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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 649 records · Page 36
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NASA NTRS1987

Second harmonic plasma emission involving ion sound waves

The theory for second harmonic plasma emission by the weak turbulence (or random phase) processes L + L + or - S to T, proceeding in two three-wave steps, L + or - S to L prime and L + L prime to T, where L, S and T denote Langmuir, ion sound and electromagnetic waves, respectively, is developed. Kinematic constraints on the characteristics and growth lengths of waves participating in the wave processes, and constraints on the characteristics of the source plasma, are derived. Limits on the brightness temperature of the radiation and the levels of the L prime and S waves are determined. Expressions for the growth rates and path-integrated wave temperatures are derived for simple models of the wave spectra and source plasma.

Cairns, Iver H.↗
NASA NTRS1987

Third and higher harmonic plasma emission due to Raman scattering

The theory for third and higher harmonic plasma emission by the weak turbulence (or random phase) process L + T prime to T (where L denotes a Langmuir wave, and T and T prime denote transverse waves) is developed. Kinematic constraints on the characteristics and growth lengths of waves participating in the wave processes are identified. The cases of L waves produced either directly by a streaming instability, or by the decay L to L prime + S (S is an ion sound wave) of L waves generated by a streaming instability, are considered. Limits on the brightness temperature of the radiation are determined, and expressions for the growth rate and path-integrated wave temperatures are derived.

Cairns, Iver H.↗
NASA NTRS1987

Whistler mode emissions in the Uranian radiation belts

Voyager 2 detected intense whistler mode emissions and fluxes of energetic electrons during the outbound pass through the region of auroral L shells. The observed energetic (E greater than 22 keV) electron distribution, a model warm (E less than 27.5 keV) electron distribution, and the cold plasma density profile deduced by Kurth et al. (1987) are used to calculate the ray path-integrated spatial amplification of whistlers which arrive at Voyager 2 from the magnetic equator. By matching the calculated amplification and the relative gains at different frequencies deduced from the observed whistler power spectrum, the pitch angle anisotropy parameters of the electron distributions are determined to within a fairly narrow range of values. The estimated bounce average pitch angle diffusion coefficient indicates that electrons are on strong diffusion over a wide range in energies. The electron precipitation energy flux is sufficient to produce the observed auroral light emissions.

Coroniti, F. V.↗
NASA NTRS1988

Supersonic combustion performance of hydrogen/hydrocarbon mixtures as determined by a nonintrusive temperature monitor

A simple and reliable OH absorption technique was developed and applied to measure path integrated temperature and OH number density in scramjet combustor hardware. The first series of measurements was made in premixed combustion products at the exit of a Mach 2 nozzle mounted on a hydrogen fueled vitiated heater. The second series of tests was conducted during supersonic combustion evaluation of hydrogen/hydrocarbon fuel mixtures. These measurements were made near the exit of a 48-inch long diverging supersonic combustor. The OH number density measurements indicated that both the nozzle and the combustor flow were not in equilibrium.

Northam, G. Burton↗
NASA NTRS1990

Estimated accuracy of ground-based liquid water measurements during FIRE

Since on goal of the First ISCCP Regional Experiment (FIRE) project is to improve our understanding of the relationships between cloud microphysics and cloud reflectivity, it is important that the accuracy of remote liquid measurements by microwave radiometry be thoroughly understood. The question is particularly relevant since the uncertainty in the absolute value of the radiometric liquid measurement is greatest at low liquid water contents (less than 0.1 mm). However it should be stressed that although uncertainty exists in the absolute value of liquid, it is well known that the observed radiometric signal is proportional to the amount of liquid in the antenna beam. As a result, changes in amounts of liquid are known to greater accuracy than the absolute value, which may contain a bias. Here, an assessment of the liquid measurement accuracy attained at San Nicolas Island (SNI) is presented. The vapor and liquid water data shown were computed from the radiometric brightness temperatures using statistical retrieval algorithms. The retrieval coefficients were derived from the 69 soundings made by Colorado State University during the SNI observations. Sources of error in the vapor and liquid measurements include cross-talk in the retrieval algorithms (not a factor at low liquid contents), uncertainties in the brightness temperature measurement, and uncertainties in the vapor and liquid attenuation coefficients. The relative importance of these errors is discussed. For the retrieval of path-integrated liquid water, the greatest uncertainty is caused by the temperature dependence of the absorption at microwave frequencies. As a result, the accuracy of statistical retrieval of liquid depends to large measure upon how representative the a priori radiosonde data are of the conditions prevailing during the measurements. The microwave radiometer measurements at SNI were supplemented by an infrared (IR) radiometer modified for measurement of cloud-base temperature. Thus, the IR system provides the means to incorporate continuous measurements of the liquid temperature into the retrieval process.

Snider, Jack B.↗
NASA NTRS1990

Ion cyclotron absorption at the second harmonic of the oxygen gyrofrequency

A hot ray tracing code (HOTRAY) is used to establish the ultimate demise of the wave energy generated inside the plasmasphere during storm conditions. The code uses the WKB approximation of geometric optics to calculate the paths of electromagnetic and electrostatic waves in a hot, multiion plasma. Ray tracing calculations with HOTRAY are detailed and path integrated absorption is discussed. Unducted waves which are preferentially generated in the field aligned direction are rapidly refracted to large wave normal angles. The waves are observed to reflect at frequencies between oxygen and helium gyrofrequencies once their frequency falls below the bi-ion frequency and the waves bounce back accross the equator. Either Landau resonance with plasmaspheric electrons or second harmonic cyclotron resonance with thermal oxygen ultimately absorb the wave energy. It is suggested that both processes may provide a significant heating mechanism for either population during a storm.

Horne, R. B.↗
NASA NTRS1990

Retrieval of precipitation profiles from airborne radar and passive radiometer measurements - Comparison with dual-frequency radar measurements

Precipitation-rate profiles derived from a single-frequency radar and a radiometer are compared with profiles derived from a dual-frequency radar, using data obtained during the 1985-1986 Communication Research Laboratory/NASA rain measuring experiment over the Atlantic Ocean from a dual-frequency X- and Ka-band radars and an X-band passive radiometer. Profiles were retrieved using a modification of the Hitschfeld-Bordan (1954) algorithm constrained by a measurement of the path integrated extinction derived from passive radiometry. It was found that the two techniques under comparison yielded average rainfall rates that agreed within about 25 percent. It is suggested that, while a single-frequency radar operating in conjunction with multifrequency passive radiometers might provide cost-effective spaceborne measurements of tropical rainfall distributions, a dual-frequency radar might be able to remove some ambiguities that were encountered in this study.

Weinman, J. A.↗
NASA NTRS1990

Pacific-North America plate motions - New results from very long baseline interferometry

The state of Pacific-North America plate interaction is updated using newest VLBI measurements and newly developed rigid plate tectonic models. Particular attention is given to examining the extent of relative motion between the Pacific plate and the North America plate as measured from their stable interiors, the evidence of Pacific plate deformation off the central California coast, and the distribution of path integrated deformaton east of the San Andreas fault. The information obtained on these questions is discussed in the framework of implications for lithospheric rheology and earthquake hazard.

Ward, Steven N.↗
NASA NTRS1991

Dual-parameter radar rainfall measurement from space - A test result from an aircraft experiment

An aircraft experiment has been conducted with a dual-frequency (X/Ka-bands) radar to test various rainfall retrieval methods from space. The authors test a method to derive raindrop size distribution (DSD) parameters from the combination of a radar reflectivity profile and a path-integrated attenuation derived from surface return, which may be available from most spaceborne radars. The estimated DSD parameters are reasonable in that the values generally fall within the range of commonly measured ones and that shifts in DSD parameters appear to be correlated with changes in storm type. The validity of the estimation result is also demonstrated by a consistency check using the Ka-band reflectivity profile which is independent of the DSD estimation process. Although errors may occur in the cases of nonuniform beam filling, these test results indicate the feasibility of the dual-parameter radar measurement from space in achieving a better accuracy in quantitative rainfall remote measurements.

Kozu, Toshiaki↗
NASA NTRS1992

The contribution of ion-cyclotron waves to electron heating and SAR-arc excitation near the storm-time plasmapause

The potential role of ion-cyclotron waves in the electron heating process has been studied, using the HOTRAY code. It is demonstrated that ion-cyclotron waves can play an important role in both the energy transfer to plasmaspheric electrons and the subsequent downward heat conduction to SAR arc altitudes. In particular, such waves can experience enhanced path integrated amplification along the steep plasmapause density gradient. The latter tends to keep the wave normal angle small on several successive bounces across the equator, thus allowing cyclotron-resonant amplification leading to a total gain of up to 20 e-foldings. When the wave propagation vector becomes highly oblique, absorption occurs during Landau resonance with thermal plasmaspheric electrons, increasing the electron temperature in the direction parallel to the ambient field and leading directly to heat conduction into ionosphere.

Thorne, Richard M.↗
NASA NTRS1990

Tropical Rainfall Measuring Mission (TRMM) project. VII - Techniques for radar data processing

The paper describes algorithms for rain-rate profiling with an airborne or space-borne radar. Some problems involved in the radar measurements from an airborne or space-borne platform are discussed. An outline of a dual-frequency algorithm is described and its performance is confirmed by a computer simulation and an airborne experiment. A single-frequency algorithm is developed by introducing a path-integrated rain rate estimated from an attenuation of surface echoes or from microwave brightness temperature. The computer simulation shows good performance for an airborne or space-borne radar.

Meneghini, Robert↗
NASA NTRS1992

Ion-cyclotron waves at Jupiter - Possibility of detection by Ulysses

Recent thermal plasma data and a computer code by Horne (1989) are employed to evaluate the linear-path-integrated gain of waves propagating through the Io to predict the Jovian plasma-wave environment. Estimates of the nonlinear saturation amplitudes are utilized with the thermal plasma data from two frequency bands to study the convective growth of the ion-cyclotron (IC) waves. Strong cyclotron resonant damping is theorized to prevent wave propagation to the lower latitudes, and the thermal plasma and cyclotron resonant energetic ions are expected to further confine the IC waves. L-mode waves below the O(+) gyrofrequency in the equatorial region of the torus are shown to inhabit an unstable region. The IC waves probably achieve nonlinear amplitudes regardless of plasma properties due to the rapid amplification in this region. It is suggested that the Ulysses data complicate the identification of the waves because the magnetometer is not adequately sensitive and because of the low frequency of the plasma-wave detector.

Mei, YI↗
NASA NTRS1992

CW laser strategies for simultaneous, multi-parameter measurements in high-speed gas flows

Strategies utilizing continuous wave (CW) lasers are considered which are capable of simultaneously measuring the flow parameters of velocity, temperature, and pressure at sampling rates exceeding 3 kHz. Velocity is determined from the Doppler shift of the spectral profile, temperature is extracted from intensity ratios of multiple lines, and pressure is measured from either the collision of broadening or the magnitude of absorption. Distinctions between strategies concern the specifics of probe spacies (NO, OH, O2, and H2O) in terms of nominal probe wavelength, equipment, and detection scheme. CW lasers were applied to path-integrated absorption measurements of transient shock-tube flows and spatially resolved laser-induced fluorescence measurements of underexpanded jets.

Di Rosa, M. D.↗
NASA NTRS1993

Quantum harmonic oscillator in a thermal bath

The influence functional path-integral treatment of quantum Brownian motion is briefly reviewed. A newly derived exact master equation of a quantum harmonic oscillator coupled to a general environment at arbitrary temperature is discussed. It is applied to the problem of loss of quantum coherence.

Zhang, Yuhong↗
NASA NTRS1991

Propagation of high-energy laser beams through the earth's atmosphere II; Proceedings of the Meeting, Los Angeles, CA, Jan. 21-23, 1991

Consideration is given to turbulence at the inner scale, modeling turbulent transport in laser beam propagation, variable wind direction effects on thermal blooming correction, realistic wind effects on turbulence and thermal blooming compensation, wide bandwidth spectral measurements of atmospheric tilt turbulence, remote alignment of adaptive optical systems with far-field optimization, focusing infrared laser beams on targets in space without using adaptive optics, and a simplex optimization method for adaptive optics system alignment. Consideration is also given to ground-to-space multiline propagation at 1.3 micron, a path integral approach to thermal blooming, functional reconstruction predictions of uplink whole beam Strehl ratios in the presence of thermal blooming, and stability analysis of semidiscrete schemes for thermal blooming computation.

Ulrich, Peter B.↗
NASA NTRS1990

Forecast model applications of retrieved three dimensional liquid water fields

Forecasts are made for tropical storm Emily using heating rates derived from the SSM/I physical retrievals described in chapters 2 and 3. Average values of the latent heating rates from the convective and stratiform cloud simulations, used in the physical retrieval, are obtained for individual 1.1 km thick vertical layers. Then, the layer-mean latent heating rates are regressed against the slant path-integrated liquid and ice precipitation water contents to determine the best fit two parameter regression coefficients for each layer. The regression formulae and retrieved precipitation water contents are utilized to infer the vertical distribution of heating rates for forecast model applications. In the forecast model, diabatic temperature contributions are calculated and used in a diabatic initialization, or in a diabatic initialization combined with a diabatic forcing procedure. Our forecasts show that the time needed to spin-up precipitation processes in tropical storm Emily is greatly accelerated through the application of the data.

Raymond, William H.↗
NASA NTRS1994

Evolution of wave function in a dissipative system

For a dissipative system with Ohmic friction, we obtain a simple and exact solution for the wave function of the system plus the bath. It is described by the direct product in two independent Hilbert space. One of them is described by an effective Hamiltonian, the other represents the effect of the bath, i.e., the Brownian motion, thus clarifying the structure of the wave function of the system whose energy is dissipated by its interaction with the bath. No path integral technology is needed in this treatment. The derivation of the Weisskopf-Wigner line width theory follows easily.

Yu, Li-Hua↗