• 드라이브 ㆍ 컨트롤
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• 제12권3호
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• pp.52-59
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• 2015

An electro hydraulic poppet valve (EHPV) and a variable orifice poppet are assembled in a single block, which is referred to as a RHINO but is also generally called a pilot-operated flow control valve. In this study, we analyzed the structure and the operating principle for a RHINO applied in a 21-ton electric excavator system. The RHINO was experimentally tested to measure the dynamic responses and the pressure energy loss. In this test, we investigated the variation in the conductance coefficient according to the increase in the supply pressure under a constant current and a variation in the flow rate according to the increase in the current. Then, the geometrical shapes and the spring stiffness of the RHINO were considered to develop an analysis model. The characteristics (current-force and hysteresis) for the solenoid based on the experimental data were reflected in the analysis model that was developed, and the reliability of the analysis model was also verified by comparing the experimental and analytical results. The developed model is thus considered to be reliable for use in a wide range of applications, including optimum design, sensitivity analysis, parameter tuning, etc.

• Bulletin of the Korean Chemical Society
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• 제22권9호
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• pp.979-983
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• 2001

Thermoanaerobacter ethanolicus is a strictly anaerobic and thermophilic bacterium whose optimum temperature ranges over $65-68^{\circ}C.$ T. ethanolicus was known to contain a bipolar very long chain fatty acyl component such as $\alpha$, $\omega-1316-dimethyloctacosanedioate$, as one of the major membrane components. However, exact physiological role of this unusual component in the membrane remains unknown. Such a very long chain fatty acyl component, $\alpha$, ${\omega}-1316-dimethyloctacosanedioate$, dimethyl ester (DME C30), was isolated, and purified from the membrane of T. ethanolicus. As a function of added concentrations of the $\alpha$, $\omega-1316-dimethyloctacosanedioate$, dimethyl ester (DME C30) or cholesterol into the standard liposomes, the acyl chain ordering effect was investigated by the steady-state anisotropy with 1,6-diphenyl-1,3,5-hexatriene (DPH) as a fluorescent probe. Acyl chain order parameter (S) of vesicles containing DME C30 is higher comparing with phosphatidylcholine (PC) only vesicles. This result was discussed thermodynamically with the aid of the simulated annealing molecular dynamics simulations. Through the investigation of all the possible conformational changes of DME C30 or cholesterol, we showed that DME C30 is very flexible and its conformation is variable depending on the temperature comparing with cholesterol, which is rigid and restricted at overall temperature. We propose that the conformational change of DME C30, not the configurational change, may be involved in the regulation of the membrane fluidity against the changes of external temperature.

• Membrane and Water Treatment
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• 제10권6호
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• pp.471-484
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• 2019

The complex combination of organic contaminants in the wastewater made water treatment challenging; hence, organic matter in water bodies is usually measured in terms of organic carbon. Since it is important to identify the types of compounds when deciding suitable treatment methods, this study implemented a quantitative and qualitative analysis of the organic matter content in an actual graywater sample from Ulsan, Republic of Korea using mass spectroscopy (MS). The graywater was treated using adsorption to remove the organic contaminants. Using orbitrap MS, the organic matter content between an untreated graywater and the treated effluent were compared which yielded a significant formula count difference for the samples. It was revealed that CHON formula has the highest removal count. Isotherm studies found that the Freundlich equation was the best fit with a coefficient of determination ($R^2$) of 0.9705 indicating a heterogenous GAC surface with a multilayer characteristic. Kinetics experiments fit the pseudo-second order equation with an $R^2$ of 0.9998 implying that chemisorption is the rate-determining step between the organic compounds and GAC at rate constant of $52.53g/mg{\cdot}h$. At low temperatures, the reaction between GAC and organic compounds were found to be spontaneous and exothermic. The conditions for optimization were set to achieve a maximum DOC and TN removal which yielded removal percentages of 94.59% and 80.75% for the DOC and TN, respectively. The optimum parameter values are the following: pH 6.3, 2.46 g of GAC for every 30 mL of graywater sample, 23.39 hrs contact time and $38.6^{\circ}C$.

• 농업생명과학연구
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• 제52권6호
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• pp.13-25
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• 2018

Appropriate water level is the primary factor for the optimal yield of crop plants. The required water level varies according to the variety of the crops. In the present study, we investigated the optimum requirement of groundwater level(GWL) to grow sorghum and adzuki bean under paddy field soil. Here, we cultivated sorghum and adzuki bean using lysimeter filled with paddy soil under GWL 0 cm(NT) and GWL(20, 40 cm) where GWL 20 cm is maintained as a waterlogging condition. The plant growth promoting attributes were measured on the first day after treatment(0 DAT), 10 DAT and 20 DAT. The results showed that the growth parameter such as shoot length, leaf length, leaf width, and stem thickness of both sorghum and adzuki bean were constantly increased and were found higher at GWL 40 cm(except stem thickness and leaf width in sorghum at 20 DAT). The physiological parameters such as chlorophyll content and stomatal conductance were also found higher at GWL 40 cm in all DAT. In addition, the elements like P and K contents in adzuki bean, and Ca content in sorghum were constantly increased and was found higher in GWL 40 cm at all DAT. These results suggest that the GWL of 40 cm is appropriate for production of sorghum and adzuki bean especially in case of paddy soil.

• 한국전자통신학회논문지
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• 제14권3호
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• pp.453-460
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• 2019

짧은 참조 신호를 이용한 차동 카오스 편이 변조 (SR-DCSK)는 DCSK의 변형으로, 추가적인 복잡성 없이 데이터 전송 속도를 높이고 에너지 효율성을 향상시킨다. 그러나 최적 길이의 기준 신호를 적용해도 기존 DCSK 대비 SR-DCSK의 BER성능의 장점은 보이지 않는다. 본 논문에서는 기준 신호와 정보를 가진 신호에 각각 두 개의 스케일 계수 (scale coefficient)를 적용하여 SR-DCSK의 성능을 향상시키는 방법을 제안한다. 그리고 제안된 방법의 성능은 가우스 근삿법을 사용하여 BER로 분석한다. 그 후 도출한 BER 표현식을 기반으로, 주어진 시스템 파라미터에 대해 BER을 최소화하여 두 계수의 비율을 최적화한다. 제안된 방법의 BER은 두 스케일 계수의 최적 비율을 적용할 때 SR-DCSK 보다 많은 부분 개선되었다는 것을 시뮬레이션 결과로 확인한다.

• 한국항해항만학회:학술대회논문집
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• 한국항해항만학회 2019년도 춘계학술대회
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• pp.38-39
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• 2019

선박의 최적 항로 계획은 주어진 해양 환경에서 운항 시간 혹은 연료 소모량을 최소로 하는 항로 계획이다. 대양을 운항하는 선박의 최적 항로에 관한 기존 연구와 다르게, 본 연구에서는 연안에서 좌초 위험을 회피하는 선박의 항로 계획을 위한 최적화 방법을 제안하였다. Dijkstra 알고리즘을 사용하여 항로의 변경 지점을 찾고, 최적화 설계 변수를 엔진 회전수로 설정하여 연료 소모량이 최소가 되도록 최적화를 수행하였다. 엔진 회전수를 설정하는 방법은 출발지에서 도착지까지 고정 회전수로 설정하는 방법과 구간을 나누어 구간별 고정 회전수를 설정하는 방법을 사용하였다. 항로 탐색을 위해 고려한 해양 환경 요소는 바람, 파고, 조류이며 좌초 위험을 계산하기 위해 수심 정보를 사용하였다. 본 연구에서 제안한 방법을 목포와 제주를 오가는 선박을 대상으로 적용하여 최적의 항로를 결정하였으며, 최적 항로를 기존에 항해했던 항로와 비교하여 연료 소모량이 절감된 것을 확인하였다.

• 한국기계가공학회지
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• 제20권8호
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• pp.93-98
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• 2021

The complex effects of the machining parameters make it is difficult to control and predict surface roughness. The theoretical surface roughness observed during mechanical machining with a round tool is determined by the tool radius and pitch. However, it was revealed that other parameters, such as the depth of cut and cutting speed, also affect surface roughness. This study adapted the Taguchi method, which can analyze the effects of cutting parameters quantitatively with an efficient number of experiments, to optimize the parameters for better surface roughness. Experiments were designed based on an orthogonal array, and the quantitative effects on the surface roughness were analyzed using the S/N ratio. The surface roughness was affected by all parameters, especially the tool radius. The optimum cutting parameter values obtained in this study showed better surface roughness than the other combinations of the parameters.

• Computers and Concrete
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• 제29권 6호
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• pp.393-405
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• 2022

Lightweight concrete is a superior material due to its light weight and high strength. There however remain significant lacunae in engineering knowledge with regards to shear failure of lightweight fiber reinforced concrete beams. The main aim of the present study is to investigate the optimum usage of steel fibers in lightweight fiber reinforced concrete (LWFRC). Multi-scale finite element model calibrated with experimental results is developed to study the effect of steel fibers on the mechanical properties of LWFRC beams. To decrease the amount of steel fibers, it is preferred to reinforce only the middle section of the LWFRC beams, where the flexural stresses are higher. For numerical simulation, a multi-scale finite element model was developed. The cement matrix was modeled as homogeneous and uniform material and both steel fibers and lightweight coarse aggregates were randomly distributed within the matrix. Considering more realistic assumptions, the bonding between fibers and cement matrix was considered with the Cohesive Zone Model (CZM) and its parameters were determined using the model update method. Furthermore, conformity of Load-Crack Mouth Opening Displacement (CMOD) curves obtained from numerical modeling and experimental test results of notched beams under center-point loading tests were investigated. Validating the finite element model results with experimental tests, the effects of fibers' volume fraction, and the length of the reinforced middle section, on flexural and residual strengths of LWFRC, were studied. Results indicate that using steel fibers in a specified length of the concrete beam with high flexural stresses, and considerable savings can be achieved in using steel fibers. Reducing the length of the reinforced middle section from 50 to 30 cm in specimens containing 10 kg/m3 of steel fibers, resulting in a considerable decrease of the used steel fibers by four times, whereas only a 7% reduction in bearing capacity was observed. Therefore, determining an appropriate length of the reinforced middle section is an essential parameter in reducing fibers, usage leading to more affordable construction costs.

• 한국산업융합학회 논문집
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• 제25권4_2호
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• pp.699-706
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• 2022

In this study, Directed energy deposition (DED) among additive manufacturing is applied to repair damaged spindle key parts of planner miller. The material of the spindle key is SCM415, and the P21 Powder is used. In order to find the optimal deposition conditions for DED equipment, a single-line deposition experiment is conducted to analysis five parameters. The laser power affects the width, and the height is a parameter affected by coaxial gas and powder gas. In addition, laser power, powder feed rate, coaxial gas, and powder gas are parameters that affect dilution. Otimal deposition is that 400 W of laser power, 4.0 g/min of powder feed rate, 6.5 L/min of coaxial gas, 3.0 L/min of powder gas and 4.5 L/min of shield gas. By setting the optimum conditions, a uniform deposition cross section in the form of an ellipse can be obtained. Damage recovery process of spindle key consists of 3D shape design of the base and deposition parts, deposition path creation and deposition process, and post-processing. The hardness of deposited area with P21 powder on the SCM415 spindle key is 336 HV for the surface of the deposition, 260 HV for the boundary area, and 165 HV for the base material.

• 청정기술
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• 제29권1호
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• pp.53-58
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• 2023

This study shows the summary of the economic performance of excess electricity conversion to hydrogen as well as methane and returned conversion to electricity using a fuel cell. The methane production process has been examined in a previous study. Here, this study focuses on the conversion of methane to electricity. As a part of this study, capital expenditure (CAPEX) is estimated under various sized plants (0.3, 3, 9, and 30 MW). The study shows a method for economic optimization of electricity generation using a fuel cell. The CAPEX and operating expenditure (OPEX) as well as the feed cost are used to calculate the discounted cash flow. Then the levelized cost of returned electricity (LCORE) is estimated from the discounted cash flow. This study found the LCORE value was ¢10.2/kWh electricity when a 9 MW electricity generating fuel cell was used. A methane production plant size of 1,500 Nm³/hr, a methane production cost of $11.47/mcf, a storage cost of $1/mcf, and a fuel cell efficiency of 54% were used as a baseline. A sensitivity analysis was performed by varying the storage cost, fuel cell efficiency, and excess electricity cost by ±20%, and fuel cell efficiency was found as the most dominating parameter in terms of the LCORE sensitivity. Therefore, for the best cost-performance, fuel cell manufacturing and efficiency need to be carefully evaluated. This study provides a general guideline for cost performance comparison with LCORE.