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At least 235 records · Page 13
All sourcesNASA NTRSDOE OSTI
NASA NTRS2000

Rapid Changes in Mercury's Sodium Exosphere

Sodium in the atmosphere of Mercury can be detected by sunlight scattered in the D1 and D2 resonance lines. Images of the sodium emission show that the sodium density changes from day to day and is often concentrated in regions at high or mid latitudes. Drew Potter (NASA/JSC) and Tom Morgan (SWRI) suggested that sputtering by magnetospheric particles was the origin of the sodium. A problem with this is that the magnetic field of Mercury is strong enough that it is believed to shield the surface from solar particles much of the time, although particle precipitation at the magnetospheric cusps could deposit particles to the surface at high latitudes. Ann Sprague (UA/LPL) noted that the "spots" of sodium emission tended to coincide with major geologic features, such as the Caloris Basin. She proposed that the sodium is released from sodiumrich surface rocks that are associated with these features; however, some spots have appeared where there are no obvious geologic features. Some of the difficulty in ascribing a source for the sodium arises from the effect of terrestrial atmospheric blurring of the image. It is hard to tell exactly where the sodium emission originates after the atmosphere has blurred the image. Potter, Killen (SWRI), and Morgan recently developed a technique for correcting sodium images for atmospheric blurring, using images made with a large-area image slicer. They applied this technique to a series of Mercury sodium observations made in November, 1997 at the McMath-Pierce Solar Telescope. Their technique for producing images from the spectroscopic data provides images of both the sodium emission and of the sunlight reflected from the surface.

Potter, Drew↗
NASA NTRS2000

Non-Intrusive, Laser-Based Imaging of Jet-A Fuel Injection and Combustion Species in High Pressure, Subsonic Flows

The emphasis of combustion research efforts at NASA Glenn Research Center (GRC) is on collaborating with industry to design and test gas-turbine combustors and subcomponents for both sub- and supersonic applications. These next-generation aircraft combustors are required to meet strict international environmental restrictions limiting emissions. To meet these goals, innovative combustor concepts require operation at temperatures and pressures far exceeding those of current designs. New and innovative diagnostic tools are necessary to characterize these flow streams since existing methods are inadequate. The combustion diagnostics team at GRC has implemented a suite of highly sensitive, nonintrusive optical imaging methods to diagnose the flowfields of these new engine concepts. By using optically accessible combustors and flame-tubes, imaging of fuel and intermediate combustion species via planar laser-induced fluorescence (PLIF) at realistic pressures are now possible. Direct imaging of the fuel injection process through both planar Mie scattering and PLIF methods is also performed. Additionally, a novel combination of planar fuel fluorescence imaging and computational analysis allows a 3-D examination of the flowfield, resulting in spatially and temporally resolved fuel/air volume distribution maps. These maps provide detailed insight into the fuel injection process at actual conditions, thereby greatly enhancing the evaluation of fuel injector performance and other combustion phenomena. Stable species such as CO2, O2, N2, H2O, and hydrocarbons are also investigated by a newly demonstrated 1-D, spontaneous Raman spectroscopic method. This visible wavelength Raman technique allows the acquisition of quantitative, stable species concentration measurements from the flow.

Locke, R. J.↗
NASA NTRS2001

Non-Intrusive, Laser-Based Imaging of Jet-A Fuel Injection and Combustion Species in High Pressure, Subsonic Flows

The emphasis of combustion research efforts at NASA Glenn Research Center (GRC) is on collaborating with industry to design and test gas-turbine combustors and subcomponents for both sub- and supersonic applications. These next-generation aircraft combustors are required to meet strict international environmental restrictions limiting emissions. To meet these goals, innovative combustor concepts require operation at temperatures and pressures far exceeding those of cur-rent designs. New and innovative diagnostic tools are necessary to characterize these flow streams since existing methods are inadequate. The combustion diagnostics team at GRC has implemented a suite of highly sensitive, nonintrusive optical imaging methods to diagnose the flowfields of these new engine concepts. By using optically accessible combustors and flametubes, imaging of fuel and intermediate combustion species via planar laser-induced fluorescence (PLIF) at realistic pressures are now possible. Direct imaging of the fuel injection process through both planar Mie scattering and PLIF methods is also performed. Additionally, a novel combination of planar fuel fluorescence imaging and computational analysis allows a 3-D examination of the flowfield, resulting in spatially and temporally resolved fuel/air volume distribution maps. These maps provide detailed insight into the fuel injection process at actual conditions, thereby greatly enhancing the evaluation of fuel injector performance and other combustion phenomena. Stable species such as CO2, O2, N2O. and hydrocarbons are also investigated by a newly demonstrated 1-D, spontaneous Raman spectroscopic method. This visible wavelength Raman technique allows the acquisition of quantitative. stable species concentration measurements from the flow.

Locke, Randy J.↗
NASA NTRS2004

Scanning Tunneling Optical Resonance Microscopy Developed

The ability to determine the in situ optoelectronic properties of semiconductor materials has become especially important as the size of device architectures has decreased and the development of complex microsystems has increased. Scanning Tunneling Optical Resonance Microscopy, or STORM, can interrogate the optical bandgap as a function of its position within a semiconductor micro-structure. This technique uses a tunable solidstate titanium-sapphire laser whose output is "chopped" using a spatial light modulator and is coupled by a fiber-optic connector to a scanning tunneling microscope in order to illuminate the tip-sample junction. The photoenhanced portion of the tunneling current is spectroscopically measured using a lock-in technique. The capabilities of this technique were verified using semiconductor microstructure calibration standards that were grown by organometallic vapor-phase epitaxy. Bandgaps characterized by STORM measurements were found to be in good agreement with the bulk values determined by transmission spectroscopy and photoluminescence and with the theoretical values that were based on x-ray diffraction results.

Bailey, Sheila G.↗
NASA NTRS1983

Laser-induced fluorescence spectroscopy for combustion diagnostics

The types of spectroscopic and collisional measurements that are needed to develop laser-induced fluorescence as a diagnostic technique are discussed, with emphasis placed on combustion measurements. The spectroscopic measurements under collision-free conditions include production of radicals, excitation scan studies, lifetime measurements, and fluorescence scans. The collisional studies discussed here are quenching, energy transfer, and polarization phenomena. The results of recent laboratory experiments are presented.

Crosley, D. R.↗
NASA NTRS1983

New absolute spectroscopic measurement of the solar equatorial rotation rate

An atomic-beam resonance-scattering technique applied to the 7699 A solar potassium absorption line is used to make an absolute spectroscopic determination of the solar equatorial rotation rate. This is believed to be a new method which has not previously been used for studying solar rotation. The measurements were made during 1979-82, initially with a permanent apparatus at Oberlin College and more recently with a portable apparatus installed at the Snow Telescope on Mt. Wilson. After carefully allowing for possible systematic errors, it is concluded that the solar sidereal equatorial rotation rate is 13.8 + or - 0.3 deg/day and that it has not varied significantly over the period of these observations.

Snider, J. L.↗
NASA NTRS1988

Vertical resolution of middle atmospheric measurements by ground-based microwave radiometry

The vertical resolution obtainable through measurement of trace constituents in the middle atmosphere by ground-based microwave spectroscopy has remained somewhat ambiguous. In order to explore this question, the Backus-Gilbert (1967, 1968, 1970) inversion technique, which automatically yields quantitative estimates of the inversion spatial resolution was applied to this particular inverse problem. This indicated that the optimum resolution of Backus-Gilbert inversions of microwave spectroscopic measurements is about 10 km. A general technique, based on inversion of delta function simulated profiles, was then developed, for evaluating the resolution of any inversion technique and applied to the Chahine (1970) inversion technique. These results indicated that the optimum resolution of the Chahine technique is about 6 or 7 km, or nearly a factor of 2 better than the equivalent Backus-Gilbert results.

Bevilacqua, Richard M.↗
NASA NTRS1975

Spectroscopic analysis of solar and cosmic X-ray spectra. 1: The nature of cosmic X-ray spectra and proposed analytical techniques

Techniques for the study of the solar corona are reviewed as an introduction to a discussion of modifications required for the study of cosmic sources. Spectroscopic analysis of individual sources and the interstellar medium is considered. The latter was studied via analysis of its effect on the spectra of selected individual sources. The effects of various characteristics of the ISM, including the presence of grains, molecules, and ionization, are first discussed, and the development of ISM models is described. The expected spectral structure of individual cosmic sources is then reviewed with emphasis on supernovae remnants and binary X-ray sources. The observational and analytical requirements imposed by the characteristics of these sources are identified, and prospects for the analysis of abundances and the study of physical parameters within them are assessed. Prospects for the spectroscopic study of other classes of X-ray sources are also discussed.

Walker, A. B. C., Jr.↗
NASA NTRS2002

Distant Cluster Hunting: A Comparison of X-Ray and Optical Cluster Detection Techniques and Catalogs from the ROSAT Optical X-Ray Survey - II

We present and analyze the optical and X-ray catalogs of moderate-redshift cluster candidates from the ROSA TOptical X-Ray Survey, or ROXS. The survey covers the sky area contained in the fields of view of 23 deep archival ROSA T PSPC pointings, 4.8 square degrees. The cross-correlated cluster catalogs were con- structed by comparing two independent catalogs extracted from the optical and X-ray bandpasses, using a matched-filter technique for the optical data and a wavelet technique for the X-ray data. We cross-identified cluster candidates in each catalog. As reported in Paper 1, the matched-filter technique found optical counter- parts for at least 60% (26 out of 43) of the X-ray cluster candidates; the estimated redshifts from the matched filter algorithm agree with at least 7 of 1 1 spectroscopic confirmations (Az 5 0.10). The matched filter technique. with an imaging sensitivity of ml N 23, identified approximately 3 times the number of candidates (155 candidates, 142 with a detection confidence >3 u) found in the X-ray survey of nearly the same area. There are 57 X-ray candidates, 43 of which are unobscured by scattered light or bright stars in the optical images. Twenty-six of these have fairly secure optical counterparts. We find that the matched filter algorithm, when applied to images with galaxy flux sensitivities of mI N 23, is fairly well-matched to discovering z 5 1 clusters detected by wavelets in ROSAT PSPC exposures of 8000-60,000 s. The difference in the spurious fractions between the optical and X-ray (30%) and IO%, respectively) cannot account for the difference in source number. In Paper I, we compared the optical and X-ray cluster luminosity functions and we found that the luminosity functions are consistent if the relationship between X-ray and optical luminosities is steep (Lx o( L&f). Here, in Paper 11, we present the cluster catalogs and a numerical simulation of the ROXS. We also present color-magnitude plots for several of the cluster candidates, and examine the prominence of the red sequence in each. We find that the X-ray clusters in our survey do not all have a prominent red sequence. We conclude that while the red sequence may be a distinct feature in the color-magnitude plots for virialized massive clusters, it may be less distinct in lower mass clusters of galaxies at even moderate redshifts. Multiple, complementary methods of selecting and defining clusters may be essential, particularly at high redshift where all methods start to run into completeness limits, incomplete understanding of physical evolution, and projection effects.

Donahue, Megan↗
NASA NTRS1977

Asteroid surface compositions from infrared spectroscopic observations - Results and prospects

Advances in IR detector technology, the increased availability of large aperture telescopes, and the techniques of Fourier transform spectroscopy now permit IR (with wavelengths greater than 1 micron) spectroscopic observations of asteroid surfaces. Asteroids already observed include Ceres, Vesta, and Eros. These initial results demonstrate that such studies can contribute new data concerning asteroid compositions. Some of the most diagnostic features of mineral spectra are in the IR spectral region, and for featureless spectra characterized only by slopes the extension of the spectral reflectivity curve into the IR provides tighter constraints on possible mineralogies. A systematic study of additional asteroids should exploit even further this new observational link to problems of meteorite origin and solar system evolution.

Larson, H. P.↗
NASA NTRS1986

Etching Silicon Films With Xenon Difluoride

Microscopic circuit structures prepared for probing. Xenon difluoride removes relatively large amounts of silicon from integratedcircuit or solar-cell structures while leaving SiO2, Si3N4, Al2O3, and other compounds intact. In Etching Apparatus, solid XeF2 sublimated in vacuum, then allowed to flow over sample at controlled rate and pressure. Wafer etched from back to expose SiO2 and Al layers for spectroscopic analysis of SiO2/Al interface. Using XeF2 technique, silicon wafer with oxide layer reduced in thickness from standard 300 micrometer to as little as 10 nanometer without adversely affecting oxide.

Hecht, M. H.↗
NASA NTRS1987

Mass spectroscopic characterization of the GeSe:GeI4 vapor transport system

The GeSe:GeI4 vapor crystal growth system was characterized mass spectroscopically. A steady-state Knudsen effusion technique was developed to simulate the equilibrium conditions at one end of a vapor transport ampoule. It was found that the previously neglected equilibrium GeSe2(s) = GeSe(v) + 1/2Se2(v) reduces the Se2(v) concentration to an extent that sublimation/condensation of GeSe becomes the dominant transport mechanism. At total pressures near 1 atm the concentration of an additional Ge-Se-I vapor species becomes comparable to that of GeSe(v).

Buchan, Nicholas I.↗
NASA NTRS1988

Theoretical studies of the monoxides and monosulfides of Y, Zr, and Nb

Modified-CPF and CASSCF/multireference-CI theoretical calculations are presented for the ground and low-lying states of YO and YS, ZrO and ZS, and NbO and NbS. The techniques employed are explained, and the calculated spectroscopic constants are presented in extensive tables. Good agreement is found with published experimental data on the oxides, and it is inferred that the sulfide results are accurate as well. Particular attention is given to the high-lying quartet manifold of states in YO and the (1) 3Pi-a3Delta transition of ZrS (possibly the source of the IR Keenan bands seen in S-star spectra).

Langhoff, Stephen R.↗
NASA NTRS2007

324GHz CMOS VCO Using Linear Superimposition Technique

Terahertz (frequencies ranged from 300GHz to 3THz) imaging and spectroscopic systems have drawn increasing attention recently due to their unique capabilities in detecting and possibly analyzing concealed objects. The generation of terahertz signals is nonetheless nontrivial and traditionally accomplished by using either free-electron radiation, optical lasers, Gunn diodes or fundamental oscillation by using III-V based HBT/HEMT technology[1-3]... We have substantially extended the operation range of deep-scaled CMOS by using a linear superimposition method, in which we have realized a 324GHz VCO in 90nm digital CMOS with 4GHz tuning range under 1V supply voltage. This may also pave the way for ultra-high data rate wireless communications beyond that of IEEE 802.15.3c and reach data rates comparable to that of fiber optical communications, such as OC768 (40Gbps) and beyond.

voltage controlled oscillators (VCO)↗
NASA NTRS1995

Fabricating Sub-Collimating Grids for an X-Ray Solar Imaging Spectrometer Using LIGA Techniques

A proposed NASA mission uses a High Energy Solar Spectroscopic Imager (HESSI) to image solar X-rays. The HESSI instrument consists of twelve rotating pairs of high aspect ratio, high Z grids, each pair of which is separated by 1.7 meters and backed by a single Ge detector. Discussed are the fabrication of these proof-of-concept sub-collimating X-ray grids which are to be used in HESSI.

solar↗
NASA NTRS2002

Applications of Kalman filtering to real-time trace gas concentration measurements

A Kalman filtering technique is applied to the simultaneous detection of NH3 and CO2 with a diode-laser-based sensor operating at 1.53 micrometers. This technique is developed for improving the sensitivity and precision of trace gas concentration levels based on direct overtone laser absorption spectroscopy in the presence of various sensor noise sources. Filter performance is demonstrated to be adaptive to real-time noise and data statistics. Additionally, filter operation is successfully performed with dynamic ranges differing by three orders of magnitude. Details of Kalman filter theory applied to the acquired spectroscopic data are discussed. The effectiveness of this technique is evaluated by performing NH3 and CO2 concentration measurements and utilizing it to monitor varying ammonia and carbon dioxide levels in a bioreactor for water reprocessing, located at the NASA-Johnson Space Center. Results indicate a sensitivity enhancement of six times, in terms of improved minimum detectable absorption by the gas sensor.

Non-NASA Center↗
NASA NTRS2012

Developing Wide-Field Spatio-Spectral Interferometry for Far-Infrared Space Applications

Interferometry is an affordable way to bring the benefits of high resolution to space far-IR astrophysics. We summarize an ongoing effort to develop and learn the practical limitations of an interferometric technique that will enable the acquisition of high-resolution far-IR integral field spectroscopic data with a single instrument in a future space-based interferometer. This technique was central to the Space Infrared Interferometric Telescope (SPIRIT) and Submillimeter Probe of the Evolution of Cosmic Structure (SPECS) space mission design concepts, and it will first be used on the Balloon Experimental Twin Telescope for Infrared Interferometry (BETTII). Our experimental approach combines data from a laboratory optical interferometer (the Wide-field Imaging Interferometry Testbed, WIIT), computational optical system modeling, and spatio-spectral synthesis algorithm development. We summarize recent experimental results and future plans.

Leisawitz, David↗
NASA NTRS1980

Spectroscopic characterization of titanium 6-4 surfaces after chemical pretreatments

Several techniques have been used to study pretreated Ti 6-4 surfaces including scanning electron microscopy (SEM), electron spectroscopy of chemical analysis (ESCA), and, reflectance visibile spectroscopy. Each pretreatment type gives a characteristic surface morphology as seen by SEM. Elemental analysis of the Ti 6-4 surfaces was done using ESCA. Trace residual contaminants from particular chemical pretreatments are identified readily. Reflectance visible spectroscopy using indicator dyes placed on Ti 6-4 surfaces appears to be a feasible approach to establish surface acidity. Differences in surface acidity have been observed using bromthymol blue on Ti 6-4 surfaces pretreated by two different methods.

Chen, W.↗