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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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NASA NTRS1972

A two component model of the diurnal variations in the thermospheric composition

A self-consistent, two-dimensional, two-component diffusion model is presented to describe the diurnal component of thermosphere dynamics. In the regions where oxygen and helium are the minor constituents, diffusion is shown to increase the amplitudes of these constituents and to advance the times of their diurnal maxima by several hours with respect to the gas temperature and the major species. Both effects are in basic agreement with satellite observations. The diffusion process is relatively insignificant for temperature, total mass density, and wind fields. The magnitude of the temperature-density phase delay is discussed with respect to its dependence on the electron density distribution.

Mayr, H. G.↗
NASA NTRS1978

Solitons and second harmonic radiation in type III bursts

The emission at the second harmonic of the plasma frequency from self-consistent Langmuir solitons is calculated. The theory predicts, in a natural way, the observed transition from the region where the intensity is linearly proportional to the electron flux to the region where the radio intensity is proportional to the square of the electron flux. A detailed comparison of the radiation observed at the second harmonic for the burst of 18:10 UT March 31, 1976, with the one expected on the assumption of radiation from solitons, using the correlated in situ measurements of the electric fields at the second harmonic, and their spatial structure, provides strong evidence that, for the first time, Langmuir solitons have been observed in space.

Papadopoulos, K.↗
NASA NTRS1994

Three-dimensional numerical simulation of current collection by a probe in a magnetized plasma

A three-dimensional numerical model for current collection in a magnetized plasma is reported. The model is based on an electrostatic particle-in-cell code. The model yields self-consistent sheath structure including distributions of plasma and the electric potential around the body and the collection of electrons. The analytical theory of current collection by a body in a magnetized plasma yields an upper bound for the collected current determined by the conservation of energy and canonical angular momentum. The theory shows that the collected charged particles come from a cylindrical volume aligned with the magnetic shadow of the body; the maximum radius r(sub o) of this volume is determined by the body size, body potential, and the ambient magnetic field. This theory does not deal with the sheath structure around the body. The condition for the actual current to approach the upper-bound value has been a matter of debate. Our simulations reveal when and why the collected current becomes equal to its upper-bound value. Sheath size in the radial direction perpendicular to the axial ambient magnetic field is determined by the current-limiting radius r(sub o). Our simulation yields time-average current in good agreement with its upper bound. This feature of the current collection is explained as follows: Once electrons enter the sheath, some of them are freely accelerated perpendicular to the magnetic field because they are demagnetized by the large gradients in the perpendicular electric fields. Simulations show a large perpendicular acceleration, producing perpendicular energy as large as that determined by the potential on the body, especially in the region where perpendicular electric fields (E perpendicular) are the strongest. An analysis shows that the demagnetization of electrons occurs above a threshold potential on the body. This threshold condition follows from the breakdown of the adiabaticity of the electron dynamics inside the sheath.

Singh, Nagendra↗
NASA NTRS1976

Diamagnetic boundary layers - A kinetic theory

A kinetic theory is presented for boundary layers associated with MHD tangential 'discontinuities' in a collisionless magnetized plasma, such as those observed in the solar wind. The theory consists of finding self-consistent solutions of Vlasov's equation and Maxwell's equation for stationary one-dimensional boundary layers separating two Maxwellian plasma states. Layers in which the current is carried by electrons are found to have a thickness of the order of a few electron gyroradii, but the drift speed of the current-carrying electrons is found to exceed the Alfven speed, and accordingly such layers are not stable. Several types of layers in which the current is carried by protons are discussed; in particular, cases are considered in which the magnetic-field intensity, direction, or both, changed across the layer. In every case, the thickness was of the order of a few proton gyroradii, and the field changed smoothly, although the characteristics depended somewhat on the boundary conditions. The drift speed was always less than the Alfven speed, consistent with stability of such structures. These results are consistent with observations of boundary layers in the solar wind near 1 AU.

Lemaire, J.↗
NASA NTRS1993

Diffusion coefficients of energetic water group ions near Comet Giacobini-Zinner

Data from the ultralow-energy charge analyzer and energetic particle anisotropy spectrometer sensors, acquired when the ICE spacecraft flew past Comet Giacobini-Zinner on September 11, 1985, are combined, and a single, self-consistent analysis technique is applied to derive a single-particle spectrum from about 200 to 1600 km/s. This information, together with the deduced bulk flow speed of the ions, is used to calculate a parallel diffusion coefficient in the transition region downstream of the bow wave (2.3 +/- 0.5) x 10 exp 17 sq cm/s; the corresponding scattering mean free path is (6 +/- 1) x 10 exp 4 km. The parallel diffusion coefficient is found to depend on the collision frequency of water group ions with Alfven waves, which are assumed to be propagating parallel (antiparallel) to the magnetic field.

Tan, L. C.↗
NASA NTRS1984

The structure of oblique subcritical bow shocks - ISEE 1 and 2 observations

ISEE 1 and 2 spacecraft magnetic field data are used to determine the scale lengths of various elements of shock structure, as well as wavelengths and wave polarizations, in a study of structural elements which include shock ramps and precursor wave trains over a series of oblique, low Mach number terrestrial bow shocks. Dissipative processes are reflected in the damping of the precursors, and dissipative scale lengths are of 200-800 km, or several times greater than shock thicknesses. The source of dissipation in the shocks does not appear to be the wave-wave decay of the whistlers, for which no evidence is found. The interaction of the whistler itself with upstream electrons is suggested as a simple and self-consistent explanation for the observed wave train damping.

Mellott, M. M.↗
NASA NTRS1983

Ponderomotive force in a warm two-fluid plasma

A general expression for the ponderomotive force of electromagnetic field with slowly varying amplitude in a warm plasma is obtained in the collisionless two-fluid model. Compared to the existing expression obtained for a cold and stationary plasma, this result contains two additional terms for the general case. One of them is involved with the density gradient and the wavenumber derivative of the dielectric tensor of a plasma. Thus, for an inhomogeneous plasma, it accounts for the effects of spatial dispersion, hence of finite temperature of the plasma. The other term is proportional to the time derivative of the density and the frequency derivative of the dielectric tensor, and is nonzero unless the plasma is stationary or nondispersive. Inclusion of these new terms in the ponderomotive force will enable self-consistent analysis of the general behavior of nonlinear waves with finite wavelengths in a warm plasma.

Lee, N. C.↗
NASA NTRS1993

Heat Transfer from Radiatively Heated Material in a Low Reynolds Number Microgravity Environment

A mathematical model of the transient three-dimensional heat transfer between a slowly moving ambient gas stream and a thermally thick or thin flat surface heated by external radiation in a microgravity environment is presented. The problem is motivated in part by fire safety issues in spacecraft. The gas phase is represented by variable property convection-diffusion energy and mass conservation equations valid at low Reynolds numbers. The absence of gravity and low Reynolds number together permit the flow to be represented by a self-consistent velocity potential determined by the ambient velocity and the thermal expansion in the gas. The solid exchanges energy with the gas by conduction/convection and with the surroundings by surface absorption and re-emission of radiation. Heat conduction in the solid is assumed to be one dimensional at each point on the surface as a consequence of the limited times (of order of 10 seconds) of interest in these simulations. Despite the apparent simplicity of the model, the results show a complex thermally induced flow near the heated surface. The thermal exchange between the gas and solid produces an outward sourcelike flow upstream of the center of the irradiated area and a sinklike flow downstream. The responses of the temperature fields and the associated flows to changes in the intensity of the external radiation and the ambient velocity are discussed.

Yamashita, H.↗
NASA NTRS1994

Multiparameter radar study of rainfall: Potential application to area-time integral studies

Multiparameter radars measure one or more additional parameters in addition to the coventional reflectivity factor. The combination of radar observations from a multiparameter radar is used to study the time evolution of rainstorms. A technique is presented to self-consistently compare the area-time integral (ATI) and rainfall volume estimates from convective storms, using two different measurements from a multiparameter radar. Rainfall volumes for the lifetime of individual storms are computed using the reflectivity at S band (10-cm wavelength) as well as one-way specific attenuation at X band (3-cm wavelength). Area-time integrals are computed by summing all areas in each radar snapshot having reflectivities (S band) in excess of a preselected threshold. The multiparameter radar data used in this study were acquired by the National Center for Atmospheric Research (NCAR) CP-2 radar during the Cooperative Huntsville Meteorological Experiment (COHMEX) and the Convection and Precipitation/Electrification Experiment (CaPE), respectively. ATI studies were accomplished in this work using multiparameter radar data acquired during the lifetime of six convective events that occurred in the COHMEX radar coverage area. A case study from the COMHEX field campaign (20 July 1986) was selected to depict the various stages in the evolution of a storm over which the ATI and rainfall volume computations were performed using multiparameter radar data. Another case study from the CaPE field campaign (12 August 1991) was used to demonstrate the evolution of a convective cell based on differential reflectivity observations.

Raghavan, R.↗
NASA NTRS1994

The interstellar medium in the starburst regions of NGC 253 and NGC 3256

We discuss observations of the (C II) 158 micrometers, (O I) 63 micrometers, (Si II) 35 micrometers, (O III) 52,88 micrometers, and (S III) 33 micrometers fine-structure transitions toward the central 45 seconds of the starburst galaxies NGC 253 and NGC 3256. The (C II) and (O I) emission probably originates in photodissociated gas at the surfaces of molecular clouds, although a small (less than or approximately 30%) contribution to the (C II) flux from H II regions cannot be ruled out. The (O III) and (S III) lines originate in H II regions and the (Si II) flux is best explained as originating in H II regions with some contribution from photodissociation regions (PDRs). The gas phase silicon abundance is nearly solar in NGC 253, which we interpret as evidence for grain destruction in the starburst region. We find that the photodissociated atomic gas has densities approximately 10(exp 4)/cu cm and temperature 200-300 K. About 2% of the gas is in this phase. The thermal gas pressure in the PDRs, P(PDR)/k approximately 1-3 x 10(exp 6) K/cu cm, might represent the 'typical' interstellar gas pressure in starburst systems. The Far Ultraviolet (FUV) radiation fields illuminating the clouds are 10(exp 3)-10(exp 4) stronger than the local Galactic FUV field and come from the contribution of many closely packed O and B stars. For the central 250 pc of NGC 253, we find that the H II gas has an average density n(sub e) is approximately 400/cu cm. This corresponds to a thermal pressure P(H II)/k approximately 7 x 10(exp 6) K/cu cm which is approximately P(PDR)/k, suggesting that the ionized gas is in pressure equilibrium with the photodissociated gas at the surfaces of molecular clouds. The H II gas fills a significant fraction, approximately 0.01-0.3, of the volume between the clouds. The effective temperature of the ionizing stars in NGC 253 is greater than or approximately 34,500 K; 2 x 10(exp 5) O7.5 stars would produce the observed Lyman countinuum photon luminosity. The average separation between the stars is approximately 3 pc. Applying the simple model for the interstellar medium in galactic nuclei of Wolfire, Tielens, & Hollenbach (1990), we find the molecular gas in the central regions of NGC 253 and NGC 3256 to be distributed in a large number (5 x 10(exp 3) to 5 x 10(exp 5)) of small (0.5-2 pc), dense (approximately 10(exp 4)/cu cm) clouds (or alternatively 'thin-flattened' structures) with volume filling factors 10(exp -3) to 10(exp -2), very different from the local Interstellar Medium (ISM) of the Galaxy. We suggest a self-consistent scenario for the ISM in NGC 253 in which clouds and H II gas are in pressure balance with a supernova-shocked, hot 1-3 x 10(exp 6) K, low-density (approximately 10(exp 4)/cu cm), all pervasive medium. A feedback mechanism may be indicated in which the pressure generated by the supernovae compresses the molecular clouds and triggers further massive star formation. The similarity of ISM parameters deduced for NGC 253, NGC 3256, and M82 (Lord et al. 1993) suggests that the ISM properties are independent of the luminosity of the starburst or the triggering mechanism, but are rather endemic to starburst systems. The starburst in NGC 3256 appears to be a scaled-up version of the NGC 253 and M82 starbursts.

Carral, P.↗
NASA NTRS1994

Airborne boundary layer flux measurements of trace species over Canadian boreal forest and northern wetland regions

Airborne heat, moisture, O3, CO, and CH4 flux measurements were obtained over the Hudson Bay lowlands (HBL) and northern boreal forest regions of Canada during July - August 1990. The airborne flux measurements were an integral part of the NASA/Arctic Boundary Layer Expedition (ABLE) 3B field experiment executed in collaboration with the Canadian Northern Wetlands Study (NOWES). Airborne CH4 flux measurements were taken over a large portion of the HBL. The surface level flux of CH4 was obtained from downward extrapolations of multiple-level CH4 flux measurements. Methane source strengths ranged from -1 to 31 mg m(exp -2)/d, with the higher values occurring in relatively small, isolated areas. Similar measurements of the CH4 source strength in the boreal forest region of Schefferville, Quebec, ranged from 6 to 27 mg m(exp -2)/d and exhibited a diurnal dependence. The CH4 source strengths found during the ABLE 3B expedition were much lower than the seasonally averaged source strength of 51 mg m(exp -2)/d found for the Yukon-Kuskokwim delta region of Alaska during the previous ABLE 3A study. Large positive CO fluxes (0.31 to 0.53 parts per billion by volume (ppbv) m/s) were observed over the inland, forested regions of the HBL study area, although the mechanism for the generation of these fluxes was not identified. Repetitive measurements along the same ground track at various times of day near the Schefferville site also suggested a diurnal dependence for CO emissions. Measurements of surface resistance to the uptake of O3 (1.91 to 0.80 s/cm) for the HBL areas investigated were comparable to those observed near the Schefferville site (3.40 to 1.10 s/cm). Surface resistance values for the ABLE 3B study area were somewhat less than those observed over the Yukon-Kuskokwim delta during the previous ABLE 3A study. The budgets for heat, moisture, O3, CO, and CH4 were evaluated. The residuals from these budget studies indicated, for the cases selected, a moderate net photochemical production of O3 present in the boundary layer over the HBL that coincided with an in situ destruction of CO, although the mechanism responsible for the destruction of CO was not identified. Results from the O3 budget analysis indicate the importance of in situ photochemical production and its possible dominance over surface deposition to the local O3 budget at the Schefferville site. Measurements of the in situ production of O3 indicated a direct relationship between the presence of biomass burning or large-scale pollution effects. Residuals from budget calculations for conserved quantities (heat, moisture, and CH4) were compared with their respective surface fluxes to provide a measure of the internal self-consistency of the flux measurements.

Ritter, John A.↗
NASA NTRS1976

Calculations of molecular ionization energies using a self-consistent-charge Hartree-Fock-Slater method

A numerical-variational method for performing self-consistent molecular calculations in the Hartree-Fock-Slater (HFS) model is presented. Molecular wavefunctions are expanded in terms of basis sets constructed from numerical HFS solutions of selected one-center atomlike problems. Binding energies and wavefunctions for the molecules are generated using a discrete variational method for a given molecular potential. In the self-consistent-charge (SCC) approximation to the complete self-consistent-field (SCF) method, results of a Mulliken population analysis of the molecular eigenfunctions are used in each iteration to produce 'atomic' occupation numbers. The simplest SCC potential is then obtained from overlapping spherical atomlike charge distributions. Molecular ionization energies are calculated using the transition-state procedure; results are given for CO, H2O, H2S, AlCl, InCl, and the Ni5O surface complex. Agreement between experimental and theoretical ionization energies for the free-molecule valence levels is generally within 1 eV. The simple SCC procedure gives a reasonably good approximation to the molecular potential, as shown by comparison with experiment, and with complete SCF calculations for CO, H2O, and H2S.

Rosen, A.↗
NASA NTRS1978

Structure of current sheets in magnetic holes at 1 AU

Current density profiles in several types of interplanetary magnetic holes were calculated assuming that the currents flow in planar sheets and that the magnetic field varies only in the direction normal to the sheet. The planarity was verified in four holes which were observed by two suitably spaced spacecraft. The structure of the current sheets ranges from very simple in some holes to very complex in others. The observed structures are found to be qualitatively consistent with models based on self-consistent solutions of Vlasov's equation and Maxwell's equations. Examples of complex, irregular magnetic holes are also presented, and they are shown to contain multiple, current sheets in which currents flow parallel to one another.

Fitzenreiter, R. J.↗
NASA NTRS1981

The self-consistent calculation of pseudo-molecule energy levels, construction of energy level correlation diagrams and an automated computation system for SCF-X(Alpha)-SW calculations

The self consistent calculation of the electronic energy levels of noble gas pseudomolecules formed when a metal surface is bombarded by noble gas ions is discussed along with the construction of energy level correlation diagrams as a function of interatomic spacing. The self consistent field x alpha scattered wave (SCF-Xalpha-SW) method is utilized. Preliminary results on the Ne-Mg system are given. An interactive x alpha programming system, implemented on the LeRC IBM 370 computer, is described in detail. This automated system makes use of special PROCDEFS (procedure definitions) to minimize the data to be entered manually at a remote terminal. Listings of the special PROCDEFS and of typical input data are given.

Schlosser, H.↗
NASA NTRS1986

Self-consistent modelling of the polar thermosphere and ionosphere to magnetospheric convection and precipitation (invited review)

It has recently been demonstrated that the dramatic effects of plasma precipitation and convection on the composition and dynamics of the polar thermosphere and ionosphere include a number of strong interactive, or feedback, processes. To aid the evaluation of these feedback processes, a joint three dimensional time dependent global model of the Earth's thermosphere and ionosphere was developed in a collaboration between University College London and Sheffield University. This model includes self consistent coupling between the thermosphere and the ionosphere in the polar regions. Some of the major features in the polar ionosphere, which the initial simulations indicate are due to the strong coupling of ions and neutrals in the presence of strong electric fields and energetic electron precipitation are reviewed. The model is also able to simulate seasonal and Universal time variations in the polar thermosphere and ionospheric regions which are due to the variations of solar photoionization in specific geomagnetic regions such as the cusp and polar cap.

Rees, D.↗
NASA NTRS1985

Alfvenic heating of the chromosphere and corona

The behavior in the chromosphere of Alfven waves propagating on closed magnetic field lines (e.g. coronal loops) is considered. It is found that the observed chromospheric nonthermal velocities are consistent with the predicted behavior of Alfven waves. If they are indeed Alfven waves, then the observed motions imply energy fluxes which are sufficient to heat the corona and chromosphere. It is further shown that the observed motions can reproduce the observed chromospheric heating, if the heating occurs via a Kolmogoroff cascade. But a definitive analysis will require a self-consistent treatment of nonlinear effects.

Hollweg, J. V.↗
NASA NTRS1990

Spiral structure of M51: Streaming motions across the spiral arms

The atomic hydrogen (HI) and the H alpha emission line in the grand-design spiral galaxy M51 have been observed with the Westerbork Synthesis Radio Telescope and the Taurus Fabry-Perot imaging spectrometer, respectively. Across the inner spiral arms significant tangential and radial velocity gradients are detected in the H alpha emission after subtraction of the axi-symmetric component of the velocity field. The shift is positive on the inside and negative on the outside of the northern arm. Across the southern arm this situation is reversed. The direction of the shifts is such that the material is moving inward and faster compared to circular rotation in both arms, consistent with the velocity perturbations predicted by spiral density wave models for gas downstream of a spiral shock. The observed shifts amount to 20 to 30 km (s-1), corresponding to streaming motions of 60 to 90 km (s-1) in the plane of the disk (inclination angle 20 degrees). Comparable velocity gradients have also been observed by Vogel et al. in the CO emission from the inner northern arm of M51. The streaming motions in M51 are about 2 to 3 times as large as the ones found in HI by Rots in M81, and successfully modelled by Visser with a self-consistent density wave model. Researchers have not been able to detect conclusively streaming motions in the HI emission from the arms, perhaps due to the relatively poor angular resolution (approx. 15 seconds) of the HI observations.

Tilanus, R. P. J.↗
NASA NTRS1991

Extension of convection modeling into the high-latitude ionosphere - Some theoretical difficulties

The Rice Convection Model (RCM) is extended and merged with empirical models so as to cover the entire high-latitude ionosphere with the aim of providing precipitation and electric field inputs for ionosphere and thermosphere modelers and producing a model in which the boundaries of the precipitation and electric field patterns maintain physically consistent relationships to each other. The computed auroral electron energy flux, plotted as a function of latitude, exhibited an exaggerated two-peak structure. When no floor was placed under the precipitation rate, the minimum between the two peaks was much too deep to be consistent with typical observations. The regions of excessively weak precipitation map to equatorial distances of 15-35 RE and thus to the regions of the plasma sheet that were not included in previous self-consistent convection calculations.

Wolf, R. A.↗