Bulletin of the American Physical Society
2013 Annual Fall Meeting of the APS Prairie Section
Volume 58, Number 15
Thursday–Saturday, November 7–9, 2013; Columbia, Missouri
Session F1: Poster Session (5:40 - 7:00 PM) |
Hide Abstracts |
Chair: Carlos Wexler, University of Missouri Room: Memorial Union Mark Twain |
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F1.00001: Detection of Rare Molecular Transitions in a Sample of Massive Star Forming Regions Li Lee, Esteban D. Araya The study of molecular transitions is key to characterize the medium where massive stars form. Several molecular species have been used to study star formation, e.g., CH3OH and H2O. Molecular line studies at mm/submm wavelength are difficult due to confusion of blending spectral lines and atmospheric opacity. In contrast, observations at $\sim$ 6 GHz are not affected by the atmosphere, and blending of bright spectral lines is unusual. Thus, molecular lines in the $\sim$ 6 GHz range could become new probes to study massive star formation. We report a project aimed to detect rare molecular transitions toward 12 massive star forming regions. The observations were conducted with the 305m Arecibo Telescope. We detected four rare molecular transitions, including the second ever detection of 6.28 GHz H2CS. We also report tentative detections of 6.85 GHz and 7.28 GHz transitions of CH3OH, and 7.35 GHz CH emission toward the massive star forming region IRAS18566$+$0408. These tentative detections are weak but their velocities agree with the velocities of other molecular lines in IRAS18566$+$0408. We recently submitted an Arecibo proposal to re-observe these lines. If confirmed, we would have discovered three new astrophysical maser transitions. [Preview Abstract] |
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F1.00002: ABSTRACT WITHDRAWN |
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F1.00003: Optical absorption properties of Neodymium ions (Nd$^{3+})$ doped lead boro tellurite glasses Kinnary Patel, P.K. Babu, Saisudha Mallur The optical absorption properties of Nd$^{3+}$ ions in PbO-TeO$_{2}$-B$_{2}$O$_{3}$ glasses were studied as a function of PbO content varying from 30 to 70 mol{\%}. Glasses were prepared by the usual melt quench technique. Glasses were annealed at 400$^{\circ}$C for 3 hours to remove thermal strains. Annealed glass samples were then polished. In order to understand the effect of host glass on the absorption properties of Nd$^{3+}$ ions in these glasses, oscillator strength, intensity parameters and radiative transition probabilities of Nd$^{3+}$ ions were calculated using the Judd-Ofelt theory. The variation of the intensity parameters $\Omega _{\mathrm{t}}$ (t$=$2,4,6) with PbO content has been attributed to the changes in the asymmetry of the ligand field at the rare-earth ($R)$ site (due to the structural changes) and to changes in $R$-O covalency. [Preview Abstract] |
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F1.00004: Direct calculation of exciton binding energies with time-dependent density-functional theory Zenghui Yang, Carsten Ullrich Excitons are coupled electron-hole pairs below the band gap in bulk semiconductors. They are vital to photovoltaics, but they are hard to obtain in a TDDFT calculation, due to usually employed exchange-correlation kernels lacking the long-range part. Another difficulty comes from the usual method of applying TDDFT on bulk materials which calculate the spectrum - though suitable for continuum excitations, this approach does not upfront yield the binding energy of the discrete excitonic excitations. We develop a method in analog with the Casida equation formalism, in which exciton binding energies are obtained directly. We calculate exciton binding energies for both small- and large-gap semiconductors with this method. We study the recently published ``bootstrap'' exchange-kernel within our method, and we extend the formalism to treat triplet excitons. [Preview Abstract] |
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F1.00005: Molecular Dynamics Simulations of Melting of Nitromethane Initiated at Crystal-Rare Gas Interfaces Ganesh Kamath, Ali Siavosh-Haghighi, Thomas Sewell, Donald Thompson The melting of nitromethane initiated at the (100), (010), and (001) crystallographic faces in contact with rare gases at pressures over the interval 1 kbar to 16 kbar has been investigated using molecular dynamics simulations with an all atom force field. Simulations were performed to evaluate the melting point of nitromethane crystal in contact with He, Ar, and Kr. The calculated melting curve is in good agreement with experiment and previous simulation results. The molecular-level mechanism of melting initiated at a crystal surface in contact with rare gas was compared with that for melting at the bare crystal surface and void-nucleated melting. Orientational disordering of the molecules at the melt front precedes the onset of translational freedom of molecules both at the crystal-fluid interface and in the core of the crystal. There is an increase of the time gap between the occurence of molecular reorientation and translational mobility in the nitromethane molecules. The predicted melting points for nitromethane in contact with He, Ar, and Kr are within 20 K of each other for all state points and can be correlated to the diffusion of the rare gas atoms into the nitromethane crystal. The diffusion of rare gas atoms into the crystalline solid eliminates the dependence of melting temperature on the crystallographic orientation reported previously for melting at bare surfaces. [Preview Abstract] |
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F1.00006: Generalized Stacking Fault Energies in the Basal Plane of Triclinic Molecular Crystal 1,3,5-Triamino-2,4,6-Trinitrobenzene (TATB) Nithin Mathew, Thomas Sewell Molecular dynamics and molecular mechanics simulations were used in conjunction with a fully flexible force field to calculate the generalized stacking fault energies in the basal plane (that is, the $a-b$ plane, where $a$, $b$, and $c$ define the edge vectors of the primitive unit cell) of the triclinic molecular crystal 1,3,5-triamino-2,4,6-trinitrobenzene (TATB). Crystal symmetry and molecular stacking arrangement result in two glide plane types for the same glide plane normal vector. The unstable stacking fault energies are found to be less than 10 mJ/m$^{2}$ at 0 K and atmospheric pressure, indicating easy dislocation glide. Glide in the $a$ and $a-b$ directions are favored to that in the $b$ direction. Asymmetric unstable stacking fault energies indicate an asymmetric barrier to dislocation glide. Stable stacking faults with energies less than 1 mJ/m$^{2}$ are predicted for the $a$ and $a-b$ directions. A compound twin is observed in the $a$ direction with energy of 2.52 mJ/m$^{2}$. Nitro (NO$_{2})$ groups on the molecules undergo out-of-plane rotations during glide. The extremely small barriers to twinning and dislocation glide might be sources for observed second harmonic generation in the nominally centrosymmetric crystal. [Preview Abstract] |
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F1.00007: Radial distribution function of liquid argon in modified hard sphere model Michael Korth, Saesun Kim We begin with a geometric model of colliding hard spheres and calculate probability densities in an iterative sequence of calculations that lead to the pair correlation function. The model is based on a kinetic theory approach developed by Shinomoto [Phys. Lett A, 89, 19 (1982)]. We added a weak attractive interatomic potential for argon based on the work of Aziz [J. Chem. Phys. 99, 4518 (1993)] in order to find radial distribution function of liquid argon. Results are in partial agreement with experiment. We are exploring additional modifications to the model. [Preview Abstract] |
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F1.00008: Effects of Annealing on the Structure and Properties of Mn$_{\mathrm{5-x}}$Fe$_{\mathrm{x}}$Si$_{3}$ Zachary Spence, Cody Dawson, Peggy Hill, Igor Dubenko, Abdiel Quetz, Naushad Ali Materials forming with the Mn$_{5}$Si$_{3}$ crystal structure have been found to exhibit interesting magnetic, magnetocaloric, and spin polarization properties. In particular, alloys of Mn$_{\mathrm{5-x}}$T$_{\mathrm{x}}$Si$_{3}$ (T $=$ transition metal) have been investigated as possible magnetocaloric materials. Previous research has shown that Mn$_{\mathrm{5-x}}$Fe$_{\mathrm{x}}$Si$_{3}$, with x $=$ 4, exhibits the largest magnetic entropy of the system (4 J/kgK) and orders ferromagnetically just below 300 K, making it a possible candidate for room temperature magnetic refrigeration applications.\footnote{Songlin, et al., J. of Alloys and Compounds. \textbf{334} (2002) 249} Our work aims to study changes in the magnetic and magnetocaloric properties of MnFe$_{4}$Si$_{3}$ as a result of substitution at the silicon site. The effect of annealing, without quenching, on crystal structure homogeneity was investigated for the parent compounds Fe$_{5}$Si$_{3}$ and Mn$_{5}$Si$_{3}$ and for Mn$_{4}$FeSi$_{3}$ by x-ray diffraction. A reduction in x-ray diffraction peaks due to impurities was observed after annealing the Mn$_{5}$Si$_{3}$ and Mn$_{4}$FeSi$_{3}$ samples. The x-ray profile of Fe$_{5}$Si$_{3}$ was greatly improved by annealing and it adopted the proper Mn$_{5}$Si$_{3}$ D8$_{8}$ hexagonal crystal structure without quenching. [Preview Abstract] |
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F1.00009: Missing Material At The Buried Interface For Ag/Si(111)7x7 Thin Films Deposited at Glancing Angle S.T. Hayden, Yiyao Chen, M.W. Gramlich, R.S. Gari, G.M. King, P.F. Miceli Missing material (vacancies) below the exposed surface has not been widely investigated during film growth because conventional surface science experiments do not probe below the surface (STM, LEED, etc.). X-ray scattering techniques, however, can uniquely explore the role of buried defects in epitaxial crystal growth, owing to its sensitivity to both the surface and the subsurface. Our prior work has shown the presence of vacancies in homoepitaxial film growth (Kim et al., Appl. Phys. Lett. 91, 093131 (2007) and Phys. Rev. B 86, 155446 (2012)). In the present study of heteroepitaxial Ag/Si grown at glancing angles, X-ray reflectivity and atomic force microscopy (AFM) measurements each yield the same surface height distribution. However, there is a significant portion of sub-surface missing material that is concealed to the AFM, but, which is revealed by the X-ray reflectivity measurements that detect the electron density profile. This missing material is determined to be concentrated at the buried film-substrate interface for deposition-angle-dependent grown Ag/Si(111)7x7. [Preview Abstract] |
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F1.00010: Boron Doping of Activated Carbon Matthew Connolly, Alexander St. John, Matthew Beckner, Peter Pfeifer, Carlos Wexler Efficient storage of hydrogen is one of the challenges to be solved for the H2-based fuelling systems. Carbon-based materials show promise, given their light weight, large surface areas and low cost. Unfortunately, the interaction of H2 and carbon, ~5kJ/mol, is insufficient for room-temperature operation, the interaction energy for optimal delivery being >15kJ/mol. It has been proposed that boron doping of carbon materials could raise the binding energy of H2 to ~12kJ/mol. However, the nature of the incorporation of boron into a carbon structure has not been studied in detail. Here, we address the energetics of boron incorporation into a carbon matrix via adsorption and decomposition of decaborane. First principles calculations demonstrate: (1) A strong adsorption of decaborane to carbon (70-80kJ/mol) resulting in easy incorporation of decaborane, sufficient for up to 10-20\% B:C at low decaborane vapour pressures. (2) Identification that boron acts as an electron acceptor when incorporated substitutionally into a graphene-like material, as expected due to its valence. (3) The electrostatic field near the molecule is responsible for ca. 2/3 of the enhancement of the H2-adsorbent interaction. Supported by DOE DE-FG36-08GO18142, ACS-PRF 52696-ND5, and NSF 1069091. [Preview Abstract] |
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F1.00011: Fabrication and characterization of single-supported bilayer membranes of anionic lipids. Andrew Miskowiec, Mengjun Bai, Haskell Taub, Flemming Hansen We report the fabrication of bilayer membranes of the anionic lipid DMPG (1,2-dimyristoyl-\textit{sn-}glycero3-phosphoglycerol) deposited on a silicon substrate. Due to electrostatic effects associated with the DMPG molecule, traditional vesicle fusion methods for producing supported bilayers must be modified to encourage rupture. In particular, high divalent salt concentrations in the buffer solution are necessary to ``prime'' the substrate for vesicle adsorption; furthermore, lower DMPG concentrations are required than for the neutral analogue DMPC (1,2-dimyristoyl-\textit{sn-}glycero3-phosphocholine). We speculate that lower DMPG concentrations allow neutralization of the bilayer with hydrogen ions, increasing the membrane fluidity. We also investigated the temperature dependence of the bilayer thickness in order to monitor the gel-to-fluid phase transition of the DMPG and DMPC membranes. Both show a higher transition temperature than found for spherical vesicles. However, the effect is greater for the DMPG bilayer for which the phase transition is shifted to 70 $^{\circ}$C, 45 $^{\circ}$C above the free-vesicle value. [Preview Abstract] |
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F1.00012: Interfacial structure and morphology of nano-crystalline Ag on Si(111)7x7: an in-situ x-ray scattering study Yiyao Chen, M.W. Gramlich, S.T. Hayden, M.C. Tringides, P.F. Miceli There is intense interest to understand the factors that control the growth of nano-scale metals on supported substrates and, although the Ag/Si(111) system has been extensively studied for this purpose, little is known about the buried interface of the Ag nano-islands because most experimental probes only detect the top surface. Here, we present the results of in situ synchrotron x-ray scattering studies that reveal previously unknown and unexpected features of the buried nano-island/substrate interface. It is found that the incommensurate FCC Ag nano-islands consume the wetting layer upon which they grow and the islands extend to the reconstructed 7x7 Si surface. Consequently, the Ag island height distribution is one monolayer thicker than previously assumed, with a trilayer being the most stable island height at low coverage. Moreover, the lattice spacing of the islands is determined to be the same as bulk Ag, contrary to several prior STM measurements. These results are discussed in terms of the competition between electron confinement effects versus the role of interfacial energy, both of which are important for determining the growth morphology of nano-scale metals on supported substrates. [Preview Abstract] |
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F1.00013: Spin-Orbit Interaction and Rashba Effect in the 2D metal dichalcogenides Mohammad Mahdi Valizadeh, Shanavas K. Veedu, Sashi Satpathy The monolayer metal dichalcogenides such as MoS$_2$ and WS$_2$ are currently an emerging class of 2D materials owing to their possible applications in 2D electronics including spintronics. The Rashba effect which describes the momentum-dependent spin-splitting of the band structure originates from the spin-orbit interaction and inversion symmetry breaking. The effect is expected to be much stronger in the dichalcogenides with high-Z elements such as WS$_2$, WO$_2$, etc. Here, we study the Rashba effect in WS$_2$ from a tight-binding model as well as from density-functional calculations. We find a strong Rashba effect leading to the possibility of applications in spintronics such as spin-valves. [Preview Abstract] |
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F1.00014: Magnetic and Magnetocaloric Properties of MnFe$_4$Si$_{3-x}$In$_x$ Cody Dawson, Zachary Spence, P. Hill, Igor Dubenko, Abdiel Quetz, Naushad Ali The magnetocaloric effect has attracted pressing curiosity for its application in magnetic refrigeration because it presents an alternative to current refrigeration technology that is more efficient and environmentally friendly. Previous research on the Mn$_{5-x}$Fe$_x$Si$_3$ system has shown that magnetic entropy changes are enhanced in the MnFe$_4$Si$_3$ compound [1]. We have prepared samples of MnFe$_4$Si$_{3-x}$In$_x$ in order to investigate how In substitution for Si affects the properties of this system. Samples were prepared by arc melting and annealed for 5 days at 900$^{\circ}$C and the crystal structure of each sample was systematically studied through X-ray diffraction techniques to determine phase purity. Then the system was investigated by measuring magnetization as a function of temperature and magnetic field. Here we report on the magnetic and magnetocaloric properties of the pseudo ternary MnFe$_4$Si$_{3-x}$In$_x$ system for x = 0, 0.5, 1, and 1.5, and discuss its applicability in magnetic refrigeration.\\[4pt] [1] Songlin, Dagula, O. Tegus, E. Br\"uck, J.C.P. Klaasse, F.R. de Boer, K.H.J. Buschow, J. Alloys Compd. 334 (2002) 249. [Preview Abstract] |
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F1.00015: Forbidden Reflections and Interference Effects in X-ray Reflectivity from Si(111)7x7 J.W. Kremenak, Yiyao Chen, S.T. Hayden, M.W. Gramlich, P.F. Miceli In diffraction, X-ray reflections from diamond crystal structures with Miller indices that satisfy h$+$k$+$l $=$ 4n$+$2, where n is an integer, are considered to be forbidden by crystal symmetry. However, these ``forbidden reflections'' have been observed experimentally, starting with W.H. Bragg over 90 years ago. Asymmetric charge distributions and anharmonic vibrations break the crystal symmetry and result in weak, but non-zero, intensities for these reflections. In the present work, we investigate the forbidden reflections in x-ray reflectivity and crystal truncation rods where we have discovered that the interference between bulk and surface waves can distinguish between the charge and vibrational origins of the reflections. Synchrotron x-ray scattering results, as well as a model, are presented. Understanding the properties of the forbidden reflections in diamond crystal structures not only provides greater insight into the crystal bonding and vibrations, but will also lead to better models for surface structures. [Preview Abstract] |
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F1.00016: Scaling analysis of the magnetic field-tuned quantum phase transition in superconducting amorphous Pb films Nicholas Olson, Ashwani Kumar Quantum phase transitions are the transitions (QPTs) that take place at absolute zero, where the crossing of the phase boundary changes the quantum mechanical ground state. Superconductor to insulator transitions is the prime examples of the QPTs. In these transitions the phase boundary can be crossed using various parameters such as disorder, magnetic field, charge carrier density etc. In this presentation we will talk about the scaling analysis of the magnetic field tuned superconductor to insulator quantum phase transition. [Preview Abstract] |
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F1.00017: Probing charge transfer complex (CTC) states in organic solar cells using photocurrent spectroscopy Dhanashree Moghe, Ping Yu, Catherine Kanimozhi, Satish Patil, Suchismita Guha Diketopyrrolopyrrole (DPP) containing copolymers have generated considerable amount of interest in bulk heterojunction organic photovoltaics due their high power conversion efficiency (above 10 percent) and mobility. Within a bulk heterojunction solar cell, the combination of a donor and acceptor chromophores facilitates charge transfer from the donor to the acceptor and may result in the formation of interfacial electronic state at the donor-acceptor interface. Here, we present photocurrent studies to identify the interfacial charge complex states in five DPP based copolymer (donor): fullerene devices using Fourier transform photocurrent spectroscopy (FTPS) and monochromatic photocurrent spectroscopy. The optical band gap of DPP based copolymer ranges from 1.4-1.7eV. Our studies show that a larger optical band gap difference between the donor and the acceptor prohibit the formation of a stable charge transfer complex state. Further, we also observe that devices in which no charge transfer state was observed show a better efficiency than devices in which charge transfer state is observed. [Preview Abstract] |
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F1.00018: Single Molecule Relaxation in Crystalline Nitromethane Luis Rivera-Rivera, Ali Siavosh-Haghighi, Thomas Sewell, Donald Thompson Classical molecular dynamics simulation results for the relaxation of a single molecule in perfect crystalline nitromethane (CH$_{3}$NO$_{2})$ at 250 K and 1 atm hydrostatic pressure will be presented. The molecule was instantaneously excited by statistically distributing excitation energy between 25.0 kcal/mol and 125.0 kcal/mol, initially all in the form of kinetic energy, among the 21 degrees of freedom. Following a subpicosecond interval dominated by intramolecular reequilibration of kinetic and potential energy, loss of kinetic energy from the excited molecule is approximately exponential, with time constants between 11.7 ps and 13.7 ps. A non-linear and non-monotonic correlation between the exponential relaxation time constant and excitation energy is predicted. Energy transfer from the excited molecule to surrounding quasi-spherical shells of molecules occurs concurrently to the first and second shells, but with more energy per molecule transferred more rapidly to the first shell. [Preview Abstract] |
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F1.00019: Theoretical determination of anisotropic thermal conductivity for crystalline 1,3,5-triamino-2,4,6-trinitrobenzene (TATB) Matthew Kroonblawd, Thomas Sewell Bond stretching and three-center angle bending potentials have been developed to extend an existing rigid-bond TATB molecular dynamics force field [D. Bedrov, O. Borodin, G. D. Smith, T. D. Sewell, D. M. Dattelbaum, and L. L. Stevens, J. Chem. Phys. \textbf{131}, 224703 (2009)] for simulations requiring fully-flexible molecules. The potentials were fit to experimental vibrational spectra and electronic structure predictions of vibrational normal modes using a combination of zero kelvin eigenmode analysis for the isolated molecule and power spectra for the isolated molecule and crystal. A reverse non-equilibrium molecular dynamics method [F. M\"{u}ller-Plathe, J. Chem. Phys. \textbf{106}, 6082 (1997)] was used to obtain the room temperature, atmospheric pressure thermal conductivity along three directions in a well-defined, non-orthogonal basis. The thermal conductivity was found to be significantly anisotropic with values 1.13, 1.07, and 0.65 W$\cdot $m$^{-1}\cdot $K$^{-1}$ for directions nominally parallel to the \textbf{a}, \textbf{b}, and \textbf{c} lattice vectors, respectively. [Preview Abstract] |
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F1.00020: Concentration-dependent embedded atom method potential for Al-Cu system Suleiman Oloriegbe, Sewell Thomas, Thompson Donald, Zhen Chen, Shan Jiang, Yong Gan A concentration-dependent interatomic potential for Al-Cu alloys has been carefully constructed in the framework of embedded atom method (EAM) refer to here as CDEAM potential. The interatomic interaction terms for the pure components Al and Cu were adapted from a previously published EAM work. The new potential incorporate interactions between Cu and Al using a pair potential function that is augmented with a fourth order polynomial function to account for concentration dependence. The potential was optimized using experimental heat of mixing for liquid Al-Cu alloys at 1467 K, second-order elastic constants and zero Kelvin formation energies from DFT for various alloy configurations and compositions. The resulting potential is able to reasonably reproduce the heat of formation across the entire composition. The heat of formation at zero Kelvin and mixing enthalpy at 1467 K as well as the second-order elastic constants are compared with existing Al-Cu potentials in the literature. Our potential reasonably reproduces the alloy mixing enthalpies at 1467 K. As a further test, we computed properties not included in the fit, such as liquid structures, self-diffusion coefficient, liquid densities, enthalpies and heat capacities as a function of temperature. The results of these properties computed using CDEAM potential are in good agreement with experimental data. [Preview Abstract] |
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F1.00021: Rotational -Vibrational Energy Transfer in OH(v,J)$+$ Ar at High Pressures Rezvan Chitsazi, Donald Thompson The exchange of energy in collisions of atoms, molecules and radicals has attracted interest since the introduction of kinetic theory and its subsequent applications in chemistry. We have studied the effects of pressure on the relaxation of excited OH radical. In most modeling of gas phase chemistry it is assumed that it occurs via isolated elementary bimolecular collisions; that is, the fundamental energy transfer and reactions occur between pairs of species. Our interest is to explore the relaxation of an internally excited radical at pressures for which the bimolecular collision assumption breaks down. We will present results for molecular dynamics simulations of the rotational-vibrational energy transfer for OH(v,J) in an Ar bath for internal energies up to the dissociation limit and over pressure and temperature ranges that include and exceed those achievable in the laboratory. [Preview Abstract] |
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F1.00022: A Study of the Effects of Basis Functions in Interpolating Moving Least Squares Methods for Fitting Potential Energy Surfaces Yi Shi, Donald Thompson The interpolating moving least-squares (IMLS) method is an efficient means for potential energy surface fitting [R. Dawes, D. L. Thompson, A. F. Wagner, M. Minkoff, J. Chem. Phys., \textbf{128}, 084107 (2008)]. To date no studies have been carried out on the effects of basis functions on the accuracy and fidelity of IMLS. Power functions are the only basis functions that have been used in IMLS. In our study, different basis functions have been used to fit different dimensional potential energy surfaces with IMLS. The efficiencies of various basis functions have been compared. The potential energy surfaces selected to fit are the Morse potential and an accurate analytical H$_{2}$O$_{2}$ potential energy surface. Our results show that other functions can be more efficient than power functions. [Preview Abstract] |
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F1.00023: Super-resolved Microscopy via Coherent Population Oscillations Kishor Kapale, Girish Agarwal We present a microscopy scheme to attain sub-nanoscale resolution based on the phenomena of coherent population oscillation (CPO). We build on the success of our earlier super-resolution methods based the phenomena of coherent population trapping (CPT). For microscopy applications it is crucial to make sure the effect being employed for super-resolution is attainable in a large class of materials. In this context, it becomes necessary to resort to a phenomena-which is similar to CPT but can be potentially observed in a larger class of materials including gases, liquids, and room-temperature solids--such as CPO. The CPO based schemes involve two-level atoms coupled to two optical fields slightly different in frequency. The CPT-like nonlinear effects such as group velocity manipulations within the CPO schemes have been observed in room temperature solids and biological samples as opposed to in atomic vapors and cold atomic gases in the case of CPT. This parallel allows us to extend our CPT-based work to CPO-based microscopy schemes and makes them attainable in much larger class of materials including solids and biological samples. We show that the CPO-based schemes offer similar resolution as the CPT-based schemes and are attainable in a larger class of materials. [Preview Abstract] |
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F1.00024: A DFT and \textit{Ab Initio} Study of the Thermal Decomposition of 1,3,3-Trinitroazetidine (TNAZ) Jeffrey Veals, Donald Thompson Density functional theory (DFT) and \textit{ab initio} methods are employed to investigate unimolecular decomposition pathways of 1,3,3-trinitroazetidine (TNAZ) initiated by loss of NO$_{2}$ or HONO. Geometry optimizations are performed using M06/cc-pVTZ for all species commonly included in the initial decomposition mechanisms. Coupled-cluster (CC) theory with single, double, and perturbative triple excitations [CCSD(T)], is used to calculate more accurate single point energies at the M06/cc-pVTZ geometries. The CCSD(T)/cc-pVTZ energies for NO$_{2}$ elimination by N-N and C-N bond fission are 43.21 kcal/mol and 50.46 kcal/mol, respectively. The decomposition route initiated by \textit{trans}-HONO elimination can occur by a concerted H-atom and nitramine NO$_{2}$ elimination or by loss of an alkyl NO$_{2}$ group and H-atom with energy barriers calculated using CCSD(T)/cc-pVTZ, respectively, 47.0 kcal/mol and 48.27 kcal/mol. At the CCSD(T)/cc-pVTZ level, the energy ordering of these four decomposition steps from most favored to least favored is as follows: N-N bond fission (43.21 kcal/mol), HONO elimination involving the nitramine NO$_{2}$ group (47.0 kcal/mol), HONO elimination involving the alkyl NO$_{2}$ group (48.27 kcal/mol), and finally C-N bond fission (50.46kcal/mol). Therefore the most likely initial decomposition route of TNAZ is predicted to be N-N bond fission. [Preview Abstract] |
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F1.00025: Controlled Focusing Properties with Cylindrical Vector Beams Maojin Yun, Lifeng Dong, Wei Lv The rapid increase of interest in cylindrical vector beams was driven largely by the unique focusing properties of such beams discovered recently. Particularly, it was found that radially polarized light can be forced into a tighter spot than those of spatially homogeneous polarization. In addition, the longitudinal component experiences an apodization effect that is different from the transverse component and is spatially separated from the transverse focal field. These effects enable three-dimensional tailoring of the focus shape. Focusing properties of cylindrical vector beams have attracted great attention and quickly became the subject of extensive worldwide research due to their applications in lithography, optical storage, and optical tweezers. In this study, pure phase plate was used to modulate phase distribution of the cylindrical vector beams to investigate their focusing properties. By using the Richards-Wolf vector diffraction theory, the simulation results show that two optical bubbles of stronger light intensity around dark spots can be obtained with the incoming cylindrical vector. [Preview Abstract] |
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F1.00026: ABSTRACT WITHDRAWN |
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F1.00027: Effect of Potentiator VX-770 on the Kinetics of Disease-Associated Mutant CFTR Channels Zuleyha Yuksek, Zoia Kopeikin, Silvia Bompadre CFTR (Cystic Fibrosis Transmembrane Conductance Regulator) is a Cl- channel whose malfunction results in the genetic disease CF. One of the most common CF-associated mutations is the deletion of Phe 508 ($\Delta$F508) resulting in channels with poor membrane expression and impaired function. Several functional abnormalities were demonstrated: infrequent openings, shorter locked-open time, reduced resident-time for the ATP molecule bound in the first nucleotide binding domain NBD1. Recently, the drug VX-770 was approved for clinical use, which increases the activity of $\Delta$F508-CFTR. We studied the effect of VX-770 on the functional defects associated with $\Delta$F508-CFTR: the Po of the channels is increased 12x due to the increase of opening rate and open time. Response to ATP analogues is decreased when channels are treated in conjunction with VX-770, suggesting that the potentiator by itself repairs gating defects. The potentiation effect was observed for temperature-corrected channels as well as channels treated with corrector VX-809. The shorter locked-open time of hydrolysis-deficient mutants is prolonged by VX-770 suggesting a stabilizing effect on the NBD dimer. The ATP resident time at NBD1, reflecting a partial NBD dimer configuration, is not affected by VX-770. [Preview Abstract] |
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F1.00028: The Isolated Nucleotide Binding Domains of CFTR Form Bipartate ATPase To Regulate ATP Consumption Mark Palmier, Silvia Bompadre The CFTR Cl- channel belongs to the ATP binding cassette (ABC) family. Contains 2 transmembrane domains that form the channel pore, 2 nucleotide-binding domains (NBDs) and a regulatory domain. Channel opening is primed by ATP binding to NBDs and their dimerization. The stable dimer forms a bipartite ATPase. With ATP at its center hydrolysis occurs, leading to dimer separation and channel closure. Progress has been achieved in the characterization of CFTR gating. But conformational changes behind the gating transitions can only be inferred on structural data from other ABC transporters. The structural dynamics governing CFTR mechanisms are still unknown. Advancements in purification technology make it possible to address the question of dynamics. Our goal is to investigate the dynamics of NBD dimer formation and separation using Single Molecule Fluorescence. Here we show our progress: that dimerization is a tight binding event ($Kd\sim 1\mu$M), hydrolysis competence only when dimerized and FRET demonstrating the association of the two isolated domains in presence of ATP. The goal of this project is to discern the molecular mechanisms governing the CFTR function. When completed, our findings will increase the overall understanding of the relationship between function and dynamics. [Preview Abstract] |
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F1.00029: Monitoring the uniformity of alpha helices in lipophilic environments Anahita Zare, Jian Xiong, Jason Cooley, Renee Jiji It is known that membrane-embedded alpha helices are more uniform structurally than their aqueous counterparts. Despite this uniformity, protein dynamics are thought to be common in these proteins in order for them to conduct their cellular tasks. However, how amino acid sequence facilitates these dynamics remains unknown as methods for investigating structural heterogeneity in transmembrane proteins are limited. Circular dichroism (CD) is often used to characterize the secondary structure of the protein, but its sensitivity to specific non-helical structural configurations is low. Deep-ultraviolet resonance Raman spectroscopy (DUVRR) is a structurally sensitive spectroscopy technique emerging for analyzing membrane protein structures. A set of \textit{de novo} designed peptides have been constructed that contain varying contents of helix breaking residues (HBR) in order to test their role helical instability in lipophilic environments. The secondary structure of each peptide was monitored through the measured by DUVRR spectroscopy, where changes in the Amide III and S modes indicate that HBRs actually cause the ``unwinding'' or the helix when solubilized in detergent environments. This observation has implications towards the role of water presentation in membrane protein dynamics. [Preview Abstract] |
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F1.00030: Structured mRNA induces the ribosome into a hyper-rotated state Peter Cornish, Peiwu Qin, Dongmei Yu, Xiaobing Zuo During protein synthesis, mRNA and tRNA are moved through the ribosome by the process of translocation. The small diameter of the mRNA entrance tunnel only permits unstructured mRNA to pass through. However, there are structured elements within mRNA that present a barrier for translocation that must be unwound. The ribosome has been shown to unwind RNA in the absence of additional factors, but the mechanism remains unclear. Here, we show using single molecule F\"{o}rster resonance energy transfer and small angle X-ray scattering experiments a new global conformational state of the ribosome. In the presence of the frameshift inducing dnaX hairpin, we observed that the ribosomal subunits were driven into a hyper-rotated state and the L1 stalk was predominantly in an open conformation. This previously unobserved conformational state provides structural insight into the helicase activity of the ribosome and may have important implications for understanding the mechanism of reading frame maintenance. [Preview Abstract] |
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F1.00031: Single molecule studies of the protein export system Raghavendar Reddy Sanganna Gari, Nathan Frey, Linda Randall, Gavin King Numerous proteins are exported across or into cell membranes to carry out critical cellular functions. In \textit{Escherichia coli,} pathway through the membrane is provided by the translocon SecYEG, which is highly conserved and has homologs across the kingdoms of life. At the cytoplasmic membrane SecA binds SecYEG and provides energy for protein translocation through the cycle of binding and hydrolysis of ATP. SecA makes large surface area contact ($\sim$ 6,800 {\AA}$^{2})$ with cytoplasmic loops spanning TM helices 6-7 and 8-9 of SecY. Despite their functional significance, measurements of these flexible and disordered protein regions remain a significant experimental challenge. Major challenges in protein export system include: determining the oligomeric state of SecYEG and SecA during protein export, and elucidating the mechanism of SecA driving precursor through translocon. Structural details at single molecule level in near native conditions can address these major questions. Recently, atomic force microscopy (AFM) has emerged as an important complementary tool to study membrane proteins. In contrast to other techniques AFM can directly monitor conformational changes and dynamics of bio-molecules. In this work we present the structural details of major components of protein export system at single molecule level in native conditions determined via AFM. [Preview Abstract] |
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F1.00032: Development of quantum mechanics laboratory for undergraduate teaching Harrison Knoll, Paul Miceli, Ping Yu We present our recent development of a quantum mechanics laboratory for undergraduate instruction. The experiments are based on detecting entangled photon pairs from the spontaneous down conversion in a beta-barium borate (BBO) crystal using low level light detection techniques. We address two issues in this work: (1) a demonstration of low level light detection by using a sensitive CCD camera to show the down conversion photon pairs from the BBO crystal and the statistics of photons in a slow time scale. (2) Experiments to show the transitions from classical states, semi-classical states, and quantum states. The wave nature of light is described by Maxwell's equations of electromagnetic fields as well as classical statistics. The construction of a Hanbury-Brown and Twiss interferometer gives an opportunity to examine wave nature of light in non-classical statistics. The quantum nature of light, proposed by Einstein, has been used to explain the phenomena of the photoelectric effect. A detection of second-order correlation for photons through a beam-splitter using their entangled photons as a gate provides experimental proof of quantum nature of photons. We offer this laboratory for the first time in the Department of Physics and Astronomy, University of Missouri during the fall semester 2013. [Preview Abstract] |
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F1.00033: Opposite Thought Experiment Florentin Smarandache Let's consider the opposite case: when we have the astronaut measures the elapse interval time of the event on the earth. It is alike the rocket stands still and the Earth is moving in the opposite direction with speed v. The observer on earth measures the elapsed proper time of the event on earth, $\Delta t_{E} '$ The elapsed non-proper time of the event on earth as measured by the astronaut is $\Delta t_{E} $. Using the same calculations, with $\Delta t_{E} '$ and $\Delta t_{E} $as the elapsed proper and respectively non-proper time of the event on earth as measured by the observer on earth and respectively by the astronaut, we get: $\Delta t_{E} =\frac{\Delta t'_{E} }{\sqrt {1-\frac{v^{2}}{c^{2}}} }$. Therefore the time dilation is measured by the astronaut in the rocket. This result is contradictory with the time dilation on the earth from the previous thought experiment. But, according to Einstein's Thought Experiment with the Light Clocks, one has: $\Delta t=\frac{\Delta t'}{\sqrt {1-\frac{v^{2}}{c^{2}}} }$, where $\Delta t$ is the elapsed time interval in the rocket as measured by the observer on earth, and $\Delta t'$ is the elapsed time interval in the rocket, as measured by the astronaut. Then who is right, the observer on earth or the astronaut? Where is really the time dilation: on earth or in the rocket? The advocates of special theory of relativity say that there is no answer to this question. They pretend that's okay. But what kind of theories are those that have undecidable propositions? Incomplete or inconsistent ones! [Preview Abstract] |
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F1.00034: Hierarchical micro/nanostructure effect on the thermal performance of oscillating heat pipes Feng Zhang, Robert Winholtz, Vitaly Gruzdev, Hongbin Ma Oscillating heat pipes (OHPs) are a promising new technology for electronics cooling. When hierarchical micro/nanostructures are introduced within the OHP, the overall thermal performance is expected to improve due to the enhancement of thin film evaporation on the interior channel surfaces. Such structures, consisting of hierarchical micron sized waves and nanometer sized pores, were fabricated using a femtosecond laser at different scanning speeds and angles of incidence. Differences in surface topography were characterized with SEM. Contact angle measurements for the hierarchical structured surfaces were conducted with water and ethanol to determine the wettability of these working fluids. Experimental comparisons of the thermal performance of micro/nanostructured OHPs and conventional OHPs will be assessed. [Preview Abstract] |
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F1.00035: Photovoltaic Properties of Electrochemical Deposited Cu2O/ZnO p-n Heterojunction Mingwei Shang, Lifeng Dong In order to fabricate a Cu2O/ZnO heterojunction, single-crystal n-type zinc oxide (ZnO) nanorod arrays and p-type cuprous oxide (Cu2O) thin film were deposited on FTO glass respectively by electrochemical deposition method using an electrochemical workstation. The Cu2O/ZnO heterjunctions were also deposited by electrochemical deposition method. A series of characterization and measurements were taken to indicate its properties. It was found that the diameter of ZnO nanorods increased with the increase of the concentration of ZnCl2 during the deposition of ZnO nanorod arrays. Formation of a p-n junction between Cu2O film and ZnO nanorod arrays were demonstrated through electrical properties measurements. The efficiency of this solar cell was also calculated. The higher external quantum efficiency of the Cu2O/ZnO heterojunctions than that of ZnO nanorod arrays and Cu2O film also indicates the formation of a p-n junction, which can efficiently facilitate the separation and transport of charge carriers for applications in solar cells. But some evidence shows that a weak contact/interface between ZnO nanorods and Cu2O film resulted from solution corrosion may affect its photovoltaic properties. [Preview Abstract] |
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F1.00036: Realization of one-way electromagnetic modes at the interface of two lossless metals Mehul Dixit, David Stroud One-way electromagnetic waveguides are of special interest because of complete suppression of back-scattering by disorder. Such waveguides support a unique class of photonic modes that completely forbid propagation in the opposite direction. We show that a one-way electromagnetic waveguide can be realized at the interface of two dissimilar lossless metals in an external magnetic field parallel to the interface. Electromagnetic surface plasmon modes bound to the interface of the two metals and propagating parallel to it and normal to the direction of the external magnetic field, with the electric field polarized normal to the plane of the interface, support one-way electromagnetic propagation in a range of frequencies. Increasing the magnetic field increases the window of frequencies for one-way propagation. Adding damping reduces the range of frequencies. Details of the calculation and plots showing the dispersion relation will be presented. [Preview Abstract] |
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F1.00037: The Paradox of Special vs. General Theory of Relativity Florentin Smarandache Two clocks \textit{C1} and \textit{C2} are synchronized on the earth. Then clock \textit{C2} is flying with a uniform speed at an altitude \textit{h \textgreater 0} above the earth. \begin{enumerate} \item According to the Special Theory of Relativity there is \underline {symmetry} of time dilation between \textit{C1} and \textit{C2} \item But, according to the General Theory of Relativity, there is an \underline {asymmetry} of time between \textit{C1} and \textit{C2}, since the clock \textit{C1} is running slower down in the gravitational field than the clock \textit{C2} which is running faster at a higher altitude \end{enumerate} [Preview Abstract] |
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F1.00038: Crustal Structure Beneath the Ozark Plateau and Illinois Basin using the OIINK Flexible Array Joshua Russell, Hersh Gilbert, Gary Pavlis The Ozarks Illinois INdiana Kentucky (OIINK) FlexArray seismic deployment provides an opportunity to learn more about the assembly and evolution of North America by comparing tectonic boundaries to variations in crustal thickness. We analyze P-to-S receiver functions to measure crustal thickness across eastern Missouri and southern Illinois. These observations indicate that crustal thickness across the region ranges from 55km at its thickest along the eastern part of the Ozark Plateau, to 43km beneath the southern portion of the Illinois Basin. The crust thins from the Ozark Plateau southeastward into Illinois where the thinnest crust in the Illinois Basin is found beneath the region where the basin reaches its greatest depth. By examining how the arrival times of converted phases of receiver functions vary as a function of incidence angle, we identify that complications resulting from the reverberation of converted waves within the low velocity sediments of the Illinois Basin influence our crustal thickness measurements. Incorporating the low velocity, shallow sedimentary layers into the velocity model used to migrate receiver function arrival times to depth reduces the crustal thickness by 3-4 km compared to depths calculated without considering basin effects. By understanding how the basin geometry effects crustal arrivals, we can more accurately estimate crustal thickness and determine how it relates to the evolution of structures in the mid-continent. [Preview Abstract] |
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F1.00039: Neutron Diffraction of Li-Ion Battery Electrode Materials Tyler Fears, Helmut Kaiser, Haskell Taub The performance characteristics of Li-ion batteries are largely dependent upon the crystalline structure of the intercalation electrodes. Li insertion and de-insertion modify the crystal structure cyclically during charging and discharging; this process also induces irreversible changes to the structure which lead to capacity fade. Significant advancements have been made with synchrotron radiation which allow diffraction during electrochemical cycling. Unfortunately, Li (a very important component of Li intercalation materials) is transparent to x-rays. Neutron diffraction is sensitive to Li atoms but has its own drawbacks. Unlike intense synchrotron radiation, neutron characterizations are flux-limited and require large sample sizes and/or long data collection times. Additionally, while the transition metal electrode materials are often the strongest x-ray scatterers in typical electrochemical cells, neutrons interact strongly with other cell components, necessitating the use of non-traditional materials for in-situ experiments. In this presentation, we will discuss the advantages of neutron diffraction with in-situ electrochemical cycling, the hurdles that must be overcome for high-resolution pattern collection, and the various strategies for the next phase of the project. [Preview Abstract] |
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F1.00040: The Nuts and Bolts of Running a Graduate Student-Led Science Outreach Program Matthew McCune, Deepika Menon, Kevin Tarwater, Christopher Owens The Public Outreach Committee of the MU Physics and Astronomy Graduate Student Association (PAGSA) was founded in 2012 to increase involvement of its members in science outreach in the community. The committee's goal was to increase the acceptance and understanding of science by the general public while also inspiring the next generation of scientists. Over the past two years the committee has managed events for the Missouri Science Olympiad State Tournament, manned booths at NSTA Science Matter's Night, entertained students at the Mizzou Adventures in Graduate Education event, judged a Junior High and High School Science Fair for the CCAA Conference, as well as helped Smithton Middle School students prepare for the Science Olympiad. The committee's dedication and hard work has been recognized the past two years with the 2012 and 2013 Chancellor's Award in Public Outreach. This poster will show how graduate students can acquire funding, organize volunteers, plan and carry out a successful science outreach program by effective use of department and university resources. [Preview Abstract] |
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F1.00041: Generation of N-particle Dicke-Class States and their Application to Quantum Information Processing Daniel DeYoung, Kishor Kapale Dicke class states are maximally entangled states of atoms or atom-like two-state entities involving a small number of excitations (much less that the total number of atoms). It has been shown in the literature [Z.H. Peng, J. Zou, X.J. Liu, Eur. Phys. J. D 58, 403-407 (2010)] that the so-called asymmetric Dicke states, which carry different relative phases for different permutations corresponding to different atomic entity being in the excited state, are more useful for quantum information processing tasks than the symmetric Dicke states. We have devised a practical conceptual proposal for generation of asymmetric Dicke states based on a proposal to generate symmetric Dicke states [Thiel et al. Phys. Rev. Lett. 99, 193602 (2007)]. We shot that the asymmetric Dicke-class states can be used for perfect teleportation [Agrawal and Pati, Phys. Rev. A 74 062320 (2006)] and dense coding. [Preview Abstract] |
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F1.00042: Kitchen inspired nanochemistry: dispersive, exfoliation and hybridization of functional MoS$_{2}$ nanosheets using culinary hydrocolloids Sudhir Ravula, Jeremy B. Essner, Gary A. Baker As a material, molybdenum disulfide (MoS$_{2})$ has drawn wide attention due to its broad applications and fascinating properties. In order to access its valuable properties, however, van der Waals interactions between the sheets within the bulk crystalline material must be overcome in order to produce stable single- or few-layer nanosheets (S/FLNS). Previous methods to exfoliate MoS$_{2}$ into nanoscale sheets were time consuming, employed expensive, environmentally unfriendly methods, or produced poorly stabilized nanosheets (yielding sheet aggregation). Known exfoliation methods also suffer poor scalability and reproducibility, making them ill-suited for the development of large scale devices and nanocomposites. In light of these facts, a simple and efficient approach to exfoliate bulk MoS$_{2}$ and generate stable S/FLNS using approaches that embrace the principles of green chemistry is long-awaited. We present results on the sonication-assisted aqueous phase exfoliation of bulk MoS$_{2}$ into dispersed S/FLNS using popular culinary agents, including guar gum, tannic acid, and xanthan gum. Subsequent decoration of the sterically-stabilized nanosheets with gold nanoparticles via in situ reduction by the sorbed culinary agent gave a plasmonic nanocatalyst hybrid exhibiting excellent activity toward 4-nitrophenol reduction using sodium borohydride. These agents are green and inexpensively available commercially, opening up interesting possibilities that will be discussed. [Preview Abstract] |
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