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991.
Héléne Gispert 《ZDM》2002,34(4):158-163
Evolutions of mathematical curricula in French society have been marked by the successive answers intitutions have given to the following question since one century: Why and whom teaching mathematics? Here I present two of these, one given in 1908 and one in 1967. Each symbolises a breaking period of reforms in secondary mathematics teaching in France. We will see in the two first part of this paper that they belong to two different worlds, with social, institutional, ideological and mathematical specific features. In the third part, I’ll focus on geometry, showing the effects of the different answers concerning the public and the aims of mathematical teaching. 相似文献
992.
J.J. THOMSEN 《Journal of sound and vibration》2002,253(4):807-831
Mechanical high-frequency (HF) excitation provides a working principle behind many industrial and natural applications and phenomena. This paper concerns three particular effects of HF excitation, that may change the apparent characteristics of mechanical systems: (1) stiffening, by which the apparent linear stiffness associated with an equilibrium is changed, along with derived quantities such as stability and natural frequencies; (2) biasing by which the system is biased towards a particular state, static or dynamic, which does not exist or is unstable in the absence of the HF excitation; and (3) smoothening, referring to a tendency for discontinuities to be effectively “smeared out” by HF excitation. Illustrating first these effects for a few specific systems, analytical results are provided that quantify them for a quite general class of mechanical systems. This class covers systems that can be modelled by a finite number of second order ordinary differential equations, generally non-linear, with periodically oscillating excitation terms of high frequency and small amplitude. The results should be useful for understanding the effects in question in a broader perspective than is possible with specific systems, for calculating effects for specific systems using well-defined formulas, and for possibly designing systems that display prescribed characteristics in the presence of HF excitation. 相似文献
993.
We prove that the average order of the remainder in counting the number of points of a random lattice inside a disc of radius
. Our proof is spectral in nature.
Submitted: July 2001, Revised: August 2001, Revised: March 2002. 相似文献
994.
X.T Zhang Y.C LiuZ.Z Zhi J.Y ZhangY.M Lu D.Z ShenW Xu X.W FanX.G Kong 《Journal of luminescence》2002,99(2):149-154
The properties of the excitonic luminescence for nanocrystalline ZnO thin films are investigated by using the dependence of excitonic photoluminescence (PL) spectra on temperature. The ZnO thin films are prepared by thermal oxidation of ZnS films prepared by low-pressure metalorganic chemical vapor deposition (LP-MOCVD) technique. The X-ray diffraction (XRD) indicates that ZnO thin films have a polycrystalline hexagonal wurtzite structure with a preferred (0 0 2) orientation. A strong ultraviolet (UV) emission peak at 3.26 eV is observed, while the deep-level emission band is barely observable at room temperature. The strength of the exciton-longitudinal-optical (LO) phonon coupling is deduced from the temperature dependence of the full-width at half-maximum (FWHM) of the fundamental excitonic peak, decrease in exciton-longitudinal-optical (LO) phonon coupling strength is due to the quantum confinement effect. 相似文献
995.
On free entropy dimension of finite von Neumann algebras 总被引:3,自引:0,他引:3
996.
A. Thomasson S. Geffroy E. Frejafon D. Weidauer R. Fabian Y. Godet M. Nominé T. Ménard P. Rairoux D. Moeller J.P. Wolf 《Applied physics. B, Lasers and optics》2002,74(4-5):453-459
Continuous mapping of an ozone episode in Paris in June 1999 has been performed using a differential absorption lidar system.
The 2D ozone concentration vertical maps recorded over 33 h at the Champ de Mars are compiled in a video clip that gives access
to local photochemical dynamics with unprecedented precision. The lidar data are compared over the whole period with point
monitors located at 0-, 50-, and 300-m altitudes on the Eiffel Tower. Very good agreement is found when spatial resolution,
acquisition time, and required concentration accuracy are optimized. Sensitivity to these parameters for successful intercomparison
in urban areas is discussed.
Received: 11 February 2002 / Published online: 14 March 2002 相似文献
997.
F.F. Karpeshin J. da Providência C. Providência J. da Providência Jr 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,18(3):319-326
Two types of extreme collective motion, large-amplitude many-phonon vibration of the ionic core and rotation of the cluster
with high angular momenta, are considered. The interplay between vibration and collective motion towards fission is discussed.
A new mechanism of formation and rupture of the neck is proposed which is based on the Franck-Condon principle, and accounts
for the interplay between vibration and fission. Under rotation, the change of the shape of the cluster and a phase transition
from axially symmetric to triaxial ellipsoid are predicted. For studying the effects, vibrational motion can be induced by
laser radiation. Rotational motion may arise in collisions of clusters.
Received 26 April 2001 and Received in final form 15 October 2001 相似文献
998.
Frédéric Coquel Thierry Gallouët Jean-Marc Hérard Nicolas Seguin 《Comptes Rendus Mathematique》2002,334(10):927-932
Closure laws for interfacial pressure and interfacial velocity are proposed within the frame work of two-pressure two-phase flow models. These enable us to ensure positivity of void fractions, mass fractions and internal energies when investigating field by field waves in the Riemann problem. To cite this article: F. Coquel et al., C. R. Acad. Sci. Paris, Ser. I 334 (2002) 927–932. 相似文献
999.
We compute Green's functions of a Bosonic field theory with cutoffs by means of a “minimal” expansion which in a single move,
interpolating a generalized propagator, performs the usual tasks of the cluster and Mayer expansion. In this way it allows
a direct construction of the infinite volume or thermodynamic limit and it brings constructive Bosonic expansions closer to
constructive Fermionic expansions and to perturbation theory.
Received: 18 May 2000 / Accepted: 21 March 2001 相似文献
1000.
We study the vibration of an elastic thin shell which is pre-constrained by a large displacement with a small deformation. In this first Note we prove the solutions exist and we investigate both the interior regularity and the boundary regularity which is known to be important in the shape differentiation of hyperbolic equations. To cite this article: J. Cagnol, J.-P. Zolésio, C. R. Acad. Sci. Paris, Ser. I 334 (2002) 161–166 相似文献