Effect of composition on the matrix transformation of the Co-Re-Cr-Ta-C alloys

Neutron diffraction measurement was performed in-situ at high temperatures on Co-Re-Ta-C alloys with and without Cr addition. This included alloys containing different C content with the C/Ta ratio varying between 0.5 and 1.0. The Co-Re-solid solution matrix of the experimental alloys is polymorphic (like in pure cobalt) and transformed from low temperature hexagonal ? phase to high temperature cubic γ phase on heating. This transformation is reversible and show hysteresis. The main alloying addition, Re, stabilizes the ? Co-phase and increases the transformation temperature to above 1273 K. The onset of the \(\varepsilon \rightleftharpoons \gamma\) transformation during heating and cooling was found to differ depending on the alloy composition. In alloys without Cr addition the transformation was not completed on cooling and the high temperature γ phase was partly retained at room temperature in metastable state with the amount depending on the cooling rate from high temperature. The diffraction and microstructural results showed that Cr is ? stabilizer (similar as Re) but the role of Ta is not clear. The C/Ta ratio has no direct effect on the matrix phase transformation. Nevertheless, it influences indirectly by determining the amount of Ta which is freely available in the matrix.     

Mechanisms of N2O production in biological wastewater treatment under nitrifying and denitrifying conditions

Nitrous oxide (N₂O) is an important greenhouse gas and a major sink for stratospheric ozone. In biological wastewater treatment, microbial processes such as autotrophic nitrification and heterotrophic denitrification have been identified as major sources; however, the underlying pathways remain unclear. In this study, the mechanisms of N₂O production were investigated in a laboratory batch-scale system with activated sludge for treating municipal wastewater. This relatively complex mixed population system is well representative for full-scale activated sludge treatment under nitrifying and denitrifying conditions.Under aerobic conditions, the addition of nitrite resulted in strongly nitrite-dependent N₂O production, mainly by nitrifier denitrification of ammonia-oxidizing bacteria (AOB). Furthermore, N₂O is produced via hydroxylamine oxidation, as has been shown by the addition of hydroxylamine. In both sets of experiments, N₂O production was highest at the beginning of the experiment, then decreased continuously and ceased when the substrate (nitrite, hydroxylamine) had been completely consumed. In ammonia oxidation experiments, N₂O peaked at the beginning of the experiment when the nitrite concentration was lowest. This indicates that N₂O production via hydroxylamine oxidation is favored at high ammonia and low nitrite concentrations, and in combination with a high metabolic activity of ammonia-oxidizing bacteria (at 2 to 3 mgO₂/l); the contribution of nitrifier denitrification by AOB increased at higher nitrite and lower ammonia concentrations towards the end of the experiment.Under anoxic conditions, nitrate reducing experiments confirmed that N₂O emission is low under optimal growth conditions for heterotrophic denitrifiers (e.g. no oxygen input and no limitation of readily biodegradable organic carbon). However, N₂O and nitric oxide (NO) production rates increased significantly in the presence of nitrite or low dissolved oxygen concentrations.     

Intersublevel Spectroscopy on Single InAs-Quantum Dots by Terahertz Near-Field Microscopy

Using scattering-type near-field infrared microscopy in combination with a free-electron laser, intersublevel transitions in buried single InAs quantum dots are investigated. The experiments are performed at room temperature on doped self-assembled quantum dots capped with a 70 nm GaAs layer. Clear near-field contrast of single dots is observed when the photon energy of the incident beam matches intersublevel transition energies, namely the p-d and s-d transition of conduction band electrons confined in the dots. The observed room-temperature line width of 5-8 meV of these resonances in the mid-infrared range is significantly below the inhomogeneously broadened spectral lines of quantum dot ensembles. The experiment highlights the strength of near-field microspectroscopy by demonstrating signals from bound-to-bound transitions of single electrons in a probe volume of the order of (100 nm)(3).     

Complexes of Silver(I) Ions and Silver Phosphate Nanoparticles with Hyaluronic Acid and/or Chitosan as Promising Antimicrobial Agents for Vascular Grafts

Polymers are currently widely used to replace a variety of natural materials with respect to their favourable physical and chemical properties, and due to their economic advantage. One of the most important branches of application of polymers is the production of different products for medical use. In this case, it is necessary to face a significant disadvantage of polymer products due to possible and very common colonization of the surface by various microorganisms that can pose a potential danger to the patient. One of the possible solutions is to prepare polymer with antibacterial/antimicrobial properties that is resistant to bacterial colonization. The aim of this study was to contribute to the development of antimicrobial polymeric material ideal for covering vascular implants with subsequent use in transplant surgery. Therefore, the complexes of polymeric substances (hyaluronic acid and chitosan) with silver nitrate or silver phosphate nanoparticles were created, and their effects on gram-positive bacterial culture of Staphylococcus aureus were monitored. Stages of formation of complexes of silver nitrate and silver phosphate nanoparticles with polymeric compounds were characterized using electrochemical and spectrophotometric methods. Furthermore, the antimicrobial activity of complexes was determined using the methods of determination of growth curves and zones of inhibition. The results of this study revealed that the complex of chitosan, with silver phosphate nanoparticles, was the most suitable in order to have an antibacterial effect on bacterial culture of Staphylococcus aureus. Formation of this complex was under way at low concentrations of chitosan. The results of electrochemical determination corresponded with the results of spectrophotometric methods and verified good interaction and formation of the complex. The complex has an outstanding antibacterial effect and this effect was of several orders higher compared to other investigated complexes.