pH control of the condensation reaction and its effect on the properties of formaldehyde/urea resins

The conditions of the preparation of formaldehyde/urea (F/U) resins have been supervised with the aim to reduce formaldehyde emission by influencing the ratio of methylene/dimethylene-ether-bridge linkages in the product. The most crucial point of this task is to keep the pH values of the reacting mixtures on the required level. The effect of formic acid, unevitably present in industrial formaldehyde solutions, was neutralized by applying a new buffer system, containing boric acid and ethylene glycol.     

Water uptake of water-borne paint resin films as studied by impedance spectroscopy and gravimetry

Impedance spectroscopy and gravimetry were employed to characterize alkyd-acrylate and styrene-acrylate water-borne resin film properties during wetting-through (i.e. during water uptake).     

Optimized Schwarz methods without overlap for highly heterogeneous media

In this paper an original variant of the Schwarz domain decomposition method is introduced for heterogeneous media. This method uses new optimized interface conditions specially designed to take into account the heterogeneity between the sub-domains on each sides of the interfaces. Numerical experiments illustrate the dependency of the proposed method with respect to several parameters, and confirm the robustness and efficiency of this method based on such optimized interface conditions. Several mesh partitions taking into account multiple cross points are considered in these experiments.     

Incremental wrapper-based gene selection from microarray data for cancer classification

Gene expression microarray is a rapidly maturing technology that provides the opportunity to assay the expression levels of thousands or tens of thousands of genes in a single experiment. We present a new heuristic to select relevant gene subsets in order to further use them for the classification task. Our method is based on the statistical significance of adding a gene from a ranked-list to the final subset. The efficiency and effectiveness of our technique is demonstrated through extensive comparisons with other representative heuristics. Our approach shows an excellent performance, not only at identifying relevant genes, but also with respect to the computational cost.     

Electrodeposition of nickel on vitreous carbon: Influence of potential on deposit morphology

The initial stages of the deposition of nickel on vitreous carbon from aqueous NiCl₂ (10^–2M adjusted to 1 M in chloride) has been studied using voltammetric and potentiostatic methods. The morphology of the deposits was observed by scanning electron and optical microscopy. A discussion of the relation between the deposition mechanism and the morphology is presented.     

Protein kinase C activity in the hippocampus following spatial learning tasks in mice

We have tested the effect of several bile acids on the proliferation and differentiation of the HL60 human promyelocytic leukemia cell line in vitro. Deoxycholate, chenodeoxycholate and lithocholic acid caused dose-dependent inhibition of cell proliferation and induction of differentiation along the monocyte/macrophage pathway as determined by morphology, NBT test, non-specific esterase, and staining by monoclonal antibodies against specific cell-surface antigens. Optimal effects were obtained at 100, 75, and 60 microM of the 3 bile acids respectively. Cell-cycle flow-cytometric analysis showed that a substantial fraction of HL60 cells accumulated at the G0/G1 transition. Protein-kinase-C inhibitors such as sphinganine and H-7 inhibited the differentiation-inducing effect of bile acids, suggesting a possible role for PKC in this regulation. When bile acids were combined with non-effective concentrations of all-trans retinoic acid, enhancement of the monocytic differentiation of THP-1 human leukemia cells was observed. Our findings demonstrate induction of tumor-cell differentiation by bile acids, compounds that present minimal undesirable effects in humans.     

Influence of water and accelerated aging on the shear fracture properties of glass/epoxy composite

The degradation of interlaminar shear strength and shear fracture toughness of glass/epoxy composites due to uptake of distilled water and sea water has been studied. The composites were immersed in water for up to eight months at temperatures up to 70 °C. Unreinforced matrix resin samples were also immersed for periods up to 2 years. Sea water was absorbed less rapidly than distilled water. Weight gains below 1% did not influence the shear strength while higher weight gains reduced shear strength up to 25%. The loss in apparent interlaminar shear strength was uniquely related to specimen weight gain. Mode II fracture toughness, G _IIc, also decreased with increasing immersion time after an initial incubation period, but the accelerated tests were found to reduce G _IIc less than the room temperature tests at comparable weight gains.     

Using the Percolation Theory to Explain the Release Behavior from Inert Matrix Systems

A novel analysis of drug release process from binary matrix systems has been realized and a study of the initial stage of the process has been carried out. A fast and easy technique has allowed the acquisition of one experimental datum per second. Release data have been analyzed by means of a detailed statistical study. The dissolution profiles were studied applying different kinetic models (zero order, logarithmic, and Higuchi equation). In all the cases studied, a starting process of zero or first order, indicative of a surface-dependent mechanism, has been found. Then, a parameter, named as critical time of kinetic change (t_c), has enabled the authors to establish the instant at which a diffusion release mechanism, according to Higuchi equation, is consolidated. From this time until the end of the process, release mechanism of matrices was shown to be diffusion controlled. The influence of the drug loading and the particle size over the release properties of tablets has also been investigated and it has been evaluated on the basis of percolation theory. The results show a major significance of particle size over the initial drug release and a decrease of its influence along the time. On the other hand, the drug loading variable shows an important influence over the release properties along the whole process.