• Membrane Journal
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• v.26 no.6
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• pp.463-469
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• 2016

In this research, a new expectation in enhancing the PES (polyethersulfone) polymer phase inversion membrane performances with nanoparticles is proposed by using ZnO. This paper investigated the synthesis of PES phase inversion membranes including ZnO nanoparticles and evaluates the performance of these mixed matrix membranes. The PES-ZnO mixed matrix membranes were fabricated by phase inversion method using the PES-ZnO-NMP(N-methyl-1-pyrrolidone) casting solutions with low ZnO nanoparticles content of 0.375 wt%. The influence of ZnO nanoparticles on the characteristics of PES-ZnO mixed matrix membranes was investigated with scanning electron microscope observations of membrane cross-sections, contact angle measurements, tensile strength measurements, pure water flux measurements and ultrafiltration experiments of BSA solution. Those results showed that the performance advancements in comparison with the pure PES membrane without ZnO in terms of increasing hydrophilicity as well as reducing membrane fouling by adding ZnO nanoparticles even in low concentration.

• The Journal of the Korea institute of electronic communication sciences
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• v.11 no.12
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• pp.1201-1208
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• 2016

Radio Frequency Identification (RFID) technology has a significant attraction throughout various industry sites, along with the development of wireless communication technologies. The typical applications of RFID include medical, logistics, and distribution, and, specially, it is effectively applied to non-contact environments, because it employs radio waves. Although, recently, construction cases of the RFID management systems for the inventory management of the construction materials have been increased, the related researches and experiments for the reused materials are not actively performed. In this paper, we propose the RFID system with the localization function for effectively managing the reuse of the construction materials, adding to the conventional inventory management system. The proposed system consists of a RFID reader unit and a receiver unit, and the location information of the material with the attached RFID tag is obtained by estimating the position of a RFID reader. The distance value for estimating the reader position is calculated using the Received Signal Strength Indicator (RSSI) value of Zigbee, and the performance evaluation of the proposed system is performed in the indoor space of $5m{\times}5m$.

• Tunnel and Underground Space
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• v.9 no.4
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• pp.328-336
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• 1999

To characterize the hydro-mechanical behavior of a rock joint, a rotary shear testing apparatus was devised in this study. Shear stress was driven by twisting the end of a sample in the rotary shear testing apparatus. The test results show that the rotary shear test underestimates the peak shear strength of a rock joint. The torque is known as a function of the radial distance from the axis of rotation, resulting in the radial variation of the shear stress. Fluid flow through rock joints is mainly dependent on the Joint roughness, contact area, initial aperture. To examine the dependency, the relationship between the hydraulic and the mechanical apertures for shear-flow was established by measuring the initial aperture. It shows that the mechanical aperture and the hydraulic aperture increase linearly with the dilatancy. The difference between the hydraulic and mechanical apertures describes the deviation from the behavior predicted by the parallel plate model.

• 한국신재생에너지학회:학술대회논문집
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• 2011.05a
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• pp.68-68
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• 2011

본 연구에서는 PV cell이 직달 일사에 노출되는 경우와 집광된 태양광에 조사되는 경우의 성능을 비교하는 한편 집광기의 형태에 따른 열적 성능을 검토하고자 하였다. PV cell은 본질적으로 반도체의 특성을 가지므로 작동온도의 상승에 따라 성능이 저하된다는 사실이 알려져 있으며, 태양조사의 강도 및 밀도 등 특성에 따라서도 성능의 변화를 예상할 수 있다. 그러나 이러한 성능변화에 관련된 인자들과 그 영향의 크기에 대한 정량적인 기술자료가 부족하므로 설치와 이용에 한계가 있는 것이 현실이다. 인공태양 장치(solar simulator)를 이용하여 0.7에서 1.2 sun 범위의 태양 조사 환경에서 결정질 실리콘계 PV cell과 집광형 PV cell의 성능을 검토하였다. 집광에 사용한 PTC는 집광면적의 폭이 500 mm이며, 집광 조사면적이 최소 10 mm인 경우 이론적 최대 집광비가 50이었다. PTC의 축방향으로는 균일한 태양조사가 있게된다는 것을 가정하여 모델의 길이는 간편한 실험을 위해 150에서 500 mm의 범위에서 제작하였다. 수평으로 놓인 PTC의 상부 초점 위치로부터 집광면이 아래 쪽에 위치할수록 집광 조사 면적이 증가하므로 PV cell의 크기에 따라 PTC 초점의 위치로부터 거리를 결정하였다. 한편, PTC 자체의 성능도 촛점거리와 집광면 폭의 비에 따라 달라질 수 있다는 가정 하에, 포물면의 최저 위치로부터 촛점거리는 각각 300, 400 및 500 mm가 되도록 세가지 형태를 제작하여 사용하였다. 동일한 형태의 PTC에서 PV cell의 동일한 설치 위치에서도 최고 $110^{\circ}C$ 범위의 PV cell의 작동 (표면) 온도에 따른 성능의 차이를 관찰하기 위해 셀의 후면을 냉각시키는 경우와 그렇지 않은 경우를 비교하였다. PV cell의 표면 온도 측정을 위해서, 후면의 온도와 같이 광선 차단 효과의 우려가 없는 경우에는 열전대를 설치하였으며, 셀의 전면 온도 측정을 위해서는 비접촉식 적외선 온도계를 사용하였다. 냉각 방법으로는 공기를 이용한 자연대류와 액체를 사용하는 강제대류의 경우를 고려하였으며, 필요에 따라 적절히 설계된 히트싱크를 설치하여 비교 실험을 진행하였다. 강제대류 냉각의 경우는 항온조를 사용하여 순환하는 냉각수의 유량과 공급온도를 변화시킴으로써 PV cell의 작동온도를 조절하고, 이에 따른 발전 성능의 변화를 관찰하였다. 본 연구에서 도출한 실험 및 분석 결과는 PV cell의 설치 환경과 작동온도의 변화에 따라 그 성능 변화를 예측할 수 있는 기술적 자료를 제공함으로써 에너지 이용의 합리화를 도모하는데 기여할 수 있을 것이다.

• Journal of the Korean Society for Railway
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• v.17 no.1
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• pp.7-13
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• 2014

Stiffness variations and wave propagation/reflection in railway catenaries are the primary sources of contact loss between a pantograph and a railway contact wire. This paper analyzes which design parameter is more important for 200km/h conventional rail and 300km/h high-speed rail, in order to effectively reduce the contact loss. For the high-speed rail, the wave propagation and reflection in the overhead contact lines are more influential than the stiffness variation over a span. When the high-speed rail needs to speed-up, it is necessary to develop higher strength contact wires in order to increase the wave propagation speed. In addition, the dropper clamp mass should be reduced in order to alleviate the wave reflection. However, it is noted that the increase in the tension to a messenger wire could deteriorate the current collection quality, which contrasts with expectations. For the 200km/h conventional rail, the stiffness variation over a span is more influential than the wave propagation and reflection. Therefore, shortening span length, increasing the tension in the contact wire and optimizing the location of the droppers are recommended for a smoother stiffness variation over the span.

• Journal of the Korean Society for Railway
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• v.13 no.1
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• pp.37-43
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• 2010

Catenary (Overhead Contact Lines) and Pantograph are used to transmit electrical energy to electric railways. An Arc occurs by unstable contact between catenary and pantograph during electric railways operation, which causes malfunctioning or even an accident. Therefore, to prevent a arc or electric contact loss are required arc detection systems with catenary maintenance capability. This paper describes developing of catenary arc detection system using photo detector in order to detect arc incidence in a indirect way. This developed system can also achieve Video-recordings and environmental conditions such as wire voltage/current, pantograph height, speed, position of electric railways, and temperature/humidity. This system have been evaluated at the section that bounds for dongdaegu from seoul. From the experimental results, the occurrence of arc and intensity of arc are mainly effected by wire voltage/current, pantograph height and speed of electric railways.

• Journal of Adhesion and Interface
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• v.6 no.2
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• pp.6-12
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• 2005

The plasma generally, ionized gas state, is the 4th material state composed the universe. Generating the plasma artificially has been studied by spending energy and it has a lot of applications in human's life. There are several merits to modify the surface of polymer using plasma. Above all, plasma maintains the property of polymer because of it changes the property of surface only. Also, it doesn't use a organic solvent and it is the environment friendship because of there are no waste under processing. Furthemore, in case of high-pressure plasma, it is possible that automated-processing continuously. In this study, we tried the reforming of surface to rise the adhesive strength between the material of polymer, experimented the rising of adhesive strength through a experiment of peel strength by virtue of processing time and using gas, confirmed the change of polymer's surface through measuring the surface contact angle analyzer and scanning electron microscopy (SEM).

• Polymer(Korea)
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• v.34 no.1
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• pp.38-44
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• 2010

Core-shell particles of inorganic/organic pair were synthesized from $CaCO_3$ absorbed sodium dodecyl benzene sulfonate(SDBS) surfactant. Shell components were synthesized by sequential emulsion polymerization. Various monomers were used as shell components such as methyl methacrylate(MMA), ethyl acrylate(EA), butyl acrylate(BA), and styrene(St). Ammonium persulfate(APS) was used as an initiator and 2-ethylhexyl acylate(2-EHA) was used as a functional monomer, In the $CaCO_3$/organic core-shell particle polymerization, $CaCO_3$ absorbed surfactant SDBS of 0.5 wt% was prepared first and then core $CaCO_3$ was encapsulated by emulsion polymerization. 0.1 wt% of APS was added sequentially to minimize the formation of new monomer particle during shell polymerization. The structure of inorganic/organic core-shell particles were characterized by measuring the decomposition degree of $CaCO_3$ using HCl solution, thermogravimetric analyzer, scanning electron microscope, and transmission electron microscope.

• Composites Research
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• v.15 no.6
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• pp.16-23
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• 2002

In this work, the effect of anodic oxidation on surface characteristics of high strength PAN-based carbon fibers was investigated in mechanical interfacial properties of composites. The surface properties of the carbon fibers were determined by acid-base values, scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and contact angles. And their mechanical interfacial properties of the composites were studied in interlaminar shear strength (ILSS) and critical stress intensity factor ($K_{IC}$). As a result, the acidity or the $O_{ls}/C_{ls}$ ratio of carbon fiber surfaces was increased, due to the development of the oxygen functional groups. Consequently, the anodic oxidation led to an increase in surface free energy of the carbon fibers, mainly due to the increase of its specific (or polar) component. The mechanical interfacial properties of the composites, including ILSS and $K_{IC}$, had been improved in the anodic oxidation on fibers. These results were explained that good wetting played an important role in improving the degree of adhesion at interfaces between fibers and epoxy resin matrix.

• Applied Chemistry for Engineering
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• v.24 no.5
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• pp.476-482
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• 2013

In this work, the effects of electrochemical oxidation of carbon fiber surfaces on mechanical interfacial properties of carbon fibers-reinforced polarized-polypropylene matrix composites were studied with various current densities during the treatments. Surface properties of the fibers before and after treatments were observed by SEM, AFM, XPS, and contact angle measurements. Mechanical interfacial properties of the composites were measured in terms of critical stress intensity factor ($K_{IC}$). From the results it was found that $O_{1s}$ peaks of the fiber surfaces were strengthened after electrochemical oxidation which led to the enhancement of surface free energy of the fiber, resulting in good mechanical performance of the composites. It can be concluded that electrochemical oxidation of the carbon fiber surfaces can control the interfacial adhesion between the carbon fibers and polarized-polypropylene in this composites system.