-pure submodules.
Sagbi bases of Cox–Nagata rings
We degenerate Cox–Nagata rings to toric algebras by means of sagbi bases induced by configurations over the rational function field. For del Pezzo surfaces, this degeneration implies the Batyrev–Popov conjecture that these rings are presented by ideals of quadrics. For the blow-up of projective -space at points, sagbi bases of Cox–Nagata rings establish a link between the Verlinde formula and phylogenetic algebraic geometry, and we use this to answer questions due to D’Cruz–Iarrobino and Buczyńska–Wiśniewski....
Sagbi bases with applications to blow-up algebras.
Schälbare Cohen-Macauley-Komplexe und ihre Parametrisierung.
S-divisible modules over domains.
Secondary characteristic classes and intermediate Jacobians.
Segre-Veronese embeddings of P1 x P1 x P1 and their secant varieties.
In this paper we compute the dimension of all the sth higher secant varieties of the Segre-Veronese embeddings Yd of the product P1 × P1 × P1 in the projective space PN via divisors of multidegree d = (a,b,c) (N = (a+1)(b+1)(c+1) - 1). We find that Yd has no deficient higher secant varieties, unless d = (2,2,2) and s = 7, or d = (2h,1,1) and s = 2h + 1, with defect 1 in both cases.
Sekiguchi-Suwa theory revisited
We present an account of the construction by S. Sekiguchi and N. Suwa of a cyclic isogeny of affine smooth group schemes unifying the Kummer and Artin-Schreier-Witt isogenies. We complete the construction over an arbitrary base ring. We extend the statements of some results in a form adapted to a further investigation of the models of the group schemes of roots of unity.
Self-dual normal bases for infinite odd abelian Galois ring extensions
Semi -ideals of commutative rings
Let be a commutative ring with identity. A proper ideal is said to be an -ideal of if for , and imply . We give a new generalization of the concept of -ideals by defining a proper ideal of to be a semi -ideal if whenever is such that , then or . We give some examples of semi -ideal and investigate semi -ideals under various contexts of constructions such as direct products, homomorphic images and localizations. We present various characterizations of this new class of...
Semicontinuity for representations of one-dimensional Cohen-Macaulay rings.
Semicontinuity for the Local Hilbert Function.
Semifields and a theorem of Abhyankar
Abhyankar proved that every field of finite transcendence degree over or over a finite field is a homomorphic image of a subring of the ring of polynomials (for some depending on the field). We conjecture that his result cannot be substantially strengthened and show that our conjecture implies a well-known conjecture on the additive idempotence of semifields that are finitely generated as semirings.
Semigroup of Two Irreducible Algebroid Plane Curves.
Semigroups associated to singular points of plane curves.
Semigroup-theoretical characterizations of arithmetical invariants with applications to numerical monoids and Krull monoids
Arithmetical invariants—such as sets of lengths, catenary and tame degrees—describe the non-uniqueness of factorizations in atomic monoids.We study these arithmetical invariants by the monoid of relations and by presentations of the involved monoids. The abstract results will be applied to numerical monoids and to Krull monoids.
Semi-invariants of binary forms and identities for Bernoulli, Euler and Hermite polynomials
Semi-local lattices
Seminormal graded rings and weakly normal projective varieties.
Semiprime factorizations in unions of Dedekind domains.