Dissertations / Theses on the topic 'Dessication'

Stomatal apertures on leaves of the resurrection plant Xerophyta humilis were monitored microscopically in order to characterize stomatal regulation during a dehydration time course. In addition, the effect of exogenous application of the stress hormone ABA on stomatal regulation was followed. X humilis stomatal regulation appears to be initially similar to that typical of desiccation sensitive plants, but differed in that stomata did not all close at once but at a slower rate to control the drying rate of the plant, this gave time for protection mechanisms to be laid down. The signal hormone ABA was found to have strong stomatal control on the adaxial surfaces of leaves but weak control on the abaxial leaf surfaces, thus it is difficult to say that ABA regulates the process until RWC of below 50%, where stomatal apertures open as a result of shrinkage of guard cells due to loss of water.

Ce travail cherche à élaborer un cadre théorique unifié et cohérent, fondé sur les principes rigoureux de la thermodynamique et permettant de modéliser une classe étendue de phénomènes physiques intervenant dans les milieux poreux non saturés, ainsi que leur interaction avec l'état mécanique des structures. Cette classe est celle des phénomènes réactifs, parmi lesquels le changement de phase (la dessiccation), modélisé dans l'ensemble de ses conséquences (fluage, mais surtout retrait) sera abordé comme exemple particulier d'application. Le premier chapitre rappelle les fondements de la description adoptée du milieu poreux, ainsi que le cadre thermodynamique global qui sous-tend l'ensemble de la modélisation. Le chapitre II s'attache à la formulation essentiellement nouvelle et à l'identification d'une loi de comportement élastique non linéaire du milieu. Différents éléments de réflexion liés aux comportements microscopiques des constituants et à l'expérience, orientent le modèle vers certaines hypothèses fortes qui permettent la détermination complète et explicite de loi de comportement macroscopique. Le chapitre III expose les différentes expériences à disposition pour l'identification de la loi de comportement et permet de les intégrer, en tant que caractéristiques comportementales, dans le modèle théorique. Chapitre IV et chapitre V sont des exemples d'application: le chapitre IV étudie le problème du retrait et du fluage de dessiccation en comportement couple élastique linéaire ; le chapitre V se limite au cas du retrait de dessiccation, par application numérique du modèle élastique non linéaire complet. Les résultats obtenus présentent une bonne adéquation avec l'expérience

F. A. Vit en milieu sec et subit des variations climatiques extremes. Il est capable de reguler ses pertes hydriques. Il est peu resistant au froid et a la secheresse. Il survit grace a son aptitude a rentrer en anhydrobiose, grace a une deshydratation lente et progressive. Le metabolisme respiratoire, suivi par l'activite de la cytochrome oxydase, decroit pendant l'anhydrobiose et augmente pendant la rehydratation. Le metabolisme des glacides est aussi modifie: diminution des reserves de glycogene pendant l'anhydrobiose, restauration apres rehydratation

L’objectif de cette thèse était le développement d’un mycoherbicide efficace contenant les propagules stables de Plectosporium alismatis, un mycoherbicide potentiel de riz. Le champignon produit des conidies (109 L-1) et des chlamydospores (108 L-1) dans les erlens. Le nitrate est essentiel pour la production de chlamydospores qui ont une survie élevée (6. 6% germination après 4 mois) comparée aux conidies. Des agrégats hétérogènes (contenant les clilamydospores) ont été aussi observés en milieu liquide contenant du nitrate. Ces agrégats pouffaient augmenter la résistance de P. Aljymatis contre les stresses environnementaux. La production d’agrégats homogènes sphériques (les pellets) est nécessaire pour améliorer la reproductibilité. Un milieu « Aggregate Production Medium (APM) » a été développé dans lequel des pellets (~2. 8 x 105 L-1), des conidies (~6. 5 x 109 L-1) et des chlamydospores (~9. 6 x 108 L-1) ont été produits. Après la dessiccation et l’exposition aux UV, le nombre maximal de propagules libres (~104 conidies et ~2 x 102 chlamydospores) n’a pas infecté la feuille alors qu’un seul pellet était suffisant pour causer la nécrose. Nous avons donc conclu que ces pellets étaient plus pathogènes car probablement plus résistants aux UV et à la dessiccation que les conidies. Les études de survie ont montré que la formulation diatomite contenant des conidies libres, des chlamydospores libres et des pellets, stockée à 4°C, survivait après 9 mois de conservation (12% de germination) et restait pathogène. En conclusion, P. Alismatis peut produire des pellets en milieu APM, et la formulation diatomite contenant ces pellets pourrait répondre aux qualités exigées d’un mycoherbicide efficace
The objective of this thesis was to develop an efficient mycoherbicide based on the stable propagules produced by Plectosporium alismatis, a potential mycoherbicide in rice crops. The fungus produced conidia (109 L-1) and chlamydospores (108 L-1) in shake-flasks. Nitrate was required for production of chlamydospores which had a ligher shelf-life (6. 6% germination after 4 months) compared to conidia. The presence of aggregates (containing chlamydospores) ws also observed in nitrate-based medium. These aggregates may increase P. Alismatis resistance against environmental constraints. To overcome the lack of culture reproducibility due to aggregates’ heterogeneous nature, an alternative, the production of homogeneous spherical aggregates (i. E. , pellets) was developed. In a new medium “Aggregate Production Medium (APM)” in which up to 2. 8 x l05 pellets L-1, 6. 5 x l09 conidia L-1 and 9. 6 x 108 chlamydospores L-1 were produced. When maximal number of free propagules (~104 conidia and ~2 x 102 chlamydospores) was not able to infect leaf when dried and exposed to U, only a single pellet was required to induce disease in the same conditions. We conclude that pellets were far more pathogenic and tolerant to desiccation and UV compared to conidia. In shelf-life experiments, diatomite formulation containing free conidia, free chlamydospores and pellets, stored at 4°C survived for a long period (12% germination after 9 months) and remained pathogenic. In conclusion, P. Alismatis can produce pellets in APM, and diatomite formulations based on these pellet-containing cultures could satisfy the requirements for an efficient mycoherbicide

Les schistes carton sont constitués par des marnes feuilletées d'apparence schisteuse et fortement surconsolidées. À l'état sain ils sont très compacts. À l'état altéré, ils deviennent très friables et se transforment en argile très plastique. Cette altération provoque deux types de problèmes en géotechnique: la stabilité des pentes et les désordres causés par le gonflement. L’altération et le gonflement des schistes carton s'effectuent en deux phases: la première phase d'altération par fissurations, provoque des gonflements indépendants de la présence des minéraux argileux et des déchargements. Les fissurations par rupture de liens interparticules sont dues aux pressions capillaires et se produisent lorsque la valeur de succion appliquée dépasse celle de la pression d'entrée d'air du matériau. Ce phénomène, mis en évidence lors de la dessiccation du matériau, prend toute son ampleur lors des restaurations ultérieures. Des essais cycliques d'humidification-dessiccation nous ont permis de reproduire les phénomènes observes in-situ. L’étude de gonflement aboutit à la proposition d'un modèle restreint pour le gonflement du matériau. Une caractérisation de ses propriétés hydrauliques lors du séchage a été également mise en œuvre dans le but de connaitre l'évolution d'un front de dessiccation lors de travaux de déblayage. La deuxième phase d'altération est due à des transformations minéralogiques. L’oxydation de la pyrite en est la principale ; elle peut s'effectuer chimiquement en présence d'oxygène. Cependant, la présence des bactéries Thiobacilles ferrooxydans augmente considérablement la vitesse d'oxydation. Cette oxydation produit de l'acide sulfurique et des sulfates de fer ferriques qui attaquent d'autres minéraux pour former du gypse, de la jarosite et de la goethite. Ceci provoque à nouveau un gonflement et une dégradation du matériau

La thèse présente un ensemble de résultats expérimentaux sur des sols fins très plastiques compactés au voisinage de l’optimum Proctor normal (OPN). Elle est réalisée dans le cadre du projet ANR TerreDurable qui traite de la conception des ouvrages en terre en sols fins. Après l’étude de l’effet de compactage sur des chemins de drainage-humidification, la fissuration induite par la dessiccation est mise en évidence et analysée. Par ailleurs, des relations entre différents paramètres mécaniques (module, IPI, Résistance à la compression) et hydriques (succion, perméabilité, ..) en fonction de l’énergie de compactage et du mode de préparation sont présentées. Le comportement mécanique des sols fins compactés est étudié sur des chemins œdométriques et triaxiaux saturés et non saturés, drainés et non drainés. Dans ce dernier cas, l’évolution des paramètres de pression interstitielle de Skempton est analysée sur des chemins isotropes et déviatoires. Ceci a nécessité la mise au point d’une cellule triaxiale équipée de psychromètres à effet Peltier, de tensiomètre et de jauges de déformations
The thesis presents an experimental study on very high plasticity soils compacted near of the standard Proctor optimum (SPO). It is performed as part of the ANR TerreDurable project which is devoted on the design of earthworks with fine soils. After the study of the effect of compaction on drying-wetting paths, induced cracking of drying is highlighted and analyzed. Furthermore, relationships between different mechanical parameters (modulus, IPI, compressive strength) and water (suction, permeability) according to the energy of compaction and method of preparation are shown. The mechanical behavior of soils compacted fine soils is studied on saturated and unsaturated, drained and undrained oedometer and triaxial. For the unsaturated undrained triaxial, the change in Skempton parameters pore pressure is analyzed on isotropic and deviatoric paths. This required the development of a triaxial cell equipped with psychrometers, tensiometer and strain gauges

Orientador: Prof. Dr. Danilo da Cruz Centeno
Dissertação (mestrado) - Universidade Federal do ABC, Programa de Pós-Graduação em Evolução e Diversidade, 2016.
O conhecimento sobre padrões de distribuição das espécies é crucial para estratégias de manejo e conservação. "Leis" biogeográficas como a Relação Espécies-Área (REA) e o Gradiente Latitudinal de Riqueza (GLR) são ferramentas fundamentais para a compreensão dos fatores determinantes da biodiversidade nos níveis local, regional e global. Listas de espécies de aves são disponíveis para diversas unidades geopolíticas, desde a escala de países até estados e cidades. Tal cenário de informação abundante é similar em poucos grupos taxonômicos (e.g. mamíferos e plantas vasculares), restringindo uma avaliação ampla da estrutura temporal e espacial das comunidades bióticas. A massa crescente de registros georreferenciados (i.e. uma observação particular de um espécime pertencente a uma espécie e associada a um par de coordenadas geográficas) poderia aumentar a acurácia de estudos envolvendo padrões descritos acima, mas estes registros também são limitados a poucos táxons e áreas amostradas. Este trabalho empregou listas de espécies de aves (do sítio Avibase) como unidades amostrais (UAs) em níveis geopolíticos distintos (países, estados e cidades) para descrever a REA e o GLR em escala global. As UAs do primeiro nível (países) de LIS (banco de dados baseado em listas de espécies) cobriram quase toda extensão de terras emersas, englobando cerca de 98% das 10.405 espécies de aves conhecidas. No terceiro nível de LIS (cidades), com apenas um milésimo do território emerso, aproximadamente metade das espécies foi amostrada. LIS também foi comparado a bancos de dados oriundos de registros georreferenciados dos sítios eBird e GBIF usando (i) as mesmas fronteiras geopolíticas como delimitadores das UAs (banco de dados GEO) e (ii) UAs com tamanho e forma circular fixos (banco de dados FIX). Valores elevados de riqueza para um dado nível geopolítico foram detectados em LIS, estando associados a variâncias reduzidas para o indicador biológico neste banco de dados. Por meio da análise de regressão linear, os três bancos de dados apresentaram curvas significantes para REA. A inclinação destas curvas não diferiu entre os níveis em LIS e GEO nem entre os níveis correspondentes destes dois bancos de dados (exceto para o nível 1). O GLR foi evidenciado em LIS (todos os níveis) e GEO (níveis 1 e 3), mas não em FIX. O efeito latitudinal contribuiu com uma fração reduzida da variância explicada da riqueza, quando comparado ao efeito da área, utilizando-se apenas esses dois fatores explanatórios numa análise de regressão múltipla. Essa contribuição relativa foi menor nos primeiros níveis de LIS e GEO. Todos os níveis dos bancos de dados possuem um componente robusto da proximidade geográfica entre UAs na similaridade entre faunas: ele reflete quase que indistintamente a estrutura da comunidade para todo o planeta. Os resultados indicam que listas de espécies disponíveis são ferramentas poderosas para a avaliação de padrões na distribuição da biodiversidade, independentemente da escala amostral. Lacunas regionais e locais nos levantamentos podem ser identificadas e preenchidas, para estender tais explanações a outros táxons além das aves. Registros massivos de locação precisa de espécies poderiam possibilitar descrições mais acuradas destes e de outros padrões biogeográficos, inclusive em escalas inferiores.
Knowledge on patterns of species distribution is crucial for management and conservation strategies. Biogeographic "Laws" as the Species-Area (SAR) and the Latitudinal Gradient Richness (LGR) are fundamental tools for understanding factors that determine the biodiversity at local, regional or even global level. Checklists of bird species are available for a large amount of geopolitical units, ranging in scale from countries to states and cities.This scenario of abundant information achieve similar status only in a few taxonomic groups (e.g. mammals and vascular plants), restricting a broad assessment of temporal and spatial structure of biotic assemblages. A growing body of georreferenced records of species (i.e. a particular observation of a specimen pertaining to a given species and associated to a pair of geographic coordinates) should improve the accuracy of studies involving the patterns described above, but it is also limited to a few taxa and sampled units (SUs). In this work, we used checklists (from Avibase) as sampling units (SUs) for different geopolitical levels to describe SAR and LGR at global scale. The first level (countries) of LIS (database from species checklists) encompasses almost the entire area of emersed land, covering about 98% of the 10,405 known bird species. The third level (cities), with only a thousandth of the emersed territory, almost half of all species was sampled. This database (LIS) was also compared to that generated from georeferenced records eBird and GBIF (database GEO) using (i) the same geopolitical frontiers as delimiters of UAs and (ii) SUs with size and circular shape fixed (database FIX). Higher richness values for a given geopolitical level were detected in LIS, associated with reduced variances in such biological indicator for this database. By using linear regression analysis, all three databases presented significant SAR curves. Slopes of such relationships did not differ among levels in LIS and GEO or between corresponding levels of these two databases (except for level 1). LGR was presented by LIS (all levels) and GEO (levels 1 and 3), but not by FIX. The latitudinal effect contributed a small fraction of explained variance of richness compared to the area effect when only these explanatory factors were used in the multiple regression analysis. This relative contribution was lower in the first LIS and GEO levels. All levels of databases presented a strong component of geographical proximity between SUs in the similarity between faunas: they reflect almost indistinctly the speciesbased community structure for the entire planet. The results indicate that species checklists are powerful tools available for evaluating patterns of biodiversity distribution despite sample scales. Regional and local gaps in inventories should be identified and filled to reinforce such extension to taxa other than birds. Massive records based on precise location of species could enable more accurate descriptions of these and other biogeographic patterns, even at smaller scales.

Les enceintes de confinement des centrales nucléaires françaises sont réalisées en béton précontraint de 1,2 m d'épaisseur. L'étanchéité de la structure dépend principalement de la précontrainte résiduelle du béton. Or les dispositifs de surveillance des déformations différées font apparaître des différences sensibles, suivant les sites, que les modèles de calcul réglementaires ne prennent pas en compte d'une façon satisfaisante. Pour améliorer la gestion du parc de centrales, au sens durée de vie, EDF a lancé en 1991 un vaste programme d'étude centré sur le matériau béton, et visant à prévoir le comportement réel en fluage des enceintes déjà construites. Ici, nous analysons une par une les différentes déformations différées du béton. Une analyse fine des phénomènes physico chimiques qui en sont à l'origine, nous conduit à proposer une modélisation d'ingénieur, sur la base d'un modèle du type milieu continu équivalent. Enfin, nous présentons les résultats de nos simulations et nous concluons en donnant les enseignements théoriques et pratiques de cette étude ainsi que quelques propositions réglementaires.

Cellulose is the most abundant biopolymer on Earth as it is found in every plant cell wall; therefore, it represents one of the most promising natural resources for the fabrication of sustainable materials. In plants, cellulose is mainly used for structural integrity, however, some species organise cellulose in helicoidal nano-architectures generating strong iridescent colours. Recent research has shown that cellulose nanocrystals, CNCs, isolated from natural fibres, can spontaneously self-assemble into architectures that resemble the one producing colouration in plants. Therefore, CNCs are an ideal candidate for the development of new photonic materials that can find use to substitute conventional pigments, which are often harmful to humans and to the environment. However, various obstacles still prevent a widespread use of cellulose-based photonic structures. For instance, while the CNC films can display a wide range of colours, a precise control of the optical appearance is still difficult to achieve. The intrinsic low thermal stability and brittleness of cellulose-based films strongly limit their use as photonic pigments at the industrial scale. Moreover, it is challenging to integrate them into composites to obtain further functionality while preserving their optical response. In this thesis, I present a series of research contributions that make progress towards addressing these challenges. First, I use an external magnetic field to tune the CNC films scattering response. Then, I demonstrate how it is possible to tailor the optical appearance and the mechanical properties of the films as well as to enhance their functionality, by combining CNCs with other polymers. Finally, I study the thermal properties of CNC films to improve the retention of the helicoidal arrangement at high temperatures and to explore the potential use of this material in industrial fabrication processes, such as hot-melt extrusion.

The current practice of red blood cell banking for transfusion medicine relies primarily on a six-week liquid storage. A growing demand for red blood cell (RBC) products has prompted the search for alternative preservation methods including dry storage. Being desiccation sensitive, attempts to recover RBCs from the dry state have failed. This dissertation offers a new mechanistic understanding of desiccation-induced cellular injury that is correlated with the oxidative state of the hemoglobin. The general hypothesis states that RBC desiccation is accompanied with non-physiological oxidation of hemoglobin and, consequently, the release of toxic products capable of compromising cellular recovery through oxidative injury. Data acquired for this dissertation demonstrates that water loss induces a drastic increase in the rate of hemoglobin oxidation, formation of intracellular reactive oxygen species (ROS), and hemolysis. Pharmacological treatments of the hemoglobins oxygen binding site reveal that hemoglobin-induced cellular injury is more prominent in RBC samples that are partially dehydrated (about 3.5 to 5.5 g H2O/g dry weight) than in samples that are relatively dry ( 2 g H2O/g dry weight). Furthermore, partially dehydrated RBC samples contain higher levels of oxidized lipids than more fully dried samples. This dissertation also examined the role that glucose and glutathione play in enhancing desiccation tolerance of RBCs. Glucose treatment (5 mmol/L) significantly reduced ROS formation and hemolysis levels in partially dehydrated RBC samples (5.8 0.3 g H2O/g dry weight), but not in samples that are relatively dry (2.8 0.5 g H2O/g dry weight). Treating RBCs with DL-buthionine-(S,R)-sulfoximine, a glutathione depleting agent, was correlated with reduced levels of desiccation-induced hemolysis. This study suggests that desiccation-induced oxidative injury in RBCs is water dependent corresponding to earlier stages of water loss, in which cells can retain metabolic activity. Pharmacological treatments at this stage can significantly affect cell recovery as demonstrated with modifying the hemoglobins oxygen binding site, glutathione depletion, and glucose supplementation. On the other hand, increased cytoplasmatic viscosity compromises biochemical reactions at lower residual moisture contents, and cellular injury is likely the result of physical and mechanical stress. These differences should be taken into consideration in the design of innovative approaches to RBC preservation.

Desmids are an important part of the phytobenthos in the wetland ecosystems. These ecosystems are often ephemeral and changes in the hydrological regime is a typical characterisic of this habitat type. Dessication is a significant stress factor that affects water organisms. Different species differ in their extent of tolerance to dessication stress and it can affect their community structure and also their phylogenetic diversity. Two sites, the nature reserve Borkovická Blata and the nature locality Na Plachtě, were selected for this work. Ephemeral (seasonally dessicating) and permanent pools differed in the structure of desmid communities but the difference was signifacant only for Borkovická blata. At both localities, the samples from the dessicating pools showed in average lower species richness and Shannon's diversity index than samples from non-dessicating pools, but the differences between these groups of samples were not statistically significant. Phylogenetic analysis showed that the desmids community were phylogenetically overdispersed; closely related species tended to not appear together on the same sites at both localities. The difference in the phylogenetic structure between ephemeral and permanent was detected only in the Borkovická blata site, where the ephemeral pools exhibited weaker...