Background values for evaluation of heavy metal contamination in sediments

The contamination of sediments can be evaluated from comparison of the current concentration with the estimated background value. Although it is known that grain size affects background concentrations, there have been difficulties in evaluating this effect. The specific surface area of sediments, which can be calculated from the grain size distribution, is introduced as a property index for correlation of background values. The results show that for sandy-to-sandy silt sediments, the background values of metals are expressed in terms of fines content, which can be correlated with the corresponding specific surface area. However, for silty clay or clayey silt sediments, which would have a high metal retention capacity, the level of the background may be constrained by the relatively low concentrations of metals in seawater. Finally, background levels of Zn, Cu and Pb are presented.     

Stress intensity factors for cracks initiated from a center-holed plate with unsymmetrical lengths under tension

The values of stress intensity factors of unsymmetrical cracks initiated from hole edges under tension were calculated in a center-holed plate, that is a plate having a hole in the center of a front face. The correction factor for stress intensity in the case of the holed plate with cracks was compared with that of a center-cracked plate whose crack length was equal to the total of the hole diameter and the lengths of the cracks in the case of the holed plate. In the present study, to understand the variation of the stress intensity factor, counterplots of the stress intensity factor K_I and the correction factor F_I are employed. Also, the variation of ratio R_F of correction factors between the holed plate with crack and the center-cracked plate were investigated. Where non-dimensional hole diameter a/W is smaller than 0.2, the ratio R_F is less than 1.1 after crack growth length c/W reaches 0.1. Where, 2a, 2c and 2W are hole diameter, the growth length of the crack from hole edge, and plate width, respectively. Therefore, the stress intensity factor for cracks initiated from a holed plate can be approximated within 10% error to that of a center-cracked plate where a/W is smaller than 0.2, though the unsymmetrical cracks are initiated from the edges. Where a/W is larger than 0.3, R_F becomes larger than 1.1 in the wide range of c/W.     

A new method of damping harmonic resonance at the DC link in a large‐capacity rectifier‐inverter system

This paper proposes a new method of damping harmonic resonance in the DC link of a large‐capacity rectifier‐inverter system, such as in rapid‐transit railways. A voltage‐source PWM converter is connected in series to the DC capacitor of the rectifier through a matching transformer, acting as a damping resistor to the DC capacitor current. No filters are needed to extract harmonic components from the DC capacitor current. This results in a quick response and highly stable damping. The relationship between the control gain of the PWM converter and the required rating is theoretically discussed. We show that the required rating is less than one‐thousandth of that previously proposed. In particular, regenerating the power consumed by the PWM converter is very important because of the large power in practical systems. Normally, an additional PWM inverter is connected to the DC bus of the PWM converter to regenerate the consumed power. The additional inverter regenerates the DC power to the AC source through a transformer. This method, however, makes the damping circuit complex, thus the proposed method for the DC‐link harmonic resonance is less practicable. In this paper, a simple and novel scheme that utilizes the DC‐link voltage of the rectifier as a DC source for the PWM converter is proposed. The excellent practicability of the proposed damping method with the novel regenerating scheme is confirmed using digital computer simulation. © 2003 Wiley Periodicals, Inc. Electr Eng Jpn, 144(2): 53–62, 2003; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10172     

Metal electrodes bonded on solid polymer electrolyte membranes (SPE)—The behaviour of platinum bonded on SPE for hydrogen and oxygen electrode processes

The electrochemical characteristics of a platinum electrode directly bonded to one side of a solid polymer electrolyte membrane (Pt-SPE) were studied. Current-potential relations of hydrogen and oxygen adsorbed on Pt-SPE were observed to be similar to those on a platinum metal electrode independently of the presence/absence of electrolytic solution at the platinum side of Pt-SPE. Hydrogen evolution, hydrogen ionisation, and oxygen reduction were examined at the condition that the side at the platinum of Pt-SPE was free from liquid but filled with the gases concerned     

Microcomputer control for an industrial sewing machine

The application of the microcomputer to various industrial machinery or equipment is expanding. The sewing industry is no exception to this trend, positively employing microcomputers for more advanced automation, labour saving and further industrialization. To satisfy recent needs, a sewing machine motor equipped with eddy current variable-speed clutch, LIMI-STOP Z, was developed. The LIMI-STOP Z features, besides a friction-free low inertial clutch used instead of the conventional friction type clutch, the use of a 4-bit microcomputer in the control system. This paper describes the principle, composition and functions of the LIMI-STOP Z.     

The effects of stacking faults on the electrical properties of a high voltage power transistor

High voltage power transistors were produced using epitaxially grown Si wafers which contain many stacking faults in base region. The reverse biased characteristics of the emitter-base and the base-collector junctions of these transistors showed “soft” breakdown under a sufficiently high reverse bias. A detailed analysis of the effect by stacking faults was carried out with a scanning electron microscope (SEM). It was observed that the junctions of the transistors are not uniform by the stacking faults.