• Title/Summary/Keyword: vibrational power spectra

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A Molecular Dynamics Simulation Study of Hydroxyls in Dioctahedral Phyllosilicates (분자동역학 시뮬레이션을 이용한 이팔면체 점토광물 수산기 연구)

  • Son, Sangbo;Kwon, Kideok D.
    • Journal of the Mineralogical Society of Korea
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    • v.29 no.4
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    • pp.209-220
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    • 2016
  • Clay minerals are a major player to determine geochemical cycles of trace metals and carbon in the critical zone which covers the atmosphere down to groundwater aquifers. Molecular dynamics (MD) simulations can examine the Earth materials at an atomic level and, therefore, provide detailed fundamental-level insights related to physicochemical properties of clay minerals. In the current study, we have applied classical MD simulations with clayFF force field to dioctahedral clay minerals (i.e., gibbsite, kaolinite, and pyrophyllite) to analyze and compare structural parameters (lattice parameter, atomic pair distance) with experiments. We further calculated vibrational power spectra for the hydroxyls of the minerals by using the MD simulations results. The MD simulations predicted lattice parameters and interatomic distances respectively deviated less than 0.1~3.7% and 5% from the experimental results. The stretching vibrational wavenumber of the hydroxyl groups were calculated $200-300cm^{-1}$ higher than experiment. However, the trends in the frequencies among different surface hydroxyl groups of each mineral was consistent with experimental results. The angle formed by the surface hydroxyl group with the (001) plane and hydrogen bond distances of the surface hydroxyls were consistent with experimental result trends. The inner hydroxyls, however, showed results somewhat deviated from reported data in the literature. These results indicate that molecular dynamics simulations with clayFF can be a useful method in elucidating the roles of surface hydroxyl groups in the adsorption of metal ions to clay minerals.

Effect of power law index for vibration of armchair and zigzag single walled carbon nanotubes

  • Khadimallah, Mohamed Amine;Hussain, Muzamal
    • Steel and Composite Structures
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    • v.37 no.5
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    • pp.621-632
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    • 2020
  • This research deals with the study of vibrational behavior of armchair and zigzag single-walled carbon nanotubes invoking extended Love shell theory. The effects of different physical and material parameters on the fundamental frequencies are investigated. By using volume fraction for power law index, the fundamental natural frequency spectra for two forms of single-walled carbon nanotubes are calculated. The influence of frequencies against length-to-diameter ratios with varying power law index are investigated in detail for these tubes. To discretize the governing equation in eigen-value form, wave propagation approach is developed. Complex exponential functions have been used and the axial model depends on boundary condition that has been described at the edges of carbon nanotubes to calculate the axial modal dependence. Computer software MATLAB is utilized for the frequencies of single-walled carbon nanotubes and current results shows a good stability with comparison of other studies.

A Molecular Dynamics Simulation Study of Trioctahedral Clay Minerals (삼팔면체 점토광물에 대한 분자동역학 시뮬레이션 연구)

  • Lee, Jiyeon;Lee, Jin-Yong;Kwon, Kideok D.
    • Journal of the Mineralogical Society of Korea
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    • v.30 no.4
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    • pp.161-172
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    • 2017
  • Clay minerals play a major role in the geochemical cycles of metals in the Critical Zone, the Earth surface-layer ranging from the groundwater bottom to the tree tops. Atomistic scale research of the very fine particles can help understand the fundamental mechanisms of the important geochemical processes and possibly apply to development of hybrid nanomaterials. Molecular dynamics (MD) simulations can provide atomistic level insights into the crystal structures of clay minerals and the chemical reactivity. Classical MD simulations use a force field which is a parameter set of interatomic pair potentials. The ClayFF force field has been widely used in the MD simulations of dioctahedral clay minerals as the force field was developed mainly based on dioctahedral phyllosilicates. The ClayFF is often used also for trioctahedral mineral simulations, but disagreement exits in selection of the interatomic potential parameters, particularly for Mg atom-types of the octahedral sheet. In this study, MD simulations were performed for trioctahedral clay minerals such as brucite, lizardite, and talc, to test how the two different Mg atom types (i.e., 'mgo' or 'mgh') affect the simulation results. The structural parameters such as lattice parameters and interatomic distances were relatively insensitive to the choice of the parameter, but the vibrational power spectra of hydroxyls were more sensitive to the choice of the parameter particularly for lizardite.

AKARI near-infrared spectral observations on the shocked H2 gas of a supernova remnant IC 443

  • Shinn, Jong-Ho;Koo, Bon-Chul;Seon, Kwang-Il;Lee, Ho-Gyu
    • The Bulletin of The Korean Astronomical Society
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    • v.35 no.1
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    • pp.69.1-69.1
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    • 2010
  • IC 443 is famous for its interaction with nearby molecular clouds and intense H2 emission lines in infrared. Therefore, it has been studied extensively for the understanding of molecular shocks. We observed H2 mission lines toward the shock-cloud interaction regions of IC 443, known as clumps B, C, and G. The observations were performed with the InfraRed Camera (IRC) onboard a satellite AKARI over 2.5-5.0 um, where previous space observations, e.g. Infrared Space Observatory (ISO) and Spitzer, do not cover. Our AKARI observations provide spectra of sequential pure-rotational and ro-vibrational H2 emission lines. For the clumps C and G, combining with previous mid-infrared observational results, we found that the H2 level populations show a significant separation between v=0 and v=1 levels; v=1 levels are under-populated than v=0 levels, therefore, the population cannot be described by two temperature LTE model, as many people have analyzed for the shocked H2 gas. We also applied the thermal admixture model, dN(H2; T)~T^(-b) dT, with varying ortho-to-para ratios according to the temperature, to describe the level population, and obtained plausible ranges of the H2 gas density and power-law index b.

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Fabrication of Microcrystalline NaPbLa(WO4)3:Yb3+/Ho3+ Phosphors and Their Upconversion Photoluminescent Characteristics

  • Lim, Chang Sung;Atuchin, Victor V.;Aleksandrovsky, Aleksandr S.;Denisenko, Yuriy G.;Molokeev, Maxim S.;Oreshonkov, Aleksandr S.
    • Korean Journal of Materials Research
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    • v.29 no.12
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    • pp.741-746
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    • 2019
  • New triple tungstate phosphors NaPbLa(WO4)3:Yb3+/Ho3+ (x = Yb3+/Ho3+ = 7, 8, 9, 10) are successfully fabricated by microwave assisted sol-gel synthesis and their structural and frequency upconversion (UC) characteristics are investigated. The compounds crystallized in the tetragonal space group I41/a and the NaPbLa(WO4)3 host have unit cell parameters a = 5.3927(1) and c = 11.7961(3) Å, V = 343.05(2) Å3, Z = 4. Under excitation at 980 nm, the phosphors have yellowish green emissions, which are derived from the intense 5S2/5F45I8 transitions of Ho3+ ions in the green spectral range and strong 5F55I8 transitions in the red spectral range. The optimal Yb3+:Ho3+ ratio is revealed to be x = 9, which is attributed to the quenching effect of Ho3+ ions, as indicated by the composition dependence. The UC characteristics are evaluated in detail under consideration of the pump power dependence and Commission Internationale de L'Eclairage chromaticity. The spectroscopic features of Raman spectra are discussed in terms of the superposition of Ho3+ luminescence and vibrational lines. The possibility of controlling the spectral distribution of UC luminescence by the chemical content of tungstate hosts is demonstrated.