• 한국전자파학회논문지
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• 제24권1호
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• pp.82-90
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• 2013

본 논문에서는 고주파 회로 모델링을 이용하여 전기자동차의 모터 구동 시스템으로부터 방출되는 전도성 전자파 노이즈를 시스템-레벨에서 분석하였다. 관련 전도 방출의 주요 원인은 모터 구동 시스템에서 사용하는 펄스폭 변조방식의 스위칭 동작에 기인하며, 이러한 전도 방출은 공통-임피던스 결합 및 유도성 결합을 통해 AM/FM 주파수 대역에서의 무선주파수 간섭을 유발한다. 이러한 문제를 분석하기 위해 모터 구동 시스템을 구성하고 있는 IGBT와 고압 커패시터, 인버터, 모터 및 고전압 케이블과 버스 바에 대한 기본 회로는 물론, 각 부분에서 존재하는 기생 성분 및 비선형 특성을 해석하여 모터 구동 시스템 전체를 포함한 시스템-레벨의 고주파 등가회로 모델을 제안하였다. 이러한 모델을 이용한 모터 구동시스템의 전도 방출 특성을 시뮬레이션하고, 측정하였으며, 비교적 큰 해석구조임에도 불구하고 두 결과가 비교적 잘 일치함을 확인하였다. 향후 이러한 접근방법이 전기자동차의 전자파 적합성 설계에 효과적으로 사용될 수 있을 것으로 기대한다.

• 한국전자파학회논문지
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• 제27권11호
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• pp.1019-1022
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• 2016

본 논문에서는 드레인 분기 커패시터를 사용하여 입 출력 간 동위상을 제공함과 동시에 각 트랜지스터에 최적 부하 임피던스를 제공하는 비균일 분산 전력증폭기 설계 기법을 2~16 GHz GaN 광대역 전력증폭기 MMIC 설계에 적용하고, 칩을 제작하여 결과를 평가하였다. Win Semiconductors사의 $0.25{\mu}m$ GaN HEMT 공정으로 제작된 MMIC 칩은 크기가 $3.9mm{\times}3.1mm$이며, 주파수 대역 내에서 12 dB 이상의 선형 이득 및 10 dB 이상의 입력 반사 손실을 보였다. 연속파모드 포화출력 조건에서 측정된 출력 전력은 36.2~38.5 dBm의 값을 보였고, 전력부가효율은 약 8~16 %를 나타내었다.

• 대한치과보철학회지
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• 제43권2호
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• pp.218-231
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• 2005

Statement of problem. In the partially edentulous patients, removable partial dentures have been working as a important treatment modality. Clasps, a kind of direct retainers, received some amount of stresses during the insertion and removal of partial denture on the abutment tooth. Purpose. The study is to investigate stresses of the different clasps. Material and methods. In order to investigate the degree of stresses, maxillary partial edentulism (Kennedy Class II modification I) was assumed and removable partial dentures were designed on it with three kinds of metallic materials; cobalt-chromium alloy, type IV gold alloy and commercially pure (c.p.) titanium. Aker's clasp was applied on the left second molar. RPA (mesial rest-proximal plate-Aker's) clasp was on the left first premolar and wrought wire clasp was on the right first premolar. Three dimensional, non-linear, dynamic finite element analysis method was run to solve this process. Results. 1. Cobalt-chromium alloy had the highest von Mises stress value and c.p. titanium had the lowest one irrespective of the types of clasps. 2. In the Aker's clasps, stress on the retentive tips was shown shortly after the appearance of stresses of the middle and minor connector areas. These time lag was much shorter in the RPA clasps than in the Aker's clasp. 3. In general. retentive tips of wrought wire clasps had much less amount of stress than other clasps. Conclusion. The amount of stress was the highest in the RPA clasp and the lowest in the wrought wire clasp, in general.

• 한국정보통신학회:학술대회논문집
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• 한국정보통신학회 2015년도 추계학술대회
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• pp.397-400
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• 2015

본 논문에서는 낮은 듀티 동작의 센서 노드를 위한 저비용 MPPT 제어기능을 갖는 빛에너지 하베스팅 회로를 제안한다. 환경, 구조물 모니터링 센서와 같은 연속적인 동작이 요구되지 않는 센서 노드가 어플리케이션이며, 기존의 MPPT(Maximum Power Point Tracking) 제어방법과 다르게 간단한 회로들을 이용하여 저비용 MPPT 제어 방법을 구현하였다. 제안된 MPPT 방법은 솔라셀의 개방회로전압과 MPP 전압간의 비례관계를 이용하여, 솔라셀의 개방회로 전압을 주기적으로 샘플링함으로써 최대 가용전력이 생성되는 지점을 추적하고 이를 부하로 전달한다. 제안된 회로는 $0.35{\mu}m\;CMOS$ 공정으로 설계되었으며, 칩 면적은 패드를 포함하여 $975{\mu}m{\times}1025{\mu}m$이다. 제작된 칩을 측정한 결과 주기적으로 솔라셀의 개방회로를 샘플링하여 솔라셀의 MPP를 실시간 추적하는 것을 확인하였다.

• 산업공학
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• 제25권2호
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• pp.241-254
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• 2012

This paper studies the relationship between SCM(Supply Chain Management) metrics and corporate value (Tobin's Q) for manufacturing and wholesale/retail firms in Korea. Specifically, the multiple regression analysis is used to investigate the relationships 1) between inventory level, inventory turns, and days of inventory and Tobin's Q and 2) between cash-to-cash (C2C) cycle time including its components such as days of inventory, days sales outstanding, and days payable outstanding and Tobin's Q. The results indicate that there exist statistically significant negative relationships between inventory levels and days of inventory (DOI) and Tobin's Q. Also, we found that there exist commonly known negative correlations between days of raw materials inventory and days of work in process (WIP) inventory and Tobin's Q. For the C2C cycle time, we found that there -exists a statistically significant negative relationship between the C2C cycle time and Tobin's Q. Also, we found that there exist commonly known correlations between the two components of C2C cycle time and Tobin's Q such as the negative for DOI and days sales outstanding. This study clearly shows the negative relationship in general between inventory levels and corporate value and between C2C time and corporate value, and this kind of result has not been found by previous studies in Korea.

• Journal of Power Electronics
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• 제16권3호
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• pp.1209-1217
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• 2016

This paper presents a novel charge pump scheme that combines the advantages of Fibonacci and Dickson charge pumps to obtain 30 V voltage for display driver integrated circuit application. This design only requires four external capacitors, which is suitable for a small-package application, such as smart card displays. High-amplitude (<6.6 V) clocks are produced to enhance the gate drive of a Dickson charge pump and improve the system's current drivability by using a voltage-doubler charge pump with a pulse skip regulator. This regulation engages many middle-voltage devices, and approximately 30% of chip size is saved. Further optimization of flying capacitors tends to decrease the total chip size by 2.1%. A precise and simple model for a one-stage Fibonacci charge pump with current load is also proposed for further efficiency optimization. In a practical design, its voltage error is within 0.12% for 1 mA of current load, and it maintains a 2.83% error even for 10 mA of current load. This charge pump is fabricated through a 0.11 μm 1.5 V/6 V/32 V process, and two regulators, namely, a pulse skip one and a linear one, are operated to maintain the output of the charge pump at 30 V. The performances of the two regulators in terms of ripple, efficiency, line regulation, and load regulation are investigated.

• ETRI Journal
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• 제28권3호
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• pp.329-336
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• 2006

This paper investigates the problem of protecting multicast sessions in mesh wavelength-division multiplexing (WDM) networks against single link failures, for example, a fiber cut in optical networks. First, we study the two characteristics of multicast sessions in mesh WDM networks with sparse light splitter configuration. Traditionally, a multicast tree does not contain any circles, and the first characteristic is that a multicast tree has better performance if it contains some circles. Note that a multicast tree has several branches. If a path is added between the leave nodes on different branches, the segment between them on the multicast tree is protected. Based the two characteristics, the survivable multicast sessions routing problem is formulated into an Integer Linear Programming (ILP). Then, a heuristic algorithm, named the adaptive shared segment protection (ASSP) algorithm, is proposed for multicast sessions. The ASSP algorithm need not previously identify the segments for a multicast tree. The segments are determined during the algorithm process. Comparisons are made between the ASSP and two other reported schemes, link disjoint trees (LDT) and shared disjoint paths (SDP), in terms of blocking probability and resource cost on CERNET and USNET topologies. Simulations show that the ASSP algorithm has better performance than other existing schemes.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2010년도 제35회 추계학술대회논문집
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• pp.590-593
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• 2010

추진제를 추진제 탱크에 충전하는 과정은 발사 준비 과정에서 중요한 역할을 하며, 추진제 충전량의 정확도는 발사체 전체 무게와 관련되어 있다. 발사체에 사용되는 추진제 중에는 액체산소와 같은 극저온 추진제도 사용되며, 극저온 추진제는 탱크 내의 환경에 따라 쉽게 액상에서 기상으로 변화된다. 따라서 추진제 탱크 내의 추진제 표면 주위에서 추진제 수위를 판별할 수 있는 액상과 기상의 경계면을 명확하게 파악 할 수 있는 수위 측정시스템이 필요하다. 본 연구에서는 정전용량형 3전극 원리를 이용한 측정시스템의 제작과정과 예비시험을 통하여 액체의 높이가 변화할 때 전기신호가 변화되는 것을 확인하였다. 시험 결과로부터 물의 높이 변화에 비례하게 전압이 선형적으로 증감하는 경향을 파악하였다.

• Structural Engineering and Mechanics
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• 제56권6호
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• pp.959-982
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• 2015

In this study, a non-stationary random earthquake Clough-Penzien model is used to describe earthquake ground motion. Using stochastic direct integration in combination with an equivalent linear method, a solution is established to describe the non-stationary response of lead-rubber bearing (LRB) system to a stochastic earthquake. Two parameters are used to develop an optimization method for bearing design: the post-yielding stiffness and the normalized yield strength of the isolation bearing. Using the minimization of the maximum energy response level of the upper structure subjected to an earthquake as an objective function, and with the constraints that the bearing failure probability is no more than 5% and the second shape factor of the bearing is less than 5, a calculation method for the two optimal design parameters is presented. In this optimization process, the radial basis function (RBF) response surface was applied, instead of the implicit objective function and constraints, and a sequential quadratic programming (SQP) algorithm was used to solve the optimization problems. By considering the uncertainties of the structural parameters and seismic ground motion input parameters for the optimization of the bearing design, convex set models (such as the interval model and ellipsoidal model) are used to describe the uncertainty parameters. Subsequently, the optimal bearing design parameters were expanded at their median values into first-order Taylor series expansions, and then, the Lagrange multipliers method was used to determine the upper and lower boundaries of the parameters. Moreover, using a calculation example, the impacts of site soil parameters, such as input peak ground acceleration, bearing diameter and rubber shore hardness on the optimization parameters, are investigated.

• Wind and Structures
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• 제13권6호
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• pp.529-556
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• 2010

This paper investigates the correlation of wind characteristics monitored on a cable-stayed bridge. Total five anemoscopes are implemented into the bridge. Two out of 5 anemoscopes in inflow and two out of 5 anemoscopes in wake-flow along the longitudinal direction of the bridge are installed. Four anemoscopes are respectively distributed at two cross-sections. Another anemoscope is installed at the top of the tower. The correlation of mean wind speed and direction, power spectral density, the turbulent intensity and integral length of wind in flow at two cross-sections are investigated. In addition, considering the non-stationary characteristics of wind, the spatial correlation in time-frequency is analyzed using wavelet transform and different phenomenon from those obtained through FFT is observed. The time-frequency analysis further indicates that intermittence, coherence structures and self-similar structures are distinctly observed from fluctuant wind. The flow characteristics around the bridge deck at two positions are also investigated using the field measurement. The results indicate that the mean wind speed decrease when the flow passing through the deck, but the turbulence intensity become much larger and the turbulence integral lengths become much smaller compared with those of inflow. The relationship of RMS (root mean square) of wake-flow and the mean wind speed of inflow is approximately linear. The special structures of wake-flow in time-frequency domain are also analyzed using wavelet transform, which aids to reveal the forming process of wake-flow.