314 research outputs found
Shear stresses in elastic beams: an intrinsic approach
No full textThe theory of non-uniform flexure and torsion of Saint-Venant's beam with arbitrary multiply connected cross section is revisited in a coordinate-free form to provide a computationally convenient context. Numerical implementations, by Matlab, are performed to evaluate the maximum elastic shear stresses in beams with rectangular cross sections for different Poisson's ratios. The deviations between the maximum and mean stresses are then diagrammed to adjust the results provided by Jourawski's method
On Maupertuis principle in dynamics
No full textA new statement of Maupertuis principle of extremal action is contributed on the basis of a constrained action principle in the velocity phase-space in which the condition of energy conservation is imposed on virtual velocities. Dynamical systems governed by time-dependent Lagrangians on nonlinear configuration manifolds and subject to the action of time-dependent forces are considered. In time-independent systems, and in particular in conservative systems, the constrained action principle specializes to a formulation of the original Maupertuis least action principle in which however conservation of energy along the trajectory is a natural consequence of the variational principle and not an a priori assumption as in classical statements
On wave propagation in nanobeams
No full textWave propagation in Rayleigh nanobeams resting on nonlocal media is investigated in this paper. Small-scale structure-foundation problems are formulated according to a novel consistent nonlocal approach extending the special elastostatic analysis in Barretta et al. (2022). Nonlocal effects of the nanostructure are modelled according to a stress-driven integral law. External elasticity of the nano-foundation is instead described by a displacement-driven spatial convolution. The developed methodology leads to well-posed continuum problems, thus circumventing issues and applicative difficulties of the Eringen–Wieghardt nonlocal approach. Wave propagation in Rayleigh nanobeams interacting with nano-foundations is then analysed and dispersive features are analytically detected exploiting the novel consistent strategy. Closed form expressions of size-dependent dispersion relations are established and connection with outcomes available in literature is contributed. A general and well-posed methodology is thus provided to address wave propagation nanomechanical problems. Parametric studies are finally accomplished and discussed to show effects of length scale parameters on wave dispersion characteristics of small-scale systems of current interest in Nano-Engineering
Wave solutions in nonlocal integral beams
No full textWave propagation in slender beams is addressed in the framework of nonlocal continuum mechanics. The elastodynamic problem is formulated exploiting consistent methodologies of pure integral, mixture and nonlocal strain gradient elasticity. Relevant wave solutions are analytically provided, with peculiar attention to reflection and near field phenomena occurring in presence of boundaries. Notably, the solution field is got as superimposition of incident, reflected, primary near field and secondary near field waves. The latter contribution represents a further effect due to the size dependent mechanical behaviour. Limit responses for vanishing nonlocal parameter are analytically evaluated, consistently showing a zero amplitude of the secondary near field wave. Parametric analyses are carried out to show how length scale parameter, amplitude of incident wave and geometric and elastic properties of the beam affect the amplitudes of reflected, primary near field and secondary near field waves. The results obtained exploiting different nonlocal integral elasticity approaches are compared and discussed
Reticulocyte Hemoglobin Content Helps Avoid Iron Overload in Hemodialysis Patients: A Retrospective Observational Study
No full textAnemia in patients suffering from end-stage renal failure is currently treated with Erythropoiesis-Stimulating Agents (ESA). This treatment needs sufficient iron supplementation to avoid an inadequate dosage of ESA. Nowadays modern analytical instruments allow to accurately calculate the content of Hemoglobin (Hb) in reticulocytes (CHr), that can be used as a guide for prescribing patients with the appropriate amount of iron
"Si tout sujet est portrait” : figurations du moi dans Le Monde désert de Jouve et La Mort difficile de Crevel
No full textThe analysis of two novels from the 1920s selected as emblematic cases – Le Monde désert by Jouve and La Mort difficile by Crevel – leads the author to point out the connections between the figuration of the subject in literature and the portrait in painting. Indeed, the survival of the portrait itself as a pictorial genre can be seen as a sign of its involvement in the enquiry of identity and subjectivity. This article describes the three main axes that organise subjectivity as a portrait: the fluctuation between stasis and movement, the relational dimension and the fictional one. The portrait becomes the ideal model of a subject conceived as the result of a creative process. Hence, painting is not to be considered a mere narrative theme but a key to the interpretation of the novels and a metaphor of the construction of the subject
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