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Can anaerobic digestion be a suitable end-of-life scenario for biodegradable plastics? A critical review of the current situation, hurdles, and challenges
Get PDFpromoted interest in biodegradable plastics. The intensification of separate biowastes collection in most European countries has also contributed to the development of biodegradable plastics, and the subject of their end-of-life is becoming a key issue. To date, there has been relatively little research to evaluate the biodegradability of biodegradable plastics by anaerobic digestion (AD) compared to industrial and home composting. However, anaerobic digestion is a particularly promising strategy for treating biodegradable organic wastes in the context of circular waste management. This critical review aims to provide an in-depth update of anaerobic digestion of biodegradable plastics by providing a summary of the literature regarding process performance, parameters affecting biodegradability, the microorganisms involved, and some of the strategies (e.g., pretreatment, additives, and inoculum acclimation) used to enhance the degradation rate of biodegradable plastics. In addition, a critical section is dedicated to suggestions and recommendations for the development of biodegradable plastics sector and their treatment in anaerobic digestion
Spontaneous moisture-driven formation of Cs2Pb1-xMxCl2I2 single crystals with M = Bi, In, Ga and Cr
Get PDFMicrometer to millimeter platelets-like single crystals of the 2D-derivated perovskite structure Cs2PbCl2I2 were synthesized by a very simple route using the humid ambient environment surrounding a DMSO solution containing the salt precursors. Cs2Pb1-xMxCl2I2 formation was also evidenced by single crystal X-ray diffraction, with M = Bi, Ga, In and Cr. X-ray photoelectron spectroscopy (XPS) confirmed the presence of each dopant, with an amount of x ∼ 5 ato.% for the last three materials. For the Bi-doped sample, XPS showed a larger quantity of dopant that can be due to XPS difficulty to discriminate too close elements for a few nanometers of analysis or higher concentrations in some crystals due to the affinity of both elements to integrate this structure on the same crystallographic site. A decrease of Bi concentration was determined by ion-beam and XPS simultaneous analysis. Finally, a photoluminescence (PL) peak was observed at ∼420 nm for all samples. Peak widening and blue-shift can be ascribed to the doping, and attributed to photon recycling and radiative self-trapped states. These results show the great versatility of ionic substitution and adaptive optoelectronic properties of the 2D phase that is stable in temperature
Crop monitoring and detection of anomalous crop development at the parcel-level with multispectral and synthetic aperture radar satellite data
Get PDFCrop monitoring will become a major challenge in the coming years. Under the pressure of climate change on the one hand, and the increase of the world population on the other hand, food supply chains are likely to be strongly constrained, impacting food security in many areas of the planet. In this context, using remote sensing to acquire information on vegetation status will be a key asset. One of the areas directly concerned is precision agriculture, which consists in optimizing yields and agricultural practices. With the arrival of the Copernicus mission satellites, Sentinel-1 (synthetic aperture radar) and Sentinel-2 (multispectral imagery), the possibilities of applications in this area have increased drastically. Indeed, Sentinel data are freely available, with a temporal and spatial resolution adapted to crop monitoring at the parcel level. The main objective of this thesis is to propose a strategy to automatically detect agricultural parcels with abnormal agronomic development. Special attention was given to the joint use of Sentinel-1 and Sentinel-2 data. Moreover, in order to be easily deployed in an operational context, a constraint is to have a method able to analyzing a single growth cycle (or a part of it). To meet the objectives of the thesis, we first propose a processing chain allowing the extraction of agronomic indicators at the parcel-level. These indicators are calculated in two steps: 1) calculation of agronomic indicators at the pixel level and 2) calculation of spatial statistics at the plot level. Then, these indicators are used to detect parcels with abnormal phenological behavior. The detection is unsupervised and performed using an anomaly detection algorithm. A comparison of several approaches was made to find the most suitable method for our problem. Among the different algorithms tested, the most efficient method is the isolation forest, which also has the advantage of being fast and not very sensitive to the choice of its parameters. Thanks to the proposed method, it is possible to detect plots with abnormal behavior with a high accuracy. The results obtained were validated on two different types of crops, wheat and rapeseed. In a second step, we addressed the problem of anomaly detection in the presence of missing data. This problem is fundamental in remote sensing, in particular for multispectral data because they are sensitive to cloud cover. To solve this problem, we propose to reconstruct the missing data (at the parcel-level) using Gaussian mixture models. This approach has been found to be significantly better than the other tested approaches for reconstructing missing data and for detecting anomalies on parcels with incomplete time series. In addition, we also have proposed a method for estimating Gaussian mixture models that are robust to the presence of outliers in the data. This method is particularly useful in the presence of strong outlier values, for example in the presence of parcels coming from a different crop type than the one analyzed. Finally, we explore in this thesis anomaly detection approaches that take into account the temporal structure of the data. In particular, we propose a method based on an ensemble of hidden Markov models. One of the interests of this approach is to be able to localize the anomalies in time
Aviation and climate: the state-of-the-art
Get PDFAs a human activity, the aviation sector is a contributor to climate change due the CO2 emissions and also non-CO2 effects which result from the interactions of the engine effluents with the atmosphere. The understanding and quantification of the impact of the aviation sector on climate is an intricate topic, whose evaluation largely depends on the scope considered. Furthermore, identifying the possible and efficient levers to mitigate such impact is of interest. This paper proposes a short review of the scientific literature regarding aviation and climate. Furthermore, it proposes an analysis of prospective decarbonisation scenarios for the sector in the context of the Paris Agreement. The results indicate that the ability of the aviation sector to reduce its CO2 emissions by 2050 thanks to technological levers (including progresses in
aerodynamics and propulsion) alone depends on the objective for the limitation of temperature increase by 2100. For an objective of +1.5 °C, if air traffic grows at the rate predicted by the aviation industry, it will consume a larger share of the carbon budget than its current share of CO2 emissions. Also, the results are compelling in regard of the low-carbon energy availability for the aviation sector
Ecodesign with topology optimization
Get PDFIn order to mitigate the impact of the transportation sector on climate change, light and ecological parts must be designed. A lifecycle oriented design methodology with C02 footprint minimization of parts used in various transports is presented in this work. Only material production and use phase are considered in this work, to have a better understanding of the different contributions. Simultaneous topological design and material choice are investigated for 2D examples. The results show that considering out-of-plane thickness as a variable, both problems can now be decoupled for simple load cases. It is shown that a very simple material index depending only on the type of transport can be used. An optimal volume fraction is obtained, specific only to each topology problem, but unrelated to the material chosen or the loads applied. The method is promising for fast ecodesign and its simple implementation enables easy future improvements
Parametric sub-structuring models of large space truss structures for structure/control co-design
Get PDFModern and future high precision pointing space missions face increasingly high challenges related to the widespread use of large flexible structures. The development of new modeling tools which are able to account for the multidisciplinary nature of this problem becomes extremely relevant in order to meet both structure and control performance criteria. This paper proposes a novel methodology to analytically model large truss structures in a sub-structuring framework. A three dimensional unit cube element has been designed and validated with a Finite Element commercial software. This model is composed by multiple two-dimensional sub-mechanisms assembled using block-diagram models. This constitutes the building block for constructing complex truss structures by repetitions of the element. The accurate vibration description of the system and its minimal representation, as well as the possibility of accounting for parametric uncertainties in its mechanical parameters, make it an appropriate tool to perform robust Structure/Control co-design. In order to demonstrate the strengths of the proposed approach, a structure/control co-design study case is proposed and solved using structured robust ????∞-synthesis. The objective is to optimize the pointing performances of an antenna, minimizing the perturbations coming from the Solar Array Driving Mechanisms (SADM) of two solar panels, performing active control by means of multiple Proof Mass Actuators (PMA), and simultaneously reduce the mass of the truss-structure which connects the antenna to the main spacecraft body
A general square exponential kernel to handle mixed-categorical variables for Gaussian process
Get PDFRecently, there has been a growing interest for mixed categorical meta-models based on Gaussian process (GP) surrogates. In this setting, several existing approaches use different strategies. Among the recently developed methods, we could cite: GP models built using continuous relaxation of the variables, Gower distance based models or GP models derived from direct estimation of the correlation matrix.
In this paper, we present a kernel-based approach that extends continuous Gaussian kernels to handle mixed-categorical variables. The proposed kernel leads to a GP surrogate that generalizes continuous relaxation and Gower distance based GP models. The good potential of the proposed framework is shown on analytical mixed-categorical variables test cases. On different settings, our proposed GP models is as accurate as the state-of-the-art GP models
The effect of initial conditions on the evolution of a turbulent mixing region induced by the Richtmyer-Meshkov instability
Get PDFTime-resolved Schlieren Photography was used to visualise the mixing zones induced by the Richtmyer-Meshkov (RM) instability initiated with four different initial conditions: three of them with monotonic, single-mode shape and one with a non-monotonic, multi-mode shape. Results of this experimental campaign showthat the shape of the initial air-helium interface has an effect on the resultant mixing region. These also confirm that the evolution of the RMI-induced mixing width follows an exponential law. The growth-rate of the mixing width depends on the monotonicity of the initial air-helium interface: while the mixing widths originating from single-mode initial conditions are almost superimposed, a lower growth-rate is found for the mixing width evolution arising from a multi-mode initial condition. The macro-scale Reynolds number based on the width of the mixing zone suggests that both flows initiated with single- and with multi-mode initial conditions reach a fully turbulent state after the reshock phenomenon. The Schlieren Photography visualisations presented here allow to illustrate the flow topologies of the induced mixing and highlight the effect of the initial conditions on the large-scale structures of the RM instability-induced mixing
Improving mechanical ice protection systems with substrate shape optimization
Get PDFMechanical and electro-mechanical de-icing systems are low-energy ice protection solutions based on fracture
mechanisms. It can, however, be difficult to obtain the protection of an entire surface due to the limited prop
agation of fractures for some mechanisms. This article shows how it is possible to reshape the substrate in order
to favor the propagation of adhesive fracture at the ice/substrate interface. The first part of the paper introduces
an analytical beam theory approach for running computations quickly, making it possible to achieve parametric
optimization of the substrate thickness and maximize the propagation length. The optimization results were
validated using FEM software and tests on an aluminum prototype. A second method is also studied in this paper,
topology optimization is used on a 2D finite element model to minimize the substrate mass of the proposed
solution and adhesive crack propagation is assessed in comparison with the mass impact. For different boundary
conditions, propagation ranges can be increased by up to 150% with a mass increase limited to 50%. Using
topology optimization, the additional mass could be reduced by 60% while maintaining the same
performances
Hybrid Material for Radiation Protection in Lunar Environment
Get PDFIn the context of an overview of radiation as the prime showstopper of human deep space exploration and a regolith-based material as a candidate for protection, this synthetic paper presents an original possible technology for hybrid hybrid protection- wall. This concept takes advantage of different elements available on site in a planetary base, in particular in the lunar regolith