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Your search keyword '"Exarchakos, Georgios"' showing total 125 results
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125 results on '"Exarchakos, Georgios"'

1. Communication protocol for a satellite-swarm interferometer

Author

Nagy, Oliver, Pandey, Manish, Exarchakos, Georgios, Bentum, Mark, and van der Hofstad, Remco

Subjects
Electrical Engineering and Systems Science - Signal Processing, Astrophysics - Instrumentation and Methods for Astrophysics
Abstract

Orbiting low frequency antennas for radio astronomy (OLFAR) that capture cosmic signals in the frequency range below 30MHz could provide valuable insights on our Universe. These wireless swarms of satellites form a connectivity graph that allows data exchange between most pairs of satellites. Since this swarm acts as an interferometer, the aim is to compute the cross-correlations between most pairs of satellites. We propose a k-nearest-neighbour communication protocol, and investigate the minimum neighbourhood size of each satellite that ensures connectivity of at least 95% of the swarm. We describe the proportion of cross-correlations that can be computed in our method given an energy budget per satellite. Despite the method's apparent simplicity, it allows us to gain insight into the requirements for such satellite swarms. In particular, we give specific advice on the energy requirements to have sufficient coverage of the relevant baselines.

Published
2023

3. In-network Hebbian Plasticity for Wireless Sensor Networks

Author

van der Lee, Tim, Exarchakos, Georgios, de Groot, Sonia Heemstra, Goos, Gerhard, Founding Editor, Hartmanis, Juris, Founding Editor, Bertino, Elisa, Editorial Board Member, Gao, Wen, Editorial Board Member, Steffen, Bernhard, Editorial Board Member, Woeginger, Gerhard, Editorial Board Member, Yung, Moti, Editorial Board Member, Montella, Raffaele, editor, Ciaramella, Angelo, editor, Fortino, Giancarlo, editor, Guerrieri, Antonio, editor, and Liotta, Antonio, editor

Published
2019
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8. Data Driven Transmission Power Control for Wireless Sensor Networks

Author

Kotian, Roshan, Exarchakos, Georgios, Liotta, Antonio, Hutchison, David, Series editor, Kanade, Takeo, Series editor, Kittler, Josef, Series editor, Kleinberg, Jon M., Series editor, Mattern, Friedemann, Series editor, Mitchell, John C., Series editor, Naor, Moni, Series editor, Pandu Rangan, C., Series editor, Steffen, Bernhard, Series editor, Terzopoulos, Demetri, Series editor, Tygar, Doug, Series editor, Weikum, Gerhard, Series editor, Di Fatta, Giuseppe, editor, Fortino, Giancarlo, editor, Li, Wenfeng, editor, Pathan, Mukaddim, editor, Stahl, Frederic, editor, and Guerrieri, Antonio, editor

Published
2015
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9. Predicting Battery Depletion of Neighboring Wireless Sensor Nodes

Author

Kotian, Roshan, Exarchakos, Georgios, Mocanu, Decebal Constantin, Liotta, Antonio, Hutchison, David, editor, Kanade, Takeo, editor, Kittler, Josef, editor, Kleinberg, Jon M., editor, Mattern, Friedemann, editor, Mitchell, John C., editor, Naor, Moni, editor, Nierstrasz, Oscar, editor, Pandu Rangan, C., editor, Steffen, Bernhard, editor, Sudan, Madhu, editor, Terzopoulos, Demetri, editor, Tygar, Doug, editor, Vardi, Moshe Y., editor, Weikum, Gerhard, editor, Aversa, Rocco, editor, Kołodziej, Joanna, editor, Zhang, Jun, editor, Amato, Flora, editor, and Fortino, Giancarlo, editor

Published
2013
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10. Tackling the Sheer Scale of Subjective QoE

Author

Menkovski, Vlado, Exarchakos, Georgios, Liotta, Antonio, Akan, Ozgur, Series editor, Bellavista, Paolo, Series editor, Cao, Jiannong, Series editor, Dressler, Falko, Series editor, Ferrari, Domenico, Series editor, Gerla, Mario, Series editor, Kobayashi, Hisashi, Series editor, Palazzo, Sergio, Series editor, Sahni, Sartaj, Series editor, Shen, Xuemin (Sherman), Series editor, Stan, Mircea, Series editor, Xiaohua, Jia, Series editor, Zomaya, Albert, Series editor, Coulson, Geoffrey, Series editor, Atzori, Luigi, editor, Delgado, Jaime, editor, and Giusto, Daniele, editor

Published
2012
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12. DACON: A reconfigurable application-centric optical network for disaggregated data center infrastructures [Invited]

Author

Guo, Xiaotao, Xue, Xuwei, Yan, Fulong, Pan, Bitao, Exarchakos, Georgios, Calabretta, Nicola, Guo, Xiaotao, Xue, Xuwei, Yan, Fulong, Pan, Bitao, Exarchakos, Georgios, and Calabretta, Nicola

Abstract

To solve the issues of low resource utilization and performance bottleneck in current server-centric data center networks (DCNs), we propose and experimentally demonstrate a disaggregated application-centric optical network (DACON) for data center infrastructures based on hybrid optical switches. DACON achieves flexible provision and dynamic reconfiguration of hardware nodes exploiting the softwared-define networking (SDN) orchestration plane. A four-node SDN-enabled disaggregated prototype is implemented with a field-programmable-gate-array-based controller of hardware nodes and nanosecond optical switches, performing a minimal node-to-node network latency of 378.6 ns and zero packet loss. Based on the unmodified Linux kernel and two different applications (distributed computing and a Memcached database), the application runtime of the disaggregated prototype is investigated and compared with the server-centric architecture. Experimental results show that the disaggregated prototype performs better with Memcached database applications, achieving a 1.46× faster runtime than the server-centric network at a memory node access ratio of 0.9. Based on the customized control plane orchestrator and dynamic resource reallocation, the node-to-node latency is reduced by 21% when CPU nodes access memory nodes. The scalability of DACON is then numerically assessed based on experimentally measured parameters. Results show that the intra-rack node-to-node latency is less than 404.8 ns with a 6144-node network and memory node access ratio of 0.9. Finally, the cost and power consumption are also studied and compared with current DCN architectures. Results indicate DACON saves 13.4% of the cost of an interconnect network compared with current disaggregated architecture and consumes up to 31.1% less power with respect to server-centric DCN architectures.

Published
2022

19. Experimental demonstration of SDN-enabled reconfigurable disaggregated data center infrastructure

Author

Universitat Politècnica de Catalunya. Departament de Teoria del Senyal i Comunicacions, Universitat Politècnica de Catalunya. GCO - Grup de Comunicacions Òptiques, Guo, Xiaotao, Agraz Bujan, Fernando, Xue, Xuwei, Pan, Bitao, Pagès Cruz, Albert, Zhang, Shaojuan, Exarchakos, Georgios, Spadaro, Salvatore, Calabretta, Nicola, Universitat Politècnica de Catalunya. Departament de Teoria del Senyal i Comunicacions, Universitat Politècnica de Catalunya. GCO - Grup de Comunicacions Òptiques, Guo, Xiaotao, Agraz Bujan, Fernando, Xue, Xuwei, Pan, Bitao, Pagès Cruz, Albert, Zhang, Shaojuan, Exarchakos, Georgios, Spadaro, Salvatore, and Calabretta, Nicola

Abstract

A 4-node prototype of SDN-controlled disaggregated data-center network is experimentally demonstrated based on the nanoseconds optical switch, enabling flexible hardware resource provisioning and dynamic resource reallocation. Experimental results show that, based on monitoring statistics, real-time reconfiguration reduces the memory node access latency by 21%., Peer Reviewed, Postprint (published version)

Published
2021

37. Distributed Reliable and Energy-Efficient Scheduling for LR-WPANs.

Author

VAN DER LEE, TIM, EXARCHAKOS, GEORGIOS, and DE GROOT, SONIA HEEMSTRA

Subjects
WIRELESS personal area networks, RESOURCE allocation, SCHEDULING, COMPUTER scheduling
Abstract

Pervasiveness of wireless networks drives the heterogeneity and density of devices in a vast diversity of environments. To achieve high reliability and low energy consumption while enabling pervasiveness is inherently a resource allocation problem. In low-rate wireless personal area networks, multi-frequency timedivision multiple access methods are identified as compelling solutions to resource allocation via scheduling transmissions in time and frequency. This work presents the TREE (TRaffic-aware Energy Efficient) algorithm, an adaptive and distributed scheduling algorithm, designed to provide high reliability in terms of packet reception ratio while optimizing the energy consumption of each device. This algorithm schedules communications according to the packets in the queue and short-memory performance. Decisions are made locally, and low-interference scheduling emerges at the network level. TREE is an adaptive threshold-based model that allocates more network resources (e.g., timeslots) when the communication queue size crosses a threshold and frees resources if the resource was underutilized. Implemented over IEEE-802.15.4-TSCH and extensively tested in simulation and on real deployments up to 81 devices, the algorithm is compared to MSF, Alice, and Orchestra, the state of the art in time-slotted channel hopping scheduling. Results highlight a high reliability regarding packet reception ratio and a lower energy consumption compared to the state of the art. [ABSTRACT FROM AUTHOR]

Published
2020
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45. The role of technetium Tc99m-tetrofosmin as head and neck tumor-seeking agent: a preliminary report

Author

Sioka, Chrissa, primary, Exarchopoulos, Thomas, additional, Skloupiotis, Vlasis, additional, Papathanassiou, Vaios, additional, Ragos, Vasileios, additional, Argyropoulou, Maria, additional, Gousia, Anna, additional, Tsekeris, Periklis, additional, Exarchakos, Georgios, additional, Assimakopoulos, Dimitrios, additional, and Fotopoulos, Andreas, additional

Published
2016
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49. Adaptation and Assessment of Reliability and Validity of the Greek Version of the Ohkuma Questionnaire for Dysphagia Screening.

Author

Papadopoulou, Soultana L., Exarchakos, Georgios, Christodoulou, Dimitrios, Theodorou, Stavroula, Beris, Alexandre, and Ploumis, Avraam

Subjects
*DEGLUTITION disorders, *CRONBACH'S alpha, *COHEN'S kappa coefficient (Statistics)
Abstract

Introduction The Ohkuma questionnaire is a validated screening tool originally used to detect dysphagia among patients hospitalized in Japanese nursing facilities. Objective The purpose of this study is to evaluate the reliability and validity of the adapted Greek version of the Ohkuma questionnaire. Methods Following the steps for cross-cultural adaptation, we delivered the validated Ohkuma questionnaire to 70 patients (53 men, 17 women) who were either suffering from dysphagia or not. All of them completed the questionnaire a second time within a month. For all of them, we performed a bedside and VFSS study of dysphagia and asked participants to undergo a second VFSS screening, with the exception of nine individuals. Statistical analysis included measurement of internal consistency with Cronbach's α coefficient, reliability with Cohen's Kappa, Pearson's correlation coefficient and construct validity with categorical components, and One-Way Anova test. Results According to Cronbach's α coefficient (0.976) for total score, there was high internal consistency for the Ohkuma Dysphagia questionnaire. Test-retest reliability (Cohen's Kappa) ranged from 0.586 to 1.00, exhibiting acceptable stability. We also estimated the Pearson's correlation coefficient for the test-retest total score, which reached high levels (0.952; p = 0.000). The One-Way Anova test in the two measurement times showed statistically significant correlation in bothmeasurements (p = 0.02 and p = 0.016). Conclusion The adapted Greek version of the questionnaire is valid and reliable and can be used for the screening of dysphagia in the Greek-speaking patients. [ABSTRACT FROM AUTHOR]

Published
2017
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