A novel electrocatalyst support with proton conductive properties for polymer electrolyte membrane fuel cell applications

The objective of this study is to graft the surface of carbon black, by chemically introducing polymeric chains (Nafion^® like) with proton-conducting properties. This procedure aims for a better interaction of the proton-conducting phase with the metallic catalyst particles, as well as hinders posterior support particle agglomeration. Also loss of active surface can be prevented. The proton conduction between the active electrocatalyst site and the Nafion^® ionomer membrane should be enhanced, thus diminishing the ohmic drop in the polymer electrolyte membrane fuel cell (PEMFC). PtRu nanoparticles were supported on different carbon materials by the impregnation method and direct reduction with ethylene glycol and characterized using amongst others FTIR, XRD and TEM. The screen printing technique was used to produce membrane electrode assemblies (MEA) for single cell tests in H₂/air (PEMFC) and methanol operation (DMFC). In the PEMFC experiments, PtRu supported on grafted carbon shows 550 mW cm⁻² gmetal⁻¹ power density, which represents at least 78% improvement in performance, compared to the power density of commercial PtRu/C ETEK. The DMFC results of the grafted electrocatalyst achieve around 100% improvement. The polarization curves results clearly show that the main cause of the observed effect is the reduction in ohmic drop, caused by the grafted polymer.     

Cognitive preconditions for responses to fairness: An object retrieval test of inhibitory control in capuchin monkeys (Cebus apella).

The authors explore the evolution of one cognitive mechanism required for altruistic behavior: the capacity to inhibit prepotent responses. Specifically, the authors used an object retrieval task to investigate whether capuchins (Cebus apella) can inhibit a prepotent strategy of reaching directly for a food reward. Success in this task varies across species and across development, but is also known to depend critically on the maturity of dorsolateral prefrontal cortex, the cortical area implicated in rejecting small payoffs in an Ultimatum Game. Capuchins easily inhibit the tendency to reach directly for food in the object retrieval task, successfully employing an alternative reaching strategy even in the first session of performance. This contrasts with the performance of closely related tamarin monkeys, who performed less well despite extensive training. These results provide the first evidence that capuchins likely exhibit human-like inhibitory control in tasks previously linked to the function of the dorsolateral prefrontal cortex, such as the Ultimatum Game. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Distribution of micro-essential (Fe, Cu, Zn) and toxic (Hg) metals in tissues of two nutritionally distinct hydrothermal shrimps

Hydrothermal ecosystems of the Mid Atlantic Ridge (MAR) are dominated by shrimps and mussels that are naturally exposed to elevated levels of heavy metals providing unique in situ laboratories for ecotoxicological investigations. This study reports on the tissue compartmentalization of both micro-essential (Fe, Zn, Cu) and toxic metals (Hg) in two nutritionally distinct cariddean vent shrimps: Rimicaris exoculata and Mirocaris fortunata, in order to shed light on organism-biota interactions at hydrothermal vents. High metal concentrations in shrimps confirmed extreme exposure levels at both geochemically different hydrothermal vents (Rainbow and Lucky Strike). However, Hg concentrations were below those reported in species for human consumption that may either suggest low bioavailability of the metal, or its effective detoxification/depuration by the hydrothermal shrimp that needs to be confirmed by post-capture toxicological investigations. Distribution of metals in different tissues had very similar patterns in both shrimp species, the target organs being gill and pylorus. Tissue levels correlated well with end-member fluid composition with regard to element ratios, i.e. Fe/Zn and Fe/Cu ratios in end-member fluids reported for Rainbow and L. Strike were conserved in the gills of M. fortunata. Moreover, R. exoculata that lives closer to venting exits as compared to M. fortunata, had similar or often less metals accumulated in selected organs, possibly owing to its higher degree of adaptation to hydrothermal conditions. Despite of high concentrations in tissues micro essential metals only represented a small fraction (14-36%) of the whole body burden indicating preponderance of minerals on the surface and/or in the gut, and thus points to improper use of whole body concentration in metal bioavailability interpretations at hydrothermal vents.     

Multipulse converters and controls for HVDC and FACTS systems

Contents  For very high power applications, it is imperative to limit switching losses in the power converter. Multipulse converters are made up from several converter modules, switching at the fundamental frequency, but properly phase shifted to produce a nearly sinusoidal output voltage. Robust controls for HVDC and FACTS systems based on multipulse converters were developed. The developed HVDC system makes the rectifier station to control the instantaneous active (real) power through the HVDC voltage link, whereas the inverter station controls the instantaneous reactive (imaginary) power generation. The control of real and imaginary powers is independent one from the other and there is no control signal that is shared by both converter stations. A complete model of a 100 MW, 33 kVac, 50/60 Hz, 24-pulse HVDC system was implemented in the electromagnetic transient program (EMTP/ATP). The static synchronous compensator (STATCOM) is a shunt type of FACTS controller. It regulates the voltage magnitude of a controlled ac bus by drawing variable reactive current from the power system. The fast dynamic of the STATCOM controller avoids high fluctuations of the dc voltage caused by transients. A complete model of a 100 MW, 33 kV, 60 Hz, 24-pulse STATCOM was implemented and the results have confirmed the robustness of the proposed voltage control. Received: 21 December 2000     

Automatic defects classification — a contribution

The objective of this work is to provide a contribution to defect classification. More precisely, we try to prove that it is possible to identify and classify defects of different types using the pulse-echo technique. The classification process makes use of the time and frequency domain responses of the ultrasonic echo signals acquired from different specimens simulating defects with three different shapes (cylindrical, spherical and planar with rectangular cross-section) and sizes. Although the final goal is the characterisation of practical defects (for instance, voids, cracks, delaminations, and so on) appearing in composite materials during manufacturing and in service, we first use the already mentioned reflectors for simplicity reasons. In these experiments 66 reflectors are used with water as matrix material. The inclusion (reflector) materials are brass, copper, steel and polystyrene. From the time domain signals we extract three features, namely, pulse duration, pulse decay rate and peak-to-peak relative amplitude of the third cycle. From the spectra of the echoes we extract the frequency for maximum amplitude and the standard error estimate from the deconvolved spectrum responses.All experimental signals were obtained using only one normal incident ultrasonic transducer aligned to maximise the direct reflected signal. In spite of the fact that this kind of configuration does not provide complete information about the characteristics of the geometries being studied, all the extracted features proved to be important discriminating factors of the geometrical classes considered, as will be demonstrated by making use of a pattern recognition technique for classification.     

Reinforcement of hydroxyapatite by adding P2O5-CaO glasses with Na2O, K2O and MgO

Commercial hydroxyapatite was reinforced by adding small amounts (2 and 4 wt%) of P₂O₅-based glasses during its sintering process. The composites prepared had a chemical composition closely related to the mineral part of bone tissues in terms of trace elements usually detected, such as Na, K and Mg. X-ray diffraction analysis (XRD) showed that the glass reinforced-HA composites were composed of a HA matrix and variable amounts of tricalcium phosphate phase, depending on sintering temperature and glass composition. These composites were shown to have much higher biaxial bending strength than sintered HA, 107 MPa for Ha/2% of 35P₂O₅-35CaO-10Na₂O-10K₂O-10MgO glass composite and 28 MPa for sintered HA. The presence of -tricalcium phosphate in the microstructure of the composites is an important factor in the reinforcement process.This paper was accepted for publication after the 1995 Conference of the European Society of Biomaterials, Oporto. Portugal, 10–13 September.     

The effect of left displacement of abomasum corrected by toggle-pin suture on lactation,reproduction, and health of Holstein dairy cows

Our objectives were to evaluate the effect of left displacement of abomasum (LDA) after correction by toggle-pin suture (TPS) on lactation performance, reproduction and health in Holstein dairy cows in a commercial dairy farm. Cows diagnosed with LDA and corrected by the TPS procedure (188 cows) during the first 70 d postpartum were matched with control herd-mates (186 controls) according to lactation number, calving date, and previous lactation 305-d mature equivalent milk yield. Cows were grouped according to parity and days in milk and fed the same total mixed ration throughout a 321-d lactation. Data collected included yields of milk and 3.5% fat-corrected milk (FCM), concentration and yields of milk fat, somatic cell count, incidence of mastitis, abortion, death and culling, in addition to reproductive measures. Cows affected with LDA corrected by the TPS procedure produced less milk and tended to produce less 3.5% FCM than control cows, but the decrease in production occurred only during the first 4 mo of lactation. Left displacement of abomasum did not affect the interval from calving to conception and conception rates, but it extended the period from calving to first postpartum artificial insemination. Incidences of abortions and mastitis were not influenced by LDA. Cows affected with LDA remained in the study for a shorter period than their control herdmates, and higher proportions of cows with LDA were sold or died. Death and culling were more pronounced immediately after the diagnosis of LDA and the TPS procedure.     

An industry experiment on the effects of test-driven development on external quality and productivity

Existing empirical studies on test-driven development (TDD) report different conclusions about its effects on quality and productivity. Very few of those studies are experiments conducted with software professionals in industry. We aim to analyse the effects of TDD on the external quality of the work done and the productivity of developers in an industrial setting. We conducted an experiment with 24 professionals from three different sites of a software organization. We chose a repeated-measures design, and asked subjects to implement TDD and incremental test last development (ITLD) in two simple tasks and a realistic application close to real-life complexity. To analyse our findings, we applied a repeated-measures general linear model procedure and a linear mixed effects procedure. We did not observe a statistical difference between the quality of the work done by subjects in both treatments. We observed that the subjects are more productive when they implement TDD on a simple task compared to ITLD, but the productivity drops significantly when applying TDD to a complex brownfield task. So, the task complexity significantly obscured the effect of TDD. Further evidence is necessary to conclude whether TDD is better or worse than ITLD in terms of external quality and productivity in an industrial setting. We found that experimental factors such as selection of tasks could dominate the findings in TDD studies.     

Mechanosynthesis of the multiferroic cubic spinel Co2MnO4: Influence of the calcination temperature

Multiferroic materials showing magnetoelectric coupling are required in various technological applications. Many synthetical approaches can be used to improve the magnetic and/or electrical properties, in particular when the materials exhibit cationic valence fluctuations, as in the Co₂MnO₄ cubic spinel. In this compound, Co and Mn ions are in competition at the tetrahedral and octahedral positions, depending on their various oxidation states. The Co₂MnO₄ was prepared following two techniques: by a soft chemical route based on a modified polymer precursor method, and by a mechanoactivation route. Both approaches yield polycrystalline powders, but their crystallites sizes and particles morphologies differ as a function of the calcination conditions. The magnetic characterization (ZFC/FC cycles, ordering temperatures, ferromagnetic coercive fields and saturation magnetizations) showed that the synthesis procedure influenced the physical properties of Co₂MnO₄ mainly through the size of the magnetic domains, which play an important role on the magnetic interactions between the Co/Mn cations.