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Exploring the oxidation characteristics of binary and ternary transition metal carbide coatings
No full textThis study explores the oxidation properties of binary and ternary Al/Si alloyed transition metal carbide (TMC) thin films, focusing on group IV to VI metals, specifically Ti, Zr, Hf, Ta, and W. TMCs are classified as ultra-high temperature ceramics (UHTCs) and are recognized for their high melting temperatures, exceeding 3000 °C, along with their exceptional thermal stability. However, they typically suffer from poor oxidation resistance. Binary TMC thin films start to oxidize at temperatures below 600 °C. To expand the application possibilities of TMCs, particularly in high-temperature fields such as aerospace, automotive, and tooling industries, alloying concepts with Al and Si are being explored to enhance their oxidation resistance. In detail, ten different sputter deposited ternary TM-X-C coating families were isothermally oxidized at 750 °C for 1 h and their oxidation kinetics have been benchmarked. For Al alloyed thin films, the best performing systems are Ti-Al-C and Ta-Al-C, forming scales below 750 nm at alloy contents above 25 at.% Al. In contrast, Ti-Si-C only requires around 20 at.% Si to form a dense and adherent scale (below 300 nm). Both Ti0.26Al0.32C0.42 and Ti0.29Si0.26C0.45 exhibit a two-layered oxide scale, consisting of a metal oxycarbide zone at the interface to the unaffected, nonporous Ti-Al/Si-C coating, followed by a mixed Ti-(Al/Si)-oxide scale on top. Based on detailed TEM analysis Al alloyed TiC obtains a better ability to act as an oxygen diffusion barrier
Graph transformers express monadic second-order logic
No full textWe quantify the expressive power of graph transformers by establishing a formal connection to monadic second-order logic (MSO). Expressivity analysis for graph learning algorithms commonly focuses on their ability to produce distinct embeddings for non-isomorphic graphs. This line of research is well established for message-passing graph neural networks and their tight connection to the Weisfeiler-Leman color refinement algorithm. In contrast, graph transformers have mostly been evaluated empirically, with little theoretical investigation thus far. The expressive power of transformers can be quantified by their ability to simulate certain formal languages in the context of natural language processing. Here, we focus on graph learning and MSO and show that transformers can produce distinct embeddings for graphs that differ in MSO-definable properties. MSO is a powerful logic for graph-related tasks, as it allows to decide decision problems for graphs with bounded treewidth in linear time
Access Nature
No full textRecent research has paid more and more attention towards the intersection of accessibility, technology and environmental justice, which indicates a growing recognition of the challenges people with mobility disabilities (PMD) face in accessing natural environments. The topic becomes even more important with the wide-spread acknowledgement of the positive effects of physical activity in natural environments (PANE) on mental and physical health for everyone. However, PMD are often excluded from PANE due to a lack of accessibility measures. Factors influencing access to nature are not just established at the interplay of impairment and the physical environment but are often social and policy related and manifested in intra- and interpersonal aspects. Derakhshan et al 2024(1) categorized the resulting barriers into different levels based on a social ecological model to be able to effectively address them. In reference to this categorization, we augment this analysis with a technological perspective allowing us to better understand the potential to address accessibility factors at the different levels of interaction. We analyze each technology in terms of its potential to facilitate access, the possible risks involved and its overall availability. All of this is compared to human assistance and its socializing factor. Our aim is to present a catalogue of different options of assistive technologies addressing a wide range of interaction challenges for PMDs in nature. Our analysis functions both as a design guide for technical interventions as well as for interested PMDs to choose the desired assistance to engage in PANE
One step closer to circularity: recycling post-consumer PE-HD into shampoo bottles
No full textDue to their dominance in the extrusion blow-moulded plastic packaging, post-consumer PE-HD bottles pose a promising material stream for increasing current recycling rates. Several studies already considered the circularity potential of PE-HD post-industrial milk bottles as well as material from multicoloured post-consumer waste streams and highlighted the addition of virgin resins to enhance the properties of these materials. However, little is known about the baseline performance of current, multicoloured post-consumer PE-HD (rPE-HD) and its suitability for blow-moulding. Consequently, a cold-washed batch of rPE-HD from the Austrian source separated waste collection system was obtained, granulated and extrusion blow-moulded at industrial scale. The corresponding flakes, regranulate pellets and produced bottles were investigated to gain insights on the recycling feedstock and impacts of melt processing on material performance. The collected samples underwent comprehensive laboratory-scale analysis including flake composition via infrared spectroscopy, thermal analysis via DSC and TGA, rheological shear and extension experiments, energy dispersive x-ray (EDX) scans of cryo-fractured tensile specimens, regular tensile tests as well as bottle drop- and strain hardening behaviour assessments. The obtained results demonstrated that extrusion blow-moulding grade rPE-HD can be successfully converted into recycled bottles, yet remains an underutilised feedstock for mechanical recycling. Despite containing ~ 4 wt% of PP contamination, the extrusion blow-moulded rPE-HD bottles exhibit high ductility in the side wall regions (> 1000%) and drop resistance from a height of 0.8 m. However, to realise the “100% rPE-HD bottle” at scale, the cooperation of all value cycle participants is much-needed