A note on stability conditions for planar switched systems

This paper is concerned with the stability problem for the planar linear switched system $\dot x(t)=u(t)A_1x(t)+(1-u(t))A_2x(t)$, where the real matrices $A_1,A_2\in \R^{2\times 2}$ are Hurwitz and $u(\cdot) [0,\infty[\to\{0,1\}$ is a measurable function. We give coordinate-invariant necessary and sufficient conditions on $A_1$ and $A_2$ under which the system is asymptotically stable for arbitrary switching functions $u(\cdot)$. The new conditions unify those given in previous papers and are simpler to be verified since we are reduced to study 4 cases instead of 20. Most of the cases are analyzed in terms of the function \Gamma(A_1,A_2)={1/2}(\tr(A_1) \tr(A_2)- \tr(A_1A_2)).Comment: 9 pages, 3 figure

Local properties of almost-Riemannian structures in dimension 3

A 3D almost-Riemannian manifold is a generalized Riemannian manifold defined locally by 3 vector fields that play the role of an orthonormal frame, but could become collinear on some set \Zz called the singular set. Under the Hormander condition, a 3D almost-Riemannian structure still has a metric space structure, whose topology is compatible with the original topology of the manifold. Almost-Riemannian manifolds were deeply studied in dimension 2. In this paper we start the study of the 3D case which appear to be reacher with respect to the 2D case, due to the presence of abnormal extremals which define a field of directions on the singular set. We study the type of singularities of the metric that could appear generically, we construct local normal forms and we study abnormal extremals. We then study the nilpotent approximation and the structure of the corresponding small spheres. We finally give some preliminary results about heat diffusion on such manifolds

Targeting the Structural Balance

This paper discusses whether a country should conduct fiscal policy by targeting a structural (or cyclically adjusted) fiscal balance. The paper is divided into three sections. The first section discusses the concept of cyclically adjusted balance (CAB) and points out practical and conceptual problems related to the interpretation and the measurement of a CAB. The second section discusses the theoretical rationale for having a fiscal rule in general and a rule defined in terms of a cyclically adjusted balance in particular. The third section discusses conceptual and practical problems with adopting fiscal rules and rules that target the structural balance.

Indagini dirette e fonti amministrative: dall'alternativa all'ancora incompiuta integrazione

The focus of the paper is about the relationships between registers (an censuses) and surveys in the in the Italian official statistics. After a brief introduction on the historical background, marked by a polarization between the two strategies of data collection, the focus is on the 1980s and early '90s. Under the presidency of Guido M. Rey a new strategy is embraced, based on the integration of different data sources. The main accomplishments, and shortcomings, of this strategy are presented and discussed. The final part of the paper is devoted to a critical assessment of the still unsatisfactory state of the art today, and to broad suggestions for a reasonable way out

Preparation and voltammetric characterization of electrodes coated with Langmuir-Schaefer ultrathin films of Nafion®

Ultrathin films of Nafion® perfluorinated polymer were deposited on indium-tin oxide electrodes (ITO) by using Langmuir-Schaefer (LS) technique, after optimization of the subphase composition conditions. Morphological characteristics of these coatings were obtained by Atomic Force Microscopy (AFM). Nafion® LS films showed a good uniformity and complete coverage of the electrode surface, however a different organization degree of the polymer layer was evidenced with respect to thin films deposited by spin-coating. ITO electrodes modified with Nafion® LS coatings preconcentrate by ion-exchange electroactive cations, such as Ru[(NH3)6]3+, dissolved in diluted solutions. The electroactive species is retained by the Nafion® LS coated ITO also after transfer of the modified electrode into pure supporting electrolyte. This allowed the use of the ruthenium complex as voltammetric probe to test diffusion phenomena within the Nafion® LS films. Apparent diffusion coefficients (Dapp) of Ru[(NH3)6]3+ incorporated in Nafion® LS films were obtained by voltammetric measurements. Dapp values decrease slightly by increasing the amount of ruthenium complex incorporated in the ultrathin film. They are significantly lower than values typical for recasted Nafion® films, in agreement with the highly condensed nature of the Nafion® LS fims. Filmes ultrafinos do polímero perfluorado Nafion® foram depositados em eletrodos de óxido índio-titânio (ITO) usando a técnica de Langmuir-Scaefer (LS), depois da otimização das condições de composição da subfase. As características morfológicas das camadas foram obtidas por Microscopia de Força Atômica (AFM). Filmes de Nafion® LS mostraram boa uniformidade e cobertura completa da superfície do eletrodo. No entanto, diferentes graus de organização das camadas poliméricas ficaram evidentes com respeito a filmes finos depositados por revestimento rotacional. Eletrodos ITO modificados com camadas de Nafion® LS, pré-concentrados por cátions eletroativos de troca iônica, como o Ru[(NH3)6]3+, dissolveram-se em soluções diluídas. A espécie eletroativa foi retida pelo ITO com camada de Nafion® LS, mesmo depois da mudança do eletrodo modificado para eletrodo de suporte purificado. Isto possibilitou o uso do complexo de rutênio como padrão voltamétrico para o teste do fenômeno de difusão nos filmes de Nafion® LS. Os coeficientes de difusão aparentes (Dapp) do Ru[(NH3)6]3+ incorporado no filme de Nafion® LS foram obtidos por medidas voltamétricas. Os valores de Dapp diminuíram levemente com o aumento da quantidade de complexo de rutênio incorporado no filme ultrafino e foram significativamente mais baixos do que os valores para filmes de Nafion® recapados, em acordo com a natureza altamente condensada dos filmes de Nafion® LS

Light Logics and the Call-by-Value Lambda Calculus

The so-called light logics have been introduced as logical systems enjoying quite remarkable normalization properties. Designing a type assignment system for pure lambda calculus from these logics, however, is problematic. In this paper we show that shifting from usual call-by-name to call-by-value lambda calculus allows regaining strong connections with the underlying logic. This will be done in the context of Elementary Affine Logic (EAL), designing a type system in natural deduction style assigning EAL formulae to lambda terms.Comment: 28 page

VOLTAMMETRIC NANOELECTRODE ENSEMBLES\ud BASED ON TEMPLATED METAL NANOWIRES\ud IN TRACK-ETCHED POLYMER MEMBRANES

This chapter reviews the recent advances taking place in the field of polymer based electrochemical sensors, in particular nanoelectrode ensembles (NEEs). In these sensors the polymer plays a crucial role in determining the specific characteristics and analytical performances. Synthetic approaches as well as principles of functioning and specific advantages and limits of NEEs are critically discussed. Useful examples of application to determinations of trace and ultratrace concentrations of inorganic and organic electroactive molecules of interest for environmental and biomedical analysis are given along with prospects in the future development of polymer based electrochemical sensors