Mean distance of closest approach of ions: Lithium salts in aqueous solutions

Numerical values for the mean distance of closest approach of ions, “a”, for lithium salts in aqueous solutions are presented and discussed. These values were obtained from both experimental activity and diffusion coefficients, and estimated by using different theoretical approaches.     

NaNbO3 crystals dispersed in a B2O3 glass matrix – Structural characteristics versus electrical and dielectrical properties

Sodium niobate (NaNbO₃) is a crystal with a perovskite structure that exhibits, at room temperature, an antiferroelectric behaviour. It is a very interesting material due to the several phase transitions that it presents as a function of the temperature (ferroelectric–antiferroelectric–paraelectric). Thus, the preparation of glass-ceramics containing NaNbO₃ crystals is scientifically and technologically important. Besides, there is actually few works available about the preparation of NaNbO₃ crystals embedded in a glass matrix. The present work reports the preparation process and the study of glass and glass-ceramics in the B₂O₃–NaNbO₃ system.The glass with the molar composition 60B₂O₃–30Na₂O–10Nb₂O₅ (mol%) was prepared by the melt-quenching method. Sodium niobate (NaNbO₃) crystallites were precipitated through a controlled heat-treatment (HT) process. NaNbO₃ crystallites were detected by X-ray diffraction (XRD) in the samples treated above 500 °C. The treatments above 600 °C favour also the formation of Na₂B₄O₇ and Nb₂O₅ crystalline phases.Scanning electron microscopy (SEM) reveals that the crystallization occurs in volume and that the number of particles increases with the rise in HT temperature.The number of network modifier ions (Na⁺ and Nb⁵⁺) in the glass network is the main factor in the dc and ac conductivity behaviours. The dielectric constant (?′) value increases with the increase of the volume ratio between the particles and the glass matrix. The sample heat-treated at 550 °C shows two thermally stimulated depolarization current (TSDC) peaks. The high temperature peak can be related to the presence of NaNbO₃ particles.     

Nitrogen and water adsorption in aluminum methylphosphonate alpha: a molecular simulation study

We present here Monte Carlo simulation and experimental results on the adsorption of nitrogen and water in aluminum methylphosphonate polymorph alpha (AlMePO-alpha). We have assumed a detailed atomic model for the material, using experimental information to construct the simulation cell. Nitrogen was modeled with two different approaches: as a simple Lennard-Jones (LJ) sphere with no charges, and as a diatomic molecule with charges explicitly included. Water was represented by the TIP4P model. Experimental adsorption isotherms were used to tune the proposed molecular model for the adsorbent. Simulated adsorption capacities were in agreement with the experimental results obtained for the studied systems. The influence of the surface model on the adsorption behavior was taken into account by considering different values of the surface methyl group size parameter. Our results corroborate the strong sensitivity of the simulation results to this parameter, as previously observed by Schumacher and co-workers. It is also observed that charged models are essential to accurately describe the low-pressure region of the adsorption isotherm, where the solid-fluid interaction rules the system behavior. However, a simple uncharged molecular model for nitrogen is able to describe the three loci arrangement at maximum loading. Experimental and simulation results presented here also confirm the low water affinity of AlMePO-alpha. These results enforce the application of this methodology to achieve quantitative predictions on similar systems, with the appropriate transferability of the molecular parameters.     

Viscosity Solution of the Hamilton-Jacobi Equation Arising from a Thin Film Blistering Model

The paper deals with a dynamical nonlinear model describing the self-driven delamination of compressed thin films. Some assumptions on the buckled shape allow us to describe the moving boundary of the film by a single Hamilton-Jacobi equation. We prove the existence and uniqueness of a viscosity solution to the associated evolution problem.     

3-D QSAR studies on histone deacetylase inhibitors. A GOLPE/GRID approach on different series of compounds

Docking simulation and three-dimensional quantitative structure-activity relationships (3D-QSARs) analyses were conducted on four series of HDAC inhibitors. The studies were performed using the GRID/GOLPE combination using structure-based alignment. Twelve 3-D QSAR models were derived and discussed. Compared to previous studies on similar inhibitors, the present 3-D QSAR investigation proved to be of higher statistical value, displaying for the best global model r2, q2, and cross-validated SDEP values of 0.94, 0.83, and 0.41, respectively. A comparison of the 3-D QSAR maps with the structural features of the binding site showed good correlation. The results of 3D-QSAR and docking studies validated each other and provided insight into the structural requirements for anti-HDAC activity. To our knowledge this is the first 3-D QSAR application on a broad molecular diversity training set of HDACIs.     

Beam search heuristics for quadratic earliness and tardiness scheduling

In this paper, we present beam search heuristics for the single machine scheduling problem with quadratic earliness and tardiness costs, and no machine idle time. These heuristics include classic beam search procedures, as well as filtered and recovering algorithms. We consider three dispatching heuristics as evaluation functions, in order to analyse the effect of different rules on the performance of the beam search procedures. The computational results show that using better dispatching heuristics improves the effectiveness of the beam search algorithms. The performance of the several heuristics is similar for instances with low variability. For high variability instances, however, the detailed, filtered and recovering beam search (RBS) procedures clearly outperform the best existing heuristic. The detailed beam search algorithm performs quite well, and is recommended for small- to medium-sized instances. For larger instances, however, this procedure requires excessive computation times, and the RBS algorithm then becomes the heuristic of choice.