In-situ Molibdenum X-ray powder diffraction study of the early hydration of cementitious systems on a humidity chamber

The durability of cement-based construction materials depends on the environmental conditions during their service life. A further factor is the microstructure of the cement bulk, established by formation of cement hydrates. The development of the phases and microstructure under given conditions is responsible of the high strength of cementitious materials. The investigation on the early hydration behavior of cements and cementing systems has been for a long time a very important area of research: understanding the chemical reactions that lead to hardening is fundamental for the prediction of performances and durability of the materials. The production of 1 ton of Ordinary Portland Cement, OPC, releases into the atmosphere ~0.97 tons of CO2. This implies that the overall CO2 emissions from the cement industry are 6% of all anthropogenic carbon dioxide. An alternative to reduce the CO2 footprint consists on the development of eco-cements composed by less calcite demanding phases, such as belite and ye'elimite. That is the case of Belite-Ye’elimite cements (BY). Since the reactivity of belite is not quick enough, these materials develop low mechanical strengths at intermediate hydration ages. A possible solution to this problem goes through the production of cements which jointly contain alite with the two previously mentioned phases, named as Belite-Alite-Ye’elimite (BAY) cements. The reaction of alite and ye'elimite with water will develop cements with high mechanical strengths at early ages, while belite will contribute to later values. The final goal is to understand the hydration mechanisms of a variety of cementing systems (OPC, BAY and pure phases) as a function of water content, superplasticizer additives and type and content of sulfate source. In order to do so, in-situ laboratory humidity chambers with Molybdenum X-ray Powder diffraction are employed. In the first 2h of hydration, reaction degree (α) of ye'elimite had been decreased for superplasticizer.

Hallazgos tomográficos como predictores del resultado funcional en edema macular secundario a oclusiones venosas retinianas

INTRODUCCIÓN: El Edema Macular (EM) es la principal causa de perdida de agudeza visual en pacientes con Oclusión Venosa Retiniana (OVR); luego del tratamiento, algunos pacientes persisten con mala agudeza visual. OBJETIVO: Realizar una Revisión Sistemática de la Literatura (RSL), para identificar la evidencia existente sobre factores tomográficos que predicen el resultado visual en pacientes con EM secundario a OVR. FUENTE DE LA INFORMACIÓN: PUBMED, MEDLINE, EMBASE, LILACS, COCHRANE, literatura gris. SELECCIÓN DE LOS ESTUDIOS: Ensayos Clínicos Controlados (ECC) y estudios observacionales analíticos. EXTRACCIÓN Y SÍNTESIS DE LOS DATOS: Dos investigadores seleccionaron los artículos de forma independiente. Se realizó una síntesis cualitativa de la información siguiendo las recomendaciones de la declaración PRISMA 2009. MEDIDAS Y DESENLACE PRINCIPAL: Grosor Retiniano Central (GRC), integridad de Banda Elipsoide e Integridad de Membrana Limitante Externa (MLE), determinados por SD OCT. El desenlace principal es la Agudeza Visual Mejor Corregida (AVMC) a los 6, 12,18 y/o 24 meses. RESULTADOS: Se identificaron 872 abstract y se incluyeron 8 artículos en el análisis cualitativo. Seis estudios evaluaron el GRC sin encontrar asociación con resultado visual final. Solo 2 estudios evaluaron y encontraron asociación estadísticamente significativa de la integridad de la MLE con el desenlace visual, Kang, H 2012 (r2 0,51 p 0,000), Rodriguez, F 2014 (p< 0,001). La integridad de la BE fue asociada a pronostico visual en 4 de 5 estudios que evaluaron esta variable, con resultados estadísticamente significativos. La AVMC de base también se asocio con desenlace visual en 4 de 5 estudios que la evaluaron. El mejor modelo que predice el resultado funcional según el estudio de Kang, H 2012 fue: Integridad de MLE, integridad de BE y AVMC de base (R2 0,671 p 0,000), a los 12 meses de seguimiento. CONCLUSION: La evidencia actual sugiere que la integridad de la BE y la MLE son predictores del resultados funcional en pacientes con EM secundario a OVR después de 6 o mas meses de seguimiento. Es necesario la realización de estudios controlados para llegar a resultados mas concluyentes.

Weed occurrence in sugarcane as function of variety and ground straw management.

2016

Weed occurrence in sugarcane as function of variety and ground straw management.

2016

An approximate method for the solution of an influence function foil rolling model

Fleck and Johnson (Int. J. Mech. Sci. 29 (1987) 507) and Fleck et al. (Proc. Inst. Mech. Eng. 206 (1992) 119) have developed foil rolling models which allow for large deformations in the roll profile, including the possibility that the rolls flatten completely. However, these models require computationally expensive iterative solution techniques. A new approach to the approximate solution of the Fleck et al. (1992) Influence Function Model has been developed using both analytic and approximation techniques. The numerical difficulties arising from solving an integral equation in the flattened region have been reduced by applying an Inverse Hilbert Transform to get an analytic expression for the pressure. The method described in this paper is applicable to cases where there is or there is not a flat region.

Smoothing a Discrete Hazard Function for the Number of Patients Colonized with Methicillin-Resistance Staphylococcus Aureus in an Intensive Care Unit

A new method for estimating the time to colonization of Methicillin-resistant Staphylococcus Aureus (MRSA) patients is developed in this paper. The time to colonization of MRSA is modelled using a Bayesian smoothing approach for the hazard function. There are two prior models discussed in this paper: the first difference prior and the second difference prior. The second difference prior model gives smoother estimates of the hazard functions and, when applied to data from an intensive care unit (ICU), clearly shows increasing hazard up to day 13, then a decreasing hazard. The results clearly demonstrate that the hazard is not constant and provide a useful quantification of the effect of length of stay on the risk of MRSA colonization which provides useful insight.