13,861 research outputs found

    High-harmonic generation from arbitrarily oriented diatomic molecules including nuclear motion and field-free alignment

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    We present a theoretical model of high-harmonic generation from diatomic molecules. The theory includes effects of alignment as well as nuclear motion and is used to predict results for N2_2, O2_2, H2_2 and D2_2. The results show that the alignment dependence of high-harmonics is governed by the symmetry of the highest occupied molecular orbital and that the inclusion of the nuclear motion in the theoretical description generally reduces the intensity of the harmonic radiation. We compare our model with experimental results on N2_2 and O2_2, and obtain very good agreement.Comment: 12 pages, 8 figures, 2 tables; legends revised on Figs. 1,3,4,6 and

    Hot-wire and hot-film anemometry

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    The circuit techniques, electronics, dynamic properties, and the applications of the anemometers are given

    How physics instruction impacts students' beliefs about learning physics: A meta-analysis of 24 studies

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    In this meta-analysis, we synthesize the results of 24 studies using the Colorado Learning Attitudes about Science Survey (CLASS) and the Maryland Physics Expectations Survey (MPEX) to answer several questions: (1) How does physics instruction impact students' beliefs? (2) When do physics majors develop expert-like beliefs? and (3) How do students' beliefs impact their learning of physics? We report that in typical physics classes, students' beliefs deteriorate or at best stay the same. There are a few types of interventions, including an explicit focus on model-building and/or developing expert- like beliefs that lead to significant improvements in beliefs. Further, small courses and those for elementary education and non-science majors also result in improved beliefs. However, because the available data oversamples certain types of classes, it is unclear whether these improvements are actually due to the interventions, or due to the small class size, or student population typical of the kinds of classes in which these interventions are most often used. Physics majors tend to enter their undergraduate education with more expert-like beliefs than non-majors and these beliefs remain relatively stable throughout their undergraduate careers. Thus, typical physics courses appear to be selecting students who already have strong beliefs, rather than supporting students in developing strong beliefs. There is a small correlation between students' incoming beliefs about physics and their gains on conceptual mechanics surveys. This suggests that students with more expert-like incoming beliefs may learn more in their physics courses, but this finding should be further explored and replicated. Some unanswered questions remain. To answer these questions, we advocate several specific types of future studies.Comment: 30 pages. Accepted to Phys Rev ST-PE
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