An atomistic investigation of the effect of strain on frictional properties of suspended graphene

We performed molecular dynamics (MD) simulations of a diamond probe scanned on a suspended graphene to reveal the effect of strain on the fictional properties of suspended graphene. The graphene was subjected to some certain strain along the scanning direction. We compared the friction coefficient obtained from different normal loads and strain. The results show that the friction coefficient can be decreased about one order of magnitude with the increase of the strain. And that can be a result of the decreased asymmetry of the contact region which is caused by strain. The synthetic effect of potential energy and the fluctuation of contact region were found to be the main reason accounting for the fluctuation of the friction force. The strain can reduce the fluctuation of the contact region and improve the stability of friction

Evolution of surface grain structure and mechanical properties in orthogonal cutting of titanium alloy

In this study, a mesoscale dislocation simulation method was developed to study the orthogonal cutting of Titanium alloy. The evolution of surface grain structure and its effects on the surface mechanical properties were studied by using two-dimensional climb assisted dislocation dynamics technology. The motions of edge dislocations such as dislocation nucleation, junction, interaction with obstacles and grain boundaries, and annihilation were tracked. The results indicated that the machined surface has a microstructure composed of refined grains. The fine-grains bring appreciable scale effect and a mass of dislocations are piled up in the grain boundaries and persistent slip bands. In particular, dislocation climb can induce a perfect softening effect, but this effect is significantly weakened when grain size is less than 1.65 μm. In addition, a Hall-Petch type relation was predicted according to the arrangement of grain, the range of grain sizes and the distribution of dislocations

A genetic variation map for chicken with 2.8 million single-nucleotide polymorphisms

We describe a genetic variation map for the chicken genome containing 2.8 million single-nucleotide polymorphisms ( SNPs). This map is based on a comparison of the sequences of three domestic chicken breeds ( a broiler, a layer and a Chinese silkie) with that of their wild ancestor, red jungle fowl. Subsequent experiments indicate that at least 90% of the variant sites are true SNPs, and at least 70% are common SNPs that segregate in many domestic breeds. Mean nucleotide diversity is about five SNPs per kilobase for almost every possible comparison between red jungle fowl and domestic lines, between two different domestic lines, and within domestic lines - in contrast to the notion that domestic animals are highly inbred relative to their wild ancestors. In fact, most of the SNPs originated before domestication, and there is little evidence of selective sweeps for adaptive alleles on length scales greater than 100 kilobases

Identifying absolute subjects: A systemic functional approach

The absolute subject refers to the subject of absolute nominative clauses in traditional grammar. It can be either nominative or accusative. Corpora data show that the number of nominatives has been decreasing, and that of accusatives, increasing over time. Absolute nominative clauses of appositive, attendant circumstance and clausal adjunct in traditional grammar correspond to the non-finite clauses of elaboration, extension and enhancement with subject in the framework of Systemic Functional Linguistics. In addition, absolute subjects can also be used in non-finite clauses of projection and embedding. The relationships between absolute subjects in different non-finite clauses and the primary clauses are different in independence. The tendency to be independent can be embodied in the dimension of the absolute subjects and that of the primary clauses. From either dimension, the tendency to be independent can form a cline. The primary clause based tendency is more in line with the characteristics of absolute subjects

Reflections on the grammatical category of the than element in English comparative constructions: A corpus-based systemic functional approach

It is generally accepted that in comparative constructions, when the clausal element compared is the subject of the matrix clause, the personal pronoun following than can be either nominative which is usually used in formal English, where than is considered as a conjunction, or accusative which is usually used in informal English, where than is considered as a preposition. However, the data collected from the COCA corpus indicate that nominative pronouns do not tend to end a comparative construction in either formal or informal English. Based on the fundamentals of Systemic Functional Linguistics, it is improper to consider the accusative form of personal pronouns in comparative constructions as the object of than; rather they are the stressed personal pronouns. It is concluded that in comparative constructions than is always a conjunction, and the personal pronoun following than can be expanded into a finite clause. However, if the nominal group following than has no comparee in the matrix clause, it is not a comparative clause and the than-phrase is a prepositional phrase. It is further concluded that in comparative constructions than is best considered as a paratactic conjunction because comparative constructions cannot be transpositioned with the primary clauses in clause complexes

A multiscale simulation investigation on subsurface dislocation motion evolution mechanism in ultra-precision machining process

During practical ultra-precision cutting, the titanium alloy specimens suffer a combination of various deformations, has great influence on machining precision and properties. Here we report, the microstructure changes and surface mechanical properties evolutions were studied using two-dimensional climb assisted discrete dislocation dynamic technology. The plastic deformation is modeled through the motion of edge dislocations in an elastic matrix with dislocation nucleation, lock, interaction with obstacle and grain boundary, annihilation incorporated a series of constitutive equations. It was found that the micro-structure was obviously refined due to the variation of cutting force, which can be described as following: the formation and development of dislocation lines in initial grain, the formation of dense dislocation walls, the transformation of dislocation lines and walls into subgrain boundaries. In addition, the variation of surface microstructure results in higher flow strength and hardening rate due to the accumulation of geometrically necessary dislocations. The numerical result is helpful to reveal the effects of these microstructural factors on the surface generation mechanism in ultra-precision machining

SPR9 encodes a 60 S ribosomal protein that modulates panicle spreading and affects resistance to false smut in rice (Oryza sativa. L)

Abstract Background The architecture of inflorescence in crops is a key agronomic feature determining grain yield and thus has been a major target trait of cereal domestication. Results In this study, we show that a simple spreading panicle change in rice panicle shape, controlled by the Spreading Panicle 9 (SPR9) locus, also has a significant impact on the resistance to rice false smut (RFS). Meanwhile, we mapped a novel spr9 mutant gene between markers Indel5-18 and Indel5-22 encompassing a genomic region of 43-kb with six candidate genes. Through gene prediction and cDNA sequencing, we confirmed that LOC_Os05g38520 is the target gene in the spr9 mutant, which encodes 60 S ribosomal protein L36-2. Further analysis showed that the spr9 mutant is caused by a 1 bp deletion in the first exon that resulted in premature termination. Knockout experiments showed that the SPR9 gene is responsible for the spreading panicle phenotype of the spr9 mutant. Interestingly, the spr9 mutant was found to improve resistance to RFS without affecting major agronomic traits. Taken together, our results revealed that the spr9 allele has good application prospects in rice breeding for disease resistance and panicle improvement. Conclusions We report the map-based cloning and functional characterization of SPR9, which encodes a 60 S ribosomal protein that regulates spreading panicles and affects the resistance to false smut in rice