Reaction mechanism and microstructure evolution of reaction sintered <Emphasis Type="Italic">h</Emphasis>-BN

Hexagonal boron nitride ceramic (h-BN) based on the nitridation of B powders was obtained by reaction sintering method. The effects of sintering temperature on the mechanical properties and microstructure of the resultant products were investigated and the reaction mechanism was discussed. Results showed that the reaction between B and N₂ occurred vigorously at temperatures ranging from 1 000 °C to 1 300 °C, which resulted in the generation of t-BN. When the temperature exceeded 1 450 °C, transformation from t-BN to h-BN began to occur. As the sintering temperature increased, the spherical particles of t-BN gradually transformed into fine sheet particles of h-BN. These particles subsequently displayed a compact arrangement to achieve a more uniform microstructure, thereby increasing the strength.     

多视无人机影像环形拼接算法

由于多视无人机影像拼接时误差的传播和累计经常导致拼接图扭曲偏斜或者拼接的失败.针对这个问题提出了构建拼接环并以多级拼接作为辅助的拼接策略.首先将待拼接图像分为多组,每组中以环形方式进行拼接,然后利用SIFT进行匹配,RANSAC实现误匹配的去除,而后计算透视变换关系,最后通过平差方程将误差削弱.通过实拍无人机影像进行的拼接实验表明该方式可以有效减少累计误差的影响,提高拼接精度.该方法的提出可以作为影像拼接消除累计误差的有效方式之一.     

Dynamic data packing towards the optimization of QoC and QoS in networked control systems

A class of networked control systems is investigated whose communication network is shared with other applications. The design objective for such a system setting is not only the optimization of the control performance but also the efficient utilization of the communication resources. We observe that at a large time scale the data packet delay in the communication network is roughly varying piecewise constant, which is typically true for data networks like the Internet. Based on this observation, a dynamic data packing scheme is proposed within the recently developed packet-based control framework for networked control systems. As expected this proposed approach achieves a fine balance between the control performance and the communication utilization: the similar control performance can be obtained at dramatically reduced cost of the communication resources. Simulations illustrate the effectiveness of the proposed approach.     

损伤变量对复合材料损伤演化过程的影响分析

复合材料层合板损伤模型中的刚度退化需要通过损伤变量来实现。针对通常采用的2种损伤变量定义,给出了统一表达式。此外,损伤刚度矩阵是损伤变量的函数,基于应变等效假设推导了三维损伤刚度矩阵,从而避免了对损伤刚度矩阵的人为假定。最后,通过复合材料层合板在冲击载荷作用下的数值模拟,讨论了损伤变量的2种定义对数值结果的影响,表明损伤变量的不同定义对分层和基体损伤分布存在一定的影响,对冲击载荷的影响不大。建议在复合材料损伤模拟中,应予关注损伤变量。     

A novel spherical-ordered macroporous CuO nanocatalyst for the electrochemical reduction of carbon dioxide

Journal of Applied Electrochemistry - The electrocatalytic reduction of CO2 is a promising research direction in resource utilization and sustainable energy development. However, there is still a...     

纳米金刚石的应用

纳米金刚石不仅具有金刚石所固有优异特性，而且还具有纳米材料所拥有的奇异性能。正是这些综合技术特性，使得它在传统的和新的技术领域中得到应用，并初见成效，本文从超精抛光、润滑、复合镀、磁性录音系统和医疗等方面的应用做了扼要的叙述，指出，纳米金刚石颗粒具有球形和准球形的特点，使得摩擦表面形成滚珠轴承效应，而表现出良好的润滑性，从而避免于摩现象的发生，而对一些主要因接触疲劳或高温磨损而失效的工件，纳米金刚石金属的复合涂层，则具有明显的优越性。     

Sensitivity analysis based preform die shape design using the finite element method

This paper uses a finite element-based sensitivity analysis method to design the preform die shape for metal forming processes. The sensitivity analysis was developed using the rigid visco-plastic finite element method. The preform die shapes are represented by cubic B-spline curves. The control points or coefficients of the B-spline are used as the design variables. The optimization problem is to minimize the difference between the realized and the desired final forging shapes. The sensitivity analysis includes the sensitivities of the objective function, nodal coordinates, and nodal velocities with respect to the design variables. The remeshing procedure and the interpolation/transfer of the history/dependent parameters are considered. An adjustment of the volume loss resulting from the finite element analysis is used to make the workpiece volume consistent in each optimization iteration and improve the optimization convergence. In addition, a technique for dealing with fold-over defects during the forming simulation is employed in order to continue the optimization procedures of the preform die shape design. The method developed in this paper is used to design the preform die shape for both plane strain and axisymmetric deformations with shaped cavities. The analysis shows that satisfactory final forging shapes are obtained using the optimized preform die shapes.     

叔胺萃取分离精炼铂的新工艺

用三烷基胺（Ｎ２３５）萃取分离铂，考察了稀释剂、改质剂浓度、料液酸度对分配系数的影响，从复杂的工业料液中，用Ｎ２３５萃取、洗涤、反萃、再生及精炼铂的工艺技术。     

Electrochemical properties of some cobalt antimonides as anode materi-als for lithium- ion batteries

Some cobalt antimonides have been prepared and studied as the candidate anode materials for lithium ion batter-ies. Reversible capacities of 424,423 and 546 mA·h·g-1 were measured at the first cycle for as-solidified CoSb2, CoSb3 and annealed CoSb3 respectively. A low lithium ions diffusion coefficient in the order of 10-16 m2·s-1 was estimated from the coulometric titration measurements in the annealed CoSb3 electrode. It was found that the electrochemical properties of fine powders are significantly better than coarse powders. However the SEM picture shows that the nano-sized CoSb3 powders gathered to larger granules, which worsens somewhat the capacity retention of the nano-sized materials, although the volume capacities of the annealed and ball milled CoSb3 remain near twice of that of graphite after 50 cycles.     

Temperature Dependence of the Magnetocrystalline Anisotropy in Nd_2Co_(14)B Compound

Easy and hard magnetization curves of Nd_2Co_(14)B compound have been measured withextracting-sample-magnetometer(μ_0H_(max)=6T)at 10～300 K.Magnetic anisotropy constants K_1 and K_2have been determined by fitting the hard magnetization curves,in which only K_1 ,K_2 and misalignment anglehave been taken as fitting parameters.The values of K_1 and K_2 at 4.2 K were derived by extrapolation.Anisotropy coefficients,x_2~° and x_4~°were derived from the anisotropy constants.The anisotropy constant K_2increases rapidly with increasing temperature when TT_(sr).The temperature depen-dence of the magnetic anisotropy coefficient x_2~° was fitted with the formula.The anisotropy coefficients x_2~°can be well described by the tenth-power law from 4.2 K to T_(sr)and by the sixth-power law from T_(sr_ to 300 K.