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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 847 records · Page 47
All sourcesNASA NTRSDOE OSTI
NASA NTRS1982

The geochemical coherence of Pu and Nd and the Pu-244/U-238 ratio of the early solar system

Two very different sets of Pu-244/U-238 ratios have been reported for early solar system materials, one high and the other low, and this paper examines how one of these groups may yield an incorrect ratio. Recently measured partition coefficients for Pu and Sm (Jones, 1981) are used to evaluate Pu-Nd fractionation during achondrite genesis, and Pu-244/U-238 ratios of chondrites, achondrites, and Ca-Al-rich inclusions are compared and discussed. A low Pu-244/U-238 ratio is favored, and some implications of this low ratio for galactic nucleosynthesis and meteorite age dating are briefly discussed.

Jones, J. H.↗
NASA NTRS1981

The effects of transmitter/receiver clock time base instability on coherent communication system performance

The purpose of this paper is to present a model and associated analysis of the deleterious effects which both transmitter and receiver data clock time-base instability have on bit error probability. The types of time-base instability modeled and analyzed include bit jitter (epoch jitter), bit jitter rate (time interval jitter) and data asymmetry. The bit error probability is determined as a function of the statistical characteristics of the time-base instability, the data transition density, the signal-to-noise ratio in the bit rate bandwidth and the mechanizations of both the data bit detector and bit synchronizer. Numerical results are provided.

Chie, C. M.↗
NASA NTRS1984

Spatial interferometry for white light processing: The coherence interferometer

An optical systems design approach for a parallel optical processor that has an information throughput capacity in excess of one petabit per second is discussed. This system enables predetection processing of white light, passively illuminated scenes. Integrated with a programmable Van der Lugt filter, this system is an effective data compression method. A program to implement this parallel optical processing by interferometry system is discussed.

Breckinridge, J. B.↗
NASA NTRS1984

LANDSAT-4 MSS and TM Spectral Class Comparison and Coherent Noise Analysis

A detailed spectral analysis is conducted of thematic mapper and MSS data for an area near Des Moines, Iowa. Data are utilized from 7 blocks distributed throughout the area which included agricultural, forest, suburan, urban, and water scene types. The blocks are processed using a clustering algorithm to produce up to 18 cluster groupings for each block. Each cluster class is then identified with a ground-cover class using aerial photography and maps of the area. The clusters from each of the 7 blocks are inspected with regard to separability, mean, and variances. The separability measure used in the transformed divergence function or processor measures the statistical distance between classes based on class means and covariance matrices. The measure has a maximum value of 2,000 and the minimum of 0. Spectrally, very close classes will typically have values as low as 50 to 500.

Anuta, P. E.↗
NASA NTRS1984

Atmospheric effects on coherent lidar systems

Atmospheric effects on lidar systems at 10.6 micron wavelength involving molecular absorption, aerosol scattering and refractive turbulence effects are discussed. Work on the combined effects of beam truncation and atmospheric refractive turbulence on the system performance are discussed, as well as the modeling of backscattering characteristics of atmospheric aerosols.

Murty, R.↗
NASA NTRS1984

Pioneer 10 search for gravitational waves - No evidence for coherent radiation from Geminga

Attempts to identify a periodic gravitational wave signal from the binary Geminga in the reduced Doppler data from the Pioneer 10 spacecraft are reported. The study was performed to examine the possibility that the observed 160 min solar oscillation is driven by a gravitational wave from the binary, which has a period exactly one cycle different from the solar oscillation. Three 12 hr passes of Doppler data from Pioneer 10, now beyond the orbit of Neptune, were subjected to FFT analysis to detect a spectral gravitational wave signature. None was found. Least squares analysis of all low noise data from 1981 to characterize the amplitude and phase of a signal from Geminga also produced a null result. Finally, an upper bound was calculated for the polarization component of the potentially observable gravitational strain.

Anderson, J. D.↗
NASA NTRS1984

A generalization of the near-optimum binary coherent state receiver concept

The structure of a maximum a posteriori decoder is derived for binary optical fields processed according to Kennedy's near-optimum scheme, but operating in the presence of random optical phase-error and interfering background fields. An exact expression is found for the error probability, and examples to illustrate decoder performance under various operating conditions of interest are provided.

Vilnrotter, V. A.↗
NASA NTRS1984

Large-scale coherent structure and far-field jet noise

The phenomenon of broadband noise amplification/suppression under controlled excitation is investigated. The suppression is found to occur only at low jet speeds when the exit boundary layer is laminar; excitation at a Strouhal St(theta) number of about 0.017 results in optimum suppression of the far-field broadband noise as well as of the near-flow-field turbulence. The noise amplification is found to be a function of the Mach number, the amplification is higher at higher Mach number for a given excitation Strouhal number and level. The amplification also depends on the Strouhal number (St D), the maximum occurring in the range 0.65-0.85. Vortex pairing induced by the excitation appears to be at the heart of the noise amplification phenomenon under excitation.

Zaman, K. B. M. Q.↗
NASA NTRS1984

Phase coherent effects in a collisional turbulent plasma

The presence of mode-mode coupling in turbulent fluctuations in the positive column of a glow discharge in argon is studied experimentally and analytically. The auto-power spectra, the cross power spectra, the phase spectra, the cross correlation functions and the bispectrum are determined. The results are relevant to the theoretical speculations of Grabec and Mikac (1974) and it is shown that ionization instability is the primary cause of the turbulence. The phase spectra indicate that the system is nearly linear at low frequency and the bispectrum plots show that nonlinear wave-wave interactions play a role in the development of the fluctuation components in the turbulent spectrum. Distinctions are made between the azimuthal and axial behaviors of the fluctuations and the results imply a trend toward longer azimuthal scales and shorter axial scales for characterizing fluctuation wave-packets as the density of the turbulent environment increases.

Johnson, J. A., III↗
NASA NTRS1984

Coherent optical system of modular imaging collectors (COSMIC) - An approach for a large aperture high angular resolution telescope in space

Very high angular resolution can be achieved in UV/optical astronomy through interferometers in space. A concept analysis of COSMIC, which may be placed into orbit by the Space Shuttle in the late 1990's, is discussed. The photon-collecting area is three times larger than that of Space Telescope (ST), and exceeds its resolution by approximately an order of magnitude. Several alternative configurations are presented to scope the extent of design approaches which may be achievable within the transportation capability of the Space Shuttle.

Davis, B.↗
NASA NTRS1985

Bounds and approximations for rapid evaluation of coherent MPSK error probabilities

The error probability for MPSK detection is expressed here as a sum of a familiar upper-bound approximation and a correction term which is well suited for numerical integration. An asymptotic expansion of the correction term is derived, from which simple and extremely tight upper and lower bounds are obtained. Relative errors in using these bounds and approximations of them are graphed for cases of practical interest.

Chie, C. M.↗
NASA NTRS1985

Influence of coherent mesoscale structures on satellite-based Doppler lidar wind measurements

Efforts to develop display routines for overlaying gridded and nongridded data sets are discussed. The primary objective is to have the capability to review global patterns of winds and lidar samples; to zoom in on particular wind features or global areas; and to display contours of wind components and derived fields (e.g., divergence, vorticity, deformation, etc.). Current considerations in support of a polar orbiting shuttle lidar mission are discussed. Ground truth for a shuttle lidar experiment may be limited to fortuitous alignment of lidar wind profiles and scheduled rawinsonde profiles. Any improvement on this would require special rawinsonde launches and/or optimization of the shuttle orbit with global wind measurement networks.

Emmitt, G. D.↗
NASA NTRS1986

Coherent fluctuations of extratropical geopotential height and tropical convection in intraseasonal time scales

Northern-Hemisphere twice-daily 500-mb-geopotential-height data for November-March 1975-1980 and November-December 1981 and NOAA satellite measurements of outgoing longwave radiation for the same period are processed to remove seasonal cycles and Fourier-decomposition bandpassed to study variations with 20-70-d periods. The results of analysis using correlation, complex EOF, and composite techniques are presented in extensive maps and graphs and characterized. Extratropical wavetrains are found to evolve systematically from Eurasia eastward to North America and the North Atlantic on 5-6-d time scales, while the intraseasonal variation in tropical convection is dominated by a dipolelike east-west feature propagating from the western Indian Ocean to the dateline with a quasi-period of 40-50 d. The possibility that normal modes coupled between the tropics and midlatitudes may be responsible for these phenomena is considered.

Lau, K.-M.↗
NASA NTRS1986

Coherent lidar technology for global wind profiling

Current lidar systems are proven sensors for atmospheric wind measurement. Ground-based and airborne continuous wave and pulsed CO2 systems were developed and applied to several wind measuring applications. Analytical and hardware feasibility studies indicte the feasibility of measuring the global wind field from a space splatform. A Global Backscater Experiment is planned by NASA to develop a global model of aerosol backscatter using a CO2 laser. Ground-based aerosol backscatter profiles will also be obtained using a ruby and a pulsed CO2 lidar.

Huffaker, R. M.↗