Lefschetz Center for Dynamical Systems Seminar
Brown University Center for Statistical Sciences Seminar
School of Public Health, University of Michigan, | |
*Lectureship Series on Statistical Genetics and Bioinformatics |
Abstract: In many disease and scientific settings, understanding the spatial distribution of transcription is quite important. In a variety of settings, ranging from yeast biology to cancer, the role of the location of transcriptional events is important. In this talk, we discuss the use of several techniques for the analysis of such data with a particular emphasis on the use of scan statistics. The methods are highlighted by several examples. This is joint work with Al Levin and Sharon Kardia.
Brown University
Joint Materials/Solid Mechanics Seminar Series
Abstract: The mechanical behavior of thin metal films has been subject of investigation for some time. Because of the small microstructural length scales involved, thin film behavior is often very different from that of the corresponding bulk material. Stresses found in thin films, for instance, tend to be significantly higher than those in bulk samples of the same material. Various theoretical models have been developed to describe plasticity in thin films - from a single threading dislocation running down the length of a film to complicated analyses involving many discrete dislocation. At the same time, continuum plasticity theory has been expanded to include the hardening effects of strain gradients and associated geometrically necessary dislocations. While often negligible for bulk materials, these effects are important for thin films with fine microstructures. In this presentation, I will give a brief overview of some of the theories that have been proposed to describe size effects in thin film plasticity and will present the results of an experimental study on the behavior of freestanding electroplated Cu thin films. Two sets of Cu films will be considered: one set consisting of films with the as-deposited microstructure and with varying thickness and one set of films for which the microstructure is independent of film thickness. The latter films were obtained by progressive thinning of Cu films using chemical mechanical polishing (CMP). I will discuss the results of an extensive microstructural and mechanical characterization of the films in light of some of the theories developed for thin film plasticity. Time permitting, I will also present some preliminary results on the mechanical behavior of thin films of $Fe{_{3}}Pd$, a ferromagnetic shape memory alloy.
Center for Fluid Mechanics Seminar
This Seminar is Joint with The Fluids, Thermal and
Chemical Processes Group of the Division of Engineering
Hatsopoulos Microfluids Laboratory, Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, MA | |
Abstract: We describe the design and construction of two new microrheometers designed to facilitate the study of complex biological fluids and food stuffs using very small sample volumes (1-10 µl). The shear-rate-dependent viscosity and gap-dependent yield stress of biological gels is measured using a sliding plate microrheometer with optical flats (polished flat to within \lambda/20, or 30nm) as the shearing surfaces. White light interferometry and a three-point nanopositioning stage employing piezo-stepping motors are used to control the parallelism of the upper and lower surfaces. A compound flexure system is used to hold the fluid sample between a drive spring and an independent sensor spring. Alignment fidelity, device orthogonality and total error stack-up are all optimized by machining the entire instrument frame from a single monolithic aluminum block using water-jet and EDM technology. Displacements in the sensing flexure are detected using an inductive proximity sensor with a resolution of ± 3 nm allowing the detection of loads up to 6 N with an accuracy of 3 mN. The lower plate is attached to a drive flexure which is moved by an `inchworm' motor with a resolution of 0.1 nm and a maximum displacement of 6 mm, thus allowing large strains to be obtained. The transient extensional rheology is also measured using a 1 µl fluid droplet in a microscale capillary break-up extensional rheometer. In this device the extensional flow is driven by capillarity and resisted by the viscous and elastic stresses in the elongating fluid thread.
These devices are used to quantify the rheological properties of a wide range of complex fluids from consumer products to biopolymer solutions. Four specific examples we will focus on include; full fat vs. fat-free mayonnaise, the spinning dope extracted {\it ex vivo} from the silk worm, {\it Bombyx mori} and from the major ampullate gland of a {\it Nephila clavipes} spider, plus the physically-crosslinked mucin gel of slugs and snails.
Brown Analysis Seminar
Scientific Computing Seminar
Professor of Applied & Computational Mathematics & Computer Science California Institute of Technology, Caltech, Pasadena, CA 91125 | |
Abstract: In the simulation of high velocity fluid and solid mechanics (such as arise for example in penetration and impact problems) it is sometimes advantageous to utilize a Lagrangian description for the solid and an Eulerian description for the fluid. The Lagrangian description is a natural approach to describing phenomena such as plastic deformation of the solid while the Eulerian approach deals well with instances where there exist regions of large strain rate but where strength effects are unimportant.
There exist several approaches in the literature that adopt this approach. For example one can track the evolution of the solid boundary and compute, at every time step, a conforming fluid mesh. Alternatively one can use Arbitrary Lagrangian Eulerian methods (ALE) to allow the coordinate system to transition smoothly from pure Lagrangian in the solid to pure Eulerian in the fluid. In this talk we present an alternative approach wherein the solid boundary is captured using level set based techniques. The level set information is used to inform the fluid mechanics solver of the location, velocities and accelerations of the solid and in turn can inform the solid solver of the load induced by the fluid. An advantage of this approach is there is no need to generate dynamically conforming meshes for the fluid mechanics. While the current version of this algorithm has first order accuracy, it has the advantage that it allows one to easily couple diverse solid and fluid mechanics approaches even on parallel architectures.
One potential difficulty with this approach is the need to repeatedly generate a distance function in the fluid domain from the solid boundary. In three dimensions, conventional algorithms make such a procedure potentially more costly than the solution of the fluid or solid mechanics problems which can effectively be performed in a time that is linearly proportional to the number of mesh points in the fluid or elements in the solid. To overcome this difficulty we also present a new linear time algorithm for generation of the level set from a triangular surface mesh.
We describe in this talk the major aspects of the solvers and coupling algorithm. We then provide some examples of this approach implented on parallel architectures.
PDE Seminar
Department of Mathematics Colloquium
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