Potentials for the modified Cam-Clay model

Energy and dissipation pseudo-potentials are employed to derive constitutive relationships, in the context of thermodynamic concepts, for the widely used Modified Cam-Clay (MCC) model for soil mechanics. A variational formulation of the MCC evolution equations is proposed in this paper. Since plastic collapse of MCC soils cannot be embedded in the classical limit analysis theory, finding the critical amplification of the load that produces plastic collapse is formulated in the form of a system of equations and inequalities. Then, a mixed minimization principle is proposed for the plastic collapse analysis of MCC soils. This principle is obtained by the application of the variational formulation for the flow law introduced in the first part of the article.     

Extension of the finite volume particle method to viscous flow

The finite volume particle method (FVPM) is a mesh-free method for fluid dynamics which allows simple and accurate implementation of boundary conditions and retains the conservation and consistency properties of classical finite volume methods. In this article, the FVPM is extended to viscous flows using a consistency-corrected smoothed particle hydrodynamics (SPH) approximation to evaluate velocity gradients. The accuracy of the viscous FVPM is improved by a higher-order discretisation of the inviscid flux combined with a second-order temporal discretisation. The higher-order inviscid FVPM is validated for a 1-D shock tube problem, in which it demonstrates an enhanced shock capturing ability. For two-dimensional simulations, a small arbitrary Lagrange–Euler correction to fully Lagrangian particle motion is beneficial in maintaining a favourable particle distribution over long simulation times. The viscous FVPM is validated for two-dimensional Poiseuille, Taylor–Green and lid-driven cavity flows, and good agreement is achieved with analytic or reference numerical solutions. These results establish the viability of FVPM as a tool for mesh-free simulation of viscous flows in engineering.     

Experimental and theoretical study of the structure and vibrational spectra of valpromide,C7H15CONH2

In this work, we present results of the conformational and vibrational properties of valpromide (Vpd), an amide with antiepileptic activity, studied by IR and Raman spectroscopy at 300 and 77 K, and 300 K, respectively. Experimental data are compared against ab initio calculations performed at B3LYP level with the inclusion of solvatation effects. Experimental results, reinforced by theoretical calculations, point out that Vpd has three conformers on the potential energy surface, with different structures that can be identified in the CO and NH spectral regions. These conformers are defined by different angular arrays of the dihedral angles formed with the CO, C N and C〈 H, C C of the aliphatic chain bonds. The existence of different conformations and structures are discussed on the basis of results derived from electronic localization function (ELF) and natural orbital bond (NBO) analysis. Copyright © 2008 John Wiley & Sons, Ltd.     

Non-invasive and non-destructive micro-XRF and micro-Raman analysis of a decorative wallpaper from the beginning of the 19th century

Non-destructive and non-invasive micro-Raman fibre optic and micro-XRF analyses were performed to study a wallpaper from the beginning of the 19th century. The complementarity of these two non-destructive techniques is shown in this work. The analysed artwork is considered one of the most beautiful wallpapers ever manufactured according to the catalogues and books; it is known as Chasse de Compiègne, manufactured by Jacquemart, Paris, in 1812. During the analysis, an unexpected pigment was detected by both analytical techniques: lead-tin yellow type II. This pigment was used until ca. 1750, when other yellow pigments replaced it, thus it is very difficult to find it in paintings afterwards. Together with this pigment, red lead, Prussian blue, brochantite, yellow iron oxide, calcium carbonate, vermilion, carbon black of animal origin (bone black), lead white, and raw and burnt sienna were also determined by combining the analytical information provided by both techniques. A possible degradation of brochantite to antlerite is also discussed.     

Electronic structure and optical properties of an alternated fluorene-benzothiadiazole copolymer: interplay between experimental and theoretical data

The donor-acceptor copolymer containing benzothiadiazole (electron acceptor), linked to functionalized fluorene (electron donor), [poly[9,9-bis(3'-(tert-butyl propanoate))fluorene-co-4,7-(2,1,3-benzothiadiazole)] (LaPPS40), was synthesized through the Suzuki route. The polymer was characterized by scanning electron microscopy, gel permeation chromatography, NMR, thermal analysis, cyclic voltammetry, X-ray photoelectron spectroscopy, UV-vis spectrometry, and photophysical measurements. Theoretical calculations (density functional theory and semiempirical methodologies) used to simulate the geometry of some oligomers and the dipole moments of molecular orbitals involved were in excellent agreement with experimental results. Using such data, the higher energy absorption band was attributed to the π-π* (S(0) → S(4)) transition of the fluorene units and the lower lying band was attributed to the intramolecular (ICT) (S(0) → S(1)) charge transfer between acceptor (benzothiadiazole) and donor groups (fluorene) (D-A structure). The ICT character of this band was confirmed by its solvatochromic properties using solvents with different dielectric properties, and this behavior could be well described by the Lippert-Mataga equation. To explain the solvatochromic behavior, both the magnitude and orientation of the dipole moments in the electronic ground state and in the excited state were analyzed using the theoretical data. According to these data, the change in magnitude of the dipole moments was very small for both transitions but the spatial orientation changed remarkably for the lower energy band ascribed to the ICT band.     

Transmission electron microscopy studies on structure and defects in crystalline yttria and lanthanum oxide thin films grown on single crystal sapphire by molecular beam synthesis

The Molecular beam synthesis and characterization are reported for Y₂O₃ thin films grown on Al₂O₃ (0001) substrate. The Y₂O₃ layer was highly oriented in the [111] direction with predominant orientation relations (111) Y₂O₃ ‖ (0001) Al₂O₃ and [110] Y₂O₃ ‖ [2110] Al₂O₃, corresponding to a lattice mismatch of ～20% at the interface. No significant interfacial layers were found at the Y₂O₃/Al₂O₃ interface and the large lattice misfit was accommodated by formation of stacking faults, dislocations and secondary orientation in the Y₂O₃ layer. A La₂O₃ interlayer improved the quality of the Y₂O₃ films. Full width at half maximum (FWHM) of the Y₂O₃ (222) peak decreased from 3.12° to 1.43° and the defect density in the Y₂O₃ layer was significantly reduced. These results may be relevant in the broader context of designing oxide heterolayers with controlled microstructures.