Graduate Student Seminar Scheduled for October 8

The Fall 2009 Beckman Institute Graduate Student Seminar series continues on Thursday, October 8. The seminar will feature three short talks from graduate students Dae-Hyeong Kim, Dwarak Krishnan and Wladimir Benalcazar. The seminar will be held in Beckman Institute Room 5602 and a pizza lunch will be served.

The Beckman Institute Graduate Student Seminar Series presents the work of outstanding graduate students working in Beckman research groups. The seminar starts at Noon in Beckman Institute Room 5602 and is open to the public. Lunch will be served.

High-speed, high-resolution cardiac electrophysiology in-vivo using conformal electronics
Dae-Hyeong Kim

Mapping cardiac arrhythmias with standard, clinical electrophysiology (EP) devices can be a tedious, lengthy process, particularly over the epicardial surface. Probes with small numbers (4-10) of widely spaced (2-5 mm) passive electrodes sequentially record electrical activity from small areas of heart muscle as they are moved manually, point to point, across regions of interest.  Because each electrode requires a separate connection to external processors, spatial resolution and mapping speed are limited by practical constraints on the number and configuration of electrodes and wires that can fit in the device.  Here we develop a high resolution, high speed system, built from over 2,000 single crystal silicon nanoribbon transistors, that eliminates these constraints.  The device uses fully integrated, conformal electronic circuits to simultaneously record from 288 multiplexed (16:1) channels, each with its own on-board amplifier. The device maps activity at high spatial (sub-mm) and temporal (sub-ms) resolutions over large areas in a single pass, without human intervention. We propose this technology as a platform for a new generation of intelligent, implantable medical devices.

Optical properties of soft photonic crystals undergoing symmetry-breaking pattern transformations
Dwarak Krishnan

Soft material photonic crystals are prospective material systems for optomechanical sensors and for templates on which to fabricate higher dielectric contrast photonic crystals. They are fabricated using a variety of techniques such as lithography, colloidal synthesis and replica molding among others. Many issues pertaining to the effects of deformation on the optical performance of these structures are not well understood. In this work three structures are considered – a 2D photonic crystal of circular holes in an elastomer material, a 3D elastomeric photonic crystal fabricated by holographic lithography, and a 3D hydrogel based structure fabricated by colloidal synthesis. In experimental work reported in literature, large localized mechanical instabilities contribute to the deformation of each of these structures. Simulation results incorporating poroelastic and hyperelastic behavior of the matrix materials confirm this buckling-like behavior that leads to symmetry breaking pattern transformations, and reveal the common features in the behavior of these complex, soft periodic structures. Real-space light transmittance and reciprocal-space band structure calculations for both the undeformed and deformed structures show that the secondary peak in the reflectance spectra undergoes mode decoupling due to the pattern transformation. Based on simulation evidence, we propose an innovative photonic crystal made of a photosensitive liquid crystal elastomer that exploits this pattern transformation.

Imaging quantum vibrational signatures of biological tissues.
Wladimir Benalcazar

As research in pathology, biology and medicine gain complexity, the key requirements imposed on optical imaging techniques are no longer restricted to chemical selectivity and high sensitivity, but also to noninvasiveness. In this talk, Nonlinear Interferometric Vibrational Imaging (NIVI) will be presented. This is a microscopic technique that provides chemical selectivity without the need to introduce exogenous markers (i.e. fluorophores). Instead, it uses “coherent anti-Stokes Raman scattering” to chemically interrogate the samples by probing its intrinsic vibrational modes. Recent advances in the instrumentation of our system have made it possible to acquire hyperspectral cubes of images containing vibrational spectra of material and biological samples, allowing identification and differentiation of chemical domains in tissues (i.e. breast and skin).