Raman scattering features of lead pyroantimonate compounds. Part I: XRD and Raman characterization of Pb2Sb2O7 doped with tin and zinc

Yellow pyroantimonates Pb Sb, Pb Sb Sn and Pb Sb Zn were synthesized by solid‐state reactions at high temperature and characterized by X‐ray diffraction and Raman spectroscopy. The lattice size of cubic pyrochlores increases with Sn and Zn doping and with Pb overstoichiometry, indicating the replacement of Sb⁵⁺ by the larger cations. This fact permits the understanding of the corresponding Raman spectral modifications as a consequence of the changes in the local symmetry of the Sb O polyhedra, justifying the exploitation of Raman spectroscopy to noninvasively identify structural modifications of pyroantimonate pigments in artworks. Copyright © 2008 John Wiley & Sons, Ltd.     

Microanalytical investigation of degradation issues in Byzantine wall paintings

The St. Euthymius wall paintings, in the Cathedral of Thessaloniki, dated 1303 AD., are stylistically attributed to the School of Panselinos, one of the most important painters of Palaeologean Art. An in situ non-invasive study has been carried out as part of a MOLAB project (a mobile laboratory accessible through the Eu-ARTECH project, funded by the EC 6th FP) combining different analytical techniques such as XRF, mid-FTIR and UV-vis diffuse reflectance spectroscopy. It was during this comprehensive in situ study that certain scientific queries were raised about sensitive areas, where indications of the phenomena of decay requested further attention. A subsequent laboratory study of selected cross-sections using microscopic analysis with μFTIR, SEM-EDS and μRaman, further confirmed the identification of only the atypical in situ observations. The comparative interpretation of all respective results on the specific regions of interest permitted the identification of several degradation phenomena which justify certain aesthetic or stylistic incoherences in the representations. Namely, (i) thermal dehydration of the yellow ochre explaining the reddish appearance of the flesh tones and halos as an accidental effect of the fire; (ii) thermal degradation of azurite converted to tenorite explaining the atypical instance of dark lightings on the purple garments; (iii) degradation of red lead employed in the lightings of the red garments; (iv) widespread presence of oxalates in the paint surface. PACS  87.64.Je; 87.64.Rr; 87.64.Ee     

The Equivalence of Ergodicity and Weak Mixing for Infinitely Divisible Processes

The equivalence of ergodicity and weak mixing for general infinitely divisible processes is proven. Using this result and [9], simple conditions for ergodicity of infinitely divisible processes are derived. The notion of codifference for infinitely divisible processes is investigated, it plays the crucial role in the proofs but it may be also of independent interest.     

Non-invasive in-situ investigations versus micro-sampling: a comparative study on a Renoirs painting

In this paper, a multi-technique in-situ non-invasive approach has been followed for the study of the materials used for a painting by Pierre-Auguste Renoir, “A woman at her toilette”. The study was carried out using five portable spectroscopic techniques, namely X-ray fluorescence, mid-infrared reflectance spectroscopy, near infrared reflectance spectroscopy, and UV-Vis spectroscopy in absorption and emission. The painting was selected as a case study because it was examined in advance of the current investigation using conventional micro-sampling techniques. This provided the opportunity to evaluate potential and limitations of the non-invasive approach to the complex case of the modern painting. PACS 82.80.GK; 78.70.En; 33.50.Dq     

Raman scattering features of lead pyroantimonate compounds: implication for the non‐invasive identification of yellow pigments on ancient ceramics. Part II. In situ characterisation of Renaissance plates by portable micro‐Raman and XRF studies

The effectiveness of Raman spectroscopy (using a bench‐top system on standard pigments) for the characterisation of modified lead antimonate yellows was demonstrated in the already published Part I. The knowledge gained is employed here for the study of yellow glazes on genuine Renaissance plates with the aim of identifying non‐invasively lead pyroantimonate compounds by portable micro‐Raman equipment. The investigation was carried out directly on site, at the Victoria and Albert Museum (London, UK) and at the Museo Statale d'Arte Medievale di Arezzo (Arezzo, Italy), combining Raman and X‐ray fluorescence analyses. In addition to the spectral features of both unmodified Naples yellow and Sn‐ and Zn‐modified lead antimonate compounds, the Raman patterns related to partially modified pyrochlore structures were observed. For this reason, the possible Sn‐induced modification of Naples yellow by cassiterite (SnO₂), present within the glaze as opacifier was explored on lead antimonate yellow glaze mock‐ups fired at different temperatures. Copyright © 2010 John Wiley & Sons, Ltd.     

Acceleration of uncertainty updating in the description of transport processes in heterogeneous materials

The prediction of thermo-mechanical behaviour of heterogeneous materials such as heat and moisture transport is strongly influenced by the uncertainty in parameters. Such materials occur e.g., in historic buildings, and the durability assessment of these therefore needs a reliable and probabilistic simulation of transport processes, which is related to the suitable identification of material parameters. In order to include expert knowledge as well as experimental results, one can employ an updating procedure such as Bayesian inference. The classical probabilistic setting of the identification process in Bayes’ form requires the solution of a stochastic forward problem via computationally expensive sampling techniques, which makes the method almost impractical.     

Formation of O3+ upon ionization of O2: the role of isomeric O4+ complexes

The course of the reaction of electronically and vibronically excited metastable O(2) (+)((4)Pi(u), nu') ions with O(2), known to produce O(3) (+), was examined by the joint application of computational and mass spectrometric methods. The results show that the reaction does not proceed by a direct mechanism and that it involves instead the intermediacy of the [O(2) (+)((4)Pi(u)) x O(2)] and [O(3) (+)((4)A(2)) x O] complexes, both theoretically characterized, and the latter one positively identified by structurally diagnostic mass spectrometric techniques. The reaction is a potential source of stratospheric ozone, in that O(3) (+) ions are known to undergo efficient charge exchange with oxygen to yield neutral O(3).     

A new peptide-based method for the design and synthesis of nanoparticle superstructures: construction of highly ordered gold nanoparticle double helices

Left-handed gold nanoparticle double helices were prepared using a new method that allows simultaneous synthesis and assembly of discrete nanoparticles. This method involves coupling the processes of peptide self-assembly of and peptide-based biomineralization of nanoparticles. In this study, AYSSGAPPMPPF (PEPAu), an oligopeptide with an affinity for gold surfaces, was modified with an aliphatic tail to generate C12-PEPAu. In the presence of buffers and gold salts, amphiphilic C12-PEPAu was used to both control the formation of monodisperse gold nanoparticles and simultaneously direct their assembly into left-handed gold nanoparticle double helices. The gold nanoparticle double helices are highly regular, spatially complex, and they exemplify the utility of this methodology for rationally controlling the topology of nanoparticle superstructures and the stereochemical organization of discrete nanoparticles within these structures.     

Capillary electrophoresis in the evaluation of ischemic injury: simultaneous determination of purine compounds and glutathione

An understanding of tissue energy metabolism and antioxidant status is of major interest in the field of organ preservation for transplantation. Nucleotide and glutathione are indicators of cell damage occurring during ischemia and reperfusion. A high performance capillary electrophoresis (HPCE) method with UV detection (185 nm) for the simultaneous analysis of intracellular free ribonucleotides, nucleosides, bases and glutathione (oxidized and reduced form) in myocardial tissues is described. The method does not involve thiol derivatization. The separations were carried out in an uncoated fused-silica capillary, 60 cm long, 52.5 cm to detector, 75 microm ID, with 20 mM Na-borate buffer, pH 10.00, at 20 kV voltage and reading at 185 nm. Injection was hydrostatic for 12 s and total analysis time was 20 min. The technique enables optimum separation of all the compounds examined and has a resolution similar to that of HPLC analysis, with the advantage of fast simultaneous measurement of cell nucleotide metabolism and redox state, not possible with HPLC.