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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 1,693 records · Page 94
All sourcesNASA NTRSDOE OSTI
NASA NTRS1983

Radar modeling of space diversity associated with slant path rain attenuation at variable path angles, frequencies, and drop size distributions

Single and joint terminal slant path attenuation statistics at frequencies of 28.56 and 19.04 GHz were derived from radar data. Statistics were independently obtained for path angles of 20, 45, and 90 deg, in order to examine how path angle influences both single terminal and joint probability distributions. A prediction technique is demonstrated to work well for calculating both single and joint terminal distributions at other path angles. Diversity gains and autocorrelation function dependence on site spacing were determined employing the radar modeling results.

Goldhirsh, J.↗
NASA NTRS1983

Effect of carbide distribution on rolling-element fatigue life of AMS 5749

Endurance tests with ball bearings made of corrosion resistant bearing steel which resulted in fatigue lives much lower than were predicted are discussed. Metallurgical analysis revealed an undesirable carbide distribution in the races. It was shown in accelerated fatigue tests in the RC rig that large, banded carbides can reduce rolling element fatigue life by a factor of approximately four. The early spalling failures on the bearing raceways are attributed to the large carbide size and banded distribution.

Parker, R. J.↗
NASA NTRS1983

Thermal Analysis of Antenna Structures. Part 2: Panel Temperature Distribution

This article is the second in a series that analyzes the temperature distribution in microwave antennas. An analytical solution in a series form is obtained for the temperature distribution in a flat plate analogous to an antenna surface panel under arbitrary temperature and boundary conditions. The solution includes the effects of radiation and air convection from the plate. Good agreement is obtained between the numerical and analytical solutions.

Schonfeld, D.↗
NASA NTRS1982

Description and planned use of a data distribution evaluation system for fiber optic data buses

A general description of a laboratory data distribution evaluation system (DDES) is given and some plans to use the system. The DDES is a microprocessor-based evaluation system consisting of three identical terminals. The DDES provides the capability for evaluating different system protocols and data word structures by making appropriate software changes, and different transmission medias and modulation schemes by making front-end hardware changes. A data multiplexing standard for fiber optic data transmission which parallels MIL-STD-1553B has proposed four different data modulation schemes. These modulation schemes will be described along with the plans to evaluate each of them. NASA-Langley has also been developing a data distribution approach which utilizes optical wavelength division multiplexing (WDM). A four-port, four-wavelength WDM system will be described along with the planned use of the DDES to evaluate its performance.

Spencer, J. L.↗
NASA NTRS1982

Remote sensing /Nimbus-7 CZCS/ analysis of phytoplankton distribution in coastal waters of the Gulf of Lions /northwestern Mediterranean/

The distribution of phytoplankton in the northwestern Mediterranean was studied using the experimental satellite Nimbus 7, which is equipped with a coastal zone color scanner (CZCS). The most characteristic boundaries of this biomass and its variations throughout the year of 1979 were also investigated by treating the CZCS data, collected through different channels with defined wavelengths, with a computer. Using specially adapted algorithms, characteristic features such as mesoscale cyclonic eddy, out-flow of freshwater from the Rhone river, and coastal upwelling were revealed. It is confirmed that the biomass of phytoplankton is a good indicator for the mesoscale distribution of water masses, and that the remote sensing in the visible spectrum can permit the study of frontal boundaries in the sea.

Caraux, D.↗
NASA NTRS1982

Infrared remote sensing of the vertical and horizontal distribution of clouds

An algorithm has been developed to derive the horizontal and vertical distribution of clouds from the same set of infrared radiance data used to retrieve atmospheric temperature profiles. The method leads to the determination of the vertical atmospheric temperature structure and the cloud distribution simultaneously, providing information on heat sources and sinks, storage rates and transport phenomena in the atmosphere. Experimental verification of this algorithm was obtained using the 15-micron data measured by the NOAA-VTPR temperature sounder. After correcting for water vapor emission, the results show that the cloud cover derived from 15-micron data is less than that obtained from visible data.

Chahine, M. T.↗
NASA NTRS1982

An instrument for rapidly measuring plasma distribution functions with high resolution

An instrument which can rapidly measure plasma particle distribution functions has been developed based upon recent innovations in electrostatic analyzer design and position sensitive particle detection. The new analyzer uses a quadrispherical geometry, but has a completely uniform 360 deg fan-shaped field of view. The polar angular distribution of entering particles is spatially imaged onto a position sensitive detector at the annular exit aperture after a deflection through 90 deg. Several methods of position sensitive detection have been successfully used in conjunction with this analyzer. The simplest is individual channel multipliers spaced around the annular exit. Microchannel plate electron multipliers permit greater position resolution to be obtained, and a detector using microchannel plates followed by a resistive anode image converter obtains angular resolution of about one degree, i.e., 360 individual angle pixels. Instruments of this type were flown on a sounding rocket in early 1982 and will be included on the Giotto comet mission and the AMPTE ion release module (IRM).

Carlson, C. W.↗
NASA NTRS1983

Dynamics of directional reflectance factor distributions for vegetation canopies

Directional reflectance factors that span the entire exitance hemisphere are collected on the ground for a variety of homogeneous vegetation canopies and bare soils. NOAA 6/7 AVHRR bands 1 (0.58-0.68 micron) and 2 (0.73-1.1 microns) are used. When possible, geometric measurements of leaf orientation distributions are taken simultaneously with each spectral measurement. Other supporting structural and optical measurements are made. These data sets are taken at various times of the day for each cover type. These unique sets, together with pertinent data in the literature, are used to investigate the dynamics of the directional reflectance factor distribution as a function of the geometric structure of the scene, solar zenith angle, and optical properties of the scene components (leaves and soil). For complete homogeneous vegetation canopies, the principal trend observed at all sun angles and spectral bands is a minimum reflectance near nadir and increasing reflectance with increasing off-nadir view angle for all azimuth directions.

Kimes, D. S.↗
NASA NTRS1983

Ionospheric and Birkeland current distributions inferred from the MAGSAT magnetometer data

Ionospheric and field-aligned sheet current density distributions are presently inferred by means of MAGSAT vector magnetometer data, together with an accurate magnetic field model. By comparing Hall current densities inferred from the MAGSAT data and those inferred from simultaneously recorded ground based data acquired by the Scandinavian magnetometer array, it is determined that the former have previously been underestimated due to high damping of magnetic variations with high spatial wave numbers between the ionosphere and the MAGSAT orbit. Among important results of this study is noted the fact that the Birkeland and electrojet current systems are colocated. The analyses have shown a tendency for triangular rather than constant electrojet current distributions as a function of latitude, consistent with the statistical, uniform regions 1 and 2 Birkeland current patterns.

Zanetti, L. J.↗
NASA NTRS1983

Finite-dimensional discrete-time control of linear distributed parameter systems

Systems described by partial differential equations have an infinite-dimensional state space. Feedback control of such distributed parameter systems must be accomplished by finite-dimensional controllers to be implemented by on-line digital computers. A further practical constraint is that the controller must operate in discrete (rather than continuous) time. This paper investigates the stability of such distributed parameter feedback controllers in closed-loop with the actual system.

Balas, M. J.↗
NASA NTRS1983

Charged particle distributions in Jupiter's magnetosphere

In situ data from the Pioneer and Voyager spacecraft, supplemented by earth-based observations and theoretical considerations, are used as the basis for the present quantitative, compact model of the 1 eV-several MeV charged particle distribution in the Jovian magnetosphere. The thermal plasma parameters of convection speed, number density, and characteristic energy, are specified as functions of position for electrons and for the ion species H(+), O(+), O(2+), S(+), S(2+), S(3+), and Na(+). Major features of the magnetic field, thermal plasma, and trapped particle distributions, are modeled and results for each plasma region are compared with observed spectra. Comparisons show that the model represents the data to within a factor of 2 + or - 1, except where time variations are significant. Practical applications of the model to spacecraft near Jupiter are given.

Divine, N.↗
NASA NTRS1983

The non-Maxwellian energy distribution of ions in the warm Io torus

Observations of Io's torus indicate that the majority of ions have energies of 55-75 eV, with a high-energy tail extending up to the corotation energy. It was found that such a distribution can be established via the Coulomb cooling of ions heated at the corotation energy onto the cold 5-eV electrons. The energy E(asterisk) of the main body of the ions and the shape of the energy distribution are functions of the transport loss time. Matching E(asterisk) with the data (E/asterisk/ = 55-75 eV) requires transport loss times in the range 25-1000 days.

Richardson, J. D.↗
NASA NTRS1983

Distributed acceleration of cosmic rays

It is proposed that the acceleration of cosmic rays is distributed over their propagation through interstellar space. Thus after most nuclear fragmentation reactions in the interstellar medium, cosmic rays gain about a factor of 5 in energy. This hypothesis resolves several discrepancies in composition at different energies. The present results suggest that after the principal acceleration and during their galactic confinement, cosmic rays are further accelerated by the weak shocks of widely distributed old supernova remnants.

Silberberg, R.↗
NASA NTRS1983

Radial evolution of ion distribution functions

A survey of solar wind ion velocity distributions and derived parameters (temperature, ion differential speed, heat flux, adiabatic invariants) is presented with emphasis on the heliocentric distance range between 0.3 and 1 AU traversed by the Helios solar probe. The radial evolution of nonthermal features are discussed which are observed to be most pronounced at perihelion. Within the framework of quasilinear plasma theory, wave particle interactions that may shape the ion distributions are considered. Some results of a self consistent model calculation are presented accounting for ion acceleration and heating by resonant momentum and energy exchange with ion cyclotron and magnetosonic waves propagating away from the Sun along the interplanetary magnetic field. Another tentative explanation for the occurrence of large perpendicular proton temperatures is offered in terms of heating by Landau damping of lower hybrid waves.

Marsch, E.↗
NASA NTRS1984

Method for Accessing Distributed Heterogeneous Databases

A scenario of relational, hierarchial, and network data bases is presented and a distributed access view integrated data base system (DAVID) is described for uniformly accessing data bases which are heterogeneous and physically distributed. The DAVID system is based on data base logic so that the relational approach is generalized to the heterogeneous approach. The global data manager is explained as are global data manipulation languages which can operate on all the data bases and can query the data dictionary and the data directory.

Jacobs, B. E.↗
NASA NTRS1984

The implementation and use of Ada on distributed systems with high reliability requirements

The use and implementation of Ada (a trade mark of the US Dept. of Defense) in distributed environments in which the hardware are assumed to be unreliable were investigated. The possibility that a distributed system is programmed entirely in Ada so that the individual tasks of the system are unconcerned with which processors they are executing on and failures occurring in the underlying hardware were examined.

Knight, J. C.↗
NASA NTRS1984

IPAD 2: Advances in Distributed Data Base Management for CAD/CAM

The Integrated Programs for Aerospace-Vehicle Design (IPAD) Project objective is to improve engineering productivity through better use of computer-aided design and manufacturing (CAD/CAM) technology. The focus is on development of technology and associated software for integrated company-wide management of engineering information. The objectives of this conference are as follows: to provide a greater awareness of the critical need by U.S. industry for advancements in distributed CAD/CAM data management capability; to present industry experiences and current and planned research in distributed data base management; and to summarize IPAD data management contributions and their impact on U.S. industry and computer hardware and software vendors.

Bostic, S. W.↗