Dependence of calibration sensitivity of a polysulfone/Ru(II)-tris(4,7-diphenyl-1,10-phenanthroline)-based oxygen optical sensor on its structural parameters

The optimum performance of an optical oxygen sensor based on polysulfone (PSF)/[Ru(II)-Tris(4,7-diphenyl-1,10-phenanthroline)] octylsulfonate (Ru(dpp)OS) was checked by carefully tuning the parameters affecting the membrane preparation. In particular, membranes having thickness ranging between 0.2 and 8.0 μm with various luminophore concentrations were prepared by dip-coating and tested. The membrane thickness was controlled by tuning the solution viscosity, and was measured both by secondary ion mass spectrometry (SIMS) and by visible spectroscopy (Vis). Luminescence-quenching-based calibration was a single value of the Stern-Volmer constant (K^′SV) for membranes containing up to 20 mmol Ru(dpp) g⁻¹ PSF (1.35 μm average thickness). The K^′SV value decreased for larger concentration. The highest sensitivity was obtained with membrane thickness around 1.6 μm, having a response time close to 1 s. Thicker membranes exhibited an emission saturation effect and were characterized by longer response time. The K^′SV behavior was interpreted on the basis of a mathematical approach accounting for the contribution of luminescence lifetime (τ₀), oxygen diffusion coefficient (DO₂) and oxygen solubility inside the membrane (sO₂) establishing the role of all of them and allowing their experimental determination. Moreover, a simple experimental way to estimate K^′SV without needing calibration was proposed. It was based either on the light emission asymmetry or on the percent variation of light emission on passing from pure nitrogen to pure oxygen.     

Nonstochastic behavior of atomic surface diffusion on Cu(111) down to low temperatures

Atomic diffusion is usually understood as a succession of random, independent displacements of an adatom over the surface's potential energy landscape. Nevertheless, an analysis of molecular dynamics simulations of self-diffusion on Cu(111) demonstrates the existence of different types of correlations in the atomic jumps at all temperatures. Thus, the atomic displacements cannot be correctly described in terms of a random walk model. This fact has a profound impact on the determination and interpretation of diffusion coefficients and activation barriers.     

Two-Photon Absorption Enhancement by the Inclusion of a Tropone Ring in Distorted Nanographene Ribbons

A new family of distorted ribbon-shaped nanographenes was designed, synthesized, and their optical and electrochemical properties were evaluated, pointing out an unprecedented correlation between their structural characteristics and the two-photon absorption (TPA) responses and electrochemical band gaps. Three nanographene ribbons have been prepared: a seven-membered-ring-containing nanographene presenting a tropone moiety at the edge, its full-carbon analogue, and a purely hexagonal one. We have found that the TPA cross-sections and the electrochemical band gaps of the seven-membered-ring-containing compounds are higher and lower, respectively, than those of the fully hexagonal polycyclic aromatic hydrocarbon (PAH). Interestingly, the inclusion of additional curvature has a positive effect in terms of non-linear optical properties of those ribbons.     

Spherical and tubular dimyristoylphosphatidylcholine liposomes

Journal of Thermal Analysis and Calorimetry - A physicochemical study of the interaction of pinocembrin with dimyristoylphosphatidylcholine (DMPC) liposomes was carried out. Unilamellar vesicles of...     

Mixing method influence on compatibility and polymorphism studies by DSC and statistical analysis

Most of the pharmaceutical products are formulated as solid dosage form, which may present drug–excipient interactions that lead to changes in the chemical nature of the drug, such as solubility and bioavailability and may compromise its safety and effectiveness. Differential scanning calorimetry (DSC) is a widely used method for the rapid evaluation of the drug-excipient compatibility and the stability of the mixture formed; however, there is no consensus on the preparation methods of the drug–excipient mixtures. The aim of this study was to investigate the influence of the mixing method on the drug–excipient compatibility studies by means of DSC analysis, using tenofovir disoproxil fumarate as a drug model. Statistical analysis revealed significant differences in the heat of fusion of the drug in the mixtures prepared by several mixing methods. Vortex Mixer with a Pop-Off Cup used for 3 min proved to be very satisfactory for these studies. A polymorphic transition was observed in the mixture prepared with the mortar and pestle. Therefore, this method should be avoided since it may induce errors in the interpretation of DSC results. In this way, the mixing method used to prepare a mixture for studies of interactions between the API and the excipients in a pharmaceutical formulation has a great influence on the results and it must be chosen carefully.     

The effect of argon bombardment on the oxidation of Fe(110) by oxygen and water

The oxidation of Fe(110) by O₂ and H₂O vapour has been studied by AES and LEED at room temperature in well ordered and in Ar bombarded surfaces. Ion irradiation causes in both cases an enhancement of the rate of oxidation. For O₂ adsorption, it has been found that ion bombardment increases the rate of surface oxide growth, whereas in the case of H₂O adsorption, the effect of the irradiation consists in facilitating the penetration of oxygen into the crystal bulk.     

Development and validation of a new LBM-MRT hybrid model with enthalpy formulation for melting with natural convection

This article presents a new model to simulate melting with natural convection of a phase change material. For the phase change problem, the enthalpy formulation is used. Energy equation is solved by a finite difference method, whereas the fluid flow is solved by the multiple relaxation time (MRT) lattice Boltzmann method. The model is first verified and validated using the data from the literature. Then, the model is applied to a tall brick filled with a fatty acid eutectic mixture and the results are presented. The main results are (1) the spatial convergence rate is of second order, (2) the new model is validated against data from the literature and (3) the natural convection plays an important role in the melting process of the fatty acid mixture considered in our work.     

Optimization model for a production,inventory, distribution and routing problem in small furniture companies

Production and distribution are two key decisions in supply chain planning. In order to achieve an effective operational performance, it is important for these two decisions to be integrated, especially in supply chains with low inventory levels. In this paper, we propose a mixed integer programming model to integrate production, inventory, distribution and routing decisions in a single framework. The model was inspired by small Brazilian furniture companies and focuses on production and distribution decisions at an operational level. In particular, we consider a scenario in which only one production line and one vehicle, which makes multiple trips over the planning horizon, are available to produce items and deliver final products, respectively. We also take into account some features rarely considered in the literature, but commonly found in real-world applications, such as producing and stocking multiple items, distribution routes extending over one or more periods, multiple time windows and customers’ due dates. Computational tests on a set of randomly generated instances were carried out using a well-known optimization software and six relax-and-fix heuristics, which explore different criteria for partitioning and fixing variables. We also implemented two hybrid heuristics in which an initial solution is first constructed and then fed into the optimization software to improve it. The results showed that one relax-and-fix and the two hybrid heuristics performed better than the solver on the largest instances.     

Existence and fractional regularity of solutions for a doubly nonlinear differential inclusion

This article considers the issues of existence and regularity of solutions to the following doubly nonlinear differential inclusion $$\omega_t+\alpha (\omega_t)-\Delta \omega-\Delta_p{\omega} \ni f$$ where α is a maximal monotone operator in ${\mathbb{R}^2}$ and Δ _p denotes the p-Laplacian with p > 2. The investigation on fractional regularity is based on the Galerkin method combined with a suitable basis for W ^1,p , which we exhibit as a preliminary result. This approach also allows the obtaining of estimates in the so-called Nikolskii spaces, since it balances the interplay between the maximal monotone operator with the appearing higher order nonlinear terms.