n-Heptane is the most important straight chain paramn in the fossil-fuel industry. In this work, pyrolysis behavior of n-heptane at high temperature is investigated by a se- ties of ReaxFF based reactive molecular dyn...n-Heptane is the most important straight chain paramn in the fossil-fuel industry. In this work, pyrolysis behavior of n-heptane at high temperature is investigated by a se- ties of ReaxFF based reactive molecular dynamics simulations. Temperature effects on the n-heptane pyrolysis and related products distributions have been detailedly analyzed. The simulation results indicate that the temperature effect is characterized in stages. High tern- perature can accelerate the decomposition of n-heptane, but the influence becomes small after it reaches a certain level. According to the different reaction behaviors, pyrolysis of n-heptane could be divided into three stages. The variation trends of the mass fraction evolu- tion of ethylene （C2H4）, C3, and C4 calculated from reactive molecular dynamics simulations are in good agreement with the previous experimental results. The apparent activation en- ergy extracted from the first-order kinetic analysis is 53.96 kcal/mol and a pre-exponential factor is 55.34×10^13 s-1, which is reasonably consistent with the experimental results.展开更多
This paper reconstructs,based on American and Chinese primary sources,the visits of Chinese mathematicians Shiing-shen Chern陈省身(Chen Xingshen)and Hua Luogeng华罗庚(Loo-Keng Hua)4 to the Institute for Advanced Study...This paper reconstructs,based on American and Chinese primary sources,the visits of Chinese mathematicians Shiing-shen Chern陈省身(Chen Xingshen)and Hua Luogeng华罗庚(Loo-Keng Hua)4 to the Institute for Advanced Study in Princeton in the United States in the 1940s,especially their interactions with Oswald Veblen and Hermann Weyl,two leading mathematicians at the IAS.It argues that Chern’s and Hua’s motivations and choices in regard to their transnational movements between China and the US were more nuanced and multifaceted than what is presented in existing accounts,and that socio-political factors combined with professional-personal ones to shape their decisions.The paper further uses their experiences to demonstrate the importance of transnational scientific interactions for the development of science in China,the US,and elsewhere in the twentieth century.展开更多
在科技日新月异的今天,想要记录下自己的美丽瞬间,你只需拿出智能手机,摆好p ose,来张自拍即可。在智能手机尚未诞生的很久很久以前,人们是否也有将自己的容颜记录和保存下来的想法呢?答案当然是肯定的,而且他们的方式并不比我们的自拍...在科技日新月异的今天,想要记录下自己的美丽瞬间,你只需拿出智能手机,摆好p ose,来张自拍即可。在智能手机尚未诞生的很久很久以前,人们是否也有将自己的容颜记录和保存下来的想法呢?答案当然是肯定的,而且他们的方式并不比我们的自拍落后,甚至还更为高明。Here are five self-portraits that are predecessors1)to the modern-day selfie.Perhaps they are not the best展开更多
基金This work was supported by the National Natural Science Foundation of China （No.20273066）.
文摘n-Heptane is the most important straight chain paramn in the fossil-fuel industry. In this work, pyrolysis behavior of n-heptane at high temperature is investigated by a se- ties of ReaxFF based reactive molecular dynamics simulations. Temperature effects on the n-heptane pyrolysis and related products distributions have been detailedly analyzed. The simulation results indicate that the temperature effect is characterized in stages. High tern- perature can accelerate the decomposition of n-heptane, but the influence becomes small after it reaches a certain level. According to the different reaction behaviors, pyrolysis of n-heptane could be divided into three stages. The variation trends of the mass fraction evolu- tion of ethylene （C2H4）, C3, and C4 calculated from reactive molecular dynamics simulations are in good agreement with the previous experimental results. The apparent activation en- ergy extracted from the first-order kinetic analysis is 53.96 kcal/mol and a pre-exponential factor is 55.34×10^13 s-1, which is reasonably consistent with the experimental results.
文摘This paper reconstructs,based on American and Chinese primary sources,the visits of Chinese mathematicians Shiing-shen Chern陈省身(Chen Xingshen)and Hua Luogeng华罗庚(Loo-Keng Hua)4 to the Institute for Advanced Study in Princeton in the United States in the 1940s,especially their interactions with Oswald Veblen and Hermann Weyl,two leading mathematicians at the IAS.It argues that Chern’s and Hua’s motivations and choices in regard to their transnational movements between China and the US were more nuanced and multifaceted than what is presented in existing accounts,and that socio-political factors combined with professional-personal ones to shape their decisions.The paper further uses their experiences to demonstrate the importance of transnational scientific interactions for the development of science in China,the US,and elsewhere in the twentieth century.
文摘在科技日新月异的今天,想要记录下自己的美丽瞬间,你只需拿出智能手机,摆好p ose,来张自拍即可。在智能手机尚未诞生的很久很久以前,人们是否也有将自己的容颜记录和保存下来的想法呢?答案当然是肯定的,而且他们的方式并不比我们的自拍落后,甚至还更为高明。Here are five self-portraits that are predecessors1)to the modern-day selfie.Perhaps they are not the best
