Applications de la résonance magnétique nucléaire (RMN) en milieu poreux Lissage des courbes de relaxation RMN du domaine du temps par une méthode discrète et continue

Dans un champ magnétique hétérogène, le signal RMN de précession libre (FID) suit une évolution gaussienne. Le traitement du signal par une méthode discrète peut donner des composantes qui ne correspondent pas à un état physique réel. Par contre l'utilisation d'une méthode de déconvolution continue nous a donné des résultats quantitatifs tout à fait satisfaisants permettant de déterminer les distributions de temps de relaxation correspondant à des états intermédiaires entre les phases solides et liquides. La RMN du domaine du temps peut ainsi être considérée comme une méthode analytique complémentaire des techniques habituellement utilisées pour l'étude de composés complexes hétérogènes ATD, ACD, isothermes de sorption, etc

Polymorphism of sugars studied by time domain NMR

The $T_1$ NMR relaxation time measured by time domain NMR spectroscopy was used to compare the mobility of the solid state of different sugars. To avoid time consuming experiments, a relaxation delay inferior to 5. $T_1$ has been used for crystalline samples. In this case, the commonly used relationship can no longer be used. The analysis of relaxation curves by a continuous method (CONTIN program) allowed to obtain quantitative results for crystalline and amorphous phases in mixtures, well related to experimental values. Photos by electronic scanning microscopy of crushed crystalline sucrose show pieces of sucrose with rounded corners, probably due to a partial melting of sucrose during crushing. This layer must be in an amorphous state. However, X-ray diffraction spectra did not show a significant amount of an amorphous phase. The very slight difference in the position of the $T_1$ distribution between rough crystalline sucrose and crushed sucrose could be due to the occurrence of an amorphous phase at the surface of the crystals

Determination of Water Droplet Size Distributions by Low Resolution PFG-NMR

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Ambivalent Types for Principal Type Inference with GADTs

Abstract. GADTs, short for Generalized Algebraic DataTypes, which allow constructors of algebraic datatypes to be non-surjective, have many useful applications. However, pattern matching on GADTs introduces local type equality assumptions, which are a source of ambiguities that may destroy principal types— and must be resolved by type annotations. We introduce ambivalent types to tighten the definition of ambiguities and better confine them, so that type inference has principal types, remains monotonic, and requires fewer type annotations.