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At least 1,441 records · Page 80

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NASA NTRS1980

On the origin of corotating energetic particle events

The paper examines energetic corotating particle events produced by acceleration at the forward and reverse shock pair which bounds a corotating interaction region by the process of successive multiple reflections. In the steady state, the energetic particle intensity at the shock depends only on the intensity of shock particles, and measurements of energetic particles show systematic variations between intensities at the forward and reverse shocks. It is concluded that the solar wind is the original particle population that is accelerated in the stationary shocks up to several MeV.

Scholer, M.↗

NASA NTRS1980

The Galaxy as the origin of gamma-ray bursts

The gamma-ray burst spectrum N(greater than S) versus S is reviewed and found to be inconsistent with a completely isotropic distribution. Extragalactic distributions are considered but rejected in favor of a galactic origin. Spherical halo models, particularly those with central concentration, are found to be unacceptable. Noncentrally concentrated disk models are acceptable, especially those with larger scale height (beta) distributions. Spiral structure effects prevent the total rejection of small beta distributions but impose space density requirements which exclude many extreme Population I candidates. Integrated burst luminosities range from about 10 to the 38th to 2 x 10 to the 39th ergs while burst rate densities vary between about 10 to the -6th and 10 to the -8th/cu pc yr; both are uniquely determined by the distribution scale height. It is shown that galactic burst sources must be repetitive with repetition rates between about 10 to the -5th/yr and about 10 to the 6th/yr depending on the source space density and the importance of beaming. Bursts are unimportant in the galactic energy balance and, on average, in the energy history of their sources. They may, however, dominate specific events.

Jennings, M. C.↗

NASA NTRS1980

Stellar winds, supernovae, and the origin of the H I supershells

It is shown that the H I shells and supershells, recently reported by Heiles, are a natural by-product of the interaction of the stellar winds and supernovae, originating from stars in typical OB associations, with the surrounding interstellar medium. The validity of this model is supported by its ability to reproduce observed characteristics of the shells such as the shell sizes and shapes as a function of their distances from the galactic center. This process may also be responsible for injecting synthesized elements into the galactic halo.

Bruhweiler, F. C.↗

NASA NTRS1980

Carbynes in meteorites - Detection, low-temperature origin, and implications for interstellar molecules

The presence, origin and implications of carbynes in meteorites are investigated. A sample of the Allende meteorite was pyrolyzed at temperatures from 25 to 750 C and examined by solid probe time-of-flight mass spectrometry and high-resolution mass spectrometry. Fragments released upon heating at 250 to 330 C are found to be composed of macromolecules containing triply bonded carbon units and cyanoacetylenes, as well as some methyl- and phenylacetylenes. Although carbynes are well known to form from the condensation of carbon vapors above 2600 K or by shock greater than 600 kbar, which would be unlikely in Allende, it is found that carbynes rather than graphite are formed metastably by the disproportionation of CO at low temperatures when chromite is present as a catalyst. Results imply that metastable formation mechanisms may be the principal source of interstellar polycyanoacetylenes and meteoritic and terrestrial carbynes.

Hayatsu, R.↗

NASA NTRS1980

Studies of the chemical basis of the origin of protein synthesis Initiation and direction of peptide growth

The data presented in this paper show that the ease of nonenzymatic activation of carboxylic acids by ATP at pH 5 varies directly with the pKa of the carboxyl group, and is consistent with the idea that it is the protonated form of the carboxyl group which participates in the activation reaction. Consequently, since most N-blocked amino acids have higher pKas than do their unblocked forms, they are activated more readily, and it has been demonstrated that this principle applies to peptides as well, which are activated more rapidly than single amino acids. It is proposed that this fact may be partly responsible for the origin of two important features still observed in contemporary protein synthesis: (1) initiation in prokaryotes is accomplished with an N-blocked amino acid, and (2) elongation in all living systems occurs at the carboxyl end of the growing peptide.

Mullins, D. W., Jr.↗

NASA NTRS1980

Origin and chemistry of comets

Long-period and short-period comets are all derived from a steady flux of 'new' comets coming straight from the margin of a sphere whose radius is 50,000 AU (the Oort's cloud). No empirical evidence requires that the Oort's cloud be older than a few million years, but all satisfactory theories have so far linked its formation to the origin of the solar system. 'New' comets have a size distribution consistent with the accretion of planetesimals, in contrast with older comets that are consistent with a fragmentation distribution. The H, C, N, O elemental ratios to Si suggest the comets are more primitive than the most primitive meteorites, namely the C I chondrites. Their chemistry is poorly known, but observational data suggest a protosolar ratio of C/O at least as large as 0.66, and a drastic depletion of hydrogen in the solar nebula. This could for instance imply that the T Tauri phase of the sun happened prior to the condensation of comets. An alternate explanation is possible: the interstellar grains were relatively unprocessed during their contraction in the solar nebula, and their mantles, barely modified, would have followed suit in the accretion of comets.

Delsemme, A. H.↗

NASA NTRS1980

The nature and origin of ureilites

A theory of the origin of ureilites is presented based on mineralogical and petrological investigation of eight species including Kenna, Novo Urei, and Goalpara. The theory suggests that ureilites are primarily olivine-pigeonite cumulates crystallized from a silicate liquid which also contained suspended solid carbon phases. The carbon induced reduction of the melt and affected the ureilite mineral compositions. Petrofabric analyses show that mafic silicates are oriented in lineated and foliated patterns similar to cumulate rocks; strain rate of silicates suggests that ureilites were deformed after lithification by a mild tectonic stress and a moderate to severe shock.

Berkley, J. L.↗

NASA NTRS1980

The origin of the solar system

A review is presented of the recent evidence that a supernova outburst may have played a decisive role in the origin of the solar system. This evidence has been largely based on the precision isotopic abundance measurements made in meteoritic material. These measurements are reviewed; emphasis is placed on the observed short lived isotopes Al-26 and Pd-107.

Schramm, D. N.↗

NASA NTRS1980

The origin of interplanetary sectors

The coronal magnetic models of Altschuler and Newkirk (1969), Schatten, Wilcox, and Ness (1969), and Schatten (1971), that allowed calculation of the coronal magnetic field from the observed photometric magnetic field, are reviewed with reference to coronal holes and the origin of interplanetary magnetic field sectors. Some misconceptions about interplanetary magnetic field sectors are examined. It is suggested that interplanetary sector structure should be confined to studies of the outer corona, interplanetary space, and objects therein, but not the sun itself.

Schatten, K. H.↗

NASA NTRS1980

Transient phenomena originating at the sun - An interplanetary view

Analyses of several transient phenomena which occurred in 1978 and 1979 are presented using data from the Pioneer Venus, ISEE, and Pioneer 10 and 11 spacecraft. The interplanetary phenomena studied are associated with solar flares and coronal holes. The observations show that phenomena originating at the sun affect the structure of the particle and field regimes throughout the explored solar system, extending out to at least 17-20 AU in the vicinity of the elliptic plane over a range of azimuthal angles greater than 90 deg. High frequency fluctuations in the interplanetary medium appear beyond 1 AU, indicating that transient phenomena are significantly modified by their passage through this medium.

Intriligator, D. S.↗

NASA NTRS1980

Theoretical interpretation of Traveling Interplanetary Phenomena and their solar origins

A review is made of recent theoretical studies on Traveling Interplanetary Phenomena (TIP) and their possible solar origins in the context of mathematical methods and physical processes. Flare-generated interplanetary shocks are used as examples to illustrate the following set of contrasting approaches to the phenomena: analytical vs numerical, hydrodynamic vs magnetohydrodynamic, dissipative vs non-dissipative, continuum/macroscopic vs kinetic/microscopic. It is suggested in conclusion that future research should emphasize continuum/macroscopic physical processes together with the kinetic approach to deepen understanding of microscopic interactions.

Wu, S. T.↗

NASA NTRS1981

Composition of hot ions /0.1-16 keV/e/ as observed by the GEOS and ISEE mass spectrometers and inferences for the origin and circulation of magnetospheric plasmas

The composition of hot magnetospheric plasma through different regions of the magnetosphere is described on the basis of mass spectrometer measurements by the GEOS 1, GEOS 2, and ISEE-1 spacecraft. Coordinated composition measurements on the different spacecraft also provide information on the spatial and temporal characteristics of the plasma during storms. Data on ion origins are also provided.

Balsiger, H.↗

NASA NTRS1981

Isotopically anomalous xenon in meteorites - A new clue to its origin

The CCF xenon component in primitive meteorites, which has been attributed either to fission of a superheavy element or to nucleosynthesis in a supernova, does not show the large enrichment in Xe-129 (from decay of 16 Myr I-129) expected for supernova ejecta. Although this problem can be circumvented by ad hoc assumptions, a fission origin of CCFXe seems more likely.

Lewis, R. S.↗

NASA NTRS1981

The stochastic evolution of asteroidal regoliths and the origin of brecciated and gas-rich meteorites

A model is constructed which views regolith evolution on asteroids as a stochastic process. Average values are shown to be poor descriptors of regolith depth. The utility of the average depth is not significantly increased by avoiding large craters or thick ejecta deposits, a procedure adopted in previous regolith studies. The statistical uncertainty associated with regolith depth severely limits the power of regolith models in predicting parent-body size for brecciated meteorites. A Monte Carlo algorithm was used to simulate the random walks and corresponding charged-particle irradiation histories of grains in regoliths. On rocky asteroids, only about 20 percent of the grains was exposed to solar cosmic ray ions. Results based on present-day conditions in the asteroid belt agree well with irradiation features observed in gas-rich meteorites. An origin during epochs of early solar system evolution is not required.

Housen, K. R.↗

NASA NTRS1982

Protein folding, protein structure and the origin of life: Theoretical methods and solutions of dynamical problems

Theoretical methods and solutions of the dynamics of protein folding, protein aggregation, protein structure, and the origin of life are discussed. The elements of a dynamic model representing the initial stages of protein folding are presented. The calculation and experimental determination of the model parameters are discussed. The use of computer simulation for modeling protein folding is considered.

Weaver, D. L.↗

NASA NTRS1981

Composition and origin of the unusual Oktibbeha County iron meteorite

Oktibbeha County, the most Ni-rich iron meteorite, has been analyzed for Ni, Co, Cu, Ga, Ge, As, Sb, Ir, and Au. Cu and Sb are higher than in any other iron, but other trace elements are within the ranges typically found in iron meteorites. Extrapolation of trace element trends in group IAB indicates that Oktibbeha County is a member of this group. This sheds light on the origin of groups IAB and IIICD, which are thought to be derived from impact melts on parent bodies of chondritic composition. Lafayette (iron), another sample reported in the literature to have a similarly high Ni content, is probably a pseudometeorite.

Kracher, A.↗

NASA NTRS1981

Upstream energetic ions and electrons - Bow shock-associated or magnetospheric origin

An analysis is made of 35 proton bursts observed with the Max-Planck-Institut/University of Maryland sensor system on ISEE 3 far upstream of the earth's bow shock. These upstream bursts are found to fall into two distinctive groups. The first is accompanied by energetic electrons (more than about 75 keV), and the proton spectrum extends up to energies greater than about 300 keV and higher and bends over toward lower energies (less than about 30 keV). The second group, which is unaccompanied by energetic electron bursts, exhibits spectra which can be represented extremely well by exponentials in energy with a mean e-folding energy of approximately 15 keV. The first group is thought to be of a magnetospheric origin, and the second to be bow-shock associated.

Scholer, M.↗

NASA NTRS1981

Energetic particle events /greater than or equal to 30 keV/ of Jovian origin observed by Voyager 1 and 2 in interplanetary space

Detailed observations of ion events of Jovian origin as observed by the low energy charge particle (LECP) instrumentation on Voyager 1 and 2 during the inbound and outbound pass for both spacecraft are reported. The general characteristics of these events are examined, and a comparison is made with similar observations at earth. Careful attention is given to the compositional signature of the Jovian ion events. Two of the specific events discussed in detail are selected to display the range of variability and complexity of the Jovian-produced interplanetary ion events. The observations are seen as strongly implying that the Jovian magnetosphere is the source of a significant fraction of the particles.

Zwickl, R. D.↗