laboratoire de physique statistique
 
 
laboratoire de physique statistique

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PHYSICA B-CONDENSED MATTER 


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2009
Thermal effects in the dynamics of disordered elastic systems - Bustingorry, S. and Kolton, A. B. and Rosso, A. and Krauth, W. and Giamarchi, T.
PHYSICA B-CONDENSED MATTER 404444-446 (2009)

Abstract : Many seemingly different macroscopic systems (magnets, ferroelectrics, CDW, vortices, etc.) can be described as generic disordered elastic systems. Understanding their static and dynamics thus poses challenging problems both from the point of view of fundamental physics and of practical applications. Despite important progress many questions remain open. In particular the temperature has drastic effects on the way these systems respond to an external force. We address here the important question of the thermal effect close to depinning, and whether these effects can be understood in the analogy with standard critical phenomena, analogy so useful to understand the zero temperature case. We show that close to the depinning force temperature leads to a rounding of the depinning transition and compute the corresponding exponent. In addition, using a novel algorithm it is possible to study precisely the behavior close to depinning, and to show that the commonly accepted analogy of the depinning with a critical phenomenon does not fully hold, since no divergent lengthscale exists in the steady state properties of the line below the depinning threshold. (c) 2008 Elsevier B.V. All rights reserved.
 
2007
The hydraulic jump and ripples in liquid helium - Rolley, E. and Guthmann, C. and Pettersen, M. S.
PHYSICA B-CONDENSED MATTER 39446-55 (2007)

Abstract : We have studied the characteristics of the circular hydraulic jump using liquid helium. Surprisingly, the radius of the jump does not change at the superfluid transition. We think that the flow is still dissipative below the lambda point because the velocity exceeds the critical one. The jump radius R-j is compared with various models. In our parameter range, we find that the jump can be treated as a shock, and that capillary effects are important. Below the superfluid transition, we observed a standing capillary wave between the impact of the jet and the jump. Assuming that the superfluid flow can be described with an effective viscosity, we calculate the wave vector and thus obtain the value of the liquid thickness, which is in reasonable agreement with predictions. However, the spatial variation of the wave amplitude depends much more strongly on temperature than we calculate. (c) 2007 Elsevier B.V. All rights reserved.