• Imaging Science in Dentistry
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• 제40권3호
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• pp.115-121
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• 2010

Purpose : The purpose of this study was to accurately analyze the radiographic characteristics of dentigerous cyst (DC) with multiplanar images of cone beam computed tomography (CBCT). Materials and Methods : Thirty eight radiographically and histopathologically proven cases of DCs were analyzed with panoramic radiograph and CBCT, retrospectively. The radiographic CT pattern, symmetry of radiolucency around the unerupted tooth crown, ratio of long length to short length, degree of cortical bone alternation, effects on adjacent tooth, and cyst size were analyzed. Relative frequencies of these radiographic features were evaluated. In order to compare the CBCT features of DC with those of odontogenic keratocyst (OKC), 9 cases of OKCs were analyzed with the same method radiographically. Results : DCs consisted of thirty unilocular cases (79.0%), seven lobulated cases (18.4%) and one multilocular case (2.6%). Eight were asymmetric (21.0%) and thirty were symmetric (79.0%). Maxillary DC showed rounder shape than mandibular DC (L/S ratio; maxilla 1.32, mandible 1.67). Alternations of lingual cortical bone (14 cases, 48.2%) were more frequent than those of buccal side (7 cases, 24.1%). CBCT images of DC showed definite root resorption and bucco-lingual tooth displacement. These findings were hardly observed on panoramic radiographs of DCs. Comparison of CBCT features of DC with those of OKC showed several different features. Conclusions : CBCT images of DC showed various characteristic radiographic features. Therefore, CBCT can be helpful for the diagnosis of DC radiographically.

• 한국정보전자통신기술학회논문지
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• 제12권1호
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• pp.13-21
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• 2019

내용기반 영상검색은 영상 내의 정보인 색상, 질감, 형태 등의 특징 값을 추출하여 검색에 이용한다. 본 논문에서는 $8{\times}8$ 이산여현변환, 즉 $8{\times}8$ DCT(Discrete Cosine Transform) 후 얻어지는 DC, AC계수를 이용하여 필터뱅크(filter-bank)를 생성하고, 이를 영상의 내용기반 검색에 이용하는 검색방법을 제안한다. 제안된 방법은 생성된 DCT 필터뱅크에서 DC성분과 주요한 AC성분인 AC01, AC10, AC11 만을 이용하며, DC성분에 대한 양자화를 수행하여 계산량을 최소화한다. 그리고 양자화된 DC성분에 대한 히스토그램 정보를 기반으로 영상 검색에 필요한 특징 값을 산출한다. AC성분에 대해서는 Otsu 이진화를 통하여 개괄적인 형태정보를 취득한 다음 이에 대한 수평/수직 방향으로의 투영 히스토그램을 계산하여 특징 값을 취득한다. 추출된 AC성분의 특징 값은 DC성분의 특징 값과 함께, 특징벡터 빈(feature vector bins)을 구성하여 검색을 수행한다. 실험은 1000장의 데이터베이스를 이용하여 수행 되었으며, 기존의 색상정보를 이용한 검색방법보다 우수한 성능을 보임을 확인하였다.

• 반도체디스플레이기술학회지
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• 제21권3호
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• pp.80-86
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• 2022

In this paper, the optimal design and circuit simulation verification results of an LLC resonant half-bridge dc-dc converter using a steady-state model with internal loss resistance are reported. Above all, the input/output voltage gain and frequency characteristic equations in the steady-state were derived by reflecting the internal loss resistance in the equivalent circuit. Based on the results, an LLC resonant half-bridge dc-dc converter with an input voltage of 360-420V, an output voltage of 54V, and a maximum power of 3kW was designed, and to verify the design, the PSIM circuit simulation was executed to compare and analyze the result. In particular, the operating range of the converter could be drawn from the frequency characteristic graph of the voltage gain, and when the converter was operated under light and maximum load conditions, it was confirmed that similar results were obtained by comparing simulation results and calculation results in the switching frequency characteristic graph. In addition, the change of the switching frequency with respect to the load current at each input voltage was compared with the calculated value and the simulation result. As a result, it was possible to confirm the usefulness of the analysis result reflecting the internal loss resistance proposed in this paper and the process of the optimal design.

• Journal of the Korean Association of Oral and Maxillofacial Surgeons
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• 제49권6호
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• pp.339-346
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• 2023

Objectives: This analysis details the characteristics of dental trauma in South Korea during the coronavirus disease 2019 (COVID-19) (DC) pandemic and compares them in patients before and after COVID-19 (BC and AC, respectively). Materials and Methods: Data were collected from medical records of patients who visited Seoul National University Bundang Hospital's Emergency Dental Care Center during three 12-month periods: BC, DC, and AC (BC from March 1, 2019 to February 29, 2020; DC from March 1, 2020 to February 28, 2021; AC from March 1, 2022 to February 28, 2023). A retrospective review was conducted to investigate patient age, sex, time of visit, cause, and diagnosis. The study included 1,544 patients: 660 BC, 374 DC, and 510 AC. Results: Significant difference in age and sex was not observed among the three periods; 1-9 years of age was the largest group (38.3% in BC, 29.6% in DC, and 27.8% in AC), and the percentage of male patients was greater than of female patients (male proportion as 63.5% in BC, 67.4% in DC, and 64.9% in AC). The number of patients generally peaked at a Saturday night in spring (for BC: May, Saturday, 18:00-19:59; for DC: March, Saturday, 18:00-19:59; for AC: April as the second most (October as the most peaked), Saturday, 20:00-21:59). The primary etiology of the dental trauma was identical in the three periods: falls, followed by sports. The most frequent diagnosis was laceration, followed by tooth avulsion and jaw fracture. Conclusion: Significant differences were not found between the characteristics and patterns of dental trauma in the BC, DC, and AC periods. However, due to the pandemic and social distancing, activities decreased and associated dental trauma-related incidents declined.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 1998년도 추계종합학술대회 논문집
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• pp.633-636
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• 1998

In this study, power AlGaAs/InGaAs/GaAs PM-HEMT's for mm wave's were fabricated using Electron beam lithography and air-bridge techniques, and so on. DC and AC characteristics of the fabricated power PM-HEMTs were measured under the various bias conditions. For example, DC and RF characteristics such as S21 gain of 3.6 dB at 35 ㎓, current gain cut-off frequencies of 45 ㎓ and maximum oscillation frequencies of 100 ㎓ were carefully analyzed for design methodology of sub-mm wave power devices.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2008년도 추계학술대회 논문집 전기설비전문위원
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• pp.308-309
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• 2008

태양광발전산업은 21세기의 청정에너지 및 대체에너지로 주목받으면서 그 관련 산업이 매년 큰 성장세에 있다. 그러나 태양광발전시스템의 DC계통 사고 보호에 대한 안정성이 확보되지 않고 보급 설치되므로 이에 대한 대책이 필요한 것이 현실이다. 본 논문은 DC계통사고 등의 문제점을 지적하고 그 대책을 연구하여 계통의 안전성 확보와 인체 감전보호론 목적으로 연구하였다.

• 전력전자학회:학술대회논문집
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• 전력전자학회 2014년도 추계학술대회 논문집
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• pp.21-22
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• 2014

본 논문은 5-레벨 NPC/H-브릿지 (Neutral Point Clamped/H-bridge) 인버터의 최적 제어 세트 (finite-control-set) 모델 예측 제어 (MPC: Model Predictive Control) 방법을 제안한다. NPC/H-브릿지 인버터의 출력 전류 제어 및 DC-link 커패시터 전압 균형을 유지하기 위해 출력 전류와 DC-link 커패시터 전압을 예측하고, 하나의 비용 함수 (cost function)을 통해 최적의 스위칭 상태를 출력한다. PSIM 시뮬레이션을 통해 제안된 제어 알고리즘의 검증하였다.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2005년도 춘계학술대회 논문집
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• pp.114-118
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• 2005

In this study, the DC dielectric breakdown of epoxy composites used for molding material was experimented and then its data were simulated by Weibull distribution equation. From the analysis of Weibull distribution, it was confirmed that as the allowed breakdown probability was given by 0.1[%], the applied field value needed to be under 21.5[kV/mm].

• 전력전자학회:학술대회논문집
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• 전력전자학회 2007년도 하계학술대회 논문집
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• pp.19-21
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• 2007

This paper proposes an input waveform improvement using VIENNA Rectifier(three-phase/level/switch). VIENNA Rectifier is based on the combination of a three-phase diode bridge and dc/dc converter. It features low input current ripple and sinusoidal mains current form.

• 전력전자학회논문지
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• 제21권5호
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• pp.388-395
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• 2016

Electric vehicles (EV) and hybrid EVs (HEV) are designed and manufactured by GM, Toyota, Honda, and Hyundai motors. The propulsion system design process for EV requires integrating subsystem designs into an overall system model to maximize the performance of a given propulsion architecture. Therefore, high-power density and high-torque density are important attributes required for EV applications. To improve torque and power density, propulsion motors are designed for saturation during high-torque operation. The nonlinearity associated with core saturation is modeled by incorporating the cross-coupling inductances, which also behave nonlinearly. Furthermore, in EV environments, the battery is directly connected to the DC link, and the battery changes depending on the state of charge. It will be onerous if as many optimal current commands as different $V_{dc}$ were made. This paper presents the optimal current commands in the various operating condition and the current control technique in EV environments.