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At least 955 records · Page 53
All sourcesNASA NTRSDOE OSTI
NASA NTRS1989

Supernova 1987A: 18 months later

An overview of the significance for physics of the closest visual supernova in almost 400 years is presented. The supernova occurred in the Large Magellanic Cloud (LMC), approx. 50 kpc away. The supernova star was a massive star of approx. 15 to 20 solar mass. Observations now show that it was once a red giant but lost its outer envelope. The lower than standard luminosity and higher observed velocities are a natural consequence of the pre-supernova star being a blue rather than a red (supergiant). Of particular importance to physicsts is the detection of neutrinos from the event by detectors in the United States and Japan. Not only did this establish extra-solar system neutrino astronomy, but it also constrained the properties of neutrino. It is shown that the well established Kamioka-IMB neutrino burst experimentally implies an event with about 2 to 4 x 10 to the 53rd power ergs emitted in neutrinos and a temperature, T sub nu e, of between 4 and 4.5 MeV. This event is in excellent agreement with what one would expect from the gravitational core collapse of a massive star. The anticipated frequency of collapse events in our Galaxy is discussed.

Schramm, David N.↗
NASA NTRS1988

A numerical study of viscous vortex rings using a spectral method

Viscous, axisymmetric vortex rings are investigated numerically by solving the incompressible Navier-Stokes equations using a spectral method designed for this type of flow. The results presented are axisymmetric, but the method is developed to be naturally extended to three dimensions. The spectral method relies on divergence-free basis functions. The basis functions are formed in spherical coordinates using Vector Spherical Harmonics in the angular directions, and Jacobi polynomials together with a mapping in the radial direction. Simulations are performed of a single ring over a wide range of Reynolds numbers (Re approximately equal gamma/nu), 0.001 less than or equal to 1000, and of two interacting rings. At large times, regardless of the early history of the vortex ring, it is observed that the flow approaches a Stokes solution that depends only on the total hydrodynamic impulse, which is conserved for all time. At small times, from an infinitely thin ring, the propagation speeds of vortex rings of varying Re are computed and comparisons are made with the asymptotic theory by Saffman. The results are in agreement with the theory; furthermore, the error is found to be smaller than Saffman's own estimate by a factor square root ((nu x t)/R squared) (at least for Re=0). The error also decreases with increasing Re at fixed core-to-ring radius ratio, and appears to be independent of Re as Re approaches infinity). Following a single ring, with Re=500, the vorticity contours indicate shedding of vorticity into the wake and a settling of an initially circular core to a more elliptical shape, similar to Norbury's steady inviscid vortices. Finally, we consider the case of leapfrogging vortex rings with Re=1000. The results show severe straining of the inner vortex core in the first pass and merging of the two cores during the second pass.

Stanaway, S. K.↗
NASA NTRS1983

Windward fraction of the total mass or heat transport for flow past a circular cylinder

The windward fraction of the total mass or heat transport for flow past a cylindrical aerodynamic object was estimated using the available experimental data for the angular distribution of the Nusselt transfer coefficient, Nu(theta, Re). The Re dependence of the windward surface fraction was calculated for the values of Re between 2 and 400,000. The results obtained from polar integrations of data from eight sources indicate that, for Reynolds numbers up to about 2000, more than 70 percent of the total transfer occurs on the windward surface. For the Re values above 100,000, the windward percentage is less than 50 percent.

Gokoglu, S.↗
NASA NTRS1989

Diffuse interstellar clouds as a chemical laboratory - The chemistry of diatomic carbon species

The chemistry of C2, CH, and CO in diffuse interstellar clouds is analyzed and compared to absorption line measurements toward background stars. Analytical expressions in terms of column densities are derived for the rate equations. The results indicate that in clouds with 4 mag of visual extinction, the abundance of C+ has to decrease by a factor of about 15 from the value traditionally used for clouds with 1 mag of extinction. The rate coefficients for the reactions C+ + CH - C2+ + H and C+ + H2 - CH2+ + h-nu need to be reduced from previous estimates. Chemical arguments are presented for the revised rate coefficients.

Federman, S. R.↗
NASA NTRS1988

Neutrinos from SN 1987A and cooling of the nascent neutron star

The implications of the detection of neutrinos from SN 1987A for the cooling of the nascent neutron star are considered. The nu-bar(e) number N, the apparent temperature, the cooling time scale measured by the Kamioka and IMB detectors, and the inferred neutron star apparent radius and binding energy are all found to provide striking verification of current supernova theory.

Lamb, D. Q.↗
NASA NTRS1989

Finite element applications to explore the effects of partial bonding on metal matrix composite properties

The mechanics of materials approach (definition of E, G, nu, and alpha) and the finite element method are used to explore the effects of partial bonding and fiber fracture on the behavior of high temperature metal matrix composites. Composite ply properties are calculated for various degrees of disbonding to evaluate the sensitivity of these properties to the presence of fiber/matrix disbonding and fiber fracture. The mechanics of materials approach allows for the determination of the basic ply material properties needed for design/analysis of composites. The finite element method provides the necessary structural response (forces and displacements) for the mechanics of materials equations. Results show that disbonding of fractured fibers affect only E-l(11) and alpha-l(11) significantly.

Caruso, J. J.↗
NASA NTRS1989

Infrared fluorescence efficiencies for the nu1 and nu5 bands of formaldehyde in the solar radiation field

Formaldehyde scattering strengths have been determined for equilibrium distributions of 100 K, 50 K, 20 K, and for the the non-LTE case of an essentially fully relaxed distribution. Integrated band g factors of 2.89 x 10 to the -4th photons/s per molecule for nu1 and 3.83 x 10 to the -4th for nu 5 are obtained. The results indicate that the most promising regions to search for cometary H2CO are at about 2782/cm, at 2794.5/cm, and at about 2835/cm.

Reuter, D. C.↗
NASA NTRS1989

Predictions of Poisson's ratio in cross-ply laminates containing matrix cracks and delaminations

A damage-dependent constitutive model for laminated composites has been developed for the combined damage modes of matrix cracks and delaminations. The model is based on the concept of continuum damage mechanics and uses second-order tensor valued internal state variables to represent each mode of damage. The internal state variables are defined as the local volume average of the relative crack face displacements. Since the local volume for delaminations is specified at the laminate level, the constitutive model takes the form of laminate analysis equations modified by the internal state variables. Model implementation is demonstrated for the laminate engineering modulus E(x) and Poisson's ratio nu(xy) of quasi-isotropic and cross-ply laminates. The model predictions are in close agreement to experimental results obtained for graphite/epoxy laminates.

Harris, Charles E.↗
NASA NTRS1989

New LRS spectra for 356 bright IRAS sources

The low-resolution spectra of all IRAS point sources with F(nu) (12 microns) greater than 40 Jy that were not included in the Atlas of Low-Resolution Spectra are presented. These have been classified into eight groups based upon the spectral morphology. Silicate emission spectra and red-continuum spectra associated with H II region sources form about 60 percent of this sample. All types of spectra in the LRS Atlas are represented in the sample except for emission-line sources. The sample is used to test a recent classification scheme for IRAS sources based on broadband colors. The spectra is used to test a recent classification scheme for IRAS sources based on broadband colors. The spectra are consistent with the classifications from the colors in most cases.

Volk, Kevin↗
NASA NTRS1989

Big Bang nucleosynthesis and the Quark-Hadron transition

An examination and brief review is made of the effects of quark-hadron transistion induced fluctuations on Big Bang nucleosynthesis. It is shown that cosmologically critical densities in baryons are difficult to reconcile with observation, but the traditional baryon density constraints from homogeneous calculations might be loosened by as much as 50 percent, to 0.3 of critical density, and the limit on the number of neutrino flavors remains about N(sub nu) is less than or approximately 4. To achieve baryon densities of greater than or approximately 0.3 of critical density would require initial density contrasts R is much greater the 10(exp 3), whereas the simplest models for the transition seem to restrict R to less than of approximately 10(exp 2).

Kurki-Suonio, Hannu↗
NASA NTRS1989

Cosmology and the weak interaction

The weak interaction plays a critical role in modern Big Bang cosmology. Two of its most publicized comological connections are emphasized: big bang nucleosynthesis and dark matter. The first of these is connected to the cosmological prediction of neutrine flavors, N(sub nu) is approximately 3 which in now being confirmed. The second is interrelated to the whole problem of galacty and structure formation in the universe. The role of the weak interaction both for dark matter candidates and for the problem of generating seeds to form structure is demonstrated.

Schramm, David N.↗
NASA NTRS1989

Big-bang nucleosynthesis revisited

The homogeneous big-bang nucleosynthesis yields of D, He-3, He-4, and Li-7 are computed taking into account recent measurements of the neutron mean-life as well as updates of several nuclear reaction rates which primarily affect the production of Li-7. The extraction of primordial abundances from observation and the likelihood that the primordial mass fraction of He-4, Y(sub p) is less than or equal to 0.24 are discussed. Using the primordial abundances of D + He-3 and Li-7 we limit the baryon-to-photon ratio (eta in units of 10 exp -10) 2.6 less than or equal to eta(sub 10) less than or equal to 4.3; which we use to argue that baryons contribute between 0.02 and 0.11 to the critical energy density of the universe. An upper limit to Y(sub p) of 0.24 constrains the number of light neutrinos to N(sub nu) less than or equal to 3.4, in excellent agreement with the LEP and SLC collider results. We turn this argument around to show that the collider limit of 3 neutrino species can be used to bound the primordial abundance of He-4: 0.235 less than or equal to Y(sub p) less than or equal to 0.245.

Olive, Keith A.↗
NASA NTRS1990

Search for interstellar methane

Researchers searched for interstellar methane in the spectra of infrared sources embedded in molecular clouds. New observations of several lines of the P and R branches of the nu 3 band of CH4 near 3.3 microns give column densities in the range N less than 1(-2) times 10 to the minus 16th power cm(-2). Resulting abundance ratios are (CH4)/(CO) less than 3.3 times 10 to the minus 2nd power toward GL961 in NGC 2244 and less than 2.4 times 10 to the minus 3rd power toward GL989 in the NGC 2264 molecular cloud. The limits, and those determined in earlier observations of BN in Orion and GL490, suggest that there is little methane in molecular clouds. The result agrees with predictions of chemical models. Exceptions could occur in clouds where oxygen may be depleted, for example by H2O freezing on grains. The present observations probably did not sample such regions.

Knacke, R. F.↗
NASA NTRS1989

Foreign-gas pressure broadening parameters of propane near 748/cm

The pressure-broadening coefficients of the nu sub 19 band of propane near 748/cm due to H2, N2, and He are determined using a tunable diode laser spectrometer at room temperature. The coefficients obtained were 0.183(5)/cm/atm for C3H8-H2, 0.119(2) for C3H8-N2, and 0.105(2) for C3H8-He. The possible implications of the results for propane on Titan, the earth, and Saturn are noted.

Nadler, Schachar↗
NASA NTRS1989

Kinetics and product studies of the reaction ClO + BrO using flash photolysis-ultraviolet absorption

The reaction between BrO and ClO was studied over the pressure range 50-700 torr and temperature range 220-400 K, using the flash photolysis-ultraviolet absorption method described by Watson et al. (1979). In order to investigate the mechanism of the BrO + ClO reaction, the product branch reactions Br + Cl2O yielding ClO + BrCl and Cl2O + h(nu) yielding products were examined. The rate constant for the overall reaction and the Arrhenius expression for the Br + Cl2O reaction are given, as well as the quantum yield for the production of atomic oxygen from the Cl2O photolysis.

Sander, Stanley P.↗
NASA NTRS1990

Big bang nucleosynthesis and the quark-hadron transition

An examination and brief review is made of the effects of quark-hadron transition induced fluctuations on Big Bang nucleosynthesis. It is shown that cosmologically critical densities in baryons are difficult to reconcile with observation, but the traditional baryon density constraints from homogeneous calculations might be loosened by as much as 50 percent, to 0.3 of critical density, and the limit on the number of neutrino flavors remains about N(sub nu) is less than or approximately 4. To achieve baryon densities of greater than or approximately 0.3 of critical density would require initial density contrasts R is much greater the 10(exp e), whereas the simplest models for the transition seem to restrict R to less than of approximately 10(exp 2).

Kurki-Suonio, Hannu↗
NASA NTRS1990

Infrared spectroscopic detection of sulfur hexafluoride (SF6) in the lower stratosphere and upper troposphere

This paper reports the detection and identification of the unresolved SF6 nu-3 band Q branch at 947.9/cm in high-resolution solar occultation spectra of the lower stratosphere and upper troposphere, which was made from the analysis of data recorded on April 30 to May 1, 1985 by the spaceborne Atmospheric Trace Molecule Spectroscopy Fourier transform spectrometer as part of the Spacelab 3 mission. On the basis of SF6 line-by-line parameters obtained from the laboratory studies of Bobin et al. (1987) and Schatz and Hornig (1953), the measured absorption was analyzed to deduce SF6 volume mixing ratios in the altitude range 12-22 km. It was found that, in this altitude range, the SF6 volume mixing ratio is independent of altitude, with an average measured value of 1.42 parts per trillion by volume (pptv) at 31 deg N latitude.

Rinsland, C. P.↗
NASA NTRS1990

A large-scale cosmic microwave background anisotropy measurement at millimeter and submillimeter wavelengths

A balloon-borne experiment to measure the anisotropy of the cosmic microwave background radiation at angular scales of 4 deg or greater is reported. The instrument simultaneously measures in four spectral bands centered on 5.6, 8.7, 15.8, and 22.5/cm. Three results are presented: (1) the 95-percent confidence limit for monochromatic anisotropies is 0.0001 or less on angular scales of 10 deg; (2) the Galactic plane dust emission at l = 42 deg is consistent with a nu-squared emissivity law at frequencies above 15/cm, with excess emission below 15/cm; and (3) atmospheric ozone at an altitude of 35 km may form clumps as large as Delta emissivity/emissivity = 0.002.

Page, Lyman A.↗