454 research outputs found
On modular forms of characteristic p>0
We compare modular forms of characteristic (i.e. Drinfeld's modular
forms) and automorphic forms. We prove that spaces of these modular forms
(which are of characteristic ) can be described by function spaces of
characteristic zero, close to those of automorphic forms
Galois theory of q-difference equations
Choose with 0<|q|<1. The main theme of this paper is the
study of linear q-difference equations over the field K of germs of meromorphic
functions at 0. It turns out that a difference module M over K induces in a
functorial way a vector bundle v(M) on the Tate curve . As a corollary one rediscovers Atiyah's classification of
the indecomposable vector bundles on the complex Tate curve. Linear
q-difference equations are also studied in positive characteristic in order to
derive Atiyah's results for elliptic curves for which the j-invariant is not
algebraic over . A universal difference ring and a universal
formal difference Galois group are introduced. Part of the difference Galois
group has an interpretation as `Stokes matrices', the above moduli space is the
algebraic tool to compute it. It is possible to provide the vector bundle v(M)
on E_q, corresponding to a difference module M over K, with a connection
. If M is regular singular, then is essentially determined
by the absense of singularities and `unit circle monodromy'. More precisely,
the monodromy of the connection coincides with the action of
two topological generators of the universal regular singular difference Galois
group. For irregular difference modules, will have singularities and
there are various Tannakian choices for . Explicit
computations are difficult, especially for the case of non integer slopes.Comment: Corrected versio
Le recyclage des éléments minéraux par la strate herbacée dans un peuplement naturel à Acacia et dans une plantation d'Eucalyptus au Sénégal
Le recyclage des Ă©lĂ©ments minĂ©raux par la strate herbacĂ©e a Ă©tĂ© Ă©tudiĂ© dans la vĂ©gĂ©tation naturelle d'un sol pauvre de la zone soudano-sahĂ©lienne au SĂ©nĂ©gal, et dans un reboisement en #Eucalyptus camaldulensis$. La biomasse herbacĂ©e aĂ©rienne est du mĂȘme ordre de grandeur dans les deux milieux, variant de 0,2 Ă 3,2 t/ha selon les annĂ©es. On n'observe pas de relation directe avec la pluviomĂ©trie totale annuelle car la rĂ©partition des pluies joue un rĂŽle important. Les teneurs en Ă©lĂ©ments minĂ©raux sont, Ă l'exception de la teneur en P, plus faibles sous plantation oĂč l'horizon supĂ©rieur du sol est appauvri. L'immobilisation de N, K et Ca est plus Ă©levĂ©e en vĂ©gĂ©tation naturelle (23, 45 et 23 kg/ha respectivement) qu'en plantation (14, 26 et 11 kg/ha respectivement). Dans les deux milieux K est l'Ă©lĂ©ment le plus abondant. Les variations inter-anuelles montrent qu'au-delĂ d'un certain seuil, la minĂ©ralomasse n'augmente plus avec la biomasse dont la teneur diminue. Cette relation ne s'observe pas pour P. (RĂ©sumĂ© d'auteur
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