Applying relation algebra and R<Emphasis Type="SmallCaps">el</Emphasis>V<Emphasis Type="SmallCaps">iew</Emphasis> to solve problems on orders and lattices

Relation algebra is well suited for dealing with many problems on ordered sets. Introducing lattices via order relations, this suggests to apply it and tools for its mechanization for lattice-theoretical problems, too. We combine relation algebra and the BDD-based specific purpose Computer Algebra system RelView to solve some algorithmic problems on orders and lattices and to visualize their solutions.     

Embedding mappings and splittings with applications

We present relation-algebraic specifications of injective embedding mappings and splittings of partial equivalence relations and show in each case that the axioms characterize these constructions up to isomorphism, i.e., in an essentially unique way. Based on the specifications, we develop a relational program for computing splitting and demonstrate some applications. The examples originate from a relation-algebraic treatment of processes, graph theory, and the decomposition of specific relations.     

Integrated Optimal Cell Site Selection and Frequency Allocation for Cellular Radio Networks

Two major planning problems are encountered when designing a cellular radio network. The initial question is where to locate the base transmitter stations such that full coverage is achieved at low interference. This is relevant for frequency division (FDMA) as well as code division multiple access (CDMA) technology. If the locations of base stations are given, then for an FDMA-system frequencies have to be assigned such that there is a sufficient number of channels per cell available at a low total interference level. Since cell site selection and frequency allocation have mutual influences on each other, the ultimate goal is to deal with both problems in a single design step. The main intention of this paper is to model the above planning issues as linear integer programs, and to discuss solution methods for the corresponding NP-hard problems. According to their increasing complexity we proceed from channel allocation via cell site selection to an integrated single setup.     

Corrosion of friction stir welded magnesium alloy AM50

The microstructure of a friction stir welded magnesium alloy AM50 was examined by means of optical light microscopy. The chemical composition, particularly the iron content, and morphology of the oxide film were analyzed and discerned via auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS). Corrosion behaviour of the welds and base materials were investigated by virtue of neutral salt spray tests and potentiodynamic polarization measurements in conventional cells and in a mini cell. The results demonstrate that minor increases in iron concentration as might be speculated to occur as a consequence of tool/work piece interaction during the welding process on the corrosion resistance of the weld can be ignored. The corrosion morphology was predominantly influenced by the distribution of the Mg₁₇Al₁₂ phase. Here, it was also found that the corrosion resistance of the friction stir weld varied in response to changes in the joint microstructure.