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

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

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

Early degradation of PV modules and guaranty conditions

CIEMAT PVLabDER has largely increased its demand on testing and characterizing PV plants, according to the fast growth of PV installed capacity in Spain. One of the topics in which manufacturers, promoters, and owners of the plants are more interested in, is the possible degradation of PV modules and its relationship to guarantee contracts, as it is related to subsidies. This paper presents some findings in campaigns of PV plants evaluation carried out during last years. This evaluation usually consists of visual inspection, I-V curve measurement in the fields (the whole plant or selected areas), thermal evaluation by IR imaging, and, in some cases, measurement of the I-V characteristic and thermal behaviour of selected modules in the plant, chosen by the laboratory. It must be noticed that new defects that grow when the module is into operation may appear in modules initially free of them (named as hidden manufacturing defects). Usually some of these hidden defects that only appear in normal operation are not detected in reliability tests (EN61215 or EN 61646) [4][5] due to the different operational conditions of the module in the standard tests and in the field (serial-parallel connection of many PV modules, power inverter influence, over voltage on wires, etc.

El control parlamentario de la política exterior de España

Tesis inédita, presentada en la Universidad Complutense de Madrid, Facultad de Derecho, 1973.Fac. de DerechoTRUEProQuestpu

El control parlamentario de la política exterior de España

Tesis inédita, presentada en la Universidad Complutense de Madrid, Facultad de Derecho, 1973.Fac. de DerechoTRUEProQuestpu

Early degradation of PV modules and guaranty conditions

CIEMAT PVLabDER has largely increased its demand on testing and characterizing PV plants, according to the fast growth of PV installed capacity in Spain. One of the topics in which manufacturers, promoters, and owners of the plants are more interested in, is the possible degradation of PV modules and its relationship to guarantee contracts, as it is related to subsidies. This paper presents some findings in campaigns of PV plants evaluation carried out during last years. This evaluation usually consists of visual inspection, I-V curve measurement in the fields (the whole plant or selected areas), thermal evaluation by IR imaging, and, in some cases, measurement of the I-V characteristic and thermal behaviour of selected modules in the plant, chosen by the laboratory. It must be noticed that new defects that grow when the module is into operation may appear in modules initially free of them (named as hidden manufacturing defects). Usually some of these hidden defects that only appear in normal operation are not detected in reliability tests (EN61215 or EN 61646) [4][5] due to the different operational conditions of the module in the standard tests and in the field (serial-parallel connection of many PV modules, power inverter influence, over voltage on wires, etc.