Dynamic Programmable Wireless Environment with UAV-mounted Static Metasurfaces

Reconfigurable intelligent surfaces (RISs) are artificial planar structures able to offer a unique way of manipulating propagated wireless signals. Commonly composed of a number of reconfigurable passive cell components and basic electronic circuits, RISs can almost freely perform a set of wave modification functionalities, in order to realize programmable wireless environments (PWEs). However, a more energy-efficient way to realize a PWE is through dynamically relocating static metasurfaces that perform a unique functionality. In this paper, we employ a UAV swarm to dynamically deploy a set of lowcost passive metasurfaces that are able to perform only one electromagnetic functionality, but with the benefit of requiring no power. Specifically, the UAV-mounted static metasurfaces are carefully positioned across the sky to create cascaded channels for improved user service and security hardening. The performance evaluation results, based o

Fast and Fair Handling of Multimedia CAPTCHA Flows

Multimedia CAPTCHAs play a crucial role in bot filtering policies for VoIP applications. Network flows carrying CAPTCHA content have a very small lifespan and require high transmission quality, making for special handling at transport layer. The present study introduces an analysis-derived, rapidly converging control mechanism for CAPTCHA flows. Instead of relying on generic heuristics, the novel scheme enables the flows to estimate their deviation from the equilibrium and adapt to it in a single step. Simulations demonstrate the high efficiency and convergence speed of the scheme, highlighting its unique fitness for the appointed task

Fast and Fair Handling of Multimedia CAPTCHA Flows

Multimedia CAPTCHAs play a crucial role in bot filtering policies for VoIP applications. Network flows carrying CAPTCHA content have a very small lifespan and require high transmission quality, making for special handling at transport layer. The present study introduces an analysis-derived, rapidly converging control mechanism for CAPTCHA flows. Instead of relying on generic heuristics, the novel scheme enables the flows to estimate their deviation from the equilibrium and adapt to it in a single step. Simulations demonstrate the high efficiency and convergence speed of the scheme, highlighting its unique fitness for the appointed task

A Holistic Virtual Laboratory on Wireless Communications and Sensor Networks

Virtual laboratories have evolved into an adequately mature educational tool for multiple fields of study. Their use is especially beneficial to modern topics such as modern wireless communications. Related solutions in this field explored various approaches and architectures in designing such a virtual environment. The presented software package combines these fragmentary conclusions to a holistic and extensible laboratory architecture. Classic and modern topics, such as propagation, green networking, indoor communications and sensor networks are discussed through interactive 2D/3D environments. The student is also introduced to field measurement procedures and ray tracing principles. Statistical assessment in the context of a postgraduate course in wireless communications demonstrates the educational benefits of the approach

A Holistic Virtual Laboratory on Wireless Communications and Sensor Networks

Virtual laboratories have evolved into an adequately mature educational tool for multiple fields of study. Their use is especially beneficial to modern topics such as modern wireless communications. Related solutions in this field explored various approaches and architectures in designing such a virtual environment. The presented software package combines these fragmentary conclusions to a holistic and extensible laboratory architecture. Classic and modern topics, such as propagation, green networking, indoor communications and sensor networks are discussed through interactive 2D/3D environments. The student is also introduced to field measurement procedures and ray tracing principles. Statistical assessment in the context of a postgraduate course in wireless communications demonstrates the educational benefits of the approach

Impact of parietal cell autoantibodies and non-organ-specific autoantibodies on the treatment outcome of patients with hepatitis C virus infection: A pilot study

AIM: Various side effects have been reported in patients infected with hepatitis C virus (HCV) who were treated with interferon-alpha (IFN-alpha), including the appearance or exacerbation of underlying autoimmune diseases and the development of a variety of organ and non-organ specific autoantibodies (NOSA). However, very few studies in adults have been strictly designed to address: whether the prevalence and the titre of organ and NOSA in serial samples of HCV-treated patients were affected by IFN-alpha, and the impact of these autoantibodies on the treatment outcome of HCV patients. METHODS: We investigated whether parietal cell autoantibodies (PCA) and/or NOSA were related with treatment-outcome in 57 HCV-treated patients (19 sustained-responders, 16 relapsers, 22 non-responders). Serum samples from patients were studied blindly at three time-points (entry, end of treatment and end of followup). For the detection of autoantibodies we used indirect immunofluorescence, commercial and in-house ELISAs. RESULTS: Sustained biochemical response was associated with ANA-negativity at the entry or end of follow up. Sustained virological response was associated with the absence of PCA at the entry. Combined virological and biochemical sustained response (CVBSR) was associated with the absence of antinuclear antibodies (ANA) at the end of follow up and PCA-negativity at the entry. Sustained virological and CVBSR were associated with a reduction of ANA and SMA titers during therapy. CONCLUSION: Although PCA and/or NOSA seropositivity should not affect the decision to treat HCV patients, the presence of some of them such as ANA, PCA and SMA before treatment or their increase during therapy with IFN-alpha may predict a worse response, indicating the need for a closer monitoring during treatment of HCV patients positive for these autoantibodies. (C) 2005 The WJG Press and Elsevier Inc. All rights reserved

Zero-Energy Reconfigurable Intelligent Surfaces (zeRIS)

A primary objective of the forthcoming sixth generation (6G) of wireless networking is to support demanding applications, while ensuring energy efficiency. Programmable wireless environments (PWEs) have emerged as a promising solution, leveraging reconfigurable intelligent surfaces (RISs), to control wireless propagation and deliver exceptional quality-ofservice. In this paper, we analyze the performance of a network supported by zero-energy RISs (zeRISs), which harvest energy for their operation and contribute to the realization of PWEs. Specifically, we investigate joint energy-data rate outage probability and the energy efficiency of a zeRIS-assisted communication system by employing three harvest-and-reflect (HaR) methods, i) power splitting, ii) time switching, and iii) element splitting. Furthermore, we consider two zeRIS deployment strategies, namely BS-side zeRIS and UE-side zeRIS. Simulation results validate the provided analysis and examine which HaR method performs better depending on the zeRIS placement. Finally, valuable insights and conclusions for the performance of zeRISassisted wireless networks are drawn from the presented results

On the Mobility Effect in UAV-Mounted Absorbing Metasurfaces: A Theoretical and Experimental Study

In this work, we focus on the theoretical modeling and experimental evaluation of absorbing metasurfaces mounted on unmanned aerial vehicles (UAVs) as facilitators for secure wireless communication channels. Specifically, we present a network architecture based on UAV-mounted metasurfaces and conduct a comprehensive analysis of its components. Furthermore, by utilizing physical optics, namely the Fresnel-Kirchhoff diffraction formula, we develop a comprehensive path loss model that accurately calculates the scattering of wavefronts from metasurfaces with arbitrary configurations; this model enables the quantification of path loss and mobility effects, including pointing accuracy, misalignment, and UAV flying stability, for both near- and far-field conditions. Finally, experimental measurements are conducted using a state-of-the-art static absorbing metasurface and a commercial UAV in an anechoic chamber environment and close agreement between theoretical and experimental results, down to the radiative near-field region, is illustrated. Specifically, our findings indicate that absorbing metasurfaces can act as notch filters with minimal impact on pointing and positioning accuracy, exhibiting a 3 dB beamwidth of ±15° compared to ideal static conditions