Brown University, Division of Biology and Medicine
Center for Statistical Sciences
Fall 2005 Seminar Series
Department of Statistics, North Carolina State University
1st fFl Conference Room 106
Abstract: In a recent clinical trial "ESPRIT" of patients with coronary heart disease who were scheduled to undergo percutaneous coronary intervention (PCI), patients randomized to receive integrilin therapy had significantly better outcomes than patients randomized to placebo.
The protocol recommended that integrilin be given as a continuous infusion duration in this 18-24 hour range, and we were asked to study this question statistically. Two issues complicated this analysis: (i) The choice of treatment duration was left to the discretion of the physician and (ii) treatment duration would have to be terminated (censored) if the patient experienced serious complications during the infusion period. To formalize the question, "What is the optimal infusion duration?" in terms of a statistical model, we developed a framework where the problem was cast using ideas developed for adaptive treatment strategies in causal inference. The problem is defined through parameters of the distribution of (unobserved) conterfactual random variables. We then show how, under some reasonable assumptions, these parameters could be estimated. The methods are illustrated using the data from the ESPIRIT trial.
Joint Materials/Solid Mechanics Seminar Series
Abstract: Electrons confined in a nanostructure are quantized into discrete energy levels, well-known as quantum well states (QWS), which has proven to greatly modulate the electronic distribution near the Fermi level, and thus significantly affect physical and chemical properties of the system. In the first part of this talk, we show the Pb wedge islands display intriguing morphology dynamics and swing between two extreme states favored by quantum size effect and classical step free energy minimization effect. It is shown that the quantum force plays a vital role in the observed novel growth processes, such as double-layer growth, selective growth and growth-rate breathing. Inthe second part, atomically flat Pb films are prepared on Si(111) substrates by a low temperature growth method, and the electronic structure and growth behaviors are investigated by scanning tunneling microscopy and angle-resolved photoemission spectroscopy. Well-defined and atomic-layer-resolved QWS were observed for coverage from 10 ML to 32ML. We employed the phase accumulation model to model the experimental data under free-electron approximation, and for the first time, determine experimentally the accurate energy dispersion of the Pb films. The results are in excellent agreement with empirical information by the first principle calculations, and explain the energy landscape of the 9ML beating patterns superimposed on a fast oscillation of 2ML. The special growth mode with a period of two monolayer stability can be understood well from the point of the total energy. The properties, such as electron-phonon coupling, thermal expansion coefficient, superconducting transition temperature, work function, adsorption, are also observed to be modulated by the quantum well states.
Graduate School, Dissertation Defense,
Abstract: Kinetic equations are commonly used to describe multiple scattering of acoustic waves in a complex medium. However, there are very few rigorous results on the transition from the wave equation to the kinetic models. As an example where the diffusive limit may be obtained rigorously we consider wave propagation in the regime of random geometric acoustics. We show, starting from the wave equation that in the long time - large distance limit wave energy density behaves diffusively and identify the diffusion coefficient in terms of the statistics of the random medium. This is a joint work with T. Komorowski.
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