• Journal of Korean Society of Water and Wastewater
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• v.31 no.6
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• pp.511-519
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• 2017

Multi-regional water supply system, which installed for supplying multiple water demands, is characterized by large-sized, long-distance, tree-type layout. This system is vulnerable to long-standing service interruption when a pipe breaks is occurred. In this study, a numerical method is proposed to calculate drainage time that directly affects time of service interruption. To begin with, governing equations are formulated to embed the delayed drainage effect by the friction loss, and to resolve complicated connection of pipelines, which are derived from the continuity and energy equations. The nonlinear hydraulic equations are solved by using explicit time integration method and the Newton-Raphson method. The developed model is verified by comparing the result with analytical solution. Furthermore, the model's applicability is validated by the examples of pipelines in serial, in parallel, and complex layout. Finally, the model is utilized to suggest an appropriate actions to reduce the deviation of draining time in the C transmission line of the B multi-regional water supply system.

• Proceedings of the Korea Water Resources Association Conference
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• 2008.05a
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• pp.345-351
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• 2008

미래의 기후변화 영향평가에 있어 전지구모형(General Circulation Model)은 가장 중요한 자료 중 하나이다. 즉, 온실가스 방출(emission) 시나리오에 기초한 전지구모형의 모의결과를 이용하면 미래 수자원에 대한 정보를 얻을 수 있다. 하지만 미래 수자원은 방출 시나리오, 상세화(downscaling) 기법, 강우-유출모형, 전지구모형의 종류에 따라 크게 달라질 수 있어 매우 큰 불확실성(uncertainty)을 포함하고 있다. 이러한 불확실성을 줄이는 방법 중 하나로 전지구모형의 모의능력에 따라 가중치(weight)를 부여하고 결합(combining)하는 multi-model 앙상블(ensemble) 기법이 선진국을 중심으로 활발히 연구되고 있다. 본 연구에서는 우선 기후변화 영향평가를 위하여 국내에서 사용가능한 전지구모형을 조사하고 그 중CCSM3, CSRIO, ECHAM4, GFDL, MIRCO를 선택하였다. 한강 충주댐 유역에 대하여 과거($1980{\sim}1999$년)와 미래($2030{\sim}2049$년) 기간에 대하여 전지구모형의 기후정보를 간단한 선형보간법을 이용하여 상세화하였다. 다음으로 multi-model 앙상블 기법을 조사하였다. 본 연구에서는 Giorgi et al.(2002)이 제안한 Reliability Ensemble Average(REA) 기법을 적용하여 선형보간법으로 상세화한 전지구모형의 모의결과에 가중치를 주어 불확실성을 줄이는 연구를 수행하였다. 특히 REA를 구성하는 식 중 모형의 편차(bias) 뿐만 아니라 분산(variance)까지 고려함으로서 이를 개선하는 Modified-REA를 제안하였다. 제안한 방안을 이용하여 결합한 전지구모형의 모의결과가 기존 REA의 결과보다 기후정보의 불확실성을 더 줄일 수 있는 것으로 나타났다.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.11 no.1
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• pp.18-38
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• 2017

Infrastructure-as-a-Service (IaaS) clouds provide infrastructure as a pool of virtual resources, and the public IaaS clouds, e.g. Amazon Web Service (AWS) and private IaaS cloud toolkits, e.g. OpenStack, CloudStack, etc. provide their own application programming interfaces (APIs) for managing the cloud resources they offer. The heterogeneity of the APIs, however, makes it difficult to access and use the multiple cloud services concurrently and collectively. In this paper, we explore previous efforts to solve this problem and present our own implementation of an integrated cloud API, which can make it possible to access and use multiple clouds collectively in a uniform way. The implemented API provides a RESTful access and hides underlying cloud infrastructures from users or applications. We show the implementation details of the integrated API and performance evaluation of it comparing the proprietary APIs based on our cloud testbed. From the evaluation results, we could conclude that the overhead imposed by our interface is negligibly small and can be successfully used for multi-cloud access.

• Journal of Soil and Groundwater Environment
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• v.16 no.6
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• pp.46-57
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• 2011

In this study, analytical solution of multip-species transport equations coupled with a first-order reaction network under constant concentration boundary condition or total flux boundary condition is obtained using similarity transformation approach of Clement et al. (2000). The study shows the schematic process about how multi-species transport equations with first-order sequential reaction network is transformed through the similarity transformation approach into independent and uncoupled single species transport equations with first-order reaction. The analytical solution was verified through the comparison with popular commercial programs such as 2DFATMIC and RT3D. The analytical solution can be utilized in nuclear waste sites where radioactive contaminants and their daughter products occur and in industrial complex cities where chlorinated solvent such as PCE, TCE, and its biodegradation products produces. In addition, it can help the verification of the developed numerical code.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.11 no.2
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• pp.670-686
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• 2017

MapReduce (MRV1), a popular programming model, proposed by Google, has been well used to process large datasets in Hadoop, an open source cloud platform. Its new version MapReduce 2.0 (MRV2) developed along with the emerging of Yarn has achieved obvious improvement over MRV1. However, MRV2 suffers from long finishing time on certain types of jobs. Speculative Execution (SE) has been presented as an approach to the problem above by backing up those delayed jobs from low-performance machines to higher ones. In this paper, an adaptive SE strategy (ASE) is presented in Hadoop-2.6.0. Experiment results have depicted that the ASE duplicates tasks according to real-time resources usage among work nodes in a cloud. In addition, the performance of MRV2 is largely improved using the ASE strategy on job execution time and resource consumption, whether in a multi-job environment.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.7 no.8
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• pp.1805-1824
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• 2013

Recently, the use of wireless body area networks (WBAN) has been increasing rapidly in medical healthcare applications. WBANs consist of smart nodes that can be used to sense and transmit vital data such as heart rate, temperature and ECG from a human body to a medical centre. WBANs depend on limited resources such as energy and bandwidth. In order to utilise these resources efficiently, a very well organized medium access control (MAC) protocol must be considered. In this paper, a new, adaptive and energy-efficient MAC protocol, entitled isMAC, is proposed for WBANs. The proposed MAC is based on multi-channel communication and aims to prolong the network lifetime by effectively employing (i) a collision prevention mechanism, (ii) a coordinator node (WCN) selection algorithm and (iii) a transmission power adjustment approach. The isMAC protocol has been developed and modelled, by using OPNET Modeler simulation software. It is based on a networking scenario that requires especially high data rates such as ECG, for performance evaluation purposes. Packet delay, network throughput and energy consumption have been chosen as performance metrics. The comparison between the simulation results of isMAC and classical IEEE 802.15.4 (ZigBee) protocol shows that isMAC significantly outperforms IEEE 802.15.4 in terms of packet delay, throughput and energy consumption.

• Journal of the Korea Computer Industry Society
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• v.9 no.2
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• pp.53-62
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• 2008

Intensive studies have been made in the area of IPTV VOD server. The basic goal of the study is to find an efficient mechanism to allow maximum number of users under the limited resources such as Buffer utilization, disk performance and network bandwidth. The overlay multicast that has been recently presented as an alternative for the IP multicast has been getting much persuasion by the system resource and the network bandwidth and the advancement of the network cost. we propose a efficient overlay multi_casting network policy for multimedia services with multi media partition storage. Simulation results show that the rate of service number and service time of proposed scheme are about 23% performance improved than that of traditional methods. This implies that our method can allow much more users for given resources.

• Korean Journal of Remote Sensing
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• v.21 no.5
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• pp.393-404
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• 2005

As multi-source spatial data fusion mainly deal with various types of spatial data which are specific representations of real world with unequal reliability and incomplete knowledge, proper data representation and uncertainty analysis become more important. In relation to this problem, this paper presents and applies an advanced data representation methodology for different types of spatial data such as categorical and continuous data. To account for the uncertainties of both categorical data and continuous data, fuzzy boundary representation and smoothed kernel density estimation within a fuzzy logic framework are adopted, respectively. To investigate the effects of those data representation on final fusion results, a case study for landslide hazard mapping was carried out on multi-source spatial data sets from Jangheung, Korea. The case study results obtained from the proposed schemes were compared with the results obtained by traditional crisp boundary representation and categorized continuous data representation methods. From the case study results, the proposed scheme showed improved prediction rates than traditional methods and different representation setting resulted in the variation of prediction rates.

• International Journal of Computer Science & Network Security
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• v.21 no.12
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• pp.175-182
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• 2021

Deadlock is a situation in which two or more processes competing for resources are waiting for the others to finish, and neither ever does. There are two different forms of systems, multi-unit and single-unit resource systems. The difference is the number of instances (or units) of each type of resource. Deadlock problem can be modeled as a constrained combinatorial problem that seeks to find a possible scheduling for the processes through which the system can avoid entering a deadlock state. To solve deadlock problem, several algorithms and techniques have been introduced, but the use of metaheuristics is one of the powerful methods to solve it. Genetic algorithms have been effective in solving many optimization issues, including deadlock Problem. In this paper, an improved parallel framework of the genetic algorithm is introduced and adapted effectively and efficiently to deadlock problem. The proposed modified method is implemented in java and tested on a specific dataset. The experiment shows that proposed approach can produce optimal solutions in terms of burst time and the number of feasible solutions in each advanced generation. Further, the proposed approach enables all types of crossovers to work with high performance.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.16 no.9
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• pp.3152-3171
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• 2022

This work investigates the physical layer secrecy of a multi-antenna hybrid satellite-terrestrial relay networks (HSTRN) with jamming, in which a satellite aims to make communication with a destination user by means of a relay, along with spatially random eavesdroppers. In order to weaken the signals of eavesdroppers, the conventional relay can also generate intentional interference, besides forwarding the received signal. Shadowed-Rician fading is adopted in satellite link, while Rayleigh fading is adopted in terrestrial link, eavesdropper link and jamming link. The analytical and asymptotic formulas for the system secrecy outage probability (SOP) are characterized. Practical insights on the diversity order of the network are revealed according to the asymptotic behavior of SOP at high signal-to-noise ratio (SNR) regime. Then, analysis of the system throughput is examined to assess the secrecy performance. In the end, numerical simulation results are presented to validate the theoretical analysis and point out: (1) The secrecy performance of the considered network is affected by the channel fading scenario, the system configuration; (2) Decrease of the relay coverage airspace can provide better SOP performance; (3) Jamming from the relay can improve secrecy performance without additional network resources.