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Application of an electromagnetic analysis for coal characterization is attempted. By time domain reflectometry (TDR), dispersion spectra in the DC – 5 GHz range of a wide variety of coals are obtained for room temperature. Static permittivity and relaxation frequency of the different samples are compared with parameters obtained by chemical analysis. Comparison reveals the usefulness of the electromagnetic characterization for the establishment of coal rank, and shows how an analysis of the dielectric characteristic parameters can provide approximate ideas about moisture, elemental carbon, hydrogen, and sulphur contents. PACS Nos.: 39.30+w, 82.53Kp, 77.22Gm

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Structure cristalline et mol6culaire du cycladi~ne (di6neoestrolThe structure determination of dienestrol: C1802H18 (Pbca, Z=4) was performed by direct methods. Although the unit-cell dimensions (a=18.969, b= 14.296, c=5-380 A) look like those of the previously described orthorhombic form of diethylstilboestrol (DES), the molecular conformation is strongly perturbed and here the central dienic chain is nearly perpendicular (85.9 °) to the phenyl planes. The hydrogen bonds which explain the crystalline cohesion are even weaker than for DES (3.063 A) but really exist as is proved by the value of the corresponding O-H...O angle (167°).

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The temperature dependence of the complex dielectric permittivity of ten primary amines (from propylamine to dodecylamine) has been measured at frequencies of 2 MHz and 3.26, 9.23, 15.05 and 35.25 GHz. From the analysis of the experimental results the authors conclude that the Davidson-Cole model is the most suitable to describe the dielectric relaxation phenomena in those amines. For this model they obtain the usual relaxation process characteristic parameters; that is to say the relaxation time, tau 0, and the constant beta which expresses the typical asymmetry of the relaxation times' zero-distribution function. The influence of the chain length and the behaviour of the NH2 group in the relaxation process is shown. Finally, the dielectric behaviour of the amines has been compared with that of their analogous alcohols.

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