• Journal of the Korea Institute of Information and Communication Engineering
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• v.13 no.11
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• pp.2447-2458
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• 2009

Ad hoc wireless networks operate without any infrastructure where a node can be a source and a router at the same time. This indispensably requires high throughput and low delay performance throughout the wireless network coverage span, particularly under heavy traffic conditions. Recent research on using multiple antennas in beam-forming or multiplexing modes over a wireless channel has shown promising results in terms of high throughput and low delay. Directional antennas have shown to increase spatial reuse by allowing multiple transmitters and receivers to communicate using. directional beams as long as they do not significantly interfere with each other. However directional antenna performance asymptotically approaches the omni-directional performance in a high density ad hoc network. Simulation results in QualNet validate that average throughput and packet corruption ratio of directional antenna approach omni-directional performance. Moreover, we further highlight some important issues pertaining to the directional antenna performance in wireless networks.

• Proceedings of the Korean Society for Rock Mechanics Conference
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• 2000.09a
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• pp.171-181
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• 2000

Many Studies of tunnel and tunnelling safety have been developed continuously based on the increasing social interests in underground space since 1990's in Korea. Because the growth of population in metropolitan has been accelerated at a faster pace than the development of the cities, underground facilities have been created as a great extent in view of less land space available. In this study, a lot of types of tunnel failure were surveyed and the detail causes were studied after many cases of tunnel failure were collected. There were suggested brief countermeasure of tunnel failure through case study. An expert system was developed to predict the safety of tunnel and choose proper tunnel reinforcement system using fuzzy quantification theory and fuzzy inference rule based on tunnel information database. The comparison result between the predicted reinforcement system level and measured ones was very similar. In-situ data were obtained in three tunnel sites including subway tunnel under Han river. This system will be very helpful to make the most of in-situ data and suggest proper applicability of tunnel reinforcement system developing more resonable tunnel support method from dependance of some experienced experts for the absent of guide.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.27 no.2
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• pp.208-211
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• 2016

Device-to-Device communication(D2D) enables devices in proximity to communicate directly without going through the network infrastructure. In particular, D2D communications in a cellular network can improve the spectral efficiency by allowing the reuse of cellular resources. However, it is not easy to maintain the channel quality of the D2D links and to protect the cellular links from the D2D interferences, since the resource allocations for the cellular users will change with time due to the time-varying nature of the cellular channels. To mitigate the performance degradation of D2D links, we propose to exploit unlicensed bands as auxiliary resources when the D2D links share the uplink cellular resources. The effectiveness of the proposed scheme is verified through simulations.

• Proceedings of the Korea Water Resources Association Conference
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• 2021.06a
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• pp.392-392
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• 2021

자료동화(data assimilation) 기법은 관측 자료와 예측 모형의 정보를 동시에 활용, 모형의 상태량(state variables)이나 매개변수(model parameters)를 실시간으로 업데이트하는 Bayesian 필터링 이론에 근거한 방법으로, 최근 이를 활용한 수문 모의 정확도 향상 기술이 빠르게 발전하고 있다. 본 연구에서는 앙상블 자료동화의 정확성을 향상시키기 위한 세부 방법인 along-the-stream localization과 inflation 기법의 분포형 수문 모형에 대한 적용성을 대규모 지역 단위(regional-scale) 모의를 통해 검토한다. 분포형 수문모형과 자료동화 framework로는 WRF-Hydro(Weather Research and Forecasting Model Hydrological Modeling System)와 DART(Data Assimilation Research Testbed)를 각각 적용한다. WRF-Hydro는 미국의 전 대륙지역(CONUS; continental United States)에 대한 수문 모델링 framework인 National Water Model의 핵심엔진이고, DART는 미국 National Center for Atmospheric Research(NCAR) 연구소에서 개발한 범용 자료동화 도구이다. 본 연구에서는 지표수 수문모형의 자료동화를 위해 개발된 기법인 along-the-stream localization과 inflation 기법이 하도 추적에 미치는 영향을 분석한다. along-the stream localization 기법은 공간적 근접도 외에 하도의 수문학적 연관관계를 고려하는 localization 기법으로, 상대적으로 수문학적 상관도가 떨어지는 하도에 대한 과도한 자료동화를 줄여줄 수 있다. inflation 기법은 앙상블의 다양성을 증가시키는 기법으로, 칼만 필터(Kalman filter)에 의한 업데이트의 이전이나 이후 적용하여 앙상블 예측의 정확도를 추가적으로 향상시킬 수 있다. 본 고에서는 앙상블 자료동화 기법을 지표수 수문 모의에 적용할 경우 남아 있는 난제와 적용 가능한 방법에 대해 중점적으로 논의한다.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.34 no.5
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• pp.503-514
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• 2016

Delineation of accurate object boundaries is crucial to provide reliable spatial information products such as digital topographic maps, building models, and spatial database. In LiDAR(Light Detection and Ranging) data, real boundaries of the buildings exist somewhere between outer-most points on the roofs and the closest points to the buildings among points on the ground. In most cases, areas of the building footprints represented by LiDAR points are smaller than actual size of the buildings because LiDAR points are located inside of the physical boundaries. Therefore, building boundaries determined by points on the roofs do not coincide with the actual footprints. This paper aims to estimate accurate boundaries that are close to the physical boundaries using airborne LiDAR data. The accurate boundaries are determined from the non-gridded original LiDAR data using initial boundaries extracted from the gridded data. The similar method implemented in this paper is also found in demarcation of the maritime boundary between two territories. The proposed method consists of determining initial boundaries with segmented LiDAR data, estimating accurate boundaries, and accuracy evaluation. In addition, extremely low density data was also utilized for verifying robustness of the method. Both simulation and real LiDAR data were used to demonstrate feasibility of the method. The results show that the proposed method is effective even though further refinement and improvement process could be required.

• International Area Studies Review
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• v.22 no.4
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• pp.189-208
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• 2018

This study validates if this relationship results in differences of significance levels between first time and repeat visitors and analyzes if there exist any differences in the spatial characteristics of tourist attractions using Social Network Analysis(SNA) for the spacial attributes of movement network Focusing on Hwaseong city, South Korea. It is important for balanced development between tour sites in Hwaseong by enhancing the value of tourism resources and applying the concept of hub-and-spoke tourism development. Based on the analyzing the centrality of tourist movement networks, degree centrality, closeness centrality, and betweenness centrality all did not show much variation for 20 tourist attractions versus the top five. That is, the attractions that both first time and repeat visitors visit are concentrated in well-known, famous places. The authors hope that this study, which defines practical interactions among attractions based movement, will be used as practical data for developing tourist retention marketing strategies.

• Journal of Korean Tunnelling and Underground Space Association
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• v.11 no.2
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• pp.175-188
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• 2009

When a new tunnel is excavated by the drill and blast method near pre-existing underground structures or tunnels due to the region restricted condition such as urban area, the ground will be relaxed by the excavation. In this case, issues can be created in terms of stability of pre-existing underground structures. One of major factors determining the stability of pre-existing underground structures can be a separation distance between pre-existing underground structures and a newly excavated tunnel. The region of ground relaxation defined by the plastic zone due to new excavation can be varied by separation distance. In this study, in other to estimate an influence of new tunnel excavation in terms of separation distance on the stability of pre-existing large pipelines, two-dimensional scaled model tests using plaster were performed for six models which have a different separation distance, The results show that based on the analysis of induced displacement during tunnel construction, the displacement decreases as the separation distance between large pipeline and new tunnel is increased until the distance is 2.5 times of pipeline diameter. Beyond this point, however, the displacement has become stabilized.

• Radiation Oncology Journal
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• v.21 no.3
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• pp.238-244
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• 2003

Purpose: The Planning of High-Dose-Rate (HDR) brachytherapy treatments are becoming individualized and more dependent on the treatment planning system. Therefore, computer software has been developed to perform independent point dose calculations with the integration of an isodose distribution curve display into the patient anatomy images. Meterials and Methods: As primary input data, the program takes patients'planning data including the source dwell positions, dwell times and the doses at reference points, computed by an HDR treatment planning system (TPS). Dosimetric calculations were peformed in a $10\times12\times10\;Cm^3$ grid space using the Interstitial Collaborative Working Group (ICWG) formalism and an anisotropy table for the HDR Iridium-192 source. The computed doses at the reference points were automatically compared with the relevant results of the TPS. The MR and simulation film images were then imported and the isodose distributions on the axial, sagittal and coronal planes intersecting the point selected by a user were superimposed on the imported images and then displayed. The accuracy of the software was tested in three benchmark plans peformed by Gamma-Med 12i TPS (MDS Nordion, Germany). Nine patients'plans generated by Plato (Nucletron Corporation, The Netherlands) were verified by the developed software. Results: The absolute doses computed by the developed software agreed with the commercial TPS results within an accuracy of $2.8\%$ in the benchmark plans. The isodose distribution plots showed excellent agreements with the exception of the tip legion of the source's longitudinal axis where a slight deviation was observed. In clinical plans, the secondary dose calculations had, on average, about a $3.4\%$ deviation from the TPS plans. Conclusion: The accurate validation of complicate treatment plans is possible with the developed software and the qualify of the HDR treatment plan can be improved with the isodose display integrated into the patient anatomy information.

• Journal of Korean Tunnelling and Underground Space Association
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• v.18 no.5
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• pp.499-509
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• 2016

In recent years, the use of underground spaces becomes more frequent and the demands for urban tunnels are rapidly increasing. The urban tunnels constructed in the ground with a shallow and soft cover might be deformed in various forms on the face, which would lead, the tunnels to behavior 3-dimensionally, which may have a great impact on the longitudinal load transfer. The tunnel face might deform in various forms depending on the construction method, overburden and the heterogeneity of the ground. And accordingly, the type and size of the distribution of the load transferred to the ground adjacent to the tunnel face as well as the form of the loosened ground may appear in various ways depending on the deformation form of the tunnel face. Therefore, in this study was conducted model tests by idealizing the deformation behavior of the tunnel face, that were constant deformation, the maximum deformation on the top and the maximum deformation on the bottom. And the test results were analyzed focusing on the deformation of the face and the longitudinal load transfer at the ground above the tunnel. As results, it turned out that the size and the distribution type of the load, which was transferred to the tunnel as well as the earth pressure on the face were affected by the deformation type of the face. The largest load was transferred to the tunnel when the deformation was in a constant form. Less load was transferred when the maximum deformation on the bottom, and the least load was transferred when the maximum deformation on the top. In addition, it turned out that, if the cover became more shallow, a longitudinal load transfer in the tunnel would limited to the region close to the face; however, if the cover became higher than a certain value, the area of the load transfer would become wider.

• Archives of design research
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• v.17 no.3
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• pp.283-292
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• 2004

Today's fast-paced world is becoming increasingly characterized by technology-facilitated transactions. Growing numbers of customers interact with technology to create service outcomes instead of interacting with a service firm employee. Self-service technologies provide technological interfaces that enable customers to produce a service independent of direct service employee involvement. To investigate on the customer satisfaction with self-technological based product design in Subway. I used the critical incident technique developed by Flanagan(1954) with quantitative measures of attributions. In this research, it results that customers are considered more important the value of technological-function and easy to use than the aspect of automated machine. It is likely that the technological aspect of many self-service options has a unique influence on customer perceptions of self-service encounters. Also, Research has shown that customer's needs are defined as situations in which external environmental factors add a sense of urgency to the transaction and saved time. On the other hand, customers realize that their favorable image of self-technological based product follows as ; first, customers prefer to the simple & modern image on the aspect of product design, secondly, customers prefer to the hitech-functional image to do its job fast in a short time by automated technology on the aspect of functional service, thirdly, customers prefer to the comfortable and sanitary image to be suitable for the underground circumstance.