Influence of aluminum precursors on structure and acidic properties of hollow silica–alumina composite spheres,and their activity for hydrolytic dehydrogenation of ammonia borane

In this study, we investigated the influence of aluminum precursors on structure and acidic properties of hollow silica–alumina composite spheres, as well as their activity for hydrolytic dehydrogenation of ammonia borane. Hollow silica–alumina composite spheres were prepared via the sol–gel method using polystyrene particles as templates. Activities of the hollow spheres prepared using various aluminum precursors for hydrolytic dehydrogenation of ammonia borane were compared. The molar ratios of evolved hydrogen to ammonia borane introduced were 1.0, 2.8, 1.5, and 3.0 in the presence of the hollow spheres prepared using aluminum ethoxide, aluminum isopropoxide, aluminum tributoxide, and aluminum-tri-sec-butoxide, respectively. Hollow spheres prepared using aluminum precursors with branched alkyl groups exhibit more hydrogen evolution than those prepared using aluminum precursors with normal alkyl groups. From the result of solid-state ²⁷Al nuclear magnetic resonance spectra and temperature-programmed desorption of ammonia, 4-coordinated aluminum species are related to Brønsted acid sites, and highly dispersed aluminum species increase the number of Brønsted acid sites.     

Constitutive modeling for compacted bentonite buffer materials as unsaturated and saturated porous media

Bentonite has remarkable swelling characteristics and low permeability that enhance the stability of the buffer materials in repositories for the geological disposal of radioactive waste. It is necessary to apply reliable numerical simulation techniques to assess the safety and mechanical stability of repositories over a long period of time. Having a constitutive model that can describe the mechanical behavior of bentonite is key to such numerical simulations. This paper proposes an elasto-plastic constitutive model to describe the changes in the mechanical properties of bentonite due to saturation in the progress of a repository becoming submerged under groundwater. In the proposed model, the swelling index is formulated as a function of the degree-of-saturation to express not only the swelling behavior, but also the dependency of the degree-of-saturation on the dilatancy characteristics. The montmorillonite content is used as a material parameter to determine the normal consolidation line. The experimental results of swelling volume and swelling pressure tests in previous literature are shown to have been satisfactorily predicted by the proposed model.     

Negative effect of divalent metal cations on production of gassericin T, a bacteriocin produced by Lactobacillus gasseri, in milk-based media

A broad-spectrum bacteriocin named gassericin T is produced by Lactobacillus gasseri LA158 in MRS broth, but is minimally produced in milk-based media. Gassericin T production in MRS broth was specifically inhibited by adding divalent metal cations. Such inhibition of gassericin T production depended on the concentration of divalent cations. The addition of trisodium citrate dihydrate (TSC), which is a food-grade chelator of divalent cations, restored gassericin T production both in modified MRS broth containing divalent cations and in milk-based medium. In modified MRS broth, 50 mmol L⁻¹ TSC promoted an over-production of gassericin T. Furthermore, it was confirmed that TSC had a synergistic antibacterial effect with gassericin T. In this study, a cheese-whey-based medium, supplemented with proteose peptone, TSC, and Tween 80, was developed for gassericin T production. These results may contribute to the effective use of bacteriocins for food preservation.     

Copper-oxide whisker growth on tin–copper alloy coatings caused by the corrosion of Cu6Sn5 intermetallics

This paper reports the effect of corrosion caused by high temperature and humidity on pure tin and tin–copper alloy coatings. A new phenomenon was observed; the development of copper-oxide whiskers on tin–copper alloys plated on copper substrates (1–5 % copper content stored at 105 °C/100 % relative humidity). The copper-oxide whiskers showed similar growth properties to tin whiskers. We have made a model to understand the development of copper-oxide whiskers. Localized corrosion of the tin coating reaches the Cu₆Sn₅ intermetallic layer, and copper oxide accumulates after the corrosion of Cu₆Sn₅. The dilating SnO _x compresses and extrudes out the copper oxide in a whisker form.     

5—THE FINITE-DEFORMATION THEORY OF PLAIN-WEAVE FABRICS. PART III: THE SHEAR-DEFORMATION THEORY

The over-all shear deformation, that is, the combined deformation of biaxial tensile and shear deformation is considered generally, and a theory by which the mechanical behaviour of fabrics in this slate can be determined is presented.

Experiments are also described that were made to confirm the accuracy of these theories by using a new biaxial tensile tester for the measurement of the tensile and shearing properties of the fabrics and by using newly designed testing instruments for the measurement of yarn properties.

Good agreement between the theoretical and observed data is shown, and the theories appear to have considerable potentialities in the practical design of fabrics.     

Improvement of High-Temperature Performance of Zn-Sn Solder Joint

Pb-based solders are used as high-temperature solders in power semiconductor devices. Although the use of Pb is globally restricted, alternative materials cannot replace the Pb-based solder. This study proposes that the Pb-based solder can be replaced by Zn-Sn alloys. Die shear tests revealed that some Zn-Sn solder joints between Cu substrates had a higher shear strength between 300 K and 543 K than those between Fe-42Ni substrates. The microstructure of the Zn-Sn solder joints between Cu substrates showed network microstructures consisting of a Zn phase and ε-CuZn₅ phase and direct connection between the network microstructures and intermetallic compound layer. These morphologies of the high melting phase should improve the shear strength even at the elevated temperature of 543 K.     

Development of high‐efficiency switched reluctance motor

In this paper, several techniques of the efficiency improvement of SRM drives are described. One of these improvements is the optimization of applied voltage waveform. Drive efficiency is further increased by application of new low‐iron‐loss materials such as Super E‐Core brand steel strip. Another step of the efficiency improvement consists in optimization of components incurring iron and copper losses by using computer program PC‐SRD. As a result, the highest efficiency level achieved in the study was 94.3%. © 2007 Wiley Periodicals, Inc. Electr Eng Jpn, 162(2): 73–82, 2008; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20523