• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.4 no.4
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• pp.360-369
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• 1992

A heat pump system is constructed to evaluate its performance and heat transfer characteristics with mixtures of R22/R142b as working fluids. The heat transfer in the evaporator and the overall performance are measured and analyzed in terms of the compositions and relevant variables. Possibility of capacity modulation by changing composition is observed without degradation of heat transfer coefficients and coefficient of performance. The cooling capacity is varied continuously within 200 percent based on minimum capacity at constant compressor speed. For similar cooling capacity, COP is improved by mixing two refrigerants and shows maximum value at 60％ mass fraction of R22. Average heat transfer coefficients of mixtures decrease in comparison with pure refrigerants at similar cooling capacity and mass flow rate. However, the overall heat transfer coefficients decrease moderately. A cycle simulation is performed in order to manifest the advantages of using refrigerant mixtures, considering experimentally observed heat transfer characteristics.

• Journal of the Korean Institute of Telematics and Electronics S
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• v.36S no.4
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• pp.45-54
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• 1999

본 논문에서는 웨이브렛 변환 대역에서 영역분할 기법을 적용하여 얻어진 각 영역을 중요 영역과 비 중요 영역으로 분류하고 각각의 영역을 그의 특성에 적합한 방식으로 부호화 하는 기법을 제안하였다. 중요 영역은 전체 영역가운데 매우 작은 부분을 차지하지만 영상 복원에 매우 큰 영향을 주기 때문에 이러한 영역 부호화를 위해 기존의 EZW 방식보다 성능이 우수하며 단일계수 전송에 성능이 뛰어난 SPIHT 알고리즘을 적용하였다. 그러나 비 중요영역은 영상복원에 미치는 영향이 적을 뿐만 아니라, 매우 큰 동질 영역을 형성하기 때문에 텍스춰 모델링을 이용할 경우 높은 압축률을 얻을 수 있다. 또한 이 방식을 이용할 경우 인위적인 에러가 거의 없기 때문에 이용할 경우 높은 압축률을 얻을 수 있다. 또한 이 방식을 이용할 경우 인위적인 에러가 거의 없기 때문에 시각적으로도 좋은 영상을 복원 할 수 있다. 실험결과 제안한 시스템은 다양한 영상에 대하여 적응성이 있음을 보였고 특히 0.2bpp 이하의 매우 낮은 비트 율에서도 EZW 와 같은 기존의 웨이브렛 기반 부호화기보다 좋은 성능을 나타내었다.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.11 no.5
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• pp.624-632
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• 1999

In order to replace CFC-502 which has been widely used in transportation and low temperature refrigeration system, performance tests using HFC-407A, HFC-404A and HFC-507 have been carried out. Measurements were conducted at two different condensing temperatures of $43.3^{\circ}C$and $54.5^{\circ}C$ for each refrigerant. System performance characteristics and heat transfer characteristics of each refrigerant were obtained at several compressor speeds and evaporating temperatures ranging from$-25^{\circ}C$ to $-10^{\circ}C$ Test results show that the use of tested alternative refrigerants without changing system components offers the potential performance improvement of a refrigeration system.

• Proceedings of the Korean Institute of Intelligent Systems Conference
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• 1997.10a
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• pp.291-295
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• 1997

현재에 주로 개발되어 상용화가 시작되고 있는 음성인식 시스템의 대부분은 단어인식을 기분으로 하는 시스템으로 적용 단어수를 늘려줌으로서 인식범위를 늘일 수 있으나, 그에 따라 검색해야하는 단어수가 늘어남으로서 전체적인 시스템의 속도 및 성능이 저하되는 경향이 있다. 이러한 단점의 극복을 위하여 본 논문에서는 HMM(Hidden Markov Model)과 GA(Genetic Algorithm)를 이용한 한국어 음성의 음소단위 인식 시스템을 구현하였다. 음성 특징으로는 LPC Cepstrum 계수를 사용하였으며, 인식시는 인식대상이 되는 단어에 대하여 GA(Genetic Algorithm)을 통하여 각 음소를 분리하고, 음소단위로 학습된 HMM 파라미터를 적용하여 인식함으로써 각각의 음소별 가능하도록 하는 방법을 제안하였다.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.10 no.1
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• pp.32-38
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• 2009

In this paper, cycle performance analysis for cooling capacity, compression work and COP of R744($CO_2$) transcritical vapor compression refrigeration system is presented to offer the basic design data for the operating parameters of the system. The operating parameters considered in this study include superheating degree, outlet temperature of gas cooler and evaporating temperature in the R744 vapor compression cycle. The main results were summarized as follows : The cooling capacity of R744 increases with superheating degree, but decreases with the increasing evaporating temperature and outlet temperature of gas cooler. The compression work increases with superheating degree and cooling pressure of R744, but decreases with the increasing evaporating temperature. And, The COP increases with outlet temperature and evaporating temperature of R744 gas cooler, but decreases with the increasing superheating degree. Therefore, superheating degree, outlet temperature and evaporating temperature of R744 vapor compression refrigeration system have an effect on the cooling capacity, compression work and COP of this system. With a thorough grasp of these effect, it is necessary to design the compression refrigeration cycle using R744.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.37A no.12
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• pp.1023-1030
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• 2012

The diversity techniques can benefit underwater acoustic communications when the distance between sensors is sufficiently apart, and this leads to the increases in the physical size of the communication system: thus it is very hard to practically use such systems in real-environments. Therefore, in this paper, we have collected data from real underwater cannel environments in order to analyze the usability of diversity combined with beamforming techniques. And we have estimated the fading characteristics from the measurement data, and analyzed the correlation coefficients using the estimated fading characteristics. After analyzing the estimated fading characteristics from the measurements data, we found out that by applying diversity techniques on the output signals from beamformers that perform beamforming from different multipath directions, we can reduce the distance between sensors and at the same time benefit from the diversity gain.

• Journal of the Korea Concrete Institute
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• v.13 no.6
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• pp.544-552
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• 2001

Korea is classified into low and moderate seismic zone from the view-point of seismic hazard level. Korean seismic provisions has been developed based on UBC and ATC 3-06. Thus, in calculation of design base shear according to Korean provisions response modification factor (R) is included in the formula of design base shear. The major role of this factor is to reduce the elastic design base shear whereby structures can behave in inelastic range during design level earthquake ground motions(mean return period of 475 yrs.). R factor is assigned according to material and structural systems. In this study, R factor for bearing wall system is considered. Most of the walls of apartment buildings in Korea resist gravity and seismic loads simultaneously so that this wall system can be classified into bearing wall system. Structural details of these walls are different from those used in Japan and U.S.. They are all rectangular in sectional shape rather than barbell in shape, and also have special lateral reinforcement details at the boundaries of a wall. In Korean seismic design provisions(1988), two different values(3.0 and 3.5) of R factor are assigned to the bearing wall systems according to the wall details. However, in updated seismic provisions(2000), only one value is assigned to R factor(3.0) irrespective of wall details. In this study, the design base shear values in Korean seismic design provisions(1988, 2000), ATC 3-06, UBC are compared. Also experimental study was carried out to evaluate the seismic performance of structural walls. For this purpose, five test specimens were made which have special details used in apartment bearing wall systems in Korea. Based on the results of this study, response modification factor for bearing wall system is discussed.

• Proceedings of the IEEK Conference
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• 2001.09a
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• pp.69-72
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• 2001

본 논문에서는 디지털 통신 시스템의 블라인드 등화에 있어서, 다중레벨 modulus를 기준 신호로 사용하여 등화기의 탭 계수 갱신 식에 사용되는 오차 신호를 형성함으로써 등화기의 블라인드 수렴 특성을 개선한 다중레벨 modulus 알고리즘들의 성능을 분석하였다. 다중경로 채널 하에서 QAM 신호점에 대해 컴퓨터 모의실험을 통하여 단일/다중레벨 modulus 알고리즘(SMMA)과 기존의 modified constant modulus algorithm(MCMA) 및 최근에 제안된 다중레벨 modulus 알고리즘(MMA) 등의 블라인드 수렴 및 정상 상태 성능을 비교하였다.

• Journal of Advanced Marine Engineering and Technology
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• v.24 no.2
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• pp.24-30
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• 2000

The high-pressure natural refrigerant $CO_2$ is now being evaluated for use in the motor vehicle air-conditioning systems and for several types of unitary equipment. In this study thermodynamic properties of $CO_2$ is compared to those of R-22 and R-134a and the performance characteristics of $CO_2$ refrigeration cycle is analyzed. The results show that the optimum discharge pressure for the cycle performance exists. New design concept for the $CO_2$ refrigeration system should be developed due to the high-operating pressure of itself.

• 한국신재생에너지학회:학술대회논문집
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• 2006.11a
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• pp.9-14
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• 2006

Open loop or ground water heat pump systems are the oldest of ground-source systems. Standing column wells can be used as highly efficient ground heat exchanger in geo-thermal heat pump systems, where hydrological and geological conditions are suitable. These systems require some careful considerations for well design, ground water flow, heat exchanger selection etc This paper describes 9round water temperature variations, performances in heat ins and cool ing mode and the results of ground water analysis.