Systematic Study on Coherent Control of Electronic Population and Vibrational Coherence in the One-Photon Regime

In the scope of this thesis, a systematic study about coherent control with shaped femtosecond pulses in the one-photon regime was performed. This regime is especially important in nature as photochemical and -physical reactions are driven by sun light, i.e. at very low intensities. Apart from the relevance of these conditions in nature, coherent control experiments at low intensity are well suited to gain understanding of the underlying processes as well as to control them by using shaped laser light fields. For the experimental shaping in the visible spectral range, a liquid-crystal spatial light modulator (LCM) was utilized. Here, it was shown for the first time that such an LCM introduces noise on the tailored spectral phase. The detailed characterization of the noise implied that molecular properties like the mobility of the liquid crystals cause the noise. Reliable pulse shapes on a pulse-to-pulse basis were achieved by externally cooling the LCM. Due to appropriate data averaging, coherent control experiments were successfully performed, where even small differences in the shaped pulses are important. These control experiments aimed at the enhancement of electronic population and vibrational coherence in the ground and excited state in dependence on the temporal shape of the excitation pulses for various excitation spectra. The temporal shape of the excitation pulse was tailored to linearly chirp pulses, multipulses, whose interpulse distance matches the period of the dominant molecular mode, and the sum of both as chirped multipulses. While the ideal choice to enhance the population and the vibrational coherence in the ground state is a resonant negatively chirped multipulse, the excited state is enhanced best with a blue-detuned positively chirped multipulse. These transient absorption experiments were performed on a prototype chromophore. However, the results should be applicable to other systems. These kinds of control experiments should be transferred to DNA bases and prototype molecules, which can be easily addressed theoretically. As many organic molecules absorb light in the ultraviolet wavelength regime, an experimental set-up for the shaping of femtosecond pulses in the spectral range between 250 nm and 350 nm was developed and characterized in detail. This setup provides the basis for future experiments with organic samples

Histone deacetylase activity is essential for the expression of HoxA9 and for endothelial commitment of progenitor cells

The regulation of acetylation is central for the epigenetic control of lineage-specific gene expression and determines cell fate decisions. We provide evidence that the inhibition of histone deacetylases (HDACs) blocks the endothelial differentiation of adult progenitor cells. To define the mechanisms by which HDAC inhibition prevents endothelial differentiation, we determined the expression of homeobox transcription factors and demonstrated that HoxA9 expression is down-regulated by HDAC inhibitors. The causal involvement of HoxA9 in the endothelial differentiation of adult progenitor cells is supported by the finding that HoxA9 overexpression partially rescued the endothelial differentiation blockade induced by HDAC inhibitors. Knockdown and overexpression studies revealed that HoxA9 acts as a master switch to regulate the expression of prototypical endothelial-committed genes such as endothelial nitric oxide synthase, VEGF-R2, and VE-cadherin, and mediates the shear stress–induced maturation of endothelial cells. Consistently, HoxA9-deficient mice exhibited lower numbers of endothelial progenitor cells and showed an impaired postnatal neovascularization capacity after the induction of ischemia. Thus, HoxA9 is regulated by HDACs and is critical for postnatal neovascularization

Non-target effects of a glyphosate-based herbicide on Common toad larvae (Bufo bufo, Amphibia) and associated algae are altered by temperature

Background Glyphosate-based herbicides are the most widely used pesticides in agriculture, horticulture, municipalities and private gardens that can potentially contaminate nearby water bodies inhabited by amphibians and algae. Moreover, the development and diversity of these aquatic organisms could also be affected by human-induced climate change that might lead to more periods with extreme temperatures. However, to what extent non-target effects of these herbicides on amphibians or algae are altered by varying temperature is not well known. Methods We studied effects of five concentrations of the glyphosate-based herbicide formulation Roundup PowerFlex (0, 1.5, 3, 4 mg acid equivalent glyphosate L−1 as a one time addition and a pulse treatment of totally 4 mg a.e. glyphosate L−1) on larval development of Common toads (Bufo bufo, L.; Amphibia: Anura) and associated algae communities under two temperature regimes (15 vs. 20 °C). Results Herbicide contamination reduced tail growth (−8%), induced the occurrence of tail deformations (i.e. lacerated or crooked tails) and reduced algae diversity (−6%). Higher water temperature increased tadpole growth (tail and body length (tl/bl) +66%, length-to-width ratio +4%) and decreased algae diversity (−21%). No clear relation between herbicide concentrations and tadpole growth or algae density or diversity was observed. Interactive effects of herbicides and temperature affected growth parameters, tail deformation and tadpole mortality indicating that the herbicide effects are temperature-dependent. Remarkably, herbicide-temperature interactions resulted in deformed tails in 34% of all herbicide treated tadpoles at 15 °C whereas no tail deformations were observed for the herbicide-free control at 15 °C or any tadpole at 20 °C; herbicide-induced mortality was higher at 15 °C but lower at 20 °C. Discussion These herbicide- and temperature-induced changes may have decided effects on ecological interactions in freshwater ecosystems. Although no clear dose-response effect was seen, the presence of glyphosate was decisive for an effect, suggesting that the lowest observed effect concentration (LOEC) in our study was 1.5 mg a.e. glyphosate L−1 water. Overall, our findings also question the relevance of pesticide risk assessments conducted at standard temperatures

Contact fatigue behavior of a-Al2O3-Ti(C,N) CVD coated WC-Co under dry and wet conditions

The response to cycling contact fatigue load of a WC-6%Co carbide coated with a Ti(C,N)/a-Al2O3 CVD multilayer was investigated in dry and wet conditions. Imprints in dry conditions were characterized by small thin cracks forming a circumference at the maximum radii of the imprint. The damaged coating was totally present in the final imprint of the dry test. Wet indentations showcase an area in the imprint where the a-Al2O3 layer has been removed throughout a ring but was kept at the center of the indentation, suggesting that the coating damage under cycling contact load in wet conditions is dominated by a-Al2O3 degradation, associated with a fretting effect or tangential loads accelerating the fatigue-corrosion of the alumina layer.Peer ReviewedPostprint (author's final draft