Influences of temperature and Sn-addition on microstructural evolution of Ag during FSW

ABSTRACT

The microstructural evolutions of pure Ag and Ag-0.75 wt-%Sn during rapid cooling friction stir welding (FSW) were examined. At the lower welding temperature of FSW conditions, the annealing twinning was highly suppressed and the microstructural evolution was dominated by the discontinuous dynamic recrystallisation (DDRX) via the high angle boundary (HAB) bulging. The fully recrystallised microstructure was remarkably finer than that formed through the frequent annealing twinning at the higher welding temperature. Moreover, the Sn-addition caused the HAB bulging due to the inhibition of dynamic recovery and decreased mobility of grain boundaries. With decreasing the ratio of the peak temperature to the recrystallisation temperature, the dominant grain refinement mechanism is implied to change from the annealing twinning to the DDRX.     

Basic design of 70-MW-class superconducting generators

The application of superconductivity technology to electric power apparatus is very important from the viewpoint of energy saving. Especially, the superconducting generators using superconductors as the field windings have many merits compared with conventional generators. Super-GM has been researching and developing 70-MW-class model machines since FY 1988 for a scheduled period of eight years, aiming at a 200-MW-class superconducting generator. This paper describes the basic specifications and designs of 70-MW-class superconducting generators by Super-GM and also describes the propriety of these basic specifications and designs.     

Relationship between coagulase toxin-type and drug susceptibility in Staphylococcus aureus strains isolated in all the Japanese National University Hospitals

Drug susceptibility of 430 Staphylococcus aureus strains isolated in 1991 from clinical specimens at all of the Japanese national university hospitals was evaluated in relationship with the epidemiological markers, namely, coagulase typing, and staphylococcal enterotoxins (SE) and toxic shock syndrome toxin 1 (TSST-1) production. There were five major methicillin-resistant Staphylococcus aureus (MRSA) groups in all the 252 MRSA strains: coagulase-type II-SEC + TSST-1- producing strains (II-SEC + TSST-1): 34.5%; coagulase-type II-no toxin-producing strains (II-): 15.4%; coagulase-type IV-SEA-producing strains (IV-SEA): 10.3%; coagulase-type II-SEA + SEC + TSST-1- producing strains (II-SEA + SEC + TSST-1): 8.7%; and coagulase-type III-no toxin-producing strains (III-): 7.1%. II-SEA + SEC + TSST-1 group was highly resistant to OFLX, whereas half of the other strain groups were sensitive to OFLX. Seventy-eight percent of the IV-SEA group was sensitive to FMOX, but there was no sensitive strain to FMOX in the II-SEA + SEC + TSST-1 group. More than 50% of the IV-SEA, III- and II-groups were sensitive to IPM, while the II-SEC + TSST-1 and II-SEA + SEC + TSST-1 groups were highly resistant to IPM. The III- and II-groups showed very good sensitivity to MINO, but the sensitivity to it of the II-SEA + SEC + TSST-1 group was very low. All of the strain groups were sensitive to ST except for the IV-SEA group. These results may provide useful information in the choice of antibacterial agents for MRSA infection.     

Transient changes in the power output from the concentration difference cell (dialytic battery) between seawater and river water

Experimental study on the concentration difference cell between seawater and river water (dialytic battery) has been made with special attention to the transient change in the power output. The cell consists of 59 compartments made with 29 ion-exchange membrane pairs, each of which has an effective area of 80 cm² per sheet. It has been found that the voltage drop across the load decreases exponentially with two different short and long time constants, of which values are about 50 and 800 s, respectively. Accordingly the power also decreased to about one fourth (from 259 to 68.9 mW/m² pair) after sufficient time passed. These transient behaviors have been successfully interpreted by the capacitor-type equivalent circuit model. From comparisons between the experimental and the model results, values of the internal resistance and two kinds of capacitor were determined, of which values were 114 Ω, 1.35 and 66.4 F, respectively. It was suggested that the short and long time constants came from charge double layers formed at the cathode and the anode, respectively. Measurements of potential difference between saline water compartments in the case with and without external current by reference electrodes showed that voltage losses occurred due to the concentration polarization near the ion-exchange membranes and the activation polarization at the electrode surfaces.     

Salt shock enhances the expression of ZrATP2, the gene for the mitochondrial ATPase beta subunit of Zygosaccharomyces rouxii

In the course of a study of cell wall proteins from the salt-tolerant yeast Zygosaccharomyces rouxii, a protein that increased its expression as the NaCl concentration of the culture medium increased was identified. Several degenerate primers were constructed based on partial amino acid sequences of this protein and were used in PCR amplification of a gene termed ZrATP2. The amino acid sequence deduced from nucleotide sequence of the gene revealed that ZrATP2 encodes the beta subunit of mitochondrial F1 ATPase. Northern blot analysis demonstrated that NaCl shock induced an elevation in ZrATP2 expression, which corresponded with the resumption of Z. rouxii cell growth after salt shock.