Through the theoretical analysis and computer simulation,the optimized design principles for Si/SiGe PMOSFETs are given,including the choice of gate materials,the determination of Ge percentage and the profile in SiGe...Through the theoretical analysis and computer simulation,the optimized design principles for Si/SiGe PMOSFETs are given,including the choice of gate materials,the determination of Ge percentage and the profile in SiGe channel,the thickness optimization of dioxide and silicon cap layer,and the adjustment of threshold voltage.In light of them,a SiGe PMOSFET is designed and fabricated successfully.The measurements indicate that the transconductance is 45mS/mm (300K) and 92mS/mm (77K) for SiGe PMOSFET's (L=2μm),while it is 33mS/mm (300K) and 39mS/mm (77K) for Si PMOSFET.展开更多
By decoupling control plane and data plane,Software-Defined Networking(SDN) approach simplifies network management and speeds up network innovations.These benefits have led not only to prototypes,but also real SDN dep...By decoupling control plane and data plane,Software-Defined Networking(SDN) approach simplifies network management and speeds up network innovations.These benefits have led not only to prototypes,but also real SDN deployments.For wide-area SDN deployments,multiple controllers are often required,and the placement of these controllers becomes a particularly important task in the SDN context.This paper studies the problem of placing controllers in SDNs,so as to maximize the reliability of SDN control networks.We present a novel metric,called expected percentage of control path loss,to characterize the reliability of SDN control networks.We formulate the reliability-aware control placement problem,prove its NP-hardness,and examine several placement algorithms that can solve this problem.Through extensive simulations using real topologies,we show how the number of controllers and their placement influence the reliability of SDN control networks.Besides,we also found that,through strategic controller placement,the reliability of SDN control networks can be significantly improved without introducing unacceptable switch-to-controller latencies.展开更多
Wind energy is a clean and renewable energy for which technology has developed rapidly in recent years.Wind turbines are commonly supported on tubular steel towers.As the turbine size is growing and the towers are ris...Wind energy is a clean and renewable energy for which technology has developed rapidly in recent years.Wind turbines are commonly supported on tubular steel towers.As the turbine size is growing and the towers are rising in height,steel towers are required to be sufficiently strong and stiff,consequently leading to high construction costs.To tackle this problem,a new type of prestressed concrete tower was designed employing a novel tower concept having a regular octagon cross section with interior ribs on each side,which was optimized by comparing the natural frequency and stress difference under the same lateral load in different directions of the tower.The designed tower features a tapered profile that reduces the area subjected to wind;the tapered profile reduces the total weight,applied moment and the capital cost.An optimization method was developed employing ABAQUS software and a genetic algorithm.A target function was defined on the basis of the minimum cost of the concrete and prestressed tendon used,and constraints were applied by accounting for the stress,displacements and natural frequency of the tower.Employing the method,a 100 m prestressed concrete tower system for a 5 MW turbine was optimized and designed under wind and earthquake loads.The paper also reports a systematic design procedure incorporating the finite element method and the optimization method for the prestressed concrete wind-turbine towers.展开更多
文摘Through the theoretical analysis and computer simulation,the optimized design principles for Si/SiGe PMOSFETs are given,including the choice of gate materials,the determination of Ge percentage and the profile in SiGe channel,the thickness optimization of dioxide and silicon cap layer,and the adjustment of threshold voltage.In light of them,a SiGe PMOSFET is designed and fabricated successfully.The measurements indicate that the transconductance is 45mS/mm (300K) and 92mS/mm (77K) for SiGe PMOSFET's (L=2μm),while it is 33mS/mm (300K) and 39mS/mm (77K) for Si PMOSFET.
基金supported in part by the National High Technology Research and Development Program(863 Program)of China under Grant No.2011AA01A101the National High Technology Research and Development Program(863 Program)of China under Grant No.2013AA01330the National High Technology Research and Development Program(863 Program)of China under Grant No.2013AA013303
文摘By decoupling control plane and data plane,Software-Defined Networking(SDN) approach simplifies network management and speeds up network innovations.These benefits have led not only to prototypes,but also real SDN deployments.For wide-area SDN deployments,multiple controllers are often required,and the placement of these controllers becomes a particularly important task in the SDN context.This paper studies the problem of placing controllers in SDNs,so as to maximize the reliability of SDN control networks.We present a novel metric,called expected percentage of control path loss,to characterize the reliability of SDN control networks.We formulate the reliability-aware control placement problem,prove its NP-hardness,and examine several placement algorithms that can solve this problem.Through extensive simulations using real topologies,we show how the number of controllers and their placement influence the reliability of SDN control networks.Besides,we also found that,through strategic controller placement,the reliability of SDN control networks can be significantly improved without introducing unacceptable switch-to-controller latencies.
基金supported by the National Natural Science Foundation of China(Grant No.51078231)
文摘Wind energy is a clean and renewable energy for which technology has developed rapidly in recent years.Wind turbines are commonly supported on tubular steel towers.As the turbine size is growing and the towers are rising in height,steel towers are required to be sufficiently strong and stiff,consequently leading to high construction costs.To tackle this problem,a new type of prestressed concrete tower was designed employing a novel tower concept having a regular octagon cross section with interior ribs on each side,which was optimized by comparing the natural frequency and stress difference under the same lateral load in different directions of the tower.The designed tower features a tapered profile that reduces the area subjected to wind;the tapered profile reduces the total weight,applied moment and the capital cost.An optimization method was developed employing ABAQUS software and a genetic algorithm.A target function was defined on the basis of the minimum cost of the concrete and prestressed tendon used,and constraints were applied by accounting for the stress,displacements and natural frequency of the tower.Employing the method,a 100 m prestressed concrete tower system for a 5 MW turbine was optimized and designed under wind and earthquake loads.The paper also reports a systematic design procedure incorporating the finite element method and the optimization method for the prestressed concrete wind-turbine towers.
