Energy-level statistics of interacting trapped bosons

It is a well-established fact that statistical properties of energy-level spectra are the most efficient tool to characterize nonintegrable quantum systems. The statistical behavior of different systems such as complex atoms, atomic nuclei, two-dimensional Hamiltonians, quantum billiards, and noninteracting many bosons has been studied. The study of statistical properties and spectral fluctuations in interacting many-boson systems has developed interest in this direction. We are especially interested in weakly interacting trapped bosons in the context of Bose-Einstein condensation (BEC) as the energy spectrum shows a transition from a collective nature to a single-particle nature with an increase in the number of levels. However this has received less attention as it is believed that the system may exhibit Poisson-like fluctuations due to the existence of an external harmonic trap. Here we compute numerically the energy levels of the zero-temperature many-boson systems which are weakly interacting through the van der Waals potential and are confined in the three-dimensional harmonic potential. We study the nearest-neighbor spacing distribution and the spectral rigidity by unfolding the spectrum. It is found that an increase in the number of energy levels for repulsive BEC induces a transition from a Wigner-like form displaying level repulsion to the Poisson distribution for P(s). It does not follow the Gaussian orthogonal ensemble prediction. For repulsive interaction, the lower levels are correlated and manifest level-repulsion. For intermediate levels P(s) shows mixed statistics, which clearly signifies the existence of two energy scales: external trap and interatomic interaction, whereas for very high levels the trapping potential dominates, generating a Poisson distribution. Comparison with mean-field results for lower levels are also presented. For attractive BEC near the critical point we observe the Shnirelman-like peak near s = 0, which signifies the presence of a large number of quasidegenerate states.

Properties of a new poly-ether-glycol copolymer.

Triblock copolymers are made of monomer segments, being the central part usually hydrophobic and the outer parts hydrophilic. By varying sizes, molecular weights and monomer types of the segments one obtains different final molecules, with different physico-chemical properties, which are directly related to the performance of the final product. Looking for new products to be used, among other possibilities, in biological applications, a new polymer (Figure 1) was synthesized by the Dow Chemical and studied by Size Exclusion Chromatography, Fourier Transformed Infrared Spectrometry, Small-angle X-ray Scattering (SAXS) and its cloud point was determined by measuring light transmittance. The studies showed low molecular polydispersivety, but different polarities in the macromolecules fractions. Due to the low solubility of Diol in water, a mixture of water/butyl diglycol was used as solvent. An extensive analysis by SAXS was performed for concentrations from 50 wt% to 80 wt% of Diol in solution. Small concentrations showed very low signal to noise ratio, making it impossible to be analysed. The scattering intensity including the form factor of polydisperse non-homogeneous spheres, and the structure factor of interacting hard spheres was fitted to the curves. As the polymer concentration is high, the fitting of form factors of direct and reverse micelles were compared. The results for direct micelles were better up to 80 wt%, whereas at 90 wt% and 95 wt% the curves were better fitted by reverse micelles. It might seem odd that direct micelles are present up to such high concentrations, but it might have been caused by the presence of butyl diglycol, which increases the solubility of Diol in water. The inner and outer radius of the micelles, electron density distribution, and interaction radius of the micelles were obtained. The polydispersivety increases with Diol concentration. Besides, the interaction radius increases with solvent concentration, even when reversed micelles are present. In the last case, accompanied by an increase of inner radius (water content), as there are fewer Diol molecules to involve the water nuclei, which become larger, further apart, and in less number.

Representations as tools of appropriation, creating meaning through activities.

Based on some constructs of the Activity Theory (Leontiev, 1978), we point to the need to develop activities that reveal the meaning of representations. We examine use of representations in teaching and propose some suggestions. Shaaron Ainsworth (1999) asserted that, in order to learn from engaging with multiple representations of scientific concepts, students need to be able to (a) understand the codes and signifiers in a representation, (b) understand the links between the representation and the target concept or process, (c) translate key features of the concept across representations and (d) know which features to emphasize in designing their own representations.

Metodi numerici per lo studio di centri di lavoro ad alta velocità

A Machining Centre is nowadays a complex mechanical, electronic, electrical system that needs integrated design capabilities which very often require a high time-consuming effort. Numerical techniques for designing and dimensioning the machine structure and components usually requires different knowledge according to the system that have to be designed. This Ph. D Thesis is related about the efforts of the Authors to develop a system that allows to perform the complete project of a new machine optimized in its dynamic behaviour. An integration of the different systems developed, each of which respond to specific necessities of designer, is here presented. In particular a dynamic analysis system, based on a lumped mass approach, that rapidly allows to setup the drives of the machine and an Integrated Dynamic Simulation System, based on a FEM approach, that permit a dynamic optimization, are shown. A multilevel Data Base, and an operator interface module provide to complete the designing platform. The proposed approach represents a significant step toward the virtual machining for the prediction of the quality of the worked surface.

Acerca del concepto de educación

Grupo de Investigación en Educación Social (GIES). Línea: Educación de Adultos y Aprendizaje a lo Largo de la Vida (Adult Education and Lifelong Learning)

La educación permanente

Grupo de Investigación en Educación Social (GIES. Línea: Educación de Adultos y Aprendizaje a lo Largo de la Vida (Adult Education and Lifelong Learning)

Expressiveness of Concurrent Languages

The aim of this thesis is to go through different approaches for proving expressiveness properties in several concurrent languages. We analyse four different calculi exploiting for each one a different technique. We begin with the analysis of a synchronous language, we explore the expressiveness of a fragment of CCS! (a variant of Milner's CCS where replication is considered instead of recursion) w.r.t. the existence of faithful encodings (i.e. encodings that respect the behaviour of the encoded model without introducing unnecessary computations) of models of computability strictly less expressive than Turing Machines. Namely, grammars of types 1,2 and 3 in the Chomsky Hierarchy. We then move to asynchronous languages and we study full abstraction for two Linda-like languages. Linda can be considered as the asynchronous version of CCS plus a shared memory (a multiset of elements) that is used for storing messages. After having defined a denotational semantics based on traces, we obtain fully abstract semantics for both languages by using suitable abstractions in order to identify different traces which do not correspond to different behaviours. Since the ability of one of the two variants considered of recognising multiple occurrences of messages in the store (which accounts for an increase of expressiveness) reflects in a less complex abstraction, we then study other languages where multiplicity plays a fundamental role. We consider the language CHR (Constraint Handling Rules) a language which uses multi-headed (guarded) rules. We prove that multiple heads augment the expressive power of the language. Indeed we show that if we restrict to rules where the head contains at most n atoms we could generate a hierarchy of languages with increasing expressiveness (i.e. the CHR language allowing at most n atoms in the heads is more expressive than the language allowing at most m atoms, with m

Centrifuge modeling of earth-reinforced retaining walls

Object of this thesis has been centrifuge modelling of earth reinforced retaining walls with modular blocks facing in order to investigate on the influence of design parameters, such as length and vertical spacing of reinforcement, on the behaviour of the structure. In order to demonstrate, 11 models were tested, each one with different length of reinforcement or spacing. Each model was constructed and then placed in the centrifuge in order to artificially raise gravitational acceleration up to 35 g, reproducing the soil behaviour of a 5 metre high wall. Vertical and horizontal displacements were recorded by means of a special device which enabled tracking of deformations in the structure along its longitudinal cross section, essentially drawing its deformed shape. As expected, results confirmed reinforcement parameters to be the governing factor in the behaviour of earth reinforced structures since increase in length and spacing improved structural stability. However, the influence of the length was found out to be the leading parameter, reducing facial deformations up to five times, and the spacing playing an important role especially in unstable configurations. When failure occurred, failure surface was characterised by the same shape (circular) and depth, regardless of the reinforcement configuration. Furthermore, results confirmed the over-conservatism of codes, since models with reinforcement layers 0.4H long showed almost negligible deformations. Although the experiments performed were consistent and yielded replicable results, further numerical modelling may allow investigation on other issues, such as the influence of the reinforcement stiffness, facing stiffness and varying backfills.

New synthetic strategies to tethered bilayer lipid membranes

Tethered bilayer lipid membranes provide an efficient, stable and versatile platform for the investigation of integrated membrane proteins. However, the incorporation of large proteins, as well as of proteins with a large submembrane part is still a very critical issue and therefore, further optimisation of the system is necessary. The central element of a tBLM is a lipid bilayer. Its proximal leaflet is, at least to some extend, covalently attached to a solid support via a spacer group. The anchor lipid consists of three distinct parts, a lipid headgroup, a spacer group and an anchor. All parts together influence the final bilayer properties. In the frame of this work, the synthesis of new thiolipids for tBLMs on gold has been investigated. The aim was to obtain molecules with longer spacers in order to increase the submembrane space. The systems obtained have been characterized using SPR and EIS. The results obtained during this study are multiple. First, the synthesis of a previously synthesized architecture was successfully scaled up in an industrial lab using a new synthetic approach. The synthesis of large amounts is now feasible. Then, the synthesis of the new thiolipids was carried out taking into account the following requirements: the increase of the submembrane space by having longer ethyleneglycol spacers, the attachment of the molecules to a gold substrate via a thiol bond, and the tunability of the lateral mobility by changing the lipid headgroup. Three different synthetic strategies have been investigated. The polymeric approach did not prove to be successful, merely because of the broad molecular weight distribution. The synthesis of heterofunctionally protected oligoethyleneglycols allowed to obtain ethyleneglycol moieties with 6 and 8 units, but the tedious purification steps gave very low yields. Finally, the block by block synthesis using ethyleneglycol precursors proved to be an efficient and fast method to synthesize the target molecules. Indeed, these were obtained with very high yields, and the separation was very efficient. A whole family of new compounds was obtained, having 6, 8 and 14 ethyleneglycol units and with mono- or diphytanyl lipid headgroups. This new pathway is a very promising synthetic strategy that can be used further in the development of new compounds of the tether system. The formation of bilayers was investigated for the different thiolipids mainly by using EIS. The electrical properties of a bilayer define the quality of the membrane and allow the study of the functionality of proteins embedded in such a system. Despite multiple trials to improve the system using self assembly, Langmuir Blodgett transfer, and detergent mixed vesicles, the new polymer thiolipids did not show as high electrical properties as tBLMs reported in the literature. Nevertheless, it was possible to show that a bilayer could be obtained for the different spacer lengths. These bilayers could be formed using self assembly for the first monolayer, and two different methods for bilayer formation, namely vesicle fusion and solvent exchange. We could furthermore show functional incorporation of the ion carrier valinomycin: the selective transport of K+ ions could be demonstrated. For DPHL, it was even possible to show the functional incorporation of the ion channel gramicidin. The influence of the spacer length is translated into an increase of the spacer capacitance, which could correspond to an increase in the capacity of charge accumulation in the submembrane space. The different systems need to be further optimised to improve the electrical properties of the bilayer. Moreover, the incorporation of larger proteins, and proteins bearing submembrane parts needs to be investigated.

Hsp90 characterization and inhibition: a multi-methodological study

Many physiological and pathological processes are mediated by the activity of proteins assembled in homo and/or hetero-oligomers. The correct recognition and association of these proteins into a functional complex is a key step determining the fate of the whole pathway. This has led to an increasing interest in selecting molecules able to modulate/inhibit these protein-protein interactions. In particular, our research was focused on Heat Shock Protein 90 (Hsp90), responsible for the activation and maturation and disposition of many client proteins [1], [2] [3]. Circular Dichroism (CD) spectroscopy, Surface Plasmon Resonance (SPR) and Affinity Capillary Electrophoresis (ACE) were used to characterize the Hsp90 target and, furthermore, its inhibition process via C-terminal domain driven by the small molecule Coumermycin A1. Circular Dichroism was used as powerful technique to characterize Hsp90 and its co-chaperone Hop in solution for secondary structure content, stability to different pHs, temperatures and solvents. Furthermore, CD was used to characterize ATP but, unfortunately, we were not able to monitor an interaction between ATP and Hsp90. The utility of SPR technology, on the other hand, arises from the possibility of immobilizing the protein on a chip through its N-terminal domain to later study the interaction with small molecules able to disrupt the Hsp90 dimerization on the C-terminal domain. The protein was attached on SPR chip using the “amine coupling” chemistry so that the C-terminal domain was free to interact with Coumermycin A1. The goal of the experiment was achieved by testing a range of concentrations of the small molecule Coumermycin A1. Despite to the large difference in the molecular weight of the protein (90KDa) and the drug (1110.08 Da), we were able to calculate the affinity constant of the interaction that was found to be 11.2 µm. In order to confirm the binding constant calculated for the Hsp90 on the chip, we decided to use Capillary Electrophoresis to test the Coumermycin binding to Hsp90. First, this technique was conveniently used to characterize the Hsp90 sample in terms of composition and purity. The experimental conditions were settled on two different systems, the bared fused silica and the PVA-coated capillary. We were able to characterize the Hsp90 sample in both systems. Furthermore, we employed an application of capillary electrophoresis, the Affinity Capillary Electrophoresis (ACE), to measure and confirm the binding constant calculated for Coumermycin on Optical Biosensor. We found a KD = 19.45 µM. This result compares favorably with the KD previously obtained on biosensor. This is a promising result for the use of our novel approach to screen new potential inhibitors of Hsp90 C-terminal domain.

A Design Methodology for Computer Security Testing

The field of "computer security" is often considered something in between Art and Science. This is partly due to the lack of widely agreed and standardized methodologies to evaluate the degree of the security of a system. This dissertation intends to contribute to this area by investigating the most common security testing strategies applied nowadays and by proposing an enhanced methodology that may be effectively applied to different threat scenarios with the same degree of effectiveness. Security testing methodologies are the first step towards standardized security evaluation processes and understanding of how the security threats evolve over time. This dissertation analyzes some of the most used identifying differences and commonalities, useful to compare them and assess their quality. The dissertation then proposes a new enhanced methodology built by keeping the best of every analyzed methodology. The designed methodology is tested over different systems with very effective results, which is the main evidence that it could really be applied in practical cases. Most of the dissertation discusses and proves how the presented testing methodology could be applied to such different systems and even to evade security measures by inverting goals and scopes. Real cases are often hard to find in methodology' documents, in contrary this dissertation wants to show real and practical cases offering technical details about how to apply it. Electronic voting systems are the first field test considered, and Pvote and Scantegrity are the two tested electronic voting systems. The usability and effectiveness of the designed methodology for electronic voting systems is proved thanks to this field cases analysis. Furthermore reputation and anti virus engines have also be analyzed with similar results. The dissertation concludes by presenting some general guidelines to build a coordination-based approach of electronic voting systems to improve the security without decreasing the system modularity.

Applicazione della Metodologia LCA(Life Cycle Assesment): La sostenibilità ambientale di Impianti a Biomassa della regione Emilia Romagna

Lo studio che la candidata ha elaborato nel progetto del Dottorato di ricerca si inserisce nel complesso percorso di soluzione del problema energetico che coinvolge necessariamente diverse variabili: economiche, tecniche, politiche e sociali L’obiettivo è di esprimere una valutazione in merito alla concreta “convenienza” dello sfruttamento delle risorse rinnovabili. Il percorso scelto è stato quello di analizzare alcuni impianti di sfruttamento, studiare il loro impatto sull’ambiente ed infine metterli a confronto. Questo ha consentito di trovare elementi oggettivi da poter valutare. In particolare la candidata ha approfondito il tema dello sfruttamento delle risorse “biomasse” analizzando nel dettaglio alcuni impianti in essere nel Territorio della Regione Emilia-Romagna: impianti a micro filiera, filiera corta e filiera lunga. Con la collaborazione di Arpa Emilia-Romagna, Centro CISA e dell’Associazione Prof. Ciancabilla, è stata fatta una scelta degli impianti da analizzare: a micro filiera: impianto a cippato di Castel d’Aiano, a filiera corta: impianto a biogas da biomassa agricola “Mengoli” di Castenaso, a filiera lunga: impianto a biomasse solide “Tampieri Energie” di Faenza. Per quanto riguarda la metodologia di studio utilizzata è stato effettuato uno studio di Life Cycle Assesment (LCA) considerando il ciclo di vita degli impianti. Tramite l’utilizzo del software “SimaPro 6.0” si sono ottenuti i risultati relativi alle categorie di impatto degli impianti considerando i metodi “Eco Indicator 99” ed “Edip Umip 96”. Il confronto fra i risultati dell’analisi dei diversi impianti non ha portato a conclusioni di carattere generale, ma ad approfondite valutazioni specifiche per ogni impianto analizzato, considerata la molteplicità delle variabili di ogni realtà, sia per quanto riguarda la dimensione/scala (microfiliera, filiera corta e filiera lunga) che per quanto riguarda le biomasse utilizzate.

Bewertungsportale im Internet – Meinungsfreiheit versus Datenschutz und Haftungsfragen der Portalbetreiber

Die vorliegende Arbeit beschäftigt sich mit rechtlichen Fragestellungen rund um Bewertungs-portale im Internet. Zentrale Themen der Arbeit sind dabei die Zulässigkeit der Veröffentlichung der von den Nutzern abgegebenen Bewertungen vor dem Hintergrund möglicherweise entgegenstehender datenschutzrechtlicher Bestimmungen und der Persönlichkeitsrechte der Betroffenen. Des weiteren wird der Rechtsschutz der Betroffenen erörtert und in diesem Zusammenhang die haftungsrechtlichen Risiken der Forenbetreiber untersucht. Gegenstand der Arbeit sind dabei sowohl Online-Marktplätze wie eBay, auf denen sowohl der Bewertende als auch der Bewertete registriert und mit dem Bewertungsverfahren grundsätz-lich einverstanden sind (geschlossene Portale), als auch Portale, auf denen – oftmals unter einem Pseudonym und ohne vorherige Anmeldung – eine freie Bewertungsabgabe, zu Pro-dukteigenschaften, Dienstleistungen bis hinzu Persönlichkeitsmerkmalen des Bewerteten möglich ist (offene Portale). Einleitung und Erster Teil Nach einer Einleitung und Einführung in die Problematik werden im ersten Teil die verschie-denen Arten der Bewertungsportale kurz vorgestellt. Die Arbeit unterscheidet dabei zwischen so genannten geschlossenen Portalen (transaktionsbegleitende Portale wie eBay oder Ama-zon) auf der einen Seite und offenen Portalen (Produktbewertungsportale, Hotelbewertungs-portale und Dienstleistungsbewertungsportale) auf der anderen Seite. Zweiter Teil Im zweiten Teil geht die Arbeit der Frage nach, ob die Veröffentlichung der durch die Nutzer abgegebenen Bewertungen auf den offenen Portalen überhaupt erlaubt ist oder ob hier mögli-cherweise das Persönlichkeitsrecht der Betroffenen und hier insbesondere das Recht auf in-formationelle Selbstbestimmung in Form der datenschutzrechtlichen Bestimmungen die freie Bewertungsabgabe unzulässig werden lässt. Untersucht werden in diesem Zusammenhang im einzelnen Löschungs- bzw. Beseitigungsan-sprüche der Betroffenen aus § 35 Abs. 2 Satz 2 Nr. 1 BDSG bzw. §§ 1004 i. V. m. 823 Abs. 1 BGB (allgemeines Persönlichkeitsrecht). Die Arbeit kommt in datenschutzrechtlicher Hinsicht zu dem Schluss, dass die Bewertungen personenbezogene Daten darstellen, die den datenschutzrechtlichen Bestimmungen unterlie-gen und eine Veröffentlichung der Bewertungen nach dem im deutschen Recht geltenden da-tenschutzrechtlichen Erlaubnisvorbehalt grundsätzlich nicht in Betracht kommt. Vor dem Hintergrund dieser den tatsächlichen Gegebenheiten und Interessenlagen im Internet nicht mehr gerecht werdenden Gesetzeslage diskutiert der Autor sodann die Frage, ob die datenschutzrechtlichen Bestimmungen in diesen Fällen eine Einschränkung durch die grund-gesetzlich garantierten Informationsfreiheiten erfahren müssen. Nach einer ausführlichen Diskussion der Rechtslage, in der auf die Besonderheiten der ein-zelnen Portale eingegangen wird, kommt die Arbeit zu dem Schluss, dass die Frage der Zuläs-sigkeit der Veröffentlichung der Bewertungen von einer Interessenabwägung im Einzelfall abhängt. Als Grundsatz kann jedoch gelten: Ist die bewertete Tätigkeit oder Person in Bezug auf die bewertete Eigenschaft ohnehin einer breiten Öffentlichkeit zugänglich, erscheint eine Veröffentlichung der Daten nicht bedenklich. Dagegen wird man einen Löschungs- bzw. Be-seitigungsanspruch bejahen müssen für die Bewertungen, die Tätigkeiten oder Eigenschaften des Bewerteten, die in keinem Zusammenhang mit ihm als öffentlicher Person stehen, betref-fen. Anschließend geht die Arbeit auf die Persönlichkeitsrechte der Betroffenen und der sich hier-aus ergebenden Beseitigungs- und Unterlassungsansprüchen gemäß der §§ 1004 Abs. 1, 823 Abs. 1 BGB ein, verneint jedoch wegen dem Vorrang der spezialgesetzlichen Bestimmungen aus dem Bundesdatenschutzgesetz letztlich eine Anwendbarkeit der Anspruchsgrundlagen. Schließlich wird in diesem Teil noch kurz auf die Zulässigkeit der Bewertung juristischer Per-sonen eingegangen, die im Grundsatz bejaht wird. Dritter Teil Sofern der zweite Teil der Arbeit zu dem Schluss kommt, dass die Veröffentlichung der Be-wertungen zulässig ist, stellt sich im dritten Teil die Frage, welche Möglichkeiten das Recht dem Bewerteten bietet, gegen negative Bewertungen vorzugehen. Untersucht werden, dabei datenschutzrechtliche, deliktsrechtliche, vertragliche und wettbe-werbsrechtliche Ansprüche. Ein Schwerpunkt dieses Teils liegt in der Darstellung der aktuellen Rechtsprechung zu der Frage wann eine Bewertung eine Tatsachenbehauptung bzw. ein Werturteil darstellt und den sich hieraus ergebenden unterschiedlichen Konsequenzen für den Unterlassungsanspruch des Betroffenen. Diejenigen Bewertungen, die eine Meinungsäußerung darstellen, unterstehen dem starken Schutz der Meinungsäußerungsfreiheit. Grenze der Zulässigkeit sind hier im wesentlichen nur die Schmähkritik und Beleidigung. An Tatsachenbehautpungen dagegen sind schärfere Maßstäbe anzulegen. In diesem Zusammenhang wird der Frage nachgegangen, ob vertragliche Beziehungen zwischen den Beteiligten (Bewertenden, Bewertete und Portalbetreiber) die Meinungsäußerungsfreiheit einschränkt, was jedenfalls für die geschlossenen Portale bejaht wird. Vierter Teil Der vierte Teil der Arbeit beschäftigt sich mit den „Zu-gut-Bewertungen“. Es geht dabei um wettbewerbsrechtliche Ansprüche im Falle verdeckter Eigenbewertungen. Solche Eigenbewertungen, die unter dem Deckmantel der Pseudonymität als Werbemittel zur Imageverbesserung in entsprechenden Bewertungsportale verbreitet werden ohne den wahren Autor erkennen zu lassen, sind in wettbewerbsrechtlicher Hinsicht grundsätzlich unzulässig. Fünfter Teil Im letzten Teil der Arbeit wird schließlich der Frage nach der Verantwortlichkeit der Portal-betreiber für rechtswidrige Bewertungen nachgegangen. Zunächst wird die Feststellung getroffen, dass es sich bei den von den Nutzern abgegebenen Bewertungen um fremde Inhalte handelt und somit die Haftungsprivilegierungen der § 11 Abs. 1 TDG, § 9 Abs. 1 MDStV eingreifen, wonach die Forenbetreiber für die rechtswidrigen Bewertungen jedenfalls so lange nicht verantwortlich sind, solange sie hiervon keine Kenntnis haben. Da von dieser Haftungsprivilegierung nach der Rechtsprechung des Bundesgerichtshofs die Störerhaftung nicht umfasst ist, wird die Reichweite die Forenbetreiber aus der Störerhaftung treffenden Überwachungspflichten diskutiert. Die Arbeit kommt hier zu dem Ergebnis, dass in den Fällen, in denen dem Adressaten der Bewertung die Identität des Verfassers bekannt ist, sich die Verpflichtungen der Forenbetrei-ber auf die Beseitigung bzw. Sperrung der rechtswidrigen Bewertung beschränken. Sofern die Identität des Bewertenden unbekannt ist, haften die Forenbetreiber als Mitstörer und dem Be-troffenen stehen Unterlassungsansprüche auch gegen die Forenbetreiber zu.

Photovernetzbare flüssigkristalline Polymere unterschiedlicher Kettentopologien

„Photovernetzbare flüssigkristalline Polymere unterschiedlicher Kettentopologien“, Patrick Beyer, Mainz 2007 Zusammenfassung In der vorliegenden Arbeit wurde die Synthese und Charakterisierung flüssigkristalliner Elastomere unterschiedlicher Polymertopologien vorgestellt. Dabei wurden Systeme synthetisiert, bei denen die mesogenen Einheiten entweder als Seitengruppen an ein Polymerrückgrat angebunden (Seitenkettenelastomere) oder direkt in die Polymerkette integriert (Hauptkettenelastomere) sind (siehe Abbildung). Bezüglich der Seitenkettensysteme konnten erstmals photovernetzbare smektische Seitenkettenpolymere, in denen aufgrund der Anknüpfung eines photoisomerisierbaren Azobenzols eine Photo- modulation der ferroelektrischen Eigenschaften möglich ist, dargestellt werden. Homöotrop orientierte freistehende Filme dieser Materialien konnten durch Spincoaten dargestellt und unter Ausnutzung des Dichroismus der Azobenzole durch geeignete Wahl der Bestrahlungsgeometrie photovernetzt werden. Aufbauend auf diesen Untersuchungen wurde anhand eines nicht vernetzbaren Modellsystems im Detail der Einfluss der trans-cis Isomerisierung des Azobenzols auf die ferroelektrischen Parameter untersucht. Durch zeitaufgelöste Messungen der Absorption der Azobenzole, der spontanen Polarisation und des Direktorneigungswinkels und Auswertung der kinetischen Prozesse konnte eine lineare Abhängigkeit der ferroelektrischen Eigenschaften vom Grad der Isomerisierungsreaktion festgestellt werden. Durch Vergleich dieser in der flüssigkristallinen Phase erhaltenen Ergebnisse mit der Kinetik der thermischen Reisomerisierung in Lösung (Toluol) konnte ferner eine deutliche Reduzierung der Relaxationszeiten in der anisotropen flüssigkristallinen Umgebung festgestellt und auf eine Absenkung der Aktivierungsenergie zurückgeführt werden. Makroskopische Formänderungen der Seitenkettenelastomere am Phasenübergang von der flüssigkristallinen in die isotrope Phase konnten jedoch nicht festgestellt werden. Aus diesem Grund wurden neue Synthesestrategien für die Darstellung von Hauptkettenelastomeren entwickelt, die sich aufgrund der direkten Kopplung von flüssigkristallinem Ordnungsgrad und Polymerkettenkonformation besser für die Herstellung thermischer Aktuatoren eignen. Auf Basis flüssigkristalliner Polymalonate konnten dabei lateral funktionalisierte smektische Hauptkettenpolymere synthetisiert werden, welche erstmals die Darstellung von LC-Hauptkettenelastomeren durch Photovernetzung in der flüssigkristallinen Phase erlauben. Durch laterale Bromierung konnte in diesen Systemen die Kristallisationstendenz der verwendeten Biphenyleinheiten unterdrückt werden. Bezüglich der Photovernetzung konnten zwei neue Synthesemethoden entwickelt werden, bei denen der Vernetzungsschritt entweder durch radikalische Polymerisation lateral angebundener Acrylatgruppen oder durch photoaktive Benzophenongruppen erfolgte. Basierend auf den Benzophenon funktionalisierten Systemen konnte ein neuartiges Verfahren zur Darstellung makroskopisch orientierter Hauptkettenelastomere durch Photovernetzung entwickelt werden. Die Elastomerproben, deren Ordnungsgrad durch Röntgenuntersuchungen ermittelt werden konnte, zeigen am Phasenübergang von der flüssigkristallinen in die isotrope Phase eine reversible Formänderung von 40%. Im Gegensatz zu anderen bekannten smektischen Systemen konnten die in dieser Arbeit vorgestellten Elastomere ohne Zerstörung der Phase bis zu 60% entlang der smektischen Schichtnormalen gestreckt werden, was im Kontext einer geringen Korrelation der smektischen Schichten in Hauptkettenelastomeren diskutiert wurde.

Optical resonances of sphere-on-plane geometries

The optical resonances of metallic nanoparticles placed at nanometer distances from a metal plane were investigated. At certain wavelengths, these “sphere-on-plane” systems become resonant with the incident electromagnetic field and huge enhancements of the field are predicted localized in the small gaps created between the nanoparticle and the plane. An experimental architecture to fabricate sphere-on-plane systems was successfully achieved in which in addition to the commonly used alkanethiols, polyphenylene dendrimers were used as molecular spacers to separate the metallic nanoparticles from the metal planes. They allow for a defined nanoparticle-plane separation and some often are functionalized with a chromophore core which is therefore positioned exactly in the gap. The metal planes used in the system architecture consisted of evaporated thin films of gold or silver. Evaporated gold or silver films have a smooth interface with their substrate and a rougher top surface. To investigate the influence of surface roughness on the optical response of such a film, two gold films were prepared with a smooth and a rough side which were as similar as possible. Surface plasmons were excited in Kretschmann configuration both on the rough and on the smooth side. Their reflectivity could be well modeled by a single gold film for each individual measurement. The film has to be modeled as two layers with significantly different optical constants. The smooth side, although polycrystalline, had an optical response that was very similar to a monocrystalline surface while for the rough side the standard response of evaporated gold is retrieved. For investigations on thin non-absorbing dielectric films though, this heterogeneity introduces only a negligible error. To determine the resonant wavelength of the sphere-on-plane systems a strategy was developed which is based on multi-wavelength surface plasmon spectroscopy experiments in Kretschmann-configuration. The resonant behavior of the system lead to characteristic changes in the surface plasmon dispersion. A quantitative analysis was performed by calculating the polarisability per unit area /A treating the sphere-on-plane systems as an effective layer. This approach completely avoids the ambiguity in the determination of thickness and optical response of thin films in surface plasmon spectroscopy. Equal area densities of polarisable units yielded identical response irrespective of the thickness of the layer they are distributed in. The parameter range where the evaluation of surface plasmon data in terms of /A is applicable was determined for a typical experimental situation. It was shown that this analysis yields reasonable quantitative agreement with a simple theoretical model of the sphere-on-plane resonators and reproduces the results from standard extinction experiments having a higher information content and significantly increased signal-to-noise ratio. With the objective to acquire a better quantitative understanding of the dependence of the resonance wavelength on the geometry of the sphere-on-plane systems, different systems were fabricated in which the gold nanoparticle size, type of spacer and ambient medium were varied and the resonance wavelength of the system was determined. The gold nanoparticle radius was varied in the range from 10 nm to 80 nm. It could be shown that the polyphenylene dendrimers can be used as molecular spacers to fabricate systems which support gap resonances. The resonance wavelength of the systems could be tuned in the optical region between 550 nm and 800 nm. Based on a simple analytical model, a quantitative analysis was developed to relate the systems’ geometry with the resonant wavelength and surprisingly good agreement of this simple model with the experiment without any adjustable parameters was found. The key feature ascribed to sphere-on-plane systems is a very large electromagnetic field localized in volumes in the nanometer range. Experiments towards a quantitative understanding of the field enhancements taking place in the gap of the sphere-on-plane systems were done by monitoring the increase in fluorescence of a metal-supported monolayer of a dye-loaded dendrimer upon decoration of the surface with nanoparticles. The metal used (gold and silver), the colloid mean size and the surface roughness were varied. Large silver crystallites on evaporated silver surfaces lead to the most pronounced fluorescence enhancements in the order of 104. They constitute a very promising sample architecture for the study of field enhancements.