• Journal of Mechanical Science and Technology
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• 제18권12호
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• pp.2158-2173
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• 2004

In this paper, the higher order terms in the crack tip stress fields are investigated macroscopically for more realistic assessment of structural material behaviors. For reactor pressure vessel material of A533B ferritic steel, effects of crack size and temperature have been evaluated using 3-point SENB specimens through a series of finite element analyses, tensile tests and fracture toughness tests. The T-stress, Q-parameter and q-parameter as well as the K and J-integral are calculated and mutual relationships are investigated also. Based on the evaluation, it has proven that the effect of crack size from standard length (a/W=0.53) to shallow length (a/W=0.11) is remarkable whilst the effect of temperature from -20$^{\circ}C$ to -60$^{\circ}C$ is negligible. Finally, the cleavage fracture toughness loci as a function of the promising Q-parameter or q-parameter are developed using specific test results as well as finite element analysis results, which can be applicable for structural integrity evaluation considering constraint effects.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2004년도 추계학술대회
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• pp.142-147
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• 2004

In this paper, a new procedure is proposed to accomplish the primary plus secondary stress(P+Q) at the 'structural element' instead of 'transition element'. For the P+Q evaluation, the calculated stresses by FEA are linearized along a stress classification line to extract the stress category, then the stress intensity is calculated to compare with the $3S_{m}$ limit. Also, in this paper, the 'design by analysis' criteria, adopted fundamental concepts and a new approach to calculate $K_{e}$ factors are explained. The new procedure combined with 3-D FEA has been applied to motor operated valve in order to the over conservatism and the rack of margin. The evaluation results show a good applicability and can be utilized for fatigue life evaluation by using P+Q.

• Journal of Microbiology and Biotechnology
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• 제20권2호
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• pp.346-349
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• 2010

Coenzyme $Q_{10}$ ($CoQ_{10}$) production from Rhizobium radiobacter T6102 was monitored under various oxygen supply conditions by controlling the agitation speeds, aeration rates, and dissolved oxygen levels. As the results, the $CoQ_{10}$ production was enhanced by limited oxygen supply. To investigate whether the $CoQ_{10}$ production is associated with its physiological functions of electron carrier and antioxidant, the effects of sodium azide and hydrogen peroxide on the $CoQ_{10}$ production were studied, showing that the $CoQ_{10}$ contents were slightly enhanced with increasing sodium azide (up to 0.4 mM) and hydrogen peroxide (up to $10\;{\mu}M$) concentrations. These results suggest the plausible mechanism where the limited electron transfer stimulating the environments of limited oxygen supply and oxidative stress could accumulate the $CoQ_{10}$, providing the relationship between the $CoQ_{10}$ physiological functions and its regulation system.

• Clinical Nutrition Research
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• 제12권4호
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• pp.257-268
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• 2023

Migraine is a common neurological disease correlated with oxidative stress and lipid profile disorders. The present study was designed to determine the effects of Coenzyme Q10 (Co-Q10) supplementation on oxidative status and lipid profile in migraine individuals. This clinical trial was conducted on 84 females aged 18-50 years, diagnosed for episodic migraine according to the International Headache Society. Subjects were randomized to receive either Co-Q10 supplement (400 mg/day) or placebo for 12 weeks. Lipid profile and oxidative stress indices including malondialdehyde (MDA) and total antioxidant capacity (TAC) were measured before and after intervention in both groups. Also, anthropometric indices, dietary intakes, and clinical features were collected. Data analysis was conducted using SPSS version 16. Seventy-seven of the participants, with mean age of 33.70 ± 7.75 years, completed the study. After 12-week intervention, Co-Q10 led to a significant decrease in MDA levels compared to placebo (p = 0.009), with no effect on TAC levels (p = 0.106). A significant increase in serum Co-Q10 concentration and high-density lipoprotein cholesterol (HDL-C) level in Co-Q10 group was observed, but no significant differences were found in other lipid profile variables (low-density lipoprotein cholesterol, triglycerides and total cholesterol). Among anthropometric variables, Co-Q10 only caused a significant reduction in body fat percentage (BFP), but we did not find any significant changes in others. A 12-week Co-Q10 supplementation led to significant improvement in clinical features, BFP, and HDL-C level among migraine individuals.

• 한국직업건강간호학회지
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• 제18권1호
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• pp.22-32
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• 2009

Purpose: This study was conducted to measure job stress and to explore risk factors of female workers in the retail and sales industries in Seoul, Gyeonggi and Incheon. Methods: A total of 321 participants responded to a self-administered questionnaire that included 24 items of the KOSS(Korean Occupational Stress Scale) and sociodemographic characteristics. The 240 questionnaires were collected from January to March 2007 and analyzed. Results: The mean scores of female workers' job stress in the retail and sales industries ranged in Q50~74 compared with the average scores of female Koreans. The level of job insecurity was significantly high, and ranged in Q75~. However, the level of insufficient job control ranged in Q~24. Multiple regression analysis was used to explain the risk factors of female workers: monthly salary and insufficient sleep were of statistical significance. Conclusion: High level of job stress suggested that appropriate stress management programs be implemented for female workers in the retail and sales industries.

• 대한기계학회논문집A
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• 제28권7호
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• pp.1021-1028
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• 2004

Kim et al. suggested an experimental method to determine the Q parameter in situ from the out-of-plane displacement and the in-plane strains on the surface of side necking near the crack tip. In this paper, the procedure to evaluate the stress triaxiality near a crack tip such as the Q parameter is to be polished in the details for simplicity and accuracy. That is, Q and hydrostatic stress are determined only from the out-of-plane displacement, but not using in-plane strain, which is hard to measure. And also, the plastic modulus is determined by an alternative way. Through three-dimensional finite element analyses for a standard CT specimen with 20% side-grooves, the validities of the new procedures are examined in comparison to the old ones. The effect of location where the displacements are measured to determine the stress triaxiality is explored.

• Transactions on Electrical and Electronic Materials
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• 제16권4호
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• pp.173-178
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• 2015

In lieu of the excellent radio frequency (RF) performance of microelectromechanical system ( MEMS) switches, these micro switches need higher actuation voltage for their operation. This requirement is secondary to concerns over the swtiches’ reliability. This paper reports high reliability operation of RF MEMS switches with low voltage requirements. The proposed switch is optimised to perform in the Q-band, which results in actuation voltage of just 16.4 V. The mechanical stress gradient in the thin micro membrane is computed by simulating von Mises stress in a multi-physics environment that results in 90.4 MPa stress. The computed spring constant for the membrane is 3.02 N/m. The switch results in excellent RF performance with simulated isolation of above 38 dB, insertion loss of less than 0.35 dB and return loss of above 30 dB in the Q-band.

• Clinical and Experimental Reproductive Medicine
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• 제48권2호
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• pp.97-104
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• 2021

Male infertility has a complex etiopathology, which mostly remains elusive. Although research has claimed that oxidative stress (OS) is the most likely underlying mechanism of idiopathic male infertility, the specific treatment of OS-mediated male infertility requires further investigation. Coenzyme Q10 (CoQ10), a vitamin-like substance, has been found in measurable levels in human semen. It exhibits essential metabolic and antioxidant functions, as well as playing a vital role in mitochondrial bioenergetics. Thus, CoQ10 may be a key player in the maintenance of biological redox balance. CoQ10 concentrations in seminal plasma directly correlate with semen parameters, especially sperm count and sperm motility. Seminal CoQ10 concentrations have been shown to be altered in various male infertility states, such as varicocele, asthenozoospermia, and medical or surgical regimens used to treat male infertility. These observations imply that CoQ10 plays an important physiological role in the maintenance and amelioration of semen quality. The present article thereby aimed to review the possible mechanisms through which CoQ10 plays a role in the regulation of male reproductive function, and to concisely discuss its efficacy as an ameliorative agent in restoring semen parameters in male infertility, as well as its impact on OS markers, sperm DNA fragmentation, pregnancy, and assisted reproductive technology outcomes.

• 한국학교보건학회지
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• 제6권1호
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• pp.78-92
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• 1993

The purpose of this study is to find out the stress causes of the primary students in Korea, through the three major methods, life event score, multiple regression about stress causes and G.H.Q. path-diagram. A survey was made of 889 students who were selected among students of six primary schools in seoul and Ka-pyeng, from Sep. 28 to Oct. 2. 1992. The results of this study are summarized as follows : 1. Life event score Among the children's life events, (deaths of family) (degrade of school record) (the increase of absence days) (divorce of parents) (trouble with relationship) are high ranking in life event score. Besides, (scolded by teacher and parents) (beginning of extracurricular work) are spread stress causes. In conclusion, these stress causes are shown by two aspects, home, school, and so children are under stress circumstance in both places. These stress causes vary with area and sex. 2. Multiple regression about stress causes and G.H.Q. This study analysed how a stress caused by home life affects the children's health of mind and body. The most influential factors are , and these factors vary with area and sex. 3. Path-diagram This study proved that socio-psychological school environment raises children to secede from school, and this secession that operates as a stress cause affects children's health of mind and body. This serial process is analysed by path analysis, and made out a path-diagram. In conclusion, as expected socio-psychological,school environment affects the children's health of mind and body. This is shown by two aspects : positive, negative. This stress causes vary with area and sex.

• 한국지반공학회논문집
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• 제22권10호
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• pp.151-163
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• 2006

본 논문에서는 모래의 비배수 정적전단거동과 반복전단거동의 상호관계를 분석하기 위하여 낙동강 모래를 사용하여 비배수 정적 및 반복삼축시험을 실시하였다. 정적삼축시험은 반복전단거동과의 상호비교를 위하여 인장시험을 포함하여 실시하였다. 그리고 반복삼축시험은 초기정적전단응력$(q_{st})$과 반복응력$(q_{cy})$조건을 조합하여 여러 응력조건 하에서 실시하였다. 시험결과 반복전단거동의 응력경로는 정적전단거동의 한계응력비(CSR)선을 지나면서 유동변형이 발생하여 정적전단거동과 일치하였으며, 그 후 정적전단거동의 파괴선(FL)을 따라 파괴가 발생하였다. 이러한 반복 전단거동의 응력경로는 시험방법이 다름에 따른 약간의 차이는 있으나 정적전단거동의 응력경로와 본질적으로 동일함을 알 수 있었다.