
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
longstanding 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 SaffmanTaylor 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, CNRSUniversity 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 scaleup of cohesive
interactions? (2) What are the respective roles of adhesion and
volume fraction in the case of binding materials?
