293 research outputs found
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.
Low load Pt catalyst with surface functionalised carbon supports for PEM fuel cells: half and full cell asssessments
ABSTRACT: Current US DOE 2020 targets for electrocatalysts aim for a total platinum group metals (PGM) loading of 0.125 mgcm-2 on membrane-electrode assemblies. The catalysts are expected to endure an elevated number of load cycles in order to comply with the expected 5000 h stack lifetime. At the stated PGM low loading attributes of performance, power and durability, as well as costs, are simultaneously required. The
present paper deals with performance assessment of new catalyst using Pt nanoparticles and a surface functionalized carbon support. Due to its relevance to fuel cell operation, the stability and durability were assessed in half cell mode, through the application of demanding aging cycling protocols (30000 cycles). Full fuel cell assessments were also conducted entailing power density curves and cell electrochemical impedance. Results denote significant improvements in cell performance as well as in catalyst stability, regarding a commercial catalyst tested in the same conditions, at Pt loadings of 0.1 mgcm-2.N/
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 impact of artificial intelligence on commercial management
The essence of this research is to shed light on use and importance of artificial intelligence (AI) in commercial activity. As such, the objective of the present study is to understand the impact of AI tools on the development of business functions and if they can be affirmed as a means of help or as a substitute for these functions. In-depth interviews were conducted with 15 commercial managers from technological SMEs. The results indicate that all the participants use AI systems frequently, that these tools assist in developing of their functions, allowing having more time and better preparing to solve the commercial problems. The findings also indicate that the tools used by commercials are still somewhat limited, and companies should focus on their training and development in AI, as well as the training of their commercials. Furthermore, the results show that firms intend to use the data collection and the analytical tool that enable real-time response and customization according to customer needs.info:eu-repo/semantics/publishedVersio
the next frontier in medicine
PM003/2016publishersversionpublishe
2,2'-(2,2'-oxybis(ethane-2,1-diyl)bis(oxy))bis(N-(2,2'-bithiophen-5-ylmethylene)aniline)
We would like to thank Xunta de Galiza (Spain) for project 09CSA043383PR and the University of Vigo, Vicou for projects INOU UVIGO/VICOU/K914-122P64702/2009 and UVIGO/VICOU/K912-122P64702/2009. Thanks to the FCT-MCTES/FEDER (Portugal) through national projects POCI/QUI/55519/2004 and PDTC/QUI/66250/2006. B. P thanks FCT/Portugal for the PhD Grant SFRH/BD/27786/2006. C.L. and J.L. thank Xunta de Galicia for the Isidro Parga Pondal Research Program.A new flexible fluorescent compound L derived from 1,5-bis(2-aminophenoxy)-3-oxapentane (A) has been synthesized by classical Schiff-base reaction between (A) and 2,2 ́-bithiophene carbaldehyde (B). The same synthesis was reproduced by a green methodology using an ultrasonication reaction in a classical sonication bath. The structure of the new compound was confirmed by elemental analysis, IR, 1H-NMR, MALDI-TOF-MS and EI-MS-spectra, UV-vis and fluorescence emission spectroscopy.publishersversionpublishe
Light, medium-weight or heavy? The nature of the first supermassive black hole seeds
Observations of hyper-luminous quasars at reveal the rapid growth of
supermassive black holes (SMBHs ) whose origin is still
difficult to explain. Their progenitors may have formed as remnants of massive,
metal free stars (light seeds), via stellar collisions (medium-weight seeds)
and/or massive gas clouds direct collapse (heavy seeds). In this work we
investigate for the first time the relative role of these three seed
populations in the formation of SMBHs within an Eddington-limited gas
accretion scenario. To this aim, we implement in our semi-analytical
data-constrained model a statistical description of the spatial fluctuations of
Lyman-Werner (LW) photo-dissociating radiation and of metal/dust enrichment.
This allows us to set the physical conditions for BH seeds formation, exploring
their relative birth rate in a highly biased region of the Universe at .
We find that the inclusion of medium-weight seeds does not qualitatively change
the growth history of the first SMBHs: although less massive seeds () form at a higher rate, the mass growth of a
SMBH at is driven by efficient gas accretion (at a sub-Eddington rate)
onto its heavy progenitors (). This conclusion holds
independently of the critical level of LW radiation and even when medium-weight
seeds are allowed to form in higher metallicity galaxies, via the so-called
super-competitive accretion scenario. Our study suggests that the genealogy of
SMBHs is characterized by a rich variety of BH progenitors, which
represent only a small fraction () of all the BHs that seed
galaxies at .Comment: (21 pages, 18 figures, 2 tables. Accepted for publication in MNRAS
Observation of aerodynamic instability in the flow of a particle stream in a dilute gas
Forming macroscopic solid bodies in circumstellar discs requires local dust
concentration levels significantly higher than the mean. Interactions of the
dust particles with the gas must serve to augment local particle densities, and
facilitate growth past barriers in the metre size range. Amongst a number of
mechanisms that can amplify the local density of solids, aerodynamic streaming
instability (SI) is one of the most promising. This work tests the physical
assumptions of models that lead to SI in protoplanetary disks (PPDs). We
conduct laboratory experiments in which we track the three-dimensional motion
of spherical solid particles fluidized in a low-pressure, laminar,
incompressible, gas stream. The particle sizes span the Stokes-Epstein drag
regime transition and the overall dust-to-gas mass density ratio is close to
unity. Lambrechts et al. (2016) established the similarity of the laboratory
flow to a simplified PPD model flow. We obtain experimental results suggesting
an instability due to particle-gas interaction: i) there exist variations in
particle concentration in the direction of the mean drag forces; ii) the
particles have a tendency to 'catch up' to one another when they are in
proximity; iii) particle clumping occurs on very small scales, which implies
local enhancements above the background dust-to-gas mass density ratio by
factors of several tens; v) the presence of these density enhancements occurs
for a mean dust-to-gas mass density ratio approaching or greater than 1; v) we
find evidence for collective particle drag reduction when the local particle
number density becomes high and when the background gas pressure is high so
that the drag is in the continuum regime. The experiments presented here are
precedent-setting for observing SI under controlled conditions and may lead to
a deeper understanding of how it operates in nature.Comment: Accepted for publication in A&A; abstract abridged for arXi
Identification of genomic loci associated with genotypic and phenotypic variation among Pseudomonas aeruginosa clinical isolates from pneumonia
In this work, a genotype-phenotype survey of a highly diversified Pseudomonas aeruginosa collection was conducted, aiming to detail pathogen-associated scenarios that clinicians face nowadays. Genetic relation based on RAPD-PCR of 705 isolates, retrieved from 424 patients and several clinical contexts, reported an almost isolate-specific molecular-pattern. Pneumonia-associated isolates HB13 and HB15, clustered in the same RAPD-PCR group, were selected to evaluate the genomic background underlying their contrasting antibiotic resistance and virulence. The HB13 genome harbors antibiotic-inactivating enzymes-coding genes (e.g. aac(3)-Ia, arr, blaVIM-2) and single-nucleotide variations (SNVs) in antibiotic targets, likely accounting for its pan-resistance, whereas HB15 susceptibility correlated to predicted dysfunctional alleles. Isolate HB13 showed the unprecedented rhl-cluster absence and variations in other pathogen competitiveness contributors. Conversely, HB15 genome comprises exoenzyme-coding genes and SNVs linked to increased virulence. Secretome analysis identified signatures features with unknown function as potential novel pathogenic (e.g. a MATE-protein in HB13, a protease in HB15) and antibiotic resistance (a HlyD-like secretion protein in HB13) determinants. Detection of active prophages, proteases (including protease IV and alkaline metalloproteinase), a porin and a peptidase in HB15 highlights the secreted arsenal likely essential for its virulent behavior. The presented phenotype-genome association will contribute to the current knowledge on Pseudomonas aeruginosa pathogenomics.This work was supported by the strategic programme UID/BIA/0050/2013 (POCI-01-0145-FEDER-007569) funded by national funds through FCT I.P., by ERDF through the COMPETE2020 - Programa Operacional Competitividade e Internacionalização (POCI) and through a PhD grant (SFRH/BD/98558/2013) attributed to C.S.M. The facility for Biological Mass Spectrometry Isabel Moura was funded by Proteomass Scientific Society. H.M.S. is funded by the FCT 2015 Investigator Program (IF/00007/2015)
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
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