205 resultados para 985:316


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采用该实验室研制的强声波发生装置来产生交变应力场,研究了不同强度和频率的交变应力场作用后烟草细胞膜蛋白结构的变化。从细胞和分子水平研究交变应力对植物生长、发育的影响及其作用机制。

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二十世纪八十年代,当比利时冶金研究中心(CRM)开发出CO_2激光毛化冷轧辊技术后,尝试用YAG激光进行轧辊毛化一直吸引着众多的研究者,这是因为YAG(1.06μm)激光波长比CO_2(10.6μm)激光波长短一个量级,材料对YAG激光有更高的吸收率,并用YAG激光可以聚焦到更小的光斑尺寸,同时使用电信号驱动的声光开关技术便于对毛化分布进行可设定控制。但是用传统声光调制的YAG激光虽然可以碇以很高的脉冲频率(>30kHz),但单脉冲有量仅为10mJ左右,难以达到辊面毛化粗糙度的要求,因此人们认为YAG激光用于毛化的主要困难是脉冲能量太小。

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The conventional direct simulation Monte Carlo (DSMC) method has a strong restriction on the cell size because simulated particles are selected randomly within the cell for collisions. Cells with size larger than the molecular mean free path are generally not allowed in correct DSMC simulations. However, the cell-size induced numerical error can be controlled if the gradients of flow properties are properly involved during collisions. In this study, a large cell DSMC scheme is proposed to relax the cell size restriction. The scheme is applied to simulate several test problems and promising results are obtained even when the cell size is greater than 10 mean free paths of gas molecules. However, it is still necessary, of course, that the cell size be small with respect to the flow field structures that must be resolved.

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In this paper, multi-hole cooling is studied for an oxide/oxide ceramic specimen with normal injection holes and for a SiC/SiC ceramic specimen with oblique injection holes. A special purpose heat transfer tunnel was designed and built, which can provide a wide range of Reynolds numbers (10(5)similar to 10(7)) and a large temperature ratio of the primary flow to the coolant (up to 2.5). Cooling effectiveness determined by the measured surface temperature for the two types of ceramic specimens is investigated. It is found that the multi-hole cooling system for both specimens has a high cooling efficiency and it is higher for the SiC/SiC specimen than for the oxide/oxide specimen. Effects on the cooling effectiveness of parameters including blowing ratio, Reynolds number and temperature ratio, are studied. In addition, profiles of the mean velocity and temperature above the cooling surface are measured to provide further understanding of the cooling process. Duplication of the key parameters for multi-hole cooling, for a representative combustor flow condition (without radiation effects), is achieved with parameter scaling and the results show the high efficiency of multi-hole cooling for the oblique hole, SiC/SiC specimen. (C) 2008 Elsevier Ltd. All rights reserved.

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We propose a scheme for realizing negative refractive index in a four-level atomic system. It is shown that such a system can simultaneously exhibit negative permittivity and negative permeability in an optical frequency range. Furthermore, by analysing the dispersion property of the left-handed material, we find that the probe beam can be controlled from superluminal to subluminal or vice versa via choosing appropriate parameters.

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从几何光学角度讨论了积分棒的匀光原理,介绍了积分棒在步进扫描投影光刻系统中的应用,分析了积分棒入射光束的数值孔径对刀口狭缝面上光强分布的影响,得到了积分棒尺寸与刀口狭缝面上照明视场的关系,为步进扫描投影光刻系统中积分棒的设计提供了依据。

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采用热键合技术,制作中运用不同的工艺参量制作出12片Yb∶Y3Al5O12/Y3Al5O12(Yb∶YAG/YAG)复合晶体。利用偏光显微镜对其键合界面进行了观察,研究了样品的透射光谱,从而确定出复合晶体合适的制作工艺。通过透射光谱的形状和透射率来表征复合晶体键合界面的质量。研究表明Yb∶YAG/YAG复合晶体键合质量较好,可实现一体化。

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这次调查获取了大量具有历史价值的资料.其中包括广东海岛及其海域的自然条件、自然资源和社会经济条件的基本资料。海岛综合调查共登岛142个,占广东省759个面积大于500m2的海岛的18.7%,共布设调查断面316条,站点3919个,采样品7933个,采标本49000号.共获得资料数据104万多个;资料汇编288册;编制图幅1159幅,编写并出版海区调查报告7册,调查研究论文集3册、专业调查报告12册和100万字的《广东海岛资源综合调查报告》。广东海岛资源综合调查填补了广东海岛环境、资源综合调查的空白,不仅概括和揭示了海岛自然环境和自然资源的基本情况,而且揭示了海岛经济开发的规律,为发展当地经济作出了突出贡献。

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