Brown University, Center for Statistical Sciences Seminar
Center for Statistical Sciences | |
Abstract : A sample of 560 smokers enrolled in a smoking cessation trial (91% white, 53% male, ave. age = 44 years, ave. cigarettes/day=24) provided baseline measurements on the Fagerstrom Tolerance Questionnaire (FTQ) and DSM-IV criteria for nicotine dependence using SCID-NP. We will use an Empirical Bayes approach to estimation of the 2-parameter logistic model (2PL). Item Response Theory will be used to evaluate the measurement properties of each set of diagnostic criteria. In particular, we will provide optimal weights for each criterion, consider whether the scales should be modified by either adding or dropping individual items and evaluate the information loss when a scale is summarized either using a total score (FTQ) or a 3/7 rule (DSM-IV ND). Further, we shall explore the dimensionality of each latent construct and argue in favor of a 2-factor solution.
This is joint work with Ray Niaura, Ph.D. and Shang-Ying Shiu, M.S., funded by NCI research grant #P50 CA84719.
Center for Fluid Mechanics Seminar
Abstract: Non-conventional Large Eddy Simulation (LES) techniques have been the subject of considerable interest during the last decade. Properties to be anticipated from a given LES model can be investigated based on the partial differential equations satisfied by the numerical solution -- the modified LES equations, which reveal the competing effects of discretization and explicit SGS modeling. From the perspective of these modified equations, {\it all} numerical schemes provide a built-in {\it implicit} subgrid scale (SGS) model enforced by the leading order discretization errors, and some can be effective by themselves when suitable algorithms are used. In the Monotonically Integrated LES (MILES) approach, flux limiting numerical schemes are used to emulate (near the LES cut-off) the high-wavenumber end of the inertial subrange region of turbulence characterized by thin filaments of intense vorticity embedded in a background of weak vorticity, mathematical and physical aspects of {\it implicit} SGS modeling using non-linear flux-limiters are addresssed. Analysis of representative results using MILES is presented based on databases of simulated flows, including homogeneous box turbulence, rectangular jets, channel flows, and buoyant contaminant transport within buildings and urban areas. Major unresolved issues relevant to LES of complex practical turbulent flows are discussed in this context, including aspects of boundary condition modeling and overall computational model validation.
Stochastic Systems Seminar
Brown Applied Mathematics Pattern Theory and Vision Seminar
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Brown Analysis Seminar
Applied Mathematics Colloquium
Scientific Computing Seminar
Abstract: There has been an ongoing interest in computational methodology by numerous researchers in every field of science and engineering. Most effort has been centered in developing either global methods or local methods for solving a variety of problems. Global methods, such as Fourier or Chebyshev spectral methods, are usually highly accurate. But local methods, such as finite element and finite difference methods, are much more flexible for handling complex boundaries and geometries. We introduce a wavelet-like approach for achieving global methods' accuracy and local methods' flexibility in solving problems with complex boundaries and geometries. The mathematical foundation of the proposed method is the theory of distributions. Example applications are discussed to fluid dynamics, electromagnetics, solid mechanics and nonlinear waves.
PDE Seminar
Department of Mathematics Colloquium
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