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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 361 records · Page 20
All sourcesNASA NTRSDOE OSTI
NASA NTRS1982

The Halley dust model

The properties of dust ejecta from Comet Halley are studied on the basis of (a) evidence from the comet's past apparitions and (b) analogy with recent, physically similar comets. Specifically discussed are the light curve and spectrum, discrete phenomena in the head, the physical properties of the nucleus (size, albedo, rotation, surface temperature, and morphology), and an interaction between the nucleus and dust atmosphere. Also reviewed are constraints on the size and mass distributions of dust particles, information on submicron-size and submillimeter-size grains from the comet's dust tail and antitail, and the apparent existence of more than one particle type. Similarities between the jet patterns of Halley and the parent comet of the Perseid meteor stream are depicted, and effects of the surface heterogeneity (discrete active regions) on the dust flow are assessed. Current dust models for Halley are summarized and the existence of short-term variations in the dust content in the comet's atmosphere is suggested.

Sekanina, Z.↗
NASA NTRS1983

Saturn's E, G, and F rings - Modulated by the plasma sheet?

Saturn's broad E ring, the narrow G ring, and the structured and apparently time-variable F ring(s) contain many micron and submicron-sized particles, which make up the 'visible' component. These rings (or ring systems) are in direct contact with magnetospheric plasma. Fluctuations in the plasma density and/or mean energy, due to magnetospheric and solar wind processes, may induce stochastic charge variations on the dust particles, which in turn lead to an orbit perturbation and spatial diffusion. In addition, Coulomb drag forces may be important, in particular for the E ring. The possibility that electromagnetic effects may play a role in determining the F ring structure and its possible time variations is critically examined. Sputtering of micron-sized dust particles in the E ring by magnetospheric ions yields lifetimes of 100 to 10,000 years. This effect as well as the plasma induced transport processes require an active source for the E ring, probably Enceladus.

Morfill, G. E.↗
NASA NTRS1983

The function and response of an improved stratospheric condensation nucleus counter

An improved condensation nucleus counter (CNC) for use in the stratosphere is described. The University of Minnesota CNC (UMCNC) has a sequential saturator and condenser and uses n-butyl alcohol as the working fluid. The use of a coaxial saturator flow, with aerosol in the center and filtered, alcohol-laden air around it, speeds the response of this instrument and improves its stability as pressure changes. The counting efficiency has been studied as a function of particle size and pressure. The UMCNC provides an accurate measure of submicron aerosol concentration as long as the number distribution is not dominated by sub-0.02 micron diameter aerosol. The response of the UMCNC is compared with that of other stratospheric condensation nucleus counters, and the results of a (near) comparison with a balloon-borne condensation nucleus counter are presented. The UMCNC has operated 14 times on a NASA U-2 aircraft at altitudes from 8 to 21.5 km.

Wilson, J. C.↗
NASA NTRS1983

Plasma polymerized high energy density dielectric films for capacitors

High energy density polymeric dielectric films were prepared by plasma polymerization of a variety of gaseous monomers. This technique gives thin, reproducible, pinhole free, conformable, adherent, and insoluble coatings and overcomes the processing problems found in the preparation of thin films with bulk polymers. Thus, devices are prepared completely in a vacuum environment. The plasma polymerized films prepared all showed dielectric strengths of greater than 1000 kV/cm and in some cases values of greater than 4000 kV/cm were observed. The dielectric loss of all films was generally less than 1% at frequencies below 10 kHz, but this value increased at higher frequencies. All films were self healing. The dielectric strength was a function of the polymerization technique, whereas the dielectric constant varied with the structure of the starting material. Because of the thin films used (thickness in the submicron range) surface smoothness of the metal electrodes was found to be critical in obtaining high dielectric strengths. High dielectric strength graft copolymers were also prepared. Plasma polymerized ethane was found to be thermally stable up to 150 C in the presence of air and 250 C in the absence of air. No glass transitions were observed for this material.

Yamagishi, F. G.↗
NASA NTRS1984

Micronized coal burner facility

A combustor or burner system in which the ash resulting from burning a coal in oil mixture is of submicron particle size is described. The burner system comprises a burner section, a flame exit nozzle, a fuel nozzle section, and an air tube by which preheated air is directed into the burner section. Regulated air pressure is delivered to a fuel nozzle. Means are provided for directing a mixture of coal particles and oil from a drum to a nozzle at a desired rate and pressure while means returns excess fuel to the fuel drum. Means provide for stable fuel pressure supply from the fuel pump to the fuel nozzle.

Calfo, F. D.↗
NASA NTRS1984

Powder fed sheared dispersal particle generator

A particle generating system is described which is capable of breaking up agglomerations of particles and producing a cloud of uniform, submicron-sized particles at high pressure and high flow rates. This is achieved by utilizing a tubular structure which has injection microslits on is periphery to accept and disperse the desired particle feed. By suppling a carrying fluid at a pressure, of approximately twice the ambient pressure of the velocimeter's settling chamber, the microslits operate at choked flow conditions. The shearing action of this choked flow is sufficient to overcome interparticle bonding forces, thereby breaking up the agglomerates of the particles feed into individual particles.

Morrisette, E. L.↗
NASA NTRS1982

Characterization of silicon-gate CMOS/SOS integrated circuits processed with ion implantation

The procedure used to generate MEBES masks and produce test wafers from the 10X Mann 1600 Pattern Generator Tape using existing CAD utility programs and the MEBES machine in the RCA Solid State Technology Center are described. The test vehicle used is the MSFC-designed SC102 Solar House Timing Circuit. When transforming the Mann 1600 tapes into MEBES tapes, extreme care is required in order to obtain accurate minimum linewidths when working with two different coding systems because the minimum grid sizes may be different for the two systems. The minimum grid sizes are 0.025 mil for MSFC Mann 1600 and 0.02 mil for MEBES. Some snapping to the next grid is therefore inevitable, and the results of this snapping effect are significant when submicron lines are present. However, no problem was noticed in the SC102 circuit because its minimum linewidth is 0.3 mil (7.6 microns). MEBES masks were fabricated and wafers were processed using the silicon-gate CMOS/SOS and aluminum-gate COS/MOS processing.

Woo, D. S.↗
NASA NTRS1983

Investigation of supersonic separated flow in a compression corner by laser Doppler anemometry

A single-component, computer-operated, three dimensional traversing laser Doppler velocimetry system was designed and constructed for a supersonic wind tunnel. The model was a 10 deg compression corner, providing an example of laminar boundary layer separation. Static pressure data and color schlieren photographs were taken. The Mach number was 2.42 and the Reynolds number was 213,000. The flow was seeded with submicron sized oil droplets. The trend of decreasing upstream influence with increasing Reynolds number was confirmed. Mean velocity profiles provided experimental evidence of reversed flow. Points of separation and reattachment were consistent with those determined by schlieren and pressure scans. The flow was of the laminar type until downstream of reattachment. Individual mean velocity and turbulence profiles, as well as velocity histograms are presented.

Baroth, E. C.↗
NASA NTRS1983

Size-specific composition of aerosols in the El Chichon volcanic cloud

A NASA U-2 research aircraft flew sampling missions in April, May, July, November, and December 1982 aimed at obtaining in situ data in the stratospheric cloud produced from the March-April 1982 El Chichon eruptions. Post flight analyses provided information on the aerosol composition and morphology. The particles ranged in size from smaller than 0.05 m to larger than 20 m diameter and were quite complex in composition. In the April, May, and July samples the aerosol mass was dominated by magmatic and lithic particles larger than about 3 m. The submicron particles consisted largely of sulfuric acid. Halite particles, believed to be related to a salt dome beneath El Chichon, were collected in the stratosphere in April and May. On the July 23 flight, copper-zinc oxide particles were collected. In July, November, and December, in addition to the volcanic ash and acid particles, carbon-rich particles smaller than about 0.1 m aerodynamic diameter were abundant.

Woods, D. C.↗
NASA NTRS1983

A new layered mineral from the Mighei carbonaceous chondrite

The poorly characterized phase (PCP) of the Mighei CM2 carbonaceous chondrite is investigated using high-resolution TEM. Electron-microprobe analyses of samples from both olivine chondrules and the matrix are included in a table. Chondrule PCP is found to have higher concentrations of S and Ni and lower concentrations of Si, Mg, and Al than matrix PCP. TEM shows that PCP in this chondrite is an intergrowth of three phases (in various proportions): a major component containing Fe, S, Ni, and O in wavy rolled layers spaced about 5.4 A apart, an Fe-rich serpentinelike phyllosilicate with 7-A layer spacing, and submicron grains of magnetite, chromite, and phosphate. It is proposed that chondrule PCP contains mainly the 5-A phase with some grains, while matrix PCP consists mostly of the 5-A and 7-A phases.

Tomeoka, K.↗
NASA NTRS1984

Sulfur dioxide - Episodic injection shows evidence for active Venus volcanism

Pioneer Venus ultraviolet spectra from the first 5 years of operation show a decline (by more than a factor of 10) in sulfur dioxide abundance at the cloud tops and in the amount of submicron haze above the clouds. At the time of the Pioneer Venus encounter, the values for both parameters greatly exceeded earlier upper limits. However, Venus had a similar appearance in the late 1950's, implying the episodic injection of sulfur dioxide possibly caused by episodic volcanism. The amount of haze in the Venus middle atmosphere is about ten times that found in earth's stratosphere after the most recent major volcanic eruptions, and the thermal energy required for this injection on Venus is greater by about an order of magnitude than the largest of these recent earth eruptions and about as large as the Krakatoa eruption of 1883. The episodic behavior of sulfur dioxide implies that steady-state models of the chemistry and dynamics of cloud-top regions may be of limited use.

Esposito, L. W.↗
NASA NTRS1984

Processing of sintered alpha SiC

Processing methods of sintered alpha SiC for engine applications are developed in a cost effective manner, using a submicron sized powder blended with sintering aids (boron and carbon). The processes for forming a green powder compact, such as dry pressing, cold isostatic pressing and green machining, slip casting, aqueous extrusion, plastic extrusion, and injection molding, are described. Dry pressing is the simplest route to component fabrication, and is carried out at approximately 10,000 psi pressure, while in the cold isostatic method the pressure could go as high as 20,000 psi. Surfactants are added to control settling rates and casting characteristics in the slip casting. The aqueous extrusion process is accomplished by a hydraulic ram forcing the aqueous mixture through a die. The plastic forming processes of extrusion and injection molding offer the potential of greater diversity in shape capacity. The physical properties of sintered alpha SiC (hardness, Young's modulus, shear modulus, and thermal diffusivity) are extensively tested. Corrosion resistance test results of silicon carbide are included.

Storm, R. S.↗
NASA NTRS1983

Laboratory dust experiments - Tracing the composition of cometary dust

The structure and composition of the comet nucleus are investigated theoretically on the basis of aggregation models and laboratory simulations of interstellar-grain evolution. The results are presented in graphs, diagrams, and drawings and discussed in detail. The nucleus is described as a loose tangle of rodlike grains containing about 28 percent H2O, 10 percent CO2 and CO, and 33 percent nonvolatile submicron-size grit particles (silicates, complex organics, and carbon). Evidence from meteorites suggests that the C-12/C-13 ratio of the volatile components is greater than 100.

Greenberg, J. M.↗
NASA NTRS1984

Transmission electron microscopy of the 'LOW-CA' hydrated interplanetary dust particle

Transmission electron microscopy of a hydrated interplanetary dust particle indicates that it consists largely of a poorly crystalline phyllosilicate containing Fe, Mg and Al with an interlayer spacing of 10 to 12 A and so is distinct from the major phyllosilicate in CI and CM carbonaceous chondrites. The silicate is probably an Fe- and Mg-rich smectite or mica. Submicron, spherical to euhedral pyrrhotite and pentlandite are prominent. Unusual, low-Ni pentlandite is also common and typically occurs as rectangular platelets. Unlike many chondritic interplanetary dust particles, olivine is rare and pyroxene was not observed. Other less abundant phases are magnetite, chromite, and an unidentified phase containing Fe, Mg, Si, Ca, and Mn. This particle differs from a hydrated micrometeorite described previously by Brownlee (1978), indicating there are mineralogically different subsets of hydrated interplanetary dust particles. Despite gross similarities in mineralogy between the particle and the carbonaceous chondrites, they show appreciable differences in detail.

Tomeoka, K.↗
NASA NTRS1984

Fine-grained millimeter-sized objects in type 3 ordinary chondrites and their relation to chondrules and matrix

Fine-grained, opaque, silicate-rich matrix material, occurring as rims on chondrules and clasts, discrete clasts, and between chondrule and mineral fragments is a primitive component of chondrites and may resemble the material from which chondrules formed. To elucidate the relationship between chondrules and matrix and to help identify chondrule precursor material, the nimeralogy and bulk compositions of 30 mm-sized, fine-grained objects in Tieschitz (h3.6), Sharps (H3.4), Allan Hills A77299 (H3.7), Yamato 74191 (L3.6), Semarkona (LL3.0), and St. Mary's Co. (LL3.3) were studied. All are composed of submicron to micron sized material and may contain larger mineral fragments. Three texturally and mineralogically distinct types of objects were identified; all are minor components of the chondrites studied ( 1% except Sharps where melt-breccia-textured objects are approximately minus 1%). Bulk compositions of network and melt-breccia-textured objects define a rather narrow trend on a plot of Si/Al vs. Mg/Al, emphasizing a possible genetic relationship. Data show that Si/Mg is higher for network and melt-breccia-textured objects than for porphyritic and barred olivine chondrules. Melting in vaccuo of network-textured objects would cause a loss of Si relative to Mg (3), suggesting that material compositionally similar to fine grained objects could have been precursors to some chondrules.

Recca, S. I.↗
NASA NTRS1984

Si MOS devices at low temperatures

Low temperature operation of micron and submicron size Si MOSFETs (metal-oxide-semiconductor field-effect-transistors) results in their improved device characteristics. Various low temperature device properties such as increase in mobility, shift in the theshold voltage, increased reliability, etc., were considered. Other device characteristics such as the subthreshold behavior, delay times and miniaturization at low temperatures are discussed. Discussion includes presenting experimental results along with physical models explaining the observed effects.

Kamgar, A.↗
NASA NTRS1982

The gravito-electrodynamics of charged dust in planetary ring systems

The dynamics of micron and submicron sized dust grains moving under the combined influence of planetary gravitation and the electromagnetic forces within the corotating regions of planetary magnetospheres are discussed. Magnetogravitational capture of charged grains in planetary rings is outlined. The adiabatic motion of charged dust is reviewed.

Mendis, D. A.↗
NASA NTRS1984

Structure of the Uranian rings. I - Square-well model and particle-size constraints

A least squares fitting is added to the diffraction model for the Uranian rings and the model is then used to determine the relative optical depths of the rings at visible and near-IR wavelengths. Light transmission is assumed constant on a scale of a few radial km in the rings. The amount of starlight passing through the rings is calculated from occultations with account taken of a monolayer ring, diffraction effects, and multiple ring layers. A diffracted occultation profile is generated with consideration given to the angular diameter of the star, the impulse response of the detector, and atmospheric aberrations. Calculation procedures which remove noise are outlined and results are compared with the observational data base. The wavelength dependence of optical depth is formulated. It is shown that occultation data do not support the presence of a large fraction of submicron particles. No optical depth variations are projected for 0.88-2.2 microns wavelengths. Unchopped data are needed to verify the model predictions.

Elliot, J. L.↗