Browsing by Author "König, Simon"

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Open Access
Design and implementation of a measurement framework for time-sensitive networks
(2021) König, Simon
Networks in industrial control and automation applications must be capable of providing highly predictable delivery, both in terms of latency and latency variation. Thus, a network must guarantee deterministic behavior for time-sensitive traffic. Currently, dedicated and highly engineered networking solutions such as field buses are commonly used for time-critical traffic in industrial applications. Current trends in network convergence combine mixed-criticality traffic flows into the same real-time-capable networks. Currently, the IEEE Time-Sensitive Networking (TSN) Task Group are augmenting the widely supported Ethernet standard to provide time-critical flows alongside best-effort traffic. For its capabilities in high bandwidth, mixed-application and real-time-support, TSN is expected to be widely adapted in industries. In TSN, many of the guarantees on deterministic behavior have their basis in a traffic scheduling mechanism called Time-Aware Shaper (TAS). The development and integration of TSN-capable networks require increasingly powerful diagnosis and measurement tools. However, no such framework is publicly available at this point. The focus of this thesis is the development of a framework fulfilling requirements for performance analysis of physical networks with real-time constraints. This framework enables high-performance measurement tasks for TSN, which makes measurable the inaccuracies of physical network devices. As a first result of this insight, we show that many of the assumptions researchers often make about TSN networks are simplified and do not properly model the real world. Moreover, scheduling algorithms for the TAS often disregard the same inaccuracies in the synthesis of the traffic schedule. This could render invalid the guarantees on determinism for out-of-the-box scheduling. We propose a mechanism to improve the determinism of low-quality senders and the overall network bandwidth utilization, proving its effectiveness in a proof-of-concept setup.
Open Access
High‐performance carbon fibers prepared by continuous stabilization and carbonization of electron beam‐irradiated textile grade polyacrylonitrile fibers
(2021) König, Simon; Bauch, Volker; Herbert, Christian; Wego, Andreas; Steinmann, Mark; Frank, Erik; Buchmeiser, Michael R.
The manufacturing of high‐performance carbon fibers (CFs) from low‐cost textile grade poly(acrylonitrile) (PAN) homo‐ and copolymers using continuous electron beam (EB) irradiation, stabilization, and carbonization on a kilogram scale is reported. The resulting CFs have tensile strengths of up to 3.1 ± 0.6 GPa and Young's moduli of up to 212 ± 9 GPa, exceeding standard grade CFs such as Toray T300. Additionally, the Weibull strength and modulus, the microstructure, and the morphology of these CFs are determined.
Open Access
Lignin/poly(vinylpyrrolidone) multifilament fibers dry‐spun from water as carbon fiber precursors
(2023) Kreis, Philipp; Frank, Erik; Clauß, Bernd; Bauch, Volker; Stolpmann, Heiko; Kuske, Lisa; Schneck, Tanja; König, Simon; Buchmeiser, Michael R.
The preparation of lignin-based carbon fibers by dry spinning from aqueous solution followed by stabilization and continuous carbonization to endless yarns is reported. The influence of carbonization temperature and draw ratio on the morphology and mechanical properties of the final carbon fibers is investigated by single-fiber testing, wide-angle X-ray scattering, scanning electron microscopy, and Raman spectroscopy. A draw ratio of 5% (1.05) with a carbonization temperature of 1400 °C leads to the best mechanical properties. The resulting multifilament carbon fibers have an average diameter between 10-12 µm, an average tensile strength of 1.30 ± 0.32 GPa, a Young's modulus of 101 ± 18 GPa, and an elongation at break of 1.31 ± 0.23%. The maximum Weibull strength (𝜎0) is 1.04 GPa with a Weibull modulus (m) of 5.1. The use of a water-soluble system is economically advantageous; also, unlike melt-spun lignin fibers, the dry-spun precursor fibers can be thermally converted without any additional crosslinking step.
Open Access
Melt spinning of propylene carbonate‐plasticized poly(acrylonitrile)‐co‐poly(methyl acrylate)
(2020) König, Simon; Kreis, Philipp; Reinders, Leonie; Beyer, Ronald; Wego, Andreas; Herbert, Christian; Steinmann, Mark; Frank, Erik; Buchmeiser, Michael R.
The primary use of poly(acrylonitrile) (PAN) fibers, commonly referred to as acrylic fibers, is in textile applications like clothing, furniture, carpets, and awnings. All commercially available PAN fibers are processed by solution spinning; however, alternative, more cost‐effective processes like melt spinning are still highly desired. Here, the melt spinning of PAN‐co‐poly(methyl acrylate) (PMA) plasticized with propylene carbonate (PC) at 175°C is reported. The use of methyl acrylate (MA) as comonomer and PC as an external plasticizer renders the approach a combination of internal and external plasticization. Various mixtures of PAN and PC used in this work were examined by rheology, subjected to melt spinning, followed by discontinuous and continuous washing, respectively. The best fibers were derived from a PAN‐co‐PMA copolymer containing 8.1 mol‐% of MA having a number‐average molecular weight Mn of 34 000 g/mol, spun in the presence of 22.5 wt.‐% of PC. The resulting fibers were analyzed by scanning electron microscopy and wide‐angle X‐ray scattering (WAXS), and were subjected to mechanical testing.
Open Access
Melt-spinning of an intrinsically flame-retardant polyacrylonitrile copolymer
(2020) König, Simon; Kreis, Philipp; Herbert, Christian; Wego, Andreas; Steinmann, Mark; Wang, Dongren; Frank, Erik; Buchmeiser, Michael R.
Poly(acrylonitrile) (PAN) fibers have two essential drawbacks: they are usually processed by solution-spinning, which is inferior to melt spinning in terms of productivity and costs, and they are flammable in air. Here, we report on the synthesis and melt-spinning of an intrinsically flame-retardant PAN-copolymer with phosphorus-containing dimethylphosphonomethyl acrylate (DPA) as primary comonomer. Furthermore, the copolymerization parameters of the aqueous suspension polymerization of acrylonitrile (AN) and DPA were determined applying both the Fineman and Ross and Kelen and Tüdõs methods. For flame retardancy and melt-spinning tests, multiple PAN copolymers with different amounts of DPA and, in some cases, methyl acrylate (MA) have been synthesized. One of the synthesized PAN-copolymers has been melt-spun with propylene carbonate (PC) as plasticizer; the resulting PAN-fibers had a tenacity of 195 ± 40 MPa and a Young’s modulus of 5.2 ± 0.7 GPa. The flame-retardant properties have been determined by Limiting Oxygen Index (LOI) flame tests. The LOI value of the melt-spinnable PAN was 25.1; it therefore meets the flame retardancy criteria for many applications. In short, the reported method shows that the disadvantage of high comonomer content necessary for flame retardation can be turned into an advantage by enabling melt spinning.
Open Access
Ordering transactions on distributed persistent objects
(2023) König, Simon
Resilient and consistent data storage is critical for applications and services across all industries. As such, various persistent storage layers, such as database storage systems, have been developed. These either require complex data translations, commonly tackled through Object-Relational Mapping (ORM), or force the application to use data types specifically developed for persistent storage (e. g., Intel PMDK). Persistent objects describe a novel storage system that is able to persist and transactionally modify application-defined objects. With persistent objects, applications transactionally execute arbitrary functions on their existing data objects. However, they only allow local transactional modifications on individual objects, as there are no consistency guarantees across sequences of transactions. In this work, we present a novel distributed transaction coordination algorithm called Two-Phase Ordering (2PO) that provides isolation between concurrently executing clients. The algorithm uses application-specific knowledge, which becomes available through the use of application-native objects in the local persistent storage layer. Moreover, the distributed transaction execution order of 2PO depends entirely on the user’s desired semantics. Thus, the system accomodates both linearizable consistency as well as arbitrary interleavings of non-transactional interactions at the same time. By proving the consistency guarantees of 2PO in the general case, we show that our work is applicable to traditional transactional storage systems (e. g., databases) as well. Our evaluations show that 2PO supports linearizability as well as highly available transaction consistency models, such as Monotonic Atomic View (MAV), both with high commit rates (above 97 % under high contention), all while scaling linearly with the number of nodes.