• Macromolecular Research
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• 제14권5호
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• pp.510-516
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• 2006

Lactide was produced from oligomeric PLA by back-biting reaction of the OH end groups. For optimization of the reaction conditions, the effects of temperature, pressure, PLA molecular weight, and catalyst type on the lactide synthesis were examined. The fraction of D,L-lactide decreased with increasing temperature. Among the various Sn-based catalysts, the D,L-lactide fraction was maximized when SnO was used. A higher yield with lower racemization was observed at lower pressure. The conversion of PLA was maximized at an oligomeric PLA molecular weight of ca. 1380. The yield of lactide increased but the fraction of D,L-lactide decreased with increasing molecular weight. The highest conversion with the lowest racemization degree was obtained at a catalyst concentration of 0.1 wt%. The lactide was more sensitive to racemization because of the entropic effect.

• 물과 미래
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• 제23권4호
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• pp.477-486
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• 1990

지하수 오염처리에 관한 문제는 수공학 이외에도 지질학, 화학, 독극물학 등의 전문지식이 요구된다는 점에서 Expert System(이하 ES)가 설계되기에 이상적인 환경을 지니고 있는 분야이다. 본 연구의 목적은 오염물질로 오염된 지하수의 처리에 대한 조언과 그것에 대한 추적을 위한 소프트웨어의 개발에 있다. Prolog 언어를 사용하여 개발된 이 프로그램은 현장 실무자에게 독극성의 정도와 화학반응의 축연성, 특정지점의 농도계산을 통하여 현 상황에 대한 심각성의 정도와 대응책을 조언하게 된다.

• 한국건축시공학회지
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• 제14권3호
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• pp.273-284
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• 2014

Ultra-high-performance concrete (UHPC) consists of cement, silica fume (SF), sand, fibers, water and superplasticizer. Typical water/binder ratios are 0.15 to 0.20 with 20 to 30% silica fume. In the production of ultra-high performance concrete, a significant temperature rise at an early age can be observed because of the higher cement content per unit mass of concrete. In this paper, by considering the production of calcium hydroxide in cement hydration and its consumption in the pozzolanic reaction, a numerical model is proposed to simulate the hydration of ultra-high performance concrete. The heat evolution rate of UHPC is determined from the contributions of cement hydration and the pozzolanic reaction. Furthermore, by combining a blended-cement hydration model with the finite-element method, the temperature history in the hardening of UHPC is evaluated using the degree of hydration of the cement and the silica fume. The predicted temperature-history curves were compared with experimental data, and a good correlation was found.

• Preventive Nutrition and Food Science
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• 제3권1호
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• pp.10-14
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• 1998

The hydrolysis conditions of blue mussel were evaluated by response surface methodology(RSM) for the alkaline protease Optimise TM APL-440 . Conditions favoring the highest degree of hydrolysis in blue mussel were pH 9,8, 58$^{\circ}C$ reaction temperature, 2,9 hrs reaction time, 46.8%(w/v) substrate concentration, and 0.34%(v/w) enzym $e_strate ratio. Levels of n-3 fatty acids, e.g.C18 : 3, C18 : 4, and C20 : 5, did not change after hydrolysis in blue mussel sample.le.

• 한국어업기술학회:학술대회논문집
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• 한국어업기술학회 2001년도 춘계 수산관련학회 공동학술대회발표요지집
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• pp.530-531
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• 2001

Out of 20 primers, 6 generated 1349 highly reproducible RAPD markers, producing approximately 5.2 polymorphic bands per primer in catfish(Sizurus asotus) population from Kunsan. The electrophoretic analysis of polymerase chain reaction-random amplified polymorphic DNAs (PCR-RAPD) products showed the middle levels of similarity between different individuals in population from Kunsan. That is to say, the degree of similarity varied from 0.40 to 0.54, with the average of 0.46, as calculated by bandsharing analysis. (omitted)

• Bulletin of the Korean Chemical Society
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• 제11권1호
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• pp.1-7
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• 1990

We present a theoretical investigation on the etching of an Al solid by $SiCl_4$ molecules at a collision energy of 600 eV. The classical trajectory method is employed to calculate Al etching yields, degree of anisotropy, kinetic energy distribution and angular distribution. The calculated results are compared with the reaction of a Cu solid by $SiCl_4$. The major products of the reaction are aluminum monomers and dimers together with considerable quantities of multimers. The Al solid shows better etching yield and better anisotropy than the Cu solid. This is consistent with the problem in the CMOS micro-fabrication of the CuAl and CuAlSi alloys. The relevance of these calculations for the dry etching of CuAl alloy is discussed.

• Bulletin of the Korean Chemical Society
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• 제13권1호
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• pp.59-64
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• 1992

The contrasting behaviour of meso-and d,l-$D_3$-trishomocubylidene-$D_3$-trishomocubane (1 and 2) in the electrophilic addition reaction, the former giving rearranged spiro compound (1a and 1b) and the latter giving 1,2-adduct (2a and 2b), has been explained as arising from the secondary steric effects based on computational evidence. As the degree of out-of-plane deformation of the olefinic carbon atoms increases with reaction progress, the resulting internal congestion in the region behind the double bond becomes unbearably large in meso-1. The absence of symmetry plane across the double bond of d,l-2 helps for the closing fragments to adjust themselves.

• Bulletin of the Korean Chemical Society
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• 제5권3호
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• pp.126-129
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• 1984

The reaction of aryl halides with phenoxides and alkoxides were investigated under phase transfer catalytic conditions. 2,4-Dinitro- and 4-nitrohalobenzenes reacted readily with phenoxides in NaOH(aq)-benzene in the presence of Bu4N+Br, affording the products quantitatively. Although the aryl halides did not react with alkoxides under the same condition, the reactions were completed within 2 hours at room temperature when conducted under solid-liquid phase transfenr catalytic condition. The reactivity of aryl halides was in the order, Ar = 2,4-dinitrophenyl > 4-nitrophenyl, and X = F > Cl, consistent with the SNAr mechanism. The reactivity of oxyanions increased with the change of reaction condition from liquid-liquid to solid-liquid phase transfer catalysis. The results were explained with the concentration and the degree of hydration of the anion in benzene.

• Bulletin of the Korean Chemical Society
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• 제11권5호
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• pp.455-460
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• 1990

2,5-Disubstituted tetrahydrofurans 11-13 were prepared by phenylselenoetherification of 1-alkyl-4-phenyl-(3E)-butenols 8-10 under kinetic conditions. Their stereochemical outcome and reactivity were controlled by solvent, reaction temperature and the alkyl substituent. While the cyclization was stereorandom in dichloromethane, its stereoinduction was moderate to good in propionitrile and good to excellent in diethyl ether. The reaction went to completion in dichloromethane and propionitrile, but it did not in diethyl ether. The results can be rationalized by the degree of reversibility in the formation of episelenonium cation and 1,3-diaxial interactions in the transition state of the formation of tetrahydrofuranonium cation.

• Bulletin of the Korean Chemical Society
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• 제15권7호
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• pp.576-581
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• 1994

The secondary deuterium kinetic isotope effects (SDKIE) involving deuterated aniline nucleophiles are reported for the reactions of benzyl bromides and chlorides and benzoyl chlorides in acetonitrile. The benzyl systems behave normally as to the trend of changes in SDKIE with the magnitude of ${\rho}X({\rho}_{nuc})$, whereas benzoyl system shows ananomaly; ${\mid}{\rho}_X{\mid}$ decreases with increase in the extent of bond making estimated by the SDKIE. This has been ascribed to the negative charge accumulation at the reaction center carbon in the transition state. The magnitude of ${\rho}_{XY}$ is found to decrease by ca. 0.03 with ten degree rise in the reaction temperature.