1,722,896 research outputs found
Trajectories of collaborative scientific conceptual change: middle school students learning about ecosystems in a CSCL environment
No full textThe dissertation aims to achieve two goals. First, it attempts to establish a new theoretical framework -- the collaborative scientific conceptual change model, which explicitly attends to social factor and epistemic practices of science, to understand conceptual change. Second, it report the findings of a classroom study to investigate how to apply this theoretical framework to examine the trajectories of collaborative scientific conceptual change in a CSCL environment and provide pedagogical implications. Two simulations were designed to help students make connections between the macroscopic substances and the aperceptual microscopic entities and underlying processes. The reported study was focused on analyzing the aggregated data from all participants and the video and audio data from twenty focal groups' collaborative activities and the process of their conceptual development in two classroom settings. Mixed quantitative and qualitative analyses were applied to analyze the video/audio data. The results found that, overall participants showed significant improvements from pretest to posttest on system understanding. Group and teacher effect as well as group variability were detected in both students' posttest performance and their collaborative activities, and variability emerged in group interaction. Multiple data analyses found that attributes of collaborative discourse and epistemic practices made a difference in student learning. Generating warranted claims in discourse as well as the predicting, coordinating theory-evidence, and modifying knowledge in epistemic practices had an impact on student's conceptual understanding. However, modifying knowledge was found negatively related to students' learning effect. The case studies show how groups differed in using the computer tools as a medium to conduct collaborative discourse and epistemic practices. Only with certain combination of discourse features and epistemic practices can the group interaction lead to successful convergent understanding. The results of the study imply that the collaborative scientific conceptual change model is an effective framework to study conceptual change and the simulation environment may mediate the development of successful collaborative interactions (including collaborative discourse and epistemic practices) that lead to collaborative scientific conceptual change.Ph.D.Includes bibliographical references (p. 120-129)by Lei Li
Dynamic characteristics of torus involute gear drive
No full textThe torus involute gear drive originates from the involute spur gear drive, which is composed of a gear with convex teeth and the one with concave teeth. Previous researches of its mesh principle indicate that the torus involute gear can compensate large axial misalignments in parallel-shaft transmission, while its dynamic behavior has not been investigated comprehensively, or compared with that of the standard involute gear. This paper focuses on the dynamic performance of this type of gear. Considering the time variation of meshing stiffness, a 6-degree-of-freedom dynamics model of the torus involute gear pair is established, which counts in the effect of alternate meshing of single-double tooth pairs. Sliding friction in elastohydrodynamic lubrication is also included in the model. The numerical analysis for six cases is conducted, and the dynamic characteristics such as the dynamic transmission error, mechanical efficiency, sliding friction forces and minimum oil-film thickness are compared with those of the standard involute gear. The results show that, the torus involute gear drive exhibits good performances as the standard involute gear drive in transmission accuracy and mechanical efficiency, while, it has a better performance in lubrication condition. The study in this paper may lay theoretical foundations for practical application of the torus involute gears
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Robust adaptive finite-time fault-tolerant tracking control for uncertain systems
No full textThe adaptive finite-time fault-tolerant tracking issue of a class of uncertain systems is taken into consideration in this paper. The unknown time-varying actuator faults and uncertainties of both the system matrix and the input matrix are considered simultaneously when designing the control scheme. The unknown control parameters and gains caused by the actuator faults and model uncertainties are estimated by the designed adaptive laws to construct the fault-tolerant controller. Lyapunov stability analysis shows that the finite-time convergence property of the closed-loop system can be accomplished with great robustness to actuator faults and uncertainties guaranteed. Simulation results of an application to an aircraft model are illustrated to highlight the effectiveness of the proposed methodology.</p
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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