Pitfalls on computing liquid-liquid phase equilibria using the k-value method

Poster presented in the 11th Mediterranean Congress of Chemical Engineering, Barcelona, October 21-24, 2008.

Syntactic and Semantic Relationships in Models of Complex Systems: An Ecological Case

In this paper, the authors extend and generalize the methodology based on the dynamics of systems with the use of differential equations as equations of state, allowing that first order transformed functions not only apply to the primitive or original variables, but also doing so to more complex expressions derived from them, and extending the rules that determine the generation of transformed superior to zero order (variable or primitive). Also, it is demonstrated that for all models of complex reality, there exists a complex model from the syntactic and semantic point of view. The theory is exemplified with a concrete model: MARIOLA model.

The emergence of classical behaviour in magnetic adatoms

A wide class of nanomagnets shows striking quantum behaviour, known as quantum spin tunnelling (QST): instead of two degenerate ground states with opposite magnetizations, a bonding-antibonding pair forms, resulting in a splitting of the ground-state doublet with wave functions linear combination of two classically opposite magnetic states, leading to the quenching of their magnetic moment. Here we study how QST is destroyed and classical behaviour emerges in the case of magnetic adatoms, where, contrary to larger nanomagnets, the QST splitting is in some instances bigger than temperature and broadening. We analyze two different mechanisms for the renormalization of the QST splitting: Heisenberg exchange between different atoms, and Kondo exchange interaction with the substrate electrons. Sufficiently strong spin-substrate and spin-spin coupling renormalize the QST splitting to zero allowing the environmental decoherence to eliminate superpositions between classical states, leading to the emergence of spontaneous magnetization. Importantly, we extract the strength of the Kondo exchange for various experiments on individual adatoms and construct a phase diagram for the classical to quantum transition.

Postproduciendo (casi) nada

Postproducci��n es un t��rmino extra��do de la industria audiovisual que alude a todas las operaciones realizadas sobre un material YA grabado o existente: m��sica, fotograf��as, videos, pel��culas, pinturas, etc. Tiene mayoritariamente un car��cter entr��pico, de liberaci��n continua e irreversible de energ��as y nuevos productos reprogramados que revisan productos ya anteriormente reprogramados, y as�� de manera sucesiva hasta el infinito. ��Podr��amos imaginar una postproducci��n de sentido contrario? ��Una postproducci��n cuyo esfuerzo tienda a cero? ��Y si ahora preferimos seguir postproduciendo pero haci��ndolo desde (casi) nada? Si extrapolamos esta otra acepci��n directamente hacia la pr��ctica arquitect��nica, estar��amos reivindicando una forma expl��cita de eficacia donde la manera de proceder (la mejor opci��n, la m��s sostenible) puede ser precisamente ���no hacer��� o ���hacer muy poco���. Una semejanza que nos emparentar��a con Bartleby, el personaje de Herman Melville y su c��lebre frase: ���preferir��a no hacerlo���.

Heavy metal release due to aging effect during zero valent iron nanoparticles remediation

Zero valent iron nanoparticles (nZVI) represent a promising agent for environmental remediation. Nevertheless, their application presents some limitations regarding their rapid oxidation and aggregation in the media. The aim of this study was to determine the effect that nZVI aging has in heavy metal remediation in water. Contaminants studied were Zn, Cd, Ni, Cu and Cr, which are typical elements found in ground and wastewater. Results show a high contaminant removal capacity by the nZVI in the first 2 h of reaction. Nevertheless, for longer reaction times, some of the metal ions that had already been adsorbed in the nZVI were delivered to the water. Cd and Ni show the maximum delivery percentages (65 and 27% respectively after 21 days of contact time). The starting delivery time was shortened when applying lower nZVI amounts. No re-dissolution of Cr was observed in any circumstance because it was the only element incorporated into the nanoparticles core, as TEM images showed. Contaminant release from nZVI is probably due to nanoparticles oxidation caused by aging, which produced a pH decrease and nZVI surface crystallization.