Equality-friendly well-founded semantics and applications to description logics

We tackle the problem of defining a well-founded semantics (WFS) for Datalog rules with existentially quantified variables in their heads and nega- tions in their bodies. In particular, we provide a WFS for the recent Datalog± family of ontology languages, which covers several important description logics (DLs). To do so, we generalize Datalog± by non-stratified nonmonotonic nega- tion in rule bodies, and we define a WFS for this generalization via guarded fixed point logic. We refer to this approach as equality-friendly WFS, since it has the advantage that it does not make the unique name assumption (UNA); this brings it close to OWL and its profiles as well as typical DLs, which also do not make the UNA. We prove that for guarded Datalog± with negation under the equality- friendly WFS, conjunctive query answering is decidable, and we provide precise complexity results for this problem. From these results, we obtain precise defi- nitions of the standard WFS extensions of EL and of members of the DL-Lite family, as well as corresponding complexity results for query answering

Well-Founded Semantics for Extended Datalog and Ontological Reasoning

The Datalog± family of expressive extensions of Datalog has recently been introduced as a new paradigm for query answering over ontologies, which captures and extends several common description logics. It extends plain Datalog by features such as existentially quantified rule heads and, at the same time, restricts the rule syntax so as to achieve decidability and tractability. In this paper, we continue the research on Datalog±. More precisely, we generalize the well-founded semantics (WFS), as the standard semantics for nonmonotonic normal programs in the database context, to Datalog± programs with negation under the unique name assumption (UNA). We prove that for guarded Datalog± with negation under the standard WFS, answering normal Boolean conjunctive queries is decidable, and we provide precise complexity results for this problem, namely, in particular, completeness for PTIME (resp., 2-EXPTIME) in the data (resp., combined) complexity

Übergänge stärken. Zur Gewinnung beruflich qualifizierter Personengruppen für das Studium zum Lehramt an berufsbildenden Schulen

Vor dem Hintergrund des Lehrkräftebedarfs und den Bestrebungen Niedersachsens zur Öffnung der Hochschulen wurde in Zusammenarbeit mit zwei Einrichtungen der Erwachsenenbildung (Heimvolkshochschulen), der Historisch-Ökologischen Bildungsstätte in Papenburg und dem Ludwig-Windthorst-Haus in Lingen sowie der Universität Osnabrück eine kooperative Weiterbildung entwickelt und erprobt, die auf den Übergang zwischen beruflicher und hochschulischer Bildung zielt. Das über den Europäischen Sozialfonds geförderte Projekt NeWeLe fokussierte dabei beruflich qualifizierte Personen mit Interesse am beruflichen Lehramt. Die Ergebnisse kennzeichnen das Format als eine zukunftsfähige Variante zur Förderung von Durchlässigkeit. Es konnte innerhalb der Teilnehmer:innengruppe ein reges Interesse am Lehramtsberuf festgestellt werden. Der Weg über ein Vollzeitstudium stellt für die berufsqualifizierte Personengruppe jedoch ein nicht unerhebliches Hindernis dar

Feasibility of fast-particle channeling in quasicrystals

The feasibility of ion channeling in quasicrystalline structures is investigated in a computer experiment. For this purpose, a quasilattice is constructed by the grid method. As this model crystal shows, in a quasicrystal also the lattice points are arranged in strings and planes and form pronounced axial and planar channels. Their occupation by lattice points is, however, not constant, but exhibits a wide density distribution in contrast to periodic crystals. Manganese atoms were placed at the lattice points and backscattering yield profiles of 750-keV He+ ions were obtained in a channeling computer simulation. Pronounced channeling minima are observed in the profiles for axial as well as planar channeling

Применение высоконапорных полимерных труб "Anaconda" на нефтегазовых промыслах в климатических условиях заполярья

Сокращение аварийных ситуаций и повышение эксплуатационной надежности трубопроводов - главная задача инженеров и проектировщиков. В результате, остро стоит вопрос о необходимости строительства промысловых трубопроводов с учётом прокладки в условиях вечной мерзлоты и коррозионного износа. Необходимость предусматривать в проекте развития высокой скорости коррозии и разрушающего воздействия грунтов заполярного круга- факторы, влияющие на безотказную работу трубопровода. Обсуждается вопрос о возможности применения высоконапорных полимерных труб "Anaconda" на промысловых нефтегазопроводах в климатических условиях заполярья и их роли в повышения эксплуатационной надежности трубопроводов

Ion channeling in T-phase quasicrystals: an investigation by Rutherford backscattering and particle induced X-ray emission

The channeling properties of a T-phase A1 62Cu 20Co 15Si 3 quasicrystal are investigated in a Rutherford backscattering study employing 2 MeV He-ions. Besides axial channeling along the decagonal axis, also planar channeling is observed in planes having the decagonal axis in common and showing the decagonal symmetry of the quasicrystal. Besides a system of main planes, various planes exhibiting only weak channeling properties are observed; they correspond to linear arrangements of vertices in a two-dimensional Penrose grid, demonstrating the close relationship between T-phase quasicrystal and Penrose pattern. Rutherford backscattering (RBS) has also been used to study the decoration of the T-phase structure by Co/Cu- and Al/Si-atoms; in addition, particle induced X-ray emission PIXE served to distinguish between Co- and Cu-atoms. The experimental data are compared with channeling computer simulations on a model T-phase quasicrystal proposed by Steurer and Kuo

Minimization of negative influence of electrode wear on generated plasma in DC arc torches

The present work offers a new approach to a problem of electrode wear in DC arc plasma torches with gas stabilization. A new torch with a moveable nozzle equipped with both normal and worn cathodes has been tested. The results have shown that change of the nozzle-cathode tip distance lead to change of the arc voltage and the generated plasma so it can help to counteract the cathode wear and prolong the lifetime of the electrode