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Rome, Italy

Favata A.,University of Trento | Micheletti A.,Polytechnic University of Mozambique | Podio-Guidugli P.,Accademia Nazionale Dei Lincei | Podio-Guidugli P.,University of Rome Tor Vergata
International Journal of Engineering Science

The discrete modeling of a large class of mechanical structures can be based on a stick-and-spring concept. We here present a stick-and-spring theory with potential application to the statics and the dynamics of such nanostructures as graphene, carbon nanotubes, viral capsids, and others. A key feature of our theory is its geometrical nonlinearity: we combine exactly defined strain measures with a general linear stress response; another, rarely found feature is a careful account of prestress states. A linear version is firstly proposed, where attention is restricted to study small displacements from an unstressed reference placement. Next, a theory linearized about a prestressed (preloaded or not) placement is displayed, which is based on a careful analysis of the tangent stiffness operator and its two parts, the elastic and prestress stiffness operators. Finally, two examples are proposed and solved; when an analytical solution is of prohibitive complication, numerical solutions are given, by the use of a specifically implemented 'stick-and-spring' code. © 2014 Elsevier B.V. All rights reserved. Source

Atti della Societa Toscana di Scienze Naturali, Memorie Serie A

Polytypism in Hanjiangite, sheet silicate-carbonate-fluoride of calcium, aluminium, vanadium and barium. The crystal structure of hanjiangite, sheet silicate-carbonate-fluoride of calcium, aluminium, vanadium and barium is described and its polytypic character is indicated. It is shown that hanjiagite is built up by two distinct structural layers (building layers BL1 and BL2) which alternate along the direction normal to the layers. The analysis of the possible sequences shows that there are three main polytypes: one, hanjiangite-2M, corresponding to the structure of the phase found in nature and studied by Liu et al. (2012), in which two layers of each type alternate for two times in a monoclinic cell; the two other polytypes, hanjiangite-1M and hanjiangite-3T, present a single alternation of BL1 and BL2 layers in a monoclinic cell (hanjiangite-1M) and a triple alternation of BL1 and BL2 in a trigonal cell (hanjiangite-3T). The close metrical and compositional relationships of hanjiangite-1M with a pair of other complex layered minerals are discussed. Source

De Martini F.,Accademia Nazionale Dei Lincei | Santamato E.,University of Naples Federico II
International Journal of Theoretical Physics

The principles and methods of the Conformal Quantum Geometrodynamics (CQG) based on the Weyl’s differential geometry are presented. The theory applied to the case of the relativistic single quantum spin $\frac{1}{2}$ leads a novel and unconventional derivation of Dirac’s equation. The further extension of the theory to the case of two spins $\frac{1}{2}$ in EPR entangled state and to the related violation of Bell’s inequalities leads, by a non relativistic analysis, to an insightful resolution of the enigma implied by quantum nonlocality. © 2013, Springer Science+Business Media New York. Source