• Bulletin of the Korean Chemical Society
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• v.19 no.9
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• pp.923-926
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• 1998

Spectral diffusion following direct triplet excitation from the ground state in glassy Methylbenzophenone as a function of transition energy has been studied. The concentrations of donor and acceptor have been determined for different transition energies. The geometrical distribution was determined by a computer simulation. The cluster size increases gradually with concentration and cluster percolation is observed at 0.31 mole fraction for a three dimensional system. The average distance between a donor and an acceptor also has been determined for different concentrations. The energy transfer efficiency changes abruptly at a critical concentration of 0.054, corresponding to a critical distance of 9.8 Å. The γvalue was evaluated to be 1.17.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.13 no.11
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• pp.5487-5495
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• 2012

The important issue that applies security key are secure rekeying, processing time and cost reduction. Because of sensor node's limited energy, energy consumption for rekeying affects lifetime of network. Thus it is necessary a secure and efficient security key management method. In this paper, I propose an energy efficient group-based cluster key management (EEGCK) in the large scale sensor networks. EEGCK uses five security key for efficient key management and different polynomial degree using security fitness function of sector, cluster and group is applied for rekeying and security processing. Through both analysis and simulation, I also show that proposed EEGCK is better than previous security management method at point of network energy efficiency.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.60 no.6
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• pp.1215-1224
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• 2011

Recently, a lot of research for the smart grid technology have been carried out to achieve energy efficiency for the electronic products. In order to practically apply this study, smart instruments which are capable of the AMI (Advanced Metering Infrastructure) and DR (Demand Response) function are necessary. However, it is difficult to apply the function of the smart grid to the electronic product that cannot support the smart grid. Accordingly, the efficient use of electric energy is impossible. In order to solve this problem, the electronic product has to be changed into the exclusive electronic product supporting smart grid technology or the smart controller has to be attached the outside of the device. In this study, we developed the smart controller for connecting the electric appliances to the smart grid system. It can be attached to the illumination and the smart grid-based lamp control system at home. We additionally designed the message frame and the protocol to operate the smart controller with the AMI based EMS (Energy Management Server). We developed an experimental system to practically verify functions of the smart controller which is attached to the lighting device. From the system, we showed that the electric source of the illumination can be controlled according to the load change and saved energy effectively. We also confirmed the structural benefit and the energy-efficient effect through the verification of the smart controller.

• Journal of Hydrogen and New Energy
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• v.16 no.4
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• pp.364-371
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• 2005

Fuel cell systems(FCS) have a financial and environmental advantage by providing electricity at a high efficiency and useful heat. For use in a residence, a polymer electrolyte fuel cell system(PEFCS) with a battery pack and a hot water storage tank has been modelled and simulated. The system is operated without connection to grid line. Its electric conversion efficiency and heat recovery performance are highly dependent on operation strategies and also on the seasonal thermal and electric load pattern. The output of the fuel cell is controlled stepwise as a function of the state of the battery and/or the storage water tank. In this study various operation strategies for cogeneration fuel cell systems are investigated. Average fuel saving rates at different seasons are calculated to find proper load management strategy. The scheme can be used to determine the optimal operating strategies of PEFCS for residential and building applications.

• Journal of Communications and Networks
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• v.16 no.2
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• pp.121-129
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• 2014

The trend of an increasing demand for a high-quality user experience, coupled with a shortage of radio resources, has necessitated more advanced wireless techniques to cooperatively achieve the required quality-of-experience enhancement. In this study, we investigate the critical problem of rate splitting in heterogeneous cellular networks, where concurrent transmission, for instance, the coordinated multipoint transmission and reception of LTE-A systems, shows promise for improvement of network-wide capacity and the user experience. Unlike most current studies, which only deal with spectral efficiency enhancement, we implement an optimal rate splitting strategy to improve both spectral efficiency and energy efficiency by exploring and exploiting cooperation diversity. First, we introduce the motivation for our proposed algorithm, and then employ the typical cooperative bargaining game to formulate the problem. Next, we derive the best response function by analyzing the dual problem of the defined primal problem. The existence and uniqueness of the proposed cooperative bargaining equilibrium are proved, and more importantly, a distributed algorithm is designed to approach the optimal unique solution under mild conditions. Finally, numerical results show a performance improvement for our proposed distributed cooperative rate splitting algorithm.

• Advances in Energy Research
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• v.6 no.1
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• pp.1-15
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• 2019

The objective of the study is to examine the relationship between water resources, energy demand, food production, and environmental pollutants in selected SAARC nations, namely, Bangladesh, India, Pakistan, and Sri Lanka, during the period of 1990-2016. The results show that water, energy, and food (WEF) resources substantially affected air quality in the form of high mass carbon emissions, fossil fuel energy demand, methane discharges, nitrous oxide emissions, and greenhouse gas emissions in these countries. Food production and food deficit largely increase $CO_2$ emissions due to unsustainable production and malnutrition, while land use under cereal production increases $CH_4$ and $N_2O$ emissions. Electricity production escalates $CO_2$ emissions and fossil emissions across countries. The results support the carbon EKC hypothesis, while monotonic increasing function exists in case of fossil fuel energy. The study emphasizes the need to ensure environmental sustainability agenda by adopting cleaner production technologies in WEF resources.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2008.11a
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• pp.67-67
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• 2008

Application of organic materials with low cost, easy fabrication and advantages of flexible device are increasing attention by research work. Recently, one of them, organic solar cells were rapidly increased efficiency with regioregular poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl-C61-butyricacidmethylester (PCBM) used typical material. To increased efficiency of organic solar cell has tried control of domain of PCBM and crystallite of P3HT by thermal annealing and solvent vapor annealing. [4-6] In those annealing effects, be made inefficiently efficiency, which is increased fill factor (FF), and current density by phase-separated morphology with blended P3HT and PCBM. In addition, increased conductivity by modified hole transfer layer (HTL) such as Poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT:PSS), increased both optical and conducting effect by titanium oxide (TiOx), and changed cathode material for control work function were increased efficiency of Organic solar cell. In this study, we had described effect of organic photovoltaics by conductivity of interlayer such as PEDOT:PSS and TCO (Transparent conducting oxide) such as ITO, which is used P3HT and PCBM. And, we have measured with exactly defined shadow mask to study effect of solar cell efficiency according to conductivity of hole transfer layer.

• Journal of the East Asian Society of Dietary Life
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• v.9 no.3
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• pp.325-335
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• 1999

The aim of the present study was to evaluate the relations among nutrient intake. self body image and satisfaction, and physical fitness of college students in Taegu. A total of 213 apparently healthy college students living in Taegu were selected for the study. The following anthropometric measurements were made on all participants : weight, height: waist and hip circumferences, and bioimpedence. Using weight and height, the body mass index (kg/$m^2$) was calculated. The 24-hour recall were obtained from subjects. Dietary habits and energy expenditure were examined through questionnaires. Nutrients intake were analyzed by computer aided nutritional analysis program. Variables of Physical fitness were consisted of body fat, muscular strength and endurance, agility. power, flexibility, cardiorespiratory function, physical efficiency index(PEI). Data were analyzed by computer using the SAS 6.12(Statistical Analysis System). The mean heights and weights of these students were similar to those reported for the 50th percentile in a national survey. Nutrient intake of the college students in Taegu was considerably lower than RDA. The male subjects' mean intake of two nutrients, vitamin B$_2$ and calcium, were less than 55% of the RDAs. the female subjects' mean intake of two nutrients, iron and calcium, were less than 55% of the RDAs. A most variables of physical fitness except sit and reach in male students showed a significant higher values than those of female students. There was a significant positive relationship between PEI and the intake of animal protein, fat, Ca. and B$_2$ in male students. Also there was a significant positive relationship between exercise duration of PWC 170 and protein, fat, iron, vitamin A, B$_2$, niacin, and energy intake in female students. The muscular strength showed the significant correlation with weight, height, and waist circumference in male and female students. The cardiorespiratory function and Physical efficiency index showed significantly negative correlation with tricep and subscapular skin thickness in the female students. There were significantly positive correlations between WHR and body efficiency index in male students, and significantly positive correlations between WHR and the cardiorespiratory function in female students. There was no significant level of correlation between the degree of satisfaction of body image and physical efficiency index. However. there was a significant positive correlation between waist circumference (and weight) and physical efficiency index in male and female students and almost all of the surveyed male and female college students wanted less waist circumference or weight even though they were in the criteria of standard waist circumference or weight. In conclusion, a beneficial effect of adequate nutrient intake on physical fitness was found, college students must increase their energy and nutrient intake if it is below than the RDA for improving their physical fitness.

• Journal of Radiation Protection and Research
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• v.38 no.4
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• pp.172-178
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• 2013

In this study, neutron detection efficiency of the UNDA system, which has been developed for study on nuclear material accountancy in a future pyro-process facility, was evaluated by using the MCNPX code. The detection efficiency was evaluated as a function of (1) positions of $^{252}Cf$ neutron source in the axial and radial directions, and (2) thicknesses and locations of the container filled with the depleted uranium materials for two different designs of the UNDA. In the case of $^{252}Cf$ source positions, detection efficiency was distributed from 6.83% to 13.35%. As $^{252}Cf$ source was positioned at upper part in the axial direction, detection efficiency was decreased after a slight increase. On the other hands, as $^{252}Cf$ source was positioned at outer part in the radial direction, detection efficiency was increased. In the case of container thickness, there was a slight decline when the thickness was increased. As the container was located at upper part, detection efficiency was decreased and as the container was located at outer part, detection efficiency was increased. Detection efficiency was varied from 10.31% to 13.61%. These values were higher than that of $^{252}Cf$ source case. The UNDA with polyethylene cover has about 2% higher detection efficiency than the UNDA without the cover.

• The Transactions of the Korean Institute of Power Electronics
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• v.20 no.1
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• pp.11-18
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• 2015

This paper proposes a high-efficiency 3-kW hybrid ESS with emergency power supply. The proposed system enables efficient use of power from photovoltaic (PV) cells and energy storage system (ESS). The proposed system can operate as an uninterruptible power supply (UPS) when grid fault occurs, providing seamless transfer from grid-connected mode to stand-alone mode. The LLC converter for PV achieves ZVS turn-on of switches and ZCS turn-off of diodes, and the isolated bidirectional DC-DC converter for ESS achieves ZCS turn-off regardless of load condition, resulting in high efficiency. The efficiency and performance of the proposed hybrid ESS has been verified by a 3-kW prototype.