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At least 289 records · Page 16
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NASA NTRS1982

Pressure-induced H2 opacity in the 5-micron region

The H2 opacity arising from the pure-rotational hexadecapole-induced transitions occurring during H2-H2 and H2-He collisions, and from the hexadecapole-induced and the quadrupole-induced transitions in H2-He collisions, has been calculated. The hexadecapole-induced and quadrupole-induced contributions from H2-H2 collisions are important H2 opacities in the frequency range from 700-3000/cm for temperatures appropriate to the outer planets. It is concluded that this opacity is needed in addition to the opacity from the extrapolation of the 0-0 and 1-0 H2-H2 collisionally-induced bands to interpret the spectrum at 5 microns for the outer planets.

Goorvitch, D.↗
NASA NTRS1981

Anisotropy of the cosmic microwave background radiation

Theoretical predictions of the angular anisotropy in the cosmic microwave background radiation on both small and large angular scales are presented, and the effect of massive neutrinos on both the background radiation anisotropy and on the galaxy correlation function over very large scales is reviewed. Current observations show that the quadrupole anisotropy provides the greatest constraint on theory, and the values for the gravitational potential fluctuations indicate that small amplitude but sufficiently large-scale density fluctuations, both at the present epoch and on the surface of last scattering, can produce significant large angular scale variations in the radiation temperature. Most importantly, it is proposed that the quadrupole moment is most simply and elegantly interpreted in terms of the density fluctuations on very large scales whose presence is inferred from the requirement that an initial fluctuation spectrum is required in order for structure to develop.

Silk, J.↗
NASA NTRS1982

Axially symmetric gravitational two-body problem of Cooperstock, Lim, and Hobill

Cooperstock, Lim, and Hobill have constructed and analyzed a model spacetime describing the head-on free-fall from rest of two fluid balls under their mutual gravitational attraction. These authors find a gravitational radiation energy flux having a different dependence on the parameters of the problem than would be expected on the basis of the quadrupole formula. It is shown that this dependence is due to their having incorrectly solved Einstein's gravitational field equations. The correct solution is consistent with the quadrupole formula.

Walker, M.↗
NASA NTRS1985

Magnetic and thermodynamic structure of the solar corona during sunspot minimum

A model of the solar corona during sunspot minimum was constructed. It was suggested that pole-equator asymmetry is caused by interaction of global azimuthal electric currents in the corona and potential magnetic fields originating below the corona. The problem was reduced to a nonlinear ordinary differential equation for a structural function. Taking the difference in electron density between the equatorial plane and the polar direction from observations, the basic equation was solved and the global electric current distribution around the Sun along with the magnetic and thermodynamic structures of the solar corona was derived. The asymmetry between the two hemispheres, which can be due to the magnetic quadrupole, is considered in detail. It is shown that an additional quadrupole term in the magnetic field representation affects the position of polar coronal hole boundaries differently in the two hemispheres. As a result, the outflow from the two polar regions is found to be different.

Osherovich, V. A.↗
NASA NTRS1984

Theoretical model of the solar corona during sunspot minimum. I - Quasi-static approximation

The model of the solar corona (1.5 to 5 solar radius) during sunspot minimum is constructed. It is suggested that pole-equator asymmetry is caused by the interaction between global azimuthal electric currents in the corona and potential magnetic fields originated below. The asymmetry between the two hemispheres, which can be due to the magnetic quadrupole, is considered in detail. It is shown that an additional quadrupole term in the magnetic field representation affects the position of polar coronal hole boundaries differently in the two hemispheres. As a result, the outflow from the two polar regions is found to be different.

Osherovich, V. A.↗
NASA NTRS1985

A map of the cosmic background radiation at 3 millimeters

Data from a series of balloon flights covering both the Northern and Southern Hemispheres, measuring the large angular scale anisotropy in the cosmic background radiation at 3.3 mm wavelength are presented. The data cover 85 percent of the sky to a limiting sensitivity of 0.7 mK per 7 deg field of view. The data show a 50-sigma (statistical error only) dipole anisotropy with an amplitude of 3.44 + or - 0.17 mK and a direction of alpha = 11.2 h + or - 0.1 h, and delta = -6.0 deg + or - 1.5 deg. A 90 percent confidence level upper limit of 0.00007 is obtained for the rms quadrupole amplitude. Flights separated by 6 months show the motion of earth around the sun. Galactic contamination is very small, with less than 0.1 mK contribution to the dipole quadrupole terms. A map of the sky has been generated from the data.

Lubin, P.↗
NASA NTRS1985

Real-time measurement of sodium chloride in individual aerosol particles by mass spectrometry

The method of particle analysis by mass spectrometry has been applied to the quantitative measurement of sodium chloride in individual particles on a real-time basis. Particles of known masses are individually introduced, in the form of a beam, into a miniature Knudsen cell oven (1600 K). The oven is fabricated from rhenium metal sheet (0.018 mm thick) and is situated in the ion source of a quadrupole mass spectrometer. A particle once inside the oven is trapped and completely volatilized; this overcomes the problem of partial volatilization due to particles bouncing from the filament surface. Individual particles are thermally volatilized and ionized inside the rhenium oven, and produce discrete sodium ion pulses whose intensities are measured with the quadrupole mass spectrometer. An ion pulse width of several milliseconds (4-12 ms) is found for particles in the mass range 1.3 x 10 to the -13th to 5.4 x 10 to the -11th g. The sodium ion intensity is found to be proportional to the particle mass to the 0.86-power. The intensity distribution for monodisperse aerosol particles possesses a geometric standard deviation of 1.09, showing that the method can be used for the determination of the mass distribution function with good resolution in a polydisperse aerosol.

Sinha, M. P.↗
NASA NTRS1987

The uses and abuses of the acoustic analogy in helicopter rotor noise prediction

The generation of noise by helicopter rotor blades is considered theoretically, reviewing recent analyses based on the acoustic analogy (where the effect of fluid motion is replaced by fictitious sources in an undisturbed fluid). The fundamental principles of the acoustic approach are explained and illustrated with diagrams; the governing Ffowcs-Williams/Hawkings equations are written with a reformulated quadrupole term; and the directivity of noise produced (1) by regions with steep gradients (such as shock surfaces) and (2) by boundary-layer quadrupoles (tip-vortex and blade wakes) is shown to be the same as that of thickness noise. The need to include both (1) and (2) in acoustic-analogy computations is indicated.

Farassat, F.↗
NASA NTRS1989

Silicon chemistry in interstellar clouds

Interstellar SiO was discovered shortly after CO but it has been detected mainly in high density and high temperature regions associated with outflow sources. A new model of interstellar silicon chemistry that explains the lack of SiO detections in cold clouds is presented which contains an exponential temperature dependence for the SiO abundance. A key aspect of the model is the sensitivity of SiO production by neutral silicon reactions to density and temperature, which arises from the dependence of the rate coefficients on the population of the excited fine structure levels of the silicon atom. This effect was originally pointed out in the context of neutral reactions of carbon and oxygen by Graff, who noted that the leading term in neutral atom-molecule interactions involves the quadrupole moment of the atom. Similar to the case of carbon, the requirement that Si has a quadrupole moment requires population of the J = 1 level, which lies 111K above the J = 0 ground state and has a critical density n(cr) equal to or greater than 10(6)/cu cm. The SiO abundance then has a temperature dependence proportional to exp(-111/T) and a quadratic density dependence for n less than n(cr). As part of the explanation of the lack of SiO detections at low temperatures and densities, this model also emphasizes the small efficiencies of the production routes and the correspondingly long times needed to reach equilibrium. Measurements of the abundance of SiO, in conjunction with theory, can provide information on the physical properties of interstellar clouds such as the abundances of oxygen bearing molecules and the depletion of interstellar silicon.

Langer, William D.↗
NASA NTRS1990

The symmetry properties of planetary magnetic fields

This paper provides a comparative study of the geometrical structures of the magnetic fields of earth, Jupiter, Saturn, and Uranus, starting from the traditional multipolar representations of these fields. For earth, Jupiter, and Saturn, the centered dipole, quadrupole, and octupole contributions are included, while at Uranus only the dipole and quadrupole contributions are considered. It is found that there are a number of common features of the magnetic fields of earth and Jupiter. Compared to earth and Jupiter, the Saturnian field exhibits not only a high degree of symmetry about the rotation axis but also a high degree of antisymmetry about the equatorial plane. The Uranian field shows strong deviations from both such symmetries. Nevertheless, there remain features common to all four planets.

Raedler, Karl-Heinz↗
NASA NTRS1989

The polarizabilities of neon

The static dipole polarizability, second hyperpolarizability, quadrupole polarizability and dipole-dipole-quadrupole hyperpolarizability for the Ne atom are computed, using large Gaussian basis sets and coupled cluster wavefunctions. Correlation effects are substantial, ranging from 15 percent for the dipole polarizability to 40 percent for the second hyperpolarizability. It is confirmed by explicit calculation earlier hypotheses that g-type and higher angular momentum functions and core correlation effects make almost no contribution to these properties in Ne. Triple excitations, on the other hand, are very important, accounting for as much as 25 percent of the correlation contribution to the second hyperpolarizability. The best estimate of the second hyperpolarizability is 119 + or - 4 au, in good agreement with the recent calculations of Maroulis and Thakkar (1989) and the latest experimental result of Shelton (1989).

Taylor, Peter R.↗
NASA NTRS1990

The sound of moving bodies

The importance of the quadrupole source term in the Ffowcs, Williams, and Hawkings (FWH) equation was addressed. The quadrupole source contains fundamental components of the complete fluid mechanics problem, which are ignored only at the risk of error. The results made it clear that any application of the acoustic analogy should begin with all of the source terms in the FWH theory. The direct calculation of the acoustic field as part of the complete unsteady fluid mechanics problem using CFD is considered. It was shown that aeroelastic calculation can indeed be made with CFD codes. The results indicate that the acoustic field is the most susceptible component of the computation to numerical error. Therefore, the ability to measure the damping of acoustic waves is absolutely essential both to develop acoustic computations. Essential groundwork for a new approach to the problem of sound generation by moving bodies is presented. This new computational acoustic approach holds the promise of solving many problems hitherto pushed aside.

Brentner, Kenneth Steven↗
NASA NTRS1990

Multipole radiation in charged-particle scattering

This paper formulates the general problem of photon emission in particle scattering using a classical and quantum mechanical approach. The connection between the classical short collision time (SCT) and Born results is examined for various special classifications of problems. In the dipole case the two formulations yield results that can be expressed in the same form and for arbitrary scattering potential. For quadrupole emission the SCT and Born results are the same only for a short-range potential, however. The quadrupole problem is more sensitive to details in the process because the calculation requires an expansion of the total amplitude for the process to lowest order in the photon wave number or momentum. The special case of photon emission associated with spin-flip transitions during scattering is considered for spin-1/2 particles. Like classical magnetic dipole radiation, there is no infrared divergence feature for this type of emission.

Gould, Robert J.↗
NASA NTRS1990

A dipole moment of the microwave background as a cosmological effect

A spherically symmetrical Tolman-Bondi cosmological model is presented in which the curvature of space and the entropy variety with distance from the center. The dipole and quadrupole moments in the distribution of the microwave background radiation are calculated as a function of cosmic time and position of an observer, assuming that the distance to the horizon is much smaller than any characteristic scale in the model. The quadrupole moment is found to be affected mostly by the gradient in the curvature of space while the dipole moment is dominated by the gradient of entropy. The results indicate that the observed dipole in the microwave background may be cosmological in origin. Observational tests of this argument are suggested.

Paczynski, Bohdan↗
NASA NTRS1990

Application of reversal electron attachment for ultrasensitive detection of thermal electron-attaching molecules - CCl4 and C6H5O2

A standard gas-dilution method was used to determine the selective response of the reversal electron attachment detector to carbon tetrachloride concentrations in nitrogen. Data are provided that determine the lowest concentration of sample detectable with the present instrumental configuration as being below 1.0 part per trillion by volume. The incorporation of a 90-deg electrostatic deflector with the quadrupole mass spectrometer is shown to be vital, and with it, negative-ion quadrupole mass spectrometry is used to characterize the ionization process. Observations are also made of the reversal electron attachment response to nitrobenzene. The analytical potential of reversal electron capture negative-ion mass spectrometry is examined, and areas for future development are discussed.

Bernius, Mark T.↗
NASA NTRS1991

Oscillations of rotating neutron stars

A perturbation technique is used to compute the rotational corrections to the nonradial oscillation spectrum of a realistic neutron star model. The l = l(0) oscillations are coupled to l = l(0) + or - 1 oscillations by the Coriolis force. To calculate the rotational corrections to the quadrupole, l(0) = 2, oscillation modes, previous calculations of the nonradial oscillation spectrum of this neutron star model are extended to include l(0) = 1 and l(0) = 3 modes, as well as many higher overtones at each value of l(o). As an example of this technique, the rotational corrections to two quadrupole toroidal modes are computed. For these modes the coupling to the spheroidal class of oscillations produced by the Coriolis force introduces a nonzero radial component to the velocity field, as well as a nonvanishing Lagrangian density perturbation. This result is used to compute the neutrino damping rates for these toroidal modes of a rotating neutron star. The neutrino damping time can approach the gravitational radiation damping time in rotating neutron stars if the central temperature is high enough. The rotationally induced coupling of spheroidal oscillations to toroidal modes can also produce significant displacements at the stellar surface in some of the toroidal modes. The damping rates due to this process for the rotationally corrected toroidal modes are estimated. The coupling of surface motions to the toroidal modes also have interesting implications for channeling energy, e.g., that associated with a glitch in the crust, to the surface of the star. Perhaps this might produce observable effects in the pulsar emission process or a gamma-ray burst event.

Strohmayer, Tod E.↗
NASA NTRS1991

Critical problems of computational aeroacoustics

The aeroacoustics of rigid boundaries is discussed. Lighthill gave a formulation of this problem in which he showed that the sources of the acoustic field were quadrupole in nature. We have preferred a different formulation of the problem, in which the quadrupoles are sources for a nonlinear wave equation, as opposed to the linear one used by Lighthill. This is given here in a figure which also gives further details of a solution procedure for the Euler equations appropriate for the aeroelastic problem and motivated by the analysis of Crow. In accordance with our formulation, we contend that an algorithm for accurate solutions of an inhomogeneous nonlinear wave equation is of prime importance.

Rogers, Joel C. W.↗