Analyzing chaos in higher order disordered quartic-sextic Klein-Gordon lattices using <i>q</i>-statistics

Antonopoulos, Chris G.,Skokos, Charalampos,Bountis, Tassos,Flach, Sergej Elsevier 2017 Chaos, solitons, and fractals Vol.104 No.-

<P><B>Abstract</B></P> <P>In the study of subdiffusive wave-packet spreading in disordered Klein–Gordon (KG) nonlinear lattices, a central open question is whether the motion continues to be chaotic despite decreasing densities, or tends to become quasi-periodic as nonlinear terms become negligible. In a recent study of such KG particle chains with quartic (4th order) anharmonicity in the on-site potential it was shown that q − Gaussian probability distribution functions of sums of position observables with <I>q</I> > 1 always approach pure Gaussians ( q = 1 ) in the long time limit and hence the motion of the full system is ultimately “strongly chaotic”. In the present paper, we show that these results continue to hold even when a sextic (6th order) term is gradually added to the potential and ultimately prevails over the 4th order anharmonicity, despite expectations that the dynamics is more “regular”, at least in the regime of small oscillations. Analyzing this system in the subdiffusive energy domain using <I>q</I>-statistics, we demonstrate that groups of oscillators centered around the initially excited one (as well as the full chain) possess strongly chaotic dynamics and are thus far from any quasi-periodic torus, for times as long as t = <SUP> 10 9 </SUP> .</P> <P><B>Highlights</B></P> <P> <UL> <LI> We contribute to the debate concerning the asymptotic behavior of wavepacket spreading in nonlinear, disordered lattices, which is an issue of interest in the last years. </LI> <LI> Using numerical techniques of chaos theory (computations of Lyapunov exponents) and statistical physics (q-statistics, Tsallis entropy) we provide, for a set of Klein–Gordon disordered lattices with higher than 4th order nonlinearity in their on-site potential, strong numerical evidences that wave packet spreading remains strongly chaotic for very long times. </LI> <LI> Our findings clearly suggest that the overall motion in the considered systems does not approach the quasi-periodic regime of invariant tori as conjectured by some authors. </LI> </UL> </P>

Aseismic protection of historical structures using modern retrofitting techniques

Syrmakezis, C.A.,Antonopoulos, A.K.,Mavrouli, O.A. Techno-Press 2008 Smart Structures and Systems, An International Jou Vol.4 No.2

For historical masonry structures existing in the Mediterranean area, structural strengthening is of primary importance due to the continuous earthquake threat that is posed on them. Proper retrofitting of historical structures involves a thorough understanding of their structural pathology, before proceeding with any intervention measures. In this paper, a methodology is presented for the evaluation of the actual state of historical masonry structures, which can provide a useful tool for the seismic response assessment before and after the retrofitting. The methodology is mainly focused on the failure and vulnerability analysis of masonry structures using the finite element method. Using this methodology the retrofitting of historical structures with innovative techniques is investigated. The innovative technique presented here involves the exploitation of Shape Memory Alloy prestressed bars. This type of intervention is proposed because it ensures increased reversibility and minimization of interventions, in comparison with conventional retrofitting methods. In this paper, a case study is investigated for the demonstration of the proposed methodologies and techniques, which comprises a masonry Byzantine church and a masonry Cistern. Prestressed SMA alloy bars are placed into the load-bearing system of the structure. The seismic response of the non-retrofitted and the retrofitted finite element models are compared in terms of seismic energy dissipation and displacements diminution.

A New Modulation Method for the Modular Multilevel Converter Allowing Fundamental Switching Frequency

K. Ilves,A. Antonopoulos,S. Norrga,H-P. Nee 전력전자학회 2011 ICPE(ISPE)논문집 Vol.2011 No.5

This paper presents a new modulation method for the modular multilevel converter. The proposed method is based on a fixed pulse pattern where harmonic elimination methods can be applied. Modulation methods with harmonic elimination based on calculated pulse patterns have been presented for other multilevel topologies. However, similar modulation schemes have not yet been presented for the modular multilevel topology. In the proposed modulation method, the pulse pattern is chosen in such a way that the stored energy in each submodule remains stable. It is shown that this can be done at the fundamental switching frequency without measuring the capacitor voltages or using any other form of feedback control. Such a modulation scheme has not been presented before. The theoretical results are verified by both simulations and experimental results. The simulation results show successful operation at the fundamental switching frequency with a larger number of submodules. When a smaller number of submodules are used, harmonic elimination methods may be applied. This is verified experimentally on a converter with eight submodules per phase leg. The experimental results verify that stable operation can be maintained at the fundamental switching frequency while successfully eliminating the fifth harmonic in the ac-side voltage.

Rehabilitation of hospital buildings using passive control systems

Syrmakezis, C.A.,Mavrouli, O.A.,Antonopoulos, A.K. Techno-Press 2006 Smart Structures and Systems, An International Jou Vol.2 No.4

In the case of hospital buildings, where seismic design requirements are very high, existing structuresand especially those attacked by past earthquakes, appear, often, unable to fulfil the necessary safety prerequisites. In this paper, the retrofitting of hospital buildings is investigated, using alternative methods of repair and strengthening. Analysis of an existing hospital building in Patras, Greece, is performed. The load-bearing system is a reinforced concrete system. Two solutions are proposed: strengthening using concrete jackets around column and beam elements and application of viscoelastic dampers for the increase of the stability of the structure. Adequate finite element models are constructed for each case and conclusions are drawn on the efficiency of each rehabilitation method.

Cardiac Decompression by Pericardiectomy for Constrictive Pericarditis: Multimodality Imaging to Identify Patients at Risk for Prolonged Inotropic Support

Alessia Azzu,Marco Morosin,Alexios S. Antonopoulos,Massimo Capoccia,Ulrich Rosendahl,Raad Mohiaddin 한국심초음파학회 2021 Journal of Cardiovascular Imaging (J Cardiovasc Im Vol.29 No.4

BACKGROUND: Post-pericardiectomy right ventricular (RV) failure has been reported but it remains not well-studied. To investigate imaging parameters that could predict RV function and the outcome of patients post-pericardiectomy. METHODS: We analysed data from a total of 53 CP patients undergoing pericardiectomy. Preoperative, early and at 6 months postoperative echocardiographic (echo) imaging datasets were analysed and correlated with preoperative cardiac magnetic resonance (CMR), cardiac computed tomography scans and histology. The primary endpoint of the study was RV functional status early postoperatively and at 6 months. Secondary endpoint was the need for prolonged inotropic support. RESULTS: A cause of CP was identified in 26 patients (49%). Inotropic support ≥ 48 hours was required in n = 28 (53%) of patients and was correlated with lower preoperative RV areas by echo or RV volumes by CMR (p < 0.05 for all). A pericardial score based on pericardial thickness/calcification and epicardial fat thickness had good diagnostic accuracy to identify patients requiring prolonged use of inotropes (area under the curve, 0.825; 95% confidence interval, 0.674–0.976). Pericardiectomy resulted in RV decompression and impaired RV function early postoperatively (fractional area change: 40.5% ± 8.8% preoperatively vs. 31.4% ± 10.4% early postoperatively vs. 42.5% ± 10.2% at 6 months, p < 0.001). CONCLUSIONS: We show that a smaller RV cavity size and a pericardial scoring system are associated with prolonged inotropic support in CP patients undergoing pericardiectomy. RV systolic impairment post decompression is present in most patients, but it is only transient.

Aseismic protection of historical structures using modern retrofitting techniques

C. A. Syrmakezis,A. K. Antonopoulos,O. A. Mavrouli 국제구조공학회 2008 Smart Structures and Systems, An International Jou Vol.4 No.2

For historical masonry structures existing in the Mediterranean area, structural strengthening is of primary importance due to the continuous earthquake threat that is posed on them. Proper retrofitting of historical structures involves a thorough understanding of their structural pathology, before proceeding with any intervention measures. In this paper, a methodology is presented for the evaluation of the actual state of historical masonry structures, which can provide a useful tool for the seismic response assessment before and after the retrofitting. The methodology is mainly focused on the failure and vulnerability analysis of masonry structures using the finite element method. Using this methodology the retrofitting of historical structures with innovative techniques is investigated. The innovative technique presented here involves the exploitation of Shape Memory Alloy prestressed bars. This type of intervention is proposed because it ensures increased reversibility and minimization of interventions, in comparison with conventional retrofitting methods. In this paper, a case study is investigated for the demonstration of the proposed methodologies and techniques, which comprises a masonry Byzantine church and a masonry Cistern. Prestressed SMA alloy bars are placed into the load-bearing system of the structure. The seismic response of the non-retrofitted and the retrofitted finite element models are compared in terms of seismic energy dissipation and displacements diminution.

Environmental assessment of a BIPV system

Demetrios N. Papadopoulos,Constantinos N. Antonopoulos,Vagelis G. Papadakis Techno-Press 2022 Advances in energy research Vol.8 No.1

The application of Photovoltaic (PV) power in the building sector, is expanding as part of the ongoing energy transition into renewables. The article addresses the question of sustainability of energy generated from PVs through an environmental assessment of a building-integrated PV system (BIPV) connected to the grid through net metering. Employing retrospective life cycle analysis (LCA), with the CCaLC2 software and ecoinvent data, the article shows that the carrying structure and other balance of system (BOS) components are responsible for a three times higher energy payback time than the literature average. However, total environmental impact can be lowered through reuse or reinstallation of PVs on the same building structure after the 30-year interval. Further ways to improve environmental efficiency include identifying the most polluting materials for each LCA parameter. The results of this study are of interest to researchers and producers of PVs and organizations investing and promoting decentralized power production through PVs.

Rehabilitation of hospital buildings using passive control systems

C.A. Syrmakezis,O.A. Mavrouli,A.K. Antonopoulos 국제구조공학회 2006 Smart Structures and Systems, An International Jou Vol.2 No.4

In the case of hospital buildings, where seismic design requirements are very high, existing structures and especially those attacked by past earthquakes, appear, often, unable to fulfil the necessary safety prerequisites. In this paper, the retrofitting of hospital buildings is investigated, using alternative methods of repair and strengthening. Analysis of an existing hospital building in Patras, Greece, is performed. The load-bearing system is a reinforced concrete system. Two solutions are proposed: strengthening using concrete jackets around column and beam elements and application of viscoelastic dampers for the increase of the stability of the structure. Adequate finite element models are constructed for each case and conclusions are drawn on the efficiency of each rehabilitation method.