• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.27 no.5
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• pp.303-306
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• 2014

In this paper, by using a dual frequency liquid crystal material, we propose a liquid crystal device with a fast response characteristics. The dual frequency liquid crystal material has a positive dielectric anisotropy value at a low frequency. With a high frequency, the dielectric anisotropy becomes negative. Therefore, the relaxation process is governed by not only the elastic deformation, but also the dielectric interaction. The measured decay time and rise time were 0.88 ms and 0.33 ms, respectively.

• Asian-Australasian Journal of Animal Sciences
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• v.16 no.6
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• pp.818-822
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• 2003

In order to investigate the effect of different sources of energy on intake and nutrient utilization from urea molasses mineral block (UMMB), rumen fermentation pattern and blood biochemical constituents, 18 intact and 9 rumen fistulated male Murrah buffaloes aged about 3 years and average weight 310.8 kg were randomly allocated into three groups of 9 animals in each, thus each group having 6 intact and three rumen fistulated buffaloes. All animals were fed individually for 90 days. All buffaloes were offered wheat straw as basal roughage and urea molasses mineral block for free choice of licking. Three different energy sources viz., barley grain, (group I), maize grain (group II) and jowar green (group III) were offered to meet their nutrient requirement as per Kearl (1982). At the end of feeding trial, a metabolism trial of 7 days duration was carried out on intact animals to determine the digestibility of nutrients. Rumen fermentation studies were carried out on rumen fistulated animals. After the metabolism trial blood was collected from intact animals to estimate the nitrogen constituents in blood serum of animals fed on different sources of energy. Results revealed no significant difference in the intake of UMMB in three groups. Similarly, the intake of DM (kg), DCP (g) and TDN (kg) per day was similar in three groups statistically. The apparent digestibility of dry matter (DM), organic matter (OM), ether extract (EE) and nitrogen free extract (NFE) was significantly (p<0.05) more in group II than group III, whereas the digestibility of DM, OM and NFE was similar in group I and II. The digestibility of crude fiber (CF) and all the fiber fractions i.e. NDF, ADF, cellulose and hemicellulose was alike in 3 groups. Nitrogen balance (g/d) was significantly (p<0.05) more in group III as compared to group I and II, which were alike statistically, though the N intake (g/d) was similar in 3 groups but N balance (g/d) was significantly (p<0.05) less in group III as compared to other 2 groups. Significantly (p<0.05) higher concentration of total volatile fatty acids (TVFA), total nitrogen (TN) and its fractions were observed in group I and II as compared to group III. There was no effect on rumen pH, rumen volume and digesta flow rate due to different sources of energy in 3 groups. Similarly the blood serum biochemical parameters (NH3-N, urea-N and total protein) were statistically identical in 3 groups.

• Electronics and Telecommunications Trends
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• v.26 no.6
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• pp.21-36
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• 2011

우리나라 전체 에너지 사용량의 40% 정도를 차지하고 있는 아파트형 주거 밀집공간, 대규모 상업건물, 정부 및 대기업의 사무용 공공건물에서 에너지 사용을 절감하기 위한 방안으로 기존 건물 위주의 수동적 제어방법에서 한 단계 앞선 최신의 ICT 기술을 접목하여 능동적으로 건물 에너지를 관리하는 방법이 강구되고 있다. 특히 소비자의 움직임 및 사용공간 정보를 활용하여 소비자의 만족도를 저해하지 않으면서 건물의 에너지 사용량을 최소화하기 위한 기술이 논의되고 있다. 즉, 조명, 냉난방/공조, 전기기기의 에너지 사용량을 30%까지 절감하기 위한 기술이 연구되고 있는데, 본 고에서는 사용자의 만족도는 향상시키면서 건물 에너지는 절약할 수 있는 기술동향에 대해 언급한다.

• Journal of the Korean Society of Industry Convergence
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• v.24 no.4_1
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• pp.377-385
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• 2021

High voltage direct current(HVDC) systems has been an alternative method of a power transmission to replace high voltage alternate current(HVAC), which is a traditional AC transmission method. Due to technical limitations, Line commutate converter HVDC(LCC-HVDC) was mainly used. However, result from many structural problems of LCC-HVDC, the voltage source converter HVDC(VSC-HVDC) are studied and applied recently. In this paper, after analyzing the reactive power and output voltage ripple, which are the main problems of LCC-HVDC, the characteristics of each HVDC are summarized. Based on this result, a new LCC-HVDC structure is proposed by combining LCC-HVDC with the MMC structure, which is a representative VSC-HVDC topology. The proposed structure generates lower reactive power than the conventional method, and greatly reduces the 12th harmonic, a major component of output voltage ripple. In addition, it can be easily applied to the already installed LCC-HVDC. When the proposed method is applied, the control of the reactive power compensator becomes unnecessary, and there is an advantage that the cut-off frequency of the output DC filter can be designed smaller. The validity of the proposed LCC-HVDC is verified through simulation and experiments.

• Applied Chemistry for Engineering
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• v.23 no.1
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• pp.119-123
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• 2012

This study presents the effect of oxygen on the $NH_3$ selective catalytic reduction (SCR) by Mn/$TiO_2$ catalyst. The lattice oxygen of catalysts is participate in the low temperature SCR, and the gaseous oxygen directly takes part in the rexoidtion of reduced catalyst. These redox properties of oxygen an play important role in SCR activity and the available capability of lattice oxygen depends on the manganese oxidation state of the catalyst surface. $MnO_2$ species has a higher redox property than that of $Mn_2O_3$ species on deposited $TiO_2$ surface and these manganese oxide states strongly depend on the $TiO_2$ surface area.

• 한국신재생에너지학회:학술대회논문집
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• 2010.06a
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• pp.152.2-152.2
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• 2010

기후변화, 석유자원 고갈 우려 등으로 인하여 그린에너지기술 개발에 대한 중요성은 크게 증가하고 있다. 그 가운데, 글로벌화된 경쟁구도 확대와 급속한 기술개발 속도로 인하여 국가간 또는 기업간 기술 개발 경쟁은 더욱 심해지고 있다. 이러한 상황하에서 그린에너지기술 개발을 위한 국제협력의 중요성은 더욱 증가하고 있다. 이에 각 국은 제도적, 경제적 지원을 통한 그린에너지기술 개발 및 국제협력을 적극 지원하고 있다. 그러나 우리나라의 경우 에너지기술 관련 R&D 예산 중 국제공동연구 비중은 0.6%로 선진국에 비해 지원 규모가 부족한 실정이며, 그린에너지기술 국제협력을 위한 기초 정보 역시 부족한 상황이다. 따라서 본 연구에서는 그린에너지기술 분야의 국외 선도 업체 및 기관을 대상으로 기술수준 및 협력의향을 조사하여 대외협력 맵을 구축하였다. 우선 '그린에너지 전략로드맵'상의 15대 기술 분류에서 상세 분석을 위한 주요 에너지기술을 선정하고 기술별 하위 전략품목별로 현황 조사를 실시하였다. 국내 전문가를 대상으로 1차, 2차 설문을 통하여 국제협력 추천 업체 및 기관, 기술수준을 조사하였으며, 조사된 국외 추천 선도 업체 및 기관을 대상으로 설문을 통하여 협력의향과 협력유형을 조사하였다. 조사된 자료를 통해 기술수준과 협력의향을 기준으로 4가지 유형으로 분류하여 대외협력 맵을 구성하고 구축된 대외협력 맵을 통해 국제협력 추진을 위한 시사점을 도출하였다.

• Journal of the Korean Society of Marine Environment & Safety
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• v.26 no.5
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• pp.561-568
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• 2020

A performance analysis was conducted according to changes in inflow velocity and the tip speed ratio of a portable horizontal-axis hydro turbine that can be used for marine leisure sports and outdoor activities by using the commercial computational fluid dynamics software ANSYS CFX. By using the analysis result and flow field analysis, the design was reviewed and the performance of the device was confirmed. In addition, data necessary to improve the performance of the hydro turbine were acquired by performing an additional performance analysis according to the variable blade pitch angle. The results among the numerical analysis cases show that the highest performance at all inflow velocities and blade pitch angles if achieved at a tip speed ratio of 4. The output power was found to be 30 W even under some conditions below the design flow rate. Among the numerical analysis cases, the highest output power (~ 85 W) and power coefficient (~ 0.30) were observed at an inlet flow rate of 1.5 m/s, a blade pitch angle of 3°, and a tip speed ratio of 4.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.41 no.7
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• pp.683-689
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• 2017

We have carried out the development for hydraulic breaker which can be operated by optimal mode with ICT convergence technology. This developed system can predict the rock properties. Moreover, this system can maximize the energy efficient with intelligent control of hydraulic system. In order to provide the optimal impact force, this system can measure the descending depth of piston with the proximity sensor and discriminate the rock properties with the measuring data and control the piston stroke using solenoid valve eventually. In addition, we have developed the controller, display module and operating device for cascade (multi-level impact) system and applied the module which can communicate each system by wireless communications. In conclusion, the control system which can control the multi-level impact in accordance with strength of rocks has been developed and approved by several field tests.

• Composites Research
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• v.34 no.1
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• pp.1-7
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• 2021

Fiber-reinforced thermoplastic composites are applied to transport industries to lightweight of body, and applications will be expanded gradually. In this study, the impregnation and mechanical properties of continuous glass fiber (GF) reinforced polycarbonate (PC) composites were evaluated with different molecular weights of PC. The continuous GF reinforced PC composite were prepared by using GF fabric and PC film via continuous compression molding method. The melting flow index and tensile strength of PC matrix were evaluated with different molecular weights. Mechanical properties (tensile, flexural, and compressive) and pore rate of GF/PC composite were evaluated with different molecular weights of PC. The fracture behavior was analyzed to fracture surface of GF/PC composite using FE-SEM images. As these results, it was condition of representing the best mechanical property that the GF/PC composite was prepared by using PC of 20,000 g/mol as matrix.

• Composites Research
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• v.33 no.6
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• pp.346-352
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• 2020

In mobility industries, the use of thermoplastic composites increased dynamically. In this study, the mechanical and impregnation properties of continuous glass fiber (GF)/polypropylene (PP) composite were evaluated with different GF contents. The GF/PP commingled fiber was manufactured with different GF contents and continuous GF/PP composite was manufactured using continuous compression molding process. Tensile, flexural, and impact test of specimens were evaluated with different GF contents. The fracture behavior of specimens was proved using field emission-scanning electron microscope images of fracture area and impregnation property was evaluated using dynamic mechanical analyzer and interlaminar shear strength. Finally, the GF/PP composite was the optimized mechanical and impregnation properties using 50 wt.% GF/PP commingled fiber.