• 한국분말재료학회지
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• 제22권2호
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• pp.116-121
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• 2015

$WS_2$-W-WC embedded carbon nanofiber composites were fabricated by using electrospinning method for use in high-performance supercapacitors. In order to obtain optimum electrochemical properties for supercapacitors, $WS_2$ nanoparticles were used as precursors and the amounts of $WS_2$ precursors were controlled to 4 wt% (sample A) and 8 wt% (sample B). The morphological, structural, and chemical properties of all samples were investigated by means of field emission photoelectron spectroscopy, transmission electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. These results demonstrated that the embedded phases of samples A and B were changed from $WS_2$ to $WS_2$-W-WC through carbothermal reaction during carbonization process. In particular, sample B presented high specific capacitance (~119.7 F/g at 5 mV/s), good high-rate capacitance (~60.5%), and superb cycleability. The enhanced electrochemical properties of sample B were explained by the synergistic effect of the using 1-D structure supports, increase of specific surface area, and improved conductivity from formation of W and WC phases.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2008년도 추계 학술발표회 제20권2호
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• pp.485-488
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• 2008

터널 화재시 화재강도는 매우 높으며 터널 내부에서 화재 발생은 높은 화재강도에 의해 구조요소인 숏크리트 및 콘크리트 라이닝의 화재 노출표면에서 폭열 발생을 유발시키는 동시에 터널 안정에 있어 중요한 역할을 수행하는 앵커 등의 터널에 매입된 강재 또한 고온의 노출로 인한 열전달로 급격한 응력감소가 발생하게 된다. 따라서 본 실험에서는 화재강도(Modified Hydrocarbon Curve)와 매입된 강재의 내화 유무를 변수로 정하여 콘크리트 라이닝의 내부에 매입된 강재의 열전도를 알아보기 위한 화재시험을 수행하였다. 또한 최근 ITA(International Tunneling Association)에서 연구한 도로 터널내화구조 기준에 따라 강재의 열손상 임계 온도범위를 산정하여 열적 손상 정도를 평가하였다.

• 마이크로전자및패키징학회지
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• 제11권1호
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• pp.29-36
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• 2004

초 박형 실리콘 칩을 이용하여 실리콘 칩들을 포함한 모듈 전체가 굽힘이 자유로운 유연 패키징 기술을 구현하였으며 bending test와 FEA를 통해 초 박형 실리콘 칩의 기계적 거동을 살펴보았다. 초박형 실리콘 칩(t<30$\mu\textrm{m}$)은 표면손상의 가능성을 배제하기 위해 KOH및 TMAH둥을 이용한 화학적 thinning 방법을 이용하여 제작되었으며 열압착 방식에 의해 $Kapton^{Kapton}$에 바로 실장 되었다. 실리콘칩과 $Kapton^\circledR$ 기판간의 단차가 적기 때문에 전기도금 방식으로 전기적 결선을 이를 수 있었다. 이러한 방식의 패키징은 이러한 공정은 flip chip 공정에 비해 공정 간단하고 wire 본딩과 달리 표면 단차 적어서 연성회로 기판을 비롯한 인쇄회로기판의 표면뿐만 아니라 기판 자체에 삽입이 가능하여 패키징 밀도 증가를 기대할 수 있으며 실질적인 실장 가능면적을 극대화 할 수 있다.

• Smart Structures and Systems
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• 제1권4호
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• pp.369-384
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• 2005

The main objectives of this paper are to demonstrate the feasibility of using newly developed smart GFRP reinforcements to effectively monitor reinforced concrete beams subjected to flexural and creep loads, and to develop non-linear numerical models to predict the behavior of these beams. The smart glass fiber-reinforced polymer (GFRP) rebars are fabricated using a modified pultrusion process, which allows the simultaneous embeddement of Fabry-Perot fiber-optic sensors within them. Two beams are subjected to static and repeated loads (until failure), and a third one is under long-term investigation for assessment of its creep behavior. The accuracy and reliability of the strain readings from the embedded sensors are verified by comparison with corresponding readings from surface attached electrical strain gages. Nonlinear finite element modeling of the smart concrete beams is subsequently performed. These models are shown to be effective in predicting various parameters of interest such as crack patterns, failure loads, strains and stresses. The strain values computed by these numerical models agree well with corresponding readings from the embedded fiber-optic sensors.

• ETRI Journal
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• 제41권6호
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• pp.731-738
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• 2019

We proposed a novel electromagnetic band-gap (EBG) cell-embedded antenna structure for reducing the interference that radiates at the antenna edge in wireless access in vehicular environment (WAVE) communication systems for vehicle-to-everything communications. To suppress the radiation of surface waves from the ground plane and vehicle, EBG cells were inserted between micropatch arrays. A simulation was also performed to determine the optimum EBG cell structure located above the ground plane in a conformal linear microstrip patch array antenna. The characteristics such as return loss, peak gain, and radiation patterns obtained using the fabricated EBG cell-embedded antenna were superior to those obtained without the EBG cells. A return loss of 35.14 dB, peak gain of 10.15 dBi at 80°, and improvement of 2.037 dB max at the field of view in the radiation beam patterns were obtained using the proposed WAVE antenna.

• 한국해양공학회지
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• 제14권4호
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• pp.23-29
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• 2000

When the concrete structures were being made with sand containing chloride ion it was knows that corrosion rate of reinforced steel embedded in concrete with chloride ion was higher than that of concrete with on chloride ion. In this study, the operation of Friedel salts affecting the corrosion behavior of reinforced steel embedded in cement mortar was investigated with electrochemical view. Corrosion potential of reinforced steel embedded in cement mortar with sand containing chloride ion was shifted noble direction than that of cement mortar with no chloride ion after immersed 5 month in natural sea water and also corrosion current density decreased with shifting corrosion potential to noble direction. However Friedel salts appeared from surface to 2.5cm of inside direction of mortar specimen, which is located at 11.5$\circ$(2$\theta$) in XRD analysis and the amount of Ca(OH)2 by SEM photograph in cement mortar with chloride ion was larger than that of cement mortar with mo chloride ion. Eventually it is suggested that Friedel salts was resulted from chloride ion and it acted as the corrosion inhibitor.

• Steel and Composite Structures
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• 제20권6호
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• pp.1275-1303
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• 2016

Steel plates and carbon-fiber-reinforced polymer (CFRP) laminates or plates bonded to concrete substrates have been widely used for concrete strengthening. However, this technique cause plate debonding, which makes the strengthening system inefficient. The main objective of this study is to enhance the bond strength of externally bonded steel plates and CFRP laminates to the concrete surface by proposing new embedded adhesive and steel connectors. The effects of these new embedded connectors were investigated through the tests on 36 prism specimens. Parameters such as interfacial shear stress, fracture energy and the maximum strains in plates were also determined in this study and compared with the maximum value of debonding stresses using a relevant failure criterion by means of pullout test. The study indicates that the interfacial bond strength between the externally bonded plates and concrete can be increased remarkably by using these connectors. The investigation verifies that steel connectors increase the shear bond strength by 48% compared to 38% for the adhesive connectors. Thus, steel connectors are more effective than adhesive connectors in increasing shear bond strength. Results also show that the use of double connectors significantly increases interfacial shear stress and decrease debonding failure. Finally, a new proposed formula is modified to predict the maximum bond strength of steel plates and CFRP laminates adhesively glued to concrete in the presence of the embedded connectors.

• 대한기계학회논문집B
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• 제25권3호
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• pp.381-388
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• 2001

Presented are heat data which describe the effect of interaction between bulk flow pulsations and a vortex embedded in a turbulent boundary layer. The pulsation frequencies are 3 Hz, 15 Hz and 30 Hz. A half delta wing with the same height as the boundary layer thickness is used to generate the vortex flow. The convection heat transfer coefficients on a constant heat-flux surface are measured by embedded 77 T-type thermocouples. Spanwise profiles of convection heat transfer coefficients show that upwash region of vortex flow is influenced by bulk flow pulsations. The local heat transfer coefficient increases approximately by 7 percent. The increase in the local change of convection heat transfer coefficient is attributed to the spanwise oscillatory motion of vortex flow especially at the low Strouhal number and to the periodic change of vortex size.

• 한국해양공학회지
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• 제23권4호
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• pp.85-90
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• 2009

Although most of existing hydration heat control methods show a certain degree of hydration heat control, generally, there are many problems as mentioned above. Therefore, our laboratory previously developed a hydration heat control method using an exposed heat pipe, which solves most of these problems and simultaneously displays excellent hydration heat control. Unfortunately, even this method had some problems such as the processing, transport, and assembly of heat pipes, and the surface treatment of a cut plane after pouring, and hardening concrete. Therefore, in this study, a hydration heat control method using an embedded pipe has been developed with the expectation that this method solves those problems in hydration heat control using an exposed heat pipe. As a result of the experiment, the peak temperature of ECHP and ICHP specimen about $4.5{\sim}6.5^{\circ}C$ than the OPC specimen and the probability of thermal cracked generated in ECHP and ICHP specimen decreased up to $13{\sim}20%$. Finally, it was confirmed in this study that the hydration heat control method using an embedded heat pipe is significantly more superior and cost effective than the existing method of an exposed one.

• 한국재료학회지
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• 제25권3호
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• pp.113-118
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• 2015

To improve the methanol electro-oxidation in direct methanol fuel cells(DMFCs), Pt electrocatalysts embedded on porous carbon nanofibers(CNFs) were synthesized by electrospinning followed by a reduction method. To fabricate the porous CNFs, we prepared three types of porous CNFs using three different amount of a styrene-co-acrylonitrile(SAN) polymer: 0.2 wt%, 0.5 wt%, and 1 wt%, respectively. A SAN polymer, which provides vacant spaces in porous CNFs, was decomposed and burn out during the carbonization. The structure and morphology of the samples were examined using field emission scanning electron microscopy and transmission electron microscopy and their surface area were measured using the Brunauer-Emmett-Teller(BET). The crystallinities and chemical compositions of the samples were examined using X-ray diffraction and X-ray photoelectron spectroscopy. The electrochemical properties on the methanol electro-oxidation were characterized using cyclic voltammetry and chronoamperometry. Pt electrocatalysts embedded on porous CNFs containing 0.5 wt% SAN polymer exhibited the improved methanol oxidation and electrocatalytic stability compared to Pt/conventional CNFs and commercial Pt/C(40 wt% Pt on Vulcan carbon, E-TEK).