The Analysis of the Differences between Electromechanical Transients Simulation and Electromagnetic Transients Simulation

The paper firstly interprets the differences between electromechanical transients program BPA and electromagnetic transients program EMTDC in the field of principle, model and algorithm. Then the authors carry out the simulation based on single-machine infinite-bus system and draw some conclusions. The time consumption of the simulation using EMTDC is much longer than the simulation using BPA under the same length of time. The results of BPA are close to those of EMTDC under steady conditions. The fundamental frequency component of the EMTDC results seems closer to the BPA results than its original value, but they still away from completely consistent. In this simulation of single-machine infinite-bus system, the transient stability results of BPA and EMTDC are close, but the results of BPA are apt to be more conservative. All the conclusions above have a certain reference value to both hybrid simulation and comprehensive analysis method in the study of the AC/DC digital simulation of large power grid.

Two-Dimensional Coupling Vibration Analysis of Laterally Acoustically Coupled Two-Port Thin-Film Bulk Acoustic Resonators

In this paper,we present an approach to studying the mode coupling vibrations in two-port thin-film bulk acoustic wave resonator(FBAR)devices with two pairs of electrodes deposited on the zinc oxide film.The two-dimensional plate theory established in our previous work is employed,which takes into account the coupling of the operating thickness-extensional mode with the extensional,flexural,fundamental and second-order thickness-shear modes.The propagation of straight-crested waves in the plate is studied,and the state-vector approach is successfully used to simplify the derivation process.For a structurally symmetric device,the modes are separated into quasi symmetric and antisymmetric ones.Frequency spectra and corresponding mode shapes are obtained under the stress-free boundary conditions,respectively,and then coupling effects and energy trapping phenomenon are discussed in detail.Some results for structures with asymmetric electrode distributions are also shown.It is found that the choice of aspect ratio has a great effect on mode couplings of FBAR devices.This study will be useful for the design of FBAR filters and sensors.

Mechanical Manipulation of Electrical Behaviors of Piezoelectric Semiconductor Nanofibers by Time-Dependent Stresses

We study electric currents in a piezoelectric semiconductor fiber under a constant voltage and time-dependent axial stresses applied locally.From a nonlinear numerical analysis based on a one-dimensional phenomenological model using the commercial software COMSOL,it is found that pulse electric currents can be produced by periodic or time-harmonic stresses.The pulse currents can be tuned by the amplitude and frequency of the applied stress.The result obtained provides a new approach for the mechanical control of electric currents in piezoelectric semiconductor fibers and has potential applications in piezotronics.

In situ coupled MoO_(3)with CoP/rGO to construct three-dimensional self-supported catalyst for highly efficient alkaline hydrogen evolution reaction

In order to solve the crisis of energy depletion and protect the beautiful natural environment,the development of efficient,cost-effective and stable hydrogen evolution reaction(HER)electrocatalyst has attracted great attention,but it is still an urgent challenge to fabricate an abundant and low cost electrocatalyst.In this article,a novel HER catalyst with heterogeneous structure interfaces was in situ synthesized by multi-step electrodeposition method,and the mechanism of the enhancement of its electrocatalytic activity was elucidated by the combination of density functional theory(DFT)calculation and multi-characterizations.The initial overpotential is only 83 mV and the Tafel slope is only 58.5 mV/dec,which is better than most of other reported CoP-based electrocatalyst.At the meantime,DFT calculations show that the incorporation of MoO_(3)and rGO leads to electron redistribution among different components,which ensures efficient adsorption and activation of H_(2)O molecules and hydrogen atoms.Therefore,this work will contribute to the understanding of the mechanisms associated with heterojunctions and provide guidance for the rational design of a hybrid catalyst.