• Journal of Ginseng Research
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• v.46 no.4
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• pp.543-549
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• 2022

Background: In physical activity or labor, the human body is in a state of high intensity stress, and all parts or physiological functions of the body respond positively to maintain or balance the need for movement. The human body has many physiological changes in the process of movement, and fatigue is the external manifestation of various complex changes inside the human body. Fatigue is also a physiological mechanism of self-protection after the body reaches a certain level of activity, which can prevent the occurrence of life-threatening excessive functional failure. The generation of fatigue is a very complex process, and its mechanism has not been concluded yet. Therefore, it is an important work to search and screen the effective components of natural plants that have anti-fatigue effect and to explore their mechanism. Methods: This was a 8-week, randomized, double-blind, placebo-controlled clinical trial. A total of 110 subjects who passed physical examination were included according to the scheme design, and randomly divided into a test group which was given KRG and a placebo control group. The calculation is carried out according to the standard of sub-high-intensity exercise test. Results: There was no adverse effect on safety index of subjects after taking red ginseng capsule. After KRG treatment, subjective strength grade is significant lower than placebo treatment. Blood lactic acid content is significantly get lower after trial in KRG group, and significant lower than placebo group. Creatine phosphokinase(CK) content is significantly get lower after trial in KRG group, and significant lower than placebo group. Conclusion: According to the criterion in the test scheme, the result shows that KRG is helpful on relieving physical fatigue.

• Nuclear Engineering and Technology
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• v.54 no.10
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• pp.3631-3640
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• 2022

Uranium mill tailing ponds (UMTPs) are risk source of debris flow and a critical source of environmental U and Rn pollution. The technology of microbial induced calcium carbonate precipitation (MICP) has been extensively studied on reinforcement of UMTs, while little attention has been paid to the effects of MICP on U & Rn release, especially when incorporation of metakaolin and bacillus subtilis (MBS). In this study, the reinforcement and U & Rn immobilization role of MBS -MICP solidification in different grouting cycle for uranium mill tailings (UMTs) was comprehensively investigated. The results showed that under the action of about 166.7 g/L metakaolin and ~50% bacillus subtilis, the solidification cycle of MICP was shortened by 50%, the solidified bodies became brittle, and the axial stress increased by up to 7.9%, and U immobilization rates and Rn exhalation rates decrease by 12.6% and 0.8%, respectively. Therefore, the incorporation of MBS can enhance the triaxial compressive strength and improve the immobilization capacity of U and Rn of the UMTs bodies solidified during MICP, due to the reduction of pore volume and surface area, the formation of more crystals general gypsum and gismondine, as well as the enhancing of coprecipitation and encapsulation capacity.

• Geomechanics and Engineering
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• v.30 no.4
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• pp.373-382
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• 2022

Unsaturated soil at high suctions is widespread. Many civil engineering projects are related to the hydro-mechanical behavior of unsaturated soils at high suctions, particularly in arid and semiarid areas. To investigate water retention behaviors of nine clayey soils (one is classified as fat clay and the others are classified as lean clay according to the unified soil classification system), the high suction (3.29-286.7 MPa) was imposed on the specimens at zero net stress by the vapor equilibrium technique. In this paper, the effect of void ratio on the water retention behavior at high suction was discussed in detail. Validation data showed that soil types, i.e., different mineralogical compositions, are critical in the soil water retention behavior at a high suction range. Second, the hysteresis behavior at a high suction range is mainly related to the clay content and the specific surface area. And the mechanism of water retention and hysteresis behavior at high suctions was discussed. Moreover, the maximum suction is not a unique value, and it is crucial to determine the maximum suction value accurately, especially for the shear strength prediction at high suctions. If the soil consists of hydrophilic minerals such as montmorillonite and illite, the maximum suction will be lower than 10⁶ kPa. Finally, using the area of hysteresis to quantify the degree of hysteresis at a high suction range is proposed. There was a good correlation between the area of hydraulic hysteresis and the specific surface area.

• Geomechanics and Engineering
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• v.25 no.3
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• pp.233-243
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• 2021

Rib spalling is a major issue affecting the safety of steeply inclined coal seam. And the failure coal face and support system can be affected with each other to generate a vicious cycle along with inducing large-scale collapse of surrounding rock in steeply inclined coal seam. In order to analyze failure mechanism and propose the corresponding prominent control measures of steeply inclined coal working face, mechanical model based on coal face-support-roof system and mechanical model of coal face failure was established to reveal the disaster mechanism of rib spalling and the sensitive analysis of related factors was performed. Furthermore, taking 3402 working face of Chen-man-zhuang coal mine as engineering background, numerical model by using FLAC3D was built to illustrate the propagation of displacement and stress fields in steeply inclined coal seam and verify the theory analysis as mentioned in this study. The results show that the coal face slide body in steeply inclined working face can be observed as the failure height of upper layer smaller than that of lower layer exhibiting with an irregular quadrilateral pyramid shape. Moreover, the cracks were originated from the upper layer of sliding body and gradually developed to the lower layer causing the final rib spalling. The influence factors on the stability of coal face can be ranked as overlying strata pressure (P) > mechanical parameters of coal body (e.g., cohesion (c), internal fraction angle (φ)) > support strength (F) > the support force of protecting piece (F') > the false angle of working face (Θ). Moreover, the corresponding control measures to maintain the stability of the coal face in the steeply inclined working face were proposed.

• Geomechanics and Engineering
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• v.27 no.5
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• pp.527-535
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• 2021

The creep characteristics of rock is of great significance for the study of long-term stability of engineering, so it is necessary to carry out indoor creep test and creep model of rock. First of all, in different water-bearing state and different positive pressure conditions, the granite is graded loaded to conduct indoor shear creep test. Through the test, the shear creep characteristics of granite are obtained. According to the test results, the stress-strain isochronous curve is obtained, and then the long-term strength of granite under different conditions is determined. Then, the fractional-order calculus software element is introduced, and it is connected in series with the spring element and the nonlinear viscoplastic body considering the creep acceleration start time to form a nonlinear viscoplastic creep model with fewer elements and fewer parameters. Finally, based on the shear creep test data of granite, using the nonlinear curve fitting of Origin software and Levenberg-Marquardt optimization algorithm, the parameter fitting and comparative analysis of the nonlinear creep model are carried out. The results show that the test data and the model curve have a high degree of fitting, which further explains the rationality and applicability of the established nonlinear visco-elastoplastic creep model. The research in this paper can provide certain reference significance and reference value for the study of nonlinear creep model of rock in the future.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.20 no.11
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• pp.67-73
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• 2021

Tanks are key weapons of ground combat that are equipped with powerful weapons and have strong protective bodies. One tank component, the engine clutch flange, is located in the part of the tank where the engine and transmission are installed, and it is a key part of the power transfer and shutoff. The engine clutch flange transmits high power to secure the mobility of the tank; thus, it must have high strength and hardness. In addition, high durability and safety must be ensured because tank operations must exclude concerns about damage. In this study, an engine clutch female flange for tanks made of SNCM439 was developed. The 2D design used AutoCAD programs, and the 3D shape design used CATIA programs. The structural analysis was conducted using ANSYS. The mesh grid has a tetrahedron shape and is created by adding a mid-side node. After the mechanical properties and constraints of SNCM439 were entered, the changes in the safety factor, total deformation, and Von-Mises stress were identified according to the increase in torque. Prototype processing was performed to verify the engine clutch female flange for the tank. To determine the productivity of the product, the cutting processing time was measured when processing the prototypes. Based on the results of measuring the cutting processing time, it is concluded that research is needed to improve productivity because MCT slot cutting processing is time consuming.

• Journal of the Korean Wood Science and Technology
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• v.31 no.5
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• pp.23-34
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• 2003

This study was carried out to investigate the mechanical properties of fabric E-glass fiber reinforced laminated timber. Specimens used to Korean red pine(Pinus densiflora) and Japanese larch(Larix kaemferi). Fabric E-glass fiber was inserted in the solid wood with aqueous polymer-isocyanate resin(MPU-500). The results were as follows: 1. Aqueous polymer-isocyanate resin(MPU-500) was good resin to manufacture laminated timber. specially, it was satisfied to property standard of construction laminated timber(KS F 3021) except for two ply glass fiber. 2. Bending and shear strengths of solid wood inserted with fabric glass fibers were not different from control solid wood. But, proportional limit bending stress was increased following the number of fabric glass fibers. Therefore, it was considered that to improve the bending and shear strength of fabric glass fiber reinforced laminated timber, the glass fiber thickness and its mesh should be modified to fitness following working conditions.

• The Journal of Korean Society for School & Community Health Education
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• v.23 no.1
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• pp.1-16
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• 2022

Background & Objectives: Self-rated health has been widely used to evaluate health status and accepted as a subjective measurement of quality of life. This study aimed to analyze the associations between self-rated health, health promotion behaviors, and mental health factors and suggest the approaches to improve health status among university students. Methods: Two thousand six hundred seventy-seven students who had stayed at dormitories on campus participated in the DU health survey by self-reported questionnaire from April 10 to 14, 2017. Multivariate logistic regression analysis was performed to estimate the odds ratios and 95% confidence intervals of association of self-rated health with health-related factors among male and female students. Results: 38.6% of the respondents reported good self-rated health. Male and first-year students were more likely to report good self-rated health than female and third-year students. There were significant differences in sex, grade, health problems, BMI, sleeping hours, eating breakfast, consumption of fruits and vegetables, physical activity (regular walking, strength exercise, moderate exercise, vigorous exercise), perceived stress, depression, and suicide thought (p<0.05). Conclusion: Although health promotion programs for university students are essential to support their adaptation to campus life and academic achievement, evidence-based health programs to encourage their participation are still insufficient. Therefore, it should establish a campus-based health policy and develop health promotion programs to increase self-rated health levels and prevent mental health problems for university students.

• KOREAN JOURNAL OF PACKAGING SCIENCE & TECHNOLOGY
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• v.28 no.2
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• pp.143-149
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• 2022

PCS needs to freely switch AC and DC to connect the battery, external AC loads and renewable energy in both directions for energy efficiency. Whenever converting happens, power loss inevitably occurs. Minimization of the power loss to save electricity and convert it for usage is a very critical function in PCS. PCS plays an important role in the ESS(Energy Storage System) but the importance of stabilizing semiconductors on PCB(Printed Circuit Board) should be empathized with a risk of failure such as a fire explosion. In this study, the temperature variation inside PCS was reviewed by cooling fan on top of PCS, and the vibration characteristics of PCS were analyzed during truck transportation for reliability of the product. In most cases, a cooling fan is mounted to control the inner temperature at the upper part of the PCS and components generating the heat placed on the internal aluminum cooling plate to apply the primary cooling and the secondary cooling system with inlet fans for the external air. Results of CFD showed slightly lack of circulating capacity but simulated temperatures were durable for components. The resonance points of PCS were various due to the complexity of components. Although they were less than 40 Hz which mostly occurs breakage, it was analyzed that the vibration displacement in the resonance frequency band was very insufficient. As a result of random-vibration simulation, the lower part was analyzed as the stress-concentrated point but no breakage was shown. The steel sheet could be stable for now, but for long-term domestic transportation, structural coupling may occur due to accumulation of fatigue strength. After the test completed, output voltage of the product had lost so that extra packaging such as bubble wrap should be considered.

• Journal of ILASS-Korea
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• v.28 no.1
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• pp.16-23
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• 2023

The objective of this numerical study is to investigate the effect of the shape and material of the blower blade for the electrified speed sprayer on the blowing performance. The shape of the blade was changed to the bonding angle, the number of blades, the width of the blade, and the blade length based on the existing model. In order to obtain the reliability of the numerical model, the analysis of the grid dependence was performed in the numerical analysis. The numerical analysis results were compared and analyzed in terms of the agricultural chemical penetration length characteristics, flow uniformity characteristics, and velocity distribution characteristics. Furthermore, the effect of material change on weight reduction and structural characteristics was also compared and analyzed. As a result of the analysis, it was found that the optimal condition was that the blade angle was 45°, the number of blades was 12, and the width was 115 mm, which was confirmed through a comparison of the inlet mass flow rate. As a result of the equivalent stress lower than the yield strength due to the material change from aluminum to steel compared to the existing steel, structural defects do not appear, and it is judged that the operation time compared to the battery capacity will be improved through the weight reduction of the blade.