• 한국결정학회:학술대회논문집
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• 한국결정학회 2002년도 정기총회 및 추계학술연구발표회
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• pp.12-12
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• 2002

Lanthanum manganites have been extensively studied for the application to magnetic devices since the colossal magnetoresistance of these compounds has been observed [1]. The critical temperatures, Tc, of manganites La/sub 0.7/Ca/sub 0.3-x/Ba/sub x/MnO₃ increased as the content of Ba increased except the abrupt jump near the critical concentration. The step like behavior of the critical temperature for a similar compound has been known to be related to the structural phase transition [2]. To understand the step like behavior of Tc, the EXAFS technique is applied to the La/sub 0.7/Ca/sub 0.3-x/Ba/sub x/MnO₃ compound system. The ordering between the manganese and oxygen was examined by this method. The EXAFS analysis shows that the coordination numbers were not changed before and after the phase transition, the bonding distance between manganese and oxygen is about 1.94 ± 0.02 Å, which is consistent with other work [3] and the Debye waller parameters were about σ²= 0.0037 ± 0.0005 Ų for x=0.0 and x=3.0, respectively. The value of Debye-Waller parameter for x=0.09 is about σ² = 0.0050 ± 0.0005 Ų in about phase transition concentration. Based on the Debye-Waller parameters, it is shown that the ordering between manganese and oxygen is significantly reduced near the phase transition concentration.

• 한국응용과학기술학회지
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• 제23권2호
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• pp.160-168
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• 2006

The conductances of trimethyltetradecylammonium bromide (TTAB) plus triphenyltetradecyl phosphonium bromide (TTPB) and TTAB plus trimethylhexadecylammonium bromide (HTAB) over the entire mole fraction range of TTAB were measured in water and in cyclodextrin plus water mixtures at fixed 4 and 8 mM of cyclodextrin at $30^{\circ}C$. The conductivity plot for both binary mixtures shows a single break from which the mixed critical micelle concentration and degree of micelle ionization were computed. From the slope of the conductivity curve, the equivalent ionic conductivities of the monomeric, associated, and the micelle states were calculated and discussed with respect to the surfactant-cyclodextrin complexation in the whole mole fraction range of both surfactant binary mixtures. The association constant K between the respective monomeric surfactant and cyclodextrin cavity of fixed 4 mM cyclodextrin was computed by considering 1:1 association from the surface tension measurement. A comparison among the K values for HTAB-cyclodetrin, TTAB-cyclodextrin, and TTPB-cyclodextrin shows that the former complexation is significantly stronger in comparison to the other ones due to the longer hydrophobic tail.

• 한국수자원학회논문집
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• 제31권1호
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• pp.115-120
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• 1998

본 논문에서는 수심적분 2차원 모형을 하나 소개하고, 이 모형이 가질 수 있는 오차의 한계를 민감도분석을 통해 제시하였다. 민감도 분석 결과, Manning 조도계수, 혼합계수, 침강속도, 한계전단력 등이 부유사농도에 대해 모형에 미치는 영향은 매우 크게 나타났으며, 조위와 확산계수의 영향은 거의 없는 것으로 나타났다.

• Bulletin of the Korean Chemical Society
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• 제12권4호
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• pp.411-413
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• 1991

The effects of electrolyte on the critical micelle concentration (cmc) and bromide counterion binding in the micelles of cetylpyridinium bromide (CPB) have been investigated by UV spectroscopy and conductance measurements. Salts used in this study decreased cmc in the order $Cl^-\;<\;Br^-\;<\;NO3^-$ (which parallels the lyotropic series for the inorganic anions) and the effects on cmc followed the equation proposed by Shinoda: log cmc = A - B log (cmc + [NaX]). In the equation, constant B represents the counterion binding to the micelles at cmc and for the micelle of CPB at $25^{\circ}C$, B=80.76%. The association constant for the binding of counterions to long chain cations within micelles was also derived from the cmc values and counterion binding constant to the micelles.

• 한국대기환경학회:학술대회논문집
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• 한국대기환경학회 2008년도 춘계학술대회 논문집
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• pp.532-534
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• 2008

• 펄프종이기술
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• 제46권6호
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• pp.1-7
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• 2014

Dissolving part of xylan and lignin in lignocellulosic biomass by base can be used as pretreatment technique. Cork oak was pretreated with sodium hydroxide solution and the pretreatment effects were evaluated with two critical factors - NaOH concentration and pretreatment temperature. Some of xylan and lignin were removed by base pretreatment. At $90^{\circ}C$ and 13% NaOH pretreatment, 22.0% of lignin and 78.8% of xylan removed by base treatment. Enzymatic hydrolysis of cork oak which was pretreated at higher temperature or concentration was further improved. After pretreatment of cork oak with 13% NaOH at $90^{\circ}C$, the conversion rate of cellulose to fermentable sugars were reached up to 91.3%. At ethanol fermentation with enzymatic hydrolysate from different pretreatment conditions, all enzymatic saccharification liquids were well fermented by Saccharomyces cerevisiae.

• 유기물자원화
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• 제9권1호
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• pp.119-126
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• 2001

PAHs로 오염된 토양을 슬러리 생물반응기로 처리할 경우, 재순환수와 계면활성제 첨가가 PAHs 제거율에 미치는 영향을 살펴보고자 하였다. 대부분 실험결과에서 1차 반응모델이 0차 반응모델보다 phenanthren과 pyrene의 제거율을 설명하는데 높은 상관계수를 나타냈다. 재순환수 및 CMC(critical micelle concentration)이상으로 계면활성제를 첨가한 실험에서 첨가하지 않은 경우 보다 phenanthrene과 pyrene의 제거율이 향상되었다.

• Korea-Australia Rheology Journal
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• 제14권4호
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• pp.189-201
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• 2002

The interaction between hydrophobically modified hydroxyethyl cellulose (hmHEC), containing approximately 1 wt% side-alkyl chains of $C_{16}$, and an anionic sodium dodecyl sulphate (SDS) surfactant was investigated. For a semi-dilute solution of 0.5 wt% hmHEC, the previously observed behaviour of a maximum in solution viscosity at intermediate SDS concentrations, followed by a drop at higher SDS concentrations, until above the cmc of surfactant when the solution resembles that of the unsubstituted polymer, was confirmed. Additionally, a two-phase region containing a hydrogel phase and a water-like supernatant was found at low SDS concentrations up to 0.2 wt%, a concentration which is akin to the critical association concentration, cac, of SDS in the presence of hmHEC. Above this concentration, SDS molecules bind strongly to form mixed micellar aggregates with the polymer alkyl side-chains, thus strengthening the network junctions, resulting in the observed increase in viscosity and elastic modulus of the solution. The shear behaviour of this polymer-surfactant complex during steady and step stress experiments was examined In great detail. Between SDS concentrations of 0.2 and 0.25 wt%, the shear viscosity of the hmHEC-polymer complex network undergoes shear-induced thickening, followed by a two-stage shear-induced fracture or break-up of the network. The thickening is thought to be due to structural rearrangement, causing the network of flexible polymers to expand, enabling some polymer hydrophobic groups to be converted from intra- to inter-chain associations. At higher applied stress, a partial local break-up of the network occurs, while at even higher stress, above the critical or network yield stress, a complete fracture of the network into small microgel-like units, Is believed to occur. This second network rupture is progressive with time of shear and no steady state in viscosity was observed even after 300 s. The structure which was reformed after the cessation of shear is found to be significantly different from the original state.

• Asian-Australasian Journal of Animal Sciences
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• 제12권3호
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• pp.422-428
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• 1999

The mineral status of native goats and forage species, namely; Cynodon plectostachyus, Pennisetum purpureum. Eleusine indica, Cynodon dactylon, Calopogonium muconoides, Centrosema pubescens, Leucaena leococephala, and Mimosa pudica in lahar affected areas of Concepcion, Tarlac, Philippines were determined. Forage and blood samples were collected six times in 1996-97, and analyzed for calcium, phosphorus, magnesium, sulfur, copper, iron, molybdenum, selenium, and zinc. Forage calcium and sulfur are non-limiting. Most species had low phosphorus, copper and selenium, while some had magnesium and zinc levels lower than the critical limit because of low mineral content and high percolation rate of lahar deposits. Iron and molybdenum were in excess. The effect of seasonal variation was observed only in copper, sulfur and iron. Average blood mineral concentration of the animals was above critical limit, but there were no significant differences between seasons. All the animals had plasma phosphorus and magnesium above critical level; but 20 % had low copper, zinc and selenium especially in dry season possibly due to insufficient amount of these elements and excessive molybdenum and iron in most forage. Conversely, calcium in forage was high; but 40 % of the animals had low plasma calcium concentration. Although no clinical signs of mineral deficiencies were observed, supplemental feeding would be important since the condition of the pasture in lahar-laden areas is not expected to improve in the next five years. Intensified use of L. leucocephala with better mineral profile would be ideal.

• Bulletin of the Korean Chemical Society
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• 제5권5호
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• pp.182-187
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• 1984

The polarographic and conductometric studies of methyl viologen $(MV^{++})$ solutions with varying concentration of sodium dodecyl sulfate (SDS) showed strong association of $MV^{++}$ and its cationic radical, $MV^+$., with SDS below the critical micelle concentration. The stoichiometries of these associations were found to be their electric charge ratios. Both electrostatic and hydrophobic interactions were found to contribute to the associations. The formation constant of$MV^+.DS^-$ in 0.1 M NaCl was $7{\times}10^3M$. The $MV^{++}$-SDS association was observed to be cooperative leading to formation of large aggregates. In the presence of $MV^{++}$, the micellization of SDS was formation of SDS homo-micelle without direct involvement of $MV^{++}$.