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EDITORS' PREFACE 总被引：1，自引：0，他引：1
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The purpose of this paper is to present an analysis of the difficulties faced by students when working with different representations of vectors, planes and their intersections in \(\mathbb {R}^{3}\). Duval’s theoretical framework on semiotic representations is used to design a set of evaluating activities, and later to analyze student work. The analysis covers three groups of undergraduate students taking introductory courses in linear algebra. Different types of treatments and conversions are required to solve the activities. One important result shows that, once students choose a register to solve a task, they seldom make transformations between different registers, even though this facilitates solving the task at hand. Identifying these difficulties for particular transformations may help teachers design specific activities to promote students cognitive flexibility between representation registers. 相似文献
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Research in Science Education - The first phase of this multiphase study involves modeling of college students’ thinking of friction at the microscopic level. Diagnostic interviews were... 相似文献
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Edgar F. Smith 《Journal of The Franklin Institute》1889,128(6):490-492
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Willis G. Hazard 《Journal of The Franklin Institute》1934,217(5):571-590
An apparatus is described for recording general atmospheric dust. The full-scale range of the present model of approximately 120 × 106 particles per cubic foot of air may be increased or decreased as desired. The dust concentrations measured are far below smoke concentrations. The method is to impinge dust on a slowly moving strip of transparent film, and to measure the deposit by a comparison of two beams of light, one passing through the dusty film, the other through clean film. The decrease in transmitted light due to the dust is balanced automatically by a motor-driven optical wedge in the unobstructed beam. The position of this wedge is recorded on a chart. Dusty air is sampled continuously for long periods. Rapid fluctuations of a few minutes in length are registered. In this, and in the fact that it is direct-reading, without tedious laboratory quantitation, the recorder offers distinct advantages over the present dust determinators, almost all of which take momentary samples. A different calibration is needed for different dusts. The machine may be adapted to laboratory or field use. In factories, auxiliary blowers may be operated through relays, when the dustiness exceeds a specified level. 相似文献