• Journal of the Korean Crystal Growth and Crystal Technology
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• v.31 no.1
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• pp.24-31
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• 2021

We report structural, mechanical, and thermal properties of diecast ADC12 aluminum alloys characterized using synchrotron X-ray diffraction (XRD), scanning electron microscopy, energy dispersive X-ray (EDX) analysis, thermal conductivity (λ), Vickers hardness (Hv), and stress-strain measurements. We also studied the effect of post-annealing performed in a vacuum atmosphere on the mechanical properties of diecast ADC12 alloys. EDX and XRD results revealed that Al2Cu and AlCu3 grains are formed, well dispersed in Al base and highly crystalline. Ultimate tensile strength (UTS) of 307.9 ± 9.1 MPa and elongation of 2.98 ± 0.62 % were estimated. λ was 129.3 ± 0.27 W/m·K and Hv was approximately 130. Both values were significantly higher than the reported values. At annealing temperatures ranging from 25 to 200℃, UTS and Hv values remained constant, while as the annealing temperature increased to 500℃, these values gradually decreased. This is because stabilization of the microstructure improves toughness and ductility.

• Korean Security Journal
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• no.24
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• pp.33-51
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• 2010

The purpose of this study was to analyze the variation of muscle function and gait ability according to regular spinal stabilization exercise program for private security guards and the conclusion as follows. First, it increased lumbar extension strength and lumbar flexion strength both exercise and non exercise group according to the variation of muscle function with the spinal stabilization exercise program. There was significant difference between exercise and non exercise group after the program but not before the program. Second, it appeared the functional vanishment of lumbar extensor before the program both exercise and non exercise group according to the variation of muscle function with the spinal stabilization exercise program for lumbar flexor extensor ratio. Third, it analyzed for the spinal stabilization with 8 ways according to the variation of muscle function with the spinal stabilization exercise program for the change of the spinal stabilization. The spinal stabilizaton increased each angle for the execise group but decreased or not changed for non exercise group. Fourth, it used 10m gait test for the speed and step length according to the variation of muscle function with the spinal stabilization exercise program. It appeared the increasement of gait ability for exercise group and there was significant difference between exercise and non exercise group. In conclusion, there was a positive effect for lumbar extension strength, lumbar flexion strength, lumbar flexor extensor ratio, spinal stabilization, and gait ability with regular spinal stabilization exercise program. This means that spinal stabilization exercise program give positive effect to the decrease of back pain and the development of muscular strength for private security guard, also will help to recover and return to work more faster. Also, it seems that the exercise prescription program may be applicable to prevent or to improve the function for private security guard.

• Korean Journal of Optics and Photonics
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• v.21 no.2
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• pp.82-88
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• 2010

Photopolymer is a material for recording three dimensional holograms containing photo information. Photopolymer has been found to be a proper material due to many advantages such as high DE value, easy processing, and low price. Compositions of PVA, monomer, initiater and photosensitizer were determined by previous experiments and the compositions of $SeO_2$ and $TiO_2$ were considered as variable to find out the effects of $TiO_2$ on DE. The DE values were constant for the varying compositions of $TiO_2$ (0.1 mg~1.0 mg). In other words, $TiO_2$ is not directly effective on the DE values. Composition change experiments from $SeO_2$ 0.1 mg, $TiO_2$ 0.9 mg to $SeO_2$ 0.9 mg, $TiO_2$ 0.1 showed a maximum DE value of 73.75% at a component of $SeO_2$ 0.8 mg, $TiO_2$ 0.2 mg. It seemed that regardless of the amount of $TiO_2$, increasing the amount of $SeO_2$ gently increases DE`s. If nano particles are heavily added, transparent films could not be made due to the separation of particles by the solubility decrease. Photopolymer films could be made with high DE values for an extensive angle range if $TiO_2$ additions were kept minimum and $SeO_2$ additions were kept maximum.