• Proceedings of the Korean Vacuum Society Conference
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• 2013.08a
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• pp.196.2-196.2
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• 2013

본 연구에서는 분자선 에피택시 (MBE)법으로 성장된 InAs submonolayer quantum dot (SML-QD)을 태양전지에 응용하여 광학 및 전기적 특성을 평가하였다. 본 연구에서 사용된 양자점 태양전지(quantum dot solar cell, QDSC)의 구조는 n+-GaAs 기판 위에 n+-GaAs buffer와 n-GaAs base layer를 차례로 성장 한 후, 활성영역에 InAs/InGaAs SML-QD와 n-GaAs spacer layer를 8주기 형성하였다. 그 위에 p+-GaAs emitter, p+-AlGaAs window layer를 성장하고 ohmic contact을 위하여 p+-GaAs 를 성장하였다. SML-QD 구조의 두께는 0.3 ML 이며, 이때 SML-QD의 적층수를 4 stacks 으로 고정하였다. SML-QD 와의 비교를 위하여 2.0 ML크기의 InAs자발 형성 양자점 태양전지(SK-QDSC)과 GaAs 단일 접합 태양전지 (reference-SC)를 동일한 성장조건에서 제작하였다. PL 측정 결과, 300 K에서 SML-QD의 발광 피크는 SK-QD 보다 고에너지에서 나타나는데(1.349 eV), 이것은 SML-QD가 SK-QD보다 작은 크기를 가지기 때문으로 사료된다. SML-QD는 single peak를 보이는 반면, SK-QD는 dual peaks (1.112 / 1.056 eV)을 확인하였다. SML-QD의 반치폭(full width at half maximum, FWHM)이 SK-QD에 비하여 작은 것으로 보아 SML-QD가 SK-QD보다 양자점 크기 분포의 균일도가 높은 것으로 해석된다. Illumination I-V 측정 결과, SML-QDSC의 개방 전압(VOC) 과 단락전류밀도(JSC)는 SK-QDSC의 값과 비교해 보면, 각각 47 mV와 0.88 mA/cm2만큼 증가하였다. 이는 SK-QD보다 상대적으로 작은 크기를 가진 SML-QD로 인해 VOC가 증가되었으며, SML-QD가 SK-QD 보다 태양광을 흡수할 수 있는 영역이 비교적 적지만, QD내에 존재하는 energy level에서 탈출 할 수 있는 확률이 더 높음으로써 JSC가 증가한 것으로 분석 된다.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.35 no.9
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• pp.1119-1129
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• 2011

Shot-peening effects on the fatigue behavior of bearing steel were investigated under the high cyclic loading. Hourglass shape specimens were made of bearing steel(JIS-SUJ2) for rotary bending fatigue tests. Two kinds of treatments were performed : a heat treatment and a shot-peened surface treatment after the heat treatment. The fracture surfaces of specimens were classified into two types of fracture mode : the surface fracture mode induced by a surface defect and the internal fracture mode induced by a nonmetallic inclusion. Inclusion depth and shape affected considerably the fatigue life. Shot-peening treatment improved much the fatigue life of the bearing steel under low and high levels of cyclic loads. Probabilistic-stress-life (P-S-N) curves were suggested for the reliable fatigue life estimation of the improved bearing steel.

• Journal of the Korea institute for structural maintenance and inspection
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• v.14 no.1
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• pp.156-164
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• 2010

A total of 6 stepwise constructions were made for building the floating mass concrete foundation. The optimal curing strategies and specialized construction guidelines were adoptively extracted from the 1.5m cube mock-up test prior to the main concrete work. Two different thermal crack index(TCI) calculations from current construction manual exhibit relatively low values as comparing the measured temperature data. This implies that the hydration-induced cracking could be developed in parts of concrete mass. However, the controversial phenomenons in reality were observed. No significant surface cracks are detected at the successive construction stages. Thereby, this paper raises the question regarding on the existence of characteristic length with varying size and shape of a target specimen which are missing in the current construction manual. The isothermal core area and high thermal gradient area in the edge volume should be identified and be introduced to TCI calculation for the purpose of an accuracy.

• Journal of the Korean Society for information Management
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• v.38 no.3
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• pp.1-22
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• 2021

An online experiment was conducted to test the subject-knowledge view of relevance theory in order to find evidence of a conceptual basis for relevance. Six experts in Library and Information Science (LIS), nine Master's students of LIS, and twelve non-experts judged the relevance of 14 abstracts within and outside of the LIS domain. Consistency among the judges was calculated by joint-probability agreement (PA) and interclass correlation coefficients (ICC). When using PA to analyze the judgements, non-experts had a higher consensus regardless of the task or division of groups. However, ICC calculations found Master's candidates had a higher level of consensus than non-experts within LIS, although the experts did not; and the agreement rates on the non-LIS task for all groups were only poor to moderate. It was only when the groups were analyzed as two groups (experts including Master's candidates and non-experts) that the expected trend of higher consistency among experts in the LIS task was seen.

• The Mathematical Education
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• v.58 no.3
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• pp.383-401
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• 2019

This study started with the idea that it is necessary to focus on common concepts and ideas among the subjects when conducting integrated education in high school. This is a preliminary study for developing materials that can be taught in mathematics in the context of already learning scientific concepts in high school. For this purpose, Mendel 's law of genetics was studied among the contents of biological subjects which are known to have relatively little connection with mathematics. The more common links between the two subjects are, the better, in order to integrate math and other subjects and develop materials for teaching. Therefore, in this study, we investigated not only the probability domain but also the concept of statistical domain. We have been wondering if there is a more abundant idea to connect between 'Mendel's law' and 'probability and statistics'. Through these anxieties, we could find that concepts such as 'likely equality' and 'permutation and combination' including 'a large number of laws' can be a link between two subjects. Based on this, we were able to develop class materials that correspond to classes. This study is expected to help with research related to development of integrated education support materials, focusing on mathematics.

• The Korean Journal of Applied Statistics
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• v.34 no.4
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• pp.537-556
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• 2021

Properties of statistical process control procedures may not be derived analytically in many cases; however, the application of a Markov chain can solve such problems. This article shows how to derive the properties of the process control procedures using the generated Markov chains when the control statistic satisfies the Markov property. Markov chain approaches that appear in the literature (such as the statistical design and economic design of the control chart as well as the variable sampling rate design) are reviewed along with the introduction of research results for application to a new control procedure and reset chart. The joint application of a Markov chain approach and analytical solutions (when available) can guarantee the correct derivation of the properties. A Markov chain approach is recommended over simulation studies due to its precise derivation of properties and short calculation times.

• Journal of the Korea Society for Simulation
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• v.31 no.4
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• pp.11-22
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• 2022

Unlike a short-range, a long-range underwater acoustic communication(UWAC) uses low frequency signal and deep sound channel to minimize propagation loss. In this case, even though communication signals are modulated using a covert transmission technique such as spread spectrum, it is hard to conceal the existence of the signals. The unconcealed communication signal can be utilized as active sonar signal by enemy and presence of underwater vehicles may be exposed to the interceptor. Since it is very important to maintain stealthiness for underwater vehicles, the detection probability of friendly underwater vehicles should be considered when interceptor utilizes our long-range UWAC signal. In this paper, we modeled a long-range UWAC environment for analyzing the detection performance of underwater vehicles and proposed the region of interest(ROI) setup method and the measurement of detection performance. By computer simulations, we yielded parameters, analyzed the detection probability and the detection performance in ROI. The analysis results showed that the proposed detection performance analysis method for underwater vehicles could play an important role in the operation of long-range UWAC equipment.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.27 no.1
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• pp.62-68
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• 2023

An aerial relay system utilizing an unmanned aerial vehicle(UAV) or drone is addressed for event-driven operations such as temporary communication services for disaster affected area, military and first responder support. UAV relay system (URS) targets to provide a reliable communication service to a remote user equipment or an operator, therefore, a fast UAV placement to guarantee a minimum quality of service(QoS) is important when an operation is requested. Researches on UAV utilization in communication systems mostly target to derive the optimal position of UAV to maximize the performance, however, fast deployment of UAV is much more important than optimal placement under emergency situations. To this end, this paper derives the feasible area for UAV placement, investigates the effect of performance requirements on that area, and suggests UAV placement to certainly guarantee the performance requirements. Simulation results demonstrate that the feasible area derived in this paper matches that obtained by an exhaustive search.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.25 no.12
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• pp.1846-1852
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• 2021

In modern society, various digital devices are being distributed in a wide range of fields due to the fourth industrial revolution and the development of IoT technology. However, noise is generated in the process of acquiring or transmitting an image, and not only damages the information, but also affects the system, causing errors and incorrect operation. AWGN is a representative noise among image noise. As a method for removing noise, prior research has been conducted, and among them, AF, A-TMF, and MF are the representative methods. Existing filters have a disadvantage that smoothing occurs in areas with high frequency components because it is difficult to consider the characteristics of images. Therefore, the proposed algorithm calculates the standard deviation distribution to effectively eliminate noise even in the high frequency domain, and then calculates the final output by applying the probability density function weight of the Laplace distribution using the curve fitting method.

• Journal of the Korean Society of Radiology
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• v.18 no.1
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• pp.11-20
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• 2024

As the importance of intervention has recently increased, interest in the health of medical staff performing the procedure is increasing. Existing radiation shielding devices have limited the operator's movement and have not been properly used due to the risk of infection, and adequate radiation shielding of the operator's gonads and furthermore, the entire area of the procedure room has not been achieved. An auxiliary shielding device was manufactured by attaching a Bismuth to the elbow support used in the procedure, and the radiation shielding effect was measured. As a result of the measurement, the average spatial dose rate decreased by about 64.8%, and the independent sample t-test analysis showed statistically significant below the significance probability (p<0.05). The use of an auxiliary shielding device is considered to be an effective shielding method that can shield the operator's gonads and reduce the radiation spatial dose rate of the entire area of the procedure room.