• The Transactions of The Korean Institute of Electrical Engineers
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• v.68 no.1
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• pp.69-76
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• 2019

Microheaters with different structures were fabricated and compared to find an optimal configuration enhancing the performances of $C_2H_2$ gas sensor. Three temperature sensors were integrated on the surface of the insulation layer over the microheater, and resistance changes were observed to check the generated heat from the microheater. A low operating voltage of 1mV was applied to the temperature sensor to minimize any influence of thermal heat from the resistance type temperature sensor, whereas high voltages in the range between 10 and 20V were applied to the microheater. A microheater structure generating maximum heat at low voltage was determined. The generated heat was verified by the temperature sensors on the top of the $Si_3N_4$ and infrared camera. A long term stability and accuracy of the microheater were observed. The developed microheater was applied to enhance the performances of $C_2H_2$ gas sensor and successfully confirmed that the developed microheater greatly contributes to the improvement of sensitivity and selectivity of gas sensor.

• Korean Journal of Materials Research
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• v.29 no.3
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• pp.189-195
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• 2019

The effect of C, Mn, and Al additions on the tensile and Charpy impact properties of austenitic high-manganese steels for cryogenic applications is investigated in terms of the deformation mechanism dependent on stacking fault energy and austenite stability. The addition of the alloying elements usually increases the stacking fault energy, which is calculated using a modified thermodynamic model. Although the yield strength of austenitic high-manganese steels is increased by the addition of the alloying elements, the tensile strength is significantly affected by the deformation mechanism associated with stacking fault energy because of grain size refinement caused by deformation twinning and mobile dislocations generated during deformation-induced martensite transformation. None of the austenitic high-manganese steels exhibit clear ductile-brittle transition behavior, but their absorbed energy gradually decreases with lowering test temperature, regardless of the alloying elements. However, the combined addition of Mn and Al to the austenitic high-manganese steels suppresses the decrease in absorbed energy with a decreasing temperature by enhancing austenite stability.

• Journal of Electrochemical Science and Technology
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• v.13 no.1
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• pp.159-166
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• 2022

The assembly of the micron-sized Si/CNT/carbon composite wrapped with graphene (SCG composite) is designed and synthesized via a spray drying process. The spherical SCG composite exhibits a high discharge capacity of 1789 mAh g^-1 with an initial coulombic efficiency of 84 %. Moreover, the porous architecture of SCG composite is beneficial for enhancing cycling stability and rate capability. In practice, a blended electrode consisting of spherical SCG composite and natural graphite with a reversible capacity of ~500 mAh g^-1, shows a stable cycle performance with high cycling efficiencies (> 99.5%) during 100 cycles. These superior electrochemical performance are mainly attributed to the robust design and structural stability of the SCG composite during charge and discharge process. It appears that despite the fracture of micro-sized Si particles during repeated cycling, the electrical contact of Si particles can be maintained within the SCG composite by suppressing the direct contact of Si particles with electrolytes.

• Journal of Institute of Convergence Technology
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• v.12 no.1
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• pp.31-35
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• 2022

This study has been carried out in order to improve the rolling problem by enhancing steering stability compared to the 2021 Student Car of the KNUT_EV team for KSAE. Among the various factors affecting steering performances, it was focused on the height of the centroid of weight, the motion ratio, and the spring deflection. In the 2022 Car, a pull rod suspension was used to reduce the height of the centroid of weight and designed with a structure of the rod and rocker to satisfy the target motion ratio. The spring deflection was testified by ADAMS and ABAQUS analysis, and the spring stiffness was selected at 350lb/inch and 450lb/inch for the front and rear wheels, respectively. As a result, the rolling angle of the 2022 Car was reduced compared to the 2021 Car, and the rolling phenomenon was improved.

• Korean Journal of Exercise Nutrition
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• v.25 no.3
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• pp.23-27
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• 2021

[Purpose] Functional beverages are intended to support those who want to maintain optimal physical condition and improve their quality of life through the enhancement of heart health, immunity, and digestion. The purpose of this study was to investigate the performance of top-level athletes consuming immune-strengthening conditioning nutritional drinks. [Methods] A total of 107 top-level athletes (baseball (56 players), pro volleyball (17), athletics (16), cycling (8), golf (6), and fencing (6)) participated in the experiment. They consumed an immune-enhancing functional beverage once a day for 8 weeks and responded to a survey before, during, and after drinking the beverage. [Results] Three total aspect-based subfactors were drawn from 24 questions in the factor analysis: physical, satisfaction with mental stability, and activity in performance. The physical, mental stability and performance changes of athletes significantly increased in period 2 (4 weeks after intake) and period 3 (after 8 weeks of intake). [Conclusion] We evaluated the efficacy of a new conditioned beverage containing Lactobacillus B240 and protein in improving the performance and physiological utility of top athletes. This functional drink may gain popularity among those seeking health benefits and improved exercise performance.

• Polymer(Korea)
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• v.39 no.1
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• pp.180-184
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• 2015

PP-grafted GO was prepared by the reaction of graphene oxide (GO) containing 2-bromoisobuyryl groups and polypropylene (PP) having hydroxyl groups (PP-OH) via a "grafting-to" method. GO-Br was synthesized by the reaction of GO and 2-bromoisobutyryl bromide under a basic condition. PP-MAH was reacted with ethanolamine to produce PP-OH. The melting temperature of PP-grafted GO was shifted to the higher temperature than that of PP-OH. Also, the thermal stability of PP-grafted GO was increased as compared to PP-OH and GO. These results demonstrated that the grafted coating polymer PP was effective for enhancing the thermal stability of GO. The higher surface roughness of PP-grafted GO was resulted from the chemical attachment of PP on the surface of GO. The characterization of PP-grafted GO was conducted from Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and scanning electron microscope (SEM).

• Transactions of the Korean Society of Mechanical Engineers A
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• v.28 no.12
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• pp.1914-1922
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• 2004

This paper provides a comprehensive study of optimum design of a helicopter tailrotor driveshaft made of the flexible matrix composites (FMCs). Since the driveshaft transmits power while subjected to large bending deformation due to aerodynamic loadings, the FMCs can be ideal for enhancing the drivetrain performance by absorbing the lateral deformation without shaft segmentation. However, the increased lateral flexibility and high internal damping of the FMCs may induce whirling instability at supercritical operating conditions. Thus, the purpose of optimization in this paper is to find a set of tailored FMC parameters that compromise between the lateral flexibility and the whirling stability while satisfying several criteria such as torsional buckling safety and the maximum shaft temperature at steadystate conditions. At first, the drivetrain was modeled based on the finite element method and the classical laminate theory with complex modulus approach. Then, an objective function was defined as a combination of an allowable bending deformation and external damping and a genetic algorithm was applied to search for an optimum set with respect to ply angles and stack sequences. Results show that an optimum laminate consists of two groups of layers: (i) one has ply angles well below 45$^{\circ}$ and the other far above 45$^{\circ}$ and (ii) the number of layers with low ply angles is much bigger than that with high ply angles. It is also found that a thick FMC shaft is desirable for both lateral flexibility and whirling stability. The genetic algorithm was effective in converging to several local optimums, whose laminates exhibit similar patterns as mentioned above.

• PNF and Movement
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• v.16 no.2
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• pp.259-266
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• 2018

Purpose: This study aimed to compare balance ability according to the immersion level of virtual reality-based training for the balance enhancement of the elderly. Methods: This study included 48 elderly people aged 65 years and older (male 16, female 32). According to the immersion level of applied virtual reality training, 16, 17, and 15 persons were randomly assigned to full immersion, semi-immersion, and control groups. The subjects who were assigned to the full immersion group and semi-immersion group received virtual reality training for 6 weeks at 20 min at a time, 3 times per week. The control group received no intervention. Balance ability was evaluated by measuring the stability limit and the tandem walking test before and after the intervention. Results: Results showed significant differences among the three groups in the limit of stability of all directions and the tandem walking test after the intervention. The results of the limit of stability showed a significantly higher value in the full-immersion group than in the control group, and the results of the tandem walking test showed a significantly lower value in the full-immersion and semi-immersion groups than in the control group. Conclusion: The results indicate that the head-mounted display equipment for applying full-immersion virtual training is the most effective in enhancing the balance ability of the elderly.

• Food Science of Animal Resources
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• v.23 no.1
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• pp.86-95
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• 2003

Potential mechanisms by which vitamin E improves oxidative stability of myoglobin are documented. The basis by which this lipid-soluble antioxidant, ${\alpha}$-tocopherol, protects water-soluble oxymyoglobin is beginning to be understood. Recent evidence suggests that ${\alpha}$-tocopherol delays the release of prooxidative products of lipid oxidation from biomembranes, which in turn delays oxymyoglobin oxidation and the concomitant loss of desirable beef color. ${\alpha}$, ${\beta}$-Unsaturated aldehydes are one class of lipid oxidation products that enhance oxymyoglobin oxidation in vitro and appear to act by covalently binding to the protein. If ${\alpha}$-tocopherol delays the formation of these reactive aldehydes, then this could inhibit the prooxidative effect of these oxidation products toward oxymyoglobin. Additionally, ${\alpha}$-tocopherol may exert part of its color-stabilizing effect in beef by enhancing the metmyoglobin reduction.

• Journal of the Society of Cosmetic Scientists of Korea
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• v.25 no.4 s.34
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• pp.145-154
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• 1999

A novel retinol derivative, polyethoxylated retinamide(Medimin A) was synthesized, as an anti-aging agent. Collagen synthesis, skin permeation, stability, and toxicity of Medimin A were evaluated and compared with those of retinol and retinyl palmitate. In vitro collagen synthesis was evaluated by quantitative assay of $[^3H]-proline$ incorporation into collagenase sensitive protein in fibroblast cultures. For in vitro skin permeation experiments, Franz diffusion cells(effective diffusion area: 1,766 $cm^2$) and the excised skin of female hairless mouse aged 8 weeks were used, The stabilities of retinoids were evaluated at two different temperature($25^{\circ}C\;and\;40^{\circ}C$) and under UV in solubilized state and in O/W emulsion. To estimate the safety, acute oral toxicity, acute dermal toxicity, primary skin irritation, acute eye irritation and human patch test were performed. The effect of Medimin A on collagen synthesis was similar to that of retinol. The skin permeability of Medimin A was higher than those of retinol and retinyl palmitate. The Medimin A was more stable than retinol and retinyl palmitate. Medimin A was nontoxic in various toxicological tests. These results suggest that Medimin A would be a good anti-aging agent for enhancing bioavailability and stability.