A voltametria cíclica e de varrimento linear unidirecional: suas potencialidades na caraterização de processos de corrosão

Artigo licenciado sob uma Licença Creative Commons: https://creativecommons.org/licenses/by-nc/4.0/deed.pt"O artigo apresenta as técnicas da voltametria cíclica e da voltametria de varrimento linear unidirecional, que são métodos eletroquímicos extremamente úteis e versáteis no estudo do comportamento de um metal ou liga, face a ambientes mais ou menos agressivos. As potencialidades das técnicas são realçadas, assim como as vantagens introduzidas pela instrumentação digital. Trata-se de um artigo de divulgação, tendo por objetivo ser acessível a engenheiros, técnicos e outros, a trabalhar na área da corrosão. Para exemplificar o tipo de informação que pode ser obtida são apresentados resultados de vários estudos realizados pelos autores.

Galvanic corrosion of two non noble dental alloys

Artigo licenciado sob uma Licença Creative Commons: https://creativecommons.org/licenses/by/4.0/"This study aims to evaluate the corrosion resistance of two nonnoble dental alloys, namely, the Wiron®88 (Ni–Cr–Mo) and the Remanium 2000+ (Co–Cr–Mo–W). A noble alloy, the V-Gnathos® Plus (AuPt) previously studied was also considered for the purpose of comparison. The study was conducted in artificial saliva, pH 7.1, at 37 °C, by cyclic and linear sweep voltammetry, electrochemical impedance spectroscopy and chronoamperometry. The Rp value of the alloy of high contents of Ni, the Wiron®88, was 26.2±0.2 kΩ cm2 and of the one with high contents of Co, the Remanium 2000+, was 22.5±0.6 kΩ cm2. Data from linear polarization resistance and electrochemical impedance spectroscopy lead to the same order for the resistance against corrosion. The order from the less to the more reactive alloy is: Wiron®88 → Remanium 2000+. The galvanic cell obtained by coupling the two nonnoble alloys presents very low cell potential (a few mV, -18 mV), while the galvanic cell between one noble alloy (the V-Gnathos® Plus) and the Wiron®88 showed a higher cell potential (-104 mV). Both galvanic couples, under short circuit, have lead to the release of cations, namely, Co2+, in the case of the Wiron®88|Remanium 2000+ and Ni2+ for the Wiron®88|V-Gnathos® Plus, galvanic couples, respectively, with the ionic concentrations reaching values of 12.15 and 7.30 μg L-1 (7.30 ppb), respectively. SEM micrographs obtained after 25 days immersion in artificial saliva, at 37 °C, showed the formation of well-defined pits on the surface of the two non-noble alloys.

The polytropic approximation and X-ray scaling relations: constraints on gas and dark matter profiles for galaxy groups and clusters

We constrain gas and dark matter (DM) parameters of galaxy groups and clusters, by comparing X-ray scaling relations to theoretical expectations, obtained assuming that the gas is in hydrostatic equilibrium with the DM and follows a polytropic relation. We vary four parameters: the gas polytropic index Gamma, its temperature at large radii T_xi, the DM logarithmic slope at large radii zeta and its concentration c_vir. When comparing the model to the observed mass-temperature (M-T) relation of local clusters, our results are independent of both T_xi and c_vir. We thus obtain constraints on Gamma, by fixing the DM profile, and on zeta, by fixing the gas profile. For an NFW DM profile, we find that 6/5<Gamma<13/10, which is consistent with numerical simulations and observations of individual clusters. Taking 6/5<Gamma<13/10 allows the DM profile to be slightly steeper than the NFW profile at large radii. Upon including local groups, we constrain the mass-dependence of Gamma and the value of T_xi. Interestingly, with Gamma=6/5 and zeta=-3, we reproduce the observed steepening/breaking of the M-T relation at low M, if 10^6 K<T_xi<10^7 K, consistent with simulations and observations of the warm-hot intergalactic medium. When extrapolated to high redshift z, the model with a constant Gamma reproduces the expected self-similar behaviour. We also account for the observed, non-self-similar relations provided by some high-z clusters, as they provide constraints on the evolution of Gamma. Comparing our model to the observed luminosity-temperature relation, we discriminate between different M-c_vir relations: a weak dependence of c_vir on M is currently preferred by data. This simple theoretical model accounts for much of the complexity of recent, improved X-ray scaling relations, provided that we allow for a mild dependence of Gamma on M or for T_xi consistent with intercluster values. [abridged]Comment: 20 pages, 18 figures, 2 tables. Accepted for publication in MNRAS, with minor changes. Accepted version plus two typos corrected. Abstract abridged for astro-ph submissio

Intramolecular excimer formation and sensing behavior of new fluorimetric probes and their interactions with metal cations and barbituric acids

A new family of compounds able to promote host-guest interactions with specific molecules (e.g., cyanuric and parabanic acids) and to coordinate metal ions, namely Zn(II) and Cu(II), has been synthesized and fully characterized. The new probes derive from the attachment of two methylaminopyrene units to the carbonyl precursor 2,6-bis(2-formylphenoxymethyl)pyridine.http://www.sciencedirect.com/science/article/B6THH-4HF5KD3-1/1/ef66847d1e019d05e2068bef93cfbd9

A population of luminous accreting black holes with hidden mergers

Major galaxy mergers are thought to play an important part in fuelling the growth of supermassive black holes. However, observational support for this hypothesis is mixed, with some studies showing a correlation between merging galaxies and luminous quasars and others showing no such association. Recent observations have shown that a black hole is likely to become heavily obscured behind merger-driven gas and dust, even in the early stages of the merger, when the galaxies are well separated (5 to 40 kiloparsecs). Merger simulations further suggest that such obscuration and black-hole accretion peaks in the final merger stage, when the two galactic nuclei are closely separated (less than 3 kiloparsecs). Resolving this final stage requires a combination of high-spatial-resolution infrared imaging and high-sensitivity hard-X-ray observations to detect highly obscured sources. However, large numbers of obscured luminous accreting supermassive black holes have been recently detected nearby (distances below 250 megaparsecs) in X-ray observations. Here we report high-resolution infrared observations of hard-X-ray-selected black holes and the discovery of obscured nuclear mergers, the parent populations of supermassive-black-hole mergers. We find that obscured luminous black holes (bolometric luminosity higher than 2x10^44 ergs per second) show a significant (P<0.001) excess of late-stage nuclear mergers (17.6 per cent) compared to a sample of inactive galaxies with matching stellar masses and star formation rates (1.1 per cent), in agreement with theoretical predictions. Using hydrodynamic simulations, we confirm that the excess of nuclear mergers is indeed strongest for gas-rich major-merger hosts of obscured luminous black holes in this final stage.Comment: To appear in the 8 November 2018 issue of Nature. This is the authors' version of the wor

Enhancing the teaching-research nexus in the undergraduate curriculum through assessment

Successful linkages between teaching and research in the undergraduate curriculum are strongly dependent on academics’ ability to encourage and facilitate an inquiry based approach to learning. An assessment strategy in which students become active participants in the assessment process is crucial to facilitate the development of this inquiry based approach. Developing this so-called research-mindedness is central to helping students' to become independent learners and to be more effective professionals in their future careers. This paper describes a distributed systems approach to assessment implemented in the undergraduate module Molecular Biology. The assessment comprised a series of sequence identification, database use and analysis steps, with each student being given a different starting gene. In combination, the students analysed an entire genetic pathway. This approach allows the assignments generated to be combined and used to address a single larger question, which can be either teaching or research based. This is then fed back into the teaching. This direct link between the assessment outcomes and the learning process increases student engagement with the subject and sense of ownership of the work carried out. This approach to assessment, in which students undertake a small part of a larger task, is ideal for various technical, skills-based, assignments, such as those central to the many types of bioinformatics analyses. However, it can be adapted to various types of meta-review. The paper discusses the details for the implementation, as well as the benefits and potential pitfalls of the approach

A Feedback Learning and Mental Models Perspective on Strategic Decision Making

This study aims to be a contribution to a theoretical model that explains the effectiveness of the learning and decision-making processes by means of a feedback and mental models perspective. With appropriate mental models, managers should be able to improve their capacity to deal with dynamically complex contexts, in order to achieve long-term success. We present a set of hypotheses about the influence of feedback information and systems thinking facilitation on mental models and management performance. We explore, under controlled conditions, the role of mental models in terms of structure and behaviour. A test based on a simulation experiment with a system dynamics model was performed. Three out of the four hypotheses were confirmed. Causal diagramming positively influences mental model structure similarity, mental model structure similarity positively influences mental model behaviour similarity, and mental model behaviour similarity positively influences the quality of the decision

Crowdsourced Mapping in Crisis Zones: Collaboration, Organisation and Impact

Crowdsourced mapping has become an integral part of humanitarian response, with high profile deployments of platforms following the Haiti and Nepal earthquakes, and the multiple projects initiated during the Ebola outbreak in North West Africa in 2014, being prominent examples. There have also been hundreds of deployments of crowdsourced mapping projects across the globe, that did not have a high profile. This paper, through an analysis of 51 mapping deployments between 2010–2016, complimented with expert interviews, seeks to explore the organisational structures that create the conditions for effective mapping actions, and the relationship between the commissioning body, often a Non-Governmental Organisation (NGO) and the volunteers who regularly make up the team charged with producing the map. The research suggests that there are three distinct areas that need to be improved in-order to provide appropriate assistance through mapping in humanitarian crisis; regionalise; prepare; and research. The paper concludes, based on the case studies, how each of these areas can be handled more effectively, concluding that failure to implement one area sufficiently can lead to overall project failure

Palynological evidence for environmental and climatic change in the lower Guadiana valley, Portugal, during the last 13 000 years

Pollen analysis of a 48 m AMS radiocarbon-dated sediment sequence from the Guadiana estuary provides the first record of Lateglacial and Holocene vegetation history in the Algarve province of Portugal. This paper focuses on the record of terrestrial pollen taxa, which document a series of forest expansions and declines during the period 13 000 cal. BP to 1600 cal. BP and provide insights into climate evolution in southwestern Iberia. The main vegetation phases identified in the Guadiana valley are (1) Lateglacial interstadial (Allerød) forest with Quercus and Pinus under a temperate, moist, continental climate; (2) a Younger Dryas forest decline (Quercus) and expansion of pinewoods, xeric scrub and open ground habitats (with Juniperus, Artemisia, Ephedra distachya type, Centaurea scabiosa type) under arid and cold conditions; (3) an early Holocene forest/scrub/open-ground vegetation mosaic developing under a warm, dry and continental climate; (4) a maximum of Quercus forest and thermomediterranean evergreen taxa (Olea, Phillyrea, Pistacia) reflecting a warm, moist oceanic climate between c. 9000 cal. BP and c. 5000 cal. BP; and (5) the expansion of shrublands with Cistaceae and Ericaceae under a drier climatic regime and increasing anthropogenic activity since c. 5000 cal. BP. Holocene episodes of maximum climatic aridity are identified in the record of xerophytic taxa (Juniperus, Artemisia, Ephedra distachya type) centred around 10 200 cal. BP, 7800 cal. BP, 4800 cal. BP, 3100 cal. BP and 1700 cal. BP. Regional comparisons suggest a correlation of arid phases across southern Iberia and northwest Africa, which can be related to abrupt North Atlantic coolings (Bond events).Research Council studentship for WJF (NERC/S/A/2001/06109), with the support of Trinity College and the Department of Geography, University of Cambridg