Mechanism of resistance microwelding of crossed fine nickel wires

Resistance microwelding of fine crossed nickel wires is of increasing industrial importance for electrical connections in downsized electronic and medical devices, but the understanding of the process is very limited. A study has, therefore, been performed to clarify the basic joining mechanisms, in which the effects of main process parameters (welding current and force and weld time) were investigated by detailed mechanical testing and metallurgical examinations. A bonding mechanism with main process stages (wire cold collapse, surface melting, molten-phase squeeze-out and, solid-state bonding) was proposed. A new technique has also been developed to optimize the process by initiating the welding current well before the electrode force has reached its full nominal value.     

In situ polymerization and characterization of polyester‐based polyurethane/nano‐silica composites

Polyester‐based polyurethane/nano‐silica composites were obtained via in situ polymerization and investigated by Fourier‐transform infrared spectroscopy (FTIR), or FTIR coupled with attenuated total reflectance (FTIR‐ATR), Transmission electron microscopy (TEM), atomic force microscopy (AFM), an Instron testing machine, dynamic mechanical analysis (DMA) and ultraviolet‐visible spectrophotometry (UV‐vis). FTIR analysis showed that in situ polymerization provoked some chemical reactions between polyester molecules and nano‐silica particles. FTIR‐ATR, TEM and AFM analyses showed that both surface and interface contained nano‐silica particles. Instron testing and DMA data showed that introducing nano‐silica particles into polyurethane enhanced the hardness, glass temperature and adhesion strength of polyurethane to the substrate, but also increased the resin viscosity. UV‐vis spectrophotometry showed that nano‐silica obtained by the fumed method did not shield UV radiation in polyurethane films. Copyright © 2003 Society of Chemical Industry     

Effect of processing history on the properties of Ag-based tapes

The Bi-system tapes and coils were prepared by the powder-in-tube method. The effect of processing and heat treatment on the properties of the tapes and coils was studied. It is found that the shearing stress produced by the rolling process may destroy the 2223 phase, and the destroyed 2223 phase cannot be recovered by heat treatment, whereas the pressing stress produced by the uniaxial pressing process only makes the 2223 phase grains break, and the broken 2223 phase can be closed by the heat treatment. TheJ _c values of the rolling samples, pressing sample, and the coil with a diameter of 35 mm are over 1.3×10⁴, 2.5×10⁴, and 4×10³ A/cm² (77 K, 0 T), respectively.     

Eigenvalue-based algorithms for testing positive realness of SISO systems

A computational test for scalar positive real and strictly positive real functions is proposed in this paper. The input for this algorithm is state space representation, not necessarily minimal. It is derived for the discrete time problem, based on numerical stable eigenvalue computations. The test can be used in the continuous counterpart, which is in fact an improvement of an algorithm posed by Bai and Freund. Differences between the discrete and continuous time problems are also pointed out.     

不锈钢绕带容器环板与绕带端头的焊接

本文通过焊接试验对奥氏体不锈钢绕带容器环板与绕带焊接工艺进行了研究分析,并得出了合理的焊接方法和工艺参数。     

石家庄市室内氡及其子体浓度

本文报道了用双滤膜法对石家庄市室内空气中氡及其子体浓度的调查结果。47个房间室内氡年平均浓度为17.0Bq·m~(-3),氡子体平均浓度是7.14Bq·m~(-3)。氡及其子体浓度的日变化是清晨4—8时出现峰值。季节变化是夏秋季低,冬季高,全年的最低值出现在8月,最高值出现在11月。     

用于重离子核反应实验测量的纵向电场气体电离室

本文报道了一种新型的大动态范围，多叠层探测器系统组件之一的纵向电场气体电离室的构造，性能和在中能得离子核反应实验中的应用。     

~（60）Co辐照对聚四氟乙烯表面润湿性的影响

研究了具有低表面能的氟聚合物聚四氟乙烯（ＰＴＦＥ），经６０Ｃｏγ射线辐照后表面状态的变化，以及其对液体介质蒸馏水的润湿性。较详细地论述了辐照后表面粗糙度、结晶度以及表面化学基因等不同因素对ＰＴＦＥ表面润湿性的影响。通过对ＰＴＦＥ及其表面的红外、Ｘ光衍射，表面粗糙度的分析，弄清了辐照后ＰＴＦＥ表面化学基团的改变对有机氟聚合物表加的润湿性影响很大，而粗糙度和结晶度的变化对润湿性影响较小。