Brownian cluster dynamics with short range patchy interactions: its application to polymers and step-growth polymerization.

We present a novel simulation technique derived from Brownian cluster dynamics used so far to study the isotropic colloidal aggregation. It now implements the classical Kern-Frenkel potential to describe patchy interactions between particles. This technique gives access to static properties, dynamics and kinetics of the system, even far from the equilibrium. Particle thermal motions are modeled using billions of independent small random translations and rotations, constrained by the excluded volume and the connectivity. This algorithm, applied to a single polymer chain leads to correct static and dynamic properties, in the framework where hydrodynamic interactions are ignored. By varying patch angles, various local chain flexibilities can be obtained. We have used this new algorithm to model step-growth polymerization under various solvent qualities. The polymerization reaction is modeled by an irreversible aggregation between patches while an isotropic finite square-well potential is superimposed to mimic the solvent quality. In bad solvent conditions, a competition between a phase separation (due to the isotropic interaction) and polymerization (due to patches) occurs. Surprisingly, an arrested network with a very peculiar structure appears. It is made of strands and nodes. Strands gather few stretched chains that dip into entangled globular nodes. These nodes act as reticulation points between the strands. The system is kinetically driven and we observe a trapped arrested structure. That demonstrates one of the strengths of this new simulation technique. It can give valuable insights about mechanisms that could be involved in the formation of stranded gels.

Do cement nanotubes exist?

Using atomistic simulations, this work indicates that cement nanotubes can exist. The chemically compatible nanotubes are constructed from the two main minerals in ordinary Portland cement pastes, namely calcium hydroxide and a calcium silicate hydrate called tobermorite. These results show that such nanotubes are stable and have outstanding mechanical properties, unique characteristics that make them ideally suitable for nanoscale reinforcements of cements.

Aluminum incorporation to dreierketten silicate chains.

This work explores, from a theoretical viewpoint, the aluminum incorporation into silicate chains with dreierketten conformation relevant in the cementitious calcium-silicate-hydrate (C-S-H) gel and in other minerals, such as wollastonite and hillebrandite. To this end, we have investigated by means of ab initio calculations both the stability and the formation of aluminosilicate chains. Our results show that only certain aluminosilicate chains are stable, namely, those whose tetrahedra length m obey the m = 3n-1 rule with n = 1, 2, 3, ..., in agreement with experiments. Moreover, our detailed analyses explain why A1 ions prefer the bridging sites and introduce new insights on the growth process.

Silicate chain formation in the nanostructure of cement-based materials.

Cement-based materials are ubiquitous in almost all built environment. In spite of this, little is known about the formation and the role played by the silicate chains always present in the cement nanostructure. By means of first principles simulations we provide compelling evidence on the pivotal role played by certain ionic species in the formation of the silicate chains inside the cementitious matrix. Moreover, we corroborate the experimental evidence which shows that the length of the most stable chains with m Si atoms follows a magic-number sequence: m = 3n-1 with n = 1,2,... Our results have been applied in the development of new higher performance cement-based materials by adding nanosilica.

Site and lattice resonances in metallic hole arrays.

A powerful analytical approach is followed to study light transmission through subwavelength holes drilled in thick perfect-conductor films, showing that full transmission (100%) is attainable in arrays of arbitrarily narrow holes as compared to the film thickness. The interplay between resonances localized in individual holes and lattice resonances originating in the array periodicity reveals new mechanisms of transmission enhancement and suppression. In particular, localized resonances obtained by filling the holes with high-index-of-refraction material are examined and experimentally observed through large enhancement in the transmission of individual holes.

Enhanced millimeter-wave transmission through subwavelength hole arrays.

We explore, both experimentally and theoretically, the existence in the millimeter-wave range of the phenomenon of extraordinary light transmission through arrays of subwavelength holes. We have measured the transmission spectra of several samples made on aluminum wafers by use of an AB Millimetre quasi-optical vector network analyzer in the wavelength range 4.2-6.5 mm. Clear signals of the existence of resonant light transmission at wavelengths close to the period of the array appear in the spectra.

Diferencias clínicas y psicosociales entre jóvenes reclusos con episodios de autolesiones / Clinical and psychosocial differences between self-injured youth inmates

En el área de la psiquiatría forense y penitenciaria uno de los problemas de mayor repercusión son los episodios de autolesiones entre los reclusos. El propósito de la presente investigación se divide en dos etapas. En la primera, se describen las características psicosociales de encarcelados con episodios de autolesión. en la segunda, buscaremos las diferencias clínicas significativas entre dos grupos de contraste, encarcelados con episodios de autolesión y reclusos sin episodios. Los sujetos seleccionados fueron 107 reclusos. El rango de edad osciló desde los 18 a los 25 años. Los datos se recogieron conforme a una revista estructurada y el instrumento psicométrico MMPI-2 Las técnicas estadísticas empleadas fueron diversos indicadores, U de Mann-Withney y ANOVA. Los resultados mostraron que existen diversas variables que se asociaron a episodios de autolesiones. Reclusos con episodios de autolesión se diferenciaron en diversas escalas del instrumento MMPI-2 del grupo de control (AU)