• Journal of the Society of Naval Architects of Korea
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• v.36 no.3
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• pp.41-49
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• 1999

A feasibility study is performed for practical application of a Ventilating Water-Jet(VWJ) propulsor which attracts new attention as a candidate propulsor for super-high speed vessels. Super-cavitating foil sections are adopted for the rotor blades since the rotor is operating at ventilating condition. Wedge type and cavitator type foil sections are used for the design of rotor blades. Other geometric characteristics of rotors are selected from the Kaplan type ducted propeller rotors. The test section of KRISO cavitation tunnel is modified to perform open-water tests of the VWJ propulsors. The tests are performed both at fully-submerged and free-jet conditions. Ventilation occurred at the free-jet condition by sucking the air in the downstream side of the rotor, which easily develops as super-cavitation when the rotor operates at lower advance coefficients. Spoilers are attached at the trailing end of the pressure side of the blade section, in order to increase the lift force.

• Journal of Radiation Protection and Research
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• v.21 no.4
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• pp.285-296
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• 1996

The energy spectra in the air and water of several ${\gamma}-ray$ sources such as Cr-51, Cs-137, Mn-54, Zn-65 have been investigated using the NaI(T1) scintillation detector. General response functions, which can curve fit the measured spectra, have been constructed. We have found that the constructed response functions can successfully represent the measured spectra in the water as well as in the air, It is possible, by comparing the relevant parameters of the response functions, to quantitatively characterize the changing features of the measured spectra as obtained with varying the water depth. Of the response function parameters, those which affect the shape of the full-energy Peak have most notably changed. Besides, those parameters which affect the shapes of the flat continuum, the Compton continuum and edge have also shown slight changes with varying the water depth.

• Proceedings of the Korean Vacuum Society Conference
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• 1999.07a
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• pp.48-48
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• 1999

티타늄 알루미나이드 합금은 이들의 강도나 고온 특성 때문에 초음속 비행기의 구조물질이나 수소를 연료로 사용하는 비행기의 엔진물질로 각광받고 있다. 그러나 티타늄 알루미나이드 합금들은 이들이 갖는 규칙적인 미세구조로 인하여 실온에서 낮은 연성을 나타내는 단점이 있다. 실온에서 낮은 연성을 갖는 티타늄 알루미나이드 합금의 단점은 텅스텐, 물리브덴, 니오비움, 탄타륨, 바나디움 등의 베타 안정화 물질들을 첨가함으로서 어느정도 극복되고 있다. 따라서 티타늄 알루미나이드 합금이 초음속 비행기의 구조 물질이나 수소를 사용하는 엔진 물질로 사용되기 위해서는 이 물질들의 산화연구가 필수적이다. 지금까지 티타늄의 산화연구에서 알루미늄이나 니오비움의 역할에 대해서는 여러 연구자들이 연구를 한 바 있다. Chaze와 Coddet는 알루미늄이 티타늄에서 산소의 용해도를 감소시키고, Chen과 Rosa는 니오비움이 티타늄에서 산화물 형성율을 낮춘다는 것을 각각 알아냈다. 그러나 지금까지 티타늄 알루미나이드의 산화연구는 충분하지 못했다. 지금까지 티타늄 알루미나이드의 산화연구에서 밝혀진 산화운동학의 내용은 가열온도와 가열시간에 따라 크게 다른 두 개 혹은 그 이상의 산화물을 갖는다는 것이다. 본 연구의 목적은 여러 가지 티타늄 알루미나이드 합금의 산화특성을 밝히는 것이다. 이를 위하여 첫 번째 실험은 실온 공기 중에서 자연적으로 산화된 여러 가지 티타늄 알루미나이드 합금들($\alpha$2,$\beta$,${\gamma}$)을 초고진공($\leq$10-11Torr)속에 넣고, 시료의 온도를 실온에서 100$0^{\circ}C$까지 변화시키면서 AES(Auger Electron Spectroscopy)와 ISS(Ion Scattering Spectroscopy)를 사용하여 각각의 온도에서 여러 가지 시료들의 표면조성을 조사했다. 두 번째 실험은 티타늄 알루미나이드 시료를 고순도 공기(hydrocarbon$\leq$0.1^g , pp m) 중에서 각각 $600^{\circ}C$에서 100$0^{\circ}C$까지 가열하여 산화시켰다. 이 시료의 산화도는 각각의 가열온도에서 가열시간을 변하시키면서 TGA(Thermogravimetric Apparatus)로 측정했다. 실온 공기중에서 자연적으로 산화된 여러 가지 티타늄 알루미나이드 합금들을 초고진공속에 넣어 100$0^{\circ}C$까지 가열한 실험에서는 이들 시료에 포함된 알루미늄의 양에 따라서 표면 조성이 크게 다른 것을 알 수 있었다. 그리고 고순도 공기 중에서 100$0^{\circ}C$까지 가열하여 산화시킨 티타늄 알루미나이드 산화물의 산화기구는 명백한 3단계 포물선 산화의 특성을 나타냈다.

• Journal of the Korea institute for structural maintenance and inspection
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• v.20 no.5
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• pp.116-122
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• 2016

This study was intended to evaluate the properties of concrete incorporating stone powders which are created during crushing natural stones to produce crushed aggregates. For concretes with 0~30 wt.% partial replacement fine aggregates with stone powders, experiments of slump, air content, strength and drying shrinkage were carried out. The experiments found that the increase of the amount of stone powders sharply decreased slump and air content. Partially using stone powders instead of fine aggregates was found to increase both compressive and tensile strength slightly. Substituting higher amount of stone powders presented higher drying shrinkage. When HRWRA was added into the concrete with stone powders in order to obtain workability similar to that of plain concrete without stone powders for the same water-cement ratio and unit weight of cement, air content increased with the amount of HRWRA but strength and drying shrinkage were hardly affected by adding HRWRA.

• Journal of the Korea institute for structural maintenance and inspection
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• v.20 no.5
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• pp.1-8
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• 2016

This paper presents an evaluation of engineering properties in TDFA(Tire Derived Fuel Ash)- based concrete in early age. Concrete containing 0.5 of w/b(water to binder) ratio and 20% of FA(Fly Ash) replacement ratio are prepared, and FA content are replaced with TDFA from 3% to 12% for evaluating the effect of TDFA on fresh and hardened concrete properties. With higher than 6% of TDFA replacement ratio, workability is significantly worsened but it is improved with more SP(Super plasticizer) and AE(Air Entrainer) agent. Concrete with 6~12% of TDFA shows reasonable strength development and better resistance to carbonation and chloride attack in spite of early-aged condition. However concrete with 6% TDFA shows poor resistance to freezing and thawing action due to insufficient air content. If air content and workability are obtained, replacement of TDFA to 12% can be used for concrete with FA.

• Magazine of the Korea Concrete Institute
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• v.4 no.1
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• pp.89-96
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• 1992

It is generally known that the frost-resistance of concrete is much affected by the air content in concrete and by the air void system or air distribution. And also the frost-resistance is believed to vary with the stre¬ngth of concrete. This article is prepared to describe, based on experiment, the effect of the air content and the air void system, particularly the effect of the spacing factor, on the freeze-thaw resistance of the high strength conc¬rete. For this purpose, I first worked on Non-AE concrete to make its compressive strength set about 400 to 500 kg/em'. However, the freeze-thaw test on the Non-AE concrete resulted in low durability factor, I.e., 10-2~0%. Thus to enhance the durability, another supplementary step was needed. I used AE admixture. which enhanced durability by changing the air content from 2% to 12%. The frost-thaw test was then performed 500 cycles on the 20 kind of concrete mixtures which differ in unit cement content and in water-cement ratio. Keywords : frost -resistance, air content, air void system, air distribution, spacing factor, freeze-thaw test, dur ability factor. capillary cavity, Linear Traverse Method.

• Journal of Environmental Science International
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• v.1 no.1
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• pp.47-51
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• 1992

Volatile organic rompounds(VOCs) present in the VOCs-contaminated water are released to air while showering and their air concentrations depend on the shower parameters, resulting in the variation of the VOCs breath concentration. The present study evaluated the key shower parameters(water temperature and inhalation duration) that affect the inhalation exposure to air chloroform while showering, by determining chloroform breath concentration. The chloroform breath concentrations increased with water temperature and inhalation duration increase. The two inhalation exposure conditions which resulted in the greatest chloroform breath contentration difference were a 5 min-inhalation exposure with warm water and a 15 min-inhalation exposure with hot water. The chloroform breath concentration was almost three times higher after later exposure. The mathematical model analyzing the relationship between two key shower parameters and breath concentration normalized to water concentration fits quite Ivell with the experimental data at a probability of p : 0.0001.

• Journal of the Korea Institute of Building Construction
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• v.10 no.5
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• pp.87-94
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• 2010

Construction projects are based on the actual field, so if the construction schedule that is established in the construction plan is delayed or extended for various reasons, construction companies are vulnerable to claims, and thus strive to complete a building within the planned timeline by shortening the construction time. Therefore, this study surveyed technicians in apartment construction in Gwangju, and studied their perceptions of the actual conditions of process control, construction time needs, goals, and methods. The results showed that the organization of the process control department and professional employees was lacking compared to other regions. The need for construction time was perceived as high, while the reduction of the construction cost was perceived as low. Regarding the reduction goal, they perceived highly the preparation for the delay of construction time and various claims, and for the reduction method, they mentioned the extension of working hours and the increase in employees. Based on the results of this study, technicians should consider that a reduction of construction time not only can make up for a delay in construction, but is also closely related to improvements in production through reduction of cost, and increased international competitiveness.

• Journal of the Korean Society of Radiology
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• v.13 no.7
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• pp.1025-1033
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• 2019

Although magnetic resonance imaging without linear hardening of CT is recognized as a method of obtaining high contrast of tissue and excellent resolution image in brain disease and head and neck examination, magnetic susceptibility artifact is generated in case of metal implants in the oral cavity, which is an obstacle to image diagnosis. Therefore, an effort was made in this thesis to find a method to reduce artifacts caused by dental implants and prosthesis in MRI. Implant-induced artifacts in magnetic resonance imaging showed that the signal size increased with shorter TE in GE technique and was inconsistent with water temperature change. In SE technique as well, the signal size of water was generally higher than that of air, but the signal to noise ratio (SNR) was not different by air and temperature. In EPI technique, images with fewer artifacts were obtained quantitatively and qualitatively when there was more water than air, and the signal to noise ratio was measured the highest, especially at water temperatures of 20° and 30°. In conclusion, when examining using the EPI technique rather than the SE or the GE technique, obtaining brain diffusion using a 20° and 30° water bag reduces the magnetic susceptibility artifacts caused by implants and prosthesis, suggesting that it may provide images with high diagnostic value.

• 한국전기화학회:학술대회논문집
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• 1998.10a
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• pp.16-16
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• 1998