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Thermal convection in 2D and Stresses in roots*

Ramon Peralta-Fabi

à 11h en salle C. Brot

1) When a fluid is heated, it expands ; becoming less dense, it moves upwards (against gravity). Boussinesq’s approximation addresses the theoretical analysis of this phenomenon. We study a very thin circular cell in which a fluid is constrained to move in two dimensions. This is accomplished by imposing two different temperatures at diametrically opposed points on the rim. By tilting the cell, the component of gravity in the plane of the fluid varies, as well as its direction. The system is analyzed theoretically and experimentally.

2)* Roots provide support to plants, structurally and energetically. They interact with the soil, modifying it and adapting to its characteristics. The tip (apex) of the root explores the environment and reacts accordingly, penetrating when feasible. Roots become thicker as the plant grows, exercising stresses on the surroundings. We design methods to measure such stresses *in situ* in the earlier stages of growth, using photo-elastic materials and elastic elements in the local surroundings, while developing a graphic history. Simple theoretical reasoning and calculations provide access to previously unknown information.