99 research outputs found
High performance optical spectroscopy for the study of isotopic CO2 anomalies in natural carbonates.
No full textL'étude de la composition isotopique des matériaux naturels ('traceurs isotopiques') est une des principales sources d'information pour l'étude des environnements et des grands cycles physico-chimiques dans la nature (ex : cycle du carbone, ou celui de l'eau). En géosciences, la plupart des mesures isotopiques se font par spectrométrie de masse et requièrent des niveaux de sensibilité́ et de précision extrêmes. En collaboration avec des géochimistes du Laboratoire des Sciences du Climat et de l'Environnement (LSCE, UMR 8212), le LIPhy développe depuis plusieurs années des instruments de mesure reposant sur la spectroscopie infra-rouge (« VCOF-CRDS »), dédies à l'analyse des isotopes et isotopologues dans diverses molécules (CO2, H2O, H2S ...). L'objectif de cette thèse est, dans un premier temps, d'optimiser la dernière génération de ces prototypes pour atteindre des mesures ultra-précises sur des petits échantillons de CO2, correspondant à des gains considérables en terme de rapidité et de simplicité de mesure pour plusieurs importants traceurs isotopiques (Δ17O, Δ16O13C18O), et permettant d'accéder pour la première fois à de nouveaux traceurs isotopiques (Δ18O12C18O) auparavant inaccessibles. Dans un second temps, le/la doctorant(e) mettra en œuvre cette technique, en collaboration étroite avec les géochimistes du LSCE, pour valider de nouvelles approches permettant de reconstruire les climats du passé (paléotempératures enregistrées dans les spéléothèmes) et de mieux comprendre certains mécanismes de biocalcification sur lesquels repose en partie la régulation naturelle du carbone atmosphérique. A plus long terme, les résultats issus de cette thèse contribueront à la montée en puissance d'une nouvelle génération de spectromètres laser ultra-précis, adaptée à l'étude de nombreuses autres molécules (H2O , CH4, N2O, H2S...), avec une très large gamme d'applications scientifiques en spectroscopie moléculaire comme en géosciences.The study of the isotopic composition of natural materials ('isotopic tracers') is one of the main sources of information for the study of environments and major physico-chemical cycles in nature (e. g. carbon or water cycles). In geosciences, most isotope measurements are made by mass spectrometry and require extreme levels of sensitivity and accuracy. In collaboration with geochemists from the Laboratoire des Sciences du Climat et de l'environnement (LSCE, UMR 8212), LIPhy has been developing for several years measurement instruments based on infrared spectroscopy ('VCOF-CRDS'), dedicated to the analysis of isotopes and isotopologues in various molecules (CO2, H2O, H2S, etc.). The objective of this thesis is, in a first step, to optimize the last generation of these prototypes to achieve ultra-precise measurements on small CO2 samples, corresponding to considerable gains in terms of measurement speed and simplicity for several important isotopic tracers (Δ17O, Δ16O13C18O), allowing access - for the first time - to new isotopic tracers (Δ18O12C18O) previously inaccessible. In a second step, the doctoral student will apply this technique, in close collaboration with LSCE geochemists, to validate new approaches to reconstruct past climates (paleo-temperatures recorded in speleothems) and to better understand certain bio-calcification mechanisms on which the natural regulation of atmospheric carbon is partly based. In the longer term, the results of this thesis will contribute to the development of a new generation of ultra-precise laser spectrometers, suitable for the study of many other molecules (H2O, CH4, N2O, H2S...), with a very wide range of scientific applications in molecular spectroscopy and geoscience
CAVITY-ENHANCED ABSORPTION SPECTROSCOPY WITH A MODE-LOCKED FEMTOSECOND LASER
No full textAuthor Institution: Laboratoire de Spectrom\'{e}trie Physique --- CNRS UMR 5588, Universit\'{e} J. Fourier-Grenoble IThe wide spectral coverage and high sensitivity of Mode-Locked Cavity Enhanced Absorption Spectroscopy (ML-CEAS) are illustrated by the observation of a very high overtone transition of in the blue spectral region (420 nm, 8 quanta of CH stretch excitation), which was easily accessed by frequency-doubling a modelocked femtosecond Ti:Sapphire laser. The detection limit is about . The rotational analysis of this parallel band, centred at , is presented and the vibrational assignment is discussed. T.Gherman, S. Kassi, A. Campargue, D. Romanini Chem. Phys. Lett. 383, 353-358 (2004
Methodologies for the mechanistic study of compartment-specific hydrogen peroxide perturbations
No full textThis electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.Thesis: Ph. D., Massachusetts Institute of Technology, Department of Chemical Engineering, 2019Cataloged from student-submitted PDF version of thesis.Includes bibliographical references.Reactive oxygen species (ROS) are an interesting class of molecules because of their ability to promote contradictory phenotypes depending on their intracellular concentration. Most significantly, their elevation has been linked with several pathologies, including cancer. The selective cancer killing hypothesis hinges on the idea that certain cancers will be more susceptible to toxicity via a redox-based mechanism than their surrounding healthy counterparts, and provides an attractive target for those studying redox biology. In order to effectively leverage this strategy, quantitative knowledge of intracellular ROS, specifically hydrogen peroxide (H₂O₂) and its associated pathway proteins, is necessary. This thesis developed tools and methodology for quantitative and mechanistic studies of H₂O₂ in the mitochondria.Both experimental and computational tools were developed and implemented to analyze mitochondrial H₂O₂, peroxiredoxin (Prx) proteins, and primary patient tumor cells. It was established that the toxicity of H₂O₂ perturbations localized to the mitochondrial matrix is dose- and time-dependent. A computational model of the mitochondrial H₂O₂ reaction network predicted that basal steady-state mitochondrial H₂O₂ concentrations are in the low nM range, and that Prx3 is responsible for H₂O₂ dynamics. Preliminary data in primary patient tumor cells of paraganglioma and related tumors with succinate dehydrogenase b (SDHB) mutations suggested these cancers are potentially sensitive to the investigational chemotherapeutic piperlongumine.And finally, analysis on the Prx family using statistical coupling analysis suggested evolutionarily conserved clusters of residues at the C-terminus of the Prx2 and Prx1 protein families that may point to a structure-function mechanism for their ability to complex with other proteins. All in all, these tools can be used in other cancer cell systems to better understand the quantitative H₂O₂ signaling mechanisms and possible chemotherapeutic targets within those pathways.by Kassi Taylor Stein.Ph. D.Ph.D. Massachusetts Institute of Technology, Department of Chemical Engineerin
Métamorphoses de l\u27écrivain dans le roman francophone subsaharien
No full textIn his very first novel - La vie et demie - the question was put forward: wherefrom shall Sony Labou Tansi write so as to be? With a stunning lucidity, the author observed the irreducible gap that separates him from (and yet links him to) his writing: I who speak of the absurdity of the absurd [ ... ] wherefrom do you think I speak if not from the outside? (1979: 9). Starting from that novel, this paper explores the way the figure of the author is revealed by the writing. To that end, it explores five takes on such a role through four more novels by Aminata Sow Fall, Ahmadou Kourouma, Kassi Efoui and Patrice Nganang
Analyse De La Diversité Floristique De La Forêt Classée D’agbo I (Côte d’Ivoire)
No full textThis study was carried out in the Agbo I classified forest (6 ° 24 '- 6 ° 41' N, 4 ° 50 '- 4 ° 09' W), which covers 15,575 ha. It contributes to a better knowledge of the dense semi-deciduous moist forest of Nesogordonia papaverifera (A. Chev.) Cap. (Malvaceae) and Khayaivorensis A. Chev. (Meliaceae). The surface surveys coupled with the itinerant inventories made it possible to have an inventory of 686 species, which are divided into 428 genera and 101 families. The most abundant families are Fabaceae, Rubiaceae, Malvaceae, Apocynaceae, and Euphorbiaceae. Out of these species, 84.11% are phanerophytes and 3.50% are hemicryptophytes. In conclusion, this study improves the knowledge which is based on the composition, structure, and diversity of the woody vegetation of the Agbo I forest. The results show that the species richness of the Agbo I classified forest is important. However, this floristic richness of the Agbo I listed forest is sufficient to justify its protection and sustainable management for the conservation of biodiversity in Côte d'Ivoire
Successional patterns of plant species and community diversity in a semi‐deciduous tropical forest under shifting cultivation
No full textImpact of Anthropogenic Activities and Urban Proximity on the Conservation of Trees Outside Forests on Agricultural Lands in the Mongala Province, Democratic Republic of Congo
No full textThis study analysed the influence of charcoal production, artisanal logging, and urban proximity on the conservation of Trees Outside Forests on Agricultural Lands (TOF-AL) in the Mongala Province (Democratic Republic of Congo). A stratified random sampling methodology was applied to 45 villages distributed across the three territories of the province (Bongandanga, Bumba, and Lisala). Within each village, an inventory of TOF-AL was conducted using linear transects and systematic sampling, allowing for the evaluation of the conservation index, species richness, density, and diversity of TOF-AL. The practice of extractive activities, including charcoal production and artisanal logging, was documented in each village, and the distance to major cities was determined. The results indicate that charcoal production and artisanal logging have a significant negative impact on all measured conservation parameters of TOF-AL. The conservation index, species richness, density, and diversity of TOF significantly decrease in villages where these activities are associated with slash-and-burn agriculture. The Bumba territory showed the lowest values for the conservation index, species richness, and density. The lowest values observed in Bumba suggest an increased anthropogenic pressure on forest resources in this area. Furthermore, a positive correlation was observed between the distance to major cities and the conservation of TOF-AL. In remote villages, the conservation index, species richness, density, and diversity of TOF-AL were significantly higher than in peri-urban areas. These results suggest that differentiated conservation strategies should be prioritised to ensure the effective conservation of TOF-AL in this region and beyond. These differentiated conservation strategies should consider territorial specificities, socio-economic activities, and spatial dynamics of rural landscapes
MICROWAVE SPECTROSCOPY OF ARGON-THIIRANE AND NEON-THIIRANE COMPLEXES
No full textAuthor Institution: Laboratoire de Physique des Lasers, Atomes et Mol\'{e}cules and CERLA, Universit\'{e} des Sciences et Technologies de LilleThe rotational spectra of Ar-thiirane (or ethylene sulfide ) and Ne-thiirane van der Waals complexes have been measured with a MWFT spectrometer between 6 and 20 GHz. The analysis of the spectra of the isotopic species and the determination of the geometrical structure of theses complexes are discussed
ULTRA SENSITIVE CAVITY RING DOWN SPECTROSCOPY OF MAJOR ATMOSPHERIC SPECIES BETWEEN 1.20 AND 1.71 m
No full textAuthor Institution: Universite Grenoble 1/CNRS, UMR5588 \mbox{LIPhy}, Grenoble, F-38041, FranceDuring recent years, we have developed a fibered DFB laser CW-CRDS spectrometer providing routine noise equivalent absorption of cm, over the 5850-8350 cm range. A detection limit of cm has been recently achieved by averaging spectra over a small spectral interval. The performances of this set up have allowed extending significantly the knowledge of the absorption spectra of molecules of major importance: methane, oxygen, water, ozone, carbon dioxide, hydrogen, nitrogen. The most striking results will be presented
Diversité floristique et infiltration humaine de la forêt classée de la Besso (Côte d’Ivoire)
No full textObjectif: Contribuer à une meilleure connaissance de la flore de la forêt classée de la Besso et de caractériser les populations infiltrées et les cultures pratiquées dans cette forêt classée.Méthodologie et résultats: La forêt classée de Besso (Côte d’Ivoire) couvre 23 100 ha sur est une forêt dense semi-décidue à Celtis spp. et Triplochiton scleroxylon. La création de clairières culturales entre 1966 et 2012 malgré le classement de la forêt est à l’origine d’une mosaïque de végétations secondaires incluses dans une matrice de forêt « primaire » que nous avons plus particulièrement étudié. Les relevés de surfaces couplés aux inventaires itinérants ont permis d’inventorier 474 espèces, qui se repartissent en 330 genres et 91 familles. Les familles les plus abondantes sont Fabaceae, les Rubiaceae, les Euphorbiaceae, les Moraceae, les Malvaceae, les Meliaceae, les Moraceae, les Annonaceae, les Sapindaceae et les Poaceae. Parmi ces espèces, 79 % sont des phanérophytes et 3 % des hémicryptophytes.Conclusion: Malheureusement, cette forêt est en progressive dégradation à cause des activités humaines qui menacent la biodiversité végétale et animale de cette forêt. Ainsi, pour réduire le phénomène de dégradation des forêts en générale, plusieurs actions de gestion durable pourraient être entreprises par l’État, les ONG et la population. Notamment par la création des zones de conservation de plantes par des mises en défens de jachères.Mots clés: Biodiversité végétale, Forêt classée de la Besso, Côte d’IvoireEnglish AbstractEnglish Title: Floristic diversity and human impact on Besso forest in Ivory CoastObjective: To contribute significantly to the knowledge of the flora of Besso forest and to evaluate the human impact.Methodology and results: The Besso forest in Ivory Coast) covers 23 100 ha and determines a potential vegetation corresponding to the Celtis spp.-Triplochiton scleroxylon semi-deciduous tropical forest. Shifting cultivation between 1966 and 2012 has led to a mosaic of secondary plant communities that are included in an old-growth forest matrix. For hundred seventy for (474) species were recorded in this forest during the field investigations, distributed among 330 genera and 91 families. The most common families were Fabaceae, Rubiaceae, Euphorbiaceae, Moraceae, Malvaceae, Meliaceae, Moraceae, Annonaceae, Sapindaceae and Poaceae. Among those species, 79 % and 3 % are phanerophytes and hemicryptophytes, respectively.Conclusion: Unfortunately, this forest is gradual degradation due to uncontrolled human’s activity. Thus, to reduce the degradation phenomenon of the forets in general, several actions of sustainable managements could be undertaken by the state, Non-Governmental Organisation (NGO) and the population. In particular by the creation of preservation zones of plants, the creation of collective gardens of plants.Keywords: Plant biodiversity, Besso forest, Ivory Coas
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