The effect of contact pressure on fretting fatigue behavior has been studied using a high strength steel and a Ti-6Al-4V alloy. In steel, at higher stress amplitude, the fretting fatigue life decreased monotonously with increasing contact pressure. At lower stress amplitude, it exhibited a minimum at a low contact pressure and a maximum at an intermediate contact pressure, then decreased again and became constant at high contact pressures. The fretting fatigue strength at 107 cycles was high at an intermediate contact pressure. In titanium alloy, the fretting fatigue life showed a similar contact pressure dependence. The frictional force increased monotonously with increasing contact pressure. The initiation site of the main crack depended on the contact pressure and had a close relation to the width of stick region at the fretted area. The contact pressure dependence was discussed in terms of stress concentration at the fretted area.
For carotenogenesis, two biosynthetic pathways from phytoene to lycopene are known. Most bacteria and fungi require only phytoene desaturase (PDS, CrtI), whereas land plants require four enzymes: PDS (CrtP), ζ-carotene desaturase (ZDS, CrtQ), ζ-carotene isomerase (Z-ISO) and cis-carotene isomerase (CrtISO, CrtH). The gene encoding Z-ISO has been functionally identified in only two species, Arabidopsis thaliana and Zea mays, and has been little studied in other organisms. In this study, we found that the deduced amino acid sequences of Arthrospira Z-ISO and Euglena Z-ISO have 58% and 62% identity, respectively, with functional Z-ISO from Arabidopsis. We studied the function of Z-ISO genes from the cyanobacterium Arthrospira platensis and eukaryotic microalga Euglena gracilis. The Z-ISO genes of Arthrospira and Euglena were transformed into Escherichia coli strains that produced mainly 9,15,9′-tri-cis-ζ-carotene in darkness. In the resulting E. coli transformants cultured under darkness, 9,9′-di-cis-ζ-carotene was accumulated predominantly as Z-ISO in Arabidopsis. This indicates that the Z-ISO genes were involved in the isomerization of 9,15,9′-tri-cis-ζ-carotene to 9,9′-di-cis-ζ-carotene in darkness. This is the first functional analysis of Z-ISO as a ζ-carotene isomerase in cyanobacteria and eukaryotic microalgae. Green sulfur bacteria and Chloracidobacterium also use CrtP, CrtQ and CrtH for lycopene synthesis as cyanobacteria, but their genomes did not comprise Z-ISO genes. Consequently, Z-ISO is needed in oxygenic phototrophs, whereas it is not found in anoxygenic species.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.