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At least 919 records · Page 51
All sourcesNASA NTRSDOE OSTI
NASA NTRS1986

The radial velocity, velocity dispersion, and mass-to-light ratio of the Sculptor dwarf galaxy

The radial velocity, velocity dispersion, and mass-to-light ratio for 16 K giants in the Sculptor dwarf galaxy are calculated. Spectra at the Ca II triplet are analyzed using cross-correlation techniques in order to obtain the mean velocity of + 107.4 + or - 2.0 km/s. The dimensional velocity dispersion estimated as 6.3 (+1.1, -1.3) km/s is combined with the calculated core radius and observed central surface brightness to produce a mass-to-light ratio of 6.0 in solar units. It is noted that the data indicate that the Sculptor contains a large amount of mass not found in globular clusters, and the mass is either in the form of remnant stars or low-mass dwarfs.

Armandroff, T. E.↗
NASA NTRS1986

A note on the total mass of comets in the solar system

The assumption that the very low albedo determined for Halley's comet is typical of all short period comets, taken together with the assumption that the average sizes of long and short-period comets are approximately equal, leads to an increase in the total mass of comets in the solar system by almost two orders of magnitude. If gravitational ejection from the Uranus-Neptune zone during the later phases of planet formation is indeed responsible for the classical Oort cloud between 0.0001 and 0.00001 AU, then the mass of comets in this transplanetary region during cosmogonic times has to exceed the combined masses of Uranus and Neptune by over an order of magnitude. Furthermore, if the recent arguments for as many as 10 to the 14th comets in an 'inner' Oort cloud between about 40 and 10,000 AU are valid, then the total mass of comets in the solar system approaches 2 percent of a solar mass.

Mendis, D. A.↗
NASA NTRS1986

Turbulent heat and mass transfers across a thermally stratified air-water interface

Rates of heat and mass transfer across an air-water interface were measured in a wind-wave research facility, under various wind and thermal stability conditions (unless otherwise noted, mass refers to water vapor). Heat fluxes were obtained from both the eddy correlation and the profile method, under unstable, neutral, and stable conditions. Mass fluxes were obtained only under unstable stratification from the profile and global method. Under unstable conditions the turbulent Prandtl and Schmidt numbers remain fairly constant and equal to 0.74, whereas the rate of mass transfer varies linearly with bulk Richardson number. Under stable conditions the turbulent Prandtl number rises steadily to a value of 1.4 for a bulk Richardson number of about 0.016. Results of heat and mass transfer, expressed in the form of bulk aerodynamic coefficients with friction velocity as a parameter, are also compared with field data.

Papadimitrakis, Y. A.↗
NASA NTRS1987

The coronal mass ejection of July 6, 1980 - A candidate for interpretation as a coronal shock wave

The July 6, 1980 looplike coronal mass ejection observed with the Solar Maximum Mission coronagraph is described and analyzed. Two observations are given special consideration: (1) the sides of the loop moved laterally while they were visible and did not form stationary bright columns, or 'legs', in the late stage, and (2) raylike features initially outside the mass ejection loop were not pushed aside or bent until the laterally moving loop sides passed over them. These observations, as well as the results of quantitative analysis of the motion of the bright loop, are consistent with the identification of the bright loop as a shock front. The loop top moved outward faster (at about 1000 km/s) than most mass ejections studied previously, and possibly faster than the Alfven speed in the corona, while the loop sides moved laterally at a speed of about 800 km/s and showed no evidence of deceleration. The excess mass in the bright loop is estimated to be less than about 2 x 10 to the 14th g, well below the value found to be typical of coronal mass ejections.

Sime, D. G.↗
NASA NTRS1986

The convective noise floor for the spectroscopic detection of low mass companions to solar type stars

The threshold mass for the unambiguous spectroscopic detection of low mass companions to solar type stars is defined here as the time when the maximum acceleration in the stellar radial velocity due to the Doppler reflex of the companion exceeds the apparent acceleration produced by changes in convection. An apparent acceleration of 11 m/s/yr in integrated sunlight was measured using near infrared Fourier transform spectroscopy. This drift in the apparent solar velocity is attributed to a lessening in the magnetic inhibition of granular convection as solar minimum approaches. The threshold mass for spectroscopic detection of companions to a one solar mass star is estimated at below one Jupiter mass.

Deming, D.↗
NASA NTRS1986

Mass, heat and freshwater fluxes in the South Indian Ocean

Six hydrographic sections were used to examine the circulation and property fluxes in the South Indian Ocean from 10 to 32 deg S. The calculations were made by applying an inverse method to the data. In the interior of the South Indian Ocean, the geostrophic flow is generally northward. At 18 deg S, the northward interior mass flux is balanced by the southward Ekman mass flux at the surface, whereas at 32 deg S the northward interior mass flux is balanced by the southward mass flux of the Agulhas Current. There is a weak, southward mass flux of 6 x 10 to the 9th kg/s in the Mozambique Channel. The rate of water exchange between the Pacific Ocean and the Indian Ocean is dependent on the choice of the initial reference level used in the inverse calculation. The choice of 1500 m, the depth of the deep oxygen minimum, has led to a flux of water from the Pacific Ocean to the Indian Ocean at a rate of 6.6 x 10 to the 9th kg/s. Heat flux calculations indicate that the Indian Ocean is exporting heat to the rest of the world's oceans at a rate of -0.69 x 10 to the 15th W at 18 deg S and -0.25 x 10 to the 15th W at 32 deg S (negative values being southward).

Fu, Lee-Lueng↗
NASA NTRS1988

Effective-Mass Theory For Inhomogeneous Semiconductors

Five papers present derivations in effective-mass theory for semiconducing materials of gradually varying spatial composition. In paper entitled "Position-Dependent Effective Masses in Semiconductor Theory," concept of spatially-varying effective masses reviewed and shown unworkable. Second paper considers compound semiconductor having gradual spatial variation of composition. Third paper shows effective masses depend on average of chemical composition over entire crystal. Pair of papers entitled "Forces Acting on Free Carriers in Semiconductors of Inhomogeneous Composition" show it is incorrect to apply extended Wannier-Slater theorem using spatially changing effective masses, and quasi-electric fields due to spatial variations in chemical composition do not depend explicitly on temperature.

Von Roos, Oldwig↗
NASA NTRS1987

Mass distributions in elliptical galaxies at large radii

Recently, X-ray observations have shown that elliptical galaxies generally contain large quantities of hot gas. Central dominant cluster ellipticals have even more gas, which they have accreted from the surrounding clusters. The mass distributions in these galaxies can be derived from the condition of hydrostatic equilibrium. M87, the best studied central dominant galaxy, has a massive, dark halo with a total mass of about 4 x 10 to the 12th solar masses within a radius of 300 kpc. The total mass-to-light ratio within this radius is at least 150 solar mass/solar luminosity. The X-ray observations of normal ellipticals also strongly suggest that they have heavy halos, although the distribution of the mass is much less certain than in M87.

Sarazin, Craig L.↗
NASA NTRS1988

Crystal growth of CdTe in space and thermal field effects on mass flux and morphology

The primary, long-range goals are the development of vapor phase crystal growth experiments, and the growth of technologically useful crystals in space. The necessary ground-based studies include measurements of the effects of temperature variations on the mass flux and crystal morphology in vapor-solid growth processes. For in-situ mass flux measurements dynamic microbalance techniques will be employed. Crystal growth procedures and equipment will be developed to be compatible with microgravity conditions and flight requirements. Emphasis was placed on the further development of crystal growth and the investigation of relevant transport properties of CdTe. The dependence of the mass flux on source temperature was experimentally established. The CdTe synthesis and pretreatment procedures are being developed that yield considerable improvements in mass transport rates, and mass fluxes which are independent of the amount of source material. A higher degree of stoichiometric control of CdTe than before was achieved during this period of investigation. Based on this, a CdTe crystal growth experiment, employing physical vapor transport, yielded very promising results. Optical microscopy and X-ray diffraction studies revealed that the boule contained several large sized crystal grains of a high degree of crystallinity. Further characterization studies of CdTe crystals are in progress. The reaction chamber, furnace dimensions, and ampoule location of the dynamic microbalance system were modified in order to minimize radiation effects on the balance performance.

Wiedemeier, H.↗
NASA NTRS1988

Late Frasnian mass extinction: Conodont event stratigraphy, global changes, and possible causes

Several abrupt changes in conodont biofacies are documented to occur synchronously at six primary control sections across the Frasnian-Famennian boundary in Euramerica. These changes occurred within a time-span of only about 100,000 years near the end of the latest Frasnian linguiformis Zone, which is formally named to replace the Uppermost gigas Zone. The conodont-biofacies changes are interpreted to reflect a eustatic rise followed by an abrupt eustatic fall immediately preceding the late Frasnian mass extinction. Two new conodont species are named and described. Ancyrognathus ubiquitus n.sp. is recorded only just below and above the level of late Frasnian extinction and hence is a global marker for that event. Palmatolepispraetriangularis n.sp. is the long-sought Frasnian ancestor of the formerly cryptogenic species, Pa. triangularis, indicator of the earliest Famennian Lower triangularis Zone. The actual extinction event occurred entirely within the Frasnian and is interpreted to have been of brief duration-from as long as 20,000 years to as short as several days. The eustatic rise-and-fall couplet associated with the late Frasnian mass extinction is similar to eustatic couplets associated with the demise of most Frasnian (F2h) reefs worldwide about 1 m.y. earlier and with a latest Famennian mass extinction about 9.5 m.y. later. All these events may be directly or indirectly attributable to extraterrestrial triggering mechanisms. An impact of a small bolide or a near miss of a larger bolide may have caused the earlier demise of Frasnian reefs. An impact of possibly the same larger bolide in the Southern Hemisphere would explain the late Frasnian mass extinction. Global regression during the Famennian probably resulted from Southern-Hemisphere glaciation triggered by the latest Frasnian impact. Glaciation probably was the indirect cause of the latest Famennian mass extinction.

Sandberg, Charles A.↗
NASA NTRS1989

Hot oxygen geocorona as inferred from neutral exospheric models and mass spectrometer measurements

Summer hot oxygen densities of 10,000-30,000 per cubic cm at 1100 km (or 100,000-300,000 at 550 km) for low to moderate solar activities are inferred from differences between satellite drag and mass-spectrometer-based models. At high solar activities, densities at 925 km from 100,000-400,000 (or 5 x 10 to the 5th to 2 x 10 to the 6th at 550 km) are inferred from a limited number of Dynamics Explorer mass spectrometer measurements. The densities are of the same order as those reported previously from ground-based optical measurements. It is pointed out that a detailed theoretical calculation of the hot oxygen distribution consistent with the cool populations in mass-spectrometer-based models would provide the basis for a more complete interpretation of mass spectrometer data and of high-altitude differences between drag-based and mass-spectrometer-based models. It is concluded that hot oxygen could be providing the major contribution to satellite drag in the summer lower exosphere during low solar activity.

Hedin, A. E.↗
NASA NTRS1989

A mass-independent sulfur isotope effect in the nonthermal formation

A nonmass-dependent sulfur isotope effect is present in the rotationally symmetric S2F10 molecule, produced in an electrical discharge through sulfur tetrafluoride. A similar isotopic fractionation was observed in the product S2F10 from the electrodissociation of SF5Cl and in the reaction between fluorine atoms produced by F2 photolysis and SF2, collectively ruling out the SF5 formation process as the source of the mass-independent fractionation. The secondary dissociation of S2F10 as a source of the mass-independent fractionation is ruled out by control S2F10 dissociation experiments which are shown to produce small mass-dependent fractionations. Mass-dependent effects such as sulfur isotopic exchange and secondary dissociation reactions are significant processes for the system under study, and have been quantitatively accounted for. The role of symmetry in nonmass-dependent isotope effects is strengthened by the present experiments, and the search and characterization of mass-independent effects is extended to sulfur-containing molecules.

Bains-Sahota, Swroop K.↗
NASA NTRS1989

The effect of mass loading on the temperature of a flowing plasma

How the addition of ions at rest (mass loading) affects the temperature of a flowing plasma in a MHD approximation is investigated, using analytic theory and time dependent, three-dimensional MHD simulations of plasma flow past Io. The MHD equations show that the temperature can increase or decrease relative to the background, depending on the local sonic Mach number M(S), of the flow. For flows with M(S) of greater than sq rt 9/5 (when gamma = 5/3), mass loading increases the plasma temperature. However, the simulations show a nonlinear response to the addition of mass. If the mass loading rate is large enough, the temperature increase may be smaller than expected, or the temperature may actually decrease, because a large mass loading rate slows the flow and decreases the thermal energy of the newly created plasma.

Linker, Jon A.↗
NASA NTRS1989

Discovery of low mass objects in Taurus

In infrared (2.2 micron, K-band) search of small regions (25 in square) near 26 members of the Taurus star-forming association has revealed 20 dim (K = 13-16 mag) stellar objects near 13 of them. Of these 20 objects, 9 are exceptionally red. It is argued that these 9 are probably also Taurus members. From the luminosities (0.4 to 4 times 10 the -3 power luminosity) and ages (estimated at 10(exp 6) years), masses can be determined by reference to theoretical low-mass cooling curves. The masses are in the range 0.005 to 0.015 solar mass, i.e., low-mass brown dwarfs. Proper motion studies of 7 of the objects visible on the POSS plates conducted by Burton Jones establish that 4 are highly probable Taurus members while 1 is a possible member.

Forrest, W. J.↗
NASA NTRS1990

An analysis of space power system masses

Various space electrical power system masses are analyzed with particular emphasis on the power management and distribution (PMAD) portion. The electrical power system (EPS) is divided into functional blocks: source, interconnection, storage, transmission, distribution, system control and load. The PMAD subsystem is defined as all the blocks between the source, storage and load, plus the power conditioning equipment required for the source, storage and load. The EPS mass of a wide range of spacecraft is then classified as source, storage or PMAD and tabulated in a database. The intent of the database is to serve as a reference source for PMAD masses of existing and in-design spacecraft. The PMAD masses in the database range from 40 kg/kW to 183 kg/kW across the spacecraft systems studied. Factors influencing the power system mass are identified. These include the total spacecraft power requirements, total amount of load capacity and physical size of the spacecraft. It is found that a new utility class of power systems, represented by Space Station Freedom, is evolving.

Kenny, Barbara H.↗
NASA NTRS1989

The shape of the mass distribution in M31 from its globular cluster system

The velocity dispersion and rotation velocity of the M31 globular cluster system depend on the relative division of mass between the flat disk and a spherically symmetric halo. Using the tensor virial theorem, it is shown in detail how the mass ratio can be constrained. Radial velocities have been collected for 149 globular clusters in M31. With no assumptions about the isotropy of the velocity distribution, the globular cluster kinematics are consistent with the mass distribution inferred by the rotation curve but otherwise place no strong constraints on the relative division of the mass. If the velocity distribution is isotropic, models with the disk mass ranging between 1/2 and 1 times its maximum possible value are marginally favored.

Kent, Stephen M.↗
NASA NTRS1988

Technology thrust areas for mass constrained spacecraft

This paper discusses a study that identifies technology thrust areas that could yield significant mass reductions for future spacecraft programs. The work involved analyzing past Jet Propulsion Laboratory interplanetary spacecraft mass data to determine how spacecraft mass is distributed by technology area. It was discovered that over a 22-yr period an almost constant 64 percent of the total spacecraft dry mass is concentrated in the two technology areas of structure and packaged electronics. Also discussed are the methods for achieving significant mass reductions through advances in materials, integration, design, and miniaturization of electronics.

Muirhead, B.↗
NASA NTRS1990

A search for eclipses of HD 114762 by a low-mass companion

HD 114762 has an unseen companion with a dynamical mass that satisfies the constraint mass sin i = 2.5 x 10 to the 31st gm. The companion is a good candidate for a planetary-mass object, but the inclination of its orbit is unknown and its mass is indeterminate. Tests were conducted for the specific case of a nearly edge-on orbit by looking for eclipses of HD 114762 by the companion. Although the a priori probability of an eclipse is low, this is a crucial case because the companion has its minimum mass if the orbit is edge on. No eclipses were found with a depth greater than 0.01 mag and, therefore, the inclination of the orbit of HD 114762 is less than 89 deg.

Robinson, Edward L.↗