In snow-icy road environment, the survey data indicate that the largest decrease in traffic flow running characters occurs when snow and ice begin to accumulate on the road surface. Saturation flow is decreased by 16%...In snow-icy road environment, the survey data indicate that the largest decrease in traffic flow running characters occurs when snow and ice begin to accumulate on the road surface. Saturation flow is decreased by 16% , speed is decreased by 30% , and start-up lost time is increased by 27%. Based on the signal control theory of HCM and Webster, the character values of traffic flow in different urban road environments were investigated, and the evolvement regularity of signal control parameters such as cycle, split, green time, offset, yellow time and red time in snow-icy road environment was analyzed. The impact factors and the changes in the scope of signal control parameters were achieved. Simulation results and practical application show that the signal control plan of road enviromnent without snow and ice will increase the vehicle delay, stop length and traffic congestion in snow-icy road environment. Thus, the traffic signal control system should address a suitable signal control plan based on different road environments.展开更多
By means of the Keldysh Green's function method,we investigate the spin-polarized electron transport in a three-terminal device,which is composed of three normal metal leads and two serially-coupled quantum dots(Q...By means of the Keldysh Green's function method,we investigate the spin-polarized electron transport in a three-terminal device,which is composed of three normal metal leads and two serially-coupled quantum dots(QDs).The Rashba spin-orbit interaction(RSOI) is also considered in one of the QDs.We show that the spin-polarized charge current with arbitrary spin polarization can be obtained because of the quantum spin interference effect arising from the Rashba spin precession phase,and it can be modulated by the system parameters such as the applied external voltages,the RSOI strength,the QD levels,as well as the dot-lead coupling strengths.Moreover,a fully spin-polarized current or a pure spin current without any accompanying charge current can also be controlled to flow in the system.Our findings indicate that the proposed model can serve as an all-electrical spin device in spintronics field.展开更多
基金Sponsored by the National Basic Research and Development Program of China(Grant No.2006CB705505) Research Fund for the Doctoral Program of Higher Education of China(Grant No.200802131012)
文摘In snow-icy road environment, the survey data indicate that the largest decrease in traffic flow running characters occurs when snow and ice begin to accumulate on the road surface. Saturation flow is decreased by 16% , speed is decreased by 30% , and start-up lost time is increased by 27%. Based on the signal control theory of HCM and Webster, the character values of traffic flow in different urban road environments were investigated, and the evolvement regularity of signal control parameters such as cycle, split, green time, offset, yellow time and red time in snow-icy road environment was analyzed. The impact factors and the changes in the scope of signal control parameters were achieved. Simulation results and practical application show that the signal control plan of road enviromnent without snow and ice will increase the vehicle delay, stop length and traffic congestion in snow-icy road environment. Thus, the traffic signal control system should address a suitable signal control plan based on different road environments.
基金Supported by National Natural Science Foundation of China under Grant Nos. 10704016,110704032,110704033Natural Science Foundation of Jiangsu Province under Grant No. BK2010416National Basic Research Project of China under Grant No. 2009CB945504
文摘By means of the Keldysh Green's function method,we investigate the spin-polarized electron transport in a three-terminal device,which is composed of three normal metal leads and two serially-coupled quantum dots(QDs).The Rashba spin-orbit interaction(RSOI) is also considered in one of the QDs.We show that the spin-polarized charge current with arbitrary spin polarization can be obtained because of the quantum spin interference effect arising from the Rashba spin precession phase,and it can be modulated by the system parameters such as the applied external voltages,the RSOI strength,the QD levels,as well as the dot-lead coupling strengths.Moreover,a fully spin-polarized current or a pure spin current without any accompanying charge current can also be controlled to flow in the system.Our findings indicate that the proposed model can serve as an all-electrical spin device in spintronics field.
