• KSII Transactions on Internet and Information Systems (TIIS)
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• 제6권12호
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• pp.3046-3060
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• 2012

Low power listening (LPL) MAC protocols based on duty-cycling mechanism have been studied extensively to achieve ultra low energy consumption in wireless sensor networks (WSNs). Especially, recent ACK-based LPL schemes such as X-MAC employ strobe preambles and an early ACK, and show fair performances in communications and energy efficiencies. However, the state-of-the-art ACK-based LPL scheme still suffers from collision problems due to the protocol incompleteness. These collision effects are not trivial and make WSNs unstable, aggravate energy consumptions. In this paper, we propose two novel schemes; (i) ${\tau}$-duration CCA to mitigate the collision problem in ACK-based LPL MAC protocols. (ii) Short Preamble Counter (SPC) to conserve more energy by reducing unnecessary overhearing. We demonstrate the performance improvement of our scheme via a mathematical analysis and real-time experiments. Both analysis and experimental results confirm that our proposed scheme saves energy by up to 36% compared to the naive ACK-based LPL MAC protocol thanks to ${\tau}$-duration CCA and SPC.

• 한국측량학회지
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• 제23권4호
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• pp.359-366
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• 2005

3차원 지형정보에 대한 사용자 요구의 증가에 따라 GPS/INS, 레이저 스캐너 시스템이 조합된 항공레이저측량 기술이 각광받고 있다. 본 논문에서는 항공레이저측량(LiDAR) 시스템의 정확도 확보를 위해 검정장에서의 측량데이터를 바탕으로 시스템 검정을 실시하였다. 검정결과, 수평 정확도는 ${\pm}15{\sim}30\;cm$ 이내, 수직정확도는 ${\pm}15cm$ 이내로 나타났다. 이를 통해 항공레이저측량 데이터를 이용하여 정밀 DEM 및 등고선 제작. 도시지역의 3차원 모델 제작, 엔지니어링 설계 등의 활용에 충분함을 입증하였다.

• Steel and Composite Structures
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• 제18권1호
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• pp.1-28
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• 2015

In this paper, the dynamic response of functionally gradient steel (FGS) composite cylindrical panels in steady-state thermal environments subjected to impulsive loads is investigated for the first time. FGSs composed of graded ferritic and austenitic regions together with bainite and martensite intermediate layers are analyzed. Thermo-mechanical material properties of FGS composites are predicted according to the microhardness profile of FGS composites and approximated with appropriate functions. Based on the three-dimensional theory of thermo-elasticity, the governing equations of motionare derived in spatial and time domains. These equations are solved using the hybrid Fourier series expansion-Galerkin finite element method-Newmark approach for simply supported boundary conditions. The present solution is then applied to the thermo-elastic dynamic analysis of cylindrical panels with three different arrangements of material compositions of FGSs including ${\alpha}{\beta}{\gamma}M{\gamma}$, ${\alpha}{\beta}{\gamma}{\beta}{\alpha}$ and ${\gamma}{\beta}{\alpha}{\beta}{\gamma}$ composites. Benchmark results on the displacement and stress time-histories of FGS cylindrical panels in thermal environments under various pulse loads are presented and discussed in detail. Due to the absence of similar results in the specialized literature, this paper is likely to fill a gap in the state of the art of this problem, and provide pertinent results that are instrumental in the design of FGS structures under time-dependent mechanical loadings.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제11권9호
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• pp.4398-4417
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• 2017

Multi-user Multiple-Input and Multiple-Output (MU-MIMO) has potential for prominently enhancing the capacity of wireless network by simultaneously transmitting to multiple users. User selection is an unavoidable problem which bottlenecks the gain of MU-MIMO to a great extent. Major state-of-the-art works are focusing on improving network throughput by using Channel State Information (CSI), however, the overhead of CSI feedback becomes unacceptable when the number of users is large. Some work does well in balancing tradeoff between complexity and achievable throughput but is lack of consideration of fairness. Current works universally ignore the rational utilizing of time resources, which may lead the improvements of network throughput to a standstill. In this paper, we propose TOUSE, a scalable and fair user selection scheme for MU-MIMO. The core design is dynamic-time-warping-based user selection mechanism for downlink MU-MIMO, which could make full use of concurrent transmitting time. TOUSE also presents a novel data-rate estimation method without any CSI feedback, providing supports for user selections. Simulation result shows that TOUSE significantly outperforms traditional contention-based user selection schemes in both throughput and fairness in an indoor condition.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제17권12호
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• pp.3383-3397
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• 2023

Scene graphs serve as semantic abstractions of images and play a crucial role in enhancing visual comprehension and reasoning. However, the performance of Scene Graph Generation is often compromised when working with biased data in real-world situations. While many existing systems focus on a single stage of learning for both feature extraction and classification, some employ Class-Balancing strategies, such as Re-weighting, Data Resampling, and Transfer Learning from head to tail. In this paper, we propose a novel approach that decouples the feature extraction and classification phases of the scene graph generation process. For feature extraction, we leverage a transformer-based architecture and design an adaptive calibration function specifically for predicate classification. This function enables us to dynamically adjust the classification scores for each predicate category. Additionally, we introduce a Distribution Alignment technique that effectively balances the class distribution after the feature extraction phase reaches a stable state, thereby facilitating the retraining of the classification head. Importantly, our Distribution Alignment strategy is model-independent and does not require additional supervision, making it applicable to a wide range of SGG models. Using the scene graph diagnostic toolkit on Visual Genome and several popular models, we achieved significant improvements over the previous state-of-the-art methods with our model. Compared to the TDE model, our model improved mR@100 by 70.5% for PredCls, by 84.0% for SGCls, and by 97.6% for SGDet tasks.

• 예술인문사회 융합 멀티미디어 논문지
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• 제7권2호
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• pp.227-236
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• 2017

양자점 셀룰라 오토마타(QCA: quantum-dot cellular automata)는 나노 규모의 크기와 낮은 전력 소비로 각광받고 있으며, CMOS 기술 규모의 한계를 극복할 수 있는 대체 기술로 떠오르고 있다. 다양한 QCA 회로들이 연구되고 있고, 그 중 카운터와 상태 제어에 필요한 래치는 순차 회로의 구성 요소로서 제안되어 왔다. 래치는 이전 상태를 유지하기 위한 피드백 구조의 형태를 가지고 있으며, 이를 QCA 상에서 구현하기 위해 4 클럭을 소모하는 사각형 형태의 루프 구조를 사용한다. 기존의 QCA 상에서 제안된 래치는 동일 평면상에서 제안되었으며, 피드백 구조를 구현하기 위해 많은 셀과 클럭이 소모되었다. 본 논문에서는 이러한 단점을 개선하기 위해서 다층 구조를 이용한 새로운 형태의 SR 래치와 D 래치를 제안한다. 제안한 3차원 루프 구조는 다층 구조 기반의 설계이며 총 3개의 층으로 구성한다. 각 층의 배선은 다른 층과 영향을 받지 않도록 인접한 배선 간 2 클럭 차이를 주어 설계한다. 설계된 래치 구조는 시뮬레이션을 수행하고 기존의 래치와 비교 및 분석한다.

• 국제초고층학회논문집
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• 제1권1호
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• pp.37-51
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• 2012

New generation of tall and complex buildings systems are now introduced that are reflective of the latest development in materials, design, sustainability, construction, and IT technologies. While the complexity in design is being overcome by the availability and advances in structural analysis tools and readily advanced software, the design of these buildings are still reliant on minimum code requirements that yet to be validated in full scale. The involvement of the author in the design and construction planning of Burj Khalifa since its inception until its completion prompted the author to conceptually develop an extensive survey and real-time structural health monitoring program to validate all the fundamental assumptions mad for the design and construction planning of the tower. The Burj Khalifa Project is the tallest structure ever built by man; the tower is 828 meters tall and comprises of 162 floors above grade and 3 basement levels. Early integration of aerodynamic shaping and wind engineering played a major role in the architectural massing and design of this multi-use tower, where mitigating and taming the dynamic wind effects was one of the most important design criteria established at the onset of the project design. Understanding the structural and foundation system behaviors of the tower are the key fundamental drivers for the development and execution of a state-of-the-art survey and structural health monitoring (SHM) programs. Therefore, the focus of this paper is to discuss the execution of the survey and real-time structural health monitoring programs to confirm the structural behavioral response of the tower during construction stage and during its service life; the monitoring programs included 1) monitoring the tower's foundation system, 2) monitoring the foundation settlement, 3) measuring the strains of the tower vertical elements, 4) measuring the wall and column vertical shortening due to elastic, shrinkage and creep effects, 5) measuring the lateral displacement of the tower under its own gravity loads (including asymmetrical effects) resulting from immediate elastic and long term creep effects, 6) measuring the building lateral movements and dynamic characteristic in real time during construction, 7) measuring the building displacements, accelerations, dynamic characteristics, and structural behavior in real time under building permanent conditions, 8) and monitoring the Pinnacle dynamic behavior and fatigue characteristics. This extensive SHM program has resulted in extensive insight into the structural response of the tower, allowed control the construction process, allowed for the evaluation of the structural response in effective and immediate manner and it allowed for immediate correlation between the measured and the predicted behavior. The survey and SHM programs developed for Burj Khalifa will with no doubt pioneer the use of new survey techniques and the execution of new SHM program concepts as part of the fundamental design of building structures. Moreover, this survey and SHM programs will be benchmarked as a model for the development of future generation of SHM programs for all critical and essential facilities, however, but with much improved devices and technologies, which are now being considered by the author for another tall and complex building development, that is presently under construction.

• 스마트미디어저널
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• 제13권1호
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• pp.86-100
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• 2024

최근 문화정책 기반 연구과제 및 공공기업들의 홍보수단으로 가상현실 전시형 콘텐츠 서비스가 적지 않게 제작되고 있다. 특히 시각, 예술, 기록 등 문화자원을 기초로 하는 대부분의 아카이브 자료들이 엔티티 기반 데이터모델링 개념으로 활용되고 있는 점이 두드러진다. 하지만 3차원 예술작품을 데이터화하여 축적하는 일은 결코 쉬운 일이 아니다. 현재 공공기관 메타데이터들의 실태를 살펴보면 오래된 국제표준을 기반으로 구축되었기 때문에 디지털트윈을 개발할 때 자원 디지털화의 부재가 있었다. 기존 시스템의 기능을 뛰어넘는 용량과 속도로 다차원 데이터들을 연결함에 데이터모델링 진화가 불가피하다는 점을 발견하였다. 따라서 우선 선행연구 중에 데이터모델링 설계의 요소들과 개념들을 고찰하였고 가상현실 콘텐츠를 개발할 때 3차원 모델링 데이터들의 마이그레이션을 위해 설계되는 경우 기존에 작성된 메타데이터를 분석하여 3차원 모델링에서 추가되어야만 하는 상위요소들을 개선하는 연구를 하였다. 나아가 본 연구에서는 새롭게 작성된 메타데이터를 데이터모델링 프로세스에 맞게 가상현실 콘텐츠에서 활용되는 과정을 직접 구현하여 가능성을 실증해 보았다. 이를 통해 개발자들이 가상현실 전시콘텐츠 제작에서 시소러스를 어떻게 데이터로 연결하는 과정을 검증하였고 메타데이터를 작성하는 사용자에게는 디지털 요소로 추가되어야 하는 필수요소들을 제안하였다. 향후 본 연구에서 도출된 데이터 방식으로 시각예술기록 및 3차원 모델링 데이터모델링 구조를 점진적으로 발전해 나간다면 앞으로 메타데이터 기반 데이터모델링이 현재보다 유의미해지고 개발자들의 공공데이터 활용성에 대해 더욱 향상할 것을 기대해 본다.

• Earthquakes and Structures
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• 제5권1호
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• pp.49-65
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• 2013

This article presents the statistical characteristics of elastic floor acceleration spectra that represent the peak response demand of non-structural components attached to a nonlinear supporting frame. For this purpose, a set of stiff and flexible general moment resisting frames with periods of 0.3-3.6 sec. are analyzed using forty-nine near-field strong ground motion records. Peak accelerations are derived for each single degree of freedom non-structural component, supported by the above mentioned frames, through a direct-integration time-history analysis. These accelerations are obtained by Floor Acceleration Response Spectrum (FARS) method. They are statistically analyzed in the next step to achieve a better understanding of their height-wise distributions. The factors that affect FARS values are found in the relevant state of the art. Here, they are summarized to evaluate the amplification and/or reduction of FARS values especially when the supporting structures undergo inelastic behavior. The properties of FARS values are studied in three regions: long-period, fundamental-period and short-period. Maximum elastic acceleration response of non-structural component, mounted on inelastic frames, depends on the following factors: inelasticity intensity and modal periods of supporting structure; natural period, damping ratio and location of non-structural component. The FARS values, corresponded to the modal periods of supporting structure, are strongly reduced beyond elastic domain. However, they could be amplified in the transferring period domain between the mentioned modal periods. In the next step, the amplification and/or reduction of FARS values, caused by inelastic behavior of supporting structure, are calculated. A parameter called the response acceleration reduction factor ($R_{acc}$), has been previously used for far-field earthquakes. The feasibility of extending this parameter for near-field motions is focused here, suggested repeatedly in the relevant sources. The nonlinearity of supporting structure is included in ($R_{acc}$) for better estimation of maximum non-structural component absolute acceleration demand, which is ordinarily neglected in the seismic design provisions.

• Smart Structures and Systems
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• 제20권2호
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• pp.163-173
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• 2017

Structural health monitoring (SHM) of civil infrastructure using fiber Bragg grating sensor networks (FBGSNs) has received significant public attention in recent years. However, there is currently little research on the health-monitoring technology of high-piled wharfs in coastal ports using the fiber Bragg grating (FBG) sensor technique. The benefits of FBG sensors are their small size, light weight, lack of conductivity, resistance corrosion, multiplexing ability and immunity to electromagnetic interference. Based on the properties of high-piled wharfs in coastal ports and servicing seawater environment and the benefits of FBG sensors, the SHM system for a high-piled wharf in the Tianjin Port of China is devised and deployed partly using the FBG sensor technique. In addition, the health-monitoring parameters are proposed. The system can monitor the structural mechanical properties and durability, which provides a state-of-the-art mean to monitor the health conditions of the wharf and display the monitored data with the BIM technique. In total, 289 FBG stain sensors, 87 FBG temperature sensors, 20 FBG obliquity sensors, 16 FBG pressure sensors, 8 FBG acceleration sensors and 4 anode ladders are installed in the components of the back platform and front platform. After the installation of some components in the wharf construction site, the good signal that each sensor measures demonstrates the suitability of the sensor setup methods, and it is proper for the full-scale, continuous, autonomous SHM deployment for the high-piled wharf in the costal port. The South 27# Wharf SHM system constitutes the largest deployment of FBG sensors for wharf structures in costal ports to date. This deployment demonstrates the strong potential of FBGSNs to monitor the health of large-scale coastal wharf structures. This study can provide a reference to the long-term health-monitoring system deployment for high-piled wharf structures in coastal ports.