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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 307 records · Page 17
All sourcesNASA NTRSDOE OSTI
NASA NTRS1979

Resonant charge transfer in He/+/-He collisions studied with the merging-beams technique

Absolute cross sections are reported for the resonant charge-transfer reaction He(+) + He yields He + He(+) at collision energies between 0.1 and 187 eV. The results, obtained using a new merging-beam apparatus are in agreement both with theory and with measurements made using other experimental techniques. The experimentally determined cross sections between 0.5 and 187 eV fall about a line given by sigma exp 1/2(sq-A) = 5.09-2.99 lnW, where W is the collision energy in eV. Considerable attention is paid to the configuration and operation of the apparatus. Tests and calculations which confirm the interpretation of the experimental data in a merging-beam experiment are discussed.

Rundel, R. D.↗
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 NTRS1979

Intensities and N2 collision-broadening coefficients measured for selected H2O absorption lines between 715 and 732 nm

Intensities and N2 collision-broadening coefficients are measured for 62 water vapor absorption lines between 715 and 732 nm potentially applicable to laser remote sensing of atmospheric water vapor. Absolute line strengths and widths were determined from spectra corrected for instrument resolution, air-path absorption and Lorentz and Doppler broadening for pure water vapor and water vapor-nitrogen mixtures in a multipass absorption cell with a base path length of 25 m (White cell). Line strengths are observed to range from 4 x 10 to the -25th to 4 x 10 to the -23rd kayser/molecule per sq cm, and collision broadening coefficients are found to be approximately equal to 0.1 kayser/atm.

Wilkerson, T. D.↗
NASA NTRS1979

Effects of hydrogen atom spin exchange collisions on atomic hydrogen maser oscillation frequency

Frequency shifts due to collisions between hydrogen atoms in an atomic hydrogen maser frequency standard are studied. Investigations of frequency shifts proportional to the spin exchange frequency shift cross section and those proportional to the duration of exchange collisions are discussed. The feasibility of operating a hydrogen frequency standard at liquid helium temperatures is examined.

Crampton, S. B.↗
NASA NTRS1979

Calculation of total cross sections for charge exchange in molecular collisions

Areas of investigation summarized include nitrogen ion-nitrogen molecule collisions; molecular collisions with surfaces; molecular identification from analysis of cracking patterns of selected gases; computer modelling of a quadrupole mass spectrometer; study of space charge in a quadrupole; transmission of the 127 deg cylindrical electrostatic analyzer; and mass spectrometer data deconvolution.

Ioup, J.↗
NASA NTRS1979

Quantum-mechanical calculation of three-dimensional atom-diatom collisions in the presence of intense laser radiation

A formalism is presented for describing the collision of fluorine with the hydrogen molecule in the presence of intense radiation. For a laser frequency on the order of the spin-orbit splitting of fluorine, the interaction of the molecular system with the radiation occurs at relatively long range where, for this system, the electric dipole is vanishingly small. Hence the interaction occurs due to the magnetic dipole coupling. Even so, at low collision energies a substantial enhancement of the quenching cross section is found for a radiation intensity of 10 to the 11th W/sq cm.

Devries, P. L.↗
NASA NTRS1979

An angular momentum approximation for molecular collisions in the presence of intense laser radiation

An approximation to a previously presented rigorous description of molecular (atom-atom) collisions occurring in the presence of intense radiation is investigated. This rigorous description explicitly considers the angular momentum transferred between the molecule and the radiation field in the absorption or emission of a photon, but involves a complicated system of close-coupled equations which must be solved independently for each projection M of the initial, total molecular angular momentum. (This is a direct consequence of the lack of rotational invariance in the molecule-field problem). These equations are solved for a model system which mimics the collision of a halogen with a rare gas atom. Empirical observations made in the course of performing these calculations lead to the development of an approximation which avoids the repeated calculations for each initial M. This orientational average approximation greatly reduces the effort required to describe the system, and for the model calculation, yields accurate results for field intensities as high as 10 GW/sq cm.

Devries, P. L.↗
NASA NTRS1979

Earth-crossing asteroids - Orbital classes, collision rates with earth, and origin

Asteroids that can intersect the orbit of the earth are discussed, which include Aten asteroids (semimajor axis (a) less than 1 AU, aphelion greater than 0.983 AU), Apollo asteroids (a greater than 1 AU, perihelion less than 1.017 AU), and Amor asteroids (perihelion distance between 1.017 and 1.3 AU). The principal sources of earth-crossing asteroids appear to be extinct comet nuclei and collision fragments from regions in the main asteroid belt. The total population of earth-crossers is estimated at 13,000, of which approximately 8% are Atens, 50% are Apollos, and 40% are Amors,and the present collision rate of such asteroids with the earth is estimated at about 3.5 objects, to absolute magnitude 18, per million years.

Shoemaker, E. M.↗
NASA NTRS1979

Chronology of asteroid collisions as recorded in meteorites

Because meteorites are derived from asteroidal objects, the chronology of meteorites give age information on the histories of the asteroidal parents. With a few possible exceptions, the radiometric chronology of less than 4.4 Gyr determined in meteorites can be attributable to collisions among meteorite parent bodies. Three types of collisional chronologies which have been determined are: (1) cosmic ray exposure ages, which generally date the time of the last fragmentation of the parent object when the meteorite is reduced to meter size, and which generally fall over the wide range of 1-1000 Myr; (2) the collisional shock ages shown by many meteorites, which are believed to date the times of major collisions among parent bodies in the asteroid belt in the time interval of 30-700 Myr; and (3) the brecciation ages of several meteorites which are believed to date the times of their collisional formation from regoliths of larger parent bodies over the period of 1.4-4.4 Gyr.

Bogard, D. D.↗
NASA NTRS1980

Computational study of alkali-metal-noble gas collisions in the presence of nonresonant lasers - Na + Xe + h/2/pi/omega sub 1 + h/2/pi/omega sub 2 system

The collision of Na with Xe in the presence of both the rhodamine-110 dye laser and the Nd-glass laser is investigated within a quantum-mechanical close-coupled formalism, utilizing ab initio potential curves and transition dipole matrix elements. Both one- and two-photon processes are investigated; the Na + Xe system is not asymptotically resonant with the radiation fields, so that these processes can only occur in the molecular collision region. The one-photon processes are found to have measurable cross sections at relatively low intensities; even the two-photon process has a significant section for field intensities as low as 10 MW/sq cm.

Devries, P. L.↗
NASA NTRS1981

Feasibility of collision warning, precision approach and landing using GPS, volume 1

The use of GPS, with an appropriately configured data link, to enhance general aviation avionic functions encountered in the terminal area and on approach was investigated with emphasis on approach and landing guidance and collision warning. The feasibility of using differential GPS to obtain the precision navigation solutions required for landing was studied. Results show that the concept is sound. An experimental program was developed to demonstrate this concept. The collision avoidance/warning concept was examined through the development of a functional system specification.

Ruedger, W. H.↗
NASA NTRS1981

Low-temperature He-Na collision rate measurements

The foreign-gas collision broadening of the Na D2 line by He at a temperature of 8 K is measured. These data combined with those of other investigators provide an empirical scaling of the collision rates and cross sections over a wide range of temperatures and relative velocities, respectively.

Zimmermann, M.↗
NASA NTRS1981

Oscillator strengths and collision strengths for S v

Observations of the optical extreme-ultraviolet spectrum of the Jupiter planetary system during the Voyager space mission revealed bright emission lines of some sulfur ions. The spectra of the torus at the orbit of Io are likely to contain S V lines. The described investigation provides oscillator strengths and collision strengths for the first four UV lines. The collision strengths from the ground state to four other excited states are also obtained. Use is made of a two-state calculation which is checked for convergence for some transitions by employing a three-state or a four-state approximation. Target wave functions for S V are calculated so that the oscillator strengths calculated in dipole length and dipole velocity approximations agree within 5%.

Van Wyngaarden, W. L.↗
NASA NTRS1981

Speed-dependent collision effects on radar back-scattering from the ionosphere

A computer code to accurately compute the fluctuation spectrum for linearly speed dependent collision frequencies was developed. The effect of ignoring the speed dependence on the estimates of ionospheric parameters was determined. It is shown that disagreements between the rocket and the incoherent scatter estimates could be partially resolved if the correct speed dependence of the i-n collision frequency is not ignored. This problem is also relevant to the study of ionospheric irregularities in the auroral E-region and their effects on the radio communication with satellites.

Theimer, O.↗
NASA NTRS1982

Fluid dynamical description of relativistic nuclear collisions

On the basis of both a conventional relativistic nuclear fluid dynamic model and a two fluid generalization that takes into account the interpenetration of the target and projectile upon contact, collisions between heavy nuclei moving at relativistic speeds are calculated. This is done by solving the relevant equations of motion numerically in three spatial dimensions by use of particle in cell finite difference computing techniques. The effect of incorporating a density isomer, or quasistable state, in the nuclear equation of state at three times normal nuclear density, and the effect of doubling the nuclear compressibility coefficient are studied. For the reaction 20Ne + 238U at a laboratory bombarding energy per nucleon of 393 MeV, the calculated distributions in energy and angle of outgoing charged particles are compared with recent experimental data both integrated over all impact parameters and for nearly central collisions.

Nix, J. R.↗
NASA NTRS1982

Water absorption lines, 931-961 nm - Selected intensities, N2-collision-broadening coefficients, self-broadening coefficients, and pressure shifts in air

Intensities were measured for 97 lines of H2O vapor between 932 and 961 nm. The lines were selected for their potential usefulness for remote laser measurements of H2O vapor in the earth's atmosphere. The spectra were obtained with several different H2O vapor abundances and N2 broadening gas pressures; the spectral resolution was 0.046/cm FWHM. Measured H2O line intensities range from 7 x 10 to the -25th to 7 x 10 to the -22nd/cm per (molecules/sq cm). H2O self-broadening coefficients were measured for 13 of these strongest lines; the mean value was 0.5/cm per atm. N2-collision-broadening coefficients were measured for 73 lines, and the average was 0.11 cm per atm HWHM. Pressure shifts in air were determined for a sample of six lines between 948 and 950 nm; these lines shift to lower frequency by an amount comparable to 0.1 of the collision-broadened widths measured in air or N2. The measured intensities of many lines of 300-000 band are much larger than expected from prior computations, in some cases by over an order of magnitude. Coriolis interactions with the stronger 201-000 band appear to be the primary cause of the enhancement of these line intensities.

Giver, L. P.↗
NASA NTRS1982

Neutron star collisions and the r-process

It is shown that a natural consequence of the binary pulsar's evolution is a neutron star collision. Such a collision is expected to eject neutron-rich matter of an r-process character. Taking reasonable estimates for the number of such events over the history of the galaxy, it may be that they account for all of the r-process nuclei.

Symbalisty, E.↗
NASA NTRS1983

Collisions and merging of disk galaxies

The stable disks required as initial states for an experiment are produced by embedding the disk (which is visible) in a halo (invisible). The disk is a luminous tracer that represents only 1 percent of the total mass of the system. The stability of the initial state of the model is confirmed experimentally. Collisions with various combinations of initial orbital energy and angular momentum and of disk orientations are investigated. Two initially parabolic cases with different impact parameters are followed in time until the interactions lead to a merger. The interpenetration of the two galaxies gives rise to a contraction and subsequent disruption of the entire system. A variety of responses is found for the visible disks, ranging from stretched-out nearly linear features to rapidly propagating ringlike patterns. It is noted that these forms depend critically on initial disk orientations but do not depend strongly on the sense of disk rotation. The ringlike patterns are found even for collisions with significant impact parameters.

Smith, B. F.↗