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Institute
Beschreibung finiter plastischer Deformationen von Einkristallen mittels materieller Isomorphismen
(1995)
Projektbericht Stadtmarketing : Ergebnisse einer Passantenbefragung in Brandenburg an der Havel
(1996)
Modular process nets are a graphical and formal notation for the representation of technical and business process models containing concurrent activities. Originally this class of Petri nets was developed for the modeling, analysis, simulation and control of workflows and computer-based process control systems, but it is also suitable for use in all other areas where a formal but comprehensible description of complex processes is needed. After a description of the basic aims and design decisions for modular process nets, the report gives a brief introduction to low-level Petri nets including different types of transition rules and aspects of the descriptive and prescriptive use of process models. The main and most innovative points which are explained in more detail are the introduction of a hierarchical module concept for nets and the definition of elementare process nets. The module concept is part of a more general ("object-based") approach to Petri nets allowing severaltypes of ab straction, whereas the main points of elementary process nets are synchronous and asynchronous communication between separately interpreted net instances via events and token passing. Modular process nets are low-level Petri nets equipped with these module and communication concepts and optionally enhanced by die use of a task concept, a method known from the areas of computer-supported cooperative work (CSCW) and work-flow management. Because the report is aimed at a systematic and easy-to-understand introduction to modular process nets, it provides a precise explanation of this net class which is kept as informal as possible and enhanced by some typical application examples
Two new optical imaging methods with submonolayer surface sensitivity are applied together to investigate pattern formation of adsorbate concentrations on surfaces during heterogeneously catalysed reactions. Ellipso-microscopy for surface imaging (EMSI) is based on an ellipsometric effect, reflection anisotropy microscopy (RAM) on the polarising properties of surface anisotropies. For the CO oxidation reaction on a Pt(110) surface features like front propagation, target patterns and spiral waves are observed, similar as in prior investigations by photoemission electron microscopy (PEEM). By applying EMSI and RAM simultaneously and imaging the same spot of the surface, supplementary information is gained on the properties of the reaction diffusion fronts. When observing a reaction front by EMSI and RAM at temperatures between 330 and 420 K the image of the front in RAM trails behind its image in EMSI. EMSI seems to display changes in the coverage of adsorbates while RAM relates to variations in surface structure.
Neutron diffraction experiments on powders are used to investigate the quantum mechanical behaviour of uniaxial rotators, i.e. NH3-molecules in Ni(NH3)6(PF6)2, Co(NH3)6(PF6)2 and Ni(NH3)6I2. A diffuse temperature dependent component of the total scattering, modulated ∼ sin QrH-H/QrH-H, is observed at a temperature of ≃ 20 K and below. This observation is due to the fact, that on cooling the sample to kT ∼ B (rotational constant) the rotational ground state is strongly populated. The ground state of a uniaxial free rotator, however, is completely polarized. As a consequence the scattering of those NH3 groups being in the ground state becomes coherent and is observable in diffraction experiments.