A unified observability result for non-autonomous observation problems

A final-state observability result in the Banach space setting for non-autonomous observation problems is obtained that covers and extends all previously known results in this context, while providing a streamlined proof that follows the established Lebeau-Robbiano strategy.Comment: 9 page

Parametrically polarization shaped pulses guided via a hollow core photonic crystal fiber for coherent control

We present ultrafast polarization pulse shaping through a micro structured hollow core photonic crystal fiber. The pulses are shaped in pulse sequences in which the energy, distance, phases, and chirps as well as the state of polarization of each individual sub-pulse can be independently controlled. The application of these pulses for coherent control is demonstrated for feedback loop optimization of the multi-photon ionization of potassium dimers. In a second experiment, this process is investigated by shaper-assisted pump–probe spectroscopy which is likewise performed with pulses that are transmitted through the fiber. Both techniques reveal the excitation pathway including the dynamics in the participating electronic states and expose the relevance of the polarization. These methods will be valuable for endoscopic applications

Asymmetrische 1,4-Addition anspruchsvoller Nukleophile mit Hilfe von Olefinliganden auf Basis von Kohlenhydraten

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Experimentelle Untersuchungen zur Fluid-Struktur-Interaktion im Wet Compression Molding Prozess

Der Wet Compression Molding Prozess und dessen Prozesskette, zur großvolumigen Herstellung kontinuierlich faserverstärkter Verbundbauteile mit duromerer Matrix, ist seit 2013 in der Serienproduktion im Einsatz. Geringere Zykluszeiten lassen sich aufgrund des gleichzeitigen Drapierens des mit Matrix benetzten textilen Halbzeugs in Kombination mit der Parallelisierung der Prozessschritte Aushärtung und Matrixapplikation realisieren. Während des Kompressionsschritts findet, zusätzlich zur Umformung des initial getränkten textilen Halbzeugs, eine erzwungene Fluidausbreitung der Matrix sowohl über der, als auch durch die permeable Faserstruktur statt. In Abhängigkeit der Prozessparameter können sich Fluid-Struktur-Interaktionen ergeben, die zu Verschiebungen von Fasern, als auch zur Beeinflussung der Faserimprägnierung führen können. Beides beeinflusst die Bauteilqualität negativ. So führen bereits geringe Änderungen der Faserorientierung in Relation zur Lastrichtung zur Minderung der mechanischen Performance. Gleichzeitig kann eine inhomogene Tränkung die Häufigkeit von Lufteinschlüssen und somit Poren innerhalb der Bauteilstruktur erhöhen. Dementsprechend ist das Ziel dieser Arbeit die Identifizierung kritischer Prozessparameter während des Kompressionsschritts beim WCM Prozess. Des Weiteren sollen Mechanismen, die zur Entstehung fluidinduzierter Faserverschiebungen führen, evaluiert werden. Im weiteren Verlauf der Arbeit folgt eine vergleichende Betrachtung der Fluidausbreitung beim WCM Prozess mit und ohne simultane Umformung des textilen Halbzeugs. Hierzu wird die Fluidausbreitung mit Hilfe eines transparenten Werkzeugs anhand einer generischen Geometrie auf Prüfstandebene visualisiert. Zur weiteren Analyse der Formfüllung findet abschließend eine makroskopische Betrachtung der Fluidausbreitung mit und ohne simultaner Umformung anhand eines komplexen generischen Demonstrators statt

Towards numerical prediction of flow-induced fiber displacements during wet compression molding (WCM)

Wet compression molding (WCM) provides large-scale production potential for continuous fiber-reinforced structural components due to simultaneous infiltration and draping during molding. Due to thickness-dominated infiltration of the laminate, comparatively low cavity pressures are sufficient – a considerable economic advantage. Experimental and numerical investigations prove strong mutual dependencies between the physical mechanisms, especially between resin flow (mold filling) and textile forming (draping), similar to other liquid molding techniques (LCM). Although these dependencies provide significant benefits such as improved contact, draping and infiltration capabilities, they may also lead to adverse effects such as flow-induced fiber displacement. To support WCM process and part development, process simulation requires a fully coupled approach including the capability to predict critical process effects. This work aims to demonstrate the suitability of a macroscopic, fully coupled, three-dimensional process simulation approach, to predict the process behavior during WCM, including flow-induced fiber displacements. The developed fluid model is superimposed to a suitable 3D forming model, which accounts for the deformation mechanisms including non-linear transverse compaction behavior. A strong Fluid-Structure-Interaction (FSI) enforced by Terzaghi’s law is applied to assess flow-induced fiber displacements during WCM within a porous UD-NCF stack in a homogenized manner. Accordingly, resulting local deformations are considered within the pressure field. All constitutive equations are formulated with respect to fiber deformation under finite strains. Results of a parametric study underline the relevance of contact conditions within the dry and infiltrated stack. The numerically predicted results are benchmarked and verified using both own and available experimental results from literature

Simultaneous phase, amplitude, and polarization control of femtosecond laser pulses

We present a serial pulse shaper design which allows us to shape the phase, amplitude, and polarization of fs laser pulses independently and simultaneously. The capabilities of this setup are demonstrated by implementing a method for generating parametrically tailored laser pulses. This method is applied on the ionization of NaK molecules by feedback loop optimization, employing a temporal sub pulse encoding. Moreover, we introduce and characterize a further development of this common path pulse shaper scheme for full control of all light field parameters

A 3D process simulation model for wet compression moulding

Wet Compression Moulding (WCM) provides large-scale production potential for continuously fibre-reinforced structural components due to simultaneous infiltration and draping during moulding. Due to thickness-dominated infiltration of the laminate, comparatively low cavity pressures are sufficient - a considerable economical advantage. Similar to other Liquid Compression Moulding (LCM) processes, forming and infiltration strongly interact during process. However, the degree of forming is much higher in WCM, which disqualifies a sequential modelling approach. This is demonstrated in this work via experimental characterisation of the interaction between compaction and permeability of a woven fabric and by trials with a transparent double dome geometry, which facilitates an in situ visualization of fluid progression during moulding. In this light, and in contrast to existing form filling approaches, a forming-inspired, three-dimensional process simulation approach is presented containing two fully-coupled macroscopic forming and fluid-submodels. The combined model is successfully benchmarked using experimental double dome trials with transparent tooling