Substitutional 4d and 5d Impurities in Graphene

We describe the structural and electronic properties of graphene doped with substitutional impurities of 4d and 5d transition metals. The binding energy and distances for 4d and 5d metals in graphene show similar trends for the later groups in the periodic table, which is also well-known characteristic of 3d elements. However, along earlier groups the 4d impurities in graphene show very similar binding energies, distances and magnetic moments to 5d ones, which can be related to the influence of the 4d and 5d lanthanide contraction. Surprisingly, within the manganese group, the total magnetic moment of 3$\mu_{B}$ for manganese is reduced to 1$\mu_{B}$ for technetium and rhenium. We find that with compared with 3d elements, the larger size of the 4d and 5d elements causes a high degree hybridization with the neighbouring carbon atoms, reducing spin splitting in the d levels. It seems that the magnetic adjustment of graphene could be significantly different is 4d or 5d impurities are used instead of 3d impurities.Comment: 16 pages, 4 figure

An Array of Layers in Silicon Sulfides: Chain-like and Ground State Structures

While much is known about isoelectronic materials related to carbon nanostructures, such as boron nitride layers and nanotubes, rather less is known about equivalent silicon based materials. Following the recent discovery of phosphorene, we herein discuss isoelectronic silicon monosulfide monolayers. We describe a set of anisotropic ground state structures that clearly have a high stability with respect to the near isotropic silicon monosulfide monolayers. The source of the layer anisotropy is related to the presence of Si-S double chains linked by some Si-Si covalent bonds, which lye at the core of the increased stability, together with a remarkable spd hybridization on Si. The involvement of d orbitals brings more variety to silicon-sulfide based nanostructures that are isoelectronic to phosphorene, which could be relevant for future applications, adding extra degrees of freedom.Comment: 16 pages, 6 figure

Theoretical characterization in the functionalization and design of low dimensional systems: carbon transition metal nanostructures and phosphorene isoelectronic compounds

167 p.El trabajo de esta tesis consiste en el estudio teórico mediante cálculos computacionalesbasados en la teoría del funcional de la densidad (DFT) de las propiedades electrónicas ymagnéticas de nanomateriales. Dentro de los nanomateriales destaca el grafeno, unmaterial bidimensional constituido por una red hexagonal de átomos de carbono. Se haestudiado el efecto que tiene en las propiedades electrónicas y magnéticas el dopado degrafeno con impurezas sustitucionales de metales de transición, así como el enlace entreagregados metálicos de cobalto y grafeno.La interacción entre metales de transición y átomos de carbono en una red hexagonal tipografeno se da también en los hidrocarburos aromáticos policíclicos. En esta tesis hemosestudiado esta interacción para el circumcoronene, compuesto por 19 anillos aromáticos,con átomos y agregados pequeños de cobalto. De igual manera se ha estudiado lainteracción de los metales de transición manganeso, cobalto y níquel con moléculas debenceno, la unidad más pequeña con un hexágono de carbonos, dando lugar aestructuras con el agregado metálico recubierto por los bencenos. En estas estructurashemos encontrado comportamientos novedosos como distancias ultracortas de 1.8 A parael enlace manganeso-manganeso, soluciones magnéticas no colineales para el caso delcobalto, o cambios en el eje fácil de magnetización para el caso del níquel.Por otro lado, hoy en día se trata de encontrar nuevos materiales bidimensionalessiguiendo el camino marcado por el grafeno o más recientemente por una capa de fósforonegro. En esta tesis estudiamos dos nuevos materiales isoelectrónicos (con el mismonúmero de electrones de valencia) al fósforo negro, silicio azufre y carbono azufre,caracterizando diferentes nanoestructuras como monocapas, películas delgadas ycadenas. Encontramos fases semiconductoras y metálicas estables a temperaturaambiente que podrían ser utilizadas para aplicaciones en el futuro

Photospheric activity, rotation, and star-planet interaction of the planet-hosting star CoRoT-6

The CoRoT satellite has recently discovered a hot Jupiter that transits across the disc of a F9V star called CoRoT-6 with a period of 8.886 days. We model the photospheric activity of the star and use the maps of the active regions to study stellar differential rotation and the star-planet interaction. We apply a maximum entropy spot model to fit the optical modulation as observed by CoRoT during a uninterrupted interval of about 140 days. Photospheric active regions are assumed to consist of spots and faculae in a fixed proportion with solar-like contrasts. Individual active regions have lifetimes up to 30-40 days. Most of them form and decay within five active longitudes whose different migration rates are attributed to the stellar differential rotation for which a lower limit of \Delta \Omega / \Omega = 0.12 \pm 0.02 is obtained. Several active regions show a maximum of activity at a longitude lagging the subplanetary point by about 200 degrees with the probability of a chance occurrence being smaller than 1 percent. Our spot modelling indicates that the photospheric activity of CoRoT-6 could be partially modulated by some kind of star-planet magnetic interaction, while an interaction related to tides is highly unlikely because of the weakness of the tidal force.Comment: 9 pages, 7 figures, accepted to Astronomy & Astrophysic

Ultrashort Mn-Mn Bonds in Organometallic Complexes

Manganese metallocenes larger than the experimentally produced sandwiched MnBz$_2$ compound are studied using several density functional theory methods. First, we show that the lowest energy structures have Mn clusters surrounded by benzene molecules, in so-called rice-ball structures. We then find a strikingly short bond length of 1.8 {\AA} between pairs of Mn atoms, accompanied by magnetism depletion. The ultrashort bond lengths are related to Bz molecules caging a pair of Mn atoms, leading to a Mn-Mn triple bond. This effect is also found when replacing benzenes by other molecules such as borazine or cyclopentadiene. The stability of the Mn-Mn bond for Mn$_2$Bz$_2$ is further investigated using dissociation energy curves. For each spin configuration, the energy versus distance plot shows different spin minima with barriers, which must be overcome to synthesize larger Mn-Bz complexes.Comment: 9 pages, 8 figure

Properties of starspots on CoRoT-2

As a planet eclipses its parent star, a dark spot on the surface of the star may be occulted, causing a detectable variation in the light curve. A total of 77 consecutive transit light curves of CoRoT-2 were observed with a high temporal resolution of 32 s, corresponding to an uninterrupted period of 134 days. By analyzing small intensity variations in the transit light curves, it was possible to detect and characterize spots at fixed positions (latitude and longitude) on the surface of the star. The model used simulates planetary transits and enables the inclusion of spots on the stellar surface with different sizes, intensities (i.e. temperatures), and positions. Fitting the data by this model, it is possible to infer the spots physical characteristics. The fits were either in spot longitude and radius, with a fixed intensity, or in spots longitude and intensity, for spots of constant size. Before the modeling of the spots were performed, the planetary radius relative to the star radius was estimated by fitting the deepest transit to minimize the effect of spots. A slightly larger (3%) radius, 0.172 Rstar, resulted instead of the previously reported 0.1667 Rstar . The fitting of the transits yield spots, or spot groups, with sizes of ranging from 0.2 to 0.7 planet radius, Rp, with a mean of (0.41 +/- 0.13) Rp (~100,000 km), resulting in a stellar area covered by spots within the transit latitudes of 10-20%. The intensity varied from 0.4 to 0.9 of the disk center intensity, Ic, with a mean of (0.60 +/- 0.19) Ic, which can be converted to temperature by assuming an effective temperature of 5625 K for the stellar photosphere, the spots temperature ranges mainly from 3600 to 5000 K. The results from the spot modeling are in agreement with those found for magnetic activity analysis from out of transit data of the same star.Comment: 7 pages, 11 figure

Theoretical characterization in the functionalization and design of low dimensional systems: carbon transition metal nanostructures and phosphorene isoelectronic compounds

167 p.El trabajo de esta tesis consiste en el estudio teórico mediante cálculos computacionalesbasados en la teoría del funcional de la densidad (DFT) de las propiedades electrónicas ymagnéticas de nanomateriales. Dentro de los nanomateriales destaca el grafeno, unmaterial bidimensional constituido por una red hexagonal de átomos de carbono. Se haestudiado el efecto que tiene en las propiedades electrónicas y magnéticas el dopado degrafeno con impurezas sustitucionales de metales de transición, así como el enlace entreagregados metálicos de cobalto y grafeno.La interacción entre metales de transición y átomos de carbono en una red hexagonal tipografeno se da también en los hidrocarburos aromáticos policíclicos. En esta tesis hemosestudiado esta interacción para el circumcoronene, compuesto por 19 anillos aromáticos,con átomos y agregados pequeños de cobalto. De igual manera se ha estudiado lainteracción de los metales de transición manganeso, cobalto y níquel con moléculas debenceno, la unidad más pequeña con un hexágono de carbonos, dando lugar aestructuras con el agregado metálico recubierto por los bencenos. En estas estructurashemos encontrado comportamientos novedosos como distancias ultracortas de 1.8 A parael enlace manganeso-manganeso, soluciones magnéticas no colineales para el caso delcobalto, o cambios en el eje fácil de magnetización para el caso del níquel.Por otro lado, hoy en día se trata de encontrar nuevos materiales bidimensionalessiguiendo el camino marcado por el grafeno o más recientemente por una capa de fósforonegro. En esta tesis estudiamos dos nuevos materiales isoelectrónicos (con el mismonúmero de electrones de valencia) al fósforo negro, silicio azufre y carbono azufre,caracterizando diferentes nanoestructuras como monocapas, películas delgadas ycadenas. Encontramos fases semiconductoras y metálicas estables a temperaturaambiente que podrían ser utilizadas para aplicaciones en el futuro

Occurrence of Nine Grapevine Viruses in Commercial Vineyards of Mendoza, Argentina

Grapevine is a widely grown fruit crop that is seriously affected by different viruses, reducing grape yield and quality, as well as threatening profitability. Vineyard disease management requires accurate identification of viral infections. This study aimed to survey the presence of ten grapevine viruses in four geographic sites in the Mendoza province of Argentina. Two hundred twenty-three composite cane samples from 1060 plants of six cultivars were collected from 26 blocks distributed across 11 vineyards. The cane samples were screened by RT-PCR for the following viruses: grapevine leafroll-associated viruses 1–4 (GLRaV 1, 2, 3, and 4), grapevine fanleaf virus (GFLV), grapevine fleck virus (GFkV), grapevine virus A (GVA) and B (GVB), grapevine rupestris stem pitting associated virus (GRSPaV), and arabis mosaic virus (ArMV). The results showed an uneven occurrence of viruses through the sampled regions, with GRSPaV being prevalent (71.1%), followed by GFLV (28.9%), GFkV (20.6%), and GLRaV-2 (14.7%). GVB was not detected. This study revealed a moderate prevalence of viruses associated with economically impactful diseases in the vineyards surveyed.Fil: Gómez Talquenca, Sebastián. Instituto Nacional de Tecnología Agropecuaria. Centro Regional Mendoza-San Juan. Estación Experimental Agropecuaria Mendoza; ArgentinaFil: Alonso, Rodrigo Emanuel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto de Biología Agrícola de Mendoza. Universidad Nacional de Cuyo. Facultad de Ciencias Agrarias. Instituto de Biología Agrícola de Mendoza; ArgentinaFil: Luna, Facundo Nicolás. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza; Argentina. Instituto Nacional de Tecnología Agropecuaria. Centro Regional Mendoza-San Juan. Estación Experimental Agropecuaria Mendoza; ArgentinaFil: Lanza Volpe, Melisa. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza; Argentina. Instituto Nacional de Tecnología Agropecuaria. Centro Regional Mendoza-San Juan. Estación Experimental Agropecuaria Mendoza; ArgentinaFil: Buscema, Fernando. Bodega Catena Zapata; Argentin