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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 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
NASA NTRS1993

Collision cross sections and diffusion parameters for H and D in atomic oxygen

Modeling the behavior of H and D in planetary exospheres requires detailed knowledge of the differential scattering cross sections for all of the important neutral-neutral and ion-neutral collision processes affecting these species over their entire ranges of interaction energies. In the upper atmospheres of Earth, Venus, and other planets as well, the interactions of H and D with atomic oxygen determine the rates of diffusion of escaping hydrogen isotopes through the thermosphere, the velocity distributions of exospheric atoms that encounter the upper thermosphere, the lifetimes of exospheric orbiters with periapsides near the exobase, and the transfer of momentum in collisions with hot O. The nature of H-O and D-O collisions and the derivation of a data base consisting of phase shifts and the differential, total, and momentum transfer cross sections for these interactions in the energy range 0.001 - 10 eV are discussed. Coefficients of mutual diffusion and thermal diffusion factors are calculated for temperatures of planetary interest.

Hodges, R. R., Jr.↗
NASA NTRS1984

Collision-induced transport processes in planetary rings

The physics of collision-dominated particle disks around planets is analyzed from both the analytical and numerical point of view. The existence of Saturn's ringlet structure is analyzed in terms of a radial instability induced by viscous diffusion. The detailed model described is based on the assumption of uniform particle size. Modifications caused by finite particle size, gravitational effects, and a distribution of particle sizes are discussed.

Stewart, G. R.↗
NASA NTRS1974

Immiscible materials and alloys

Only immiscible materials which involve a fluid phase have a potential advantage when considered for space processing. Processing of such systems at low gravity can lead to a material which is very homogeneous and contains a finely dispersed mixture of phases. Materials with such structures may exhibit potentially useful properties for such applications as superconductors, dispersion-strengthened materials, superplastic materials, permanent magnets, etc. These conclusions have resulted from review of past efforts in the field of low-g processing of materials containing a liquid phase miscibility gap and from present efforts dealing with such systems. These studies have concentrated on precipitation of liquid droplets in a host liquid during cooling through the miscibility gap. This effort has been to study the agglomeration of the droplets both experimentally and through computer simulation in order to understand the mechansism involved and to deduce the effect of gravity on the droplet distribution and resulting structure of the solidified material. The agglomeration mechanisms treated in detail are those due to diffusional growth and collision processes caused by Stokes on convection current-induced droplet migration.

Markworth, A. J.↗
NASA NTRS2003

Laboratory Studies in UV and EUV Solar Physics

The Ion Beam Experiment at the Center for Astrophysics is dedicated to the study of ion-electron collision processes of importance in solar physics. A paper describing our most recent measurement 'Absolute cross section for Si(2+)(3s3p(sup 3)Rho (sup 0) yields 3s3p(sup 1)Rho(sup 0)) electron-impact excitation' was published during the past year. Dr. Paul Janzen received his PhD. from the Harvard Physics Department on the basis of this and other work, such as the new electron cyclotron resonance (ECR) ion source. The ion source is producing stable beams with large currents for our present work on C(2+), and it also produces stable beams with large currents of more highly charged systems, for future work on systems such as O(4+). The past year has been focussed on our current program to measure absolute cross sections for Electron Impact Excitation (EIE) in C(2+), one of the primary ions used for probing the solar transition region. C(2+) beams produced by the ion source have been transported to the interaction region of the experiment, where the collisions are studied, and Visiting Scientist Dr. Adrian Daw is currently collecting data to measure the C(2+)(2s2p(sup 3)Rho(sup 0) yields 2p(sup 2)(sup 3)Rho) EIE cross section as a function of collision energy, under the guidance of Drs. John Kohl, Larry Gardner and Bill Parkinson. Also this year, modifications were made to the ECR ion source in order to produce greater currents of highly charged ions. Testing of the ion source was completed. Modifications were designed to extend the photon detection capabilities of the apparatus to shorter UV wavelengths, or EUV. Following the work on C(2+)(2s2p(sup 3)Pho(sup 0) yields 2p(sup 2)(sup 3)Rho), the extended UV detection capabilities will be used to measure the C(2+)(2s(sup 2)(sup 1)S yields 2s2p(sup 1)Rho(sup 0)) EIE cross section. The EUV modifications complement those of the new ion source, by enabling detection of EUV light generated by high charge state ions and putting us in a position to measure the excitation cross sections for more highly charged ions as well.

Parkinson, William↗
NASA NTRS1969

Dielectronic recombination

Dielectronic recombination rate coefficient determined by quantum theory of resonance- collision processes, considering coupling, degeneracy and overlapping resonances

Shore, B. W.↗
NASA NTRS1969

Inelastic molecular collisions

Collision cross sections direct measurement for determining macroscopic reaction rates in inelastic molecular collision processes in gas dynamics

Utterback, N. G.↗
NASA NTRS1971

The propagation of solar cosmic-ray bursts.

Description of a model showing analytically the three phases of anisotropy which occur during solar cosmic-ray events in the 7.5 to 21 MeV kinetic-energy interval and reported by McCracken et al. (1971): (1) a highly anisotropic, near field-aligned, initial phase, (2) a convective phase, and (3) a late-time phase in which the anisotropy is approximately perpendicular to the mean interplanetary magnetic field. The model is based on the cosmic-ray particles being convectively transported out from the sun, undergoing anisotropic diffusion along the interplanetary magnetic-field lines, and losing energy by adiabatic deceleration or by collision processes. The event is seen simply as a pulse moving outward from the sun after a cosmic-ray burst with a negative density-gradient in front of it and a positive gradient behind.

Ng, C. K.↗
NASA NTRS1972

A plausible energy source and structure for quasi-stellar objects.

If a collision of two large, massive, fast gas clouds occurs, their kinetic energy is converted to radiation in a pair of shock fronts at their interface. Basic constraints imposed on such a model by observations of QSOs are considered. It is shown that a very large shock area is required if such a collision process is to provide the energy for a QSO. Details regarding the anticipated spectrum are discussed together with the opacity of the neutral clouds.

Daltabuit, E.↗
NASA NTRS1972

Linear momentum transfer effects in molecular dissociation produced by electron impact.

In this study of molecular dissociation produced by electron impact, diatomic systems and polyatomic molecules are considered, and attention is given to the effects of thermal motion and of momentum transfer in the collision process. A procedure is described which makes it possible to 'construct' both the laboratory angular distribution and velocity distribution of the atomic fragments (or, alternatively, the time-of-flight distribution). The calculation assumes that s-wave electron scattering predominates, i.e., that excitation occurs near threshold. The computational procedure may also be reversed to allow construction of possible molecular models to fit given experimental angular and velocity distribution data.

Misakian, M.↗
NASA NTRS1973

High intensity copper atom beam - Preliminary results

The development of a nozzle which gas-dynamically accelerates neutral copper atoms at controlled energy levels and flux rates suitable for the investigation of inelastic copper atom collision processes is reported. Preliminary test data demonstrate that vapor-deposited rhenium nozzles do not degrade in the presence of copper vapor at high temperatures. Operation with high purity helium gas at nozzle stagnation temperatures in the range 2650-2700 K and total stagnation pressures from 1/4 to 2 atm with continuous copper atom flux rates of approximately 10 to the 18th power per second has been maintained, for a total time of 8-1/2 h to date.

Kelly, A. J.↗
NASA NTRS1974

Magnetic field dependence of plasma relaxation times

A previously derived Fokker-Planck collision integral for an electron plasma in a dc magnetic field is examined in the limit in which the Debye length is greater than the thermal gyroradius, which is in turn greater than the mean distance of closest approach. It is demonstrated that the collision integral can be satisfactorily approximated by the classical Landau value (which ignores the presence of a dc magnetic field) if the following replacement is made: In the Coulomb logarithm, the Debye length is replaced by the gyroradius. This induces a fundamental logarithmic dependence on magnetic field in the relaxation times. Numerical comparison of the asymptotic approximations with the previously derived exact results is made, and good agreement is found. The simplification this introduces into the description of collision processes in magnetized plasma is considerable.

Montgomery, D.↗
NASA NTRS1976

Spacecraft self-contamination due to back-scattering of outgas products

The back-scattering of outgas contamination near an orbiting spacecraft due to intermolecular collisions was analyzed. Analytical tools were developed for making reasonably accurate quantitative estimates of the outgas contamination return flux, given a knowledge of the pertinent spacecraft and orbit conditions. Two basic collision mechanisms were considered: (1) collisions involving only outgas molecules (self-scattering) and (2) collisions between outgas molecules and molecules in the ambient atmosphere (ambient-scattering). For simplicity, the geometry was idealized to a uniformly outgassing sphere and to a disk oriented normal to the freestream. The method of solution involved an integration of an approximation of the Boltzmann kinetic equation known as the BGK (or Krook) model equation. Results were obtained in the form of simple equations relating outgas return flux to spacecraft and orbit parameters. Results were compared with previous analyses based on more simplistic models of the collision processes.

Robertson, S. J.↗
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

Reactions between NO/+/ and metal atoms using magnetically confined afterglows

A new method of studying thermal energy ion-neutral collision processes involving nongaseous neutral atoms is described. A long magnetic field produced by a solenoid in a vacuum chamber confines a thermal-energy plasma generated by photoionization of gas at very low pressure. As the plasma moves toward the end of the field, it is crossed by a metal atom beam. Ionic products of ion-atom reactions are trapped by the field and both the reactant and product ions move to the end of the magnetic field where they are detected by a quadrupole mass filter. The cross sections for charge transfer between NO(+) and Na, Mg, Ca, and Sr and that for rearrangement between NO(+) and Ca have been obtained. The charge-transfer reaction is found strongly dominant over the rearrangement reaction that forms metallic oxide ions.

Lo, H. H.↗
NASA NTRS1978

On the origin of Uranus' rings

The role of Miranda-Ariel orbital resonances in determining the structure of the rings of Uranus is discussed. In particular, it is argued that the three-body orbital resonances of Miranda and Ariel may function as a mechanism for the formation of narrow rings, rather than as a mechanism for trapping freely orbiting particles; the formation of narrow rings, in this hypothesis, would involve an inelastic collision process. The narrowness of the resonances may account for the sharply defined ring boundaries.

Ip, W.-H.↗
NASA NTRS1978

Rotational inelasticity in high-energy H2-H2 collisions

Rotational cross sections for transitions in the H2-H2 system have been calculated for energies up to about 2.0 eV and for rotor levels up to j = 11 in the effective potential approximation. The cases of para H2-para H2, ortho H2-ortho H2 and ortho H2-para H2 are considered. Correlations and trends in the cross sections have been examined, and it is shown that the high-energy collisions are dominated by coupling effects. The results of this analysis also suggest that the collision process may be profitably viewed as a diffusion of probability among the levels.

Ramaswamy, R.↗
NASA NTRS1980

Gamma rays from Penrose powered black holes in Centaurus A, 3C 273, and NGC 4151

Gamma-ray observations of Cen A, 3C 273, and NGC 4151 are examined under the assumption that Penrose collision processes in the ergospheres of massive black holes power their nuclei. The observed sharp break in the MeV region of the NGC spectrum is attributed to Penrose Compton scattering, and the absence of an MeV break in the spectra of Cen A and 3C 273 implies Penrose pair production. Central black hole masses of tens of millions of solar masses for NGC 4151 and Cen A, and tens of billions of solar masses for 3C 273, are obtained. Attention is also given to accretion rate, the efficiency of accretion, QSOs and Seyferts.

Kafatos, M.↗