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At least 1,045 records · Page 58
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NASA NTRS1986

Thermophoretically augmented mass transfer rates to solid walls across laminar boundary layers

Predictions of mass transfer (heavy vapor and small particle deposition) rates to solid walls, including the effects of thermal (Soret) diffusion ('thermophoresis' for small particles), are made by numerically solving the two-dimensional self-similar forced convection laminar boundary-layer equations with variable properties, covering the particle size range from vapor molecules up to the size threshold for inertial (dynamical nonequilibrium) effects. The effect of thermophoresis is predicted to be particularly important for submicron particle deposition on highly cooled solid surfaces, with corresponding enhancement factors at atmospheric conditions being over a thousand-fold at T(w)/T(e) equal to about 0.6. As a consequence of this mass transfer mechanism, the particle size dependence of the mass transfer coefficient to a cooled wall will be much weaker than for the corresponding case of isothermal capture by Brownian-convective diffusion.

Gokoglu, S. A.↗
NASA NTRS1985

Mass loss from red giants - Results from ultraviolet spectroscopy

New instrumentation in space, primarily the IUE spacecraft, has enabled the application of ultraviolet spectroscopic techniques to the determination of physical properties and reliable mass loss rates for red giant winds. One important result is the determination of where in the H-R diagram are found stars with hot outer atmospheres and with cool winds. So far it appears that single cool stars, except perhaps the so-called hybrid stars, have either hot outer atmospheres or cool winds but not both. The C II resonance (1335 A) and intersystem (2325 A) multiplets have been used to derive temperatures, densities, and geometrical extents for the chromospheric portions of red giant winds, with the result that the red giants and the earlier giants with hot coronae have qualitatively different chromospheres. Mass loss rates can now be derived accurately from the analysis of asymmetric emission lines, such as the Mg II resonance lines, and from P Cygni profile lines of atoms in the dominant ionization stage when a hot star is available to probe the wind of a red giant. The Zeta Aur systems, consisting of a K-M supergiant and a main sequence B star are important systems for reliable mass loss rates for the red supergiant components are becoming available.

Linsky, J. L.↗
NASA NTRS1985

Hydrogen deficiency and mass loss from AGB stars

Theoretical studies predict that mass loss from stars should accelerate once stars on the AGB begin thermal pulsations (TP). It has been discovered that the stars on this part of the AGB are apparently hydrogen deficient. This development may be related to the mass loss predicted by theory. Hydrogen deficiency is also supported by the nondetection of H2 in non-Mira stars, S stars, and carbon stars. The possibility that the observed apparent hydrogen deficiency has resulted from a mass loss process is considered. Observations indicate that TP-AGB stars become hydrogen deficient before the Mira phase.

Augason, G. C.↗
NASA NTRS1986

Dust counter and mass analyser (DUCMA) measurements of comet Halley's coma from Vega spacecraft

Measurements of dust particles in comet Halley's coma from Vega spacecraft made with instruments using a new principle of dust detection and having a high time resolution over a large range of dust fluxes and masses are reported. The dust coma, whether quiescent (as seen by Vega 2) or containing a major jet structure, (as seen by Vega 1) displays large, short-term variations throughout which are at times quasi-periodic. The integral mass spectra increase in intensity to the lowest masses measured, and the flux levels lie approximately in the ranges estimated previously from ground-based observations. The coma is highly dynamical on all spatial and temporal scales, suggesting a complex structure of localized regions of dust emission from the nucleus.

Simpson, J. A.↗
NASA NTRS1986

Theories of mass loss from T Tauri stars

The available database on T Tauri stars is examined in order to develop criteria for modeling the physical processes occurring within and around pre-main sequence stars. Observational data on the temperature structures, mass loss rates, and mass motions in T Tauri envelopes are reviewed to form a basis for discussing the possible mechanisms for mass loss in the T Tauri objects. Analytical models are explored for thermally-driven, wave-driven and rotationally-driven winds. The possible interactions of the T Tauri stellar winds with processes occurring in the nearby FU Dri stars are noted, as is the necessity of momdeling physical processes such as turbulent velocity fields through accurate radiative transfer calculations in order to model the envelopes of the T Tauri stars.

Hartmann, L.↗
NASA NTRS1986

Protoearth mass shedding and the origin of the moon

Darwin's (1980) theory of lunar formation from the earth by means of a rotationally driven dynamic fission instability is presently considered in view of viscous shear's maintenance of solid body rotation throughout the protoearth's accretion phase. Assuming the appropriateness of a polytropic account of the protoearth, it is unlikely that dynamic fission could have occurred; instantaneous spin-up following a giant impact would instead have led to mass shedding. The dynamical phenomenon of mass shedding is here explored on the basis of numerical models for a self-gravitating, axisymmetric, polytropic and dissipative protoearth. It is concluded that mass shedding from the protoearth mantle after a giant impact and explosion could have contributed substantial matter to a lunar disk.

Boss, A. P.↗
NASA NTRS1986

Equivalence of active and passive gravitational mass using the moon

Based on an asymmetry in the composition of the moon, a limit is established for the violation of the equity of passive and active gravitational mass. It is suggested that the 2-km offset between the moon's center of figure and center of mass imply an asymmetry in the distribution of Fe and Al, and that the Fe on one side and the Al on the other must attract another with equal force in order for the moon to follow the orbit predicted by classical mechanics. Based on laser ranging data and a model for the moon's interior, the ratios of active to passive mass for Fe and Al are found to be equal to a precision of 4 x 10 to the -12th.

Bartlett, D. F.↗
NASA NTRS1986

Do stars that lose mass expand or contract? A semianalytical approach

Semianalytic methods are used to determine whether a star of polytropic index n expands or contracts following an insentropic loss of mass. It is found that most stars shrink, including radiative stars which can be approximated by polytropes of index roughly three. However, stars that have a ratio of specific heats gamma only slightly larger than 1 + 1/n do expand if the perturbation of the core density is sufficiently large. For stars that shrink, the fractional change in the radius is not a linear function of the fractional change in mass. Using Lane's theorem, it is shown that a star with gamma = 4/3 cannot lose mass isentropically, although the radius increases if the core density is reduced.

Heisler, J.↗
NASA NTRS1986

Mass spectrometric studies of the electrical breakdown of thin polymer films

The composition of the neutral particles released during the electrical breakdown of 50-micron and 75-micron insulating films of the type used on spacecraft exteriors investigated experimentally using a time-of-flight mass spectrometer triggered by the breakdown event. The experimental apparatus is described in detail, and the results are presented in photographs. It is found that the particle flux from Teflon FEP and PFA films comprise mainly fluorocarbon fragments, some with mass 350 amu or greater, but the flux from Kapton oxygen-ion-beam treated Kapton, Tefzel, and Mylar comprises mainly molecules of mass 44 amu or less.

Kendall, B. R. F.↗
NASA NTRS1986

Mass return to the interstellar medium from highly-evolved carbon stars

Data produced by the Infrared Astronomy Satellite (IRAS) was surveyed at the mid- and far-infrared wavelengths. Visually-identified carbon stars in the 12/25/60 micron color-color diagram were plotted, along with the location of a number of mass-losing stars that lie near the location of the carbon stars, but are not carbon rich. The final sample consisted of 619 objects, which were estimated to be contaminated by 7 % noncarbon-rich objects. The mass return rate was estimated for all evolved circumstellar envelopes. The IRAS Point Source Catalog (PSC) was also searched for the entire class of stars with excess emission. Mass-loss rates, lifetimes, and birthrates for evolved stars were also estimated.

Latter, W. B.↗
NASA NTRS1987

A survey of nested grid techniques and their potential for use within the MASS weather prediction model

A survey of various one- and two-way interactive nested grid techniques used in hydrostatic numerical weather prediction models is presented and the advantages and disadvantages of each method are discussed. The techniques for specifying the lateral boundary conditions for each nested grid scheme are described in detail. Averaging and interpolation techniques used when applying the coarse mesh grid (CMG) and fine mesh grid (FMG) interface conditions during two-way nesting are discussed separately. The survey shows that errors are commonly generated at the boundary between the CMG and FMG due to boundary formulation or specification discrepancies. Methods used to control this noise include application of smoothers, enhanced diffusion, or damping-type time integration schemes to model variables. The results from this survey provide the information needed to decide which one-way and two-way nested grid schemes merit future testing with the Mesoscale Atmospheric Simulation System (MASS) model. An analytically specified baroclinic wave will be used to conduct systematic tests of the chosen schemes since this will allow for objective determination of the interfacial noise in the kind of meteorological setting for which MASS is designed. Sample diagnostic plots from initial tests using the analytic wave are presented to illustrate how the model-generated noise is ascertained. These plots will be used to compare the accuracy of the various nesting schemes when incorporated into the MASS model.

Koch, Steven E.↗
NASA NTRS1986

Coronal mass ejections and coronal structures

Research on coronal mass ejections (CMF) took a variety of forms, both observational and theoretical. On the observational side there were: case studies of individual events, in which it was attempted to provide the most complete descriptions possible, using correlative observations in diverse wavelengths; statistical studies of the properties CMEs and their associated activity; observations which may tell us about the initiation of mass ejections; interplanetary observations of associated shocks and energetic particles even observations of CMEs traversing interplanetary space; and the beautiful synoptic charts which show to what degree mass ejections affect the background corona and how rapidly (if at all) the corona recovers its pre-disturbance form. These efforts are described in capsule form with an emphasis on presenting pictures, graphs, and tables so that the reader can form a personal appreciation of the work and its results.

Hildner, E.↗
NASA NTRS1987

Masses, luminosities and dynamics of galactic molecular clouds

Star formation in galaxies takes place in molecular clouds and the Milky Way is the only galaxy in which it is possible to resolve and study the physical properties and star formation activity of individual clouds. The masses, luminosities, dynamics, and distribution of molecular clouds, primarily giant molecular clouds in the Milky Way are described and analyzed. The observational data sets are the Massachusetts-Stony Brook CO Galactic Plane Survey and the IRAS far IR images. The molecular mass and infrared luminosities of glactic clouds are then compared with the molecular mass and infrared luminosities of external galaxies.

Solomon, P. M.↗
NASA NTRS1987

Reduction and scientific analysis of data from the charge-energy-mass (CHEM) spectrometer on the AMPTE/CCE spacecraft

The Charge-Energy-Mass (CHEM) spectrometer instrument on the AMPTE/Charge Composition Explorer (CCE) spacecraft is designed to measure the mass and charge-state abundance of magnetospheric and magnetosheath ions between 0.3 and 315 keV/e, an energy range that includes the bulk of the ring current and the dynamically important portion of the plasma sheet population. Continuing research is being conducted using the AMPTE mission data set, and in particular, that of the CHEM spectrometer which has operated flawlessly since launch and still provides excellent quality data. The requirted routine data processing and reduction, and software develpment continues to be performed. Scientific analysis of composition data in a number of magnetospheric regions including the ring current region, near-earth plasma sheet and subsolar magnetosheath continues to be undertaken. Correlative studies using data from the sister instrument SULEICA, which determines the mass and charge states of ions in the energy range of approximately 10 to 250 keV/e on the IRM, as well as other data from the CCE and IRM spacecraft, particularly in the upstream region and plasma sheet have also been undertaken.

Gloeckler, G.↗
NASA NTRS1986

High-mass star formation due to cloud-cloud collisions

Observational evidence is presented for the compression of molecular gas in the interface between colliding GMCs, and it is proposed that this is the dominant mode for high-mass star formation in the Galaxy. For a sample of 94 GMCs associated with high-luminosity radio H II regions, the efficiency of OB star formation decreases significantly with increasing cloud mass over the observed mass range. It is concluded that star formation is generally not stimulated by an internal mechanism. The formation of OB stars by cloud-cloud collisions is suggested by the observed quadratic dependence of the Galactic H II region distribution on the local density of H2. The preference for OB star formation in spiral arms is then naturally accounted for by orbit crowding and the increased collision frequency of clouds in the spiral arms.

Scoville, N. Z.↗
NASA NTRS1987

Mass loss from FU Orionis objects

Estimates are presented for the mass loss rates of FU Ori, V1057 Cyg and V1515 Cyg. The approximations are made on the basis of models of the physical conditions required to generate the P Cygni profiles of the observed H-alpha and Na I lines. The spectra were obtained in 1985 using Reticons at the Whipple Observatory and Mt. Hopkins Multiple Mirror Telescope. FU Ori and V1515 Cyg each exhibited an estimate mass loss rate of 1/100,000 solar mass/yr, while that of V1507 Cyg is 10 times smaller. Magnetic wave acceleration is proposed as the driving force for the stellar winds associated with the mass losses, which are at a temperature near 5000 K when leaving the disks proposed around the T Tauri objects.

Croswell, Ken↗
NASA NTRS1987

Centrifugal field line breaking - An upper limit to Io mass injection

The magnetic field generated by the current needed to balance the centrifugal force on the Io torus plasma is considered to find a self-consistent equation for radial mass transport. Solutions are obtained which give plasma density and field strength as a function of distance for different mass transport rates. The solutions are subjected to a stability analyses to find where the field lines break about 3 x 10 to the 30th atoms/sec (about 100,000 kg/sec) it reaches Io. This sets an upper limit on the magnetosphere's ability to off-load mass from Io. The effect of corotation lag was ignored.

Huang, T. S.↗