Two kinds of Ag-graphite composites reinforced with spherical graphite(SG)and conventional flake graphite(FG)were prepared by powder metallurgy technology.The effect of graphite morphology on the tribological behavior...Two kinds of Ag-graphite composites reinforced with spherical graphite(SG)and conventional flake graphite(FG)were prepared by powder metallurgy technology.The effect of graphite morphology on the tribological behavior for the Ag-SG and Ag-FG under the dry sliding wear was investigated with a pin-on-disk tribometer at a load of 3.0 N in atmosphere condition.The results indicated that the minimum wear rate of 3.5×10^-5 mm^3/(N·m)for Ag-FG was achieved and it reduced by nearly an order of magnitude,reaching 1.6×10^-6 mm^3/(N·m)for the Ag-SG.The obviously different tribological behaviors between the Ag-SG and Ag-FG were closely related to the formation of cracks in the sub-surface.The stress concentration tended to generate at the edges of flake graphite during sliding process,which resulted in the cracks and severe delamination wear of Ag-FG.However,no cracks were found around the spherical graphite in Ag-SG.The spherical graphite can effectively inhibit the initiation and propagation of cracks,achieving high wear resistance.展开更多
Academic writing is social interaction between writer and reader,during which writers can employ discursive and non-discursive features to construct their identities.However,many student writers who are users of Engli...Academic writing is social interaction between writer and reader,during which writers can employ discursive and non-discursive features to construct their identities.However,many student writers who are users of English as an additional language(EAL)may find it challenging to construct their identities in academic writing.Properly constructed identity in academic writing can help EAL student writers develop a stronger sense of self,exercise their agency,and negotiate the academic discourse.Therefore,this paper reviews empirical studies on EAL student writers'identity construction when they write in English to investigate the features of identities that EAL student writers construct in texts and the factors that influence their identity construction.The findings show that,compared with expert writers and native-English-speaking(NES)counterparts,EAL student writers tend to present a weak authorial identity.Furthermore,EAL student writers tend to be more engaged with texts than with readers and lack commitment to their claims.The identities that EAL student writers construct in academic writing are also interwoven with EAL students'English proficiency levels,educational experience,disciplinary conventions,genre affordances,and audience awareness.The findings of this literature review can help teachers and educators raise EAL students’identity awareness and facilitate students in strategically constructing writer identities in academic writing.展开更多
基金Project(51674304)supported by the National Natural Science Foundation of ChinaProject(2018JJ3677)supported by Natural Science Foundation of Hunan Province,China。
文摘Two kinds of Ag-graphite composites reinforced with spherical graphite(SG)and conventional flake graphite(FG)were prepared by powder metallurgy technology.The effect of graphite morphology on the tribological behavior for the Ag-SG and Ag-FG under the dry sliding wear was investigated with a pin-on-disk tribometer at a load of 3.0 N in atmosphere condition.The results indicated that the minimum wear rate of 3.5×10^-5 mm^3/(N·m)for Ag-FG was achieved and it reduced by nearly an order of magnitude,reaching 1.6×10^-6 mm^3/(N·m)for the Ag-SG.The obviously different tribological behaviors between the Ag-SG and Ag-FG were closely related to the formation of cracks in the sub-surface.The stress concentration tended to generate at the edges of flake graphite during sliding process,which resulted in the cracks and severe delamination wear of Ag-FG.However,no cracks were found around the spherical graphite in Ag-SG.The spherical graphite can effectively inhibit the initiation and propagation of cracks,achieving high wear resistance.
文摘Academic writing is social interaction between writer and reader,during which writers can employ discursive and non-discursive features to construct their identities.However,many student writers who are users of English as an additional language(EAL)may find it challenging to construct their identities in academic writing.Properly constructed identity in academic writing can help EAL student writers develop a stronger sense of self,exercise their agency,and negotiate the academic discourse.Therefore,this paper reviews empirical studies on EAL student writers'identity construction when they write in English to investigate the features of identities that EAL student writers construct in texts and the factors that influence their identity construction.The findings show that,compared with expert writers and native-English-speaking(NES)counterparts,EAL student writers tend to present a weak authorial identity.Furthermore,EAL student writers tend to be more engaged with texts than with readers and lack commitment to their claims.The identities that EAL student writers construct in academic writing are also interwoven with EAL students'English proficiency levels,educational experience,disciplinary conventions,genre affordances,and audience awareness.The findings of this literature review can help teachers and educators raise EAL students’identity awareness and facilitate students in strategically constructing writer identities in academic writing.
