• 대한전기학회:학술대회논문집
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• 대한전기학회 2009년도 제40회 하계학술대회
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• pp.1161_1162
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• 2009

The recent environmental protection trend requires more strict energy saving, therefore every transportation system should reduce energy consumption to the minimum value. High-efficiency operation system, energy saving and $CO_2$ emissions shall be addressed as important issue in railway system. These issues are the most essential factors of railway, compared to major public transportation system. Recently, saving energy in the electric railway system has been studied. For such new energy saving, the energy storage system is considered for saving energy. Energy saving is possible by efficient use of regenerated energy. Regenerated energy is recycled amongst vehicles by mean of charge and discharge corresponding to powering and braking of electric vehicle operations. This energy saving contributes to cut $CO_2$ to reduce greenhouse gas emissions. Recycling regenerated energy demonstrate significant effect on peak cut of consumption energy in railway substation. Absorption of excess energy avoids regeneration failure due to high traction voltage. Therefore, the energy storage system is needed to be adopted to use regeneration energy when the vehicle is braking.

• 전기학회논문지
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• 제66권3호
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• pp.486-492
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• 2017

In recent years, renewable energy sources have been mentioned as solution to environmental regulation and energy supply-demand. Energy storage systems are needed to mitigate the intermittent output characteristics of renewable energy sources and to operate micro grid efficiently using renewable energy generation systems. However, despite the necessity of energy storage system, this cannot secure the economical efficiency of the energy storage system by high initial cost. In this paper, a micro grid is constructed to supply electric power to industrial customers by using solar power generation system and energy storage system among renewable energy generation power sources and operated to improve energy independence. In the case study, we use photovoltaic system which is representative renewable energy generation system. Unlike conventional photovoltaic system, this system uses floating photovoltaic system with the advantage of having high output and no land area limitations. It is operated for the purpose of improving energy independence in the micro grid. In order to secure economical efficiency, the energy storage system operates a micro grid with a minimum capacity. Finally, this paper calculates the appropriate subsidy for the energy storage capacity.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2016년도 제50회 동계 정기학술대회 초록집
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• pp.297.2-297.2
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• 2016

Photoacoustic generation of ultrasound is an effective approach for development of high-frequency and high-amplitude ultrasound transmitters. This requires an efficient energy converter from optical input to acoustic output. For such photoacoustic conversion, various light-absorbing materials have been used such as metallic coating, dye-doped polymer composite, and nanostructure composite. These transmitters absorb laser pulses with 5-10 ns widths for generation of tens-of-MHz frequency ultrasound. The short optical pulse leads to rapid heating of the irradiated region and therefore fast thermal expansion before significant heat diffusion occurs to the surrounding. In this purpose, nanocomposite thin films containing gold nanoparticles, carbon nanotubes (CNTs), or carbon nanofibers have been recently proposed for high optical absorption, efficient thermoacosutic transfer, and mechanical robustness. These properties are necessary to produce a high-amplitude ultrasonic output under a low-energy optical input. Here, we investigate carbon nanotube (CNT)-polydimethylsiloxane (PDMS) composite transmitters and their nanostructure-originated characteristics enabling extraordinary energy conversion. We explain a thermoelastic energy conversion mechanism within the nanocomposite and examine nanostructures by using a scanning electron microscopy. Then, we measure laser-induced damage threshold of the transmitters against pulsed laser ablation. Particularly, laser-induced damage threshold has been largely overlooked so far in the development of photoacoustic transmitters. Higher damage threshold means that transmitters can withstand optical irradiation with higher laser energy and produce higher pressure output proportional to such optical input. We discuss an optimal design of CNT-PDMS composite transmitter for high-amplitude pressure generation (e.g. focused ultrasound transmitter) useful for therapeutic applications. It is fabricated using a focal structure (spherically concave substrate) that is coated with a CNT-PDMS composite layer. We also introduce some application examples of the high-amplitude focused transmitter based on the CNT-PDMS composite film.

• 한국분말재료학회지
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• 제20권1호
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• pp.53-59
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• 2013

Fe-TiC composite powder was fabricated via two steps. The first step was a high-energy milling of FeO and carbon powders followed by heat treatment for reduction to obtain a (Fe+C) powder mixture. The optimal condition for high-energy milling was 500 rpm for 1h, which had been determined by a series of preliminary experiment. Reduction heat-treatment was carried out at $900^{\circ}C$ for 1h in flowing argon gas atmosphere. Reduced powder mixture was investigated by X-ray Diffraction (XRD), Field Emission-Scanning Electron Microscopy (FE-SEM) and Laser Particle Size Analyser (LPSA). The second step was a high-energy milling of (Fe+C) powder mixture and additional $TiH_2$ powder, and subsequent in-situ synthesis of TiC particulate in Fe matrix through a reaction of carbon and Ti. High-energy milling was carried out at 500 rpm for 1 h. Heat treatment for reaction synthesis was carried out at $1000{\sim}1200^{\circ}C$ for 1 h in flowing argon gas atmosphere. X-ray diffraction (XRD) results of the fabricated Fe-TiC composite powder showed that only TiC and Fe phases exist. Results from FE-SEM observation and Energy-Dispersive X-ray Spectros-copy (EDS) revealed that TiC phase exists uniformly dispersed in the Fe matrix in a form of particulate with a size of submicron.

• Fisheries and Aquatic Sciences
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• 제5권3호
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• pp.219-228
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• 2002

Based on the five-year (October 1992 through September 1997) Topex/Poseidon altimeter measurements, we describe the statistical characteristics of the eddy variability in the East Sea in terms of sea surface height anomaly, slope variability, and eddy kinetic energy (EKE). The sea surface height anomalies in the East Sea are produced with standard corrections from Topex/Poseidon measurements. In order to eliminate the high frequency noise in the sea surface height anomaly data, the alongtrack height anomaly data was filtered by about 40 km low-pass Lanczos filter based on Strub et al. (1997) and Kelly et a1. (1998). We find that there exists a distinct spatial contrast of high eddy variability in the south and low eddy energy in the north, bordering the Polar Front. In the northwestern area $(north\;of\;39^{\circ}N\;and\;west\;of\;133^{\circ}E)$ from the Polar Front where the eddies frequently appear, the EKE is also considerabel. The high kinetic energy in the southern East Sea reveals a close connection with the paths of the Tsushima Warm Current, suggesting that the high variability in the south is mainly generated by the baroclinic instability process of the Tsushima Warm Current. This finding is supported by other studies (Fu and Zlontnicki, 1989; Stammer, 1997) wh.ch have shown the strong eddy energy coupled in the major current system. The monthly variation of the EKE in both areas of high and low eddy variability shows a strong seasonality of a high eddy kinetic energy from October to February and a relatively low one from March to September. The sequential pattern of wind stress curl shows resemblance with those of monthly and seasonal EKE and the two sequences have a correlation of 0.82 and 0.67, respectively, providing an evidence that wind stress curl can be the possible forcing for the monthly and seasonal variation of the EKE in the East Sea. The seasonality of the EKE also seems to correlate with the seasonality of the Tsushima Warm Current. There also exists the large spatial and interannual variabilities in the EKE.

• 청정기술
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• 제20권4호
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• pp.359-366
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• 2014

연소전 $CO_2$ 흡수제인 PKM1-SU와 원유의 접촉분해 촉매인 FCC (fluid catalytic cracking)입자의 고온, 고압 조건 마모 실험을 수행하였다. 지름 15.1 cm, 높이 120 cm에 스파저 튜브(sparger tube, 1 mm 오리피스)를 장착한 원통형 기포유동층반응기를 이용하여, 다양한 온도조건($0{\sim}400^{\circ}C$), 압력조건(0~20 bar)에서 입자마모 실험을 수행하였다. BET, 광학현미경, 입도분석기 등을 이용하여 실험 전, 후 입자를 분석 하였다. 또한 기존의 마모도 측정 방법인 ASTM D5757-95방법을 이용하여 층물질의 높이(4.4~10.2 cm) 및 수분 주입이 입자 마모에 미치는 영향에 대하여 확인하였다.

• 한국재료학회지
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• 제21권11호
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• pp.596-603
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• 2011

The very high temperature gas reactor (VHTR) is one of the next generation nuclear reactors for its safety, long-term stability, and proliferation-resistance. The high operating temperature of over 800$^{\circ}C$ enables various applications with high energy efficiency. Heat is transferred from the primary helium loop to the secondary helium loop through the intermediate heat exchanger (IHX). The IHX material requires creep resistance, oxidation resistance, and corrosion resistance in a helium environment at high operating temperatures. A Ni-based superalloy such as Alloy 617 is considered as a primary candidate material for the intermediate heat exchanger. In this study, the microstructures of Alloy 617 crept in pure helium and air environments at 950$^{\circ}C$ were observed. The rupture time in helium was shorter than that in air under small applied stresses. As the exposure time increased, the thickness of outer oxide layer of the specimens clearly increased but delaminated after a long creep time. The depth of the carbide-depleted zone was rather high in the specimens under high applied stress. The reason was elucidated by the comparison between the ruptured region and grip region of the samples. It is considered that decarburization caused by minor gas impurities in a helium environment caused the reduction in creep rupture time.

• 방사성폐기물학회지
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• 제19권2호
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• pp.161-176
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• 2021

In this study, the electrochemical behavior of Sm on the binary liquid Al-Ga cathode in the LiCl-KCl molten salt system is investigated. First, the co-reduction process of Sm(III)-Al(III), Sm(III)-Ga(III), and Sm(III)-Ga(III)-Al(III) on the W electrode (inert) were studied using cyclic voltammetry (CV), square-wave voltammetry (SWV) and open circuit potential (OCP) methods, respectively. It was identified that Sm(III) can be co-reduced with Al(III) or Ga(III) to form Al_zSm_y or Ga_xSm_y intermetallic compounds. Subsequently, the under-potential deposition of Sm(III) at the Al, Ga, and Al-Ga active cathode was performed to confirm the formation of Sm-based intermetallic compounds. The X-ray diffraction (XRD) and scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS) analyses indicated that Ga₃Sm and Ga₆Sm intermetallic compounds were formed on the Mo grid electrode (inert) during the potentiostatic electrolysis in LiCl-KCl-SmCl₃-AlCl₃-GaCl₃ melt, while only Ga₆Sm intermetallic compound was generated on the Al-Ga alloy electrode during the galvanostatic electrolysis in LiCl-KCl-SmCl₃ melt. The electrolysis results revealed that the interaction between Sm and Ga was predominant in the Al-Ga alloy electrode, with Al only acting as an additive to lower the melting point.

• 대한영양사협회학술지
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• 제22권2호
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• pp.131-142
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• 2016

The purpose of this study was to assess the physical activity and energy balance of weekdays and weekend in male high school students. Fifty healthy male high school students participated in this study. Anthropometric data were collected. Physical activity level (PAL) and energy intake for weekdays and weekend were calculated from a physical activity diary and food diary using the 24-hour recall method and interview. The resting metabolic rate (RMR) and estimated energy requirement (EER) were calculated from the prediction equations suggested in 2015 KDRIs. Total energy expenditure (TEE) was calculated by multiplying RMR by PAL. Mean age of subjects was $15.9{\pm}0.33years$. The daily pedometer counts were significantly higher in the weekdays (12,837 steps) than in weekend (6,661 steps) (P<0.001). The PAL of the weekdays ($1.63{\pm}0.17$) was significantly higher than that ($1.37{\pm}0.26$) of the weekend (P<0.001). PAL was significantly correlated with pedometer counts on the weekdays (r=0.495) and weekend (r=0.686). The total energy intakes ($2,847.2{\pm}681.5kcal$) and TEE ($3,046.3{\pm}437.3kcal$) of weekdays were significantly higher than those of the weekend. The results of this study would be useful to develop nutrition and exercise programs for male high school students on weekdays and weekend, respectively.

• Journal of Electrochemical Science and Technology
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• 제10권3호
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• pp.302-312
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• 2019

The voltage produced from the salinity gradient in reverse electrodialysis (RED) increases proportionally with the number of cell pairs of alternating cation and anion exchange membranes. Large-scale RED systems consisting of hundreds of cell pairs exhibit high voltage of more than 10 V, which is sufficient to utilize water electrolysis as the electrode reaction even though there is no specific strategy for minimizing the overpotential of water electrolysis. Moreover, hydrogen gas can be simultaneously obtained as surplus energy from the electrochemical reduction of water at the cathode if the RED system is equipped with proper venting and collecting facilities. Therefore, RED-driven water electrolysis system can be a promising solution not only for sustainable electric power but also for eco-friendly hydrogen production with high purity without $CO_2$ emission. The RED system in this study includes a high membrane voltage from more than 50 cells, neutral-pH water as the electrolyte, and an artificial NaCl solution as the feed water, which are more universal, economical, and eco-friendly conditions than previous studies on RED with hydrogen production. We measure the amount of hydrogen produced at maximum power of the RED system using a batch-type electrode chamber with a gas bag and evaluate the interrelation between the electric power and hydrogen energy with varied cell pairs. A hydrogen production rate of $1.1{\times}10^{-4}mol\;cm^{-2}h^{-1}$ is obtained, which is larger than previously reported values for RED system with simultaneous hydrogen production.