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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 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1986

A two-fluid solar wind model with Alfven waves - Parameter study and application to observations

The effects of Alfven waves from the inner corona on the solar wind density profile, flow velocity and on the random motion of protons are studied. Different base densities, temperatures, and wave velocity amplitudes, as well as different flow geometries, are considered. The model calculations are compared to simultaneous observations of the electron density profile and the resonantly scattered Lyman alpha line. Present observations, out to 4 solar radii, can be used to place limits on the coronal base density and temperature, and put an upper limit on the wave amplitude. It is pointed out that future observations of the electron density and the Lyman alpha line, out to larger heliocentric distances, and of lines from heavier elements, should be used to place more stringent constraints on the amplitudes of MHD waves in the corona.

Esser, R.↗
NASA NTRS1995

Estimating gravity wave parameters from oblique high-frequency backscatter: Modeling and analysis

A new technique for estimating electron density perturbation amplitudes of traveling ionospheric disturbances (TIDs), using HF radar data, is presented. TIDs are observed in HF radar data as enhancements of the ground-scattered power which propagate through the radar's field of view. These TIDs are the ionospheric manifestation of atmospheric acoustic-gravity waves. TID electron density perturbation amplitudes were estimated by simulating the radar returns, using HF ray tracing through a model ionosphere perturbed by a model gravity wave. The simulation determined the return power in the ground-scattered portion of the signal as a function of range, and this was compared to HF radar data from the Goose Bay HF radar at a time when evidence of gravity waves was present in the data. By varying the amplitude of the electron density perturbation in the model it was possible to estimate the perturbation of the actual wave. It was found that the perturbations that are observed by the Goose Bay HF radar are of the order of 20% to 35%. It was also found that the number of observable power enhancements, and the relative amplitudes of these enhancements, depended on the vertical thickness of the gravity wave's source region. From the simulations and observations it was estimated that the source region for the case presented here was approximately 20 km thick. In addition, the energy in the wave packet was calculated and compared to an estimate of the available energy in the source region. It was found that the wave energy was about 0.2% of the estimated available source region energy.

Bristow, W. A.↗
NASA NTRS1979

On the connection of interplanetary shock wave parameters and energetic storm particle events

A series of energetic storm particle (ESP) events is investigated on the basis of observations of energetic solar protons by IMPs IV and V between 1967 and 1972. The total number and energy of particles associated with 20 ESP events are analyzed in connection with several plasma parameters at the shock surface; i.e., magnetic and thermal pressure, magnetic field and plasma mass flux. Correlation is established between the total energy of ESPs in the energy range of 1-80 MeV and the jump in the total pressure. It is pointed out that the amount of shock energy converted to the acceleration of ESP particles is not negligible and could, in principle, contribute to the deceleration of the shock wave.

Gombosi, T.↗
NASA NTRS2006

Effect of DC Offset on the T-Wave Residuum Parameter

The T-wave residuum (TWR) is a relatively new 12-lead ECG parameter that may reflect cardiac repolarization heterogeneity. TWR shows clinical promise and may become an important diagnostic tool if accurate, consistent, and convenient methods for its calculation can be developed. However, there are discrepancies between the methods that various investigators have used to calculate TWR, as well as some questions about basic methodology and assumptions that require resolution. The presence of a DC offset or very low frequency AC component to the ECG is often observed. Many researchers have attempted to compensate for these by high pass filters and by median beat techniques. These techniques may help minimize the contribution of a low frequency AC component to the TWR, but they will not eliminate a DC offset inherent within the instrumentation. The present study examined the presence of DC offsets in the ECG record, and their effect on TWR. Specifically, in healthy individuals, a DC offset was added to all 8 channels collectively or to each channel selectively. Even with offsets that were relatively small compared to T-wave amplitude, the addition of either collectively or individually applied offsets was observed to produce very significant changes in the TWR, affecting its value by as much as an order of magnitude. These DC offsets may arise from at least two possible sources: a transient artifact from EMG or electrode movement resulting in a transient baseline offset in one or more channels. Since highpass filters have a settling time of several seconds, these artifacts will contribute to a transitory baseline offset lasting 1020 cycles. The machine hardware may also introduce an offset. Regardless of the cause or source of a DC offset, this study demonstrates that offsets have a very significant impact on TWR, and that future studies must not ignore their presence, but rather more appropriately compensate for them.

Scott, N.↗
NASA NTRS2007

New and Improved T-wave Morphology Parameters to Differentiate Healthy Individuals from those with Cardiomyopathy and Coronary Artery Disease

We investigated the ability of several known as well as new ECG repolarization parameters to differentiate healthy individuals from patients with obstructive coronary artery disease (CAD) and cardiomyopathy (CM). Advanced high-fidelity 12-lead ECG tests (approx. 5-min supine) were first performed on a "training set" of 99 individuals: 33 with ischemic or dilated CM and low ejection fraction (EF less than 40%); 33 with catheterization-proven obstructive CAD but normal EF; and 33 age-/gender-matched healthy controls. The following multiple parameters of T-wave morphology (TWM) were derived via signal averaging and singular value decomposition (SVD, which yields 8 eigenvalues, rho(sub 1) greater than rho(sub 2)...greater than rho(sub 8) and studied for their retrospective accuracy in detecting underlying disease: 1) Principal component analysis ratio of the T wave (T-PCA) = 100*rho(sub 2)/rho(sub 1); 2) Relative T-wave residuum (rTWR) = 100* SIGMA (rho(sub 4)(sup 2) +...+ rho(sub 8)(sup 2)); 3) Modified complexity ratio of the T wave (T-mCR) = 100*SIGMA(rho(sub 3)(sup 2) +...+rho(sb 8) (sup 2)); and 4) Normalized 3-dimensional volume of the T wave (nTV) = 100*(rho(sub 2)*rho(sub 3)/rho(sub 1)(sup 2). All TWM parameters significantly differentiated CAD from controls (p less than 0.0001), and also CM from controls (p less than 0.0001). Retrospective areas under the ROC curve were 0.77, 0.81, 0.82, and 0.83 (CAD vs. controls) and 0.93, 0.89, 0.95 and 0.96 (CM vs. controls) for T-PCA, rTWR, T-mCR and nTV respectively. The newer TWM parameters (T-mCR and nTV) thus outperformed the more established parameters (T-PCA and rTWR), presumably by putting a greater emphasis on the third T-wave eigenvalue, which in most healthy subjects has little energy compared to the first two eigenvalues. Subsequent prospective analyses have also yielded similar results, such that we conclude that diagnostic differentiation of pathology from non-pathology may be especially aided by detecting the transference of energy from the first and second T-wave eigenvalues into the third T-wave eigenvalue.

Greco, E. C.↗
NASA NTRS1975

Application of monochromatic ocean wave forecasts to prediction of wave-induced currents

The use of monochromatic wind-wave forecasts in prediction of wind-wave-induced currents was assessed. Currents were computed for selected combinations of wind conditions by using a spectrum approach which was developed by using the Bretschneider wave spectrum for partially developed wind seas. These currents were compared with currents computed by using the significant and average monochromatic wave parameters related to the Bretschneider spectrum. Results indicate that forecasts of significant wave parameters can be used to predict surface wind-wave-induced currents. Conversion of these parameters to average wave parameters can furnish reasonable estimates of subsurface current values.

Poole, L. R.↗
NASA NTRS1987

Rayleigh lidar observations of gravity wave activity in the stratosphere and lower mesosphere

Forty-two monochromatic gravity wave events were observed in the 25 to 55 km altitude region during 16 nights of Rayleigh lidar measurements at Poker Flat, Alaska and Urbana, Illinois. The measured wave parameters were compared to previous radar and lidar measurements of gravity wave activity. Vertical wavelengths, lambda(z), between 2 and 11.5 km with vertical phase velocities, c(z), between 0.1 and 1 m/s were observed. Measured values of lambda(z) and c(z) were used to infer observed wave periods, T(ob), between 50 and 1000 minutes and horizontal wavelengths, lambda(x), from 25 to 2000 km. Dominant wave activity was found at vertical wavelengths between 2 to 4 km and 7 to 10 km. No seasonal variations were evident in the observed wave parameters. Vertical and horizontal wavelengths showed a clear tendency to increase with T(ob), which is consistent with recent sodium lidar studies of monochromatic wave events near the mesopause. Measured power law relationships between the wave parameters were lambda(z) varies as T(ob) sup 0.96, lambda(x) varies as T(ob) sup 1.8, and c(z) varies as T(ob) sup -0.85. The kinetic energy calculated for the monochromatic wave events varied as k(z) sup -2, k(x) sup -1, and f(ob) sup -1.7. The atmospheric scale heights calculated for each observation date range from 6.5 to 7.6 km with a mean value of 7 km. The increase of rms wind perturbations with altitude indicated an amplitude growth length of 20.9 km. The altitude profile of kinetic energy density decreased with height, suggesting that waves in this altitude region were subject to dissipation or saturation effects.

Miller, M. S.↗
NASA NTRS1979

On the role of the Kelvin wave in the westerly phase of the semiannual zonal wind oscillation

The role of the Kelvin wave, discovered by Hirota (1978), in producing the westerly accelerations of the semiannual zonal wind oscillation in the tropical upper stratosphere is examined quantitatively. It is shown that, for reasonable values of the wave parameters, this Kelvin wave could indeed give rise to the observed accelerations. For the thermal damping rates of Dickinson (1973), the most likely range of phase speeds for a wavenumber 1 disturbance is from 45 to 60 m/sec. For 'photochemically accelerated' damping rates (Blake and Lindzen, 1973), a phase speed in excess of 70 m/sec would be required. The possibility of a significant modulation of the semiannual westerlies by the quasi-biennial oscillation is also suggested.

Dunkerton, T.↗
NASA NTRS1983

Meteorological and dynamical requirements for MST radar networks: Waves

Studies of wave motions using the MST radar have concentrated on single station time series analyses of gravity waves and tides. Since these radars collect high time resolution data they have the potential to become a significant tool for mesoscale research. In addition, radars are operated almost continuously unattended and, consequently, data sets are available for analyzing longer period wave motions such as tides and planetary scale waves. Although there is much to learn from single station data, the possibilities of new knowledge from a network of radars is exciting. The scales of wave motions in the atmosphere cover a broad range. Consequently the choice of a radar network depends to a large extent on the types of wave motions that are studied. There are many outstanding research problems that would benefit from observations from a MST radar network. In particular, there is a strong need for measurements of gravity wave parameters and equatorial wave motions. Some of the current problems in wave dynamics are discussed.

Avery, S. K.↗
NASA NTRS1986

Hydromagnetic waves at low latitudes - A symposium review from the fifth IAGA assembly

The aim of the symposium was to bring together investigators with interests in low latitude hydromagnetic waves in order to review the present state of knowledge in this area of magnetospheric physics. Of particular importance is the means by which wave energy is transferred to low latitudes to produce geomagnetic pulsations on the ground. The group of contributed papers reviewed shows that definitive experiments are underway and new theories capable of providing resonant wave energy at low latitudes are being developed. Particular topics covered by the review include solar wind control, wave spectra, array studies of wave parameters, storm time waves, and global wave resonance theory involving the coupling of compressional and transverse waves in the magnetosphere.

Fraser, B. J.↗
NASA NTRS1989

Picture of the global field of quasi-monochromatic gravity waves observed by stratospheric balloons and MST radars

In MAP observations, it was found that: (1) gravity waves in selected or filtered portions of data are fit for monochromatic structures, whereas (2) those in fully continuous and resolved observations take universal continuous spectra. It is possible to explain (2) by dispersion of quasi-monochromatic (or slowly varying) wave packets observed locally as (1), since the medium atmosphere is unsteady and nonuniform. Complete verification of the wave-mean flow interactions by tracking individual wave packets seems hopeless, because the wave induced flow cannot be distinguished from the basic flow independent of the waves. Instead, the primitive picture is looked at before MAP, that is, the atmosphere is just like an entertainment stage illuminated by cocktail lights of quasi-monochromatic gravity waves. The wave parameters are regarded as functions of time and spatial coordinates. The observational evidences (1) and (2) suggest that the wave parameter field is rather homogeneous, which can be explained by interference of quasi-monochromatic wave packets.

Yamanaka, M. D.↗
NASA NTRS1986

A study of the relationship among wind speed, sea state, and the drag coefficient for a developing wave field

Controlled laboratory experiments are reported which demonstrate directly and quantitatively the influence of wave conditions in determining the drag law at the air-sea interface under neutral stability conditions. It is concluded that the analytic form first proposed by Kitaigorodskii (1970) models the roughness scale very well when the sea is dominated by the locally generated waves. It is demonstrated that, by using a unified two-parameter wave spectral model by Huang et al. (1981), Kitaigorodskii's result can be shown to contain the formulas of Charnock (1955) and Hsu (1974) as special cases. The results also identify two wind and wave-related parameters as important in determining the drag coefficient for developing wave fields.

Huang, N. E.↗
NASA NTRS1983

Seismic properties of the crust and uppermost mantle of North America

Seismic refraction profiles for the North American continent were compiled. The crustal models compiled data on the upper mantle seismic velocity (P sub n), the crustal thickness (H sub c) and the average seismic velocity of the crystalline crust (V sub p). Compressional wave parameters were compared with shear wave data derived from surface wave dispersion models and indicate an average value for Poisson's ratio of 0.252 for the crust and of 0.273 for the uppermost mantle. Contour maps illustrate lateral variations in crustal thickness, upper mantle velocity and average seismic velocity of the crystalline crust. The distribution of seismic parameters are compared with a smoothed free air anomaly map of North America and indicate that a complidated mechanism of isostatic compensation exists for the North American continent. Several features on the seismic contour maps also correlate with regional magnetic anomalies.

Braile, L. W.↗
NASA NTRS1989

MU radar observation of a mesospheric gravity wave breaking caused by convective instability

In recent measurements of mesospheric winds with the MU radar at Shigaraki (34.9 N, 136.1 E), Japan, a couple of wind velocity data was obtained showing that a monochromatic inertia-gravity wave was propagating vertically in the mesosphere. The data show that the velocity amplitude of the wave did not increase exponentially above a height and further show that the wave form had broken down at a level. Evaluating the changes of the atmospheric stability in the wave field from the measured wind data and from the estimated wave parameters, the breakdown of the wave was shown to be connected with the occurrence of convective instability in the wave field.

Muraoka, Y.↗
NASA NTRS2007

Effect of Oblique Electromagnetic Ion Cyclotron Waves on Relativistic Electron Scattering: CRRES Based Calculation

We consider the effect of oblique EMIC waves on relativistic electron scattering in the outer radiation belt using simultaneous observations of plasma and wave parameters from CRRES. The main findings can be s ummarized as follows: 1. In 1comparison with field-aligned waves, int ermediate and highly oblique distributions decrease the range of pitc h-angles subject to diffusion, and reduce the local scattering rate b y an order of magnitude at pitch-angles where the principle absolute value of n = 1 resonances operate. Oblique waves allow the absolute va lue of n > 1 resonances to operate, extending the range of local pitc h-angle diffusion down to the loss cone, and increasing the diffusion at lower pitch angles by orders of magnitude; 2. The local diffusion coefficients derived from CRRES data are qualitatively similar to the local results obtained for prescribed plasma/wave parameters. Conseq uently, it is likely that the bounce-averaged diffusion coefficients, if estimated from concurrent data, will exhibit the dependencies similar to those we found for model calculations; 3. In comparison with f ield-aligned waves, intermediate and highly oblique waves decrease th e bounce-averaged scattering rate near the edge of the equatorial lo ss cone by orders of magnitude if the electron energy does not excee d a threshold (approximately equal to 2 - 5 MeV) depending on specified plasma and/or wave parameters; 4. For greater electron energies_ ob lique waves operating the absolute value of n > 1 resonances are more effective and provide the same bounce_averaged diffusion rate near the loss cone as fiel_aligned waves do.

Gamayunov, K. V.↗
NASA NTRS1974

Effect of Faraday rotation on the circular polarization of the Crab Nebula

The effect of Faraday rotation on the circular polarization of an electromagnetic wave propagating through a magnetized plasma is calculated for various limits of the plasma and wave parameters appropriate to a 30-Hz wave in the Crab Nebula. It is shown that a static magnetic field of the proper geometry and only a few times stronger than the wave field can reduce the circular polarization of the nonlinear inverse Compton radiation to a value below the observed upper limit.-

Gerver, M. J.↗