Speaker
Nicholas Moloney

Description We examine the cost-minimisation problem posed by Ferrer i Cancho and Solé in their information-theory based communication model (R. Ferrer i Cancho and R. V. Solé, PNAS 100, 788 (2003)), proposed in efforts to explain Zipf’s Law (power law frequency-rank relation for words in written texts). We obtain the exact minimum-cost solutions as obtained previously via other methods. The model exhibits three qualitatively different behaviours according to the relative importance of speaker and listener costs. At the phase transition, the minimum-cost solutions do not correspond to a power law except for a vanishingly small subset.

Speaker
David Sprinzak

Description Many signaling pathways rely on direct cell-cell contacts to transduce signaling between neighboring cells. For example, the Notch signaling pathway, which is the canonical signaling pathway between neighboring cells during development, involves interaction between membrane-bound receptors on one cell and membrane-bound ligands on a neighboring cell. Such intercellular signaling mechanisms are affected not only by the concentrations and binding affinities of the involved proteins, but may also depend on the morphology of the cells and the contact area between them. In this talk, I will discuss our theoretical and experimental efforts to understand how intercellular Notch signaling depends on the geometry and properties of the contact area between cells. Theoretically, we developed a simple mathematical model which provides insight into how the biochemical and biophysical processes as well as the geometry of the system control cell-cell signaling. Experimentally, we developed methods to measure the relevant biophysical parameters of the Notch signaling system and to study the dynamics of Notch receptors and ligands on the cell membrane. I will discuss the implications of our findings in various biological contexts.

Description

A meeting characterized by the emphasis in interdisciplinary will take place during the upcoming February 7th 2013 in the Main Lecture Hall (Aula Magna) of the historical building of the University of Barcelona. The leading thread of the meeting consists on a series of thematic sessions where young researchers with common interests but not necessarily from the same field will present the research they carry out. The sessions will have a divulgative but formal character.

 

Organizers
Anna Alemany, Albert Bruix, Marc Caballero, Joan Camuñas, Blai Garolera, David Martí, Narcís Miguel, Rubén Pérez, Daniel Pérez, José Manuel Rebled, Oleguer Segarra.

Speaker
Eduard Vives

Description Among known hydrodynamic instabilities, boiling crisis is one of the most poorly understood [1]. It may be described as a sudden loss of liquid contact with a heating surface (dryout) when a small increase of heat flux transforms nucleate boiling regime into film boiling reaching the critical heat flux results in thermal blocking and temperature increase with often devastating consequences for various nuclear and electronic systems (burnout). In this work [2] we study boiling crisis from a fundamental point of view because it marks a transition between two different non-equilibrium dynamic steady states, each incorporating liquid flow, phase transition, contact line dynamics and heat transfer. At subcritical values of the heat flux separate bubbles are released from the hot surface (nucleate boiling), while at the CHF a vapor layer suddenly covers the hot surface. At supercritical heat flux values the system stabilizes again in a film boiling regime where bubbles are released from a detached liquid vapor surface. We present an experimental study (based on the Acoustic Emission technique )of intermittancy and avalanche distribution during boiling crisis. To understand the emergence of power law statistics we also propose a simple spin model capturing the measured critical exponent. The model suggests that behind the critical heat flux there is a percolation phenomenon involving drying-rewetting competition close to the hot surface. [1] V.K.Dhir, Annu. Rev. Fluid Mech. 30, 365 (1998) [2] P. Lloveras, F. Salvat-Pujol, L.Truskinovsky and E.Vives, Phys. Rev. Lett.108, 215701 (2012)

Speaker
Nikos Kouvaris

Description Traveling fronts and stationary localized patterns in bistable reaction-diffusion systems have been broadly studied for classical continuous media and regular lattices. Analogs of such non-equilibrium patterns are also possible in networks. Here, we consider traveling and stationary patterns in bistable one-component systems on random Erdös-Rényi, scale-free and hierarchical tree networks. As revealed through numerical simulations, traveling fronts exist in network-organized systems. They represent waves of transition from one stable state into another, spreading over the entire network. The fronts can furthermore be pinned, thus forming stationary structures. While pinning of fronts has previously been considered for chains of diffusively coupled bistable elements, the network architecture brings about significant differences. An important role is played by the degree (the number of connections) of a node. For regular trees with a fixed branching factor, the pinning conditions are analytically determined. Furthermore, effects of feedbacks on pattern formation phenomena are investigated. Localized stationary activation patterns, which resemble stationary spots in continuous media, have been observed in the networks. The active nodes in such a pattern form a subnetwork, whose size and structure can be controlled by the feedback intensity.