• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2008년도 춘계 학술발표회 제20권1호
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• pp.1069-1072
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• 2008

매립된 철근의 부식이 진행될 경우, 부착강도 및 강성이 감소되며, 구조물의 열화가 발생하여 사용 수명이 단축된다. 이러한 문제를 해결하기 위하여 RC 부재의 부착특성에 대한 평가가 인위적으로 철근을 빠르게 부식시키는 방법을 통하여 지금까지 연구되어왔다. 그러나, 이러한 인위적인 부식방법은 실제 부식 상황과 일치하지 않으며, 결과적으로 실제 상황에서의 RC 부재에 대한 부식 가능성을 과대평가할 수 있다. 따라서, 본 연구는 인위적인 방법과 자연적인 방법에 의해 RC 부재를 부식시킴으로써 부착 강성의 차이를 평가하고자 하였다. 자연적인 부식의 경우, 부식면적 50%에서 취성파괴가 발생했으며, 부식면적 80%이상에서는 부착강도가 약 10%이상 감소하였다. 특히, 자연적 부식의 경우 낮은 부식수준에서 콘크리트의 열화가 발생하였다. 따라서 향후 부식에 따른 부재의 성능저하를 평가하고자 할 경우에는 인위적으로 부식시킨 시험체로부터 평가하는 것은 곤란하며 반드시 자연적으로 부식시킨 시험체를 사용하여 성능을 평가해야 한다고 판단된다.

• 한국세라믹학회지
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• 제35권1호
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• pp.79-87
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• 1998

Melt spun YbBa2Cu3Agx(x=0, 5, 12, 16 and 53) precursor alloy ribbons were oxidized at 263-330$^{\circ}C$ and treated at 820$^{\circ}C$, 855$^{\circ}C$ and 885$^{\circ}C$ under 1.0 atm oxygen pressure. In the ribbons treated at 820$^{\circ}C$, 855$^{\circ}C$and 885$^{\circ}C$ 1-2-4 phase (YbBa2Cu4O8) and 1-2-3 phase (YbBa2Cu3O{{{{ OMICRON _7-$\delta$ }})were formed respectively. The shape of 1-2-4 phase was distorted or ellipsoid. The 2-4-7 and 1-2-3 phases tooked the shape of bar. All the ribbons showed zero critical current density Jc at 77K in zero magnetic field. By considering the shape and the highest critical temperature (among the three phases) of the 1-2-3 phase we tried to increase the critical current density of the ribbons treated at 885$^{\circ}C$ by press deformation. About tenribbons were stacked and coupled by press deformation and then treated at 885$^{\circ}C$ These 1-2-3 phase did not show any texture in any of the ribbons. However they exhibited weak texture in the multilayered specimens. Among the multilayered specimens YbBa2Cu3Ag16 exhibited a Jc of 180 A/cm2 Among the above ribbons YbBa2Cu3Ag16 ribbon has the optimum composition to produce textured superconducting oxide with improved Jc by press deformation. Onset critical temperatures Ton of the multilayered YbBa2Cu3Agx(x=5, 12, 16 and 53) were measured as 88-90 K.

• 한국수소및신에너지학회논문집
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• 제20권6호
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• pp.471-478
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• 2009

The specific some types of compressors are appropriate for a use in hydrogen gas station. Metal diaphragm type of hydrogen compressor is one of them, which can satisfy the critical requirements of maintaining gas purity and producing high pressure over 850 bar. The objective of this study is to investigate an characteristics of compression through two-way Fluid-Structure-Interaction (FSI) analysis as bulk modulus and initial volume of oil independently varies. Deflection of diaphragm, oil density, gas and oil pressure were analyzed during a certain period of compression process. According to the analysis results, bulk modulus and initial volume remarkably affected deflection of diaphragm, oil density, gas and oil pressure. The highest gas pressure were attained with the highest bulk modulus of $7e^9\;N/m^2$ and the lowest initial oil volume of 80 cc.

• Structural Engineering and Mechanics
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• 제74권1호
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• pp.1-18
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• 2020

For the large deformation of shear walls under vertical and horizontal loads, there are difficulties in obtaining accurate simulation results using the response analysis method, even with fine mesh elements. Furthermore, concrete material nonlinearity, stiffness degradation, concrete cracking and crushing, and steel bar damage may occur during the large deformation of reinforced concrete (RC) shear walls. Matrix operations that are involved in nonlinear analysis using the traditional finite-element method (FEM) may also result in flaws, and may thus lead to serious errors. To solve these problems, a planar four-node element was developed based on vector mechanics. Owing to particle-based formulation along the path element, the method does not require repeated constructions of a global stiffness matrix for the nonlinear behavior of the structure. The nonlinear concrete constitutive model and bilinear steel material model are integrated with the developed element, to ensure that large deformation and damage behavior can be addressed. For verification, simulation analyses were performed to obtain experimental results on an RC shear wall subjected to a monotonically increasing lateral load with a constant vertical load. To appropriately evaluate the parameters, investigations were conducted on the loading speed, meshing dimension, and the damping factor, because vector mechanics is based on the equation of motion. The static problem was then verified to obtain a stable solution by employing a balanced equation of motion. Using the parameters obtained, the simulated pushover response, including the bearing capacity, deformation ability, curvature development, and energy dissipation, were found to be in accordance with the experimental observation. This study demonstrated the potential of the developed planar element for simulating the entire process of large deformation and damage behavior in RC shear walls.

• Bulletin of the Korean Chemical Society
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• 제33권7호
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• pp.2325-2332
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• 2012

A series $[C_3Omim]$[X] of imidazolium cation-based ILs, with ether functional group on the alkyl side-chain have been synthesized and structure of the materials were confirmed by various techniques like $^1H$, $^{13}C$ NMR spectroscopy, MS-ESI, FTIR spectroscopy and EA. More specifically, the influence of changing the anion with same cation is carried out. The absorption capacity of $CO_2$ for ILs were evaluated at 30 and $50^{\circ}C$ at ambient pressure (0-1.6 bar). Ether functionalized ILs shows significantly high absorption capacity for $CO_2$. In general, the $CO_2$ absorption capacity of ILs increased with a rise in pressure and decreased when temperature was raised. The obtained results showed that absorption capacity reached about 0.9 mol $CO_2$ per mol of IL at $30^{\circ}C$. The most probable mechanism of interaction of $CO_2$ with ILs were investigated using FTIR spectroscopy, $^{13}C$ NMR spectroscopy and result shows that the absorption of $CO_2$ in ether functionalized ILs is a chemical process. The $CO_2$ absorption results and detailed study indicates the predominance of 1:1 mechanism, where the $CO_2$ reacts with one IL to form a carbamic acid. The $CO_2$ absorption capacity of ILs for different anions follows the trend: $BF_4$ < DCA < $PF_6$ < TfO < $Tf_2N$. Moreover, the as-synthesized ILs is selective, thermally stable, long life operational and can be recycled at a temperature of $70^{\circ}C$ or under vacuum and can be used repeatedly.

• 분석과학
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• 제15권6호
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• pp.540-549
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• 2002

The arrangement of encapsulated Ar atoms in the molecular-dimensioned cavities of fully dehydrated zeolite A of unit-cell composition $Cs_3Na_8HSi_{12}Al_{12}O_{48}$ ($Cs_3$-A) has been studied crystallographically to probe the confinement effect of guest species in microporous environment. Atoms of Ar were encapsulated in the cavities of $Cs_3$-A by treatment with 410 atm of Ar at $400^{\circ}C$ for two days, followed by cooling at room temperature. The crystal structure of $Cs_3Na_8H$-A(4Ar) ($P_e$ = 410 atm, $a=12.245(2){\AA}$, $R_1=0.0543$, and $R_2=0.0552$) has been determined by single crystal X-ray diffraction technique in the cubic space group $Pm\bar{3}m$ at 21 (1) $^{\circ}C$ and 1 atm. Encapsulated Ar atoms are distributed in three crystallographic distinct positions: 1.5 Ar atoms per unit cell opposite 6-rings, 1.5 opposite four-rings in the large cavity, and finally 1.0 in the sodalite-unit. The possible structures of argon clusters, such as $Ar_2$, $Ar_3$, and $Ar_4$, are proposed.

• 한국구조물진단유지관리공학회 논문집
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• 제16권1호
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• pp.18-26
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• 2012

최근 FRP를 이용한 철근콘크리트 구조물의 보강방법으로서, 표면매입 보강 (Near-Surface-Mounted Retrofit, NSMR)방법의 연구가 활발히 진행되고 있다. 이 방법은 콘크리트에 홈을 형성하는 추가의 작업이 필요하지만 보강효과를 높일 수 있고 FRP가 표면에 노출되지 않기 때문에 환경의 영향을 저감시킬 수 있다. 본 연구에서는 이와 같은 표면매입 보강공법 즉, FRP판을 세워서 표면에 매입보강하는 공법의 보강효과를 실험적으로 규명하고자 하였다. 이를 위하여 철근콘크리트 보를 제작한 뒤 기존의 표면부착 보강과 표면매입 보강을 실시한 뒤 실험을 통하여 보강성능을 비교하였다. 또한 매입보강의 경우에는 중앙부를 부분적으로 비부착시켜 그 효과를 관찰하였다. 연구결과, FRP판을 이용한 철근콘크리트 부재의 휨보강방법으로서 FRP판을 세워서 표면에 매입하는 보강방법은 기존의 판 부착보강에 비하여 높은 보강성능을 발휘하는 것으로 나타났다. ACI 440-2R의 휨보강시 내력산정방법을 따르고 정착부분의 세가지 파괴형태를 고려함으로써 표면매입 보강된 부재의 내력을 평가할 수 있는 것으로 나타났다.

• Structural Engineering and Mechanics
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• 제74권3호
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• pp.395-406
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• 2020

Many prefabricated concrete frame joints have been proposed, and most of them showed good seismic performance. However, there are still some limitations in the proposed fabricated joints. For example, for prefabricated prestressed concrete joints, prefabricated beams and prefabricated columns are assembled as a whole by the pre-stressed steel bar and steel strand in the beams, which brings some troubles to the construction, and the reinforcement in the core area of the joints is complex, and the mechanical mechanism is not clear. Based on the current research results, a new type of fabricated joint of prestressed concrete beams and confined concrete columns is proposed. To study the seismic performance of the joint, the quasi-static test is carried out. The test results show that the nodes exhibit good ductility and energy dissipation. According to the experimental fitting method and the "fixed point pointing" law, the resilience model of this kind of nodes is established, and compared with the experimental results, the two agree well, which can provides a certain reference for elasto-plastic seismic response analysis of this type of structure. Besides, based on the analysis of the factors affecting the shear capacity of the node core area, the formula of shear capacity of the core area of the node is proposed, and the theoretical values of the formula are consistent with the experimental value.

• 대한토목학회논문집
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• 제39권5호
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• pp.587-594
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• 2019

하천 내 흐름에 대한 식생 밀도의 영향을 조사하기 위해 버드나무가 활착된 하천 규모의 자연형 수로에서 유동 측정 실험을 수행하였다. 식생 내 흐름에 대한 하천 규모 실험은 식생의 반 잠김 조건에 대해 수행되었다. 수로 내 식생대(vegetation patch)는 교차로 형성된 사주의 형상으로 배열되었고 식생 구간과 비식생 구간에서의 흐름을 비교하였다. 3차원 유동 구조는 초음파 유속계(Acoustic Doppler Velocimeter)에 의해 측정되었고 종방향 속도의 연직 분포는 다양한 지점에서의 측정값으로부터 분석되었다. 유속은 식생대의 밀도에 따라 다른 양상을 보여 주는데, 식생 구간와 비식생 구간에서의 흐름 속도의 차이는 밀집된 식생대 주변에서 크게 나타나며 흐름 분포의 형태는 식생대의 하류방향 하단에서 복잡한 모습을 나타낸다. 하류에 위치한 식생대 주변의 흐름은 상류에 설치된 식생대에 의해 교란된 흐름에도 불구하고 유사한 분포를 보여준다.

• 한국기후변화학회지
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• 제7권3호
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• pp.249-256
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• 2016

Porous $Al_2O_3$ hollow fiber membranes were successfully prepared by dry-wet spinning/sintering method. The SEM image shows that the $Al_2O_3$ hollow fiber membrane consists mostly of sponge pore structure. The contact angle and the breakthrough pressure were $126^{\circ}$ and 1.91 bar, respectively. This results indicate that the $Al_2O_3$ hollow fiber membranes were successfully modified to hydrophobic surface. The hydrophobic modified $Al_2O_3$ hollow fiber membranes were assembled into a membrane contactor system to separate $CO_2$ from a model gas mixture of the flue gas at elevated gas velocity. The $CO_2$ absorption flux was enhanced when the gas velocity increased from $1{\times}10^{-3}$ to $6{\times}10^{-3}$ m/s. Whereas the $CO_2$ absorption flux was decreased with the number of hollow fiber membrane of a module because of the concentration polarization. Furthermore, we developed an lab-scale $Al_2O_3$ hollow fiber membrane contactor modules and their system (i.e., $CO_2$ absorption using the $Al_2O_3$ membrane and monoethanolamine (MEA)) that could dispose of over $0.02Nm^3/h$ mixture gas (15% $CO_2$) with the removal efficiency higher than 95%. The results can be useful in a field of the membrane contactor for $CO_2$ separation, helping to design and extend a equipment.