• Applied Chemistry for Engineering
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• v.21 no.2
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• pp.205-210
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• 2010

In this study, a brass electrode gas discharge tube (GDT) was prepared to investigate its discharge characterization, which affects surge protection efficiency and lifetime of GDT. Discharge characterization of GDT using a brass electrode was investigated by changing applied voltage gradient and nitrogen gas pressure inside the GDT. As applied voltage gradient in GDT increased, electrical breakdown voltage and threshold energy largely increased and electrical breakdown time delay decreased. It was found that electrical breakdown voltage, electrical breakdown time delay, and threshold energy were largely decreased with decreasing the nitrogen gas pressure in GDT. As a result, electrical breakdown voltage, electrical breakdown time delay, threshold energy needed to be decreased to increase surge protection efficiency and lifetime. It was also found that the nitrogen gas pressure of GDT influenced strongly the performances as well as life span of it.

• The KIPS Transactions:PartC
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• v.16C no.6
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• pp.731-736
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• 2009

In wireless sensor network, many sensor nodes are distributed in the field. They communicate the sensing data each other and forward it to sink. Routing protocols, which define the delivery methods of sending data, affect to the lifetime of sensor network. This paper proposes RTAF that is a routing-tree construction algorithm of sensor nodes by a single flooding process in wireless sensor network. A routing tree is constructed by selecting a parent node using the forward-direction flooding packet and gathering children nodes using the reverse-direction flooding packet. In this process, a node with much energy becomes the parent node. And the routing tree is periodically reconstructed in order to distribute the loads of parent nodes. The proposed algorithm compared performance with Modified-LEACH using NS2 network simulation tool. The simulation result shows that the proposed algorithm constructs a routing-tree faster and reduced 40-80% in routing-tree construction packet.

• Journal of the Korean Magnetics Society
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• v.19 no.5
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• pp.186-190
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• 2009

We investigated the magneto-optical properties and application of diluted magnetic semiconductors Cd$_{1-x}$Mn$_x$Te crystals with various Mn contents grown using a vertical Bridgman method. This material crystallizes in the zinc-blende structure for values of x < 0.82. The band-gap energy was depended on Mn mole fraction x linearly and increased with decreasing temperature. The Faraday rotation was increased as the photon energy increased near to that of the fundamental band gap and its increased with increasing Mn mole fraction. Optical isolator using the Cd$_{0.62}$Mn$_{0.38}$Te crystal shows that the isolation and insertion loss are 45 dB and 0.35 dB at 650 nm, respectively.

• Journal of Energy Engineering
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• v.20 no.1
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• pp.26-29
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• 2011

A promising alternative technology is the potential use of ice slurries as a secondary refrigerant in conventional cooling process. Ice slurries behave almost like a liquid and can be pumped through pipes although the energy capacity of ice slurries per unit volume is considerably higher than that for chilled water or brine due to the latent heat capacity of the ice particles. To give the basic data for the design of cooling systems using ice slurries, experimental study has been conducted to find out the performance of the cooling coil of show-case with ice slurries. Despite the fact that ice slurries entering the cooling coil had at least $5^{\circ}C$ higher temperature than that of R22, it was still capable of providing a similar cooling performance than that obtained with R22.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.11 no.1
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• pp.9-16
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• 1991

The concept of damage is all-pervasive in structural engineering. It can be considered a state variable and defined to vary from 0(no damage) to 1(failure). Thus, the factor of safety against failure, the most important aspect of a structure, cannot be assessed without evaluating the damageability of a structure under load. It is the objective of the research reported herein to study the behavior of concrete under repeated load applications. Concrete is known to deteriorate under such loading, i.e., it suffers damage of increasing degree. Its response to future loading is a function of the amount of damage sustained during previous load exposures. The same can be said about reinforced concrete members and entire structures, but here we wish to consider only plain concrete and express some of its material properties as functions of the degree of sustained damage. The work described herein is based on the stipulation that the energy dissipation capacity of plain concrete is a material property and the damage accumulates in direct proportion to the degree to which the energy dissipation capacity is being exhausted, in some analogy to both high- and low-cycle failure behavior of materials.

• 한국신재생에너지학회:학술대회논문집
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• 2010.06a
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• pp.185.1-185.1
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• 2010

원격탐사(remote sensing)란 관측 대상과의 접촉 없이 멀리서 정보를 얻어내는 기술을 말한다. 기상관측분야에는 이미 소다(SODAR) 장비가 폭넓게 사용되거 왔으나 최근 풍력자원평가(wind resource assessment)를 위한 풍황측정에 SODAR와 더불어 라이다(LIDAR)가 적극적으로 활용되기 시작하고 있다. 참고로 SODAR(SOnic Detection And Ranging)는 수직 및 동서 남북 방향으로 음파를 발생시키고 대기유동에 의해 산란 반사된 에코를 수신하여 진동수 변화와 반사에코 강도를 측정하여 각 방향의 에코자료를 벡터 합성함으로써 풍향 및 풍속을 산출하는 원리이다. 반면 LIDAR(Light Detection And Ranging)는 비교적 최근에 풍황측정 용도로 개발된 레이저 탐지에 바탕을 둔 원거리 센서로, 공기입자(먼지, 수증기, 구름, 안개, 오염물질 등)에 의해 산란된 레이저 발산의 도플러 쉬프트(Doppler shift)를 이용하여 풍향 및 풍속을 측정하는 원격탐사 장비이다. 풍력자원평가 측면에서 라이다는 그 정확도가 IEC61400-12에 의거한 풍황탑(met-mast) 측정자료 다수와의 비교검증 실측평가(Albers et al., 2009)를 통하여 입증된 바 있다. 한편 한국에너지기술연구원에서 운용 중인 라이다 시스템은 그림 1의 우측 그림과 같이 1초에 $360^{\circ}$를 스캔하여 50지점에서 반사되는 레이저를 스펙트럼으로 측정하되 설정된 관측높이에서 풍속은 샘플링 부피(sampling volume)의 평균값으로 정의된다. 그런데 샘플링 부피는 설정된 관측높이로부터 상하 12.5m, 총 25m의 높이구간에서 관측한 스펙트럼의 평균값을 그 중앙지점에서의 풍속으로 환산하는 알고리듬(algorithm)을 채택하고 있다. 따라서 비선형적으로 변화하는 풍속연직분포 관측 시 풍속환산 알고리듬에 의한 측정오차가 개입될 가능성이 존재하는 것이다. 이에 본 연구에서는 라이다에 의한 풍속연직분포 측정 시 샘플링 부피의 구간 평균화 과정에서 발생하는 불확도(uncertainty)를 정량적으로 분석함으로써 라이다에 의한 풍속연직분포 관측의 불확도를 정량평가하고자 한다.

• 한국신재생에너지학회:학술대회논문집
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• 2010.06a
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• pp.217.2-217.2
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• 2010

자연 상태에서의 가스하이드레이트의 존재는 물의 빙점보다 높은 온도에서 가스 수송관이 막히는 사고가 관내에 생성된 하이드레이트에 의한 것으로 규명된 이후영구동토지역이나 심해저에 부존되어 있는 막대한 매장량으로 인해 매우 활발한 연구가 최근에 진행되고 있다. 가스하이드레이트는 수분의 량에 비해 대량의 가스를 함유하므로 인위적인 가스하이드레이트를 제조하기 위하여 여러 가지 연구 중 하이드레이트 반응을 촉진하는 촉진제(promoter)와 생성을 억제하는 억제제(inhibitor)를 찾는 연구가 활발히 이루어지고 있다. 계면활성제와 고분자물질이 이들의 다양한 첨가제로 현제 사용되고 있다. 이러한 연구에서 메탄가스하이드레이트 형성에 영향을 미치는 대상물질로 선택한 DME(Dimethane Ether)는 산소 함유율이 34.8wt%인 함산소연료로 최근 신에너지로 부상하고 있으며, 해외 가스전 개발과 맞물려서 상용화단계에 들어와 있다. DME의 물리화학적인 특성으로는 상온의 온도에서 약5기압의 압력으로 액화 시킬 수 있다. 마취성이 강한 디에틸에테르와는 달리 마취성이 없을 뿐만 아니라 인체에 무해한 무색기체로 세탄가가 60가까이되어 경유(세탄가 55) 대체연료로 내연기관의 실증사업이 진행되고 있다. 이러한 특성을 갖고 있는 DME가 메탄가스 하이드레이트 생성에는 어떤 영향을 미치는지를 본 연구에서는 실험을 통해서 분석을 수행하였다. 실험과정에는 세 단계로 구분하여 진행하였는데 첫 번째 단계에서는 메탄가스만으로 하이드레이트 생성조건을 실험분석하였고, 두 번째 단계에서는 DME가스를 먼저 주입한후 동일 온도에서 메탄가스를 주입시켜 하이드레이트 생성 압력을 실험측정하였다. 마지막 단계에서는 DME가스를 약 두 배 정도 많이 주입한 후 동일 온도에서 메탄가스를 주입하여 하이드레이트 생성 압력을 측정하였디. 이러한 단계별 과정을 다소 온화한 $-5^{\circ}C{\sim}4^{\circ}C$의 온도 범위에서 반복적으로 수행하였다. 실험결과에서는 메탄만의 하이드레이트 형성보다 빙점($0^{\circ}C$) 이하의 온도 범위에서는 DME가 메탄하이드레이트 형성에 촉진제 역할을 하였고, 빙점 이상의 온도에서는 억제제의 역할을 하는 것으로 측정되었다. 또한 첨가된 DME의 양에 따라 촉진제의 역할과 억제제의 역할에 확연한 차이를 보였다. 추후 실험에서는 좀더 넓은 농도, 온도 및 압력범위에서 재현성 실험을 추가로 수행할 것도 제안한다.

• Journal of Digital Contents Society
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• v.19 no.4
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• pp.815-819
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• 2018

In this study, we investigate balance of a biped robot applying Foot Placement Estimator (FPE) in simulation. FPE method is used to determine a stable foot location for balancing the biped robot when an initial orientation of the robot body is statically unstable. In this case, the 6-DOF biped robot with point foot is modelled considering contact and friction between foot and the ground. For simulation, the mass of the robot is 1 kg assuming the center of robot mass (COM) is located at the center of the robot body. The height from the ground to the COM is 1 m. Robot balance is achieved applying stable foot locations calculated from FPE method using linear and angular velocities, and the height of the COM. The initially unstable angular postures, $5^{\circ}$ and $-5^{\circ}$, of the robot body are simulated. Simulation results confirm that the FPE method provides stable balance of the robot for all given unstable initial conditions.

• Transactions of the Korean Society of Mechanical Engineers
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• v.17 no.5
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• pp.1227-1236
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• 1993

In conventional thermodynamics, energy is regarded as a physical quantity transferring from one system to another, but in present study, the real energy is regarded as a physical quantity coming out from one interaction and absorbing into another interaction between two systems. To reconstruct thermodynamics with such a point of view, available work is distinguished from half work in conventional work concepts, and a special space named reversible world is proposed in which every process is reversible and the only measurable quantity is available work and just the equality between the intensities of two systems can be verified. As results, thermodynamic laws are arranged into two principles in the reversible world-conservations of energy elements and conservation of available energy. It means the exsistences of state properties corresponding to transferring energy elements and the available work. The former are extensive properties and the later is named potential work which is a property of the composite system and a kind of mathematical distance. The conventional available energy (exergy) and internal energy can be explained as the special cases of potential work, and the conventional first law of thermodynamics can be derived from the principle of the conservation of available energy. With these new concepts, the description of thermodynamic processes is more comprehensive. The second law of thermodynamics is no longer needed in the reversible world.

• Applied Biological Chemistry
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• v.47 no.1
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• pp.33-40
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• 2004

Thermodynamic properties of ubiquitin transient folding intermediate were studied by measuring folding kinetics in varying temperatures and denaturant concentrations. Through quantitative kinetic modeling, the equilibrium constant, hence folding free energy, between unfolded state and intermediate state in several different temperatures were calculated. Using these values, the thermodynamic parameters were estimated. The heat capacity change $({\Delta}C_p)$ upon formation of folding intermediate from unfolded state were estimated to be around 80% of the overall folding reaction, indicating that ubiquitin folding intermediate is highly compact. At room temperature, the changes of enthalpy and entropy upon formation of the intermediate state were observed to be positive. The positive enthalpy change suggests that the breaking up of the highly ordered solvent structure surrounding hydrophobic side-chain upon formation of intermediate state. This positive enthalpy was compensated for by the positive entropy change of whole system so that formation of transient intermediate has negative free energy.