• Magazine of the Korea Concrete Institute
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• v.11 no.2
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• pp.167-175
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• 1999

Many composite girder bridges have been constructed for about thirty five years. Nowadays they are aged or deteriorated because of the increase in traffic and vehicle loads. In this study, the effect of strengthening with glass fiber sheet is investigated to estimate the possibility for applying to damaged prestressed concrete bridges. One normal and eight cracked specimens which had been preloaded were tested. The cracked specimens were strengthened with either external prestressing or bonding glass fiber sheet, or using both methods. The results showed that the maximum loads are almost same for both methods. So it seems that the strengthening with glass fiber sheet can be used for strengthening damaged prestressed concrete girders. It is important that proper devices should be selected to prevent glass fiber sheet from premature bonding failure below its maximum load, which is similar to end anchorage problem in external prestressing method. It is proved that the devices proposed in this paper have sufficient anchoring capability to increase load carrying capacity.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.04a
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• pp.357-360
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• 2008

This study was performed to estimate the workability and the static behavior for Bi Prestressed Concrete Girder(Bicon girder) which could introduce effectively prestressed forces into concrete girders. A bicon girder is manufactured by means of introducing pure bending moment that prestress simultaneously the compressive member(steel bar) and the tensile member(steel tendon). Static test was executed for 20m railway bridge girder specimen and evaluated whether pure bending moment was introduced or not, and the behaviors after cracking, and at the ultimate load. Test results showed that a bicon girder had the enough safety in the introduction of pure moment, the serviceability, and the ultimate behavior.

• Proceedings of the KIEE Conference
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• 2001.11a
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• pp.241-244
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• 2001

절연체의 수명과 직접적인 관련이 있는 전기트리의 개시특성을 연구하는데 있어서, 전기트리의 개시시간이 매우 길기 때문에 실험적으로 절연재료의 수명을 구하는데 어려움이 있다. 따라서. 본 논문에서는 Weibull 해석을 이용하여, 일반적으로 사용되는 가속시험법에 의하여 얻어진 전기트리 개시전계를 사용하여 일정전압 인가시에 전기트리 개시시간을 추정하는 방법을 이론적으로 고찰하여 실험에 적용하였다. 또한 기계적 스트레스에 의한 전기트리 개시특성을 평가하기 위하여 기계적 스트레스를 모의한 XLPE 시료에 대하여 이러한 기계적 스트레스가 전기트리 개시전계 및 개시시간 특성에 미치는 영향을 평가하였다. 기계적 스트레스가 전기트리 개시전계 뿐만 아니라 개시시간을 현저하게 감소시켰으며, XLPE의 장기적인 신뢰성을 보증하기 위해서는 이러한 기계적 스트레스를 완화시키는 것이 매우 중요하다.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.38 no.11
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• pp.1221-1229
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• 2014

This paper proposes an approach for predicting the fatigue life of a propeller shaft of a forklift truck by an accelerated life test method. The accelerated life test method adopted in this study is the calibrated accelerated life test, which is highly effective in the prediction of the lifetime and enables significant reduction of the test time as well as a quantification of reliability in the case of small sample sizes. First, the fatigue test was performed under two high stress levels, and then, it was performed by setting low stress levels in consideration of the available test time and extrapolation. Major reliability parameters such as the lifetime, accelerated power index, and shape parameter were obtained experimentally, and the experimentally predicted lifetime of the propeller shaft was verified through comparison with results of an analysis of load spectrum data under actual operating conditions.

• Journal of Music and Human Behavior
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• v.6 no.1
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• pp.81-109
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• 2009

The purpose of this study was to determine the effectiveness the Song Psychotherapy Program in decreasing test anxiety in adolescent students. For this study, twelve sessions were conducted in five stages for four 14-year-old middle school students at D Middle School on Daejeon. To measure the effects of the Song Psychotherapy Program, the researcher compared the results of Test Anxiety Inventory of Korea (TAI-K) before and after the program. The researcher also analyzed the contents of the participants' verbal responses and answers to repeated questionnaires to find out what participants experienced in Song Psychotherapy. The results of this study were as follows. First, a comparison of test anxiety scores prior to and following the program showed an average decrease from 91.75 to 60.5. Second, the subjects reported a positive musical experience in the program. The results of the research as described above show that the Song Psychotherapy Programis effective in decreasing test anxiety levels and general examination stress in adolescent students.

• Journal of the Microelectronics and Packaging Society
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• v.9 no.4
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• pp.61-68
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• 2002

Thermal shock testing was used to evaluate reliability that appeared in the solder joints of electronic devices when they were subjected to thermal cycling. Recently, mobile devices have come smaller and multi-functional, with the increasing need for high-density packaging, BGA or CSP has become the main trend for surface mounting technology, and therefore mechanical stress life for solder joints in BGA/CSP type packages has required. Reliability of BGA/CSP solder joints was evaluated with electric resistivity change of daisy chain pattern and stress-strain curve measured using strain gage attached on the surface of PCB under mechanical impact loading. In this report, applications of PCB Universal Testing Machine we have developed and experimental datum of SONY estimating dynamic behavior of mechanical stress in BGA/CSP solder joints are introduced.

• Journal of dental hygiene science
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• v.15 no.4
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• pp.509-517
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• 2015

This study attempted to identify the entrance exam stress levels in high school students and analyze the relationship this entrance exam stress and perceived oral health status. Self-administered survey was conducted in total 304 students attending in academic high schools in Bucheon. For analysis, SPSS was used to perform t-test and one-way ANOVA. As a result of the study, the entrance exam stress level of academic high school students was 2.71. The level of sub-factors were that tension for exam/poor result was highest by 3.08 and the next were future uncertainty (2.81), parents pressure (2.56), and insufficient free time (2.52). The group with high entrance exam stress showed significantly high perceived degrees of temporomandibular disorder, oral mucosal disease and xerostama. Among sub-factors of stress, the group with high tension for exam/poor result stress had significantly high perceived degrees of dental caries, teporomandibular disorder, oral mucosal disease and xerostama. Because perception on oral health issues increased with high entrance exam stress in high school students, it is necessary to seek some ways to decrease oral health problems even though entrance exam stress is intensified. To do so, it is inferred that it will be very important to promote oral health education to develop ability of high school students to practice correct oral management method.

• Korean Journal of Psychosomatic Medicine
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• v.7 no.2
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• pp.196-202
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• 1999

The purpose of the study was to determine the effect of vitamin B complex on stress-induced immune alteration. 21 medical students participated in the study 4 weeks before an academic examination period(baseline), 2 weeks before the exam period and during the exam period. Among them, 10 subjects were given vitamin B complex for 4 weeks, and 11 were not given vitamin B during the whole period. Cell-mediated immune function was measured by lymphocyte proliferative response to phytohemagglutinin(PHA) and interleukin-2(IL-2) production. Global assessment of recent stress(GARS) scale and symptom checklist-90-revised(SCL-90-R) were used to measure the level of subjective stress and psychopathology. Vitamin group had significantly lower scores of anxiety scale on SCL-90-R than non-vitamin group. No significant differences were found in lymphocyte proliferative response to PHA and IL-2 production between vitamin and non-vitamin groups during each period. There were no significant differences in change of of each of the two immune parameters over time as well as between vitamin and non-vitamin groups. However, lymphocyte proliferative response to PHA was significantly increased over time. In conclusion, it was suggested that vitamin B complex is likely to decrease anxiety level, and that exam stress might enhance lymphocyte proliferation regardless of vitamin B.

• Journal of the Korea Convergence Society
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• v.10 no.12
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• pp.465-476
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• 2019

This study was convergence study to determine sleep and its factors in university students on the basis of Spielman's 3P model. The participants were 191 graduate and undergraduate students who were scheduled to take the exam after 1~2 weeks. The related variables of quality of sleep were self-control, stress, test anxiety, smartphone dependence, and daytime sleepiness. Chi-square test and t-test were used to make a comparison of the quality of sleep between the good and the bad sleep quality group. Pearson's coefficient correlation analysis was performed for correlation between the quality of sleep and the general characteristics, self-control, stress, test anxiety, smartphone dependence, and daytime sleepiness. Stress and test anxiety as precipitating factors for sleep disturbance, smartphone dependency as a perpetuating factor for sleep disorder, and daytime sleepiness as a sleep-related factor were correlated with the quality of sleep; no statistically significant correlation was found with self-control as a predisposing factor in the biopsychological area. It is necessary to solve such problems with mental health as stress and test anxiety, which are factors for sleep disturbance, and smartphone dependency as a perpetuating factor for sleep disorder, in pursuit of higher quality of sleep for university students.

• Journal of Korean Society of Industrial and Systems Engineering
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• v.31 no.4
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• pp.153-161
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• 2008

신뢰성 평가 시험은 종종 성능 평가에 장기간의 시간이 요구되며, 전체 생산비용까지 증가시키는 문제점을 안고 있다 스트레스를 이용한 가속수명시험은 제품의 신뢰성 고장과 밀접한 관련이 있는 고장 메커니즘의 촉진을 통해 고장에 이르는 기간을 단축함으로써 신뢰성 평가의 효율성을 도모할 수 있다. 본 연구에서는 이러한 스트레스 가속 시험에 빈도가속(Usage-Rate Acceleration) 또는 판정가속(Tightening Critical-Values) 등을 결합하여 한층 높은 가속효과를 도모하는 방법을 제안하고, 국내에서 생산되고 있는 2차 전지 제품에 대한 실제 시험 사례분석을 통해 결합된 가속방법의 효과를 실증적으로 보여주고 있다.