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Robust FD-DFE equalization for optical OTFS-based NOMA multi-user MIMO in visible light communication systems
No full textInternational audienceVisible Light Communication (VLC) has emerged as a promising indoor optical wireless communication (IOWC) solution, complementing traditional RF systems by offering high-speed and cost-effective data transmission. However, challenges such as limited modulation bandwidth in multi-user (MU) VLC systems hinder high data rates. This study introduces a framework based on optical orthogonal time frequency space (OTFS) and non-orthogonal multiple access (NOMA) for MU multiple-input multiple-output (MIMO) systems. The proposed system leverages decision feedback equalization (DFE) with maximum likelihood (ML) estimation to address inter-symbol and inter-user interference in the 2D delay-Doppler domain. Optimization of waveform parameters under peak power constraints ensures balanced communication performance. Extensive evaluations confirm that DFE-ML outperforms benchmarks like minimum mean square error (MMSE) with the successive interference cancellation (SIC) and FD-ZFE, achieving better bit error ratio (BER) performance at a high signal-to-noise ratio (SNR). A provided numerical comparison of power spectrum density (PSD) for optical OTFS modulation derivatives and mitigating interference, spectral efficiency (SE), and sum rates under imperfect channel state information (CSI). Developed optical OTFS framework for next-generation VLC systems, integrating precise sensing with high-performance communication to enable intelligent wireless sensing and efficient connectivity
Investigating Impacts of Local Pressure and Temperature on CVD Growth of Hexagonal Boron Nitride on Ge(001)/Si
No full textInternational audienceThe chemical vapor deposition (CVD) growth of hexagonal boron nitride (hBN) on Ge substrates is a promising pathway to high-quality hBN thin films without metal contaminations for microelectronic applications, but the effect of CVD process parameters on the hBN properties is not well understood yet. The influence of local changes in pressure and temperature due to different reactor configurations on the structure and quality of hBN films grown on Ge(001)/Si is studied. Injection of the borazine precursor close to the sample surface results in an inhomogeneous film thickness, attributed to an inhomogeneous pressure distribution at the surface, as shown by computational fluid dynamics simulations. The additional formation of nanocrystalline islands is attributed to unfavorable gas phase reactions due to the radiative heating of the injector. Both issues are mitigated by increasing the injector-sample distance, leading to an 86% reduction in pressure variability on the sample surface and a 200 °C reduction in precursor temperature. The resulting hBN films exhibit no nanocrystalline islands, improved thickness homogeneity, and high crystalline quality (Raman FWHM = 23 cm−1). This is competitive with hBN films grown on other non-metal substrates but achieved at lower temperature and with a low thickness of only a few nanometers
Tuned Y-shaped Electromagnetic Switch for Directional Signal Control in Photonic Circuits
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Temporal fusion strategy for violence detection: utilising convolutional and LSTM neural networks for surveillance videos
No full textInternational audienceIn the latest intelligent cities, there is a pursuit for the utmost degree of automation and integration of services. One of the major challenges in the surveillance industry is the need to automate real-time video analysis to identify critical cases. This paper introduces sophisticated models using Convolutional Neural Networks (CNN), specifically MobileNet V3, VGG16, and InceptionV3 networks, as well as networks using LSTM and feedforward networks. These models are designed to accurately categorise videos into two completely separate classes, namely: ("Non-Violence" and "Violence"). The RLVS database is used for this classification task. Various data representations are used by Temporal Fusion approaches. The highest attained outcome was an Accuracy of 91.03 %, and an F1-score of 90.90 %, which is superior to the results obtained in similar research performed on the same database for achieving the goal of recognising actions that are violent in Surveillance Videos.</div
Optimization of CRC-Based Single-Bit Error Correction Using a Perfect Hash Table Structure
No full textInternational audienceThis work introduces a novel approach for correcting a single-bit error in a CRC-protected message, which is based on a perfect hash table that can be queried by a non-zero CRC syndrome. The paper primarily focuses on presenting the new table structure and includes a comparative analysis of various CRC-based error correction methods, demonstrating that ours strikes an excellent balance between correction complexity and memory requirements. Complexity evaluation is performed in terms of the number of 2-input gate operations
Frequency Comb Generation Induced by Internal Mode Coupling in Silicon Nitride Drum Resonators
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Effects of temperature, humidity and disorder in phase transformation phenomena of multi-stable systems
No full textInternational audienceMulti-stable behavior at the microscopic length-scale is fundamental for phasetrans- formation phenomena observed in many materials. These phenomenacan be driven not only by external mechanical forces but are also cruciallyinfluenced by disorder and thermal fluctuations. Disorder, arising from structuraldefects or fluctuations in external stimuli, disrupts the homogeneity ofthe material and can significantly alter the system’s response, often leadingto the suppression of cooperativity in the phase transition. Temperaturecan further introduce novel effects, modifying energy barriers and transitionrates. We study prototypical models able to represent the behavior ofseveral biomacro- molecules and phase transformation phenomena in solidmechanics. In the framework of Statistical Mechanics we can interpret theexperimentally observed thermal effects with the theoretical force–extensionrelation characterized by a temperature-dependent force plateau (Maxwellstress) and a force peak (nucleation stress) [1]. Moreover, by using a meanfield approach, we are able to include the effects of disorder in the frameworkof a replica symmetry theory [2]. Finally, we consider a predictive model forthe hygro-thermo- mechanical behavior of complex materials such as spidersilks, exhibiting an effect known as supercontraction, conceptualizing thisphenomenon as a solid-solid phase transition driven by humidity [3]. As wettingincreases, the system undergoes a transition, at the network scale, froma hard dry state to a soft amorphous wet state. We model these states byusing a two-well free energy function dependent on molecular stretch, withtransition energy modulated by humidity. We are thus able to deduce thatsupercontraction can be interpreted as a solid-solid phase transition.References[1] Cannizzo, A., Bellino, L., Florio, G., Puglisi, G., Giordano, S.: Thermalcontrol of nucleation and propagation transition stresses in discrete latticeswith non-local interactions and non-convex energy. Eur. Phys. J. Plus, 137,569 (2022)[2] Florio, G., Giordano, S., Puglisi, G.: Effects of Temperature and RandomForces in Phase Transformation of Multi-Stable Systems. Entropy, 26, 1109(2024)[3] Fazio, V., Florio, G., Pugno, N.M., Puglisi, G.: Modeling spider silk supercontraction as a hydration- driven solid–solid phase transition. J. Mech.Phys. Solids, 195, 105959 (2025
Advanced Refinement of Geopolymer Composites for Enhanced 3D Printing via In-Depth Rheological Insights
No full textInternational audienceThe advancement of 3D printing technology has been remarkable, yet the quality of printed prototypes heavily relies on the rheological behavior of the materials used. This study focuses on optimizing geopolymer-based composite formulas to achieve high-quality 3D printing, with particular attention given to rheological analysis. Three metakaolins, Argical M1200s, Metamax, and Tempozz M88, were used as alumino-silicate precursors for the preparation of the geopolymer binders. Rheological studies were conducted on viscosity, shear stress, and responses to oscillations in amplitude and frequency. The Tempozz M88-based binder was identified as the most effective for the extrusion due to its optimal rheological properties. Subsequently, the study investigated the influence of the amount, up to 55%, and morphology of the fillers, comprising feldspar and wollastonite, on the rheology of the pastes. Also, the addition of Xanthan gum, a gelling agent in the geopolymer paste, was analyzed, revealing improved extrusion quality and more stable bead structures. Finally, a comprehensive comparison was carried out between two formulations chosen according to rheological observations, utilizing image sequences captured during 3D printing. This comparison highlighted the formulation that ensures structural stability, design accuracy, and minimized sagging. This study underscores the significance of geopolymer formula optimization, leveraging rheology as a pivotal tool to enhance 3D printing quality, thereby facilitating more precise and reliable applications of additive manufacturing