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The work examines the influence of the microstructure on the in vitro bioactivity of two glass-ceramics with the same chemical composition in the SiO 2 –CaO system. Ceramizing a glass, via powder technology route (W1), and by sol–gel method (W2), formed two glass-ceramics composed of the same crystalline phases, but differed in microstructure. Both glass-ceramics were soaked in simulated body fluid up to 4 weeks using the same conditions. An hydroxyapatite (HA)-like layer formed on the surfaces of both samples but a different formation rates yielded differences in the microstructure. The W2 glass-ceramic showed faster HA-like formation because its smaller crystalline grains dissolved more readily. In addition, the thicker glassy phase at the grain boundaries facilitated a faster formation of silanol groups on the surface of the amorphous SiO 2 interlayer, a reaction that is considered to be a prerequisite for HA-like formation. Comparison of glass-ceramics synthesized by the two preparation methods was carried out. The interfacial reaction product was examined by scanning and transmission electron microscopy. Both instruments were fitted with energy-dispersive X-ray analyzers. Additional changes in ionic concentration, using inductively couple plasma atomic emission spectroscopy, were determined.

This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0). Cushioning is an important aspect in hydraulic cylinder performance. The piston has to be decelerated before it strikes the end cap in order to avoid stresses in the cylinder components and reduce vibration that can be transmitted to the machine. One of the least-studied methods is internal cushioning by grooves in the piston. In this method, the flow is throttled with adequately designed grooves when the piston reaches the outlet port position. The purpose of the present work is to present a method to estimate the pressure-drop coefficients for a certain design of piston grooves in order to provide a model to develop a dynamic system simulation of the cushion system. The method is based on a computational fluid dynamic simulation of flow through piston grooves to the outlet port for each piston’s static position. The results are compared with experimental measurements, and a correction, based on Reynolds number, is proposed. Good agreement, below 16%, was obtained for all the positions but particularly for the last grooves, for which the numerical result’s deviation to the experimental measurements was less than 10%. In general, the numerical simulation tended to underestimate the pressure drop for the first grooves and overestimate the calculation for the last grooves.

Existe una importante vulnerabilidad individual a la adiccion que puede estar relacionada con factores de personalidad. Uno de los rasgos de personalidad mas estudiado en relacion a la susceptibilidad a la adiccion ha sido el de busqueda de sensaciones o de novedades. En esta revision se analizan principalmente datos de investigacion basica sobre la relacion entre adiccion y busqueda de sensaciones. En modelos animales este rasgo ha sido valorado principalmente mediante la actividad motora en un ambiente nuevo, estableciendose dos tipologias de ratas, las denominadas LR (low-responders) y las HR (high-responders) que muestran respectivamente niveles bajos y altos de actividad en dicho ambiente nuevo. Los animales HR son mas sensibles a los efectos estimulantes motores de diversas drogas y muestran mayor sensibilizacion conductual ante la administracion repetida de la droga respecto a los LR. Ademas, los sujetos HR adquieren inicialmente mas facilmente la conducta de autoadministracion operante de diversas drogas de abuso. La reactividad del eje hipotalamo-pituitario-adrenal ante ciertas situaciones de estres tambien es mayor en los animales HR que en los LR. A nivel del sistema nervioso central, los sujetos HR tambien presentan una mayor actividad del eje hipotalamico-pituitarioadrenal. Respecto al sistema dopaminergico, estudios de microdialisis muestran que la cocaina ejerce un mayor efecto neuroquimico (mayor incremento en los niveles de dopamina) en los animales HR que en los LR. Estos datos en animales a grandes rasgos se replican tambien en humanos, aunque existen tambien resultados contradictorios tanto en animales como en humanos, indicando que el tema es complejo y aun no esta resuelto.