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        검색결과 7

        4.
        2018.05 구독 인증기관·개인회원 무료
        In Korea, concrete pavements were first applied to highways in 1981 and as a result of continued increase in length over the past years, 2,592 km of concrete pavement network is currently in service, of which 1,399 km(54%) of concrete pavements is 10 years or older, and 233km(9%) is 20 years or older. The length of concrete pavement sections nationwide has been steadily on the rise every year (EXTRI, 2017). Approximately 54% of current concrete pavement highway network will reach the service life limit in 2025 which means around 660 billion won is needed for future pavement repair project (EXTRI, 2017). Given that concrete pavements beyond design life still have a remaining service life, it is economically advantageous to repair them before reconstruction. Asphalt overlays are a major repair method for older concrete pavements. Depending on the concrete pavement condition, thickness and mixture of asphalt overlays are determined. Service life of asphalt overlays varies by the presence, time and size of cracks in existing concrete pavements and reflecting crack at joints. Temperature change of concrete pavement is among the major reaction parameters of reflecting crack. Reflecting crack develops when asphalt bottom-up cracking by longitudinal shrinkage and expansion due to temperature change of the concrete base layer, top-down cracking by temperature difference between top and bottom of concrete, and shear stress by traffic loading are combined (Baek, 2010). Crack and joint behaviors of concrete pavement vary between the base layer and the concrete surface of composite pavement system, and different conductivity by mixture and thickness of asphalt overlay leads to temperature change of concrete base course. This study measured temperatures of each layer of diverse composite pavements in place on site and analyzed differences in temperature change of concrete base layer depending on mixture and thickness of asphalt overlays. Overlay thickness parameters were 5cm and 10cm, two values most widely used, while mixture parameters were SMA and porous asphalt. Based on temperature change of concrete surface, this study also evaluated the difference of temperature change in concrete base layer with an asphalt overlay on top. Findings from this study are expected to be utilized for studies on mechanism and modeling of reflecting crack in old concrete pavements with asphalt overlays.
        7.
        2012.06 구독 인증기관·개인회원 무료
        True hermaphrodites are animals of equivocal sex in which both male and female gonads develop simultaneously. The frequency of true hermaphroditism is higher in pigs than in other domestic animals. Two Korean pigs were diagnosed with true hermaphroditism showing ovotestes, epididymes, penes, and uteri. Histomorphologically, the testicular tissues consisted of Sertoli cells that were devoid of spermatogenic germ cells and showed proliferation of interstitial cells. However, the uteri were of normal architecture and had well-developed uterine endometrial glands. The samples were 38, XX female karyotype without the sex-determining region Y (SRY) gene. The findings of this study could contribute to the understanding of true hermaphroditism in the Korean pig industry. * This work was supported by a grant (Code# PJ008148) from BioGreen21 Program, Rural Development Administration, Republic of Korea.