• 폴리머
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• 제29권3호
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• pp.308-313
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• 2005

광감응성 azobenzene 그룹이 분자의 주위 환경에 따라 광이성화 반응이 변화하는 것을 in-situ UV/Vis 분광 실험법과 광학 이방성 측정법을 이용하여 조사하였다. 4-Hyhoxyazobenzene을 포함하는 필름에 광조사함과 동시에 trans-isomer와 cis-isomer 특성 피크의 세기 변화를 측정하여 azobenzene 그룹의 가역적이며 반복적인 광이성화 반응을 알수 있었다. Azobenzene 자기조립체 박막이 입혀진 기판을 액정 셀의 배향막으로 사용하여 액정의 배향을 유도하였을 때, trans-azobenzene 그룹들이 조밀한 packing을 하며 기판에 수직으로 배열한 자기조립체 구조 때문에 액정 분자들도 수직 homeotropic 배향을 하였다. 이와 같은 자기조립체 박막의 액정 셀에 UV 빛을 노광하면 azobenzene그룹이 광이 성화 반응을 일으켜 cis-isomer로 변하게 되며, 이로 인해 액정의 배향이 수직에서 수평 planar 배향으로 변함을 알 수있었다.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2014년도 제46회 동계 정기학술대회 초록집
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• pp.429.2-429.2
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• 2014

ZnO nanowire is known as synthesizable and good mechanical properties. And, stimuli-responsive polymer is widely used in the application of tunable sensing device. So, we combined these characteristics to make precise tunable sensing devise. In this work, we investigate the dependence of ZnO nanowire alignment and morphology on si substrate using nanosphere template with various conditions via hydrothermal process. Also, pH-temperature dependant tuning ability of nanostructure was studied. The brief experimental scheme is as follow. First, Zno seed layer was coated on a si wafer ($20{\times}20mm$) by spin coater. And then $1.15{\mu}m$ sized close-packed PS nanospheres were formed on a cleaned si substrate by using gas-liquid-solid interfacial self-assembly method. After that, zinc oxide nanowires were synthesized using hydrothermal method. Before the wire growth, to specify the growth site, heat treatment was performed. Finally, NIPAM(N-Isopropylacrylamide) was coated onto as-fabricated nanostructure and irradiated by UV light to form the PNIPAM network. The morphology, structures and optical properties are investigated by FE-SEM(Field Emission Scanning electron Microscopy), XRD(X-ray diffraction), OM(Optical microscopy), and WCA(water contact angle).

• 분석과학
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• 제10권2호
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• pp.126-130
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• 1997

염화마그네슘이 있을 때 비스(2,2'-비피리딜)구리(II)(${Cu(bpy)_2}^{2+}$)-도데실황산나트륨(SDS)의 전기화학적거동이 고찰되었다. SDS가 존재하지 않을 때에 비해 SDS가 있을 때 ${Cu(bpy)_2}^{2+/1+}$의 $E_{pa}$ 및 $E_{1/2}$값은 양의 방향으로 이동된다. 1.0mM ${Cu(bpy)_2}^{2+}$의 100mM NaCl+27mM $MgCl_2$용액에서, ${\Delta}E_p$대-log[SDS]로 도시되는 두 선을 교차점이 임계미셀농도(CMC)이다. 염화마그네슘이 있을 때, 환원형 ${Cu(bpy)_2}^{1+}$이 산화형 ${Cu(bpy)_2}^{2+}$보다 도데실황산이온과 더욱 쉽게 화합한다. 염화마그네슘 첨가에 의해 이온세기가 증가할수록, 이중층이 더욱 좁아지고 미셀형성이 더욱 어렵게 된다.

• 마이크로전자및패키징학회지
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• 제6권2호
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• pp.13-21
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• 1999

Flip chip assembly directly on organic boards offers miniaturization of package size as well as reduction in interconnection distances resulting in a high performance and cost-competitive Packaging method. This paper describes the investigation of alternative low cost flip-chip mounting processes using electroless Ni/Au bump and anisotropic conductive adhesives/films as an interconnection material on organic boards such as FR-4. As bumps for flip chip, electroless Ni/Au plating was performed and characterized in mechanical and metallurgical point of view. Effect of annealing on Ni bump characteristics informed that the formation of crystalline nickel with $Ni_3$P precipitation above $300^{\circ}C$ causes an increase of hardness and an increase of the intrinsic stress resulting in a reliability limitation. As an interconnection material, modified ACFs composed of nickel conductive fillers for electrical conductor and non-conductive inorganic fillers for modification of film properties such as coefficient of thermal expansion(CTE) and tensile strength were formulated for improved electrical and mechanical properties of ACF interconnection. The thermal fatigue life of ACA/F flip chip on organic board limited by the thermal expansion mismatch between the chip and the board could be increased by a modified ACA/F. Three ACF materials with different CTE values were prepared and bonded between Si chip and FR-4 board for the thermal strain measurement using moire interferometry. The thermal strain of ACF interconnection layer induced by temperature excursion of $80^{\circ}C$ was decreased with decreasing CTEs of ACF materials.

• Bulletin of the Korean Chemical Society
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• 제22권2호
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• pp.213-218
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• 2001

Presented are the STM images of self-assembled monolayer of 2-mercaptoethanol on Au(111). Striped structures of ($6{\times}3_{\frac{1}{2}}$), ($5{\times}3_{\frac{1}{2}}$), ($4{\times}3_{\frac{1}{2}}$) and compact-($5{\times}3_{\frac{1}{2}}$) were observed after annealing at $80^{\circ}C.$ Analysis of the ordered structures revealed that the basic fundamental units of the ordered structures were three crystallographically non-equivalent ($3_{\frac{1}{2}}{\times}3_{\frac{1}{2}}$) $R30^{\circ}$ assemblies, and that the way of combination of the assemblies produced the four different structures. The($6{\times}3_{\frac{1}{2}}$) structure ( $\theta$ = 0.33) was composed of one ($3_{\frac{1}{2}}{\times}3_{\frac{1}{2}}$)$R30^{\circ}$ assembly, while the ($5{\times}3_{\frac{1}{2}}$) ( $\theta$ = 0.30) and ($4{\times}3_{\frac{1}{2}}$) ( $\theta$ = 0.38) structures were consisted of two ($3_{\frac{1}{2}}{\times}3_{\frac{1}{2}}$) $R30^{\circ}$ assemblies, separated by 5a and 4a, respectively. Furthermore, the compact-(5X 3½) structure ( $\theta$ = 0.50) was obtained by overlapping three ($3_{\frac{1}{2}}{\times}3_{\frac{1}{2}}$) $R30^{\circ}$ assemblies. In spite of the diversity in the adsorption structures, all the adsorption sites of 2-mercaptoethanol were fundamentally identical. On the other hand, the unannealed primitive SAM of 2-mercaptoethanol was characterized by two observations: a short-range order keeping the adsorbed molecules at approximately $3_{\frac{1}{2}}$ a and the small domains of the striped structures supporting that the observed surface structures on the annealed surface were the extension of the primitive layer of 2-mercaptoethanol. Comparing these observations with the already published structures of ethanthiol, it was concluded that the interaction between the hydroxyl groups of 2-mercaptoethanol might play a significant role in the adsorption step of 2-mercaptoethanol on Au(111) to organize the adsorption structures different from those of ethanthiol.

• Korean Chemical Engineering Research
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• 제40권6호
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• pp.659-663
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• 2002

에틸알코올의 첨가로 과포화가 유도되는 NaF 결정화 과정을 수정진동자를 이용하여 측정하였다. 준안정 상태의 NaF 용액에 에틸알코올을 첨가하면 NaF의 용해도가 감소하여 NaF 과포화가 형성되어 결과적으로 NaF 결정이 생성 및 성장한다. NaF 용액의 과포화에서 결정 생성 및 성장하는 변화를 감지하기 위하여 수정진동자의 금전극 표면을 염산시스테아민(cysteamine hydrochloride; 2-mercaptoethylamine hydrochloride)으로 self-assembly하여 수식하여 응용 가능성을 검토하였다. 과포화 과정을 통해 생성된 NaF 결정이 염산시스테아민 표면 위에 흡착되면 흡착된 양에 비례하여 수정진동자 주파수가 변화하기 때문에 주파수 변화를 측정함으로써 간접적으로 NaF 결정과정을 분석할 수 있었다. 알코올의 주입량을 1-5 ml로 변화시킴으로써 용액 중에 형성되는 NaF의 과포화 농도의 수준을 변화시켜 주었으며, 염산시스테아민 박막에 대한 주파수 변화를 분석함으로써 주입량에 따른 NaF 결정화 정도를 해석할 수 있었다. 이들 결과들을 통하여 수정진동자를 이용한 NaF 결정화 과정의 분석이 가능함을 알 수 있었다.

• Journal of the Korean Data Analysis Society
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• 제20권6호
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• pp.2873-2881
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• 2018

유권자들의 올바른 투표행위에 기여하기 위하여 또는 후보나 정당의 적절한 선거전략 수립을 위하여, 선거여론조사를 통하여 신뢰성 있고 객관적인 정보를 확보하는 것은 매우 중요한 문제이다. 따라서 정당, 언론기관, 조사회사 등 관련 기관에서는 여론조사의 결과와 선거예측의 정확도 향상을 위해 지속적으로 노력해 왔다. Kim et al.(2017)에서는 선거여론조사에서 지지후보가 없다고 응답한 무응답층을 분류하여 득표율 예측의 정확도를 높일 수 있는지를 분석하였는데, 결과적으로 무응답층에 대하여 적절한 분류를 수행함으로써 득표율 추정의 정확도를 상당히 높일 수 있음을 확인한 바 있다. 본 연구에서는 특정 선거구(지역)에 대하여 전체 투표율이 주어져 있다는 조건 하에서 각 층(성, 연령대)별 투표율을 추정하는 방안을 제안하고, 투표율을 반영하여 득표율을 예측하는 절차를 제시하였다. 또한 2016년 20대 국회의원선거에 대한 여론조사에서 전화면접조사를 통해 얻어진 자료를 사용하여 사례 분석을 수행하였다.

• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2009년도 춘계학술대회 논문집
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• pp.288-294
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• 2009

Various polymer electrolyte membrane fuel cell (PEMFC) startup procedures were tested to explore possible techniques for reducing performance decay and improving durability during repeated startup-shutdown cycles. The effects of applying a dummy load, which prevents cell reversal by consuming the air at the cathode, on the degradation of a membrane electrode assembly (MEA) were investigated via single cell experiments. The electrochemical results showed that application of a dummy load during the startup procedure significantly reduced the performance decay, the decrease in the electrochemically active surface area (EAS), and the increase in the charge transfer resistance ($R_{ct}$), which resulted in a dramatic improvement in durability. After 1200 startup-shutdown cycles, post-mortem analyses were carried out to investigate the degradation mechanisms via various physicochemical methods including FESEM, an on-line $CO_2$ analysis, EPMA, XRD, FETEM, SAED, FTIR. After 1200 startup-shutdown cycles, severe Pt particle sintering/agglomeration/dissolution and carbon corrosion were observed at the cathode catalyst layer when starting up a PEMFC without a dummy load, which significantly contributed to a loss of Pt surface area, and thus to cell performance degradation. However, applying a dummy load during the startup procedure remarkably mitigated such severe degradations, and should be used to increase the durability of MEAs in PEMFCs. Our results suggest that starting up PEMFCs while applying a dummy load is an effective method for mitigating performance degradation caused by reverse current under a repetition of unprotected startup cycles.

• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2007년도 춘계학술대회
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• pp.101-104
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• 2007

금속 분리판으로 제작된 연료전지 스택의 기계적인 거동을 유한요소 해석을 통하여 살펴보았다. 연료전지의 구성요소는 크게 금속 분리판, 가스켓, MEA, GDL, 엔드 플레이트로 나눌 수 있다. 각각의 요소들은 적절한 힘에 의하여 체결되어야 하고 이에 의해 연료전지 스택의 성능이 많아 좌우된다. 유한 요소해석을 위해 가스켓, GDL을 금속 분리판 위에서 변위에 따른 힘의 변화를 실험을 통해 구했으며, 금속 분리판의 유로 부분을 단순 평판으로 치환하여 유한 요소해석을 진행하였고, 해석 결과와 실험결과가 일치함을 확인하였다. 이를 통해 금속 분리판 스택이 체결되었을 때의 기계적 거동을 유추할 수 있다.

• Structural Monitoring and Maintenance
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• 제1권3호
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• pp.249-271
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• 2014

This paper presents a unique study of Structural Health Monitoring (SHM) for the maintenance decision making about a real life movable bridge. The mechanical components of movable bridges are maintained on a scheduled basis. However, it is desired to have a condition-based maintenance by taking advantage of SHM. The main objective is to track the operation of a gearbox and a rack-pinion/open gear assembly, which are critical parts of bascule type movable bridges. Maintenance needs that may lead to major damage to these components needs to be identified and diagnosed timely since an early detection of faults may help avoid unexpected bridge closures or costly repairs. The fault prediction of the gearbox and rack-pinion/open gear is carried out using two types of Artificial Neural Networks (ANNs): 1) Multi-Layer Perceptron Neural Networks (MLP-NNs) and 2) Fuzzy Neural Networks (FNNs). Monitoring data is collected during regular opening and closing of the bridge as well as during artificially induced reversible damage conditions. Several statistical parameters are extracted from the time-domain vibration signals as characteristic features to be fed to the ANNs for constructing the MLP-NNs and FNNs independently. The required training and testing sets are obtained by processing the acceleration data for both damaged and undamaged condition of the aforementioned mechanical components. The performances of the developed ANNs are first evaluated using unseen test sets. Second, the selected networks are used for long-term condition evaluation of the rack-pinion/open gear of the movable bridge. It is shown that the vibration monitoring data with selected statistical parameters and particular network architectures give successful results to predict the undamaged and damaged condition of the bridge. It is also observed that the MLP-NNs performed better than the FNNs in the presented case. The successful results indicate that ANNs are promising tools for maintenance monitoring of movable bridge components and it is also shown that the ANN results can be employed in simple approach for day-to-day operation and maintenance of movable bridges.