Temperature stability of a pure metakaolin based K-geopolymer: Part 1. Variations in the amorphous mineral network

The thermal behavior of a model MK based K-geopolymer (Si/Al = 1.38 and K/Al = 0.68; obtained by alkaline activation of a very pure metakaolin) was investigated between room temperature and 1400°C in order to evaluate its potentiality for high-temperature applications. The purpose of our study was to monitor the behavior of a geopolymer during a temperature rise in order to better understand its variations with respect to temperature. The works from the present paper focus only variations in the internal structure of the mineral matrix. The results presented here show that the amorphous mineral matrix is preserved up to 900°C. The results also show that there is a densification of the internal structure of tetrahedral network during heating, due to changes in the Q³ environments in fully-connected Q⁴ for both silicates and aluminates. Thus, our work provides a new more precise vision of the 3D geopolymeric mineral matrix for which the silicoaluminous network is not exclusively composed of Q⁴ entities, contrary to what is frequently encountered in the literature before.     

Development of biomass in a drinking water granular active carbon (GAC) filter

Indigenous bacteria are essential for the performance of drinking water biofilters, yet this biological component remains poorly characterized. In the present study we followed biofilm formation and development in a granular activated carbon (GAC) filter on pilot-scale during the first six months of operation. GAC particles were sampled from four different depths (10, 45, 80 and 115 cm) and attached biomass was measured with adenosine tri-phosphate (ATP) analysis. The attached biomass accumulated rapidly on the GAC particles throughout all levels in the filter during the first 90 days of operation and maintained a steady state afterward. Vertical gradients of biomass density and growth rates were observed during start-up and also in steady state. During steady state, biomass concentrations ranged between 0.8-1.83 x 10⁻⁶ g ATP/g GAC in the filter, and 22% of the influent dissolved organic carbon (DOC) was removed. Concomitant biomass production was about 1.8 × 10¹² cells/m²h, which represents a yield of 1.26 × 10⁶ cells/μg. The bacteria assimilated only about 3% of the removed carbon as biomass. At one point during the operational period, a natural 5-fold increase in the influent phytoplankton concentration occurred. As a result, influent assimilable organic carbon concentrations increased and suspended bacteria in the filter effluent increased 3-fold as the direct consequence of increased growth in the biofilter. This study shows that the combination of different analytical methods allows detailed quantification of the microbiological activity in drinking water biofilters.     

Comparative Study of Different Milk Samples Preservation Procedures for Bacteriologic Examination

The control of pathogenic bacteria present in foods, as well as scientific data concerning their behavior, are closely linked to analytical methods used and the way they are implemented. To assess the capacity of the laboratories to conduct correctly microbiological analyses, national and international proficiency testing schemes are organized. To set up these inter-laboratory studies (ILS), it is necessary to prepare artificially contaminated samples, which contamination level is sufficiently stable regarding their transportation conditions to the participating laboratories. In this context, we tested several procedures to maintain the concentration of Listeria monocytogenes and coagulase-positive staphylococci in milk samples: freezing temperature and addition of bacteriostatic agents at refrigeration temperatures, such as nystatin, boric acid, sodium azide, the lactoperoxidase system, or a boric acid mixture. Through this study we selected preservation procedures, which could be used to stabilize the contamination level of artificially contaminated milk samples during transportation without preventing the growth of the target bacteria during the analysis and after the initial dilution step. Boric acid mixture and boric acid were found to be effective in stabilizing the contamination level of Staphylococcus aureus in milk samples, whereas freezing, a boric acid mixture, and boric acid were suitable for milk samples containing L. monocytogenes, depending on the samples’ contamination rate. An erratum to this article can be found at     

Quantitative measurement of protein stability from unfolding equilibria monitored with the fluorescence maximum wavelength

The fluorescence of tryptophan is used as a signal to monitor the unfolding of proteins, in particular the intensity of fluorescence and the wavelength of its maximum lambda(max). The law of the signal is linear with respect to the concentrations of the reactants for the intensity but not for lambda(max). Consequently, the stability of a protein and its variation upon mutation cannot be deduced directly from measurements made with lambda(max). Here, we established a rigorous law of the signal for lambda(max). We then compared the stability DeltaG(H(2)O) and coefficient of cooperativity m for a two-state equilibrium of unfolding, monitored with lambda(max), when the rigorous and empirical linear laws of the signal are applied. The corrective terms involve the curvature of the emission spectra at their lambda(max) and can be determined experimentally. The rigorous and empirical values of the cooperativity coefficient m are equal within the experimental error for this parameter. In contrast, the rigorous and empirical values of the stability DeltaG(H(2)O) generally differ. However, they are equal within the experimental error if the curvatures of the spectra for the native and unfolded states are identical. We validated this analysis experimentally using domain 3 of the envelope glycoprotein of the dengue virus and the single-chain variable fragment (scFv) of antibody mAbD1.3, directed against lysozyme.     

Measurements of Chlorpyrifos Levels in Forager Bees and Comparison with Levels that Disrupt Honey Bee Odor-Mediated Learning Under Laboratory Conditions

Chlorpyrifos is an organophosphate pesticide used around the world to protect food crops against insects and mites. Despite guidelines for chlorpyrifos usage, including precautions to protect beneficial insects, such as honeybees from spray drift, this pesticide has been detected in bees in various countries, indicating that exposure still occurs. Here, we examined chlorpyrifos levels in bees collected from 17 locations in Otago, New Zealand, and compared doses of this pesticide that cause sub-lethal effects on learning performance under laboratory conditions with amounts of chlorpyrifos detected in the bees in the field. The pesticide was detected at 17 % of the sites sampled and in 12 % of the colonies examined. Amounts detected ranged from 35 to 286 pg.bee^?1, far below the LD₅₀ of ~100 ng.bee^?1. We detected no adverse effect of chlorpyrifos on aversive learning, but the formation and retrieval of appetitive olfactory memories was severely affected. Chlorpyrifos fed to bees in amounts several orders of magnitude lower than the LD₅₀, and also lower than levels detected in bees, was found to slow appetitive learning and reduce the specificity of memory recall. As learning and memory play a central role in the behavioral ecology and communication of foraging bees, chlorpyrifos, even in sublethal doses, may threaten the success and survival of this important insect pollinator.     

The effect of nanostructure on the thermal properties of fluorinated carbon nanofibres

Using thermogravimetic analysis in air, the thermal properties of fluorinated carbon nanofibres have been investigated. The fluorination level, the C–F bonding, the number of structural defects and the distribution of fluorine atoms in the carbon matrix have been modified using three fluorination routes, (i) a direct process using a flux of pure molecular fluorine F₂ (dynamic process), (ii) a filling of a closed reactor by this reactive gas (static process) and (iii) controlled fluorination using the thermal decomposition of a solid fluorinating agent TbF₄. At given fluorine contents, only the location of the fluorine atoms within the nanofibre changes the thermal stability, which can be increased up to 480 °C; such improvement is obtained when the fluorinated regions are located in the outer shell (tubes).     

Isothermal Oxidation Behaviour of NiCoCrAlYTa Coatings Produced by HVOF Spraying and Tribomet™ Process

Protective NiCoCrAlYTa coatings are used on gas turbine single crystal superalloy blades to provide environmental resistance. They can be deposited by several processes. In this study, isothermal oxidation behaviour of NiCoCrAlYTa coatings produced by HVOF spraying and Tribomet? process and deposited on single crystal nickel-based superalloy CMSX-4 were compared between 950 and 1,150 °C for several exposure durations. Microstructure and chemical composition of both coatings were examined before and after oxidation testing and quite similar observations were made for both coating processes. The combination of phase and chemical analyses allowed the establishment of an occurrence diagram of phases for both coating processes, according to temperature and duration of exposure. The obtained diagrams seemed similar for both processes. Finally both processes appeared to be equivalent for the protection of CMSX-4 superalloy in isothermal oxidation conditions.     

μm-resolved high resolution X-ray diffraction imaging for semiconductor quality control

We present a method and an equipment for performing μm-resolved X-ray diffraction area maps, and apply it to wafer defect analysis and industrial wafer quality inspection. The method determines simultaneously the macroscopic warpage, the mesoscopic curvature and the microscopic defect structure of semiconductor wagers. It is based on X-ray diffraction rocking curve imaging of the whole wafer with down to 1 μm² resolution. The new wafer testing equipment determines the maximal and integral peak intensities, the peak position and the half width of the rocking curves with a microscopic resolution, thus imaging simultaneously the macroscopic quality parameters and the microscopic defect structure. This permits to establish a direct one-to-one correlation between the microscopic defects and the resulting macroscopic effects. As an example, wafers of different materials, fabrication technology and resulting perfection are studied. When investigating layered samples, the technique allows furthermore to determine the influence of the wafer quality on the layer properties. The method can be applied generally to characterize non-destructively the quality of all kinds of crystalline structures, like, e.g. microelectronic and optoelectronic devices.