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Now showing items 1 - 16 of 84


    Disclosed is an image forming apparatus employing an electrophotograph image forming unit and an inkjet image forming unit and thereby being capable of printing images respectively on the front and back of paper.
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  • Fast Lithium Ion Migration in Room Temperature LiBH4

    Lee, Young-Su   Cho, Young Whan  

    The defect structure and the Li ion diffusion mechanism of orthorhombic LiBH4 (o-LiBH4) are studied by first-principles calculations to elucidate the Li ion transport in o-LiBH4. Two metastable Li interstitial sites are identified, and the formation energies of the Schottky and Frenkel defect pair are calculated to be 1.2-1.4 eV, the former being slightly easier to form. The energy required to form intrinsic defects is higher than that of hexagonal LiBH4 (h-LiBH4). On the other hand, the migration energy barrier of the Li vacancy or interstitial ranges from 0.1 to 0.3 eV, which is comparable to that of hLiBH(4). Therefore, the higher defect formation energy mainly accounts for the much lower Li ion conductivity of o-LiBH4. The calculated overall activation barrier for the Li ion conduction in fair agreement with the experimental activation energy. Molecular,dynamics simulation demonstrates that both the interstitial and the interstitialcy mechanisms are operative for the Li interstitial diffusion and that the interconnected interstitial sites compose a fast diffusion path. The simulation results point out that the enhancement of the carrier density via defect or interface engineering may significantly raise the ionic conductivity of o-LiBH4.
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  • Interface-enhanced Li ion conduction in a LiBH4-SiO2 solid electrolyte

    Choi, Yong Seok   Lee, Young-Su   Oh, Kyu Hwan   Cho, Young Whan  

    We have developed a fast solid state Li ion conductor composed of LiBH4 and SiO2 by means of interface engineering. A composite of LiBH4-SiO2 was simply synthesized by high energy ball-milling, and two types of SiO2 (MCM-41 and fumed silica) having different specific surface areas were used to evaluate the effect of the LiBH4/SiO2 interface on the ionic conductivity enhancement. The ionic conductivity of the ball-milled LiBH4-MCM-41 and LiBH4-fumed silica mixture is as high as 10(-5) S cm(-1) and 10(-4) S cm(-1) at room temperature, respectively. In particular, the conductivity of the latter is comparable to the LiBH4 melt-infiltrated into MCM-41. The conductivities of the LiBH4-fumed silica mixtures at different mixing ratios were analyzed employing a continuum percolation model, and the conductivity of the LiBH4/SiO2 interface layer is estimated to be 10(5) times higher than that of pure bulk LiBH4. The result highlights the importance of the interface and indicates that significant enhancement in ionic conductivity can be achieved via interface engineering.
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  • Lithium Ion Disorder and Conduction Mechanism in LiCe(BH4)(3)Cl

    Lee, Young-Su   Ley, Morten B.   Jensen, Torben R.   Cho, Young Whan  

    We investigate the diffusion mechanism of Li ions in LiCe(BH4)(3)Cl, which exhibits fast Li ion conduction. It was previously shown that eight Li ions partially occupy the 12d Wyckoff sites in the I (4) over bar 3m structure and the Li ion diffusion takes place via jumping through the three-dimensional network of the 12d sites. In this study, we employ first-principles-nudged elastic band simulation to elucidate the diffusion mechanism and discover that the Li ion does not directly jump to the neighboring 12d site, but instead passes through the closest 6b site. Moreover, the 6b site turns out to be another stable Li ion site, not just a transient point during a jump event. The occupation of the 6b site and the Li ion diffusion mechanism were assured by first-principles molecular dynamics simulations. The partial occupancy of the 12d site and 6b site at 500 K is approximately 1/2 and 1/3, respectively. The experimental diffraction data can be consistently interpreted. The peculiar crystal structure of LiCe(BH4)(3)Cl allowing efficient and fast Li ion diffusion is again highlighted together with the role of [BH4](-) ion in thermodynamically stabilizing LiCe(BH4)(3)Cl.
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    The present invention relates to a method for artificially breeding Illeis koebelei, which provides an optimized artificial breeding environment based on the ecological characteristics of the Illeis koebelei that are indigenous fungivorous natural predators and which supplies feed that enables excellent phased growth, thus leading to the artificial breeding of Illeis koebelei having superior viability and fecundity. Particularly, the method of the present invention comprises: a step of taking eggs from imagoes so as to obtain hatched larvae; a step of raising the hatched larvae so as to obtain fully grown larvae; a step of enabling the fully grown larvae to pupate so as to obtain pupae; a step of enabling the pupae so as to eclose to obtain imagoes; and a step of inducing natural copulation and spawning of the imagoes, thus enabling the artificial breeding of the Illeis koebelei.
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    The present invention relates to a skin care apparatus using micro bubbles, which provides skin with washing water and micro bubbles to create a closer contact with the skin by sucking and removing any foreign matters that cause skin troubles such as dead skin cells, sebum and demodex in pores, as well as by reducing and easily eliminating adhesiveness of the foreign matters through the micro bubbles that are contained in the washing water such that the skin can be toned up and become cleaner so as to enhance the skin condition in an effective way. According to the present invention, the skin care apparatus comprises: a hand-piece having a contact tip to come in contact with the skin and a hole formed at the contact tip; a vacuum pump for providing a vacuum pressure to the hand-piece; a foreign matter container disposed on the path of the vacuum pressure from the vacuum pump to the hand-piece to collect foreign matters; a washing water container for supplying washing water to the hand-piece, the washing water being applied to the skin through the hole of the contact tip; and a micro bubble generator for providing micro bubbles to the washing water container, thereby providing both the washing water and the micro bubbles to the skin.
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  • Enhanced Li Ion Conductivity in LiBH4-Al2O3 Mixture via Interface Engineering

    Choi, Yong Seok   Lee, Young-Su   Choi, Dong-Jun   Chae, Keun Hwa   Oh, Kyu Hwan   Cho, Young Whan  

    A new solid-state Li ion conductor composed of LiBH4 and Al2O3 was synthesized by a simple ball-milling process. The element distribution map obtained by transmission electron microscopy demonstrates that the LiBH4 and Al2O3 are well mixed and form a large interface after ball-milling. The ionic conductivity of the mixture reaches as high as 2 X 10(-4) S cm(-1) at room temperature when the volume fraction of Al2O3 is approximately 44%. The ionic conductivity of the interface between LiBH4 and Al2O3 was extracted by using a continuum percolation model, which turns out to be about 10(-3) S cm(-1) at room temperature, being 10(5) times higher than, that of pure LiBH4. This remarkable rise in conductivity is accompanied by the lowered activation energy for the Li ion conduction in the mixture, indicating that the interface layer facilitates Li ion conduction. Near-edge X-ray absorption fine structure analysis reveals the presence of B-O bondings in the mixture, which was not detected by X-ray diffraction. This disruption of the chemical bondings at the interface may allow an increase in carrier concentration and/or mobility thereby resulting, in the pronounced enhancement in conductivity. This result provides a guideline for designing fast Li ion conductor through interface engineering.
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  • Stability of quadratic functional equations in generalized functions

    Lee, Young-Su  

    In this paper, we consider the following generalized quadratic functional equation with n-independent variables in the spaces of generalized functions: Sigma(1 <= i
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  • On the stability of a mixed type quadratic-additive functional equation

    Lee, Young-Su   Na, Junyeop   Woo, Heejong  

    In this paper we establish the general solutions of the following mixed type quadratic-additive functional equation: 9f(x+y+z/3) + 4[f(x-y/2) + f(y-z/2) + f(z-x)/2] = 3[f(x) + f(y) + f(z)] in the class of functions between real vector spaces. Moreover, we prove the generalized Hyers-Ulam-Rassias stability of this equation in Banach spaces.
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  • A mixed-cation mixed-anion borohydride NaY(BH4)(2)Cl-2

    Ravnsbaek, Dorthe B.   Ley, Morten B.   Lee, Young-Su   Hagemann, Hans   D'Anna, Vincenza   Cho, Young Whan   Filinchuk, Yaroslav   Jensen, Torben R.  

    A new sodium-yttrium borohydride-chloride, NaY(BH4)(2)Cl-2, is obtained by a combination of mechanochemical synthesis and annealing of NaBH4-YCl3 mixtures and is characterized by in-situ synchrotron radiation X-ray powder diffraction, density functional theory, thermal analysis and vibrational spectroscopy. Several simultaneous and coupled reactions occur during the synthesis, also yielding Na3YCl6 and Na(BH4)(1-x)Cl-x besides the title compound. The polymeric pseudo-orthorhombic crystal structure of NaY(BH4)(2)Cl-2 (space group P2/c) is built of edge- and corner-sharing octahedral coordination polyhedra of yttrium (4Cl + 2BH(4)) and sodium (2Cl + 4BH(4)). The structure is isomorphous to the high temperature polymorph of NaYCl4. The BH4 units in NaY(BH4)(2)Cl-2 are located only on the larger of the two independent anion sites in NaYCl4. Density functional theory optimization of the experimental structure suggests that the BH4 units act as eta(3)-ligands (face-sharing) towards yttrium and eta(1)-ligands (corner-sharing) towards sodium. Raman spectroscopy confirms this BH4 configuration. NaY(BH4)(2)Cl-2 decomposes at similar to 300 degrees C under formation of Na3YCl6, while the latter compound at higher temperatures reacts with Na(BH4)(1-x)Cl-x to form NaCl and possibly amorphous products. The reactions are associated with mass losses of 2.62 and 3.78 wt% for the NaBH4-YCl3 (3:1) and (4:1) samples, respectively. Copyright (C) 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.
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  • Stability of quadratic functional equations in tempered distributions

    Lee, Young-Su  

    We reformulate the following quadratic functional equation: f(kx + y) + f(kx - y) = 2k(2)f(x) + 2f(y) as the equation for generalized functions. Using the fundamental solution of the heat equation, we solve the general solution of this equation and prove the Hyers-Ulam stability in the spaces of tempered distributions and Fourier hyperfunctions.
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    The present invention relates to a manual pipe cutter for cutting a pipe while being rotated. In particular, the present invention allows a pipe cutter to rotate smoothly so as to prevent malfunction and facilitate the cutting work. The pipe cutter is provided with an auxiliary cutting blade so that a cutting blade can be immediately and easily substituted with the auxiliary cutting blade when the cutting blade wears out.
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  • Synthesis and Structural Investigation of Zr(BH4)(4)

    Rude, Line H.   Corno, Marta   Ugliengo, Piero   Baricco, Marcello   Lee, Young-Su   Cho, Young Whan   Besenbacher, Flemming   Overgaard, Jacob   Jensen, Torben R.  

    Zirconium tetraborohydride, Zr(BH4)(4), was synthesized by a metathesis reaction between LiBH4 and ZrCl4 using high-energy ball milling. Initially, a white powder was produced, and during storage at -30 degrees C in a closed vial, transparent rectangular single crystals formed under the lid by vapor deposition. Single-crystal X-ray diffraction data revealed a cubic unit cell (a = 5.8387(4) angstrom, space group P-43m, determined at T = 100 K), which consists of neutral Zr(BH4)4 molecules. The BH4- anions coordinate to Zr via the tetrahedral faces (eta(3)). The shortest distance between neighboring molecules in the solid is defined by B-H-2 center dot center dot center dot H-2-B interactions of 2.77 angstrom. DFT calculations, based on the experimental structure, have been performed with the CRYSTAL code. A phonon instability in the Gamma point was observed for space-group symmetry P-43m, which can be eliminated by a symmetry reduction to the cubic space group P23. Computed IR spectra for the two structural models turned out to be very similar. Synthesis and decomposition was further investigated using in situ synchrotron radiation powder X-ray diffraction.
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  • Fast Lithium Ion Migration in Room Temperature LiBH\r <sub/>4sub>

    Lee, Young-Su   Cho, Young Whan  

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  • A modified embedded-atom method interatomic potential for the V-H system

    Shim, Jae-Hyeok   Lee, Young-Su   Fleury, Eric   Cho, Young Whan   Ko, Won-Seok   Lee, Byeong-Joo  

    An interatomic potential for the vanadium-hydrogen binary system has been developed based on the second nearest-neighbor modified embedded-atom method (2NN MEAM) potential formalism, in combination with the previously developed potentials for V and H. Also, first-principles calculation has been carried out to provide data on the physical properties of this system, which are necessary for the optimization of the potential parameters. The developed potential reasonably reproduces the fundamental physical properties (thermodynamic, diffusion, elastic and volumetric properties) of V-rich bcc solid solution and some of the vanadium hydride phases. The applicability of this potential to the development of V-based alloys for hydrogen applications is discussed. (C) 2011 Elsevier Ltd. All rights reserved.
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  • Stability in Generalized Functions

    Lee, Young-Su  

    We consider the following additive functional equation with n-independent variables: f (Sigma(n)(i-1) x(i)) = Sigma(n)(i-1) f(x(i)) + Sigma(n)(i-1) f(x(i) - x(i-1)) in the spaces of generalized functions. Making use of the heat kernels, we solve the general solutions and the stability problems of the above equation in the spaces of tempered distributions and Fourier hyperfunctions. Moreover, using the mollifiers, we extend these results to the space of distributions.
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