超高压泵头体材料模拟平台数据采集控制系统研究

本文介绍了一种基于超高压泵头体材料模拟平台的数据采集控制系统,该系统为模拟平台采集压力、温度、应力等信息,并可对压力（50MPa 200MPa）进行连续调节,实时监测被测材料的开裂情况.本文介绍了该系统的设计背景,并对系统的工作原理进行了详细的介绍.     

Isothermal crystallization kinetics and morphology development of isotactic polypropylene blends with atactic polypropylene

The crystallization kinetics and morphology development of pure isotactic polypropylene (iPP) homopolymer and iPP blended with atactic polypropylene (aPP) at different aPP contents and the isothermal crystallization temperatures were studied with differential scanning calorimetry, wide‐angle X‐ray diffraction, and polarized optical microscopy. The spherulitic morphologies of pure iPP and larger amounts of aPP for iPP blends showed the negative spherulite, whereas that of smaller amounts of aPP for the iPP blends showed a combination of positive and negative spherulites. This indicated that the morphology transition of the spherulite may have been due to changes the crystal forms of iPP in the iPP blends during crystallization. Therefore, with smaller amounts of aPP, the spherulitic density and overall crystallinity of the iPP blends increased with increasing aPP and presented a lower degree of perfection of the γ form coexisting with the α form of iPP during crystallization. However, with larger amounts of aPP, the spherulitic density and overall crystallinity of the iPP blends decreased and reduced the γ‐form crystals with increasing aPP. These results indicate that the aPP molecules hindered the nucleation rate and promoted the molecular motion and growth rate of iPP with smaller amounts of aPP and hindered both the nucleation rate and growth rate of iPP with larger amounts of aPP during isothermal crystallization. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 1093–1104, 2007     

车载安全应用广播性能分析*

在仿真软件NS-2.29和VanetMobiSim1.1下,搭建了车载通信网络仿真平台,讨论了广播信标信息在不同距离下的接收率,并对两类广播信息在EDCA方式下的接收率和接入时延进行了深入的分析和比较。仿真结果表明,隐藏终端导致广播数据的严重丢包而且不同竞争窗口对接入时延有很大的影响,尤其是在信道负荷比较重时。最后指出了可行的解决思路。     

处理工艺对纯镁表面植酸转化膜性能的影响

文章采用植酸水溶液对纯镁进行化学转化处理,通过SEM、EDS、电化学极化曲线法研究了温度、时间、浓度以及pH值对表面转化膜性能的影响.结果表明,转化膜的厚度和表面裂纹尺寸随着转化处理液浓度及处理时间的增加而增大,但时间过长或浓度过大均会导致转化膜的耐蚀性下降;溶液pH从1增大到5时,转化膜的裂纹尺寸呈现减小趋势,耐蚀性先增大后减小;转化膜表面裂纹尺寸随温度升高先增大后减小,温度在20℃～60℃之间,形成的转化膜耐蚀性较好,80℃和90℃时,形成的转化膜耐蚀性显著降低.     

深部软岩巷道锚喷支护参数优化设计

采用正交设计方法对望峰岗煤矿巷道锚喷加固方案进行优化,得出加固优化方案,此方案对巷道塑性区、位移都有一定程度的抑制,而且使巷道周边围岩卸荷区所承受的应力有所增高,应力增高区和集中应力区的应力下降,更有利于巷道的稳定,发挥围岩的自承载能力.     

A perturbation-incremental scheme for studying Hopf bifurcation in delayed differential systems

A new method, called perturbation-incremental scheme (PIS), is presented to investigate the periodic solution derived from Hopf bifurcation due to time delay in a system of first-order delayed differential equations. The method is summarized as three steps, namely linear analysis at critical value, perturba- tion and increment for continuation. The PIS can bypass and avoid the tedious calculation of the center manifold reduction (CMR) and normal form. Meanwhile, the PIS not only inherits the advantages of t...     

Preparation of freestanding and crack-free titania–silica aerogels and their performance for gas phase, photocatalytic oxidation of VOCs

Freestanding and crack-free titania–silica aerogels with high titanium content (i.e., Ti/Si = 1) were successfully prepared by adjusting the hydrolysis of the two alkoxide precursors to a comparable rate during the sol–gel processing. Two titania–silica aerogels were prepared by ethanol and CO₂ supercritical drying methods. Well-dispersed, nanometer-sized anatase crystal domains (ca. 10 nm) were crystallized by high temperature, ethanol supercritical drying. The crystalline domains were solidly anchored to the aerogel network by Ti–O–Si bonds. Titania–silica aerogels prepared by CO₂ supercritical drying method were devoid of TiO₂ crystals. A molecular-level mixing was achieved and anatase TiO₂ was only crystallized with difficulty by high temperature calcination (1073 K). Both aerogels were mesoporous and displayed similar open pore structure that is readily accessible to reactant molecules. However, only the titania–silica aerogel with anatase TiO₂ prepared by ethanol supercritical drying was active for the gas phase, photocatalytic oxidation of volatile organic compounds (i.e., isopropanol and trichloroethylene). Catalysts prepared from Degussa P25 TiO₂ displayed lower activity under similar reaction conditions.     

基于J2EE技术的可配置化系统的设计开发

科技项目在线申报已成为项目申报的主流方式.为适应新形势、新要求,原有的在线项目申报系统需要升级.文章介绍了基于J2EE技术的可配置化项目申报管理系统的开发、实现过程,对系统的需求分析、方案论证、系统设计、数据库设计、模块设计等环节进行详尽的分析和描述.该可配置化系统在处理大规模定制化的项目申报流程时具有适用性和可操作性.     

Broadband high‐gain slot grid array antenna for millimeter wave applications

A broadband high‐gain slot grid array antenna (SGAA) is proposed in this paper. Based on the electromagnetic complementarity principle, the metal elements in the traditional microstrip grid array antenna (GAA) are replaced by a wide slot element. Compared with the GAA, the proposed SGAA achieves broadband and high‐gain performance. In order to demonstrate this concept, a prototype with 9‐element SGAA is designed using wide slot radiation elements and fabricated on Rogers 5880 printed circuit board (PCB) substrates, which is fed by a 50 Ω coaxial probe. The measured and simulated results show a good agreement. The proposed SGAA achieves a measured peak gain of 14.8 dBi at 26.0 GHz, a 10‐dB impedance bandwidth from 22.2 to 28.5 GHz with a fractional bandwidth of 24.9%. These results indicate that the SGAA is with high performance and it is suitable for the fifth‐generation (5G) millimeter wave (mmW) wireless communication system.     

移动边缘计算中基于Lyapunov的任务卸载与资源分配算法

移动边缘计算（MEC）通过将计算和存储资源部署在无线网络边缘,使得用户终端可将计算任务卸载到边缘服务器进行处理,从而缓解终端设备资源受限与高性能任务处理需求之间的冲突。但随着任务卸载规模的不断增加,执行任务所产生的功耗急剧上升,严重影响了MEC系统的收益。建立任务队列动态调度模型,以队列上溢概率为约束构建最大化系统平均收益的资源优化模型。考虑到资源优化问题为不同时隙下的耦合问题,运用Lyapunov优化理论设计一种基于单时隙的资源分配算法,将优化问题转化为用户本地计算资源分配、功率和带宽资源分配以及MEC服务器计算资源分配3个子问题并分别进行求解。仿真结果表明,该算法在满足用户QoS需求的同时能够有效提高MEC系统的时间平均收益。