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At least 415 records · Page 23
All sourcesNASA NTRSDOE OSTI
NASA NTRS1994

On the apparent velocity of integrated sunlight. 2: 1983-1992 and comparisons with magnetograms

We report additional results in our program to monitor the wavelength stability of lines in the 2.3 micrometer spectrum of integrated sunlight. We use the McMath Fourier transform spectrometer (FTS) of the National Solar Observatory to monitor 16 delta V = 2 lines of (12)C(16)O, as well as five atomic lines. Wavenumber calibration is achieved using a low-pressure N2O absorption cell and checked against terrestrial atmospheric lines. Imperfect optical integration of the solar disk remains the principal source of error, but this error has been reduced by improved FTS/telescope collimation and observing procedures. The present results include data from an additional 13 quarterly observing runs since 1985. We continue to find that the apparent velocity of integrated sunlight is variable, in the sense of having a greater reshift at solar maximum. This is supported by the temporal dependence of the integrated light velocity, and by the presence of a correlation between velocity and the disk-averaged magnetic flux derived from Kitt Peak magnetograms. The indicated peak-to-peak apparent velocity amplitude over a solar cycle is approximately the same as the velocity amplitude of the Sun's motion about the solar system barycenter. This represents about half the amplitude which we inferred in Paper I (Deming et al. 1987), but the present result has a much greater statistical significance. Our results have implications for those investigations which search for the Doppler signatures of planetary-mass companions to solar-type stars. We contrast our results to the recent finding by McMillan et al. 1993 that solar absorption lines in the violet spectral region are wavelength-stable over the solar cycle.

Deming, Drake↗
NASA NTRS1993

Robots for Aircraft Maintenance

Marshall Space Flight Center charged USBI (now Pratt & Whitney) with the task of developing an advanced stripping system based on hydroblasting to strip paint and thermal protection material from Space Shuttle solid rocket boosters. A robot, mounted on a transportable platform, controls the waterjet angle, water pressure and flow rate. This technology, now known as ARMS, has found commercial applications in the removal of coatings from jet engine components. The system is significantly faster than manual procedures and uses only minimal labor. Because the amount of "substrate" lost is minimal, the life of the component is extended. The need for toxic chemicals is reduced, as is waste disposal and human protection equipment. Users of the ARMS work cell include Delta Air Lines and the Air Force, which later contracted with USBI for development of a Large Aircraft Paint Stripping system (LARPS). LARPS' advantages are similar to ARMS, and it has enormous potential in military and civil aircraft maintenance. The technology may also be adapted to aircraft painting, aircraft inspection techniques and paint stripping of large objects like ships and railcars.

Source record↗
NASA NTRS2004

The Severe Weather Outbreak of 10 November 2002: Lightning and Radar Analysis of Storms in the Deep South

On the afternoon and evening of 10 November 2002, the Midwest and Deep South were struck by a major outbreak of severe storms that produced some 80 tornadoes. In terms of number of tornadoes, this was the largest outbreak in the United States since November 1992. Some 32 of the tornadoes occurred in Tennessee, Mississippi, Alabama and Georgia, including several long-track killers. We use the North Alabama Lightning Mapping Array (LMA) and other data sources to perform a comprehensive analysis of the structure and evolution of the outbreak. Most of the Southern tornadoes occurred in isolated, fast-moving supercell storms that formed in warm, moist air ahead of a major cold front. Storms tended to form in lines parallel to storm cell motion, resulting in many communities being hit multiple times by severe storms that evening. Supercells in Tennessee produced numerous strong tornadoes with short to medium-length track paths, while the supercells further south produced several very long-track tornadoes. Radar data indicate that the Tennessee storms tended to split frequently, apparently limiting their ability to sustain long-lived tornadoes, while storms further south split at most one time. The differences between these storms appear to be related to the presence of stronger jetstream winds in Tennessee relative to those present in Mississippi, Alabama and Georgia. LMA-derived flash rates associated with most of the supercell storm cores were about 1-2 flashes per second. Rapid increases in lightning rates (or "jumps") occurred prior to tornado touchdown in many instances. Lightning "holes" (lightning-free regions associated with the echo-free vault) occurred in two of the Tennessee supercells. The complexity of the relationship between lightning and storm severity is revealed by the behavior of one Alabama supercell, which produced a peak flash rate of nearly 14 flashes per second, well after the end of its long-track tornado, while interacting and ultimately merging with a daughter supercell on its southwest flank. Close examination of this powerful storm indicates that its prodigious flash rate was the result of strong flash activity over an unusually large area, rather than a concentrated core of extremely high flash rate activity.

Buechler, D. E.↗
NASA NTRS2011

Spatial Correlation of Rain Drop Size Distribution from Polarimetric Radar and 2D-Video Disdrometers

Spatial correlations of two of the main rain drop-size distribution (DSD) parameters - namely the median-volume diameter (Do) and the normalized intercept parameter (Nw) - as well as rainfall rate (R) are determined from polarimetric radar measurements, with added information from 2D video disdrometer (2DVD) data. Two cases have been considered, (i) a widespread, long-duration rain event in Huntsville, Alabama, and (ii) an event with localized intense rain-cells within a convection line which occurred during the MC3E campaign. For the first case, data from a C-band polarimetric radar (ARMOR) were utilized, with two 2DVDs acting as ground-truth , both being located at the same site 15 km from the radar. The radar was operated in a special near-dwelling mode over the 2DVDs. In the second case, data from an S-band polarimetric radar (NPOL) data were utilized, with at least five 2DVDs located between 20 and 30 km from the radar. In both rain event cases, comparisons of Do, log10(Nw) and R were made between radar derived estimates and 2DVD-based measurements, and were found to be in good agreement, and in both cases, the radar data were subsequently used to determine the spatial correlations For the first case, the spatial decorrelation distance was found to be smallest for R (4.5 km), and largest fo Do (8.2 km). For log10(Nw) it was 7.2 km (Fig. 1). For the second case, the corresponding decorrelation distances were somewhat smaller but had a directional dependence. In Fig. 2, we show an example of Do comparisons between NPOL based estimates and 1-minute DSD based estimates from one of the five 2DVDs.

Thurai, Merhala↗
NASA NTRSDate not supplied

Initial testing of the Uncrewed Aerial System Pilot Kit (UASP-kit) in Operational Settings

Remote pilots for small uncrewed aerial systems (sUAS) are at a disadvantage for building situation awareness of the airspace in which they are flying, because of limited sight lines and distance from cell towers. A tool to provide increased air traffic situation awareness for an sUAS pilot is being developed. The “UASP-kit” is small and self-contained, with its chief capability being to collect and display Automatic Dependent Surveillance-Broadcast reports of local aircraft. UASP-kits were taken into the field, introduced to users during a training course, and then left with them for the summer fire season. sUAS pilots used the prototypes when it was appropriate throughout the summer. The UASP-kits were operational for a total of 79 flight-days. Users noted that the UASP-kits supported their situation awareness but also identified several usability issues. The findings contribute to validation of the UASP-kit, and support continuing the work to improve the tool and develop additional functionality.

STEReO↗
NASA NTRS1997

Improvement in Suppression of Pulsed Nd:YAG Laser Light With Iodine Absorption Cells for Filtered Rayleigh Scattering Measurements

Filtered Rayleigh scattering using iodine absorption cells is an effective technique for obtaining density, temperature, and velocity measurements in high speed confined flows. By tuning a single frequency laser to a strong iodine absorption line, stray scattered laser light can be greatly suppressed. For example, the minimum transmission predicted by an iodine absorption model calculation is less than 10(exp -5) at the 18788.44/cm line using a 200 mm absorption cell containing iodine vapor at 0.46 T. Measurements obtained by other researches using a CW Nd:YAG laser agree with the model calculations. However, measurements made by us and by others using Q-switched, injection-seeded, frequency doubled Nd:YAG lasers only show minimum transmission of about 3 x 10(exp -3). This greatly reduces the applicability of the filtered Rayleigh scattering technique using these lasers in experiments having large amounts of stray scattered laser light. The purposes of the present study are to characterize the spectrum of the excess light transmitted by the iodine cell and to make changes to the laser to reduce the transmitted laser light. Transmission data as a function of laser frequency for the iodine absorption line at 18788.44/cm are presented. A planar mirror Fabry-Perot interferometer was used to characterize the frequency spectrum of the light passed through the cell. Measurements taken with the laser tuned to the center of the iodine absorption line show the light transmitted through the iodine cell to have a component with a bandwidth of about 40 GHz. This is probably caused by other modes in the laser that exist in spite of the single frequency injection beam. A second broadband component was also observed, possibly caused by the laser flash lamps or by fluorescence. An intracavity etalon was installed in the laser oscillator cavity to suppress the 40 GHz component. Measurements taken with the etalon tuned to the injection frequency showed a reduction in the transmitted laser light. This improvement allows the iodine cell to block significantly more of the stray laser light in filtered Rayleigh scattering experiments. Examples are given of filtered Rayleigh scattering measurements showing the effect of the etalon on measurements taken in a Mach 3 flow in the NASA Lewis 4 inch by 10 inch supersonic wind tunnel.

Seasholtz, Richard G.↗
NASA NTRS1982

Process Research ON Semix Silicon Materials (PROSSM)

A cost effective process sequence was identified, equipment was designed to implement a 6.6 MW per year automated production line, and a cost analysis projected a $0.56 per watt cell add-on cost for this line. Four process steps were developed for this program: glass beads back clean-up, hot spray antireflective coating, wave soldering of fronts, and ion milling for edging. While spray dopants were advertised as an off the shelf developed product, they were unreliable with shorter than advertised shelf life.

Wohlgemuth, J. H.↗
NASA NTRS1996

Optical Properties of Selective Emitter Materials for Thermophotovoltaic Applications

We investigate the optical properties of new "selective emitter" materials for possible use in high-efficiency thermophotovoltaic power systems. These are systems which directly convert heat to radiation at a wavelength closely matched to the bandgap energy of the solar cell. Candidate materials which have strong absorption lines fairly close to the bandgap of good solar-cell materials were chosen for study. Their emittance was measured as a function of wavelength to evaluate their promise as selective TPV emitters. Useful and informative results were obtained. Some of these results were presented at a January 1996 solar energy conference of the American Institute of Aeronautics and Astronautics.

Hambourger, Paul D.↗
NASA NTRS2002

An Optical Oxygen Sensor for Long-Term Continuous Monitoring of Dissolved Oxygen in Perfused Bioreactors

For long-term growth of man1ITlalian cells in perfused bioreactors, it is essential to monitor the concentration of dissolved oxygen (DO) present in the culture medium to quantitate and control level of DO. Continuous measurement of the amount of DO in the cell culture medium in-line under sterile conditions in NASA's perfused bioreactor requires that the oxygen sensor provide increased sensitivity and be sterilizable and nontoxic. Additionally, long-term cell culture experiments require that the calibration be maintained several weeks or months. Although there are a number of sensors for dissolved oxygen on the market and under development elsewhere, very few meet these stringent conditions. An optical oxygen sensor (BOXY) based on dynamic fluorescent quenching and a pulsed blue LED light source was developed in our laboratory to address these requirements. Tris( 4,7 -diphenyl-l, 1 O-phenanthroline )ruthenium(II) chloride is employed as the fluorescent dye indicator. The sensing element consists of a glass capillary (OD 4.0 mm; ID 2.0 mm) coated internally with a thin layer of the fluorescent dye in silicone matrix and overlayed with a black shielding layer. Irradiation of the sensing element with blue light (blue LED with emission maximum at 475 nm) generates a red fluorescence centered at 626 nm. The fluorescence intensity is correlated to the concentration of DO present in the culture medium, following the modified non-linear Stern-Volmer equation. By using a pulsed irradiating light source, the problem of dye-bleaching, which is often encountered in long-term continuous measurements of tIns type, 'is minimized. To date we achieved sensor resolution of 0.3 mmHg at 50 mmHg p02, and 0.6 mmHg at 100 mmHg p02, with a response time of about one minute. Calibration was accomplished in sterile phosphate-buffered saline with a blood-gas analyzer (BGA) measurement as reference. Stand-alone software was also developed to control the sensor and bioreactor as well as to acquire data. Two HOXY sensors with a single calibration were employed to continuously monitor the DO in GTSF-2 medium during a Baby Hamster Kidney (BHK-21) cell culture in a Rotating Wall Perfused Vessel (RWPV) bioreactor for 90 days. HOXY sensors were located at the inlet to and outlet from the bioreactor. One of the sensors was placed between an oxygenator and the inlet to the bioreactor. The dissolved oxygen concentrations determined by both sensors were compared with those measured regularly with the BGA reference. The cell culture was maintained for 110 days. Sensor output was found to correlate well with the BGA data throughout the experiment, where the DO of the medium ranged between 25 and 50 mmHg at the bioreactor outlet and 90-130 mmHg at the bioreactor inlet. Measuring DO with the HOXY sensors versus the BGA reference indicated bias values of -2 mmHg and -15 mmHg, and precision values of +/-3mmHg and +/-16 mmHg at the bioreactor inlet and outlet, respectively.

Gao, F. G.↗
NASA NTRS1985

Integrating Residential Photovoltaics With Power Lines

Report finds rooftop solar-cell arrays feed excess power to electric-utility grid for fee are potentially attractive large-scale application of photovoltaic technology. Presents assessment of breakeven costs of these arrays under variety of technological and economic assumptions.

Borden, C. S.↗
NASA NTRS2004

Space Shuttle Upgrades: Long Life Alkaline Fuel Cell

NASA has utilized the alkaline fuel cell technology to provide electrical power for manned launch vehicles such as Gemini, Apollo, and the Space Shuttle. The current Shuttle alkaline fuel cells are procured from UTC Fuel Cells, a United Technologies Company. The alkaline fuel cells are very reliable but the operating life is limited to 2600 hours due to voltage degradation of the individual cells. The main limiting factor in the life of the cells is corrosion of the cell's fiberglass/epoxy frame by the aqueous potassium hydroxide electrolyte. To reduce operating costs, the orbiter program office approved the Long Life Alkaline Fuel Cell (LLAFC) program as a shuttle upgrade in 1999 to increase the operating life of the fuel cell powerplant to 5000 hours. The LLAFC program incorporates improving the cell by extending the length of the corrosion path, which reduces the cell frame corrosion. UTCFC performed analysis to understand the fundamental mechanisms that drive the cell frame corrosion. The analysis indicated that the corrosion path started along the bond line between the cathode and the cell frame. Analysis also showed that the oxygen available at the cathode, the catalyst on the electrode, and the electrode substrate all supported or intensified the corrosion. The new cell design essentially doubled the corrosion path to mitigate the problem. A 10-cell stack was tested for 5000 hours during the development phase of this program to verify improved cell performance. A complete 96-cell stack was then tested for 5000 hours during the full manned-space qualification phase of this program. Additional upgrades to the powerplant under this program are: replacing the aluminum body in the pressure regulator with stainless steel to reduce corrosion, improving stack insulator plate with improved resistance to stress failure and improved temperature capability, and replacing separator plate elastomer seals with a more durable material and improved seal retention.

Kerri McCurdy↗
NASA NTRS1974

Methods of improving the efficiency of photovoltaic cells

Work on aluminum-alloyed silicon grating cells is continued. Optimization of the geometry (grating line width and spacing) confirms the analysis of such cells. A 1 sq cm grating cell was fabricated and its i-V characteristic was measured under an AMO solar simulator. It is found that the efficiency of this cell would be about 7.9%, if it were covered by the usual antireflection coating. The surface of the cell is not covered by a diffused junction. The response is blue shifted; the current is somewhat higher than that produced by a commercial Si cell. However, the open circuit voltage is low, and attempts to optimize the open circuit voltage of the aluminum-alloy junctions are described. A preliminary X-ray topographic examination of GaAs specimens of the type commonly used to make solar cells is studied. The X-ray study shows that the wafers are filled with regions having strain gradients, possibly caused by precipitates. It is possible that a correlation exists between the presence of low mechanical perfection and minority carrier diffusion lengths of GaAs crystals.

Loferski, J. J.↗
NASA NTRS1972

Automatic microscopy for mitotic cell location.

Advances are reported in the development of an automatic microscope with which to locate hematologic or other cells in mitosis for subsequent chromosome analysis. The system under development is designed to perform the functions of: slide scanning to locate metaphase cells; conversion of images of selected cells into binary form; and on-line computer analysis of the digitized image for significant cytogenetic data. Cell detection criteria are evaluated using a test sample of 100 mitotic cells and 100 artifacts.

Herron, J.↗
NASA NTRS1980

Fast-response atmospheric-pollutant monitor

Fast infrared spectrometer measures atmospheric C0, CH4, and HC1 over range of 1 to 12 ppm. With modifications it could measure other pollutants and use natural light as source. Cell filled with sample to be measured filters out spectral lines of interest. Infrared beam passes through rotating cell holder that produces chopped signals at two frequencies. Difference in signal amplitudes depends on amount of test gas in sample. Signal processing circuitry amplifies and separates test-gas and reference signals.

Sebacher, D. I.↗
NASA NTRS1990

Airborne water vapor DIAL system development

A differential absorption lidar (DIAL) system developed at NASA Langley Research Center for the remote measurement of atmospheric H2O and aerosols from an aircraft is briefly discussed. This DIAL system utilizes a Nd:YAG laser-pumped dye laser as the off-line transmitter and a narrowband, tunable Alexandrite laser as the on-line transmitter. A 1-m monochromator and a multipass absorption cell are used to position the on-line laser to the center of the H2O line. The receiver system has a 14-in. diameter, f/7 Celestron telescope to collect the backscattered laser light and focus in into the detector optics. Return signals are converted to electrical signals by the optical detector and are digitalized and stored on magnetic tape. The results of fligh tests of the system are shown.

Higdon, Noah S.↗
NASA NTRS2003

Afferent innervation of the utricular macula in pigeons

Biotinylated dextran amine (BDA) was used to retrogradely label afferents innervating the utricular macula in adult pigeons. The pigeon utriclar macula consists of a large rectangular-shaped neuroepithelium with a dorsally curved anterior edge and an extended medioposterior tail. The macula could be demarcated into several regions based on cytoarchitectural differences. The striola occupied 30% of the macula and contained a large density of type I hair cells with fewer type II hair cells. Medial and lateral extrastriola zones were located outside the striola and contained only type II hair cells. A six- to eight-cell-wide band of type II hair cells existed near the center of the striola. The reversal line marked by the morphological polarization of hair cells coursed throughout the epithelium, near the peripheral margin, and through the center of the type II band. Calyx afferents innervated type I hair cells with calyceal terminals that contained between 2 and 15 receptor cells. Calyx afferents were located only in the striola region, exclusive of the type II band, had small total fiber innervation areas and low innervation densities. Dimorph afferents innervated both type I and type II hair cells with calyceal and bouton terminals and were primarily located in the striola region. Dimorph afferents had smaller calyceal terminals with few type I hair cells, extended fiber branches with bouton terminals and larger innervation areas. Bouton afferents innervated only type II hair cells in the extrastriola and type II band regions. Bouton afferents innervating the type II band had smaller terminal fields with fewer bouton terminals and smaller innervation areas than fibers located in the extrastriolar zones. Bouton afferents had the most bouton terminals on the longest fibers, the largest innervation areas with the highest innervation densities of all afferents. Among all afferents, smaller terminal innervation fields were observed in the striola and large fields were located in the extrastriola. The cellular organization and innervation patterns of the utricular maculae in birds appear to represent an organ in adaptive evolution, different from that observed for amphibians or mammals.

Non-NASA Center↗
NASA NTRS1981

Laser processing of silicon solar cells

Results of a study to utilize an Nd:glass laser for production line annealing of ion implantation induced damage in solar cells are reported. Czochralski-grown and sawn Si wafers 7.6 cm in diam, 0.35 mm thick, were implanted with phosphorus junctions and boron BSFs. Annealing with electron beam, laser, and firing of an Al paste to form the BSFs in different cells was compared. The laser was employed at 1.06 and 0.53 micron and in combination of both, with a 20-50 nsec pulsewidth, and energy densities of 1.2, 1.5, 1.9, and 2.1 J/sq cm. Best optical coupling was observed with the combined wavelengths and a 20 nsec pulse, using energy densities less than 1.5 J/sq cm. Although the Al sintered cells displayed the best characteristics, laser annealing is concluded to offer electrically active, defect-free, shallow junction Si substrates for high efficiency cells.

Katzeff, J. S.↗
NASA NTRS1991

Quasi-periodic structures in the large-scale galaxy distribution and three-dimensional Voronoi tessellation

It has been suggested that the void and wall structure associated with the large-scale galaxy distribution might be qualitatively, or perhaps even physically, modeled by a Voronoi tessellation, and that such structure might account for the surprisingly regular, sharp peaks in the galaxy redshift distributions obtained from 'pencil beam' surveys. Taking cell wall crossings by random line segments to correspond to such redshift peaks, an exact expression is derived for the distribution of spacings of these intersections in a three-dimensional Voronoi tessellation. This result verifies that the spacings are nonrandom and quasi-periodic, qualitatively resembling the observed pattern, even though the cell wall structure is generated from randomly placed seeds. Finally, moments of the spacing distribution are used to show that apparently periodic samples, similar to those recently reported, represent only one to two sigma fluctuations in a Voronoi tesselation.

Ikeuchi, Satoru↗