3,559 research outputs found
A note on stability conditions for planar switched systems
This paper is concerned with the stability problem for the planar linear
switched system , where the real
matrices are Hurwitz and is a measurable function. We give coordinate-invariant
necessary and sufficient conditions on and under which the system
is asymptotically stable for arbitrary switching functions . 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 NafionÂź
Ultrathin films of NafionÂź 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). NafionÂź 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 NafionÂź 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 NafionÂź 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 NafionÂź LS films. Apparent diffusion coefficients (Dapp) of Ru[(NH3)6]3+ incorporated in NafionÂź 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 NafionÂź films, in agreement with the highly condensed nature of the NafionÂź LS fims. Filmes ultrafinos do polĂmero perfluorado NafionÂź foram depositados em eletrodos de Ăłxido Ăndio-titĂąnio (ITO) usando a tĂ©cnica de Langmuir-Scaefer (LS), depois da otimização das condiçÔes de composição da subfase. As caracterĂsticas morfolĂłgicas das camadas foram obtidas por Microscopia de Força AtĂŽmica (AFM). Filmes de NafionÂź LS mostraram boa uniformidade e cobertura completa da superfĂcie do eletrodo. No entanto, diferentes graus de organização das camadas polimĂ©ricas ficaram evidentes com respeito a filmes finos depositados por revestimento rotacional. Eletrodos ITO modificados com camadas de NafionÂź LS, prĂ©-concentrados por cĂĄtions eletroativos de troca iĂŽnica, como o Ru[(NH3)6]3+, dissolveram-se em soluçÔes diluĂdas. A espĂ©cie eletroativa foi retida pelo ITO com camada de NafionÂź LS, mesmo depois da mudança do eletrodo modificado para eletrodo de suporte purificado. Isto possibilitou o uso do complexo de rutĂȘnio como padrĂŁo voltamĂ©trico para o teste do fenĂŽmeno de difusĂŁo nos filmes de NafionÂź LS. Os coeficientes de difusĂŁo aparentes (Dapp) do Ru[(NH3)6]3+ incorporado no filme de NafionÂź LS foram obtidos por medidas voltamĂ©tricas. Os valores de Dapp diminuĂram levemente com o aumento da quantidade de complexo de rutĂȘnio incorporado no filme ultrafino e foram significativamente mais baixos do que os valores para filmes de NafionÂź recapados, em acordo com a natureza altamente condensada dos filmes de NafionÂź 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
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