Theoretical study of Ga-based nanowires and the interaction of Ga with single-wall carbon nanotubes

Gallium displays physical properties which can make it a potential element to produce metallic nanowires and high-conducting interconnects in nanoelectronics. Using first-principles pseudopotential plane method we showed that Ga can form stable metallic linear and zigzag monatomic chain structures. The interaction between individual Ga atom and single-wall carbon nanotube (SWNT) leads to a chemisorption bond involving charge transfer. Doping of SWNT with Ga atom gives rise to donor states. Owing to a significant interaction between individual Ga atom and SWNT, continuous Ga coverage of the tube can be achieved. Ga nanowires produced by the coating of carbon nanotube templates are found to be stable and high conducting.Comment: 8 pages, 8 figure

Development of urban bird indicators using data from monitoring schemes in two large European cities

Bird monitoring projects have provided valuable data for developing biological indicators to evaluate the state of natural and agricultural habitats. However, fewer advances have been made in urban environments. In this study we used bird monitoring data from 2002 to 2012 in two cities with different climates (Brussels and Barcelona), to generate two multi–species urban indicators to evaluate temporal trends on abundance of urban avifauna. To do this we used two different conceptual approaches, one based on a list of widespread species in European cities (WSEC) and another based exclusively on species widespread at city level (WCS) regardless of the birds occurring in other cities. The two indicators gave a similar general pattern, although we found a 3% difference in the mean annual change in both cities, thus suggesting that the values provided by urban indicators may differ depending on the conceptual approach and, hence, by the species list used to generate them. However, both indicators may have their own value and could be treated as complementary indices

Microplate tectonics and environmental factors as distribution drivers in Western Mediterranean freshwater planarians

AIM: Species biogeography mainly focuses on palaeogeographical events, while environmental factors are generally overlooked despite their importance in species diversification. Here, we use an integrative approach to understand how palaeogeographical and environmental processes shape species distribution and focus on freshwater planarians as the model system. LOCATION: Western Mediterranean. TAXON: Dugesia METHODS: We inferred the phylogenetic relationships of most known Dugesia species in the area using six molecular markers. We then estimated their divergence times and reconstructed their ancestral distribution ranges. We also performed environmental niche modelling analyses using Dugesia subtentaculata as a model to evaluate the effects of several hydro-environmental variables and the likely existence of interspecific competition on Dugesia distributions. RESULTS: Our results provide a new phylogenetic scheme for Dugesia from the Western Mediterranean and show that the time splits between the lineages and their putative ancestral distribution ranges are correlated with microplate tectonic dynamics within the region during the Oligocene–Miocene period. Our environmental niche modelling analyses indicate that the type of land cover and the slope of the terrain are the most important abiotic factors driving the distribution of Dugesia from this region. Finally, we found a partial niche overlap between D. subtentaculata and two other common planarian species from the Iberian Peninsula. MAIN CONCLUSIONS: The microplate tectonic dynamics of the Western Mediterranean during the Oligocene–Miocene period, together with the position of the mountain ranges and posterior climate changes, may have played crucial roles in driving the biogeographical history of Dugesia in this region. Moreover, both interspecific competition and changes in fluvial characteristics driven by human activities may affect the current diversity and distribution of Dugesia in the Western Mediterranean. This study highlights the importance of integrating different types of information to study the biogeographical history of a species. <br

Conferencia clínico-patológica de la Societat Catalana de Neurología: sesión del 3 de mayo de 1990

Caso clínico: paciente de 32 años de edad que ingresa por cuadro de cefalea, náuseas, vómitos, pérdida brusca de fuerza y sensibilidad faciobraquial derecha y afasia

Direct Calculation of Spin-Stiffness for Spin-1/2 Heisenberg Models

The spin-stiffness of frustrated spin-1/2 Heisenberg models in one and two dimensions is computed for the first time by exact diagonalizations on small clusters that implement spin-dependent twisted boundary conditions. Finite-size extrapolation to the thermodynamic limit yields a value of $0.14\pm 0.01$ for the spin-stiffness of the unfrustrated planar antiferromagnet. We also present a general discussion of the linear-response theory for spin-twists, which ultimately leads to the moment sum-rule.Comment: 11 pgs, TeX, LA-UR-94-94 (to be published in Phys. Rev. B

Magnetism in Dense Quark Matter

We review the mechanisms via which an external magnetic field can affect the ground state of cold and dense quark matter. In the absence of a magnetic field, at asymptotically high densities, cold quark matter is in the Color-Flavor-Locked (CFL) phase of color superconductivity characterized by three scales: the superconducting gap, the gluon Meissner mass, and the baryonic chemical potential. When an applied magnetic field becomes comparable with each of these scales, new phases and/or condensates may emerge. They include the magnetic CFL (MCFL) phase that becomes relevant for fields of the order of the gap scale; the paramagnetic CFL, important when the field is of the order of the Meissner mass, and a spin-one condensate associated to the magnetic moment of the Cooper pairs, significant at fields of the order of the chemical potential. We discuss the equation of state (EoS) of MCFL matter for a large range of field values and consider possible applications of the magnetic effects on dense quark matter to the astrophysics of compact stars.Comment: To appear in Lect. Notes Phys. "Strongly interacting matter in magnetic fields" (Springer), edited by D. Kharzeev, K. Landsteiner, A. Schmitt, H.-U. Ye