• Journal of the Korean Crystal Growth and Crystal Technology
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• v.27 no.3
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• pp.143-147
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• 2017

To evaluate surface characteristics and improve crystalline quality of AlN single crystal grown by physical vapor transport (PVT) method, wet chemical etching process using $KOH/H_2O_2$ mixture in a low temperature condition and thermal annealing process was proceeded respectively. Conventional etching process using strong base etchant at a high temperature (above $300^{\circ}C$) had formed over etching phenomenon according to crystalline quality of materials. When it occurred to over etching phenomenon, it had a low reliability of dislocation density because it cannot show correct number of etch pits per estimated area. Therefore, it was proceeded to etching process in a low temperature (below $100^{\circ}C$) using $H_2O_2$ as an oxidizer in KOH aqueous solution and to be determined optimum etching condition and dislocation density via scanning electron microscope (SEM). For improving crystalline quality of AlN single crystal, thermal annealing process was proceeded. When compared with specimens as-prepared and as-annealed, full width at half maximum (FWHM) of the specimen as-annealed was decreased exponentially, and we analyzed the mechanism of this process via double crystal X-ray diffraction (DC-XRD).

• Nuclear Engineering and Technology
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• v.7 no.3
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• pp.243-256
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• 1975

1. 기초실험 1) 안전성의 검토 대형고속로의 안전성확보를 위한 Doppler효과, Na void 효과 등의 검토 2) 노심의 제특성 측정 청계질양, 비균질효과, 중성자내분포, 중성자 energy 분포, 제물광의 반응도채치, 증식비, Doppler계수, Na의 void 계수 3) 중성자 energy 측정법의 확립 대형노심에 었어서의 중성자 spectrum을 정도높게 정하는 것은 고속노물리자험의 전제조건이 되는 동요한 역천이다, 현재로서는 측정기, 긴정법자체가 업분치 못하기 때문에 많은 연구가 필요하다. 4) 고원여심의 군정수 정비 고동로심의 군정수가 정비 확립 안된것이 계산신업가 낮은 원인이 되고 있기 때문에 제채험의 결과와 대조하여 신뢰성있는 군정수를 정비하여 고속노설계에 양지를 시공한다. 5) 동특성 및 Pulse 체험원자로 내전운전과 핵연료의 효율적인 연소관리를 위한 동특실험과 Pulse 실험을 행하여 동특성해석을 한다. 2. 핵적 Mock-up 실험 관발 건조하고져하는 책험노, 원형노, 책용노의 대심을 모남하여 제물리적인 Parameter를 측정, 최적화를 수행한다.

• Food Science and Preservation
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• v.12 no.3
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• pp.209-215
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• 2005

Response surface methodology(RSM) was applied to monitor the elimination rate of heavy metals(Pb, Cd) and soluble solids depending on the steaming and roasting conditions of Polygonatum odoratum roots. Experiments of 16 different steaming and roasting conditions based on a central composite design for steaming time($60{\sim}180$ min), roasting temperature($110{\sim}150^{\circ}C$), and roasting time($10{\sim}50$ min) were conducted, thereby predicting the steaming and roasting conditions for the maximal responses; soluble solids($71.47\%$) at 65.24 min, $126.93^{\circ}C$ and 37.58 min; Pb removal rate($18.87\%$) at 71.23 min, $119.81^{\circ}C$ and 24.35 min; Cd removal rate($50,85\%$) at 160.89 min, $126.43^{\circ}C$ and 15.81 min, respectively. The optimum conditions estimated by RSM for the maximized values of soluble solids and heavy metal elimination rates were $165{\sim}180$ min of steaming time, $120{\sim}135^{\circ}C$ of roasting temperature, and $30{\sim}45$ min of roasting time, respectively. These estimated values were in agreement with those measured by real experiments.

• Journal of the Korean Magnetics Society
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• v.12 no.6
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• pp.224-230
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• 2002

The statistical experiment method is employed to optimize the deposition condition of Co film with DC magnetron sputtering process. The statistical treatment results showed the significance value below 0.05, low RMS error and R-sq value close to 1, which implied that our experiment and design were very reliable. We found that the sheet resistance decreased to -1.83Ω/$\square$ with the deposition temperature, increased to 11.17Ω/$\square$ with the deposition pressure, and decreased into -0.65Ω/$\square$ with the DC power. We also confirmed that the sheet resistance uniformity was mainly influenced by the deposition temperature as it decreased -4.04％ at the temperature range of 25$\^{C}$∼147$\^{C}$. Finally, we report that the optimum condition of Co film using our statistical method of design of experiment is the deposition temperature of 25$\^{C}$, the deposition pressure of 12mTorr, and the DC power of 1500W.

• Environmental and Resource Economics Review
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• v.16 no.1
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• pp.171-197
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• 2007

In this paper we provide a methodology that permits test of feasibility of Porter hypothesis under limited data environment by utilizing two types of output distance function: Shephard distance function and directional distance function. The production technology supported by Porter hypothesis is embodied in the directional distance function. The average annual marginal abatement cost for $SO_2$ obtained by estimating the directional distance function is higher than the one obtained with the Shephard distance function by about 50 percent in the Korean electric power industry over the period 1970~1998. This result implies that feasibility of Porter hypothesis depends upon whether investment in production capital and process can bring more than a 50 percent increase in the average productivity.

• Membrane Journal
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• v.15 no.4
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• pp.297-309
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• 2005

As a number of potential endocrine disrupting compounds (EDCs) are released into the environment, recently growing attention has been drawn to them. Therefore sensitive and reliable analytical methods are essential to monitor those compounds. In this study, complementary CC-MS and LC-MS were employed to analyze the endocrine disrupters, and the results of two methods were compared for di(2-ethylhexyl)phthalate (DEHP), benzylbutylphthalate (BBP), pentachlorophenol (PCP), and 4,4'-Isopropylidenediphenol (Bisphenol-A, or BPA). The results indicate that it was possible to lower the detection limits of EDCs by LC-MS. Also, LC-MS enabled to identify the EDCs as almost intact molecules. Furthermore, this study presented a nanofiltration membrane (MWCO 250) and a ultrafiltration membrane (MWCO 1,000) filtration system as methods far removing EDCs from drinking water containing $\gamma$-BHC, p,p'-DDE, BBP, p,p'-DDT, DEHP, PCP, and BPA. Cross-flow type nanofiltrations showed $100\%$ removal of EDCs, and the result implies that MWCO 250 nanofilter was sufficient for treatment of EDCs. The ratio of permeate flux to mass transfer coefficient of nanofiltration, high flux ultrafiltration, and low flux ultrafiltration with ultrapure water were 0.67, 3.4, and 0.44, respectively. It was found that nanofiltration and low flux ultrafiltration were operated at a diffusion dominant condition, and the high flux ultrafiltration was operated at a convection dominant condition. Furthermore, a diffusion dominant process attained reasonable rejection of EDCs. The removal in the ultrafiltration was depending on the molecular weight of an EDC, and the filtration was governed by diffusion-dominant hydrodynamic conditions.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.15 no.3
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• pp.389-398
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• 2002

The mixed mode problem (I and II) of a peny-shaped interface cracks in remote tension loading on a bi-material cylinder is studied using finite element method. The energy release rates for the tip of the crack in the interface were calibrated for several different moduli combinations and crack ratios using the modified crack closure integral technique and J-integral method, with numerical results obtained from a commercial finite element program. Numerical results show that non-dimensional value of$\sqrt{G_{II}E^*}/\sqrt[p]{\pi a}$ increases as the crack size or moduli ratio increases. Meanwhile, non-dimensional value of$\sqrt{G_{I}E^*}/\sqrt[p]{\pi a}$ decreases as the moduli ratio increases, but above the moduli ratio of 3 its value decreases then increases again as the crack size increases. Reliability of the numerical analysis in this study was acquired with comparison to an analytical solution for the peny-shaped interface crack in an infinite medium.

• Journal of the Korea institute for structural maintenance and inspection
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• v.27 no.5
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• pp.120-129
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• 2023

Hanger cable tension is a major response that can determine the integrity and safety of suspension bridges. In general, the vibration method is used to estimate hanger cable tension on operational suspension bridges. It measures natural frequencies from hanger cables and indirectly estimates tension using the geometry conditions of the hanger cables. This study estimated the hanger cable tension of the Palyeong Bridge using a vision-based system. The vision-based system used digital camcorders and tripods considering the convenience and economic efficiency of measurement. Measuring the natural frequencies for high-order modes required for the vibration method is difficult because the hanger cable response measured using the vision-based system is displacement-based. Therefore, this study proposed a back analysis technique for estimating tension using the natural frequencies of low-order modes. Optimization for the back analysis technique was performed by defining the difference between the natural frequencies of hanger cables measured in the field and those calculated using finite element analysis as the objective function. The direct search method that does not require the partial derivatives of the objective function was applied as the optimization method. The reliability and accuracy of the back analysis technique were verified by comparing the tension calculated using the method with that estimated using the vibration method. Tension was accurately estimated using the natural frequencies of low-order modes by applying the back analysis technique.

• The Korean Journal of Pesticide Science
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• v.15 no.4
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• pp.529-544
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• 2011

Many international organizations, such as the International Organization for Standardization (ISO) and Collaborative International Pesticide Analytical Council (CIPAC), have published a guide to quality control requirements, proficiency testing and method validation for pesticide formulation. In general, proficiency testing is to determine the performance of individual laboratories from the comparison of test results and to monitor a laboratory's performance abilities. One of quality assurance (QA) scheme would be include the validation of analytical method that implies a performance characteristics, specificity, selectivity, linearity and so on. According to many international organizations, the quantification methods of active substance in formulated pesticide products are required to be reproducible, accurate and precise. This study was conducted to compare the international guidelines for the quality control, proficiency testing and method validation of analytical laboratories and to propose a general guidance for the establishment of quality control system in the analytical chemistry laboratories of pesticide formulation in domestic.

• Journal of the Korean Society for Precision Engineering
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• v.12 no.7
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• pp.158-168
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• 1995

연삭숫돌 선택은 공작물제거량, 숫돌의 소모량, 표면정도 및 공작물의 물리적,화학적 특성을 고려하여 설정하는 것을 기본으로 한다. 연삭가공은 구성인자의 상호관계가 복잡하여 이중에서 어느한 요소만을 고려하여 설정하기 어렵고 정량적 기준 또한 정해져있지 않아 현실적으로는 숙련자의 정성적이고 경험적 지식에 따른 주관적 척도에 의존하는 것이 대부분이다. 또한, 연삭숫돌은 작업조건중에서 대량생산을 제외하고는 되도록이면 현장에 구비되어 있는 작업가능한 연삭숫돌 중에서 선택하는 것이 바람직하다. 따라서 본시스템에서는 이와같은 점을 고려하여 최적 연삭숫돌선택을 퍼지이론에 기초한 현장 숙련자의 지식을 활용하므로써 연삭숫돌선택의 효율성을 도모하는 동시에 현장에 연삭숫돌이 구비되지 않은 경우도 고려하여 연삭숫돌설정에 우선순위를 제시하므로써 작업자에 연삭숫돌선택의 유연성을 부여하였다. 또한, 실용성있는 전문가시스템의 구축을 위해 정성적이고 경험적인 지식의 활용을 위한 지식표현으로 설문조사에서 얻은 테이타를 x$^{2}$-분포에 따른 추정신뢰구간을 구해, 이를 토대로한 비대칭 삼각퍼지함수의 결정법을 제시하고, 이를 이용해서 구축한 시스템의 실행결과의 타당성을 비교하고자 한다.