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See detailUnter Beobachtung. Das frühpädagogische Feld und die Ethnographie der Frühpädagogik
Neumann, Sascha UL

in Zeitschrift für Soziologie der Erziehung und Sozialisation = Journal for Sociology of Education and Socialization (2013), 33(1), 10-25

In the slipstream of increasing research activities in early childhood education and care (ECEC) during the last decades also ethnographic studies became an important resource for the production of ... [more ▼]

In the slipstream of increasing research activities in early childhood education and care (ECEC) during the last decades also ethnographic studies became an important resource for the production of scientific knowledge in this research area. Going out from a review of relevant literature the paper intends to enquire about the status the field of ECEC has in different studies for the production of ethnographic knowledge about ECEC. After working out that the idea of „field” in ECEC-related ethnography mainly is defined in relation to a certain place the paper discusses the limits of this idea and the possibilities of an alternative conceptualization of the research field in ECEC-related ethnography, which may allow the field of ECEC becoming a discrete object of investigation. [less ▲]

Detailed reference viewed: 74 (4 UL)
See detailUnter französischer Herrschaft: Cond von 1794 bis 1814
Kreutz, Bernhard René UL

in Dorfgemeinschaft Pumpenfest Cochem-Cond (Ed.) Leben am Fluss. Cond an der Mosel in Vergangenheit und Gegenwart (2010)

Detailed reference viewed: 97 (0 UL)
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See detailUnternehmertum in der Frühpädagogik - Berufsentscheidungen in Luxemburg
Ricken Geb. Weber, Kathrin Hannelore UL

Doctoral thesis (2015)

The observations, that founders of private crèches in Luxemburg possibly have a mainly non-pedagogic, but economic driven professional background, hire for the pedagogic management of their crèches ... [more ▼]

The observations, that founders of private crèches in Luxemburg possibly have a mainly non-pedagogic, but economic driven professional background, hire for the pedagogic management of their crèches qualified personnel and, compared to the gender ratio of specialized staff, are mainly male persons, cannot be confirmed with this qualitative research. The results show a certain dichotomy, but not, as suggested, concerning the job profiles ‘employed nursery nurse’ and ‘entrepreneur’. In contrast, within the group of entrepreneurs a tendency towards a dichotomy in terms of practicing tasks, early pedagogic or managerial, and size of the business, single or several crèches, appears. The assumption, that mainly male persons found private crèches cannot be confirmed. In contrary women appear to be in majority in all fields of business activity, so that there might possibly be a tendency towards a permeant feminisation of the whole private early pedagogic market. This is insofar surprising, as in this commercial part of the early pedagogic market with the new professional opportunity of being an entrepreneur due to the reflection of the literature more heterogeneity was expected. [less ▲]

Detailed reference viewed: 143 (2 UL)
See detailUnterrichtete Mündigkeit? Reflexionen auf die Aporien des Bildungssystems
Mein, Georg UL

Book published by Blaue Eule (2002)

Detailed reference viewed: 62 (1 UL)
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: 68 (6 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: 55 (10 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: 108 (15 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: 77 (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: 103 (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: 31 (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: 70 (13 UL)
See detailUnterschiedliche Lehrstrategien und ihr Niederschlag in der Lernerproduktion
Ehrhart, Sabine UL

Presentation (2003, March 07)

Detailed reference viewed: 24 (0 UL)
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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)

Detailed reference viewed: 29 (3 UL)
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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 ▲]

Detailed reference viewed: 148 (26 UL)
See detailUNTERSUCHUNG DER METALLURGISCHEN PHASENBILDUNG UND DEREN EINFLUSS AUF DIE VERBINDUNGSEIGENSCHAFTEN SOWIE AUF DIE VERSAGENSURSACHEN VON LASERGESCHWEIßTEN HARTMETALL-STAHL-VERBUNDEN
Schiry, Marc UL

Doctoral thesis (2020)

Laser beam welding of hard metal to steel offers multiple advantages regarding resource saving, mechanical strength of the joint and automation capability. The present work focuses on the fundamental ... [more ▼]

Laser beam welding of hard metal to steel offers multiple advantages regarding resource saving, mechanical strength of the joint and automation capability. The present work focuses on the fundamental research and development of the laser based welding process of tungsten carbide-cobalt hard metals with a tempering steel. Metallurgical analysis of the welding process showed that the formation of intermetallic and/or intermediate phases has a significant influence on the properties and mechanical strength of the dissimilar joint. The amount of molten hard metal in the steel melt bath plays a key role for the formation of the different phases. Therefore, a new parameter dy was defined, which correlates with the hard metal content in the melt pool. It is shown that for hard metals with 12 wt.% of cobalt binder, the phase transformation in the weld seam starts with a relative hard metal content of 10 vol.%. This threshold is dependent on the relative cobalt concentration in the hard metal. The tungsten carbide grain size has a low influence on the phase transformation in the weld seam. Steel melt pools with hard metal content lower than 10 vol.% show under metallographic observation a martensitic/bainitic microstructure. Simulation of the stress formation in the joint showed that due to the volume expansion of martensite during the transformation, tensile stress in the hard metal part was formed. Under shear load, these tensile stresses compensate with the induced compressive stresses and results an almost stress free interface. High shear strengths of the dissimilar joints are possible. A higher percentage of hard metal melting during the welding process increases the carbon and tungsten content in the melt bath. Consequently, the martensite start temperature decreases significantly. When the initiating temperature for martensite transformation falls under room temperature, the weld seam transforms into an austenitic microstructure. Because of the missing volume expansion during cooling of the weld seam volume, low stresses in the hard metal are generated. Under shear load of the joint area, high tensile stresses appear in the sintered part. These stress concentration decreases the shear strength of the weld and lead to premature failure. For the industrial use case, high mechanical strength and a robust manufacturing process is needed. Therefore, the laser welding process of hard metal to steel was optimized. The joint properties strongly depend on the weld bead geometry. Weld seams with x- or v-shaped profiles enable local concentrated metallurgical bonding of the sintered part to the steel sheet. Reduction of the horizontal focal distance of the laser beam to the interface increases the bonding ratio, but also intensifies the melting of the hard metal part and lead to the metallurgical transformation. By tilting a v-shape weld seam, it was possible to optimize the bonding behavior and to minimize the amount of liquefied hard metal in the melt bath. Hard metal with low amounts of binder showed a high temperature sensitivity. After laser welding of these grades, hot cracks were found in the sinter material. These cracks were formed due to the high stresses, which are generate during cooling of the dissimilar joint. Therefore, a laser based heat treatment process was developed and applied. With a defined pre- and post-heating of the joint area, the cooling rate was reduced significantly and the stresses in the hard metal part minimized. High shear strengths were the result. [less ▲]

Detailed reference viewed: 29 (4 UL)