共查询到10条相似文献，搜索用时 234 毫秒
1.
Laser shock processing (LSP), also known as laser peening, is a novel surface treatment technique in the past few years. Compressive
residual stresses which imparted by LSP are very important for improving fatigue, corrosion and wear resistance of metals.
Finite element analysis (FEA) simulation using ABAQUS software has been applied to predict residual stresses induced by LSP
on Ti-6Al-4V titanium alloy with laser pulse duration 30 ns and water confined ablation mode. The residual stress field generated
by different shape laser spots was studied, and the square laser spot is shown the most suitability for avoiding stress lack
phenomenon and overlapping LSP. Surface residual stresses and plastically affected depth within single square spot both increased
with the increase of laser intensity and laser shock times. Furthermore, compared with circle and ellipse spot, the residual
stress distribution in overlapping square spots is very uniform only with small overlapping ratio. LSP with square spot can
process advantageous residual stress field, and this technique will be used widely. 相似文献
2.
弧焊机器人的主要工艺问题之一是需要保证零件焊接的一致性,当焊缝接头位置因工件加工、夹具装配以及热应力变形等因素发生变化时,需借助传感器实时准确引导机器人来确定焊缝位置.激光视觉传感赋予机器人“看”的功能,大大促进了焊接自动化程度.为此,以Panasonic-TA1400六自由度弧焊机器人为试验平台,针对V型坡口MAG焊焊缝视觉传感实时图像处理技术进行了研究.采用领域平均滤波和小波降噪相结合的方法,有效地滤除了焊接背景噪声.采用小波边缘检测算法获取了激光光带边缘.对焊缝图像处理的关键技术——中心线抽取和特征点检测提出了逐行搜索求平均值和模板匹配法等切实可行的算法.试验表明,该图像处理流程效果良好,能够满足后续跟踪系统实时性要求. 相似文献
3.
Philip Riley 《欧洲师范教育杂志》1989,12(2):69-80
Summary This article examines the notions of ‘specialisation’ or ‘specificity’ as they are used in expressions such as ‘English for special purposes’ (ESP) or languages for specific purposes’ (LSP). It is argued that a given variety of language is not ‘special’ or ‘specific’ in some absolute or objective way, inherent to its formal structures, topics and norms. ‘Specificity’ is, rather, the result of a particular relationship between participant and discourse, between two cultures or worlds of knowledge. For these reasons, it is often not particularly helpful to attempt to describe specific varieties in terms of linguistic features. Instead, we need to situate the problem within a general theory of the sociology of knowledge by asking fundamental questions such as ‘Specialised for who?’ and ‘Who knows what?’, ‘How do they acquire and use their knowledge?’. Such a theory will necessarily be both relative and social: relative to the individual and to the way in which knowledge is socially distributed. But it will also be a theory of discourse, since interactive language‐use is the principal mechanism by which individuals acquire, stock and share all knowledge, ‘specialised’ or otherwise. It is suggested that two factors need to be kept in mind by the didactician interested in LSP. First, is the discourse asymmetric?, i.e. does it assume or contain knowledge which the learner does not have? Secondly, is the discourse non‐collaborative?, i.e. one where no attempt is made to share the knowledge with uninitiated participants. 相似文献
4.
教育学以"教育"活动作为逻辑起点具有研究对象与逻辑起点重合的缺陷,相应地教育技术学以"借助于技术的教育"活动作为逻辑起点也具有同样的问题。对教育技术学的逻辑起点的认识只有当教育技术学发展到一定阶段之后才成为可能,在这个过程中,需要处理好逻辑起点与研究起点、历史起点的关系。最后,作者提出了重新认识逻辑起点的问题及其重要性。 相似文献
5.
共享知识作为语境的一部分,在话语理解中起着非常重要的作用。Sperber&Wilson的关联理论中谈到语境作用越强,关联性越大,说话人与受话人的话语活动更易于成功。同时,根据语境的动态性,共享知识也是处于动态之中,并不是固定的,而是随着话语的发展而不断丰富发展的,反之,共享知识的发展又推动了整个话语向前发展。本文主要结合关联理论来论述共享知识在话语理解过程中的作用及其动态性。 相似文献
6.
7.
朱逸韬黄卫东 《福建工程学院学报》2020,(6):570-575
设计了以激光功率、扫描速度、扫描间距、铺粉厚度为因素的正交实验,研究了SLM 成型18Ni-300 模具钢粉末过程中各个工艺参数对成型件致密度的影响规律,并进行了工艺参数优化。实验表明,在选定范围内,成型件致密度随激光功率的增加先增大后减小?随扫描速度的增加持续减小?随扫描间距的增加先增加后减小?随铺粉厚度的增加持续减小。最优工艺参数组为激光功率260 W、扫描速度500 mm/ s、扫描间距0.11 mm、铺粉厚度0.02 mm 时,成型件致密度99.99%,为所有实验中的最优值。 相似文献
8.
A CO2 laser die-cutting system, which does not need die board any more, is a new technique for manufac-turing packing box. Two optical paths, the galvanometer scanning system and the flying optical system, are used to satisfy different processing needs. The scanning system is composed of galvanometer scanning mirrors and F-θ lens. And the flying optical system is driven by two servo motors. This paper presents the software and hardware design of the laser die-cutting system, the difference between the two optical paths, as well as the relationship among the cutting speed, thickness of wrapping paper and laser power. The cutting speed and thickness of wrapping paper are linearly increased by the incremental laser power, while the cutting speed is hyperbolically decreased by the incremental thickness of wrapping paper when the laser power is constant. The amount of incision is reduced by 20% and the processing time by 40% when tested by a low power RF CO2 laser die-cutting system using the optimized program. This tech- nique is also used for the reference of other rapid laser processing systems. 相似文献
9.
本文阐述了LDP、RSVP、LSP的原理、方法,并详细分析论述利用LDP或RSVP协议的扩展实现LSP建立的方法. 相似文献
10.
Signs of Erosion: Reflections on Three Decades of Problem-based Learning at Maastricht University 总被引：1，自引：0，他引：1
Nowadays many schools in higher education implement problem-based learning to foster active learning processes by students.
In some schools with a number of years of experience with this approach, phenomena can be observed which indicate signs of
wear. The implementation of a large-scale innovation such as problem-based learning (PBL) seems to provoke different activities
and attitudes in those actors who are most involved. Students and staff members seem to behave in a way which could be counterproductive
to the development of self-directed learning. In the first part of this paper, we briefly describe the cognitive psychological
background of PBL. In the second part various adjustments observed in problem-based curricula and their effects on students’
learning are analyzed. Arguments are presented about adverse effects on the implementation of this educational innovation.
Special attention is given to teachers’ concerns. In the third part suggestions are made about ways to revitalize PBL processes
as well as suggestions about effecting educational innovations on a more solid basis 相似文献