• 대한전자공학회논문지SD
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• 제40권4호
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• pp.27-33
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• 2003

최근, 원통형 DFB전송 구조들은 다양한 광 소자들과 결합하여 광통신용 필터로 널리 사용되고 있다. 이 원통형 Bragg 격자 구조들의 광 필터특성을 분석하기 위하여 본 논문에서는 Floquet-Babinet의 원리에 의존한 새롭고 쉬운 모드 전송선로 이론 (Modal Transmission-Line Theory)을 제시하였다. 수치해석 결과, 제안한 해석법은 원통형 DFB전송 구조들의 필터특성을 분석하기 위한 유용한 프로그래밍 알고리즘을 제공하고, 다층 원통형 주기 구조들의 전송특성을 분석하기 위하여 쉽게 발전시킬 수 있음을 보였다.

• 한국표면공학회지
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• 제50권5호
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• pp.315-321
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• 2017

Antireflective pyramid arrays can be readily obtained via anisotropic etching in alkaline solution (KOH, NaOH), which is widely used in crystalline-Si (c-Si) solar cells. The periodic inverted pyramid arrays show even lower light reflectivity because of their superior light-trapping characteristics. Since this inverted pyramidal structures are mostly achieved using very complex techniques such as photolithograpy and laser processes requiring extra costs, here, we demonstrate the Cu-nanoparticle assisted chemical etching processes to make the inverted pyramidal arrays without the need of photolithography. We have mainly controlled the concentration of $Cu(NO_3)_2$, HF, $H_2O_2$ and temperature as well as time factors that affecting the reaction. Optimal inverted pyramid structure was obtained through reaction parameters control. The reflectance of inverted pyramid arrays showed < 10% over 400 to 1100 nm wavelength range while showing 15~20% in random pyramid arrays.

• 국제초고층학회논문집
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• 제10권2호
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• pp.149-164
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• 2021

Most of high-rise buildings in Japan^*1 are structure with damping systems recently. The design procedure is performance-based design (PBD), which is based on the nonlinear response history procedure (NRHP) using 2 or 3-dimentional frame model. In addition, hysteretic property of steel plates or velocity-dependent property of viscous dampers are common practice for the damping system. However, for the selection of damping system, the easy dynamic analysis of recent date may lead the most of engineers to focus attention on the maximum response only without thinking how it shakes. By nature, the seismic design shall be to figure out the action of inertia forces by complex & dynamic loads including periodic and pulse-like characteristics, what we call seismic ground motion. And it shall be done under the dynamic condition. On the contrary, we engineers engineers have constructed the easy-to-use static loads and devoted ourselves to handle them. The structures with damping system shall be designed considering how the stiffness & damping to be applied to the structures against the inertia forces with the viewpoint of dynamic aspect. In this paper we reconsider the role of damping in vibration and give much thought to the basic of shake with damping from a standpoint of structural design. Then, we present some design examples based on them.

• Steel and Composite Structures
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• 제48권3호
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• pp.251-262
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• 2023

There are many examples of steel structures subjected to severe environmental conditions with bolted connections directly exposed to extreme climatic agents such as freeze-thaw cycles or low temperatures. Some examples are: steel bridges, mining transfer towers, wind towers... These service conditions neither are included in Eurocode 3 or EN1090-2, nor there are references in other international standards. In this experimental research, 46 specimens of non-slip joints with HV M20 bolts and four different types of contact surfaces have been studied. Half of the specimens were subjected to fourteen twelve-hours freeze-thaw cycles, with periodic immersion in water and temperature oscillation. Subsequently, half of the connections were subjected to a slip test under monotonic load at temperature of -20 ± 0.5 ℃ and the other half at room temperature. The results were compared with others equal joints not subjected to freeze-thaw cycles and kept at room temperature for the same time. This finally resulted in 4 sets of joints by combining the freeze-thaw degradation or not with the low-temperature conditions or not in the slip testing. Therefore, a total of 16 different conditions were studied by also considering 4 different contact surfaces between the joined plates in each set. The results obtained show influence of environmental conditions on the slip resistant capacity of these joints.

• 고무기술
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• 제9권1호
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• pp.25-28
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• 2008

By combining the multi-faceted environmental responsiveness of polymer hydrogels with photonically active structures, there has been a significant effort to create color-tunable photonic crystal sensors by changing either the periodic spacing of the structure or the dielectric constants of the materials. Here, we show that reversible spiral and helical opal switches with both dimensional and optical functionalities that respond to environmental chemistry can be constructed. When the transparent opal switch is swollen in hydrophilic acetic acid, right-handed spirals and helices that exhibit angularly dependent colors from Bragg diffraction are formed. When the transparent opal switch is swollen in hydrophobic hexane, left-handed spirals which exhibit angularly dependent colors from Bragg diffraction are formed. When the transparent opal switch is swollen in hydrophobic hexane solvent, a left-handed spiral and helix with an angularly independent bluish color is formed. After deswelling, all switches returned back to the transparent planar state. These color-tunable, reversible spiral and helical opal switches can be useful as mechanical actuators, and electrical devices as well as optical components.

• 한국지진공학회:학술대회논문집
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• 한국지진공학회 2000년도 춘계 학술발표회 논문집 Proceedings of EESK Conference-Spring
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• pp.3-16
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• 2000

The ultimate safety-goal of nuclear power plants should be targeted at preventing release of nuclear radiation compared to general structures, Accordingly the phases of siting design construction and operation of NPPs are severely regulated by codes of aseismic design so as to assure safety of NPPs. To accomplish this goal strict quality assurace and seismic qualification tests should be conducted for all phases of NPP construction. In addition seismic monitoring systems should be installed and always in operation to provide proper post-earhquake procedures. Besides periodic safety review should be performed during operation along with the seismic margin assessment. In this paper general procedures to secure seismic safety of NPPs are systematically reviewed and additional considerations for improvement are suggested.

• Structural Engineering and Mechanics
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• 제9권4호
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• pp.397-416
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• 2000

The present study deals with the nonlinear dynamics and stability of autonomous dissipative either imperfect potential (limit point) systems or perfect (bifurcational) non-potential ones. Through a fully nonlinear dynamic analysis, performed on two simple 2-DOF models corresponding to the classes of systems mentioned above, and with the aid of basic definitions of the theory of nonlinear dynamical systems, new important phenomena are revealed. For the first class of systems a third possibility of postbuckling dynamic response is offered, associated with a point attractor on the prebuckling primary path, while for the second one the new findings are chaos-like (most likely chaotic) motions, consecutive regions of point and periodic attractors, series of global bifurcations and point attractor response of always existing complementary equilibrium configurations, regardless of the value of the nonconservativeness parameter.

• 제어로봇시스템학회논문지
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• 제20권2호
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• pp.107-111
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• 2014

An SIW cavity is a useful tool to design an FSS which shows a rapid roll-off rate and insensitivity to polarizations and incident angles of electromagnetic waves. However, due to its high Q-factor, the FSS also shows narrow bandwidth which is undesirable for high-capacity communication. To address this drawback, we propose a novel technique to enhance the bandwidth while maintaining similar frequency response characteristics and minimizing the increase of the overall thickness of the SIW cavity FSS. In order to verify the performance of the technique, simulated frequency responses will be provided. Also, a parameter which affects the bandwidth will be studied. Finally the stability to polarizations and incident angles will be observed through the simulated results.

• Journal of electromagnetic engineering and science
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• 제12권4호
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• pp.280-286
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• 2012

The conventionally classified waves are reclassified in this paper, including the waves associated with metamaterial (MTM) transmission lines. Various types of guided waves in periodic structures are analyzed for 1D Composite Right/Left Handed (CRLH) transmission lines (TL). In addition, dispersion diagrams for 1D CRLH, RH, and LH TLs are presented in terms of radiation conditions. We have refined the design equations of the conventional 1D CRLH TL and proposed a condition to realize the desired phase shift and its slope per unit cell. This condition has been applied to the conventional Wilkinson power divider and realized into MTM added $90^{\circ}$ hybrid coupler. Based on the 10 dB return loss and the $90{\pm}10^{\circ}$ phase shift, the bandwidths of the MTM added $90^{\circ}$ hybrid coupler are 82.25% and 103.5% against the conventional 23% and 52.5%, respectively.

• 한국음향학회:학술대회논문집
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• 한국음향학회 2000년도 하계학술발표대회 논문집 제19권 1호
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• pp.287-290
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• 2000

In periodic structures where two or more materials of different density and sound speeds are arranged, there exist stop bands, in which waves cannot propagate. In this paper noise and vibration reduction by using band gap phenomena is discussed. The general theoretical background is presented and experimental results for acoustic wave attenuation in 2D cylinder arrays are described.