• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2018.06a
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• pp.106-106
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• 2018

해양환경용 선박재료는 전기화학적인 부식을 발생시키는 염소이온($Cl^-$)이 다량 포함된 부식 환경에 장기간 노출되어 있어 부식에 대해 취약하다. 따라서 우수한 내식성 및 내침식성을 가진 재료를 선정하는 것은 매우 중요하다. 알루미늄 합금은 충분한 강도와 부동태 피막 형성으로 인해 내식성이 우수하여 해양환경용 선박 재료로서 널리 이용되고 있으며, 이에 따른 부식 특성에 관한 연구도 활발히 이뤄지고 있다. 그러나 선박에서는 부식에 의한 손상뿐만 아니라 전식에 의한 부식 손상도 발생할 수 있다. 특히 선미 부분은 프로펠러의 동합금과 알루미늄 합금의 이종금속 간 전위차에 의한 전식이 발생하여 선체의 다른 부위에 비해 부식이 더 심하게 진행될 수도 있다. 또한 전식은 해안 부두에 접안된 선박의 용접 시미주전류(stray current)에 의한 부식손상이 발생할 수 있으나 이에 대한 연구는 미미한 실정이다. 따라서 본 연구는 해양환경에서의 전식을 인위적으로 모사할 수 있는 부식 정전류 시험법을 이용하여 다양한 크기의 전식 손상을 유발시켰으며, 해양환경 하에서 선박재료로 주로 사용되는 알루미늄 합금인 Al5083-H321, Al5052-O, Al6061-T6에 대한 전식 특성을 비교, 분석하였다. 실험 방법으로 작동전극은 각 재료의 시험편을 $2cm{\times}2cm$ 으로 절단하여 sand paper # 2000 번까지 연마 후 아세톤과 증류수로 세척하고 건조하였으며, 제작된 시험편은 자체 제작한 홀더를 이용하여 $1cm^2$만 노출시킨 후 정전류 가속 실험을 실시하였다. 기준전극은 은/염화은(Ag/AgCl) 전극을, 대응전극은 백금(Pt) 전극을 사용하였다. 정전류 가속 조건은 $0.001mA/cm^2$, $0.1mA/cm^2$, $1mA/cm^2$, $5mA/cm^2$, $10mA/cm^2$의 전류 밀도를 천연해수에서 30분간 인가하였다. 각 재료에 대한 전식 특성은 실험 전후의 무게 감소량으로 전식의 저항 특성을 확인하였다. 그리고 3D 현미경으로 표면 손상 경향과 깊이를 측정하였으며, 주사전자현미경 (SEM)을 통해 표면 형상을 미시적으로 관찰하였다. 부식 정전류 시험 결과 모든 시편에서 $0.01mA/cm^2$에서 미세한 국부적인 부식이 일어났으며, 전류밀도가 증가할수록 표면 전반에 부식이 진행되고 성장하였다. 그리고 모든 인가 전류밀도의 조건에서 Al6061-T6가 5000계열(Al5083-H321, Al5052-O)보다 더 우수한 내식성을 나타났다.

• Journal of the Institute of Convergence Signal Processing
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• v.9 no.1
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• pp.31-38
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• 2008

Ad-Hoc network is a network architecture which has no backbone network and is deployed temporarily and rapidly in emergency or war without fixed mobile infrastructures. All communications between network entities are carried in ad-hoc networks over the wireless medium. Due to the radio communications being extremely vulnerable to propagation impairments, connectivity between network nodes is not guaranteed. Therefore, many new algorithms have been studied recently. This study proposes the secondary header approach to the cluster based routing protocol (CBRP). The primary header becomes abnormal status so that the primary header can not participate in the communications between network entities, the secondary header immediately replaces the primary header without selecting process of the new primary header. This improves the routing interruption problem that occurs when a header is moving out from a cluster or in the abnormal status. The performances of proposed algorithm ACBRP(Advanced Cluster Based Routing Protocol) are compared with CBRP. The cost of the primary header reelection of ACBRP is simulated. And results are presented in order to show the effectiveness of the algorithm.

• Korea journal of population studies
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• v.19 no.2
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• pp.77-105
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• 1996

The rural problems which we are facing start from the extremely small sized population and the skewed population structure by age and sex. Thus we analyzed the change of the rural population. And we analyzed the recent return migration to the rural areas by comparing the recent in-migrants with out-migrants to rural areas. And by analyzing the rural village survey data which was to show the current characteristics of rural population, we found out the effects of the in-migrants to the rural areas and predicted the futures of rural villages by characteristics. The changes of rural population composition by age was very clear. As the out-migrants towards cities carried on, the population composition of young children aged 0~4 years was low and the aged became thick. The proportion of the population aged 0~4 years was 45.1% of the total population in 1970 and dropped down to 20.4% in 1995, which is predicted to become under 20% from now on. In the same period(1970~1995), the population aged 65 years and over rose from 4.2% to 11.9%. In 1960, before industrialization, the proportion of the population aged 0~4 years in rural areas was higher than that of cities. As the rural young population continuously moves to cities it became lower than that in urban areas from 1975 and the gap grew till 1990. But the proportion of rural population aged 0~4 years in 1995 became 6.2% and the gap reduced. We can say this is the change of the characteristics of in-migrants and out-migrants in the rural areas. Also considering the composition of the population by age group moving from urban to rural area in the late 1980s, 51.8% of the total migrants concentrates upon age group of 20~34 years and these people's educational level was higher than that of out-migrants to urban areas. This fact predicted the changes of the rural population, and the results will turn out as a change in the rural society. However, after comparing the population structure between the pure rural village of Boeun-gun and suburban village of Paju-gun which was agriculture centered village but recently changed rapidly, the recent change of the rural population structure which the in-migrants to rural areas becomes younger is just a phenomenon in the suburban rural areas, not the change of the total rural areas in general. From the characteristics of the population structure of rural village from the field survey on these villages, we can see that in the pure rural villages without any effects from cities the regidents are highly aged, while industrialization and urbanization are making a progress in suburban villages. Therefore, the recent partial change of the rural population structure and the change of characteristics of the in-migrants toward rural areas is effecting and being effected by the population change of areas like suburban rural villages. Although there are return migrants to rural areas to change their jobs into agriculture, this is too minor to appear as a statistic effect.