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Peer Reviewed
See detailUnterschätzungen der Schülerfähigkeit durch Lehrkräfte: Prädiktoren und Konsequenzen
Baudson, Tanja Gabriele; Fischbach, Antoine UL; Wollschläger, Rachel UL et al

Scientific Conference (2013, September)

Detailed reference viewed: 59 (6 UL)
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See detailUnterschiede zwischen Schulformen
Keller, Ulrich UL; Villanyi, Denise UL; Fischbach, Antoine UL et al

in Martin, Romain; Ugen, Sonja; Fischbach, Antoine (Eds.) Épreuves Standardisées: Bildungsmonitoring für Luxemburg. Nationaler Bericht 2011 bis 2013 (2015)

Detailed reference viewed: 98 (15 UL)
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See detailUnterschiede zwischen Schulformen
Keller, Ulrich UL; Lorphelin, Dalia UL; Muller, Claire UL et al

in Martin, Romain; Brunner, Martin (Eds.) Épreuves Standardisées. Nationaler Bericht 2011‐2012 (2012)

Detailed reference viewed: 50 (10 UL)
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See detailUnterschiede zwischen Schulformen und das Pilotprojekt PROCI
Keller, Ulrich UL; Sonnleitner, Philipp UL; Villanyi, Denise UL et al

in SCRIPT; EMACS (Eds.) PISA 2012. Nationaler Bericht Luxemburg (2013)

Detailed reference viewed: 67 (10 UL)
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See detailUnterschiede zwischen Schulformen und Schulen
Keller, Ulrich UL; Reichert, Monique UL; Brunner, Martin UL et al

in SCRIPT; EMACS (Eds.) PISA 2009. Nationaler Bericht Luxemburg (2010)

Detailed reference viewed: 99 (11 UL)
See detailUnterschiede zwischen Schulformen und Schulen PISA 2006
Keller, Ulrich UL; Reichert, Monique UL; Burton, Réginald UL et al

in Nationaler Bericht Luxemburg (2007)

Detailed reference viewed: 27 (2 UL)
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See detailUnterschiede zwischen Schullaufbahnen
Fischbach, Antoine UL; Lorphelin, Dalia UL; Keller, Ulrich UL et al

in Martin, Romain; Ugen, Sonja; Fischbach, Antoine (Eds.) Épreuves Standardisées: Bildungsmonitoring für Luxemburg. Nationaler Bericht 2011 bis 2013 (2015)

Detailed reference viewed: 67 (13 UL)
See detailUnterschiedliche Lehrstrategien und ihr Niederschlag in der Lernerproduktion
Ehrhart, Sabine UL

Presentation (2003, March 07)

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Peer Reviewed
See detailUnterstützung der juristisch-informatischen Kommunikation im Hinblick auf elektronische Wahlprotokolle
Neumann, Stephan; Kahlert, Anna; Henning, Maria et al

in Proc.\ 16. Internationales Rechtsinformatik Symposion (IRIS2013) (2013)

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See detailUntersuchung der Ermüdungsfestigkeit von komplexen innendruckbelasteten Aluminiumgeometrien und der Lebensdauersteigerung durch Autofrettage
Sellen, Stephan UL

Doctoral thesis (2014)

Introducing gaseous high-pressure hydrogen storage for fuel cell vehicles requires safe light-weight valves for the automotive gas management. In contrast to thin-walled pressure vessels, there are no ... [more ▼]

Introducing gaseous high-pressure hydrogen storage for fuel cell vehicles requires safe light-weight valves for the automotive gas management. In contrast to thin-walled pressure vessels, there are no calculation or design guidelines available due to the huge variety of possible geometries and integrated functions. However, hydraulic cyclic pressure tests are compulsory for a finite-life fatigue strength certification of hydrogen valves. The valve body, linking different functional devices with each other via internal bore intersections, is the most critical part since the sharp-edged bore crossings cause high stress concentrations which distinctively limit the fatigue strength of such internally pressurized parts. Due to demands for light-weight design and manufacturing advantages it is aluminium which should be used as an appropriate material for the valve body. However, its fatigue properties need to be proved. Because of the complex valve body geometry, local fatigue evaluation concepts are initially applied to a simplified internally pressurized bore intersection and compared to the results of tested samples under pulsating pressure. However, those tests revealed an early crack initiation and a fast spreading of cracks in the aluminium under cyclic load and, thus, the requirements of the applicable testing regulation are not fulfilled. The present work focuses further on a method to increase the fatigue life by inducing residual compressive stresses at the areas of high stress concentrations. Here, the so called autofrettage, which is typically used for internally pressurized geometries, is a promising technology since it induces residual compressive stresses at the hotspots due to a unique static overload pressure with a distinctively higher pressure level than the subsequent cyclic pressure during operation. Although this is a well-known method, its potential for aluminium is not understood sufficiently. This is also the cast for the geometry dependent choice of a suitable autofrettage pressure range which is still inadequately clarified for the herein studied complex valve body geometry. An efficient design method based on a non-linear finite element method is derived from and applied to the valve body geometry. In order to perform the non-linear simulations, additional information about the plastification behaviour for reverse loading is necessary and being derived from uniaxial material tests. Fatigue testing of the valve body under cyclic pressure load shows a highly increased fatigue life and a design rule for the choice of an appropriate autofrettage pressure is verified. Besides sharp-edged bore intersections, high stress concentrations are also existent at the threads in the aluminium valve body, leading to an early crack initiation and a fast crack growth. In contrast to the typical implementation of the autofrettage process, it is shown that also even a unique static overload on the threads leads to an increased fatigue life. Thus, the end plugs should be used during the autofrettage process which causes residual compressive stresses at the thread root and a stress homogenisation over the carrying threads. These effects are studied with the help of non-linear finite element simulations considering the detailed thread geometry, the non-linear material behaviour and frictional contact. This leads to the conclusion that the effects of autofrettage as a method to increase the fatigue life by inducing residual compressive stresses for valve bodies for high-pressure hydrogen applications are being analysed in detail. As a result, it can be stated that with an appropriate selection of the autofrettage pressure and the suitable implementation of the process towards the valve body geometry, the required number of pressure cycles according to the applicable regulation can be successfully achieved. [less ▲]

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See detailUntersuchung der Rissentwicklung an zementgebundenen Sichtestrichen
Weiler, Michael UL; Waldmann, Danièle UL

in Beton (2016), (66), 248-252

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See detailUntersuchung der Rissentwicklung an zementgebundenen Sichtestrichen
Weiler, Michael; Waldmann, Danièle UL

in Beton (2016), (66), 248-252

Detailed reference viewed: 26 (3 UL)
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Peer Reviewed
See detailUntersuchung des thermischen Komforts und der Luftqualität an vier neuen energieeffizienten Luxemburger Schulen mit und ohne Lüftungsanlagen
Maas, Stefan UL; Brensing, Jessica UL; Flies, Max et al

in Bauphysik (2017), 39. Jahrgang

A study was conducted in four new energy efficient schools in Luxembourg with excellent primary energy consumption values, where the indoor thermal comfort and the air quality was assessed by technical ... [more ▼]

A study was conducted in four new energy efficient schools in Luxembourg with excellent primary energy consumption values, where the indoor thermal comfort and the air quality was assessed by technical measurements and by surveys. Two schools were equipped with mechanical ventilation with heat recovery and two were without, i.e. ventilation there was manually controlled by opening the windows. Further to the C02-concentration as indicator for the air quality all other important comfort parameters were measured, why the well-known indicators according to FANGER could be calculated, i.e. the „Predicted Mean Vote (PMV)“ and the „Predicted Percentage of Dissatisfied (PPD)“. The individual perceived indoor comfort was analyzed by standardized questionnaires for a period of four weeks. One aim of the study was to compare natural ventilation by opening and closing the windows with the mechanical ventilation in all named aspects. In total there was a good agreement between the measurements and the survey. The results show that in general mechanical ventilation in schools lead to better physical measured values and to better subjective perception of the users. However those buildings suffer from a very low relative humidity, though it is rarely sensed by the occupants. Furthermore, in one of the mechanically ventilated buildings the air velocity was very high and led to draft-perception. The detected air temperature was heterogeneous and independent of the ventilation concept, leading to an individual judgement of PMV for the different buildings. Users should always have the possibility of interaction and control to adjust the indoor climate according to their individual needs and to correct smaller technical shortcomings. [less ▲]

Detailed reference viewed: 189 (11 UL)
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See detailUntersuchung dünnwandiger Silostrukturen unter exzentrischer Entleerung
Reinstädler, Sven; Dinkler, Dieter; Zilian, Andreas UL

in Baustatik-Baupraxis 11 (2011)

Detailed reference viewed: 54 (1 UL)
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Peer Reviewed
See detailUntersuchung nichtlinearer Schwingungseigenschaften zur zerstörungsfreien Zustandsprüfung am Beispiel von Stahlbetonbalken
Waltering, Markus UL; Waldmann, Danièle UL; Maas, Stefan UL et al

in Beton- und Stahlbetonbau (2007), 09/ 2007(Ernst & Sohn. Verlag für Architektur und technische Wissenschaften GmbH & Co.KG;),

Detailed reference viewed: 88 (11 UL)