A relative completeness theorem

Archiv der Mathematik - We prove a relative n-completeness theorem asserting that a complex space Y that fibers over a complex space X of dimension less than n is n-complete provided that Y admits...     

A relative backward perturbation theorem for the eigenvalue problem

Summary A-posteriori bound is given for the computed eigenpair ( ), of the eigenvalue problemAx=x, which is shown to be more realistic than the available one. A simple expression is further presented for calculating the backward error.     

A central limit theorem for Gibbs measures relative to Brownian motion

We study a Gibbs measure over Brownian motion with a pair potential which depends only on the increments. Assuming a particular form of this pair potential, we establish that in the infinite volume limit the Gibbs measure can be viewed as Brownian motion moving in a dynamic random environment. Thereby we are in a position to use the technique of Kipnis and Varadhan and to prove a functional central limit theorem.     

The relative isomorphism theorem for Bernoulli flows

In this paper we extend the work of Thouvenot and others on Bernoulli splitting of ergodic transformations to ergodic flows of finite entropy. We prove that ifA is a factor of a flowS, whereS ₁ is ergodic andA has a Bernoulli complement inS ₁, thenA has a Bernoulli complement inS. Consequently, Bernoulli splitting for flows is stable under taking intermediate factors and certain limits. In addition it follows that the property of isomorphism with a Bernoulli × zero entropy flow is similarly stable.     

A relative interpolation theorem for infinitary universal Horn logic and its applications

In this paper we deal with infinitary universal Horn logic both with and without equality. First, we obtain a relative Lyndon-style interpolation theorem. Using this result, we prove a non-standard preservation theorem which contains, as a particular case, a Lyndon-style theorem on surjective homomorphisms in its Makkai-style formulation. Another consequence of the preservation theorem is a theorem on bimorphisms, which, in particular, provides a tool for immediate obtaining characterizations of infinitary universal Horn classes without equality from those with equality. From the theorem on surjective homomorphisms we also derive a non-standard Beth-style preservation theorem that yields a non-standard Beth-style definability theorem, according to which implicit definability of a relation symbol in an infinitary universal Horn theory implies its explicit definability by a conjunction of atomic formulas. We also apply our theorem on surjective homomorphisms, theorem on bimorphisms and definability theorem to algebraic logic for general propositional logic.     

On the Shafarevich conjecture for genus-2 fibrations

We prove a result about fundamental group of a smooth projective surface with ample canonical divisor which admits a genus two fibration. As a corollary we prove that the universal cover of such a surface is holomorphically convex. This proves the conjecture of Shafarevich for such surfaces. This article is dedicated to Madhav V. Nori.     

A robust Kantorovich’s theorem on the inexact Newton method with relative residual error tolerance

We prove that under semi-local assumptions, the inexact Newton method with a fixed   relative residual error tolerance converges Q$Q$-linearly to a zero of the nonlinear operator under consideration. Using this result we show that the Newton method for minimizing a self-concordant function or to find a zero of an analytic function can be implemented with a fixed relative residual error tolerance.     

Reflection theorem for divisor class groups of relative quadratic function fields

We present the reflection theorem for divisor class groups of relative quadratic function fields. Let K be a global function field with constant field Fq. Let L₁ be a quadratic geometric extension of K and let L₂ be its twist by the quadratic constant field extension of K. We show that for every odd integer m that divides q+1 the divisor class groups of L₁ and L₂ have the same m-rank.     

A comparison theorem

The existence of an explosive singularity in the unsteady boundary layer on a rotating disc in a counter-rotating fluid has now been shown incontrovertibly following the work of K. Stewartson, C. J. Simpson, and R. J. Bodonyi (J. Fluid. Mech.121 (1982), 507–515). Here, we develop some asymptotic results for the governing differential equations to help gain an understanding of the mechanism behind this phenomenon. No definite conclusions are possible, but the presence of inertial oscillations at the edge of the boundary layer could well play a definite role.