Reversible formation-melting of nano-crystals in supercooled oxyfluoride germanate liquids

The nanocrystals play a critical role in generating and affecting functionalities of glass materials. Therefore, scientists have made considerable efforts in clarifying microscopic mechanisms of nanocrystal formation in glass to obtain the desired type of nanocrystals. However, the phase transitions of nanocrystals during heating have not been well understood. Here we report on a discovery of the reversible melting-formation of nanocrystals in an oxyfluoride germanate glass during heating-cooling circles. Using a differential scanning calorimetry (DSC), we detected a striking endothermic event at 925 K during heating, after the glass underwent a DSC upscan to a temperature between 925–986 K and subsequent cooling. Based on Raman spectroscopy, X-ray diffraction and transmission electron microscopy, the endotherm is attributed to the melting of nano-crystal BaGeF₆ (˜20 nm). An exothermal response was observed at 890 K during the DSC downscan, implying the re-formation of BaGeF₆ nano-crystals. This suggests that the melting-formation of BaGeF₆ nano-crystals is a typical first-order transition.     

Experimental investigation of power management and control of a PV/wind/fuel cell/battery hybrid energy system microgrid

This paper presents an experimental study of a standalone hybrid microgrid system. The latter is dedicated to remote area applications. The system is a compound that utilizes renewable sources that are Wind Generator (WG), Solar Array (SA), Fuel Cell (FC) and Energy Storage System (ESS) using a battery. The power electronic converters play a very important role in the system; they optimize the control and energy management techniques of the various sources. For wind and solar subsystem, the speed and Single Input Fuzzy Logic (SIFL) controllers are used respectively to harvest the maximum power point tracking (MPPT). To maintain a balance of energy in the hybrid system, an energy management strategy based on the battery state of charge (SOC) has been developed and implemented experimentally. The AC output voltage regulation was achieved using a Proportional Integral (PI) controller to supply a resistive load with constant amplitude and frequency. According to the obtained performances, it was concluded that the proposed system is very promising for potential applications in hybrid renewable energy management systems.     

Uncertainty analysis and robust control of fuel delivery systems considering nitrogen crossover phenomenon

In this paper, the fuel delivery subsystem (FDS) with hydrogen recirculation and anode bleeding is applied in proton exchange membrane fuel cell (PEMFC) system, which is utilized to supply hydrogen to the anode of stack and recirculate fuel back to the supply line. As the diffusion of nitrogen from cathode to anode is inevitable in a real PEMFC during long-term operation. To prevent system performance decline due to nitrogen accumulation. Therefore, this paper firstly develops a control-oriented nonlinear dynamic FDS model involving gas diffusion. Additionally, the FDS is very sensitive to operating environment, uncontrolled operation conditions may cause stack degradation. Specifically, a method based on Monte Carlo simulation is proposed to identify the key parameter boundaries. Then the gas distribution in FDS due to nitrogen crossover is analyzed in detail. After this, a hybrid robust methodology based on sliding mode algorithm is also proposed to maintain adequate hydrogen pressure supply, suitable hydrogen and nitrogen content in the system in presence of nitrogen crossover and renewed uncertainties. Finally, the performance of the presented controller is compared with nonlinear PID (NPID) control and nonlinear multi-input-multi-output (NMIMO) control through a hardware-in-the-loop test bench. Experimental results show that the hybrid controller is accurate and suitable for control purpose, the nitrogen content is restricted to the given range and the variation of output voltage is limited to the desired boundaries, the feasibility and effectiveness are validated.     

机械制图课改中三维模型库的开发和研究

针对机械制图课程教学中普遍存在的教学模型及挂图数量不足、教学难度大等问题,简述了使用SolidWorks软件建立三维实体模型的过程以及机械制图虚拟模型库的设计流程、内容组成、网络发布等。实践证明,该模型库的设计是成功的,不仅弥补了实物模型库的不足,而且具有更多优势。     

光学像差图像随机波前编码混合成像

研究了一种采用随机相位板消除光学像差的波前编码和数字图像处理混合成像方法.用激光散斑干涉法制作随机相位板,放置在系统成像面之前的光路中,光学像差图像被转变为随机编码中间像,使光学系统固定像差淹没在随机编码中受到削弱.建立了基于频域梯度优化的盲反卷积解码算法,用于解码中间像为无像差图像,由于采用频域共轭梯度优化,提高了解...     

虚拟现实技术应用于光环境可视化研究的前沿动态

近年来,虚拟现实技术(virtual reality,VR)发展迅速,应用范围广阔,成为众多领域的研究热点。VR是图像技术、人机交互技术等多维整合形成的沉浸式展示方式,其基础是光环境的可视化和视觉交互,对于光环境可视化的模拟精度一定程度上也决定了VR技术的应用边界及深度。因此,探索VR对光环境进行精确可视化对推动其在更广阔的领域进行更深层次的应用具有较大的经济价值及学术价值。本文系统梳理了VR技术在光环境可视化领域研究的发展进程及前沿热点;介绍了当下沉浸式虚拟光环境(immersive virtual lighting environment,IVLE)的构建原理、常用方法、软件及设备;剖析了国内外应用IVLE替代真实空间光环境探索人因光环境研究的优势、评价方法及评价因子;最后,对既有研究进行了分类分析,梳理出VR技术在光环境可视化研究领域的发展方向及科研、应用价值。本文可以为VR技术用于光环境领域的工程及科研工作提供较系统的认识,为相关研究提供理论及经验支持。     

基于高频分量的高压直流输电线路单端保护方法

输电线路是高压直流输电系统中故障率最高的元件。针对现有输电线路行波保护耐过渡电阻能力差,存在难以识别区内高阻故障和远端区外金属性故障的问题,提出了一种高压直流输电线路单端保护方法。基于高压直流输电系统拓扑,分析了高压直流输电线路区内和区外故障电流的特征,从而利用小波变换提取高频分量电流构建保护方法。仿真结果表明,该方法不受过渡电阻、故障距离影响,保护可靠性高。     

考虑刚体稳定性约束条件的变形监测数据处理方法研究

在各种变形监测工程中,部分监测对象可以假设成为刚体进行处理,而刚体的稳定性始终没有被引入到变形监测数据处理中。本文旨在讨论变形监测数据处理时,如何引入刚体的稳定性,并获取整体位移信息。     

铁路大跨梁拱组合桥粘滞阻尼器减震研究

采用不同分析方法和计算理论对设有粘滞阻尼器的兰渝铁路(82+172+82)m连续梁—拱组合桥进行了地震反应分析,并对其减震性能进行了研究,通过计算分析,得出设粘滞阻尼器后,桥梁结构地震反应时所受水平力比单墩时明显减小。