• Structural Monitoring and Maintenance
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• 제8권4호
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• pp.329-344
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• 2021

The use of structural control devices to minimize structural response to seismic/dynamic excitations has attracted increased attention in recent years. The use of magnetorheological (MR) dampers as a control device have captured the attention of researchers in this field due to its flexibility, adaptability, easy control, and low power requirement compared to other control devices. However, little attention has been paid to the effect of configuration and number of dampers installed in a structure on responses reduction. This study assesses the control of a five-story structure using one and two MR dampers at different stories to determine the optimal damper positions and configurations based on performance indices. This paper also addresses the fail-safe current value to be applied to the MR damper at each floor in the event of feedback or control failure. The model is mathematically simulated in SIMULINK/MATLAB environment. Linear control strategies for current at 0 A, 0.5 A, 1 A, 1.5 A, 2 A, and 2.5 A are implemented for MR dampers, and the response of the structure to these control strategies for different configurations of dampers is compared with the uncontrolled structure. Based on the performance indices, it was concluded that the dampers should be positioned starting from the ground floor, then the 2^nd floor followed by 1^st and rest of the floors sequentially. The failsafe value of current for MR dampers located in lower floors (G+1) should be kept at a higher value compared to dampers at top floors for effective passive control of multi-story structures.

• 한국안전학회지
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• 제37권3호
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• pp.52-59
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• 2022

Conventionally, all the unsafe acts by human beings in relation to industrial accidents have been regarded as unintentional human errors. Exceptionally, however, in the cases with fatalities, seriously injured workers, and/or losses that evoked social issues, attention was paid to violating related laws and regulations for finding out some people to be prosecuted and given judicial punishments. As Heinrich stated, injury or loss in an accident is quite a random variable, so it can be unfair to utilize it as a criterion for prosecution or punishment. The present study was conducted to comprehend how categorizing intentional violations in unsafe acts might disrupt conventional conclusions about the industrial accident process. It was also intended to seek out the right direction for countermeasures by examining unsafe acts comprehensively rather than limiting the analysis to human errors only. In an analysis of 150 industrial accident cases that caused fatalities and featured relatively clear accident scenarios, the results showed that only 36.0% (54 cases) of the workers recognized the situation they confronted as risky, out of which 29.6% (16 cases) thought of the risk as trivial. In addition, even when the risks were recognized, most workers attempted to solve the hazardous situations in ways that violated rules or regulations. If analyzed with a focus on human errors, accidents can be attributed to personal deviations. However, if considered with an emphasis on safety rules or regulations, the focus will naturally move to the question of whether the workers intentionally violated them or not. As a consequence, failure of managerial efforts may be highlighted. Therefore, it was concluded that management should consider unsafe acts comprehensively, with violations included in principle, during accident investigations and the development of countermeasures to prevent future accidents.

• 산업경영시스템학회지
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• 제45권4호
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• pp.150-156
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• 2022

As the 4th industrial revolution emerges, the implementation of smart factories are essential in the manufacturing industry. However, 80% of small and medium-sized enterprises that have introduced smart factories remain at the basic level. In addition, in root industries such as injection molding, PLC and HMI software are used to implement functions that simply show operation data aggregated by facilities in real time. This has limitations for managers to make decisions related to product production other than viewing data. This study presents a method for upgrading the level of smart factories to suit the reality of small and medium-sized enterprises. By monitoring the data collected from the facility, it is possible to determine whether there is an abnormal situation by proposing an appropriate algorithm for meaningful decision-making, and an alarm sounds when the process is out of control. In this study, the function of HMI has been expanded to check the failure frequency rate, facility time operation rate, average time between failures, and average time between failures based on facility operation signals. For the injection molding industry, an HMI prototype including the extended function proposed in this study was implemented. This is expected to provide a foundation for SMEs that do not have sufficient IT capabilities to advance to the middle level of smart factories without making large investments.

• Structural Engineering and Mechanics
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• 제87권4호
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• pp.317-332
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• 2023

Understanding and analysing the behaviour and response of historical structures in the face of climate changes and environmental conditions is of utmost significance for their preservation. There are several structural hazards associated with climate and hydrology changes in the region, including the settlement of piers, the rotation of piers, and temperature changes. The present study investigates the experimental and numerical structural behaviour of skewed and non-skewed Persian brick masonry barrel vaults under various conditions. The external loading conditions included pier rotation in five modes, settlement, and temperature variations in four states. Initially, the experiments extracted the mechanical properties of the scaled materials. Then, three semi-circular brick barrel vaults were tested with gravitational loads. The outcomes were used to develop and validate the finite element model. Following the development of the finite element model, numerical and parametric studies were conducted on the effect of the aforementioned structural hazards on the response of brick masonry barrel vaults with various Persian geometries (semi-circular, drop pointed, and four-centred), angles of skew (0, 15, 30, and 45 degrees), and dimensional ratios. According to the findings, the fragility of masonry materials makes historical structures susceptible to failure under different loading. A brick barrel vault fails in the presence of minor rotation and settlement of the piers. The four-centred geometric shape has the lowest performance among the seven Persian geometries; therefore, its health monitoring and retrofitting should be prioritised. In Isfahan, Iran, temperature variations, particularly during the warm seasons, cause critical conditions in such structures.

• 한국지반공학회논문집
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• 제39권12호
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• pp.103-114
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• 2023

흙막이 현장에서 계측은 굴착으로 인한 지보재와 지반의 안정성 확인을 위해 필수적으로 수행해야 하는 중요한 요소이다. 특히, 굴착지반에서 전달되는 버팀대의 하중 전달 추이를 확인하는 하중계는 정확도 유지가 필수적이다. 그러나, 건설 현장에서는 하중계의 정확도를 파악할 수 있는 검증 방법, 규정 등의 연구가 부족하여 제대로 된 성능검사 없이 설치됨에 따라 문제가 되고 있다. 본 연구에서는 국내 현장에 사용되는 하중계를 전수조사하여 성능검사를 실시하고 외국 제품과의 비교를 통해 불량 원인을 파악하였다. 하중계의 성능검증을 통해 성능검사 기준을 제시하였으므로 본 연구 결과는 신뢰성 높은 하중계를 선택하는 데 도움이 될 것으로 판단된다.

• Journal of Chest Surgery
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• 제57권1호
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• pp.36-43
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• 2024

Background: Coronavirus disease 2019 (COVID-19) can lead to acute respiratory failure, which frequently necessitates invasive mechanical ventilation and extracorporeal membrane oxygenation (ECMO). However, the limited availability of ECMO resources poses challenges to patient selection and associated decision-making. Consequently, this retrospective single-center study was undertaken to evaluate the characteristics and clinical outcomes of patients with COVID-19 receiving ECMO. Methods: Between March 2020 and July 2022, 65 patients with COVID-19 were treated with ECMO and were subsequently reviewed. Patient demographics, laboratory data, and clinical outcomes were examined, and statistical analyses were performed to identify risk factors associated with mortality. Results: Of the patients studied, 15 (23.1%) survived and were discharged from the hospital, while 50 (76.9%) died during their hospitalization. The survival group had a significantly lower median age, at 52 years (interquartile range [IQR], 47.5-61.5 years), compared to 64 years (IQR, 60.0-68.0 years) among mortality group (p=0.016). However, no significant differences were observed in other underlying conditions or in factors related to intervention timing. Multivariable analysis revealed that the requirement of a change in ECMO mode (odds ratio [OR], 366.77; 95% confidence interval [CI], 1.92-69911.92; p=0.0275) and the initiation of continuous renal replacement therapy (CRRT) (OR, 139.15; 95% CI, 1.95-9,910.14; p=0.0233) were independent predictors of mortality. Conclusion: Changes in ECMO mode and the initiation of CRRT during management were associated with mortality in patients with COVID-19 who were supported by ECMO. Patients exhibiting these factors require careful monitoring due to the potential for adverse outcomes.

• 디지털산업정보학회논문지
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• 제20권1호
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• pp.109-118
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• 2024

Recently, a social issue has arisen involving RDDoS attacks following the sending of threatening emails to security administrators of companies and institutions. According to a report published by the Korea Internet & Security Agency and the Ministry of Science and ICT, survey results indicate that DDoS attacks are increasing. However, the top response in the survey highlighted the difficulty in countering DDoS attacks due to issues related to security personnel and costs. In responding to DDoS attacks, administrators typically detect anomalies through traffic monitoring, utilizing security equipment and programs to identify and block attacks. They also respond by employing DDoS mitigation solutions offered by external security firms. However, a challenge arises from the initial failure in early response to DDoS attacks, leading to frequent use of detection and mitigation measures. This issue, compounded by increased costs, poses a problem in effectively countering DDoS attacks. In this paper, we propose a system that creates detection rules, periodically collects traffic using mail detection and IDS, notifies administrators when rules match, and Based on predefined threshold, we use IPS to block traffic or DDoS mitigation. In the absence of DDoS mitigation, the system sends urgent notifications to administrators and suggests that you apply for and use of a cyber shelter or DDoS mitigation. Based on this, the implementation showed that network traffic was reduced from 400 Mbps to 100 Mbps, enabling DDoS response. Additionally, due to the time and expense involved in modifying detection and blocking rules, it is anticipated that future research could address cost-saving through reduced usage of DDoS mitigation by utilizing artificial intelligence for rule creation and modification, or by generating rules in new ways.

• 한국터널지하공간학회 논문집
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• 제24권6호
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• pp.451-464
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• 2022

고준위방사성폐기물 처분장은 심지층 처분시스템으로 사용후핵연료를 취급하는 특성상 고온, 방사선 및 지하수 등의 복합적인 환경조건에 노출되어 있다. 지속적인 노출에 의해 시간이 지남에 따라 구조물의 균열 및 열화가 발생할 수 있다. 한편 고준위방사성폐기물 처분장은 초장기 기대수명이 요구되며 이에 따른 장기적인 구조물 건전성 모니터링이 필수적이다. 구조물 건전성 모니터링에는 가속도계, 토압계, 변위계 등 다양한 센서들이 활용될 수 있으며, 이 중 일반적으로 피에조센서가 사용된다. 따라서 피에조센서의 내구성 평가를 바탕으로 고내구성 센서를 개발할 필요가 있다. 본 연구에서는 피에조센서의 내구성 평가 및 수명예측을 위한 가속수명시험을 설계하였다. 문헌연구를 바탕으로 단일 스트레스 인자에 대한 가속 스트레스 수준 수 및 각 수준 별 시료 수를 선정하였다. 또한 고준위방사성폐기물 처분장 환경조건에서 발생할 수 있는 피에조센서의 고장모드 및 고장메커니즘을 분석하였다. 온도 스트레스 인자에 대한 최대 가혹조건 탐색 실험을 두 가지 방법으로 제안하였으며 피에조센서의 신뢰도 높은 동작한계를 도출하였다. 이를 이용하여 가속수명시험의 합리적인 가속 스트레스 수준을 설정하였다. 본 연구에서 제시된 최대 가혹조건 탐색 실험방법은 경제적이며 실용적인 아이디어를 담고 있으며, 추후 피에조센서의 가속수명시험 설계에 널리 활용될 수 있을 것으로 판단된다.

• 한국콘텐츠학회논문지
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• 제20권4호
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• pp.396-405
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• 2020

본 연구에서는 초고속인터넷 상품에 관련된 고객 불만사항(VOC, Voice of Customer)의 빅데이터를 활용하여 고객이 지각하는 품질이상의 원인과 선제적 서비스의 가능성을 살펴보았다. 선제적 서비스의 가능성을 검증하기 위해 실제 이동통신 서비스기업의 시설·장비의 총 13개 장애경보에 관련된 품질이상 VOC를 수집한 후, 𝒙²검증을 통해 품질이상 VOC 실제관측값과 기대값이 통계적으로 유의한 차이가 있는 지 검증하였다. 연구결과, 시설·장비의 총 13개 장애경보 관련 품질이상 VOC 중 6개의 장애경보로서, 'FTTH-R 장비 ON/OFF', 'FTTH-E,V 회선오류 감지', '포트불량, FTTH-R 회선오류 감지', '네트워크 LOOP 감지', 그리고 '비정상 트래픽 제한'은 실시간 모니터링을 통한 선제적 서비스가 가능하다는 통계적 근거를 찾았다. 기업들은 이러한 선제적 서비스를 이용하여 시잠점유율을 향상키시고 고객서비스 비용을 절감하는 데 적용할 수 있을 것이다. 본 연구의 결과는 통신서비스 분야의 선제적 서비스의 가능성을 진단하고, 나아가 효과적인 선제적 서비스 제공 방안에 대한 시사점을 제시하였다는 점에서 실제 산업 적용에 대한 공헌점이 기대된다.

• 한국임상약학회지
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• 제23권4호
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• pp.307-315
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• 2013

Objective: Colistimethate was first became available in 1950s and used until the early 1980s to treat infections caused by gram-negative bacteria and was abandoned due to its nephrotoxicity and neurotoxicity. However, it was recently reintroduced into the clinical practices due to emergence of multidrug-resistance gram-negative bacteria, particularly Pseudomonas aeruginosa and Acinetobacter baumanii. Therefore, it is increasingly used in the intensive care unit settings as a salvage therapy. This study was designed to investigate the incidence rates and risk factors of acute kidney injury associated with colistimethate by using the standardized definition in critically ill patients. Methods: This study retrospectively reviewed the electronic medical records of 71 adult patients above 18 years old receiving intravenous colistimethate at least 48 hours at intensive care unit, university-affiliated hospital from Nov 2012 to Aug 2013 and excluded patients with end-stage renal disease (ESRD) and required renal replacement therapy before initiation of the colistimethate therapy. Acute kidney injury (AKI) was determined by using the standardized RIFLE criteria, classified with risk, injury, failure, loss and ESRD according to serum creatinine (Scr) levels. Results: Among the 71 patients included in the analysis, AKI developed in 40 patients (56.3%) and 6 patients (8.4%) had irreversible kidney injury. AKI occurred within 5 days in 20 patients (50.0%). Maximum Scr level showed a significant increase in the patients with AKI ($1.92{\pm}0.86mg/dL$ vs. $1.12{\pm}0.46mg/dL$ p=0.001), maximum BUN also increased ($64.2{\pm}28.7mg/dL$ vs. $48.4{\pm}24.9mg/dL$ p=0.017) and minimum creatinine clearance (CLcr) was significantly decreased in the patients with AKI than non-AKI ($34.5{\pm}18.6ml/min$ vs. $64.4{\pm}33.7ml/min$ p=0.185). The patients with AKI had significantly longer duration of colistimethate therapy ($21.1{\pm}17.0$ days vs. $13.0{\pm}11.5$ days, p=0.020) and larger cumulative doses of colistimethate ($6465.9{\pm}4717.0mg$ vs. $4438.1{\pm}3426.7mg$, p=0.040). Conclusion: The incidence and severity of AKI associated with colistimethate in critically ill patients was high and serious. Drug monitoring program should be performed to shorten duration of therapy and reduce cumulative dose from initiation of colistimethate therapy for minimizing AKI of colistimethate.