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NASA NTRS1981

Enhancement of peptide bond formation by polyribonucleotides on clay surfaces in fluctuating environments

The selective effects of polyribonucleotides on the formation of glycine peptide bonds in glycine on clay surfaces are investigated as a model for a template mechanism for the effects of polynucleotides on peptide bond formation. Free oligoglycine yields were determined for the cycling reaction of glycine in the presence and absence of clay and polyribonucleotides or polydeoxyribonucleotides. The polyribonucleotides are observed to lead to increases of up to fourfold increases in oligoglycine formed, with greater enhancements for poly-G nucleotides than for poly-A, poly-U and poly-C, indicating a codonic bias. Polydeoxyribonucleotides are found to provide no enhancement in peptide formation rates, and yields were also greatly reduced in the absence of clay. A mechanism for peptide synthesis is proposed which involves the activation of glycine on the clay surface, followed by the formation of esters between glycine and the 2-prime OH groups of the polyribonucleotide and peptide bonds between adjacent amino acyl esters. It is pointed out that if this mechanism is correct, it may provide a basis for a direct template translation process, which would produce a singlet genetic code.

White, D. H.↗

NASA NTRS1981

Stochastic self-propagating star formation in the Large Magellanic Cloud

The considered investigation provides a unifying theoretical basis for an understanding of a variety of observations on the Large Magellanic Cloud (LMC). It is demonstrated that an intrinsically statistical theory can supply a model for individual objects. With the aid of the model of stochastic self-propagating star formation described by Gerola and Seiden (1978), many structural features, both in the stars and in the gas are related to the process of star formation and the evolution of the LMC. It is found that the pattern of massive star formation in the LMC is partially ordered. The stars occur in large clumps and their global pattern is basically irregular and asymmetric with respect to the rotation center. The mean rate of chemical evolution of the LMC is smaller than that of the Milky Way. This fact is largely explained by the model in terms of the difference in shear for these galaxies. The formation of large, dense regions of massive stars has a great effect on the gas.

Feitzinger, V.↗

NASA NTRS1981

Dissipational galaxy formation - Confrontation with observations

An exploration is presented of the hypothesis that a protogalaxy consists of an aggregate of interacting gas clouds which undergo mergers with neighboring systems, as envisaged by both the hierarchical clustering and fragmentation schemes of galaxy formation. Both gaseous dissipation and violet relaxation play fundamental roles in this galaxy formation model, in order to account for such diverse structural and dynamical properties of spheroidal galaxies as velocity anisotropy and metallicity gradients. Protogalaxy mergers during the initial stages of galaxy clustering can account for the observed spatial distribution of spiral, S0, and elliptical galaxies, and galaxy formation can occur slowly and at late epochs, since the time scale for disk formation is less than about 10 to the 10th years.

Silk, J.↗

NASA NTRS1982

Evidence for arrested bone formation during spaceflight

Addressing the question of whether the bone formed in space is unusual, the morphology of bone made at the tibial diaphysis of rats before, during, and after spaceflight is studied. Evidence of arrest lines in the bone formed in space is reported suggesting that bone formation ceases along portions of the periosteum during spaceflight. Visualized by microradiography, the arrest lines are shown to be less mineralized than the surrounding bone matrix. When viewed by scanning electron microscopy, it is seen that bone fractures more readily at the site of an arrest line. These observations are seen as suggesting that arrest lines are a zone of weakness and that their formation may result in decreased bone strength in spite of normalization of bone formation after flight. The occurrence, location, and morphology of arrest lines are seen as suggesting that they are a visible result of the phenomenon of arrested bone formation.

Turner, R. T.↗

NASA NTRS1983

Glass formation - A contemporary view

The process of glass formation is discussed from several perspectives. Particular attention is directed to kinetic treatments of glass formation and to the question of how fast a given liquid must be cooled in order to form a glass. Specific consideration is paid to the calculation of critical cooling rates for glass formation, to the effects of nucleating heterogeneities and transients in nucleation on the critical cooling rates, to crystallization on reheating a glass, to the experimental determination of nucleation rates and barriers to crystal nucleation, and to the characteristics of materials which are most conducive to glass formation.

Uhlmann, D. R.↗

NASA NTRS1983

Standard free energy of formation of iron iodide

An experiment is reported where silver iodide is used to determine the standard free energy of formation of iron iodide. By using silver iodide as a solid electrolyte, a galvanic cell, Ag/AgI/Fe-FeI2, is formulated. The standard free energy of formation of AgI is known, and hence it is possible to estimate the standard free energy of formation of FeI2 by measuring the open-circuit emf of the above cell as a function of temperature. The free standard energy of formation of FeI2 determined by this method is -38784 + 24.165T cal/mol. It is estimated that the maximum error associated with this method is plus or minus 2500 cal/mol.

Khandkar, A.↗

NASA NTRS1983

Thiol-catalyzed formation of lactate and glycerate from glyceraldehyde

The rate of lactate formation from glyceraldehyde, catalyzed by N-acetyl-cysteine at ambient temperature in aqueous sodium phosphate (pH 7.0), is more rapid at higher sodium phosphate concentrations and remains essentially the same in the presence and absence of oxygen. The dramatic increase in the rate of glycerate formation that is brought about by this thiol, N-acetylcysteine, is accompanied by commensurate decreases in the rates of glycolate and formate production. It is suggested that the thiol-dependent formation of lactate and glycerate occurs by way of their respective thioesters. Attention is given to the significance of these reactions in the context of molecular evolution.

Weber, A. L.↗

NASA NTRS1983

The formation of galaxies

Current models of galaxy formation are examined in a review of recent observational and theoretical studies. Observational data on elliptical galaxies, disk galaxies, luminosity functions, clustering, and angular fluctuations in the cosmic microwave background are summarized. Theoretical aspects discussed include the origin and early evolution of small fluctuations, matter and radiation fluctuations, the formation of large-scale structure, dissipationless galaxy formation, galaxy mergers, dissipational galaxy formation, and the implications of particle physics (GUTs, massive neutrinos, and gravitinos) for cosmology.

Efstathiou, G.↗

NASA NTRS1984

Climatic Impact of a Change in North Atlantic Deep Water Formation

The response of the ocean to climate changes is one of the most uncertain questions regarding the impact of increasing CO2 on climate and society. North Atlantic deep water (NADW) formation apparently depends on a complex confluence of different water masses originating in different areas, all of which will presumably be affected by changes in wind, evaporation, etc., as the atmosphere warms. To analyze from first principles what the effect will be on NADW formation is a task which requires an ocean modeling capability not yet available. As a substitute, past climates can be investigated to see if there is any evidence for alterations in NADW formation. In addition, the possible impact of such changes on climate can be explored. An estimate of NADW sensitivity (at least in the past) and of the climate consequences can be studied. The North Atlantic surface water temperatures can be reconstructed to indicate a substantial cooling between 11,000 and 10,000 years B.P. Were NADW formation to have ceased, it would have resulted in cooler surface waters; whether the reconstructed temperatures were due to this or some other effect cannot be determined at this time. Nevertheless, it was decided that it would be useful to see what the effect these colder temperatures would have had on the climate.

Rind, D.↗

NASA NTRS1985

Nebular volatile fractionations associated with chondrule formation

Chondrules are ubiquitous constituents of primitive solar system matter, indicating that chondrule formation was an important and widespread process in the early history of the solar system. If chondrules formed from fine grained CI like precursors, some volatile fractionation must have accompanied chondrule formation. This is not likely related to a separation of chondrules from gas (and dust, fine enough to be coupled to gas) shortly after formation, a process required by most models of chondrule formation. If chondrules are continuously formed in and removed from a region of the solar nebula, the chemical environment in this region will change. Vaporization of solid increases both oxygen and sulfur in the gas relative to H. Depending on the oxygen/sulfur ratio, which may vary widely as a function of precursor composition and temperature, two cases can be distinguished: (1) sulfur requires reaction with solid to condense, and thus may become much more enriched than 0; (2) if a significant amount of silicate is vaporized together with sulfides and does not recondense, changes in H/O outweigh S enrichment. In combination, these two effects may be able to account for much of the chemical variation among various types of chondrites. Opaque, fine grained matrix in unequilibrated chondrites, which is thought to derive from dust, has indeed been found to have a volatile element abundance complementary to chondrules.

Kracher, A.↗

NASA NTRS1985

On instruction sets and their formats

Central to instruction set design is the issue of the instruction format. Some common format encoding techniques are discussed, and a method of representing high-level language parse trees by means of formats that cover successively larger portions of a tree is introduced. Variations are introduced on the method that represent directed acyclic graphs as well as simple parse trees, and that encode constants in a special fashion. For a particular representation, the number of times each format is executed to run a sample program to completion is measured.

Flynn, M. J.↗

NASA NTRS1986

A model for the biological precipitation of Precambrian iron-formation

A biological model for the precipitation of Precambrian iron formations is presented. Assuming an oxygen deficient atmosphere and water column to allow sufficient Fe solubility, it is proposed that local oxidizing environments, produced biologically, led to precipitation of iron formations. It is further suggested that spheroidal structures about 30 mm in diameter, which are widespread in low grade cherty rion formations, are relict forms of the organic walled microfossil Eosphaera tylerii. The presence of these structures suggests that the organism may have had a siliceous test, which allowed sufficient rigidity for accumulation and preservation. The model involves precipitation of ferric hydrates by oxidation of iron in the photic zone by a variety of photosynthetic organisms. Silica may have formed in the frustules of silica secreting organisms, including Eosphaera tylerii. Iron formates formed, therefore, by a sediment rain of biologically produced ferric hydrates and silica and other organic material. Siderite and hematite formed diagenetically on basin floors, and subsequent metamorphism produced magnetite and iron silicates.

Laberge, G. L.↗

NASA NTRS1986

Shock-tube pyrolysis of chlorinated hydrocarbons - Formation of soot

Soot formation in pyrolysis of chlorinated methanes, their mixtures with methane, and chlorinated ethylenes were studied behind reflected shock waves by monitoring the attenuation of an He-Ne laser beam. An additional single-pulse shock-tube study was conducted for the pyrolysis of methane, methyl chloride, and dichloromethane. The experiments were performed at temperatures 1300-3000 K, pressures of 0.4-3.6 bar, and total carbon atom concentrations of 1-5 x 10 to the 17th atoms cu cm. The amounts of soot produced in the pyrolysis of chlorinated hydrocarbons are larger than that of their nonchlorinated counterparts. The sooting behavior and product distribution can be generally explained in terms of chlorine-catalyzed chemical reaction mechanisms. The pathway to soot from chlorinated methanes and ethylenes with high H:Cl ratio proceeds via the formation of C2H, C2H2, and C2H3 species. For chlorinated hydrocarbons with low H:Cl ratio, the formation of C2 and its contribution to soot formation at high temperatures becomes significant. There is evidence for the importance of CHCl radical and its reactions in the pyrolysis of dichloromethane.

Frenklach, M.↗

NASA NTRS1987

Integration of altitude and airspeed information into a primary flight display via moving-tape formats

A ground-based aircraft simulation study was conducted to determine the effect on pilot performance of replacing the electromechanical altimeter and airspeed indicators with electronically generated representations integrated into the primary flight display via moving-tape (linear moving scale) formats. Several key factors relating to moving-tape formats were examined during the study: tape centering, secondary (trend) information, and tape orientation. The factor of centering refers to whether the tape was centered about the actual airspeed or altitude or about some defined reference value. Tape orientation refers to whether the values represented are arranged in either descending or ascending order. Six pilots participated in this study, with each subject performing 18 runs along a single, known flight profile. Subjective results indicated that the moving-tape formats were generally better than that of the conventional instruments. They also indicated that an actual-centered fixed pointer was preferred to a reference-centered pointer. Performance data for a visual secondary task showed that formats not containing trend information produced better performance; however, no difference was noted in airspeed tracking or altitude tracking performance. Regarding tape orientation, subjective comments indicated that there was lower work load and better performance when the airspeed tape had the high numbers at the top.

Abbott, Terence S.↗

NASA NTRS1986

Recent observations of the formation of filaments

Two examples of the formation of small filaments in H alpha are described and illustrated. In both cases, the formation is seen to be the spontaneous appearance of strands of absorbing mass that evolve from no previous structure. The initial development of the filaments appears to consist of the accumulation of these absorptive strands along approximately parallel paths in a channel between large-scale, opposite polarity magnetic fields on either side of the filaments. The strands exhibit continuous changes in shape and degree of absorption which can be due to successive condensations resulting in new strands, mass motions within the strands, and outflow of the mass from the strands. For at least several hours before the formation of both filaments, small-scale fragments of opposite polarity, line-of-sight magnetic flux adjacent to or immediately below the filaments, and at the ends of the filaments, were cancelling. This type of magnetic flux disappearance continued during the development of the filaments and is commonly observed in association with established filaments. Cancellation is interpreted as an important evolutionary change in the magnetic field that can lead to configurations suitable for the formation of filaments.

Martin, Sara F.↗

NASA NTRS1987

Star formation in the Magellanic clouds

Because of their proximity, the Magellanic Clouds provide the opportunity to conduct a detailed study of the history and current state of star formation in dwarf irregular galaxies. There is considerable evidence that star formation in the Clouds was and is proceeding in a manner different from that found in a typical well-ordered spiral galaxy. Star formation in both Clouds appears to have undergone a number of relatively intense bursts. There exist a number of similarities and differences in the current state of star formation in the Magellanic Clouds and the Milky Way. Examination of Infrared Astronomy Satellite (IRAS) sources with ground based telescopes allows identification of highly evolved massive stars with circumstellar shells as well as several types of compact emission line objects.

Frogel, Jay A.↗

NASA NTRS1987

A simple theory of bimodal star formation

A model of bimodal star formation is presented, wherein massive stars form in giant molecular clouds (GNC), at a rate regulated by supernovae energy feedback through the interstellar medium, the heat input also ensuring that the initial mass function (IMF) remains skewed towards massive stars. The low mass stars form at a constant rate. The formation of the GMC is governed by the dynamics of the host galaxy through the rotation curve and potential perturbations such as a spiral density wave. The characteristic masses, relative normalizations, and rates of formation of the massive and low mass modes of star formation may be tightly constrained by the requirements of the chemical evolution in the Solar Neighborhood. Good fits were obtained for the age metallicity relation and the metallicity structure of thin disk and spheroid stars only for a narrow range of these parameters.

Wyse, Rosemary F. G.↗

NASA NTRS1987

Innovative design of composite structures: Use of curvilinear fiber format to improve structural efficiency

To increase the effectiveness and efficiency of fiber-reinforced materials, the use of fibers in a curvilinear rather than the traditional straightline format is explored. The capacity of a laminated square plate with a central circular hole loaded in tension is investigated. The orientation of the fibers is chosen so that the fibers in a particular layer are aligned with the principle stress directions in that layer. Finite elements and an iteration scheme are used to find the fiber orientation. A noninteracting maximum strain criterion is used to predict load capacity. The load capacities of several plates with different curvilinear fibers format are compared with the capacities of more conventional straightline format designs. It is found that the most practical curvilinear design sandwiches a group of fibers in a curvilinear format between a pair of +/-45 degree layers. This design has a 60% greater load capacity than a conventional quasi-isotropic design with the same number of layers. The +/-45 degree layers are necessary to prevent matrix cracking in the curvilinear layers due to stresses perpendicular to the fibers in those layers. Greater efficiencies are achievable with composite structures than now realized.

Hyer, M. W.↗