A MIXED ELECTRIC BOUNDARY VALUE PROBLEM FOR AN ANTI－PLANE PIEZOELECTRIC CRACK

The analytical continuation method is adopted to solve a mixed electric boundary value problem for a piezoelectric medium under anti-plane deformation. The crack face is partly conductive and partly impermeable. The results show that the stress intensity factor is identical with the mode III stress intensity factor independent of the conducting length. But the electric field and the electric displacement are dependent on the electric boundary conditions on the crack faces and are singular not only at the crack tips but also at the junctures between the impermeable part and conducting portions.     

Inertia effects of the fluid and cylinder in coaxial cylindrical rheometer

The inertias of the fluid and the inner cylinder in coaxial cylinder rheometer (CACR) have great influence on the unsteady flow of non-Newtonian fluid. Even for the Newtonian fluid there exist the so called “stress overshoot” phenomenon. In the present article this phenomenon was studied in detail and a method correcting the measured results for an unsteady flow in the rheometer was proposed. It is found that the inertia effect of the fluid can be ignored when the gap between cylinders is small. The project was supported by the Youth Foundation of the Fourth Military Medical University     

氧化物超导体的真空失超

处在超导态的Bi-2223相和Y-123相样品,在抽真空的条件下,会迅速失去超导电性转变为正常态,无论测量Tc时的恒流变大还是变小,失去超导的现象都是明显的。即使在十几K的范围内减压降温仍能保持在正常态。失超的直接原因可能是由于样品氧含量急剧减少而引起了超导相的变化,也说明了一种与氧含量有关的超导机制的存在。     

Thin and high conductive multi-walled carbon nanotubes/polydimethylsiloxane composite film prepared via solvent method as strain sensors

Flexible strain sensors based on conductive fillers and flexible polymers possessed significant advantages in human motion detection. Preparing a strain sensing layer with high electrical conductivity and excellent mechanical property under high content of conductive filler contributed to the stability of flexible strain sensors. In this study, MWCNTs/PDMS composite film was prepared by the organic solvent method. The microstructure, electrical conductivity, mechanical property, and piezoresistive characteristics of the composite film at different MWCNTs contents were characterized and discussed. When the mass fraction of MWCNTs in the composite film was 5%, the composite film exhibited a high electrical conductivity of 9.56 S/m while maintaining ideal mechanical properties, and the film thickness was just about 180 μm. The relationship between electrical signals and film strain was performed. The piezoresistive characteristic results demonstrated that the prepared composite film could be used as flexible strain sensor for human motion detection. The prepared thin MWCNTs/PDMS composite film in this paper illustrated high conductive and desired flexibility, and was an alternative material for human motion detection.     

应用次生相富集系数评价柴河沉积物重金属污染

目前,国外学者提出的几种关于河流沉积物重金属污染评价方法,具有其本身的特点和应用性,但也存在着某些局限性。为弥补这些评价方法的不足,提出了次生相富集系数法,并应用此法对柴河流域沉积物重金属的污染水平进行了评价。     

抽油杆表面感应淬火引起的残余应力

本文讨论了抽油杆通过感应线圈和水冷装置时的温度场和由温度场引起的相变。在有限元计算中，通过与实验数据对比，认为考虑温度对弹性模量有影响的计算模型更合理，并用此模型计算了由温度和相变共同作用的弹塑性应力场，及最终的残余应力。结果表明淬火层超过一定厚度后，残余应力分布的合理性降低；淬火前抽油杆的强度与残余应力的大小关系较弱。     

多足爬壁机器人新型足—掌机构运动学和力解析

本文介绍了一种新型足－掌机构，利用该机构可以解决多足爬壁机器人从地面向壁面过渡行走的难题。通过对机构的运动学正、逆问题的求解，推导出足端的工作空间以及可达的极限位置，同时对机构进行了受力分析，为规划多足爬壁机器人地壁过渡行走、机构参数的选择以及优化设计提供了理论依据。     

科技报刊要尽快适应“两个转变”

科技报刊还不适应“两个转变”的需求,主要表现为一般性载体,被动性服务,滞后性反映,散漫性观照,要更新观念,在“两个转变”中充分发挥作用,就必须改变单纯反映为适应性选择,改变愿者上钩为主动性服务,改变短视行为为前沿性拓展,改变不计成本为效益性增长,寻求最佳办刊途径以拓展市场;重新定位,突出实践性,明确指出,突出专业性,开拓新路,突出开放性;左挂右联,突出增益性。     

YBCO在氮纯化过程中的催化氧化作用

高温超导材料YBa2Cu3O7-x(即YBCO)在加氢的普氮气流中,在100～300 ℃的温区里就能生成H2O和高纯N2. 系列的X-光谱和热重分析以及相应的氮纯度测量表明,它是一种很有应用前景的氧化催化剂. 实验明确给出130～150 ℃是它的最佳催化温区,还根据YBCO的等温特性曲线和Langmuir理论讨论了YBCO在氮纯化过程中催化氧化作用的机制.     

Study on Active Drive System for Colonoscope

The paper deals with active drive system for colonoscope. The system is mainly composed of soft mobile mechanism for earthworm locomotion and turning mechanism based on shape memory effect. The soft mobile mechanism contacts colon wall with airin inflatable balloons, so the robot has better soft and non invasive properties. The turning mechanism can be actively bent by shape memory alloy components. It ensures the colonoscope to adapt to the tortuous shape of colon. Some experiment results are given in the paper.