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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 145 records · Page 8
All sourcesNASA NTRSDOE OSTI
NASA NTRS1980

Cycles till failure of silver-zinc cells with completing failures modes: Preliminary data analysis

One hundred and twenty nine cells were run through charge-discharge cycles until failure. The experiment design was a variant of a central composite factorial in five factors. Preliminary data analysis consisted of response surface estimation of life. Batteries fail under two basic modes; a low voltage condition and an internal shorting condition. A competing failure modes analysis using maximum likelihood estimation for the extreme value life distribution was performed. Extensive diagnostics such as residual plotting and probability plotting were employed to verify data quality and choice of model.

Sidik, S. M.↗
NASA NTRS1980

A search for isotopic anomalies in uranium

The U-238/U-235 ratios for nine bulk chondritic meteorites and a terrestrial basalt were measured. The total range in U-238/U-235 determined for both total meteorites and for acid leaches was from 137.2 terrestrial U. The typical errors in a single determination are plus or minus 6 per thousand (2 sigma m) for a 2 ng U sample from a chondrite. Taking the extreme values of delta U-235 for each measurement the maximum amount of excess U-235 that can be allowed to be present ranges from 200 million to 2 billion atoms per gram of bulk meteorite. These results do not support the claims of variations in U-238/U-235 at the percentage levels or number of excess U-235 atoms in some of the same meteorites as reported by several other previous workers.

Chen, J. H.↗
NASA NTRS1980

Cycles till failure of silver-zinc cells with competing failure modes - Preliminary data analysis

The data analysis of cycles to failure of silver-zinc electrochemical cells with competing failure modes is presented. The test ran 129 cells through charge-discharge cycles until failure; preliminary data analysis consisted of response surface estimate of life. Batteries fail through low voltage condition and an internal shorting condition; a competing failure modes analysis was made using maximum likelihood estimation for the extreme value life distribution. Extensive residual plotting and probability plotting were used to verify data quality and selection of model.

Sidik, S. M.↗
NASA NTRS1983

Significant events in low-level flow conditions hazardous to aircraft

Atmospheric parameters recorded during high surface winds are analyzed to determine magnitude, frequency, duration, and simultaneity of occurrence of low level flow conditions known to be hazardous to the ascent and descent of conventional aircraft and the space shuttle. Graphic and tabular presentations of mean and extreme values and simultaneous occurrences of turbulence (gustiness and a gust factor), wind shear (speed and direction), and vertical motion (updrafts and downdrafts), along with associated temperature inversions are included as function of tower height, layer and/or distance for six 5 sec intervals (one interval every 100 sec) of parameters sampled simultaneously at the rate of 10 speeds, directions and temperatures per second during an approximately 10 min period.

Alexander, M. B.↗
NASA NTRS1981

A time Fourier analysis of zonal averaged ozone heating rates

A time-Fourier analysis is presented for the yearly variation of the zonal averaged ozone heating rates in the middle atmosphere based on a model study. The ozone heating rates are determined by utilizing two-dimensional ozone distributions, the altitude and latitude, and by including the effect of the curved earth's atmosphere. In addition, assumptions are introduced to the yearly variations of the ozone distributions due to the lack of sufficient existing ozone data. Among other results, it is shown that the first harmonic component indicates that the heating rates are completely out of phase between the northern and southern hemispheres. The second Fourier component shows a symmetric pattern with respect to the equator, as well as five distinct local extreme values of the ozone heating rate. The third harmonic component shows a pattern close to that of the first component except in the regions above 70 deg between 45-95 km in both hemispheres.

Wang, P.-H.↗
NASA NTRS1984

A study of environmental characterization of conventional and advanced aluminum alloys for selection and design. Phase 2: The breaking load test method

A technique is demonstrated for accelerated stress corrosion testing of high strength aluminum alloys. The method offers better precision and shorter exposure times than traditional pass fail procedures. The approach uses data from tension tests performed on replicate groups of smooth specimens after various lengths of exposure to static stress. The breaking strength measures degradation in the test specimen load carrying ability due to the environmental attack. Analysis of breaking load data by extreme value statistics enables the calculation of survival probabilities and a statistically defined threshold stress applicable to the specific test conditions. A fracture mechanics model is given which quantifies depth of attack in the stress corroded specimen by an effective flaw size calculated from the breaking stress and the material strength and fracture toughness properties. Comparisons are made with experimental results from three tempers of 7075 alloy plate tested by the breaking load method and by traditional tests of statistically loaded smooth tension bars and conventional precracked specimens.

Sprowls, D. O.↗
NASA NTRS1985

Formation, distribution and variability in snow cover on the Asian territory of the USSR

A description is given of maps compiled for annual and average multiple-year water reserves. The annual and average multiple-year maximum snow cover height for winter, extreme values of maximum snow reserves, and the average height and snow reserves at the end of each decade are shown. These maps were made for the entire Asian territory of the USSR, excluding Central Asia, Kamchatka Peninsula, and the Sakhalin Islands.

Pupkov, V. N.↗
NASA NTRS1987

Far-infrared activity and starburst galaxies

After the IRAS discovery of galaxies with large far-infrared to blue luminosity ratio, it has been proposed that an enhanced star formation could be the origin of the far-infrared emission through dust heating. Whether a simple photometric model is able to account for the FIR and optical properties of IRAS galaxies was investigated. The L sub IR/L sub B ratio, (B-V) color and H sub alpha equivalent width of normal spirals are well reproduced with smooth star formation histories. In the case of starburst galaxies, several theoretical diagrams allow us to estimate the burst strength and extinction. L sub IR/L sub B ratio up to 100 can be rather easily reached, whereas extreme values probably require IMF truncated at the low end.

Belfort, P.↗
NASA NTRS1986

A statistical rain attenuation prediction model with application to the advanced communication technology satellite project. 1: Theoretical development and application to yearly predictions for selected cities in the United States

A rain attenuation prediction model is described for use in calculating satellite communication link availability for any specific location in the world that is characterized by an extended record of rainfall. Such a formalism is necessary for the accurate assessment of such availability predictions in the case of the small user-terminal concept of the Advanced Communication Technology Satellite (ACTS) Project. The model employs the theory of extreme value statistics to generate the necessary statistical rainrate parameters from rain data in the form compiled by the National Weather Service. These location dependent rain statistics are then applied to a rain attenuation model to obtain a yearly prediction of the occurrence of attenuation on any satellite link at that location. The predictions of this model are compared to those of the Crane Two-Component Rain Model and some empirical data and found to be very good. The model is then used to calculate rain attenuation statistics at 59 locations in the United States (including Alaska and Hawaii) for the 20 GHz downlinks and 30 GHz uplinks of the proposed ACTS system. The flexibility of this modeling formalism is such that it allows a complete and unified treatment of the temporal aspects of rain attenuation that leads to the design of an optimum stochastic power control algorithm, the purpose of which is to efficiently counter such rain fades on a satellite link.

Manning, Robert M.↗
NASA NTRS1988

A self-consistent interpretation of the solar flare extreme-ultraviolet to hard X-ray ratio in large events

This paper shows quantitatively that when a limiting X-ray yield is considered, a universal area of 10 to the 17th sq cm used in the thick-target electron bombardment model of McClymont and Canfield (1986) cannot explain the observed hard X-ray flux in large solar flare events without recourse to extreme values of the physical parameters of the flaring corona. The return current ohmic heating produced by a beam of flux 10 to the 13th ergs/sq cm/s results in a coronal temperature in excess of 100 million K. In this case, the thermal hard X-ray emission dominates the nonthermal emission and the EUV-to-hard X-ray ratio would not decrease with increasing hard X-ray flux, as observed. Hence, any model that requires a beam flux of 10 to the 13th ergs/sq cm/s is untenable. It is proposed that these apparently contradictory results can be reconciled if the X-ray emitting area is substantially larger than the area of the chromospheric precipitation site.

Larosa, T. N.↗
NASA NTRS1988

Speculative histories of the Uranian satellite system

The hypothetical histories presently considered for the Uranian satellite system are very sensitive to the assumed satellite masses, within the errors of their determinations, as well as to the Uranian tidal effective dissipation function. A determination is made of the resonances that could have been encountered in these histories, and of the orbital eccentricity constraints that would have led to certain capture. It is found that if the mass of Miranda were of the upper extreme value, it would have been locked in a long-term 2/1 orbital resonance with Ariel to form a Laplacelike, three-body resonance that encompassed Umbriel.

Peale, S. J.↗
NASA NTRS1988

A comparison of single-cycle versus multi-cycle proof testing strategies

Proof testing was a useful supplement to conventional nondestructive evaluation (NDE) of space shuttle main engine (SSME) components. Since many of these components involve thin sections and high toughness materials, such as Inconel 718, conventional single-cycle proof test logic is not applicable due to the propensity for stable crack growth during the proof tests. Experience with five-cycle proof testing of SSME components is summarized and a framework is outlined for understanding multi-cycle proof testing using the fracture mechanics concept of a resistance curve. Extreme value statistics are also used to propose an empirical approach to compare the advantages and disadvantages of single- versus multi-cycle proof testing. The importance of the initial flaw size distribution and specimen thickness in such a comparison is also discussed.

Hudak, Stephen J., Jr.↗
NASA NTRS1989

Confusion-limited galaxy fields. II - Classical analyses

Chokshi and Wright presented a detailed model for simulating angular distribution of galaxy images in fields that extended to very high redshifts. Standard tools are used to analyze these simulated galaxy fields for the Omega(O) = 0 and the Omega(O) = 1 cases in order to test the discriminatory power of these tools. Classical number-magnitude diagrams and surface brightness-color-color diagrams are employed to study crowded galaxy fields. An attempt is made to separate the effects due to stellar evolution in galaxies from those due to the space time geometry. The results show that this discrimination is maximized at near-infrared wavelengths where the stellar photospheres are still visible but stellar evolution effects are less severe than those observed at optical wavelenghts. Rapid evolution of the stars on the asymptotic giant branch is easily recognized in the simulated data for both cosmologies and serves to discriminate between the two extreme values of Omega(O). Measurements of total magnitudes of individual galaxies are not essential for studying light distribution in galaxies as a function of redshift. Calculations for the extragalactic background radiation are carried out using the simulated data, and compared to integrals over the evolutionary models used.

Chokshi, Arati↗
NASA NTRS1989

Designing ceramic components with the CARES computer program

NASA-Lewis has developed a public-domain computer program, designated 'Ceramic Analysis and Reliability Evaluation of Structures' (CARES) for calculating the fast-fracture reliability of macroscopically isotropic ceramic components subjected to the complex thermomechanical loadings typical of heat engines. The design methodology employed by CARES encompasses linear elastic fracture mechanics theory, extreme value statistics, and material microstructures; component integrity is conceived as a function of the entire field solution of the stresses, rather than being based solely on the most highly stressed point.

Nemeth, Noel N.↗
NASA NTRS1991

IRAS observations of classical novae. II - Modeling the detections

The analysis of IRAS data on 64 classical novae extracted since an initial study of 41 novae (Harrison and Gehrz, 1988) is reported, and it is concluded that 45 of the 105 novae investigated were detected by IRAS. A model is presented that compares the IRAS detections of novae with predictions of the strength of the far-infrared forbidden line emission from the gaseous ejecta. The distances are known for 23 of the 45 detected novae so that this sample of 23 can be used to compare the fluxes observed at earth with fluxes predicted by the line emission model. The fluxes from 9 of these 23 novae can be explained by line emission given relatively conservative assumptions about the physical conditions in their shells. Accepting more extreme values for these parameters makes it possible to attribute three more detections to possible line emission. There are 11 novae whose IRAS detections remain difficult to explain, even when dust emission and free-free emission are considered as alternatives to line emission.

Harrison, T. E.↗
NASA NTRS1991

A constitutive relation for the viscous flow of an oriented fiber assembly

A constitutive relation for an equivalent, homogeneous fluid is developed for the anisotropic viscous flow of an oriented assembly of discontinuous fibers suspended in a viscous fluid. The anisotropic viscous compliance matrix can be expressed in terms of three constants by assuming the equivalent fluid to be incompressible and the microstructure to have axial symmetry (transversely isotropic). By means of a micromechanics analysis, the three terms of the constitutive relation are expressed in terms of the viscosity of the matrix fluid, the fiber aspect ratio, and the fiber volume fraction. A comparison of the viscosity terms reveals that the elongational viscosity in the fiber direction varies as the square of the fiber aspect ratio and a complex function of the fiber volume fraction. Furthermore, the ratio of the axial elongational viscosity to the transverse elongational viscosity and both axial and transverse shear viscosities was shown to be 10 exp 4 - 10 exp 6 for fiber aspect ratio of 100-1000, except at extreme values of the fiber volume fraction.

Pipes, R. B.↗
NASA NTRS1992

Great magnetic storms

The five largest magnetic storms that occurred between 1971 to 1986 are studied to determine their solar and interplanetary causes. All of the events are found to be associated with high speed solar wind streams led by collisionless shocks. The high speed streams are clearly related to identifiable solar flares. It is found that: (1) it is the extreme values of the southward interplanetary magnetic fields rather than solar wind speeds that are the primary causes of great magnetic storms, (2) shocked and draped sheath fields preceding the driver gas (magnetic cloud) are at least as effective in causing the onset of great magnetic storms (3 of 5 events) as the strong fields within the driver gas itself, and (3) precursor southward fields ahead of the high speed streams allow the shock compression mechanism (item 2) to be particularly geoeffective.

Tsurutani, Bruce T.↗