Synthesis of an AlN Polycrystalline Bulk Layer and Nanotubes by Using NH3 and Bi

A bulk layer of aluminum nitride (AlN) polycrystals was synthesized on a boron nitride crucible surface by heating Al chunks with 5 mol% of bismuth at 1273 K for 3 h under NH₃ gas flow. The fragments of the layer were characterized by X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. The platelet grains of AlN with a size of 0.1–1.0 μm and having preferred orientation of the c -axis perpendicular to the layer were formed at the crucible side. Nanotubes 6–15 μm long and about 20–100 nm thick grew on the gas phase side of the layer.     

A PAM control method for a matrix converter based on a virtual AC/DC/AC conversion method

In this paper, a novel control method for a matrix converter is proposed. The proposed method is a PAM (Pulse Amplitude Modulation) control method based on a virtual AC/DC/AC conversion method. Output voltage amplitude is controlled by controlling a virtual DC link voltage with a virtual rectifier. Output frequency is controlled by a virtual inverter. First, the proposed method is explained. Next, the validity of the proposed method is confirmed through simulation and experiment using a 750‐W prototype matrix converter. Moreover, various characteristics of the proposed method and conventional virtual AC/DC/AC method are compared through experiment. As a result of the experiment, it has been understood that total harmonic distortion of output current and common‐mode voltage can be reduced compared with the case of using a conventional virtual AC/DC/AC conversion method. © 2008 Wiley Periodicals, Inc. Electr Eng Jpn, 166(4): 88–96, 2009; Published online in Wiley InterScience ( www.interscience. wiley.com ). DOI 10.1002/eej.20601     

Preparation of Cu2ZnSnS4 thin films by sulfurizing electroplated precursors

Cu₂ZnSnS₄ (CZTS) thin films were prepared by sulfurizing precursors deposited by electroplating. The precursors (Cu/Sn/Zn stacked layers) were deposited by electroplating sequentially onto Mo-coated glass substrates. Aqueous solutions containing copper sulfate for Cu plating, tin sulfate for Sn plating and zinc sulfate for Zn plating were used as the electrolytes. The precursors were sulfurized by annealing with sulfur at temperatures of 300, 400, 500 and 600 °C in an N₂ gas atmosphere. The X-ray diffraction peaks attributable to CZTS were detected in thin films sulfurized at temperatures above 400 °C. A photovoltaic cell using a CZTS thin film produced by sulfurizing an electroplated Sn-rich precursor at 600 °C exhibited an open-circuit voltage of 262 mV, a short-circuit current of 9.85 mA/cm² and an efficiency of 0.98%.     

Effect of blending on liquefaction of coals

After solvent extraction of Taiheiyo, Miike and Balmer coals using wash oil under nitrogen atmosphere at 370 °C for 30 min, the extraction yield is always within the additivity law. Further studies used Yallourn, Soyakoishi, Taiheiyo, Horonai, Miike, Shin Yubari, Balmer coals and their blends which were hydrogenated in tetralin, wash oil or creosote oil, with or without catalyst, at 400–450 °C under 10 or 3 MPa of initial hydrogen pressure. When hydrogen is available, the additivity law exists for blended coals, but when the hydrogen supply is deficient, the experimental conversion of blended coals is always lower than calculated conversions. This may be due to the faster consumption of the hydrogen by more reactive coals and thus the less reactive coals were unable to react with hydrogen.     

Correlation of reactivity to hydrogenation and chemical structure of lignites

Three North Dakota lignites with almost the same percentage carbon have been used to determine the relation between chemical structure and reactivity to hydrogenation. Average structural indices of the lignites were estimated using the pyridine-soluble products after alcohol-alkali treatment, the structural indices obtained at various reaction times being extrapolated to zero reaction time. Hydrogenation was influenced by the average structure, with the lignite having higher aromaticity, higher molecular weight of the pyridine extract from the alcohol-alkali reaction product, larger aromatic ring size and lower content of aliphatic structure, showing a smaller degree of conversion.     

HEXHOOP: Modular Templates for Converting a Hex-Dominant Mesh to an ALL-Hex Mesh

This paper presents a new mesh conversion template called HEXHOOP, which fully automates a con-version from a hex-dominant mesh to an all-hex mesh. A HEXHOOP template subdivides a hex/prism/pyramid element into a set of smaller hex elements while main-taining the topological conformity with neighboring elements. A HEXHOOP template is constructed by assembling sub-templates, cores and caps. A dicing template for a hex and a prism is constructed by choosing the appropriate combination of a core and caps. A template that dices a pyramid without losing conformity to the adjacent element is derived from a HEXHOOP template. Some experimental results show that the HEXHOOP templates successfully convert a hex-dominant mesh into an all-hex mesh. ID="A1" Correspondence and offprint requests to: K. Shimada, Department of Mechanical Engineering, Carnegie Mellon University, 5000 Forbes Avenue, Pittsburgh, PA 15213–3890, USA. E-mail: shimada@cmu.edu     

Nonsolvent coal hydrogenation at short contact time

Yields and properties of products on hydrogenation of Japanese and Australian coals have been studied using an autoclave equipped with a magnedrive device at temperatures of 500–600 °C and hydrogen pressure 4.9–14.7 MPa (gauge) in the absence of solvent. Optimum contact time, at which maximum extraction yield was observed, shifted from 15 s to a few seconds with increasing reaction temperature and hydrogen pressure. The extracts derived from both coals reveal similar structural parameters.