Electrochemical characterization of biodeterioration of paint films containing cadmium yellow pigment

The voltammetry of microparticles (VMP) methodology was used to characterize the biological attack of different bacteria and fungi to reconstructed egg tempera and egg–linseed oil emulsion paint films containing cadmium yellow (CdS), which mimic historical painting techniques. When these paint films are in contact with aqueous acetate buffer, different cathodic signals are observed. As a result of the crossing of VMP data with attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), scanning electrochemical microscopy (SECM), field emission scanning electron microscopy (FESEM), and atomic force microscopy (AFM), these voltammetric signals can be associated with the reduction of CdS and different complexes associated to the proteinaceous and fatty acid fractions of the binders. After biological attack with different fungi (Acremonium chrysogenum, Aspergillus niger, Mucor rouxii, Penicillium chrysogenum, and Trichoderma pseudokoningii) and bacteria (Arthrobacter oxydans, Bacillus amyloliquefaciens, and Streptomyces cellulofans), the observed electrochemical signals experience specific modifications depending on the binder and the biological agent, allowing for an electrochemical monitoring of biological attack.     

On the Relationship Between Two Kinds of Besov Spaces with Smoothness Near Zero and Some Other Applications of Limiting Interpolation

Using limiting interpolation techniques we study the relationship between Besov spaces \(\mathbf B ^{0,-1/q}_{p,q}\) with zero classical smoothness and logarithmic smoothness \(-1/q\) defined by means of differences with similar spaces \(B^{0,b,d}_{p,q}\) defined by means of the Fourier transform. Among other things, we prove that \(\mathbf B ^{0,-1/2}_{2,2}=B^{0,0,1/2}_{2,2}\). We also derive several results on periodic spaces \(\mathbf B ^{0,-1/q}_{p,q}(\mathbb {T})\), including embeddings in generalized Lorentz–Zygmund spaces and the distribution of Fourier coefficients of functions of \(\mathbf B ^{0,-1/q}_{p,q}(\mathbb {T})\).     

Electrochemically-driven conformational shift in mono- and di-copper constrained macrotricyclic cyclen receptors

An electrochemical study of mono- and di-copper constrained cyclen macrotricycles is presented. Electrochemical data in DMF solution indicate that the reduction of dinuclear complexes occurs in two steps in the -0.4 to -0.8 V vs.AgCl/Ag potential range yielding CuII CuI and CuI CuI species further reduced to Cu metal at highly negative potentials. Mononuclear complexes are reduced in two steps to CuI and Cu metal. Electrochemical data suggest that reduction of both mononuclear and dinuclear complexes approach a square scheme involving electrochemically-driven conformational shifts for metal ions. The presence of endo- and exo-forms of the complexes are revealed by changes in the electrochemical response of the complexes in the presence of tetraethylammonium chloride, 1-azabicyclo[2.2.2]octane and diazabicyclo[2.2.2]octane competing ligands.     

Characterization of polyvinyl resins used as binding media in paintings by pyrolysis–silylation–gas chromatography–mass spectrometry

Polyvinyl resins, in particular poly(vinyl acetate) emulsions (PVA), are widely used in contemporary paintings as binding media, because of the optimum mechanical and optical properties these polymers confer on the paint layers. A study has been carried out to chemically characterize samples of PVA resins prepared as coating films from commercial products currently available from fine arts suppliers. For this purpose, a new method has been based on "on-line" silylation-pyrolysis using hexamethyldisilazane as derivatisation reagent in pyrolysis-gas chromatography-mass spectrometry (Py-GC-MS). This proposed procedure leads to unambiguous identification of this type of binder and improves conventional direct Py-GC-MS. PVA media used in three contemporary paintings from a private collection and from the Museum of Fine Arts of Málaga (Spain) have been successfully identified with this procedure. As a second step of this work, a study devoted to the characterization of changes in the chemical composition of the PVA commercial products studied has been carried out. Effects induced in the specimens by three different types of artificial accelerated ageing process--thermal, UV light, and in an SO(2)-polluted chamber--were compared.     

Renaissance patinas in Úbeda (Spain): mineralogic,petrographic and spectroscopic study

Different analytical techniques were used for microstructural and compositional analysis of the ochre-coloured patinas that appear on the calcarenite substrate of monuments in the historical settings of Úbeda and Baeza (Spain). Optical microscopy, scanning electron microscopy–energy dispersive x-ray spectrometry (SEM-EDX), x-ray diffraction, Raman spectroscopy and attenuated total reflection–Fourier transform infrared spectroscopy (ATR-FTIR) were employed and a critical comparison of their experimental requirements, strengths and weaknesses is presented. The study focussed on two churches in Úbeda where patinas were widespread in ornamental elements. These films contained calcite as the principal component, and traces of dolomite and feldspars. Clear identification of calcium oxalate, mainly in the form of whewellite, was achieved by infrared and Raman spectroscopic studies. Results from texture, distribution and composition of the patinas in ornamental elements suggest that ancient treatments were applied for protection of Renaissance façades and consolidation of weathered older façades. The patinas were seldom found on supporting elements. Their different composition, apatite was found together with oxalates, and location may suggest a biogenic origin here. Gypsum crusts were sometimes found over the patinas.     

Effects of lactose permease on the phospholipid environment in which it is reconstituted: a fluorescence and atomic force microscopy study

The membrane transport protein lactose permease (LacY), a member of the major facilitator superfamily containing 12 membrane-spanning segments connected by hydrophilic loops, was reconstituted in liposomes whose composition was 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphoethanolamine and 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphoglycerol in a 3:1 molar ratio. The structural order of the lipid membranes, in the presence and absence of LacY, was assessed using steady-state fluorescence anisotropy. The features of the anisotropy curves obtained with 1,6-phenyl-1,3,5-hexatriene and 1-(4-trimethylammoniumphenyl)-6-phenyl-1,3,5-hexatriene p-toluenesulfonate suggest a surface effect of LacY on the membranes. Atomic force microscopy imaging of supported planar bilayers (SPBs) deposited onto mica was used to examine the effect of LacY on the nanostructure of the phospholipid matrix. Two separated domains were observed in SPBs formed from pure phospholipid mixture. Protein assemblies segregated from the rest of the matrix were observed after the extension of proteoliposomes. The effect of the protein on the electrostatic surface potential of the bilayer was also examined using a fluorescent pH indicator, 4-heptadecyl-7-hydroxycoumarin. Changes in surface potential were enhanced in the presence of the substrate (i.e., lactose). Taken together the results indicate that LacY is segregated into the phospholipid matrix and has moderate effects on the acyl chain order of the bilayers. The changes in surface electrical properties of the bilayers suggest a role for the phospholipid headgroups in proton transfer to the amino acids involved in substrate translocation.     

Stability and Bifurcation Analysis of a Modified Geometrically Nonlinear Orthotropic Jeffcott Model with Internal Damping

In this paper, a modified Jeffcott model is proposed and studied in order to shed light into the dynamics of a complex system, the Short Electrodynamic Tether (SET), which is similar to an unbalanced rotor. Due to the internal damping, a geometrically linear SET model appears to be unstable as predicted by the linear rotordynamics theory. Some studies in the field of rotordynamics suggest that this instability caused by internal damping do not appear if geometric nonlinearities are taken into account in the system equations of motion. Stability and bifurcation analysis have been carried out on the modified Jeffcott model, which accounts for geometric nonlinearities, orthotropy in the shaft's cross section, and a viscous damping-based internal damping model. The stability results analytically obtained have been compared with a nonlinear multibody model by means of time simulations and good agreement has been found.     

Heuristic Procedures for Solving the Discrete Ordered Median Problem

We present two heuristic methods for solving the Discrete Ordered Median Problem (DOMP), for which no such approaches have been developed so far. The DOMP generalizes classical discrete facility location problems, such as the p-median and p-center. The first procedure proposed in this paper is based on a genetic algorithm developed by Moreno Vega (1996) for p-median and p-center problems. Additionally, a second heuristic approach based on the Variable Neighborhood Search metaheuristic (VNS) proposed by Hansen and Mladenović (1997) for the p-median problem is described. An extensive numerical study is presented to show the efficiency of both heuristics and compare them.     

Emerging trends in metal oxide electrocatalysis: Bifunctional oxygen catalysis,synergies and new insights from in situ studies

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