High-performance graphite materials have important roles in aerospace and nuclear reactor technologies because of their outstanding chemical stability and high-temperature performance.Their traditional production meth...High-performance graphite materials have important roles in aerospace and nuclear reactor technologies because of their outstanding chemical stability and high-temperature performance.Their traditional production method relies on repeated impregnation-carbonization and graphitization,and is plagued by lengthy preparation cycles and high energy consumption.Phase transition-assisted self-pressurized selfsintering technology can rapidly produce high-strength graphite materials,but the fracture strain of the graphite materials produced is poor.To solve this problem,this study used a two-step sintering method to uniformly introduce micro-nano pores into natural graphite-based bulk graphite,achieving improved fracture strain of the samples without reducing their density and mechanical properties.Using natural graphite powder,micron-diamond,and nano-diamond as raw materials,and by precisely controlling the staged pressure release process,the degree of diamond phase transition expansion was effectively regulated.The strain-to-failure of the graphite samples reached 1.2%,a 35%increase compared to samples produced by fullpressure sintering.Meanwhile,their flexural strength exceeded 110 MPa,and their density was over 1.9 g/cm^(3).The process therefore produced both a high strength and a high fracture strain.The interface evolution and toughening mechanism during the two-step sintering process were investigated.It is believed that the micro-nano pores formed have two roles:as stress concentrators they induce yielding by shear and as multi-crack propagation paths they significantly lengthen the crack propagation path.The two-step sintering phase transition strategy introduces pores and provides a new approach for increasing the fracture strain of brittle materials.展开更多
建模互联网中热点话题的传播过程具有重要的意义和价值,该文以网络热点话题为研究对象,基于自激霍克斯过程提出一个话题传播模型(Self-Exciting Point Process Model,SEPPM).SEPPM利用用户参与话题的自激效应,将话题传播过程建模为一个...建模互联网中热点话题的传播过程具有重要的意义和价值,该文以网络热点话题为研究对象,基于自激霍克斯过程提出一个话题传播模型(Self-Exciting Point Process Model,SEPPM).SEPPM利用用户参与话题的自激效应,将话题传播过程建模为一个随机点过程.同时,SEPPM也考虑了话题传播的外部因素,综合形成话题传播模型.为了验证该模型的有效性,该文从仿真和实证两个角度分别进行了大量的实验比较,提出话题仿真算法,仿真结果说明SEPPM可以生成多种符合热点话题传播特征的模式.实际数据上的结果说明SEPPM不仅能够很好地拟合真实话题的传播过程,还能够有效地预测话题传播趋势.展开更多
基金Natural Science Foundation of Shanghai(24ZR1400800)he Natural Science Foundation of China(U23A20685,52073058,91963204)+1 种基金the National Key R&D Program of China(2021YFB3701400)Shanghai Sailing Program(23YF1400200)。
文摘High-performance graphite materials have important roles in aerospace and nuclear reactor technologies because of their outstanding chemical stability and high-temperature performance.Their traditional production method relies on repeated impregnation-carbonization and graphitization,and is plagued by lengthy preparation cycles and high energy consumption.Phase transition-assisted self-pressurized selfsintering technology can rapidly produce high-strength graphite materials,but the fracture strain of the graphite materials produced is poor.To solve this problem,this study used a two-step sintering method to uniformly introduce micro-nano pores into natural graphite-based bulk graphite,achieving improved fracture strain of the samples without reducing their density and mechanical properties.Using natural graphite powder,micron-diamond,and nano-diamond as raw materials,and by precisely controlling the staged pressure release process,the degree of diamond phase transition expansion was effectively regulated.The strain-to-failure of the graphite samples reached 1.2%,a 35%increase compared to samples produced by fullpressure sintering.Meanwhile,their flexural strength exceeded 110 MPa,and their density was over 1.9 g/cm^(3).The process therefore produced both a high strength and a high fracture strain.The interface evolution and toughening mechanism during the two-step sintering process were investigated.It is believed that the micro-nano pores formed have two roles:as stress concentrators they induce yielding by shear and as multi-crack propagation paths they significantly lengthen the crack propagation path.The two-step sintering phase transition strategy introduces pores and provides a new approach for increasing the fracture strain of brittle materials.
文摘建模互联网中热点话题的传播过程具有重要的意义和价值,该文以网络热点话题为研究对象,基于自激霍克斯过程提出一个话题传播模型(Self-Exciting Point Process Model,SEPPM).SEPPM利用用户参与话题的自激效应,将话题传播过程建模为一个随机点过程.同时,SEPPM也考虑了话题传播的外部因素,综合形成话题传播模型.为了验证该模型的有效性,该文从仿真和实证两个角度分别进行了大量的实验比较,提出话题仿真算法,仿真结果说明SEPPM可以生成多种符合热点话题传播特征的模式.实际数据上的结果说明SEPPM不仅能够很好地拟合真实话题的传播过程,还能够有效地预测话题传播趋势.
