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At least 469 records · Page 26
All sourcesNASA NTRSDOE OSTI
NASA NTRS1985

Asteroidal source of ordinary chondrites (Meteoritical Society Presidential Address 1984)

The orbital evolution of asteroidal fragments injected into the 3-1 Kirkwood gap resonance at 2.5 AU is investigated on the basis of a Monte Carlo simulation. The diameters of the fragments in the simulation were between 10 cm and 20 km, and it was assumed that the fragments cross the orbital path of the earth every one million years. The effects of close encounter planetary perturbations, the nu dot 6 secular resonance, and the ablative effects of the earth atmosphere were also taken into account. It is found that: (1) the predicted meteorite orbits closely matched the known orbits of ordinary chondrites; and (2) the total flux was in approximate agreement with the observed fall rate of ordinary chondrites. About 90 percent of the predicted impacting bodies were created by fragmentation of larger earth crossing asteroidal fragments, the largest of which were observed in the vicinity of the Apollo-Amor objects. The numerical results are presented in a series of graphs.

Wetherill, G. W.↗
NASA NTRS1986

Evolution of primoridal gas clouds

The dynamical, chemical, and thermal evolution of zero-metal gas clouds was modeled to study conditions of star formation in the early universe. Numerical results are given for the collapse of spherical clouds of mass 1000 and 50000 solar mass. Cooling by H2 lines and by photons emitted in H + e(-) yields H(-) = h (sup nu) maintains collapse until formation of an equilibrium protostellar core of mass 0.02 solar mass. The cooling by photons produced with H is essential for low mass star formation. If the cloud is fragmented, the evolution of the pieces is similar to that of the parent cloud, but the equilibrium core has larger density and mass.

Bodenheimer, P. H.↗
NASA NTRS1985

The magnetic and thermodynamical structure of a coronal hole

A nonpolytropic model of a polar coronal hole of 2-5 solar radii constructed. The main assumptions are: (1) the magnetic structure of the sun can be described by a combination of dipole-like and radial fields; (2) in the magnetically dominated region rho(nu sq/2) much less than B sq/8 pi the influence of the outflow on the magnetic structure is negligible. The magnetic and thermodynamic structures are obtained by solving the force balance equation for plasma with the observationally derived electron density. Profiles of velocities in the acceleration regime are presented and the influence of the outflow on the thermodynamic structure of the solar corona above the polar region is discussed.

Osherovich, V. A.↗
NASA NTRS1985

Dissociation of metastable O2 as a potential source of atmospheric odd oxygen

An analysis of the possible dissociation of metastable oxygen molecules subject ot constraints imposed by selection rules for molecular transitions, airglow observations, and atmospheric chemistry leads to the following conclusions. Dissociation of O2(b1Sigma g +) must produce a negligible number of oxygen atoms at all altitudes in the earth's atmosphere. However, if the dissociation cross section of O2(a1Delta g) has a maximum value in the range 10 to the -20th to 10 to the -19th/sq cm, then the process O2(a1Delta g) + h(nu) yields O2(C3Delta u) yields O(3P) + O(3P) will constitute a significant, and potentially the major, source of odd oxygen in the uppermost stratosphere and mesosphere.

Frederick, J. E.↗
NASA NTRS1985

An upper limit for the absorption cross section of the oxygen C 3 Delta u - a 1 Delta g transition

Frederick and Cicerone (1985) have proposed that photodissociation of O2 (a 1 Delta g) by the process O2 (a 1 Delta g) + h-nu + O2 (C 3 Delta u) to O(3 P) + O(3 P) may be a major source of odd oxygen in the upper stratosphere and mesosphere. They argued that, since the process is forbidden only by change in the spin multiplicity, it might have been a cross section intermediate between a fully allowed and a strictly forbidden transition, i.e., 10 to the -20th to 10 to the -19th sq cm near 250 nm. In order to test this proposal, absorption by O2 (a 1 Delta g) has been measured in the 190-290 nm wavelength region. No absorption above the detection limit could be observed for O2 (a 1 Delta g) concentrations of (4-7) x 10 to the 15th/cu cm. An upper limit of 8 x 10 to the -22 sq cm was calculated for the cross section.

Simonaitis, R.↗
NASA NTRS1986

Direct picosecond time resolution of unimolecular reactions initiated by local mode excitation

Attention is given to the first results of direct, picosec measurements of the Delta-nu(OH) 5 local mode transition of H2O2. These time-resolved studies yield a direct measure of the unimolecular dissociation rate, and furnish a lower limit for the rate of energy redistribution from the OH stretch to the O-O reaction coordinate. The data thus determined may be used to ascertain the domain of validity for statistical unimolecular reaction rate theories.

Scherer, N. F.↗
NASA NTRS1986

Steady hydromagnetic flows in open magnetic fields. I - A class of analytic solutions

In the case of an establishment of theoretical models of the hydromagnetic solar wind, the inclusion of the effects of the magnetic field in the solar wind makes it extremely dificult to solve the mathematical problem. This paper has the objective to present a set of particular analytic solutions. The general formulation of Tsinganos (1982) is used to identify a class of analytic solutions to the equations of steady hydromagnetic flows in spherical coordinates. Flow in an open magnetic field are studied, taking into account the problem in dimensionless form, the special case of radial flows with alpha = 0, general radial flows, illustrative examples for flows in which alpha is not equal to 0, a parametric study of nonradial flows in which alpha is not equal to zero, variations in the parameter nu, and variations in the initial speed eta.

Low, B. C.↗
NASA NTRS1986

The O2 atmospheric dayglow in the thermosphere

Spectral measurements (Delta lambda = 8A) from Spacelab 1 of the O2 atmospheric bands in the dayglow at thermospheric altitudes are reported for a tangent ray height of 150 km. Vibrational levels up to nu-prime = 4 are found in the data, requiring a source in addition to the energy transfer from O(1D) to O2. It is suggested that this source is the collisional deactivation of N(2D) by O2.

Torr, M. R.↗
NASA NTRS1986

Ultraviolet spectrometer observations of Uranus

The Voyager 2 UV spectrometer was used to scan the Uranus atmosphere at wavelengths from 500-1700 A with a field of view of 0.1 x 0.86 deg. The temperature and composition of the upper atmosphere were determined through occultations of light from gamma Pegasi, nu Geminorum and the sun. The data indicated a substantial gas density (100 million H atoms/cu cm) at about 28,000 km from the Uranus center, suggesting that gas drag plays a significant role in ring evolution. The distributions of CH4 and C2H2 in the lower atmosphere were also estimated. An electroglow emission was detected on the sunlit side, and attributed to emissions from atomic and molecular hydrogen excited by low energy electrons. An auroral glow was also observed, and exhibited evidence of an energy input equal to that of the electroglow. Finally, estimates of the C2H2 mixing ratio and the vertical column abundance of H2 are calculated.

Broadfoot, A. L.↗
NASA NTRS1986

IRAS observations of binaries with compact objects

The infrared emission data, obtained on 260 binary systems by the all-sky IRAS survey in wavelengths between 12 and 100 microns, are reported. Of all the 260 sources, which contained compact objects including white dwarfs, neutron stars, or possibly black holes, only 32 contained detectable IR radiation. The X-ray emitting Be-type stars (gamma-Cas and X Per) were found to have their energy flux proportional to frequency in the range of the log nu values of 12.7-14.7. However, the GS304-1 flux distribution is unique, in that its flux rises by several orders of magnitude as the wavelength changes from 4000 A to 60 microns. A static dust cloud was detected, with a radius of about 1 AU, which has formed around the classical nova RR Pic since its 1925 eruption. The post-eruption far-IR light curve of a classical nova provides strong evidence for IR emissions from both dust grains formed during the eruption and dust grains existing from previous eruptions.

Schaefer, B. E.↗
NASA NTRS1986

The effects of space radiation on a chemically modified graphite-epoxy composite material

The effects of the space environment on the engineering properties and chemistry of a chemically modified T300/934 graphite-epoxy composite system are characterized. The material was subjected to 1.0 x 10 to the 10th power rads of 1.0 MeV electron irradiation under vacuum to simulate 30 years in geosynchronous earth orbit. Monotonic tension tests were performed at room temperature (75 F/24 C) and elevated temperature (250 F/121 C) on 4-ply unidirectional laminates. From these tests, inplane engineering and strength properties (E sub 1, E sub 2, Nu sub 12, G sub 12, X sub T, Y sub T) were determined. Cyclic tests were also performed to characterize energy dissipation changes due to irradiation and elevated temperature. Large diameter graphite fibers were tested to determine the effects of radiation on their stiffness and strength. No significant changes were observed. Dynamic-mechanical analysis demonstrated that the glass transition temperature was reduced by 50 F(28 C) after irradiation. Thermomechanical analysis showed the occurrence of volatile products generated upon heating of the irradiated material. The chemical modification of the epoxy did not aid in producing a material which was more radiation resistant than the standard T300/934 graphite-epoxy system. Irradiation was found to cause crosslinking and chain scission in the polymer. The latter produced low molecular weight products which plasticize the material at elevated temperatures and cause apparent material stiffening at low stresses at room temperature.

Reed, S. M.↗
NASA NTRS1986

HALOE science investigation

The Halogen Occulation Experiment (HALOE) gas response test simulations were completed using the HALOE spectroscopic instrument model. A new series of programs were written for routine repetitive runs of the spectroscopic model to make it more user friendly for certain studies. Some of the limitations of the model were eased for atmospheric studies. Atmospheric signal profiles were calculated for inclusion in the electronic model programs. Analysis of additional spectral bands of CO2 in the 3 micron region was continued. A program of measurement of the air broadened halfwidths of spectral lines in the nu (sub 3) fundamental band of CH4 was started and over 40 lines measured.

Benner, D. C.↗
NASA NTRS1986

The asymmetric profile of the H76 alpha line emission from MWC349

MWC349 is an emission-line star found by Merrill, Humason and Burwell (1932). Braes, Habing and Schoenmaker (1972) discovered that it is a strong radio source. The radio emission originates in a massive ionized wind that is expanding with a velocity of about 50 km s(-1). Its continuum spectrum fits well a nu(0.6) power law from the cm wavelengths to the far-IR. Radio recombination line emission from the envelope of MWC349 was first detected by Altenhoff, Strittmatter and Wendker (1981). We have obtained good signal-to-noise ratio, Very Large Array observations of the H76 alpha radio recombination line from the ionized wind of MWC349. Our data reveal that the profile is markedly asymmetric, with a steep rise on the blue side. This asymmetry could be due to non-LTE effects in the formation and transfer of the line or to intrinsic asymmetries in the envelope. Our analysis suggests that most probably the peculiar profile is caused by a non-LTE enhancement of the line emission from the side of the envelope nearer to the observer. This asymmetry has the opposite sense than that observed in optical and IR recombination lines, where a different effect (absorption of the stellar continuum by the gas in the wind between the star and the observer) is known to be dominant, leading to the classic P Cygni profile. We propose that the profiles of the radio recombination lines from ionized stellar winds will have this characteristic shape, while optical and IR recombination lines are characterized by P Cygni-like profiles. Unfortunately, at present the detection of radio recombination lines from ionized stellar winds is only feasible for MWC349 and a few other objects.

Rodriquez, L. F.↗
NASA NTRS1987

Monodeuterated methane in the outer Solar System. Part 3: Its abundance on Titan

The 3 nu 2 band of CH3D has been detected in spectra of Titan recorded at 1.6 microns with the Fourier Transform Spectrometer (FTS) at the 4 m telescope of the Kitt Peak National Observatory (NOAO). We have obtained a value of the CH3D/CH4 mixing ratio of 6.6 (+6.6 or -3.3) x 10 to the -4 from a comparison between the observed Titan spectra and synthetic spectra. This value is approx. 2 times higher than the value measured on Uranus (de Bergh et al. 1986) and approx. 6 times higher than on Jupiter and on Saturn (Courtin et al. 1984; de Bergh et al. 1986). It corresponds to D/H of 1.65 (+1.65 or -0.8) x 10 the -4, nominally 8 times higher than the most commonly accepted value for the protosolar D/H = 2 x 10 to the -5 (Geiss and Reeves 1981). The value we find on Titan for D/H in methane is comparable to the D/H ratio measured in terrestrial H2O.

Debergh, C.↗
NASA NTRS1987

Quantitative analysis of the reconstruction performance of interpolants

The analysis presented provides a quantitative measure of the reconstruction or interpolation performance of linear, shift-invariant interpolants. The performance criterion is the mean square error of the difference between the sampled and reconstructed functions. The analysis is applicable to reconstruction algorithms used in image processing and to many types of splines used in numerical analysis and computer graphics. When formulated in the frequency domain, the mean square error clearly separates the contribution of the interpolation method from the contribution of the sampled data. The equations provide a rational basis for selecting an optimal interpolant; that is, one which minimizes the mean square error. The analysis has been applied to a selection of frequently used data splines and reconstruction algorithms: parametric cubic and quintic Hermite splines, exponential and nu splines (including the special case of the cubic spline), parametric cubic convolution, Keys' fourth-order cubic, and a cubic with a discontinuous first derivative. The emphasis in this paper is on the image-dependent case in which no a priori knowledge of the frequency spectrum of the sampled function is assumed.

Lansing, Donald L.↗
NASA NTRS1987

Diffuse infrared emission of the galaxy: Large scale properties

A quantitative analysis of Infrared Astronomy Satellite (IRAS) data in the galactic plane shows that: about 66% of the power radiated in the 100 micron band comes from the diffuse medium, the other 33% coming from well identified luminous sources. The diffuse emission has almost constant colors throughout the Galaxy, similar to the local cirrus colors. The sources have a much lower 12 micron/25 micron and a much high 60 micron/100 micron emission ratio than the diffuse component, giving a very striking anticorrelation in the color-color diagrams. The separation between one narrow and a second broader component shows that the molecular component does not provide much more than one half of the diffuse emission in the molecular ring: this implies a 4 pi nuI(nu) emissivity at 100 microns for the atomic component of about 2.4 x 10 to the minus 30th watts per H atom, 10 times higher than the emissivity of the molecular component at the same galactocentric radius. The atomic component emissivity measures the interstellar radiation field density. The temperature distribution of the 2 components is discussed comparing IRAS data with measures of the 900 micron emission of the galactic plane, which appears to be dominated by cold dust in the narrow component.

Puget, J. L.↗
NASA NTRS1986

Enhanced Raman spectroscopic study of rotational isomers on metal surfaces

Surfaced-enhanced Raman spectroscopy has been used to study rotational isomers of succinonitrile and N-methyl-thioacetamide on Cu and Ag surfaces. Both the gauche and trans conformers of succinonitrile are found to chemisorb on the metal surface. The doubly degenerate nu(C-triple bond-N) in the free molecules is removed when succinonitrile adsorbs on copper, which indicates that the two (C-triple bond-N) groups are no longer chemically equivalent. Both conformers are found to coordinate to the copper surface through the pi system of one of the two (C-triple bond-N) groups. In the case of N-methyl-thioacetamide, the population of the cis isomer is greatly increased on Cu and Ag surfaces. This is probably due to surface-induced cis-trans isomerization, in which the predominant trans isomer is converted to the cis isomer.

Loo, B. H.↗
NASA NTRS1986

Monodeuterated methane in the outer solar system. II - Its detection on Uranus at 1.6 microns

The 3 nu 2 band of CH3D has been detected in the spectrum of Uranus recorded with the Fourier Transform Spectrometer at the 4 m Mayall telescope of Kitt Peak National Observatory. A scattering-model atmosphere and spectral synthesis techniques are used to derive a bulk CH3D/CH4 mixing ratio of 3.6 + 3.6 or - 2.8 x 10 to the -4th from these observations that suggests a deuterium enhancement in methane relative to that observed on Jupiter and Saturn.

De Bergh, C.↗