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We establish a new model based on fractal theory and cubic spline interpolation to study the effective thermal conductivity of isotropic porous silica low-k materials. A 3D fractal model is introduced to describe the structure of the silica xerogel and silica hybrid materials (such as methylsilsesquioxane, MSQ). Combined with fractal structure, a more suitable medium approximation is developed to study the isotropic porous silica xerogel and MSQ materials. Cubic spline interpolation for fitting discrete predictions from the fractal model is used to obtain the continuous function of the effective thermal conductivity versus porosity. Compared with other common models, the effective thermal conductivity predicted by our model presents better agreement with the experimental data for all porosity. These results indicate that the proposed model is valid.  相似文献   
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本文结合声光布拉格衍射,及动量匹配与衍射效率关系,探讨了声波波长与光波波长的定量关系,推导出光波波长测量相关公式,验证了基于声光布拉格衍射测量待测光波波长方案的可行性.并进行了实验方案的设计,实现了对不同光波的波长测量,自制出可用于实验教学的实验仪器.本波长测量方案具有实验操作步骤简单、实验装置造价低廉、受环境因素干扰较小等优势,同时可用于声光布拉格衍射的演示教学,直观的展示出布拉格衍射不同级数的衍射效率.  相似文献   
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为了解决机械式风速仪对方向测量的局限性,使用了单向叶轮传感器的矢量三维风速仪,风速传感器采用叶轮带动空心杯电机的结构,通过单片机对三维组合单向速传感器进行采集和风速矢量合成,实现了对风的大小和方向的测量.实验结果表明:该设计在对风速矢量的二维测量上,风速大小和方向的测量均具有很高的可靠性;在对风速矢量的三维测量上,风速大小的测量值也比较精确,风速方向的测量值误差比较小.  相似文献   
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董锡杰  胡一帆  吴玉莹 《中国物理 B》2010,19(1):13601-013601
Depth profiled positronium (Ps) annihilation lifetime spectroscopy (PALS) is an extremely useful probe of the pore characteristics in nanoporous low-dielectric (low-k) constant thin films. PALS has also been considered as a potential probe to investigate diffusion barrier integrity and the structural changes of porous low-k films during their integration with Cu. Hence, it is essential to understand the diffusion behaviour of positronium/Cu atoms in the films. In this work, based on the fact that porous materials possess characteristics of statistical self-similarity, a fractal model, the Menger sponge model, has been applied to simulate the structure of a promising dielectric, porous methylsilsesquioxane (MSQ) films. The diffusion behaviour of Ps out of the fractal model and into the surrounding vacuum is studied by means of the diffusion equation and traditional advective-diffusive theory. Predictive results from our model show good agreement with measurement data.  相似文献   
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