TRY plant trait database – enhanced coverage and open access

Plant traits - the morphological, anatomical, physiological, biochemical and phenological characteristics of plants - determine how plants respond to environmental factors, affect other trophic levels, and influence ecosystem properties and their benefits and detriments to people. Plant trait data thus represent the basis for a vast area of research spanning from evolutionary biology, community and functional ecology, to biodiversity conservation, ecosystem and landscape management, restoration, biogeography and earth system modelling. Since its foundation in 2007, the TRY database of plant traits has grown continuously. It now provides unprecedented data coverage under an open access data policy and is the main plant trait database used by the research community worldwide. Increasingly, the TRY database also supports new frontiers of trait‐based plant research, including the identification of data gaps and the subsequent mobilization or measurement of new data. To support this development, in this article we evaluate the extent of the trait data compiled in TRY and analyse emerging patterns of data coverage and representativeness. Best species coverage is achieved for categorical traits - almost complete coverage for ‘plant growth form’. However, most traits relevant for ecology and vegetation modelling are characterized by continuous intraspecific variation and trait–environmental relationships. These traits have to be measured on individual plants in their respective environment. Despite unprecedented data coverage, we observe a humbling lack of completeness and representativeness of these continuous traits in many aspects. We, therefore, conclude that reducing data gaps and biases in the TRY database remains a key challenge and requires a coordinated approach to data mobilization and trait measurements. This can only be achieved in collaboration with other initiatives

Climate control of terrestrial carbon exchange across biomes and continents

Peer reviewe

Computer simulation of the injection molding of viscoelastic crystalline thermoplastics

The thermomechanical history experienced by plastics melts and solids during processing leads to the development of microstructure, which directly influences the ultimate properties of the plastic articles. Therefore, besides the predictions of thermomechanical history, the prediction of microstructure represents an important aspect of the modeling of plastics processing.A comprehensive model has been developed to describe the behaviour of thermoplastic polymer melts during the injection molding process. The model, which deals with the three stages of the process (filling, packing and cooling), employs a viscoelastic constitutive equation and incorporates crystallization kinetics. All the properties of the material employed are based on experimental data. The model predicts fill times, velocity, temperature and pressure distributions, the distribution of shear and normal stresses, and stress relaxation. The predictions of the model are compared to experimental data relating to pressure distributions and variation with time, fill times, and the distributions of crystallinity, orientation and tensile modulus

Extrusion des Polymères

National audienceL'extrusion est le plus important des procédés de transformation des polymères. Dans cet ouvrage, les auteurs présentent en détail les deux procédés clés que sont l'extrusion monovis et l'extrusion bi-vis, ainsi que leur application à la fabrication de profilés, de films et de câbles. L'accent est mis sur la compréhension des mécanismes physiques se déroulant dans ces procédés et sur le développement de modèles simples, souvent analytiques, fondés sur la thermique et la mécanique des milieux continus. Ces modèles permettent d'obtenir aisément des ordres de grandeur, de dimensionner rapidement des outillages ou d'optimiser des conditions opératoires. Bien entendu, à côté de ces approches très simplifiées, des modèles plus sophistiqués sont également présentés. Sommaire : 1, Introduction. 2, Rappels de mécanique, de rhéologie et de thermique. 3, méthodes de calcul. 4, Extrusion monovis. 5, Extrusion bivis co-rotatives. 6, Fabrication des produits profilés. 7, Fabrication des films et feuilles. 8, Câbleri

Polymer Extrusion

Extrusion is by far the most important and the oldest processing and shaping method for thermoplastic polymers. This process concerns almost all synthetic polymers, as well as elastomers or food materials. Single-screw extrusion is mainly used nowadays to manufacture finished goods or semi-finished products. More than 90 million tons of thermoplastics are therefore processed every year. Twin-screw extrusion may be divided into two systems: contra-rotating systems used within the context of PVC extrusion, for the manufacture of pipes or profiles; and co-rotating systems experiencing nowadays a very significant development, because of their significant adaptability and flexibility, which enables the manufacture of specific materials (polymer alloys, thermoplastic elastomers, filled polymers, nanocomposites). Extrusion is carried out by passing molten polymer through a tool called die that will give the product its final shape (films and sheets, rolled products, and electric cables). Thanks to the design of dies, we obtain at the output a product with controlled dimensions, uniform speeds and homogeneous temperatures. The book will discuss the same production types, but only in the case of coextrusion flows, i.e. multilayer stratified products. First of all, we will present in this book the physics of the mechanisms at stake, then propose more or less complex models in order to describe these mechanisms and then go forward in the interpretation of results and the control of condition flows

Dispersive prediction of single-screw extruder with mixing head using Boundary Element Method

International audienceThe relationship between the mixing performance in extrusion and the process conditions is of great importance but is never easy to establish. Although experimental prototyping of mixing equipment provides insight into the mixing process, it is too time consuming and cost prohibitive to fully optimize the geometry and the process itself. Alternatively, numerical methods can be used to provide more detailed information on the mixing flows to alleviate the problems with experimental modeling. The Boundary Element Method is an alternative technique which offers the possibility of modeling complex systems since it requires only the discretisation of the model boundaries. In this paper, we examine the use of a Boundary Element Method (BEM) model to predict the dispersive mixing performance of Maddock-like mixing heads on single screw extruders. We use this method to calculate the flow number on the middle plan of the studied geometries and compare it between different conditions of extrusion. The experiments were conducted with a classical Maddock mixing head (in-house design). Two materials were extruded: a polypropylene/ calcium carbonate blend and a polyvinyl chloride/ red pigment blend. The numerical simulations were compared to the observed mixing behavior