Generating pairs of 2-bridge knot groups

We study Nielsen equivalence classes of generating pairs of Kleinian groups and HNN-extensions. We establish the following facts: - Hyperbolic 2-bridge knot groups have infinitely many Nielsen classes of generating pairs. - For any natural number N there is a closed hyperbolic 3-manifold whose fundamental group has N distinct Nielsen classes of generating pairs. - Two pairs of elements of a fundamental group of an HNN-extension are Nielsen equivalent iff they are so for the obvious reasons.Comment: Final version to appear in Geometriae Dedicat

On invertible generating pairs of fundamental groups of graph manifolds

We study invertible generating pairs of fundamental groups of graph manifolds, that is, pairs of elements (g,h) for which the map g --> g^{-1}, h --> h^{-1} extends to an automorphism. We show in particular that a graph manifold is of Heegaard genus 2 if and only if its fundamental group has an invertible generating pair.Comment: This is the version published by Geometry & Topology Monographs on 29 April 200

IFOAM Training Manual: Training Manual for Organic Agriculture in the Humid Tropics

The first IFOAM Training Manual for Organic Agriculture in the Tropics (the Basic Manual) was published in 2004. The Research Institute of Organic Agriculture (FiBL) together with partners of the organic movement in the Tropics were commissioned by IFOAM to complete two new training manuals that build on the Basic Manual. The new IFOAM training manuals address the two basic climatic zones of the Tropics, the Arid and Semi-Arid Tropics, and the Humid Tropics. For both new manuals, already existing material was collected, screened and condensed into comprehensive training manuals. Additionally, a large number of farmers, trainers and scientists were asked for their experience. Partner institutions from the Tropics actively collaborated in the development of the manuals. The partners of the manual for the Arid and Semi-Arid Tropics are from Asia (India), Africa (Senegal and Tunisia) and Latin America (Chile). The training manuals contain case studies of organic farming systems, describe successful organic marketing initiatives and offer guidelines for the main crops of the Tropics. With the informative text, transparencies and didactical recommendations the training manuals offer a resource basis for trainers with the idea of encouraging individual adaptation and further development of the material according to need. The training manuals are available on separate CDs in English, French and Spanish. The training manuals were commissioned by IFOAM and funded through its program IFOAM-GROWING ORGANIC II (I-GO II). The Research Institute of Organic Agriculture (FiBL) and the Swiss Import Promotion Programme (SIPPO) provided co-funding

Sprachen für parallele objektorientierte Programmierung

In letzter Zeit wurden eine ganze Reihe von objektorientierten Sprachen zur parallelen Programmierung entworfen und implementiert. Einige dieser Sprachen werden hier einander gegenübergestellt. Das Hauptaugenmerk der Arbeit liegt einerseits auf den bereitgestellten Konzepten zur Bewältigung der Komplexität, die sich durch die Parallelisierung ergibt, und andererseits auf der Flexibilisierung von Synchronisation und Kommunikation zur Optimierung der Parallelisierbarkeit von Programmausführungen

Nielsen equivalence in a class of random groups

We show that for every $n\ge 2$ there exists a torsion-free one-ended word-hyperbolic group $G$ of rank $n$ admitting generating $n$-tuples $(a_1,\ldots ,a_n)$ and $(b_1,\ldots ,b_n)$ such that the $(2n-1)$-tuples $$(a_1,\ldots ,a_n, \underbrace{1,\ldots ,1}_{n-1 \text{times}})\hbox{ and }(b_1,\ldots, b_n, \underbrace{1,\ldots ,1}_{n-1 \text{times}})$$ are not Nielsen-equivalent in $G$. The group $G$ is produced via a probabilistic construction.Comment: 34 pages, 2 figures; a revised final version, to appear in the Journal of Topolog