• 한국물환경학회지
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• 제31권3호
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• pp.295-303
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• 2015

In Korea, Total Maximum Daily Loads(TMDLs) has been enforced to restore and manage water quality in the watersheds. However, some assesment of implementation plan of TMDLs showed that the achievement of the target water quality is not related to the proper allocation loads because difference of flow duration interval. In the United States, the discharge loads are determined by water quality modeling considering standard flow conditions according to purpose. Therefore, this study tried to develop the allocation method considering economical efficiency using water quality model. For this purpose, several allocation methods being used in the management of TMDLs is investigated and develope an allocation criteria considering regional equality and uniformity. Since WARMF(Watershed Analysis Risk Management Framework) model can simulate the time varying behavior of a system and the various water quality variables, it was selected for a decision support system in this study. This model showed fairly good performance by adequately simulating observed discharge and water quality in Miho watershed. Furthermore, the scenario simulation results showed that the effect of annual average water quality improvement to remove 1kg BOD is more than 25 times, even if point pollutants treatment facility is six times more expensive to operate than non-point pollutants treatment facility.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제4권6호
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• pp.1098-1115
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• 2010

An inseparable challenge associated with every random access network is the design of an efficient Collision Resolution Algorithm (CRA), since collisions cannot be completely avoided in such network. To maximize the collision resolution efficiency of a popular CRA, namely Binary Exponential Backoff (BEB), we propose a reactive backoff algorithm. The proposed backoff algorithm is reactive in the sense that it updates the contention window based on the previously selected backoff value in the failed contention stage to avoid a typical type of collision, referred as cross-collision. Cross-collision would occur if the contention slot pointed by the currently selected backoff value appeared to be present in the overlapped portion of the adjacent (the previous and the current) windows. The proposed reactive algorithm contributes to significant performance improvements in the network since it offers a supplementary feature of Cross Collision Exclusion (XCE) and also retains the legacy collision mitigation features. We formulate a Markovian model to emulate the characteristics of the proposed algorithm. Based on the solution of the model, we then estimate the throughput and delay performances of WLAN following the signaling mechanisms of the Distributed Coordination Function (DCF) considering IEEE 802.11b system parameters. We validate the accuracy of the analytical performance estimation framework by comparing the analytically obtained results with the results that we obtain from the simulation experiments performed in ns-2. Through the rigorous analysis, based on the validated model, we show that the proposed reactive cross collision exclusionary backoff algorithm significantly enhances the throughput and reduces the average packet delay in the network.

• 한국시스템다이내믹스연구
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• 제14권3호
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• pp.25-49
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• 2013

As global competition for green car, that is environmentally friendly car, is getting tougher, the governments and the related industries are putting their core efforts in its diffusion. However, the green car sales are disappointing so far. To overcome the gridlock, it is necessary to develop concrete analytical framework to understand the diffusion process. Based on causal loop analysis from the previous work, we have identified main variables and relationships of them in the diffusion process and developed a stock-flow diagram and mathematical formula for the main components. The model would be applied for further quantitative simulation on the diffusion process of green car and other innovative goods as well. Also, we have suggested constructive insights for the policy makers and for the related industries. First, it is important to increase consumers' willingness to consider through marketing and word of mouth to accelerate the diffusion process. Second, in the perspective of the industry, the market share of green car should be increased at the earliest possible stage and this could be done by enhancing each components of green car attractiveness(e.g. price, driving range, social infra). Third, companies should develop a balanced investment between consumer and technology sector through a flexible financial policy. Fourth, the government continuously has the role of investing in the related R&D and social infra building. We expect the green car diffusion model and related formula from the research can provide meaningful tools to analyze the diffusion process of other new and innovative goods based on its deep researched literature review.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제13권10호
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• pp.4923-4939
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• 2019

In this paper, a secure transmission scheme based on the artificial noise is proposed for D2D communications underlaying the full-duplex cellular network, and a secure power allocation scheme to maximize the overall secrecy rate of both the cellular user and D2D transmitter node is presented. Firstly, the full-duplex base station transmits the artificial noise to guarantee the secure communications when it receives signals of cellular uplinks. Under this secure framework, it is found that improving the transmission power of the cellular user or the D2D transmitter node will degrade the secrecy rate of the other, although will improve itself secrecy rate obviously. Hence, a secure power allocation scheme to maximize the overall secrecy rate is presented subject to the security requirement of the cellular user. However, the original power optimization problem is non-convex. To efficiently solve it, we recast the original problem into a convex program problem by utilizing the proper relaxation and the successive convex approximation algorithm. Simulation results evaluate the effectiveness of the proposed scheme.

• Journal of Microbiology and Biotechnology
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• 제15권3호
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• pp.551-559
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• 2005

The recent rapid increase in genomic data related to many microorganisms and the development of computational tools to accurately analyze large amounts of data have enabled us to design several kinds of simulation approaches for the complex behaviors of cells. Among these approaches, dFBA (dynamic flux balance analysis), which utilizes FBA, differential equations, and regulatory events, has correctly predicted cellular behaviors under given environmental conditions. However, until now, dFBA has centered on substrate concentration, cell growth, and gene on/off, but a detailed hierarchical structure of a regulatory network has not been taken into account. The use of Boolean rules for regulatory events in dFBA has limited the representation of interactions between specific regulatory proteins and genes and the whole transcriptional regulation mechanism with environmental change. In this paper, we adopted the operon as the basic structure, constructed a hierarchical structure for a regulatory network with defined fundamental symbols, and introduced a weight between symbols in order to solve the above problems. Finally, the total control mechanism of regulatory elements (operons, genes, effectors, etc.) with time was simulated through the linkage of dFBA with regulatory network modeling. The lac operon, trp operon, and tna operon in the central metabolic network of E. coli were chosen as the basic models for control patterns. The suggested modeling method in this study can be adopted as a basic framework to describe other transcriptional regulations, and provide biologists and engineers with useful information on transcriptional regulation mechanisms under extracellular environmental change.

• 한국통신학회논문지
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• 제29권6B호
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• pp.575-583
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• 2004

본 논문에서는 MTS 정체 프레임워크를 윈도우 기반 정체 제어, 특히 TCP로 확장하고 TCP의 대역폭 소비 반응의 적극성을 LTS 자기유사성 네트워크 상태의 함수 형태에서 연구한다. RTT가 결정한 피드백 루프의 시간 한계를 초과하는 정보의 형태로 조정하는 LTS 제어모듈과 TCP를 연계시키는 방법으로 연구하며, 또 정보는 개연적인 특성을 갖고 여러 시간대에 걸쳐 분산되는 기존 윈도우를 기반으로 실현되기 때문에, 이를 효과적으로 활용할 수 있는 방법으로 개선하고, MTS TCP의 성능을 자기 유사성 트래픽의 물리적 모델링에 기반 한 시뮬레이션을 벤치마크 환경을 통해 수행된다. 본 논문은 자기유사성 트래픽 조건에서 프로토콜 스택의 전송 프로토콜 변화의 영향을 파악 및 평가하는 방법론을 활용하고, 과중한 워크로드 조건에서 시뮬레이션을 통해 성능 개선을 평가 비교한다.

• 한국통신학회논문지
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• 제34권9A호
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• pp.697-703
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• 2009

인지무선 통신장치(cognitive radio)는 일반적으로 일차 사용자(primary user)와의 간섭을 피하기 위해 어떠한 일차 사용자도 점유하고 있지 않은 주파수 자원을 활용한다. 그러나 비어있는 주파수 자원을 발견할 수 없을 경우, 인지무선 통신장치는 언더레이(underlay) 형태로 일차 사용자들과 주파수를 공유할 수 있으며, 이 때 스스로의 통신이 일차 사용자들에게 간섭을 미치지 않도록 전송 전력을 조절해야 한다. 본 논문은 셀룰라 네트워크의 상향링크 주파수 자원을 사용하는 언더레이 주파수 공유 방법을 제안한다. 셀룰라 네트워크의 범위 안에 존재하는 한쌍의 인지무선 통신장치들이 단방향 점대점(point-to-point) 통신 링크를 생성할 때 사용할 수 있는 전송 전력의 재한을 계산하고, 계산된 전송 전력을 적용할 수 있는 실용적인 상향 링크 공유 방안을 제시한다. 또한 시뮬레이션을 통해 제안된 상향 링크 공유 방안이 하향 링크 주파수 자원을 공유하는 것에 비해 인지무선 통신장치의 부담(overhead)을 줄일 뿐만 아니라 점대점 통신 링크의 수율(throughput) 성능을 향상시킬 수 있음을 보인다.

• 한국통신학회논문지
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• 제39B권10호
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• pp.708-714
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• 2014

무선 센서 네트워크는 일반적으로 에너지를 위해 배터리에 의존하는 밀집되게 배치된 센서 노드들로 구성된다. 이와 같이 여러 개로 밀집되게 배치된 센서 노드들은 에너지 낭비 및 센서 데이터의 높은 중복 전송을 야기한다. 상기 전원 관련 제약 및 높은 중복성과 같은 양자 문제는 센서 노드들 간의 적절한 노드 활동 스케줄링에 의해 해결될 수 있다. 본 논문에서는 우수한 커버리지 성능 보장 및 노드들 간 에너지 절약과 네트워크 수명의 연장을 위한 셀룰러 오토마타 (CA) 기반의 노드 스케줄링 알고리즘이 제안된다. 또한 CA 프레임워크에 기반하여 노드 스케줄링 알고리즘의 새로운 수학적 모델을 제안한다. 제안한 알고리즘은 스케줄링 결정을 위해 노드 내 지역 환경 조건의 변경 및 인접 노드들의 상태 정보를 이용한다. 본 논문은 제안한 방식을 적용한 시스템의 동작을 분석하고 시뮬레이션 결과를 통해 제안한 알고리즘이 센싱 커버리지 품질을 유지하면서 유의한 에너지 절약을 갖춘 에너지 균형을 보장함을 확인하였다.

• 한국지진공학회논문집
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• 제20권7_spc호
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• pp.435-441
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• 2016

The Korean peninsula has known as a minor-to-moderate seismic region. However, some recent studies had shown that the maximum possible earthquake magnitude in the region is approximately 6.3-6.5. Therefore, a seismic vulnerability assessment of the existing infrastructures considering ground motions in Korea is necessary. In this study, we developed seismic fragility curves for a continuous steel box girder bridge and two typical transmission towers, in which a set of seven artificial and natural ground motions recorded in South Korea is used. A finite element simulation framework, OpenSees, is utilized to perform nonlinear time history analyses of the bridge and a commercial software, SAP2000, is used to perform time history analyses of the transmission towers. The fragility curves based on Korean ground motions were then compared with the fragility curves generated using worldwide ground motions to evaluate the effect of the two ground motion groups on the seismic fragility curves of the structures. The results show that both non-isolated and base-isolated bridges are less vulnerable to the Korean ground motions than to worldwide earthquakes. Similarly to the bridge case, the transmission towers are safer during Korean motions than that under worldwide earthquakes in terms of fragility functions.

• 한국지반공학회논문집
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• 제36권8호
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• pp.7-15
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• 2020

인공신경망(ANN) 지진응답 예측모델 구성을 위해 다양한 지진파 및 지반 조건 하에서 구조물의 최대변위 및 최대 전단력 데이터베이스 구축이 필요하다. 하지만 3차원 컴퓨터 해석을 활용한 데이터베이스 구축은 많은 시간 및 인력, 비용을 발생시킨다. 본 연구에서는 주어진 지반의 포아송비와 전단파 속도에 대하여 건물의 지진응답을 예측할 수 있는 ANN 모델 개발 프레임워크를 소개하였다. 데이터베이스 구축에는 지반-상부 구조물 효과를 고려할 수 있는 간단한 단자유도 모델을 이용하였고 개발된 ANN 모델의 정확도를 결정계수(R²)를 통하여 논의하였다. 또한 구축된 데이터베이스의 백분위 90~100에서 ANN 모델을 구성하고 결정계수를 통해 각 백분위에서 ANN 모델의 정확도에 대하여 논의하였다.