Monitoring Corrosion Products on Metal Artefacts by Linear Sweep Voltammetry (LSV)

Metallic surfaces are highly sensitive to their surroundings, and prone to react with airborne pollutants to form complex layers. Electrochemical techniques have the possibility of simultaneously identifying different electroactive compounds [1]. The high sensitivity of Linear Sweep Voltammetry (LSV) allows the detection of extremely thin surface films before they became visible. LSV leads to reduction peaks, which can identify the compounds within the “tarnishing” layer and also its relative abundance [1, 2]. The potentialities of this and others electrochemical techniques has been well demonstrated in several recent works and they seem to be promising and non-invasive tools, even for in situ investigations on the metallic artifacts from cultural heritage. This communication presents data showing the application of the technique to silver and sterling silver coupons exposed, during periods of 1 and 12 months, in the Treasure Room in the Museum (inside showcases) and near the Holy Altar of the Chapel, of Porto Cathedral (Portugal). The influence of various conditions: the atmosphere (Museum and Chapel), exposure time (1 and 12 months) and season (spring, summer, autumn and winter) have been analysed. The LSV spectra of blank polished samples as well as samples covered with thin films of silver sulphide and of silver chloride, formed under controlled conditions, respectively: (i) H2S, 1000 ppm, RH= 53% ± 2, T= 21 ºC ± 1, over periods of 24, 48 and 72 h) and (ii) 3.5% of NaCl, RH=41% periods of 5 h, have been used as references. Concerning the nature of the products developed on the surface during the exposure, data has revealed that the tarnishing layers have a complex nature and are not composed only by silver sulphide. It happens even that silver sulphide is a relative minor component in the tarnish layer. Peaks corresponding to silver chloride and silver oxides were well visible. Small peaks assigned to silver sulphide were identified on the samples exposed in the Chapel. For the 12 months exposures both peaks have increased in size with the peak assigned to chloride being much higher in the case of the Chapel. The seasonal influence, even for the 1 month exposures, was particularly notable on those samples with exposures started in winter with well visible effects on the chloride peak on the tarnish layer of the samples exposed in the Chapel. Obviously, that to obtain analytical information electrochemical techniques can be complemented with spectroscopic techniques, namely, X- ray photon spectroscopy (XPS), laser induced breakdown spectroscopy (LIBS), x-rays fluorescence spectroscopy, among others. [1] A. Doménech-Carbó, M.T. Doménech-Carbó, V. Costa (2009), Electrochemical Methods in Archaeometry, Conservation and Restoration, Berlin: F. Scholz. [2] V. Costa, M. Dubus (2007), Impact of the environmental conditions on the conservation of metal artifacts: an evaluation using electrochemical techniques, in National Museum of Denmark, Museum Microclimates, Copenhagen: T. Padfield and K. Borchersen, 63-65

Phytosociologic associations and Natura 2000 habitats of Portuguese coastal sand dunes

The Portuguese coastline is quite long and the littoral ecosystems are of the outmost importance in the context of the national flora and vegetation. The diversity of vegetation types and the endemicity of their flora justify the attention paid to coastal habitats in the implementation of the Natura 2000 network. In this paper we present a synatoxonomical revision of the phanerophytic, chamaephytic and hemicryptophytic communities occurring in the sandy coastal areas of Portugal, together with their correspondence to the “Natura 2000” natural habitat types. The production of synthetic tables with all available relevés has allowed the segregation of plant community types. We also include maps concerning the distribution of all validated vegetation types occurring in the Portuguese sandy coastal areas.info:eu-repo/semantics/publishedVersio

Teaching the dynamics of the growth of a business venture through transparent simulations

Achieving rapid and sustainable growth is essential for business ventures to succeed. This being so, future entrepreneurs need to understand and manage the dynamics of business growth. Simulation-based learning environments (SBLEs) have been proposed as effective tools to help learners improve their understanding of complex business problems. However, previous research has found that learners tend to underestimate dynamic complexity. Transparent simulations allow entrepreneurship learners to explore the dynamic complexity of business ventures while accessing the model structure and growth behaviour. Previous studies have addressed some aspects of model transparency and produced inconclusive results regarding their impact on learning effectiveness. This study explores the learning and performance effects of using transparent simulations to teach the dynamics of the growth of a business venture. One such simulation experiment used a system dynamics model that represented the development of an energy service company (ESCO) venture under varying conditions of simulator transparency. Students who were subjected to the more transparent strategy achieved higher performance and demonstrated better comprehension of the business dynamics. However, our findings indicate that the effect to be gained from making only the simulator model more visible is more limited. The structural debriefing (focused on the critical variables and relations) was determinant in improving students’ learning regarding the stocks and flows structure in the prospects pipeline. Only after participating in the behavioural debriefing (focused on the relation between model structure, patterns of actions, and system behaviour), were the students able to appreciate the dynamics of the business feedback loops. The research suggests that educators who use complex business simulations should complement model transparency with structural and behavioural debriefings.info:eu-repo/semantics/acceptedVersio

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 comparison of black hole growth in galaxy mergers with Gasoline and Ramses

Supermassive black hole dynamics during galaxy mergers is crucial in determining the rate of black hole mergers and cosmic black hole growth. As simulations achieve higher resolution, it becomes important to assess whether the black hole dynamics is influenced by the treatment of the interstellar medium in different simulation codes. We here compare simulations of black hole growth in galaxy mergers with two codes: the Smoothed Particle Hydrodynamics code Gasoline, and the Adaptive Mesh Refinement code Ramses. We seek to identify predictions of these models that are robust despite differences in hydrodynamic methods and implementations of sub-grid physics. We find that the general behavior is consistent between codes. Black hole accretion is minimal while the galaxies are well-separated (and even as they "fly-by" within 10 kpc at first pericenter). At late stages, when the galaxies pass within a few kpc, tidal torques drive nuclear gas inflow that triggers bursts of black hole accretion accompanied by star formation. We also note quantitative discrepancies that are model-dependent: our Ramses simulations show less star formation and black hole growth, and a smoother gas distribution with larger clumps and filaments, than our Gasoline simulations. We attribute these differences primarily to the sub-grid models for black hole fueling and feedback and gas thermodynamics. The main conclusion is that differences exist quantitatively between codes, and this should be kept in mind when making comparisons with observations. However, reassuringly, both codes capture the same dynamical behaviors in terms of triggering of black hole accretion, star formation, and black hole dynamics.Comment: 11 pages, 7 figures. Submitted to A&A. Comments welcom

The landscape and plant communities of Serra da Arrábida

The field trip takes place in the biogeographic territories of the Sadensean-Dividing Portuguese Subprovince (Coastal Lusitan- Andalusian Province, Mediterranean Region), throughout the upper thermomediterranean thermotype and subhumid ombrotype

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.

Controlling pollution effects on metallic cultural heritage using linear sweep voltammetry

This work demonstrates the potentialities of the linear sweep voltammetry (LSV) for monitoring the composition of the tarnishing layers formed on silver and on the silver-copper alloys exposed to atmospheres contaminated with pollutants, such as H2S and chloride ions, among others. A collection of silver and sterling silver coupons exposed during periods of 1 and 12 months, at the Holy Altar of the Chapel and at the Treasure Room of the Museum, both of the Porto Cathedral (Portugal), with exposures started in march 2010 and ending in march 2011, have been analysed by LSV. The LSV spectra of blank polished samples as well as samples covered with thin films of silver sulphide and of silver chloride, formed under controlled conditions, respectively: (i) H2S, 1000 ppm, RH= 53% ± 2, T= 21˚C ± 1, over periods of 24, 48 and 72 h and (ii) 3.5% of NaCl, RH=41%, T= 43˚C, periods of 5 h, have been used as references. The influence of the atmosphere (Chapel and Museum), exposure time (1 and 12 months) and season, in which the exposures were started, (spring, summer, autumn and winter) have been analysed on the LSVs of the coupons exposed to the various conditions. For the 1 month exposures started in spring the peaks corresponding to the silver sulphide and silver chloride were, as expected, higher on the samples exposed in the Chapel. For the 12 months exposures both peaks have increased in size with the peak assigned to chloride being much higher in the case of the Chapel and the reverse observed in the case of the Museum. The seasonal influence, even for the 1 month exposures was particularly notable on those started in winter with well visible effects on the sulphide and chloride peaks respectively, in the Museum and Chapel exposures

Synthesis of gold functionalised nanoparticles with the eranthis hyemalis lectin and preliminary toxicological studies on caenorhabditis elegans

The lectin found in the tubers of the Winter Aconite (Eranthis hyemalis) plant (EHL) is a Type II Ribosome Inactivating Protein (RIP). Type II RIPs have shown anti-cancer properties and have great potential as therapeutic agents. Similarly, colloidal gold nanoparticles are successfully used in biomedical applications as they can be functionalised with ligands with high affinity and specificity for target cells to create therapeutic and imaging agents. Here we present the synthesis and characterization of gold nanoparticles conjugated with EHL and the results of a set of initial assays to establish whether the biological effect of EHL is altered by the conjugation. Gold nanoparticles functionalised with EHL (AuNPs@EHL) were successfully synthesised by bioconjugation with citrate gold nanoparticles (AuNPs@Citrate). The conjugates were analysed by UV-Vis spectroscopy, Dynamic Light Scattering (DLS), Zeta Potential analysis, and Transmission Electron Microscopy (TEM). Results indicate that an optimal functionalisation was achieved with the addition of 100 µL of EHL (concentration 1090 ± 40 µg/mL) over 5 mL of AuNPs (concentration [Au0] = 0.8 mM). Biological assays on the effect of AuNPs@EHL were undertaken on Caenorhabditis elegans, a free-living nematode commonly used for toxicological studies, that has previously been shown to be strongly affected by EHL. Citrate gold nanoparticles did not have any obvious effect on the nematodes. For first larval stage (L1) nematodes, AuNPs@EHL showed a lower biological effect than EHL. For L4 stage, pre-adult nematodes, both EHL alone and AuNPs@EHL delayed the onset of reproduction and reduced fecundity. These assays indicate that EHL can be conjugated to gold nanoparticles and retain elements of biocidal activity