• The Journal of Korean Institute of Communications and Information Sciences
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• v.37C no.12
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• pp.1328-1336
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• 2012

Compared to terrestrial RF communications, underwater acoustic communications have several limitations such as limited bandwidth, high level of fading effects, and a large underwater propagation delay. In this paper, in order to tackle those limitations of underwater communications and to make it possible to form a large underwater monitoring systems, we propose a hierarchical underwater network architecture, which consists of underwater sensors, clusterheads, underwater/surface sink nodes, autonomous underwater vehicles (AUVs). In the proposed architecture, for the maximization of packet delivery ratio and the minimization of underwater sensor's energy consumption, a hybrid routing protocol is used. More specifically, cluster members use Tree based routing to transmit sensing data to clusterheads. AUVs on optimal trajectory movements collect the aggregated data from clusterhead and finally forward the data to the sink node. Also, in order to minimize the maximum travel distance of AUVs, an Integer Linear Programming based algorithm is employed. Performance analysis through simulations shows that the proposed architecture can achieve a higher data delivery ratio and lower energy consumption than existing routing schemes such as gradient based routing and geographical forwarding. Start after striking space key 2 times.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1990.10a
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• pp.98-101
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• 1990

In order to investigate the laser effects resulted from the behaviors of carriers for BOPP film, experiment of TSC were carried out on the specimen with 15[$\mu\textrm{m}$] thick irradiated by He-Ne laser. The TSC spectras were observed in the temperature range of -100[$^{\circ}C$] to 130[$^{\circ}C$] with the electric field of 20∼60[MV/m], had show four of the distinguished peak such as ${\alpha}$$_1$, ${\alpha}$$_2$, ${\beta}$ and ${\gamma}$, which appeared at 115, 80, 17 and -30[$^{\circ}C$] respectively. Specially, ${\alpha}$$_1$ was observed and anomalous TSC flowing in the same direction as the charging current on the high-electric field such as 50∼60[MV/m]. In according on the consequences obtained from the studies, the origin of ${\alpha}$$_1$peak was attributed to the detrapping process form trap with 2.88[eV] deep of injected space charge from the chathode in the crystaline regions. The origin of ${\alpha}$$_2$ peak was regarded as the detrapping process of ions trapped with 0.9[eV] deep originated from impurity-ion remained in the specimen during production process of the material, in the crystalline regions. The origin of ${\beta}$ peak was concluded to be due to the depolarization process of "C=0"dipole with the activation energy of 0.75[eV] in the amorphous regions. The origin of ${\gamma}$ peak was responsible to the process combined with the depolarization of "CH$_3$", chain segment, with the activation energy of carriers from the shallow trap with 0.4[eV], in he amorphous regions.

• Journal of Information Processing Systems
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• v.14 no.4
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• pp.989-1009
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• 2018

Rapid advances in science and technology with exponential development of smart mobile devices, workstations, supercomputers, smart gadgets and network servers has been witnessed over the past few years. The sudden increase in the Internet population and manifold growth in internet speeds has occasioned the generation of an enormous amount of data, now termed 'big data'. Given this scenario, storage of data on local servers or a personal computer is an issue, which can be resolved by utilizing cloud computing. At present, there are several cloud computing service providers available to resolve the big data issues. This paper establishes a framework that builds Hadoop clusters on the new single-board computer (SBC) Mobile Raspberry Pi. Moreover, these clusters offer facilities for storage as well as computing. Besides the fact that the regular data centers require large amounts of energy for operation, they also need cooling equipment and occupy prime real estate. However, this energy consumption scenario and the physical space constraints can be solved by employing a Mobile Raspberry Pi with Hadoop clusters that provides a cost-effective, low-power, high-speed solution along with micro-data center support for big data. Hadoop provides the required modules for the distributed processing of big data by deploying map-reduce programming approaches. In this work, the performance of SBC clusters and a single computer were compared. It can be observed from the experimental data that the SBC clusters exemplify superior performance to a single computer, by around 20%. Furthermore, the cluster processing speed for large volumes of data can be enhanced by escalating the number of SBC nodes. Data storage is accomplished by using a Hadoop Distributed File System (HDFS), which offers more flexibility and greater scalability than a single computer system.

• The KIPS Transactions:PartC
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• v.15C no.1
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• pp.19-30
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• 2008

Sensor nodes are used as a storage space in the data centric storage method for sensor networks. Sensor nodes save the data to the node which is computed by hash table and users also access to the node to get the data by using hash table. One of the problems which the data centric storage method has is that queries from many users who are interested in the popular data could be concentrated to one node. In this case, responses for queries could be delayed and the energy of heavy loaded node could be dissipated fast. This would lead to reduction of network life time. In this paper, ALT, Data Centric Storage based on Adaptive Local Trajectory, is proposed as scalable data centric storage method for sensor network. ALT constructs trajectory around the storage node. The scope of trajectory is increased or decreased based on the query frequency. ALT distributes the query processing loads to several nodes so that delay of response is reduced and energy dissipation is also distributed.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1999.11a
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• pp.529-532
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• 1999

본 연구에서는 유기 전기 발광 소자에서 녹색 발광층으로 사용되는 terbium(Tb) complexes와 europium(Eu) complex, 정공 수송층으로 사용되는 TPD (N, N\`-diphenyl-N,\`(3-methylphenyl)-1, 1\`biphenyl-4, 4\`-diamine), 그리고 전자 수송층으로 사용되는 Alq$_{3}$ (trois(8-hydroxyquinolino)aluminum), Bebq$_2$들의 Uv/Vis. 홉광도와 PL 스펙 트럼과 같은 광학적 특성을 조사하였으며 또한 이러한 물질들을 이용하여 다양한 종류의 유기 전기 발광 소자를 제작하고 제작된 소자들의 전류밀도-전압-조도 등의 전기 . 광학적 특성을 조사하였으며, 그 결과 다 음과 같은 결곤을 얻을 수 있었다. 다양한 ligand를 갖는 Tb complex들의 경우에도 EL 스펙트럼의 파장대 (wavelength)는 546nm~548nm의 녹색 발광을 하는 것을 알 수 있었고, 제작된 소자 중에서 Tb(ACAC)$_3$(Phen) 을 발광충으로 하고, TPD, 그리고 Bebq$_2$를 각각 정공 수송층, 전자 수송 층으로 한 소자가 가장 낮은 구동 전압을 갖는다는 것을 확인하였으며 logJ-logV 특성에서도 모든 전계 구간에서 이러한 구조의 소자가 가장 높은 전류밀도를 나타냈으며 저 전계 구간에서 전류밀도 타이가 가장 컸다. 소자의 전류밀도와 휘도의 관계에 있어서는 제작된 네 종류의 소자 중 Tb(ACAC)3(Cl-Phen)를 발광층으로 하고 TPD, 그리고 Bebq2를 각각 정공 수송층, 전자 수송 층으로 한 소자가 가장 휘도가 우수한 것을 알 수 있었다. 또한 red (europium complex), green (terbium complex), 그리고 blue (TPD) 색깔을 나타내는 유기 재료를 사용하여 한 소자에서 백색 소자를 제작하여 cyclic voltametric방법을 이용하여 각 유기 물질들의 에너지 준위를 조사하여, 각각의 소자들을 에너지 밴드 다이어그램(energy band diagram)으로 자세히 설명하였다.

• Tunnel and Underground Space
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• v.30 no.1
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• pp.15-28
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• 2020

In this study, a procedure was introduced to estimate strength and deformation modulus of the 3-D discrete fracture network(DFN) systems using the distinct element method(DEM). Fracture entities were treated as non-persistent square planes in the DFN systems. Systematically generated fictitious fractures having similar mechanical characteristics of intact rock were combined with non-persistent real fractures to create polyhedral blocks in the analysis domain. Strength and deformation modulus for 10 m cube domain of various deterministic and stochastic 3-D DFN systems were estimated using the DEM to explore the applicability of suggested method and to examine the effect of fracture geometry on strength and deformability of DFN systems. The suggested procedures were found to effective in estimating anisotropic strength and deformability of the 3-D DFN systems.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.12 no.9
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• pp.4250-4256
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• 2011

Mn catalyst promoted with Cu were prepared and tested for selective catalytic reduction of $NO_x$ with $NH_3$. Performance of each catalyst was investigated for $NO_x$ activity while changing temperature, space velocity, water content and $O_2$ concentration. Hydrogen conversion efficiency of catalyst was also measured in the $H_2$-TPR system. The inhibition effect of water on catalyst was investigated with the on-off control of water supply. High activity of Mn-Cu catalyst was observed for $160{\sim}260^{\circ}C$. It is found that increase of oxygen concentration acts as a promotor to the increase of catalyst activity but water content acts as a inhibitor.

• Journal of Korea Multimedia Society
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• v.10 no.2
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• pp.236-245
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• 2007

Wireless sensor networks consist of numerous nodes equipped with small-sized and limited calculation capacities and storage space as well as low-capacity batteries. Therefore, the key issue is to reduce energy consumption of sensor nodes in sensor network environment. To reduce energy consumption of sensor nodes, consideration must be given to decreasing frequency of messages transmitted by nodes. Also, considering network application, security of sensor networks is also considered important. Therefore, this study proposes a key distribution scheme in dynamic clustering model. The dynamic clustering model used for this scheme is very effective in extending life span of wireless sensor networks. The proposed scheme provides improved security compared to the existing key distribution scheme by applying grid-based key distribution scheme and allocating polynomial s hare to the nodes forming a cluster. Also, comparison was made with the previously proposed grid-based, location-based and cluster-based key distribution schemes to illustrate the advantages of the proposed scheme.

• Journal of the Korean Solar Energy Society
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• v.28 no.4
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• pp.17-24
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• 2008

Estimation of typical solar radiation is very important for the calculations concerning many solar applications. But solar radiation measurements are not easily available because of the expensive measuring equipment and techniques required. Accordingly, for regions where no solar radiation is measured, solar radiation need to be estimated using other meteorological data. However, currently in Korea, there is no study on how to do this. In this paper, the global radiation of the six major cities in South Korea where the global radiation is measured using comparatively simple CRM model was calculated compared and analyzed. The comparison between the original coefficient and the site-fitted coefficient for these cities are as follows. Differences between the site-fitted coefficient and the original coefficient for six cities are small. Except for Gwangju, both calculations show strong correlation. In case of Seoul, the $R^2$(coefficient of determination) were 0.747 and 0.749. In case of Busan and Daegu the figures were 0.817, 0.819 and 0.820, 0.821 respectively. For Gwangju, these were 0.618 and 0.622, Thus, the site-fitted coefficients were slightly higher for these four cities. On the other hand, Daejeon and Incheon was reported 0.773, 0.772 and 0.785, 0.783, respectively.

• Tunnel and Underground Space
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• v.29 no.2
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• pp.89-107
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• 2019

Rock joints have an extremely important role in analyzing the mechanical stability and hydraulic characteristics of rock mass structures. Most rock joint parameters are generally indicated as a distribution by statistical techniques. In this research, calculation technique of Joint Center Volume (JCV) is analyzed, which is required for estimating the size distribution having the largest uncertainty among the joint parameters, then a new technique is proposed which is applicable regardless of the shape of survey window. The existing theoretical JCV calculation technique can be applied only to the plane window, and the complete enumeration techniques show the limitations in joint trace type and analysis time. This research aims to overcome the limitations in survey window shape and joint trace type through calculating JCV by using Monte Carlo simulation. The applicability of proposed technique is validated through the estimation results at non-planar survey windows such as curved surface and tunnel surface.