• Structural Engineering and Mechanics
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• v.9 no.6
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• pp.557-568
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• 2000

As time-variant reliability approaches become increasingly used for service life prediction of the aging infrastructure, the demand for computer solution methods continues to increase. Effcient computer techniques have become well established for the reliability analysis of structural systems. Thus far, however, this is largely limited to time-invariant reliability problems. Therefore, the requirements for time-variant reliability prediction of deteriorating structural systems under time-variant loads have remained incomplete. This study presents a computer program for $\underline{REL}$iability of $\underline{T}$ime-Variant $\underline{SYS}$tems, RELTSYS. This program uses a combined technique of adaptive importance sampling, numerical integration, and fault tree analysis to compute time-variant reliabilities of individual components and systems. Time-invariant quantities are generated using Monte Carlo simulation, whereas time-variant quantities are evaluated using numerical integration. Load distribution and post-failure redistribution are considered using fault tree analysis. The strengths and limitations of RELTSYS are presented via a numerical example.

• International Journal of Reliability and Applications
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• v.7 no.1
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• pp.13-25
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• 2006

A new class of life distributions is studied. This class is defined based on comparing the residual life time to the whole life in the moment generating function order giving 'the new better than used in the moment generating function order ageing class $(NBU_{mgf})$'. Fundamental properties of this class are given including some closure properties and characterizations. Finally, we consider new results about comparisons of age and block replacement policies when the underlying distribution belongs to $NBU_{mgf}$ aging classes.

• Journal of Applied Reliability
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• v.12 no.3
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• pp.165-176
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• 2012

Hydrostatic bearing improves performance and life time of a product by avoiding solid friction and reducing viscosity friction with the help of creating pressure equilibrium between two faces doing relative motion. This study suggests failure analysis and test evaluation for a ball joint that adopts the hydrostatic bearing and introduces the entire process to improve reliability of the product by design improvement. A typical failure is growth of friction torque by solid friction, and its failure cause is determined and the improvement is proposed. Finally, reliability improvement is established by analysis of the results of before and after acceleration test.

• Journal of Korean Society for Quality Management
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• v.7 no.2
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• pp.7-10
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• 1979

In this paper the Rao-Blackwell and Lehmann-$Scheff{\acute{e}}$ Theorem are used to drive the minimum variance unbiased estimators of system reliability for a number of distributions when a system consists of n Components whose random life times are assumed to be independent and identically distributed. For the case of a negative exponential life time, we obtain the maximum likelihood estimator of the system reliability and compair it with minimum variance unbiased estimator of the system reliability.

• The Journal of Korean Academy of Sensory Integration
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• v.16 no.2
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• pp.36-49
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• 2018

Objective : The purpose of this study was to examine the validity and reliability of the Korean version of Life Balance Inventory (K-LBI) and to present the relationship between life balance and sensory processing. Methods : K-LBI was constructed through forward and backward translation. Convergent validity, internal consistency, and test-retest reliability were tested for college students. To verify convergent validity, correlation analyses between K-LBI and Korean version of Perceived Stress Scale, Korean version of Satisfaction With Life Scale, and Adult Self Report-Achenbach system of empirically based assessment were performed. Split-half reliability and test-retest reliability were also obtained for reliability verification. We performed the correlation analysis between K-LBI and Korean version of Adolescent/Adult Sensory Profile. Results : A significant correlation was found between K-LBI and the scales for convergent validity. A favorable split-half reliability and test-retest reliability were calculated. The positive correlations were found between relationship life balance and sensory sensitivity/sensation avoiding quadrants. The negative correlation was found between challenges life balance and low registration. Conclusion : This study shows that K-LBI is a valid and reliable tool in Korea. It also provides an in-depth understanding of the relationship between life balance and sensory processing.

• Journal of Applied Reliability
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• v.17 no.2
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• pp.103-111
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• 2017

Purpose: Accelerated degradation tests can speed time to market and reduce the test time and costs associated with long term reliability tests to verify the required service life of a product or material. This paper proposes a service life prediction method for components or materials using an accelerated degradation tests based on the relationships between temperature and the rate of failure-causing chemical reaction. Methods: The relationship between performance degradation and the rate of a failure-causing chemical reaction is assumed and least square estimation is used to estimate model parameters from the degradation model. Results: Methods of obtaining acceleration factors and predicting service life using the degradation model are presented and a numerical example is provided. Conclusion: Service life prediction of a component or material is possible at an early stage of the degradation test by using the proposed method.

• Journal of Applied Reliability
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• v.17 no.2
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• pp.136-142
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• 2017

Purpose: In this paper, we propose a test method for evaluating the life time of the inverter which is one of the main internal configuration systems in order to evaluate the life time of the power supply for the vehicle. Methods: The performance and failure criteria required for the development of the accelerated life test method were established and the Taguchi method was used to derive the stress factors affecting performance and reliability. Results: The major stress of the product degradation were considered to be high temperature. Conclusion: The acceleration factor was estimated through a two-level high temperature test and a test methods was designed to guarantee the accelerated life time of the inverter.

• Journal of Applied Reliability
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• v.14 no.4
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• pp.213-219
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• 2014

Wind turbine, which is attracting part of the renewable energy and is researching continuously, is going to be large size for high efficiency. There is a yaw system rotating the nacelle, weighted about 600 tons, to be perpendicular with the wind direction blowing in the large wind turbine. The wind turbine is focusing on the reliability improvement because working environment effect is bigger than any other points and specially, the reliability improvement of the yaw drive is required by the customer because it is the key component of the wind turbine. Because of this, the establishment of criteria for yaw drive is required because yaw drive system is the part of the wind turbine closely related with ensuring the reliability. So, this study did the failure analysis of the yaw drive system, which is consisted with 10 sets of yaw drives through researching and analyzing the site conditions. Also this study designed the life test method based on the failure analysis and working condition of the yaw drive. To design the accelerated life test of the yaw drive, this study reviewed the torque, lubrication condition, and frequency of use and etc. Finally, this selected the torque as the acceleration factor which is affected mainly to the system and also, the test equipment was developed based on the requirement of the life and performance test.

• Journal of the Korean Society of Laryngology, Phoniatrics and Logopedics
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• v.30 no.1
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• pp.21-27
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• 2019

Background and Objectives : Voice disorder is recognized as a major problem because it negatively affects the elderly's social participation and quality of life. The purpose of this study was to examine the validity and reliability of Korean aging voice index (KAVI), which assesses the quality of life related to the voice of the elderly. Materials and Method : This study was conducted on 211 elderly people aged 65 years or older : 111 patients with voice disorder (mean age 69.8, range 65-80 years) and 100 nomorphonic participants (mean age 70.6, range 65-82 years). Aging voice index was translated into Korean and used and Korean voice-related quality of life (KVQOL) was conducted to verify KAVI. The validity (item validity, concurrent validity, and construct validity) and reliability (test-retest reliability and internal consistency reliability) of KAVI. Results : The item validity (ICC=0.895) and construct validity (r=0.765) showed a high correlation, respectively. And concurrent validity (r=0.748), test-retest reliability (0.851), and internal consistency reliability (${\alpha}=0.832$) were statistically significant in voice disorder group. In addition, there was a significant difference between the voice disorder and the nomorphonic group in AVI total score. Conclusion : KAVI is a validated and reliable quality of life tool that will be useful for assessing the presence and effectiveness of interventions in clinical settings.

• Child Health Nursing Research
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• v.26 no.3
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• pp.338-347
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• 2020

Purpose: The Life Transition Scale (LTS) consists of 24 items that assess the life transition process of parents of autistic children. This study aimed to examine the validity and reliability of the LTS in parents of children with a wide spectrum of disabilities. Methods: Data were collected from 260 parents of children with disabilities through self-report questionnaires. Validity was examined using exploratory and confirmative factor analysis to determine the factor structures of the LTS; socio-demographic differences in LTS scores were examined using the t-test or ANOVA. Reliability was examined using Cronbach's α coefficient. Results: A four-factor structure was validated (χ²=640.0, p<.001, GFI=.81, RMSEA=.07, NNFI=.89, CFI=.89, PNFI=.74, Q [χ²/df]=2.60). The validity of the LTS was verified by exploratory factor analysis, with factor loading ranging from .30 to .80. There were significant differences in the accepting phase according to children's and parents' age and the type of disability, and in the wandering phase according to parental gender, educational level, job, and socioeconomic status. The Cronbach's αs for the reliability of each of the four structures were acceptable, within a range of .80~.90. Conclusion: The LTS is a valid and reliable measurement to assess the life transition process of parents with disabled children.