## Search

Now showing items 41-50 of 61

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Preprint
The Navier-Stokes Equations with Time Delay

(2007)

In the present paper we use a time delay epsilon > 0 for an energy conserving approximation of the nonlinear term of the non-stationary Navier-Stokes equations. We prove that the corresponding initial value problem (N_epsilon)in smoothly bounded domains G \subseteq R^3 is well-posed. Passing to the limit epsilon \rightarrow 0 we show that the sequence of stabilized solutions has an accumulation point such that it solves the Navier-Stokes problem (N_0) in a weak sense (Hopf).

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Preprint
Approximate Approximations and a Boundary Point Method for the Linearized Stokes System

(2007)

The method of approximate approximations, introduced by Maz'ya [1], can also be used for the numerical solution of boundary integral equations. In this case, the matrix
of the resulting algebraic system to compute an approximate source density depends only on the position of a finite number of boundary points and on the direction of the normal vector in these points (Boundary Point Method). We investigate this approach for the Stokes problem in the whole space and for the Stokes boundary value problem in a bounded ...

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Preprint
Parity of the Number of Irreducible Factors for Composite Polynomials

(2008)

Various results on parity of the number of irreducible factors of given polynomials over finite fields have been obtained in the recent literature. Those are mainly based on Swan’s theorem in which discriminants of polynomials over a finite field or the integral ring Z play an important role. In this paper we consider discriminants of the composition of some polynomials over finite fields. The relation between the discriminants of composed polynomial and the original ones will be established. We apply this to obtain ...

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Preprint
Restarting automata with restricted utilization of auxiliary symbols

(Universität Kassel, FB 17, Mathematik/Informatik, 2005)

The restarting automaton is a restricted model of computation that was introduced by Jancar et al. to model the so-called analysis by reduction, which is a technique used in linguistics to analyze sentences of natural languages. The most general models of restarting automata make use of auxiliary symbols in their rewrite operations, although this ability does not directly correspond to any aspect of the analysis by reduction. Here we put restrictions on the way in which restarting automata use auxiliary symbols, and ...

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Preprint
Exact algorithms for p-adic fields and epsilon constant conjectures

(2006)

We develop several algorithms for computations in Galois extensions of p-adic fields. Our algorithms are based on existing algorithms for number fields and are exact in the sense that we do not need to consider approximations to p-adic numbers. As an application we describe an algorithmic approach to prove or disprove various conjectures for local and global epsilon constants.

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Preprint
Church-Rosser groups and growing context-sensitive groups

(2006)

A finitely generated group is called a Church-Rosser group (growing context-sensitive group) if it admits a finitely generated presentation for which the word problem is a Church-Rosser (growing context-sensitive) language.
Although the Church-Rosser languages are incomparable to the context-free languages under set inclusion, they strictly contain the class of deterministic context-free languages.
As each context-free group language is actually deterministic context-free, it follows that all context-free groups ...

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Preprint
On the Gap-Complexity of Simple RL-Automata

(2006)

Analysis by reduction is a method used in linguistics for checking the correctness of sentences of natural languages.
This method is modelled by restarting automata. All types of restarting automata considered in the literature up to now accept at least the deterministic context-free languages.
Here we introduce and study a new type of restarting automaton, the so-called t-RL-automaton, which is an RL-automaton
that is rather restricted in that it has a window of size one only, and that it works under a minimal ...

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Preprint
Computation of locally free class groups

(2006)

We show that the locally free class group of an order in a semisimple algebra over a number field is isomorphic to a certain ray class group. This description is then used to present an algorithm that computes the
locally free class group. The algorithm is implemented in MAGMA for the case where the algebra is a group ring over the rational numbers.

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Preprint
Orthogonal polynomials and recurrence equations, operator equations and factorization

(Universität Kassel, FB 17, Mathematik/Informatik, 2005)

This article surveys the classical orthogonal polynomial systems of the Hahn class, which are solutions of second-order differential, difference or q-difference equations. Orthogonal families satisfy three-term recurrence equations. Example applications of an algorithm to determine whether a three-term recurrence equation has solutions in the Hahn class - implemented in the computer algebra system Maple - are given. Modifications of these families, in particular associated orthogonal systems, satisfy fourth-order ...

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Preprint
Duplication coefficients via generating functions

(2006)

In this paper, we solve the duplication problem
P_n(ax) = sum_{m=0}^{n}C_m(n,a)P_m(x) where {P_n}_{n>=0} belongs to a wide class of polynomials, including the classical orthogonal polynomials (Hermite, Laguerre, Jacobi) as well as the classical discrete orthogonal polynomials
(Charlier, Meixner, Krawtchouk) for the specific case a = −1. We give closed-form expressions
as well as recurrence relations satisfied by the duplication coefficients.