关键词： 流体饱和多孔隙介质   小波多尺度方法   孔隙率   反演   正则化高斯牛顿法   小波有限元法  

摘要： 基于多尺度的思想,将小波多分辨分析和多尺度方法相结合,应用于流体饱和多孔隙介质孔隙率的反演。利用小波变换,将原始反问题分解为不同尺度上的一系列子反问题,并按照尺度从粗到细的顺序依次求解。在每一个尺度上,都采用稳定、收敛快的正则化高斯牛顿法求解,次一级尺度上求出的“全局最优解”作为上一级的初始解,依此类推,直到求出原始问题的真正的全局最优解。通过与传统的正则化高斯牛顿法相比较,显示了小波多尺度法是一个大范围收敛、能够有效节省计算量的方法,数值模拟的结果也表明了方法的有效性。

关键词： hydroxyapatite   mechanical properties   porosity   rapid prototyping   bone ingrowth   ELASTIC PROPERTIES   TRABECULAR BONE   MORPHOGENETIC PROTEIN-2   COMPRESSIVE STRENGTH   CANCELLOUS BONE   YIELD BEHAVIOR   TISSUE   SUBSTITUTES   PHOSPHATE   MACROPOROSITY  

摘要： The relative osteoconductivity and the change in the mechanical properties of hydroxyapatite (HA) scaffolds with multi-scale porosity were compared to scaffolds with a single pore size. Non-microporous (NMP) scaffolds contained only macroporosity (250-350 mu m) and microporous (MP) scaffolds contained both macroporosity and microporosity (2-8 mu m). Recombinant human bone morphogenetic protein-2 (rhBMP-2) was incorporated into all scaffolds via gelatin microspheres prior to implantation into the latissimus dorsi muscle of Yorkshire pigs. After 8 weeks, only the MP scaffolds contained bone. The result demonstrates the efficacy of the MP scaffolds as drug carriers. Implanted and as-fabricated scaffolds were compared using histology, microcomputed tomography, scanning electron microscopy, and compression testing. Implanted scaffolds exhibited a stress-strain response similar to that of cancellous bone with strengths between those of cancellous and cortical bone. The strength and stiffness of implanted NMP scaffolds decreased by 15% and 46%, respectively. Implanted NIP scaffolds lost 30% of their strength and 31% of their stiffness. Bone arrested crack propagation effectively in MP scaffolds. The change in mechanical behavior is discussed and the study demonstrates the importance of scaffold microporosity on bone ingrowth and on the mechanical behavior of HA implant materials. (c) 2006 Elsevier Ltd. All rights reserved.

关键词： 氮气   导热系数   纳米尺度   孔隙   分子动力学模拟  

摘要： 应用Lennard-Jone作用势,在300K和0·1MPa条件下,对边长20nm的立方体孔隙内氮气的导热系数进行了平衡分子动力学模拟.结果得出分子分速度和速率的分布与统计力学得到的Maxwell速度和速率分布曲线基本一致,并且分子的平均自由程受到孔隙壁的严格限制.通过Green-Kubo关系式计算得出了孔隙内氮气的导热系数,并与文献中的结果进行了比较,模拟结果接近于实验值,仅为同样条件下自由空间氮气的导热系数的1/3左右.

关键词： 孔隙气体   渗流规律   微尺度   低渗透岩石   气体流动特性   地质环境保护   运动定律   非线性渗流   气体渗流   前沿领域   渗流力学   力学机理   统一模型   特性研究   资源开发   地下流体   度条件   新模型   微流动   实验   液体  

摘要： 微尺度条件下气体流动特性的研究是现代渗流力学前沿领域之一.分析了低渗透岩石饱和气体渗 流实验结果,探索了微尺度孔隙气体渗流规律,探讨了气体非线性渗流力学机理,发现了低渗透岩石微尺度孔 隙气体与液体渗流遵循同一形式的运动定律,建立了气体与液体非线性运动定律统一模型.结果表明:新模型 与实验结果吻合很好,为微尺度孔隙气体微流动特性研究提供了新的理论依据,对工程地质环境保护及地下流 体资源开发有重要指导意义.

关键词： 孔隙度   含水系统   移速   渗透系数   尺度   运移   上升   多孔介质   连通性   三维  

摘要： 首先提出渗透系数场为非高斯分布、高方差条件下三维非均质多孔介质的渗透系数上升尺度的经验计算公式，所考虑的因素包括砂质包裹体的体积百分含量、空间统计几何尺寸、空间连通性以及各水文地质相渗透系数的算术平均值．系统对比结果表明，该经验公式优于常用的传统计算方法．然后提出三维非均质多孔介质的孔隙度必须提升尺度的概念．这是因为在多孔介质含水系统中，污染物趋向于沿着高渗透性物质构成的三维优势通道快速运移，其有效运移速度与经提升尺度获得的单一渗流速度差别很大，迫使我们对孔隙度进行尺度提升．含水系统中高渗透性物质含量的变化引起孔隙度尺度提升特征的非线性变化，其上升尺度值介于0．004～1．5之间．当高渗透性物质含量低于30％时，孔隙度的尺度提升对于正确求解污染物运移尤为重要．

关键词： 堆积散体   孔隙结构   空间结构   离散系数   散体力学  

摘要： 在传统描述孔隙空间结构方法的基础上 ,用孔隙壁间距离作为变量 ,提出了表征散体孔隙空间结构的离散系数 ,并阐释了其物理含义 ,具有重要的理论和实际应用价值。

关键词： 土壤   序列数字图像技术   孔隙   小尺度特征   荧光有机染料   树脂浸渍  

摘要： 将土壤样品用混有荧光有机染料的树脂浸渍后 ,以 1mm间距连续研磨 ,经过一定的图像转换处理 ,最后以连续数字图像方式对图像孔隙的小尺度特征进行分析。对一种美国耕作黑土和一种法国耕作黄壤的比较研究表明 ,两类土壤在图像孔隙面积、图像孔隙面积变异性、图像孔隙孔径、孔隙连接度、孔隙重叠度以及孔隙流通性等方面均有所差异 ,这与两类土壤不同的有机质含量有关。

关键词： STAPHYLOCOCCAL ALPHA-HEMOLYSIN   POLYMER TRANSLOCATION   NUCLEIC-ACIDS   DNA TRANSPORT   TOXIN   PROTEIN   DISCRIMINATION   MOLECULES   CHANNELS   NANOPORES  

摘要： The transport of biopolymers through large membrane channels is a ubiquitous process in biology. It is central to processes such as gene transfer by transduction and RNA transport through nuclear pore complexes. The transport of polymers through nanoscopic channels is also of interest to physicists and chemists studying the effects of steric, hydrodynamic, and electrostatic interactions between polymers and confining walls. Single-channel ion current measurements have been recently used to study the transport of biopolymers, and in particular single-stranded DNA and RNA molecules, through nanometre-size channels. Under the influence of an electric field, the negatively charged polynucleotides can be captured and drawn through the channel in a process termed 'translocation'. During translocation, the ion current flowing through the channel is mostly blocked, indicating the presence of the polymer inside the channel. The current blockades were found to be sensitive to the properties of the biopolymers such as their nucleotide composition, length, and secondary structure, and to physical parameters such as the driving field intensity, temperature, and ionic strength. These blockades are therefore a rich source of information regarding the dynamics of polynucleotides in the pore. The translocation process is separated into its two main steps: (a) polymer 'capture' in which one of the polymer's ends is threaded a small distance through the channel, and (b) polymer sliding through the channel. The experimental and theoretical efforts to elucidate polymer capture and the transport dynamics of biopolymers in nanoscopic pores are reviewed in this article.

关键词： 双尺度渐近分析   有限元   复合材料   周期孔隙结构  

摘要： 对于具有小周期孔隙复合材料弹性结构，在双尺度渐近分析理论结果的基础上提出了双尺度有限元计算格式，并给出了严格的误差估计．