Baryon Magnetic Moments in the 1/N_c Expansion with Flavor Symmetry Breaking

The magnetic moments and transition magnetic moments of the ground state baryons are analyzed in an expansion in 1/N_c, SU(3) flavor symmetry breaking and isospin symmetry breaking. There is clear evidence in the experimental data for the hierarchy of magnetic moments of the combined expansion in 1/N_c and flavor breaking. SU(3) breaking in the magnetic moments is expected to be enhanced relative to that of other hadronic observables, and significant SU(3) breaking is found.Comment: 21 pages, 1 figure, CLAS reference update

Exact simulation of the Wright-Fisher diffusion

The Wright-Fisher family of diffusion processes is a widely used class of evolutionary models. However, simulation is difficult because there is no known closed-form formula for its transition function. In this article we demonstrate that it is in fact possible to simulate exactly from a broad class of Wright-Fisher diffusion processes and their bridges. For those diffusions corresponding to reversible, neutral evolution, our key idea is to exploit an eigenfunction expansion of the transition function; this approach even applies to its infinite-dimensional analogue, the Fleming-Viot process. We then develop an exact rejection algorithm for processes with more general drift functions, including those modelling natural selection, using ideas from retrospective simulation. Our approach also yields methods for exact simulation of the moment dual of the Wright-Fisher diffusion, the ancestral process of an infinite-leaf Kingman coalescent tree. We believe our new perspective on diffusion simulation holds promise for other models admitting a transition eigenfunction expansion.Comment: 36 pages, 2 figure, 2 tables. This version corrects an error in the proof of Lemma 6.

Linking teaching and research in disciplines and departments

This paper supports the effective links between teaching and discipline-based research in disciplinary communities and in academic departments. It is authored by Alan Jenkins, Mick Healey and Roger Zetter

Introduction to Library Trends 55 (3) Winter 2007: Libraries in Times of War, Revolution and Social Change

published or submitted for publicatio

The Kinetics of the Exchange of Tritium between Hypophosphorous Acid and Water

We have measured the rates of exchange of radioactive hydrogen (tritium) between tritiated water, HTO, and the thwo "undissociable" hydrogens of monobasic hydrophosphorous acid, H3PO2

An asymptotic sampling formula for the coalescent with Recombination

Ewens sampling formula (ESF) is a one-parameter family of probability distributions with a number of intriguing combinatorial connections. This elegant closed-form formula first arose in biology as the stationary probability distribution of a sample configuration at one locus under the infinite-alleles model of mutation. Since its discovery in the early 1970s, the ESF has been used in various biological applications, and has sparked several interesting mathematical generalizations. In the population genetics community, extending the underlying random-mating model to include recombination has received much attention in the past, but no general closed-form sampling formula is currently known even for the simplest extension, that is, a model with two loci. In this paper, we show that it is possible to obtain useful closed-form results in the case the population-scaled recombination rate $\rho$ is large but not necessarily infinite. Specifically, we consider an asymptotic expansion of the two-locus sampling formula in inverse powers of $\rho$ and obtain closed-form expressions for the first few terms in the expansion. Our asymptotic sampling formula applies to arbitrary sample sizes and configurations.Comment: Published in at http://dx.doi.org/10.1214/09-AAP646 the Annals of Applied Probability (http://www.imstat.org/aap/) by the Institute of Mathematical Statistics (http://www.imstat.org