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The Keller–Segel system on bounded convex domains in critical spaces
Get PDFConsider the classical Keller–Segel system on a bounded convex domain Ω⊂ℝ³. In contrast to previous works it is not assumed that the boundary of Ω is smooth. It is shown that this system admits a local, strong solution for initial data in critical spaces which extends to a global one provided the data are small enough in this critical norm. Furthermore, it is shown that this system admits for given T-periodic and sufficiently small forcing functions a unique, strong T-time periodic solution
Artificial intelligence in human factors and ergonomics: an overview of the current state of research
Get PDFThe development of artificial intelligence (AI) technologies continues to advance. To fully exploit the potential, it is important to deal with the topics of human factors and ergonomics, so that a smooth implementation of AI applications can be realized. In order to map the current state of research in this area, three systematic literature reviews with different focuses were conducted. The seven observation levels of work processes according to Luczak and Volpert (1987) served as a basis. Overall n = 237 sources were found and analyzed. It can be seen that the research critically deals with human-centered, effective as well as efficient work in relation to AI. Research gaps, for example in the areas of corporate education concepts and participation and voice, identify further needs in research. The author postulates not to miss the transition between forecasts and verifiable facts
Document Structure in Long Document Transformers
Get PDFLong documents often exhibit structure with hierarchically organized elements of different functions, such as section headers and paragraphs. Despite the omnipresence of document structure, its role in natural language processing (NLP) remains opaque. Do long-document Transformer models acquire an internal representation of document structure during pre-training? How can structural information be communicated to a model after pre-training, and how does it influence downstream performance? To answer these questions, we develop a novel suite of probing tasks to assess structure-awareness of long-document Transformers, propose general-purpose structure infusion methods, and evaluate the effects of structure infusion on QASPER and Evidence Inference, two challenging long-document NLP tasks. Results on LED and LongT5 suggest that they acquire implicit understanding of document structure during pre-training, which can be further enhanced by structure infusion, leading to improved end-task performance. To foster research on the role of document structure in NLP modeling, we make our data and code publicly available
Fatigue Design with Respect to Component Related Cyclic Material Behaviour and Considerations of Size Effects
Get PDFLocal fatigue approaches, as for example the notch base approach, evaluate fatigue strength on the basis of strain controlled fatigue tests in conjunction with elastic plastic stress strain analyses of component structures, considering crack initiation as fatigue criterion. In case of constant amplitude loading, a cyclic stabilisation of the material behaviour is assumed, neglecting transient effects of cyclic straining at the start of the lifetime. Under variable amplitude loading, this simplification may not be valid, as the influences of load cycles of different magnitude on the material behaviour have to be carefully examined employing appropriate testing methods, such as incremental step tests, for the generation of cyclic material parameters. Moreover, the fatigue life estimation under variable amplitude loading with local approaches may lead to large calculation times due to the necessity of non-linear finite element analyses for the damage evaluation of each load range within the rainflow counted load-time history. A combination of the local approach with the nominal stress approach to a material based approach allows the use of the linear damage accumulation hypothesis according to Palmgren-Miner, thus substantially reducing the numerical effort for fatigue life estimation under variable amplitude loading. Although the local approach yields a reliable method for transferring material parameters from the specimen to the component geometry with the help of elastic plastic finite element analyses, the consideration of the effects of component size on fatigue life remains a complex objective. The presented work aims to convey a further development of the material based approach, including a proposal for the evaluation of mechanical and statistical size effects in the fatigue life estimation of components under variable amplitude loading
SIMD vectorization for simultaneous solution of locally varying linear systems with multiple right-hand sides
Get PDFDevelopments in numerical simulation of flows and high-performance computing influence one another. More detailed simulation methods create a permanent need for more computational power, while new hardware developments often require changes to the software to exploit new hardware features. This dependency is very pronounced in the case of vector-units which are featured by all modern processors to increase their numerical throughput but require vectorization of the software to be used efficiently. We study the vectorization of a simulation method that exhibits an inherent level of vector-parallelism. This is of particular interest as SIMD operations will hopefully be available with std::simd in a future C++ standard. The simulation method considered here results in the simultaneous solution of multiple sparse linear systems of equations which only differ by their main diagonal and right-hand sides. Such structure arises in the simulation of unsteady flow in turbomachinery by means of a frequency domain approach called harmonic balance
Experimental Investigation of Combustion Characteristics during Oxygen Carrier Aided Combustion of Solid Recovered Fuel and Coal in a 1 MWth Circulating Fluidized Bed Reactor
Get PDFThis presentation investigates results on oxygen carrier aided combustion (OCAC) of solid recovered fuel (SRF) and hard coal in a circulating fluidized bed (CFB) boiler, using ilmenite as bed material. In the OCAC process, the oxygen carrier (OC) is used as a bed material with the ability to incorporate and release oxygen, resulting in a decrease of local excesses or demands of oxygen. This effect has been proven to buffer combustion, which results in lower CO concentrations in the flue gas while at the same time allowing an increase in boiler load. During the test campaign described in this paper, a reduction of CO concentration of more than 70% has been measured. The NO concentration in the flue gas has shown varying results in different experiments. While there was a reduction in one case, increased NO values were found elsewhere, which are in line with the slight increase of up to 7 % during this test campaign. The pilot plant used to conduct the experiments has an inner diameter of 0.59 m, a height of 8.6 m, a thermal load of 1 MWth and a high operational flexibility. The combustion tests were performed using 100% SRF and a mixture of SRF and coal in the ratio of nearly 80/20 by heating value to investigate the combustion characteristics. It was found that even though an increase in SRF share shifts the combustion towards higher reactor region and lowers the pressure inside the reactor, stable operation can be maintained. The combustion conditions inside the reactor were investigated using two in-bed gas measurements, where the components O2, CO and CO2 are measured as horizontal profiles through the entire reactor width of 590 mm
Resilienz in der industriellen Produktion - Eine Aufnahme der Ist-Situation
Get PDFDie vorliegende Studie hat zum Ziel, ein umfassendes Bild der Resilienz in der Industrie zu zeichnen. Die gewonnenen Erkenntnisse zeigen, dass Resilienz ein entscheidender Faktor für den Erfolg in der industriellen Produktion ist und neben den klassischen Zielgrößen wie Kosten verstärkt in den Fokus rücken sollte. Dies ist insbesondere vor dem Hintergrund zunehmender Unsicherheiten und Störungen in globalen Lieferketten und Produktionsprozessen von großer Bedeutung. Die Studie ist das Ergebnis einer Kooperation zwischen dem Institut für Produktionsmanagement, Technologie und Werkzeugmaschinen (PTW) der Technischen Universität Darmstadt und dem Beratungsunternehmen Staufen AG. Die Studie ist Teil des Forschungsprojekts Flex4Res
Kinetic characterization of two neuraminic acid synthases and evaluation of their application potential
Get PDFNeuraminic acid synthases are an important yet underexplored group of enzymes. Thus, in this research, we performed a detailed kinetic and stability analysis and a comparison of previously known neuraminic acid synthase from Neisseria meningitidis, and a novel enzyme, PNH₅, obtained from a metagenomic library. A systematic analysis revealed a high level of similarity of PNH₅ to other known neuraminic acid synthases, except for its pH optimum, which was found to be at 5.5 for the novel enzyme. This is the first reported enzyme from this family that prefers an acidic pH value. The effect of different metal cofactors on enzyme activity, i.e. Co²⁺, Mn²⁺ and Mg²⁺, was studied systematically. The kinetics of neuraminic acid synthesis was completely elucidated, and an appropriate kinetic model was proposed. Enzyme stability study revealed that the purified enzyme exhibits changes in its structure during time as observed by differential light scattering, which cause a drop in its activity and protein concentration. The operational enzyme stability for the neuraminic acid synthase from N. meningitidis is excellent, where no activity drop was observed during the batch reactor experiments. In the case of PNH₅, some activity drop was observed at higher concentration of substrates. The obtained results present a solid platform for the future application of these enzymes in the synthesis of sialic acids.
Key points:
• A novel neuraminic acid synthase was characterized.
• The effect of cofactors on NeuS activity was elucidated.
• Kinetic and stability characterization of two neuraminic acid synthases was performed
Analytical and numerical analysis on local and global buckling of sandwich panels with strut-based lattice cores
Get PDFAdditive manufacturing (AM) offers new possibilities to fabricate and design lightweight lattice materials. Due to the superior mechanical properties of these lattice structures, they have the potential to replace honeycombs as cores in sandwich panels. In addition to the advantage of the integral fabrication thanks to AM, additively manufactured lattice core sandwich panels may be also used as heat exchangers, enabling a multifunctional use of the core. To ensure a reliable and safe structure, the mechanical response of lattice core sandwich panels under given load conditions must be predictable. In conventional sandwich panels subjected to compressive loads, the sandwich’s global buckling and the face sheets’ local buckling are the dominant failure modes. In constrast, core strut buckling may be the critical failure mode in lattice core sandwich panels. Therefore, an analytical 2D model to predict the local buckling of lattice core struts is considered in this study. Furthermore, the critical load for global buckling is obtained based on the first-order shear deformation theory. Thus, the transition from local buckling to global buckling depending on the length-to-thickness ratio is captured by the presented model. The comparison with finite element modeling of the sandwich model with truss cores has proved the accuracy of the derived model
The first in-beam reaction measurement at CRYRING@ESR using the CARME array
Get PDFIn the last decade nuclear reaction measurements using heavy ion storage rings became an important tool for nuclear astrophysics studies. The new CRYRING Array for Reaction MEasurements (CARME), recently commissioned at the low energy CRYRING@ESR storage ring (GSI/FAIR), is designed to take this novel approach one step further and perform direct nuclear reaction measurements at stellar energies, as well as indirect studies of nuclear properties of interest for nuclear astrophysics. CRYRING is unique worldwide in being able to store high quality, isotopically pure, radioactive beams produced in-flight at the low energies required for nuclear astrophysics. This paper describes the first in-beam reaction measurement with CARME at CRYRING, the first beam on (conventional) target measurement for FAIR Phase-0, and the data analysis approach required by this unprecedented, unique experimental approach