Brown University Center for Statistical Sciences Seminar
University of Pittsburgh School of Medicine | |
Abstract: Association between disease and genetic polymorphisms often contributes critical information in our search for the genetic components of common diseases. Devlin and Roeder [1999: Biometrics 55:997-1004] introduced genomic control, a statistical method that overcomes a drawback to the use of population based samples for tests of association, namely spurious associations induced by population structure. In essence, genomic control (GC) uses markers throughout the genome to adjust for any inflation in test statistics due to substructure. To date, genomic control (GC) has been developed for binary traits and bi- or multiallelic markers. Tests of association using GC have been limited to single genes. In this report, we generalize GC to quantitative traits (QT) and multilocus models. Using statistical analysis and simulations, we show that GC controls spurious associations in reasonable settings of population substructure for QT models, including gene-gene interaction. Through simulations, we explore GC power for both random and selected samples, assuming the QT locus tested is causal and its specific heritability is 2.5- 5%. We find that GC, combined with either random or selected samples, has good power in this setting, and that more complex models induce smaller GC corrections. The latter suggests greater power can be achieved by specifying more complex genetic models, but this observation only follows when such models are largely correct and specified a priori.
Center for Fluid Mechanics Seminar
The John's Hopkins University, Baltimore, MD 21218 and Faculty of Applied Physics, University of Twente, Twente Institute of Mechanics, and Burgerscentrum, AE 7500 Enschede, The Netherlands | |
Abstract: The talk describes two methods to carry out direct numerical simulations of flows with solid particles or gas bubbles. In the case of solid particles a locally valid modified Stokes solution near each particle is matched to a finite-difference Navier- Stokes solution near, but away from, the particle surface. In the case of gas bubbles, we combine ideas from the front-tracking, volume-of-fluid, and ghost-fluid methods to develop a new approach which maintains the gas-liquid interface sharp and can deal with arbitrary gas-liquid density differences. Some benchmark computations using boundary-fitted coordinates will also be briefly described.
Supported by NSF, DOE, and NASA.
Brown University
Joint Materials/Solid Mechanics Seminar Series
and its Application to Strain Localization and Damage | |
Scientific Computing Seminar
Abstract: The least-squares element method has increased in popularity in recent years largely due to its success in solving elliptic type problems. The methodology has not carried into the hyperbolic framework because of problems associated with smearing. In this talk, we offer promising evidence that the LSFEM, in a locally adapted space-time setting, may be a competent alternative to other approaches.
The talk is structured as follows. We give an overview of the attractive qualities inherent in a FOSLS (First-Order Systems Least-Squares) formulation. The methodology is extended to the first-order linear advection equation in time-space where solution quality and multigrid performance are discussed. We extend the approach, with modification, to the nonlinear conservation law and present results for Burgers equation.
PDE Seminar
Department of Mathematics Colloquium
<--- 2003 Index