• Industrial Engineering and Management Systems
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• 제2권1호
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• pp.63-70
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• 2003

In this study, we employed an arithmetic process (AP) approach to resolve gearbox maintenance problems. The approach is realistic and direct in modelling the characteristics of a deteriorating system such as a gearbox since a decreasing AP can model a gearbox's successive operating times and an increasing AP can model the corresponding consecutive repair times. First of all, two test statistics were used to check whether the process is arithmetic or not. Next, model parameters of the AP were estimated using the simple linear regression method. Finally, the optimal replacement policy based on minimising the long-run average cost per day was determined for each type of gearbox.

• 품질경영학회지
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• 제30권4호
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• pp.94-105
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• 2002

In this paper, replacement problems for a deteriorating system are considered. In the system under consideration, the successive lifetimes after repair become shorter and shorter, while the consecutive repair times become longer and longer. More specifically, the lifetimes of the system form a nonhomogeneous Poisson process, whereas the consecutive repair times constitute a stochastically increasing geometric process. Optimal replacement policies for the long-run average cost rate and the steady state availability are considered. Also taking the cost and the availability into consideration at the same time, the properties of optimal policies under the Cost Priority Policy and the Availability Priority Policy are obtained.

• 국제강구조저널
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• 제18권5호
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• pp.1761-1771
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• 2018

In this paper, a hysteretic model of rectangular hollow section (RHS) columns that includes the deteriorating range caused by local buckling is proposed. The proposed model consists of the skeleton curve, the Bauschinger part that appears before reaching the maximum strength, the strength increasing part of the deteriorating range, and the unloading part. Of these, the skeleton curve, including the deterioration range caused by local buckling, which is considered to be equivalent to the load-deformation relationship under monotonic loading, is obtained through an analytical method. Bi-linear hysteretic models based on experimental results are applied to the Bauschinger part and the strength increasing part. The elastic stiffness is applied to the unloading part. The proposed model is verified by comparing with experimental results of RHS columns under monotonic and cyclic loading.

• 대한화학회지
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• 제62권3호
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• pp.253-256
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• 2018

• Asian-Australasian Journal of Animal Sciences
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• 제31권2호
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• pp.198-207
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• 2018

Objective: This study investigated the association of yeast species with improved aerobic stability of total mixed ration (TMR) silages with prolonged ensiling, and clarified the characteristics of yeast species and their role during aerobic deterioration. Methods: Whole crop corn (WCC) silages and TMR silages formulated with WCC were ensiled for 7, 14, 28, and 56 d and used for an aerobic stability test. Predominant yeast species were isolated from different periods and identified by sequencing analyses of the 26S rRNA gene D1/D2 domain. Characteristics (assimilation and tolerance) of the yeast species and their role during aerobic deterioration were investigated. Results: In addition to species of Candida glabrata and Pichia kudriavzevii (P. kudriavzevii) previously isolated in WCC and TMR, Pichia manshurica (P. manshurica), Candida ethanolica (C. ethanolica), and Zygosaccharomyces bailii (Z. bailii) isolated at great frequency during deterioration, were capable of assimilating lactic or acetic acid and tolerant to acetic acid and might function more in deteriorating TMR silages at early fermentation (7 d and 14 d). With ensiling prolonged to 28 d, silages became more (p<0.01) stable when exposed to air, coinciding with the inhibition of yeast to below the detection limit. Species of P. manshurica that were predominant in deteriorating WCC silages were not detectable in TMR silages. In addition, the predominant yeast species of Z. bailii in deteriorating TMR silages at later fermentation (28 d and 56 d) were not observed in both WCC and WCC silages. Conclusion: The inhibition of yeasts, particularly P. kudriavzevii, probably account for the improved aerobic stability of TMR silages at later fermentation. Fewer species seemed to be involved in aerobic deterioration of silages at later fermentation and Z. bailii was most likely to initiate the aerobic deterioration of TMR silages at later fermentation. The use of WCC in TMR might not influence the predominant yeast species during aerobic deterioration of TMR silages.

• 보존과학연구
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• 통권24호
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• pp.81-98
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• 2003

The biodeterioration on Iksan Mireuksaji pagoda has been studied with fucus on application of K201 as a chemical treatment. Total of 39species, including 10 algae, 16 lichens, 6 mosses and 7 unidentified bacteria and fungi, were collected and identified on the surface of the pagoda. Most of them caused serious discoloration on the surface. The effectiveness and stability of K201 was examined by applying it on some part of the pagoda. A mild spraying of solution diluted to half of original reagent was good enough to eliminate all the deteriorating species on the surface. Most of discoloration disappeared after the treatment except the red color caused by iron substance. The effectiveness of the regent was compared with water wash. The stone was first washed with water and the dirt on the surface was scrubbed off from the surface. The initial surface of the stone was clearer in water wash. However, many of the deteriorating species reappear in 4 weeks after water wash. Although spraying of the reagent K201 could noteliminate all the remnant of dead organisms as good as scrubbing the surface, no deteriorating algae or lichen was observed until two month after treatment. Therefore, spraying method with chemicals seems more stable and reliable way to remove the biodeterioration than physical scrubbing of the surface.

• 한국물환경학회지
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• 제39권5호
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• pp.377-389
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• 2023

Chungcheongnam-do has been measuring the flow rate and water quality of streams in the province once a month since 2011 in order to water environment policies. Based on the results, after evaluating the coefficient of variation and the tendency of the water quality trend by using the Mann-Kendall test and Sen's Slope for each stream, the streams subject to priority introduction of Total Pollution Load Management at Tributaries were selected through the Stream Grouping Method. The water quality trend analysis results for 125 streams using the Mann-Kendall test and Sen's Slope were evaluated as streams showing a tendency of deteriorating water quality Biochemical oxygen demand (BOD): 13 streams, Total Phosphorus (T-P): 16 streams). Streams with deteriorating water quality were classified into A-D groups using the Stream Grouping Method. Group A, which has a high flow rate and high water quality, is a stream that requires priority management, and was selected as a stream for introduction of Total Pollution Load Management at Tributaries. There are 7 streams that need to be introduced into the BOD category, and there are 7 streams that need to be introduced into the T-P category. In this study, based on flow and water quality monitoring data accumulated over a long period of time (2011-2022), statistical techniques are used to select watersheds in which water quality is deteriorating. Accordingly, it is expected that it will be useful in establishing a water quality improvement plan in the future.

• 디지털융복합연구
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• 제19권4호
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• pp.467-475
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• 2021

목적: 병동에서 급성악화 환자가 발생할 때 환자에게 집중치료가 필요한지 여부에 대한 결정은 환자의 예후를 향상시키기 위해서는 매우 중요하나, 특히 사용 가능한 ICU 자원이 제한적일 때는 ICU 전동 여부를 결정하기에는 어려움이 있다. 따라서 본 연구는 일반병동 급성 악화 환자를 대상으로 중환자실 전동 위험요인을 확인하고자 한다. 연구방법: 후향적 조사연구로서 대상자는 일 상급종합병원 일반병동에 입원한 18세 이상의 성인 환자 중 악화상태를 보여 신속대응팀에 의뢰된 환자 2,945명을 대상으로 하였다. 중환자실 전동 위험요인을 파악하기 위해 다변량 로지스틱 회귀분석을 시행하였다. 연구결과: 다변량 로지스틱 회귀분석 결과 입원시 고형암을 진단받은 경우 (odds ratio [OR] 0.39, 95% CI 0.32-0.47), 악화원인이 호흡문제인 경우 (OR 1.51, 95% CI 1.17-1.95), MEWS (OR 1.22, 95% CI 1.17-1.28)와 SpO2/FiO2 score (OR 2.41, 95% CI 2.23-2.60)가 중환자실 전동 위험요인으로 나타났다. 결론: 본 연구 결과는 중환자실 전동 위험이 높은 환자의 조기 예측을 가능하게 하여 환자의 예후를 향상시키는데 도움이 될 것으로 사료된다.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제8권2호
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• pp.664-677
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• 2014

Wind energy has proven its viability by the emergence of countless wind turbines around the world which greatly contribute to the increased electrical generating capacity of wind farm operators. These infrastructures are usually deployed in not easily accessible areas; therefore, maintenance routines should be based on a well-guided decision so as to minimize cost. To aid operators prior to the maintenance process, a condition monitoring system should be able to accurately reflect the actual state of the wind turbine and its major components in order to execute specific preventive measures using as little resources as possible. In this paper, we propose a fault detection approach which combines cluster analysis and frequent pattern mining to accurately reflect the deteriorating condition of a wind turbine and to indicate the components that need attention. Using SCADA data, we extracted operational status patterns and developed a rule repository for monitoring wind turbine systems. Results show that the proposed scheme is able to detect the deteriorating condition of a wind turbine as well as to explicitly identify faulty components.

• Smart Structures and Systems
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• 제22권2호
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• pp.151-159
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• 2018

Maintenance activities are regarded as a key part of the repairable deteriorating system because they maintain the equipment in good condition. In practice, many maintenance policies are used in engineering fields to reduce unexpected failures and slow down the deterioration of the system. However, in traditional maintenance policies, maintenance activities have often been assumed to be performed at the same time interval, which may result in higher operational costs and more system failures. Thus, this study presents two non-periodic preventive maintenance (PM) policies for repairable deteriorating systems, employing the failure rate of the system as a conditional variable. In the proposed PM models, the failure rate of the system was restored via the failure rate reduction factors after imperfect PM activities. Operational costs were also considered, which increased along with the operating time of the system and the frequency of PM activities to reflect the deterioration process of the system. A numerical example was provided to illustrate the proposed PM policy. The results showed that PM activities performed at a low failure rate threshold slowed down the degradation of the system and thus extended the system lifetime. Moreover, when the operational cost was considered in the proposed maintenance scheme, the system replacement was more cost-effective than frequent PM activities in the severely degraded system.