A pseudo-plastic engagement effect on the toughening of discontinuous fiber-reinforced brittle composites

In brittle composites, such as whisker reinforced ceramics, the sliding of reinforcing fibers against the frictional resistance of matrix is of a pseudo-plastic deformation mechanism. High aspect-ratio whiskers possess larger pseudo-plastic deformation ability but are usually sparse, while, low aspect-ratio ones were distributed widely in the matrix and show low pseudo-plastic deformation ability (engagement effect), also. A comparative investigation was carried out in present study based on a multi-scale network model. The results indicate that the effect of low aspect-ratio whiskers is of most importance. Improving the engagement coefficient by raising the compactness of material seems a more practical way for optimization of discontinuous fiber-reinforced brittle composites in the present technological condition.

Compact difference approximation with consistent boundary condition

For simulating multi-scale complex flow fields it should be noted that all the physical quantities we are interested in must be simulated well. With limitation of the computer resources it is preferred to use high order accurate difference schemes. Because of their high accuracy and small stencil of grid points computational fluid dynamics (CFD) workers pay more attention to compact schemes recently. For simulating the complex flow fields the treatment of boundary conditions at the far field boundary points and near far field boundary points is very important. According to authors' experience and published results some aspects of boundary condition treatment for far field boundary are presented, and the emphasis is on treatment of boundary conditions for the upwind compact schemes. The consistent treatment of boundary conditions at the near boundary points is also discussed. At the end of the paper are given some numerical examples. The computed results with presented method are satisfactory.

Difference schemes on non-uniform mesh and their application

High order accurate schemes are needed to simulate the multi-scale complex flow fields to get fine structures in simulation of the complex flows with large gradient of fluid parameters near the wall, and schemes on non-uniform mesh are desirable for many CFD (computational fluid dynamics) workers. The construction methods of difference approximations and several difference approximations on non-uniform mesh are presented. The accuracy of the methods and the influence of stretch ratio of the neighbor mesh increment on accuracy are discussed. Some comments on these methods are given, and comparison of the accuracy of the results obtained by schemes based on both non-uniform mesh and coordinate transformation is made, and some numerical examples with non-uniform mesh are presented.

Nonlinear dynamics of atomic force microscopy with intermittent contact

When the atomic force microscopy (AFM) in tapping mode is in intermittent contact with a soft substrate, the contact time can be a significant portion of a cycle, resulting in invalidity of the impact oscillator model, where the contact time is assumed to be infinitely small. Furthermore, we demonstrate that the AFM intermittent contact with soft substrate can induce the motion of higher modes in the AFM dynamic response. Traditional ways of modeling AFM (one degree of freedom (DOF) system or single mode analysis) are shown to have serious mistakes when applied to this kind of problem. A more reasonable displacement criterion on contact is proposed, where the contact time is a function of the mechanical properties of AFM and substrate, driving frequencies/amplitude, initial conditions, etc. Multi-modal analysis is presented and mode coupling is also shown. (c) 2006 Published by Elsevier Ltd.

Multiscale Method for Turbulent-Flow Computations

A main method of predicting turbulent flows is to solve LES equations, which was called traditional LES method. The traditional LES method solves the motions of large eddies of size larger than filtering scale An while modeling unresolved scales less than Delta_n. Hughes et al argued that many shortcomings of the traditional LES approaches were associated with their inabilities to successfully differentiate between large and small scales. One may guess that a priori scale-separation would be better, because it can predict scale-interaction well compared with posteriori scale-separation. To this end, a multi-scale method was suggested to perform scale-separation computation. The primary contents of the multiscale method are l) A space average is used to differentiate scale. 2) The basic equations include the large scale equations and fluctuation equations. 3) The large-scale equations and fluctuation equations are coupled through turbulent stress terms. We use the multiscale equations of n=2, i.e., the large and small scale (LSS) equations, to simulate 3-D evolutions of a channel flow and a planar mixing layer flow Some interesting results are given.

Experimental Study on Subcooled Pool Boiling in Microgravity Utilizing

The Development of Biosensor with Imaging Ellipsometry

The concept of biosensor with imaging ellipsometry was proposed about ten years ago. It has become an automatic analysis technique for protein detection with merits of label-free, multi-protein analysis, and real-time analysis for protein interaction process, etc. Its principle, andrelated technique units, such as micro-array, micro-fluidic and bio-molecule interaction cell, sampling unit and calibration for quantitative detection as well as its applications in biomedicine field are presented here.

Lateral motion and departure of vapor bubbles in nucleate pool boiling on thin wires in microgravity

A space experiment on bubble behavior and heat transfer in subcooled pool boiling phenomenon has been performed utilizing the temperature-controlled pool boiling (TCPB) device both in normal gravity in the laboratory and in microgravity aboard the 22(nd) Chinese recoverable satellite. The fluid is R113 at 0.1 MPa and subcooled by 26 degrees C nominally. A thin platinum wire of 60 mu m in diameter and 30mm in length is simultaneously used as heater and thermometer. Only the lateral motion and the departure of discrete vapor bubbles in nucleate pool boiling are reported and analyzed in the present paper. A scale analysis on the Marangoni convection surrounding a bubble in the process of subcooled nucleate pool boiling leads to formulas of the characteristic velocity of the lateral motion and its observability. The predictions consist with the experimental observations. Considering the Marangoni effect, a new qualitative model is proposed to reveal the mechanism underlying the bubble departure processes and a quantitative agreement can also be acquired.

内蒙古锡林河流域空间生态学研究

本文从物种和景观两个组织水平上研究了气候、土壤、地形等自然环境因子和人类活动因子对生物空间分布格局的影响。基于锡林河流域地理信息系统各环境因子的专题数据，利用空间异质性分析方法研究了锡林河流域环境因子的空间分布格局;基于锡林河流域野外调查数据，运用空间异质性分析方法研究了重要物种的空间分布格局，并采用典范对应分析(Canomc Correspondence Analvsis，CCA)方法分析了物种分布与环境因子的关系：基于锡林河流域地理信息系统各环境因子的专题数据，研究了锡林河流域植被斑块的空间格局特征及其与环境因子的关系，并采用典范对应分析方法分析了植被类型组成与环境因子的关系：基于内蒙古草原生态系统定位研究站放牧样地的样方调查数据．采用空间异质性分析方法，研究了放牧压力对物种空间分布格局的影响：基于多年的卫星遥感数据，采用建模和对比等方法，研究了定居放牧方式下植被状况空间变化规律及植被状况时空变化与人类活动、社会经济发展的关系。通过上述分析，得到的主要结论如下： 1、锡林河流域各个环境因子都具有自己的空间特征尺度，共同形成多尺度等级体系，按特征尺度的大小可以分为如下3个组： ·小尺度组(15km左右)：有机暖、全N的较小的特征尺度 ·中尺度组(30～50km)：T1，碳酸钙含量．PER、全N和海拔高度的较小的特征尺度 ·大尺度组(100km左右)：ANNR，PER、全N和海拔高度的较大的特征尺度多尺度等级的生态学意义是它反映生态变量异质斑块的镶嵌和包含特征，环境因子多尺度等级体系反映共性，具有普遍性：反映生态关系，具有生态学意义。 2、对物种空间异质性的Mantel检验和半方差分析得到了一致的结果产即羊草、糙隐子草和星毛萎菱菜在锡林河流域的空间分布呈现随机特征，而大针茅和冷蒿则表现为十分显著的格局特征。按分布格局的显著程度从大到小排列为冷蒿>大针茅>星毛萎菱菜>糙隐子草>羊草。理论半方差图显示大针茅和冷蒿的空间自相关域分别为30．447公里和30公里。物种空间分布格局是受自然条件、人类活动以及它们自身的生理生态特征综合决定的，物种自身的生理生态特征决定了它们对外界环境变化的适应性反应机制，而自然与人类活动这两种因素在空间的交错配置决定了物种适应性反应的方向和程度，从而综合导致物种空间分布格局的形成。 3、对锡林河流域物种分布与环境因子关系的CCA分析和交叉半方差方法分析显示：1)气候因子(11个指标)、土壤性状因子(3个指标)和地形因子(3个指标)对物种分布的贡献率分别为11．2％、9．5％和11％，三者总和为31．7％。2)各个环境因子对物种分布空间作用方向具有一致性，物种分布与环境因子几乎都在135。和157．5。两个方向上具有相对明显的相关性，从锡林河流域来看，这两个方向反映了气候、土壤以及地形从东南往西北的变化梯度方向。 4、对锡林河流域14个植被景观指数进行的PCA分析表明，锡林河流域植被斑块空间分布的物理特征主要表现在斑块的数目和大小方面，其次是在斑块的多样性方面，并可将它们分为4个组，分别反映锡林河流域植被斑块的不同特征： ·第一组：NP、PRD、LPI、MPS、PSSD和TE，主要反映景观斑块在数量和大小方面的特征; ·第二组：SHDI、SIDI、SHEI和SIEI，主要反映景观斑块的多样性特征; ·第三组：PSCV和[J]．主要反映景观斑块之间的相互邻接程度; ·第四组：MSI和AWMSI，主要反映景观斑块的形状特征。 MPS和PSSD两个指数与环境因子无论是在相关系数的性质还是显著程度上都保持了很好的一致性，它们与纬度(LAT)及可能蒸散率(PER)呈极显著的正相关关系，而与经度(LNG)、海拔高度(ALT)、年平均降水量(ANNR)及土壤有机质含量(0RG)呈极显著的负相关关系：平均形状指数(MSI)只与LAT呈显著的正相关关系;多样性指数和扩散毗连指数与任何一个环境因子都没有表现出显著的相关性。 5、锡林河流域植被分布与环境因子的关系CCA排序方法分析表明，气候因子(11个指标)、土壤性状因子(3个指标)和地形因子(3个指标)对植被分布的贡献率分别为19.8%、11.1%和14.5%，三者总和为45.4％。环境因子在植被和物种两个水平上的贡献率表现了相似的特点，自然环境因子不能完全解释植被的空间分布，人类活动的影响应该受到重视。 6、放牧压力对物种空间分布格局的研究表明： ·牧压对温带典型草原物种的空间分布格局有明显的影响。随着牧云的增大，属于原生群落物种的羊草与大针茅空间分布的随机性减小，空间自相关尺度逐渐增大;而对于退化过程中的入侵物种冷蒿和星毛萎菱菜，其空间分布的随机性逐渐增大．空间自相关尺度也呈增大趋势。在牧压胁迫超过一定水平时，冷蒿空间分布的自相关尺度开始下降，而星毛萎菱菜的空间分布格局则表现出强烈的随机性。 ·物种空间格局的变化是反映群落演替过程较为稳定的特征，适用于不同放牧条件下 群落之间的比较。 7、利用遥感数据对人类活动对植被影响的研究表明： ·定居放牧方式下，NDVI随定居点距离的变化格局经历了3个阶段。第一阶段，草场处于原生阶段，NDVI不随距离变化;第二阶段，定居点附近开始局部退化，NDVI随距离增加而增大：第三阶段，退化区域扩大，NDVI不随距离变化。 ·在草场局部退化阶段，NDVI随距离的变化呈对数函数规律，定居点的放牧区具有放牧半径、原生NDVI值、NDVI变化率等特征。根据这些特征、NDVI对数规律以及NDVI与地上生物量的关系可以推测定居点的总载畜量。 ·锡林河流域从87年到85年NDVI值降低最大的区域为流域的中部和南部，这与这一区域人类活动强度以及社会经济发展具有密切关系。

Analytical method of predicating the instabilities of a micro arch-shaped beam under electrostatic loading

An arch-shaped beam with different configurations under electrostatic loading experiences either the direct pull-in instability or the snap-through first and then the pull-in instability. When the pull-in instability occurs, the system collides with the electrode and adheres to it, which usually causes the system failure. When the snap-through instability occurs, the system experiences a discontinuous displacement to flip over without colliding with the electrode. The snap-through instability is an ideal actuation mechanism because of the following reasons: (1) after snap-through the system regains the stability and capability of withstanding further loading; (2) the system flips back when the loading is reduced, i.e. the system can be used repetitively; and (3) when approaching snap-through instability the system effective stiffness reduces toward zero, which leads to a fast flipping-over response. To differentiate these two types of instability responses for an arch-shaped beam is vital for the actuator design. For an arch-shaped beam under electrostatic loading, the nonlinear terms of the mid-plane stretching and the electrostatic loading make the analytical solution extremely difficult if not impossible and the related numerical solution is rather complex. Using the one mode expansion approximation and the truncation of the higher-order terms of the Taylor series, we present an analytical solution here. However, the one mode approximation and the truncation error of the Taylor series can cause serious error in the solution. Therefore, an error-compensating mechanism is also proposed. The analytical results are compared with both the experimental data and the numerical multi-mode analysis. The analytical method presented here offers a simple yet efficient solution approach by retaining good accuracy to analyze the instability of an arch-shaped beam under electrostatic loading.

First principles based predictions of the toughness of a metal/oxide interface

We describe a first-principles-based strategy to predict the macroscopic toughness of a gamma-Ni(Al)/alpha-Al2O3 interface. Density functional theory calculations are used to ascertain energy changes upon displacing the two materials adjacent to the interface, with relaxation conducted over all atoms located within adjoining rows. Traction/displacernent curves are obtained from derivatives of the energy. Calculations are performed in mode I (opening), mode II (shear) and at a phase angle of 45 degrees. The shear calculations are conducted for displacements along < 110 > and < 112 > of the Ni lattice. A generalized interface potential function is used to characterize the results. Initial fitting to both the shear and normal stress results is required to calibrate the unknowns. Thereafter, consistency is established by using the potential to predict other traction quantities. The potential is incorporated as a traction/displacement function within a cohesive zone model and used to predict the steady-state toughness of the interface. For this purpose, the plasticity of the Ni alloy must be known, including the plasticity length scale. Measurements obtained for a gamma-Ni superalloy are used and the toughness predicted over the full range of mode mixity. Additional results for a range of alloys are used to demonstrate the influences of yield strength and length scale.

Comparison of wavelet transform methods - The compression of IR spectral data

In this paper, an introduction of wavelet transform and multi-resolution analysis is presented. We describe three data compression methods based on wavelet transform for spectral information,and by using the multi-resolution analysis, we compressed spectral data by Daubechies's compactly supported orthogonal wavelet and orthogonal cubic B-splines wavelet, Using orthogonal cubic B-splines wavelet and coefficients of sharpening signal are set to zero, only very few large coefficients are stored, and a favourable data compression can be achieved.

小波多尺度跟踪技术研究

本论文研究的主要内容为基于小波多尺度特性的序列图像目标跟踪技术。目标跟踪作为一个在军事、工业和科学研究方面有着广泛应用背景的研究领域，一直以来吸引了大批国内外学者。由于小波变换具有多分辨率分析的特点，而且在时频两域都具有表征信号局部特征的能力，使得基于小波变换的目标跟踪算法具有传统算法无法比拟的优势。针对目标跟踪技术的研究现状和存在问题，本文着重从目标分割和特征检测与匹配两个角度对基于小波变换的几种新的目标跟踪方法进行了研究。 1. 采用基于多尺度Gabor小波的特征点检测算法对序列图像进行跟踪。借助图像的金字塔变换得到多尺度的Gabor小波特征图像，并对特征图像进行特征点检测，提取对图像变换具有鲁棒性的特征。针对两种特征检测方案，提出不同的特征匹配准则，按照分层匹配的策略由粗到精逐步定位目标的准确位置，具有较快的搜索速度。 2. 采用多尺度小波函数所提取的相位一致性特征进行基于目标分割和基于角点特征的跟踪。 对目标图像进行相位一致性检测，得到一个具有光照不变性的无量纲特征量—相位一致系数。利用相位一致性检测的这种特性，针对孤立目标的情况，提出了两种自适应目标分割和跟踪的算法。基于区域增长的目标分割算法利用从相位一致图像中找到的对比度最大点及其法线方向两边的灰度分布确定目标和背景的种子像素，进行自适应目标分割。基于相位一致性检测的目标分割算法只需确定一个阈值即可利用相位一致特征图像的方向性，依据目标在不同方向响应的不同将目标和背景区分开，适应于复杂纹理背景中的目标分割。最后，分别将两种算法所得的分割结果向水平和垂直方向投影即可确定各自的质心位置，实现自适应的质心跟踪。 进一步提取相位一致性图像的最小矩特征就能得到目标的角点信息。文中用实验验证了此方法检测到角点的综合性能。在此基础上，提出了利用单演相位差进行角点匹配跟踪的算法，并将其同基于灰度相关的匹配算法进行了对比，证明了本算法能够检测出更多准确匹配的角点、减少误匹配，同时具有较小的匹配运算量。 对以上提出的几种目标跟踪算法进行了大量的仿真实验，实验结果表明，这几种方法均取得了较好的跟踪效果，能够实现稳定、精确的跟踪。