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Dust Particles (dust + particle)
Selected AbstractsHydrodynamic and Kinetic Modelling of Dust Free and Dusty Radio-Frequency DischargesCONTRIBUTIONS TO PLASMA PHYSICS, Issue 5-6 2004W. J. Goedheer Abstract In this paper hydrodynamic and kinetic approaches to model low pressure capacitively coupled radio-frequency discharges are discussed. In particular approaches and results for power modulated discharges in a mixture of silane and hydrogen and for discharges containing a considerable amount of dust particles will be presented. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Wind erosion characteristics of Sahelian surface typesEARTH SURFACE PROCESSES AND LANDFORMS, Issue 12 2010Thomas Maurer Abstract The assessment of wind erosion magnitudes for a given area requires knowledge of wind erosion susceptibilities of the dominant local surface types. Relative wind erosion potentials of surfaces can hardly be compared under field conditions, as each erosion event is unique in terms of duration, intensity and extent. The objective of this study was to determine and compare relative wind erosion potentials of the most representative surface types over a transect comprising most parts of southwestern Niger. For this purpose, mobile wind tunnel experiments were run on 26 dominant surface types. The effects of surface disturbance were additionally determined for 13 of these surfaces. The results, namely measurements of wind fields and mass fluxes, can be classified according to specific surface characteristics. Three basic surface groups with similar emission behaviour and aerodynamic characteristics were identified: (1) sand surfaces, (2) rough stone surfaces and (3) flat crusted surfaces. Sand surfaces feature a turbulent zone close to the surface due to the development of a saltation layer. Their surface roughness is medium to high, as a consequence of the loss of kinetic energy of the wind field to saltating particles. Sand surfaces show the highest mass fluxes due to the abundance of loose particles, but also fairly high PM10 fluxes, as potential dust particles are not contained in stable crusts or aggregates. Rough stone surfaces, due to their fragmented and irregular surface, feature the highest surface roughness and the most intense turbulence. They are among the weakest emitters but, due to their relatively high share of potential dust particles, PM10 emissions are still average. Flat crusted surfaces, in contrast, show low turbulence and the lowest surface roughness. This group of surfaces shows rather heterogeneous mass fluxes, which range from moderate to almost zero, although the share of PM10 particles is always relatively high. Topsoil disturbance always results in higher total and PM10 emissions on sand surfaces and also on flat crusted surfaces. Stone surfaces regularly exhibit a decrease in emission after disturbance, which can possibly be attributed to a reorganization which protects finer particles from entrainment. The results are comparable with field studies of natural erosion events and similar wind tunnel field campaigns. The broad range of tested surfaces and the standardized methodology are a precondition for the future regionalization of the experimental point data. Copyright © 2010 John Wiley & Sons, Ltd. [source] Techniques to measure the dry aeolian deposition of dust in arid and semi-arid landscapes: a comparative study in West NigerEARTH SURFACE PROCESSES AND LANDFORMS, Issue 2 2008Dirk Goossens Abstract Seven techniques designed to measure the dry aeolian deposition of dust on a desert surface were tested during field experiments in Niger, central-west Africa. Deposition fluxes were measured during eight periods of 3,4 days each. Experimental techniques tested were the MDCO (marble dust collector) method, the Frisbee method, the glass plate method (optical analysis of dust deposited on glass surfaces using particle imaging software), the soil surface method (deposition on a simulated desert floor) and the CAPYR (capteur pyramidal) method. Theoretical techniques tested were the inferential method and the combination method (gradient method extended with a deposition term for coarse dust particles). The results obtained by the MDCO, Frisbee, inferential and combination methods could be directly compared by converting the data to identical standard conditions (deposition on a water surface producing no resuspension). The results obtained by the other methods (glass plate, soil surface, CAPYR) were compared relatively. The study shows that the crude (unconverted) deposition fluxes of the five experimental techniques were similar, while the crude deposition fluxes calculated by the two theoretical techniques were substantially higher, of the order of four to five times as high as for the experimental techniques. Recalculation of the data to identical environmental conditions (the standard water surface) resulted in nearly identical deposition fluxes for the MDCO, Frisbee, inferential and combination techniques, although the latter two still had slightly higher values (but the differences remained small). The measurements illustrate the need to include a grain shape factor in theoretical dust deposition models. Without such a factor, theoretical models overestimate the deposition. The paper also discusses the advantages and disadvantages of the techniques tested. Copyright © 2007 John Wiley & Sons, Ltd. [source] Formation of Porous SiC Ceramics by Pyrolysis of Wood Impregnated with SilicaINTERNATIONAL JOURNAL OF APPLIED CERAMIC TECHNOLOGY, Issue 6 2006Kateryna Vyshnyakova Biomorphous ,-SiC ceramics were produced at 1400°C from pine wood impregnated with silica. This one-step carbothermal reduction process decreases the cost of manufacturing of SiC ceramics compared with siliconization of carbonized wood in silicon vapor. The synthesized sample exhibits a 14 m2/g surface area and has a hybrid pore structure with large 5,20 ,m tubular macropores and small (<50 nm) slit-shaped mesopores. SiC whiskers of 20,400 nm in diameter and 5,20 ,m in length formed within the tubular pores. These whiskers are expected to improve the filtration by removing dust particles that could otherwise penetrate through large pores. After ultrasonic milling, the powdered sample showed an average particle size of ,30 nm. The SiC nanopowder produced in this process may be used for manufacturing SiC ceramics for structural, tribological, and other applications. [source] Micro-organisms and dust exposure in an Italian grain millJOURNAL OF APPLIED MICROBIOLOGY, Issue 1 2005C. Dacarro Abstract Aims:, In order to assess possible occupational risk for workers in a grain mill, we evaluated aerial microbiological contamination in different areas of the mill and at different points of the production line. We also measured the concentration of aerodispersed dust particles. Methods and Results:, An assessment of microbiological contamination levels based on a Global Index of Microbial Contamination per cubic metre (GIMC per m3), an Index of Mesophilic Bacterial Contamination, and an Amplification Index is proposed. The indices were obtained from total and fungal counts. The cleaning sector is the most contaminated area of the mill: the mean GIMC per m3 was 17 213·6. In this area, the average microbial contamination was 11·41 times higher than that in the external environment. The highest concentrations of aerodispersed dust (inhalable 2·763 mg m,3; respirable 1·400 mg m,3) were found in the cleaning area. Conclusions:, The proposed microbiological indices and the concentrations of aerodispersed dust particles show that the most hazardous section of the mill is the cleaning area. The large variation in the data does not depend on seasonal factors, but rather on not easily identifiable conditions of the internal environment which facilitate diffusion and/or proliferation of the micro-organisms. Significance and Impact of the Study:, The proposed microbiological contamination indices and the evaluation of the concentration of dust particles allow the identification of critical positions during the production cycle so that suitable measures to prevent the aerial contamination can be taken. [source] Raman spectroscopy of ion-irradiated astrophysically relevant materialsJOURNAL OF RAMAN SPECTROSCOPY, Issue 2 2008G. A. Baratta Abstract Solid objects in space (interstellar grains, comets, interplanetary dust particles, etc.) are continuously exposed to energetic processes, such as cosmic ion irradiation, that influence their evolution. In this paper we present an experimental study, carried out by Raman spectroscopy, of the effects induced by ion irradiation on frozen ices and refractory materials. If the irradiated ice mixture contains a relevant amount of carbon atoms, the ice is converted into an organic residue (stable at room temperature), which at high irradiation dose evolves toward a hydrogenated amorphous carbon. Here we show that material similar to that produced in the laboratory by ion irradiation of frozen ice mixtures and refractory materials can be formed in space by cosmic ion irradiation. This finding has been recently confirmed by the Stardust mission, which revealed in some of the cometary particles collected in space and returned to earth carbonaceous materials that have been processed by cosmic ion irradiation. Copyright © 2008 John Wiley & Sons, Ltd. [source] Stardust glass: Indigenous and modified comet Wild 2 particlesMETEORITICS & PLANETARY SCIENCE, Issue 11 2009Frans J. M. Rietmeijer Glass is used here to include all types of amorphous materials that could be either indigenous or modified comet Wild 2 grains, and all amorphous phases in chondritic aggregate interplanetary dust particles (IDPs). The answer is that it probably does, but very little is known of their compositions to allow a definitive answer to be given. There is no evidence among the collected comet dust for interstellar glass with embedded metals and sulfides. There is, however, ample evidence for melting of the smallest, sub-micrometer comet particles of nanometer-scale grains similar to those in the matrix of chondritic aggregate IDPs, including pyrrhotite. Massive patches of Mg-SiO, Al-SiO, or Ca-Si-O glass are incorporated in the familiar, vesicular Si-rich glass are melted Wild 2 silicates. Magnesiosilica glass has a deep metastable eutectic smectite-dehydroxylate composition. It indicates that very high temperatures well above the liquidus temperatures of forsterite were achieved very rapidly and were followed but ultra-rapid quenching. This predictable and systematic response is not limited to Mg-silicates, and recognizing this phenomenon among massive glass will provide a means to complete the reconstruction of this comet's original minerals, as well as constrain the physiochemical environment created during aerogel melting and evaporation. [source] Organic matter from comet 81P/Wild 2, IDPs, and carbonaceous meteorites; similarities and differencesMETEORITICS & PLANETARY SCIENCE, Issue 10 2009S. Wirick Sections were analyzed using a scanning transmission X-ray microscope (SXTM) and carbon X-ray absorption near edge structure (XANES) spectra were collected. We compared the carbon XANES spectra of these Wild 2 samples with a database of spectra on thirty-four interplanetary dust particles (IDPs) and with several meteorites. Two of the particles analyzed are iron sulfides and there is evidence that an aliphatic compound associated with these particles can survive high temperatures. An iron sulfide from an IDP demonstrates the same phenomenon. Another, mostly carbon free containing particle radiation damaged, something we have not observed in any IDPs we have analyzed or any indigenous organic matter from the carbonaceous meteorites, Tagish Lake, Orgueil, Bells and Murchison. The carbonaceous material associated with this particle showed no mass loss during the initial analysis but chemically changed over a period of two months. The carbon XANES spectra of the other four particles varied more than spectra from IDPs and indigenous organic matter from meteorites. Comparison of the carbon XANES spectra from these particles with 1. the carbon XANES spectra from thirty-four IDPs (<15 micron in size) and 2. the carbon XANES spectra from carbonaceous material from the Tagish Lake, Orgueil, Bells, and Murchison meteorites show that 81P/Wild 2 carbon XANES spectra are more similar to IDP carbon XANES spectra then to the carbon XANES spectra of meteorites. [source] Analytical SuperSTEM for extraterrestrial materials researchMETEORITICS & PLANETARY SCIENCE, Issue 10 2009John P. Bradley The improved technical capabilities enable analyses previously not possible. Mineral structures can be directly imaged and analyzed with single-atomic-column resolution, liquids, and implanted gases can be detected, and UV-VIS optical properties can be measured. Detection limits for minor/trace elements in thin (<100 nm thick) specimens are improved such that quantitative measurements of some extend to the sub-500 ppm level. Electron energy-loss spectroscopy (EELS) can be carried out with 0.10,0.20 eV energy resolution and atomic-scale spatial resolution such that variations in oxidation state from one atomic column to another can be detected. Petrographic mapping is extended down to the atomic scale using energy-dispersive X-ray spectroscopy (EDS) and energy-filtered transmission electron microscopy (EFTEM) imaging. Technical capabilities and examples of the applications of SuperSTEM to extraterrestrial materials are presented, including the UV spectral properties and organic carbon K-edge fine structure of carbonaceous matter in interplanetary dust particles (IDPs), X-ray elemental maps showing the nanometer-scale distribution of carbon within GEMS (glass with embedded metal and sulfides), the first detection and quantification of trace Ti in GEMS using EDS, and detection of molecular H2O in vesicles and implanted H2 and He in irradiated mineral and glass grains. [source] Stardust in Antarctic micrometeoritesMETEORITICS & PLANETARY SCIENCE, Issue 8 2008Toru YADA The oxygen isotopic compositions of the eighteen presolar silicate (and one oxide) grains found are similar those observed previously in primitive meteorites and interplanetary dust particles, and indicate origins in oxygen-rich red giant or asymptotic giant branch stars, or in supernovae. Four grains with anomalous C isotopic compositions were also detected. 12C/13C as well as Si ratios are similar to those of mainstream SiC grains; the N isotopic composition of one grain is also consistent with a mainstream SiC classification. Presolar silicate grains were found in three of the seven AMMs studied, and are heterogeneously distributed within these micrometeorites. Fourteen of the 18 presolar silicate grains and 3 of the 4 C-anomalous grains were found within one AMM, T98G8. Presolar silicate-bearing micrometeorites contain crystalline silicates that give sharp X-ray diffractions and do not contain magnesiowüstite, which forms mainly through the decomposition of phyllosilicates and carbonates. The occurrence of this mineral in AMMs without presolar silicates suggests that secondary parent body processes probably determine the presence or absence of presolar silicates in Antarctic micrometeorites. [source] Acrylic embedding of Stardust particles encased in aerogelMETEORITICS & PLANETARY SCIENCE, Issue 11 2006G. Matrajt In this report we describe a new embedding technique that uses acrylic resin instead of epoxy. This method offers several important advantages for sectioning small extraterrestrial samples. One is that the acrylic resin is soluble and can be removed after ultramicrotomy to leave a sample that is free of the mounting media. This is important for studying carbon and insoluble organic components. A second major advantage of acrylic is that, when combined with pre-embedding compression, it provides a very effective method of mounting samples collected in silica aerogel. Acrylic embedding is currently being used to mount comet particles collected by NASA's Stardust mission. Combined with a flattening process, the acrylic embedding and sectioning preserves all pieces of collected samples in their collection matrix. In addition to Stardust, acrylic may be applied to other samples collected in aerogel such as those from the Russian Mir space station (Hörz et al. 2000) and future missions such as Sample Collection for Investigation of Mars (SCIM) (Leshin 2003), a proposed mission to collect atmospheric dust particles from Mars. [source] Opportunities for the stratospheric collection of dust from short-period cometsMETEORITICS & PLANETARY SCIENCE, Issue 11 2002Scott MESSENGER These comets have had the rare characteristics of low eccentricity, low inclination orbits with nodes very close to 1 AU. Dust from these comets is directly injected into Earth-crossing orbits by radiation pressure, unlike the great majority of interplanetary dust particles collected in the stratosphere which spend millennia in space prior to Earth-encounter. Complete dust streams from these comets form within a few decades, and appreciable amounts of dust are accreted by the Earth each year regardless of the positions of the parent comets. Dust from these comets could be collected in the stratosphere and identified by its short space exposure age, as indicated by low abundances of implanted solar-wind noble gases and/or lack of solar flare tracks. Dust from Grigg-Skjellerup probably has the highest concentration at Earth orbit. We estimate that the proportion of dust from this comet will reach at least several percent of the background interplanetary dust flux in the >40 ,m size range during April 23,24 of 2003. [source] Combined noble gas and trace element measurements on individual stratospheric interplanetary dust particlesMETEORITICS & PLANETARY SCIENCE, Issue 10 2002K. Kehm Trace element compositions are generally similar to CI meteorites, with occasional depletions in Zn/Fe with respect to CI. Noble gases were detected in all but one of the IDPs. Noble gas elemental compositions are consistent with the presence of fractionated solar wind. A rough correlation between surface-normalized He abundances and Zn/Fe ratios is observed; Zn-poor particles generally have lower He contents than the other IDPs. This suggests that both elements were lost by frictional heating during atmospheric entry and confirms the view that Zn can serve as an entry-heating indicator in IDPs. [source] The role of Kelvin,Helmholtz instability in dusty and partially ionized outflowsMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 3 2008Mohsen Shadmehri ABSTRACT We investigate the linear theory of Kelvin,Helmholtz instability at the interface between a partially ionized dusty outflow and the ambient material analytically. We model the interaction as a multifluid system in a planar geometry. The unstable modes are independent from the charge polarity of the dust particles. Although our results show a stabilizing effect for charged dust particles, the growth time-scale of the growing modes gradually becomes independent of the mass or charge of the dust particles when the magnetic-field strength increases. We show that growth time-scale decreases with increasing the magnetic field. Also, as the mass of the dust particles increases, the growth time-scale of the unstable mode increases. [source] On Different Approaches to Estimate the Mass Fractal Dimension of Coal AggregatesPARTICLE & PARTICLE SYSTEMS CHARACTERIZATION, Issue 5 2005Jimmy Y. H. Liao Abstract Several methods to measure the structures of coal aggregates are compared. Loose and compact coal aggregates were generated through flocculation of ultrafine coal particles (mean volume diameter of 12,,m) under specific shearing conditions. Aggregate structure in terms of mass fractal dimension, Df, was determined using various methods; namely 2D and 3D image analysis, interpretation of intensity patterns from small angle light scattering, changes in aggregation state through light obscuration, and settling behavior. In this study, the measured values of Df ranged from 1.84,2.19 for coal aggregates with more open structures, and around 2.27,2.66 for the compact ones. All of these approaches could distinguish structural differences between aggregates, albeit with variation in Df values estimated by the different techniques. The discrepancy in the absolute values for fractal dimension is due to the different physical properties measured by each approach, depending on the assumptions used to infer Df from measurable parameters. In addition, image analysis and settling techniques are based on the examination of individual aggregates, such that a large number of data points are required to yield statistically representative estimations. Light scattering and obscuration measure the aggregates collectively to give average Df values of the particulate systems; consequently ignoring any structural variation between the aggregates, and leaving possible small contaminations undetected (e.g. by dust particles or air bubbles). Appropriate utilization of a particular method is thus largely determined by system properties and required data quality. [source] Deposition of SnO2:F Thin Films on Polycarbonate Substrates by PECVD for Antifouling PropertiesPLASMA PROCESSES AND POLYMERS, Issue S1 2007Marie Jubault Abstract SnO2:F thin films were deposited on polycarbonate and glass substrates by RF capacitively coupled plasma enhanced chemical vapor deposition (PECVD) using a mixture of tetramethyltin (TMT) [Sn(CH3)4], argon, oxygen as precursors. The effects of the substrate temperature, deposition time and doping on the resistivity and the morphology of the films have been studied. The as-deposited films appear to have higher carrier mobilities than amorphous ones, in the range of 5 and 7.5 cm2,·,V,1,·,s,1, which could be explained by the presence of nanocrystallites. In order to understand the nanostructure of the films, we studied the formation of nanoparticles and dust particles in the discharge. Finally, we have shown that the incorporation of less than 3% of F in the tin oxide layer could decrease the resistivity down to 3,·,10,3 ,,·,cm. [source] | |||||||||||||