Desarrollo de un sistema de videoconferencia en HTML 5.0

[ES] Webcam App es una aplicación que tiene como principal objetivo social que las personas puedan realizar videoconferencias a través de la web de forma gratuita y sencilla. Para el desarrollo de la misma, fueron de gran utilidad los elementos que brinda HTML5.0 para dar soporte multimedia: y . También, se usan dos de las APIs que implementa WebRTC para la trasmisión de audio y video en tiempo real, obtenidos desde la webcam: MediaStream (getUserMedia) y RTCPeerConnection. Para soportar esta aplicación se elige Node.js como servidor web, pues entre sus puntos fuertes está la capacidad de mantener varias conexiones abiertas, característica fundamental en una aplicación de videollamadas, donde miles de usuarios crean y envían solicitudes de conexión simultáneamente. Con el fin de aportarle una apariencia agradable a la aplicación, un entorno usable y conocido para los usuarios, se utiliza CMS Elgg como marco de red social. CMS Elgg provee de funcionalidades comunes, como por ejemplo: conectar con amigos, enviar mensajes, compartir contenido. Como metodología base se usa el Proceso Unificado de Desarrollo de Software, posibilitando que la realización de este trabajo se haya hecho de una manera organizada y se obtuvieran artefactos para el desarrollo. Como resultado del trabajo, se obtiene una solución Open Source que sirve como un modelo de comunicación en tiempo real sin necesidad de descargar, instalar o actualizar ningún complemento de terceros y que demuestra la fiabilidad de los sistemas basados en HTML5 y WebRTC.

Simulación URANS 2D del flujo alrededor de un cilindro para 104 ≤ Re ≤ 106 con tratamiento de paredes

Máster Universitario en Sistemas Inteligentes y Aplicaciones Numéricas en Ingeniería (SIANI)

Finanza Imprenditoriale: Teoria del Portafoglio e Costo del Capitale

This thesis focuses on the limits that may prevent an entrepreneur from maximizing her value, and the benefits of diversification in reducing her cost of capital. After reviewing all relevant literature dealing with the differences between traditional corporate finance and entrepreneurial finance, we focus on the biases occurring when traditional finance techniques are applied to the entrepreneurial context. In particular, using the portfolio theory framework, we determine the degree of under-diversification of entrepreneurs. Borrowing the methodology developed by Kerins et al. (2004), we test a model for the cost of capital according to the firms' industry and the entrepreneur's wealth commitment to the firm. This model takes three market inputs (standard deviation of market returns, expected return of the market, and risk-free rate), and two firm-specific inputs (standard deviation of the firm returns and correlation between firm and market returns) as parameters, and returns an appropriate cost of capital as an output. We determine the expected market return and the risk-free rate according to the huge literature on the market risk premium. As for the market return volatility, it is estimated considering a GARCH specification for the market index returns. Furthermore, we assume that the firm-specific inputs can be obtained considering new-listed firms similar in risk to the firm we are evaluating. After we form a database including all the data needed for our analysis, we perform an empirical investigation to understand how much of the firm's total risk depends on market risk, and which explanatory variables can explain it. Our results show that cost of capital declines as the level of entrepreneur's commitment decreases. Therefore, maximizing the value for the entrepreneur depends on the fraction of entrepreneur's wealth invested in the firm and the fraction she sells to outside investors. These results are interesting both for entrepreneurs and policy makers: the former can benefit from an unbiased model for their valuation; the latter can obtain some guidelines to overcome the recent financial market crisis.

Effetti degli accordi Euro-Mediterrani sul comparto dell'ortofrutta fresca

In 1995, the European Union (EU) Member States and 12 Mediterranean countries launched in Barcelona a liberalization process that aims at establishing a free trade area (to be realized by 2010) and at promoting a sustainable and balanced economic development by the adoption of a new generation of Agreements: the Euro-Mediterranean Agreements (EMA). For the Mediterranean partner countries, the main concern is a better access for their fruit and vegetable exports to the European market. These products represent the main exports of these countries, and the EU is their first trading partner. On the other side, for the EU the main issue is not only the promotion of its products, but also the protection of its fruit and vegetables producers. Moreover, the trade with third countries is the key element of the Common Market Organization of the sector. Fruit and vegetables represent a very sensitive sector since their high seasonality, high perishability, and especially since the production of the Mediterranean countries is often similar to the European Mediterranean’s countries one. In fact, the agreements define preferences at the entrance of the EU market providing limited concessions for each partner, for specific products, limited quantities and calendars. This research tries to analyze the bilateral trade volume for fresh fruit and vegetables in the European and Italian markets in order to assess the effects of Mediterranean liberalization on this sector. Free trade of agricultural products represents a very actual topic in international trade and the Mediterranean countries, recognised as big producers of fruit and vegetables, as big exporters of their crops and actually significantly present on the European market, could be high competitors with the inward production because the outlet could be the same. The goal of this study is to provide some considerations about the competitiveness of mediterranean fruit and vegetables productions after Barcelona Process, in a first step for the European market and then also for the Italian one. The aim is to discuss the influence of the euro-mediterranean agreements on the fruit and vegetables trade between 10 foreign Mediterranean countries (Algeria, Egypt, Israel, Jordan, Libya, Lebanon, Morocco, Tunisia, Syria, and Turkey) and 15 EU countries in the period 1995-2007, by means of a gravity model, which is a widespread methodology in international trade analysis. The basic idea of gravity models is that bilateral trade from one country to another (as the dependent variable) can be explained by a set of factors: - factors that capture the potential of a country to export goods and services; - factors that capture the propensity of a country to imports goods and services; - any other forces that either attract or inhibit bilateral trade. This analysis compares only imports’ flows by Europe and by Italy (in volumes) from Mediterranean countries, since the exports’ flows toward those foreign countries are not significant, especially for Italy. The market of fruit and vegetables appears as a high heterogeneous group so it is very difficult to show a synthesis of the analysis performed and the related results. In fact, this sector includes the so called “poor products” (such as potatoes and legumes), and the “rich product”, such as nuts or exotic fruit, and there are a lot of different goods that arouse a dissimilar consumer demand which directly influence the import requirements. Fruit and vegetables sector includes products with extremely different biological cycles, leading to a very unlike seasonality. Moreover, the Mediterranean area appears as a highly heterogeneous bloc, including countries which differ from the others for economic size, production potential, capability to export and for the relationships with the EU. The econometric estimation includes 68 analyses, 34 of which considering the European import and 34 the Italian import and the products are examined in their aggregated form and in their disaggregated level. The analysis obtains a very high R2 coefficient, which means that the methodology is able to assess the import effects on fruit and vegetables associated to the Association Agreements, preferential tariffs, regional integration, and others information involved in the equation. The empirical analysis suggests that fruits and vegetables trade flows are well explained by some parameters: size of the involved countries (especially GDP and population of the Mediterranean countries); distances; prices of imported products; local production for the aggregated products; preferential expressed tariffs like duty free; sub-regional agreements that enforce the export capability. The euro-mediterranean agreements are significant in some of the performed analysis, confirming the slow and gradual evolution of euro- Mediterranean liberalization. The euro-mediterranean liberalization provides opportunities from one side, and imposes a new important challenge from the other side. For the EU the chance is that fruit and vegetables imported from the mediterranean area represent a support for local supply and a possibility to increase the range of products existing on the market. The challenge regards the competition of foreign products with the local ones since the types of productions are similar and markets coincide, especially in the Italian issue. We need to apply a strategy based not on a trade antagonism, but on the realization of a common plane market with the Mediterranean countries. This goal could be achieved enhancing the industrial cooperation in addition to commercial relationships, and increasing investments’ flows in the Mediterranean countries aiming at transforming those countries from potential competitors to trade partners and creating new commercial policies to export towards extra European countries.

Untersuchungen zur Beteiligung der Preseniline an den molekularen Mechanismen der Amyloid-ß Entstehung

ZusammenfassungMorbus Alzheimer ist eine progressive, neurodegenerative Erkrankung, die weltweit die häufigste Form der Demenz darstellt und im mittleren bis späten Lebensabschnitt auftritt. Die neuropathologischen Merkmale beinhalten das Auftreten von extrazellulären Ablagerungen aus fibrillogenem Aß42 Peptiden in senilen Plaques und intraneuronalen Akkumulationen von hyperphosphoryliertem Tau in sogenannten neurofibrillären Bündeln. Obwohl die meisten Alzheimer Fälle sporadisch und Alters-assoziiert auftreten, gibt es eine autosomal dominant vererbte Form (FAD; Familial Alzheimer Disease), die schon in einem frühen Lebensabschnitt (ab 28 Jahren) ausbrechen kann. Diese aggressive Alzheimer Form wird durch Mutationen im Amyloid-Precursor-Protein-Gen (APP) oder den Presenilin-Genen (PS-1 und PS-2) ausgelöst. Die Presenilin (PS) Proteine sind entscheidend an der Entstehung von Aß beteiligt. So erhöhen FAD-assoziierte Mutationen in PS-1 und PS-2 die Bildung von Aß42. Außerdem verhindern sowohl homozygote PS-1 Null-Mutationen (PS-1-/-) in transgenen Mäusen, als auch dominant negative PS-1 Mutationen in Kulturzellen die Ab Bildung. Diese Belege sprechen für die zur Zeit favorisierte Amyloid Hypothese, in der die toxische Wirkung des Aß-Peptides in der Entstehung der Alzheimer Erkrankung eine zentrale Rolle einnimmt. Die y-Sekretase ist eine Protease, deren Aktivität für die Entstehung von Ab aus dem Vorläuferprotein APP essentiell ist. Damit bildet sie einen möglichen Ansatzpunkt, um grundlegend in den Prozeß der Ab Bildung einzugreifen. Die y-Sekretase ist allerdings noch nicht identifiziert oder kloniert. Es gibt Hinweise, daß die Preseniline y-Sekretase Aktivität besitzen könnten. Diese Theorie ist bis heute jedoch nicht eindeutig belegt. In dieser Arbeit sollten die molekularen Mechanismen der Ab Entstehung und insbesondere die Beteiligung der Preseniline an diesem Prozeß untersucht werden. Dazu wurde zunächst die subzelluläre Verteilung der endogenen Preseniline analysiert. Es konnte erstmalig ein Unterschied in der subzellulären Verteilung zwischen PS-1 und PS-2 festgestellt werden. PS-1 war vorwiegend im ER lokalisiert, wogegen PS-2 stark im Golgi-Apparat angereichert war. Im zweiten Teil der Arbeit wurde nach möglichen Interaktionen der Preseniline mit C-terminalen APP Fragmenten gesucht, die die Substrate der y-Sekretase darstellen. Es konnte gezeigt werden, daß die Preseniline mit einem 21 kDa großen C-terminalen APP Fragment interagieren. Dabei band die Mutante-Form der Preseniline mehr C-terminales APP Fragment als die Wildtyp-Form. Weiterhin wurde ein zellfreies System zur indirekten Bestimmung der y-Sekretase Aktivität etabliert. Mit Hilfe dieses Systems wird es möglich, Inhibitoren der y-Sekretase zu identifizieren. Die Spezifität des zellfreien Testsystems konnte dadurch deutlich gemacht werden, daß das PS-1, das schon in Zellkultur als essentielle Proteinkomponente zur Entstehung von Aß beschrieben wurde, auch in diesem zellfreien y-Sekretase System notwendig war. Allgemeine Proteaseinhibitoren, die alle bekannten Proteasemechanismen abdeckten, zeigten keinen Einfluß auf die de novo Bildung von Aß. Es konnte festgestellt werden, daß neben der y-Sekretase als Aß produzierende Protease auch Aß abbauende Proteasen vorlagen. Das pH-Optimum der y-Sekretase wurde im neutralen Bereich festgestellt. Weiterhin konnte gezeigt werden, daß die y-Sekretase eine transmembrane oder zumindest membranassoziierte Protease ist, die keine cytosolischen Komponenten benötigt.

Johannes Driessler - Leben und Werk

Die vorliegende Arbeit über den Komponisten Johannes Driessler besteht aus einer Biographie, Werkanalysen und einem Werkverzeichnis inklusive Verlagsangaben. Johannes Driessler - geboren am 26. Januar 1921 in Friedrichsthal, gestorben am 4. Mai 1998 in Detmold - entfaltet, neben seiner pädagogischen Tätigkeit als Kompositionslehrer an der Nordwestdeutschen Musikakademie in Detmold, zwischen 1946 und 1971 ein reiches kompositorisches Schaffen. Sein Werk umfaßt geistliche und weltliche Chormusik - A-cappella-Werke, Kantaten, Oratorien, Opern, eine Messe - Liedkompositionen, Kammermusik, Klavier- und Orgelmusik, Orchesterwerke und Symphonien. Johannes Driesslers Werk ist in der geistlichen Musik verwurzelt, er entwickelt eine eigene Tonsprache: Die Gestaltung von Werken aus einer Grundidee, der Bogen, der Ostinato, das Kontrapunktische im Kanon, in der Fuge, in der Passacaglia und eine ungebundene Harmonik sind Elemente seines intellektuellen Kompositionsstils. Johannes Driesslers ureigenes Feld liegt im Vokalbereich. Hier gibt es hervorragende Werke wie zum Beispiel das erste Oratorium Dein Reich komme. Die zyklischen geistlichen Werke durch das Kirchenjahr sind wichtige Bausteine in den Gattungen Orgelmusik und Evangelienspruch im 20. Jahrhundert. Die frühe Kammermusik und die Opern des Komponisten sollten neu entdeckt werden. Auch die didaktisch wertvolle Musik in den Lehrwerken für Schüler und Studierende hat Bestand.

Tropospheric carboxylic acids in tropical rainforest environments

Der Übergang der Grenzschicht von stark ozeanisch auf kontinental beeinflusst wurde in 2 tropischen Küstenwaldgebieten Amerikas untersucht, wo Luftmassen vom Meer kommend über den Kontinent transportiert werden.Zwei Feldkampagnen wurden durchgeführt; in Costa Rica (CR; 07.1996) und in Surinam (04.1998). In CR wurde im nordöstlichen Flachgebiet (etwa 10°25' N; 84°W) Regenwasser gesammelt, in dem später Carboxylate, anorganischen Anionen, Ca2+, K+, NH4+ und Mg2+ gemessen wurden. Die Proben wurden an 5 verschiedenen Stellen entlang der Windrichtung 1, 20, 60, 60 und 80 km von der Küste gesammelt. In Surinam (Sipaliwini, 2°02' N, 56°08' W) wurden organischen Säuren aus der Gasphase gesammelt etwa 550 km von der Küste entfernt, sowohl wie O3 und CO. Die Proben wurden mittels Ionenchromatographie und Kapillarelektrophorese analysiert. Morgendliche Einmischung der nächtlichen residualen Schicht und Luft der unteren freien Troposphäre war Hauptquelle für HCOOH und CH3COOH in der Tagesmischschicht. Es wurde gezeigt, dass lokale Produktion dieser Säuren durch chemische Reaktionen eine kleine Rolle gespielt hat und dass direkte Emission vernachlässigbar war.Aus den beiden Feldkampagnen folgt, dass die Konzentrationen der sekundären Verbindungen HCOOH, CH3COOH, Ozon und CO in der Tagesmischschicht von Importen bestimmt wurden, was gilt für Regen- und Trockenzeit bis zu Entfernungen von 550 km zur Küste.

Climate impact studies of sediment transport on the Adriatic coastal zone

The study of the impact of climate change on the environment has been based, until very recently, on an global approach, whose interest from a local point of view is very limited. This thesis, on the contrary, has treated the study of the impact of climate change in the Adriatic Sea basin following a twofold strategy of regionalization and integration of numerical models in order to reproduce the present and future scenarios of the system through a more and more realistic and solid approach. In particular the focus of the study was on the impact on the physical environment and on the sediment transport in the basin. This latter is a very new and original issue, to our knowledge still uninvestigated. The study case of the coastal area of Montenegro was particularly studied, since it is characterized by an important supply of sediment through the Buna/Bojana river, second most important in the Adriatic basin in terms of flow. To do this, a methodology to introduce the tidal processes in a baroclinic primitive equations Ocean General Circulation Model was applied and tidal processes were successfully reproduced in the Adriatic Sea, analyzing also the impacts they have on the mean general circulation, on salt and heat transport and on mixing and stratification of the water column in the different seasons of the year. The new hydrodynamical model has been further coupled with a wave model and with a river and sea sediment transport model, showing good results in the reproduction of sediment transport processes. Finally this complex coupled platform was integrated in the period 2001-2030 under the A1B scenario of IPCC, and the impact of climate change on the physical system and on sediment transport was preliminarily evaluated.

Mechanische Eigenschaften von freitragenden artifiziellen und nativen Membranen

This thesis presents a new method to explore the local mechanical properties such as bending modulus or surface tension of artificial and native pore-spanning membranes. Therefore the elastic response of a free-standing membrane to a local indentation by the means of atomic force microscopy is measured. Starting point are highly hexagonal ordered pores in alumina produced by electrochemical anodization of planar aluminium. The homogeneous pore radius can by tailored in the range of 10 nm up to 200 nm, but radius of 33 nm, 90 nm and 200 nm turned out to be best suited for investigation of the mechanical properties of pore-spanning native or artificial membranes. In this work artificial membrane systems consisting of DODAB as a bilayer in gel phase or DOTAP as a fluide membrane are spreaded by vesicle absorption on hexagonal structured pores after chemisorption of a 3-mercaptopropionic acid monolayer. Centrally indenting these nanodrums with an atomic force microscope tip yields force-indentation curves, which are quantitatively analyzed by solving the corresponding shape equations of continuum curvature elasticity. Since the measured response depends in a known way on the system geometry (pore size, tip radius) and on material parameters (bending modulus, lateral tension, adhesion), this opens the possibility to monitor local elastic properties of lipid membranes in a well-controlled setting. Additionally the locally distributed mechanical properties of pore-spanning artificial membranes are compared to those of native pore-spanning membranes. Therefore the basal membrane of MDCK II cells was prepared on porous alumina assays and their mechanical properties were analyzed by means of atomic force microscopy. Finally the elastic behavior such as the Young modulus of living MDCK II cells under various osmotic pressures is investigated. By changing the osmolarity in the extracellular region of MDCK II cells a volume change is induced according to hydration and dehydration of the cells, respectively. This volume change induces also a change in the elastic behavior of the cell, which is quantified by the means of force spectroscopy.

Synthesis and characterization of Poly(vinylphosphonic acid) for proton exchange membranes in fuel cells

Vinylphosphonic acid (VPA) was polymerized at 80 ºC by free radical polymerization to give polymers (PVPA) of different molecular weight depending on the initiator concentration. The highest molecular weight, Mw, achieved was 6.2 x 104 g/mol as determined by static light scattering. High resolution nuclear magnetic resonance (NMR) spectroscopy was used to gain microstructure information about the polymer chain. Information based on tetrad probabilities was utilized to deduce an almost atactic configuration. In addition, 13C-NMR gave evidence for the presence of head-head and tail-tail links. Refined analysis of the 1H NMR spectra allowed for the quantitative determination of the fraction of these links (23.5 percent of all links). Experimental evidence suggested that the polymerization proceeded via cyclopolymerization of the vinylphosphonic acid anhydride as an intermediate. Titration curves indicated that high molecular weight poly(vinylphosphonic acid) PVPA behaved as a monoprotic acid. Proton conductors with phosphonic acid moieties as protogenic groups are promising due to their high charge carrier concentration, thermal stability, and oxidation resistivity. Blends and copolymers of PVPA have already been reported, but PVPA has not been characterized sufficiently with respect to its polymer properties. Therefore, we also studied the proton conductivity behaviour of a well-characterized PVPA. PVPA is a conductor; however, the conductivity depends strongly on the water content of the material. The phosphonic acid functionality in the resulting polymer, PVPA, undergoes condensation leading to the formation of phosphonic anhydride groups at elevated temperature. Anhydride formation was found to be temperature dependent by solid state NMR. Anhydride formation affects the proton conductivity to a large extent because not only the number of charge carriers but also the mobility of the charge carriers seems to change.

Synthesis and characterization of structurally well-defined polymer-layered silicate nanocomposites

Zusammenfassung Nanokomposite aus Polymeren und Schichtsilikaten werden zumeist auf der Basis natürlicher Tone wie Montmorillonit hergestellt. Für NMR- und EPR-Untersuchungen der Tensidschicht, die das Silikat mit dem Polymer kompatibilisiert, ist der Eisengehalt natürlicher Tone jedoch abträglich, weil er zu einer Verkürzung der Relaxationszeiten und zu einer Linienverbreiterung in den Spektren führt. Dieses Problem konnte überwunden werden, indem als Silikatkomponente eisenfreies, strukturell wohldefiniertes Magadiit hydrothermal synthetisiert und für die Kompositbildung eingesetzt wurde. Die Morphologie des Magadiits wurde durch Rasterelektronenmikroskopie charakterisiert und der Interkalationsgrad von schmelzinterkalierten Polymer-Nanokompositen wurde durch Weitwinkelröntgenstreuung bestimmt. Polymere mit Carbonylgruppen scheinen leichter zu interkalieren als solche ohne Carbonylgruppen. Polycaprolacton interkalierte sowohl in Oragnomagadiite auf der Basis von Ammoniumtensiden als auch in solche auf der Basis von Phosphoniumtensiden. Die Dynamik auf einer Nanosekundenzeitskala und die Struktur der Tensidschicht wurden mittels ortsspezifisch spinmarkierter Tensidsonden unter Nutzung von Dauerstrich- (CW) und Puls-Methoden der elektronenparamagnetischen Resonanzspektroskopie (EPR) untersucht. Zusätzlich wurde die statische 2H-Kernmagnetresonanz (NMR) an spezifisch deuterierten Tensiden angewendet, um die Tensiddynamik auf einer komplementären Zeitskala zwischen Mikrosekunden und Millisekunden zu erfassen. Sowohl die CW-EPR- als auch die 2H-NMR-Ergebnisse zeigen eine Beschleunigung der Tensiddynamik durch Interkalation von Polycaprolacton auf, während sich in den nichtinterkalierten Mikrokompositen mit Polystyrol die Tensiddynamik verlangsamt. Die Rotationskorrelationszeiten und Aktivierungsenergien offenbaren verschiedene Regime der Tensiddynamik. In Polystyrol-Mikrokompositen entspricht die Übergangstemperatur zwischen den Regimen der Glasübergangstemperatur von Polystyrol, während sie in Polycaprolacton-Nanokompositen bei der Schmelztemperatur von Polycaprolacton liegt. Durch die erhebliche Verlängerung der Elektronenspin-Relaxationszeiten bei Verwendung von eisenfreiem Magadiit können Messdaten hoher Qualität mit Puls-EPR-Experimenten erhalten werden. Insebsondere wurden die Vier-Puls-Elektron-Elektron-Doppelresonanz (DEER), die Elektronenspinechoenveloppenmodulation (ESEEM) und die Elektronen-Kern-Doppelresonanz (ENDOR) an spinmarkierten sowie spezifisch deuterierten Tensiden angewandt. Die ENDOR-Ergebnisse legen ein Model der Tensidschicht nahe, in dem zusätzlich zu den Oberflächenlagen auf dem Silikat eine wohldefinierte mittlere Lage existiert. Dieses Modell erklärt auch Verdünnungseffekte durch das Polymer in Kompositen mit Polycaprolacton und Polystyrol. Die umfangreiche Information aus den Magnetresonanztechniken ergänzt die Information aus konventionellen Charakterisierungstechniken wie Röntgendiffraktion und Transmissionselektronenmikroskopie und führt so zu einem detaillierteren Bild der Struktur und Dynamik der Tensidschicht in Nanokompositen aus Polymeren und Schichtsilikaten.

Structuring of polymer surface by evaporation of sessile microdrops

In this thesis, we investigated the evaporation of sessile microdroplets on different solid substrates. Three major aspects were studied: the influence of surface hydrophilicity and heterogeneity on the evaporation dynamics for an insoluble solid substrate, the influence of external process parameters and intrinsic material properties on microstructuring of soluble polymer substrates and the influence of an increased area to volume ratio in a microfluidic capillary, when evaporation is hindered. In the first part, the evaporation dynamics of pure sessile water drops on smooth self-assembled monolayers (SAMs) of thiols or disulfides on gold on mica was studied. With increasing surface hydrophilicity the drop stayed pinned longer. Thus, the total evaporation time of a given initial drop volume was shorter, since the drop surface, through which the evaporation occurs, stays longer large. Usually, for a single drop the volume decreased linearly with t1.5, t being the evaporation time, for a diffusion-controlled evaporation process. However, when we measured the total evaporation time, ttot, for multiple droplets with different initial volumes, V0, we found a scaling of the form V0 = attotb. The more hydrophilic the substrate was, the more showed the scaling exponent a tendency to an increased value up to 1.6. This can be attributed to an increasing evaporation rate through a thin water layer in the vicinity of the drop. Under the assumption of a constant temperature at the substrate surface a cooling of the droplet and thus a decreased evaporation rate could be excluded as a reason for the different scaling exponent by simulations performed by F. Schönfeld at the IMM, Mainz. In contrast, for a hairy surface, made of dialkyldisulfide SAMs with different chain lengths and a 1:1 mixture of hydrophilic and hydrophobic end groups (hydroxy versus methyl group), the scaling exponent was found to be ~ 1.4. It increased to ~ 1.5 with increasing hydrophilicity. A reason for this observation can only be speculated: in the case of longer hydrophobic alkyl chains the formation of an air layer between substrate and surface might be favorable. Thus, the heat transport to the substrate might be reduced, leading to a stronger cooling and thus decreased evaporation rate. In the second part, the microstructuring of polystyrene surfaces by drops of toluene, a good solvent, was investigated. For this a novel deposition technique was developed, with which the drop can be deposited with a syringe. The polymer substrate is lying on a motorized table, which picks up the pendant drop by an upward motion until a liquid bridge is formed. A consecutive downward motion of the table after a variable delay, i.e. the contact time between drop and polymer, leads to the deposition of the droplet, which can evaporate. The resulting microstructure is investigated in dependence of the processes parameters, i.e. the approach and the retraction speed of the substrate and the delay between them, and in dependence of the intrinsic material properties, i.e. the molar mass and the type of the polymer/solvent system. The principal equivalence with the microstructuring by the ink-jet technique was demonstrated. For a high approach and retraction speed of 9 mm/s and no delay between them, a concave microtopology was observed. In agreement with the literature, this can be explained by a flow of solvent and the dissolved polymer to the rim of the pinned droplet, where polymer is accumulated. This effect is analogue to the well-known formation of ring-like stains after the evaporation of coffee drops (coffee-stain effect). With decreasing retraction speed down to 10 µm/s the resulting surface topology changes from concave to convex. This can be explained with the increasing dissolution of polymer into the solvent drop prior to the evaporation. If the polymer concentration is high enough, gelation occurs instead of a flow to the rim and the shape of the convex droplet is received. With increasing delay time from below 0 ms to 1s the depth of the concave microwells decreases from 4.6 µm to 3.2 µm. However, a convex surface topology could not be obtained, since for longer delay times the polymer sticks to the tip of the syringe. Thus, by changing the delay time a fine-tuning of the concave structure is accomplished, while by changing the retraction speed a principal change of the microtopolgy can be achieved. We attribute this to an additional flow inside the liquid bridge, which enhanced polymer dissolution. Even if the pendant drop is evaporating about 30 µm above the polymer surface without any contact (non-contact mode), concave structures were observed. Rim heights as high as 33 µm could be generated for exposure times of 20 min. The concave structure exclusively lay above the flat polymer surface outside the structure even after drying. This shows that toluene is taken up permanently. The increasing rim height, rh, with increasing exposure time to the solvent vapor obeys a diffusion law of rh = rh0  tn, with n in the range of 0.46 ~ 0.65. This hints at a non-Fickian swelling process. A detailed analysis showed that the rim height of the concave structure is modulated, unlike for the drop deposition. This is due to the local stress relaxation, which was initiated by the increasing toluene concentration in the extruded polymer surface. By altering the intrinsic material parameters i.e. the polymer molar mass and the polymer/solvent combination, several types of microstructures could be formed. With increasing molar mass from 20.9 kDa to 1.44 MDa the resulting microstructure changed from convex, to a structure with a dimple in the center, to concave, to finally an irregular structure. This observation can be explained if one assumes that the microstructuring is dominated by two opposing effects, a decreasing solubility with increasing polymer molar mass, but an increasing surface tension gradient leading to instabilities of Marangoni-type. Thus, a polymer with a low molar mass close or below the entanglement limit is subject to a high dissolution rate, which leads to fast gelation compared to the evaporation rate. This way a coffee-rim like effect is eliminated early and a convex structure results. For high molar masses the low dissolution rate and the low polymer diffusion might lead to increased surface tension gradients and a typical local pile-up of polymer is found. For intermediate polymer masses around 200 kDa, the dissolution and evaporation rate are comparable and the typical concave microtopology is found. This interpretation was supported by a quantitative estimation of the diffusion coefficient and the evaporation rate. For a different polymer/solvent system, polyethylmethacrylate (PEMA)/ethylacetate (EA), exclusively concave structures were found. Following the statements above this can be interpreted with a lower dissolution rate. At low molar masses the concentration of PEMA in EA most likely never reaches the gelation point. Thus, a concave instead of a convex structure occurs. At the end of this section, the optically properties of such microstructures for a potential application as microlenses are studied with laser scanning confocal microscopy. In the third part, the droplet was confined into a glass microcapillary to avoid evaporation. Since here, due to an increased area to volume ratio, the surface properties of the liquid and the solid walls became important, the influence of the surface hydrophilicity of the wall on the interfacial tension between two immiscible liquid slugs was investigated. For this a novel method for measuring the interfacial tension between the two liquids within the capillary was developed. This technique was demonstrated by measuring the interfacial tensions between slugs of pure water and standard solvents. For toluene, n-hexane and chloroform 36.2, 50.9 and 34.2 mN/m were measured at 20°C, which is in a good agreement with data from the literature. For a slug of hexane in contact with a slug of pure water containing ethanol in a concentration range between 0 and 70 (v/v %), a difference of up to 6 mN/m was found, when compared to commercial ring tensiometry. This discrepancy is still under debate.

Numerical investigation of turbulent/non-turbulent interface

The subject of this work is the diffusion of turbulence in a non-turbulent flow. Such phenomenon can be found in almost every practical case of turbulent flow: all types of shear flows (wakes, jet, boundary layers) present some boundary between turbulence and the non-turbulent surround; all transients from a laminar flow to turbulence must account for turbulent diffusion; mixing of flows often involve the injection of a turbulent solution in a non-turbulent fluid. The mechanism of what Phillips defined as “the erosion by turbulence of the underlying non-turbulent flow”, is called entrainment. It is usually considered to operate on two scales with different mechanics. The small scale nibbling, which is the entrainment of fluid by viscous diffusion of turbulence, and the large scale engulfment, which entraps large volume of flow to be “digested” subsequently by viscous diffusion. The exact role of each of them in the overall entrainment rate is still not well understood, as it is the interplay between these two mechanics of diffusion. It is anyway accepted that the entrainment rate scales with large properties of the flow, while is not understood how the large scale inertial behavior can affect an intrinsically viscous phenomenon as diffusion of vorticity. In the present work we will address then the problem of turbulent diffusion through pseudo-spectral DNS simulations of the interface between a volume of decaying turbulence and quiescent flow. Such simulations will give us first hand measures of velocity, vorticity and strains fields at the interface; moreover the framework of unforced decaying turbulence will permit to study both spatial and temporal evolution of such fields. The analysis will evidence that for this kind of flows the overall production of enstrophy , i.e. the square of vorticity omega^2 , is dominated near the interface by the local inertial transport of “fresh vorticity” coming from the turbulent flow. Viscous diffusion instead plays a major role in enstrophy production in the outbound of the interface, where the nibbling process is dominant. The data from our simulation seems to confirm the theory of an inertially stirred viscous phenomenon proposed by others authors before and provides new data about the inertial diffusion of turbulence across the interface.

Anhydrous proton conducting polymer electrolytes based on polymeric ionic liquids

Imidazolium types of ionic liquids were immobilized by tethering it to acrylate backbone. These imidazolium salt containing acrylate monomers were polymerize at 70oC by free radical polymerization to give polymers poly(AcIm-n) with n being the side chain lenght. The chemical structure of the polymer electrolytes obtained by the described synthetic routes was investigated by NMR-spectroscopy. The polymers were doped with various amounts of H3PO4 and LiN(SO2CF3)2, to obtain poly(AcIm-n) x H3PO4 and poly(AcIm-2-Li) x LiN(SO2CF3)2. The TG curves show that the polymer electrolytes are thermally stable up to about 200◦C. DSC results indicates the softening effect of the length of the spacers (n) as well as phosphoric acid. The proton conductivity of the samples increase with x and reaches to 10-2 Scm-1 at 120oC for both poly(AcIm-2)2H3PO4 and poly(AcIm-6)2H3PO4. It was observed that the lithium ion conductivity of the poly(AcIm-2-Li) x LiN(SO2CF3)2 increases with blends (x) up to certain composition and then leveled off independently from blend content. The conductivity reaches to about 10-5 S cm-1 at 30oC and 10-3 at 100oC for poly(AcIm-2-Li) x LiN(SO2CF3)2 where x is 10. The phosphate and phosphoric acid functionality in the resulting polymers, poly(AcIm-n) x H3PO4, undergoes condensation leading to the formation of cross-linked materials at elevated temperature which may improve the mechanical properties to be used as membrane materials in fuel cells. High resolution nuclear magnetic resonance (NMR) spectroscopy was used to obtain information about hydrogen bonding in solids. The low Tg enhances molecular mobility and this leads to better resolved resonances in both the backbone region and side chain region. The mobile and immobile protons can be distinguished by comparing 1H MAS and 1H-DQF NMR spectra. The interaction of the protons which may contribute to the conductivity is observed from the 2D double quantum correlation (DQC) spectra.