• Journal of Korean Society of Water and Wastewater
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• v.30 no.2
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• pp.155-165
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• 2016

Pipe Deterioration Prediction (PDP) and Pipe Failure Risk Prediction (PFRP) models were developed in an attempt to predict the deterioration and failure risk in water mains using fuzzy technique and the markov process. These two models were used to determine the priority in repair and replacement, by predicting the deterioration degree, deterioration rate, failure possibility and remaining life in a study sample comprising 32 water mains. From an analysis approach based on conservative risk with a medium policy risk, the remaining life for 30 of the 32 water mains was less than 5 years for 2 mains (7%), 5-10 years for 8 (27%), 10-15 years for 7 (23%), 15-20 years for 5 (17%), 20-25 years for 5 (17%), and 25 years or more for 2 (7%).

• Journal of Korean Society of Industrial and Systems Engineering
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• v.45 no.3
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• pp.18-30
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• 2022

Predicting remaining useful life (RUL) becomes significant to implement prognostics and health management of industrial systems. The relevant studies have contributed to creating RUL prediction models and validating their acceptable performance; however, they are confined to drive reasonable preventive maintenance strategies derived from and connected with such predictive models. This paper proposes a data-driven preventive maintenance method that predicts RUL of industrial systems and determines the optimal replacement time intervals to lead to cost minimization in preventive maintenance. The proposed method comprises: (1) generating RUL prediction models through learning historical process data by using machine learning techniques including random forest and extreme gradient boosting, and (2) applying the system failure time derived from the RUL prediction models to the Weibull distribution-based minimum-repair block replacement model for finding the cost-optimal block replacement time. The paper includes a case study to demonstrate the feasibility of the proposed method using an open dataset, wherein sensor data are generated and recorded from turbofan engine systems.

• Journal of dental hygiene science
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• v.13 no.3
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• pp.281-289
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• 2013

The purpose of this study is to find out potential factors associated with the quality of life in South Korean senior people, on the basis of their oral health, so that it may provide basic reference materials in developing and assessing national policies for improving the quality of life in senior people. The data of 3,882 senior citizens who were at the Western age of 65 and up and got a dental checkup were selected from the first-, second- and third-year raw data of the 4th National Health and Nutrition Survey that were conducted from July 2007 to December 2009. And the statistical package SPSS 19.0 was employed to analyze the selected data. The findings of the study were as follows: The senior citizens whose remaining tooth was larger in number and who didn't need partial or full denture lead a better quality of life. Therefore, dental loss without any prosthetic appliance has significant negative effects on the quality of life in senior people, so it is urgently demanded to try to increase the number of remaining teeth and apply dental prosthesis to senior people for recovery of their oral health.

• Journal of Applied Tourism Food and Beverage Management and Research
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• v.9
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• pp.243-271
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• 1998

The changes of life-style by improving the standard of living produce the development of food service industry. But, the consequence is that food waste also increase. I think that the problems about the food waste become more critical. There are some reports about counting the amount of remaining foods until now. But, I can not find reports about the calory analysis of the remaining foods. So, I analysis the amounts and calories of the food and remaining food served at the restaurants for the purpose of groping how to reduce the remaining food and conclude as follows. First, the average amount of the food giving to one person is 1007gm(from 300gm to 1367gm), and the average amount of the remaining food is 126gm(from 29gm to 172gm). Second, the average calory of the food giving to one person is 795.5kcal(from 464kcal to 1225kcal), and the average calory of the remaining food is 140.8kcal(from 29kcal to 289kcal). So, we gain 130kcal more than recommending calory to woman. Therefore, we need to studies of developing menu, controlling the amount of supplied food, and improving how to supply. Also we need to study about the using of food bank and publish and use about recycling of food waste.

• Journal of the Korean Society of Safety
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• v.16 no.3
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• pp.26-30
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• 2001

Creep crack growth lift of high temperature pressure equipments was assessed for various crack locations and for various material properties. Surface cracks at the inner and outer surface of the vessel in the axial and circumferential directions were considered. The crack was located in the weld metal, in the parent metal or at the weld interface. Results shored that the crack at the weld interface was the most dangerous one. The crack located outside is weaker than that located inside. Safety factors of the case in which improper material properties were used the to unavailability of the correct material properties were discussed.

• Steel and Composite Structures
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• v.28 no.3
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• pp.349-362
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• 2018

This paper presents a semi-analytical solution for the creep analysis and life assessment of 304L austenitic stainless steel thick truncated conical shells using multilayered method based on the first order shear deformation theory (FSDT). The cone is subjected to the non-uniform internal pressure and temperature gradient. Damages are obtained in thick truncated conical shell using Robinson's linear life fraction damage rule, and time to rupture and remaining life assessment is determined by Larson-Miller Parameter (LMP). The creep response of the material is described by Norton's law. In the multilayer method, the truncated cone is divided into n homogeneous disks, and n sets of differential equations with constant coefficients. This set of equations is solved analytically by applying boundary and continuity conditions between the layers. The results obtained analytically have been compared with the numerical results of the finite element method. The results show that the multilayered method based on FSDT has an acceptable amount of accuracy when one wants to obtain radial displacement, radial, circumferential and shear stresses. It is shown that non-uniform pressure has significant influences on the creep damages and remaining life of the truncated cone.

• The Journal of Information Systems
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• v.29 no.1
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• pp.75-91
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• 2020

Purpose Retrofit, defined to be addition of new technologies or features to the old system to increase efficiency or to abate GHG emissions, is considered as an important alternative for the old coal-fired power plant. The purpose of this study is to propose mathematical method to model multiple alternative retrofit in Generation Capacity Expansion Planning(GCEP) problem, and to get insight to the retrofit patterns from realistic case studies. Design/methodology/approach This study made a multi-alternative retrofit GECP model by adopting some new variables and equations to the existing GECP model. Added variables and equations are to ensure the retrofit feature that the life time of retrofitted plant is the remaining life time of the old power plant. We formulated such that multiple retrofit alternatives are simultaneously compared and the best retrofit alternative can be selected. And we found that old approach to model retrofit has a problem that old plant with long remaining life time is retrofitted earlier than the one with short remaining life time, fixed the problem by some constraints with some binary variables. Therefore, the proposed model is formulated into a mixed binary programming problem, and coded and run using the GAMS/cplex. Findings According to the empirical analysis result, we found that approach to model the multiple alternative retrofit proposed in this study is comparing simultaneously multiple retrofit alternatives and select the best retrofit satisfying the retrofit features related to the life time. And we found that retrofit order problem is cleared. In addition, the model is expected to be very useful in evaluating and developing the national policies concerning coal-fired power plant retrofit.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.49 no.7
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• pp.565-572
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• 2021

In this study, a study on the performance and aging of explosive bolts stored for a long time among pyrotechnic mechanical devices(PMD) used as separation devices in the defense field is conducted. For this, explosive bolts that had been installed in the weapon system for about 10 years are secured. Performance and life extension test procedures are established based on the AIAA Standard and MIL-STD. Before performance evaluation, non-functional tests are performed to check whether external changes or failures occurred. Next, circuit inspection and X-ray tests are conducted to check the failure in internal circuits and structures. After that, performance test is carried out to confirm the operation of the samples that passed the non-functional test. Through this test, separation of bolt and separation time are measured, and some samples are tested after a high temperature storage test to confirm the remaining life and the possibility of extension. Finally, the remaining life and reliability are predicted based on the results of the test and the Arrhenius model to identify remaining shelf life and reliability depend on time.

• Journal of the Korean Society of Industry Convergence
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• v.6 no.3
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• pp.223-230
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• 2003

Generally, the life-span of a multi-housing complex is over 50 years, but in reality they are usually demolished after 20 years in spite of its remaining life expectancy. Thus, this research focuses on the estimation of the optimum economic life-span of a multi-housing complex. To estimate the minimum total cost point of start to finish of a multi-housing complex, we'll apply MAPI(Machinery and Allied Product Institute) and LCC(Life Cycle Cost) theory.

• Journal of Korean society of Dental Hygiene
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• v.18 no.6
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• pp.903-910
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• 2018

Objectives: The study aimed to identify the oral health factors that affect the nutritional status of the elderly. Methods: The study was conducted over ten months from September 2013 to June 2014, and included senior citizens who were supported by the visiting health service. The rate of saliva release, the number of remaining teeth, and the ability of the elderly to identify nutritional conditions were evaluated. Statistical analyses were performed using the t-test, ANOVA, and multiple linear regression using SAS 9.4 (SAS Institute Inc., Cary, NC, USA.). Results: The study participants had an average irritation saliva secretion rate of $2.26{\pm}1.11mg$ per minute. The higher the rate of saliva secretion, the higher the mini nutritional assessment (MNA) score (p<0.001). The average number of remaining teeth was $8.21{\pm}9.76$. The MNA scores were highest in groups with 11 or more remaining teeth (p=0.001). The factors that affected the nutritional condition of the elderly were their ability to perform activities of daily living, saliva flow rate, and number of remaining teeth. The highest correlation among them was that of the standardized regression coefficient was - 0.386 by activity daily living, followed by a 0.170 saliva secretion rate and 0.118 remaining teeth in daily life performance. Conclusions: Activities of daily living and rate of saliva secretion showed the highest correlations to nutritional status of the elderly.