Speaker
Marcelo Nollmann

Description ATP-fuelled molecular motors are responsible for rapid and specific transfer of double-stranded DNA during several fundamental processes, such as cell division, sporulation, bacterial conjugation, and viral DNA transfer. A dramatic example of intercompartmental DNA transfer occurs during sporulation in Bacillus subtilis, in which ~3Mbp of chromosomal DNA are transported across a division septum by the SpoIIIE ATPase. We previously showed that SpoIIIE translocates DNA at ~5kbp/s while specifically interacting with highly skewed chromosomal sequences (SRS) that guide its directional motion. In addition, our data suggested that SpoIIIE assembles on a compartment-specific manner, though other reports proposed a different scenario. Here, we use photoactivated localization microscopy, a recently developed super-resolution microscopy method, to directly visualize the architecture and the assembly dynamics of the SpoIIIE complex in live cells.

Speaker
Antonio Pons

Description Planar crack propagation becomes universally unstable under tension loading (mode I) with the superposition of a shear stress parallel to the crack front (mode III). Under this mixed-mode (I-III) loading configuration, an initially flat parent crack segments into an array of daughter cracks that rotate towards a direction of maximum tensile stress. This segmentation produces stepped fracture surfaces with characteristic ‘lance-shaped’ markings observed in a wide range of engineering and geological materials. We perform large-scale simulations of mixed-mode I-III brittle fracture using a continuum phase-field method that describes the complete three-dimensional crack-front evolution. We show that the dynamically preferred unstable wavelength is governed by the balance of the destabilizing effect of far-field stresses and the stabilizing effect of cohesive forces on the process zone scale, and we derive a theoretical estimate for this scale using a new propagation law for curved cracks in three dimensions. The simulations reveal that planar crack propagation evolve nonlinearly into a segmented array of finger-shaped daughter cracks which gradually coarsen owing to the growth competition of daughter cracks. The rotation angles of coarsened facets are also compared to theoretical predictions and available experimental data.

Speaker
Carme Calderer

Speaker
Carles Calero

Speaker
Aurora Hernández-Machado

Description Interface dynamics is one of the most challenging fields of research of Condensed Matter Physics due to its importance in the current miniaturization trend. At ever smaller scales the surface to volume ratio becomes increasingly large and system frontiers play a crucial role due to roughness and wetting conditions. The seminar will present experimental and theoretical results on membranes, avalanche fronts, viscoelastics flowsand drops at the microscale.