Periodic solutions of semi-explicit differential-algebraic equations with time-dependent constraints

In this paper we investigate the properties of the set of T-periodic solutions of semi-explicit parametrized Differential-Algebraic Equations with non-autonomous constraints of a particular type. We provide simple, degree theoretic conditions for the existence of branches of T-periodic solutions of the considered equations. Our approach is based on topological arguments about differential equations on implicitly defined manifolds, combined with elementary facts of matrix analysis

Qualitative effects of the addition of withered grapes to a freshly produced red wine: the traditional governo all'uso toscano practice

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Sociophonetics, at the crossroads of speech variation, processing and communication

On December 14th-15th, 2010, the international workshop “Sociophonetics, at the crossroads of speech variation, processing and communication” was held in Pisa, Scuola Normale Superiore, with the participation of eleven invited speakers and over ninety scholars coming from Europe, USA, Asia and Africa (http://linguistica.sns.it/Sociophonetics/home.htm). The local organizing committee, headed by Pier Marco Bertinetto and Chiara Celata from Scuola Normale Superiore and Silvia Calamai from Siena University, received forty submissions for poster presentation. The evaluation and reviewing of which could not have been achieved without the help of a small but generous scientific committee, composed by (in alphabetical order) Hans Basbøll, Gaetano Berruto, Wolfgang U. Dressler, Olle Engstrand, Alberto M. Mioni, Bruno Moretti and Daniel Recasens. The twenty papers collected in this volume are a selection of the works that were presented as posters at the conference. By covering a broad range of topics and introducing different theoretical and experimental perspectives in sociophonetic research, they fully demonstrate the popularity of the conference, and the widespread need for the sharing of ideas within a truly international community. We gratefully acknowledge all those who have contributed to producing these proceedings and in particular Pier Marco Bertinetto, Director of the Laboratorio di Linguistica “Giovanni Nencioni” at Scuola Normale Superiore, Pisa, who supported our editorial initiative and pleaded the sociophonetic cause by the Edizioni della Normale publishing house. This volume is dedicated to the memory of Edda Farnetani (1936-2010)

System identification via fast relaxed vector fitting for the structural health monitoring of masonry bridges

The increasingly request for the maintenance of the architectural heritage has led in the last decades to the extensive use of System Identification (SI) techniques for Structural Health Monitoring (SHM) purposes. These proved to be useful tools for assessing the state of conservation of the built environment and its behaviour in operating conditions. In particular, historical masonry structures and infrastructures present several compelling difficulties. Masonry is non-linear and its mechanical properties are uncertain due to the presence of local irregularities and its internal texture. Moreover, centuries-old buildings are severely affected by deterioration, eventual restoration interventions, and exposure to weather conditions. In this work, the Fast Relaxed Vector Fitting (FRVF) approach is proposed as a rapid, efficient, and reliable instrument for the vibration-based SI of such structures. The method is preliminarily validated on simple numerical examples and a multi-damaged cantilevered box beam, then tested on a true 1:2 scaled model of a masonry two-span arch bridge. The results match well the estimations from other well-established SI techniques, such as the Eigensystem Realization Algorithm (ERA), and can be utilised for damage assessment (with all the standard advantages and limitations of modal-based outlier detection). Stabilisation diagrams and frequency-damping plots are also proposed for FRVF

Experimental modal analysis of structural systems by using the fast relaxed vector fitting method

System identification (SI) techniques can be used to identify the dynamic parameters of mechanical systems and civil infrastructures. The aim is to rapidly and consistently model the object of interest, in a quantitative and principled manner. This is also useful in establishing the capacity of a structure to serve its purpose, thus as a tool for structural health monitoring (SHM). In this context, input–output SI techniques allow precise and robust identification regardless of the actual input. However, one of the most popular and widely used approaches, the Rational Fraction Polynomial (RFP) method, has several drawbacks. The fitting problem is nonlinear and generally non‐convex, with many local minima; even if linearised via weighting, it can become severely ill‐conditioned. Here, a novel proposal for the broadband macro‐modelling of structures in the frequency domain with several output and/or input channels is presented. A variant of the vector fitting approach, the Fast Relaxed Vector Fitting (FRVF), applied so far in the literature only for the identification of electrical circuits, is translated and adapted to serve as a technique for structural SI and compared with other traditional techniques. A study about the robustness of the FRVF method with respect to noise is carried out on a numerical system. Finally, the method is applied to two experimental case studies: a scaled model of a high‐aspect‐ratio (HAR) wing and the well known benchmark problem of the three‐storey frame of Los Alamos laboratories. Promising results were achieved in terms of accuracy and computational performance