Recent Additions

  • Publication
    Additive manufacturing of WE43 and modified AZ91D magnesium alloys using the laser engineered net shaping process
    ( 2024)
    Hartmann, Christoph
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    Venkatesan, Kishore
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    Looze, Geoffrey de
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    Takashima, Kazuki
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    Shen, Shirley
    ;
    Wilson, Robert
    Magnesium alloys WE43 and AZ91D offer weight savings for structural applications. WE43 contains rare-earth elements such as yttrium and neodymium, whereas AZ91D and the AZ class of alloys are lower-cost containing aluminium and zinc. This work uses a modified version of the latter, identified as AZ91D*, where calcium and yttrium have been added. Laser Engineered Net Shaping (LENS) equipment was used to investigate the 3D printing behaviour of gas-atomized WE43 and AZ91D* material. Process evaluations were first done using single track laser scans across wrought substrates of WE43 and AZ31. Process parameters were then developed that enabled deposition of build coupons with less than 1% porosity. These were used for microstructural and mechanical property assessments. The energy densities used were in the range of 40 – 60 J/mm² for AZ91D*, while for WE43 a value of 50 J/mm² was selected. A focus of the work was managing the tendency of magnesium materials to fume heavily during deposition, while achieving a deposit with close to nominal density, i.e. having a low incidence of voids or other micro- or macro-structural defects. The porosity of AZ91D* builds did not seem to correlate with increasing deposition energy density, however WE43 builds did, up to a practical limit imposed by generation of excessive fume. WE43 generated much less fume than AZ91D*. Analysis of the input powder materials indicate the presence of oxides on the particle surfaces. The WE43 powders had a noticeable shell of yttrium oxide. The microstructures of WE43 builds show the presence of arc-shaped structures that are likely the same yttrium oxides, partially, or fully ‘unfolded’. Tensile testing was conducted on WE43 build coupons to assess the effect of a T6 heat treatment. The effect on the ultimate tensile and yield strengths was negligible, however the % elongation at break almost doubled. Inspection of the fracture surfaces suggests this was due to a change in mechanism from fracture initiation at sites of lack-of-fusion/un-melted particles, to a more ductile micro-void coalescence. Furthermore, a not previously described microstructure anomaly was observed: the presence of pure elemental magnesium crystallites and films on the fracture surface. These are attributed to condensation of magnesium vapour on previously built layers and are a possible reason for the existence of lack-of-fusion defects. The in-depth study of process fundamentals will enable future work on process fume inhibition based on process optimization and alloy composition with the goal of producing parts for biomedical and lightweighting applications.
  • Publication
    Deepfakes und manipulierte Realitäten - Technologiefolgenabschätzung und Handlungsempfehlungen für die Schweiz
    (vdf - Hochschulverlag AG an der ETH Zürich, 2024) ;
    Frei, Nula
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    Puppis, Manuel
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    Vogler, Daniel
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    Raemy, Patric
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    ; ;
    Rauchfleisch, Adrian
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    Seta, Gabriela de
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    Gurr, Gwendolin
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    Rovelli, Sophia
    Die Imitation von Stimmen und Gesichtern mittels neuer KI-Technologien wird zunehmend einfacher – und die Resultate sind schon heute kaum mehr von echten Stimmen und Gesichtern zu unterscheiden. Diese Technologien bieten viele kreative und innovative Nutzungspotenziale, sowohl für Privatnutzende als auch für verschiedene Wirtschaftsbereiche. Andererseits sind Deepfake-Videos und Deepfake-Audios auch Quell zahlreicher Risiken: Sie können z.B. politische Desinformation vereinfachen, Mobbing Vorschub leisten und kriminelle Aktivitäten begünstigen. Angesichts der fortwährenden Debatten über die Chancen und Risiken von Deepfakes wird in der Studie der Umgang mit einer veränderten Realität diskutiert, in der täuschend echte Fälschungen mit Originalmedien um die Aufmerksamkeit der Zuschauer konkurrieren. Was ist technisch möglich? Welche Grenzen setzt das Recht? Was weiss und denkt die Bevölkerung über Deepfakes? Wie geht der Journalismus mit dem Phänomen um? Welche Rolle könnten Deepfakes in Politik und Wirtschaft spielen? Die Studie bietet zu diesen und weiteren Fragen fundierte Orientierung und zeigt darauf basierende Handlungsmöglichkeiten auf.
  • Publication
    Benefits of multi-voltage-level grid control in future distribution grids
    ( 2020)
    Biener, Wolfgang
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    Kumm, Thomas
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    Operators of distribution grids will be confronted with new challenges caused by a high share of distributed fluctuating generators (PV, wind) together with new load profiles of a fleet of electric vehicles (EV), decentralized storage systems or electricity-heat-converters (like heat-pumps or direct heaters). Conventional grid reinforcement is an expensive and inflexible way to handle upcoming grid problems like the violation of voltage limits or the thermal overloading of operating equipment. By controlling flexible components (like on-load tap changers or reactive power generation from inverters) grid operators can counteract violations of operational limits. A grid simulation study has been performed to compare benefits of intelligent multi-voltage-level grid control with single-voltage-level control solutions and conventional grid control methods. The starting point for this work was a number of scenarios for the future grid penetration by PV, wind and EV. Representative type grids consisting of interconnected grid segments for rural and municipal distribution grids were modelled within a probabilistic load flow calculation framework. To quantify the probability of voltage violations or thermal overload situations, a probabilistic assignment of grid components (PV, wind, EV) to grid nodes was implemented. Four grid control approaches have been studied by use of the simulation, representing different distributed and centralized control methods. The results of the investigation show the benefits of multi-voltage-level grid control for distribution grids with a high share of distributed wind, PV and EV. While conventional grid operation solutions might be able to counteract local voltage problems, a combined control algorithm for the LV and MV grid segments is able to prevent the violation of given voltage and current limits in many cases quite effectively. The effectiveness of using transformers with variable on-load tap changers (OLTC) might improve significantly if communication based multi-voltage-level grid control concepts are applied. Overloading of cables resulting from solving local voltage maintenance problems by means of reactive power injection can be avoided. Multi-voltage-level grid control avoids or delays grid extension and increases grid capacity towards the installation of additional PV, wind or EV-charging units.
  • Publication
    Design of electrical contact surfaces for fast charging systems
    E-mobility is of high interest for the energy transition and the achievement of climate targets. Nevertheless, this forward-looking technology still has a number of drawbacks. One example is the very long charging time of battery systems. To counteract this, an innovative fast charging system using a face contact instead of classic plug-in contacts is being developed that significantly reduces conventional charging times. To enable this, an electrical contact surface is functionalized in such a way that, on the one hand, the contact resistance is reduced and, on the other hand, the thermal as well as mechanical properties are improved. This can be achieved by a special design of the microstructure of the electrical contact surface. In the following, the procedure is described in detail. First, a single microcontact is designed to break up the oxide layers and minimize the constriction resistance. The thermal, mechanical and the electrical properties are described and optimized using analytical and numerical methods. Special attention must be paid to the heating of an a-spot during current flow. Then, the single microcontact is multiplied to exploit the principle of a parallel connection. This can significantly reduce the constriction resistance. Finally, this designed microstructure is manufactured and tested in experiments. Consequently, high charging currents can be transmitted via a face contact on a relatively small contact area.

Most viewed

  • Publication
    Contactless recording of vital parameters to evaluate the quality of sleep in the nursing environment
    ( 2023-09-08)
    Alić, Belmin
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    Seidel, Roman
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    ; ; ;
    Hirtz, Gangolf
    Chronic Fatigue Syndrome (CFS) is a nervous system disorder that causes severe physical weakness in patients worldwide. The number of people affected in Europe is currently estimated at two million, including around 300,000 in Germany. Due to the COVID-19 pandemic, a sharp increase in the number of affected people can be expected. The post-viral symptoms such as fatigue, muscle pain, and neurocognitive symptoms that occur after a corona infection are known as long-COVID. It is assumed that around 30% of those infected with COVID-19 suffer from these symptoms. The goal of this work is to develop contactless monitoring of body parameters of CFS patients, quantify the level of activity and thus avoid overexertion of patients. Measurable parameters include vital and sleep parameters. The measurement hardware consists of a multispectral 3D sensor system with an RGB camera and two near-infrared cameras, as well as dedicated narrow-band infrared LEDs. Sleep parameters are estimated through the estimation of the pose of the person lying in the bed although a blanket obscures the person. Vital parameters are determined by measuring and analyzing the time course of color, spectral, and temperature values of human skin. Using ensemble learning approaches, the body parameters are bundled into a sleep protocol and quantified to a sleep score. A connection to a database and the design of a visualization system allows for two-way feedback, for both the patient and the physician. The measurements are carried out with reference to polysomnography, the gold standard in sleep diagnostics. The visualized results are evaluated by sleep physicians. The proposed solution for contactless sleep quality monitoring of CFS patients has the potential of improving the assessment of available energy during the day and therefore reduce overexertion events. This hypothesis shall be validated and quantified with respect to polysomnography in the continuation of this study.
  • Publication
    The individualized electronic newspaper
    (GMD, 1993)
    Haake, A.
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    Hüser, C.
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    Reichenberger, K.
  • Publication
    Multilevel finite element Riesz bases in Sobolev spaces
    ( 1997)
    Lorentz, R.A.
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    Oswald, P.
  • Publication
    Methode zur Reduktion technischer Nebenzeiten in der spanenden Fertigung
    (Fraunhofer Verlag, 2016)
    Bosch, Thomas
    Die Effizienz von Fertigungsprozessen kann durch die Reduktion technischer Nebenzeiten deutlich gesteigert werden. Hierzu wird eine Methode vorgestellt, welche die äußerst komplexe Aufgabe der Optimierung des Fertigungsprozesses vereinfachen kann. Die Methode besteht aus Verfahren der Potenzialanalyse und der Optimierung. Diese Verfahren werden anschließend exemplarisch an Fertigungsprozessen der automobilen Großserienfertigung angewandt und die daraus resultierenden Erfolge aufgezeigt.
  • Publication
    Elektromobilität in gewerblichen Flotten
    (Fraunhofer ISI, 2014) ; ;
    Ullrich, Sandra
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    Haendel, Michael
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    Globisch, Joachim
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