Applying a constructivist and collaborative methodological approach in engineering education

In this paper, a methodological educational proposal based on constructivism and collaborative learning theories is described. The suggested approach has been successfully applied to a subject entitled “Computer Architecture and Engineering” in a Computer Science degree in the University of La Laguna in Spain.     

Cytogenetic changes in fish exposed to water of the river Rhine

The induction of chromosome aberrations in fishes, exposed to Rhinewater, was investigated. The mudminnow, Umbra pygmaea, was chosen for this study, because of its ideal karyotype of 22 large chromosomes. Gill cells were used for chromosome studies.Fish, kept in Rhinewater for 11 days had chromosome breaks in approximately 30% of the metaphases studied. Control fish, exposed to a very good quality of untreated groundwater had breaks in about 8% of the metaphases.Several Rhinewater extracts were tested for their mutagenic potential in the Salmonella-microsome test. The fraction of aromatic compounds was found to be positive. This may indicate that one or more of the compounds present in this fraction were also responsible for the cytogenetic changes found in the fish.     

Poly(hydroxybutyrate-co-hydroxyvalerate) microspheres loaded with atrazine herbicide: screening of conditions for preparation,physico-chemical characterization,and in vitro release studies

Due to their widespread use in agriculture as well as in urban areas, agricultural chemicals are globally some of the most commonly encountered substances in waters. The objective of this study is to develop (including preparation and characterization) a new modified release system for the herbicide atrazine, employing poly(hydroxybutyrate-co-hydroxyvalerate) (PHBV) microspheres. The microspheres were prepared by the emulsification/solvent evaporation method, emulsifying an organic phase (atrazine and PHBV dissolved in chloroform) into an aqueous phase containing polyvinyl alcohol (PVA) as surfactant, under stirring, and then evaporating the solvent. A 2^4-1 fractional factorial design, investigating the influence of four variables at two levels, was performed to obtain formulations with optimized association efficiencies. There was a greater dependence of association efficiency on PVA concentration (negative) and the mass of polymer (positive) with lesser influence of both stirring speed and organic phase volume. The size of the particles was assessed using scanning electron microscopy, which showed that the particles were rough-surfaced spheres. The results obtained are promising, since the formulations presented encapsulation efficiency near 25% and the release kinetics profile of atrazine was altered when it was encapsulated in the microparticles, indicating that these systems may be efficient in reducing the environmental impact caused by the herbicide, hence making it safer to use.     

Trace-metal contamination in proton exchange membrane fuel cells caused by laser-cutting stains on carbon-coated metallic bipolar plates

Trace-metal contamination poses a threat to performance and stability of proton exchange membrane fuel cells (PEMFCs). In this study the source of origin and degree of metal dissolution from carbon-coated 316L bipolar plates (BPPs) are evaluated after a long-term PEMFC test run under conditions resembling a real-life automotive application. Despite intact carbon-coating, metal dissolution occurs from uncoated oxycarbide stains on the plates’ surface. Which correlates with post-mortem detection of chromium, iron and nickel in the membrane electrode assembly. The rate of cell voltage decrease throughout the high current operations is found to be twice as high in the presence of metal ions. Metal dissolution can be correlated with transients in cell voltage during dynamic current load cycling as a result of temporary global fuel starvation. The observed difference in metal dissolution on the anode and cathode BPP indicates weak galvanic coupling between the bipolar plate(s) and the electrode layer(s).     

Arsenate adsorption and desorption kinetics on a Fe(III)-modified montmorillonite

The adsorption-desorption kinetics of arsenate on a Fe(III)-modified montmorillonite (Fe-M) was studied at different arsenate concentrations, pH and stirring rates. The synthesized solid was a porous sample with Fe(III) present as a mix of monomeric and polymeric Fe(III) species in the interlayer and on the external surface. Adsorption took place in a two-step mechanism, with an initial fast binding of arsenate to Fe(III) species at the external surface (half-lives of 1 min or shorter) followed by a slower binding to less accessible Fe(III) species in pores and the interlayer (half-lives of around 1 h). Desorption kinetics also reflected the presence of externally and internally adsorbed arsenate. At pH 6 the maximum adsorbed arsenate was 52 μmol/g, a value that is low as compared to adsorption on ferrihydrite (700 μmol/g) and goethite (192-220 μmol/g). However, since the Fe(III) content of Fe-M is much lower than that of ferrihydrite and goethite, Fe(III) species in Fe-M are more efficient in binding arsenate than in ferrihydrite or goethite (one As atom is attached every 8.95 iron atoms). This high binding efficiency indicates that Fe(III) species are well spread on montmorillonite, forming small oligomeric species or surface clusters containing just a few iron atoms.     

Recycling of aluminum and caustic soda solution from waste effluents generated during the cleaning of the extruder matrixes of the aluminum industry

Anodising industries use a concentrated caustic soda solution to remove aluminum from extruder matrixes. This procedure produces very alkaline effluents containing high amounts of aluminum. The work reported here was focussed on recycling aluminum, as aluminum hydroxide, from these effluents and regenerating an alkaline sodium hydroxide solution. Briefly, the method comprises a dilution step (necessary for reducing the viscosity of the effluent and allowing the subsequent filtration) followed by a filtration to eliminate a substantial amount of the insoluble iron. Then, sulphuric acid was added to neutralize the waste solution down to pH 12 and induce aluminum precipitation. The purity of the aluminum salt was improved after washing the precipitate with deionised water. The characterization of the solid recovered, performed by thermogravimetric analysis, Fourier transform infrared spectroscopy and X-ray diffraction, indicated characteristics typical of bayerite. The proposal method allowed recovering 82% of the aluminum present in the wastewater with high purity (99.5%). Additionally, a sufficiently concentrated caustic soda solution was also recovered, which can be reused in the anodising industries. This procedure can be easily implemented and ensures economy by recycling reagents (concentrated caustic soda solution) and by recovering commercial by-products (aluminum hydroxide), while avoiding environmental pollution.     

Asymmetric Synthesis of α‐Amino Acids under Operationally Convenient Conditions

A new multipurpose glycine equivalent for the general asymmetric synthesis of α‐amino acids is introduced. The chiral reagent can be transformed to various amino acids by alkylations with alkyl halides as well as aldol and Michael addition reactions under operationally convenient reaction conditions at room temperature with virtually complete stereochemical control.

     

Validation and application of an LC-MS/MS method for the determination of cyclic oligomers originating from polyamide 6 and polyamide 66 in food simulant

Polyamides (PAs) are used in the production of various food contact materials (FCMs) and articles such as kitchen utensils and packaging material. Cyclic oligomers have been identified as potential migrants from PA. This study describes the development, validation and application of a multi-oligomer analytical method based on LC-ESI-MS/MS for the identification and quantification of eight cyclic oligomers of PA 6 and four PA 66 migrating from FCMs into food simulant B (3% acetic acid) and beverages. It was proved that doubly charged precursor ions of the cyclic PA 6 and PA 66 oligomers above a mass of 500 Da are formed during the ionisation process of the electrospray technique used. Direct injection of a diluted food simulant into the LC-ESI-MS/MS system after migration makes the validated method a valuable tool for investigating migration of cyclic PA oligomers. The validation results demonstrate that the multi-oligomer method is applicable for the analysis of cyclic PA 6 and PA 66 oligomers in food simulant B. For all investigated cyclic PA oligomers, detection limits were in the range of 0.1–1.1 µg/l. Linearity (r² ≥ 0.99), trueness values between 91% and 122%, and intra-day (RSD_r < 10%) and inter-day precision (RSD_R < 19%) were determined and satisfied validation criteria set out by the European Reference Laboratory for FCMs. The method was extended to tap water and tea. Finally, the multi-oligomer method was successfully applied to determine cyclic PA oligomers in migration solutions originating from different PA FCMs. In all migration solutions, concentrations of cyclic PA oligomers were determined above the LOQ. A preliminary risk assessment based on in silico tools was performed. The results demonstrate the urgent need for toxicological data that would facilitate the evaluation of the health risk of cyclic PA oligomers.     

Coronary artery bypass grafting versus percutaneous coronary intervention in end-stage kidney disease: A systematic review and meta-analysis of clinical studies

The most significant complication of end-stage kidney disease (ESKD) is cardiovascular disease, mainly coronary artery disease (CAD). Although the effective treatment of CAD is an important prognostic factor, whether percutaneous coronary intervention (PCI) or coronary artery bypass grafting (CABG) is better for treating CAD in this group of patients is still controversial. We searched Pubmed/Medline, Web of Science, Embase, the Cochrane Central Register of Controlled Trials articles that compared the outcomes of CABG versus PCI in patients with ESKD requiring dialysis. A total of 10 observational studies with 39,666 patients were included. Our analysis showed that when compared to PCI, CABG had lower risk of need for repeat revascularization (relative risk [RR] = 2.25, 95% confidence interval [CI] 2.1–2.42, p < 0.00001) and cardiovascular death (RR = 1.19, 95% CI 1.14–1.23, p < 0.00001) and higher risk for short-term mortality (RR = 0.43, 95% CI 0.38–0.48, p < 0.00001). There was no statistically significant difference between the PCI and CABG groups in the risk for late mortality (RR = 1.05, 95% CI 0.97–1.14, p = 0.25), myocardial infarction (RR = 1.05, 95% CI 0.46–2.36, p = 0.91) or stroke (RR = 1.02, 95% CI 0.64–1.61, p = 0.95). This meta-analysis showed that in ESKD patients requiring dialysis, CABG was superior to PCI in regard to cardiovascular death and need for repeat revascularization and inferior to PCI in regard to short term mortality. However, this meta-analysis has limitations and needs confirmation with large randomized controlled trials.