Chain metallicity and antiferro-paramagnetism competition in underdoped YBa2_2Cu3_3O6+x_{6+x}: a first principles description

We describe from advanced first principles calculations the energetics of oxygen doping and its relation to insulator-metal transitions in underdoped YBa$_2$Cu$_3$O$_{6+x}$. We find a strong tendency of doping oxygens to order into non-magnetic Cu$^{1+}$O$_x$ chains at any $x$. Ordering produces one-dimensional metallic bands, while configurations with non-aligned oxygens are insulating. The Cu$^{2+}$O$_2$ planes remain insulating and antiferromagnetic up to a threshold between $x$=0.25 and 0.5, above which a paramagnetic normal-metal state prevails. The in-plane antiferro-paramagnetic competition depends on $x$, but only weakly on the ordering state of the chains.Comment: 4 pages, 6 figures, 2 table

Extracting convergent surface energies from slab calculations

The formation energy of a solid surface can be extracted from slab calculations if the bulk energy per atom is known. It has been pointed out previously that the resulting surface energy will diverge with slab thickness if the bulk energy is in error, in the context of calculations which used different methods to study the bulk and slab systems. We show here that this result is equally relevant for state-of-the-art computational methods which carefully treat bulk and slab systems in the same way. Here we compare different approaches, and present a solution to the problem that eliminates the divergence and leads to rapidly convergent and accurate surface energies.Comment: 3 revtex pages, 1 figure, in print on J. Phys. Cond. Mat

Large phonon-drag enhancement induced by narrow quantum confinement at the LaAlO3/SrTiO3 interface

The thermoelectric power of the two-dimensional electron system (2DES) at the LaAlO3/SrTiO3 interface is explored below room temperature, in comparison with that of Nb-doped SrTiO3 single crystals. For the interface we find a region below T =50 K where thermopower is dominated by phonon-drag, whose amplitude is hugely amplified with respect to the corresponding bulk value, reaching values ~mV/K and above. The phonon-drag enhancement at the interface is traced back to the tight carrier confinement of the 2DES, and represents a sharp signature of strong electron-acoustic phonon coupling at the interface

Prediction of Ferromagnetic Ground State of NaCl-type FeN

Ab-initio results for structural and electronic properties of NaCl-type FeN are presented in a framework of plane-wave and ultrasoft pseudopotentials. Competition among different magnetic ordering is examined. We find the ferromagnetic phase stable overall. Stabilization over the unpolarized phase is obtained by splitting one flat t_2g-type band crossing the Fermi energy. A comparison with CrN is considered. We find large differences in the properties of the two systems that can be addressed to the smaller ionicity and magnetization of FeN.Comment: 5 pages, 4 figures, twocolumn latex style Sentence changed in Section III line 1

Concepciones de niños y niñas sobre la inteligencia ¿Qué papel se otorga a las funciones ejecutivas y a la autorregulación?

Intelligence is a construct of notable impact in our sociocultural context, related to a wide range of conceptual and operational definitions which originate positions that highlights cognitive and abstract elements and emotional and social skills, as well was perspectives that are focused on processes underlying the intelligent performance, such as in the case of executive functions (EFs), which are configured as cognitive processes that make it possible the self-regulation (Miyake & Friedman, 2012). Similarly, there are approaches that give intelligence a relevant and predictive role of school performance, an aspect strengthened by the psychometric perspective, where the concept of intelligence has been closely linked to learning. In this line, we also find the classical perspective of crystallized Intelligence of Cattell (1943), which refers to the knowledge acquired through educational and cultural processes. The aim of this study is to know the conceptualizations of intelligence of children aged 8-12, the features they give to them, and the assessment of their own intellectual capacities. The data analysis was carried out through the grounded theory and the results mainly show that participants attribute components referred to the management of school contents and quantitative performance to intelligence. Moreover, the answers show elements related to EFs and self-regulation not only when considering the meaning of the construct, but also while characterizing and evaluating the intelligence performance.La inteligencia constituye un constructo de notable impacto en nuestro contexto sociocultural, evidenciado en un amplio desarrollo de definiciones conceptuales y operacionales, donde surgen aseveraciones que van desde privilegiar elementos de tipo cognitivo y abstracto, a elementos emocionales y sociales, hasta perspectivas que se enfocan en los procesos que subyacen al desempeño inteligente, como es el caso de las funciones ejecutivas (FE), las cuáles se configuran como procesos cognitivos que posibilitan la autorregulación (Miyake & Friedman, 2012). De igual modo, existen enfoques que otorgan a la inteligencia un rol relevante y predictivo del rendimiento escolar, aspecto fortalecido por la perspectiva psicométrica donde el concepto de inteligencia se ha vinculado estrechamente con el aprendizaje. En esta línea, también encontramos la perspectiva clásica de inteligencia cristalizada de Cattell (1943), la cual hace alusión al conocimiento adquirido a través de procesos educativos y culturales. El objetivo de este estudio fue conocer las concepciones que niñas y niños, de edades comprendidas entre 8 y 12 años, otorgan al concepto de inteligencia, las características que le atribuyen y la valoración que hacen de las propias capacidades intelectuales. El análisis de los datos se llevó a cabo mediante la teoría fundamentada y los resultados evidencian principalmente que los participantes atribuyen al constructo de inteligencia componentes referidos al manejo de contenidos escolares y al rendimiento cuantitativo; además de poner en manifiesto elementos relacionados con las FE y la autorregulación no sólo en la significación que hacen del constructo, sino también al caracterizar y valorar el desempeño inteligente

Concepciones de niños y niñas sobre la inteligencia ¿Qué papel se otorga a las funciones ejecutivas y a la autorregulación?

Intelligence is a construct of notable impact in our sociocultural context, related to a wide range of conceptual and operational definitions which originate positions that highlights cognitive and abstract elements and emotional and social skills, as well was perspectives that are focused on processes underlying the intelligent performance, such as in the case of executive functions (EFs), which are configured as cognitive processes that make it possible the self-regulation (Miyake & Friedman, 2012). Similarly, there are approaches that give intelligence a relevant and predictive role of school performance, an aspect strengthened by the psychometric perspective, where the concept of intelligence has been closely linked to learning. In this line, we also find the classical perspective of crystallized Intelligence of Cattell (1943), which refers to the knowledge acquired through educational and cultural processes. The aim of this study is to know the conceptualizations of intelligence of children aged 8-12, the features they give to them, and the assessment of their own intellectual capacities. The data analysis was carried out through the grounded theory and the results mainly show that participants attribute components referred to the management of school contents and quantitative performance to intelligence. Moreover, the answers show elements related to EFs and self-regulation not only when considering the meaning of the construct, but also while characterizing and evaluating the intelligence performance.La inteligencia constituye un constructo de notable impacto en nuestro contexto sociocultural, evidenciado en un amplio desarrollo de definiciones conceptuales y operacionales, donde surgen aseveraciones que van desde privilegiar elementos de tipo cognitivo y abstracto, a elementos emocionales y sociales, hasta perspectivas que se enfocan en los procesos que subyacen al desempeño inteligente, como es el caso de las funciones ejecutivas (FE), las cuáles se configuran como procesos cognitivos que posibilitan la autorregulación (Miyake & Friedman, 2012). De igual modo, existen enfoques que otorgan a la inteligencia un rol relevante y predictivo del rendimiento escolar, aspecto fortalecido por la perspectiva psicométrica donde el concepto de inteligencia se ha vinculado estrechamente con el aprendizaje. En esta línea, también encontramos la perspectiva clásica de inteligencia cristalizada de Cattell (1943), la cual hace alusión al conocimiento adquirido a través de procesos educativos y culturales. El objetivo de este estudio fue conocer las concepciones que niñas y niños, de edades comprendidas entre 8 y 12 años, otorgan al concepto de inteligencia, las características que le atribuyen y la valoración que hacen de las propias capacidades intelectuales. El análisis de los datos se llevó a cabo mediante la teoría fundamentada y los resultados evidencian principalmente que los participantes atribuyen al constructo de inteligencia componentes referidos al manejo de contenidos escolares y al rendimiento cuantitativo; además de poner en manifiesto elementos relacionados con las FE y la autorregulación no sólo en la significación que hacen del constructo, sino también al caracterizar y valorar el desempeño inteligente

Diversity assessment of seedlings from self-pollinated Sangiovese grapevines by ampelography and microsatellite DNA analysis

A population of Vitis vinifera L. seedlings deriving from a single self-pollinated Sangiovese vine were assayed for diversity by ampelographic and genetic techniques. After field-transplantation in 1987, the seedlings were initially screened in 1995. Twenty-four seedlings were of standard Vigour and grape production. Woody cuttings from the 24 seedlings and the mother plant were self-rooted in 1995, and each Vine was morphologically analysed and compared in 1997 using 31 descriptors of the ampelographic data sheet (OIV 1983) which are also recommended by UPOV for varietal identification - three for young shoots, 7 for shoots at bloom, 17 for adult leaves, one for flowers and 3 for berries. - In 1996 DNA was extracted from young apical leaves of the mother plant and the 24 seedlings. Ten molecular microsatellites, VVS1, VVS2, VVS5, VVS16, VVS29, VVMD5, VVMD6, VVMD7, VVMD17 and VVMD28, were used for progeny and mother plant comparison. The descriptor-based analysis showed that 12 of the 24 seedlings were morphologically similar amongst themselves and not different fr-om the mother; the remaining 12 differing from each other and from the parent. The microsatellite analysis differentiated all 24 seedlings from the mother plant. Only two seedlings showed the same allele patterns at the 10 tested loci, although they differed morphologically. The results of both analyses indicate that self-pollination can generate phenotypically similar individuals that are difficult to distinguish morphologically, while their genetic polymorphism can easily be detected by microsatellite analysis. Thus it is possible, as suggested by RIVES (1961), that certain ancient cultivars comprise a number of clones that derive via vegetative propagation from closely related mother plants. Corroboration of the polyclonal origin in such cases can be performed by techniques combining morphological and molecular approaches

Giant Oscillating Thermopower at Oxide Interfaces

Understanding the nature of charge carriers at the LaAlO3/SrTiO3 interface is one of the major open issues in the full comprehension of the charge confinement phenomenon in oxide heterostructures. Here, we investigate thermopower to study the electronic structure in LaAlO3/SrTiO3 at low temperature as a function of gate field. In particular, under large negative gate voltage, corresponding to the strongly depleted charge density regime, thermopower displays record-high negative values of the order of 10^4 - 10^5 microV/K, oscillating at regular intervals as a function of the gate voltage. The huge thermopower magnitude can be attributed to the phonon-drag contribution, while the oscillations map the progressive depletion and the Fermi level descent across a dense array of localized states lying at the bottom of the Ti 3d conduction band. This study is the first direct evidence of a localized Anderson tail in the two-dimensional (2D) electron liquid at the LaAlO3/SrTiO3 interface.Comment: Main text: 28 pages and 3 figures; Supplementary information: 29 pages, 5 figures and 1 tabl

Magnetic stress as a driving force of structural distortions: the case of CrN

We show that the observed transition from rocksalt to orthorhombic P$_{nma}$ symmetry in CrN can be understood in terms of stress anisotropy. Using local spin density functional theory, we find that the imbalance between stress stored in spin-paired and spin-unpaired Cr nearest neighbors causes the rocksalt structure to be unstable against distortions and justifies the observed antiferromagnetic ordering. This stress has a purely magnetic origin, and may be important in any system where the coupling between spin ordering and structure is strong.Comment: 4 pages (two columns) 4 figure