• 항공우주시스템공학회지
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• 제14권spc호
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• pp.31-38
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• 2020

항공기의 개발 및 인증 과정에서 중요성이 강조되고 있는 시스템 안전성 평가는 고장 또는 결함으로 인해 발생할 수 있는 위험을 사전에 식별하고, 이에 대한 영향성을 판단하여 요구되는 수준의 안전성을 확보하기 위해 적용하는 시스템 엔지니어링 기법이다. 항공기 시스템이 복잡해지고, 통합적인 기능 및 성능이 요구되면서 항공기 개발 초기부터 적절한 안전성 목표를 수립하고, 체계적인 평가를 통해 이에 대한 검증 및 후속 조치를 이행하여야 한다. 본 논문에서는 고장 데이터의 확률 분석을 수행하는 방안을 제시하여 항공기의 전체 수명주기에 걸쳐 리스크를 진단하고 효율적인 안전성 평가를 수행하기 위한 방법론을 제시하였고, 항공기 인증 및 안전성 확보를 위해 고려해야 할 사항을 제시하였다.

• 산업경영시스템학회지
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• 제40권3호
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• pp.92-98
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• 2017

The rapid growth of engineering technology and the emergence of systemized and large-scale engineering systems have resulted in complexity and uncertainty throughout the lifecycle activities of engineering systems. This complex and large-scale engineering system consists of numerous components, but system failure can be caused by failure of any one of a number of components. There is a real difficulty in managing such a complex and large-scale system as a part. In order to efficiently manage the system and have high reliability, it is necessary to structure a system with a complex structure as a sub-system. Also, in the case of a system in which cause of failures exist at the same time, it is required to identify the correlation of the components lifetime and utilize it for the design policy or maintenance activities of the system. Competitive risk theory has been used as a theory based on this concept. In this study, we apply the competitive risk theory to the models with combined structure of series and parallel which is the basic structure of most complex engineering systems. We construct a competing risks model and propose a mathematical model of net lifetime and crude lifetime for each cause of failure, assuming that the components consisting a parallel system are mutually dependent. In addition, based on the constructed model, the correlation of cause of failure is mathematically analyzed and the hazard function is derived by dividing into net lifetime and crude lifetime.

• Journal of the Korean Data and Information Science Society
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• 제28권2호
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• pp.349-359
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• 2017

본 논문에서는 미국 국립암연구소의 SEER 프로그램에서 제공하는 우측 대장암 3기 자료에 Cox 비례위험모형을 적합하여 생존분석을 하였다. 우측 대장암 3기 환자의 사망률에 유의한 영향을 미치는 공변량들을 파악하고, 관심있는 공변량들을 가진 환자의 생존율을 추정하였다. Schoenfeld 잔차를 기반한 검정과 Schoenfeld 잔차 도표, $log[-log\{{\hat{S}}(t)\}]$ 도표를 이용하여 분석에 사용된 공변량들이 비례위험 가정을 만족함을 확인하였다. 적합된 Cox 비례위험모형의 타당성을 검증하기 위해 10-fold 교차 검증을 이용하여 calibration 도표와 시간에 의존하는 ROC 곡선 아래 면적을 계산하였다. 이를 통해 적합된 Cox 비례위험모형의 타당성을 확인하였다.

• 조명전기설비학회논문지
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• 제25권6호
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• pp.68-74
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• 2011

The touch or step voltages which exist in the vicinity of a grounding electrode are closely related to the earth structure and resistivity and the ground current. The grounding design approach is required to determine the grounding electrode location where the hazardous voltages are minimized. In this paper, in order to propose a method of mitigating the electric shock hazards caused by the ground surface potential rise in the vicinity of a counterpoise, the hazards relevant to touch voltage were evaluated as a function of the soil resistivity ratio $\rho_2/\rho_1$ for several practical values of two-layer earth structures. The touch voltage and current on the ground surface just above the test electrode are calculated with CDEGS program. As a consequence, it was found that burying a grounding electrode in the soil with low resistivity is effective to reduce the electric shock hazards. In the case that the bottom layer soil where a counterpoise is buried has lower resistivity than the upper layer soil, when the upper layer soil resistivity is increased, the surface potential is slightly raised, but the current through the human body is reduced with increasing the upper layer soil resistivity because of the greater contact resistance between the earth surface and the feet. The electric shock hazard in the vicinity of grounding electrodes is closely related to soil structure and resistivity and are reduced with increasing the ration of the upper layer resistivity to the bottom layer resistivity in two-layer soil.

• 대한설비공학회:학술대회논문집
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• 대한설비공학회 2007년도 동계학술발표대회 논문집
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• pp.305-309
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• 2007

FTL(Fuel Test Loop) is a facility that confirms performance of nuclear fuel at a similar irradiation condition with that of nuclear power plant. FTL construction work began on August, 2006 and ended on March, 2007. During Construction, ensuring the worker's safety was the top priority and installation of the FTL without hampering the integrity of the HANARO was the next one. The installation works were done successfully overcoming the difficulties such as on the limited space, on the radiation hazard inside the reactor pool, and finally on the shortening of the shut down period of the HANARO. The Commissioning of the FTL is to check the function and the performance of the equipment and the overall system as well. The FTL shall start operation with high burn up test fuels in early 2008 if the commissioning and licensing progress on schedule.

• 패션비즈니스
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• 제24권3호
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• pp.30-39
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• 2020

This study was conducted to identify problems in domestic flame-retardant performance specifications. Currently, the domestic wallcovering anti-inflammatory regulations are not prepared for damage caused by smoke, with the carbonized area as the main function. In particular, given that smoke is the main cause of human casualties and injuries in a fire, it is reasonable that the flame density and toxicity of the wallcovering should also be the main performance indicators. The scope and method of research in this study were as follows. First, a prior study related to fire on various wallcoverings was considered. Second, it raised questions about the effects of smoke in the event of a fire and domestic anti-inflammatory performance tests. Third, textile wallcovering samples were manufactured with viscose rayon for experimental verification of the problems and tested by Korean and EU standards without flame retardant processing to analyze the differences between each regulation. Fourth, the performance of flame retardant wallcovering according to Korean standards was evaluated using smoke density and harmful gas testing methods. The results of each test were as follows. Non-fire retardant wallcovering was rejected by Korea standards. However, B-s1.d0 in Europe. Smoke density testing and harmful gas by domestic combustion processing on the same sample showed that the smoke density increased about 4.3 times more than before, and the harmful gas test showed that the suspension of the post-processing sample slowed earlier than the non-processed sample.

• 한국방재학회:학술대회논문집
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• 한국방재학회 2008년도 정기총회 및 학술발표대회
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• pp.743-746
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• 2008

Recently, due to the effect of global warming and extreme rainfall, the magnitude of flood disaster and the frequency of flood is rapidly increasing. In order to mitigate the damage of human and property from this kind of meteorological phenomenon and manage water resources scientifically, effective operation of dam and reservoir is very important. In case of Andong dam which was not performed a flood control function needs to develop new types of dam safety management measure because of recent extraordinary flood by typhoons. In case of Andong dam and Imha dam, I am using HEC-5 model in order to apply reservoir simulation. In this case, complex conditions among 100-year floods , 200-year floods and PMF was used. Also, I modified the maximum outflow 3,800m3/s into 3,490m3/s and applied this modified discharge in order to secure freeboard in the downstream. In an analysis that I applied modified outflow by 100-year floods and 200-year floods to, the result showed that river didn't overflow in Andong area but some other places have relatively low freeboard. In the cases that I modified maximum outflow, results showed that freeboard of levee is larger than existed simulation. In the simulation that I applied 200-year floods and PMF to and under a condition connected with PMF, results showed overflowing the levees. Because of the difference between the frequency of dam outflow and the design flood in river, it is required to improve the existed flood plan in the downstream of Andong dam. As a result of this study, the optimal operation of reservoir systems can be proposed to mitigate the flood damage in the downstream of Andong dam and also can be used to establish the flood plans.

• Journal of Preventive Medicine and Public Health
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• 제45권4호
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• pp.219-226
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• 2012

Objectives: To evaluate the risk of fractures related with zolpidem in elderly insomnia patients. Methods: Health claims data on the entire South Korean elderly population from January 2005 to June 2006 were extracted from the Health Insurance Review and Assessment Service database. We applied a case-crossover design. Cases were defined as insomnia patients who had a fracture diagnosis. We set the hazard period of 1 day length prior to the fracture date and four control periods of the same length at 5, 10, 15, and 20 weeks prior to the fracture date. Time independent confounding factors such as age, gender, lifestyle, cognitive function level, mobility, socioeconomic status, residential environment, and comorbidity could be controlled using the case-crossover design. Time dependent confounding factors, especially co-medication of patients during the study period, were adjusted by conditional logistic regression analysis. The odds ratios and their 95% confidence intervals (CIs) were estimated for the risk of fracture related to zolpidem. Results: One thousand five hundred and eight cases of fracture were detected in insomnia patients during the study period. In our data, the use of zolpidem increased the risk of fracture significantly (adjusted odds ratio [aOR], 1.72; 95% CI, 1.37 to 2.16). However, the association between benzodiazepine hypnotics and the risk of fracture was not statistically significant (aOR, 1.00; 95% CI, 0.83 to 1.21). Likewise, the results were not statistically significant in stratified analysis with each benzodiazepine generic subgroup. Conclusions: Zolpidem could increase the risk of fracture in elderly insomnia patients. Therefore zolpidem should be prescribed carefully and the elderly should be provided with sufficient patient education.

• Kidney Research and Clinical Practice
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• 제37권4호
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• pp.384-392
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• 2018

Background: A very low protein diet (VLPD) with ketoacid analogs of essential amino acids (KA/EAA) administration can remarkably influence protein synthesis and metabolic disturbances of patients with advanced chronic kidney disease (CKD), and may also slow the decline in renal function. Methods: A retrospective cohort study was carried out to monitor renal progression and metabolic and nutritional status among 140 patients with CKD stage III or IV. One group (n = 70) was on a low protein diet (LPD) with 0.6 g of protein intake, and another group (n = 70) was on a VLPD with 0.3 g of protein and KA/EAA supplementation of 100 mg/kg/day for 12 months. Results: At 12-month follow-up, estimated glomerular filtration rate (GFR) significantly decreased from $41.6{\pm}10.2$ to $36.4{\pm}8.8mL/min/1.73m^2$ (P < 0.001) and urine protein increased from $0.6{\pm}0.5$ to $0.9{\pm}1.1g/day$ (P = 0.017) in the LPD group, but no significant changes in estimated GFR and urine protein were found in the VLPD plus KA/EAA group. A significant mean difference in rate of change in estimated GFR ($-5.2{\pm}3.6mL/min/1.73m^2$ per year; P < 0.001) was observed between the two groups. After Cox regression analysis, treatment with VLPD plus KA/EAA significantly protected against the incidence of declining GFR > 10% annually (adjusted hazard ratio, 0.42; 95% confidence interval, 0.23-0.79; P = 0.006) and significant correlations were found between using VLPD plus KA/EEA and increased GFR. Conclusion: VLPD supplementation with KA/EAA is associated with delayed renal progression while preserving the nutritional status in the patients with CKD. Co-administration of VLPD and KA/EAA may prove an effective alternative to conservative management of CKD.

• 당뇨병
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• 제19권3호
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• pp.135-139
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• 2018

The sodium-glucose cotransporter-2 inhibitor (SGLT2i) is a new anti-hyperglycemic agent that have function to concomitantly inhibit the reabsorption of glucose and sodium in the renal proximal convoluting tubule. Recent two cardiovascular outcome trials showed that a lower risk of cardiovascular events with SGLT2i in people with type 2 diabetes. In addition, prior real-world data demonstrated similar SGLT2i effects, but these studies were limited to the United States and Europe. Thus, the CVD-REAL (Comparative Effectiveness of Cardiovascular Outcomes in New Users of Sodium-Glucose Cotransporter-2 Inhibitors) 2 Study was investigated cardiovascular outcomes in those initiated on SGLT2i versus other glucose-lowering drugs (oGLDs) across 6 countries in the Asia Pacific, the Middle East, and North American regions. In Korea, 336,644 episodes of initiation in SGLT2i or oGLD group between September 2014 and December 2016 were identified in Korea National Health Insurance database after propensity score matching. SGLT2i users was associated with a lower risk of all-cause death (hazard ratio [HR], 0.72; 95% confidence interval [CI], 0.67~0.77), hospitalization for heart failure (HHF) (HR, 0.87; 95% CI, 0.82~0.92), all-cause death or HHF (HR, 0.81; 95% CI, 0.78~0.85), myocardial infarction (HR, 0.81; 95% CI, 0.74~0.89), and stroke (HR, 0.82; 95% CI, 0.78~0.86) compared with oGLD users. In conclusion, initiation of SGLT2i had a lower risk of cardiovascular events in people with type 2 diabetes compared with oGLDs.