45 research outputs found
The ceab's marine observatory in the catalan sea : consolidating long time series observations?
Peer Reviewe
Factors controlling interannual variability of vertical organic matter export and phytoplankton bloom dynamics – a numerical case-study for the NW Mediterranean Sea
Mid-latitude spring blooms of phytoplankton show considerable year-to-year variability in timing, spatial extent and intensity. It is still unclear to what degree the bloom variability is connected to the magnitude of the vertical flux of organic matter. A coupled three-dimensional hydrodynamic-biogeochemical model is used to relate interannual variability in phytoplankton spring-bloom dynamics to variability in the vertical export of organic matter in the NW Mediterranean Sea. Simulation results from 2001 to 2010, validated against remote-sensing chlorophyll, show marked interannual variability in both timing and shape of the bloom. Model results show a tendency for the bloom to start later after cold and windy winters. However, the onset of the bloom occurs often when the mixed layer is still several hundred metres deep while the heat flux is already approaching zero and turbulent mixing is low. Frequency and intensity of wind episodes control both the timing and development of the bloom and the consequent export flux of organic matter. The wintertime flux is greater than zero and shows relatively low interannual variability. The magnitude of the interannual variability is mainly determined in March when the frequency of windy days positively correlates with the export flux. Frequent wind-driven mixing episodes act to increase the export flux and, at the same time, to interrupt the bloom. Perhaps counterintuitively, our analysis shows that years with discontinuous, low-chlorophyll blooms are likely to have higher export flux than years with intense uninterrupted blooms. The NW Mediterranean shows strong analogy with the North Atlantic section within the same latitude range. Hence, our results may also be applicable to this quantitatively more important area of the world ocean
A critical analysis on the sensitivity enhancement of surface plasmon resonance sensors with graphene
The use of graphene in surface plasmon resonance sensors, covering a metallic (plasmonic) film, has a number of demonstrated advantages, such as protecting the film against corrosion/oxidation and facilitating the introduction of functional groups for selective sensing. Recently, a number of works have claimed that few-layer graphene can also increase the sensitivity of the sensor. However, graphene was treated as an isotropic thin film, with an out-of-plane refractive index that is identical to the in-plane index. Here, we critically examine the role of single and few layers of graphene in the sensitivity enhancement of surface plasmon resonance sensors. Graphene is introduced over the metallic film via three different descriptions: as an atomic-thick two-dimensional sheet, as a thin effective isotropic material (same conductivity in the three coordinate directions), and as an non-isotropic layer (different conductivity in the perpendicular direction to the two-dimensional plane). We find that only the isotropic layer model, which is known to be incorrect for the optical modeling of graphene, provides sizable sensitivity increases, while the other, more accurate, models lead to a negligible contribution to the sensitivity.This work was funded by FAPESP (grant nos. 2018/07276-5 and 2018/25339-4), the Brazilian Nanocarbon Institute of Science and Technology (INCT/Nanocarbon), and CAPES-PrInt (grant no. 88887.310281/2018-00). N.M.R.P. acknowledges PORTUGAL 2020, FEDER, and the FCT through projects: UIDB/04650/2020 strategic project, QML-HEP-CERN/FIS-COM/0004/2021 and PTDC/FIS-MAC/2045/2021, and the European Commission through the project GrapheneDriven Revolutions in ICT and Beyond (Ref. No. 881603, CORE 3).https://www.mdpi.com/2079-4991/12/15/256
Venus Express radio occultation observed by PRIDE
Context. Radio occultation is a technique used to study planetary atmospheres
by means of the refraction and absorption of a spacecraft carrier signal
through the atmosphere of the celestial body of interest, as detected from a
ground station on Earth. This technique is usually employed by the deep space
tracking and communication facilities (e.g., NASA's Deep Space Network (DSN),
ESA's Estrack). Aims. We want to characterize the capabilities of the Planetary
Radio Interferometry and Doppler Experiment (PRIDE) technique for radio
occultation experiments, using radio telescopes equipped with Very Long
Baseline Interferometry (VLBI) instrumentation. Methods. We conducted a test
with ESA's Venus Express (VEX), to evaluate the performance of the PRIDE
technique for this particular application. We explain in detail the data
processing pipeline of radio occultation experiments with PRIDE, based on the
collection of so-called open-loop Doppler data with VLBI stations, and perform
an error propagation analysis of the technique. Results. With the VEX test case
and the corresponding error analysis, we have demonstrated that the PRIDE setup
and processing pipeline is suited for radio occultation experiments of
planetary bodies. The noise budget of the open-loop Doppler data collected with
PRIDE indicated that the uncertainties in the derived density and temperature
profiles remain within the range of uncertainties reported in previous Venus'
studies. Open-loop Doppler data can probe deeper layers of thick atmospheres,
such as that of Venus, when compared to closed-loop Doppler data. Furthermore,
PRIDE through the VLBI networks around the world, provides a wide coverage and
range of large antenna dishes, that can be used for this type of experiments
Dirac Spectrum in Piecewise Constant One-Dimensional Potentials
We study the electronic states of graphene in piecewise constant potentials
using the continuum Dirac equation appropriate at low energies, and a transfer
matrix method. For superlattice potentials, we identify patterns of induced
Dirac points which are present throughout the band structure, and verify for
the special case of a particle-hole symmetric potential their presence at zero
energy. We also consider the cases of a single trench and a p-n junction
embedded in neutral graphene, which are shown to support confined states. An
analysis of conductance across these structures demonstrates that these
confined states create quantum interference effects which evidence their
presence.Comment: 10 pages, 12 figures, additional references adde
Advancing fishery-independent stock assessments for the Norway lobster (Nephrops norvegicus) with new monitoring techn
The Norway lobster, Nephrops norvegicus, supports a key European fishery.
Stock assessments for this species are mostly based on trawling and
UnderWater TeleVision (UWTV) surveys. However, N. norvegicus are
burrowing organisms and these survey methods are unable to sample or
observe individuals in their burrows. To account for this, UWTV surveys
generally assume that “1 burrow system = 1 animal”, due to the territorial
behavior of N. norvegicus. Nevertheless, this assumption still requires in-situ
validation. Here, we outline how to improve the accuracy of current stock
assessments for N. norvegicus with novel ecological monitoring technologies,
including: robotic fixed and mobile camera-platforms, telemetry,
environmental DNA (eDNA), and Artificial Intelligence (AI). First, we outline
the present status and threat for overexploitation in N. norvegicus stocks. Then,
we discuss how the burrowing behavior of N. norvegicus biases current stock
assessment methods. We propose that state-of-the-art stationary and mobile
robotic platforms endowed with innovative sensors and complemented with AI
tools could be used to count both animals and burrows systems in-situ, as well
as to provide key insights into burrowing behavior. Next, we illustrate how
multiparametric monitoring can be incorporated into assessments of
physiology and burrowing behavior. Finally, we develop a flowchart for the
appropriate treatment of multiparametric biological and environmental data
required to improve current stock assessment methods
The Biodiversity of the Mediterranean Sea: Estimates, Patterns, and Threats
The Mediterranean Sea is a marine biodiversity hot spot. Here we combined an extensive literature analysis with expert opinions to update publicly available estimates of major taxa in this marine ecosystem and to revise and update several species lists. We also assessed overall spatial and temporal patterns of species diversity and identified major changes and threats. Our results listed approximately 17,000 marine species occurring in the Mediterranean Sea. However, our estimates of marine diversity are still incomplete as yet—undescribed species will be added in the future. Diversity for microbes is substantially underestimated, and the deep-sea areas and portions of the southern and eastern region are still poorly known. In addition, the invasion of alien species is a crucial factor that will continue to change the biodiversity of the Mediterranean, mainly in its eastern basin that can spread rapidly northwards and westwards due to the warming of the Mediterranean Sea. Spatial patterns showed a general decrease in biodiversity from northwestern to southeastern regions following a gradient of production, with some exceptions and caution due to gaps in our knowledge of the biota along the southern and eastern rims. Biodiversity was also generally higher in coastal areas and continental shelves, and decreases with depth. Temporal trends indicated that overexploitation and habitat loss have been the main human drivers of historical changes in biodiversity. At present, habitat loss and degradation, followed by fishing impacts, pollution, climate change, eutrophication, and the establishment of alien species are the most important threats and affect the greatest number of taxonomic groups. All these impacts are expected to grow in importance in the future, especially climate change and habitat degradation. The spatial identification of hot spots highlighted the ecological importance of most of the western Mediterranean shelves (and in particular, the Strait of Gibraltar and the adjacent Alboran Sea), western African coast, the Adriatic, and the Aegean Sea, which show high concentrations of endangered, threatened, or vulnerable species. The Levantine Basin, severely impacted by the invasion of species, is endangered as well
Population abundance and seasonal migration patterns indicated by commercial catch-per-unit-effort of hakes (Merluccius capensis and M. paradoxus) in the northern Benguela Current Large Marine Ecosystem
Este artículo contiene 14 páginas, 8 figuras, 2 tablas.We developed generalised additive models (GAMs) to estimate standardised time-series of population abundance
indices for assessment purposes and to infer ecological and behavioural information on northern Benguela
hakes, Merluccius capensis and M. paradoxus, using haul-by-haul commercial trawl catch-rate data as proxies for
hake densities. The modelling indicated that individual ship identifiers should be used rather than general vessel
characteristics, such as vessel size. The final models explained 79% and 68% of the variability in the commercial
catch rates of M. capensis and M. paradoxus, respectively. The spatial density patterns were consistent and
confirmed existing knowledge about these species in the northern Benguela system. Furthermore, seasonal migration
patterns were described for the first time and were found to correspond to the known spawning areas and seasons
for M. capensis and M. paradoxus. Spatial density patterns were validated using the geostatistical modelling results
of fisheries-independent trawl survey data. Improved understanding of the relationships between fleet dynamics and
fish movement can be achieved by taking into consideration the present catch-rate model and spatial and seasonal
distribution maps. We conclude that the yearly standardised CPUE time-series are problematic as proxies for
total stock abundance because of spatial coverage issues. Consequently, such CPUE data should not be used for
stock-size assessments and fisheries advice concerning northern Benguela hakes until this is solved. We generally
recommend the exclusion of standardised CPUE time-series from stock assessments when important and changing
parts of the stock distribution cannot be targeted by the fishery, such as due to closed areas or seasons.The work by JNK and TJ was funded from
Europe Aid through the EcoFish project (CRIS number C-222387).Peer reviewe
The ceab's marine observatory in the catalan sea : consolidating long time series observations?
Peer Reviewe
A Comparative Assessment of Emerging Solvents and Adsorbents for Mitigating CO2 Emissions From the Industrial Sector by Using Molecular Modeling Tools
The possibilities offered by molecular modeling tools to obtain relevant data at process conditions, while also gaining molecular insights on the techniques used for CO2 capture and separation, are presented here using selected case studies. Two different technologies, absorption with amine-based systems and adsorption on porous materials, were explored, using the molecular-based equation of state, soft-Statistical Associating Fluid Theory (SAFT), and Grand Canonical Monte Carlo simulations, respectively. The aqueous monoethanolamine (MEA) system was set as the benchmark for absorption and compared to the performance of 8 alternative amine-based systems, while 16 adsorbents belonging to different families (zeolites, metal–organic frameworks, amorphous silicas, and activated carbons), bare or functionalized with alkylamines, were investigated for the separation of CO2 by adsorption. In addition to obtaining molecular information on the CO2 capture process, the models were further used to examine the CO2 capture performance in terms of cyclic working capacity and energy index as key performance indicators, allowing the identification of promising systems that can improve the current ones to be further evaluated for separation in non-power industries. Results show that for the same total amine mass concentration, non-aqueous amine solvents have a 5–10% reduction in cyclic working capacity, and a 10–30% decrease in the energy index compared to their aqueous counterparts due to their lower heat of vaporization and specific heat capacity. In addition, M-MOF-74, NaX, and NaY structures present the best results for adsorption in temperature swing adsorption (TSA) processes. Similar values of energy requirements to those of amine-based systems (2–2.5 MJ kg CO2–1) were obtained for some of the adsorbent; however, the disadvantage of the TSA process versus absorption should be considered. These results confirm the reliability of molecular modeling as an attractive and valuable screening tool for CO2 capture and separation processes. © Copyright © 2020 Bahamon, Alkhatib, Alkhatib, Builes, Sinnokrot and Vega