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At least 271 records · Page 15

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NASA NTRS1990

Radio emission from rapidly-rotating cool giant stars

The results of a VLA program are reported to examine the radio continuum emission from 11 rapidly-rotating cool giant stars, all of which were originally believed to be single stars. Six of the 11 stars were detected as radio sources, including FK Com and HR 9024, for which there exist multifrequency observations. HD 199178, UZ Lib (now known to be a binary system), and HD 82558, for which there is only 6-cm data. The radio properties of these stars are compared with those of the active, rapidly rotating evolved stars found in the RS CVn binary systems.

Drake, Stephen A.↗

NASA NTRS1991

Chromospherically active stars. IX - HD 33798 = V390 Auirigae - A lithium-rich rapidly rotating single giant

Results are presented of spectroscopic observations of HD 33798 obtained to determine if this star is a short-period binary and to examine its evolutionary status. Analysis of 40 radial velocities indicates no periodic velocity variations, suggesting that the star is single, so its rapid rotation is highly unusual. This rotation is inconsistent with the rotational brake hypothesis advanced by Gray (1989). It is proposed that HD 33798 is in a post-main-sequence phase of evolution. Its space motion is similar to FK Com, suggesting that it is a coalesced binary in the process of spinning down. Scenarios are presented to explain its large lithium abundance. A version in which material is transferred from a rapidly rotating core is suggested as the most likely.

Fekel, Francis C.↗

NASA NTRS1992

Tracking performance with two breathing oxygen concentrations after high altitude rapid decompression

Current military aircraft Liquid Oxygen (LOX) systems supply 99.5 pct. gaseous Aviator's Breathing Oxygen (ABO) to aircrew. Newer Molecular Sieve Oxygen Generation Systems (MSOGS) supply breathing gas concentration of 93 to 95 pct. O2. The margin is compared of hypoxia protection afforded by ABO and MSOGS breathing gas after a 5 psi differential rapid decompression (RD) in a hypobaric research chamber. The barometric pressures equivalent to the altitudes of 46000, 52000, 56000, and 60000 ft were achieved from respective base altitudes in 1 to 1.5 s decompressions. During each exposure, subjects remained at the simulated peak altitude breathing either 100 or 94 pct. O2 with positive pressure for 60 s, followed by a rapid descent to 40000 ft. Subjects used the Tactical Life Support System (TLSS) for high altitude protection. Subcritical tracking task performance on the Performance Evaluation Device (PED) provided psychomotor test measures. Overall tracking task performance results showed no differences between the MSOGS breathing O2 concentration of 94 pct. and ABO. Significance RMS error differences were found between the ground level and base altitude trials compared to peak altitude trials. The high positive breathing pressures occurring at the peak altitudes explained the differences.

Nesthus, Thomas E.↗

NASA NTRS1991

Ada and the rapid development lifecycle

JPL is under contract, through NASA, with the US Army to develop a state-of-the-art Command Center System for the US European Command (USEUCOM). The Command Center System will receive, process, and integrate force status information from various sources and provide this integrated information to staff officers and decision makers in a format designed to enhance user comprehension and utility. The system is based on distributed workstation class microcomputers, VAX- and SUN-based data servers, and interfaces to existing military mainframe systems and communication networks. JPL is developing the Command Center System utilizing an incremental delivery methodology called the Rapid Development Methodology with adherence to government and industry standards including the UNIX operating system, X Windows, OSF/Motif, and the Ada programming language. Through a combination of software engineering techniques specific to the Ada programming language and the Rapid Development Approach, JPL was able to deliver capability to the military user incrementally, with comparable quality and improved economies of projects developed under more traditional software intensive system implementation methodologies.

Deforrest, Lloyd↗

NASA NTRS1992

Satellite-derived surface latent heat fluxes in a rapidly intensifying marine cyclone

Surface latent heat fluxes are estimated in the vicinity of a rapidly deepening cyclone before and during its period of most rapid intensification. This was done with a bulk parameterization scheme and remotely sensed input data. A method is studied for estimating the difference in specific humidity between the surface and a ten meter height using the Special Sensor Microwave/Imager (SSM/I) observed integrated water vapor field and a sea surface temperature analysis. The surface latent heat flux fields generally have estimated errors below 40 pct. south of 40 deg. N and outside the region of high integrated water vapor values associated with frontal bands. The method of estimating surface latent heat fluxes for the case study was found to be usable in most regions of the Northwest Atlantic Ocean except for those locations directly adjacent to coastlines in instances of offshore flow and in the vicinity of surface fronts.

Miller, Douglas K.↗

NASA NTRS1990

An experimental study of the effects of rapid rotation on turbulence

Experiments, large eddy simulations and direct numerical simulations all show that rapid rotation has a striking effect on homogeneous nearly isotropic turbulence. The cascade process is effectively inhibited by rotation, and thus dissipation is greatly reduced. Some attempts have been made to incorporate this effect in turbulence models. Numerical simulation further showed the somewhat surprising result that anisotropic homogeneous turbulence subjected to rotation tended towards an isotropic state; however, the residual anisotropy was not zero. Reynolds (1989) performed a detailed analysis using Rapid Distortion Theory (RDT) and showed that a reduction in the anisotropy is indeed expected and if the anisotropy is produced by irrotational strain then the anisotropy tensor b(sub ij) is asymptotically driven to half its initial value. Our objective is to extend the work of the experiments mentioned above to lower turbulent Rossby numbers and to confirm some of the results obtained by Reynolds (1989) for anisotropic turbulence.

Veeravalli, S. V.↗

NASA NTRS1992

Rapid development of the X-31 simulation to support flight-testing

The X-31 Enhanced Fighter Maneuverability Program has been recognized to form the International Test Organization, with the NASA Dryden Flight Research Facility (NASA-Dryden) as the responsible test organization. The two X-31 research aircraft and engineering support personnel were colocated at NASA-Dryden, with flight test operations beginning in Apr. 1992. Therefore, rapid development of a hardware-in-the-loop simulation was needed to support the flight test operations at NASA-Dryden, and to perform verification and validation of flight control software. The X-31 simulation system requirements, distributed simulation system architecture, simulation components math models to the visual system, and the advanced capabilities the X-31 simulation provides. In addition, unique software tools and the methods used to rapidly develop this simulation system will be highlighted.

Mackall, Dale↗

NASA NTRS1991

Containerless processing and rapid solidification of Nb-Si alloys in the niobium-rich eutectic range

Containerless processing and rapid solidification techniques were used to process Nb-Si alloys in the Nb-rich eutectic range. Electromagnetically levitated drops were melted and subsequently splat-quenched from different temperatures. A variety of eutectic morphologies was obtained as a function of the degree of superheating or undercooling of the drops prior to splatting. Metallic glass was observed only in drops quenched from above the melting temperature. Microstructures of splats deeply undercooled prior to quenching were very fine and uniform. These results are discussed in terms of classic nucleation theory concepts and the expected heat evolution at different regions of the splat during the rapid quenching process. The locations of the coupled-zone boundaries for the alpha-Nb + Nb3Si eutectic are also suggested.

Hofmeister, W. H.↗

NASA NTRS1991

Microstructural and magnetic characterization of rapidly solidified and annealed Pt-Co-B alloys

Significant increases in intrinsic coercivity (Hic) of Pt-Co alloys have been obtained by the addition of boron and the application of rapid solidification processing. After rapid solidification by double anvil splat quenching with subsequent annealing at 650 C for 30 min, an alloy of Pt42Co45B13 exhibits an Hic as high as 14 kOe. Annealing of the Pt-Co-B influences the L1(0) superlattice structure and grain size of the matrix, the crystal structure and size of Co-boride precipitate, and the distribution of magnetic domain walls. A microstructural analysis shows that the maximum H(ic) occurs when Co borides, having the Co3B structure, are within the single magnetic domain size. The magnetic hardening mechanism in Pt-Co-B is believed to be a combination of inhibited magnetic domain nucleation and difficult reverse magnetic domain growth caused by the interaction of the magnetically anisotropic Co borides with the L1(0) Pt-Co matrix.

Qiu, N.↗

NASA NTRS1992

The Jodrell bank 'C' pulsar survey - A survey of the northern Galactic plane for rapidly rotating pulsars

Nearly 1500 sq deg of the northern Galactic plane were surveyed for rapidly rotating pulsars using the 76-m Lovell telescope. The sampling rate was such that there was sufficient nominal sensitivity to detect pulsars with periods as short as 0.6 ms. To overcome the effects of dispersion, scattering, and galactic background radiation, the high frequency of 1420 MHz was used to survey the inner Galaxy, while lower frequencies of 928 and 610 MHz were used for regions further from the Galactic center. PSR 1937 + 21 was detected in the survey, but no new pulsars were discovered. This is consistent with the results of other recent surveys and suggests that rapidly rotating, high-luminosity pulsars are not very common in the Galactic disk.

Biggs, J. D.↗

NASA NTRS1992

Instantaneous response of elastic thin-walled structures with arbitrary open cross section to rapid heating

A generalized modeling and analysis approach of thermally-induced coupled vibrations of elastic thin-walled configurations with arbitrary open cross sections are presented in conjunction with a unified implicit transient methodology. Limited research appears in literature which takes into account the influence of rapid thermal heating effects on structures involving various forms of coupling. As a consequence, the dynamic response of such thin-walled structures of arbitrary open cross section due to rapid heating are described here. Effects involving triple, double, and no coupling between bending and torsional vibrations caused by sudden heating on these structures are examined. Numerical test cases are presented which describe the influence of sudden heating on elastic thin-walled structures of arbitrary open cross sections.

Chen, Xiaoqin↗

NASA NTRS1992

The relation between the bolometric flux and the blackbody temperature at the peak of type II bursts from the Rapid Burster

During about 6 hr of Ginga observations of the Rapid Burster in August 1988, the source emitted type II bursts with durations between about 3 and about 35 s and with peak fluxes which varied by factors of about 5. The Rapid Burster was active in two bursting modes as defined by Marshall et al. (1979): mode I characterize by a burst energy distribution which is 'double-peaked' and mode II by a distribution which is 'single-peaked'. A study of the relationship between the maximum bolometric burst flux, F(max), and the associated blackbody temperature, Tc, shows that mode I bursts consistently show higher Tc values than bursts of mode II. These results, together with previous work, suggest that the relation between F(max) and Tc is dependent on mode. In mode I the color temperature is approximately independent of the burst peak flux, whereas in mode II the two properties are correlated.

Lubin, Lori M.↗

NASA NTRS1992

Satellite-derived surface latent heat fluxes in a rapidly intensifying marine cyclone

The aim of this article is to estimate surface latent heat fluxes in the vicinity of a rapidly deepening cyclone before and during its period of most rapid intensification. This is done with a bulk parameterization scheme and remotely sensed input data. A method for estimating the difference in specific humidity between the surface and a 10-m height is investigated using the Special Sensor Microwave/Imager-observed integrated water vapor field and a sea surface temperature analysis. The surface latent heat flux fields generally have estimated errors below 40 percent south of 40 deg N and outside the region of high integrated water vapor values associated with frontal bands. The method of estimating surface latent heat fluxes for the case study was found to be usable in most regions of the northwest Atlantic Ocean except for those locations directly adjacent to coastlines in instances of offshore flow and in the vicinity of surface fronts.

Miller, Douglas K.↗

NASA NTRS1992

Rapid detection and quantification of features such as damage or flaws in composite and metallic structures

An apparatus, system, and method for non-destructible evaluation (NDE) of a material use thermography to rapidly detect and/or generally locate a feature such as, for example, damage or a defect in the material. The apparatus, system, and method also use ultrasound to specifically locate the feature in the material for quantification and/or evaluation either by an operator or by an external device suited for such purpose. Accordingly, the apparatus, system and method are particularly useful for NDE in applications such as the analysis of the structure of an aircraft, for example, in which the scale of the material to be analyzed is large, thus requiring the rapid NDE afforded by thermography, and in which quantification and/or evaluation of a feature must be performed with precision, thus requiring the relatively high-resolution NDE afforded by ultrasound.

Farley, Gary L.↗

NASA NTRS1993

A rapid-distortion-theory turbulence model for developed unsteady wall-bounded flow

A new approach to turbulence modeling in unsteady developed flows has recently been introduced, based on results of rapid distortion theory. The approach involves closing the k-epsilon equations for the organized unsteady component of the flow by modeling local unsteadiness as a rapid distortion of the local structure of the parent turbulent flow, in terms of an effective strain parameter alpha(sub eff). In this paper, the phase-conditioned equations of motion are developed to accommodate a new unsteady dissipation model and local effects of the slow-relaxation time scale of the parent flow. The model equations are tested against measurements of the response of a fully-developed turbulent pipe flow to the superposition of sinusoidal streamwise oscillation. Good agreement is found between measurements and predictions over a wide range of frequencies of unsteadiness, indicating that this approach may be particularly well suited to modeling of unsteady turbulent flows which are perturbations about a well characterized mean.

Brereton, G. J.↗

NASA NTRS1992

Rapid development of the X-31 simulation to support flight-testing

Mackall, Dale↗

NASA NTRS1993

A seven-year northern sky survey of Ap stars for rapid variability

A high-speed photometric survey of 120 Ap stars in the northern sky, has been conducted, between 1985 and 1991, in order to search for rapid variability. Stars of spectral types, namely from B8 to F4, have been selected for the survey. The selected pulsational variable stars occupy the hotter regions of the instability strip of the Hertzsprung-Russel diagram. Noted is the absence of pulsations in the hotter B8-A3 Ap stars; this does not, however, preclude the existence of pulsations, since HD 218495 was recently discovered to be a rapidly oscillating Ap (roAp) star. The primary result of this study is that various combinations of photometric indices, while pointing towards roAp stars having the characteristic signatures of cool, SrCrEu stars, still fail to isolate the roAp phenomenon from similar nonpulsating Ap stars. Color-magnitude and color-color diagrams are presented in order to complete this survey.

Nelson, Matthew J.↗

NASA NTRS1993

Infrared radiative properties of rapidly cooling, initially molten Al2O3 particles

A shock tube technique was used to investigate the effects of rapid cooling of molten Al2O3 particles on their radiative signatures below the melt. Optically thin clouds of submicron Al2O3 particles in an Ar bath were shock-heated and then quench-cooled by a rarefaction wave. Visible pyrometry monitored the temperature history of the particles and infrared detectors quantified the IR signatures at several wavelengths. Data analysis gave values of the imaginary refractive index, k. As the particles cooled to submelt temperatures (1600 to 2300 K), the values of k remained near 0.1, comparable to the liquid values and several orders of magnitude larger than those for bulk alpha-Al2O3. This results in an enhancement of SWIR radiation by three or more orders of magnitude. These results give strong evidence that a rapid-cooling solidification process is primarily responsible for discrepancies between observed and predicted radiation in SRM tests.

Rawlins, W. T.↗