Multiperiod fringe projection interferometry using a backpropagation method for surface profile measurement

Interference fringes with different periods are projected on an object surface. There is a constant phase point where the phase of the fringe is kept at a constant value while the period is scanning. Multiple optical fields with different periods on the object surface are made from detected phases of the fringes. The multiple optical fields are backpropagated to the constant phase point of the phase where all of the phases of the multiple backpropagated fields become the same value and the amplitude of the sum of the multiple backpropagated fields becomes maximum. The distance of the backpropagation provides the position of the object surface. Some experiments show that this method can measure an object surface with discontinuities of several millimeters with high accuracy of several micrometers.     

Grating projection system for surface contour measurement

A grating projection system is a low-cost surface contour measurement technique that can be applied to a wide range of applications. There has been a resurgence of interest in the technique in recent years because of developments in computer hardware and image processing algorithms. We describe a method that projects a phase-shifted grating through a lens on an object surface. The deformed grating image on the object surface is captured by a CCD camera for subsequent analysis. Phase variation is achieved by a linear translation stage on which the grating is mounted. We compare the experimental results with the test results using a mechanical stylus method.     

一种基于三维模型投影的人脸识别新方法

研究了使用三维人脸模型进行不同姿势下的人脸识别问题,提出了一种三维建模二维识别的人脸识别算法,首先使用该方法将三维模型向不同方向投影,进而将不同姿势的二维图像与不同方向的投影结果相匹配,进行人脸识别。研究了使用Minolta Vivid 910进行数据获取,创建三维模型的方法和过程。实验结果表明,在进行不同姿势的人脸识别时,该方法的识别速度快于三维可变形模型方法,识别率远优于使用二维正面图像作为模板的人脸识别方法。     

Metallic film optimization in a surface plasmon resonance biosensor by the extended Rouard method

The extended Rouard method is applied to the computation of a multi-absorbing-layer system for the optimization of surface plasmon resonance (SPR) sensors. Specifically, the effect of the properties of a metallic layer on the shape of the reflectivity and sensitivity curve is demonstrated in the case of a Kretschmann configuration. This theoretical investigation allows us to establish the best optical properties of the metal to obtain a localized SPR, given the illuminating beam properties. Toward the development of a sensitive biosensor based on SPR, we quantify the changes in reflectivity of such an optical biosensor induced by the deposition of a nanometric biochemical film as a function of the metal film characteristics and the illumination operating conditions. The sensitivity of the system emphasizes the potential of such biophotonic technology using metallic multilayer configurations, especially with envisioned metamaterials.     

Three-dimensional nonplanar fracture model using the surface integral method

A computer code based on the use of the surface integral method, which represents a crack as a distribution of force dipoles, has been developed for modeling 3D nonplanar fractures. The nonplanar geometry was approximated as piecewise linear by subdividing the fracture surface into triangular elements that assume constant crack opening in the interior, and a p ^1/2 variation of opening along the crack front. The resulting singular integral equations were integrated using a combination of numerical and analytical techniques.Convergence studies using the surface integral formulation have yielded accurate stress intensity factors and crack opening displacements for both planar and nonplanar cracks under a variety of mixed mode loading conditions. Elliptical meshes were mapped on to cylindrical and spherical surfaces to model nonplanar fractures that could be compared to published results. Also, a high aspect ratio rectangular mesh was used to model a nonplanar kinked crack under plane strain conditions.     

Automatic parameter optimization of the local model fitting method for single-shot surface profiling

The local model fitting (LMF) method is a single-shot surface profiling algorithm. Its measurement principle is based on the assumption that the target surface to be profiled is locally flat, which enables us to utilize the information brought by nearby pixels in the single interference image for robust LMF. Given that the shape and size of the local area is appropriately determined, the LMF method was demonstrated to provide very accurate measurement results. However, the appropriate choice of the local area often requires prior knowledge on the target surface profile or manual parameter tuning. To cope with this problem, we propose a method for automatically determining the shape and size of local regions only from the single interference image. The effectiveness of the proposed method is demonstrated through experiments.     

Calculating the extended defect contrast for the X-ray-beam-induced current method

The contrast of extended defects representing dislocations and grain boundaries has been calculated for the X-ray-beam-induced current (XBIC) method. It is established that the maximum contrast increases with the diffusion length of excess charge and decreases with increasing X-ray beam width. The simulated XBIC profile contrasts are compared to experimentally measured patterns.     

An extended mathematical model for failure kinetics

In practice we often observe some kind of ‘self-acceleration’ when degradation causes the local temperature to increase, and in turn the temperature accelerates degradation. In this paper an extended model for failure kinetics is proposed to describe the phenomenon mentioned above. It is a common belief that a non-linear relation between logarithmic lifetime and inverse temperature reveals a change of failure mechanisms. The results of the paper tell us that non-linearity may be produced by a single failure process with more complex failure kinetics than the simple reaction of the first order.     

A projection iterative algorithm boundary element method for the Signorini problem

We propose a projection iterative algorithm based on a fixed point equation for solving a certain class of Signorini problem. The satisfaction of the Signorini boundary conditions is verified in a projection iterative manner, and at each iterative step, an elliptic mixed boundary value problem is solved by a boundary element method which is suitable for any domain. We prove the convergence of the algorithm by the property of projection. The advantage of this algorithm is that it is easy to be implemented and converge quickly. Some numerical results show the accuracy and effectiveness of the algorithm.     

A model for the compressive buckling of extended chain polymers

A model for the compressive buckling of an extended polymer chain is presented. The application of classical elastic instability analysis to an idealized polymer chain reveals that the bending rigidity and critical buckling loads for a chain are proportional to the force constants for valence bond angle bending and torsion. Highly oriented polymer fibres are treated as a collection of elastic chains that interact laterally. The critical stresses to buckle this collection of chains are calculated following a procedure developed to predict the compressive strengths of fibre-reinforced composites. This buckling stress is predicted to be equal to the shear modulus of the fibres and is the limiting value of compressive strength. Comparison of experimental and predicted values shows that the theory overestimates the compressive strength, but that there is a correlation of shear modulus with axial compressive strength. Consideration of flaws in both the theory and the material indicate that the compressive strength should be proportional to either the shear modulus or shear strength of the fibres.Nomenclature P axial compressive load (force) - P _cr critical buckling load (force) - M,M _i bending moments - l length of a link - p number of links - k elastic hinge constant - , _i angular rotation of hinges - L overall chain or column length - v,v _i lateral deflection of buckled chain or column - x, y, z Cartesian coordinate axes - E Young's modulus of isotropic column - I moment of inertia - a _ij matrix coefficients - A _p coefficient for exact buckling loads of chains - T energy change due to work of external load on buckled column or chain - U ₁ bending strain energy change of buckled column or chain - U ₂, U ₂ ^e , U ₂ ^s strain energy changes in elastic foundation, where e refers to extension mode buckling and s refers to shear mode buckling - E _t transverse modulus - G longitudinal shear modulus - b dimension associated with chain packing - A cross-sectional area per chain (=b ²) - f(x) curve fitted to shape of buckled chain - m,n,r integers - a _n coefficients of trigonometric series - _y normal strain iny-direction - _y normal stress iny-direction - xy shear strain inxy plane - xy shear stress inxy plane - u _x displacement inx-direction - u _y displacement iny-direction - V volume     

A robust preconditioning technique for the extended finite element method

The extended finite element method enhances the approximation properties of the finite element space by using additional enrichment functions. But the resulting stiffness matrices can become ill‐conditioned. In that case iterative solvers need a large number of iterations to obtain an acceptable solution. In this paper a procedure is described to obtain stiffness matrices whose condition number is close to the one of the finite element matrices without any enrichments. A domain decomposition is employed and the algorithm is very well suited for parallel computations. The method was tested in numerical experiments to show its effectiveness. The experiments have been conducted for structures containing cracks and material interfaces. We show that the corresponding enrichments can result in arbitrarily ill‐conditioned matrices. The method proposed here, however, provides well‐conditioned matrices and can be applied to any sort of enrichment. The complexity of this approach and its relation to the domain decomposition is discussed. Computation times have been measured for a structure containing multiple cracks. For this structure the computation times could be decreased by a factor of 2. Copyright © 2010 John Wiley & Sons, Ltd.     

基于多项式拟合的C臂投影全局校正法

针对C臂影像增强器采集的投影图像因失真变形而无法直接用于计算机辅助手术的问题,提出了一种基于多项式拟合的C臂投影全局校正法.该方法统一考虑C臂投影图像的3种类型的失真--针垫失真、S型扭曲、图像偏移,利用N阶多项式拟合图像的复合失真,然后利用最小二乘法求解最优化校正系数,从而具有所需标记点数量较少,校正区域连续,步骤简单,易于在线使用的优点.校正误差实验表明:该方法在3阶和4阶多项式的情况下所有标记点最大误差小于0.5像素,误差均方根小于0.26像素,并且对不同姿态的C臂投影图像的校正结果具有稳定性.该方法可用于计算机辅助手术导航、器械定位和术中X光三维锥束重建.     

一种基于投影层析方法的水下目标成像方法

投影层析是一种在几何上基于多角度投影实现目标与情景的像重构方法。水下散射目标具有数量众多、散射特性复杂的特点,为了有效探测到感兴趣的目标,需要重构出目标及所在情景高可靠分辨的像。因此,该文从逆问题求解的角度出发,分析了实现投影层析方法的物理条件及数学原理;并提出了一种水下目标投影层析成像的可行性方法及实现流程;通过在不同的扫描角度范围下的仿真进一步验证了投影层析方法对指定区域反射性目标探测的可行性。     

A multiscale projection method for macro/microcrack simulations

We present a new multiscale method for crack simulations. This approach is based on a two‐scale decomposition of the displacements and a projection to the coarse scale by using coarse scale test functions. The extended finite element method (XFEM) is used to take into account macrocracks as well as microcracks accurately. The transition of the field variables between the different scales and the role of the microfield in the coarse scale formulation are emphasized. The method is designed so that the fine scale computation can be done independently of the coarse scale computation, which is very efficient and ideal for parallelization. Several examples involving microcracks and macrocracks are given. It is shown that the effect of crack shielding and amplification for crack growth analyses can be captured efficiently. Copyright © 2007 John Wiley & Sons, Ltd.