• 한국재료학회:학술대회논문집
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• 한국재료학회 2010년도 춘계학술발표대회
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• pp.48.2-48.2
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• 2010

The effect of additives as rare-earth in dielectric materials has been studied to meet the development trend in electronics on the miniaturization with increasing the capacitance of MLCCs (multi-layered ceramic capacitors). It was reported that the addition of rare-earth oxides in dielectrics would contribute to enhance dielectric properties and high temperature stability. Especially, dysprosium and thulium are well known to the representative elements functioned as selective substitution in barium titanate with perovskite structure. The effects of these additives on microstructure and electric properties were studied. The 0.8 mol% Dy doped $BaTiO_3$ and the 1.0 mol% Tm doped $BaTiO_3$ had the highest electric properties as optimized composition, respectively. According to the increase of rare-earth contents, the growth of abnormal grains was suppressed and pyrochlore phase was formed in more than solubility limits. Furthermore, the effect of two rare-earth elements co-doped $BaTiO_3$ on the dielectric properties and insulation resistance was investigated with different concentration. The dielectric specimens with $BaTiO_3-Dy_2O_3-Tm2O_3$ system were prepared by design of experiment for improving the electric properties and sintered at $1320^{\circ}C$ for 2h in a reducing atmosphere. The dielectric properties were evaluated from -55 to $125^{\circ}C$ (at $1KHz{\pm}10%$ and $1.0{\pm}0.2V$) and the insulation resistance was examined at 16V for 2 min. The morphology and crystallinity of the specimens were determined by microstructural and phase analysis.

• 농업과학연구
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• 제50권3호
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• pp.539-549
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• 2023

Domestic processed food exports might increase due to the free trade agreement (FTA) and spread of the Korean Wave, Hallyu. However, the share of the domestic raw materials in the domestic processed food industry is very low at 31.4%, which limits the spillover effect on domestic agriculture. Therefore, we selected frozen dumplings as a representative processed food whose exports are growing rapidly and conducted a multiple regression analysis to examine the effects of Hallyu and FTA variables on the frozen dumpling exports. We tried to link them to an increase in agricultural income through the expansion of demand for the domestic raw materials. This study analyzed tariff indicator as the FTA variable, cosmetics export value indicator as the Hallyu Wave variable, and other variables expected to change the trade environment such as gross domestic product (GDP) and the relative exchange rate by country as the key explanatory variables that affect changes in the trade environment. The analysis showed that the core hypothesis, the Hallyu variable and the FTA variable, have a positive impact on frozen dumpling exports. Frozen dumpling exports are expected to increase as the FTAs and the spread of Hallyu are expected to continue for the foreseeable future. Therefore, we should seek ways to increase the proportion of domestically produced ingredients in the frozen dumplings to spread the economic impact to domestic agriculture. We reviewed previous studies and determined, the price-related factors play a major role in the use of imported ingredients, and that price stability and competitiveness are essential to increase the share of the domestically produced ingredients. Based on these conclusions, we reviewed the current status of food industry-related policies and determined measures needed to expand the use of domestically produced ingredients.

• The Journal of Advanced Prosthodontics
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• 제7권2호
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• pp.151-159
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• 2015

PURPOSE. To describe and characterize the surface topography and cleanliness of CAD/CAM manufactured zirconia abutments after steaming and ultrasonic cleaning. MATERIALS AND METHODS. A total of 12 ceramic CAD/CAM implant abutments of various manufacturers were produced and randomly divided into two groups of six samples each (control and test group). Four two-piece hybrid abutments and two one-piece abutments made of zirconium-dioxide were assessed per each group. In the control group, cleaning by steam was performed. The test group underwent an ultrasonic cleaning procedure with acetone, ethyl alcohol and antibacterial solution. Groups were subjected to scanning electron microscope (SEM) analysis and Energy-dispersive X-ray spectroscopy (EDX) to verify and characterize contaminant chemical characterization non- quantitatively. RESULTS. All zirconia CAD/CAM abutments in the present study displayed production-induced wear particles, debris as well as organic and inorganic contaminants. The abutments of the test group showed reduction of surface contamination after undergoing an ultrasonic cleaning procedure. However, an absolute removal of pollutants could not be achieved. CONCLUSION. The presence of debris on the transmucosal surface of CAD/CAM zirconia abutments of various manufacturers was confirmed. Within the limits of the study design, the results suggest that a defined ultrasonic cleaning process can be advantageously employed to reduce such debris, thus, supposedly enhancing soft tissue healing. Although the adverse long-term influence of abutment contamination on the biological stability of peri-implant tissues has been evidenced, a standardized and validated polishing and cleaning protocol still has to be implemented.

• 한국지반환경공학회 논문집
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• 제20권12호
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• pp.49-55
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• 2019

사면 붕괴에 대한 해석은 지반특성과 여러 가지 복합적인 인자들로 인해 정확한 해석은 어려운 것이 사실이다. 지속적으로 발생하는 사면재해로 인하여 사면재해 발생 원인을 규명하기 위한 많은 연구가 이루어지고 있지만, 사면 붕괴의 가장 중요한 요소인 강우특성 및 강우로 인한 침투능에 따른 사면 안정성 평가는 미흡한 실정이다. 본 연구에서는 주문진표준사를 이용하여 단위중량별 정수위 투수시험을 통한 투수계수를 산정하였으며, 투수계수와 강우강도의 영향을 고려하여 침투능 및 침투량을 산정할 수 있는 강우강도별 일차원 침투실험을 실시하였다. 실험결과를 바탕으로 사질토지반에서의 기존 경험식의 적용성을 분석하였다.

• 터널과지하공간
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• 제28권5호
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• pp.493-511
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• 2018

본 논문에서는 그라운드 앵커의 긴장력 손실에 대응하고자 긴장력 상시확인을 위한 앵커 긴장력 상시 육안확인장치에 대한 내용을 다루었다. 그라운드 앵커는 사회적 인프라 시설의 안정성을 확보하기 위해 시공되었지만 지속적인 긴장력 손실로 인해 시설물에 대한 안전이 심각하게 우려되고 있는 실정이다. 이에 앵커의 유지관리가 요구되지만 현재 잔존긴장력의 계측은 경제적인 측면을 고려하여 표본조사로 이루어지고 있어 정밀도에 대한 한계점을 지니고 있다. 따라서 본 논문에서는 앵커의 긴장력을 육안으로 확인할 수 있는 앵커 긴장력 상시 육안확인장치의 개발을 목적으로 개념설계, 실내 인장실험을 통한 규격화를 수행하였으며, 현장시험을 통해 성능을 확인하였다.

• 디지털융복합연구
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• 제11권11호
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• pp.37-52
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• 2013

현재 정부는 본격적인 전력 스마트그리드 확대에 앞서 제주도 구좌읍 6,000호를 대상으로 스마트그리드 실증사업을 추진 중에 있다. 하지만, 관련 기업들은 정부와 한전 주도의 한국 전력시장의 한계, 기존 전력망의 높은 안정성 및 효율성, 신재생에너지 활용도 미흡, 전기요금 인상 우려 등을 이유로 스마트그리드 확산에 대한 부정적인 시각을 가지고 있다. 본 연구는 스마트그리드 시장을 활성화하기 위한 핵심 이슈들을 1) 이해관계자들의 대립 문제, 2) 실시간 요금제 도입에 따른 효과 문제, 3) 소비자들의 수요 반응 참여 부족, 4) 스마트그리드의 비즈니스 모델부재, 5) 스마트그리드 거점지구 확산 문제 등의 5가지로 분류하고, 이에 대한 전략적 방안을 제시하였다.

• 한국광학회지
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• 제17권5호
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• pp.412-419
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• 2006

초정밀 비구면 기공기로 제작한 구경 300 mm이고 f-수가 1.98인 알루미늄 쌍곡면 거울의 형상을 측정하기 위하여 자동무수차점 널(null) 렌즈 광학계를 설계하고 제작하였으며, 이를 이용하여 이 대구경 쌍곡면 거울의 형상을 측정하였다. 이때 널 렌즈간 정렬은 구조적으로 안정하고 부피가 작은 경통고정식을 선택하였고, 널 렌즈 및 경통의 제작 허용오차는 요구되는 측정 정밀도를 만족하도록 공차분석기법을 통하여 계산하고 제작하였다.

• PNF and Movement
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• 제21권2호
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• pp.255-263
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• 2023

Purpose: This study aims to investigate the immediate effects of electromyography (EMG) biofeedback training of the gluteus medius on dynamic balance during single leg squats in healthy individuals. Methods: The sample size in this study was estimated using the G-power program at an effect size of 0.4, a significance level (α) of 0.05, and a testing power of 0.90. In addition, as a result of considering the 10% dropout rate, this study recruited 21 healthy individuals (8 males and 13 females). All subjects measured the Y-balance test-lower quarter (YBT-LQ) and limits of stability (LOS) before and after a single leg squat (SLS) and SLS with EMG biofeedback training of the gluteus medius (SLSEB). They were trained for 10 minutes for each exercise, and two dynamic balance tests were performed three times. Results: There was a significant difference in the YBT-LQ score between the two exercises (p < 0.05). In the YBT-LQ score, there was a significant difference before and after SLS and SLSEB (p < 0.05). SLSEB showed a significantly higher YBT-LQ score than SLS (p < 0.05). There was a significant difference in LOM between the two exercises (p < 0.05). However, there was no significant difference between the two exercises. Conclusion: A single-leg squat with EMG biofeedback exercises is an effective method to improve dynamic balance, such as the YBT-LQ.

• Structural Monitoring and Maintenance
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• 제8권4호
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• pp.345-360
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• 2021

This paper presents an analytical approach to calculate the buckling load of the cylindrical ring structures subjected to both hydrostatic and hydrodynamic pressures. Based on the conservative law of energy and Timoshenko beam theory, a theoretical formula, which can be used to evaluate the critical pressure of buckling, is first derived for the simplified cylindrical ring structures. It is assumed that the hydrodynamic pressure can be treated as an equivalent hydrostatic pressure as a cosine function along the perimeter while the thickness ratio is limited to 0.2. Note that this paper limits the deformed shape of the cylindrical ring structures to an elliptical shape. The proposed analytical solutions are then compared with the numerical simulations. The critical pressure is evaluated in this study considering two possible failure modes: ultimate failure and buckling failure. The results show that the proposed analytical solutions can correctly predict the critical pressure for both failure modes. However, it is not recommended to be used when the hydrostatic pressure is low or medium (less than 80% of the critical pressure) as the analytical solutions underestimate the critical pressure especially when the ultimate failure mode occurs. This implies that the proposed solutions can still be used properly when the subsea vehicles are located in the deep parts of the ocean where the hydrostatic pressure is high. The finding will further help improve the geometric design of subsea vehicles against both hydrostatic and hydrodynamic pressures to enhance its strength and stability when it moves underwater. It will also help to control the speed of the subsea vehicles especially they move close to the sea bottom to prevent a catastrophic failure.

• 천문학회지
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• 제56권2호
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• pp.277-286
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• 2023

It is difficult to distinguish the pure signal produced by an orbiting planetary companion around giant stars from other possible sources, such as stellar spots, pulsations, or certain activities. Since 2003, we have obtained radial (RV) data from evolved stars using the high-resolution, fiber-fed Bohyunsan Observatory Echelle Spectrograph (BOES) at the Bohyunsan Optical Astronomy Observatory (BOAO). Here, we report the results of RV variations in the binary star HD 135438. We found two significant periods: 494.98 d with eccentricity of 0.23 and 8494.1 d with eccentricity of 0.83. Considering orbital stability, it is impossible to have two companions in such close orbits with high eccentricity. To determine the nature of the changes in the RV variability, we analyzed indicators of stellar spot and stellar chromospheric activity to find that there are no signals related to the significant period of 494.98 d. However, we calculated the upper limits of rotation period of the rotational velocity and found this to be 478-536 d. One possible interpretation is that this may be closely related to the rotational modulation of an orbital inclination at 67-90 degrees. The other signal corresponding to the period of 8494.1 d is probably associated with a stellar companion orbiting the giant star. A Markov Chain Monte Carlo (MCMC) simulation considering a single companion indicates that HD 135438 system hosts a stellar companion with 0.57^+0.017 _-0.017 M_⊙ with an orbital period of 8498 d.