Preparation and Optical Characterization of Organoeuropium-Doped Silica Gels

Gels have been investigated as potential matrices for rare earth luminescence. The use of complexing ligands in the sol-gel synthesis of the rare-earth doped glasses has been suggested to improve the rare earth ion luminescence properties in these matrices due to the changes in the local environment experienced by the rare earth ion. In this work, transparent Eu3+-doped gels were prepared from Si(OCH3)4 and fluorinated and/or complex-forming Eu3+ precursors (Eu(fod)3, (CF3 SO3)3Eu, (CF3CO2)Eu · 3H2O, Eu(thd)3 and Eu(acac)3). Results of emission, fluorescence line narrowing and lifetimes studies of Eu3+-doped gels derived from Si(OCH3)4 and fluorinated/chelate Eu3+ precursors are presented. The results were interpreted in terms of the evolution of the Eu3+ fluorescence in systems varying from solutions to the gels densified to 800°C. Analysis of the fluorescence decays of the 5D0 state suggests that the use of the fluorinated Eu3+ precursors reduces the hydrophobic content in the silica gels matrices. FLN studies indicate that Eu3+ clustering occurred in all densified samples.     

Characterization of Lewis acid sites on the (100) surface of beta-AlF3: Ab initio calculations of NH3 adsorption

The current study employs hybrid-exchange density functional theory to show that the Lewis base, NH(3), binds to the beta-AlF(3) (100) surface with a binding energy (BE) of up to -1.96 eV per molecule. This is characteristic of a strong Lewis acid. The binding of NH(3) to the surface is predominately due to electrostatic interactions. There is only a small charge transfer from the NH(3) molecule to the surface. The BE as a function of coverage is computed and used to develop a lattice Monte Carlo model which is used to predict the temperature programed desorption (TPD) spectrum. Comparison with experimental TPD studies of NH(3) from beta-AlF(3) strongly suggests that these structural models and binding mechanisms are good approximations to those that occur on real AlF(3) surfaces.     

Advances in the study of elementary cellular automata regular language complexity

Cellular automata (CA) are discrete dynamical systems that, out of the fully local action of its state transition rule, are capable of generating a multitude of global patterns, from the trivial to the arbitrarily complex ones. The set of global configurations that can be obtained by iterating a one‐dimensional cellular automaton for a finite number of times can always be described by a regular language. The size of the minimum finite automaton corresponding to such a language at a given time step provides a complexity measure of the underlying rule. Here, we study the time evolution of elementary CA, in terms of such a regular language complexity. We review and expand the original results on the topic, describe an alternative method for generating the subsequent finite automata in time, and provide a method to analyze and detect patterns in the complexity growth of the rules. © 2015 Wiley Periodicals, Inc. Complexity 21: 267–279, 2016     

Spatial energy estimates in dynamical problems for a semi-infinite piezoelectric beam

The behaviour of the total energy for a semi-infinite piezoelectricbeam, with uniform or variable cross-section, in dynamical conditionsis investigated. Precisely, we obtain some estimates in termsof the data for the energy of the portion of the body at distancegreater than z from the base and for its norm in L¹(0,t) (wheret is an arbitrary positive time). We obtain some estimates whichdepend on the initial data if t z/V (where V is a computablepositive material constant); if t > z/V, by using also theKorn inequality, we show that the bounds depend on all the data.Under mild hypotheses on the initial data we derive the asymptoticbehaviour of the energy as z +. All possible combinations ofboundary conditions are examined and the kind of the estimateis formally the same for all the problems whether the beam isa cylinder or not.     

Structural Control in Poly(butyl acrylate)-Silica Hybrids by Modifying Polymer-Silica Interactions

Porous organic-inorganic hybrids of poly(n-butyl acrylate) (PBA) and silica were synthesized with different polymer contents via sol-gel process. With the aim of controlling interfacial properties in hybrids, the bonding agent 3-methacryloxypropyl-trimethoxysilane (MPTS) was copolymerized with n-butyl acrylate (BA) at different proportions. Copolymers P(BA-co-MPTS) and hybrids obtained were characterized by infrared spectroscopy and thermogravimetric analysis. Nitrogen sorption analyses of hybrids determined that the increase in polymer content leads to the formation of non-porous hybrids only if bonding agent content is sufficiently large. Otherwise, hybrids with large pore volumes and sizes, nearly reaching macropore range, are obtained even for polymer content as high as 45% in the absence or low content of MPTS. Scanning electron microscopy images showed that the addition of bonding agent changes the aspect of hybrid surface from rough, with loosely bound particles with a few hundreds nanometers, to relatively smooth, with particles typically smaller than 100 nm. These results were explained considering that a more homogeneous medium provided by the presence of MPTS may lead to easier condensation of PBA-silica particles due to the smaller polymeric domains. This idea is supported by the fact that, after polymer degradation, smaller uniform-sized pores arise for hybrids with larger bonding agent contents.