Directional solidification experiments were conducted for Ti-46Al-8Nb alloy at the growth rates ranging from 3 to 70 pards. The microstructure evolution and microsegregation pattern were investigated. In the range of ...Directional solidification experiments were conducted for Ti-46Al-8Nb alloy at the growth rates ranging from 3 to 70 pards. The microstructure evolution and microsegregation pattern were investigated. In the range of growth rate, a regular dendritic structure appears and the primary dendrite spacing decreases with increasing growth rate. The peritectic reaction is observed during the solidification and the final microstructure is composed of α2/γ lamellar structure and retained β（B2） after directional solidification The lamellar orientation is found to be parallel and 45° to the primary growth direction ofβ dendrite. Peritectic reaction leads to significant chemical inhomogeneity, in which aluminum is rich in interdendritic liquid and niobium is rich in the core ofβ dendrite during the solidification. With the nucleation and growth of a phase, the segregation amplitude of niobium increases, which promotes the formation of B2 phase, while aluminum rich in the interdendritic becomes homogeneous gradually.展开更多
The influence of supercooled melt forced lamina flow on microsegregation was investigated. The concentration distribution at solid-liquid boundary of binary alloy Ni-Cu was simulated using phase field model coupled wi...The influence of supercooled melt forced lamina flow on microsegregation was investigated. The concentration distribution at solid-liquid boundary of binary alloy Ni-Cu was simulated using phase field model coupled with flow field. The microsegregation, concentration maximum value, boundary thickness of concentration near upstream dendrite and normal to flow dendrite, and downstream dendrite were studied quantitatively in the case of forced lamia flow. The simulation results show that solute field and flow field interact complexly. Compared with melt without flow, in front of upstream dendrite tip, the concentration boundary thickness is the lowest and the concentration maximum value is the smallest for melt with flow. However, in front of downstream dendrite tip, the results are just the opposite. The zone of poor Cu in upstream dendrite where is the most severely microsegregation and shrinkage cavity is wider and the concentration is lower for melt with flow than that without flow.展开更多
A personalized trustworthy service selection method is proposed to fully express the features of trust, emphasize the importance of user preference and improve the trustworthiness of service selection. The trustworthi...A personalized trustworthy service selection method is proposed to fully express the features of trust, emphasize the importance of user preference and improve the trustworthiness of service selection. The trustworthiness of web service is defined as customized multi-dimensional trust metrics and the user preference is embodied in the weight of each trust metric. A service selection method combining AHP （analytic hierarchy process） and PROMETHEE （preference ranking organization method for enrichment evaluations） is proposed. AHP is used to determine the weights of trust metrics according to users＇ preferences. Hierarchy and pairwise comparison matrices are constructed. The weights of trust metrics are derived from the highest eigenvalue and eigenvector of the matrix. to obtain the final rank of candidate services. The preference functions are defined according to the inherent characteristics of the trust metrics and net outranking flows are calculated. Experimental results show that the proposed method can effectively express users＇ personalized preferences for trust metrics, and the trustworthiness of service ranking and selection is efficiently improved.展开更多
Al-Mg alloys are considered to have potentials to form twins during deformation because Mg can reduce the intrinsicstacking fault energy?ISFE of Al.Nevertheless,twinning has rarely been found in Al-Mg alloys even subj...Al-Mg alloys are considered to have potentials to form twins during deformation because Mg can reduce the intrinsicstacking fault energy?ISFE of Al.Nevertheless,twinning has rarely been found in Al-Mg alloys even subjected to various severeplastic deformation(SPD)techniques.In order to probe the twinning propensity of Al-Mg alloys,first-principles calculations werecarried out to investigate the effects of Mg and vacancies on the generalized planar fault energy(GPFE)of Al.It is found that bothMg and vacancies exhibit a Suzuki segregation feature to the stacking fault,and have the influence of decreasing the?ISFE of Al.However,?ISFE does not decrease and the twinnability parameterτa of Al does not increase monotonically with increasing Mgconcentration in the alloy.On the basis ofτa evaluated from the calculated GPFE of Al-Mg alloys,we conclude that deformationtwinning is difficult for Al-Mg alloys even with a high content of Mg.Besides,the decrease of?ISFE caused by the introduction ofMg and vacancies is supposed to have the effect of improving the work-hardening rate and facilitating the formation of bandstructures in Al-Mg alloys subjected to SPD.展开更多
This study examined public attitudes concerning the value of outdoor spaces which people use daily. Two successive analyses were performed based on data from common residents and college students in the city of Hangzh...This study examined public attitudes concerning the value of outdoor spaces which people use daily. Two successive analyses were performed based on data from common residents and college students in the city of Hangzhou, China. First, citizens registered various items constituting desirable values of residential outdoor spaces through a preliminary questionnaire. The result proposed three general attributes (functional, aesthetic and ecological) and ten specific qualities of residential outdoor spaces. An analytic hierarchy process (AHP) was applied to an interview survey in order to clarify the weights among these attributes and qualities. Second, principal factors were extracted from the ten specific qualities with principal component analysis (PCA) for both the common case and the campus case. In addition, the variations of respondents’ groups were classified with cluster analysis (CA) using the results of the PCA. The results of the AHP application found that the public prefers the functional attribute, rather than the aesthetic attribute. The latter is always viewed as the core value of open spaces in the eyes of architects and designers. Fur-thermore, comparisons of ten specific qualities showed that the public prefers the open spaces that can be utilized conveniently and easily for group activities, because such spaces keep an active lifestyle of neighborhood communication, which is also seen to protect human-regarding residential environments. Moreover, different groups of respondents diverge largely in terms of gender, age, behavior and preference.展开更多
基金Projects (50801019,51071062) supported by the National Natural Science Foundation of ChinaProject (2011CB605504) supported by the National Basic Research Program of China
文摘Directional solidification experiments were conducted for Ti-46Al-8Nb alloy at the growth rates ranging from 3 to 70 pards. The microstructure evolution and microsegregation pattern were investigated. In the range of growth rate, a regular dendritic structure appears and the primary dendrite spacing decreases with increasing growth rate. The peritectic reaction is observed during the solidification and the final microstructure is composed of α2/γ lamellar structure and retained β（B2） after directional solidification The lamellar orientation is found to be parallel and 45° to the primary growth direction ofβ dendrite. Peritectic reaction leads to significant chemical inhomogeneity, in which aluminum is rich in interdendritic liquid and niobium is rich in the core ofβ dendrite during the solidification. With the nucleation and growth of a phase, the segregation amplitude of niobium increases, which promotes the formation of B2 phase, while aluminum rich in the interdendritic becomes homogeneous gradually.
基金Project (10964004) supported by the National Natural Science Foundation of ChinaProject (20070731001) supported by Research Fund for the Doctoral Program of ChinaProject (096RJZA104) supported by the Natural Science Foundation of Gansu Province,China
文摘The influence of supercooled melt forced lamina flow on microsegregation was investigated. The concentration distribution at solid-liquid boundary of binary alloy Ni-Cu was simulated using phase field model coupled with flow field. The microsegregation, concentration maximum value, boundary thickness of concentration near upstream dendrite and normal to flow dendrite, and downstream dendrite were studied quantitatively in the case of forced lamia flow. The simulation results show that solute field and flow field interact complexly. Compared with melt without flow, in front of upstream dendrite tip, the concentration boundary thickness is the lowest and the concentration maximum value is the smallest for melt with flow. However, in front of downstream dendrite tip, the results are just the opposite. The zone of poor Cu in upstream dendrite where is the most severely microsegregation and shrinkage cavity is wider and the concentration is lower for melt with flow than that without flow.
基金The National Natural Science Foundation of China(No.60973149)the Open Funds of State Key Laboratory of Computer Science of the Chinese Academy of Sciences(No.SYSKF1110)+1 种基金the Doctoral Fund of Ministry of Education of China(No.20100092110022)the College Industrialization Project of Jiangsu Province(No.JHB2011-3)
文摘A personalized trustworthy service selection method is proposed to fully express the features of trust, emphasize the importance of user preference and improve the trustworthiness of service selection. The trustworthiness of web service is defined as customized multi-dimensional trust metrics and the user preference is embodied in the weight of each trust metric. A service selection method combining AHP （analytic hierarchy process） and PROMETHEE （preference ranking organization method for enrichment evaluations） is proposed. AHP is used to determine the weights of trust metrics according to users＇ preferences. Hierarchy and pairwise comparison matrices are constructed. The weights of trust metrics are derived from the highest eigenvalue and eigenvector of the matrix. to obtain the final rank of candidate services. The preference functions are defined according to the inherent characteristics of the trust metrics and net outranking flows are calculated. Experimental results show that the proposed method can effectively express users＇ personalized preferences for trust metrics, and the trustworthiness of service ranking and selection is efficiently improved.
基金Project(222173) supported by the FRINATEK project ‘BENTMAT’ from the Research Council of Norway
文摘Al-Mg alloys are considered to have potentials to form twins during deformation because Mg can reduce the intrinsicstacking fault energy?ISFE of Al.Nevertheless,twinning has rarely been found in Al-Mg alloys even subjected to various severeplastic deformation(SPD)techniques.In order to probe the twinning propensity of Al-Mg alloys,first-principles calculations werecarried out to investigate the effects of Mg and vacancies on the generalized planar fault energy(GPFE)of Al.It is found that bothMg and vacancies exhibit a Suzuki segregation feature to the stacking fault,and have the influence of decreasing the?ISFE of Al.However,?ISFE does not decrease and the twinnability parameterτa of Al does not increase monotonically with increasing Mgconcentration in the alloy.On the basis ofτa evaluated from the calculated GPFE of Al-Mg alloys,we conclude that deformationtwinning is difficult for Al-Mg alloys even with a high content of Mg.Besides,the decrease of?ISFE caused by the introduction ofMg and vacancies is supposed to have the effect of improving the work-hardening rate and facilitating the formation of bandstructures in Al-Mg alloys subjected to SPD.
文摘This study examined public attitudes concerning the value of outdoor spaces which people use daily. Two successive analyses were performed based on data from common residents and college students in the city of Hangzhou, China. First, citizens registered various items constituting desirable values of residential outdoor spaces through a preliminary questionnaire. The result proposed three general attributes (functional, aesthetic and ecological) and ten specific qualities of residential outdoor spaces. An analytic hierarchy process (AHP) was applied to an interview survey in order to clarify the weights among these attributes and qualities. Second, principal factors were extracted from the ten specific qualities with principal component analysis (PCA) for both the common case and the campus case. In addition, the variations of respondents’ groups were classified with cluster analysis (CA) using the results of the PCA. The results of the AHP application found that the public prefers the functional attribute, rather than the aesthetic attribute. The latter is always viewed as the core value of open spaces in the eyes of architects and designers. Fur-thermore, comparisons of ten specific qualities showed that the public prefers the open spaces that can be utilized conveniently and easily for group activities, because such spaces keep an active lifestyle of neighborhood communication, which is also seen to protect human-regarding residential environments. Moreover, different groups of respondents diverge largely in terms of gender, age, behavior and preference.
