• Journal of the Korean Data and Information Science Society
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• 제21권4호
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• pp.765-775
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• 2010

For the accelerated failure time (AFT) model a lot of effort has been devoted to develop effective estimation methods. AFT model assumes a linear relationship between the logarithm of event time and covariates. In this paper we propose a semiparametric support vector machine to consider situations where the functional form of the effect of one or more covariates is unknown. The proposed estimating equation can be computed by a quadratic programming and a linear equation. We study the effect of several covariates on a censored response variable with an unknown probability distribution. We also provide a generalized approximate cross-validation method for choosing the hyper-parameters which affect the performance of the proposed approach. The proposed method is evaluated through simulations using the artificial example.

• 한국철도학회논문집
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• 제9권5호
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• pp.606-611
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• 2006

This paper presents a procedure and an analysis method to evaluate reliability of the Korea high-speed train. The rolling stock system is divided into 6 sub-systems and each subsystem is classified into sub-assemblies. Functional analysis has been conducted to draw reliability block diagrams for the sub-systems. First, failure rates has been calculated for each sub-assembly from the failure data obtained during commissioning tests. Then a reliability block diagram is used to evaluate the MKBF(Mean Kilometers Before Failure) of the sub-systems. Activities to increase reliability have been carried out throughout the test runs and analysis results show that the reliability of the rolling stock system is gradually growing in time.

• 한국안전학회지
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• 제15권4호
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• pp.62-68
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• 2000

Static electricity in electronics manufacturing plants causes the economic loss, yet it is one of the least understood and least recognized effects haunting the industry today. Today's challenge in semiconductor devices is to achieve greater functional density pattern and to miniaturize electronic systems of being more fragile by electrostatic discharges(ESD) phenomena. As the use of automatic handling equipment for static-sensitive semiconductor components is rapidly increased, most manufacturers need to be more alert to the problem of ESD. One of the most common causes of electrostatic damage is the direct transfer of electrostatic charge from the human body or a charged material to the static-sensitive devices. To evaluate the ESD hazards by charged human body and devices, in this paper, characteristics of electrostatic attenuation in domestic semiconductor devices is investigated and the voltage to cause electronic component failures is investigated by field-induced charged device model(FCDM) tester. The FCDM simulator provides a fast and inexpensive test that faithfully represents ESD hazards in plants. Also the results obtained in this paper can be used for the prevention of semiconductor failure from ESD hazards.

• 전자공학회논문지A
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• 제33A권4호
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• pp.11-17
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• 1996

In the case of redundancy control performed by a netowrk management system, it can not be ignored some delay of control time and break of control by failure of the system. This paper proposed a new method to improve the performacne of a redundancy control system interfaced to the network management system. At first, it produced the modelling of the total system and analyzed the functional relation of reliability and failure rate for a transmission system having an one-to-one active redundancy structure controlled by itself. After describing the loss rate of transmission data and the time required for the redundancy control process of the network management system when a failure is occurred, it proposed the new redundancy method of complex system control mode as an effective redundancy control method to improve reliability of a redundancy control system. Finally, it proved the effect by comparing the new result to the previous result.

• 전기학회논문지
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• 제63권11호
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• pp.1526-1532
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• 2014

The Electronic Interlocking unit in railway signalling system is safety-related facilities to determine route and speed for train running. In particular, the SSI(Solid State Interlocking) is Electronic Interlocking unit for high-speed railway, and it performs safety-critical function by MPM(Micro-Processor Module). Meanwhile, MPM is composed of the PES(Programmable Electronic System)-based system, and the PES-based system in railway safety-related facilities should be implemented by complying with the safety requirements defined in IEC 62425 and IEC 61508. In this paper, we performed modeling of failure rate and reliability for MPM implemented by fault tolerance methods and analyzed functional safety for MPM. Moreover, we determined SIL(Safety Integrity Level) for MPM according to the safety requirements defined in IEC 61508 based on an analyzed functional safety.

• 한국철도학회논문집
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• 제16권2호
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• pp.104-109
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• 2013

The paper will outline how hazard identification and risk evaluation can effectively be performed to obtain Tolerable Hazard Rates (THR). As a target group manufacturers are addressed, who face the situation, that for a generic application THRs are needed for compliance with EN 50129 [1]. Focusing on functional hazards this paper shows a possible hazard log and the relevant analysis methods. The terms safety barrier and barrier function will be introduced and used instead of the term "safety function". As functional hazards and barrier functions depend on each other, emphasis will be put on a comprehensive and detailed definition of barrier functions and the usage of function lists. By using detailed and complete hazard and barrier function definitions THRs can be obtained while at the same time the approach becomes clear how the hazard rates (HR) will be established.

• 대한안전경영과학회지
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• 제15권3호
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• pp.105-112
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• 2013

To meet the growing needs from a variety of stakeholders, the development of modern systems is getting more complex and thus, the systems failure in the actual operations can potentially become more serious. This is why several international or military standards on systems safety have been published. In spite of the importance of meeting those standards such as IEC 61508 and ISO 26262 in the systems development, the associated practical methods seem deficient since those standards do not provide them. The objective of this paper is to present a method to identify potential hazards in fulfilling the requirements of the safety standards. In particular, the approach taken here is based on applying the functional analysis that covers several levels of the system under development. Note, however, that in the most of the conventional methods for hazards identification, the analysis has been focused on the failure at or underneath the component level of the system. The hazards identification method in this paper would cover the level up to the system by utilizing the functions-oriented approach. The case study of the safety enhancement for locomotive cabs is also discussed.

• 한국안전학회지
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• 제39권1호
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• pp.16-26
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• 2024

This study aims to introduce a method for risk assessment analysis aimed at preventing electrical fires within the manufacturing industry. Initially, we provided a functional block diagram illustrating the electrical equipment employed in various processes within a food manufacturing company in Chungcheongbuk-do. Subsequently, we categorized the components of each machine outlined in the functional block diagram and determined the priority of failure for each classified component. Upon implementing the model in the frying process of the food manufacturing company, specific components, including MC, motor, mixer heater, electric wiring, and terminal block, exhibit a risk priority number (RPN) of 40 or higher. This identified an electrical issue within the manufacturing process and environment. Consequently, we propose a methodology to identify latent failure modes that could escalate into fires or systemic issues if not promptly addressed. It is essential to note that while the FMEA presented in this study may not immediately impact food manufacturing, its applicability extends to various workplaces.

• Journal of Chest Surgery
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• 제23권6호
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• pp.1180-1190
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• 1990

96 patients underwent cardiac valve replacement for valvular heart diseases consecutively between February 1986 to February 1990 in the Department of Thoracic and Cardiovascular Surgery of Yeungnam University Hospital. The follow up period was between 6 months and 4.5 years postoperatively[mean 23.4$\pm$13.1 months]. 75 cases got mitral valve replacement, 6 cases, aortic valve replacement, 15 cases, double valve replacement. 30[31.2%] patients were male and 66[68.8%] were female and the age ranged from 14 to 66 years old. Early hospital death within 30 days postoperation were 5 patients[5.2%], consisting of by low cardiac output in 2, infective endocarditis in 1, multiple organ failure with sepsis in 1 patient. There was no late postoperative death. Most common early postoperative complication was wound disruption [8.7%] and then low cardiac output, pneumothorax, pleural effusion in order. Most common late postoperative complications were minor bleeding episodes[8.7%] related to anticoagulant therapy which were consisted of frequent epistaxis in 3, gum bleeding in 2, hemorrhagic gastritis in 1, hypermenorrhea in 1, hematoma in right arm in 1 patient. Valve-related complications included valve thrombosis [1.6%/ patient-year], valve failure due to pannus formation[1.1% /patient-year], prosthetic valve endocarditis[1, 1%o/patient-year] and minor anticoagulant hemorrhage[4.4% /patient-year]. 5 cases of reoperations were performed in 4 patients due to valve failure and all of them were in the mitral positions[2.7% /patient-year]. Cardiothoracic ratios in the chest X-ray decreased at the 6th month and 1st year postoperation in all patients. But in New York Heart Association[NYHA] functional class IV, no change in cardiothoracic ratio was found between 6 months and 1 year postoperation. In the echocardiogram, the size of the cardiac chambers decreased, but ejection fraction increased postoperatively in each functional class. In the electrocardiogram, decreases were found in the incidence of atrial fibrillation, left atrial enlargement, left ventricular hypertrophy with right bundle branch block increasing postoperatively in each functional class. The actuarial survival rate was 98.4% for all patients, 98.7% for mitral valve replacement, 83.8% for aortic valve replacement, and 80% for double valve replacement at the end of a 4.5 year follow up period. Meanwhile the actuarial freedom rate was 91.5% for prosthetic valve endocarditis, 91.6% for thromboembolism, 89.0% for prosthetic valve failure and 83.7% for minor anticoagulant hemorrhage. Preoperative NYHA class III and IV were 75% of all patients, but 95% of all patients were up graded to NYHA class I and II postoperatively.

• 한국산학기술학회논문지
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• 제17권9호
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• pp.308-313
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• 2016

사용자의 요구사항 증대와 기술의 발전으로 인해 현대 시스템은 계속해서 복잡해지고 있어 시스템 설계 오류 및 고장 등으로 인한 시스템 운용 중의 사고도 빈번해지고 있다. 특히 사고로 인한 인적 및 물적 피해가 심각할 수 있는 시스템을 안전중시 시스템이라고 부른다. 이러한 시스템에 대해서는 안전성을 확보하기 위한 특별한 노력이 필요한데 이에 부응하여 본 논문에서는 개발 초기 단계부터 안전성을 반영하면서 시스템 설계를 수행할 수 있는 방법을 연구하였다. 특히 안전 메타모델을 활용해서 기능의 고장 탐지를 수행할 수 있는 시스템 설계 방법을 제시하였다. 구체적으로 국제 안전 표준들을 참고하여 안전 데이터를 추출하고, 시스템 모델링 표준 언어인 SysML을 이용하여 안전 데이터 메타모델을 생성한 후, 시스템 설계에서 안전 데이터 메타모델을 효과적으로 활용하는 모델 기반 안전 시스템 설계 방법을 제시하였고, 이를 기반으로 안전요구사항 생성 및 시뮬레이션 방법에 관하여 논의하였다. 마지막으로 사례연구로서 자동차 시스템 설계에서 SysML 기반 모델링 및 시뮬레이션을 통해 기능 고장의 탐지나 안전 요구사항의 검증이 가능한 것을 보여 주었다. 본 연구에서 안전 데이터에 대한 메타모델의 활용을 통해 안전 데이터 및 정보의 구성 및 관리를 효율적으로 수행할 수 있는 것과, 메타모델 기반 시스템 설계와 시뮬레이션을 활용하여 설계 오류를 줄임으로써 요구사항에 맞는 시스템 설계를 할 수 있음을 제시하였다.