Brown University
Joint Materials/Solid Mechanics Seminar Series
Department of Aerospace Engineering, Department of Mechanical Engineering, Iowa State University, Ames, Iowa | |
Abstract: In recent years, Chemical-Mechanical Planarization (CMP) has emerged as the process of choice for microelectronic processing due to its local and global planarization capability over the entire stepper field. In CMP, however, the manufacturing technique has outdistanced its underlying science. This talk will provide a summary of how basic mechanics concepts can provide insight on the design space of the CMP process. For example, the material removable rate is affected by a range of process parameters, which span several length scales. The morphology and stiffness of the utilized porous pad controls the level of the transfer loads to the active abrasive particles. At the particle level, the synergistic role of chemical dissolution and mechanical abrasion controls the local rate of material removal. The experimental observations of these various deformation/material removal mechanisms are utilized into simplified phenomenological MRR models to explore the CMP-process space. The model reveals the importance of the slurry-pad interaction, and the associated force partitioning in determining the variation of MRR with particle size and concentration. The developed understanding is the basis for further investigation of the various process-induced defects.
Note: There will be a dinner following the seminar.
Please contact Ms. Pat Capece at x3-1501 if you plan to attend.
Center For Fluid Mechanics
And
The Fluids, Thermal And Chemical Processes Group
Of
The Division Of Engineering
Seminar Series
Department of Mechanical Engineering Northwestern University, Evanston, IL | |
Abstract: A Direct Numerical Simulation (DNS) scheme, named Fluctuating Immersed MATerial (FIMAT) dynamics, for the Brownian motion of rigid particles will be presented. In this approach the thermal fluctuations are included in the fluid equations via random stress terms. Solving the fluctuating hydrodynamic equations coupled with the particle equations of motion result in the Brownian motion of the particles. There is no need to add a random force term in the particle equations. The particles acquire random motion through the hydrodynamic force acting on its surface from the surrounding fluctuating fluid. The random stress in the fluid equations is easy to compute unlike the random terms in the conventional Brownian/Stokesian Dynamics type approaches. The approach is tested for a variety of cases including single spheres, single ellipsoids and many spheres by considering quasi-steady simulations in the long time limit. Translational and rotational diffusion of the particles are considered. Unsteady simulations are also performed to test the short time behavior of the velocity autocorrelations. The method correctly reproduces the algebraic tail of the velocity autocorrelation.
Center For Fluid Mechanics
And
The Fluids, Thermal And Chemical Processes Group
Of
The Division Of Engineering
Seminar Series
Department of Mechanical Engineering, University of Houston, Houston, TX | |
Abstract: Transient growth is studied in a normal-mode-stable vortex column via linear analysis and direct numerical simulation (DNS). Energetically "optimal" perturbations -- attaining over thousand-fold amplification at moderate Reynolds numbers, $Re ~ 10^{4} $ -- grow via two inviscid mechanisms: (a) 2-D perturbations with "positive-tilt" streamlines (contributing positive Reynolds stress, hence production) grow until the mean swirl transforms the streamlines to "negative tilt" (negative stress); (b) 3-D perturbations grow via the tilting and stretching of perturbation radial vorticity. Competition between the amplifying effect of mean strain and growth-arresting effect of mean vorticity, in addition to viscous damping, fixes the optimal radius of initial perturbation. With increasing growth, axisymmetric modes originate at increasingly larger radii outside the core, whereas bending wave modes are localized close to the vortex axis, where they resonantly excite vortex core waves. Resulting strong growth of bending waves appears likely to cause core transition, hence enhanced vortex decay -- a phenomenon of interest in high-$Re$ practical flows, e.g. aircraft wake.
Center for Computational Molecular Biology Seminar
Massachusetts Institute of Technology, Department of Mathematics, Cambridge, MA Faculty Search Candidate Center for Computational Molecular Biology | |
Abstract: Whole genome alignment methods rely fundamentally on a seed and extend approach, where the first step is typically the identification of "confident" exact matches, followed by a chaining step, and further refinement. The presence of repetitive sequence in higher order eukaryotes undermines the relationship between confidence of a match and its length. One heuristic is to filter by considering only matches which can be built out of much shorter bi-unique matches, but the quality of this heuristic is difficult to assess without being able to compare the results against differing heuristic lengths. I will describe a method of characterizing the uniqueness of a sequence, which also allows one to quickly filter matches for a range of heuristic lengths. When combined with a fast method for chaining, one can produce draft whole-genome alignments quickly for a range of parameter settings.
Peptide identification via mass spectrometry is at the heart of high throughput proteomics. The successful analysis of such experiments typically relies on amino-acid sequence databases to provide a set of biologically relevant peptide examples to examine against the observed peaks in the mass spectrum. In order to solve this problem efficiently, we must deal not only with the redundancy of our amino-acid database at the substring level, but also with the redundancy of our set of observed peptide masses. I will describe how these issues were dealt with in the Celera proteomics effort.
Scientific Computing Seminar
PDE Seminar
Abstract: We study the problem of supersonic flow onto a solid wedge. There are two possible steady solutions, a strong and a weak(er) shock. We study numerically which one occurs and is stable under which circumstances.
To settle the question mathematically, we construct an exact self-similar solution to a model problem using compressible potential flow. The problem is mixed-type with degeneracy, with a free boundary and other technical obstacles.
(Joint work with Tai-Ping Liu)
Brown University Center for Statistical Sciences Seminar
Presents "The Future of Biostatistics,"
A Series of Lectures Celebrating The 10th Anniversary of the Center
Johns Hopkins University | |
Department of Mathematics Colloquium
University of British Columbia and Brown University | |
Abstract: This is joint work with Andrei Okounkov. Given a polygon P with 3n sides, when can you find a degree-n rational curve inscribed in P? We answer this question for the family of polygons having sides with slopes 0,1,infinity. This result arose from a completely different area, studying the so-called dimer model of statistical mechanics. We'll show the connection and give a sketch of the proof.
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