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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 343 records · Page 19
All sourcesNASA NTRSDOE OSTI
NASA NTRS1978

Minimum energy control of a class of electrically driven vehicles

Theoretical and experimental results are obtained in the investigation of a minimum energy control problem associated with a class of electrically driven vehicles. Analytical results are obtained by making several justifiable approximations in the dynamical equations of the plant, the performance index of which is related to the minimization of system energy consumption for any required control action. The control problem of interest is simplified and solved by using Bellman's invariant imbedding technique. The optimality of the resulting control law is compared with those of the bang-bang control law, which is the exact solution for the case of speed-setting control action, and the classical control laws under identical conditions. A stochastic optimization problem is then formulated and solved by using Bellman's dynamic programming technique. The resulting control law is mechanized for a particular vehicle configuration which is simulated in the laboratory.

Sahinkaya, Y. E.↗
NASA NTRS1978

Discrimination of rock classes and alteration products in southwestern Saudi Arabia with computer-enhanced LANDSAT data

Digital LANDSAT MSS data for an area in the southwestern Arabian Shield were computer-enhanced to improve discrimination of rock classes, and recognition of gossans associated with massive sulphide deposits. The test area is underlain by metamorphic rocks that are locally intruded by granites; these are partly overlain by sandstones. The test area further includes the Wadi Wassat and Wadi Qatan massive sulphide deposits, which are commonly capped by gossans of ferric oxides, silica, and carbonates. Color patterns and boundaries on contrast-stretched ratio color composite imagery, and on complementary images constructed using principal component and canonical analyses transformations, correspond exceptionally well to 1:100,000 scale field maps. A qualitative visual comparison of information content showed that the ratio enhancement provided the best overall image for identification of rock type and alteration products.

Blodget, H. W.↗
NASA NTRS1977

Search for correlation between asteroid families and classes

A correlation between membership in a dynamically defined asteroid family and membership in a given asteroid spectral class is sought. Examination of 10 families each with five or more classified members indicates a correlation for the 4 families whose existence is best established, and no correlation for the remaining 6 families. This conclusion supports the break-up hypothesis for the origin of some families, while not contradicting that hypothesis for any family.

Hansen, O.↗
NASA NTRS1977

Utilization of the vacuum developed in the wake zone of space vehicles in the LDEF class

Contaminating fluxes from upper atmospheric molecules found in the wake of a typical spacecraft of the Long Duration Exposure Facility class are studied with the aim of determining vacuum levels which may be employed by experiments mounted on the vehicle. A simplified representation for the spacecraft, the velocity-shifted Maxwellian distribution (to evaluate ambient flux which has a velocity sufficient to overtake the spacecraft), and a calculation for the backscattered contribution to the flux density of the wake figure in the study are presented. Results indicate that direct and backscattered fluxes of about 10 to the seventh power molecules per sq cm can be expected in the wake of a spacecraft at 550 km altitude.

Oran, W. A.↗
NASA NTRS1978

A theoretical and observational analysis of He I triplet lines in class 1 Seyfert galaxy spectra

The equations of statistical equilibrium are solved for 11 levels of the helium atom that are most relevant to the production and radiative transfer of He I triplet lines. Solutions are obtained for several densities and temperatures over a run of optical depth in the 10,830-A line, and the results for emission-line strengths are plotted. Spectrophotometric scans and pertinent line strengths are presented for the class 1 Seyfert galaxies 3C 120, NGC 7469, and Mrk 618, as well as for Mrk 335, which exhibits a 'more normal' He I 5876/H-beta ratio. A comparison of the theoretically determined line intensities with the observational results verifies that the He I triplet line intensities are significantly enhanced by electron collisional excitation from 2(3)P and 2(3)S. It is suggested that the gas which gives rise to the broad He I lines in 3C 120, Mrk 618, and NGC 7469 is characterized by a number density of about 5 billion per cu cm, a temperature of approximately 15,000 K, and an optical depth of 100 to 120 in the 10,830-A line.

Feldman, F. R.↗
NASA NTRS1978

Numerical solution of a class of integral equations arising in two-dimensional aerodynamics

We consider the numerical solution of a class of integral equations arising in the determination of the compressible flow about a thin airfoil in a ventilated wind tunnel. The integral equations are of the first kind with kernels having a Cauchy singularity. Using appropriately chosen Hilbert spaces, it is shown that the kernel gives rise to a mapping which is the sum of a unitary operator and a compact operator. This allows the problem to be studied in terms of an equivalent integral equation of the second kind. A convergent numerical algorithm for its solution is derived by using Galerkin's method. It is shown that this algorithm is numerically equivalent to Bland's collocation method, which is then used as the method of computation. Extensive numerical calculations are presented establishing the validity of the theory.

Fromme, J.↗
NASA NTRS1978

Measurement and analysis of magnetic field variation during a class 2b flare

A digital analysis of high-time-resolution videomagnetograms taken during a class 2b flare that occurred at 60 deg east is reported. The data were obtained at the Big Bear Observatory and calibrated by a Mt. Wilson magnetogram. Changes of weak magnetic fields (less than 100 G) with an amplitude of 30% to 100% have been detected over 55% of the optical flare region, apparently taking place at the initial phase of the flare. Statistical considerations suggest a real flare association with most of these changes. H-alpha observations show that large changes took place over the footpoints of heavily inclined structures like penumbral fibrils, while smaller changes took place over the plage region. An apparent polarity reversal was found at the feet of erupted fibrils. Based on force-free field calculations these changes can be reasonably explained as a transformation of the current-carrying fields to potential fields which produced large changes in the field-line inclination and rotation.

Tanaka, K.↗
NASA NTRS1978

Cargo Logistics Airlift Systems Study (CLASS). Volume 1: Analysis of current air cargo system

The material presented in this volume is classified into the following sections; (1) analysis of current routes; (2) air eligibility criteria; (3) current direct support infrastructure; (4) comparative mode analysis; (5) political and economic factors; and (6) future potential market areas. An effort was made to keep the observations and findings relating to the current systems as objective as possible in order not to bias the analysis of future air cargo operations reported in Volume 3 of the CLASS final report.

Burby, R. J.↗
NASA NTRS1979

Interstellar scattering, the North Polar Spur, and a possible new class of compact galactic radio sources

Claims for a galactic-latitude dependence of interstellar angular broadening based on interplanetary-scintillation (IPS) observations are investigated. Analysis of the statistics of the angular sizes in an IPS survey shows that there is no evidence for increased angular broadening in the galactic plane. A region of sky about 500 sq deg of arc in area is considered in which significant angular broadening is thought to exist. An association between this region and the nearby North Polar Spur is proposed on the basis of the former's extension off the galactic plane to high latitudes. An evaluation of two-frequency angular-broadening measurements suggests that the data used to support the conclusion about a galactic-latitude dependence are not statistically significant. A study of pulsar data and implications for the angular broadening expected in the interstellar medium for sources at galactic latitudes below + or - 10 deg indicates the possible existence of a previously unsuspected class of compact galactic nonthermal radio sources, designated 'scintars'.

Rickard, J. J.↗
NASA NTRS1979

A special class of planetary collisions - Theory and evidence

Collisions between comparable-sized planetary bodies are a special class of collisions, rarer than other collisions, but producing interesting products, such as unfractured dumbbell-shaped contact binaries, partly brecciated elongated bodies, totally brecciated spheroidal bodies, and perhaps co-orbiting binary pairs or swarms. Qualitative and rough quantitative theories are presented to indicate collision outcomes. Contact binaries or fractured elongated bodies as large as tens or hundreds of kilometers across can be produced - larger than hitherto considered. Lengths about 20 to 200 km are most probable for igneous or ordinary chondritic elongated objects formed by collision, but other lengths could result from tidal evolution of pairs. Though most elongated asteroids are probably collision fragments, as usually assumed, some may instead be accretionary products. Trojan asteroid 624 Hektor is a candidate. Some polymict, genomict, and monomict brecciated meteorites may be better explained by large-scale fragmentation and immediate gravitational re-assembly of parent bodies than by local-scale processes of cratering on parent-body surfaces.

Hartmann, W. K.↗
NASA NTRS1980

Air cargo market outlook and impact via the NASA CLASS project

An overview is given of the Cargo/Logistics Airlift Systems Study (CLASS) project which was a 10 man-year effort carried out by two contractor teams, aimed at defining factors impacting future system growth and obtaining market requirements and design guidelines for future air freighters. Growth projection was estimated by two approaches: one, an optimal systems approach with a more efficient and cost effective system considered as being available in 1990; and the other, an evolutionary approach with an econometric behavior model used to predict long term evolution from the present system. Both approaches predict significant growth in demand for international air freighter services and less growth for U.S. domestic services. Economic analysis of air freighter fleet options indicate very strong market appeal of derivative widebody transports in 1990 with little incentive to develop all new dedicated air freighters utilizing the 1990's technology until sometime beyond the year 2000. Advanced air freighters would be economically attractive for a wide range of payload sizes (to 500 metric tons), however, if a government would share in the RD and T costs by virtue of its needs for a slightly modified version of a civil air freighter design (a.g. military airlifter).

Winston, M. M.↗
NASA NTRS1981

A class of unsteady, three-dimensional flow structures in turbulent boundary layers

A restricted class of mathematically admissible, unsteady, three dimensional flows was identified which may constitute part of the structure observed in turbulent boundary layers. The development of the model and some general results are discussed. The resulting solution has characteristics which suggest how upwelling low speed flow can trigger a downward jetting of irrotational high speed fluid into the boundary layer.

Ash, R. L.↗
NASA NTRS1981

Acquisition of background and technical information and class trip planning

Instructors who are very familiar with a study area, as well as those who are not, find the field trip information acquisition and planning process speeded and made more effective by organizing it in stages. The stage follow a deductive progression: from the associated context region, to the study area, to the specific sample window sites, and from generalized background information on the study region to specific technical data on the environmental and human use systems to be interpreted at each site. On the class trip and in the follow up laboratory, the learning/interpretive process are at first deductive in applying previously learned information and skills to analysis of the study site, then inductive in reading and interpreting the landscape, imagery, and maps of the site, correlating them with information of other samples sites and building valid generalizations about the larger study area, its context region, and other (similar and/or contrasting) regions.

Mackinnon, R. M.↗
NASA NTRS1981

A nonparametric identification method for a class of non-linear systems

A relatively simple nonparametric method for the identification of a class of close-coupled nonlinear multi-degree-of-freedom systems has been developed. The identification of arbitrary memoryless nonlinearities is possible through knowledge of the accelerations, velocities, and displacements of the various masses. These quantities are used to obtain the surfaces of the restoring forces as functions of the intermass displacements and velocities. The method was demonstrated by application to a four-degree-of-freedom system to identify the restoring forces. It is found that the identification results are relatively insensitive to measurement noise.

Udwadia, F. E.↗
NASA NTRS1981

Stable boundary approximations for a class of implicit schemes for the one-dimensional inviscid equations of gas dynamics

The applicability to practical calculations of recent theoretical developments in the stability analysis of difference approximations for initial-boundary-value problems of the hyperbolic type. For the numerical experiments, select the one-dimensional inviscid gas-dynamic equations in conservation-law form is selected. A class of implicit schemes based on linear multistep methods for ordinary differential equations is chosen and the use of space or space-time extrapolations as implicit or explicit boundary schemes is emphasized. Some numerical examples with various inflow-outflow conditions highlight the commonly discussed issues: explicit versus implicit boundary schemes, unconditionally stable schemes, and underspecification or overspecification of boundary conditions.

Yee, H. C.↗
NASA NTRS1981

Teaching graphics in technical communication classes

Graphic aids convey and clarify information more efficiently and accurately than words alone therefore, most technical writing includes the use of graphics. Ways of accumulating and presenting graphics illustrations on a shoestring budget are suggested. These include collecting graphics from companies, annual reports and laminating them for workshop use or putting them on a flip chart for classroom presentation, creating overhead transparencies to demonstrate different levels of effectiveness of graphic aids, and bringing in grahic artists for question/answer periods or in class workshops. Also included are an extensive handout as an introduction to graphics, sample assignments, and a selected and annotated bibliography.

Spurgeon, K. C.↗
NASA NTRS1981

Use of an automatic procedure for determination of classes of land use in the Teste Araras area of the peripheral Paulist depression

An evaluation of the multispectral image analyzer (system Image 1-100), using automatic classification, is presented. The region studied is situated. The automatic was carried out using the maximum likelihood (MAXVER) classification system. The following classes were established: urban area, bare soil, sugar cane, citrus culture (oranges), pastures, and reforestation. The classification matrix of the test sites indicate that the percentage of correct classification varied between 63% and 100%.

Dejesusparada, N.↗
NASA NTRS1981

Methodology evaluation: Effects of independent verification and intergration on one class of application

The effects of an independent verification and integration (V and I) methodology on one class of application are described. Resource profiles are discussed. The development environment is reviewed. Seven measures are presented to test the hypothesis that V and I improve the development and product. The V and I methodology provided: (1) a decrease in requirements ambiguities and misinterpretation; (2) no decrease in design errors; (3) no decrease in the cost of correcting errors; (4) a decrease in the cost of system and acceptance testing; (5) an increase in early discovery of errors; (6) no improvement in the quality of software put into operation; and (7) a decrease in productivity and an increase in cost.

Page, J.↗