Spanish National Research Council

About: Spanish National Research Council is a government organization based out in Madrid, Spain. It is known for research contribution in the topics: Population & Galaxy. The organization has 79563 authors who have published 220470 publications receiving 7698991 citations. The organization is also known as: CSIC & Consejo Superior de Investigaciones Científicas.

Electronic properties of disordered two-dimensional carbon

Abstract: Two-dimensional carbon, or graphene, is a semimetal that presents unusual low-energy electronic excitations described in terms of Dirac fermions. We analyze in a self-consistent way the effects of localized (impurities or vacancies) and extended (edges or grain boundaries) defects on the electronic and transport properties of graphene. On the one hand, point defects induce a finite elastic lifetime at low energies with the enhancement of the electronic density of states close to the Fermi level. Localized disorder leads to a universal, disorder independent, electrical conductivity at low temperatures, of the order of the quantum of conductance. The static conductivity increases with temperature and shows oscillations in the presence of a magnetic field. The graphene magnetic susceptibility is temperature dependent (unlike an ordinary metal) and also increases with the amount of defects. Optical transport properties are also calculated in detail. On the other hand, extended defects induce localized states near the Fermi level. In the absence of electron-hole symmetry, these states lead to a transfer of charge between the defects and the bulk, the phenomenon we call self-doping. The role of electron-electron interactions in controlling self-doping is also analyzed. We also discuss the integer and fractional quantum Hall effect in graphene, the role played by the edge states induced by a magnetic field, and their relation to the almost field independent surface states induced at boundaries. The possibility of magnetism in graphene, in the presence of short-range electron-electron interactions and disorder is also analyzed.

Behavior of Ylides Containing N, O, and C Atoms as Hydrogen Bond Acceptors

Abstract: The hydrogen bond (HB) basicity of a series of ylides containing nitrogen, oxygen, or carbon as heavy atoms, as well as the influence of the formation of the HB complexes on their structure, has been studied. In addition, in this paper we propose the formation of some rather strong HBs (that could be considered low-barrier hydrogen bonds, LBHBs) between ylides and different neutral molecules. The ylides chosen for the study were H3N+−N-H, Me3N+−N-H, H2O+−N-H, Me2O+−N-H, H2O+−O-, Me2O+−O-, and Me3N+−C-H2. As HB donors, classical donors such as HF, HCN, and HCCH were used. The analysis of the protonation energies of the ylides and the optimized geometries, interaction energies, and characteristics of the electron density of the complexes shows that these ylides are very good HB acceptors, forming stable complexes even with weak HB donors. With strong donors, when the proton transfer did not take place, very strong HBs were formed with quite large interaction energies and very short HB distances which could ...

Germanene: a novel two-dimensional germanium allotrope akin to graphene and silicene

Abstract: We have grown an atom-thin, ordered, two-dimensional multi-phase film in situ through germanium molecular beam epitaxy using a gold (111) surface as a substrate. Its growth is similar to the formation of silicene layers on silver (111) templates. One of the phases, forming large domains, as observed in scanning tunneling microscopy, shows a clear, nearly flat, honeycomb structure. Thanks to thorough synchrotron radiation core-level spectroscopy measurements and advanced density functional theory calculations we can identify it as a ?3????3 R(30?) germanene layer in conjunction with a ?7????7 R(19.1?) Au(111) supercell, presenting compelling evidence of the synthesis of the germanium-based cousin of graphene on gold.

JASMONATE-INSENSITIVE1 Encodes a MYC Transcription Factor Essential to Discriminate between Different Jasmonate-Regulated Defense Responses in Arabidopsis

Abstract: In spite of the importance of jasmonates (JAs) as plant growth and stress regulators, the molecular components of their signaling pathway remain largely unknown. By means of a genetic screen that exploits the cross talk between ethylene (ET) and JAs, we describe the identification of several new loci involved in JA signaling and the characterization and positional cloning of one of them, JASMONATE-INSENSITIVE1 (JAI1/JIN1). JIN1 encodes AtMYC2, a nuclear-localized basic helix-loop-helix-leucine zipper transcription factor, whose expression is rapidly upregulated by JA, in a CORONATINE INSENSITIVE1–dependent manner. Gain-of-function experiments confirmed the relevance of AtMYC2 in the activation of JA signaling. AtMYC2 differentially regulates the expression of two groups of JA-induced genes. The first group includes genes involved in defense responses against pathogens and is repressed by AtMYC2. Consistently, jin1 mutants show increased resistance to necrotrophic pathogens. The second group, integrated by genes involved in JA-mediated systemic responses to wounding, is activated by AtMYC2. Conversely, Ethylene-Response-Factor1 (ERF1) positively regulates the expression of the first group of genes and represses the second. These results highlight the existence of two branches in the JA signaling pathway, antagonistically regulated by AtMYC2 and ERF1, that are coincident with the alternative responses activated by JA and ET to two different sets of stresses, namely pathogen attack and wounding.

Temperature dependence of Raman scattering in ZnO

Abstract: We present a Raman scattering study of wurtzite $\mathrm{ZnO}$ over a temperature range from 80 to $750\phantom{\rule{03em}{0ex}}\mathrm{K}$ Second-order Raman features are interpreted in the light of recent ab initio phonon density of states calculations The temperature dependence of the Raman intensities allows the assignment of difference modes to be made unambiguously Some weak, sharp Raman peaks are detected whose temperature dependence suggests they may be due to impurity modes High-resolution spectra of the ${E}_{2}^{\mathrm{high}}$, ${A}_{1}(\mathrm{LO})$, and ${E}_{1}(\mathrm{LO})$ modes were recorded, and an analysis of the anharmonicity and lifetimes of these phonons is carried out The ${E}_{2}^{\mathrm{high}}$ mode displays a visibly asymmetric line shape This can be attributed to anharmonic interaction with transverse and longitudinal acoustic phonon combinations in the vicinity of the $K$ point, where the two-phonon density of states displays a sharp edge around the ${E}_{2}^{\mathrm{high}}$ frequency The temperature dependence of the linewidth and frequency of the ${E}_{2}^{\mathrm{high}}$ mode is well described by a perturbation-theory renormalization of the harmonic ${E}_{2}^{\mathrm{high}}$ frequency resulting from the interaction with the acoustic two-phonon density of states In contrast, the ${A}_{1}(\mathrm{LO})$ and ${E}_{1}(\mathrm{LO})$ frequencies lie in a region of nearly flat two-phonon density of states, and they exhibit a nearly symmetric Lorentzian line shape with a temperature dependence that is well accounted for by a dominating asymmetric decay channel