1,721,771 research outputs found
Determination of the cabibbo-kobayashi-maskawa matrix element |Vcb|
No full textIn this review we present and discuss the determination of the magnitude of the Cabibbo-Kobayashi-Maskawa (CKM) matrix parameter Vcb. The CKM matrix parametrizes the weak charged current interactions of quarks in the standard model (SM), and a precise determination of its elements has always been one of the most important targets of particle physics. The precise knowledge of the |Vcb| value plays a pivotal role in testing the flavour sector of the SM and in the analyses of the unitarity of the CKM matrix. The SM does not predict the values of the CKM matrix elements, which have to be extracted by experimental data. Given the variety of channels that allow the extraction of |Vcb|, different theoretical and experimental techniques are mustered for the |Vcb| determination. The exertion towards precision represents not only a significant test of our theoretical procedures but a stimulus towards better detection performances. The most precise measurements of |Vcb| come from semileptonic decays, that being tree level at the lowest order in the SM are generally considered unaffected by physics beyond the SM. After summarizing the characteristics of the SM that set the frame for the determination of |Vcb|, we discuss inclusive and exclusive semileptonic B decays. We analyse the |Vcb| extraction methods and recent results, detailing both the theoretical and experimental techniques, and, finally, outline future prospects. We also comment on exclusive decays into heavy leptons, on the observables R(D) and R(D∗), on decays to excited D meson states and on baryon decays
A continuous vibration analysis model for cables with sag and bending stiffness
No full textThe paper reports an investigation on a continuous model for dynamics of large-diameter sagged cables, taking bending stiffness and sag extensibility into account. Following the classical guidelines of cable dynamics, and by making some simplifications, a continuous model is found in this work; frequency and mode shape equations have been obtained in non-dimensional form. Comparison with Finite Element (FE) and Finite Difference (FD) models has been made to validate the proposed method. Moreover, it allows us to represent local effects at the end zones of cable correctly, if clamped boundary conditions are assumed. To obtain comparable results, the FE model would require a large subdivision, with consequently, a large number of elements. The proposed eigenfunctions allow us to solve the dynamic problem without a large computational effort compared to FE or FD approaches. Finally, in order to show the usefulness of the developed continuous model, an application on the main cables of the designed Messina Strait Bridge has been made. © 2007 Elsevier Ltd. All rights reserved
Indagine sperimentale sulla dispersione di fibre di vetro da pannelli usati per la coibentazione.
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