Interfacial Reaction between Zn-Al-Based High-Temperature Solders and Ni Substrate

The Zn-Al(-Cu) eutectic alloys (melting point 381°C) are candidates for use as Pb-free high-temperature solders as a substitute for Pb-based solders, which are suitable for severe working environments such as the engine room of hybrid vehicles equipped with an inverter system as well as a heat engine. In this study, the interfacial reaction between Zn-Al(-Cu) alloys and the Ni substrate during soldering, aging, and thermal cycling was investigated. Semiconductor chips and Ni substrates were soldered with Zn-Al(-Cu) alloys at various temperatures under a nitrogen atmosphere. The soldered assemblies were then heat-treated at 200°C and 300°C to examine the microstructural evolution at the soldered interface. The effect of severe thermal cycles between −40°C and 250°C in air on the microstructure and fracture behavior at the solder joint was investigated. Even after a 1000-cycle test, the thickness of the Al₃Ni₂ layer formed at the interface between the Zn-Al-based solder and the Ni substrate, which is responsible for the damage of the soldered assemblies, was quite small.     

Band-edge luminescence from SrTiO3: No polaron effect

We studied the band-edge photoluminescence (PL) of electron-doped SrTiO₃ and strongly photoexcited SrTiO₃ crystals. Two band-edge PL peaks are clearly observed at low temperatures. The PL peak energies coincide with the high- and low-temperature onsets of the optical absorption, corresponding to the phonon-assisted band-to-band optical transition. This result is the direct evidence that the free electrons and holes exist in the conduction and valence bands, and radiative recombination of free electrons and free holes causes the band-edge PL.     

Controlled Crystallization of Calcite Under Surface Electric Field Due to Polarized Hydroxyapatite Ceramics

We examined effects of surface electric fields for the crystallization of calcite on polarized hydroxyapatite ceramics with and without polyacrylic acid (PAA) as soluble additive. Both on negatively and positively charged surfaces without PAA, the only precipitates were rhombohedra calcite crystals with the face of the {10.4} plane favorably oriented parallel to the surfaces. This oriented growth was explained by the nucleation theory in the presence of an external electric field. However, the addition of PAA drastically changed the situation of the calcite crystals, i.e., the crystallites were the hemispheric aggregates of calcite needles with a facetted rhombohedral {10.4} end face and flat island-shaped aggregates of ones with a rough (00.1) end face having a triangular shape. The calcite needles grew along the crystallographic [00.1] axis. This oriented growth was explained by epitaxy on the PAA–Ca²⁺ complexes adsorbing on the surfaces. The morphology of the PAA–Ca²⁺ complex assemblies adsorbing on the surfaces before the calcite nucleation was an important factor to control the structure of calcite aggregates formed following. This morphology was controlled by properties of the surface electric field and the spatial distribution of the negatively and positively charged sites in the PAA–Ca²⁺ complexes.     

Ultrasound-assisted capillary microreactor for aqueous–organic multiphase reactions

A simple capillary microreactor was tested as a potential reactor to carry out a multiphase reaction. The hydrolysis of benzyl chloride in a biphasic system was investigated. The capillary microreactor was irradiated by 28 kHz ultrasound at different temperatures, capillary lengths and phase flow rates. It was found that the combination of microreactor technique and the ultrasound irradiation provides a promising protocol for process intensification. Under sonication conditions, higher conversions were obtained compared to silent conditions. The presence of ultrasound has affected the multiphase slug size and promoted better internal circulation within these slugs. Similar reactivities were noticed at higher temperature for both sonication and silent conditions.     

Level set‐based topology optimization targeting dielectric resonator‐based composite right‐ and left‐handed transmission lines

In the last decade, metamaterials have been gaining attention and have been investigated because of their unique characteristics, which conventional materials do not have, such as negative refraction indexes. However, it is sometimes difficult to design metamaterials on the basis of experience and theoretical considerations because the relationship between their electromagnetic characteristics and structure is often vague. A mathematical structural design methodology targeting metamaterials may therefore be useful for expanding the engineering applications of metamaterials in industry. In this paper, a new level set‐based topology optimization method is proposed for designing composite right‐ and left‐handed transmission lines, each of which consists of a waveguide and periodically located dielectric resonators. Such transmission lines function as a fundamental metamaterial. In the proposed method, the shape and topology of the dielectric resonators are represented by the level set function, and topology optimization problems are formulated on the basis of the level set‐based representation. Copyright © 2011 John Wiley & Sons, Ltd.     

Expression and purification of recombinant human annexin A2 in Pichia pastoris and utility of expression product for detecting annexin A2 antibody

Annexin A2, a Ca2+-dependent phospholipid binding protein, is abundantly expressed in various human organs, which exists as either a membrane-associated, cytosolic or soluble form in serum. We constructed expression systems for recombinant human annexin A2 (rhA2) using Pichia pastoris. The systems are designed to secrete rhA2 as either the N- or C-terminally His6-tagged form to facilitate purification. Both types of rhA2 were overexpressed, but in the N-terminal-truncated form as revealed from the results of N-terminal amino acid sequencing and Western blotting. Therefore, further purification of N-terminally His6-tagged rhA2 was not feasible because of the removal of the N-terminal His6-tag sequence. C-terminally His6-tagged rhA2 was expressed as either a glycosylated or a nonglycosylated form, and the nonglycosylated form was purified using the combination of nickel-immobilized affinity, concanavalin A and cation exchanged column chromatographies. The solid-phase binding of rhA2 was examined by enzyme-linked immunosorbent assay (ELISA), which revealed the specific reactivity of rhA2 against an anti-annexin A2 monoclonal antibody. These results suggest that the expression system using P. pastoris is useful for the preparation of rhA2 that is applicable to the ELISA detection of the anti-annexin A2 antibody.     

Experimental and numerical evaluation of bearing capacity of steel plate girder affected by end panel corrosion

The present study deals with the effect of uniform and non-uniform local corrosion damages at the bearing stiffener and nearby web on the bearing capacity of plate girder. Five plate girder ends simulated with different uniform and non-uniform types of corrosion damage, at the base of the bearing stiffener are used in the experimental program. The experimental results are modeled and verified on a Finite Element (FE) software ABAQUS, considering shell-solid coupling elements formulation. The study is further extended to various damage cases i.e., stiffener damage, stiffer plus web damages etc. considering different damage heights and residual thicknesses. The study concludes that minimum thickness within any damage height may be used to simulate the corrosion damage in a FE analysis. At the end, some empirical relationships are also proposed to estimate the bearing strength of the plate girder affected by the local corrosion damage at plate girder end.     

Survey of a catalyst system for living cationic polymerization of glucose‐carrying vinyl ethers with acetyl and isopropylidene protecting groups

This study concerns the living cationic polymerization of two vinyl ethers (VEs) having pendant glucose residues, in which the hydroxyl groups are protected by acetyl and isopropylidene functions. Living cationic polymerization of VE having an acetyl‐protected glucose was achieved by employing an initiating system consisting of the CF₃COOH adduct of isobutyl VE (IBVE) and ethylaluminium dichloride in the presence of an added base at 0 °C. In contrast, the use of the HCl adduct of IBVE in conjunction with zinc iodide at ?15 °C was more suitable for the controlled polymerization of VE having an isopropylidene‐protected glucose. Polymers obtained under these reaction conditions had narrow molecular weight distributions (M_w/M_n ～ 1.1) and controlled molecular weights. © 2001 Society of Chemical Industry