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Tests were made at a mean inlet Mach number of 0.2 with area suction applied to conical diffusers with expansion angles of 30 degrees and 50 degrees and exit to inlet area ratios of 2. Air-flow separation was eliminated with suction mass flows of 3 and 4 percent of the inlet mass flows for the 30 degrees and 50 degrees diffusers, respectively.
Young massive stars produce sufficient Lyman continuum photon luminosity Phi(sub i) to significantly affect the structure and evolution of the accretion disks surrounding them. A nearly static, ionized, isothermal 10(exp 4) K atmosphere forms above the neutral disk for disk radii r less than r(sub g) = 10(exp 15) M(sub 1) cm, where M(sub *) = 10 solar mass M(sub 1) is the stellar mass. For r approximately greater than r(sub g) the diffuse field created by hydrogen recombinations to the ground state in the photoionized gas above the disk produces a steady evaporation at the surface of the disk, and this H II gas flows freely out to the ISM (the 'disk wind'). The detailed structure depends on the mass-loss rate dot-M(sub w) of the fast, approximately greater than 1000 km/sec, stellar wind from the massive star. A critical mass-loss rate dot-M(sub cr) is defined such that the ram pressure of the stellar wind equals the thermal pressure of the H II atmosphere at r(sub g). In the weak stellar wind solution, dot-M(sub w) less than dot-M(sub cr), the diffuse photons from the atmosphere above r(sub g) produce a photoevaporative mass-loss rate from the disk at r approximately greater than r(sub g) of order 1 x 10(exp -5)(Phi(sub 49))(exp 1/2)(M(sub 1))(exp 1/2) solar mass/year, where Phi(sub i) = 10(exp 49) Phi(sub 49)/sec. The resulting slow (10 to 50 km/sec) ionized outflow, which persists for approximately greater than 10(exp 5) year for disk masses M(sub d) approximately 0.3 M(sub *), may explain the observational characteri stics of unresolved, ultracompact H II regions. In the strong stellar wind solution, dot-M(sub w) greater than dot-M(sub cr), the ram pressure of the stellar wind blows down the atmosphere for r less than r(sub g) and allows the stellar photons to penetrate to greater radii and smaller heights. A slow, ionized outflow produced mainly by diffuse photons is again created for r less than r(sub g); however, it is now dominated by the flow at r(sub w)(greater than r(sub g)), the radius at which the stellar wind ram pressure equals the thermal pressure in the evaporating flow. The mass-loss rate from the disk is of order 6 x 10(exp -5)dot-M(sub w-6) v(sub w8)(Phi (sub 49))(exp -1/2) solar mass/year, where dot-M(sub w-6) = M(sub w)/10(exp -6) solar mass/year and v(sub w8) = v(sub w)/1000 km/sec is the stellar wind velocity. The resulting outflow, which also persists for approximately greater than 10(exp 5) year may explain many of the more extended (r approximately greater than 10(exp 16) cm) ultracompact H II regions. Both the weak-wind and the strong-wind models depend entirely on stellar parameters Phi(sub i), M(sub *), dot-M(sub w)) and are independent of disk parameters as long as an extended r much greater than (r(sub g)), neutral disk exists. We compare both weak-wind and strong-wind model results to the observed radio free-free spectra and luminosities of ultracompact H II regions and to the interesting source MWC 349.
Despite its lack of intrinsic magnetic field Venus has a well defined magnetotail, containing about 3 megawebers of magnetic flux in a tail about 4 Venus radii across with perhaps a slightly elliptical cross section. This tail arises through the mass-loading of magnetic flux tubes passing by the planet. Mass-loading can occur due to charge exchange and photoionization as well as from the diffusion of magnetic field into the ionosphere. Various evidence exists for the mass-loading process, including the direct observation of the picked up ions with both the Venera and Pioneer Venus plasma analyzers.
The paper provides a theoretical description of the development of the boundary layer on the lip and diffuser surface of a subsonic inlet at arbitrary operating conditions of mass flow rate, freestream velocity and incidence angle. Both laminar separation on the lip and turbulent separation in the diffuser are discussed. The agreement of the theoretical results with model experimental data illustrates the capability of the theory to predict separation. The effects of throat Mach number, inlet size, and surface roughness on boundary-layer development and separation are illustrated.
Photoionization mass spectrometer for ion-molecule reaction studies, determining ion residence times, drift velocities, diffusion coefficients and ion temperatures
The passage of debris from a high altitude ( 400 km) nuclear burst over the ionospheric plasma is found to be capable of exciting large amplitude whistler waves which can act to structure a collisionless shock. This instability will occur in the loss cone exits of the nuclear debris bubble, and the accelerated ambient ions will freestream along the magnetic field lines into the magnetosphere. Using Starfish-like parameters and accounting for plasma diffusion and thermalization of the propagating plasma mass, it is found that synchronous orbit plasma fluxes of high temperature electrons (near 10 keV) will be significantly greater than those encountered during magnetospheric substorms. These fluxes will last for sufficiently long periods of time so as to charge immersed bodies to high potentials and arc discharges to take place.
A study is presented of several mechanisms which may reduce crystal growth rates and or terminate crystal growth. It is found that salt gradients which change the local chemical potential of the protein are insufficient to account for the slow crystal growth rates which have been reported. Contaminants which adsorb protein from solution may reduce the effective protein concentration, but the impurity's concentration and its affinity for protein are unknown. Association of protein molecules in bulk solution can reduce the monomer concentration significantly, but extant theory and experiment are not sensitive enough to determine the actual concentration of aggregates in solution. For systems of interest, shear-induced effects were found to be too weak to interfere with normal binding of incoming protein molecules. Although we found that most crystal growth occurs in a regime where both interfacial kinetics and diffusion influence crystal growth, the role of mass transfer rates on the terminal size of crystals is unknown, primarily because no data exist which cover the size range of interest (0.1 mm to 1 mm in length).
Flight in the atmosphere is examined from the viewpoint of including real gas phenomena in the flow field about a vehicle flying at hypervelocity. That is to say, the flow field is subject not only to compressible phenomena, but is dominated by energetic phenomena. There are several significant features of such a flow field. Spatially, its composition can vary by both chemical and elemental species. The equations which describe the flow field include equations of state and mass, species, elemental, and electric charge continuity; momentum; and energy equations. These are nonlinear, coupled, partial differential equations that have been reduced to a relatively compact set of equations in a self-consistent manner (which allows mass addition at the surface at a rate comparable to the free-stream mass flux). The equations and their inputs allow for transport of these quantities relative to the mass-average behavior of the flow field. Thus transport of mass by chemical, thermal, pressure, and forced diffusion; transport of momentum by viscosity; and transport of energy by conduction, chemical considerations, viscosity, and radiative transfer are included. The last of these complicate the set of equations by making the energy equations a partial integrodifferential equation. Each phenomenon is considered and represented mathematically by one or more developments. The coefficients which pertain are both thermodynamically and chemically dependent. Solutions of the equations are presented and discussed in considerable detail, with emphasis on severe energetic flow fields. Hypervelocity flight in low-density environments where gaseous reactions proceed at finite rates chemical nonequilibrium is considered, and some illustrations are presented. Finally, flight where the flow field may be out of equilibrium, both chemically and thermodynamically, is presented briefly.
Flight in the atmosphere is examined from the viewpoint of including real gas phenomena in the flow field about a vehicle flying at hypervelocity. That is to say, the flow field is subject not only to compressible phenomena, but is dominated by energetic phenomena. There are several significant features of such a flow field. Spatially, its composition can vary by both chemical and elemental species. The equations which describe the flow field include equations of state and mass, species, elemental, and electric charge continuity; momentum; and energy equations. These are nonlinear, coupled, partial differential equations that were reduced to a relatively compact set of equations of a self-consistent manner (which allows mass addition at the surface at a rate comparable to the free-stream mass flux). The equations and their inputs allow for transport of these quantities relative to the mass-averaged behavior of the flow field. Thus transport of mass by chemical, thermal, pressure, and forced diffusion; transport of momentum by viscosity; and transport of energy by conduction, chemical considerations, viscosity, and radiative transfer are included. The last of these complicate the set of equations by making the energy equation a partial integrodifferential equation. Each phenomenon is considered and represented mathematically by one or more developments. The coefficients which pertain are both thermodynamically and chemically dependent. Solutions of the equations are presented and discussed in considerable detail, with emphasis on severe energetic flow fields. For hypervelocity flight in low-density environments where gaseous reactions proceed at finite rates, chemical nonequilibrium is considered and some illustrations are presented. Finally, flight where the flow field may be out of equilibrium, both chemically and thermodynamically, is presented briefly.
A significant effort to determine the effects of low earth orbit (LEO) exposure on silver backed fluorinated ethylene-propylene (FEP) blankets from the Long Duration Exposure Facility (LDEF) was performed, and the results of this investigation are described. Extensive measurements of surface, optical, chemical, and mechanical properties were conducted. Effects of contamination and erosion rates of the FEP layer were determined. Specific results are reported on solar absorptance, thermal emittance, diffuse reflectance, cross sectional microphotography, secondary ion mass spectroscopy, electron scattering for chemical analysis, scanning electron microscopy, percent elongation, and tensile strength. These measurements show the effects of two distinctly different exposure environments, solar exposure, and simultaneous atomic oxygen (AO) and solar exposure.
The resonance lines of singly ionized magnesium, the MgII h&k lines at about 280 nm, are two of the small number of lines in the solar spectrum that are optically thick in the chromospheric part of the solar atmosphere. Potentially these lines contain information on the initial temperature rise that occurs at the top of the photosphere. Unfortunately, few good observations of the lines exist due to their wavelength near 280 nm the ultraviolet. However, a fair number of observations (on the order of 200) are available from the data base of the UltraViolet Polarimeter and Spectrometer (UVSP) instrument that flew on board of NASA's Solar Maximum Mission (SMM) satellite. In addition, this data base contains a number of spectra that include the Mg I resonance line at (lambda)285.2nm, just longward of the h&k lines. The neutral magnesium line is not as strong as its ionic counterparts and samples slightly lower parts of the atmosphere. Its width is a sensitive diagnostic of the ionization balance between neutral and singly ionized magnesium, which determines the opacity scale (and formation height) of other diagnostically important MgI lines like the 457.1 nm intercombination line, the magnesium b lines and the infrared MgI emission lines near 12 microns. Analysis of the observed line profiles shows that it is necessary to include the effects of partial frequency redistribution (PRD) in the formation of the line as in the case of the h&k lines. This implies that the core of the line is very sensitive to the way scattering is treated in the modeling of the line, and in turn this allows us to separate the uncertain effects in the atomic data (viz. the Van der Waals broadening) from the uncertainties in the underlying atmospheric model. The main objective of this research was to compare observed spectra of the magnesium resonance lines against theoretical line profiles calculated from recent models of the solar atmosphere by Fontenla et al., hereafter called FAL. These models extend earlier solar models by Avrett et al. and provide yet a better match between observed and calculated spectra, in particular of the hydrogen Lyman line, by including the effects of ambipolar diffusion of hydrogen and helium in the mass and energy transport equations for the chromosphere-corona transition region. Although the transition region models can be built self-consistently (without additional observational input) once the proper boundary conditions are given at the top of the chromosphere, there are uncertainties in the models precisely because these boundary conditions are not well known. With the analysis of UVSP magnesium observations we strive to constrain these uncertainties.
A fully prognostic Arctic ice-ocean model is used to study the interannual variability of deepwater formation in the Greenland Sea Gyre based on the simulations for the Arctic ice-ocean system for the period 1955 and 1960 - 1985. The model uses monthly climatology for thermodynamic forcing components (such as air temperature and cloudiness), together with constant annual net precipitation and river runoff. The daily wind forcing is derived from analyzed sea level air pressures from the National Center for Atmospheric Research (NCAR). In summary, the model shows that the occurence of deep convection in the Greenland Sea Gyre is controlled by the extensive Fram Strait ice export and/or local wind conditions in the Greenland Sea. In the latter case the weakening of the local wind curl allows the Polar Front to move eastward. The movement of the Polar Front causes adverse ice conditions, often together with much larger than normal ice export from the Arctic, such as in 1968, which can block convection in the gyre. The density difference between upper and lower layers is investigated as an indication of water mass formation through convection, occurring as strong diffusion in the model. The model-simulated density difference between the average top 100 m and deep levels reveals that the period 1960 - 1985 had only a few distinct years with weak stratification, and, especially, the model predicts no deep convection since the nid-1970s. The common factor for the years of the weakest decrease of the model-predicted heat content of the upper 2000 m which can, to a high degree, be explained by local heat loss.
The concept of "numerical speed of sound" is proposed in the construction of numerical flux. It is shown that this variable is responsible for the accurate resolution of' discontinuities, such as contacts and shocks. Moreover, this concept can he readily extended to deal with low speed and multiphase flows. As a results, the numerical dissipation for low speed flows is scaled with the local fluid speed, rather than the sound speed. Hence, the accuracy is enhanced the correct solution recovered, and the convergence rate improved. We also emphasize the role of mass flux and analyze the behavior of this flux. Study of mass flux is important because the numerical diffusivity introduced in it can be identified. In addition, it is the term common to all conservation equations. We show calculated results for a wide variety of flows to validate the effectiveness of using the numerical speed of sound concept in constructing the numerical flux. We especially aim at achieving these two goals: (1) improving accuracy and (2) gaining convergence rates for all speed ranges. We find that while the performance at high speed range is maintained, the flux now has the capability of performing well even with the low: speed flows. Thanks to the new numerical speed of sound, the convergence is even enhanced for the flows outside of the low speed range. To realize the usefulness of the proposed method in engineering problems, we have also performed calculations for complex 3D turbulent flows and the results are in excellent agreement with data.
Mixing driven by buoyancy-induced flows is of particular interest to microgravity processes, as the body force that governs the intensity of flow fields can be directly controlled. We consider a model experimental system to explore the dynamics of mixing which employs two miscible liquids inside a cavity separated initially by a divider. The two liquids are oriented vertically inside a rectangular cavity with constant width and height, and varying depths to span the range of a Hele-Shaw cell to a 3-[) configuration. The two miscible liquids can be sufficiently diluted and died, for example water and deuterium oxide, such that a distinct interface exists across the divider. The transient mixing characteristic of the two fluids is addressed by following the Lagrangian history of the interface for various aspect ratios in the z-plane (depth variation) as well as a range of pulling velocities of the divider. The mixing characteristics of the two fluids are quantified from measurement of the length stretch of the interface and its flow field using respectively image processing techniques and Particle Imaging Velocimetry. Scaling analysis shows that the length stretch depends on four governing parameters, namely the Grashof number (Gr), Schmidt number (Sc), aspect ratio (Ar), and Reynolds number (Re). Variation of the Schmidt number is taken into account through thermophysical property variation. Thus our problem reduces to a codimension three bifurcation in parametric space for Gr, Ar, and Re. Our experimental results show that for Gr on the order of 106 and a nominal cavity aspect ratio Ar = 0.2, the net effect of removal of the divider and the overwhelming buoyancy force causes an overturning motion which stretches and folds the interface to produce ml internal breakwave. The structure of the breakwave is similar to the ubiquitous Rayleigh-Taylor instability morphology. The breakwave is dissipated either through internal or wall collision depending on the impulsive velocity of the divider as prescribed by the Reynolds number. The decay of the collision event occurs through sloshing oscillations over a short time scale. The two fluids then become stably stratified with a diffusive band at the interface indicating local mass transport. The local bifurcation of the internal breakwave is investigated as a function of aspect ratio. Results show that for narrow cavities on the order of 2mm (Ar = 0.04) folding does not occur, the interface only stretches. As the cavity size increases folding occurs through a supercritical bifurcation. Insight into the mechanism of folding is obtained from measurement of the flow field which shows that in the neighborhood of the folding event, there exists hyperbolic points caused by multiple vortex interactions. The global length stretch of the interface as a function of time is nearly Gaussian; calculations of finite-time Liapunov exponents as well as construction of horseshoe maps indicate the likelihood of a chaotic transient.
We investigate how magnetic reconnection is influenced by an inflow of a dense cold ion population. We compare two 2.5D Particle-In-Cell simulations, one containing the cold population and one without. We find that the cold population influences the reconnection process on both global and kinetic scales, and that the dominant contribution can be explained through mass-loading. We provide an analysis of how these multiscale changes are related through kinetic processes in the ion diffusion region, the so-called micro-macro coupling of mass-loading. The inertia of the cold ion population is found to be the significant link that connects the changes on different scales. The cold and warm populations exhibit counter streaming behavior when and after the ion diffusion region reorganizes itself in response to the arrival of the cold population. This signature of the cold population should be observable by spacecraft observatories such as MMS.
A description is presented of the development of the boundary layer on the lip and diffuser surface of a subsonic inlet at arbitrary operating conditions of mass flow rate, free stream velocity and incidence angle. Both laminar separation on the lip and turbulent separation in the diffuser are discussed. The agreement of the theoretical results with model experimental data illustrates the capability of the theory to predict separation. The effects of throat Mach number, inlet size, and surface roughness on boundary layer development and separation are illustrated.
A comparison is made between indium phosphide solar cells whose p-n junctions were processed by open tube capped diffusion, and closed tube uncapped diffusion, of sulfur into Czochralski grown p-type substrates. Air mass zero, total area, efficiencies ranged from 10 to 14.2 percent, the latter value attributed to cells processed by capped diffusion. The radiation resistance of these latter cells was slightly better, under 1 MeV electron irradiation. However, rather than being process dependent, the difference in radiation resistance could be attributed to the effects of increased base dopant concentration. In agreement with previous results, both cells exhibited radiation resistance superior to that of gallium arsenide. The lowest temperature dependency of maximum power was exhibited by the cells prepared by open tube capped diffusion. Contrary to previous results, no correlation was found between open circuit voltage and the temperature dependency of Pmax. It was concluded that additional process optimization was necessary before concluding that one process was better than another.
As stars of 2-5 solar mass evolve across the Hertzsprung Gap they should first deplete their surface lithium by convective dilution and then, when convection penetrates deeper, begin to bring CN processed material to their surfaces. To investigate this process we have observed 52 giants, 25 of which have known C/N ratios, for their Li abundances. After eliminating four stars that may actually be dwarfs and including the two components of Capella analyzed by Pilachowski and Sowell we have compared our (Li/Fe) ratios with models of Swenson. For stars showing v sin i greater than 50 km/s we find (Li/Fe) to be uneffected by mixing for B - V less than 0.7 as predicted. For stars cooler than B - V = 0.7 both v sin i and (Li/Fe) drop to smaller values. For the sharp lined stars (v sin i less than 50 km/s) we find a drop in Li between B - V = 0.45 and 0.60 which cannot be understood in terms of dilution by convection. Various possible causes of such an early depletion or dilution of surface Li are discussed including diffusion at the base of the convection zone, mass loss possibly enhanced by pulsation, and magnetic activity as in the magnetic A and B type stars. The models of Richer & Michaud (1993) with diffusion point toward a satisfactory solution. A few giants with low v sin i values stand out with much higher than expected (Li/Fe) values despite their cool effective temperatures. We do not understand why those stars have not depleted their lithium as have most giants of similar color. The correlation of (N/C) with (Li/Fe) follows expectations in so far as almost all stars with enhanced (N/C) have depleted their Li as well.