Room and pillar sizes are key factors for safe mining and ore recovery in open-stope mining. To investigate the influence of room and pillar configurations on stope stability in highly fractured and weakened areas, an...Room and pillar sizes are key factors for safe mining and ore recovery in open-stope mining. To investigate the influence of room and pillar configurations on stope stability in highly fractured and weakened areas, an orthogonal design with two factors, three levels and nine runs was proposed, followed by three-dimensional numerical simulation using ANSYS and FLAC3~. Results show that surface settlement after excavation is concentrically ringed, and increases with the decrease of pillar width and distances to stope gobs. In the meantime, the ore-control fault at the ore-rock boundary and the fractured argillaceous dolomite with intercalated slate at the hanging wall deteriorate the roof settlement. Additionally, stope stability is challenged due to pillar rheological yield and stress concentration, and both are induced by redistribution of stress and plastic zones after mining. Following an objective function and a constraint function, room and pillar configuration with widths of 14 m and 16 m, respectively, is presented as the optimization for improving the ore recovery rate while maintaining a safe working environment.展开更多
International standards impose several constraints concerning the electric power quality and require that the harmonic content of the line current of grid connected equipment is below assigned limits; for this reason,...International standards impose several constraints concerning the electric power quality and require that the harmonic content of the line current of grid connected equipment is below assigned limits; for this reason, operating of AC-DC converters with high power factor and low line current distortion has become essential. In this paper, the prototypal realization of a three-phase AC-DC 48 V power electronic converter for telecom system supplying is described and experimental testing results are discussed. The main constraints in the power supply design are the required power density of about 900 W per dm3 as well as the absence of the neutral wire in the supply grid. The carried out investigation is focused on three-level power converter configurations which are considered in order to reduce voltage rating of power switches. As a result of the reduced voltage, low on-resistance metal-oxide-semiconductor field effect transistors can be used in the power stage, solution which allows to achieve improved efficiency as well as increased switching frequency with respect to the insulated gate bipolar transistors based two-level topologies.展开更多
The process described here is well at the heart of the appearance of pigmentary materials and their interactions with light. It is indeed based on the property of colored materials to reflect, in a selective way, the ...The process described here is well at the heart of the appearance of pigmentary materials and their interactions with light. It is indeed based on the property of colored materials to reflect, in a selective way, the colored radiations of light. The innovation is here based on a more subtle and more complete process, using the trichromy, i.e., all the possibilities of the white light, which is split in three primary radiations： red^een--blue. One can, indeed, animate a pigmentary surface by the alternate projection of these three colors, and thus reveal three different images on the same support, or create a motion effect. However, in this process, the weakness of bhie, compared to green and red, might constitute an obstacle. But that will be compensated by the use of fluorescent colors, instead of ordinary colors. This process may provide very spectacular applications in the fields of lighting, architecture, design, scenography, booths, display windows, etc.. We shall propose a step-to-step approach.展开更多
基金Projects(50934002,51074013,51104100)supported by the National Natural Science Foundation of ChinaProject(IRT0950)supported by the Program for Changjiang Scholars and Innovative Research Team in University of China
文摘Room and pillar sizes are key factors for safe mining and ore recovery in open-stope mining. To investigate the influence of room and pillar configurations on stope stability in highly fractured and weakened areas, an orthogonal design with two factors, three levels and nine runs was proposed, followed by three-dimensional numerical simulation using ANSYS and FLAC3~. Results show that surface settlement after excavation is concentrically ringed, and increases with the decrease of pillar width and distances to stope gobs. In the meantime, the ore-control fault at the ore-rock boundary and the fractured argillaceous dolomite with intercalated slate at the hanging wall deteriorate the roof settlement. Additionally, stope stability is challenged due to pillar rheological yield and stress concentration, and both are induced by redistribution of stress and plastic zones after mining. Following an objective function and a constraint function, room and pillar configuration with widths of 14 m and 16 m, respectively, is presented as the optimization for improving the ore recovery rate while maintaining a safe working environment.
文摘International standards impose several constraints concerning the electric power quality and require that the harmonic content of the line current of grid connected equipment is below assigned limits; for this reason, operating of AC-DC converters with high power factor and low line current distortion has become essential. In this paper, the prototypal realization of a three-phase AC-DC 48 V power electronic converter for telecom system supplying is described and experimental testing results are discussed. The main constraints in the power supply design are the required power density of about 900 W per dm3 as well as the absence of the neutral wire in the supply grid. The carried out investigation is focused on three-level power converter configurations which are considered in order to reduce voltage rating of power switches. As a result of the reduced voltage, low on-resistance metal-oxide-semiconductor field effect transistors can be used in the power stage, solution which allows to achieve improved efficiency as well as increased switching frequency with respect to the insulated gate bipolar transistors based two-level topologies.
文摘The process described here is well at the heart of the appearance of pigmentary materials and their interactions with light. It is indeed based on the property of colored materials to reflect, in a selective way, the colored radiations of light. The innovation is here based on a more subtle and more complete process, using the trichromy, i.e., all the possibilities of the white light, which is split in three primary radiations： red^een--blue. One can, indeed, animate a pigmentary surface by the alternate projection of these three colors, and thus reveal three different images on the same support, or create a motion effect. However, in this process, the weakness of bhie, compared to green and red, might constitute an obstacle. But that will be compensated by the use of fluorescent colors, instead of ordinary colors. This process may provide very spectacular applications in the fields of lighting, architecture, design, scenography, booths, display windows, etc.. We shall propose a step-to-step approach.
