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In this paper we study the L p-Minkowski problem for p=鈭n鈭1, which corresponds to the critical exponent in the Blaschke鈥揝antalo inequality. We first obtain volume estimates for general solutions, then establish a priori estimates for rotationally symmetric solutions by using a Kazdan鈥揥arner type obstruction. Finally we give sufficient conditions for the existence of rotationally symmetric solutions by a blow-up analysis. We also include an existence result for the L p-Minkowski problem which corresponds to the super-critical case of the Blaschke鈥揝antalo inequality.

Nous etudions Ie Laplacien sur une bande rectiligne plane, avec des conditions aux bords de Neuman sur un intervalle de largeur 2a Ie long de la frontiere et de Dirichlet ailleurs. Pour a suffisamment petit cet operateur a une valeur propre simple 6 (a); nous montrons quil existe deux nombres positifs c1, c2 tels que E (a)-(03C0/d) 2~-c2a4. La meme conclusion s applique pour une paire de bandes paralleles avec conditions aux bords de Dirichlet, de largeurs differentes et, sur la frontiere commune, une fenetre de largeur 2a. de lInstitut Henri Poincar-Physique theorique-0246-0211 Vol. 65/96/0!/$4.00/@ Gauthier-Villars

We analyze a family of singular Schrdinger operators describing a Neumann waveguide with a periodic array of singular traps of a delta\prime type. We show that in the limit when perpendicular size of the guide tends to zero and the delta\prime interactions are appropriately scaled, the first spectral gap is determined exclusively by geometric properties of the traps.