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Grain-size Distribution (grain-size + distribution)
Selected AbstractsAeolian dust dynamics in agricultural land areas in Lower Saxony, GermanyEARTH SURFACE PROCESSES AND LANDFORMS, Issue 7 2001Dirk Goossens Abstract The dynamics of fine aeolian dust emitted from agricultural land was investigated over 15 months near Grönheim, Lower Saxony, Germany. The following aspects were studied: airborne dust concentration, the ratio of mineral versus organic dust, the vertical distribution of the particles in the atmosphere, horizontal and vertically integrated horizontal dust flux, vertical dust flux, dust deposition at ground level, grain-size distribution of the mineral dust component, and vertical distribution of organic matter in the dust. Standard meteorological parameters (wind speed and direction, precipitation) were measured as well. Dust activity in Grönheim is high in spring (March,May) and autumn (October,November) and low to very low during the rest of the year. There is a strong relationship between the periods of tillage and the intensity of dust activity. Also, there is high dust activity during wind erosion events. For the year 1999, dust emission due to tillage was 6·6 times higher than dust emission due to wind erosion. A dust transport of 15·8 ton km,1 a,1 was calculated for the first 10 m of the atmosphere in 1999. Total dust transport (in the entire mixing layer) was estimated between 16 and 20 ton km,1 a,1. About 25,30 per cent of this dust is mineral dust, emitted from the fields during tillage or during wind erosion events. In spring and autumn there is a strong vertical stratification in the airborne sediment, with much (coarse) dust in the lower air layers and significantly less (and finer) dust at higher altitudes. In summer and winter, when there is no local dust production, there is no stratification: equal amounts of dust are transported at all heights. The stratification in spring and autumn is exclusively caused by the mineral part of the dust. The organic particles are much better mixed in the atmosphere because of their lower density. Copyright © 2001 John Wiley & Sons, Ltd. [source] Size distributions of suspended particles in open channel flow over bed materialsENVIRONMETRICS, Issue 2 2005B. S. Mazumder Controlled experiments have shown that the grain-size distribution of suspended sediments is related to bed material, flow velocity and height of suspension above the sand bed in an open channel flow. A theoretical model has been developed for computation of suspended grain-size distribution on the basis of continuity equations of sediment and water, using the computed bed-layer concentration as a reference. The proposed model includes the effect of suspension concentration into the mean velocity, turbulent and viscous shear stresses owing to the dynamic coupling between the flow and sediments in suspension. The effect of hindered settling due to the increased concentration in suspension is also taken into account. The model is considered to be a more general one than the existing models, and the results of the present model compare well with the experimental data. Copyright © 2004 John Wiley & Sons, Ltd. [source] Magnetic grain-size distribution of the enhanced component in the loess,palaeosol sequences in the western Loess Plateau of ChinaGEOPHYSICAL JOURNAL INTERNATIONAL, Issue 2 2001Toshiaki Mishima SUMMARY Rock magnetic measurements of Chinese loess,palaeosol samples from the Beiyuan section in Linxia City suggest the presence of two magnetic components: a background component and an enhanced component. The magnetic properties of the enhanced component suggest strong grain-size control, which is in contrast with variable grain-size distribution in loess,palaeosol from the central Loess Plateau. Chemically formed magnetic grains do not fulfil the requirements in the case of the western Loess Plateau because they may show shifts in the grain-size distribution. The difference in climate between the western and central Loess Plateau may lead to different origins and different preservation conditions of the pedogenic magnetite. [source] First indication of Storegga tsunami deposits from East Greenland,JOURNAL OF QUATERNARY SCIENCE, Issue 4 2007Bernd Wagner Abstract A 2.73,m long sediment sequence from Loon Lake, located at 18,m a.s.l. on outer Geographical Society Ø, East Greenland, was investigated for its chronology and changes in physical and biogeochemical properties, macrofossils, and grain-size distribution. The predominance of marine fossils throughout the sequence, dated by 14C AMS to between 8630 and 7535 cal. yr BP, shows that the Loon Lake at that time was a marine basin, which according to existing sea-level curves was about 15,35,m deep. The sequence mainly consists of fine grained homogeneous sediments, which are interrupted by a 0.72,m thick sandy horizon with erosive basis and distinct fluctuations in the grain-size distribution and in the physical and biogeochemical properties. According to the radiocarbon dates, this sandy horizon was deposited after 8500,8300 cal. yr BP and is interpreted as originating from the Storegga tsunami. The record from Loon Lake provides the first indication of Storegga tsunami deposits from East Greenland. Copyright © 2006 John Wiley & Sons, Ltd. [source] Effect of Twin-Plane Reentrant Edge on the Coarsening Behavior of Barium Titanate GrainsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 4 2002Ho-Yong Lee When BaTiO3 ceramics were sintered at relatively low temperatures (,1250°C), the grains with reentrant edges caused by a (111) double twin grew exclusively. As a result, a microstructure with a bimodal grain-size distribution composed of platelike large grains and fine matrix grains was obtained. In contrast, at the usual sintering temperature between 1250° and 1350°C, grains containing a (111) double twin did not exhibit any growth advantage. In this case, a coarse and uniform microstructure was obtained. When this coarse-grained specimen was further heat-treated at 1365°C, the grains possessing a double twin were observed to grow exclusively again. The results were explained in terms of a coarsening process controlled by two-dimensional nucleation. [source] Single-Step Synthesis of Chemically Cross-Linked Polysilastyrene and Its Conversion to ,-Silicon CarbideJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 2 2002Venkatasubbaiah Krishnan A new method for chemically cross-linking polysilastyrene using divinylbenzene as the cross-linking agent is reported. The procedure involves a single-step synthesis using the alkali-metal sodium to promote the polymerization of dimethyldichlorsilane in the presence of the comonomers phenylmethyldichlorosilane and divinylbenzene. The cross-linked polymer can be readily converted to ,-SiC on pyrolysis at 1500°C. The ,-SiC obtained by this procedure is nanocrystalline and has a grain-size distribution of 8,20 nm. [source] A comparative study of laser- and electric-field-induced effects on the crystallinity, surface morphology and plasmon resonance of indium and gold thin filmsPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 4 2010Prashant Kumar Abstract The effects of post-deposition treatment of In and Au thin films by excimer laser and electric field are reported. The films were subjected to an electric field in the range of 0.1,3.3,kV/cm and laser irradiation in the range from 0.01 to 0.1,J/cm2. The effect of this treatment on the morphology and crystallinity of indium and gold thin films (10,100,nm thickness) is investigated. Indium films exhibited a three-fold grain growth at an electric field of 3.3,kV/cm. Gold thin film, on the other hand, showed significant grain growth at a much lower field of 0.6,kV/cm. The as-deposited thin films of indium and gold were amorphous but turned nanocrystalline with average crystallite sizes of 57,nm at 3.33,kV/cm and 35,nm at 0.66,kV/cm, respectively. When indium thin films were laser irradiated, flat disc-shaped grains for as-deposited thin films were transformed to spherical grains at a laser fluence of 0.02,J/cm2 and cubical grains at 0.05,J/cm2. At 0.05,J/cm2, as-deposited amorphous indium and gold thin films turned nanocrystalline with crystallite sizes of 50,nm and 10,nm, respectively. Significantly, laser treatment causes the grain-size distribution to become narrower with a shift in mean size to larger values. Electric-field treatment on the other hand leads to a shifting of the mean grain size to larger values without affecting the distribution. [source] | ||||||||||