Precision Engineering is the discipline that encompasses the design,development,fabrication,and measurement of parts of a mechanical,optical,or electronic system,in software or in fixtures and other structures.For example,a precision instrument or machine should be able to function or perform at a high accuracy that is many orders of magnitude smaller than the size of the instrument or machine itself.It is critical that such accuracy and accurate performance are repeatable and stable over a designated period.Precision engineering also involves the generation of new knowledge-bases and creation of new technologies which will advance the innovation of such machines,instruments,or systems.

Overall,precision engineering deals with anything that requires accuracy in its creation,from finding solutions to scientific and technological problems,developing new production methods to turning theory into reality.The field plays a crucial role in today's world,from aircraft engines,pharmaceuticals manufacture,agricultural machinery,food processing,silicon chips,mobile phones,cameras,supercomputers,robots,and unmanned vehicles to artificial intelligence—we are surrounded by the numerous products from precision engineering.The discipline is becoming more important in the development of future technologies,where accuracy and repeatability are increasingly needed to improve product performance by delivering better accuracy,reliability,and improved product life and enhancing safety;or to increase manufacturability by allowing for automation and,of course,by lowering costs.

A number of trends are evident in precision engineering:additive manufacturing,such as three-dimensional(3D)printing;micro-and nano-processing,which require precision,machine rigidity,physical machine control and accurate tooling;the processing of new engineered materials,such as composites,where traditional approaches to manufacturing and machining lead to many defects and surface integrity problems;and the growing demand for autonomous machine operation.We can also see ‘‘molecular manufacturing”on the horizon:industries making biomedical implants,prosthetics,and pharmaceuticals,which increasingly rely on nanotechnology—an area where precision engineering is paramount.

In this issue,a group of eight papers present some methods and processes related to two aspects of precision engineering:miniaturised surface texture generation and precision metrology.

The possible development of electrical equivalent molecular components—such as molecular transistors,capacitors,and diodes—is reviewed by Mathew and Fang,and provides newcomers to the field with an overview of some previous publications.

A prospective alternative to single large expensive satellites is to utilize multiple satellites flying in formation with the advantage of increased redundancy and cheaper and simpler satellite designs.Formation flying,though,requires satellites to accurately measure and maintain desired distances from each other;dual-comb absolute distance ranging systems have been proposed and tested in laboratory conditions.Zhu and Wu provide a review of absolute distance measurement using dual-comb ranging and argue that,using two coherent frequency combs,dual-comb ranging can enable the fast measurement of time and phase response,and thus can overcome the existing difficulty in using conventional ranging tools.

Micro/nano-machining based on mechanical tooling is an important process in micro/nano-scale fabrication,in which the material removal mechanisms and the associated surface integrity achievable are fundamental to the quality fabrication of micro-components.However,it is not simple to scale down a mechanical machining process to micro/nano-scales due to tooling restrictions.Wang et al.discuss the advantage of a picosecond laser in the manufacture of Stavax steel surfaces with miniaturised micro/nano-scale features,and seek to demonstrate that the wettability of the textured surfaces can be tailored.

An investigation of surface microprocessing of the biomedical metallic materials,alloys Mg-6Gd-0.6Ca and decorated Ti6Al4V,using laser technology is presented by Hu et al.The reason for this study is that the impressive mechanical and functional properties,as well as the biocompatibility,of metallic biomaterials make them attractive for increasing use in medical applications.Poor surface topologies,however,hinder bio-integration and hence their full application.This study aims to understand the applicability of the microprocessed surfaces to cell adhesion and liquid biopsy.

“我骗杰克说我要把瓷瓶送给朋友，可是他一点儿也不好糊弄。为了不被发现，我就把现场伪造成我和杰克都被绑架的样子。”教授苦笑着说道，“我本想等把这个瓷瓶卖了换些钱之后，就把杰克放了，然后出去躲一段时间……”

传统教学观认为教师在教学活动中处于主导地位，学生是学习知识的“容器”，语文教学活动被当作是单纯的知识习得过程，其核心目的是要将课本中所涉及的知识“吃透”，正如叶澜教授所说：“把丰富复杂、变动不拘的课堂教学过程简约化为特殊的认识活动，把他从整体生命活动中抽象、隔离出来，是传统教学观的最大缺陷”。因此，语文教学应在让学生掌握必要的语文知识的基础上，不断发掘蕴含在教材中的人文内涵，将课堂知识与实际生活进行对接，让学生在语文学习中舒展自己的生命，探索生命存在的意义。

Freeform specular surfaces are encountering more and more applications in precision manufacturing and measurement systems,thanks to improved capabilities in the manufacture of optical components where high potential in accuracy and repeatability are required.Xu et al.discuss the effect of geometric parameters on the measurementaccuracy in stereo deflectometry,and propose a measurement system based on the analysis to measure a stock concave mirror.

基于关键词共现网络可视化结果拓扑结构的分析，结合社会网络分析法的理论和对原始文献的研读，本研究将日本移民研究领域的研究热点分为三大方面：日本在东北地区的移民侵略研究、日本移民其他国家地区的政策研究以及侨居广州的日本移民社会学研究。

Lasers with ultrashort pulses are useful in materials processing,as they can significantly minimise the thermal effect on workpiece material,and also process transparent materials due to the mechanism of nonlinear multiphoton absorption.A review of micromachining using ultrashort pulse lasers is provided by Yu et al.,describing the processes and providing some manufactured samples.