• 한국정보통신학회:학술대회논문집
• /
• 한국정보통신학회 2014년도 추계학술대회
• /
• pp.581-584
• /
• 2014

본 논문에서는 에너지 분배 기능을 이용하여 MPPT(Maximum Power Point Tracking) 제어 기능을 구현한 마이크로 빛에너지 하베스팅 시스템을 제안한다. 소형 PV(Photovoltaic) 셀에서 출력되는 에너지와 전압 레벨은 작기 때문에 직접 MPPT 제어회로를 구동하기 어렵다. 따라서 제안된 회로에서는 시동회로를 사용하여 Vcp를 MPPT 제어회로를 구동하기 위해 필요한 전압까지 승압시킨다. Vcp가 원하는 전압 값에 도달하면 전압감지기가 이를 감지하여 PV 셀로부터 시동회로에 공급되는 에너지는 차단하고, 전력변환기에 에너지를 공급한다. Vcp가 감소하여 MPPT 제어회로가 동작하기 어렵게 되면 전력변환기로의 에너지 전달을 차단하고 시동회로를 다시 구동한다. 이렇게 에너지 분배 기능을 이용하여 시동회로와 전력변환기를 번갈아 동작시키면서 에너지를 수확하여 PMU(Power Management Unit)를 통해 부하에 전달한다. 제안된 회로는 0.35um CMOS 공정으로 설계 되었으며 모의실험을 통해 동작을 검증하였다. 설계된 회로의 칩 면적은 패드를 포함하여 $1430um{\times}1110um$이다.

• 한국전자통신학회논문지
• /
• 제14권2호
• /
• pp.309-316
• /
• 2019

본 논문은 로컬 클록 왜곡을 보상하는 낮은 지터 성능의 지연 고정 루프를 제시한다. 제안된 DLL은 위상 스플리터, 위상 검출기(PD), 차지 펌프, 바이어스 생성기, 전압 제어 지연 라인(Voltage Controlled Delay Line) 및 레벨 변환기로 구성된다. VCDL(: Voltage Controlled Delay Line)은 CML(: Current Mode Logic)을 사용하는 자체 바이어스 지연 셀을 사용하여 온도에 민감하지 않고 잡음을 공급한다. 위상 스플리터는 VCDL의 차동 입력으로 사용되는 두 개의 기준 클록을 생성한다. 제안된 회로의 PD는 CML에 비해 적은 전력을 소비하는 CMOS 로직을 사용하기 때문에 PD는 위상 스플리터의 유일한 단일 클록을 사용한다. 따라서 VCDL의 출력은 로컬 클록 분배 회로뿐만 아니라 PD에 사용되므로 레벨 변환기에 의해 레일-투-레일 신호로 변환된다. 제안된 회로는 $0.13{\mu}m\;CMOS$ 공정으로 설계되었으며, 주파수가 1GHz인 클록이 외부에서 인가된다. 약 19 사이클 후에 제안된 DLL은 잠금이 되며, 클록의 지터는 1.05ps이다.

• 한국물환경학회지
• /
• 제36권6호
• /
• pp.546-558
• /
• 2020

While industrialization has provided in abundance, the pollution it creates has caused untold damage to the environment, increasing the frequency and severity of natural disasters through changes in global climate patterns. The World Risk Forum's (WEF) World Risk Report presented the results of a survey of experts from around the world detailing the most influential risk factors over the next decade. Notably, the failure to respond to climate change ranked first and the global water crisis third. The extreme drought in the western Chungnam province was unexpected in 2016. At the time, the water level of Boryeong Dam was drastically decreased due to receiving less than half the average recorded rainfall in the region that year. The Boryeong Dam diversion pipeline has the capacity to solve the water shortage problem between these two regions by providing water from Geumgang to the western part of Chungnam, including Boryeong City. Current weather trends suggest drought is likely to continue in western Chungnam, which uses the Boryeong Dam as an intake source. This makes it necessary to operate Boryeong Dam diversion pipeline in an efficient and effective manner. SWAT is a watershed scale model developed to predict the impact of land management practices on water. The SWAT model was used in this study to evaluate the adequacy of the Boryeong Dam diversion pipeline operational plan by comparing it to present Boryeong Dam diversion pipeline operation. By investigating the number of days required to reach each reservoir stage, we determined that the number of days required to reach the boundary stage was less than that of the current operation. This determination accounts for the caveats that the Boryeong Dam waterway was not operated and only one pump will be operated from October to May of next year. As our results suggest, the most stable operation scenario is to operate two pumps at all times. This can be accomplished by operating two pumps from the caution stage to increase the number of pumps whenever the stage is raised. In addition to the stable operation of the Boryeong Dam pipeline, policy considerations are required with regard to imposing a water use charge on users of the Boryeong Dam region.

• Journal of Chest Surgery
• /
• 제35권5호
• /
• pp.365-368
• /
• 2002

배경: 관상동맥우회술은 많은 비용이 소요되며 시술의 방법이나 질적 수준에 따라 환자의 생존율이나 진료비와 같은 진료결과에 큰 영향을 미칠 수 있다. 저자들은 체외순환 없는 관상동맥우회술과 전통적인 관상동맥우회술의 병원내 자원소모량을 비교함으로써 체외순환 없는 관상동맥우회 술의 경제적 측면에서의 유용성을 평가하고자 하였다. 재료 및 방법: 1998년 1월부터 1999년 7월까지 관상동맥우회술을 받은 184명을 대상으로 하였다. 이들 중 체외순환 없는 관상동맥우회술을 받은 환자(1군)은 111명이었고, 전통적인 관상동맥우회술을 받은 환자(2군)은 73명이었다. 환자의 진료결과 및 진료비에 영향을 미칠 수 있는 환자의 수술 전 위험요인과 병원 내 자원소모량을 조사하였다. 결과: 수술전 위험요인들의 분포와 술후 합병증의 발생율 및 술후 재원일수 등은 두 군간에 차이가 없었다. 하지만 두 군간의 중환자실 재원시간 (51.3$\pm$49.8 hr vs 128.3$\pm$150.2 hr; p<0.01)과 인공호흡기 사용시간 (14.9$\pm$22.7 hr vs 56.2$\pm$ 124.9 hr ; p<0.01)에는 유의한 차이가 있었다. 환자 본인 부담금과 의료보험공단 부담금을 합한 총 진료비는 1군이 1,722만 원, 2군이 7,125만 원으로 두 군간에 유의한 차이가 있었다(p<0.01). 항목별 진료비 중에서는 수술료, 재료대, 수혈료, 방사선검사료가 두 군간에 유의한 차이가 있었다. 1군에서 방사선검사료를 제외한 모든 항목별 진료비가 2군에 비하여 낮았다. 결론: 체외순환없는 관상동맥우회 술은 전통적인 수술법에 비해 저렴한 비용으로 우수한 효과를 얻을 수 있는 좋은 방법이다.

• 설비공학논문집
• /
• 제21권12호
• /
• pp.715-732
• /
• 2009

This article reviews the papers published in the Korean Journal of Air-Conditioning and Refrigeration Engineering during 2008. It is intended to understand the status of current research in the areas of heating, cooling, ventilation, sanitation, and indoor environments of buildings and plant facilities. Conclusions are as follows. (1) Research trends in thermal and fluid engineering have been surveyed in the categories of general fluid flow, fluid machinery and piping, new and renewable energy, and fire. Well-developed CFD technologies were widely applied in developing facilities and their systems. New research topics include fire, fuel cell, and solar energy. Research was mainly focused on flow distribution and optimization in the fields of fluid machinery and piping. Topics related to the development of fans and compressors had been popular, but were no longer investigated widely. Research papers on micro heat exchangers using nanofluids and micro pumps were also not presented during this period. There were some studies on thermal reliability and performance in the fields of new and renewable energy. Numerical simulations of smoke ventilation and the spread of fire were the main topics in the field of fire. (2) Research works on heat transfer presented in 2008 have been reviewed in the categories of heat transfer characteristics, industrial heat exchangers, and ground heat exchangers. Research on heat transfer characteristics included thermal transport in cryogenic vessels, dish solar collectors, radiative thermal reflectors, variable conductance heat pipes, and flow condensation and evaporation of refrigerants. In the area of industrial heat exchangers, examined are research on micro-channel plate heat exchangers, liquid cooled cold plates, fin-tube heat exchangers, and frost behavior of heat exchanger fins. Measurements on ground thermal conductivity and on the thermal diffusion characteristics of ground heat exchangers were reported. (3) In the field of refrigeration, many studies were presented on simultaneous heating and cooling heat pump systems. Switching between various operation modes and optimizing the refrigerant charge were considered in this research. Studies of heat pump systems using unutilized energy sources such as sewage water and river water were reported. Evaporative cooling was studied both theoretically and experimentally as a potential alternative to the conventional methods. (4) Research papers on building facilities have been reviewed and divided into studies on heat and cold sources, air conditioning and air cleaning, ventilation, automatic control of heat sources with piping systems, and sound reduction in hydraulic turbine dynamo rooms. In particular, considered were efficient and effective uses of energy resulting in reduced environmental pollution and operating costs. (5) In the field of building environments, many studies focused on health and comfort. Ventilation. system performance was considered to be important in improving indoor air conditions. Due to high oil prices, various tests were planned to examine building energy consumption and to cut life cycle costs.

• 설비공학논문집
• /
• 제20권6호
• /
• pp.427-446
• /
• 2008

A review on the papers published in the Korean Journal of Air-Conditioning and Refrigeration Engineering in 2006 has been accomplished. Focus has been put on current status of research in the aspect of heating, cooling, ventilation, sanitation and building environments. The conclusions are as follows. (1) The research trends of fluid engineering have been surveyed as groups of general fluid flow, fluid machinery and piping, etc. New research topics include micro heat exchanger and siphon cooling device using nano-fluid. Traditional CFD and flow visualization methods were still popular and widely used in research and development. Studies about diffusers and compressors were performed in fluid machinery. Characteristics of flow and heat transfer and piping optimization were studied in piping systems. (2) The papers on heat transfer have been categorized into heat transfer characteristics, heat exchangers, heat pipes, and two-phase heat transfer. The topics on heat transfer characteristics in general include thermal transport in a cryo-chamber, a LCD panel, a dryer, and heat generating electronics. Heat exchangers investigated include pin-tube type, plate type, ventilation air-to-air type, and heat transfer enhancing tubes. The research on a reversible loop heat pipe, the influence of NCG charging mass on heat transport capacity, and the chilling start-up characteristics in a heat pipe were reported. In two-phase heat transfer area, the studies on frost growth, ice slurry formation and liquid spray cooling were presented. The studies on the boiling of R-290 and the application of carbon nanotubes to enhance boiling were noticeable in this research area. (3) Many studies on refrigeration and air conditioning systems were presented on the practical issues of the performance and reliability enhancement. The air conditioning system with multi indoor units caught attention in several research works. The issues on the refrigerant charge and the control algorithm were treated. The systems with alternative refrigerants were also studied. Carbon dioxide, hydrocarbons and their mixtures were considered and the heat transfer correlations were proposed. (4) Due to high oil prices, energy consumption have been attentioned in mechanical building systems. Research works have been reviewed in this field by grouping into the research on heat and cold sources, air conditioning and cleaning research, ventilation and fire research including tunnel ventilation, and piping system research. The papers involve the promotion of efficient or effective use of energy, which helps to save energy and results in reduced environmental pollution and operating cost. (5) Studies on indoor air quality took a great portion in the field of building environments. Various other subjects such as indoor thermal comfort were also investigated through computer simulation, case study, and field experiment. Studies on energy include not only optimization study and economic analysis of building equipments but also usability of renewable energy in geothermal and solar systems.