Slow flow across macroscopically semi-circular fibre lattices and a free-flow region of variable width—visualisation by magnetic resonance imaging

Slow flow of an incompressible Newtonian fluid across a fibrous porous medium bounded by a free-flow region of variable width was studied experimentally by magnetic resonance imaging velocimetry. The fibrous porous medium (fibre lattice) comprised of aligned rows of cylindrical rods, which were macroscopically arranged in a semi-circular fashion in a Hele-Shaw cell. The local aspects of the flow in the interior of and exterior to the fibre lattices were studied for (i) three individual semi-circular fibre lattices of different porosity and/or cylinder size, with each lattice bounded by an open channel and (ii) an assembly of five fibre lattices with the interstitial space between them forming a free-flow region. The symmetry (in a practical sense) of slow flow over symmetrical lattice-channel arrangements is demonstrated. The subtle characteristics of the flow within the lattices are seen as considerable local velocity enhancements (LVE) transverse to and in the direction of superficial flow. These LVE within the lattices strongly depend on the interface configuration of the lattice-channel arrangement, the gap size between the cylinders and the lattice porosity. The penetration depth of the LVE may even extend to the lattice centre. When a fibre lattice is a part of an assembly, the surface irregularities of neighbouring lattices create more complex tortuous flow pathways in the free-flow region. These pathways produce recurrent LVE within the fibre lattice. The implications that the above findings have for the flow, heat transfer and mass transfer in conceptually similar heterogeneous porous media used in, for example, liquid composite moulding processes and filtration processes are discussed.     

Sparse representation of precision matrices used in GMMs

The paper presents a novel precision matrix modeling technique for Gaussian Mixture Models (GMMs), which is based on the concept of sparse representation. Representation coefficients of each precision matrix (inverse covariance), as well as an accompanying overcomplete matrix dictionary, are learned by minimizing an appropriate functional, the first component of which corresponds to the sum of Kullback-Leibler (KL) divergences between the initial and the target GMM, and the second represents the sparse regularizer of the coefficients. Compared to the existing, alternative approaches for approximate GMM modeling, like popular subspace-based representation methods, the proposed model results in notably better trade-off between the representation error and the computational (memory) complexity. This is achieved under assumption that the training data in the recognition system utilizing GMM have an inherent sparseness property, which enables application of the proposed model and approximate representation using only one dictionary and a significantly smaller number of coefficients. Proposed model is experimentally compared with the Subspace Precision and Mean (SPAM) model, a state of the art instance of subspace-based representation models, using both the data from a real Automatic Speech Recognition (ASR) system, and specially designed sets of artificially created/synthetic data.     

Capacity Fade Analysis of a Battery/Super Capacitor Hybrid and a Battery under Pulse Loads – Full Cell Studies

A detailed analysis of the capacity fade of a battery/supercapacitor hybrid and a battery alone has been carried out at 55 °C by discharging them at three different pulse rates. The applied peak current amplitudes were 5C (7 A), 3C (4.2 A), and 1C (1.4 A), respectively. The results indicated that for hybrids the pulse discharge run time was extended for all pulse discharge rates. The ohmic resistances estimated as a function of the pulse discharge rates were smaller for hybrids when compared with those for batteries. The variation of the ohmic resistance under pulse discharge with cycling, irrespective of the pulse discharge rate was smaller for hybrids than that for the batteries. The batteries and hybrids cycled at the lowest pulse discharge rate (high pulse discharge time) have larger capacity fade when compared with the capacity fade of the batteries and the hybrids discharged using higher discharge rates (low pulse discharge time). Impedance, cyclic voltammogram, and the rate capability studies were carried out on batteries cycled alone and on batteries cycled as part of the hybrid. The battery showed larger increase in the interfacial impedance with cycling when compared with the hybrid system.     

Anticorrosive epoxy/clay nanocomposite coatings: rheological and protective properties

The preparation of epoxy/clay nanocomposites (NCs) and their insertion into coatings are of great importance since the NCs could enhance the protective performances. In this study, epoxy NCs with 1–10 wt% of nanoclay Cloisite 30B (C30B) were prepared by the sonication-assisted solution method. The rheological measurements of epoxy/C30B suspensions revealed non-Newtonian, shear-thinning behavior of the uncured NCs, with an increase in the viscosity, yield stress, and shear modules with increasing organoclay content, while the dispersion effectiveness of C30B decreased. A significant enhancement of the rheological parameters was observed at the second percolation threshold (4.1 vol%) due to the formation of a continuous network of 45-layer-thick tactoids. Although NCs with 1–3 wt% C30B exhibited slightly reduced mechanical and adhesion properties compared with the cured reference epoxy resin, the epoxy primer and topcoat based on NC with 1 wt% C30B generally displayed improved impact resistance and maintained flexibility, pendulum hardness, and good adhesion properties. Two-layer coating systems, i.e., NC-based primers and topcoats, had higher corrosion stability in a salt spray chamber compared to the unmodified system.     

Diffusion of drugs from hydrogels and liposomes as drug carriers

BACKGROUND: The mass transfer of model drugs Lidocaine hydrochloride and Dihydroquercetin from hydrogels (the usual carriers for topical drugs), and hydrogels containing liposomes, as novel drug vehicles, was studied. Diffusion experiments were performed using a Franz diffusion cell. Experimental data were used to calculate drug diffusion coefficients across membranes, and their effective diffusion coefficients from hydrogels and liposome containing hydrogels. For the first time the diffusion resistance of all drug carriers was determined from corresponding diffusion coefficients. The main aim of this work was the study of drug diffusion coefficients from liposomes and their comparison with related diffusion coefficients from hydrogels to find how liposomes contribute to prolonged and controlled drug release. RESULTS: Drug diffusion coefficients were: 1.38 · 10^?8m² s^?1 for Lidocaine hydrochloride and 5.96 · 10^?9m² s^?1 for Dihydroquercetin, while corresponding effective diffusion coefficients from hydrogels were: 7.82 · 10^?10m² s^?1 and 7.98 · 10^?10m² s^?1, respectively. Effective diffusion coefficients from liposome‐containing hydrogels were:4.82 · 10^?10m² s^?1 (Lidocaine hydrochloride) and 4.305 · 10^?10m² s^?1 (Dihydroquercetin). Diffusion resistances for the two hydrogels were almost the same. Very similar values of diffusion resistances for all liposome dispersions were obtained. CONCLUSION: Calculated diffusion coefficients and resistances demonstrate that liposomes, as drug carriers, significantly affect diffusion rates. The results obtained could be used whenever diffusion‐controlled drug release is required. Copyright © 2010 Society of Chemical Industry     

Influence of mechanical activation on sphene based ceramic material synthesis

Sphene (CaTiSiO₅), a calcium titanosilicate ceramic has been prepared from a powder mixture of CaCO₃, TiO₂ and SiO₂ using vibro-milling for homogenization and activation of precursors. The mechanochemical process initially yielded amorphous powders, which on further calcination, crystallized to yield sphene ceramic. The evolution of the phase composition with thermal treatment was investigated by X-ray powder diffraction (XRPD). Powder morphology and particle size distribution were analyzed by scanning electron microscopy (SEM) and laser diffraction, respectively. Rietveld refinement was employed to get the structural information of the synthesized powder. Densification and microstructure evolution was determined by means of density and scanning electron microscopy (SEM). The most favorable conditions for mechanical activation and synthesis of sphene based ceramic material are reported.     

Classification of Slovak white wines using artificial neural networks and discriminant techniques

This work demonstrates the possibility to use artificial neural networks (ANN) for the classification of white varietal wines. A multilayer perceptron technique using quick propagation and quasi-Newton propagation algorithms was the most successful. The developed methodology was applied to classify Slovak white wines of different variety, year of production and from different producers. The wine samples were analysed by the GC–MS technique taking into consideration mainly volatile species, which highly influence the wine aroma (terpenes, esters, alcohols). The analytical data were evaluated by means of the ANN and the classification results were compared with the analysis of variance (ANOVA). A good agreement amongst the applied computational methods has been observed and, in addition, further special information on the importance of the volatile compounds for the wine classification has been provided.     

Evaluation of alginate hydrogels under in vivo–like bioreactor conditions for cartilage tissue engineering

Alginate hydrogels in forms of discs and packed beds of microbeads (~800 μm) were tested in a novel bioreactor at 10% strain using two regimes: at a loading rate of 337.5 μm/s and at sequential increments of 50 μm displacement every 30 min. Compressive strength increased with the increase in alginate concentration (1.5 vs. 2% w/w) and the content of guluronic residues (38.5 vs. 67%). Packed beds of microbeads exhibited significantly higher (~1.5–3.4 fold) compression moduli than the respective discs indicating the effects of gel form and entrapped water. Short-term cultivation of microbeads with immobilized bovine calf chondrocytes (1.5% w/w, 33 × 10⁶ cells/ml) under biomimetic conditions (dynamic compression: 1 h on/1 h off, 0.42 Hz, 10% strain) resulted in cell proliferation and bed compaction, so that the compression modulus slightly increased. Thus, the novel bioreactor demonstrated advantages in evaluation of biomaterial properties and cell-biomaterial interactions under in vivo–like settings.     

Synthesis, structure and magnetic properties of the first copper(II) complex with an (E)-4-aryl-4-oxo-2-butenoato ligand

A new binuclear Cu(II) complex with an (E)-4-(2,4-diisopropylphenyl)-4-oxo-2-butenoato ligand (L) was successfully synthesized and characterized by elemental analysis and IR-spectroscopy. The structures of (E)-4-(2,4-diisopropylphenyl)-4-oxo-2-butenoic acid (HL), and the corresponding (tetrakis)-μ-[(E)-4-(2,4-diisopropylphenyl)-4-oxo-2-butenoato]-bis(ethanol)-copper(II) complex, [Cu₂L₄(C₂H₅OH)₂], were determined by single crystal X-ray analyses and are preliminarily discussed. This is the first complex of a transition metal with ligand L, as well as the first determined crystal structure of a metal complex with this type of ligand. Analysis of the magnetic susceptibility measurements of the isolated [Cu₂L₄(C₂H₅OH)₂] · H₂O complex shows the existence of a strong anti-ferromagnetic intradimer coupling, with an exchange integral value 2J of −260 cm⁻¹.