• Proceedings of the Korean Society of Broadcast Engineers Conference
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• 2015.11a
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• pp.35-38
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• 2015

OFDM 변조방식의 특징 중 하나가 SFN(Single Frequency Network) 기능이다. 최근 지상파 UHDTV방송을 기대하면서 OFDM 변조방식의 SFN기능을 이용한 가정 내 무선수신 환경에 대한 관심이 높아지고 있다. 그러나 SFN기능이 가능할지라도 송 중계기와 갭 필러 측면에서 보면 프로그램을 전달하는 별도의 백본망 없이 수신과 송신이 동일한 주파수로 이루어지려면 송신된 전파가 다시 자기 안테나로 수신되는 Feedback현상에 대해 좀 더 많은 연구가 요구되고 있다. 본 연구에서는 현재 가정과 사무실 등에서 사용하고 있는 저가의 가정용 T-DMB 갭 필러를 이용한 수신실태와 Feedback 현상에 대해 몇 가지 실험을 실행해 보았다. 가정용 갭 필러의 Feedback현상과 사용 형태를 분석함으로써 향후 UHDTV방송의 원활한 SFN망 구축과 가정 내 무선 수신환경 구축을 위한 방안을 제시하고자 한다.

• Polymer(Korea)
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• v.38 no.2
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• pp.232-239
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• 2014

Poly(lactic acid)(PLA) nanocomposites containing various nanofillers were synthesized using the solution intercalation method. Organically modified bentonite clay (NSE), octadecylamine-graphene oxide (ODA-GO), and an NSE/ODA-GO complex were utilized as nanofillers in the fabrication of PLA hybrid films. PLA hybrid films with varying nanofiller contents in the range of 0-10 wt% were examined and compared in terms of their thermomechanical properties, morphologies, and oxygen permeabilities. Transmission electron microscopy (TEM) confirmed that most of the NSE and ODA-GO nanofillers were dispersed homogeneously throughout the PLA matrix on the nanoscale, although some agglomerate NSE/ODA-GO complex particles were also formed. Among the three nanofillers for PLA hybrid films, the NSE/ODA-GO complex showed the best improvement in film thermal stability. In contrast, NSE and ODA-GO exhibited the best improvement in tensile mechanical properties and oxygen barrier properties of the PLA hybrid films, respectively.

• Tunnel and Underground Space
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• v.23 no.2
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• pp.130-140
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• 2013

In this study, scaled model tests were performed to investigate the stability of twin tunnels with small clearance, where the pillar widths were 0.5D and 0.25D, respectively. The tunnels were supposed to be constructed in anisotropic weathered rocks with $30^{\circ}$ inclined bedding planes, and the model tests were conducted under the condition of lateral pressure ratio, 1. Six types of test models which had respectively different pillar widths and support conditions were experimented, where crack initiating pressures, maximum pressures, failure modes of pillar and deformation behaviors around tunnels were investigated. The models with wider pillar were cracked under higher pressure than the models with shallower pillar. The models with lining support were cracked under higher pressure and showed less tunnel convergence than the unsupported models. The models with both lining and pillar reinforcement were proved to be most stable among the tested models. In particular, as the model of 0.25D pillar width with only lining support showed shear failure of pillar according to the existing bedding planes, so both lining and pillar reinforcement were thought to be indispensable in that case of tunnel.

• Tunnel and Underground Space
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• v.20 no.3
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• pp.131-144
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• 2010

The design and construction of tunnels has been followed an large parallel tunnels with a small clearance because of the various conditions. Rock pillar between each single tunnel is supposed to be under heavy load by rock mass. The stability of pillar is very important for the ensure the stability of the large parallel tunnels. In this study, the analysis of stress state of pillar at various construction cases is reviewed to investigate the mechanical behaviour of tunnels and stability of the pillar.

• Composites Research
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• v.35 no.4
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• pp.223-231
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• 2022

With the rapid growth of the future mobility market, a large number of electronic parts are being used in automobile, and the importance of electromagnetic interference (EMI) shielding in the automobile market is growing to minimize malfunctioning among the parts. Accordingly, conductive polymer composites (CPCs) are getting a lot of attention as EMI shielding materials for the automotive, but there are still challenges in CPCs like high content of conductive filler to achieve proper EMI shielding effectiveness, and poor mechanical properties. This paper introduces main methods to manufacture CPCs with segregated filler structure, which can significantly reduce the filler content, and analyzes EMI shielding performance of each manufacturing method.

• Polymer(Korea)
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• v.39 no.3
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• pp.468-474
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• 2015

Electrically conductive polymer nanocomposites were prepared by the inclusion of graphene-based nanofillers. Graphene oxide (GO) and reduced graphene oxide wrapped by poly(styrene sulfonate) (PSS-RGO) were used as nanofillers to make good dispersion with the aqueous dispersion of polystyrene (PS) particles. GO sheets were synthesized by the modified Hummers' method from graphite, and PSS-RGO sheets were prepared by the reduction of GO-dispersed PSS solution with hydrazine monohydrate. Morphology and properties of PS/GO and PS/PSS-RGO nanocomposites via latex technology were investigated. Both nanofillers showed well dispersed morphology in PS matrix. Rheological and electrical percolation thresholds were 0.28 and 0.51 wt% for GO, and 0.50 and 1.01 wt% for PSS-RGO respectively. It is speculated that PS/GO nanocomposites showed better conductivity than PS/PSS-RGO counterparts due to the partial recovery of GO by thermal reduction during molding.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.9 no.5
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• pp.1279-1283
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• 2008

Satellite Digital Multimedia Broadcasting(SDMB) needs Gap Fillers(GFs) to cover the non-service areas. However, SDMB mobile phones which are not located in GFs service area receive signals directly from the satellite because it is impossible to cover all SDMB service with GFs. Therefore, there is a border between the GFs service coverage and the satellite service coverage and it causes a time delay in signals which are from the GFs or the satellite. The time delay is the reason why SDMB service deteriorates. In this paper, I show how to reduce the deterioration of SDMB service in the border area between the GFs and the satellite adding the time delay to the satellite signal and the GFs signal. I think that this method is helpful in reducing the deterioration, especially in the early stages of SDMB service, which the GFs are not spread all over the nation yet.

• Journal of Adhesion and Interface
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• v.10 no.1
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• pp.30-34
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• 2009

The effect of pressure on the thermal conductivity in two-phase composite system was studied. Thermally conductive polypropylene (PP)/silicon carbide (SiC) composites were prepared by applying various pressures from 0 to 20 MPa. The thermal conductivity of the composite was 1.86 W/mK at 20 MPa, increased by 40% compared to the value of at 0 MPa. It was 9 times higher than that of unfilled polypropylene. It implies the pressure induces the easy path for phonon transport. Also, the experimental values were compared with Maxwell's prediction and Agari's prediction. Agari's prediction gave a better agreement compared to that of Maxwell's prediction due to the consideration of interactions between filler-filler and filler-polymer.

• Journal of Korean Tunnelling and Underground Space Association
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• v.6 no.2
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• pp.171-182
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• 2004

This study is focused on finding out the mechanical behavior of pillars and the ground adjacent to the tunnel depending on the central tunnel size and the invert during the construction of 2 arch tunnels in the sandy ground. Model tests were performed in the trap door system, which was composed of 3 separately movable plates. Central pillar was installed on the central movable plate to measure the pillar loads during the excavation of pilot tunnel and the main tunnel. The load-transfer and the loosening load were measured at the bottom plates adjacent to the 2 arch tunnels. The ground settlement and displacement of the tunnel lining were also measured. As results, not only pillar load but also the load transfer mechanism was influenced by the construction sequences, central tunnel size, and the invert.

• Tunnel and Underground Space
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• v.29 no.6
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• pp.425-438
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• 2019

A scaled model test was performed to evaluate the stability of subway twin tunnels excavated in the sedimentary rocks with subhorizontal bedding planes. The size of studied tunnel was 6.2 m×6.8 m and pillar width was 4 m. The anisotropic model test specimen was manufactured with the modeling materials suitable for in-situ rocks by way of dimensional analysis. Fracture and deformation behaviors of tunnels according to applied loads were investigated through the biaxial compression test. As the load was increased on the model specimen, the first crack occurred in the middle part of the pillar across twin tunnels and the gradual fractures progressed at crown and floor of twin tunnels. All the cracks in pillar were generated along the existing bedding planes so that they were found to be the main cause of the pillar failure. In addition, the test results were verified by numerical analysis on the experimental conditions using FLAC ubiquitous joint model. The distribution of plastic regions obtained from numerical analysis were in general agreement with test results, confirming the reliability of the scaled model test conducted in this study.