• 한국통신학회논문지
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• 제33권9A호
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• pp.891-899
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• 2008

cdma2000 1xEV-DO 시스템은 기지국이 전송하는 이진(binary) 정보와 간단한 확률모델에 의해 역방향 링크의 전송속도를 제어한다. 하지만, 이 트래픽 제어방식은 각 단말이 자율적으로 전송속도를 결정하기 때문에 역방향 링크를 효과적으로 제어하기 어렵고 역방향 링크의 안성성을 보장하기도 쉽지 않다. 본 논문에서는 역방향 링크의 안정성을 향상시키기 위하여 트래픽 부하에 따른 단계별 전송속도 제어방법을 제안하고, 이를 이산시간 마르코프 프로세스로 모델링하여 성능을 분석한다. 다양한 환경에서 실시한 분석 결과를 통해 제안한 방법이 기존의 방법과 비교하여 보다 높은 전송속도를 지원함을 확인할 수 있다. 더불어, 제안한 방식은 표준규격에서 정의한 물리계층 구조를 변경하지 않으므로 이미 구축되어 있는 1xEV-DO 시스템과 호환이 가능한 장점을 가진다.

• 인간식물환경학회지
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• 제24권6호
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• pp.639-649
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• 2021

Background and objective: Various images from visual display terminals (VDTs) as well as living lighting are important parts of our daily life; thus, properly controlling the lighting environment - that is, illuminance, color temperature and good images from VDTs - can have a substantial effect on improving the mental health and work efficiency in everyday life. We examined electroencephalography (EEG) and heart rate variability (HRV) responses to various lighting conditions in 25 university students as they viewed images of a green landscape or traffic congestion. Methods: EEG was performed in darkness and when the room was illuminated with 10 different light-emitting diode (LED) color temperatures, while the EEG and HRV responses to green landscape or traffic congestion image stimuli were measured in darkness and during room illumination with three different LED color temperatures. Results: We found a significant difference between darkness and high LED illumination (400 lx) at 7 (CZ, F4, FZ, O1, O2, OZ, and T6) of 30 channels, while the alpha wave activity increased during darkness. In the second experiment, the green landscape image stimuli in the 30 lx-2600 K lighting condition elicited theta wave activity on the EEG, whereas the traffic congestion image stimuli under high LED illumination elicited high beta and gamma wave activities. Moreover, the subjects exhibited better stress coping ability and heart rate stability in response to green landscape image stimuli under illuminated conditions, according to their HRV. Conclusion: These results suggest that lower color temperatures and illumination levels alleviate tension, and that viewing green landscape image stimuli at low illumination, or in darkness, is effective for reducing stress. Conversely, high illumination levels and color temperatures are likely to increase tension and stress in response to traffic congestion image stimuli.

• International Journal of Control, Automation, and Systems
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• 제6권6호
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• pp.915-927
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• 2008

Networked control systems(NCSs) have gained increasing attention in recent years due to their advantages and potential applications. The network Quality-of-Service(QoS) in NCSs always fluctuates due to changes of the traffic load and available network resources. To handle the network QoS variations problem, this paper presents an intelligent scheduling control method for NCSs, where the sampling period and the control parameters are simultaneously scheduled to compensate the effect of QoS variation on NCSs performance. For NCSs with network-induced delays and packet dropouts, a discrete-time switch model is proposed. By defining a sampling-period-dependent Lyapunov function and a common quadratic Lyapunov function, the stability conditions are derived for NCSs in terms of linear matrix inequalities(LMIs). Based on the obtained stability conditions, the corresponding controller design problem is solved and the performance optimization problem is also investigated. Simulation results are given to demonstrate the effectiveness of the proposed approaches.

• Structural Engineering and Mechanics
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• 제59권2호
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• pp.373-385
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• 2016

During recent years researchers performed large effort to increase the service life and asphalt stability of the roads against traffic loads and weather conditions. Investigations carried out in various aspects such as changes in gradation, addition of various additives, changes in asphalt textures and etc. The objective of this research is to evaluate the advantages of adding recycled glass powder (RGP), Crumb Rubber (CR), styrene-butadiene rubber (SBR) and styrene butadiene styrene (SBS) to base bitumen with grade of 60/70 for modification of asphalt concrete. Initial studies conducted for determining the physical properties of bitumen and modifiers. A series of asphalt concrete samples made using various combinations of RGP, CR, SBR, SBS and base bitumen. All samples tested using Indirect Tensile Strength (ITS), Indirect Tensile Strength Modulus (ITSM) and Marshall Stability Tests. The new data compared with the results of control samples. The results showed that replacing RGP with known polymers improved ITS and ITSM results considerably. Also the Marshall Stability of modified mixtures using RGP is more than what is found for the base blend. Ultimately, the new RGP modifier had a huge impact on pavement performance and results in high flexibility which can be concluded as high service life for the new modified asphalt concrete.

• Smart Structures and Systems
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• 제18권2호
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• pp.217-231
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• 2016

The present work aims to develop piezoresistive sensors of excellent piezoresistive response attributable to change in nanoscale structures of multi-wall carbon nanotube (MWNT) embedded in cement. MWNT was distributed in a cement matrix by means of polymer wrapping method in tandem with the ultrasonication process. DC conductivity of the prepared samples exhibited the electrical percolation behavior and therefore the dispersion method adopted in this study was deemed effective. The integrity of piezoresistive response of the sensors was assessed in terms of stability, the maximum electrical resistance change rate, and sensitivity. A composite sensor with MWNT 0.2 wt.% showed the lowest stability and sensitivity, while the maximum electrical resistance change rate exhibited by this sample was the highest (96 %) among others and even higher than those found in the literature. This observation was presumably attributed by the percolation threshold and the tunneling effect. As a result of the MWNT content (0.2 wt.%) of the sensor being near the percolation threshold (0.25 wt.%), MWNTs were close to each other to trigger tunneling in response of external loading. The sensor with MWNT 0.2 wt.% was able to maintain the repeatable sensing capability while sustaining a vehicular loading on road, demonstrating the feasibility in traffic flow sensing application.

• 대한토목학회논문집
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• 제6권2호
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• pp.45-55
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• 1986

본(本) 연구(硏究)는 도시교통계획(都市交通計劃)에서 장래교통발생예측시(將來交通發生豫測時) 항상 문제(問題)로 되는 설명변수선택(說明變數選擇)의 애매성(曖昧性)을 해결(解決)하기 위하여 교통발생(交通發生)의 설명지표(說明指標)를 제안(提案)하는 동시(同時)에 최량(最良)의 도시교통발생(都市交通發生) Model을 작성(作成)하였다. 제안(提案)된 설명지표(說明指標)를 사용(使用)하여 목적별(目的別) 교통발생중회귀(交通發生重回歸) 모델을 작성(作成)하고, 단일변수(單一變數)로 설명(說明)이 가능(可能)한 것은 교통발생(交通발生)의 비손성(非負性)을 확보(確保)하기 위하여 단회귀(單回歸)모델로 수정(修正)하였다. 그러나 다변수(多變數)가 도입(導入)되어도 설명(說明)이 불충분(不充分)한 목적별(目的別) 교통(交通)(등교집중(等校集中)과 자유목적(自由目的)의 발생(發生)모델)은 동질(同質)의 토지이용활동(土地利用活動)으로부터 발생(發生)하는 교통(交通)의 발생특성(發生特性)이 유이(類似)함에 주목(注目)하여 각(各) zone을 특성별(特性別)로 분류(分類)하고 zone 군별(群別)로 교통발생(交通發生) 모델을 작성(作成)하여 통계적(統計的)으로 유의성(有意性)을 검토(檢討)하였다. 그리고 장래교통발생예측(將來交通發生豫測)은 단순(單純)하면서도 예측정도(豫測精度)의 제고(提高)가 바람직하므로 토지이용활동별(土地利用活動別)로 교통발생원단위(交通發生原單位)를 작성(作成)하고 안정성(安定性)을 고찰(考察)하여 교통발생예측시(交通發生豫測時) 실용가능(實用可能)한 원단위(原單位)를 제안(提案)하였다.

• 한국터널지하공간학회 논문집
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• 제19권1호
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• pp.41-56
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• 2017

최근 대도시에서는 교통량 증가 등으로 인해 대심도 터널 건설의 필요성이 날로 증대되고 있어서, 대심도 복층터널의 분기에 대한 연구가 필요한 실정이다. 때문에 본 연구에서는 FLAC 2D 프로그램을 이용하여 지반의 종류, 측압계수, 보강방법, 토피고를 매개변수로 선정하여 민감도 분석을 실시하였다. 궁극적으로 터널 분기부에서 최적의 분기부 형상 및 보강방법을 찾고자 하였다. 본 연구결과 일반적인 생각과 달리 박스형 확폭단면이 아치형보다 안정성이 높게 나타났다. 이는 아치형 굴착면적이 박스형보다 약 30% 정도 넓었기 때문인 것으로 판단된다. 또한 지반이 좋지 않은 경우는 록볼트 보강보다 강관그라우팅 보강 시의 안정성이 더 높았으며, 강관그라우팅의 보강두께와 범위는 확폭부의 안정성에 큰 영향을 끼치지 못하였다.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2009년도 춘계 학술발표회
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• pp.579-584
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• 2009

Arrangement of the facilities for improving harbor functions depends on sea and land conditions such as the ship's arrival and departure conditions, waves and tide. And the plan and the size of the facilities depend much on harbor and marine environment condition such as cargo quantity, ship size, ship traffic and seawater circulation. Among these, waves have so much effect on a breakwater design that it is the most important to understand their characteristics and to apply them to breakwater design. Therefore, to analyze the effect of waves characteristics over a rubble mound breakwater, we have calculated wave pressure by using numerical analysis at each tide level and have analyzed the effect of wave pressure on structure stability by conducting the stability analysis with the wave pressure. As a result, it is found that during low and mean tide level time the biggest wave pressure is estimated near calm water level. But during high tide time, the biggest wave pressure is estimated in front of capping. And the stability analysis indicates also that a structure is most unstable when low tide time wave pressure is acting on. After reviewing the stability of a structure by applying vertical and horizon wave forces, it is concluded that safety factor is lower than ordinary time(max. about 15%), is also reviewed when designing a rubble mound breakwater.

• 한국지반신소재학회논문집
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• 제21권1호
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• pp.49-56
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• 2022

본 연구에서는 공동이 발생된 도로 하부지반에서의 영향인자 분석과 지반의 안정성을 평가하기 위하여 다양한 영향인자(공동형상 및 규모, 포장층 두께, 교통하중의 크기)를 고려한 유한요소 수치해석을 수행하였다. 본 연구에서 적용된 수치해석 방법 및 결과에 대한 신뢰성을 검증하기 위하여 기존 연구 및 현장계측 결과와 비교·분석하였다. 수치해석 결과로부터 얻은 연직변위분포, 지표침하분포 및 침하량, 응력비 분포, 안전율 분포를 통해 영향인자 간의 상관관계를 분석하였으며, 도로 하부지반의 전반적인 역학적 거동 분석을 통해 지반의 안정성을 평가하였다. 그 결과, 공동규모 및 교통하중이 증가하고 포장층 두께가 감소할수록 공동 상부의 연직변위 및 지표침하량이 크게 나타났으며 허용안전율 미만의 위험지반영역이 증가하여 지반의 안정성 감소가 크게 나타난 것을 확인할 수 있었다. 또한 공동의 형상이 사각형일 경우 원형의 공동일 때보다 지반의 안정성 감소가 크게 나타났다. 이러한 결과를 통해 공동이 발생된 도로 하부지반의 전반적인 안정성에 대해 확인할 수 있었다.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제11권1호
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• pp.146-170
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• 2017

Joint channel assignment and routing is a well-known problem in multi-radio wireless mesh networks for which optimal configurations is required to optimize the overall throughput and fairness. However, other objectives need to be considered in order to provide a high quality service to network users when it deployed with high traffic dynamic. In this paper, we propose a re-configuration optimization model that optimizes the network throughput in addition to reducing the disruption to the mesh clients' traffic due to the re-configuration process. In this multi-objective optimization model, four objective functions are proposed to be minimized namely maximum link-channel utilization, network average contention, channel re-assignment cost, and re-routing cost. The latter two objectives focus on reducing the re-configuration overhead. This is to reduce the amount of disrupted traffic due to the channel switching and path re-routing resulted from applying the new configuration. In order to adapt to traffic dynamics in the network which might be caused by many factors i.e. users' mobility, a centralized heuristic re-configuration algorithm called State-Aware Joint Routing and Channel Assignment (SA-JRCA) is proposed in this research based on our re-configuration model. The proposed algorithm re-assigns channels to radios and re-configures flows' routes with aim of achieving a tradeoff between maximizing the network throughput and minimizing the re-configuration overhead. The ns-2 simulator is used as simulation tool and various metrics are evaluated. These metrics include channel-link utilization, channel re-assignment cost, re-routing cost, throughput, and delay. Simulation results show the good performance of SA-JRCA in term of packet delivery ratio, aggregated throughput and re-configuration overhead. It also shows higher stability to the traffic variation in comparison with other compared algorithms which suffer from performance degradation when high traffic dynamics is applied.