Jaume Casademunt - Academia.edu (original) (raw)

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Papers by Jaume Casademunt

Nature Physics, Feb 4, 2019

The physical basis of flagellar and ciliary beating is a major problem in biology which is still ... more The physical basis of flagellar and ciliary beating is a major problem in biology which is still far from completely understood. The fundamental cytoskeleton structure of cilia and flagella is the axoneme, a cylindrical array of microtubule doublets connected by passive cross-linkers and dynein motor proteins. The complex interplay of these elements leads to the generation of self-organized bending waves. Although many mathematical models have been proposed to understand this process, few attempts have been made to assess the role of dyneins on the nonlinear nature of the axoneme. Here, we investigate the nonlinear dynamics of flagella by considering an axonemal sliding control mechanism for dynein activity. This approach unveils the nonlinear selection of the oscillation amplitudes, which are typically either missed or prescribed in mathematical models. The explicit set of nonlinear equations are derived and solved numerically. Our analysis reveals the spatio-temporal dynamics of dynein populations and flagellum shape for different regimes of motor activity, medium viscosity and flagellum elasticity. Unstable modes saturate via the coupling of dynein kinetics and flagellum shape without the need of invoking a nonlinear axonemal response. Hence, our work reveals a novel mechanism for the saturation of unstable modes in axonemal beating.

57th International Astronautical Congress, Oct 2, 2006

Nature Physics, Dec 8, 2022

Physics Reports, Oct 1, 2000

Proceedings of the 1993 ASME Winter Annual Meeting, Dec 1, 1993

Physical review, Aug 1, 1999

Physical review, Aug 1, 1993

AIAA Journal, Sep 1, 2020

Low activity flagellar dynamics

Subharmonic oscillations of collective molecular motors

The behavior of chemical waves advancing through a disordered excitable medium is investigated in... more The behavior of chemical waves advancing through a disordered excitable medium is investigated in terms of percolation theory and autowave properties in the framework of the light-sensitive Belousov-Zhabotinsky reaction. By controlling the number of sites with a given illumination, different percolation thresholds for propagation are observed, which depend on the relative wave transmittances of the two-state medium considered.

Soft Matter, 2017

Collective cell migration in spreading epithelia in controlled environments has become a landmark... more Collective cell migration in spreading epithelia in controlled environments has become a landmark in our current understanding of fundamental biophysical processes in development, regeneration, wound healing or cancer. Epithelial monolayers are treated as thin layers of a viscous fluid that exert active traction forces on the substrate. The model is exactly solvable and shows a broad range of applicabilities for the quantitative analysis and interpretation of force microscopy data of monolayers from a variety of experiments and cell lines. In addition, the proposed model provides physical insights into how the biological regulation of the tissue is encoded in a reduced set of time-dependent physical parameters. In particular the temporal evolution of the effective viscosity entails a mechanosensitive regulation of adhesion. Besides, the observation of an effective elastic tensile modulus can be interpreted as an emergent phenomenon in an active fluid.

We propose a model for membrane-cortex adhesion that couples membrane deformations, hydrodynamics... more We propose a model for membrane-cortex adhesion that couples membrane deformations, hydrodynamics, and kinetics of membrane-cortex ligands. In its simplest form, the model gives explicit predictions for the critical pressure for membrane detachment and for the value of adhesion energy. We show that these quantities exhibit a significant dependence on the active acto-myosin stresses. The model provides a simple framework to access quantitative information on cortical activity by means of micropipette experiments. We also extend the model to incorporate fluctuations and show that detailed information on the stability of membrane-cortex coupling can be obtained by a combination of micropipette aspiration and fluctuation spectroscopy measurements.

Noise and Nonlinear Phenomena in Nuclear Systems, 1989

The effects of the nonlinearities in the steady state dynamics of nuclear reactor models have not... more The effects of the nonlinearities in the steady state dynamics of nuclear reactor models have not been considered until recently1,2. The nonlinear terms appear, for example, in the Langevin equation for the number of neutrons, due to an adiabatic elimination of the fast variables (delayed neutrons, fuel temperature, refrigerator temperature, etc.) The reduction in the number of variables gives a more tractable problem in the sense that the validity of the approximations that one uses are more easily known, but the price that is paid is the nonlinearity of the equations. Then, the usual procedure is the linearization of the resulting equations around the deterministic steady state. The validity of this approximation has been considered by many authors3–6. All of these studies agree that the linearization is a good approximation far from the instability points, but it breaks down near them.

Springer Proceedings in Physics, 1991

Branching in Nature, 2001

The phenomenon of branching has already proven to have some universality throughout this book. Mi... more The phenomenon of branching has already proven to have some universality throughout this book. Misbah has even shown in the present chapter how the whole dynamics of a problem — including this branching phenomenon — can be mapped onto a different one in some approximation. In this spirit, the use of a unifying mathematical formulation in different physical models of branching can serve as a basis to understand why so different problems share the same branching phenomenon.