Odd counts of partitions

Speaker: 

Dennis Eichhorn

Institution: 

UCI

Time: 

Thursday, May 29, 2008 - 3:00pm

Location: 

MSTB 254

How many ways can an integer n be expressed as a sum of positive integers? This question is the cornerstone of Partition Theory, and it is surprisingly difficult to answer. For example, if we let p(n) be the number of these expressions of n, even the parity of p(n) remains something of a mystery, despite the fact that it has been studied for over a century. In particular, although empirical evidence (the first several million values) seems to indicate that Po(N) = [the number of odd values of p(n) up to N] is asymptotic to N/2, no one has even been able to show that Po(N) is larger than the square root of N for N sufficiently large. Many advances in discovering the mod 2 behavior of p(n) have been made over the past several years, and most of them have required properties of l-adic Galois representations and the theory of modular forms. However, one lower bound for Po(N) (which was the state-of-the-art for a brief period) was proven using only elementary generating function techniques and results from classical analytic number theory. In this talk, we develop the history of the mystery, and we prove the latter lower bound. The talk will be aimed at the partition theoretically uninitiated, and a great deal of background will be provided.

Peristaltic pumping and irreversibility of a Stokesian viscoelastic fluid

Speaker: 

Professor Joseph Teran

Institution: 

UCLA

Time: 

Monday, November 17, 2008 - 4:00pm

Peristaltic pumping by wavelike contractions is a fundamental
biomechanical mechanism for fluid and material transport and is used
in the esophagus, intestine, oviduct, and ureter. While peristaltic
pumping of a Newtonian fluid is well understood, in many important
settings, as in the fluid dynamics of reproduction, the fluids have
non-Newtonian responses. Here, I will present a numerical method for
simulating an Oldroyd-B fluid coupled to contractile, moving walls. A
marker and cell grid-based projection method is used for the fluid
equations and an immersed boundary method is used for coupling to a
Lagrangian representation of the deforming walls. We examine
numerically the peristaltic transport of a highly viscous Oldroyd-B
fluid over a range of Weissenberg numbers and peristalsis wavelengths
and amplitudes

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