• Journal of Biosystems Engineering
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• 제15권1호
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• pp.14-22
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• 1990

For efficient use of solar energy in plastic greenhouse, thermal storage system was developed. The system was constructed with the counter-flow type air-water heat exchanger using a thin polyethylene film as a medium of heat exchange parts. Experiments were carried out to investigate the heat exchange rate, optimum water flow rate, overall heat transfer coefficient, and the effectiveness of the counter-flow type air-water heat exchanger with polyethylene film bags. Mathematical model to predict air temperature leaving heat exchanger was developed. The results obtained in the present study are summarized as follows. 1. Heat exchange rate in the counter-flow type air-water heat exchanger with polyethylene film bags was compared to that of polyethylene film. Heat exchange rate was almost identical at air velocity of 0.5m/s on polyethylene film surface. But, heat exchange rate of heat exchanger with polyethylene film bag was $32{\sim}55KJ/m^2$ hr higher than that of polyethylene film at air velocity of 1.0m/s. 2. Considering the formation of uniform water film and the sufficient heat exchange rate of polyethylene film bags, optimum water flow rate in polyethylene film bags was $3.0{\sim}6.0{\ell}/m^2$ min. 3. The overall heat transfer coefficient of polyethylene film bags was found to be $35.0{\sim}130.0KJ/m^2\;hr\;^{\circ}C$ corresponding to the air velocity ranging 0.5 to 4.0 m/s on polyethylene film surface. And the overall heat transfer coefficient showed almost linearly increasing tendency to the variation of air velocity. 4. Mathematical model to predict air temperature leaving the heat exchanger was developed, resulting in a good agreement between the experimental and predicted values. But, the experimental results were a little lower than predicted. 5. Effectiveness of heat exchanger for the experiment was found to be 0.40~0.81 corresponding to the number of transfer units due to the variation of air velocity ranging 0.6 to 1.7 m/s.

• 한국통신학회논문지
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• 제21권12호
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• pp.3132-3143
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• 1996

In the evaluation of Broadband-ISDN, the main issue is to interconnect existing LANs and MANs to B-ISDN based on Asynchrous Transfer Mode. However, LANs provide connectionless services, whereas the ATM network provides connection-oriented services. So some problem arises from accessing ATM switchs to transparently transmit connectionless data via B-ISDN. Two methods then were recommended by ITU-TS to support the connectionaless services. In the paper, we do the numerical analysis, using the stochastic fluid flow method, of dynamic bandwidth allocation sheme with two class traffics in the virtual path established between Interworking Units(JWUS) interconnecting LANs to an ATM network and Connectionless Servers(CLSs). The loss mechanism of each traffic is controlled by the contents of buffer. The vandwidth which the IWU requests the CLS is estimated by the number of On-Off sources in the On state. We use the stochsastic fluide flow method which is to find the steady-state joint probability in each level of the IWU buffer. The length of the IWU buffer as the real random variable is changed by traffics entering the IWU.

• 생물환경조절학회지
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• 제2권1호
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• pp.1-8
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• 1993

Experimental and theoretical analyses were carried out to investigate the heat exchange characteristics of the nutrient solution cooling system utilizing ground water. The material of heat exchanger used in the experiment was polyethylene and the cross-flow type was adapted in which nutrient solution was mixed and ground water unmixed. For the exchanger surface area of 0.33$m^2$ and flow rates of ground water of 1-6$\ell$/min, NTU(number of transfer units) and effectiveness of experimental heat exchanger were 0.1-0.45 and 10-35％, respectively. Therefore these results showed that the hydroponic greenhouse of 1,000$m^2$(300 pyong) with the ground water of 10$m^2$/day could cover about 55-70％ of maximum cooling load in summer.

• 한국수자원학회:학술대회논문집
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• 한국수자원학회 2015년도 학술발표회
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• pp.217-217
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• 2015

The objective of this study was mainly to evaluate the water resources potential of Lake Tana Basin (LTB) by using Soil and Water Assessment Tool (SWAT). From SWAT simulation of LTB, about 5236 km2 area of LTB is gauged watershed and the remaining 9878 km2 area is ungauged watershed. For calibration of model parameters, four gauged stations were considered namely: Gilgel Abay, Gummera, Rib, and Megech. The SWAT-CUP built-in techniques, particle swarm optimization (PSO) and generalized likelihood uncertainty estimation (GLUE) method was used for calibration of model parameters and PSO method were selected for the study based on its performance results in four gauging stations. However the level of sensitivity of flow parameters differ from catchment to catchment, the curve number (CN2) has been found the most sensitive parameters in all gauged catchments. To facilitate the transfer of data from gauged catchments to ungauged catchments, clustering of hydrologic response units (HRUs) were done based on physical similarity measured between gauged and ungauged catchment attributes. From SWAT land use/ soil use/slope reclassification of LTB, a total of 142 HRUs were identified and these HRUs are clustered in to 39 similar hydrologic groups. In order to transfer the optimized model parameters from gauged to ungauged catchments based on these clustered hydrologic groups, this study evaluates three parameter transfer schemes: parameters transfer based on homogeneous regions (PT-I), parameter transfer based on global averaging (PT-II), and parameter transfer by considering Gilgel Abay catchment as a representative catchment (PT-III) since its model performance values are better than the other three gauged catchments. The performance of these parameter transfer approach was evaluated based on values of Nash-Sutcliffe efficiency (NSE) and coefficient of determination (R2). The computed NSE values was found to be 0.71, 0.58, and 0.31 for PT-I, PT-II and PT-III respectively and the computed R2 values was found to be 0.93, 0.82, and 0.95 for PT-I, PT-II, and PT-III respectively. Based on the performance evaluation criteria, PT-I were selected for modelling ungauged catchments by transferring optimized model parameters from gauged catchment. From the model result, yearly average stream flow for all homogeneous regions was found 29.54 m3/s, 112.92 m3/s, and 130.10 m3/s for time period (1989 - 2005) for region-I, region-II, and region-III respectively.

• 한국콘텐츠학회논문지
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• 제14권5호
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• pp.211-223
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• 2014

본 연구는 일반 병동으로 전실 예정된 중환자실 환자 가족을 대상으로 중환자실 환자 가족의 부담감에 영향을 미치는 요인을 규명하기 위해 시도된 서술적 횡단조사연구이다. 연구대상은 C시에 소재한 일 대학병원 중환자실에서 일정기간 집중치료를 받고 신체상태가 안정적으로 회복되어 일반병동으로 전실 예정된 환자의 가족 중 연구대상자 선정기준에 적합한 101명이 연구 분석대상에 포함되었다. 자료수집 기간은 2010년 8월부터 11월까지였으며, SPSS 18.0 프로그램을 이용하여 자료 분석을 시행하였다. 연구 결과, 중환자실 환자 가족의 객관적 부담감은 전실 시 환자의 의식수준, 환자 몸에 부착된 기계장치의 수, 기관절개관 여부에서 통계적으로 유의한 차이가 나타났으며, 환자 가족의 주관적 부담감의 경우 환자의 성별, 환자의 교육수준, 환자와의 관계 항목에서 통계적으로 유의한 차이가 나타났다. 중환자실 환자 가족의 전실불안은 객관적 주관적 부담감과 통계적으로 유의하게 순상관관계를 보였고, 본 연구의 주요 결과인 회귀분석에서 환자 가족의 부담감 영향요인으로 객관적 부담감의 경우 전실불안이, 주관적 부담감은 환자 성별과 전실불안이 통계적으로 유의한 독립변인으로 제시되었고, 각각의 설명력은 12.7%와 23.8%로 나타났다. 본 연구결과, 일반 병동으로 전실 예정된 환자 가족의 전실불안이 환자 가족의 객관적, 주관적 부담감을 증가시키는 요인으로 나타나, 향후 본 연구결과를 토대로 중환자실 퇴실 환자와 그 가족을 대상으로 각 대상자의 요구도를 반영한 맞춤형 전실교육을 통해 환자가족의 부담감을 적극적으로 낮출 수 있는 방안이 마련되어야 할 것이다.

• 대한기계학회논문집
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• 제14권2호
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• pp.422-429
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• 1990

The experimental study investigates two aspects of counterflow sensible heat regenerator operation. First, it examines the regenerator performance in periodic steady state operation with spatially nonuniform inlet temperature in one of the fluid stream. Second, the study examines the transient response of a regenerator to a step change in the inlet temperature of one of the fluid streams. The effect of transient inlet temperatures is analyzed in terms of the response of the outlet fluid temperatures to a step change in temperature of one of the inlet fluid streams. The effect of temperature nonuniformities is analyzed in terms of the change of temperature nonuniformities is analyzed in terms of the change in steady state effectiveness due to a circumferential temperature distribution in one of the inlet fluid streams. an experimental analysis has been conducted using a counterflow, parallel passage, and rotary regenerator made from polyethylene film. Efficiencies follow similar trends with increasing matrix to fluid capacity rate ratio for the balanced and symmetric regenerator with nonuniform inlet temperature.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제14권4호
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• pp.1502-1519
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• 2020

Recently, new devices have been developed for the Internet of Things concept. The devices commonly use RF (Radio Frequency) based wireless communication. With the increase in the number of devices, the space allocated for the radio frequency band in wireless communication fills rapidly. Visible Light Communication (VLC) is an alternative, secure and economical communication technology that uses light instead of radio frequencies. While Web of Things (WoT) is the adaptation of the experience and knowledge acquired from the web into the internet of things ecosystems. By combining these two technologies, the development of the Visible Light Communication for Web of Things (VLC4WoT) system, which can use VLC and WoT technologies, has been our motivation. In our study, microcontroller control circuit was created for VLC4WoT system. Control of the circuits over the internet was performed. VLC based receiver and transmitter units have been developed for wireless communication. Web based interface was created for control. The test apparatus consisting of four objects with four outputs and a transfer unit was carried out. In this test, communication was achieved successfully. It was presented in the study that VLC can be used in the web of things architecture. In the future, it is envisaged to use this system as a safe and economical system in indoor environments.

• International Journal of Aeronautical and Space Sciences
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• 제11권1호
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• pp.19-25
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• 2010

A computational study for the optimal design of heat exchangers (HX) used in a high temperature and high pressure system is presented. Two types of air to air HX are considered in this study. One is a single-pass cross-flow type with straight plain tubes and the other is a two-pass cross-counter flow type with plain U-tubes. These two types of HX have the staggered arrangement of tubes. The design models are formulated using the number of transfer units ($\varepsilon$-NTU method) and optimized using a genetic algorithm. In order to design compact light weight HX with the minimum pressure loss and the maximum heat exchange rate, the weight of HX core is chosen as the object function. Dimensions and tube pitch ratio of a HX are used as design variables. Demanded performance such as the pressure loss (${\Delta}P$) and the temperature drop (${\Delta}T$) are used as constraints. The performance of HX is discussed and their optimal designs are presented with an investigation of the effect of design variables and constraints.

• 기술혁신연구
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• 제17권2호
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• pp.131-158
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• 2009

각 의사결정단위(decision making unit: DMU)의 효율성을 추정하는 기법의 하나인 '확률적 프론티어 분석'(Stochastic Frontier Analysis)을 사용하여 국내 공공 연구기관에 소속된 기술이전조직의 기술이전 관련 활동들의 성과에 영향을 미치는 요인들의 효과를 분석하였다. 확률 프론티어 분석에서 독립변수들은 효율적 생산기술('생산 프론티어')에 직접 영향을 미치거나 생산 프론티어와 관측치의 거리로 표현되는 DMU의 효율성에 영향을 미치는 것으로 가정된다. 해외의 선행 연구에서는 인력, 연구개발비 등의 투입변수들은 생산 프론티어에 영향을 미치고, 그 밖의 환경 또는 조직 관련 변수들은 효율성에 영향을 미치는 것으로 가정되었다. 본 연구에서는 환경 및 조직변수들이 선행 연구의 영향 경로와 다른 방식으로 성과에 영향을 미치는지 여부를 밝히기 위해 여러 형태의 모형을 추정하였다. 본 연구에서 도출된 주요 결과는 다음과 같다. 첫째, 투입 요소 가운데 연구개발비가 성과의 증가에 가장 확실한 영향을 미치는 것으로 나타났다. 둘째, 기관유형, 기관의 소재 지역 등의 환경변수들이 성과에 영향을 미치는 것으로 나타났나. 셋째, 기술이전과 관련된 보상시스템 등의 일부 조직변수들이 성과에 영향을 미치는 것으로 나타났다. 넷째, 환경변수와 조직변수들은 DMU의 효율성에 영향을 주기 보다는 생산 프론티어에 직접 영향을 미치는 것으로 나타났다. 다섯째, 일부 모형에서는 거의 모든 DMU의 효율성이 1에 가까운 것으로 나타났는데 이는 효율성을 기준으로 공공 연구기관의 기술이전 활동성과를 평가하는 것은 효과적이지 못하다는 것을 시사한다. 본 연구의 결과는 추가적인 자료를 통해 보완되어야 한다. 또한 더욱 일반적인 생산함수 형태를 고려할 필요가 있으며 산출 거리함수 등의 개념을 이용하여 복수산출물의 경우까지 분석 범위를 확장할 필요가 있다.

• Journal of Mechanical Science and Technology
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• 제17권10호
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• pp.1507-1519
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• 2003

The two-phase flow patterns for both non-loop and loop type oscillating capillary tube heat pipes (OCHPs) were presented in this study. The detailed flow patterns were recorded by a high-speed digital camera for each experimental condition to understand exactly the operation mechanism of the OCHP. The design and operation conditions of the OCHP such as turn number, working fluid, and heat flux were varied. The experimental results showed that the representative flow pattern in the evaporating section of the OCHP was the oscillation of liquid slugs and vapor plugs based on the generation and growth of bubbles by nucleate boiling. As the oscillation of liquid slugs and vapor plugs was very speedy, the flow pattern changed from the capillary slug flow to a pseudo slug flow near the annular flow. The flow of short vapor-liquid slug-train units was the flow pattern in the adiabatic section. In the condensing section, it was the oscillation of liquid slugs and vapor plugs and the circulation of working fluid. The oscillation flow in the loop type OCHP was more active than that in the non-loop type OCHP due to the circulation of working fluid in the OCHP. When the turn number of the OCHP was increased, the oscillation and circulation of working fluid was more active as well as forming the oscillation wave of long liquid slugs and vapor plugs in the OCHP. The oscillation flow of R-142b as the working fluid was more active than that of ethanol and the high efficiency of the heat transfer performance of R -142b was achieved.