Dielectric Characterization of Solutions of Galactomannan Extracted from Adenanthera pavonina L.: Effects of Purification and Ethanol Concentration.

Galactomannans are polysaccharides obtained from legume seed extraction. They present a chemical structure consisting of D-mannose chains linked by glycosidic bonds and galactose branches. The main focus lies in their use as thickeners in the food industry, aimed at improving the dielectric properties of food during heating processes within the radiofrequency and microwave ranges. In this work, the prepared galactomannan samples were electrically analyzed through impedance spectroscopy, which is a powerful physical technique. From the experimental measurements, the dielectric permittivity and loss tangent of the galactomannan solutions were analyzed and the electrical modulus formalism was used to study the dielectric relaxations. Crude galactomannans exhibited higher values of permittivity, conductivity, and losses compared to purified galactomannans. Increasing ethanol concentration in galactomannan purification causes an increase in the permittivity and conductivity of galactomannan solutions. In a 1% solution, at 1 kHz, the permittivity increased from 378.56 to 538.09, while in the 2% solution, this increase was from 656.22 to 1103.24. Regarding the conductivity, at the same frequency, the increase was from 1.6 × 10-3 to 3.3 × 10-3 Ω-1m-1 and from 2.9 × 10-3 to 5.5 × 10-3 Ω-1m-1, respectively. The rise of the ethanol concentration in galactomannan purification led to a decrease in the relaxation time, from 448.56 to 159.15 µs and from 224.81 to 89.50 µs in the solution with 1 and 2%, respectively. The results suggest that galactomannan from Adenanthera pavonina L. has potential for use in the food industry.

A 3D-Printed Ceramics Innovative Firing Technique: A Numerical and Experimental Study.

Additive manufacturing (AM), also known as three-dimensional (3D) printing, allows the fabrication of complex parts, which are impossible or very expensive to produce using traditional processes. That is the case for dinnerware and artworks (stoneware, porcelain and clay-based products). After the piece is formed, the greenware is fired at high temperatures so that these pieces gain its mechanical strength and aesthetics. The conventional (gas or resistive heating elements) firing usually requires long heating cycles, presently requiring around 10 h to reach temperatures as high as 1200 °C. Searching for faster processes, 3D-printed stoneware were fired using microwave (MW) radiation. The pieces were fired within 10% of the conventional processing time. The temperature were controlled using a pyrometer and monitored using Process Temperature Control Rings (PTCRs). An error of 1.25% was calculated between the PTCR (1207 ± 15 °C) and the pyrometer (1200 °C). Microwave-fast-fired pieces show similar mechanical strength to the references and to the electrically fast-fired pieces (41, 46 and 34 (N/mm2), respectively), presenting aesthetic features closer to the reference. Total porosities of ~4%, ~5% and ~9% were determined for microwave, electrically fast-fired and reference samples. Numerical studies have shown to be essential to better understand and improve the firing process using microwave radiation. In summary, microwave heating can be employed as an alternative to stoneware conventional firing methods, not compromising the quality and features of the processed pieces, and with gains in the heating time.

Influence of the Preparation Method on the Structural, Morphological and Dielectric Properties of FeNbO4 Ceramics.

In this work, iron niobate (FeNbO4) was prepared via two processes based on the sol-gel method: colloidal gel and polymeric gel. The obtained powders were submitted to heat treatments at different temperatures based on the results obtained via differential thermal analysis. The structures of the prepared samples were characterized via X-ray diffraction and the morphology was characterized via scanning electron microscopy. The dielectric measurements were performed in the radiofrequency region using the impedance spectroscopy technique and in the microwave range using the resonant cavity method. The influence of the preparation method was noticeable in the structural, morphological and dielectric properties of the studied samples. The polymeric gel method promoted the formation of monoclinic and orthorhombic iron niobate at lower temperatures. The differences in the samples' morphology were also remarkable, both in the size and shape of the grains. The dielectric characterization revealed that the dielectric constant and the dielectric losses had the same order of magnitude and similar trends. A relaxation mechanism was identified in all the samples.

Tuning Green to Red Color in Erbium Niobate Micro- and Nanoparticles.

Tetragonal Er0.5Nb0.5O2 and monoclinic ErNbO4 micro- and nanoparticles were prepared by the citrate sol-gel method and heat-treated at temperatures between 700 and 1600 °C. ErNbO4 revealed a spherical-shaped crystallite, whose size increased with heat treatment temperatures. To assess their optical properties at room temperature (RT), a thorough spectroscopic study was conducted. RT photoluminescence (PL) spectroscopy revealed that Er3+ optical activation was achieved in all samples. The photoluminescence spectra show the green/yellow 2H11/2, 4S3/2→4I15/2 and red 4F9/2→4I15/2 intraionic transitions as the main visible recombination, with the number of the crystal field splitting Er3+ multiplets reflecting the ion site symmetry in the crystalline phases. PL excitation allows the identification of Er3+ high-energy excited multiplets as the preferential population paths of the emitting levels. Independently of the crystalline structure, the intensity ratio between the green/yellow and red intraionic transitions was found to be strongly sensitive to the excitation energy. After pumping the samples with a resonant excitation into the 4G11/2 excited multiplet, a green/yellow transition stronger than the red one was observed, whereas the reverse occurred for higher excitation photon energies. Thus, a controllable selective excited tunable green to red color was achieved, which endows new opportunities for photonic and optoelectronic applications.

Prótesis expansiva en un lactante neumonectomizado / Expandable prosthesis in a pneumonectomized patient

Una niña de 45 días de vida fue sometida a neumonectomía derecha por daño pulmonar extenso, debido a enfisema pulmonar intersticial persistente generalizado. Para evitar el síndrome postneumonectomía derecha y la torsión del pedículo vascular mediastinal, se colocó en el hemitórax derecho una prótesis de silástico de las que habitualmente se emplean para expander la piel, con buen resultado

Follicular gastritis and its association with Helicobacter pylori infection

Cincuenta biopsias endoscópicas con gastritis folicular (GF) fueron revisadas con el fin de definir la frecuencia de infección por Helicobacter phylori (H pylori). Todas las biopsias fueron estudiadas en cortes convencionales teñidos sólo con hematoxilina y eosina. En cuarenta y dos de las 50 biopsias (84 porciento) se identificó el microorganismo y la mayoría presentaron datos de actividad. No existió correlación entre el número de folículos y la cantidad de H pylori. Así, algunos casos donde se encontraron numerosos folículos mostraron escasos microorganismos y veceversa. Tampoco existió relación entre la presencia de los folículos y la distribución del H pylori; en algunas biopsias el microorganismo se encontró en el fragmento donde había folículos hiperplásicos, pero en otros, el H pylori se observó en fragmentos vecinos sin folículos linfoides. La elevada frecuencia de asociación entre la GF y la infección por H pylori sugiere que este microorganismo posee propiedades antigénicas que condicionan la hiperplasia del tejido linfoide en la mucosa gástrica. Se concluye que la gastritis folicular debe ser considerada un hallazgo de importancia y su presencia debe conducir a la búsqueda cuidadosa de H pylori, el cual puede ser identificado en la mayoría de las biopsias en cortes rutinarios teñidos con hematoxilina y eosina.