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     

铁磁偶合的Gd（Ⅲ）Cu（Ⅱ）配合物──组装分子基铁磁体的一种重要元件

铁磁偶合的Ｇｄ（Ⅲ）Ｃｕ（Ⅱ）配合物──组装分子基铁磁体的一种重要元件缪明明，廖代正，王耕霖（南开大学化学系天津３０００７１）摘要分子基磁体的设计是自然界向化学家挑战的一个热点课题。铁磁偶合的Ｇｄ（Ⅲ）Ｃｕ（Ⅱ）配合物是组装分子基磁体的一种重要元件。...     

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本文通过对在用钻机井架的现场实际测试,建立数据库、测评模型,对实测的数据用计算机技术进行分析,提出了初始弯曲应力;数据正态分布检验——x～2检验;建立回归方程;在给定置信度下测评当前承载能力的技术概念。解决了在用钻机A型井架的安全性评估问题,是一种较为合理、可靠、科学的测评技术和方法。     

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。