The effect of zirconium addition on the microstructure and properties of chopped carbon fiber/carbon composites

Carbon/carbon composites containing zirconium were prepared using chopped carbon fiber, mesophase pitch and Zr powder by the traditional process including molding, carbonization, densification and graphitization. The influence of Zr on the microstructure and properties of the composites were investigated. Results show that Zr can improve the interface bonding, promote more perfect and larger crystallites and enhance the conductive/mechanical properties of the composites. The high in-plane thermal conductivity of 464 W/(m K) and excellent bending strength of 83.6 MPa was obtained for a Zr content of 13.9 wt% at heat treatment temperature(HTT) of 2500 °C. However the conductive/mechanical properties of the composites decrease dramatically for an higher HTT of 3000 °C. SEM micrograph of the fracture surface for the composites shows that lower disorder crystallite arrangement of fiber and carbon matrix come into being in the composites during HTT of 3000 °C, which should be responsible for the low properties. Correlation between the content of Zr and the microstructure and properties are discussed.     

Fluidised pellet bed bioreactor: a promising technology for onsite wastewater treatment and reuse.

A pilot-scale fluidised pellet bed (FPB) bioreactor, which combines chemical coagulation, biological degradation, particle pelletisation and separation in one unit, was applied for onsite wastewater treatment and reuse. As a result of rational use of inorganic coagulant and organic polymer and moderate mechanical agitation, spherical particles were generated in the upflow column and a well-fluidised bed was formed. With a continuous supply of dissolved oxygen through a recycling loop, an aerobic condition was kept in the bottom section of the FPB column. Under such conditions the pellets in the FPB column showed the following characteristics: (1) compact structure and high density; (2) rich in microorganisms; and (3) high MLSS and MLVSS concentrations. Therefore, the FPB bioreactor achieved more than 90% removal of SS, COD, BOD and TP from raw domestic wastewater within a total hydraulic retention time (HRT) of only about 30 minutes. It also showed nitrification and denitrification ability and the TN removal could be about 50% as the recycling ratio was increased to 1:1. The treated water quality is generally competitive with the secondary effluent from a conventional activated sludge process. With these advantages the FPB bioreactor is recommendable as a compact system for onsite wastewater treatment and reuse.     

活性炭吸附硫脲溶液中的金离子之形态

由实验得出活性炭从硫脲溶液中吸附金的特点,根据络合化学原理找到溶液中被吸附离子形态是AuTu~+,AuTu_2~+和Au~+,并解释了实验现象。     

模糊解耦控制在集散控制中的应用

该文结合循环流化床锅炉的特点,采用了霍尼韦尔公司的EPKS控制系统对锅炉进行控制,设计了硬件的配置,主要设计了控制策略,将模糊解耦控制应用在控制策略中,进行了实验仿真,实验结果表明模糊解耦控制具有良好的解耦效果。     

Dynamic behavior of an aggregate material at simultaneous high pressure and strain rate: SHPB triaxial tests

Low velocity impacts on energetic materials induce plastic deformations and sliding friction which can lead to ignition. If some ignition criteria have been proposed, the remaining difficulty is to characterize the mechanical behavior of the material when submitted to the corresponding solicitations (high pressure and high strain rate). Thus, a technique based on the Split Hopkinson Pressure Bars system is proposed to carry out a triaxial compression test. A cylindrical specimen is placed into a confining ring and is compressed by the system of bars. The ring prevents the radial extension of the specimen and creates a lateral confining pressure. The material and dimensions chosen for the ring maintain a constant radial pressure during the test. Some tests were carried out on an inert aggregate material and proved the validity of this experimental device. The experimental data processing shows the influence of both the pressure and the strain rate. The shear stresses, which contribute to thermal dissipation and then to the ignition threshold, increase according to the pressure.     

一种三电平高压变频器IGBT驱动电路的实现

三电平高压变频器对IGBT驱动电路有特殊的要求,比如:高低压侧的隔离问题、绝缘等级、动态驱动能力以及快速保护功能都有严格的要求。采用美国Unitrode公司生产的UC3726/3727驱动IGBT芯片对,两芯片可组合使用,从而可以达到理想的驱动效果。测试结果表明了该方法的可行性。     

智能迷宫机器人系统设计与搜寻算法研究

智能迷宫机器人利用红外传感器,探测正前方及左右两侧的实时路况信息实现避障功能,采用相关算法搜寻行进路线,在无人控制的情况下自主地破解迷宫。在此介绍了智能迷宫机器人的具体设计与实现,并着重对迷宫算法进行研究。考虑到实际系统内存容量和运算速度的限制以及常用算法的优缺点,提出一种优化的深度优先算法,它具有占用内存空间少,对处理器的速度要求低等特点。经实验验证,该算法可以准确快速地找到终点。     

Bias effects on heat transfer measurements in microchannel flows

This work is devoted to both experimental and numerical investigations of the hydrodynamics and associated heat transfer in two-dimensional microchannels from 700 μm to 200 μm in height. The design of the test section enabled to vary the channel height and to set a quasi-constant heat flux at the microchannel surface. Laminar developing, transitional and turbulent regimes of water flows were explored (200 < Re < 8000). A significant decrease in the Nusselt number was observed in the laminar regime when the channel spacing was decreased while the Poiseuille number remained unchanged in regard to conventional channel flow. It is shown that a bias effect in the solid/fluid interface temperature measurements is most likely responsible for this scale effect. The temperature error was estimated and accounted for in the determination of the Nusselt number. The corrected values have been found to be consistent with the conventional laws both in the laminar and in the beginning of the turbulent regime.     

一种改进的全四边形网格生成方法及优化

在任意二维区域的全四边形网格生成方法中,铺砌法是目前较好的一种方法。但是当边界出现不规则区域时,网格生成完毕后内部会产生一些质量较差的单元,且判断网格交叉现象是否发生和解决网格交叉问题比较困难。为了提高该方法的适应性和可靠性,提出一种新的改进算法,它对边界不规则区域网格生成和解决网格交叉问题等关键技术进行改进,并加入四边形网格优化方法。将改进后的铺砌法应用于船舶有限元网格划分中,取得了较好的应用效果,最后给出算例进行了验证。     

Co-coating effect of GdPO4 and carbon on LiFePO4 cathode surface for lithium ion batteries

The electronic conductivity enhanced has been extensively studied and reported in lithium iron phosph-ate (LiFePO₄). However, only few existing literatures are available for researchers to enhance simultaneously the ion and electronic conductivity of LiFePO₄. Herein, we disclose that the LiFePO₄ is co-coated with novel GdPO₄ and Carbon via a hydrothermal-assisted solid-phase method, contributing to particle size and dispersibility. What surprising is that the ionic and electronic conductivity of the material is significantly enhanced, and the interfacial side reaction is effectively inhibited between the materials and the electrolytes. The diverse proportions of the mixed coating (LiFePO₄/C&xGdPO₄ (x = 0, 1 wt%, 2 wt%, 3 wt%, 4 wt%)) are synthesized compared with bare LiFePO₄. The experimental results suggest that LiFePO₄/C&0.03GdPO₄ exhibits the most excellent electrochemical performance. There is discharge capacity of 158, 148.8, 141.6, 134.9, 121.8, 104.9, and 86.7mAh/g at 0.1, 0.2, 0.5, 1, 2, 5, and 10 C rates, respectively.