真空热处理对CoFe薄膜结构及电磁特性的影响

在本底真空度优于5×10-4Pa的室温条件下,利用电子束蒸发方法沉积CoFe薄膜,研究了不同退火温度对CoFe薄膜结构和电磁特性的影响。样品采用热氧化Si为基片,在3×10-5Pa真空度下分别进行了150、280、330、450和500℃的60min退火处理。电阻率和磁电阻测量表明,450℃退火处理能够明显降低CoFe薄膜电阻率和提高磁电阻变化率,因为这时的X射线衍射谱显示CoFe薄膜的结构已明显改善。还发现沉积在热氧化Si基片上的CoFe薄膜(111)晶面面间距明显小于靶材相应晶面面间距,而退火处理会使薄膜(111)晶面面间距接近恢复到靶材。透射电镜对沉积态样品分析表明,样品呈多晶结构但结晶不太理想。振动样品磁强计(VSM)的磁特性测量发现,500℃真空退火处理,薄膜的矫顽力和饱和磁化强度都提高近一倍,分别由室温沉积态的2337 A/m和327 emu/cm3上升到退火后的4746 A/m和649 emu/cm3。     

Energy flux characteristics of inhomogeneous waves in anisotropic thermoviscoelastic media

This study aims to calculate the wave-field characteristics of four attenuating waves in anisotropic thermoviscoelastic medium. An energy balance equation relates the complex-valued energy flux vector to the time-averaged densities of kinetic energy, strain energy and dissipated energy of plane harmonic waves in the medium. A complex slowness vector defines the inhomogeneous propagation of an attenuating wave in the medium. This slowness vector is specified with the phase velocity and the two non-dimensional attenuation parameters of the wave. One of the attenuation parameter defines the inhomogeneity strength of the wave as a measure of its deviation from homogeneous propagation. The phase velocity, attenuation parameters, polarizations of particles, propagation direction are combined to define the group velocity, ray direction and quality factor of attenuation of an inhomogeneous wave in the medium. Numerical examples are considered to study the variations of these characteristics of energy flux with propagation direction and inhomogeneity strength for each of the four attenuating waves in the medium. The effects of anisotropic symmetries are analyzed on the velocities of waves. The decay-rate of energy densities is exhibited with offset in the propagation-attenuation plane.     

Validation of Analytical Multiparameter Homogenization Models for Out-of-Plane Loaded Masonry Walls by Means of the Finite Element Method

The linear elastic analysis of in-plane and out-of-plane loaded masonry walls is still significant under service loads and is required by codes of practice, therefore the knowledge of the homogenized mechanical properties of masonry is of relevant interest. The aim of this paper is to discuss the problem of the out-of-plane loaded masonry walls in detail and to assess the accuracy and reliability of different homogenization approaches presented in the technical literature, with particular interest in recent explicit formulas obtained through an asymptotic model (as reported by Cecchi and Sab in 2002). Several meaningful comparisons are presented for different types of new and historical masonry structures currently employed in Italy. The validation of the analytical models is carried out by means of a three-dimensional (3D) finite-element (FE) out-of-plane homogenization. A final structural comparison among analytical models, FE out-of-plane homogenization, and a computationally expensive heterogeneous 3D FE model is discussed for a simply supported square panel laterally loaded.     

Torsional Surface Waves in an Initially Stressed Anisotropic Porous Medium

It is well known that the homogeneous elastic half space does not allow the torsional surface wave to propagate. The present article attempts to study the possibility of propagation of such waves in a liquid-filled initially stressed poroelastic layer over nonhomogeneous half space. The study concludes that torsional surface waves may propagate in the poroelastic layer. The presence of fluid in pores and initial compressive stresses diminishes the velocity. The nonhomogeneity in rigidity and density of the half space also has a certain role to play in initiating, enhancing, or diminishing the velocity of torsional surface waves.     

一种改进的各向异性扩散去噪模型

为了既能有效地去除噪声,又能够较好地保持图像的边缘以及重要的细节信息,在Perona和Malik提出的各向异性扩散模型(P-M模型)的基础上,通过对扩散方程中扩散函数的改进,提出了一种具备自适应性的去噪扩散模型,该模型对图像去噪处理更加高效。改进的扩散函数在梯度较小时为一个常数,大于某个阈值后变为单调递减函数,直至某个梯度时递减为零。以上扩散函数特性使各向异性扩散模型能够达到在同质区加速平滑、在边缘区停止平滑的目的。实验结果表明,改进的扩散模型是一种更为理想的保边缘平滑模型。     

Multi-scale weighted gradient-based fusion for multi-focus images

Anisotropic blur and mis-registration frequently happen in multi-focus images due to object or camera motion. These factors severely degrade the fusion quality of multi-focus images. In this paper, we present a novel multi-scale weighted gradient-based fusion method to solve this problem. This method is based on a multi-scale structure-based focus measure that reflects the sharpness of edge and corner structures at multiple scales. This focus measure is derived based on an image structure saliency and introduced to determine the gradient weights in the proposed gradient-based fusion method for multi-focus images with a novel multi-scale approach. In particular, we focus on a two-scale scheme, i.e., a large scale and a small scale, to effectively solve the fusion problems raised by anisotropic blur and mis-registration. The large-scale structure-based focus measure is used first to attenuate the impacts of anisotropic blur and mis-registration on the focused region detection, and then the gradient weights near the boundaries of the focused regions are carefully determined by applying the small-scale focus measure. Experimental results clearly demonstrate that the proposed method outperforms the conventional fusion methods in the presence of anisotropic blur and mis-registration.     

再辐射边界条件在FDTD中的应用

目前的吸收边界条件存在编程复杂,占有内存空间与计算量过大等缺点。再辐射边界条件通过在截断边界处引入与入射波等效电磁流符号相反的源,使得穿过边界的电磁场得到有效的衰减。与传统的吸收边界条件相比,再辐射边界条件具有吸收性能优越,设计思路清晰,编程简单,内存占有少,计算时间短的优点。推导了在离散网格中再辐射边界的反射系数与时间及空间步长的关系,通过时域有限差分方法（FDTD）进行了验证,与理论值基本相符。     

Ultrasound speckle reduction by a SUSAN-controlled anisotropic diffusion method

An ultrasound speckle reduction method is proposed in this paper. The filter, which enhances the power of anisotropic diffusion with the Smallest Univalue Segment Assimilating Nucleus (SUSAN) edge detector, is referred to as the SUSAN-controlled anisotropic diffusion (SUSAN_AD). The SUSAN edge detector finds image features by using local information from a pseudo-global perspective. Thanks to the noise insensitivity and structure preservation properties of SUSAN, a better control can be provided to the subsequent diffusion process. To enhance the adaptability of the SUSAN_AD, the parameters of the SUSAN edge detector are calculated based on the statistics of a fully formed speckle (FFS) region. Different FFS estimation schemes are proposed for envelope-detected speckle images and log-compressed ultrasonic images. Adaptive diffusion threshold estimation and automatic diffusion termination criterion are employed to enhance the robustness of the method. Both synthetic and real ultrasound images are used to evaluate the proposed method. The performance of the SUSAN_AD is compared with four other existing speckle reduction methods. It is shown that the proposed method is superior to other methods in both noise reduction and detail preservation.     

各务异性网格生成及其在曲面三角化中的应用

网格生成技术在工程分析，科学计算可视化等领域有着重要的意义，为了快速进行曲面三角化，提出了一种二维各向异性网格生成方法，通过引入椭圆距离和椭圆矩阵，定义了三角形的外接椭圆，从而将Delaunay三角化方法扩展到各向异性环境中，并讨论了各向异性网格的性质，随后将各向异性网格方法应用在曲面三角化当中，并将曲面的第一基本形式作为参数域的椭圆矩阵，同时给出了曲面Delaunay三角化的定义，从而成功地利用了各向异性网格方法对曲面进行三角化，实践证明，不仅其速度要大大快于传统的三角化方法，并且该方法能统一处理各种二次曲面和裁剪NURBS曲面。