• 한국응용과학기술학회지
• /
• 제22권2호
• /
• pp.96-105
• /
• 2005

Core-shell polymers of methyl methacrylate-styrene system were prepared by sequential emulsion polymerization in the presence of sodium dodecyl benzene sulfonate(SDBS) as an emulsifier using ammonium persulfate(APS) in an initiator and the characteristics of these core-shell polymers were evaluated. Core-shell composite latex has the both properties of core and shell components in a particle, whereas polymer blends or copolymers show a combined physical properties of two homopolymers. This unique behavior of core-shell composite latex can be used in various industrial fields. However, in preparation of core-shell composite latex, several unexpected matters are observed, for examples, particle coagulation, low degree of polymerization, and formation of new particles during shell polymerization. To solve this matters, we study the effects of surfactant concentrations, initiator concentrations, and reaction temperature on the core-shell structure of PMMA-PSt and PSt-PMMA. Particle size and particles distribution were measured by using particle size analyzer, and the morphology of the core-shell composite latex was observed by using transmission electron microscope. Glass temperature was also measured by using differential scanning calorimeter. To identify the core-shell structure, pH of the composite latex solutions was measured.

• Bulletin of the Korean Chemical Society
• /
• 제31권8호
• /
• pp.2309-2314
• /
• 2010

Design and syntheses of four red phosphorescent heteroleptic cationic iridium(III) complexes containing two substituted phenylquinoxaline (pqx) or benzo[b]thiophen-2-yl-pyridin (btp) main ligands and one 2,2'-biimidazole (H2biim) ancillary ligand are reported: [$(pqx)_2$Ir(biim)]Cl (1), [$(dmpqx)_2$Ir(biim)]Cl (2), [$(dfpqx)_2$Ir(biim)]Cl (3), [$(btp)_2$Ir(biim)]Cl (4). Complex 1 showed a distorted octahedral geometry around the iridium(III) metal ion with cis metallated carbons and trans nitrogen atoms. The absorption, emission and electrochemical properties were systematically evaluated. The complexes exhibited red phosphorescence in the spectral range of 580 to 620 nm with high quantum efficiencies of 0.58 - 0.78 in both solution and solid-state at room temperature depending on the cyclometalated main ligands. The cyclic voltammetry of the complexes (1-3) showed a metal-centered irreversible oxidation in the range of 1.40 to 1.90 V as well as two quasi reversible reduction waves from -1.15 to -1.45 V attributed to the sequential addition of two electrons to the more electron accepting heterocyclic portion of two distinctive cyclometalated main ligands, whereas complex 4 showed a reversible oxidation potential at 1.24 V and irreversible reduction waves at -1.80 V.

• 한국전자파학회논문지
• /
• 제25권3호
• /
• pp.311-318
• /
• 2014

소형 위성 발사체 나로호의 전자파 적합성 성능은 탑재 위성과 우주센터에 설치되는 지상 장비, 그리고 다른 무선통신망 사이에서 정상적인 동작을 보장하도록 확보되고 검증되어야 한다. 전자파 적합성 성능을 검증하기 위해서는 서브 시스템과 시스템에 대한 적절한 시험 규격과 방법, 그리고 절차가 발사체의 운용 특성과 전자기 환경을 고려하여 수립되어야 한다. 그리고 프로그램 종료단계까지 결정된 규격에 따라 지속적으로 전자파 적합성 특성을 유지 관리하는 것이 요구된다. 본 논문에서는 나로호의 발사체 개발 전 주기 동안 수행된 순차적인 관리 업무를 기술하고, 나로호와 각 서브 시스템의 각 모델에 대한 단계별 시험계획뿐만 아니라, 시험 방법, 규격, 검증시험 결과 등이 제시된다. 또한, 멀티팩션 분석에 대한 결과를 기술한다.

• Asian-Australasian Journal of Animal Sciences
• /
• 제26권4호
• /
• pp.588-595
• /
• 2013

Mesenchymal stem cells (MSCs) are often known to have a therapeutic potential in the cell-mediated repair for fatal or incurable diseases. In this study, canine umbilical cord MSCs (cUC-MSCs) were isolated from umbilical cord matrix (n = 3) and subjected to proliferative culture for 5 consecutive passages. The cells at each passage were characterized for multipotent MSC properties such as proliferation kinetics, expression patterns of MSC surface markers and self-renewal associated markers, and chondrogenic differentiation. In results, the proliferation of the cells as determined by the cumulative population doubling level was observed at its peak on passage 3 and stopped after passage 5, whereas cell doubling time dramatically increased after passage 4. Expression of MSC surface markers (CD44, CD54, CD61, CD80, CD90 and Flk-1), molecule (HMGA2) and pluripotent markers (sox2, nanog) associated with self-renewal was negatively correlated with the number of passages. However, MSC surface marker (CD105) and pluripotent marker (Oct3/4) decreased with increasing the number of subpassage. cUC-MSCs at passage 1 to 5 underwent chondrogenesis under specific culture conditions, but percentage of chondrogenic differentiation decreased with increasing the number of subpassage. Collectively, the present study suggested that sequential subpassage could affect multipotent properties of cUC-MSCs and needs to be addressed before clinical applications.

• Smart Structures and Systems
• /
• 제21권5호
• /
• pp.591-600
• /
• 2018

The probabilistic characterization of wind field characteristics is a significant task for fatigue reliability assessment of long-span railway bridges in wind-prone regions. In consideration of the effect of wind direction, the stochastic properties of wind field should be represented by a bivariate statistical model of wind speed and direction. This paper presents the construction of the bivariate model of wind speed and direction at the site of a railway arch bridge by use of the long-term structural health monitoring (SHM) data. The wind characteristics are derived by analyzing the real-time wind monitoring data, such as the mean wind speed and direction, turbulence intensity, turbulence integral scale, and power spectral density. A sequential quadratic programming (SQP) algorithm-based finite mixture modeling method is proposed to formulate the joint distribution model of wind speed and direction. For the probability density function (PDF) of wind speed, a double-parameter Weibull distribution function is utilized, and a von Mises distribution function is applied to represent the PDF of wind direction. The SQP algorithm with multi-start points is used to estimate the parameters in the bivariate model, namely Weibull-von Mises mixture model. One-year wind monitoring data are selected to validate the effectiveness of the proposed modeling method. The optimal model is jointly evaluated by the Bayesian information criterion (BIC) and coefficient of determination, $R^2$. The obtained results indicate that the proposed SQP algorithm-based finite mixture modeling method can effectively establish the bivariate model of wind speed and direction. The established bivariate model of wind speed and direction will facilitate the wind-induced fatigue reliability assessment of long-span bridges.

• 분석과학
• /
• 제26권3호
• /
• pp.211-221
• /
• 2013

본 연구는 원주 법천사지에서 출토된 분청사기의 화학조성과 미세조직, 결정상을 X-선형광분석기와 주사전자현미경-에너지분산형엑스선분석기, X-선회절분석기를 이용하여 알아보았다. 태토의 화학성분 분석 결과, 낮은 실리카($RO_2$) 함량과 높은 융제(RO+$R_2O$) 함량임을 알 수 있다. 유약의 경우 융제 성분 중 CaO 함량이 높은 전형적인 석회계열(lime type)과 석회-알칼리 계열(lime-alkali type) 유약을 사용하였으며 태토의 결정상으로는 quarts, mullite, microcline, albite가 확인되었다. 특히 원주 법천사지에서 출토된 분청사기 태토의 화학적 조성은 제겔식을 이용하여 이미 연구된 다른 유적에서 출토된 분청사기와 비교하였으며 화학조성은 서로 상이한 결과를 보였다.

• 응용통계연구
• /
• 제30권1호
• /
• pp.1-12
• /
• 2017

많은 확률과정이 Markov 특성을 만족하거나 근사적으로 만족하는 것으로 가정된다. Markov 과정에서 특히 관심을 끄는 것은 최초통과시간이다. 최초통과시간에 대한 연구는 Wald의 축차분석에서 시작하여 근사적 특성에 대한 많은 연구가 되어왔고 컴퓨터의 발달로 통계계산적 방법이 사용되면서 근사적 결과가 참값에 가까운 값을 계산할 수 있게 되었다. 이 논문은 Markov 과정의 예로서 지수가중 이동평균 관리도를 사용할 때 평균런길이를 계산하는 과정과 계산상의 주의점, 문제점 등을 연구하였다. 이 결과는 다른 모든 Markov 과정에 적용될 수 있으며 특히 Markov 연쇄로의 근사는 확률과정의 특성의 연구에 유용하고 계산적 접근을 용이하게 한다.

• 공업화학
• /
• 제23권2호
• /
• pp.153-156
• /
• 2012

본 연구에서 직접 메탄올형 연료전지용 담지 촉매의 전기 화학적 효율을 높이기 위하여 담지 촉매의 합성을 위한 2가지 다른 방법을 조사하였다. 담지 촉매에 있어서 합금을 형성하여 동시 담지하는 방법과 금속을 순차적으로 담지하는 방법을 비교하였다. 금속의 총 함량을 20 wt%를 사용하였으며, Pt-Pd의 금속비를 1 : 2로 하였다. 순환 전류-전압곡선(CVs), TEM 이미지와 XRD분석을 이용하여 두가지 다른 방법으로 제조된 촉매 간의 전기화학적 특성, 입자의 평균 크기 및 결정의 구조 변화를 비교 분석하였다. 그 결과, 순차적 금속 담지 촉매가 동시 담지 촉매보다 단위 무게당 산화전류 수치를 나타내어 보다 높은 전기활성 특성을 보였다.

• Food Science and Biotechnology
• /
• 제14권3호
• /
• pp.375-379
• /
• 2005

Physicochemical properties, intestinal microbial growth, and inhibitory effects of alcohol-insoluble polysaccharide (AIP) extracted from cucumber peel were investigated. AIP was composed of 14.54% crude protein, 1.04% crude lipid, 13.74 % crude ash, 9.1% soluble dietary fiber, and 41.2% insoluble dietary fiber. AIP showed low bulk density (0.18 g/mL) and water-holding capacity (6.39 g/g), and high oil-holding capacity (3.96 g/g). Pectic substance fractions [water-soluble pectic substance (WSP), ethylenediaminetetraacetic acid-soluble pectic substance (ESP), and alkali-soluble pectic substances (ASP)] and hemicellulose fractions [1 M KOH-soluble hemicellulose (KHP1) and 4 M KOH-soluble hemicellulose (KHP4)] were obtained from sequential chemical fractionation of AIP. WSP showed higher total sugar contents than total uronic acid contents, whereas opposite results were observed in ESP and ASP. Molecular weight distributions of three pectic substance fractions were in order of ASP>ESP>WSP. Ion exchange chromatogram pattern of WSP was different from those of ESP and ASP. Major component of WSP was fraction eluted by 0.05 M ammonium acetate buffer, whereas that of ESP and ASP was fraction eluted by 0.2 M NaOH. WSP and ASP showed growth-promoting activities against Lactobacillus brevis, Bifidobacterium bifidum, and B. longum, whereas B. bifidum and B. longum for ESP. KHP1 and KHP4 fractions had significant growth-promoting activities against B. bifidum.

• Nuclear Engineering and Technology
• /
• 제46권1호
• /
• pp.117-124
• /
• 2014

The effect of various process variables on the powder properties of recycled $U_3O_8$ from MnO-$Al_2O_3$ doped large grain $UO_2$ pellets and the effect of those recycled $U_3O_8$ powders on the sintered density and grain size of MnO-$Al_2O_3$ doped large grain $UO_2$ pellets have been investigated. The evolution of morphology, size, and BET surface area of the recycled $U_3O_8$ powders according to the respective variation of the thermo-mechanical treatment variables of oxidation temperature, powder milling, and sequential cyclic heat treatment of oxidation and then reduction was examined. The correlation between the BET surface area of recycled $U_3O_8$ powder and the sintered pellet properties of MnO-$Al_2O_3$ doped pellets showed that the pellet density and grain size of doped pellets were increased and then saturated by increasing the BET surface area of the recycled $U_3O_8$ powder. The density and grain size of the pellets were maximized when the BET surface area of the recycled $U_3O_8$ powder was in the vicinity of $3m^2/g$. Among the process variables applied in this study, the cyclic heat treatment followed by low temperature oxidation was a potential process combination to obtain the sinter-active $U_3O_8$ powder.