• Journal of the Korea Academia-Industrial cooperation Society
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• v.13 no.5
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• pp.2219-2231
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• 2012

This study conducted to investigate incidence rate and association of serum lipid profiles with incidence of ischemic heart disease. Study subjects consisted of 417,642 adults aged 30 years and over, who underwent physical examination and responded to questionnaire from health examination center of 19 university general hospitals. Hazard ratio of risk factor for ischemic heart disease (IHD) were calculated by Cox's proportional hazard regression model adjusted for ages, BMI and lifestyle (drinking, smoking and exercising). For TC/HDL ratio, hazard ratio of IHD in male increased from 1.21 times to 1.84 times increase with TC/HDL ratio, and that in female also increased from 1.26 times to 1.86 times. For TG/HDL ratio, hazard ratio of IHD in male increased from 1.17 times to 1.49 times increase with TG/HDL ratio, and that in female also increased from 1.42 times to 1.97 times. For LDL/HDL ratio, hazard ratio of IHD in male increased from 1.26 times to 1.82 times increase with LDL/HDL ratio, and that in female also increased from 1.26 times to 1.68 times. In conclusion serum lipid indexes are the significant risk factors for cardiovascular diseases. The higher the concentration of TC, LDL and TG is, the lower the concentration of HDL is, hazard ratio for IHD increased. Ratio of TC/HDL, TG/HDL and LDL/HDL were also verified to be significant risk factors for IHD.

• Structural Engineering and Mechanics
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• v.6 no.7
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• pp.773-784
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• 1998

To assess the collapse risk of transmission line structures subject to natural hazards, it is important to identify what hazard may cause the structural collapse. In Australia and many other countries, a large proportion of failures of transmission line structures are caused by severe thunderstorms. Because the wind loads generated by thunderstorms are not only random but time-variant as well, a time-dependent structural reliability approach for the risk assessment of transmission line structures is essential. However, a lack of appropriate stochastic models for thunderstorm winds usually makes this kind of analysis impossible. The intention of the paper is to propose a stochastic model that could realistically and accurately simulate wind loading due to severe thunderstorms. With the proposed thunderstorm model, the collapse risk of transmission line structures under severe thunderstorms is assessed numerically based on the computed failure probability of the structure.

• International Journal of Reliability and Applications
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• v.17 no.1
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• pp.1-19
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• 2016

The Exponentiated Quasi Lindley (EQL) distribution which is an extension of the quasi Lindley Distribution is introduced and its properties are explored. This new distribution represents a more flexible model for the lifetime data. Some statistical properties of the proposed distribution including the shapes of the density and hazard rate functions, the moments and moment generating function, the distribution of the order statistics are given. The maximum likelihood estimation technique is used to estimate the model parameters and finally an application of the model with a real data set is presented for the illustration of the usefulness of the proposed distribution.

• Journal of Korean Institute of Industrial Engineers
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• v.33 no.2
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• pp.273-281
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• 2007

The decision of how long performing system burn-in must be answered with a probabilistic model of a system lifetime at which infant mortality failures created during assembly processes are quantified. In this paper, we propose such a model which is modified from previous results. Using the system model, we derived system reliability in terms of component and system burn-in times for the two cases of minimal repair at system failure and of component replacement and connection repair at their failure times. The procedure is illustrated with a bridge system and the optimal system burn-in times are obtained for maximizing system reliability. The result suggests that an assumption of minimal repair at system failure may underestimate the optimal burn-in time in practice.

• Communications for Statistical Applications and Methods
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• v.23 no.2
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• pp.147-161
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• 2016

This paper introduces the four parameter new generalized inverse Weibull distribution and investigates the potential usefulness of this model with application to reliability data from engineering studies. The new extended model has upside-down hazard rate function and provides an alternative to existing lifetime distributions. Various structural properties of the new distribution are derived that include explicit expressions for the moments, moment generating function, quantile function and the moments of order statistics. The estimation of model parameters are performed by the method of maximum likelihood and evaluate the performance of maximum likelihood estimation using simulation.

• Journal of the Korean Data and Information Science Society
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• v.23 no.2
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• pp.257-269
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• 2012

Global crisis expedites the change in the environment of industry and puts small size enterprises in danger of mass bankruptcy. Because of this, domestic small size enterprises is an urgent need of restructuring. Based on the small business data registered in the Credit Guarantee Fund, we estimated the survival probability in the context of the survival analysis. We also analyzed the survival time which are distinguished depending on the types of business in the small business. Financial variables were also conducted using COX regression analysis of small businesses by types of business. In terms of types of business wholesale and retail trade industry and services were relatively high in the survival probability than light, heavy, and the construction industries. Especially the construction industry showed the lowest survival probability. In addition, we found that construction industry, the bigger BIS (bank of international settlements capital ratio) and current ratio are, the smaller default-rate is. But the bigger borrowing bond is, the bigger default-rate is. In the light industry, the bigger BIS and ROA (return on assets) are, the smaller a default-rate is. In the wholesale and retail trade industry, the bigger bis and current ratio are, the smaller a default-rate is. In the heavy industry, the bigger BIS, ROA, current ratio are, the smaller default-rate is. Finally, in the services industry, the bigger current ratio is, the smaller a default-rate is.

• Journal of Periodontal and Implant Science
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• v.54 no.1
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• pp.44-52
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• 2024

Purpose: This study aimed to evaluate the clinical outcomes of a single type of narrow-diameter implant (NDI) by investigating its survival rate and peri-implant marginal bone loss (MBL). In addition, variables possibly related to implant survival and MBL were investigated to identify potential risk factors. Methods: The study was conducted as a retrospective study involving 49 patients who had received 3.0-mm diameter TSIII implants (Osstem Implant Co.) at Seoul National University Dental Hospital. In total, 64 implants were included, and dental records and radiographic data were collected from 2017 to 2022. Kaplan-Meier survival curves and a Cox proportional hazard model were used to estimate the implant survival rate and to investigate the effects of age, sex, jaw, implant location, implant length, the stage of surgery, guided bone regeneration, type of implant placement, and the surgeon's proficiency (resident or professor) on implant survival. The MBL of the NDIs was measured, and the factors influencing MBL were evaluated. Results: The mean observation period was 30.5 months (interquartile range, 26.75-45 months), and 6 out of 64 implants failed. The survival rate of the NDIs was 90.6%, and the multivariate Cox regression analysis showed that age was associated with implant failure (hazard ratio, 1.17; 95% confidence interval, 1.04-1.31, P=0.01). The mean MBL was 0.44±0.75 mm, and no factors showed statistically significant associations with greater MBL. Conclusions: NDIs can be considered a primary alternative when standard-diameter implants are unsuitable. However, further studies are required to confirm their long-term stability.

• Journal of the Korean Institute of Gas
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• v.6 no.1 s.17
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• pp.81-85
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• 2002

This paper presents the calculation methods of liquid release rate in the transition region when hazardous materials leak from the pipeline due to an unwanted accident. For the laminar and turbulent flow region, liquid release rate from a pipeline can be calculated by using a commercial software or by using calculator based on the models(equations) suggested by Crowl and Louvar et al. However, there has been no corresponding model for the transition flow region. In this paper. we showed that the turbulent model may be used as an equation generally used in the transition region for conservative hazard analysis if safety factor $30\%$ is added to the value calculated by the turbulent model. In this regard, we first calculated the release rate from liquid pipeline in the transition region by using experimental data on Fanning friction factor depending on Reynolds number which Lap-Mou Tam et al. had introduced, then compared it with that of the laminar and turbulent models in transition region.

• 한국방재학회:학술대회논문집
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• 2008.02a
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• pp.191-194
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• 2008

Labyrinth weir is a hydraulic structure that can maintain constant water depth and increase overflow rate by increasing overflow width of weir through complicated displacement of its cross section. The labyrinth weir can be widely applied to various hydraulic facilities such as dam spillway, irrigation facilities, and canal structures. To date, however, few labyrinth weirs were applied to hydraulic facilities in Korea. Hence, in-depth research on labyrinth weir is highly required to efficiently apply the labyrinth weir to hydraulic facilities. This study was performed to analyze the hydraulic characteristics according to triangle labyrinth weir using hydraulic model experiments. The hydraulic characteristics provided in this study, which make it feasible to increase the overflow rate, and are expected to be widely applied to design of hydraulic facilities such as dam spillway and irrigation system.

• Journal of the Korean Geophysical Society
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• v.9 no.3
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• pp.171-179
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• 2006

Predictive equations of ground motions are one of the most important factors in the seismic hazard analysis. Unfortunately, studies on predictive equations of ground motions in Korea had been hampered due to the lack of seismic data. To overcome the lack of data, seismologists adopted the stochastic method based on the seismological model. Korean predictive equations developed by the stochastic method show large differences in their predictions. It was turned out through the analysis of the existing studies that the main sources of the differences are the uncertainties in the (Brune) stress drop and spectral decay rate . Therefore, it is necessary to focus the future research on the reduction of the uncertainties in the two parameters.