Residual stresses in Y-TZP crowns due to changes in the thermal contraction coefficient of veneers

Objective. To test the hypothesis that the difference in the coefficient of thermal contraction of the veneering porcelain above (˛liquid) and below (˛solid) its Tg plays an important role in stress development during a fast cooling protocol of Y-TZP crowns. Methods. Three-dimensional finite element models of veneered Y-TZP crowns were developed. Heat transfer analyses were conducted with two cooling protocols: slow (group A) and fast (groups B–F). Calculated temperatures as a function of time were used to determine the thermal stresses. Porcelain ˛solid was kept constant while its ˛liquid was varied, creating different ˛/˛solid conditions: 0, 1, 1.5, 2 and 3 (groups B–F, respectively). Maximum ( 1) and minimum ( 3) residual principal stress distributions in the porcelain layer were compared. Results. For the slowly cooled crown, positive 1 were observed in the porcelain, orientated perpendicular to the core–veneer interface (“radial” orientation). Simultaneously, negative 3 were observed within the porcelain, mostly in a hoop orientation (“hoop–arch”). For rapidly cooled crowns, stress patterns varied depending on ˛/˛solid ratios. For groups B and C, the patterns were similar to those found in group A for 1 (“radial”) and 3 (“hoop–arch”). For groups D–F, stress distribution changed significantly, with 1 forming a “hoop-arch” pattern while 3 developed a “radial” pattern. Significance. Hoop tensile stresses generated in the veneering layer during fast cooling protocols due to porcelain high ˛/˛solid ratio will facilitate flaw propagation from the surface toward the core, which negatively affects the potential clinical longevity of a crown.

Sintering and model of thermal residual stress for getting cutting tools from functionally gradient materials

Cutting tools with higher wear resistance are those manufactured by powder metallurgy process, which combines the development of materials and design properties, features of shape-making technology and sintering. The annual global market of cutting tools consumes about US$ 12 billion; therefore, any research to improve tool designs and machining process techniques adds value or reduces costs. The aim is to describe the Spark Plasma Sintering (SPS) of cutting tools in functionally gradient materials, to show this structure design suitability through thermal residual stress model and, lastly, to present two kinds of inserts. For this, three cutting tool materials were used (Al2O3-ZrO2, Al2O3-TiC and WC-Co). The samples were sintered by SPS at 1300 °C and 70 MPa. The results showed that mechanical and thermal displacements may be separated during thermal treatment for analysis. Besides, the absence of cracks indicated coherence between experimental results and the residual stresses predicted.

Introducción a la contaminación biológica

Máster en Medio Ambiente Litoral y Marino

Diseño de un sistema de captación de energía residual basado en el acondicionador EH300 de la empresa Advanced Linear Devices

Proyecto y presentación del Proyecto Fin de Carrera titulado "DISEÑO DE UN SISTEMA DE CAPTACIÓN DE ENERGÍA RESIDUAL BASADO EN EL ACONDICIONADOR EH300 DE LA EMPRESA ADVANCED LINEAR DEVICES"

Teoría de contaminación biológica

Facultad de Ciencias del Mar, Departamento de Biología

Evaluación del impacto medioambiental sobre zonas costeras en condiciones de oleaje y contaminación extremales

[ES] En este trabajo se utilizan los principios generales de la óptica geométrica y la forma del espectro teórico de oleaje TMA (basado en datos experimentales) para derivar un modelo numérico aplicable en aguas de poca profundidad, cuyo objetivo final es prever los impactos medioambientales provocados en condiciones de oleaje y contaminación extremales. Este modelo es puesto en práctica en una zona costera del archipiélago canario, siendo sus resultados bastante coherentes con los observados en situaciones reales.

Caracterización y cuantificación de la contaminación producida por hidrocarburos en el entorno de las centrales térmicas de la provincia de Las Palmas

[ES] En el entorno de las centrales térmicas de Las Palmas (Barranco de Tirajana, Jinámar- Gran Canaria-, Punta Grande -Lanzarote- y Las Salinas -Fuerteventura-) se produce frecuentemente contaminación por hidrocarburos debido a vertidos ocasionales de las propias centrales y de los entornos habitados. Los vertidos que se producen en la zona son de carácter heterogéneo, por lo que sería conveniente estudiar el tipo de compuestos orgánicos existentes (Hidrocarburos aromáticos policíclicos y PCBs, fundamentalmente) a fin de poder identificar el grado de contaminación de esas zonas y las fuentes de los mismos. La finalidad de este trabajo reside en la determinación de métodos selectivos de análisis de este tipo de contaminantes y en concreto de los hidrocarburos orgánicos persistentes (PCBs y los PAHs).