Computer-assisted optimization of cobalt-base alloy compositions

Cobalt-base hard metals are known for their wear and corrosion resistance and also for their ability to retain hardness at elevated temperatures.

Considering the matrix of these alloys it can be predicted that (a) the performance against corrosive media will improve when the Cr content is increased, (b) a higher W content will be advantageous because of its solid solution strengthening effect, and (c) care has to be taken in the course of liquid phase sintering to avoid unwished-for carbides and/or intermetallic phases, because these would be detrimental with respect to mechanical properties of the alloys.

To locate ranges for optimal matrix and carbide compositions thermodynamic calculations with were carried out on the basis of recently published data which were improved by a new optimization routine.

A series of phase diagrams was calculated and the optimal compositions of alloys were derived. Furthermore, calculated transition temperatures and phase compositions of some selected alloys compare reasonably with published experimental results.     

On the transfer matrix of a neutral system: Characterizations of exponential stability in input—output terms

This paper investigates the stability of linear autonomous multivariable neutral systems from an input—output viewpoint. Several frequency-domain and input—output characterizations for exponential stability of neutral systems are given. We provide two examples which illustrate that the behaviour of neutral systems may be quite different from that of retarded systems. Moreover we give necessary and sufficient conditions for the transfer functions of a neutral system to belong to certain algebras of meromorphic functions introduced in this paper.     

Petri net modules in the transformation-based component framework

Component-based software engineering needs to be backed by thorough formal concepts and modeling techniques. This paper combines two concepts introduced independently by the two authors in previous papers. On one hand, the concept of Petri net modules introduced at IDPT 2002 in Padberg [J. Padberg, Petri net modules, Journal on Integrated Design and Process Technology 6 (4) (2002) 105–120], and on the other hand a generic component framework for system modeling introduced at FASE 2002 in Ehrig et al. [H. Ehrig, F. Orejas, B. Braatz, M. Klein, M. Piirainen, A generic component concept for system modeling, in: Proceedings of FASE ’02, Lecture Notes in Computer Science, vol. 2306, Springer, 2002]. First we develop a categorical formalization of the transformation based approach to components that is based on pushouts. This is the frame in which we show that Petri net modules can be considered as an instantiation of the generic component framework. This allows applying the transformation based semantics and compositionality result of the generic framework to Petri net modules. In addition to general Petri net modules we introduce Petri net modules preserving safety properties which can be considered as another instantiation of pushout based formalization of the generic framework.     

Adaptive QoS for Mobile Web Services through Cross-Layer Communication

Web services providers can use the WS-QoS framework to achieve QoS differentiation by integrating various aspects of distinct communication layers. An architecture based on the framework supports resource-constrained mobile devices, which will generate a large percentage of Web service requests in the future     

Partially Bio-Based Polyester Bead Foams via Extrusion Foaming of Poly(butylene terephthalate)/Poly(butylene furanoate) Blends

The interest in bio-based alternatives to classical polyesters such as poly(ethylene terephthalate) (PET) and poly(butylene terephthalate) (PBT) is steadily growing to achieve a more sustainable approach to polymer materials. In this study, PBT/poly(butylene furanoate) (PBF) blends are prepared, characterized and extrusion foamed. PBF as a bio-based polyester offers two advantages. The ecological footprint of the material is reduced, and additionally, it can be used in Diels-Alder reactions at the blend surface to support fusion of the foamed beads. The blending behavior of the polyesters is investigated using samples prepared in a microcompounder, particularly focused on the miscibility of the blends and transesterification reactions. The blends are thermodynamically immiscible but show a certain degree of transesterification according to nuclear magnetic resonance (NMR) spectroscopy. The morphology of blend beads produced by an extrusion foaming process is analyzed regarding their cell density, cell size distribution, and open-cell content. It is shown that PBF has a positive effect on the bead foam morphology. The use of a bifunctional linker designed for chemical fusion of the bead surfaces allows to obtaining of molded parts, in contrast to beads containing pure PBT.     

Enzymatic Late-Stage Halogenation of Peptides

The late-stage site-selective derivatisation of peptides has many potential applications in structure-activity relationship studies and postsynthetic modification or conjugation of bioactive compounds. The development of orthogonal methods for C−H functionalisation is crucial for such peptide derivatisation. Among them, biocatalytic methods are increasingly attracting attention. Tryptophan halogenases emerged as valuable catalysts to functionalise tryptophan (Trp), while direct enzyme-catalysed halogenation of synthetic peptides is yet unprecedented. Here, it is reported that the Trp 6-halogenase Thal accepts a wide range of amides and peptides containing a Trp moiety. Increasing the sequence length and reaction optimisation made bromination of pentapeptides feasible with good turnovers and a broad sequence scope, while regioselectivity turned out to be sequence dependent. Comparison of X-ray single crystal structures of Thal in complex with d -Trp and a dipeptide revealed a significantly altered binding mode for the peptide. The viability of this bioorthogonal approach was exemplified by halogenation of a cyclic RGD peptide.     

Implementation of a geographical routing scheme for low Earth orbiting satellite constellations using intersatellite links

A major problem for low Earth orbit (LEO) constellations with intersatellite links is the efficient routing of the data packets through such a highly dynamic network. In order to achieve a worldwide coverage even in remote areas and Internet access with a limited amount of gateway stations, intersatellite links are a promising approach. Since LEO constellations represent a distinct, highly dynamic routing environment, specific strategies are needed. To this end, a suitable geographical routing scheme is proposed and investigated in two Walker Star constellations. The proposed scheme targets reliable transmissions with low latency and high data rates. The approach is based on a geographical address identifier in Layer 2 of the communication stack. The globe is thus divided into geographical areas that determine this identifier in the MAC address of the terminals. As mobile terminals are considered, the MAC addressing scheme is flexible, whereas the IP addresses of the terminals remain static. This decoupling allows for flexibility in the choice of the address resolution scheme. Moreover, the geographical identifier in the MAC address enables fast routing table lookups and switching. The proposed routing scheme also takes possible overloads of the satellites due to traffic into account and applies a rerouting procedure. When a packet arrives in the geographical area of the destination terminal, a local rerouting scheme is applied if needed. The proposed approaches take handover events that possibly occur during a transmission into account. Furthermore, the scan angles of the satellites have been adapted to the constellations to provide full coverage and high elevation angles. So a robust and adaptable routing scheme is provided for a dynamic environment where satellites and terminals are constantly moving. The proposed definitions and procedures have been implemented in a system level simulator, which allows for comparisons with adjustable parameters in various scenarios. In this work, an Iridium‐like constellation and a megaconstellation are investigated and compared regarding the address resolution procedures, the average end‐to‐end transmission delay, and the dropping and rerouting rates. Additionally, the signaling overhead is compared with other approaches. The simulator and results of the simulations provide grounds for further research w.r.t. the routing in satellite constellations using intersatellite links.