• 한국진공학회:학술대회논문집
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• 한국진공학회 2013년도 제44회 동계 정기학술대회 초록집
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• pp.430-430
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• 2013

Field effect transistor based on semiconductor nanowires has been attracting lots of concerns and studies of scientists because of its different characteristic comparing with other morphology like thin film. Nowadays, graphene is introducing a great promise as an active layer in field effect transistor due to its unique electronic and optoelectronic properties. Thus, a mix structure between etched graphene and semiconductor nanowires is believed to expose novel electrical characteristics. In this study, CuO nanowires (20~80 nm in diameter and $1{\sim}10{\mu}m$ length) were grown during oxidizing Cu foil at $450^{\circ}C$ for 24 h. Besides, 3-layersetched graphene was deposited on Cu foil at $1,000^{\circ}C$ using a feedstock of $CH_4$/$H_2$ mixed gas in CVD system. A structure of Ni/Au electrode + CuO nanowires + etched graphene was fabricated, afterward. Finally, field effect properties of the device was revealed and compared with individual devices of just nanowires and just graphene.

• Elastomers and Composites
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• 제23권4호
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• pp.289-298
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• 1988

The thermal degradation of poly(methyl methacrylate)(PMMA) and poly($\alpha$-methylstyrene-co-acrylonitrile)(SAN) mixtures were carried out using the thermogravimetry(TG) and differential scanning calorimetry(DSC) in the stream of nitrogen and air with 50 ml/min at the various heating rate from 4 to $20^{\circ}C/min$ and temperature from 20 to $500^{\circ}C$. The value of activation energies of thermal degradation determined by TG and DSC in the various PMMA/SAN mixtures were 34-54 kcal/mol in the stream of nitrogen. The value of activation energy of SAN 60% mixture were appeared high in comparison with addition rule. PMMA/SAN mixtures by the analysis of infrared spectrophotometer were decomposed by main chain scission in the stream of nitrogen.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2008년도 춘계 학술발표회 제20권1호
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• pp.181-184
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• 2008

콘크리트는 비교적 내화성이 있는 재료이다. 그러나 화재 등의 고온에 장기 노출될 경우는 콘크리트 강도 등이 급격하게 저하하는 현상이 발생한다. 이와 같은 경우, 저강도 콘크리트를 일반 비파괴검사 강도추정식을 이용하여 추정하는 것은 적절하지 않다. 이 문제를 해결하기 위해 각종 배합조건의 콘크리트시편을 200, 400, 600, $800^{\circ}C$의 온도변화 조건에서 가열한 후, 초음파속도와 콘크리트강도간의 상관관계를 분석하였다. 아울러 이들 결과를 통해 고온에서 손상된 콘크리트 비파괴검사 강도추정식을 제안하였다.

• Computers and Concrete
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• 제13권4호
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• pp.531-545
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• 2014

The purpose of this paper is to develop a prediction model for the compressive strength of waste LCD glass applied in concrete by analyzing a series of laboratory test results, which were obtained in our previous study. The hyperbolic function was used to perform the nonlinear-multivariate regression analysis of the compressive strength prediction model with the following parameters: water-binder ratio w/b, curing age t, and waste glass content G. According to the relative regression analysis, the compressive strength prediction model is developed. The calculated results are in accord with the laboratory measured data, which are the concrete compressive strengths of different mix proportions. In addition, a coefficient of determination $R^2$ value between 0.93 and 0.96 and a mean absolute percentage error MAPE between 5.4% and 8.4% were obtained by regression analysis using the predicted compressive analysis value, and the test results are also excellent. Therefore, the predicted results for compressive strength are highly accurate for waste LCD glass applied in concrete. Additionally, this predicted model exhibits a good predictive capacity when employed to calculate the compressive strength of washed glass sand concrete.

• 한국구조물진단유지관리공학회 논문집
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• 제6권1호
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• pp.149-158
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• 2002

The carbonation process is affected by both the concrete material properties such as W/C ratio, types of cement and aggregates, admixture characteristics and the environmental factors such as $CO_2$ concentration, temperature, humidity. Based on results of preliminary study on carbonation, this study is to develop a carbonation prediction model by taking account of $CO_2$ concentration, temperature, humidity ad W/C ratio among major factor affecting the carbonation process. And to constitute a model formula which correspond to the mix design of the nuclear power plant, test coefficient that correspond to the design of the nuclear power plant is obtained based on the results of accelerated carbonation test. Also a field coefficient which is obtained based on results of the field examination is included to improve the conformity of the actual structures of nuclear power plant.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2007년도 추계학술대회 논문집
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• pp.81-82
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• 2007

The stochiometric mix of evaporating materials for the $CdGa_2Se_4$ single crystal thin films was prepared from horizontal furnace. To obtain the single crystal thin films, $CdGa_2Se_4$ mixed crystal was deposited on thoroughly etched semi-insulating GaAs(100) substrate by the Hot Wall Epitaxy (HWE) system. The source and substrate temperature were $630^{\circ}C\;and\;420^{\circ}C$, respectively. After the as-grown single crystal $CdGa_2Se_4$ thin films were annealed in Cd-, Se-, and Ga -atmospheres, the origin of point defects of single crystal $CdGa_2Se_4$ thin films has been investigated by PL at 10 K. The native defects of $V_{Cd},\;V_{Se},\;Cd_{int},\;and\;Se_{int}$ obtained by PL measurements were classified as donors or acceptors. And we concluded that the heat-treatment in the Cd-atmosphere converted single crystal $CdGa_2Se_4$ thin films to an optical p-type. Also, we confirmed that Ga in $CdGa_2Se_4$/GaAs did not form the native defects because Ga in single crystal $CdGa_2Se_4$ thin films existed in the form of stable bonds.

• 한국안전학회지
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• 제34권5호
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• pp.111-118
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• 2019

Recently, a variety of special concrete structures have been designed in domestic and overseas construction markets and more advanced construction technology is required. Therefore, it is necessary to secure quantitative construction technology. For this purpose, it is essential to develop a standard reference material having a constant flow performance and quality to evaluate quantitative performance. On the other hand, the flowability of the concrete is greatly influenced by the flowability of the cement paste. Also, in consideration of design strength and workability, mix design is carried out at various mixing ratios according to the purpose of the site. Therefore, in this study, based on the derived components of standard reference materials for cement paste, we suggested mixing ratio of standard reference materials that can uniformly simulate the flow characteristics of cement paste according to W/C. As a result, it was found that the yield stress was determined by the ratio of water and glycerol but plastic viscosity was controled by limestone content. Finally, the ratio of standard reference materials to simulate the rheological range of cement paste by W/C was suggested.

• Advances in concrete construction
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• 제4권1호
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• pp.49-69
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• 2016

This work investigates the mechanical properties of conventional concrete (CC) and self compacting concrete (SCC) using fine rubber and silpozz were accompanied by a comparative study between conventional rubberized concrete (CRC) and self compacting rubberized concrete (SCRC). Fine rubber (FR) from scrap tires has replaced the fine aggregate (FA) and Silpozz has been used as a replacement of cement at the proportions of 5, 10 and 15%. Silpozz as a partial replacement of cement in addition of superplasticiser (SP) increases the strength of concrete. Fresh concrete properties such as slump test, compaction factor test for CRC, whereas for SCRC slump flow, $T_{500}$, V-funnel, L-box, U-box, J-ring tests were conducted along with the hardened properties tests like compressive, split tensile and flexural strength test at 7, 28 and 90 days of curing. The durability and microstructural behavior for both CRC and SCRC were investigated. FR used in the present study is 4.75 mm passing with fineness modulus 4.74.M30 grade concrete is used with a mix proportion of 1:1.44:2.91 and w/c ratio as 0.43. The results indicate that as FR quantity increases, workability of both CRC and SCRC decreases. The results also show that the replacement of natural fine aggregate (NFA) with FR particles decreases the compressive strength with the increase of flexural strength observed upto 5% replacement of FR. Also replacement of cement with silpozz resulted enhancement of strength in SCRC.

• Computers and Concrete
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• 제24권1호
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• pp.19-35
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• 2019

In this paper, the effect of the type and amount of fibers on the physicomechanical properties of concrete containing fine recycled refractory brick (RRB) and natural aggregate subjected to elevated temperatures was investigated. For this purpose, forta-ferro (FF), polypropylene (PP), and polyvinyl alcohol (PVA) fibers with the volume fractions of 0, 0.25, and 0.5%, as well as steel fibers with the volume fractions of 0, 0.75, and 1.5% were used in the concrete containing RRB fine aggregate replacing natural sand by 0 and 100%. In total, 162 concrete specimens from 18 different mix designs were prepared and tested in the temperature groups of 23, 400, and $800^{\circ}C$. After experiencing heat, the concrete properties including the compressive strength, ultrasonic pulse velocity (UPV), weight loss, and surface appearance were evaluated and compared with the corresponding results of the reference (unheated) specimens. The results show that using RRB fine aggregate replacing natural fine aggregate by 100% led to an increase in the concrete compressive strength in almost all the mixes, and only in the PVA-containing mixes a decrease in strength was observed. Furthermore, UPV values at $800^{\circ}C$ for all the concrete mixes containing RRB fine aggregate were above those of the natural aggregate concrete specimens. Finally, regarding the compressive strength and UPV results, steel fibers demonstrated a better performance relative to other fiber types.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1997년도 하계학술대회 논문집 C
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• pp.1462-1464
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• 1997

The spinel $LiMn_2O_4$ has been synthesized by solid-state reaction. $LiMn_2O_4$ which includes 3 mix $Li_2CO_3$ or $LiNO_3$ and $MnO_2$ prepared by Prelim heating at $350^{\circ}C$ for 24hr. $LiMn_2O_4$ fired at temp range from $600^{\circ}C$ to $800^{\circ}C$ for 48hr. The structure a electrochemical characteristics of spinel $LiMn_2O_2$ wh fabricated by changing sintering condition from st materials are investigated. The spinel $LiMn_2O_4$ prepared by the mixture of L CMD at $800^{\circ}C$ for 48hr showed an initial charge ca of 146mAh/g. The spinel $LiMn_2O_4$ prepared by the m of $LiNO_3$/CMD at $600{\sim}800^{\circ}C$ for 48hr stabilized ch discharge capacity after 50th cycles.