Doped AB_2 Hubbard Chain: Spiral, Nagaoka and RVB States, Phase Separation and Luttinger Liquid Behavior

We present an extensive numerical study of the Hubbard model on the doped AB$_2$ chain, both in the weak coupling and the infinite-U limit. Due to the special unit cell topology, this system displays a rich variety of phases as function of hole doping ($\delta$) away from half-filling. Near half-filling, spiral states develop in the weak coupling regime, while Nagaoka itinerant ferromagnetism is observed in the infinite-U limit. For higher doping the system phase-separates before reaching a Mott insulating phase of short-range RVB states at $\delta=1/3$. Moreover, for $\delta>1/3$ we observe a crossover, which anticipates the Luttinger liquid behavior for $\delta > 2/3$.Comment: 11 pages, 13 figure

Magnetism and Electronic Correlations in Quasi-One-Dimensional Compounds

In this contribution on the celebration of the 80th birthday anniversary of Prof. Ricardo Ferreira, we present a brief survey on the magnetism of quasi-one-dimensional compounds. This has been a research area of intense activity particularly since the first experimental announcements of magnetism in organic and organometallic polymers in the mid 80s. We review experimental and theoretical achievements on the field, featuring chain systems of correlated electrons in a special AB2 unit cell structure present in inorganic and organic compounds

Potencialidades hídricas superficiais de Fernando de Noronha, PE, e alternativas para incremento da oferta.

A disponibilidade de recursos hídricos para usos múltiplos, com ênfase no abastecimento público, é questão da mais alta relevância e depende de aspectos edáficos, hidrológicos, ambientais e de gestão. Avaliou-se o potencial hídrico de bacias hidrográficas da Ilha de Fernando de Noronha, com vistas a dar suporte à gestão da água no arquipélago; para isto se delimitaram e caracterizaram cinco bacias representativas e se estimou a precipitação efetiva através do método da Curva Número. Adicionalmente, foram investigadas as características de infiltração dos principais solos do arquipélago. Verifica-se que, em geral, as bacias hidrográficas têm limitada infiltrabilidade e elevado potencial de escoamento, constatando-se o potencial de incremento de oferta de água superficial superior a 90%, desde que se contemple a utilização racional das principais bacias existentes. Dentre os solos analisados, os Cambissolos Háplicos Vertissólicos e os Vertissolos são os solos de menor infiltrabilidade e, portanto, de maior contribuição à macrodrenagem do arquipélago. Sugere-se a utilização das bacias estudadas no abastecimento doméstico da Ilha, de modo a incrementar a disponibilidade de água no local

Chemistry in isolation: High CCH/HCO+ line ratio in the AMIGA galaxy CIG 638

Multi-molecule observations towards an increasing variety of galaxies have been showing that the relative molecular abundances are affected by the type of activity. However, these studies are biased towards bright active galaxies, which are typically in interaction. We study the molecular composition of one of the most isolated galaxies in the local Universe where the physical and chemical properties of their molecular clouds have been determined by intrinsic mechanisms. We present 3 mm broad band observations of the galaxy CIG 638, extracted from the AMIGA sample of isolated galaxies. The emission of the J=1-0 transitions of CCH, HCN, HCO+, and HNC are detected. Integrated intensity ratios between these line are compared with similar observations from the literature towards active galaxies including starburst galaxies (SB), active galactic nuclei (AGN), luminous infrared galaxies (LIRG), and GMCs in M33. A significantly high ratio of CCH with respect to HCN, HCO+, and HNC is found towards CIG 638 when compared with all other galaxies where these species have been detected. This points to either an overabundance of CCH or to a relative lack of dense molecular gas as supported by the low HCN/CO ratio, or both. The data suggest that the CIG 638 is naturally a less perturbed galaxy where a lower fraction of dense molecular gas, as well as a more even distribution could explain the measured ratios. In this scenario the dense gas tracers would be naturally dimmer, while the UV enhanced CCH, would be overproduced in a less shielded medium.Comment: Letter accepted for publication in A&