Poisson’s ratio of porous and cellular materials with randomly distributed isometric pores or cells

The porosity dependence of Poisson's ratio of materials with random microstructure is investigated via analytical and numerical modeling. It is shown that all analytical models predict porosity independence if the solid Poisson ratio is 0.2 and for low porosities a converging trend toward this value with increasing porosity. From all theory-based relations, only power-law and exponential relations allow for auxetic behavior. Numerical calculations on computer-generated digital microstructures (overlapping and isolated spherical pores, pores between overlapping spherical grains, wall-based cellular materials/closed-cell foams, and strut-based cellular materials/open-cell foams) confirm the general qualitative trends of the analytical models, although a closer look reveals significant quantitative differences. Cellular materials and foams exhibit similar features as porous materials in general, but lack their converging trend toward values around 0.2. Comparison of our results with the classical Roberts-Garboczi results shows good agreement, with subtle differences due to the different microstructures generated.     

ANN modeling applied to NO x reduction with octane in a new microreactor

A silver/alumina catalyst was tested for its NO _x reduction activity during oxygen-rich conditions and during variation in the input parameters (nitric oxide, octane and oxygen). The experimental data using the microreactor was investigated by means of artificial neural networks (ANN).     

Ocratoxin A in human plasma and coffee from Costa Rica by ELISA

Costa Rica is not an exception in the prevalence of ochratoxin A in human plasma, in this research the presence of the micotoxin was found in 95% of the 149 samples studied. The presence of ocratoxina A also was studied in 110 samples of toasted and grounded coffee from the most important 12 coffee factories of the country and from 7 supermarkets. With the exception of one negative sample the rest of them have concentrations of micotoxin below 4000 ng/kg. An association between the coffee consumption and the presence of ochratoxin A in plasma was attempted to be found as well as in the consumption of beer, but there were any statistically significant difference in the average level of mycotoxin between the coffee consumers and non coffee consumers neither between beer consumers and no beer consumers.     

Comparison of NMR investigation of chemically crosslinked polyethylene and polypropylene

Summary Chemically crosslinked polyethylene and polypropylene were investigated by the means of NMR. Basing on this investigation the comparison of MR relaxation times and structure of both polymers are made as a function of the concentration of the crosslinking agent.Presented at the 7th IUPAC Discussion Conference Polymer Networks, Karlovy Vary, CSSR, September 15–19, 1980     

Density and electrical conductivity of molten NaCl-KCl-AlCl3 mixtures

The density and specific electrical conductivity were investigated for molten ternary NaCl-KCl-AlCl₃ mixtures of interest to new industrial processes for electrolytic aluminium deposition. A method for the calculation of density and electrical conductivity of molten ternary mixtures on the basis of experimentally determined values for the binary systems NaCl-AlCl₃, NaCl-KCl and KCl-AlCl₃ has been proposed. The difference between the experimental and calculated density and electrical conductivity values of the ternary system was less than ± 1.5% for the density and ± 5% for the electrical conductivity, respectively.     

Mechanical properties and thermal shock in thin ZrO2–Y2O3–Al2O3 films obtained by the sol-gel method

Thin multilayer coatings of ZrO₂–Y₂O₃–Al₂O₃ were prepared using the sol-gel method and dip-coating technique in order to advance in the study of what influence the incorporation of Al₂O₃ has on films of Y₂O₃-doped ZrO₂, investigating its role in the synthesis of the solutions and in the characteristics and properties of the coatings. After the characterization of the solutions used in the process, the microstructure of the films was studied and their mechanical behaviour and resistance to thermal shock were determined so as to optimize the characteristics and functionality of these coatings. With increased alumina content, 3YSZ-Al₂O₃ (20 mol%), the cubic phase of the zirconia disappeared completely at the sintering temperature used (700 °C), resulting in the tetragonal phase with Al in solution. There was also a decrease in the coatings' hardness and Young's modulus, and an increase in toughness and resistance to thermal shock. These results allow guidelines to be established for the design of multilayer structures that are, tougher, more resistant, and have improved surface properties.