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At least 325 records · Page 18
All sourcesNASA NTRSDOE OSTI
NASA NTRS1972

Dipole antenna in space - Time periodic media.

Study and solution of the problem of dipole radiation in sinusoidally space-time periodic media. The space-time periodicity can be considered as due to a strong pump wave and is expressed as a traveling-wave type change in the dielectric constant or the plasma density. The solution also covers the limit case of a sinusoidally stratified medium. The solution is formulated in a matrix form such that the basic results and diagrams apply, with minor changes, to the different cases studied: electric and magnetic dipole in a dielectric, plasma, and uniaxial plasma. The wave-vector diagram is used extensively in studying and presenting the different properties of the solution: caustics, effect of the disturbance (pump wave) motion, harmonics, radiation outside the allowed cone in a uniaxial plasma. Many dipole radiation patterns are given, and their features are explained physically. Finally, the solution and results obtained are extended to certain generally space-time periodic media.

Elachi, C.↗
NASA NTRS1972

Recent developments in global cloud statistics.

The cloud-type and cloud-layer statistics were stratified by cloud climatological regime, month, and time of day at the three hourly intervals beginning with 01 LST. Use was made of the format previously adopted for the derivation of cloud cover statistics by Sherr et al. (1968) and Greaves et al. (1971). With the new data, it is now possible to provide realistic simulations of the four-dimensional aspects of the cloud field. Furthermore, by the addition of models of the microphysical properties of each of the major cloud types, such as those developed by Gaut and Reifenstein (1969), it will be possible to extend the cloud simulation to the specification of the vertical distributions of such intensive parameters as drop size distribution and liquid water content.

Chang, D. T.↗
NASA NTRS1972

Fluid mechanics and meteorological studies directed toward improved forecasting of CAT.

Discussion of fluid mechanics experiments designed to verify theoretical understanding of the stability of stratified shear flows. Meteorological analyses of CAT encounters are reviewed, and attempts are made to tie this information together to investigate possible improvements in CAT forecasting methods. The essential facts are presented in a form intended to be useful to forecasters and flight crews.

Stoeffler, R. C.↗
NASA NTRS1972

Space-charge dynamics of liquids.

The propagation and instability characteristics of small-signal electro-fluid-mechanical space-charge and polarization waves in nonhomogeneous fluids are developed. Stratified equilibrium configurations with fluid properties and space-charge density constant within planar, cylindrical, and spherical surfaces, are emphasized. Equilibrium electric fields due both to charges in the fluid and to externally imposed potentials are normal to these surfaces. The liquid is modeled as incompressible, inviscid, and perfectly insulating, with domains of sufficiently high frequency or growth rate to validate the last assumption defined in terms of electrical conductivity or mobility. A general set of relations for perturbation field and flow variables on the perturbed surfaces of fluid layers having constant properties and space charge are derived in each of the configurations.

Zahn, M.↗
NASA NTRS1972

Cerenkov and transition radiation in space-time periodic media.

The solution to the problem of determining the radiation emitted by a uniformly moving charged particle in a sinusoidally space-time periodic medium is obtained. The space-time periodicity can be considered as due to a strong pump wave and is expressed as a traveling-wave-type change in the dielectric constant or the plasma density. The solution covers also the limiting case of sinusoidally stratified media. The expression and spectrum of the radiated electromagnetic field are determined for different media: dielectric, isotropic and uniaxial plasma. Depending on the nature of the medium and the velocity of the particle, the radiated field is of the Cerenkov and/or transition type. The Brillouin diagram is used extensively in understanding and determining the nature, extent, and spectrum of the different modes of radiation, and a focusing effect is also studied.

Elachi, C.↗
NASA NTRS1972

Theoretical frameworks for testing relativistic gravity. IV - A compendium of metric theories of gravity and their post-Newtonian limits.

Metric theories of gravity are compiled and classified according to the types of gravitational fields they contain, and the modes of interaction among those fields. The gravitation theories considered are classified as (1) general relativity, (2) scalar-tensor theories, (3) conformally flat theories, and (4) stratified theories with conformally flat space slices. The post-Newtonian limit of each theory is constructed and its Parametrized Post-Newtonian (PPN) values are obtained by comparing it with Will's version of the formalism. Results obtained here, when combined with experimental data and with recent work by Nordtvedt and Will and by Ni, show that, of all theories thus far examined by our group, the only currently viable ones are general relativity, the Bergmann-Wagoner scalar-tensor theory and its special cases (Nordtvedt; Brans-Dicke-Jordan), and a recent, new vector-tensor theory by Nordtvedt, Hellings, and Will.

Ni, W.-T.↗
NASA NTRS1972

Effects of circular geometry in simulation of convection in rotating spacecraft tanks

For computational simulation of the convection and mixing of stratified fluid in a rotating tank (such as used in Apollo flights) with time-dependent rotation, the Navier-Stokes convection problem was formulated for a circular tank configuration. The final equations results from a general approximate theory for combined forced and contained natural convection in a time-dependent rotating system. The equations are cast in terms of vorticity and stream function in a form convenient for computation, with a transformed coordinate system, and appropriate boundary conditions are derived. Accurate representations for the cryogenic supercritical oxygen thermodynamic properties are used in the computations, and an efficient numerical finite difference scheme and computational method are employed.

Martin, E. D.↗
NASA NTRS1972

Numerical methods for reduction of topside ionograms

Several alternative methods for solving the group height equation are presented. Three of these are now in operation at Ames Research Center and use data contained in a single ionogram trace. From the data an electron density profile N(h) is computed. If the ionogram also exhibits other traces, reverse ionogram traces are computed, using the N(h) profile, for comparison with the redundant data. When agreement is poor, the initial data trace is reinterpreted, another N(h) profile computed, and the reverse traces generated once again. This process is repeated until a desired degree of consistency is achieved. To reduce the necessity for human intervention and eliminate decision making required in conjunction with the preceding methods, a method is proposed that accepts as input, all data from a single ionogram. In general, no electron density function will satisfy these data exactly, but a best N(h) profile can be computed. Finally, a method is described that eliminates the need to assume that the ionosphere is spherically stratified. Horizontal gradients in electron density are detected and accounted for by processing several ionograms from the same satellite pass simultaneously. This idea is derived as an extension of one of the basic methods.

Mcculley, L.↗
NASA NTRS1973

Inventory and monitoring of natural vegetation and related resources in an arid environment by the use of ERTS-1 imagery

The author has identified the following significant results. An evaluation of information content of ERTS-1 reconstituted photography in comparison with Apollo 6 and Gemini 4 photography has been accomplished for some landforms through the use of an image groupability testing procedure. Analysis of terrain feature-vegetation relationships has been completed. Ground truth data collected in the southern Arizona test site have indicated that many of the plants can be categorized as either evergreen, cool season deciduous, or warm season deciduous. Results from image groupability testing have been utilized to stratify an Apollo 6 scene and an ERTS-1 scene of the same area.

Schrumpf, B. J.↗
NASA NTRS1973

An evaluation of space acquired data as a tool for management to wildlife habitat in Alaska

The Bureau of Sport Fisheries and Wildlife ERTS experiment in Alaska attempts to yield information useful for three primary functions in the State. They are: (1) to test the feasibility of using ERTS data, in conjunction with aircraft acquired multispectral photography, to develop effective stratified sampling techniques, (2) to provide near real time assessment and evaluation of the quantity, quality, and distribution of waterfowl breeding habitat through frequent ERTS measurements of hydrologic, phenological and vegetational parameters, and (3) to provide basic mapping of vegetation and terrain in certain remote areas of the State for which little or no biological data now exist.

Vantries, B. J.↗
NASA NTRS1973

ERTS-1 data applications to Minnesota forest land use classification

The author has identified the following significant results. Color-combined ERTS-1 MSS spectral slices were analyzed to determine the maximum (repeatable) level of meaningful forest resource classification data visually attainable by skilled forest photointerpreters for the following purposes: (1) periodic updating of the Minnesota Land Management Information System (MLMIS) statewide computerized land use data bank, and (2) to provide first-stage forest resources survey data for large area forest land management planning. Controlled tests were made of two forest classification schemes by experienced professional foresters with special photointerpretation training and experience. The test results indicate it is possible to discriminate the MLMIS forest class from the MLMIS nonforest classes, but that it is not possible, under average circumstances, to further stratify the forest classification into species components with any degree of reliability with ERTS-1 imagery. An ongoing test of the resulting classification scheme involves the interpretation, and mapping, of the south half of Itasca County, Minnesota, with ERTS-1 imagery. This map is undergoing field checking by on the ground field cooperators, whose evaluation will be completed in the fall of 1973.

Sizer, J. E.↗
NASA NTRS1973

Apollo 16 exploration of Descartes - A geologic summary.

The Cayley Plains at the Apollo 16 landing site consist of crudely stratified breccias to a depth of at least 200 meters, overlain by a regolith 10 to 15 meters thick. Samples, photographs, and observations by the astronauts indicate that most of the rocks are impact breccias derived from an anorthosite-gabbro complex. The least brecciated members of the suite include coarse-grained anorthosite and finer-grained, more mafic rocks, some with igneous and some with metamorphic textures. Much of the transverse area is covered by ejecta from North Ray and South Ray craters, but the abundance of rock fragments increases to the south toward the younger South Ray crater.

Source record↗
NASA NTRS1972

The Washougal meteorite.

Optical study of the Washougal (Wash.), howardite, and determination of the ranges of composition of plagioclase and pyroxenes from measurements of densities and indices of refraction. Notable among many unique xenoliths are a round object whose morphology is that of an armored chondrule; a stratified fragment; and a centimeter-sized dunite xenolith (olivine Fa sub 12.8). The abundances of 27 elements, including all major elements and 15 trace elements are reported. To a first approximation, the composition of Washougal corresponds to a mixture of 51 wt per cent of eucritic material and 49 per cent of a diogenitic component, but excesses of some elements suggest a minor component of chondritic composition.

Jerome, D. Y.↗
NASA NTRS1973

The core paradox.

Rebuttal of suggestions from various critics attempting to provide an escape from the seeming paradox originated by Higgins and Kennedy's (1971) proposed possibility that the liquid in the outer core was thermally stably stratified and that this stratification might prove a powerful inhibitor to circulation of the outer core fluid of the kind postulated for the generation of the earth's magnetic field. These suggestions are examined and shown to provide no reasonable escape from the core paradox.

Kennedy, G. C.↗
NASA NTRS1973

Amplification and decay of long nonlinear waves.

The interaction of weakly nonlinear waves with slowly varying boundaries is considered. Special emphasis is given to rotating fluids, but the analysis applies with minor modifications to waves in stratified fluids and shallow-water waves. An asymptotic solution of a variant of the Korteweg-de Vries equation with variable coefficients is developed that produces a 'Green's law' for the amplification of waves of finite amplitude. For shallow-water waves in water of variable depth, the result predicts wave growth proportional to the -1/3 power of the depth.

Leibovich, S.↗
NASA NTRS1973

Corrections of satellite positions in near-real time.

The influence of sudden increases of electron content on the accurate determination of the position of a satellite is investigated based on a spherically stratified ionospheric model. Using the total electron content information from Faraday rotation measurements, a procedure is presented whereby the corrections of satellite position due to the unpredicted electron increase can be accounted for without the need to know the spatial distribution of the additional electrons.

Poularikas, A. D.↗
NASA NTRS1973

Laboratory vortices in rotating, sheared flow.

By placing a small convective source (electrical heater) in a rotating, vertically sheared, stratified flow in a rotating annulus, a well-organized vortex flow is generated. A qualitative description of the flow is given. The flow is always cyclonic below the heater and anticyclonic above, and is quite persistent in the sheared flow.

Kaiser, J. A. C.↗
NASA NTRS1973

Radiative damping of trapped gravity waves in the solar atmosphere.

The radiative damping of trapped gravity waves in an optically thin atmosphere is studied for a stratified Boussinesq fluid. The character of the atmospheric eigenmodes depends on the distribution of the Brunt-Vaisala frequency N and the radiative relaxation time tau. The calculations for simple layer models show that if N x tau is large over some finite fraction of the trapping region, then modes of long lifetime can exist. In order to suppress gravity waves entirely, it is necessary that N x tau be less than or equal to 1 over the entire trapping region. Qualitative application of the results to the solar atmosphere leads to the conclusion that gravity wave eigenmodes of the solar atmosphere, although damped, are by no means eliminated by radiative effects.

Clark, P. A.↗