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We clarify the way in which cosmological perturbations of quantum origin, produced during inflation, assume classical properties. Two features play an important role in this process: First, the dynamics of fluctuations which are presently on large cosmological scales leads to a very peculiar state (highly squeezed) that is indistinguishable, in a precise sense, from a classical stochastic process. This holds for almost all initial quantum states. Second, the process of decoherence by interaction with the environment distinguishes the field amplitude basis as the robust pointer basis. We discuss in detail the interplay between these features and use simple analogies such as the free quantum particle to illustrate the main conceptual issues. 相似文献
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K. Rßner M. Hümmer A. Benkert A. Forchel 《Physica E: Low-dimensional Systems and Nanostructures》2005,30(1-2):159-163
We have successfully fabricated and characterized room temperature continuous wave (cw) GaInAsSb/AlGaAsSb distributed feedback lasers emitting in the wavelength region between 2.499 and 2.573 μm. To the best of our knowledge, this is the longest emission wavelength realized with a GaSb-based DFB laser diode. The laser structure used for DFB processing was grown by solid source molecular beam epitaxy. A DFB concept requiring no subsequent overgrowth step was used by defining first-order Cr-Bragg gratings laterally patterned to a ridge waveguide. Threshold currents smaller than 60 mA and room temperature cw output powers up to 6.5 mW were obtained. The laser diodes show single mode emission with side mode suppression ratios (SMSR) of up to 32 dB. 相似文献
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Christian J. Bordé Claus Lämmerzahl Ernst M. Rasel 《General Relativity and Gravitation》2004,36(10):2193-2196
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Claus Scheiderer 《Mathematische Zeitschrift》1989,201(2):249-271
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Claus Michelsen 《ZDM》2006,38(3):269-280
It is difficult for the students to transfer concepts, ideas and procedures learned in mathematics to a new and unanticipated situation in science. An alternative to this traditional transfer method stresses the importance of modelling activities in an interdisciplinary context between mathematics and science. In the paper we introduce a modelling approach to the concept of function in upper secondary school is introduced. We discuss pedagogical and didactical issues concerning the interplay between mathematics and science. The discussion is crystallized into a didactical model for interdisciplinary instruction in mathematics and science. The model is considered as an iterative movement with two phases: (1) the horizontal linking of the subjects: Situations from science are embedded in contexts which are mathematized by the students, (2) the vertical structuring in the subjects: The conceptual anchoring of the students' constructs from the horizontal linking in the systematic and framework of mathematics and science respectively. 相似文献