• The Korean Journal of Applied Statistics
• /
• v.31 no.4
• /
• pp.427-446
• /
• 2018

Korea will have a super-aged society within only 30 years according to the United Nations' definition of an aging society and the statistics on Korea's Population projections (2016), indicates that Korea has the fastest ageing speed in the world. There is a lack of data on long-term time-series data on death as related to pension and welfare policies compared to the rapid rate of aging. This paper estimates life expectancy over 245 years (from 1955 to 2200) through past and future forecasts as well as compares the expected life expectancy of the synthetic cohort and the real cohort. In addition, an international comparisons were made to understand the level of aging in Korea. Estimates of the back-projection period were compared with previous studies and the LC model to improve accuracy and objectivity. In addition, the predictions after 2016 reflected the declined mortality rate effect of Korea using the LC-ER model. The results showed an increase in life expectancy of about 30 years over 60 years (1955-2015) with an expected life expectancy of the real cohort over the second century (1955-2155) higher than the synthetic cohort. The comparative advantage of life expectancy of real cohorts was confirmed to be a common trend among comparative countries. In addition, Japan and Korea have a higher life expectancy and starting from 85 to 90 years old, all comparative countries show that the growth rate for the life expectancy of synthetic and real cohorts is less than previous years.

• Journal of the Korean Data and Information Science Society
• /
• v.25 no.6
• /
• pp.1273-1281
• /
• 2014

As a variety of industrial technology advances with various materials developed, cosmetics industry in general is witnessing many kinds of new cosmetic products. At the same time, Cosmetics Act becomes effective, and cosmetics ingredient labeling is implemented. Concerns with life pattern such as life management, biorhythm, right posture, and stress symptoms are on the increase in order to seek high-quality life as well. These life patterns are closely connected not only with life quality and health but with skin management, and thus this paper conducts a survey on the connection between functional cosmetics awareness and life pattern. Results show that out of 16 questions concerning cosmetics awareness, responses to question number 3, 5, 6 and 11 have relevant differences among colleges. Furthermore, the results of cross analysis with life pattern show that there are relevant differences between the year of responses and stress symptoms and between the year of responses and right posture. Lastly, it is shown that answers to questions regarding gender and biorhythm, gender and right posture, and gender and stress symptoms are relevantly different. Further research is needed to reveal the differences between college students and ordinary people at large.

• Imaging Science in Dentistry
• /
• v.51 no.1
• /
• pp.73-80
• /
• 2021

Purpose: The purpose of this study was to evaluate the cone-beam computed tomographic (CBCT) imaging and histopathological characteristics of osteoradionecrosis(ORN) and medication-related osteonecrosis of the jaw(MRONJ). Materials and Methods: Ten surgical specimens from segmental mandibulectomy (3 ORN and 7 MRONJ) were analyzed using CBCT. The CBCT parameters were as follows: high-resolution mode (tube voltage, 90.0 kV; tube current, 4.00 mA; rotation time, 16.8 s; field of view, 56 mm×56 mm; thickness, 0.099 mm). Histopathological characteristics were evaluated using histological slides of the surgical specimens. The Pearson chi-square test was used to compare ORN and MRONJ in terms of CBCT findings(internal texture, sequestrum, periosteal reaction and cortical perforation) and histopathological characteristics(necrotic bone, inflammatory cells, reactive bone formation, bacteria, Actinomyces, and osteoclasts). A P value less than 0.05 was considered to indicate statistical significance. Results: MRONJ showed periosteal reaction on CBCT more frequently than ORN (7 of 7 [100%] vs. 0 of 3 [0%], P<0.05). Regarding histopathological characteristics, MRONJ showed osteoclasts more frequently than ORN (6 of 7 [85.7%] vs. 0 of 3 [0%], P<0.05). Conclusion: This study evaluated the CBCT imaging and histopathological characteristics of ORN and MRONJ, and the findings suggest that CBCT could be useful for the evaluation of ORN and MRONJ.

• Journal of Technologic Dentistry
• /
• v.34 no.3
• /
• pp.249-261
• /
• 2012

Purpose: This study was carried out in order to examine the relationship of job satisfaction and quality of life on the dental technicians and to analyze its influence. Methods: A self-reported questionnaire survey was carried out by having convenience sampling as 220 dental technicians who work in Seoul Metropolis, Gyeonggi-do Province, Daejeon and Chungnam Province from March 12, 2012 to April 13. A research tool was used questionnaire that was proved reliability and validity. It was prepared with totally 50 questions such as 12 items for subjects' general characteristics, 18 items for job satisfaction measurement, and 20 items for life quality measurement. An analysis of the collected data was computationally processed by using SPSS Win 17.0 program. An analytical technique was made by using statistical techniques such as frequency & percentage, T-test or One-way ANOVA analysis. The following are the analytical results of the collected materials. Results: As a result of analyzing research subjects' job satisfaction level, there was significant difference(P<0.05) in items of religion, hobby life, working environment, and rest time out of daily work. The whole mean in job satisfaction was indicated to be relatively high with 3.13. However, job satisfaction with social recognition, salary, and safety was indicated lowly. As a result of analyzing research subjects' life quality level, there was significant difference(P<0.05) in items of religion, hobby life, working environment, and rest time out of daily work. The whole mean in quality of life was indicated to be relatively high with 3.10. However, the satisfaction was indicated lowly in the whole life quality and the life environment sphere. As a result of analyzing correlation between job satisfaction and life quality, all variables were indicated to be positive correlation in high significance level, thereby having been indicated that the higher job satisfaction leads to the higher life quality. Conclusion: As a result of research, the dental technicians' job satisfaction was indicated to have high correlation with quality of life. An effort is judged to be necessary for establishing fair compensation system, improving welfare policy and enhancing social recognition and position in order to promote dental technicians' quality of life.

• Journal of the Korean Society of Industry Convergence
• /
• v.5 no.1
• /
• pp.3-9
• /
• 2002

In the field of design of mechanical structure and expectation of life time, characteristic of fatigue limit comes out to he the most important problem. In this paper, in order to get fatigue limit, (I) investigate the aspects of economy, time and confidence comparing two methods: the method by fracture probability introducing statistical conception and the staircase method. And (II) examine the experience approaching fatigue limit and coaxing effect. The value of fatigue limit by staircase method in very effective in view of practical use, and coaxing comes out by the same material effect as restraining crack progress, not as strengthening the tip of crack alone.

• Earthquakes and Structures
• /
• v.9 no.4
• /
• pp.851-873
• /
• 2015

A methodology for estimation of statistical properties (viz. mean and standard deviation) of the expected seismic damage to reinforced concrete framed structures subject to corrosion of reinforcement, over a specified reference time (typically the service life of the structure) is proposed in this paper. The damage to the structure under the earthquake loading is characterised by the damage index, determined using the modified Park and Ang damage model. The reduction in area, yield strength and strain at ultimate of steel reinforcement, and the reduction in compressive strength of cover concrete due to corrosion are taken into account in the estimation of damage. The proposed methodology is illustrated through an example problem. From the results obtained, it is noted that there is an increase of about 70% in the mean value of expected seismic damage to the reinforced concrete frame considered over a reference time of 30 years when effect of corrosion is taken into consideration. This indicates that there is a need to consider the effect of corrosion of reinforcement on the estimation of expected seismic damage.

• Journal of Korean Society for Quality Management
• /
• v.34 no.3
• /
• pp.19-30
• /
• 2006

For highly reliable products, it is difficult to assess the lifetime of the products with traditional life tests. Accordingly, a recent approach is to observe the performance degradation of product during the test rather than regular failure time. This study compares performances of three methods(i.e. the approximation, analytical and numerical methods) to estimate the parameters and quantiles of the lifetime when the time-to-failure distribution follows Weibull and lognormal distributions under a random coefficient degradation rate model. Numerical experiments are also conducted to investigate the effects of model error such as measurements in a random coefficient model.

• Journal of Korean Institute of Industrial Engineers
• /
• v.43 no.2
• /
• pp.147-153
• /
• 2017

In order to demonstrate a target reliability with a specified confidence level, a new two-stage Bayesian Reliability Demonstration Test (RDT) plans that is known to be more effective than a corresponding single-stage one is proposed and developed by Bayesian framework with beta prior distribution for Weibull life time distribution. A numerical example is provided to illustrate the proposed RDT plans and compared with other non-Bayesian and Bayesian plans. Comparative results show that the proposed Bayesian two-stage plans have some merits in terms of required and expected testing time and probability of acceptance.

• Journal of the Korean Data and Information Science Society
• /
• v.28 no.4
• /
• pp.875-888
• /
• 2017

The Rayleigh distribution has been commonly used in life time testing studies of the probability of surviving until mission time. We focus on a reliability function of the Rayleigh distribution and deal with prior distribution on R(t). This paper is an effort to obtain Bayes estimators of rayleigh distribution with three different prior distribution on the reliability function; a noninformative prior, uniform prior and inverse gamma prior. We have found the Bayes estimator and predictive density function of a future observation y with each prior distribution. We compare the performance of the Bayes estimators under different sample size and in simulation study. We also derive the most plausible region, prediction intervals for a future observation.

• The Korean Journal of Applied Statistics
• /
• v.25 no.6
• /
• pp.897-915
• /
• 2012

This paper examines the relationship between the stock and futures markets in terms of lead-lag relationship, correlation and the hedge ratio using wavelet analysis. The basic finding is that the relationship between the two markets significantly depends on the time-scale. First, there is a feedback relationship between the stock and futures markets in the long-run scale; however, weaker evidence is observed in shorter-run scales. Second, wavelet correlation between the two markets increases for a longer time scale. Third, the hedge ratio and the effectiveness of hedging strategies increase as the investment horizon gets longer. The results in this paper indicate that the stock and futures series are perfectly correlated in the long run and are tied together over long horizons.