Speaker
Description
Within a living cell, motor proteins like kinesin are responsible of the transport of intracellular components. The functioning of this active transport is well known, and it has been employed to build synthetic assemblies of microtubules, which are stirred at the level of the single components and evolve out of thermal equilibrium. Such system is a paradigmatic example of an active material, and its realisation has originated lasting efforts, aimed to understand its crucial properties.
The presence of activity drives chaotic flow at the large scale and a sustained proliferation of topological defects, that retain some unique properties compared with passive liquid crystals. We use numerical simulations of a simple model of nematic liquid crystals in the presence of a microscopic active stress to study the morphology and dynamics of these topological defects to deduce fundamental properties of the turbulent state.
In a 3D periodic geometry, a statistically relevant wrapping component is present and quantitatively compatible with a phenomenon of defects percolation. Moreover, while the linear size of finite defects scales linearly with active length, it verifies an inverse quadratic dependence for wrapping defects. The shorter is the active length scale, the more times the defect lines wrap around the periodic boundaries, resulting in extremely long and tangled structures.
