• 드라이브 ㆍ 컨트롤
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• 제12권4호
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• pp.60-70
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• 2015

A front-end loader (FEL) mounted on an agricultural tractor is one of the most commonly used implements for farm work. However, when the tractor carries material using the bucket attached to the FEL on a sloping ground, the materials can spill or roll back over the operator due to the tilted body, thereby requiring the bucket surface to remain level at a constant value regardless of varying slopes. In this study, an active system for controlling the angle of the FEL bucket on a tractor based on the real-time measurement of ground slopes was developed to enable the bucket to constantly remain level. A FEL simulator operated based on an electro hydraulic proportional valve (EHPV) was constructed in the laboratory to develop a proportional-integral-derivative (PID) controller forming a virtual electronic control unit (ECU) on the computer, which could automatically adjust the bucket angles depending on varying input angles while sending SAE-J1939 associated messages via CAN BUS to the EHPV. The different parameter values for the PID controller due to the gravity effect of the bucket were determined using a manual PID tuning method while assuming that the tractor travels on either an ascending slope or a descending slope. The developed PID control-based self-leveling system showed a mean of steady-state errors of within $1^{\circ}$ and a mean of delayed times of ~ 0.8s when the step input of $+20^{\circ}$ was given, implying that the developed system and control algorithm would be effective in maintaining the bucket angle at a certain value. Future studies include the improvement of the control algorithm to reduce such a time delay as well as the application of the developed algorithm to the FEL mounted on a tractor tested at a testing ground.

• Nuclear Engineering and Technology
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• 제51권8호
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• pp.1939-1950
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• 2019

The MELCOR code useful for a plant-specific hydrogen risk analysis has inevitable limitations in prediction of a turbulent flow of a hydrogen mixture. To investigate the accuracy of the hydrogen risk analysis by the MELCOR code, results for the turbulent gas behavior at pipe rupture accident were compared with CFX results which were verified by the American National Standard Institute (ANSI) model. The postulated accident scenario was selected to be surge line failure induced by station blackout of an Optimized Power Reactor 1000 MWe (OPR1000). When the surge line failure occurred, the flow out of the surgeline was strongly turbulent, from which the MELCOR code predicted that a substantial amount of hydrogen could be released. Nevertheless, the results indicated nonflammable mixtures owing to the high steam concentration released before the failure. On the other hand, the CFX code solving the three-dimensional fluid dynamics by incorporating the turbulence closure model predicted that the flammable area continuously existed at the jet interface even in the rising hydrogen mixtures. In conclusion, this study confirmed that the MELCOR code, which has limitations in turbulence analysis, could underestimate the existence of local combustible gas at pipe rupture accident. This clear comparison between two codes can contribute to establishing a guideline for computational hydrogen risk analysis.

• 한국통신학회논문지
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• 제39C권2호
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• pp.191-198
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• 2014

NMEA(National Marine Electronic Association) 2000은 선박에서 사용되는 다양한 데이터(위치정보, 엔진 상태 등)들을 다른 전자장비에 통신하기 위한 규격으로, 이 선박 네트워크를 기반으로 한 범용 게이트웨이를 구현하였다. 이를 위해 NMEA 2000 Stack(ssJ1939) source와 CAN device driver source를 다양한 통신프로토콜을 사용할 수 있는 보드에 포팅하고 CAN, RS232, USB, Ethernet port를 갖추고 있는 이 보드에 연결하였다. 개발한 게이트웨이에서 변환된 선박 데이터의 검증을 위해, PC 기반의 시뮬레이터 프로그램과 모니터링 프로그램을 이 보드에 연결하여 NMEA 2000 network를 통해 선박의 데이터를 볼 수 있게끔 구성하였다. PC의 시뮬레이터 프로그램에서 생성된 선박 데이터정보를 게이트웨이와 NMEA 2000 network를 통해 모니터링 프로그램에서 분석하고 게이트웨이의 성능을 검증하였다. 기존의 게이트웨이가 주로 단일의 특정한 통신 프로토콜을 지원하는 것에 대비하여 Wi-Fi, Ethernet, Bluetooth, USB, RS232 등 다양한 통신 프로토콜을 지원함으로써 사용자가 원하는 통신방식을 이용하여 원격에서 데이터를 모니터링 하도록 설계하고 구현하였다.

• Nuclear Engineering and Technology
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• 제52권9호
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• pp.1939-1944
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• 2020

Pool boiling heat transfer of a copper microporous coating was experimentally studied in borated water with a concentration of boric acid from 0.0 to 5.0 vol percent (vol%) to determine the effect of boric acid on boiling heat transfer in water. A high-temperature, thermally conductive microporous coating (HTCMC) was created by sintering copper powder with an average particle size of 67 ㎛ onto a 1 cm × 1 cm plain copper surface with a coating thickness of ~300 ㎛ within a furnace in a vacuum environment. The tests showed that the nucleate boiling heat transfer coefficient (NBHT) of HTCMC became slightly less enhanced as the concentration of boric acid increased but the NBHT coefficient values were still significantly higher than those of the plain surface. The critical heat flux (CHF) values from 0 to 1.0 vol% were maintained at ~2,000 kW/㎡, and then, they gradually decreased down to ~1,700 kW/㎡ as the concentration increased further to 5.0 vol%. It is believed that the micro-scale pores of the HTCMC were partially blocked by the high boric acid concentration during the nucleate boiling such that the small bubbles were not effectively created using the HTCMC reentrant cavities as the boric acid concentration increased.

• Asian-Australasian Journal of Animal Sciences
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• 제31권12호
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• pp.1939-1945
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• 2018

Objective: This study was conducted with the objectives to examine the impacts of inorganic selenium (Se) and different types and levels of organic selenium on the serum and tissues Se status and antioxidant capacity in broiler breeders. Methods: Five hundred and forty 48-wk-old Lingnan Yellow broiler breeders were randomly assigned to 6 dietary treatments, provided same basal diet (0.04 mg/kg of Se) with 0.15 mg/kg, or 0.30 mg/kg of Se from sodium selenite (SS) or from selenium-enriched yeast (SY) or from selenomethionine (SM). The broiler breeders were slaughtered after an 8-wk experiment. Results: The results showed that SM was better than SY and SS, 0.30 mg/kg level was better than 0.15 mg/kg level in Se deposition (p<0.05) in serum, liver, kidney, pancreas and muscle; in antioxidant status, organic selenium had better effects than SS in broiler breeders (p<0.05), but SM and SY had a similar result, and 0.15 mg/kg level was better than 0.30 mg/kg (p<0.05). Conclusion: The results demonstrated the evident advantage of supplementation of broiler breeders with 0.15 mg/kg SM, which improved tissue Se concentrations and antioxidant status, and can be considered as the best selenium source.

• Journal of Plant Biology
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• 제38권3호
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• pp.305-317
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• 1995

한반도 중, 남부지역에서 가장 높은 산악지역인 지리산지의 냉온대 및 아고산대의 침광혼효림과 상록침엽수림의 임상선태류군락을 식물사회학적 관점에서 연구하였다. 그 결과 고등식물군락의 조성과 관련하여 다섯 임상선태류군락을 식별하였다. A 조릿대-구상나무/비꼬리이끼-수저잎산주목이끼군락, B. 비비추-구상나무/곱슬명주실이끼-등덩굴초롱이끼군락, C. 구상나무/아기호랑꼬리이끼-가지윤이끼군락, D. 구상나무-가문비나무/아기호랑이끼-깃털이끼군락, E. 구상나무-가문비나무/수풀이끼-겉창발이끼군락. 이들 군락 중 A, B, C, D 등 네 군락은 비교적 낮은 해발영역 (1200-1700m)의 침광혼효림에 분포하며, 냉온대의 종요소에 의해 특징화되었다. 이들 군락은 쇠물푸레-구상나무군집에 속하는 하나의 분층군락으로 확인되었다. E군락은 보다 높은 해발영역(1700m 이상)에 분포하며, 아한대; 아고산대와 한 대; 고산대에 한정분포하는 주극요소의 종군에 의해 특징화되었다. 또 이 군락은 월귤-가문비나무군강에 속하는 구상나무-가문비나무군집의 하나의 분층군락임이 밝혀졌다. 지금까지 많은 연구자들이 지리산지 1200m 이상에서 정상 근처까지 분포하는 침엽수림을 아고산대의 식생으로 취급하였다. 그렇지만, 현 연구결과는 식물사회학적 입장에서 침광혼효림과 진성아고산침엽수림의 경계가 1700m가 된다는 사실을 명백히 하였다. 선태류의 종의 풍부성은 E군락에서 가장 높았으며, 나머지 네 군락은 비슷한 수준이었다. 선태류의 종다양도지수에 있어서 H'와 D는 B와 E군락에서 높았으며, A와 C군락에서 낮고, D군락은 중간적인 값을 나타내었다. 균등도지수(J')의 값은 고도의 증가와 함께 감소하여, 높은 해발영역의 E군락에서 가장 낮았다. Bray-Curtis 서열법의 결과는 이 다양성 분석과 상기의 두 삼림대의 구분이 정당함을 나타내었다. 조사된 지리산지의 선태류의 분류군은 25과, 46속, 73종, 1아종, 2변종으로 구성되었다.