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At least 415 records · Page 23
All sourcesNASA NTRSDOE OSTI
NASA NTRS1972

The occultation of beta Scorpii by Jupiter and Io. I - Jupiter.

Use of computer-controlled one-dimensional area-scanning photometers to observe the occultation of the Beta Scorpii system by Jupiter on May 13, 1971. Six high-quality light curves were obtained; three of the occultations of the brighter component Beta Sco A and three of Beta Sco C. The mean scale height of the Jovian upper atmosphere is 32 plus or minus 6 km near -10 deg zenographic latitude, 31 plus or minus 2 km at -47 deg zenographic latitude, and 24 plus or minus 2 km at -57 deg zenographic latitude. The determination of the atmospheric scale height is highly sensitive to the background level subtracted, providing a possible explanation of an earlier result by Baum and Code (1953) placing the scale height at about 8 km. Correlated departures of the light curve from a theoretical isothermal curve are reproduced in the three bright-star curves, and are thus not due to random density fluctuations in the Jovian atmosphere, but are rather due to global stratification. Details of the stratification, which includes at least a number of warm layers, are examined by deconvolution of the light curves. There is evidence for a high-temperature (T greater than 300 K) thermosphere on two of the bright-star light curves.

Hubbard, W. B.↗
NASA NTRS1972

Comparison of calcium and phosphorus excretion with bone density changes during restraint in immature Macaca nemestrina primates.

Calcium and phosphorus balance data on Macaca nemestrina monkeys during immobilization are presented and correlated with X-ray bone densitometry findings. A positive mineral balance was maintained during the immobilized period. A reduced bone density was observed in most skeletal sites examined with increased density observed in epiphyseal regions. Migration of mineral from one site to another is suggested as a possible explanation for the findings.

Hoffman, R. A.↗
NASA NTRS1972

The response of covered silicon detectors to monoenergetic gamma rays.

Measurements have been made of the efficiency in detecting gamma rays of a 0.3-mm-, 3-mm-, and 5-mm-thick silicon detector covered with different absorbers. Calibrated sources over the range from 279 keV to 2.75 MeV were used. The need for the absorbers to obtain meaningful results and their contribution to the response of the detectors at electron biases from 50 to 200 keV are discussed in detail. It is shown that the results are virtually independent of the atomic number of the absorber. In addition, the role of the absorber in increasing the efficiency with increasing photon energy for low bias settings is demonstrated for the 0.3-mm crystal. Qualitative explanations are given for the shapes of all curves of efficiency versus energy at each bias.

Reier, M.↗
NASA NTRS1972

Nonuniform concentration - A mechanism for drag reduction.

A large reduction in drag coefficient has been observed in certain external flows of aqueous solutions with high molecular weight polymer additives. A change in the near wake configuration is phenomenologically responsible for the drag reduction, but the underlying mechanism is presently unknown. An analogy to known phenomena in particulate suspensions is drawn which suggests nonuniform concentration of the polymer additive as an explanation. An analysis of the boundary layer on a sphere with varying viscosity was made to investigate the effect. The results indicate early transition to turbulence for concentration variations whose length scale is small compared with the momentum boundary layer thickness. Stabilization and delayed transition are indicated for thicker concentration layers. Observations are suggested for the thin concentration layers.

Rivard, W. C.↗
NASA NTRS1972

Quiet-time electron increases - A measure of conditions in the outer solar system.

Discussion of a possible explanation for the increases in the intensity range of 3- to 12-MeV interplanetary electrons that McDonald et al. (1972) have labeled as 'quiet-time electron increases.' It is argued that the electrons in quiet-time increases are galactic in origin but that the observed increases are not the result of any variation in the modulation of these particles in the inner solar system. It is suggested instead that quiet-time increases may occur when more electrons than normal penetrate a modulating region that lies far beyond the orbit of the earth. The number of electrons penetrating this region may increase when field lines that have experienced an unusually large random walk in the photosphere are carried by the solar wind out to the region. As evidence of this increased random walk, it is shown that five solar rotations before most of the quiet-time increases occur there is an extended period when the amplitude of the diurnal anisotropy (measured by the Deep River neutron monitor) is relatively low. A delay time of five rotations implies that the proposed modulating region lies at about 30 AU from the sun if the average solar-wind speed is assumed to be constant at about 400 km/sec over this distance. The implications for the correlation between periods of low-amplitude diurnal anisotropy and quiet-time increases on interplanetary conditions out to about 30 AU and some possible models for the proposed modulating region are also considered.

Fisk, L. A.↗
NASA NTRS1972

Photoelectron emission from Io as the cause of enhancements of the Jovian decametric radiation.

A theoretical explanation for the dependence of the Jovian decametric radiation on the position of its satellite Io is advanced in terms of electrostatic instabilities created by injection into the hot natural plasma of cold photoelectrons from Io. This may be tested with appropriately positioned and presently planned deep-space probes that search for variations of the Jovian decametric radiation at times following local sunset and sunrise at Io.

Mozer, F. S.↗
NASA NTRS1972

Abnormal grain growth in TD-nickel.

Characteristics of the coarse grain transformation occurring in TD-nickel 1 in. bar under certain conditions of deformation and annealing were examined. The transformation exhibits Avrami-type kinetics, with an activation energy of 250 kcal per mole. Characteristics of untransformed regions are like those of the as-received state. The transformed grain size increases with increasing deformation and decreasing annealing temperature. The coarse grain transformation is significantly different from primary recrystallization in pure nickel. Its characteristics cannot be rationalized in terms of primary recrystallization concepts, but may be explained in terms of an abnormal grain growth description. The coarse grain transformation in TD-nickel is abnormal grain growth rather than primary recrystallization. The analysis suggests an explanation for the effect of thermomechanical history on the deformation and annealing behavior of TD-nickel.

Petrovic, J. J.↗
NASA NTRS1972

Nonlinear interaction of resonant plasma oscillations.

Using the water-bag model of an electron plasma the nonlinear interaction of two plasma wave pulses (each of sufficiently narrow wave-number spectrum) is discussed. It is shown that for the special case of a resonant (zero group velocity) pulse interacting with a nonresonant pulse, the interaction produces an effective slowing down of the group velocity of the nonresonant pulse. An application of this theory to the explanation of the apparent resonances at fractions of the plasma frequency observed in the ionosphere is discussed.

Lewak, G. J.↗
NASA NTRS1972

Circumsolar radiation and the International Pyrheliometric Scale.

Issue is taken with the ascription of the 2% discrepancy in values of solar irradiance at the surface of the earth, found between the measurements performed by the absolute radiometers of Kendall and Wilson and those obtained by Eppley-Angstrom pyrheliometers, to the possibility that the two types of instruments might collect different amounts of circumsolar radiation. It is shown that this explanation is very unlikely.

Geist, J.↗
NASA NTRS1972

The relative age of the transition zone between Hellas and the Martian cratered terrain.

Consideration of the relationships of craters to scarps and ridges and of the antiquity of Hellas relative to the cratered terrain. Scarps and ridges in the transition zone between Hellas and the cratered terrain both postdate and predate large craters. It appears that there are a number of craters which are older than the transition zone structures, which in turn are presumably related in some way to the formation of Hellas. Sharp et al. (1971) have suggested impact, large-scale volcanic explosion, or subsidence for the origin of Hellas. Volcanic explosion seems the least likely explanation, for the resulting deficiency of mass beneath Hellas should induce later isostatic rebound, contrary to observations of the transition zone which imply subsidence relatively late in the history of the Martian surface. An origin of Hellas by impact with later isostatic subsidence (because of a dense mass under its floor, as suggested by Sharp et al.) to account for the characteristics of the transition zone seems to be the best model, and may also account for the featureless floor of the basin.

Thorman, C. H.↗
NASA NTRS1972

ELF noise bands associated with auroral electron precipitation.

Observation of a new type of ELF noise band that is closely associated with low-energy auroral electron precipitation. These observations have been made at relatively low altitudes (less than 3000 km) with the polar-orbiting satellite Injun 5. The noise bands typically have a center frequency of 100 to 300 Hz and often appear to consist of many nearly monochromatic bursts, typically of a few seconds' duration, superimposed to produce the observed noise band. These ELF noise bands are observed only in a relatively narrow range of latitudes (a few degrees) in the auroral zone and are almost always associated with intense fluxes of precipitating electrons with energies from a few hundred electron volts to several kiloelectron volts. On the dayside of the magnetosphere the region where the ELF noise bands and the associated low-energy electron precipitation are observed has been identified as the polar cusp. In considering the possible explanations of these ELF noise bands, it is noted that the spectral characteristics of this noise are very similar to a type of narrowband electromagnetic noise called 'lion's roar,' which has been observed at much higher altitudes in the magnetosheath with the satellite Ogo 5. It is suggested that the ELF noise bands observed at low altitudes with Injun 5 are caused by lion's roar emissions that have propagated down 'open' magnetic-field lines to low altitudes from the magnetosheath region.

Gurnett, D. A.↗
NASA NTRS1972

Voltages induced in superconductors in the absence of transport currents.

Experimental observations of the production of dc and harmonic voltages are described in superconductors subjected to superimposed dc and oscillatory magnetic fields. The attempt is made to account for these observations in a qualitative manner by relating them to the asymmetric flux flow induced by the magnetic fields in the superconductor samples. The observed effects are quite complex and depend on the values of the many parameters in the experiment. Regarding some of the observed phenomena, for which no satisfactory explanation is as yet available, further understanding is expected to come from detailed work on samples with asymmetric surfaces produced in a controlled fashion.

Ohmer, M. C.↗
NASA NTRS1972

Intermodulation characteristics of X-band IMPATT amplifiers.

Measurement of the intermodulation products produced when two equal amplitude signals are applied to the input of an X-band IMPATT diode amplifier. A Si p(+)nn(+) IMPATT diode was operated in a double-slug-tuned reflection amplifier circuit that was tuned to provide 20 dB of small-signal gain at 9.340 GHz. The intermodulation tests consist of measurements of the magnitudes and frequencies of the amplifier output signals as a function of the input signal drive levels and frequency separations. The gain and single-frequency characteristics of the amplifier were also measured and are used along with the theoretical device and circuit admittance characteristics as a basis for explanation of the intermodulation results. A low-frequency dominance mechanism is found to exist in which the low-frequency signals are amplified more than the high-frequency signals. This mechanism becomes more significant as the amplifier drive level is increased.

Trew, R. J.↗
NASA NTRS1972

A theory for energetic electron lifetimes within the plasmasphere.

The removal of radiation belt electrons through pitch-angle scattering by the observed obliquely propagating plasmaspheric whistler wave band is investigated. Electron lifetimes are calculated as a function of L and energy. The effects of high latitude interactions and of oblique wave propagation with the resulting diffusion at all cyclotron harmonics are quantitatively incorporated into the calculations. The inclusion of these effects appears to extend the role of whistler-driven electron pitch-angle diffusion to provide an explanation of the positioning of the quiet time radiation belt electron slot and the electron losses within the slot region.

Lyons, L. R.↗
NASA NTRS1972

Perturbation guidance for minimum time flight paths of spacecraft.

The problem of transferring a rocket vehicle from a given circular orbit to a larger coplanar circular orbit in minimum time, using a constant low-thrust rocket engine, is considered. Parameters are chosen to correspond to a transfer from the earth's orbit in heliocentric space to the orbit of Mars. A path satisfying the first order necessary conditions of variational calculus is shown to be locally minimizing by application of a set of second order conditions. A physical explanation is offered to justify the retrothrust period occurring during the flight. A neighboring optimum feedback control law, based on estimated time-to-go, is applied to this problem. State variable and terminal constraint feedback gains are calculated while one of the second order conditions, involving the backward integration of a matrix Riccati equation, is being tested.

Wood, L. J.↗
NASA NTRS1972

Numerical averaging in orbit prediction.

This paper is a presentation of some useful aspects of a numerical averaging technique that has been applied with considerable success to the orbit prediction problem for artificial satellites. The method has been tested in a variety of situations wherein the satellite is subjected to combinations of perturbations for which adequate analytic theories are practically impossible. The technique provides many of the advantages of analytic averaging while retaining the ability to simulate the effects of any kind of small force that can be deterministically modeled. The theoretical basis for the method is straightforward but the details of its implementation are somewhat confusing and need some explanation. A particularly useful set of averaged equations is presented along with a description of an efficient algorithm for their solution. Examples of the advantages to be obtained by use of the method are included.

Uphoff, C.↗
NASA NTRS1972

Non-planar tests using the wind tunnel free-flight technique.

Results from the first bi-planar wind tunnel free-flight test program designed to investigate the difference between planar and nonplanar dynamic stability are presented. The test provides perhaps the best free-flight angular documentation of arbitrary nonplanar motion yet obtained. Two widely different configurations, a blunt 60-deg cone and a sharp 10-deg half-angle cone, were tested. Comparisons between the angular motion from raw data and the analytical fits indicate a phasing difference. An examination of possible causes discounts experimental errors as an explanation and points strongly toward an inadequacy of the theoretical force model.

Jaffe, P.↗
NASA NTRS1972

Temporal evolution of velocity structures in the solar wind

Generally poor correlations were obtained of solar wind flow speed measurements at one point in the ecliptic plane with measurements at the same point 28 days (one solar rotation) earlier or with measurements at other points in the ecliptic plane separated by 50 deg or more in solar longitude. This is evidence that either the flow speed is a very sensitive function of solar latitude or that temporal processes typically alter the speed of the wind emanating from particular solar regions on a time scale of about 4 days. From a measure of the persistence of the flow speed at the orbit of the earth, it appears that the temporal explanation is more likely to be the correct one.

Gosling, J. T.↗