Bulletin of the American Physical Society
2018 Annual Meeting of the APS Mid-Atlantic Section
Volume 63, Number 20
Friday–Sunday, November 9–11, 2018; College Park, Maryland
Session B01: Poster Session (Day 1) |
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Chair: Wendell T. Hill, III, University of Maryland, College Park Room: Edward St. John Lounge |
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B01.00001: Photodissociation Dynamics of SO2 from the Electronically Excited C State Paul B Diss, Christopher R Lukowski, Andrew J Pommersheim, Amy S Mullin The early earth rock record shows unusual sulfur mass independent fractionation that is potentially caused by the UV photodissociation of SO2. We investigate the dynamics of SO2 photodissociation from the electronically excited C state, using tunable, pulsed UV light (λ = 210-220 nm) to initiate the dissociation and state-resolved high-resolution transient IR spectroscopy to measure the appearance of SO(v=0) product state. Individual ro-vibrational states of nascent SO products are measured along with the fluorescence excitation spectrum to determine anisotropy parameters and the dissociation quantum yield. UV wavelength dependent studies were used to obtain rotational energy distributions. The measurements near the photodissociation threshold at λ = 220 nm provide insight into the dissociation dynamics of SO2 from the C state. |
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B01.00002: The Intrinsic Density of a Nanoconfined Liquid Samuel R Cohen, John S Bender, Benoit Coasne, John T Fourkas Liquids confined to nanoscale geometries are ubiquitous in nature and important in many areas of science and technology. However, connecting the microscopic structure and dynamics of a confined liquid to its macroscopic behavior is a fundamental, unsolved problem in liquid-state physics. One key macroscopic property, the density, is highly fluid-dependent, and there is currently no rigorous way of assessing a confined liquid’s accessible volume. Here we present our work using the spectrum of intermolecular vibrational modes to probe the intrinsic density of a confined liquid. In particular, molecular simulations to probe the density will be discussed. |
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B01.00003: A colloidal lithography route to zero mode waveguides. Ryan M. Jamiolkowski, Kevin Y. Chen, Shane A. Fiorenza, Alyssa M. Tate, Shawn H. Pfeil, Yale E. Goldman Zero mode waveguides (ZMWs) are nano-apertures in a conducting film that enable single-molecule fluorescence measurements in the presence of up to micromolar concentrations of probes in solution. Here, we report on a method for fabricating ZMWs using a self-assembled mask made of polystyrene microspheres, thermal annealing, and metal evaporation. Data is presented characterizing the performance of these devices. Importantly, this fabrication technique provides a route to fully functional ZMWs without the need for expensive electron beam or deep-UV lithography. |
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B01.00004: Variation of Parameters in Metal-Assisted Catalytic Etching Joseph D Swanson, Benjamine M Roe, Teresa Lee, Kurt Wolfgeng Kolasinski, Shawn H Pfeil, Konstantin Tamarov Porous silicon powders were produced by Ag-catalyzed etching in an aqueous solution of HF and CH3COOH to which H2O2 is injected. This research investigates how variations in the amount of Ag and H2O2 as well as the injection time affect metal-assisted catalytic etching (MACE). This was done by analyzing the percent yield of the product and by examining SEM images of the products before and after exfoliation of silicon nanowires (SiNW). Atomic force microscopy (AFM) analysis was also used to characterize the size and aspect ratios of the nanowires. We demonstrate that the amount of silver catalyst that was used during etching, the time of the etching, and the amount of hydrogen peroxide that was used can be used to control the structure and yield of the product of MACE. |
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B01.00005: Stereo-chemical Analysis of Surface Functionalized C60 and Radiotracers Used in Detection of Tumor Cells and Alzheimer’s Disease Mia Moon, Amanda Kyung In the case of the neurodegenerative diseases such as Alzheimer’s Disease (AD), an accumulation of a misfolded protein called beta amyloid form amyloid plaques between nerve cells in the brain. While the occurrence of these neuronal degeneration is still unclear, research suggests that these amyloid molecules produce free radicals and induce oxidative stress in the brain. Under such oxidative stress, reactive oxygen species (ROS) are overproduced and trigger a chain of reactions. In recent years, multi-target directed ligands (MTDLs) have been effective tools in various medical treatments. In AD, fullerene molecules can be used to deliver electrons to the free radicals that cause damage to neurons. The purpose of this research paper is to study the efficiency of delivering electrons to the ROS in the brain by using C60 fullerene derivatives. Using the molecular editing software, various information was extracted about fullerenes and other forms of C60 molecules with different types of elements and compounds bonded to them. Optimization energies (kJ/mol) of the molecules were found and used to determine the stability of the molecules while dipole moments were used to determine the reactivity and efficiency of the molecule to donate or accept electrons from the ROS molecules. |
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B01.00006: Stereo-chemical Analysis of Nano-scaled Biomolecules and Reactive Oxygen Species (ROS) in Cancer Disease Lauren Chung, Ho Jeong Kwon Multiple pathways through oxidative stress can cause cancer via cell injury. The oxidative reactions in biomembranes are particularly important, because it can result in the impairment of lipid–protein interaction, modification and fragmentation of membrane proteins. A free-radical chain reaction capable of propagating in space is the major oxidative reaction in biomembranes. Information on the subcellular localization of oxidative stress is not provided in detail so far. It is highly desirable to visualize the activities of Reactive Oxygen Species (ROS) causing cancer and antioxidants in living cells on a nano-scaled level for the proper mechanism of the role of fullerene derivatives and metal oxides. This project aims to determine the thermodynamic stability of various compounds used in cancer treatment using a computational chemistry. Density Functional Theory (DFT) is used in order to model the electron properties of the fullerenes and metal oxide compounds. Molecular editing programs such as Avogadro and Chemcraft allow performing such computations for those compounds. The programs show the optimized geometry energy levels and they fully determines the theoretical values of the structure’s atomic properties. |
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B01.00007: Stereochemical and thermodynamic analysis of functionalized chocolate molecules and their derivatives: Applications in food and molecular chemistry Richard Kyung, Jiho Song Theobromine contains several psychoactive chemicals such as Phenylethylamine, Theophylline, and Tele-methylhistamine that it dramatically impacts blood pressure and sugar levels. Theobromine is an isomer of theophylline, which is a bitter alkaloid of the cacao plant and it is used as heart stimulant instigating the body to naturally produce fat-burning hormones. Pharmaco-toxicological and clinical studies with psychoactive chemicals show that digestion of a substantial amount of the product induces greater alertness or feelings of contentment. In this paper, biophysical and pharmacokinetic modeling on the chocolate molecules and their derivatives has been performed by computational and theoretical methods. The commercial programs and freewares such as Avogadro and Chemcraft have been used in an effort to discover the optimal method and to compute the enthalpy of each product. This research utilizes computational optimization theory, DFT, that can determine the physical and chemical properties of the molecules as well as the efficiencies. Optimization configuration energies were collected for all the chocolate molecules to compare chemical compounds’ stability.
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B01.00008: On the reversibility of granular rotations and translations Zackery A Benson, Anton Peshkov, Michelle Girvan, Derek C. Richardson, Wolfgang Losert We analyze reversibility of both displacements and rotations of spherical grains in three-dimensional compression experiments. We track grain motion during cyclical compression achieved via compressing a moving wall in a rectangular box. Using transparent acrylic beads with cylindrical holes and index matching techniques, we are not only capable of tracking displacements but also, for the first time, rotations. We observe that for compression amplitudes up to the bead diameter, the bead's translational displacements after each cycle eventually become mostly reversible. By contrast, granular rotations appear to be largely irreversible. Our results indicate a weak correlation between translational and rotational displacements, indicates that rotational reversibility depends on more subtle changes in the contact distributions and contact forces between grains compared with displacement reversibility. These experimental results are corroborated by our molecular dynamics simulations. |
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B01.00009: Broadband terahertz time domain spectroscopy with a femtosecond oscillator laser Jimmy Iannone, Dogeun Jang, Ki-Yong Kim We have investigated broadband coherent terahertz (THz) generation and detection using a femtosecond oscillator laser. Our time-domain THz spectroscopic system adopts nonlinear crystals to generate and detect broadband (0.1~10 THz) THz radiation. Here we have used various nonlinear crystals (ZnTe, GaP, and LiNbO3 in many different thicknesses) as THz emitters and detectors and optimized their performance to maximize THz output power and/or spectral bandwidth. In particular, thin (0.1-0.3 mm) GaP crystals are used to achieve a large spectral bandwidth (~10 THz) with moderate laser power (<400 mW). |
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B01.00010: Ultrafast response of thin film vanadium dioxide grown on titanium dioxide doped with niobium Scott E Madaras, Jason Creeden, Douglas Beringer, Irina Novikova, R. Ale Lukaszew We have studied vanadium dioxide (VO2) films grown on titanium dioxide (TiO2) substrates to investigate the properties of the heterojunction that forms at the interface between substrate and film with the purpose of applying it as an UV photodetector. The use of niobium as dopant on TiO2 substrates has been shown to favorably modify the energy levels at the heterojunction thus promoting photocurrent generation when illuminated with UV light. To further investigate this electronic structure modifications we study the ultrafast dynamics of the insulator-metal-transition (IMT) in such samples by using a pump probe configuration. The samples are pumped with ~150 fs pulses of 400nm wavelength light, and the changes in electronic structure of the heterojunction region are detected via change in relative optical reflectance (∆R/R) of a 800nm probe light. The VO2 on TiO2:Nb doped samples generate distinctive ∆R/R effects compared with the VO2films deposited on plain TiO2substrates samples that are undoped. |
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B01.00011: Towards an in situ, full-power intensity profiler for petawatt-class lasers Calvin Z He, Wendell Talbot Hill A technique to measure the intensity profile of a focused laser pulse at full power is a long-standing desire. Nearly 40 years ago, Sarachik and Schappert suggested an approach, and worked out many of the details, to measure the intensity that is based on relativistic Thomson scattering (RTS), which consists of a rich spectrum of Doppler shifted radiation of the laser light, and its harmonics. It is straightforward to show that intensities can be extracted from the nth-order RTS harmonic spectrum from: I(λ,θ;n)=2πmec3/[r0λ02(1-cos2θ)](nλ/λ0-1), where λ0, λ, me, r0, θ, n and c are the laser wavelength, nth harmonic wavelength, the electron mass, classical electron radius, angle of observation, harmonic order and speed of light respectively. This expression was recently used to measure the intensity of VEGA 2, 200 TW pulses generated at the Centro de Láseres Pulsados (CLPU) facility in Salamanca, Spain. Specifically, 30 fs pulses with energies between 1 and 2.5 J were focused to w0 ~ 20 μm and captured by microscope objectives and dispersed by an Andor iStar spectrometer. This presentation will include a description of the apparatus, our initial results and a discussion of prospects for exploiting RTS to develop an in situ intensity profiler for intensities above 1018 W/cm2. |
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B01.00012: Single Photons for a Modular Ion Trap Quantum Network Sophia Scarano, Martin Lichtman, Clayton Crocker, Ksenia Sosnova, Allison Carter, Christopher Monroe Trapped atomic ions of different species are an ideal candidate for a modular quantum computing network partially due to low crosstalk between memory and communication qubits. A dual species Yb+/Ba+ ion trap is used to create entanglement between memory spin qubits and photonic qubits. The flying qubits are emitted via the 6S1/2 ↔ 6P1/2 transition in 138Ba+. It is advantageous to excite the atom on the 5D3/2 ↔ 6P1/2 transition at 650 nm, while still collecting 493 nm photons. This removes the excitation light as a source of noise and reduces double excitation errors. Most significantly, the D ↔ P transition allows us to use a slower excitation, such that instead of requiring a picosecond pulsed laser, we can gate a CW laser using AO modulators. We demonstrate a single photon source for quantum networking based on a trapped barium ion subject to pulsed excitation with a second-order coherence of g(2)(0) = (8.1 ± 2.3) × 10-5 without background subtraction, a state-of-the-art result for replicable single photon sources. |
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B01.00013: Creating and imaging atomic wave functions beyond the diffraction limit Tsz-Chun Tsui, Sarthak Subhankar, Yang Wang, Przemyslaw Bienias, Mateusz Lacki, Mikhail Baranov, Alexey Gorshkov, Peter Zoller, James V Porto, Steven L Rolston In cold atom experiments, the application of optical fields is the cornerstone for the manipulation and imaging of atoms. The wavelength of the light field sets a limit on the size of features that can be resolved. To beat this diffraction limit, we exploit the non-linear optical response of a three-level atom coupled by two light fields and create ultra-narrow potential barriers with widths less than lambda/50, physically realizing a Kronig-Penney potential. We also demonstrate a new imaging technique for probing the wavefunction of atoms trapped in an optical lattice with a spatial resolution of lambda/50 and a sub-microsecond temporal resolution, thereby introducing super-resolution microscopy to the field of cold atom systems. With this technique, we study the static and dynamic properties of the wavefunctions of atoms in the unit cell of an optical lattice. |
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B01.00014: Optimization of Polarization Self-Rotation Squeezing in Rubidium Vaporvia Spatial Optimization of the Pump Beam Austin Kalasky, Eugeniy Mikhailov High precision optical detection is fundamentally limited by quantum noise. Such limits can be bypassed with the use of squeezed states of light with modified quantum noise. We study squeezed states of light, with a focus on optimization of squeezing generated via polarization self-rotation (PSR) in hot Rubidium vapor. The goal of our research is to reduce quantum noise by optimizing various experimental parameters, such as cell temperature and focusing parameters of the input pump field. After such preliminary optimization, we found that the squeezing level is optimal for the temperature of Rb vapor of 69-70°C, reaching quantum noise suppression around 2.3 ± 0.10 dB below shot noise. Currently, we focus on optimization of the spatial intensity and phase profile of the pump field, using complex amplitude and phase cluster masks. |
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B01.00015: Optical Angular Momentum manipulations in a Four Wave Mixing process Nikunj Prajapati, Nathan P Super, Robert N Lanning, Irina Novikova, Jonathan P Dowling We investigate the spatial and quantum intensity correlations between the probe and Stokes optical fields produced via four-wave mixing in a double-λ configuration. When both fields carry non-zero optical orbital angular momentum (OAM), we observed that the topological charge of the generated Stokes field obeyed the angular momentum conservation law and that the intensity squeezing between the two fields were mostly independent on their OAM value. We also investigated the case of a composite-vortex pump field, containing two closely-positioned optical vortices, and showed that the generated Stokes field carried the OAM corresponding to the total topological charge of the pump field. Our current work focuses on showing squeezing and polarization entanglement using a dual-rail experimental arrangement, for which we are developing a simplified version of a truncated SU (1,1) interferometer. |
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B01.00016: Design of Magneto-Ellipsometer with Vortex Beam Capability K. Watt, Z. Oertel, T. N. Stanislavchuk, A. A. Sirenko We present a design of an optical system for measuring ellipsometric spectra in a magnetic field up to 7T and at low temperatures down to 5K. Synchrotron radiation at NSLS-II, BNL will be used as a light source. Conversion of synchrotron radiation into a source of vortex beam with a non-zero orbital angular momentum (OAM) is also developed. The optical setup will be operational in broad-band spectral range from 20 cm-1 up to 4000 cm-1 using Si axicone retarders producing OAM with l=+/-1. Beams with higher order OAM l=+/-1, +/-2, +/-3, +/-4 and +/-5 will be achieved with a motorized phase-shifting spiral mirror with continuous plate and staircase designs. Quantum materials will be studied using vortex beams. This work is supported by NFS-MRI grant. |
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B01.00017: Dispersion Enhanced Laser Frequency Response via Four-wave Mixing in an Active Cavity Savannah Cuozzo, Eugeniy Mikhailov Lasers are used for precision metrology, and by introducing a dispersive medium into the cavity, one can drastically enhance the sensitivity of such devices. We present experimental results demonstrating enhanced and suppressed lasing-frequency response to cavity-length variations in an active ring laser. Pumping on an N-type level scheme in $^{87}$Rb, we tune the cavity dispersion by varying experimental parameters, such as pump-laser frequency, atomic density, and pump power. As a result, we can control the sensitivity of the laser so that the lasing-frequency response to the empty cavity length change is increased greater than a factor of 2 in the enhanced regime and completely eliminated in the suppressed regime. |
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B01.00018: The Unruh Effect: Insight from the Laws of Thermodynamics Stephen J Crothers, Pierre-Marie L Robitaille When an observer experiences uniform acceleration it has been postulated that empty space will appear as an infinite extent emitting a blackbody spectrum at a temperature proportional to the acceleration: the Unruh Effect. The Effect has been tied to the Hawking temperature of a black hole and is purportedly one account of the origin of black hole thermal emission, where the acceleration in the black hole case is due to gravity. The Unruh and Hawking temperatures have the same mathematical form: T = ha/4π2ckB, were T is temperature, h is Planck’s constant, a is acceleration, c is the speed of light in vacuo, and kB is Boltzmann’s constant. Acceleration for Hawking temperature is a = GM/(rS)2 where rS = 2GM/c2 (Schwarzschild radius) where G is the universal constant of gravitation, M the black hole mass. Temperature is always an intensive property. Acceleration is not an intensive property. The Unruh temperature, as with the Hawking temperature, although dimensionally balanced, is not thermodynamically balanced. Temperature cannot be equated to a term, or combination of terms, that is not intensive. The Unruh temperature therefore, violates the 0th and 2nd laws of thermodynamics, as does Hawking temperature. Consequently, it is invalid. The Unruh Effect does not exist. |
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B01.00019: Lattice Simulation of Gravitational Wave Spectra from Varying Reheating Models Gibson H Porter IV, Jeffrey M Hyde During reheating, gravitational waves could be produced. The spectrum of these gravitational waves could teach us something about the inflation potential and possible couplings to other fields. In principle, such a gravitational wave spectrum could be observed today. We are studying gravitational wave production using a lattice simulation and analytic analysis, with the goal of directly relating features of the spectrum to underlying models. We will show our preliminary results in comparison to a few well-studied models. |
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B01.00020: Application of a Retired Burst Gravitational Wave Data Analysis Method to Investigate the Origin of the Blip Glitch Sarah Choate, Amber Stuver The Laser Interferometer Gravitational-Wave Observatory (LIGO) is a collaboration with the goal to observe and study events that create gravitational waves detectable on Earth. During the process of data acquisition, glitches in the data can occur as a result of the observation of transient noise. One class of these glitches that occurs in burst data analysis is the blip glitch, which results in an almost identical signal to that of a gravitational wave detection and has an unknown origin. SLOPE is a data analysis method originally used for gravitational wave detection. This research has redeveloped SLOPE for the purpose of investigating glitches and has readied the algorithm to be applied to auxiliary channels to search for glitches. Results presented include operating parameters for which SLOPE can be effectively run. |
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B01.00021: Biomedical Analysis of Amine Compounds Causing Cancer Using Computational and Chemical Simulations Yeon Su Park, Elise Kang In this research, the biomedical and thermodynamic stability of ammonia derivatives were studied in the light of their potentially harmful role in cosmetic products. For instance, pigments in cosmetics such as amine compounds contain restrictions for their usage due to the fact that they release carcinogens. A certain commercial products show rather low in toxicity and are can be safely used for patients, having shown that there is an absence of evidence of carcinogenicity. Other compounds show immediate side effects such as rashes or long-term side effects. The focus of this paper is the stereochemical stability and toxicity of ammonia compounds which
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B01.00022: Diffusive and Deterministic Transport in Gels Nathalya Ramirez, Mark E Reeves We present a novel lab for teaching diffusion and electrostatics in ionic solutions. Two challenging topics in our introductory university physics course with a bio focus are diffusion and electrostatics in salty solutions. In the diffusion unit, the students work through a laboratory in which they observe two dyes diffuse in agarose gels. In the second semester course, electrostatics is introduced and the students investigate and model interactions between charges in conducting solutions. We developed a new laboratory in which the students investigate the movement of dye molecules with different charges and sizes under electric field in agarose gels. In this lab, the students make observations in gels made with pure water, as well as in media prepared with salt and buffered solution. The lab also allows students to use image analysis to determine pH change, how far the dyes have traveled, the effect of additional ions in the solution on the dyes and their interactions in different media, the change in current over time, and to estimate the unknown molar mass of one of the dyes. |
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B01.00023: Nanoprobe Diffusion in Concentrated Polyethylene Glycol Solutions Keyanna Ryan, Julius Allen, Hacene Boukari We applied fluorescence correlation spectroscopy (FCS) to measure changes of the translational diffusion of several nanoprobes (Alexa488, fluorescein, GFP proteins) dispersed in Polyethylene Glycol (PEG) solutions prepared at different concentrations (up 900 mg/ml). The measured FCS correlations of each nanoprobe showed a systematic and uniform shift to longer delay times, indicating slowing down of the diffusion. Further, the measured FCS correlations could be readily fit with the closed-form expression describing freely diffusing nanoparticles. The concentration dependence of the nanoprobe diffusion could not be accounted for by the corresponding increase of the bulk viscosity of the PEG solution as would be suggested by the Stokes-Einstein relation. Instead, we fitted the data with a stretched exponential [exp(-acn)] where c denotes the PEG concentration, n is related to the solvent quality, and a is proportional to the hydrodynamic size of the diffusing nanoprobe. We determined that n is close to 3/4, indicating that water solvent is good solvent and that a is proportional to the nanoprobe size. |
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B01.00024: Electrotaxis and actin wave dynamics across cell types Abby L Bull, Qixin Yang, Leonard J Campanello, Matt Hourwitz, John T Fourkas, Wolfgang Losert Electric fields are instrumental in various life processes including wound healing, embryonic development and cancer metastasis via directing cell migration. Few studies have focused on intracellular dynamics of cells in electric fields to better characterize electrotactic responses or determined how electric fields affect cells in a dynamic manner. Here, we investigate actin steady states, waves and oscillations under direct current electric stimulation to better understand electrotaxis of neutrophil-like HL60 cells and model organism Dictyostelium. Both cell types have fast dynamic actin waves that may be influenced by the electric field as well as by nano-topographical surfaces and biochemical cues. Additionally, variances in cell sizes enable us to explore actin dynamics on different scales. |
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B01.00025: Comparison of Dark-Field Microscopic and Fluorescence Spectral Studies on the Interaction of AuNPs/AgNPs with GUVs Sanna Kamara, Tiana Cooks, Qi Lu Giant unilamellar vesicles (GUVs) are well-established model systems for studying lipid packing and membrane dynamics. With diameters in tens of microns, GUVs are easily observable using optical microscopy. Gold nanoparticles (AuNPs) are well known for their biocompatibility and biomedical applications in drug and gene delivery. Meanwhile, silver nanoparticles (AgNPs) have long been known for their potent antimicrobial and anti-inflammatory effects for such applications as biomedical implants. In this study, we compare morphological data from the dark-field microscopy and the spectral data from the fluorescence of a lipid packing probe to understand how AuNPs and AgNPs interact with GUVs in different ways. What’s learned from this study can be used for future applications in nanomedicine and nanotechnology. |
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B01.00026: Comparison of 440 Hz vs. 432 Hz Tuning through EEG of Human Brain Waves Romuald Kenmegne, Qi Lu 440 Hz is the standard pitch of the musical note A4 above middle C, which was adopted for the tuning of musical instruments by the International Organization of Standardization (ISO) in 1955 and reaffirmed in 1975. On the other hand, there is a recent movement of returning the music tuning to A4=432 Hz, a scientific pitch that leads to middle C being at 256 Hz, the eighth power of 2. Many music uploads tuned at 432 Hz on YouTube.com are claimed to render relaxation and healing for the brain. There was even better audience response reported for music performances tuned to 432 Hz. In this investigation, we collected human brain waves (including alpha, beta, delta and theta waves) upon external sound stimuli tuned at 440 Hz and 432 Hz, with a BIOPAC system through the EEG (electroencephalogram) setup. EEG is the recording of the brain’s activity through electrodes placed on the scalp in detection of the collective electrical activity from thousands of neurons right beneath. The EEG data collected from the human subjects will be analyzed for evaluation and comparison of the effects of sounds tuned at 440 Hz vs. 432 Hz on human brain waves. |
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B01.00027: Nanoprobe Diffusion in Concentrated Polyethylene Glycol Solutions Keyanna Ryan, Julius Allen, Hacene Boukari We applied fluorescence correlation spectroscopy (FCS) to measure changes of the translational diffusion of several nanoprobes (Alexa488, fluorescein, GFP proteins) dispersed in Polyethylene Glycol (PEG) solutions prepared at different concentrations (up 900 mg/ml). We found that the measured FCS correlations of each nanoprobe showed systematic and uniform shift to longer delay times, indicating slowing down of the diffusion. Further, the measured FCS correlations could be readily fit with the closed-form expression describing freely diffusing nanoparticles. Remarkably, changes of the diffusion due to PEG concentration could not be accounted for by the corresponding increase of the bulk viscosity of the PEG solution as would be suggested by the Stokes-Einstein relation. Instead, we fitted the concentration dependence of the diffusion coefficient with a stretched exponential [exp(-acn)] where cdenotes the PEG concentration, nis related to the solvent quality, and ais proportional to the hydrodynamic size of the diffusing nanoprobe. We determined that nis close to 3/4, indicating that water solvent is good solvent, and that ais proportional to the nanoprobe size.
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B01.00028: Feedback and Learning: Lessons from the pocket guitar Adebanjo A Oriade Student centered active learning depends on use of feedback. In this presentation we explore different dimensions of feedback - kind and utility. This is a presentation of effects, on learning and instruction, of tuning an assessment from a primarily summative exercise to (in addition) partly formative in nature. This happend in a physics for non-science majors course. The weekly quizzes are primarily summative but when, after grading the quizzes students were afforded the opportunity to reclaim up to 10% of the maximum credit back, it became a partly formative assessment. Students earned points back by visiting with an instructor (including Graduate teaching assistants) and explaining what they missed, why the error happened and how it can be fixed. Data from meetings with students was recorded and analyzed. Reflections from the analysis will be presented. This instructor gets a personal glimpse of how hard learning can be by learning a new skill: playing a score with a guitar. To support learning this new skill the pocket guitar was purchased - it became a metaphor for the effects diverse kinds of feedback, used in optimal ways, has on learning. |
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B01.00029: Developing new experimental techniques to understand neuronal networks Samira Aghayee, Patrcik Kanold, Wolfgang Losert All optical manipulation and read out of neuronal activity has provided new opportunities for investigating neuronal network dynamics in real time. However there exists technical issues that need to be overcome to allow these techniques to reach their potential. To correct for the persistent jitter that is present in in-vivo recordings we introduced a particle-tracking based motion correction algorithm that is fast enough for realtime motion compensation. The speckles and non-uniform existing in holographic illumination prevents reliable targeting of neurons. To address this problem and to preserve the optical accessibility of the FOV we use a non-conventional optical configuration that implements a virtual lens. Finally, to over come the limited time resolution induced by the refreshing rate of the spatial light modulator, we implement a fast switching holographic technique that is capable of targeting different neurons on relevant timescales to activity propagation. |
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B01.00030: Collective dynamics over long time scales and large length scales reveals distinct cell migration phenotypes Rachel Lee, Haicen Yue, Christina Stuelten, Wouter-Jan Rappel, Carole Parent, Wolfgang Losert In this study, we investigate multiple length and time scales in the collective migration of cell sheets and show that particle image velocimetry (PIV) based measurements yield insight into biological mechanisms. Comparing experimental PIV flow fields from migrating cells to the behavior of simulated cell groups, we connect individual cell properties to collective behavior over the millimeter-scale of the cell monolayer. We find that cell migration at the boundary can affect migration within the monolayer without the need to specify large-scale features in the simulations. In addition to tissue-scale trends in collective behavior, migrating cells have localized dynamic features which can change over multiple time scales. We developed a set of measurement techniques to extract multiple features of collective motion, and apply these techniques to both non-malignant and tumorigenic breast epithelial cells. |
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B01.00031: A Method for the Large-Scale Production of Nanotopographical Surfaces for Cellular Studies Matt J Hourwitz, Xiaoyu Sun, Eleni M Baker, Sebastian Schmidt, Wolfgang Losert, John T Fourkas The physical environment of cells impacts their behavior and plays a role in biological processes. Finding ways to mimic in vivo characteristics of cells’ physical surroundings can give a clearer picture of their response to natural textures. We developed a method for fabricating patterns of arbitrary shape and replicating them on a large scale for use in cellular studies. Multiphoton absorption polymerization (MAP), a two-photon lithographic technique, was used to design and fabricate the topographical features. Solvent-assisted nanotransfer molding allowed for the creation of a negative-relief mold made of poly(dimethylsiloxane) (PDMS). Replica molding, with this PDMS mold and a photocurable resin, can reproduce the original pattern made with MAP. The replica nanotopographies can be adapted to fit specific experimental requirements, including surface coating. The patterned films have been shown to be biocompatible. To demonstrate their use, we examined the cytoskeletal arrangement of MCF10A cells on one nanotopographical pattern. |
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B01.00032: CHARACTERIZATION OF HALOTAG FLUORESCENT LIGANDS IN PLANT AND ANIMAL MODEL SYSTEMS Tiana Cooks, Timothy Chaya, Alex Nedo, Kun Huang, Ramona Neunuebel, Jeffrey Caplan The isolation of green fluorescent protein (GFP) from the jellyfish revolutionized cell biology, making it possible to tag proteins for localization and dynamics by light microscopy. However, FPs still suffer from low brightness and photostability compared to fluorescent dyes. This lead to the development of genetically-encoded tags that bind to fluorescent dyes, specifically the HaloTag, a modified haloalkane dehalogenase that irreversibly binds a ligand. Like FPs, it only requires a single genetically-encoded fusion construct, but it has the superior photophysical characteristics of fluorescent dyes, yet, is still difficult to use in some organisms, such as plants, due to low cell permeability. Here we show that a newly developed HaloTag fluorescent ligand has a high permeability in plants compared to Promega TMR ligand normally used. Overall, the JF dyes extend the advantages of HaloTag to plants and provide new, fluorescent ligands for researchers using mammalian cells. |
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B01.00033: Long-term Brillouin imaging of live cells with reduced photodamage at 660nm wavelength Milos Nikolic, Giuliano Scarcelli Brillouin microscopy is an all-optical, non-contact method for characterizing mechanical properties of materials by measuring the spectrum of light which scatters from spontaneous (thermally induced) density waves inside a material. Due to the weak efficiency of the scattering, for Brillouin imaging of live samples, photodamage imposes a significant limitation on both speed and the SNR. To overcome this barrier, we evaluated Brillouin microscopy at different illumination wavelengths. We show that red wavelengths represent the best compromise between scattering efficiency (proportional to λ-4) and minimal photodamage. We demonstrate that a Brillouin microscope based on 660 nm laser has a significantly higher limit on illumination powers that can be used to image live cells due to the reduced photodamage of 660 nm light, compared to standard 532 nm lasers. Low photodamage allows for longer integration times or using higher power without damaging live samples. This opens doors for improved accuracy and/or higher speed Brillouin imaging of live biological samples. |
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B01.00034: Folding Kinetics of Human Telomeric G Quadruplex (HTG) Sequence Abbas M Husain, Shawn H Pfeil G-Quadruplex (GQ) DNA sequences exhibit a novel secondary structure, where four tracts of guanines participate in Hoogsteen base pairing to make a stable structure. While much work has been done on these structures, their folding kinetics are still not completely understood. Here, we report on the conformation dynamics of the Human Telomeric G-Quadruplex sequence (HTG) monitored via F rester Resonance Energy Transfer (FRET), a technique which can monitor the nanoscale separation of two extrinsic fluorescent dye labels. Our data is consistent with the kinetic scheme of Gray et al., where the unfolded quadruplex passes through a long-lived intermediate on the way to the folded state. Preliminary kinetic data taken in various sucrose concentrations, a viscogen and molecular crowding agent, shows an appreciable effect. We seek to correlate and rationalize this dependence to understand GQ folding dynamics in the crowded and viscous environment of the cell. |
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B01.00035: Comparative Studies of the Superparamagnetic Properties of Engineered H-rich and L-rich Human Ferritins Reconstituted with 500 57Fe-atoms / Protein Thomas Longo, Lauren Hurley, Kaixuan Ji, Lara Varden, Britannia Smith, Fadi Bou-Abdallah, Paolo Arosio, Arthur Viescas, Georgia Papaefthymiou Ferritin, the iron storage protein, consists of an inorganic ferrihydrite core surrounded by an organic protein shell, and in humans, it is found in the liver, spleen, brain, and heart. The shell consists of 24 amino acid subunits of two types: heavy (H) and light (L). In the liver and spleen, it is L-rich, while in the brain and heart it is H-rich. Since iron deposits in the brain have been linked to neurodegenerative diseases, like Parkinson’s and Alzheimer's, it is important to study the structure/function relations in these types of ferritin. Thus, we used Mӧssbauer Spectroscopy (MS) to analyze the physical properties of the cores within L-rich and an H-rich human ferritin. The MS signatures obtained in the temperature range of 4.2 < T < 300K show that magnetic spitting of the L-rich core collapses to a quadrupole doublet at a higher temperature (TB=21K) than the H-rich core (TB=11K). We used the Néel uniaxial magnetic anisotropy model for spin-relaxation-time processes in magnetic nanoparticles to extract information on core size. We found that H-rich proteins tend to form smaller cores with a larger surface-to-volume ratio, favoring high iron trafficking; while L-rich proteins form larger cores with a smaller surface-to-volume ratio, favoring long-term storage. |
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B01.00036: Combinatorial Synthesis & High Throughput Characterization of Shape Memory Alloy Thin Film Libraries for Thermoelastic Cooling Naila Al Hasan We utilize combinatorial deposition of metallic alloy thin films and high throughput characterization to generate large sets of data for machine learning. Autonomous capability designed in our group to achieve rapid characterization with upgradable feedback loops is applied to shape memory alloy thin film libraries to determine composition with ambient transformation temperatures. We demonstrate the clustering analysis of crystal structure for fast identification, grouping, and qualitative assessment. |
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B01.00037: Determination of the Nonlinear Photocurrent Response of AlGaN via 2-Beam Action Spectroscopy Daniel Jovinelli, Nikolaos Liaros, John T. Fourkas Despite the increasingly growing demand for materials able to undergo multiphoton absorption, the accurate characterization of the nonlinear responses of such materials remains challenging. We employ 2-beam constant-amplitude photocurrent (2-BCAmP) spectroscopy to study nonlinear photocurrent generation in the wide band gap semiconductor AlGaN. Through the use of 2-BCAmP, the nonlinear photocurrent response of the AlGaN photodiodes was studied at a wavelength range of 740-840nm using a mode locked, Ti:sapphire excitation source. The 2-BCAmP experiments reveal the presence of two different orders of absorption in the photodiode. 2-BCAmP experiments at different photocurrents further show that the contributing mechanism is a combination of 2-photon absorption and linear absorption. |
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B01.00038: Probing the Superconducting Energy Gaps of an Assymetrical all-MgB2 Josephson Junction Joseph Lambert, Masahito Sakoda, Michio Naito, Roberto C Ramos We have previously reported high-resolution tunneling spectroscopy measurements of substructure within the two superconducting energy gaps of Magnesium diboride (MgB2) [1,2]. The samples used consisted of 1-gap/2-gap heterojunctions, where the counter-electrode is a conventional single-gap superconductor (Pb or Sn). Here, we report similar measurements of 2-gap/2-gap all-MgB2 Josephson junctions. The crystal orientations of the two MgB2 films are mostly c-axis parallel to the tunneling direction, with very small contribution from the larger σ gap. Due to differences in growth conditions, we find that the two MgB2 electrodes have different Tc's and gap values. We analyze our dI/dV measurements using a modified tunneling model where each electrode is represented as a weighted sum of two BCS densities of states. We observe (1) a transition from SIS to NIS behavior as temperature increases past the lower Tc electrode, and (2) the presence of multiple quasiparticle peaks due to the sums and differences in pairwise combinations of disparate π and σ gap values within each electrode. [1] S. Carabello, et. al., Supercond. Sci. Technol. 28, 055015 (2015). [2] K. Chen, et. al., Nat. Comm., 3, 619, (2012). |
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B01.00039: Characterizing the Nonlinear Optical Properties of CsPbBr3 Nanocrystals Using Two-Beam Action Spectroscopy and Nonlinear Fluorescence Excitation Renee A Stover, Nikolaos Liaros, Xiuquan Zhou, Efrain E Rodriguez, John T Fourkas Halide perovskites have gained considerable attention in recent years due to their potential as easily processable and efficient photovoltaic materials. These materials also exhibit efficient multiphoton absorption (MPA). However, the characterization of MPA in halide perovskites has led to many conflicting reports. Here we apply a technique that we recently developed, two-beam constant emission intensity (2-BCEIn) spectroscopy, to the study of MPA-generated emission in CsPbBr3nanocrystals. 2-BCEIn allows for the measurement of the order(s) of nonlinear absorption without requiring high dynamics range, allowing us to elucidate the photophysics of multiphoton excitation in this system. We also demonstrate that this material undergoes efficient MPA even with continuous-wave light at 800 nm. |
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B01.00040: Size and Fluorescence characterization of Silicon Nanoparticles for Sensing Applications. Benjamin M Roe, Teresa Lee, Joseph D Swanson, Shawn H Pfeil, Kurt Wolfgeng Kolasinski We characterize the size distribution and fluorescence properties of Silicon nanoparticles prepared by Metal Assisted Catalytic Etching (MACE) for use in bio-sensing applications. Silicon is an ideal candidate due to the photo-stability inherent to semiconductor photoluminescence (PL) in comparison to organic fluorophores, and low toxicity relative to CdSe quantum dots. Importantly, Silicon nanostructures prepared via MACE have photoluminescence spectra in the visible, which makes them compatible with standard biological microscopy and imaging systems. Nanoparticles were characterized using Atomic Force and Scanning Electron Microscopy (AFM and SEM respectively) to examine height and width distributions. The effect of solvents on the PL spectra of particles was also investigated as a first step toward engineering their properties for bio-sensing applications. |
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B01.00041: On the nature of cosmic ray spectrum hardening at 230 GV Hongyi Wu, Vladimir Ptuskin, Eun-Suk Seo The high-accuracy measurements of protons and nuclei energy spectra in the cosmic ray experiment AMS-02 confirmed the earlier experimental results of ATIC-2, CREAM and PAMELA measurements on the presence of spectral hardening at magnetic rigidity about 230 GV. The AMS-02 data on the secondary nuclei Li, Be and B indicated that the hardening is most probably due to the transition to weaker rigidity dependence of cosmic ray confinement time in the Galaxy above 230 GV. However, the possible hardening of the source spectrum is also not excluded. To study the origin of spectrum hardening, we use the numerical code GALPROP to compute the propagation of cosmic rays under different assumptions on the rigidity dependence of cosmic ray source and propagation parameters in a few Galactic models. |
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B01.00042: Performance of the ISS-CREAM Calorimeter Zhiyu Yin Cosmic rays are energetic particles, primarily atomic nuclei, traveling to Earth from astrophysical sources in the Milky Way Galaxy or even beyond. We are currently exploring the properties of cosmic rays with the ISS-CREAM (Cosmic Ray Energetic And Mass) experiment, deployed on the International Space Station (ISS) in August, 2017. In this presentation, we will report on the status of flight data analysis and operations. We will focus on the behavior of the high voltage systems and corresponding current draw from the calorimeter electronics as markers of overall instrument performance. |
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B01.00043: The Physics of Light and Food: Enabling a Physics Summer Camp for Middle School Girls Kristiana Ramos, Roberto C Ramos In the United States, only 20-22% of the STEM labor force are women. To help contribute to the pipeline of women STEM workers, the Philadelphia-based Physics Wonder Girls Camp aims to sustain girls’ interest in STEM during middle school years – which is when research shows girls are more likely to lose interest in science. The camp is free and has been featured on Philadelphia's ABC News and Fox News TV networks, the SPS Observer, and international science blogs. We discuss the mechanics of organizing the camp and its optics- and food processing-themed activities that included building telescopes, physics experiments, lab and industrial plant tours, and career talks by women scientists and engineers from private industry and academia. Experiments measured properties of light (reflection, refraction, polarization, diffraction) and real-world applications, thereof and food processing (phase transitions, thermodynamics), culminating in a Girls' Physics Presentation. We use blind surveys, letters and other feedback from the girls, parents and physics-major-crew to assess the camp's effectivity. |
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B01.00044: Transient Magnesium-Based Color Pixels Thomas G Farinha, Marina Leite Optical devices applied in research and industry environments utilize wavelength filtering to achieve optical responses necessary for proper function. Most optical signal filters require power during usage and/or modification, and so the development of a power-free reconfigurable photonic alternative is desired. We realize Mg-based nanophotonic color pixels with transient functionality which filter visible light based on nanocavity interference. These transient color pixels can be fabricated to transmit any hue within the sRGB gamut. We determine the transient optical response of the Mg-based pixels during their dissolution in water under pH neutral, room temperature conditions. Color is completely negated in under 10 minutes, making these pixels useful for encryption and anti-counterfeiting. Our spectroscopic ellipsometry experiments are corroborated by 3D full-field computation using finite-difference time-domain (FDTD) simulations. The application of Mg as a material for transient photonic devices allows for the rapid, inexpensive adjustment of optical responses for wavelength filtering. |
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B01.00045: Electric fields influence the propagation of electrical activity in primary neurons and in neuron-like cells Sylvester J Gates, Kate O'Neill, Phillip Alvarez, Samira Aghayee, Yuan Wang, Houpu Li, Quan Qing, Gloria Ortiz, Evan Miller, Stephan Brenowitz, Wolfgang Losert Coupling between excitable systems is well known, and recent work has focused on excitability in neural & cardiovascular systems through recording microelectrodes. Building on this, we use noninvasive voltage indicators to probe the electrical dynamics of in vitro primary rat cortical neurons & a human embryonic kidney (HEK-293) cell line that has been engineered to be electrically excitable through expression of sodium (Na+) & potassium (K+) channels (NK-HEKs). To accomplish this, we 1) apply direct current (DC) or alternating current (AC) stimulation to cells, 2) image changes in transmembrane potential using fast acting voltage sensitive dyes, & 3) quantify signal propagation. We observe that NK-HEKs respond to both DC & AC stimulation, though the response to DC fields is more rapid. Neurons can also be electrically activated by DC fields, but the response depends on cell (and synapse) maturity. While the NK-HEKs “action potentials” are slower than those of neurons, NK-HEKs are tightly coupled, allowing for fast spiral waves &/or propagation of waves. In future work, we hope to use what we have learned about electrical dynamics & coupling in these cell types to make inferences about other excitable systems. |
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B01.00046: Metal Halide Perovskite Dynamics Driven by Water and Light John M. Howard, Marina S. Leite Hybrid organic-inorganic perovskites present ideal properties for light-emitting diodes and photovoltaics, but are limited by their stability under multiple operating conditions [1]. We first elucidate the impact of relative humidity (rH) cycling on the luminescence properties of four CsxFA1-xPb(IyBr1-y) perovskites using environmentally-controlled in situ micro-photoluminscence (PL) and discover PL hysteresis for all compositions but the 17%-Cs/38%-Br [2]. Next, we shift focus to light, and quantify the wavelength-dependent voltage dynamics in three perovskite compositions: (i) CH3NH3PbBr3, (ii) (MA,FA,Cs)Pb(I,Br)3, and (iii) CH3NH3PbI3 across a dark-light-dark illumination cycle using heterodyne Kelvin Probe voltage measurements [3]. We conclude with a discussion of the potential for machine learning to identify and control the impact of all environmental parameters [1].
[1] J. M. Howard, et al., Joule, Accepted (2018) - Invited Perspective. [2] J. M. Howard, et al., Journal of Physical Chemistry Letters, 9, 3463 (2018). [3] E. M. Tennyson*, J. M. Howard*, et al., to be submitted (2018). |
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B01.00047: Studying Supernova Remnants at High Energies with the High Altitude Water Cherenkov Observatory Leah M Hunt, Miguel A Mostafa There is still much to be understood regarding supernova remnants (SNRs). In working with data collected with the High Altitude Water Cherenkov (HAWC) Gamma-Ray Observatory, I have been able to produce spectra for several SNRs in the field of view of HAWC in the multi-TeV energy range. I then compare the energy spectra I measure with lower energy data from other experiments -such as Fermi-LAT, VERITAS, and MAGIC- to gain a better understanding of the particle acceleration processes at these sources. |
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B01.00048: Point Contact Spectroscopy of Iron Pnictides: Probing Superconductors to Observe the Gap Structures of Phosphorus Doped Iron Pnictides Brett A Conti, Roberto C Ramos, Oberon O Wackwitz, Luke A Conover, Pengcheng Dai, Chengling Zhang, Yu Song, Guotai Tan We used a four-wire point contact spectroscopy system to obtain differential conductance (dI/dV) measurements in order to observe the energy gap structures of phosphorus doped iron-pnictides (x ~ 0.2 - 0.7) at 2K. We were motivated to study the phosphorus doped family of iron pnictides because our initial literature searches indicated that not many groups had taken differential conductance measurements of this family in order to identify gap structures, and also because the iron pnictides can exhibit multi-gap structures like those of magnesium di-boride. Our goal was to obtain the differential conductance measurements for varying x values of phosphorus, and observe the gap structures to further characterize and understand the superconducting transition of these iron pnictides. We observed both single and double gap structures for various x values, with delta 1 ~ 2-5 meV, and delta 2 ~ 7-10 meV. However, there were some interesting measurements in which we observed a possible delta 2 much further out than normal, at around 17-20 meV. |
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