• Journal of the Korean Institute of Intelligent Systems
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• v.3 no.2
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• pp.18-35
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• 1993

The water level control system of the steam generator in a pressurized water reactor and its control problems are analysed. In this work the stable control strategy during the low power operation and transient states is studied. To solve the problem, a fuzzy logic control method is applied as a basic algorithm of the controller. The control algorithm is based on the operator's knowledges and the experiences of manual operation for water level control at the compact nuclear simulator set up in Korea Atomic Energy Research Institute. From a viewpoint of the system realization, the control variables and rules are established considering simpler tuning and the input-output relation. The control strategy includes the dynamic tuning method and employs a substitutional information using the bypass valve opening instead of incorrectly measured signal at the low flow rate as the fuzzy variable of the flow rate during the pressure control mode of the steam generator. It also involves the switching algorithm between the control valves to suppress the perturbation of water level. The simulation results show that both of the fine control action at the small level error and the quick response at the large level error can be obtained and that the performance of the controller is improved.

• Health Policy and Management
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• v.6 no.1
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• pp.163-190
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• 1996

본 논문은 미국 농촌병원의 경영전략과 관련하여 몇가지 가설을 검증한 연구결과이다. 구체적으로 1987년부터 1991년 사이의 미국 농촌병원들의 기본적 경영전략 지향 형태와 변화 추세, 경영전략과 환경 및 병원특성과의 관계, 그리고 경영전략과 재정적 성과의 관계 등이 연구되었다. 본 연구의 자료수집은 미국 농촌지역의 모든 종교병원과 영리병원, 그리고 무작위 표본추출로 뽑힌 50%의 공공병원 및 기타 비영리 병원의 최고경영자를 대상으로 1989년에 우편설문조사를 통해 이루어졌으며 회수된 설문지 중 사용가능한 640개 병원 (응답율 43%)의 자료가 분석 이용되었다. 조사대상병원의 환경적 특성자료는 지역자원 파일(Area Resource File)에서 수집하였고, 병원특성 및 재정적 성과자료는 미국병원협회 연감(Annual Survey of Hospitals)에서 구하였다. 응답병원과 비응답병원간에 환경 및 병원특성에 유의한 차이는 없는 것으로 나타났다. 본 연구에서는 Miles와 Snow가 개발한 방어형(defender), 분석형(analyzer), 진보형(prospector), 반응형(reactor)의 네가지 경영전략지향 형태를 사용하여 분석하였다. 본 연구의 결과를 요약하면 다음과 같다. 1) 미국 농촌 병원들은 과거에는 방어형 및 분석형의 경영전략 지향을 보이다가 점차 반응형과 진보형으로 변화해 가고 있다. 2) 가장 뚜렷한 경영전략 지향의 변화추세는 방어형이 급격히 줄고 반응형이 크게 늘어나고 있다는 점이다. 이는 많은 병원들이 급격한 환경변화에 적응하기 위해 일관된 전략 지향보다 융통성 있고 탈력적인 경영전략을 선호하고 있음을 나타낸다. 3) 농촌병원들은 경영전략의 급격한 변화를 추구하지는 않을 것이라는 가설을 뒷받침할 근거는 없는 것으로 나타났다. 이는 급격한 의료환경의 변화로 인해 병원들이 다양한 경영전략의 변화를 모새하고 있는 것으로 볼 수 있다. 4) 대부분의 외부환경 및 병원특성은 병원의 전략지향의 선택에 큰 영향을 미치지 않는 것으로 나타났으나 인구 10,000명당 의사수, 병상규모, 위탁경영 여부, 병상점유율, 소유형태 등의 변수들이 경영전략 지향 형태에 따라 유의한 차이가 있는 것으로 나타났다. 5) 경영전략 지향이 상이한 병원들은 세부 실천전략에 있어서도 치이가 있을 것이라는 가설을 일부 전략에 있어서 사실인 것으로 나타났다. 즉 방어형 병원들은 진보형이나 반응형 병원들보다 내부관리전략, 다양화 전략, 의사유치전략, 직원복지전략 등에 있어서 소극적인 것으로 나타났다. 6) 비록 방어형 병원들이 다른 형태의 병원보다 낮은 재정적 성과를 보이고 있었지만 본 연구의 자료로는 경영전략지향과 재정적 성과간의 인과관계를 구명할 수 없었다. 또한 재정적성과에 따른 전략지향의 변화여부도 통계적으로 유의한 관계가 있지는 않은 것으로 나타났다. 이는 각각의 전략지향들이 환경에 따라 나름대로 장점을 가질 수 있으며 반드시 어느 한가지의 전략지향만이 최선은 아님을 시사해주고 있다. 7) 병원의 경영전략 변화는 환경의 변화와 더블어 그러한 변화에 적응할 수 있는 내부의 능력과도 관계가 있는 것으로 보인다. 이상의 연구결과에 따르면 미국의 농촌병원들은 급격한 환경변화에 적응하기 위하여 다수의 병원들이 환경 및 벼원특성에 관계없이 생존을 위한 전략적 노력을 기울이고 있음을 알 수 있다. 끝으로 이러한 연구결과는 최근 어려운 경영환경에 처한 한국의 농촌병원들도 합리적인 경영을 위해서는 병원이 처한 외부환경분석과 함께 내부의 능력에 적합한 경영전략의 방향을 설정하고 그에 따른 실천적 세부 경영전략을 수립해야만 한다는 것을 시사해 주고 있다.

• Applied Chemistry for Engineering
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• v.10 no.2
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• pp.252-258
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• 1999

Tetramethyl orthosilicate (TMOS) was obtained by the direct synthesis of methanol with metallic silicon including copper compound as a catalyst and zinc compound as a promoter. The effects of the preheating temperature and the preparation method of the contact mass on TMOS synthesis were investigated. The composition effects of the contact mass which was composed of metallic silicon with copper catalyst and various metallic halide promoters including Zn, Sn or Cd compound were studied also. The best performance on TMOS synthesis was observed on a mixed bed reactor containing metallic silicon preheated with CuCl as a catalyst and $ZnCl_2$ as a promoter. When Cu/Si = 7 wt %, Zn/Cu = 7 wt % was mixed in a slurry phase and activated into contact mass at $380^{\circ}C$, the average selectivity was 87.2% in the silicon consumption of 69.2% at $220^{\circ}C$.

• International Journal of Advanced Culture Technology
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• v.3 no.1
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• pp.21-30
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• 2015

Ceramic foams are prepared as positive images corresponding to a plastic foam structure which exhibits high porosities (85-90%). This structure makes the ceramic foams attractive as a catalyst in a dry reforming process, because it could reduce a high pressure drop problem. This problem causes low mass and heat transfers in the process. Furthermore, the reactants would shortly contact to catalyst surface, thus low conversion could occur. Therefore, this research addressed the preparation of dry reforming catalysts using a sol-gel catalyst preparation via a polymeric sponge method. The specific objectives of this work are to investigate the effects of polymer foam structure (such as porosity, pore sizes, and cell characteristics) on a catalyst performance and to observe the influences of catalyst preparation parameters to yield a replica of the original structure of polymeric foam. To accomplish these objectives industrial waste foams, polyurethane (PU) and polyvinyl alcohol (PVA) foams, were used as a polymeric template. Results indicated that the porosity of the polyurethane and polyvinyl alcohol foams were about 99% and 97%. Their average cell sizes were approximate 200 and 50 micrometres, respectively. The cell characteristics of polymer foams exhibited the character of a high permeability material that can be able to dip with ceramic slurry, which was synthesized with various viscosities, during a catalyst preparation step. Next, morphology of ceramic foams was explored using scanning electron microscopy (SEM), and catalyst properties, such as; temperature profile of catalyst reduction, metal dispersion, and surface area, were also characterized by $H_2-TPR$ and $H_2-TPD$ techniques, and BET, respectively. From the results, it was found that metal-particle dispersion was relatively high about 5.89%, whereas the surface area of ceramic foam catalysts was $64.52m^2/g$. Finally, the catalytic behaviour toward hydrogen production through the dry reforming of methane using a fixed-bed reactor was evaluated under certain operating conditions. The approaches from this research provide a direction for further improvement of marketable environmental friendly catalyst production.

• Clean Technology
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• v.18 no.2
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• pp.216-220
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• 2012

The objective of the present study was to evaluate catalytic performance of a commercial catalyst (Co/$ZrO_2-Al_2O_3$) for the decomposition of perfluorinated chemicals in a pilot scale reactor containing 30 L of catalysts. At a reaction condition of GHSV $1,800h^{-1}$, $T_{95}$ of $SF_6$ was increased from 580 to $610^{\circ}C$ with increasing of $SF_6$ concentration from 1,000 to 10,000 ppm. $T_{95}$ of $SF_6$ in catalytic decomposition was much smaller than that of thermal decomposition ($1,600^{\circ}C$). The 99% conversion of $SF_6$ was maintained for 72 hours a reaction temperature of $650^{\circ}C$. In order to maintain the $SF_6$ conversion more than 99%, it is necessary to operate at a reaction condition of GHSV less than $2,000h^{-1}$. An operating temperature of $710^{\circ}C$ was required to achieve >95% destruction of the $CF_4$, which was much higher than that of catalytic decomposition of $SF_6$.

• Journal of Korean Society of Environmental Engineers
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• v.27 no.2
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• pp.206-214
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• 2005

This study was initiated to evaluate efficiencies of suspenced-growth processes(CAS; Conventional Activated Sludge, MLE; Modified Ludzack-Ettinger) and hybrid process(Modified-Dephanox) on removal of organic matter(C), nitrogen(N) and phosphorus(P) in municipal wastewater. M-Dephanox process was designed to improve the performance of Dephanox process on denitrification efficiency. As the results, removal efficiencies of total chemical oxygen demand(TCOD), total nitrogen(T-N) and total phosphorus(T-P) in M-Dephanox process, which is hybrid process, were 12,3, 18.6 and 28.2% higher than those in MLE, which is suspended-growth process. The better removal efficiencies of TCOD, T-N and T-P in M-Dephanox than those in MLE result that M-Dephanox is not only hybrid or multi-sludge process but also process using biosorption mechanism which is possible to use organics in denitrification, effectively. Ammonia removal efficiency in nitrification reactor of M-Dephanox was 96.7% at short hydraulic retention time(HRT) of 2 hr which was 3 hr more short HRT than that(HRT 5 hr) reported in other related papers. This indicates that M-Dephanox process can reduce HRT of whole process.

• Journal of Microbiology and Biotechnology
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• v.27 no.2
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• pp.321-334
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• 2017

Process surveillance within agricultural biogas plants (BGPs) was concurrently studied by high-throughput 16S rRNA gene amplicon sequencing and an optimized quantitative microscopic fingerprinting (QMF) technique. In contrast to 16S rRNA gene amplicons, digitalized microscopy is a rapid and cost-effective method that facilitates enumeration and morphological differentiation of the most significant groups of methanogens regarding their shape and characteristic autofluorescent factor 420. Moreover, the fluorescence signal mirrors cell vitality. In this study, four different BGPs were investigated. The results indicated stable process performance in the mesophilic BGPs and in the thermophilic reactor. Bacterial subcommunity characterization revealed significant differences between the four BGPs. Most remarkably, the genera Defluviitoga and Halocella dominated the thermophilic bacterial subcommunity, whereas members of another taxon, Syntrophaceticus, were found to be abundant in the mesophilic BGP. The domain Archaea was dominated by the genus Methanoculleus in all four BGPs, followed by Methanosaeta in BGP1 and BGP3. In contrast, Methanothermobacter members were highly abundant in the thermophilic BGP4. Furthermore, a high consistency between the sequencing approach and the QMF method was shown, especially for the thermophilic BGP. The differences elucidated that using this biphasic approach for mesophilic BGPs provided novel insights regarding disaggregated single cells of Methanosarcina and Methanosaeta species. Both dominated the archaeal subcommunity and replaced coccoid Methanoculleus members belonging to the same group of Methanomicrobiales that have been frequently observed in similar BGPs. This work demonstrates that combining QMF and 16S rRNA gene amplicon sequencing is a complementary strategy to describe archaeal community structures within biogas processes.

• Korean Chemical Engineering Research
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• v.50 no.3
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• pp.516-521
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• 2012

This study developed a simple model to investigate effects of important operating parameters on performance of a bubbling-bed adsorber and regenerator system collecting $CO_2$ from flue gas. The chemical reaction rate was used with mean particles residence time of a reactor to determine the extent of conversion in both adsorber and regenerator reactors. Effects of process parameters - temperature, gas velocity, solid circulation rate, moisture content of feed gas - on $CO_2$ capture efficiency were investigated in a laboratory scale process. The $CO_2$ capture efficiency decreased with increasing temperature or gas velocity of the adsorber. However, it increased with increasing the moisture content of the flue gas or the regenerator temperature. The calculated $CO_2$ capture efficiency agreed to the measured value reasonably well. However the present model did not agree well to the effect of the solid circulation rate on $CO_2$ capture efficiency. Better understanding on contact efficiency between gas and particles was needed to interpret the effect properly.

• Korean Chemical Engineering Research
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• v.46 no.5
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• pp.922-930
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• 2008

The selective non-catalytic reduction(SNCR) performance is sensitive to the process parameters such as flow velocity, reaction temperature and mixing of reagent(ammonia or urea) with the flue gases. Therefore, the knowledge of the velocity field, temperature field and species concentration distribution is crucial for the design and operation of an effective SNCR injection system. In this work, a full-scale two-dimensional computational fluid dynamics(CFD)-based reacting model involving a droplet model is built and validated with the data obtained from a pilot-scale urea-based SNCR reactor installed with a 150 kW LPG burner. The kinetic mechanism with seven reactions for nitrogen oxides($NO_x$) reduction by urea-water solution is used to predict $NO_x$ reduction and ammonia slip. Using the turbulent reacting flow CFD model involving the discrete droplet phase, the CFD simulation results show maximum 20% difference from the experimental data for NO reduction. For $NH_3$ slip, the simulation results have a similar tendency with the experimental data with regard to the temperature and the normalized stoichiometric ratio(NSR).

• Korean Chemical Engineering Research
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• v.46 no.4
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• pp.806-812
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• 2008

The ammonia decomposition reaction has been of increasing interest as a means of treating ammonia in flue gas in the presence of precious metal catalyst. Various catalysts, $Pt-Rh/Al_2O_3$, $Pt-Rh/TiO_2$, $Pt-Rh/ZrO_2$, $Pt-Pd/Al_2O_3$, $Pd-Rh/Al_2O_3$, $Pd-Rh/TiO_2$, $Pd-Rh/ZrO_2$, $Pt-Pd-Rh/Al_2O_3$, $Pd/Ga-Al_2O_3$, $Rh/Ga-Al_2O_3$, and Ru/Ga-$Al_2O_3$, were synthesized by using excess wet impregnation method. Using a homemade 1/4" reactor at $10,000{\sim}50,000hr^{-1}$ of space velocity in the presence of precious metal catalyst ammonia decomposition reactions were carried out to investigate the catalyst activity. The inlet ammonia concentration was maintained at 2,000 ppm, with an air balance. Both $T_{50}$ and $T_{90}$, defined as the temperatures where 50% and 90% of ammonia, respectively, are converted, decreased significantly when alumina-supported catalysts were applied. In terms of catalytic performance on the ammonia conversion in the presence of hydrogen sulfide, $Pt-Rh/Al_2O_3$ catalyst showed no effect on the poisoning caused by hydrogen sulfide. These results indicate that platinum-rhodium bimetallic catalyst is a useful catalyst for ammonia decomposition.