On the exceptional series,and its descendantsLa série exceptionnelle,et sa descendance

Many of the striking similarities which occur for the adjoint representation of groups in the exceptional series (cf. [1–3]) also occur for certain representations of specific reductive subgroups. The tensor algebras on these representations are easier to describe (cf. [4,5,7]), and may offer clues to the original situation.The subgroups which occur form a Magic Triangle, which extends Freudenthal's Magic Square of Lie algebras. We describe these groups from the perspective of dual pairs, and their representations from the action of the dual pair on an exceptional Lie algebra. To cite this article: P. Deligne, B.H. Gross, C. R. Acad. Sci. Paris, Ser. I 335 (2002) 877–881.     

Temperaturmessung

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Magnetic properties of lanthanum orthoferrite fine powders prepared by different chemical routes

Fine powders of lanthanum iron oxide, LaFeO₃, have been prepared by solid state reaction as well as sol-gel synthesis and nebulized spray pyrolysis. Structures, morphologies and magnetic susceptibility measurements of these powders have been examined. The powders prepared by all the three low-temperature routes contain nearly spherical particles with an average diameter of 40 nm. These samples show a lower Neel temperature than the powder prepared by solid state reaction besides showing much lower magnetic susceptibility at low temperatures. Dedicated to Professor C N R Rao on his 70th birthday     

Gas-phase copolymerization of sulfur dioxide and butene-1

Mixtures of sulphur dioxide and butene-1 have been polymerized in the gas phase to the 1:1 alternating copolymer by electron irradiation. The rate of polymerization, measured by the decrease in gas pressure, decreased with increase in temperature over the range ?20 to +30°C. The initial G(-monomer) values decreased from 500 to 50 giving an Arrhenius activation energy of ?30 kJ mol^?1. These results are consistent with a ceiling temperature-pressure relationship. The ceiling temperature is about 60°C lower than that observed previously in the liquid phase in accord with thermo-dynamic prediction.