Thermoelectrics

Metallic Ag microsphere in a ceramic matrix Thermoelectricity is the direct solid-state conversion between thermal and electrical energy, without any moving parts, due to the well-known Seebeck effect. Currently, more than half of the energy produced ends up in the form of wasted heat: thermoelectric harvesting and energy conversion constitutes an solution to improve the energy efficiency of classical industrial and domestic energy transforming processes, through thermoelectric modules

The Effect of Slamming Impact on Out-of-Autoclave Cured Prepregs of GFRP Composite Panels for Hulls

This paper proposes a methodology that employs an experimental apparatus that reproduces, in pre-impregnated and cured out-of-autoclave Glass Fiber Reinforced Polymer (GFRP) panels, the phenomenon of slamming or impact on the bottom of a high-speed boat during planing. The pressure limits in the simulation are defined by employing a finite element model (FEM) that evaluates the forces applied by the cam that hits the panels in the apparatus via microdeformations obtained in the simulation. The methodology requires that various impact series be performed at different energies and that the evolution of the damage be followed via immersion ultrasound inspection to quantify how the material behaves, in addition to evaluating the delamination process via penetrating dyes using UV radiation. Slamming impacts were performed on the order of 105, and the micromechanisms of interlaminar and intralaminar damage propagation were observed with scanning electron microscopy (SEM). The results were analyzed by correlating them with pressure, deformation, impact energy, and applied cycles, in addition to conducting compression experiments after impact to relate the material damage with the residual strength of the impacted panels

Thermoelectric doping effect in Ca3Co4-xNixO9 ceramics

Ca3Co4-xNixO9 (x=0.01, 0.03, and 0.05) polycrystalline thermoelectric ceramics have been prepared by the classical solid state method. As a result of the Ni addition an increase in porosity has been detected. Moreover, the presence of Ni has been related with the increase of Ca2Co3O6 secondary phase and the appearance of a new NiO-CoO solid solution. However, for the 0.01-Ni doped samples an improvement in the thermoelectric performances has been measured. This effect has been related with a decrease in the resistivity values and an increase in the Seebeck coefficient. The raise in the power factor for the 0.01-Ni doped samples, compared with the undoped ones, is between 10 and 25% at 50 and 800 °C respectively. Moreover, the maximum power at 800 °C, around 0.25 mW/K2.m, is significantly higher than the best results obtained in Ni doped samples reported previously in the literature

In-situ measurements of temperature distribution during transmission laser welding of poly(aryletherketone)

In this work, the temperature distribution inside the specimens has been measured during transmission laser welding. The material studied is a high performance thermoplastic of the polyaryletherketone (PAEK) family. The assembly consists of a quasi-amorphous sample as the upper part and a semi-crystalline sample as the lower part. The temperature fields were measured by infrared thermography with the camera sensor perpendicular to the welded interface. With an energy beam of 28 J.mm-2 and irradiation time of 15s, we have noticed that the maximum temperature inside the sample is kept far from the PAEK degradation one. Moreover, the temperature at the interface reaches the melting temperature thus assuring enough mobility for polymeric chains to get adhesion at the interface. Finally, the location and size of the heat-affected zone (HAZ) has been determined

Role of Ag in textured-annealed Bi2Ca2Co1.7Ox thermoelectric ceramic

Bi2Ca2Co1.7Ox thermoelectric ceramics with small Ag additions (0, 1, 2, 3, 4, and 5 wt.%) have been successfully grown from the melt, using the laser floating zone method and subsequently annealed at 800 °C for 24 h. The microstructure has shown a reduction of the amount of secondary phases for Ag contents up to 4 wt.%. This microstructural evolution leads to a decrease of the electrical resistivity values until an Ag content of 4 wt.%, whereas Seebeck coefficient has been maintained unchanged. This is in agreement with the presence of metallic Ag in all samples, confirmed not only by Energy Dispersive Spectrometry but also by X-ray photoelectron and Auger spectroscopy. These electrical properties lead to maximum power factor values of about 0.30 mW/K2.m at 650 °C for the 4 wt.% Ag containing samples, which is among the best results obtained for this type of materials

Exploring the high-temperature electrical performance of Ca3-xLaxCo4O9 thermoelectric ceramics for moderate and low substitution levels

Aliovalent substitutions in Ca3Co4O9 often result in complex effects on the electrical properties and the solubility, and impact of the substituting cation also depends largely on the preparation and processing method. It is also well-known that the monoclinic symmetry of this material’s composite crystal structure allows for a significant hole transfer from the rock salt-type Ca2CoO3 buffer layers to the hexagonal CoO2 ones, increasing the concentration of holes and breaking the electron-hole symmetry from the latter layers. This work explored the relevant effects of relatively low La-for-Ca substitutions, for samples prepared and processed through a conventional ceramic route, chosen for its simplicity. The obtained results show that the actual substitution level does not exceed 0.03 (x < 0.03) in Ca3-xLaxCo4O9 samples with x = 0.01, 0.03, 0.05 and 0.07 and that further introduction of lanthanum results in simultaneous Ca3Co4O9 phase decomposition and secondary Ca3Co2O6 and (La, Ca)CoO3 phase formation. The microstructural effects promoted by this phase evolution have a moderate influence on the electronic transport. The electrical measurements and determined average oxidation state of cobalt at room temperature suggest that the present La substitutions might only have a minor effect on the concentration of charge carriers and/or their mobility. The electrical resistivity values of the Ca3-xLaxCo4O9 samples with x = 0.01, 0.03 and 0.05 were found to be ~1.3 times (or 24%) lower (considering mean values) than those measured for the pristine Ca3Co4O9 samples, while the changes in Seebeck coefficient values were only moderate. The highest power factor value calculated for Ca2.99La0.01Co4O9 (~0.28 mW/K2m at 800 °C) is among the best found in the literature for similar materials. The obtained results suggest that low rare-earth substitutions in the rock salt-type layers can be a promising pathway in designing and improving these p-type thermoelectric oxides, provided by the strong interplay between the mobility of charge carriers and their concentration, capable of breaking the electron-hole symmetry from the conductive layers. © 2021 by the authors

Vascular NADH/NADPH oxidase is involved in enhanced superoxide production in spontaneously hypertensive rats

This study was designed to test the hypothesis that stimulation of nicotinamide adenine dinucleotide/nicotinamide adenine dinucleotide phosphate (NADH/NADPH) oxidase is involved in increased vascular superoxide anion (*O(2)(-)) production in spontaneously hypertensive rats (SHR). The study was performed in 16-week-old and 30-week-old normotensive Wistar-Kyoto rats (WKY(16) and WKY(30), respectively) and in 16-week-old and 30-week-old SHR (SHR(16) and SHR(30), respectively). In addition, 16-week-old SHR were treated with oral irbesartan (average dose 20 mg/kg per day) for 14 weeks (SHR(30)-I). Aortic NADH/NADPH oxidase activity was determined by use of chemiluminescence with lucigenin. The expression of p22phox messenger RNA was assessed by competitive reverse transcription-polymerase chain reaction. Vascular responses to acetylcholine were determined by isometric tension studies. Aortic wall structure was studied, determining the media thickness and the cross-sectional area by morphometric analysis. Whereas systolic blood pressure was significantly increased in the 2 groups of hypertensive animals compared with their normotensive controls, no differences were observed in systolic blood pressure between SHR(30) and SHR(16). No other differences in the parameters measured were found between WKY(16) and SHR(16). In SHR(30) compared with WKY(30), we found significantly greater p22phox mRNA level, NADH/NADPH-driven *O(2)(-) production, media thickness, and cross-sectional area and an impaired vasodilation in response to acetylcholine. Treated SHR had similar NADH/NADPH oxidase activity and p22phox expression as the WKY(30) group. The vascular functional and morphological parameters were improved in SHR(30)-I. These findings suggest that an association exists between p22phox gene overexpression and NADH/NADPH overactivity in the aortas of adult SHR. Enhanced NADH/NADPH oxidase-dependent *O(2)(-) production may contribute to endothelial dysfunction and vascular hypertrophy in this genetic model of hypertension

Effects of ispaghula husk and guar gum on postprandial glucose and insulin concentrations in healthy subjects

P. 235-243The aim of this study was to evaluate, under the same experimental conditions and in the same subjects, the effects of ispaghula husk and guar gum on postprandial glucose and insulin concentrations in healthy female subjects(ten healthy female volunteers aged 30 ± 48 y with normal body mass indices).S

Sex dimorphism in the myocardial response to aortic stenosis

Objectives: The goal of this study was to explore sex differences in myocardial remodeling in aortic stenosis (AS) by using echocardiography, cardiac magnetic resonance (CMR), and biomarkers. Background: AS is a disease of both valve and left ventricle (LV). Sex differences in LV remodeling are reported in AS and may play a role in disease phenotyping. Methods: This study was a prospective assessment of patients awaiting surgical valve replacement for severe AS using echocardiography, the 6-min walking test, biomarkers (high-sensitivity troponin T and N-terminal pro-brain natriuretic peptide), and CMR with late gadolinium enhancement and extracellular volume fraction, which dichotomizes the myocardium into matrix and cell volumes. LV remodeling was categorized into normal geometry, concentric remodeling, concentric hypertrophy, and eccentric hypertrophy

Self-induced and induced transparencies of two-dimensional and three- dimensional superlattices

The phenomenon of transparency in two-dimensional and three-dimensional superlattices is analyzed on the basis of the Boltzmann equation with a collision term encompassing three distinct scattering mechanisms (elastic, inelastic and electron-electron) in terms of three corresponding distinct relaxation times. On this basis, we show that electron heating in the plane perpendicular to the current direction drastically changes the conditions for the occurrence of self-induced transparency in the superlattice. In particular, it leads to an additional modulation of the current amplitudes excited by an applied biharmonic electric field with harmonic components polarized in orthogonal directions. Furthermore, we show that self-induced transparency and dynamic localization are different phenomena with different physical origins, displaced in time from each other, and, in general, they arise at different electric fields.Comment: to appear in Physical Review