Speaker
Charles Newman

Speaker
Matteo Nicoli

Description Pressure sensitive adhesives (PSAs) are viscoelastic or viscoplastic materials that adhere to a substrate upon the application of light pressure. The debonding mechanism is an interfacial process due to different phenomena, e.g. the creation of cavities and fibrils, the propagation of interfacial cracks and the lateral invasion of air fingers. The studies of adhesive performances of PSAs are carried out through the probe tack tester. We developed a boundary recognition algorithm to analyze the top-view images from probe tack experiments, allowing us to detect the nucleation of cavities, track their growth and measure various geometrical quantities. We tested three PSAs with different viscoelastic features, ranging from a more liquid to a more elastic behavior, at two debonding velocities (1 and 10 µm / s). We measured the load bearing area and estimated the magnitude of the shear stress from the nominal force and the uniaxial tensile stress. From the characterization of the projected radius of each bubble, we tested the assumption of spherical growth of these cavities after the onset of their nucleation. The probe tack test combined with our methodology provides valuable data to understand the interfacial processes leading to the debonding of PSAs.

Speaker
Jordan Muscatello

Speaker
Per Sebastian Skardal

Description The study of synchronization of oscillators in complex networks has become a large and important research area in complexity theory. Examples and applications range from the very small, e.g. sub-cellular protein interactions, to the very large, e.g. trends in interconnected world economies. Previous work combines elements from the internal dynamics (e.g. natural frequencies) of each oscillator and the overall network structure (e.g. one or more eigenvalues of the adjacent matrix) to describe synchronization dynamics. However, many of these results break down when when networks develop modular, or community, structure, i.e. groups of strongly connected oscillators that are weakly connected to oscillators in other groups. In such networks, synchronization often occurs hierarchically: first locally within communities, then globally as communities synchronize with one another. I will present a framework for studying and characterizing synchronization in such networks via a series of dimensionality reductions. I will also show how these results generalize to other scenarios, e.g. to networks with several layers of hierarchical structure.

Speaker
Josep Lluís Solé

Description lliçó inaugural dels cursos de Matemàtiques i d'Estadística 2012-2013