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At least 199 records · Page 11

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NASA NTRS1976

Angular distributions of electrons of energy greater than 0.06 MeV in the Jovian magnetosphere

Measurements of the angular distribution of electron intensity in the Jupiter magnetosphere were made by the University of Iowa experiment on Pioneer 10. The data were from three directional particle detectors with effective integral threshold of 0.06, 0.55 and 0.5 MeV respectively. It was discovered that the central core of the magnetosphere for radial distances less than 12 Jovian radii is dominated by pitch angle distributions strongly peaked at alpha = 90 degrees, while the region of radial distances 12-25 Jovian radii shows bidirectional and approximately equal maxima at alpha = 0 and 180 degrees. Substantial field-aligned streaming was detected on two occasions, each of about 1 hour duration. No distinctive effects on angular distributions were observed near the L shells of satellites.

Sentman, D. D.↗

NASA NTRS1976

Diffraction effects on angular response of X-ray collimators

Angular responses have been measured for X-ray collimators with half-widths ranging from minutes of arc down to 10 arcsec. In the seconds-of-arc range, diffraction peaks at off-axis angles can masquerade as side lobes of the collimator angular response. Measurements and qualitative physical arguments lead to a rule of thumb for collimator design; namely, the angle of first minimum in the Fraunhofer single-slit diffraction pattern should be less than one-fourth of the collimator geometrical full-width at half-maximum intensity.

Blake, R. L.↗

NASA NTRS1977

Angular distribution of Auger electrons due to 3d-shell ionization of krypton

Cross sections for electron impact ionization of krypton due to ejection of a 3rd shell electron have been calculated using screened hydrogenic and Hartree-Slater wave functions for target atom. While the total ionization cross sections in the two approximations are within 10% of each other, the Auger electron angular distribution, related to cross sections for specific magnetic quantum numbers of the 3rd electrons, is widely different in the two approximations. The angular distribution due to Hartree-Slater approximation is in excellent agreement with measurement. The physical reason for the discrepancies in the two approximations is explained.

Omidvar, K.↗

NASA NTRS1977

Modification of the DSN radio frequency angular tropospheric refraction model

The previously derived DSN Radio Frequency Angular Tropospheric Refraction Model contained an assumption which was subsequently seen to be at a variance with the theoretical basis of angular refraction. The modification necessary to correct the model is minor in that the value of a constant is changed.

Berman, A. L.↗

NASA NTRS1977

Angular distribution of Auger electrons due to 3d-shell impact ionization of krypton

Cross sections for electron impact ionization of krypton due to ejection of a 3d-shell electron have been calculated using screened hydrogenic and Hartree-Slater wavefunctions for the target atom. While the total ionization cross sections in the two approximations are within 10% of each other, the Auger electron angular distribution, related to cross sections for specific magnetic quantum numbers of the 3d electrons, are widely different in the two approximations. The angular distribution due to the Hartree-Slater approximation is in excellent agreement with measurement. The physical reason for the discrepancies in the two approximations is explained.

Omidvar, K.↗

NASA NTRS1978

Neutrino angular momentum loss in rotating stars

We consider how an axisymmetric, uniformly and slowly rotating homogeneous star might be affected by the loss of energy and angular momentum via neutrino emission. For example, these losses can cause a collapsing, rotating star to flatten either faster or slower than would be the case if these losses were not taken fully into account, depending on the efficiency of the angular momentum loss mechanism.

Epstein, R.↗

NASA NTRS1978

Analytical inversions in remote sensing of particle size distributions. I - Multispectral extinctions in the anomalous diffraction approximation. II Angular and spectral scattering in diffraction approximations

Consideration is given to analytical inversions in the remote sensing of particle size distributions, noting multispectral extinctions in anomalous diffraction approximation and angular and spectral scattering in diffraction approximation. A closed-form analytical inverse solution is derived in order to reconstruct the size distribution of atmospheric aerosols. The anomalous diffraction approximation to Mie's solution is used to describe the particles. Experimental data yield the geometrical area of aerosol polydispersion. Size distribution is thus found from a set of multispectral extinction measurements. In terms of the angular and spectral scattering of light in a narrow forward cone, it is shown that an analytical inverse solution may also be found for the Fraunhofer approximation to the Kirchhoff diffraction, and for an improved expression of this approximation due to Penndorf (1962) and Shifrin-Punina (1968).

Fymat, A. L.↗

NASA NTRS1978

On the information content of natural frequency spectra associated with different angular numbers

The problem of inferring the speed of sound in a contained spherically symmetric fluid solely from its natural frequencies of vibration is considered. An investigation of the case in which the data consist of the two spectra associated with the angular numbers 0 and 1, suggests the possibility that a one-parameter family of slowness profiles can be constructed. These profiles are compatible with the data, up to first order in the non-uniformity of the fluid. It is conjectured that for other angular numbers, the loss of information increases as the difference between them increases.

Barcilon, V.↗

NASA NTRS1978

Quantum-mechanical theory including angular momenta analysis of atom-atom collisions in a laser field

The problem of two atoms colliding in the presence of an intense radiation field, such as that of a laser, is investigated. The radiation field, which couples states of different electronic symmetry, is described by the number state representation while the electronic degrees of freedom (plus spin-orbit interaction) are discussed in terms of a diabatic representation. The total angular momentum of the field-free system and the angular momentum transferred by absorption (or emission) of a photon are explicitly considered in the derivation of the coupled scattering equations. A model calculation is discussed for the Xe + F collision system.

Devries, P. L.↗

NASA NTRS1980

Solar cell angular position transducer

An angular position transducer utilizing photocells and a light source is disclosed. The device uses a fully rotatable baffle which is connected via an actuator shaft to the body whose rotational displacement is to be measured. The baffle blocks the light path between the light source and the photocells so that a constant semicircular beam of light reaches the photocells. The current produced by the photocells is fed through a resistor, a differential amplifier measures the voltage drop across the resistor which indicates the angular position of the actuator shaft and hence of the object.

Sandford, M. C.↗

NASA NTRS1979

An angular momentum approximation for molecular collisions in the presence of intense laser radiation

An approximation to a previously presented rigorous description of molecular (atom-atom) collisions occurring in the presence of intense radiation is investigated. This rigorous description explicitly considers the angular momentum transferred between the molecule and the radiation field in the absorption or emission of a photon, but involves a complicated system of close-coupled equations which must be solved independently for each projection M of the initial, total molecular angular momentum. (This is a direct consequence of the lack of rotational invariance in the molecule-field problem). These equations are solved for a model system which mimics the collision of a halogen with a rare gas atom. Empirical observations made in the course of performing these calculations lead to the development of an approximation which avoids the repeated calculations for each initial M. This orientational average approximation greatly reduces the effort required to describe the system, and for the model calculation, yields accurate results for field intensities as high as 10 GW/sq cm.

Devries, P. L.↗

NASA NTRS1979

A method of evaluating quantitative magnetospheric field models by an angular parameter alpha

The paper introduces an angular parameter, termed alpha, which represents the angular difference between the observed, or model, field and the internal model field. The study discusses why this parameter is chosen and demonstrates its usefulness by applying it to both observations and models. In certain areas alpha is more sensitive than delta-B (the difference between the magnitude of the observed magnetic field and that of the earth's internal field calculated from a spherical harmonic expansion) in expressing magnetospheric field distortions. It is recommended to use both alpha and delta-B in comparing models with observations.

Sugiura, M.↗

NASA NTRS1982

Regionally applicable angular reflectance models

Determination of the angular variation of the reflected radiance field in order to infer the reflected component of the Earth radiation budget from medium or narrow field of view radiometer measurements is discussed. An average angular model applicable at 250 to 1000 km is presented and evaluated. The nature of the convergence of the radiance patterns to the regional means is also discussed. Radiances measured during summer Monex 1979, from Hudson Bay to Saudi Arabia, were averaged and then normalized by multiplying by pi and dividing by the scene-averaged reflected flux density. This casts the model into the inverse of the bidirectional reflectance normalization coefficient, which has the value of unity for an isotropic surface. The reflected component of the Earth's radiation budget is inferred to an accuracy of about 2.5%.

Davis, J. M.↗

NASA NTRS1982

Interannual atmospheric angular momentum variability 1963-1973 and the Southern Oscillation

The Oort (1981) data set is used to determine the total angular momentum variability of the atmosphere below 75 mbar over the 120-month period from May 1963 to April 1973. These results are in turn compared with the observed length of day variations of the same period. When the mean, annual and semi-annual cycles are removed, the angular momentum displays an irregular oscillation with periods of three to four years and a corresponding relative change in the length of day of about + or - 0.2 x 10 to the -8th. This oscillation, which agrees with the observed interannual length of day variations for the period, appears to be related to the oscillation in tropical air and sea surface temperatures which lags behind the temperature oscillation by a few months. A relative change in the rotation of the earth on the order of 0.2 x 10 to the -8th can be produced by an observed tropical temperature oscillation of 1.0 C, according to a thermal wind argument.

Stefanick, M.↗

NASA NTRS1983

Dynamics of Tisserand's frame for an elastic spacecraft with stored angular momentum

Tisserand's frame represents a frame in which the deformations in elastic members and the motions in a central rigid body add zero translational and angular momenta to the overall momentum of the vehicle. The considered relations have been known for some time in the case of nongyroscopic spacecraft. The present investigation is concerned with an extension of the relations to gyroscopic systems, taking into account an entirely elastic spacecraft with significant stored angular momentum. A two-dimensional free, rectangular, elastic structure with axisymmetric rotors is considered. Equations of motion are obtained with the aid of the Newton-Eulerian technique and Hamilton's principle. An analysis is conducted of the dynamics of an elastic gyroscopic free vehicle, and the dynamics of the Tisserand's frame in response to external stimuli is examined.

Hablani, H. B.↗

NASA NTRS1984

Angular momentum drain - A mechanism for despinning asteroids

The new mechanism of angular momentum drain is proposed to account for the relatively slow rotation rates of intermediate-sized asteroids. Impact ejecta on a spinning body preferentially escape in the direction of rotation, systematically draining away spin angular momentum and leading to the counterintuitive result that collisions can reduce the spin of midsized objects. The existing theory of asteroid rotation is reviewed, and the escape of ejecta from hypervelocity impacts on bodies of different sizes and physical properties is described. The effect of this mass loss on asteroidal rotation is calculated and shown to be a significant brake on the spins of intermediate-sized asteroids. Finally, this new process is incorporated in a revised theory of collisional evolution, its predictions are compared with observational data, and its applications are discussed.

Dobrovolskis, A. R.↗

NASA NTRS1985

Measurements of the angular distribution of auroral-zone bremsstrahlung in the middle atmosphere

The angular distributions of atmospheric electron bremsstrahlung at 45-65 km are determined by analyzing NaI-scintillation-detector measurements of X-rays in energy ranges upward of 5, 10, 20, and 40 keV obtained in two rocket flights over Alaska during March 1978 as part of the Aurorozone II project (Goldberg et al., 1984). The data are presented graphically and characterized, with a focus on periods of post-breakup auroral precipitation events. Findings reported include generally uniform upward and downward intensities, with the upward intensity typically 1-10 percent of the total; a smooth zenith-nadir transition of angular width less than + or - 20 deg at 40 keV; a downward energy spectrum dominated by direct X-rays at 65 km but much less so at lower altitudes (where Compton-scattered X-rays play a greater role); and a completely scattered-X-ray-dominated upward energy spectrum. Reasonable agreement is found when these data are compared with the theoretical bremsstrahlung calculations of Berger and Seltzer (1972).

Barcus, J. R.↗

NASA NTRS1986

Inference of stress and texture from angular dependence of ultrasonic plate mode velocities

The theory for the angular dependence of the ultrasonic wave velocity in a symmetry plane of an orthorhombic, stressed material is presented. The two waves having polarizations in this plane are shown to have velocities which can be estimated from measurements of the SH sub 0 and S sub 0 guided modes of a thin plate: the relationship being exact for the SH sub 0 mode and requiring a 10% correction for the S sub 0 mode at long wavelength. It is then shown how stress and texture can be independently inferred from various features of the angular dependence of these two velocities. From the SH sub 0 data, the ability to determine the directions and differences in magnitudes of principal stresses is described and supported by experimental data on several materials. From a combination of the SH sub 0 and S sub 0 data, a procedure is proposed for determining the coefficients W sub 400, W sub 420 and W sub 440 of an expansion of the crystallite orientation distribution function in terms of generalized Legendre functions. Possible applications in process control are indicated.

Thompson, R. B.↗