• 한국표면공학회지
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• 제51권1호
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• pp.79-85
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• 2018

We systematically investigated the optical properties of sub-micron sized methylammonium lead tribromide ($CH_3NH_3PbBr_3$) cubes in the range of 100 to 700 nm, which were prepared by a surfactant-free precipitation method. We found that despite the strong absorbance, their photoluminescence quantum yield (PLQY) is very low as 0.009~0.011 % for whole range of sizes. Surfactant-free synthesis approach results in nanocubes that has no surface passivating reagents (e.g. surfactants) on their surface. As-prepared particles contain a large number of surface defects that may cause the low PLQY. The role of the surface defects were investigated in their photoluminescence decay process, which can be correlated with the particle size. Larger particles are characterized by a slower decay rate compared to smaller particles due to a large number of surface defects in the smaller particles that trap more excitons in the fluorescence decay process. These experimental results provide new insights into the fundamental relationship between surface state and optical properties.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2003년도 사면안정학술발표회
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• pp.65-81
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• 2003

During the last few decades in Korea, the development of hillside or mountain areas has rapidly increased for infrastructure construction such as railroads, highways and housing. Many landslides have occurred during these constructions. Also, the amount and scale of damage caused by landslides have increased every year. In the case of Far East Asia including Korea, the damage of landslides is consequently reported during the wet season. In this paper, the effect of stabilizing piles on slope stability is checked and the behavior of slope soil and piles are observed throughout the year by field measurements in the large-scale cut slopes. In particular a large-scale cut slope situated on the construction site for the express highway in Donghae, Korea. First of all, The behavior of the slope soil was measured by inclinometers during slope modification. Landslides occurred in this area due to the soil cutting for slope modification. The horizontal deformations of slope soil gradually increased and rapidly decreased at depth of sliding surface indicating that the depth of sliding surface below the ground surface can be predicted. On the basis of being able to predict the depth of the sliding surface, stabilizing piles were designed and constructed in this slope. To ensure the stability of the reinforced slope using stabilizing piles, an instrumentation system was installed. The maximum deflection of piles is measured at the pile head and it is noted that the piles deform like deflection on a cantilever beam. The maximum bending stress of piles is measured at the soil layer. The pile above the soil layer is subjected to lateral earth pressure due to driving force of the slope, while pile below soil layer is subjected to subgrade reaction against pile deflection. As a result of research, the effect and applicability of stabilizing piles in large-scale cut slopes could be confirmed sufficiently.

• 비파괴검사학회지
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• 제23권5호
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• pp.475-479
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• 2003

재료에 존재하는 미소균열을 검출하기 위한 일반적인 초음파 탐상법은 고주파수 집속형 수직 초음파 탐촉자를 이용한 펄스-에코법을 사용하거나 표면파를 발생시키는 사각 탐상법을 사용한다. 이러한 방법들은 압연 롤, 세라믹 롤등 대형 구조물의 표면에 존재하는 미소 크랙의 존재 여부 및 위치 측정을 위한 자동화 초음파 탐상장치를 구성하기에는 다랑의 검사 데이터, 결함 위치정보의 불확실성 등 현실적으로 많은 어려움이 있다. 본 연구에서는 고정밀도 초음파 현미경(scanning acoustic microscope)에 비교적 저주파수의 대구경 초음파 탐촉자를 사용하여 미세균열의 존재 여부 및 위치 등의 검사결과를 실시간 A, B, C-Scan으로 표시할 수 있으며, 기존의 방법보다 검사 속도 및 시간을 10배 이상으로 향상된 파동화 초음파 탐상법 및 초음파 현미경법의 실용성을 검증하였다.

• 한국분말재료학회지
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• 제24권1호
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• pp.46-52
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• 2017

Fecralloy coating layer with large surface area is suitable for use as a filter media for efficient removal of hot gaseous pollutants exhausted from combustion processes. For uniform preparation of a Fecralloy coating layer with large surface area and strong adhesion to substrate, electrospray coating and thermal treatment processes are experimentally optimized in this study. A nano-colloidal solution with 0.05 wt% Fecralloy nanoparticles is successfully prepared. Optimized electrospraying conditions are experimentally discovered to prepare a uniform coating layer of Fecralloy nano-colloidal solution on a substrate. Drying the electrospray coated Fecralloy nano-colloidal solution layer at $120^{\circ}C$ and subsequent heating at $600^{\circ}C$ are the best post-treatment for enhancing the adhesion force and surface roughness of the Fecralloy coating layer on a substrate. An electrospray coating system, consisting of several multi-groove nozzles, is also experimentally confirmed as a reasonable device for uniform coating of Fecralloy nano-colloid on a large area substrate.

• 한국의류학회지
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• 제28권3_4호
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• pp.396-402
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• 2004

The purpose of this study was to investigate the difference of cotton fabric texture perceived between on-line(screening fabric) and off-line(real fabric), and to analyze fabric characteristics having an effect on the difference. The similarity of 55 various cotton fabrics perceived between on-line and on-line were measured showing simultaneously real fabrics and screening fabrics by 7-scale questionnaire. And the characteristics of cotton fabrics such as weave structure, thickness, weight, fabric density, stiffness, Hunter's L, a, b, and hue were measured. Cotton fabrics were classified into 3 groups by extent of similarity. There were no significant differences in weft density, stiffness, Hunter's L, a, b, and hue among 3 groups. But there were significant differences in weave structure, thickness, weight, warp density, and difference of warp ＆ weft density. The fabrics having large similarity were thick and heavy, had small warp density and difference of warp ＆ weft density, and distinct surface texture. The group having medium similarity included fabrics of medium thickness and weight, having weak surface texture, large warp density and difference of warp ＆ weft density. The group having small similarity, which the differences between on-line and off-line were large, included thin and light fabrics having smooth surface and large warp density and difference of warp ＆ weft density.

• 정보저장시스템학회논문집
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• 제1권2호
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• pp.182-187
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• 2005

A large area micro mirror is an optical element that functions as changing an optical path by reflection in integrated optical system. We fabricated the large area silicon mirror by anisotropic etching using MEMS for implementation of integrated optical pickup. In this work, we report the optimum conditions to better fabricate and design, greatly improve mirror surface quality. To obtain mirror surface of $45^{\circ},\;9.74^{\circ}$ off-axis silicon wafer from (100) plane was used in etching condition of $80^{\circ}C$ with 40wt.% KOH solution. After wet etching, polishing process by MR fluid was applied to mirror surface for reduction of roughness. In the next step, after polymer coating on the polished Si wafer, the Si mirror was fabricated by UV curing using a trapezoid bar-type way structure. Finally, we obtained peak to valley roughness about 50 nm in large area of $mm^2$ and it is applicable to optical pickup using blu-ray wavelength as well as infrared wavelength.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2005년도 춘계학술대회 논문집
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• pp.1522-1526
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• 2005

In this study, the fabrication of large area silicon mirror is accomplished by anisotropic etching using MEMS for implementation of integrated optical pickup and the process condition is also established for improving the mirror surface roughness. Until now, few results have been reported about the production of highly stepped $9.74^{\circ}$ off-axis-cut silicon wafer using wet etching. In addition rough surface of the mirror is achieved in case of long etching time. Hence a novel method called magnetorheolocal finishing is introduced to enhancing the surface quality of the mirror plane. Finally, areal peak to valley surface roughness of mirror plane is reduced about 100nm in large area of $mm^2$ and it is applicable to optical pickup using infrared wavelength.

• 대한전자공학회논문지SD
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• 제45권8호
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• pp.11-16
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• 2008

본 논문에서는 먼저 RTP(Rapid Thermal Processor) 장치를 스트레스 측정에 용이한 구조로 제작하고 PC에서 통합 공정관리 시스템을 설계하였다. 다음으로는 Large deformation 이론을 바탕으로 반도체 웨이퍼 표면의 변형검사를 위한 레이져 인터페로미터리를 구성하였다. 궁극적으로 이러한 레이져장치로부터 웨이퍼 표면의 영상을 추출하고 세선화, 블록화 그리고 스트레스 분포도의 순서로 영상처리 하여 스트레스로 인한 웨이퍼 표면의 변형을 검사하였다. 실험을 하기 위해 변형이 이루어지도록 웨이퍼의 후면을 1mm정도 갈아낸 후 약 1000도에서 $3\sim4$회 열처리를 수행하였으며, 열처리를 가한 영상과 가하지 않은 영상을 통하여 웨이퍼 열처리 후 심각한 변형이 이루어졌음을 알 수 있었다.

• 한국해양공학회지
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• 제20권6호
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• pp.67-74
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• 2006

A high-order spectral/boundary-element method is newly adapted as an efficient numerical tool. This method is one of the most efficient numerical methods by which the nonlinear gravity waves can be simulated and hydrodynamic forces also can be calculated in time-domain. In this method, the velocity potential is expressed as the sum of surface potential and body potential. Then, surface potential is solved by using the high-order spectral method and body potential is solved by using the high-order boundary element method. By the combination of these two methods, the wave-making problems by a submerged sphere oscillating with large amplitude under the free~surface are solved in time-domain. Through the example calculations, nonlinear effects on free-surface profiles and hydrodynamic forces are shown and discussed.

• Journal of Ship and Ocean Technology
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• 제10권1호
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• pp.1-9
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• 2006

The resistance reduction by an air lubrication effect of a large air cavity covering the hull bottom surface and the similarity relations involved have been investigated with a series of towing tank tests of three geometrically similar models. The test results of geometrically similar models have indicated that a large air cavity was formed beneath the bottom having a backward-facing step by artificially supplying air is effective for resistance reduction. The areas of air cavity and the required flow rates of air are directly related to the effective wetted surface area. The traditional extrapolation methods seem to be applicable to the estimation of the resistance in the tested range if corrections are made to account the changes in the frictional resistance caused by the changes in the effective wetted surface area. To investigate the effectiveness of air lubrication in improving the resistance performance of a practical ship, a small test boat having a backward-facing step under its bottom has been manufactured and speed trials in a river have been performed. Air has been supplied artificially into the downstream region of the bottom step to form a large air cavity covering the bottom surface. The results have confirmed the practical applicability of air lubrication for the resistance reduction of a small high-speed boat.