共查询到20条相似文献，搜索用时 765 毫秒
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赵升升 《深圳职业技术学院学报》2013,12(3):64-69,74
文章讨论了几种薄膜残余应力测试方法的优缺点,介绍了氮化物薄膜应力沿层深分布趋势的最新研究,偏压和N2分压工艺对薄膜应力的影响及几种调节薄膜残余应力的有效方法．脉冲偏压增大,薄膜残余应力显著增加：N2分压增大,薄膜残余应力显著增加．采用独立变化脉冲偏压或变化N2分压工艺制备的薄膜,其残余应力沿层深分布趋势明显均匀,薄膜残余应力可得到有效调整． 相似文献
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为了研究天然牙与种植体联合支持附着体连接式固定桥的骨组织应力分布情况,选择一左侧下颌第一磨牙缺失病例,分别设计刚性连接(模型Ⅰ)和Ceka附着体连接(模型Ⅱ)天然牙与种植体联合支持固定桥模型.分别在分散垂直和分散斜向两种载荷情况下,采用三维有限元法分析基牙及种植体周围骨组织的应力分布情况.研究结果表明,在两种载荷情况下,种植体周围骨组织的应力值都大于天然牙周围骨组织的应力值,模型Ⅰ中的种植体周围骨组织的应力值明显大于模型Ⅱ中的种植体周围骨组织的应力值,而天然牙周围骨组织的应力值在两组模型中变化不大.因此可以认为,Ceka附着体能缓冲种植体周围骨组织的部分应力,但对垂直应力和侧向应力的缓冲能力区别不大.进行天然牙与种植体联合支持固定桥修复时,可以设计附着体连接体,以缓冲种植体周围骨组织的应力水平,防止或减轻种植体支持组织的损伤. 相似文献
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为了研究吊索内钢丝腐蚀损伤后的应力分布规律,采用有限元软件ANSYS弹簧单元与节点耦合模拟钢丝间相互作用,考虑温度变化时护套对钢丝的握裹力影响,提出了一种改进的平行钢丝吊索纤维束理论计算模型,研究了钢丝束长度、层数,锈坑尺寸、数量和位置分布等参数以及护套握裹力对吊索内钢丝应力分布的影响规律。结果表明：拉伸荷载作用下,改进的纤维束模型可准确反映吊索钢丝间应力分布,中心层与内层钢丝应力略大于外层钢丝应力;锈坑参数对吊索钢丝应力分布影响显著;锈坑角度为60°时,吊索受力最为不利;护套握裹力对最外层钢丝应力有较大影响。 相似文献
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《莆田学院学报》2017,(5):19-23
分析慢性踝关节外侧失稳时距骨的Von Mises应力分布规律及易发生骨折部位。创建正常踝足三维有限元模型和53个踝关节外侧失稳模型,以距骨为观察对象做有限元分析,获得拥有solid45六面体单元488482个,总节点129108个的正常踝足模型及踝足诸骨应力分布云图。踝关节外侧失稳时,距骨较大应力集中在距舟关节、距骨颈和距骨外突,较正常应力区范围变小,局部应力增加。距骨应力主要受内旋影响,内旋角度超过40°时,外踝、距骨颈有骨折危险。结果表明:踝关节外侧失稳是骨性关节炎和功能障碍的主要原因,临床治疗应以矫正内旋,纠正失稳,增强力学性能为主。 相似文献
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吕偿 《实验室研究与探索》2023,(7):33-37
为了研究铣削参数对TC4钛合金加工表面残余应力分布的影响，建立了硬质合金立铣刀铣削TC4钛合金的三维铣削模型。以刀具角速度和进给速度作为输入载荷变量，探讨不同铣削参数TC4钛合金加工表面残余应力的分布情况。仿真结果表明，残余应力随刀具进给方向不断减小，在进刀槽处残余应力值大于退刀槽处的残余应力值；在进(退)刀槽纵向深度方向残余应力随着距离铣削面越远应力值越小，最大应力值分布在距离铣削面0.2～0.25 mm区域；当纵向深度距离铣削面0.5 mm时，残余应力急剧减小至300 MPa左右；当刀具角速度为314 rad/s、进给速度为1 800 mm/min时，铣削面残余应力相对较小。该仿真结果为不同铣削参数对铣削面及其纵向深度的残余应力分布情况的研究提供参考。 相似文献
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在应力-强度干涉模型中,当应力服从伽玛分布,强度服从指数分布情况下讨论了给定验前分布情况下可靠度的Bayes估计,并给出了数值例子.通过分析表明,Bayes模拟结果较好. 相似文献
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《新课程实验教材小一数学教案设计合订本》2003,(2):14-15
结合某工程深基坑边墙单孔复合型锚杆施工，选取4根锚杆作为试验锚杆，通过在锚固体范围埋设多个应变测试元件，对锚固体在不同张拉载荷条件下的应力分布状态进行了现场测试研究。根据单孔复合型锚杆的结构特点，对代表性锚固体建立有限元数值模型，并对锚固体的应力．应变特征进行了数值分析。根据现场测试和数值分析结果，对单孔复合型锚杆锚固体的应力分布规律和锚固机理进行了研究。 相似文献
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We developed a computerised simulation that utilises embodied modelling by letting students play the role of particles in a liquid. We compared the learning of two eight-grade classrooms that used the embodied modelling simulation during a weeklong learning module on phase change, with a comparison group that used an ordinary simulation with no embodied modelling. In the pre-test, neither group mentioned inter-molecular forces in their explanations. In the post-test, significantly more students from the embodied modelling group mentioned inter-molecular bonds in their explanations than their counterparts who used the regular simulation, and realised that inter-molecular forces influence the motion of particles. However, we found little difference between the groups in students’ ability to relate the magnitude of the inter-molecular forces to the magnitude of the boiling point of the material, showing not only the potential but also the limits in developing complex conceptualisations through this approach. Building on these findings, we discuss the affordances of embodied modelling for learning complex models, and suggest future directions for research into embodied modelling. 相似文献
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Peter Frejd 《Educational Studies in Mathematics》2013,84(3):413-438
This paper presents a critical review of literature investigating assessment of mathematical modelling. Written tests, projects, hands-on tests, portfolio and contests are modes of modelling assessment identified in this study. The written tests found in the reviewed papers draw on an atomistic view on modelling competencies, whereas projects are described to assess a more holistic modelling competence but obstacles regarding reliability of assessing projects are identified. The outcome of this investigation also indicates that the criteria used in frameworks or modes of assessment seldom are derived from a theoretical analysis, but more often based on ad hoc constructions, experience from assessment situations or empirical studies of students’ work. Finally, this study suggests that an elaborated view on the meaning of quality of mathematical models is needed in order to assess the quality of students’ work with mathematical models. 相似文献
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J. Bernardino Lopes 《International Journal of Science Education》2013,35(7):811-851
Modelling is an inherent process for the construction and use of science concepts that mobilize diverse specific competences. The aims of this work are to put forward a means of evaluating modelling competences that is relevant for physics teaching and science education research and to identify the potentials and constraints in the development of modelling competences. A written test, which embraces a wide range of modelling aspects in mechanics domain, was drawn up and validated, and a theoretically based evaluation methodology was specified. In the validation process, the test was given to 75 subjects distributed across seven levels of physics education. The answers were analysed and later cluster analysis was carried out in order to identify categories of answers among the diverse answers. The results indicate that the test identified and delimitated modelling competences. Some results are in agreement with those obtained through other research into this issue and other results better elucidate certain aspects of modelling. The way in which evaluation methodology can be used in other areas of physics is discussed, such as in research and in teaching. Also discussed is how the constraints and potentials identified in the development of modelling competences can be taken into account in teaching and learning sciences. 相似文献
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Gjalt T. Prins Astrid M. W. Bulte Jan H. van Driel Albert Pilot 《International Journal of Science Education》2013,35(14):1867-1890
In science education, students should come to understand the nature and significance of models. In the case of chemistry education it is argued that the present use of models is often not meaningful from the students' perspective. A strategy to overcome this problem is to use an authentic chemical modelling practice as a context for a curriculum unit. The theoretical framework for this strategy is activity theory rooted in socio‐cultural theories on learning. An authentic chemical modelling practice is characterized by a set of motives for model development through a well‐defined modelling procedure using only relevant issue knowledge. The aim of this study was to explore, analyse, and select authentic chemical modelling practices for use in chemistry education. The suitability of the practices was reviewed by applying a stepwise procedure focused on criteria such as students' interest and ownership, modelling procedure, issue knowledge, and feasibility of the laboratory work in the classroom. It was concluded that modelling drinking‐water treatment and human exposure assessment are both suitable to serve as contexts, because both practices exhibit clear motives for model construction and the applied modelling procedures are in line with students' pre‐existing procedural modelling knowledge. The issue knowledge involved is consistent with present Dutch science curriculum, and it is possible to carry out experimental work in the classroom for model calibration and validation. The method described here to select and evaluate practices for use as contexts in chemistry education can also be used in other science domains. 相似文献
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This article presents knowledge modelling in an intelligent tutoring system, in which the modelling approach allows the knowledge representation to somewhat depart from its actual or most obvious basis to fit specifically pedagogical needs. The knowledge domain is cost engineering. Although the formulae used in cost engineering problem-solving are usually considered as relations between variables, our approach makes use of these formulae to identify new concepts, the factors, of a more pedagogical nature. The introduction of these concepts should help the student to concentrate either on computations or on economic analysis, and the system to make more accurate and more useful tutoring interventions. Moreover, it leads to important qualitative aspects of the domain modelling and of the tutorial interactions that should also help the learning process. Finally, this concept creation brings to light a hierarchy of intermediate abstraction levels, which can then be used to derive an order of presentation of these concepts, an order of the corresponding prerequisites and an order of the exercise types. All these should facilitate the student's learning. 相似文献
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This paper reports on a project that incorporated mathematical modelling within a pre-university subject at a secondary college. The program emphasised modelling rather than models and extended over two years. A qualitative methodology was used to evaluate the program with information collected in a variety of forms including student written reports, oral interviews, video reports, diaries, questionnaire data, as well as informal observation. The program was evaluated in terms of five criteria derived from the stated aims. Erom the synthesis and triangulation of the data it was inferred that the program aims were achieved to an encouraging degree. The paper describes and illustrates key aspects of the program and its evaluation. 相似文献
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Klaus-Dieter Schewe Bernhard Thalheim Aleksander Binemann-Zdanowicz Roland Kaschek Thomas Kuss Bernd Tschiedel 《Education and Information Technologies》2005,10(1-2):83-110
Starting from a general framework for web-based e-learning systems that is based on an abstraction layer model, this paper presents a conceptual modelling approach, which captures the modelling of learners, the modelling of courses, the personalisation of courses, and the management of data in e-learning systems. Courses are modelled by outline graphs, which are further refined by some form of process algebra. The linguistic analysis of word fields referring to an application domain helps to set up these course outlines. Learners are modelled by classifying value combinations for their characteristic properties. Each learner type gives rise to intentions as well as rights and obligations in using a learning system. Intentions can be formalised as postconditions, while rights and obligations lead to deontic constraints. The intentions can be used for the personalisation of the learning system to a learner type. Finally, the management of data in an e-learning system is approached on two different levels dealing with the content of individual learning units and the integrated content of the whole system, respectively. This leads to supporting databases and views defined on them. 相似文献
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数学建模是联系数学与实际问题的桥梁,是数学在各个领域广泛应用的具体体现。本文首先简要介绍了数学建模的概念、数学建模竞赛的发展概况和数学建模竞赛中使用的重要数学软件一Matlab,然后重点介绍了笔者在这几年参加全国大学生数学建模竞赛集训中关于Matlab软件教学的一些点滴体会。 相似文献
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The technology of knowledge-based systems undoubtedly offers potential for educational modelling, yet its practical impact on today's school classrooms is very limited. To an extent this is because the tools presently used in schools are mostly rule-based expert system shells, which lack usability. We developed three alternative tools, using ideas from knowledge acquisition research, and compared their effectiveness to that of an established rule-based shell. Children working with the new tools produced higher quality models and developed more positive attitudes. We relate these findings to the forms of representation provided by the new tools and present evidence that modelling increases children's representational skill. We conclude that knowledge acquisition systems and alternative forms of representation can contribute to improved forms of knowledge-based modelling. 相似文献
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Gjalt T. Prins Astrid M. W. Bulte Albert Pilot 《International Journal of Science Education》2013,35(11):1539-1569
Science education should foster students’ epistemological view on models and modelling consistent with formal epistemology in science and technology practices. This paper reports the application of a curriculum unit in the classroom using an authentic chemical practice, ‘Modelling drinking water treatment’, as the context for learning. An authentic practice is defined as professionals working on an issue guided by common motives and purposes, according to a similar type of procedure and applying relevant knowledge. The epistemology on models and modelling in the practice was analysed and anchored in the curriculum unit. The knowledge involved was captured in a design principle ‘content modelling’. A design principle provides heuristic guidelines to reach the intended pedagogic effects in the classroom. Throughout the field tests, research data were collected by means of classroom observations, interviews, audio‐taped discussions, completed worksheets, and written questionnaires. Students were able to evaluate the advanced model features of goodness of fit and reliability, and, to a lesser extent, validity. However, reflection on the modelling approach applied can be improved. The findings were used to reconsider the current completion of the design principle ‘content modelling’. This study contributes to the acquisition of a knowledge base concerning the use of authentic practices as contexts for learning in chemistry education as well as in science education in a broader sense. 相似文献