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arXiv 2024年

作者： Castro-Correa, Jhon A. Giraldo, Jhony H. Badiey, Mohsen Malliaros, Fragkiskos D. Department of Electrical and Computer Engineering University of Delaware NewarkDE United States LTCI Télécom Paris Institut Polytechnique de Paris Palaiseau France Gif-sur-Yvette France

Reconstructing time-varying graph signals (or graph time-series imputation) is a critical problem in machine learning and signal processing with broad applications, ranging from missing data imputation in sensor networks to time-series forecasting. Accurately capturing the spatio-temporal information inherent in these signals is crucial for effectively addressing these tasks. However, existing approaches relying on smoothness assumptions of temporal differences and simple convex optimization techniques have inherent limitations. To address these challenges, we propose a novel approach that incorporates a learning module to enhance the accuracy of the downstream task. To this end, we introduce the Gegenbauer-based graph convolutional (GegenConv) operator, which is a generalization of the conventional Chebyshev graph convolution by leveraging the theory of Gegenbauer polynomials. By deviating from traditional convex problems, we expand the complexity of the model and offer a more accurate solution for recovering time-varying graph signals. Building upon GegenConv, we design the Gegenbauerbased time Graph Neural Network (GegenGNN) architecture, which adopts an encoder-decoder structure. Likewise, our approach also utilizes a dedicated loss function that incorporates a mean squared error component alongside Sobolev smoothness regularization. This combination enables GegenGNN to capture both the fidelity to ground truth and the underlying smoothness properties of the signals, enhancing the reconstruction performance. We conduct extensive experiments on real datasets to evaluate the effectiveness of our proposed approach. The experimental results demonstrate that GegenGNN outperforms state-of-the-art methods, showcasing its superior capability in recovering time-varying graph signals. Copyright © 2024, The Authors. All rights reserved.

关键词： Graph neural networks

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The Influence of V-Defects, Leakage, and Random Alloy Fluctuations on the Carrier Transport in Red InGaN MQW LEDs

arXiv

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arXiv 2025年

作者： Huang, Huai-Chin Chen, Shih-Min Weisbuch, Claude Speck, James S. Wu, Yuh-Renn Graduate Institute of Photonics and Optoelectronics Department of Electrical Engineering National Taiwan University Taipei10617 Taiwan Materials Department University of California Santa BarbaraCA93106 United States Laboratoire de Physique de la Matière Condensée CNRS Ecole polytechnique Institut Polytechnique de Paris Palaiseau91120 France

Red InGaN-based light-emitting diodes (LEDs) exhibit lower internal quantum efficiencies (IQEs) than violet, blue, and green InGaN LEDs due to a reduction in radiative recombination rates relative to non-radiative recombination rates as the indium composition increases. Additionally, the larger polarization and band offset barriers between high indium content InGaN quantum wells and GaN quantum barriers increase the forward voltage. In blue and green LEDs, random alloy fluctuations and V-defects play a key role in reducing the forward voltage. When V-defects are present, either naturally or intentionally introduced, they create an alternative path for carrier injection into the MQWs through the V-defect sidewalls. This injection mechanism explains the turn-on voltages of green LEDs. However, in InGaN red LEDs, these two phenomena do not reduce the forward voltage as effectively as in blue and green LEDs, and consequently, the computed forward voltage remains significantly higher than the measured one. Furthermore, currents are observed at low voltages before the turn-on voltage (V © 2025, CC BY.

关键词： Semiconductor quantum wells

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Efficient handling of ACL policy change in SDN using reactive and proactive flow rule installation ( vol 14 , 14976 , 2024 )

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SCIENTIFIC REPORTS 2024年第1期14卷 1-19页

作者： Hussain, Mudassar Amin, Rashid Gantassi, Rahma Alshehri, Asma Hassan Frnda, Jaroslav Raza, Syed Mohsan Department of Computer Science and Creative Technologies Global College of Engineering and Technology CPO Ruwi 112 P.O Box 2546 Muscat Sultanate of Oman Department of Computer Science and IT University of Chakwal Chakwal 48800 Pakistan Department of Computer Science University of Engineering and Technology Taxila 47050 Pakistan Department of Electrical Engineering Chonnam National University Gwangju 61186 South Korea Department of Computer Science College of Computer Engineering and Science Prince Sattam Bin Abdulaziz University Alkharj 16273 Saudi Arabia Department of Quantitative Methods and Economic Informatics Faculty of Operation and Economics of Transport and Communications University of Zilina 01026 Zilina Slovakia Department of Telecommunications Faculty of Electrical Engineering and Computer Science VSB Technical University of Ostrava 70800 Ostrava Czech Republic SAMOVAR Telecom SudParis Institut Polytechnique de Paris 91120 Paris France

Software-defined networking (SDN) is a pioneering network paradigm that strategically decouples the control plane from the data and management planes, thereby streamlining network administration. SDN's centralized network management makes configuring access control list (ACL) policies easier, which is important as these policies frequently change due to network application needs and topology modifications. Consequently, this action may trigger modifications at the SDN controller. In response, the controller performs computational tasks to generate updated flow rules in accordance with modified ACL policies and installs flow rules at the data plane. Existing research has investigated reactive flow rules installation that changes in ACL policies result in packet violations and network inefficiencies. Network management becomes difficult due to deleting inconsistent flow rules and computing new flow rules per modified ACL policies. The proposed solution efficiently handles ACL policy change phenomena by automatically detecting ACL policy change and accordingly detecting and deleting inconsistent flow rules along with the caching at the controller and adding new flow rules at the data plane. A comprehensive analysis of both proactive and reactive mechanisms in SDN is carried out to achieve this. To facilitate the evaluation of these mechanisms, the ACL policies are modeled using a 5-tuple structure comprising Source, Destination, Protocol, Ports, and Action. The resulting policies are then translated into a policy implementation file and transmitted to the controller. Subsequently, the controller utilizes the network topology and the ACL policies to calculate the necessary flow rules and caches these flow rules in hash table in addition to installing them at the switches. The proposed solution is simulated in Mininet Emulator using a set of ACL policies, hosts, and switches. The results are presented by varying the ACL policy at different time instances, inter-packet de

关键词： ACL policy change Management Proactive flow rule installation Reactive flow rule installation SDN Security

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Lightning Precursor Discharges and Terrestrial Gamma Ray Flashes

Lightning Precursor Discharges and Terrestrial Gamma Ray Fla...

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US National Committee of URSI National Radio Science Meeting (USNC-URSI NRSM)

作者： Victor P. Pasko Sebastien Celestin Anne Bourdon Reza Janalizadeh Zaid Pervez Jaroslav Jansky Pierre Gourbin School of Electrical Engineering and Computer Science Penn State University PA USA Laboratory of Physics and Chemistry of the Environment and Space (LPC2E) CNRS University of Orleans Orleans France Plasma Physics Laboratory (LPP) Ecole Polytechnique Palaiseau France Department of Mathematics and Physics University of Defense Brno Czechia

ISBN: (数字)9781946815200

ISBN: (纸本)9798331513979

Spectacular naturally occurring bursts of X-rays with tens of mega electron-volt energies are observed in association with lightning activity in the Earth's atmosphere. These events were first discovered in 1994 by NASA's Compton Gamma Ray Observatory [Fishman et al., 1994] and are commonly referred to as terrestrial gamma-ray flashes (TGFs). Although since then many other orbital observatories captured these high energy events [Smith et al., 2005; Marisaldi et al., 2010; Briggs et al., 2011; Neubert et al., 2020] and these events have been clearly linked to very intense but short (approximately 10–50 microseconds) bursts of electromagnetic radiation [Ostgaard et al., 2021], the physical nature of these events remains unclear. It is widely recognized that these electromagnetic bursts are also the strongest naturally occurring sources of terrestrial very high frequency (VHF) radiation [Jacobson et al., 2012]. The most puzzling unexplained aspect of these events is that the extreme gamma ray and electromagnetic energy fluxes originate from very compact regions with spatial extent on the order of 100 meters [Lu et al., 2010; Rison et al., 2016; Tilles et al., 2019; Tilles et al., 2020; Kohn et al., 2020; Heumesser et al., 2021], yet they are light-deficient and often even optically undetectable compared to ordinary lightning discharges [Jacobson et al., 2012]. In this work we report on the mechanism that allows precise quantitative explanation of the vast majority of currently accumulated observations of these events at different altitudes in the Earth's atmosphere. The specifics includes TGF fluences and durations, optical darkness, magnitudes and specific waveform characteristics of low and very low frequency radio emissions termed narrow bipolar events and energetic in cloud pulses that are associated with TGFs, the peculiar observations of very fast (typically one tenths of the speed of light) spatial propagation features termed fast positive breakdown in the prese

关键词： Jacobian matrices Observatories Stimulated emission Optical propagation Gamma-rays Lightning X-rays Orbits Discharges (electric) Optical pulses

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Statistical Characterization of RIS-assisted UAV Communications in Terrestrial and Non-Terrestrial Networks Under Channel Aging

arXiv

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arXiv 2024年

作者： Nguyen, Thanh Luan Kaddoum, Georges Do, Tri Nhu Haas, Zygmunt J. MontréalQC Canada Artificial Intelligence & Cyber Systems Research Center Lebanese American University Lebanon Electrical Engineering Department Polytechnique Montréal MontréalQC Canada Department of Computer Science University of Texas DallasTX75080 United States School of Electrical and Computer Engineering Cornell University IthacaNY14853 United States

This paper studies the statistical characterization of ground-to-air (G2A) and reconfigurable intelligent surface (RIS)assisted air-to-ground (A2G) communications with unmanned aerial vehicles (UAVs) in terrestrial and non-terrestrial networks under the impact of channel aging. We first model the G2A and A2G signal-to-noise ratios (SNRs) as non-central complex Gaussian quadratic random variables (RVs) and derive their exact probability density functions, offering a unique characterization for the A2G SNR as the product of two scaled non-central chi-square RVs. Moreover, we also find that, for a large number of RIS elements, the RIS-assisted A2G channel can be characterized as a single Rician fading channel. Our results reveal the presence of channel hardening in A2G communication under low UAV speeds, where we derive the maximum target spectral efficiency (SE) for a system to maintain a consistent required outage level. Meanwhile, high UAV speeds, exceeding 50 m/s, lead to a significant performance degradation, which cannot be mitigated by increasing the number of RIS elements. © 2024, CC BY.

关键词： Signal to noise ratio

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Physical limits on Raman scattering: The critical role of pump and signal co-design

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Physical Review A 2024年第6期110卷 L061501-L061501页

作者： Alessio Amaolo Pengning Chao Thomas J. Maldonado Sean Molesky Alejandro W. Rodriguez Department of Chemistry Princeton University Princeton New Jersey 08544 USA Department of Mathematics Massachusetts Institute of Technology Cambridge Massachusetts 02139 USA Department of Electrical and Computer Engineering Princeton University Princeton New Jersey 08544 USA Department of Engineering Physics Polytechnique Montréal Montréal Québec H3T 1J4 Canada

We present a method for deriving limits on Raman scattering in structured media and exploit it to constrain the maximum Raman signal resulting from a plane wave incident on either a single Raman molecule in the vicinity of a structured medium or a designable Raman medium. Results pertaining to metallic and dielectric structures illustrate the importance of accounting for the nonlinear interplay between pump and signal fields, showing that treating the pump-focusing and signal-extraction processes separately, as in prior work, leads to unrealistic enhancements. The formulation could readily find applications in further enhancing surface-enhanced Raman scattering (SERS) spectroscopy and Raman-assisted lasing.

关键词： Nanophotonics Nonlinear optics Photonics Numerical techniques Raman spectroscopy Surface-enhanced Raman spectroscopy

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Limitations on bandwidth-integrated passive cloaking

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Physical Review A 2024年第6期110卷 063513-063513页

作者： Benjamin Strekha Alessio Amaolo Jewel Mohajan Pengning Chao Sean Molesky Alejandro W. Rodriguez Department of Electrical and Computer Engineering Princeton University Princeton New Jersey 08544 USA Department of Chemistry Princeton University Princeton New Jersey 08544 USA Department of Mathematics Massachusetts Institute of Technology Cambridge Massachusetts 02139 USA Department of Engineering Physics Polytechnique Montréal Montréal Québec H3T 1J4 Canada

We present a general framework for the computation of structure-agnostic bounds on the performance of passive cloaks over a nonzero bandwidth. We apply this framework in two dimensions to the canonical scenario of cloaking a circular object. We find that perfect cloaking using a finite-sized isotropic cloak is impossible over any bandwidth, with the bounds scaling linearly with the bandwidth before saturating due to the finite size of the cloak and the presence of material loss. The bounds also exhibit linear scaling with material loss in the cloak and linear scaling with the inverse of the radial thickness of the design region before saturation due to finite-size effects or the presence of material loss. The formulation could readily find applications in the development of cloaking devices, setting expectations, and benchmarks for optimal performance.

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Second-order optical nonlinearities in ferroelectric ScAlN for quantum photonics

Second-order optical nonlinearities in ferroelectric ScAlN f...

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IEEE Photonics Conference (IPC)

作者： Jiangnan Liu Pierre-Luc Thériault Shuai Liu Ding Wang Wade Wu Qiannan Wen Zheshen Zhang Moe Soltani Mackillo Kira Stéphane Kéna-Cohen Zetian Mi Department of Electrical Engineering and Computer Science University of Michigan Ann Arbor USA Department of Engineering Physics École Polytechnique de Montréal Montréal Canada Raytheon BBN Technologies Cambridge USA

High quality ScAlN are epitaxially grown on sapphire by molecular beam epitaxy, which shows relatively low propagation loss, as well as significantly enhanced second-order optical nonlinearity compared to conventional...

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Comparison of Machine Learning Methods for Cryptocurrency Price Prediction

Comparison of Machine Learning Methods for Cryptocurrency Pr...

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International Conference of Signal Processing and Intelligent Systems (ICSPIS)

作者： Atieh Armin Ali Shiri Behnam Bahrak School of Electrical and Computer Engineering University of Tehran Tehran Iran Department of Mathematics and Industrial Engineering Polytechnique Montreal Montreal Canada

ISBN: (纸本)9781665476249

In recent years, cryptocurrencies have received much attention due to their recent price surge and crash. In fact, their prices have been volatile, making them very difficult to predict. Accordingly, various machine learning methods have been used by researchers to investigate factors that affect cryptocurrencies prices and the patterns behind their fluctuations. From various machine learning and deep learning methods, this study aims to find an efficient and accurate model for predicting Bitcoin, Ethereum, and Binance Coin prices. Our experiments show that the Ridge regression model outperforms more complicated prediction models, such as RNNs and LSTM, in predicting the exact closing price. On the other hand, LSTM can anticipate the direction of the cryptocurrency price better than others.

关键词： Time series analysis Linear regression Signal processing algorithms Predictive models Signal processing Prediction algorithms Surges

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On-Demand Routing in LEO Mega-Constellations with Dynamic Laser Inter-Satellite Links

arXiv

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arXiv 2024年

作者： Bhattacharjee, Dhiraj Madoery, Pablo G. Chaudhry, Aizaz U. Yanikomeroglu, Halim Kurt, Güneş Karabulut Hu, Peng Ahmed, Khaled Martel, Stéphane Lab Department of Systems and Computer Engineering Carleton University Canada The Poly-Grames Research Center Department of Electrical Engineering Polytechnique Montréal Canada The Digital Technologies Research Center National Research Council Canada Canada Satellite Systems MDA Canada

Low Earth orbit (LEO) satellite mega-constellations are beginning to include laser inter-satellite links (LISLs) to extend the Internet to the most remote locations on Earth. Since the process of establishing these links incurs a setup delay on the order of seconds, a static network topology is generally established well in advance, which is then used for the routing calculations. However, this involves keeping links active even when they are not being used to forward traffic, leading to a poor energy efficiency. Motivated by technological advances that are gradually decreasing the LISL setup delays, we foresee scenarios in which it will be possible to compute routes and establish dynamic LISLs on demand. This will require considering setup delays as penalties that will affect the end-to-end latency. In this paper, we present a non-linear optimization model that considers these penalties in the cost function and propose three heuristic algorithms that solve the problem in a tractable way. The algorithms establish different trade-offs in terms of performance and computational complexity. We extensively analyze metrics including average latency, route change rate, outage probability, and jitter, in Starlink’s Phase I version 2 constellation. The results show the benefit of adaptive routing schemes according to the link setup delay. In particular, more complex schemes are able to decrease the average end-to-end latency, in exchange for an increase in the execution time. On the other hand, depending on the maximum values of tolerated latency, it is possible to use less computationally complex schemes which will be more scalable for the satellite mega-constellations of the future. Copyright © 2024, The Authors. All rights reserved.

关键词： Satellites

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