A new method for soldering particle-reinforced aluminum metal matrix composites

Soldering of aluminum metal matrix composites (Al–SiC) to other structural materials, or even to themselves, has proved unsuccessful mainly due to the poor wetting of these composites by conventional soldering alloys. This paper reports a new approach, which improves the wetting properties of these composites by molting solder alloys to promote stronger bonds. The new approach relies on nickel-plating of the composite's faying surface prior to application of a solder alloy. Based on this approach, an aluminum metal matrix composite containing 55 vol.% SiC particles is successfully soldered to a Fe–Ni–Co alloy (commercially known as Kovar 4J29). The solder material is a zinc-based alloy (Zn–Cd–Ag–Cu) with a melting point of about 400 °C. Microscopic examinations of the aluminum metal matrix composites (Al-MMCs)–Kovar interfaces show that the nickel-plating, prior to soldering, could noticeably enhance the reaction between the molten solder and composites. The fractography of the shear-tested samples revealed that fracture occurs within the composite (i.e. cohesive failure), indicating a good adhesion between the solder alloy and the Al–SiC composite.     

智能点阵显示屏HCMS-29xx/39xx及其应用

HCMS-29xx／HCMS-39xx系列是安捷伦科技公司推出的智能LED点阵显示屏，它采用CMOS工艺制造，能够直接与微处理器和微控制器相连而无需接口电路和元件，可广泛用于医疗设备、打印机、扫描仪、复印机和消费类电子。文中介绍了HCMS-29xx／HCMS-39xx系列产品的引脚功能、内部结构和操作时序，给出了HCMS-2912与8751H的接口电路。     

Numerical Recovery of Conductivity at the Boundary from the Localized Dirichlet to Neumann Map

Numerical implementation of the reconstruction formulae of Nakamura and Tanuma [Recent Development in Theories and Numerics, International Conference on Inverse Problems 2003] is presented. With the formulae, the conductivity and its normal derivative can be recovered on the boundary of a planar domain from the localized Dirichlet to Neumann map. Such reconstruction method is needed as a preliminary step before full reconstruction of conductivity inside the domain from boundary measurements, as done in electrical impedance tomography. Properties of the method are illustrated with reconstructions from simulated data.     

Univariate Strip Interpolations by Nonlinear Parametric Splines

 In this paper, we develop algorithms for treating several constrained interpolation problems using the parametric cubic splines introduced in reference [11]. Explicit bounds for the parameters occurring in the spline class are given such that within these bounds the considered problems are always solvable. Received March 9, 2000     

G92指令在FANUC-0M系统中的灵活运用

在数控加工中,一般习惯上使用G54来设置工件坐标系的零点,实际上FANUC-OM系统中的G92指令的功能有一定的灵活性,在G54失效或不使用G54的情况下同样可以使数控机床正常使用.     

重卡后围强度试验的有限元分析

依据ECE29法规,对重卡驾驶室后围强度试验进行有限元仿真。当施加水平载荷后,测量结果表明驾驶室方向盘到座椅靠背的X向距离大于法规中人胸部厚度,证明了驾驶室具有足够的生存空间．     

MAS NMR studies of ZSM-5 zeolites: Correlation to para selectivity and SEM observations

²⁷Al and²⁹Si MAS NMR studies of various ZSM-5 zeolites of different Si/Al ratio, crystal size synthesized with and without alkali metal salt addition by the hydrothermal technique were carried out. The NMR observations clearly showed that the technique can be employed to differentiate Si/Al ratio, framework tetrahedral content and the crystal size. The last observation has been confirmed by SEM and catalytic activity test for para ethylation of ethylbenzene. A good correlation was found between the catalytic activity and the data from NMR and SEM.     

温度对大掺量粉煤灰水泥水化C-S-H聚合度的影响

采用固体29Si核磁共振、FTIR、XRD测试方法研究了养护温度、温度变化对大掺量粉煤灰水泥基材料水化C-S-H凝胶硅氧四面体聚合程度的影响规律。结果表明:粉煤灰掺量为50%时,C-S-H凝胶硅氧四面体的聚合程度和C-S-H凝胶中铝氧四面体的比例随着养护温度的升高而呈现先增加后稳定的趋势。在7d至28d龄期阶段,常温养护更加有利于C-S-H凝胶硅氧四面体聚合程度的增加,也更有利于Al原子取代Si原子。     

Regional differences in personal saving rates in Spain

The aim of this article is to analyze, from an aggregate perspective, the differences in personal saving rates among the Spanish regions at the NUTS II level from 1986 to 1994. In accordance with the postulates of the life cycle hypothesis, we present the main economic determinants for personal saving rates obtained from an aggregate personal saving model. Correcting for temporal and spatial dependence in the empirical model, the analysis suggests the existence of a significant and negative relationship between aggregate personal saving rates and wealth, access to credit and direct tax burdens. Likewise, a nearly significant positive relationship between personal saving rates and per capita gross disposable personal income has been detected. Received: 29 January 1999 / Accepted: 31 July 2000     

秦南凹陷秦皇岛29-2油气田原油来源及其勘探意义

秦皇岛29-2油气田的发现是秦南凹陷首次重大勘探突破,其影响意义深远.通过对原油物性和地球化学特征分析发现,虽然该油气田凝析油、正常原油和稠油3类原油的物性变化较大,但其母质来源和沉积环境相同、具有同源的特征.以规则甾烷C2920S/(20S+20R)为约束条件,综合利用ααα20RC27/C29规则甾烷和原油碳同位素2种油源对比参数,证实该油气田原油来自沙三段烃源岩.进一步利用回归方程求得原油所对应烃源岩镜质组反射率为0.71％ ～0.72％,与研究区钻井揭示的沙三段烃源岩的成熟度相当,表现出近源供烃的特征.研究结果表明,秦南凹陷内小型次洼已具备较大的生排烃能力,而与之相邻的烃源岩厚度更大、埋藏更深的秦南凹陷东洼周边勘探前景应更为广阔.