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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Caractérisation biogéochimique et potentiel de méthylation du mercure de biofilms en milieu tropical (retenue de Petit Saut et estuaire du Sinnamary, Guyane Française) / Biogeochemical characterization and mercury methylation potentiel of tropical biofilms (Petit Saut reservoir and Sinnamary Estuary, French Guiana)

Huguet, Lucie 04 June 2009 (has links)
Le barrage de Petit Saut a été construit sur le fleuve Sinnamary en Guyane française en 1994. De la forêt tropicale laissée en place lors de la mise en eau, subsistent encore aujourd'hui de nombreux troncs d'arbres dans toute la retenue. Des biofilms ont colonisés la surface de ces troncs et sont également retrouvés en abondance sur plusieurs dizaines de km à l'aval du barrage. L'objectif de la thèse a été de caractériser ces biofilms et de déterminer leur rôle dans la méthylation du mercure. Dans un premier temps, les biofilms ont été caractérisés par une approche multidisciplinaire. La composition de la matière organique des biofilms et de la couche néphéloïde des sédiments a été décrite par l'identification de biomarqueurs (isotopes stables du carbone d13C et de l'azote d15N et acides gras). Dans le réservoir, les particules en suspension sont une source importante du matériel accumulé dans les biofilms. Ils contiennent plus de matière organique réfractaire que les biofilms à l'aval et que la couche néphéloïde de la retenue. D'autre part, les éléments fer, soufre et manganèse, ainsi que le mercure et le méthylmercure présentent une stratification avec la profondeur. Des Chlorobiaceae ont été identifiées à l'oxycline tandis que les bactéries ferri-réductrices prédominent par rapport aux bactéries sulfato-réductrices dans l'hypolimnion anoxique. Dans le Sinnamary aval, les biofilms sont essentiellement constitués de fer (50 % du poids sec). Les bactéries ferri-réductrices y sont prépondérantes par rapport aux bactéries sulfato-réductrices. La matière organique est majoritairement labile et permet le développement de différents groupes métaboliques bactériens dont les bactéries méthanotrophes à la station Passerelle. La présence de consortia de bactéries (observés en FISH) appartenant à la famille des Firmicutes et d’Archaea méthanogènes dans des enrichissements de biofilms de la station Passerelle et de la couche néphéloïde des sédiments permet de proposer une voie anaérobie d’oxydation du méthane par une synthrophie de ces micro-organismes. Dans un deuxième temps, ce travail présente une nouvelle application de l’utilisation d’isotopes stables pour déterminer le potentiel de méthylation du mercure de biofilms tropicaux. Les biofilms de l’oxycline présentent des taux de méthylation les plus faibles après 3 mois d’incubation dans l’eau du réservoir. Les taux de méthylation les plus élevés sont obtenus par les micro-organismes planctoniques de la colonne d’eau, la couche néphéloïde des sédiments, les biofilms situés à 20 m de profondeur et ceux de la station Passerelle. L’ajout de nutriments augmente le potentiel de méthylation des différents échantillons, en particulier à l’aval du barrage, même s’il ne favorise pas uniquement la croissance des micro-organismes méthylants mais aussi celle d’autres groupes (capables de déméthyler le MeHg ou n’intervenant pas dans les transformations du mercure). Les différences de potentiel de méthylation observées sont dues soit à la diversité des microorganismes soit à la composition des biofilms qui modifie la biodisponibilité du mercure. / The Petit Saut dam was built on the Sinnamary River in French Guiana in 1994 and its flooding has resulted to the final immersion of 350 km² of uncleared tropical rainforest. All immersed surfaces (rocks, immersed tree branches and trunks, roots…) in the reservoir lake and in the downstream are recovered by abundant biofilms. The aim of the present work was to characterize biofilms in terms of elemental composition, organic matter content and microbial communities and to define their role in mercury methylation. A multidisciplinary approach, applied to the biofilms and the nepheloid layer of the reservoir sediment, consisted in (i) assessing carbon, nitrogen, iron, sulfur, manganese, mercury and methylmercury concentrations, (ii) characterizing the nature of organic matter using its carbon and nitrogen isotopic composition (?13C and ?15N), its C/N ratio and its fatty acids composition (focusing on bacterial biomarkers). In the reservoir, suspended particles matter is an important source of accumulating material in biofilms. Reservoir biofilms contain higher refractory organic matter than the biofilms of the estuary and than the reservoir nepheloid layer. Iron, sulfur and manganese, mercury and methylmercury concentration are stratified with depth. Even if the relative contribution of bacterial fatty acids biomarkers was low, Chlorobiaceae was identified above the oxycline, whereas iron reducing bacteria were predominant in the hypolimnion as regards sulphate reducing bacteria. In the estuary, iron weights for the major part of the biofilm and higher IRB amount is present than SRB. The more labile organic matter allows the development of various microbial metabolic groups such as methanotrophs at the Passerelle station. Presence of Firmicutes-Archaea consortia (FISH analysis) in enrichment of Passerelle biofilms and of the reservoir nepheloid layer suggests that methane could also be oxidized under anaerobic synthrophy. This study shows a new application of stable isotope incubation to determine mercury methylation potential in tropical biofilms. Methylation potential is the lowest in the biofilm from the oxycline whereas higher methylation rates are obtained for microorganisms of the water column (planktonic), nepheloid layer, biofilms sampled at -20 m and at the Passerelle station. Adding nutrient enhances mercury methylation, especially in the estuary but it doesn’t only promote growth of methylating microorganisms but also that of demethylating or not involved in Hg transformation microorganisms Differences in methylation potential could be explained by either the bacterial communities diversity and/or by biofilm composition modifying Hg bioavailability.
2

Correlation of some features of tropical preventive medicine, and their application to the tropical areas under Australian control

Cilento, Raphael, Sir, 1893-1985 January 1922 (has links)
[Typewritten copy] / 210 p. : / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (M.D.)--University of Adelaide, 1923
3

Creating R&D incentives for medicines for neglected diseases an economic analysis of parallel imports, patents, and alternative mechanisms to stimulate pharmaceutical research /

Müller-Langer, Frank. January 1900 (has links)
Diss.-- Hamburg Univ., 2008. / Includes bibliographical references and index.
4

UPWELLING INTO THE LOWER STRATOSPHERE & TROPICAL WAVE BREAKING: EVIDENCE FROM CHEMICAL TRACERS

Engida, Zelalem 16 August 2012 (has links)
We use 2005 - 2010 measurements from the Microwave Limb Sounder (MLS) instrument to calculate the deseasonalized anomalies of tropical mean water vapor (H2O), carbon monoxide (CO), and nitrous oxide (N2O) on the 68 hPa surface. We then calculate the spatial maps of the coherence between the tropical mean tracer measurements and reanalysis temperature on the 100 hPa surface, in both the subseasonal and multiyear time windows. In the multiyear time window, the spatial pattern of the coherence, and the time lags, indicate that fluctuations in 100 hPa temperature affect 68 hPa H2O through changes in dehydration efficiency. In the subseasonal time window, the coherence between 100 hPa temperature and 68 hPa H2O is mediated through changes in upwelling driven by the dissipation of tropical Rossby waves. On subseasonal timescales, the 68 hPa anomalies in tropical mean CO are strongly coherent with the Madden Julian Oscillation (MJO).
5

Correlation of some features of tropical preventive medicine, and their application to the tropical areas under Australian control.

Cilento January 1900 (has links) (PDF)
Thesis (M.D.) -- University of Adelaide, 1923. / [Typewritten copy].
6

The phytosociology of a tropical seasonal forest in southeastern Mexico

Shepherd, John Dorsey, January 1975 (has links)
Thesis (M.S.)--University of Wisconsin--Madison. / Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 114-120).
7

Complete Tropical Bezout's Theorem and Intersection Theory in the Tropical Projective Plane

Rimmasch, Gretchen 11 July 2008 (has links) (PDF)
In this dissertation we prove a version of the tropical Bezout's theorem which is applicable to all tropical projective plane curves. There is a version of tropical Bezout's theorem presented in other works which applies in special cases, but we provide a proof of the theorem for all tropical projective plane curves. We provide several different definitions of intersection multiplicity and show that they all agree. Finally, we will use a tropical resultant to determine the intersection multiplicity of points of intersection at infinite distance. Using these new definitions of intersection multiplicity we prove the complete tropical Bezout's theorem.
8

A study of Equatorial superrotation in a two-level model of the atmosphere

Woolnough, Steven James January 1997 (has links)
No description available.
9

The ecology of seedlings in Central Amazonian forest fragments

Malvido-Benitez, Julieta January 1995 (has links)
No description available.
10

The effects of root competition on saplings and seedlings in Amazonian caatinga forest in southern Venezuela

Coomes, David Anthony January 1995 (has links)
No description available.

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