Bulletin of the American Physical Society
APS March Meeting 2011
Volume 56, Number 1
Monday–Friday, March 21–25, 2011; Dallas, Texas
Session D10: SPS Undergraduate Research II |
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Sponsoring Units: SPS Chair: Crystal Bailey, American Physical Society Room: D221 |
Monday, March 21, 2011 2:30PM - 2:42PM |
D10.00001: The $^{11}$C Project:Measurement of Root Exudation at Elevated CO2 Levels in Low and High Nutrient Solutions Verida Leandre, Calvin Howell Understanding the plant kingdom's mechanisms of resource management in variable environments is integral to predicting how plants will respond to an increase in atmospheric CO$_{2}$. The goal of this study is to determine the effects of changing nutrient conditions on the root exudation of barley plants at elevated CO$_{2}$ levels. The $^{11}$C group at the Triangle Universities Nuclear Laboratory (TUNL) tags various species of plants with short-lived positron-emitting radioisotopes in order to analyze metabolite transport in response to changes in the environment. $^{11}$C is produced at TUNL using a tandem Van de Graaff particle accelerator, then transported from TUNL to the Duke Univ. Phytotron (100m) where plants are labeled with $^{11}$C in a growth chamber. The chamber allows researchers to control the light intensity, air temperature, humidity and concentration of CO$_{2}$ in the air. The plant absorbs $^{11}$CO$_{2}$ in a leaf that is placed inside a cuvette through which radioactive $^{11}$CO$_{2}$ gas flows. The sugars in the labeling leaf are tagged with $^{11}$C and translocated throughout the plant similar to $^{12}$C. Scintillation detectors are used to track the tagged sugars as they are translocated through the plant and exudated from the root into the nutrient solution or $^{11}$CO$_{2}$ gas is respired by the root. The labeling system, detector arrangement, electronics and data analysis will be described and preliminary results will be presented. [Preview Abstract] |
Monday, March 21, 2011 2:42PM - 2:54PM |
D10.00002: A One Dimensional Stochastic Susceptible-Infectious-Recovered Model and its Variations: a Hamiltonian Approach Ali Hamed, Dia'a Bisharat, Mohamad Amine, Irina Mazilu The spread of an infectious disease is a random process, and a stochastic approach to the problem is justified. The susceptible-infectious-recovered model (SIR) describes the evolution of three types of individuals (in a small community) which undergo an infection and recovery mechanism. The model (and its variations) predicts the number of infected individuals over a certain period of time, gives an estimate of the maximum possible number of infected people, and predicts how long the disease will be threat to the examined community. Using a quantum mechanical approach, we investigate four variations of the original SIR model and compare our analytical findings with the computer simulation results. We also calculate correlations between infected and recovered individuals, and find a good agreement between theory and computer simulations. [Preview Abstract] |
Monday, March 21, 2011 2:54PM - 3:06PM |
D10.00003: Exploring a Parasite-Host Model with Monte Carlo Simulations Nyles Breecher, JiaJia Dong We explore parasite-host interactions, a less investigated subset of the well-established predator-prey model. In particular, it is not well known how the numerous parameters of the system affect its characteristics. Parasite-host systems rely on their spatial interaction, as a parasite must make physical contact with the host to reproduce. Using C++ to program a Monte Carlo simulation, we study how the speed and type of movement of the host affect the spatial and temporal distribution of the parasites. By drawing on mean-field theoretics, we find the exact solution for the parasite distribution with a stationary host at the center and analyze the distributions for a moving host. The findings of the study provide rich behavior of a non-equilibrium system and bring insights to pest-control and, on a larger scale, epidemics spreading. [Preview Abstract] |
Monday, March 21, 2011 3:06PM - 3:18PM |
D10.00004: Optical design of a robotic TV camera probe for minimally invasive abdominal surgery Susanna Todaro, Weiyi He, Dennis Killinger Minimally invasive techniques are a promising new field of surgery; however, they limit the surgeon's access points and maneuverability. In order to increase the number of access points in minimally invasive abdominal surgery, a proposed implantable medical probe braces to the abdominal wall and provides illumination and video signal. The probe is cylindrical, about 25 mm long and 10 mm in diameter. A ring of LEDs on the end of the probe illuminates the tissue, and the resulting image is focused onto an HD video detector. It was necessary to apply beam-shaping reflectors to collimate the light onto a small target area, to avoid illuminating areas not picked up by the video. These reflectors were designed and simulated using the optical ray tracing software TracePro. Two LED chip geometries and three types of reflector geometries were analyzed, and the parameters for each geometry were optimized. For the straight-edged reflectors, the intensity patterns and optimization were compared to experimental results. Although parabolic reflectors produced the best collimation, cone reflectors with a 20-degree half-angle produced significant collimation at a much cheaper price. [Preview Abstract] |
Monday, March 21, 2011 3:18PM - 3:30PM |
D10.00005: Developing a Procedure for the Characterization of Mechanical Properties of Collagen Gels Christopher Chambers, Heather Lovelady, Garrett Matthews The characterization of bulk mechanical properties of type I collagen gels is critical to understanding the role of collagen in the extracellular matrix (ECM), and developing biocompatible devices for use in the human body. Understanding the mechanical properties of the gel state of collagen can lead to the ability to adjust these properties for multiple uses. Here, we examined the Young's modulus of the synthesized gels. This project used a microrheological approach to discover these properties. Gels were first formed using a known process and magnetic microspheres were embedded in the gel prior to formation. An optical microscope was fitted with a magnetic chamber used to drive the embedded beads in two modes, an oscillatory motion and a pulse motion. Tracking software was modified and used to analyze the motion of the beads recorded with a CCD camera on the microscope. These techniques should be sufficient to obtain a reliable value for the Young's modulus of collagen gels, as well as other similar materials. [Preview Abstract] |
Monday, March 21, 2011 3:30PM - 3:42PM |
D10.00006: ABSTRACT WITHDRAWN |
Monday, March 21, 2011 3:42PM - 3:54PM |
D10.00007: Does Thioflavin-T Detect Oligomers Formed During Amyloid Fibril Assembly Christopher Persichilli, Shannon E. Hill, Jason Mast, Martin Muschol Recent results have shown that oligomeric intermediates of amyloid fibril assembly represent the main toxic species in disorders such as Alzheimer's disease and type II diabetes. Thioflavin-T (ThT) is among the most commonly used indicator dyes for mature amyloid fibrils \textit{in vitro}. We used ThT to monitor amyloid fibril formation of lysozyme (HEWL), and correlated ThT fluorescence to concurrent dynamic light scattering and atomic force microscopy measurements. Specifically, we tested the ability of ThT to discern among oligomer-free \textit{vs.} oligomeric fibril assembly pathways. We found that ThT fluorescence did not detect oligomer growth; however, fluorescence increases did coincide with the formation of monomeric filaments in the oligomer-free assembly pathway. This implies that ThT fluorescence is not generally suitable for the detection of oligomeric intermediates. The results further suggest different internal structures for oligomeric \textit{vs. }monomeric filaments. [Preview Abstract] |
Monday, March 21, 2011 3:54PM - 4:06PM |
D10.00008: The Design and Fabrication of Bismuth Hall Effect Biosensors A.J. Sigillito, M. Rudolph, V. Soghomonian, J.J. Heremans Because of their high sensitivity, accuracy, and low cost, the use of Hall biosensors promises to be an effective diagnostic technique that may aid in the early diagnosis of diseases. In this research, Hall sensors were fabricated from thermally evaporated bismuth thin films. The bismuth films were deposited under high vacuum onto heated Si/SiO$_{2}$ substrates using a two layer deposition technique. The films varied in thickness from 60 nm to 75 nm and were etched into Hall bar geometries using photolithography and wet chemical etching. Magnetoresistance and Hall measurements were taken from 4 K to 300 K. The data indicate that the sensors may be characterized using a two carrier model with high mobility, low density holes and low mobility, high density electrons. Additionally, the sensors were exposed to magnetite nanoparticles and characterized using atomic force microscopy. The results will be reported. This research was funded by the National Science Foundation (NSF Grant DMR-0851662). [Preview Abstract] |
Monday, March 21, 2011 4:06PM - 4:18PM |
D10.00009: EPR Study of Lithium Borovanadate and Lithium Silicate Glasses Bikesh Dahal, D. Blane Baker, Steve Feller Lithium borovanadate and lithium silicate samples with varying molar ratios were prepared using both roller quenching and plate quenching methods. Electron paramagnetic resonance EPR spectra of those samples show that resolution of the hyperfine structure lines(hfs) depend on their molar ratio. When the molar ratio (K) is less than 0.5 in the borovanadate system, the hyperfine structure lines are well resolved and defined. However, when the molar ratio becomes greater than 0.5; the spectra starts to get less resolved; at molar ratio 0.7 there is no hyperfine resolution. Well resolved samples were modeled by using a modeling program in MATLAB to obtain Hamiltonian parameters. The Hamiltonian parameters that were obtained were g $_{parallel}$, g $_{perpendicular}$, A $_{parallel}$ and A $_{perpendicular}$. The Hamiltonian parameters were calculated to learn about the orientation of V$^{4+}$ ions and electrons in the glass samples. According to our calculation g $_{parallel} \quad <$g$_{perpendicular}<$ g $_{e}$ which suggests that crystal field of the V$^{4+}$ ions has a octahedral site with a tetragonal compression in the glass samples. [Preview Abstract] |
Monday, March 21, 2011 4:18PM - 4:30PM |
D10.00010: EPR study of radical trapping of RAFT polymerization of Multifunctional Acrylates Aayush Regmi, Ashutosh Dahal, D. Blane Baker, John Pojman, Patrick Bunton Electron Paramagnetic Resonance (EPR) was used to monitor radical trapping during Reversible Addition-Fragmentation chain Transfer (RAFT) polymerization of acrylate monomers with different degrees of functionality. Monomers used for the study were 1, 6-Hexanidiol \underline {Di}acrylate (HDODA), Trimethylopropane \underline {Tri}acrylate (TMPTA), and Pentaerythritol \underline {Tetra}crylate (PETA). X-band EPR spectra were obtained for approximately 0.2 g of samples in a 4 mm quartz tube heated at 50$^{0 }$C inside the cavity. The trapped radicals' signals were first observed after the samples were heated for 400-500 minutes. Radical density continued to increase for an additional 180 -190 minutes. EPR spectra of RAFT samples of TMPTA and PETA were compared with subsequent spectra produced by traditional free radical polymerization. [Preview Abstract] |
Monday, March 21, 2011 4:30PM - 4:42PM |
D10.00011: EPR study of Frontally Polymerized Multifunctional Acrylates Ashutosh Dahal, Aayush Regmi, Anna Thoma, Alecia Valencia, Veronika Viner, Rafael Cueto, D. Blane Baker, John Pojman, Patrick Bunton Electron Paramagnetic Resonance(EPR) study of frontally polymerized Trimethylopropane Trimethacrylate(TMPTMA), Trimethylopropane Triacrylate(TMPTA), 1,6-Hexanidiol Diacrylate(HDODA) and Pentaerythritol Tetracrylate(PETA) was done to determine the absolute radical concentration. Higher radical concentrations were found in the frontally polymerized samples compared to the bulk polymerized samples for TMTPMA and PETA. The concentration of radicals was highest in TMPTMA frontal sample at 8.74 X 10$^{-3}$ moles/kg. The lowest measureable concentration was in the HDODA bulk samples at 0.0266 X 10$^{-3}$ moles/kg. For all frontally polymerized samples high radical concentrations were observed at the point of initiation after which the signal intensity decreased to steady state within a few centimeters down the front. An exponential growth in the radical signal was observed in the mixture of TMPTMA and TMPTA when the concentration of the TMPTMA was increased. [Preview Abstract] |
Monday, March 21, 2011 4:42PM - 4:54PM |
D10.00012: First-principles investigation of graphene-metal interfaces Andrew Ross, Lyudmyla Adamska, You Lin, Ivan Oleynik Epitaxial growth of graphene on Ni(111) substrates is one promising method of large-scale, high-quality graphene wafer production, due to the small lattice mismatch between these two materials. We present results of first-principles density functional theory (DFT) investigation of thestructural, electronic, and magnetic properties of graphene/Ni(111) interfaces relevant to experimental studies of graphene growth on nickel substrates. DFT calculations were performed to identify the favored interface geometries and binding sites for different interface configurations. Additional adlayers of Ni and Cu were either adsorbed on top of the graphene/metal interface, or placed between the graphene and substrate to model processes of metal intercalation. It was also found that the interaction between graphene/Ni(111) and the top Cu adlayer is much weaker compared to that for Ni adlayer. The atomic, electronic, and magnetic properties of these interfaces, including induced magnetic moments in graphene/Ni(111) and Cu,Ni/graphene/Ni(111) systems are also discussed. [Preview Abstract] |
Monday, March 21, 2011 4:54PM - 5:06PM |
D10.00013: Growth of Graphene on Metal Substrates Travis Miller, Jayeeta Lahiri, Rafik Addou, Matthias Batzill Graphene, a single layer of graphite, has large potential as an electronic material. For these applications large scale, high quality graphene wafers are required. A promising approach to achieve this is by growth on metal substrates. In this REU project I used Auger electron spectroscopy to study the growth of graphene on Ni(111) and its modification by Cu or Al additions. On pure nickel we found two graphene growth regimes. Below 480 $^{\circ}$C graphene grows by converting a surface carbide phase while above 480 $^{\circ}$C graphene grows on pure nickel. Addition of copper destabilizes the nickel carbide enabling the growth of graphene in the absence of a carbide at lower temperatures. Finally, aluminum intercalation through the Ni- supported graphene layer was investigated in an attempt to form an ordered Ni-Al alloy underneath the graphene. Surprisingly, we found that this intercalation process already occurs at only 100 $^{\circ}$C. Furthermore, the intercalated Al is protected by the graphene against oxidation. [Preview Abstract] |
Monday, March 21, 2011 5:06PM - 5:18PM |
D10.00014: Single-Walled Carbon Nanotubes in Epoxy -- Investigating Behavior under Strain and Alignment Using Fluorescence Spectroscopy Tamika Thomas, Kena Senegal, Sarena Senegal, Paul Withey, Sergei Bachilo, R. Bruce Weisman Single-walled carbon nanotubes (SWCNTs) have been successfully embedded into EPON 862/W epoxy both with and without a surfactant. Applying strain to the nanocomposite permitted the interfacial adhesion between the SWCNT and host to be studied at the single-particle level using near-infrared fluorescence spectroscopy. Load transfer from the host to an embedded CNT is clearly observed as a shift in the nanotube's spectral emission. Loss of adhesion, or slipping, is also detected. Attempts at enhancing CNT-alignment within the nanocomposite will also be discussed. Near-infrared fluorescence imaging and spectroscopy prove to be ideal methods for monitoring the behavior of SWCNTs within nanocomposites, especially at the single-particle level. Much of this work has been carried out by undergraduate physics and chemistry majors. [Preview Abstract] |
Monday, March 21, 2011 5:18PM - 5:30PM |
D10.00015: An Ab-initio Study of Folded Armchair Graphene Nanoribbons Adam Iaizzi, Nam Lee, Lilia Woods We present a first principles approach to the characterization of armchair graphene nanoribbons folded along their long axis using density functional theory, along with ultrasoft psuedopotentials and the local density approximation for the exchange-correlation functional. Based on past studies, we anticipate that folding nanoribbons will produces changes in the band structure, possibly turning normally semiconducting nanoribbons into metallic nanowires. We determine the energy required to produce a number of different folded structures from nanoribbons as well as the energy and band structure as a function of width in single-fold structures. Ribbons as narrow as 13 carbon atoms formed stable folded structures. [Preview Abstract] |
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