Charge localization at the interface between La1-xSrxMnO3 and the infinite layers cuprate CaCuO2

(CaCuO2)m/(La0.7Sr0.3MnO3)n superlattices, consisting of the infinite layers cuprate CaCuO2 and the optimally doped manganite La1-xSrxMnO3, were grown by pulsed laser deposition. The transport properties are dominated by the manganite block. X-Ray Absorption spectroscopy measurements show a clear evidence of an orbital reconstruction at the interface, ascribed to the hybridization between the Cu 3d3z2-r2 and the Mn 3d3z2-r2 orbitals via interface apical oxygen ions. Such a mechanism localizes holes at the interfaces, thus preventing charge transfer to the CaCuO2 block. Some charge (holes) transfer occurs toward the La0.7Sr0.3MnO3 block in strongly oxidized superlattices, contributing to the suppression of the magnetotransport properties.Comment: 20 pages, 6 figure

Current profiles and AC losses of a superconducting strip with elliptic cross-section in perpendicular magnetic field

The case of a hard type II superconductor in the form of strip with elliptic cross-section when placed in transverse magnetic field is studied. We approach the problem in two steps, both based on the critical-state model. First we calculate numerically the penetrated current profiles that ensure complete shielding in the interior, without assuming an a priori form for the profiles. In the second step we introduce an analytical approximation that asumes that the current profiles are ellipses. Expressions linking the sample magnetization to the applied field are derived covering the whole range of applied fields. The theoretical predictions are tested by the comparison with experimental data for the imaginary part of AC susceptibility.Comment: 12 pages; 3 figure

Electrodynamic properties of an artificial heterostructured superconducting cuprate

We perform infrared conductivity measurements on a series of CaCuO2/SrTiO3 heterostructures made by the insulating cuprate CaCuO2 (CCO) and the insulating perovkite SrTiO3 (STO). We estimate the carrier density of various heterostructures, with different level of hole doping from the integral of the optical conductivity and we measure the corresponding degree of correlation by estimating the ratio between the Drude weight and the integral of the infrared spectrum. The analysis demonstrates a large degree of correlation, which increases as the doping is reduced. The experimental results can be reproduced by Dynamical Mean-Field Theory calculations which strongly support the role of correlations in the CCO/STO heterostructures and their similarities with the most common cuprate superconductors. Our results suggest that cuprate superconductors can be looked at as natural superlattices, where the properties of the CuO2 conducting planes and charge reservoir blocks can be completely disentangled

Adenosine A2A receptor modulation of hippocampal CA3-CA1 synapse plasticity during associative learning in behaving mice

© 2009 Nature Publishing Group All rights reservedPrevious in vitro studies have characterized the electrophysiological and molecular signaling pathways of adenosine tonic modulation on long-lasting synaptic plasticity events, particularly for hippocampal long-term potentiation(LTP). However, it remains to be elucidated whether the long-term changes produced by endogenous adenosine in the efficiency of synapses are related to those required for learning and memory formation. Our goal was to understand how endogenous activation of adenosine excitatory A2A receptors modulates the associative learning evolution in conscious behaving mice. We have studied here the effects of the application of a highly selective A2A receptor antagonist, SCH58261, upon a well-known associative learning paradigm - classical eyeblink conditioning. We used a trace paradigm, with a tone as the conditioned stimulus (CS) and an electric shock presented to the supraorbital nerve as the unconditioned stimulus(US). A single electrical pulse was presented to the Schaffer collateral–commissural pathway to evoke field EPSPs (fEPSPs) in the pyramidal CA1 area during the CS–US interval. In vehicle-injected animals, there was a progressive increase in the percentage of conditioning responses (CRs) and in the slope of fEPSPs through conditioning sessions, an effect that was completely prevented (and lost) in SCH58261 (0.5 mg/kg, i.p.)-injected animals. Moreover, experimentally evoked LTP was impaired in SCH58261- injected mice. In conclusion, the endogenous activation of adenosine A2A receptors plays a pivotal effect on the associative learning process and its relevant hippocampal circuits, including activity-dependent changes at the CA3-CA1 synapse.This study was supported by grants from the Spanish Ministry of Education and Research (BFU2005-01024 and BFU2005-02512), Spanish Junta de Andalucía (BIO-122 and CVI-02487), and the Fundación Conocimiento y Cultura of the Pablo de Olavide University (Seville, Spain).B. Fontinha was in receipt of a studentship from a project grant (POCI/SAU-NEU/56332/2004) supported by Fundação para a Ciência e Tecnologia (FCT, Portugal), and of an STSM from Cost B30 concerted action of the EU

Superconducting properties of [BaCuO_x]_2/[CaCuO_2]_n artificial structures with ultrathick CaCuO_2 blocks

The electrical transport properties of [BaCuO_x]_2/[CaCuO_2]_n (CBCCO-2xn)underdoped high temperature superconducting superlattices grown by Pulsed Laser Deposition have been investigated. Starting from the optimally doped CBCCO-2x2 superlattice, having three CuO_2 planes and T_c around 80 K, we have systematically increased the number n up to 15 moving toward the underdoped region and hence decreasing T_c. For n>11 the artificial structures are no longer superconducting, as expected, for a uniformly distributed charge carriers density inside the conducting block layer. The sheet resistance of such artificial structures (n nearly equal to 11) turns out to be quite temperature independent and close to the 2D quantum resistance 26 kOhm. A further increase of the number of CuO_2 planes results in an insulator-type dependence of R(T) in the wide range of temperatures from room temperature to 1 K. The value of the sheet resistance separating the Superconducting and the Insulating regimes supports the fermionic scenario of the Superconductor-Insulator transition in these systems.Comment: 12 pages, 5 figures. Corresponding author: [email protected]

Is the functional interaction between adenosine A2A receptors and metabotropic glutamate 5 receptors a general mechanism in the brain? Differences and similarities between the striatum and the hippocampus

The aim of the present paper was to examine, in a comparative way, the occurrence and the mechanisms of the interactions between adenosine A2A receptors (A2ARs) and metabotropic glutamate 5 receptors (mGlu5Rs) in the hippocampus and the striatum. In rat hippocampal and corticostriatal slices, combined ineffective doses of the mGlu5R agonist 2-chloro-5-hydroxyphenylglycine (CHPG) and the A2AR agonist CGS 21680 synergistically reduced the slope of excitatory postsynaptic field potentials (fEPSPs) recorded in CA1 and the amplitude of field potentials (FPs) recorded in the dorsomedial striatum. The cyclic adenosine monophosphate (cAMP)/protein kinase A (PKA) pathway appeared to be involved in the effects of CGS 21680 in corticostriatal but not in hippocampal slices. In both areas, a postsynaptic locus of interaction appeared more likely. N-methyl-D-aspartate (NMDA) reduced the fEPSP slope and FP amplitude in hippocampal and corticostriatal slices, respectively. Such an effect was significantly potentiated by CHPG in both areas. Interestingly, the A2AR antagonist ZM 241385 significantly reduced the NMDA-potentiating effect of CHPG. In primary cultures of rat hippocampal and striatal neurons (ED 17, DIV 14), CHPG significantly potentiated NMDA-induced lactate dehydrogenase (LDH) release. Again, such an effect was prevented by ZM 241385. Our results show that A2A and mGlu5 receptors functionally interact both in the hippocampus and in the striatum, even though different mechanisms seem to be involved in the two areas. The ability of A2ARs to control mGlu5R-dependent effects may thus be a general feature of A2ARs in different brain regions (irrespective of their density) and may represent an additional target for the development of therapeutic strategies against neurological disorders

High Tc superconductivity in superlattices of insulating oxides

We report the occurrence of superconductivity, with maximum Tc = 40 K, in superlattices (SLs) based on two insulating oxides, namely CaCuO2 and SrTiO3. In these (CaCuO2)n/(SrTiO3)m SLs, the CuO2 planes belong only to CaCuO2 block, which is an antiferromagnetic insulator. Superconductivity, confined within few unit cells at the CaCuO2/SrTiO3 interface, shows up only when the SLs are grown in a highly oxidizing atmosphere, because of extra oxygen ions entering at the interfaces. Evidence is reported that the hole doping of the CuO2 planes is obtained by charge transfer from the interface layers, which act as charge reservoir.Comment: 18 pages, 8 figure

Control of magnetic anisotropy by orbital hybridization in (La0.67Sr0.33MnO3)n/(SrTiO3)n superlattice

The asymmetry of chemical nature at the hetero-structural interface offers an unique opportunity to design desirable electronic structure by controlling charge transfer and orbital hybridization across the interface. However, the control of hetero-interface remains a daunting task. Here, we report the modulation of interfacial coupling of (La0.67Sr0.33MnO3)n/(SrTiO3)n superlattices by manipulating the periodic thickness with n unit cells of SrTiO3 and n unit cells La0.67Sr0.33MnO3. The easy axis of magnetic anisotropy rotates from in-plane (n = 10) to out-of-plane (n = 2) orientation at 150 K. Transmission electron microscopy reveals enlarged tetragonal ratio > 1 with breaking of volume conservation around the (La0.67Sr0.33MnO3)n/(SrTiO3)n interface, and electronic charge transfer from Mn to Ti 3d orbitals across the interface. Orbital hybridization accompanying the charge transfer results in preferred occupancy of 3d3z2-r2 orbital at the interface, which induces a stronger electronic hopping integral along the out-of-plane direction and corresponding out-of-plane magnetic easy axis for n = 2. We demonstrate that interfacial orbital hybridization in superlattices of strongly correlated oxides may be a promising approach to tailor electronic and magnetic properties in device applications

The automatized workflow of a radiation oncology department: a complete integration of the oncology information system MOSAIQ with hospital information system

OBJECTIVE: To fully integrate the OIS (MOSAIQ by Elekta) and the Hospital Information System (HIS) to increase efficiency, quality, and safety of care and to streamline clinical workflows and processes. MATERIALS AND METHODS: More than 25 dedicated staff members are currently working at the Radiotherapy Unit of our Institute and treat approximately 700 patients per year with two Elekta linear accelerators. Within a radiation treatment, there is a series of clinical and organizational steps that it is indispensable to do to avoid errors or excessive resource consumption. Our experience has led to the creation of structured workflows to overcome these critical issues through the optimization and integration of HIS and OIS, respectively our hospital and our Radiotherapy Unit data management systems. RESULTS: Through the integration of the main management programs available and the creation of standardized therapeutic paths based on logistical and clinical needs, we managed to optimize both quality of care and accounting services provided. CONCLUSIONS: The integration of different operating systems and the definition of standardized steps within the workflow has led to the abolition of unnecessary operations, making it easier to manage patients’ care and prescription accounting. Furthermore, clinical records have become more readily and accessible by health care providers of our unit. All this translates into a decreased risk of misinformation, or time loss due to bureaucratic and organizational issues, therefore, allowing a significant increase in staff efficiency

Analysis of charge transfer mechanism on (Ba1-xNdxCuO2+d)2/(CaCuO2)n superconducting superlattices by thermoelectric power measurements

We have investigated the charge transfer mechanism in artificial superlattices by Seebeck effect measurements. Such a technique allows a precise determination of the amount of charge transferred on each CuO2 plane. A systematic characterization of thermoelectric power in (BaCuO2+d)2/(CaCuO2)n and (Ba0.9Nd0.1CuO2+d)2/(CaCuO2)n superlattices demonstrates that electrical charge distributes uniformly among the CuO2 planes in the Ca-block. The differences observed in the Seebeck effect behavior between the Nd-doped and undoped superlattices are ascribed to the different metallic character of the Ba-block in the two cases. Finally, the special role of structural disorder in superlattices with n=1 is pointed out by such analysis.Comment: subitted to PRB, 15 pages, 3 figure