Copyright (c)JCPDS-International Centre for Diffraction Data

ABSTRACT This paper describes the effect of renitriding for hot work die steel. We noticed a decrease of compressive residual stress on the nitrided die surface during thermal fatigue process. X-ray stress measurement was used to detect the decomposition of nitride layer on hot work die steel (H13). As a result, compressive residual stress decreased gradually during the thermal fatigue test, almost restoring to the pre-test level by renitriding. The number of cracks decreased with the frequency of test by surface removal effect of shot peening while renitriding. Comparing the renitrided specimen with non renitrided specimen (single nitride), the number of cracks had decreased. 1.INTRODUCTION On the surface of hot work die, such as die-casting die, heat cycles are applied during the operation. Then, the cracks occurred due to thermal stresses caused by thermal cycles. To extend die-casting die life, nitriding is often applied to the die surface 1) . Even with nitriding, the nitride layer is damaged by heat during the die-casting operation. Thus, if renitriding will be available with the detecting damaged layer quantitatively, extension of die life can be expected. On the other hand, high compressive residual stress about -900MPa is caused on the surface of hot work die steel (AISI-H13) by nitriding. And the reheating decreases the residual stress 2) . We noticed the compressive residual stress, and tried to detect decomposition of nitride layer in thermal fatigue process by X-ray stress measurement. And repair effect of nitride layer by renitriding with shot peening was investigated. During the thermal fatigue test, renitriding was applied several times and changes of residual stress and half-value breadth were measured. After the test, distribution of residual stress, maximum crack length and number of cracks were measured

DNA Microarray Analysis of Redox-Responsive Genes in the Genome of the Cyanobacterium Synechocystis sp. Strain PCC 6803

Whole-genome DNA microarrays were used to evaluate the effect of the redox state of the photosynthetic electron transport chain on gene expression in Synechocystis sp. strain PCC 6803. Two specific inhibitors of electron transport, 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU) and 2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone (DBMIB), were added to the cultures, and changes in accumulation of transcripts were examined. About 140 genes were highlighted as reproducibly affected by the change in the redox state of the photosynthetic electron transport chain. It was shown that some stress-responsive genes but not photosynthetic genes were under the control of the redox state of the plastoquinone pool in Synechocystis sp. strain PCC 6803