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NASA NTRS1984

Properties of the Upper Tropospheres of Uranus and Neptune Derived from Observations at Visible to Near-Infrared Wavelengths

Photons at wavelengths between 0.3 and 4.5 microns penetrate the atmospheres of Uranus and Neptune to pressures between about 0.01 bar and 10 bars. This pressure range brackets the radiative convective boundary in both atmospheres and is therefore designated upper troposphere. Physical processes which govern the transfer of radiation in Uranus's and Neptune's atmospheres at these wavelengths include Rayleigh/Raman scattering by hydrogen, scattering and broadband absorption by suspended aerosol particles and absorption in discrete bands and lines by methane and hydrogen. Consequently, tropospheric properties constrained by observations at these wavelengths include optical properties and distribution of aerosol particles, methane/hydrogen ratio, and ortho/para hydrogen ratio. Recent observations of Uranus and Neptune in this spectral range, are reviewed and compared with predictions based on models of the atmospheric structures. Significant results for Uranus include the presence of an opaque lower boundary to the visible atmosphere very near the level corresponding to 2 bars pressure, and consequently a methane/hydrogen ratio no less than 3 percent.

Bergstralh, J. T.↗

NASA NTRS1984

Cosmic ray propagation in the local superbubble

It is suggested that a ring of HI gas lying in the galactic plane is part of a supershell which formed some 3 x to the 7th power years ago. The consequences of a closed magnetic supershell for cosmic ray propagation are examined and it is concluded that there is no evidence which precludes the production and trapping of cosmic rays in such a region. A consequence of superbubble confinement is that the mean age of cosmic rays would be independent of energy. This can be tested by high energy observations of the isotopic composition of Be.

Steitmatter, R. E.↗

NASA NTRS1985

Galileo internal electrostatic discharge program

The Galileo spacecraft which will orbit Jupiter in 1988 will encounter a very harsh environment of energetic electrons. These electrons will have sufficient energy to penetrate the spacecraft shielding, consequently depositing charges in the dielectric insulating materials or ungrounded conductors. The resulting electric field could exceed the breakdown strength of the insulating materials, producing discharges. The transients produced from these Internal Electrostatic Discharges (IESD) could, depending on their relative location, be coupled to nearby cables and circuits. These transients could change the state of logic circuits or degrade or even damage spacecraft components, consequently disrupting the operation of subsystems and systems of the Galileo spacecraft during its expected mission life. An extensive testing program was initiated for the purpose of understanding the potential threats associated with these IESD events. Data obtained from these tests were used to define design guidelines.

Leung, P. L.↗

NASA NTRS1985

Gravity Reception and Cardiac Function in the Spider

The following features of the arachnid gravity system were studied. (1) the absolute threshold to hyper-gz is quite low indicating fine proprioreceptive properties of the lyriform organ, the Gz/vibration detector; (2) the neurogenic heart of the spider is a good dependent variable for assessing its behavior to Gz and other stimuli which produce mechanical effects on the exoskeleton; (3) Not only is the cardiac response useful but it is now understood to be an integral part of the system which compensates for the consequences of gravity in the spider (an hydraulic leg extension); and (4) a theoretical model was proposed in which a mechanical amplifier, the leg lever, converts a weak force (at the tarsus) to a strong force (at the patella), capable of compressing the exoskeleton and consequently the lyriform receptor.

Finck, A.↗

NASA NTRS1985

Cosmic ray propagation in the local superbubble

It is suggested that a ring of HI gas lying in the galactic plane is part of a supershell which formed some 3 x 10 to the 7th power years ago. The consequences of a closed magnetic supershell for cosmic ray propagation are examined and it is concluded that there is no evidence which precludes the production and trapping of cosmic rays in such a region. A consequence of superbubble confinement is that the mean age of cosmic rays would be independent of energy. This can be tested by high energy observations of the isotopic composition of Be.

Streitmatter, R. E.↗

NASA NTRS1986

Supernova nucleosynthesis in low-metallicity populations

The mass loss rate in low-metallicity stars is discussed, and the consequences of that rate for the fate of such stars are considered. It is shown that, if radiation pressure on dust is important in driving the mass loss from red giants, and if these stars do not dredge up large amounts of processed material during their evolution, then the total amount of mass lost by Population II stars with low metallicity is small. Consequently, the rate of supernovae in populations of low metallicity is much higher than in populations of solar abundances. This conclusion leads to the prediction that the supernova rate should be high in galaxies that have some intermediate mass stars and have metallicity less than about 0.1 of the solar value.

Jura, M.↗

NASA NTRS1986

Heat transport in steep temperature gradients. I - Small flaring solar loops

Results on nonlocal heat transport which properly takes into account the presence of fast electrons with mean free paths much longer than the temperature scale height L are reviewed. In terms of the mean free path for the slow bulk electrons, lambda(s), the nonlocal effects are important whenever lambda(s)/L greater than 0.001, with the following consequences. The heat flux in the hot part of the gradient is reduced relative to the Spitzer-Haerm value q(SH) which does not take into account the heat carried away by the fast electrons. The heat flux in the cold part of the gradient is enhanced relative to the value q(SH) which does not take into account the heat deposited by the fast electrons. These quite general results, which should have several applications in astrophysics, are applied to the problem of thermal hard X-ray burst models. It is shown that heat is not bottled up as effectively as in some past models, and temperatures achieved for realistic energy input rates are consequently not as high. As a result such sources can be effective only in the soft part (10-30 keV) of the hard X-ray range for energy input rates up to 6,400 ergs/cu cm s. The analysis is based on a fluid model and does not consider the X-ray signature of fast electrons which escape to distances far beyond the conduction fronts formed. It is shown that such electrons could at most be effective in the soft part of the hard X-ray range.

Smith, D. F.↗

NASA NTRS1986

The tail lobe ion spectrometer

A two-dimensional kinetic 'tail lobe ion spectrometer' model for the transport of ionospheric ions from polar cleft ionosphere into the tail lobes is developed to semiquantitatively simulate the behavior of the observed O(+) ion streams in the magnetotail lobes. The consequences of the present model include: (1) the increase in velocity of the O(+) streams away from the tail midplane; (2) the existence of 'tongues' of O(+) density from the cleft ionosphere into the tail lobes whose distribution configuration depends on the convection electric field and the source thermal energies; and (3) very low parallel thermal energies and speeds in the lobes which are correlated with the parallel ion bulk velocities. These consequences are reasonably consistent with the trends in lobe streams observed by recent spacecraft.

Horwitz, J. L.↗

NASA NTRS1986

Geometrization of spin and the Weyssenhoff fluid conjecture

It is shown that the logical treatment of spinning perfect fluids occurs in a metric-torsion space-time with or without mass conservation. The Lagrangian formulation of a spin density fluid is reviewed, concentrating on the relationship between spin and torsion for metric-torsion space-times. The significance of the mass constraint is discussed, and its consequences for the variation of the Lagrangian is given. That consequence is the geometrization of spin; that is, the Weyssenhoff form relating spin and the trace-free torsion is obtained without any ad hoc assumption.

Smalley, L. L.↗

NASA NTRS1986

Use of the Sun to determine pointing of ST radar beams

Verification of the beam pointing direction for ST (stratosphere troposphere) radars is a technically difficult problem. Consequently it is not usually done. For measurement of horizontal wind, the lack of precise knowledge of the beam pointing direction is usually of little consequence as any errors cause only a small uncertainty in the measured velocity. However, instantaneous vertical velocities are typically more than an order of magnitude less than horizontal velocities and average vertical velocities are more than two orders of magnitude less than average horizontal velocities. Hence small pointing errors for vertical beams can result in large errors due to contamination by horizontal winds. Experimental confirmation of pointing accuracy using the measured winds is difficult but has been achieved where horizontal and vertical winds are measured at the same site. Using the techniques described by Balsley and Riddle, 1984 and Riddle and Balsley, 1985, pointing accuracy was measured at Ponape, Federated States of Micronesia. The experiment is described in detail.

Riddle, A. C.↗

NASA NTRS1988

Turbulence modeling in non-inertial frames of reference

The effect of an arbitrary change of frame on the structure of turbulence models is examined from a fundamental theoretical standpoint. It is proven, as a rigorous consequence of the Navier-Stokes equations, that turbulence models must be form invariant under arbitrary translational accelerations of the reference frame and should only be affected by rotations through the intrinsic mean vorticity. A direct application of the invariance property along with the Taylor-Proudman Theorem, material frame-indifference in the limit of two-dimensional turbulence and Rapid Distortion Theory is shown to yield powerful constraints on the allowable form of turbulence models. Most of the commonly used turbulence models are demonstrated to be in serious violation of these constraints and consequently are inconsistent with the Navier-Stokes equations in non-inertial frames. Alternative models with improved non-inertial properties are developed and some simple applications to rotating turbulent flows are considered.

Speziale, Charles G.↗

NASA NTRS1987

Stimulated dissipation of magnetic discontinuities and the origin of solar flares

It is proposed that the principal cause of the confined solar flare is the dissipation of magnetic energy at the many small-scale pre-existing tangential discontinuities in the local bipolar magnetic field. The discontinuities are a consequence of the continuous shuffling and intermixing of the footpoints of the bipolar field by the turbulent photospheric granules. The X-ray corona within the bipolar field is presumed to be a consequence of the continuing dissipation by reconnection at these discontinuities. A flare results when static deformation and/or internal agitation of the field stimulates the onset of rapid reconnection at the many small internal discontinuities. The discontinuities are partially exhausted by the flare, so that the post-flare X-ray emission of that particular loop is substantially below the pre-flare level for a period of some hours while the discontinuities are being rejuvenated.

Parker, E. N.↗

NASA NTRS1988

Large molecules in diffuse interstellar clouds

The effects of the presence of a substantial component of large molecules on the chemistry of diffuse molecular clouds are explored, and detailed models of the zeta Persei and zeta Ophiuchi clouds are constructed. The major consequence is a reduction in the abundances of singly charged atomic species. The long-standing discrepancy between cloud densities inferred from rotational and fine-structure level populations and from the ionization balance can be resolved by postulating a fractional abundance of large molecules of 1 x 10 to the -7th for zeta Persei and 6 x 10 to the -7th for zeta Ophiuchi. If the large molecules are polycyclic aromatic hydrocarbons (PAH) containing about 50 carbon atoms, they contain 1 percent of the carbon in zeta Persei and 7 percent in zeta Ophiuchi. Other consequences of the possible presence of PAH molecules are discussed.

Lepp, S.↗

NASA NTRS1988

On the formation of black holes

The paper explores the consequences of the existence of a burning process beyond ordinary nuclear processes (which stop at iron), involving the 'strange' particles. In effect, this idea has already had considerable discussion within the high energy physics community in terms of 'quark' matter. A possible consequence is that neutron stars may explode rather than collapse to black holes. It should be evident that such a possibility suggests radically new scenarios for activity in galactic nuclei and gamma ray burst sources.

Michel, F. Curtis↗

NASA NTRS1987

Model for the geomagnetic ion spectrometer in the magnetotail lobes

A two-dimensional kinetic tail-lobe ion spectrometer model for the transport of ionospheric ions from the polar-cleft ionosphere into the tail lobes is developed to simulate semiquantitatively the behavior of the observed O(+) ion streams in the magnetotail lobes. The consequences of the present model include: (1) the increase in velocity of the O(+) streams away from the tail midplane and (2) the existence of tongues of O(+) density from the cleft ionosphere into the tail lobes whose distribution configuration depends on the convection electric field and the source thermal energies. These consequences are reasonably consistent with the trends in lobe streams observed by recent spacecraft.

Horwitz, J. L.↗

NASA NTRS1988

Functional reasoning in diagnostic problem solving

This work is one facet of an integrated approach to diagnostic problem solving for aircraft and space systems currently under development. The authors are applying a method of modeling and reasoning about deep knowledge based on a functional viewpoint. The approach recognizes a level of device understanding which is intermediate between a compiled level of typical Expert Systems, and a deep level at which large-scale device behavior is derived from known properties of device structure and component behavior. At this intermediate functional level, a device is modeled in three steps. First, a component decomposition of the device is defined. Second, the functionality of each device/subdevice is abstractly identified. Third, the state sequences which implement each function are specified. Given a functional representation and a set of initial conditions, the functional reasoner acts as a consequence finder. The output of the consequence finder can be utilized in diagnostic problem solving. The paper also discussed ways in which this functional approach may find application in the aerospace field.

Sticklen, Jon↗

NASA NTRS1988

Is the great attractor really a great wall

Some of the cosmological consequences are discussed of a late time phase transition which produces light domain walls. The observed peculiar velocity field of the Universe and the observed isotropy of the microwave background radiation severely constrain the wall surface density in such a scenario. The most interesting consequence of such a phase transition is the possibility that the local, coherent streaming motion reported by the Seven Samurai could be explained by the repulsive effect of a relic domain wall with the Hubble volume (the Great Wall).

Stebbins, Albert↗

NASA NTRS1988

Rocks, resolution, and the record at the terrestrial K/T boundary, eastern Montana and western North Dakota

Reconstructions of mass extinction events are based upon faunal patterns, reconstructed from numerical and diversity data ultimately derived from rocks. It follows that geological complexity must not be subsumed in the desire to establish patterns. This is exemplified at the Terrestrial Cretaceous-Tertiary (K/T) boundary in eastern Montana and western North Dakota, where there are represented all of the major indicators of the terrestrial K/T transition: dinosaurian and non-dinosaurian vertebrate faunas, pollen, a megaflora, iridium, and shocked quartz. It is the patterns of these indicators that shape ideas about the terrestrial K/T transition. In eastern Montana and western North Dakota, the K/T transition is represented lithostratigraphically by the Cretaceous Hell Creek Formation, and the Tertiary Tullock Formation. Both of these are the result of aggrading, meandering, fluvial systems, a fact that has important consequences for interpretations of fossils they contain. Direct consequences of the fluvial depositional environments are: facies are lenticular, interfingering, and laterally discontinuous; the occurrence of fossils in the Hell Creek and Tullock formations is facies-dependent; and the K/T sequence in eastern Montana and western North Dakota is incomplete, as indicated by repetitive erosional contacts and soil successions. The significance for faunal patterns of lenticular facies, facies-dependent preservation, and incompleteness is discussed. A project attempting to reconstruct vertebrate evolution in a reproducible manner in Hell Creek-type sediments must be based upon a reliable scale of correlations, given the lenticular nature of the deposits, and a recognition of the fact that disparate facies are not comparable in terms of either numbers of preserved vertebrates or depositional rates.

Fastovsky, D. E.↗