516 research outputs found
Resiliencia en sistemas dunares litorales altamente antropizados: la restauración del sistema dunar de la playa del Remolar (Viladecans, Barcelona)
Con el fin de recuperar y restaurar el sistema playa-duna del Remolar (700 m de longitud y más de 100 m de ancho, de dirección 070N), se propusieron en 2004 una serie de medidas de restauración blanda. Para valorar dichas medidas, transcurridos 10 años, se efectuó un estudio de la morfología, sedimentología y de la vegetación del ecosistema. Se realizó el levantamiento de perfiles topográficos y de GPR, un análisis granulométrico y un análisis de las comunidades vegetales encontradas a lo largo de los perfiles topográficos. Los datos obtenidos han sido comparados con datos de un estudio previo, realizado en el 2004. Los resultados muestran que la morfología dunar se ha recuperado, originándose una nueva duna primaria. El sistema presenta actualmente un proceso mayor de agradación que de progradación. La vegetación ha recuperado una composición global de sistema dunar, con una comunidad típica de duna embrionaria y otras de duna primaria, en bandas paralelas a la costa. A pesar de esta mejora, la componente de tipo oportunista y ruderal de la vegetación de duna primaria denota una fuerte herencia antrópica en el sistema
CVD synthesis of carbon spheres using NiFe-LDHs as catalytic precursors: structural, electrochemical and magnetoresistive properties
The gram-scale synthesis of carbon spheres with a diameter of ca. 740 nm has been achieved by means of a chemical vapour deposition method using NiFe-layered double hydroxides as a solid catalytic precursor. The presence of the catalyst (FeNi3) allows controlling the final size distribution, resulting in a monodisperse sample. Their structural properties exhibited a high degree of graphitization according to their ID/IG ratio. In addition, their morphological features were unveiled by FIB-SEM and HRTEM, showing that they are formed by solid inner cores, and presenting labile chain-like structures due to accretion procedures. The solution and posterior sonication of the samples in toluene gave rise to the well-defined isolated spheres. The textural and electrochemical properties of the spheres have been tested showing non-mesoporous structures with a good behaviour as electrode materials for supercapacitors due to the presence of redox functionalities on their surface. Finally, magneto-transport measurements have been carried out, demonstrating semiconductor behaviour, as well as a positive magnetoresistance effect (ca. 72%) for the lowest studied temperature (2 K)
Assessment of the Restoration of the Remolar Dune System (Viladecans, Barcelona): The Resilience of a Coastal Dune System
The Remolar beach-dune system (700 m long and more than 100 m wide, 070N direction) borders a campground that was closed (2003), due to the Barcelona airport expansion. In order to recover and restore the dune ecosystem, a series of soft measures were performed. After 10 years, a study of the morphology, sedimentology, and vegetation of the ecosystem was carried out to evaluate the results of these measures. For this purpose, a series of topographic and groundpenetrating radar (GPR) profiles, grain-size analysis, and an analysis of plant communities found along the profiles were carried out. The data obtained were compared with data from a former 2004 study. The results show that the morphology of the dunes recovered, and a new primary dune has arisen. The system now has a greater process of aggradation than of progradation. The vegetation has recovered the global composition of dune systems, with a typical community of embryo dunes and others of primary dunes that are set in strips parallel to the coast. Despite this improvement, the opportunistic and ruderal component in the primary dune vegetation evidences a strong anthropic inheritance in the system
Global variability of high-nutrient low-chlorophyll regions using neural networks and wavelet coherence analysis
We examine 20 years of monthly global ocean color data and
modeling outputs of nutrients using self-organizing map (SOM) analysis to
identify characteristic spatial and temporal patterns of high-nutrient low-chlorophyll (HNLC) regions and their association with different climate
modes. The global nitrate-to-chlorophyll ratio threshold of
NO3 : Chl > 17 (mmol NO3 mg Chl−1) is estimated to be a good indicator
of the distribution limit of this unproductive biome that, on average,
covers 92 × 106 km2 (∼ 25 % of the ocean). The
trends in satellite-derived surface chlorophyll (0.6 ± 0.4 % yr−1 to 2 ± 0.4 % yr−1) suggest that HNLC regions in polar and subpolar areas
have experienced an increase in phytoplankton biomass over the last decades,
but much of this variation, particularly in the Southern Ocean, is produced
by a climate-driven transition in 2009–2010. Indeed, since 2010, the extent
of the HNLC zones has decreased at the poles (up to 8 %) and slightly
increased at the Equator (< 0.5 %). Our study finds that
chlorophyll variations in HNLC regions respond to major climate variability
signals such as the El Niño–Southern Oscillation (ENSO) and Meridional
Overturning Circulation (MOC) at both short (2–4 years) and long (decadal)
timescales. These results suggest global coupling in the functioning of
distant biogeochemical regions.</p
Seasonal and El Niño–Southern Oscillation-related ocean variability in the Panama Bight
In the Panama Bight, two different seasonal surface circulation patterns
coincide with a strong mean sea level variation, as observed from 27 years
of absolute dynamic topography (ADT) and the use of self-organizing maps.
From January to April, a cyclonic gyre with a strong southwestward Panama
Jet Surface Current (PJSC) dominates the basin circulation, forced by the
Panama surface wind jet that also produces upwelling, reducing sea surface
temperature (SST), increasing sea surface salinity (SSS) and causing an ADT
decrease. From June to December, the Choco surface wind jet enhances SST,
precipitation and river runoff, which reduces SSS, causing an ADT rise, which in turn forces a weak circulation in the bight, vanishing the PJSC. Interannual
variability in the region is strongly affected by El Niño–Southern Oscillation (ENSO); however this
climatic variability does not modify the seasonal circulation patterns in
the Panama Bight. In contrast, the positive (negative) ENSO phase increases
(decreases) SST and ADT in the Panama Bight, with a mean annual difference
of 0.9 ∘C and 9.6 cm, respectively, between the two conditions,
while its effect on SSS is small. However, as the strong seasonal SST, SSS
and ADT ranges are up to 2.2 ∘C, 2.59 g kg−1 and 28.3 cm,
the seasonal signal dominates over interannual variations in the bight.</p
Impact of HF radar current gap-filling methodologies on the Lagrangian assessment of coastal dynamics
High-frequency radar, HFR, is a cost-effective monitoring
technique that allows us to obtain high-resolution continuous surface currents,
providing new insights for understanding small-scale transport processes in
the coastal ocean. In the last years, the use of Lagrangian metrics to study
mixing and transport properties has been growing in importance. A common condition
among all the Lagrangian techniques is that complete spatial and temporal
velocity data are required to compute trajectories of virtual particles in the
flow. However, hardware or software failures in the HFR system can compromise the
availability of data, resulting in incomplete spatial coverage fields or
periods without data. In this regard, several methods have been widely used
to fill spatiotemporal gaps in HFR measurements. Despite the growing
relevance of these systems there are still many open questions concerning the
reliability of gap-filling methods for the Lagrangian assessment of
coastal ocean dynamics. In this paper, we first develop a new methodology to
reconstruct HFR velocity fields based on self-organizing maps (SOMs). Then, a
comparative analysis of this method with other available gap-filling
techniques is performed, i.e., open-boundary modal analysis (OMA) and data
interpolating empirical orthogonal functions (DINEOFs). The performance of
each approach is quantified in the Lagrangian frame through the computation
of finite-size Lyapunov exponents, Lagrangian coherent structures and
residence times. We determine the limit of applicability of each method
regarding four experiments based on the typical temporal and spatial gap
distributions observed in HFR systems unveiled by a K-means clustering
analysis. Our results show that even when a large number of data are missing,
the Lagrangian diagnoses still give an accurate description of oceanic
transport properties.</p
Bottlenose dolphins (Tursiops truncatus) do also cast neutrophil extracellular traps against the apicomplexan parasite Neospora caninum
Neutrophil extracellular traps (NETs) are web-like structures composed of nuclear DNA decorated with histones and cytoplasmic peptides which antiparasitic properties have not previously been investigated in cetaceans. Polymorphonuclear neutrophils (PMN) were isolated from healthy bottlenose dolphins (Tursiops truncatus), and stimulated with Neospora caninum tachyzoites and the NETs-agonist zymosan. In vitro interactions of PMN with the tachyzoites resulted in rapid extrusion of NETs. For the demonstration and quantification of cetacean NETs, extracellular DNA was stained by using either Sytox Orange® or Pico Green®. Scanning electron microscopy (SEM) and fluorescence analyses demonstrated PMN-derived release of NETs upon exposure to tachyzoites of N. caninum. Co-localization studies of N. caninum induced cetacean NETs proved the presence of DNA adorned with histones (H1, H2A/H2B, H3, H4), neutrophil elastase (NE), myeloperoxidase (MPO) and pentraxin (PTX) confirming the molecular properties of mammalian NETosis. Dolphin-derived N. caninum-NETosis were efficiently suppressed by DNase I and diphenyleneiodonium (DPI) treatments. Our results indicate that cetacean-derived NETs represent an ancient, conserved and relevant defense effector mechanism of the host innate immune system against N. caninum and probably other related neozoan parasites circulating in the marine environment
Singularities of surface mixing activity in the Western Mediterranean influence bluefin tuna larval habitats
Understanding how the surface dynamics of the ocean influence the spawning and larval ecology of many large pelagic species, in particular tuna species, is a major challenge. For temperate tunas, the selection of geographically restricted spawning grounds is influenced by environmental conditions, but the influence of surface mixing properties on the early life stages of these species remains poorly understood. Here, based on ichthyoplankton samples collected over 4 yr and satellite-derived finite size Lyapunov exponents (FSLEs), we examined how horizontal mixing activity drives the probability of presence of Atlantic bluefin tuna Thunnus thynnus larvae. We further analyzed the spatial and temporal scales of the FSLE variability at which the relationship between larval presence and mesoscale activity is maximized. We found that moderate mixing activity strongly favors the spatial-temporal distribution of larval habitats, evidencing an optimal environmental window of bluefin tuna spawning and early life development within the mesoscale dynamics. During the spawning season, the Balearic Sea presents a unique spatial and temporal hydrodynamic scenario within the Western Mediterranean. These results can be used for developing oceanographic indicators and improving larval abundance indices that are currently used in Atlantic bluefin tuna stock assessments.En prensa2,48
Small-pore driven high capacitance in a hierarchical carbon via carbonization of Ni-MOF-74 at low temperatures
A hierarchical porous carbon prepared via direct carbonization of Ni-MOF-74 loaded with furfuryl alcohol at 450 °C displays high specific capacitance in comparison with other MOF-derived carbons as a result of the formation of micropores smaller than 1 nm
CVD synthesis of carbon spheres using NiFe-LDHs as catalytic precursors: structural, electrochemical and magnetoresistive properties
The gram-scale synthesis of carbon spheres with a diameter of ca. 740 nm has been achieved by means of a chemical vapour deposition method using NiFe-layered double hydroxides as a solid catalytic precursor. The presence of the catalyst (FeNi3) allows controlling the final size distribution, resulting in a monodisperse sample. Their structural properties exhibited a high degree of graphitization according to their ID/IG ratio. In addition, their morphological features were unveiled by FIB-SEM and HRTEM, showing that they are formed by solid inner cores, and presenting labile chain-like structures due to accretion procedures. The solution and posterior sonication of the samples in toluene gave rise to the well-defined isolated spheres. The textural and electrochemical properties of the spheres have been tested showing non-mesoporous structures with a good behaviour as electrode materials for supercapacitors due to the presence of redox functionalities on their surface. Finally, magneto-transport measurements have been carried out, demonstrating semiconductor behaviour, as well as a positive magnetoresistance effect (ca. 72%) for the lowest studied temperature (2 K)
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