Preparation of single crystals of MoB2 by the aluminium-flux technique and some of their properties

Crystal growth of MoB₂ (R-3m;a _hex. = 0.30136(6) nm,c _hex. = 2.0961 (4) nm) from high-temperature aluminium solutions (1000 to 1500°C) has been investigated, and the optimum conditions for obtaining single crystals of this compound were examined. Starting with about 33 to 53 g of a mixture of molybdenum, boron and aluminium, in which the atomic ratio is 1 : 2.5 : 53.3 to 88.9, MoB₂ single crystals of about 1.5 mm in size were grown without being accompanied by any other crystal phases. The stoichiometry and the crystal structure were corroborated by chemical analysis and single-crystal X-ray diffractometry. The Vickers microhardness measured in the (001) plane is in the range 2170 to 2470 kg mm^–2. The oxidation of the crystal in air is examined by thermogravimetric and differential thermal analyses up to 1200°C.     

Analysis of dibenzothiophene metabolic pathway in Mycobacterium strain G3

The dibenzothiophene (DBT) metabolic pathway in Mycobacterium strain G3, which is classified as a desulfurizing microorganism with the 4S pathway, was analyzed. 2-Hydroxybiphenyl (HBP), which is an end metabolite in the DBT desulfurization reaction, and 2-methoxybiphenyl (MBP) were found in the reaction mixture, and the methoxylation pathway from HBP to MBP was clarified. Although the substrate in the methoxylation reaction was HBP, there was no relationship between expression of the methoxylation activity and that of the desulfurization activity. Then, 4,6-dimethyl DBT, 4,6-diethyl DBT and benzo[b]naphtho[2,1-d]thiophene were metabolized to their methoxy forms via the desulfurization pathway. We established the methoxylation pathway in Mycobacterium G3.     

Structome of Saccharomyces cerevisiae determined by freeze-substitution and serial ultrathin-sectioning electron microscopy

The cell structure has been studied using light and electron microscopies for centuries, and it is assumed that the whole structure is clarified by now. Little quantitative and three-dimensional analysis of cell structure, however, has been undertaken. We have coined a new word, 'structome', by combining 'structure' and '-ome', and defined it as the 'quantitative and three-dimensional structural information of a whole cell at the electron microscopic level'. In the present study, we performed structome analysis of Saccharomyces cerevisiae, one of the most widely researched biological materials, by using freeze-substitution and serial ultrathin-sectioning electron microscopy. Our analysis revealed that there were one to three mitochondria, ~220 000 ribosomes in a cell, and 13-28 endoplasmic reticula/Golgi apparatus which do not form networks in the cytoplasm in the G1 phase. Nucleus occupied ~10.5% of the cell volume; cell wall occupied ~17%; vacuole occupied ~5.8%; cytoplasm occupied ~64%; and mitochondria occupied only ~1.7% in the G1 phase. Structome analysis of cells would form a base for the post-genome research.     

Determination of back-pressure profile for forward extrusion using sequential approximate optimization

This paper proposes a method for determining optimal back-pressure profile in forging of aluminum alloy using a sequential approximate optimization (SAO). In forging, it is important to improve the mold filling for the product quality. In addition, it is preferable to produce a product with a minimum forming energy. To achieve these objectives simultaneously, a forging method with back-pressure profile is proposed. Here, the back-pressure profile implies that the back-pressure varies through the stroke. In this paper, a multi-objective optimization (MOO) problem is formulated. To improve the mold filling, an unfilled area is taken as the first objective function. Furthermore, a forming energy during the forging is taken as the second objective function. Numerical simulation in the forging is so expensive that the SAO using the radial basis function (RBF) network is adopted, and the pareto-frontier is identified with a small number of simulation runs. Based on the numerical result, the experiments are also conducted. It can be found from these results that, the back-pressure profile approach is valid for improving the mold filling as well as the forming energy.     

Application of photoreflectance to advanced multilayer structures for photovoltaics

Photoreflectance (PR) is a convenient characterization tool able to reveal optoelectronic properties of semiconductor materials and structures. It is a simple non-destructive and contactless technique which can be used in air at room temperature. We will present experimental results of the characterization carried out by means of PR on different types of advanced photovoltaic (PV) structures, including quantum-dot-based prototypes of intermediate band solar cells, quantum-well structures, highly mismatched alloys, and III–V-based multi-junction devices, thereby demonstrating the suitability of PR as a powerful diagnostic tool. Examples will be given to illustrate the value of this spectroscopic technique for PV including (i) the analysis of the PR spectra in search of critical points associated to absorption onsets; (ii) distinguishing signatures related to quantum confinement from those originating from delocalized band states; (iii) determining the intensity of the electric field related to built-in potentials at interfaces according to the Franz–Keldysh (FK) theory; and (v) determining the nature of different oscillatory PR signals among those ascribed to FK-oscillations, interferometric and photorefractive effects. The aim is to attract the interest of researchers in the field of PV to modulation spectroscopies, as they can be helpful in the analysis of their devices.     

Charge–discharge and high temperature reaction of LiCoO2 in ionic liquid electrolytes based on cyano-substituted quaternary ammonium cation

The charge–discharge performance of LiCoO₂ positive electrode was observed in a mixed electrolyte system consisting of two ionic liquids: cyano-substituted quaternary ammonium bis(trifluoromethane)sulfoneimide (TFSI) and a same-anion salt of 1-ethyl-3-methyl imidazolium (EMI). The positive electrode exhibited a discharge capacity rather close to the theoretical one when N,N,N,N-cyanoethyl trimethyl ammonium salt was applied. Differential scanning calorimetry (DSC) studies revealed that these electrolytes exhibited exotherm only around 260 °C, 50 °C higher than conventional carbonate-based electrolytes. This is the first attempt to reveal the thermal stability of ionic liquid electrolyte under a practical situation.     

Modification of HPLC conditions for the determinations of raw materials, intermediates and subsidiary colors in 5 kinds of food azo colors

Modification of HPLC conditions for the determinations of raw materials, intermediates and subsidiary colors (organic impurities) in 5 kinds of food azo colors were studied in order to analyze them simply and rapidly. The organic impurities were determined by HPLC using L-column ODS and a gradient system (0.02 mol/L ammonium acetate solution for 10 min, and a gradient with a mixture of acetonitrile and water (7:3)). The organic impurities in 163 samples of azo colors subjected to inspection in fiscal year 1999 were determined under the proposed HPLC conditions. It was found that the contents of organic impurities in 163 samples were less than the limit of Japan's Specifications and Standards for Food Additives, 7th Edition.     

Carbon nano-fiber interlayer that provides high catalyst utilization in direct methanol fuel cell

The introduction of a carbon nano-fiber (CNF) interlayer to the interface between the carbon paper and the catalyst layer was investigated for providing a highly active catalyst layer with PtRu nano-particles on it for the direct methanol fuel cell (DMFC) anode. A precipitation method was used for applying the CNF layer and the catalyst layer. The effects of the loadings of the CNF and the catalyst on the DMFC power generation were evaluated. The CNF interlayer covered the large openings of the carbon paper resulting in a dense and smooth surface. The PtRu black catalyst prepared on the surface of the CNF layer provided a higher power density of DMFC than that obtained by using carbon black, suggesting that the dense and crackless surface of the CNF layer reduced the catalyst loss that leaks into the crack and increases the active reaction sites on the anode surface.