Energy harvesting using porous piezoelectric beam with impacts

An analytical model of impact energy harvester consisting of a cantilever beam with integrated piezoelectric patches and a ball is developed in this paper. The material chosen to extract the energy is porous PZT, a composite material made of two phases: air and PZT. This material offers good control of the capacitance and the stiffness of the resultant composite material and expands the design space for the harvester. The cantilever beam is modelled using a single degree-of-freedom approximation, and a load resistor is used to represent the external circuit. The response of the energy harvester and the power output is obtained for harmonic base excitation, and the effect of excitation frequency, boundary distance, load resistance and porosity of the PZT material. The results highlight the potential for the impact harvester and motivate further studies to optimize the harvester

Electric field distribution in porous piezoelectric materials during polarization

High piezoelectric coupling coefficients enable the harvesting of more energy or increase the sensitivity of sensors which work using the principle of piezoelectricity. These coefficients depend on the material properties, but the manufacturing process can have a significant impact on the resulting overall coefficients. During the manufacturing process, one of the main steps is the process of polarization where a poling electric field aligns the ferroelectric domains in a similar direction in order to create a transversely isotropic material able to generate electric fields or deformations. The degree of polarization depends on multiple factors and it can strongly influence the final piezoelectric coefficients. In this paper, a study on the electric field distribution on the sensitivity of the main piezoelectric and dielectric coefficients to the polarization process is performed, focusing on porous piezoelectric materials. Different inclusion geometries are considered, namely spherical, ellipsoidal and spheres with cracks. The electric field distribution at the micro scale within a representative volume element is modelled to determine the material polarization level using the finite element method. The results show that the electric field distribution is highly dependent on the inclusion geometries and cracks and it has a noticeable impact on the equivalent piezoelectric coefficients. These results are compared with experimental measurements from published literature. Good agreement is found between the ellipsoidal model and the experimental data

Impact of physical activity and cardiovascular fitness on total homocysteine concentrations in European adolescents : The HELENA Study

We examined the association of physical activity (PA), cardiovascular fi tness (CVF) and fatness with total homocysteine (tHcy) concentrations in European adolescents. The present study comprised 713 European adolescents aged 14.81.2 y (females 55.3%) from the multicenter HELENA cross-sectional study. PA was assessed through accelerometry, CVF by the 20-m shuttle run test, and body fat by skinfold thicknesses with the Slaughter equation. Plasma folate, cobalamin, and tHcy concentrations were measured. To examine the association of tHcy with PA, CVF, and fatness after controlling for a set of confounders including age, maturity, folate, cobalamin, creatinine, smoking, supplement use, and methylenetetrahydrofolate reductase 677 genotype (CC 47%, CT 43%, TT 10%), bivariate correlations followed by multiple regression models were performed. In the bivariate correlation analysis, tHcy concentrations were slightly negatively correlated (p0.05) with CVF in females (measured both by stages: r 0.118 and by VO2max: r 0.102) and positively with body mass index (r 0.100). However, daily time spent with moderate and vigorous PA showed a weak positive association with tHcy in females (p0.05). tHcy concentrations showed a tendency to decrease with increasing CVF and increase with increasing BMI in female European adolescents. However, tHcy concentrations were positively associated with moderate and vigorous PA in female European adolescents

Healthcare workers hospitalized due to COVID-19 have no higher risk of death than general population. Data from the Spanish SEMI-COVID-19 Registry

Aim To determine whether healthcare workers (HCW) hospitalized in Spain due to COVID-19 have a worse prognosis than non-healthcare workers (NHCW). Methods Observational cohort study based on the SEMI-COVID-19 Registry, a nationwide registry that collects sociodemographic, clinical, laboratory, and treatment data on patients hospitalised with COVID-19 in Spain. Patients aged 20-65 years were selected. A multivariate logistic regression model was performed to identify factors associated with mortality. Results As of 22 May 2020, 4393 patients were included, of whom 419 (9.5%) were HCW. Median (interquartile range) age of HCW was 52 (15) years and 62.4% were women. Prevalence of comorbidities and severe radiological findings upon admission were less frequent in HCW. There were no difference in need of respiratory support and admission to intensive care unit, but occurrence of sepsis and in-hospital mortality was lower in HCW (1.7% vs. 3.9%; p = 0.024 and 0.7% vs. 4.8%; p<0.001 respectively). Age, male sex and comorbidity, were independently associated with higher in-hospital mortality and healthcare working with lower mortality (OR 0.211, 95%CI 0.067-0.667, p = 0.008). 30-days survival was higher in HCW (0.968 vs. 0.851 p<0.001). Conclusions Hospitalized COVID-19 HCW had fewer comorbidities and a better prognosis than NHCW. Our results suggest that professional exposure to COVID-19 in HCW does not carry more clinical severity nor mortality

Clonal chromosomal mosaicism and loss of chromosome Y in elderly men increase vulnerability for SARS-CoV-2

The pandemic caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2, COVID-19) had an estimated overall case fatality ratio of 1.38% (pre-vaccination), being 53% higher in males and increasing exponentially with age. Among 9578 individuals diagnosed with COVID-19 in the SCOURGE study, we found 133 cases (1.42%) with detectable clonal mosaicism for chromosome alterations (mCA) and 226 males (5.08%) with acquired loss of chromosome Y (LOY). Individuals with clonal mosaic events (mCA and/or LOY) showed a 54% increase in the risk of COVID-19 lethality. LOY is associated with transcriptomic biomarkers of immune dysfunction, pro-coagulation activity and cardiovascular risk. Interferon-induced genes involved in the initial immune response to SARS-CoV-2 are also down-regulated in LOY. Thus, mCA and LOY underlie at least part of the sex-biased severity and mortality of COVID-19 in aging patients. Given its potential therapeutic and prognostic relevance, evaluation of clonal mosaicism should be implemented as biomarker of COVID-19 severity in elderly people. Among 9578 individuals diagnosed with COVID-19 in the SCOURGE study, individuals with clonal mosaic events (clonal mosaicism for chromosome alterations and/or loss of chromosome Y) showed an increased risk of COVID-19 lethality

Electric field distribution in porous piezoelectric materials during polarization

High piezoelectric coupling coefficients enable the harvesting of more energy or increase the sensitivity of sensors which work using the principle of piezoelectricity. These coefficients depend on the material properties, but the manufacturing process can have a significant impact on the resulting overall coefficients. During the manufacturing process, one of the main steps is the process of polarization. The degree of polarization depends on multiple factors and it can strongly influence the final piezoelectric coefficients. In this paper, a study on the electric field distribution on the sensitivity of the main piezoelectric and dielectric coefficients to the polarization process is performed, focusing on porous piezoelectric materials. Different inclusion geometries are considered, namely spherical, ellipsoidal and spheres with cracks. The electric field distribution at the micro scale within a representative volume element is modelled to determine the material polarization level using the finite element method. The results show that the electric field distribution is highly dependent on the inclusion geometries and cracks and it has a noticeable impact on the equivalent piezoelectric coefficients. These results are compared with experimental measurements from published literature. Good agreement is found between the ellipsoidal model and the experimental data.</p

Homogenization of porous piezoelectric materials

This paper presents a homogenization study of porous piezoelectric materials through analytical and numerical analysis. Using two of the most well-known analytical methods for theoretical homogenization, the Mori–Tanaka and self-consistent schemes, the full set of material properties are obtained. These results are compared to two different theoretical bounds, the Halpin–Tsai and Hashin–Sthrikman bounds. A numerical model of a representative volume element is then developed using finite element analysis for different percentages of inclusions. Finally, the analytical and numerical results are compared and discussed; a good agreement between the analytical and numerical methods is shown

Model Validation of a Porous Piezoelectric Energy Harvester Using Vibration Test Data

In this paper, a finite element model is coupled to an homogenisation theory in order to predict the energy harvesting capabilities of a porous piezoelectric energy harvester. The harvester consists of a porous piezoelectric patch bonded to the root of a cantilever beam. The material properties of the porous piezoelectric material are estimated by the Mori&ndash;Tanaka homogenisation method, which is an analytical method that provides the material properties as a function of the porosity of the piezoelectric composite. These material properties are then used in a finite element model of the harvester that predicts the deformation and voltage output for a given base excitation of the cantilever beam, onto which the piezoelectric element is bonded. Experiments are performed to validate the numerical model, based on the fabrication and testing of several demonstrators composed of porous piezoelectric patches with different percentages of porosity bonded to an aluminium cantilever beam. The electrical load is simulated using a resistor and the voltage across the resistor is measured to estimate the energy generated. The beam is excited in a range of frequencies close to the first and second modes using base excitation. The effects of the porosity and the assumptions made for homogenisation are discussed

Effective Elastic Properties Using Maxwell’s Approach for Transversely Isotropic Composites

International audienceIn this contribution an analysis of static properties of transversely isotropic, porous and nano-composites is considered. Present work features explicit formulas for effective coefficient in these types of composites. The reinforcements of the composites are a set of spheroidal inclusions with identical size and shape. The center is randomly distributed and the inclusions are embedded in an homogeneous infinite medium (matrix). An study of theoretical predictions obtained by Maxwell approach using two different density distribution functions, which describe the alignment inclusions is done. The method allows to report the static effective elastic coefficients in composites ensemble with inclusions of different geometrical shapes and configurations embedded into a matrix. The effective properties of composites are computed using the Maxwell homogenization method in Matlab software. Another novelty of this contribution is the calculation of new explicit analytical formulas for the control of the alignment tensors N* and Ns∗ which is in charged of the alignment distribution of inclusions within matrix through disorder parameters λ and s, respectively. The alignment tensors N∗ and Ns∗ are obtained as average of all possible alignments of the inclusions inside the composite. Numerical results are obtained and compared with some other theoretical approaches reported in the literature

En marcha con las TIC : recopilación de un año de noticias TICs

Se recopilan aportaciones de docentes extremeños que han llevado a cabo iniciativas relacionadas con las nuevas tecnologías, el acceso libre a la información y el software libre. Se describen los proyectos llevados a cabo por la administración educativa extremeña para promocionar el uso de las tecnologías de la información y la comunicación, entre otras: la plataforma educativa Rayuela, el proyecto de formación a distancia Avanza, el portal del docente Profex, etc..ExtremaduraConsejería de Educación. Dirección General de Política Educativa; Calle Delgado Valencia, 6; 06800 Mérida (Badajoz); +34924006714; +34924006716; [email protected]