Brown University
Cognitive & Linguistic Sciences
Spring 2005 Colloquium and CG233 Speakers
Brown University Division of Biology and Medicine
Center for Statistical Sciences Seminar Series
Academic Medical Center, University of Amsterdam, The Netherlands | |
Abstract: In some diagnostic accuracy studies the test results of a series of patients with an established diagnosis are compared with those of a control group. Such case-control designs are intuitively appealing but they have also been criticized for leading to inflated estimates of accuracy. To discuss the mechanisms that can lead to variation in estimates of diagnostic accuracy in studies with separate sampling schemes for diseased and non-diseased subjects, using results from meta-analyses and literature reviews. To discuss the similarities and differences between diagnostic and etiologic case-control studies.
Diagnostic case-control studies difffer from etiologic case-control studies and are prone to different forms of bias. Diagnostic accuracy studies are cross-sectional and descriptive in nature, while etiological case-control studies focus on causality and consider a time window between exposure and disease occurrence. The efficiency benefits of etiological case-control studies do not easily apply to diagnostic studies. Researchers and readers should be aware of spectrum effects in diagnostic case-control studies as a result of the restricted sampling of cases and/or controls, as these can lead to biased estimates of diagnostic accuracy. These spectrum effects may be advantageous in the early investigation of a new diagnostic test. For an overall evaluation of the performance of a diagnostic test in a clinical situation, case-control studies should closely mimic cross-sectional diagnostic studies.
As variability in accuracy across patient groups is the rule rather than the exception, one should carefully consider the potential for spectrum effects in any diagnostic accuracy study. This applies in particular to diagnostic case-control studies.
Brown University Division of Biology and Medicine
Center for Gerontoloty and Health Care Research and
Center for Statistical Sciences Seminar
Assistant Professor of Biostatistics and Computational Biology, Candidate for Open Rank Professor (research track) in the Public Health Program/Department of Community Health | |
An Application to Pulmonary Function and Cholesterol Levels in the Normative Aging Study | |
Abstract: There is continued debate regarding the exact relation between lower cholesterol levels and increased respiratory disease mortality. One of the goals of this study is to reveal the relationship between subcomponents of cholesterol and pulmonary function. We consider the subcomponents of total cholesterol, namely high-density lipoprotein cholesterol and low-density lipoprotein cholesterol, to investigate the relationship of cholesterol levels with pulmonary function in a longitudinal study. To answer these questions, we propose new methodology for hierarchical reciprocal graphical models. We consider the identification and estimation of these models, and propose maximum likelihood estimation using a generalized EM algorithm. A simulation study of the algorithm and the corresponding estimates reveals excellent performance of the proposed procedures. Application of this methodology to the Normative Aging Study reveals complicated associations between pulmonary function and the subcomponents of total cholesterol.
Brown University
Joint Materials/Solid Mechanics Seminar Series
Abstract: When either the sample or grain size of a metal is reduced below roughly a micrometer, unusual mechanical properties are observed. For example, the yield stress of fine-grained bulk metals or thin metal films can be as much as one order of magnitude larger than in their large-grained bulk counterparts. Similarly, the fatigue resistance is dramatically increased once the microstructural length scale or sample size falls below a few micrometers. More recently, uniaxial compression tests of micron-sized single crystal metal columns (Al, Ag, and Cu) have shown that a combination of increased yield stress and strain hardening can lead to stresses as large as the theoretical stress in sub-micron diameter columns. These results are explained in terms of dislocation processes, such as dislocation nucleation and "starvation" and the interaction of dislocations with each other and with surfaces. The work highlights the need for a better understanding of deformation under conditions where only a few dislocations are present. It also has important implications for the design and mechanical integrity of small metal structures and fine-grained metals used in many technological applications.
PLEASE NOTE CHANGE IN DAY AND TIME FOR THIS SEMINAR ONLY
Center for Fluid Mechanics
And
The Fluids, Thermal and Chemical Processes Group
Of
The Division of Engineering
Seminar Series
Benjamin Levich Institute for Physico-Chemical Hydrodynamics and Department of Chemical Engineering City College of New York, New York, NY | |
Abstract: The processing of polymer melts and concentrated solutions, in which the mobility and time dependence of the liquid is determined by macromolecular "entanglements," is often limited by the onset of material failure in the form of shape distortions or mechanical rupture. Failure mechanisms in polymeric liquids have been studied for more than half a century, but they are still not well understood. This lecture will illustrate some of the important features of failure in polymeric liquids and examine the current level of understanding and the major open questions.
Scientific Computing Seminar
Department of Mechanical & Industrial Engineering, University of Illinois at Chicago, 842 West Taylor Street, Chicago, IL 60607 | |
Abstract: Particle-laden flows have been the subject of many investigations due to their widespread presence in industrial applications and natural phenomena. From a theoretical point of view, mathematical modeling and numerical simulation of these flows present many challenges and have led to two approaches. In the first approach, the particles are tracked in the Lagrangian frame whereas the carrier phase is solved in the Eulerian frame. This approach, although more natural for description of the dispersed phase, could become computationally prohibitive for complex systems embedded with a large number of particles. This has motivated the second approach involving the development of (Eulerian) fluid equations for the dispersed phase. In this talk, we will discuss development and implementation of these two approaches. Application of the methods resulting from these approaches will be considered for two problems of current interest in our group. The first problem involves dispersion of particles in a turbulent flow with a specific application for preliminary design of liquid-fuel combustors. The second application concerns the design and optimization of a dusty plasma reactor for deposition of nano-layer coatings on nano- and micron-sized particles.
Division of Applied Mathematics Student Pizza Seminar
PDE Seminar
Abstract: The movement of cells along surfaces is an important biological process that has been studied by the biologists for decades. There are only a few mathematical models which described the complete cell motion using mechanics principle. We will describe and analyze the one-dimensional Mogilner-Verzi model which is a moving boundary problem. There are key differences with the classical Stefan problem. We will establish the global existence of solution to the cell motility problem.
The model also accepts a `traveling cell' solution, in the sense that the cell moves with a uniform speed. It differs from a usual traveling wave solution in infinite domain since both the speed and the length of a moving cell need to be predicted. We will also give some partial results on the stability of such a traveling cell solution.
Department of Mathematics Colloquium
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