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At least 901 records · Page 50
All sourcesNASA NTRSDOE OSTI
NASA NTRS1974

Analysis of effect of the solubility on gas exchange in nonhomogeneous lungs

A comparison is made of the gas exchange in nonhomogeneous lung models and in homogeneous lung models with the same total blood flow and ventilation. It is shown that the ratio of the rate of gas transfer of the inhomogeneous lung model over the rate of gas transfer of the homogeneous lung model as a function of gas solubility always has the qualitative features for gases with linear dissociation curves. This ratio is 1 for a gas with zero solubility and decreases to a single minimum. It subsequently rises to approach 1 as the solubility tends to infinity. The early portion of the graph of this function is convex, then after a single inflection point it is concave.

Colburn, W. E., Jr.↗
NASA NTRS1974

Primitive control of cellular metabolism

It is pointed out that control substances must have existed from the earliest times in the evolution of life and that the same control mechanisms must exist today. The investigation reported is concerned with the concept that carbon dioxide is a primitive regulator of cell function. The effects of carbon dioxide on cellular materials are examined, taking into account questions of solubilization, dissociation, changes of charge, stabilization, structural changes, wettability, the exclusion of other gases, the activation of compounds, changes in plasticity, and changes in membrane permeability.

Mitz, M. A.↗
NASA NTRS1975

A model of the Venus ionosphere

Results of model calculations of the Venus ionosphere from 120 to 300 km are presented. The chemical scheme and reaction rates used are the same as given by Kumar and Hunten (1974) except that the electron temperature dependence of the dissociative recombination rates is taken into account. Calculations are made for low and high atomic oxygen models in which the O/CO2 ratios are 0.4% and 4% respectively at 140 km, and the results agree well in shape and magnitude with the Mariner 5 and 10 occultation results in the chemically controlled region. Reasonable agreement is obtained at higher altitudes if diffusive equilibrium and high vertical flow velocities (10 km/s) are assumed as upper boundaries for the Mariner 5 and 10 conditions respectively, although solar wind-ionosphere interactions are considered to be the controlling mechanism for the Mariner 10 results.

Nagy, A. F.↗
NASA NTRS1975

Conversion of laser energy to gas kinetic energy

Techniques for the gas phase absorption of laser radiation for conversion to gas kinetic energy are discussed. Absorption by inverse Bremsstrahlung, in which laser energy is converted at a gas kinetic rate in a spectrally continuous process, is briefly described, and absorption by molecular vibrational rotation bands is discussed at length. High pressure absorption is proposed as a means of minimizing gas bleaching and dissociation, the major disadvantages of the molecular absorption process. A band model is presented for predicting the molecular absorption spectra in the high pressure absorption region and is applied to the CO molecule. Use of a rare gas seeded with Fe(CO)5 for converting vibrational modes to translation modes is described.

Caledonia, G. E.↗
NASA NTRS1974

Determination of the rate constant for the reaction O + NO yields N + O2

A shock-tube technique was used to determine the rate constant for the reaction O + NO yields N + O2 in the 2500-4100 K range. Mixtures of NO, N2O, and an inert gas (Ar or Kr) were shock-heated, and the decay of infrared emission from the fundamental vibration-rotation band of NO at 5.3 microns was monitored. The N2O dissociates quickly to provide a source of O atoms for the above reaction. An expression for the rate constant is derived which fits these data and previous data at higher and lower temperatures.

Hanson, R. K.↗
NASA NTRS1975

Evidence for an elemental sulfur component of the clouds from Venus spectrophotometry

The decrease in the reflectivity of Venus in the near-UV can be explained if the clouds contain particles of elemental sulfur in addition to sulfuric acid. The low-resolution McDonald-Pittsburgh spectrum can be fitted by two sulfur-containing, multiple-scattering cloud models: (1) a mixed cloud consisting of one particle of elemental sulfur of radius 10 microns for every 670 particles of sulfuric acid of radius 1 micron, and (2) a layered cloud of optical thickness tau = 1.0 consisting of one-micron particles of sulfuric acid overlying a thick cloud of elemental sulfur particles of radius 3.6 microns. Some of the sulfur is incompletely polymerized. The source of the sulfur is photo-dissociation of COS, although some may also be recycled from the lower atmosphere. The sulfur plays a crucial role in the planetary meteorology of Venus since it is responsible for the bulk of the absorption of solar energy.

Hapke, B.↗
NASA NTRS1976

Formation of the 0.511.-MeV line in solar flares

The gamma-ray line produced at 0.51-MeV was studied and is shown to be the result of either of free annihilation of positrons with electrons or of the decay of positronium by 2-photon emission. Positron annihilation from the bound state of positronium may also proceed by 3-photon emission, resulting in a continuum with energies up to 0.51-MeV. Accurate calculations of the rates of free annihilation and positronium formation in a solar-flare plasma are presented. Estimates of the positronium-formulation rates by charge exchange and the rates of dissociation and quenching are also considered. The temperature and density dependence of the ratio of 3-photon to 2-photon emission was obtained. It is shown that when the ratio of free electrons to neutral atoms in the plasma is approximately unity or greater, the Doppler width of the 0.51-MeV line is a function of the temperature of the annihilation region. For the small ion densities characteristics of the photosphere, the width is predominantly a function of the density.

Crannell, C. J.↗
NASA NTRS1976

Researches on interactions of satellite-speed helium atoms with aluminum and quartz surfaces

Three major areas were experimentally studied: (1) energy transfer in collisions of satellite-speed (700 m/sec) helium atoms with a cleaned satellite-type aluminum surface was investigated using the molecular-beam technique. Spatial and energy distributions of reflected helium atoms were measured and analyzed, (2) The gross accommodation coefficient for a satellite-speed (7000 m/sec) helium beam entering a 2-inch-diameter aluminum spherical cavity was determined by measuring the exit velocity distribution of the leaving helium atoms using a metastable time-of-flight method. Results indicate that the 7000-m/sec satellite-speed helium atoms entering the cavity gain full accommodation with the room-temperature inner surface of the sphere through a large number of collisions before leaving the spherical cavity; and (3) the feasibility of producing a satellite-speed atomic hydrogen beam by arc-heating, for use in studies of interactions of satellite-surfaces with hydrogen atoms under laboratory conditions, was investigated. It was found that a stable arc-heated molecular hydrogen beam can be obtained using the arc-heater, and that a partially dissociated hydrogen beam can be produced. Photographs of laboratory equipment are shown.

Liu, S. M.↗
NASA NTRS1976

Sulfidation of 310 stainless steel at sulfur potentials encountered in coal conversion systems

The sulfidation of SAE 310 stainless steel was carried out in gas mixtures of hydrogen and hydrogen sulfide over a range of sulfur potentials anticipated in advanced coal gasification processes. The kinetics, composition, and morphology of sulfide scale formation were studied at a fixed temperature of 1,065 K over a range of sulfur potentials from .00015 Nm to the -2nd power to 900 Nm to the -2nd power. At all sulfur potentials investigated, the sulfide scales were found to be multilayered. The relative thickness of the individual layers as well as the composition was found to depend on the sulfur potential. The reaction was found to obey the parabolic rate law after an initial transient period. Considerably longer transient periods were found to be due to unsteady state conditions resulting from compositional variations in the spinel layer. The sulfur pressure dependence on the parabolic rate constant was found to best fit the equation K sub p equals const. (P sub S2) to the 1/nth power, where n equals 3.7. The growth of the outer layers was found to be primarily due to the diffusion of metal ions, iron being the predominant species. The inner layer growth was due to the dissociation of the primary product at the alloy scale interface and depended on the activity of chromium.

Rao, D. B.↗
NASA NTRS1976

In situ measurements of the mesosphere and stratosphere

The operation of a subsonic, Gerdien condenser probe for in situ measurements of the mesosphere and stratosphere is presented. The inclusion of a flashing Lyman alpha ultraviolet source provides an artifically produced ionization of particular constituents. Detailed theory of operation is presented and the data results from two flights are shown. A great deal of fine structure in mobility is observed due to the presence of various hydrated positive ions. The effect of the Lyman alpha source in the 35 km region was to dissociate a light hydrate ion rather than produce additional ionization. At the 70 km region, photodissociation of the heaviest ions (probably ice crystals) was also observed.

Crosky, C.↗
NASA NTRS1976

Absolute rate constant determinations for the deactivation of O/1D/ by time resolved decay of O/1D/ yields O/3P/ emission

Absolute rate constants for the deactivation of O(1D) atoms by some atmospheric gases have been determined by observing the time-resolved emission of O(1D) at 630 nm. O(1D) atoms were produced by the dissociation of ozone via repetitive laser pulses at 266 nm. Absolute rate constants for the relaxation of O(1D) at 298 K are reported for N2, O2, CO2, O3, H2, D2, CH4, HCl, NH3, H2O, N2O, and Ne. The results obtained are compared with previous relative and absolute measurements reported in the literature.

Davidson, J. A.↗
NASA NTRS1975

Hydrogen chemistry - Perspective on experiment and theory

A review is presented of the advantages and limitations of various experimental methods for the investigation of the kinetics of hydrogen chemistry, including classic thermal and photochemical methods and the crossed molecular beam method. Special attention is given to the flash photolysis-resonance fluorescence apparatus developed by Braun et al, in which repetitive vacuum UV flashes result in the photolytic generation of the desired species, and to the discharge-flow technique. The use of various theoretical methods for the selection or elimination of kinetic data is considered in a brief discussion of the rate theory of two-body encounters and recombination-dissociation processes in neutral reactions. Recent kinetic studies of a series of OH reactions and of a major loss process for odd H in the stratosphere are summarized.

Kaufman, F.↗
NASA NTRS1975

OGO-6 observations of 5577 A

A brief review is given of the data obtained by the horizon-scanning 5577-A airglow photometer flown aboard OGO 6. Data are presented which show the contributions to the 5577-A emission from the F-1 region and the Chapman airglow layer. Emission rates are calculated for both regions on the basis of the dissociative-recombination and Chapman reactions, and the atomic oxygen density and downward flux are inferred from the emission rates and several assumptions concerning the temperature dependence of the rate constants. Latitude variations in the emission rates are discussed along with variations in the altitude of the 5577-A airglow. It is shown that there is a large semiannual variation in the average effective transport properties of the lower thermosphere, that the atomic oxygen profiles near 110 km suggest a maximum in eddy diffusion at about that altitude, and that systematic variations in the altitude of the atomic oxygen maximum probably do not exceed 2 km.

Donahue, T. M.↗
NASA NTRS1976

Metastable 2D atomic nitrogen in the mid-latitude nocturnal ionosphere

The only source at night at midlatitudes of N(2D) in the F region is the dissociative recombination of the positive NO ion, and the only important sinks are quenching by atomic oxygen and electrons. Ground-based measurements of the 5200 angstrom emission line resulting from the transition from N(2D) to N(4S) combined with satellite observations of neutral and ion densities and temperatures and the shape of the 5200 angstrom profile are used to relate the rate of quenching by atomic oxygen and the efficiency of production of N(2D) to the rate of quenching by electrons. A rate of quenching by atomic oxygen of 1.5-2.5 x 10 to the minus 12th cu cm/s and an efficiency of (0.8-1.0) plus or minus 30% for the production of N(2D) are obtained.

Torr, M. R.↗
NASA NTRS1976

Microwave measurement of mesospheric carbon monoxide

Ground-based observations of atmospheric absorption of solar radiation at a wavelength of 2.6 millimeters has provided the first measurement of mesospheric carbon monoxide. The measurement agrees with photochemical predictions of a carbon monoxide source in the lower thermosphere due to dissociation of carbon dioxide by solar radiation, and has implications for the magnitude of vertical transport in the mesosphere.

Waters, J. W.↗
NASA NTRS1976

Laser engines operating by resonance absorption

Basic tutorial article on the thermodynamic feasibility of laser engines at the present state of the art. Three main options are considered: (1) laser power applied externally to a heat reservoir (boiler approach); (2) internal heating of working fluid by resonance absorption; and (3) direct conversion of selective excitation into work. Only (2) is considered practically feasible at present. Basic concepts and variants, efficiency relations, upper temperature limits of laser engines, selection of absorbing gases, engine walls, bleaching, thermodynamic cycles of optimized laser engines, laser-powered turbines, laser heat pumps are discussed. Photon engines and laser dissociation engines are also considered.

Garbuny, M.↗
NASA NTRS1976

Absolute measurement of the photoionization cross section of atomic hydrogen with a shock tube for the extreme ultraviolet

The paper reports an experiment which is part of a program to measure the absolute values of the atomic photoionization cross sections of astrophysically abundant elements, particularly in stars and planetary atmospheres. An aerodynamic pressure-driven shock tube constructed from stainless steel with a quadratic cross section was used to measure the photoionization cross section of H I at 19 wavelength points from 910 to 609 A with experimental uncertainties between 7 and 20%. The shock tube was used to produce fully dissociated hydrogen and neon mixtures for the photoabsorption measurements.

Palenius, H. P.↗
NASA NTRS1976

On disequilibrated rotational distributions of CN/X/ produced in the photolysis of ClCN

The rotational-vibrational product state distributions of the CN(X 2Sigma (+)) radicals which are produced in photolysis at a wavelength of about 160 nm were monitored by laser-induced fluorescence detection. A nitrogen laser pumped dye laser was used to excite the violet band fluorescence of CN. The number of collisions the radicals undergo between formation and detection was controlled by the total pressure and the time delay between the flash lamp pulse and the laser pulse. An argon flash lamp with a Suprasil transmission window was used to dissociate the ClCN. Disequilibrated rotational distributions of CN(X) are displayed, the spectrum showing that the nu = 0 and 1 levels are rotationally hot. The rotational distributions of CN(X 2 Sigma (+), nu = 0) are shown as a function of collision number. At a pressure of 0.070 torr and a delay of 2.0 microsecs, the distribution shows clearly that the excited rotational levels peak near N equals 66-70.

Sabety-Dzvonik, M.↗