Morphogenesis of highly connected structures : from termite nests to sea urchin spines.
Orateur : Giulio Facchini
Abstract : Self-organisation is a powerful tool as it can produce complexity through the bare combination of minimal mechanisms and variable boundary conditions. Simple mechanisms borrowed from chemo-physical processes can thus explain the morphogenesis of complex biological patterns. In this frame we have recently focused on the impressive nests built by termites. In a first study we have shown that using a phase-field approach and a single non-linear equation we can reproduce the nest growth process and retrieve the main geometrical features of real nests geometry. Our model equation relies on the hypothesis that building activity is locally enhanced where the convexity of the nest walls is high. More recently we have run laboratory experiments with small group of termites constrained in a humid clay arena decorated with topographic cues. Observations confirm that convexity drives building activity and points toward evaporation flux as the genuine physical quantity perceived by termites. Remarkably, nest construction resembles to other growth phenomena, known as Laplacian, which grow at the tips and express tips splitting. However, differently from them, the growth of our nests also express reconnections which are necessary to produce high connectivity. This puzzle inspires my current research which aims to understand how highly connected biotic structures can form and whether similar structures can be expressed by abiotic systems.
Dynamics and instabilities of concentrated vortices
Orateur : Andrés Castillo-Castellanos
Abstract : A vortex ring and a uniform helical vortex are examples of elongate concentrated vortices which move in space without deformation. Their stability to long- and short-wavelength perturbations has been the subject of numerous analytical, numerical, and experimental works. Such stability analyses are relatively scarce in systems composed of multiple vortices or complex geometries. We present a general approach based on the free vortex method to study the dynamics and stability of the wake behind a horizontal axis wind turbine with single and tip-splitting rotors, where helical symmetry is not present.
Date et lieu : Vendredi 11/03 11h00, en ligne sur Zoom