Chemomechanical Simulation of Microtubule Dynamics With Explicit Lateral Bond Dynamics

We introduce and parameterize a chemomechanical model of microtubule dynamics on the dimer level, which is based on the allosteric tubulin model and includes attachment, detachment and hydrolysis of tubulin dimers as well as stretching of lateral bonds, bending at longitudinal junctions, and the possibility of lateral bond rupture and formation. The model is computationally efficient such that we reach sufficiently long simulation times to observe repeated catastrophe and rescue events at realistic tubulin concentrations and hydrolysis rates, which allows us to deduce catastrophe and rescue rates. The chemomechanical model also allows us to gain insight into microscopic features of the GTP-tubulin cap structure and microscopic structural features triggering microtubule catastrophes and rescues. Dilution simulations show qualitative agreement with experiments. We also explore the consequences of a possible feedback of mechanical forces onto the hydrolysis process and the GTP-tubulin cap structure.

Tracking time with ricequakes in partially soaked brittle porous media

When brittle porous media interact with chemically active fluids, they may suddenly crumble. This has reportedly triggered the collapse of rockfill dams, sinkholes, and ice shelves. To study this problem, we use a surrogate experiment for the effect of fluid on rocks and ice involving a column of puffed rice partially soaked in a reservoir of liquid under constant pressure. We disclose localized crushing collapse in the unsaturated region that produces incremental global compaction and loud audible beats. These “ricequakes” repeat perpetually during the experiments and propagate upward through the material. The delay time between consecutive quakes grows linearly with time and is accompanied by creep motion. All those new observations can be explained using a simple chemomechanical model of capillary-driven crushing steps progressing through the micropores.

A Chemomechanical Model for Stress Evolution and Distribution in the Viscoplastic Oxide Scale During Oxidation

Using the location-dependent growth strain, a chemomechanical model is developed for the analysis of the stress evolution and distribution in the viscoplastic oxide scale during high-temperature oxidation. The problem of oxidizing a semi-infinite substrate is formulated and solved. The numerical results reveal high compressive stress and significant stress gradient. The maximum stress is at the oxide/substrate interface and the minimum stress at the oxygen/oxide interface in short oxidation time, while the maximum stress is no longer at the oxide/substrate interface in long oxidation time. The stress evolutions at different locations are also presented. The predicted results agree well with the experimental data.