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

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

Seguimiento de dependientes del alcohol y/o de la cocaína después de su salida de una Comunidad Terapéutica: estudio piloto

En España, las Comunidades Terapéuticas (CT) constituyen un modelo de tratamiento común en las adicciones, aunque apenas existe investigación acerca de su eficacia y la persistencia de sus logros. Objetivos: Evaluar los efectos a corto, medio y largo plazo del tratamiento de la adicción al alcohol o cocaína en las CT de la “Fundación Salud y Comunidad”. Diseño: Estudio piloto descriptivo, con un diseño secuencial de cohorte. Se aplicó una encuesta diseñada ad hoc a 91 usuarios para conocer su evolución en los diferentes periodos de seguimiento (1, 3, 5 ó 10 años después de su salida de la CT): variables sociodemográficas, de uso de la/s sustancia/s psicoactiva/s y relacionadas con la estancia en la CT. Se describe el cambio entre antes de la CT y en la actualidad respecto a variables académicas, laborales, de consumo de droga/s, salud, adaptación socio-familiar y comportamiento delictivo. Resultados: las cohortes mostraron un patrón previo relativamente común, recibiendo un tratamiento similar. Los usuarios afirman haber disminuido el hábito de consumo frecuente de la droga principal, encontrando un 48.9% que no ha recaído ni siquiera mediante un consumo ocasional de la/s droga/s. También perciben haber mejorado su salud y sus relaciones familiares, así como el comportamiento agresivo y problemas legales derivados del consumo de droga/s. Conclusiones: tras su rehabilitación en una CT, los usuarios manifiestan una disminución global del consumo de drogas y perciben una mejora a nivel de salud, familia, violencia y problemáticas derivadas del consumo

Les enquestes a pescadors com a instrument per a detectar processos erosius al litoral rocallós de Menorca (Illes Balears)

En aquest article s'ha realitzat una enquesta de percepció sobre processos de caigudes de blocs i esllavissades a la població de pescadors professionals i recreatius de l'illa de Menorca. Els resultats indiquen els indrets de la costa on els pescadors aprecien fenòmens geomorfològics de caigudes de blocs. A l'hora, ens permet tenir un punt de partida per a l'estudi dels processos inestables a la costa rocosa de Menorca. S'ha pres una mostra representativa de 48 enquestes a pescadors professionals i 88 enquestes a pescadors recreatius delimitant 39 zones amb processos actius. En el cas dels pescadors professionals s'han pres com a zones de mostreig els ports base de: Maó, sa Nitja, Macaret, Fornells, Ciutadella, Biniancolla, es Grau, Alcalfar, Canutells i cales Fonts. Amb el resultat de les enquestes es troben algunes respostes associades a la manca de blocs de tempesta o tsunami a les costes rocoses que ens han animat a explorar tot el perímetre de la costa de Menorca

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