激光激励下厚尺度样品光热参数分布反演

为了实现厚尺度样品光热参数分布反演的目的,提出并建立厚尺度样品光热参数的反演模型,采用光热技术,正则化方法、格林函数法及奇异值分解方法,进行了激光致热正反问题的理论计算及数值模拟,分别在样品上下表面采集信号,反演得到了厚尺度样品内有2个光吸收层的模拟结果.结果表明,该方法有较好的稳定性和实用性.     

SIFT特征分布式并行提取算法

SIFT(scale invariant feature transform)特征在物体检测和识别、图像配准与融合、纹理识别、场景分类、人脸检测、图像检索、三维重建、数字水印、影像追踪等领域具有广泛应用,但存在计算量大、消耗时间长的缺点.基于消息传递机制,采用数据并行策略,提出了在PC机群或COW(cluster ofworkstation)上提取图像SIFT特征的分布式并行算法(DP-SIFT算法):根据特征空间-高斯尺度金字塔的特点提出了高度宽度受限的数据块划分算法,设计了数据分配和特征调整方法;研究了数据块划分和数据发送方法对通信时间的影响,提出了基于消息传递机制的并行图像处理中数据块划分与数据发送方式协同对通信优化的策略;实验结果表明DP-SIFT算法具有良好的加速性能和较高的处理器利用效率,千兆以太网连接32核的PC机群系统图像规模为1024×768时,加速比和处理器效率分别可以达到20和0.6;图像规模为2048×1536时可达18和0.56.     

可重构阵列的同步性能优化算法

可重构多处理器阵列上的容错技术可用来重构含有故障单元的处理器阵列,以便获得最大可用的目标阵列。现有的研究成果主要侧重于重构算法的构造,还没有涉及对重构后目标阵列的同步通讯性能的研究。提出了一种改善目标阵列同步通讯性能的电路优化算法,用来降低目标阵列行与行之间通讯的延时,使得相邻两行处理器的通讯尽可能达到同步。实验结果表明,提出的算法对不同大小、不同故障率的阵列都有相应的同步通讯性能的改善。     

高效软硬件划分算法及其提升技术

软硬件划分是软硬件协同设计的关键环节,它决定系统中哪些组件由软件实现,哪些由硬件实现。软硬件划分问题已被证明是NP完全问题。将一类软硬件划分问题看作变异的0-1背包问题,在求解背包问题的算法基础上构造出软硬件划分问题的优质启发解。此外,采用禁忌搜索(Tabu Search)算法对求得的启发解进行改进,在软件开销和通信开销满足一定约束的条件下,使得硬件开销尽可能小。实验结果证明,所提算法对当前最新算法的改进最大可达到28%。     

The effects of pulse frequency and substrate bias to the mechanical properties of CrN coatings deposited by pulsed DC magnetron sputtering

The chromium nitride coatings have been prepared by the bipolar symmetric pulsed DC magnetron reactive sputtering process at 2 kHz and 20 kHz pulse frequencies, respectively. Different substrate bias was applied with a pulsed DC bias unit with 50 kHz pulse frequency. Oscilloscope traces of the I–V waveforms indicate high power and high current density outputs during the symmetric bipolar pulsed mode. It is concluded that the (200) orientation of CrN films is observed. The grain size decreases with increasing pulse frequency and substrate bias. The substrate bias has a strong influence on the mechanical properties of CrN films. The scratch tests of the CrN coatings show that almost only tiny chipping failure is occurred. Sufficient adhesion strength quality of the coating is also observed. The substrate bias for the deposition of CrN films with sufficient hardness and adhesion properties combination is − 290 V at 20 kHz and − 408 V at 2 kHz pulse frequency, respectively.     

Process parameters design of a three-dimensional and five-directional braided composite joint based on finite element analysis

This paper presents an analytical method for designing the configuration of composite joint with three-dimensional (3D) five-directional braided composites. Based on the analysis of 3D braided structure characteristics, the elastic properties of the 3D five-directional braided composites were determined by the volume averaging method. The effects of the braiding angle and fiber volume fraction on the elastic constants of the braided composites were also discussed. Finite element analysis on the load capacity of the 3D five-directional braided composite joint was implemented using the software ANSYS Workbench 14.0. The influence of braiding angle on the stress, strain and deformation of the composite joint under tensile loading were calculated. The results show that when the fiber volume fraction of the 3D five-directional braided preform is given, the equivalent stress of the composite joint decreases monotonically as the braiding angle increases, while the normal stress, maximum principal stress and total deformation firstly decreases and then increases. Based on the finite element analysis, we found that at the fiber volume fraction of 60%, the braiding angle within the range of 30–35° are the optimum processing parameters for the 3D five-directional braided composite joint structure that used in the tensile load 320 N condition.     

A direct two-dimensional pressure formulation in molecular dynamics

Two-dimensional (2D) pressure field estimation in molecular dynamics (MD) simulations has been done using three-dimensional (3D) pressure field calculations followed by averaging, which is computationally expensive due to 3D convolutions. In this work, we develop a direct 2D pressure field estimation method which is much faster than 3D methods without losing accuracy. The method is validated with MD simulations on two systems: a liquid film and a cylindrical drop of argon suspended in surrounding vapor.     

Effects of high temperature treatment on microstructure and mechanical properties of laser-clad NiCrBSi/WC coatings on titanium alloy substrate

Laser-clad composite coatings on the Ti6Al4V substrate were heat-treated at 700, 800, and 900 °C for 1 h. The effects of post-heat treatment on the microstructure, microhardness, and fracture toughness of the coatings were investigated by scanning electron microscopy, X-ray diffractometry, energy dispersive spectroscopy, and optical microscopy. The wear resistance of the coatings was evaluated under dry reciprocating sliding friction at room temperature. The coatings mainly comprised some coarse gray blocky (W,Ti)C particles accompanied by the fine white WC particles, a large number of black TiC cellular/dendrites, and the matrix composed of NiTi and Ni₃Ti; some unknown rich Ni- and Ti-rich particles with sizes ranging from 10 nm to 50 nm were precipitated and uniformly distributed in the Ni₃Ti phase to form a thin granular layer after heat treatment at 700 °C. The granular layer spread from the edge toward the center of the Ni₃Ti phase with increasing temperature. A large number of fine equiaxed Cr₂₃C₆ particles with 0.2–0.5 μm sizes were observed around the edges of the NiTi supersaturated solid solution when the temperature was further increased to 900 °C. The microhardness and fracture toughness of the coatings were improved with increased temperature due to the dispersion-strengthening effect of the precipitates. Dominant wear mechanisms for all the coatings included abrasive and delamination wear. The post-heat treatment not only reduced wear volume and friction coefficient, but also decreased cracking susceptibility during sliding friction. Comparatively speaking, the heat-treated coating at 900 °C presented the most excellent wear resistance.     

Microstructure evolution and mechanical properties of ultrasonic assisted laser clad yttria stabilized zirconia coating

Yttria stabilized zirconia (YSZ) coatings were fabricated on a titanium alloy substrate by ultrasonic assisted laser cladding technique and the effect of ultrasonic vibration on the microstructureevolution and mechanical properties was investigated. Experimental results indicated that with the increase of ultrasonic output power, the clad depth increased, the wettability between coating and substrate was improved, the size of equiaxed grains in the cladding zone decreased, and the band structures were broken up gradually. Simultaneously, the element content distribution along the thickness of coating in the transition region changed from exponential to linear distribution gradually, together with the increase of dilution rate. With the increase of ultrasonic output power, the microhardness distribution of fusion zone also converted from an exponential to a linear distribution. Additionally, the friction and wear tests showed that the wear mechanism of coatings both with and without ultrasonic vibration was abrasive wear while the friction coefficients of coating with ultrasonic vibration were lower than that without ultrasonic vibration, which was related to the refined microstructures within the YSZ coatings.