As coal and gas outburst is one of the most serious mine disasters, it is very important to at least control it if not prevent it from occurring. Injecting cement slurry or grouting into the coal seam can strengthen t...As coal and gas outburst is one of the most serious mine disasters, it is very important to at least control it if not prevent it from occurring. Injecting cement slurry or grouting into the coal seam can strengthen the seam, increase its rigidity coefficient(f), and reduce the volumetric expansion due to gas energy release.This paper reports the results of laboratory experiments on cement-based high water content slurry having different water-cement ratios(W/C) to be used for coal injection. The results show that as the W/C increases, the mobility of the slurry and its setting time increase. The compressive strength and rupture strength, however, are reduced. Furthermore, high W/C grout shows early strength after 7 days, which can be 80% of its 14-day compressive strength. To achieve rapid setting and early strength, the addition of Na_2SiO_3has proven to give the best result, when the concentration of the additive is 3%. The initial and final setting times are 13 and 21 min shorter than samples without Na_2SiO_3, while the compressive strength is more than double. As a retarder, the initial setting time can be extended to 83 min when tartaric acid of 0.4% concentration is added. Through the orthogonal experiment, the optimum recipe of the new high water content slurry has been determined to be: W/C = 2, tartaric acid = 0.2%, Na_2SiO_3= 3%, and12% bentonite. Reinforcement by injection simulation experiments show that the grouting radius of the new slurry mix is 250 mm when the applied grouting pressure is 60 k Pa, 7-day rupture strength and compressive strength are 5.2 and 6.4 MPa, respectively, and are 37% and 88% higher than ordinary cement grout. It can be concluded that the newly developed slurry mix is more effective than the ordinary mix for reinforcing coal and controlling gas outburst.展开更多
Against the backdrop of China's socio-economic transition, there is a growing imperative to examine neighborhood renovation initiatives in addressing the emerging needs of residents. Developing Granovetter's c...Against the backdrop of China's socio-economic transition, there is a growing imperative to examine neighborhood renovation initiatives in addressing the emerging needs of residents. Developing Granovetter's classic work on embeddedness, this paper proposes a conceptual framework of spatial embeddedness to understand changes in the physical space brought about by neighborhood renovation, in order to explore how it affects residents' satisfaction in a dynamic temporal and spatial process. It presents whether and why residents' real feelings produced from their interaction with neighborhood renovation are(un)different, and how their feelings are shaped based on six months of fieldwork in a danwei neighborhood in Xi'an, China. The paper conceptualizes the relationship between the neighborhood space and embeddedness by adopting spatial embeddedness to capture the interplay of temporal, spatial, and social factors in the process of danwei neighborhood renovation. This framework not only integrates multiple perspectives and scales, but also reflects different levels of residents' satisfaction, trying to establish a connection between the abstract space and the renovation space. It suggests that spatial embeddedness should be considered as a response to the negative social impacts resulting from changes in the physical space in neighborhood renovation.展开更多
Starting with the self-organized evolution of the trader group’s structure, a parsimonious percolation model for stock market is established, which can be considered as a kind of betterment of the Cont-Bouchaud model...Starting with the self-organized evolution of the trader group’s structure, a parsimonious percolation model for stock market is established, which can be considered as a kind of betterment of the Cont-Bouchaud model. The return distribution of the present model obeys Lévy form in the center and displays fat-tail property, in accord with the styl-ized facts observed in real-life financial time series. Fur-thermore, this model reveals the power-law relationship be-tween the peak value of the probability distribution and the time scales, in agreement with the empirical studies on the Hang Seng Index.展开更多
基金financial support of the National Natural Science Foundation of China (No. 51474017)the Natural Science Foundation of Xinjiang Uygur Autonomous Region of China (No. 2014211B013)
文摘As coal and gas outburst is one of the most serious mine disasters, it is very important to at least control it if not prevent it from occurring. Injecting cement slurry or grouting into the coal seam can strengthen the seam, increase its rigidity coefficient(f), and reduce the volumetric expansion due to gas energy release.This paper reports the results of laboratory experiments on cement-based high water content slurry having different water-cement ratios(W/C) to be used for coal injection. The results show that as the W/C increases, the mobility of the slurry and its setting time increase. The compressive strength and rupture strength, however, are reduced. Furthermore, high W/C grout shows early strength after 7 days, which can be 80% of its 14-day compressive strength. To achieve rapid setting and early strength, the addition of Na_2SiO_3has proven to give the best result, when the concentration of the additive is 3%. The initial and final setting times are 13 and 21 min shorter than samples without Na_2SiO_3, while the compressive strength is more than double. As a retarder, the initial setting time can be extended to 83 min when tartaric acid of 0.4% concentration is added. Through the orthogonal experiment, the optimum recipe of the new high water content slurry has been determined to be: W/C = 2, tartaric acid = 0.2%, Na_2SiO_3= 3%, and12% bentonite. Reinforcement by injection simulation experiments show that the grouting radius of the new slurry mix is 250 mm when the applied grouting pressure is 60 k Pa, 7-day rupture strength and compressive strength are 5.2 and 6.4 MPa, respectively, and are 37% and 88% higher than ordinary cement grout. It can be concluded that the newly developed slurry mix is more effective than the ordinary mix for reinforcing coal and controlling gas outburst.
基金supported by the National Natural Science Foundation of China (Nos. 7227419742371238)。
文摘Against the backdrop of China's socio-economic transition, there is a growing imperative to examine neighborhood renovation initiatives in addressing the emerging needs of residents. Developing Granovetter's classic work on embeddedness, this paper proposes a conceptual framework of spatial embeddedness to understand changes in the physical space brought about by neighborhood renovation, in order to explore how it affects residents' satisfaction in a dynamic temporal and spatial process. It presents whether and why residents' real feelings produced from their interaction with neighborhood renovation are(un)different, and how their feelings are shaped based on six months of fieldwork in a danwei neighborhood in Xi'an, China. The paper conceptualizes the relationship between the neighborhood space and embeddedness by adopting spatial embeddedness to capture the interplay of temporal, spatial, and social factors in the process of danwei neighborhood renovation. This framework not only integrates multiple perspectives and scales, but also reflects different levels of residents' satisfaction, trying to establish a connection between the abstract space and the renovation space. It suggests that spatial embeddedness should be considered as a response to the negative social impacts resulting from changes in the physical space in neighborhood renovation.
基金Th is work was supported by the National Natural Science Foundation of China (Grant Nos． 70171053． 70271070，70471033& 10472ll61)the Specialized Research Fund for the Doctoral Program of Higher Education (SRFDP No．20020358009) the Foundation for Graduate Students of University of Science and Tech—nology of China(Grant No．KD 200408)．
文摘Starting with the self-organized evolution of the trader group’s structure, a parsimonious percolation model for stock market is established, which can be considered as a kind of betterment of the Cont-Bouchaud model. The return distribution of the present model obeys Lévy form in the center and displays fat-tail property, in accord with the styl-ized facts observed in real-life financial time series. Fur-thermore, this model reveals the power-law relationship be-tween the peak value of the probability distribution and the time scales, in agreement with the empirical studies on the Hang Seng Index.
