New England problem town: public relations factors in rehabilitating a community which has lost its major industry

Thesis (M.S.)--Boston Universit

Accelerating Wilson Fermion Matrix Inversions by Means of the Stabilized Biconjugate Gradient Algorithm

The stabilized biconjugate gradient algorithm BiCGStab recently presented by van der Vorst is applied to the inversion of the lattice fermion operator in the Wilson formulation of lattice Quantum Chromodynamics. Its computational efficiency is tested in a comparative study against the conjugate gradient and minimal residual methods. Both for quenched gauge configurations at beta= 6.0 and gauge configurations with dynamical fermions at beta=5.4, we find BiCGStab to be superior to the other methods. BiCGStab turns out to be particularly useful in the chiral regime of small quark masses.Comment: 25 pages, WUB 94-1

Deflation of Eigenvalues for Iterative Methods in Lattice QCD

Work on generalizing the deflated, restarted GMRES algorithm, useful in lattice studies using stochastic noise methods, is reported. We first show how the multi-mass extension of deflated GMRES can be implemented. We then give a deflated GMRES method that can be used on multiple right-hand sides of $Ax=b$ in an efficient manner. We also discuss and give numerical results on the possibilty of combining deflated GMRES for the first right hand side with a deflated BiCGStab algorithm for the subsequent right hand sides.Comment: Lattice2003(machine

07071 Abstracts Collection -- Web Information Retrieval and Linear Algebra Algorithms

From 12th to 16th February 2007, the Dagstuhl Seminar 07071 ``Web Information Retrieval and Linear Algebra Algorithms\u27\u27 was held in the International Conference and Research Center (IBFI), Schloss Dagstuhl. During the seminar, several participants presented their current research, and ongoing work and open problems were discussed. Abstracts of the presentations given during the seminar as well as abstracts of seminar results and ideas are put together in this paper. The first section describes the seminar topics and goals in general. Links to extended abstracts or full papers are provided, if available

Preconditioning of Improved and ``Perfect'' Fermion Actions

We construct a locally-lexicographic SSOR preconditioner to accelerate the parallel iterative solution of linear systems of equations for two improved discretizations of lattice fermions: the Sheikholeslami-Wohlert scheme where a non-constant block-diagonal term is added to the Wilson fermion matrix and renormalization group improved actions which incorporate couplings beyond nearest neighbors of the lattice fermion fields. In case (i) we find the block llssor-scheme to be more effective by a factor about 2 than odd-even preconditioned solvers in terms of convergence rates, at beta=6.0. For type (ii) actions, we show that our preconditioner accelerates the iterative solution of a linear system of hypercube fermions by a factor of 3 to 4.Comment: 27 pages, Latex, 17 Figures include

Heterologous expression of a plant uracil transporter in yeast: improvement of plasma membrane targeting in mutants of the Rsp5p ubiquitin protein ligase.

Plasma membrane proteins involved in transport processes play a crucial role in cell physiology. On account of these properties, these molecules are ideal targets for development of new therapeutic and agronomic agents. However, these proteins are of low abundance, which limits their study. Although yeast seems ideal for expressing heterologous transporters, plasma membrane proteins are often retained in intracellular compartments. We tried to find yeast mutants potentially able to improve functional expression of a whole set of heterologous transporters. We focused on Arabidopsis thaliana ureide transporter 1 (AtUPS1), previously cloned by functional complementation in yeast. Tagged versions of AtUPS1 remain mostly trapped in the endoplasmic reticulum and were able to reach slowly the plasma membrane. In contrast, untagged AtUPS1 is rapidly delivered to plasma membrane, where it remains in stable form. Tagged and untagged versions of AtUPS1 were expressed in cells deficient in the ubiquitin ligase Rsp5p, involved in various stages of the intracellular trafficking of membrane-bound proteins. rsp5 mutants displayed further plasma membrane stabilization of untagged AtUPS1, and improved steady state amounts of tagged versions of AtUPS1. rsp5 cells are thus powerful tools to solve the many problems inherent in heterologous expression of membrane proteins in yeast, including ER retention