Quasi-linear theory of plasma waves.
Plasma wave quasi-linear theory, noting nonlinear effect treatment via distribution function, electric field, Fourier component decay, etc
DISTRIBUTION FUNCTION↗
SEARCH · Engineering Papers
Results for “wave function”
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.
Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.
Optimization of a Deep Convective Cloud Technique in Evaluating the Long-Term Radiometric Stability of MODIS Reflective Solar Bands
MODIS reflective solar bands are calibrated on-orbit using a solar diffuser and near-monthly lunar observations. To monitor the performance and effectiveness of the on-orbit calibrations, pseudo-invariant targets such as deep convective clouds (DCCs), Libya-4, and Dome-C are used to track the long-term stability of MODIS Level 1B product. However, the current MODIS operational DCC technique (DCCT) simply uses the criteria set for the 0.65- m band. We optimize several critical DCCT parameters including the 11- micrometer IR-band Brightness Temperature (BT11) threshold for DCC identification, DCC core size and uniformity to help locate DCCs at convection centers, data collection time interval, and probability distribution function (PDF) bin increment for each channel. The mode reflectances corresponding to the PDF peaks are utilized as the DCC reflectances. Results show that the BT11 threshold and time interval are most critical for the Short Wave Infrared (SWIR) bands. The Bidirectional Reflectance Distribution Function model is most effective in reducing the DCC anisotropy for the visible channels. The uniformity filters and PDF bin size have minimal impacts on the visible channels and a larger impact on the SWIR bands. The newly optimized DCCT will be used for future evaluation of MODIS on-orbit calibration by MODIS Characterization Support Team.
Mu, Qiaozhen↗
The low-frequency continuum as observed in the solar wind from ISEE 3 - Thermal electrostatic noise
The low frequency continuum (LFC) noise between 30 and 200 kHz has been investigated from the ISEE 3 spacecraft in the solar wind by means of a radio astronomy experiment more sensitive than previously available. It is demonstrated that the LFC radiation observed in the solar wind is in the form of longitudinal plasma waves rather than transverse electromagnetic waves. The observed spectral characteristics are found to be a function of antenna length. In addition, both the absence of antenna spin modulation and the fact that these plasma waves do not propagate to large distances imply a local origin for the LFC.
Hoang, S.↗
Experimental and theoretical study of Rayleigh-Lamb waves in a plate containing a surface-breaking crack
Scattering of Rayleigh-Lamb waves by a normal surface-breaking crack in a plate has been studied both theoretically and experimentally. The two-dimensionality of the far field, generated by a ball impact source, is exploited to characterize the source function using a direct integration technique. The scattering of waves generated by this impact source by the crack is subsequently solved by employing a Green's function integral expression for the scattered field coupled with a finite element representation of the near field. It is shown that theoretical results of plate response, both in frequency and time, are similar to those obtained experimentally. Additionally, implication for practical applications are discussed.
Paffenholz, Joseph↗
Electrostatic turbulence in the earth's central plasma sheet produced by multiple-ring ion distributions
Attention is given to a mechanism to generate a broad spectrum of electrostatic turbulence in the quiet time central plasma sheet (CPS) plasma. It is shown theoretically that multiple-ring ion distributions can generate short-wavelength (less than about 1), electrostatic turbulence with frequencies less than about kVj, where Vj is the velocity of the jth ring. On the basis of a set of parameters from measurements made in the CPS, it is found that electrostatic turbulence can be generated with wavenumbers in the range of 0.02 and 1.0, with real frequencies in the range of 0 and 10, and with linear growth rates greater than 0.01 over a broad range of angles relative to the magnetic field (5-90 deg). These theoretical results are compared with wave data from ISEE 1 using an ion distribution function exhibiting multiple-ring structures observed at the same time. The theoretical results in the linear regime are found to be consistent with the wave data.
Huba, J. D.↗
Practical method for highly accurate large-scale surface calculations
An accurate and efficient film linearized muffin-tin orbital (FLMTO) technique for surface electronic-structure calculations is presented which uses only 60-70 basis functions, as opposed to the 300 functions used in the linear augmented plane-wave method. Calculations for three different (3d and 4d) transition-metal films resulted in high quality results for five-layer slabs of Cu(001), Fe(001), and Ru(001), in addition to good results for the work functions and projected density of states. By retaining the LMTO small basis size, computer time and memory are reduced, making practical the study of systems with a larger number of atoms in the two-dimensional unit cell.
Fernando, G. W.↗
Switchback Boundary Dissipation and Relative Age
We examine Parker Solar Probe (PSP) magnetic field and plasma observations during its first encounter with the Sun in early 2018 November. During this perihelion time, impulsive reversals in the magnetic field, called "switchbacks," were found in the data set characterized by a quick rotation in B along with a simultaneous increase in solar wind flow. In this work, we examine the structure and morphology of 920 switchback boundaries as PSP enters and exits the structures, specifically looking for evidence of boundary degradation, dissipation, and associated ultralow frequency (ULF) magnetic wave activity. We find that boundaries with the most abrupt, step-function-like change in Br and Vr also show little evidence of dissipation and ULF wave activity. In contrast, there is a set of boundaries that appears highly degraded with ULF magnetic activity in the vicinity of the boundary. We thus infer that the steep, step-like boundaries with little ULF activity are relatively young in comparison to the degraded boundaries. The distribution in relative ages suggests that the switchback boundary formation process is dynamic and evolving, even occurring near the PSP observation point inside of 40 Rs.
W. M. Farrell↗
A two-scale Bragg scattering model for microwave backscatter from wind generated waves
A model for the wavenumber spectrum for fully developed seas is derived as a function of the mean wind gradient. The high wavenumber part of the spectrum, which defines the Bragg wavenumbers, is an equilibrium spectrum in balance by a wind forcing term determined by viscous dissipation, which is a strong function of water temperature, and dissipation by breaking and microbreaking. The low wavenumber spectrum, constructed from surface elevation observations of gravity waves, is merged with the high wavenumber spectrum. Parameters are adjusted to fit circle flight data for Ku-band. The full spectrum is used in the two-scale Bragg scattering theory, plus specular reflection, to compute backscatter as a function of wind speed, direction, incidence angle, and water temperature (which determines viscosity) for Ku-band.
Donelan, M. A.↗
The influence of the directional energy distribution on the nonlinear dispersion relation in a random gravity wave field
The influence of the directional distribution of wave energy on the dispersion relation is calculated numerically using various directional wave spectrum models. The results indicate that the dispersion relation varies both as a function of the directional energy distribution and the direction of propagation of the wave component under consideration. Furthermore, both the mean deviation and the random scatter from the linear approximation increase as the energy spreading decreases. Limited observational data are compared with the theoretical results. The agreement is favorable.
Huang, N. E.↗
Acoustic resonances and sound scattering by a shear layer
The reflection and transmission characteristics of plane waves scattered by a finite-thickness shear layer having a linear velocity profile and bounded by two otherwise uniform parallel flows is examined using the pressure perturbation equation solutions in the shear layer shown previously to be in terms of Whittaker M functions. In addition to the angle of plane wave incidence and the relative Mach number of the flows bounding the shear layer, it is found that the scattering properties of the shear layer depend crucially upon a parameter tau in such a manner that the case tau approaching zero characterizes the long wavelength properties of the layer and the case tau approaching infinity characterizes the short wavelength properties of the layer. In contrast to the region of ordinary reflection in the cases where the corresponding vortex sheet does not have a Brewster angle, the values of the reflection coefficient up to tau of 2 follow those of the vortex sheet; for the case for which the corresponding vortex sheet has a Brewster angle, the magnitude of the reflection coefficient may be sensitive to even small changes in tau in certain cases.
Koutsoyannis, S. P.↗
High-frequency modulation of ion-acoustic waves.
A large amplitude, high-frequency electromagnetic oscillation is impressed on a nonrelativistic, collisionless plasma from an external source. The frequency is chosen to be far from the plasma frequency (in fact, lower). The resulting electron velocity distribution function strongly modifies the propagation of ion-acoustic waves parallel to the oscillating electric field. The complex frequency is calculated numerically.
Albright, N. W.↗
Propagation of sound waves in tubes of noncircular cross section
Plane-acoustic-wave propagation in small tubes with a cross section in the shape of a flattened oval is described. Theoretical descriptions of a plane wave propagating in a tube with circular cross section and between a pair of infinite parallel plates, including viscous and thermal damping, are expressed in similar form. For a wide range of useful duct sizes, the propagation constant (whose real and imaginary parts are the amplitude attenuation rate and the wave number, respectively) is very nearly the same function of frequency for both cases if the radius of the circular tube is the same as the distance between the parallel plates. This suggests that either a circular-cross-section model or a flat-plate model can be used to calculate wave propagation in flat-oval tubing, or any other shape tubing, if its size is expressed in terms of an equivalent radius, given by g = 2 x (cross-sectional area)/(length of perimeter). Measurements of the frequency response of two sections of flat-oval tubing agree with calculations based on this idea. Flat-plate formulas are derived, the use of transmission-line matrices for calculations of plane waves in compound systems of ducts is described, and examples of computer programs written to carry out the calculations are shown.
Richards, W. B.↗
Trapped particles and waves, and what can be learned from multisatellite experiments
Calculations concerning the pitch-angle diffusion resulting from resonant wave-particle interactions can lead to definitive predictions of equatorial pitch-angle distributions and rates of particle loss as a function of particle energy and L-value. Thus, given simultaneous high-altitude measurements of pitch-angle distributions and low-altitude measurements of precipitating fluxes as a function of energy and L, the importance of proposed wave-particle interactions can be verified or discarded. Since many wave-particle phenomena occur over large spatial and temporal scales, exact simultaneity in longitude and time is not necessary. Simultaneous low and high altitude (preferably nearly equatorial) particle measurements could thus greatly increase our understanding of trapped particles and their effects on the ionosphere. Furthermore, given a verified pitch-angle diffusion mechanism and simultaneous low- and high-altitude measurements, accurate lowto high-altitude mappings of field lines and magnetospheric boundaries (such as the plasmapause) could be obtained.
Lyons, L. R.↗
Electron beams and Langmuir turbulence in solar type III radio bursts observed in the interplanetary medium
Results are presented of in situ observations of electron beams, plasma waves, and associated solar type II radio emission in the interplanetary medium near 1 AU, which were provided by the ISEE-3 spacecraft. It is shown that electron beams are formed by the faster electrons arriving before the slower ones, following an impulsive injection at the sun. The resulting bump-on-tail in the reduced 1D distribution function is unstable to the growth of electrostatic electron plasma (Langmuir) waves. The Langmuir waves are observed to be highly impulsive in nature. The onset and temporal variations of the observed plasma waves are in good qualitative agreement with the wave growth expected from the evolution of the measured 1D distribution function. The lack of obvious plateauing of the bump-on-tail suggests that the waves were removed from resonance with the beam electrons by some wave-wave interaction.
Lin, R. P.↗
The microscopic state of the solar wind: Links between composition, velocity distributions, waves and turbulence
An overview is given of the microscopic state of the solar wind with emphasis on recent Ulysses high-latitude observations and previous Helios in-ecliptic observations. The possible links between composition, ionization state. velocity distribution functions of electrons, protons and heavy ions. kinetic plasma waves and MHD-scale turbulence are elaborated. Emphasis is placed on a connection of interplanetary kinetic-scale phenomena with their generating microscopic processes in the corona. The fast streams seem to consist of mesoscale pressure-balanced plasma filaments and magnetic flux tubes, reminiscent of the supergranular-size structures building the open corona, from which copious Alfven waves emanate. The wind from the magnetically structured and active corona shows developed compressive turbulence and considerable abundance and ionization state variations. Some modelling attempts to explain the observed element fractionation are briefly reviewed. The causes of the nonthermal particle features. such as proton-ion differential streaming, ion beams. temperature anisotropies, and skewed distributions associated with collisionless heat conduction, are ultimately to be searched in the fact, that the corona is never quiescent but fundamentally variable in space and time. Consequently, the radial evolution of the internal state of the wind resembles at all latitudes a complicated relaxation process, in the course of which the free (in comparison with LTE conditions) particle kinetic energy is converted into plasma waves and MHD turbulence on a wide range of scales. This leads to intermittent wave-particle interactions and unsteady anomalous transport, mixed with the weak effects of the rare Coulomb collisions. Spherical expansion and large-scale inhomogeneity forces the wind to attain microscopically a complex internal state of dynamic statistical equilibrium.
Marsch, E.↗
Theory of thin-screen scintillations for a spherical wave
A thin-screen scintillation theory for a spherical wave is presented under the 'quasi-optical' approximation. The 'scattering angle', the 'observed angle', the intensity correlation function, and the temporal pulse broadening are calculated for the random wave. It is found that as the wave propagates outward away from the phase screen, the correlation scale of the intensity fluctuation increases linearly while the 'observed angle' decreases linearly. The calculations are carried out for both Gaussian and power-law spectra of the turbulent medium. The results are applied to an analysis of the scattering data for the Crab Nebula's radiation.
Lee, L. C.↗
Tether as a dynamic transmission line
The effect of longitudinal impulses on a satellite when a continuum tether from the Shuttle or Space Station is included is investigated. It is demonstrated that, taking the continuum nature of the tether into account, the sharp onset of a forcing impulse at the Shuttle end is perceived on board the satellite. The magnitude of the satellite response is diminished from that of the forcing impulse, and the response exhibits a broadened exponential tailoff. These are due primarily to the coupling between the tether and the satellite and its influence on an impinging impulsive wave, and not on the whole system as in the spring-mass model. The full impulse response function can be quite complex, showing repeated impulses as the tether wave bounces back and forth between the satellite and Shuttle, and having a different shape at each impingement on the satellite.
Gullahorn, Gordon E.↗
Studies of pressure oscillations in a research dump combustor
A coaxial research dump combustor was used to investigate the acoustic modes structure and its effect on the inlet shock system. Acoustic wave structure was determined including the amplitude, frequency, and phase as a function of position. Inlet shock position, shock displacement, shock displacement frequency, and phase relative to acoustic wave structure were also defined. All results were compared to with one dimensional modeling.
Schadow, K. C.↗