New approaches for facility distribution in chemical plants are proposed including an improved non-overlapping constraint based on projection relationships of facilities and a novel toxic gas dispersion constraint. In...New approaches for facility distribution in chemical plants are proposed including an improved non-overlapping constraint based on projection relationships of facilities and a novel toxic gas dispersion constraint. In consideration of the large number of variables in the plant layout model, our new method can significantly reduce the number of variables with their own projection relationships. Also, as toxic gas dispersion is a usual incident in a chemical plant, a simple approach to describe the gas leakage is proposed, which can clearly represent the constraints of potential emission source and sitting facilities. For solving the plant layout model, an improved genetic algorithm (GA) based on infeasible solution fix technique is proposed, which improves the globe search ability of GA. The case study and experiment show that a better layout plan can be obtained with our method, and the safety factors such as gas dispersion and minimum distances can be well handled in the solution.展开更多
This paper proposes a modification to distributed coordination function （DCF） to improve the channel utilization in IEEE 802.11 wireless local area networks （ WLANs）. In the modified DCF, when a station has conten...This paper proposes a modification to distributed coordination function （DCF） to improve the channel utilization in IEEE 802.11 wireless local area networks （ WLANs）. In the modified DCF, when a station has contended for the channel, it may transmit multiple data frames continuously to the same destination, which is called transmission burst（TB）. When the maximum number of data packets transmitted continuously in a TB is set to be 2, the performance is expected to be the best. The theoretical analysis and simulation results show that compared with the standard DCF, the modified DCF can increase the throughput and decrease the delay of the WLAN, and the modification does not introduce any additional control overhead.展开更多
基金Supported by the National Natural Science Foundation of China （61074153, 61104131）, and the Fundamental Research Funds for Central Universities of China （ZY1111, JD1104）.
文摘New approaches for facility distribution in chemical plants are proposed including an improved non-overlapping constraint based on projection relationships of facilities and a novel toxic gas dispersion constraint. In consideration of the large number of variables in the plant layout model, our new method can significantly reduce the number of variables with their own projection relationships. Also, as toxic gas dispersion is a usual incident in a chemical plant, a simple approach to describe the gas leakage is proposed, which can clearly represent the constraints of potential emission source and sitting facilities. For solving the plant layout model, an improved genetic algorithm (GA) based on infeasible solution fix technique is proposed, which improves the globe search ability of GA. The case study and experiment show that a better layout plan can be obtained with our method, and the safety factors such as gas dispersion and minimum distances can be well handled in the solution.
基金Supported by National Natural Science Foundation of China (No. 60472078 and No. 90604013).
文摘This paper proposes a modification to distributed coordination function （DCF） to improve the channel utilization in IEEE 802.11 wireless local area networks （ WLANs）. In the modified DCF, when a station has contended for the channel, it may transmit multiple data frames continuously to the same destination, which is called transmission burst（TB）. When the maximum number of data packets transmitted continuously in a TB is set to be 2, the performance is expected to be the best. The theoretical analysis and simulation results show that compared with the standard DCF, the modified DCF can increase the throughput and decrease the delay of the WLAN, and the modification does not introduce any additional control overhead.
