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At least 505 records · Page 28
All sourcesNASA NTRSDOE OSTI
NASA NTRS1994

Hot gas in the interstellar medium: A reanalysis of O VI absorption data

The Copernicus O(+5) column densities toward 72 stars provide a rare and valuable tracer of 10(exp 5.5) K gas in the interstellar medium. The original analysis of the data by Jenkins provided important clues about the distribution of interstellar O(+5) ions, but our understanding of the local interstellar medium has since grown substantially. We revisit that work, including the possibility that local hot gas may contribute a significant O(+5) column density to most lines of sight. Our reanalysis also includes slight improvements in the statistics and was found to be reliable when tested on simulated data sets. In the end, we come to conclusions about the distribution of interstellar O(+5) ions that differ considerably from those of the original analysis. With our reanalysis, some theoretical models now show promise. For example, our Local Bubble column density compares favorably with the estimated quantity of O(+5) within the remnant of an ancient local explosion. Similarly, our mean O(+5) column density per feature in more distant regions is like that found in models of hot interstellar bubbles from either stellar winds or ancient supernova explosions in a warm diffuse interstellar environment, suggesting that the hot gas in interstellar space may exist primarily within discrete regions of modest volume occupation rather than in a continuous and pervasive phase.

Shelton, R. L.↗
NASA NTRS1994

Atomic data from the iron project. 3: Rate coefficients for electron impact excitation of boron-like ions: Ne VI, Mg VIII, Al IX, Si X, S XII, Ar XIV, Ca XVI and Fe XXII

Collison strengths and maxwellian averaged rate coefficients have been calculated for the 105 transitions among all 15 fine structure levels of the 8 LS terms 2s(sup 2) 2 P(P-2(sup 0 sub 1/, 3/2)), 2s2p(sup 2)(P-4(sub 1/2,3/2,5/2), D-2(sub 3/2, 5/2), S-2(sub 1/2), P-2(sub 1/2, 3/2)), 2p(sup 3)(S-4(sup 0)(sub 3/2), D-2(sup 0 sub 3/2, 5/2), P-2(sup 0 sub 1/2, 3/2)) in highly- charged B-like Ne, Mg, Al, Si, S, Ar, Ca and Fe. Rate coefficients have been tabulated at a wide range of temperatures, depending on the ion charge and abundance in plasma sources. Earlier work for O IV has also been extended to include the high temperature range. A brief discussion of the calculations, sample results, and comparison with earlier works is also given. While much of the new data should be applicable to UV spectral diagnostics, the new rates for the important ground state fine structure transition P-2(sup 0 sub 1/2)-P-2(sup 0 sub 3/2) should result in significant revision of the IR cooling rates in plasmas where B-like ions are prominent constituents, since the new rate coefficients are generally higher by several factors compared with the older data.

Zhang, Hong Lin↗
NASA NTRS1999

High Resolution Triple Axis X-Ray Diffraction Analysis of II-VI Semiconductor Crystals

The objective of this research program is to develop methods of structural analysis based on high resolution triple axis X-ray diffractometry (HRTXD) and to carry out detailed studies of defect distributions in crystals grown in both microgravity and ground-based environments. HRTXD represents a modification of the widely used double axis X-ray rocking curve method for the characterization of grown-in defects in nearly perfect crystals. In a double axis rocking curve experiment, the sample is illuminated by a monochromatic X-ray beam and the diffracted intensity is recorded by a fixed, wide-open detector. The intensity diffracted by the sample is then monitored as the sample is rotated through the Bragg reflection condition. The breadth of the peak, which is often reported as the full angular width at half the maximum intensity (FWHM), is used as an indicator of the amount of defects in the sample. This work has shown that high resolution triple axis X-ray diffraction is an effective tool for characterizing the defect structure in semiconductor crystals, particularly at high defect densities. Additionally, the technique is complimentary to X-ray topography for defect characterization in crystals.

Volz, H. M.↗
NASA NTRS1999

Fe(VI) as a Possible Oxidant on the Martian Surface

The essential findings of the three biological experiments (Gas Exchange, Labeled Released, and Pyrolitic Release) aboard the Viking Mars landers were the discovery of the presence of one or more strong oxidants on the Martian surface. The Gas Exchange experiments showed that wetting Martian soil leads to the evolution of oxygen, while in the Labeled Release experiment addition of a nutrient solution containing C-14-labeled formate, glycine, lactate, alanine, and glycolic acid induced CO2 evolution. A general consensus was reached that all data taken together pointed to the presence on Martian surface of a strong oxidant, or most probably several different types of oxidants. Several candidates have been proposed as oxidants, including superoxides, hydrogen peroxide, and iron oxides (possibly gamma-Fe2O3). Additional information is contained in the original extended abstract.

Tsapin, A. I.↗
NASA NTRS2002

Hot HB Stars in Globular Clusters - Physical Parameters and Consequences for Theory. VI. The Second Parameter Pair M3 and M13

We present the results of spectroscopic analyses of hot horizontal branch (HB) stars in M13 and M3, which form a famous second parameter pair. From the spectra we derived - for the first time in M13 - atmospheric parameters (effective temperature and surface gravity) as well as abundances of helium, magnesium, and iron. Consistent with analyses of hot HB stars in other globular clusters we find evidence for helium depletion and iron enrichment in stars hotter than about 12,000 K in both M3 and M13. Accounting for the iron enrichment substantially improves the agreement with canonical evolutionary models, although the derived gravities and masses are still somewhat too low. This remaining discrepancy may be an indication that scaled-solar metal-rich model atmospheres do not adequately represent the highly non-solar abundance ratios found in blue HB stars with radiative levitation. We discuss the effects of an enhancement in the envelope helium abundance on the atmospheric parameters of the blue HB stars, as might be caused by deep mixing on the red giant branch or primordial pollution from an earlier generation of intermediate mass asymptotic giant branch stars.

Moehler, S.↗
NASA NTRS2003

Thermophysical Properties of Te-based II-VI Semiconductors: Reduced Algorithms for Thermal Diffusivity Determination

This paper presents methodologies for measuring the thermal diffusivity using the difference between temperatures measured at two, essentially independent, locations. A heat pulse is applied for an arbitrary time to one region of the sample; either the inner core or the outer wall. Temperature changes are then monitored versus time. The thermal diffusivity is calculated from the temperature difference versus time. No initial conditions are used directly in the final results.

Banish, R. Michael↗
NASA NTRS2003

Hot HB Stars in Globular Clusters: Physical Parameters and Consequences for Theory: The Second Parameter Pair M 3 and M 13 - VI

We present the results of spectroscopic analyses of hot horizontal branch (HB) stars in M 13 and M 3, which form a famous "second parameter" pair. F rom the spectra and Stromgren photometry we derived - for the first time in M 13 - atmospheric parameters (effective temperature and surface gravity). For stars with Stromgren temperatures between 10,000 and 12,000 K we found excellent agreement between the atmospheric parameters derived from Stromgren photometry and those derived from Balmer line profile fits. However, for cooler stars there is a disagreement in the parameters derived by the two methods, for which we have no satisfactory explanation. Stars hotter than 12,000 K show evidence for helium depletion and iron enrichment, both in M 3 and M 13. Accounting for the iron enrichment substantially improves the agreement with canonical evolutionary models, although the derived gravities and masses are still somewhat too low. This remaining discrepancy may be an indication that scaled-solar metal-rich model atmospheres do not adequately represent the highly non-solar abundance ratios found in blue HB stars affected by diffusion. We discuss the effects of an enhancement in the envelope helium abundance on the atmospheric parameters of the blue HB stars, as might be caused by deep mixing on the red giant branch or primordial pollution from an earlier generation of intermediate mass asymptotic giant branch stars. Key words. Stars: atmospheres - Stars: evolution - Stars: horizontal branch - Globular clusters: individual: M 3 - Globular clusters: individual: M 13

Moehler, S.↗
NASA NTRS1989

Gravitropism in higher plant shoots. VI. Changing sensitivity to auxin in gravistimulated soybean hypocotyls

Although the Cholodny-Went model of auxin redistribution has been used to explain the transduction phase of gravitropism for over 60 years, problems are apparent, especially with dicot stems. An alternative to an auxin gradient is a physiological gradient in which lower tissues of a horizontal stem become more sensitive than upper tissues to auxin already present. Changes in tissue sensitivity to auxin were tested by immersing marked Glycine max Merrill (soybean) hypocotyl sections in buffered auxin solutions (0, 10(-8) to 10(-2) molar indoleacetic acid) and observing bending and growth of upper and lower surfaces. The two surfaces of horizontal hypocotyl sections responded differently to the same applied auxin stimulus; hypocotyls bent up (lower half grew more) in buffer alone or in low auxin levels, but bent down (upper half grew more) in high auxin. Dose-response curves were evaluated with Michaelis-Menten kinetics, with auxin-receptor binding analogous to enzyme-substrate binding. Vmax for the lower half was usually greater than that for the upper half, which could indicate more binding sites in the lower half. Km of the upper half was always greater than that of the lower half (unmeasurably low), which could indicate that upper-half binding sites had a much lower affinity for auxin than lower-half sites. Dose-response curves were also obtained for sections scrubbed' (cuticle abraded) on top or bottom before immersion in auxin, and gravitropic memory' experiments of L. Brauner and A. Hagar (1958 Planta 51: 115-147) were duplicated. [1-14C]Indoleacetic acid penetration was equal into the two halves, and endogenous plus exogenously supplied (not radiolabeled) free auxin in the two halves (by gas chromatography-selected ion monitoring-mass spectrometry) was also equal. Thus, differential growth occurred without free auxin redistribution, contrary to Cholodny-Went but in agreement with a sensitivity model.

NASA Discipline Number 29-20↗
NASA NTRS2004

Space Resources Roundtable VI

The topics addressed in the conference paper abstracts contained in this document include: extracting resources from the Moon and Mars, equipment for in situ resource utilization, mission planning for resource extraction, drilling on Mars, and simulants for lunar soil and minerals.

Source record↗
NASA NTRS1996

The HST Key Project on the Extragalactic Distance Scale VI. The Cepheids in NGC925

We report the detection of Cepheid Variable stars in the barred spiral galaxy NGC925, using the Hubble Space Telescope (HST) Wide Field and Planetary Camera 2 (WFPC2). Twelve V (F555W), four I (F814W) and three B (F439W) epochs of cosmic ray split observations were obtained. Eighty Cepheids were discovered, with periods from 6 to +-80 days. Light curves of the Cepheids are presented, and their corresponding period-luminosity diagrams are discussed.

Cepheids Cepheid Cepheid Variable stars barred spi↗
NASA NTRS1948

Performance of Compressor of XJ-41-V Turbojet Engine VI - Analysis of Compressor Flow Choking: Analysis of Compressor Flow Choking - 6

An extended analysis was made of the previously reported performance investigation of the original compressor from the XJ-41-v turbojet engine and a similar compressor revised a to obtain a 33-percent increase in the geometric passage area at the vaned-collector entrance. This analysis was based on the concept of the vaned-collector entrance as the throat section of a nozzle. Because of nonuniform air distribution at the vaned-collector entrance, approximately 90 percent of the available flow area was utilized in the original compressor and 94percent in the revised com$ressor. The increase in maximum weight flow obtained with the revised compressor was disproportionate to the increased effective critical throat area because. the air density at the revised vaned-collector entrance for maximum flow was lower than that obtained in the original compressor. This reduction in density resulted from the large pressure losses near the impeller inlet of the revised compressor, which is indicative of impending flow choking in the impeller, The.calculated maximum corrected weight-flow capacity of a compressor consisting of the revised vaneless diffuser and vaned collector with a theoretical impeller that combined peak impeller pressure ratio and peak impeller efficiency at the . maximum flow point would be 112 pounds per second for an equivalent impeller speed of 11,500 rpm;

Creagh, John W. R.↗
NASA NTRS1955

Aerodynamic Design of Axial-flow Compressors. VI - Experimental Flow in Two-Dimensional Cascades

Available experimental two-dimensional cascade data for conventional compressor blade sections are correlated at a reference incidence angle in the region of minimum loss. Variations of reference incidence angle, total-pressure loss, and deviation angle with cascade geometry, inlet Mach number, and Reynolds number are investigated. From the analysis and the correlations of the available data, rules and relations are evolved for the prediction of blade-profile performance. These relations are developed in simplified forms readily applicable to compressor design procedures.

Lieblein, Seymour↗
NASA NTRS2010

Minnowbrook VI: 2009 Workshop on Flow Physics and Control for Internal and External Aerodynamics

Topics covered include: Flow Physics and control for Internal and External Aerodynamics (not in TOC...starts on pg13); Breaking CFD Bottlenecks in Gas-Turbine Flow-Path Design; Streamwise Vortices on the Convex Surfaces of Circular Cylinders and Turbomachinery Blading; DNS and Embedded DNS as Tools for Investigating Unsteady Heat Transfer Phenomena in Turbines; Cavitation, Flow Structure and Turbulence in the Tip Region of a Rotor Blade; Development and Application of Plasma Actuators for Active Control of High-Speed and High Reynolds Number Flows; Active Flow Control of Lifting Surface With Flap-Current Activities and Future Directions; Closed-Loop Control of Vortex Formation in Separated Flows; Global Instability on Laminar Separation Bubbles-Revisited; Very Large-Scale Motions in Smooth and Rough Wall Boundary Layers; Instability of a Supersonic Boundary-Layer With Localized Roughness; Active Control of Open Cavities; Amplitude Scaling of Active Separation Control; U.S. Air Force Research Laboratory's Need for Flow Physics and Control With Applications Involving Aero-Optics and Weapon Bay Cavities; Some Issues Related to Integrating Active Flow Control With Flight Control; Active Flow Control Strategies Using Surface Pressure Measurements; Reduction of Unsteady Forcing in a Vaned, Contra-Rotating Transonic Turbine Configuration; Active Flow Control Stator With Coanda Surface; Controlling Separation in Turbomachines; Flow Control on Low-Pressure Turbine Airfoils Using Vortex Generator Jets; Reduced Order Modeling Incompressible Flows; Study and Control of Flow Past Disk, and Circular and Rectangular Cylinders Aligned in the Flow; Periodic Forcing of a Turbulent Axisymmetric Wake; Control of Vortex Breakdown in Critical Swirl Regime Using Azimuthal Forcing; External and Turbomachinery Flow Control Working Group; Boundary Layers, Transitions and Separation; Efficiency Considerations in Low Pressure Turbines; Summary of Conference; and Final Plenary Session Transcript.

LaGraff, John E.↗
NASA NTRS2008

Limits on O VI Emission from the Shocked Circumstellar Gas of SN 1987A

The Far Ultraviolet Spectroscopic Explorer (FUSE) was used to search for emission from the shock interaction of the ejecta of SN 1987A with its circumstellar material. FUSE observations of SN 1987A between 2000 and 2007 did not detect broad OVI emission. However, OVI emission was detected in 2000-2001 with a narrow line width (FWHM <35 kms t ) and a heliocentric radial velocity of +280 km/s. This places the emitting gas at rest relative to the supernova and is interpreted as emission from unshocked circumstellar gas. This narrow emission had disappeared in 2007 (and possibly earlier) as a result of the advancing shock overtaking the H II region that was flash ionized by the supernova explosion in 1987.

Sonneborn, George↗
NASA NTRS2003

Navier-Stokes and Comprehensive Analysis Performance Predictions of the NREL Phase VI Experiment

A vortex lattice code, CAMRAD II, and a Reynolds-Averaged Navier-Stoke code, OVERFLOW-D2, were used to predict the aerodynamic performance of a two-bladed horizontal axis wind turbine. All computations were compared with experimental data that was collected at the NASA Ames Research Center 80- by 120-Foot Wind Tunnel. Computations were performed for both axial as well as yawed operating conditions. Various stall delay models and dynamics stall models were used by the CAMRAD II code. Comparisons between the experimental data and computed aerodynamic loads show that the OVERFLOW-D2 code can accurately predict the power and spanwise loading of a wind turbine rotor.

NREL (NATIONAL RENEWABLE ENERGY LABORATORY)↗