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Shear

Slow Relaxations in Complex Fluids: Origin and Nature of Dynamical Heterogeneities Bulbul Chakraborty, Brandeis University, DMR 0549762.

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Shear

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  1. Slow Relaxations in Complex Fluids: Origin and Nature of Dynamical HeterogeneitiesBulbul Chakraborty, Brandeis University, DMR 0549762 A visually striking feature of dry granular materials is the inhomogeneous network of force chains that develop in response to external stresses (as shown in figure). Although visually striking, a quantitative characterization of these heterogeneities has been difficult. Shear Pressure We have constructed a theory of stress fluctuations in static packings and quasistatic granular flows. Some of the most interesting results are: Shear fluctuations exhibit long-range spatial correlations in packings under pure hydrostatic compression, but pressure fluctuations are short-ranged. Figures show comparison between theory and simulations of correlations in q-space Under shear, granular packings exhibit a logarithmic increase with shear rate. We have explained this by combining our stress-based ensemble (Henkes,O’Hern,Chakraborty, PRL 99, 038002 (2007) with an activated process controlled by a stress fluctuation “temperature”, x (Behringer,Chakraborty,Henkes, Hartley, submitted to Phys. Rev. Lett, Bi,Henkes, Chakraborty, in preparation)

  2. Slow Relaxations in Complex Fluids: Origin and Nature of Dynamical HeterogeneitiesBulbul Chakraborty, Brandeis University, DMR 0549762 News • Silke Henkes, who has been the main force behind the construction of the statistical ensemble received a KITP graduate fellowship for Fall 2007. She will be joining the Van Saarloos group in Leiden as a postdoc in August, 2008 http://www.kitp.ucsb.edu/people/grad_fellows/ • A new student, Mitch Mailman is working with Corey O’Hern of Yale University to study jamming of soft anisotropic grains and the applicability of the statistical ensemble. • Another new student, Max Bi, has taken Silke’s work and extended it to dynamics. http://www.physics.brandeis.edu/people/gradstudents.html • BC has been invited to a Royal Society Discussion Meeting in March, 2009. She was a discussion leader at the 2008 Godon conference on Granular Materials, and she has been invited to be a dicsussant at the Leiden Workshop on Dynamical Heterogeneities in August 2008.

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