Effect of Surface Roughness and Structure Features on Tribological Properties of Electrodeposited Nanocrystalline Ni and Ni/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> Coatings

Metal matrix composite coatings obtained by electrodeposition are one of the ways of improving the surfaces of materials to enhance their durability and properties required in different applications. This paper presents an analysis of the surface topography, microstructure and properties (residual stresses, microhardness, wear resistance) of Ni/Al₂O₃ nanocomposite coatings electrodeposited on steel substrates from modified Watt’s-type baths containing various concentrations of Al₂O₃ nanoparticles and a saccharin additive. The residual stresses measured in the Ni/Al₂O₃ coatings decreased with an increasing amount of the co-deposited ceramics. It was established that the addition of Al₂O₃ powder significantly improved the coatings’ microhardness. The wear mechanism changed from adhesive-abrasive to abrasive with a rising amount of Al₂O₃ particles and coating microhardness. Nanocomposite coatings also exhibited a lower coefficient of friction than that of a pure Ni-electrodeposited coating. The friction was found to depend on the surface roughness, and the smoother surfaces gave lower friction coefficients.     

Electrochemical impedance spectroscopy and corrosion behaviour of Al2O3-Ni nano composite coatings

In this paper, the results on the electrochemical impedance spectroscopy and corrosion properties of electrodeposited nanostructured Al₂O₃-Ni composite coatings are presented. The nanocomposite coatings were obtained by codeposition of alumina nanoparticles (13 nm) with nickel during plating process. The coating thickness was 50 μm on steel support and an average of nano Al₂O₃ particles inside of coatings at 15 vol.% was present. The structure of the coatings was investigated by scanning electron microscopy (SEM). It has been found that the codeposition of Al₂O₃ particles with nickel disturbs the nickel coating's regular surface structure. The electrochemical behavior of the coatings in the corrosive solutions was investigated by polarization potentiodynamic and electrochemical impedance spectroscopy methods. As electrochemical test solutions 0.5 M sodium chloride and 0.5 M potassium sulphate were used in a three electrode open cell. The corrosion potential is shifted to more negative values for nanostructured coatings in 0.5 M sodium chloride. The polarization resistance in 0.5 M sodium chloride decreases in 24 h, but after that increases slowly. In 0.5 M potassium sulphate solution the polarization resistance decreases after 2 h and after 30 h of immersion the polarization resistance is higher than that of the beginning value. The corrosion rate calculated by polarization potentiodynamic curves obtained after 30 min from immersion in solution is smaller for nanostructured coatings in 0.5 M potassium sulphate (4.74 μm/year) and a little bit bigger in 0.5 M sodium chloride (5.03 μm/year).     

Distribution of respiratory droplets in enclosed environments under different air distribution methods

The dispersion characteristics of respiratory droplets are important in controlling transmission of airborne diseases indoors. This study investigates the spatial concentration distribution and temporal evolution of exhaled and sneezed/coughed droplets within the range of 1.0 − 10.0μm in an office room with three air distribution methods, specifically mixing ventilation (MV), displacement ventilation (DV), and under-floor air distribution (UFAD). The diffusion, gravitational settling and deposition mechanism of particulate matter were accounted by using an Eulerian modeling approach with one-way coupling. The simulation results indicate that exhaled droplets up to 10μm in diameter from normal human respiration are uniformly distributed in MV. However, they become trapped in the breathing zone by thermal stratifications in DV and UFAD, resulting in a higher droplet concentration and an increased exposure risk to other room occupants. Sneezed/coughed droplets are more slowly diluted in DV/UFAD than in MV. Low air speed in the breathing zone in DV/UFAD can lead to prolonged human exposure to droplets in the breathing zone.     

Detection of Yersinia spp. in meat products by enrichment culture, immunomagnetic separation and nested PCR

The prevalence of Yersinia enterocolitica in meat products was assessed by four methods: cold enrichment in trypticase soy broth (A), enrichment in modified Rappaport broth at 25 °C (B), concentration by immunomagnetic separation (C) and yadA nested PCR (D). Furthermore, the pathogenic potentials of the isolates were established by phenotypic and genotypic tests, and their genomic relationships were determined by pulsed-field gel electrophoresis (PFGE). A total of 238 samples were collected at retail level in the city of San Luis, Argentina, during the period 2007–2008. The highest Yersinia prevalence in meat products was observed by method D (92 positive samples), followed by methods A (13 positive samples) and C (5 positive samples); however, no isolation was obtained by method B. Fourteen Y. enterocolitica and 4 Yersinia intermedia strains were recovered by culture. All Y. enterocolitica 2/O:9 strains gave results related to virulence by phenotypic tests and exhibited the genotype virF⁺myfA⁺ail⁺ystA⁺. Two biotype 1A strains showed a genotype virF⁻myfA⁻ail⁺ystA⁺ystB⁺. The 14 Y. enterocolitica strains isolated during this work plus one reference strain were separated into 11 genomic types by PFGE. This genomic heterogeneity of the isolates shows the diversity of Y. enterocolitica strains in our region. It is the first time that IMS was used to search Y. enterocolitica strains from naturally contaminated meat products.     

Facile synthesis of budding yeast a-factor and its use to synchronize cells of α mating type

The ease with which populations of the budding yeast Saccharomyces cerevisiae can be synchronized using the mating pheromone α-factor has been invaluable for studies of the cell cycle. The α-factor response pathway has also remained an important model to study the molecular mechanism of G-protein coupled receptor signalling. α-Factor is a 13 amino acids long peptide that is readily available by automated peptide synthesis. However, only cells of the a mating type respond to α-factor. Cells of the opposite α mating type respond to a-factor, a farnesylated and C-terminally methylated 12 amino acids peptide. Because of its more difficult chemical synthesis, a-factor is not readily available and consequently the a-factor response is less well understood. Here we describe an improved strategy for producing a-factor, based on solid-phase peptide synthesis, followed by two simple steps in solution that show favourable characteristics and good yield. We demonstrate the successful use of the resulting a-factor to synchronize cell cycle progression of α cells. Notably, the a-factor concentrations required for cell synchronization are an order of magnitude lower than typically used α-factor concentrations. Despite a similar cell cycle response, shmoo formation was less pronounced compared to α-factor-treated a cells. Our protocol makes a-factor widely accessible, extending the ease of cell cycle synchronization to budding yeast cells of both mating types and facilitating the study of a-factor signalling.     

Production of dihydroxyacetone from an aqueous solution of glycerol in the reaction catalyzed by an immobilized cell preparation of acetic acid bacteria Gluconobacter oxydans ATCC 621

Dihydroxyacetone (1,3-dihydroxy-2-propanone, DHA) is applied in the food and cosmetic industries as well as in pharmacy and medicine. It is produced as a result of incomplete oxidation of glycerol by acetic acid bacteria Gluconobacter oxydans. This reaction is catalyzed by PQQ-dependent membrane-bound glycerol dehydrogenase. The research developed a method of obtaining DHA by oxidation of a 3?% aqueous solution of glycerol (pH 7.5) at a temperature of 23?°C, with the only reaction biocatalyst being an immobilized cell preparation obtained from G. oxydans cells. After 5?days of the process, DHA concentration in the solution accounted for 27.2?g/L and the reaction efficiency for 94?%. After 4?days of the reaction run in culture media with pH 5.0, at a temperature of 28?°C, free or immobilized cells of G. oxydans produced on average 25?g of DHA/L at the reaction efficiency of 87?%.     

Determination of Iron Species in Samples of Iron-Fortified Food

The paper presents the determination of iron forms in food products. The procedure of sample extraction was developed and optimized, preserving the content of particular forms of iron. The colorimetric method using 2,2′-bipirydyl (measurements at 520 nm) was applied in Fe(II) determinations, while in Fe(III) determinations, the colorimetric method with potassium thiocyanate (measurements at 470 nm) was applied. The total content of iron was determined by the technique of atomic absorption spectrometry, which allowed for the determination of iron content in organic and inorganic complex compounds. Detection limits of 1 mg kg^?1 were obtained for all determined iron forms, with the precision ranging between 0.7 % and 1.5 % for 10 mg kg^?1 concentration. The optimized analytical procedure was applied in the determinations of iron forms in iron-fortified food products.