• Journal of Korean Society of Coastal and Ocean Engineers
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• v.29 no.6
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• pp.363-368
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• 2017

The tsunami flood the coastal cities and damage the land structures. The study on wave pressure and force on land structures is one of the important factors in designing the stability of inland structures. In this study, two - dimensional wave flume tests on the horizontal wave force and pressure of tsunamis on a simplified box-type structure was conducted. Vertical distribution and wave power of horizontal wave pressure over time were measured by pressure sensors and force transducer. Also, those were measured from the different wave breaking types. The vertical distribution of horizontal wave pressure was uniform at the moment when the horizontal wave force to the structure was maximum under the breaking wave condition. A surf similarity parameter was employed in order to figure out the relationship between the maximum horizontal wave force on the structure as a function of various incident wave conditions. As a result, the non - dimensionalized horizontal wave force tends to decrease exponentially as the surf similarity parameter increases.

• Journal of the Korean Wood Science and Technology
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• v.44 no.5
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• pp.760-766
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• 2016

This study explored the effects of heating temperature and laminae thicknesses on the time required to heat the center of air-dried Paulownia tomentosa, Pinus sp., Abies sp., and Larix sp. laminae to $56^{\circ}C$, which is a minimum core temperature of wood packaging materials defined by ISPM 15 standard, and maintain for 30 minutes in dry heat treatment schedule. Heating times were different among wood species and were Pinus sp. ${\geq}$ Abies sp. > Paulownia tomentosa > Larix sp. in decreasing order. The differences in heating times of some species were significantly different statistically, but were not different enough in practical terms to warrant heating four species separately. Heating times decreased as heating temperature increased and followed approximately power-function relationship. Also, heating times increased linearly with increasing laminae thickness. These relationships make it possible to calculate intermediate heating times relative to experimentally observed heating times. The results of this study will serve as a guideline for heat sterilization of Chinese laminae species to meet heat treatment requirements for protection against invasive pests.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.16 no.12
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• pp.8700-8706
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• 2015

The first driving device of the power bogies for the Korean high-speed railway vehicle consists of the traction motor (TM) and the motor reduction gears unit (MRU). Although TM and MRU are the mechanically integrated structures, their time between overhauls (TBO) have two separate intervals due to different technical requirements(i.e. TBO of MRU: $1.8{\times}10^6km$, TBO of TM: $2.5{\times}10^6km$). Therefore, to reduce the unnecessary number of preventive maintenances, it is important to evaluate the optimal TBO with a viewpoint of reliability-center maintenance towards cost-effective solution. In this study, derived from the field data in maintenance, fault tree analysis and failure rate of the subsystem considering criticality of the components are evaluated respectively. To minimize the conventional total maintenance cost, the same optimal TBO of the components is derived from genetic algorithm considering target reliability and improvement factor. In this algorithm, a chromosome which comprised of each individual is the minimum preventive maintenance interval. The fitness function of the individual in generation is acquired through the formulation using an inverse number of the total maintenance cost. Whereas the lowest common multiple method produces only a four percent reduction compared to what the existing method did, the optimal TBO of them using genetic algorithm is $2.25{\times}10^6$km, which is reduced to about 14% comparing the conventional method.

• Journal of Korea Water Resources Association
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• v.42 no.8
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• pp.643-657
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• 2009

The major reason to construct large dams is to store surplus water during rainy seasons and utilize it for water supply in dry seasons. Reservoir storage has to meet a pre-defined target to satisfy water demands and cope with a dry season when the availability of water resources are limited temporally as well as spatially. In this study, a Hedging rule that reduces total reservoir outflow as drought starts is applied to alleviate severe water shortages. Five stages for reducing outflow based on the current reservoir storage are proposed as the Hedging rule. The objective function is to minimize the total discrepancies between the target and actual reservoir storage, water supply and demand, and required minimum river discharge and actual river flow. Mixed Integer Linear Programming (MILP) is used to develop a multi-reservoir operation system with the Hedging rule. The developed system is applied for the Han River basin that includes four multi-purpose dams and one water supplying reservoir. One of the fours dams is primarily for power generation. Ten-day-based runoff from subbasins and water demand in 2003 and water supply plan to water users from the reservoirs are used from "Long Term Comprehensive Plan for Water Resources in Korea" and "Practical Handbook of Dam Operation in Korea", respectively. The model was optimized by GAMS/CPLEX which is LP/MIP solver using a branch-and-cut algorithm. As results, 99.99% of municipal demand, 99.91% of agricultural demand and 100.00% of minimum river discharge were satisfied and, at the same time, dam storage compared to the storage efficiency increased 10.04% which is a real operation data in 2003.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2009.06a
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• pp.260-260
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• 2009

초박형 절연막은 현재 다양한 전자소자의 제작과 향상을 위하여 활용되고 있으며, 일반적인 화학 기상 증착 방법으로는 균일도를 확보하기 어려운 문제점을 가지고 있다. 본 논문에서는 디스플레이의 구동소자로 활용되는 박막 트랜지스터의 특성 향상과 비휘발성 메모리 소자의 터널링 박막에 응용하기 위하여 초박형 실리콘 옥시나이트라이드 박막의 증착과 이의 특성을 분석하였다. 실리콘 옥시나이트라이드 박막은 실리콘 산화막에 질소가 주입되어 있는 형태로 실리콘 산화막과 실리콘 계면상에 존재하는 질소는 터널링 전류와 결함 형성을 감소시키며, bulk 내에 존재하는 질소는 단일 실리콘 산화막에 비해 더 두꺼운 박막을 커패시턴스의 감소없이 이용할 수 있는 장점이 있다. 플라즈마 처리 기법을 이용하였을 경우에는 초박형의 균일한 박막을 얻을 수 있으며, 본 연구에서는 이산화질소 플라즈마를 이용하여 활성화된 질소 및 산소 라디칼들이 실리콘 계면을 개질하여 초박형 실리콘 옥시나이트라이드 박막을 형성활 수 있다. 플라즈마 처리 시간과 RF power의 변화에 따라 형성된 실리콘 옥시나이트라이드 박막의 두께 및 광학적 특성은 엘립소미터를 통하여 분석하였으며, 전기적인 특성은 금속-절연막-실리콘의 MIS 구조를 형성하여 커패시턴스-전압 곡선과 전류-전압 곡선을 사용하여 평가하였다. 이산화질소 플라즈마 처리 방법을 사용한 실리콘 옥시나이트라이드 박막을 log-log 스케일로 시간과 박막 두께의 함수로 전환해보면 선형적인 증가를 나타내며, 이는 초기적으로 증착률이 높고 시간이 지남에 따라 두께 증가가 포화상태에 도달함을 확인할 수 있다. 실리콘 옥시나이트라이드 박막은 초기적으로 산소의 함유량이 많은 형태의 박막으로 구성되며, 시간의 증가에 따라서 질소의 함유량이 증가하여 굴절률이 높고 더욱 치밀한 형태의 박막이 형성되었으며, 이는 시간의 증가에 따라 플라즈마 챔버 내에 존재하는 활성종들은 실리콘 박막의 개질을 통한 실리콘 옥시나이트라이드 박막의 두께 증가에 기여하기 보다는 형성된 박막의 내부적인 성분 변화에 기여하게 된다. 이산화질소 플라즈마 처리 시간의 변화에 따라 형성된 박막의 정기적인 특성의 경우, 2.3 nm 이상의 실리콘 옥시나이트라이드 박막을 가진 MIS 구조에서 accumulation과 inversion의 특성이 명확하게 나타남을 확인할 수 있다. 아산화질소 플라즈마 처리 시간이 짧은 실리콘 옥시나이트라이드 박막의 경우 전압의 변화에 따라 공핍영역에서의 기울기가 현저히 감소하며 이는 플라즈마에 의한 계면 손상으로 계면결합 전하량이 증가에 기인한 것으로 판단된다. 또한, 전류-전압 곡선을 활용하여 측정한 터널링 메카니즘은 2.3 nm 이하의 두께를 가진 실리콘 옥시나이트라이드 박막은 직접 터널링이 주도하며, 2.7 nm 이상의 두께를 가진 실리콘 옥시나이트라이드 박막은 F-N 터널링이 주도하고 있음을 확인할 수 있다. 즉, 2.5 nm 두께를 경계로 하여 실리콘 옥시나이트라이드 박막의 터널링 메카니즘이 변화함을 확인할 수 있다. 결론적으로 2.3 nm 이상의 두께를 가진 실리콘 옥시나이트라이드 박막에서 전기적인 안정성을 확보할수 있어 박막트랜지스터의 절연막으로 활용이 가능하며 2.5 nm 두께를 경계로 터널링 메커니즘이 변화하는 특성을 이용하여 비휘발성 메모리 소자 제작시 전하 주입 및 기억 유지 특성을 확보를 위한 실리콘 옥시나이트라이드 터널링 박막을 효과적으로 선택하여 활용할 수 있다.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.43 no.6 s.348
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• pp.23-29
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• 2006

It is difficult to apply conventional security algorithms to the wireless sensor networks composed of nodes that have resource constraints such as memory, computing, power resources limitation. Generally, shared key based algorithms with low resource consumption and short key length are used for broadcast packets in authentication of base station. But it is not suitable that all the nodes hold the same shared key only for packet authentication. Recently, broadcast authentication algorithm for sensor network is proposed, which uses key chain generation by one-way hash function, Message Authentication Code generation by each keys of the key chains and delayed key disclosure. It provides suitable authentication method for wireless sensor networks but may leads to inefficient consequence with respect to network conditions such as broadcast ratio, key chain level, and so on. In this paper, we propose an improved broadcast authentication algorithm that uses key chain link and periodical key disclosure. We evaluated the performance of proposed algorithm using TOSSIM(TinyOS Simulator) in TinyOS. The results show that the proposed algorithm ensures low authentication delay, uses memory and computing resource of receiving nodes efficiently and reduces the amount of packet transmitting/receiving.

• Journal of the Korean Vacuum Society
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• v.15 no.2
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• pp.216-222
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• 2006

In this paper, we investigated the effect of hydrogen-plasma (H-plasma) treatment on the electrical and optical properties of a quantum dot infrared photodetector (QDIP) with a 5-stacked InAs dots in an InGaAs/GaAs well structure and $Al_{0.3}Ga_{0.7}As/GaAs$ SL (superlattice) current blocking layer. It has been observed that H-plasma treatment didn't affect the band structure of QDIP. It has been also observed that the H-plasma treatment on the QDIP not only enhance the electrical property of QDIP by curing the defect channels in $Al_{0.3}Ga_{0.7}As/GaAs$ SL but also introduce defects in QDIP structure. The H-plasma treatment for 10 min with 20 W of RF power provided the lowest dark current, which made it possible to measure the photo-current (PC) of QDIP whose PC was not detectable without the H-plasma treatment due to the high dark current.

• Journal of Korea Water Resources Association
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• v.37 no.12
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• pp.1019-1032
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• 2004

Flood frequency estimate is an essential index for determining the scale of small and middle hydraulic structure. However, this flood quantity could not be estimated directly for practical design purpose due to the lack of available flood data, and indirect method like design rainfall-runoff method have been used for the estimation of design flood. To give the good explain for design flood estimates, regional flood frequency analysis was performed by flood index method in this study. First, annual maximum series were constructed by using the collected data which covers from Japanese imperialism period to 1999. Wakeby distribution recommended by WMO(1989) was used for regional flood frequency analysis and L-moment method by Hosking (1990) was used for parameter estimation. For the homogeneity of region, the discordance and heterogeneity test by Hosking and Wallis(1993) was carried for 4 major watersheds in Korea. Physical independent variable correlated with index flood was watershed area. The relationship between specific discharge and watershed area showed a type of power function, i.e. the specific discharge decreases as watershed area increases. So flood quantity according to watershed area and return period was presented for each watershed(Han rivet, Nakdong river, Geum river and Youngsan/Seomjin river) by using this relation type. This result was also compared with the result of point frequency analysis and its regionalization. It was shown that the dam construction couldn't largely affect the variation of peak flood. The property of this study was also examined by comparison with previous studies.

• KOREAN JOURNAL OF CROP SCIENCE
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• v.46 no.3
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• pp.202-208
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• 2001

Under the constant daylength of 13 hours and growth temperatures of 15$^{\circ}C$ to 27$^{\circ}C$, the final number of loaves (FNL) on the main culm was constant as 15 regardless of temperature in rice variety 'Kwanganbyeo'. Leaf appearance rate (LAR) increased with rising temperature and decreased with phenological development. Threshold temperature (T$_{o}$) was not constant across growth stages, but increased with phenological development. Effective accumulated temperature (EAT), which is calculated by the summation of values subtracting T0 from daily mean temperature, is closely related with number of leaves appeared (LA). LA was fitted to bilinear, quadratic, power and logistic function of EAT. Among the functions, logistic function had the best fitness of which coefficient of determination was $R^2$=0.995. Therefore, LAR prediction model was established by differentiating this function in terms of time: (equation omitted). where dL/dt is LAR, T$_1$ is daily mean temperature, L is the number of leaves appeared, and a, b, and c are constants that were estimated as 41.8, 1098.38, and -0.9273, respectively. When predictions of LA were made by LAR prediction model using data independent of model establishment, the observed and predicted LA showed good agreement of $R^2$$\geq$0.99.

• Journal of Korea Water Resources Association
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• v.44 no.7
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• pp.553-563
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• 2011

According to the improvement of computer's performance, the development of Geographic Information System (GIS), and the activation of offering information, a distributed model for analyzing runoff has been studied a lot in recently years. The distribution model is a theoretical and physical model computing runoff as making target basin subdivided parted. In the distributed model developed by this study, the volume of runoff at the surface flow is calculated on the basis of the parameter determined by landcover data and a two-dimensional diffusion wave equation. Most of existing runoff models compute velocity and discharge of flow by applying Manning-Strickler's mean velocity equation and Manning's roughness coefficient. Manning's roughness coefficient is not matched with dimension and ambiguous at computation; Nevertheless, it is widely used in because of its convenience for use. In order to improve those problems, this study developed the runoff model by applying not only Manning-Strickler's equation but also Chezy's mean velocity equation. Furthermore, this study introduced a power law of exponential friction factor expressed by the function of roughness height. The distributed model developed in this study is applied to 6 events of fan-shape basin, oblong shape test basin and Anseongcheon basin as real field conditions. As a result the model is found to be excellent in comparison with the exiting runoff models using for practical engineering application.