Protective effect of Staphylococcus chromogenes infection against Staphylococcus aureus infection in the lactating bovine mammary gland

The susceptibility of uninfected or Staphylococcus chromogenes-infected quarters to challenge with Staphylococcus aureus was measured. Seventeen S. chromogenes-infected quarters were challenged by infusion of S. aureus into the teat sinus; 47% (8 of 17) became infected and all 18 uninfected quarters challenged similarly with S. aureus became infected. No differences in daily milk yield were seen between uninfected quarters and S. chromogenes-infected quarters prior to S. aureus infusion. Postinfusion, milk yield for S. aureus-infected, S. chromogenes-infected, and S. chromogenes- and S. aureus-infected quarters differed. Somatic cell counts were elevated in S. chromogenes-infected quarters compared with uninfected quarters prior to S. aureus infusion. Somatic cell counts were not different between S. aureus- and S. chromogenes- and S. aureus-infected quarters postinfusion, but were different for S. chromogenes-infected quarters. Chloride concentrations in S. chromogenes- and S. aureus-infected quarters were different from either S. aureus-infected or S. chromogenes-infected quarters. Staphylococcus aureus colony forming units in quarters with preexisting S. chromogenes infections were lower than S. aureus colony-forming units in previously uninfected quarters. Possible protective mechanisms induced by S. chromogenes against superinfection by S. aureus are discussed.     

Investigation into etching mechanism of polyethylene terephthalate (PET) films treated in helium and oxygenated‐helium atmospheric plasmas

This research makes an investigation into the etching mechanism of atmospheric plasma conditions on the surface of polyethylene terephthalate (PET) films. Two types of untreated PET films (S/200 and S/500) were exposed to plasma for 0 to 5.0 min in 30‐s increments. The first set of each film type was treated in helium plasma, while the second was treated in oxygenated‐helium plasma. Differential Scanning Calorimetry (DSC) was used to characterize pre‐ and post‐exposure films. Weight changes and the degree of solubility were also determined. Based on peak area results, the percent crystallinity of PET S/200 increased by an average of 4.57% (helium treated) and 13.56% (oxygenated‐helium treated), while the S/500 showed only a small increase. There was no significant change in the melting or crystallization temperatures of either film type, indicating a decrease in amorphous content versus an increase in crystalline material. Weight loss analysis supports this theory. Solubility testing revealed a continual decrease in swelling as exposure time was increased. A model was developed to predict the change in the degree of solubility for polyphase surfaces considering the etching rate per phase. The model was applied to PET with good correlation between the model and experimental data. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 2383–2389, 2004     

Radical styrene polymerization in the presence of trace levels of sulfonic acids

The bulk polymerization of styrene in the presence of the vinyl functional sulfonic acid 2‐sulfoethylmethacrylate (SEM) was found to have utility for making polystyrenes with narrow polydispersity, bimodal polydispersity, and ultrahigh molecular weight at fast polymerization rates. Narrow polydispersity polymers were made by the addition of SEM to nitroxide‐mediated polymerizations. Bimodal polydispersity polymers were made by the ultrahigh molecular weight component being made in the presence of SEM in the absence of an initiator and the low molecular weight component being made in the presence of an initiator and/or chain‐transfer agent. Ultrahigh molecular weight monomodal polystyrenes were prepared at much faster polymerization rates than possible via spontaneous polymerization in the absence of SEM. SEM was found to be more effective, by an order of magnitude, than camphor sulfonic acid on a weight basis and, because it is copolymerized into the polymer chain, should not lead to corrosion problems during fabrication of the polymer. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 869–875, 2003     

Porometry, porosimetry, image analysis and void network modelling in the study of the pore-level properties of filters

We present fundamental and quantitative comparisons between the techniques of porometry (or flow permporometry), porosimetry, image analysis and void network modelling for seven types of filter, chosen to encompass the range of simple to complex void structure. They were metal, cellulose and glass fibre macro- and meso-porous filters of various types. The comparisons allow a general re-appraisal of the limitations of each technique for measuring void structures. Porometry is shown to give unrealistically narrow void size distributions, but the correct filtration characteristic when calibrated. Shielded mercury porosimetry can give the quaternary (sample-level anisotropic) characteristics of the void structure. The first derivative of a mercury porosimetry intrusion curve is shown to underestimate the large number of voids, but this error can be largely corrected by the use of a void network model. The model was also used to simulate the full filtration characteristic of each sample, which agreed with the manufacturer's filtration ratings. The model was validated through its correct a priori simulation of absolute gas permeabilities for track etch, cellulose nitrate and sintered powder filters.     

Characterisation and tribological evaluation of nitrogen-containing molybdenum–copper PVD metallic nanocomposite films

This paper reports on the structural, mechanical and tribological properties of molybdenum–copper nanocomposite films ‘doped’ with small amounts of nitrogen, which contain either no nitride phase (i.e. the nitrogen is held in interstitial solid solution, mainly in molybdenum) or small amounts of lower nitrides (i.e. Mo₂N). All films were deposited on Si wafers, AISI M2 high speed steel and AISI 316 stainless steel by reactive sputtering using a hot-filament-enhanced dc unbalanced magnetron system. A systematic approach was adopted to investigate the evolution of metal/metal and ceramic/metal phase combinations with increasing nitrogen content (up to 40 at.% N) in the film. Coating composition and microstructure were determined by cross-sectional TEM, SEM and XPS. XRD was used to identify (where possible) metallic and metal-nitride phases. Mechanical properties such as hardness and elastic modulus were determined by low load Knoop and instrumented Vickers indentation measurements. Reciprocating sliding, micro-abrasion and impact tests were performed to assess tribological performance.

It was found that increasing the nitrogen gas flow rate from 0 to 15 sccm (and therefore nitrogen content in the film from 0 to 24 at.% N), refined significantly the coating microstructure from columnar to a dense and more equiaxed morphology, increasing the hardness whilst maintaining (almost constant) elastic modulus values, close to that of molybdenum metal. Further increases in the nitrogen gas flow rate resulted in films that appeared to contain significant fractions of the Mo₂N ceramic phase. SEM and cross-sectional TEM analyses of the film deposited at a nitrogen flow rate of 20 sccm (containing 36 at.% N) demonstrated a microstructure consisting of 50–100 nm wide columns, which contain small regions of contrast in dark-field images, of the order of 3–5 nm wide. A maximum hardness of 32 GPa and the highest hardness/modulus ratio was however found in the (predominantly metallic) film deposited at a nitrogen gas flow rate of 15 sccm. This film also performed best in both micro-abrasion and impact wear tests; in contrast, the ‘ceramic’ film (deposited at 20 sccm nitrogen flow rate) performed better in reciprocating sliding wear.     

Erosion of oxide scales formed on Cr3C2-NiCr thermal spray coatings

Cr₃C₂-NiCr thermal spray coatings are extensively used to mitigate high temperature erosive wear in fluidised bed combustors and power generation/transport turbines. The aim of this work was to characterise the variation in oxide erosion response as a function of the Cr₃C₂-NiCr coating microstructure. Erosion was carried out at 700 °C and 800 °C with erodent impact velocities of 225-235 m/s. The erosion behaviour of the oxide scales formed on these coatings, was influenced by the coating microstructure and erosion temperature. Development of the carbide microstructure with extended heat treatment lead to variations in the erosion-corrosion response of the Cr₃C₂-NiCr coatings.     

The Effect of Heat Treatment on the Oxidation Mechanism of Blended Powder Cr3C2-NiCr Coatings

The advantageous oxidation and wear properties of Cr₃C₂-NiCr thermal spray coatings have resulted in them being extensively applied to combat erosion at high temperatures. Under these conditions, oxide layers take on an ever more significant role in determining the composite response. The response of blended powder-based carbide coatings for erosion applications has formed the basis for application of cermet-based coatings at elevated temperature. In this study, the oxidation mechanisms of as-sprayed and heat-treated Cr₃C₂-NiCr blended powder-based coatings are characterized. Interdiffusion between the coating phases with long-term exposure increased the Cr content of the matrix phase. This had a significant effect on the oxidation mechanism. The implications of the change in oxidation mechanism and oxide morphology on the coating response to high-temperature erosion are discussed.     

Surface characterisation of DC plasma electrolytic oxidation treated 6082 aluminium alloy: Effect of current density and electrolyte concentration

Plasma electrolytic oxidation (PEO) is a specialised but well-developed process which has found applications in aerospace, oil/gas, textile, chemical, electrical and biomedical sectors. A novel range of coatings having technologically attractive physical and chemical properties (e.g. wear- and corrosion-resistance) can be produced by suitable control of the electrolyte as well as electrical parameters of the PEO process. Oxide ceramic films, 3 to 40 μm thick, were produced on 6082 aluminium alloy by DC PEO using 5 to 20 A/dm² current density in KOH electrolyte with varied concentration (0.5 to 2.0 g/l). Phase analysis (composition and crystallite size) was carried out using X-ray diffraction and TEM techniques. Residual stresses associated with the crystalline coating phase (α-Al₂O₃) were evaluated using the X-ray diffraction Sin²ψ method. Nanoindentation studies were conducted to evaluate the hardness and elastic modulus. SEM, SPM and TEM techniques were utilised to study surface as well as cross-sectional morphology and nano features of the PEO coatings. Correlations between internal stress and coating thickness, surface morphology and phase composition are discussed. It was found that, depending on the current density and electrolyte concentration used, internal direct and shear stresses in DC PEO alumina coatings ranged from − 302 ± 19 MPa to − 714 ± 22 MPa and − 25 ± 12 MPa to − 345 ± 27 MPa, respectively. Regimes of PEO treatment favourable for the production of thicker coatings with minimal stress level, dense morphology and relatively high content of α-Al₂O₃ phase are identified.     

PEO coatings obtained on an Mg-Mn type alloy under unipolar and bipolar modes in silicate-containing electrolytes

Protective surface layers with high corrosion resistance (R_p = 3.3·105 ohm cm²) and significant microhardness (H = 4.8 GPa), as compared to the substrate material, were obtained on MA8 magnesium alloy by bipolar Plasma Electrolytic Oxidation (PEO) in a silicate-fluoride electrolyte. The phase and elemental composition and morphology of the coatings were investigated. It was found that the application of the bipolar PEO mode enables one to synthesise on the alloy's surface a high-temperature phase of magnesium silicate, forsterite (Mg₂SiO₄) having good anticorrosion and mechanical properties.