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0341341c_Nijs

First quantitative observation of critical opalescence in a biological system Marcel den Nijs, DMR 0341341, and Michael Schick, DMR 0503752, (University of Washington).

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0341341c_Nijs

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  1. First quantitative observation of critical opalescence in a biological system Marcel den Nijs, DMR 0341341, and Michael Schick, DMR 0503752, (University of Washington) Cell membranes are bi-layers containing various types of lipid molecules. They can phase separate with temperature and composition. This is thought to play an important role in the formation of membrane “rafts”. Sarah Keller’s biophysics group at the University of Washington recently observed critical opalescence in such vesicles at optical length scales, using thermo luminescence groups attached to one type of lipid molecule, and by fine tuning the composition of the two lipid species and (passive) cholesterol. The familiar critical Ising like fractal structures appeared. This observation provided an unique opportunity to establish quantitatively for the first time equilibrium criticality in the context of a biological system. We confirmed the values of the two dimensional Ising critical exponents from the surface tension, the structure factor (comparing it to the scaling limit of the exact Ising spin-spin correlation function), and from the evolution of the width of the distribution of pixel intensities (above Tc).

  2. First quantitative observation of critical opalescence in a biological system Marcel den Nijs, DMR 0341341, and Michael Schick, DMR 0503752, (University of Washington) This project brought together three research groups: Sarah Keller’s experimental biophysics group, Michael Schick’s theoretical biophysics group, and Marcel den Nijs’ statistical physics group. It was a pleasure to expose the biophysics community to the quantitative aspects of equilibrium critical phenomena and illustrate its relevance to biophysics. Aurelia Honerkamp-Smith, Pietro Cicuta, Marcus Collins, Sarah Veatch, Marcel den Nijs, Michael Schick, and Sarah Keller, “Line tensions, correlation lengths, and critical exponents in lipid membranes near critical points”, Biophysical Journal Vol.35, July 2008, 1-11. Support includes NSF grants: MCB-0133484, DGE-0504573, DMR-0341341 and DMR-0503752.

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