Based on the theory of concrete structure, a new expression was derived for lagged strain of fiber-reinforced polymer （FLIP） laminates in reinforced concrete （RC） beams strengthened with FRP. The influence of diff...Based on the theory of concrete structure, a new expression was derived for lagged strain of fiber-reinforced polymer （FLIP） laminates in reinforced concrete （RC） beams strengthened with FRP. The influence of different preloaded states and nonlinear stress-strain relationship of compressed concrete were both taken into account in this approach. Then a simplified expression was given by ignoring tensile resistance of concrete. Comparison of analytical predictions with experimental results indicates satisfactory accuracy of the procedures. The errors are less than 8% and 10% respectively when the tensile resistance of concrete is or not considered. While the maximum error of existing procedures is up to 60%.展开更多
直升机低空突防已逐渐成为现代空战察打任务的核心,而低空航迹规划算法是实现该技术的关键。尽管现有的航迹规划算法已经被应用于实际低空突防任务,但基于“前端-后端”式的传统航迹规划算法依然存在规划航迹机动执行性差与复杂动态场...直升机低空突防已逐渐成为现代空战察打任务的核心,而低空航迹规划算法是实现该技术的关键。尽管现有的航迹规划算法已经被应用于实际低空突防任务,但基于“前端-后端”式的传统航迹规划算法依然存在规划航迹机动执行性差与复杂动态场景下易碰撞的缺陷。针对上述问题,本文提出一种基于Hybrid State A^(*)与增强安全管道的改进算法。首先,基于Hybrid State A^(*)算法的联合轨迹优化,可以在状态空间中完成兼顾直升机机动特性的初始航迹高效搜索,有效保证直升机航迹的可达性。其次,基于初始航迹膨胀的增强安全管道,将后端航迹优化参数限制在安全的可行域内,进而有效提升复杂动态场景下规划航迹的安全性。在实验环节,本研究结合ROS机器人仿真环境与Rviz数据可视化工具完成仿真验证,通过算法间的综合对比实验,论证了本研究所提算法对规划的航迹机动性与安全性有明显的提升。展开更多
Background:Global spread and impact of the coronavirus disease 2019(COVID-19)pandemic are determined to a large extent,by resistance to the pandemic and public response of all countries in the world;while a country...Background:Global spread and impact of the coronavirus disease 2019(COVID-19)pandemic are determined to a large extent,by resistance to the pandemic and public response of all countries in the world;while a country's resistance and response are in turn determined by its political and socio economic conditions.To inform future disease prevention and control,we analyzed global data to exam the relationship between state vulnerabilities and COVID-19 incidences and deaths.Methods:Vulnerability was measured using the Fragile States Index(FSI).FSI is created by the Fund for Peace to assess levels of fragility for individual countries.Total FSI score and scores for 12 specific indicators were used as the predictor variables.Outcome variables were national cumulative COVID-19 cases and deaths up to September 16,2020,derived from the World Health Organization.Cumulative incidence rates were computed using 2019 National population derived from the World Bank,and case fatality rates were computed as the ratio of deaths/COVID-19 cases.Countries with incomplete data were excluded,yielding a final sample of 146 countries.Multivariate regression was used to examine the association between the predictor and the outcome measures.Results:There were dramatic cross-country variations in both FSI and COVID-19 epidemiological measurements.FSI total scores were negatively associated with both COVID-19 cumulative incidence rates(β=-0.0135,P<0.001)and case fatality rates(β=-0.0147,P<0.05).Of the 12 FSI indicators,three negatively associated with COVID-19 incidences were E1(Economic Decline and Poverty),E3(Human Flight and Brain Drain),and S2(Refugees and Internally Displaced Persons);two positively associated were P1(State Legitimacy)and X1(External Intervention).With regard to association with case fatality rates,C1(Security Apparatus)was positive,and P3(Human Rights and Rule of Law)and X1 was negative.Conclusion:With FSI measures by the Fund of Peace,overall,more fragile countries are less likely to be affected by the COVID-19 pandemic,and even if affected,death rates were lower.However,poor in state legitimacy and lack of external intervention are risk for COVID-19 infection and lack of security apparatus is risky for COVID-19 death.Implications of the study findings are discussed and additional studies are needed to examine the mechanisms underpinning these relationships.展开更多
基金Project(2002G043) supported by the Science & Technology Research Program of Chinese Railway MinistryProject (05JJ30101)supported by the Natural Science Foundation of Hunan Province, China
文摘Based on the theory of concrete structure, a new expression was derived for lagged strain of fiber-reinforced polymer （FLIP） laminates in reinforced concrete （RC） beams strengthened with FRP. The influence of different preloaded states and nonlinear stress-strain relationship of compressed concrete were both taken into account in this approach. Then a simplified expression was given by ignoring tensile resistance of concrete. Comparison of analytical predictions with experimental results indicates satisfactory accuracy of the procedures. The errors are less than 8% and 10% respectively when the tensile resistance of concrete is or not considered. While the maximum error of existing procedures is up to 60%.
文摘直升机低空突防已逐渐成为现代空战察打任务的核心,而低空航迹规划算法是实现该技术的关键。尽管现有的航迹规划算法已经被应用于实际低空突防任务,但基于“前端-后端”式的传统航迹规划算法依然存在规划航迹机动执行性差与复杂动态场景下易碰撞的缺陷。针对上述问题,本文提出一种基于Hybrid State A^(*)与增强安全管道的改进算法。首先,基于Hybrid State A^(*)算法的联合轨迹优化,可以在状态空间中完成兼顾直升机机动特性的初始航迹高效搜索,有效保证直升机航迹的可达性。其次,基于初始航迹膨胀的增强安全管道,将后端航迹优化参数限制在安全的可行域内,进而有效提升复杂动态场景下规划航迹的安全性。在实验环节,本研究结合ROS机器人仿真环境与Rviz数据可视化工具完成仿真验证,通过算法间的综合对比实验,论证了本研究所提算法对规划的航迹机动性与安全性有明显的提升。
基金This paper was supported by the National Natural Science Foundation of China(No.72042014).
文摘Background:Global spread and impact of the coronavirus disease 2019(COVID-19)pandemic are determined to a large extent,by resistance to the pandemic and public response of all countries in the world;while a country's resistance and response are in turn determined by its political and socio economic conditions.To inform future disease prevention and control,we analyzed global data to exam the relationship between state vulnerabilities and COVID-19 incidences and deaths.Methods:Vulnerability was measured using the Fragile States Index(FSI).FSI is created by the Fund for Peace to assess levels of fragility for individual countries.Total FSI score and scores for 12 specific indicators were used as the predictor variables.Outcome variables were national cumulative COVID-19 cases and deaths up to September 16,2020,derived from the World Health Organization.Cumulative incidence rates were computed using 2019 National population derived from the World Bank,and case fatality rates were computed as the ratio of deaths/COVID-19 cases.Countries with incomplete data were excluded,yielding a final sample of 146 countries.Multivariate regression was used to examine the association between the predictor and the outcome measures.Results:There were dramatic cross-country variations in both FSI and COVID-19 epidemiological measurements.FSI total scores were negatively associated with both COVID-19 cumulative incidence rates(β=-0.0135,P<0.001)and case fatality rates(β=-0.0147,P<0.05).Of the 12 FSI indicators,three negatively associated with COVID-19 incidences were E1(Economic Decline and Poverty),E3(Human Flight and Brain Drain),and S2(Refugees and Internally Displaced Persons);two positively associated were P1(State Legitimacy)and X1(External Intervention).With regard to association with case fatality rates,C1(Security Apparatus)was positive,and P3(Human Rights and Rule of Law)and X1 was negative.Conclusion:With FSI measures by the Fund of Peace,overall,more fragile countries are less likely to be affected by the COVID-19 pandemic,and even if affected,death rates were lower.However,poor in state legitimacy and lack of external intervention are risk for COVID-19 infection and lack of security apparatus is risky for COVID-19 death.Implications of the study findings are discussed and additional studies are needed to examine the mechanisms underpinning these relationships.
