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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 1,135 records · Page 63
All sourcesNASA NTRSDOE OSTI
NASA NTRS1978

Rate constant for the fraction of atomic chlorine with formaldehyde from 200 to 500K

A flash photolysis - resonance fluorescence technique was used to measure rate constant. The results were independent of substantial variations in H2CO, total pressure (Ar), and flash intensity (i.e., initial Cl). The rate constant was shown to be invariant with temperature, the best representation for this temperature range being K = (7.48 + or - 0.50) x 10 to the minus 11 power cu cm molecule-1 s-1 where the error is one standard deviation. The rate constant is theoretically discussed and the potential importance of the reaction in stratospheric chemistry is considered.

Michael, J. V.↗
NASA NTRS1979

The communications industry's requirements and interests

Of interest to the communications industry are the amplitude, waveshape, duration and frequency of lightning-originated voltage surges and transients on the communications network, including the distribution system and AC power supply circuits. The cloud-to-ground lightning discharge and its characteristics are thought to be most meaningful. Of specific interest are peak current, waveshape, number of flashes, strokes per flash, and zone of influence. Accurate and meaningful lightning data at the local level (telephone district office) is necessary for a decision on the appropriate protection level. In addition to lightning, the protection engineer must consider other factors such as: AC induction, switching surges, ground potential rise, soil resistivity, bonding and grounding techniques, shielding and isolation, and exposure of the telephone loop.

Wanaselja, O.↗
NASA NTRS1979

Rate constant for the reaction of atomic chlorine with formaldehyde from 200 to 500 K

The absolute rate constant for the reaction of atomic chlorine with formaldehyde has been measured from 200 to 500 K using the flash photolysis-resonance fluorescence technique. The results were independent of substantial variations in (H2CO), total pressure (Ar), and flash intensity (i.e., initial (Cl)). The rate constant was shown to be invariant with temperature, the best representation for this temperature range being k-sub-1 = (7.48 + or - 0.50) times 10 to the -11 cu cm/molecule sec, where the error is one standard deviation. This result is compared with the only previous determination of k-sub-1, which was a relative value obtained at 298 K. The rate constant is theoretically discussed, and the potential importance of the reaction in stratospheric chemistry is considered.

Michael, J. V.↗
NASA NTRS1979

Simmer-enhanced flashlamp-pumped dye laser

It has been demonstrated experimentally that by enhancing the simmer current in the flash lamps before the energy discharge, the lamp inductance is reduced and the dye laser efficiency is thus remarkably improved. This technique has advantages over the prepulsing technique for conditioning flash lamps; the electronic circuit for the simmer enhancement is simple, inexpensive and reliable, and accurate timing is not required. Furthermore, the simmer enhancement consumes much less power, thus minimizing the attendant thermal effects and improving overall laser efficiency.

Yee, T. K.↗
NASA NTRS1978

Measurement of the Li/B abundance ratio above 650 MeV/nucleon

A balloon-borne cosmic-ray telescope containing 4 Cerenkov counters and a neon flash tube hodoscope was flown from Sioux City, Iowa in September 1974. The data have been reanalyzed, using information of flashed tubes to reject events due to proton and He interactions. The new event selection has reduced charge overlap between He and Li to an insignificant level, so that abundance ratios involving Li can now be measured with the instrument. Precise correction factors for events lost by inefficiency of the hodoscope have been derived from flight data; they lead to improved accuracy in measurements of light elements.

Byrnak, B.↗
NASA NTRS1979

Persistent emission from X-ray burst sources and the nature of galactic bulge X-ray sources

Intrinsic persistent emission from galactic bulge X-ray sources and the ratio of the average persistent X-ray luminosity to the time-averaged burst luminosity associated with Type I burst sources are discussed in the light of the thermonuclear flash model of X-ray burst emission. Values of the ratio between average persistent luminosity and time-averaged burst luminosity for a large collection of SAS 3 sources are presented to confirm the predictions of the burst model of thermonuclear flashes in freshly accreted matter on a neutron star. The model also predicts a critical value of the persistent accretion rate, below which bursts can occur. It is suggested that the galactic bulge X-ray sources represent neutron stars undergoing accretion, with burst sources accounting for a subset in which the accretion rate is below the critical value.

Van Paradijs, J.↗
NASA NTRS1979

First results on Jovian lightning

Longitudes and latitudes of 20 Jovian lightning flashes are plotted on the basis of observations of the dark side of Jupiter by an unidentified spacecraft. It is suggested that the mechanisms of lightning generation on Jupiter and earth may be similar, that convective electrification is the most plausible mechanism, and that observations of lightning may be used as a tracer of upwelling in the Jovian circulation. The observation of lightning flashes at high latitudes is shown to be consistent with the concept of convective cloud systems generated by internal heating.

Cook, A. F., II↗
NASA NTRS1980

Rate constant for the reaction of hydroxyl radical with formaldehyde over the temperature range 228-362 K

Absolute rate constants for the reaction OH ? H2CO measured over the temperature range 228-362 K using the flash photolysis-resonance fluorescence technique are given. The results are independent of variations in H2CO concentration, total pressure Ar concentration, and flash intensity (i.e., initial OH concentration). The rate constant is found to be invariant with temperature in this range, the best representation being k sub 1 = (1.05 ? or - 0.11) x 10 to the 11th power cu cm molecule(-1) s(-1) where the error is two standard deviations. This result is compared with previous absolute and relative determinations of k sub 1. The reaction is also discussed from a theoretical point of view.

Stief, L. J.↗
NASA NTRS1980

Rate statistics for radio noise from lightning

Radio frequency noise from lightning was measured at several frequencies in the HF - VHF range at the Kennedy Space Center, Florida. The data were examined to determine flashing rate statistics during periods of strong activity from nearby storms. It was found that the time between flashes is modeled reasonably well by a random variable with a lognormal distribution.

Levine, D. M.↗
NASA NTRS1979

Photochemistry of bromoacetylene - Formation of HBr and quenching of excited Br/4 2P 0 1/2/

The photolysis of bromacetylene is examined by means of vacuum ultraviolet flash photolysis-kinetic spectroscopy, with attention given to the production of Br atoms in the 2P 0 3/2 and 2P 0 1/2 states, the production of HBr, and UV absorption attributable to the ethynyl radical. Although Br(2P 0 1/2) and Br(2P 0 3/2) were both directly observed at the shortest delay time after the flash, strongly indicating the presence of the ethynyl radical, transient absorption by C2H was not detected in the range 125 to 180 nm. Quenching rate constants for the decay of the 2P 0 1/2 state of Br, which is observed to form concurrently with the ground state, are derived for quenching by He, CH2Br, CF4, and D2 from the pseudo-first-order decay rates. HBr was observed as a secondary photolysis product, and a model of its formation by the exothermic reaction of ground-state atoms with C2HBR, coupled with the secondary production of Br atoms, is found to agree well with the experiment.

Laufer, A. H.↗
NASA NTRS1979

Pressure and temperature dependence kinetics study of the NO + BrO yielding NO2 + Br reaction - Implications for stratospheric bromine photochemistry

The reactivity of NO with BrO radicals over a wide range of pressure (100-700 torr) and temperature (224-398 K) is investigated using the flash photolysis-ultraviolet absorption technique. The flash photolysis system consists of a high-pressure xenon arc light source, a reaction cell/gas filter/flash lamp combination, and a 216.5 half-meter monochromator/polychromator/spectrography for wavelength selectivity. The details of the reaction and its corresponding Arrhenius expression are identified. The results are compared with previous measurements, and atmospheric implications of the reaction are discussed. The NO + BrO yielding NO2 + Br reaction is shown to be important in controlling the concentration ratios of BrO/Br and BrO/HBr in the stratosphere, but this reaction does not affect the catalytic efficiency of BrOx in ozone destruction.

Watson, R. T.↗
NASA NTRS1980

Three flares with blue continuum, one with a D3 preflare shell

Three flares with short-lived flashes observed with a 65 A wide filter centered on 3835 A are discussed. Observations at other wavelengths indicated it is a 'blue continuum'; the flashes occur in pairs at the ends of flux loops and result from the precipitation of energetic particles. A shell of D3 absorption was observed in one of the flares, considered to be a compressed sheet of dense, hot material that limits the flare until it breaks out as a surge. It is concluded that the blue continuum may be the same as that seen in flare stars.

Zirin, H.↗
NASA NTRS1980

Rate constant for the reaction of hydroxyl radical with formaldehyde over the temperature range 228-362 K

Absolute rate constants for the reaction OH + H2CO have been measured over the temperature range 228-362 K using the flash photolysis-resonance fluorescence technique. The results were independent of variations in forbidden H2CO, total pressure of forbidden Ar and flash intensity (i.e., initial forbidden OH). The rate constant was found to be invariant with temperature in this range, the best representation being k1 = (1.05 + or - 0.11) x 10 to the -11th cu cm/molecule sec where the error is two standard deviations. This result is compared with previous absolute and relative determinations of k1. The reaction is also discussed from a theoretical point of view.

Stief, L. J.↗
NASA NTRS1981

Turbulence in deep radio occultations

The effects of turbulence in the focal region of spherical or weakly oblate refracting bodies on the evolute flashes associated with the crossing of the evolute of the planetary limb by an occulted spacecraft are investigated. The approximate theory of focal evolutes in oblate refractivity fields developed by Eshleman et al. (1979) is combined with a generalized weak scattering scintillation theory that includes the effect of focusing around a curved limb to obtain expressions for the scintillation index and power spectrum. Results are then applied to the radio observations of the crossing of the focal evolute of Jupiter by Voyager 1, in which no flash was detected, and to the effects of the solar coronal plasma on the gravitational lens of the sun.

Haugstad, B. S.↗
NASA NTRS1980

The spectrum of radiation from lightning

A theory is presented for the spectrum of radiation from lightning applicable in the range LF to VHF. This is done by adopting the hypothesis that all events in the flash (e.g., return strokes, K-changes, etc.) can be modelled in terms of a current pulse propagating along a tortuous channel. Using a Fraunhofer approximation for radiation in the far field, a formula for the electric field radiated from an arbitrary event is obtained, and then this result is summed over all events to obtain an expression for the spectrum of the composite flash. The result predicts a spectral decrease as the inverse of frequency (1/v) in agreement with data.

Le Vine, D. M.↗
NASA NTRS1982

Lightning to the ionosphere

It is pointed out that most lightning discharges take place within clouds or between clouds and the ground. There are a few reports, however, of a much rarer form of lightning that has been observed to come out of the top of the thunderstorm cloud and extend vertically for some distance into the clear air above it. A description is presented of the observations of such an incident made by a NASA pilot. The incident occurred when the pilot was flying a T-38 jet aircraft at an altitude of about 40,000 feet over Amarillo in Texas. The pilot found himself behind an extremely fast-moving very large cold front. A large number of lightning flashes could be seen. While most of the lightning flashes were typical, approximately every 50th or 100th discharge would go from the top of a cloud vertically upwards through the clear air towards the ionosphere. Explanations for these observations are discussed.

Vaughan, O. H., Jr.↗
NASA NTRS1982

Lightning attachment patterns and flight conditions for storm hazards, 1980

As part of the NASA Langley Research Center Storm Hazards Program, 69 thunderstorm pentrations were made in 1980 with an F-106B airplane in order to record direct strike lightning data and the associated flight conditions. Ground based weather radar measurements in conjunction with these penetrations were made by NOAA National Severe Storms Laboratory in Oklahoma and by NASA Wallops Flight Center in Virginia. In 1980, the airplane received 10 direct lightning strikes; in addition, lightning transient data were recorded from 6 nearby flashes. Following each flight, the airplane was thoroughly inspected for evidence of lightning attachment, and the individual lightning attachment points were plotted on isometric projections of the airplane to identify swept flash patterns. This report presents pilot descriptions of the direct strikes to the airplane, shows the strike attachment patterns that were found, and discusses the implications of the patterns with respect to aircraft protection design. The flight conditions are also included. Finally, the lightning strike scenarios for three U.S. Air Force F-106A airplanes which were struck during routine operations are given in the appendix to this paper.

Fisher, B. D.↗
NASA NTRS1981

A combined visible and IR technique for the estimation of rainfall amounts from GOES data

The use of visible and infrared techniques for estimating precipitation for flash flood, hydrological, and agricultural applications is discussed. Satellite derived rainfall estimates supplement other data or are the only data available. The Scofield/Oliver convective rainfall technique is used for analyzing a half hour period of heavy rainfall during a Chicago flash flood event. The results of a real time hydrological application of the Scofield/Oliver technique for the Hurricane Allen event are also presented. Visible and IR techniques for agricultural applications are also discussed.

Austin, G. L.↗