• 대한화학회지
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• 제59권3호
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• pp.215-224
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• 2015

Unsymmetrical tetradentate Schiff base N-(2-hydroxy-5-methylacetophenone)-N'-(2-hydroxy acetophenone) ethylene diamine (H₂L) and its complexes with Cr(III), Mn(II), Fe(III), Co(II), Ni(II) and Cu(II) have been synthesized and characterized by elemental analyses, magnetic susceptibility measurements, IR, electronic spectra and thermogravimetric analyses. ¹H, ¹³C-NMR and FAB Mass spectra of ligand clearly indicate the presence of OH and azomethine groups. Elemental analyses of the complexes indicate that the metal to ligand ratio is 1:1 in all complexes. Infrared spectra of complexes indicate a dibasic quadridentate nature of the ligand and its coordination to metal ions through phenolic oxygen and azomethine nitrogen atoms. The thermal behavior of these complexes showed the loss of lattice water in the first step followed by decomposition of the ligand in subsequent steps. The thermal data have also been analyzed for the kinetic parameters by using Horowitz-Metzger method. The dependence of the electrical conductivity on the temperature has been studied over the temperature range 313-403 K and the complexes are found to show semiconducting behavior. XRD and SEM images of some representative complexes have been recorded. The antimicrobial activity of the ligand and its complexes has been screened against various microorganisms and all of them were found to be active against the test organisms. The Fe(III) and Ni(II) complex have been tested for the catalytic oxidation of styrene.

• Structural Engineering and Mechanics
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• 제76권2호
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• pp.223-237
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• 2020

Transmission towers have come to represent one of the most important infrastructures in today's society, which may suffer severe earthquakes during their service lives. However, in the conventional seismic analyses of transmission towers, the towers are normally assumed to be fixed on the ground without considering the effect of soil-structure interaction (SSI) on the pile-supported transmission tower. This assumption may lead to inaccurate seismic performance estimations of transmission towers. In the present study, the seismic response and failure analyses of pile-supported transmission towers considering SSI are comprehensively performed based on the finite element method. Specifically, two detailed finite element (FE) models of the employed pile-supported transmission tower with and without consideration of SSI effects are established in ABAQUS analysis platform, in which SSI is simulated by the classical p-y approach. A simulation method is developed to stochastically synthesize the earthquake ground motions at different soil depths (i.e. depth-varying ground motions, DVGMs). The impacts of SSI on the dynamic characteristic, seismic response and failure modes are investigated and discussed by using the generated FE models and ground motions. Numerical results show that the vibration mode shapes of the pile-supported transmission towers with and without SSI are basically same; however, SSI can significantly affect the dynamic characteristic by altering the vibration frequencies of different modes. Neglecting the SSI and the variability of earthquake motions at different depths may cause an underestimate and overestimate on the seismic responses, respectively. Moreover, the seismic failure mode of pile-supported transmission towers is also significantly impacted by the SSI and DVGMs.

• 한국강구조학회 논문집
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• 제16권5호통권72호
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• pp.505-517
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• 2004

상자형보와 윈형기둥으로 구성된 강재교각 정합부의 응력평가식 제안에 대한 연구이다. 원형기둥을 각형으로 치환하여 사용하고 있는 기존의 응력평가식은 정합각도가 감소함에 따라 전단지언능력은 과소평가되고, 전단응력은 접협각도가 증가함에 따라 과대하게 평가되는 문제점이 있다. 따라서 이라한 문제점 을 보완하기 위해 다양한 매개변수, 즉 접합각도 (${\alpha}$), 전단지간/보의 폭비 (L/B) 기둥의 휨강성/보의 휨강성비 (k) 를 사용하여 유한요소해석을 수행하고 해석결과를 이용하여 기존 응력평가식의 문제점을 보완할 수 있는 응력평가식을 제안하였다. 한편, 허용응력 대비 극한내하력의 안전율을 검토하기 위해 재료 및 기하 비선형해석을 수행하여 제안식의 타당성을 확인하였다.

• 한국기계가공학회지
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• 제20권12호
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• pp.113-122
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• 2021

Complicated residual stress distributions occur in the vicinity of a deposited region via directed energy deposition (DED) process owing to the rapid heating and cooling cycle of the deposited region and the substrate. The residual stress can cause defects and premature failure in the vicinity of the deposited region. Several heat treatment technologies have been extensively researched and applied on the part deposited by the DED process to relieve the residual stress. The aim of this study was to investigate the residual stress characteristics of a specimen fabricated by DED and a quenching process using thermomechanical analyses. A coupled thermomechanical analysis technique was adopted to predict the residual stress distribution in the vicinity of the deposited region subsequent to the quenching step. The results of the finite element (FE) analyses for the deposition and the cooling measures show that the residual stress in the vicinity of the deposited region significantly increases after the completion of the elastic recovery. The results of the FE analyses for the heating and quenching stages further indicate that the residual stress in the vicinity of the deposited region remarkably increases at the initial stage of quenching. In addition, it is observed that the residual stress for quenching is lesser than that after the elastic recovery, irrespective of the deposited material.

• 한국재료학회지
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• 제14권10호
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• pp.688-695
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• 2004

The capacitor contact barrier(CCB) layers have been introduced in the FeRAM integration to prevent the Pt/Al reaction during the back-end processes. Therefore, the interdiffusion and intermetallic formation in $Pt(1500{\AA})/Al(3000{\AA})$ film stacks were investigated over the annealing temperature range of $100\sim500^{\circ}C$. The interdiffusion in Pt/Al interface started at $300^{\circ}C$ and the stack was completlely intermixed after annealing over $400^{\circ}C$ in nitrogen ambient for 1 hour. Both XRD and SBM analyses revealed that the Pt/Al interdiffusion formed a single phase of $RtAl_2$ intermetallic compound. On the other hand, in the presence of TiN($1000{\AA}$) barrier layer at the Pt/Al interface, the intermetallic formation was completely suppressed even after the annealing at $500^{\circ}C$. These were in good agreement with the predicted effect of the TiN diffusion barrier layer. But the conventional TiN CCB layer could not perfectly block the Pt/Al reaction during the back-end processes of the FeRAM integration with the maximum annealing temperature of $420^{\circ}C$. The difference in the TiN barrier properties could be explained by the voids generated on the Pt electrode surface during the integration. The voids were acted as the starting point of the Pt/Al reaction in real FeRAM structure.

• 한국자기학회지
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• 제25권2호
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• pp.39-42
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• 2015

우리는 탄소가 도핑 된 FePt 박막을 스퍼터링 방법으로 제작한 후 시간 분해능을 가진 모크 장비를 이용해서 매우 빠른 자기소거 후 그 회복 과정을 관찰하였다. 탄소의 함량이 늘어 날수록 격자 구조가 $L1_0$에서 벗어나는 것을 확인하였으며 보자력의 변화 또한 확인하였다. 모든 시료가 펨토 초 펄스로 열을 받으면 5 피코초 안에 자기 소거되었다. 그 후 흥미롭게도 탄소 함량이 많을수록 매우 빠른 자기 회복 시간이 길어지는 것이 관측되었다.

• 한국세라믹학회지
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• 제54권2호
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• pp.137-140
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• 2017

A $TiO_2$ nanofilm was deposited on ${\alpha}-Fe_2O_3$ nanopowders using the atomic layer deposition method. The $TiO_2$ film was prepared at $300^{\circ}C$ using $Ti(N(CH_3)_2)_4$ and $H_2O$ as the precursor and reactant gas, respectively. The thickness and composition of the $TiO_2$ surface were characterized by TEM and EDS measurements. The TEM results showed that the growth rate of the film was about $0.12{\AA}/cycle$. The EDS and SAED analyses showed the presence of titanium oxide on the surface of the ${\alpha}-Fe_2O_3$ nanopowders, confirming the deposition of the $TiO_2$ nanofilm. The Zeta potential and sedimentation test results showed that the dispersibility of the coated nanopowders was higher than that of the uncoated nanopowders. This is attributed to the electrostatic repulsion between the $TiO_2$-coated layers on the surface of the ${\alpha}-Fe_2O_3$ nanopowders. The results revealed that the $TiO_2$-coated layers modified the surface characteristics of the ${\alpha}-Fe_2O_3$ nanopowders and improved their dispersibility.

• 한국세라믹학회지
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• 제42권11호
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• pp.722-728
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• 2005

A wet-chemical route was utilized to obtain nanosized crystalline goethite ($\alpha$-FeOOH) particle, which was known as an oxidation catalyst in reducing carbon monoxide (CO) and dioxine during incineration. A cost-effective $FeSO_4{\cdot}7H_2O$ was used as starting raw material and a successive process of hydrolysis-oxidation was utilized as synthetic method. The effects of the initial $Fe^{2+}$ concentration, hydrolysis time and oxidation period on the crystalline phase and particle characteristics were systematically investigated by X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM) and BET analyses. It was found that the spindle-shaped crystalline $\alpha$-FeOOH particle with the width of 70 nm and the length of 200 nm could be obtained successfully when the initial concentration of 1.5 M, hydrolysis time of 4h, and oxidation period of 10 h, respectively. In addition, it was observed that the spindle-shaped $\alpha$-FeOOH particle consisted of nano-sized primary crystallites of $30\~50\;nm$, which were de-agglomerated into individual particle and successively re­agglomerated into spherical or irregular-shaped agglomerates beyond certain periods in the hydrolysis and oxidation process.

• 한국결정성장학회지
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• 제24권2호
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• pp.77-83
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• 2014

본 연구는 순환자원인 저회, 잔사회 그리고 준설토로 인공 경량골재를 제조할 때 철분의 종류와 양이 발포기구에 미치는 영향을 분석하는 것이다. 원료의 화학적 특성을 X선 회절 분석과 X선 형광 분석으로 측정하였다. 준설토 50 %, 저회 15 % 그리고 잔사회 35 %를 무게비로 혼합하고 철분함량을 5 % 단위로 30 %까지 첨가하였으며, 철분의 종류는 $Fe_2O_3$와 $Fe_3O_4$로 선정하였다. 성형된 골재는 급속 소성법으로 $40^{\circ}C$ 간격으로 $1060^{\circ}C$에서 $1180^{\circ}C$까지 소결하고, 비중과 흡수율을 측정하였다. 인공 경량골재는 철분 함유량이 10~15 %일 때 가장 낮은 비중을 보이며, 철분량이 증가할수록 액상 소결이 되어 비중이 증가하였다.

• Nuclear Engineering and Technology
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• 제40권1호
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• pp.77-86
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• 2008

This paper describes the nonlinear analyses of a 1:4 scale model of a prestressed concrete containment vessel (PCCV) using an axisymmetric model and a three-dimensional model. These two models are refined by comparison of the analysis results and with testing results. This paper is especially focused on the analysis of behavior under pressure and the temperature effects revealed using an axisymmetric model. The temperature-dependent degradation properties of concrete and steel are considered. Both geometric and material nonlinearities, including thermal effects, are also addressed in the analyses. The Menetrey and Willam (1995) concrete constitutive model with non-associated flow potential is adopted for this study. This study includes the results of the predicted thermal and mechanical behaviors of the PCCV subject to high temperature loading and internal pressure at the same time. To find the effect of high temperature accident conditions on the ultimate capacity of the liner plate, reinforcement, prestressing tendon and concrete, two kinds of analyses are performed: one for pressure only and the other for pressure with temperature. The results from the test on pressurization, analysis for pressure only, and analyses considering pressure with temperatures are compared with one another. The analysis results show that the temperature directly affects the behavior of the liner plate, but has little impact on the ultimate pressure capacity of the PCCV.