Crystallographic analysis of fatigue fracture initiation in 8Ni-0.1C martensitic steel

The present paper investigated characteristics of fatigue fracture behavior, particularly initiation stage of fatigue fracture (Stage I), in an as-quenched martensitic steel from microstructural and crystallographic points of view. The detailed crystallographic orientation analysis using EBSD revealed that block boundaries in lath martensite structure were the most preferential initiation sites for fatigue cracks. We found that incompatibility of plastic strains between adjacent blocks was the origin for the formation of initial fatigue cracks at block boundaries. Moreover, plastic deformation along {0 1 1} slip planes also played an important role on the transgranular crack propagation

Effect of hydrogen on evolution of deformation microstructure in low-carbon steel with ferrite microstructure

In this study, the deformation microstructure of hydrogen-charged ferritic-pearlitic 2Mn-0.1C steel was characterized using SEM-BSE, SEM-EBSD, TEM, and neutron diffraction. The microscopic mechanism of hydrogen-related quasi-cleavage fracture along the {011} planes was also discussed. It was found that hydrogen increased the relative velocity of screw dislocations to edge dislocations, leading to a tangled dislocation morphology, even at the initial stage of deformation (e = 3%). In addition, the density of screw dislocations at the later stage of deformation (e = 20%) increased in the presence of hydrogen. Based on the experimental results, it is proposed that a high density of vacancies accumulated along {011} slip planes by jog-dragging of screw dislocations, and coalescence of the accumulated vacancies led to the hydrogen-related quasi-cleavage fracture along the {011} slip planes

Strain localization and hydrogen-related fracture in martensitic steels investigated by combined digital image correlation and electron backscatter diffraction

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Improvement of resistance against hydrogen embrittlement by controlling carbon segregation at prior austenite grain boundary in 3Mn-0.2C martensitic steels

This study challenged to improve the resistance against hydrogen embrittlement by increasing the concentration of carbon segregated at prior austenite grain boundary (PAGB), XPAGB, in low-carbon martensitic steels. The specimens with/without carbon segregation treatment (Non-seg and Seg specimens, respectively) had almost the same microstructure, other than higher XPAGB in the Seg specimen. While the uncharged Non-seg and Seg specimens exhibited similar mechanical properties, the maximum stress of the hydrogen-charged specimen was much higher in the Seg specimen than that in the Non-seg specimen even when diffusible hydrogen contents were almost the same. In addition, the fraction of intergranular fracture surface was much smaller in the Seg specimen. Based on these results, we conclude that the segregated carbon suppressed the accumulation of hydrogen around PAGB by site competition and increased cohesive energy of PAGB, leading to the significantly improved resistance against hydrogen-related intergranular fracture

Improvement of resistance against hydrogen embrittlement by increasing carbon segregationat prior austenite grain boundary in low-carbon martensitic steels

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Dehydrocostus lactone, a naturally occurring polar auxin transport inhibitor, inhibits epicotyl growth by interacting with auxin in etiolated Pisum sativum seedlings

We have isolated germacranolide-type sesquiterpene lactones with an α-methylene-γ-lactone moiety, dehydrocostus lactone (DHCL), costunolide, santamarine, and a novel compound denoted artabolide [3-hydroxy-4,6,7(H)-germacra-1(10),11(13)-dien-6,12-olide] from oriental medicinal Asteraceae plants as novel naturally occurring inhibitors of polar auxin transport detected by the radish hypocotyl bioassay. To investigate the mode of action of natural sesquiterpene lactones on the inhibition of polar auxin transport as well as its relation to the growth of seedlings, the function of DHCL on growth and auxin dynamics in etiolated pea seedlings was studied intensively. DHCL reduced polar auxin transport in a dose-dependent manner together with the inhibition of the accumulation of mRNA of PsAUX1 and PsPIN1 genes encoding influx and efflux carrier proteins of auxin, respectively. DHCL applied to the apical hook region as a lanolin paste substantially inhibited elongation growth in the subapical region of epicotyls in intact etiolated pea seedlings, coupled with a significant reduction of endogenous levels of indole-3-acetic acid (IAA). DHCL also revealed the inhibition of IAA-induced cell elongation in etiolated pea epicotyl segments by affecting IAA-induced changes in the mechanical properties of cell walls. These facts suggest that germacranolide-type sesquiterpene lactones with an α-methylene-γ-lactone moiety affect the expression of PsAUX1 and PsPINs genes, and then inhibit polar auxin transport and reduce endogenous levels of IAA necessary for stem growth in etiolated pea seedlings. These compounds are also suggested to show the inhibitory effects on auxin action in pea stem growth

Three-dimensional crack propagation behavior in hydrogen-related fracture of high-strength martensitic steel

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Histone H4 Lys 20 Monomethylation of the CENP-A Nucleosome Is Essential for Kinetochore Assembly

SummaryIn vertebrate cells, centromeres are specified epigenetically through the deposition of the centromere-specific histone CENP-A. Following CENP-A deposition, additional proteins are assembled on centromeric chromatin. However, it remains unknown whether additional epigenetic features of centromeric chromatin are required for kinetochore assembly. Here, we used ChIP-seq analysis to examine centromere-specific histone modifications at chicken centromeres, which lack highly repetitive sequences. We found that H4K20 monomethylation (H4K20me1) is enriched at centromeres. Immunofluorescence and biochemical analyses revealed that H4K20me1 is present at all centromeres in chicken and human cells. Based on immunoprecipitation data, H4K20me1 occurs primarily on the histone H4 that is assembled as part of the CENP-A nucleosome following deposition of CENP-A into centromeres. Targeting the H4K20me1-specific demethylase PHF8 to centromeres reduces the level of H4K20me1 at centromeres and results in kinetochore assembly defects. We conclude that H4K20me1 modification of CENP-A nucleosomes contributes to functional kinetochore assembly

Integrative Annotation of 21,037 Human Genes Validated by Full-Length cDNA Clones

The human genome sequence defines our inherent biological potential; the realization of the biology encoded therein requires knowledge of the function of each gene. Currently, our knowledge in this area is still limited. Several lines of investigation have been used to elucidate the structure and function of the genes in the human genome. Even so, gene prediction remains a difficult task, as the varieties of transcripts of a gene may vary to a great extent. We thus performed an exhaustive integrative characterization of 41,118 full-length cDNAs that capture the gene transcripts as complete functional cassettes, providing an unequivocal report of structural and functional diversity at the gene level. Our international collaboration has validated 21,037 human gene candidates by analysis of high-quality full-length cDNA clones through curation using unified criteria. This led to the identification of 5,155 new gene candidates. It also manifested the most reliable way to control the quality of the cDNA clones. We have developed a human gene database, called the H-Invitational Database (H-InvDB; http://www.h-invitational.jp/). It provides the following: integrative annotation of human genes, description of gene structures, details of novel alternative splicing isoforms, non-protein-coding RNAs, functional domains, subcellular localizations, metabolic pathways, predictions of protein three-dimensional structure, mapping of known single nucleotide polymorphisms (SNPs), identification of polymorphic microsatellite repeats within human genes, and comparative results with mouse full-length cDNAs. The H-InvDB analysis has shown that up to 4% of the human genome sequence (National Center for Biotechnology Information build 34 assembly) may contain misassembled or missing regions. We found that 6.5% of the human gene candidates (1,377 loci) did not have a good protein-coding open reading frame, of which 296 loci are strong candidates for non-protein-coding RNA genes. In addition, among 72,027 uniquely mapped SNPs and insertions/deletions localized within human genes, 13,215 nonsynonymous SNPs, 315 nonsense SNPs, and 452 indels occurred in coding regions. Together with 25 polymorphic microsatellite repeats present in coding regions, they may alter protein structure, causing phenotypic effects or resulting in disease. The H-InvDB platform represents a substantial contribution to resources needed for the exploration of human biology and pathology