• Nuclear Engineering and Technology
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• 제55권2호
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• pp.452-459
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• 2023

The core power control is an important issue for the study of dynamic characteristics in China initiative accelerator driven subcritical system (CiADS), which has direct impact on the control strategy and safety analysis process. The CiADS is an experimental facility that is only controlled by the proton beam intensity without considering the control rods in the current engineering design stage. In order to get the optimized operation scheme with the stable and reliable features, the variation of beam intensity using the continuous and periodic control approaches has been adopted, and the change of collimator and the adjusting of duty ratio have been proposed in the power control process. Considering the neutronics and the thermal-hydraulics characteristics in CiADS, the physical model for the core power control has been established by means of the point reactor kinetics method and the lumped parameter method. Moreover, the multi-inputs single-output (MISO) logical structure for the power control process has been constructed using proportional integral derivative (PID) controller, and the meta-heuristic algorithm has been employed to obtain the global optimized parameters for the stable running mode without producing large perturbations. Finally, the verification and validation of the control method have been tested based on the reference scenarios in considering the disturbances of spallation neutron source and inlet temperature respectively, where all the numerical results reveal that the optimization method has satisfactory performance in the CiADS core power control scenarios.

• Korean Chemical Engineering Research
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• 제45권2호
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• pp.166-171
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• 2007

칼슘 이온에 의해 젤화되는 알지네이트를 내부가 고상인 비드와 내부가 액상인 캡슐 형태로 각각 만들어 납이온 흡착 특성을 비교하여 보았다. 흡착 키네틱과 흡착 등온선 분석을 통해 칼슘-알지네이트 비드와 캡슐의 흡착 특성 차이를 pH 및 경화 시간에 따른 변화, 흡착시 칼슘 이온 방출량의 모니터링을 통해 검토하였다. 비드와 캡슐의 구조적 차이에 상관없이 두 흡착제 모두 표면착화(surface complexation)와 이온교환(ion exchange) 메커니즘에 의해 납 이온을 흡착하였고, 흡착량에 상관없이 두 메커니즘 간의 비율은 유사하였다. 납이온 흡착에 대한 pH 의존성은 비드와 캡슐이 유사하였으며, 이는 두 흡착제에 존재하는 표면 작용기가 유사함을 의미한다. 반면에 흡착 키네틱 분석에서는 캡슐에 비해 비드에서의 납이온 흡착 속도가 느렸으며, 흡착 등온선 분석에서 얻은 납이온의 최대 흡착량($Q_{max}$)은 알지네 이트 비드가 캡슐의 약 49% 정도로 나타났다. 이러한 납이온 흡착 거동의 차이는 비드와 캡슐 간의 구조적 차이에 기인한 것으로, 알지네이트 비드는 확산 저항에 의해 상대적으로 느린 흡착 속도 및 단위 무게당 적은 흡착량을 보이는 것으로 판단된다.

• Bulletin of the Korean Chemical Society
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• 제29권6호
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• pp.1115-1120
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• 2008

The adsorption of CO on W(110) surfaces was studied using thermal desorption spectroscopy (TDS), and core and valence level spectroscopy. At 120 K, CO forms a tilted structure at lower coverages ($\alpha$ 1), whereas it adsorbs normal to the surface at higher coverages ($\alpha$ 2). Tilted structures have been suggested to be precursors of dissociative chemisorption; however, experimental evidence is provided for the non-dissociative chemisorption of CO at temperatures above 900 K (which is referred to as the $\beta$ -state): TDS shows first order desorption kinetics. The core and valence level spectra of O/W(110) and those of $\beta$ -CO/W(110) are different. Most importantly, the 4$\sigma$ molecular orbital of CO can be identified in the valence level spectra of the $\beta$ -CO.

• Journal of Pharmaceutical Investigation
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• 제22권1호
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• pp.33-40
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• 1992

This study was aimed to control the release characteristics of ketoprofen by microencapsulating $ketoprofen-{\beta}-cyclodextrin\;(KF-{\beta}-CyD)$ solid dispersion with Eudragit RS by the phase separation method using a nonaqueous vehicle. KF alone was also microencapsulated with Eudragit RS by the evaporation process in water phase. The results obtained showed that it was not possible to microencapsulate KF alone by phase separation in a chloroform-cyclohexane system while it was easy to microencapsulate $(KF-{\beta}-CyD)$ solid dispersion system. For the microcapsules, the release test was performed in the first fluid (pH 1.2) and the second fluid (pH 6.8) of K.P.V disintegration medium at $37^{\circ}C$. The release of KF from $(KF-{\beta}-CyD)$ solid dispersion microcapsules (1:1 core wall ratio) was more sustained than that from KF microcapsules, and followed zero-order kinetics. Especially, solid dispersion microcapsules showed pH-independent release patterns with higher wall to core ratio (1:1 w/w).

• Journal of Pharmaceutical Investigation
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• 제39권4호
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• pp.269-273
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• 2009

The objective of this investigation was to develop a gastro-retentive(GR) dosage form of gabapentin and was to evaluate of its dissolution characteristics. GR tablet consists of expandable core tablet matrix and semi-permeable membrane coating. Poloxamer 407 and sodium bicarbonate were used to prepare the core matrix. Polyvinly acetate dispersion (Kollicoat $SR30D^{(R)}$) and polyvinyl alcohol-polyethylene glycol copolymer ((Kollicoat $IR^{(R)}$)) were employed to form the semi-permeable membrane. The GR tablets significantly expanded up to fivefold in simulated gastrointestinal fluids with no apparent damage of the coating membrane over 12 hours. Also, the swelling rate was controllable with the amount of sodium bicarbonate. The drug release was observed to be substantially sustained based on coating level. The release rate of gabapentin from the GR tablet was gradually slowed down as the coasting amount was increased. The gabapentin GR tablet with 8% coating level showed a pseudo-zero order release kinetics over 12 hours. These results suggest that this swellable GR tablet system having semi-permeable membrane coating can be applicable for hydrophilic drug substances like gabapentin.

• Elastomers and Composites
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• 제37권2호
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• pp.124-133
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• 2002

온화한 조건($80{\sim}110^{\circ}C$, 대기압)하에서 비누화반응에 의해 폐 PBT의 입자를 해중합하여다. PBT의 해중합은 KOH 보다 NaOH가 보다 효과적이었으며, 반응온도가 증가하고 입자의 크기가 작을수록 해중합은 증가하였다. 해중합속도는 표면반응이 율속단계로서 PBT 입자표면에 생성물이 형성되지 않은 미반응핵 모델에 의해 표현할수 있었다. 겉보기활성화에너지는 98.1KJ/mol 이었으며, 85.1, $105{\mu}m$인 PBT 입자를 6시간 동안 해중합하였을때 TPA의 회수율은 약 95%정도였다.

• Nuclear Engineering and Technology
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• 제37권1호
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• pp.25-78
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• 2005

As a key and core knowledge for the design of various types of nuclear reactors, the discipline of reactor physics has been advanced continually in the past six decades and has led to a very sophisticated fabric of analysis methods and computer codes in use today. Notwithstanding, the discipline faces interesting challenges from next-generation nuclear reactors and innovative new fuel designs in the coming. After presenting a brief overview of important tasks and steps involved in the nuclear design and analysis of a reactor, this article focuses on the currently-used design and analysis methods, issues and limitations, and current activities to resolve them as follows: (1) Derivation of the multi group transport equations and the multi group diffusion equations, with representative solution methods thereof. (2) Elements of modem (now almost three decades old) diffusion nodal methods. (3) Limitations of nodal methods such as transverse integration, flux reconstruction, and analysis of UO2-MOX mixed cores. Homogenization and related issues. (4) Description of the analytic function expansion nodal (AFEN) method. (5) Ongoing efforts for three-dimensional whole-core heterogeneous transport calculations and acceleration methods. (6) Elements of spatial kinetics calculation methods and coupled neutronics and thermal-hydraulics transient analysis. (7) Identification of future research and development areas in advanced reactors and Generation-IV reactors, in particular, in very high temperature gas reactor (VHTR) cores.

• 한국재료학회지
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• 제28권8호
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• pp.466-473
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• 2018

Nickel oxide(NiO) thin films, nanorods, and carbon nanotube(CNT)/NiO core-shell nanorod structures are fabricated by sputtering Nickel at different deposition time on alumina substrates or single wall carbon nanotube templates followed by oxidation treatments at different temperatures, 400 and $700^{\circ}C$. Structural analyses are carried out by scanning electron microscopy and x-ray diffraction. NiO thinfilm, nanorod and CNT/NiO core-shell nanorod structurals of the gas sensor structures are tested for detection of $H_2S$ gas. The NiO structures exhibit the highest response at $200^{\circ}C$ and high selectivity to $H_2S$ among other gases of NO, $NH_3$, $H_2$, CO, etc. The nanorod structures have a higher sensing performance than the thin films and carbon nanotube/NiO core-shell structures. The gold catalyst deposited on NiO nanorods further improve the sensing performance, particularly the recovery kinetics.

• Nuclear Engineering and Technology
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• 제19권3호
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• pp.192-197
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• 1987

다량의 중수반사체를 가진 조밀한 노심에서는 핵분열시 발생하는ｒ선과 중수소와의 (ｒ,n) 반응에 의해 지발 광중성자가 다량 생성되므로 이러한 계통을 기술하기 위하여 광중성자와 그 모핵종의 공간적 분리에 역점을 두어 2-점노 운동방정식을 정립하였다. 여러 반응도를 주입하여 출력 천이를 모사계산하므로써 노심과 반사체사이의 관련 효과를 조사하였다. 이 모델에 의한 모사계산 결과와 공간 종속 운동방정식에 의한 계산결과를 비교하였다. 반사체 영역에서의 광중성자 효과가 포함되므로써, 이를 포함하지 않은 모델에 비해 출력 천이현상을 감소시켰다. 실제로 출력을 측정하는 계측기는 이러한 공간적 분리영 향을 제거하기 위하여 노심 내부에 위치하여야 한다.

• 한국생물정보학회:학술대회논문집
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• 한국생물정보시스템생물학회 2005년도 BIOINFO 2005
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• pp.272-277
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• 2005

We introduce a new approach to optimize the parameters in biological kinetic models by quantifier elimination (QE), in combination with numerical simulation methods. The optimization method was applied to a model for the inhibition kinetics of HIV proteinase with ten parameters and nine variables, and attained the goodness of fit to 300 points of observed data with the same magnitude as that obtained by the previous optimization methods, remarkably by using only one or two points of data. Furthermore, the utilization of QE demonstrated the feasibility of the present method for elucidating the behavior of the parameters in the analyzed model. The present symbolic-numeric method is therefore a powerful approach to reveal the fundamental mechanisms of kinetic models, in addition to being a computational engine.