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At least 379 records · Page 21
All sourcesNASA NTRSDOE OSTI
NASA NTRS1972

High energy-resolution studies of electron impact optical excitation functions. I - The second positive system of N2.

The relative emission cross section for the N2 second positive system (0,0) and (1,0) bands excited by electron impact was measured for incident electron energies from threshold to 17 eV. The use of a high energy-resolution electron spectrometer coupled to an optical detection system made it possible to obtain the measurements with an incident electron beam having an energy half width of 50 meV. Calibration of the incident electron energy was provided by observing the scattering resonances in nitrogen and helium. The maximum of the (0,0) and (1,0) bands were found to be at approximately 14.02 and 14.3 eV, respectively. A small structural feature that was pressure-independent appeared only in the (0,0) band emission cross section. Another such feature was pressure-dependent and appeared more strongly in the (1,0) band cross section.

Finn, T. G.↗
NASA NTRS1975

A study of lunar impact crater size-distributions

In view of the discrepancies in published crater frequency data, effects modifying production size distributions of impact craters are discussed. The resulting criteria are applied to the determination of the size distributions of unmodified impact crater populations in selected lunar regions of different ages. The measured cumulative crater frequencies are used to obtain a general calibration size distribution curve by a normalization procedure. Deviations of measured size distributions from the calibration distribution are strongly suggestive of the existence of processes having modified the primary impact crater population.

Neukum, G.↗
NASA NTRS1976

A model study of the impact of emission control strategies on Los Angeles air quality

A generalized cell model is developed for the calculation of city-wide averages of photochemical smog components in Los Angeles. This model takes into account the effects of variations with time and within the city of the source strengths, the wind field, and the mixing depth. The effect of the influx of background pollution from outside the modeled volume is also included. Several control strategies for reducing automobile emissions are then introduced into the model, and their impact on predicted pollutant levels, particularly those of O3, are investigated.

Hameed, S.↗
NASA NTRS1981

UV studies of electron impact excitation of CS2

The first measurements of emission cross sections of CS2 by electron impact over the wavelength interval 110-510 nm are reported. Absolute emission cross sections are obtained at 100 eV for all spectral features observed in this interval. Emission cross sections as a function of electron energy (0-125 eV) are reported for several of the principal electronic transitions.

Ajello, J. M.↗
NASA NTRS1985

Vacuum ultraviolet studies of electron impact of helium Excitation of He n1P0 Rydberg series and ionization-excitation of He(+) nl Rydberg series

The cross sections for the He I 1s2 1S-1snp 1P0 series have been measured using a relative flow method, with the absolute scale fixed by the H Ly-alpha dissociative excitation cross section standard. The results are compared with those obtained using a relative cross section data analysis by modified Born approximation, and good agreement is found. Cross sections for the ionization-excitation of the He II 121.51 nm and He II 164.04 nm transmissions have been measured, and the results strongly suggest that theoretical calculations of the reactions differ fundamentally from physical reality. The failure of the theory to describe experimental results stems from the neglect in the theory of electron correlation effects between the two orbital electrons.

Shemansky, D. E.↗
NASA NTRS1987

Search for, and study of, paleozoic impact ejecta: Progress made during the past year

Nodule-like objects which the author believes to be impact bombs had been found in Middle Ordovician rocks of southeastern Wisconsin and northern Illinois. In northern Illinois, rock fragments containing oolith-like spherules, which the author believes to be solidified impact droplets, and numerous large bubble-holes, had been found at the same stratigraphic level. The discovery of bomb-like nodules in Lower Ordovician rocks of southeastern Wisconsin was reported. Bomb-type nodules associated with droplet-type spherules have been found in Lower Ordovician rocks of central Pennsylvania. These discoveries, in the authors opinion, suffice to show that impact ejecta are widespread in marine sediments of Ordovician age and are likely to be widespread also in marine sediments of other ages. Unfortunately, according to the author, there is little indication so far that this evidence has been accepted as valid by the concerned scientific community.

Read, William F.↗
NASA NTRS1993

A study of the impact of the Space Shuttle environment on faint far-UV geophysical and astronomical phenomena

FAUST is a far ultraviolet (1400-1800 A) photon-counting imaging telescope featuring a wide field of view (7.6 deg) and a high sensitivity to extended emission features. During its flight as part of the ATLAS-1 payload aboard the STS-45 mission in March 1992, 19 deep-space nighttime viewing opportunities were utilized by FAUST. Here we report the observed fluxes and their time and space variations, and identify the signatures of postsunset airglow phenomena and Orbiter Vernier attitude control thruster firing events. We find that the Space Shuttle nighttime environment at 296 km altitude is often sufficiently dark to permit geophysical and astronomical UV observations down to levels on the order of 1000 photons/sq cm sr A sec, or 0.01 Rayleighs/A. We also find evidence for occasional geophysical fluxes of some tens or hundreds of Rayleighs in the upward-looking direction.

Lampton, Michael↗
NASA NTRS1993

A preliminary study of the impact of the ERS 1 C band scatterometer wind data on the European Centre for Medium-Range Weather Forecasts global data assimilation system

A preliminary assessment of the impact of the ERS 1 scatterometer wind data on the current European Centre for Medium-Range Weather Forecasts analysis and forecast system has been carried out. Although the scatterometer data results in changes to the analyses and forecasts, there is no consistent improvement or degradation. Our results are based on comparing analyses and forecasts from assimilation cycles. The two sets of analyses are very similar except for the low level wind fields over the ocean. Impacts on the analyzed wind fields are greater over the southern ocean, where other data are scarce. For the most part the mass field increments are too small to balance the wind increments. The effect of the nonlinear normal mode initialization on the analysis differences is quite small, but we observe that the differences tend to wash out in the subsequent 6-hour forecast. In the Northern Hemisphere, analysis differences are very small, except directly at the scatterometer locations. Forecast comparisons reveal large differences in the Southern Hemisphere after 72 hours. Notable differences in the Northern Hemisphere do not appear until late in the forecast. Overall, however, the Southern Hemisphere impacts are neutral. The experiments described are preliminary in several respects. We expect these data to ultimately prove useful for global data assimilation.

Hoffman, Ross N.↗
NASA NTRS1994

Development of techniques for the in situ observation of OH and HO2 for studies of the impact of high-altitude supersonic aircraft on the stratosphere

This three-year project supported the construction, calibration, and deployment of a new instrument to measure the OH and HO2 radicals on the NASA ER-2 aircraft. The instrument has met and exceeded all of its design goals. The instrumentation represents a true quantum leap in performance over that achieved in previous HO(x) instruments built in our group. Sensitivity for OH was enhanced by over two orders of magnitude as the weight fell from approximately 1500 to less than 200 Kg. Reliability has been very high: HO(x) data are available for all flights during the first operational mission, the Stratospheric Photochemistry, Aerosols, and Dynamics Expedition (SPADE). The results of that experiment have been reported in the scientific literature and at conferences. Additionally, measurements of H2O and O3 were made and have been reported in the scientific literature. The measurements demonstrated the important role that OH and HO2 play in determining the concentration of ozone in the lower stratosphere. During the SPADE, campaign the measurements demonstrated that the catalytic removal is dominated by processes involving the odd-hydrogen and halogen radicals-and extremely important constraint for photochemical models that are being used to assess the potential deleterious effects of super-sonic aircraft effluent on the burden of stratospheric ozone.

Anderson, James G.↗
NASA NTRS1994

Development of techniques for the In Situ observation of OH and HO2 for studies of the impact of high-altitude supersonic aircraft on the stratosphere

This three-year project supported the construction, calibration, and deployment of a new instrument to measure the OH and HO2 radicals on the NASA Er-2 aircraft. The instrument has met and exceeded all of its design goals. The instrumentation represents a true quantum leap in performance over that achieved in previous HO(x) instruments built in our group. Sensitivity of OH was enhanced by over two orders of magnitude as the weight fell from approximately 1500 to less than 200 Kg. Reliability has been very high: HO(x) data are available for all flights during the first operational mission, the Stratospheric Photochemistry, aerosols, and Dynamics Expedition (SPADE). The results of that experiment have been reported in the scientific literature and at conferences. Additionally, measurements of H2O and O3 were made and have been reported in the scientific literature. The measurements demonstrate the important role that OH and HO2 play in determining the concentration of ozone in the lower stratosphere. During the SPADE campaign, the measurements demonstrate that the catalytic removal is dominated by processes involving the odd-hydrogen and halogen radicals-an extremely important constraint for photochemical models that are being used to assess the potential deleterious effects of super-sonic aircraft effluent on the burden of stratospheric ozone.

Anderson, James G.↗