Diffusion soldering for stable high-temperature thin-film bonds

Diffusion soldering is a special bonding technique to produce joints at a moderate temperature that are subsequently stable at higher temperatures. The search for material systems extending the upper-temperature limit of stability requires information from the pertinent phase diagrams and the reaction kinetics. Combining experimental studies on phase equilibration in powder samples with bulk and thin-film diffusion couples is a useful approach for a systematic search. Promising candidates for dsoldering are Pt-In or Pd-In, and molybdenum is also an effective diffusion barrier against the attack of liquid tin.     

Charactersitics of Stress-strain Curve of High Strength Steel Fiber Reinforced Concrete under Uniaxial Tension

A whole of 110 specimens divided into 22 groups were tested with varying the volume fraction of steel fibers and the matrix strength of these specimens. The stress-strain behaviors of four types of steel fiber reinforced concrete （SFRC） under uniaxial tension were studied experimentally. When the matrix strength and the fiber content increase, the tensile stress and tensile strain vary differently according to the fiber type. The mechanisms of reinforcing effect for different types of fiber were analyzed and the stress-strain curves of the specimens were plotted. Some experimental factors for stress or strain of SFRC were given. A tensile toughness modulus Re0.5 was introduced to evaluate the toughness characters of SFRC under uniaxial tension. Moreover, the formula of the tensile stress-strain curve of SFRC was regressed. The theoretical curve and the experimental ones fit well, which can be used for references in construction.     

Qualitative representation of spatial knowledge in two-dimensional space

Various relation-based systems, concerned with the qualitative representation and processing of spatial knowledge, have been developed in numerous application domains. In this article, we identify the common concepts underlying qualitative spatial knowledge representation, we compare the representational properties of the different systems, and we outline the computational tasks involved in relation-based spatial information processing. We also describesymbolic spatial indexes, relation-based structures that combine several ideas in spatial knowledge representation. A symbolic spatial index is an array that preserves only a set of spatial relations among distinct objects in an image, called the modeling space; the index array discards information, such as shape and size of objects, and irrelevant spatial relations. The construction of a symbolic spatial index from an input image can be thought of as a transformation that keeps only a set of representative points needed to define the relations of the modeling space. By keeping the relative arrangements of the representative points in symbolic spatial indexes and discarding all other points, we maintain enough information to answer queries regarding the spatial relations of the modeling space without the need to access the initial image or an object database. Symbolic spatial indexes can be used to solve problems involving route planning, composition of spatial relations, and update operations.     

Relationship between Multi-Phase Formation and Molecular Structure for Liquid Crystal System

4 mechanical model of liquid crystals （ LCs ） was used to explain the phase formation and thermal properties . The LC plusses in the model are micro- machine systems consisting of an ensemble of molecular rotors, and some dynamie parameters in a semi-experiment molecular orbit method. A novel explanation on the multi-phase formation of LC system is obtained. It is found that the value of the critical rotational velueity is a key parameter for the characterization of each homologous series. The dipole moment of the molecules was also discussed.     

建筑艺术与科学的比较研究

本文通过对建筑艺术与科学在成就、社会文化中的地位、评判方式及时间感等方面的比较研究,阐明了两者之间的异相,并指出中国当代建筑理论的发展方向是加强科学理性的基础研究。     

Preparing high- and low-aspect ratio AlB2 flakes from borax or boron oxide

The commercial preparation of aluminum-diboride flakes in aluminum relies on relatively expensive starting materials. A new synthesis has been developed that allows AlB₂ to be prepared directly from the reaction of borax (Na₂B₄O₇·10H₂O) or boron oxide (B₂O₃) with aluminum. Aluminum metal at temperatures higher than 900°C has been shown to reduce these boron-containing compounds, producing an Al₂O₃-containing slag and AlB₂. A natural separation occurs, leaving AlB₂ in the molten aluminum and Al₂O₃ as part of a slag that forms at the melt surface. Samples containing up to 10 vol.% AlB₂ in an aluminum matrix have been directly prepared using this method. For more information, contact A.C. Hall, Sandia National Labs., P.O. Box 5800, Mail Stop 0340, Albuquerque, New Mexico 87185; (505) 284-6964; fax (505) 845-9659.     

Why High-Speed Railway Stations Continue China’s Leapfrog Urbanization:Institutional Parameters of Urban Development

An ambitious program of High-Speed Railway (HSR) is under construction in China and already soon the network will overtake its counterparts in Europe. Reflecting on experiences in Europe, the authors explore the conditions for place making qualities of six new HSR station areas in China. The superb inter-city connectivity of the new infrastructure nodes raises a lot of expectations about the economic and social potential of the station areas, but the experiences in Europe thus far are very differentiated. With regards to the attraction of economic activities usually the existing differences between different economic regions are reproduced rather than shaping completely new conditions. Also the expectations of developing completely new integrated urban centers around stations in the urban periphery are rather ambitious. The paper questions the planning responses to HSR development in Chinese cities and investigates the institutional conditions that frame these responses. The authors explore how the plans for Chinese HSR station development account for their objectives and reflect on the potential of the station area planning by investigating the institutional parameters of urban development.     

Development of a Hybrid Photopolymer for Stereolithography

1 IntroductionRapid Prototyping (RP) was developed as a newmanufacture technique and considered a significant break-through in the field of manufacturing in the past 20years[1-4].The principle of RPis based on layer additivefabrication. Firstly, a three-dimensional object modelfromcomputer-aided design (CAD) is divided into manythinlayers by delaminatingsoftware .Thetwo-dimensionaldata of eachthinlayer control alaser beam,whichirradi-ates many materials like resin point-by-point ,and solid…     

Processing,structure, and property relationships in Nd-Fe-B magnets

Rare-earth permanent magnets, whose prototypical representative is Nd₂Fe₁₄B, are rapidly becoming established as important hard magnets because of their excellent intrinsic magnetic properties. Currently, however, the highest values for coercivity and energy product achieved in production are only 40% and 60%, respectively, of the theoretical values. Since coercivity and energy product are structure-sensitive properties, improving the microstructure is a major challenge. This article compares the microstructure-property relationships of Nd-Fe-B magnets as a function of processing condition.