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Grain boundaries are important microstructures in metallic materials, and dislocation nucleation on grain boundaries plays a crucial role in material deformation. Studies on P segregation on grain boundaries typically focus on segregation behavior at substitution or interstitial positions. Less attention is given to the interaction of a certain amount of P with dislocation nucleation and grain boundary structural units during deformation. Previous deformation mechanism studies often qualitatively determine mechanisms, struggling to quantitatively explain their roles. This paper offers an atomic mechanism for grain boundary dislocation nucleation, aiding in understanding of the effect of P segregation in BCC Fe on mechanical properties. In this paper, a large-scale atomic/molecular massively parallel simulation (LAMMPS) program was employed. It investigated the effect of P segregation in BCC Fe grain boundary on the tensile deformation behavior. Binary Fe-P embedded atom potential was used for the calculation of stress-strain curves and dislocation activation energy densities. The analysis of P segregation behavior on different grain boundary structures and the effect of temperature was conducted using visual analysis software (OVITO.3.10). To illustrate the elastic-plastic component of the strain during loading, a set of kinematic parameters based on continuum medium mechanics was employed. The atomic deformation tensor of the deformation gradient was calculated using the nearest-neighbor table approximation of the continuum medium field around each atom. Additionally, the mechanisms of dislocation nucleation and twinning were discussed for the symmetrically inclined grain boundaries in BCC Fe. For the (111) grain boundary system, dislocation nucleation extends and dominates the deformation behavior. For the (112) twin grain boundary system, tensile deformation is mainly controlled by twin grain boundary, resulting in BCC-FCC phase transitions. Tensile loads were applied to different grain boundaries at temperatures of 300 K and 600 K. The results indicate that, in the Fe-P system with P concentrations ranging from 0.05at.% to 0.2at.%, compared to enhancing the strength of (111) grain boundary systems, P segregation leads to a decrease in strength for (112) systems, but the effect is minor. The P segregation hinders dislocation nucleation on the (111) and (113) grain boundaries, while it promotes dislocation nucleation at (112) grain boundaries, and P segregation has no significant effect on dislocation nucleation at (114) grain boundaries. The degree of deformation of the E structural unit at the P segregated site on the (111) grain boundary is small, and the dislocations are more inclined to nucleate in the unsubstituted structural unit near the P atom.

Abstract: Reactor pressure vessel (RPV) is an irreplaceable component in pressurized water reactors. It carries internal components, fuel assemblies and primary cooling water. Its integrity plays an important role in the safe operation of the reactor. Microscopic defects caused by neutron irradiation can cause radiation hardening and radiation embrittlement of RPV steel, increasing the risk of brittle fracture of RPV steel. Accurately characterizing the microscopic defects is of great significance for predicting the macroscopic properties of RPV steel. Solute defect clusters are the dominant radiation defects in RPV steel. Because they are rich in solute atoms Cu, Mn, Ni, etc., they can also be called Cu-rich precipitates and Mn-Ni-rich precipitates. At present, there are few studies on the nucleation and growth of precipitates dominated by vacancy clusters. Due to the limitations of microscopic characterization technology, it is difficult to directly observe solute-vacancy clusters in RPV steel. In this work, the solute-vacancy clusters generated in RPV steel after irradiation were focused. Taking the FeCuMnNi alloy system as the research object, the nucleation and growth process of solute-vacancy clusters were explored. The Metropolis Monte Carlo method was used to simulate the stable configurations of the solute-vacancy clusters in different RPV model alloys. The molecular statics method was used to study the interaction mechanism between solute atoms and vacancy clusters. The results show that in FeCuMnNi alloy system, Cu atoms preferentially segregate on the surface of vacancy clusters than Mn and Ni atoms, and the solute-vacancy clusters have a spherical shell structure. Mn can promote the growth of solute-vacancy clusters, while Ni has little effect on the growth of solute-vacancy clusters. Mn and Ni elements have a synergistic effect, which can promote the growth of solute-vacancy clusters. There is a correlation between the structure and energy of solute atoms in solute-vacancy clusters. Vacancy clusters can directly change the structures of solute atoms nearby, causing the inner solute atoms have significantly higher energy than the outer atoms. The growth process of solute-vacancy clusters can change from being dominated by vacancy clusters to outer solute atoms. The results are helpful to understand the formation and evolution behaviors of microscopic defects in RPV steel under neutron irradiation, and promote the prediction of irradiation embrittlement. In the future, to fully reveal the nucleation and growth process of solute-vacancy clusters, we will carry out research from a kinetic perspective using the kinetic Monte Carlo method or the cluster dynamics method.

Abyssal (3501–6500 m) and hadal (>6500 m) fauna evolve under harsh abiotic stresses, characterized by high hydrostatic pressure, darkness and food shortage, providing unique opportunities to investigate mechanisms underlying environmental adaptation. Genomes of several hadal species have recently been reported. However, the genetic adaptation of deep sea species across a broad spectrum of ocean depths has yet to be thoroughly investigated, due to the challenges imposed by collecting the deep sea species. To elucidate the correlation between genetic innovation and vertical distribution, we generated a chromosome‐level genome assembly of the macrourids Coryphaenoides yaquinae, which is widely distributed in the abyssal/hadal zone ranging from 3655 to 7259 m in depth. Genomic comparisons among shallow, abyssal and hadal‐living species identified idiosyncratic and convergent genetic alterations underlying the extraordinary adaptations of deep‐sea species including light perception, circadian regulation, hydrostatic pressure and hunger tolerance. The deep‐sea fishes (Coryphaenoides Sp. and Pseudoliparis swirei) venturing into various ocean depths independently have undergone convergent amino acid substitutions in multiple proteins such as rhodopsin 1, pancreatic and duodenal homeobox 1 and melanocortin 4 receptor which are known or verified in zebrafish to be related with vision adaptation and energy expenditure. Convergent evolution events were also identified in heat shock protein 90 beta family member 1 and valosin‐containing protein genes known to be related to hydrostatic pressure adaptation specifically in fishes found around the hadal range. The uncovering of the molecular convergence among the deep‐sea species shed new light on the common genetic innovations required for deep‐sea adaptation by the fishes. [ABSTRACT FROM AUTHOR]

Whether nitrogen (N)-metabolic versatility is a common trait of N-transforming microbes or if it only occurs in a few species is still unknown. We collected 83 soil samples from six soil types across China, retrieved 19 publicly available metagenomic marine sample data, and analyzed the functional traits of N-transforming microorganisms using metagenomic sequencing. More than 38% and 35% of N-transforming species in soil and marine ecosystems, respectively, encoded two or more N-pathways, although N-transforming species differed greatly between them. Furthermore, in both soil and marine ecosystems, more than 80% of nitrifying and N-fixing microorganisms at the species level were N-metabolic versatile. This study reveals that N-metabolic versatility is a common trait of N-transforming microbes, which could expand our understanding of the functional traits of drivers of nitrogen biogeochemistry. [ABSTRACT FROM AUTHOR]

As an important part of modern comprehensive transportation system, high-speed railway (HSR), whether it is a transregional trunk line or an intercity line, always shapes the industrial layout and changes the living environment at different levels. Based on the analysis of the railway network topology and organization process of passenger train, this paper clarifies the connotation of passenger train operation scheme of HSR considering network survivability, and further explains the connotation of railway network system and its relationship with passenger train operation scheme. In this paper, a comprehensive quantitative index of the importance of key nodes and key edges is established, and an evaluation index of the survivability of railway service network based on the operating mileage of passenger trains is constructed, which is applied to the real local HSR network in China. With the aim of improving the survivability of HSR system, an alternative operation route of passenger trains between some OD stations is given according to the specific railway interruption situation., Author(s): Yong Xian [1]; Yinzhen Li (corresponding author) [1]; Haijun Li [1]; Changxi Ma [1]; Tianxiang Zhang [2]; Yongpeng Zhao [1] 1. Introduction Railway plays an important role in economic [...]