Seminars & Discussions

How does a drop of water rest on a solid surface? The textbook answer to this simple question has unphysical implications. It suggests that a meager drop of water applies a divergent stress to its substrate at the contact line where solid, liquid and vapor meet. We measure the deformation of a soft elastic solid near a contact line and find that the solid sidesteps this singularity by mimicking a liquid. If time permits, I will discuss striking similarities between the wetting of simple liquids and the spreading of cohesive cells.

This talk is for everyone who is interested in how bacteria "do it". Although bacteria are asexual organisms and they reproduce by binary fission, they also have a mechanism called conjugation which allows them to exchange portions of genetic code. Including conjugation in population-genetics equations is not difficult, but as I will show, it leads to some interesting effects.

We identify a new mechanism for the spontaneous formation of an oil-in-water emulsion [1]. Our classical density functional, which describes electrostatics, ionic surface reactions, and nanoparticle adsorption, predicts kinetically and even thermodynamically stable emulsion droplets with a tunable mesoscopic size. Our results closely match recent experiments [2][3], and may open new pathways for the reversible dispersion of particle-coated droplets that are desired in the fields of catalysis, controlled drug delivery and particle synthesis. The last part of the presentation will highlight the structural and thermodynamic properties of electrolytes of the primitive model, at low temperatures, and near (dielectric) boundaries, as predicted by both classical and recently developed theories [4]. [1] JZ, K. Ioannidou, D. Kraft, and R. van Roij, Soft Matter 7, 11093 (2011). [2] S. Sacanna et al., Phys. Rev. Lett., (2007), 98, 158301. [3] D. Kraft et al., J. Phys. Chem. B, (2010), 114, 10347. [4] JZ, P. K. Jha, and M. Olvera de la Cruz, J. Chem. Phys. 135, 064106 (2011).

Adaptation is the essential process by which an organism becomes better suited to its environment. The benefits of adaptation are well documented, but the cost it incurs remains poorly understood. Here, by analysing a stochastic model of a minimum feedback network underlying many sensory adaptation systems, we show that adaptive processes are necessarily dissipative, and continuous energy consumption is required to stabilize the adapted state. Our study reveals a general relation among energy dissipation rate, adaptation speed and the maximum adaptation accuracy. This energy-speed-accuracy relation is tested in the Escherichia coli chemosensory system, which exhibits near-perfect chemoreceptor adaptation. We identify key requirements for the underlying biochemical network to achieve accurate adaptation with a given energy budget. Moreover, direct measurements confirm the prediction that adaptation slows down as cells gradually de-energize in a nutrient-poor medium without compromising adaptation accuracy. Our work provides a general framework to study cost-performance trade-offs for cellular regulatory functions and information
Nature Physics Advance Online Publication
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