No description available.

Monolayers of the cationic surfactant hexadecyltrimethylammonium halide (CTAX, where X = F¯, Cl¯, Br¯, and I¯) have been studied at the air-water and oilwater interfaces. At the air-water interface, the effects of the halide counterion and the addition of counterion were investigated. Sum-frequency spectroscopy (SFS), ellipsometry, and surface tensiometry indicated that the counterion changed the efficiency and effectiveness of the surfactant, both decreasing in the order of Br¯> Cl¯>F¯. The addition of salt in the form of 0.1 M KX was found to reduce the cmc but had little effect on the limiting area per molecule attained at the cmc, which increased from 44 Ų for CTAB to 65 Ų for CTAC and ca. 94 Ų for CTAF. Neither SFS nor ellipsometry provided any firm evidence for specific effects of the halide ions on the structure of the surfactant monolayers. For CTAB monolayers in the absence of excess electrolyte, the effect of area per molecule on the sum-frequency (SF) spectra was studied. Mixed monolayers of CTAB and tetradecane at the air-water interface exhibit a first-order phase transition from a conformationally disordered to a conformationally ordered state as the temperature is lowered. The phase transition occurs ca. 11 °C above the bulk melting point of tetradecane. A new experimental arrangement is described for acquiring SF spectra from surfactants at the oil-water interface. The key features of this approach are the stabilisation of a thin oil film between a sapphire prism and an aqueous phase, and the use of total internal reflection to enhance the total signal and discriminate against signals from other interfaces in the system. With this new methodology, the first SF vibrational spectra of surfactant monolayers at an alkane-water interface were obtained. Surface tensiometry was used to characterise the monolayers further. The structure of CTAB monolayers at the hexadecane-water interface was determined by SFS and compared with monolayers of CTAB at the air-water interface. At low concentrations, CTAB/hexadecane showed the expected features in the C-H stretching region, characteristic of a conformationally disordered monolayer. As the bulk concentration approached the critical micelle concentration, the spectra changed to one characteristic of a more ordered, upright conformation. Ellipsometric measurements supported this conclusion. This qualitative structural change is not observed in analogous monolayers at the air-water interface or CCl₄-water interface, or in surfactant solutions in contact with a hydrophobic solid surface.

During development of tissues, cells collectively organize to form complex patterns and morphologies. A general feature of many developing epithelia is their distinct organization into cellular compartments of different cell lineages. The interfaces between these compartments, called compartment boundaries, maintain straight and sharp morphologies. The interfaces play key roles in tissue development and pattern formation. An important model system to study the morphology of compartment boundaries during development is the wing disc of the fruit fly. Two compartment boundaries exist in the fly wing disc, the anteroposterior (AP) boundary and the dorsoventral (DV) boundary. A crucial question is how compartment boundaries are shaped and remain stable during growth. In this work, we discuss the dynamics and mechanisms of compartment boundaries in developing epithelia. We analyze the general features of interfacial phenomena in coarse- grained models of passive and active fluids. We introduce a continuum description of tissues with two cell types. This model allows us to study the propagation of interfaces due to the interplay of cell dynamics and tissue mechanics. We also use a vertex model to describe cellular compartments in growing epithelia. The vertex model accounts for cell mechanics and describes a 2D picture of tissues where the network of adherens junctions characterizes cell shapes. We use this model to study the general physical mechanisms by which compartment boundaries are shaped. We quantify the stresses in the cellular network and discuss how cell mechanics and growth influence the stress profile. With the help of the anisotropic stress profile near the interfaces we calculate the interfacial tension. We show that cell area pressure, cell proliferation rate, orientation of cell division, cell elongation created by external stress, and cell bond tension all have distinct effects on the morphology of interfaces during tissue growth. Furthermore, we investigate how much different mechanisms contribute to the effective interfacial tension. We study the mechanisms shaping the DV boundary in wing imaginal disc at different stages during the development. We analyze the images of wing discs to quantify the roughness of the DV boundary and average cell elongation in its vicinity. We quantify increased cell bond tension along the boundary and analyze the role of localized reduction in cell proliferation on the morphology of the DV boundary. We use experimentally determined values for cell bond tension, cell elongation and bias in orientation of cell division in simulations of tissue growth in order to reproduce the main features of the time-evolution of the DV boundary shape.

The European legislation prohibits the use of lead containing solders in Europe. However, lead free solders have a higher melting point (typical 20%) and their mechanical characteristics are worse. Additional problems are aging and adhesion of the solder on the electronic circuits. Thus, research activities must focus on the optimization of the properties of Sn-Ag-Cu based lead free solders chosen by the industry. Two main objectives are treated in this work. In the center of the first one is the study of curious hysteresis effects of metallic cadmium-antimony alloys after thermal cycles by measuring electronic transport phenomena (thermoelectric power and electrical resistivity). The second objective, within the framework of “cotutelle” between the universities of Metz and of Chemnitz and supported by COST531, is to study more specifically lead free solders. A welding must well conduct electricity and well conduct and dissipate heat. In Metz, we determined the electrical conductivity, the thermoelectric power and the thermal conductivity of various lead free solders (Sn-Ag-Cu, Sn-Cu, Sn-Ag, Sn-Sb) as well in the liquid as well in the solid state. The results have been compared to classical lead-tin (Pb-Sn) solders. In Chemnitz we measured the surface tension, the interfacial tension and the density of lead free solders. We also measured the viscosity of these solders without and with additives, in particular nickel. These properties were related to the industrial problems of wettability and spreadability. Lastly, we solidified alloys under various conditions. We observed undercooling. We developed a technique of mixture of nanocristalline powder with lead free solders "to sow" the liquid bath in order to obtain "different" solids which were examined using optical and electron microscopy. / Die europäische Gesetzgebung verbietet die Benutzung von Lötmitteln, die Blei enthalten. Bleilose Lote haben aber einen höheren Schmelzpunkt (typisch 20%) und ihre mechanischen Eigenschaften sind schlechter. Zusätzliche Probleme sind das Alterungsverhalten und das Haftvermögen des Lots an den Leiterbahnen. Daher müssen sich Forschungsaktivitäten auf die Optimierung der Eigenschaften von bleifreien Sn-Ag-Cu (SAC) Loten konzentrieren, die von der Industrie gewählt wurden. Zwei Hauptgebiete werden in dieser Arbeit bearbeitet. Im Zentrum des Ersten stehen seltsame Hysterese-Effekte von metallischen Kadmium- Antimon Legierungen bei thermischen Zyklen, wobei Transporteigenschaften wie die thermoelektrische Kraft und der elektrische Widerstand untersucht werden. Die zweite Aktivität, die in einer Kooperation der Universitäten Metz und Chemnitz (cotutelle) bearbeitet und die durch COST531 unterstützt wird, besteht in der detaillierten Erforschung des Lötprozesses ohne Blei. Eine Lötverbindung muß den Strom gut führen und die Wärme gut ableiten. In Metz haben wir die elektrische Leitfähigkeit, die thermoelektrische Kraft und das Wärmeleitvermögen bestimmt für verschiedene bleilose Lote (Sn-Ag-Cu, Sn-Cu, Sn-Ag, Sn-Sb), sowohl im flüssigen als auch festen Zustand. Die Ergebnisse wurden mit dem klassischen bleihaltigen Lötzinn (Sn-Pb) verglichen. In Chemnitz haben wir die Oberflächen- und Grenzflächenspannung und die Dichte bleifreier Lote gemessen. Ebenfalls wurde die Viskosität dieser Lote ohne und mit Zusätzen (insbesondere Nickel) gemessen. Diese Eigenschaften wurden in Beziehung gesetzt zu den industriellen Problemen der Benetzbarkeit und des Fließverhaltens. Schließlich haben wir Legierungen unter verschiedenen Bedingungen verfestigt. Wir haben Unterkühlung beobachtet. Wir haben eine Technik entwickelt, basierend auf einer Mischung von Lot mit Pulver. Durch "Einsäen" von Nanokristallen in das flüssige Bad erhielten wir "verschiedene" Festkörper, die mit optischer und Elektronenmikroskopie untersucht wurden.

The European legislation prohibits the use of lead containing solders in Europe. However, lead free solders have a higher melting point (typical 20%) and their mechanical characteristics are worse. Additional problems are aging and adhesion of the solder on the electronic circuits. Thus, research activities must focus on the optimization of the properties of Sn-Ag-Cu based lead free solders chosen by the industry. Two main objectives are treated in this work. In the center of the first one is the study of curious hysteresis effects of metallic cadmium-antimony alloys after thermal cycles by measuring electronic transport phenomena (thermoelectric power and electrical resistivity). The second objective, within the framework of “cotutelle” between the universities of Metz and of Chemnitz and supported by COST531, is to study more specifically lead free solders. A welding must well conduct electricity and well conduct and dissipate heat. In Metz, we determined the electrical conductivity, the thermoelectric power and the thermal conductivity of various lead free solders (Sn-Ag-Cu, Sn-Cu, Sn-Ag, Sn-Sb) as well in the liquid as well in the solid state. The results have been compared to classical lead-tin (Pb-Sn) solders. In Chemnitz we measured the surface tension, the interfacial tension and the density of lead free solders. We also measured the viscosity of these solders without and with additives, in particular nickel. These properties were related to the industrial problems of wettability and spreadability. Lastly, we solidified alloys under various conditions. We observed undercooling. We developed a technique of mixture of nanocristalline powder with lead free solders "to sow" the liquid bath in order to obtain "different" solids which were examined using optical and electron microscopy. / Die europäische Gesetzgebung verbietet die Benutzung von Lötmitteln, die Blei enthalten. Bleilose Lote haben aber einen höheren Schmelzpunkt (typisch 20%) und ihre mechanischen Eigenschaften sind schlechter. Zusätzliche Probleme sind das Alterungsverhalten und das Haftvermögen des Lots an den Leiterbahnen. Daher müssen sich Forschungsaktivitäten auf die Optimierung der Eigenschaften von bleifreien Sn-Ag-Cu (SAC) Loten konzentrieren, die von der Industrie gewählt wurden. Zwei Hauptgebiete werden in dieser Arbeit bearbeitet. Im Zentrum des Ersten stehen seltsame Hysterese-Effekte von metallischen Kadmium- Antimon Legierungen bei thermischen Zyklen, wobei Transporteigenschaften wie die thermoelektrische Kraft und der elektrische Widerstand untersucht werden. Die zweite Aktivität, die in einer Kooperation der Universitäten Metz und Chemnitz (cotutelle) bearbeitet und die durch COST531 unterstützt wird, besteht in der detaillierten Erforschung des Lötprozesses ohne Blei. Eine Lötverbindung muß den Strom gut führen und die Wärme gut ableiten. In Metz haben wir die elektrische Leitfähigkeit, die thermoelektrische Kraft und das Wärmeleitvermögen bestimmt für verschiedene bleilose Lote (Sn-Ag-Cu, Sn-Cu, Sn-Ag, Sn-Sb), sowohl im flüssigen als auch festen Zustand. Die Ergebnisse wurden mit dem klassischen bleihaltigen Lötzinn (Sn-Pb) verglichen. In Chemnitz haben wir die Oberflächen- und Grenzflächenspannung und die Dichte bleifreier Lote gemessen. Ebenfalls wurde die Viskosität dieser Lote ohne und mit Zusätzen (insbesondere Nickel) gemessen. Diese Eigenschaften wurden in Beziehung gesetzt zu den industriellen Problemen der Benetzbarkeit und des Fließverhaltens. Schließlich haben wir Legierungen unter verschiedenen Bedingungen verfestigt. Wir haben Unterkühlung beobachtet. Wir haben eine Technik entwickelt, basierend auf einer Mischung von Lot mit Pulver. Durch "Einsäen" von Nanokristallen in das flüssige Bad erhielten wir "verschiedene" Festkörper, die mit optischer und Elektronenmikroskopie untersucht wurden.

During development of tissues, cells collectively organize to form complex patterns and morphologies. A general feature of many developing epithelia is their distinct organization into cellular compartments of different cell lineages. The interfaces between these compartments, called compartment boundaries, maintain straight and sharp morphologies. The interfaces play key roles in tissue development and pattern formation. An important model system to study the morphology of compartment boundaries during development is the wing disc of the fruit fly. Two compartment boundaries exist in the fly wing disc, the anteroposterior (AP) boundary and the dorsoventral (DV) boundary. A crucial question is how compartment boundaries are shaped and remain stable during growth. In this work, we discuss the dynamics and mechanisms of compartment boundaries in developing epithelia. We analyze the general features of interfacial phenomena in coarse- grained models of passive and active fluids. We introduce a continuum description of tissues with two cell types. This model allows us to study the propagation of interfaces due to the interplay of cell dynamics and tissue mechanics. We also use a vertex model to describe cellular compartments in growing epithelia. The vertex model accounts for cell mechanics and describes a 2D picture of tissues where the network of adherens junctions characterizes cell shapes. We use this model to study the general physical mechanisms by which compartment boundaries are shaped. We quantify the stresses in the cellular network and discuss how cell mechanics and growth influence the stress profile. With the help of the anisotropic stress profile near the interfaces we calculate the interfacial tension. We show that cell area pressure, cell proliferation rate, orientation of cell division, cell elongation created by external stress, and cell bond tension all have distinct effects on the morphology of interfaces during tissue growth. Furthermore, we investigate how much different mechanisms contribute to the effective interfacial tension. We study the mechanisms shaping the DV boundary in wing imaginal disc at different stages during the development. We analyze the images of wing discs to quantify the roughness of the DV boundary and average cell elongation in its vicinity. We quantify increased cell bond tension along the boundary and analyze the role of localized reduction in cell proliferation on the morphology of the DV boundary. We use experimentally determined values for cell bond tension, cell elongation and bias in orientation of cell division in simulations of tissue growth in order to reproduce the main features of the time-evolution of the DV boundary shape.

The process of cell-sorting is essential for development and maintenance of tissues. With the Differential Adhesion Hypothesis, Steinberg proposed that cellsorting is determined by quantitative differences in cell-type-specific intercellular adhesion strengths. An implementation of the Differential Adhesion Hypothesis is the Differential Migration Model by Voss-Böhme and Deutsch. There, an effective adhesion parameter was derived analytically for systems with two cell types, which predicts the asymptotic sorting pattern. However, the existence and form of such a parameter for more than two cell types is unclear. Here, we generalize analytically the concept of an effective adhesion parameter to three and more cell types and demonstrate its existence numerically for three cell types based on in silico time-series data that is produced by a cellular-automaton implementation of the Differential Migration Model. Additionally, we classify the segregation behavior using statistical learning methods and show that the estimated effective adhesion parameter for three cell types matches our analytical prediction. Finally, we demonstrate that the effective adhesion parameter can resolve a recent dispute about the impact of interfacial adhesion, cortical tension and heterotypic repulsion on cell segregation. / Der Prozess der Zellsortierung ist für die Entwicklung und Erhaltung von Geweben unerlässlich. Mit der Differentiellen Adhäsionshypothese schlug Steinberg vor, dass die Zellsortierung durch quantitative Unterschiede in den zelltypspezifischen interzellulären Adhäsionsstärken bestimmt wird. Eine Umsetzung der Differentiellen Adhäsionshypothese ist das Differentielle Migrationsmodell von Voss-Böhme und Deutsch. In diesem wurde für Systeme mit zwei Zelltypen ein effektiver Adhäsionsparameter analytisch hergeleitet, der das asymptotische Sortiermuster vorhersagt. Die Existenz und Form eines solchen Parameters für mehr als zwei Zelltypen ist jedoch unklar. Hier verallgemeinern wir analytisch das Konzept eines effektiven Adhäsionsparameters für drei und mehr Zelltypen und zeigen numerisch seine Existenz für drei Zelltypen auf der Basis von in silico Zeitreihendaten, die von einem zellulären Automaten des Differentiellen Migrationsmodells erzeugt werden. Darüber hinaus klassifizieren wir das Segregationsverhalten mithilfe statistischer Lernverfahren und zeigen, dass der geschätzte effektive Adhäsionsparameter für drei Zelltypen mit unserer analytischen Vorhersage übereinstimmt. Schließlich zeigen wir, dass der effektive Adhäsionsparameter eine kürzlich aufgekommene Diskussion über den Einfluss von Grenzflächenadhäsion, Kortikalspannung und heterotypischer Abstoßung auf die Zellsegregation lösen kann.