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TREND Fair 2007

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August 10, 2007

On this page... TREND 2007 Presentations

Trend Group 2007
Left to right: John Platig, Sereres Johnston, Rebecca Taft, Abby Goldman, Nicholas LeCompte, Mark Patrick, Caitlin Williams, Katarzyna Oldak, Rose Faghih, Zhigang Pan

Trend photoElectron Energization inside Magnetic Islands


Katarzyna Oldak, Case Western Reserve University

Advisors: Professor James F. Drake and Dr. Marc Swisdak

Magnetic reconnection occurs throughout the universe, transferring magnetic energy into kinetic energy by energizing particles found in interstellar plasmas. It drives solar flares and is present in the Earth's magnetotail. Some of the energized particles have been detected, but had energies much greater than what existing theories would predict. However, according to a recent theory of contracting islands, already fast electrons can attain very high velocities by bouncing inside contracting magnetic islands during reconnection. This project investigated the fate of the slower electrons within these contracting islands by studying what happens to the initial Maxwellian distribution of electrons.

Trend photoEntrainment of Weakly Coupled Oscillators by External Driving


Rose Faghih, University of Maryland College Park
John Platig, Wright State University

Advisors: Professor Edward Ott, Professor Thomas Antonsen, and Assistant Professor Michelle Girvan

The Kuramoto model describes a large population of weakly coupled oscillators whose frequencies are distributed around some average value. This model is relevant to a host of interesting phenomena, from beating of the heart, to synchronization of firefly flashing, to synchronization in Josephson diode circuits. In our work, we have expanded the Kuramoto model to include an external forcing input to the coupled system. We present parameter studies which show the entrainment properties of the expanded model. In doing this, we hope to add insight into the effects of synchronization in cellular clocks in the brain.


Trend photoCell Migration on Chemically and Topographically Modified Surfaces


Abby Goldman, Mount Holyoke College

Advisors: Associate Professor Wolfgang Losert, Colin McCann, Meghan Driscoll,and Rael Kopace

In living systems, cells maneuver in a complex three-dimensional environment. For instance, white blood cells, when chasing down invaders, adhere to blood vessel walls and penetrate deep into tissue. We explore how cell affinity for the substrate and the topology of the surface affect the cell motion. We utilize a well-characterized motility model organism, the social amoeba D. discoidium. We capture time-lapsed movies of D. discoidium cells as the move on amine-treated glass, amine-treated acrylic, and use image analysis to track changes in cell speed and directionality. To examine the role of small-scale topology changes, we monitored the cell motion over glass slides coated with gold nanoparticles. In addition, we studied the effect of large-scale topographical modifications by monitoring the cell motion along microscale ramps.

Trend photoDynamics of Granular Matter under Localized Stress


Rebecca Taft, Yale University

Advisors: Associate Professor Wolfgang Losert, Professor Core O'Hern, Steven Slotterback, Krisztian Ronaszegi,and  Andrew Pomerance

To understand granular flows under stress, we performed experiments in which we push a "penetrometer" into a sample of glass beads and track their movement using 3D imaging techniques. Improvements were made to the existing imaging system by automating the data collection and refining the image processing software. To determine the influence of sample preparation on material failure, we compressed the samples perpendicular and parallel to gravitational loading before inserting the penetrometer. We also performed frictional molecular dynamics (MD) simulations of penetrometer insertion using experiment particle coordinates as initial conditions to predict the failure regions. To account for experimental uncertainty, we first adjusted the positions and radii using a geometric algorithm we designed to bring the system near mechanical equilibrium.

Trend photoElectrodeposition of Copper with an Alternating Electric Field


Nicholas LeCompte, Worcester Polytechnic Institute

Advisor: Professor. Daniel Lathrop

In electrodeposition, two metal electrodes immersed in a salt of that metal have a potential difference applied between them. If this difference is sufficiently high, the anode becomes ionized. This causes a deposition of ions on the cathode. An aggregate of these ions can exhibit diverse morphologies, ranging from fractal tree-like structures to dense, homogeneous clumps. We investigate the effect of an alternating electric field on the morphology of the aggregate, using copper electrodes in a cupric sulfate solution. The parameters we vary are the frequency and the ratio of AC to DC voltage, and we look at two-dimensional and three-dimensional systems. Quantities such as fractal dimension, growth velocity, tip-splitting frequency, and dendrite thickness are measured, and qualitative observations on the morphologies are made. We also test a hypothesis which predicts that a characteristic length scale of the aggregate is proportional to the inverse square root of the frequency. In addition, chemical properties of the electrocell are examined indirectly from qualities of the aggregate such as color and abrupt morphological transitions.

Trend photoDiffusion: The Key to Understanding Why Photocathodes Die


Zhigang Pan, University of Maryland College Park

Advisors: Professor Patrick O'Shea, Dr. Eric J. Montgomery, and Dr. Kevin L.Jensen

Robust and highly efficient laser-driven photocathodes are an important source of bright electron beams. Photocathodes are coated with a partial monolayer of cesium to increase quantum efficiency (i.e., the number of electrons per photon). During operation, cesium atoms come up through pores onto the cathode surface, diffuse, and undergo desorption. Having a theoretical model to predict evolution of the cesium surface density is of great interest in furthering the development of high quality photocathodes. Currently, I am developing a model of cesium diffusion through a porous surface. This model would be useful in designing experiments and optimizing photocathode quantum efficiency and lifetime.

Trend photoChaotically Oscillating Gate Networks


Sereres Johnston, Andrews University

Advisors: Professor Daniel Lathrop and Dr. John Rodgers

Random Boolean Networks (RBNs) can model complex systems such as neural pathways and gene expression. Usually RBN studies simulate multinode networks of idealized logic gates, but this TREND project focused on networks of five or fewer 74AC04 CMOS inverters. System parameters such as the power supply voltage, circuit time delay, and loop gain were adjusted. Later in the project, AC current with a DC bias was used. Reduced loop gain widened the range in which chaos was observed, while combining time delay with gain reduction resulted in intermittency. Self-synchronization through weak external coupling was observed for sets of free-running devices. The networks' sensitivity and their self-synchronizing capability indicate that they or similar systems may be useful as intrusion detectors.

Numerical Models of Semiconductor Lasers with Time-Delayed Optoelectronic Feedback


Mark Patrick, University of Maryland College Park

Advisors: Professor Rajarshi Roy, Associate Professor. Thomas E. Murphy, Adam Cohen, Bhargava Ravoori, and Caitlin Williams

We examine numerical models of a system of two optoelectronically cross-coupled semiconductor lasers. We implemented a Runge-Kutta integration method to analyze the deviations from the steady state intensities with a band-pass filter in the feedback loop. Through comparison with experiment, we made our model more accurate. We explored the dependence of the dynamics on the coupling strength between the two lasers, as well as the coupling time delays in both the symmetric and asymmetric cases. Numerically, we observed the fast relaxation oscillations of the laser, oscillations on the order of the total delay time, and an unexpected slower bursting behavior that was similar to experiment.

Trend photoDynamics of Semiconductor Lasers with Optoelectronic Time-Delayed Feedback:  Experimental Observations


Caitlin Williams, Grove City College

Advisors: Professor Rajarshi Roy, Associate Professor Thomas E. Murphy, Adam Cohen, Bhargava Ravoori, and Mark Patrick

A system of two semiconductor lasers cross-coupled optoelectronically with time delays is a simple prototype element of a sensor network. In this system periodic intensity oscillations are present for coupling strengths above a threshold level. The goal of this project was to understand the dynamics of this system with asymmetric time delays over a wide range of coupling strengths. The laser intensities displayed periodic behavior on two different timescales: one on the order of nanoseconds and a second longer timescale of microseconds. Their periods and phases were analyzed using FFT, Hilbrert transforms, and cross-correlation functions.