Die Flüssigkeitsring-Vakuumpumpe als verfahrenstechnische Maschine

Liquid ring vacuum pumps have many and diversified applications in the process industry. Primarily they are used to transfer gases and vapours from a lower to a higher pressure level. Due to the specific principles of operation, a heat and mass transfer between the gas or vapour and the sealing liquid takes place also. This can be utilised to perform unit operations. Beside transportation and compression of gases the pump can perform the following operations: exchange of heat, condensation/evaporation, absorption/desorption as well as chemical reactions. Because of these features is the liquid ring vacuum pump a ?process engine”? and an interesting alternative to other process apparatus. Following the definition of H. Brauer (1985) is the objective function of a process engine achieved by a moving element, whereas the objective function of a process apparatus is achieved without any moving element. For nearly all possible combinations of sealant, gases and vapours reliable empirical principles to determine the suction volume and the power requirements of liquid ring vacuum pumps are at hand. Besides has the use of liquid ring vacuum pumps to perform unit operations a long successful tradition. However, the field of applicability can be enlarged if the feasibility of the engine for individual unit Operations can be predicted with the help of physical models. Due to the eccentrically arranged rotor a sickle shaped space is formed between rotor hub and liquid ring where suction, compression and discharge of an gas/vapour mixture can be realised if the suction and discharge slots are arranged in a suitable manner. As the seal liquid is in direct contact with the gases and vapours all reactions inside the pump develop in the direction of a thermodynamical equilibrium between the two phases. An important consequence of this feature is the limit of operation of liquid ring vacuum pumps: the suction pressure has to be above the vapour pressure of the seal liquid. Another consequence is the possibility to utilise this type of pumps for unit operations. The turbulent surface of the liquid ring which is formed by a dense hale of droplets is ideal for heat and mass transfer processes. Following an attempt of C. Pfleiderer, the azimuthale distribution of the static pressure and the contour of the liquid ring can be determined under considerably simplifying assumptions. One of these simplifications is that the condensation and evaporation in the pump is neglected. The further simplifications deal with the significant idealisation of the geometry. Taking back the simplifying assumptions step-by-step and including the thermodynamical circumstances it is possible to calculate the azimuthale distribution of the static pressure and the real contour of the liquid ring for the condensation and the evaporation. These attempts can be carried on to taking several components in the vapour-portion of the gas/vapour mixture into account and form the basis of the calculation of the absorption and desorption. In this case the assumption that the thermodynamical equilibrium is attained instantly is no longer valid.     

Sputtering of Surfaces of the Solid Hydrogens

Sputtering of the solid hydrogens by electrons and ions exhibits features that may be related to quantum properties of these solids, i.e. a drastic enhancement of the yield for electron–bombarded thick deuterium films and a thermal peak at low ejection energies in the energy distribution of the sputtered particles.     

System-Level Synthesis Using Evolutionary Algorithms

In this paper, we consider system-level synthesis as the problem of optimally mapping a task-level specification onto a heterogeneous hardware/software architecture. This problem requires (1) the selection of the architecture (allocation) including general purpose and dedicated processors, ASICs, busses and memories, (2) the mapping of the specification onto the selected architecture in space (binding) and time (scheduling), and (3) the design space exploration with the goal to find a set of implementations that satisfy a number of constraints on cost and performance. Existing methodologies often consider a fixed architecture, perform the binding only, do not reflect the tight interdependency between binding and scheduling, do not consider communication (tasks and resources), or require long run-times preventing design space exploration, or yield only one implementation with optimal cost. Here, a model is introduced that handles all mentioned requirements and allows the task of system-synthesis to be specified as an optimization problem. The application and adaptation of an Evolutionary Algorithm to solve the tasks of optimization and design space exploration is described.     

Linguistically based functions in information retrieval: PADOK and the German Patent Information System

This paper reports on methodological considerations and the results of the Information Retrieval (IR) project PADOK I and II. PADOK has been carried out by the Linguistic Information Science Group of the University of Regensburg (LIR) since November 1984 and has been sponsored by the German Ministry for Research and Technology. The long term objective is to integrate artificial intelligence topics and the methods of information retrieval research without neglecting traditional IR methodology. In PADOK we consider a type of mass data IR system which indexes its documents rather shallowly (freetext or morphological components) and adds an intelligent information retrieval component to this kernel system. So far we have obtained, on the basis of two large-scale retrieval tests of the German Patent Information System results which show how the linguistically based functions of an indexing system contribute to its performance, and indicate what is the most reasonable basic content analysis program for a German Patent Information System. This paper focusses on the general principles and aims of PADOK I and PADOK R and on the statistical evaluation of the retrieval tests.Christa Womser-Hacker has a Ph.D. in Linguistic Information Science. From 1985 until 1990 she was involved in several LIR-Projects concerning text processing, evaluation of the German Patent Information System, man-machine-interaction, intelligent interfaces for databases. Since May 1990 she has been an LIR staff member. She is interested in information retrieval, (statistical) evaluation methods of man-machine-interaction, intelligent interfaces. She has published Der PADOK-Retrieval-test (1989) and Die statistische Auswertung des Retrievaltests (1990).Jürgen Krause is professor of Linguistic Information Science at the University of Regensburg. He is a member of the editorial boards of the periodicals Computer and the Humanities and GLDV-Forum, and co-editor of Sprache and Computer. His research interests include office automation, artificial intelligence help system, information retrieval, evaluation of natural language systems. He is co-editor (with Christa Womser-Hacker) of Das Deutsche Patentinformationssystem, Entwicklungstendenzen, Retrievaltests and Bewertungen (1990) and co-editor of Computer Talk (1991).     

Die Versprödungsneigung der hochkorrosionsbeständigen Legierung NiMo28 (2.4617) im Chemie-Apparatebau und Maßnahmen zu ihrer Vermeidung

The ductility loss of the highly corrosion resistant alloy NiMo28 (Alloy B-2) during manufacturing of components for chemical plants and precautions to prevent it

1 Vortrag anläßlich der Achema '91, Frankfurt/Main, 09.–15. Juni 1991; überarbeitete und ergänzte Fassung.

Alloy B-2 exhibits an excellent corrosion resistance in reducing media, especially in a wide range of concentration and temperature of hydrochloric acid and sulphuric acid. In spite of its almost binary constitution and therefore simple phase equilibria the alloy revealed in the past difficulties in workability, creating considerable problems when the alloy had to be manufactured into components for chemical plants. This is caused by formation of the intermetallic phase Ni₄Mo which is an ordered phase of the Ni-rich solid solution. The susceptibility to the ductility loss of the alloy NiMo28 (alloy B-2) has been evaluated by time-temperature-impact strength diagrams. Furthermore, the positive effect of adjustments of the alloy composition (Fe and Cr) within the limits of the actual standards on the workability is pointed out. The influence of a 5% cold forming operation on the ductility loss is demonstrated, too. Recommendations for manufacturing of the alloy are given in order to avoid detrimental internal stresses by an additional heat treatment.     

The relationship between KLM and MAK models for nonmonotonic inference operations

The purpose of this note is to make quite clear the relationship between two variants of the general notion of a preferential model for nonmonotonic inference: the models of Kraus, Lehmann and Magidor (KLM models) and those of Makinson (MAK models). On the one hand, we introduce the notion of the core of a KLM model, which suffices to fully determine the associated nonmonotonic inference relation. On the other hand, we slightly amplify MAK models with a monotonic consequence operation as additional ingredient. We give two equivalent characterizations of the cores of KLM models: they are precisely the amplified MAK models whose satisfaction relation:

may be expressed as the intersection of some non-empty family of satisfaction relations each of which is classically well-behaved; or

satisfies certain syntactic conditions.

This gives corollary characterizations of certain particular classes of KLM models, notably those that are (in their terminology) cumulative and more specifically those they call preferential.