Javier Rodriguez-Rodriguez

Spatio-temporal analysis of eukaryotic cell motility by improved force cytometry

Cell motility plays an essential role in many biological systems, but precise quantitative knowledge of the biophysical processes involved in cell migration is limited. Better measurements are needed to ultimately build models with predictive capabilities. We present an improved force cytometry method and apply it to the analysis of the dynamics of the chemotactic migration of the amoeboid form of Dictyostelium discoideum. Our explicit calculation of the force field takes into account the finite thickness of the elastic substrate and improves the accuracy and resolution compared with previous methods. This approach enables us to quantitatively study the differences in the mechanics of the migration of wild-type (WT) and mutant cell lines. The time evolution of the strain energy exerted by the migrating cells on their substrate is quasi-periodic and can be used as a simple indicator of the stages of the cell motility cycle. We have found that the mean velocity of migration v and the period of the strain energy T cycle are related through a hyperbolic law v = L/T, where L is a constant step length that remains unchanged in mutants with adhesion or contraction defects. Furthermore, when cells adhere to the substrate, they exert opposing pole forces that are orders of magnitude higher than required to overcome the resistance from their environment.

Negatively buoyant starting jets

The initial development of negatively buoyant jets has been investigated experimentally and numerically, focusing on the role played by gravity in the evolution of the leading vortex ring. Under the experimental conditions considered in this work, the densimetric Froude number, Fr=ρjUj2/[(ρ0−ρj)gD], which represents the ratio between the jet momentum and the buoyancy forces, emerges as the most relevant parameter characterizing the dynamics of the flow. Two different flow regimes have been observed depending on the Froude number: for sufficiently small Fr, the vortex ring generated initially is pushed radially away by gravity forces before it has time to detach from the shear layer originating at the orifice. On the other hand, when the Froude number is larger than a critical value, Fr>Frc∼1, the vortex ring detaches from the injection orifice and propagates downstream into the stagnant ambient followed by a trailing jet until it eventually reaches a maximum penetration depth. In order to clarify the mech...

Bubble break-up in a straining flow at finite Reynolds numbers

It has recently been shown that the behaviour of a gas bubble in a uniaxial straining flow can be used as a simplified model to describe some important aspects of the more complex, turbulent bubble break-up problem, provided that the Reynolds and the Weber numbers are sufficiently large. In the present investigation, we extend that work and, using a level-set numerical scheme, we analyse the influence of the bubble Reynolds number on break-up time,

Transient effects in the translation of bubbles insonated with acoustic pulses of finite duration

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Intraoperative brain ultrasound: A new approach to study flow dynamics in intracranial aneurysms

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Dynamics of large turbulent structures in a steady breaker

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Dissolution of a spherical cap bubble adhered to a flat surface in air-saturated water

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Formation regimes of vortex rings in negatively buoyant starting jets

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Diffusion of dissolved CO2 in water propagating from a cylindrical bubble in a horizontal Hele-Shaw cell

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Why does a beer bottle foam up after a sudden impact on its mouth

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