1,721,881 research outputs found
Structure and evolution of mammoth molar enamel
No full textThis work investigates the structure of Eurasian Plio–Pleistocene Mammuthus enamel, with attention to diagenesis and individual variability. A focal point of this study was to determine whether morphological trends in Mammuthus molars were accompanied by correlated enamel microstructure changes. In the examined four taxa the enamel of the cheek teeth consists of three layers delimited by two major discontinuities in enamel prism direction. Noticeably, the enamel capping the occlusal end of the unworn molar plates retains a less derived two−layered structure, similar to that found in the basal proboscidean Moeritherium. In Mammuthus meridionalis the third deciduous premolar is differentiated from all other teeth in having more strongly decussating Hunter−Schreger bands in the middle layer, as a possible reinforcement of the very thin enamel. Evidence from this analysis shows that, in the transition from late Middle Pliocene M. rumanus to Late Pleistocene M. primigenius, the middle enamel layer, which is made up of prisms at an angle to the occlusal surface, providing greater resistance against wear, increased its relative thickness. This is consistent with the hypothesis that Mammuthus adapted to a more abrasive diet. Comparison with other proboscidean taxa indicates that the schmelzmuster (enamel pattern) found in Mammuthus is a synapomorphy of the Elephantoidea
Federico Ubaldini esegeta e apologista di Dante nel Seicento
Full text linkIl lavoro prende in esame l'attiva erudita, in particolar modo dantesca, del medievista secentesco Federico Ubaldini, il quale all'interno del suo dialogo 'Il Giordano o vero Nuova difesa di Dante' controbatte alle critiche del letterato Nicola Villani, che aveva accusato il poeta fiorentino di aver inserito, all'interno del suo poema, contraddizioni, oscurità linguistiche e storie false
Flexural torsional buckling of uniformly compressed beam-like structures
No full textA Timoshenko beam model embedded in a 3D space is introduced for buckling analysis of multi-store buildings, made by rigid floors connected by elastic columns. The beam model is developed via a direct approach, and the constitutive law, accounting for prestress forces, is deduced via a suitable homogenization procedure. The bifurcation analysis for the case of uniformly compressed buildings is then addressed, and numerical results concerning the Timoshenko model are compared with 3D finite element analyses. Finally, some conclusions and perspectives are drawn
"Emporium". Parole e figure tra il 1895 e il 1964, atti dell’incontro di studio (Pisa, 30-31 maggio 2007)
No full textDynamic modeling of taut strings carrying a traveling mass
No full textIn this paper, a new consistent dynamic model is proposed, aimed at studying linear vibrations induced in an elastic wire by a bilaterally constrained single mass moving with a constant velocity. Starting from a variational formulation, through the Hadamard’s condition, a corrective term to the local linear stiffness is determined in the continuum model as a function of the moving mass velocity; in this way, the boundary conditions are properly found. The representation of the solutions of the hyperbolic equations governing the motion of the wire presents some difficulties, which are solved by means of a suitable coordinate transformation in a time-invariant domain and a judicious choice of the set of shape functions, to be used in the discrete formulation of the problem. This new description allows an easy estimation of high-order deformations that are neglected by a purely linear approach. When the mass velocity is sufficiently high, displacements near the supports show high gradients: in these cases, it is necessary to use an unknown velocity or introduce an advanced mechanical model in order to correctly describe the motion of the mass. Numerical examples confirm the stability of the proposed solution in all conditions examined
Buckling disappearance via merging/divergence in a nonlinear three-d.o.f. system with linear constitutive law
Full text linkThe phenomenon of buckling disappearance, occurring in a parameter-dependent family of systems admitting a nontrivial fundamental path, is studied. Two different forms of disappearance are detected, namely: (i) the divergence, in which the critical load continuously tends to infinity, and (ii) the merging, in which two critical loads approach each other, coalesce, and then disappear at a finite value of the critical load. It is shown that the two phenomena can be exhibited by the same mechanical system, when a suitable elasto-geometric parameter is varied. More importantly, it is proved that merging continuously changes into divergence when a second parameter is changed. A paradigmatic system is chosen to illustrate the two forms of buckling, i.e., a three degree-of-freedom spherical pendulum, elastically constrained at the ground, loaded by a transverse force and/or a conservative couple, made of two longitudinal potential forces. The springs are taken elastically linear, to stress the fact that divergence not necessarily calls for introducing a nonlinear constitutive law, as also mentioned in literature. Only a linear bifurcation analysis is carried out here, aimed to find the bifurcation points along the nonlinear fundamental path. However, due to the presence of non-negligible prestrains, such a bifurcation problem is governed by nonlinear algebraic equations, whose number of roots cannot be predicted in advance
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