Science et Ingénierie des Matériaux et Procédés

There are numerous examples where animals or plants synthesize extracellular high-performance skeletal biocomposites consisting of a matrix reinforced by fibrous biopolymers. Cellulose, the world's most abundant natural, renewable, biodegradable polymer, is a classical example of these reinforcing elements, which occur as whisker-like microfibrils that are biosynthesized and deposited in a continuous fashion. In many cases, this mode of biogenesis leads to crystalline microfibrils that are almost defect-free, with the consequence of axial physical properties approaching those of perfect crystals. This quite "primitive" polymer can be used to create high performance nanocomposites presenting outstanding properties. This reinforcing capability results from the intrinsic chemical nature of cellulose and from its hierarchical structure. Aqueous suspensions of cellulose crystallites can be prepared by acid hydrolysis of cellulose. The object of this treatment is to dissolve away regions of low lateral order so that the water-insoluble, highly crystalline residue may be converted into a stable suspension by subsequent vigorous mechanical shearing action. During the past decade, many works have been devoted to mimic biocomposites by blending cellulose whiskers from different sources with polymer matrixes.

1 Once neglected, the role of facilitative interactions in plant communities has received considerable attention in the last two decades, and is now widely recognized. It is timely to consider the progress made by research in this field. 2 We review the development of plant facilitation research, focusing on the history of the field, the relationship between plant–plant interactions and environmental severity gradients, and attempts to integrate facilitation into mainstream ecological theory. We then consider future directions for facilitation research. 3 With respect to our fundamental understanding of plant facilitation, clarification of the relationship between interactions and environmental gradients is central for further progress, and necessitates the design and implementation of experiments that move beyond the clear limitations of previous studies. 4 There is substantial scope for exploring indirect facilitative effects in plant communities, including their impacts on diversity and evolution, and future studies should connect the degree of non-transitivity in plant competitive networks to community diversity and facilitative promotion of species coexistence, and explore how the role of indirect facilitation varies with environmental severity. 5 Certain ecological modelling approaches (e.g. individual-based modelling), although thus far largely neglected, provide highly useful tools for exploring these fundamental processes. 6 Evolutionary responses might result from facilitative interactions, and consideration of facilitation might lead to re-assessment of the evolution of plant growth forms. 7 Improved understanding of facilitation processes has direct relevance for the development of tools for ecosystem restoration, and for improving our understanding of the response of plant species and communities to environmental change drivers. 8 Attempts to apply our developing ecological knowledge would benefit from explicit recognition of the potential role of facilitative plant–plant interactions in the design and interpretation of studies from the fields of restoration and global change ecology. 9 Synthesis: Plant facilitation research provides new insights into classic ecological theory and pressing environmental issues. Awareness and understanding of facilitation should be part of the basic ecological knowledge of all plant ecologists.

In this paper, we reflect on the implications for science, policy and practice of the recently introduced concept of Nature-Based Solutions (NBS), with a focus on the European context. First, we analyse NBS in relation to similar concepts, and reflect on its relationship to sustainability as an overarching framework. From this, we derive a set of questions to be addressed and propose a general framework for how these might be addressed in NBS projects by funders, researchers, policy-makers and practitioners. We conclude that: NBS need to be developed and discussed in relation to existing concepts to clarify their added value; When considering and implementing NBS, the ‘relabelling’ of related concepts and the misuse of the concept have to be prevented in order to avoid misunderstanding, duplication and unintended consequences; NBS as currently framed by the European Commission provides an opportunity for: a) transdisciplinary research into the design and implementation of solutions based on nature; and b) overcoming a bias towards development alternatives with narrow perspectives that focus on short-term economic gains and effectiveness; The strength of the NBS concept is its integrative, systemic approach which prevents it from becoming just another “green communication tool” that provides justification for a classical model of natural resource exploitation and management measures. To realise their full potential, NBS must be developed by including the experience of all relevant stakeholders such that ‘solutions’ contribute to achieving all dimensions of sustainability. As NBS are developed, we must also moderate the expectations placed on them since the precedent provided by other initiatives whose aim was to manage nature sustainably demonstrates that we should not expect NBS to be cheap and easy, at least not in the short-term.

Animal movement is fundamental for ecosystem functioning and species survival, yet the effects of the anthropogenic footprint on animal movements have not been estimated across species. Using a unique GPS-tracking database of 803 individuals across 57 species, we found that movements of mammals in areas with a comparatively high human footprint were on average one-half to one-third the extent of their movements in areas with a low human footprint. We attribute this reduction to behavioral changes of individual animals and to the exclusion of species with long-range movements from areas with higher human impact. Global loss of vagility alters a key ecological trait of animals that affects not only population persistence but also ecosystem processes such as predator-prey interactions, nutrient cycling, and disease transmission.

The unique combination of very large strains, high temperatures and high strain rates inherent to friction stir welding (FSW) and friction stir processing (FSP) and their dependency on the processing parameters provides an opportunity to tailor the microstructure, and hence the performance of welds and surfaces to an extent not possible with fusion processes. While a great deal of attention has previously been focused on the FSW parameters and their effect on weld quality and joint performance, here the focus is on developing a comprehensive understanding of the fundamentals of the microstructural evolution during FSW/P. Through a consideration of the mechanisms underlying the development of grain structures and textures, phases, phase transformations and precipitation, microstructural control across a very wide range of similar and dissimilar material joints is examined. In particular, when considering the joining of dissimilar metals and alloys, special attention is focused on the control and dispersion of deleterious intermetallic compounds. Similarly, we consider how FSP can be used to locally refine the microstructure as well as provide an opportunity to form metal matrix composites (MMCs) for near surface reinforcement. Finally, the current gaps in our knowledge are considered in the context of the future outlook for FSW/P.

Past and present pressures on forest resources have led to a drastic decrease in the surface area of unmanaged forests in Europe. Changes in forest structure, composition, and dynamics inevitably lead to changes in the biodiversity of forest-dwelling species. The possible biodiversity gains and losses due to forest management (i.e., anthropogenic pressures related to direct forest resource use), however, have never been assessed at a pan-European scale. We used meta-analysis to review 49 published papers containing 120 individual comparisons of species richness between unmanaged and managed forests throughout Europe. We explored the response of different taxonomic groups and the variability of their response with respect to time since abandonment and intensity of forest management. Species richness was slightly higher in unmanaged than in managed forests. Species dependent on forest cover continuity, deadwood, and large trees (bryophytes, lichens, fungi, saproxylic beetles) and carabids were negatively affected by forest management. In contrast, vascular plant species were favored. The response for birds was heterogeneous and probably depended more on factors such as landscape patterns. The global difference in species richness between unmanaged and managed forests increased with time since abandonment and indicated a gradual recovery of biodiversity. Clearcut forests in which the composition of tree species changed had the strongest effect on species richness, but the effects of different types of management on taxa could not be assessed in a robust way because of low numbers of replications in the management-intensity classes. Our results show that some taxa are more affected by forestry than others, but there is a need for research into poorly studied species groups in Europe and in particular locations. Our meta-analysis supports the need for a coordinated European research network to study and monitor the biodiversity of different taxa in managed and unmanaged forests.

$\ensuremath{\gamma}\ensuremath{-}{\mathrm{Fe}}_{2}{\mathrm{O}}_{3}$ magnetic nanoparticles, with a very high surface to volume ratio, exhibit both strong exchange anisotropy and magnetic training effect. At the same time high field irreversibility in $M\left(H\right)$ curves and zero field cooled--field cooled (ZFC-FC) processes has also been detected. A low temperature spin-glass-like transition is evidenced at ${T}_{F}\ensuremath{\approx}42\mathrm{K}$ with strong irreversibility even at $H\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}55\mathrm{kOe}$. ${T}_{F}\left(H\right)$ evolves following the well known de Almeida--Thouless line $\ensuremath{\delta}{T}_{F}\ensuremath{\propto}{H}^{2/3}$. The thermal dependence of the exchange anisotropy field ${H}_{E}$ is described by the random-field model of exchange anisotropy. In the framework of this theory, a surface spin-glass layer about 0.6 nm thick is determined.

Summary 1. Many recent statistical applications involve inference under complex models, where it is computationally prohibitive to calculate likelihoods but possible to simulate data. Approximate Bayesian computation (ABC) is devoted to these complex models because it bypasses the evaluation of the likelihood function by comparing observed and simulated data. 2. We introduce the R package ‘abc’ that implements several ABC algorithms for performing parameter estimation and model selection. In particular, the recently developed nonlinear heteroscedastic regression methods for ABC are implemented. The ‘abc’ package also includes a cross‐validation tool for measuring the accuracy of ABC estimates and to calculate the misclassification probabilities when performing model selection. The main functions are accompanied by appropriate summary and plotting tools. 3. R is already widely used in bioinformatics and several fields of biology. The R package ‘abc’ will make the ABC algorithms available to a large number of R users. ‘abc’ is a freely available R package under the GPL license, and it can be downloaded at http://cran.r‐project.org/web/packages/abc/index.html .

A ‘grafting from’ approach was used to graft poly(ε-caprolactone) (PCL) polymers to cellulose nanocrystals by Sn(Oct)2-catalyzed ring-opening polymerization (ROP). The grafting efficiency was evidenced by the long-term stability of suspension of PCL-grafted cellulose nanocrystals in toluene. These observations were confirmed by Fourier Transform Infrared Spectroscopy (FT-IR) and Time-of-Flight Secondary Ion Mass Spectrometry (TOF-SIMS). Extracted nanohybrids were characterized by Differential Scanning Calorimetry (DSC), X-ray photoelectron spectroscopy (XPS), and contact angle measurements. The morphology and crystalline structure of the PCL-grafted cellulose nanocrystals was examined by transmission electron microscopy (TEM) and X-Ray diffraction, respectively. Results showed that cellulose nanocrystals kept their initial morphological integrity and their native crystallinity. Nanocomposites with high content of cellulose nanocrystals were prepared using either neat cellulose nanocrystals or PCL-grafted cellulose nanocrystals and high molecular weight PCL as matrix using a casting/evaporation technique. Thermo-mechanical properties of processed nanocomposites were studied by DSC, dynamical mechanical analyses (DMA) and tensile tests. A significant improvement in terms of Young's modulus and storage modulus was obtained.

There are several facets of aluminum when it comes to sustainability. While it helps to save fuel due to its low density, producing it from ores is very energy-intensive. Recycling it shifts the balance towards higher sustainability, because the energy needed to melt aluminum from scrap is only about 5% of that consumed in ore reduction. The amount of aluminum available for recycling is estimated to double by 2050. This offers an opportunity to bring the metallurgical sector closer to a circular economy. A challenge is that large amounts of scrap are post-consumer scrap, containing high levels of elemental contamination. This has to be taken into account in more sustainable alloy design strategies. A “green aluminum” trend has already triggered a new trading platform for low-carbon aluminum at the London Metal Exchange (2020). The trend may lead to limits on the use of less-sustainable materials in future products. The shift from primary synthesis (ore reduction) to secondary synthesis (scrap melting) requires to gain better understanding of how multiple scrap-related contaminant elements act on aluminum alloys and how future alloys can be designed upfront to become scrap-compatible and composition-tolerant. The paper therefore discusses the influence of scrap-related impurities on the thermodynamics and kinetics of precipitation reactions and their mechanical and electrochemical effects; impurity effects on precipitation-free zones around grain boundaries; their effects on casting microstructures; and the possibilities presented by adjusting processing parameters and the associated mechanical, functional and chemical properties. The objective is to foster the design and production of aluminum alloys with the highest possible scrap fractions, using even low-quality scrap and scrap types which match only a few target alloys when recycled.

Abstract The normal spectral absorptance of a number of metal, ceramic and polymer powders susceptible to be utilised for selective laser sintering (SLS) technique was experimentally determined. The measurements were performed with two laser wavelengths of 1.06μm and 10.6μm obtained by using two lasers – Nd‐YAG and CO2 respectively. The change in the powder absorptance with time during laser processing was also investigated. The effect of the absorptance characteristics on the sintering process is discussed.

We report on the formation by mechanical alloying of fcc solid solution of Fe and Cu, which are immiscible. Intense codeformation of Cu with Fe and other high-melting bcc metals generates small fragments with tip radii of the order 1 nm such that capillary pressures force the atoms on these fragments to dissolve. The critical radius for dissolution is found to increase with solute content inside the spinodal thus leading to full dissolution of one of the components. The fcc-FeCu solid solutions have Curie temperatures similar to those of vapor-deposited alloys and a positive heat of mixing that is in accord with theoretical results.

Order, Order The structure of glassy materials, which are known to have short-range order but no long-range pattern, continues to be a puzzle. One current theory is that some glassy materials possess icosahedral ordering, a motif that cannot show translational periodicity. Hirata et al. (p. 376 , published online 11 July) obtained diffraction patterns from subnanometer volumes in a metallic glass, which show some, but not all, of the expected features of an icosahedron. Simulations suggest that the patterns arise from icosahedrons distorted to include features of the face-centered cubic structure. This observation is different from the predictions of molecular dynamics simulations and provides pivotal information in understanding the competition between the formation of the globally inexpensive long-range order and the locally inexpensive short-range order.

The stability of carbon-supported electrocatalysts has been largely investigated in acidic electrolytes, but the literature is much scarcer regarding similar stability studies in alkaline medium. Herein, the degradation of Vulcan XC-72-supported platinum nanoparticles (noted Pt/C), a state-of-the-art proton exchange membrane fuel cell electrocatalyst, is investigated in alkaline medium by combining electrochemical measurements and identical location transmission electron microscopy; electrochemical surface area (ECSA) losses were bridged to electrocatalyst morphological changes. The results demonstrate that the degradation in 0.1 M NaOH at 25 °C is severe (60% of ECSA loss after only 150 cycles between 0.1 and 1.23 V vs RHE), which is about 3 times worse than in acidic media for this soft accelerated stress test. Severe carbon corrosion has been ruled out according to Raman spectroscopy and X-ray photoelectron spectroscopy measurements, and it seems that the chemistry of the carbon support (in particular, the interface (chemical bounding)) between the Pt nanoparticles and their carbon substrate does play a significant role in the observed degradations.

The impact of the carbon structure, the aging protocol, and the gas atmosphere on the degradation of Pt/C electrocatalysts were studied by electrochemical and spectroscopic methods. Pt nanocrystallites loaded onto high-surface area carbon (HSAC), Vulcan XC72, or reinforced-graphite (RG) with identical Pt weight fraction (40 wt %) were submitted to two accelerated stress test (AST) protocols from the Fuel Cell Commercialization Conference of Japan (FCCJ) mimicking load-cycling or start-up/shutdown events in a proton-exchange membrane fuel cell (PEMFC). The load-cycling protocol essentially caused dissolution/redeposition and migration/aggregation/coalescence of the Pt nanocrystallites but led to similar electrochemically active surface area (ECSA) losses for the three Pt/C electrocatalysts. This suggests that the nature of the carbon support plays a minor role in the potential range 0.60 < E < 1.0 V versus RHE. In contrast, the carbon support was strongly corroded under the start-up/shutdown protocol (1.0 < E < 1.5 V versus RHE), resulting in pronounced detachment of the Pt nanocrystallites and massive ECSA losses. Raman spectroscopy and differential electrochemical mass spectrometry were used to shed light on the underlying corrosion mechanisms of structurally ordered and disordered carbon supports in this potential region. Although for Pt/HSAC the start-up/shutdown protocol resulted into preferential oxidation of the more disorganized domains of the carbon support, new structural defects were generated at quasi-graphitic crystallites for Pt/RG. Pt/Vulcan represented an intermediate case. Finally, we show that oxygen affects the surface chemistry of the carbon supports but negligibly influences the ECSA losses for both aging protocols.

A thorough investigation of the acid-catalyzed polycondensation of furfuryl alcohol was conducted with the specific aim of understanding the mechanisms responsible for the main reaction, but more particularly for the transformation of linear unconjugated oligomers into black cross-linked final materials. The originality of the present approach, compared with previous unsuccessful attempts, consisted in calling upon numerous model compounds simulating specific features of both the monomer and its condensation products. The formation of conjugated sequences along the poly(furfuryl) chains is caused by repetitive cycles involving the loss of hydride ions followed by the deprotonation of the carbenium ions thus formed. This reaction was simulated and accelerated by using cationic hydride-ion abstractors. The branching reactions only occur after the appearance of the multiple unsaturations and owe their origin to interchain cycloadditions between furan rings and conjugated structures. A long-standing puzzle has thus been solved.

Cellulose and starch nanocrystals obtained from the acid hydrolysis of ramie fibers and waxy maize starch granules, respectively, were subjected to isocyanate-mediated reaction to graft polycaprolactone (PCL) chains with various molecular weights on their surface. Grafted nanoparticles were characterized by X-ray diffraction analysis and contact angle measurements. We observed that the nanoparticles kept their initial morphological integrity and native crystallinity. Nanocomposite films were processed from both unmodified and PCL-grafted nanoparticles and PCL as matrix using a casting/evaporation technique. We showed that mechanical properties of resulting films were notably different. Compared to unmodified nanoparticles, the grafting of PCL chains on the surface results in lower modulus values but significantly higher strain at break. This unusual behavior clearly reflects the originality of the reinforcing phenomenon of polysaccharide nanocrystals resulting from the formation of a percolating network thanks to chain entanglements and cocrystallization.

We connected dislocation-based atomic-scale and continuum models of plasticity in crystalline solids through numerical simulations of dislocation intersections in face-centered cubic crystals. The results contradict the traditional assumption that strain hardening is governed by the formation of sessile junctions between dislocations. The interaction between two dislocations with collinear Burgers vectors gliding in intersecting slip planes was found to be by far the strongest of all reactions. Its properties were investigated and discussed using a multiscale approach.

Abstract An automated technique for the mapping of nanocrystal phases and orientations in a transmission electron microscope is described. It is primarily based on the projected reciprocal lattice geometry that is extracted from electron diffraction spot patterns. Precession electron diffraction patterns are especially useful for this purpose. The required hardware allows for a scanning-precession movement of the primary electron beam on the crystalline sample and can be interfaced to any older or newer mid-voltage transmission electron microscope (TEM). Experimentally obtained crystal phase and orientation maps are shown for a variety of samples. Comprehensive commercial and open-access crystallographic databases may be used in support of the nanocrystal phase identification process and are briefly mentioned.

The purpose of this study was to investigate a new way of processing cellulose whiskers reinforced polymer. A stable suspension of tunicin whiskers was obtained in an organic solvent (N,N-dimethylformamide) without a surfactant addition or a chemical surface modification. Both the high value of the dielectric constant of DMF and the medium wettability of tunicin whiskers were supposed to control the stability of the suspension. The nanocomposite materials were prepared by UV cross-linking using an unsaturated polyether as matrix. The resulting films were characterized by SEM, DSC, and mechanical testing in both the linear and nonlinear domains. The processing technique from a N,N-dimethylformamide suspension was found to be successful and led to materials whose properties are similar to those obtained with aqueous medium. It could be a good alternative to broaden the number of possible polymer matrices and to allow the processing of nanocomposite materials from an organic solvent solution instead of using aqueous suspensions.