Weighted variational inequalities in non-pivot Hilbert spaces with applications

We introduce variational inequalities defined in non-pivot Hilbert spaces and we show some existence results. Then, we prove regularity results for weighted variational inequalities in non-pivot Hilbert space. These results have been applied to the weighted traffic equilibrium problem. The continuity of the traffic equilibrium solution allows us to present a numerical method to solve the weighted variational inequality that expresses the problem. In particular, we extend the Solodov-Svaiter algorithm to the variational inequalities defined in finite-dimensional non-pivot Hilbert spaces. Then, by means of a interpolation, we construct the solution of the weighted variational inequality defined in a infinite-dimensional space. Moreover, we present a convergence analysis of the method.     

MnO x /ZrO2 gel-derived materials for hydrogen peroxide decomposition

Manganese-yttrium-zirconium mixed oxide nanocomposites with three different Mn loadings (5, 15 and 30 wt%) were prepared by sol–gel synthesis. Amorphous xerogels were obtained for each composition. Their structural evolution with the temperature and textural properties were examined by thermogravimetry/differential thermal analysis, X-ray diffraction, diffuse reflectance UV–vis spectroscopy and N₂ adsorption isotherms. Mesoporous materials with high surface area values (70–100 m² g⁻¹) were obtained by annealing in air at 550 °C. They are amorphous or contain nanocrystals of the tetragonal ZrO₂ phase (T-ZrO₂) depending on the Mn amount and exhibit Mn species with oxidation state higher than 2 as confirmed by temperature programmed reduction experiments. T-ZrO₂ is the only crystallizing phase at 700 °C while the monoclinic polymorph and Mn₃O₄ start to appear only after a prolonged annealing at 1,000 °C. The samples annealed at 550 °C were studied as catalysts for H₂O₂ decomposition in liquid phase. Their catalytic activity was higher than that of previously studied Mn/Zr oxide systems prepared by impregnation. Catalytic data were described by a rate equation of Langmuir type. The decrease of catalytic activity with time was related to dissolution of a limited fraction (up to 15%) of Mn into the H₂O₂/H₂O solution.     

Comparison of physical-mechanical features of polyethylene based polymers employed as sealants in solar cells

In this article, we compared the sealing strength, flexibility, thermal stability, and moisture-barrier properties of two polymeric films, both based on linear low density poly ethylene (LLDPE), which can be successfully used as sealant materials in electrical devices. One example is the dye-sensitized solar cell (DSSC), a low-cost third generation device, based on a photo-electrochemical system. Characterization of LLDPE modified with maleic anhydride (PE-MAH) or with ionomeric ethylene-acrylic acid co-polymer (EMAA) was carried out. Results highlighted as PE-MAH exhibits better adhesion features toward glass, higher thermal stability, and lower wet ability even at high temperatures (80?°C) compared to EMAA. Sealant’s features have been correlated to their chemical and structural composition.     

Spectroscopic Characterisation of a Bio-Inspired Ni-Based Proton Reduction Catalyst Bearing a Pentadentate N2S3 Ligand with Improved Photocatalytic Activity

Inspired by the sulfur-rich environment found in active hydrogenase enzymes, a Ni-based proton reduction catalyst with pentadentate N₂S₃ ligand was synthesised. When coupled with [Ru(bpy)₃]²⁺ (bpy=2,2′-bipyridine) as photosensitiser and ascorbate as electron donor in a 1:1 mixture of dimethylacetamide and aqueous ascorbic acid/ascorbate buffer, the catalyst showed improved photocatalytic activity compared with a homologous counterpart bearing a tetradentate N₂S₂ ligand. The mechanistic pathway of photoinduced hydrogen evolution was comprehensively analysed through optical transient absorption and time-resolved X-ray absorption spectroscopy, which revealed important electronic and structural changes in the catalytic system during photoirradiation. The Ni^II catalyst undergoes a photoinduced metal-centred reduction to form a Ni^I intermediate with distorted square-bipyramidal geometry. Further kinetic analyses revealed differences in charge-separation dynamics between the pentadentate and tetradentate forms.     

Inner cladding influence on mode interaction in symmetry-free photonic crystal fibers under heat load

A further output power scaling of Yb-doped double-cladding photonic crystal fiber lasers, required for practical applications in many industrial fields, is currently prevented by thermal effects, which significantly worsen the beam quality. In this work the mode interaction and, consequently, the single-mode regime of Yb-doped air-silica symmetry-free photonic crystal fibers have been numerically investigated in different heat load conditions using simulation tools based on the finite element method. The effect of the main inner cladding geometric parameters, in particular of the inner cladding dimension, on the guided-mode delocalization has been analyzed, with the aim to identify a design of the large mode area active fiber providing single-mode operation despite the presence of thermal effects. Simulation results have demonstrated that the inner cladding enlargement causes a stronger coupling between core-guided and cladding modes, as well as an increase of the differential overlap between fundamental and first higher-order mode for moderate heat load values. However, the inner cladding influence becomes less important under severe heat load, being the fiber behaviour mainly affected by the thermally-induced refractive index change in the doped core.     

The normal approximation rate for the drift estimator of multidimensional diffusions

We consider the problem of the density and drift estimation by the observation of a trajectory of an \mathbbR^d{\mathbb{R}^{d}}-dimensional homogeneous diffusion process with a unique invariant density. We construct estimators of the kernel type based on discretely sampled observations and study their asymptotic distribution. An estimate of the rate of normal approximation is given.     

SPME in environmental analysis: biotransformation pathways

Solid-phase microextraction (SPME) is an organic solvent-free sample preparation tool suitable for direct adsorption of analytes from the headspace or the aqueous phase of a matrix followed by desorption into a gas chromatograph (GC) or high-performance liquid chromatograph (HPLC) for subsequent analysis. The SPME technique is designed to accommodate the use of fibers coated with different polymers suitable for the extraction of chemicals with varied hydrophobic and polar properties. Also, the technique can minimize interference from other artefacts associated with complex samples, such as those encountered in biological matrices or reaction mixtures. The preceding characteristics of SPME make the technique suitable for real-time measurements of intermediate reaction products and, thus, able to provide insight into the fate of target chemicals and their degradation pathways. In the present article, the current state of knowledge on the use of SPME-GC and SPME-HPLC in the determination of frequently encountered environmental chemicals and their (bio)transformation pathways are critically reviewed. Future opportunities of SPME in real time in situ process monitoring such as the use of agricultural feed stocks to bio-based industrial products termed henceforth "process analytical chemistry" are also discussed.     

Product Gauss quadrature rules vs. cubature rules in the meshless local Petrov–Galerkin method

A crucial point in the implementation of meshless methods such as the meshless local Petrov–Galerkin (MLPG) method is the evaluation of the domain integrals arising over circles in the discrete local weak form of the governing partial differential equation. In this paper we make a comparison between the product Gauss numerical quadrature rules, which are very popular in the MLPG literature, with cubature formulas specifically constructed for the approximation of an integral over the unit disk, but not yet applied in the MLPG method, namely the spherical, the circularly symmetrical and the symmetric cubature formulas. The same accuracy obtained with 64×64 points in the product Gauss rules may be obtained with symmetric quadrature formulas with very few points.     

Second‐Sphere Biomimetic Multipoint Hydrogen‐Bonding Patterns to Boost CO2 Reduction of Iron Porphyrins

Inspired by nature's orchestra of chemical subtleties to activate and reduce CO₂, we have developed a family of iron porphyrin derivatives in to which we have introduced urea groups functioning as multipoint hydrogen‐bonding pillars on the periphery of the porphyrinic ring. This structure closely resembles the hydrogen‐bond stabilization scheme of the carbon dioxide (CO₂) adduct in the carbon monoxide dehydrogenase (CODH). We found that such changes to the second coordination sphere significantly lowered the overpotential for CO₂ reduction in this family of molecular catalysts and importantly increased the CO₂ binding rate while maintaining high turnover frequency (TOF) and selectivity. Entrapped water molecules within the molecular clefts were found to be the source of protons for the CO₂ reduction.     

A new synthesis of butadienyl- and styrylboronic esters: highly reactive intermediates for Suzuki cross-coupling

Alkoxy-functionalized butadienyl- and styrylboronic esters have been synthesized starting from alpha,beta-unsaturated acetals. These derivatives readily cross-couple with aryl substrates, and the obtained products can be transformed under mild conditions into aromatic ketones, achieving the same result as an acylation reaction. [reaction: see text]