<p> The question of how the plastic strength of alloys depends on composition is critical to alloy design. Numerous classical works have tackled this question in the past. Yet, the models available to date primarily focus on the strength of alloys at the onset of yielding and seldom address the role of alloy composition in the hardening and dislocation microstructure evolution regime. The above question becomes even more important in situations in which the alloys are compositionally nonuniform at the mesoscale, as in spinodally decomposed alloys, irradiated alloys, high entropy alloys, and additive-manufactured alloys. In this work, the interaction between alloy plasticity and compositional inhomogeneity is addressed from a discrete dislocation dynamics (DDD) perspective. A framework comprising of three components: (1) analysis of the 3D composition morphology in inhomogeneous alloys with tendency to undergo spinodal/spinodal-like instability, (2) atomistic simulations of the dislocation mobility as a function of the local composition, and (3) dislocation dynamics simulations, has been utilized to understand the collective dynamics of dislocations and mesoscale plasticity in inhomogeneous alloys. Irradiated FeCrAl has been used as a model alloy for the implementation of the current framework and subsequent investigations. The investigation reveals that the composition inhomogeneity plays a crucial role in influencing microplasticity and macroscopic plasticity in inhomogeneous alloys. This happens due to the motion of dislocations taking place in a wavy fashion due to coherency stresses and locally varying dislocation velocities. </p> <p>To further understand alloy microplasticity from a single dislocation perspective, Cahn’s theory of hardening in compositionally modulated alloys based on coherency stresses has been modified to account for superposition of solid solution strengthening on spinodal strengthening due to the composition modulation. A new definition for the CRSS in compositionally modulated alloys is provided. Subsequently, CRSS is determined as a function of dislocation line direction, amplitude, and wavelength of the composition fluctuations.</p> <p>Lastly, an application of the developed framework is demonstrated where plasticity in irradiated FeCrAl nanopillars is investigated using DDD, with a comparison to transmission electron microscopic in situ tensile tests of ion- and neutron-irradiated commercial FeCrAl C35M alloy.</p>

Combustion phenomena are complex in theory and expensive to test, analysis techniques<br>provide handles with which we may describe them. Just as simultaneous experimental tech-<br>niques provide complementary descriptions of flame behavior, one might assume that no<br>analysis technique for any kind of flame measurement would cover the full description of<br>the flame. To this end, the search continues for complementary descriptions of engineering<br>flames that capture enough information for the engine designer to make informed decisions.<br>The kinds of flames I have encountered are high pressure transverse jet flames issuing into a<br>vitiated crossflow which is itself generated from combustion of a gaseous fuel and oxidizer.<br>Summarizing the behavior of these flames has required my understanding of experimen-<br>tal techniques such as Planar Laser Induced Fluorescence of a reaction intermediate -OH,<br>Particle Image Velocimetry of a passive tracer in the flame and OH * chemiluminescence of<br>another reaction intermediate. The analysis tools applied to these measurements must reveal<br>as much information as is laden in these measurements.<br>In this work I have also used wavelet optical flow to track flow features in the visualization<br>of combustion intermediates using OH * chemiluminescence. There are many limitations to<br>the application of this technique to engineering flames especially due to the interpretation<br>of the data as a 2-D motion field in 3-D world. The interpretation of such motion fields<br>as generated by scalar fields is one subject matter discussed in this dissertation. Some<br>inferences from the topology of the ensuing velocity field has provided insight to the behavior<br>of reacting turbulent flows which appear attached to an injector in the mean field. It gives<br>some understanding to the robustness of the attachment mechanism when such flames are<br>located near walls.

Diese Dissertation umfasst vier Aufsätze welche die Effekte von nicht-zufälliger Selektion betrachten. Im ersten Aufsatz wird analysiert welche Rolle die geänderte Zusammensetzung der Erwerbsbevölkerung für die Entwicklung der Lohnungleichheit spielt. Vollzeit-Erwerbstätige weisen zunehmend Episoden von Teilzeitarbeit und Erwerbsunterbrechungen in ihren Biographien auf. Dies hat maßgeblich zum Anstieg der Lohnungleichheit beigetragen. Der zweite Aufsatz betrachtet die Effekte von gesunkener Arbeitslosigkeit auf Lohnungleichheit.. Wenn sich die Selektion in Vollzeit oder Arbeitslosigkeit ändert, kann dies zu steigender Lohnungleichheit führen. Dies ist insbesondere dann der Fall wenn Personen neu in Beschäftigung kommen, die eine Negativauswahl der Erwerbsbevölkerung sind. Jedoch zeigt sich, als Resultat einer Analyse mit selektionskorrigierten Quantilsregressionen, dass diese veränderte Selektion nicht zum Anstieg der Lohnungleichheit beigetragen hat. Im dritten Aufsatz geht es um nicht-monotone Selektion bei Regression Discontinuity Designs (RDD). Die Annahmen, auf welchen RDDs beruhen, können verletzt sein wenn sich sowohl Individuen in die Maßnahmengruppe hinein, als auch aus ihr heraus selektieren. Der Aufsatz beschreibt diesen Selektionsmechanismus und zeigt seine praktische Relevanz. Zudem wird ein Spezifikationstest vorgestellt um das Problem im Vorfeld der Analyse zu erkennen. Der vierte Aufsatz untersucht Wählerpräferenzen für das Geschlecht politischer Kandidaten. Es wird analysiert ob das Zusammenspiel von Berufsinformationen und Geschlecht die geringere Repräsentation von Frauen erklären kann. Dazu wurde ein Feldexperiment durchgeführt. Es zeigt sich dass weibliche Kandidaten einen Stimmvorteil genießen solange keine Berufsinformationen angegeben sind. Sobald jedoch die Berufe der Kandidaten bekannt sind kehrt sich dies in einen Stimmvorteil für männliche Kandidaten um. / This thesis comprises four essays which study effects of non-random selection. The first essay analyzes the role of changes in labor force composition for the development of wage inequality among full-time workers. Of particular interest are the effects of increasingly common episodes of temporary part-time work and nonemployment among full-time workers. Such episodes, have contributed substantially to the rise in wage inequality. The second essay studies the effects of declining unemployment on inequality of wages. Changing selection over time between unemployment and full-time work could lead to increasingly diverse wages, particularly if sinking unemployment implies an influx of negatively selected workers into employment. However, results from a selection corrected quantile regression approach show that changing selection with respect to unobservables is not a contributor to the rise in wage inequality. The third essay studies non-monotonic selection in regression discontinuity designs (RDD). When similar numbers of individual select into and out of treatment simultaneously, the identifying assumption of the RDD can be violated. The essay describes the selection mechanisms and demonstrates it’s practical relevance. It then suggests an enhancement to the standard specification tests for RDDs, which can detect non-monotonic sorting in advance. The fourth essay studies voter’s valuation of candidate gender. It examines whether the presence of profession information coupled with voter preferences for stereotypical male occupations may explain part of the gender gap in parliaments. The analysis is conducted as a field experiment built into an exit-poll of voters in Germany in 2014. The results show a vote share bonus for women in the absence of profession information. Once voters know the profession of candidates, however, this changes towards a small edge for male candidates.