Iron and molybdenum valences in double-perovskite (Sr,Nd)2FeMoO6: electron-doping effect

Double perovskite, (Sr1-xNdx)2FeMoO6, was doped with electrons through partial substitution of divalent Sr by trivalent Nd (0 < x < 0.2). The Fe valence and the degree of B-site order were probed by 57Fe Mossbauer spectroscopy. Replacing Sr by Nd increased the fraction of Fe and Mo atoms occupying wrong sites, i.e. antisite disorder. It had very little effect on the Fe valence: a small but visible increase in the isomer shift was seen for the mixed-valent FeII/III atoms occupying the right site indicating a slight movement towards divalency of these atoms, which was more than counterbalanced by the increase in the fraction of antisite Fe atoms with III valence state. It is therefore argued that the bulk of the electron doping is received by antisite Mo atoms, which - being surrounded by six MoV/VI atoms - prefer the lower IV/V valence state. Thus under Nd substitution, the charge-neutrality requirement inflicts a lattice disorder such that low-valent MoIV/V can exist.Comment: 15 pages, 6 figures, to appear in Solid State Commu

Iron valence in double-perovskite (Ba,Sr,Ca)2FeMoO6: Isovalent substitution effect

In the Fe-Mo based B-site ordered double-perovskite, A2FeMoO6.0, with iron in the mixed-valence II/III state, the valence value of Fe is not precisely fixed at 2.5 but may be fine-tuned by means of applying chemical pressure at the A-cation site. This is shown through a systematic 57Fe Mossbauer spectroscopy study using a series of A2FeMoO6.0 [A = (Ba,Sr) or (Sr,Ca)] samples with high degree of Fe/Mo order, the same stoichiometric oxygen content and also almost the same grain size. The isomer shift values and other hyperfine parameters obtained from the Mossbauer spectra confirm that Fe remains in the mixed-valence state within the whole range of A constituents. However, upon increasing the average cation size at the A site the precise valence of Fe is found to decrease such that within the A = (Ba,Sr) regime the valence of Fe is closer to II, while within the A = (Sr,Ca) regime it is closer to the actual mixed-valence II/III state. As the valence of Fe approaches II, the difference in charges between Fe and Mo increases, and parallel with this the degree of Fe/Mo order increases. Additionally, for the less-ordered samples an increased tendency of clustering of the anti-site Fe atoms is deduced from the Mossbauer data.Comment: 19 pages, 6 figures, submitted to Phys. Rev.

Corpus-based lexeme ranking for morphological guessers

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Electroactive Polyhydroquinone Coatings for Marine Fouling Prevention—A Rejected Dynamic pH Hypothesis and a Deceiving Artifact in Electrochemical Antifouling Testing

Nanometer-thin coatings of polyhydroquinone (PHQ), which release and absorb protons upon oxidation and reduction, respectively, were tested for electrochemically induced anti-biofouling activity under the hypothesis that a dynamic pH environment would discourage fouling. Antifouling tests in artificial seawater using the marine, biofilm-forming bacterium Vibrio alginolyticus proved the coatings to be ineffective in fouling prevention but revealed a deceiving artifact from the reactive species generated at the counter electrode (CE), even for electrochemical bias potentials as low as |400| mV versus Ag|AgCl. These findings provide valuable information on the preparation of nanothin PHQ coatings and their electrochemical behavior in artificial seawater. The results further demonstrate that it is critical to isolate the CE in electrochemical anti-biofouling testing

Generalized Elliptic Integrals and the Legendre M-function

We study monotonicity and convexity properties of functions arising in the theory of elliptic integrals, and in particular in the case of a Schwarz-Christoffel conformal mapping from a half-plane to a trapezoid. We obtain sharp monotonicity and convexity results for combinations of these functions, as well as functional inequalities and a linearization property.Comment: 28 page

Gromov hyperbolicity of Denjoy domains with hyperbolic and quasihyperbolic metrics

15 pages, 2 figures.-- MSC2000 codes: 30F45, 53C23, 30C99.-- ArXiv pre-print available at: http://arxiv.org/abs/0806.0097SubmittedWe derive explicit and simple conditions which in many cases allow one decide, whether or not a Denjoy domain endowed with the Poincare or quasihyperbolic metric is Gromov hyperbolic. The criteria are based on the Euclidean size of the complement. As a corollary, the main theorem allows to deduce the non-hyperbolicity of any periodic Denjoy domain.First author (P.H.) was supported in part by the Academy of Finland. Third (A.P.), fourth (J.M.R.) and fifth (E.T.) authors were supported in part by three grants from M.E.C. (MTM 2006-13000-C03-02, MTM 2006-11976 and MTM 2007-30904-E), Spain. Fourth and fifth authors were also supported in part by a grant from U.C.IIIM./C.A.M. (CCG07-UC3M/ESP-3339), Spain.No publicad

Personalisation of intelligent homecare services adapted to children with motor impairments

Ambient Intelligence could support innovative application domains like motor impairments' detection at the home environment. This research aims to prevent neurodevelopmental disorders through the natural interaction of the children with embedded intelligence daily life objects, like home furniture and toys. Designed system uses an interoperable platform to provide two intelligent interrelated home healthcare services: monitoring of children¿s abilities and completion of early stimulation activities. A set of sensors, which are embedded within the rooms, toys and furniture, allows private data gathering about the child's interaction with the environment. This information feeds a reasoning subsystem, which encloses an ontology of neurodevelopment items, and adapts the service to the age and acquisition of expected abilities. Next, the platform proposes customized stimulation services by taking advantage of the existing facilities at the child's environment. The result integrates Embedded Sensor Systems for Health at Mälardalen University with UPM Smart Home, for adapted services delivery

Investigation and compensation of the nonlinear response in photomultiplier tubes for quantitative single-shot measurements.

A concept for time-sensitive optical detectors is described that shows how to confirm whether the detection device is operating in the linear response regime. By evaluating the recorded time decay of a thermographic phosphor, even weak saturation effects far from obvious situations can be identified and further related to either optical or electrical saturation. The concept has been validated by running a PMT detector close to saturation and exposing it to the optical signal decay of two different thermographic phosphors, La(2)O(2)S:Eu and CdWO(4). It was confirmed that short but intense light exposures at the beginning of an individual time decay influence the detector response for the rest of the decaying signal including temporal areas, where the anode current has dropped well below the manufacturer specified current limit. Such situations are common when applying, e.g., phosphor thermometry where it is necessary to retrieve the full decay curve from a single-shot event, i.e., standard techniques based on single-photon counting are omitted. Finally, means of compensation are introduced in order to facilitate the retrieval of useful information from the measurement data when operation in the non-linear response regime is inevitable

151Eu Mössbauer spectroscopy and x-ray-diffraction studies on the Pb2Ba2EuCu3O8+[delta] system

Simultaneous replacement of Sr by Ba and Y by Eu in the Pb-2213 system was found to yield single-phase Pb2Ba2EuCu3O8+δ samples, suitable for Eu151 Mössbauer measurements. The samples were synthesized by a solid-state reaction of metal oxides and carbonates under an inert atmosphere. An oxygen-rich sample corresponding to δ=1.79 was obtained by annealing the as-synthesized material (δ=0.16) in oxygen. The oxygen annealing increased the size of the lattice constants and led to an orthorhombic-to-tetragonal phase transition of the structure. The samples were also oriented in an 11.7-T magnetic field. The x-ray-diffraction spectra showed that the c axes tended to orient perpendicular to the applied field. The measured Mössbauer spectra exhibited an electric quadrupole interaction typical of the Eu site in high-Tc cuprates. The average orientation angles obtained from fittings of the Mössbauer spectra were in accordance with the results from the x-ray-diffraction measurements.Peer reviewe