Publications Search Results

Now showing 1 - 10 of 323
  • Publication
    A computational multi-scale model for the stiffness degradation of short-fiber reinforced plastics subjected to fatigue loading
    ( 2021)
    Köbler, J.
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    Magino, N.
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    Andrä, H.
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    Welschinger, F.
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    Müller, R.
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    Schneider, M.
    In this work, we investigate a model for the anisotropic and loading-direction dependent stiffness degradation of short-fiber reinforced thermoplastics subjected to high-cycle fatigue loading. Based upon the variational setting of generalized standard materials, we model the stiffness degradation of the matrix in cycle space by a simple isotropic fatigue-damage model with minimum number of model parameters, and consider the fibers to be linear elastic. The stiffness degradation upon cyclic loading is determined, for fixed damage state, by standard linear elastic homogenization. We thoroughly investigate the influence of the involved numerical and material parameters on the effective stiffness degradation of short-fiber reinforced volume elements, and also pay close attention on the dependence on geometric parameters of the composite like fiber-volume fraction and the fiber-orientation state. To enable component-scale simulations, we use a model-order reduction strategy for identifying a suitable macroscopic model. This reduction is possible because our free energy involves polynomial powers in the fields not exceeding two, and our dissipation potential is assumed quadratic. For resolving the balance of linear momentum on the microscopic scale, we rely upon a fast Fourier transform based non-local micromechanics solver. We investigate the clever identification of the modes and demonstrate the capabilities of our model on the microscopic and on the component scale by pertinent numerical examples.
  • Publication
    Understanding kinetic and thermodynamic properties of blended cathode materials for lithium-ion batteries
    ( 2021)
    Liebmann, T.
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    Heubner, C.
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    Schneider, M.
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    Michaelis, A.
    Using electrodes with multiple types of active materials has been shown to be a promising approach to improve critical properties of Li-ion batteries, such as cost, lifetime, safety, and rate performance and is already applied in automotive applications. However, the impact of the type and content of components in the blend is still poorly understood, making it difficult to identify the most beneficial compositions and designs. The present work systematically investigates how specific electrochemical properties of the components affect the resulting electrochemical kinetics and thermodynamics of blended electrodes. The impact of component type and mass ratio on the voltage and entropy profiles, charge transfer kinetics, and lithium diffusivity is examined by thermodynamic analyses, galvanostatic titration, impedance spectroscopy, and chronoamperometry. Comparison of the results with models based on physical mixtures shows that the basic electrochemical properties of the blended electrodes correspond to expectations based on the components' properties. Based on the present findings, direct mixing effects can be ruled out for future simulations and model-based design studies to effectively search for optimal compositions and electrode structures.
  • Publication
    The PICASO cloud platform for improved holistic care in rheumatoid arthritis treatment - experiences of patients and clinicians
    ( 2021)
    Richter, J.G.
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    Chehab, G.
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    Schwartz, C.
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    Ricken, E.
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    Tomczak, M.
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    Acar, H.
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    Gappa, H.
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    Velasco, C.A.
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    Rosengren, P.
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    Povilionis, A.
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    Schneider, M.
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    Thestrup, J.
    Background Multimorbidity raises the number of essential information needed for delivery of high-quality care in patients with chronic diseases like rheumatoid arthritis (RA). We evaluated an innovative ICT platform for integrated care which orchestrates data from various health care providers to optimize care management processes. Methods The Horizon2020-funded research project PICASO (picaso-project.eu) established an ICT platform that offers integration of care services across providers and supports patients' management along the continuum of care, leaving the data with the owner. Strict conformity with ethical and legal legislations was augmented with a usability-driven engineering process, user requirements gathering from relevant stakeholders, and expert walkthroughs guided developments. Developments based on the HL7/FHIR standard granting interoperability. Platform's applicability in clinical routine was an essential aim. Thus, we evaluated the platform according to an evaluation framework in an observational 6-month proof-of-concept study with RA patients affected by cardiovascular comorbidities using questionnaires, interviews, and platform data. Results Thirty RA patients (80% female) participated, mean age 59 years, disease duration 13 years, average number of comorbidities 2.9. Home monitoring data demonstrated high platform adherence. Evaluations yielded predominantly positive feedback: The innovative dashboard-like design offering time-efficient data visualization, comprehension, and personalization was well accepted, i.e., patients rated the platform ""overall"" as 2.3 (1.1) (mean (SD), Likert scales 1-6) and clinicians recommended further platform use for 93% of their patients. They managed 86% of patients' visits using the clinician dashboard. Dashboards were valued for a broader view of health status and patient-physician interactions. Platform use contributed to improved disease and comorbidity management (i.e., in 70% physicians reported usefulness to assess patients' diseases and in 33% potential influence on treatment decisions; risk manager was used in 59%) and empowered patients (i.e., 48% set themselves new health-related goals, 92% stated easier patient-physician communications). Conclusion Comprehensive aggregation of clinical data from distributed sources in a modern, GDPR-compliant cloud platform can improve physicians' and patients' knowledge of the disease status and comorbidities as well as patients' management. It empowers patients to monitor and positively contribute to their disease management. Effects on patients' outcome, behavior, and changes in the health care systems should be explored by implementing ICT-based platforms enriched by upcoming Artificial Intelligence features where possible. Trial registration DRKS-German Clinical Trials Register, DRKS00013637, prospectively registered. 17 January 2018.
  • Publication
    Diving into Email Bomb Attack
    ( 2020)
    Schneider, M.
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    Shulman, H.
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    Sidis, A.
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    Sidis, R.
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    Waidner, M.
    We explore Email Bomb - a particularly devastating type of Denial of Service (DOS) attack that recently gained traction. During the attack Email account of a victim is targeted with a flood of Emails. Existing anti-spam defences fail at filtering this Emails' flood, since the Emails are not sent from spoofed addresses, but originate from legitimate web services on the Internet which are exploited as reflectors. We perform a two-year study of the Email bomb attack and the affected actors - the victims and the reflectors. We show that although the attack is rented for one day, the Email flood proceeds over longer time periods often lasting months after the initial attack. We identify the properties that allow the attackers to recruit web sites as potential reflectors and demonstrate how the attackers harvest web reflectors. We show that even popular Alexa web sites, such as booking.com, are exploited to launch Email bomb attacks. The main problem is that such attacks are extremely simple to launch and can be rented for 5USD on darknet. We setup a tool which periodically collects and analyses the Emails received during the attack, the analysis as well as the data is presented online at http://emailbombresearch.xyz. We argue that email bomb attacks do not only pose inconvenience and hinder the ability of victims to function, but also we provide the first demonstration how such attacks can be leveraged for hiding other devastating attacks which take place in parallel. We show that existing countermeasures fall short of preventing email bomb attacks and provide effective mitigation recommendations that are based on our study of this attack.
  • Publication
    Data Management at the Tool. The Electronic Tool Logbook as a Combination of Operating Manual and Check List
    ( 2020)
    Seul, T.
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    Wenzel, A.
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    Rönnecke, S.
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    Schneider, M.
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    Köllner, U.
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    Gutterau, A.
    A tool logbook on paper is often not to hand just when you need it most. Or it is incomplete, since it is time consuming to keep the information up to date. A cloud-independent, electronic tool log, which is directly integrated into the tool could make all the relevant data available directly. Digital access would allow authorized users to read or enter content, and, if needed, provide important operating instructions and information about the condition of the tool.
  • Publication
    Digital sand core physics: Predicting physical properties of sand cores by simulations on digital microstructures
    ( 2020)
    Ettemeyer, F.
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    Lechner, P.
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    Hofmann, T.
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    Andrä, H.
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    Schneider, M.
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    Grund, D.
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    Volk, W.
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    Günther, D.
    In this work, we compare measurements of strength, permeability and thermal conductivity of blown anorganically bound sand cores to simulation results on digitally generated unit cell models resolving the fine sand grain-binder aggregate on the micrometer scale. The quality and operationality of sand cores used in foundry applications is strongly affected by different characteristics of the sand and binder used, for instance chemical composition, porosity, grain size distributions and binder volume fraction. On the one hand, sand cores should be strong enough to survive the casting process. On the other hand, after casting extracting the sand should be easy. Currently, in industry, finding cost-efficient recipes for mixing sand and binder types requires tedious calibration and expert's knowledge. This originates from an incomplete understanding of the sensitivity of the physical properties of the resulting sand core w.r.t. the sand-binder characteristics. Furthermore, even with a controlled sand shooting process, the final sand core exhibits a heterogeneity, for instance in density, which needs to be accounted for during the design process. In a previous work, we have introduced a method to generate stochastic microstructure models based on X-ray micro-computed tomography scans and simulated compactification, which serves as the starting point for further simulation studies. In this work, we improve the previously introduced method towards better applicability to industrial problems: Firstly, we dispense with the time-consuming morphological dilation and use background CAD models instead. Secondly, we include a broader variety of real sand shapes by utilizing modern image processing tools. With this tool at hand, we simulate strength, permeability and thermal conductivity on these microstructures, and subsequently compare those to dedicated experiments, laying the foundation for ""Digital Sand Core Physics"".
  • Publication
    Bewertung von Produktionsprozessen mit Verfahren der Künstlichen Intelligenz
    ( 2020)
    Greifzu, N.
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    Schneider, M.
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    Werner, M.
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    Fränzel, N.
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    Walther, C.
    In der industriellen Fertigung wird zunehmend die zuverlässige Vorhersage der Produktqualität verlangt. Im Bereich des Kunststoffspritzgießprozesses existieren dabei grundlegende Herausforderungen, welche auf der teilweise sehr komplexen Geometrie der Produkte, der unterschiedlichen Qualitätsanforderungen und der Fülle der einzuhaltenden Prozessparameter begründet sind. Im vorliegenden Beitrag wird die Bauteilqualität eines individuellen Produktes anhand von gezielten Versuchsreihen mit einer Methode des Maschinellen Lernens bewertet. Unter Verwendung einer Aufzeichnungs- und Analysesoftware wird der Versuch unternommen, eine Gutteil-Schlechtteil-Aussage basierend auf den im Werkzeug erfassten Prozessdaten zu ermitteln.
  • Publication
    Datenmanagement am Werkzeug. Das elektronische Werkzeuglogbuch als Kombination von Betriebsanleitung und Checkheft
    ( 2020)
    Seul, T.
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    Wenzel, A.
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    Rönnecke, S.
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    Schneider, M.
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    Köllner, U.
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    Gutterau, A.
    Ein Werkzeuglogbuch in Papierform ist, gerade wenn es benötigt wird, oft nicht greifbar. Oder unvollständig, denn die Pflege der Informationen ist mit erheblichem Aufwand verbunden. Ein Cloud-unabhängiges elektronisches Werkzeugbegleitheft, das direkt in das Werkzeug integriert ist, könnte alle relevanten Daten direkt zur Verfügung stellen. Durch den digitalisierten Zugriff würden das Lesen bzw. Hinzufügen von Inhalten durch autorisierte Personen ermöglicht und im Bedarfsfall wichtige Anleitungen zum Gebrauch sowie Informationen über den Zustand des Werkzeugs bereitgestellt.
  • Publication
    Lippmann-Schwinger solvers for the explicit jump discretization for thermal computational homogenization problems
    ( 2019)
    Dorn, C.
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    Schneider, M.
    We present a variational formulation and a Lippmann-Schwinger equation for the explicit jump discretization of thermal computational homogenization problems, together with fast and memory-efficient matrix-free solvers based on the fast Fourier transform (FFT). Wiegmann and Zemitis introduced the explicit jump discretization for volumetric image-based computational homogenization of thermal conduction. In contrast to Fourier and finite difference-based discretization methods classically used in FFT-based homogenization, the explicit jump discretization is devoid of ringing and checkerboarding artifacts. Originally, the explicit jump discretization was formulated as the discrete equivalent of a boundary integral equation for the jump in the temperature gradient. The resulting equations are not symmetric positive definite, and thus solved by the BiCGSTAB method. Still, the numerical scheme exhibits stable convergence behavior, also in the presence of pores. In this work, we exploit a reformulation of the explicit jump system in terms of harmonically averaged conductivities. The resulting system is intrinsically symmetric positive definite and admits a Lippmann-Schwinger formulation. A seamless integration into existing FFT-based software packages is ensured. We demonstrate our improvements by numerical experiments.
  • Publication
    Update of the DevTox data database for harmonized risk assessment and alternative methodologies in developmental toxicology: Report of the 9th Berlin Workshop on Developmental Toxicity
    ( 2019)
    Solecki, R.
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    Rauch, M.
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    Gall, A.
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    Buschmann, J.
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    Kellner, R.
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    Kucheryavenko, O.
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    Schmitt, A.
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    Delrue, N.
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    Li, W.
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    Hu, J.
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    Fujiwara, M.
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    Kuwagata, M.
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    Mantovani, A.
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    Makris, S.L.
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    Paumgartten, F.
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    Schönfelder, G.
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    Schneider, S.
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    Vogl, S.
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    Kleinstreuer, N.
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    Schneider, M.
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    Schulze, F.
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    Fritsche, E.
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    Clark, R.
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    Shiota, K.
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    Chahoud, I.
    Representatives of applied science (e.g. governmental organizations, academia, and industry) met to discuss the progress towards a harmonized human health risk assessment in developmental toxicology of plant protection products, biocidal products, and other environmental chemicals at the 9th Berlin Workshop on Developmental Toxicity held in September 2018. Within the focus of the scientific discussion were the future of in-vitro methods for developmental and reproductive toxicology, the potential relevance of alternative species in testing of developmental effects, and risk and hazard assessment of developmental and endocrine effects. Furthermore, the need for a harmonized terminology for classification of anomalies in laboratory animals in developmental toxicity studies aiming for human health risk assessment was determined. Here, the DevTox database was identified as an extremely valuable tool. Overall, the participants agreed that still one of the biggest challenges for testing developmental toxicity in the 21st century is the development of animal-free test strategies and alternatives to animal testing that could provide human-relevant information in a rapid, efficient, and mechanistically informative manner.