Jian-Min Chen

Enhanced thermoelectric performance in p-type BiSbTe bulk alloy with nanoinclusion of ZnAlO

p-type BiSbTe/xu2002wtu2009%u2002ZnAlO (x=0, 0.25, 0.5, 0.75, and 1.0) composites were prepared by zone melting method. A peak thermoelectric figure of merit (ZT) of 1.33 at 370 K was achieved for the sample with x=0.75, about 34% higher than that of BiSbTe at the same temperature, making these composites more attractive for commercial applications. This enhancement of ZT can be mainly ascribed to a remarkable increase of the electrical conductivity and a simultaneous decrease of the lattice thermal conductivity by the introduction of ZnAlO nanopowder.

Overview of plasma-facing materials and components for EAST

By the end of September 2006, the engineering commissioning of the Experimental Advanced Superconducting Tokamak (EAST) was completed and the first H2 plasma was achieved with stainless steel as the plasma-facing material (PFM). In the following phases, with gradual increase in the heating power, the EAST divertor targets have to handle expected heat loads up to ~10 MW m−2. The PFMs to be employed include doped graphite and W coatings. The former will be used to cover the whole plasma-facing surface in the first phase, and then the latter applied to replace the graphite tiles gradually in the second phase, and finally a whole W plasma-facing surface will be expected. Graphite has been studied for many years and contributed greatly to the HT-7 to achieve long pulses of some 100 s. The W coatings are being developed and the latest R&D development is reported in the paper.

Investigation of superlubricity in a two-dimensional Frenkel-Kontorova model with square lattice symmetry

A two-dimensional Frenkel–Kontorova model with a square symmetry substrate potential for a square lattice layer driven by an external driving force with an arbitrary direction α and an arbitrary misfit angle θ between upper and lower layers is presented in this paper. The effects of the system parameters have been investigated. The application of our results to the tribology is discussed and the dependence of the static friction force on the system parameters is studied. How to make the material with superlubricity is suggested.

Rectification and phase locking in overdamped two-dimensional Frenkel-Kontorova model

The rectification phenomena and the phase locking for an overdamped two-dimensional Frenkel-Kontorova model system with commensurate structure under ac- and dc-driven external forces are demonstrated. As a function of longitudinal dc amplitude, the longitudinal velocity increases in a series of steps of height jν0. In the steps, rectifications in the transverse direction occur though there are no net dc force in the transverse direction. Our results can be applied to vortices in superconductors, classical electron motion, biomolecules moving through 2D arrays of posts, and especially in tribology. In these active ratchets the rectified velocities can be controlled by jν0.

Hysteresis in the pinning-depinning transition in underdamped two-dimensional Frenkel-Kontorova model

Hysteretic phenomenon is studied in the 2D Frenkel-Kontorova model system. In the depinning process, two critical points Fs1 and Fs2 are found. In the pinning process, two critical points Fb1 and Fb2 are also found. The dependence of four critical forces Fs1, Fs2, Fb1, Fb2 on the system parameters such as external driving force, misfit angle, winding number, interatomic strength is investigated. The winding number b/a substantially affect the depinning forces of Fs1 and Fs2, but not the pinning forces of both Fb1 and Fb2. The pinning force of Fb2 linearly increases as the interatomic interaction strength (K) increase. The dependence of both Fb1 and Fb2 on the misfit angle θ is not in fractal structure which is different from the depinning force of Fs1.

Effect of multicomponent dust grains in a cold quantum dusty plasma

By employing the quantum hydrodynamic model for electron—ion—dust plasma, we derive a dispersion relation of the quantum dusty plasma. The effects of the dust size distribution on the dispersion relation in a cold quantum dusty plasma are studied. Both analytical and numerical results are given to compare the differences between the dusty plasma by considering the dust size distribution and the mono-sized dusty plasma. It is shown that many system parameters can significantly influence the dispersion relation of the quantum dusty plasma.

Synchronization in the Frenkel-Kontorova type system

Synchronization in the Frenkel–Kontorova model is studied by molecular-dynamics simulations. We employ the similarity function to investigate the lag synchronization (LS) and complete synchronization, and provide evidence that the type of synchronization depends not only on the coupling strength but also on the differences of the initial conditions. The LS of the system is affected by nonlinear effects due to the difference of the initial momentum of the two particles. The phase diagram is also given. The results can be better understood with coupled oscillations.

Synchronization and phase transition in the Frenkel–Kontorova-type model system

A coupled Hamiltonian system of the Frenkel–Kontorova model is studied in this paper, including the measure synchronization and the complete synchronization of the model. The measure synchronization depends not only on the coupling strength but also on the initial conditions. In a certain range of initial conditions, complete synchronization is reached when the system is in the measure synchronization, which means that as the coupling strength increases the energy can be transferred from one particle to another more easily. In other words, the average vibration amplitude of two particles tends to be identical as the coupling strength increases. The critical point Kc depends on both the initial total energy of two particles and the initial energy difference between two particles. Moreover, it is also related to the initial velocity directions of the two particles.

Frictional Dynamics in a Two Dimensional Frenkel-Kontorova Model with Square Lattice Symmetry

A two-dimensional (2D) Frenkel-Kontorova (FK) model with a square symmetry substrate potential for a square lattice layer driven by an external driving force with an arbitrary direction α and an arbitrary misfit angle θ between upper and lower layers is presented. Both the theoretical and the numerical study of the lock-to-sliding transition for this 2D FK model are given. The results show that both the misfit angle θ and the direction (cosα, sinα) of the external driving force play crucial roles in the scenario of the lock-to-sliding transition and the determination of the structure of the sliding state. The effects of the system parameters such as the magnitude of the adhesive force between the two layers, the stiffness of the interatomic bonds, and the viscous damping constant to the lock-to-sliding transition have also been investigated. The application of our results to the tribology is discussed and the dependence of the static friction force on the system parameters is studied. It is noted that the parameters of both θ and α play important roles in the magnitude of the static friction force Fs. The numerical results show that the possibility to obtain superlubricity is larger between two same material layers than that for different materials. How to make the material with superlubricity is suggested.