Center for Fluid Mechanics
and
The Fluids, Thermal and Chemical Processes Group
of
The Division of Engineering
Seminar Series
Department of Chemical Engineering, University of Massachusetts, Amherst, Massachusetts | |
Abstract: Nanocrystals or "quantum dots" of compound semiconductors (e.g. CdSe, ZnSe, CdS, PbSe, etc.) that confine electron-hole pairs (excitons) in zero dimensions are attracting a lot of attention because of their unique size-dependent properties and their potential to revolutionize clinical diagnostics, photovoltaics, and high-density optoelectronics.
This presentation will focus on process engineering issues related to the synthesis and functionalization of ZnSe nanocrystals. Two new synthesis techniques have been developed in our laboratory offering distinct advantages for large-scale production of these materials:
(a) Microemulsion-gas contacting: This technique exploits the dispersed phase of self-assembled microemulsions and liquid crystals to form numerous identical nanoreactors producing almost monodisperse nanocrystal populations. Recent results on templated growth nanowires, nanorods and free-standing quantum wells in liquid crystals will also be discussed.
(b) Vapor-phase synthesis in a counterflow jet reactor: This technique is compatible with the existing infrastructure of the microelectronics industry and produces nanocrystals with superior purity.
Studies of the fundamental links between transport phenomena, reaction kinetics, particle nucleation, cluster coalescence, and nanocrystal properties are being performed in order to identify optimal synthesis conditions. We employ a combination of experiments and multi-scale process models to probe the underlying phenomena. Surface passivation and functionalization protocols have been developed to exploit the size-dependent luminescence of the nanocrystals in novel multiplexed biosensors and DNA arrays. A procedure for conjugating nanocrystals with oligonucleotides in water will be discussed that results in significant amplification of their luminescence intensity. Applications of these materials in clinical diagnostics will be outlined.
Center for Computational Molecular Biology Seminar Series
Center for Studies in Physics and Biology | |
Abstract: Structural modeling of protein-DNA complexes is complementary to genomic sequence based bioinformatics methods - the two can be used together to understand transcriptional regulatory networks. Using structural analysis, evolution of transcription factor binding sites due to mutations at the protein-DNA binding interface can be characterized. I will demonstrate how genome-wide sequence-structure threading can be used to study the degree of protein-DNA interface conservation across multiple genomes. Focusing on protein-DNA interfaces provides classification of transcription factors by their binding specificity, and allows us to find orthologs and paralogs in related species, complementing existing algorithms based on the overall sequence similarity. When a suitable structural template for modeling a transcription factor is available, transcription factor binding sites and energies can be directly predicted by computational modeling, and compared with experimental data.
Scientific Computing Seminar
Abstract: Reconstruction of piecewise smooth functions from their Fourier spectral coefficients is often studied. Applications arise in various scientific fields, in particular, the use of Fourier methods are common in medical magnetic resonance imaging (MRI) because of their relationship to Radon transforms. Such images are not free from Gibbs phenomenon, as various tissue regions can be seen as piecewise smooth functions. Filtering is frequently used to alleviate the ringing in the images. However abnormal developments often begin near the edges of tissues regions, and it is well known that filtering compromises the integrity of the image there. Hence we are motivated to use high order reconstruction techniques for purposes of earlier and better diagnosis.
Recently spectral reprojection methods, notably the Gegenbauer reconstruction method, have been developed to reconstruct piecewise smooth functions in their smooth sub-intervals and restore the exponential properties of spectral methods. Specifically, unlike standard filtering, the convergence rate does not deteriorate as the discontinuities are approached. This talk discusses these methods and demonstrate their capabilities in fields such as MRI reconstruction.
Another type of problem occurs when the given information is discrete (non-uniform) grid point data. Spectral reprojection methods can only be used if the data has a Gaussian type distribution. However, here we show that a similarly designed projection method, based on discrete variable orthogonal polynomials, can reconstruct piecewise smooth functions with spectral accuracy. The method is computationally efficient and robust.
Division of Applied Mathematics Graduate Student Seminar
Abstract: I intend to talk about the determinant function of square matrices. The inspiration for this presentation is Peter Lax's book on linear algebra. This book has a short chapter on the determinant, in which Lax uses the concepts of volume/signed volume of polyhedrons to motivate/define this important function. It is a very intuitive (and rigorous) approach that quickly bears fruits. Lax attributes this signed volume based development of the determinant to Emil Artin. There are no new or even remotely recent research results in this talk. It will be in the spirit of an afternoon gossip over tea (or pizza if you will).
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