laboratoire de physique statistique
 
 
laboratoire de physique statistique

Publications

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AMERICAN JOURNAL OF PHYSICS 


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2012
Chaotic motors - Laroche, C. and Labbe, R. and Petrelis, F. and Fauve, S.
AMERICAN JOURNAL OF PHYSICS 80113-121 (2012)

Abstract : We show that electric motors and dynamos can be used to illustrate most elementary instabilities or bifurcations discussed in courses on nonlinear oscillators and dynamical systems. These examples are easier to understand and display a richer behavior than the ones commonly used from mechanics, electronics, hydrodynamics, lasers, chemical reactions, and population dynamics. In particular, an electric motor driven by a dynamo can display stationary, Hopf, and codimension-two bifurcations by tuning the driving speed of the dynamo and the electric current in the stator of the electric motor. When the dynamo is driven at constant torque instead of constant rotation rate, chaotic reversals of the generated current and of the angular rotation of the motor are observed. Simple deterministic models are presented which capture the observed dynamical regimes. (C) 2012 American Association of Physics Teachers.
 
2011
Capillary rise and condensation in a cone as an illustration of a spinodal - Pettersen, M. S. and Rolley, E. and Treiner, J.
AMERICAN JOURNAL OF PHYSICS 79831-837 (2011)

Abstract : Spinodal decomposition can be observed only in systems whose dynamics are slow enough to quench through the metastable region where the phase transition occurs by nucleation. We discuss the capillary rise of a fluid in a cone inserted into a bulk fluid, with the wide end down. The rise displays a first-order phase transition with a spinodal and is easily accessible both theoretically and experimentally. (C) 2011 American Association of Physics Teachers. [DOI: 10.1119/1.3599073]
 
2008
Experimental high Reynolds number turbulence with an active grid - Mordant, Nicolas
AMERICAN JOURNAL OF PHYSICS 761092-1098 (2008)

Abstract : This article describes the wind tunnel used in the Physics Department of the Ecole Normale Superieure in Paris for undergraduate laboratory courses. By using an active grid, which consists of a grid of shafts fitted with randomly rotating wings, a fully turbulent flow is observed. The velocity of the air flow is measured with a low cost hot wire probe. The Reynolds number is large enough so that predictions of the 1941 Kolmogorov theory of turbulence can be observed, such as the famous k(-5/3) spectrum, in spite of the small size of the tunnel. Deviations from the Kolmogorov theory are also observed and quantified. The moderate cost and size of the wind tunnel due to the use of the active grid make it a valuable teaching tool for introducing the phenomenology of turbulence to undergraduates. (C) 2008 American Association of Physics Teachers.