In this paper, proportional fairness(PF)-based energy-efficient power allocation is studied for multiple-input multiple-output(MIMO) non-orthogonal multiple access(NOMA) systems. In our schemes, statistical channel st...In this paper, proportional fairness(PF)-based energy-efficient power allocation is studied for multiple-input multiple-output(MIMO) non-orthogonal multiple access(NOMA) systems. In our schemes, statistical channel state information(CSI) is utilized for perfect CSI is impossible to achieve in practice. PF is used to balance the transmission efficiency and user fairness. Energy efficiency(EE) is formulated under basic data rate requirements and maximum transmitting power constraints. Due to the non-convex nature of EE, a two-step algorithm is proposed to obtain sub-optimal solution with a low complexity. Firstly, power allocation is determined by golden section search for fixed power. Secondly total transmitting power is determined by fractional programming method in the feasible regions. Compared to the performance of MIMO-NOMA without PF constraint, fairness is obtained at expense of decreasing of EE.展开更多
Fast flow simulation is imperative in the design of pulsating ventilation,which is potentially efficient in indoor air contaminant removal.The execution of the conventional CFD method requires considerable amount of c...Fast flow simulation is imperative in the design of pulsating ventilation,which is potentially efficient in indoor air contaminant removal.The execution of the conventional CFD method requires considerable amount of computational resources.In this study,five different numerical schemes were proposed based on fast fluid dynamics(FFD)and fractional step(FS)methods,and were evaluated to achieve quick simulation of airflow/contaminant dispersion.One of these numerical schemes was identified with the best overall computing efficiency for investigating the performance of pulsating ventilation.With this numerical scheme at hand,the air contaminant removal effectiveness of different ventilation types was evaluated.Two kinds of pulsating ventilation and one kind of steady ventilation were tested upon a benchmark isothermal mixing chamber.The effect of adjusting supply velocity parameters on the ventilation performance was also investigated.CO_(2)concentration,airflow pattern,and vortex structure of different ventilation types were illustrated and analyzed.The results reveal that the FS method is more suitable for transient simulation of wall-bounded indoor airflow than the FFD method,and 34%–51%of computing time could be saved compared to the conventional CFD method.Regarding the choice of ventilation type,steady ventilation might result in short-circuit airflow and stagnant zones;alternatively,pulsating ventilation has greater potential in air contaminant removal due to its ever-changing vortex structure.展开更多
Fibrous filters are often used to remove contaminants including both dusts and liquid droplets from natural gas. This paper aims to evaluate the gas-liquid separation performance of three types of cartridge filters us...Fibrous filters are often used to remove contaminants including both dusts and liquid droplets from natural gas. This paper aims to evaluate the gas-liquid separation performance of three types of cartridge filters used in the West-East natural gas transmission project. The comparison of the original pressure drop of clean filters and the evolution of pressure drop as liquid droplets deposited in the filter media are described. The original pressure drops of these filters were similar but the pressure drops at a steady state were different. Fractional efficiency was used to study the separation performance of cartridge filters. Droplets at the outlet of the filters had small diameters, no more than 3 μm, but were very numerous. The effect of filtration velocity on gas-liquid separation performance was analyzed. Higher filtration velocity indicated better gas-liquid separation performance. Finally the quality factor related to pressure drop and filtration efficiency was applied to evaluate the gas-liquid separation performance.展开更多
If Hall plates are used as magnetic field sensors they are usually powered up by a current source connected to a pair of non-neighboring contacts. The output voltage is tapped at another pair of non-neighboring contac...If Hall plates are used as magnetic field sensors they are usually powered up by a current source connected to a pair of non-neighboring contacts. The output voltage is tapped at another pair of non-neighboring contacts. In this paper we study more general operating conditions of Hall plates with an arbitrary number of contacts. In such hybrid operating modes current sources are connected to a first set of contacts and voltage sources to a second set of contacts. Output voltages are tapped at the first set of contacts and output currents are measured at the second set of contacts. All these output signals are multiplied by coefficients and added up. The purpose of this work is to figure out which operating mode and which Hall plate achieve maximum signal at minimum thermal noise and power dissipation. To this end we develop a theory, which gives the ratio of signal over noise and power as a function of the resistance matrix of Hall plates, of the supply voltages and currents, and of the coefficients. Optimization is done analytically in closed form and numerically for specific examples. The results are: 1) all operating modes have identical noise performance if their parameters are optimized;2) for any Hall plate one can measure its resistance matrix and insert its values into our formulae to obtain the optimum supply currents and coefficients for optimum noise performance.展开更多
To reduce carbon intensity, an improved management method balancing the reduction in costs and greenhouse gas(GHG)emissions is required for Tianjin's waste management system. Firstly, six objective functions, name...To reduce carbon intensity, an improved management method balancing the reduction in costs and greenhouse gas(GHG)emissions is required for Tianjin's waste management system. Firstly, six objective functions, namely, cost minimization, GHG minimization, eco-efficiency minimization, cost maximization, GHG maximization and eco-efficiency maximization, are built and subjected to the same constraints with each objective function corresponding to one scenario. Secondly, GHG emissions and costs are derived from the waste flow of each scenario. Thirdly, the range of GHG emissions and costs of other potential scenarios are obtained and plotted through adjusting waste flow with infinitely possible step sizes according to the correlation among the above six scenarios. And the optimal scenario is determined based on this range. The results suggest the following conclusions. 1) The scenarios located on the border between scenario cost minimization and GHG minimization create an optimum curve, and scenario GHG minimization has the smallest eco-efficiency on the curve; 2) Simple pursuit of eco-efficiency minimization using fractional programming may be unreasonable; 3) Balancing GHG emissions from incineration and landfills benefits Tianjin's waste management system as it reduces GHG emissions and costs.展开更多
基金supported by the National Natural Science Foundation of China (No. 61671252)
文摘In this paper, proportional fairness(PF)-based energy-efficient power allocation is studied for multiple-input multiple-output(MIMO) non-orthogonal multiple access(NOMA) systems. In our schemes, statistical channel state information(CSI) is utilized for perfect CSI is impossible to achieve in practice. PF is used to balance the transmission efficiency and user fairness. Energy efficiency(EE) is formulated under basic data rate requirements and maximum transmitting power constraints. Due to the non-convex nature of EE, a two-step algorithm is proposed to obtain sub-optimal solution with a low complexity. Firstly, power allocation is determined by golden section search for fixed power. Secondly total transmitting power is determined by fractional programming method in the feasible regions. Compared to the performance of MIMO-NOMA without PF constraint, fairness is obtained at expense of decreasing of EE.
基金supported by the National Natural Science Foundation of China under the grant number of 52278116.
文摘Fast flow simulation is imperative in the design of pulsating ventilation,which is potentially efficient in indoor air contaminant removal.The execution of the conventional CFD method requires considerable amount of computational resources.In this study,five different numerical schemes were proposed based on fast fluid dynamics(FFD)and fractional step(FS)methods,and were evaluated to achieve quick simulation of airflow/contaminant dispersion.One of these numerical schemes was identified with the best overall computing efficiency for investigating the performance of pulsating ventilation.With this numerical scheme at hand,the air contaminant removal effectiveness of different ventilation types was evaluated.Two kinds of pulsating ventilation and one kind of steady ventilation were tested upon a benchmark isothermal mixing chamber.The effect of adjusting supply velocity parameters on the ventilation performance was also investigated.CO_(2)concentration,airflow pattern,and vortex structure of different ventilation types were illustrated and analyzed.The results reveal that the FS method is more suitable for transient simulation of wall-bounded indoor airflow than the FFD method,and 34%–51%of computing time could be saved compared to the conventional CFD method.Regarding the choice of ventilation type,steady ventilation might result in short-circuit airflow and stagnant zones;alternatively,pulsating ventilation has greater potential in air contaminant removal due to its ever-changing vortex structure.
文摘Fibrous filters are often used to remove contaminants including both dusts and liquid droplets from natural gas. This paper aims to evaluate the gas-liquid separation performance of three types of cartridge filters used in the West-East natural gas transmission project. The comparison of the original pressure drop of clean filters and the evolution of pressure drop as liquid droplets deposited in the filter media are described. The original pressure drops of these filters were similar but the pressure drops at a steady state were different. Fractional efficiency was used to study the separation performance of cartridge filters. Droplets at the outlet of the filters had small diameters, no more than 3 μm, but were very numerous. The effect of filtration velocity on gas-liquid separation performance was analyzed. Higher filtration velocity indicated better gas-liquid separation performance. Finally the quality factor related to pressure drop and filtration efficiency was applied to evaluate the gas-liquid separation performance.
文摘If Hall plates are used as magnetic field sensors they are usually powered up by a current source connected to a pair of non-neighboring contacts. The output voltage is tapped at another pair of non-neighboring contacts. In this paper we study more general operating conditions of Hall plates with an arbitrary number of contacts. In such hybrid operating modes current sources are connected to a first set of contacts and voltage sources to a second set of contacts. Output voltages are tapped at the first set of contacts and output currents are measured at the second set of contacts. All these output signals are multiplied by coefficients and added up. The purpose of this work is to figure out which operating mode and which Hall plate achieve maximum signal at minimum thermal noise and power dissipation. To this end we develop a theory, which gives the ratio of signal over noise and power as a function of the resistance matrix of Hall plates, of the supply voltages and currents, and of the coefficients. Optimization is done analytically in closed form and numerically for specific examples. The results are: 1) all operating modes have identical noise performance if their parameters are optimized;2) for any Hall plate one can measure its resistance matrix and insert its values into our formulae to obtain the optimum supply currents and coefficients for optimum noise performance.
基金Project(51406133) supported by the National Natural Science Foundation of ChinaProject supported by the Scientific Research Foundation for the Returned Overseas,ChinaProject supported by Independent Innovation Fund of Tianjin University,China
文摘To reduce carbon intensity, an improved management method balancing the reduction in costs and greenhouse gas(GHG)emissions is required for Tianjin's waste management system. Firstly, six objective functions, namely, cost minimization, GHG minimization, eco-efficiency minimization, cost maximization, GHG maximization and eco-efficiency maximization, are built and subjected to the same constraints with each objective function corresponding to one scenario. Secondly, GHG emissions and costs are derived from the waste flow of each scenario. Thirdly, the range of GHG emissions and costs of other potential scenarios are obtained and plotted through adjusting waste flow with infinitely possible step sizes according to the correlation among the above six scenarios. And the optimal scenario is determined based on this range. The results suggest the following conclusions. 1) The scenarios located on the border between scenario cost minimization and GHG minimization create an optimum curve, and scenario GHG minimization has the smallest eco-efficiency on the curve; 2) Simple pursuit of eco-efficiency minimization using fractional programming may be unreasonable; 3) Balancing GHG emissions from incineration and landfills benefits Tianjin's waste management system as it reduces GHG emissions and costs.
