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The natural enemies hypothesis predicts that the abundance and diversity of antagonists such as predators and parasitoids of herbivores increases with the diversity of plants, which can lead to more effective top-down control of insect herbivores. However, although the hypothesis has received large support in agricultural systems, fewer studies have been conducted in forest ecosystems and a comprehensive synthesis of previous research is still lacking. We conducted a meta-analysis of 65 publications comparing the diversity, abundance or activity of various groups of natural enemies (including birds, bats, spiders and insect parasitoids) in pure vs. mixed forest stands. We tested the effects of forest biome, natural enemy taxon and type of study (managed vs experimental forest). We found a significant positive effect of forest tree diversity on natural enemy abundance and diversity but not on their activity. The effect of tree diversity on natural enemies was stronger towards lower latitudes but was not contingent on the natural enemy taxon level. Overall, our study contributes toward a better understanding of the "natural enemies hypothesis" in forest systems and provides new insights about the mechanisms involved. Furthermore, we outline potential avenues for strengthening forest resistance to the growing threat of herbivorous insects. [ABSTRACT FROM AUTHOR]

• Ixodes ticks are more abundant in forests than in other types of habitat. • This difference is greater with mixed forests than with deciduous forests. • Exophilic Ixodes abundance is positively correlated with the abundance of ungulates. With increasing deforestation, questions are being raised about the risk of zoonotic disease to humans. To better assess the role of forest in the emergence of tick-borne diseases, we conducted a meta-analysis of the scientific literature to compare the abundance or diversity of ticks between forest and open habitats (natural or anthropogenic) and a meta-regression to test how tick abundance is influenced by the abundance of their vertebrate hosts in forest habitats. We found that Ixodes ticks were on average more abundant in forests than in any other non-forested habitats, the difference being more pronounced with mixed deciduous- coniferous than with deciduous forests. At the forest scale, exophilic Ixodes tick abundance was positively influenced by the abundance of their ungulate hosts. Our results suggest that mixed forests represent the habitats with the highest level of tick hazard. However, more studies are needed to assess the risk of transmission of tick-borne diseases in forests, which also depends on the prevalence of pathogens and the exposure of people. [ABSTRACT FROM AUTHOR]

When the water inventory evaporates during a hypothetical loss of coolant accident in the core of a pressurized water reactor, the fuel rods temperature increases substantially, resulting in the clad ballooning and the formation of blocked sub-channels. During the reflooding phase, where water is injected into the core and a steam-droplets flow is created above the water level, the presence of ballooned zone forces the steam flow to redistribute towards intact sub-channels, which degrades the cooling of ballooned clads within blocked sub-channels. Looking to better understand this flow redistribution process, this study presents experimental results of magnetic resonance velocimetry measurements of three-component velocity fields in several 49-element ballooned bundles to evaluate geometric effects (blockage ratio, length and coplanarity) on the flow dynamics, as well as the flow rate effect (Reynolds number from 1,936 to 9,599). The flow redistribution occurred in the transition zone upstream of the balloon. Moreover, the transverse velocities at this location are higher for higher blockage ratios and they can reach nearly the same magnitude of the axial velocity. The amount of deviated flow is approximately equal to the sub-channel's blockage ratio and is virtually insensitive to the blockage length or the flow rate. Furthermore, the flow's axial velocity reduces up- and downstream of blocked sub-channels and this reduction is more substantial as the blockage ratio increases. Results with non-coplanar balloons showed that a less intense flow redistribution takes place; however, a downstream balloon can affect the flow redistribution dynamics caused by an upstream ballooned zone. Finally, for all the tested bundles and tested flow rate ranges, the flow was remarkably homogenized by the downstream mixing spacer grid, restricting the clad ballooning effects only to the portion between the two spacer grids where the ballooned zone is located regardless of the balloon geometry and the flow rate. The present results may be useful as well for other research areas involving flow blockages in heat exchangers. • 3D velocity field measurements in several 7x7 bundles with different ballooned zones. • Parametric effect analysis: blockage ratio, length and coplanarity; and flow rate. • The blockage ratio and coplanarity play important roles in the flow redistribution. • Blockage non-coplanarity can change the location of the bundle's less-cooled region. • The downstream mixing spacer grid mitigated all the flow redistribution effects. [ABSTRACT FROM AUTHOR]

The water electro-osmotic drag coefficient of a cation _ K drag (cation)_ is defined as the number of water molecules which is dragged by a cation when it goes through a membrane at equilibrium state (i.e. in the absence of water concentration gradient within membrane). This coefficient is one of the key elements for modeling the water balance through Nafion membrane in a proton Exchange membrane Fuel cell (PEMFC). In this work, we have applied the method of electrophoresis NMR (ENMR) to determine the coefficient of electro-osmotic drag (K drag ) within Nafion prepared in different cationic forms (H + , Na + and K + ). Applying, in all cases, the same method for determining K drag of Nafion membrane in many cationic forms should be appropriate in order to apprehend the mechanisms of water transport which occur in this membrane. This method consists in measuring the phase of the water NMR signal under the application of an electric current in a diffusion-like experiment, this phase being proportional to the flux of water within Nafion. The results show that the electro-osmotic coefficients of water within Nafion depend on the type of counter-cation and on the water content of Nafion. Due to proton lability, the electro-osmotic drag coefficient of water within Nafion in the acid form (K drag (H + )) is the lowest among the three studied cationic forms. In a dehydrated state of Nafion, the K drag (H + ) is lower than 1, suggesting here that the hopping mechanism is favored. In the case of Nafion in sodium and potassium forms, K drag of these cations is always higher than 1. This can be rationalized by the vehicular mechanism and also by a strong interaction between the water solvation of the cation and the cation itself. [ABSTRACT FROM AUTHOR]

Abstract: This review aims to cover the state of the art of renewable feedstock use in materials production using photopolymerization processes. This area of investigation is an emerging field of research, and it combines biosourced molecules with a cheap and rapid radiative processing method that avoids any emission of volatile organic compounds. The main classes of naturally occurring molecules and macromolecules such as lipids, amino acids, carbohydrates, polyenes, etc. are detailed. The way they are used or integrated in photopolymerizable systems are described in relation to their applications: coatings, biomaterials, biodegradable drug delivery systems, microelectronics or optoelectronics. This critical review takes into account the reactivity of the various compounds as well as their cytotoxicity, biodegradability and finally their end uses. [Copyright &y& Elsevier]

Abstract: A multiscale approach (periodic homogenization) is carried out to model clayey materials behaviour, and especially the coupled phenomena that govern electro-osmotic process. Clays are composed of a charged solid phase saturated by an aqueous electrolyte containing four ionic species Na+, Cl−, H+ and OH−. The novelty of this approach consists in the integration of chemical reactions in our description. Thus influence of ionic exchanges that occur at the platelet’s scale can be propagated at the macroscale. In particular, suction effects observed in electrokinetic soil processing can be explained by this approach. [Copyright &y& Elsevier]

A titanium Porous Transport Layer (PTL) is usually used at the anode side of PEM water electrolyzers to ensure both the gas/water transport and the electric charges transfer. In this paper, four different sintered Ti powder PTLs were characterized to determine some properties, such as the pore size distribution, the porosity, and the permeability. Their influence on the electrolysis performance was investigated by using a 30 cm2 segmented cell which allowed measuring the current density distribution, while controlling temperature and pressure conditions. For a better understanding, in-situ techniques such as the Polarization Curves and the Electrochemical Impedance Spectroscopy (EIS) were used. A local characterization of mass transport limitations caused by oxygen saturation was carried out, paying special attention to the pressure influence when using a PTL with very small pores. The results showed that current density heterogeneities can be explained by microstructure changes along the PTL. The optimal geometric characteristics of the PTL depend not only on the operating conditions such as current density, pressure, and temperature but also on the catalyst layer properties. A new model for the constriction resistance between the catalyst layer and the PTL was proposed. • The influence of the PTL properties on the electrolyzer performance was investigated. • Optimal performance was obtained for an average pore size of 10 μm and porosity of 31%. • The pressure influence on the mass transport limitations was proved. • Current density heterogeneities were observed with a segmented PEM electrolyzer. • A new model for the constriction resistance in the catalyst layer was developed. [ABSTRACT FROM AUTHOR]

The understanding of fluid flow in faulted sandstones is based on a wide range of techniques. These depend on the multi-method determination of petrological and structural features, porous network properties and both spatial and temporal variations and interactions of these features. The question of the multi-parameter analysis on fluid flow controlling properties is addressed for an outcrop damage zone in the hanging wall of a normal fault zone on the western border of the Upper Rhine Graben, affecting the Buntsandstein Group (Early Triassic). Diagenetic processes may alter the original pore type and geometry in fractured and faulted sandstones. Therefore, these may control the ultimate porosity and permeability of the damage zone. The classical model of evolution of hydraulic properties with distance from the major fault core is nuanced here. The hydraulic behavior of the rock media is better described by a pluri-scale model including: 1) The grain scale, where the hydraulic properties are controlled by sedimentary features, the distance from the fracture, and the impact of diagenetic processes. These result in the ultimate porous network characteristics observed. 2) A larger scale, where the structural position and characteristics (density, connectivity) of the fracture corridors are strongly correlated with both geo-mechanical and hydraulic properties within the damage zone. [ABSTRACT FROM AUTHOR]

Abstract: Polymer electrolyte membrane fuel cell (PEMFC) use perfluorosulfonic acid membranes (for example ) as a solid electrolyte and their performances are strongly dependent on membrane hydration. Therefore, the accurate knowledge of water distribution in the membrane and of the zone of water condensation in the fuel cell is a fundamental issue. Nuclear Magnetic Resonance is a non-destructive and non-invasive technique. It is particularly suited for observing the transport properties of water in a membrane. Magnetic Resonance Imaging (MRI) experiments of a whole fuel cell are more difficult to achieve because they require a PEMFC free of ferromagnetic species and with a minimum of paramagnetic materials. Moreover, difficulties arise because of the electric conductance of most of the fuel cell components (bipolar plates, backing layers, electrodes). These issues have been addressed and MRI experiments of a rectangular PEMFC under operation have been performed. This fuel cell proved to have performances comparable to commercially available fuel cells. Preliminary results exhibit a progressive accumulation of water close to the gas outlet while the gas inlet remains dry. [Copyright &y& Elsevier]