• Journal of the Korean Society for Nondestructive Testing
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• v.21 no.3
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• pp.261-268
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• 2001

An investigation on nondestructive evaluation of thermal stress-nduced damage in the composite laminates (3mm in thickness and $[+45_6/-45_6]_s$ lay-up angles) has been performed using the thermo-acoustic emission technique. Reduction of thermo-AE events due to repetitive thermal load cycles showed a Kaiser effect. An analysis of the thermo-AE behavior determined the stress free temperature of composite laminates. Fiber fracture and matrix cracks were observed using the optical microscopy, scanning electron microscopy and ultrasonic C-sean. Short-Time Fourier Transform of thermo-AE signals offered the time-frequency characteristics which might classily the thermo-AE as three different types to estimate the damage processes of the composites.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.21 no.3
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• pp.447-452
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• 2020

The purpose of this research was to confirm that prefrontal neurofeedback training has an impact on adolescents. The objective of this study was to prove its scientific effect through experimentation. The effect of the training was measured by the difference in neuro?frequencies before and after the training. For this research, an experimental group and a control group, each with 22 students in J High School located in the city of S participated in this study. From May to July 2019, the training was conducted three times a week and for 30 minutes per session. The neuro?frequency data collected were analyzed through the methods of F.F.T. The resulting changes from the neurofeedback training for each group were analyzed by T-Tests. The result of the study is as follows; Neurofeedback training has had a positive effect on adolescent attention and sleep. In conclusion, the environmental and educational factors also play an important role. As the interaction of the latter two factors yield an individual's unique brain structure and functionality, the impact of the neurofeedback training is important on adolescents. The derivation of the above results by utilizing scientific and objective methods reemphasizes the importance of this study.