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At least 955 records · Page 53
All sourcesNASA NTRSDOE OSTI
NASA NTRS1996

Latitudinal Dependence of the Radial IMF Component - Interplanetary Imprint

Ulysses measurements have confirmed that there is no significant gradient with respect to heliomagnetic latitude in the radial component, B(sub r,), of the interplanetary magnetic field. There are two processes responsible for this observation. In the corona, the plasma beta is much less than 1, except directly above streamers, so both longitudinal and latitudinal (meridional) gradients in field strength will relax, due to the transverse magnetic pressure gradient force, as the solar wind carries magnetic flux away from the Sun. This happens so quickly that the field is essentially uniform by 5 solar radius. Beyond 10 solar radius, beta is greater than 1 and it is possible for a meridional thermal pressure gradient to redistribute magnetic flux - an effect apparently absent in Ulysses and earlier ICE and Interplanetary Magnetic Physics (IMP) data. We discuss this second effect here, showing that its absence is mainly due to the perpendicular part of the anisotropic thermal pressure gradient in the interplanetary medium being too small to drive significant meridional transport between the Sun and approx. 4 AU. This is done using a linear analytic estimate of meridional transport. The first effect was discussed in an earlier paper.

Suess, S. T.↗
NASA NTRS1996

Latitudinal Dependence of the Radial IMF Component: Coronal Imprint

Measurements by Ulysses have confirmed that there is no significant gradient with respect to heliomagnetic latitude in the radial component, B(sub r,) of the interplanetary magnetic field. In the corona, the plasma, beta is much less than 1, except directly above streamers, so longitudinal and latitudinal gradients in field strength will relax due to the transverse magnetic pressure gradient force as the solar wind carries magnetic flux away from the Sun. This happens quickly enough so that the field is essentially uniform by 5 - 10 solar radius, apparently remaining so as it is carried to beyond 1 AU. Here, we illustrate the coronal relaxation with a qualitative physical argument and by reference to a detailed Magneto HydroDynamics (MHD) simulation.

Suess, S. T.↗
NASA NTRS1995

The Singularity Mystery Associated with a Radially Continuous Maxwell Viscoelastic Structure

The singularity problem associated with a radially continuous Maxwell viscoclastic structure is investigated. A special tool called the isolation function is developed. Results calculated using the isolation function show that the discrete model assumption is no longer valid when the viscoelastic parameter becomes a continuous function of radius. Continuous variations in the upper mantle viscoelastic parameter are especially powerful in destroying the mode-like structures. The contribution to the load Love numbers of the singularities is sensitive to the convexity of the viscoelastic parameter models. The difference between the vertical response and the horizontal response found in layered viscoelastic parameter models remains with continuous models.

Fang, Ming↗
NASA NTRS1994

Radial Variation of Elastic Properties of SCS-6 Silicon Carbide Fiber

The upper and lower bounds of the bulk, shear, and Young's moduli are calculated point-by-point along the radius of SCS-6 silicon carbide fibers using the Hashin-Shtrikman equations from considerations of the Auger spectra along the fiber radius. The calculated values are in agreement with measurements of the average Young modulus obtained over relatively large radial regions of the fiber using scanning acoustic microscopy (SAM). The validity of the Hashin-Shtrikman bounds calculations is enhanced by the agreement found between experimental SAM V(z) curves for fixed z along the fiber radius and the theoretical bounds of such curves obtained from the bounds of the calculated bulk and shear moduli.

Sathish, Shamachary↗
NASA NTRS1993

Coplanar Waveguide Radial Line Double Stub and Application to Filter Circuits

Coplanar waveguide (CPW) and grounded coplanar waveguide (GCPW) radial line double stub resonators are experimentally characterized with respect to stub radius and sector angle. A simple closed-form design equation, which predicts the resonance radius of the stub, is presented. Use of a double stub resonator as a lowpass filter or as a harmonic suppression filter is demonstrated, and design rules are given.

Simons, R. N.↗
NASA NTRS1998

South-North and radial traverses through the interplanetary dust cloud

Identical in situ dust detectors are flown on board the Galileo and Ulysses spacecraft. They record impacts of micrometeoroids in the ecliptic plane at heliocentric distances from 0.7 to 5.4 AU and in a plane almost perpendicular to the ecliptic from -79 deg to +79 deg ecliptic latitude. The combination of both Ulysses and Galileo measurements yield information about the radial and latitudinal distributions of micron and sub-micron sized dust in the solar system. Two types of dust particles were found to dominate the dust flux in interplanetary space: (1) Interplanetary micrometeoroids covering a wide mass range from 10(exp -16) to 10(exp -6) gr are mostly recorded inside 3 AU, and at latitudes below 30 deg; and (2) Interstellar grains with masses between 10(exp -14) and 10(exp -12) gr have been positively identified outside 3 AU near the ecliptic plane and outside 1.8 AU at high ecliptic latitudes (> 50 deg). Interstellar grains move on hyperbolic trajectories through the planetary system and constitute the dominant dust flux (1.5 x 10(exp -4)/ sq m sec) in the outer solar system and at high ecliptic latitudes. In order to compare and analyze the Galileo and Ulysses data sets, a new model is developed based on Divine's (1993) "Five populations of interplanetary meteoroids" model. By using this model, which takes into account the measured velocities and the effect of radiation pressure on small particles, we define four populations of meteoroids on elliptical orbits plus one population on hyperbolic orbits that all can fit the micrometeoroid flux observed by Galileo and Ulysses.

Gruen, E.↗
NASA NTRS1961

Declination, Radial Distance, and Phases of the Moon for the Years 1961 to 1971 for Use in Trajectory Considerations

As a byproduct of the preparation of solar and lunar coordinates for use in trajectory calculations a time history has been obtained of the radial distance and declination of the moon and its phases. Results are intended for use as an aid in the selection of launch dates. Results are presented for the years 1961 to 1971 in a form which permits a rapid approximate determination of the combination of declination and lighting for any calendar date. The information provides a time basis for entering tables of the moon's coordinates to obtain more precise data for use in computing insertion conditions.

Woolston, Donald S.↗
NASA NTRS1959

Estimated Performance of Radial-Flow Exit Nozzles for Air in Chemical Equilibrium

The thrust, boundary-layer, and heat-transfer characteristics were computed for nozzles having radial flow in the divergent part. The working medium was air in chemical equilibrium, and the boundary layer was assumed to be all turbulent. Stagnation pressure was varied from 1 to 32 atmospheres, stagnation temperature from 1000 to 6000 R, and wall temperature from 1000 to 3000 R. Design pressure ratio was varied from 5 to 320, and operating pressure ratio was varied from 0.25 to 8 times the design pressure ratio. Results were generalized independent of divergence angle and were also generalized independent of stagnation pressure in the temperature range of 1000 to 3000 R. A means of determining the aerodynamically optimum wall angle is provided.

Englert, Gerald W.↗
NASA NTRS1995

The Spreading of Variable-Viscosity Axisymmetric Radial Gravity Currents: Applications to the Emplacement of Venusian 'Pancake' Domes

The Magellan images of Venus have revealed a number of intriguing volcanic features, including the steep-sided or 'pancake' domes. These volcanic domes or flows have morphologies that suggest formation by a single continuous emplacement of lava with a higher viscosity than that of the surrounding basaltic plains. Numerous investigators have suggested that such high viscosity is due to high silica content, leading to the conclusion that the domes are evidence of evolved magmatic products on Venus. However, viscosity depends on crystallinity as well as on silica content: high viscosity could therefore also be due to a cooler (and therefore higher crystal content) lava. Models of dome emplacement which include both cooling and composition factors are thus necessary in order to determine the ranges of crystallinity and silica content which might lead to the observed gross dome morphologies. Accordingly, in this study domes are modelled as radial viscous gravity currents with an assumed cooling-induced viscosity increase to include both effects. Analytical and numerical results indicate that pancake dome formation is feasible with compositions ranging from basaltic to rhyolitic. Therefore, observations of gross dome morphology alone are insufficient for determining composition and the domes do not necessarily represent strong evidence for evolved magmatism on Venus.

Sakimoto, S. E. H.↗
NASA NTRS1999

Eigenmodes of Ducted Flows With Radially-Dependent Axial and Swirl Velocity Components

This report characterizes the sets of small disturbances possible in cylindrical and annular ducts with mean flow whose axial and tangential components vary arbitrarily with radius. The linearized equations of motion are presented and discussed, and then exponential forms for the axial, circumferential, and time dependencies of any unsteady disturbances are assumed. The resultant equations form a generalized eigenvalue problem, the solution of which yields the axial wavenumbers and radial mode shapes of the unsteady disturbances. Two numerical discretizations are applied to the system of equations: (1) a spectral collocation technique based on Chebyshev polynomial expansions on the Gauss-Lobatto points, and (2) second and fourth order finite differences on uniform grids. The discretized equations are solved using a standard eigensystem package employing the QR algorithm. The eigenvalues fall into two primary categories: a discrete set (analogous to the acoustic modes found in uniform mean flows) and a continuous band (analogous to convected disturbances in uniform mean flows) where the phase velocities of the disturbances correspond to the local mean flow velocities. Sample mode shapes and eigensystem distributions are presented for both sheared axial and swirling flows. The physics of swirling flows is examined with reference to hydrodynamic stability and completeness of the eigensystem expansions. The effect of assuming exponential dependence in the axial direction is discussed.

Kousen, Kenneth A.↗
NASA NTRS1999

Radially Focused Eddy Current Sensor for Detection of Longitudinal Flaws in Metallic Tubes

A radially focused eddy current sensor detects longitudinal flaws in a metal tube. A drive coil induces eddy currents within the wall of the metal tube. A pick-up cod is spaced apart from the drive coil along the length of the metal tube. The pick@up coil is positioned with one end thereof lying adjacent the wall of the metal tube such that the pick-up coil's longitudinal axis is perpendicular to the wall of the metal tube. To isolate the pick-up coil from the magnetic flux of the drive coil and the flux from the induced eddy currents. except the eddy currents diverted by a longitudinal flaw. an electrically conducting material high in magnetic permeability surrounds all of the pick-up coil except its one end that is adjacent the walls of the metal tube. The electrically conducting material can extend into and through the drive coil in a coaxial relationship therewith.

Wincheski, Russell A.↗
NASA NTRS2001

Properties and Radial Trends of Coronal Mass Ejecta and Their Associated Shocks Observed by Ulysses in the Ecliptic Plane

In this paper, magnetic and plasma measurements are used to analyze 17 interplanetary coronal mass ejections (CMEs) identified by Ulysses during its in-ecliptic passage to Jupiter. We focus on the expansion characteristics of these CMEs (as inferred from the time rate of change of the velocity profiles through the CMEs) and the properties of 14 forward shocks unambiguously associated with these CMEs. We highlight radial trends from 1 to 5.4 AU. Our results indicate that the CMEs are generally expanding at all heliocentric distances. With regard to the shocks preceding these ejecta, we note the following: (1) There is a clear tendency for the shock speed (in the upstream frame of reference) to decrease with increasing heliocentric distance as the CMEs transfer momentum to the ambient solar wind and slow down; (2) 86% of the shock fronts are oriented in the ecliptic plane such that their normals point westward (i.e., in the direction of planetary motion about the Sun), (3) 86% of the shocks are propagating toward the heliographic equator; and (4) no clear trend was found in the strength of the shocks versus heliocentric distance. These results are interpreted using simple dynamical arguments and are supported by fluid and magnetohydrodynamic (MHD) simulations.

Riley, Pete↗
NASA NTRS2001

Spacecraft Formation Flying Maneuvers Using Linear-Quadratic Regulation with No Radial Axis Inputs

Regarding multiple spacecraft formation flying, the observation has been made that control thrust need only be applied coplanar to the local horizon to achieve complete controllability of a two-satellite (leader-follower) formation. A formulation of orbital dynamics using the state of one satellite relative to another is used. Without the need for thrust along the radial (zenith-nadir) axis of the relative reference frame ' propulsion system simplifications and weight reduction may be accomplished. Several linear-quadratic regulators (LQR) are explored and compared based on performance measures likely to be important to many missions, but not directly optimized in the LQR designs. Maneuver simulations are performed using commercial ODE solvers to propagate the Keplerian dynamics of a controlled satellite relative to an uncontrolled leader. These short maneuver simulations demonstrate the capacity of the controller to perform changes from one formation geometry to another. This work focusses on formations in which the controlled satellite has a relative trajectory which projects onto the local horizon of the uncontrolled satellite as a circle. This formation has potential uses for distributed remote sensing systems.

Starin, Scott R.↗
NASA NTRS2003

IMAGE EUV Observation of a Radially, Bifurcated Plasmapause: First Observations of a Possible Standing ULF Waveform in the Inner Magnetosphere

We present EUV observations of the plasmasphere-plasmapause from 19:38-22:11 UT on 28 June 2000 characterized by the presence of bifurcated radial enhancements of the He(+) plasma distribution in the nighside sector. These features remain stable throughout the period of observation and are found to co-rotate at 67% of the expected rate. Two-dimensional simulation of the plasmasphere assuming the presence of field lines resonances at L = 1.8 and 2.5 suggest that the organization of the outer plasmasphere and plasmapause is the result convective motion driven by a standing ULF-wave. Preliminary analysis of ground-based magnetometer data provided by the IMAGE magnetometer network during the period of EUV observation indicates the presence of a discrete spectrum of field line resonances extending down to 0.68-mHz.

Adrian, M. L.↗
NASA NTRS2003

Detection of High-impedance Arcing Faults in Radial Distribution DC Systems

High voltage, low current arcing faults in DC power systems have been researched at the NASA Glenn Research Center in order to develop a method for detecting these 'hidden faults', in-situ, before damage to cables and components from localized heating can occur. A simple arc generator was built and high-speed and low-speed monitoring of the voltage and current waveforms, respectively, has shown that these high impedance faults produce a significant increase in high frequency content in the DC bus voltage and low frequency content in the DC system current. Based on these observations, an algorithm was developed using a high-speed data acquisition system that was able to accurately detect high impedance arcing events induced in a single-line system based on the frequency content of the DC bus voltage or the system current. Next, a multi-line, radial distribution system was researched to see if the arc location could be determined through the voltage information when multiple 'detectors' are present in the system. It was shown that a small, passive LC filter was sufficient to reliably isolate the fault to a single line in a multi-line distribution system. Of course, no modification is necessary if only the current information is used to locate the arc. However, data shows that it might be necessary to monitor both the system current and bus voltage to improve the chances of detecting and locating high impedance arcing faults

Gonzalez, Marcelo C.↗
NASA NTRS1991

Asymptotic expansions of the hydrogenic radial dipole integral

A method is presented for an asymptotic expansion of the hydrogenic radial dipole integral for discrete-discrete transitions from initial state n'l' to final state nl. The advantage of this simple method is that it allows all the necessary algebraic manipulations to be done by the computer programming package REDUCE-2. Expansion coefficients up to the coefficient of the l/n17 term are obtained for all initial states with n' < or = 10. However, only the coefficients which are not calculated by Klarsfeld are tabulated in this paper.

NASA Discipline Radiation Health↗
NASA NTRS2000

Model for radial dependence of frequency distributions for energy imparted in nanometer volumes from HZE particles

This paper develops a deterministic model of frequency distributions for energy imparted (total energy deposition) in small volumes similar to DNA molecules from high-energy ions of interest for space radiation protection and cancer therapy. Frequency distributions for energy imparted are useful for considering radiation quality and for modeling biological damage produced by ionizing radiation. For high-energy ions, secondary electron (delta-ray) tracks originating from a primary ion track make dominant contributions to energy deposition events in small volumes. Our method uses the distribution of electrons produced about an ion's path and incorporates results from Monte Carlo simulation of electron tracks to predict frequency distributions for ions, including their dependence on radial distance. The contribution from primary ion events is treated using an impact parameter formalism of spatially restricted linear energy transfer (LET) and energy-transfer straggling. We validate our model by comparing it directly to results from Monte Carlo simulations for proton and alpha-particle tracks. We show for the first time frequency distributions of energy imparted in DNA structures by several high-energy ions such as cosmic-ray iron ions. Our comparison with results from Monte Carlo simulations at low energies indicates the accuracy of the method.

Non-NASA Center↗
NASA NTRS1998

Ensembles of radial basis function networks for spectroscopic detection of cervical precancer

The mortality related to cervical cancer can be substantially reduced through early detection and treatment. However, current detection techniques, such as Pap smear and colposcopy, fail to achieve a concurrently high sensitivity and specificity. In vivo fluorescence spectroscopy is a technique which quickly, noninvasively and quantitatively probes the biochemical and morphological changes that occur in precancerous tissue. A multivariate statistical algorithm was used to extract clinically useful information from tissue spectra acquired from 361 cervical sites from 95 patients at 337-, 380-, and 460-nm excitation wavelengths. The multivariate statistical analysis was also employed to reduce the number of fluorescence excitation-emission wavelength pairs required to discriminate healthy tissue samples from precancerous tissue samples. The use of connectionist methods such as multilayered perceptrons, radial basis function (RBF) networks, and ensembles of such networks was investigated. RBF ensemble algorithms based on fluorescence spectra potentially provide automated and near real-time implementation of precancer detection in the hands of nonexperts. The results are more reliable, direct, and accurate than those achieved by either human experts or multivariate statistical algorithms.

Cervix Neoplasms/pathology↗