• Transactions of the Korean hydrogen and new energy society
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• v.30 no.5
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• pp.401-410
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• 2019

The operating conditions greatly impact the efficiency and performance of polymer electrolyte membrane (PEM) fuel cell systems and must be properly managed to ensure better performance and efficiency. In particular, small variations in operating conditions interact with each other and affect the performance and efficiency of PEM fuel cell systems. Thus, a systematic study is needed to understand how small changes in operating conditions affect the system performance and efficiency. In this paper, an automotive fuel cell system (including cell stack and balance of plant [BOP]) with a turbo-blower was modeled using MATLAB/Simulink platform and the sensitivity analyses of main operating parameters were performed using the developed system model. Effects of small variations in four main parameters (stack temperature, cathode air stoichiometry, cathode pressure, and cathode relative humidity) on the system efficiency were investigated. The results show that cathode pressure has the greatest potential impact on the sensitivity of fuel cell system efficiency. It is expected that this study can be used as a basic guidance to understand the importance of achieving accurate control of the fuel cell operating conditions for the robust operation of automotive PEM fuel cell systems.

• Clean Technology
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• v.20 no.4
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• pp.449-456
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• 2014

There has been increasing concerns for the problems of water security in countries, caused by the frequent occurrence of localized drought due to the climate change and uncertainty of water balance. The importance of fresh water is emphasized as considerable amount of usable fresh water is utilized for power generation sector producing electricity. PV power system, the source of renewable energy, consumes water for the every steps of life cycle: manufacturing, installation, and operation. However, it uses relatively less water than the traditional energy sources such as thermal power and nuclear power sources. In this study, to find out the use of water for the entire process of PV power system from extracting raw materials to operating the system, the footprint of water in the whole process is measured to be analyzed. Measuring the result, the PV water footprint of value chain was $0.989m^3/MWh$ and the water footprint appeared higher specially in poly-Si and solar cell process. The following two reasons explain it: poly-Si process is energy-intensive process and it consumes lots of cooling water. In solar cell process, deionized water is used considerably for washing a high-efficiency crystalline silicon. It is identified that PV system is the source using less water than traditional ones, which has a critical value in saving water. In discussing the future energy policy, it is vital to introduce the concept of water footprint as a supplementary value of renewable energy.

• Molecules and Cells
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• v.37 no.11
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• pp.827-832
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• 2014

The balance between bone formation by osteoblasts and destruction of mineralized bone matrix by osteoclasts is important for bone homeostasis. The increase of osteoclast differentiation by RANKL induces bone diseases such as osteoporosis. Recent studies have shown that insulin is one of main factors mediating the cross-talk between bone remodeling and energy metabolism. However, the systemic examination of insulin-induced differential gene expression profiles in osteoclasts has not been extensively studied. Here, we investigated the global effects of insulin on osteoclast precursors at the level of gene transcription by microarray analysis. The number of genes that were up-regulated by ${\geq}1.5$ fold after insulin treatment for 6 h, 12 h, or 24 h was 76, 73, and 39; and 96, 83, and 54 genes were down-regulated, respectively. The genes were classified by 20 biological processes or 24 molecular functions and the number of genes involved in 'development processes' and 'cell proliferation and differentiation' was 25 and 18, respectively, including Inhba, Socs, Plk3, Tnfsf4, and Plk1. The microarray results of these genes were verified by real-time RT-PCR analysis. We also compared the effects of insulin and RANKL on the expression of these genes. Most genes had a very similar pattern of expressions in insulin- and RANKL-treated cells. Interestingly, Tnfsf4 and Inhba genes were affected by insulin but not by RANKL. Taken together, these results suggest a potential role for insulin in osteoclast biology, thus contributing to the understanding of the pathogenesis and development of therapeutics for numerous bone and metabolic diseases.

• International Commerce and Information Review
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• v.16 no.4
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• pp.281-305
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• 2014

The purpose of this study is to empirically analyze the status and the trends in the international competitiveness of Korean export products against MINTs. For the study, the data were collected from the trade statistics for the period 2009-2012 produced by KITA and UN comtrade, and trade specialization index and market comparative advantage index were selected as index analysis methods. The findings from this study are as follows: First, Korea maintains a continuous increase of trade volume and trade balance in trade with MINTs, and exports finished goods, auto parts, etc. to MINTs, whlie mainly imports primary products such as energy fuels from MINTs. Second, Korea remains competitive in both product groups and individual products over MINTs. Third, even though Korean exports obtain a high competitiveness against MINTs, its competitiveness shows the differences by country. Several implications of this study are as follows: First, we need to take full advantage of energy resource-rich MINTs in securing stable energy fuels. Second, we should prepare response plans for the economic conditions which can have a negative impact on trade with MINTs, Third, we need to build strategies for maintaining the competitiveness of Korean exports over MINTs. Fourth, The differentiated export strategies should be established by country by considering differences in Korean exports' competitiveness which exist among the four countries of MINTs. Fifth, we need to prepare for such a situation which MINTs attempt to expand its influence by forming a collective economic cooperation.

• Journal of Distribution Science
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• v.10 no.7
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• pp.33-41
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• 2012

The purpose of this study is to analyse the state of the energy industry and to determine the efficiency of its functioning on the basis of energy conservation principle and application of innovative technologies aimed at improving the ecological modernisation of agricultural sectors of Kazakhstan. The research methodology is based on an integrated approach of financial and economic evaluation of the effectiveness of the investment project, based on calculation of elasticity, total costs and profitability, as well as on comparative, graphical and system analysis. The current stage is characterised by widely spread restructuring processes of electric power industry in many countries through introduction of new technical installations of energy facilities and increased government regulation in order to enhance the competitive advantage of electricity market. Electric power industry features a considerable value of creating areas. For example, by providing scientific and technical progress, it crucially affects not only the development but also the territorial organisation of productive forces, first of all the industry. In modern life, more than 90% of electricity and heat is obtained by Kazakhstan's economy by consuming non-renewable energy resources: different types of coal, oil shale, oil, natural gas and peat. Therefore, it is significant to ensure energy security, as the country faces a rapid fall back to mono-gas structure of fuel and energy balance. However, energy resources in Kazakhstan are spread very unevenly. Its main supplies are concentrated in northern and central parts of the republic, and the majority of consumers of electrical power live in the southern and western areas of the country. However, energy plays an important role in the economy of industrial production and to a large extent determines the level of competitive advantage, which is a promising condition for implementation of energy-saving and environmentally friendly technologies. In these circumstances, issues of modernisation and reforms of this sector in Kazakhstan gain more and more importance, which can be seen in the example of economically sustainable solutions of a large local monopoly company, significant savings in capital investment and efficiency of implementation of an investment project. A major disadvantage of development of electricity distribution companies is the prevalence of very high moral and physical amortisation of equipment, reaching almost 70-80%, which significantly increases the operating costs. For example, while an investment of 12 billion tenge was planned in 2009 in this branch, in 2012 it is planned to invest more than 17 billion. Obviously, despite the absolute increase, the rate of investment is still quite low, as the total demand in this area is at least more than 250 billion tenge. In addition, industrial infrastructure, including the objects of Kazakhstan electric power industry, have a tangible adverse impact on the environment. Thus, since there is a large number of various power projects that are sources of electromagnetic radiation, the environment is deteriorated. Hence, there is a need to optimise the efficiency of the organisation and management of production activities of energy companies, to create and implement new technologies, to ensure safe production and provide solutions to various environmental aspects. These are key strategic factors to ensure success of the modern energy sector of Kazakhstan. The contribution of authors in developing the scope of this subject is explained by the fact that there was not enough research in the energy sector, especially in the view of ecological modernisation. This work differs from similar works in Kazakhstan in the way that the proposed method of investment project calculation takes into account the time factor, which compares the current and future value of profit from the implementation of innovative equipment that helps to bring it to actual practise. The feasibility of writing this article lies in the need of forming a public policy in the industrial sector, including optimising the structure of energy disbursing rate, which complies with the terms of future modernised development of the domestic energy sector.

• Journal of the Korean Wood Science and Technology
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• v.17 no.1
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• pp.22-54
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• 1989

Seasonal semi-greenhouse type solar-drying of 2.5cm-and 5.0cm-thick lumber of Quercus aliena Blume and Quercus variailis Blume was carried out to investigate the possibility of solar-drying of wood and to decide the active solar-drying period in Korea. In the active solar-drying period obtained solar-dehumidification, semi-greenhouse type solar-, air- and kiln-drying of 2.5cm -thick lumber of oaks were carried out to analyze drying-rates. -defects, and -yield in each drying-method and to calculate daily total absorbed solar-radiation the solar dryers. The energy balance equations were set up, considering all the energy requirements, to analyze the heat efficiencies of semi-greenhouse type solar and solar-dehumidification-dryer. In a seasonal drying the drying rate of semi-greenhouse type solar-dryer was highest in summer, and greater in fall, spring, and winter in order. Solar-drying time was 45% in summer to 50% in winter of the air-drying rime, and more serious drying-defects occurred in air-drying than in solar-drying. In the active solar-drying period. April, May, and June, the average drying rate in solar-dehumidification-drying was 1.0%/day and greater than 0.8%/day in semi-greenhouse type solar-drying. In solar-dehumidification-drying the time required to dry lumber to 10% moisture content was less than 60 days, and solar-dehumidification-drying showed the highest drying-yield, 65.01%, than the other drying methods. The daily total absorbed solar radiations were 8.51MJ on the roof collector and 6.22 MJ on the south wall collector. In the energy blance 69.48% of total energy input was lost by heat conduction through walls, roof. and floor 11.68% by heat leakage, 0.33% by heating the internal structures of the solar-dryer and 5.38% by air-venting. Therefore the heat efficiency of semi-greenhouse type solar-dryer 13.13%, was lower than that of solar-dehumidification-dryer, 14.04%. Solar-drying of lumber in Korea showed the possibility to reduce the air-drying-time in every season and the efficiency of solar-dehumidification drying was higher than that of semi-greenhouse type solar-drying.

• Journal of Korean Medicine for Obesity Research
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• v.8 no.1
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• pp.63-70
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• 2008

Objectives Obesity is the major risk factor of the heart disease and the metabolic disease. The autonomic nervous system is a key contributor in the regulation of energy balance, so the blunted activity may contribute to the maintenance of the obese state. So we evaluated the function of the autonomic nervous system in young overweight and obese women with heart rate variability. Methods The subjects were 26 overweight and obese young women(BMI〉$23kg/m^2$) and 25 lean women who visited Kangnam Kyunghee hospital for obesity management from March 2006 to April 2008. Bioimpedance Analysis (BIA), short-term spectral analysis of heart rate variability (HRV) were performed. Results HRV of obese young group was lower than the lean young group, but there is no statistical significance. BMI had significantly a negative correlation with Low Frequency(LF) of HRV. LF power is mediated by sympathetic nervous system activity. These results indicate a decrease of sympathetic modulation in overweight and obese young women. Conclusions Overweight and obese young women have decreased sympathetic nervous system activity. In clinical practice, an assessement of HRV would be noninvasive and sensitive methods for sympathetic nervous system of young overweight and obese women.

• Journal of Biosystems Engineering
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• v.40 no.3
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• pp.296-304
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• 2015

Purpose: The balance between miscanthus production and its cost effectiveness depends greatly on its moisture content during post processing. The objective of this research was to measure the moisture content using a non-destructive and non-contact methodology for in situ applications. Methods: The moisture content of comminuted miscanthus was controlled using a closed chamber, a humidifier, a precision weigher, and a real-time monitoring software developed in this research. A CMOS sensor equipped with $50{\times}$ magnifier lens was used to capture magnified images of the conditioned materials with moisture content level from 5 to 30%. The hypothesis is that when light is incident on the comminuted particles in an inclined manner, higher moisture content results in light being reflected with a higher intensity. Results: A linear regression analysis for an initiative hypothesis based on general histogram analysis yielded insufficient correlations with low significance level (<0.31) for the determination coefficient. A significant relationship (94% confidence level) was determined at level 108 in a reverse accumulative histogram proposed based on a revised hypothesis. A linear regression model with the value at level 108 in the reverse accumulative histogram for a magnified image as the independent variable and the moisture content of comminuted miscanthus as the dependent variable was proposed as the estimation model. The calibrated linear regression model with a slope of 92.054 and an offset of 32.752 yielded 0.94 for the determination coefficient (RMSE = 0.2%). The validation test showed a significant relationship at the 74% confidence level with RMSE 6.4% (n = 36). Conclusions: To compensate the inconsistent significance between calibration and validation, an estimation model robust against various systematic interferences is necessary. The economic efficiency of miscanthus, which is a promising energy resource, can be improved by the real-time measurement of its crucial material properties.

• YAKHAK HOEJI
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• v.54 no.3
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• pp.180-186
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• 2010

Aldosterone, mineralocorticoid hormone, has important functions related to the regulation of blood pressure and balance of fluids and electrolytes in the distal region of the nephron. By genomic and non-genomic action of aldosterone, the physiological kidney functions are modulated. However, many of them except several kind of sodium channel have not been identified and analyzed yet. In this study, proteomic technologies with two-dimensional gel electrophoresis (2-DE) gel using aldosterone rat model were applied to analyze and identify the aldosterone dependently expressed proteins in rat kidney cortex. As a result, the established aldosterone rat model exhibited the normal physiological responses to aldosterone and modulated proteins were identified, which included 15 increased and 3 decreased proteins on 2-DE analysis. Among them, 11 proteins were identified as changed proteins by LC-MS/MS analysis. These proteins identified as aldosterone induced proteins were involved in several cellular pathways such as cytoskeleton remodeling, energy metabolism, amino acid metabolism, and chaperone process. In conclusion, our data could provide the insights into the new mechanism underlying regulation of kidney functions by aldosterone.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.41 no.2
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• pp.87-95
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• 2017

The concept of entransy has been proposed recently as a potential heat transfer mechanism and could be useful in analyzing and optimizing the heat-work conversion systems. This work presents an entransy analysis for the irreversible Carnot cycle by systematic balance formulations of the entransy loss, work entransy, and entransy dissipations, which are consistent with exergy balances. Additionally, several forms of system efficiency are introduced based on entransy for the appreciation of the optimal system performance. The effects of the source temperature and irreversible efficiencies on the optimal conditions for system efficiencies are systematically investigated for both dumping and non-dumping cases of used source fluid. The results show different trends in entransy efficiencies when compared to the conventional efficiencies of energy and exergy, and represent another method to assess the effective use of heat source in power generation systems.