Plan for the week:

Sunday:   Jennifer Chayes and Christian Borgs arrive late evening.

Monday:   3:30     Joint Math/CS Colloquium (J. Chayes) in Olsson 009
          evening  Pierre Cartier arrives
          7:00     Dinner at the Blue Bird Cafe

Tuesday:  3:30 MathPhys seminar (C. Borgs) in Clark 141
          Jennifer & Christian leave for DC early evening

Thursday: 3:30 Math Colloquium (P. Cartier) in Cabell 311

May 2:    Pierre Cartier leaves.

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                 Mathematical Physics Seminar
           Tuesday, April 24 in Clark 141 at 3:30 pm:

             Christian Borgs (Microsoft research)

            "Complex Zeros of Partition Functions: 
                A Generalized Lee-Yang Theorem"

Abstract:
It is well known that phase transitions are closely related to zeros 
in the complex temperature and field plane. In this talk I present 
a new approach to determine partition function zeros near first order 
phase transitions. I discuss the relationship of our results to the 
classic Lee-Yang theorem on the one hand, and to the theory of finite 
size scaling on the other.  Among the results I present will be a local 
Lee-Yang theorem, which states conditions under which some of the zeros
lie on pieces of circles, even when the standard, "global" Lee-Yang 
theorem fails.  No prior knowledge of the Lee-Yang theorem is assumed.

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                 Joint CS/Math  Colloquium
                 Monday, April 23 in Olsson 009 at 3:30 pm:

             Jennifer Chayes (Microsoft research)

      "Phase Transitions in Combinatorics and Computer Science"

Phase transitions are familiar phenomena in physical systems. 
But they also occur in many probabilistic and combinatoric models, 
and even in some problems in theoretical computer science. In 
this talk, I will discuss phase transitions in several systems, 
including percolation -- a simple probabilistic model which undergoes 
a critical transition from a disordered to an ordered phase; 
satisfiability -- a canonical model in theoretical computer science 
which undergoes a transition from solvability to insolvability; and 
optimum partitioning -- a fundamental problem in combinatorial 
optimization, which undergoes a different type of transition from 
solvability to insolvability.

No prior knowledge of phase transitions or of particular models will 
be assumed in this talk.

5pm: Round table  with graduate students in Olsson 228E.

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Mathmatics Colloquium 

Thursday, April 26 in Cabell 311:

          Pierre Cartier (Ecole Normale Superieure)

     "Hopf algebras as a versatile tool in algebra, geometry, combinatorics
               and even mathematical physics"


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