83 research outputs found
Filtre-amplificateur passe-haut pour la recherche et l'étude des raies de RMN ou de RQP
No full textA high-pass filter amplifier is proposed to reduce the effect of slow drift superimposed on a faster signal during the recording of NMR or NQR spectra.Le filtre-amplificateur passe-haut décrit sert à réduire l'effet des dérives lentes superposées à des signaux plus rapides pendant les enregistrements de RMN ou de RQP
Étude en fonction de la température par R. M. M. du couplage quadripolaire de l'azote 14 dans un monocristal de nitrate de sodium
No full textPrior studies by Bernheim and Gutowsky, Andrew et al. and d'Alessio and Scott on the 14N quadrupole coupling constant (q. c. c.) of sodium nitrate showed a relationship with the phase transition at T λ = 275 °C. We show the interest of studying the temperature dependence of the nitrogen q. c. c. This q. c. c. (745 kHz ± 2 % at 25 °C) could be measured between - 196 °C and + 285 °C by NMR on a single crystal. We observe that q. c. c. decreases more and more rapidly as the temperature increases up to Tλ, after which the q. c. c. continues to decrease. The intraionic contribution to the nitrogen q. c. c. in the nitrate ion is discussed in terms of the σ and π orbital populations in the nitrogen, and of the electric charges in the oxygen atoms. Estimating the crystalline contribution to the q. c. c. by two methods, we find that it is subtracting from the intraionic contribution, respectively, by an amount of 11 kHz or 38 kHz. Finally, the nitrogen q. c. c. decrease is well explained below room temperature by the Bayer- Kushida theory although its strong decrease at higher temperatures is not. This is in agreement with the recent theories about phase transition according to which NO3- ions undergo helicoïdal motions of high amplitude when the transition is approached.Après avoir rappelé les études effectuées par Bernheim et Gutowsky, Andrew et al. et d'Alessio et Scott sur le couplage quadripolaire (c. q.) du sodium en relation avec la transition de phase à Tλ = 275 °C, on montre l'intérêt que peut présenter l'étude du c. q. de l'azote en fonction de la température pour préciser le comportement des ions nitrates lorsque la température augmente. Ce c. q. (745 kHz ± 2 % à 25° C) a pu être mesuré, par R. M. N. sur un monocristal, entre - 196 °C et. + 285 °C. Il diminue de plus en plus rapidement quand la température s'élève jusqu'à Tλ et, au-delà, il décroît encore. La contribution intra-ionique au c. q. de l'azote de l'ion nitrate est ensuite discutée en fonction des populations des orbitales σ et π sur l'azote et des charges portées par les oxygènes. Deux évaluations distinctes donnent l'ordre de grandeur de la contribution cristalline (11 kHz ou 38 kHz selon le calcul) et montrent qu'elle se retranche de la contribution intra-ionique. Finalement la décroissance du c. q. de l'azote aux températures inférieures à l'ambiante s'interprète bien par la théorie de Bayer-Kushida ; par contre, cette théorie ne rend pas compte de la forte décroissance du c. q. au-dessus de l'ambiante, et cela s'explique avec les dernières théories relatives à l'existence de mouvements hélicoïdaux de grande amplitude des ions NO3- accompagnant la transition de phase
Sustainable Development Opportunities at the Climate, Land, Energy and Water Nexus in Nicaragua
No full textThere are strong interconnections between the practices needed to sustainably manage land, energy, and water resources, which become even more pronounced when the many implications of climate change are taken into consideration. An exploration of these resource sectors in Nicaragua, a country at high risk from climate change, shows how their linkages directly impact the opportunities for development available to a rapidly growing economy. In particular, these linkages may shape solutions for sustainably managing agriculture,confronting water scarcity, and promoting local energy resources, which together can provide independence from global market volatility. Here we synthesize the state of climate, land,energy, and water issues in Nicaragua and highlight the potential for integrated resource planning in the country. We focus on three ongoing, sustainable development initiatives as case studies: rain-water harvesting in the Pacific Mountain Corridor, community-scale breadfruit processing in the Caribbean Coast region, and national bioenergy production using sugarcane bagasse.Fil: Gourdji, Sharon. University of Stanford; Estados UnidosFil: Craig, Mathias. Blue Energy; Estados UnidosFil: Shirley, Rebekah. University of California at Berkeley; Estados UnidosFil: Ponce de Leon Barido, Diego. University of California at Berkeley; Estados UnidosFil: Campos, Eleonora. Instituto Nacional de Tecnología Agropecuaria; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Giraldo, Mauricio. Universidad Pontificia Bolivariana; ColombiaFil: Lopez, Mauricio. Pontificia Universidad Católica de Chile; ChileFil: Pereira de Lucena, Andre F.. Universidade Federal do Rio de Janeiro; BrasilFil: Luger, Martina. Horizont3000; NicaraguaFil: Kammen, Daniel M.. University of California at Berkeley; Estados Unido
Improved Estimates of Regional-scale Land-Atmosphere CO2 Exchange Using Geostatistical Atmospheric Inverse Models.
No full textIn order to devise strategies to reduce atmospheric CO2 concentrations and predict their future trajectories for climate change mitigation and prediction, it is important to accurately quantify and understand the drivers of regional-scale (~500 x 500 km2) land-atmosphere carbon exchange from biospheric processes and fossil fuel emissions. While CO2 fluxes at this scale cannot be directly measured, inverse models can potentially provide estimates with reasonable uncertainties by tracing back variability in atmospheric CO2 measurements to the most likely distribution of surface CO2 exchange. This dissertation applies a geostatistical approach to inversions, which relies on an estimated spatiotemporal covariance structure to infer fluxes directly at fine scales in both space and time. In addition, process-based datasets can be incorporated into the inversion in a manner analogous to multi-linear regression, improving flux
estimates and providing inference regarding significant flux drivers. In the first dissertation component, environmental datasets are incorporated into a global inversion, with results showing that Leaf Area Index and the Fraction of Photosynthetically Active Radiation explain a significant portion of biospheric flux variability, while Gross Domestic Product and Population Density are associated with the fossil fuel emission signal. However, at the continental scale, flux estimates were found to be constrained primarily by the atmospheric measurements, with the grid-scale environmental datasets having minimal impact. The second component investigates the optimal use of continuous, continental CO2 measurements influenced by the biospheric diurnal cycle, heterogeneous land-cover, and point-source fossil fuel emissions. In a series of synthetic data inversions over North America during the growing season, explicitly estimating the diurnal variability of fluxes was found to be critical for inferring unbiased fluxes at the aggregated monthly, ecoregion-scale. In the third component, a North American regional inversion is implemented using real data available from the continuous monitoring network in 2004. The biospheric portion of estimated total CO2 flux is compared to a collection of bottom-up, process-based model output. Results show some convergence in the spatial patterns, seasonal cycle and net annual CO2 flux between the inversion and bottom-up models, although inversion results at robust scales also help to provide insight into the forward model spread.PhDEnvironmental EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/84599/1/sgourdji_1.pd
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North American CO2 exchange: Inter comparison of modeled estimates with results from a fine scale atmospheric inversion
No full textProline-rich tyrosine kinase 2 mediates gonadotropin-releasing hormone signaling to a specific extracellularly regulated kinase-sensitive transcriptional locus in the luteinizing hormone beta-subunit gene
No full textG protein-coupled receptor regulation of gene transcription primarily occurs through the phosphorylation of transcription factors by MAPKs. This requires transduction of an activating signal via scaffold proteins that can ultimately determine the outcome by binding signaling kinases and adapter proteins with effects on the target transcription factor and locus of activation. By investigating these mechanisms, we have elucidated how pituitary gonadotrope cells decode an input GnRH signal into coherent transcriptional output from the LH beta-subunit gene promoter. We show that GnRH activates c-Src and multiple members of the MAPK family, c-Jun NH2-terminal kinase 1/2, p38MAPK, and ERK1/2. Using dominant-negative point mutations and chemical inhibitors, we identified that calcium-dependent proline-rich tyrosine kinase 2 specifically acts as a scaffold for a focal adhesion/cytoskeleton-dependent complex comprised of c-Src, Grb2, and mSos that translocates an ERK-activating signal to the nucleus. The locus of action of ERK was specifically mapped to early growth response-1 (Egr-1) DNA binding sites within the LH beta-subunit gene proximal promoter, which was also activated by p38MAPK, but not c-Jun NH2-terminal kinase 1/2. Egr-1 was confirmed as the transcription factor target of ERK and p38MAPK by blockade of protein expression, transcriptional activity, and DNA binding. We have identified a novel GnRH-activated proline-rich tyrosine kinase 2-dependent ERK-mediated signal transduction pathway that specifically regulates Egr-1 activation of the LH beta-subunit proximal gene promoter, and thus provide insight into the molecular mechanisms required for differential regulation of gonadotropin gene expression
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