Reactive powder concrete （RPC） is vulnerable to explosive spalling when exposed to high temperature. The characteristics of micro pore structure and vapor pressure of RPC are closely related to the thermal spalling....Reactive powder concrete （RPC） is vulnerable to explosive spalling when exposed to high temperature. The characteristics of micro pore structure and vapor pressure of RPC are closely related to the thermal spalling. Applying mercury intrusion po- rosimetry （MIP） and scanning electron microscopy （SEM） techniques, the authors probed the characteristics of micro pore structures of plain RPC200 when heated from 20-350~C. The pore characteristics such as specific pore volume, threshold pore size and most probable pore size varying with temperatures were investigated. A vapor pressure kit was developed to measure the vapor pressure and its variation inside RPC200 at various temperatures. A thin-wall spherical pore model was proposed to ana- lyze the thermo-mechanical mechanism of spalling, by which the stresses varying with the vapor pressure q（T） and the character- istic size of wall （K） at any point of interest were determined. It is shown that the pore characteristics including specific pore volume, average pore size, threshold pore size and most probable pore size rise significantly with the increasing temperature. 200~C appears to be the threshold temperature above which the threshold pore size and the most probable pore size climb up dramatically. The increase in the specific pore volume results from the growth both in quantity and in volume of the transition pores and the capillary pores. The appearance of the explosive spalling in RPC200 is mainly attributed to being unable to form pathways in favor of releasing water steam in RPC and to thin-wall sphere domain where the vapor pressure governs the the rapid accumulation of high vapor pressures as well. The spalling is bounded through the pore model.展开更多
We consider the small value probability of supercritical continuous state branching processes with immigration. From Pinsky （1972） it is known that under regularity condition on the branching mechanism and immigrati...We consider the small value probability of supercritical continuous state branching processes with immigration. From Pinsky （1972） it is known that under regularity condition on the branching mechanism and immigration mechanism, the normalized population size converges to a non-degenerate finite and positive limit PV as t tends to infinity. We provide sharp estimate on asymptotic behavior of P（W≤ε〈） as ε→ 0＋ by studying the Laplace transform of W. Without immigration, we also give a simpler proof for the small value probability in the non-subordinator case via the prolific backbone decomposition.展开更多
基金supported by the National Science Foundation for Distin-guished Young Scholars of China (Grant No. 51125017)the National Natural Science Foundation of China (Grant No. 50974125)+1 种基金the ResearchFund for Doctoral Programs of Chinese Ministry of Education (Grant No.20110023110015)the National Basic Research Program of China("973" Project)(Grant Nos. 2010CB226804,2011CB201201)
文摘Reactive powder concrete （RPC） is vulnerable to explosive spalling when exposed to high temperature. The characteristics of micro pore structure and vapor pressure of RPC are closely related to the thermal spalling. Applying mercury intrusion po- rosimetry （MIP） and scanning electron microscopy （SEM） techniques, the authors probed the characteristics of micro pore structures of plain RPC200 when heated from 20-350~C. The pore characteristics such as specific pore volume, threshold pore size and most probable pore size varying with temperatures were investigated. A vapor pressure kit was developed to measure the vapor pressure and its variation inside RPC200 at various temperatures. A thin-wall spherical pore model was proposed to ana- lyze the thermo-mechanical mechanism of spalling, by which the stresses varying with the vapor pressure q（T） and the character- istic size of wall （K） at any point of interest were determined. It is shown that the pore characteristics including specific pore volume, average pore size, threshold pore size and most probable pore size rise significantly with the increasing temperature. 200~C appears to be the threshold temperature above which the threshold pore size and the most probable pore size climb up dramatically. The increase in the specific pore volume results from the growth both in quantity and in volume of the transition pores and the capillary pores. The appearance of the explosive spalling in RPC200 is mainly attributed to being unable to form pathways in favor of releasing water steam in RPC and to thin-wall sphere domain where the vapor pressure governs the the rapid accumulation of high vapor pressures as well. The spalling is bounded through the pore model.
基金supported by National Science Foundation of US (Grant Nos. DMS-0805929 and DMS-1106938)National Natural Science Foundation of China (Grant Nos. 10928103,10971003 and 11128101)+1 种基金Specialized Research Fund for the Doctoral Program of Higher Education of Chinathe Fundamental Research Funds for the Central Universities
文摘We consider the small value probability of supercritical continuous state branching processes with immigration. From Pinsky （1972） it is known that under regularity condition on the branching mechanism and immigration mechanism, the normalized population size converges to a non-degenerate finite and positive limit PV as t tends to infinity. We provide sharp estimate on asymptotic behavior of P（W≤ε〈） as ε→ 0＋ by studying the Laplace transform of W. Without immigration, we also give a simpler proof for the small value probability in the non-subordinator case via the prolific backbone decomposition.
