EXAFS Study of Rutile and Anatase

Two crystallographic forms of TiO2 (rutile and anatase) were subject to an extended x-ray absorption fine structure study at the K threshold of titanium. Data analysis was carried out by Fourier methods and curve fitting techniques. Using the theoretical phases, Ti-O bond distances of 1.93(1) Å were derived both for rutile and anatase, as compared to the crystallographic values of 1.948 - 1.980(1) Å (rutile) and 1.934-1.980(1) Å (anatase). The ratio of the cation coordination numbers Nr/Na = 1.07 is close to the theoretical value

EXAFS characterization of oxaliplatin anticancer drug and its degradation in chloride media.

Oxaliplatin is a second-generation platinum-based anticancer drug. Its degradation is studied in solution, in the presence of chloride ions (in neutral or acidic media) in excess. In both cases the degradation product precipitates immediately. The EXAFS spectra of these products show that they are identical. EXAFS modeling and refinement of the first coordination sphere shows that two light atoms are replaced by two chloride ions. The complete refinement of the local structure is possible by studying the multiple-scattering signal. The results show that the main multiple-scattering contribution is due to the binding oxalato group and that the degradation product is [Cl(2)-(diaminocyclohexane)-Pt(II)]

EXAFS analysis of the L3 edge of Ce in CeO2: effects of multi‐electron excitations and final‐state mixed valence

Cerium oxide (IV) (CeO2) is extensively employed in heterogeneous catalysis, particularly as a promoter of noble metal action in three-way catalysts. For this reason there is a great scientific and economical interest in the development of any possible chemical or structural analysis technique that could provide information on these systems. EXAFS spectroscopy has revealed itself as a powerful technique for structural characterization of such catalysts. Unfortunately, good quality K-edge spectra of cerium are not yet easily obtainable because of the high photon energy required (>40 keV). On the other hand, at lower energies it is easy to collect very good spectra of the L3 edge (5.5 keV), but L3-edge spectra of cerium (IV) are characterized by the presence of two undesired additional phenomena that interfere with EXAFS analysis: final-state mixed-valence behaviour and intense multi-electron excitations. Here, a comparative analysis of the K, L3, L2 and L1 edges of Ce in CeO2 has been made and a procedure for obtaining structural parameters from L3-edge EXAFS, even in the presence of these features, has been developed. This procedure could allow further studies of catalytic compounds containing tetravalent cerium surrounded by oxygen ligands

Bimetallic ruthenium-gold-on-magnesia catalysts: Chemicophysical properties and catalytic activity

Bimetallic Ru-Au catalysts supported on MgO were prepared, their atomic composition varying from 100% Ru to 100% Au. Samples were characterized after impregnation and drying at 110 [deg]C and after further reduction by hydrogen at 400 [deg]C. X-Ray line broadening analysis, small-angle X-ray scattering, transmission electron microscopy, gas chemisorption, diffuse reflectance spectroscopy (DRS), X-ray photoelectron spectroscopy (XPS), and extended X-ray absorption fine structure (EXAFS) analysis were used. Catalytic activity was measured for the oxygen transfer between CO and CO2. The Ru and Au precursor compounds appear to be modified, and have probably interacted in the bimetallic samples, already after impregnation and drying. Relevant amounts of metal oxides are found in some "reduced" catalysts; a metal-support interaction is proposed for Au/MgO. The amounts of the Ru and Au oxidized species found by EXAFS in the examined bimetallic sample are significantly different from those found in Ru/MgO and Au/MgO, respectively. The DR spectra of the bimetallic samples are not a simple combination of those of the monometallic catalysts. The Ru/Au atomic ratios measured by XPS are higher than the analytical ones. The fraction of surface Ru atoms, measured by hydrogen chemisorption, increases on decreasing the bulk Ru/Au atomic ratio. The Au/MgO sample has an activity which is two orders of magnitude higher than that of the remaining samples. All of this suggests the existence of a Ru surface enrichment and also an Ru-Au chemical interaction. These conclusions are also supported by an ir study of CO chemisorbed on the same samples.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/23184/1/0000111.pd

Low Temperature Ferromagnetism in Chemically Ordered FeRh Nanocrystals

In sharp contrast to previous studies on FeRh bulk, thin films, and nanoparticles, we report the persistence of ferromagnetic order down to 3 K for size-selected 3.3 nm diameter nanocrystals embedded into an amorphous carbon matrix. The annealed nanoparticles have a B2 structure with alternating atomic Fe and Rh layers. X-ray magnetic dichroism and superconducting quantum interference device measurements demonstrate ferromagnetic alignment of the Fe and Rh magnetic moments of 3 and 1 mu(B), respectively. The ferromagnetic order is ascribed to the finite-size induced structural relaxation observed in extended x-ray absorption spectroscopy. DOI: 10.1103/PhysRevLett.110.08720

Recent progress on univariate and multivariate polynomial and spline quasi-interpolants

Polynomial and spline quasi-interpolants (QIs) are practical and effective approximation operators. Among their remarkable properties, let us cite for example: good shape properties, easy computation and evaluation (no linear system to solve), uniform boundedness independently of the degree (polynomials) or of the partition (splines), good approximation order. We shall emphasize new results on various types of univariate and multivariate polynomial or spline QIs, depending on the nature of coefficient functionals, which can be differential, discrete or integral. We shall also present some applications of QIs to numerical methods

Landscape genomics and biased FST approaches reveal single nucleotide polymorphisms under selection in goat breeds of North-East Mediterranean

<p>Abstract</p> <p>Background</p> <p>In this study we compare outlier loci detected using a <it>F<smcaps>ST </smcaps></it>based method with those identified by a recently described method based on spatial analysis (SAM). We tested a panel of single nucleotide polymorphisms (SNPs) previously genotyped in individuals of goat breeds of southern areas of the Mediterranean basin (Italy, Greece and Albania). We evaluate how the SAM method performs with SNPs, which are increasingly employed due to their high number, low cost and easy of scoring.</p> <p>Results</p> <p>The combined use of the two outlier detection approaches, never tested before using SNP polymorphisms, resulted in the identification of the same three loci involved in milk and meat quality data by using the two methods, while the <it>F<smcaps>ST </smcaps></it>based method identified 3 more loci as under selection sweep in the breeds examined.</p> <p>Conclusion</p> <p>Data appear congruent by using the two methods for <it>F<smcaps>ST </smcaps></it>values exceeding the 99% confidence limits. The methods of <it>F<smcaps>ST </smcaps></it>and SAM can independently detect signatures of selection and therefore can reduce the probability of finding false positives if employed together. The outlier loci identified in this study could indicate adaptive variation in the analysed species, characterized by a large range of climatic conditions in the rearing areas and by a history of intense trade, that implies plasticity in adapting to new environments.</p

Structure and Morphology of Silver Nanoparticles on the (111) Surface of Cerium Oxide

The structure of Ag nanoparticles of different size, supported on the cerium oxide (111) surface, was investigated by X-ray absorption fine structure at the Ag K-edge. The results of the data analysis in the near and extended energy range are interpreted with the help of the results obtained by X-ray photoelectron spectroscopy and scanning tunneling microscopy measurements and allow to obtain a detailed atomic scale description of the model system investigated. The Ag nanoparticles have an average size of a few tens of angstroms, which increases with increasing deposited Ag amount. The nanoparticles show a slight tendency to nucleate at the step edges between different cerium oxide layers and they have a face centered cubic structure with an Ag-Ag interatomic distance contracted by 3-4% with respect to the bulk value. The interatomic distance contraction is mainly ascribed to dimensionality induced effects, while epitaxial effects have a minor role. The presence of Ag-O bonds at the interface between the nanoparticles and the supporting oxide is also detected. The Ag-O interatomic distance decreases with decreasing nanoparticle size