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51.
52.
本文所介绍的高效辐射换热器是指在其环缝通道中安装有网状二次传热面的辐射换热器,用对比实验方法研究了它们在空气预热温度、给热系数和阻力系数上的差别.实验表明:高效辐射换热器可强化空气侧的传热,其综合传热系数达59W/(m2·℃),而阻力系数可控制在3000Pa以内. 相似文献
53.
初生空化与液体抗拉强度的关系 总被引:3,自引:1,他引:2
杨志明 《水动力学研究与进展(A辑)》1990,5(4):27-34
自1983年开始以液体的抗拉强度作为其空化临界压强研究初生空化的比尺效应以来,该方法已得到进一步的应用和完善。本文就研究中遇到的一些问题,如关于空化灵敏度仪的校正,“零抗拉强度”的概念,试验设备中液体抗拉强度的动态变化以及在空化试验中使用该方法的技术和意义等作详细的阐述。 相似文献
54.
Bert Slof Anouschka van Leeuwen Jeroen Janssen Paul A. Kirschner 《Journal of Computer Assisted Learning》2021,37(1):39-50
In computer-supported collaborative learning research, studies examining the combined effects of individual level, group level and within-group differences level measures on individual achievement are scarce. The current study addressed this by examining whether individual, group and within-group differences regarding engagement and prior knowledge predict individual achievement. Engagement was operationalised as group members' exhibited activities in the task space (i.e., discussing domain-content) and social space (i.e., regulating ideas, actions and socioemotional processes). Prior knowledge and achievement were operationalised as group members' performance on a domain-related pre-test and post-test, respectively. Data was collected for 95 triads of secondary education students collaborating on a complex business-economics problem. Subsequently, three different multilevel models were tested to examine the combined effect. First a model with the individual level measures (model 1) was tested and in subsequent models the group level measures (model 2) and within-group levels measures (model 3) were added. Findings indicate model 2 showed the best fit; group members' individual engagement in the social space activities as well as the groups' average prior knowledge positively predicts individual achievement. No effects were found for either group members' or groups' engagement in the task space and for the within-group differences. 相似文献
55.
Caihua Liu Didar Zowghi Matthew Kearney Muneera Bano 《Journal of Computer Assisted Learning》2021,37(1):1-23
Recent years have seen a growing call for inquiry-based learning in science education, and mobile technologies are perceived as increasingly valuable tools to support this approach. However, there is a lack of understanding of mobile technology-supported inquiry-based learning (mIBL) in secondary science education. More evidence-based, nuanced insights are needed into how using mobile technologies might facilitate students' engagement with various levels of inquiry and enhance their science learning. We, therefore, conducted a robust systematic literature review (SLR) of the research articles on mIBL in secondary school science education that have been published from 2000 to 2019. We reviewed and analysed 31 empirical studies (34 articles) to explore the types of mIBL, and the benefits and constraints of mIBL in secondary school science education. The findings of this SLR suggest new research areas for further exploration and provide implications for science teachers' selection, use and design of mIBL approaches in their teaching. 相似文献
56.
为寻求在钢的成份和二次硬化能力之间的定量关系,对国内外40多种钢按作者提出的合金化参数进行计算和整理,证明了用“平衡碳”(Cp)和“碳饱和度”(A) 两个合金化参数判别 (预报) 钢的二次硬度的可能性。 相似文献
57.
本文以二次Bernstein基函数为例,首次提出了含双参数基函数的新扩展——αβQ—Bern-stein基函数,此类基函数具有新的特点,即基函数的扩展次数一次性升高两次,且包含了二次多项式和带一个参数的三次多项式基函数的所有性质。基于这组基函数定义了αβQ—Bézier曲线,该曲线也含有参数,具有形状可调性,当α与β取某些值时曲线能达到C4连续或在某个端点处C0连续。最后与含两个参数的升一次Bézier曲线进行比较,该曲线具有调节范围广、灵活性更强的优势。 相似文献
58.
转换开关是用在工业生产自动流水线机械手中一种易磨损和大量消耗的塑料制品,以前依靠外国进口,花费了大量外汇。由于转换开关的精度极高,甚至超过金属件的制造精度。故不仅要求制品在成型加工过程中不能有微小的变形,甚至需要严格控制塑料的收缩量。使得所有成型孔的精度达到IT6级以上,平面度不大于0.02 mm,圆柱度不大于0.01 mm。通过对亚光微珠增强聚碳酸脂改性材料的选择,实现控制了制品变形量和提高了耐磨性的目的,通过超高精度孔的二次限制工艺的实施,使得制品孔的精度可达到IT4级以上,圆柱度为0.002 mm以内。国产转换开关完全取代了进口产品,且其精度和寿命远高于进口产品,为超高精度注射件加工创出了一种新方法,也为有关单位节约了大量外汇。 相似文献
59.
The programmability of RNA–RNA interactions through intermolecular base-pairing has been successfully exploited to design a variety of RNA devices that artificially regulate gene expression. An in silico design for interacting structured RNA sequences that satisfies multiple design criteria becomes a complex multi-objective problem. Although multi-objective optimization is a powerful technique that explores a vast solution space without empirical weights between design objectives, to date, no web service for multi-objective design of RNA switches that utilizes RNA–RNA interaction has been proposed. We developed a web server, which is based on a multi-objective design algorithm called MODENA, to design two interacting RNAs that form a complex in silico. By predicting the secondary structures with RactIP during the design process, we can design RNAs that form a joint secondary structure with an external pseudoknot. The energy barrier upon the complex formation is modeled by an interaction seed that is optimized in the design algorithm. We benchmarked the RNA switch design approaches (MODENA+RactIP and MODENA+RNAcofold) for the target structures based on natural RNA-RNA interactions. As a result, MODENA+RactIP showed high design performance for the benchmark datasets. 相似文献
60.
XIA Yuebo WANG Zhongguang State Key Laboratory for Fatigue Failure of Materials Institute of Metal Research Academia Sinica Shenyang China 《金属学报(英文版)》1992,5(5):330-335
SEM photos for very coarse grained and high ductile polycrystalline pure Al show followingcharacteristics:A few fracture sources are concentrated,the crack propagates in fan-shapenear them,and the fatigue striations are cyclic cleavage facets.Each striation consists of awide cleavage facet and a narrow cleavage stage.Those stages often blunt due to plasticdeformation.The fatigue striations are clear and continual,and distribute over whole zone ofstage Ⅱ crack propagation.Two kinds of fatigue striations form in different levels,areconjoined by a“twisted baked piece of pastry”band.The secondary crack along the fatiguestriations was observed frequently.Some of them have already developed into secondarymacrocracks and secondary fatigue striations were found clearly on secondary fracture sur-face.The fracture surface can be divided into two parts,initiation and propagation zone of thecrack,however,no statical-fracture zone was observed.The mechanism to form striationswas preliminarily discussed. 相似文献