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우리나라 이동전화와 유선전화의 가입수요 대체에 관한 연구
성낙일,김창건 한국산업조직학회 2002 産業組織硏究 Vol.10 No.3
As mobile telephones become widely spread, they began to compete directly with fixed telephones, first for usage and ultimately for access. The potential for mobile phones to become a substitute for fixed phones has become evident. The aim of this paper is to examine the impact of rapid growth in mobile telephones on the access demand for traditional fixed telephones. In particular, we study whether or not mobile telephones are a substitute for fixed telephones by estimating the market demand equations for new connections. The empirical analysis is carried out with Korean regional panel data for the period 1991~1998. The study shows that a 1% increase in the number of mobile telephones results in a reduction of 0.10~0.18% in new fixed connections. The study provides various implications for telecommunications policy issues.
온도 변동하의 Al 7075 합금의 크리이프 및 파단수명
강대민,구양,백남주,김창건,박경동 한국산업안전학회 1989 한국안전학회지 Vol.4 No.1
Cyclic temperature creep tests were carried out an Al 7075 alloy specimens were subjected to a constant load and step-wise temperature cycles in which temperature was fluctuated between 300℃ and 250℃ with three different cycle ratios. The highest frequency of cycling was 1 cycle per 10 hr and the lowest one was 1 cycle per 12 hr. From the creep experimental results with the above conditions the creep strain under cyclic temperature can be predicted easily by introducing the equivalent steady temperature Te as defined by Eq.(16), but the rupture life is 1.1 time than those of constant temperature because of effect of temperature history at tertiary creep range. Besides this result, the results of the creep test under cyclic temperature conditions are respectively compayied with calculated rupture lives using the life fraction law and Eq.(18). The agreement between the obseried rupture times and calculated ones is fairly good. So creep rupture lives can be respectively predicted using life fraction law and Eq.(18).