• Aerospace Engineering and Technology
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• v.6 no.1
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• pp.201-208
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• 2007

A fuel pump and turbine rotordynamic design is performed for a 75 ton thrust liquid rocket engine. A distance from the rear bearing to the turbine was considered as a design parameter for load distribution of the bearings. Asynchronous eigenvalue analysis was performed as a function of rotating speeds, turbine mass and bearing stiffness to investigate critical speed of the fuel pump and turbine. From the numerical analysis, it is found that the effect of the front bearing stiffness is negligible in the critical speed due to the large mass moment of inertia of the turbine. With the rear bearing stiffness over $2{\times}10^{8}N/m$ and the turbine mass below 20 kg, the critical speed of the fuel pump and turbine in long shaft case is at least 70 % higher than the operating speed 11,000 rpm.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.21 no.12
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• pp.2318-2324
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• 2017

Quantum cryptography, which is emerging as a next generation password, is being studied by quantum cryptographic transfer protocols and quantum secret communication. Quantum key transfer protocol can be used in combination with the modern password because of the inefficiency of the use of the password, or the use of OTP(one time password). In this paper an algorithm for direct communication by means of direct cryptographic communications rather than quantum keys. The method of implementing quantum secure direct community was adopted using 2-channel methods using Einstein gravity field. Two channels were designed to adopt a quantum secret communication protocol that applies time delay between 2-channels of channel to apply time difference between 2-channels. The proposed time delay effect reflects the time delay by reflecting the gravitational lensing phenomenon. Gravity generator with centrifugal acceleration is incorporated in the viscometer, and the time delay using this implies the correlation between the variance of the metametry.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.38 no.5
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• pp.399-406
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• 2014

Three-dimensional flow and aerodynamic loss in the tip-leakage flow region of a turbine blade equipped with both a pressure-side winglet and a suction-side squealer have been measured for the tip gap-to-span ratio of h/s = 1.36%. The suction-side squealer has a fixed height-to-span ratio of $h_s/s$ = 3.75% and the pressure-side winglet has width-to-pitch ratios of w/p = 2.64%, 5.28%, 7.92% and 10.55%. The results are compared with those for a plane tip and for a cavity squealer tip of $h_{ps}/s$ = 3.75%. The present tip delivers lower loss in the passage vortex region but higher loss in the tip-leakage vortex region, compared to the plane tip. With increasing w/p, its mass-averaged loss tends to be reduced. Regardless of w/p, the present tip provides lower loss than the plane tip but higher loss than the cavity squealer tip.

• Fire Science and Engineering
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• v.21 no.3
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• pp.41-46
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• 2007

The combustion characteristics of surface forest fire fuels was analysed using variable external irradiation level. The characteristics such as ignition time, ignition temperature, critical heat flux and mass loss rate were measured. Fuel samples were exposed to incident heat fluxes from 8 to $50\;kW/m^2$. For the measurement of various combustion characteristics, the size of specimen holder was $100\;mm{\times}100\;mm{\times}12\;mm$ and the fuel samples grinded by electric mill were the fallen leaves of Quercus variabilis and Pinus densiflora. As results, the occurrence of ignition is possible to the heat flux more than $9\;kW/m^2$. The fuel of Pinus densiflora keeps its high temperature longer than that of Quercus variabilis during the combustion process. The results of measurement shows that the maximun and average mass loss rate of Quercus variabilis larger than that of Pinus densiflora.

• Clean Technology
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• v.21 no.1
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• pp.62-67
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• 2015

We have developed a versatile method for the preparation of chemically linked graphene/multi-walled carbon nanotubes (MWNTs) hybrid materials via simple acid-catalyzed dehydration reaction between graphene oxide (GO) and amine-functionalized MWNTs (af-MWNTs). In this condition, ketone (-C=O) groups in GO and primary amine (-NH₂) moieties in af-MWNTs readily react to form imine (-C=N-) linkage. The chemical structures of graphene/MWNTs hybrid materials have been investigated using various microscopic and spectroscopic measurements. As a result of the synergetic effects of hybrid materials such as improved surface area and the superior structural restoration of graphitic networks, the hybrid materials demonstrate improved capacitance with excellent long-term stability. Furthermore, controlled experiments were conducted to optimize the weight ratio of graphene/MWNTs in hybrid materials. The highest capacitance of 132.4 F/g was obtained from the GM7.5 material, in which the weight ratio between graphene and MWNTs was adjusted to 7.5/1, in 1M KOH electrolyte at a scan rate of 100 mV/s.

• Fire Science and Engineering
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• v.24 no.1
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• pp.122-127
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• 2010

The combustion characteristics of phenol foam were analysed using variable external irradiation level (20, 25, 35, 50, and $70kW/m^2$) and in the mixture gas of oxygen/nitrogen. The oxygen index were carried out from the oxygen index tester (KS M ISO 4589-2) and ignition time, critical heat flux, and mass loss rate were carried out from the mass loss calorimeter (ISO 5660-1). As the results of this study, the critical heat flux and average mass loss rate were $28.99kW/m^2$ and $0.56{\sim}1.77g/m^2s$ respectively at the variable external irradiation level. And the limited oxygen index were 45.1% in mixture gas of oxygen/nitrogen. In conclusion, we knew that phenol foam had the best performance than other foam materials in fire safety from all data of this study.

• Journal of the Korean Recycled Construction Resources Institute
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• v.6 no.4
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• pp.304-310
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• 2018

The aim of the research is to provide possibility of quality controlling by rheological properties for lightweight foamed concrete. The lightweight foamed concrete achieves its low density by containing air bubbles (foam) produced during the mixing process. Therefore, containing foamed volume during setting period is critical for the securing the performance as an insulating material. In this research, regarding foam collapse during the setting period, rheolgocial properties of fresh state lightweight foamed concrete were assessed to get its relationship with volume stability, or foam stability. For the experiment regarding foaming factors including mixing time, mix design of contents for materials, rheological properties of fresh state lightweight foamed concrete were tested with its density and settling depth. Based on the settling depth with various factors, relationship with rheological properties was analyzed, and especially, close relationship of plastic viscosity and settling depth was found. Therefore, from the results of this research, it is considered to contribute on suggesting a new approach of quality controlling for lightweight foamed concrete using rheological test method.

• Proceedings of the Korea Water Resources Association Conference
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• 1998.05a
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• pp.395-403
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• 1998

오염원의 이송확산에 관한 많은 연구들이 수행되어 왔으나 특히 비포화 영역에서 오염원 이송확산을 측정하는 것은 매우 어려운 것으로 알려지고 있다. 비포화 토양에서의 오염원 이송확산은 매질의 함수량 변화에 영향을 받기 때문에 오염원 거동특성을 이해하려면 비포화 흐름 분석을 선행한 후 오염원의 이송확산 특성을 분석하여야 한다. 본 연구에서는 비포화 영역에서의 오염원 이송특성을 분석하기 위하여 TDR(Time Domain Reflectometry)을 이용하여 비포화 흐름 및 오염원 이송을 측정하였다. 이를 위하여 본 연구에서는 TDR을 이용하여 오염원 이송을 측정하는 방법을 개발하였으며, 이 방법을 이용하여 1차원의 토양기둥시료에서 비포화 흐름 및 오염원 이송확산에 관한 실험을 수행하고 수치모형을 적용함으로써 비포화 영역에서 오염원의 이송확산에 관한 거동특성을 규명하였다. 본 연구에서는 두 종류의 국내 토양시료(SUS, KUS)를 사용하였는데, 토양의 물리적 특성을 예비실험을 통하여 규명한 후 토양기둥시료를 이용한 본실험을 수행하였다. 비포화 천이흐름하의 오염원 이송확산 실험에서는 급격한 습윤전선의 전진에 따른 종형의 함수량변화를 관측할 수 있었고, 이때 오염원의 농도는 함수량의 천이구간의 중심점으로부터 전방영역의 농도분포가 습윤전선에서의 함수량 분포와 유사한 종형을 이루고 있음을 관측할 수 있었다. 비포화 정상흐름하의 오염원 이송확산 실험에서는 오염원이 이송하며 농도 천이구간이 확장되어지는 전형적인 형태를 보였다. 또한 예비실험에서 측정한 매개변수를 입력자료로하여 수행한 수치결과와 실험결과를 비교하였는데 비포화 흐름특성은 실험결과와 수치결과가 정량적으로 일치하는 경향을 보였으나, 오염원 이송확산 특성은 정량적으로 수치결과가 실험결과보다 더 많이 확산되는 경향을 보였다. 따라서 수치모형을 현장에 적용할 경우 확산지수 결정에 주의하여야 할 것으로 판단된다. 즉, 수치모형에 적용할 확산지수는 BTC 실험을 통하여 측정한 확산지수, 수치확산, 흡착계수, 적용영역의 크기 등을 고려하여 결정하여야 한다. 특히 본 논문에서는 TDR을 이용하여 최초로 천이상태의 함수량과 오염원 농도를 측정하였는데 이를 위하여 전기전도도와 함수량관계를 추정하는 식을 제안하였으며, 전기전도도와 토양수 농도, 전기전도도와 함수량의 관계를 이용한 천이상태의 오염원 농도 측정방법을 개발하였다. 특히 제안식에서는 한계함수량의 개념을 도입하여 전기전도도와 함수량관계를 추정하므로 추정식의 실험값 반영 정도를 증가시켰다. 본 연구에서 제안된 식을 이용하여 추정된 전기전도도와 함수량관계는 다른 제안식에 비하여 개선된 결과를 보여 주었고, 본 연구에서 개발한 오염원 농도 측정법을 이용하여 측정한 결과 함수량이 0.15이하에서는 측정오차가 크지만 함수량이 0.15이상일 경우 매우 좋은 결과를 보였는데 질량평형을 검토한 결과 약 5-10%의 오차율을 보였다. 따라서 본 논문에서 개발된 천이상태의 오염원 농도측정법은 용존 오염물질의 이송에 관한 정확한 실험을 제공할 것으로 판단된다.

• Journal of Life Science
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• v.10 no.3
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• pp.254-261
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• 2000

In order to observe the bioactivity of ovariectomized rats, ovariectomized group (Ovx), nonovariectomized group (Sham), ovariectomized Vitamin C-treat group (Ovx+Vit C), ovariectomized Vitamin E-treat group (Ovx+Vit E) and ovariectomized Vitamin C+Vitamin E-treat group(Ovx+Vit C+E) were made. Lipidperoxides of liver and kidney, serum total cholesterol and HDL-cholesterol were investigate as follows. Lipidperoxides of liver and kidney in Ovx group were 1.78 times and 1.61 times increased compared to Sham group respectively. But, they were significantly decreased in Ovx+Vit C group, Ovx+Vit E group, Ovx+Vit C+E group compared to Ovx group. Serum total cholesterol in Ovx group was increased 2.57 times compared to Sham group. Injections of each substance such as ascorbate, tocopherol, mixture (C+E) make data of Cholesterol become low. When especially Vit C is injected, the data of cholesterol lowed by about 94%. Serum HDL-cholesterol in Ovx group decreased 36.7% compared to Sham group. And as the result of the measurement of SOD, Catalase, and GPx which are antioxidant enzyme, SOD and Catalase activities in Ovx group much higher than in Sham group. Based on the results, it is supposed that more produced free radicals increased antioxidant enzyme. And it is also thought that vitamin can inhibit aging by reducing antioxidant enzyme.

• Journal of Korean Society of Steel Construction
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• v.16 no.1 s.68
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• pp.81-89
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• 2004

The vibration analysis of the circular arch as a member of a structure has been an important subject of mechanics due to its various applications to many industrial fields. In particular, circular arches with variable cross section are widely used to optimize the distribution of weight and strength and to satisfy special architectural and functional requirements. The Generalized Differential Quadrature Method (GDQM) and Differential Transformation Method (DTM) were recently proposed by Shu and Zou, respectively. In this study, GDQM and DTM were applied to the vibration analysis of circular arches with variable cross section. The governing equations of motion for circular arches with variable cross section were derived. The concepts of Differential Transformation and Generalized Differential Quadrature were briefly introduced. The non-dimensionless natural frequencies of circular arches with variable cross section were obtained for various boundary conditions. The results obtained using these methods were compared with those of previous works. GDQM and DTM showed fast convergence, accuracy, efficiency, and validity in solving the vibration problem of circular arches with variable cross section.