Development of Reference Shunt for Short‐Time Alternating High Current Tests and Study of Measuring System

Short‐circuit tests for power circuit breakers and others require alternative short‐time current measurement, from a few kA to over several tens kA. However, the reference measurement system as a national standard or a specified secondary standard instrument to directly perform comparative test as a complete calibration test in high current class has not yet been established globally. The Japan Short‐Circuit Testing Committee (hereinafter referred to as “JSTC”) has therefore developed a shunt resistor that can be used as a standard instrument for high current measurement. Reference system using this shunt resistor is also considered by JSTC. The performance of the newly developed shunt resistor has been checked through several methods, such as resistance measurement, high power current test, high frequency current test, temperature rise test, and interference test. The results of the tests proved satisfactory performance. Resistance of the shunt resistor before and after the tests was invariant and stable. This makes the shunt resistor adequate for a reference in practical use. In addition, evaluation of uncertainty of the whole reference system including this shunt resistor satisfactorily fulfills the requirements of IEC 62475 edition 1.0, 2010.     

Effects of Bismuth Sesquioxide on the Characteristics of ZnO Varistors

The nonlinearity of ZnO varistors is significantly influenced by the Bi₂O₃ and Sb₂O₃ contents, as well as by the phase composition of the Bi₂O₃. Degradation of the current-voltage characteristics due to the applied voltage is not always lowered by the β—γ transition of the Bi₂O₃ phase. Lattice parameter determinations and stress analyses suggest that the Bi₂O₃-rich phase in multigrain junctions causes mechanical strain at the grain boundary which may play an important role in the current-voltage characteristics of ZnO varistors.     

Synthesis of bismuth-based high-Tc superconducting fibres by using sodium alginate as a polyelectrolyte

The thermal pyrolysis processes and solid-state reactions in the synthesis of bismuth-based high-Tc superconducting fibre obtained by using sodium alginates are studied. This alginate is a polyelectrolyte and has not only an excellent ion-exchange property but also a gelation to synthesize long fibrous precursors. We first determined the optimum conditions to promote ion-exchange of this polyelectrolyte which yields high contents of metal ions in the precursor. The thermal pyrolysis of a precursor was studied by DTA and IR absorption. On the basis of the DTA and XRD, the solid-state reactions associated with the formation of the 2 2 1 2 phase were revealed. Our method can be applied easily to synthesize Ag-sheathed fibre having an improved tensile strength. This revised version was published online in November 2006 with corrections to the Cover Date.     

Abalone (Hariltis discus): Seasonal Variations in Chemical Composition and Textural Properties

Seasonal changes in adenosine 5′-triphosphate, total free amino acids, and total oligopeptides in abalone meat were analyzed. Levels were higher in summer and lower in winter. In both seasons, the most abundant free amino acid was taurine followed by arginine, glycine, glutamine, and glutamic acid. The largest peptide-bond amino acid was glutamic acid + glutamine. The collagen content decreased in summer and increased in winter. The breaking stress values of the meat were low in summer and high in winter, indicating that summer abalone would be more tender. Scanning electron microscopy revealed the collagen network was more compact in winter.     

Effects of Antimony Oxide on the Characteristics of ZnO Varistors

The breakdown voltage, the upturn voltage, and the nonlinearity of the ZnO varistors are significantly influenced by the Sb₂O₃ and SiO₂ contents, as well as by the β→γ transition of the Bi₂O₃ phase. The lattice parameter of spinel is influenced by the coexisting Bi₂O₃ phase. Antimony oxide disperses into the powders of ZnO and other additives in the early stage of sintering, and finally gathers again as particles of spinel which may play an important role in the improvement of the nonlinearity by stressing the interfaces of two ZnO grains.     

Gas-sensor properties of SnO2 films implanted with gold and iron ions

SnO₂ gas-sensor films were modified by implantation of gold and iron ions. The change in electrical resistivity of the films caused by inflammable gases, H₂, CO, CH₄ and C₂H₅OH, was measured in the temperature range 100–500°C, and compared to non-implanted films. The morphological changes caused by gold and iron ion implantation were also investigated by atomic force microscopy. After ion implantation and annealing at 600°C, the sensitivity to H₂ and CO gas was found to increase, and the dynamic range of the sensitivity to ethanol was improved. The sensitivity to CH₄ was low before and after ion implantation. Fe₂O₃ (3%SnO₂) film was also modified by gold ion implantation for comparison. This revised version was published online in July 2006 with corrections to the Cover Date.     

Ultra-High-Speed Performance of Ball Bearings and Annular Seals in Liquid Hydrogen at Up to 3 Million DN (120,000 rpm)©

The ultra-high-speed performance of a hybrid ceramic 25-mm-bore ball bearing, as well as that of floating-ring seals with a sealing diameter of 30 mm, was determined in liquid hydrogen at speeds to 120,000 rpm, 3 million DN, under thrust loads to 3,140 N and sealed pressures to 1.7 MPaG. The bearings had Si₃N₄ balls and a single outer land-guided retainer. The hybrid ceramic bearing exhibited excellent performance at high load, contrasting with the seized all-steel bearing; however, the ceramic balls developed superficial micro-cracks due to frictional heating. Effective cooling of the bearing was achieved by increasing the jet speed through the nozzles. The bearing power loss drastically increased with increasing speed and cooling flow rate. The critical load capacity without bearing damage was also evaluated. Furthermore, the sealing performance of the one-ring seal was superior to that of the two-ring seal in preventing the sealing ring seizure against the runner.     

MILK BASIC PROTEIN ENHANCES THE BONE STRENGTH IN OVARIECTOMIZED RATS

We studied the effects of milk basic protein (MBP) on bone metabolism in ovariectomized (OVX) rats. Five‐week‐old female Sprague‐Dawley rats were ovariectomized and fed a low‐calcium diet (0.009% Ca) for 5 weeks. The OVX rats were divided into three experimental groups: Control group (20% casein), MBP‐L group (19.9% casein, 0.1% MBP), and MBP‐H (19% casein, 1% MBP) of six animals. The rats were fed each experimental diet for 3 weeks. The bone breaking strength and energy of femur in the MBP‐H group were significantly higher than those in the control group. The bone breaking energy of femur in the MBP‐L group was also significantly higher than those in the control group. There were no differences in the amount of femoral calcium and phosphorus among the three groups, however, the amounts of femoral proline, hydroxyproline and hydroxylysine (typical amino acids of collagen) in the MBP groups were significantly higher than those in the control group. These data indicate that MBP in the whey protein increases the amount of the bone collagen and enhances the bone strength.