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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 289 records · Page 16
All sourcesNASA NTRSDOE OSTI
NASA NTRS1993

Design for testability and diagnosis at the system-level

The growing complexity of full-scale systems has surpassed the capabilities of most simulation software to provide detailed models or gate-level failure analyses. The process of system-level diagnosis approaches the fault-isolation problem in a manner that differs significantly from the traditional and exhaustive failure mode search. System-level diagnosis is based on a functional representation of the system. For example, one can exercise one portion of a radar algorithm (the Fast Fourier Transform (FFT) function) by injecting several standard input patterns and comparing the results to standardized output results. An anomalous output would point to one of several items (including the FFT circuit) without specifying the gate or failure mode. For system-level repair, identifying an anomalous chip is sufficient. We describe here an information theoretic and dependency modeling approach that discards much of the detailed physical knowledge about the system and analyzes its information flow and functional interrelationships. The approach relies on group and flow associations and, as such, is hierarchical. Its hierarchical nature allows the approach to be applicable to any level of complexity and to any repair level. This approach has been incorporated in a product called STAMP (System Testability and Maintenance Program) which was developed and refined through more than 10 years of field-level applications to complex system diagnosis. The results have been outstanding, even spectacular in some cases. In this paper we describe system-level testability, system-level diagnoses, and the STAMP analysis approach, as well as a few STAMP applications.

Simpson, William R.↗
NASA NTRS1994

Photoevaporation of disks around massive stars and application to ultracompact H II regions

Young massive stars produce sufficient Lyman continuum photon luminosity Phi(sub i) to significantly affect the structure and evolution of the accretion disks surrounding them. A nearly static, ionized, isothermal 10(exp 4) K atmosphere forms above the neutral disk for disk radii r less than r(sub g) = 10(exp 15) M(sub 1) cm, where M(sub *) = 10 solar mass M(sub 1) is the stellar mass. For r approximately greater than r(sub g) the diffuse field created by hydrogen recombinations to the ground state in the photoionized gas above the disk produces a steady evaporation at the surface of the disk, and this H II gas flows freely out to the ISM (the 'disk wind'). The detailed structure depends on the mass-loss rate dot-M(sub w) of the fast, approximately greater than 1000 km/sec, stellar wind from the massive star. A critical mass-loss rate dot-M(sub cr) is defined such that the ram pressure of the stellar wind equals the thermal pressure of the H II atmosphere at r(sub g). In the weak stellar wind solution, dot-M(sub w) less than dot-M(sub cr), the diffuse photons from the atmosphere above r(sub g) produce a photoevaporative mass-loss rate from the disk at r approximately greater than r(sub g) of order 1 x 10(exp -5)(Phi(sub 49))(exp 1/2)(M(sub 1))(exp 1/2) solar mass/year, where Phi(sub i) = 10(exp 49) Phi(sub 49)/sec. The resulting slow (10 to 50 km/sec) ionized outflow, which persists for approximately greater than 10(exp 5) year for disk masses M(sub d) approximately 0.3 M(sub *), may explain the observational characteri stics of unresolved, ultracompact H II regions. In the strong stellar wind solution, dot-M(sub w) greater than dot-M(sub cr), the ram pressure of the stellar wind blows down the atmosphere for r less than r(sub g) and allows the stellar photons to penetrate to greater radii and smaller heights. A slow, ionized outflow produced mainly by diffuse photons is again created for r less than r(sub g); however, it is now dominated by the flow at r(sub w)(greater than r(sub g)), the radius at which the stellar wind ram pressure equals the thermal pressure in the evaporating flow. The mass-loss rate from the disk is of order 6 x 10(exp -5)dot-M(sub w-6) v(sub w8)(Phi (sub 49))(exp -1/2) solar mass/year, where dot-M(sub w-6) = M(sub w)/10(exp -6) solar mass/year and v(sub w8) = v(sub w)/1000 km/sec is the stellar wind velocity. The resulting outflow, which also persists for approximately greater than 10(exp 5) year may explain many of the more extended (r approximately greater than 10(exp 16) cm) ultracompact H II regions. Both the weak-wind and the strong-wind models depend entirely on stellar parameters Phi(sub i), M(sub *), dot-M(sub w)) and are independent of disk parameters as long as an extended r much greater than (r(sub g)), neutral disk exists. We compare both weak-wind and strong-wind model results to the observed radio free-free spectra and luminosities of ultracompact H II regions and to the interesting source MWC 349.

Hollenbach, David↗
NASA NTRS1962

Time-Dependent Structure of the Upper Atmosphere

The physical properties of the upper atmosphere are determined mainly by heat conduction, the heat sources and the barometric law. An analysis of the integro-differential equation which describes these physical processes has been carried out. It is found that heating of the thermosphere due to absorption of the solar extreme ultraviolet (EUV) radiation alone cannot explain the observed diurnal variation of density and temperature, since it would yield a maximum of these properties at about 17h local time, instead of 14h where it is observed. Secondly, if the EUV flux is adjusted to give the observed average temperature, then the diurnal variation in density would be much too large compared with the observed amplitude. Thirdly, it would require an extremely high efficiency for the conversion of EUV radiation into heat, if we compare the required flux with Hinteregger's measurements of the EUV flux. Thus, it is necessary to have another heat source in addition to the heating due to absorption of EUV radiation. If an additional beat source is used, which has a maximum at about 9h local time and a flux of 1 erg cm−1 sec−1, a time-dependent model of the upper atmosphere is obtained that is in good agreement with the observed densities. There is evidence that this additional heat source derives its energy ultimately from the solar corpuscular radiation. In this paper we present the results of calculations for a model in the equatorial and temperature zones of the earth, for those times when the average solar activity corresponds to a solar radiation flux of 200×110−22 Wm−2 (cps)−1 at 10.7-cm wavelength. The physical properties (temperature, density, pressure, scale height, mean molecular weight and the number densities of N2, O2, O, He and H) are given as a function of local time and for the altitudes between 120 km and 2050 km.

ATMOSPHERE↗
NASA NTRS1979

Arctic Sea ice decay simulated for a CO2-induced temperature rise

A large scale numerical time-dependent model of sea ice that takes into account the heat fluxes in and out of the ice, the seasonal occurrence of snow, and ice motions was used in an experiment to determine the response of the Arctic Ocean ice pack to a warming of the atmosphere. The degree of warming specified is that expected for a doubling of atmospheric carbon dioxide with its associated greenhouse effect, a condition that could occur before the middle of the next century. The results of three 5-year simulations with a warmer atmosphere and varied boundary conditions were: (1) that in the face of a 5 K surface atmospheric temperature increase the ice pack disappeared completely in August and September but reformed in the central Arctic Ocean in mid fall; (2) that the simulations were moderately dependence on assumptions concerning cloud cover; and (3) that even when atmospheric temperature increases of 6-9 K were combined with an order-of-magnitude increase in the upward heat flux from the ocean, the ice still appeared in winter. It should be noted that a year-round ice-free Arctic Ocean has apparently not existed for a million years or more.

Heat flux↗
NASA NTRS1993

Geographic variations in the thermal and diffusive stability of ground ice on Mars

Time-dependent models of the thermal and diffusive behavior of the Martian regolith are developed to investigate the stability of ground ice within the top several meters of the regolith. The geographic distribution of thermal inertia and albedo as well as the latitudinal variation in insolation are included in calculations of surface and subsurface temperatures between +/- 60 deg latitude. Ground ice is found to be stable where the annual mean surface and subsurface temperatures were below the atmospheric frost point. Calculations of temperatures at high and low obliquity suggest that ground ice would be stable globally at high obliquity and would not be stable between +/- 60 deg latitude at low obliquity. The time scales for condensation of ground ice are found to be comparable to that of orbital oscillations, suggesting that the present geographic distribution of ground ice may depend on the orbital history of Mars.

Mellon, Michael T.↗
NASA NTRS1998

Fos Expression in Rat Brain During Depletion-Induced Thirst and Salt Appetite

The expression of Fos protein (Fos immunoreactivity, Fos-ir) was mapped in the brain of rats subjected to an angiotensin-dependent model of thirst and salt appetite. The physiological state associated with water and sodium ingestion was produced by the concurrent subcutaneous administration of the diuretic furosemide (10 mg/kg) and a low dose of the angiotensin-converting enzyme (ACE) inhibitor captopril (5 mg/kg; Furo/Cap treatment). The animals were killed 2 h posttreatment, and the brains were processed for Fos-ir to assess neural activation. Furo/Cap treatment significantly increased Fos-ir density above baseline levels both in structures of the lamina terminalis and hypothalamus known to mediate the actions of ANG 2 and in hindbrain regions associated with blood volume and pressure regulation. Furo/Cap treatment also typically increased Fos-ir density in these structures above levels observed after administration of furosemide or captopril separately. Fos-ir was reduced to a greater extent in forebrain than in hindbrain areas by a dose of captopril (100 mg/kg sc) known to block the actions of ACE in the brain. The present work provides further evidence that areas of lamina terminalis subserve angiotensin-dependent thirst and salt appetite.

Thunhorst, R. L.↗
NASA NTRS2004

MARIE Dose and Flux Measurements in Mars Orbit

We present results from the Martian Radiation Environment Experiment (MARIE), aboard the 2001 Mars Odyssey spacecraft in orbit around Mars. MARIE operated successfully from March 2002 through October 2003. At the time of this writing, the instrument is off due to a loss of communications during an extremely intense Solar Particle Event. Efforts to revive MARIE are planned for Spring 2004, when Odyssey's role as a communications relay for the MER rovers is completed. During the period of successful operation, MARIE returned the first detailed energetic charged particle data from Mars. Due to limitations of the instrument, normalizing MARIE data to flux or dose is not straightforward - several large corrections are needed. Thus normalized results (like dose or flux) have large uncertainties and/or significant model-dependence. The problems in normalization are mainly due to inefficiency in detecting high-energy protons (signal-to-noise problems force the trigger threshold to be higher than optimal), to the excessively high gains employed in the signal processing electronics (many ions deposit energy sufficient to saturate the electronics, and dE/dx information is lost), and to artifacts associated with the two trigger detectors (incomplete registration of dE/dx). Despite these problems, MARIE is efficient for detecting helium ions with kinetic energies above about 30 MeV/nucleon, and for detecting high-energy ions (energies above about 400 MeV/nucleon) with charges from 5 to 10. Fluxes of these heavier ions can be compared to fluxes obtained from the ACE/CRIS instrument, providing at least one area of direct comparison between data obtained at Earth and at Mars; this analysis will be presented as a work in progress. We will also present dose-rate data, with a detailed explanation of the many sources of uncertainty in normalization. The results for both flux and dose will be compared to predictions of the HZETRN model of the GCR.

Zeitlin, C.↗
NASA NTRS2023

Latitudinal Variations in Methane Abundance, Aerosol Opacity and Aerosol Scattering Efficiency in Neptune's Atmosphere Determined from VLT/MUSE

Spectral observations of Neptune made in 2019 with the Multi Unit Spectroscopic Explorer (MUSE) instrument at the Very Large Telescope (VLT) in Chile have been analyzed to determine the spatial variation of aerosol scattering properties and methane abundance in Neptune's atmosphere. The darkening of the South Polar Wave at ∼60°S, and dark spots such as the Voyager 2 Great Dark Spot is concluded to be due to a spectrally dependent darkening (λ < 650 nm) of particles in a deep aerosol layer at ∼5 bar and presumed to be composed of a mixture of photochemically generated haze and H 2 S ice. We also note a regular latitudinal variation of reflectivity at wavelengths of very low methane absorption longer than ∼650 nm, with bright zones latitudinally separated by ∼25°. This feature, which has similar spectral characteristics to a discrete deep bright spot DBS-2019 found in our data, is found to be consistent with a brightening of the particles in the same ∼5-bar aerosol layer at λ > 650 nm. We find the properties of an overlying methane/haze aerosol layer at ∼2 bar are, to first-order, invariant with latitude, while variations in the opacity of an upper tropospheric haze layer reproduce the observed reflectivity at methane-absorbing wavelengths, with higher abundances found at the equator and also in a narrow “zone” at 80°S. Finally, we find the mean abundance of methane below its condensation level to be 6%–7% at the equator reducing to ∼3% south of ∼25°S, although the absolute abundances are model dependent.

P. G. J. Irwin↗
NASA NTRS1990

Chromospheric extents predicted by time-dependent acoustic wave models

Theoretical models for chromospheric structures of late-type giant stars are computed, including the time-dependent propagation of acoustic waves. Models with short-period monochromatic shock waves as well as a spectrum of acoustic waves are discussed, and the method is applied to the stars Arcturus, Aldebaran, and Betelgeuse. Chromospheric extent, defined as the monotonic decrease with height of the time-averaged electron densities, are found to be 1.12, 1.13, and 1.22 stellar radii for the three stars, respectively; this corresponds to a time-averaged electron density of 10 to the 7th/cu cm. Predictions of the extended chromospheric obtained using a simple scaling law agree well with those obtained by the time-dependent wave models; thus, the chromospheres of all stars for which the scaling law is valid consist of the same number of pressure scale heights.

Cuntz, Manfred↗
NASA NTRS1963

HEATING OF THE UPPER ATMOSPHERE

Theoretical time-dependent model of the upper atmosphere through solutions to heat conduction equation for an equilibrium gas in a gravitational field

UPPER ATMOSPHERE↗
NASA NTRS1973

Supersonic turbulent boundary-layer flows with tangential slot injection.

An implicit finite-difference method has been developed for the solution of the compressible boundary-layer equations. This method is applied to tangential slot injection into supersonic turbulent boundary-layer flows. In addition, the effects induced by the interaction between the boundary-layer displacement thickness and the external pressure field are considered. Three different eddy viscosity models have been used to specify the turbulent momentum exchange. One model depends on the species concentration profile, and the species conservation equation has been included in the system of governing partial differential equations. For air injected into air, the freestream and injected gases are treated as separate species which have common fluid properties. Calculations were made and results were compared with experimental data at freestream Mach numbers of 2.4 and 6.0 and with results of another finite-difference method. Good agreement was obtained for the reduction of wall skin friction with slot injection.

Miner, E. W.↗
NASA NTRS1973

Lunar rock types - The role of plagioclase in non-mare and highland rock types

Some nonmare and highland rock types (14310 type KREEP and very high Al2O3 basalts) have the internal chemical variations expected for a plagioclase-liquid system. The observed Eu variations in these rock types suggest a D(Eu) 1/p of 0.6 to 0.7. The Sr variations suggest a D(Sr) 1/p of about 0.6, with values as low as 0.35 suggested for some materials from sample 14063. Common Apollo 14 KREEP and Apollo 15 KREEP do not show internal Sr, Eu, Al2O3 variations consistent with the D(Eu, Sr) 1/p values derived for 14310 type KREEP. Major element and experimental data indicate that olivine or pyroxene is a large, perhaps dominant, controller of chemical variations within common Apollo 14 KREEP. The application of these distribution coefficients to pure anorthosites like 15415 yields the model dependent conclusion that the silicate liquids with which such anorthosites may have been chemically equilibrated have not yet been analyzed and perhaps not directly sampled.

Hubbard, N. J.↗
NASA NTRS1974

Diurnal variations of HOx and NOx in the stratosphere

The diurnal variations of odd hydrogen (OH, HO2, H2O2) and odd nitrogen compounds (NO, NO2, HNO3) are investigated by using a one-dimensional time-dependent model containing both chemistry and eddy transport. These variations are discussed in terms of relevant processes.-

Whitten, R. C.↗
NASA NTRS1975

On the passage of radiation through inhomogeneous, moving media. XII - Polarized waves in a plane, sheared medium

Using the complete set of Maxwell equations, the ray paths and Stokes parameters of a polarized wave are followed which passes through a slab of differentially shearing material of variable refractive index. The polarization state of the signal leaving the top of the slab is related to the polarization state of the initial wave. In general, the two are not the same. These calculations were made to illustrate the point that the polarization properties of observed pulsar signals may be very different from those of the emitted signals due to propagation effects in the differentially shearing magnetospheres that most pulsars are believed to possess. While it is recognized that the precise amount of polarization variations is model dependent, the calculations show that even for simple situations a noticeable polarization variation occurs. Accordingly, the calculations reported here are an educative device: they show that it is, perhaps, unwise to assume that the observed polarization properties of pulsar signals are the same as the emitted signals.

Lee, M. A.↗
NASA NTRS1977

Galactic infall and cosmic ray acceleration

An estimate is made of the extent to which cosmic rays would be accelerated as a result of their scattering off material entering into the galaxy. A model of the flow is presented, and the assumptions on which the applicability of the model depends are examined. As examples, the maximum acceleration efficiencies are calculated for two ratios of disk gas to total pressure. With these results, the upper limit for power supplied by this process is found to be essentially identical to the cosmic ray power requirement. This circumstance suggests the possibility that the infall might contribute appreciably to the cosmic ray acceleration.

Hedrick, D.↗