Using an optical microscope and scanning electron microscope (SEM), the variation of eutectic Si morphology of Al-Si alloy in solution treatment was observed to study its influence on mechanical properties and fractur...Using an optical microscope and scanning electron microscope (SEM), the variation of eutectic Si morphology of Al-Si alloy in solution treatment was observed to study its influence on mechanical properties and fracture behavior. The results show that eutectic Si undergoes stubbing, necking, fragmentation, and growth in the initial stage (250 min); in the middle solution stage (250 to 400 min), the eutectic Si morphology has no significant change, only the degree of spheroidizing becomes higher; after 600 min, the growth of eutectic Si is a coarsening process controlled by diffusion and follows the Liftshitz-Slyozov-Wangner (LSW) model, and the eutectic Si morphology deteriorates due to the occurrence of facets and lap. Based on the quantitative measure and regression analysis, the eutectic Si morphology has a remarkable influence on mechanical properties and fracture behavior.展开更多
A retrogression process was applied to AA7075alloy at180,240and320°C for1,30,50,70,90and120min.After the retrogression,aging treatment was reapplied with T6conditions(120°C,24h).The mechanical properties of ...A retrogression process was applied to AA7075alloy at180,240and320°C for1,30,50,70,90and120min.After the retrogression,aging treatment was reapplied with T6conditions(120°C,24h).The mechanical properties of aged samples were determined by V-Charpy and hardness tests and also,physical properties of samples were determined by electrical conductivity tests.Moreover,microstructural properties were characterized by light microscope and transmission electron microscope.The results show that the effects of the temperature and the duration of the retrogression and reagent on the impact toughness and hardness are related to the precipitates at the grain boundary.展开更多
Nowadays, geotextile tubes hydraulically filled with dredged materials have been used in the application of cofferdam, sea reclamation and deepwater channel regulation in China. The shape and mechanical behaviors duri...Nowadays, geotextile tubes hydraulically filled with dredged materials have been used in the application of cofferdam, sea reclamation and deepwater channel regulation in China. The shape and mechanical behaviors during the process of filling, consolidation and stacked are one of the main problems concemed by designers and researchers.This paper uses the method of elliptic integrals to study the behaviors of filling and deduces the regressive formulas of shape features and circumferential tension. The results show that the proposal regressive formulas are only the function of pressure at bottom; they are very convenient and suitable for the filling design. When the filling materials are sandy, the shape and mechanical behaviors nearly remain during the process of consolidation. The behaviors of stacked geotextile tubes are very complex, because they are involved in the properties of the filling material, geotextile and foundation.Using the commercial finite element analysis program ABAQUS, this paper establishes the entire 2- D finite element load model to investigate, which include the part of filling material, geotextile and foundation. The numerical results suggest that the maximun circumferential tension varies with the properties of filling materials and foundations, whereas the largest tensile force occurs during the filling process.展开更多
AIM： To identity the factors influencing colorectal cancer （CRC） screening behavior and willingness among Chinese outpatients.METHODS： An outpatient-based face-to-face survey was conducted from August 18 to Septem...AIM： To identity the factors influencing colorectal cancer （CRC） screening behavior and willingness among Chinese outpatients.METHODS： An outpatient-based face-to-face survey was conducted from August 18 to September 7, 2010 in Changhai Hospital. A total of 1200 consecutive patients aged ≥ 18 years were recruited for interview. The patient＇s knowledge about CRC and screening was pre-measured as a predictor variable, and other pre- dictors included age, gender, educational level, month- ly household income and health insurance status. The relationship between these predictors and screening behavior, screening willingness and screening approach were examined using Pearson＇s 2 test and logistic regression analyses.RESULTS： Of these outpatients, 22.5% had undergone CRC screening prior to this study. Patients who had participated in the screening were more likely to have good knowledge about CRC and screening （OR： 5.299, 95% CI： 3.415-8.223）, have health insurance （OR： 1.996, 95% CI： 1.426-2.794） and older in age. Higher income, however, was found to be a barrier to the screening （OR： 0.633, 95% CI： 0.467-0.858）. An analysis of screening willingness showed that 37.5% of the patients would voluntarily participated in a screen at the recommended age, but 41.3% would do so under doctor＇s advice. Screening willingness was positively correlated with the patient＇s knowledge sta- tus. Patients with higher knowledge levels would like to participate in the screening （OR： 4.352, 95% CI： 3.008-6.298）, and they would select colonoscopy as a screening approach （OR： 3.513, 95% CI： 2.290-5.389）. However, higher income level was, again, a bar- rier to colonoscopic screening （OR： 0.667, 95% CI： 0.505-0.908）. CONCLUSION： Patient＇s level of knowledge and in-ome should be taken into consideration when conducting a feasible CRC screening.展开更多
Background： Sedentary behavior （SB）, physical activity （PA）, and attributes of physical fitness have been shown to be related to depressive symptoms in adolescents. The purpose of the present study was to investi...Background： Sedentary behavior （SB）, physical activity （PA）, and attributes of physical fitness have been shown to be related to depressive symptoms in adolescents. The purpose of the present study was to investigate whether SB and fitness-producing activity predicted depression in active adolescents over and above gender and fitness attributes. Methods： Participants were 249 adolescents （age： 12.85 ± 0.89 years, mean ± SD） from 3 public middle schools who wore Actical accelerometers to assess their SB and PA. Participants also completed the FITNESSGRAM health-related fitness assessment and a brief depression questionnaire. A 3-step hierarchical regression analysis was conducted with gender and fitness attributes （i.e., body mass index （BMI）, maximal volume oxygen uptake （VO2max）, curlups, and pushups）, moderate- and vigorous-intensity activity, and SB entered in respective steps. Results： Regression analysis indicated activity variables （i.e., moderate- and vigorous-intensity activity） significantly predicted depression （△R^2= 0.12, p 〈 0.01） beyond gender and fitness attributes. Overall, gender, fitness attributes, activity variables, SB explained 31% of the variance in depression. Structure coefficients revealed VO2max （rs= -0.77）, moderate-intensity activity （rs= -0.67）, vigorous-intensity activity （rs = -0.81）, and SB （rs = 0.57） were substantially correlated with the criterion variable; thus, they were the strongest predictors of depression. Conclusion： The findings of the current study indicated SB and PA were both significant predictors of depression; however, sufficient fitness-producing activity and adequate cardiorespiratory fitness may nullify the negative influence of SB on depressive symptoms in active adolescents.2018 Published by Elsevier B.V. on behalf of Shanghai University of Sport. This is an open access article under the CC BY-NC-ND license. （http：//creativecommons.org/licenses/by-nc-nd/4.0/）.展开更多
A study was conducted to better understand how different parameters, namely, regression aging time and regression aging temperature, affect the creep aging properties, i.e., the creep deformation and performance of Al...A study was conducted to better understand how different parameters, namely, regression aging time and regression aging temperature, affect the creep aging properties, i.e., the creep deformation and performance of Al-Zn-MgCu alloy during regressive reaging. The corresponding creep strain and mechanical properties of samples were studied by conducting creep tests and uniaxial tensile tests. The electrical conductivity was measured using an eddy-current conductivity meter. The microstructures were observed by transmission electron microscopy(TEM). With the increase in regression aging time, the steady creep strain first increased and then decreased, and reached the maximum at 45 min.The steady creep strain increased with the increase in regression aging temperature, and reached the maximum at 200 ℃.The level of steady creep strain was determined by precipitation and dislocation recovery. Creep aging strengthens 7B50-RRA treated with regression aging time at 190 ℃ for 10 min, and the difference in the mechanical properties of alloy becomes smaller. The diffusion of solute atoms reduces the scattering of electrons, leading to a significant improvement in electrical conductivity and stress corrosion cracking(SCC) resistance after creep aging. The findings of this study could help in the application of creep aging forming(CAF) technology in Al-Zn-Mg-Cu alloy under RRA treatment.展开更多
The random coefficient integer-valued autoregressive process was introduced by Zheng,Basawa,and Datta in 2007.In this paper we study the asymptotic behavior of this model(in particular,weak limits of extreme values an...The random coefficient integer-valued autoregressive process was introduced by Zheng,Basawa,and Datta in 2007.In this paper we study the asymptotic behavior of this model(in particular,weak limits of extreme values and the growth rate of partial sums) in the case where the additive term in the underlying random linear recursion belongs to the domain of attraction of a stable law.展开更多
The m-th order detrended Brownian motion is defined as the orthogonal component of projection of the standard Brownian motion onto the subspace spanned by polynomials of degree up to m. We obtain the Karhunen-Loeve ex...The m-th order detrended Brownian motion is defined as the orthogonal component of projection of the standard Brownian motion onto the subspace spanned by polynomials of degree up to m. We obtain the Karhunen-Loeve expansion for the process and establish a connection with the generalized （m-th order） Brownian bridge developed by MacNeill （1978） in the study of distributions of polynomial regression. The resulting distribution identity is also verified by a stochastic Fubini approach. As applications, large and small deviation asymptotic behaviors for the L2 norm are given.展开更多
Recurrent events data with a terminal event （e.g., death） often arise in clinical and ob- servational studies. Variable selection is an important issue in all regression analysis. In this paper, the authors first pr...Recurrent events data with a terminal event （e.g., death） often arise in clinical and ob- servational studies. Variable selection is an important issue in all regression analysis. In this paper, the authors first propose the estimation methods to select the significant variables, and then prove the asymptotic behavior of the proposed estimator. Furthermore, the authors discuss the computing algorithm to assess the proposed estimator via the linear function approximation and generalized cross validation method for determination of the tuning parameters. Finally, the finite sample estimation for the asymptotical covariance matrix is also proposed.展开更多
文摘Using an optical microscope and scanning electron microscope (SEM), the variation of eutectic Si morphology of Al-Si alloy in solution treatment was observed to study its influence on mechanical properties and fracture behavior. The results show that eutectic Si undergoes stubbing, necking, fragmentation, and growth in the initial stage (250 min); in the middle solution stage (250 to 400 min), the eutectic Si morphology has no significant change, only the degree of spheroidizing becomes higher; after 600 min, the growth of eutectic Si is a coarsening process controlled by diffusion and follows the Liftshitz-Slyozov-Wangner (LSW) model, and the eutectic Si morphology deteriorates due to the occurrence of facets and lap. Based on the quantitative measure and regression analysis, the eutectic Si morphology has a remarkable influence on mechanical properties and fracture behavior.
基金supported by Yildiz Technical University Scientific Research Project Unit under Contract No:2016-07-02-DOP02
文摘A retrogression process was applied to AA7075alloy at180,240and320°C for1,30,50,70,90and120min.After the retrogression,aging treatment was reapplied with T6conditions(120°C,24h).The mechanical properties of aged samples were determined by V-Charpy and hardness tests and also,physical properties of samples were determined by electrical conductivity tests.Moreover,microstructural properties were characterized by light microscope and transmission electron microscope.The results show that the effects of the temperature and the duration of the retrogression and reagent on the impact toughness and hardness are related to the precipitates at the grain boundary.
文摘Nowadays, geotextile tubes hydraulically filled with dredged materials have been used in the application of cofferdam, sea reclamation and deepwater channel regulation in China. The shape and mechanical behaviors during the process of filling, consolidation and stacked are one of the main problems concemed by designers and researchers.This paper uses the method of elliptic integrals to study the behaviors of filling and deduces the regressive formulas of shape features and circumferential tension. The results show that the proposal regressive formulas are only the function of pressure at bottom; they are very convenient and suitable for the filling design. When the filling materials are sandy, the shape and mechanical behaviors nearly remain during the process of consolidation. The behaviors of stacked geotextile tubes are very complex, because they are involved in the properties of the filling material, geotextile and foundation.Using the commercial finite element analysis program ABAQUS, this paper establishes the entire 2- D finite element load model to investigate, which include the part of filling material, geotextile and foundation. The numerical results suggest that the maximun circumferential tension varies with the properties of filling materials and foundations, whereas the largest tensile force occurs during the filling process.
文摘AIM： To identity the factors influencing colorectal cancer （CRC） screening behavior and willingness among Chinese outpatients.METHODS： An outpatient-based face-to-face survey was conducted from August 18 to September 7, 2010 in Changhai Hospital. A total of 1200 consecutive patients aged ≥ 18 years were recruited for interview. The patient＇s knowledge about CRC and screening was pre-measured as a predictor variable, and other pre- dictors included age, gender, educational level, month- ly household income and health insurance status. The relationship between these predictors and screening behavior, screening willingness and screening approach were examined using Pearson＇s 2 test and logistic regression analyses.RESULTS： Of these outpatients, 22.5% had undergone CRC screening prior to this study. Patients who had participated in the screening were more likely to have good knowledge about CRC and screening （OR： 5.299, 95% CI： 3.415-8.223）, have health insurance （OR： 1.996, 95% CI： 1.426-2.794） and older in age. Higher income, however, was found to be a barrier to the screening （OR： 0.633, 95% CI： 0.467-0.858）. An analysis of screening willingness showed that 37.5% of the patients would voluntarily participated in a screen at the recommended age, but 41.3% would do so under doctor＇s advice. Screening willingness was positively correlated with the patient＇s knowledge sta- tus. Patients with higher knowledge levels would like to participate in the screening （OR： 4.352, 95% CI： 3.008-6.298）, and they would select colonoscopy as a screening approach （OR： 3.513, 95% CI： 2.290-5.389）. However, higher income level was, again, a bar- rier to colonoscopic screening （OR： 0.667, 95% CI： 0.505-0.908）. CONCLUSION： Patient＇s level of knowledge and in-ome should be taken into consideration when conducting a feasible CRC screening.
文摘Background： Sedentary behavior （SB）, physical activity （PA）, and attributes of physical fitness have been shown to be related to depressive symptoms in adolescents. The purpose of the present study was to investigate whether SB and fitness-producing activity predicted depression in active adolescents over and above gender and fitness attributes. Methods： Participants were 249 adolescents （age： 12.85 ± 0.89 years, mean ± SD） from 3 public middle schools who wore Actical accelerometers to assess their SB and PA. Participants also completed the FITNESSGRAM health-related fitness assessment and a brief depression questionnaire. A 3-step hierarchical regression analysis was conducted with gender and fitness attributes （i.e., body mass index （BMI）, maximal volume oxygen uptake （VO2max）, curlups, and pushups）, moderate- and vigorous-intensity activity, and SB entered in respective steps. Results： Regression analysis indicated activity variables （i.e., moderate- and vigorous-intensity activity） significantly predicted depression （△R^2= 0.12, p 〈 0.01） beyond gender and fitness attributes. Overall, gender, fitness attributes, activity variables, SB explained 31% of the variance in depression. Structure coefficients revealed VO2max （rs= -0.77）, moderate-intensity activity （rs= -0.67）, vigorous-intensity activity （rs = -0.81）, and SB （rs = 0.57） were substantially correlated with the criterion variable; thus, they were the strongest predictors of depression. Conclusion： The findings of the current study indicated SB and PA were both significant predictors of depression; however, sufficient fitness-producing activity and adequate cardiorespiratory fitness may nullify the negative influence of SB on depressive symptoms in active adolescents.2018 Published by Elsevier B.V. on behalf of Shanghai University of Sport. This is an open access article under the CC BY-NC-ND license. （http：//creativecommons.org/licenses/by-nc-nd/4.0/）.
基金Project(2017YFB0306300) supported by the National key R&D Program of ChinaProjects(51675538, 51905551)supported by the National Natural Science Foundation of ChinaProject(ZZYJKT2019-11) supported by Free Exploration Project of State Key Laboratory of High performance Complex Manufacturing,China。
文摘A study was conducted to better understand how different parameters, namely, regression aging time and regression aging temperature, affect the creep aging properties, i.e., the creep deformation and performance of Al-Zn-MgCu alloy during regressive reaging. The corresponding creep strain and mechanical properties of samples were studied by conducting creep tests and uniaxial tensile tests. The electrical conductivity was measured using an eddy-current conductivity meter. The microstructures were observed by transmission electron microscopy(TEM). With the increase in regression aging time, the steady creep strain first increased and then decreased, and reached the maximum at 45 min.The steady creep strain increased with the increase in regression aging temperature, and reached the maximum at 200 ℃.The level of steady creep strain was determined by precipitation and dislocation recovery. Creep aging strengthens 7B50-RRA treated with regression aging time at 190 ℃ for 10 min, and the difference in the mechanical properties of alloy becomes smaller. The diffusion of solute atoms reduces the scattering of electrons, leading to a significant improvement in electrical conductivity and stress corrosion cracking(SCC) resistance after creep aging. The findings of this study could help in the application of creep aging forming(CAF) technology in Al-Zn-Mg-Cu alloy under RRA treatment.
文摘The random coefficient integer-valued autoregressive process was introduced by Zheng,Basawa,and Datta in 2007.In this paper we study the asymptotic behavior of this model(in particular,weak limits of extreme values and the growth rate of partial sums) in the case where the additive term in the underlying random linear recursion belongs to the domain of attraction of a stable law.
基金supported by the Fundamental Research Funds for the Central Universities(Grant No.DL13BBX10)
文摘The m-th order detrended Brownian motion is defined as the orthogonal component of projection of the standard Brownian motion onto the subspace spanned by polynomials of degree up to m. We obtain the Karhunen-Loeve expansion for the process and establish a connection with the generalized （m-th order） Brownian bridge developed by MacNeill （1978） in the study of distributions of polynomial regression. The resulting distribution identity is also verified by a stochastic Fubini approach. As applications, large and small deviation asymptotic behaviors for the L2 norm are given.
文摘Recurrent events data with a terminal event （e.g., death） often arise in clinical and ob- servational studies. Variable selection is an important issue in all regression analysis. In this paper, the authors first propose the estimation methods to select the significant variables, and then prove the asymptotic behavior of the proposed estimator. Furthermore, the authors discuss the computing algorithm to assess the proposed estimator via the linear function approximation and generalized cross validation method for determination of the tuning parameters. Finally, the finite sample estimation for the asymptotical covariance matrix is also proposed.
