• 한국지열·수열에너지학회논문집
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• 제20권2호
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• pp.11-23
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• 2024

In order to design a standing column well (SCW) for a sustainable groundwater curtain system for greenhouse heating, we conducted parameter sensitivity tests. These tests simulated the outlet temperature changes of the SCW in a groundwater recirculating greenhouse cultivation system. Our modeling considered ground thermal conductivity and hydrogeological conditions. Specifically, we examined several factors, including SCW length, enhanced thermal conductivity of the ground, and groundwater circulation rate. The simulation results indicated that there was not a significant difference in the heat exchange rate based on the characteristics of enhanced thermal conductivity. However, we anticipate a substantial difference in the case of varying SCW lengths. Therefore, we conclude that the simulation results are primarily influenced by conductive heat exchange values, as the circulating water remains at a constant groundwater level.

• 무역상무연구
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• 제61권
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• pp.165-190
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• 2014

The purpose of this study is to measure the trade insurance's macroeconomic effects by analyzing the causality between major economic variables(GDP per capita, market interest rate, inflation, unemployment rate, exchange rate) and trade insurance variable. I conducted empirical analyses using First-difference GMM(Generalized Method of Moments), System GMM and Panel-VAR Model, with panel data from 11 countries(Korea, United States, Japan, BRICs, Indonesia, Singapore, Hong Kong, Vietnam) between 1992 and 2011. There are several important findings. Above all, Trade insurance is positively and significantly related to GDP. This results show that trade insurance serves to increase economic growth. In other words, trade insurance leads to economic growth by helping increase GDP per capita. Especially, trade insurance negatively related to unemployment rate, it is for sure that trade insurance contribute to decrease unemployment rate. And trade insurance helps control of inflation. It is also confirmed that trade insurance contributes to price stability, which in turn serves to stabilize the overall economy. And this research finds as uncertainty in the market increases, seen it as increase of exchange rate, increasing trade insurance supply is stabilize the exchange rate.

• 에너지공학
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• 제10권4호
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• pp.357-362
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• 2001

충진농도, 냉매 팽창밸브 개도, 그리고 약용액의 유량 변화에 따른 벤치타입 암모니아-물 흡수식 열교환 사이클에 대한 실험을 수행한 결과 시스템의 충진농도가 증가할수록 냉방능력이 증가하였으며, 최적의 충진농도가 존재함을 알았다. 그리고 냉매 팽창 밸브의 개도는 응축기 출구의 직접적인 영향을 주고 있으며 최적의 과냉도가 0~4$^{\circ}C$임을 알았다. 또한 약용액의 유량이 증가시킬수록 증발압력과 강용액의 농도가 즐어들었으며, 냉방능력과 COP가 최대가 되는 최적의 약용액 유량이 존재하였다.

• East Asian Economic Review
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• 제20권3호
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• pp.365-390
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• 2016

This paper quantitatively compares the intrinsic features of the daily USD-GBP exchange rates in two different periods, the 1920s and the 2010s, under the same freely floating exchange rate system. Even though the foreign exchange markets in the 1920s seem to be much less organized and developed than in the 2010s, this paper finds that both the long memory volatility property and the structural break appear to be the common intrigue features of the exchange rates in the two periods by using the FIGARCH model. In particular, the long memory volatility properties in the two periods are found to be upward biased and overstated because of the structural breaks in the exchange markets. Thus this paper applies the Adaptive-FIGARCH model to consider the long memory volatility property and the structural breaks jointly. The main finding is that the structural breaks in the exchange markets affect the long memory volatility property significantly in the two periods but the degree of the long memory volatility property in the 1920s is reduced more remarkably than in the 2010s after the structural breaks are accounted for; thus implying that the structural breaks in the foreign exchange markets in the 1920s seem to be more significant.

• 동력기계공학회지
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• 제21권1호
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• pp.50-56
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• 2017

To increase the enthalpy exchange efficiency of ERV elements, the moisture exchange character must be improved. The moisture exchange efficiency depends on material characteristics. The material used for ERV is Hwang-to paper based on Han-ji which is Korean traditional paper. The paper has excellent performance in moisture exchange and heat transfer compared with polymer and other papers. To have an anti bacteria performance and to improve moisture exchange performance of Han-ji, Hwang-to is added to the Han-ji. The enthalpy exchange efficiency of the Hwang-to paper shows 5% greater than that of the conventional paper. In case of Escherichia Coli, the reduction rate of bacteria is 96.6% and in case of Pseudomonas, the reduction rate of bacteria is 97.5%. The ERV element made of Hwang-to paper has a great possibility as an ERV element.

• 동력기계공학회지
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• 제9권4호
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• pp.18-23
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• 2005

The experimental investigation was carried out to evaluate the performance of air-to-air heat exchanger with rotating porous plates newly developed in this study. The rotating porous plates are mounted with an equal interval of 18 mm inside the heat exchanger where the hot and cold airs enter at opposite ends. When flowing in opposite directions by the separating plate installed in the center of the rotating porous plates, the airs give and receive the heat each other. The material of the porous plate is cooper and its thickness is 1.0 mm. Air flow rate is varied from 10 to 120 m3/h. From the experiment of air-to-air heat exchanger with the rotating porous plates, the heat exchange performance increased with the increase in RPM of the porous rotating discs at the conditions of the same air flow rate. The sensible heat exchange efficiency was maximum 60 to 70 percent, and enthalpy exchange efficiency 50 to 60 percent.

• The Journal of Asian Finance, Economics and Business
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• 제5권2호
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• pp.5-14
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• 2018

This study is motivated based on concern from some renowned scholars and central bankers whom have raised the issue of the sustainability of the International Monetary System (IMS). Using the panel data set of four major international currencies, USD, JPY, EUR and GBP from 1973 to 2013 with Pooled Mean Group (PMG) estimator, to re-examine whether Triffin dilemma still exists through investigating the relationship between the reserve share, current account balance and real effective exchange rate. The evidence from the result indicates that Triffin dilemma exists only in the long run, and shows that in the long-run, current account balance is proportionate to the increased real effective exchange rate while varies inversely with the reserve shares. However, the estimation for the short-run is not significant to prove the existence of Triffin dilemma. In addition, we investigated the non-dollar panel sample and found that the international monetary system still suffers from Triffin dilemma even without the dollar. To overcome Triffin dilemma, immediate step such as having currency swap mechanism is recommended. In medium term, a multi-polar Monetary System is suggested, and in the longer time, a supranational currency will be used to replace all the currencies in the world.

• 한국수소및신에너지학회논문집
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• 제18권3호
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• pp.292-300
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• 2007

A dynamic system model of a proton exchange membrane fuel cell(PEMFC) has been developed. The PEMFC of this study has large active area with water cooling in order to simulate the performance of the commercially viable PEMFC system for the transportation. A PEMFC stack model is a transient thermal model which is respond to the dynamic change of the coolant temperature and the flow rate. The dynamic cooling system model has been developed to determine the coolant flow rate and the coolant temperature. Prior to the system level study, thermal management criteria have been set up and brought to the control command of the cooling system. Since the system model is designed to evaluate the effect of thermal management on the system performance, it is attempted to determine the proper control algorithm of the cooling system so that the PEMFC system is working on the thermal management criteria. As a result of simulation, feedback controlled cooling system consumes less power and produce more power comparing with that of conventionally controlled cooling system.

• 지능정보연구
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• 제28권4호
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• pp.191-209
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• 2022

2020년 코로나19 발발 이후 한국 경제를 포함한 국제 시장 환경은 급속하게 변하고 있고 한국 금융시장의 중요 경제 지표인 원/달러 환율도 요동치고 있다. 대외 의존도가 높은 한국 경제에서 환율에 대한 이해는 항상 중요한 연구 과제였고, 특히 코로나 확산이 환율에 미치는 연구는 시기적으로 많은 경제 학자들의 관심사이기도 하다. 따라서 본 연구는 코로나19 발발 이후 환율과 경제 지표의 관계를 분석하고 환율 예측을 위한 단변량 다변량 예측 모형을 구축하여 모형의 예측 성능을 비교 검증을 하였다. 코로나 전후 기간을 세 기간으로 나눠서 기간 1은 코로나 발발전과 초기, 기간 2는 코로나 대확산, 기간 3을 코로나 안정기로 나누고 기간 1의 환율 데이터를 학습한 SARIMA 모형과 같은 기간의 경제 변수와 환율 데이터를 학습한 ARDL 모형의 예측 성능을 비교하였다. 기간별 RMSE기준으로 SARIMA 모형은 기간 2에서 예측 성능이 뛰어나고 ARDL 모형은 기간 3에서 예측 성능이 가장 우수한 것으로 나타났다. 연구 결론은 환율과 경제 변수의 통상적인 관계가 나타나는 기간 3에서는 변수 관계를 반영하는 ARDL 모형이 좀 더 예측 성능이 좋은 모델이고 기존의 전형적인 환율과 경제 변수의 패턴에서 벗어난 과도기 시기인 기간 2에는 과거 환율 추이만 반영하는 SARIMA 모형이 좀 더 우수한 예측 성능을 보여주는 모델로 검증되었다.

• KIEAE Journal
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• 제14권4호
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• pp.127-131
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• 2014

The ground source heat pump (GSHP) system is a kind of the temperature differential energy system using relatively stable underground temperature as heat source of space heating and cooling. This system can achieve higher performance of system than it of conventional air source heat pump systems. However, its superiority of the system performance is different according to installation location or local climate, because the system performance depends on the underground condition which is decided by annual average air temperature. In this study, in order to estimate the feasibility of the ground source heat pump system according to the local climate, numerical simulation was conducted using the ground heat transfer model and the surface heat balance model. The case study was conducted in the condition of Seoul, Daejeon, and Busan, In the result, the heat exchange rate of Busan was 34.33 W/m as the largest in heating season and it of Seoul was 40.61 W/m as the largest in cooling.