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치과임플란트용 Ti-25Ta-xHf 합금의 플라즈마 전해 산화
김정재,최한철,Kim, Jeong-Jae,Choe, Han-Cheol 한국표면공학회 2018 한국표면공학회지 Vol.51 No.6
Plasma electrolytic oxidation of Ti-25Ta-xHf alloy in electrolyte containing Ca and P for dental implants was investigated using various experimental techniques. Ti-25Ta-xHf (x=0 and 15 wt.%) alloys were manufactured in an arc-melting vacuum furnace. Micropores were formed in PEO films on Ti-25Ta-xHf alloys in 0.15 M calcium acetate monohydrate + 0.02 M calcium glycerophosphate at 240 V, 270 V and 300 V for 3 min, respectively. The microstructure of Ti-25Ta-xHf alloys changed from (${\alpha}^{\prime}+{\alpha}^{{\prime}{\prime}}$) phase to (${\alpha}^{{\prime}{\prime}}+{\beta}$) phase by addition of Hf. As the applied potential increased, the number of pore and the area ratio of occupied by micro-pore decreased, whereas the pore size increased. The anatase phase increase as the applied potential increased. Also, the crystallite size of anatase-$TiO_2$ can be controlled by applied voltage.
초미세먼지를 이용한 오피스 내 환기유동에 대한 실험적 연구
김정재(Jeong Jae Kim),윤건영(Gunyeong Yoon) 대한기계학회 2021 대한기계학회 춘추학술대회 Vol.2021 No.11
Due to the recent COVID-19 situation, the importance of indoor ventilation has been highlighted. In particular, ventilation in residential and work spaces where most of the day is spent is important. In this study, ventilation performance was experimentally studied by measuring the concentration of ultrafine particulate matters (PM2.5) according to the opening conditions of windows and door for an office model in the wind tunnel. Furthermore, in order to find out the cause of the difference in ventilation performance, a quantitative analysis of the internal flow structure of the office model was performed through particle image velocimetry (PIV). As the opening angle of window increased, the mean velocity inside the model increased and the ventilation performance is also enhanced. In particular, the opening condition of door had a great effect on the ventilation performance in the office model. It is expected that this study would provide a guideline that can effectively improve ventilation performance in indoor space.
김정재(Jeong-Jae Kim),김원기(Won-Gi Kim) 한국콘텐츠학회 2014 한국콘텐츠학회논문지 Vol.14 No.4
본 연구의 목적은 저탄성계수 Ti-30Ta 합금에 Zr 원소를 첨가하여 표면 특성 및 부식 거동을 조사하였다. 저탄성계수 Ti-30Ta-xZr(x : 3, 7, 15 wt %)합금은 아크 멜팅기로 제조하였고, 아르곤 분위기에서 1000 ℃ 24시간 동안 열처리하였다. 합금의 미세구조는 FE-SEM 그리고 XRD를 이용하여 조사하였다. 전기화학적 특성은 시편 작업전극, 고밀도 탄소 보조전극 그리고 포화칼로멜 기준전극의 통상적인 3상을 이용하여 수행하였다. Ti-30Ta-xZr 합금의 분극 거동 결과, 균질화 처리된 Ti-30Ta-15Zr 합금의 부동태 전류밀도가 다른 합금에 비해 낮았다. In this study, surface characteristics and corrosion behaviors have been investigated in addition to Zr elements on the low elastic modulus Ti-30Ta alloy. Low elastic modulus Ti-30Ta-xZr(x : 3, 7 and 15 wt %) alloys were prepared by arc melting and then heat treated at 1000 ℃ for 24 hrs in an argon atmosphere. Microstructures of the alloys were examined by field emission scanning electron microscope(FE-SEM) and X-ray diffractometer(XRD). Electrochemical experiments were performed using a conventional three-electrode configuration with a sample working electrode, a high density carbon counter electrode and a saturated calomel reference electrode. According to the result of polarization behavior in the Ti-30Ta-xZr alloys, the current density of homogenized Ti-30Ta-15Zr in the passive region was lower than the other alloys.
김정재(Jeong-Jae Kim) 한국산업경영학회 2009 經營硏究 Vol.24 No.1
본 연구는 코스닥기업에서 회계수치의 가치관련성이 상장기간의 경과에 따라 차이가 있는지 살펴보았다. 이는 현재의 수익창출모형에 만족하지 못해 기존자산의 퇴출이나 변화를 모색하는 옵션평가모형에 근거한 기업가치 평가요인이 상장기간의 경과에 따라 달라질 수 있다는 판단에 근거한 것이다. 왜냐하면 선행연구에서 주장하는 대로 벤처기업은 영업환경이 불안정하여 새로운 수익모형으로의 전환가능성이 높아 포기옵션가치를 반영하는 장부가액의 가치관련성이 높다는 논리가 모든 벤처기업에서 상장하자마자 적용될 지는 의문이기 때문이다. 또한 본 연구에서는 일반기업과 벤처기업의 구분을 상장당시의 구분이 아니라 최근의 소속으로 하였다. 이는 상장당시에는 벤처기업이었지만 현재는 일반기업으로 전환된 기업이 벤처기업으로 계속 분류되는 것이 모순이기 때문에 이를 방지하기 위함이다. 본 연구의 의의는 첫째, 청산가치의 대용변수로서 장부가액의 가치관련성이 모든 벤처기업에서 상장하자마자 나타나는 것이 아님을 밝힌 것이며, 둘째, 일반기업과 벤처기업의 구분을 어느 시점을 기준으로 분류하느냐에 따라 분석결과가 달라질 수 있음을 보인 것이며, 셋째, 단순 시차별 분석이 간과하는 상장기간경과에 따른 벤처기업의 수익률 변화를 고려하여 벤처기업의 가치평가에 대한 이해를 증진시켰다는 점이다. Prior studies have examined the value relevance of KOSDAQ firms and found that whereas earnings have more significant value relevance in non-venture firms, book values have more significant value relevance in venture firms. These findings have been supported by the expectation that since venture firms face more unstable operating environments and volatile revenue models their firm valuation is more dependent on the liquidation or adaptation value proxied by book value. The objective of this study is to examine whether the value relevance of accounting numbers is dependent on the length of listing period of KOSDAQ firms. The reason why this study pinpoints the listing period is that in the option style valuation model liquidation or adaptation value proxied by book value could materialize as listing period passes. Since the adaptation value is derived from the adaptation of existing resources to a superior alternative future use the length of listing period could be an influential factor. In this vein, this study expects that the adaptation value of venture firms will not be reflected until profitability analysis of the current revenue model is completed and executive decision is formalized. Therefore, this study hypothesizes that the value relevance of accounting numbers will be different between venture firms and non-venture firms as the length of listing period becomes longer. To test the hypothesis this study applies a linear option model and a non-linear option model to the sample firm data collected over the period 1996-2005. The results of the study consistently support the hypothesis and are summarized as follows. First, in the non-venture firms, the value relevance of book value and income numbers has been generally observed as in the prior studies. However, in the venture firms, the value relevance of earnings has been observed in the earlier stages of listings period whereas the value relevance of book value has been observed in the latter stages of listing period. Second, in the venture firms, the difference between two groups depending on the sign of earnings or ROE level has been observed only in the earlier stages of listing period. However, in the non-venture firms, the difference between two groups depending on the sign of earnings or ROE level has been observed in the entire listing period. This evidence empirically supports the proposition that the value relevance of accounting numbers in venture firms essentially depends on the length of listing period. Overall, the results of this study indicate that, in the venture firms, earnings play pivotal role in the earlier stages of listing period whereas book values play pivotal role in the latter stages of listing period.