K-Theory for group C^*-algebras

These notes are based on a lecture course given by the first author in the Sedano Winter School on K-theory held in Sedano, Spain, on January 22-27th of 2007. They aim at introducing K-theory of C^*-algebras, equivariant K-homology and KK-theory in the context of the Baum-Connes conjecture.Comment: 22 pages, 2 figures, to be published in Springer Lecture Note

Searching for chemical inhomogeneities in Open Clusters: Analysis of the CN and CH Molecular Band Strengths in NGC 2158, NGC 2420, NGC 2682, NGC 7789 and Berkeley 29

Context: The total mass of a cluster, being the main parameter determining its ability to host more than one stellar generation, may constitute a threshold below which the cluster is able to form only a single stellar population. AIms: Our goal is to investigate the existence of star-to-star variations of CN and CH band strengths, related to the N and C abundances, respectively, among the stars in five open cluster (NGC 2158, NGC 2420, NGC 2682, NGC 7789 and Berkeley 29) similar to those observed in globular clusters and linked with the existence of multiple populations therein. Since these systems are less massive than globulars, our results may allow us to constrain the lower mass necessary to form more than one stellar population. Methods: We measured the strength of the CN and CH bands, which correlate with the C and N abundances, using four molecular indices in low-resolution SDSS/SEGUE spectra. Results: We found that for four of the open clusters (NGC 2158, NGC 2420, NGC 2682 and Berkeley 29) all the stars studied in each of them have similar CN and CH band strengths within the uncertainties since neither anomalous spreads nor bimodalities have been detected in their CN and CH distributions. In contrast, for NGC 7789 we found an anomalous spread in the strength of the CN molecular band at 3839 \AA which is larger than the uncertainties. However, the small number of stars studied in this cluster implies that further analysis is needed to confirm the existence of chemical inhomogeneities in this cluster.Comment: 11 pages, 9 figures, Accepted for publication in A&A, Tables 7, 8 and 9 will be publish onlin

Some results on thermal stress of layered plates and shells by using Unified Formulation

This work presents some results on two-dimensional modelling of thermal stress problems in multilayered structures. The governing equations are written by referring to the Unified Formulation (UF) introduced by the first author. These equations are obtained in a compact form, that doesn't depend on the order of expansion of variables in the thickness direction or the variable description (layer-wise models and equivalent single layers models). Classical and refined theories based on the Principle of Virtual Displacements (PVD) and advanced mixed theories based on the Reissner Mixed Variational Theorem (RMVT) are both considered. As a result, a large variety of theories are derived and compared. The temperature profile along the thickness of the plate/shell is calculated by solving the Fourier's heat conduction equation. Alternatively, thermo-mechanical coupling problems can be considered, in which the thermal variation is influenced by mechanical loading. Exact closed-form solutions are provided for plates and shells, but also the applications of the Ritz method and the Finite Element Method (FEM) are presented

Boredom

This Element challenges prevailing views of boredom as a modern phenomenon and as an experience occurring inside our minds

Advanced modeling of embedded piezo-electric transducers for the health-monitoring of layered structures

The present paper presents an innovative approach for the numerical modeling of piezo-electric transducers for the health-monitoring of layered structures. The numerical approach has been developed in the frameworks of the Carrera Unified Formulation. This computational tool allows refined numerical models to be derived in a unified and efficient fashion. The use of higher-order models and the capability to connect different kinematic models using the node-dependent kinematic approach has led to an efficient modeling technique for global-local analysis. This approach can refine the model only in those regions where it is required, e.g., the areas where piezo-electric transducers are placed. The model has been used to study embedded and surface-mounted sensors. The accuracy of the present model has been verified by comparing the current results with numerical and experimental data from the literature. Different modeling solutions have been developed, mixing one-, two- and three-dimensional finite elements. The results show that the use of the present modeling technique allows the computational cost to be reduced with respect to the classical approaches preserving the accuracy of the results in the critical areas

Multi-dimensional models for the global-local analysis of smart layered structures

The present paper presents a multidimensional model for the global-local analysis of smart layered structures. The use of the Carrera Unified Formulation has lead to a general framework for the development of one-, two- and three-dimensional models. The use of the node-dependent kinematic approach makes it possible to easily connect elements with incompatible kinematics, that is, refined kinematic elements can be connected with classical elements without the need of ad hoc connection strategies. The capabilities of this numerical model have been exploited to develop enhanced global-local models for smart layered structures where high-fidelity models are used only in those areas where complex phenomena appear, e.g. around a piezo-patch. The results show the accuracy and efficiency of the present approach and make it suitable for future applications in the design of smart structures