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Smaller Grains (smaller + grain)
Terms modified by Smaller Grains Selected AbstractsThe initiation and development of metamorphic foliation in the Otago Schist, Part 1: competitive oriented growth of white micaJOURNAL OF METAMORPHIC GEOLOGY, Issue 6 2005A. STALLARD Abstract The 3D shape, size and orientation data for white mica grains sampled along two transects of increasing metamorphic grade in the Otago Schist, New Zealand, reveal that metamorphic foliation, as defined by mica shape-preferred orientation (SPO), developed rapidly at sub-greenschist facies conditions early in the deformation history. The onset of penetrative strain metamorphism is marked by the rapid elimination of poorly oriented large clastic mica in favour of numerous new smaller grains of contrasting composition, higher aspect ratios and a strong preferred orientation. The metamorphic mica is blade shaped with long axes defining the linear aspect of the foliation and intermediate axes a partial girdle about the lineation. Once initiated, foliation progressively intensified by an increase in the aspect ratio, size and alignment of grains, although highest grade samples within the chlorite zone record a decrease in aspect ratio and reduction in SPO strength despite continued increase in grain size. These trends are interpreted in terms of progressive competitive anisotropic growth of blade-shaped grains so that the fastest growth directions and blade lengths tend to parallel the extension direction during deformation. The competitive nature of mica growth is indicated by the progressive increase in size and resultant decrease in number of metamorphic mica with increasing grade, from c. 1000 relatively small mica grains per square millimetre of thin section at lower grades, to c. 100 relatively large grains per square millimetre in higher grade samples. Reversal of SPO intensity and grain aspect ratio trends in higher grade samples may reflect a reduction in the strain rate or reduction in the deviatoric component of the stress field. [source] Effect of pH of Medium on Hydrothermal Synthesis of Nanocrystalline Cerium(IV) Oxide PowdersJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 10 2002Nan-Chun Wu Well-crystallized cerium(IV) oxide (CeO2) powders with nanosizes without agglomeration have been synthesized by a hydrothermal method in an acidic medium by using cerium hydroxide gel as a precursor. The relationship between the grain size, the morphology of the CeO2 crystallites, and the reaction conditions such as temperature, time, and acidity of the medium was studied. The experiments showed that with increasing reaction temperature and time, the CeO2 crystallites grew larger. The crystallites synthesized in an acidic hydrothermal medium were larger and had a more regular morphology than the ones synthesized in a neutral or alkaline medium when the reaction temperature and time were fixed. The CeO2 crystallites synthesized in an acidic medium were monodispersed; however, there was vigorous agglomeration among the grains synthesized in a neutral or alkaline medium. It was demonstrated that the hydrothermal treatment was an Ostwald ripening process and the acidity (pH) of the used hydrothermal medium played a key role in the dissolution of smaller grains. It is proposed that the dissolution process can control the kinetics of the growth of larger grains. [source] Heterogeneous agglutinitic glass and the fusion of the finest fraction (F3) modelMETEORITICS & PLANETARY SCIENCE, Issue 12 2002Abhijit Basu They include (1) theoretical expectations that shock pulses should engulf and melt smaller grains more efficiently than larger grains, (2) experimental results of impact shock, albeit at lower than presumed hypervelocity impacts of micrometeorites on the lunar regolith, and (3) new analyses confirming previous results that average compositions of agglutinitic glass are biased towards that of the finest fraction of lunar soils from which they had formed. We add another reason in support of the F3 model. Finer grains of lunar soils are also much more abundant. Hence, electrostatic forces associated with the rotating terminator region bring the finest grains that are obviously much lighter than courser grains to the surface of the Moon. This further contributes to the preferential melting of the finest fraction upon micrometeoritic impacts. New backscattered electron imaging shows that agglutinitic glass is inhomogeneous at submicron scale. Composition ranges of agglutinitic glass are extreme and deviate from that of the finest fraction, even by more than an order of magnitude for some components. Additionally, we show how an ilmenite grain upon impact would produce TiO2 -rich agglutinitic glass in complete disregard to the requirements of fusion of the finest fraction. We propose an addition to the F3 model to accommodate these observations (i.e., that micrometeorite impacts indiscriminately melt the immediate target regardless of grain size or grain composition). We, therefore, suggest that (1) agglutinitic glass is the sum of (a) the melt produced by the fusion of the finest fraction of lunar soils and (b) the microvolume of the indiscriminate target, which melts at high-shock pressures from micrometeoritic impacts, and that (2) because of the small volume of the melt and incorporating cold soil grains, the melt quenched so rapidly that it did not mix and homogenize to represent any preferential composition, for example, that of the finest fraction. [source] Quality variations in transgenic rice with a synthetic cry1Ab gene from Bacillus thuringiensisPLANT BREEDING, Issue 3 2002D. X. Wu Abstract In order to estimate the potential of transgenic rice, characteristics related to grain quality and starch viscosity were investigated in six japonica lines based on three primary transgenic lines containing a synthetic cry1Ab gene from Bacillus thuringiensis. No significant differences were found between the transgenic lines and the wild type, including negative lines and an untransformed line. All six transgenic lines were comparable in size, milling quality, appearance quality and physicochemical properties to the wild type that were derived from. One exception was that the lines derived from the primary transgenic line TR0-101 had smaller grains. Crude protein contents were equivalent in all the material tested, but Cry1Ab protein was only detected in grains of transgenic rice and was undetectable in the cooked rice. The viscosity of the starch differed between the transgenic lines, the wild type and other controls, and two transgenic lines had breakdown values (BDV) and setback values (SBV) similar to the wild type. A positional effect of T-DNA insertion on starch viscosity was found in three primary transgenic lines. [source] Role of particle size in till-fabric characteristics: systematic variation in till fabric from Vestari-Hagafellsjökull, IcelandBOREAS, Issue 4 2007Simon J. Carr Till-fabric analysis has often been used to interpret glacier flow directions and subglacial dynamics using vector-based statistics, but recent data suggest that such analysis may also effectively indicate former glacier dynamics. The results of a fabric investigation of subglacially strained till deposited during a surge of Vestari-Hagafellsjökull, Iceland, are presented. Till fabric was collected at four sites within a limited area where ice-flow direction during deposition was known from subglacial bedforms at the site. Analysis was carried out on elongate grains (axial ratio <1.5:1) at seven size fractions, with the a-axis length ranging from 0.25 to 32 mm. The largest grains tend to be parallel to ice flow, whereas smaller grains reflect a mix of parallel and transverse orientations. The implications of these data for the role and validity of till-fabric analysis are discussed, with reference to vector analyses and the compilation of fabric shape envelopes. It is noted that, in contrast to laboratory experimental data, neither March nor Jeffery mechanisms explain the fabric configurations reported. It is concluded that a standardized approach is necessary for collecting fabric data, and in many situations analysis of data populations at a range of particle sizes is desirable. [source] | ||||||||||