Lefschetz Center for Dynamical Systems Seminar
Visiting from Free University of Berlin | |
Abstract: We consider spiral waves in reaction-diffusion systems. One example is the light sensitive Belousov-Zhabotinsky reaction. In the spatially homogeneous case spiral wave patterns appear, due to Euclidean $SE(2)$-symmetry, which rotate rigidly around the fixed tip position of the spiral. We are interested in the persistence of such solutions under a symmetry breaking perturbation, which still keeps a discrete lattice symmetry. In particular we study the resulting tip motions via a reduction of the original PDE-systems to vectorfields on the two-dimensional torus. Our methods include global center manifold reductions.
Brown University -
Joint Materials/Solid Mechanics Seminar Series
The Johns Hopkins University, Baltimore, MD 21218 | |
Abstract: The mechanical behavior of nanostructured metals is considered, with a focus on bcc metals. First, a constitutive response function based on kink-dominated dislocation mobility is constructed for bcc metals, with the high-stress response determined by appeal to recent atomistic results by other researchers. The result is a constitutive model that is applicable over a wide range of strain rates at low homologous temperatures. Application of this model to the consideration of grain size effects indicates that nanostructured bcc metals should display a substantial reduction in the rate-dependence of the flow strength. This, when coupled with the dramatic increase in strength developed at small grain sizes, leads to a propensity for deformation instabilities in bcc structures. Next, a suite of experimental techniques is described for the determination of these material properties at high rates of deformation, and the predictions of the model are compared with recent experimental observations of the mechanical behaviors of nanostructured iron, vanadium and tantalum over a wide range of strain rates. Comparative studies of nanostructured fcc and hcp metals are also presented, with the goal of developing physics-based approaches to constitutive modeling.
Biographical Sketch: Professor Ramesh received his doctorate from Brown University in 1987. After a short stint as a postdoctoral fellow at the University of California, San Diego, he joined the Department of Mechanical Engineering at Johns Hopkins in 1988, becoming Department Chair from 1999-2002 and Director of the Center for Advanced Metallic and Ceramic Systems in 2001. He has just completed a sabbatical year at the University of Cambridge.
Cognitive & Linguistic Sciences Colloquium Series
Refreshments Will be Served at 3:45 in Room 124-125 |
Abstract: One normative theory of causal reasoning, sometimes known as Causal Bayes Networks, has been reasonably stable for about a decade, but has not penetrated mainstream statistical curricula. In the late 1990s, several groups collaborated to produce an online course to teach the qualitative essentials of this theory. The course materials include a virtual Causality Lab - which allows learners to setup, carry out, and analyze experiments, and to compare the results of these experiments to hypotheses they construct. In several large experiments we confirmed that our online course provides at least as good a delivery mechanism than a standard lecture version of the material. We are now set to use the Causality Lab to not only teach the normative theory, but also to investigate how students who have been taught the normative theory approach causal discovery, and to compare their behavior to naive learners as examined by researchers like Sobel, Kushnir, Sloman, Lagnado. Steyvers, Tenenbaum, Gopnik, Schulz, etc. I will show the Causality Lab, and report on a pilot experimant involving choosing experiments.
Stochastic Systems Seminar
Brown University --
Joint Materials/Solid Mechanics Seminar Series
Brown Analysis Seminar
Neural Coding Discussion
PDE Seminar
Department of Mathematics Colloquium
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