• Journal of the Korean Solar Energy Society
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• v.34 no.4
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• pp.51-56
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• 2014

In this paper, OTEC(Ocean Thermal Energy Conversion) system with vapor-vapor ejector is newly proposed. And 6 wet refrigerants are applied into the proposed OTEC system for performance comparison. The results of comparison performance are as follows. In the view of system efficiency, R32/R744(90:10) has the highest efficiency among the 6 refrigerants. In case of evaporation capacity, pump work and mass flow rate of working fluid, R744, R717 and R717 is lowest value, respectively. As this results, the vapor-vapor ejector is able to increase the efficiency of system. And It is necessary to select the optimized working fluid considering environmental and economic factors.

• Proceedings of the KSR Conference
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• 2005.05a
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• pp.712-717
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• 2005

When the weight if a concrete member makes problems, or when the cost of the concrete is relatively high, it may be economical to use a hollow concrete member. But a hollow R.C column may have poor ductility because of the brittle failure at the inner face of the hollow R.C column. This brittle failure results from the absence of the confinement at the inner face of the hollow R.C column. To avoid this brittle failure an internally confined hollow R.C column by a steel tube was developed before. In this study, a hollow R.C column is internally confined by a corrugated steel tube instead of a general flat steel tube. And a column ductility is performed. Test results show that the energy ductility ratio of a internally confined hollow R.C column by a by a corrugated steel tube corresponds to $80\%$ of the energy ductility ratio of a general solid R.C column.

• Journal of the Korean Chemical Society
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• v.54 no.6
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• pp.717-722
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• 2010

Two derivatives of star shaped compounds based on naphthylamine with symmetric trisubstituted benzene as core, methoxy and ethoxy as end substitutions are synthesized. The synthesized compounds are characterized by UV-visible, FT-IR and NMR spectrometric techniques. The electronic and thermal properties of the compounds are studied using cyclic voltametry (CV) and differential scanning calorimetry (DSC) respectively. The data's obtained have similarity with the arylamines that have been already used in optoelectronic devices. So these compounds are interesting materials for applications in such devices.

• Journal of Power System Engineering
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• v.17 no.5
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• pp.58-63
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• 2013

In this study, the effect of deep ocean condenser inlet temperature ($T_{DOI}$), condenser inlet pressure ($P_{cond,in}$), and thermal diffusivity on system efficiency of some selected refrigerants was analyzed using HYSYS. The proposed DOTEC cycle is similar to the reheat Rankine cycle but eliminates irreversibilities by bleeding a fraction of the steam between certain stages of the turbine. The evaporator inlet mass flow rate, inlet temperature of turbine 1, turbine efficiency and inlet and outlet temperature of heat source were imposed. The working fluids considered are sorted in ascending order of their molecular weights as R717, R600a and R152a. Results indicated that a fluid with a lower boiling point temperature like R717 needs a corresponding high heat source and/or evaporator inlet pressure. Also, the response of thermal diffusivity closely follows the change in TDOI as an increase in $T_{DOI}$ increases $P_{cond,in}$ which reduces thermal diffusivity and system efficiency. Furthermore, the fluid with the nominal boiling point temperature has the highest efficiency with efficiency decreasing with an increase in TDOI.

• Proceedings of the KIEE Conference
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• 2007.07a
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• pp.717-718
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• 2007

RCM(Reliability-centered Maintenance)은 Maintenance라는 사전적인 정의(사용자가 요구하는 설비의 기능을 지속적으로 유지)를 만족시키기 위하여 나온 절차로써 유지 보수하고자 하는 기기에 대하여 시스템의 신뢰도와 안정성 및 경제적 측면을 고려하여 적용이 가능하고 효율적인 유지보수 방법을 논리적으로 선택하는 기법이다. 본 논문에서는 전력 설비의 효율적인 유지보수 및 수명 평가를 위해 RCM의 설비 보전 방식에 대한 이론적 고찰과 신뢰성 공학을 기반으로 개발된 설비관리 시스템에 대하여 기술한다.

• Journal of applied mathematics & informatics
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• v.40 no.3_4
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• pp.709-717
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• 2022

The objective of this research is to prove that an additive mapping T : R → R is a left as well as right centralizer on R if it satisfies any one of the following identities: (i) T(xⁿyⁿ + yⁿxⁿ) = T(xⁿ)yⁿ + yⁿT(xⁿ) (ii) 2T(xⁿyⁿ) = T(xⁿ)yⁿ + yⁿT(xⁿ) for each x, y ∈ R, where n ≥ 1 is a fixed integer and R is any n!-torsion free semiprime ring. In addition, we talk over above identities in the setting of *-ring(ring with involution).

• KOREAN JOURNAL OF CROP SCIENCE
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• v.4 no.1
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• pp.97-101
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• 1968

Effects of weather factors on leaf tobacco yield were studied from the yield data of flue-cured yellow tobacco variety Yellow pryer and weather recordes for 13 years from 1952 to 1964. The results are summarized as follows; 1. Leaf tobacco yield variation was large and larger coefficient of variance was calculated. 2. Yield of leaf tobacco was correlated largely to leaf number, with simple correlation coefficient r=0.736. Leaf number was correlated largely to sunshine hours during May with r=0.745, and multiple correlation coefficient R=0.837 between leaf number and multiple weather factors during May to June. 3. Leaf tobacco yield was largely affected by the sunshine hours (r=0.717) and temperature (r=0.329) in May and precipitation (r=0.421) in June. 4. From the study of partial regression of leaf tobacco yield on weather factors a formulation Y=441.664-31.255$X_1$+1.19$Y_2$-0.031$X_3$ was calculated for the estimation of leaf tobacco yield. Here R=0.8074 d.f.=7 was significant.

• Journal of Advanced Marine Engineering and Technology
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• v.37 no.8
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• pp.836-842
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• 2013

In this paper, the 20 kW Ocean Thermal Energy Conversion(OTEC) is newly proposed in order to select the refrigerant that makes the cycle performance be optimized and the performance of 20 kW OTEC applying 15 pure refrigerants and 16 mixed refrigerants is analyzed. The efficiency of system, the mass flow of working fluids and TPP, which is new concepts, are analyzed. In view of cycle efficiency, R32/R152a (87:13) is the highest efficiency among the refrigerants. At the mass flow of working fluid to make the 20 kW electricity, R717 is shown as the lowest value. And in view of TPP in this study, R32/R134a 70:30 is the most optimized refrigerant. The analysis can confirm that the refrigerant is different along with the part of the system, so it is necessary to select the optimized refrigerant for 20 kW OTEC.

• Korean Journal of Ecology and Environment
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• v.48 no.4
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• pp.263-271
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• 2015

To evaluate the relationship between dynamics of cyanobacteria and odorous compounds, a monthly monitoring of water quality and phytoplankton were conducted at the three serial lakes (Lake Ui-am, Lake Cheong-pyeong and Lake Pal-dang) in the North Han River for 11 times from May 2014 to March 2015. In the three serial lakes, phytoplankton communities showed that seasonal changes in Bacillariophyceae-Cyanophyceae-Bacillariophyceae. Anabaena and Pseudanabaena were dominant species in August and September 2014. At the same time the odors (Geosmin, 2-MIB) were also detected with high concentration. Relationship between environmental factors and cyanobacterial abundance showed a significant correlation with Anabaena circinalis and geosmin (r=0.983, p<0.01). In the case of Pseudanabaena limnetica showed a significant correlation of total nitrogen (r=0.685, p<0.01) and NO3-N (r=0.723, p<0.01). In addition, similarly Pseudanabaena limnetica and 2-MIB (r=0.717, p<0.01) was high. The odorous compounds appeared in the North Han River water were considered to be a direct relationship with cyanobacteria.

• Bulletin of the Korean Mathematical Society
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• v.36 no.4
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• pp.717-722
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• 1999

The set of continuous maps of a space X to real usual space R equipped with the toplogy of pointwise convergence will be denoted by $C_p$(X). In this paper, we prove that; $C_p$(X) is hereditarily separable and hereditary Lindelof if and only if $X^n$ is hereditarily separable and hereditary Lindelof.