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Prof. Hans-Günther Döbereiner: Slime Mold Network Percolation as a Paradigm for Topological Phase Transitions

Date: 28. 3. 2012
Source: Monday physics colloquium
Ponedeljek, 2. aprila 2012, ob 16:15 v predavalnici F1, FMF UL, Jadranska 19, Ljubljana

     Slime Mold Network Percolation as a Paradigm for Topological Phase Transitions     

     Prof. Hans-Günther Döbereiner, Institut für Biophysik, Universität Bremen  

The true slime mold Physarum polycephalum forms a tubular network as a foraging strategy in order to maximize searchable area and minimize transport distances of nutrients and biochemical signals. These networks grow out of microplasmodia which oscillate in shape with a typical frequency of two minutes. We characterize concomitant calcium oscillations and cytoskeleton elasticity, and show that microplasmodia fuse to form macroplasmodia in a percolation transition. At this topological phase transition, one single giant component forms, connecting most of the previously isolated microplasmodia. Employing the configuration model of graph theory for small link degrees, we have found an exact solution for this transition. Topological constraints impose strong conditions on trajectories in the configuration space of the network.  Conditions are quite general so that all systems which form extended networks from disconnected pieces have to pass through this percolation transition in a particular way. Especially, this applies to vasculogenesis in early embryo development and within tumors. We have demonstrated that in the early stages of vascular network assembly of endothelial cells. In a broader sense, static and dynamic phase transitions may serve as a general ordering principle in complex biological systems.