1,721,047 research outputs found
A Close Look into the Low Energy Region of the XAS Spectra: The XANES Region
No full textThe interest in XANES spectroscopy is growing systematically in material sciences as it is a very unique
local probe, chemically selective, giving access to fine details of the local atomic structure and electronic
state of the photo-absorber, which are hardly reached by other techniques. The recent progresses in theory
and computation have extended the application of XANES spectroscopy in many different fields. This
chapter aims to be a guide across the different approaches to XANES data analysis, from the
phenomenological semi-quantitative methods, to accurate ab-initio modelling and data fitting
Effect of multielectronic configurations on the XAFS analysis at the FeK edge
No full textAn extensive investigation of the extended X-ray absorption fine structure (EXAFS) spectra of Fe2+ and Fe3+ in aqueous solution is presented. Anomalous peaks at 3.9 and 5.3 Angstrom(-1) have been detected and assigned to the simultaneous excitations of the 1s3p and 1s3s electrons, referred to as KM23 and KM1 channels. The Fe3+ water solution absorption cross section displays the presence of peculiar features that reflect the existence of two electronic configurations in the ground state, giving rise to two channels of comparable intensity. The influence of many-body effects on the quantitative extraction of the structural parameters from the EXAFS spectra was investigated. Omission of double-electron excitation edges from the atomic background significantly worsens the quality of the EXAFS fits and results in slightly incorrect values of the structural parameters. Conversely, the [Fe(H2O)(6)](3+) structural parameters obtained from the EXAFS data analysis, performed in the framework of the one-electron approximation, are affected by severe systematic errors, despite the perfect agreement between the experimental and theoretical data. An accurate determination of the hydration geometry of the Fe3+ ion can be only obtained using a theoretical scheme based on the multichannel multiple-scattering theory. The hydrogen contribution has been included in the EXAFS data analyses and Fe-H distances of 2.84 and 2.76 Angstrom have been obtained for Fe2+ and Fe3+, respectively, which are in excellent agreement with the results of ab initio quantum-mechanical/molecular-mechanical molecular dynamics simulations
X-ray resonant scattering as a direct probe of orbital ordering in transition-metal oxides
No full textGeometrical fitting of experimental XANES (X-ray Absorption Near Edge Structure) by a full multiple scattering procedure
No full textAdvances in theTheoretical Analysis of the XANES (X-ray Absorption Near Edge Structure) Energy Region for Quantitative Structural Use
No full textAdvances in the theoretical analysis of the XANES (X-Ray Absorption Near Edge Structure) energy region for quantitative structural use
No full textX-ray absorption analysis of the active site of Streptomyces antibioticus Tyrosinase upon binding of transition state analogue inhibitors
No full textThe key structural features that define the reaction mechanism of the binuclear copper enzyme Tyrosinase (Ty) from Streptomyces antibioticus were investigated by X-ray absorption spectroscopy. The data for the met form, the halide bound derivative and the adduct with the competitive inhibitor and transition state analogue Kojic acid were analysed using the recently developed MXAN package. This analysis permitted the definition of structural clusters that include all atoms within 5 A from the metal ions of the active site. The data obtained for the different forms provide validation of the structural models previously proposed on the basis of the magnetic properties investigated by both pulsed EPR and paramagnetic NMR spectroscopies. The structural model of the reaction center obtained in this solution study is compared with the crystallographic structures recently proposed for several derivatives of bacterial Ty to suggest that only one of these structures is relevant to solution conditions. (C) 2007 Elsevier Inc. All rights reserved
Evidence of distorted fivefold coordination of the Cu2+ aqua ion from an x-ray absorption spectroscopy quantitative analysis.
No full textA combined x-ray-absorption near-edge structure and extended x-ray-absorption fine-structure quantitative analysis, based on fitting procedures of both low- and high-energy ranges, has been carried out at the Cu K edge. This allowed an accurate determination of the structural parameters associated with the first hydration shell of the Cu2+ aqua complex. The existence of an average fivefold coordination has been evidenced, ruling out the recently proposed regular pyramidal configuration with five equal Cu-O distances. Our structural results are compared with recent neutron-diffraction data performed by the second-difference isotopic substitution method
Setaria tundra, an emerging filarioid nematode in roe deer (Capreolus capreolus) in northeast Italy.
Full text linkCoincidental with decades of warming (high temperature and humidity) in the sub-Arctic region of
Europe, the mosquito-borne filarioid nematode Setaria tundra is now associated with emerging
epidemic disease, resulting in morbidity and mortality for reindeer and moose. Similarly, roe deer is
also target of this nematode, as documented in Denmark, Germany and Bulgary. In the early 2000s,
S. tundra was first described in roe deer in Piedmont (north Italy). Aedes spp. mosquitoes seem to
be the most competent vectors for S. tundra and little is known about its pathogenicity in roe deer.
After a first report in 2013 of S. tundra in Friuli Venezia Giulia-FVG (northeast Italy) roe deers,
during 2014-2016 an investigation was undertaken to evaluate the its presence in road-killed roe
deer from the Gorizia province. Currently, parasitological dissections of 17 roe deer were
performed. During the necropsy, nematode specimens (1 to 58 per host) were found in the
abdominal cavity. Based on their morphology and biometrics, the nematodes recovered were
identified as Setaria tundra and preserved in alcohol or cryopreserved for further analysis
Moreover, pathological lesions were described, documented and damaged tissue samples were
collected for histological evaluation. The prevalence of S. tundra in FVG roe deer population is
47.1%, mean intensity 11 (range 1-58) and mean abundance 5. The adult worms were located free
in the abdominal cavity where tracks left by worm migration were also seen. Macroscopical lesions
were polysierositis with thickening spleen and liver serosa with fibrinous deposition on surface of
the abdominal organs. Whereas, histological lesions were diffuse serositis, granulomatous reactivity
with Muller's giant cells and calcifications. In our study in FVG, this the first recognition of S.
tundra and the alarming aspect has been that some road killed roe deers showed some significant
pathological peritoneal changes
Prime osservazioni italiane di attività predatoria da parte dello sciacallo dorato (Canis aureus) su ovini domestici nel Carso goriziano
Full text linkLa presenza della specie sciacallo dorato Canis aureus moreoticus (I. Geoffrey, 1835) documentata per il Friuli Venezia-Giulia
a partire dagli anni 80 è in continua espansione ed incremento con un particolare riferimento all’area carsica. Nel territorio
preso in esame, una porzione di landa e boscaglia carsica in cui è ubicato un parco rurale di circa 100 ha con annesso allevamento
ovino, la presenza di sciacallo dorato, documentata anche con l’uso di foto trappole, è passata da casi sporadici ad un numero
certo di 7 esemplari che frequentano l’area. Congiuntamente all’aumento di presenza si sono avuti casi di predazione su
ovini adulti mantenuti allo stato semibrado senza ricovero notturno. Sono state esaminate tre carcasse di ovini trovati morti in
giornate successive. Le pecore appartenevano tutte alla classe adulta ed in particolare superavano gli 8 anni di età.
Le valutazioni anatomopatologiche delle carcasse, a diversi stadi di decomposizione, hanno messo in evidenza lesioni di carattere
lacero contuso dei diversi piani tissutali nella regione del collo e nei garretti causate da morsi, con un consumo, costituito prevalentemente
dai tessuti molli delle cavità toraciche ed addominali, variabile in base al tempo intercorso tra il ritrovamento
ed il decesso. Dall’esame dei morsi ed in particolare dalla misurazione della distanza tra i canini, unite alle caratteristiche della
predazione hanno permesso di riferirla a sciacallo dorato. Tale ipotesi è stata successivamente confermata con il fototrappolaggio.
Dopo tali episodi, gli ovini sono stati ricoverati ogni notte in ovile chiuso e protetto. Tale metodologia gestionale è stata
sufficiente a ridurre notevolmente l’impatto della predazione da sciacallo dorato sugli animali allevati
- …
