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A free boundary-value problem for a nonisothermal flow of two heavy viscous incompressible capillary liquids descibing a slot coating process is mathematically studied. The problem is stationary and two-dimensional and the Boussinesq approximation for the Navier-Stokes equations is used. The existence and uniqueness of a weak solution is proved in weighted Holder spaces for small data.
Deduktionssysteme
(1994)
Exact solutions of generalized three-particle Bargmann-Wigner equations in the strong-coupling limit
(1994)
In this paper a Petri net based methodology is outlined for an integrated qualitative and quantitative analysis of parallel software systems which is based on different (Petri) net representations of die software system under consideration. The software validation methodology starts from the source text of a set of communicating processes which specify the system under development. From this source text skeleton, a Petri net representation of the general control structure of the system is generated. On this basis a set of reduction steps is defined for transforming the net into different intermediate representations all owing the validation of both qualitative and qualitative properties. Particular attention is paid to the validation of quantitative properties which is performed using a transformation into locally Markovian Object Nets (MONs). Models of this new class of modular Petri nets are obtained by property-preserving structural compression and by enhancement with quantitative i nformation This information is obtained in the form of frequency and delay parameters by monitoring testing the software on the basis of prototypes. Compared to a previous paper on the same topic /Heiner94/ the methodology as well presentation have been improved. In particular, a new, more comprehensive running example been selected and the object net approach is explained in much more detail.
Small sodium and silver particles were generated on dielectric substrates like LiF, quartz and sapphire under ultrahigh vacuum conditions. The optical transmission spectra of the clusters were measured as a function of cluster size and shape, for low and high substrate temperatures as well as for s- and p- polarization of the incident light. Excitation of dipolar surface plasmon oscillations in the directions normal and parallel to the substrate surface could be identified. Furthermore, optical spectra for Na and Ag clusters were calculated with the classical Mie theory. The measured spectra vary strongly if the experimental conditions are changed and can be exploited, for example, to characterize the particles with regard to their size and shape. In particular, the axial ratio of the spheroidal clusters could be determined. Its value is considerably different for the two investigated metals and depends on the substrate material. Furthermore, the temperature of the substrate has a pronounced influence on the shape of the particles. At low temperature of T=100 K two-dimensional island growth is predominant. The particles extend only little in the direction perpendicular to the surface and coalesce readily at small coverage of metal atoms. In contrast, the clusters are truly three-dimensional at T=300 K. At this stage, sodium particles still exhibit a rather small axial ratio whereas silver clusters appear almost spherical. Thus, measurements of the optical spectra permit direct in situ monitoring of cluster growth during the nucleation of adsorbed atoms and of temperature induced shape variations. In addition to investigations of the shape of the particles, the quadrupolar surface plasmon mode was observed for Ag clusters.
Imaging Pattern Formation in Surface Reactions from Ultrahigh Vacuum up to Atmospheric Pressures
(1995)
Two optical methods that allow pattern formation to be investigated at an arbitrary pressure are here applied to image concentration patterns of adsorbed species associated with heterogeneous catalytic reactions. In contrast to most surface physical techniques, these methods are not restricted to high vacuum conditions and thus bridge the “pressure gap.” With carbon monoxide oxidation on a (110) surface of platinum as an example, the coupling mechanisms responsible for spatiotemporal self-organization in surface reactions were followed from reaction-diffusion control to the thermokinetic region, associated with phenomena not previously observed in pattern formation.
Two surface-sensitive optical imaging methods, Ellipso-Microscopy for surface Imaging (EMSI) and Reflection Anisotropy Microscopy (RAM) are introduced. They allow imaging of pattern formation on surfaces, e.g., due to submonolayer coverages of adsorbates, at any arbitrary pressure.
In spatio-temporal pattern formation during heterogeneously catalysed reactions this bridges the ‘pressure gap’ between well-defined UHV experiments and ‘real catalysis’. For the CO oxidation on Pt(110), the parameter space for pattern formation was extended up to 100 mbar, i.e., by 5 orders of magnitude compared to earlier investigations by Photo-Emission Electron Microscopy (PEEM) which had to be conducted below 10−3 mbar. With increasing pressure, the synchronisation mechanisms responsible for the observed pattern showed a gradual shift from reaction-diffusion to thermal-kinetic coupling unveiling previously unseen features of pattern formation in catalysis.
Analysis of a nonisothermal viscous flow problem with free boundaries and a dynamic contact line
(1995)
Effective dynamics in a subfermion shell model of leptons, quarks and electroweak gauge bosons
(1995)
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