Dissertationen zum Thema „Earth and Life Sciences“
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Hode, Tomas. „The Search for Life on Mars - Preparation for Sample Return“. Doctoral thesis, Stockholm : Department of geology and geochemistry, Stockholm University, 2005. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-477.
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Cheney, David W. „Information technology, science, and public policy“. Fairfax, VA : George Mason University, 2007. http://hdl.handle.net/1920/2959.
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Thesis (Ph. D.)--George Mason University, 2007.Title from PDF t.p. (viewed Jan. 17, 2008). Thesis director: Don E. Kash Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Public Policy. Vita: p. 330. Includes bibliographical references (p. 289-329). Also available in print.
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Garai, Jozsef. „Thermodynamic description and phase transformation of highly symmetrical monoatomic structures“. FIU Digital Commons, 2007. http://digitalcommons.fiu.edu/etd/3614.
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Based on theoretical considerations an explanation for the temperature dependence of the thermal expansion and the bulk modulus is proposed. A new equation state is also derived. Additionally a physical explanation for the latent heat of fusion is presented. These theoretical predictions are tested against experiments on highly symmetrical monoatomic structures.
The volume is not an independent variable and must be broken down into its fundamental components when the relationships to the pressure and temperature are defined. Using zero pressure and temperature reference frame, the initial parameters, volume at zero pressure and temperature[VJ, bulk modulus at zero temperature[Ko], and volume coefficient of thermal expansion at zero pressure [a J are defined.
The new derived EoS is tested against the experiments on perovskite and epsilon iron. The Root-mean-square-deviations (RMSD) of the residuals of the molar volume, pressure, and temperature are in the range of the uncertainty of the experiments.
Separating the experiments into 200 K ranges, the new EoS was compared to the most widely used finite strain, interatomic potential, and empirical isothermal EoSs such as the Burch-Murnaghan, the Vinet, and the Roy-Roy respectively. Correlation coefficients, RMSD’s of the residuals, and Akaike Information Criteria were used for evaluating the fitting. Based on these fitting parameters, the new p-V-T EoS is superior in every temperature range relative to the investigated conventional isothermal EoS.
The new EoS for epsilon iron reproduces the preliminary-reference earth-model (PREM) densities at 6100-7400 K indicating that the presence of light elements might not be necessary to explain the Earth’s inner core densities.
It is suggested that the latent heat of fusion supplies the energy required for overcoming on the viscous drag resistance of the atoms. The calculated energies for melts formed from highly symmetrical packing arrangements correlate very well with experimentally determined latent heat values.
The optical investigation of carbonado-diamond is also part of the dissertation. The collected first complete infrared FTIR absorption spectra for carbonado-diamond confirm the interstellar origin for the most enigmatic diamonds known as carbonado.
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Black, Robert Xavier. „A diagnostic study of the life cycles of persistent flow anomalies“. Thesis, Massachusetts Institute of Technology, 1990. http://hdl.handle.net/1721.1/51479.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 1990.Includes bibliographical references (p. 197-202).
by Robert Xavier Black.
Ph.D.
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Hoel, Ole Andreas. „Diversity and Life Habits of Silurian Strophomenide Brachiopods of Gotland“. Doctoral thesis, Uppsala University, Department of Earth Sciences, 2005. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-4728.
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The Superfamily Strophomenoidea is a very diverse group of brachiopods in the Early Palaeozoic. In the Silurian succession on Gotland, they are among the most easily identifiable, and commonly found fossils. However, there are few detailed studies of this group from Gotland, and no new strophomenide taxa have been described from this area since 1869. The life habits of strophomenides are also poorly understood, partly because their morphology differs greatly from that of living brachiopods.
The succession on Gotland yielded 27 species belonging to the Strophomenoidea, of which two species and two subspecies are new. The remaining species have been described earlier from Gotland or Great Britain. The most important group is the Leptaeninae, which occurs commonly throughout the entire succession on Gotland. Five species (one new), two new subspecies and two taxa treated under open nomenclature were found. Leptaena rhomboidalis and Lepidoleptaena poulseni were specialized for life in shallow water environments, retaining a large apical pedicle; the remaining leptaenines were ambitopic. The Furcitellininae is represented by three genera comprising six species, of which only one persisted into the Ludlow. All were ambitopic, except Pentlandina loveni, which was specialized for high-energy environments. Six species of “strophodontids” from Gotland, belonging to the Leptostrophidae, the Strophodontidae and the Shaleriidae, share a shallow-bodied, variably concavo-convex shell with costellate ornament. Mesoleptostrophia and Brachyprion (Brachyprion) were long-ranged and ecologically tolerant, while B. (Erinostrophia), Strophodonta and Shaleria had short ranges and were ecologically specialized. The two earliest known cementing strophomenides occur on Gotland, and their hitherto unknown dorsal valves have been identified: Liljevallia was found to belong to the Douvillinidae. The cementing Leptaenoidea silurica was found to be conspecific with the ambitopic Scamnomena rugata; it was able to live ambitopically if removed from the substrate. The thickened dorsal valves allow reconstruction of its lophophore.
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Webb, Claire Isabel. „Technologies of perception : searches for life and intelligence beyond Earth“. Thesis, Massachusetts Institute of Technology, 2020. https://hdl.handle.net/1721.1/129021.
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Thesis: Ph. D. in History, Anthropology, and Science, Technology and Society (HASTS), Massachusetts Institute of Technology, Program in Science, Technology and Society, September, 2020Page 229 blank. Cataloged from PDF version of thesis.
Includes bibliographical references (pages 217-228).
Scientists in the late 1950s in the United States gained technological capabilities to test for signs of extraterrestrial life. While exobiologists developed visual techniques to detect whether sites beyond Earth might harbor microbes, "biosignatures," radio astronomers searched for extraterrestrial intelligence (SETI) in the form of "technosignatures." This dissertation explores how scientists since the Space Age have constructed experimental assemblages to imagine, relate to, and investigate the alien and exotic microbes -- unknown, indeed, as-yet-imperceptible, objects --
through familiar sensory metaphors of seeing (exobiologists) and listening (SETI scientists). From historical material gathered at various D.C. archives, the American Philosophical Society, and the National Library of Medicine, I show how exobiologists' technologies of vision rendered anew images of the Moon, Mars, Venus, and the Earth from afar and at surface, affording scientists the ability to conceptually anticipate relationships between their world and others. Through a epistemic pratice I call "gaze-scaling," they yoked the concept of "island" to "planet," casting extraterrestrial sites as fragile laboratories of life that beckoned exploration. I next draw from immersive participant observation since 2016 to engage ethnographic sonar on the SETI group Breakthrough Listen based at U.C. Berkeley, California. I analyze how they construct criteria of intelligence through "experiments of anticipation" that are parametrized to hear from a commensurable subject.
I theorize "figures of listening" in both observational protocols and as a preemptive attunement to Other intention, acts that configure an alien who would be not just perceptible, but relatable. If exobiologists envisioned universal standards of biochemistry that would map life's common origins, SETI astronomers have traded on imagined superhuman characteristics of the alien -- more benevolent, wiser, and technologically superior -- to suggest human futures. I outline how the alien has been imagined through three potent analogical figures: as artifacts, animals, and angels. Furnished by feminist epistemologies and queer theories of care around multispecies becomings -- traditions that have persistently challenged ontological stability across species, gender, race, and spacetime --
I theorize those analogies as acts of "reflexive alienation": a mode of worldmaking in which scientists imagine Others imagining them. Future-oriented extraterrestrial objects held in abeyance cultivate Earthly concepts of being..
by Claire Isabel Webb.
Ph. D. in History, Anthropology, and Science, Technology and Society (HASTS)
Ph.D.inHistory,Anthropology,andScience,TechnologyandSociety(HASTS) Massachusetts Institute of Technology, Program in Science, Technology and Society
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Araiza, Roberto. „The use of interval-related expert knowledge in processing 2-D and 3-D data with an emphasis on applications to geosciences and biosciences /“. To access this resource online via ProQuest Dissertations and Theses @ UTEP, 2007. http://0-proquest.umi.com.lib.utep.edu/login?COPT=REJTPTU0YmImSU5UPTAmVkVSPTI=&clientId=2515.
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Neilley, Peter Paul. „Interactions between synoptic-scale eddies and the large-scale flow during the life cycles of persistent flow anomalies“. Thesis, Massachusetts Institute of Technology, 1990. http://hdl.handle.net/1721.1/54966.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 1990.Includes bibliographical references (p. 259-267).
by Peter Paul Neilley.
Ph.D.
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Willman, Sebastian. „The Ediacaran Diversification of Organic-walled Microbiota : Ocean Life 600 Million Years Ago“. Doctoral thesis, Uppsala University, Department of Earth Sciences, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-8684.
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The only direct evidence of past life is provided by fossils. Fossils tell us about the evolution of life on Earth and they give us clues concerning ancient environments. The Ediacaran Period (roughly 635-542 million years ago) is characterised by the appearance and diversification of various microbiota and also the diversification of metazoans. Well-preserved organic-walled microfossils referred to as acritarchs occur abundantly in Ediacaran sedimentary successions in the Officer Basin in South Australia. Acritarch assemblages from the Giles 1 and Murnaroo 1 drillcores show a wide morphological disparity and are taxonomically diverse. Assemblages change over short stratigraphic intervals which enables the recognition of different biozones. The presence of taxa common between Australia, Siberia, Baltica and China provides a means for global correlation of the Ediacaran System. Examination of the wall ultrastructure of several acritarch specimens by use of transmission electron microscopy reveals a complexity in the cell wall that is not seen in prokaryotes but is indicative in some cases of particular clades of microalgae. Wall ultrastructures range from single-layered to three- and four-layered and from homogeneous to porous. The wall ultrastructure can be used to assess biological affinities and the affinities of the studied taxa in relation to green algae, dinoflagellates and metazoans are discussed. However, before taxonomic interpretations can be made with confidence, an understanding of taphonomic degradation of microorganisms is required. With focus on illustrated specimens, one part of this thesis explains what happens to an acritarch as it undergoes various types of degradation and why an understanding of these processes is important for taxonomic identification. A meteorite impact in South Australia spread an ejecta layer over a 550 km radius area. This ejecta layer is recognised in subsurface drillcores and provides an independent stratigraphic marker horizon that supports an acritarch-based correlation.
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Fenwick, Emily L. „The impact of an integrative 3-d virtual learning environment in diverse ninth grade earth and space science classes“. Thesis, Kansas State University, 2010. http://hdl.handle.net/2097/4231.
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Master of ScienceDepartment of Geology
Iris M. Totten
Problem-based learning in the sciences has been demonstrated to be a successful educational approach to engage students and increase content knowledge. However, the power of collaborative learning to engage students, increase content knowledge and develop problem-solving skills in the sciences has not yet been fully researched. Collaborative learning has an enormous potential not only to foster student learning, but also to increase interest in the sciences and promote cutting-edge education strategies worldwide. Collaborative learning tactics in this study take place within the virtual learning environment entitled “GeoWorlds.” GeoWorlds is an online educational gaming program within the Second Life 3-D Teen Grid. The curriculum was developed as a collaborative, investigative and engaging program to promote learning of Earth science content. The program allows students to be submersed-in and explore different geologic time periods; enabling them to observe species and geological structures while interacting with one another to complete tasks. This study investigates the educational impact, emotional response and overall feedback of the GeoWorlds virtual learning environment on Midwest ninth graders.
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BALTZINGER, Christophe. „Sélection des sites de repos par le Cerf (Cervus elaphus L.) et le Chevreuil (Capreolus capreolus L.) vivant en sympatrie en forêt tempérée de moyenne montagne“. Phd thesis, ENGREF (AgroParisTech), 2003. http://tel.archives-ouvertes.fr/tel-00005727.
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Le Cerf (Cervus elaphus) et le Chevreuil (Capreolus capreolus) sont 2 cervidés qui abondent en Europe, ils partagent souvent le même habitat. Les cervidés passent en moyenne 50% de leur temps au repos, cependant les critères de sélection des sites de repos ont été peu étudiés.L'objectif de notre travail est double : i) décrire les patrons de sélection des sites de repos, pour chaque espèce et à différentes échelles spatiales et temporelle, et ii) comparer les patrons de sélection des deux espèces.
L'étude a été menée au sein du Parc National des Cévennes, dans la Forêt Domaniale du Bougès. L'échantillonnage par transects a permis de décrire les caractéristiques de 425 reposées, au cours de 2 hivers et de 2 étés. La méthode PCR appliquée à l'ADN de poils prélevés sur les reposées s'est révélée pertinente pour distinguer Cerf et Chevreuil.
A l'échelle du peuplement forestier, nous montrons un fort chevauchement entre Cerf et Chevreuil dans l'utilisation, pour se reposer, des différents types de peuplement. Les 2 cervidés ont tendance à éviter les peuplements résineux adultes été comme hiver. Le Chevreuil est moins sélectif à cette échelle, et utilise indifféremment les peuplements forestiers en été. Le Cerf a par contre un comportement très sélectif et manifeste une préférence marquée pour les jeunes peuplements résineux.
A l'échelle du microhabitat, le Cerf et le Chevreuil recherchent toujours une bonne protection visuelle, à travers un couvert latéral important. Ce couvert est essentiellement composé de résineux pour le Cerf, alors que le Chevreuil utilise aussi les feuillus quand ils sont disponibles en été.
En hiver, le Chevreuil se couche sous un fort couvert dans la canopée, ce couvert est plus élevé que pour le Cerf. Il se repose à proximité des lisières contrairement au Cerf qui sen éloigne.
Nous discutons ces différences de patron de sélection entre le Cerf, qui occupe un domaine vital étendu, et le Chevreuil, territorial, qui vit sur un domaine beaucoup plus restreint.
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Capova, Klara Anna. „The charming science of the other : the cultural analysis of the scientific search for life beyond earth“. Thesis, Durham University, 2013. http://etheses.dur.ac.uk/8516/.
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This dissertation presents the cultural study of scientific search for extraterrestrial life conducted over the past sixty years by the scientific community. It introduces an original piece of research that conceptualises the extraterrestrial life hypothesis as a significant part of the general world-view, constantly shaped by the work and discoveries of science. It sheds light on the ways in which alien life is imagined and theorised and presents its concept in both the scientific community and in popular culture. Drawing from anthropology of science it offers elaboration of ‘culture of science’ and ‘scientific culture’ and describes the scientific search for other life as a specific culture of science, here referred to as ‘charming science’. The three scientific search methods: message sending, analysing of cosmic signals and the search for extrasolar planets are conceptualised as the three search modes: messaging, listening and exploring respectively. This work introduces the extraterrestrial ‘Other’ as a profoundly cultural concept, firstly presented as the missing subject of ‘charming science’. Exploration of public understanding the extraterrestrial life and popular imagination of the ‘Other’ is intended to introduce the scientific search in broader social context and address the role of science in contemporary Western world. The dissertation draws on the multi-sited and multi-method ethnographic fieldwork conducted over two years in the UK. The research methods included interviewing (semi-structured face-to-face interviews and interviews conducted via email), participation (conferences and scientific meetings), and data collection from the global ‘online’ community including social networks.
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Ray, Darrell. „Patterns of Sulfur Deposition in the Wood of Pinus Echinatia Mill. from the Cumberland Plateau in Kentucky“. TopSCHOLAR®, 1988. https://digitalcommons.wku.edu/theses/2749.
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Air pollution and acid precipitation have long had an influence on plant and animal life. In this study, the level of sulfur in the stem tissue of Pinus echinata Mill. was measured in trees from various sites along the western edge of the Cumberland Plateau to determine the presence and pattern of sulfur deposition in this species. Overall, a 40.28% increase in sulfur levels was observed from four sites along the plateau with levels increasing from 0.072 mgS/gdwt in the 1962-66 growth increment to 0.101 mg in the 1982-86 increment. According to a computer generated analysis of variance, the differences observed are a function of increasing levels through time and are less related to geographic differences. Significant differences were measured in the sulfur content of saplings and mature trees from the Rock Creek collection site; no changes were detected in the levels of carbon, hydrogen and nitrogen from Rock Creek between 1957-1962. A preliminary study of sulfur uptake in seedlings resulted in no conclusive results. While the effects of pollutants on plant health has been intensely studied, long term effects including pollutant influences on wood product quality are less well documented. The pattern of increased deposition seen in the current study indicates that more work is needed to understand all of the impacts and implications of sulfur deposition in important forest species such as Pinus echinata.
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Fitzpatrick, Garret R. „Searching for life where the sun don't shine : explorations to the seafloors of Earth and Europa“. Thesis, Massachusetts Institute of Technology, 2012. http://hdl.handle.net/1721.1/76138.
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Thesis (S.M. in Science Writing)--Massachusetts Institute of Technology, Dept. of Humanities, Graduate Program in Science Writing, 2012.Cataloged from PDF version of thesis.
Includes bibliographical references (p. 23-24).
Hydrothermal vents on Earth's seafloor host entire ecosystems that live off energy from chemosynthesis rather than photosynthesis. This energy process uses chemical reactions between metals and hot gases from inside Earth's mantle to fuel thriving communities of exotic organisms. Some researchers think life originated at these vents and if they're right, that means there's a chance life could have also originated near similar hydrothermal vents on other planets or moons. One of the most promising places to search is the suspected sub-ice ocean on Jupiter's moon, Europa. This is the story of humankind's efforts to understand the origins of life by looking for it in extreme environments where life thrives without relying on the sun as an energy source. It follows an oceanographic expedition to the Mid-Cayman Rise, led by Chris German of the Woods Hole Oceanographic Institution and NASA's efforts to plan a future mission to Europa. By understanding how life can live without the sun, we may discover how life began on our planet and whether or not Earth is the only place in the universe capable of supporting a biosphere.
by Garret R. Fitzpatrick.
S.M.in Science Writing
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Lin, Nai Shi. „The response of the width of the Hadley cell to global warming-like thermal forcing in a simple general circulation model“. Thesis, McGill University, 2011. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=97070.
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The response of the Hadley Cell (HC) width to the global warming is investigated using a set of dry global circulation model (GCM) integrations. In the model, global warming is mimicked by two thermal forcings: a warming in the tropical upper troposphere (THR) and a warming in polar lower atmosphere (PHR). A set of model integrations for the THR case, the PHR case and both of these cases combined (TPH) are performed with both the axisymmetric (2D) and non-axisymmetric (3D) model configurations. It is found that THR results in a clear poleward expansion of the Hadley circulation. By contrast, the PHR case tends to cause the HC in the 3D run to shrink, although its impact is minor. This sensitivity does not exist on the axisymmetric (2D) integration, indicating that baroclinic eddies play a critical role in the widening of the HC. Model integrations with TPH show a stronger HC expansion than their addition of two simulations with only THR and PHR. It suggests that baroclinic eddies, which are responsible for the HC expansion, nonlinearly interact with the THR and PHR. The widening of the HC is also found to be solely attributed to the influence of increased static stability, which is induced by tropical heating. Sensitivity tests further show the HC expansion is highly sensitive to the width of the THR. This occurs only when THR is broad enough to change the baroclinicity in the subtropics.Lèffet du réchauffement global sur la largeur de la cellule de Hadley est examiné en utilisant une série d`intégrations dùn modèle de circulation global sec. Dans le modèle, le réchauffement global est imité par deux forçages thermiques, le réchauffement de la troposphère supérieure tropicale et le réchauffement polaire est la combinaison des deux réchauffements, une série d`intégrations numériques est performée avec deux configurations de modèle : axisymétrique (2D) et non-axisymétrique (3D). Les résultats démontrent que le réchauffement tropical résulte en une expansion évidente de la cellule de Hadley. Au contraire, le réchauffement polaire diminue la largeur de la cellule de Hadley bien que lèffet soit mineur. Cette sensibilité nèxiste pas dans la simulation 2D, indiquant que les ondes baroclines jouent un rôle important dans l`élargissement de la cellule de Hadley. L`intégration combinant les réchauffements tropicaux et polaires d`émontrent une expansion supérieure de la cellule de Hadley que les intégrations de réchauffement tropical et de réchauffement polaire additionnées. Cela suggère que les ondes baroclines qui sont responsables de lèxpansion de la cellule de Hadley interagissent de manière non-linéaire avec le réchauffement tropical et le réchauffement polaire. En plus, lèxpansion de la cellule de Hadley est uniquement attribuée a l`influence dùne stabilité accrue introduite par le réchauffement tropical. Des tests de stabilité d`émontrent que lèxpansion est très sensible à la largeur du réchauffement tropical. Il a lieu seulement lorsque le réchauffement tropical est assez large pour changer la baroclinicité dans les subtropiques.
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Shahrokhi, Hanieh. „Re-processing of Shallow and Deep Crustal Reflection Seismic Data along BABEL Line 7, Central Sweden“. Thesis, Uppsala universitet, Geofysik, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-179534.
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The BABEL project (Baltic And Bothnian Echoes from the Lithosphere) was a collaboration among British, Danish, Finnish, German and Swedish geoscientists to acquire deep-crustal reflection and wide-angle refraction data in the Baltic Shield and Gulf of Bothnia. In 1989, the collection of 2,268 km of deep marine reflection seismic data was carried out. BABEL line 7, one of several BABEL profiles, is the focus of this study and runs north of the Åland islands, in an E-W direction in the Bothnian Sea, east of the city of Gävle. The previous seismic image of the BABEL line 7 displays a considerable change in the reflectivity pattern from a weak reflective lower crust in thewest to a more highly reflective lower crust in the east, interpreted to be due to a transition from a stiff crust to a plastic crust from the west to the east. The seismic results were presented by the BABEL Working Group (1993) which focused on imaging and interpreting deep crustal structures as well as assessing the seismic velocities within the crust, the depth and nature of the Moho discontinuity and the seismic reflectivity texture in the crustal geological structures. Early Proterozoic plate tectonics in the Baltic Shield was also suggested from the reflection seismic data.The BABEL line 7 reflection data were collected with a profile length of 174 km, a group of 48 air guns towed at 7.5 m depth, and 3000 m long streamer, 60 hydrophones spaced at 50 m intervals towed at 15 m depth. Seismic data were acquired for a 25 s record length using a 4 ms sampling interval and a 75 m shot interval. Seismic data are characterized by strong source-generated noise at shallow travel times and strong but randomly distributed spurious spikes at later arrival times. In this thesis, the seismic data along BABEL line 7 were recovered and re-processed. Modern processing techniques that were not available previously, were used. A special emphasis on the shallow parts of the seismic data was given and resulted in revealingreflections as shallow as 300 ms. Some of these reflections seem to be a continuation of the deeper ones and now appear to come to the surface which can now improve thecorrelation with the surface geology. Two major apparently moderately dipping shear zones are now interpreted to reach to the surface in the re-processed data in comparison with the previous work.The deep reflections are also enhanced together with the improvement in the shallow parts which provide further insights about the nature of the Moho and its geometry along BABEL line 7. The re-processed seismic image demonstrates the potential in improving shallow and deep crustal structures along the BABEL offshore seismic data.
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Garreau, Germain. „Detecting Earth-like exoplanets using high-dispersion nulling interferometry“. Thesis, KTH, Tillämpad fysik, 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-293172.
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The detection of Earth-like exoplanets and the characterization of their atmospheres is a challenge one needs to solve to assess their habitability and the presence of life in the universe. If this challenge is still unresolved today, even in the era of giant telescopes, it is mainly because of the very high contrast between these exoplanets and their host star and also their proximity. To overcome both of these constraints, a new method combining high-dispersion spectroscopy and nulling interferometry has been imagined. The idea is to use the nulling interferometry to attenuate the star light emission and detect the inner rocky planets with a high angular resolution. The high-dispersion spectroscopy is increasing the exoplanet detectability significantly which enables to relax the star attenuation requirement for an Earth-like observation. Our simulation made for an exoplanet similar to the Earth orbiting Proxima Centauri is giving a condition for the star attenuation ∼10−4 to detect it. Given this condition, we are able to evaluate the unability of a photonic device at our disposal to achieve such performance without dealing with its limitations. If a future project manages to overcome these limitations, this device could be part of a precursor instrument at IPAG to demonstrate experimentally the performance of high-dispersion nulling interferometry.Upptäckten av jordliknande exoplaneter och karakteriseringen av deras atmosfärer är en utmaning man behöver lösa för att bedöma deras beboelighet och närvaron av liv i universum. Om denna utmaning fortfarande inte är löst idag, även i jätteteleskopens tid, beror det främst på den mycket höga kontrasten mellan dessa exoplaneter och deras värdstjärna och också deras närhet. För att övervinna båda dessa begränsningar har en ny metod som kombinerar högdispersionsspektroskopi och nullingsinterferometri föreställts. Idéen är att använda nullingsinterferometrin för att minska stjärnljusemissionen och upptäcka de inre steniga planeterna med hög vinkelupplösning. Spektroskopin med hög dispersion ökar exoplanetens detekterbarhet betydligt vilket gör det möjligt att minska stjärndämpningsbehovet för en jordliknande observation. Vår simulering för en exoplanet som liknar jorden som kretsar omkring Proxima Centauri ger ett tillstånd för stjärndämpningen att ∼10−4 för att upptäcka den. Med tanke på detta villkor kan vi utvärdera oförmågan hos en fotonisk enhet till vårt förfogande för att uppnå sådan prestanda utan att hantera dess begränsningar. Om ett framtida projekt lyckas övervinna dessa begränsningar kan den här enheten vara en del av ett föregångarinstrument på IPAG för att experimentellt visa prestanda för högdispersionsnullningsinterferometri.
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Nichols, Bryan H. „Defining Earth Smarts: A Construct Analysis for Socioecological Literacy Based on Justly Maintaining Quality of Life“. Scholar Commons, 2012. http://scholarcommons.usf.edu/etd/4182.
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This paper describes the creation and validation of a new educational construct. Socioecological literacy, or earth smarts, describes the qualities we need to justly maintain or improve our quality of life in a changing world. It was created using construct analysis techniques and systems tools, drawing on an extensive, transdisciplinary body of literature. Concepts related to environmental, ecological and scientific literacy, sustainability and citizenship were combined with educational frameworks, new research in science education, and modern cognitive psychology. After the initial formulation, the results were considered by a variety of experts and professionals from the fields of ecology, environmental science and education, using surveys, conference presentations and interviews. The resulting qualitative and quantitative feedback was used to refine and validate the framework. Four domains emerged from the analysis: concepts, competencies, sense of place, and values. The first two are common in formal education, although many of the more specific components that emerged are not adequately addressed. The second two domains are unlikely to be achieved solely in traditional educational settings, although they emerged as equally important. Sense of place includes affective components such as self-efficacy, while values includes moral development, respect, and justice as fairness. To make culturally and ecologically appropriate localization as accessible as possible, the earth smarts framework (www.earthsmarts.info) is deliberately nonpartisan and was designed using free and open-source software. It can help educators, policy makers, and researchers interested in more resilient, just and adaptable communities to coordinate their efforts, particularly in the nexus between formal and informal education, which have different strengths and weaknesses.
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Kanan, Maria Isabel Correa. „An analytical study of earth and lime based buildings in the Blumenau region of Southern Brazil“. Thesis, Bournemouth University, 1995. http://eprints.bournemouth.ac.uk/327/.
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An Analytical Study of Earth and Lime Based Building Materials in the Blumenau Region, Southern Brazil. In the last fifteen years, there has been a growing state and national interest in the preservation of historic rural settlements of the nineteenth and twenty centuries in southern Brazil. This interest has generated a need to develop appropriate conservation methods which will safeguard the integrity and technology of vernacular buildings in Brazil. This study focuses on the Blumenau region, an area in the state of Santa Catarina which was settled by German and Italian immigrants in the late 19th century. As was typical in such settlements, the immigrants brought with them European methods of construction which were then adapted to the local environment and available local materials. Though somewhat deteriorated, Blumenau still retains a large number of vernacular building types and good documentary sources of information. Thus, it provided an ideal context in which to develop a methodological approach to the study and conservation of regional building materials in Santa Catarina. Twenty domestic buildings dating from approximately 1870 to 1930 and representing the four principal types of construction in the area were chosen for the pilot project. In addition to thorough historical and archival research on the architecture and technology of the region, the study includes an in-depth scientific analysis of earth and lime- based buildings materials utilised in the rural settlement. The analytical results are interpreted in light of the historical research and recommendations are made regarding appropriate conservation and repair techniques. The study concludes with general recommendations for improved conservation practice in the region including issues of material production, training, and management. The work includes an extensive bibliography relating to the characterisation and conservation of earth and lime- based building materials. Full details of analytical techniques utilised are given in the appendix.
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FRANCOU, Cédric. „STABILISATION DE LA MATIERE ORGANIQUE AU COURS DU COMPOSTAGE DE DECHETS URBAINS : Influence de la nature des déchets et du procédé“. Phd thesis, Institut national agronomique paris-grignon - INA P-G, 2003. http://tel.archives-ouvertes.fr/tel-00007519.
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Le compostage des déchets organiques reproduit le processus naturel de transformation dans le sol, des matières organiques fraîches, d'origine animale et végétale, en matière organique humifiée, communément appelée humus. C'est une pratique ancienne, dont on trouve des témoignages dans les lointaines civilisations romaine et même égyptienne. Mais l'évolution des déchets suit étroitement celle des sociétés, et les déchets du passé qui étaient essentiellement organiques (effluents d'élevages, déchets alimentaires, résidus végétaux...) renferment aujourd'hui une gamme très hétérogène de produits (déchets verts, déchets alimentaires, effluents d'élevages et industriels, papiers, emballages plastiques et métalliques,...). Aux composts « artisanaux » destinés à un usage très local se sont ajoutés les composts industriels visant à digérer les déchets des collectivités et des industries agro-alimentaires, pour les valoriser en agriculture. Cette diversité des déchets, accentuée par la diversité des procédés de compostage conduit à une grande variabilité des composts produits.
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Moberger, Allison L. „Theoretical detection limits and error reduction for radial velocity observations of an Earth-like exoplanet“. Thesis, Massachusetts Institute of Technology, 2009. http://hdl.handle.net/1721.1/114371.
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Thesis: S.B., Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences, 2009.Cataloged from PDF version of thesis.
Includes bibliographical references (page 36) and index.
The intent of this project was to determine the relationship between the number of radial velocity observations of an Earth-twin exoplanet and the error in the mass calculated from the detected signal. If the planet's period is known through prior transit observations, the mass may be measured by radial velocity more accurately; this project tested and measured the conditions for this error reduction. Simulated sets of radial velocity data taken by HARPS (accurate to 1 m/s) for an Earth-mass planet in a circular, edge-on, 1 AU orbit around a Sun-like star were used with a least-squares fit to measure the amplitude of the sinusoidal radial velocity curve. The three conditions in which the mass fit was compared were: evenly-spaced observations with the period unknown; evenly-spaced observations with the period known; and an unevenly-spaced observation method in which observation times are chosen to be very frequent and clustered around the peaks of the radial velocity curve. For evenly-spaced observations, knowledge of the period did not reduce the error in the mass measurement compared to the period-unknown case, though it did allow for the elimination of the false-negative detection case. When observations were evenly spaced, the percent error in the detected mass had a power law relationship with the number of observations of [sigma]%error 1250=N -⁰.⁵. However, when using the knowledge of the period from transits to choose clustered observation times near the peaks of the curve, the error in the mass was reduced by about 20% for the same number of total observations, and was thus approximated by the power law [sigma]%error = 1030N-⁰.⁵. This indicates that if the period of a low-mass planet is known through transits, the use of clustered observations allows its mass to be measured more accurately with the same number of radial velocity observations than if the period were unknown.
by Allison L. Moberger.
S.B.
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Chang, Chia-Yung. „Momentum transport due to a squall line system over the tropical oceans“. Thesis, Massachusetts Institute of Technology, 1988. http://hdl.handle.net/1721.1/51464.
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Vandenbussche, Sophie. „Origin of homochirality on Earth: experimental and theoretical investigations“. Doctoral thesis, Universite Libre de Bruxelles, 2009. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/210362.
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Chirality is the property of objects, including molecules, which are not superimposable on their materialized mirror image. Chiral molecules are omnipresent in living organisms and the constituents of biological macromolecules (proteins and nucleic acids) are chiral. Amino-acids (constituting proteins), ribose and 2-deoxy-ribose (the only chiral constituent of RNA and DNA nucleotides respectively) are furthermore generally present in living organisms only under one of their enantiomeric forms. This is referred to as the homochirality of the living world. The origin of this homochirality is still unexplained, even if many partial scenarios have been proposed in the literature. All scenarios involve the creation of a small enantiomeric excess for certain molecules, amplification of this excess and chirality transfer to other chiral molecules. The origin of homochirality on Earth is closely related to the origin of life, and is currently supposed to have preceded life. As no-one will ever be able to directly observe the phenomena which lead to homochirality, and life, on our planet, the only scientific approach to try and help explain how this occurred is to build scenarios, and test them taking into account all available information on the physical and chemical conditions on the primitive Earth (Earth before life appeared). In our work, we investigated three scenarios related to the origin of homochirality on Earth. One of these scenarios also relates to a very precise step of the origin of life: the selection of beta-d-ribofuranose as component of RNA nucleotides.Enantiomeric excesses (up to 15 %) of alpha-methylated alpha-amino-acids have been detected in meteorites which fell on Earth during the 20th century. No enantiomeric excess is detected for the corresponding alpha-hydroxy-acids in the same meteoritic samples and small (2% at most) or no enantiomeric excesses have been measured for non-methylated alpha-amino-acids. In the first part of our work, we investigated if photolysis by circularly polarized light (CPL) in space could be at the origin of the presence (or absence) of an enantiomeric excess for these compounds. Experiments to reproduce UV-CPL photolysis are difficult to undertake: they require high-energy circularly polarized photons, hence the use of a synchrotron. In our work, we used quantum mechanical calculations to obtain the electronic circular dichroïsm (ECD) spectra of two -methylated -amino-acids, their corresponding alpha-hydroxy-acids and one non-methylated alpha-amino-acid. Differences are observed between these spectra, and we propose a scenario to explain the experimental measurements reported here above: the enantioselective photolysis, in the gas phase at low temperatures (20K at most), of the alpha-amino-acids by UV-CPL with lambda>210 nm. Under these conditions no photolysis of the alpha-hydroxy-acids would occur. This scenario concerns the first step in the origin of homochirality on Earth: the creation of a small enantiomeric excess for some chiral molecules.
The second scenario that we investigated relates to the enantiomeric amplification step of the origin of homochirality on Earth, for which the role of the alpha-amino-acid serine has been suggested in the literature. Serine clusters have been observed in the gas phase by mass spectrometry. Among these clusters the octamer has been shown to be a magic number cluster and to have a preference for homochirality. An enantiomeric amplification via cycles of formation and dissociation of the octamer has been suggested. No complete scenario has however been proposed in the literature to explain how this could have occurred on the primitive Earth, but any scenario would most probably include an aqueous phase. We aimed at determining if the homochiral preference of serine octamers also exists in solution and therefore we first investigated if serine octamers exist in solution. For this study, we used nuclear magnetic resonance and infrared spectroscopies, which are well-adapted to the study of molecular assemblies in solution. We were able to demonstrate that most probably serine clusters are not present in solution, and if they are it could only be in extremely low concentration. The scenario suggested in the literature is discussed in the light of our results and of literature data on serine clusters.
As last hypothesis, we investigated a possible scenario for the selection of beta-d-ribofuranose as component of RNA nucleotides. The currently known prebiotic synthesis pathways to ribose also lead to the formation of many other carbohydrates, and ribose is only a minor product of these syntheses. Our hypothesis is that beta-d-ribofuranose could have been selected through favorable interactions with alpha-amino-acids already present on the primitive Earth under one enantiomeric form. Indeed, it is plausible that a peptidic world emerged before the presence of RNA and that homochiral alpha-amino-acids were present on Earth when RNA was synthesized. Under this hypothesis, we investigated the role that alpha-l-amino-acids could have played in the selection of alpha-d-ribofuranose as component of RNA nucleotides. This work is related to the last step of the origin of homochirality: chirality transfer. Our scenario was investigated via nuclear magnetic resonance studies of the interaction between alpha-amino-acids and carbohydrates. We were able to show that, in the systems that we studied, when an interaction occurs it is very weak (affinity constant less than 1M−1) and non enantioselective. Our results most probably discard the role that alpha-amino-acids alone could have played in the selection of beta-d-ribofuranose as component of RNA nucleotides, but does not discard the role that peptides could have played in this selection.
Doctorat en Sciences de l'ingénieur
info:eu-repo/semantics/nonPublished
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Ring, Michael J. 1979. „Annular mode-like responses to external forcings in a simple atmospheric general circulation model“. Thesis, Massachusetts Institute of Technology, 2008. http://hdl.handle.net/1721.1/43152.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 2008.Includes bibliographical references (p. 217-225).
In this thesis, I investigate the response of a simple atmospheric general circulation model to applied forcings to learn whether the annular mode patterns are a preferred model response to the forcings. The thesis is inspired by the appearance of annular mode patterns in Earth's atmosphere in response to a number of forcings. Climatologies of the model under the influence of applied torques or perturbations to the reference temperature profile are compiled and compared to a control run with neither type of forcing. In most cases the differences in climatologies are annular mode-like, suggesting the patterns are the preferred response of the model to the forcings. The strength of the response typically increases for either an increase in the strength of the forcing, or an increase in the strength of the projection of the forcing on the model's annular mode patterns. Trials with a response which was not annular mode-like usually featured a poor projection of the forcing on the annular modes, or substantial interference with tropical dynamics. A zonally symmetric version of the model is also used to test the direct response of the model to the forcing versus the response caused by changes in eddy feedback processes. The direct forcing alone is found to be insufficient to produce either the correct strength or shape of the annular mode patterns. Instead the changes in eddy fluxes must be included to produce the correct shape and amplitude of the anomalies.
by Michael John Ring.
Ph.D.
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Singer, Tanyew. „Wooden Photovoltaic Module Frames : Proof of Concept, Life Cycle Assessment and Cost Analysis“. Thesis, Uppsala universitet, Institutionen för geovetenskaper, 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-454318.
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To mitigate climate change and to achieve global carbon neutrality, the expansion of renewable energy sources is of paramount importance. In this context, photovoltaics (PV) are widely regarded as one of the most promising technologies to lead the transformation towards decarbonized energy systems. However, the manufacturing of PV systems is associated with initial greenhouse gas emissions linked to the procurement of PV components. Therefore, current research focuses on minimizing initial emissions to improve the overall environmental performance of PV systems. Since previous research suggests that conventional aluminum module frames contain a significant amount of embodied carbon, this study investigates a possible material substitution with wood as alternative frame material to lower the overall carbon footprint of PV modules. To test the technical feasibility of PV modules with wooden frames, a proof of concept (POC) is conducted using wood types that exhibit necessary characteristics regarding their mechanical properties and durability. Guided by the finite element method and preliminary testing, a novel frame design is conceived, and PV modules with wooden frames are realized. The prototypes are put to extensive testing, in which the mechanical stability is examined, and weathering effects are investigated in an outdoor installation. Furthermore, a life cycle assessment (LCA) is carried out to quantify potential benefits of wooden compared to aluminum frames regarding their global warming potential and other environmental impact categories. Lastly, this study compares the economic performance of wooden PV module frames with aluminum frames and considers possible optimizations in the value chain of wooden frames. POC results show that PV modules with wooden frames - in line with industrial standards - are feasible, yet mechanical stability and durability vary depending on the type of wood and overall design. LCA results suggest that wooden frames exhibit invariably better environmental performance in all impact categories although a reduced module lifetime may impair the overall life cycle performance. In regard to cost efficiency, wooden frames are more costly than aluminum frames, yet financial incentives or subsidies may make low-carbon materials more competitive in the future. It can be concluded that wooden PV module frames may be a promising alternative to standard aluminum frames provided that the overall lifetime is identical. Thus, additional studies are required to analyze the long-term performance and to identify areas of application for modules with wooden frames, for instance in the building-integrated PV sector. Lastly, further research is needed to explore additional utilizations of wood in PV systems such as in ground and roof mounting structures.
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Vigil, Miquela 1981. „H107[alpha] recombination-line emission, 4800-MHz and 1666-MHz continuum emission in the HII region RCW38“. Thesis, Massachusetts Institute of Technology, 2003. http://hdl.handle.net/1721.1/114111.
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Thesis: S.B., Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences, 2003.Cataloged from PDF version of thesis. In title on title page, "[alpha] appears as lower case Greek letter. "May 21, 2003."
Includes bibliographical references (page 31).
We present results from observations of H107[alpha] recombination-line emission and the related 4800 MHz continuum emission of the HII region RCW 38 using the Australia Telescope Compact Array. We find the continuum emission to be concentrated in a ring-like structure with the 05 star, IRS2, approximately centered in the cavity within the ring. The temperature of the ionized gas ranges from 5200 to 7500 K and the emission is optically thin. The H107[alpha] line emission appears to be confined within the continuum ring. We also find the continuum ring to encircle the peak in the diffuse X-ray gas. The radio continuum emission matches closely to NIR observations with a bright western ridge containing the peak in the 10[mu]m emission known as IRS1 (Frogel et al. 1974) apparent in both observations. From calculations of continuum and line parameters, we estimate the spectral type of the ionizing source for the region to be an 05/06 star which is consistent with the spectral type of IRS2.
by Miquela Vigil.
S.B.
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Siljeström, Sandra. „Single fluid inclusion analysis using ToF-SIMS : Implications for ancient Earth biodiversiy and paleoenvironment studies“. Doctoral thesis, Stockholms universitet, Institutionen för geologiska vetenskaper, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-54909.
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When and how life first emerged on the Earth is an area of intense research. Signs of the first life on Earth, including morphological fossils, are scarce and hard to interpret. An alternative approach is to study organic biomarkers, which are molecular fossils commonly considered as bona fide biosignatures. The main objective of the project is to develop an approach for analysis of single oil-bearing fluid inclusions and most importantly the detection of organic biomarkers in these inclusions. Analysis of oil-bearing fluid inclusions is advantageous since the inclusions may provide an uncontaminated sample source of Precambrian hopanes and steranes, which are key biomarkers for tracing the early evolution of life on Earth. Due to the presence of several inclusion generations, single inclusion analysis is desired in order to constrain biomarkers to specific inclusions. Time-of-flight secondary ion mass spectrometry (ToF-SIMS) could be an excellent tool for analysis of these types of samples. The development of the approach for analysis of single oil-bearing inclusions was done in a two-step process; i) a number of crude oils were analysed with ToF-SIMS and gas chromatography mass-spectrometry (GC-MS) to facilitate interpretation of ToF-SIMS spectra of these types of samples and, ii) a procedure that combines micrographs with ion etching and ToF-SIMS analysis was developed for analysis of inclusions. The feasibility of the technique was demonstrated for oil inclusions from the Siljan impact crater in which hopanes and steranes where detected. Single oil-bearing fluid inclusions trapped in mid-Proterozoic sandstones from Northern Australia were subsequently analyzed, and steranes and hopanes were detected in these inclusions. If applied on older inclusions this approach may help answer some of the questions regarding the emergence and evolution of life on Earth, and if applied on extraterrestrial samples, also the possibility of life on other planets and moons.Livets uppkomst och tidiga utveckling på jorden är ett hett forskningsfält. Hur och när livet och dess olika domäner (arkéer, bakterier och eukaryoter) uppstod på jorden är fortfarande oklart vilket beror på att de första tecknen på liv, vilka inkluderar morfologiska fossil, spårfossil och isotoper, är få och svåra att tolka. Ett alternativt sätt att studera det tidiga livet är att studera organiska biomarkörer som är organiska molekyler som anses unika för liv. Huvudmålet med projektet är att utveckla en metod som kan detektera organiska biomarkörer i enskilda oljebärande vätskeinneslutningar. Vätskeinneslutningar, som är små mängder vätska (picoliter) infångad in en sten, är intressanta då de är en potentiell provkälla för prekambriska (äldre än 500 miljoner år) biomarkörer, som hopaner och steraner, vilka används för att utforska livets tidiga utveckling på jorden. Analys av enskilda inneslutningar är emellertid oftast nödvändigt för att kunna tidsavgränsa biomarkörer. På grund av att de flesta inneslutningar är små (10 µm i diameter) är det inte möjligt att analysera en enskild vätskeinneslutning med standardtekniken gaskromatografi-masspektrometri (GC-MS). Time-of-flight secondary ion mass spektrometri (ToF-SIMS) med sin höga känslighet, höga massupplösning och kapacitet för 2D-representation av analysdata och djupprofilering av prover är en utmärkt teknik för analys av enskilda inneslutningar. Metoden för analys av enskilda inneslutningar utvecklades i två steg. Först analyserades ett antal råoljor med ToF-SIMS och GC-MS för att underlätta förståelsen av ToF-SIMS-spektra från dessa typer av prover. Därefter utvecklades en metod som bestod av mikroskopering för att lokalisera inneslutningen, jonetsning för att öppna inneslutningen och ToF-SIMS analys av det exponerade innehållet. Metoden testades framgångsrikt på enskilda inneslutningar i hydrotermala vener av flusspat och kalcit i ordovicisk (488-443 miljoner år sedan) kalksten. Därefter användes den utvecklade metoden för att analysera enskilda vätskeinneslutningar i 1,43 miljarder år gammal sandsten från norra Australien, i vilka hopaner och steraner detekterades. De detekterade steranerna visar att trots att havet under denna tid var syrefritt existerade det lokala syrerika miljöer där eukaryoter kunde överleva. Om den utvecklade metoden används på ännu äldre inneslutningar, vilka har daterats till 3,2 miljarder år, kan den komma att svara på några de mest fundamentala frågorna kring livets uppkomst och tidiga utveckling. Om metoden används på utomjordiska prover kan den svara på frågan om det finns liv på andra planeter eller månar.
At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 3: Manuscript. Paper 4: Submitted.
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Korbelyiova, Lucia. „Paper vs Leaf: Comparative Life Cycle Assessment Of Single-use Plates Made Of Renewable Materials“. Thesis, Uppsala universitet, Institutionen för geovetenskaper, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-386367.
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Global plastic pollution of the natural environment is extremely detrimental as it is causing deaths of animal species. More than 80 % of marine litter is made up by plastics and 70 % of those are made up by disposable items. For this reason, the European Parliament has agreed to abolish the top ten single-use plastic items found in the marine environment from the EU market from 2021. Therefore, the fossil-based disposables will need to be substituted by disposables made from renewable materials. It is thus important to investigate the environmental impact of these alternatives through their life cycle in order to support sustainable consumption and production. In this study, environmental impact of disposable plates made from two different renewable materials (paper and leaf) were analysed by means of life cycle assessment (LCA). The aim of the study was to examine the environmental performance of the two plates in the impact category global warming potential (GWP); and reveal the processes with the largest contributions to the overall GWP of each plate. The leaf plate was produced in India and the paper plate in the Nordics, however, both plates were used and disposed of in Uppsala, Sweden. The results showed that the leaf plate has a higher GWP due to its long-distance transport and electricity use derived from fossil fuels. Scenario analysis has proved that its GWP can be reduced when sea transport route is chosen instead of flying and production is increased. When it comes to the paper plate life cycle, the processing stage was identified to contribute the most to the total GWP. It could be further improved by applying a biodegradable layer for its coating. To keep the good performance in GWP the plate should be incinerated with energy recovery. The disposal of the plates has a substantial positive influence on their total carbon footprint as both plates substitute use of fossil fuels. However, the credits allocated for the different waste management options are specific to Uppsala and thus the results of this study should be applied only under similar conditions.
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Gómez, Leal Illeana. „Spectrophotometry of the infrared emission of Earth-like Planets“. Phd thesis, Université Sciences et Technologies - Bordeaux I, 2013. http://tel.archives-ouvertes.fr/tel-00962379.
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Le signal thermique d'une exoplanète tellurique est une clé pour caractériser les propriétés physiques et chimiques de son atmosphère. La résolution spectrale, et donc la caractérisation spectrale que nous pouvons réaliser des planètes extrasolaires, est malheureusement très limité, en particulier pour les planètes similaires à la Terre. Dans cette thèse, j'ai étudié la possibilité de caractériser des exoplanètes telluriques par l'analyse de la variabilité de son émission infrarouge. L'émission thermique apparente est en effet modulée par les saisons, la rotation de la planète, le mouvement et la variabilité des nuages, la phase orbitale, et aussi par la présence des satellites naturels.Premièrement, nous avons étudié l' émission thermique de la Terre vue en tant que point-source distante, ainsi que la variabilité et la dépendance du signal de la géométrie d'observation. J'ai modélisé l'émission de la Terre à l'aide des données satellitaires et des données produites par des modèles de circulation général (GCMs) du Laboratoire de Météorologie Dynamique de Paris (LMD), en comparant les deux types de données afin de valider les simulations.Pendant la deuxième partie de mon travail, j'ai utilisé des donnés du GCM pour modéliser des planètes telluriques qui diffèrent de la Terre par seulement un ou deux paramètres tels que: la vitesse de rotation (y compris des planètes synchrones), une surface planétaire entièrement recouverte par la glace ou de l'eau, l'obliquité de l'axe de rotation ou l'excentricité de l'orbite. Pour toutes ces planètes virtuelles, j'ai étudié le climat, déduit les propriétés physiques de la planète, et produit et analysé les signaux intégrés associés à différentes géométries d'observation.La dernière partie de la thèse est un travail préliminaire qui consiste en ne plus considérer l'émission bolométrique mais le signal de bandes spectrales étroites, grâce à une nouvelle génération de GCM. Parce que chaque bande explore un niveau spécifique dans l'atmosphère, l'étude de la variation du spectre en comparant les variabilités photométriques entre les bandes, permet d'étudier la dynamique, la composition, la distribution et l'évolution de l'atmosphère de la planète, ce qui ouvre un champ encore inexploré pour la caractérisation des exoplanètes.
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Bessou, Cécile. „Greenhouse gas emissions of biofuels: improving Life Cycle Assessments by taking into account local production factors“. Phd thesis, AgroParisTech, 2009. http://tel.archives-ouvertes.fr/tel-00453003.
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L'Analyse de Cycle de Vie (ACV) permet de comptabiliser les émissions de la production à la combustion d'un biocarburant mais elle ne prend pas en compte la dynamique locale de ces émissions, notamment celle des émissions de N2O, principal gaz à effet de serre agricole. Notre objectif fut d'abord d'analyse l'effet du tassement du sol sur les émissions de N2O en combinant expérimentation et modélisation. À l'aide de chambres automatiques sur des parcelles de betterave, nous avons mesuré en 2007-2008 des émissions cumulées de 944-977 g N-N2O ha-1 en sol non tassé et 1,448-1,382 g N-N2O ha-1 en sol tassé. Les émissions plus importantes sur le tassé furent surtout dues aux conditions anoxiques propices à la dénitrification. Nous avons modifié le modèle NOE pour mieux simuler la nitrification et la variation des fractions de N2O sur les produits totaux. Malgré une meilleure prédiction de la nitrification et des flux post-fertilisation, le modèle modifié NOE2 sous-estima les émissions totales. La sévère sous-estimation en été montre que les cycles sec-humides peuvent entraîner de fortes émissions dont le déterminisme n'est ni élucidé ni modélisé. Nous avons ensuite utilisé un modèle d'agro-écosystème (CERES-EGC-NOE2) pour produire les données d'inventaire pour nos ACV locales. L'éthanol de Miscanthus produit en Picardie entraîne potentiellement beaucoup moins d'impacts environnementaux que celui de betterave. Comparés à l'essence, l'éthanol de Miscanthus permettrait une réduction de gaz à effet de serre de 82-85% par MJ, celui de betterave une réduction de 28-42% par MJ en fonction des conditions pédo-climatiques et des pratiques agricoles locales.
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Rodriguez, Tablante Johiris Isabel. „Extracting 3D Information from 2D Crooked Line Seismic Data on Hardrock Environments“. Doctoral thesis, Uppsala University, Department of Earth Sciences, 2006. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-6510.
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Seismic methods have been used in sedimentary environment for almost 80 years. During that time, exploration geophysicists have developed a number of techniques to handle specific aspects of working in sedimentary areas. This is not the case for studies in the hardrock environment, where significantly less time and money have been invested on seismic investigations. Therefore, there is still a need to develop the right techniques appropriate for working in hardrock environments. The research presented here, covers aspects of acquisition, processing and interpretation in hardrock environments. A cost-effective alternative for two-dimensional data acquisition is presented. Acquisition parameters are also discussed and recommendations for future work are given. The main effort of this thesis, however, was to find appropriate processing methods to address some of the different problems present in datasets acquired in the hardrock environment. Comparison of two computer programs for first arrival seismic tomography was performed in order to find the most suitable one for processing crooked line geometries. Three-dimensional pre-stack depth migration was also tested to find a detailed near-surface image. A processing method geared to enhance the signal-to-noise ratio was applied to the dataset with the lowest signal amplitudes to improve the quality of the stack. Finally, cross-dip analysis and corrections were performed on two of the three datasets included in this thesis. Cross-dip analysis was also applied as an interpretation tool to provide the information needed for estimation of the true dip of some of the reflectors related to geological structures. The results presented in this thesis indicate that cross-dip analysis and corrections are one of the most powerful tools for processing and interpretation in the presence of complex geology. Therefore, it is recommended to include this method as a standard step in the processing and interpretation sequence of data acquired in hardrock environments.
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Wanzambi, Ellinor. „The Relationship Between a Variable Orbital Eccentricity and Climate on an Earth-Like Planet“. Thesis, Uppsala universitet, Luft-, vatten och landskapslära, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-388151.
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By using climate models based on the Earth’s climate, you can get information about how the climate on exoplanets can look like. ROCKE-3D is a general circulation model based on ModelE2, which is used for simulations of modern and prehistoric Earth’s climate. ROCKE-3D, on the other hand, is used to simulate terrestrial planets both in our solar system and around other stars. The orbital eccentricity affects a planet’s climate, if the eccentricity is high, the planet will be closer to its star certain parts of the year and further away from it for other parts. Because of this, it is interesting to study the eccentricity’s influence on the climate of exoplanets, especially since the boundaries of the habitable zone change. In this report, the climate of an Earth-like planet with varying orbital eccentricity has been investigated using ROCKE-3D. The results show that the annual average temperature increased if the eccentricity increased, even though it was expected to decrease because the planet was further away from its star for longer periods than it was closer. The reason for this was that the ocean dampened the surface temperature drop. The amount of snow and ice was also examined. As eccentricity increased, the ocean ice became thicker and snow accumulated in the northern hemisphere. This can be explained, even though the annual average temperature increased due to the warmer winters, by the fact that the temperature in the summer decreased so much that the snow and ocean ice did not melt away completely and started to accumulate for the years with higher eccentricities.
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Cole, Timothy. „Physical Properties of Tar Sand Tailings that Influence Their Ability to Sustain Plant Growth“. TopSCHOLAR®, 1985. http://digitalcommons.wku.edu/theses/1900.
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The mining of bituminous sandstone rock for the purpose of extracting bitumen has created a need for reclamation. One such mine is located in northern Logan County. Their mining operation involves removing large sections of sandstone, which is impregnated with bitumen, and crushing it to sand-sized material. The sand-sized material is then mixed with organic solvents which extract the bitumen. Once separated, the bitumen is stored for future refinement and the spent sand is stockpiled for later disposal.
The spent sands or waste material are referred to as tar sand tailings. These tailings have particular properties which make reclamation efforts difficult. One restrictive property is the 30 percent swell factor, which prevents replacement of the tailings into their respective mined area. Another property is the tailings’ hydrophobicity. This water repellence prevents merely spreading the tailings onto the surface.
Experiments were conducted at Western Kentucky University during 1984 and 1985 to determine methods to lessen the hydrophobic tendencies and allow for reclamation. These experiments included mixing the tailings with the existing soil and adding surfactants to the tailings. Water holding capacities, infiltration rates, and the ability to sustain plant life were determined and evaluated.
It appears that the residual bitumen not removed by the extraction process causes the hydrophobic tendencies of the tailings. This conclusion was based on a comparison of pure tailings and tailings which were subjected to 500°C temperatures for 24 hours which could destroy all organic material, specifically the residual bitumen. The pure tar sand tailing held 0.44 percent moisture and the tailings with the organic material removed held 27.48 percent moisture.
Mixtures of tailings and Zanesville soil were also evaluated and compared to the tailings with and without organic material. The percent moisture of the soil was not significantly different from the tailings without organic material. All mixtures were significantly lower than the soil or the tailings without organic material and significantly higher than the pure tar and tailings. However, the mixtures apparently can hold sufficient moisture for plant growth.
Water infiltration rates through various mixtures of tailings and soil with and without surfactants were also evaluated. It was concluded that a tailings/soil mixture of 75/25 percent with and without surfactant and 90/10 percent mixture with surfactant allowed the fastest water infiltration. The rate of infiltration is important since the Logan County topography is favorable for runoff erosion.
Rye (secale cereale) was grown in various mixtures of tailings and soil with and without surfactants to determine phytotoxic effects. Visual observations of the growing plants indicated no phytotoxic effects due to the bitumen or surfactants. However, dry matter yields of the plants differed significantly. The lower yield of some plants could be attributed to a lack of moisture since the lowest yields were in the pure tailings with and without surfactant.
In conclusion, the results of this study revealed that tar sand tailings do have hydrophobic tendencies apparently due to residual bitumen. These tendencies can be buffered by mixing the waste material with an existing soil or by complete combustion of the residual organic material. Also it was concluded that vegetation could be established on the mixtures of tailings and soil and thus, the land reclaimed.
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Brayard, Arnaud. „Ammonoïdes du Smithien (Trias inférieur) du Nord‐Ouest du Guangxi (Chine du Sud) et modélisation biogéographique de la récupération biotique des ammonoïdes après l'extinction de masse Permien/Trias“. Phd thesis, Université Claude Bernard - Lyon I, 2006. http://tel.archives-ouvertes.fr/tel-00254879.
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L'extinction de masse permo‐triasique (~252 Ma) a décimé plus de 90% des espèces marines vivant à cette époque. La récupération biotique consécutive était jusqu'alors considérée comme extrêmement lente (~10 millions d'années). Dans ce contexte, les ammonoïdes (céphalopodes) du Trias inférieur constituent un ensemble phylogénétiquement bien contraint d'organismes marins abondant dans le registre fossile, et donc particulièrement appropriés à l'étude de l'impact des conditions climatiques et océaniques (températures[SST], courants, etc.) sur les dynamiques macroécologiques et biogéographiques post‐crise. Afin d'appréhender l'impact relatif de ces paramètres, nous avons élaboré un modèle de simulation 2D, dit modèle « géophylétique », où les SST et les courants forcent la dispersion géographique d'un ensemble phylogénétique généré aléatoirement. Les simulations indiquent que la forme et l'intensité du gradient latitudinal de diversité résultent de la combinaison de deux effets « milieu de domaine », l'un géographique et l'autre thermique, en lien avec la forme et l'intensité du gradient de SST : plus celui‐ci est marqué, plus le gradient de diversité est accentué. Ces résultats sont comparés aux données fossiles, augmentées de plusieurs nouvelles faunes du Smithien de Chine du Sud, présentées ici sous une forme monographique. Celles‐ci indiquent que les ammonoïdes sont, après la crise permo‐triasique, parmi les organismes marins les plus rapides à se re‐diversifier et à reconquérir l'océan mondial (< ~2 ma). Le début du Trias inférieur est marqué par un gradient latitudinal de diversité très faible, avec de très nombreux genres cosmopolites. Ce gradient de diversité s'accentue progressivement durant le Trias inférieur, en lien avec une augmentation de la différentiation latitudinale et du degré d'endémisme des faunes. Cette accentuation correspond vraisemblablement au développement d'un fort gradient latitudinal de SST au cours du Trias inférieur.
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Bergström, Pauline. „Mapping surplus food redistribution initiatives in Sweden and a Life Cycle Assessment of environmental, social and economic impacts of some representatives“. Thesis, Uppsala universitet, Institutionen för geovetenskaper, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-388642.
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The Food and Agriculture Organization of the United Nations suggest that out of all food that is produced, 1/3 ends up as food waste. In high income countries, such as Sweden, the food waste mainly originates from the last stages of the food chain, e.g. at food stores and households. Sweden is a member of the EU as well as the United Nations, and follows the common legislation for waste in the EU and has adopted the Sustainable Development Goals from the United Nations. In the Sustainable Development Goal number 12, food waste in terms of reduction is addressed, although Sweden does not have a clear goal that addresses how to reduce food waste. Food banks have globally been a strategy to redistribute surplus food from the retail sector to people in need, something that has not been common in the Nordic region of Europe (including Sweden) until the 1980’s. However, in Sweden, food banks have not been used as a way to prevent food waste but as a way to help people in need, perhaps because there is a well-established well-fare system in the country. Recently, initiatives that redistribute surplus food from the retail sector have been developed - working towards different consumer groups and solutions. This study aimed to map out the different surplus food redistributing initiatives in Sweden, categorise them and analyse some of the initiatives that represented different solutions and consumer groups. The chosen initiatives were ReFood, City Mission Uppsala (Matkassen and Mikaelsgården), City Mission Stockholm (Matmissionen), Food2change, Foodloopz and Allwin. The methods used for analysing the chosen initiatives were Environmental Life Cycle Assessment, Social Life Cycle Assessment and Life Cycle Costing. To weigh the environmental-, social- and economic impacts against each other, a total sustainability ranking system was used to point out the most favourable option for a redistributing surplus food initiative, in terms of sustainability. The results showed that the environmental impacts (Green House Gases (kg CO2 equivalents/functional unit)) were the lowest for, in this order, ReFood, Mikaelsgården and Allwin, Foodloopz, Matmissionen and Matkassen, and Food2change. For the social impacts, the results showed that Allwin is the initiative that redistribute the largest amount of surplus food to the consumer group “exposed people”, followed by Matmissionen that redistribute the second largest amount of surplus food to “people with low income”. Allwin is also the initiative with the highest capacity and largest yearly environmental savings, as the company redistributes a much larger amount of food than the other initiatives. The results for the economic impacts showed that all but one initiative, Food2change, have monthly financial losses. The overall sustainability ranking showed that the initiative that is the most favourable is Matkassen followed by Matmissionen and Allwin, Food2change, Foodloopz, ReFood and Mikaelsgården.
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Schloegel, Lisa Marie. „Investigations on the dispersal of 'Batrachochytrium dendrobatidis' and Ranaviral disease through the international live animal trade in the Americas and Asia“. Thesis, Kingston University, 2012. http://eprints.kingston.ac.uk/23706/.
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Enigmatic amphibian declines are strongly associated with infectious diseases, including chytridiomycosis, caused by the fungus 'Batrachochytrium dendrobatidis' (Bd), and ranaviral disease induced by ranaviruses. A series of data analyses, field sampling, laboratory experimentation and molecular techniques were utilized to test the hypothesis that the international live animal trade is contributing to the spread of these amphibian pathogens. Regions sampled included specific locations in North America, South America and Asia. The magnitude of the live importation of amphibians into the United States (U.S.) was calculated in the millions of animals per year. Batrachochytrium dendrobatidis and ranavirus infections were identified in live food animals in: (a) U.S. wet markets (in 'Lithobates catesbeianus', the North American bullfrog); (b) frog farms in Taiwan (in 'L. catesbeianus'); and (c) wet markets in Taiwan (in 'Rana tigrina', the Chinese bullfrog). 'Batrachochytrium dendrobatidis' infections were also identified in 'L. catesbeianus' farmed in Brazil and in 8 species of amphibians in the U.S. pet trade (in captive bred and directly imported animals). Detection of Bd in individuals upon initial entry into the U.S. demonstrated definitively the trans-continental movement of this potentially lethal amphibian pathogen. Laboratory experimentation illustrated transmission of Bd from a highly traded carrier host ('L. catesbeianus') to frogs of the same species, and to a known susceptible frog species ('Litoria caerulea', White's tree-frog). Molecular data linked U.S. market frogs and their associated ranaviral infections to origins in Asia and South America. Genotyping of pure, cultured isolates of Bd from farmed 'L. catesbeianus' in Brazil showed that they were most similar to isolates from native amphibians in Latin America when compared to a global dataset, providing evidence for transmission between wild and farmed amphibians. Analysis of isolates from market 'L. catesbeianus' led to the discovery of a novel genotype of Bd in Ypsilanti, Michigan that appeared to have a disparate lineage compared with the previously identified panzootic genotypes. DNA sequence analysis from the Ypsilanti frog indicated its origin in Brazil, where the novel genotype was also discovered in native Brazilian frog populations. The demonstration of amphibian pathogens on frog farms, in live wet markets and at border crossings, the evidence of inter- and intra-species transmission, and the existence of a novel genotype in traded anurans, all indicate that international transport of amphibians and their pathogens could produce not only mixing of pathogen genotypes, but the inadvertent spread of strains of unknown virulence that could negatively impact amphibian health. In 2008, data from research contained in this thesis were instrumental in the decision to list both Bd and ranaviral disease in the World Organization for Animal Health Aquatic Animal Health Code, providing guidelines (such as quarantine procedures) to limit the spread of these pathogens through the trade. The evidence provided in this work re-enforces the need for urgent action to minimize the potential spread of amphibian diseases through international trade routes, for the benefit of amphibian populations throughout the world.
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Grönkvist, Sofia. „Social Life Cycle Assessment in the Textile Industry: a case study in a small company“. Thesis, Uppsala universitet, Institutionen för geovetenskaper, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-384470.
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Investigations of the textile industry and apparel sector often reveal unethical behaviours towards workers and lack of transparency in the value chain. As consumers are getting more conscious and the external pressure and demand for more sustainable clothing increases, companies need to implement management systems to control their operations and ensure actions are socially responsible. The Social Life Cycle Assessment (S-LCA) methodology published by the United Nations Environment Programme in 2009 are suggested to measure positive and negative social impacts on stakeholders along a products entire life cycle, from cradle to grave. The methodology is still under development and no methods have yet been standardized or internationally recognized. To contribute to the development of the S-LCA and its practical use in real world situations, the present study aims to evaluate the applicability of existing methodologies and tools by applying them to a cotton shirt from a small company in Sweden. The case study was performed by conducting an S-LCA following the four phases: Goal and scope; Life Cycle Inventory; Life Cycle Impact Assessment and; Life Cycle Interpretation. Generic country-level data and organisation specific data were collected through questionnaires, document review and desktop screening, while two different assessment tools were tested for the different data types. For generic country-level data, a Social Hotspot Assessment framework developed for this study, was applied and evaluated. For organisation specific data the existing Subcategory Assessment Method (SAM) was subject for feasibility evaluation. The S-LCA conduction involved several application issues that affect the perceived applicability and feasibility of the methods. Problems identified relate to the definition of system boundaries and uncertainties in the choice of appropriate and relevant indicators. The major problems refer to data collection both in terms of availability and quality issues both with regards to the inventory and assessment phase. Further, in the assessment and interpretation phase uncertainties regarding assessment criteria’s and aggregation of results evolved when using the framework for identifying hotspots, affecting the reliability of the results. Despite the identified issues, it is evident that it is possible to conduct and finalise a Social Hotspot Assessment using the methodology. However, based on the reliability issues of the results and the effort it requires, it is concluded that the applied framework is not feasible for smaller clothing companies with limited resources. The assessment of organisation specific data by applying SAM, is considered incomplete and identified issues reflect the incompatibility of the method and are thus not considered applicable or feasible for smaller companies.
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Welzel, Lisa. „End-Of-Life Wind Turbines in the EU : An Estimation of the NdFeB-Magnets and Containing Rare Earth Elements in the Anthropogenic Stock of Germany and Denmark“. Thesis, Uppsala universitet, Institutionen för geovetenskaper, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-394910.
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Securing rare earth elements (REE) for a stable supply require sustainable management strategies in Europe due to a missing local primary production and a dependence on China as the main producer of REE. These elements, like neodymium (Nd) and dysprosium (Dy), are contained in permanent magnets (PM) (mostly NdFeB-magnets) in wind turbines. Addressing the question whether PM-material, Nd- and Dy-contents from wind turbines could help to meet future demands of REE in Europe while reducing simultaneously the import dependence, the purpose of the present work was to analyze the urban mining opportunities, recovery - and recycling potentials for REE from end-of-life (EoL) wind turbines. This thesis aimed to identify current and upcoming stocks as well as material flows of the PM and their containing REE in the wind energy sector. Two European countries, Germany and Denmark, were chosen as case studies to be compared based on created future scenarios and the modeling of the theoretical recycling potential of Nd and Dy in both countries. It could have been identified that the German anthropogenic stock contains greater amounts of NdFeB-magnets and REE compared to the Danish stock. Overall it could be concluded that the countries’ demand could partly be met by using secondary Nd and Dy from the EoL-wind turbines. Although future scenarios were used, the results realistically illustrate the German and Danish anthropogenic stock until 2035 by relying on data of already installed turbines up to 2018, which makes an evaluation of capacities and EoL-turbines, which need to be decommissioned by 2035, achievable. The provided information is valuable for further investigations regarding recovery strategies, feasibility analysis, and future decision-making processes.För att säkra tillgången på jordartsmetaller (REE) i Europa krävs hållbara beslutsstrategier. Detta på grund av avsaknaden av en inhemsk primärproduktion samt ett beroende av Kina som en huvudprodu-cent av REE. Jordartsmetaller som neodymium (Nd) och dysprosium (Dy), finns kvar i permanenta magneter (PM) (mestadels NdFeB-magneter) i vindturbiner. För att ta itu med frågan om huruvida Nd- och Dy-innehållet i PM-material, från vindturbiner skulle kunna bidra till att uppfylla framtida efter-frågan på REE i Europa samtidigt som importberoendet skulle minskas, var syftet med detta arbete att analysera möjligheterna till urban utvininng, återvinning och materialutnyttjande av REE från vindtur-biner i uttjänt tillstånd (EoL).Syftet med denna uppsats var att identifiera nuvarande och kommande tillgångar samt materialflöden av PM och därav följande REE inom vindkraftsektorn. Två europeiska länder, Tyskland och Danmark, valdes ut som fallstudier och jämfördes i framtida scenarier och mo-dellering av Nd -och Dy teoretiska återvinningspotential i båda länderna. Det kunde konstaterats att det tyska antropogena beståndet innehåller större mängder NdFeB-magneter och REE än det danska beståndet. Sammanfattningsvis kan man dra slutsatsen att ländernas efterfrågan delvis kunde tillgodo-ses genom att man använde sekundär Nd och Dy från EoL-vindturbiner. Även om framtida scenarier användes illustreras resultatet på ett realistiskt sätt det det antropogena lagret i Tyskland och Danmark fram till 2035 genom att man förlitar sig på uppgifter om redan installerade turbiner fram till 2018, vilket gör det möjligt att göra en utvärdering av kapaciteten och antal EoL-turbiner, som måste av-vecklas senast 2035. Informationen är värdefull för ytterligare utredningar om återvinningsstrategier, genomförbarhetsanalys och framtida beslutsprocesser.
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De, Brémond D'Ars Jean. „Estimation des propriétés rhéologiques des magmas par l'étude des instabilités gravitaires : Pétrologie du complexe plutonique lite de Guernesey“. Phd thesis, Université Rennes 1, 1989. http://tel.archives-ouvertes.fr/tel-00619374.
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L'objectif principal de ce travail est de déterminer dans quelle mesure l'étude de phénomènes physiques, secondaires par rapport à la différenciation magmatique, permet d'apporter des contraintes pour la reconstitution de l'évolution des chambres magmatiques. Dans un premier temps, une étude pétrologique de l'objet choisi -le Complexe plutonique Nord de Guernesey- a été réalisée. On en retire à la fois des résultats intéressant la géologie régionale et les paramètres de base pour l'étude des phénomènes physiques secondaires. Les résultats d'ordre régional consistent en la mise en évidence ou la confirmation de plusieurs points. On a ainsi montré que le Complexe plutonique Nord de Guernesey est un massif calco-alcalin d'âge cadomien (550-560 Ma) constitué de quatre intrusions. Les deux ensembles les plus basiques: le Gabbro de Saint-Peter-Port et le Groupe Dioritique de Bordeaux sont des formations litées qui constituent les témoins d'une ancienne chambre magmatique. Les relations entre gabbros et diorites ne peuvent être établies avec certitude, mais plusieurs critères pétrographiques et géochimiques incitent à penser qu'ils se - rattachent à une même évolution magmatique. Les deux intrusions les plus acides: la Granodiorite de L'Ancresse et le Granite de Cobo apparaissent résulter du mélange d'un constituant basique apparenté aux liquides gabbro-dioritiques et d'un constituant dérivant de la fusion crustale induite par la mise en place de la chambre magmatique basique. Le Groupe Dioritique de Bordeaux, et plus précisément le type Beaucette que l'on observe sur la côte Est de l'île, présente de nombreuses figures particulières traduisant l'intervention de phénomènes magmatiques divers venant se superposer à l'évolution magmatique principale par cristallisation fractionnée. On a ainsi des indications de l'importance des phénomènes tels que les mélanges dans les chambres magmatiques calco-alcalines. Certaines structures qui évoquent des figures de charge sédimentaires sont particuiièrement bien déveioppées à ia pointe Nord-Est de l'île. Ce sont elles qui ont été choisies pour étudier l'importance des phénomènes physiques de second ordre dans les chambres magmatiques. En effet, les mécanismes d'instabilité gravitaire ont une signification suffisamment simple pour permettre ce type d'approche.
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Stevenson, Emily Isabel. „Stable strontium isotope fractionation in marine and terrestrial environments“. Thesis, University of Oxford, 2012. http://ora.ox.ac.uk/objects/uuid:a2d97fc7-3e9d-484a-8026-11c118fcc3fd.
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The work reported in this thesis applies a new isotope tracer, stable strontium isotopes (δ88/86Sr), to address questions concerning changes in global climate that occur in response to continental weathering processes, and to constrain the modern marine geochemical Sr cycle. Stable Sr isotopes are a relatively new geochemical proxy, and as such their behavior needs to be understood in differing forms of marine calcium carbonate, the archives from which records of past stable Sr variability in the oceans can be constructed. Foraminifera, coccoliths and corals (both aragonite and high Mg calcite) acquire δ88/86Sr values lighter than that of modern day seawater, (approximately 0.11, 0.05, 0.2 and 0.19 ‰ lighter than seawater at ~25°C respectively) providing a measureable offset which can be used to constrain the modern Sr outputs from the ocean and provide a better understanding of the modern Sr cycle. Using foraminifera as a sedimentary archive the first marine δ88/86Sr record of seawater over the last two glacial cycles has been constructed, and used to investigate changing carbonate input and output over this 145 kyr period. Modelling of the large excursion of δ88/86Sr to heavier values during Marine Isotope Stage (MIS) 3, reveals that this is more likely to be due to local changes in seawater or post-depositional alteration, rather then whole ocean changes. In the terrestrial environment δδ88/86Sr has been measured in the dissolved load of rivers from the Himalaya. It is found that, in general, rivers draining carbonate catchments possess lighter isotopic δ88/86Sr values than those from rivers draining silicates. Covariations of either δ88/86Sr vs. δ30Si or δ88/86Sr vs. 1/[Sr] can be used to distinguish between rivers draining different catchment areas.
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Dufour, Simon. „Contrôles naturels et anthropiques de la structure et de la dynamique des forêts riveraines des cours d'eau du bassin rhodanien (Ain, Arve, Drôme et Rhône)“. Phd thesis, Université Jean Moulin - Lyon III, 2005. http://tel.archives-ouvertes.fr/tel-00012155.
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L'effet combiné des gradients physiques, des interactions biotiques et des impacts anthropiques, le tout dans un cadre temporel évolutif, donne aux forêts alluviales l'aspect d'une mosaïque complexe où se juxtaposent, dans l'espace et dans le temps, des milieux variés et diversifiés. Si, depuis plus de trente ans, les études ont décrit, qualitativement, les liens qui unissent la végétation des plaines alluviales et la dynamique hydro-morphologique du chenal, certains aspects ont été peu abordés (Chapitre 1). C'est pourquoi, nous avons analysé, quantitativement, l'impact de l'évolution hydro-morphologique du chenal sur les flux d'eau et de sédiments et donc sur les boisements riverains dans les hydrosystèmes rhodaniens. Dans ce contexte, les contrôles anthropiques ont été explicitement intégrés dans l'analyse de l'évolution des structures et des flux. De fait, deux questions scientifiques ont été abordées.Dans un premier temps (Chapitre 2), une approche temporelle de la dynamique de la végétation riveraine à l'échelle de la seconde moitié du 20e s a été développée. Au niveau du paysage (Chapitre 2-A), le contrôle anthropique apparaît très important, aussi bien pour l'évolution des surfaces boisées, que pour la structuration spatiale du corridor naturel. Ainsi, nous avons montré que l'abandon des pratiques sylvicoles et pastorales peut être le moteur de la végétalisation des lits majeurs (Ain). A l'inverse, l'implantation de structures anthropiques dans le paysage réduit la superficie des milieux forestiers et provoque une fragmentation de l'ensemble du corridor (Arve). Lorsque la dynamique latérale du chenal peut s'exprimer, elle est à l'origine d'une plus grande diversité des unités paysagères. Cependant, nous avons mis en lumière un fort découplage géographique entre la dynamique de la zone interne du corridor et celle de la zone externe. Enfin, le caractère transitoire de la structure et de la diversité de la mosaïque paysagère a également été montré. A l'échelle des individus (Chapitre 2-B), l'analyse de la croissance ligneuse du frêne montre également que les contrôles hydro-morphologiques et anthropiques sont prépondérants pour la dynamique de la végétation riveraine à moyen terme. De fait, la position altitudinale d'une placette contrôle en grande partie son degré de connexion hydrologique ; sur l'Ain, un effet de seuil a pu être identifié pour la croissance du frêne entre des débits de connexion de 750 m3.s-1 et de 1000 m3.s-1. De plus, la structuration spatiale du substrat est également, pour le frêne, un facteur important contrôlant sa croissance radiale. L'analyse de la prospection racinaire de cette essence met en évidence un double contrôle au niveau du substrat : un contrôle édaphique (présence d'horizons impénétrables, ex. : le toit de galets) et un contrôle hydrologique (présence d'une nappe permanente ou semi-permanente). Evidemment, structure et fonctionnement sont intimement liées et nos résultats indiquent que la mobilité du chenal, en modifiant de façon significative le patron hydrologique et sédimentaire, affecte les conditions écologiques au sein de la plaine. De même, dans les corridors riverains soumis à une pression anthropique importante, le développement d'activités consommatrices d'eau entraîne une modification de la répartition spatiale et temporelle des flux au sein de l'hydrosystème.
Dans un deuxième temps (Chapitre 3), nous avons travaillé à une échelle de temps plus courte et à l'échelle spatiale de la communauté végétale. Dans la strate basse des boisements post-pionniers (frênaie) du corridor de l'Ain (Chapitre 3-A) aussi bien que dans les unités pionnières (saulaies) de la Drôme (Chapitre 3-B), nous avons montré que les conditions écologiques d'une unité varient non seulement en fonction de sa position dans l'hydrosystème à un instant donné, mais aussi au gré de l'évolution de la géométrie du chenal. Cette évolution résulte de l'ajustement aux conditions de débits, solide et liquide, au sein du chenal ; elle est donc liée à la dynamique de l'ensemble du tronçon fluvial : mobilité du chenal (incision sur l'Ain), effet des aménagements anthropiques (endiguement sur la Drôme). Concernant les communautés végétales, la position spatiale et la dynamique du tronçon se traduisent par des niveaux contrastés de connexion hydro-sédimentaire et donc de régime de perturbation. L'expression des processus hydrologiques et sédimentaires se répercute ainsi sur la communauté, en termes de composition, de structure, de régénération ou de diversité. Le rôle important joué par la dynamique des sédiments fins dans les forêts alluviales est alors souligné par nos résultats. En effet, l'érosion et le dépôt de sédiments constituent les processus primordiaux du caractère perturbant d'une crue. De plus, la granulométrie et l'épaisseur du substrat constituent un filtre à l'origine d'une sélection des espèces arbustives dans les milieux pionniers. Notons que cette dynamique des sédiments fins est sous le contrôle de la dynamique hydro-morphologique de l'ensemble du tronçon.
Les exemples développés dans notre travail font apparaître une véritable géographie des facteurs de contrôle liée à l'expression différenciée des conditions hydro-morphologiques mais aussi une empreinte anthropique toujours présente. Par exemple, l'influence de la mobilité du chenal sur la croissance et la régénération ligneuse ainsi que le contrôle exercé par la dynamique sédimentaire sur le paysage et les communautés riveraines constituent des arguments importants pour développer une gestion cohérente des lits fluviaux et de leurs marges boisées. Pour cela, après avoir rappelé la spécificité des boisements alluviaux, nous proposons des éléments stratégiques de gestion, concernant notamment : la cohérence géographique des boisements à gérer, le diagnostic fonctionnel de ces forêts, le choix des objectifs de gestion, la prise en compte du contexte hydro-morphologique et de son évolution, la réhabilitation des sites et la cohérence des outils législatifs et financiers permettant d'agir dans ce domaine (Chapitre 4).
Enfin, les résultats obtenus dans le cadre de cette thèse permettent de discuter les notions de connexion physique (hydrologique et sédimentaire), de contraintes anthropiques et de trajectoire écologique (Conclusion).
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Denison, Francis. „SPECIATION DE L'URANIUM(VI), MODELISATION, INCERTITUDE ET IMPLICATION POUR LES MODELES DE BIODISPONIBILITE. APPLICATION A L'ACCUMULATION DANS LES BRANCHIES CHEZ UN BIVALVE D'EAU DOUCE“. Phd thesis, Université de Provence - Aix-Marseille I, 2004. http://tel.archives-ouvertes.fr/tel-00009927.
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Les effets de différentes compositions de solution sur les interactions entre l'uranium(VI) et des branchies disséquées du bivalve d'eau douce Corbicula fluminea ont été étudiés dans des milieux de solution bien définis. Une réduction significative de l'accumulation de l'uranium a été observée en augmentant les concentrations de citrate et carbonates, ligands complexants de l'uranium. Des cinétiques de saturation en fonction de la concentration d'uranium ont été observées à pH 5,0, ce qui indique que l'accumulation d'uranium est un processus facilité, impliquant probablement un ou plusieurs systèmes de transport transmembranaire. Une modification relativement réduite de l'accumulation d'uranium a été constatée en fonction du pH (facteur de 2 environ), en dépit de modifications extrêmement importantes apportées à la spéciation en solution de l'uranium sur la plage de pH étudiée (5,0 – 7,5). Une revue exhaustive des données thermodynamiques relatives au domaine de composition de solution utilisé pour cette étude a été réalisée. Les estimations des incertitudes pour les constantes de formation des espèces aqueuses d'uranium(VI) ont été intégrées dans une base de données thermodynamiques. Un programme informatique a été élaboré afin de prévoir la distribution à l'équilibre de l'uranium(VI) dans les systèmes aqueux simples, à l'aide des valeurs moyennes des paramètres thermodynamiques. Le programme a été étendu afin de réaliser les analyses d'incertitude avec les méthodes de Monte Carlo et Quasi Monte Carlo, en intégrant les estimations des incertitudes de la base de données thermodynamiques, afin de prévoir de manière quantitative les incertitudes inhérentes à la prévision de la spéciation en solution de l'uranium. L'utilisation de la modélisation de l'équilibre thermodynamique en tant qu'outil d'interprétation de la biodisponibilité de l'uranium(VI) a été étudiée. Le comportement d'accumulation d'uranium(VI) observé a été interprété en fonction des modifications prédites de la spéciation en solution de l'uranium. Différentes approches d'état stationnaire ou de pré-équilibre pour la modélisation de l'accumulation d'uranium ont été testées. D'autres approches de modélisation ont également été testées, en prenant en considération les modifications potentielles de l'activité du système de transport membranaire ou des caractéristiques de sorption pour des compositions de solution variables. Enfin, l'effet de l'incertitude sur l'utilisation de la modélisation de l'équilibre thermodynamique pour interpréter la biodisponibilité de l'uranium (VI), a été évalué.
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Mocquet, Christophe. „Interférence entre les processus mitotiques et la prise d'azote chez Thalassiosira weissflogii. Implications en modélisation et sur les flux globaux“. Phd thesis, Université Pierre et Marie Curie - Paris VI, 2009. http://tel.archives-ouvertes.fr/tel-00472581.
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Le modèle michaëlien d'acquisition d'azote, utilisé à l'origine pour représenter l'effet de la concentration d'un nutriment sur son taux d'absorption, s'avère insuffisant lorsque d'autres facteurs présentent des variations temporelles, à l'exemple du cycle diurne de lumière. Dans la littérature, les oscillations diurnes de l'acquisition d'azote sont généralement expliquées par la réponse du statut physiologique des microalgues au flux de photons et à la disponibilité en substrat. Cette thèse a pour but d'identifier dans quelle mesure le cycle cellulaire conditionne lui aussi la prise d'azote, et le cas échéant d'évaluer l'impact de cette propriété au niveau macroscopique. Pour cela, nous avons réalisé des expériences en cultures continues de la diatomée Thalassiosira weissflogii soumise à différentes conditions de lumière et d'azote. Notre étude met en évidence une diminution de l'acquisition d'azote lorsqu'une proportion significative de la population est en mitose. Il apparait également que les évènements mitotiques sont planifiés à la fois par les conditions de croissance et par une horloge interne. De plus, nos expériences montrent que les conséquences macroscopiques de ces propriétés individuelles sont fonction du degré de synchronisation de la population, et nous détaillons les facteurs agissant sur ce phénomène. Ensuite, nos hypothèses sont reprises dans une approche numérique afin de tester le gain de représentativité obtenu en prenant en compte le cycle cellulaire dans la modélisation de la croissance phytoplanctonique. Enfin, nous discutons de l'effet du cycle cellulaire sur l'acquisition d'azote en milieu marin et de ses possibles implications écologiques.
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Pelosi, Céline. „Modélisation de la dynamique d'une population de vers de terre Lumbricus terrestris au champ. Contribution à l'étude de l'impact des systèmes de culture sur les communautés lombriciennes“. Phd thesis, AgroParisTech, 2008. http://tel.archives-ouvertes.fr/tel-00336523.
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Les lombriciens représentent une composante majeure de la macrofaune du sol et sont souvent présentés comme bioindicateurs de la biodiversité et de la qualité du sol. Par ailleurs, ils sont des ingénieurs de l'écosystème car ils modifient directement ou indirectement la disponibilité des ressources pour d'autres organismes tels que les plantes et les microorganismes. Ils ont un rôle important dans les agrosystèmes car ils participent aux processus qui influencent les composantes physique, chimique et biologique du sol.L'enjeu majeur de ce travail est de comprendre et de modéliser l'évolution des populations de lombriciens dans un champ cultivé et d'étudier l'impact de certains systèmes de culture sur les communautés lombriciennes. L'outil que nous avons mis en place, WORMDYN est un modèle stochastique de dynamique des populations basé sur un modèle matriciel et structuré en classes de stades de développement (cocons, juvéniles, sub-adultes et adultes). Il prédit l'évolution des populations du ver L. terrestris dans des parcelles labourées et dans des parcelles travaillées superficiellement. Les paramètres de ce modèle, estimés en partie grâce à des données issues de la littérature, dépendent de la température et de l'humidité du sol qui sont les facteurs clés influençant la dynamique à court terme de cette espèce de vers de terre.
Ce travail de thèse comporte une première partie méthodologique. L'étude de la dynamique des populations lombriciennes a nécessité un nombre important de prélèvements en champ cultivé. Or, diverses méthodes sont classiquement utilisées pour l'échantillonnage des lombriciens. Nous avons donc cherché à déterminer la méthode de prélèvement la plus adéquate, c'est-à-dire alliant efficacité et sécurité du manipulateur. Une première partie est donc consacrée à l'étude et à la comparaison de trois produits chimiques utilisés pour le prélèvement des lombriciens.
Dans un deuxième temps, la thèse présente la structure du modèle WORMDYN. La capacité du modèle à représenter la réalité est testée en confrontant les sorties aux mesures faites en parcelles expérimentales. Une analyse de sensibilité désigne les paramètres influençant fortement les sorties du modèle et met ainsi en évidence des pistes d'amélioration possibles.
Enfin, dans le but de discuter des impacts de systèmes de culture sur les communautés lombriciennes, nous avons récolté des données sur un essai de longue durée comprenant trois systèmes : biologique, conventionnel et un système sous couvert végétal permanent. Par ailleurs, les résultats nous permettent d'étudier le comportement de WORMDYN dans d'autres situations et de dégager des pistes d'amélioration du modèle.
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HOSTIOU, Nathalie. „Pratiques et stratégies de gestion des ressources herbagères cultivées par des éleveurs laitiers sur un front pionnier en Amazonie brésilienne : cas du municipe de Uruar“. Phd thesis, Institut national agronomique paris-grignon - INA P-G, 2003. http://tel.archives-ouvertes.fr/tel-00007520.
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Sur les fronts pionniers amazoniens au Brésil, la production laitière est un facteur de consolidation des exploitations familiales. Dans les élevages lait-viande herbagers, les troupeauxbovins sont alimentés sur des prairies cultivées installées sur défriche forestière. Le discours scientifique considère que la durabilité de ces systèmes est étroitement liée à la pérennité des
prairies. L'objectif de la recherche est d'identifier si le maintien de prairies pérennes est une entrée clé pour appuyer et stabiliser ces exploitations lait-viande. Notre recherche est conduite auprès des éleveurs laitiers du municipe de Uruará sur le front pionnier de la Transamazonienne dans l'Etat du
Pará.
Une analyse de la diversité de ces systèmes d'élevage, à partir des structures de production et des trajectoires d'évolution, met en évidence les différentes fonctions de la production de lait dans leur fonctionnement ainsi que par leur dynamique d'évolution. L'analyse des combinaisons de pratiques, à partir de suivis d'élevages laitiers pendant une campagne annuelle, conduit à identifier quatre principales stratégies de gestion des ressources herbagères. Elles se caractérisent par leurs expressions (pratiques et modalités), leurs déterminants et justificatifs. Ces résultats permettent d'identifier les objectifs, les attentes et les capacités des éleveurs pour gérer les ressources herbagères.
En Amazonie, la pérennité des prairies cultivées ne constitue pas le seul enjeu clé ni la contrainte majeure pour la durabilité et la reproductibilité des élevages laitiers herbagers. Il s'avère nécessaire de renouveler les approches sur la gestion des prairies pour consolider les exploitations familiales tout en préservant l'écosystème forestier
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Monzon, Santos Juan Luis Andre. „Food Waste Management - Perceptions, Decisions, and Actions: The case of Guatemala City Department Restaurants“. Thesis, Uppsala universitet, Institutionen för geovetenskaper, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-324710.
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Food waste has implications for the people, the planet, and profits. It presents a global problem which normally requires a local solution. Around 6% of the global food loss occurs in Latin America. However, the region lacks a clear strategy to address the issue, which is also true at the national level for countries such as Guatemala. Furthermore, the perception of different actors in the country towards food waste and its management remains unknown. The aim of this research is to explore on the attitudes towards food waste that might exist in the country by focusing on the restaurant sector with the objective of producing a holistic understanding of the issue. Concentration on the restaurant sector provides additional information of the matter, on a sector that shows limited research on it. To fulfill this objective, a case study was conducted, one that involved the participation of three actors directly related to restaurants as either managers or owners and an actor involved in the Municipality of Guatemala City. The research utilized semi-structured interviews and a review of the literature available on the subject as means of data gathering. The analysis was supported using the Triple Bottom Line Framework, a Positional Analysis ideology, the Sustainable Development Goals and the EU Waste Framework Directive. The results showed varied perceptions from the actors on the categorization of food waste, although impacts on an economic, environmental, and social dimension derived from food waste were acknowledged by all of them; being the latter the most prominent. For the actors, the generation of food waste was significant at the customer level, but was also influenced by the type of service provided by the restaurants. Additionally, the approaches selected by them to either directly or indirectly manage food waste covered a vast range of actions. Finally, the actors understood as key for addressing the food waste issue, the raising of awareness on the subject.
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Beveridge, Susan Lynn. „Quantifying the Relationship Between Southern-end Supercells and Tornado Production“. Ohio University Honors Tutorial College / OhioLINK, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=ouhonors1556127178521766.
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Charreau, Julien. „Evolution tectonique du Tianshan au Cénozoïque liée à la collision Inde-Asie : apports de la magnétostratigraphie et de la géochronologie isotopique U-Th/He“. Phd thesis, Université d'Orléans, 2005. http://tel.archives-ouvertes.fr/tel-00011572.
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Le Tianshan est une des chaînes majeures d'Asie qui s'étend sur près de 2500 km de longitude avec des reliefs supérieurs à 7000 m. Il s'agit de l'orogène intracontinental le plus actif au monde issu d'une accrétion initiale au Paléozoïque suivie d'une réactivation majeure au Cénozoïque en réponse à la collision Inde-Asie. Mais l'âge exact d'initiation de la déformation cénozoïque reste mal contraint, ce qui est un obstacle important à la compréhension et à la détermination de l'évolution de la déformation en Asie. Les piémonts Nord et Sud du Tianshan sont constitués par deux remarquables prismes d'avant chaîne où les sédiments permiens au quaternaires des bassins flexuraux adjacents de Kuche et de la Junggarie sont très bien exposés. L'histoire de la construction du Tianshan peut être déterminée grâce à une étude de l'enregistrement sédimentaire facilement accessible au niveau des piémonts.Ainsi, nous avons réalisé trois études magnétostratigraphiques le long des coupes de la Kuitun et de la Jingou He au Nord et le long de celle de Yaha au sud pour lesquelles nous avons identifié respectivement 16, 22 et 18 chrons magnétiques que nous avons corrélés à l'échelle de référence donnant des âges compris entre, 3.1 et 10.5 Ma, 8.5 Ma et 22 Ma et 5.2 et 12.6 Ma respectivement. Les vitesses de sédimentations déduites de ces corrélations montrent une accélération à ~11 Ma sur la coupe de Yaha et celle de la Jingou He qui présente également une accélération antérieure à ~15 Ma alors que les vitesses restent stables depuis ~10 Ma sur la coupe Kuitun. Nous avons également réalisé des études de la minéralogie magnétique et des mesures de l'ASM qui montrent des changements importants de la susceptibilité magnétique (Κ) et du paramètre de forme (T) à 21, 15 et 11 Ma sur les deux piémonts. A partir des changements de vitesses de sédimentation, contraint par ailleurs par ceux des paramètres magnétiques, nous pensons que la surrection du Tianshan a probablement débuté vers 15 Ma puis s'est accélérée à ~11 Ma, ce qui est cohérent avec les études précédentes réalisées sur la zone suivant d'autres méthodes.
A partir de modèles structuraux des piémonts et des basins de la Junggarie et de Kuche, associés aux âges magnétostratigraphiques et à des datations U-Th/He de grains d'apatites et zircons détritiques , nous déterminons également: (1) l'âge d'activation et les vitesses de déformation de certaines structures des piémonts, (2) les flux et vitesses sédimentaires et (3) l'évolution des taux d'érosion. Nous discutons et décrivons ainsi l'évolution cinétique et cinématique des piémonts et de la haute chaîne.
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Charbonnier, Céline. „Biogéochimie et hydrologie d'une plage battue : la plage du Truc Vert : flux de matière dans les sédiments sableux intertidaux“. Phd thesis, Université Sciences et Technologies - Bordeaux I, 2013. http://tel.archives-ouvertes.fr/tel-00946913.
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L'étude biogéochimique des sédiments sableux perméables est un domaine nouveau : le rôle de ces environnements dans les cycles biogéochimiques a longtemps été négligé en raison de leur pauvreté en matière organique et de la complexité des processus transitoires s'y déroulant. Les plages sableuses sont en effet soumises à de nombreux forçages physiques, dont la marée, la houle et la connexion avec l'aquifère continental. Le processus d'advection y est le mode de transport dominant. De grands volumes d'eau de mer chargée en matière organique sont plus ou moins filtrés par les sédiments perméables intertidaux. Le principal objectif de cette thèse était de caractériser les processus biogéochimiques induits par la recirculation de l'eau de mer et les apports d'eau douce dans la zone intertidale dans le cas d'une plage soumise à de fortes conditions hydrodynamiques : la plage du Truc Vert. Un suivi saisonnier des propriétés physico-chimiques des eaux porales a montré que les processus de respiration aérobie interviennent en zone intertidale, dans la lentille de recirculation de l'eau de mer. A l'échelle du littoral aquitain, ces processus représentent un apport annuel de 610 tonnes de nitrate et de 4400 tonnes de carbone inorganique dissous pour l'océan côtier, soit l'équivalent des apports de la Leyre, un petit fleuve drainant un bassin versant de 2000 km2 au sud-est du Bassin d'Arcachon. La macrofaune benthique est dominée par les Crustacés. Ces individus sont caractéristiques de ces milieux complexes, qu'ils subissent mais ne contrôlent pas : la macrofaune benthique contribue faiblement aux processus de respiration aérobie. Seuls 2% du déficit en oxygène des eaux porales du bas de plage leur est attribué en moyenne : les flux biogéochimiques observés en zone intertidale sont donc majoritairement induits par les processus de respiration aérobie des micro-organismes présents dans le sédiment. Soutenus par l'apport régulier d'oxygène dissous dans le milieu poral à chaque marée, ces processus sont également contrôlés par la température et la variabilité des apports de matière organique.Le déploiement de sondes autonomes dans le sédiment de la zone intertidale a également permis de préciser la variabilité à court terme des propriétés des eaux porales. L'extension de la lentille intertidale de recirculation de l'eau de mer est ainsi variable en fonction du marnage et les teneurs en oxygène mesurées en un point fixe de la plage varient légèrement en fonction de ce cycle. Ce travail a donc permis de démontrer que les processus de respiration aérobie varient principalement à l'échelle saisonnière. L'impact ponctuel et local des conditions météorologiques et de la houle a également été mis en évidence. Nous avons démontré l'existence d'un estuaire souterrain sous la plage du Truc Vert. La dynamique de ce système a été explorée grâce à l'installation de piézomètres en haut de plage. L'apport d'eaux douces continentales représente une source supplémentaire de nitrate et de carbone inorganique dissous pour l'océan côtier. L'étude biogéochimique de la nappe phréatique en arrière dune indique l'existence d'un découplage entre le front salin et le front redox au sein de l'estuaire souterrain, ainsi que l'existence d'un intense dégazage de CO2 au niveau de la dune.Les travaux réalisés durant cette thèse permettent de mieux comprendre les processus à l'œuvre dans les sédiments sableux des plages exposées et permettront ainsi le développement de modèles numériques complexes liant hydrologie et biogéochimie. Ils entraînent également de nombreuses perspectives à propos du rôle des plages sableuses à l'échelle locale (en cas de pollution par exemple) mais aussi sur les cycles biogéochimiques globaux, notamment en lien avec le réchauffement climatique et l'élévation du niveau marin (rejets de CO2, salinisation des aquifères côtiers).
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Laporte, Marie-Aline. „Contribution à la modélisation de l'absorption du cadmium par les racines du tournesol (Helianthus annuus L.) en relation avec l'architecture racinaire“. Phd thesis, Université Sciences et Technologies - Bordeaux I, 2013. http://tel.archives-ouvertes.fr/tel-00960832.
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Le cadmium (Cd) est naturellement présent dans les sols qui sont aussi enrichis par l'activité humaine. Le Cd contamine les produits végétaux alimentaires car il est absorbé par les racines des plantes. Elément toxique pour les organismes vivants, les concentrations dans les produits consommés sont soumises aux règlementations pour l'alimentation humaine et animale. Il est donc nécessaire de comprendre le transfert sol-organe consommé du Cd, spécialement pour le tournesol (Helianthus annuus L.), notre plante modèle, pouvant accumuler plus de Cd que d'autre plantes cultivées. Ce travail a testé l'hypothèse que la quantité de Cd absorbée par le système racinaire du tournesol était liée à l'architecture de ce dernier. Nous avons caractérisé au niveau des racines individuelles une variation longitudinale de l'influx d'absorption du Cd2+ en lien avec le milieu de culture, l'ordre et l'âge des racines. Ces variations ont été attribuées à la dynamique de développement des barrières apoplasmiques (dépôts de cellulose lignine et subérine) qui limitent l'internalisation du Cd2+ dans le cytoplasme cellulaire. Par simulation, il a été montré que ces variations pouvaient théoriquement impacter l'absorption totale de Cd2+ en fonction de l'architecture racinaire en hydroponie mais beaucoup moins sur substrat solide (sable). En outre, une comparaison de 14 cultivars de tournesol cultivé en hydroponie a montré que la variabilité des teneurs en Cd dans les parties aériennes était plutôt liée à des différences d'absorption indépendantes de l'architecture racinaire et à des variations de répartition dans la plante. Les variations longitudinales d'absorption du Cd peuvent alors être considérées comme mineures face à des variations inter-cultivars dont l'origine reste à élucider. Dans une optique de modélisation du prélèvement total en conditions de sol, il serait alors possible de ne considérer qu'un influx moyen de Cd pour la totalité du système racinaire indépendamment de son architecture