15 research outputs found
Analytical Solutions in Coupled Streamflow and Groundwater Modelling
No full textThere is a growing interest in coupled modelling of Groundwater-Surface water Interaction (GSI) due to the increased stresses on available water resources from population growth and various developments (agricultural and industrial among others). Policies and technologies for integrated water management and conjunctive use of groundwater and surface water are attracting researchers and investigators worldwide
Enantioselective sensors and biosensors for clinical analysis
No full textThesis (PhD (Chemistry))--University of Pretoria, 2006.The enantioanalysis of compounds of biological importance with a chiral moiety is very important because each enantiomer is a marker for a different disease. Accordingly, very reliable methods of enantioanalysis should be employed for the correct diagnosis of the diseases. The utilization of amperometric biosensors and enantioselective, potentiometric membrane electrodes made the assay of a single enantiomer faster, easier and more reliable if one compare with the chromatographic techniques which are widely proposed for this kind of analyses. Monocrystalline diamond was proposed as matrix for amperometric electrodes and amperometric biosensors design. The advantages of using such material for electrode design are: (a) lower background currents and noise signals, which lead to improve S/B and S/N ratios, and lower detection limits; (b) good electrochemical activity (pre-treatment is not necessary); (c) wide electrochemical potential window in aqueous media; (d) very low capacitance; (e) extreme electrochemical stability; and (f) high reproducibility of analytical information. The design selected for the electrodes is simple, fast and reproducible. The carbon or diamond powders were mixed with paraffine oil to give the carbon or diamond paste which can act alone as electroactive material in the electrodes or it can be modified with a chiral selector (e.g., cyclodextrins, maltodextrins or antibiotics) or enzyme (e.g., L(D)-aminoacid oxidase, L-lysine oxidase). The results obtained by employing the amperometric electrodes and biosensors and the enantioselective, potentiometric membrane electrodes proved a high sensitivity, selectivity, accuracy and high reliability. These characteristics made them suitable to be used for the enantioanalysis of different compounds of biological importance (e.g., pipecolic acid, glyceric acid, 2-hydroxyglyceric acid, fucose, L-vesamicol and L-lysine) in serume and/or urine samples. The features of the proposed enantioselective, amperometric and potentiometric electrodes proposed in this thesis are their utilization for in vivo measurements and as detectors in flow systems (flow injection analysis or/and sequential injection analysis). This will simplify the enantioanalysis and will improve considerable the reliability of the analytical information favorazing a fast and accurate diagnosis of the diseases associated with the marker determined.Chemistryunrestricte
Enantioselective Potentiometric Membrane Electrodes Based on Antibiotics for the Determination of L- and D-Glyceric Acids
No full textGlyceric acid (GA) is a human metabolite existing in L- and D-configurations, which are considered the markers for the diseases L- and D-glyceric aciduria/academia, respectively. Enantioselective, potentiometric membrane electrodes based on carbon paste modified with antibiotics as chiral selectors, vancomycin, and teicoplanin were designed for the assay of L- and D-GA, respectively, in the concentration ranges of 10−9–10−7 and 10−4–10−2 moL/L with very low detection limits (1.5 × 10−10 moL/L for L-GA and 1.6 × 10−4 moL/L for D-GA, resp.). The surface of the electrodes can be regenerated simply by polishing in order to obtain a fresh surface ready to be used in a new assay. The proposed electrodes can be successfully applied for the enantioanalysis of L- and D-glyceric acids in serum samples
Experimental and numerical study of diffusion and trapping of hydrogen in plastically deformed A508.Cl.3 steel at room temperature
No full textDetermination of<scp>l</scp>- and d-fucose using amperometric electrodes based on diamond paste
No full textDecontamination of Dental Implant Surfaces by the Er:YAG Laser Beam: A Comparative in Vitro Study of Various Protocols
No full textOral rehabilitation with dental implants has revolutionized the field of dentistry and has been proven to be an effective procedure. However, the incidence of peri-implantitis has become an emerging concern. The efficacy of the decontamination of the implant surface, by means of lasers, is still controversial. Previous studies have revealed a reduction in osteoblast adhesion to carbon-contaminated implant surfaces. This in-vitro study aimed to evaluate the decontamination of failed implants by assessing the carbon proportion, after irradiation by low-energy erbium yttrium-aluminum-garnet laser (Er:YAG) (Fotona; 2940 nm, Ljubljana, Slovenia) for a single and for multiple passages, until getting a surface, free of organic matters; to find the appropriate procedure for dental-implant surface-decontamination. Ninety implants were used. Thirty sterile implants were kept as a negative control. Thirty failed implants were irradiated by the Er:YAG laser, for a single passage, and the other thirty, for multiple passages. The parameters used in our experiments were an irradiation energy of 50 mJ, frequency of 30 Hz, and an energy density of 3.76 J/cm2. A sapphire tip, with a length of 8 mm, was used with concomitant water spray irrigation, under air 6 and water spray 4. Super short pulse mode (SSP) was of 50 μs; irradiation speed being 2 mm/s. We used energy-dispersive X-ray spectroscopy (EDX) to evaluate the carbon proportion on the surfaces of the sterile implants, the contaminated, and the lased implants, with one (LX1) and with three passages (LX3). Statistical analysis was performed by ANOVA. Results showed mean difference between the three groups (contaminated, LX1, and LX3) with p < 0.0001, as between LX1 and Group A (p < 0.0001), while the difference between LX3 and the control group was not statistically significant. The decontamination of the implant surfaces with a low-energy Er:YAG laser with three passages, appeared to be an encouraging approach
COMPARISON BETWEEN THE BEHAVIOR OF PURE AND COMMERCIAL UNSTABLE AUSTENITIC STAINLESS STEELS IN THE PRESENCE OF HYDROGEN
No full textThe Impact of Pro-Government Militias on Human Rights Violations
No full textNew data show that between 1982 and 2007, in over 60 countries governments were linked to and cooperated with informal armed groups within their own borders. Given the prevalence of these linkages, we ask how such links between governments and informal armed groups influence the risk of repression. We draw on principal-agent arguments to explore how issues of monitoring and control help understanding of the impact of militias on human rights violations. We argue that such informal agents increase accountability problems for the governments, which is likely to worsen human rights conditions for two reasons. First, it is more difficult for governments to control and to train these militias, and they may have private interests in the use of violence. Second, informal armed groups allow governments to shift responsibility and use repression for strategic benefits while evading accountability. Using a global dataset from 1982 to 2007, we show that pro-government militias increase the risk of repression and that the presence of militias also affects the type of violations that we observe
Towards the directed evolution of an L-aspartate oxidase from Pseudomonas putida
No full textAmino acid oxidases (AAOs) are enantioselective flavoenzymes that catalyse the oxidation of amino acids into imino acids, which spontaneously hydrolyse in water to form keto acids. AAOs have several potential applications, most notably as biocatalysts in the production of enantiomerically pure amino acids and keto acids, or in enzymatic biosensors. Therefore, there is a demand for a range of AAOs with specific activity against various substrates, encouraging the characterisation of less well understood oxidases.
Seven putative oxidases were cloned into the pET-YSBLIC-3C expression vector, expressed in E. coli-DE3 expression strains and assayed for activity against all proteinogenic amino acids. Of these seven targets, the L-amino acid oxidase from Pseudomonas putida (PpLAAO) was found to be highly soluble, had detectable activity against L-aspartate and L-asparagine and had not been investigated in depth previously.
The purified PpLAAO protein showed high substrate specificity against L-aspartate and lower activity with substrate inhibition against L-asparagine. Very low activity was also detected against L-glutamate. The purified protein had optimal activity around pH 7.5 and at temperatures between 4°C and 30°C.
To investigate the role of residues in the active site area of the PpLAAO protein thirteen active site residues, determined by comparison with the structure of the L-aspartate oxidase from E. coli (L-AspO), were mutated to alanine. Eleven of these mutants were purified and assayed against L-aspartate, L-asparagine and L-glutamate. Results were largely consistent with knowledge of L-AspO.
Ingenza Ltd. has an interest in potential applications of L-tyrosine and L-alanine oxidases. Because of this iterative combinatorial active site saturation testing, using the active structure of L-AspO was performed alongside a small scale epPCR mutagenesis in an attempt to introduce activity against L-alanine and L-tyrosine. L-homoserine was also targeted as part of a substrate walking approach towards L-alanine; however no novel activity was detected in any transformants
Rivers are social–ecological systems: Time to integrate human dimensions into riverscape ecology and management
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