• 한국전기전자재료학회논문지
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• 제13권8호
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• pp.675-680
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• 2000

In this study the temperature coefficient of resonant frequency(TC $F_{r}$) dielectric and piezoelectric properties of Pb[(S $b_{1}$2//N $b_{1}$2/)$_{0.065}$)-(Z $r_{x}$, $Ti_{1-x}$ )$_{0.90}$] $O_3$ceramics were investigated with Zr/Ti ratio. The compositions near the morphotropic phase boundary (MPB) appeared when Zr/Ti ratio was 49.5/50.5 The dielectric constant and electromechanical coupling factor( $k_{p}$) also showed the highest values of 1,257, 0.653 respectively when the Zr/Ti ratio was 49.5/50.5 Moreover the mechanical quality factor( $Q_{m}$) showed th lowest value of 713 when the Zr/Ti ratio. The temperature coefficient of resonant frequency(TC $F_{r}$) abruptly change at the morphotropic phase boundary(MPB) which existed between the rhombohedral phase with highly negative TC $F_{r}$ of -106ppm/$^{\circ}C$ and the tetragonal phase with highly positive TC $F_{r}$ of +64pp $m^{\circ}C$ as Zr/Ti ratio varied from 50/50 to 49.5/50.5.50.5..50.5.

• 한국전자파학회논문지
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• 제15권11호
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• pp.1082-1089
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• 2004

본 논문에서는 개방 루프 공진기로 구현된 타원응답 필터의 소형화 및 결합행렬의 유사변환을 통한 설계의 유연성에 관해 연구하였다. 더불어 제안한 방법에 의하여 보다 큰 비대역폭을 갖는 필터를 제시하였다. 제안한 방법의 유효성을 확인하기 위해 개방 루프 공진기를 이용하여 중심 주파수(f$_{c}$) 2.0 GHz에서 0.04의 비대역폭(FBW)을 가지는 4차 타원응답 대역통과 필터를 설계하였다. 개방 루프 공진기의 혼합결합이 일어나는 부분의 선폭을 좁게 함으로써 구현된 두 개의 필터는 일정한 선폭을 가지는 공진기로 구현된 필터에 비해 각각 13%와 25%의 크기 감소 효과를 나타내었다. 또한, 요구되는 결합량을 만족시키기 위한 공진기 사이의 간격이 실현 불가능할 경우 결합행렬의 유사변환을 통하여 기존 구조와 동일한 특성을 나타내는 두 가지 다른 구조를 제시함으로써 필터 설계의 유연성을 보여주었으며 이로 인해 보다 큰 비대역폭(FBW=0.08)을 갖는 필터 설계가 가능함을 나타내었다.

• 한국자동차공학회논문집
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• 제24권2호
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• pp.137-143
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• 2016

The fifth wheel coupler is a heavy automotive coupling structure which connects a tractor and a trailer used for heavy-duty trucks widely. It is subjected to various loads simultaneously such as rolling, pitching and yawing loads as well as coupling frictional and impact loadings. Most of existing couplers have been overdesigned and, therefore, it is necessary to reduce the dead weight to increase the fuel efficiency. The topology optimization was applied in order to find conceptual layout designs which could show major load paths and ribs locations, and then the size structural optimization was performed in order to determine the heights and thicknesses of coupler ribs with the predetermined various loading conditions for the development of a new slim coupler with a minimum weight and high enough strength and stiffness. As the results of the topology optimum design, an efficient new coupling structure for truck trailers was designed. The weight of the new fifth wheel coupler was reduced by 4.9 %, compared with the existing one, even though all strength requirements were satisfied. The fatigue test of the new coupler was performed with cyclic vertical loads (+78.4 to +235.2 kN) and horizontal loads (-91.2 to +91.2 kN) simultaneously at 1 Hz and the life of 2,000,000 cycles were achieved without failure.

• 한국우주과학회:학술대회논문집(한국우주과학회보)
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• 한국우주과학회 2003년도 한국우주과학회보 제12권2호
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• pp.82-82
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• 2003

It is well known that electromagnetic (EM) waves are mode converted to electrostatic (ES) waves in inhomogeneous plasmas. We examine this issue in a three-dimensional multi-fluid numerical model. First, we derive a set of coupled linear wave equations when a one-dimensional inhomogeneous density profile is assumed in a cold and collisionless plasma. The massive ions are considered as fixed because we are interested in high frequency waves in plasmas. It is shown that the EM mode satisfies the 0th order modified Bessel equation near the resonant region where the frequency matches the local electron plasma frequency. It is expected that the EM waves are coupled and damped to the ES waves owing to the logarithmic singular behavior at such resonances. Second, we numerically test the same case in a 3-D multi-fluid model. An impulsive input is assumed to excite EM waves in the inhomogeneous 3-D box model. The wave spectra of electric and magnetic fields are presented and compared with the analytical results. Our results suggest that the EM energy is irreversibly converted into the ES energy wherever the resonant condition is satisfied. Finally we discuss how the mode conversion appears in both electric and magnetic fields by analyzing time histories of each component. We also compare our results with MHD wave coupling. It is numerically confirmed in this study that the coupling of EM and ES waves is similar to that of compressional and transverse MHD waves.

• 한국정보통신학회논문지
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• 제25권8호
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• pp.1074-1081
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• 2021

최근 무선통신 사용자들의 기술 요구사항과 고속 데이터 기술 개발의 필요성이 증가되면서 비면허 무선접속 기술 개발이 주목되고 있다. 더 높은 주파수와 더 넓은 대역폭을 가진 WiFi (Wireless Fidelity)와 같은 저전력 근접 무선통신 서비스와 더불어 광범위한 비면허 기술의 응용성을 위해 다양한 주파수 대역에서의 스펙트럼 공존 및 공유 연구가 필수적이다. 본 논문에서는 지하철 내의 6GHz 비면허 대역의 WiFi와 기존 무선업무인 이동방송중계 시스템간의 간섭의 정도를 평가하고 공존을 위한 두 서비스간의 이격거리를 제안한다. 간섭 평가를 위해 최소결합손실 (MCL: Minimum Coupling Loss)방법과 몬테카를로 (MC: Monte Carlo)방법 기반의 간섭 시나리오를 설정하였으며, 두 시스템간의 동 대역과 주파수 이격에 따른 이격거리를 도출하였다.

• 한국정보통신학회논문지
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• 제26권7호
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• pp.1032-1039
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• 2022

이동통신 중계기에 사용하는 SAW(Surface Acoustic Wave) 방식의 대역통과필터를 대체할 수 있는 5G 이동통신 중계기용 군 지연 특성이 개선된 크로스 커플링 등화기 구조를 결합한 캐비티 대역통과필터를 설계하고 이를 구현하였다. 3D EM 시뮬레이션 툴 (HFSS)을 이용하여 공진 주파수, 공진기 간 결합 계수와 공진기 사이 외부 품질 계수를 계산하였고, 이를 바탕으로 메탈 캐비티 구조로 주파수대역 3500MHz~3600MHz, 대역폭 97.85MHz로 대역 양쪽 가장자리 주파수(edge)단에서 20dB 이상의 감쇄 특성을 가지도록 12차 대역 통과 필터를 제작 하였다. 설계 제작한 대역통과필터는 5G 이동통신 표준에 요구하는 군 지연 시간 조건과 인-밴드, 아웃-밴드 주파수 응답을 만족하였다.

• Nuclear Engineering and Technology
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• 제52권2호
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• pp.248-257
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• 2020

This study presents an initial design for a novel system consisting in a coupled nuclear reactor and a phase change material-based thermal energy storage (TES) component, which acts as a buffer and regulator of heat transfer between the primary and secondary loops. The goal of this concept is to enhance the capacity factor of nuclear power plants (NPPs) in the case of high integration of renewable energy sources into the electric grid. Hence, this system could support in elevating the economics of NPPs in current competitive markets, especially with subsidized solar and wind energy sources, and relatively low oil and gas prices. Furthermore, utilizing a prismatic-core advanced high temperature reactor (PAHTR) cooled by a molten salt with a high melting point, have the potential in increasing the system efficiency due to its high operating temperature, and providing the baseline requirements for coupling other process heat applications. The present research studies the neutronics and thermal hydraulics (TH) of the PAHTR as well as TH calculations for the TES which consists of 300 blocks with a total heat storage capacity of 150 MWd. SERPENT Monte Carlo and MCNP5 codes carried out the neutronics analysis of the PAHTR which is sized to have a 5-year refueling cycle and rated power of 300 MW_th. The PAHTR has 10 metric tons of heavy metal with 19.75 wt% enriched UO₂ TRISO fuel, a hot clean excess reactivity and shutdown margin of $33.70 and -$115.68; respectively, negative temperature feedback coefficients, and an axial flux peaking factor of 1.68. Star-CCM + code predicted the correct convective heat transfer coefficient variations for both the reactor and the storage. TH analysis results show that the flow in the primary loop (in the reactor and TES) remains in the developing mixed convection regime while it reaches a fully developed flow in the secondary loop.

• 방사선산업학회지
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• 제17권4호
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• pp.333-344
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• 2023

To validate the numerical model used in the study of deep disposal of spent nuclear fuel, we selected benchmark cases and performed numerical model validation. We selected the DECOVALEX-THMC Task D_THM1 FEBEX Type benchmark case, which was conducted from 2003 to 2007. We analyzed the thermal-hydraulic (TH) behavior using the finite element program CODE_BRIGHT and verified the results against previous studies. The temperature results were similar to the results of DECOVALEX-THMC Task D. The saturation results showed a similar trend to the results of DECOVALEX-THMC Task D, but the time to reach full saturation was different.

• Advances in Energy Research
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• 제5권2호
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• pp.91-105
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• 2017

Thermal hydraulic (TH) analysis of nuclear power reactors is utmost important. In this way, the numerical codes that preparing TH data in reactor core are essential. In this paper, a subchannel analysis of a Russian pressurized water reactor (WWER1000) core with enhanced numerical code is carried out. For this, in fluid domain, the mass, axial and lateral momentum and energy conservation equations for desired control volume are solved, numerically. In the solid domain, the cylindrical heat transfer equation for calculation of radial temperature profile in fuel, gap and clad with finite difference and finite element solvers are considered. The dependence of material properties to fuel burnup with Calza-Bini fuel-gap model is implemented. This model is coupled with Isotope Generation and Depletion Code (ORIGEN2.1). The possibility of central hole consideration in fuel pellet is another advantage of this work. In addition, subchannel to subchannel and subchannel to rod connection data in hexagonal fuel assembly geometry could be prepared, automatically. For a demonstration of code capability, the steady state TH analysis of a the WWER1000 core is compromised with Thermal-hydraulic analysis code (COBRA-EN). By thermal hydraulic parameters averaging Fuel Assembly-to-Fuel Assembly method, the one sixth (symmetry) of the Boushehr Nuclear Power Plant (BNPP) core with regular subchannels are modeled. Comparison between the results of the work and COBRA-EN demonstrates some advantages of the presented code. Using the code the thermal modeling of the fuel rods with considering the fission gas generation would be possible. In addition, this code is compatible with neutronic codes for coupling. This method is faster and more accurate for symmetrical simulation of the core with acceptable results.

• Journal of electromagnetic engineering and science
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• 제3권2호
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• pp.140-146
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• 2003

In this paper, the design of a channel filter and its group-delay-and-amplitude equalizer is carried out for the Ka-band satellite transponder subsystem. The 8th order dual-mode filter is employed for high selectivity around the band-edges with an elliptic-integral function response and has an in-line configuration. The 2-pole, reflection-type, group-delay equalizer is designed and manufactured to reduce the group-delay and amplitude variation, which can be large for such a high order filter. It is noted that in both the filter and equalizer, adopting the dual-mode coupling mechanism leads to less mass and volume. Through measurement, the performance of the realized group-delay-equalized filter is shown to meet the equipment requirements and to be appropriate for the satellite input multiplexer.