单振子型多自由度超声波电机研究现状

根据定子的结构特点以及工作方式,将多自由度超声波电机划分为两个主要类型,即多振子型和单振子型.综述了国内外单振子型多自由度超声波电机的研究现状,重点介绍了这类典型电机的结构、机理、性能、特点及应用;总结了该类电机主要研究成果,并指出今后研究中需要解决的关键技术.     

震后建筑内部层次化SLAM的地图模型转换方法

由于震后建筑内部环境受损程度和震害形态分布的无法预见性, 层次化SLAM地图模型转换难以直接预设划分参数. 本文提出一种基于图形分割的区域划分方法, 实现层次化SLAM地图模型转换. 通过对机器人里程和观测信息进行图形映射, 基于信息熵生成节点集, 将环境相似度作为边的权重, 构建无向加权图及相似度矩阵; 并采用归一化割策略对图形进行划分, 得到以机器人观测视角的环境空间划分结果; 方法在解决SLAM计算量递增问题的基础上, 最小化相关信息损失, 确保全局一致性. 最后, 通过仿真及模拟废墟实验, 验证算法的有效性和可行性.     

软件开发活动数据的数据质量问题

问题追踪系统和版本控制系统等软件开发支持工具已被广泛应用于开源和商业软件的开发中,产生了大量的数据,即软件开发活动数据.软件开发活动数据被广泛应用于科学研究和开发实践,为智能化开发提供支持.然而数据质量对相关的研究和实践有重大影响,却还没有得到足够的重视.为了能够更好地警示数据使用者潜在的数据质量问题,通过文献调研和访谈,并基于自有经验对数据进行分析,总结出了9种数据质量问题,覆盖了数据产生、数据收集和数据使用这3个不同的阶段.进一步地,提出了相应的方法以帮助发现和解决数据问题.发现问题是指加强对数据上下文的理解和通过统计分析及数据可视化发现潜在的数据质量问题,解决问题是指利用冗余数据或者挖掘用户行为模式进行修正.     

基于Logistic回归的电梯健康评估

电梯的隐患故障与其运行状态存在着一定的关联性.根据电梯的组成要素、体现电梯健康状况表征,合理选择评价参数,基于logistic回归方法建立评价模型.通过分析评价模型基本原理,整合原始数据、引入惩罚因子、交叉验证、高阶拟线性等方法,解决了数据不均衡现状和差异性,提高了评价模型准确度,达到了对电梯健康实时监控并预警.     

Optical,structural and photophysical properties of Ga2BiTaO7 compound

The Ga₂BiTaO₇ compound was synthesized by solid-state reaction method and characterized by powder X-ray diffraction method and the Rietveld structure refinement. This compound crystallizes in the pyrochlore-type structure, cubic system with space group Fd3m and the lattice parameter a = 10.4544(2) Angstrom. The band gap of the Ga₂BiTaO₇ compound was estimated to be about 2.47(1) eV. It shows strong optical absorption in the visible light region (λ > 420 nm). This indicates that the Ga₂BiTaO₇ compound has the ability to respond to wavelength of visible light region and has potential for splitting water into H₂ and O₂ under visible light irradiation. Photocatalytic degradation of methylene blue (MB) dye on the Ga₂BiTaO₇ compound was first investigated under ultraviolet light and visible light irradiation. MB was obviously degraded after visible light irradiation for 140 min with the photocatalyst at room temperature in air. The high activity has potential to be kept in a wide range of wavelength up to 505 nm.     

Investigation on the durability of direct dimethyl ether fuel cell. Part II: Cathode degradation

Cathodic Pt/C catalyst degradation for a direct dimethyl ether fuel cell (DDFC) has been investigated after a 70.5 h galvostatic operation at 60 °C under ambient pressure. The cathode electrochemical active surface (EAS) reduces from 349 to 267 cm² mg^?1 Pt after durability test. Cathode EAS loss is associated with the growth of Pt catalyst particles. XRD and TEM results show that the particle size of cathodic Pt catalyst increases from an original value of 3.0 nm to 5.4 nm. Furthermore, the anode failure accelerates dimethyl ether (DME) crossover, and consequently, poisoning of catalyst by absorbed DME and/or intermediates aggravates the degradation of cathodic Pt/C catalyst. The effect of anode degradation on the long-term performance of DDFC has been reported in companion article (Part I).     

Pore-scale investigation of residual oil displacement in surfactant–polymer flooding using nuclear magnetic resonance experiments

Research on the Gangxi III area in the Dagang Oilfield shows that there was still a significant amount of oil remaining in oil reservoirs after many years of polymer flooding.This is a potential target for enhanced oil recovery(EOR).Surfactant–polymer(SP) flooding is an effective chemical EOR method for mobilizing residual oil and improving displacement efficiency macroscopically,but the microscopic oil displacement efficiency in pores of different sizes is unclear.Nuclear magnetic resonance(NMR) is an efficient method for quantifying oil saturation in the rock matrix and analyzing pore structures.In this paper,the threshold values of different pore sizes were established from the relationship between mercury injection curves and NMR T2 spectrums.The distribution and migration of residual oil in different flooding processes was evaluated by quantitatively analyzing the change of the relaxation time.The oil displaced from pores of different sizes after the water flood,polymer flood,and the SP flood was calculated,respectively.Experimental results indicate that(1) the residual oil in medium pores contributed the most to the incremental oil recovery for the SP flood,ranging from 40 % to 49 %,and small pores usually contributed \30 %;(2) the residual oil after the SP flood was mainly distributed in small and medium pores;the residual oil in medium pores accounted for 47.3 %–54.7 %,while that trapped in small pores was 25.7 %–42.5 %.The residual oil in small and medium pores was the main target for EOR after the SP flood in oilfields.     

CaCu3Ti4O12陶瓷深陷阱松弛特性研究

研究了固相反应法及共沉淀法制备的CaCu3Ti4O12陶瓷深陷阱松弛特性.测试了CaCu3Ti4O12陶瓷在频率为0.1～107Hz,温度为–100～100℃的范围内的介电频谱及温谱.通过对不同温度下介电频谱的分析,研究了双Schottky势垒结构中深陷阱松弛特性.研究表明:在交流小信号作用下,由于Schottky势垒中深陷阱与Fermi能级的上下关系发生变化,引起深陷阱电子发射和俘获即电子松弛过程,在介电频谱中表现为松弛峰;并且由介电谱的分析结果可得深陷阱能级等微观参数.比较不同试样的深陷阱参数可知:在CaCu3Ti4O12陶瓷中,在导带以下约0.52和0.12 eV的能级处存在由本征缺陷产生的深陷阱.介电温谱与频谱的分析类似,二者可以互为补充.     

Reduced leakage current of nickel induced crystallization poly-Si TFTs by a simple chemical oxide layer

Ni-metal-induced crystallization (MIC) of amorphous Si (α-Si) has been used to fabricate low-temperature polycrystalline silicon (poly-Si) thin-film transistors (TFTs). However, the leakage current of MIC-TFT is high. In this study, a chemical oxide layer was used to avoid excess of Ni atoms into α-Si layer during MIC process, which was simple and without extra expensive instrument. The minimum leakage current and on/off current ratio were significantly improved.