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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1995

Stellar Activity at the End of the Main Sequence: GHRS Observations of the M8 Ve Star VB 10

We present Goddard High Resolution Spectrograph observations of the M8 Ve star VB 10 (equal to G1 752B), located very near the end of the stellar main sequence, and its dM3.5 binary companion G1 752A. These coeval stars provide a test bed for studying whether the outer atmospheres of stars respond to changes in internal structure as stars become fully convective near mass 0.3 solar mass (about spectral type M5), where the nature of the stellar magnetic dynamo presumably changes, and near the transition from red to brown dwarfs near mass 0.08 solar mass (about spectral type M9), when hydrogen burning ceases at the end of the main sequence. We obtain upper limits for the quiescent emission of VB 10 but observe a transition region spectrum during a large flare, which indicates that some type of magnetic dynamo must be present. Two indirect lines of evidence-scaling from the observed X-ray emission and scaling from a time-resolved flare on AD Leo suggest that the fraction of the stellar bolometric luminosity that heats the transition region of VB 10 outside of obvious flares is comparable to, or larger than, that for G1 752A. This suggests an increase in the magnetic heating rates, as measured by L(sub line)/L(sub bol) ratios, across the radiative/convective core boundary and as stars approach the red/brown dwarf boundary. These results provide new constraints for dynamo models and models of coronal and transition-region heating in late-type stars.

Linsky, Jeffrey L.↗
NASA NTRS1987

Direct infrared imaging of VB 8

Near-infrared images of VB 8 taken at K (2.2 microns) and L-prime (3.75 microns) during a period of good seeing at the IRTF show no evidence of the brown dwarf companion reported by McCarthy et al. (1985). Any companion 1.0 arcsec away from the primary must be at least 4 mag fainter than the primary at K and 3 mag fainter at L-prime in order to escape detection. A faint nebula centered on the star with scattering properties similar to a nebula detected near another main-sequence M star, Lalande 21185 (reported by McCarthy in 1986), may account for the extended emission detected by speckle observations.

Skrutskie, M. F.↗
NASA NTRS2000

Control of Convection by Dynamic Magnetic Fields for VB, FZ and THM Crystal Growth Application

The Traveling Magnetic Field (TMF) technique, recently proposed to control meridional flow in electrically conducting melts is reviewed. In particular, the natural convection damping capability of this technique has been numerically demonstrated with the implication of significantly improving crystal quality. Advantages of the traveling magnetic field, in comparison to the more mature rotating magnetic field method, are discussed. Finally, a detailed one-dimensional planar TMF model has been developed and is presented.

Mazuruk, Konstantin↗
NASA NTRS1982

Radiation-induced loss of unsaturation in 1,2-polybutadiene

The radiation induced loss of unsaturation and methyl production in 1,2-polybutadiene (VB) was studied using IR spectroscopy. It was found that G(-1,2), which depends on the initial vinyl content, decreased from approximately 550 for VB with 98.5% 1,2 initially, to approximately 270 for VB with 85% 1,2 initially. G(-trans-1,4) ranged from approximately 21 for VB with 14% trans-1,4 to nearly zero for VB with less than 1% trans-1,4 initially. Methyl production was found to equal one methyl group formed for every 4-5 vinyl units consumed in the radiation-cyclized VB, in contrast to one methyl formed for every two vinyls reacted during cationic cyclization to give monocyclic structures. The IR spectra of gamma-irradiated VB were very similar to the spectra of UV-irradiated or thermally-treated VB at the same residual vinyl contents. It is suggested that the radiation-induced cyclization of VB occurs by a nonionic, nonradical 'energy chain' mechanism, which apparently holds for the cyclization of VB, whether induced by gamma-rays, UV radiation, or heat.

Golub, M. A.↗
NASA NTRS1994

Coronal X-ray sources in the Hyades: A 40 kilosecond ROSAT pointing

We present results of a 40 ks ROSAT pointed observation of the Hyades cluster. The limiting L(sub x) is approximately = 2 x 10(exp 27) ergs/sec at field center, increasing to approximately = 2 x 10(exp 28) ergs/sec at 40 min off-axis. This represents the most sensitive X-ray observation to date in the Hyades region. More than 30 sources have been detected in the Position Sensitive Proportional Counter (PSPC) standard processing, of which 15 are Hyades members, five are cluster candidates that are likely non-members, four are foreground or background stars, and the remainder are unidentified. One Hyad, VB 173 (= VA 276), lies in a confused region, but is detected as a distinct source in the soft band only (E approximately less than 0.5 keV). We report upper limits for four other Hyades members in our field, all M dwarfs. Of the 16 Hyades detections, two represent the optically faintest members seen to date in X-rays; VA 260 (V = 16.68) and VA 368 (V = 16.25). These are both M dwarfs of mass approximately = 0.15-0.2 solar mass and are fully convective stars according to current theory. Analysis of X-ray light curves using 1 ks bins indicates some variability in the strongest sources and a possible flare in VA 383. Two Hyades stars, VB 141 and VB 71, were also detected with the co-aligned Wide Field Camera (WFC) EUV instrument. VB 141, the second brightest X-ray source in the Hyades, remains an enigma: a rapidly rotating FO star with a fainter, long-period companion, this object has an X-ray spectrum indicative of strong coronal activity. X-ray pulse-height analysis demonstrates that coronal models with at least two temperatures are required for most of the stronger X-ray sources. The ROSAT X-ray spectra generally require higher temperatures for the hotter component in the M dwarfs compared to the F-G dwarfs.

Stern, Robert A.↗
NASA NTRS1987

Low-energy X-ray observations of the Wolf 630 system

The Exosat channel multiplier array is used to resolve the septuplet of M dwarfs into three components (Wolf 630ABab, Wolf 629ab, and VB 8AB) with widely different X-ray characteristics. An isothermal plasma temperature of between 800,000 and 550,000 K (which is very low in the known range of coronal temperatures) is found for any relatively quiescent state of VB 8. It is shown from the count rate during 18,112 sec of effective exposure with Exosat that VB 8 flared once in 0.05-2 keV flux.

Johnson, Hugh M.↗
NASA NTRS2005

Re-Configurable Electronics Characterization under Extreme Thermal Environment

The need for reconfigurable electronics is driven by requirements to survive longer missions and harsher environments. It is possible to compensate for degradations in Extreme Environments (EE). EE has effect on electronics: circuits are designed to exploit device characteristics and when a certain temperature or radiation range is exceeded the circuit function gradually degrades. It is possible to employ Hardening by reconfiguration (HBR) to mitigate drifts, degradation, or damage on electronic devices in EE by using reconfigurable devices and an adaptive self-reconfiguration of circuit topology. In this manner degraded components can be salvaged, and completely damaged components can be bypassed. The challenge of conventional design is replaced with that of designing a recover process that automatically performs the (re) design in place of the designer. The objective of testing a Digital Signal Processor (DSP) under the extreme temperatures was to determine the lowest temperature at which the DAP can operate. The objective of testing a Xilinx VirtexII Pro FPGA board was to initially find our whether the evaluation board and the FPGA would survive and continue at temperature ranges from -180 C, and 120 C. The Virtex II functioned correctly at the temperatures tested. The next test was done on the GM-C filter building block using the same temperature range as the Virtex II. The current lower and upper limits were shown to be reduced as the temperature gets lower. The device function can be recovered by increasing the Vb from .08V to .85V. The negative and positive saturation voltages increases as the temperature gets higher. The function of the device can be recovered by decreasing the Vb from .8V to around .75V. The next test was performed to test the recovery of the GmC low pass filter through Vb in a filter circuit. The test indicate that bias voltage control adjustment is an efficient mechanism for circuit recovery at extreme temperatures.

reliability↗
NASA NTRS2010

Control of Vortex Breakdown in Critical Swirl Regime Using Azimuthal Forcing

We finally go back to the four swirl cases and see how the flow responds to either forcing m = -1 or m = -2. On the left we see the flow forced at m = -1 We see that the PVC locks onto the applied forcing also for lower swirl number causing this high TKE at the jet center. The amplification of this instability causes VB to occur at a lower swirl number. The opposite can be seen when forcing the flow at m=-2 which is basically growing in the outer shear layer causing VB to move downstream . There is no energy at the center of the vortex showing that the precessing has been damped. The mean flow is most altered at the swirl numbers were VB is unstable.

Oberleithner, Kilian↗
NASA NTRS1985

On the nature of the companion to Van Biesbroeck 8

Results of the first numerical evolutionary calculations for very low-mass stars with ages up to the age of the Galaxy are presented. The calculations shed new light on the nature of the recently discovered object VB 8B, the companion to Van Biesbroeck's star no. 8, and support the identification of this object as a low-mass star in which hydrogen burning was never able to establish thermal equilibrium. For plausible ages of this binary stellar system, the mass of VB 8B is estimated to be in the range 0.04-0.08 solar mass. The object is supported primarily by degenerate electron pressure; its present values of central density and temperature are found to be 500-2000 g/cu cm and 1.0-1.5 million K. An orbital period of more than about 40 yr is predicted for the binary system. The presented evolutionary tracks are also applicable to the interpretation of observations of other very low-luminosity dwarfs.

Nelson, L. A.↗
NASA NTRS1985

Emerging monochromatic fluxes and colors of red degenerate stars

The emerging monochromatic fluxes and the B-V, V-I, J-H, and V-K color indices are presented for red degenerate stars with helium atmospheres which were calculated using an equation of state and opacities based on a hot Thomas-Fermi model of the helium gas. The effective temperature range is 4500-2500 K. It is found that although the emerging fluxes resemble blackbody curves, red degenerates emit more radiation than blackbodies in the short wavelength range and less in the long wavelength range. Thus, red degenerates appear bluer than blackbodies of the same temperature. The calculated colors of these models are compared to the colors of some of the coolest known non-DA degenerate stars. In particular it is found that the B-V and V-I colors of the cool white dwarf VB 11, whose temperature had been previously estimated to be higher than 4000 K, suggest a temperature of 3750 K. If this result is correct, then VB 11 is probably the coolest known white dwarf.

Kapranidis, S.↗
NASA NTRS1987

Reactions of Atomic Oxygen (O(3P)) with Polybutadienes and Related Polymers

Thin films of the following polymers were exposed at ambient temperature to ground-state oxygen atoms (O(3P)), generated by a radio-frequency glow discharge in O2: cis- and trans-1,4-polybutadienes (CB and TB), amorphous 1,2-polybutadiene (VB), polybutadienes with different 1,4/1,2 contents, trans polypentenamer (TP), cis and trans polyoctenamers (CO and TO), and ethylene-propylene rubber (EPM). Transmission infrared spectra of CB and TB films revealed extensive surface recession, or etching, unaccompanied by any microstructural changes within the films, demonstrating that the reactions were confined to the surface layers. Contrary to the report by Rabek, Lucki, and Ranby (1979), there was no O(3P)-induced cis-trans isomerization in CB or TB. From weight-loss measurements, etch rates for polybutadienes were found to be markedly dependent on vinyl content, decreasing by two orders of magnitude from CB (2% 1,2) to structures with 30 to 40% 1,2 double bonds, thereafter increasing by half an order of magnitude to VB (97% 1,2). Relative etch rates for EMP and the polyalkenamers were in the order: EMP is greater than CO (or TO) is greater than TP is greater than CB. The sole non-elastomer examined, TB, had an etch rate about six times that of CB, ascribable to a morphology difference. Cis/trans content had a negligible effect on the etch rate of the polyalkenamers. Mechanisms involving crosslinking through units are proposed for the unexpected protection imparted to polybutadienes by the 1,2 double bonds.

Golub, Morton A.↗
NASA NTRS1981

Thermal Rearrangements of Polybutadienes with Different Vinyl Contents

A study was made of the loss of double bonds in equibinary (1,4-1,2) polybutadiene (EB) and in polybutadienes with 30% 1,2, 70% 1,4 (FI), and 10% 1,2, 90% 1,4 (DI) double-bond content, when heated in vacuum under nonpyrolitic conditions (temperature range 220-280 C). These polymers were found to undergo second-order loss of 1,2 unsaturation with similar activation energies (E(sub a) = 34.0 +/- 3 kcal/mole), by analogy to the previously reported thermally induced loss of double bonds in 1,2-polybutadiene (VB) (E(sub a) = 33.6 +/- 3 kcal/mole). Moreover, EB and Fl exhibited also second-order loss of 1,4 unsaturation, with E(sub a) ca. 36 and 40 kcal/mole, respectively, while DI showed negligible loss of 1,4 unsaturation below 260 C, in common with cis-1,4-polybutadiene (CB) (with 2% 1,2 double bonds) examined earlier. The loss of 1,2 double bonds in the various polybutadienes with different vinyl contents is accompanied by substantial methyl production, ranging from about one methyl group formed for every 4-5 vinyl units lost in VB, to one methyl for every two vinyls lost in EB,and to almost one methyl for each vinyl lost in DI or CB. Mechanisms are proposed for the thermally induced loss of 1,2 and 1,4 unsaturation in various polybutadienes and for the accompanying methyl production.

Golub, Morton A.↗
NASA NTRS1998

EUVE Observations of the Hyades Giants

The contractor describes EUVE and ROSAT observations of the Hyades K0 III giants theta(sup 1(vB 71 = HR 1411) and gamma$ (vB 28 = HR 1346) Tau, and ASCA observations of theta(sup 1) Tau. The coronal activity of these "clump" giants is intermediate between that of the Sun and of high-activity stars such as RS CVn systems. There is no evidence for significant short or long term variability up to several years. Modeling of the individual and combined spectra suggest that these two X-ray and EUV- bright Hyades giants resemble in their activity levels another clump giant, beta Cet, with a peak in the emission measure distribution near log T approx. 6.8, reminiscent of the Capella emission measure "bump."

Stern, Robert A.↗
NASA NTRS1998

EUVE Observations of the Hyades Giants

We describe EUVE and ROSAT observations of the Hyades K0 III giants theta(sup 1) (vB 71 = HR1411) and gamma (vB 28 = HR1346) Tau. We also discuss ASCA observations of theta(sup 1)Tau. The coronal activity of these "clump" giants is intermediate between that of the Sun and of high activity stars such as RS CVn systems. There is no evidence for significant short or long term variability up to several years. Modeling of the individual and combined spectra suggest that these two X-ray and EUV-bright Hyades giants resemble in their activity levels another clump giant, beta Cet, with a peak in the emission measure distribution near log T approx. 6.8, reminiscent of the Capella emission measure "bump."

Stern, Robert A.↗
NASA NTRS1996

Quantitative changes of GABA-immunoreactive cells in the hindlimb representation of the rat somatosensory cortex after 14-day hindlimb unloading by tail suspension

The present study was aimed at evaluating quantitatively gamma-aminobutyric acid (GABA) immunoreactivity in the hindlimb representation of the rat somatosensory cortex after 14 days of hindlimb unloading by tail suspension. A reduction in the number of GABA-immunoreactive cells with respect to the control animals was observed in layer Va and Vb. GABA-containing terminals were also reduced in the same layers, particularly those terminals surrounding the soma and apical dendrites of pyramidal cells in layer Vb. On the basis of previous morphological and behavioral studies of the neuromuscular system of hindlimb-suspended animals, it is suggested that the unloading due to hindlimb suspension alters afferent signaling and feedback information from intramuscular receptors to the cerebral cortex due to modifications in the reflex organization of hindlimb muscle groups. We propose that the reduction in immunoreactivity of local circuit GABAergic neurons and terminals is an expression of changes in their modulatory activity to compensate for the alterations in the afferent information.

Non-NASA Center↗
NASA NTRS1992

Effects of dimethyl prostaglandin A1 on herpes simplex virus and human immunodeficiency virus replication

We have investigated the direct effect of dimethyl prostaglandin A1 (dmPGA1) on the replication of herpes simplex virus (HSV) and human immunodeficiency virus type 1 (HIV-1). dmPGA1 significantly inhibited viral replication in both HSV and HIV infection systems at concentrations of dmPGA1 that did not adversely alter cellular DNA synthesis. The 50% inhibitory concentration (ID50) for several HSV type 1 (HSV-1) strains ranged from 3.8 to 5.6 micrograms/ml for Vero cells and from 4.6 to 7.3 micrograms/ml for human foreskin fibroblasts. The ID50s for two HSV-2 strains varied from 3.8 to 4.5 micrograms/ml for Vero cells; the ID50 was 5.7 micrograms/ml for human foreskin fibroblasts. We found that closely related prostaglandins did not have the same effect on the replication of HSV; dmPGE2 and dmPGA2 caused up to a 60% increase in HSV replication compared with that in untreated virus-infected cells. HIV-1 replication in acutely infected T cells (VB line) and chronically infected macrophages was assessed by quantitative decreases in p24 concentration. The effective ID50s were 2.5 micrograms/ml for VB cells acutely infected with HIV-1 and 5.2 micrograms/m for chronically infected macrophages. dmPGA1 has an unusual broad-spectrum antiviral activity against both HSV and HIV-1 in vitro and offers a new class of potential therapeutic agents for in vivo use.

Non-NASA Center↗
NASA NTRS2009

Interactive, Automated Management of Icing Data

IceVal DatAssistant is software (see figure) that provides an automated, interactive solution for the management of data from research on aircraft icing. This software consists primarily of (1) a relational database component used to store ice shape and airfoil coordinates and associated data on operational and environmental test conditions and (2) a graphically oriented database access utility, used to upload, download, process, and/or display data selected by the user. The relational database component consists of a Microsoft Access 2003 database file with nine tables containing data of different types. Included in the database are the data for all publicly releasable ice tracings with complete and verifiable test conditions from experiments conducted to date in the Glenn Research Center Icing Research Tunnel. Ice shapes from computational simulations with the correspond ing conditions performed utilizing the latest version of the LEWICE ice shape prediction code are likewise included, and are linked to the equivalent experimental runs. The database access component includes ten Microsoft Visual Basic 6.0 (VB) form modules and three VB support modules. Together, these modules enable uploading, downloading, processing, and display of all data contained in the database. This component also affords the capability to perform various database maintenance functions for example, compacting the database or creating a new, fully initialized but empty database file.

Levinson, Laurie H.↗