158 research outputs found
239 + 240Pu from “contaminant” to soil erosion tracer: Where do we stand?
As soil erosion is the major threat to one of the most essential resources of humankind, methods to quantify soil redistribution are crucial for agro-environmental assessment as well as for optimisation of soil conservation practices. The use of fallout radionuclides (FRN) as soil redistribution tracers is, next to modelling, currently the most promising approach for assessing soil erosion. This review aims to evaluate the suitability of Plutonium (Pu) in general and the 239+240Pu isotopes in particular as soil redistribution tracers. It provides information on its origin, distribution and behaviour in soils and in the environment. Analytical methods, their recent advances as well as limitations, are discussed. To establish the current state of knowledge and to deepen our understanding, particular attention is given to the main existing achievements and findings based on using 239+240Pu as soil erosion tracer in agroecosystems. We further discuss similarities and differences to other more mature FRN techniques such as the 137Cs based approach which has been until now the most widely used method. We conclude that 239+240Pu has the potential to become the next generation of soil redistribution tracer compared to the more mature FRN techniques mostly due to (i) its long half-life guaranteeing its long-term availability in the environment, (ii) its analytical advantage in terms of measurement precision and measurement time and (iii) its greater homogeneity at reference sites due to its main origin from past atmospheric nuclear weapon tests. In identifying some key future research opportunities and needs, we hope to refine the efficiency of this promising agro-environmental tracer for effective soil redistribution studies under future climate and land use change
Are plankton nets a thing of the past? An assessment of in situ imaging of zooplankton for large-scale ecosystem assessment and policy decision-making
Zooplankton are fundamental to aquatic ecosystem services such as carbon and nutrient cycling. Therefore, a robust evidence base of how zooplankton respond to changes in anthropogenic pressures, such as climate change and nutrient loading, is key to implementing effective policy-making and management measures. Currently, the data on which to base this evidence, such as long time-series and large-scale datasets of zooplankton distribution and community composition, are too sparse owing to practical limitations in traditional collection and analysis methods. The advance of in situ imaging technologies that can be deployed at large scales on autonomous platforms, coupled with artificial intelligence and machine learning (AI/ML) for image analysis, promises a solution. However, whether imaging could reasonably replace physical samples, and whether AI/ML can achieve a taxonomic resolution that scientists trust, is currently unclear. We here develop a roadmap for imaging and AI/ML for future zooplankton monitoring and research based on community consensus. To do so, we determined current perceptions of the zooplankton community with a focus on their experience and trust in the new technologies. Our survey revealed a clear consensus that traditional net sampling and taxonomy must be retained, yet imaging will play an important part in the future of zooplankton monitoring and research. A period of overlapping use of imaging and physical sampling systems is needed before imaging can reasonably replace physical sampling for widespread time-series zooplankton monitoring. In addition, comprehensive improvements in AI/ML and close collaboration between zooplankton researchers and AI developers are needed for AI-based taxonomy to be trusted and fully adopted. Encouragingly, the adoption of cutting-edge technologies for zooplankton research may provide a solution to maintaining the critical taxonomic and ecological knowledge needed for future zooplankton monitoring and robust evidence-based policy decision-making
Domain Walls in Two-Component Dynamical Lattices
We introduce domain-wall (DW) states in the bimodal discrete nonlinear
Schr{\"{o}}dinger equation, in which the modes are coupled by cross phase
modulation (XPM). By means of continuation from various initial patterns taken
in the anti-continuum (AC) limit, we find a number of different solutions of
the DW type, for which different stability scenarios are identified. In the
case of strong XPM coupling, DW configurations contain a single mode at each
end of the chain. The most fundamental solution of this type is found to be
always stable. Another solution, which is generated by a different AC pattern,
demonstrates behavior which is unusual for nonlinear dynamical lattices: it is
unstable for small values of the coupling constant (which measures the
ratio of the nonlinearity and coupling lengths), and becomes stable at larger
. Stable bound states of DWs are also found. DW configurations generated by
more sophisticated AC patterns are identified as well, but they are either
completely unstable, or are stable only at small values of . In the case of
weak XPM, a natural DW solution is the one which contains a combination of both
polarizations, with the phase difference between them 0 and at the
opposite ends of the lattice. This solution is unstable at all values of ,
but the instability is very weak for large , indicating stabilization as the
continuum limit is approached. The stability of DWs is also verified by direct
simulations, and the evolution of unstable DWs is simulated too; in particular,
it is found that, in the weak-XPM system, the instability may give rise to a
moving DW.Comment: 14 pages, 14 figures, Phys. Rev. E (in press
Nonlinear atom optics and bright gap soliton generation in finite optical lattices
We theoretically investigate the transmission dynamics of coherent matter
wave pulses across finite optical lattices in both the linear and the nonlinear
regimes. The shape and the intensity of the transmitted pulse are found to
strongly depend on the parameters of the incident pulse, in particular its
velocity and density: a clear physical picture for the main features observed
in the numerical simulations is given in terms of the atomic band dispersion in
the periodic potential of the optical lattice. Signatures of nonlinear effects
due the atom-atom interaction are discussed in detail, such as atom optical
limiting and atom optical bistability. For positive scattering lengths, matter
waves propagating close to the top of the valence band are shown to be subject
to modulational instability. A new scheme for the experimental generation of
narrow bright gap solitons from a wide Bose-Einstein condensate is proposed:
the modulational instability is seeded in a controlled way starting from the
strongly modulated density profile of a standing matter wave and the solitonic
nature of the generated pulses is checked from their shape and their
collisional properties
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The ocean sampling day consortium.
Ocean Sampling Day was initiated by the EU-funded Micro B3 (Marine Microbial Biodiversity, Bioinformatics, Biotechnology) project to obtain a snapshot of the marine microbial biodiversity and function of the world's oceans. It is a simultaneous global mega-sequencing campaign aiming to generate the largest standardized microbial data set in a single day. This will be achievable only through the coordinated efforts of an Ocean Sampling Day Consortium, supportive partnerships and networks between sites. This commentary outlines the establishment, function and aims of the Consortium and describes our vision for a sustainable study of marine microbial communities and their embedded functional traits
Wet Granular Materials
Most studies on granular physics have focused on dry granular media, with no
liquids between the grains. However, in geology and many real world
applications (e.g., food processing, pharmaceuticals, ceramics, civil
engineering, constructions, and many industrial applications), liquid is
present between the grains. This produces inter-grain cohesion and drastically
modifies the mechanical properties of the granular media (e.g., the surface
angle can be larger than 90 degrees). Here we present a review of the
mechanical properties of wet granular media, with particular emphasis on the
effect of cohesion. We also list several open problems that might motivate
future studies in this exciting but mostly unexplored field.Comment: review article, accepted for publication in Advances in Physics;
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Capillary Bridge Formation and Breakage: A Test to Characterize Antiadhesive Surfaces
In order to characterize very weak adhesive surfaces, we have developed a
quantitative test inspired by the Johnson, Kendall, and Roberts adhesion test
for soft adhesives, which relies on the formation and then the rupture of a
capillary bridge between the surface to be tested and a liquid bath. Both the
shape and the kinetics of breakage of the capillary bridge for various coatings
put into contact with liquids of various viscosities and surface tensions have
been studied. Several pull off regimes can be distinguished. For low pull off
velocities, a quasi-static regime is observed, well described by capillary
equations and sensitive to the hysteresis of the contact angle of the fluid on
the coating. Above a critical pull off velocity that depends on the fluid
viscosity, a dynamic regime is observed, characterized by the formation of a
flat pancake of fluid on the coating that recedes more slowly than the
capillary bridge itself. After the breakage of the capillary bridge, a small
drop can remain attached to the surface. The volume of this drop depends on the
dynamical regime and is strongly affected by very small differences between the
coatings. The aptitude of this test in characterizing very weakly adhesive
surfaces is exemplified by a comparison between three different perfluorinated
coatings
The ocean sampling day consortium
Ocean Sampling Day was initiated by the EU-funded Micro B3 (Marine Microbial Biodiversity, Bioinformatics, Biotechnology) project to obtain a snapshot of the marine microbial biodiversity and function of the world’s oceans. It is a simultaneous global mega-sequencing campaign aiming to generate the largest standardized microbial data set in a single day. This will be achievable only through the coordinated efforts of an Ocean Sampling Day Consortium, supportive partnerships and networks between sites. This commentary outlines the establishment, function and aims of the Consortium and describes our vision for a sustainable study of marine microbial communities and their embedded functional traits
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