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At least 829 records · Page 46
All sourcesNASA NTRSDOE OSTI
NASA NTRS1991

The x ray morphology of the relaxed cluster of galaxies A2256. 2: Sources around the extended cluster emission

X-ray emission from cluster galaxies as well as from 'dark objects' (i.e. not visible on the Palomar Observatory Sky Survey (POSS)) seen in the x-ray observation of A2256 with the imaging proportional counter on board ROSAT (x-ray astronomy satellite), is reported. This observation revealed significantly more sources in the field around the extended cluster emission than one would expect by chance. In a preliminary investigation, 14 sources were discovered at the limiting flux for this exposure, whereas about 7 sources would have been expected by chance. At least two of those sources are coincident with cluster member galaxies, having x-ray luminosities of approximately 10(exp +42) erg/s in the ROSAT energy band from 0.1 to 2.4 keV, but at least four more are from 'dark' objects. The similarity of these objects to those in A1367 suggests the existence of a new class of x-ray sources in clusters.

Henry, J. Patrick↗
NASA NTRS1992

Biophysical, morphological, canopy optical property, and productivity data from the Superior National Forest

Described here are the results of a NASA field experiment conducted in the Superior National Forest near Ely, Minnesota, during the summers of 1983 and 1984. The purpose of the experiment was to examine the use of remote sensing to provide measurements of biophysical parameters in the boreal forests. Leaf area index, biomass, net primary productivity, canopy coverage, overstory and understory species composition data are reported for about 60 sites, representing a range of stand density and age for aspen and spruce. Leaf, needle, and bark high-resolution spectral reflectance and transmittance data are reported for the major boreal forest species. Canopy bidirectional reflectance measurements are provided from a helicopter-mounted Barnes Multiband Modular Radiometer (MMR) and the Thematic Mapper Simulator (TMS) on the NASA C-130 aircraft.

Hall, F. G.↗
NASA NTRS1992

Morphological instability of a thermophoretically growing deposit

The stability of the planar interface of a structureless solid growing from a depositing component dilute in a carrier fluid is studied when the main solute transport mechanism is thermal (Soret) diffusion. A linear stability analysis, carried out in the limit of low growth Peclet number, leads to a dispersion relation which shows that the planar front is unstable either when the thermal diffusion factor of the condensing component is positive and the latent heat release is small or when the thermal diffusion factor is negative and the solid grows over a thermally-insulating substrate. Furthermore, the influence of interfacial energy effects and constitutional supersaturation in the vicinity of the moving interface is analyzed in the limit of very small Schmidt numbers (small solute Fickian diffusion). The analysis is relevant to physical vapor deposition of very massive species on cold surfaces, as in recent experiments of organic solid film growth under microgravity conditions.

Castillo, Jose L.↗
NASA NTRS1992

Infrared morphology of mass outflow from GL 2591

Results are presented of a spectrophotometric study of a young stellar object, GL 2591, at wavelengths covering 2.10 to 2.27 microns, employing the KPNO long-slit cryogenic spectrometer. H2 emission was discovered in this source. A map of the v = 1-0 S(1) emission line shows a bipolar structure extending over 0.9 d (d/2 kpc) pc in an east-west direction roughly centered around GL 2591 IRS, with four bright knotty peaks. Br-gamma emission was detected in this source. A map of the Br-gamma emission line delineates a monopolar jetlike structure emanating over 0.2 d (d/2 kpc)pc from NIRS 1 to the southwest. The map of 2-micron continuum emission shows a multilooplike structure extending predominantly to the west. The dust distribution derived from this continuum map reveals a monopolar shell structure composed of several clumps. The spatial distribution of the H2, Br-gamma and 2-micron continuum emission is consistently explained by an outflow and dust disk model around GL 2591, if this emission is interpreted as shocked gas, ionized, gas, and swept-up dust, respectively, associated with the outflow from GL 2591.

Tamura, Motohide↗
NASA NTRS1992

Stratospheric sulfate aerosol in and near the Northern Hemisphere polar vortex - The morphology of the sulfate layer, multimodal size distributions, and the effect of denitrification

Measurements were made of stratospheric sulfate aerosols using a passive cavity aerosol spectrometer and a condensation nucleus counter on a NASA ER-2 aircraft in the Airborne Arctic Stratospheric Experiment of 1989. The problems of representative and accurate sampling and particle evaporation were explicitly addressed in the design of the inlets and reduction of the data. The measurements suggest that the sulfate aerosol is bimodal in the polar vortex above the mass mixing ratio maximum in the sulfate layer. It appears that a nuclei mode of small, newly formed particles exists in this region. A stronger case is made for a nuclei mode in the upper few kilometers of the troposphere and in the lower few kilometers of the stratosphere. This mode is probably a global phenomenon occurring in all seasons. Comparison of denitrified and nondenitrified air suggests that denitrification removes some of the larger sulfate particles.

Wilson, J. G.↗
NASA NTRS1992

Ultraviolet and optical spectral morphology of Melnick 42 and Radcliffe 136a in 30 Doradus

HST/GHRS ultraviolet spectrograms of the individual O3 If*/WN6-A object Mk 42 in 30 Dor and the adjacent, central multiple system R136a are compared with each other and with an appropriate sequence of O3 If* and WN6-A standards from the IUE archive. The analogous spectral montages covering the blue-violet regino, based on new, homogeneous, digital observations of the same stars with the CTIO 4 m telescope, are also presented. These comparisons show clearly the intermediate O3/WN nature of the Mk 42 spectrum, in terms of both emission-line strength (increasing with envelope density) and stellar-wind velocity (decreasing with envelope density). It is also shown that R136a possesses stronger WN spectral characteristics than Mk 42, in agreement with HST narrow-band imaging by the WF/PC Team.

Walborn, Nolan R.↗
NASA NTRS1992

CCD photometry of the globular cluster NGC 5897 - Morphology of the color-magnitude diagram

The paper presents CCD photometry in the B and V bands of the Galactic globular cluster NGC 5897. The color-magnitude diagram (CMD) obtained for this cluster is used to examine the properties of the cluster and to compare the NGC 5897 to the well-known globular cluster M3. It was found that the metallicity of the NGC 5897 is in the range of the metallicity of M3 and that the age of NGC 5897 is about 2 Gyr greater than that of M3. The CMD for NGC 5897 also reveals a significant population of blue straggler stars (BSS) more massive than the cluster subgiant branch stars. A pseudomain sequence is constructed for NGC 5897 and the previously studied (Sarajedini and Da Costa, 1991) global cluster 6101, which includes the BSS and extends to the faintest regions of the unevolved main sequence.

Sarajedini, Ata↗
NASA NTRS1992

Morphological studies of bone and tendon

The Soviet biosatellite Cosmos 2044 carried adult rats on a spaceflight that lasted 13.8 days and was intended to repeat animal studies carrier out on Cosmos 1887. Skeletal tissue and tendon from animals flown on Cosmos 2044 were studied by light and electron microscopy, histochemistry, and morphometric techniques. Studies were confined to the bone cells and vasculature from the weight-bearing tibias. Results indicated that vascular changes at the periosteal and subperiosteal region of the tibia were not apparent by light microscopy or histochemistry. However, electron microscopy indicated that vascular influsions were present in bone samples from the flight animals. A unique combination of microscopy and histochemical techniques indicated that the endosteal osteoblasts from this same middiaphyseal region demonstrated a slight (but not statisticallly significant) reduction in bone cell activity. Electron-microscopic studies of the tendons from metatarsal bones showed a collagen fibril disorganization as a result of spaceflight. Thus changes described for Cosmos 1887 were present in Cosmos 2044, but the changes ascribed to spaceflight were not as evident.

Doty, Stephen B.↗
NASA NTRS1992

Ground testing of bioconvective variables such as morphological characterizations and mechanisms which regulate macroscopic patterns

Conditions simulating low- and high-gravity, reveal changes in macroscopic pattern formation in selected microorganisms, but whether these structures are gravity dependent is not clear. Two theories have been identified in the fluid dynamics community which support macroscopic pattern formation. The first one is gravity dependent (fluid density models) where small concentrated regions of organisms sink unstably, and the second is gravity independent (wave reinforcement theory) where organisms align their movements in concert, such that either their swimming strokes beat in phase or their vortices entrain neighbors to follow parallel paths. Studies have shown that macroscopic pattern formation is consistent with the fluid density models for protozoa and algae and wave reinforcement hypothesis for caprine spermatozoa.

Johnson, Adriel D.↗
NASA NTRS1992

Morphology and composition of condensates on Apollo 17 orange and black glass

Lunar soil sample 74220 and core samples 74001/2 consist mainly of orange glass droplets, droplet fragments, and their crystallized equivalents. These samples are now generally accepted to be pyroclastic ejecta from early lunar volcanic eruptions. It has been known since early examination of these samples that they contain surface coatings and material rich in volatile condensible phases, including S, Zn, F, Cl, and many volatile metals. The volatiles associated with these orange and black glasses (and the Apollo 15 green glasses) may provide important clues in understanding the differentiation and volcanic history of the Moon. In addition, condensible volatiles can be mobilized and concentrated by volcanic processes. We have reviewed many of our existing photomicrographs and energy dispersive analysis (EDXA) of grain surfaces and have reexamined some of our older SEM mounts using an improved EDXA system capable of light-element detection and analysis (oxygen, nitrogen, and carbon). The results from these investigations are presented.

Mckay, David S.↗
NASA NTRS1993

Is a local bar a good place to find a companion? The near infrared morphology of Maffei 2

Maffei 2 is one of the closest large spiral galaxies lying just beyond the Local Group. It would probably be one of the most heavily studied galaxies in the sky were it not for the approximately 5 magnitudes of visual extinction resulting from its position behind the Galactic plane. It is the site of a burst of nuclear star formation indicated by strong infrared and radii continuum emission. Interferometric maps of CO-12 and CO-13 emission indicate that star formation is associated with a barlike structure consisting of arms of molecular gas that extend from within approximately 50 pc of the dynamical center out to a radius of at least 500 pc. HI maps have shown the galaxy to have an angular extent of approximately 15 feet and a neutral gas mass typical of a large spiral galaxy.

Hurt, Robert L.↗
NASA NTRS1992

The metal-rich globular cluster NGC 6553 - Clump morphology and age

Stellar evolutionary tracks for metal-rich HB stars have been used to construct synthetic population models for the peculiar HB clump in NGC 6553. Although the uncertainties are large, it is possible to derive an age for NGC 6553 in the range 8-13 Gyr, which supports the idea that the disk globular cluster system is younger than the oldest stars in the Galactic halo and bulge.

Demarque, P.↗
NASA NTRS1992

The morphology of 20 x 10 exp 6 K plasma in large non-impulsive solar flares

We have examined images of 10 flares observed by the Soft X-ray Telescope on-board the Yohkoh spacecraft. These images show that the hottest portion of the soft X-ray flare is located in compact regions that appear to be situated at the tops of loops. These compact regions form at, or shortly after, flare onset, and persist well into the decay phase of the flares. In some cases, the compact regions are only a few thousand kilometers in size and are small compared to the lengths of flaring loops. This is inconsistent with the smoother intensity distribution along the loops expected from models of chromospheric evaporation.

Acton, Loren W.↗
NASA NTRS1993

The origin of morphological asymmetries in bipolar active regions

A series of 3D numerical simulations was carried out to examine the dynamical evolution of emerging flux loops in the solar convective envelope. The innermost portions of the loops are anchored beneath the base of the convective zone by the subadiabatic temperature gradient of the underlying overshoot region. It is found that, as the emerging loops approach the photosphere, the magnetic field strength of the leading side of each rising loop is about twice as large as that of the following side at the same depth. The evacuation of plasma out of the leading side of the rising loop results in an enhanced magnetic field strength there compared with the following side. It is argued that this result provides a natural explanation for the fact that the preceding (leading) polarity tends to have a less organized and more fragmented appearance, and that the preceding spots tend to be larger in area and fewer in number, and have a longer lifetime than the following spots.

Fan, Y.↗
NASA NTRS1993

The morphology of flare phenomena, magnetic fields, and electric currents in active regions. I - Introduction and methods

Electric current systems in solar active regions and their spatial relationship to sites of electron precipitation and high-pressure in flares were studied with the purpose of providing observational evidence for or against the flare models commonly discussed in the literature. The paper describes the instrumentation, the data used, and the data analysis methods, as well as improvements made upon earlier studies. Several flare models are overviewed, and the predictions yielded by each model for the relationships of flares to the vertical current systems are discussed.

Canfield, Richard C.↗
NASA NTRS1992

Position and morphology of the compact non-thermal radio source at the Galactic Center

We have determined with VLBI the position of the compact nonthermal radio source at the Galactic Center, commonly referred to as SgrA*, in the J2000.0 reference frame of extragalactic radio sources. We have also determined the size of SgrA* at 1.3, 3.6, and 13 cm wavelengths and found that the apparent size of the source increases proportionally to the observing wavelength squared, as expected from source size broadening by interstellar scattering and as reported previously by other authors. We have also established an upper limit of about 8 mJy at 3.6 cm wavelength for any ultracompact component. The actual size of the source is less than 15 AU. Fourier analysis of our very sensitive 3.6 cm observations of this source shows no significant variations of correlated flux density on time scales from 12 to 700 s.

Marcaide, J. M.↗
NASA NTRS1992

Quantitative analysis of surface characteristics and morphology in Death Valley, California using AIRSAR data

The Jet Propulsion Laboratory Airborne Synthetic Aperture Radar (JPL-AIRSAR) is used to collect full polarimetric measurements at P-, L-, and C-bands. These data are analyzed using the radar analysis and visualization environment (RAVEN). The AIRSAR data are calibrated using in-scene corner reflectors to allow for quantitative analysis of the radar backscatter. RAVEN is used to extract surface characteristics. Inversion models are used to calculate quantitative surface roughness values and fractal dimensions. These values are used to generate synthetic surface plots that represent the small-scale surface structure of areas in Death Valley. These procedures are applied to a playa, smooth salt-pan, and alluvial fan surfaces in Death Valley. Field measurements of surface roughness are used to verify the accuracy.

Kierein-Young, K. S.↗
NASA NTRS1992

Analysis of lightning flash videos from the Space Shuttle using blob and morphological techniques

Flash rates measured from the Space Shuttle range from 27.8 flashes per minute to 77 flashes per minute. The cloud is an optically thick medium which effectively scatters the energy from a lightning discharge and thereby broadens the risetime and duration of each lightning pulse. Because of the small size, spacecraft sensors with resolutions of 1 km or more are unlikely to detect the individual lightning channels. Instead, the energy from the lightning channel is scattered within the cloud, thereby broadening the apparent area. All of these measurements of lightning flash area and flash rate have involved manual manipulation and analysis of the video or film data. Only a small percentage of the Space Shuttle lightning video has been analyzed. An attempt is made to combine the use of real-time digital disk system and an automated analysis routine in order to overcome this limitation and make processing of a sequence of video frames a much less labor-intensive task.

Pitts, David E.↗