In the case of a severe accident involving nuclear reactors,an important aspect that should be considered is the leakage of molten material from the inside of the reactor into the environment.These molten materials da...In the case of a severe accident involving nuclear reactors,an important aspect that should be considered is the leakage of molten material from the inside of the reactor into the environment.These molten materials damage other reactor components,such as electrical tubes,grid plates and core catchers.In this study,the moving particle semi-implicit(MPS)method is adopted and improved to analyze the twodimensional downward relocation process of molten Wood’s metal as a representation of molten material in a nuclear reactor.The molten material impinges the Wood’s metal plate(WMP),which is mounted on a rigid dummy stainless steel in a cylindrical test vessel.The breaching process occurs because of heat transfer between the molten material and WMP.The formed breach areas were in good agreement with the experimental results,and they showed that the molten Wood’s metal spread above the WMP.The solid WMP fraction decreased with time until it reached the termination time of the simulation.The present results show that the MPS method can be applied to simulate and analyze the downward relocation process of molten material in the grid plate of a nuclear reactor.展开更多
At the normal pool level of 175 m, the inundated areas of the Three Gorges Reservoir involve 2 cities, 11 county seats and 140 towns. The population of the cities and towns under the inundated line totals 393 000 peop...At the normal pool level of 175 m, the inundated areas of the Three Gorges Reservoir involve 2 cities, 11 county seats and 140 towns. The population of the cities and towns under the inundated line totals 393 000 people(1985). These affected cities and towns will be rebuilt by means of moving backward to a higher elevation or to other places.The cities and towns to be relocated are the regional political, economic and cultural centres, and serve as traffic complexes and places of goods gathering and distributing. They are also the seats containing some important cultural relics and historic sites, landscaping and scenic spots. The relocation of the cities and towns will generate far-reaching impacts on regional socio-economy and environment. The unreasonable excavation and fill or the improper protective measures adopted may induce land slide,collapse and soil loss. The ruins and wastes will affect the water quality in the early period of impoundment of the Three Gorges Reservoir. A large demand of timber may result in forest fall excessively in the local area of the reservoir region, and lower forest and vegetation coverage rate may lead to soil loss. The relocation of the cities and towns will increase urbanization in reservoir, improve the infrastructure, enhance their location function and economic radiation capacity. The negative impact will reach its maximum during relocation peak period, and the environmental quality will be progressively improved with the recovery of the functions of the relocated cities and towns and the implementation of environmental protection measures. Finally, the negative impact will be offset, and the negative impact will be changed into positive environmental elements.展开更多
It is widely acknowledged that the improved accessibility enabled by investment in public transport services can, under favorable market conditions, impact the local real estate market within the zone of influence of ...It is widely acknowledged that the improved accessibility enabled by investment in public transport services can, under favorable market conditions, impact the local real estate market within the zone of influence of the service＇s stations. The motivation for this study is to establish the nature of two such impacts, specifically the spatial and socio-economic patterns of residential relocations that are driven by the new light rail transit （LRT） service. Using empirical data （n = 1,023） from the Hudson-Bergen Light Rail system in New Jersey （US）, we report findings regarding the impacts of the introduction of the new LRT service. We investigate two linked dimensions; the first is the distinctive socio-economic profile of LRT passengers who self-report having relocated to the new transit corridor due, at least in part, to the new transit service. The second is their proximity （following their resi- dential relocation） to the new LRT line＇ s stations. We present a novel analysis that accounts for endogeneity between these two dimensions of residential relocation. Of light rail passengers who engaged in a residential relocation in the 5 years prior to the survey, two-thirds （69 %） indicate that proximity to the light rail service was a ＇somewhat＇ or ＇very＇ important consideration. Via the multivariate analysis, we demonstrate that small household size, low income, youth （as opposed to older age）, and low car ownership are each positively linked, ceteris paribus, with having engaged in a residential reloca- tion motivated by the new transit service. Finally, higher household income is found to be associated with distance （after relocation） to the nearest transit station, which is consistent with bid-rent theory.展开更多
In this paper, we present a multiobjective approach for solving the one-way car relocation problem.We fix three objectives that include the number of remaining rejected demands, the number of jockeys used for the relo...In this paper, we present a multiobjective approach for solving the one-way car relocation problem.We fix three objectives that include the number of remaining rejected demands, the number of jockeys used for the relocation operations, and the total time used by these jockeys. For this sake, we propose to apply two algorithms namely NSGA-Ⅱ and an adapted memetic algorithm(MA) that we call MARPOCS which stands for memetic algorithm for the one-way carsharing system. The NSGA-Ⅱ is used as a reference to compare the performance of MARPOCS. The comparison of the approximation sets obtained by both algorithms shows that the hybrid algorithm outperforms the classical NSGA-Ⅱ and so solutions generated by the MARPOCS are much better than the solutions generated by NSGA-Ⅱ. This observation is proved by the comparison of different quality indicators’ values that are used to compare the performance of each algorithm. Results show that the MARPOCS is promising to generate very good solutions for the multiobjective car relocation problem in one-way carsharing system. It shows a good performance in exploring the search space and in finding solution with very good fitness values.展开更多
Because surface-based monitoring of hydraulic fracturing is not restricted by borehole geometry or the difficulties in maintaining subsurface equipment, it is becoming an increasingly common part of microseismic monit...Because surface-based monitoring of hydraulic fracturing is not restricted by borehole geometry or the difficulties in maintaining subsurface equipment, it is becoming an increasingly common part of microseismic monitoring. The ability to determine an accurate velocity model for the monitored area directly affects the accuracy of microseismic event locations. However, velocity model calibration for location with surface instruments is difficult for several reasons： well log measurements are often inaccurate or incomplete, yielding intractable models; ori- gin times of perforation shots are not always accurate; and the non-uniqueness of velocity models obtained by inver- sion becomes especially problematic when only perforation shots are used. In this paper, we propose a new approach to overcome these limitations. We establish an initial velocity model from well logging data, and then use the root mean square （RMS） error of double-difference arrival times as a proxy measure for the misfit between the well log velocity model and the true velocity structure of the medium. Double-difference RMS errors are reduced by using a very fast simulated annealing for model perturbance, and a sample set of double-difference RMS errors is then selec- ted to determine an empirical threshold. This threshold value is set near the minimum RMS of the selected samples, and an appropriate number of travel times within the threshold range are chosen. The corresponding velocity models are then used to relocate the perforation-shot. We use the velocity model with the smallest relative location errors as the basis for microseismic location. Numerical analysis with exact input velocity models shows that although large differences exist between the calculated and true velocity models, perforation shots can still be located to their actual positions with the proposed technique; the location inaccuracy of the perforation is 〈2 m. Further tests on field data demonstrate the validity of this technique.展开更多
基金supported by the Pendidikan Magister Menuju Doktor untuk Sarjana Unggul(PMDSU)a research program from the Ministry of Research,Technology and Higher Education,IndonesiaThe authors wish to thank Prof.S.Koshizuka,Prof.M.Sakai and Dr.K.Shibata of the University of Tokyo for their helpful comments and for providing the basic MPS code for fluids。
文摘In the case of a severe accident involving nuclear reactors,an important aspect that should be considered is the leakage of molten material from the inside of the reactor into the environment.These molten materials damage other reactor components,such as electrical tubes,grid plates and core catchers.In this study,the moving particle semi-implicit(MPS)method is adopted and improved to analyze the twodimensional downward relocation process of molten Wood’s metal as a representation of molten material in a nuclear reactor.The molten material impinges the Wood’s metal plate(WMP),which is mounted on a rigid dummy stainless steel in a cylindrical test vessel.The breaching process occurs because of heat transfer between the molten material and WMP.The formed breach areas were in good agreement with the experimental results,and they showed that the molten Wood’s metal spread above the WMP.The solid WMP fraction decreased with time until it reached the termination time of the simulation.The present results show that the MPS method can be applied to simulate and analyze the downward relocation process of molten material in the grid plate of a nuclear reactor.
文摘At the normal pool level of 175 m, the inundated areas of the Three Gorges Reservoir involve 2 cities, 11 county seats and 140 towns. The population of the cities and towns under the inundated line totals 393 000 people(1985). These affected cities and towns will be rebuilt by means of moving backward to a higher elevation or to other places.The cities and towns to be relocated are the regional political, economic and cultural centres, and serve as traffic complexes and places of goods gathering and distributing. They are also the seats containing some important cultural relics and historic sites, landscaping and scenic spots. The relocation of the cities and towns will generate far-reaching impacts on regional socio-economy and environment. The unreasonable excavation and fill or the improper protective measures adopted may induce land slide,collapse and soil loss. The ruins and wastes will affect the water quality in the early period of impoundment of the Three Gorges Reservoir. A large demand of timber may result in forest fall excessively in the local area of the reservoir region, and lower forest and vegetation coverage rate may lead to soil loss. The relocation of the cities and towns will increase urbanization in reservoir, improve the infrastructure, enhance their location function and economic radiation capacity. The negative impact will reach its maximum during relocation peak period, and the environmental quality will be progressively improved with the recovery of the functions of the relocated cities and towns and the implementation of environmental protection measures. Finally, the negative impact will be offset, and the negative impact will be changed into positive environmental elements.
文摘It is widely acknowledged that the improved accessibility enabled by investment in public transport services can, under favorable market conditions, impact the local real estate market within the zone of influence of the service＇s stations. The motivation for this study is to establish the nature of two such impacts, specifically the spatial and socio-economic patterns of residential relocations that are driven by the new light rail transit （LRT） service. Using empirical data （n = 1,023） from the Hudson-Bergen Light Rail system in New Jersey （US）, we report findings regarding the impacts of the introduction of the new LRT service. We investigate two linked dimensions; the first is the distinctive socio-economic profile of LRT passengers who self-report having relocated to the new transit corridor due, at least in part, to the new transit service. The second is their proximity （following their resi- dential relocation） to the new LRT line＇ s stations. We present a novel analysis that accounts for endogeneity between these two dimensions of residential relocation. Of light rail passengers who engaged in a residential relocation in the 5 years prior to the survey, two-thirds （69 %） indicate that proximity to the light rail service was a ＇somewhat＇ or ＇very＇ important consideration. Via the multivariate analysis, we demonstrate that small household size, low income, youth （as opposed to older age）, and low car ownership are each positively linked, ceteris paribus, with having engaged in a residential reloca- tion motivated by the new transit service. Finally, higher household income is found to be associated with distance （after relocation） to the nearest transit station, which is consistent with bid-rent theory.
文摘In this paper, we present a multiobjective approach for solving the one-way car relocation problem.We fix three objectives that include the number of remaining rejected demands, the number of jockeys used for the relocation operations, and the total time used by these jockeys. For this sake, we propose to apply two algorithms namely NSGA-Ⅱ and an adapted memetic algorithm(MA) that we call MARPOCS which stands for memetic algorithm for the one-way carsharing system. The NSGA-Ⅱ is used as a reference to compare the performance of MARPOCS. The comparison of the approximation sets obtained by both algorithms shows that the hybrid algorithm outperforms the classical NSGA-Ⅱ and so solutions generated by the MARPOCS are much better than the solutions generated by NSGA-Ⅱ. This observation is proved by the comparison of different quality indicators’ values that are used to compare the performance of each algorithm. Results show that the MARPOCS is promising to generate very good solutions for the multiobjective car relocation problem in one-way carsharing system. It shows a good performance in exploring the search space and in finding solution with very good fitness values.
基金supported by the National Natural Science Foundation of China(No.41074074)
文摘Because surface-based monitoring of hydraulic fracturing is not restricted by borehole geometry or the difficulties in maintaining subsurface equipment, it is becoming an increasingly common part of microseismic monitoring. The ability to determine an accurate velocity model for the monitored area directly affects the accuracy of microseismic event locations. However, velocity model calibration for location with surface instruments is difficult for several reasons： well log measurements are often inaccurate or incomplete, yielding intractable models; ori- gin times of perforation shots are not always accurate; and the non-uniqueness of velocity models obtained by inver- sion becomes especially problematic when only perforation shots are used. In this paper, we propose a new approach to overcome these limitations. We establish an initial velocity model from well logging data, and then use the root mean square （RMS） error of double-difference arrival times as a proxy measure for the misfit between the well log velocity model and the true velocity structure of the medium. Double-difference RMS errors are reduced by using a very fast simulated annealing for model perturbance, and a sample set of double-difference RMS errors is then selec- ted to determine an empirical threshold. This threshold value is set near the minimum RMS of the selected samples, and an appropriate number of travel times within the threshold range are chosen. The corresponding velocity models are then used to relocate the perforation-shot. We use the velocity model with the smallest relative location errors as the basis for microseismic location. Numerical analysis with exact input velocity models shows that although large differences exist between the calculated and true velocity models, perforation shots can still be located to their actual positions with the proposed technique; the location inaccuracy of the perforation is 〈2 m. Further tests on field data demonstrate the validity of this technique.
