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See detailStaatliche Forschungsförderung der Sozialwissenschaften: Die Deutsche Forschungsgemeinschaft und die amerikanische National Science Foundation im Vergleich
Powell, Justin J W UL

Bachelor/master dissertation (1999)

Why have the social sciences been more successful at gaining funding from Germany's national science foundation, the Deutsche Forschungsgemeinschaft (DFG), than from the U.S. National Science Foundation ... [more ▼]

Why have the social sciences been more successful at gaining funding from Germany's national science foundation, the Deutsche Forschungsgemeinschaft (DFG), than from the U.S. National Science Foundation (NSF)? Historical-institutional case studies of the DFG's difficult reconstruction and NSF's complicated birth show how scientists negotiated postwar political conditions. Further, comparative analysis examines postwar research and development trends through 1997, including organization-level data on funding distributions between branches of science. Postwar consensus about the increasing importance of science enabled the rapid growth of government-sponsored research funds and distributing organizations, with the DFG and the NSF created to allocate basic research funds among and within disciplines. While institutionalized peer review systems balanced external political control and scientific freedom, competition between levels and branches of government and complex decision making processes affected federal research-sponsoring agencies' expansion as intermediary institutions. While both organizations attempt to shield themselves from political control by nonscientists, the NSF has been less successful than the DFG in maintaining its autonomy from federal policymakers. In Germany, the federal science ministry with its comprehensive budgeting process and constitutionally guaranteed academic freedoms strengthen the equilibrium of the science-politics nexus. In contrast, the US still lacks an executive branch department of science or technology and American social scientists only obtained a full-fledged social science directorate at the NSF in the 1990s. Comparative analysis shows significant differences in political decision-makers' control of these organizations, especially with respect to the natural sciences' dominance over the social sciences. German social scientists have maintained higher levels of government funding for basic research than their American peers, who suffered both lost autonomy and diminished funding, especially at NSF. [less ▲]

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See detailStaatliche Lehrerbildung in der Zeit der Helvetik und die Rolle Pestalozzis
Tröhler, Daniel UL

in Beiträge zur Lehrerbildung (1997), 15(3), 293-303

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See detailStaatsbildung und Staatsangehörigkeitsrecht in Luxemburg: zwischen Inklusion und Exklusion (1804-1940)
Scuto, Denis UL

in Franz, Norbert; Lehners, Jean-Paul (Eds.) Nationenbildung und Demokratie: Europäische Entwicklungen gesellschaftlicher Partizipation (2013)

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See detailStaatsdenken bei Max Weber und Pierre Bourdieu
Connor, Ulla UL

Presentation (2017)

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See detailStaatsgarantie für die Einlagensicherung, Icesave und der Weg zur grenzüberschreitenden Einlagensolidarität
Zetzsche, Dirk Andreas UL; Gruenewald, S.

in Wertpapiermitteilungen (WM) (2013)

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See detailStaatsgewalt und Kindsmord: zum sozialphilosophischen Hintergrund von Pestalozzis Schrift: "Über Gesetzgebung und Kindermord" (1780/83)
Tröhler, Daniel UL

in Schweizerische Zeitschrift fur Bildungswissenschaften = Rivista svizzera di scienze dell'educazione = Revue suisse des sciences de l'education (1995), (1), 34-35

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See detailDer Staatsrat - eine umstrittene Institution
Pauly, Michel UL

Article for general public (2006)

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See detailStabilisation des systèmes bilinéaires fractionnaires
Ndoye, Ibrahima UL; Zasadzinski, Michel; Nour-Eddine, Radhy et al

in Sixième Conférence Internationale Francophone d'Automatique, CIFA 2010, Nancy, France (2010)

Cet article traite de la stabilisation des systèmes bilinéaires fractionnaires par l'approche de la nouvelle généralisation du lemme de Gronwall-Bellman. L'utilisation de cette nouvelle approche permet de ... [more ▼]

Cet article traite de la stabilisation des systèmes bilinéaires fractionnaires par l'approche de la nouvelle généralisation du lemme de Gronwall-Bellman. L'utilisation de cette nouvelle approche permet de montrer sous certaines hypothèses adéquates, qu'on peut garantir une stabilisation asymptotique par retour d'état statique et par retour de sortie statique des systèmes bilinéaires fractionnaires. La méthodologie est illustrée par l'intermédiaire d'un exemple numérique. [less ▲]

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See detailUne stabilisation difficile. La chlorpromazine dans les années 1950 en Belgique
Majerus, Benoît UL

in Gesnerus (2010), 67(1), 57-72

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See detailDie Stabilität von akademischen Selbstkonzept-Profilen: Befunde einer „latent transition analysis“
Franzen, Patrick UL; Arens, A Katrin; Niepel, Christoph UL

Scientific Conference (2019, September)

Nach dem „internal-external frame of reference“ Modell (Marsh, 1986), spielen u.a. dimensionale Vergleiche (Vergleich der eigenen Leistung in einem Fach mit der eigenen Leistung in einem anderen Fach ... [more ▼]

Nach dem „internal-external frame of reference“ Modell (Marsh, 1986), spielen u.a. dimensionale Vergleiche (Vergleich der eigenen Leistung in einem Fach mit der eigenen Leistung in einem anderen Fach) eine Rolle für die Ausbildung fachspezifischer akademischer Selbstkonzepte (ASKs). Dabei kommt es zu Kontrasteffekten: Eine gute Leistung in Mathematik stärkt das Mathematik-ASK, schwächt aber das Deutsch-ASK und vice versa. Schüler schätzen sich daher oft als fähiger in einem der beiden Fächer ein. Diese Typisierung ließ sich auch in personenzentrierten Ansätzen zeigen. Eine Profilanalyse von Marsh, Lüdtke, Trautwein und Morin (2009) ergab, dass ASK-Profile entweder einem Mathematik-Typ (höheres Mathe-ASK, niedrigeres Sprach-ASK), einem Sprach-Typ (niedrigeres Mathe-ASK, höheres Sprach-ASK) oder einem Mischtyp (gleich hohe ASKs in allen Domänen) folgten. Ob diese Profile über die Zeit hinweg stabil sind oder Schüler in Abhängigkeit ihrer Erfahrungen im Schulalltag zwischen den Typen wechseln können, ist bisher unklar. Ziel der vorliegenden Studie ist es, diese Frage zu beantworten. Eine Stichprobe von N = 382 Schülern aus 18 Klassen und vier Bundesländern beantwortete einen Fragebogen zum Mathematik-, Physik-, Deutsch- und Englisch-ASK an zwei Messzeitpunkten, mit einem Intervall von vier Wochen. Eine „latent transition analysis“ ergab eine Vier-State Lösung (BIC = 7797.8, Entropie = 0.884). Die vier States beschrieben einen Mathematik-Typ (höhere ASKs in Mathematik und Physik, niedrigere ASKs in Deutsch und Englisch), einen Sprach-Typ (höhere ASKs in Deutsch und Englisch, niedrigere ASKs in Mathematik und Physik), und zwei Mischtypen (gleich hohe ASKs für alle Fächer mit generell höheren ASKs bzw. niedrigeren ASKs). Die Ergebnisse zeigten eine hohe Stabilität der States: Alle Personen wurden an beiden Messzeitpunkten demselben State zugewiesen; die Transitionswahrscheinlichkeiten lagen bei 0% bis 5%. Weitere Ergebnisse zur Stabilität von ASK-Profilen bei noch kürzeren Zeitabständen, basierend auf „Experience Sampling“ Daten, werden diskutiert. Marsh, H.W. (1986). Verbal and math self-concepts: An internal/external frame of reference model. American Educational Research Journal, 23, 129-149. Marsh, H.W., Lüdtke, O., Trautwein, U., & Morin, A.J.S. (2009). Classical latent profile analysis of academic self-concept dimensions: Synergy of person- and variable-centered approaches to theoretical models of self-concept. Structural Equation Modeling, 16, 191–225. [less ▲]

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See detailStabilität wechselrichtergeführter Inselnetze
Jostock, Markus UL

Book published by Books on Demand (2013)

The book investigates the stability of inverter driven power island grids, thus power grids, in which only renewable energy resourced feed their energy exclusively with voltage source inverters. Research ... [more ▼]

The book investigates the stability of inverter driven power island grids, thus power grids, in which only renewable energy resourced feed their energy exclusively with voltage source inverters. Research on stability of power grids has been conducted for decades. Due to the increased feed-in of renewable energy sources, in the future there will be the possibility to run parts of the power grids in island mode, e.g. during large grid blackouts, disconnected from the large interconnected European power grid. This rises some concerns about the stability of such purely inverter driven power grids, as inverter do not have stabilising rotating masses - and thus no inertia. Their controllers and actuators are by orders of magnitude faster than classic synchronous generator governors, which guarantee a degree frequency stability due to their large rotor inertia. If energy is fed in with inverters with much smaller time constants, only small amounts of energy suffice to introduce disturbances in the grid. The analysis presented in the book is not limited to specific grid structures or topologies and can be applied to grids of different voltage levels. The number of inverters in the analysed grid can be very high and arbitrary inverter models can be used for the analysis. Until now no generic, analytic model existed for this type of analysis of widely distributed grids with high numbers of generators. [less ▲]

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See detailStabilität wechselrichtergeführter Inselnetze
Jostock, Markus UL

Doctoral thesis (2013)

The PhD thesis develops a control model for island grids, where voltage source inverters with droop control adapt frequency and voltage amplitude and no classic rotating generators are present. The ... [more ▼]

The PhD thesis develops a control model for island grids, where voltage source inverters with droop control adapt frequency and voltage amplitude and no classic rotating generators are present. The presented linear, time invariant model is based on a state space control model of inverters and linearised power flow equations for the grid lines, the grid topology is captured in a node incidence matrix. Such a compound model for inverter driven island grids has not yet been developed to the author’s knowledge. Most existing models have been formulated for very small grids or inverter constellations. The presented control model allows to investigate grids with a very high number of inverters and with arbitrary grid structures and facilitates the calculation of the compound state space model and the MIMO transfer function matrix. No explicit re-formulation of the differential equations is necessary for different grid topologies, as this information is captured in the node incidence matrix. The thesis further investigates the stability of inverter driven island grids, i.e. power grids decoupled from the interconnected European power grid and in which most of the primary sources are renewable energy sources, injected via voltage source inverters. As inverters do not have rotating masses and thus no rotational inertia, they can be actuated much faster than classical synchronous generators. The effect of this property on the overall system stability is investigated in this work. The grid frequency is considered as a distributed parameter, where during transient phases, each grid node has its own valid phase angle speed. During transient phases, the inverters adjust injection frequency according to their droop, due to a local active power change. Until all inverters have adapted their injection frequencies, in each grid node a separate phase speed is valid. This behaviour could be verified with laboratory experiments and is integrated into the formal model with a graph theory approach. The power flow through grid lines due to voltage changes is a physical effect and practically immediate, while the adaptation of voltage amplitude and frequency through the inverters is a slower action depending on the inverter control algorithm. The separate modelling of inverters with their droop control on the one hand and the passive grid structure with the load flows on the other hand is justified by singular perturbation. An inverter driven island grid in droop mode can become unstable. Different parameters of the model have an influence on the system stability. A stability analysis is performed on simple grid structures as line, ring and lattice structure based on pole-zero plots. The influence of single parameters on the pole positions is investigated. Three pole regions appear for the compound model, their position and form is depending on the model parameters. For the model of the inverter two time constants are assumed: the smaller time constant Tm models the physically minimal possible delay in a PT1 element, while the larger time constant TWR can be adjusted arbitrarily by programming in an inverter. Both time constants determine more or less the position and form of one pole region each. If both time constants approach each other, conjugate complex poles appear. For large values of TWR the system can become unstable as poles move into the right half pane. This thesis reaches the following conclusions: Small rated power values of the inverters lead to potential instability as small power perturbations may cause large frequency changes. Since this effect is related to the value of the time constants, a stabilising effect can be observed when the time constants of the inverters are minimised, which enables the inverters to react more quickly to the frequency changes. An increasing number of inverters in the grid increases the system order and thus the number of poles. Under unfavourable conditions these poles may be badly damped and may develop into dominant complex conjugate poles. Similar effects can be observed for short grid lines: in systems with short grid connections, the inverters have a stronger electric coupling, bringing forward dominant pole pairs. The control of voltage and frequency by droops has been developed for in- ductive high voltage grids. In low voltage grids with ohmic line characteristics the droops lead to cross coupling between the voltage and frequency controller, causing an additional voltage reaction due to an active power change and an additional frequency reaction due to a reactive power change. This effect can be counteracted by the rotation of the measured P and Q coordinates in the droop control. The rotation angle is strongly related to the impedance angle at the point of connection of the inverter. Using P/Q rotation reduces the number of dominant pole pairs and fosters the integration of higher numbers of inverters without reaching the stability limits of the grid. Based on the laboratory results, a method for detection of the optimal P/Q rotation angle has been filed for patent. [less ▲]

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See detailStabilité de systèmes de murs en blocs de béton emboîtables sans joints en mortier
Agaajani, Shahriar; Waldmann, Danièle UL

Scientific Conference (2012)

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See detailStability Analysis of Power Networks under Cyber-Physical Attacks: an LPV-Descriptor Approach
Bezzaoucha, Souad UL; Voos, Holger UL

in Bezzaoucha, Souad (Ed.) International Conference on Control, Decision and Information Technologies (2019, April)

This paper proposes a unified and advanced framework for the modeling, stability study and stabilization of a Power Networks subject to an omniscient adversary (i.e. cyber-attack). From the system model ... [more ▼]

This paper proposes a unified and advanced framework for the modeling, stability study and stabilization of a Power Networks subject to an omniscient adversary (i.e. cyber-attack). From the system model developed in [24], based on the well-known sector non-linearity approach and the convex polytopic transformation, the attacked system (descriptor model) is re-written in a more convenient form (Linear Parameter Varying-LPV) with unmeasurable premise variables. The so-called Lyapunov-based methods are applied in order to study the stability and security problems despite the presence of cyber-attacks. The conditions will be given in terms of Linear- Bilinear Matrix Inequality LMI- BMI constraints. [less ▲]

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See detailStability and cooperative solution in stochastic games
Parilina, Elena; Tampieri, Alessandro UL

E-print/Working paper (2014)

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See detailStability comparison of two absolute gravimeters: optical versus atomic interferometers
Gillot, P.; Francis, Olivier UL; Landragin, A. et al

in Metrologia (2014), 51(5), 15-17

We report the direct comparison between the stabilities of two mobile absolute gravimeters of different technology: the LNE-SYRTE Cold Atom Gravimeter (CAG) and FG5X#216 of the Université du Luxembourg ... [more ▼]

We report the direct comparison between the stabilities of two mobile absolute gravimeters of different technology: the LNE-SYRTE Cold Atom Gravimeter (CAG) and FG5X#216 of the Université du Luxembourg. These instruments rely on two different principles of operation: atomic and optical interferometry. The comparison took place in the Walferdange Underground Laboratory for Geodynamics in Luxembourg, at the beginning of the last International Comparison of Absolute Gravimeters, ICAG-2013. We analyse a 2h10 duration common measurement, and find that the CAG shows better immunity with respect to changes in the level of vibration noise, as well as a slightly better short term stability. [less ▲]

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See detailStability Criteria for Clusterhead Selection in Mobile Ad-hoc Networks
Brust, Matthias R. UL; Andronache, Adrian UL; Rothkugel, Steffen UL et al

in Proceedings of International Conference on Wireless and Information Technology (CEWIT 2007) (2007)

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See detailStability of a spin-triplet nematic state near to a quantum critical point
Hannappel, Gregor; Pedder, Christopher UL; Kruger, Frank et al

in Physical Review. B: Condensed Matter and Materials Physics (2016), 93(23), 5105

We analyze a model of itinerant electrons interacting through a quadrupole density-density repulsion in three dimensions. At the mean field level, the interaction drives a continuous Pomeranchuk ... [more ▼]

We analyze a model of itinerant electrons interacting through a quadrupole density-density repulsion in three dimensions. At the mean field level, the interaction drives a continuous Pomeranchuk instability towards d-wave, spin-triplet nematic order, which simultaneously breaks the SU(2) spin-rotation and spatial rotational symmetries. This order results in spin antisymmetric, elliptical deformations of the Fermi surfaces of up and down spins. We show that the effects of quantum fluctuations are similar to those in metallic ferromagnets, rendering the nematic transition first-order at low temperatures. Using the fermionic quantum order-by-disorder approach to self-consistently calculate fluctuations around possible modulated states, we show that the first-order transition is pre-empted by the formation of a nematic state that is intertwined with a helical modulation in spin space. Such a state is closely related to d-wave bond density wave order in square-lattice systems. Moreover, we show that it may coexist with a modulated, p-wave superconducting state. [less ▲]

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See detailThe stability of academic self-concept profiles – a latent transition analysis
Franzen, Patrick UL; Arens, A. Katrin; Niepel, Christoph UL

Poster (2019, November 06)

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