It is very difficult to obtain mechanical properties of oxide films formed on a
material in high temperature environments despite its importance of estimating material
degradation caused by such as thermal stress. Corrosion/oxidation tests were conducted for
pure titanium and titanium alloy in high temperature corrosive environments of wet air and
water vapor with hydrogen chloride at temperatures from 673 K to 973 K to look into basic
behavior of degradation and the growth of titanium oxide films. It was found that oxide films
were usually formed on the specimen surface and the growth was accelerated by the
corrosiveness of the environment. In order to examine mechanical properties and exfoliation of
corrosion products or oxide films formed on titanium and its alloy, tests of single particle
impact on the specimen surface with a glass bead were performed in high temperature
corrosive environments. The piling-up surfaces around impact craters were formed and
plastically strained. The oxide film formed on the metal surface was detached in a wide range
of the circumference and fractured a little far from the rim of the crater. Then fracture and
exfoliation stress of the oxide film were estimated by the calculation of impact energy and
fractured and detached areas. It was found that both the fracture and exfoliation stress of the
oxide films were different depending on the corrosive environment and chemical composition
of titanium alloy.
Cephonodes hylas, the coffee bee hawkmoth is a hawkmoth species with unique characteristics, such as larvae feeding on gardenia, overcoming the toxicity of its iridoid glycosides, diurnal adults, and transparent wings. Although C. hylas is a fascinating model for molecular biological research, genome sequence analysis-based genetic approaches to elucidate these peculiarities have not yet been undertaken. We successfully achieved de novo genome assembly at the chromosome level of C. hylas comparable to the Lepidoptera model organism, silkworm. Additionally, 16,854 protein-coding genes were annotated, and the constructed genome sequence and annotated genes were of the highest quality BUSCO completion compared to closely related species. Comparative genome analysis revealed the process of chromosomal evolution from the Bombycoidea ancestral (n = 31) genome and changes in turnover at the chromosome level associated with chromosomal fusion events, such as the rate of repetitive sequence insertion. These analyses were only possible because the genome was constructed at the chromosome level. Additionally, increased the nonsynonymous/synonymous rate (dN/dS) ratios were observed in multiple photoreceptor-related genes that were strongly associated with the acquisition of diurnal activity. Furthermore, tandemly duplicated expanded genes containing many digestive and other enzymes and larval midgut-specific expression were also confirmed. These genes may be involved in the metabolism of genipin, a toxin found in gardenias. Using the genome sequence of C. hylas determined at the chromosome level, we have successfully identified new insights into the chromosomal evolution of Bombycoidea, as well as the relationship between the genome sequence and its characteristic traits.
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