On the statistics of correlator outputs
Characteristic function, probability density function, and probability distribution function computations for correlation detector output, and correlator output statistics
Wintz, P. A.↗
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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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On the probability of cycle-slipping in first-order phase-locked loops.
The first-passage time boundary value problem for first-order phase-locked loops (PLL) is analyzed, and spectral representations are developed for the probability density function (pdf), the distribution function, and the moments of the first time to passage (or cycle-slip). For the sinusoidal PLL, an asymptotic formula, that is surprisingly accurate even at low loop SNR's and large frequency offsets, is obtained for the pdf of the time to cycle-slip, in terms of the mean time to slip.
La Frieda, J. R.↗
Properties of the Io plasma torus inferred from Voyager EUV data
A physical model for the Io plasma torus is constructed to explain the EUV radiative emission observed by the Voyager UV spectrometer. Electron impact excitation rate coefficients for electronic transitions of S III, S IV, O II and O III are calculated by the method of distorted waves (Davis, Kepple, and Blaha, 1976); these coefficients account for the asymmetric shape of the 686 A feature. It is concluded that the electron gas must have a distribution function with a non-Maxwellian tail. An approximate representation of the distribution function as two temperature components requires a cold component of 3.5-4 eV and density of 2000 per cu cm and a hot component of about 100 eV and density of 50-100 per cu cm to satisfy observational constraints.
Strobel, D. F.↗
Martian Crater Size Distributions and Terrain Age
The crater size/frequency distributions of large ( 8 km) craters on the Moon and terrestrial planets display two very different curves representing two crater populations. The heavily cratered regions of the Moon, Mercury, and Mars show the same highly structured curve which cannot be represented by a single slope distribution function. In contrast, the lunar post mare crater population has a size/frequency distribution which differs significantly from that in the highlands over the same diameter range, and can be represented by a single-slope distribution function of -2.8 differential. On areas of martian lightly cratered northern plains, the crater population is essentially identical to that of the post mare population. This indicates that the same two families of impacting objects were responsible for the cratering records on both Moon and Mars. The thickness of mantling material varies among the various plains units, and can be calculated from the depth/diameter scaling relations for martian craters.
Nadine G Barlow↗
A multiple scattering theory for EM wave propagation in a dense random medium
For a dense medium of randomly distributed scatterers an integral formulation for the total coherent field has been developed. This formulation accounts for the multiple scattering of electromagnetic waves including both the twoand three-particle terms. It is shown that under the Markovian assumption the total coherent field and the effective field have the same effective wave number. As an illustration of this theory, the effective wave number and the extinction coefficient are derived in terms of the polarizability tensor and the pair distribution function for randomly distributed small spherical scatterers. It is found that the contribution of the three-particle term increases with the particle size, the volume fraction, the frequency and the permittivity of the particle. This increase is more significant with frequency and particle size than with other parameters.
Karam, M. A.↗
Particle distributions in a two-dimensional reconnection field geometry
In order to understand space phase density variations near the magnetopause and in the geomagnetic tail, particle trajectories in a two-dimensional steady state reconnection field geometry are studied by tracing particles from a spacecraft position back in time. The distribution function at the spacecraft is calculated using Liouville's theorem and known distribution functions in the source regions. It is found, in particular, that multiple ion beams in the plasma sheet boundary layer are a natural consequence of reconnection. In the center of the central plasma sheet, the omnidirectional flux of keV ions should be at a minimum. The depth of this minimum is very large near the neutral point but decreases as the distance from the neutral point increases.
Gurran, D. B.↗
A self-consistent model for the particles and fields upstream of an outgassing comet. I - Gyrotropic and isotropic ion distributions
The magnetic field and solar wind flow parameters in the vicinity of a weakly outgassing comet are determined using a self-consistent model which treats the cometary ions kinetically. Two different assumptions are made concerning the cometary ion distribution function; the pickup cometary ions from either a velocity space gyrotropic ring distribution or a velocity space isotropic shell distribution in the solar wind frame of reference. The individual currents due to the solar wind and cometary ions, which determine the magnetic field, are calculated in each case. Using theoretically determined parameters which reflect the conditions expected to comet Kopff (a typical short-period comet and one possible target for the future CRAF/Cassini mission) for various heliocentric distances, the way in which global field and flow characteristics are influenced by the nature of the cometary ion distribution function is determined.
Flammer, K. R.↗
Probabilistic material degradation model for aerospace materials subjected to high temperature, mechanical and thermal fatigue, and creep
A probabilistic general material strength degradation model has been developed for structural components of aerospace propulsion systems subjected to diverse random effects. The model has been implemented in two FORTRAN programs, PROMISS (Probabilistic Material Strength Simulator) and PROMISC (Probabilistic Material Strength Calibrator). PROMISS calculates the random lifetime strength of an aerospace propulsion component due to as many as eighteen diverse random effects. Results are presented in the form of probability density functions and cumulative distribution functions of lifetime strength. PROMISC calibrates the model by calculating the values of empirical material constants.
Boyce, L.↗
Wave generation by contaminant ions
Investigations dealing with the generation of waves by contaminant ions are reported. The studies included the properties of the velocity distribution function of such ions. It was found that it takes about one ion-cyclotron period for the distribution function to transform from a beam to a ring distribution. A linear instability analysis was performed to examine the possibility of wave excitation by an ion beam streaming perpendicular to the ambient magnetic field in an ionospheric type of plasma. A simulation code was developed to study the nonlinear behavior of the waves excited by beam and ring types of ion distributions. The code treats both electrons and ions as particles kinetically to also factor in the possible involvement of lower-hybrid waves.
Singh, N.↗
Advanced S-Band studies using the TDRSS communications satellite
This report will describe the design, implementation, and results of a propagation experiment which used TDRSS to transmit spread signals at S-Band to an instrumented mobile receiver. The results consist of fade measurements and distribution functions in 21 environments across the Continental United States (CONUS). From these distribution functions, some idea may be gained about what system designers should expect for excess path loss in many mobile environments. Some of these results may be compared against similar measurements made with narrowband beacon measurements. Such comparisons provide insight into what gains the spread signaling system may or may not have in multipath and shadowing environments.
Jenkins, Jeffrey D.↗
Stellar Photon Archaeology with Gamma-Rays
Ongoing deep surveys of galaxy luminosity distribution functions, spectral energy distributions and backwards evolution models of star formation rates can be used to calculate the past history of intergalactic photon densities and, from them, the present and past optical depth of the Universe to gamma-rays from pair production interactions with these photons. The energy-redshift dependence of the optical depth of the Universe to gamma-rays has become known as the Fazio-Stecker relation (Fazio & Stecker 1970). Stecker, Malkan & Scully have calculated the densities of intergalactic background light (IBL) photons of energies from 0.03 eV to the Lyman limit at 13.6 eV and for 0$ < z < $6, using deep survey galaxy observations from Spitzer, Hubble and GALEX and have consequently predicted spectral absorption features for extragalactic gamma-ray sources. This procedure can also be reversed. Determining the cutoff energies of gamma-ray sources with known redshifts using the recently launched Fermi gamma-ray space telescope may enable a more precise determination of the IBL photon densities in the past, i.e., the "archaeo-IBL.", and therefore allow a better measure of the past history of the total star formation rate, including that from galaxies too faint to be observed.
Stecker, Floyd W.↗
Application of the Global Precipitation Forecast dataset for Global Landslide Forecasting System
Landslides are extremely damaging, pervasive and cause fatalities and economic impacts. Extreme rainfall events, coupled with inopportune surface conditions, are the primary triggers of landslides around the world. Forecasting landslide events represent an area of open research. A global Landslide Hazard Assessment for Situational Awareness (LHASA) model has been created that provides near real-time dynamic landslide characterization using Integrated Multi-Satellite Retrievals for Global Precipitation Mission (IMERG). However, it does not provide information on prediction of landslides into future. This study considers how global precipitation forecast data compares to satellite rainfall at different spatiotemporal scales and outlines the potential for its use in landslide hazard prediction/forecasting system. NASA Goddard Earth Observing System (GEOS)-Forecast model assimilates new observations every 6 hours, at 00, 06, 12, and 18 UTC. The GEOS-Forecast model is initialized at 00 UTC and is evaluated with IMERG Early, using Multi-Radar Multi-Sensor gauge corrected (MRMS-GC) precipitation product as a reference over contiguous United States (CONUS). Categorical and continuous statistics along with probability density functions and cumulative distribution functions are considered to assess the performance of the precipitation products, with a focus on landslide hotspots. Seasonality appears to influence the performance of both the GEOS-Forecast and IMERG Early product. Moreover, the global comparison between the GEOS-Forecast and IMERG Early is carried out in terms of percentile difference, correlation, and bias maps. For extreme rainfall events in regions such as Mekong, Colombia, and Tajikistan, GEOS-Forecast appears to resolve high rainfall relative to IMERG Early more frequently. Validation over landslide points reveal that for 24hr rainfall accumulations > 100mm, GEOS-Forecast and IMERG coincide. GEOS-Forecast and IMERG Early precipitation matches more closely for tropical cyclones than other types of storms. Overall, the performance varies with respect to location, rainfall intensities, and type of precipitation events.
Sana Khan↗
Studies of magnetopause structure
From the International Sun-Earth Explorers (ISEE) 1 magnetopause crossings on November 10, 1977, three-dimensional distribution functions for energetic ions were studied in the magnetosphere, through the magnetopause, and in the magnetosheath (Speiser and Williams, 1982). The particle distributions were particularly examined at and near the times that Russell and Elphic (1978) identified as flux transfer events (FTE). Using a simple, one-dimensional, quasi-static model, particle orbits were followed numerically, from the magnetosphere into the sheath. The inner, trapped, distribution initializes the distribution function. Liouville's theorem allows the inner distribution to be mapped into the sheath following the orbits. This mapping is shown for four mangetosheath ion flows (MIF's) corresponding to four flux transfer events. Results from the studies are discussed. A brief discussion of current sheet particle motion is presented.
Speiser, Theodore W.↗
Optimum structural design based on reliability and proof-load testing
Proof-load test eliminates structures with strength less than the proof load and improves the reliability value in analysis. It truncates the distribution function of strength at the proof load, thereby alleviating verification of a fitted distribution function at the lower tail portion where data are usually nonexistent.
Shinozuka, M.↗
Comparison of flare bremsstrahlung resulting from energetic thermal and nonthermal electrons
The paper investigates the behavior of the X-ray bremsstrahlung spectra resulting from two distinct types of electron distribution functions impinging on a target atmosphere during flare activity. A power-law distribution function is compared with two double-peaked Maxwellians. The results of these calculations show that it would be difficult to rule out multithermal interpretations for the emitted high-energy X-rays.
Davis, J.↗
A universal spectrum for AGNs and QSOs
The effects of the feedback of e+-e- pair reinjection in a plasma due to photon photon absorption of its own radiation is examined. Under the assumption of continuous electron injection with a power law spectrum and Compton losses only, it is shown that for power law index 2 the steady state electron distribution function has a unique form independent of the primary injection spectrum. This electron distribution function can by then reproduce the general characteristics of AGN, QSO spectra from radio to X-rays. It also implies gamma ray emission from these objects consistent with the observations of the diffuse gamma ray background.
Kazanas, D.↗
Nonlinear upper hybrid drift waves for a longitudinal electric field perpendicular to a uniform magnetic field in the Vlasov-Maxwell approximation
Upper hybrid drift waves are found as a special solution to a Vlasov-Maxwell plasma which has a longitudinal electric field and a perpendicular uniform magnetic field. A single-species plasma with a constant-density mobile neutralizing background supports spatially varying disturbances that oscillate at the upper hybrid frequency. The general functional dependences of the electric field, the plasma number density, and the one-particle distribution function for the special case are found from more general Vlasov-Maxwell equations invariant under a Lie group point transformation. The one-particle distribution function for the plasma is a function of the Liouville invariant, which is the energy in the generalized Bernstein-Greene-Kruskal (BGK) reference frame, and the momentum in the drift direction.
Abraham-Shrauner, B.↗
Nonequilibrium molecular motion in a hypersonic shock wave
Molecular velocities have been measured inside a hypersonic, normal shock wave, where the gas experiences rapid changes in its macroscopic properties. As first hypothesized by Mott-Smith, but never directly observed, the molecular velocity distribution exhibits a qualitatively bimodal character that is derived from the distribution functions on either side of the shock. Quantitatively correct forms of the molecular velocity distribution function in highly nonequilibrium flows can be calculated, by means of the Direct Simulation Monte Carlo technique.
Pham-Van-diep, G.↗