• Computers and Concrete
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• 제6권2호
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• pp.155-165
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• 2009

Splitting tensile strength (STS) of high-performance concrete (HPC) is one of the important mechanical properties for structural design. This property is related to compressive strength (CS), water/binder (W/B) ratio and concrete age. This paper presents a clustering-based fuzzy model for the prediction of STS based on the CS and (W/B) at a fixed age (28 days). The data driven fuzzy model consists of three main steps: fuzzy clustering, inference system, and prediction. The system can be analyzed directly by the model from measured data. The performance evaluations showed that the fuzzy model is more accurate than the other prediction models concerned.

• Advances in concrete construction
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• 제10권1호
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• pp.81-92
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• 2020

Flexural and splitting strength behavior of conventional concrete can significantly be improved by incorporating the fibers in it. A significant number of research studies have been conducted on various types of fibers and their influence on the tensile capacity of concrete. However, as an important property, tensile capacity of fiber reinforced concrete (FRC) is not modelled properly. Therefore, this paper intends to formulate a model based on experiments that show the relationship between the fiber properties such as the aspect ratio (length/diameter), fiber content, compressive strength, flexural strength and splitting strength of FRC. For the purpose of modeling, various FRC mixes only with steel fiber are adopted from the existing research papers. Automated neural network search (ANS) is then developed and used to investigate the effect of input parameters such as fiber content, aspect ratio and compressive strength to the output parameters of flexural and splitting strength of FRC. It is found that the ANS model can be used to predict the flexural and splitting strength of FRC in a sensible precision.

• 한국표면공학회지
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• 제56권4호
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• pp.265-272
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• 2023

Photoelectrochemical (PEC) water splitting is one of the promising methods for hydrogen production by solar energy. Iron oxide has been effectively investigated as a photoelectrode material for PEC water splitting due to its intrinsic property such as short minority carrier diffusion length. However, iron oxide has a low PEC efficiency owing to a high recombination rate between photoexcited electrons and holes. In this study, we synthesized nanoporous structured iron oxide by anodization to overcome the drawbacks and to increase surface area. The anodized iron oxide was annealed in Ar atmosphere with different purging times. In conclusion, the highest current density of 0.032 mA/cm² at 1.23 V vs. RHE was obtained with 60 s of pursing for iron oxide(Fe-60), which was 3 times higher in photocurrent density compared to iron oxide annealed with 600 s of pursing(Fe-600). The resistances and donor densities were also evaluated for all the anodized iron oxide by electrochemical impedance spectra and Mott-Schottky plot analysis.

• 대한수학회지
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• 제42권4호
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• pp.773-793
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• 2005

We consider interesting conditions, one of which will be called the disjoint $(A^2,\;D^2)-pair$ property, on genus $g{\geq}2$ Heegaard splittings of compact orient able 3-manifolds. Here a Heegaard splitting $(C_1,\;C_2;\;F)$ admits the disjoint $(A^2,\;D^2)-pair$ property if there are an essential annulus Ai normally embedded in $C_i$ and an essential disk $D_j\;in\;C_j((i,\;j)=(1,\;2)\;or\;(2,\;1))$ such that ${\partial}A_i$ is disjoint from ${\partial}D_j$. It is proved that all genus $g{\geq}2$ Heegaard splittings of toroidal manifolds and Seifert fibered spaces admit the disjoint $(A^2,\;D^2)-pair$ property.

• 멤브레인
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• 제25권2호
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• pp.152-161
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• 2015

본 연구에서는 이온교환막을 이용한 전기화학적 수처리 공정의 효율을 향상시키기 위해 낮은 전기적 저항, 높은 이온선택 투과성, 및 농도분극 조건에서 낮은 물분해 플럭스 특성을 갖는 새로운 세공충진 음이온 교환막을 개발하였다. 다공성 폴리올레핀 기재에 이온교환능이 우수한 4급 암모늄기를 포함한 공중합 고분자를 충진하여 상용막 이상의 성능을 갖는 기저 멤브레인을 제조하였다. 또한 기저 막 표면에 이미다졸륨 고분자를 코팅하여 전기화학적 성능을 유지하며 동시에 물분해 플럭스를 효과적으로 제어할 수 있음을 확인하였다. 제조된 세공충진 음이온 교환막은 상용막 대비 약 1/6~1/8 수준의 매우 낮은 전기적 저항을 나타내었으며 동시에 농도분극 조건에서 양이온 교환막 수준의 낮은 물분해 플럭스를 나타내었다.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 1994년도 가을 학술발표회 논문집
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• pp.99-104
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• 1994

Recently, nonlinear fracture mechanics was applied to analyze concrete structures more accurately, and new materials property such as fracture energy(Gf) was used for its application. The fracture energy was influenced by many parameters, especially the strength of concrete. Many researches on the relation between the strength of concrete and the fracture energy were performed. In spite of many researches on the relation between the strength of concrete and the fracture energy, there is no distinct conclusion. This research includes various the strength levels from low-strength of concrete to high-strength, and then intends to estimate relation between the strength of concrete and the fracture energy. Concrete used crushed sand is also included, which is going to be used much. In this research, the wedge splitting test method proposed by Prof. Linsbauer is adopted to investigate the fracture energy. Fracture behavior of concrete used natrual sand and crushed sand has the similar trend. In the strength range of 200~500 kg/$\textrm{cm}^2$, the fracture energy and the maximum splitting forces(F) increase as the strength of concrete increases. In the range of the higher strength, however, the maximum splitting forces(F) increases but the fracture energy decreases as the strength of concrete increases. Through this investigation the fracture energy of concrete was not proportional to the strength of concrete.

• Bulletin of the Korean Chemical Society
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• 제33권7호
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• pp.2200-2206
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• 2012

One-dimensional $TiO_2$ array grown on optically transparent electrode holds a promise as a photoelectrode for photoelectrochemical water splitting; however, its crystal structure is rutile, imposing constraints on the potent use of this nanostructure. To address this issue, a heterojunction with type-II band alignment was fabricated using atomic layer deposition (ALD) technique. One-dimensional core/shell structured $TiO_2$/ZnO heterojunction was superior to $TiO_2$ in the photoelectrochemical water splitting because of better charge separation and more favorable Fermi level. The heterojunction also possesses better light scattering property, which turned out to be beneficial even for improving the photoelectrochemical performance of semiconductor-sensitized solar cell.

• 한국재료학회지
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• 제32권1호
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• pp.30-35
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• 2022

The development of advanced materials to improve the efficiency of photoelectrochemical (PEC) water splitting paves the way for widespread renewable energy technologies. Efficient photoanodes with strong absorbance in visible light increases the effectiveness of solar energy conversion systems. MoS₂ in a two-dimensional semiconductor that has excellent absorption performance in visible light and high catalytic activity, showing considerable potential as an agent of PEC water splitting. In this study, we successfully modulated the MoS₂ morphology on indium tin oxide substrate by using the metalorganic chemical vapor deposition method, and applied the PEC application. The PEC photocurrent of the vertically grown MoS₂ nanosheet structure significantly increased relative to that of MoS₂ nanoparticles because of the efficient transfer of charge carriers and high-density active sites. The enhanced photocurrent was attributed to the efficient charge separation and improved light absorption of the MoS₂ nanosheet structure. Meanwhile, the photocurrent property of thick nanosheets decreased because of the limit imposed by the diffusion lengths of carriers. This study proposes a valuable photoelectrode design with suitable nanosheet morphology for efficient PEC water splitting.

• Computers and Concrete
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• 제12권4호
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• pp.377-392
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• 2013

This paper investigates prediction models estimating the hydration properties of concrete, such as the compressive strength, the splitting tensile strength, the elastic modulus,and the autogenous shrinkage. A prediction model is suggested on the basis of an equation that is formulated to predict the compressive strength. Based on the assumption that the apparent activation energy is a characteristic property of concrete, a prediction model for the compressive strength is applied to hydration-related properties. The hydration properties predicted by the model are compared with experimental results, and it is concluded that the prediction model properly estimates the splitting tensile strength, elastic modulus, and autogenous shrinkage as well as the compressive strength of concrete.

• Advances in concrete construction
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• 제1권4호
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• pp.305-318
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• 2013

Engineering properties such as compressive strength, splitting tensile strength, modulus of rupture, modulus of elasticity and Poisson's ratio of geopolymer concrete (GPC) and steel fibre reinforced geopolymer concrete (SFRGPC) have been obtained from standard tests and compared. A total of 15 specimens were tested for determining each property. The grade of concrete used was M 40. The percentages of steel fibres considered include 0.25%, 0.5%, 0.75% and 1%. In general, the addition of fibres improved the mechanical properties of both GPC and SFRGPC. However the increase was found to be nominal in the case of compressive strength (8.51%), significant in the case of splitting tensile strength (61.63%), modulus of rupture (24%), modulus of elasticity (64.92%) and Poisson's ratio (50%) at 1% volume fraction of fibres. An attempt was made to obtain the relation between the various engineering properties with the percentage of fibres added.