• Transactions of the Korean Society of Mechanical Engineers
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• v.16 no.9
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• pp.1615-1626
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• 1992

In this study, vibrations and resulting acoustic radiations from an elastic beam impacted by a steel ball were studied theoretically and experimentally. First the transverse vibrations of free-free elastic beams are analysed with modal analysis technique. The impact forces are modeled with the Hertz's theory and the contanct duration is compared with the measured values. Also the calculated beam vibrations are verified with the experimental results. Then the acoustic radiations due to the beam vibration are studied numberically and experimentally. The acousticpressure is calculated assuming the beam has an elliptical cross-section. The predicted acoustic pressure is compared with the measured value. It was found that both the predicted beamvibrations using the Hertz's theory and the estimated acoustic pressure under the assumption of an elliptical cross- section are in very good agreements with the measured values.

• Journal of Adhesion and Interface
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• v.2 no.1
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• pp.18-22
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• 2001

Surface morphology of [poly(vinylidene fluoride)/poly(methyl methacrylate)] (PVDF/PMMA) was investigated on the basis of atomic force microscopy and differential scanning calorimeter measurements. The surface of (PMMA/PVDF) and (H14-PMMA/PVDF) blend films was fully composed with PVDF crystals. Although the difference of surface free energy between PMMA and PVDF is increased with increasing carboxyl group content in PMMA, however, in the case of (H24-PMMA/PVDF) blend film surface, the existence of aggregated H-PMMA was observed. It was found that the degree of surface enrichment of the blend is more affected by the magnitude of intermolecular interaction than the surface free energy difference, Besides, the introduction of carboxyl group for miscible (PVDF/PMMA) blend decreased the miscibility in the blend.

• Computational Structural Engineering
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• v.11 no.1
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• pp.191-204
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• 1998

The general formulation for free vibration and stability analysis of unsymmetric thin-wared space frames is presented in case where the shear deformation effects are neglected. The kinetic and total potential energies are derived by applying the extended virtual work principle, introducing displacement parameters defined at the arbitrarily chosen axis and including warping deformation and second order terms of finite semitangential rotations. In formulating the finite element procedure, cubic Hermitian polynomials are utilized as shape functions of the two node space frame element. Mass, elastic stiffness, and geometric stiffness matrices for the unsymmetric thin-walled section are evaluated, and load-correction stiffness matrices for off-axis distributed loadings are considered. In order to illustrate the accuracy and practical usefulness of this formulation, finite element solutions for the free vibration and stability problems of thin-walled beam-columns and space frames are presented and compared with available solutions.

• Journal of Wetlands Research
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• v.23 no.3
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• pp.234-241
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• 2021

This paper contributes to the understanding of the effect of pulley on the performance of the vortex turbine in free water surface. The experimental work was to analyze the rotation, voltage and current of the turbine due to physical factors (vortex height, velocity, effective head, etc.) at flow rates ranging from 0.0069 to 0.0077 m³/s in the inlet channel. As a result, the experimental values showed that voltage, current and rotational speed of the vortex turbine decreased with increasing the pulley ratio regardless of the blade type. The efficiency of straight blade and twisted blade was 52 % at the gear ratio of 0.45, whereas the efficiency of small twisted blade was 54 % at the pulley ratio of 0.21. The highest amount of the energy generated by the water free vortex turbine occurred within a pulley ratio of 0.5. The efficiency of this vortex turbine was observed at 0.2 ~ 58 % depending on the pulley ratio.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.48 no.9
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• pp.691-701
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• 2020

An actuator mixer design using convex optimization technique situation where the propulsion system of an electric VTOL UAV during vertical take-off and landing maneuvers is proposed. The attainable control set to analyze the impact from failure of each motor and propeller can be calculated and illustrated using the properties of the convex function. The control allocation can be defined as a convex function optimization problem to obtain an optimal solution in real time. The mixer is implemented using a convex optimization solver, and the performance of the control allocation methods is compared to the attainable control set. Finally, the proposed mixer is compared with other techniques with nonlinear sux degree-of-freedom simulation.

• Korean Journal of Optics and Photonics
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• v.29 no.2
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• pp.77-84
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• 2018

We analyze the link availability of terrestrial free-space optical (FSO) communication systems in Korea. For this purpose, we utilize several theoretical models to calculate the power losses induced by absorption and scattering in the atmospheric channel, using five-year meteorological data for three major cities in Korea (Seoul, Busan, and Daejeon). Also, we estimate the power variations at the receiver caused by scintillation in the data. Those power losses and variations are used to estimate the availability of FSO links in the three cities. The results show that link availability is estimated to be over 95% in Daejeon for a 3.5-km FSO link, when the transmitter power and receiver diameter are greater than 10 dBm and 7 cm respectively. Slightly worse link availabilities are obtained for Busan and Seoul.

• Journal of Korean Philosophical Society
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• v.116
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• pp.181-206
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• 2010

It is widely recognized that human beings have moral responsibility for their actions because they have free will to choose and control their acts. Unlike natural phenomena, however, human acts cannot be interpreted with simple, visible ones. Human acts are quite different from natural phenomena because they come about through a number of complicated, invisible phases taking place in our mind. In addition, human actions are under the influence of internal and external factors. Those various internal and external factors are divided into four sectors as follows; (1) the factors that can fall under control of our free will, (2) the factors in the interim phase that could come under our control, (3) the factors that are partially determined that we cannot choose or control over, and (4) the factors that completely determined, and can't be chosen or controlled. we have to pay attention to the fact that we can choose or control the internal and external factors that influence human action. However, there are still factors that are impossible to choose or control with our will. So it is highly unreasonable to hold accountable for actors by means of the factors that can't be chosen or controlled. Hence, the society should be also accountable for the acts of actors influenced by heredity and environment. For this, Politics should affect the external, undesirable, and uncontrollable factors beyond actors power. Education has to exert its influence over the internal and genetic factors by instilling sound values in human mind, too. It is because happy and desirable future will be possible by giving equal opportunities to us including the youth.

• Journal of Korean Society of Environmental Engineers
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• v.22 no.2
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• pp.241-249
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• 2000

In this study, UV-catalyzed $H_2O_2$ oxidation and $H_2O_2$ oxidation to remove contaminants from photo processing chemicals were investigated at various conditions. Photo processing chemicals contains high concentrations of organic compounds and has very low biodegradability. Hydrogen peroxide is subjected to gradual decomposition as metastable substance. In the process, short-lived and highly reactive hydroxyl radicals are formed. The decomposition can be significantly accelerated by use of appropriate catalyst, such as ultraviolet radiation. The experiments were conducted in a UV-free reflecting reactor in batch and a high-pressure mercury lamp was used as UV source. Mixing, cooling and ventilation of the reactor were operated during experiments. In $UV/H_2O_2$ oxidation and $H_2O_2$ oxidation, the removal efficiencies of $COD_{Cr}$, TOC and chromaticity increased with the increase of $H_2O_2$ dosage and were higher in the controlled pH condition of 3 than in original pH condition of 8. In $UV/H_2O_2$ oxidation under the optimum condition of pH 8 and 1.3 stoichiometric $H_2O_2$ dosage, the removal efficiencies of $COD_{Cr}$, TOC and chromaticity were 47.5%, 75.0% and 91.5% respectively and $BOD/COD_{Cr}$ ratio was significantly increased from 0.04 to 0.21.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.40 no.1
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• pp.105-110
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• 2020

This study provides a method and data for predicting the flight initiation wind speed of wind-borne debris. From the force equilibrium acting on debris including aerodynamic and inertia forces, the equation for predicting the flight initiation wind speeds are presented. Wind tunnel tests were carried out to provide necessary aerodynamic data in the equation for the debris with various aspect ratios. The proposed equation for flight initiation wind speeds was validated from free flying tests in the wind tunnel. The flights of debris were mostly initiated by slip when width to thickness was less than 10, otherwise overturning were dominant. The actual flight initiation speeds were lower than that of the computed ones. The surface boundary layer flow and the gap between the debris and surface might affect the prediction error.

• Proceedings of the Korea Society of Costume Conference
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• 2001.04a
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• pp.49-49
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• 2001

SP(sales promotion)전략을 지향하는 백화점은 강 한 개성으로 다양하게 변화해 가는 소비자의 욕구충 족을 위해 대 고객차원의 편의성 및 쾌적한 쇼핑환 경을 마련하며 아이디어는 항상 특별하고 새로워야 한다. SP 전략으로서의 VMD (visual merchandi sing)는 상품의 시각화계획 등 통일된 시각(visual identity) 연 출을 통해 고객의 그룹이나 개인의 취향에 맞는 타켓 마케팅 (target marketing) 으로 백 화점 은 고객 의 중심에서 그들의 삶을 윤태하게 하며 아름답고 즐거 운 소비문화를 주도해갈 수 있는 환경을 제공해야 할 것이다. 1999년 말 IMF 이후 최근 막강한 자금력과 경쟁 력을 가진 대형 외국 할인 업체의 부상과 계속되는 장기적인 경제위축으로 백화점의 마케팅활동은 기존 고객과 관련된 단기적 욕구만을 충족시키는 점에서 벗어날 수 없었다. 이렇게 심각한 경기불안과 유통환 경의 급변으로 인해 소비자의 구매력이 약화되고 매 출이 감소하는 등 백화점의 한계성과 업태간의 경쟁 이 심화되어 갈수록 진정한 서비스개념의 합리적 목 적을 띤 VMD가 SP전략의 실질적인 형태로써 존재 되어야 한다. VMD는 이러한 불경기에 대응하는 백화점의 생존 고용식 전략으로서 좀더 강하고 적극적인 글로벌 마인드 ( (global mind)를 갖고 보다 넓은 시장에 대한 장기적 안목을 필요로 한다. 특히 대 고객 감성의 글로벌화 로 광범위한 상품의 장르와 감각적인 투자로써 신 고객창출을 도모하는 한편 고객에 대한 세심한 배려 와 구체화된 전략을 통해 불황을 극복하는 등 국내 유통문화의 선진화를 가속시켜 나갈 수 있는 것이다. "손쉬운 장사벌이"라는 무책임한 사고를 버리고 철저한 고객친화의 중심에 서서 그들에게 즐거웅을 주고 풍요로운 문화의 장(場)을 마련하는 등 지금의 무한경쟁 시대에 가장 감성적인 경쟁력으로서 고객에게는 쇼핑을 통한 즐거움과 여유로움, 풍성한 정보 와 화제성, 독특한 서비스와 볼거리 등이 지속적으로 제공되어야 하며 상품의 시각화 계획인 VMD는 세 련된 드라마처럼 감동적 연출로 그 이야기가 전개되 어야한다. 고객의 구매행동을 기초로 유통시장의 무한 자유 경쟁이란 현 시점에서 판매촉진의 전략에 대한 체계 적 접근과 합목적성을 가진 VMD의 전개 방향 및 향후 백화점업계의 차별화 방안과 전략은 단순한 행 위의 출발이 아닌 주변환경과의 밀접한 연관 속에서 지극히 창조적인 예술적 자극이 요구되며 그 과정에 따른 결과적인 "반응"을 기대한다.quot;반응"을 기대한다.기대한다.