Le microclimat urbain à haute résolution : mesures et modélisation

Le confort thermique des habitants d'une ville est principalement affecté par l'îlot de chaleur urbain. Ce phénomène se traduit par des températures plus chaudes en ville que dans sa périphérique, principalement la nuit. Il est causé par les relâchements de chaleur stockée dans les bâtiments et la route le jour mais aussi par des sources anthropiques comme le chauffage ou le trafic routier. L'îlot de chaleur urbain peut atteindre jusqu'à 10°C la nuit pour les plus grandes mégapoles. Mais au cœur d'un quartier, la variabilité de la température, en fonction des ombrages ou de la présence d'eau et de parcs peut aussi atteindre quelques degrés. Elle peut donc être de la même amplitude que l'îlot de chaleur urbain. L'objectif de cette thèse est d'étudier la variabilité de la température à l'échelle de la ville et à l'échelle de la rue. Le but est de mettre en place une chaîne de modélisation de la température à l'échelle de rue à partir de données de stations météorologiques opérationnelles en périphérie d'une ville. Cette chaîne de modélisation doit être rapide et faire appel à des données accessibles au plus grand nombre afin de pouvoir simuler des scénarios d'aménagement urbains sur le long terme en dehors des laboratoires de recherche. La première partie de la chaîne de modélisation s'appuie sur un modèle numérique physique, le générateur de climat urbain spatialisé, permettant de calculer l'îlot de chaleur à l'échelle du quartier à partir de données se situant en dehors d'une ville et d'un modèle de surface de ville comme le modèle TEB. La deuxième partie permet de modéliser statistiquement la variabilité de température à l'échelle de la rue à partir des conditions météorologiques simulées par le générateur au sein d'un quartier et d'une cartographie précise du tissu urbain du quartier considéré. Cette modélisation statistique s'appuie sur des campagnes de mesures effectuées en 2013 et 2014 dans des quartiers des villes de Marseille, Paris et Toulouse.The thermal comfort of the inhabitants of a city is mainly affected by the urban heat island (difference in air temperature between urban and surrounding area. This effect is caused by anthropogenic sources, low vegetated areas and heat stored in buildings and roads during the night. The urban heat island can reach 10°C at night for the biggest cities. But inside a neighborhood, the temperature variability can reach a few degrees with the effect of the shadow of the trees or the presence of lake or parks. This variability may have the same magnitude than the urban heat island. The objective of this thesis is to study the temperature variability at the city-scale and at the street-scale. The aim of this PhD work is to develop a modeling chain of the temperature at the street-scale from data from operational weather stations located in airports.The modeling chain has to be fast in order to simulate long term urban planning scenarios and have a low computational cost in order to be run outside of atmospheric sciences laboratories. The first step of the modeling chain is the spatialized urban weather generator, a numerical physical scheme which calculated the urban heat island at the neighborhood scale from data of an operational weather station located outside of the city and with sur urban surface model TEB. The second part is a statistical model of temperature variability at the street scale calculated with meteorological data coming from the generator and a mapping of the urban tissue. The statistical model relies on field campaigns achieved in 2013 and 2014 in the neighborhoods of Marseille, Paris and Toulouse

Cellulose Nanocrystals: From Classical Hydrolysis to the Use of Deep Eutectic Solvents

During the last two decades, interest in cellulosic nanomaterials has greatly increased. Among these nanocelluloses, cellulose nanocrystals (CNC) exhibit outstanding properties. Indeed, besides their high crystallinity, cellulose nanocrystals are interesting in terms of morphology with high aspect ratio (length 100–1000 nm, width 2–15 nm), high specific area, and high mechanical properties. Moreover, they can be used as rheological modifier, emulsifier, or for barrier properties, and their surface chemistry opens the door to numerous feasible chemical modifications, leading to a large panel of applications in medical, electronic, composites, or packaging, for example. Traditionally, their extraction is performed via monitored sulfuric acid hydrolysis, leading to well-dispersed aqueous CNC suspensions; these last bearing negative charges (half-sulfate ester groups) at their surface. More recently, natural chemicals called deep eutectic solvents (DESs) have been used for the production of CNC in a way of green chemistry, and characterization of recovered CNC is encouraging

Chemically extracted nanocellulose from sisal fibres by a simple and industrially relevant process

International audienceA novel type of acetylated cellulose nanofibre (CNF) was extracted successfully from sisal fibres using chemical methods. Initially, a strong alkali treatment was used to swell the fibres, followed by a bleaching step to remove the residual lignin and finally an acetylation step to reduce the impact of the intermolecular hydrogen bonds in the nanocellulose. The result of this sequence of up-scalable chemical treatments was a pulp consisting mainly of micro-sized fibres, which allowed simpler handling through filtration and purification steps and permitted the isolation of an intermediate product with a high solids content. An aqueous dispersion of CNF could be obtained directly from this intermediate pulp by simple magnetic stirring. As a proof of concept, the dispersion was used directly for preparing a highly translucent CNF film, illustrating that there are no large aggregates in the prepared CNF dispersion. Finally, CNF films with alkali extracts were also prepared, resulting in flatter films with an increased mass yield and improved mechanical strength

Isolation and characterization of cellulose nanofibers from argentine tacuara cane (Guadua angustifolia kunth)

New trends in the area of material improvement are the use of natural nano-charges from renewable biomass, improving the value and sustainability of our country’s natural products. Bamboo is widely used in many countries of the world, although in Argentina, despite being commercialized and exported for the manufacture of wood floors, it goes unnoticed despite having native species. Therefore, researchers identified the native and exotic species present in our country and are working on novel uses. In this context, it is proposed the Argentine Tacuara Cane (Guadua Angustifolia Kunth), endemic plant as a new source of nanocellulosic materials, where stem fibers have been isolated using a green method achieving with yield of 45.9% of cellulose. The cellulose nanofibrils (CNF) were obtained using a green homogenization method. The CNF exhibited web-like long fibrous structure with the diameter of 10-20 nm. The crystallinity was 65.5%, as for the onset temperature of thermal decomposition was 212°C. The nanocellulose isolated from the Tacuara Cane seed fibers has a high potential to be used as a new source of cellulose-based nanofiller for the reinforcement of bionanocomposite films.Fil: Rodriguez Ramirez, Carlos Alejandro. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Centro de Investigaciones en Hidratos de Carbono. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Centro de Investigaciones en Hidratos de Carbono; ArgentinaFil: Rol, Fleur. Université Grenoble Alpes; FranciaFil: Bras, Julien. Université Grenoble Alpes; FranciaFil: Dufresne, Alain. Université Grenoble Alpes; FranciaFil: Garcia, Nancy Lis. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Centro de Investigaciones en Hidratos de Carbono. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Centro de Investigaciones en Hidratos de Carbono; ArgentinaFil: D'accorso, Norma Beatriz. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Centro de Investigaciones en Hidratos de Carbono. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Centro de Investigaciones en Hidratos de Carbono; Argentina. Universidad de Buenos Aires; Argentin

Multilayers of Renewable Nanostructured Materials with High Oxygen and Water Vapor Barriers for Food Packaging

Natural biopolymers have become key players in the preparation of biodegradable food packaging. However, biopolymers are typically highly hydrophilic, which imposes limitations in terms of barrier properties that are associated with water interactions. Here, we enhance the barrier properties of biobased packaging using multilayer designs, in which each layer displays a complementary barrier function. Oxygen, water vapor, and UV barriers were achieved using a stepwise assembly of cellulose nanofibers, biobased wax, and lignin particles supported by chitin nanofibers. We first engineered several designs containing CNFs and carnauba wax. Among them, we obtained low water vapor permeabilities in an assembly containing three layers, i.e., CNF/wax/CNF, in which wax was present as a continuous layer. We then incorporated a layer of lignin nanoparticles nucleated on chitin nanofibrils (LPChNF) to introduce a complete barrier against UV light, while maintaining film translucency. Our multilayer design which comprised CNF/wax/LPChNF enabled high oxygen (OTR of 3 +/- 1 cm(3)/m(2).day) and water vapor (WVTR of 6 +/- 1 g/m(2).day) barriers at 50% relative humidity. It was also effective against oil penetration. Oxygen permeability was controlled by the presence of tight networks of cellulose and chitin nanofibers, while water vapor diffusion through the assembly was regulated by the continuous wax layer. Lastly, we showcased our fully renewable packaging material for preservation of the texture of a commercial cracker (dry food). Our material showed functionality similar to that of the original packaging, which was composed of synthetic polymers.Peer reviewe

Oxygen and water vapor permeability of fully substituted long chain cellulose esters (LCCE)

Fully-substituted cellulose esters with acyl substituents ranging in size from C2 to C18 were synthesized using the acyl chloride method. Films were prepared from the purified esters by either solvent-casting or compression-molding at elevated temperatures. Oxygen and water vapor permeability was determined under different conditions of pressure and moisture. The relationship between cellulose ester structure and barrier properties was examined. The results revealed linear relationships between water vapor and oxygen permeabilities and molar ester substituent volume as well as several structural factors relating to polymer polarity and hydrophobicity, such as aliphatic (methylene) content, solubility parameter, and contact angle. Films from long chain cellulose esters (LCCE) with acyl substituents in the size range between C8 and C18 were found to represent effective barriers to water vapor transport while their obstruction to the transfer of oxygen remained low. It was concluded that the hydrophobic nature of LCCEs is responsible for the control of water vapor transport, and that spatial factors dominate the transfer of oxygen

Simulation basis for a techno-economic evaluation of chitin nanomaterials production process using Aspen Plus® software

Process simulation is a useful tool that has been widely used to analyze, design and optimize energy balances in chemical technologies including those related to biomass processing, biorefinery processes and chemical engineering. The presented data set serves as basis for the simulation of chitin purification, nanofibers and nanocrystals production processes, considering laboratory experimental procedures described in previous experimental articles.Peer ReviewedPostprint (published version

NIR Study of Chemically Modified Cellulosic Biopolymers

Near-infrared spectral analysis was useful to quantify the ester content of chemically modified cellulose and lignocellulosics. Two kinds of samples were studied, as long aliphatic-chain cellulose esters and wood sawdust chemically-modified either by anhydrides or by ethylene carbonate. It was possible to determine the degree of substitution (DS) of such samples through a correlation by partial least square (PLS) of second-order derivative of NIR spectra. This technique was efficient even when DS values were low, which is difficult to do by using FTIR. It was also possible to distinguish reagent molecules that were attached to the cellulosic substrate by hydrogen bonding from those linked by covalent bonding

Curr Biol

Efference copies are neural replicas of motor outputs used to anticipate the sensory consequences of a self-generated motor action or to coordinate neural networks involved in distinct motor behaviors. An established example of this motor-to-motor coupling is the efference copy of the propulsive motor command, which supplements classical visuo-vestibular reflexes to ensure gaze stabilization during amphibian larval locomotion. Such feedforward replica of spinal pattern-generating circuits produces a spino-extraocular motor coupled activity that evokes eye movements, spatiotemporally coordinated to tail undulation independently of any sensory signal. Exploiting the developmental stages of the frog, studies in metamorphing Xenopus demonstrated the persistence of this spino-extraocular motor command in adults and its developmental adaptation to tetrapodal locomotion. Here, we demonstrate for the first time the existence of a comparable locomotor-to-ocular motor coupling in the mouse. In neonates, ex vivo nerve recordings of brainstem-spinal cord preparations reveal a spino-extraocular motor coupled activity similar to the one described in Xenopus. In adult mice, trans-synaptic rabies virus injections in lateral rectus eye muscle label cervical spinal cord neurons closely connected to abducens motor neurons. Finally, treadmill-elicited locomotion in decerebrated preparations evokes rhythmic eye movements in synchrony with the limb gait pattern. Overall, our data are evidence for the conservation of locomotor-induced eye movements in vertebrate lineages. Thus, in mammals as in amphibians, CPG-efference copy feedforward signals might interact with sensory feedback to ensure efficient gaze control during locomotion.Corrélats neurophysiologiques de l'évolution et du développement des stratégies de stabilisation du regard pendant la locomotion chez les vertébrésUniversité de Pari