A circulating current control scheme for multiple three‐level NPC inverter systems

In recent years, motor drive systems for steel rolling mills have been steadily increasing in capacity. In particular, the development of three‐level NPC (Neutral Point Clamped) inverters is now focusing on the replacement of cycloconverters. In order to satisfy such a requirement, in this paper a multiple three‐level NPC inverter system is proposed. The configuration consists of two three‐level NPC inverters with the same configuration connected in parallel by current limiting reactors. In this case, the circulating current flowing between the two three‐level NPC inverters must be controlled to prevent a decrease in the maximum output capacity. In particular, a new method for control of the circulating current is a major topic of discussion. The method is based on space voltage vector‐based PWM (Pulse Width Modulation) control for the three‐level NPC inverters and the circulating current is controlled by adjusting the output durations of the respective space voltage vectors. In this method the circulating current controller can be decoupled from the motor current controller. Therefore, it is possible to design the different controllers independently. In addition, the experimental results obtained using an induction motor show that the circulating current can be reduced to within 2% of the rated motor current when the motor current response exceeds 1000 rad/s. © 2001 Scripta Technica, Electr Eng Jpn, 136(2): 38–48, 2001     

First-Principles Study on the Grain Boundary Embrittlement of Metals by Solute Segregation: Part II. Metal (Fe,Al, Cu)-Hydrogen (H) Systems

The microscopic mechanism of grain boundary (GB) embrittlement in metals by hydrogen segregation (trapping) has been not well understood for many years. From first-principles calculations, we show here that the calculated cohesive energy of bcc Fe Σ3(111) and fcc Al(Cu) Σ5(012) symmetrical tilt GBs can be significantly reduced if many hydrogen atoms segregate at the GBs. This indicates that the reduction of the cohesive energy of the GB may cause the hydrogen-induced GB embrittlement in Fe, Al, and Cu. Considering the “mobile” effect of hydrogen during fracture, especially for the Fe system, more hydrogen atoms coming from solid solution state can segregate on the gradually formed two fracture surfaces and reduce further the cohesive energy. We suggest a new idea about the upper and lower critical stresses observed in the constant-load test of hydrogen-induced delayed fracture in high-strength steels; the upper critical stress is determined by the amount (density) of “immobile” hydrogen atoms segregated at the GB before fracture, and the lower critical stress is determined by the total amount (density) of immobile and mobile hydrogen atoms, the latter of which segregate on the two fracture surfaces during fracture.     

Triple‐junction effect and its electric field relaxation in three dielectrics

This paper analyzes the electric field distribution near a wedge‐like edge in arrangements consisting of three dielectrics using analytical and numerical methods. The electric potential behaves exponentially as rⁿ (r is the distance from the edge) near the edge, leading to an infinitely high field with decreasing r for all cases. The value of the analytically derived exponent n agreed well with that obtained from the numerical field calculations. It has also been demonstrated that rounded contact of the spacer with a zero contact angle can make the electric field constant without showing an exponential rise near the edge. © 2009 Wiley Periodicals, Inc. Electr Eng Jpn, 167(1): 1– 8, 2009; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20670     

Quantitative separation of antioxidant pigments in purple sea urchin shells using a reversed-phase high performance liquid chromatography

Sea urchin shells are generally discarded as food waste after removal of edible gonads, although they possess significant amount of polyhydroxylated naphtoquinone pigments having potent antioxidant property. In this study, separation and quantification of the pigment mixtures from purple sea urchin shells were performed using a C18 reversed-phase HPLC with isocratic elution of 50% mixture of solvent (A) formic acid: water (0.1: 100, v/v) and solvent (B) MeOH: acetonitrile (5: 9, v/v) at a flow rate of 0.5 mL/min. The pigment mixtures were separated into four major peaks in 30 min, which assumed to be spinochromes A, B and C and echinochrome A on the basis of UV-Vis absorption spectra obtained by a diode array detector. LC-MS analysis also supported these results by producing the predominant base peaks at m/z 221.1, 279.1, 265.1, and 263.1 corresponding to the pseudomolecular ions [M-H]⁻ of the respective compounds. The HPLC method also showed good correlations (r² > 0.98) between injected amounts of these pigments and peak areas recorded at 340 and 520 nm. These results indicated that the HPLC method developed in this study would be applicable for the separation and quantification of these major pigments in sea urchin shells.     

Studies on Epoxy Resin Film Coating by the Flame Spraying Method

The authors have shown that special formulations are required to give complete covering of steel surface (with no swelling, break away, cracks, etc) with flame sprayed film coating of epoxy resin. For this purpose, there should be minimum stress in the film, and it was concluded that treatments effective for this purpose involve adding adequate filler to reduce the thermal expansion coefficient, controlling the degree of cure, holding small closed pores in the film and semi-curing immediately after spray to keep the required tensile strength.     

Framework for Performance-Based Design of Building Structures

Abstract:   This article proposes a new framework for performance-based design (PBD) of building structures. This framework was proposed under the 3-year Japanese Government Comprehensive Research and Development Project on "Development of a New Engineering Framework for Building Structures" launched in the fiscal year of 1995. The primary objective of the project is to create a system in which the performance of buildings is clearly stated, and consumers, that is, occupants, are well informed of how their buildings will perform and how much it will cost to maintain their performance. The framework emphasizes the establishment of target performance, the performance evaluation, and the performance statement as the main three elements. It also stresses that an institutional framework and support systems need to be provided to enable PBD to be practiced efficiently. The implementation of the proposed framework is also expected to promote engineering innovation, progress in building engineering, and globalization. The new framework will also bring other benefits, such as improved design techniques, greater design flexibility, and international harmonization. It is also important for building structural performance to become one of the most important indexes for consumers to define a building's value. The Japanese building code was changed to the performance-based code, based in the clear and comprehensive manner proposed in this article. In the United States, "Vision 2000" ( SEAOC, 1995 ) was published, then many research activities were conducted simultaneously.     

Hydrothermal flames in supercritical water oxidation: investigation in a pilot scale continuous reactor

Hydrothermal flames at 25 MPa supercritical water environment were investigated using a 4800 ml reaction tower, in which the sapphire windows were fitted for optical access. Down flowing hydrothermal flames were observed for oxidation of 2-propanol when the reactor was fed with inlet organic concentration higher than 2 vol% and air ratio higher than 1.8. Flame temperature, as high as 1100 °C, was measured by means of a thermocouple and the temperature was found to be strongly influenced by air ratio. Effective and stable oxidation of organics with TOC removal rate of 99.9% was achieved. Dioxins were also decomposed with a ratio higher than 99.9%, within 1 min reaction time in this reactor configuration.