• 한국결정성장학회지
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• 제30권1호
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• pp.1-6
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• 2020

본 연구에서는 패턴화된 사파이어 기판 위에 HVPE(Hydride Vapor Phase Epitaxy System) 법에 의해 50 nm 두께의 AlN thin film을 증착한 뒤, 에피층 구조가 MO CVD에서 성장되었다. AlN 버퍼층 박막의 표면형상이 SEM, AFM에 의해서, 에피층 구조의 GaN 박막의 결정성은 X-선 rocking curve에 의해 분석되었다. 패턴화된 사파이어 기판 위에 증착된 GaN 박막은, 사파이어 기판 위에 증착된 GaN 박막의 경우보다 XRD 피크 세기가 다소 높은 결과를 나타냈다. AFM 표면 형상에서 사파이어 기판 위에 AlN 박막이 증착된 경우, GaN 에피층 박막의 p-side 쪽의 v-pit 밀도가 상대적으로 낮았으며, 결함밀도가 낮게 관찰되었다. 또한, AlN 버퍼층이 증착된 에피층 구조는 AlN 박막이 없는 에피층의 광출력에 비해 높은 값을 나타냈다.

• 대한수학회보
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• 제55권4호
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• pp.1103-1107
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• 2018

Let M be a complete spacelike hypersurface in the (n + 1)-dimensional Minkowski space ${\mathbb{L}}^{n+1}$. Suppose that every unit speed curve X(s) on M satisfies ${\langle}X^{\prime\prime}(s),X^{\prime\prime}s){\rangle}{\geq}-1/r^2$ and there exists a point $p{\in}M$ such that for every unit speed geodesic X(s) of M through the point p, ${\langle}X^{\prime\prime}(s),X^{\prime\prime}s){\rangle}=-1/r^2$ holds. Then, we show that up to isometries of ${\mathbb{L}}^{n+1}$, M is the hyperbolic space $H^n(r)$.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1992년도 하계학술대회 논문집 B
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• pp.753-756
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• 1992

The piezoelectric ceramics of PMS-PZT was made in the radial mode disk. As the results, in the application of filter required conditions: that is, higher-values for piezoelectric properties($K_p$, $Q_m$) and lower-values for stabilities of $F_{\tau}$(temp. coefficient, aging rate), 5PMS-51PT-44PZ composition statified well. This composition was made in the dot-ring type. Asthe results, with increasing $n^2$ both $Q_m$ and S had high values, decreasing $n^2$ both $K_p$ and BW had low values when the diameter of sintered bodies were constant. Therefore, curve of filter characteristic have sharped with increasing $n^2$ and BW broadened with decreasing $n^2$.

• 대한수학회보
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• 제59권5호
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• pp.1105-1117
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• 2022

In this paper, we obtain a second main theorem for holomorphic curves and moving hyperplanes of Pⁿ(C) where the counting functions are truncated multiplicity and have different weights. As its application, we prove a uniqueness theorem for holomorphic curves of finite growth index sharing moving hyperplanes with different multiple values.

• Nuclear Engineering and Technology
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• 제38권3호
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• pp.277-284
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• 2006

In order to ensure the structural integrity of nuclear welded structures during design life, the fatigue life has to be evaluated by fatigue analysis procedures presented in technical codes such as ASME B&PV Code Section III. However, existing fatigue analysis procedures do not explicitly consider the presence of welded joints. A new fatigue analysis procedure based on a structural stress/fracture mechanics approach has been recently developed in order to reduce conservatism by erasing uncertainty in the analysis procedure. A recent review of fatigue crack growth data under various mean loading conditions using the structural stress/fracture mechanics approach, does not consider the mean loading effect, revealed some significant discrepancies in fatigue crack growth curves according to the mean loading conditions. In this paper, we propose the use of the stress intensity factor range ${\Delta}K$ characterized with loading ratio R effects in terms of the structural stress. We demonstrate the effectiveness in characterizing fatigue crack growth and S-N behavior using the well-known data. It was identified that the S-N data under high mean loading could be consolidated in a master S-N curve for welded joints.

• Journal of Chest Surgery
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• 제45권3호
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• pp.166-170
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• 2012

(VATS) lobectomy to junior surgeons, and to review the first year experience of a new surgeon performing VATS lobectomies who had not performed a VATS lobectomy unassisted during his training period. Materials and Methods: A young surgeon opened a division of general thoracic surgery at a medical institution. The surgeon had performed about 100 lobectomies via conventional thoracotomy during his training period, but had never performed a VATS lobectomy unassisted while under the supervision of an expert. After opening the division of general thoracic surgery, the surgeon performed a total of 38 pulmonary lobectomies for various pulmonary diseases from March 2009 to February 2010. All data were collected retrospectively. Results: There were 14 lobectomies via thoracotomy, 14 VATS lobectomies, and 10 cases of attempted VATS lobectomies that were converted to open thoracotomies. The number of VATS lobectomies increased from the second quarter (n=0) to the third quarter (n=5). The lobectomies that were converted from VATS into thoracotomies decreased from the second quarter (n=5) to the third quarter (n=1) (p=0.002). Conclusion: It can take 6 months for young surgeons without experience in VATS lobectomy in their training period to be able to reliably perform a VATS lobectomy.

• 대한전기학회논문지
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• 제41권7호
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• pp.712-722
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• 1992

Several voltage instability/collapse problems that have occurred in the electric utility industry worldwide have gained the attention of engineers and researchers of electric power systems. This paper proposes an effective calculation scheme of the extreme loading point and nose curves(P-V curves) using modified Newton-Raphson(N-R) load flow method and the Continuation Method. This method provides detail and visual information of the power system voltage profile and operating margin ro operators and planners. In this paper, a modified load flow claculation method for ill-conditioned power systems is introduced for the purpose of seeking more precise load flow solutions and nose curves, and the Continuation Method is also used as a part of the solution algorithm for the calculation of extreme loading point and nose curves. The conventional polar coordinate based N-R load flow program is modified to avoid numerical difficulties caused by the singularity of the Jacobian matrix occuring in the vicinity of extreme loading point of heavily loaded systems. Application results of the proposed method to Klos-Kerner 11-bus system and modified IEE-30-bus system are presented to assure the usefulness of the approach.

• 대한조선학회논문집
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• 제56권2호
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• pp.161-167
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• 2019

In general, fatigue analysis is performed by using deterministic model to estimate the optimal parameters. However, the deterministic model is difficult to clearly describe the physical phenomena of fatigue failure that contains many uncertainty factors. With regard to this, efforts have been made in this research to compare with the deterministic model and the stochastic models. Firstly, One deterministic S-N curve was derived from ordinary least squares technique and two P-S-N curves were estimated through Bayesian-linear regression model and Markov-Chain Monte Carlo simulation. Secondly, the distribution of Long-term fatigue damage and fatigue life were predicted by using the parameters obtained from the three methodologies and the long-term stress distribution.

• 한국물환경학회지
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• 제28권3호
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• pp.409-417
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• 2012

SWAT model was applied for the Nakdong River Basin to characterize water quality variability and assess the feasibility of using the load duration curve to water quality management. The basin was divided into 67 sub-basins considering various watershed environment, and rainfall runoff and pollutant loading were simulated based on 6 year measurements of meteo-hydrological data, discharge data of treatment plants, and water quality data (SS, T-N and T-P). The results demonstrate that non-point source loads during wet season increase by 80 ~ 95% of total loads. Although the rate of water flow governs the amount of SS that is transported to the main streams, nutrient concentrations are highly elevated during dry season by being concentrated. This phenomenon is more pronounced in the lower basin, receiving large amounts of urban point source discharges such as treated sewages. Also, the load duration curves (LDC) demonstrate dominant source problems based on the load exceedances, showing that SS concentrations are associated with the rainy season and nutrients, such as T-P, may be more concentrated at low flow and more diluted at higher flow. Overall, the LDC method could be used conveniently to assess watershed characteristics and pollutant loads in watershed scale.

• 한국습지학회지
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• 제26권1호
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• pp.1-9
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• 2024

이 연구에서는 서낙동강을 구성하는 소유역 중 대지면적 비율이 크고 인구밀도가 높은 해반천 유역의 유출 및 수질을 모의하기 위한 HSPF(Hydrological Simulation Program-FORTRAN)모형을 개발하였다. 유역에서 발생하는 비점오염 부하량을 관리하기 위한 세 가지 시나리오가 개발되어 모형에 적용되었고, 오염부하량의 감소와 부하지속곡선에 대비한 수질 기준 초과율이 분석되었다. 시나리오는 비점오염의 발생을 줄이기 위한 도로 청소, 다양한 저영향 개발 기법을 고려한 유출 저감 조치, 그리고 강으로 들어가는 비점오염원을 완화하기 위한 유입 저감 조치로 구성되었다. 첫 번째 시나리오에서는 김해시의 도로 청소 차량 수와 같은 실제 조건이 고려되었으며, 두 번째와 세 번째 시나리오에서는 적용 가능한 토지 이용별 면적의 50%에 저영향 개발 기법을 적용하는 것으로 적용되었다. 모든 세 가지 조치를 적용한 결과, BOD 오염 물질 부하가 58.28%, T-N은 58.49%, T-P는 51.56% 감소할 수 있는 것으로 도출되었다. 또한, 5년간 누적된 수질 측정의 60번째 백분위수를 목표 수질로 설정하고 구축된 유량지속곡선에 의한 초과율분석 결과, 결과적으로, BOD의 경우 조치 적용 전 41.57%의 초과율이 조치 후 16.32%로 감소하여, 초과율이 25.25% 감소하였다. T-N의 경우 조치 전 40.31%에서 조치 후 22.84%로, T-P의 경우 62.43%에서 27.22%로 감소하였다.