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니켈도금된 S45C강의 연속파형 Nd:YAG 레이저 겹치기용접 특성
유영태,신호준,Yoo, Young-Tae,Shin, Ho-Jun 대한용접접합학회 2007 대한용접·접합학회지 Vol.25 No.3
Laser welding process is widely used in the industrial field due to its numerous advantages: a small heat affected zone(HAZ), deep penetration, high welding speed, ease of automation, single-pass thick section capability, enhanced design flexibility, and small distortion after welding. The objective of this research works is to investigate the influence of the process parameters, such as the welding fur metals with CW Nd:YAG lasers. The bead-on-plate and Lap welding experiments are carried out for several combinations of the experimental conditions. In order to quantitatively examine the characteristics of the welding quality of the cross section, tensile stress behavior and the hardness of the welded part are investigated in comparison of the Nickel coated and Nickel uncoated S45C steel. As a result of experiment, nickel coated S45C Steel showed more even weld zone than Nickel uncoated counterpart upon lap welding. Also, it showed relatively small amount of internal defects and spatter, and Nickel coated S45C showed better weldability than Nickel uncoated S45C steel. The optimum welding process upon lap welding of Nickel coated S45C steel is when each laser power is 1900W; focal positions is -1mm; welding speed is $0.9{\sim}1.0m/min$. The heat input was $4.178{\sim}4.36{\times}103J/cm^2$.
유영태(Young-Tae Yoo),최병재(Byeong-Jae Choi),김진우(Jin-Woo Kim) 한국기계가공학회 2021 한국기계가공학회지 Vol.20 No.3
Typical implants are not specified the screw structure and the surface process according to the bone quality of the human body. The purpose of this study is to complement the shortcomings of the existing implant surface processing method. It is to propose a surface processing method that increases the adhesion between the implant and bone tissue by increasing the surface area per unit area of the implant. It is very important to establish precise and systematic process parameters when surface treatment of implants using lasers. Therefore, we intend to develop a process so that the implant can be a biocompatible structure using a Q-switching Nd:YAG laser with a wavelength of 1.06um. Implant surface treatment technology through this study will be used in the industry.
유영태 ( Young Tae Yoo ),김창수 ( Chang Soo Kim ),송기홍 ( Gi Hong Song ) 한국회계학회 2012 회계저널 Vol.21 No.5
본 연구의 목적은 우리나라 자본시장에서 선택적으로 자산재평가를 실시한 기업들의 장단기성과를 측정하고, 장단기성과와 재평가를 실시한 기업의 재무특성 사이의 관계를 실증적으로 분석하고자 함에 있다. 자산재평가실시 공시가 의무화된 2009년 4월 15일 이후부터 2011년 12월까지 자산재평가실시를 공시한 237개 기업을 대상으로 보유기간초과수익률(BHAR), 누적초과수익률(CAR)을 이용하여 장기성과를 측정하였다. 분석결과는 다음과 같다. 첫째, 재평가실시 공시일 이후 누적평균초과수익률이 사건일부터 연속하여 8일간 유의한 양의 값을 보여 자산재평가가 단기적으로 자본시장에서 긍정적으로 받아들여지고 있음이 확인되었다. 둘째, 장기성과측정치인 보유기간초과수익률(BHAR)과 누적초과수익률(CAR)이 모두 통계적으로 유의한 정의 값을 보여 자산재평가실시라는 긍정적인 정보가 주가에 충분히 반영되지 못하고 장기간에 걸쳐 반영되는 과소반응가설을 지지하고 있다. 셋째, 단기성과와 손실보고여부의 회귀계수가 유의한 양의 관계를 보여 적자기업이 재평가를 실시할 경우 가시적인 청산가치가 높아지므로 기업가치가 향상됨을 보여주고 있다. 넷째, 장기성과와 재무특성사이의 관계를 회귀분석한 결과 총자산이 작은 기업이큰 기업보다 장기성과가 높아 총자산이 작은 기업이 더 과소반응가설을 지지하는 것으로 나타났다. 이러한 결과는 규모가 작은 그룹들의 정월초과수익률이 규모가 큰 그룹보다 더 높았기 때문인 데 자산재평가를 실시한 기업들 사이에서도 정월효과(January effect)가 나타나고 있음을 보여 주고 있다. This study investigates the short- and long-term performances of companies which selectively carried out asset revaluation. It also examines the relationship between short- and long-term performances and financial characteristics of firms which implemented asset revaluation. The sample is composed of 237 firms that announced asset revaluation during the period from April 15, 2009, when public announcement of asset revaluation became mandatory, to December, 2011. Two long-term performance measures are used, i. e. , Buy and Hold Abnormal Return (hereafter, BHAR) and Cumulative Abnormal Return (hereafter, CAR). The results are as follows: First, the announcement of asset revaluation has a significantly positive influence on stock prices in the short run. The CARs become significantly positive on the day of announcement and remain statistically significant during the following eight days. Since the CARs were never significant before announcement day, the result is consistent with a semi-strong form market efficiency. Second, asset revaluation firms show a positive long-term performance as measured by either BHAR or CAR. This result is consistent with the under-reaction hypothesis that the positive information associated with asset revaluation is not fully reflected during the announcement period and is rather gradually reflected over a long period of time. Third, the regression analysis shows a significantly positive relationship between short-term performance and a dummy variable for negative earnings. It suggests that the positive impact of asset revaluation is even larger for firms with negative earnings since their liquidation value gets higher due to asset revaluation. Fourth, small firms are found to have a higher long-term performance than large firms, which is also consistent with under-reaction hypothesis. This result is driven by January effect where small capitalization firms have a higher return than large firms in January.
유영태(Young-Tae Yoo),황희주(HeeJu Hwang) 한국산업경영학회 2023 경영연구 Vol.38 No.1
Due to COVID-19, people around the world have to adapt to a new lifestyle, and the real economy has been hit hard. Firms have considered and implemented various strategies to survive the economic shock starting in 2020. In this study, the free cash flow of individual firms was mainly observed at the period of COVID-19. It was found that firms listed on the Korean capital market during and after the pandemic strategically use free cash flow. At the time of the pandemic with high uncertainty, free cash flow was held, and it was confirmed that free cash flow was exhausted by reducing uncertainties and securing stable investment in new industries. This study has a contribution in that it reviewed the entire Korean capital market for free cash flow control activities. In preparation for similar shocks that may occur in the future, it is possible to confirm the expected response of the capital market in advance, and at the same time propose the necessary policy implications for the government authorities. COVID-19로 인하여 전 세계인은 새로운 생활방식에 적응해야 했으며 실물경제도 엄청난 타격을 받았다. 기업들은 2020년을 기점으로 경제 충격에서 생존하기 위한 다양한 전략을 고민하였으며 이를 실행해 왔다. 본 연구에서는 COVID-19 시점에 개별 기업의 잉여현금흐름(Free Cash Flow)을 주로 관찰하였다. 팬데믹기간 및 그 직후 한국 자본시장에 상장한 기업들은 잉여현금흐름을 전략적으로 사용하는 것으로 나타났다. 불확실성이 매우 높은 팬데믹 시점에는 잉여현금흐름을 보유하였으며, 팬데믹 이후 기간에는 불확실성 감소와신산업에 대한 안정적 투자처 확보 등으로 잉여현금흐름을 소진하는 것을 확인하였다. 본 연구는 잉여현금흐름 조절 활동에 대하여 한국 자본시장 전체를 검토하였다는 데에 그 기여점이 있다. 향후 발생하는 유사 충격에 대비하여 예상되는 자본시장의 반응을 미리 확인할 수 있고, 정부 당국에 필요한 정책적 함의를 동시에제안한다.
펄스레이저 조사가 타이타늄 임플란트 표면처리 특성에 미치는 영향
유영태(Young-Tae Yoo),최병재(Byeong-Jae Choi),김진우(Jin-Woo Kim) 한국기계가공학회 2023 한국기계가공학회지 Vol.22 No.3
Recently, the clinical efficiency of dental components based on titanium has been demonstrated. The surface shape and roughness characteristics of the implants are evaluated after laser surface treatment. When material with high thermal conductivity is processed with a laser, the energy of the laser beam is instantaneously diffused into the material. Therefore, a laser beam oscillating in the form of a pulse was used. After the laser beam was irradiated on the surface of the implant, a 3D surface roughness meter and an optical microscope were used to analyze it. In this study, the surface area increased owing to testing the implant by applying the scribing method to the implant surface.