• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.34 no.1
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• pp.73-77
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• 2021

Inorganic-organic hybrid perovskite solar cells have demonstrated considerable improvements, reaching 25.5% of certified power conversion efficiency in 2020 from 3.8% in 2009. In normal structured perovskite solar cells, TiO2 electron-transporting materials require heat treatment process at a high temperature over 450℃ to induce crystallinity. Inverted perovskite solar cells have also been studied to exclude the additional thermal process by using [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) as a non-oxide electron-transporting layer. However, the drawback of the PCBM layer is a charge accumulation at the interface between PCBM and a metal electrode. The impact of bathocuproin (BCP) buffer layer on photovoltaic performance has been investigated herein to solve the problem of PCBM. 2-mM BCP-modified perovskite solar cells were observed to exhibit a maximum efficiency of 12.03% compared with BCP-free counterparts (5.82%) due to the suppression of the charge accumulation at the PCBM-Au interface and the resulting reduction of the charge recombination between perovskite and the PCBM layer.

• Korean Journal of Materials Research
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• v.34 no.4
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• pp.215-222
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• 2024

Because collagen is inherently piezoelectric, research is being actively conducted to utilize it to harvest energy. In this study, a collagen solution was prepared using edible low-molecular-weight peptide collagen powder, and collagen films were fabricated using a dip coating method. The collagen films prepared by dip coating showed a smooth surface without defects such as pinholes or cracks. Dehydrothermal treatment of the collagen films was performed to induce a stable molecular structure through cross-linking. The collagen film subjected to dehydrothermal treatment at 110 ℃ for 24 h showed a thickness reduction rate of 19 %. Analysis of the collagen films showed that the crystallinity of the collagen film improved by about 7.9 % after dehydrothermal treatment. A collagen film-based piezoelectric nanogenerator showed output characteristics of approximately 13.7 V and 1.4 ㎂ in a pressure test of 120 N. The generator showed a maximum power density of about 2.91 mW/m² and an output voltage of about 8~19 V during various human body movements such as finger tapping. The collagen film-based piezoelectric generator showed improved output performance with improved crystallinity and piezoelectricity after dehydrothermal treatment.

• Information Systems Review
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• v.12 no.1
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• pp.189-207
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• 2010

We applied IT ecosystem analysis to Smart Grid system in this paper and thereby compared various arguments about Smart Grid technologies against the reality of the power generation and distribution in South Korea with a special attention to the power distribution side. Our work attempts to propose policy implications in the government-level based on a firm-level analysis using the framework of the competitive strategy and advantage. The Smart Grid initiative is expected to enhance the efficiency in the power generation and distribution. In addition, the Smart Grid initiative aims at capturing the opportunities in the electric power business such as parts, components, supplies, and system products in the global arena. Prerequisites of smart distribution system include building infrastructure based on smart distribution parts, information systems, communication technologies, and developing various application programs and interfaces that would interact with the consumers. Consumers are expected to play an integral role by changing their consumption patterns in response to dynamic pricing and quality choices enabled by the smart distribution technologies. In order to induce the consumers to participate actively in the program, firms and policy makers should consider providing consumers economic incentives and proper education for better understanding of new technologies. Our work helps policy makers and firm better understand the nature of technology and stakeholders for the successful implementation of smart distribution technologies.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.36 no.3
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• pp.277-284
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• 2012

In this study, a heat-transfer performance analysis is carried out for a multi-channel volumetric air receiver for a solar power tower. On the basis of a series of reviews regarding the relevant literature, a calculation process is proposed for the prediction of the wall- and air- temperature distributions of a single channel at given geometric and input conditions. Furthermore, a unique mathematical model of the receiver effectiveness is presented through analysis of the temperature profile. The receiver is made of silicon carbide. A total of 225 square straight channels per module are molded to induce the air flow, and each channel has the dimensions of $2mm(W){\times}2mm(H){\times}0.2mm(t){\times}320mm(L)$. The heat-transfer rate, temperature distribution and effectiveness are presented according to the variation of the channel and module number under uniform irradiation and mass flow rate. The available air outlet temperature applied to the solar power tower should be over $700^{\circ}C$. This numerical model was actually used in the design of a 200 kW-level commercial solar air receiver, and the required number of modules satisfying the thermal performance could be obtained for the specified geometric and input conditions.

• Journal of Life Science
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• v.20 no.9
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• pp.1345-1352
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• 2010

We investigated the effect of brown-rice vinegar (BRV) ingestion after strenuous Wingate tests on energy substrates during a 2 hr recovery period. For this, seven healthy male adolescents were chosen as subjects. They performed 3 Wingate tests to induce fatigue, after which they ingested brown-rice vinegar (BRV) drink and/or water as a control (CON) after 15 min of the test. Blood was obtained pre-exercise and 30 min, 60 min, and 120 min post-exercise, and blood glucose, lactate, free fatty acids, ammonia, and cortisol were analyzed. After 120 min of recovery period, the 4th Wingate test was conducted to calculate the power recovery ratio of the 3rd and 4th trials. Breathing frequency, oxygen saturation, and heart rate did not show significant changes. Blood glucose level was lower in CON than BRV after 120 min of recovery, and blood lactate and ammonia levels were lower in BRV at 60 and 120 min. The higher free fatty acids were found at 60 and 120 min in BRV. In addition, Wingate power recovery ratio of peak power and peak power/body weight was significantly higher in BRV compared to CON. These results suggested that BRV ingestion after strenuous exercise facilitates fatigue recovery. Therefore, BRV might be effectively used as an ergogenic aid for events in which competitors compete two or more times a day.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.37C no.11
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• pp.1064-1076
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• 2012

This study is an attempt to identify factors determining the success of international standardization and understand the relationship between the factors, such as government-driven standardization activities. Six factors were identified through factor analysis; namely, 'Direct government support', 'Indirect government support', 'Utilization of standardization bodies', 'Standardization strategy', 'Attainment of a dominant market power', and 'Adoption as an international standard.' The results showed that firstly, support from the government, whether direct or indirect, had no direct effect on the outcome of international standardization efforts, but produced an indirect influence on it through mediating factors such as the attainment of a dominant market power. Secondly, the attainment of a dominant market power proved to be the most important success factor of international standardization, suggesting that the government must direct its efforts to help boost the market power of target standards through measures like promoting a timely market entry and the development of high-quality standards, in a manner to induce market satisfaction, increasing lock-in effects and building a quasi-vertical integration system. Thirdly, direct support from the government holds the key to the success of international standardization with de jure standardization bodies, while the strategic use of standardization bodies appears the most important for the positive outcome of standardization concerning de facto standardization bodies.

• Journal of Energy Engineering
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• v.23 no.1
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• pp.46-57
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• 2014

This study analyzes whether the value-added structure of Korean wind power industry exhibits a virtuous cycle through the value chain(VC) within wind power firms and the value system(VS) among the wind power industries, using a regression analysis based on a survey about Korean wind power companies. According to the VC, the government's R&D support is analyzed to have contributed to an increase in the R&D investments of the wind power companies. An increase in corporates' R&D investments has led to an increase in corporates' R&D outputs, and in turn, induced a remarkable increase in the amounts of production. But an increase in production has not led to a decrease in the costs of production, not resulting in an increase in profit rates per sales amount. In addition, while an increase in profit rates is analyzed to have contributed to an increase in production, this did not induce further investments in corporate's R&D. The virtuous cycle of the value chain in Korean wind power firms is, therefore, analyzed to be weak. Next, the VS is analyzed by dividing the whole chain into the system group including rotor blades, gear boxes, and power generators, and the structure group, such as towers. Two groups are analyzed to have mutually positive effects in the processes of the government's support for corporates' R&D, corporates' investment in R&D, R&D outputs, and profit rates per sales amount. Such mutual positive effects are, however, not found in the processes of the amounts of production and the costs of production. These results demonstrates that the value system of Korean wind power industry is not completed. This study has a policy implication to need further efforts to create the virtuous cycle in the VC and VS of Korean wind power industry.

• The Korean Journal of Financial Management
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• v.27 no.2
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• pp.169-204
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• 2010

This paper examines the dynamic relationship between fund flow and market risk at the aggregate level and explores whether sudden sharp changes in fund flow (fund run) can cause a systemic risk in the Korean financial markets. We use daily and weekly data and regression and VAR analysis. Main results of the paper are as follows: First, in the stock market, a concurrent and a lagged unexpected fund flows have a positive relationship with market volatility. A positive shock in fund flow predicts an increase in stock market volatility. In the bond market, an unexpected fund flow has a negative relationship with the default risk premium, but a positive relationship with the term premium. And an unexpected fund flow of the money market fund has a negative relationship with the liquidy risk, but the explanatory power is very low. Second, for examining whether changes in fund flow induce a systemic risk, we construct a spillover index based on the forecast error variance decomposition of VAR model. A spillover index represents that how much the shock in fund flow can explain the change of market risk in a market. In general, explanatory powers from spillover indexes are so fluctuant and low. In the stock market, the impact of shocks in fund flow on market risk is relatively high and persistent during the period from the end of 2007 to 2008, which is the subprime-mortgage crisis period. In bond market, since the end of 2008, the impact of shocks in fund flow spreads to default risk continually, while in the money market, such a systematic effect doesn't take place. The persistent patterns of spillover effect appearing around a certain period in the stock market and the bond market suggest that the shock to the unexpected fund flow may increase the market risk and can be a cause of systemic risk in the financial markets. However, summarizing the results of regression and VAR model analysis, and considering the very low explanatory power of spillover index analysis, we can conclude that changes in fund flow have a very limited power in explaining changes in market risk and it is not very likely to induce the systemic risk by a fund run in the Korean financial markets.

• Science of Emotion and Sensibility
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• v.23 no.2
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• pp.3-12
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• 2020

The purpose of this work is to suggest the optimal color temperature, which induces a sense of comfort for autonomous vehicle users through the analysis of biosignal using electroencephalography (EEG) and photoplethysmography (PPG). To achieve this purpose, we applied lighting with a color temperature of 3000 K, 4000 K, 5000 K, and 6000 K to the autonomous driving environment. We experimented in a laboratory equipped with a graphic driving simulator. The experimental procedure is as follows: 1) stabilization (5 min). 2) Uchida-Kraepelin test (3 min). 3) Automatic driving + lighting (3 min). This procedure was repeated four times under different color temperatures. We performed frequency analysis on a collected time-series data and calculated the power value for each frequency band through power spectrum analysis. In the case of EEG, we analyzed α- and β-waves, which are indicators of stability and arousal, respectively. In the case of PPG, we analyzed the sympathetic nervous system activity. To reduce deviations between the subjects, we normalized the data before analysis. The result of the first analysis revealed that α-wave increased only at 5000 K, while the β-wave increased at almost all color temperatures. In addition, in the case of PPG, sympathetic nervous system activity (SNSA) increased under driving conditions. The result of the second analysis revealed that the difference between β-wave and SNSA is insignificant. In conclusion, the increase in α-waves showed that EEG was most stable at 5000 K. The results of this study can be applied to the upcoming autonomous driving era to induce high driver satisfaction. Furthermore, this approach could eventually lead to the acceptance of autonomous vehicles by suggesting a positive effect of autonomous driving.

• KEPCO Journal on Electric Power and Energy
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• v.3 no.1
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• pp.65-72
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• 2017

This study analyzed causal relationship between electricity consumption and economic output (GDP) for Korea from 2001 to 2014 employing the vector error-correction model estimation by manufacturing sector. The results of unit-roots tests show that all sectoral GDP and electricity consumptions were not stationary. And cointegration tests show that processed foods, Wood Pulp Paper, electricity apparatus, Precision Medical sectors had a linear combinations in the long run between electricity consumptions and economic growth. With respect to the direction of causality, manufacturing sector has a uni-directional running from economic output (GDP) to electricity consumption in short term. The results of study show that sectoral causal relation were different each other in short term and long term. These findings imply that electricity demand management policy focusing on efficiency improvement is necessary to minimize negative impacts on economic growth and to adopt suitable structural policies can induce energy conservation.