Visible light mediated activation of vinyl halides

This thesis starts with a brief introduction to vinyl radicals in organic chemistry. Beginning with early examples such as the combination of SnBu3H and AIBN in the 1980s, it later focuses on the generation of such intermediates through more benign visible light. After a short introduction to photoredox catalysis, it summarizes major contributions in this field from 2010 until the very recent date. The main part of this thesis deals with the activation of vinyl bromides and chlorides via visible light photoredox catalysis. The initial situation is based on previous investigations on α-bromo chalcones. Although these substrates readily undergo single electron reduction, this principle of activation could barely be transferred to less extended π-systems such as α-bromo cinnamates. The chapter “Preliminary studies with vinyl bromides” illustrates that the inert reactivity of α-bromo cinnamates is predominantly based on the more negative reduction potential. Several efforts to overcome this previously observed limitation are described. Unfortunately, all of these attempts were found to be unproductive and gave only mediocre results at best. The two subsequent chapters cover research results with vinyl chlorides as radical precursors. The chapter “Visible light mediated activation of α-chloro cinnamates” starts with a brief comparison of both vinyl halides and reveals that the chloro derivative surprisingly outcompetes the vinyl bromide in the visible light mediated coupling with enol acetates. The investigation of the reaction and its conditions demonstrates that α-chloro cinnamates represent excellent radical precursors and these substrates can be readily coupled with enol acetates in high yields. Subsequent studies regarding the substrate scope reveal the limitations of the described reaction. This coupling proves to be suitable for photochemical up-scaling and the corresponding products can be readily converted to biologically active γ-butyrolactones. These substrates are first accessed as racemates in a Luche reduction and subsequently enantioenriched in a CBS reduction. This chapter later focuses on solving this current halogen paradox. Numerous control experiments and theoretical calculations reveal that the major difference between both substrates does not rely on the initial bond fragmentation but is rather based on efficient catalyst deactivation in the case of the vinyl bromide. It provides evidence that, in direct comparison to the chloride, the vinyl bromide is consumed faster but nevertheless gives rise to lower yields due to poor conversion of the starting material. In the end, acetyl bromide which is formed as stoichiometric by-product in the described reaction is convicted as gradual but efficient catalyst poison for the photocatalyst

Consequences of Postnatally Elevated Insulin-Like Growth Factor-II in Transgenic Mice: Endocrine Changes and Effects on Body and Organ Growth.

Insulin-like growth factor-II (IGF-II) is an important regulator of embryonic growth and differentiation, but its function in postnatal life is unclear. To address this point, we generated transgenic mice harboring fusion genes in which a human IGF-II complementary DNA is placed under the transcriptional control of the rat phosphoenolpyruvate carboxykinase promoter. Transgene-specific messenger RNA was detected in liver, kidney, and several parts of the gut. Serum IGF-II levels in transgenic mice were 2-3 times higher than those in controls and increased after starvation. Circulating IGF-I correlated negatively and IGF-binding protein-2 (IGFBP-2) positively with IGF-II levels, suggesting that IGF-I is displaced from IGFBPs by IGF-II and that IGFII is a major regulator of IGFBP-2. Serum levels of IGFBP-3 and IGFBP-4 tended to be higher in phosphoenolpyruvate carboxykinase- IGF-II transgenic mice than in controls, as evaluated by ligand blot analysis. Starvation reduced serum IGF-I, but increased IGFBP-2 in transgenic mice more markedly than in controls. Fasting insulin levels were significantly reduced in transgenic mice, whereas glucose levels were not influenced by elevated IGF-II. The body growth of 4- and 12- week-old mice was not significantly influenced by elevated IGF-II, but transgenic mice displayed increased kidney and testis weight at the age of 4 weeks, and increased adrenal weight at the age of 12 weeks. Our results demonstrate that elevated IGF-II in postnatal life has multiple endocrine consequences and subtle time-specific effects on organ growth

ALIGNING IS CURRICULUM WITH INDUSTRY SKILL EXPECTATIONS: A TEXT MINING APPROACH

Digitalization offers both great opportunities as well as new challenges and uncertainties. In particular, students in their role as future employees will have to cope with the new digital environments, which makes lifelong learning and up-to-date skills even more important than they already are. Key players in this long-term development are the universities as providers of the necessary skills and knowledge. By now, it is clear that digitalization will have a broad impact on the future conditions of universities. But are they already prepared for it? Against this backdrop, we present an approach to combine universities’ offerings with the required industry job skills to identify potential curricular gaps at course level that arise through ongoing digitalization and, as a consequence, changing skill requests for employees. We identify an appropriate set of methods for our project including text min-ing methods, an expert survey and an interview phase for evaluation. We illustrate our approach using a large data set of German IS curricular module descriptions and offers for IS job starters

Essays in Labor Economics and Labor Market Policy

The thesis 'Essays in Labor Economics and Labor Market Policy' contributes to the existing literature by advancing our understanding of the forces that have shaped labor market outcomes in recent decades. It consists of three independent research papers, which zoom in on the effects of financial frictions, routine-biased technical change, and judge ideology, respectively. My coauthors and I employ both empirical and analytical methods to analyze the underlying mechanisms and discuss appropriate policy implications. Chapter 2 of this thesis explores the joint role of imperfections in labor and financial markets for the cyclical adjustment of the labor market. I show that jobless recoveries emerge when, upon exiting a recession, firms are faced with deteriorating credit conditions. On the financial side, collateral requirements affect the cost of borrowing for firms. On the employment side, hiring frictions and wage rigidity increase the need for credit, making the binding collateral constraint more relevant. In a general equilibrium business cycle model with search and matching frictions, I illustrate that tightening credit conditions calibrated from data negatively affect employment adjustments during recovery periods. Wage rigidity substantially amplifies this mechanism, generating empirically plausible fluctuations in employment and output. In Chapter 3 of this thesis, using state-level labor market data, Anna Hartmann and I document a positive relationship between the two phenomena in the U.S.: the decrease in unionization rates has been significantly more pronounced in states with a higher employment share in routine-intensive occupations. Contrary to conventional wisdom, deunionization is mainly driven by large within-industry and within-occupation changes in union membership rates and not only by compositional effects. Building on this observation, we argue that the commonly assumed driver of polarization, routine-biased technical change, is also the main driving force behind the decline in union membership rates. In a model with search and matching frictions where workers choose occupations and endogenously form unions, we illustrate that shifts in the structure of labor demand in favor of low- and high-skill occupations worsen the bargaining position of unions and make participation in collective bargaining less attractive for workers. The ensuing within-industry and within-occupation decline in unionization rates in turn provides incentives for middle-wage workers to switch to low-wage occupations, which further amplifies job market polarization. In Chapter 4 of this thesis, Christian Bredemeier, Anna Hartmann, and I provide evidence on the systematic labor market effects of ideological tendencies of the judiciary, employing broad data on court rulings and labor market outcomes. Our identification strategy uses heterogenous effects of ideological shifts of the U.S. Supreme Court on U.S. district court rulings, which we derive from a theoretical model of judge decision making and document empirically. Exploiting this heterogeneity, we find that an increase in the share of conservative rulings substantially increases the employment rate and promotes labor market fluidity but also contributes to wage stagnation, job market polarization, deunionization, and rising income inequality. Our main empirical results can be rationalized in a search and matching model with wrongful-termination lawsuits

Self-organized pore formation and open-loop-control in semiconductor etching

Electrochemical etching of semiconductors, apart from many technical applications, provides an interesting experimental setup for self-organized structure formation capable e.g. of regular, diameter-modulated, and branching pores. The underlying dynamical processes governing current transfer and structure formation are described by the Current-Burst-Model: all dissolution processes are assumed to occur inhomogeneously in time and space as a Current Burst (CB); the properties and interactions between CB's are described by a number of material- and chemistry- dependent ingredients, like passivation and aging of surfaces in different crystallographic orientations, giving a qualitative understanding of resulting pore morphologies. These morphologies cannot be influenced only by the current, by chemical, material and other etching conditions, but also by an open-loop control, triggering the time scale given by the oxide dissolution time. With this method, under conditions where only branching pores occur, the additional signal hinders side pore formation resulting in regular pores with modulated diameter

Pores in n-Type InP: A Model System for Electrochemical Pore Etching

The growth mechanism of currentline-oriented pores in n-type InP has been studied by Fast-Fourier-Transform Impedance Spectroscopy (FFT IS) applied in situ during pore etching and by theoretical calculations. Several pore growth parameters could thus be extracted in situ that are otherwise not obtainable. These include the space-charge-region (SCR) width, the SCR potential, the capacitance at the pore tips, and the avalanche breakdown field strength. It could be demonstrated that the system adjusts itself in such a way that the potential across the space-charge-region at the pore tips is kept constant within a certain bandwidth of the applied potential. This provides for a constant field strength at the pore tips, ensuring that avalanche breakdown occurs, generating the necessary holes for the electrochemical dissolution of InP

Essays on Macroeconomics and Labor Markets

Over the last decades, the U.S. labor market has changed significantly. These developments can not only be attributed to cyclical components influencing labor market conditions during economic downturns but also partly to important and slow moving structural factors. How do changing labor markets affect workers? Discussing and answering this question is an important task for researchers, not only because labor earnings are a major source of income, making up around 60 percent of household income, but also because workers spent a large part of their lifetime at work, on average 34 hours a week for 38 years of their lives. I contribute to the understanding of changing labor markets by focusing on three specific aspects: technical change, selective hiring, and judicial ideology. While this thesis consists of three independent research papers, they are connected by an overarching focus on firms’ hiring behavior and associated consequences for workers’ employment conditions and opportunities. Chapter 2, which is joint work with Tobias Föll, explores the effect of routine-biased technical change on both the occupational and the union-membership choice of workers and thus analyses the connection between polarization and deunionization. In Chapter 3, I study the connection between involuntary part-time employment, workers’ job mobility, and the role of firms’ hiring behaviour. In Chapter 4, which is joint work with Christian Bredemeier and Tobias Föll, we examine how the ideological composition of the Supreme Court affects labor market conditions for workers in the U.S