Search

Abstract: A beam model aimed at describing the flexural–torsional buckling of thin-walled members with non-symmetric cross-sections is presented. Two beam axes are introduced, and strain is defined with respect to both. The shearing strain between the cross-section and one of the two axes is assumed to vanish; the warping is supposed to be linear in the twist. Non-linear hyperelastic constitutive relations are introduced; by means of standard localization and static perturbation techniques, the field equations describing the flexural–torsional buckling are obtained. One benchmark example is given and some numerical values of the critical load for various warping constraints at the beam ends are provided. [Copyright &y& Elsevier]

Abstract: The mechanical behavior of soft matter is characterized by large shape changes, often accompanied by small changes of elastic energy; non-linear elasticity, with large, inhomogeneous, and anisotropic distortions, that may evolve in time, proved to be an effective modeling tool for many of such soft materials. Here, we deal with the definition of an appropriate strain measure, called the elastic metric, upon which the elastic energy density can be defined. Moreover, we discuss two key issues about distortions: one deals with the notion of compatible distortions, that is, distortion fields yielding a global configuration without any change of the elastic energy; the other concerns the symmetries of the material responses. We also present few selected examples of non-linear, anisotropic, elastic response where distortions play a key role. [Copyright &y& Elsevier]

Abstract: We present a simplified heart model with the aim of introducing a mechanical point of view in the interpretation of the pressure–volume loops. In particular, we propose a mechanical description of muscle contraction, and discuss its implications with reference to a specific pressure–volume loop representative of a normal human patient. [Copyright &y& Elsevier]

The study describes a stand-alone photovoltaic system in which the storage is realized using electrolytic hydrogen, converted into electricity in fuel cells. The aim of the research is the optimization of the sizing of the system elements chain (photovoltaic generator, electrolyzer, tank, fuel cell) with respect to the electric load to fulfil. A positive annual balance between hydrogen production and consumption must be guaranteed; furthermore, energy production surplus that cannot be stored or converted into hydrogen due to batteries or tanks capacity limits must be avoided. The energetic analysis and that of hydrogen production and consumption have been carried out on an hourly basis using the HOMER software. The study shows that, being the load active in the evening and the system disconnected from the grid, excess energy cannot be exploited unless large tanks are used, if high gas pressures are to be avoided. Consequently, the system use in public areas or residential buildings, where visual impact generated by tanks is hardly acceptable and safety rules do not allow high gas pressures, is advisable only in grid-connected configurations. Such problems are by far reduced when a marked self consumption is present. • Hydrogen might represent the energy vector of the future. • RES can be used as a primary source for the production of electrolytic hydrogen. • Electrolysis of water from RES has only byproducts water and heat. • After electrolysis hydrogen is stored and converted into electricity by fuel cells. • The study refers to a real stand-alone PV system equipped with hydrogen storage. [ABSTRACT FROM AUTHOR]

A mechanics-based analysis of data from three-dimensional speckle tracking echocardiography is proposed, aimed at investigating deformations in myocardium and at assessing shape and function of distinct strain lines corresponding to the principal strain lines of the cardiac tissue. The analysis is based on the application of a protocol of measurement of the endocardial and epicardial principal strain lines, which was already tested on simulated left ventricles. In contrast with similar studies, it is established that endocardial principal strain lines cannot be identified with any structural fibers, not even along the systolic phase and is suggested that it is due to the capacity of the endocardial surface to contrast the dilation of the left ventricle. [ABSTRACT FROM AUTHOR]

Abstract: A question which has not been addressed so far in the analysis of the twisting motion of the heart, relates to the existence of any advantages in energetic expenditure due to differential contractile properties across the wall of the ventricles. The question is addressed in this paper by a highly simplified analytical model of the ventricular cavity, based on a cylindrical geometry and set in the context of the linear theory of elasticity; however, the anisotropy of contraction is also taken into account. It is concluded, that when oppositely directed spirals of fibres in the internal and external layers of the cylinder keep the torsion within suitable limits, i.e. mimicking the biological context, a smaller energetic expenditure is related to a transmural pattern of contraction which is not uniform, and presents a larger epicardial contraction. [Copyright &y& Elsevier]

Abstract: We set a twofold investigation: we assess left ventricular (LV) rotation and twist in the human heart through 3D-echocardiographic speckle tracking, and use representative experimental data as benchmark with respect to numerical results obtained by solving our mechanical model of the LV. We aim at new insight into the relationships between myocardial contraction patterns and the overall behavior at the scale of the whole organ. It is concluded that torsional rotation is sensitive to transmural gradients of contractility which is assumed linearly related to action potential duration (APD). Pressure–volume loops and other basic strain measures are not affected by these gradients. Therefore, realistic torsional behavior of human LV may indeed correspond to the electrophysiological and functional differences between endocardial and epicardial cells recently observed in non-failing hearts. Future investigations need now to integrate the mechanical model proposed here with minimal models of human ventricular APD to drive excitation-contraction coupling transmurally. [Copyright &y& Elsevier]

We exploit the possibility of deforming a solid volume, or a surface as well, by assigning a target metric. As well known, an elastic solid may change its shape under two different kinds of actions: one are the loadings, the other one are the distortions, aka, the pre-strains. Actually, a distortion prescribes the target metric sought by the solid, and the metric effectively realized is the one that minimize the distance, measured through an elastic energy, between the target metric and the actual one. The challenge of our work is to use the metric information taken from a pair of configurations X ¯ , X of a given body B x , to deform a different body B y , so that its deformation be as similar as possible to the one suffered by B x. In particular, we assess the metric change between the two configurations X ¯ , X of the template B x ; then, we use this information to build a target metric for B y , exploiting the notion of distortions: given a source configuration Y ¯ , we find a target configuration Y by minimizing an appropriate elastic energy. The proposed method is very effective in deforming solids as well as surfaces, and in reproducing similar deformations even when applied to different bodies. [ABSTRACT FROM AUTHOR]