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Results for “Dusty or complex plasma”

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 181 records · Page 10
All sourcesNASA NTRSDOE OSTI
NASA NTRS1981

Thermal tides in the dusty martian atmosphere - A verification of theory

Major features of the daily surface pressure oscillations observed by the Viking landers during the two great dust storms on Mars in 1977 can be explained in terms of the classical atmospheric tidal theory developed for the earth's atmosphere. The most dramatic exception is the virtual disappearance of only the diurnal tide at Viking Lander 1 just before the second storm. This disappearance is attributed to destructive interference between the usually westward-traveling tide and an eastward-traveling diurnal Kelvin mode generated by orographically induced differential heating. The continuing Viking Lander 1 pressure measurements can be used with the model to monitor future great dust storms.

Zurek, R. W.↗
NASA NTRS1983

H2O heating in molecular clouds - Line transfer and thermal balance in a warm dusty medium

An investigation is undertaken into the possibility of the heating of molecular gas through collisions with radiatively pumped H2O, in the context of the overall thermal balance of optically thick molecular clouds with embedded sources. In order to solve the line transfer equation, which includes warm dust grains, an extended method of escape probability approximation is developed in which the equilibrium gas temperature arises from the balance of heating by cosmic ray ionization of H2, and by collisions with warm dust grains and radiatively pumped H2O molecules against cooling by collisions with CO and C I. The equilibrium gas temperature for a given dust temperature strongly depends on the efficiency of the cooling species, and is therefore most sensitive to the cloud optical depth. It is less dependent, in decreasing order, on H2O abundance, gas density, and velocity dispersion.

Takahashi, T.↗
NASA NTRS1984

The dusty, luminous broad-line radio galaxy 3C 109

In the present optical polarimetry and IR photometry for the broad line radio galaxy 3C 109, the absence of variability, in conjunction with a polarization in H-alpha that is identical to that of the adjacent continuum, suggests that the strong polarization of this galaxy is due to extinction by aligned dust grains. This is the process which gives rise to interstellar polarization within the Galaxy. The energy output of 3C 109, from the optical to 20 microns, exceeds by a factor of 2-4 that of the Seyfert 1 galaxy Markarian 231. These observations, together with recent polarimetry of other broad line radio galaxies, indicate that their broad line regions are more heavily reddened than those of either the Seyfert 1 galaxies or quasars. Evidence for a gradual decrease in dust content with increasing source luminosity is discussed.

Rudy, R. J.↗
NASA NTRS1984

The effects of the diffuse radiation fields due to multiple scattering and thermal reradiation by dust on the dynamics and thermodynamics of a dusty cometary atmosphere

A self-consistent model of a dirty, clathrate cometary nucleus is extended to account for diffuse radiation fields caused by multiple scattering and thermal reradiation of the solar continuum by dust. The model is configured to fit conditions expected for the various spacecraft which will encounter Halley's comet at 0.89 AU. The atmosphere is assumed a chemically reactive dust-gas mixture in quasi-steady spherically symmetric expansion. The effect of electron-neutral ion collisions is accounted for, along with rate constants of the various species of clathrate ice particles and radiative transfer of the solar input in the UV, visible and near-IR intervals. The opacity of the circumnuclear dust is projected to be an order of magnitude greater than previous estimates, which severely impacts the potential visibility of the nucleus to the cameras of the flyby satellites.

Marconi, M. L.↗
NASA NTRS1985

Resonance lines in dusty gaseous nebulae

Under the assumption that dust is either homogeneously mixed throughout or confined to either 1/2 or 1/4 of the space in question, the effect of absorption and scattering by dust grains on resonance lines that were formed in static gaseous nebulae with plane-parallel stratification is studied and a comparison is made between the total emergent flux in the line from the dust-filled nebula and the emergent flux from a dust-free medium. Many line optical thickness values, and several combinations of the opacity ratio of dust and gas, dust albedo, and collision parameter, are compared. A novel method is used to analytically solve the transfer equation for a spectral line in the presence of scattering and absorbing dust. It is noted that dust distribution can have large effects on the value of the total emergent flux.

Wehrse, R.↗
NASA NTRS1986

The electrostatics of a dusty plasma

The potential distribution in a plasma containing dust grains were derived where the Debye length can be larger or smaller than the average intergrain spacing. Three models were treated for the grain-plasma system, with the assumption that the system of dust and plasma is charge-neutral: a permeable grain model, an impermeable grain model, and a capacitor model that does not require the nearest neighbor approximation of the other two models. A gauge-invariant form of Poisson's equation was used which is linearized about the average potential in the system. The charging currents to a grain are functions of the difference between the grain potential and this average potential. Expressions were obtained for the equilibrium potential of the grain and for the gauge-invariant capacitance between the grain and the plasma. The charge on a grain is determined by the product of this capacitance and the grain-plasma potential difference.

Whipple, E. C.↗
NASA NTRS1984

Optical experiments on thermophoretically augmented submicron particle deposition from 'dusty' high temperature gas flows

A real-time laser reflectivity method and Pt ribbon targets are used to obtain experimental data on the initial deposition rate of MgO(s) particles of approximately 700 nm diameter from otherwise clean combustion products as a function of target temperature (about 950-1450 K) and mainstream gas temperature (about 1500-1600 K). These preliminary data are used to demonstrate the dominant role of thermophoresis (particle drift down a temperature gradient) and to assess the utility of recently developed theoretical methods for predicting and correlating the temperature dependence of thermophoretically augmented convective-diffusion 'dust' deposition rates from flowing hot gases.

Rosner, Daniel E.↗
NASA NTRS1989

Small grains in M82 - A dusty halo surrounding the starburst

The well-known starburst in M82 at 10.8, 19.2, and 30 microns has been mapped. Scans along the galactic plane which are derived from these data reveal marked color variations with position. These color variations are correlated with the UV energy density in a manner explicable in terms of a heated mixture of dust grains extending to very small sizes. Many of the small grains may have been destroyed in the most intense regions of the starburst, but they have survived in a halo where the UV energy density is too low to destroy them but still high enough to significantly heat them. Implications of the results for interpreting IR continuum emission from starburst galaxies are considered.

Telesco, C. M.↗
NASA NTRS1990

Are high-redshift quasars hidden by dusty galaxies?

A Monte Carlo technique has been developed to compute the joint probability distribution for the reddening and extinction of quasars by galaxies along the line of sight with a realistic dust extinction curve including the 220 nm feature. Galaxies are treated as disks with random inclinations, having exponential or modified Gaussian radial profiles. This technique is used to find the distribution of the reddened quasars on multicolor diagrams such as the (U-J, J-F) plots used by Koo and Kron (1982) to find faint quasars. The multicolor search technique is not a simple UV excess approach, and the resulting color selection does not add significantly to the flux selection discussed by Wright (1981), Ostriker and Heisler (1984), and Heisler and Ostriker (1988). The quasar reddening trend observed by Wright and Malkan (1987) is about 0.35 + or - 0.50 times the mean reddening of the selected sample predicted by the Heisler and Ostriker model.

Wright, Edward L.↗
NASA NTRS1990

Aerobraking in a dusty Martian atmosphere

The effects of dust particle impacts on the erosion of the heat shield were estimated for a 26 m diameter aerobraking vehicle entering the Mars atmosphere at 8.6 km/sec. An explicit Navier-Stokes code was used to compute the flow field about the vehicle for the actual Martian atmospheric composition at a speed of 7.5 km/sec. The deceleration and melting of the dust particles within the forebody shock-layer was computed for dust spherules having initial diameters from 3 to 10 microns. Two heat shield materials were considered: Shuttle tiles with glassy surfaces and a low-density ablator known as Avcoat.

Chang, I-Dee↗
NASA NTRS1990

Far-infrared emission from dusty ellipticals

The incidence of dust lanes in elliptical galaxies has been estimated at approx. 40 percent by Sadler and Gerhard (1985), although the observed fraction is lower because of inclination effects. A similar percentage of ellipticals has been detected by the Infrared Astronomy Satellite (IRAS) at 100 microns (Knapp et al. 1989); these have far-infrared colors expected for emission from cool dust (S sub 60 micron/S sub 100 micron approx. 1/3). For the far-infrared detected galaxies, neither L sub 100 microns/L sub B nor L sub 60 microns/L sub 100 microns are very dependent on dust content, suggesting that the source of the infrared luminosity is the same in both cases; and hence that dust is responsible even when not detected optically. Despite this indication, L sub 100 microns does not prove to be a good indicator of the quantity of cool interstellar matter in elliptical galaxies, as measured by the mass of neutral hydrogen. There even exist several examples of ellipticals with dust, strong 100 micron flux density and sensitive limits on HI mass (Walsh et al. in preparation). Chief reasons for the lack of correlation include the existence of other important sources of far-IR power in ellipticals, such as nonthermal continuum emission extending from longer wavelengths in flat spectrum radio sources (Golombek, Miley and Neugebauer 1988); and the fact that far-infrared luminosity per unit dust mass is extremely sensitive to the temperature of the ambient radiation field, which is not accurately known. In addition to having their appearance distorted by dust, several ellipticals also show such features as shells, box-shaped isophotes or inner disks. These may be signatures of past mergers, which could also add to the ISM content of the system.

Walsh, Duncan↗
NASA NTRS1991

Analysis of a dusty wall jet

An analysis is given for the entrainment of dust into a turbulent radial wall jet. Equations are solved based on incompressible flow of a radial wall jet into which dust is entrained from the wall and transported by turbulent diffusion and convection throughout the flow. It is shown that the resulting concentration of dust particles in the flow depends on the difference between the applied shear stress at the surface and the maximum level of shear stress that the surface can withstand (varies as rho(sub d)a(sub g)D) i.e., the pressure due to the weight of a single layer of dust. The analysis is expected to have application to the downflow that results from helicopter and VTOL aircraft.

Lim, Hock-Bin↗
NASA NTRS1992

Heat shield erosion in a dusty Martian atmosphere

The study calculates the effects of dust particle impacts on the erosion of the forebody heat shield for a 26-m diameter aerobraking vehicle entering the Martian atmosphere at 8.6 km/s. An explicit thin-layer Navier-Stokes code is used to compute the dustless flowfield about the vehicle for the actual Martian atmospheric composition. The deceleration and melting of the dust particles within the forebody shock layer was computed for dust spherules having initial diameters from 1 to 19 microns. All the particles began vaporizing shortly after entering the shock layer, but most survived to hit the heat shield surface. The two different heat shield materials considered were Shuttle ceramic tiles with glassy surfaces and a moderate-density ablator. For a vehicle with a ballistic coefficient of 200 kg/sq m, a glassy heat shield surface experienced an average of 7 mm of surface erosion, or 20 times the thickness of the glassy layer on ceramic tiles.

Papadopoulos, Periklis↗
NASA NTRS1992

Lorentz resonances and the vertical structure of dusty rings - Analytical and numerical results

The Schaffer and Burns (1987) linear theory of Lorentz resonances (LRs) in planetary rings is extended in order to accurately compute LR locations and to elucidate the nature of grain trajectories within the LR zones. Using the perturbation theory and energy arguments, it is shown that an increase in the inclination or eccentricity of a grain must be accompanied by a shift in the mean orbital radius of the particle. This shift alters the epicyclic frequencies in such a way that the infinite response of the linear resonance theory is suppressed. Chaotic motion is found for the range of charge-to-mass ratios that cause the vertical and horizontal LRs to overlap.

Schaffer, Les↗
NASA NTRS1992

Dusty plasmas

Dust grains immersed in plasma become charged. The charge is determined by the plasma characteristics, by secondary and photoemission from the grain, by grain velocity, and at any given instant by the past time history of the charging currents. This charge affects the Coulomb drag on a grain moving through the plasma. It affects the motion of the grain in an electromagnetic field of a planetary magnetosphere, and it is involved in the formation of the spokes in Saturn's rings and in the erosion of the rings by micrometeorites. And finally, it affects the coagulation rate of dust into larger bodies.

Northrop, T. G.↗
NASA NTRS1993

An infrared study of the remarkable dusty M star HR 3126

HR 3126 is a unique M giant star embedded in the bipolar reflection nebula IC 2220. In this paper we present new photometric and spectroscopic observations of HR 3126 and combine them with existing data from the literature in an extensive reappraisal of the star's properties at infrared wavelengths. The spectral energy distribution is consistent with an optical classification of M0-3 II with infrared excess. The dust shell cannot be fitted by a single-temperature blackbody: at least three components are required, with temperatures in the range 35-1300 K. On the basis of spectroscopy at 1-4 and 7-25 microns, combined with an assessment of various color-color diagrams, we are able to reject the hypothesis that HR 3126 is carbon-rich. Weak silicate emission features are detected at 10 and 19 microns, and a previous report of silicon carbide emission at 11.2 microns is not substantiated. It seems likely that HR 2136 is in a phase of advanced and rapid postmain-sequence evolution, possibly beginning its ascent of the asymptotic giant branch.

Chiar, J. E.↗