• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2009년도 추계학술대회 논문집
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• pp.112-112
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• 2009

In this study, the effect of a long post-deposition thermal annealing(600 and 1000 $^{\circ}C$) on the surface acoustic wave (SAW) properties of polycrystalline (poly) aluminum-nitride (AlN) thin films grown on a 3C-SiC buffer layer was investigates. The poly-AlN thin films with a (0002) preferred orientation were deposited on the substrates by using a pulsed reactive magnetron sputtering system. Experimental results show that the texture degree of AlN thin film was reduced along the increase in annealing temperature, which caused the decrease in the electromechanical coupling coefficient ($k^2$). The SAW velocity also was decreased slightly by the increase in root mean square (RMS) roughness over annealing temperature. However, the residual stress in films almost was not affect by thermal annealing process due to small lattice mismatch different and similar coefficient temperature expansion (CTE) between AlN and 3C-SiC. After the AlN film annealed at 1000 $^{\circ}C$, the insertion loss of an $IDT/AlN/3C-SiC/SiO_2/Si$ structure (-16.44 dB) was reduced by 8.79 dB in comparison with that of the as-deposited film (-25.23 dB). The improvement in the insertion loss of the film was fined according to the decrease in the grain size. The characteristics of AlN thin films were also evaluated using Fourier transform-infrared spectroscopy (FT-IR) spectra and X-ray diffraction (XRD), scanning electron microscopy (SEM), and atomic force microscopy (AFM) images.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2009년도 하계학술대회 논문집
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• pp.235-235
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• 2009

This paper describes the influence of a polycrystalline (poly) 3C-SiC buffer layer on the surface acoustic wave (SAW) properties of poly aluminum nitride (AlN) thin films by comparing the center frequency, insertion loss, the electromechanical coupling coefficient ($k^2$), andthetemperaturecoefficientoffrequency(TCF) of an IDT/AlN/3C-SiC structure with those of an IDT/AlN/Si structure, The poly-AlN thin films with an (0002)-preferred orientation were deposited on a silicon (Si) substrate using a pulsed reactive magnetron sputtering system. Results show that the insertion loss (21.92 dB) and TCF (-18 ppm/$^{\circ}C$) of the IDT/AlN/3C-SiC structure were improved by a closely matched coefficient of thermal expansion (CTE) and small lattice mismatch (1 %) between the AlN and 3C-SiC. However, a drawback is that the $k^2(0.79%)$ and SAW velocity(5020m/s) of the AlN/3C-SiC SAW device were reduced by appearing in some non-(0002)AlN planes such as the (10 $\bar{1}$ 2) and (10 $\bar{1}$ 3) AlN planes in the AlN/SiC film. Although disadvantages were shown to exist, the use of the AlN/3C-SiC structure for SAW applications at high temperatures is possible. The characteristics of the AlN thin films were also evaluated using FT-IR spectra, XRD, and AFM images.

• 한국환경보건학회지
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• 제33권4호
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• pp.242-249
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• 2007

Indoor air quality has become a topic of interest and concern. Especially changes in construction design and the increased use of synthetic products may result in an increasing of complaints and health effects about the quality of indoor air at home. In this study, nitrogen dioxide($NO_2$) and volatile organic compounds(VOCs) within new and established apartments on the basis of 4 years of building year were measured every 3 days consecutively during 60 days. We selected each 10 house in Seoul, Asan and Daegu, respectively, and produced risk numbers for hazard quotients, and predicted increases in incidence of cancer. The calculations were made for the adult with default exposure values and also made for a worst case scenario using Monte-Carlo simulation as describing the reasonable exposure(RME). Mean of Monte carlo analysis by benzene, in the construction under 4 years (male: $9.2{\times}10^{-5}$, female: $1.0{\times}10^{-4}$) and over 4 years (male: $6.8{\times}10^{-5}$, female: $8.3{\times}10^{-5}$) exceeded $10^{-6}$ of permitted standards in US EPA, RME of Monte carlo analysis. In construction under 4 yews (male: $9.9{\times}10^{-3}$, female: $9.6{\times}10^{-3}$) and over 4 years (male: $9.8{\times}10^{-3}$, female: $7.8{\times}10^{-3}$) exceeded $10^{-4}$ of maximum permitted standards in US EPA. The hazard index of non-carcinogenic pollutants by nitrogen dioxide, toluene, m,p-xylene and o-xylene, both male and female in apartment constructed under 4 yews and over 4 years was found less than the permitted standards of hazardous health effects in CTE. Significant cancer risks and non-cancer hazard quotients were predicted in under 4 yews of building year.

• 대한기계학회논문집A
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• 제38권9호
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• pp.953-958
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• 2014

형상적응형 냉각회로를 구비한 사출금형 및 히트 싱크를 가지는 절삭공구 (혹은 냉각 장치) 등과 같은 많은 응용 분야에서 기능성 경사 복합재(FGM)를 사용하여 필요한 강성을 약화시키지 않으면서 열전도 특성을 향상 시킬 수 있을 것으로 기대된다. 본 논문에서는 M2 공구강과 Cu 간의 FGM 히트 싱크를 가지는 절삭 공구 제작을 위한 기초연구로, M2 와 Cu 를 각각 100:0, 80:20, 60:40, 40:60, 20:80, 0:100 wt% 비율로 사전에 혼합한 금속분말을 분말야금법으로 가압성형 및 소결 제작 하였다. 각 시편의 단면을 광학현미경으로 관찰하여 소결 상태를 분석하였으며, 열전도도, 비열 및 열팽창계수 등 열전달 관련물성을 측정하고 분석하였다.

• 대한기계학회논문집A
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• 제28권9호
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• pp.1408-1414
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• 2004

The use of flip-chip technology has many advantages over other approaches for high-density electronic packaging. ACF (anisotropic conductive film) is one of the major flip-chip technologies, which has short chip-to-chip interconnection length, high productivity, and miniaturization of package. In this study, thermal fatigue lift of ACF bonding flip-chip package has been predicted. Elastic and thermal properties of ACF were measured by using DMA and TMA. Temperature dependent nonlinear hi-thermal analysis was conducted and the result was compared with Moire interferometer experiment. Calculated displacement field was well matched with experimental result. Thermal fatigue analysis was also conducted. The maximum shear strain occurs at the outmost located bump. Shear stress-strain curve was obtained to calculate fatigue life. Fatigue model for electronic adhesives was used to predict thermal fatigue life of ACF bonding flip-chip packaging. DOE (Design of Experiment) technique was used to find important design factors. The results show that PCB CTE (Coefficient of Thermal Expansion) and elastic modulus of ACF material are important material parameters. And as important design parameters, chip width, bump pitch and bump width were chose. 2$^{nd}$ DOE was conducted to obtain RSM equation far the choose 3 design parameter. The coefficient of determination ($R^2$) for the calculated RSM equation is 0.99934. Optimum design is conducted using the RSM equation. MMFD (Modified Method for feasible Direction) algorithm is used to optimum design. The optimum value for chip width, bump pitch and bump width were 7.87mm, 430$\mu$m, and 78$\mu$m, respectively. Approximately, 1400 cycles have been expected under optimum conditions. Reliability analysis was conducted to find out guideline for control range of design parameter. Sigma value was calculated with changing standard deviation of design variable. To acquire 6 sigma level thermal fatigue reliability, the Std. Deviation of design parameter should be controlled within 3% of average value.

• 한국분말재료학회지
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• 제13권5호
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• pp.321-326
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• 2006

Electronic packaging involves interconnecting, powering, protecting, and cooling of semiconductor circuits fur the use in a variety of microelectronic applications. For microelectronic circuits, the main type of failure is thermal fatigue, owing to the different thermal expansion coefficients of semiconductor chips and packaging materials. Therefore, the search for matched coefficients of thermal expansion (CTE) of packaging materials in combination with a high thermal conductivity is the main task for developments of heat sink materials electronics, and good mechanical properties are also required. The aim of this work is to develop copper matrix composites reinforced with carbon nanofibers. The advantages of carbon nanofibers, especially the good thermal conductivity, are utlized to obtain a composite material having a thermal conductivity higher than 400 W/mK. The main challenge is to obtain a homogeneous dispersion of carbon nanofibers in copper. In this paper, a technology for obtaining a homogeneous mixture of copper and nanofibers will be presented and the microstructure and properties of consolidated samples will be discussed. In order to improve the bonding strength between copper and nanofibers, different alloying elements were added. The microstructure and the properties will be presented and the influence of interface modification will be discussed.

• 시스템엔지니어링학술지
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• 제16권1호
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• pp.18-24
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• 2020

The KSLV-II project with high difficulties technically requires thorough technical management during long-term life cycle more than 10 years for launching into space. The TRL is a quantitative indicator developed by NASA widely used all over the world to measure technology maturity of a system development objectively and consistently. The TRL is also used to make sure technology level and to establish a future direction in the KSLV-II project. The TRL has advantage enable to identify a technology level through quantitative indicators. However, it takes a lot of efforts such as trials and errors, time and cost to apply it to the project considering the project environments, and stakeholder needs. These include not only to establish TRL management plan from ideal, conceptual and abstractive standards/guidelines such as NASA's, but also to construct TRL management environment enable to apply and manage harmoniously. In the KSLV-II project, it is required to figure out current technology level and technology development trend in the future, to access conveniently, to share related data in real time, and to update periodically for the comprehensive TRL management. From the reason above, the TRL management environment was built by using the systems engineering tool already has been used for other system management data such as requirements in the project. It also could be accomplished a practical management basis of systems engineering from the traceability among system management data including TRL. In this paper, case study results are introduced to manage the TRL for the space launch vehicle using the systems engineering tool in the KSLV-II project.

• International Journal of Aeronautical and Space Sciences
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• 제18권2호
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• pp.206-214
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• 2017

In this study, measurement of thermophysical properties of materials at high temperatures was performed. This experiment employed a heater device to heat the material to a high temperature. The images of the specimen surface due to thermal load at various temperatures were recorded using charge-coupled device (CCD) cameras. Afterwards, the full-field thermal deformation of the specimen was determined using the digital image correlation (DIC) method. The capability and accuracy of the proposed technique are verified by two experiments: (1) thermal deformation and strain measurement of a stainless steel specimen that was heated to $590^{\circ}C$ and (2) thermal expansion and thermal contraction measurements of specimen in the process of heating and cooling. This research focused on two goals: first, obtaining the temperature dependence of the coefficient of thermal expansion, which can be used as data input for finite element simulation; and second, investigating the capability of the DIC method in measuring full-field thermal deformation and strain. The results of the measured coefficient of thermal expansion were close to the values available in the handbook. The measurement results were in good agreement with finite element method simulation results. The results reveal that DIC is an effective and accurate technique for measuring full-field high-temperature thermal strain in engineering fields such as aerospace engineering.

• 폴리머
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• 제34권5호
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• pp.480-484
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• 2010

무수산인 4,4'-(4,4'-isopropylidene-diphenoxy)bis(phthalic anhydride)(BPADA)와 아민계인 2,2'-bis(trifluoromethyl)benzidine(TFB), bis(3-aminophenyl)sulfone(APS), 4,4'-methylene-bis-(2-methylcyclohexylamine)(MMCA), bis[4-(3-aminophenoxy)phenyl]sulfone(BAPS)에 melamine을 각각 5 몰%로 반응시켜 N,N'-dimethylacetamide(DMAc) 용매 속에서 폴리아믹산(poly(amic acid), PAA)들을 얻었다. 용액 상태의 PAA를 캐스팅하여 각각 다른 반응 온도에서 열처리를 통해 무색 투명한 폴리이미드(PI) 필름을 얻었다. PI의 열적 성질, 광학적 특성을 다양한 아민 구조의 변화에 따라 조사하였으며, 열적 성질은 differential scanning calorimetry(DSC), thermogravimetric analysis(TGA), thermomechanical analysis(TMA)를 이용해 측정하였고, 광학적 투명도는 색차계(spectrophotometry)를 이용하였다. 제조된 모든 필름의 열 팽창계수는 $48.53-64.24ppm/^{\circ}C$ 사이의 값을 얻었으며, 모든 필름 시료의 노란색 지수(yellow index, YI)는 3 이하를 나타내었다.

• 대한본초학회지
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• 제27권4호
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• pp.73-80
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• 2012

Objectives : Under normal condition melanin protects the skin from extracellular stimuli including ultraviolet (UV)-induced oxidative skin damages, but excess production and accumulation of melanin can induce hyperpigmentation causing esthetic problems. Therefore, in this study we tried to search for natural skin whitening materials from marine natural resources. Methods : Water and ethanol extracts of marine natural resources were prepared from Porphyra thalli (PT), Laminariae thallus (LT), Ostreae concha (OC), Sargassum thallus (ST), Undaria thallus (UT), Codium thalli (CT), Enteromorpha thalli (ET), Syngnathoides biaculeatus (SB), and Hippocampus coronatus (Hc). Their effects against UVB and ${\alpha}$-melanocyte stimulating hormone (${\alpha}$-MSH)-induced melanogenesis were investigated based on melanin formation in B16 mouse melanoma cells. The mRNA and protein expression of enzymes involved in the melanogenic process were further examined by reverse transcriptase-polymerase chain reaction (RT-PCR) and Western blot analysis, respectively. Results : Water extract of Ostreae concha (OCW/E) effectively inhibited UVB and ${\alpha}$-MSH-induced melanin production in B16 melanocytes, which seemed to be mediated by inhibition of mRNA expression of tyrosinase and tyrosinase-related protein 1 (TRP-1). In another experiment, ethanol extracts from Porphyra thalli (PTE/E), Laminariae thallus (LTE/E), Sargassum thallus (STE/E), Undaria thallus (UTE/E), Codium thalli (CTE/E), Syngnathoides biaculeatus (SBE/E), and Hippocampus coronatus (HcE/E) significantly suppressed UVB and ${\alpha}$-MSH-induced melanin formation. Furthermore, ethylacetate fraction isolated form LTE/E (LTE/EEt) decreased UVB and ${\alpha}$-MSH-elevated extracellular melanin levels via inhibition of tyrosinase protein expression. Conclutions : These results suggest that marine natural resources such as Porphyra thalli, Laminariae thallus, Ostreae concha, Sargassum thallus, Undaria thallus, Codium thalli, Syngnathoides biaculeatus and Hippocampus coronatus have anti-melanogenic effects, thereby exhibiting high potentials to be utilized as one of the ingredients for the development of new whitening functional cosmetics.