• 한국운동역학회지
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• 제28권2호
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• pp.87-92
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• 2018

Objective: The purpose of this study was to investigate the factors affecting two kinds of bat swing behavior through kinematic analysis. Method: A total of 32 high school baseball players participated in this study. The ball was placed on the tee-ball in a position where the subject could easily swing and the standard bat swing was performed as quickly and as accurately as possible using aluminum bats and wooden bats. Results: The aluminum bat showed a rapid swing speed of about 1.79 m/sec compared to the wooden bat. The speed of the batted ball was found to be significantly greater for the aluminum bat than for the wooden bat. In addition, although the difference between the shoulder-pelvis rotation angle according to the type of bat was not indicated, there was a statistically significant difference between the aluminum bat and the wooden bat in terms of the rotational angular velocity. Conclusion: Even though the results can explain the difference between the bat swing speed and the speed of the batted ball depending on the bat's material, it is difficult to explain the difference depending on the type of bat at the shoulder-pelvis rotation angle. However, shoulder-pelvic rotation angular velocity appears to be higher for the aluminum bat, and the differences in the type of bat is considered to be related to the batting swing factor.

• 환경생물
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• 제36권4호
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• pp.550-553
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• 2018

집박쥐(Pipistrellus abramus)는 인간의 주거 지역을 중심으로 서식하는 대표적인 종으로, 우리나라에 광범위하게 분포하고 있다. 그러나 대부분의 박쥐류가 유사한 크기의 다른 포유동물보다 상대적으로 긴 수명을 가지는 것에 반하여 집박쥐는 매우 짧은 수명을 가지는 것으로 알려져 왔다. 지금까지 집박쥐의 장기 수명에 관한 내용으로는 암컷 5년, 수컷 3년의 확인 기록이 전부였다. 그러나 본 연구자들은 284개체에 대한 밴딩을 통하여 지금까지 알려진 집박쥐의 최대 수명보다 2배 이상 생존한 개체를 재포획 하였으며, 그 결과를 정리하였다. 집박쥐는 인간의 생활권과 가장 밀접한 종으로 서식지의 환경은 본 종의 수명에 직접적인 영향을 미친다고 볼 수 있다. 따라서 향후 서식지 환경에 따른 수명과의 연계성에 대한 연구가 이루어져야 할 것으로 판단되며, 본 자료는 집박쥐의 장기 생존과 수명에 관한 국내 첫 보고로써 향후 박쥐의 수명에 관한 기초 자료가 될 것으로 기대된다.

• Journal of Welding and Joining
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• 제35권2호
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• pp.58-62
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• 2017

A319 aluminum alloy containing 6.5% Si and 3.5% Cu as major alloying elements has been widely used in machinery parts because of its excellent castability and crack resistance. However it needs more wear resistance to extend its usage to the severe wear environments. It has been known that hyper-eutectic Al-Si alloy having more than 12.6% Si contains pro-eutectic Si particles, which give better wear resistance and lubrication characteristics than hypo-eutectic Al-Si alloy like A319 alloy. In this study, it was tried to clad hyper-eutectic Al-Si alloy on the surface of A319 alloy. In the experiments, Al-36%Si alloy powder was mixed with organic binder to make a fluidic paste. The paste was screen-printed on the A319 alloy surface, melted by pulsed Nd:YAG laser and alloyed with the A319 base alloy. As experimental parameters, the average laser power was changed to 111 W, 202 W and 280 W. With increasing the average laser power, the melting depth was changed to $142{\mu}m$, $205{\mu}m$ and $245{\mu}m$, and the dilution rate to 67.2 %, 72.4 % and 75.7 %, and the Si content in the cladding layer to 16.2 %, 14.6 % and 13.7 %, respectively. The cross-section of the cladding layer showed very fine eutectic microstructure even though it was hyper-eutectic Al-Si alloy. This seems to be due to the rapid solidification of the melted spot by single laser pulse. The average hardness for the three cladding layers was HV175, which was much higher than HV96 of A319 base alloy. From the block-on-roll wear tests, A319 alloy had a wear loss of 5.8 mg, but the three cladding layers had an average wear loss of 3.5 mg, which meant that an increase of 40 % in wear resistance was obtained by laser cladding.