• Geomechanics and Engineering
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• 제33권1호
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• pp.65-75
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• 2023

Recycled concrete aggregate (RCA) is widely used as a construction material in road construction, concrete structures, embankments, etc. However, it has been reported that calcite (CaCO₃) precipitation from RCA can be a cause of clogging when used in drainage applications. An accelerated calcite precipitation (ACP) procedure has been devised to evaluate the long-term geochemical performance of RCA in subsurface drainage systems. While the ACP procedure was useful for the French Drain application, there remained opportunities for improvement. In this study, key factors that control the formation of calcite precipitation were quantitatively evaluated, and the results were used to improve the current prototype ACP method. A laboratory parametric study was carried out by investigating the effects of reaction temperature and time on the formation of calcite precipitation of RCA, with determining an optimum reaction temperature and time which maximizes calcite precipitation. The improved ACP procedure was then applied to RCA samples that were graded for Type I Underdrain application, to compare the calcite precipitation. Two key findings are (1) that calcite precipitation can be maximized with the optimum heating temperature (75℃) and time (17 hours), and (2) the potential for calcite precipitation from RCA is not as significant as for limestone. With the improved ACP procedure, the total amount of calcite precipitation from RCAs within the life cycle of a drain system can be determined when RCAs from different sources are used as pipe backfill materials in a drain system.

• 한국세라믹학회지
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• 제25권5호
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• pp.509-517
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• 1988

The controlled Ti(CO2H5)4 hydrolysis reactions for the synthesis of Spherical Monodispersed Titania powders are described. Increasing the concentration of TEOT and the molar ratio of water to TEOT in alcohol solution decrease the reaction time and the particle size. The reaction time is delalyed by increasing the chain length and the number of carbon branches of alcohol as a solvent. The prepared powders with an average diameter of 0.8$\mu$ and the spherical monodispersed transfer to Rutile phase at 55$0^{\circ}C$.

• 약학회지
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• 제22권1호
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• pp.15-21
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• 1978

Gentamicin sulfate reacted with pyridoxal and zinc (II) ion in pyridine-methanol solution to yield highly fluorescent zinc(II) chelates of N-pyridoxylidene derivatives. This fluorescence reaction was sensitive and showed excitation maximum at 398nm, and emission maximum at 482nm. The effects of reagent concentration, reaction time and temperature, standing time and temperature were studied. And a new fluorophotometric method for the determination of gentamicin sulfate was developed. A good result was obtained and this method was applied to various preparations.

• 한국지능시스템학회:학술대회논문집
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• 한국퍼지및지능시스템학회 1993년도 Fifth International Fuzzy Systems Association World Congress 93
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• pp.1106-1108
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• 1993

This paper deals with an industrial application of a fuzzy feedback combined learning control to an industrial batch free radical polymerization reactor. As a result, the plant has reduced the batch reaction time by 50 minute and stabilized both by 40 percent reduction of the standard deviations of product qualities, such as the total solid content and the graft gum, and by 45 percent reduction of the standard deviation of the batch reaction end time.

• Bulletin of the Korean Chemical Society
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• 제16권11호
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• pp.1113-1118
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• 1995

The Schlo'gl model with the first order transition for a photochemical reaction is considered to study the dynamic behaviors in the neighborhood of the Gaussian white noise by obtaining the explicit results of the time-dependent variance and time correlation function with the aid of approximate methods based on the stationary properties of the system. Then, we discuss the effect of external noise strength on the stability of the model at steady states in detail.

• Bulletin of the Korean Chemical Society
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• 제16권11호
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• pp.1119-1121
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• 1995

The method for the Schlo"gl model with the first order transition is extended to the Scho;gl model with the second order transition for a photochemical reaction. We obtain the explicit results of the time-dependent average and the time correlation function at the unstable steady state of the model in the neighborhood of the Gaussian white noise and then discuss the effect of noise on the dynamic properties.

• 한국안전학회지
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• 제27권5호
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• pp.77-87
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• 2012

Compared to a batch reactor, where all reactants are initially charged to the reactor, the semi-batch reactor presents serious advantages. The feed of at least one of the reactants provides an additional way of controlling the reaction course, which represents a safety factor and increases the constancy of the product quality. The aim of this study was to investigate the characteristics of thermal hazard such as a feed time, catalysis concentration and solvent concentration in methylthioisocyanate(MTI) synthesis reaction process. The experiments were carried out by the Multimax reactor system and Accelerating rate calorimeter(ARC). The MTI synthesis reaction process has many reaction factors and complicated reaction mechanism of multiphase reaction. Through this study, we can use as a tool for assessment of thermal hazard of other reaction processes by applying experiment method provided.

• 자원리싸이클링
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• 제18권3호
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• pp.42-48
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• 2009

고로 수쇄 슬래그에 알칼리 자극제(NaOH+$Na_2O.SiO_2$)를 첨가한 계는 보통 포틀랜드 시멘트의 수화반응과 다르게, 수화반응 초기에 높은 농도의 $OH^-,\;[SiO_4]^{4-}$ 이온이 존재하게 되므로, 유도기가 없이 수화반응이 빠르게 진행되며, 슬래그 입자 주위에 수화물에 의한 reaction rim을 형성한다 반응기간 1일부터 고로 수쇄 슬래그 입자 주위에 $0.6{\mu}m$의 reaction rim이 형성되었고, 반응기간이 증가함에 따라 reaction rim의 두께는 증가하여 28일에 $1{\mu}m$으로 성장하였으며, 미반응 고로 수쇄 슬래그 입자는 각진 형태에서 구형의 형태로 변화되었다. 슬래그 입자의 내부로부터 reaction rim으로 갈수록 Ca/Si의 몰비는 감소하는 경향을 나타냈었다. 그리고 반응기간이 경과할수록 슬래그 입자 내부와 reaction rim간의 Ca/Si 몰비 차이는 작아졌으며, 생성된 수화물은 저결정성의 Ca/Si 몰비가 1.5 미만인 CSH(I)이었다.

• 핵의학기술
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• 제12권3호
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• pp.176-180
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• 2008

Department of Nuclear Medicine in Seoul National University Hospital (SNUH) had developed $^{18}F$-Flumazenil as Benzodiazepine receptor imaging agent for PET diagnosis of Epilepsy. But production Activity of $^{18}F$-Flumazenil is decreased owing to this method has difficult synthesis procedures and pretty long synthesis time. In this study, we can modify synthesizing method to have more simple procedure and less spend time and help to increase production Activity. Old method: Radioactivity was produced by cyclotron was captured by QMA cartridge that was activated. Captured radioactivity was eluted into the reaction vial by using kryptofix solution and delivered. After evaporation of eluent, the azeotrophic drying step repeated two times. tosylflumazenil in anhydrous Acetonitrile was added to a reaction vial while bubbling. The reaction mixture was evaporated until the mixture volume was 0.5 mL. Reaction vial washed with 20 % Acetonitrile and that solution went into the reaction vial. The reaction mixture was loaded to the HPLC loop by hand and purified $^{18}F$-Flumazenil by HPLC column. New method: We used $TBAHCO_3$ solution as a eluent. After the eluent was evaporated, tosylflumazenil in anhydrous acetonitrile was added to a reaction vial and the reaction mixture was bubbled for 15 minutes. It was evaporated until the mixture volume became 0.5 mL. It was loaded to the HPLC loop. In old method, $^{18}F$-Flumazenil was synthesized via 6 steps synthesis procedures in 105 minutes with 30~35% synthesizing yield (non-decay correction) and specific activity was about $0.5{\sim}2{\times}10^5$ Ci/mole. In new method, It had 3 steps synthesis procedures in 53 minutes with 40~45% synthesizing yield and specific activity was about $3{\sim}8{\times}10^5$ Ci/mole. This method leads to improve of minimizing synthesis time, increasing synthesis yield and specific activity. While we can load reaction mixture to the HPLC loop, we can expose high radiation field thanks to used by hand.

• 공업화학
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• 제31권2호
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• pp.147-152
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• 2020

본 연구에서는 천연오일인 cashew nut shell liquid (CNSL)의 구성성분인 cardanol을 이용하여 내화학성이 향상된 에폭시계 수지용 반응성 희석제 제조 공정을 최적화하였다. 이를 위해 반응표면분석법 중 중심합성계획법을 이용하여 최적화과정를 설계하였다. 계량인자로는 cardanol/ECH 반응몰비, 반응시간, 반응온도이고, 반응치는 수율, 에폭시 당량(EEW), 점도이다. 기초실험으로부터 계량인자 범위를 각각 cardanol/ECH 반응몰비(2~4), 반응시간(4~8 h), 반응온도(100~140 ℃)로 설정한 후 최적화과정을 진행한 결과 최적의 조건은 cardanol/ECH 반응몰비(3.33), 반응시간(6.18 h), 반응온도(120 ℃)로 산출되었으며, 이 조건에서의 예측값은 수율(100%), EEW (429.89 g/eq.), 점도(41.65 cP)로 나타났다. 실제 실험을 통해 알아본 결과 오차율은 0.3% 이하로 나타나 중심합성계획모델을 이용하여 cardanol 원료 반응성 희석제의 제조 공정을 최적화할 수 있었다.