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排序方式: 共有62条查询结果,搜索用时 20 毫秒
1.
J. B. Lagrange 《International Journal of Computers for Mathematical Learning》2005,10(2):143-189
The paper starts from classroom situations about the study of a functional relationship with help of technological tools as a ‘transposition’ of experimental approaches from research mathematical practices. It considers the limitation of this transposition in existing curricula and practices based on the use of non-symbolic software like dynamic geometry and spreadsheets. The paper focuses then on the potentialities of classroom use of computer algebra packages that could help to go beyond this shortcoming. It looks at a contradiction: while symbolic calculation is a basic tool for mathematicians, curricula and teachers are very cautious regarding their use by students. The rest of the paper considers the design and experiment of a computer environment Casyopée as means to contribute to an evolution of curricula and classroom practices to achieve the transposition in the domain of algebraic activities linked to functions. 相似文献
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Emery N Hérold C d'Astuto M Garcia V Bellin Ch Marêché JF Lagrange P Loupias G 《Physical review letters》2005,95(8):087003
We have obtained bulk samples of the graphite intercalation compound, CaC6, by a novel method of synthesis from highly oriented pyrolytic graphite. The crystal structure has been completely determined showing that it is the only member of the MC6, metal-graphite compounds that has rhombohedral symmetry. We have clearly shown the occurrence of superconductivity in the bulk sample at 11.5 K, using magnetization measurements. 相似文献
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The spinel phases Mn3-x Co x O4 are prepared directly and at low temperature (600-700°C) by means of thermal decomposition of mixed oxalate salt precursors in air or controlled atmosphere. The powders so obtained when sintered at 1200°C behave as semiconducting or insulating ceramics, depending on their cobalt content. The electrical properties of these ceramics have been found to be related to the distribution and valencies of the cations in the spinel structure. The study of their crystalline structure and stability, complemented by electrical measurements have permitted us to distinguish two types of compounds. The first type includes those given by Mn3-x Co x O4 with 0 < x < 1. These are stable at high temperature, have a tetragonal structure and are insulators. The cation distributions for them can be deduced from that of hausmannite as given by Mn2+ [Mn3+ 2]O4, by substituting Mn2+ ions with Co2+ ions. The second type of compounds correspond to the cubic phases and occur for 1 < x < 3. These are unstable at high temperature and show a lower resistivity (e.g. 360 ° cm) which is of particular interest for their application in the design of negative temperature coefficient (N.T.C.) thermistor components. 相似文献
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Ph. Caïs L. Ravera D. Lagrange M. Giard A. Baudry J. Y. Mayvial 《International Journal of Infrared and Millimeter Waves》1998,19(11):1471-1487
We have designed and built a new, wide band, modulable resolution spectrometer, in view of full astronomical qualifying tests, and to prepare future models for the FIRST satellite's heterodyne instrument. Our spectrometer, a hybrid digital Autocorrelator, offers flexibility in terms of bandwidth (from 170MHz to 680MHz) and resolution (from 700kHz to 3MHz). This spectrometer required the development of a dedicated analog filter bank, homemade samplers, and the design of full custom GaAs integrated circuits.Laboratory tests have shown excellent agreement with expected performances and observations performed with the IRAM 30-m radiotelescope have qualified its capabilities. Despite the relatively limited number of channels of our current prototype compared to others spectrometers, the main advantages are its stability (inherent to digital technique), and its spectral versatility.Recent microelectronics advances and rad-tolerance of our spectrometer components are used to prepare a new, compact, and low power consumption autocorrelator in view of a flight model for HIFI, the heterodyne instrument on the ESA cornerstone mission FIRST. 相似文献
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Saladin Ducretet Lejeune Henri Moissan Jules Violle Lagrange und Hoho 《Fresenius' Journal of Analytical Chemistry》1895,34(1):176-178
Ohne Zusammenfassung 相似文献
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