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Mon travail de thèse a porté sur le développement de nouvelles méthodes de Résonance Magnétique Nucléaire pour l’étude des solides. Les méthodes développées sont compatibles avec des champs magnétiques élevés et une rotation rapide de l’échantillon autour de l’angle magique. Nous avons notamment développé une nouvelle méthode pour observer les proximités hétéronucléaires dans les solides. Cette méthode, baptisée PT-HMQC, consiste à manipuler les populations des transitions satellites des noyaux quadripolaires pendant les temps de défocalisation et de refocalisation. Cette manipulation permet d’accélérer le transfert de cohérence hétéronucléaire et ainsi d’augmenter la sensibilité des méthodes HMQC permettant l’observation indirecte d’isotope quadripolaire. Pour manipuler les transitions satellite, nous avons introduit de nouvelles impulsions radiofréquence modulées en amplitude et en fréquence. Ces impulsions, qui réalisent un quadruple balayage en fréquence, sont plus robustes dans le cas d’échantillon contenant des sites soumis à des interactions quadripolaires différentes. Nous avons aussi introduit une nouvelle méthode pour l’acquisition et le traitement des expériences RMN bidimensionnelles. Nous avons montré que la covariance permet de traiter des expériences enregistrées avec une acquisition continue non-uniforme. Ces méthodes permettent de réduire le temps d’expérience et d’améliorer la sensibilité sans affecter la résolution. / This thesis focus on the development of novel Solid-State Nuclear Magnetic Resonance (SS-NMR) methods. The proposed methods are compatible with high magnetic fields and fast MAS. Main achievements comprise :(1) the new pulse sequence (PT-HMQC) for heteronucler experiments. The major limitation of HMQC experiments is their lack of sensitivity, especially involving quadrupolar nuclei with short T2 values. We propose a simple and robust strategy by manipulating the populations of the satellite transitions (ST) during the mixing time, to accelerate the rate of coherence transfer, and enhance the sensitivity of J-HMQC experiments with indirect detection of the quadrupolar nucleus. With the introduction of new shape pulses (quadruple sweeps pulses), we find the best method, PT-J-HMQC with QFS (Quadruple Frequency Sweep), which is more robust to samples with different sites with different CQ value.(2) the new data processing methods for homonuclear experiments. We combine covariance (COV2D) spectroscopy with non-uniform continuous acquisition (NUCA) scheme, such as linear profile (Lk) and Gaussian profile (Gk). Furthermore, we add various sampling schemes, such as NUS (non-uniform sampling) and CUO (t1 cut-off). We find that covariance treatment, combined with the CUO sampling and Gaussian accumulation profile provides better gain in experimental time, better S/N, without loss of resolution.

Abstract The experiments was studied on a rotating ribbed square duct from two different impingement position of air jets (termed as Type A and B) and at rotational speeds of 0,300 and 600 rpm¡CThe jet impinged on two different geometric types of rib (square and semi-circular ribs). The study covered jet Reynolds number 5000 to 9000 and the jet rotation number was varied from 0 to 0.0053. Results are presented and focused on the effect of two of circular jet arrangements and different geometric of ribs. Significant heat transfer enhancement was found for Type A configuration and square ribs within the ranges of operating parameters considered in the study. However, rotation induced Coriolis and centrifuged forces decreased the Nusselt number values (up to 20%) which is quitely conincided with those of previous studies.

Thesis (Ph. D.) in Plant Science--University of Maine, 2000. / Includes vita. Includes bibliographical references (leaves 147-160).