1,555 research outputs found

    a new approach for life cycle impact assessment

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    Publisher Copyright: © 2023 The AuthorsAll plastic contains additives. Once in the environment, these will start to leach out and will expose and harm aquatic biota, causing potentially lethal and sub-lethal toxic effects. Even though life cycle assessment covers the toxic impacts of several thousands of chemicals, models to assess the toxic impacts of plastic additives are only emerging. We gathered 461 data points from the literature (266 for freshwater and 195 for marine ecosystems) for 75 species belonging to 9 different phyla. The endpoints effective concentration and lethal concentration, no observed effects concentrations and lowest observed effect concentration tested in acute and chronic exposure, were harmonized into chronic values by applying extrapolation factors. The collected data points covered 75 main plastic additives. This allowed us to calculate 25 Effect factors, 19 for single chemicals and four for overarching categories (alkylphenols, benzophenones, brominated flame retardants and phosphates. In addition, we calculated an aggregated effect factor for chemicals that did not fit in any of the previous groups, as well as a Generic effect factor including 404 gathered data points. The estimated potentially affected fraction (PAF) for the single additives varied between 20.69 PAF·m3·kg−1 for diethyl phthalate and 11081.85 PAF·m3·kg−1 for 4-Nonylphenol. The factors can in future be combined with fate and exposure factors to derive a characterization factor for toxicity caused by additives in aquatic species. This is an important advancement for the assessment of the impacts of plastic debris on aquatic species, thus providing information for decision-makers, as well as guiding policies for the use of additives, ultimately aiming to make the plastic value chain more sustainable.publishersversionpublishe

    Excitation Mechanisms and Characterization of a Multi-Ionic Xenon Laser

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    The emission characteristics of an ultraviolet-visible pulsed multi-ionic xenon laser were studied through time-resolved spectroscopy and the results were interpreted using a collisional radiative theoretical model. This analysis includes more than 20 laser lines belonging to several ionic species (Xe III VIII). Depending on the experimental conditions, different temporal distributions of the laser lines and their corresponding sponta neous emissions can be observed. In particular, laser emission presents temporal oscillations near threshold. Pumping processes for the laser transitions have been analyzed by using this model. Relativistic Hartree Fock calculations of laser level lifetimes and radiative transition probabilities were performed. Experimental laser gain for several transitions were obtained and compared with the theoretical values derived from the calculations.Facultad de Ingenierí

    Excitation Mechanisms and Characterization of a Multi-Ionic Xenon Laser

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    The emission characteristics of an ultraviolet-visible pulsed multi-ionic xenon laser were studied through time-resolved spectroscopy and the results were interpreted using a collisional radiative theoretical model. This analysis includes more than 20 laser lines belonging to several ionic species (Xe III VIII). Depending on the experimental conditions, different temporal distributions of the laser lines and their corresponding sponta neous emissions can be observed. In particular, laser emission presents temporal oscillations near threshold. Pumping processes for the laser transitions have been analyzed by using this model. Relativistic Hartree Fock calculations of laser level lifetimes and radiative transition probabilities were performed. Experimental laser gain for several transitions were obtained and compared with the theoretical values derived from the calculations.Facultad de Ingenierí

    Evidence for the evolutionary steps leading to mecA-mediated ß-lactam resistance in staphylococci

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    The epidemiologically most important mechanism of antibiotic resistance in Staphylococcus aureus is associated with mecA–an acquired gene encoding an extra penicillin-binding protein (PBP2a) with low affinity to virtually all β-lactams. The introduction of mecA into the S. aureus chromosome has led to the emergence of methicillin-resistant S. aureus (MRSA) pandemics, responsible for high rates of mortality worldwide. Nonetheless, little is known regarding the origin and evolution of mecA. Different mecA homologues have been identified in species belonging to the Staphylococcus sciuri group representing the most primitive staphylococci. In this study we aimed to identify evolutionary steps linking these mecA precursors to the β-lactam resistance gene mecA and the resistance phenotype. We sequenced genomes of 106 S. sciuri, S. vitulinus and S. fleurettii strains and determined their oxacillin susceptibility profiles. Single-nucleotide polymorphism (SNP) analysis of the core genome was performed to assess the genetic relatedness of the isolates. Phylogenetic analysis of the mecA gene homologues and promoters was achieved through nucleotide/amino acid sequence alignments and mutation rates were estimated using a Bayesian analysis. Furthermore, the predicted structure of mecA homologue-encoded PBPs of oxacillin-susceptible and -resistant strains were compared. We showed for the first time that oxacillin resistance in the S. sciuri group has emerged multiple times and by a variety of different mechanisms. Development of resistance occurred through several steps including structural diversification of the non-binding domain of native PBPs; changes in the promoters of mecA homologues; acquisition of SCCmec and adaptation of the bacterial genetic background. Moreover, our results suggest that it was exposure to β-lactams in human-created environments that has driven evolution of native PBPs towards a resistance determinant. The evolution of β-lactam resistance in staphylococci highlights the numerous resources available to bacteria to adapt to the selective pressure of antibiotics

    Revised and extended analysis in four times ionized xenon Xe V

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    The atomic-emission spectrum of four times ionized xenon (Xe V) has been observed in the region 500–6700 Å; 233 lines were classified as transition between 5s5p3, 5s25p5d, 5s25p6s with 5s25p2, 5s25p6p and 5s25p4f configurations. Ninty-seven of these lines are reported for the first time. Two new energy level values corresponding to the 5s25p4f configuration have been determined, and we proposed two new values for the previously reported 3D1 and 3G5 energy levels of this configuration. The value of the 5s25p6p 1S0 energy level has also been determined, and we propose a new value for the previously reported 5s25p5d 3F4 energy level. New adjusted values for the previously known levels of the studied configurations are included. Least-squares fitted parametric calculations involving configuration interactions have been carried out to interpret the observed spectrum.Facultad de Ciencias ExactasCentro de Investigaciones Óptica

    Revised and extended analysis in four times ionized xenon Xe V

    Get PDF
    The atomic-emission spectrum of four times ionized xenon (Xe V) has been observed in the region 500–6700 Å; 233 lines were classified as transition between 5s5p3, 5s25p5d, 5s25p6s with 5s25p2, 5s25p6p and 5s25p4f configurations. Ninty-seven of these lines are reported for the first time. Two new energy level values corresponding to the 5s25p4f configuration have been determined, and we proposed two new values for the previously reported 3D1 and 3G5 energy levels of this configuration. The value of the 5s25p6p 1S0 energy level has also been determined, and we propose a new value for the previously reported 5s25p5d 3F4 energy level. New adjusted values for the previously known levels of the studied configurations are included. Least-squares fitted parametric calculations involving configuration interactions have been carried out to interpret the observed spectrum.Facultad de Ciencias ExactasCentro de Investigaciones Óptica
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