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At least 451 records · Page 25

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NASA NTRS1983

The effects of the Asselin time filter on numerical solutions to the linearized shallow-water wave equations

In the present investigation, a one-dimensional linearized analysis is used to determine the effect of Asselin's (1972) time filter on both the computational stability and phase error of numerical solutions for the shallow water wave equations, in cases with diffusion but without rotation. An attempt has been made to establish the approximate optimal values of the filtering parameter nu for each of the 'lagged', Dufort-Frankel, and Crank-Nicholson diffusion schemes, suppressing the computational wave mode without materially altering the physical wave mode. It is determined that in the presence of diffusion, the optimum filter length depends on whether waves are undergoing significant propagation. When moderate propagation is present, with or without diffusion, the Asselin filter has little effect on the spatial phase lag of the physical mode for the leapfrog advection scheme of the three diffusion schemes considered.

Schlesinger, R. E.↗

NASA NTRS1983

Large numbers hypothesis. II - Electromagnetic radiation

This paper develops the theory of electromagnetic radiation in the units covariant formalism incorporating Dirac's large numbers hypothesis (LNH). A direct field-to-particle technique is used to obtain the photon propagation equation which explicitly involves the photon replication rate. This replication rate is fixed uniquely by requiring that the form of a free-photon distribution function be preserved, as required by the 2.7 K cosmic radiation. One finds that with this particular photon replication rate the units covariant formalism developed in Paper I actually predicts that the ratio of photon number to proton number in the universe varies as t to the 1/4, precisely in accord with LNH. The cosmological red-shift law is also derived and it is shown to differ considerably from the standard form of (nu)(R) - const.

Adams, P. J.↗

NASA NTRS1982

Finite analytic numerical solution of heat transfer and flow past a square channel cavity

A numerical solution of flow and heat transfer characteristics is obtained by the finite analytic method for a two dimensional laminar channel flow over a two-dimensional square cavity. The finite analytic method utilizes the local analytic solution in a small element of the problem region to form the algebraic equation relating an interior nodal value with its surrounding nodal values. Stable and rapidly converged solutions were obtained for Reynolds numbers ranging to 1000 and Prandtl number to 10. Streamfunction, vorticity and temperature profiles are solved. Local and mean Nusselt number are given. It is found that the separation streamlines between the cavity and channel flow are concave into the cavity at low Reynolds number and convex at high Reynolds number (Re greater than 100) and for square cavity the mean Nusselt number may be approximately correlated with Peclet number as Nu(m) = 0.365 Pe exp 0.2.

Chen, C.-J.↗

NASA NTRS1983

Interstellar C2 molecules in a Taurus dark cloud

Five relatively strong interstellar absorption lines of C2 in the (2-0) Phillips band near 8670 A have been detected toward the heavily reddened, late B star HD 29647, which lies behind a substantial part of one of the darkest regions of the nearest molecular cloud complex, the dark clouds of Taurus. Stringent upper limits on the C2 absorption toward two lightly reddened stars, Nu Cyg and Omicron And, are also reported. The observations yield a column density of about 9 x 10 to the 13th/sq cm, comparable to those of widely distributed molecules like CH and H2CO. Theoretical treatment of the data yields a kinetic temperature of 14 K and a mean density of less than about 1000/cu cm. A narrow, anomalously strong, stellar Mn II line yields a projected rotational velocity of less than about 7 km/s and is explained by previous identifications of the star as Hg-Mn peculiar.

Hobbs, L. M.↗

NASA NTRS1983

Computations of the current profile influence on tearing instability

Results of computations of tearing instability of a plasma column in a strong longitudinal magnetic field are presented for different current profiles. The power current profiles j=j sub 0(1-(r/a)(P))(nu) are considered and analyzed for various values of the parameters p and v. The tearing instability of the smoothed two-step profiles is studied. Optimal smoothed two-step profiles are constructed which are stable with respect to all helical largescale perturbations.

Blekher, P. M.↗

NASA NTRS1983

The 12 micron band of ethane: A spectral catalog from 765 cm(-1) to 900 cm(-1)

The high resolution laboratory absorption spectrum of the 12 micro band of ethane gas is studied. The data were obtained using the McMath Solar Telescope 1 meter Fourier Transform interferometer at Kitt Peak National Observatory and tunable diode laser spectrometers at the University of Tennessee and NASA/Goddard Space Flight Center. Over 200 individual vibration rotation transitions were analyzed taking into account many higher order effects including torsional splitting. Line positions were reproduced to better than 0.001/cm. Both ground and upper state molecular constants were determined in the analysis. The experimental details, the analysis procedures and the results are addressed. A list of ethane transitions occurring near (14)CO2 laser lines needed for heterodyne searches for C2H6 in extraterrestrial sources is also included. A spectral catalog of the ethane nu sub g fundamental from 765/cm to 900/cm is provided. A high dispersion (1/cm 12 in.) plot of both the Kitt Peak interferometric data and a simulated spectrum with Doppler limited resolution, a table of over 8500 calculated transitions listed quantum number assignments, frequencies and intensities are provided.

Atakan, A. K.↗

NASA NTRS1984

Space Radiation Effects on Graphite-Epoxy Composite Materials

Radiation effects on engineering properties, dimensional stability, and chemistry on state of the art composite systems were characterized. T300/934 graphite-epoxy composite was subjected to 1.0 MeV electron radiation for a total dose of 1.0 x 10(10) rads at a rate of 5.0 x 10(7) rads/hour. This simulates a worst case exposure equivalent to 30 years in space. Mechanical testing was performed on he 4-ply unidirectional laminates over the temperature range of -250 F (116K) to +250 F (394K). A complete set of in-plane tensile elastic and strength properties were obtained (E sub 1, E sub 2, nu sub 12, G sub 12, X sub T, Y sub T, and S). In addition electron microscopy was used to study and analyze the fracture surfaces of all specimens tested. Results indicate that little difference in properties is noted at room temperature, but significant differences are observed at both low and elevated temperatures.

Milkovich, S. M.↗

NASA NTRS1983

C-12H3D rovibrational intensities and the Jovian D/H ratio

A tabulation is given of line intensities for the nu(2) band of CH3D which have absolute accuracies of + or - 3 percent. Using these intensities, some of the previous Jovian D/H determinations are reinterpreted.

Chackerian, C., Jr.↗

NASA NTRS1983

Observations of two peculiar emission objects in the Large Magellanic Cloud

Ultraviolet and visual wavelength spectra were obtained of two peculiar emission objects, Henize S63 and Sanduleak's star in the Large Magellanic Cloud. Previously not observed in the near- or far-ultraviolet, both objects exhibit strong permitted and semiforbidden line emissions. Estimates based on the absolute continuum flux of the hot companion star in Hen S63 indicate that it rivals the luminosity of the carbon star primary. The emission-line profile structure in both objects does not suggest Wolf-Rayet type emission. Carbon in Sanduleak's star (LMC anonymous) is conspicuously absent, while N V, semiforbidden N IV, and semiforbidden N III dominate the UV emission-line spectrum. Nitrogen is overabundant with respect to carbon and oxygen in both objects. The large overabundance of nitrogen in Sanduleak's star suggests evidence for CNO processes material similar to that seen in Nu Car.

Kafatos, M.↗

NASA NTRS1984

IUE observations of Centaurus X-4 during the 1979 May outburst

Ultraviolet spectrophotometry of the X-ray transient/burst source Centaurus X-4 at several intervals during the peak and decay of the May 1979 X-ray transient event was obtained. The spectrum was characterized by a blue continuum with alpha = 0.0 + or - 0.3 (F/nu/ varies as nu to the alpha power) and strong emission lines of N V lambda 1240, C IV lambda 1550, and Si IV lambda 1398. The relative intensities of the emission lines and the ratio of line to continuum strengths remained nearly constant during the decline. The emission lines may have arisen from a 'disk chromosphere', from X-ray heating of the K4 V companion star, or both. The ultraviolet data are combined with previously published optical and X-ray data to determine some of the physical characteristics of the system and to show that X-ray reprocessing plays an important role in producing the optical and ultraviolet continua.

Blair, W. P.↗

NASA NTRS1984

High Rayleigh number heat transfer in a horizontal cylinder with adiabatic wall

The present investigation is concerned with an experimentally guided approach to the estimation of Nusselt numbers (Nu) at high Rayleigh numbers (Ra) for a cylinder with an adiabatic side wall. The Rayleigh number dependence of the Nusselt number for a horizontal cylinder with an adiabatic wall is presented in a graph. The obtained data are compared with results reported by Shih (1981). Shih has extended a three-term expansion for velocity and temperature distributions reported by Bejan and Tien (1978).

Schiroky, G. H.↗

NASA NTRS1984

Silane in IRC +10216

Silane has been detected in the gas surrounding IRC +10216. Thirteen absorption lines in the nu-4 band around 917/cm were observed at 0.2 km/s resolution. A lower limit to the radial column density is 2 x 10 to the 15th/sq cm, and the relative strengths of the transitions indicate an average rotational temperature of 173 K.

Goldhaber, D. M.↗

NASA NTRS1984

Self-deactivation of water vapor - Role of the dimer

A phenomenological multiple-relaxation theory of the deactivation rate constant for the nu-2 (1 - 0) bending mode of water vapor is presented which incorporates the role not only of the excited monomer but also of the bound molecular complex, in particular the dimer. The deactivation takes place by means of three parallel processes: (1) collisional deexcitation of the excited monomer, (2) a two-step reaction involving association and spontaneous redissociation of an H2O collision complex, and (3) spontaneous dissociation of the stably bound H2O dimer. Oxygen, but not nitrogen or argon, serves as an effective chaperon for the formation of the activated complex. This observation explains the impurity dependence of the self-deactivation rate constant of water vapor. Analysis of an ultrasonic absorption peak based on the third process yields values for the standard entropy and enthalpy of dissociation of the stably bound H2O dimer.

Zuckerwar, A. J.↗

NASA NTRS1985

Muon and neutrino fluxes

The result of a new calculation of the atmospheric muon and neutrino fluxes and the energy spectrum of muon-neutrinos produced in individual extensive air showers (EAS) initiated by proton and gamma-ray primaries is reported. Also explained is the possibility of detecting atmospheric nu sub mu's due to gamma-rays from these sources.

Edwards, P. G.↗

NASA NTRS1984

Stratospheric HNO3 quantification from line-by-line nonlinear least-squares analysis of high-resolution balloon-borne solar absorption spectra in the 870/cm region

Line parameters for the nu(5) and 2nu(9) bands and associated hot bands of HNO3 have been calculated and compared with laboratory spectra, and the results are presented. Spectral intervals near 870/cm for which best agreement was obtained are used to quantitatively analyze HNO3 absorption features in 0.02/cm resolution stratospheric solar absorption spectra.

Goldman, A.↗

NASA NTRS1985

Spectroscopic measurements of atmospheric HCN at northern and southern latitudes

A number of lines belonging to the nu(3) fundamental vibration-rotation band of hydrogen cyanide (HCN) have been identified in atmospheric infrared absorption spectra obtained on high-altitude balloon flights at 32 deg N in 1976 and at 30 deg S in 1977. Quantitative analysis of these spectral features has resulted in the first determination of atmospheric HCN concentrations in the Southern Hemisphere, as well as an independent estimate of stratospheric HCN abundance in the Northern Hemisphere. Within the uncertainties of the present and previous measurements, the Northern Hemisphere result is consistent with those of other investigators, and Southern Hemisphere HCN concentrations appear to be similar to those in the Northern Hemisphere.

Smith, M. A. H.↗

NASA NTRS1985

Infrared measurements of atmospheric ethane (C2H6) from aircraft and ground-based solar absorption spectra in the 3000/cm region

A number of prominent Q-branches of the nu-7 band of C2H6 have been identified near 3000/cm in aircraft and ground-based infrared solar absorption spectra. The aircraft spectra provide the column amount above 12 km at various altitudes. The column amount is strongly correlated with tropopause height and can be described by a constant mixing ratio of 0.46 ppbv in the upper troposphere and a mixing ratio scale height of 3.9 km above the tropopause. The ground-based spectra yield a column of 9.0 x 10 to the 15th molecules/sq cm above 2.1 km; combining these results implies a tropospheric mixing ratio of approximately 0.63 ppbv.

Coffey, M. T.↗

NASA NTRS1985

Comparison of the frequencies of NH3, CO2, H2O, N2O, CO, and CH4 as infrared calibration standards

The absolute accuracies of infrared calibration standards for the line positions have been investigated using a 0.0056-kayser-resolution (unapodized) Fourier-transform spectrum recorded from 550 to 5000 kayser. The spectrum has been obtained using a multicell arrangement containing the various molecular species. Detailed comoparisons reveal that standards for CO2, CH4, and N2O obtained from laser research and NH3 from Fourier-transform spectrometer research are consistent within the accuracies of the present data (+ or 0.0001 kayser). However, certain N2O, H2O, and CO values in the 1100-to 2300 kayser region are systematically high by 0.0001 to 0.0004 kayser. Correction factors for the H2O and CO standards are obtained to bring these into agreement with the laser values. In addition, corrected values for the 2nu-2 and nu-1 bands of N2O at 9 microns are reported.

Brown, L. R.↗