This paper provides an overview of significant advances in nonlinear stochastic dynamics during the past two decades, including random response, stochastic stability, stochastic bifurcation, first passage problem and ...This paper provides an overview of significant advances in nonlinear stochastic dynamics during the past two decades, including random response, stochastic stability, stochastic bifurcation, first passage problem and nonlinear stochastic control. Topics for future research are also suggested.展开更多
For the uplink in the long-term evolution(LTE)systems,the physical random access channel(PRACH)adopts Zadoff–Chu(ZC) sequences as preamble sequences,and each user can choose a unique cyclic shift for user identificat...For the uplink in the long-term evolution(LTE)systems,the physical random access channel(PRACH)adopts Zadoff–Chu(ZC) sequences as preamble sequences,and each user can choose a unique cyclic shift for user identification.In high-mobility scenario,the Doppler frequency shift raises up the false alarm probability by inducing the correlation peak offsetting at the receiver side.Traditional detection method utilizes multiple search windows for searching the potential uplink users.When the Doppler frequency shift is larger than the subcarrier spacing,the energy of correlation peak leaks outside the search window and increases the false alarm probability.In this paper,we present a novel design for PRACH preamble sequence for high-speed railway scenario.Through numerical observation,we find out that the offset of the correlation peaks only depends on the initial root sequence number and the length of ZC sequences.Therefore,the root number of ZC sequences should be carefully designed to generate a preamble sequence to fight against the Doppler frequency shift.Consequently,those offsets of the correlation peaks are concentrated within a single search window,resulting in lower complexity of detection and lower probability of false alarm for random access in LTE uplink.展开更多
A modified discontinuous deformation analysis (DDA) algorithm was proposed to simulate the failure behavior of jointed rock. In the proposed algorithm, by using the Monte-Carlo technique, random joint network was gene...A modified discontinuous deformation analysis (DDA) algorithm was proposed to simulate the failure behavior of jointed rock. In the proposed algorithm, by using the Monte-Carlo technique, random joint network was generated in the domain of interest. Based on the joint network, the triangular DDA block system was automatically generated by adopting the advanced front method. In the process of generating blocks, numerous artificial joints came into being, and once the stress states at some artificial joints satisfy the failure criterion given beforehand, artificial joints will turn into real joints. In this way, the whole fragmentation process of rock mass can be replicated. The algorithm logic was described in detail, and several numerical examples were carried out to obtain some insight into the failure behavior of rock mass containing random joints. From the numerical results, it can be found that the crack initiates from the crack tip, the growth direction of the crack depends upon the loading and constraint conditions, and the proposed method can reproduce some complicated phenomena in the whole process of rock failure.展开更多
基金The project supported by the National Natural Science Foundation of China (19972059)
文摘This paper provides an overview of significant advances in nonlinear stochastic dynamics during the past two decades, including random response, stochastic stability, stochastic bifurcation, first passage problem and nonlinear stochastic control. Topics for future research are also suggested.
基金supported by National Natural Science Foundation of China(61032002,61101090 and 61471100)
文摘For the uplink in the long-term evolution(LTE)systems,the physical random access channel(PRACH)adopts Zadoff–Chu(ZC) sequences as preamble sequences,and each user can choose a unique cyclic shift for user identification.In high-mobility scenario,the Doppler frequency shift raises up the false alarm probability by inducing the correlation peak offsetting at the receiver side.Traditional detection method utilizes multiple search windows for searching the potential uplink users.When the Doppler frequency shift is larger than the subcarrier spacing,the energy of correlation peak leaks outside the search window and increases the false alarm probability.In this paper,we present a novel design for PRACH preamble sequence for high-speed railway scenario.Through numerical observation,we find out that the offset of the correlation peaks only depends on the initial root sequence number and the length of ZC sequences.Therefore,the root number of ZC sequences should be carefully designed to generate a preamble sequence to fight against the Doppler frequency shift.Consequently,those offsets of the correlation peaks are concentrated within a single search window,resulting in lower complexity of detection and lower probability of false alarm for random access in LTE uplink.
基金Projects(50479071, 40672191) supported by the National Natural Science Foundation of ChinaProject(SKLZ0801) supported by the Independent Research Key Project of State Key Laboratory of Geomechanics and Geotechnical EngineeringProject(SKLQ001) supported by the Independent Research Frontier Exploring Project of State Key Laboratory of Geomechanics and Geotechnical Engineering
文摘A modified discontinuous deformation analysis (DDA) algorithm was proposed to simulate the failure behavior of jointed rock. In the proposed algorithm, by using the Monte-Carlo technique, random joint network was generated in the domain of interest. Based on the joint network, the triangular DDA block system was automatically generated by adopting the advanced front method. In the process of generating blocks, numerous artificial joints came into being, and once the stress states at some artificial joints satisfy the failure criterion given beforehand, artificial joints will turn into real joints. In this way, the whole fragmentation process of rock mass can be replicated. The algorithm logic was described in detail, and several numerical examples were carried out to obtain some insight into the failure behavior of rock mass containing random joints. From the numerical results, it can be found that the crack initiates from the crack tip, the growth direction of the crack depends upon the loading and constraint conditions, and the proposed method can reproduce some complicated phenomena in the whole process of rock failure.
