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At least 181 records · Page 10
All sourcesNASA NTRSDOE OSTI
NASA NTRS2004

Rapid Measurements of Aerosol Ionic Composition and 3-10 nm Particle Size Distributions On The NASA P3 To Better Quantify Processes Affecting Aerosols Advected From East Asia

The Particle Into Liquid Sample (PILS) was deployed on the NASA P3 for airborne measurements of fine particle ionic chemical composition. The data have been quality assured and reside in the NASA data archive. We have analyzed our data to characterize the sources and atmospheric processing of fine aerosol particles advected from the region during the experiments. Fine particle water-soluble potassium was found to serve as a useful aerosol tracer for biomass smoke. Ratios of PILS potassium to sulfate are used as a means of estimating the percent contribution of biomass burning to fine particle mass in mixed plumes advecting from Asia. The high correlations between K+ and NO3(sup -) and NH4(sup +)' indicated that biomass burning was a significant source of these aerosol compounds in the region. It is noteworthy that the air mass containing the highest concentrations of fine particles recorded in all of ACE-Asia and TRACE-P appeared to be advecting from the Bejing/Tientsin urban region and also had the highest K(+), NO3(sup -) and NH4(sup +) concentrations of both studies. Based on K+/SO4(sup 2-) ratio's, we estimated that the plume was composed of approx. 60% biomass burning emissions, possibly from the use of bio-fuels in the urban regions.

Weber, Rodney J.↗
NASA NTRS1972

Composition of interplanetary particles at energies from 0.1 to 150 MeV/nucleon, part B

During the Apollo 16 mission, a solar flare produced an enormous amount of low-energy nuclei, many orders of magnitude greater than the level inferred from studies of tracks in the window of the Apollo 12 spacecraft during a time when the sun was quiet. The differential energy spectrum of nuclei with Z less than or equal to 6 falls by seven orders of magnitude over the interval from 0.1 to 20 MeV/nucleon, then remains almost flat up to approximately 100 MeV/nucleon. The two parts correspond to contributions from the sun and from galactic cosmic rays. Any maximum in the spectrum occurs below the lowest energy studied.

Price, P. B.↗
NASA NTRS1974

Computer simulation of a fringe type laser velocimeter

A computer simulation of a fringe type laser velocimeter has been written to determine the theoretical characteristics of the laser velocimeter when applied to a given flow field. The program includes the effect of particle size and composition on particle lag, light scattering characteristics and signal contrast. The model of the laser velocimeter includes the laser, optical system, photomultiplier, and counter type data processing electronics. The LV particle size analyzer is also modeled and incorporated in the program. An example application of the program to a Mach 5 wind tunnel using a backscatter laser velocimeter is presented.

Meyers, J. F.↗
NASA NTRS1986

Studies of the composition of solar particles and of energetic oxygen and sulfur nuclei trapped in the Jovian magnetosphere

The Cosmic Ray System (CRS) experiment on board each of the Voyager 1 and 2 spacecraft consists of four Low Energy Telescopes (LETs), two High Energy Telescopes (HETs), the Electron Telescope (TET), and associated electronics. With these instruments it is possible to measure the energy spectrum of electrons over the 3-110MeV energy range and the energy spectra and nuclear charge of atomic nuclei from hydrogen through zinc over the 3-500 MeV/nuc energy range. The exclusive use of solid-state detectors in the CRS telescopes achieves the objectives of reliability over a long mission life, high resolution determinations of energy and charge, and high-count-rate capability during large solar flares and passage through the magnetospheres of the outer planets. Summarized here are some of the many accomplishments that have resulted from the CRS measurements during the period covered by this report, May 15, 1981 to May 15, 1984, including studies of the energetic oxygen and sulfur nuclei trapped in the Jovian magnetosphere.

Stone, E. C.↗
NASA NTRS2003

Individual Aerosol Particles from Biomass Burning in Southern Africa: Compositions and Size Distributions of Carbonaceous Particles - 1

Individual aerosol particles in smoke plumes from biomass fires and in regional hazes in southern Africa were studied using analytical transmission electron microscopy (TEM), which allowed detailed characterization of carbonaceous particle types in smoke and determination of changes in particle properties and concentrations during smoke aging. Based on composition, morphology, and microstructure, three distinct types of carbonaceous particles were present in the smoke: organic particles with inorganic (K-salt) inclusions, tar ball particles, and soot. The relative number concentrations of organic particles were largest in young smoke, whereas tar balls were dominant in a slightly aged (1 hour) smoke from a smoldering fire. Flaming fires emitted relatively more soot particles than smoldering fires, but soot was a minor constituent of all studied plumes. Further aging caused the accumulation of sulfate on organic and soot particles, as indicated by the large number of internally mixed organic/sulfate and soot/sulfate particles in the regional haze. Externally mixed ammonium sulfate particles dominated in the boundary layer hazes, whereas organic/sulfate particles were the most abundant type in the upper hazes. Apparently, elevated haze layers were more strongly affected by biomass smoke than those within the boundary layer. Based on size distributions and the observed patterns of internal mixing, we hypothesize that organic and soot particles are the cloud-nucleating constituents of biomass smoke aerosols. Sea-salt particles dominated in the samples taken in stratus clouds over the Atlantic Ocean, off the coast of Namibia, whereas a distinct haze layer above the clouds consisted of aged biomass smoke particles.

Posfai, Mihaly↗
NASA NTRS1979

Elemental composition of solar energetic particles in 1977 and 1978

The elemental composition of energetic nuclei from seven major solar flare events were measured wit the cosmic ray detector systems aboard the Voyager 1 and 2 spacecraft. The energetic nuclei abundances differ significantly from those of photospheric material. They are enhanced relative to the photonsphere by a factor which is the ratio of abundance of an energetic nuclei species (relative to oxygen) over the corresponding abundance of photospheric material. This factor is common to all events and has a nonmonochromatic characteristic dependence on nuclear charge. This factor is roughly ordered by first ionization potential into two groups of elements, metallics and volatiles.

Cook, W. R.↗
NASA NTRS1989

Effect of particle size on fracture toughness of SiC/Al composite material

Discontinuous SiC/Al composites with SiC particles of different sizes were fabricated in order to study the role of particle size on the fracture process. The fracture process is confined to a very narrow band and takes place within the matrix in composites containing small SiC particle sizes. In the composite reinforced with SiC particles of 20 microns and above fracture of SiC begins to dominate. The matrix is influenced by the high density of dislocations generated at SiC/Al interfaces due to the difference in coefficient of thermal expansion between SiC and the Al matrix. Crack initiation fracture toughness does not depend on SiC particle size. Crack growth fracture toughness increases as the size of the SiC particle increase.

Flom, Y.↗
NASA NTRS1975

Heavy particle emission of unusual composition from the sun

Sustained emission of low energy (0.6-4 MeV/nuc) solar particles with a composition richer in iron than in oxygen is observed in three time periods of 1974. The relative abundances of Ne, Mg, Si, and S-Ca to O are also enhanced as compared to those of the sun and of solar cosmic rays. During all three periods, a large H-3/H-4 isotope ratio was also observed; for two cases, it is in the order of unity. On the other hand, the d/H-4 and the T/He-4 are less than 0.04 and 0.02 respectively. The solar activity during the time periods of the reported emission was low. At present, it is not clear whether the emission processes which yielded enriched heavy ions also produced the He-3 enhancement. It seems that any explanation of heavy ion enrichments in solar cosmic rays has to explain also the He-3 enrichment.

Hovestadt, D.↗
NASA NTRS1974

X-ray spectral microanalysis of composition of individual lunar regolith particles

Determinations were made of the chemical compositions of selected olivine crystals, spherical particles ranging in size from 170 to 350 micrometer, spinels, and magnetic particles. The olivines contain 30 to 50 mole percent fayalite. The spherical particles of various colors are aluminosilicate glasses, significantly enriched in CaO compared with the mean composition of the regolith. The degree of coloration depends on the FeO content and also the admixtures TiO2, MnO, and Cr2O3. Compositionally, the spinel was interpreted to be chromopicotites. Magnetic particles were shown to be complex intergrowths of nickelous iron and aluminosilicates. The composition of the metallic phase of one particle (in percent) was: Fe - 86, Ni - 13.6, and Co - 0.16 in combination with plagioclase and microinclusions of ilmenite in silicate. Kamacite was determined in another intergrowth of Fe, Ni, and Co.

Ilin, N. P.↗
NASA NTRS1980

Elemental composition of solar energetic particles in 1977 and 1978

Measurements of the elemental composition of energetic nuclei with atomic numbers between 2 and 28 from seven major solar flares from September 1977 to May 1978 are presented. The abundance observations were made with the Low Energy Telescope systems of the cosmic ray detector systems on board the Voyager 1 and 2 spacecraft between 1 and 3 AU. Examination of the abundance ratios of the flare nuclei relative to oxygen reveals significant variations from event to event and between energetic nuclei and photospheric abundances, with an average composition, except for C and N, very similar to that of the galactic cosmic ray source. For the four flare events for which the elemental abundances exhibit no significant energy dependence in the energy range observed, it is found that the enhancement of energetic nuclei relative to their photospheric abundance are similar and not monotonic with atomic number, with the metallic nuclei showing an enhancement factor of approximately 5 and the volatiles showing one closer to 1.

Cook, W. R.↗
NASA NTRS1994

Aerosol particles in the upper troposphere and lower stratosphere: Elemental composition and morphology of individual particles in northern midlatitudes

Atmospheric particles were collected in the midlatitude upper troposphere (UT) and lower stratosphere (LS) by inetrial impaction for subsequent electron microscopy and individual particle element analysis. More than 97% of particles analyzed on impactor substrates exposed in the LS contained only O and S in detectable quantities; these particles are believed to be acidic sulfate. Nonsulfate materials seen in the remaining particles included soot, other c-rich substances and crustal materials. Although not predominantly sulfate, usually carried a sulfer-rich coating in the LS. Samples collected very near and just below the tropopause were also dominated by sulfates. The fraction of sulfate particles analyzed on impactor substrates exposed in the UT was 91-94% of the total particle concentration. Nonsulfate substances observed in the UT samples included crustal-type material, hydrated marine salts, carbon-rich materials of several types, and metal-containing substances of uncertain origin. Most of these UT particles were not coated with detectable quantitites of sulfate.

Sheridan, Patrick J.↗
NASA NTRS2012

Mineralogy and Oxygen Isotope Compositions of Two C-Rich Hydrated Interplanetary Dust Particles

Oxygen isotopic compositions of chondrites reflect mixing between a O-16-rich reservoir and a O-17,O-18-rich reservoir produced via mass-independent fractionation. The composition of the O-16-rich reservoir is reasonably well constrained, but material representing the O-17,O-18-rich end-member is rare. Self-shielding models predict that cometary water, presumed to represent this reservoir, should be enriched in O-17 and O-18 18O by > 200%. Hydrated interplanetary dust particles (IDPs) rich in carbonaceous matter may be derived from comets; such particles likely contain the products of reaction between O-16-poor water and anhydrous silicates that formed in the inner solar system. Here we present mineralogy and oxygen isotope compositions of two C-rich hydrated IDPs, L2083E47 and L2071E35.

Snead, C. J.↗
NASA NTRS1990

Kinetics of gas-to-liquid and liquid-to-solid transfer of particles in metal-matrix composites

Analytical models for transfer of particles from gas to liquid and from liquid to solid are introduced. The model for calculation of the pushing/engulfment transition in directionally solidified particulate metal matrix composites, considers process thermodynamics, process kinetics, thermophysical properties and buoyant forces. Based on processing variables (solidification velocity and direction) and on material variables (interface energies, particle size, particle and liquid density, volume fraction of particles and particle/liquid thermal conductivity ratio) four types of behavior were predicted. Also, two numerical models for liquid-to-solid transfer are discussed, as well as the limitations of presently available models.

Stefanescu, D. M.↗
NASA NTRS1986

Workshop on Past and Present Solar Radiation: The Record in Meteoritic and Lunar Regolith Material

The principal question addressed in the workshop was the extent to which asteroidal and lunar regoliths have collected and preserved, in meteoritic regolith breccias and in lunar soils and regolith breccias, a record of the flux, energy, and compositional history of the solar wind and solar flares. Six central discussion topics were identified. They are: (1)Trapped solar wind and flare gases, tracks, and micrometeorite pits in regolith components; (2)Comparison between lunar regolith breccias, meteoritic regolith breccias, and the lunar soil; (3)The special role of regolith breccias and the challenge of dating their times of compaction; (4)Implications of the data for the flux and compositional history of solar particle emission, composition, and physical mechanisms in the solar source regions, and the composition of the early nebula; (5)How and to what extent have records of incident radiation been altered in various types of grains; (6)Future research directions

Pepin, R. O.↗
NASA NTRS1996

Computer Simulation of Spatial Arrangement and Connectivity of Particles in Three-Dimensional Microstructure: Application to Model Electrical Conductivity of Polymer Matrix Composite

Computer simulation is a powerful tool for analyzing the geometry of three-dimensional microstructure. A computer simulation model is developed to represent the three-dimensional microstructure of a two-phase particulate composite where particles may be in contact with one another but do not overlap significantly. The model is used to quantify the "connectedness" of the particulate phase of a polymer matrix composite containing hollow carbon particles in a dielectric polymer resin matrix. The simulations are utilized to estimate the morphological percolation volume fraction for electrical conduction, and the effective volume fraction of the particles that actually take part in the electrical conduction. The calculated values of the effective volume fraction are used as an input for a self-consistent physical model for electrical conductivity. The predicted values of electrical conductivity are in very good agreement with the corresponding experimental data on a series of specimens having different particulate volume fraction.

Louis, P.↗
NASA NTRS2015

Early Size Distributions of Chondrule Subgroups Overprinted by the Final Accumulation Process of Particle Components in Allende

Populations of compositionally distinct particles are fundamental components of undifferentiated chondritic meteorites. Many theories explain the formation of chondrites, one class of which includes mechanisms for sorting the component particles in the solar nebula prior to their accretion. Mechanisms include sorting by mass, turbulent concentration, X-winds, and photophoresis, which will produce characteristic distributions of observable properties such as particle size. Distinguishing processes that occur in specific astrophysical environments requires characterization of particle types, which include refractory Ca-Al-rich Inclusions (CAIs) and less-refractory chondrules. Previous investigations of modal abundances of CAIs and chondrules exist, but differences within and between these two groups, both of which are made up of diverse subgroups with different thermal histories and chemical compositions, remain mostly unstudied. The presence of rims, a significant event occurring after the formation of at least some chondrules, have also yet to be considered with respect to sorting. Here we present the sizes of CAIs and chondrules in Allende with attention to the smallest sizes, subgroups, and particle rims.

McCain, K. A.↗