Determination of Arsenic, Mercury and Barium in herbarium mount paper using dynamic ultrasound-assisted extraction prior to atomic fluorescence and absorption spectrometry

A dynamic ultrasound-assisted extraction method using Atomic Absorption and Atomic Flourescence spectrometers as detectors was developed to analyse mercury, arsenic and barium from herbarium mount paper originating from the herbarium collection of the National Museum of Wales. The variables influencing extraction were optimised by a multivariate approach. The optimal conditions were found to be 1% HNO3 extractant solution used at a flow rate of 1 mL min-1. The duty cycle and amplitude of the ultrasonic probe was found to be 50% in both cases with an ultrasound power of 400 W. The optimal distance between the probe and the top face of the extraction chamber was found to be 0 cm. Under these conditions the time required for complete extraction of the three analytes was 25 min. Cold vapour and hydride generation coupled to atomic fluorescence spectrometry was utilized to determine mercury and arsenic, respectively. The chemical and instrumental conditions were optimized to provide detection limits of 0.01ng g-1 and 1.25 ng g-1 for mercury and arsenic, respectively. Barium was determined by graphite-furnace atomic absorption spectrometry, with a detection limit of 25 ng g-1. By using 0.5 g of sample, the concentrations of the target analytes varied for the different types of paper and ranged between 0.4–2.55 µg g-1 for Ba, 0.035–10.47 µg g-1 for As and 0.0046–2.37 µg g-1 for Hg

The N137 and P140 amino acids in the p51 and the P95 amino acid in the p66 subunit of human immunodeficiency virus type 1 (HIV-1) reverse transcriptase are instrumental to maintain catalytic activity and to design new classes of anti-HIV-1 drugs

Amino acids N137 and P140 in the p51 subunit of HIV-1 reverse transcriptase (RT) are part of the β7-β8-loop that contributes to the formation of the base of the non-nucleoside RT inhibitor (NNRTI)-binding pocket and makes up a substantial part of the dimerization interface. Amino acid P95 in p66 also markedly contributes to the dimerization binding energy. Nine RT mutants at amino acid 137 were constructed bearing the mutations Y, K, T, D, A, Q, S, H or E. The prolines at amino acid positions 95 and 140 were replaced by alanine in separate enzymes. We found that all mutant RT enzymes showed a dramatically decreased RNA-dependent DNA polymerase activity. None of the mutant RT enzymes showed marked resistance against any of the clinically used NNRTIs but they surprisingly lost significant sensitivity for NRTIs such as ddGTP. The denaturation analyses of the mutant RTs by urea are suggestive for a relevant role of N137 in the stability of the RT heterodimer and support the view that the β7-β8 loop in p51 is a hot spot for RT dimerization and instrumental for efficient polymerase catalytic activity. Consequently, N137 and P140 in p51 and P95 in p66 should be attractive targets in the design of new structural classes of RT inhibitors aimed at compromising the optimal interaction of the β7-β8 loop in p51 at the p66/p51 dimerization interface. © 2005 Federation of European Biochemical Societies. Published by Elsevier B.V. All rights reserved.We thank Kristien Minner for excellent technical assistance. This work was supported by the European Commission [No. QLRT-2000-30291 (HIV resistance), HPAW-2002-10004 (Rene´ Descartes Prize-2001) and QLRT-2001-01311 (Virulence)], the ‘‘Fonds voor Wetenschappelijk Onderzoek – Vlaanderen’’ (No. G-0267-04), a Research Grant from GlaxoSmithKline, Verona, Italy, and a Research Grant from the Spanish MEC (Ministerio de Educacion y Ciencia) (No. SAF2003-07219-C02-01). J.A. acknowledges a Ph.D. grant from the Institute for the Promotion of Innovation through Science and Technology in Flanders (IWT-Vlaande

Probing the Canis Major stellar over-density as due to the Galactic warp

Proper-motion, star counts and photometric catalog simulations are used to explain the detected stellar over-density in the region of Canis Major (CMa), claimed to be the core of a disrupted dwarf galaxy (Martin et al. 2004, Bellazzini et al. 2003), as due to the Galactic warp and flare in the external disk. We compare the kinematics of CMa M-giant selected sample with surrounding Galactic disk stars in the UCAC2 catalog and find no peculiar proper motion signature: CMa stars mimic thick disk kinematics. Moreover, when taking into account the Galactic warp and flare of the disk, 2MASS star count profiles reproduce the CMa stellar over-density. This star count analysis is confirmed by direct comparison with synthetic color-magnitude diagrams simulated with the Besancon models (Robin et al. 2003) that include the warp and flare of the disk. The presented evidence casts doubt on the identification of the CMa over-density as the core of a disrupted Milky Way satellite. This however does not make clear the origin of over-densities responsible for the ring structure in the anticenter direction of the Galactic halo (Newberg et al. 2002; Yanny et al. 2003; Zaggia et al. 2004, in preparation).Comment: Accepted for publication in A&A Letters, 4 page

The impact of global platforms on media competition and on the results of European communication companies

The market value and capitalization of traditional media companies have dropped dramatically in the last five years. This is due to the evolution of digital platforms and the emergence of global communications mega-corporations that have since absorbed the distribution of new information and entertainment content. It is also a consequence of the aggregation of value-added services generated through incessant innovation. Communications mega-corporations, the GAFANs (Google, Amazon, Facebook, Apple and Netflix), and audiovisual and telecommunications platforms reached market capitalizations ranging from 56% to 170% in the last five years (2012-17) respectively, whilst those of traditional media did not exceed 75 percent. Asymmetries on competition regulations against traditional media and the political alarm ignited by the so-called fake news or scandals due to the mishandling of users data awakened the European states and the EU about the urgency of filling the legal gap existing around the development of such platforms, particularly in order to demand rules and responsibilities comparable to those that apply to editorial groups.La cotización y capitalización de las empresas de medios tradicionales se ha hundido en los últimos cinco años ante la evolución de las plataformas digitales y la conformación de mega grupos globales de comunicación que absorben la distribución de los nuevos contenidos informativos y de entretenimiento, así como la agregación de los servicios de valor añadido generados a través de su incesante innovación. Los mega grupos de comunicación, los GAFAN (Google, Amazon, Facebook, Apple y Netflix), y las plataformas de audiovisual y telecomunicaciones lograron en los últimos cinco años (2012-17) capitalizaciones de entre el 560 y el 170% respectivamente, frente a las de los medios tradicionales, que no pasaron del 75 por ciento. La asimetría de la regulación de la competencia frente a los medios tradicionales y la alarma política provocada por las fake news o los escándalos del uso impropio de datos de los usuarios despertó a los estados europeos y a la propia UE sobre la urgencia de llenar el vacío legal sobre el desarrollo de las plataformas para exigirles reglas de juego y responsabilidades como a los grupos editoriales

Trophic models and short-term dynamic simulations for benthic-pelagic communities at Banco Chinchorro Biosphere Reserve (Mexican Caribbean): a conservation case

Banco Chinchorro is the largest reef in the Mexican Caribbean. Historically, spiny lobster, queen conch and over 20 other reef species have been exploited here. Multispecies intervention management from an ecosystem perspective has been developed in this area; however, an assessment of the effects of such practices on ecosystem health is required. Five quantitative trophic models were constructed using Ecopath with Ecosim. The results show that, in terms of biomass, benthic autotrophs are the dominant group in all communities. Ecosystem Network Analysis indices showed that Cueva de Tiburones was the most mature, developed, complex and healthy subsystem, but, El Colorado and La Baliza were the subsystems most resistant to disturbances. The fisheries mainly concentrate on primary (La Baliza and Cueva de Tiburones sites) and secondary consumers (La Caldera, Chancay, and El Colorado). The greatest propagation of direct and indirect effects, estimated by Mixed Trophic Impacts and Ecosim simulations, were generated by the benthic autotrophs, small benthic epifauna, benthic-pelagic carnivorous fish and benthic carnivorous fish, among others. In contrast, the System Recovery Time showed different patterns among subsystems, indicating several compartments that reduce resilience. Considering the structure, dynamics, trophic functioning and ecosystem health of Banco Chinchorro, its ecological heterogeneity highlights the need for the design of a specific (by subsystem) management strategy, particularly because different species or functional groups present greater sensitivity to human interventions in each community

Experimental evidence of contamination on the dynamics of shrimp populations: susceptibility to spatial isolation

Landscape-scale ecology comprises complex structures where a flow of energy, materials and organisms among ecosystems conditions the dynamics of populations. Several natural and anthropogenic stressors are likely to affect the landscape composition, generally leading to the rupture of ecological connectivity among populations. Although contamination is considered one of the most threatening factors for biodiversity, its impact on spatial dynamics of populations (e.g., distribution, persistence and abundance) from an eco-toxicological perspective is still unknown. In the current study, the potential effect that contamination can exert on the loss of connectivity among populations (chemically fragmented habitats) leading to population isolation was assessed. The estuarine shrimp Palaemon varians was used as model organisms and a novel version of the HeMHAS (Heterogeneous Multi-Habitat Assay System) was used to simulate spatially heterogeneous landscapes. In order to provide more ecological relevance to the study, besides copper as stressor [at low (0.5 μg/L) and high (25 μg/L) levels], other two factors were simultaneously tested: fish kairomones (as a predation signal) and food availability. Different scenarios were simulated in the HeMHAS to create heterogeneous landscapes that vary depending on the presence or absence of these stressors. The behavior observed by the population of P. varians clearly showed that the shrimp detected copper and avoided the regions with the highest levels of contamination. However, when fish kairomones were added to previously preferred regions, the behavior of shrimp populations did a radical turn: they escape the predator signals, moving towards contaminated regions, but with a clear preference for less contaminated areas. When faced whether to stay in a clean area with no food or moving through disturbed regions to colonize a clean region with food, shrimps’ populations crossed the regions, but with a more dynamic transit in the region with kairomones and no copper. These results indicate that contamination might interfere in the spatial dynamics of shrimps’ populations by: (i) triggering avoidance, (ii) preventing colonization, (iii) isolating populations and (iv) making them more susceptible to local extinction

Experimental evidence of how contamination might modify the shrimps’ population dynamics and make them susceptible to spatial isolation

Contamination is likely to affect the landscape composition, usually linked to ecological fragmentation, which may impact the distribution, persistence and abundance of species. In the current study, the estuarine shrimp Palaemon varians was exposed to copper (25 and 0.5 μg/L) simultaneously to predation signal and food to evaluate the organism’s spatial distribution within a spatially heterogeneous landscape. All experimental landscapes were simulated in the Heterogeneous Multi Habitat Assay System (HeMHAS). As results, P. varians detected and avoided copper, however, predation signal shifted the response to preference over regions with conditions previously avoided, even if that meant to increase copper exposure. When confronted to move towards environments with high food availability, lower connectivity occurred among the shrimps’ populations isolated by contamination and predation risk simultaneously. This indicate that contamination might: (i) trigger avoidance in shrimps, (ii) prevent the colonisation towards foraging areas, (iii) enhance the populations’ isolation and (iv) make populations more susceptible to local extinction

Resolución de inecuaciones variacionales y aplicaciones

En esta comunicación se pretende dar una breve introducción a las inecuaciones variacionales, y exponer las líneas de trabajo que sobre este tema se desarrollan en el Departamento de Ecuaciones Funcionales de la Universidad de Santiago.Asimismo se resumen algunas contribu ciones publicadas o en curso de realización

Effect of the Modification of the Start-Up Sequence on the Thermal Stresses for a Microgas Turbine

Microgas turbines (MGT) are an alternative for small-scale energy production; however, their small size becomes a drawback since it enhances the heat transfer among their components. Moreover, heat transfer drives to temperature gradients which become higher during transient cycles like start-up. The influence of different start-up curves on temperature and thermal stresses of a microgas turbine was investigated. Stationary and rotational blades of the turbine were numerically simulated using CFD and FEM commercial codes. Conjugated heat transfer cases were solved for obtaining heat transfer from fluid toward the blades. Changes of temperature gradients within the blades during the start-ups were calculated under transient state with boundary conditions according to each curve to assess accurate thermal stresses calculations. Results showed that the modification of the start-up curves had an impact on the thermal stresses levels and on the time when highest stresses appeared on each component. Furthermore, zones highly stressed were located near the constraints of blades where thermal strains are restricted. It was also found that the curve that had a warming period at the beginning of the start-up allowed reducing the peaks of stresses making it more feasible and safer for the turbine start-up operation