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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 523 records · Page 29
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NASA NTRS1972

The excitation of O2 in auroras.

Newly measured electron impact cross sections for excitation of the a super 1 Delta sub g and b super 1 Sigma (plus) sub g electronic states of O2 have been employed to predict the absolute volume emission rates from these states under auroral conditions. A secondary electron flux typical of an IBC II nighttime aurora was used, and the most important quenching processes were included in the calculations. The new excitation cross sections for the a super 1 Delta sub g and b super 1 Sigma (plus) sub g states are more than an order of magnitude larger than previous estimates and lead to correspondingly greater intensities in the atmospheric and IR atmospheric band systems. The calculated intensity ratios of the volume emission rates of 7621 A and 1.27 micron to that for 3914 A are smaller than those obtained from aircraft observations and recent rocket experiments.

Cartwright, D. C.↗
NASA NTRS1972

The IR emission spectrum of N2 excited under auroral conditions.

Recently determined experimental and theoretical cross sections for electron impact excitation of six triplet states of N2 (A, B, W, C, E, D) have been utilized to predict the absolute IR volume emission rates from N2 under nighttime auroral conditions. Secondary electron fluxes appropriate to an IBC II normal aurora were used in the calculations. The cascade contributions coupling the various electronic states were included as well as the most important quenching processes. The results indicate that the B yields reversibly A and W yields reversibly B cascade processes, which are important in the population of the A, B, and W states, produce appreciable radiation in the 1- to 5-micron wavelength region.

Cartwright, D. C.↗
NASA NTRS1972

Supersonic electrical-discharge copper vapor laser.

A copper vapor laser, utilizing a pulsed discharge transverse to a supersonic flow of copper vapor, argon, and helium and oscillating at 5106 and 5782 A, has been built and tested. Laser energy densities per pulse of 2.5 microjoules per cu cm have been achieved to date. Laser pulse widths of up to 185 nsec have been obtained with delay times after initiation of the current pulse of 220 to 250 nsec. Both the delay time and pulse width are in good agreement with theoretical predictions. Quenching of the laser pulse is shown to be due to a rapid increase in the rate of equilibration of the lasing levels by electron collisions, and to a decrease in the differential pumping of the lasing levels from the ground state because of a decay in the electron temperature.

Russell, G. R.↗
NASA NTRS1973

Effects of contaminants in CO2 lasers.

A theoretical model which includes the effects of contaminants is developed for the high flow electric discharge CO2-N2-He laser. The model couples the excitation and relaxation processes, CO2 dissociation, and negative ion formation with the flow processes. An analysis of the effects of CO, O2, NO, and N2O impurities on the average small signal gain is presented. CO decreases the gain by collisional depopulation of the upper laser level, and O2, NO, and N2O reduce the gain by decreasing the electron density by forming stable negative ions. In particular, N2O exhibits a strong quenching effect because of its large dissociation cross section for the formation of O(-).

Smith, N. S.↗
NASA NTRS1972

Residual conductivity in unannealed amorphous germanium.

An enhanced residual conductivity which persists long after cessation of illumination has been observed in amorphous germanium at 77 K. The effect may be thermally quenched by heating to 120 K, returning the sample to its initial condition.

Burke, T. J.↗
NASA NTRS1973

The solubility of hydrogen in rhodium, ruthenium, iridium and nickel.

The temperature variation of the solubility of hydrogen in rhodium, ruthenium, iridium, and nickel in equilibrium with H2 gas at 1 atm pressure has been measured by a technique involving saturating the solvent metal with hydrogen, quenching, and analyzing in resultant solid solutions. The solubilities determined are small (atom fraction of H is in the range from 0.0005 to 0.00001, and the results are consistent with the simple quasi-regular model for dilute interstitial solid solutions. The relative partial enthalpy and excess entropy of the dissolved hydrogen atoms have been calculated from the solubility data and compared with well-known correlations between these quantities.

Mclellan, R. B.↗
NASA NTRS1973

Photometer for detection of sodium day airglow.

Description of a photometer for daytime ground-based measurements of sodium airglow emission. The photometer described can be characterized by the following principal features: (1) a narrow (4.5-A) interference filter for initial discrimination; (2) cooled photomultiplier detector to reduce noise from dark current fluctuations and chopping to eliminate the average dark current; (3) a sodium vapor resonance cell to provide an effective bandpass comparable to the Doppler line width; (4) separate detection of all light transmitted by the interference filter to evaluate the Rayleigh and Mie components within the Doppler width of the resonance cell; and (5) temperature quenching of the resonance cell to evaluate and account for instrumental imperfections.

Mcmahon, D. J.↗
NASA NTRS1973

Time-of-flight measurements of metastable state lifetimes.

A time-of-flight method for measurement of the lifetime of metastable molecules is described. The method is applicable to a molecular beam that has molecules in several different metastable excited states. As compared to methods used previously, the method has the advantages that it does not require selective excitation or quenching of the different states; moreover, it does not require a determination of the relative populations or velocity distributions of molecules in the excited states.

Kaslow, D. E.↗
NASA NTRS1973

On the reactions of N2 with O.

An application of the rigorous curve crossing theory reported by Delos and Thorson (1972) is presented and the current level of understanding regarding the reactions involving a nitrogen molecule and an oxygen atom is discussed. A theoretical analysis of these reactions had been conducted by Fisher and Bauer (1972). The characteristics of the unimolecular decomposition of nitrous oxide are considered together with the quenching of O(1 D) by molecular nitrogen and the vibrational relaxation of molecular nitrogen.

Delos, J. B.↗
NASA NTRS1974

Laser measurements of the radiative lifetime of the B state of CN

A turnable dye laser was used to measure the radiative lifetime of the individual rotational levels of the B2 Sigma (+) state of CN. The radiative lifetime of the unperturbed rotational levels is 65.6 plus or minus 1.0 nsec. A longer radiative lifetime of 72 plus or minus 1 nsec is observed for the Kaon prime = 4 level of the B state. The measured values of the perturbed and unperturbed levels support the longer lifetimes for the A2 meson pion state of CN. The quenching cross section of the B2 Sigma state of CN is 41 plus or minus 20 Angstroms squared and is independent of the rotational energy of the B state.

Jackson, W. M.↗
NASA NTRS1974

Study of recrystallization and devitrification of lunar glass

The technique of differential thermal analysis (DTA) was applied to the study of the Apollo 17 orange soil (74220,63) and the Apollo 16 glass coated anorthite (64455,21). These glasses show accentuated exotherms of strain relief in the annealing range which is indicative of rapid cooling. These are amenable to interpretation by comparison to the known history of synthetic glasses. Synthetic glasses were prepared whose similarity in behavior between the lunar glasses and their synthetic analogs is striking. Approximate rates of cooling of the lunar glasses were determined from comparative DTA of lunar and synthetic glasses and from the determination of the relation of strain relief in the annealing range to quench rate. At higher temperatures the glasses show exotherms of crystallization. The crystallization products associated with the exothermic reactions have been identified by X-ray diffraction and the surface morphologies developed by strain relief and crystallization have been characterized with scanning electron microscopy.

Ulrich, D. R.↗
NASA NTRS1974

Apparatus for inserting and removing specimens from high temperature vacuum furnaces

The apparatus comprises a high speed gate valve for isolating the interior of the furnance from an air lock chamber on the opposite side of the gate valve. The air lock chamber is provided with valve ports connected to a vacuum source, a source of inert quenching gas, and the atmosphere, respectively. Attached to the end of the air lock chamber away from the furnace is a cylindrical tube having disposed within it a rod carrying specimen pan at the end towards the furnace and having mounted at its top end an annular magnet having a diameter slightly less than the interior diameter of the tube. The top end of the tube is closed by a removeable cap. Encircling the tube in the vicinity of the magnet is a carbon steel ring which when axially moved along the tube causes the magnet to follow it and thereby controls the position of the rod and specimen pan within the tube.

Whitehead, C. W.↗
NASA NTRS1973

Synthesis of mechanisms with flexible centrifugal-inertial connections according to fixed dynamic characteristics

The criteria for the selection of dynamic characteristics of flexible centrifugal-inertial couplings are discussed. The basic properties considered are: (1) vibration isolation, (2) vibration quenching, and (3) transmission properties. It is stated that the most promising couplings are those with a nonlinear relation between the magnitude of the torque transmitted and the magnitude of deformation of the coupling. The efforts of various investigators are briefly analyzed. Mathematical models are developed to show the relationships of the parameters involved.

Ragulskis, K. M.↗
NASA NTRS1973

Amorphous magnetism in f.c.c. Vicalloy II

The results of magnetization and Mossbauer experiments are described which give evidence for superparamagnetism in the quenched face-centered-cubic (gamma) phase of the ternary system Fe .34, C .52, V .14 (Vicalloy II). Magnetometer data are given which clearly show that splat-cooled Vicalloy II does not exhibit long-range magnetic order. These data together with the Mossbauer data indicate that short-range magnetic ordering occurs which is temperature-dependent with coalescence of magnetic clusters over a limited temperature range. The model presented reasonably accounts for the observed effects and indicates that this ternary system is superparamagnetic down to 4.2 K.

Cusick, J. P.↗
NASA NTRS1973

The effects of perturbations on the flammability limits

Based on the mechanism of heat losses, the known effects of external disturbances (pressure waves or turbulences) on the flammability limits are explained. This includes the sensitivity of near-limit flames to perturbations and the flame quenching by disturbances. The significance of the unstable solution as the criterion for dynamic extinction is stressed.

T'Ien, J. S.↗
NASA NTRS1974

Origin of the high-temperature fraction of C2 chondrites

The coarse-grained fraction of C2 chondrites is composed mostly of single crystals and aggregates of crystals of Mg-rich olivine and pyroxene. They do not possess compelling textural evidence of being the solidification products of rapidly-quenched molten droplets. Metal inclusions in the silicates contain 3.82-8.88 mole% Ni, 0.16-0.70% Co, 0.17-1.07% Cr, and up to 5.70% P. Thermodynamic calculations show that alloys of these compositions may be condensates from the solar nebula. The implication is that the high-temperature fraction of C2 chondrites consists mostly of high-temperature condensates.

Grossman, L.↗
NASA NTRS1973

Antiphase domains in lunar plagioclase

The paper is a compilation of data on antiphase domains in lunar plagioclase. New observations and reports in the literature are tabulated and discussed. In the pattern which emerges (but is still very incomplete), it appears that b-domains, which except for the An 82 bytownite from the Stillwater complex have only been observed in lunar feldspars, occur in the anorthite range An 80 to 95. Especially in the sodium rich part there seems to be a close relation between an exsolution structure and b-APB's. The c-APB's are found in anorthites An 95 to 100 and for a given An-content they are larger for metamorphic than for volcanic anorthites. Near An 95, c- and b-domains can be observed in the same crystal. The c-domains disappear when heated above 1200 C; they are not affected by heating below 600 C. This implies that calcic anorthite without c-domains must have been rapidly quenched from high temperatures.

Wenk, H.-R.↗
NASA NTRS1974

An investigation of the plastic fracture of AISI 4340 and 18 nickel - 200 grade maraging steels

The mechanisms of plastic fracture (dimpled rupture) in high-purity and commercial 18 Ni, 200 grade maraging steels and quenched and tempered AISI 4340 steels have been studied. Plastic fracture takes place in the maraging alloys through void initiation by fracture of titanium carbo-nitride inclusions and the growth of these voids until impingement results in coalescence and final fracture. The fracture of AISI 4340 steel at a yield strength of 200 ksi occurs by nucleation and subsequent growth of voids formed by fracture of the interface between manganese sulfide inclusions and the matrix. The growth of these inclusion-nucleated voids is interrupted long before coalescence by impingement, by the formation of void sheets which connect neighboring sulfide-nucleated voids.

Cox, T. B.↗