Uniform denominators in Hilbert's Seventeenth Problem.
Unimodular lattices over real quadratic fields.
Unitary groups acting on hyperbolic substructures
Given a quadratic extension L/K of fields and a regular λ-Hermitian space (V, h) of finite dimension over L, we study the orbits of the group of isometries of (V, h) in the set of hyperbolic K-substructures of V.
Universal codes and unimodular lattices
Binary quadratic residue codes of length produce via construction and density doubling type II lattices like the Leech. Recently, quaternary quadratic residue codes have been shown to produce the same lattices by construction modulo . We prove in a direct way the equivalence of these two constructions for . In dimension 32, we obtain an extremal lattice of type II not isometric to the Barnes-Wall lattice . The equivalence between construction modulo plus density doubling and construction...
Universality of a non-classical integral quadratic form over ℚ(√5)
Unramified cohomology and rationality problems.
Untersuchungen über quadratische Formen in Körpern der Charakteristik 2.