• The Research Journal of the Costume Culture
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• v.27 no.1
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• pp.1-10
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• 2019

Firefighters wear Personal Protective Equipment (PPE) for protection from environmental hazards. However, due to the layers of protective functions, the PPE inevitably adds excessive weight, bulkiness, and thermal stress to firefighters. This study investigated the adverse impact of wearing PPE as an occupational stressor on the firefighter's cognitive functioning. Twenty-three firefighters who had been involved in firefighting at least for 1 year were recruited. The overall changing trend in the firefighter's cognitive functioning (short-term memory, long-term memory, and inductive reasoning) was measured by the scores of three standardized cognitive tests at the baseline and the follow-up, after participating in a moderate-intensity physical activity, wearing a full ensemble of the PPE. The study findings evinced the negative impact of the PPE on the firefighter's cognitive functioning, especially in short-term memory and inductive reasoning. No significant influence was found on the firefighter's long-term memory. The results were consistent when the participant's age and BMI were controlled. The outcomes of the present study will not only fill the gap in the literature, but also provide critical justification to stakeholders, including governments, policymakers, academic communities, and industry, for such efforts to improve human factors of the firefighter's PPE by realizing the negative consequences of the added layers and protective functions on their occupational safety. Study limitations and future directions were also discussed.

• Journal of Life Science
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• v.22 no.2
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• pp.184-191
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• 2012

The purpose of this study was to examine the effect of 16 weeks of resistance training on the fatigue factor, muscle soreness, oxidative stress, and myokine in elite weightlifters. A total of 10 subjects (six male, four female) participated in this study. The results were compared according to baseline, 8 weeks, and 16 weeks. Ammonia and Pi were increased through 16 weeks of resistance training, but this result was not significant. CK was significantly (p<0.05) increased at 8 weeks and 16 weeks compared to baseline, while LDH was significantly (p<0.05) increased at 8 weeks compared to baseline. The MDA of the oxidative stress factor was significantly (p<0.05) increased at 8 weeks compared to baseline and 16 weeks, and TAS of the antioxidant factor was significantly (p<0.05) increased at 8 weeks compared to baseline. The IL-15 of the myokine was significantly (p<0.05) increased at baseline compared to 8 weeks and 16 weeks. In conclusion, 16 weeks of high-intensity resistance training may have a positive effect on peripheral fatigue factors, muscle soreness, oxidative stress, and myokine in elite weightlifters.

• Transactions of Materials Processing
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• v.16 no.2 s.92
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• pp.126-131
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• 2007

Voids in a large rotor are formed in solidification process of a cast ingot. The voids have to be eliminated from the rotor by a forming process, because they would became stress-intensity factors which suddenly fracture the rotor in the operation. Previous studies on void-elimination of a large rotor have mainly focused on finding the process variables affecting the void-closure. But the study on the amount of void closure in a large rotor has been very rare. This study was performed to obtain an equation which predicts the amount of void-closure in a forging process of a large rotor and to evaluate the availability of the void-closure equation through finite element analyses. Firstly, 2D FE analysis was carried out to find effects of time integral of hydrostatic stress and effective strain on void volume rate of a large rotor in the upsetting process for various diameters and shapes of void, and material temperature. From the 2D FE analysis, we found that effective strain was suitable for predicting the void-closure of a large rotor, because there was a constant relationship between void volume rate and effective strain. And a void-closure equation was proposed fur predicting void-closure of a large rotor in the upsetting process. Finally, ken the 3D FE analysis, the proposed void-closure equation was verified to be useful for upsetting and cogging processes.

• Transactions of the Korean Society of Pressure Vessels and Piping
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• v.12 no.1
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• pp.62-69
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• 2016

Current guidance considers that uniaxially loaded specimen with a deep crack is used for the determination of the ductile-to-brittle transition temperature. However, reactor pressure vessel is under biaxial loading in real and the existence of deep crack is not probable through periodic in-service-inspection. The elastic stress intensity factor and the elastic-plastic J-integral which were used for crack-tip stress field and fracture mechanics assessment parameters. The difference of the loading condition and crack geometry can significantly influence on these parameters. Thus, a constraint effect caused by differences between standard specimens and a real structure can over/underestimate the fracture toughness, and it affects the results of the structural integrity assessment, consequentially. The present paper investigates the constraint effects by evaluating the master curve $T_0$ reference temperature of PCVN (Pre-cracked Charpy V-Notch) and small scale cruciform specimens which was designed to simulate biaxial loading condition with shallow crack through the fracture toughness tests and 3-dimensional elastic-plastic finite element analyses. Based on the finite element analysis results, the fracture toughness values of a small scale cruciform specimen were estimated, and the geometry-dependent factors of the cruciform specimen considered in the present study were determined. Finally, the transferability of the test results of these specimens was discussed.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.39 no.6
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• pp.583-588
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• 2015

Asymptotic method has been often used to theoretically analyze the complete contact problem. The error of the asymptotic results increases as the distance from the contact edge increases. The singularity cannot be properly obtained from a finite element (FE) analysis owing to the finiteness of the element size. In the present work, the complete contact problem in bonded condition is analyzed using a combined experimental-numerical approach to assist and/or compare with the asymptotic results. Al and Cu alloys are used for the material combination of the punch and substrate. 120 and 135 degrees are used for the punch angle. The FE models are validated by comparison of displacement distributions obtained by the FE analysis and $moir{\acute{e}}$ experiment. Generalized stress intensity factors are evaluated using the validated FE models. Stress field in the vicinity of the sharp contact edges obtained from the FE and asymptotic analyses are compared. The discrepancies are also discussed.

• Journal of Aerospace System Engineering
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• v.18 no.3
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• pp.17-26
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• 2024

Aircraft engines are exposed to high temperatures, high pressures, and stress caused by the rotation of the turbine shaft during flight. These loads can result in microcracks both on the inside and outside surfaces of the structure. Consequently, this can lead to structural defects and negatively impact the lifespan of the parts. To proactively prevent these defects, a finite element analysis is carried out to identify cracks. However, this process is time-consuming and requires significant effort due to the repetitive nature of crack modeling. This study aims to develop a crack modeling method based on the finite element model. To achieve this, the Constrained Delaunay Triangulation (CDT) technique is employed to triangulate the space while considering limitations on point connections. The effectiveness of this method is validated by comparing stress intensity factors for semi-elliptical cracks in plates and cylindrical vessels. This approach proves to be a valuable tool for crack analysis studies.

• Journal of Environmental Science International
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• v.33 no.4
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• pp.279-282
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• 2024

This study aimed to verify the results of emotional analysis with respect to canine behavior as reported in the existing animal behavior field based on the dog vestibular emotional reflex (VER) principle, and to evaluate humans and animals based on empathy gained through true communication rather than human-centered interpretation. A total of 200 canines were divided into non-daily and daily situation groups (n=100 each). To assess the psychological and emotional state of each group, these changes were applied to the principle of VER, and six measurement values were selected: positive emotion (balance and energy), negative emotion (tension/anxiety and stress), and body condition (inhibition and neuroticism). The results showed a statistically significant difference (p<0.05) in positive emotions, negative emotions, and body conditions between the two groups. In addition, balance, energy, tension/anxiety, inhibition, and neuroticism were higher in the non-daily situation group than in the daily situation group, with an exception for stress. Compared with the canine daily situation groups, canine in the non-daily situation groups instinctively observed their surroundings to cope with possible threats, had decreased concentration, and elevated vitals due to high-intensity anxiety. This can be perceived as a state of immediate reaction to possible situations/threats. In conclusion, it was confirmed through Vibra Image technology that canine instability mainly affects three factors: positive emotion, negative emotion, and physical condition.

• Journal of Korean Society of Steel Construction
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• v.10 no.3 s.36
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• pp.423-435
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• 1998

In this paper fatigue strength reduction of butt weld with penetration defect, which can be seen frequently in the steel bridge, was assessed quantitatively. S-N curves were derived and investigated through the constant amplitude fatigue test of fully or partially penetrated welded specimen made of SWS490 steel. The fracture mechanical method was applied in order to calculate the remaining fatigue life of the partially penetrated butt welds. The fatigue limit of the fully penetrated butt welds was higher than that of category A in AASHTO's fatigue design curves, and the slope of S-N curves with 5.57 was stiffer than that of other result for welded part generally accepted as 3. The fatigue strength of the partially Penetrated butt weld was strongly influenced by the size of lack of penetration, D. It decreased drastically with increasing D from 3.9 to 14.7mm. Fracture behaviour of the partially penetrated butt weld is able to be explained obviously from the beach mark test that a semi-elliptical surface crack with small a/c ratio initiates at a internal weld root and propagates through the weld metal. To estimate the fatigue life of the partially penetrated butt weld with fracture mechanics, stress intensity factors K of 3-dimensional semi-elliptical crack were calculated by appling finite elements method and fracture mechanics parameters such as C and m were derived through the fatigue test of CT-specimen. As a result, the fatigue lives obtained by using the fracture mechanical method agreed well with the experimental results. The results were applied to Sung-Su bridge collapsed due to penetration defects in butt weld of vertical member.

• Polymer(Korea)
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• v.27 no.3
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• pp.210-216
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• 2003

4-Vinyl-1-cyclohexene diepoxide (VCE)/diglycidyl ether of bisphenol-A (DGEBA) epoxy blends with benzylquinoxalinium hexafluoroanti-monate were cured using an electron-beam technique. The effect of DGEBA content to VCE on cure behavior, thermal stabilities, and mechanical properties was investigated. The composition of VCE/DGEBA blend system vaned within 100:0, 80:20, 60:40, 40:60, 20:80, and 0:100 wt%. The cure behavior and thermal stability of the cured specimens was monited by near-infrared spectroscopy and thermogravimetric analysis, respectively. Also, the critical stress intensity factor ($_{4}$) test of the cured specimens was performed to study the mechanical interfacial properties. As a result, the decreases of short side-chain structure and chain scission were observed in NIR measurements as the DGEBA content increases, resulting in varying the hydroxyl and carbonyl groups. And, the initial decomposition temperature (IDT), temperature of maximum weight loss (T$\_$max/), and decomposition activation energy (E$\_$d/) as thermal stability factors were increased with increasing the DGEBA content. These results could be explained by mean of decreasing viscosity, stable aromatic ring structure, and grafted interpenetrating polymer network with increasing of DGEBA content. Also, the maximum $_{4}$ value showed at mixing ratio of 40:60 wt% in this blend system. in this blend system.

• Tunnel and Underground Space
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• v.26 no.5
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• pp.396-408
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• 2016

Rock fracture mechanics has been widely applied to various fields of rock and civil engineering. But most researches covered mode I behavior, though mode II behavior is dominant in rock engineering. Until now, there is only one ISRM suggested method for mode II toughness of rock. A new SCC (Short Core in Compression) mode II toughness test method was developed considering 1) application of confining pressure, 2) easiness of notch creation, 3) utilization of existing equipment, 4) simple test procedure. The stress intensity factors were determined by 3D finite element method considering line and distributed loading conditions. The tests with granite specimens were carried out using MTS 815 rock test system with a loading rate of 0.002 mm/s. The mean value of mode II fracture toughness of granite showed $2.33MPa{\sqrt{m}}$. Mode I toughness of the same granite was $1.12MPa{\sqrt{m}}$, determined by Brazilian disk test and $K_{IIC}/K_{IC}=2.08$. The smooth fracture surface with rock powder formation also supported mode II behavior of SCC method. The SCC method can be used for the determination of mode II fracture toughness of rocks based on the current results.