Exponential decay of spin-spin correlation between distant defect states produced by contour hydrogenation of polycyclic aromatic hydrocarbon molecules

The first few low-lying spin states of alternant polycyclic aromatic hydrocarbon (PAH) molecules of several shapes showing defect states induced by contour hydrogenation have been studied both by ab initio methods and by a precise numerical solution of Pariser-Parr-Pople (PPP) interacting model. In accordance with Lieb's theorem, the ground state shows a spin multiplicity equal to one for balanced molecules, and it gets larger values for imbalanced molecules (that is, when the number of π electrons on both subsets is not equal). Furthermore, we find a systematic decrease of the singlet-triplet splitting as a function of the distance between defects, regardless of whether the ground state is singlet or triplet. For example, a splitting smaller than 0.001 eV is obtained for a medium size C46H28 PAH molecule (di-hydrogenated [11]phenacene) showing a singlet ground state. We conclude that π electrons unbound by lattice defects tend to remain localized and unpaired even when long-range Coulomb interaction is taken into account. Therefore they show a biradical character (polyradical character for more than two defects) and should be studied as two or more local doublets. The implications for electron transport are potentially important since these unpaired electrons can trap traveling electrons or simply flip their spin at a very small energy cost.

Visions of the Spanish Revolution: identities and conflicts in post-welfare societies

This is a case study that analyzes photographic documents of the social protest in Spain between 2011 and 2013. The analysis is qualitative and considers the use of space, the visual expression of the messages and the orientation toward the causes or effects of political, economic and social changes. Visual sociology allows us to appreciate, in the case of the Spanish Revolution, a dynamic of “reflexivity” unrecognizable from other research approaches. Two successive waves of social mobilization in response to two different shocks can be appreciated. The first is given by political corruption, unemployment and the threat to consumer society. The second shock is caused by the savage cuts in the Welfare State. Social mobilization is expressed differently in each phase, and the forms taken by the protests show how the class structure in post industrial society shapes the reactions to the crisis of the Welfare State.

No evolution but revolution: The future of the Dutch terraced house

Dealing with the environmental problems is one of the biggest challenges within the field of architectural technology. Solutions to this problem are mostly exclusively sought in materials and computer technology. However, far more attention should be paid to humans and their role in this problem. This paper presents a small part of our bachelor thesis, which started as an investigation on the Dutch terraced house and through research ended as a study on the human behaviour and motivation. The first part of this paper, the evolution, is focussed on the traditional way of problem solving. The second part, the revolution, is focussed on human behaviour and motivation. These two studies put together lead to our conclusion: The only way to structurally solve our environmental problem is to revolutionize our way of building by involving the human interaction into our solution instead of forcing it out.