Modulation of Superconducting Properties by Ferroelectric Polarization in Confined FE-S-FE Films

We show that the electric polarization at the interface with ultrathin superconducting (S) films sandwiched between ferroelectric (FE) layers allows achievement of substantially stronger modulation of inner carrier density and superconducting transition temperature as compared to FE-S bilayers typically used in superconducting FETs. We find that not only the larger penetration depths but also the pairing symmetry should be responsible for the fact that the electric field effect in high temperature superconductors is much stronger than in conventional systems. Discussing the advantages of multilayers, we propose a novel design concept for superconducting electric field-effect transistors based on ferroelectric films.Comment: 5 pages RevTex4, 6 figure

Assessment of the conservation status of natural and semi-natural patches associated with urban areas through habitat suitability indices

Urban environments rely on the surrounding natural ecosystems remnants as providers of ecosystem functions, therefore these areas not only support a unique biodiversity but also have a social value for maintaining public health and wellbeing. For this reason, urbanization is considered to be one the biggest threats to ecosystems, leading to native biodiversity simplification and, thus, to a detriment of the provided ecosystem services. Moreover, this change in land use results in high levels of landscape fragmentation and modification in areas surrounding the habitat remnants which, in consequence, become inadequate for many native species. In this context, it is important that urban planners have the information to assess the possible consequences of future changes in land use in order to increase the landscape chances of supporting both, native biodiversity and the needs of a growing human population. The objective of the present work is to evaluate the ecological integrity of natural and semi-natural vegetation patches immersed in an urban area in order to generate a conceptual framework for landscape assessment that allows urban planners to envision the best choice for city development at a given place. To do so, we developed a quantitative integral environmental evaluation index that includes ecological characterization, geological characterization, and environmental characterization (presence of anthropic disturbance) of the assessed area. We conclude that the index we have generated in this work is suitable to be used as a management tool to allow an unbiased valuation and to identify managing situations that require a short term response.Fil: Natale, Evangelina Sandra. Fundación Conservación y Desarrollo; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Villalba, G.. Fundación Conservación y Desarrollo; ArgentinaFil: Junquera, J. E.. Fundación Conservación y Desarrollo; ArgentinaFil: Zalba, Sergio Martín. Universidad Nacional del Sur. Departamento de Biología, Bioquímica y Farmacia. Grupo de Estudios en Conservación y Manejo; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentin

Interplay of couplings between antiferrodistortive, ferroelectric, and strain degrees of freedom in monodomain PbTiO3_{3}/SrTiO3_{3} superlattices

We report first-principles calculations on the coupling between epitaxial strain, polarization, and oxygen octahedra rotations in monodomain (PbTiO$_{3}$)$_{n}$/(SrTiO$_{3}$)$_{n}$ superlattices. We show how the interplay between (i) the epitaxial strain and (ii) the electrostatic conditions, can be used to control the orientation of the main axis of the system. The electrostatic constrains at the interface facilitate the rotation of the polarization and, as a consequence, we predict large piezoelectric responses at epitaxial strains smaller than those that would be required considering only strain effects. In addition, ferroelectric (FE) and antiferrodistortive (AFD) modes are strongly coupled. Usual steric arguments cannot explain this coupling and a covalent model is proposed to account for it. The energy gain due to the FE-AFD coupling decreases with the periodicity of the superlattice, becoming negligible for $n \ge 3$.Comment: 5 pages, 4 figure

Shine bright or live long: substituent effects in [Cu(N^N)(P^P)]+-based light-emitting electrochemical cells where N^N is a 6-substituted 2,2'-bipyridine

We report [Cu(P^P)(N^N)][PF6] complexes with P^P = bis(2-(diphenylphosphino)phenyl)ether (POP) or 4,5-bis(diphenylphosphino)-9,9-dimethylxanthene (xantphos) and N^N = 6-methyl-2,2′-bipyridine (Mebpy), 6-ethyl-2,2′-bipyridine (Etbpy), 6,6′-dimethyl-2,2′-bipyridine (Me2bpy) or 6-phenyl-2,2′-bipyridine (Phbpy). The crystal structures of [Cu(POP)(Phbpy)][PF6]·Et2O, [Cu(POP)(Etbpy)][PF6]·Et2O, [Cu(xantphos)(Me2bpy)][PF6], [Cu(xantphos)(Mebpy)][PF6]·CH2Cl2·0.4Et2O, [Cu(xantphos)(Etbpy)][PF6]·CH2Cl2·1.5H2O and [Cu(xantphos)(Phbpy)][PF6] are described; each copper(I) centre is distorted tetrahedral. In the crystallographically determined structures, the N^N domain in [Cu(xantphos)(Phbpy)]+ and [Cu(POP)(Phbpy)]+ is rotated ∼180° with respect to its orientation in [Cu(xantphos)(Mebpy)]+, [Cu(POP)(Etbpy)]+ and [Cu(xantphos)(Etbpy)]+; in each complex containing xantphos, the xanthene ‘bowl’ retains the same conformation in the solid-state structures. The two conformers resulting from the 180° rotation of the N^N ligand were optimized at the B3LYP-D3/(6-31G**+LANL2DZ) level and are close in energy for each complex. Variable temperature NMR spectroscopy evidences the presence of two conformers of [Cu(xantphos)(Phbpy)]+ in solution which are related by inversion of the xanthene unit. The complexes exhibit MLCT absorption bands in the range 378 to 388 nm, and excitation into each MLCT band leads to yellow emissions. Photoluminescence quantum yields (PLQYs) increase from solution to thin-film and powder; the highest PLQYs are observed for powdered [Cu(xantphos)(Mebpy)][PF6] (34%), [Cu(xantphos)(Etbpy)][PF6] (37%) and [Cu(xantphos)(Me2bpy)][PF6] (37%) with lifetimes of 9.6–11 μs. Density functional theory calculations predict that the emitting triplet (T1) involves an electron transfer from the Cu–P^P environment to the N^N ligand and therefore shows a 3MLCT character. T1 is calculated to be ∼0.20 eV lower in energy than the first singlet excited state (S1). The [Cu(P^P)(N^N)][PF6] ionic transition-metal (iTMC) complexes were tested in light-emitting electrochemical cells (LECs). Turn-on times are fast, and the LEC with [Cu(xantphos)(Me2bpy)][PF6] achieves a maximum efficacy of 3.0 cd A−1 (luminance = 145 cd m−2) with a lifetime of 1 h; on going to the [Cu(xantphos)(Mebpy)][PF6]-based LEC, the lifetime exceeds 15 h but at the expense of the efficacy (1.9 cd A−1). The lifetimes of LECs containing [Cu(xantphos)(Etbpy)][PF6] and [Cu(POP)(Etbpy)][PF6] exceed 40 and 80 h respectively

Study of cycloplatinated complexes with isocyanide ligands: isomerism, optical properties and mechanochromism

Platinum(II) cyclometalated derivatives have attracted a great interest dueto their rich photophysical properties, with interesting applications aschemical sensors, photocatalysts or in light emitting diodes (OLEDs). Thepresence of planar ligands in these complexes improves the luminescenceand the ability to form aggregates through the formation of Pt···Pt and/or··· interactions. In this context, there are very scarce examples ofheteroleptic complexes with isocyanide and alkynyl ligands.In this work, we present the synthesis and characterization of a group ofPt(II) compounds featuring 2-phenylpyridine and 2-phenylquinoline ascyclometalated ligands and 2,6-dimethylphenyl isocyanide as auxiliaryligand. The p-tolylacetylide complexes [Pt(C^N)(CCTol)(CNXyl)] (C^N =ppy 3, pq 4) have been obtained from the chloride derivatives[Pt(C^N)Cl(CNXyl)] (C^N = ppy 1, pq 2). The isomerism of thesecompounds in which the isocyanide ligand can be trans to the nitrogen or tothe carbon of the cyclometalated ligand has been determined by differenttechniques, as NMR and X-ray diffraction.The photophysical properties (absorption and emission) of all complexeshave been studied with the aid of theoretical calculations. Interestingly, thephenylpyridine derivatives exhibit mechanical stimuli responsive colour andluminescence changes correlated with the formation of different aggregateswith ··· and/or Pt···Pt interactions

Greenland Halibut Depth Variations of Catch-per-unit Effort, Length Composition, Mature Proportions and Associated By-catches in Divisions 3LMNO

In this paper we present a review of the geographic and bathimetric patterns of occurrence of the Greenland halibut catches in NAFO Divisions 3LMNO and their incidence on the catch of other stocks, namely cod, American plaice and yellowtail and witch flounders. The Greenland halibut mature proportions at depth in both the commercial catches and the spring Spanish 3NO survey indices are also presented. According to the results of the Spanish fleet, the Greenland halibut fishery does not overlap significantly with either American plaice, yellowtail flounder, skate or cod. By-catches of witch flounder in the Greenland halibut fishery have been very small, at least in 1999. The CPUE analysis indicate that Greenland halibut is best caught in the deepest strata, with catch rates comparatively poor at depths less than 600 m. Besides a sharp change in catchability is observed between 500 – 600 m. The proportion of mature fish in the catches increases with depth attaining a maximum between 1200 – 1600 m. The survey results indicate that most part of the SSB is found at depths beyond 800 m

Systematic generation of finite-range atomic basis sets for linear-scaling calculations

Basis sets of atomic orbitals are very efficient for density functional calculations but lack a systematic variational convergence. We present a variational method to optimize numerical atomic orbitals using a single parameter to control their range. The efficiency of the basis generation scheme is tested and compared with other schemes for multiple zeta basis sets. The scheme shows to be comparable in quality to other widely used schemes albeit offering better performance for linear-scaling computations

Spanish Research Report for 1994

13 páginas, 12 tablasPeer reviewe