Higher Institute on Territorial Systems for Innovation
PORTO Publications Open Repository TOrinoNot a member yet
91193 research outputs found
Sort by
Intrinsic and state parameters governing the efficiency of bentonite barriers for contaminant control
No full textThe osmotic, hydraulic and self-healing efficiency of bentonite based barriers (e.g. geosynthetic clay liners) for containment of polluting solutes are governed by both the chemico-physical intrinsic parameters of the bentonite, i.e. the solid density (rosk), the total specific surface (S), the fixed negative electric surface charge (sigma), the Stern fraction (fStern), and by the chemico-mechanical state parameters able to quantify the solid skeleton density and fabric, i.e. the total (e) and nano (en) void ratio, the average number of platelets per tactoid (Nl, AV), and the effective electric fixed-charge concentration (csk,0). In turn, looking at saturated active clays only, the state parameters seem to be controlled by the effective stress history (SH), ionic valence (vi) and related exposure sequence of salt concentrations in the pore solution (cs). A theoretical framework, able to describe chemical, hydraulic and mechanical behaviors of bentonites in the case of one-dimensional strain and flow fields, has been set up. In particular, the relationships, linking the aforementioned state and intrinsic parameters of a given bentonite with its hydraulic conductivity (k), effective diffusion coefficient (D*s), osmotic coefficient (w) and swelling pressure (usw) under different stress-histories and solute concentration sequences, are presented. The validity of the proposed theoretical hydro-chemico-mechanical framework has been tested by comparison of its predictions with some of the available experimental results on bentonites (i.e. hydraulic conductivity tests, swelling pressure tests and osmotic efficiency tests)
Resistive switching and impedance properties of soft nanocomposites based on Ag nanoparticles
No full textPolymeric nanocomposites (NCs) containing Ag nanoparticles (NPs) feature interesting properties arising from the interaction between a confined metallic system, its surface and a viscoelastic matrix whose electronic properties range between a dielectric and an ionic conductor. They are currently exploited in a number of applications as electronic materials, among the others the most promising being high-K extrinsic dielectrics and resistive switching devices (RSDs). A large diffusivity through the polymeric network permits the displacement of Ag ions to sustain reversible electrochemical states that store information in impedance states. We present a detailed study showing how the interaction between polymeric matrix and dispersed NPs, thanks to its huge specific surface, influences the resistive switching and electrical impedance in view of an application as soft neuromorphic devices, going beyond the simple superposition of effects due to the pure matrix and the filler alone
Component-wise vibration analysis of stiffened plates accounting for stiffener modes
No full textThis work has the aims to assess and compare the behavior of different finite element models in a free-vibration analysis of reinforced structures. The effects of the aspect ratio and cross-sectional shape of the stringers have been analyzed using both classical and refined FE. One- and two-dimensional classical finite element models, as well as refined one-dimensional elements, derived using the Carrera Unified Formulation, have been considered in an analysis of reinforced structures. The accuracy and efficiency of these models have been investigated. A three-dimensional model has been used as a reference solution. Three different modeling approaches have been considered in the present work. Two approaches are based on classical models provided by commercial tools: the first uses two-dimensional elements for both a plate and stringers, while the second uses two-dimensional elements to simulate the plate and the beam elements for the stringers. The third approach uses a refined one-dimensional model, based on the Carrera Unified Formulation. This refined one-dimensional model considers a variable kinematic displacement field over the beam cross section. In the present work, Lagrange polynomials are used to describe the cross-sectional displacement field. The use of a component-wise modeling approach allows the stiffeners to be modeled as independent entities. The component-wise approach was first assessed and convergence was then evaluated. The performances of these models in the analysis of reinforced structure were then compared with those from classical models. The use of refined one-dimensional models allows stiffener modes to be investigated. The results show that this approach is comparable to a full three-dimensional solution. The use of classical one- and two-dimensional models does not allow the local deformation of reinforcements to be taken into account. Therefore, these models cannot be considered accurate when the aim of the analysis is to investigate the local mode
Direct current microgrids based on solar power systems and storage optimization, as a tool for cost-effective rural electrification
No full text
Influence of actual static transmission error and contact ratio on gear engagement dynamics
No full textIn the literature, many models for depicting the gear mating dynamics are present. In addition, finite element techniques allow to perform highly representative engagement analysis, but with a high computational effort and in particular only after having defined a semi-definitive geometry. When a new gearbox is developed, its geometrical features are not completely defined, and highly refined finite element models cannot be used. On the other hand, performing parametric analysis at the early stages of the design process is mandatory to shorten the lead time. In this direction, an accurate parametric model of gear engagement, which requires a little computational effort, is an enabling technology. In the present paper, the Harmonic Balance Method is used to build a simple engagement model able to predict the dynamic effect in teeth contact and to investigate the contribution to gear dynamics due to actual static transmission error and the contact ratio. A particular emphasis is given to the actual contact ratio estimation and the relationship between the teeth stiffness and the dynamic transmission error. As principal result, the possibility to design teeth stiffness in order to minimize dynamic transmission error is investigated and HBM potential for reaching this goal is evaluated
El paisaje de la electricidad y arquitectura
No full textThe beginning of the hydroelectric energy production has deeply affected mountain areas, contributing to a significant transformation of the environment. Dams, power plants, watersheds, pipelines, penstocks can be found in almost all mountain valleys and are indelible traces of the changes that have involved these territories since the last decade of the ninetieth century. These traces are real historical and cultural resources, still waiting to be properly exploited and made readable and available to those who already normally visit or may visit in the future mountain areas, contributing to their tourism development
Easy batch-scale production of cobalt ferrite nanopowders by two-step milling: Structural and magnetic characterization
No full textCobalt ferrite (CF) powder was synthesized by solid state reaction method at two different calcination temperatures (1120 K and 1320 K) then milled in two steps, gradually reducing the milling media size. The first milling step results in CF nanoparticles with crystallite size of 33 nm showing fairly high coercivity (3.7 kOe), > 5 times higher than the non-milled material (0.7 kOe). The high coercivity was correlated to the crystallite size close to the single-domain limit, and to the strain increase up to 2.1%. This value of strain is the highest ever reported in literature for the CF and brings to the highest figure of merit for permanent magnets, (BH)max = 2.16 MGOe. After the second milling step the powder displays particle size of 9 nm, release of strain (ε = 1.2%), coercivity reduction that approaches 250 Oe and decrease of the deblocking temperature from 421 K to 317 K. The large tunability obtained by multi-step milling allows to use CF in different applications. In particular, the milled CF powder characterized by high microstrain is a good candidate for the realization of rare-earth-free permanent magnets (at least on the basis of the (BH)max product). For the first time, a correlation between the spin-canting angle and the degree of inversion, the crystallite size and the microstrain is presented and discussed