Simulation of a PCB assembly line: A modified JIT approach

In this paper, a simulation model of an existing printed circuit board (PCB) assembly line is developed in an attempt to identify strategies which tend to improve the system performance. The model is based on the concept of the JIT (Just-In-Time) production approach. Parameters investigated includes sequencing rules, lot sizes, number of Kanbans used, and number of PCB types.     

Life extension technology for steam pipe systems—I. Development of material properties

Material properties of A106B low-carbon steels were developed for life prediction analyses of steam pipes operated at elevated temperatures but in the sub-creep temperature range. Tensile, fracture toughness, fatigue crack growth rate and low-cycle fatigue properties were obtained on the piping steel at 24°C (75°F) and 288°C (550°F). The latter temperature corresponded to the highest operating temperature of nuclear plant steam piping. Increasing the test temperature from 24°C (75°F) to 288°C (550°F) decreased the yield strength and fracture toughness of the steel. Fatigue crack propagation rate properties at 24°C (75°F) and 288°C (550°F) were found to be comparable.

In the low-cycle fatigue tests, below a strain amplitude level of approximately 0.5%, cyclic softening was observed, while at higher strain levels, cyclic hardening was present. Based on the results of tensile and incremental-step fatigue testing, the strain-life curve was predicted. The predicted strain-life curve was found to be in agreement with the experimental result.

The fracture surfaces of fracture toughness specimens showed ductile fracture, while striations were observed on those of fatigue crack growth specimens. Fatigue striations were also observed on the fracture surfaces of low-cycle fatigue specimens. Fatigue initiation was associated with inclusions. It was shown that plastic straining in A106B steel could be detected by acoustic emission and by monitoring the eddy current response. These nondestructive evaluation techniques exhibit possibilities for in-situ monitoring of fatigue deformation.

While the development of material properties for the life prediction assessment of steam pipes is included in Part I of this paper, the establishment of a quantitative life prediction methodology and inspection criteria is contained in Part II. The developed life prediction methodology quantifies the effects of operating parameters on the remaining life of steam pipes using the material properties obtained in Part I.     

CAD与CAPP集成研究回转体类零件特征识别

本文研究了回转体轴类,轴套类零件的特征识别。对这类零件常用的特征单元进行了定义,描述了这类零件的特征模型:介绍了它的识别方法和特征参数定义方法。     

离散序列AR模型定阶方法研究

介绍了AR模型及其参数计算方法,结合具体实例,用Gram-Schmidt正交法、奇异值分解法、LD递推法,编写程序,确定AR模型有效阶数,并进行比较分析。结果表明:Gram-Schmidt正交法所得模型的阶数、计算时间、精确度都较为适中,适合在AR模型的研究中推广普及。     

柔性高压直流输电仿真技术研究方法综述

柔性直流输电工程应用前景广阔,采用各种高精度高效率仿真技术对柔性直流系统进行理论分析和运行特性研究是柔性直流技术发展的关键;实时数字仿真、物理动模仿真和数字物理混合仿真是常用的系统仿真研究方法。总结柔性直流输电系统结构及核心装备;分别介绍三种仿真方法,从基本理论与算法原理、实现方式和柔直装备建模方法等方面进行论述,并总结各种方法的适用性和优缺点。最后,对柔性高压直流输电仿真技术的发展趋势和关键问题进行了总结和展望,提出了几点可能的研究思路。     

一类负模量Kirchhoff - Carrier方程的解

利用变分方法和反证法研究了一类含有非线性项的Kirchhoff - Carrier方程,证明了当0<λ1时,该方程至少存在一对非平凡解,且当λ≥a λ₁时该方程不存在同号解.     

基于l1范数相干度的量子态区分

为探究区分量子态的最优策略,以相干作为资源,利用附加辅助系统的方法来区分非正交量子态,并给出了l₁范数相干度与区分量子态的成功概率之间的数值关系,同时量化了某些特定情况下不出错的量子态区分(UQSD)的最优协议所需的l₁范数相干均值.本文的研究结果表明,通过调整生成的相干度可以提高区分量子态的成功几率.     

中国耕地细碎化的理论解析与研究框架

基于演绎推理法和文献研究法,探索耕地细碎化的概念、过程、机制和效应,并构建耕地细碎化研究框架,为耕地细碎化研究提供理论指导。结果表明:①耕地细碎化是耕地在自然-人为双重因素驱动下,耕地地块在形态上不断分割、变小,耕地产权在主体上不断细分、多元的过程,并分别表现为相互关联又有所区别的耕地景观细碎化和耕地权属细碎化; ②耕地细碎化研究应遵循“诊断-机制-效应-治理”的理论框架,耕地细碎化诊断需从形态和权属两方面构建评价指标体系,形成机制可从自然切割力、利用切割力、设施切割力和管理切割力4个方面揭示不同因素的作用机制,效应需揭示不同尺度下耕地细碎化形态和产权的趋势性转折对经济、社会和生态的影响,治理研究应按照“问题识别治理潜力治理路径保障措施”的逻辑顺序构建。     

舌控智能辅助系统的通信装置研究

为提高舌控智能辅助系统舌部运动信息的采集精度,利用STM32H743和LabVIEW设计了一种对舌机接口辅助系统进行信号采集、传输的通信装置.该装置通过舌部触碰嵌入式电极传感器发出信号并传输给单片机(进行舌控信号采集),然后通过串口传给上位机以此最终实现数据的采集与保存.实验结果表明,该装置可有效完成舌控智能辅助系统对控制信号的采集与传输,并具有实时显示、自动保存和查询历史数据等功能; 因此,该装置在舌控智能辅助系统的信号采集中具有良好的应用前景.     

花斑无须鲶(Ageneiosus marmoratus)全基因组微卫星分布特征研究

根据NCBI已公布的花斑无须鲶全基因组序列,利用MISA软件对花斑无须鲶全基因组的6种完整型微卫星进行筛选并分析其分布特征. 结果如下:在花斑无须鲶全基因组(约1.03Gb)中符合条件的微卫星序列共336 037个,丰度为326个/Mb. 微卫星总长度为7 720 686 bp,占花斑无须鲶全基因组的0.75%. 其中二碱基类型的微卫星数目最多,为145 318个,占微卫星总数的43.24%,其次分别为单碱基(37.12%)、三碱基(11.00%)、四碱基(7.39%)、五碱基(1.04%)和六碱基(0.21%). 花斑无须鲶全基因组微卫星中的优势碱基类别按照数量从高到低排列依次为A、AC、AG、AT、AAT、AAAT、TATC、AAG、AAC和TGA,共有305 243个,占微卫星总数的 90.84%,A、T碱基在微卫星中占绝对优势.