Graphene–ionic liquid interfacial potential drop from density functional theory-based molecular dynamics simulations

Ionic liquids (ILs) are promising electrolytes for electrochemical applications due to their remarkable stability and high charge density. Molecular dynamics simulations are essential for a better understanding of the complex phenomena occurring at the electrode–IL interface. In this work, we have studied the interface between graphene and 1-ethyl-3-methyl-imidazolium tetrafluoroborate IL by density functional theory-based molecular dynamics (DFT-MD) simulations at variable surface charge densities. We have disassembled the electrical double layer potential drop into two main components: one involving atomic charges and the other dipoles. The former component arises due to the reorganization of ionic liquid and the latter due to the electronic polarization of the surface. It is related to concepts hotly debated in the literature, such as the Thomas–Fermi screening length, effective surface charge plane, and quantum capacitance

Unexpectedly diverse forest dung beetle communities in degraded rain forest landscapes in Madagascar

Tropical forests, which harbor high levels of biodiversity, are being lost at an alarming speed. Madagascar, a biodiversity hotspot, has lost more than half of its original forest cover. Most of the remaining forests are small fragments of primary and secondary forest with differing degrees of human impact. These forests, as well as coffee and fruit plantations, may be important in supporting the forest-dependent biodiversity in Madagascar but this has been little studied. In Madagascar, dung beetles, which offer important ecosystem services, are largely restricted to forests. We examined the ability of fragmented and degraded forests to support dung beetle diversity, compared to the large areas of primary forest in eastern Madagascar. We found a general trend of a reduction of species with a loss of forest connectivity. In contrast, a higher level of forest disturbance was associated with higher species diversity. In several sites of low-quality forest as many or more species were found as in less disturbed and primary forests. The average size of dung beetles was smaller in the lower quality localities than in the primary forests. These findings suggest that many forest dung beetles in Madagascar are better adapted to forest disturbance than earlier expected, although they require some level of connectivity to surrounding forest. in Malagasy is available with online material.Peer reviewe

Madagascan day geckos (Phelsuma spp.) exhibit differing responses along a gradient of land-use change

Madagascar is a key priority for global conservation efforts, as much of its diverse and highly endemic biota is threatened by deforestation. Despite this threat, there are limited data on the responses and tolerances of herpetofaunal species to landscape change. This study investigated the response of Madagascan day geckos (Phelsuma spp.) to deforestation in Nosy Be, Madagascar. We selected six sites along a gradient of land-use change: two in Sambirano rainforest (“Forest”), two in secondary, fragmented forest (“Fragment”), and two in agricultural plantations (“Orchard” and “Cropland”). We conducted a series of time-constrained searches at each site. The mean encounter rate of Phelsuma geckos (geckos detected per person/hour) was greater in agricultural sites than Forest sites, but no difference was detected between Forest and Fragment or Fragment and agricultural areas. Three species were encountered more frequently in agricultural land than forested sites, but this was not true for Phelsuma seippi, an endangered species on the IUCN Red List. These results suggest that adaptive, generalist species may benefit from anthropogenic land-use change, whereas specialist species will suffer. Our study emphasizes the importance of extending research beyond the borders of protected forests to include anthropogenically disturbed areas

Origin of dielectric polarization suppression in confined water from first principles.

Acknowledgements: The authors thank D. V. Matyushov for fruitful discussions. T. D. and L. F. were supported by the European Research Council (grant 819417) under the European Union Horizon 2020 Research and Innovation Programme. A. M. acknowledges support from the European Union under the “n-aqua” European Research Council project (grant 101071937). C. S. acknowledges partial financial support from the Alexander von Humboldt-Stiftung and the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) project number 500244608. J. C. and A. M. thank Beijing Municipal Natural Science Foundation (no. JQ22001) for support. We are grateful to the UK Materials and Molecular Modelling Hub for computational resources, which is partially funded by EPSRC (EP/P020194/1 and EP/T022213/1), and computational support from the UK national high performance computing service, ARCHER, for which access was obtained via the UKCP consortium, funded by EPSRC grant ref. EP/P022561/1. We are also grateful to the Research IT and the use of the High Performance Computing (HPC) Pool funded by the Research Lifecycle Programme at the University of Manchester.It has long been known that the dielectric constant of confined water should be different from that in bulk. Recent experiments have shown that it is vanishingly small, however the origin of the phenomenon remains unclear. Here we used ab initio molecular dynamics simulations (AIMD) and AIMD-trained machine-learning potentials to understand water's structure and electronic properties underpinning this effect. For the graphene and hexagonal boron-nitride substrates considered, we find that it originates in the spontaneous anti-parallel alignment of the water dipoles in the first two water layers near the solid interface. The interfacial layers exhibit net ferroelectric ordering, resulting in an overall anti-ferroelectric arrangement of confined water. Together with constrained hydrogen-bonding orientations, this leads to much reduced out-of-plane polarization. Furthermore, we directly contrast AIMD and simple classical force-field simulations, revealing important differences. This work offers insight into a property of water that is critical in modulating surface forces, the electric-double-layer formation and molecular solvation, and shows a way to compute it

Origin of dielectric polarization suppression in confined water from first principles

It has long been known that the dielectric constant of confined water should be different from that in bulk. Recent experiments have shown that it is vanishingly small, however the origin of the phenomenon remains unclear. Here we used ab initio molecular dynamics simulations (AIMD) and AIMD-trained machine-learning potentials to understand water's structure and electronic properties underpinning this effect. For the graphene and hexagonal boron-nitride substrates considered, we find that it originates in the spontaneous anti-parallel alignment of the water dipoles in the first two water layers near the solid interface. The interfacial layers exhibit net ferroelectric ordering, resulting in an overall anti-ferroelectric arrangement of confined water. Together with constrained hydrogen-bonding orientations, this leads to much reduced out-of-plane polarization. Furthermore, we directly contrast AIMD and simple classical force-field simulations, revealing important differences. This work offers insight into a property of water that is critical in modulating surface forces, the electric-double-layer formation and molecular solvation, and shows a way to compute it.<br/

Conception et évaluation de systèmes de culture maraîchers méditerranéens innovants pour gérer les nématodes à galles

Design and assessment of innovative Mediterranean vegetable cropping systems to manage root-knot nematodes. Description of the subject. A system approach based on co-design and experimental field evaluation of cropping systems (CSs), combining technical and varietal innovations, has been implemented for sustainable management of root-knot nematodes (RKN) in Mediterranean sheltered vegetable systems. Objectives. Cropping systems combining genetic resistance and cultural practices (crop rotations including susceptible, resistant, and non-host plants; intercropping management with nematicidal cover crops or soil solarization) were assessed over a period of 4 years (i) to reduce RKN populations and increase the durability of varietal resistances, (ii) to study the impact of these systems on soil ecology (plant-parasitic and free-living nematode communities), and (iii) to evaluate their acceptability by farmers. Method. Three CS prototypes, resulting from a co-design process with research and development stakeholders, were compared with CSs conventionally implemented in the Mediterranean region. The three prototypes were also evaluated using complementary methods: (i) system experiments in three commercial farms in Southern France; (ii) analytical experiments to decipher the mechanisms of action for some [agroecological??] levers; (iii) surveys to evaluate the acceptability of the prototypes by farmers. Results. All three CSs were found to be effective (90% RKN decrease, protection of partially resistant Solanaceae, no negative effect on non-phytoparasitic nematodes) and sustainable, when application conditions and soil biological equilibrium were favorable (global soil nematofauna diversified and abundant). The acceptability of the three systems depended on the type of farm where they were implemented and the attitude of the farmers towards innovation. Conclusions. These three CSs still need to be improved, in terms of their efficiency, in consultation with participating farmers, by introducing new agroecological levers, as well as innovation costs. Future research will also need to open up to a more comprehensive management of soil health