Analysis and DEM simulation of granular material flow patterns in hopper models of different shapes

By using the discrete element method (DEM) a comparison and observations on material flow patterns in plane-wedged, space-wedged, and flat-bottomed hopper were accounted for. Numerical results obtained by combining data of individual particles, statistical processing of particle assemblies and evaluation of the field variables provided the essential characteristics for different regimes of the discharge flow (within steady or unsteady state of flow) and the differences in differently shaped hoppers due to different microscopic inter-particle friction. For validation of the performed simulations, velocity patterns developed in three-dimensional flat-bottomed hopper containing 20,400 pea grains were also analysed. To represent the continuum by avoiding the local effects produced by the individual grains, the simulation results were focused on the mean velocity distributions with data smoothening. The effect of rolling resistance on granular material flow was also considered.     

Selective IR absorption in molecular nanofilms

We have formulated a microscopic theory of optical properties of ultrathin molecular films (nanofilms), i.e. quasi 2D systems parallel to XY planes bounded by two surfaces. Exposure of nanofilms to the external electromagnetic fields has result in creation of excitons - but different than bulk ones. Harmonic exciton states were calculated using the method of two-time, retarded, temperature dependent Green’s functions. It has been shown that two types of optical excitations can occur: bulk and surface exciton states. Exciton energy dispersion law shows discrete behavior with non-zero values. Analysis of the dielectric properties of these crystalline systems for low exciton concentration shows that the permittivity strongly depends on boundary parameters and the thickness of the film. In addition, permittivity shows very narrow and discrete dependence of external electromagnetic field frequency, which is a consequence of both resonance and quantum size effects. Influences of boundary conditions on optical characteristics (through analyses of dynamical absorption coefficient) of these nanostructures were specially and in details explored.     

Determination of optimal cutting edge geometry on a stamped orthotropic circular electrical steel sheet

Today engineers involved in the stamping process used for high-volume production of rotor and stator laminations are faced with a great challenge to achieve extremely narrow dimensional and geometrical tolerance on their products. Because materials are produced by different suppliers, adjustments of technological parameters to the emerging differences are required to maintain the high quality of products. An upgraded engineering method was developed in which electrical steel sheet of semi-finish grade was not treated traditionally, but as a 3D body with orthotropic material behaviour. The round profile of the cutting edge was studied from the experimental and numerical point of view. If the completely round punch was used, the profile of the cutting edge appeared as a non-round shape. With additional FEM analyses a new profile of punch was designed as a non-round shape to be able to provide much better circularity. FEM simulation showed that 10 times lower profile deviations were found on the workpiece shaped by the new cutting element profile.     

Achieving Rich and Active Alkaline Hydrogen Evolution Heterostructures via Interface Engineering on 2D 1T‐MoS2 Quantum Sheets

Large‐scale production of hydrogen from water‐alkali electrolyzers is impeded by the sluggish kinetics of hydrogen evolution reaction (HER) electrocatalysts. The hybridization of an acid‐active HER catalyst with a cocatalyst at the nanoscale helps boost HER kinetics in alkaline media. Here, it is demonstrated that 1T–MoS₂ nanosheet edges (instead of basal planes) decorated by metal hydroxides form highly active ${\text{edge}}_{{\text{1T‐MoS}}_{\text{2}}}$/ ${\text{edge}}_{\text{Ni}{(\text{OH})}_{\text{2}}}$ heterostructures, which significantly enhance HER performance in alkaline media. Featured with rich ${\text{edge}}_{{\text{1T‐MoS}}_{\text{2}}}$/ ${\text{edge}}_{\text{Ni}{(\text{OH})}_{\text{2}}}$ sites, the fabricated 1T–MoS₂ QS/Ni(OH)₂ hybrid (quantum sized 1T–MoS₂ sheets decorated with Ni(OH)₂ via interface engineering) only requires overpotentials of 57 and 112 mV to drive HER current densities of 10 and 100 mA cm^?2, respectively, and has a low Tafel slope of 30 mV dec^?1 in 1 m KOH. So far, this is the best performance for MoS₂‐based electrocatalysts and the 1T–MoS₂ QS/Ni(OH)₂ hybrid is among the best‐performing non‐Pt alkaline HER electrocatalysts known. The HER process is durable for 100 h at current densities up to 500 mA cm^?2. This work not only provides an active, cost‐effective, and robust alkaline HER electrocatalyst, but also demonstrates a design strategy for preparing high‐performance catalysts based on edge‐rich 2D quantum sheets for other catalytic reactions.     

一种新的相干信源DOA估计算法: 加权空间平滑协方差矩阵的Toeplitz矩阵拟合

文献[1]提出的最优加权空间平滑技术可以使相干源存在时的信源协方差矩阵恢复为对角阵.由于文献[1]中导出的最优权矩阵是空间信源方位的函数矩阵,本文利用最优加权空间平滑后阵列协方差矩阵的Toeplitz性,构造了一个全新的优化拟合的代价函数,并基于此提出了一种相干源方位估计的新算法.与文献[1]不同,算法的实现不需要方位估计的先验知识和协方差矩阵的去噪预处理.分辨性能的蒙特卡罗仿真实验表明,新算法对空间相干信源的分辨性能优于常规的空间平滑算法和最大似然算法,在小阵列和信源空间间隔较近时,算法的优越性尤为突出.     

基于Microsoft Visio 2002的电路图形的绘制

介绍了用商业绘图软件MicrosoftVisio2002绘制电路图形的方法，这种绘图方法比起其它的电路图形的绘制手段，具有易学易用，所绘电路图形标准美观，改动方便等优点，是广大电路教学和研究人员十分理想的制图工具。     

基于空时格形码的差分调制

提出了空时格形码的差分调制方案,并对空时格形码和系统模型以及差分调制技术进行了深入的研究。在发射天线和接收天线数量乘积大于3时,对QPSK和8-PSK的STTCM码和TSC码以及BBH码进行了仿真,仿真结果表明:STTCM码与相应的TSC和BBH码相比具有更低的帧误码率,而且STTCM码能够提供最大可能的分集增益和编码增益。     

基于混合多值离散粒子群优化的混合极性Reed-Muller最小化算法

针对布尔函数系统的混合极性Reed-Muller(Mixed-Polarity Reed-Muller,MPRM)最小化问题,该文提出了一种混合多值离散粒子群优化算法.为解决多样性损失,改善优化结果,兼顾算法的效率和精度,算法采用多群协同优化方法,并提出了概率变异更新、没有重复的更新以及群间重复最优变异3种更新和变异策略.实验结果表明,和模拟退火遗传算法相比,所构造算法能够在获得基本相同优化结果的同时,提高MPRM最小化的时间效率.     

H型栅结构的亚微米PDSOI MOS器件的跨导双峰效应研究

A bimodal effect of transconductance was observed in narrow channel PDSOI sub-micron H-gate PMOSFETs,which was accompanied with the degeneration of device performance.This paper presents a study of the transconductance bimodal effect based on the manufacturing process and electrical properties of those devices.It is shown that this effect is caused by a diffusion of donor impurities from the NC region of body contact to the PC poly gate at the neck of the H-gate,which would change the work function differences of the polysilicon gate and substrate.This means that the threshold voltage of the device is different in the width direction,which means that there are parasitic transistors paralleled with the main transistor at the neck of the H-gate.The subsequent devices were fabricated with layout optimization,and it is demonstrated that the bimodal transconductance can be eliminated by mask modification with NC implantation more than 0.2 m away from a poly gate.