• International Journal of Quality Innovation
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• 제1권1호
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• pp.89-96
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• 2000

Evolutionary operation (EVOP) is a continuous improvement system which explores a region of process operating conditions by deliberately creating some systematic changes to the process variable levels without jeopardizing the product. It is aimed at securing a satisfactory operating condition in full-scale manufacturing processes, which is generally different from that obtained in laboratory or pilot plant experiments. Information on how to improve the process is generated from a simple experimental design. Traditional EVOP procedures are established on the assumption that the variance of the response variable should be small and stable in the region of the process operation. However, it is often the case that process noises have an influence on the stability of the process. This process instability is due to many factors such as raw materials, ambient temperature, and equipment wear. Therefore, process variables should be optimized continuously not only to meet the target value but also to keep the variance of the response variables as low as possible. We propose a scheme to achieve robust process improvement. As a process performance measure, we adopted the mean square error (MSE) of the replicate response values on a specific operating condition, and used the Kruskal-Wallis test to identify significant differences between the process operating conditions.

• 상하수도학회지
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• 제24권4호
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• pp.407-412
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• 2010

The purpose of this study was to investigate removal efficiencies of contaminants in night soil treatment plant using the B3 system. The samples were collected from retaining tank and settlement tank in Yechon night soil plant. We experimented concentrations of BOD, COD, SS, TN and TP. Concentration data were processed using removal efficiencies by season and correlation analysis with pilot running parameters. Removal efficiencies of total organic carbon was over 96%, TN was 98% during summer, 80.9% during winter. In the case of TP, the highest removal efficiencies was 94.1% during fall and the lowest removal efficiencies was 82% during spring. Results of correlation analysis showed two positive correlation groups and one negative group. Positive correlations were among temperature, BOD and TN. The others were pH, BOD, COD, SS, TN and TP. Negative correlation were among MLSS, BOD, COD, SS, TN, TP.

• 상하수도학회지
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• 제22권3호
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• pp.351-358
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• 2008

The modified in-line mixer which was suggested in this study for small water treatment facilities was evaluated on the performance of coagulation. For the objectives of this research, computational fluid dynamics(CFD) simulation was applied for analysis of flow characteristics within the modified in-line mixer. For verifying the results of CFD simulation, wet tests for the pilot plant were conducted. The wet test was to measure the actual coagulant dispersion distribution on the overall cross-section at a distance of 5.5D from the chemical injection point. From the results of CFD simulation and wet test, it was shown that the coagulant dispersion within the modified in-line mixer was occurred more uniformly than within the existing PDM(Pump diffusion Mixer). The results have confirmed the modified in-line mixer had several advantages compared with the existing PDM in terms of dispersion efficiency.

• 상하수도학회지
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• 제32권5호
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• pp.411-419
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• 2018

The residual chlorine concentration is an essential factor to secure reliable water quality in the water distribution systems. The chlorine concentration decays along the pipeline system and the main processes of the reaction can be divided into the bulk decay and the wall decay mechanisms. Using EPANET 2.0, it is possible to predict the chlorine decay through bulk decay and wall decay based on the pipeline geometry and the hydraulic analysis of the water distribution system. In this study, we tried to verify the predictability of EPANET 2.0 using data collected from experimental practices. We performed chlorine concentration measurement according to various Reynolds numbers in a pilot-scale water distribution system. The chlorine concentration was predicted using both bulk decay model and wall decay model. As a result of the comparison between experimental data and simulated data, the performance of the limited $1^{st}$-order model was found to the best in the bulk decay model. The wall decay model simulated the initial decay well, but the overall chlorine decay cannot be properly predicted. Simulation also indicated that as the Reynolds number increased, the impact of the wall.

• 한국환경과학회지
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• 제14권3호
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• pp.327-333
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• 2005

The performance of ozone contactor in ozone-BAC advanced water treatment process was evaluated by the degree of decomposition of organic matters. The degree was measured by the analyses of $UV_{254}$ absorbance and the concentrations of DOC and BDOC for the sand filtered water and the ozone treated water, respectively. In addition, the ozone concentration in the contactor, required for the maximum BDOC concentration, was selected as the optimum concentration, and the appropriate residential time of ozone treated water in a reservoir was recommended based on the residual ozone concentration in the treated water. The following results were obtained from the pilot scale experiments. By ozonation $UV_{254}$ absorbance was decreased, and BDOC concentration was increased. The change of DOC concentration by ozonation was negligible, but the excess input of ozone resulted in the removal of the small amount of BDOC by complete oxidation. The optimum ozone concentration was 0.58mg $O_3/mg$ DOC. In order to remove residual ozone, 20minutes of the residential time were enough after ozonation.

• 한국안전학회지
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• 제31권1호
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• pp.54-60
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• 2016

The bottom of dikes must be kept impermeable to control hazardous chemicals spilled from storage tanks. Currently, insufficient related chemical control laws lead to a possibility to spread through the bottom. Generally, due to the high cost of installation and periodical maintenance, many businesses prefer to install the bottom with general concrete. But, since the impermeability of concrete is dependent on the kind of materials and chemical reaction, all concrete cannot be considered as impermeable material. Thus, it is necessary to make the installation standards of the dike bottom clear in order to avoid the argument over the impermeability and prevent the chemical accident. This study has suggested the standards of impermeable concrete by conducting 7-day exposure test to crude oil with the pilot dikes. The results have showed that the standards have the better impermeable performance compared with the germany standard, which have been penetrated at the maximum penetration depth of 1.9 cm. This study is expected to contribute to both the risk reduction of penetrating into the bottom and the cost reduction of spending to make the bottom of dikes impermeable.

• Membrane and Water Treatment
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• 제8권5호
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• pp.395-409
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• 2017

Membrane bioreactor (MBR) is a compact and efficient wastewater treatment and reclamation technology; but, it is limited by membrane fouling. The control of membrane fouling significantly increases operational and maintenance costs. Bacteria and their byproducts - extracellular polymeric substances (EPS) - are major contributors to membrane fouling in MBRs. A recent attempt at fouling mitigation is the development of aerobic granular sludge membrane bioreactor (AGMBR) through the integration of a novel biotechnology - aerobic granulation - and MBR. This paper provides an overview on the development of AGMBR to mitigate membrane fouling caused by bacteria and EPS. In AGMBR, EPS are used up in granule formation; and, the rigid structure of granules provides a surface for bacteria to attach to rather than the membrane surface. Preliminary research on AGMBR using synthetic wastewater show remarkable membrane fouling reduction compared to conventional MBR, thus improved membrane filtration. Enhanced performance in AGMBR using actual municipal wastewater at pilot-scale has also been reported. Therefore, further research is needed to determine AGMBR optimal operational conditions to enhance granule stability in long-term operations and in full-scale applications.

• 대한기계학회논문집B
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• 제25권2호
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• pp.244-251
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• 2001

This paper describes a design study of heat exchanger assembly to be used for low NOx condensing gas boiler. In this study, specifications of each heat exchanger components(upper and lower fin-type HEX, coil-type HEX, baffle) were investigated experimently by using model apparatus and analytical model, and comprehensive performances of the pilot gas boiler were examined. As a result, the boiler efficiency for heating and hot-water reached 90% and 94%, respectively. NOx and CO emission are less than 50ppm and 200ppm (0$_2$0% basis), respectively, which are very improved results than those of conventional bunsen-type boiler. But it is considered that supplementary investigations necessary for CO emission improvement and optimum design with boiler capacity.

• 간호행정학회지
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• 제12권3호
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• pp.373-384
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• 2006

Purpose: This is a pilot study to identify patient safety risk factors and strategies for patient safety management perceived by nurses. Methods: Data were collected and analyzed with an open questionnaire from April to May 2005, targeted on 100 nurses working in two hospitals. The issues were 'what are risk factors for patients, nurses, and other medical practitioners? How do they prevent with the aftermath of risk factors, causes of incidents?' For data analysis, types and frequency of risk factors were worked out, using the Australian Incident Monitoring System Taxonomy. Results: The types of patient safety risk factor perceived by nurses were as follows ; therapeutic devices or equipment, infrastructure and services (29.5%), nosocomial infections (16.3%), clinical processes or procedures (15.4%), behavior, human performance, violence, aggression, security and safety (12.2%), therapeutic agents (9.7%), injuries and pressure ulcers (8.7%), logistics, organization, documentation, and infrastructure technology (5.6%). Strategies for patient safety included training of prevention of infection, education about safety management for patients and medical professionals, establishment of reporting system, culture of care, pre-elimination of risk factors, cooperative system among employees, and sharing information. Conclusion: These results will be used to provide evidences for patient safety management and educational program.

• 한국정보통신학회논문지
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• 제17권3호
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• pp.556-560
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• 2013

고성능 스마트폰이 본격 보급되면서 폭발적으로 증가하고 있는 데이터 트래픽을 효과적으로 수용하기 위한 해법들에 대한 관심이 높아지고 있다. 이동통신용으로 활용할 수 있는 주파수에 제한이 있기 때문에, 최근에는 동일주파수를 사용하면서 추가적으로 용량을 확보할 수 있는 펨토셀에 대한 연구 및 개발이 활발히 진행되고 있다. 본 논문에서는 기존 매크로 신호가 존재하는 환경에서 데이터 오프로딩을 위하여 펨토셀을 구축할 경우를 가정하여, 펨토셀의 커버리지를 수학적으로 분석하였다. 분석 결과, 펨토셀의 출력이 증가할수록 그리고 파일럿 채널에 할당하는 전력의 비율이 높아질수록 펨토셀의 커버리지가 증가하지만, 매크로 기지국 신호가 강한 트래픽 밀집 지역에서는 펨토셀의 커버리지가 매우 제한적임을 알 수 있었다.