THERMODYNAMIC VARIATIONAL APPROACH FOR CLIMB OF AN EDGE DISLOCATION

A general thermodynamic variational approach is applied to study the force on an edge dislocation, which drives the dislocation to climb. Our attention is focused on the physical mechanism responsible for dislocation climb. A dislocation in a material element climbs as a result of vacancies diffusing into or out from the dislocation core, with the dislocation acting as a source or a sink for vacancy diffusion in the material element. The basic governing equations for dislocation climb and the climb forces on the dislocation are obtained naturally as a result of the present thermodynamic variational approach.     

Fuel‐Free Micro‐/Nanomotors as Intelligent Therapeutic Agents

There are many efficient biological motors in Nature that perform complex functions by converting chemical energy into mechanical motion. Inspired by this, the development of their synthetic counterparts has aroused tremendous research interest in the past decade. Among these man‐made motor systems, the fuel‐free (or light, magnet, ultrasound, or electric field driven) motors are advantageous in terms of controllability, lifespan, and biocompatibility concerning bioapplications, when compared with their chemically powered counterparts. Therefore, this review will highlight the latest biomedical applications in the versatile field of externally propelled micro‐/nanomotors, as well as elucidating their driving mechanisms. A perspective into the future of the micro‐/nanomotors field and a discussion of the challenges we need to face along the road towards practical clinical translation of external‐field‐propelled micro‐/nanomotors will be provided.     

Generalized hyperbolic perturbation method for homoclinic solutions of strongly nonlinear autonomous systems

A generalized hyperbolic perturbation method is presented for homoclinic solutions of strongly nonlinear autonomous oscillators,in which the perturbation procedure is improved for those systems whose exact homoclinic generating solutions cannot be explicitly derived.The generalized hyperbolic functions are employed as the basis functions in the present procedure to extend the validity of the hyperbolic perturbation method.Several strongly nonlinear oscillators with quadratic,cubic,and quartic nonlinearity are studied in detail to illustrate the efficiency and accuracy of the present method.     

Hamiltonian weakly damped autonomous systems exhibiting periodic attractors

The dynamic local stability of autonomous Hamiltonian, weakly damped, lumped-mass (discrete) systems is reconsidered. For such potential(conservative) systems conditions for the existence of limit cycles are discussed by studying the effect of the damping matrix on the Jacobian eigenvalues. New findings that contradict existing results are presented. Thus, undamped stable symmetric systems with the inclusion of slight damping may experience: (a) a double zero eigenvalue bifurcation, a degenerate Hopf bifurcation and a generic (usual) Hopf bifurcation, and (b) a limit cycle (dynamic) mode of instability prior to the static (divergence) mode of instability (failure of Zieglers kinetic criterion). A variety of numerical examples verified by a nonlinear analysis confirm the validity of the theoretical findings presented herein. Received: January 3, 2003; revised: July 14, 2003 and February 17, 2004     

Subspace exit properties of extremal controls

In a linear control system setting, we derive conditions under which extremal controls give rise to trajectories which exit a given subspace. An application is in determining effectiveness of linear state restraints in time-optimal problems.This work was supported by the National Research Council of Canada under Grant No. A4641.     

Tractable model discrimination for safety–critical systems with disjunctive and coupled constraints

This paper considers the model discrimination problem among a finite number of models in safety–critical systems that are subjected to constraints that can be disjunctive and where state and input constraints can be coupled with each other. In particular, we consider both the optimal input design problem for active model discrimination that is solved offline as well as the online passive model discrimination problem via a model invalidation framework. To overcome the issues associated with non-convex and generalized semi-infinite constraints due to the disjunctive and coupled constraints, we propose some techniques for reformulating these constraints in a computationally tractable manner by leveraging the Karush–Kuhn–Tucker (KKT) conditions and introducing binary variables, thus recasting the active and passive model discrimination problems into tractable mixed-integer linear/quadratic programming (MILP/MIQP) problems. When compared with existing approaches, our method is able to obtain the optimal solution and is observed in simulations to also result in less computation time. Finally, we demonstrate the effectiveness of the proposed active model discrimination approach for estimating driver intention with disjunctive safety constraints and state–input coupled curvature constraints, as well as for fault identification.     

Controlling quantum discord dynamics in cavity QED systems by applying a classical driving field with phase decoherence

We investigate a two-level atom interacting with a quantized cavity field and a classical driving field in the presence of phase decoherence and find that a stationary quantum discord can arise in the interaction of the atom and cavity field as the time turns to infinity. We also find that the stationary quantum discord can be increased by applying a classical driving field. Furthermore, we explore the quantum discord dynamics of two identical non-interacting two-level atoms independently interacting with a quantized cavity field and a classical driving field in the presence of phase decoherence. Results show that the quantum discord between two atoms is more robust than entanglement under phase decoherence and the classical driving field can help to improve the amount of quantum discord of the two atoms.     

Activity enhancement of acetate precursor prepared on MnO_x-CeO_2 catalyst for low-temperature NH_3-SCR: Effect of gaseous acetone addition

MnO_x-CeO_2 catalysts are developed by hydrolysis driving redox method using acetate precursor(3 Mn1 Ce-Ac) and nitrate precursor(3 Mn1 Ce-N) for the selective catalytic reduction(SCR) of NO_x by NH_3.A counterpart sample(Cop-3 Mn1 Ce) was prepared by the NH_3·H_2 O co-precipitation method for comparison purpose.Combining the results of physicochemical properties characterization and performance test,we find that the 3 Mn1 Ce-Ac catalyst with some nanorod structures is highly active for the deNOx process.The SCR activity of the 3 Mn1 Ce-Ac catalyst is more admirable than the 3 Mn1 Ce-N and the Cop-3 Mn1 Ce catalysts due to plentiful Lewis acid sites,excellent low-temperature reducibility,and superior surface area resulted from O_2 generation during the pre paration procedure.The 3 Mn1 Ce-Ac still exhibits the greatest performance for the deNOx process when gaseous acetone is in the SCR feed gas.The NO_x conversion and N_2 selectivity over the 3 Mn1 Ce-Ac are both improved by gaseous acetone above150℃ due to the inhibition of SCR undesired side reactions(NSCR C-O reactions) and "slow-SCR" process.     

直流供电零电流变换串联谐振激光电源

设计了一款采用串联谐振全桥逆变电路结构的灯泵浦激光电源.在对电源信号发生电路、隔离驱动电路和逆变谐振电路等模块进行分析和设计的基础上,设计了一款重频达5 Hz,最高重频达10 Hz的灯泵激光器驱动电源.该电源不但满足5 Hz灯泵激光器的技术要求,而且具有尺寸小、充电效率高和结构简单等优点.