The unified bound on the fundamental limit of quantum dynamics rate, as quietly recently obtainedby Levitin and Toffoli [Phys.Rev.Lett.103 (2009) 160502], is improved and refined.The improvement may bearbitrarily larg...The unified bound on the fundamental limit of quantum dynamics rate, as quietly recently obtainedby Levitin and Toffoli [Phys.Rev.Lett.103 (2009) 160502], is improved and refined.The improvement may bearbitrarily large in certain cases.In particular, this puts a limit on the operation rate of quantum gates allowed byquantum mechanics.展开更多
The dependence of dislocation mobility on stress is the fundamental ingredient for the deformation in crystalline materials. Strength and ductility, the two most important properties characterizing mechanical behavior...The dependence of dislocation mobility on stress is the fundamental ingredient for the deformation in crystalline materials. Strength and ductility, the two most important properties characterizing mechanical behavior of crystalline metals, are in general governed by dislocation motion. Recording the position of a moving dislocation in a short time window is still challenging, and direct observations which enable us to deduce the speed-stress relationship of dislocations are still missing. Using large-scale molecular dynamics simulations, we obtain the motion of an obstacle-free twinning partial dislocation in face centred cubic crystals with spatial resolution at the angstrom scale and picosecond temporal information. The dislocation exhibits two limiting speeds: the first is subsonic and occurs when the resolved shear stress is on the order of hundreds of megapascal. While the stress is raised to gigapascal level, an abrupt jump of dislocation velocity occurs, from subsonic to supersonic regime. The two speed limits are governed respectively by the local transverse and longitudinal phonons associated with the stressed dislocation, as the two types of phonons facilitate dislocation gliding at different stress levels.展开更多
The method of nonlinear finite element reliability analysis (FERA) of slope stability using the technique of slip surface stress analysis (SSA) is studied. The limit state function that can consider the direction of s...The method of nonlinear finite element reliability analysis (FERA) of slope stability using the technique of slip surface stress analysis (SSA) is studied. The limit state function that can consider the direction of slip surface is given, and the formula-tions of FERA based on incremental tangent stiffness method and modified Aitken accelerating algorithm are developed. The limited step length iteration method (LSLIM) is adopted to calculate the reliability index. The nonlinear FERA code using the SSA technique is developed and the main flow chart is illustrated. Numerical examples are used to demonstrate the efficiency and robustness of this method. It is found that the accelerating convergence algorithm proposed in this study proves to be very efficient for it can reduce the iteration number greatly, and LSLIM is also efficient for it can assure the convergence of the iteration of the reliability index.展开更多
Numerical computations using the finite difference code FLAC (fast Lagrangian analysis of continua) are presented to evaluate the soil bearing capacity factors Nc,Nq and Nγ for circular smooth and rough footings. The...Numerical computations using the finite difference code FLAC (fast Lagrangian analysis of continua) are presented to evaluate the soil bearing capacity factors Nc,Nq and Nγ for circular smooth and rough footings. The influence of nonassociative flow rule on the ultimate bearing capacity of a circular footing is investigated. The footing rests on the surface of a homogeneous soil mass and a Mohr-Coulomb yield criterion have been assumed for the soil behavior. The values of ultimate bearing capacity factors Nc,Nq and Nγ are obtained for a wide range of values of the friction angle for five different values of the dilation angle. The values from the numerical simulation are found to decrease significantly with the increase of nonassociativity of the soil. The results are compared with those derived from existing classical solutions.展开更多
基金Supported by the National Natural Science Foundation of China under Grant No.10771208the Science Fund for Creative Research Groups under Grant No.10721101the Key Lab of Random Complex Structures and Data Science,CAS,under Grant No.2008DP173182
文摘The unified bound on the fundamental limit of quantum dynamics rate, as quietly recently obtainedby Levitin and Toffoli [Phys.Rev.Lett.103 (2009) 160502], is improved and refined.The improvement may bearbitrarily large in certain cases.In particular, this puts a limit on the operation rate of quantum gates allowed byquantum mechanics.
基金supported by the National Natural Science Foundation of China(Grant No.11425211)
文摘The dependence of dislocation mobility on stress is the fundamental ingredient for the deformation in crystalline materials. Strength and ductility, the two most important properties characterizing mechanical behavior of crystalline metals, are in general governed by dislocation motion. Recording the position of a moving dislocation in a short time window is still challenging, and direct observations which enable us to deduce the speed-stress relationship of dislocations are still missing. Using large-scale molecular dynamics simulations, we obtain the motion of an obstacle-free twinning partial dislocation in face centred cubic crystals with spatial resolution at the angstrom scale and picosecond temporal information. The dislocation exhibits two limiting speeds: the first is subsonic and occurs when the resolved shear stress is on the order of hundreds of megapascal. While the stress is raised to gigapascal level, an abrupt jump of dislocation velocity occurs, from subsonic to supersonic regime. The two speed limits are governed respectively by the local transverse and longitudinal phonons associated with the stressed dislocation, as the two types of phonons facilitate dislocation gliding at different stress levels.
基金supported by the National Natural Science Foundation of China (No. 50748033)the Specific Foundation for PhD of Hefei University of Technology (No. 2007GDBJ044), China
文摘The method of nonlinear finite element reliability analysis (FERA) of slope stability using the technique of slip surface stress analysis (SSA) is studied. The limit state function that can consider the direction of slip surface is given, and the formula-tions of FERA based on incremental tangent stiffness method and modified Aitken accelerating algorithm are developed. The limited step length iteration method (LSLIM) is adopted to calculate the reliability index. The nonlinear FERA code using the SSA technique is developed and the main flow chart is illustrated. Numerical examples are used to demonstrate the efficiency and robustness of this method. It is found that the accelerating convergence algorithm proposed in this study proves to be very efficient for it can reduce the iteration number greatly, and LSLIM is also efficient for it can assure the convergence of the iteration of the reliability index.
基金the National Natural Science Foundation of China (No. 50679041)the Mountaineering Program of Science and Technology Commission of Shanghai Municipality (No. 04dzl 2001)
文摘Numerical computations using the finite difference code FLAC (fast Lagrangian analysis of continua) are presented to evaluate the soil bearing capacity factors Nc,Nq and Nγ for circular smooth and rough footings. The influence of nonassociative flow rule on the ultimate bearing capacity of a circular footing is investigated. The footing rests on the surface of a homogeneous soil mass and a Mohr-Coulomb yield criterion have been assumed for the soil behavior. The values of ultimate bearing capacity factors Nc,Nq and Nγ are obtained for a wide range of values of the friction angle for five different values of the dilation angle. The values from the numerical simulation are found to decrease significantly with the increase of nonassociativity of the soil. The results are compared with those derived from existing classical solutions.
