• KSII Transactions on Internet and Information Systems (TIIS)
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• 제13권3호
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• pp.1238-1259
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• 2019

Saving energy is a big challenge for Wireless Sensor Networks (WSNs), which becomes even more critical in large-scale WSNs. Most energy waste is communication related, such as collision, overhearing and idle listening, so the schedule-based access which can avoid these wastes is preferred for WSNs. On the other hand, clustering technique is considered as the most promising solution for topology management in WSNs. Hence, providing interference-free clustering is vital for WSNs, especially for large-scale WSNs. However, schedule management in cluster-based networks is never a trivial work, since it requires inter-cluster cooperation. In this paper, we propose a clustering method, called Interference-Free Clustering Protocol (IFCP), to partition a WSN into interference-free clusters, making timeslot management much easier to achieve. Moreover, we model the clustering problem as a multi-objective optimization issue and use non-dominated sorting genetic algorithm II to solve it. Our proposal is finally compared with two adaptive clustering methods, HEED-CSMA and HEED-BMA, demonstrating that it achieves the good performance in terms of delay, packet delivery ratio, and energy consumption.

• Advances in aircraft and spacecraft science
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• 제2권1호
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• pp.95-108
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• 2015

Automatic Dependent Surveillance Broadcast (ADS-B) is quickly being adopted by aviation safety authorities around the world as the standard for aircraft tracking. The technology provides the opportunity for live tracking of aircraft positions within range of an ADS-B receiver stations. Currently these receiver stations are bound by land and local infrastructural constraints. As such there is little to no coverage over oceans and poles, over which many commercial flights routinely travel. A low cost space based ADS-B receiving system is proposed as a constellation of small satellites. The possibility for a link between aircraft and satellite is dependent primarily on proximity. Calculating the likelihood of a link between two moving targets when considering with the non-periodic and non-uniform nature of actual aircraft flight-paths is non-trivial. This analysis of the link likelihood and the performance of the tracking ability of the satellite constellation has been carried out by a direct simulation of satellites and aircraft. Parameters defining the constellation (satellite numbers, orbit size and shape, orbit configuration) were varied between reasonable limits. The recent MH370 disappearance was simulated and potential tracking and coverage was analysed using an example constellation. The trend of more satellites at a higher altitude inclined at 60 degrees was found to be the optimal solution.

• Smart Structures and Systems
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• 제29권1호
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• pp.181-193
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• 2022

Data-driven structural health monitoring (SHM) of civil infrastructure can be used to continuously assess the state of a structure, allowing preemptive safety measures to be carried out. Long-term monitoring of large-scale civil infrastructure often involves data-collection using a network of numerous sensors of various types. Malfunctioning sensors in the network are common, which can disrupt the condition assessment and even lead to false-negative indications of damage. The overwhelming size of the data collected renders manual approaches to ensure data quality intractable. The task of detecting and classifying an anomaly in the raw data is non-trivial. We propose an approach to automate this task, improving upon the previously developed technique of image-based pre-processing on one-dimensional (1D) data by enriching the features of the neural network input data with multiple channels. In particular, feature engineering is employed to convert the measured time histories into a 3-channel image comprised of (i) the time history, (ii) the spectrogram, and (iii) the probability density function representation of the signal. To demonstrate this approach, a CNN model is designed and trained on a dataset consisting of acceleration records of sensors installed on a long-span bridge, with the goal of fault detection and classification. The effect of imbalance in anomaly patterns observed is studied to better account for unseen test cases. The proposed framework achieves high overall accuracy and recall even when tested on an unseen dataset that is much larger than the samples used for training, offering a viable solution for implementation on full-scale structures where limited labeled-training data is available.

• 무역상무연구
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• 제17권
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• pp.251-293
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• 2002

The study is a comparative and analytical study which comprises of the analysis of the rules of the buyer's right to withhold performance where the seller delivers defective goods or documents of three legal systems; the CISG, English law and Korean law. The purposes underlying this study are twofold. The first is to clarify the current position as to the right of withholding performance in the event of the seller's tender of defective goods or documents in Korean law, CISG and English law so that it may assist the parties in drafting the buyer's right to withhold performance in their own contract. The second is to compare the rules of one jurisdiction with those of other jurisdictions and to evaluate the rules in light of the practical functions and benefits of the right to withhold performance and the discipline of comparative law the basic question of which is whether a solution from one jurisdiction may facilitate the systematic development and reform of another jurisdiction. It shows that each jurisdiction does not have any provision or case law specifically dealing with the buyer's right to withhold performance where the seller delivers the goods which are defective in terms of quality or quantity. The absence of such provision or case in each jurisdiction has resulted in either disputes or uncertainty. However, the study executed in light of the primary functions and benefits of the right in practice and the discipline of comparative law reveals that, first, the view in English law which is against recognizing the right may not be justified when one considers the practical importance of having the right and the position taken by the CISG as a well developed and modernized law, second, the view in Korean law which argues that the principle of specific goods dogma on which it is based is extended even to substitutable or repairable goods cannot be also justified on the ground of one's ordinary expectation and the position under the CISG and English law which imposes a contractual duty to deliver non-defective goods on the seller insofar as the buyer's payment is deemed to be made in exchange for the seller's delivery of non-defective goods and they are substitutable or repairable. Regarding the right to withhold performance in the event of the seller's tender of defective documents, the study shows that the relatively detailed rules in English law may be utilized as a guideline to fill the gap in the CISG and Korean law in terms of the practicability and appropriateness to govern documentary sales. Furthermore, it is found that the position in English law which confers on the buyer the right to withhold performance for a trivial defect in documents may be unreasonable in terms of one's need to enable justice to be done in individual cases.