• 한국통신학회논문지
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• 제36권6C호
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• pp.376-383
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• 2011

UWB(Ultra Wide Band) 다중경로 채널에서 첫번째 경로를 통해 수신되는 신호가 가장 큰 신호가 아닐 경우가 종종 있으며, 이러한 경우 ToA(Time-of-Arrival) 추정의 정밀도를 유지하는 것은 매우 어려운 문제가 된다. 또한 UWB 신호의 초광대역 특성상 동기식 시스템을 구현할 경우 수신기는 매우 높은 표본화율을 이용해 신호를 수신해야 하기 때문에 복잡도가 증가되는데, 압축센싱(Compressed Sensing) 이론을 이용함으로써 시스템의 복잡도를 효율적으로 낮출 수 있다. 이에 본 논문은 압축센싱 기반의 UWB 수신기의 장점을 이용하면서도 정밀 추정성능을 제공할 수 있는 개선된 ToA 추정 기법을 제안한다. 모의실험 결과를 통해 광범위한 신호대잡음비 환경에서 제안된 기법이 다른 저복잡도 기법들의 성능보다 우수함을 확인하였다.

• 한국인터넷방송통신학회논문지
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• 제15권3호
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• pp.137-141
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• 2015

모바일 클라우드 컴퓨팅은 모바일 기기의 자원 제약적인 문제를 해결하기 위해 클라우드 서비스를 활용한다. 이렇게 모바일 기기에서 수행해야할 작업을 클라우드로 위임하는 것을 오프로딩이라고 하고 에너지 소모의 관점에서 많은 연구들이 진행되고 있다. 본 논문에서는 응답 시간의 관점에서 오프로딩 기법 적용의 효율성을 측정하기 위해 센 싱 데이터 동기화를 고려한 응답 시간 모델을 설계하였다. 제안 모델에서는 클라우드에서 모바일 기기가 요청한 작업 을 처리할 때 필요한 센싱 데이터에 대한 동기화 작업을 고려하여 정교한 응답 시간 예측을 가능하도록 했으며 모의실험을 통해 새로운 센서 데이터의 발생 비율과 동기화 주기가 응답 시간에 어떤 영향을 주는지를 확인하였다.

• Journal of Communications and Networks
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• 제14권5호
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• pp.471-480
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• 2012

Reliable detection of primary user activity increases the opportunity to access temporarily unused bands and prevents harmful interference to the primary system. By extracting a global decision from local sensing results, cooperative sensing achieves high reliability against multipath fading. For the effective combining of sensing results, which is generalized by a likelihood ratio test, the fusion center should learn some parameters, such as the probabilities of primary transmission, false alarm, and detection at the local sensors. During the training period in supervised learning, the on/off log of primary transmission serves as the output label of decision statistics from the local sensor. In this paper, we extend unsupervised learning techniques with an expectation maximization algorithm for cooperative spectrum sensing, which does not require an external primary transmission log. Local sensors report binary hard decisions to the fusion center and adjust their operating points to enhance learning performance. Increasing the number of sensors, the joint-expectation step makes a confident classification on the primary transmission as in the supervised learning. Thereby, the proposed scheme provides accurate parameter estimates and a fast convergence rate even in low signal-to-noise ratio regimes, where the primary signal is dominated by the noise at the local sensors.

• 한국소음진동공학회논문집
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• 제26권6_spc호
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• pp.651-659
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• 2016

Condition monitoring (CM) encounters a large data problem due to sensors that measure vibration data with a continuous, and sometimes, high sampling rate. In this study, compressive sensing approaches for condition monitoring are proposed to demonstrate the efficiency in handling a large amount of data and to improve the damage detection capability of the current condition monitoring process. Compressive sensing is a novel sensing/sampling paradigm that takes much fewer samples compared to traditional sampling methods. For the experiments a built-in rotating system was used and all data were compressively sampled to obtain compressed data. Optimal signal features were then selected without the reconstruction process and were used to detect and classify damage. The experimental results show that the proposed method could improve the data processing speed and the accuracy of condition monitoring of rotating systems.

• Smart Structures and Systems
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• 제30권2호
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• pp.183-193
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• 2022

Structural health monitoring and structural vibration control are multidisciplinary and frontier research directions of civil engineering. As intelligent materials that integrate sensing and actuation capabilities, shape memory alloys (SMAs) exhibit multiple excellent characteristics, such as shape memory effect, superelasticity, corrosion resistance, fatigue resistance, and high energy density. Moreover, SMAs possess excellent resistance sensing properties and large deformation ability. Superfine NiTi SMA wires have potential applications in structural health monitoring and micro-drive system. In this study, the mechanical properties and electrical resistance sensing characteristics of superfine NiTi SMA wires were experimentally investigated. The mechanical parameters such as residual strain, hysteretic energy, secant stiffness, and equivalent damping ratio were analyzed at different training strain amplitudes and numbers of loading-unloading cycles. The results demonstrate that the detwinning process shortened with increasing training amplitude, while austenitic mechanical properties were not affected. In addition, superfine SMA wires showed good strain-resistance linear correlation, and the loading rate had little effect on their mechanical properties and electrical resistance sensing characteristics. This study aims to provide an experimental basis for the application of superfine SMA wires in engineering.

• 한국구조물진단유지관리공학회 논문집
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• 제27권5호
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• pp.139-146
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• 2023

In this study, compressive strength and adhesion strength were measured as repair materials to evaluate the mechanical and electrical properties of compression and shear specimens with self-sensing repair materials. As a result of the experiment, the strength improvement rate of the compression test specimen was higher than the section enlargement area ratio, but the shear test specimen did not show an improvement in strength as much as the section enlargement area ratio. Compression experiments under load showed high correlation between FCR-Strain and FCR-Stress, confirming self-sensing performance. However, the shear test did not show as much correlation as the compression test. Accordingly, it is judged that the self-sensing repair material is suitable for the compression member on which the compression load acts in the building.

• Agricultural and Biosystems Engineering
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• 제7권1호
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• pp.18-26
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• 2006

In-field site-specific nitrogen (N) management increases crop yield, reduces N application to minimize the risk of nitrate contamination of ground water, and thus reduces farming cost. Real-time N sensing and fertilization is required for efficient N management. An 'on-the-go' site-specific N management system was developed and evaluated for the supplemental N application to com (Zea mays L.). This real-time N sensing and fertilization system monitored and assessed N fertilization needs using a vision-based spectral sensor and controlled the appropriate variable N rate according to N deficiency level estimated from spectral signature of crop canopies. Sensor inputs included ambient illumination, camera parameters, and image histogram of three spectral regions (red, green, and near-infrared). The real-time sensor-based supplemental N treatment improved crop N status and increased yield over most plots. The largest yield increase was achieved in plots with low initial N treatment combined with supplemental variable-rate application. Yield data for plots where N was applied the latest in the season resulted in a reduced impact on supplemental N. For plots with no supplemental N application, yield increased gradually with initial N treatment, but any N application more than 101 kg/ha had minimal impact on yield.

• 센서학회지
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• 제16권6호
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• pp.434-440
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• 2007

Two kinds of new NOx sensing mechanism was proposed and examined. One of those was potentiomtric sensor based on the measurement of decomposed oxygen from NO using YSZ porous diffusion barrier and Pd catalytic electrode. The sensor based on decomposed oxygen measurement responded to the range of 300 - 1000 ppm NO in $N_{2}$ environment and the sensitivities were coincident with theoretical values at 700 and $800^{\circ}C$ but the decomposition rate depended on gas flow rate. The other sensor was equilibrium potentiometric type using $Gd_{2}O_{3}$-nitrates solid solution as sensing material. The sensor using $Gd_{2}O_{3}$-nitrates solid solution was suitable for NOxxsensing at $700^{\circ}C$ in 5 % oxygen and the sensitivity was 19.3 mV/decade. However, long term stability of the sensing material at high temperature was not sufficient.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제13권6호
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• pp.2873-2892
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• 2019

Reducing the interference to the licensed mobile users and obtaining the energy efficiency are key issues in cognitive heterogeneous networks. A corresponding rate loss constraint is proposed to be used for the sensing-based spectrum sharing (SBSS) model in cognitive heterogeneous networks in this paper. Resource allocation optimization strategy is designed for the maximum energy efficiency under the proposed interference constraint together with average transmission power constraint. An efficiency algorithm is studied to maximize energy efficiency due to the nonconvex optimal problem. Furthermore, the relationship between the proposed protection criterion and the conventional interference constraint strategy under imperfect sensing condition for the SBSS model is also investigated, and we found that the conventional interference threshold can be regarded as the upper bound of the maximum rate loss that the primary user could tolerate. Simulation results have shown the effectiveness of the proposed protection criterion overcome the conventional interference power constraint.

• 한국환경과학회지
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• 제30권5호
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• pp.369-378
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• 2021

In this study, we investigated the effects of indole on biofilm formation inhibition in Pantoea agglomerans (P. agglomerans). In the biofilm growth assay, indole inhibited biofilm formation across all the growth time. Depending on biofilm growth stage, indole exhibited biofilm inhibition and anti-bacterial effects on planktonic cells. Through the analysis of the proportion rate between biofilm and Colony Forming Units (CFU) and inhibition rate of indole, we confirmed that depending on the biofilm stage of P. agglomerans, indole treatment timing was more important than the treatment duration. By comparing gene expression rates through rt-qPCR P.agglomerans affected by indole was found to significantly change quorum sensing (pagI/R) and indole transportation (bssS) gene expressions. Throughout all, indole exhibited both antimicrobial and anti-biofilm effects on P. agglomerans. In addition, we confirmed the anti-biofilm effects of indole on mature biofilm. In conclusion, indole as a signal molecule, can exhibit anti-biofilm effects through bacterial quorum sensing inhibition and indole affects. Therefore, indole can regulate biofilm bacteria especially gram-negative opportunistic pathogens.