• Journal of Aerospace System Engineering
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• v.15 no.2
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• pp.16-25
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• 2021

Reliability of fatigue strength on Aircraft Composites(GFRP) Structures was assessed in this paper. Fatigue strength of GFRP was used through the existing fatigue test data with Monte Carlo method. The S_a-N_f curve of composites fatigue strength was assumed as normal distribution and reliability was analyzed using SSIT model. Fatigue stress was designed IAW ASTM F3114-15 with special safety factor of S_sf=1.2~2.0. Reliability was calculated by analytic method and FORM. Sensitivity for the effect of mean and standard deviation of fatigue strength as well as fatigue stability was evaluated. This result can be usefully applied to reliability and fatigue design for composite structures of light weight aircraft.

• Economic Analysis
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• v.25 no.3
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• pp.70-99
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• 2019

Using a stochastic volatility-in-mean VAR model consisting of the KOSPI index, the foreign exchange rate, the government bond rate, and the credit spread, this study investigates the effects of financial market uncertainty on financial markets. We find that higher uncertainty has recessionary effects on financial markets. The effects are especially stronger in equity markets and in won-dollar exchange markets. We also find that the effects of uncertainty become stronger during times of financial market stress compared to normal times. Finally, the results imply that financial market uncertainty may potentially affect the real sector, too.

• Korean Journal of Biological Psychiatry
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• v.25 no.3
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• pp.79-87
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• 2018

Objectives Internet gaming disorder (IGD) is known to be related to stress and the serotonin-transporter-linked polymorphic region (5-HTTLPR) that is known to be associated with stress and has been studied to affect various psychiatric illness outbreaks. We tried to examine the relationship between stress, 5-HTTLPR and IGD. Methods A total of 59 participants with IGD, diagnosed according to the 5th edition of the Diagnostic and Statistical Manual of Mental Disorders (DSM-5) criteria and 67 normal controls (NC) were enrolled. The IGD group and the NC were compared using chisquare test and independent sample t-test, and logistic regression analysis was used to examine the relationship between stress, the 5-HTTLPR, and IGD. Results The mean scores for anxiety, impulsivity and stress were significantly higher in the IGD group than in the NC. In addition, there was a significant association between stress and IGD [odds ratio (OR) = 1.172, 95% confidence interval (CI) = 1.008-1.362]. Conclusions This study showed that stress would affect IGD. Therefore, the evaluation and management of stress should be included in the diagnosis and treatment of IGD.

• Journal of Hospice and Palliative Care
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• v.22 no.3
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• pp.125-133
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• 2019

Purpose: The purpose of this study was to investigate the relationship between end of life care competencies and terminal care stress of nurses in long term care hospitals. Methods: For this study, 140 nurses were sampled among those that have over 6-month end of life care experience and were working at long term care hospitals located in A city and C city of Chungcheongnam-do. Using a questionnaire, data were collected from January 2018 through March 2018. Data were analyzed using the SPSS, Windows version 21.0, according to the purpose of the study and analyzed by descriptive statistics, t-test, one way ANOVA, $Sch\acute{e}ffe^{\prime}s$ test, and Pearson's correlation coefficient. Results: The mean score on terminal care stress of nurses was above the normal level. The scores on end of life care competencies significantly varied by age, total career at hospitals, death/hospice and palliative care education, and bereavement experience. The mean score of end of life care competencies was negatively correlated with the mean score of lack of knowledge and skills among the subitems of the terminal care stress category (r=-0.260, P=0.002). Conclusion: To decrease the terminal care stress of long term care hospital nurses, it is suggested to carry out end of life care education tailored to nurses characteristics.

• Sleep Medicine and Psychophysiology
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• v.25 no.1
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• pp.15-20
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• 2018

Objectives: This study was designed to assess the change of heart rate variability (HRV) at resting, upright, and psychological stress states in depressive disorder patients. Methods: HRV was measured at resting, upright, and psychological stress states in 62 depressive disorder patients. We used visual analogue scale (VAS) score to assess tension and stress severity. Beck depression inventory (BDI) and state trait anxiety inventories I and II (STAI-I and II) were used to assess depression and anxiety severity, respectively. Differences between HRV indices and VAS score were evaluated using paired t-tests. Gender difference analysis was conducted with ANCOVA. Results: SDNN (standard deviation of normal to normal intervals), LF/HF (low frequency/high frequency), and VLF (very low frequency) were significantly increased, while NN50 and pNN50 were significantly decreased in the upright position compared to resting state. SDNN, RMSSD (root mean square of the differences of successive normal to normal intervals), and VLF were significantly increased, while pNN50 was significantly decreased in the psychological stress state compared to resting state. SDNN, NN50, and pNN50 were significantly lower in an upright position compared to a state of psychological stress, and LF, HF, and LF/HF showed no significant differences Conclusion: The LF/HF ratio was significantly increased after physical stress in depressive disorder. However, the LF/HF ratio was not significantly increased after psychological stress, and the change in LF/HF ratio after physical stress and psychological stress did not significantly differ from each other. Significant increase in SDNN, NN50, and pNN50 in an upright posture compared to psychological stress suggests that depressive patients react more sensitively to physical stress than psychological stress.

• Journal of the Korean earth science society
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• v.25 no.1
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• pp.22-31
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• 2004

Laboratory experiments were conducted in order to find effects of the intermediate principal stress of ${\sigma}_{2}$ on rock fractures and faults. Polyaxial tests were carried out under the most generalized compressive stress conditions, in which different magnitudes of the least and intermediate principal stresses ${\sigma}_{3}$ and ${\sigma}_{2}$ were maintained constant, and the maximum stress ${\sigma}_{1}$, was increased to failure. Two crystalline rocks (Westerly granite and KTB amphibolite) exhibited similar mechanical behavior, much of which is neglected in conventional triaxial compression tests in which ${\sigma}_{2}$ = ${\sigma}_{3}$. Compressive rock failure took the form of a main shear fracture, or fault, steeply dipping in ${\sigma}_{3}$ direction with its strike aligned with ${\sigma}_{2}$ direction. Rock strength rose significantly with the magnitude of ${\sigma}_{2}$, suggesting that the commonly used Mohr-type failure criteria, which ignore the ${\sigma}_{2}$ effect, predict only the lower limit of rock strength for a given ${\sigma}_{3}$ level. The true triaxial failure criterion for each of the crystalline rocks can be expressed as the octahedral shear stress at failure as a function of the mean normal stress acting on the fault plane. It is found that the onset of dilatancy increases considerably for higher ${\sigma}_{2}$. Thus, ${\sigma}_{2}$ extends the elastic range for a given ${\sigma}_{3}$ and, hence, retards the onset of the failure process. SEM inspection of the micromechanics leading to specimen failure showed a multitude of stress-induced microcracks localized on both sides of the through-going fault. Microcracks gradually align themselves with the ${\sigma}_{1}$-${\sigma}_{2}$ plane as the magnitude of ${\sigma}_{2}$ is raised.

• Environmental Analysis Health and Toxicology
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• v.18 no.4
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• pp.295-303
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• 2003

Physiological cellular activities responses to cadmium (Cd) exposure in green algae with several reductases activities and viability of the cell were examined. The cell division of green algae, Selenastrum capricornutum treated with 5ppm was significantly decreased than that of normal algae. The mean cell number of normal algal culture was as twice much as than that of algae at 6 days after Cd treatment. The cellular viability of algae was analysed by flow-cytometry with fluorescent dye after esterase reaction on cell membrane. The 85.35% of cellular viability of normal culture was decreased to 34.35% when algae was treated with 5 ppm of Cd at 6 days after treatment. It was considered that those method of flow-cytometry is useful tool for toxicity test on micro-organisms in the respect of identifying cellular viability. Also, the activities of both glutathione peroxidase (GPX) and ascorbate peroxidase (APX), which are indirectly react against oxidative stress through reduction of glutathione by Cd were significantly increased with 25%. It is considered that both GPX and APX are involved in the metabolic pathway of Cd -detoxification with similar portion in Selenasturm capricornutum.

• The Journal of Korean Academy of Sensory Integration
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• v.22 no.1
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• pp.43-53
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• 2024

Objective : The aim of this study was to investigate the differences in academic and mental health status (generalized anxiety, depression, stress, loneliness, and suicidal thoughts) between adolescents exhibiting normal and excessive smartphone use patterns. Methods : The smartphone use times and academic and mental health status of 51,850 adolescents were analyzed using raw data from the 2022 Korea Youth Risk Behavior Web-Based Survey. Descriptive statistics of complex sample analysis, frequency analysis and linear regression analysis were performed. Results : The mean smartphone use time of middle and high school students was 6 hours 43 minutes on weekends and 4 hours 39 minutes on weekdays. There were significant differences in smartphone use time according to gender and grade. As a result of comparing differences in academic status between adolescents with excessive smartphone use times and those with normal use times. In terms of mental health status, adolescents with excessive use times had higher generalized anxiety, depression, stress, loneliness, and suicidal thought scores than adolescents with normal use times. Conclusion : This study can be used as a basic reference for research on smartphone overuse.

• Geomechanics and Engineering
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• v.9 no.1
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• pp.115-124
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• 2015

Determination of mobilized shear strength parameters (that identify stresses on the failure plane) is required for analyzing the stability by limit equilibrium method. Generalized Hoek-Brown (GHB) and Mohr-Coulomb (MC) failure criteria are usually used for obtaining stresses on the plane of failure. In the present paper, the applicability of these criteria for determining the stresses on failure plane is investigated. The comparison is based on stresses on the real failure plane which are obtained from the Mohr stress circle. To do so, 18 sets of data (consist of principal stresses and angle of failure plane) presented in the literature are used. In addition, the values account for (VAF) and the root mean square error (RMSE) indices were calculated to check the determination performance of the obtained results. Values of VAF and RMSE for the normal stresses on the failure plane evaluated from MC are 49% and 31.5 where for GHB are 55% and 30.5, respectively. Also, for the shear stresses on failure plane, they are 74% and 36 for MC, 76% and 34.5 for GHB. Results show that the obtained stresses and angles of failure plane for each criterion differ from real ones, but GHB results are closer to the empirical results. Also, it is inferred that results are affected by the failure envelope not real failure plane. Therefore, obtained shear strength parameters are not mobilized. Finally, a multivariable regressed relation is presented for determining the stresses on the failure plane.

• Journal of Oriental Neuropsychiatry
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• v.22 no.1
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• pp.1-12
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• 2011

Objectives : This study was conducted to assess effects of oriental medicine music therapy on heart rate variability(HRV) in normal subjects under mental stress. Methods : 34 healthy volunteers(control group:17, experimental group:17) participate in this study. The volunteers were randomly allocated into two groups. After 10-minutes rest period and instrumentation, both groups performed a mental stress test for 12-minutes. HRV was recorded before and after the mental stress. And then the experimental group applied oriental medicine music therapy for 10-minutes. In the control group, they rested for 10-minutes. And HRV was recorded. Results : After giving mental stress stimulation to both groups, LF and LF/HF ratio were significantly increased and HF, mean HRV were decreased. In experimental group, LF, LF/HF ratio were significantly decreased and HF, SDNN were significantly increased after applying oriental medicine music therapy. In control group, LF was significantly decreased. And LF/HF ratio was decreased and HF, SDNN were increased, but it was not significant. Conclusions : This results show that oriental medicine music therapy could be relatively useful to decrease sympathetic activity and prevent the alteration of autonomic nervous system due to mental stress.