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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 523 records · Page 29
All sourcesNASA NTRSDOE OSTI
NASA NTRS1985

Endocrine and fluid metabolism in males and females of different ages after bedrest, acceleration and lower body negative pressure

Space shuttle flight simulations were conducted to determine the effects of weightlessness, lower body negative pressure (LBNP), and acceleration of fluid and electrolyte excretion and the hormones that control it. Measurements were made on male and female subjects of different ages before and after bedrest. After admission to a controlled environment, groups of 6 to 14 subjects in the age ranges 25 to 35, 35 to 45, 45 to 55 to 65 years were exposed to +3 G sub z for 15 minutes (G1) and to LBNP (LBNP1) on different days. On 3 days during this prebedrest period, no tests were conducted. Six days of bedrest followed, and the G sub z (G2) and LBNP (LBNP2) tests were run again. Hormones, electrolytes, and other parameters were measured in 24-hour urine pools throughout the experiment. During bedrest, cortisol and aldosterone excretion increased. Urine volume decreased, and specific gravity and osmolality increased. Urinary electrolytes were statistically unchanged from levels during the non-stress control period. During G2, cortisol increased significantly over its control and bedrest levels. Urine volume, sodium, and chloride were significantly lower; specific gravity and osmolality were higher during the control period or bedrest. The retention of fluids and electrolytes after +G sub z may at least partially explain decreased urine volume and increased osmolality observed during bedrest in this study. There were some who indicated that space flight would not affect the fluid and electrolyte metabolism of females or older males any more severely than it has affected that of male astronauts.

Leach, C. S.↗
NASA NTRS1986

The relative effect of noise at different times of day: An analysis of existing survey data

This report examines survey evidence on the relative impact of noise at different times of day and assesses the survey methodology which produces that evidence. Analyses of the regression of overall (24-hour) annoyance on noise levels in different time periods can provide direct estimates of the value of the parameters in human reaction models which are used in environmental noise indices such as LDN and CNEL. In this report these analyses are based on the original computer tapes containing the responses of 22,000 respondents from ten studies of response to noise in residential areas. The estimates derived from these analyses are found to be so inaccurate that they do not provide useful information for policy or scientific purposes. The possibility that the type of questionnaire item could be biasing the estimates of the time-of-day weightings is considered but not supported by the data. Two alternatives to the conventional noise reaction model (adjusted energy model) are considered but not supported by the data.

Fields, J. M.↗
NASA NTRS1985

On the differences in continental rifting at the Earth, Mars and Venus

During the process of continental rifting on Earth, the lower ductile crust stretches, forming a neck, while the upper brittle crust is broken in blocks by faults, and the blocks sink down the thinned lower crust; if the stretching continues, the neck may break and a newly originated oceanic crust is formed at this place. The rift system structure depends on the depth of the boundary surface between the brittle crust and the ductile crust, the litospheric thickness, the tension value, etc.. The rigid brittle rifting when narrow necks form in the lower crust is characteristic of the contemporary Earth; on Mars the brittle rifting with large subsidence was characteristic of the Tharsis upland formation epoch. The ductile rifting is typical of the Venus. The differences in rheologic features of the lithospheres of different planets causes the variation in types of rifting.

Nikishin, A. M.↗
NASA NTRS1985

Finite difference solutions of the Euler equations in the vicinity of sharp edges

Attempts have been made to explain why finite difference solutions of the Euler equations can describe flows with large vortical structures around sharp-edged bodies. The present paper is concerned with the influence of a singular sharp edge on the truncation error for a set of discretized Euler equations. An analysis is conducted of the distribution of the truncation error of one finite difference approximation of the Euler equations near a sharp edge of a thin plate. The analysis leads to a determination of the size of the region of the neighborhood of such a singularity. Attention is given to the consistency of a discretization of the Euler equations, and numerical experiments.

Hartwich, P.-M.↗
NASA NTRS1985

Finite-difference computations of rotor loads

This paper demonstrates the current and future potential of finite-difference methods for solving real rotor problems which now rely largely on empiricism. The demonstration consists of a simple means of combining existing finite-difference, integral, and comprehensive loads codes to predict real transonic rotor flows. These computations are performed for hover and high-advance-ratio flight. Comparisons are made with experimental pressure data.

Caradonna, F. X.↗
NASA NTRS1986

Finite difference simulations of seismic scattering Implications for the propagation of short-period seismic waves in the crust and models of crustal heterogeneity

Synthetic seismographs that were obtained by the finite difference method are presently applied to the study of elastic and acoustic wave scattering in two-dimensional media with random spatial variations in seismic velocity. The seismograms are analyzed to determine the variation in travel times and waveforms across arrays of receivers. The random media with Gaussian and exponential correlation functions considered differ in the spectral falloff of their velocity fluctuations at wavelengths smaller than 2pi times the correlation distance. It is found that alternative models of crustal heterogeneity can be tested by improved measurements of the frequency dependence of the crustal Q at frequencies greater than about 1 Hz, assuming that scattering is responsible for most of the attenuation at such frequencies.

Frankel, A.↗
NASA NTRS1986

An implicit flux-difference splitting scheme for three-dimensional, incompressible Navier-Stokes solutions to leading edge vortex flows

A new, implicit finite-difference scheme designed to solve the conservative, flux-difference split Navier-Stokes equations is used to compute incompressible vortex flows around delta wings. The completely vectorizable hybrid algorithm is constructed in delta form for steady state solutions independent of the time-step sizes. The scheme combines approximate factorization in crossflow planes with a symmetric planar Gauss-Seidel relaxation in the remaining spatial direction. The governing equations are solved in curvilinear, body-fitted coordinates for treating complex geometries. The computed flow field results are compared with other theoretical and experimental data.

Hartwich, P.-M.↗
NASA NTRS1986

Effects of different convection models upon the high-latitude ionosphere

The plasma convection models of Volland (1975) and Heelis (1982) are utilized to study the ionosphere. The parameters for the two models are evaluated. The two-cell convection models have similar total cross tail electric potential, diameter of the polar cap, and potential falloff rate outside the polar cap; however, they differ in maximum potential, and the electric field in the polar cap. The input parameters for the high-latitude ionospheric model are described. Two high-latitude ionospheric model runs were conducted and the data are compared in terms of electron density at and above the F 2 peak, attitude of the F 2 peak, ion temperature, and molecular-atomic ion transition height. The altitude dependence of electron density is analyzed using coherent scatter radar data. The data reveal differences between the two models in the height of the F 2 peak and in the ion temperature. The altitude values of the Heelis model are higher than the Volland model in the region where plasma is transported into the polar cap and lower in the region plasma is transported out of the polar cap; the Heelis model also produces an increase in ion temperature. It is noted that the ionosphere has a limited dependence upon the details of the convection models.

Rasmussen, C. E.↗
NASA NTRS1985

On marching to two different drummers - Perceptual aspects of the difficulties

Three experiments which reveal that the difficulties involved in processing conflicting rhythms occur when monitoring a stimuli and indicating termination of one rhythmic sequence or tapping with one hand are described. The relation between perceiving and acting in temporal tapping tasks is studied. The effects of varying temporal compatibility on perceptual monitoring and one-hand tapping are examined. It is observed that the difficulty of two-handed tapping to polyrhythms with two different tones decreases as pitch differences between tones decrease, and the difficulty of rhythmic coordination can be perceptually controlled. It is noted that the evaluation of polyrhythmic performance provides a useful means of examining the interactions of perceptual and motor organizations.

Klapp, S. T.↗
NASA NTRS1986

Convenient total variation diminishing conditions for nonlinear difference schemes

Convenient conditions for nonlinear difference schemes to be total-variation diminishing (TVD) are reviewed. It is shown that such schemes share the TVD property, provided their numerical fluxes meet a certain positivity condition at extrema values but can be arbitrary otherwise. The conditions are invariant under different incremental representations of the nonlinear schemes, and thus provide a simplified generalization of the TVD conditions due to Harten and others.

Tadmor, Eitan↗
NASA NTRS1986

A theoretical analysis of the round-off propagation in different Kalman filter implementations

A theoretical analysis is made of the error propagation due to numerical round-off for four different Kalman filter implementations: the conventional Kalman filter, the square root covariance filter, the square root information filter and the Chandrasekhar square root filter. From these error models, new insights about the applicability of the different filters and their sensitivity to round-off, is obtained. It is shown that the CKF may become completely unreliable when the original plant is unstable, and that this is easily circumvented by a number of techniques. The square root filters, often quoted to possess a conditioning or sensitivity that is the square root of that of the CKF, are shown to possess this property only for the computation of the covariance of the filtered signal and not for the computation of the Kalman gain or the filtered estimate. Finally, the Chandrasekhar filter is shown to be numerically unstable.

Verhaegen, M.↗
NASA NTRS1986

Comparison of abrasion model differences in heavy ion fragmentation - Optical versus geometric models

Two different abrasion formalisms, one based on an energy-independent geometric model and the other based on a quantum-mechanical optical model, are shown to yield comparable fragmentation cross section predictions when used as input to an abrasion-ablation frictional-spectator interaction fragmentation calculation which includes electromagnetic dissociation contributions. The results suggest that any dependence upon the incident ion's kinetic energy above 200 MeV/nucleon is weak. It is also noted that the larger surface diffusiveness of the optical model densities only affects nuclear cross sections for near-projectile-mass fragments, while for heavier nuclei, the sizable cross-section contributions from electromagnetic dissociation negate these differences.

Townsend, L. W.↗
NASA NTRS1988

Applications of an exponential finite difference technique

An exponential finite difference scheme first presented by Bhattacharya for one dimensional unsteady heat conduction problems in Cartesian coordinates was extended. The finite difference algorithm developed was used to solve the unsteady diffusion equation in one dimensional cylindrical coordinates and was applied to two and three dimensional conduction problems in Cartesian coordinates. Heat conduction involving variable thermal conductivity was also investigated. The method was used to solve nonlinear partial differential equations in one and two dimensional Cartesian coordinates. Predicted results are compared to exact solutions where available or to results obtained by other numerical methods.

Handschuh, Robert F.↗
NASA NTRS1988

Trace element differences between Archean, Proterozoic and Phanerozoic crustal components: Implications for crustal growth processes

Critical to models for continental crust growth and recycling are the processes through which crustal growth takes place. In particular, it is important to know whether these processes have changed fundamentally with time in response to the earth's thermal evolution, and whether the crustal compositions generated are compatible with crustal remobilization, crustal recycling, or represent primary additions. There are some significant and consistent differences in the major and trace element compositions of crustal components with time which have important implications for crustal growth processes. These will be illustrated with reference to Archean rocks from a number of shield areas, Proterozoic granitoids from Australia and elsewhere, Palaeozoic granitoids from Australia and Scotland, and Mesozoic - recent granitoids from present continental margin belts. Surprisingly some rather simple and consistent patterns energy using this technique. There are then significant differences in compositions of granitoid crustal additions throughout geological time, with a particular type of granitoid apparently dominating a particular time period. This implies that the tectonic processes giving rise to granite generation have changed in response to the earth's thermal evolution.

Tarney, J.↗
NASA NTRS1987

A mapped finite difference study of noise propagation in nonuniform ducts with mean flow

The primary objective of this work is to study noise propagation in acoustically lined variable area ducts with mean fluid flow. The method of study is numerical in nature and involves a body-fitted grid mapping procedure in conjunction with a factored-implicit finite difference technique. The mean fluid flow model used is two-dimensional, inviscid, irrotational, incompressible, and nonheat conducting. Fully-coupled solutions of the linearized gasdynamic equations are obtained for both positive and negative Mach numbers as well as for hard and soft wall conditions. The factored-implicit finite difference technique used did give rise to short wavelength perturbations, but these were dampened by the introduction of higher order artificial dissipation terms into the scheme. Results compared favorably with available numerical and experimental data.

Raad, Peter E.↗
NASA NTRS1988

The difference in hydrogen abundance between two classes of type I X-ray bursts

The hypothesis that the bright type I X-ray bursts differ from faint bursts in that a hydrogen-rich envelope is ejected in the former type and not in the latter is theoretically discussed and experimentally investigated. Color-temperature versus luminosity diagrams of X-ray bursts from MXB 1636-536 and MXB 1608-522 are constructed based on observations from the Tenma satellite and are used to study the hydrogen richness of the surface of the neutron stars resulting from the outbursts. Systematic differences between the bright and faint class diagrams are found which confirm the hypothesis.

Ebisuzaki, Toshikazu↗
NASA NTRS1987

Individual differences and subjective workload assessment - Comparing pilots to nonpilots

Results by two groups of subjects, pilots and nonpilots, for two subjective workload assessment techniques (the SWAT and NASA-TLX tests) intended to evaluate individual differences in the perception and reporting of subjective workload are compared with results obtained for several traditional personality tests. The personality tests were found to discriminate between the groups while the workload tests did not. It is concluded that although the workload tests may provide useful information with respect to the interaction between tasks and personality, they are not effective as pure tests of individual differences.

Vidulich, Michael A.↗