Title: Active tangentially-driven polymers in ordered media

Speaker: Mohammed Fazelzadeh (UvA)

Abstract:

Investigating the active transport of polymers in crowded environments, we explore the impact of spatial order of obstacles on their conformation and dynamics in comparison to disordered media. Our computational study focuses on semiflexible tangentially-driven polymers in two-dimensional square lattices of obstacles. Tight periodic confinement induces distinct conformational changes and transport modes for flexible and stiff active filaments. Flexible polymers with low activity become caged inside the inter-obstacle pores and their migration occurs via hopping events, akin to disordered media but with slower dynamics. Stiff polymers travel in straight paths within periodic channels, while occasionally changing their direction of motion, showing extended conformation and enhanced dynamics compared to disordered media. At high active forces, polymers overcome confinement effects, moving swiftly through inter-obstacle pores regardless of the spatial arrangement of obstacles. We present an analytical theory linking center of mass dynamics of semiflexible polymers to active force and the conformation of chains.

Title: Low energy excitations in glasses

Speaker: Tommaso Pettinari (UvA)

Abstract:

The mechanical properties of glasses are closely related to the presence of “soft spots” in the structure of the material: disorder-induced defects originated during the quenching of the glass. These “soft spots” can be also identified as the core region of the so-called Quasi-Localized Excitations (QLEs), which are low energy, non-phononic, vibrational modes appearing in disorder structures, in addition to the usual phonons. In this talk, I will present you a minimal model for glasses that we developed to shed some light on the link between macroscopic mechanical properties and the underlying microscopical structure, focusing in particular on the low energy excitation spectrum. The model consists in a random network of springs where we introduce mechanical frustration, which plays the role of a control parameter for the disorder in the system. Time permitting, I will relate this model to a mean-field model of coupled anharmonics oscillators.

This seminar will take place in room C4.174