Y Trinuclear Cu-II structural isomers coordination, magnetism, electrochemistry and catalytic activity towards the oxidation of alkanes

The reaction of the Schiff base (3,5-di-tert-butyl-2-hydroxybenzylidene)-2-hydroxybenzohydrazide (H3L) with copper(II) nitrate, acetate or metaborate has led to the isomeric complexes [Cu-3(L)(2)(MeOH)(4)] (1), [Cu-3(L)(2)(MeOH)(2)]2MeOH (2) and [Cu-3(L)(2)(MeOH)(4)] (3), respectively, in which the ligand L exhibits dianionic (HL2-, in 1) or trianionic (L3-, in 2 and 3) pentadentate 1O,O,N:2N,O chelation modes. Complexes 1-3 were characterized by elemental analysis, IR spectroscopy, single-crystal X-ray crystallography, electrochemical methods and variable-temperature magnetic susceptibility measurements, which indicated that the intratrimer antiferromagnetic coupling is strong in the three complexes and that there exists very weak ferromagnetic intermolecular interactions in 1 but weak antiferromagnetic intermolecular interactions in both 2 and 3. Electrochemical experiments showed that in complexes 1-3 the Cu-II ions can be reduced, in distinct steps, to Cu-I and Cu-0. All the complexes act as efficient catalyst precursors under mild conditions for the peroxidative oxidation of cyclohexane to cyclohexyl hydroperoxide, cyclohexanol and cyclohexanone, leading to overall yields (based on the alkane) of up to 31% (TON = 1.55x10(3)) after 6 h in the presence of pyrazinecarboxylic acid.

Low temperature structural transitions in dipolar hard spheres: the influence on magnetic properties

We investigate the structural chain-to-ring transition at low temperature in a gas of dipolar hard spheres (DRS). Due to the weakening of entropic contribution, ring formation becomes noticeable when the effective dipole-dipole magnetic interaction increases, It results in the redistribution of particles from usually observed flexible chains into flexible rings. The concentration (rho) of DI-IS plays a crucial part in this transition: at a very low rho only chains and rings are observed, whereas even a slight increase of the volume fraction leads to the formation of branched or defect structures. As a result, the fraction of DHS aggregated in defect-free rings turns out to be a non-monotonic function of rho. The average ring size is found to be a slower increasing function of rho when compared Lo that of chains. Both theory and computer simulations confirm the dramatic influence of the ring formation on the rho-dependence of the initial magnetic susceptibility (chi) when the temperature decreases. The rings clue to their zero total dipole moment are irresponsive to a weak magnetic field and drive to the strong decrease of the initial magnetic susceptibility. (C) 2014 Elsevier B.V. All rights reserved.

Temperature-induced structural transitions in self-assembling magnetic nanocolloids

With the help of a unique combination of density functional theory and computer simulations, we discover two possible scenarios, depending on concentration, for the hierarchical self-assembly of magnetic nanoparticles on cooling. We show that typically considered low temperature clusters, i.e. defect-free chains and rings, merge into more complex branched structures through only three types of defects: four-way X junctions, three-way Y junctions and two-way Z junctions. Our accurate calculations reveal the predominance of weakly magnetically responsive rings cross-linked by X defects at the lowest temperatures. We thus provide a strategy to fine-tune magnetic and thermodynamic responses of magnetic nanocolloids to be used in medical and microfluidics applications.

Sistemas e soluções pós-tensão na reabilitação de obras de arte

Trabalho Final de Mestrado para obtenção do grau de Mestre em Engenharia Civil

Materials selection for a set of multiple parts considering manufacturing costs and weight reduction with structural isoperformance using direct multisearch optimization

Materials selection is a matter of great importance to engineering design and software tools are valuable to inform decisions in the early stages of product development. However, when a set of alternative materials is available for the different parts a product is made of, the question of what optimal material mix to choose for a group of parts is not trivial. The engineer/designer therefore goes about this in a part-by-part procedure. Optimizing each part per se can lead to a global sub-optimal solution from the product point of view. An optimization procedure to deal with products with multiple parts, each with discrete design variables, and able to determine the optimal solution assuming different objectives is therefore needed. To solve this multiobjective optimization problem, a new routine based on Direct MultiSearch (DMS) algorithm is created. Results from the Pareto front can help the designer to align his/hers materials selection for a complete set of materials with product attribute objectives, depending on the relative importance of each objective.

Formación de profesores post Bolonia: los desafíos de un proceso en dos etapas

En los últimos años, las políticas de formación de profesores se han convertido en un foco de interés para gobernantes, investigadores y profesionales de la educación. En Portugal, como en otros países europeos, la reestructuración de la formación de profesores estuvo marcada por las políticas, directrices y tendencias de la Comisión Europea, adecuándolas a las especificidades propias de la cultura e historia nacionales. Actualmente, la formación de profesores para los primeros años (0-12) se realiza en instituciones de enseñanza superior, bajo una estructura de dos etapas, constituida por el primer ciclo (licenciatura en Educación Básica) y el segundo ciclo (maestros en educación de infancia y/o ciclo de Enseñanza Básica), con una duración de 4,5 a 5 años. Esta organización en dos etapas ha traído nuevos desafíos a la coherencia y consistencia de los cursos de formación, sobre todo, por lo que respecta a la articulación de la formación académica con la formación práctica. Los problemas generados se vuelven especialmente relevantes en el 6º semestre de la licenciatura en Educación Básica, periodo de transición entre la conclusión de una etapa y el inicio de otra. En este artículo, relatamos el recorrido realizado en la organización de la formación en Educación Básica en una escuela superior de educación en Portugal. El proyecto duró 4 años e incidió en la orientación, organización y procesos de apoyo a la iniciación a la práctica profesional en el 6º semestre del curso. En este proceso, la participación e implicación de los estudiantes, a través de la evaluación de la formación, fue el rasgo fundamental y distintivo.