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At least 775 records · Page 43

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NASA NTRS1976

Investigation of forbidden transitions in argon ions

An attempt has been made to observe the visible forbidden argon coronal lines at 553.6 nm (Ar X), 691.7 nm (Ar XI), 847.6 nm (Ar XIII), and 441.2 nm (Ar XIV) in a deuterium-argon plasma produced in a large theta pinch. The electron temperature (250 eV) and the electron density (5 by 10 to the 16th power per cu cm) were measured by Thomson scattering of ruby laser radiation. This temperature is adequate to produce ionization stages up to Ar XIV, as was verified by photographic observation of Ar XIV lines. No line corresponding to the coronal lines was observed from the high-temperature plasma, but lines with wavelengths very nearly identical to those of two of the forbidden transitions were observed; these lines were due to allowed transitions of Ar II in a cooler portion of the plasma. Calculation of rate coefficients in the Coulomb-Born approximation shows that for laboratory experiments, electron collisions are much more important than radiative decay in depopulating the upper state of the forbidden lines.

Jalufka, N. W.↗

NASA NTRS1976

New observations of pulsed X-ray emission from NP 0532

Large-area proportional counters sensitive from 0.6 to 23 keV were used to observe about 3 min of pulsed X-ray emission from NP 0532 during two lunar-occultation experiments. A detailed pulse profile with 65-microsec resolution shows that the X-ray primary-pulse shape is essentially identical to its optical counterpart. Spectral data on the pulsed X-ray emission are presented. A pulse-by-pulse examination of the data shows no evidence for temporal variability.

Kestenbaum, H. L.↗

NASA NTRS1976

Irreducibility of large-scale dynamical systems of uni-modules

We consider the class of large-scale dynamical systems consisting of identical subsystems, but with complex connectivity. It is shown that the irreducibility of this large system is directly related to the irreducibility of a simple system, which is obtained by a replacement of the subsystems by integrators.

Singh, S. P.↗

NASA NTRS1976

Heat flow anomaly associated with dike intrusion. II

An investigation reported by Horai (1974) is continued. A special case of the steady state temperature field associated with dike intrusion is studied, taking into account an infinite vertical downward extension of the isotherm of rectangular shape approximating the dike. The considered case represents a problem of two-dimensional steady state thermal conduction. The technique of conformal mapping used is identical to the method employed by Horai (1974). The characteristics of surface heat flow associated with an infinitesimal thin dike of certain temperature with the considered extension are shown in a graph.

Horai, K.-I.↗

NASA NTRS1976

Climate stability for a Sellers-type model

We study a diffusive energy-balance climate model governed by a nonlinear parabolic partial differential equation. Three positive steady-state solutions of this equation are found; they correspond to three possible climates of our planet: an interglacial (nearly identical to the present climate), a glacial, and a completely ice-covered earth. We consider also models similar to the main one studied, and determine the number of their steady states. All the models have albedo continuously varying with latitude and temperature, and entirely diffusive horizontal heat transfer. The diffusion is taken to be nonlinear as well as linear. We investigate the stability under small perturbations of the main model's climates. A stability criterion is derived, and its application shows that the 'present climate' and the 'deep freeze' are stable, whereas the model's glacial is unstable. A variational principle is introduced to confirm the results of this stability analysis. For a sufficient decrease in solar radiation (about 2%) the glacial and interglacial solutions disappear, leaving the ice-covered earth as the only possible climate.

Ghil, M.↗

NASA NTRS1976

Linear polarimeter with rapid modulation, achromatic in the 0.3-1.1-micron range

A polarimeter is described, which provides achromatic modulation over the spectral range 0.3 to 1.1 microns, with very small light losses. The instrument is the first one to use superachromatic half-wave plates; such a plate is made of three achromatic half-wave plates of quartz and magnesium fluoride cemented with the optical axis of the central plate making an angle of 1.00 rad with the axes of the parallel-oriented outer half-wave plates. Wavelength dependence of the axis direction of the optical axis was eliminated by using two identical such plates in front of a Wollaston prism. The plate closer to the prism is stationary, while the other is continuously rotated by a stepper motor. In the polarimeter constructed, the range of instrumentally induced wavelength dependence of the plane of polarization did not exceed 0.002 rad. Using the polarimeter on a 228-cm telescope, a 10-min integration through the blue filter of the UBV photometric system for a star of magnitude 10.0 gives the percentage polarization with a mean error of + or - 0.014%.

Frecker, J. E.↗

NASA NTRS1976

The interplanetary acceleration of energetic nucleons

Corotating proton and electron streams are the dominant type of low-energy (i.e., 0.1-10 MeV per nucleon) particle event observed at 1 AU. The radial dependence of these events has been studied between 1 and 4 AU using essentially identical low-energy detector systems on IMP-7, Pioneer-10, and Pioneer-11. It had been expected that at a given energy, the intensity of these streams would decrease rapidly with heliocentric distance due to the effects of interplanetary adiabatic deceleration. Instead, it is observed that from event to event, the intensity either remains roughly constant or increases significantly (more than an order of magnitude) between 1 and 4 AU. It appears that interplanetary acceleration processes are the most plausible explanation. Several possible acceleration models are discussed.

Mcdonald, F. B.↗

NASA NTRS1975

On the origin of cosmic rays

Using recent surveys of molecular clouds and gamma-rays in the galaxy, it has become possible to determine the distribution of 1 to 10 GeV cosmic-ray nucleons in the galaxy. This distribution appears to be identical to the supernova remnant distribution to within experimental error, providing strong support for the hypothesis that supernovae produce most of the observed cosmic rays. This distribution resembles that of OB associations of an average age of 30 million years, suggesting that cosmic rays are produced by population I objects about 30 million years after their birth.

Stecker, F. W.↗

NASA NTRS1975

On the quiet-time increases of low energy cosmic ray electrons

With a detector on board the OGO-5 satellite, the flux and energy spectrum of electrons in the 10-30 MeV range has been continuously monitored from 1968 to 1972. Sudden increases by factors of up to 300 percent have been observed during solar quiet periods. These 'Quiet-Time Increases' abruptly die out above 30 MeV and correlate well with identical increases reported at lower energies leading to a flat relative energy spectrum. A large fraction of these electrons is most likely of Jovian origin.

Lheureux, J.↗

NASA NTRS1975

Solar and galactic cosmic ray abundances - A comparison and some comments

We have compared the abundances of galactic cosmic rays at their source and solar cosmic-rays utilizing new data which includes the first determination of the abundances of Na and Al in the solar cosmic ray population. We find the relative abundances of the solar and galactic species to be identical within experimental error for 8 elements. One clear abundance difference exists for C. He and Fe have a variable solar cosmic ray abundance, and the unbiased abundance of both of these nuclei is also probably different than that in the galactic cosmic ray sources. We also have compared the cosmic ray abundances with solar system and solar atmospheric abundance determinations. We find an abundance ratio which depends on the first ionization potential for galactic cosmic rays; however, in addition, we find this same dependence on ionization potential for solar cosmic ray abundance ratios. The implications of this result are discussed.

Webber, W. R.↗

NASA NTRS1975

Relation of large-scale coronal X-ray structure and cosmic rays. II - Coronal control of interplanetary injection of 300 keV protons

We report the striking coronal control of low-energy solar particles from the solar flare of September 7, 1973. The flare was at S18, W46 (Carrington longitude 188 deg) in McMath Plage Region 12307. We find strong intensity gradients in heliolongitude (about 10% per deg) that are nearly identical in protons, helium, and medium nuclei at energies about 0.5 MeV/nuc, as well as relativistic electrons and 3 MeV protons. This pervasive gradient occurs at longitudes over bright X-ray emission structures east of the flare site which interconnect large-scale chromospheric polarity regions identifiable in H-alpha filtergrams.

Roelof, E. C.↗

NASA NTRS1975

Further studies of the new component of cosmic rays at low energies

Recent observations with cosmic ray telescopes aboard the Pioneer 10 space probe have revealed an anomalous spectrum of nitrogen and oxygen nuclei relative to other nuclei such as carbon in the quiet time cosmic radiation below about 40 MeV/nuc. These observations are extended with additional data from Pioneer 10 and considerable new data from an identical telescope aboard Pioneer 11. In addition to the enhancement of nitrogen and oxygen nuclei observed earlier, the intensity of neon is enhanced as well. The spectra of boron, magnesium, and silicon appear to be similar to that of carbon. Data on the isotopic composition, solar modulation, and radial gradient of these nuclei are presented.

Webber, W. R.↗

NASA NTRS1975

The sources of material comprising a mass ejection coronal transient

The origin of the material ejected during a white-light coronal transient on August 26 and 27, 1973, is investigated using simultaneous observations of a slowly ascending prominence and the more rapid accompanying coronal transient. Nearly identical simultaneous images of the prominence were obtained over a six-hour period in the H-alpha and He II (304 A) emission lines; contemporaneous Skylab coronograph observations over approximately 1.5 hours showed that the mass-ejection coronal transient rose above the ascending prominence. Based on analysis of these observations, it is concluded that: (1) the bulk of the ejected material originated in the lower corona, despite the lack of an observed depletion there; (2) the material in the transient was at coronal temperature and was visible in polarized radiation due to Thomson scattering of photospheric light by free electrons; and (3) the total event was far larger, more energetic, and longer lasting than would have been inferred from the prominence observations alone.

Hildner, E.↗

NASA NTRS1976

Scattering of high-velocity He atoms by C/CH3/4 and Si/CH3/4

Fast helium beams are employed to probe short-range potentials in tetramethylmethane and tetramethylsilane, and throw light on the relations between these more complex reactions and such reactions as He-CH4 and He-SiH4. Earlier work on scattering of helium and argon beams by polyatomic molecules (fluorinated methanes, sulfur hexafluoride, silane, germane) are at variance with these results, as neither of the above systems can be represented as a cluster of four CH4 molecules, Effective He-H potentials based on scattering data are identical for the two systems studied but are much larger than the corresponding CH4 potential. A model in which centers of force are located along the bonds rather than at the nuclei is suggested for further testing.

Amdur, I.↗

NASA NTRS1975

A note on the consistency of maximum likelihood estimates for finite families of stochastic processes

The note considers families of stochastic processes indexed by a finite number of alternative parameter values. For general classes of stochastic processes, it is shown that maximum-likelihood estimates converge almost surely to the correct parameter value. This is established by use of a submartingale property of the sequence of maximized-likelihood ratios together with a technique first employed by Wald (1949) in the case of independent identically distributed random variables.

Caines, P. E.↗

NASA NTRS1975

Stereomolecular interactions and microsystems in experimental protobiogenesis

A theory on the origin of the first reproducing (in the sense of Fox, 1973) cells on earth is presented. A degree of self-ordering has been observed in the selective thermal reactions of certain ones of the amino acids which have been found in samples of meteorites, lunar samples, and terrestrial lava, and which have been synthesized from formaldehyde and ammonia under conditions modeling those assumed to have been present in the primitive earth. The genetic code is supposed to have arisen from a nonrandom matrix of preproteins. The ordering of preproteins specified limitations in the identity of the pre-enzymes and primordial microsystems which gave rise to contemporary living systems. The evolution of progresively more complex system was largely determined by stereochemical forces involving the shapes of the molecules themselves and the regulatory effects of the confines of the microsystems.

Fox, S. W.↗

NASA NTRS1976

Relative toxicity of pyrolysis products of some foams and fabrics

A limited number of foams and fabrics was evaluated in the course of developing test procedures for determining the relative toxicity of materials. The principal variable studied, heating rate, did not affect the relative ranking of the materials tested. Two pyrolysis test procedures using the same basic approach but employing different sample weights, chamber volumes, laboratory animals, heating rates, and upper temperature limits, resulted in identical rankings of relative toxicity. The data obtained show that modification of conventional flexible polyurethane foams with flame retardants to comply with California upholstered furniture flammability regulations seems to consistently reduce toxicity under pyrolysis conditions.

Hilado, C. J.↗

NASA NTRS1976

Microwave remote sensing of a two-layer random medium

A two-variable expansion technique is used to solve for the mean Green's. function from the Dyson equation under the nonlinear approximation. The Bethe-Salpeter equation then gives rise to a set of modified radiative transfer (MRT) equations which accommodate coherent effects essential to bounded media. It is found that the nonlinear approximation, instead of the more popular bilocal approximation, should be used for the case of bounded media. The two approximations yield identical results for unbounded media. The MRT equations are then solved for a two-layer random medium. The MRT equations give rise to simple and useful solutions which are applicable to both active and passive microwave remote sensing.

Tsang, L.↗