• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.23 no.8
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• pp.617-621
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• 2010

($K_{0.5}Na_{0.5}$)($Nb_{0.96}Sb_{0.04}$)$O_3$+1.2 mol% $K_4CuNb_8O_{23}$ ceramics doped with iron oxide ($Fe_2O_3$) were prepared by a conventional mixed oxide method. And then, their piezoelectric and dielectric properties were investigated as a function of $Fe_2O_3$ addition. X-ray diffraction studies reveal that $Fe^{3+}$ diffuses into the NKN lattices to form a solid solution with a pure perovskite structure at room temperature. At the sintering temperature of $1,060^{\circ}C$, when 0.2 mol% $Fe_2O_3$ was doped, the piezoelectric constant ($d_{33}$), electromechanical coupling factor (Kp), and mechanical quality factor ($Q_m$) showed the excellent values of 131.67 pC/N, 0.436, and 696.36, respectively. Results show that $Fe_2O_3$ deped ($K_{0.5}Na_{0.5}$)($Nb_{0.96}Sb_{0.04}$)$O_3$+1.2 mol% $K_4CuNb_8O_{23}$ lead-free piezoelectric ceramics are a promising lead free material for piezoelectric transformer applications.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.13 no.2
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• pp.492-497
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• 2012

In this paper, we determined the scintillation and thermoluminescence properties of $Cs_2NaCeBr_6$ elpasolite scintillation crystal. The emission spectrum of $Cs_2NaCeBr_6$ is located in the range of 300 ~ 450 nm, peaking at 377 nm and 400 nm. And, the fluorescence decay time of the crystal is composed two components. The fast component is 140 ns (94%), and the slow component is 880 ns (6%) of the crystal. The after-glow is caused by the electron and hole traps in the crystal lattices. We determined thermoluminescence parameters of the traps in the crystal. The determined activation energy(E), kinetic order and frequency factor of the traps are 0.67 eV, 1.71 and $2.51{\times}10^8s^{-1}$ respectively. In this crystal, re-combination rate is more dominant phenomenon than the re-trapping rate.

• Korean Institute of Interior Design Journal
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• v.21 no.4
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• pp.163-171
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• 2012

The objective of this study was to analyze the characteristics of traditionality expressions at modernized Chinese restaurant in Hong Kong. As a case study, the study examined 12 modernized Chinese restaurants in Hong Kong. The gathered data were categorized and examined according to the ways of traditionality expressions, which included reproduction, transformation, and reinterpretation of traditional components. Each of the components was measured for the amount of traditional or modernity expression on a five-point scale. The five-point scoring system put an emphasis on heritage; 1 point was given to principal modernity(modernity: 90-100% + tradition: 0-10%), 2 points were given to principal modernity + auxiliary tradition(modernity: 70-90% + tradition: 10-30%), 3 points were given to the same ratio between tradition and modernity(modernity: 40-60% + tradition: 40-60%), 4 points were given to principal tradition + auxiliary modernity(modernity: 10-30% + tradition: 70-90%), and 5 points were given to principal tradition(modernity: 0-10% + tradition: 90-100%). The analysis performed according to those criteria and methodologies led to the following findings and conclusions: Traditional components were most reproduced in the ornaments placed all over the restaurant and applied to the chirography of the restaurant logos, walls, and windows/doors in a big number. The methodology of transforming tradition was evenly applied to each of the spatial components. With the most transformations occurring to the lattices, there were many different ways to transform tradition including the partition, chirography, pattern, red lantern, furniture and ornament, and traditional materials that were turned into modern ones. Few examples of reinterpreting tradition were observed in the restaurant titles, inside floors, and ceilings, but plenty of examples were found in the walls, windows/doors, lighting, and furniture in a range of ways. Most of them reinterpreted the traditional forms and added altered patterns to them to remind customers of tradition. In short, all of the three ways of expressing tradition were actively applied to each component in an array of ways.

• Membrane Journal
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• v.27 no.3
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• pp.216-225
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• 2017

Since the experimental proof of one-atom-thick graphene single layer from graphite in 2004, graphene, as a leading material opening two-dimensional world, has been tremendously investigated owing to its intrinsic extraordinary physical properties. Among many promising graphene applications, it is believed that membranes might be one of the first significant applications for graphene and its derivatives (e.g., graphene oxide). Recently, a number of simulation results and proof-of-concept experimental approaches towards graphene membranes reflect such positive prospects. Moreover, graphene and graphene oxide already show many outstanding intrinsic properties suitable for promising membrane platforms, such as the minimum membrane thickness, excellent mechanical strength, high chemical and thermal stability, and the ability to generate nanopores in the two-dimensional, rigid hexagonal lattices or to create slit-like nanochannels between adjacent sheets. In this paper, important theoretical and experimental developments in graphene or graphene oxide-based membranes for gas separation based on intrinsic properties of graphene and its derivatives will be discussed, emphasizing on transport behavior, membrane formation methods, and challenging issues for actual membrane applications.

• Proceedings of the Materials Research Society of Korea Conference
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• 2003.11a
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• pp.56-56
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• 2003

BaTiO$_3$, SrTiO$_3$단일막과 BaTiO$_3$ (BTO)/SrTiO$_3$ (STO) 산화물 인공격자를 pulsed laser deposition (PLD) 법에 의해서 100 nm 두께의 (La,Sr)CoO3 (LSCO) 산화물 전극이 코핑된 MgO 단결정 기판 위에 증착시켰다. 이러한 기판위에서 2 unit cell의 적층 두께를 갖는 BTO/STO 초격자 (=BTO2/STO2)를 100～5 nm까지 변화시켰다. 또한 BTO와 STO 단일막도 같은 두께로 변화시켰다. 이러한 두께 범위에서 BTO, STO 단일막과 초격자의 격자변형에 따른 유전특성을 살펴 보았다. 두께 변화에 따른 단일막과 초격자의 구조 분석은 포항 방사광 가속기의 x-ray 회절에 의해서 이루어졌다. 다양한 두께를 갖는 BTO2/STO2 초격자에서 BTO와 STO 충은 in-plane 방향으로 격자정합을 유지하면서 변형되었다. 두께가 얇아지면서 하부 LSCO영향으로 BTO, STO의 n-plane 격자상수는 LSCO 격자상수 쪽으로 접근하였다. Out-of-plane 방향의 BTO 격자상수는 두께가 얇아지면서 증가하였고 반면에 STO 격자상수는 감소하였다. STO와 BTO 단일막의 격자변형은 두께가 얇아지면서 in-plane 방향으로 압축응력으로 인해 증가하였다. 그러나, 격자부정합도가 큰 BTO격자에서 더 많이 변형되었다. 또한 초격자에서 BTO격자가 BTO 단일막보다 더 많이 변형되었는데 초격자에서는 BTO, STO 두 층의 발달된 변형뿐만 아니라 하부 LSCO/MgO 기판의 영향을 함께 받고 있기 때문이다. 초격자와 단일막의 유전상수를 살펴보면은 두께가 감소하면서 유전상수가 감소하는 size effect을 보이고 있다. 하지만 초격자에서의 유전상수가 단일막보다 우수한 유전특성을 보이고 있다. 이러한 결과로 볼 때 격자변형이 size effect 영향을 끼치는 중요한 요소임을 확인하였다.

• Proceedings of the Materials Research Society of Korea Conference
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• 2003.11a
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• pp.55-55
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• 2003

Ferroelectric 물질은 고유전성, 자발분극과 전기장에 따른 유전상수의 변화 등의 특성을 가지고 있으므로 많은 연구가 진행중이다. 이러한 ferroelectric 물질의 유전 특성에 미치는 요소로는 물질의 조성비, 박막의 스트레스, 결정성 등이 있다. 특히 스트레스에 대한 연구가 활발히 진행중이다. 본 연구에서 산화물 인공격자를 이용하여 단일박막에서 얻을 수 없는 격자변형도를 얻어 격자 변형이 박막의 유전특성에 미치는 영향을 연구하였다. BaTiO$_3$ (BTO)/SrTiO$_3$ (STO) 산화물 인공격자를 Pulsed laser deposition (PLD)법으로 (La,Sr)CoO$_3$ 전극이 코팅된 MGO (100) 단결정 기판위에 증착시켰다. 적층 주기에 변화를 주어 BTO와 STO 각각 1.01~1.095와 0.925 ~ 1.003의 단일 막에서는 얻을 수 없는 격자 변형도를 얻었다. 이 실험적 데이터를 기초로 하여 density functional theory (DFT)라고 불리는 범함수밀도론를 기초한 제일원리적 계산 방법을 통하여 격자 변형된 SrTiO$_3$의 구조적, 전기적 특성을 계산하였다. SrTiO$_3$와 BaTiO$_3$ 격자의 안정성을 분석하기 위하여 Vienna Ab-intio Simulation Package (VASP) code가 사용되었다. SrTiO$_3$와 BaTiO$_3$ 산화물 격자의 안정성 분석 후, frozen-phonon 계산 방법을 사용하여 zone-centered optical phonon mode가 계산되었으며, mode effective charge는 Berry-phase polarization 으로부터 얻어졌다. SrTiO$_3$ 격자가 격자변형이 일어나지 않은 상태로부터 c/a= 0.985로 격자 변형 이 일어남에 따라 optical phonon mode는 점차 hardening되었다. BaTiO$_3$ 격자의 경우 SrTiO$_3$ 격자와는 달리 격자 변형이 1.01~1.023으로 진행됨에 따라 optical phonon mode의 증가를 가져왔으나 Born effective charge의 증가하였으며, 더 이상 격자 변형이 진행됨에 따라 optical phonon mode의 감소를 가져왔으나 Born effective charge의 증가 유전상수는 증가했다. 격자 변형이 SrTiO$_3$ 와 BaTiO$_3$ 산화물 격자의 optical phonon mode와 Born effective charge에 크게 영향을 미쳤다.

• Journal of Powder Materials
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• v.19 no.2
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• pp.146-150
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• 2012

The effects of nano $Fe_xC$ addition to superconducting properties of $in$ $situ$ processed $MgB_2$ superconductors was examined. 0.1 wt.% and 1 wt.% nano $Fe_xC$ powders were mixed with boron and magnesium powders by ball milling. The powder mixtures were made into pellets by uniaxial pressing. The pellets were heat-treated at $700^{\circ}C-900^{\circ}C$ in argon atmosphere for $MgB_2$ formation. It was found by powder X-ray diffraction that the raw powders were completely converted into $MgB_2$ after the heat treatment. The superconducting transition temperature ($T_c$) and critical current density ($J_c$), estimated from susceptibility-temperature and $M-H$ curves, were decreased by nano $Fe_xC$ addition. The $T_c$ and $J_c$ decrease by nano $Fe_xC$ addition are attributed to the incorporation of iron and carbon with $MgB_2$ lattices (Fe substitution for Mg and C substitution for B) due to the high reactivity of the nano $Fe_xC$ powder.

• Proceedings of the Korea Contents Association Conference
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• 2007.11a
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• pp.209-211
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• 2007

The computational time of Stocahstic Diagonalization (SD) calculation for 2-dimensional interacting fermion systems is reduced by using several methods including symmetry operations. First, each lattice is subdivided into spin-up and spin-down lattices separately, thus allowing a bi-partite lattice. A valid basis state is then obtained from stacking up an up-spin configuration on top of a down-spin configuration. As a consequence, the memory space to be used in saving the trial basis state reduces significantly. Secondly, the matrix elements of a Hamiltonianin are reconrded in a look-up table when making basis state set. Thus the repeated calculation of the matrix elements of the Hamiltonian are avoided during SD process. Thirdly, by applying symmetry operations to the basis state set the original basis state is transformed to a new basis state whose elements are the eigenvectors of the symmetry operations. The ground state wavefunction is constructed from the elements of symmetric - bonding state - basis state set. As a result, the total number of basis states involved in SD calculation is reduced upto 50 percentage by using symmetry operations.

• Korean Chemical Engineering Research
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• v.48 no.3
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• pp.292-299
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• 2010

Graphene is a two-dimensional nanosheet consisting of honeycomb lattices of $sp^2$ carbon atoms. It is one of promising active materials for the anode of lithium-ion battery and the electrode of supercapacitor, due to its large specific surface area(theoretically $2600m^2\;g^{-1}$), high electric conductivity(typically $8{\times}10^5S\;cm^{-1}$), and mechanical strength. In this review, the synthetic methods of graphene nanosheet and graphene-based nanocomposite are introduced. Also, the electrochemical properties obtainable when the graphene-based materials are adopted to the electrodes of lithium-ion battery and supercapacitor are discussed along with their nanostructures.

• Proceedings of the SCSK Conference
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• 2003.09a
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• pp.192-202
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• 2003

The wrinkles correspond to the most obvious expression of skin ageing and are manifested by changes on the organization and dermal structure. In the extracellular matrix, decreased quantities of collagens and glycosaminoglycans as well as a deterioration of the fibrillary network is noted, result in a reduction of dermal thickness. In addition, the activity of the collagenases increases in contrast to the synthesis of collagen fibers. Nor are cells spared during the aging process. We thus studied and compared the contractile capacity as well as the synthesis capacity of normal human fibroblasts and human fibroblasts obtained from biopsies of forehead wrinkles. The capacity of the fibroblasts to be adhered to the collagen network and to maintain a three-dimensional structure of dermis was studied on a model of equivalent dermis. The metabolic activity was studied by evaluating the capacities of synthesis of collagen I, main component of dermis. Human fibroblasts resulting from the forehead wrinkle contract less the gel of collagen than the normal human fibroblasts and present an activity of biosynthesis of collagen I less important than normal human fibroblasts. These results show that fibroblasts with aging present a deceleration of their metabolic activity and lose their capacity of adhesion to collagen fibers thus limiting the possibility of organizing the dermal tissue. We investigated the potential of an active ingredient able to compensate for the reduction of the metabolic activity and to restore the contractile capacity of fibroblasts obtained from forehead wrinkles. This effect was compared with a reference molecule: the vitamin C.