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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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At least 811 records · Page 45
All sourcesNASA NTRSDOE OSTI
NASA NTRS1988

A statistical study of properties of Seyfert and starburst galaxies

Spectral and morphological data for 282 Seyfert and emission-line galaxies spanning radio to X-ray wavelengths are compiled. The data include a large number of optical emission-line measurements which have not been reported previously. These data are intended to provide a convenient summary of the relevant properties of these galaxies, as well as a data base to search for correlations among the various parameters in order to obtain a better understanding of the active galaxy phenomenon. The paper presents the data and analyzes the distributions of various properties of Seyfert 1 and Seyfert 2 galaxies and starburst galaxies. It is found that Seyferts 2s have a higher 60 micron/forbidden O III 5007 A flux ratio than Seyfert 1s. This result, combined with the fact that Seyfert 2s are more heavily reddened, indicate that they have a higher dust content. It is also found that starburst nuclei are comparable to Seyfert 2s in far-infrared and 20 cm luminosities, although their optical spectra are markedly different.

Dahari, Oved↗
NASA NTRS1989

The sunspot cycle variations of the neutral line on the source surface

The earlier presentation method of the sunspot cycle variations of the neutral line on the source surface by introducing the view longitude is defined. It is shown that the neutral line seen from the view longitude and the equivalent dipole (determined by Hoeksema, 1984) showed a trend of rotation throughout the sunspot cycle. However, the surface bounded by the neutral line is generally far from a circle. In fact, our combined presentation of both the equivalnet dipole and the nuetral line indicates graphically that such a simple description of the rotating (equivalent) dipole may be misleading. The concept of an inclined dipole with respect to the rotation axis may also be misleading.

Saito, T.↗
NASA NTRS1987

Design and test of an NLF wing glove for the variable-sweep transition flight experiment

Gloves for M = 0.7 and 0.8 design points were computationally designed and analyzed at conditions over the proposed flight test envelope. The resulting computational pressure distributions were analyzed in a boundary layer stability code. These results indicate that the available pressure distributions offer a wide range of combinations of cross flow and Tollmien-Schlichting N-factors. The glove designs along with the baseline configuration were tested in an entry into the National Transonic Facility. Analysis of the force and moment data showed no significant differences in the performance and stability and control characteristics between the baseline and gloved configurations. The rolling moment constraint was met over the entire flight test envelope for the gloved configuration. Pressure distributions for the NTF test confirmed the design pressure distributions were achieved. However, it was decided that with minor modifications to the inboard region of the glove, useful available data could be significantly increased by adding another row of pressure orifices at span station 167.

Waggoner, Ed G.↗
NASA NTRS1990

Time dependence of the earth's radiation fields determined from ERBS and NOAA-9 satellites

Satellite measurements from the Earth Radiation Budget Experiment (ERBE) are providing important quantitative data on the diurnal variability of broadband shortwave and longwave radiation. The results derived from the combination of the Earth Radiation Budget Satellite (ERBS) and NOAA-9 indicate that the largest diurnal variations in longwave radiation occur typically over deserts and over land areas which experience intense convective activity. Maximum values of the albedo diurnal amplitude factor are over oceans. Seasonal and cloud cover variations have important effects on the diurnal cycles of earth's radiation budget. ERBE results derived for individual regions are in substantial agreement with the diurnal results derived from the Geostationary Operational Environmental Satellite (GOES) measurements.

Harrison, E. F.↗
NASA NTRS1991

Cosmological structure formation

A summary of the current forefront problem of physical cosmology, the formation of structures (galaxies, clusters, great walls, etc.) in the universe is presented. Solutions require two key ingredients: (1) matter; and (2) seeds. Regarding the matter, it now seems clear that both baryonic and non-baryonic matter are required. Whether the non-baryonic matter is hot or cold depends on the choice of seeds. Regarding the seeds, both density fluctuations and topological defects are discussed. The combination of isotropy of the microwave background and the recent observations indicating more power on large scales have severly constrained, if not eliminated, Gaussian fluctuations with equal power on all scales, regardless of the eventual resolution of both the matter and seed questions. It is important to note that all current structure formation ideas require new physics beyond SU(3) x SU(2) x U(1).

Schramm, David N.↗
NASA NTRS1991

Thermal structure and energy balance of Uranus

The present study determines the basic properties of the atmospheric temperature field of Uranus through a combination of earth-based and Voyager measurements. Stellar occultation observations indicate both spatial and temporal variability at microbar pressure levels. The tropospheric and stratospheric vertical structure are established via Voyager radio occultation and infrared measurements as well as earth-based full-disk infrared observations. It is found that the measured lapse rate at pressures greater than about 600 microbar exceeds that for fully equilibrated ortho and para hydrogen. The latitude dependence of the upper tropospheric temperatures is determined from Voyager infrared measurements; remarkably little contrast is found. The weak horizontal structure is consistent with tropospheric zonal winds which decay with height and are directed prograde at midlatitudes but retrograde at low latitudes.

Conrath, B. J.↗
NASA NTRS1991

Clouds and aerosols in the Uranian atmosphere

Data accumulated from ground-based instruments, the IUE satellite, and Voyager experiments are used to determine the properties of at least three types of cloud and haze layers in the Uranian atmosphere. Studies of ground-based and IUE spectrophotometry data suggest an optically thin stratospheric haze, and optically thicker but surprisingly thin methane cloud near or above the 2-bar level, and a deeper cloud top of unknown composition near the 3-bar level. A strong increase in the intensity of scattered light from about 147 to 157 deg phase angle, as observed with the imaging experiment, provides definitive evidence for the presence of haze in the stratosphere. A combined radiative-transfer, microphysical, and photochemical model of these data indicates that the haze is located chiefly at pressures in excess of 1 microbar; that it is composed of condensed ethane, acetylene, and diacetylene; that its optical depth is on the order of 0.01 in the stratosphere; that the typical particle size is approximately 0.1; and that the haze is being produced at a rate of about 10 exp -16 g/ cm

West, Robert A.↗
NASA NTRS1992

A neuro-collision avoidance strategy for robot manipulators

The area of collision avoidance and path planning in robotics has received much attention in the research community. Our study centers on a combination of an artificial neural network paradigm with a motion planning strategy that insures safe motion of the Articulated Two-Link Arm with Scissor Hand System relative to an object. Whenever an obstacle is encountered, the arm attempts to slide along the obstacle surface, thereby avoiding collision by means of the local tangent strategy and its artificial neural network implementation. This combination compensates the inverse kinematics of a robot manipulator. Simulation results indicate that a neuro-collision avoidance strategy can be achieved by means of a learning local tangent method.

Onema, Joel P.↗
NASA NTRS1992

The Use of Subcarriers in Future DSN Missions

The performance of deep space telemetry signals that employ a residual carrier modulation technique is compared in the presence and absence of a subcarrier. When the subcarrier is present, the performance for the resulting pulse-coded modulation/phase-shift keyed/phase-modulated (PCM/PSK/PM) scheme is evaluated for both sine wave and square wave subcarriers and non-return-to zero (NRZ) data. When the subcarrier is absent, the performance for the resulting PCM/PM technique is evaluated for both the NRZ and the bi-phase data format. The comparison is based on telemetry performance as well as bandwidth efficiency. The first criterion is characterized in terms of the symbol error rate (SER) as a function of symbol SNR, loop bandwidth-to-data rate ratio, and modulation index. The bandwidth efficiency is characterized by the occupancy factor. The results of both the analysis and measurements show that when the interference-to-carrier ratio (ICR) is less than -15 dB, the performance degradation in the absence of a subcarrier is negligible. Various combinations of loop bandwidth-to-data rate ratios and modulation indices that achieve this performance are derived and listed. Bandwidth occupancy comparison indicates that PCM/PM/NRZ is the most efficient in this regard. Therefore, by eliminating the subcarrier and using the PCM/PM/NRZ scheme, many advantages can be realized without any sacrifice in performance.

Shihabi, M. M.↗
NASA NTRS1993

Infrared studies of circumstellar matter around Herbig Ae/Be and related stars

The study presents high spatial resolution data at 50 and 100 microns for seven young intermediate-mass stars with flat or rising spectral energy distributions. Five stars, namely, LkH-alpha 198, R Mon, CD -42 deg 11721, R CrA, and V645 Cyg, are resolved at 100 microns. The emission comes from spatially extended envelopes, with sizes varying between 0.025 and 0.4 pc. The wavelengths are optically thin at mid-IR and FIR wavelengths but become optically thick in the visual where the extinction amounts to 5-10 mag. In two cases, R CrA and V 645 Cyg, dust density distributions with steep density gradients are obtained, alpha is approximately equal to 2, while for LkH-alpha, R Mon, and CD -42 deg 11721, alpha is approximately equal to 0.5. Model fitting to the spectral energy distributions, combined with the constraints on the size of the emitting regions, indicates that inside the circumstellar envelopes a large fraction of the stellar radiation is already degraded to longer wavelengths.

Natta, Antonella↗
NASA NTRS1995

On the nature of the companion to HD 114762

The results of a recent study of coplanarity tendencies between stellar-equatorial and binary-orbital planes are applied to the low-metal F9 V star HD 114762, for which a possible substellar companion was reported by Latham et al. (1989). High-resolution spectroscopy is performed on HD 114762 in order to extract its projected rotational velocity (v sin i). This is then combined with an expected rotational velocity determined via age-scaling, providing an estimate of the star's equatorial inclination, which then combined with the results of the coplanarity study provides an approximate indication of the companion's orbital inclination. Although the formal uncertainties in this process preclude an accurate estimate of the companion's inclination, the results suggest that the inclination is low, possibly low enough to force the companion's mass above the limit for hydrogen fusion. It is thus possible the companion may be nothing more exotic than a low-mass M star, as opposed to a brown dwarf. These results add support to a similar conclusion recently obtained by Cochran et al. (1991).

Hale, Alan↗
NASA NTRS1994

Possible Halo Depictions in the Prehistoric Rock Art of Utah

In western American rock art the concentric circle symbol, which is widely regarded as a sun symbol, is ubiquitous. We provide evidence from Archaic and Fremont Indian rock art sites in northwestern Utah that at least one depiction was motivated by an observation of a complex halo display. Cirrus cloud optical displays are linked in both folklore and meteorology to precipitation-producing weather situations, which, in combination with an abundance of weather-related rock art symbolism, indicate that such images reflected the ceremonial concerns of the indigenous cultures for ensuring adequate precipitation. As has been shown to be the case with rock art rainbows, conventionalization of the halo image may have resulted in simple patterns that lacked recognizable details of atmospheric optical phenomena. However, in one case in which an Archaic-style petroglyph (probably 1500 yr or more old) satisfactorily reproduced a complicated halo display that contained parhelia and tangent arcs, sufficient geometric information is rendered to indicate a solar elevation angle of approx. 40 deg. at the time of observation.

Sassen, Kenneth↗
NASA NTRS1994

A Comparison of Telemetry Signals in the Presence and Absence of a Subcarrier

The performance of deep-space telemetry signals that employ a residual carrier modulation technique is compared in the presence and absence of a subcarrier. When the subcarrier is present, the performance for the resulting pulse-coded modulation/phase-shift keyed/phase-modulated (PCM/PSK/PM) scheme is evaluated for both sine-wave and square-wave subcarriers and Non-Return-to Zero (NRZ) data. When the subcarrier is absent, the performance for the resulting PCM/PM technique is evaluated for both the NRZ and the bi-phase data format. The comparison is based on telemetry performance as well as bandwidth efficiency. The first criterion is characterized in terms of the Symbol Error Rate (SER) as a function of symbol SNR, loop bandwidth-to-data rate ratio, and modulation index. The bandwidth efficiency is characterized by the occupancy factor. The results of both the analysis and measurements show that when the Interference-to-Carrier Ratio (ICR) is less than -20 dB, the performance degradation in the absence of a subcarrier is negligible. Various combinations of loop bandwidth-to-data rate ratios and modulation indices that achieve this performance are derived and listed. Bandwidth occupancy comparison indicates that PCM/PM/NRZ is the most efficient in this regard. Therefore, by eliminating the subcarrier and using the PCM/PM/NRZ scheme, many advantages can be realized without any sacrifice in performance.

Shihabi, Mazen M.↗
NASA NTRS1998

Nonlinear Response of Thin Cylindrical Shells with Longitudinal Cracks and Subjected to Internal Pressure and Axial compression Loads

The results of an analytical study of the nonlinear response of a thin unstiffened aluminum cylindrical shell with a longitudinal crack are presented. The shell is analyzed with a nonlinear shell analysis code that maintains the shell in a nonlinear equilibrium state while the crack is grown. The analysis accurately accounts for global and local structural response phenomena. Results are presented for internal pressure, axial compression, and combined internal pressure and axial compression loads. The effects of varying crack length on the nonlinear response of the shell subjected to internal pressure are described. The effects of varying crack length on the prebuckling, buckling and postbuckling responses of the shell subjected to axial compression, and subjected to combined internal pressure and axial compression are also described. The results indicate that the nonlinear interaction between the in-plane stress resultants and the out-of-plane displacements near a crack can significantly affect the structural response of the shell. The results also indicate that crack growth instabilities and shell buckling instabilities can both affect the response of the shell as the crack length is increased.

Starnes, James H.↗
NASA NTRS1999

Microgravity Two-Phase Flow Transition

Two-phase flows under microgravity condition find a large number of important applications in fluid handling and storage, and spacecraft thermal management. Specifically, under microgravity condition heat transfer between heat exchanger surfaces and fluids depend critically on the distribution and interaction between different fluid phases which are often qualitatively different from the gravity-based systems. Heat transfer and flow analysis in two-phase flows under these conditions require a clear understanding of the flow pattern transition and development of appropriate dimensionless scales for its modeling and prediction. The physics of this flow is however very complex and remains poorly understood. This has led to various inadequacies in flow and heat transfer modeling and has made prediction of flow transition difficult in engineering design of efficient thermal and flow systems. In the present study the available published data for flow transition under microgravity condition are considered for mapping. The transition from slug to annular flow and from bubbly to slug flow are mapped using dimensionless variable combination developed in a previous study by the authors. The result indicate that the new maps describe the flow transitions reasonably well over the range of the data available. The transition maps are examined and the results are discussed in relation to the presumed balance of forces and flow dynamics. It is suggested that further evaluation of the proposed flow and transition mapping will require a wider range of microgravity data expected to be made available in future studies.

Parang, M.↗
NASA NTRS2000

BEAM-ish: A Graphical User Interface for the Physical Characterization of Macromolecular Crystals

Crystal mosaicity is determined from the measurement of the reflection angular width and can be used as an indicator of crystal perfection. A new method has been developed that combines the use of unfocused synchrotron radiation, super-fine phi slicing and a CCD area detector to simultaneously measure the mosaicity of hundreds of reflections . The X-ray beam characteristics and Lorentz correction are deconvoluted from the resulting reflection widths to calculate the true crystal mosaicity.

Lovelace, Jeff↗
NASA NTRS2002

Quantitative analysis of aortic regurgitation: real-time 3-dimensional and 2-dimensional color Doppler echocardiographic method--a clinical and a chronic animal study

BACKGROUND: For evaluating patients with aortic regurgitation (AR), regurgitant volumes, left ventricular (LV) stroke volumes (SV), and absolute LV volumes are valuable indices. AIM: The aim of this study was to validate the combination of real-time 3-dimensional echocardiography (3DE) and semiautomated digital color Doppler cardiac flow measurement (ACM) for quantifying absolute LV volumes, LVSV, and AR volumes using an animal model of chronic AR and to investigate its clinical applicability. METHODS: In 8 sheep, a total of 26 hemodynamic states were obtained pharmacologically 20 weeks after the aortic valve noncoronary (n = 4) or right coronary (n = 4) leaflet was incised to produce AR. Reference standard LVSV and AR volume were determined using the electromagnetic flow method (EM). Simultaneous epicardial real-time 3DE studies were performed to obtain LV end-diastolic volumes (LVEDV), end-systolic volumes (LVESV), and LVSV by subtracting LVESV from LVEDV. Simultaneous ACM was performed to obtain LVSV and transmitral flows; AR volume was calculated by subtracting transmitral flow volume from LVSV. In a total of 19 patients with AR, real-time 3DE and ACM were used to obtain LVSVs and these were compared with each other. RESULTS: A strong relationship was found between LVSV derived from EM and those from the real-time 3DE (r = 0.93, P <.001, mean difference (3D - EM) = -1.0 +/- 9.8 mL). A good relationship between LVSV and AR volumes derived from EM and those by ACM was found (r = 0.88, P <.001). A good relationship between LVSV derived from real-time 3DE and that from ACM was observed (r = 0.73, P <.01, mean difference = 2.5 +/- 7.9 mL). In patients, a good relationship between LVSV obtained by real-time 3DE and ACM was found (r = 0.90, P <.001, mean difference = 0.6 +/- 9.8 mL). CONCLUSION: The combination of ACM and real-time 3DE for quantifying LV volumes, LVSV, and AR volumes was validated by the chronic animal study and was shown to be clinically applicable.

Validation Studies↗
NASA NTRS1992

N-methyl-D-aspartate increases acetylcholine release from rat striatum and cortex: its effect is augmented by choline

We examined the effects of N-methyl-D-aspartate (NMDA), a glutamate agonist, and of glutamate itself, on acetylcholine (ACh) release from superfused rat striatal slices. In a Mg(++)-free medium, NMDA (32-1000 microM) as well as glutamate (1 mM) increased basal ACh release by 35 to 100% (all indicated differences, P less than .05), without altering tissue ACh or choline contents. This augmentation was blocked by Mg++ (1.2 mM) or by MK-801 (10 microM). Electrical stimulation (15 Hz, 75 mA) increased ACh release 9-fold (from 400 to 3660 pmol/mg of protein): this was enhanced (to 4850 pmol/mg of protein) by NMDA (100 microM). ACh levels in stimulated slices fell by 50 or 65% depending on the absence or presence of NMDA. The addition of choline (40 microM) increased ACh release both basally (570 pmol/mg of protein) and with electrical stimulation (6900 pmol/mg of protein). In stimulated slices choline acted synergistically with NMDA, raising ACh release to 10,520 pmol/mg of protein. The presence of choline also blocked the fall in tissue ACh. No treatment affected tissue phospholipid or protein levels. NMDA (32-320 microM) also augmented basal ACh release from cortical but not hippocampal slices. Choline efflux from striatal and cortical (but not hippocampal) slices decreased by 34 to 50% in Mg(++)-free medium. These data indicate that NMDA-like drugs may be useful, particularly in combination with choline, to enhance striatal and cortical cholinergic activity. ACh release from rat hippocampus apparently is not affected by NMDA receptors.

Non-NASA Center↗