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At least 883 records · Page 49
All sourcesNASA NTRSDOE OSTI
NASA NTRS1974

Approach to the origin of turbulence on the basis of two-point kinetic theory

Equations for the fluctuation correlation in an incompressible shear flow are derived on the basis of kinetic theory, utilizing the two-point distribution function which obeys the BBGKY hierarchy equation truncated with the hypothesis of 'ternary' molecular chaos. The step from the molecular to the hydrodynamic description is accomplished by a moment expansion which is a two-point version of the thirteen-moment method, and which leads to a series of correlation equations, viz., the two-point counterparts of the continuity equation, the Navier-Stokes equation, etc. For almost parallel shearing flows the two-point equation is separable and reduces to two Orr-Sommerfeld equations with different physical implications.

Tsuge, S.↗
NASA NTRS1974

Anisotropies of galactic cosmic rays outside the orbit of earth measured on Pioneer 10

Preliminary results of observations of the directional distribution of cosmic rays being conducted by the University of Chicago experiment on the Pioneer 10 spacecraft are presented. The unusual geometry of the directional scan is described and some features of the response of a bidirectional coincidence telescope are discussed. Selected periods free from the presence of low-energy solar particles exhibit transient deviations from uniform directional distributions for the bidirectional flux of nuclei greater than 67 MeV/nucleon. These deviations are typically 2 to 4 (plus or minus 1) percent and are oriented very roughly in a N-S direction. Such nonuniformities observed with a bidirectional detector can only be due to even order terms in the angular distribution function.

Lentz, G. A.↗
NASA NTRS1974

Coherent propagation of charged-particle bunches in random magnetic fields

When the distribution function for energetic particles moving in interplanetary space is expressed in terms of eigenfunctions of an operator which describes pitch-angle scattering by random magnetic fields, the familiar phenomenon of diffusion is the dominant solution of the transport equations provided that the spectrum of magnetic fluctuations is not too steep. However, if the power-versus-wavenumber spectrum of the random fields has a spectral index greater than 2, the dominant solution of the same equations is a qualitatively different mode of transport in which density inhomogeneities propagate coherently along the guiding field with a characteristic velocity equal to half the particle speed. The present work, which extends classical transport theory to give a detailed treatment of the new mode, presents explicit formulae which describe the spatial and temporal structure of the coherent disturbance. It is shown that this disturbance evolves asymptotically into a moving Gaussian pulse whose width increases with time.

Earl, J. A.↗
NASA NTRS1974

Transport coefficients of gaseous ions in an electric field

A general theory of ion mobility formulated by Kihara (1953) is extended to ion diffusion and to mixtures of neutral gases. The theory assumes that only binary collisions between ions and neutral particles need to be taken into account and that the velocity distribution function of the neutral particles is Maxwellian. These assumptions make it possible to use a linearized Boltzmann equation. Questions of mobility are considered along with aspects of diffusion and deviations from Fick's law of diffusion.

Whealton, J. H.↗
NASA NTRS1974

Statistical properties of interstellar clouds

Scans of the interstellar 7699-A line of K I in the spectra of 26 stars show that the K I lines are highly appropriate for a study of the local statistical distributions of several observable properties of interstellar clouds and, in principle, of the intercloud medium. A description is presented of the distribution functions obtained from the currently available sample of 37 interstellar clouds, measured toward 17 stars. It is pointed out that a very considerable expansion of this sample should be possible in the immediate future.

Hobbs, L. M.↗
NASA NTRS1974

Current constraints on hidden mass in the Coma Cluster

Various possible means of accounting for the dynamical mass of the Coma Cluster are reviewed. We intentionally choose to emphasize conventional forms of hidden mass, specifically gas and low-luminosity stars, while adopting conventional mass-to-luminosity ratios for the observed luminous material in galaxies. We have attempted to combine all previous work relating to assumed gas parameters in order to examine precisely what constraints current observations, together with theoretical and observational upper limits, place on any gas in the Coma Cluster. In particular, we make use of a density distribution function that is consistent with the dynamical data and express all constraints in a manner which explicitly displays their dependence on Hubble constant, current observational flux levels, distance from the dynamical center of the cluster, and the mass of gas postulated.

Tarter, J.↗
NASA NTRS1974

Termination of the solar wind in the hot, partially ionized interstellar medium

Theoretical foundations for understanding the problem of the termination of the solar wind are reexamined in the light of most recent findings concerning the states of the solar wind and the local interstellar medium. The investigation suggests that a simple extention of Parker's (1961) analytical model provides a useful approximate description of the combined solar wind, interstellar wind plasma flowfield under conditions presently thought to occur. A linear perturbation solution exhibiting both the effects of photoionization and charge exchange is obtained for the supersonic solar wind. A numerical algorithm is described for computing moments of the non-equilibrium hydrogen distribution function and associated source terms for the MHD equations. Computed using the algorithm in conjunction with the extended Parker solution to approximate the plasma flowfield, profiles of hydrogen number density are given in the solar wind along the upstream and downstream axes of flow with respect to the direction of the interstellar wind. Predictions of solar Lyman-alpha backscatter intensities to be observed at 1 a.u. have been computed, in turn, from a set of such hydrogen number density profiles varied over assumed conditions of the interstellar wind.

Lombard, C. K.↗
NASA NTRS1975

Thermodynamics and phase separation of dense fully-ionized hydrogen-helium fluid mixtures

The free energy of a hydrogen-helium fluid mixture is evaluated for the temperatures and densities appropriate to the deep interior of a giant planet such as Jupiter. The electrons are assumed to be fully pressure-ionized and degenerate. In this regime, an appropriate first approximation to the ionic distribution functions can be found by assuming hard sphere interactions. Corrections to this approximation are incorporated by means of the perturbation theory of Anderson and Chandler. Approximations for the three-body interactions and the nonlinear response of the electron gas to the ions are included. It is predicted that a hydrogen-helium mixture, containing 10% by number of helium ions, separates into hydrogen-rich and helium-rich phases below about 8000 K, at the pressures relevant to Jupiter (4-40 Megabars). It is also predicted that the alloy occupies less volume per ion than the separated phases. The equations of state and other thermodynamic derivatives are tabulated. Implications of these results are discussed.

Stevenson, D. J.↗
NASA NTRS1974

Estimations of the smoothing operator response characteristics

The mean response characteristic of the graphical smoothing method is discussed. The method is illustrated by analysis of latitude observations at Washington from 1915.9 to 1941.0. Spectral density, frequency distribution, and distribution functions are also discussed.

Yatskiv, Y. S.↗
NASA NTRS1975

Treatment of atomic and molecular line blanketing by opacity sampling

An opacity sampling (OS) technique for treating the radiative opacity of large numbers of atomic and molecular lines in cool stellar atmospheres is presented. Tests were conducted and results show that the structure of atmospheric models is accurately fixed by the use of 1000 frequency points, and 500 frequency points is often adequate. The effects of atomic and molecular lines are separately studied. A test model computed by using the OS method agrees very well with a model having identical atmospheric parameters computed by the giant line (opacity distribution function) method.

Johnson, H. R.↗
NASA NTRS1975

When is quasi-linear theory exact

We use the cumulant expansion technique of Kubo (1962, 1963) to derive an integrodifferential equation for the average one-particle distribution function for particles being accelerated by electric and magnetic fluctuations of a general nature. For a very restricted class of fluctuations, the equation for this function degenerates exactly to a differential equation of Fokker-Planck type. Quasi-linear theory, including the adiabatic assumption, is an exact theory only for this limited class of fluctuations.

Jones, F. C.↗
NASA NTRS1975

The ground state properties of spin-aligned atomic hydrogen, deuterium, and tritium

The internal energy, pressure, and compressibility of ground-state, spin-aligned atomic hydrogen, deuterium, and tritium are calculated assuming that all pair interactions occur via the atomic triplet (spin-aligned) potential. The conditions required to obtain atomic hydrogen and its isotopes in bulk are discussed; such a development would be of value in propulsion systems because of the light mass and energetic recombination of atomic hydrogen. Results show that atomic triplet hydrogen and deuterium remain gaseous at 0 K, and that tritium forms a liquid with a binding energy of approximately -0.75 K per atom at a molar volume of 130 cu cm per mole. The pair distribution function for these systems is calculated, and the predicted superfluid behavior of atomic triplet hydrogen and tritium is briefly discussed.

Etters, R. D.↗
NASA NTRS1974

Observation of a driver gas-tangential discontinuity

A complete analysis of an interplanetary disturbance of Nov. 19, 1970 using the Apollo 12-SIDE (Suprathermal Ion Detector Experiment) is presented. The SIDE detectors were pointing at 26.3 degrees from the normal solar-wind direction during the observations. The data were least-squares fitted (using a parabolic hypersurface approximation) to a convected Maxwell-Boltzmann distribution function. The results of the fit combined with two other experiments showed a drastic change in the wind speed (from an steady 352 km/sec down to 219 km/sec), direction, and temperature. Except for a delta-function increase at the onset, the density remained constant. There was a considerable enhancement in the abundance of He and probably of heavier elements. The interplanetary magnetic field exhibited a jump of 21 gamma with a change in latitude from -56 to -76 degrees in solar ecliptic coordinates. It is concluded that the disturbance was due to the driver gas-tangential discontinuity of a solar flare-induced shock wave. The characteristic of the tangential discontinuity fit well with theoretical prediction.

Medrano, R. A.↗
NASA NTRS1974

Critical point parameters of helium

Calculations of the critical point parameters of the helium isotopes using integral equation closures for the pair distribution function are reported for two pair potentials.

Bruch, L. W.↗
NASA NTRS1975

Current-driven plasma instabilities at high latitudes

Earlier Ogo 5 discussions of high-latitude magnetospheric wave-particle interaction phenomena associated with field aligned current systems are extended by considering some September 7, 1968, out-bound measurements and corresponding March 11, 1969, observations, when the spacecraft was traversing auroral L shells in midafternoon. It is shown that during moderate magnetospheric disturbances the most intense waves and currents were detected near sharp boundaries in the density of polar cleft electrons, and it is possible that local wave-particle interactions produced anomalous resistivity. Some observed changes in the electron distribution functions might be explained in terms of local acceleration, but significant causal questions about the dynamics remain open if one can use only local data from a single spacecraft in this region.

Scarf, F. L.↗
NASA NTRS1974

Thermal histories and crystal distributions in partly devitrified lunar glasses cooled by radiation

Calculations of the expected crystallization behavior of selected lunar compositions (60095 and 14259) are presented. Knowledge of this behavior combined with measurements of the state of crystallinity in partially devitrified lunar samples permits the determination of the thermal history of the samples. The state of crystallinity of a specimen is described by a statistical crystal distribution function psi. The heat flow problems of a plate of opaque glass quenched on an aluminum block and of a semi-transparent glass sphere cooling by radiation are analyzed. The results are combined with laboratory measurements of the crystal growth velocity and the viscosity, and with theoretical expressions for the nucleation frequency (homogeneous and heterogeneous) to obtain psi. It is found that the calculated psi is much too large in comparison with laboratory experiments on lunar samples. Possible reasons for the discrepancy are discussed, and the most likely cause is that the assumed nucleation barrier is too small. It also appears likely that these materials have relatively few nucleating heterogeneities.

Hopper, R. W.↗
NASA NTRS1975

Distribution and moments of radial error

An investigation of the moments and probability distribution of the resultant of two normally distributed random variables is presented. This is the so-called generalized Rayleigh distribution which has many applications in the study of wind shear, random noise, and radar. The most general formula was derived, and two special cases were considered for which tables of the moments and probability distribution functions are included as an appendix. One of the special cases was generalized to n-dimensions.

White, R. G.↗