Scientific Computing Seminar
Brown University Center for Statistical Sciences Seminar
Abstract: This article develops methods for estimating treatment effects in mixed effects models using outcome data gathered from serial dilution assays. Our application allows us to estimate the viral burden of HIV infection before and after antiviral treatment from cell dilution assays. This assay is designed to determine the infectious units per patient peripheral blood mononuclear cell (PBMC). The infectious unit is the amount of virus required to produce detectable HIV infection in PBMCs from healthy, uninfected donors. At each dilution level of the patient cells, one observes whether or not it was possible for the virus from these cells to infect donor cells. Thus the assay result for each subject consists of a series of repeated binary outcomes. We propose an analytic approach in which patient-specific titers (measures of viral burden) are modeled as random effects from an unknown distribution, and treatment effects are modeled as fixed. This approach makes use of all assay results, even if many assays fail to reach endpoint (turn negative at the highest dilution level) and the assay design (dilution scheme) changes over time.
Center for Fluid Mechanics Seminar
Stochastic Systems Seminar
Brown Applied Mathematics Pattern Theory and Vision Seminar
Abstract: In this talk I will describe a hierarchical approach to character recognition based on principles of asymmetry,maximum understanding and emergence of shape.I will concentrate on printed characters,possibly multi-font and describe efficient solutions to various problems in computational geometry which arise in the context of the above approach to character recognition.The goal is to develop a practical system which will work for many fonts ( perhaps as many as 50).We are creating a computational environment where systematic experimentation can take place.
Brown Analysis Seminar
Applied Mathematics Colloquium
Abstract: We present a high-efficiency parallel spectral element method for solution of the unsteady Navier-Stokes equations in general two- and three- dimensional domains. The method is based upon semi-implicit time stepping schemes coupled with Jacobi and overlapping Schwarz preconditioned iterative solvers for the elliptic subproblems associated with the viscous and pressure operators. The Schwarz additive procedure requires the solution of local independent problems on subdomains and a global "coarse grid" problem to propagate long wavelength information. The local problems are independent and fully parallel. They are treated via efficient tensor-product solvers which attain excellent vector performance. In addition, a fast direct method for parallel solution of the global coarse grid problem is derived in the context of general projection strategies. It attains the minimum possible number of contention-free message cycles and significantly less data traffic than competing methods, making it ideally suited to communication intensive architectures such as networks of workstations and multi-thousand node teraflops- level machines. Numerous fluid mechanics and heat transfer applications illustrate the capabilities of the parallel spectral element method for problems of scientific and engineering interest.
Scientific Computing Seminar
Abstract: High field resistive magnets generate an enormous quantity of heat that must be extracted by deionized, chilled water flowing through special cooling channels. The effect of cooling channel roughness on the heat and momentum transfer is poorly understood, and limits the design optimization process. A spectral element code is being developed to perform large-eddy simulations of the flows. Key aspects of the code will be described, and difficulties associated with the implementation of LES in spectral element codes will be discussed.
PDE Seminar
Department of Mathematics Colloquium
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