A comparison between different propagative schemes for the simulation of tapered step index slab waveguides

The performance and accuracy of a number of propagative algorithms are compared for the simulation of tapered high contrast step index slab waveguides. The considered methods include paraxial as well as nonparaxial formulations of optical field propagation. In particular attention is paid to the validity of the paraxial approximation. To test the internal consistency of the various methods the property of reciprocity is verified and it is shown that for the paraxial algorithms the reciprocity can only be fulfilled if the paraxial approximation of the power flux expression using the Poynting vector is considered. Finally, modeling results are compared with measured fiber coupling losses for an experimentally realized taper structure

Synthese eines Polymerlinkersystems für T-Zellaktivierung

Abweichender Titel nach Übersetzung der Verfasserin/des VerfassersKurzfassung Im Bereich der biomedizinischen Anwendungen, wurde die Herstellung und das Design von Polymer-brushes in letzter Zeit sehr attraktiv, da diese, spezielle Fähigkeiten und eine Vielzahl an wichtigen architektonischen Eigenschaften kontrollieren können. Polymer-brushes werden verwendet um spezielle Biointerfaces und Anwendungen im Nanotechnologiebereich zu realisieren. Im Zuge dieser Arbeit wurde eine Strategie für ein Polymer-Linker-System auf Glassubstraten erstellt, um T-Zellen Aktivierung zu ermöglichen. Endgruppen-funktionalisierte Polymer-brushes sollten eine mögliche Kupplung mit Biomolekülen ermöglichen. Für die Implementierung eines solchen Biointerface-Systems wurde als Methode die sogenannte oberflächeninduzierte Reversible Additions-Fragmentierungs Kettenübertragungs (RAFT) Polymerisation gewählt, da diese Methode bestimmte Vorteile mit sich bringt, wie milde Polymerisationsbedingungen, Abwesenheit von toxischen Katalysatoren, ein breites Spektrum an möglichen Endgruppen-Modifikationen, einheitliche Kettenlängen und definierte Molekulargewichte. Als biokompatible Monomere in diesem System wurden N-Acryloylmorpholin (NAM) und Methoxypropylacrylamid (MPAA) verwendet. Kinetische Studien wurden mit diesen Monomeren und den RAFT Reagenzien 4-Cyano-4-[(dodecylsulfanylthiocarbonyl)-sulfanyl]pentansäure (CDTPA) und 2-(Dodecylthiocarbonothioylthio)-2-methyl-propionsäure (DDMAT) durchgeführt, welche im ersten Schritt gemäß der Literatur synthetisiert wurden. Beide RAFT Reagenzien zeigten hohe Monomerumsätze in kurzen Polymerisationszeiten. Die hergestellten Polymere polyNAM und polyMPAA wurden anschließend auf ihre Morphologie in wässriger Umgebung mittels Lichtstreumethoden und Kleinwinkelröntgenstreuung untersucht, um ihre Anordnung bei Verwendung als Polymer-brushes vorherzusagen. Es wurde herausgefunden, dass beide Polymere fadenähnliche Aggregate in Wasser und in PBS Puffer Lösung formten. Studien zur Endgruppen-Modifizierung von polyNAM und polyMPAA wurden durchgeführt, mittels Aminolyse und Radikal-induzierter Endgruppen-Modifizierung. Es wurde herausgefunden, dass die radikalisch induzierte Endgruppen-Modifizierung mit 4,4'-Azobis(4-cyanovaleriansäure) mit guten Umsätzen funktionierte und leicht durchzuführen war. Für das Pfropfpolymerisieren auf der Glasoberfläche wurden weitere Studien durchgeführt. Zwei Methoden wurden getestet: Die erste war die Immobilisierung von Aminopropyltriethoxysilan (APTES) auf der Glasoberfläche mit anschließender Kupplung zu einem RAFT Reagenz, die zweite war die Immobilisierung eines mit APTES gekuppelten RAFT Reagenzes auf die Oberfläche. Diese Modifizierungen wurden mittels Kontaktwinkel (CA) Messungen, totaler interner Reflexion Fluoreszenz Mikroskopie (TIRFM), Ellipsometrie und Röntgen Photoelektronen Spektroskopie charakterisiert. Mit den Erkenntnissen aus diesen Funktionalisierungsversuchen kann in Zukunft ein geeignetes Polymer-brush System realisiert werden.Abstract In the field of biomedical application, the generation and design of polymer brushes became very attractive due to their ability to control a number of important architectural features1 for the creation of particular biointerfaces2-4 and applications in nanotechnologies4-6. In the course of this thesis, a strategy for a polymer linker system on glass substrates for T-cell activation was established, in form of end-group functionalized polymers designed for the coupling to biomolecules. For the implementation of this polymer brush system, surface-induced reversible addition fragmentation chain transfer (RAFT) polymerization was selected, delivering gentle polymerization conditions, absence of toxic catalysts, a variety of possible end-group modifications, uniform chain lengths and defined molecular weights. Acryloylmorpholine (NAM)7 and methoxypropylacrylamide (MPAA)8 were chosen as biocompatible monomers. Kinetic studies were performed on the RAFT polymerization of these monomers using 4-cyano-4-(((dodecylthio) carbonothioyl)thio)pentanoic acid (CDTPA) and 2-(((dodecylthio)carbonothioyl)thio)-2-methylpropanoic acid (DDMAT) as RAFT reagents, which were synthesized in the first step according to literature. Both RAFT reagents showed high monomer conversions within short polymerization times. The generated polymers pNAM and pMPAA were investigated on their morphology in aqueous environment with light scattering methods and small angle X-ray scattering, to predict their arrangement in a polymer brush system. It was found out that both polymers formed worm-like shaped aggregates in water and PBS buffer solution. Studies on end-group modification of pNAM and pMPAA polymers were performed by aminolysis and radical induced end-group formation. It proved, that radical induced end-group formation with 4,4'-azobis(4-cyanovaleric acid) performed in good yields and was easy to establish. For the grafting of the polymers from glass substrates by surface immobilized RAFT reagents, further studies were performed. Two approaches were tested: First, to immobilize aminopropyl triethoxysilane (APTES) on the glass surface and then couple the RAFT reagent onto it, second, to immobilize APTES modified RAFT reagents to the surface. These modifications were monitored by contact angle (CA) measurement, total internal reflection fluorescence microscopy (TIRFM), ellipsometry and X-ray photoelectron spectroscopy (XPS). With knowledge gained from these functionalization experiments, a future system for surface induced RAFT polymerization of a suitable polymer brush system will be possible.16

Introduction to micro- and nanooptics

This first textbook on both micro- and nanooptics introduces readers to the technological development, physical background and key areas.The opening chapters on the physics of light are complemented by chapters on refractive and diffractive optical elements. The internationally renowned authors present different methods of lithographic and nonlithographic fabrication of microoptics and introduce the characterization and testing of microoptics.The second part of the book is dedicated to optical microsystems and MEMS, optical waveguide structures and optical nanostructures, including ph

Energieeffizienz in der zerspanenden Industrie

Im Rahmen des Projekts ETA-Transfer werden bei neun Industriepartnern Produktionsanlagen sowie die entsprechenden Energieversorgungsnetze hinsichtlich energetischer Optimierungspotenziale untersucht. Hierzu wurden unter anderem Messkampagnen zum Erfassen elektrischer und thermischer Leistungsaufnahmen durchgeführt. Um ein Benchmarking zu erlauben, wurde eine Datenbank aufgesetzt, welche einen Vergleich auf verschiedenen Ebenen mittels Key Performance Indicators ermöglicht

High-velocity streams of dust originating from Saturn

High-velocity submicrometre-sized dust particles expelled from the jovian system have been identified by dust detectors on board several spacecraft. On the basis of periodicities in the dust impact rate, Jupiter's moon Io was found to be the dominant source of the streams. The grains become positively charged within the plasma environment of Jupiter's magnetosphere, and gain energy from its co-rotational electric field. Outside the magnetosphere, the dynamics of the grains are governed by the interaction with the interplanetary magnetic field that eventually forms the streams. A similar process was suggested for Saturn. Here we report the discovery by the Cassini spacecraft of bursts of high-velocity dust particles ( 100 km s-1) within approx70 million kilometres of Saturn. Most of the particles detected at large distances appear to originate from the outskirts of Saturn's outermost main ring. All bursts of dust impacts detected within 150 Saturn radii are characterized by impact directions markedly different from those measured between the bursts, and they clearly coincide with the spacecraft's traversals through streams of compressed solar wind

Composition of Saturnian Stream Particles

During Cassini's approach to Saturn, the Cosmic Dust Analyser (CDA) discovered streams of tiny (less than 20 nanometers) high-velocity (100 kilometers per second) dust particles escaping from the saturnian system. A fraction of these impactors originated from the outskirts of Saturn's dense A ring. The CDA time-of-flight mass spectrometer recorded 584 mass spectra from the stream particles. The particles consist predominantly of oxygen, silicon, and iron, with some evidence of water ice, ammonium, and perhaps carbon. The stream particles primarily consist of silicate materials, and this implies that the particles are impurities from the icy ring material rather than the ice particles themselves

Interaction of the solar wind and stream particles, results from the Cassini dust detector

The stream particles are nanometer-size dust particles ejected from the jovian and the saturnian systems with velocities greater than 100kms -1. Due to their small size, stream particles are more sensitive to the electromagnetic force than to gravity. It has been shown by the simulations that the stream - particle dynamics in interplanetary space should be dominated by the interplanetary magnetic field (IMF) [15]. Based on the measurements by the dust detector on board the Cassini spacecraft, we found that the detection patterns of the stream particles are well correlated with the IMF structures. As the spacecraft crosses the compression regions of the Co - rotation Interaction Regions (CIRs), not only the directionality of the impacts changes with the field direction, but also the impact signal and rate vary with an increase of field strength. By understanding the interaction of stream particles and the solar wind, the data provide important insight to the formation environments of the stream particles and is an unique opportunity to study the dust-moon-magnetosphere system of Jupiter and Saturn.</p