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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 91 records · Page 5
All sourcesNASA NTRSDOE OSTI
NASA NTRS2017

Global Distribution and Parameter Dependences of Gravity Wave Activity in the Martian Upper Thermosphere Derived from MAVEN NGIMS Observations

Wavelike perturbations in the Martian upper thermosphere observed by the Neutral Gas Ion Mass Spectrometer (NGIMS) onboard the Mars Atmosphere and Volatile EvolutioN (MAVEN) spacecraft have been analyzed. The amplitudes of small-scale perturbations with apparent wavelengths between approx. 100 and approx. 500 km in the Ar density around the exobase show a clear dependence on temperature (T(sub 0)) of the upper thermosphere. The average amplitude of the perturbations is approx. 10% on the dayside and approx. 20% on the nightside, which is about 2 and 10 times larger than those observed in the Venusian upper thermosphere and in the low-latitude region of Earths upper thermosphere, respectively. The amplitudes are inversely proportional to T(sub 0), suggesting saturation due to convective instability in the Martian upper thermosphere. After removing the dependence on T(sub 0), dependences of the average amplitude on the geographic latitude and longitude and solar wind parameters are found to be not larger than a few percent. These results suggest that the amplitudes of small-scale perturbations are mainly determined by convective breaking saturation in the upper thermosphere on Mars, unlike those on Venus and Earth.

Thermosphere↗
NASA NTRS1997

Effect of Helical Slow-Wave Circuit Variations on TWT Cold-Test Characteristics

Recent advances in the state of the art of computer modeling offer the possibility for the first time to evaluate the effect that slow-wave structure parameter variations, such as manufacturing tolerances, have on the cold-test characteristics of helical traveling-wave tubes (TWT's). This will enable manufacturers to determine the cost effectiveness of controlling the dimensions of the component parts of the TWT, which is almost impossible to do experimentally without building a large number of tubes and controlling several parameters simultaneously. The computer code MAFIA is used in this analysis to determine the effect on dispersion and on-axis interaction impedance of several helical slow-wave circuit parameter variations, including thickness and relative dielectric constant of the support rods, tape width, and height of the metallized films deposited on the dielectric rods. Previous computer analyses required so many approximations that accurate determinations of the effect of many relevant dimensions on tube performance were practically impossible.

Kory, Carol L.↗
NASA NTRS1998

Effect of Helical Slow-Wave Circuit Variations on TWT Cold-Test Characteristics

Recent advances in the state of the art of computer modeling offer the possibility for the first time to evaluate the effect that slow-wave structure parameter variations, such as manufacturing tolerances, have on the cold-test characteristics of helical traveling-wave tubes (TWT's). This will enable manufacturers to determine the cost effectiveness of controlling the dimensions of the component parts of the TWT, which is almost impossible to do experimentally without building a large number of tubes and controlling several parameters simultaneously. The computer code MAFIA is used in this analysis to determine the effect on dispersion and on-axis interaction impedance of several helical slow-wave circuit parameter variations, including thickness and relative dielectric constant of the support rods, tape width, and height of the metallized films deposited on the dielectric rods. Previous computer analyzes required so many approximations that accurate determinations of the effect of many relevant dimensions on tube performance were practically impossible.

Kory, Carol L.↗
NASA NTRS1998

Effect of Helical Slow-Wave Circuit Variations on TWT Cold-Test Characteristics

Recent advances in the state of the art of computer modeling offer the possibility for the first time to evaluate the effect that slow-wave structure parameter variations, such'as manufacturing tolerances, have on the cold-test characteristics of helical traveling-wave tubes (TWT's). This will enable manufacturers to determine the cost effectiveness of controlling the dimensions of the component parts of the TWT, which is almost impossible to do experimentally without building a large number of tubes and controlling several parameters simultaneously. The computer code MAxwell's equations by the Finite Integration Algorithm (MAFIA) is used in this analysis to determine the effect on dispersion and on-axis interaction impedance of several helical slow-wave circuit parameter variations, including thickness and relative dielectric constant of the support rods, tape width, and height of the metallized films deposited on the dielectric rods. Previous computer analyzes required so many approximations that accurate determinations of the effect of many relevant dimensions on tube performance were practically impossible.

Kory, Carol L.↗
NASA NTRS1973

Relations among low ionosphere parameters and high frequency radio wave absorption

Charged particle conductivities measured in the very low ionosphere at White Sands Missile Range, New Mexico, and Wallops Island, Virginia, are compared with atmospheric parameters and high frequency radio wave absorption measurements. Charged particle densities are derived from the conductivity data. Between 33 and 58 km, positive conductivity correlated well with neutral atmospheric temperature, with temperature coefficients as large as 4.6%/deg K. Good correlations were also found between HF radio wave absorption and negative conductivity at altitudes as low as 53 km, indicating that the day-to-day absorption variations were principally due to variations in electron loss rate.

Cipriano, J. P.↗
NASA NTRS1989

Analysis of the fetch-related bias in altimeter wind speed measurements

The present interpretation of the radar cross section sigma exp 0 measured by satellite altimeters implies that the rms wave slope gamma is controlled solely by the local wind. However, parameters of wave spectra, including the exponent in the power law for the equilibrium range, depend on sea maturity. The latter is characterized by the nondimensional fetch, x = gX/U-squared. Consequently, gamma and sigma exp 0 are controlled by both U and the wind fetch X. Geosat data for one year are used jointly with in-situ wind and wave observations to assess the fetch-related error trend in altimeter wind speeds. This trend results in overestimated winds in the regions and seasons characterized by a high x, and vice versa. A procedure for wind speed retrieval based on processing sigma exp 0 jointly with the significant wave height information contained in the altimeter wave forms is proposed.

Glazman, Roman E.↗
NASA NTRS1976

Whistler wave propagation in a large magnetoplasma

A large collisionless quiescent plasma source is developed for investigating the phase and amplitude distribution of antenna-launched whistler waves in a specified parameter regime relating wave frequency to electron cyclotron frequency. Wave dispersion is studied both by interferometer techniques with monochromatic waves and by propagation of short phase-coherent wave bursts. The wave damping mechanism is examined by propagating perfectly ducted whistler waves. The dispersion of single frequency waves and wave packets is demonstrated. Trough ducting for wave frequency to electron cyclotron frequency ratio greater than 1/2 is verified, and new eigenmodes in nonuniform plasmas at ratio values less than 1/2 are observed. It is shown that geometric effects due to ray divergence and wave refraction dominate over collisional damping.

Stenzel, R. L.↗
NASA NTRS1973

Automation of measurement of spatial damping parameters

A traveling wave unit was built to process measurement data on spatial damping parameters and to simplify statistical treatment of the results. Mean values of the loss coefficient, lengths of flexual waves, and wave propagation velocities for a given set of discrete functions were determined. Results are given in a table.

Akolzin, A. N.↗
NASA NTRS1976

A comparative study of three techniques for using the spectral matrix in wave analysis

Three techniques - power spectral analysis, coherency analysis, and wave analysis - for studying ULF waves in the magnetosphere are described. These techniques, while mathematically dissimilar, are all based on the assumption that, at any single frequency, a single plane wave, propagating along the normal to the plane, is present. Wave polarization parameters provided by these techniques are important in the development of models of wave generation. A comparative study of the three techniques was carried out using simulated data involving known wave and noise properties and real ULF event data from ATS 1 and 6.

Arthur, C. W.↗
NASA NTRS2015

Gravitational Waves: Search Results, Data Analysis and Parameter Estimation. Amaldi 10 Parallel Session C2

The Amaldi 10 Parallel Session C2 on gravitational wave(GW) search results, data analysis and parameter estimation included three lively sessions of lectures by 13 presenters, and 34 posters. The talks and posters covered a huge range of material, including results and analysis techniques for ground-based GW detectors, targeting anticipated signals from different astrophysical sources: compact binary inspiral, merger and ringdown; GW bursts from intermediate mass binary black hole mergers, cosmic string cusps, core-collapse supernovae, and other unmodeled sources; continuous waves from spinning neutron stars; and a stochastic GW background. There was considerable emphasis on Bayesian techniques for estimating the parameters of coalescing compact binary systems from the gravitational waveforms extracted from the data from the advanced detector network. This included methods to distinguish deviations of the signals from what is expected in the context of General Relativity.

Tests of general relativity↗
NASA NTRS1981

Temperature minimum heating in solar flares by resistive dissipation of Alfven waves

The possibility that the strong heating produced at temperature-minimum levels during solar flares is due to resistive dissipation of Alfven waves generated by the primary energy release process in the corona is studied. It is shown how, for suitable parameters, these waves can carry their energy essentially undamped into the temperature-minimum layers and can then produce a degree of heating consistent with observations.

Emslie, A. G.↗
NASA NTRS1979

Hydromagnetic waves and turbulence in the solar wind

The paper presents a state-of-the-art review of interplanetary fluctuations, their origins, and their effects on the solar wind. Typical values of parameters to waves and turbulence in the solar wind are examined, along with a classification of large-amplitude waves. Cases where description by the MHD theory is qualitatively correct and where it can be misleading are noted. An attempt is made to state rigorously the essential points of hydromagnetic-wave theory and to identify areas in which theoretical research needs to be extended. The review covers the observed hydromagnetic fluctuations, their interpretation in terms of current theory, and the degree of closure between observation and theory. The spatial distribution and origins of waves in the solar wind are discussed.

Barnes, A.↗
NASA NTRS1985

Hierarchical structure of stratospheric wind fluctuations

In order to verify the gravity-wave-breaking theories, high resolution observations of middle-stratospheric winds were carried out by balloon-borne anemometers. The observed features were summarized, the parameters of waves generating the turbulence were estimated, and the effect on the general circulation and the transport process were discussed.

Yamanaka, M. D.↗
NASA NTRS1990

Dependence of millimeter wave surface resistance on the deposition parameters of laser ablated YBa2Cu3O(x) thin films

Measurements of millimeter-wave surface resistance versus temperature have been performed for YBa2Cu3O(x) thin films on 100 line-type SrTiO(3) substrates using a TE(011) cylindrical copper cavity at 80 GHz. The 0.6-micron thick films were grown at several deposition temperatures in the range 690 C to 810 C by means of a pulsed excimer laser ablation technique. A surface resistance minimum (60 milliohm at 77 K) near 770 C is shown to correlate with a minimum in c-axis lattice parameter (11.72 A). The highest value of Tc also occurs near this temperature. The surface resistance of films deposited at 790 C on 110 line-type LaAlO3 subtrates is lower, reaching 8 milliohm at 98 GHz and 80 K, demonstrating the influence of substate material on film quality.

Wosik, J.↗
NASA NTRS1989

Wavelet analysis introduction and application to radar scattering from water waves

Double-parameter expansions, leading to an instantaneous multiscale analysis, are used to obtain time-frequency graphs from time-series data for interpretation of scatterometer response to sea surface geometry. This method is used to define, as well as possible, one-dimensional signal input (elevation and slope). However, some important fundamental parameters, such as the asymmetric development of short scales in crests and troughs, the long-wave amplitude modulation, the different zero-crossings, and so forth, are easily extracted from the wavelet images.

Chapron, B.↗