Special Issue on the Internet of Things (ISCC 2020)

Journal of Signal Processing Systems -     

Spatio-temporal evolution of the deformation around the Rio-Patras fault (Greece) observed by synthetic aperture radar interferometry from 1993 to 2017

We analysed the ground deformation across two blocks defined by the Rio-Patras fault from 1993 to 2017 using multi-temporal Synthetic Aperture Radar Interferometry (InSAR) techniques. Our main objective was to contribute to the assessment of seismic hazard near the large city of Patras. Multiple data-sets were used, each one covering different temporal periods. Descending and ascending acquisitions, providing different viewing geometries contribute to fully determine the ground displacement in 3D. The data-sets used are from the European Space Agency’s (ESA) European Remote Sensing (ERS), Environmental Satellite (ENVISAT) and SENTINEL-1 as well as German Aerospace Center (DLR) ’s TERRASAR-X missions. Considering ESA’s missions covering both acquisition geometries and long periods, the southern block, showing lack of a sufficient number of scatterers does not allow the displacement characterization. In contrary, the northern block is characterized by a high number of scatterers having values of maximum likehood ranging from ?3.5 to ?4.3 mm year^?1 for ascending geometry and from ?1.6 to ?2.7 mm year^?1 for the descending one. The fact that both geometries show negative values of displacements are consistent with downlift movement and at the same time the quantitative differentiation probably indicates an horizontal component as well.     

Constitutive modelling and numerical simulation of multivariant phase transformation in superelastic shape‐memory alloys

This work concerns the micromechanical constitutive modelling, algorithmic implementation and numerical simulation of polycrystalline superelastic alloys under multiaxial loading. The model is formulated in finite deformations and incorporates the effect of texture. The numerical implementation is based on the constrained minimization of the Helmholtz free energy with dissipation. Simulations are conducted for thin tubes of Nitinol under tension–torsion, as well as for a simplified model of a biomedical stent. Copyright © 2004 John Wiley & Sons, Ltd.     

Control-canonical-form method applied to generating systems to improve dynamic stability characteristics

Contents The control-canonical-form (CCF) method is introduced for the purpose of applying it to high-order state-space single-input single or multiple-output (SISO or SIMO) and multiple-input multiple-output (MIMO) linear time-invariant system models to determine closed-loop systems (i.e. design robust controllers) from which enchanced dynamic stability characteristics and overall performance of these systems is achieved. The method has been applied successfully to a SISO 6th-order linearized state-space open-loop model (representing a simplified hydro power system), and to a MIMO 8th-order linearized state-space open-loop model (representing an 87.5 kVA synchronous machine with conventional exciter supplying power to an electric utility system through an interconnection network)

---

Anwendung der kanonischen Form der Zustandsrückführung auf Erzeugersysteme zur Verbesserung der dynamischen Stabilitätseigenschaften

Übersicht Die Methode der kanonischen Form wird auf lineare zeitinvariante Systeme höherer Ordnung im Zustandsraum angewendet, die eine oder mehrere Eingangsgrößen bei einer oder mehreren Ausgangsgrößen aufweisen. Damit werden robuste Regler entworfen, welche die dynamische Stabilität und das gesamte Betriebsverhalten verbessern. Die Methode wurde erfolgreich auf ein linearisiertes Modell sechster Ordnung mit einem Eingang und einem Ausgang angewendet, das vereinfachend eine Wasserkraftanlage darstellt; außerdem auf ein linearisiertes Zustandsmodell achter Ordnung einer Synchronmaschine 87,5kVA mit konventioneller Erregung, die über ein Verbindungsnetzwerk in das öffentliche Netz einspeist.

     

Improving Awareness in Mobile CSCW

The diffusion of mobile devices in the working landscape is promoting collaboration across time and space. Following through this development, we investigate opportunities for improving awareness in mobile environments with a view to enable collaboration under power constraints and transitory network disconnections. We elaborate in particular on synchronous CSCW and expose with it significant details of group awareness, while we contribute a protocol for awareness support over large areas that strikes a balance between energy consumption and notification time. To avoid user disruption, this protocol notifies awareness information in a multicast fashion, while the bandwidth is allocated dynamically among notifications and data requests, thus minimizing the time needed by each one of them and ensuring the isochronous delivery of information to all clients. The efficiency and scalability of our protocol are evaluated with simulation experiments, whereby we compare various notification schemes and finally choose one that changes dynamically over time.     

On scaling the IEEE 802.11 to facilitate scalable wireless networks

The IEEE 802.11 MAC protocol has gained widespread popularity and has been adopted as the de-facto layer 2 protocol for wireless local area networks (WLANs). However, it is well known that as the number of competing stations increases, the performance of the protocol degrades dramatically. Given the explosive growth in WLANs’ usage, the question of how to sustain each user’s perceived performance when a large number of competing stations are present, is an important and challenging open research problem.Motivated by this, in this paper we analyze the behavior of 802.11-based WLANs as the number of competing stations increases, and attempt to provide concrete answers to the following fundamental questions: (i) is there a set of system and protocol parameters that we can scale in order to sustain each individual user’s perceived performance, and (ii) what is the minimum scaling factor?Using theoretical analysis coupled with extensive simulations we show that such a set of parameters exists, and that the minimum scaling factor is equal to the factor by which the number of users increases. Our results reveal several important scaling properties that exist in today’s 802.11-based wireless networks, and set guidelines for designing future versions of such networks that can efficiently support a very large number of users.     

A comprehensive solution for application‐level adaptation

Driven by the emergence of mobile and pervasive computing there is a growing demand for context‐aware software systems that can dynamically adapt to their run‐time environment. We present the results of project MADAM that has delivered a comprehensive solution for the development and operation of context‐aware, self‐adaptive applications. The main contributions of MADAM are (a) a sophisticated middleware that supports the dynamic adaptation of component‐based applications, and (b) an innovative model‐driven development methodology that is based on abstract adaptation models and corresponding model‐to‐code transformations. MADAM has demonstrated the viability of a general, integrated approach to application‐level adaptation. We discuss our experiences with two real‐world case studies that were built using the MADAM approach. Copyright © 2008 John Wiley & Sons, Ltd.