Beckman Graduate Student Seminar Series Continues October 11

The Beckman Institute Graduate Student Seminar Series presents the work of outstanding graduate students working in Beckman research groups. The seminars are open to the UIUC campus. The next seminar takes place on Wednesday, October 11 at noon in Room 1005 of the Beckman Institute.

Speakers and abstracts are listed below:

Joule Heating and Phonon Transport in Silicon
Zlatan Aksamija (CE)

Joule heating is caused by emission of phonons as electrons traverse through a semiconductor device. In silicon MOSFETs, most of the emission is concentrated in the small region where the channel meets the drain. It has been noted in the literature that this causes a hot-spot in the device where strong non-equilibrium conditions exist. The emission of phonons has previously been examined, but the resulting non-equilibrium temperature conditions in a typical device have never been established. This work aims at using full-band Monte Carlo simulation coupled with phonon transport to quantify the extent and the location of Joule heating in a silicon MOSFET.

Separation of Functionalized Single-Walled Carbon Nanotubes via Electrophoresis
Monica Usrey (NANO)

The separation of single-walled carbon nanotubes (SWNT) by electronic structure remains a hurdle to their application. An electronic structure selective chemistry was developed using an aryl diazonium salt to selectively react metallic nanotubes. Using this chemistry with a hydroxyl moiety allows for the control of metallic SWNT formal charge depending upon the extent of reaction. In this work, we investigate the separation of functionalized and non-functionalized carbon nanotubes using both gel electrophoresis and solution electro-diffusion. The separation efficiency is measured using UV-vis-nIR photoabsorption and Raman spectroscopy. Electrophoretic mobility is dependent upon the charge of a particle, which promotes mobility, and its hydrodynamic drag, which resists movement. A model based upon flexible rod diffusion theory is used to study the effect of covalent reaction upon the net charge and the frictional resistance in various electrophoretic systems. The predictive capabilities of the model are used to estimate optimal separation conditions.

Context-Specific Recognition
Michael Diaz (CS)

Most theories of recognition agree that a matching process is utilized that compares a sought-after stimulus to the contents of memory as a whole. However, these theories are asymptotically inefficient because, with increasing age and experience, the matching process becomes noisier and eventually useless. This research examines whether humans limit the set of memory traces that are considered by using knowledge about the circumstances of the prior presentation of the stimulus. Such a mechanism might underlie, for example, the common experience of only being able to remember a familiar face when we are reminded of the circumstances in which we had met that person previously. On each trial, participants studied a list of 2-6 words, 1-3 of which were presented in blue and 1-3 of which were presented in red. After each list, participants were told to only endorse (say "yes" to) a test item only if it had been studied in a particular color, but not if had been presented in the other color . Recognition times varied with the size of the relevant-color set-size, but not with the size of the irrelevant-color set-size, indicating that subjects were successful in searching only a limited portion of recent memory traces.