Analysis of real-time properties and rules for setting protocol parameters of MAP networks

This paper reports on an evaluation of real-time properties of MAP (Manufacturing Automation Protocol) networks by analytical considerations and measurements. Based on a model of the time schedule of a communication cycle figures for response times (transport system) and message delays (MAC layer) are given. The influence of some options for handling acknowledgments within the transport layer is shown. The message delay at MAC layer is separated into an implementation-dependent and a protocol-dependent protion, and an upper bound is derived. Rules for selecting protocol parameters affecting real time behavior are given. Aspects for improved implementations of communication controllers for MAP networks are discussed.     

Structured document storage and refined declarative and navigational access mechanisms in HyperStorM

The combination of SGML and database technology allows to refine both declarative and navigational access mechanisms for structured document collection: with regard to declarative access, the user can formulate complex information needs without knowing a query language, the respective document type definition (DTD) or the underlying modelling. Navigational access is eased by hyperlink-rendition mechanisms going beyond plain link-integrity checking. With our approach, the database-internal representation of documents is configurable. It allows for an efficient implementation of operations, because DTD knowledge is not needed for document structure recognition. We show how the number of method invocations and the cost of parsing can be significantly reduced. Edited by Y.C. Tay. Received April 22, 1996 / Accepted March 16, 1997     

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The role of cysteine residues of spinach ferredoxin-NADP+ reductase As assessed by site-directed mutagenesis

To investigate the functional role of the cysteine residues present in the spinach ferredoxin-NADP+ oxidoreductase, we individually replaced each of the five cysteine residues with serine using site-directed mutagenesis. All of the mutant reductases were correctly assembled in Escherichia coli except for the C42S mutant protein. C114S and C137S mutant enzymes apparently showed structural and kinetic properties very similar to those of the wild-type reductase. However, C272S and C132S mutations yielded enzymes with a decreased catalytic activity in the ferredoxin-dependent reaction (14 and 31% of the wild type, respectively). Whereas the C132S was fully competent in the diaphorase reaction, the C272S mutant flavoprotein showed a 35-fold reduction in catalytic efficiency with respect to the wild-type enzyme (0.4 versus 14.28 microM-1 s-1) due to a substantial decrease of kcat. NADP+ binding by the C272S mutant enzyme was apparently quantitatively the same (Kd = 37 microM) but qualitatively different, as shown by the differential spectrum. Stopped-flow experiments showed that the enzyme-FAD reduction rate was considerably decreased in the C272S mutant reductase, along with a much lower yield of the charge-transfer transient species. It is inferred from these data that the charge transfer (FAD-NADPH) between the reductase and NADPH is required for hydride transfer from the pyridine nucleotide to flavin to occur with a rate compatible with catalysis.     

Verbesserung des Vakuums in Isoliergefäßen aus Glas

Improving the vacuum would increase the insulation capacity of commercially available glass containers by a factor of about two. To do this, pressures of 10^?4 mbar must be attained. Different approaches were taken to meet this objective. As an alternative to today's commonly practiced sealing method, three possibilities are introduced which eliminate the necessity of pump stub narrowing which causes reduced conductance. Furthermore, depending on the sealing process used, the gases occuring during sealing are either avoided completly or they can at least be reduced by having the chance of exact temperature control resp. by a lower separation temperature. A completly different approach was taken by using Getters, of which a metal hydride on a TiVMn base proved especially suitable. It is activated by heat and can be integrated into the normal production process without any problem. Aside from a shorter pump period, the added advantage here is the containment of the gasses occuring during sealing as well as that of the longterm gasses.