• Journal of the Korean Geosynthetics Society
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• v.10 no.4
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• pp.19-28
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• 2011

This paper presents the results of an investigation into the effect of cyclic wetting-drying on the compressive strength characteristics of decomposed granite soils. A series of plane strain compression (PSC) tests were performed on test specimens with varying fine contents under different wetting-drying cycles to investigate the change in compressive strength under the process of wetting-drying cycles. The effect of wetting-drying cycles on the structural particle rearrangement at a micro-scale level was also examined using scanning electron microscope (SEM) tests. It was shown that the soil containing larger fines showed more significant decrease in compressive strength compared with the soils with less fines. Also found was that the wetting-drying cycle did not have significant effect on the particle arrangement.

• Proceedings of the Korean Institute of Intelligent Systems Conference
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• 2008.04a
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• pp.37-40
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• 2008

본 논문은 2차전지의 최적화된 충 ${\cdot}$ 방전 제어를 위한 지능형 제어 알고리즘을 제안한다. 고용량화된 2차 전지는 높은 에너지 밀도를 갖게 되고, 과충전에 의한 발화와 과방전에 의한 열화 특성으로 위험성이 존재하므로 정밀하게 전안, 전류를 제어하지 않으면 그 성능을 발휘하기 어렵다. 전지의 위험성을 제거하고 성능을 최대로 활용하기 위해서는 모든 전지 셀의 충방전 전류량을 조절하여 모든 전지의 셀간 전압 차이를 밸런스 제어 해야 한다. 하지만 전지의 특성에 영향을 미치는 임피던스가 사이클 라이프와 온도 변화 등 외부 환경에 의해 비선형적으로 변화하기 때문에 전지의 셀간 밸런스 제어에 어려움이 있다. 따라서 본 논문에서는 지능형 충 ${\cdot}$ 방전 제어 알고리즘을 이용하여 임피던스의 변화에도 적응 가능 하고 2차 전지가 가질 수 있는 최대 에너지를 사용할 수 있는 최적화된 방법을 제안한다. 또한 제안하는 알고리즘과 제어회로의 컴퓨터 시뮬레이션을 통해 그 효용성을 입증한다.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.8 no.6
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• pp.1325-1331
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• 2007

In order to investigate the cooling capacity of an air-conditioner applying a variable capacity compressor and the temperature characteristics on a condenser and an evaporator, the experiment on the operation characteristics of the air-conditioner was performed along a compressor operation ratio and an indoor/outdoor temperatures, under a cooling operation mode. The system characteristics were measured by the psychrometric calorimeter. The cooling capacity increased with decreasing the outdoor temperature and increasing the indoor temperature. Also, it increased with increasing the compressor operation ratio. The temperature of the condenser was more sensitive for the variation of the outdoor temperature and the temperature of the evaporator was more sensitive for the variation of the indoor temperature. The operation characteristics of the cycle used in this present were also analyzed by a pressure-enthalpy chart.

• Journal of the Korean Society for Nondestructive Testing
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• v.20 no.4
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• pp.269-275
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• 2000

It is well recognized that damage resulting from freeze-thaw cycles is a serious problem causing deterioration and degradation of concrete. In general, freeze-thaw cycles change the microstructure of the concrete ultimately leading to internal stresses and cracking. In this study, a new method for one-sided stress wave velocity measurement has been applied to evaluate freeze-thaw damage in concrete by monitoring the velocity change of longitudinal and surface waves. The freeze-thaw damage was induced in a $400{\times}350{\times}100mm$ concrete specimen in accordance with ASTM C666 using s commercial testing apparatus. A cycle consisted of a variation of the temperature from -14 to 4 degrees Celsius. A cycle takes 4-5 hours with approximately equal times devoted to freezing-thawing. Measurement of longitudinal and surface wave velocities based on one-sided stress wave velocity measurement technique was made every 5 freeze-thaw cycle. The variation of longitudinal and surface wave velocities due to increasing freeze-thaw damage is demonstrated and compared to determine which one is more effective to monitor freeze-thaw cyclic damage progress. The variation in longitudinal wave velocity measured by one-sided technique is also compared with that measured by the conventional through transmission technique.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.36 no.2
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• pp.171-179
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• 2012

Cooling of hot sections, especially the turbine nozzle and rotor blades, has a significant impact on gas turbine performance. In this study, the influence of precooling of the cooling air on the performance of gas turbines and their combined cycle plants was investigated. A state-of-the-art F-class gas turbine was selected, and its design performance was deliberately simulated using detailed component models including turbine blade cooling. Off-design analysis was used to simulate changes in the operating conditions and performance of the gas turbines due to precooling of the cooling air. Thermodynamic and aerodynamic models were used to simulate the performance of the cooled nozzle and rotor blade. In the combined cycle plant, the heat rejected from the cooling air was recovered at the bottoming steam cycle to optimize the overall plant performance. With a 200K decrease of all cooling air stream, an almost 1.78% power upgrade due to increase in main gas flow and a 0.70 percent point efficiency decrease due to the fuel flow increase to maintain design turbine inlet temperature were predicted.

• Journal of the Korean Society of Marine Environment & Safety
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• v.24 no.6
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• pp.834-840
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• 2018

In this study, the characteristics of air pollutant emissions from ships' engines have been investigated by conducting E2 and E3 cycle mode tests. A engine 360Ps (Doosan L126TIH engine) and 400kW dynamometer Horiba-Schenck were utilized for engine tests. The FTIR analyzer and SPC were used to measure exhaust gas (NOx, SOx etc.) and PM (particulate matter), respectively. The results showed that the emissions of THC and CO produced from engine were increased with the increase of sulfur content in fuel oils at E2 and E3 cycle modes. The kinetic viscosity of the fuel increased as the sulfur content of the fuel increased, thereby the specific fuel oil consumption (SFC) of the engine improved. This result is considered to be due to improved combustion conditions due to increased average diameters of sprayed particles and due to increased kinetic viscosity under constant fuel injection pressure in this study. In the case of NOx emission, this study showed no significant change in amount of sulfur content.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.35 no.12
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• pp.1285-1292
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• 2011

The characteristics of a semiconductor chiller system with EEV have been experimentally studied. Three experiments on temperature changes (increase and decrease), load variation, and control precision were conducted to investigate the operating characteristics of the semiconductor chiller. The power consumption was 8.9 kW during increase in temperature. The required time was 37.5 min for CH1 and 39.5 min for CH2. Moreover, the time required for falling temperature was 26.5 min. The control precision for partial load operation was relatively low compared to that of a full load operation. In addition, the CH2 equipped with a step motor showed better control precision. The power consumed by the chiller for process cooling water was 1.8 kW, which was one-half of that consumed during the refrigeration cycle. The objective of this study is to provide an optimal control guideline for the semiconductor chiller design.

• Korean Chemical Engineering Research
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• v.59 no.3
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• pp.339-344
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• 2021

In order to improve the PEMFC (Proton Exchange Membrane Fuel Cell) durability, it is important to accurately evaluate the durability of the membrane in a short time. Recently, DOE (Department of Energy) reported a protocol that combines the chemical and mechanical durability of membranes to evaluate them effectively. This protocol applies chemical/mechanical deterioration to the membrane by repeating wet/dry while OCV (Open Circuit Voltage) holding. The problem of this protocol is that it is highly affected by electrode degradation due to change cycles in OCV and that the evaluation time is long. By using oxygen instead of air as the cathode gas while leaving the other conditions of the DOE protocol as it is, the durability evaluation time could be reduced from 408 hours to 144 hours. By reducing the number of voltage change cycles to 1/3, the electrode degradation due to the voltage change cycle was reduced to 1/12 when oxygen was used compared to air at the end, thereby enabling more accurate evaluation of polymer membrane durability.

• Korean Chemical Engineering Research
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• v.62 no.3
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• pp.246-252
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• 2024

In this study, impurities such as Li and F were removed from waste graphite through citric acid treatment, and changes in structural properties, capacity, and cycle stability of regenerated graphite were observed accordingly. Regenerated graphite pretreated in a nitrogen atmosphere was treated with citric acid, and its structure and characteristics were analyzed through SEM (Scanning Electron Microscope), FT-IR (Fourier Transform Infrared spectroscopy), XRD (X-ray Diffraction), and XPS (X-ray Photoelectron Spectroscopy). Waste graphite that was not treated with acid had a rapid decrease in capacity before 70 cycles, but graphite that had been treated with citric acid showed a capacity of 302.9 mAh g^-1 and a capacity retention rate of 93.1% at 100 cycles. In addition, despite changes in current density in rate performance, samples treated with citric acid showed 340.2 mAh g^-1 performance at 1.0C without change in capacity. As a result, it was confirmed that citric acid treatment not only effectively removed impurities and showed a high capacity retention rate, but also showed stability even at high current densities.

• Journal of Korea Game Society
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• v.15 no.1
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• pp.115-124
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• 2015

This research analyzed the case of Ncsoft to study the organizational learning, exploitation and exploration that create dynamic capability in hypercompetitive environment. First of all, we demonstrated the activities of exploitation and exploration in Ncsoft according to the life cycle of online game industry. An exploitation related to routine, learning and fit with existing environment brings about incremental innovation. In contrast, an exploration associated with non-learning, flexibility with changing environment results in radical innovation. We examined them based on the life cycle of its various game services. NCsoft that built the leading position in online game industry focused the exploitation activities at the stage of beginning period and growth, whereas NCsoft has increased the activities of exploration at period of mature. In addition, the firm conducts an exploration for its brand new game services and R&D. Conversely, An exploitation is conducted for sustainable updating of patch service and marketing and system building. The result implies that online game companies create sustainable competitive advantage using the balance between exploitation and exploration.