Structural dichroism in the antiferromagnetic insulating phase of V_2O_3

We performed near-edge x-ray absorption spectroscopy (XANES) at V K edge in the antiferromagnetic insulating (AFI) phase of a 2.8% Cr-doped V_2O_3 single crystal. Linear dichroism of several percent is measured in the hexagonal plane and found to be in good agreement with ab-initio calculations based on multiple scattering theory. This experiment definitively proves the structural origin of the signal and therefore solves a controversy raised by previous interpretations of the same dichroism as non-reciprocal. It also calls for a further investigation of the role of the magnetoelectric annealing procedure in cooling to the AFI phase.Comment: 4 pages 3 figures. To be published in Phys. Rev. B (2005

Comment on a recent sensitivity analysis of radial base function and multi-layer feed-forward neural network models - Response

Contains fulltext : 112420.pdf (publisher's version ) (Open Access

The structure of ZrO2 phases and devetrification processes in a Ca-Zr-Si-O-based glass ceramic: a combined a-XRD and XAS study

The structure of Zr atomic environment in a CaO-ZrO2-SiO2 glass-ceramic has beenstudied combining x-ray absorption spectroscopy (XAS), X-ray diffraction (XRD) andanomalous-XRD (a-XRD) techniques as a function of thermal treatments. The analysisof XRD patterns demonstrates that the devitrification process, as a function ofthermal treatment, proceeds through the partial segregation of Zr-depleted phases(Wollastonite-like) and Zr-rich phases (Zr-oxides). The XAS and a-XRD measurementsat the Zr K edge have been exploited to get a closer insight on the atomicstructure around Zr ions. In the as quenched glass the Zr is 6-fold coordinated to Oxygenatoms in an amorphous environment rich of Ca and Si. Thermal treatment firstly(T=1000 - 1050 oC) determines the partial segregation of Zr in form of oxide whichcrystalline structure is that of tetragonal Zirconia (t-ZrO2). Raising the temperature(T=1100 oC) provokes the formation of ZrO2 crystallites in the monoclinic crystallographicphase (Baddeleyite: m-ZrO2). The analysis of XAS data demonstrates that aconsiderable amount of Zr still remains in an amorphous Calcium-Silicate phase

Recent studies of cements and concretes by synchrotron radiation crystallographic and cognate methods

The portfolio of available synchrotron radiation techniques is increasing notably for cements and pastes. Furthermore, sometimes the terminology is confusing and an overall picture highlighting similarities and differences of related techniques was lacking. Therefore, the main objective of this work is to review recent advances in synchrotron techniques providing a comprehensive overview. This work is not intended to gather all publications in cement chemistry but to give a unified picture through selected examples. Crystallographic techniques are used for structure determination, quantitative phase analyses and microstructure characterization. These studies are not only carried out in standard conditions but synchrotron techniques are especially suited to non-ambient conditions: high temperatures and pressures, hydration, etc., and combinations. Related crystallographic techniques, like Pair Distribution Function, are being used for the analysis of ill-crystalline phase(s). Furthermore, crystallographic tools are also employed in imaging techniques including scanning diffraction microscopy and tomography and coherent diffraction imaging. Other synchrotron techniques are also reviewed including X-rays absorption spectroscopy for local structure and speciation characterizations; small angle X-ray scattering for microstructure analysis and several imaging techniques for microstructure quantification: full-field soft and hard X-ray nano-tomographies; scanning infrared spectro-microscopy; scanning transmission and fluorescence X-ray tomographies. Finally, a personal outlook is provided.I am grateful to all my coauthors, collaborators, colleagues and PhD students, for all our work together during more than two decades. I thank the University of Malaga and ALBA Synchrotron Light Source for the support and the stirring environments. I acknowledge the Spanish science funding agencies (they change the name quite often) for funding my studentship, to do the PhD and the three summer research stays at Oxford University, to the last ongoing research project. To all synchrotrons I have been allowed to enjoy carrying out experiments: SRS, ESRF, Max-Lab, DLS, APS, SLS and ALBA. Finally, this work has been supported by the Spanish MINECO through the BIA2014-57658-C2-1-R research grant

High-Pressure Phase Diagram in the Manganites: a Two-site Model Study

The pressure dependence of the Curie temperature $T_C$ in manganites, recently studied over a wide pressure range, is not quantitatively accounted for by the quenching of Jahn-Teller distortions, and suggests the occurrence of a new pressure-activated localizing processes. We present a theoretical calculation of $T_C$ based on a two-site double-exchange model with electron-phonon coupling interaction and direct superexchange between the $t_{2g}$ core spins. We calculate the pressure dependence of $T_C$ and compare it with the experimental phase diagram. Our results describe the experimental behavior quite well if a pressure-activated enhancement of the antiferromagnetic superexchange interaction is assumed

NGPaaS framework for enriched and customized virtual network functions-as-a-service

This paper describes how the novel Next Generation Platform-as-a-Service (NGPaaS) framework can facilitate major benefits for Network Operators and Vertical Service Providers (VSPs) who wish to leverage Virtual Network Functions-as-a-Service (VNFaaS) capabilities. Network Operators can benefit by providing an "on demand" PaaS with required features for the VSPs, thus generating new revenue streams but with low operational overhead due to the high degree of automation. VSPs can benefit from the PaaS-oriented approach, by being able to flexibly on-board new VNF types and "value-added" service capabilities like monitoring, healing and profiling, to deliver customized service blueprints to meet the needs of their end customers. The paper outlines the design of an early prototype, built on the Open-CORD platform and using industry-standard Virtualised Network Functions (VNFs)