Numerical studies of colloidal systems

The interplay of hydrodynamic and electrostatic forces is of great importance for the understanding of colloidal dispersions. Theoretical descriptions are often based on the so called standard electrokinetic model. This Mean Field approach combines the Stokes equation for the hydrodynamic flow field, the Poisson equation for electrostatics and a continuity equation describing the evolution of the ion concentration fields. In the first part of this thesis a new lattice method is presented in order to efficiently solve the set of non-linear equations for a charge-stabilized colloidal dispersion in the presence of an external electric field. Within this framework, the research is mainly focused on the calculation of the electrophoretic mobility. Since this transport coefficient is independent of the electric field only for small driving, the algorithm is based upon a linearization of the governing equations. The zeroth order is the well known Poisson-Boltzmann theory and the first order is a coupled set of linear equations. Furthermore, this set of equations is divided into several subproblems. A specialized solver for each subproblem is developed, and various tests and applications are discussed for every particular method. Finally, all solvers are combined in an iterative procedure and applied to several interesting questions, for example, the effect of the screening mechanism on the electrophoretic mobility or the charge dependence of the field-induced dipole moment and ion clouds surrounding a weakly charged sphere. In the second part a quantitative data analysis method is developed for a new experimental approach, known as "Total Internal Reflection Fluorescence Cross-Correlation Spectroscopy" (TIR-FCCS). The TIR-FCCS setup is an optical method using fluorescent colloidal particles to analyze the flow field close to a solid-fluid interface. The interpretation of the experimental results requires a theoretical model, which is usually the solution of a convection-diffusion equation. Since an analytic solution is not available due to the form of the flow field and the boundary conditions, an alternative numerical approach is presented. It is based on stochastic methods, i. e. a combination of a Brownian Dynamics algorithm and Monte Carlo techniques. Finally, experimental measurements for a hydrophilic surface are analyzed using this new numerical approach.

Design of nanoparticle systems with antimicrobial properties

Infektiöse Komplikationen im Zusammenhang mit Implantaten stellen einen Großteil aller Krankenhausinfektionen dar und treiben die Gesundheitskosten signifikant in die Höhe. Die bakterielle Kolonisation von Implantatoberflächen zieht schwerwiegende medizinische Konsequenzen nach sich, die unter Umständen tödlich verlaufen können. Trotz umfassender Forschungsaktivitäten auf dem Gebiet der antibakteriellen Oberflächenbeschichtungen ist das Spektrum an wirksamen Substanzen aufgrund der Anpassungsfähigkeit und Ausbildung von Resistenzen verschiedener Mikroorganismen eingeschränkt. Die Erforschung und Entwicklung neuer antibakterieller Materialien ist daher von fundamentaler Bedeutung.rnIn der vorliegenden Arbeit wurden auf der Basis von Polymernanopartikeln und anorganischen/polymeren Verbundmaterialien verschiedene Systeme als Alternative zu bestehenden antibakteriellen Oberflächenbeschichtungen entwickelt. Polymerpartikel finden Anwendung in vielen verschiedenen Bereichen, da sowohl Größe als auch Zusammensetzung und Morphologie vielseitig gestaltet werden können. Mit Hilfe der Miniemulsionstechnik lassen sich u. A. funktionelle Polymernanopartikel im Größenbereich von 50-500 nm herstellen. Diese wurde im ersten System angewendet, um PEGylierte Poly(styrol)nanopartikel zu synthetisieren, deren anti-adhesives Potential in Bezug auf P. aeruginosa evaluiert wurde. Im zweiten System wurden sog. kontakt-aktive kolloide Dispersionen entwickelt, welche bakteriostatische Eigenschaften gegenüber S. aureus zeigten. In Analogie zum ersten System, wurden Poly(styrol)nanopartikel in Copolymerisation in Miniemulsion mit quaternären Ammoniumgruppen funktionalisiert. Als Costabilisator diente das zuvor quaternisierte, oberflächenaktive Monomer (2-Dimethylamino)ethylmethacrylat (qDMAEMA). Die Optimierung der antibakteriellen Eigenschaften wurde im nachfolgenden System realisiert. Hierbei wurde das oberflächenaktive Monomer qDMAEMA zu einem oberflächenaktiven Polyelektrolyt polymerisiert, welcher unter Anwendung von kombinierter Miniemulsions- und Lösemittelverdampfungstechnik, in entsprechende Polyelektrolytnanopartikel umgesetzt wurde. Infolge seiner oberflächenaktiven Eigenschaften, ließen sich aus dem Polyelektrolyt stabile Partikeldispersionen ohne Zusatz weiterer Tenside ausbilden. Die selektive Toxizität der Polyelektrolytnanopartikel gegenüber S. aureus im Unterschied zu Körperzellen, untermauert ihr vielversprechendes Potential als bakterizides, kontakt-aktives Reagenz. rnAufgrund ihrer antibakteriellen Eigenschaften wurden ZnO Nanopartikel ausgewählt und in verschiedene Freisetzungssysteme integriert. Hochdefinierte eckige ZnO Nanokristalle mit einem mittleren Durchmesser von 23 nm wurden durch thermische Zersetzung des Precursormaterials synthetisiert. Durch die nachfolgende Einkapselung in Poly(L-laktid) Latexpartikel wurden neue, antibakterielle und UV-responsive Hybridnanopartikel entwickelt. Durch die photokatalytische Aktivierung von ZnO mittels UV-Strahlung wurde der Abbau der ZnO/PLLA Hybridnanopartikel signifikant von mehreren Monaten auf mehrere Wochen verkürzt. Die Photoaktivierung von ZnO eröffnet somit die Möglichkeit einer gesteuerten Freisetzung von ZnO. Im nachfolgenden System wurden dünne Verbundfilme aus Poly(N-isopropylacrylamid)-Hydrogelschichten mit eingebetteten ZnO Nanopartikeln hergestellt, die als bakterizide Oberflächenbeschichtungen gegen E. coli zum Einsatz kamen. Mit minimalem Gehalt an ZnO zeigten die Filme eine vergleichbare antibakterielle Aktivität zu Silber-basierten Beschichtungen. Hierbei lässt sich der Gehalt an ZnO relativ einfach über die Filmdicke einstellen. Weiterhin erwiesen sich die Filme mit bakteriziden Konzentrationen an ZnO als nichtzytotoxisch gegenüber Körperzellen. Zusammenfassend wurden mehrere vielversprechende antibakterielle Prototypen entwickelt, die als potentielle Implantatbeschichtungen auf die jeweilige Anwendung weiterhin zugeschnitten und optimiert werden können.

Neuartige kryogene Penning-Falle für den Nachweis von Spin-Übergängen eines Protons und Bestimmung seines g-Faktors

In dieser Arbeit wird der Entwurf, der Aufbau, die Inbetriebnahme und die Charakterisierung einer neuartigen Penning-Falle im Rahmen des Experiments zur Bestimmung des g-Faktors des Protons präsentiert. Diese Falle zeichnet sich dadurch aus, dass die Magnetfeldlinien eines äußeren homogenen Magnetfeldes durch eine ferromagnetische Ringelektrode im Zentrum der Falle verzerrt werden. Der inhomogene Anteil des resultierenden Magnetfeldes, die sogenannte magnetische Flasche, lässt sich durch den Koeffizient B2 = 297(10) mT/mm2 des Terms zweiter Ordnung der Ortsabhängigkeit des Feldes quantifizieren. Eine solche ungewöhnlich starke Feldinhomogenität ist Grundvoraussetzung für den Nachweis der Spinausrichtung des Protons mittels des kontinuierlichen Stern-Gerlach-Effektes. Dieser Effekt basiert auf der im inhomogenen Magnetfeld entstehenden Kopplung des Spin-Freiheitsgrades des gefangenen Protons an eine seiner Eigenfrequenzen. Ein Spin-Übergang lässt sich so über einen Frequenzsprung detektieren. Dabei ist die nachzuweisende Änderung der Frequenz proportional zu B2 und zum im Fall des Protons extrem kleinen Verhältnis zwischen seinem magnetischen Moment nund seiner Masse. Die durch die benötigte hohe Inhomogenität des Magnetfeldes bedingten technischen Herausforderungen erfordern eine fundierte Kenntnis und Kontrolle der Eigenschaften der Penning-Falle sowie der experimentellen Bedingungen. Die in der vorliegenden Arbeit entwickelte Penning-Falle ermöglichte den erstmaligen zerstörungsfreien Nachweis von Spin-Quantensprüngen eines einzelnen gefangenen Protons, was einen Durchbruch für das Experiment zur direkten Bestimmung des g-Faktors mit der angestrebten relativen Genauigkeit von 10−9 darstellte. Mithilfe eines statistischen Verfahrens ließen sich die Larmor- und die Zyklotronfrequenz des Protons im inhomogenen Magnetfeld der Falle ermitteln. Daraus wurde der g-Faktor mit einer relativen Genauigkeit von 8,9 × 10−6 bestimmt. Die hier vorgestellten Messverfahren und der experimentelle Aufbau können auf ein äquivalentes Experiment zur Bestimmung des g-Faktors des Antiprotons zum Erreichen der gleichen Messgenauigkeit übertragen werden, womit der erste Schritt auf dem Weg zu einem neuen zwingenden Test der CPT-Symmetrie im baryonischen Sektor gemacht wäre.

Mechanical properties and structure of gel systems

Understanding the origins of the mechanical properties and its correlation withrnthe microstructure of gel systems is of great scientific and industrial interest. Inrngeneral, colloidal gels can be classified into chemical and physical gels, accordingrnto the life time of the network bonds. The characteristic di↵erences in gelationrndynamics can be observed with rheological measurements.rnAs a model system, a mixture of sodium silicate and low concentration sulfuric acidrnwas used. Nano-sized silica particles grow and aggregate to a system-spanning gelrnnetwork. The influence of the finite solubility of silica at high pH on the gelationrnwas studied with classical and piezo rheometer. The storage modulus of therngel grew logarithmically with time with two distinct growth laws. A relaxationrnat low frequency was observed in the frequency dependent measurements. I attributernthese two behaviors as a sign of structural rearrangements due to the finiternsolubility of silica at high pH. The reaction equilibrium between formation andrndissolution of bonds leads to a finite life time of the bonds and behavior similar tornphysical gel. The frequency dependence was more pronounced for lower water concentrations,rnhigher temperatures and shorter reaction times. With two relaxationrnmodels, I deduced characteristic relaxation times from the experimental data. Besidesrnrheology, the evolution of silica gels at high pH on di↵erent length scales wasrnstudied by NMR and dynamic light scattering. The results revealed that the primaryrnparticles existed already in sodium silicate and aggregated after the mixingrnof reactants due to a chemical reaction. Throughout the aggregation process thernsystem was in its chemical reaction equilibrium. Applying large oscillatory shearrnstrain to the gel allowed for modifying the gel modulus. The e↵ect of shear andrnshear history on the rheological properties of the gel were investigated. The storagernmodulus of the final gel increased with increasing strain. This behavior can be explained with (i) shear-induced aggregate compaction and (ii) combination ofrnbreakage and new formation of bonds.rnIn comparison with the physical gel-like behavior of the silica gel at high pH, typicalrnchemical gel features were exhibited by other gels formed from various chemicalrnreactions. Influences of the chemical structure modification on the gelation wererninvestigated with the piezo-rheometer. The external stimuli can be applied to tunernthe mechanical properties of the gel systems.

Il modello green office come nicchia strategica per la transizione sostenibile del sistema universita the green office model as strategic niche for sustainability transition of hei systems

Nella prima parte di questo progetto di tesi, ho analizzato tutte le nozioni teoriche rilevanti in merito alla teoria della transizione. Il primo concetto condiviso in questa trattazione è quello di transizione. Nella parte finale del capitolo, il focus si sposta sul ruolo, in una generica transizione, delle nicchie. Lo strumento centrale in questa struttura sono gli esperimenti di transizione, i quali forniscono un approccio alternativo ai progetti di innovazione classica che sono incentrati nell'ottenimento di soluzioni a breve termine. Vi è dunque una forte relazione tra nicchia e sperimentazione. Infine la trattazione si concentra sul tema dello Strategic Niche Management. Nel secondo capitolo, analizzo il tema della sostenibilità inserita in un contesto universitario. Questa sezione si focalizza sulle strategie di alto livello richieste per dare avvio alla transizione universitaria verso la sostenibilità, identificando gli ostacoli e gli elementi portanti, e definendo una vision al fine di concretizzarla. Il capitolo guida, passo per passo, le università che tentano di mettere in pratica il proprio obiettivo e la vision di sviluppo sostenibile. Una delle problematiche principali per stimare gli sforzi verso la sostenibilità nelle università è costituita in modo particolare dagli strumenti di valutazione. Per questo motivo, è stata sviluppata la valutazione grafica della sostenibilità nell'università (GASU). Al fine di riassumere quanto detto fin qui ed avere un quadro generale più chiaro dell'organizzazione di un campus universitario che mira a diventare sostenibile, ho utilizzato lo strumento gestionale della SWOT Analysis. Negli ultimi due capitoli, infine, analizzo nel dettaglio il modello Green Office. La teorizzazione di questo modello e l'elaborazione dei 6 principi del Green Office sono state effettuate da rootAbility. Le seguenti pagine presentano 3 casi studio di come i 6 principi dei Green Office sono stati adattati alle 3 unità di sostenibilità guidate da studenti e supportate da staff qualificato. L'oggetto della trattazione sono i principali GO affermatisi nei Paesi Bassi. A seguito dell'introduzione del modello relativo al Green Office e dell'illustrazione degli esempi presi in esame, è stato sfruttato lo strumento della feasibility analysis al fine di giudicare se l'idea di business sia praticabile. Il mezzo con cui ho condotto l'analisi sotto riportata è un questionario relativo al modello di Green Office implementato, nel quale viene chiesto di valutare gli aspetti relativi alla organizational feasibility e alla financial feasibility. Infine nella sezione finale ho considerato i Green Office come fossero un unico movimento. L'analisi mira a considerare l'impatto globale del Green Office Movement nei sistemi universitari e come, a seguito del loro consolidarsi nella struttura accademica, possano divenire prassi comune. La struttura proposta contiene elementi sia da il SNM (Strategic Niche Management) che dal TE (Transition Experiment).

Influence of curing rate on softening in ethanol, degree of conversion, and wear of resin composite

PURPOSE: To investigate the effect of curing rate on softening in ethanol, degree of conversion, and wear of resin composites. METHOD: With a given energy density and for each of two different light-curing units (QTH or LED), the curing rate was reduced by modulating the curing mode. Thus, the irradiation of resin composite specimens (Filtek Z250, Tetric Ceram, Esthet-X) was performed in a continuous curing mode and in a pulse-delay curing mode. Wallace hardness was used to determine the softening of resin composite after storage in ethanol. Degree of conversion was determined by infrared spectroscopy (FTIR). Wear was assessed by a three-body test. Data were submitted to Levene's test, one and three-way ANOVA, and Tukey HSD test (alpha = 0.05). Results: Immersion in ethanol, curing mode, and material all had significant effects on Wallace hardness. After ethanol storage, resin composites exposed to the pulse-delay curing mode were softer than resin composites exposed to continuous cure (P< 0.0001). Tetric Ceram was the softest material followed by Esthet-X and Filtek Z250 (P< 0.001). Only the restorative material had a significant effect on degree of conversion (P< 0.001): Esthet-X had the lowest degree of conversion followed by Filtek Z250 and Tetric Ceram. Curing mode (P= 0.007) and material (P< 0.001) had significant effect on wear. Higher wear resulted from the pulse-delay curing mode when compared to continuous curing, and Filtek Z250 showed the lowest wear followed by Esthet-X and Tetric Ceram.

Tempering the EU? NGO Advocacy in the Area of Freedom, Security, and Justice

The European Union’s (EU) area of Freedom, Security and Justice (AFSJ) portfolio comprises policy areas such as immigration and asylum, and police and judicial cooperation. Steps were taken to bring this field into the mandate of the EU first by the Maastricht Treaty, followed by changes implemented by the Amsterdam and Lisbon Treaties, the last one ‘normalizing’ the EU’s erstwhile Third Pillar. As the emergent EU regime continues to consolidate in this field, NGOs of various kinds continue to seek to influence policy-making and implementation, with varying success. This article seeks to establish the context in which NGOs carry out their work and argues that the EU-NGO interface is impacted both by the institutional realities of the European Union and the capacities of EU-oriented NGOs to seize and expand opportunities for access and input into the policy cycle. Using EU instruments representing three different policy bundles in AFSJ (immigration, asylum and judicial cooperation in criminal matters), the article seeks to map out NGO strategies in engaging and oftentimes resisting European Union policy instruments.

Deviation from Murray's law is associated with a higher degree of calcification in coronary bifurcations

Murray's law describes the optimal branching anatomy of vascular bifurcations. If Murray's law is obeyed, shear stress is constant over the bifurcation. Associations between Murray's law and intravascular ultrasound (IVUS) assessed plaque composition near coronary bifurcations have not been investigated previously.

Rapid assessment of cerebral autoregulation by near-infrared spectroscopy and a single dose of phenylephrine

Rapid bedside determination of cerebral blood pressure autoregulation (AR) may improve clinical utility. We tested the hypothesis that cerebral Hb oxygenation (HbDiff) and cerebral Hb volume (HbTotal) measured by near-infrared spectroscopy (NIRS) would correlate with cerebral blood flow (CBF) after single dose phenylephrine (PE). Critically ill patients requiring artificial ventilation and arterial lines were eligible. During rapid blood pressure rise induced by i.v. PE bolus, ΔHbDiff and ΔHbTotal were calculated by subtracting values at baseline (normotension) from values at peak blood pressure elevation (hypertension). With the aid of NIRS and bolus injection of indocyanine green, relative measures of CBF, called blood flow index (BFI), were determined during normotension and during hypertension. BFI during hypertension was expressed as percentage from BFI during normotension (BFI%). Autoregulation indices (ARIs) were calculated by dividing BFI%, ΔHbDiff, and ΔHbTotal by the concomitant change in blood pressure. In 24 patients (11 newborns and 13 children), significant correlations between BFI% and ΔHbDiff (or ΔHbTotal) were found. In addition, the associations between Hb-based ARI and BFI%-based ARI were significant with correlation coefficients of 0.73 (or 0.72). Rapid determination of dynamic AR with the aid of cerebral Hb signals and PE bolus seems to be reliable.

Single application of low-dose mycophenolate mofetil-OX7-immunoliposomes ameliorates experimental mesangial proliferative glomerulonephritis

IgA nephropathy, one of the most frequent forms of glomerulonephritis, characterized by mesangial hypercellularity and glomerular extracellular matrix (ECM) expansion, often leads to end-stage renal disease over a prolonged period. We investigated whether antiproliferative treatment in a single low dose specifically targeted to the glomerular mesangium by immunoliposomes (ILs) results in an amelioration of mesangial proliferative glomerulonephritis in rats (anti-Thy1.1 nephritis). Mycophenolate mofetil (MMF) containing ILs was generated that targets the Thy1.1 antigen (OX-7) in rat mesangial cells. Treatment benefit of a single intravenous dose of these ILs given 2 days after disease induction was investigated by stereology, immunohistochemistry, and functional analyses (creatinine, albuminuria) until day +9 and was compared among untreated and free MMF-treated rats using six male Wistar rats per group. MMF-loaded OX7-IL prevented creatinine increase and albuminuria. Stereological analyses of MMF OX7-IL-treated animals yielded 30% reduction of mesangial cells on day +9 and a 40% reduction of glomerular ECM volume on day +5, compared with all of the other nephritic animals. Furthermore, at days +5 and +9 we observed decreased ECM content and decreased glomerular volume (day +5) in the MMF-OX7-IL-treated group compared with the nephritic group treated with free MMF. In conclusion, MMF-OX7-IL-based directed drug delivery represents a novel approach for treating mesangial cell-mediated forms of glomerulonephritis.