CNCS Center for Nonlinear and Complex Systems

CNCS Seminar series

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Upcoming Seminars:
  • Tuesday, March 31, 2015, 2:50pm, 119 Physics, CNCS Seminar
    The role of exponentially small effects in the physical sciences
    Philippe H. Trinh (Mathematical Institute, Oxford University)
     
    Recently, the development of specialized techniques in mathematics known as exponential asymptotics has led to the successful resolution of long-standing problems in topics as varied as crystal growth, dislocations, pattern formation, turbulence, thin film flow, and hydrodynamics. These developments have emerged from the realization that in many such problems, exponentially small effects can significantly change the solutions of the underlying mathematical models.
    In this talk, we will introduce the audience to the history, ideas, and basic techniques of exponential asymptotics, with particular emphasis on how to recognize when such approaches are necessary. We will discuss the 19th century struggles of the great Cambridge physicist G.G. Stokes to better understand what is now known as the Stokes Phenomenon. We will then show how this understanding would provide the key insight into resolving two famous problems: the problem of modelling dendritic crystal growth, and the Saffman-Taylor viscous fingering problem.
    Our discussion will conclude with a glimpse of the present and future applications of exponential asymptotics, notably within the context of hydrodynamics and ship waves, and for the mathematical modelling of rupture and singularity formation in fluid flows.

  • Tuesday, April 7, 2015, 2:50pm, 119 Physics, CNCS Seminar
    Fabric and force anisotropy in cohesive granular materials
    Farhang Radjai (LMGC, CNRS-University of Montpellier)
     
    The cohesive strength of granular materials is a consequence of either cohesive bonding (capillary bridging, van der Waals forces\'85) between the grains or the action of a binding solid or liquid material in the pore space. I first discuss the constitutive framework of the plastic behavior of granular materials with internal variables pertaining to the granular fabric. Then, I show how cohesive granular systems can be simulated by different methods accounting for capillary or solid bonding and in the presence of a binding solid or liquid. Finally, I focus on two issues: (1) How does local granular disorder affects the scale-up of cohesive interactions? (2) What are the respective roles of adhesion and volume fraction in the case of binding materials?


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