992 resultados para 113-696A


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The connection between the activity of the gonadotropic cells of the hypophysis and the neurosecretion in the pre-optico neuro-hypophysial system in different groups of vertebrates has been examined by many authors. It has been established that in many species there exists some kind of synchronism between the sexual cycle and the cellular activity of neurosecretion, a fact that has led to the prevailing idea that gonadotropic activity in the hypophysis is regulated by the hypothalamus. This paper summarises the results of experiments made in this direction on Cyclostomata. The materials for research came from adult individuals of Eudontomyson danfordi Regan taken from the rivers Somes-Rece and Ivo (Harghita district) at different times of the year.

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This partial translation of a longer article describes the phenomenon of ”Blasensand”. Blasensand is formed when sedimentation of dried out sand is suddenly flooded from above. A more detailed explanation of Blasensand is given in this translated part of the paper.

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Morphology of self-assembled GeSi quantum dot grown on Si(113) by Si molecular beam epitaxy has been studied by transmission electron microscopy and atomic force microscopy. Photoluminescence from the as-grown sample and annealed sample was studied. The results were analyzed and explained.

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The surface structures of the Si(113)-(1 X 1), Si(113)-(3 X 1) and Si(113)-(3 X 2) have been studied theoretically by means of an ab initio quantum chemical CNDO method. We address not only the importance of the surface energy but also the energy minimization and the barrier height in the different structural conversion. We found that (1) the relaxed Si(113)-(1 X 1) structure. (2) the Si(113)-(3 X 1) close to the Si(113) Ranke (3 X 1)-2 model; (3) the atomic positions of Si(113)-(3 X 2) corrugated arrangement. (C) 1997 Elsevier Science B.V.

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We present photoelectron spectroscopic and low energy electron diffraction measurements of water adsorption on flat Si samples of the orientations (001), (115), (113), (5,5,12) and (112) as well as on curved samples covering continuously the ranges (001)-(117) and (113)-(5,5,12)-(112). On all orientations, water adsorption is dissociative (OH and H) and non-destructive. On Si(001) the sticking coefficient S and the saturation coverage Theta(sat) are largest. On Si(001) and for small miscuts in the [110]-azimuth, S is constant nearly up to saturation which proves that the kinetics involves a weakly bound mobile precursor state. For (001)-vicinals with high miscut angles (9-13 degrees), the step structure breaks down, the precursor mobility is affected and the adsorption kinetics changed. On (115), (113), (5,5,12) and (112), the values of S and Theta(sat) are smaller which indicates that not all sites are able to dissociate and bind water. For (113) the shape of the adsorption curves Theta versus exposure shows the existence of two adsorption processes, one with mobile precursor kinetics and one with Langmuir-like kinetics. On (5,5,12), two processes with mobile precursor kinetics are observed which are ascribed to adsorption on different surface regions within the large surface unit cell. From the corresponding values of S and Theta(sat), data for structure models are deduced. (C) 1997 Elsevier Science B.V.

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Surface reconstructions on Si(113) induced by dissociated hydrogen adsorption have been studied using low energy electron diffraction (LEED). It has been found that: (1) at 300 K and 80 K temperatures, with the increase of hydrogen coverage on the surface, the (3 x 1) phase transferred continuously into a hydrogen saturated (1 x 1)-2H phase; (2) flashing of the (1 x 1)-2H surface at about 1100 degrees C resulted in a complete new phase of(1 x 3) and further annealing of the sample at 1250 degrees C gave back the starting surface of (3 x 1); (3) saturated hydrogen adsorption at a sample temperature of 700 degrees C resulted in a stable new phase of(1 x 2)-H and further saturation doses of hydrogen at other temperatures below 700 degrees C did not change the (1 x 2) LEED pattern; (4) annealing of the (I x 2)-H surface in the same manner as (2) gave similar results.

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用透射电子显微镜观察了Si(113)衬底上由固态源分子束外延生长的自组织量子点的形貌,测量了其原生及退火后低温下的荧光光谱。对所得结果进行了分析。

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于2010-11-23批量导入

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采用半经验分子轨道理论方法AM1研究用Si_(16)H_(21)模拟的Si(113)高指数表面及其吸附H原子的体系,得到生成热和表面原子上受力随吸附的变化。从生成热分析得知,Si(113)表面上形成Si─H_2吸附比Si─H容易,且为放热吸附;受力分析指出了表面原子再构发生的趋向,而吸附则引起趋向改变。

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于2010-11-23批量导入

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于2010-11-23批量导入

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于2010-11-23批量导入