• Title/Summary/Keyword: 2D-hexagonal

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Soft-template Synthesis of Magnetically Separable Mesoporous Carbon (자성에 의해 분리 가능한 메조포러스 카본의 소프트 주형 합성)

  • Park, Sung Soo;Ha, Chang-Sik
    • Journal of Adhesion and Interface
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    • v.18 no.2
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    • pp.75-81
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    • 2017
  • In this study, we synthesized mesoporous carbon (Carbonized Ni-FDU-15) containing nanoporous structures and magnetic nanoparticles. Carbonized Ni-FDU-15 was synthesized via evaporation-induced self-assembly (EISA) and direct carbonization by using a triblock copolymer (F127) as a structure-directing agent, a resol precursor as a carbon-pore wall forming material, and nickel (II) nitrate as a metal ion source. The mesoporous carbon has a well-ordered two-dimensional hexagonal structure. Meanwhile, nickel (Ni) metal and nickel oxide (NiO) were produced in the magnetic nanoparticles in the pore wall. The size of the nanoparticles was about 37 nm. The surface area, pore size and pore volume of Carbonized Ni-FDU-15 were $558m^2g^{-1}$, $22.5{\AA}$ and $0.5cm^3g^{-1}$, respectively. Carbonized Ni-FDU-15 was found to move in the direction of magnetic force when magnetic force was externally applied. The magnetic nanoparticle-bearing mesoporous carbons are expected to have high applicability in a wide variety of applications such as adsorption/separation, magnetic storage media, ferrofluid, magnetic resonance imaging (MRI) and drug targeting, etc.

Performance Analysis of Two-Location Distance-based Registration in Mobile Communication Network (이동통신망에서 이중영역 거리기준 위치등록의 성능 분석)

  • Suh, Jae-Joon;Luo, Yong;Baek, Jang-Hyun
    • Journal of the Korea Society for Simulation
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    • v.17 no.4
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    • pp.41-50
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    • 2008
  • In this study, an improved scheme for distance-based registration (DBR) is proposed and its performance is analyzed. In the DBR, when a mobile station (MS) enters a new cell, it calculates the distance between last registered cell and current cell and registers its location if the distance reaches reference distance D. In this study, two-location DBR (TDBR) is proposed to improve the performance of the DBR. In the TDBR, an MS stores not only last registered location area (LA) but also previously registered LA, and then no registration is needed when the MS crosses two LAs stored already. However, since the TDBR may increase paging cost, trade-off is necessary between decreased registration cost and increased paging cost. In this study, the performances of two schemes are analyzed and compared using 2-dimensional random walk mobility model in hexagonal cell configuration. We show that our mathematical analysis is accurate by comparing with simulation. From the numerical results for various circumstances, it is shown that our proposed TDBR outperforms current DBR in most cases.

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Morphology control and optical properties of ZnO nanostructures grown by ultrasonic synthesis

  • Morales-Flores, N.;Galeazzi, R.;Rosendo, E.;Diaz1d, T.;Velumani, S.;Pal, U.
    • Advances in nano research
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    • v.1 no.1
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    • pp.59-70
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    • 2013
  • ZnO nanostructures of rod-like, faceted bar, cup-end bars, and spindle shaped morphologies could be grown by a low power ultrasonic synthesis process. pH of the reaction mixture seems to plays an important role for defining the final morphology of ZnO nanostructures. While the solution pH as low as 7 produces long, uniform rod-like nanostructures of mixed phase (ZnO and $Zn(OH)_2$), higher pH of the reaction mixture produces ZnO nanostructures of different morphologies in pure hexagonal wurtzite phase. pH of the reaction as high as 10 produces bar shaped uniform nanostructures with lower specific surface area and lower surface and lattice defects, reducing the defect emissions of ZnO in the visible region of their photoluminescence spectra.

Adaptive time-step control for modal methods to integrate the neutron diffusion equation

  • Carreno, A.;Vidal-Ferrandiz, A.;Ginestar, D.;Verdu, G.
    • Nuclear Engineering and Technology
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    • v.53 no.2
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    • pp.399-413
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    • 2021
  • The solution of the time-dependent neutron diffusion equation can be approximated using quasi-static methods that factorise the neutronic flux as the product of a time dependent function times a shape function that depends both on space and time. A generalization of this technique is the updated modal method. This strategy assumes that the neutron flux can be decomposed into a sum of amplitudes multiplied by some shape functions. These functions, known as modes, come from the solution of the eigenvalue problems associated with the static neutron diffusion equation that are being updated along the transient. In previous works, the time step used to update the modes is set to a fixed value and this implies the need of using small time-steps to obtain accurate results and, consequently, a high computational cost. In this work, we propose the use of an adaptive control time-step that reduces automatically the time-step when the algorithm detects large errors and increases this value when it is not necessary to use small steps. Several strategies to compute the modes updating time step are proposed and their performance is tested for different transients in benchmark reactors with rectangular and hexagonal geometry.

Study on the Electro-Optic Characteristics of $CdS_{1-x}Se_{x}$ Photoconductive Thin Films ($CdS_{1-x}Se_{x}$ 광도전 박막의 전기-광학적 특성연구)

  • Yang, D.I.;Shin, Y.J.;Lim, S.Y.;Park, S.M.;Choi, Y.D.
    • Journal of Sensor Science and Technology
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    • v.1 no.1
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    • pp.53-57
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    • 1992
  • We report the crystal growth and the electro-optic characteristics of $CdS_{1-x}Se_{x}$ thin films. $CdS_{1-x}Se_{x}$ thin films wire deposited on the alumina plate by electron beam evaporation technique in pressure of $1.5{\times}10^{-7}$ torr, voltage of 4kV, current of 2.5mA and substrate temperature of $300^{\circ}C$. The deposited $CdS_{1-x}Se_{x}$ thin films were proved to be a polycrystal with hexagonal structure through X-ray diffraction patterns. $CdS_{1-x}Se_{x}$ photoconductive films showed high photoconductivity after annealing at $550^{\circ}C$ for 30 minutes. And the films have been investigated the Hall effect, photocurrent spectra, sensitivity, maximum allowable power dissipation and response time.

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Dedicated preparation for in situ transmission electron microscope tensile testing of exfoliated graphene

  • Kim, Kangsik;Yoon, Jong Chan;Kim, Jaemin;Kim, Jung Hwa;Lee, Suk Woo;Yoon, Aram;Lee, Zonghoon
    • Applied Microscopy
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    • v.49
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    • pp.3.1-3.7
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    • 2019
  • Graphene, which is one of the most promising materials for its state-of-the-art applications, has received extensive attention because of its superior mechanical properties. However, there is little experimental evidence related to the mechanical properties of graphene at the atomic level because of the challenges associated with transferring atomically-thin two-dimensional (2D) materials onto microelectromechanical systems (MEMS) devices. In this study, we show successful dry transfer with a gel material of a stable, clean, and free-standing exfoliated graphene film onto a push-to-pull (PTP) device, which is a MEMS device used for uniaxial tensile testing in in situ transmission electron microscopy (TEM). Through the results of optical microscopy, Raman spectroscopy, and TEM, we demonstrate high quality exfoliated graphene on the PTP device. Finally, the stress-strain results corresponding to propagating cracks in folded graphene were simultaneously obtained during the tensile tests in TEM. The zigzag and armchair edges of graphene confirmed that the fracture occurred in association with the hexagonal lattice structure of graphene while the tensile testing. In the wake of the results, we envision the dedicated preparation and in situ TEM tensile experiments advance the understanding of the relationship between the mechanical properties and structural characteristics of 2D materials.

Synthesis of Cobalt Hydroxide Nanosheets based on Sonication-induced Exfoliation for Depolymerization of Polyethylene Terephthalate (폴리에틸렌 테레프탈레이트의 해중합을 위한 초음파 박리법 기반의 코발트 수산화물 나노시트의 제조)

  • Jin, Se Bin;Son, Seon Gyu;Jeong, Jae-Min;Choi, Bong Gill
    • Applied Chemistry for Engineering
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    • v.31 no.6
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    • pp.668-673
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    • 2020
  • In this work, ultrathin and two-dimensional (2D) cobalt hydroxide [Co(OH)2] nanosheets were synthesized by a sonication assisted liquid-phase exfoliation of bulk Co(OH)2. The resulting exfoliated Co(OH)2 is a hexagonal mono-layered nanosheet with a high specific surface area of 27.5 ㎡ g-1. The depolymerization of polyethylene terephthalate (PET) based on glycolysis reaction was also performed using an exfoliated Co(OH)2 catalyst. Excellent catalytic reaction performances were demonstrated; a high PET conversion and bis(2-hydroxyethyl) terephthalate (BHET) yield of both 100% using the nanosheet catalyst were achieved within a reaction time and temperature of 30 min and 200 ℃, respectively. The long-term stability of exfoliated Co(OH)2 catalysts was also demonstrated by recyclability tests of the catalyzed glycolysis reaction of PET over four cycles, showing both 100% of high PET conversion and BHET yield.

Synthetic Characteristics of AlPO$_4$-5 Molecular Sieve (AlPO$_4$-5 분자체의 합성 특성)

  • Sung Hwa Jhung;Suk Bong Hong;Young Sun Uh;Hakze Chon
    • Journal of the Korean Chemical Society
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    • v.37 no.10
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    • pp.867-873
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    • 1993
  • Influences of crystallization time and $H_2O/Al_2O_3$ ratio of the reaction mixtures on the synthesis of AlPO$_4$-5 molecular sieve have been studied by X-ray powder diffraction, nitrogen adsorption, scanning electron microscope (SEM), and solid state $^{27}$Al magic angle spinning nuclear magnetic resonance (MAS NMR) techniques. The degree of crystallinity of AlPO$_4$-5 follows a sigmoid pattem as crystallization time increases. The induction period is shorter than 1 h when the crystallization process is carried out at 150$^{\circ}$C. The conversion of reactants to product, AlPO$_4$-5, can be clearly observed, and all of the determined physical properties change abruptly after about 2 h. It is found that increase in $H_2O/Al_2O_3$ ratio of the reaction mixtures not only changes the crystal morphology from aggregates to hexagonal single crystals, but also results in the formation of longer AlPO$_4$-5 crystals.

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Growth mechanism of three dimensionally structured TiO2 thin film for gas sensors (가스 감응용 3차원 구조체 TiO2 박막 성장기구)

  • Moon, Hi-Gyu;Yoon, Seok-Jin;Park, Hyung-Ho;Kim, Jin-Sang
    • Journal of Sensor Science and Technology
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    • v.18 no.2
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    • pp.110-115
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    • 2009
  • Polystyrene (PS) microspheres were used to good advantage as a template material to prepare macroporous $TiO_2$ thin films. This is enabled to run the thermal decomposition of the PS without the collapsing of the 3-D macroporous framework during the calcination step. $TiO_2$ thin films were deposited onto the colloidal templated substrates at room temperature by RF sputtering, and then samples were thermally treated at $450^{\circ}C$ for 40.min in air to remove the organic colloidal template and induce crystallization of the $TiO_2$ film. The macroporous $TiO_2$ thin film exhibited a quasi-ordered partially hexagonal close-packed structure. Burst holes, estimated to be formed during PS thermal decomposition, are seen as the hemisphere walls. the inner as well as the outer surfaces of the hollow hemispheres formed by the method of thermal decomposition can be easily accessed by the diffusing gas species. As a consequence, the active surface area interacting with the gas species is expected to be enlarged about by a factor of fourth as large as compared to that of a planar films. Also the thickness at neighboring hemisphere could be controlled a few nm thickness. If the acceptor density becomes as large that depletion width reaches those thickness, the device is in the pinch off-situation and a strong resistance change should be observed.

Rare-Earth Metal Complex-Functionalized Mesoporous Silica for a Potential UV Sensor (잠재적인 UV 센서를 위한 희토류 금속착물이 기능화된 메조다공성 실리카)

  • Sung Soo Park;Mi-Ra Kim;Weontae Oh;Yedam Kim;Yeeun Lee;Youngeon Lee;Kangbeom Ha;Dojun Jung
    • Journal of Adhesion and Interface
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    • v.24 no.4
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    • pp.136-142
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    • 2023
  • In this study, TEOS was used as a silica source, and a triblock copolymer (P123) was used as a template to produce mesoporous silica with a well-ordered hexagonal mesopore array through a self-assembly method and hydrothermal process under acidic condition. (Surfactant-extracted SBA-15). Surfactant-extracted SBA-15 showed the particle shape of a short rod with a size of approximately 980 nm. The surface area and pore diameter were 730 m2g-1 and 70.8 Å, respectively. Meanwhile, aminosilane (3-aminopropyltriethoxysilane, APTES) was grafted into the mesopores using a post-synthesis method. Mesoporous silica (APTES-SBA-15) modified with aminosilane had a well-ordered pore structure (p6mm) and well-maintained the particle shape of short rods. The surface area and pore diameter of APTES-SBA-15 decreased to 350 m2g-1 and 60.7 Å, respectively. APTES-modified mesoporous silica was treated with a solution of rare earth metal ions (Eu3+, Tb3+) to synthesize a mesoporous silica material in which rare earth metal complexes were introduced into the mesopores. (Eu/APTES-SBA-15, Tb/APTES-SBA-15) These materials exhibited characteristic photoluminescence spectra by λex=250 nm. (5D47F5 (543.5 nm), 5D47F4 (583.5 nm), 5D47F3 (620.2 nm) transitions for Tb/APTES-SBA-15; 5D07F0 (577.7 nm), 5D07F1 (592.0 nm), 5D07F2 (614.9 nm), 5D07F3 (650.3 nm) and 5D07F4 (698.5 nm) transitions for Eu/APTES-SBA-15)