiber surfaces for mass determinations and on Whatman-41 surfaces for elemental analysis by neutron activation for 25 elements. The elemental data are assessed in terms of distribution functions and interrelationships and are compared between locations as a function of resultant wind direction in an attempt to relate the findings to sources.

Leibecki, H. F.↗

NASA NTRS1976

Energetic electrons in the Jovian magnetosphere

Results are reported for a detailed analysis of Pioneer 10 data on energetic particle species in the magnetodisk region of Jupiter's magnetosphere. It is shown that the observed counting rates in the magnetodisk (beyond 20 Jupiter radii) were caused primarily by electrons with energies exceeding 0.06 MeV. Absolute omnidirectional electron intensities in the magnetodisk are presented for five integral energy ranges, and a model electron differential energy spectrum is found to fit the intensities throughout most of the encounter trajectory. It is suggested that the observed spectral shape results from losses of high-energy electrons by pitch-angle scattering. Observed equatorial energy spectra are used to compute distribution functions for several values of the first adiabatic invariant, mu. The radial profiles of the functions are found to have maxima at about 50 Jupiter radii inbound as well as at about 90 radii outbound and to diminish strongly for lesser radii. The large decreases in density are shown to require strong losses, and resonant electron whistler-mode pitch-angle scattering is suggested as a loss mechanism.

Baker, D. N.↗

NASA NTRS1975

An examination of the adiabatic approximation in cosmic ray propagation theory

A theory for the pitch-angle scattering of cosmic rays in a turbulent magnetic field can be derived from first principles by applying both the quasi-linear and adiabatic approximations to the master equation for the ensemble averaged distribution function. A proof of the failure of these approximations, taken together, is given. Some predictions of the quasi-linear theory, are given. New wave-like propagation modes have been discovered.

Scudder, J.↗

NASA NTRS1976

Characteristics of auroral electron acceleration regions observed by Atmosphere Explorer C

Satellite measurements of electron precipitation and ion drift velocities showed that electron acceleration regions (or inverted V's) in the 1200 to 1800 MLT quadrant exhibit the following systematic behavior: electron distribution functions in the accelerated region can be well described by Maxwellian primary electron beams accelerated through an electrostatic potential; the typical inverted V latitudinal structure is always observed in the accelerated regions, the electrostatic potential reaching a maximum and consequently decreasing to near zero over distances of 100 to 250 km; the Maxwellian temperature of the primary electron beam increases systematically with increasing electrostatic potential; rather weak acceleration regions, characterized by values of the electrostatic potential below 1 keV and values of the Maxwellian temperature between 100 and 350 eV, occur in the cusp and in the highest-latitude portion of the dusk side electron precipitation zone.

Burch, J. L.↗

NASA NTRS1976

Treatment of atomic and molecular line blanketing by opacity sampling

A sampling technique for treating the radiative opacity of large numbers of atomic and molecular lines in cool stellar atmospheres is subjected to several tests. In this opacity sampling (OS) technique, the global opacity is sampled at only a selected set of frequencies, and at each of these frequencies the total monochromatic opacity is obtained by summing the contribution of every relevant atomic and molecular line. In accord with previous results, we find that the structure of atmospheric models is accurately fixed by the use of 1000 frequency points, and 100 frequency points are adequate for many purposes. The effects of atomic and molecular lines are separately studied. A test model computed using the OS method agrees very well with a model having identical atmospheric parameters, but computed with the giant line (opacity distribution function) method.

Johnson, H. R.↗

NASA NTRS1975

Auroral electron beams near the magnetic equator

Intense beams of electrons traveling parallel to the local magnetic field have been observed at a magnetic latitude of 11 deg and a radial distance of 6.6 earth radii. The distribution function for electrons traveling within 8 deg of the field line direction is typically flat or slightly rising up to a break point beyond which it decreases as inversely as the 5-10th power of v. The energy corresponding to the break point velocity is usually between 0.1 and 10 keV. These beams are found to occur on closed field lines at the inner edge of the plasma sheet and thus at the root of the earth's magnetotail. Beams with break point energies greater than 2 keV seem to occur only within the first 10 minutes after the onset of hot plasma injection associated with a magnetospheric substorm.

Mcilwain, C. E.↗

NASA NTRS1975

Hot plasma dynamics within geostationary altitudes

The reported investigation is based on observations made with the aid of the Explorer 45 satellite. Observations of protons during geomagnetic storms are discussed and attention is given to considerations of energy densities, hot-cold plasma interactions, stable and turbulent regions, the distribution function, charge exchange losses, the formation of stable auroral red arcs, and adiabatic and nonadiabatic responses. The behavior of energetic electrons is considered along with studies of quiet-time conditions and investigations of storm and poststorm behavior.

Williams, D. J.↗

NASA NTRS1975

Characteristics of instabilities in the magnetosphere deduced from wave observations

A general summary is presented of the types of unstable plasma distributions encountered in the magnetosphere. It is shown that gyroresonant interactions play an important role in magnetospheric dynamics. Electrostatic instabilities not driven by currents are considered and a description is presented of observations related to current-driven instabilities. Attention is also given to aspects of mode coupling. It is pointed out that during the last decade much progress has been made in the identification of specific instabilities. Better measurements of magnetospheric plasma distribution functions are needed for the solution of remaining problems.

Scarf, F. L.↗

NASA NTRS1976

Ion cyclotron instability of drifting plasma clouds

The paper is concerned with a quantitative study of the frequency dispersion characteristics of the ion cyclotron mode in a realistic dipole magnetosphere where the particles are allowed to drift azimuthally. The adopted model assumes that the particles are injected at a constant L shell in an extended region around local midnight. A drift-convoluted distribution function is used to study the spatial and temporal characteristics of the ion cyclotron instability. Two cases are examined: one in which the cold plasma density is constant and the other in which the cold particle density is allowed to vary. The resulting growth rates are presented in both the frequency versus coordinate space and the frequency versus time space. Possible inferences regarding wave emissions such as IPDP (intervals of pulsations of diminishing period) events are discussed. It is shown that the frequency dispersive effects can be produced by either the drift effects or changing the cold plasma density.

Lin, C. S.↗

NASA NTRS1976

Radial distribution of meteoric particles in interplanetary space

The heliocentric distribution of meteoric particles in interplanetary space is derived, with consideration of the Poynting-Robertson effect, interparticle collision processes and cometary dust injection. Radial distribution functions were derived for zodiacal dust, radar meteors and the meteoroids of mass 10 to the -9th to about 10 to the -10th g (normalized to 1 AU). The number density was found to depend on particle size.

Rhee, J. W.↗

NASA NTRS1977

Current-limited electron beam injection

The injection of an electron beam into a weakly collisional, magnetized background plasma was investigated experimentally. The injected beam was energetic and cold, the background plasma was initially isothermal. Beam and plasma dimensions were so large that the system was considered unbounded. The temporal and spatial evolution of the beam-plasma system was dominated by collective effects. High-frequency electrostatic instabilities rapidly thermalized the beam and heated the background electrons. The injected beam current was balanced by a return current consisting of background electrons drifting toward the beam source. The drift between electrons and ions gave rise to an ion acoustic instability which developed into strong three-dimensional turbulence. It was shown that the injected beam current was limited by the return current which is approximately given by the electron saturation current. Non-Maxwellian electron distribution functions were observed.

Stenzel, R. L.↗