• 한국자원식물학회지
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• 제21권3호
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• pp.210-215
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• 2008

Gene-expression analysis is increasingly important in biological research, with real-time reverse PCR (RTPCR) becoming the method of choice for high-throughput and accurate expression profiling of selected genes. However, this technique requires important preliminary work for standardizing and optimizing the many parameters involved in the analysis. Plant stress studies are more and more based on gene expression. The analysis of gene expression requires sensitive and reproducible measurements for specific mRNA sequence. Several genes are regulated in response to abitoic stresses, such as salinity, and their gene products function in stress response and tolerance. The design of the primers and TaqMan probes for real-time PCR assays were carried out using the Primer $Express^{TM}$ software 3.0. The PCR efficiency was estimated through the linear regression of the dilution curve. To understand the expression pattern of various genes under salt stressed condition, we have developed a unique public resource of 9 stress-related genes in poplar. In this study, real-time RT-PCR was used to quantify the transcript level of 10 genes (9 stress-related genes and 1 house keeping gene) that could play a role in adaptation of Populus davidiana. Real-time RT-PCR analyses exhibited different expression ratios of related genes. The data obtained showed that determination of mRNA levels could constitute a new approach to study the stress response of P. davidiana after adaptation during growth in salinity condition.

• Nuclear Engineering and Technology
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• 제49권3호
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• pp.581-591
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• 2017

Influences of hold time and stress ratio on cyclic creep properties of Grade 91 steel were systemically investigated using a wide range of cyclic creep tests, which were performed with hold times (HTs) of 1 minute, 3 minutes, 5 minutes, 10 minutes, 20 minutes, and 30 minutes and stress ratios (R) of 0.5, 0.8, 0.85, 0.90, and 0.95 under tension loading cycles at $600^{\circ}C$. Under the influence of HT, the rupture time increased to HT = 5 minutes at R = 0.90 and R = 0.95, but there was no influence at R = 0.50, 0.80, and 0.85. The creep rate was constant regardless of an increase in the HT, except for the case of HT = 5 minutes at R = 0.90 and R = 0.95. Under the influence of stress ratio, the rupture time increased with an increase in the stress ratio, but the creep rate decreased. The cyclic creep led to a reduction in the rupture time and an acceleration in the creep rate compared with the case of monotonic creep. Cyclic creep was found to depend dominantly on the stress ratio rather than on the HT. Fracture surfaces displayed transgranular fractures resulting from microvoid coalescence, and the amount of microvoids increased with an increase in the stress ratio. Enhanced coarsening of the precipitates in the cyclic creep test specimens was found under all conditions.

• 대한인간공학회지
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• 제28권4호
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• pp.91-99
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• 2009

A visual stress may provoke migraine, cephalalgia, intervene a long term reading and learning capability and reduce the productivity of a laborer who uses computer for a good while. In this study, a web based screening tool for visual stress was developed, it applied to 72 visually normal young persons in parallel with traditional questionnaire about symptoms of visual stress. To estimate visual stress, It is proposed to measure difference of visual search time of Han Gul characters as targets between visual stressful pattern and non-visual stressful pattern as global background of characters. As a result of test, 5 subjects were screened whose mean visual search time in the stressful pattern with 6 CPD spatial frequency increase significantly more than in none stressful pattern(t-test, one-tailed, p=$1.0407\times10^{-11}$). 2 of them were diagnosed as mild visual stress syndrome in the clinic. None had visual distortion and 50% of subjects had visual discomfort in results of the questionnaire. Correlation between visual search time increase rate and normalized number of visual discomfort may be slight(C. coefficient=0.1355). This study may contribute as a basic research for screening person with migraine, visual reading disabilities and VDT syndrome. It is required to apply the test to visual reading disabilities, migraine with visual distortion and/or visual discomfort as well as normal person for higher reliability of the screening tool.

• 한국자동차공학회논문집
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• 제10권5호
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• pp.168-173
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• 2002

The durability test, along with the crashworthiness test, requires the most time and expense in the vehicle development process. The durability design using CAE tools reduces the time required for both the durability test and actual vehicle production. Existing dynamic stress analyses designed fir the analysis of vehicle fatigue mainly calculate the dynamic stress history and fatigue after performing dynamic analysis and stress analysis with relevant software applications and then superpositioning the dynamic load history and stress influence coefficient at each joint. This approach is a complex process, taking into account the flexibility of the parts. It is, however, incapable of giving accurate consideration to the contacts between components, the non-linearity of materials, and tire-road surface interactions. This approach also requires that the analysts have an expertise in software applications of various kinds or an expert in each area must perform the analysis. This requires as a great deal of manpower and time. In order to complement the existing approaches for dynamic stress analysis, this study aims at the following: (1) to suggest the simple and accurate analysis technique which is capable of producing all the possible necessary results; (2) to reduce dramatically the time and manpower needed to construct a model designed to analyze dynamics, quasi-static stress, and fatigue; and (3) to enable an accurate analysis of fatigue by improving the accuracy of dynamic stress. we verify the presented analysis method through durability evaluation of the knuckle of passenger car.

• International Journal of Precision Engineering and Manufacturing
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• 제2권2호
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• pp.5-10
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• 2001

This paper attempt to explore the shape of stress wave propagation of 3-dimensional stress field which in made in the process of the time increment. A finite element program about 3-dimensional stress wave propagation is developed for investigating the changing shape of the stress by the impact load. The finite element program, which is the solution for the 3-dimensional stress wave analysis, based on Galerkin and Newmark-${\beta}$ method at time increment step. The tensile stress and compressive stress become larger with the order of the middle , the upper and the opposite layers when the impact load is applied. In a while the shear stress become larger according to the order of the upper, the middle and the opposite layers when impact load applied.

• Ocean Systems Engineering
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• 제1권2호
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• pp.121-130
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• 2011

One of the prevailing models that describe the stress corrosion is represented by an exponential dependence between rate of corrosion and stress, suggested by Gutman, Zainullin and Zuripov. This study revisits the exponential model and derives analytical expressions for the structures' durability which is postulated as the time for stress level to reach its yield value. Comparison is conducted with other possible models, namely with linear, quadratic or cubic cases.

• 대한간호학회지
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• 제50권4호
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• pp.631-640
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• 2020

Purpose: This study aimed to examine premenstrual symptoms (PMS) of shift nurses and identify the association between PMS, sleep, and occupational stress. Methods: This study was conducted with a secondary data analysis that used data from the Shift Work Nurse's Health and Turnover study. The participants were 258 nurses who were working in shifts including night shifts. PMS, sleep patterns (sleep time and sleep time variability), sleep quality, and the occupational stress of each participant were measured using the Moos Menstrual Distress Questionnaire, a sleep diary, an actigraph, the Insomnia Severity Index, and the Korean Occupational Stress Scale, respectively. Data were analyzed using SPSS 23 and STATA 15.1 to obtain descriptive statistics, Pearson's correlation coefficients, multiple linear regression with generalized estimating equations (GEE) and Baron and Kenny's mediating analysis. Results: The average PMS score, average sleep time, average sleep time variability, average sleep quality score, and average occupational stress score of the participants was 53.95 ± 40.45, 7.52 ± 0.89 hours, 32.84 ± 8.43%, 12.34 ± 5.95, and 49.89 ± 8.98, respectively. A multiple linear regression analysis with GEE indicated that sleep time variability (B = 0.86, p = .001), and sleep quality (B = 2.36, p < .001) had negative effects on nurses' PMS. We also found that sleep quality had a complete mediating effect in the relationship between occupational stress and PMS. Conclusion: These findings indicate that both sleep time variability and sleep quality are important factors associated with PMS among shift work nurses. To improve shift nurses' PMS status, strategies are urgently needed to decrease sleep time variability and increase sleep quality.

• 전자공학회논문지A
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• 제32A권6호
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• pp.67-74
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• 1995

This paper proposes the step-stress type-I censoring model for analyzing the data of accelerated life test and reducing the time of accelerated life test. In order to obtain the data of accelerated life test, the step-stress accelerated life test was run with voltage stress to CMOS Hex Buffer. The Weibull distribution, the Inverse-power-law model and Maximum likelihood method were used. The iterative procedure using modified-quasi-linearization method is applied to solve the nonlinear equation. The proposed Weibull step-stress type-I censoring model exactly estimases the life time of units, while reducting the time of accelerated life test and the equipments of test.

• 품질경영학회지
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• 제32권4호
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• pp.208-219
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• 2004

This paper considers a nonparametric estimation of lifetime distribution for ramp stress tests with stress bound under intermittent inspection. The test items are inspected only at specified time points an⊂1 so the collected observations are grouped data. Under the cumulative exposure model, two nonparametric estimation methods of estimating the lifetime distribution at use condition stress are proposed for the situation which the time transformation function relating stress to lifetime is a type of the inverse power law. Each of items is initially put on test under ramp stress and then survivors are put on test under constant stress, where all failures in the Inspection interval are assumed to occur at the midi)oint or the endpoint of that interval. Two proposed estimators of quantile from grouped data consisting of the number of items failed in each inspection interval are numerically compared with the maximum likelihood estimator(MLE) based on Weibull distribution.

• 소음진동
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• 제10권4호
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• pp.686-691
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• 2000

In this paper a computer aided analysis method is proposed for durability assessment in the early design stages using dynamic analysis, stress analysis and fatigue life prediction method. From dynamic analysis of a vehicle suspension system, dynamic load time histories of a suspension component are calculated. From the dynamic load time histories and the stress of the suspension component, a dynamic stress time history at the critical location is produced using the superposition principle. Using linear damage law and cycle counting method, fatigue life cycle is calculated. The predicted fatigue life cycle is verified by experimental durability tests.