In 2006, SOMAIR decided to increase the uranium production by 50% using heap leaching for the treatment of low grade ores. These ores, which come from different lodes with various properties, have been studied in four...In 2006, SOMAIR decided to increase the uranium production by 50% using heap leaching for the treatment of low grade ores. These ores, which come from different lodes with various properties, have been studied in four steps： （ 1 ） Lab tests： to compare the ores （characterization, acid consumptions, recovery...）; （2） Column tests on an average sample： to define significant parameters for a feasibility study; （3） Column tests on specific samples： to optimize recovery for each ore and identify problems of percolation due to the clays; （4） Pilot tests in large boxes （stalls）： to validate process parameters. Uranium production by heap leaching started in July 2009.展开更多
In this article we consider a sequence of hierarchical space model of inverse problems.The underlying function is estimated from indirect observations over a variety of error distributions including those that are hea...In this article we consider a sequence of hierarchical space model of inverse problems.The underlying function is estimated from indirect observations over a variety of error distributions including those that are heavy-tailed and may not even possess variances or means.The main contribution of this paper is that we establish some oracle inequalities for the inverse problems by using quantile coupling technique that gives a tight bound for the quantile coupling between an arbitrary sample p-quantile and a normal variable,and an automatic selection principle for the nonrandom filters.This leads to the data-driven choice of weights.We also give an algorithm for its implementation.The quantile coupling inequality developed in this paper is of independent interest,because it includes the median coupling inequality in literature as a special case.展开更多
The nestedness property has become an increasingly important means for devising efficient algorithms for network location problems.There have been attempts to explore the nestedness property of network location proble...The nestedness property has become an increasingly important means for devising efficient algorithms for network location problems.There have been attempts to explore the nestedness property of network location problems with some special cases of the convex ordered median objectives.However,there is little research on the nestedness property for those problems with the concave ordered median objectives.This paper constructs a tree network T and shows that the nestedness property cannot hold for the concave ordered median problem,which fills a gap in the research on the nestedness property.Finally,the authors pose an open problem on identifying the nestedness property for the continuous strategic ordered median problem.展开更多
This paper uses a finite dominating set （FDS） to investigate the multi-facility ordered median problem （OMP） in a strongly connected directed network. The authors first prove that the multi-facility OMP has an FDS...This paper uses a finite dominating set （FDS） to investigate the multi-facility ordered median problem （OMP） in a strongly connected directed network. The authors first prove that the multi-facility OMP has an FDS in the node set, which not only generalizes the FDS result provided by Kalcsics, et al. （2002）, but also extends the FDS result from the single-facility Case to the multiple case, filling an important gap. Then, based on this FDS result, the authors develop an exact algorithm to solve the problem. However, if the number of facilities is large, it is not practical to find the optimal solution, because the multi-facility OMP in directed networks is NP-hard. Hence, we present a constant-approximation algorithm for the p-median problem in directed networks. Finally, we pose an open problem for future research.展开更多
文摘In 2006, SOMAIR decided to increase the uranium production by 50% using heap leaching for the treatment of low grade ores. These ores, which come from different lodes with various properties, have been studied in four steps： （ 1 ） Lab tests： to compare the ores （characterization, acid consumptions, recovery...）; （2） Column tests on an average sample： to define significant parameters for a feasibility study; （3） Column tests on specific samples： to optimize recovery for each ore and identify problems of percolation due to the clays; （4） Pilot tests in large boxes （stalls）： to validate process parameters. Uranium production by heap leaching started in July 2009.
基金supported by the Major Project of Humanities Social Science Foundation of Ministry of Education(Grant No. 08JJD910247)Key Project of Chinese Ministry of Education (Grant No. 108120)+4 种基金National Natural Science Foundation of China (Grant No. 10871201)Beijing Natural Science Foundation (Grant No. 1102021)the Fundamental Research Funds for the Central Universitiesthe Research Funds of Renmin University of China(Grant No. 10XNL018)the China Statistical Research Project (Grant No. 2011LZ031)
文摘In this article we consider a sequence of hierarchical space model of inverse problems.The underlying function is estimated from indirect observations over a variety of error distributions including those that are heavy-tailed and may not even possess variances or means.The main contribution of this paper is that we establish some oracle inequalities for the inverse problems by using quantile coupling technique that gives a tight bound for the quantile coupling between an arbitrary sample p-quantile and a normal variable,and an automatic selection principle for the nonrandom filters.This leads to the data-driven choice of weights.We also give an algorithm for its implementation.The quantile coupling inequality developed in this paper is of independent interest,because it includes the median coupling inequality in literature as a special case.
基金supported by the Macao Foundation under Grant No.0249National Natural Science Foundation of China under Grant No.70901050
文摘The nestedness property has become an increasingly important means for devising efficient algorithms for network location problems.There have been attempts to explore the nestedness property of network location problems with some special cases of the convex ordered median objectives.However,there is little research on the nestedness property for those problems with the concave ordered median objectives.This paper constructs a tree network T and shows that the nestedness property cannot hold for the concave ordered median problem,which fills a gap in the research on the nestedness property.Finally,the authors pose an open problem on identifying the nestedness property for the continuous strategic ordered median problem.
基金This research is supported by the National Natural Science Foundation of China under Grant No. 70901050 and Macao Foundation under Grant No. 0144.
文摘This paper uses a finite dominating set （FDS） to investigate the multi-facility ordered median problem （OMP） in a strongly connected directed network. The authors first prove that the multi-facility OMP has an FDS in the node set, which not only generalizes the FDS result provided by Kalcsics, et al. （2002）, but also extends the FDS result from the single-facility Case to the multiple case, filling an important gap. Then, based on this FDS result, the authors develop an exact algorithm to solve the problem. However, if the number of facilities is large, it is not practical to find the optimal solution, because the multi-facility OMP in directed networks is NP-hard. Hence, we present a constant-approximation algorithm for the p-median problem in directed networks. Finally, we pose an open problem for future research.
