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Differential cross sections for electron scattering by hydrogen with and without vibrational excitation, discussing inelastic processes
The oxygen and hydrogen free radical (atom) concentration profiles in the premixed propane/oxygen flame at 92.5% oxygen were determined using electron spin resonance (ESR) spectroscopy techniques. The ESR instrument was specially modified so that the flame can be probed for determining the oxygen and hydrogen atom population densities during the actual combustion process of propane burning in oxygen. The technique used for propane is similar to that suggested by Fristrom and Westenberg to measure the free radical concentration profiles in C-C hydrocarbon/oxygen combustion.
A cleaning and drying system for processing at least 2500 three in. diameter wafers per hour was developed with a reduction in process cost. The system consists of an ammonia hydrogen peroxide bath in which both surfaces of 3/32 in. spaced, ion implanted wafers are cleaned in quartz carriers moved on a belt past two pairs of megasonic transducers. The wafers are dried in the novel room temperature, high velocity air dryer in the same carriers used for annealing. A new laser scanner was used effectively to monitor the cleaning ability on a sampling basis.
A preprototype water electrolysis subsystem was designed and fabricated for NASA's advanced regenerative life support program. A solid polymer is used for the cell electrolyte. The electrolysis module has 12 cells that can generate 5.5 kg/day of oxygen for the metabolic requirements of three crewmembers, for cabin leakage, and for the oxygen and hydrogen required for carbon dioxide collection and reduction processes. The subsystem can be operated at a pressure between 276 and 2760 kN/sq m and in a continuous constant-current, cyclic, or standby mode. A microprocessor is used to aid in operating the subsystem. Sensors and controls provide fault detection and automatic shutdown. The results of development, demonstration, and parametric testing are presented. Modifications to enhance operation in an integrated and manned test are described. Prospective improvements for the electrolysis subsystem are discussed.
The effects of retained bound hydroxyl groups on amorphous immiscibility behavior and on the kinetics of phase separation were studied in glasses containing from 10 to 19 percent sodium oxide preparaed by the gel process. Differences in behavior as functions of preliminary thermal treatment of the gel precursor and of melting conditions were studied, employing IR spectroscopy, SAXS and WAXD to monitor the variation in glass microstructure. Both the initial gel treatment and the OH concentration in the prepared glasses were found to affect the immiscibility temperatures, and the magnitude of the maximum temperature increase was also a function of the sodium oxide concentration. It is suggested that the variation in thermodynamic behavior may be caused by the structural arrangement attained by the OH groups during the gel condensation process, which in turn affects the extent of hydrogen bonding to nonbridging oxygen ions.
A survey is presented of the available information on the flare process contained in optical observations. It is shown that the flare process is always associated with filaments and with the simplification of existing magnetic connections. The flare process also arises from the emergence and expansion of new flux. The optical flare can be divided into the impulsive phase, in which multiple flashes along the neutral line are exhibited, and the thermal phase, in which two-ribbon expansion is present. It is shown that the impulsive phase resembles tearing mode phenomena. Very high densities in these phenomena are required by the appearance of loops in emission. Several unanswered questions relating to the flare process are examined, including the ratios of the hydrogen lines, the excitation of He II 4686, and the relation of the vertical to the horizontal structures.
The identification of electrostatic modes in the ionospheric and magnetospheric plasma is a difficult process. Some success has been achieved with electrostatic hydrogen cyclotron waves where Doppler broadening is insignificant and with zero-frequency turbulence where the spectrum is entirely Doppler shifted. However, it is not yet possible to identify specific modes in regions of transverse ion acceleration. If the modes are assumed to exist, some limits can be placed on their electric field amplitudes. An experimental technique to measure wavelength directly, thereby circumventing problems created by Doppler shifting, is reviewed.
Rate constants have been obtained for CH(X 2Pi) radical reactions with cyclopropane, cyclopentane, and cyclohexane in order to establish the rate of CH insertion into secondary C-H bonds in alkanes. Data indicate that there is no measurable dependence on photolysis laser energy. The reactions all exhibited rate constants that decrease with increasing temperature. It is suggested that a possible set of pathways for the cycloalkane reactions is a ring-opening process where the excited adduct decomposes to a hydrogen atom and a diene.
The production and destruction processes for molecules in very fast protostellar winds are analyzed and modeled with a one-dimensional chemical kinetics code. Radial density and temperature distributions suggested by protostellar theory are explored as are a range of mass-loss rates. The efficiency of in situ formation of heavy molecules is found to be high if the wind temperature falls sufficiently rapidly, as indicated by theory. The degree of molecular conversion is a strong function of the mass-loss rate and of density gradients associated with the acceleration and collimation of the wind. Even in cases where essentially all of the heavy atoms are processed into molecules, a significant fraction of atomic hydrogen remains so that hghly molecular, protostellar winds are able to emit the 21-cm line. Although CO has a substantial abundance in most models relevant to very young protostars, high abundances of other molecules such as SiO and H2O signify more complete association characteristic of winds containing regions of very high density. Although the models apply only to regions close to the protostar, they are in qualitative accord with recent observations at much larger distances of both atomic and molecular emission from extremely high-velocity flow.
The observational determination of the extent, escape rate, and composition of Pluto's upper atmosphere is presently approached via calculations of the rates of production and hydrodynamic outflow of atomic H generated by methane photodissociation. Observations have been conducted with the IUE in order to detect atomic H's Lyman-alpha emission in the conjectured cloud; these results are used to derive cloud-property upper limits as a function of the extent of the cloud. It is concluded that the extent and density of the hydrogen atmosphere is more dependent on the escape process than on the atmospheric fraction of methane.
We have investigated the termolecular reaction involving concerted hydrogen exchange between three HF molecules, with particular emphasis on the effects of correlation at the various stationary points along the reaction. Using an extended basis, we have located the geometries of the stable hydrogen-bonded trimer, which is of C(sub 3h) symmetry, and the transition state for hydrogen exchange, which is of D(sub 3h) symmetry. The energies of the exchange reation were then evaluated at the correlated level, using a large atomic natural orbital basis and correlating all valence electrons. Several correlation treatments were used, namely, configration interaction with single and double excitations, coupled-pair functional, and coupled-cluster methods. We are thus able to measure the effect of accounting for size-extensivity. Zero-point corrections to the correlated level energetics were determined using analytic second derivative techniques at the SCF level. Our best calculations, which include the effects of connected triple excitations in the coupled-cluster procedure, indicate that the trimer is bound by 9 +/- 1 kcal/mol relative to three separate monomers, in excellent agreement with previous estimates. The barrier to concerted hydrogen exchange is 15 kcal/mol above the trimer, or only 4.7 kcal/mol above three separated monomers. Thus the barrier to hydrogen exchange between HF molecules via this termolecular process is very low.
It is found that in multicomponent plasmas subjected to Alfven or fast magnetosonic waves, such as are observed in regions of the outer plasmasphere and ring current-plasmapause overlap, lower hybrid oscillations are generated. The addition of a minor heavy ion component to a proton-electron plasma significantly lowers the low-frequency electric wave amplitude needed for lower hybrid wave excitation. It is found that the lower hybrid wave energy density level is determined by the nonlinear process of induced scattering by ions and electrons; hydrogen ions in the region of resonant velocities are accelerated; and nonresonant particles are weakly heated due to the induced scattering. For a given example, the light resonant ions have an energy gain factor of 20, leading to the development of a high-energy tail in the H(+) distribution function due to low-frequency waves.
It is widely held that there was a phosphate compound in prebiotic chemistry that played the role of adenosine triphosphate and that the first living organisms had ribose-phosphate in the backbone of their genetic material. However, there are no known efficient prebiotic synthesis of high-energy phosphates or phosphate esters. We review the occurrence of phosphates in nature, the efficiency of the volcanic synthesis of P4O10, the efficiency of polyphosphate synthesis by heating phosphate minerals under geological conditions, and the use of high-energy organic compounds such as cyanamide or hydrogen cyanide. These are shown to be inefficient processes especially when the hydrolysis of the polyphosphates is taken into account. For example, if a whole atmosphere of methane or carbon monoxide were converted to cyanide which somehow synthesized polyphosphates quantitatively, the polyphosphate concentration in the ocean would still have been insignificant. We also attempted to find more efficient high-energy polymerizing agents by spark discharge syntheses, but without success. There may still be undiscovered robust prebiotic syntheses of polyphosphates, or mechanisms for concentrating them, but we conclude that phosphate esters may not have been constituents of the first genetic material. Phosphoanhydrides are also unlikely as prebiotic energy sources.
The atmospheres of the terrestrial planets and satellites are generally quite thin, much thinner than might be expected given their relatively high abundances of geochemical volatiles and popular estimates of the available mass of volatile-rich impactors. In some cases a specific deficiency (e.g., water on Venus) implies a specific loss process (a runaway greenhouse effect that promoted irreversible hydrogen escape; same planet). But more generally the absence of atmophiles is broadbased and so argues for broad-based volatile loss. This talk will address the hypothesis that extant planetary atmospheres represent the small residue left between relatively large rates of supply and escape.
This paper will present technologies and concepts for novel aeropropulsion systems. These technologies will enhance the safety of operations, reduce life cycle costs, and contribute to reduced costs of air travel and access to space. One of the goals of the NASA program is to reduce the carbon-dioxide emissions of aircraft engines. Engine concepts that use highly efficient fuel cell/electric drive technologies in hydrogen-fueled engines will be presented in the proposed paper. Carbon-dioxide emissions will be eliminated by replacing hydrocarbon fuel with hydrogen, and reduce NOx emissions through better combustion process control. A revolutionary exoskeletal engine concept, in which the engine drum is rotated, will be shown. This concept has the potential to allow a propulsion system that can be used for subsonic through hypersonic flight. Dual fan concepts that have ultra-high bypass ratios, low noise, and low drag will be presented. Flow-controlled turbofans and control-configured turbofans also will be discussed. To increase efficiency, a system of microengines distributed along lifting surfaces and on the fuselage is being investigated. This concept will be presented in the paper. Small propulsion systems for affordable, safe personal transportation vehicles will be discussed. These low-oil/oilless systems use technologies that enable significant cost and weight reductions. Pulse detonation engine-based hybrid-cycle and combined-cycle propulsion systems for aviation and space access will be presented.
The atmospheres of the terrestrial planets and satellites are generally quite thin, much thinner than might be expected given their relatively high abundances of geochemical volatiles and popular estimates of the available mass of volatile-rich impactors. In some cases a specific deficiency (e.g., water on Venus) implies a specific loss process (a runaway greenhouse effect that promoted irreversible hydrogen escape; same planet). But more generally the absence of atmophiles is broad-based and so argues for broad-based volatile loss. This talk will address the hypothesis that extant planetary atmospheres represent the small residue left between relatively large rates of supply and escape.
During normal and pathological conditions, endothelial cells (ECs) are subjected to locally generated reactive oxygen species, produced by themselves or by other vessel wall cells. In excess these molecules cause oxidative injury to the cell but at moderate levels they might modulate intracellular signalling pathways. We have investigated the effect of oxidative stress on the palmitoylation and trafficking of caveolin-1 in bovine aortic ECs. Exogenous H2O2 did not alter the intracellular localization of caveolin-1 in ECs. However, metabolic labelling experiments showed that H2O2 inhibited the trafficking of newly synthesized caveolin-1 to membrane raft domains. Several mechanisms potentially responsible for this inhibition were examined. Impairment of caveolin-1 synthesis by H2O2 was not responsible for diminished trafficking. Similarly, the inhibition was independent of H2O2-induced caveolin-1 phosphorylation as shown by the markedly different concentration dependences. We tested the effect of H2O2 on palmitoylation of caveolin-1 by the incorporation of [3H]palmitic acid. Exposure of ECs to H2O2 markedly inhibited the palmitoylation of caveolin-1. Comparable inhibition was observed after treatment of cells with H2O2 delivered either as a bolus or by continuous delivery with glucose and glucose oxidase. Kinetic studies showed that H2O2 did not alter the rate of caveolin-1 depalmitoylation but instead decreased the 'on-rate' of palmitoylation. Together these results show for the first time the modulation of protein palmitoylation by oxidative stress, and suggest a cellular mechanism by which stress might influence caveolin-1-dependent cell activities such as the concentration of signalling proteins and cholesterol trafficking.
In Titan s atmosphere composed of N2 and CH4, irradiations of both solar ultraviolet light and charged particles induce active chemical reactions. In the processes of these reactions, a large amount of hydrogen (H) atoms are expected to be formed by dissociation of CH4 and other hydrocarbons [e.g., 1, 2]. Theoretical models suggest that these active H atoms need to be converted to stable hydrogen molecules (H2) efficiently to maintain unsaturated hydrocarbons and organic haze in Titan s atmosphere [e.g., 1]. Furthermore, molecular hydrogen is an important greenhouse effect gas in Titan s atmosphere, and small variation in its abundance strongly affects Titan s surface temperature [3]. Thus, the formation of H2 molecules from H atoms is a key reaction for both the atmospheric chemistry and the surface environment of Titan. Although several numerical calculations have been conducted to investigate the atmospheric chemistry of Titan with hypothesized recombination reactions of H atoms, such as catalytic scheme of C4H2 [e.g., 1, 2], it is still unclear what chemical reaction is responsible for the conversion of H atoms to H2 molecules in Titan s atmosphere.