• Membrane Journal
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• v.28 no.6
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• pp.388-394
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• 2018

Carbon nanotube (CNT) based membranes are promising candidates for separation membranes by showing high water transport rate and ion rejection rate according to their radii. The ion selectivity is an important factor to discover the full potential of CNT membranes, and it is affected by the functionalization of CNTs. With multivalent/size ion mixtures, the ion selectivity is affected by not only ion-functional groups interaction but also ion-ion interactions and ion size exclusion in a complex manner. In this study, molecular dynamics simulations are performed to study the ion selectivity of functionalized carbon nanotubes when multivalent/size ions are contained. The permeation energy barriers are calculated by plotting potential of mean force profiles, and various factors, such as CNT size and partial charges, affecting ion selectivity are investigated. The results presented here will be useful for designing CNT membranes for ion separation, biomimetic ion channels, etc.

• Journal of the Korean Chemical Society
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• v.35 no.6
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• pp.617-624
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• 1991

Nonstoichiometric solid solutions of $Y_{1-x}A_xFeO_{3-y}$ (A = Ca, Sr) systems with perovskite structure were prepared for x = 0.00, 0.25, 0.50, 0.75 and 1.00 at 1200$^{\circ}C$ under atmospheric pressure, respectively. Crystallographic structures of the solid solutions of all compositions have been determined by the analysis of X-ray diffraction patterns. Reduced lattice volume of the $Y_{1-x}Ca_xFeO_{3-y}$ system was decreased with increasing x value and that of the $Y_{1-x}Sr_xFeO_{3-y}$ system was increased with increasing the x value. The mole ratios of $ Fe^{4+}$ to $ Fe^{3+}$, ${\tau}$, values in the solid solutions have been determined by Mohr salt's method of analysis and then the mixed valency was identified by Mossbauer spectroscopic analysis at 298 K. The y values were calculated from the x and ${\tau}$, and then nonstoichiometric chemical formulas were fixed. The conduction mechanism could be explained by hopping model of the conduction electrons between the mixed valence states.

• Journal of the Korean Society of Environmental Restoration Technology
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• v.7 no.3
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• pp.48-55
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• 2004

본 연구는 중 저해상도 위성영상을 이용하여 하천주변 습지를 판별해내는 보다 개선된 기법을 개발해 내는데 그 목적이 있다. 중 저해상도 위성영상의 하나의 화소는 일반적으로 하나의 동질한 물체의 분광반사값을 나타내기보다는 다양한 분광값을 가진 물체들의 대표값으로 나타나게 된다. 특히 본 연구에서는 식생, 수문 및 토양요소의 혼합체인 습지의 판별을 위해서, 하나의 화소가 하나의 물체를 대표함을 전제로 하는 기존의 분석방법 보다는, 혼합화소 (mixed pixel)를 대상지 의 토지 피복을 가장 잘 반영 하는 순수한 화소값(endmember)들로 분해함으로써 보다 정확한 판별 및 분류를 가능케 하고자 하였다. 이를 위하여 일반적으로 극세분광 위성영상의 분석에 활용되는 기법인 분광혼합화소분석(Spectral Mixture Analysis)을 이용하였는데, 습지 각 화소의 식생, 수문 및 토양요소의 흔합정도를 분해한 후, 이들의 분할영상 (fraction images)을 추출해내고 이를 분석에 이용하였다. 팔당상수원보호구역의 소택형 습지를 대상으로 봄 가을의 Landsat 영상에 대한 분석을 수행하였으며, 도출된 결과는 다음과 같다. 첫째, 봄 가을 각각의 영상에 대하여 4개씩 endmember를 선정하였으며, 분할영상과 원자료 각각에 대하여 습지판별을 수행한 결과, 가을영상에 대하여 분할영상을 이용한 방법의 소택 형 습지 판별 정확도가 가장 높은 값을 보여주었다(생산자 정확도 : 83.3%, 사용자 정확도 : 86.5%). 둘째, 소택형 습지로 판별된 지역만을 대상으로 보다 세분화된 분류가 가능한 지 알아보기 위하여 소택형 습지로 판별된 지역의 영상에 대해 ISODATA 무감독분류를 수행한 결과 2개의 클러스터로 대별되었다. 현장조사, 기존 연구의 수심자료 및 식생에 대한 조사를 바탕으로 위의 2개의 클러스터를 조사한 결과, 수문조건에 따른 분류인 아계(subsystem) 단계의 '영구적 침수형 소택형 습지'와 '계절적 침수형 소택형 습지'로 분류할 수 있었다.

• Journal of computational fluids engineering
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• v.20 no.1
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• pp.84-91
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• 2015

SMART adopts, very unique facility, an FMHA to enhance the thermal and flow mixing capability in abnormal conditions of some steam generators or reactor coolant pumps. The FMHA is important for enhancing thermal mixing of the core inlet flow during a transient and even during accidents, and thus it is essential that the thermal mixing characteristics of flow of the FMHA be understood. Investigations for the mixing characteristics of the FMHA had been performed by using experimental and CFD methods in KAERI. In this study, the temperature distribution at the core inlet region is investigated for several abnormal conditions of steam generators using the commercial code, FLUENT 12. Simulations are carried out with two kinds of FMHA shapes, different mesh resolutions, turbulence models, and steam generator conditions. The CFD results show that the temperature deviation at the core inlet reduces greatly for all turbulence models and steam generator conditions tested here, and the effect of mesh refinement on the temperature distribution at the core inlet is negligible. Even though the uniformity of FMHA outlet hole flow increases the thermal mixing, the temperature deviation at the core inlet is within an acceptable range. We numerically confirmed that the FMHA applied in SMART has an excellent mixing capability and all simulation cases tested here satisfies the design requirement for FMHA thermal mixing capability.

• Analytical Science and Technology
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• v.14 no.4
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• pp.324-330
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• 2001

For the analysis of S, P and Zn in lubricating oil, microwave digestion method was studied by using inductively coupled plasma-atomic emission spectrometry(ICP-AES). Lubricating oil was completely decomposed with nitric acid or a mixture of nitric acid and hydrogen peroxide using and closed microwave digestion system. Digestions are completed within 50 min, a factor of at least 3~4 times faster than for the conventional digestion. A gradual heating program operated by the pulsed mode was found suitable for decomposing the lubricating oil matrix safely. The proposed method of digestion gave relative standard deviations(RSD) less than 3% for the elements determined.

• Proceedings of the KIEE Conference
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• 2000.11a
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• pp.262-264
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• 2000

원자로 내에서 연소 중인 핵연료나 저장 또는 재처리 중인 사용후핵연료의 성분으로서 시설의 공정설계, 안전성분석 및 차폐설계에 중요한 입력자료가 되는 핵분열생성물질, 방사화생성물 및 악티나이드의 핵종 농도와 이에 대응하는 방사능 강도의 기기 별 시간변 화율을 해석할 수 있는 코드 개발할 목적으로 MULTISAMS 정상 평형상태 모델을 구현하였다. MULTISAMS 코드의 반응공정 모델은 서로 연결되어 있으며 내부에 방사성물질의 혼합유체가 순환하는 세 종류의 반응기(원자로, 열교환기 및 화학반응기) 계통에서 자연적 또는 설계에 의해 일어나는 현상으로서; 반응기 간의 물질 흐름; 각 반응기 내에서 방사성 붕괴, 변환, 이동과 중성자 흡수 및 핵분열; 외부로부터 특정 핵종의 유입혹은 유출을 고려한 시간종속 핵종농도보존방정식 이론에 근거한다. 코드의 유용성 및 신뢰성을 검증하기 위해 현재 개념설계가 진행 중인 AMBIDEXTER원자력 에너지시스템을 대상으로 ORIGEN2 계산과 비교하였다. 두 코드 간의 입력조건과 배경이론차이점 때문에 절대적 비교가 불가능하므로 단순이론의 중간매개코드로서 SAMS를 이용한 2단계 비교방법을 따랐다. 결론은 MULTISAMS는 ORIGEN2 계산의 수렴치와 근사하게 일치하면서 ORIGEN2 가 다룰 수 없는 핵주기 연속후처리공정의 정상가동 시 핵종 평형농도를 기기 별로 계산할 수 있다는 장점을 확인하였다.

• Journal of the Korean Chemical Society
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• v.29 no.3
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• pp.220-225
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• 1985

An attempt was made to determine some trace metals in highly concentrated samples using micro sampling technique in flame atomic absorption spectrophotometry. Major instrumental parameters and optimun analytical conditions investigated were the measuring time of instrument (the speed of electronics), sample volume, burner height, aspiration rate, and fuel to oxidant ratio. Advantages of the present technique are not only rapid, simple, and sensitive with good precision but also capability of analyzing small volume of sample and ability to handle highly concentrated samples without serious burner clog-up problem compared to conventional flame atomic absorption.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.14 no.4
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• pp.129-134
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• 2004

In this study, we investigated the effect of a nitrogen atom on the amorphization of V-Fe alloy through solid-gas reaction during mechanical alloying (MA). MA by planetary ball mill of $V_{70}Fe_{30}$ elemental powders was carried out under the nitrogen gas atmosphere. Amorphization has been observed after 160 hours of ball milling in this case. The DSC spectrum for the mechanically alloyed ($V_{70}Fe$_{30}$)_{0.89}N_{0.11}$ powders exhibits a sharp exothermic peak due to crystallization at about $600^{\circ}C$. Structural transformation from the bcc crystalline to amorphous states was also observed through X-ray and neutron diffractions. We take a full advantage of a negligibly small scattering length of the V atom in the neutron diffraction measurement. During amorphization process the octahedral unit, which is typical of a polyhedron formed in any crystal structures, was preferentially destroyed and transformed into the tetrahedral unit. Futhermore, neutron diffraction measurements revealed that a nitrogen atom is selectively situated at a center of the polyhedron formed by V atoms.

• Applied Chemistry for Engineering
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• v.10 no.7
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• pp.990-995
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• 1999

To determine the effect of chemical structure of linear amine curing agents on thermal and mechanical properties, standard epoxy resin DGEBA was cured with ethylene diamine(EDA) and hexamethylene diamine(HMDA) in a stoichiometrically equivalent ratio. From this work, the effect of linear amine curing agents on the thermal and mechanical properties is significantly influenced by the chemical structure or chain length of curing agents. In contrast, the results show that the DGEBA/EDA system having the two carbons had higher values in the thermal stability, maximum conversion of epoxide, density, glass transition temperature, tensile modulus, flexural strength, and flexural modulus than the DGEBA/HMDA system having the six carbons, whereas the DGEBA/EDA cure system had relatively low values in the shrinkage(%), thermal expansion coefficient, tensile strength, and had similar values in the maximum exothermic temperature, and conversion of epoxide compared to the DGEBA/HMDA cure system. This findings indicate that packing ability in the HMDA structure affects the thermal and mechanical properties.

• Journal of the Korean Chemical Society
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• v.39 no.3
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• pp.204-212
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• 1995

The graphite furnace atomic absorption spectrophotometric determination of trace lead in water samples was studied using matrix modifiers. In order to modify the sample matrix, the type and optimum amount of the modifier were investigated with a given concentration of Pb solution. In fact, if the matrix is not modified, lead has low ashing and atomization temperatures as to give a low absorbance with bad reproducibility because of its volatility. Therefore, optimum modifiers should be used to stabilize the atomization. In this work, the ashing and atomization temperatures were raised from 400 and $1800^{\circ}C$, to 1,000 and $2000^{\circ}C$, by the addition of palladium to 50 ng/mL lead solution as a modifier. The concentration of palladium was 5.0 ${\mu}g/mL$ in the modified solution. Furthermore, if 1.5 ${\mu}g/mL$ of aluminum was mixed with the palladium modifier as an auxiliary modifier, the ashing temperature could be increased $150^{\circ}C$ additionally. With such a treatment, the sensitivity was improved more than 5 times of the solution unmodified and the reproducible results of less than 5% RSD were obtained in the samples of university's waste water and pipe-washing tap water. It could be concluded that this procedure was quantitative in the determination of trace lead from the recoveries of more than 88% obtained in the samples in which a given amount of lead was spiked.