Bulletin of the American Physical Society
APS March Meeting 2017
Volume 62, Number 4
Monday–Friday, March 13–17, 2017; New Orleans, Louisiana
Session E12: Undergraduate Research/SPS IVUndergraduate
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Sponsoring Units: SPS FED Chair: Crystal Bailey, American Physical Society Room: 271 |
Tuesday, March 14, 2017 8:00AM - 8:12AM |
E12.00001: Electro-spun PEDOT-PSS nano-ribbon transistor using ion-gel gate dielectric Deliris N Ortiz, Nicholas J Pinto Poly(3,4-ethylenedioxythiophene) doped with poly(styrenesulfonic acid)-PEDOT:PSS is a $p$-doped conducting polymer. Using the electrospinning technique, we have fabricated nano-ribbons of this polymer and deposited them on pre-patterned doped Si/SiO$_{2}$ wafers. Using the doped Si substrate as the back gate electrode and the SiO$_{2}$ as the dielectric insulator, the ribbon was characterized in a 3-terminal transistor configuration. No change in the channel current was observed for back gate bias under these conditions. We also used an ion-gel gate dielectric by placing a drop of the ion-gel over the ribbon and inserting a Au wire into the drop. By applying a bias to this contact (top gate), we were able to modulate the current through the ribbon at low voltages. The device operated like a field effect/electrochemical transistor, characteristic of a $p$-doped semiconductor with an on/off ratio of 350, threshold voltage of 0.7V, mobility of 5 cm$^{2}$/V-s, and a zero gate bias conductivity of 15 S/cm. The large specific capacitance of the ion-gel (as compared to SiO$_{2})$ and the formation of an electric double layer at the semiconductor/ion-gel interface was responsible for its operation below 2V. The device was also successfully tested at 100Hz making it useful in low frequency applications. [Preview Abstract] |
Tuesday, March 14, 2017 8:12AM - 8:24AM |
E12.00002: Raman Spectroscopy of 3-D Printed Polymers Vanessa Espinoza, Erin Wood, Angela Hight Walker, Jonathan Seppala, Anthony Kotula Additive manufacturing (AM) techniques, such as 3-D printing are becoming an innovative and efficient way to produce highly customized parts for applications ranging from automotive to biomedical. Polymer-based AM parts can be produced from a myriad of materials and processing conditions to enable application-specific products. However, bringing 3-D printing from prototype to production relies on understanding the effect of processing conditions on the final product. Raman spectroscopy is a powerful and non-destructive characterization technique that can assist in determining the chemical homogeneity and physical alignment of polymer chains in 3-D printed materials. Two polymers commonly used in 3-D printing, acrylonitrile butadiene styrene (ABS) and polycarbonate (PC), were investigated using 1- and 2-D hyperspectral Raman imaging. In the case of ABS, a complex thermoplastic, the homogeneity of the material through the weld zone was investigated by comparing Raman peaks from each of the three components. In order to investigate the effect of processing conditions on polymer chain alignment, polarized Raman spectroscopy was used. In particular, the print speed or shear rate and effect of strain on PC filaments was investigated with perpendicular and parallel polarizations. [Preview Abstract] |
Tuesday, March 14, 2017 8:24AM - 8:36AM |
E12.00003: Stand alone, low current measurements on possible sensing platforms via Arduino Uno microcontroller with modified commercially available sensors Meghan Tanner, Gabriel Henson, Indrajith Senevirathne Advent of cost-effective solid-state sensors has spurred an immense interest in microcontrollers, in particular Arduino microcontrollers. These include serious engineering and physical science applications due to their versatility and robustness. An Arduino microcontroller coupled with a commercially available sensor has been used to methodically measure, record, and explore low currents, low voltages, and corresponding dissipated power towards assessing secondary physical properties in a select set of engineered systems. System was assembled via breadboard, wire, and simple soldering with an Arduino Uno with ATmega328P microcontroller connected to a PC. The microcontroller was programmed with Arduino software while the bootloader was used to upload the code. High--side measurement INA169 current shunt monitor was used to measure corresponding low to ultra-low currents and voltages. A collection of measurements was obtained via the sensor and was compared with measurements from standardized devices to assess reliability and uncertainty. Some sensors were modified/hacked to improve the sensitivity of the measurements. [Preview Abstract] |
Tuesday, March 14, 2017 8:36AM - 8:48AM |
E12.00004: Memristor Circuitry via Material Implication Anna Wright, Nadine Gergel-Hackett Memristors are novel nanoelectronic devices that have advantages over traditional computer circuitry (eg., they are nonvolatile, two-terminal, and low power) and thus have potential circuit applications for both digital logic and memory. In this work, we used a simple memristor model that was designed to replicate the real-world electrical characteristics of previously fabricated and tested memristor devices. This model was developed and constructed with basic circuit elements using a free and widely available circuit simulator, LT Spice. We updated this model to more realistically simulate memristor behavior and then theoretically demonstrated that the model can be used to build memristor-based material implication gates (IMPLY gates). The development of these IMPLY gates is a critical step in the realization of memristor-based digital logic because they can be combined to act in place of any of the basic traditional logic gates (AND, NAND, etc), and thus enable efficient entirely memristor-based computing. [Preview Abstract] |
Tuesday, March 14, 2017 8:48AM - 9:00AM |
E12.00005: Molecular Modeling of a Probe in 2D IR Spectroscopy Anthony Cooper, Luca Larini Proteins must adopt a precise three dimensional structure in the folding process in order to perform its designated function. Although much has been learned about folding, there are still many details in structural dynamics that are difficult to characterize by existing experimental techniques. In order to overcome these challenges, novel infrared and fluorescent spectroscopic techniques have recently been employed to probe the molecular structure at the atomistic scale. These techniques rely on the spectroscopic properties of the nitrile group attached to a phenylalanine. In this study, we model this probe and we compute its properties in different solvents. This is done by performing Molecular Dynamics simulations with a PheCN solvated in water, urea and TMAO. We measure the decay rate of the vibrational stretching of the CN group in order to characterize the effects of different solvents on the local structure of the molecule. This data can be used to identify non-trivial conformational changes of the protein in the folding process. Preliminary results show agreement with current experimental data on 2D IR spectroscopy. [Preview Abstract] |
Tuesday, March 14, 2017 9:00AM - 9:12AM |
E12.00006: Intrinsic Mirror Birefringence Measurements for the Any Light Particle Search (ALPS) Claire Baum, Guido Mueller, David Tanner, Simon Barke, Zachary Bush, Giacomo Ciani, Hal Hollis, Tomoyuki Uehara, Gustavo Perez, Paul Fulda, Mauricio Diaz-Ortiz, Todd Kozlowski, Ryan Goetz, Joe Gleason The Standard Model is the most comprehensive theory of particle physics, yet it fails to explain phenomena such as dark matter. In the Any Light Particle Search (ALPS) experiment at the Deutsches Elektronen-Synchrotron (DESY), researchers are searching for weakly interacting sub-eV particles (WISPs). WISPs are predicted by extensions of the Standard Model that may explain dark matter and support string theory. The design of ALPS also allows researchers to measure the vacuum birefringence (BF) in a magnetic field. This vacuum magnetic BF (VMB) is predicted by QED and lacks experimental confirmation. ALPS researchers must know the BF of their optics and how it is affected by a magnetic field to make reliable VMB measurements. In my research, I used a heterodyne polarimeter to perform preliminary BF measurements on a mirror. For a mirror at 45$^{\circ}$ incidence, 0$^{\circ}$ incidence, and 0$^{\circ}$ incidence with an applied magnetic field, the effective path length difference between two 1064 nm laser beams was $\approx$26.6 nm, 4.871 $\pm$ 0.046 nm, and 16.58 $\pm$ 0.11 nm respectively. [Preview Abstract] |
Tuesday, March 14, 2017 9:12AM - 9:24AM |
E12.00007: All Optical Helicity Dependent Spin Switching Zachary Babyak, Tanner Latta, Mitsuko Korobkin, Guo-Ping Zhang It is known that the spin of an electron can be manipulated via an interaction with an external magnetic field. The phenomenon of all optical helicity dependent spin switching, or all optical switching (AOS), is novel method of spin manipulation which can invert a given spin via an interaction with an electric field in the form of ultrafast laser pulses on femtosecond timescales. In the following study, we demonstrate AOS is possible through our theory, by applying left and right circularly polarized light to a small electron spin system. We further demonstrate that AOS can be achieved through our theory using a small number of multiple laser pulses, suggesting it may align with experiment where the number of pulses is on the order of 10^3. [Preview Abstract] |
Tuesday, March 14, 2017 9:24AM - 9:36AM |
E12.00008: Time-Correlated Single-Photon Counting Fluorescence Imaging of Lipid Domains In Raft-Mimicking Giant Unilamellar Vesicles James Clarke, Kwan Cheng, Orrin Shindell, Exing Wang We have designed and constructed a high-throughput electrofusion chamber and an incubator to fabricate Giant Unilamellar Vesicles (GUVs) consisting of high-melting lipids, low-melting lipids, cholesterol and both ordered and disordered phase sensitive fluorescent probes (DiIC12, dehydroergosterol and BODIPY-Cholesterol). GUVs were formed in a 3 stage pulse sequence electrofusion process with voltages ranging from 50mVpp to 2.2Vpp and frequencies from 5Hz to 10Hz. Steady state and time-correlated single-photon counting (TCSPC) fluorescence lifetime (FLIM) based confocal and/or multi-photon microscopic techniques were used to characterize phase separated lipid domains in GUVs. Confocal imaging measures the probe concentration and the chemical environment of the system. TCSPC techniques determine the chemical environment through the perturbation of fluorescent lifetimes of the probes in the system. The above techniques will be applied to investigate the protein-lipid interactions involving domain formation. Specifically, the mechanisms governing lipid domain formations in the above systems that mimic the lipid rafts in cells will be explored. [Preview Abstract] |
Tuesday, March 14, 2017 9:36AM - 9:48AM |
E12.00009: Acoustic Properties of a Vibrating Plate in the Uniform Flow Dachuan Lu The characteristics of the sound produced by a vibrating plate is subtle and it is commonly occurred in the daily life. In this study, acoustic properties of the pure tone produced by a vibrating plate with in-plane tension in the uniform parallel flow is theoretically investigated by modifying Euler-Bernoulli beam equation combined with the mean flow theory. Explicit expression for the frequency of the pure tone is derived by eigenvalue method, in that all of the parameters can be measured in experiment. We find a new relation between the square of the frequency and the tension and the flow velocity, as $f^2\propto U^2+aT+b$, where $a$ and $b$ are constant. On the basis of our formula, the sound frequency can be precisely described. Meanwhile, the effects of the flow velocity and in-plane tension on the frequency and intensity of the sound have been investigated experimentally, our experiments have a good agreement with the theoretical results. [Preview Abstract] |
Tuesday, March 14, 2017 9:48AM - 10:00AM |
E12.00010: Topological Transformation of Defects in Nematic Liquid Crystals Zachary Pagel, Timothy Atherton, Jeffrey Guasto, Peggy Cebe A topological transformation around silica microsphere inclusions in nematic liquid crystal cells (LCC) is experimentally studied. Silica microspheres are coated to induce homeotropic LC anchoring to the spheres. Parallel rub directions of the alignment polymer during LCC construction create a splay wall that traps the microspheres. Application of an out-of-plane electric field then permits a transformation of hedgehog defects, reversing the orientation of the defect around microspheres. The transformation controllably reverses the microsphere's direction of travel during AC electrophoresis due to defect-dependent velocity anisotropy. A similar transformation is studied on chains of microspheres with hedgehog defects, where the defect orientation is reversed on the entire chain. Polarized and confocal microscopies are used to study the defect structures. Results contribute to recent developments in microsphere electrokinetics in nematic LCs, as the transformation adds an additional degree of control in the electrophoretic motion of microspheres and chains of microspheres with dipolar defects. [Preview Abstract] |
Tuesday, March 14, 2017 10:00AM - 10:12AM |
E12.00011: Reconstructing Solvent Density of Myoglobin Unit Cell from Proximal Radial Distribution Functions of Amino Acids Madeline Galbraith, GC Lynch, BM Pettitt Understanding the solvent density around a protein crystal structure is an important step for refining accurate crystal structures for use in dynamics simulations or in free energy calculations. The free energy of solvation has typically been approximated using an implicit continuum solvent model or an all atom MD simulation, with a trade-off between accuracy and computation time. For proteins, using precomputed proximal radial distribution functions (pRDFs) of the solvent to reconstruct solvent density on a grid is much faster than all atom MD simulations and more accurate than using implicit solvent models. MD simulations were run for the 20 common amino acids and pRDFs were calculated for several atom type data sets with and without hydrogens, using atom types representative of amino acid side chain atoms. Preliminary results from reconstructions suggest using a data set with 15 heavy atoms and 3 hydrogen yields results with the lowest error without a tradeoff on time. The results of using precomputed pRDFs to reconstruct the solvent density of water for the myoglobin (pdb ID 2mgk) unit cell quantifies the accuracy of the method in comparison with the crystallographic data. [Preview Abstract] |
Tuesday, March 14, 2017 10:12AM - 10:24AM |
E12.00012: Analysis of AtCry1 and Mutants Derek Burdick, Adam Purvis, Margaret Ahmad, Justin J Link, Dorothy Engle Cryptochrome is an incredibly versatile protein that influences numerous biological processes such as plant growth, bird migration, and sleep cycles. Due to the versatility of this protein, understanding the mechanism would allow for advances in numerous fields such as crop growth, animal behavior, and sleep disorders. It is known that cryptochrome requires blue light to function, but the exact processes in the regulation of biological activity are still not fully understood. It is believed that the c-terminal domain of the protein undergoes a conformational change when exposed to blue light which allows for biological function. Three different non-functioning mutants were tested during this study to gain insight on the mechanism of cryptochrome. Absorbance spectra showed a difference between two of the mutants and the wild type with one mutant showing little difference. Immunoprecipitation experiments were also conducted to identify the different c-terminal responses of the mutants. By studying non functioning mutants of this protein, the mechanism of the protein can be further characterized. This two-month research experience in Paris allowed us to experience international and interdisciplinary collaborations in science and immerse in a different culture. [Preview Abstract] |
Tuesday, March 14, 2017 10:24AM - 10:36AM |
E12.00013: Period doubling bifurcation in the zebrafish heart James Farmer, Conner Herndon, Ilija Uzelac, Flavio Fenton The study of voltage and calcium alternans in electrocardiology has vast implications in the medical field. By analyzing the bifurcations of restitution curves, we may be able to better understand the path that leads a heart into fibrillation. Zebrafish are becoming a valuable model organism for scientific research as it has many characteristics that make it useful for studying human genetics and disease. In this case, a period two bifurcation when paced at high rates. In this talk we present experimental and theoretical results for this bifurcation. We record zebrafish voltage and calcium signals via optical mapping at high spatiotemporal resolution with JPW-6003 and Rhod-2 ratiometric dyes for voltage and calcium, respectively. We find that: (1) alternans (period two) are present at pacing cycles in the range of 250ms to 150ms; (2) that alternans are enhanced when calcium is strongly reduced, indicating that the bifurcation is driven by voltage; and (3) experimental results can be reproduced by a one dimensional map model of a restitution function. [Preview Abstract] |
Tuesday, March 14, 2017 10:36AM - 10:48AM |
E12.00014: Thermodynamic Properties of Protein Folding Process Vattika Sivised, Theja De Silva Proteins are one of the fundamental building blocks of life and they are present in almost all biological and cellular processes. Proteins consist of amino acids held together in a long chain by peptide bonds. When proteins function in biological processes, they \emph{fold} in to three-dimensional structures by curling the chain. The folding of a peptide chain into a three dimensional structure is a thermodynamically driven process such that the chain naturally evolves to form domains of similar amino acids. The formation of this domain occurs by curling the one dimensional amino acid sequence by moving similar amino acids proximity to each other. We model this formation of domains or “ordering of amino acids” using q-state Potts model and study the thermodynamic Properties using a statistical mechanics approach. Converting the interacting amino acids into an effectively non-interacting model using a mean-field theory, we calculate the Helmholtz free energy (HFE). Then by investigating the HFE, we qualitatively study the properties of protein folding transition. We find that the protein folding phase transition is strongly \emph{first} order and the specific heat shows the experimental signatures of this phase transition. [Preview Abstract] |
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