环氧热熔胶的合成及其在可粘合PTFE上的应用

采用环氧树脂E -20、均苯四甲酸二酐、DMP-30合成高温快速固化环氧热熔胶粘剂,实验结果表明:E20/PMDA摩尔比为4.1/1,DMP-30用量为0.3％～0.5％,在110 ～120℃反应5～6h制得的环氧热熔胶对经过钠/萘腐蚀液处理后的聚四氟乙烯(PTFE)进行涂覆,得到可粘合PTFE板,于205℃固化90 s,与钢板粘接的剪切强度达2.129 MPa,在275.5℃下无热重损失,该胶固化迅速,粘接性和耐热性良好.     

高速网络环境下的P2P流媒体业务分析和识别方法

The growing P2P streaming traffic brings a variety of problems and challenges to ISP networks and service providers.A P2P streaming traffic classification method based on sampling technology is presented in this paper.By analyzing traffic statistical features and network behavior of P2P streaming,a group of flow characteristics were found,which can make P2P streaming more recognizable among other applications.Attributes from Netflow and those proposed by us are compared in terms of classification accuracy,a...     

Understanding the failure mechanisms of microwave bipolar transistors caused by electrostatic discharge

Electrostatic discharge(ESD) phenomena involve both electrical and thermal effects,and a direct electrostatic discharge to an electronic device is one of the most severe threats to component reliability.Therefore, the electrical and thermal stability of multifinger microwave bipolar transistors(BJTs) under ESD conditions has been investigated theoretically and experimentally.100 samples have been tested for multiple pulses until a failure occurred.Meanwhile,the distributions of electric field,current density and lattice temperature have also been analyzed by use of the two-dimensional device simulation tool Medici.There is a good agreement between the simulated results and failure analysis.In the case of a thermal couple,the avalanche current distribution in the fingers is in general spatially unstable and results in the formation of current crowding effects and crystal defects.The experimental results indicate that a collector-base junction is more sensitive to ESD than an emitter-base junction based on the special device structure.When the ESD level increased to 1.3 kV,the collector-base junction has been burnt out first.The analysis has also demonstrated that ESD failures occur generally by upsetting the breakdown voltage of the dielectric or overheating of the aluminum-silicon eutectic.In addition,fatigue phenomena are observed during ESD testing,with devices that still function after repeated low-intensity ESDs but whose performances have been severely degraded.     

塑封器件中高聚物的失效分析

文章分析了塑封器件中高聚物在封装固化过程中和使用过程中常见的损伤或失效,结果表明:封装固化过程中,当高聚物材料收缩受到周围材料的约束时,由于残余应力的存在,可引起气孔、孔隙、微裂纹,即形成了一系列微小缺陷;在后续的生产工艺以及产品使用过程中的热-机械载荷作用下,固化中产生的微小缺陷或损伤会扩展、汇合而形成宏观裂纹,导致...     

未雨绸缪,应对物联网时代的频谱需求

无所不在的"物联网"时代即将来临,它将实现人与人、物与物、人与物的智能连接,它将带动上万亿元规模的新兴科技市场……也许用不了5年,"物联网"改变的生活图景将比比皆是:当司机出现操作失误,汽车会自动报警;公文包会主动提醒主人忘带了东西;衣服会"告诉"洗衣机要怎么洗涤,等等。     

长度可调的TiO2纳米管制备及其DSSC性能的研究

采用阳极氧化法在Ti片上制备高度取向的TiO2纳米管阵列.室温下,电压60V,在含有0.5%(质量分数)NH4F,1%(体积分数)HF,2%(体积分数)H2O的乙二醇电解液中,通过改变阳极氧化时间(8～20h),反应制得管长约为6.7～19.5μm,管径约为90～110nm,管壁约为20nm的TiO2纳米管阵列.利用S...     

16通道光纤布拉格光栅解调系统的研究

鉴于单通道解调系统一次可检测的光栅波长数目有限,同时为兼顾FBG(光纤布拉格光栅)解调系统与上位机通信的稳定性与高速性,结合波分复用与空分复用技术,研制了多通道、多通信端口的FBG解调系统。通过控制16路光开关的光路切换,可实现对16通道FBG传感网的空分复用,对各通道传感器中心波长进行解调。测试结果表明,解调系统中心波长分辨率为1pm,一次采集光栅波长信息的时间为620ms,16个光通道的FBG传感信息更新最短时间不大于10s,可对约200只光纤光栅传感器进行有效监测。     

基于PID与前馈相结合的泵控马达恒速输出系统研究

针对泵控马达系统存在转速和外接负载扰动的问题,以变量泵-定量马达恒速控制系统为研究对象,阐明了系统的控制原理,建立相应液压系统的数学模型;采用了优化后的增量式PID与前馈相结合的复合方式对系统进行控制。通过Matlab的Simulink模块对系统的响应情况进行仿真,仿真结果表明:控制系统在两种扰动下反应迅速,马达输出转速能保持在较理想的状态。采用负载箱来模拟负载变化,变频器控制来模拟转速变化,进行了试验台的搭建。在输入转速为800、1 500 r/min时,当突变转速和负载时,马达输出转速能在2 s内恢复到稳定值,稳态转速偏差为0.5%,瞬时转速偏差为5.33%。分析实验结果表明该系统调速能力较好,为车载发电系统的实现提供了借鉴意义。     

基于巷道断面的掘进机截割头定位系统设计

针对无法精确定位掘进机截割头的位置、截割效率低及截割断面成形差的问题,提出了基于巷道断面的掘进机及截割头定位系统设计方法。结果表明,该定位系统在直线标准巷道内,可实现掘进机截割头准确定位,不仅提高截割效率和断面成形率,而且有利于安全生产,节约人力及支护成本。     

论地勘时期煤层瓦斯含量现场测定

论述了地勘时期煤层瓦斯含量现场测定的重要性,阐述了地勘时期煤层瓦斯含量现场测定的基本工作包括设备器具的准备、现场测定和记录,并从煤样密封罐的气密性、煤芯的钻取、瓦斯解吸速度的现场测定、气体体积校正、瓦斯损失量计算、记录和送样等方面探讨了地勘时期煤层瓦斯含量现场测定应注意的事项。