The effects of minor Sc and Zr additions on the mechanical properties and microstructure evolution of Al Zn Mg Cu alloys were studied using tensile tests, scanning electron microscopy (SEM) and transmission electron m...The effects of minor Sc and Zr additions on the mechanical properties and microstructure evolution of Al Zn Mg Cu alloys were studied using tensile tests, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The ultimate tensile strength of the peak-aged Al Zn Mg Cu alloy is improved by about 105 MPa with the addition of 0.10% Zr. An increase of about 133 MPa is observed with the joint addition of 0.07% Sc and 0.07% Zr. For the alloys modified with the minor addition of Sc and Zr (0.14%), the main strengthening mechanisms of minor addition of Sc and Zr are fine-grain strengthening, sub-structure strengthening and the Orowan strengthening mechanism produced by the Al3(Sc,Zr) and Al3Zr dispersoids. The volume of Al3Zr particles is less than that of Al3(Sc,Zr) particles, but the distribution of Al3(Sc,Zr) particles is more dispersed throughout the matrix leading to pinning the dislocations motion and restraining the recrystallization more effectively.展开更多
Based on the work of paper [1], we propose a modified Levenberg-Marquardt algoithm for solving singular system of nonlinear equations F(x) = 0, where F(x) : Rn - Rn is continuously differentiable and F'(x) is Lips...Based on the work of paper [1], we propose a modified Levenberg-Marquardt algoithm for solving singular system of nonlinear equations F(x) = 0, where F(x) : Rn - Rn is continuously differentiable and F'(x) is Lipschitz continuous. The algorithm is equivalent to a trust region algorithm in some sense, and the global convergence result is given. The sequence generated by the algorithm converges to the solution quadratically, if ||F(x)||2 provides a local error bound for the system of nonlinear equations. Numerical results show that the algorithm performs well.展开更多
Dear Editor,The emerging pandemic of coronavirus,SARS-CoV-2(pre-viously named 2019-nCoV),has posed significant threats to global public health(Wu et al,2020).The dominant symp-toms of coronavirus disease 2019(COVID-19...Dear Editor,The emerging pandemic of coronavirus,SARS-CoV-2(pre-viously named 2019-nCoV),has posed significant threats to global public health(Wu et al,2020).The dominant symp-toms of coronavirus disease 2019(COVID-19)are fever and cough(Chen et al.,2020;Huang et al.,2020).However,a proportion of patients showed multi-organ damage and dysfunction(Chen et al.,2020;Huang et al.,2020;Zhu et al.,2020).Of note,liver damage is emerging as a co existed symptom reported in patients with COVID-19.A recent epi-demiologic study in Shanghai(China)reported that 75 out of 148(50.7%)COVID-19 patients had liver function abnor-mality,indicated by key liver function parameters above the normal range,including alanine aminotransferase(ALT),aspartate aminotransferase(AST),alkaline phosphatase(ALP)or total bilrubin(TBIL)(Fan et al.,2020).展开更多
1.No global progress on youth physical activity prevalenceTagedEnd TagedPDespite hundreds of intervention studies over decennia that have been dedicated to developing and testing programs and strategies to promote phy...1.No global progress on youth physical activity prevalenceTagedEnd TagedPDespite hundreds of intervention studies over decennia that have been dedicated to developing and testing programs and strategies to promote physical activity(PA)in adolescents,14 global inactivity levels remain persistently high.Based on self-report data from 1.6 million schoolgoing adolescents from 146 countries,Guthold et al.5 confirmed previous urgent calls to get adolescents more active.Researchers from the World Health Organization(WHO)recently published global prevalence rates and the first ever global time trends for insufficient PA in youth.They reported that more than 80%of school-going adolescents globally did not meet the current recommendations of at least 1 h of PA per day.展开更多
基金国家自然科学基金(批准号:2983719030230310+5 种基金20077004和20477004)北京市自然科学基金(批准号:89910028041003)资助项目教育部高等学校博士学科点专项科研基金(20010027017)中国科学院百人计划 大气边界层物理和大气化学国家重点实验室(LAPC)以及Swedish International Development Cooperation Agency(SIDA)部分资助项目
基金Project (2016B090931004) supported by the Scientific and Research Plan of Guangdong Province, ChinaProject (51601229) supported by the National Natural Science Foundation of China。
文摘The effects of minor Sc and Zr additions on the mechanical properties and microstructure evolution of Al Zn Mg Cu alloys were studied using tensile tests, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The ultimate tensile strength of the peak-aged Al Zn Mg Cu alloy is improved by about 105 MPa with the addition of 0.10% Zr. An increase of about 133 MPa is observed with the joint addition of 0.07% Sc and 0.07% Zr. For the alloys modified with the minor addition of Sc and Zr (0.14%), the main strengthening mechanisms of minor addition of Sc and Zr are fine-grain strengthening, sub-structure strengthening and the Orowan strengthening mechanism produced by the Al3(Sc,Zr) and Al3Zr dispersoids. The volume of Al3Zr particles is less than that of Al3(Sc,Zr) particles, but the distribution of Al3(Sc,Zr) particles is more dispersed throughout the matrix leading to pinning the dislocations motion and restraining the recrystallization more effectively.
文摘Based on the work of paper [1], we propose a modified Levenberg-Marquardt algoithm for solving singular system of nonlinear equations F(x) = 0, where F(x) : Rn - Rn is continuously differentiable and F'(x) is Lipschitz continuous. The algorithm is equivalent to a trust region algorithm in some sense, and the global convergence result is given. The sequence generated by the algorithm converges to the solution quadratically, if ||F(x)||2 provides a local error bound for the system of nonlinear equations. Numerical results show that the algorithm performs well.
文摘Dear Editor,The emerging pandemic of coronavirus,SARS-CoV-2(pre-viously named 2019-nCoV),has posed significant threats to global public health(Wu et al,2020).The dominant symp-toms of coronavirus disease 2019(COVID-19)are fever and cough(Chen et al.,2020;Huang et al.,2020).However,a proportion of patients showed multi-organ damage and dysfunction(Chen et al.,2020;Huang et al.,2020;Zhu et al.,2020).Of note,liver damage is emerging as a co existed symptom reported in patients with COVID-19.A recent epi-demiologic study in Shanghai(China)reported that 75 out of 148(50.7%)COVID-19 patients had liver function abnor-mality,indicated by key liver function parameters above the normal range,including alanine aminotransferase(ALT),aspartate aminotransferase(AST),alkaline phosphatase(ALP)or total bilrubin(TBIL)(Fan et al.,2020).
文摘1.No global progress on youth physical activity prevalenceTagedEnd TagedPDespite hundreds of intervention studies over decennia that have been dedicated to developing and testing programs and strategies to promote physical activity(PA)in adolescents,14 global inactivity levels remain persistently high.Based on self-report data from 1.6 million schoolgoing adolescents from 146 countries,Guthold et al.5 confirmed previous urgent calls to get adolescents more active.Researchers from the World Health Organization(WHO)recently published global prevalence rates and the first ever global time trends for insufficient PA in youth.They reported that more than 80%of school-going adolescents globally did not meet the current recommendations of at least 1 h of PA per day.
