• Journal of Korean Society of Disaster and Security
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• v.17 no.2
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• pp.1-11
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• 2024

Most reservoirs in South Korea are earthen dams, mainly because they are cost-effective and easy to construct. However, earthen dams are highly vulnerable to seepage and overtopping, making them prone to sudden failure during excessive flooding. Such sudden failures can lead to a rapid increase in flood discharge, causing significant damage to downstream rivers and inhabited areas. This study investigates the effect of riprap placement on the slopes of earthen dams in delaying dam failure. Delaying the failure time is crucial as it allows more time for evacuation, significantly reducing potential casualties, which is essential from a disaster response perspective. Hydraulic experiments were conducted in a straight channel, using two different sizes of riprap for protection. Unlike previous studies, these experiments were performed under unsteady flow conditions to reflect the impact of rising water levels inside the dam. The target dam for the study was a cofferdam installed in a diversion tunnel. Experimental results indicated that the presence of riprap protection effectively prevented slope failure under the tested conditions. Without riprap protection, increasing the size of the riprap delayed the failure time. This delay can reduce peak discharge, mitigating damage downstream of the dam. Furthermore, these findings can serve as critical reference material for establishing emergency action plans (EAP) for reservoir failure.

• Korean Chemical Engineering Research
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• v.51 no.2
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• pp.267-271
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• 2013

Test bed studies with highly efficient amine $CO_2$ solvent (KoSol-4) developed by KEPCO research institute were performed. For the first time in Korea, evaluation of post-combustion $CO_2$ capture technology to capture 2 ton $CO_2$/day from a slipstream of the flue gas from a coal-fired power station was performed. Also the analysis of solvent regeneration energy was conducted to suggest the reliable performance data of the KoSol-4 solvent. For this purpose, we have tested 5 campaigns changing the operating conditions of the solvent flow rate and the stripper pressure. The overall results of these campaigns showed that the $CO_2$ removal rate met the technical guideline ($CO_2$ removal rate: 90%) suggested by IEA-GHG and that the regeneration energy of the KoSol-4 showed about 3.0~3.2 GJ/$tCO_2$ which was, compared to that of the commercial solvent MEA (Monoethanolamine), about 25% reduction of regeneration energy. Based on these results, we could confirm the good performance of the KoSol-4 solvent and the $CO_2$ capture process developed by KEPCO research institute. And also it was expected that the cost of $CO_2$ avoided could be reduced drastically if the KoSol-4 is applied to the commercial scale $CO_2$ capture plant.

• Journal of the Korean Society of Radiology
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• v.11 no.5
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• pp.297-302
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• 2017

Recently, building materials and air purification filters with eco-friendly charcoal are actively studying to reduce the concentration of radon gas in indoor air. In this study, radon reduction performance was assessed by designing and producing new panel-type activated carbon filter that can be handled more efficiently than conventional charcoal filters, which can reduce radon gas. For the fabrication of our panel-type activated carbon filter, first the pressed molding product after mixing activated carbon powder and polyurethane. Then, through diamond cutting, the activated carbon filter of 2 mm, 4 mm and 6 mm thickness were fabricated. To investigate the physical characteristics of the fabricated activated carbon filter, a surface area and flexural strength measurement was performed. In addition, to evaluate the reduction performance of radon gas in indoor, the radon concentration of before and after the filter passes from a constant amount of air flow using three acrylic chambers was measured, respectively. As a result, the surface area of the fabricated activated carbon was approximately $1,008m^2/g$ showing similar value to conventional products. Also, the flexural load was found to have three times higher value than the gypsum board with 435 N. Finally, the radon reduction efficiency from indoor gas improved as the thickness of the activated carbon increases, resulting in an excellent radon removal rate of more than 90 % in the 6 mm thick filter. From the experimental results, the panel-type activated carbon is considered to be available as an eco-friendly building material to reduce radon gas in an enclosed indoor environment.

• Journal of the Korean Society for Library and Information Science
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• v.4
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• pp.43-71
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• 1975

Operations research has developed rapidly since its origins in World War II. Practitioners of O. R. have contributed to almost every aspect of government and business. More recently, a number of operations researchers have turned their attention to library and information systems, and the author believes that significant research has resulted. It is the purpose of this essay to introduce the library audience to some of these accomplishments, to present some of the author's hypotheses on the subject of library management to which he belives O. R. has great potential, and to suggest some future research directions. Some problem areas in librianship where O. R. may play a part have been discussed and are summarized below. (1) Library location. It is usually necessary to make balance between accessibility and cost In location problems. Many mathematical methods are available for identifying the optimal locations once the balance between these two criteria has been decided. The major difficulties lie in relating cost to size and in taking future change into account when discriminating possible solutions. (2) Planning new facilities. Standard approaches to using mathematical models for simple investment decisions are well established. If the problem is one of choosing the most economical way of achieving a certain objective, one may compare th althenatives by using one of the discounted cash flow techniques. In other situations it may be necessary to use of cost-benefit approach. (3) Allocating library resources. In order to allocate the resources to best advantage the librarian needs to know how the effectiveness of the services he offers depends on the way he puts his resources. The O. R. approach to the problems is to construct a model representing effectiveness as a mathematical function of levels of different inputs(e.g., numbers of people in different jobs, acquisitions of different types, physical resources). (4) Long term planning. Resource allocation problems are generally concerned with up to one and a half years ahead. The longer term certainly offers both greater freedom of action and greater uncertainty. Thus it is difficult to generalize about long term planning problems. In other fields, however, O. R. has made a significant contribution to long range planning and it is likely to have one to make in librarianship as well. (5) Public relations. It is generally accepted that actual and potential users are too ignorant both of the range of library services provided and of how to make use of them. How should services be brought to the attention of potential users? The answer seems to lie in obtaining empirical evidence by controlled experiments in which a group of libraries participated. (6) Acquisition policy. In comparing alternative policies for acquisition of materials one needs to know the implications of each service which depends on the stock. Second is the relative importance to be ascribed to each service for each class of user. By reducing the level of the first, formal models will allow the librarian to concentrate his attention upon the value judgements which will be necessary for the second. (7) Loan policy. The approach to choosing between loan policies is much the same as the previous approach. (8) Manpower planning. For large library systems one should consider constructing models which will permit the skills necessary in the future with predictions of the skills that will be available, so as to allow informed decisions. (9) Management information system for libraries. A great deal of data can be available in libraries as a by-product of all recording activities. It is particularly tempting when procedures are computerized to make summary statistics available as a management information system. The values of information to particular decisions that may have to be taken future is best assessed in terms of a model of the relevant problem. (10) Management gaming. One of the most common uses of a management game is as a means of developing staff's to take decisions. The value of such exercises depends upon the validity of the computerized model. If the model were sufficiently simple to take the form of a mathematical equation, decision-makers would probably able to learn adequately from a graph. More complex situations require simulation models. (11) Diagnostics tools. Libraries are sufficiently complex systems that it would be useful to have available simple means of telling whether performance could be regarded as satisfactory which, if it could not, would also provide pointers to what was wrong. (12) Data banks. It would appear to be worth considering establishing a bank for certain types of data. It certain items on questionnaires were to take a standard form, a greater pool of data would de available for various analysis. (13) Effectiveness measures. The meaning of a library performance measure is not readily interpreted. Each measure must itself be assessed in relation to the corresponding measures for earlier periods of time and a standard measure that may be a corresponding measure in another library, the 'norm', the 'best practice', or user expectations.

• Journal of Intelligence and Information Systems
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• v.20 no.4
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• pp.121-139
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• 2014

Predicting corporate failure has been an important topic in accounting and finance. The costs associated with bankruptcy are high, so the accuracy of bankruptcy prediction is greatly important for financial institutions. Lots of researchers have dealt with the topic associated with bankruptcy prediction in the past three decades. The current research attempts to use ensemble models for improving the performance of bankruptcy prediction. Ensemble classification is to combine individually trained classifiers in order to gain more accurate prediction than individual models. Ensemble techniques are shown to be very useful for improving the generalization ability of the classifier. Bagging is the most commonly used methods for constructing ensemble classifiers. In bagging, the different training data subsets are randomly drawn with replacement from the original training dataset. Base classifiers are trained on the different bootstrap samples. Instance selection is to select critical instances while deleting and removing irrelevant and harmful instances from the original set. Instance selection and bagging are quite well known in data mining. However, few studies have dealt with the integration of instance selection and bagging. This study proposes an improved bagging ensemble based on instance selection using genetic algorithms (GA) for improving the performance of SVM. GA is an efficient optimization procedure based on the theory of natural selection and evolution. GA uses the idea of survival of the fittest by progressively accepting better solutions to the problems. GA searches by maintaining a population of solutions from which better solutions are created rather than making incremental changes to a single solution to the problem. The initial solution population is generated randomly and evolves into the next generation by genetic operators such as selection, crossover and mutation. The solutions coded by strings are evaluated by the fitness function. The proposed model consists of two phases: GA based Instance Selection and Instance based Bagging. In the first phase, GA is used to select optimal instance subset that is used as input data of bagging model. In this study, the chromosome is encoded as a form of binary string for the instance subset. In this phase, the population size was set to 100 while maximum number of generations was set to 150. We set the crossover rate and mutation rate to 0.7 and 0.1 respectively. We used the prediction accuracy of model as the fitness function of GA. SVM model is trained on training data set using the selected instance subset. The prediction accuracy of SVM model over test data set is used as fitness value in order to avoid overfitting. In the second phase, we used the optimal instance subset selected in the first phase as input data of bagging model. We used SVM model as base classifier for bagging ensemble. The majority voting scheme was used as a combining method in this study. This study applies the proposed model to the bankruptcy prediction problem using a real data set from Korean companies. The research data used in this study contains 1832 externally non-audited firms which filed for bankruptcy (916 cases) and non-bankruptcy (916 cases). Financial ratios categorized as stability, profitability, growth, activity and cash flow were investigated through literature review and basic statistical methods and we selected 8 financial ratios as the final input variables. We separated the whole data into three subsets as training, test and validation data set. In this study, we compared the proposed model with several comparative models including the simple individual SVM model, the simple bagging model and the instance selection based SVM model. The McNemar tests were used to examine whether the proposed model significantly outperforms the other models. The experimental results show that the proposed model outperforms the other models.

• Journal of Chest Surgery
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• v.29 no.7
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• pp.689-699
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• 1996

An animal experiment was designed for the evaluation of in vivo performance of the newly developed electrohydraulic type ventricular assist device and its influence on the left ventricular function during pal- satile left ventricular assist. Eight adult sheep were incorporated into the study and data were collected from seven sheep. Total as- sist time ranged from 69 minutes to 7 days. The performance of the device was satisfactory both in asyn- chr nous and synchronous mode within the range of given native heart rate. More than 4 liters of device output could be reached within the range of normal left atral pressure without development of negative pressure in the left atrium. Moderate to severe degree of hemolysis was noted as evidenced by significant increase of plasma free hemoglobin level after 3 days of left ventricular support along with the presence of the small amount of thrombi around the floating disc type polymer valve apparatus reflecting that further study and refinement of the device need to be done in regard of biocompatibility and thromboresistance. The hemodynamics showed increase in heart rate (p < 0.05), cardiac output and left ventricular minute work (p < 0.05) after placement of the device at the flow rate of 2.0∼2.5 Llmin. The left atrial pressure, left ventricular pressure and LV dpldt were decreased after the device placement(p < 0.05). The endocardial viability ratio and oxygen contents of the mixed ven us blood and coronary venous blood were all increased (p < 0.05) after the device placement suggesting effective unloading of the left ventricle was accomplished. The myocardial perfusion was thought improved in synchronous counterpulsation as suggested by sig- nificant increase in endocardial viability ratio and coronary venous blood oxygen content in synchronous assist mode comparing with asynchronous mode.

• Journal of Dairy Science and Biotechnology
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• v.33 no.4
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• pp.263-269
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• 2015

Various carbohydrates (lactose, glucose, and fructose), lactic acid, uric acid, and acetoin were separated on a ZORBAX Carbohydrate Analysis column using the Agilent 1200 HPLC ChemStation$^{TM}$, and were identified according to retention times with 325 Dual Wavelength UV-Vis Detector and Refractive Index Detector with 0.013 N $H_2SO_4$ at a flow rate of 0.8 mL/min. In addition, the lactase activity of four commercial probiotic lactic acid bacteria during 6-hour incubation was determined using a high-performance liquid chromatography (HPLC) method. Among the tested samples, Bifidobacterium animalis subsp. lactis showed the greatest lactase activity, followed by Lactobacillus rhamnosus and Lactobacillus casei, with Streptococcus salivarius subsp. thermophilus showing the lowest activity. Therefore, this HPLC technique shows potential for evaluating the fermentation processes of probiotic lactic acid bacteria and could simultaneously confirm the degree of ripening in various fermented dairy foods within only a half hour.

• Journal of Korean Society of Environmental Engineers
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• v.31 no.11
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• pp.1007-1018
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• 2009

Hydrocyclone is widely used in industry, because of its simplicity in design, high capacity, low maintenance and operational cost. The separation action of a hydrocyclone treating particulate slurry is a consequence of the swirling flow that produces a centrifugal force on the fluid and suspended particles. In spite of hydrocyclone have many advantage, the application for treatment of urban stormwater case study were rare. We conducted a laboratory scale study on treatable potential of micro particles using hydrocyclone filter (HCF) that was a combined modified hydrocyclone with perlite filter cartridge. Since it was not easy to use actual storm water in the scaled-down hydraulic model investigations, it was necessary to reproduce ranges of particles sizes with synthetic materials. The synthesized storm runoff was made with water and addition of particles; ion exchange resin, road sediment, commercial area manhole sediment, and silica gel particles. Experimental studies have been carried out about the particle separation performance of HCF-open system and HCF-closed system. The principal structural differences of these HCFs are underflow zone structure and vortex finder. HCF was made of acryl resin with 120 mm of diameter hydrocyclone and 250 mm of diameter filter chamber and overall height of 800 mm. To determine the removal efficiency for various influent concentrations of suspended solids (SS) and chemical oxygen demand (COD), tests were performed with different operational conditions. The operated maximum of surface loading rate was about 700 $m^3/m^2$/day for HCF-open system, and 1,200 $m^3/m^2$/day for HCF-closed system. It was found that particle removal efficiency for the HCF-closed system is better than the HCF-open system under same surface loading rate. Results showed that SS removal efficiency with the HCF-closed system improved by about 8~20% compared with HCF-open system. The average removal efficiency difference for HCF-closed system between measurement and CFD particle tracking simulation was about 4%.

• Journal of Korean Society of Environmental Engineers
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• v.22 no.10
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• pp.1905-1919
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• 2000

The main motivation of this research is to develop an intelligent control strategy for Activated Sludge Process (ASP). ASP is a complex and nonlinear dynamic system because of the characteristic of wastewater, the change in influent flow rate, weather conditions, and etc. The mathematical model of ASP also includes uncertainties which are ignored or not considered by process engineer or controller designer. The ASP is generally controlled by a PID controller that consists of fixed proportional, integral, and derivative gain values. The PID gains are adjusted by the expert who has much experience in the ASP. The ASP model based on $Matlab^{(R)}5.3/Simulink^{(R)}3.0$ is developed in this paper. The performance of the model is tested by IWA(International Water Association) and COST(European Cooperation in the field of Scientific and Technical Research) data that include steady-state results during 14 days. The advantage of the developed model is that the user can easily modify or change the controller by the help of the graphical user interface. The ASP model as a typical nonlinear system can be used to simulate and test the proposed controller for an educational purpose. Various control methods are applied to the ASP model and the control results are compared to apply the proposed intelligent control strategy to a real ASP. Three control methods are designed and tested: conventional PID controller, fuzzy logic control approach to modify setpoints, and fuzzy-PID control method. The proposed setpoints changer based on the fuzzy logic shows a better performance and robustness under disturbances. The objective function can be defined and included in the proposed control strategy to improve the effluent water quality and to reduce the operating cost in a real ASP.

• Archives of design research
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• v.19 no.4 s.66
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• pp.51-60
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• 2006

Nowadays, reading text from screens is prevailing in everyday life. The advent of mobile information devices such as a cellular phone, PDA, and e-book reader facilitates us to enjoy various text-based contents any time and anywhere. Most studies comparing screen and paper readability show that screens are less readable than paper. Furthermore, the decrease of line length and number of lines that can be displayed on the screen of mobile information devices deteriorate text readability. This study investigated parameters affecting text readability on small screens and designed a new text layout to improve readability. We suggested a diagonally splitted layout of rectangular column, which is supposed to facilitate eye movement to trace text flow with ease. The experiment comparing readability between a traditional rectangular column and a diagonally splitted column was conducted. The result of experiment revealed that there is no significant difference between the two text layouts in terms of subjective satisfaction of reading task and a level of comprehension. However, in the screen size of $4000mm^2\;and\;8000mm^2$, reading speed was increased 18.9% and 34.0% respectively from a traditional rectangular column to a diagonally splitted column. We conducted a consecutive experiment to scrutinize the cause that improved the performance in readability task remarkably. The readability of text in a traditional rectangular column was compared with a left triangular column and a right triangular column in the condition of $4000mm^2/3:1$ ratio screen. The performance measurements revealed that participants read 21.1% and 67.6% faster respectively with the left triangular column and right triangular column than with the rectangular column. In consequence, the improvement of readability in the diagonally splitted column was attributed mainly to the increase of reading speed in the right triangular column. This research verified that the diagonally splitted column improve text readability on a small screen and this result is expected to make a contribution to designing an efficient text layout for mobile information devices