Stratospheric aerosol extinction profile retrievals from SCIAMACHY limb-scatter observations

This dissertation presents a method for retrieving stratospheric aerosol extinction profiles from a global satellite data set. Ten years of limb radiance measurements with the instrument SCanning Imaging Absorption spectroMeter for Atmospheric CHartographY (SCIAMACHY) onboard the European environmental research satellite Envisat provides the unique opportunity to derive a stratospheric aerosol extinction data set over a long time period (2002 2012) with a good global coverage on a daily basis. Stratospheric sulfate aerosols have a significant impact on climate but the determination is still subject to large uncertainties. To improve our understanding of climate relevant processes an accurate determination of stratospheric aerosol properties is crucial. Deriving stratospheric aerosol extinction from limb radiance spectra requires complicated radiative transfer calculations. An algorithm based on a color-index approach combining normalized limb radiance spectra at 470 and 750 nm is applied to retrieve aerosol extinction profiles between 12 and 35 km altitude. A Mie phase function for typical background aerosols is implemented. The resulting SCIAMACHY stratospheric aerosol data set can serve as a foundation for climatological interpretation with respect to natural variability and anthropogenic impact

Transcriptional Regulation of the Nickel and Iron Metabolism in Helicobacter pylori

Up to 50 % of the world's population is infected with Helicobacter pylori. Colonization of the mucus layer of the human stomach by H. pylori, is lifelong unless treated with antibiotics (26). H. pylori, which is a neutralophilic bacterium, survives in the mucus layer of the human stomach with the help of the enzyme urease. Urease is an enzyme that converts urea into ammonium and carbon dioxide, thereby keeping the intracellular and periplasmic pH at neutral. It is estimated that up to 10% of the whole cell protein consists of this nickelcofactored enzyme (19). The nickel necessary to activate the urease is thought to come from foodsources, such as nuts, tea and cereals, which are rich in nickel (1). Metal ions like nickel or iron can be dangerous for bacteria, as they can react with oxygen in order to create reactive oxygen species that in turn can destroy macromolecules like nucleic acids, proteins and cell wall components (27). Therefore, the bacterial metal metabolism has to be tightly regulated. In H. pylori, regulatory proteins are scarce. Only two metal-regulatory proteins are known, the ferric uptake regulator Fur (4), and the nickel responsive regulator NikR (31). Fur is a regulatory protein that can sense and bind intracellular ferrous ions, and subsequently displays iron-dependent binding to conserved promoter sequences (Fur boxes) of its target genes (17). The classical regulation is repression of iron uptake genes in iron-replete conditions (15, 17, 33). Unlike all other Fur homologs known so far, H. pylori Fur can also bind to Fur-boxes in an iron free form (apo-Fur), as was shown for pfr (16) and sodB (Chapter 3). The second metal-dependent regulatory protein is NikR, the nickel responsive regulator, which belongs to the family of Ribbon-Helix-Helix regulatory proteins (9). NikR is directly involved in the regulation of acid resistance via urease and nickel-uptake (Chapter 4), and was previously demonstrated to mediate regulation of the ferric uptake regulator Fur (7, 12, 29). The aim of this thesis was to gain further insight into the transcriptional regulation the ferric uptake regulator Fur and the nickel responsive regulator NikR

miR-200c sensitizes breast cancer cells to doxorubicin treatment by decreasing TrkB and Bmi1 expression.

Acquired resistance to classical chemotherapeutics is a major obstacle in cancer treatment. Doxorubicin is frequently used in breast cancer therapy either as single-agent or in combination with other drugs like docetaxel and cyclophosphamide. All these chemotherapies have in common that they are administered sequentially and often result in chemoresistance. Here, we mimicked this pulse therapy of breast cancer patients in an in vitro cell culture model, where the epithelial breast cancer cell line BT474 was sequentially treated with doxorubicin for several treatment cycles. In consequence, we obtained chemoresistant cells displaying a mesenchymal-like phenotype with decreased levels of miR-200c. To investigate the involvement of miR-200c in resistance formation, we inhibited and overexpressed miR-200c in different cell lines. Thereby, the cells were rendered more resistant or susceptible to doxorubicin treatment. Moreover, the receptor tyrosine kinase TrkB and the transcriptional repressor Bmi1 were identified as miR-200c targets mediating the drug resistance. Hence, we provide a mechanism of acquired resistance to doxorubicin that is caused by the loss of miR-200c. Along with this, our study demonstrates the complex network of microRNA mediated chemoresistance highlighting the challenges in cancer therapy and the importance of novel microRNA-modulating anticancer agents

Soft Gamma Rays from Heavy WIMPs

We propose an explanation of the galactic center gamma ray excess by supersymmetric WIMPs as heavy as 500 GeV. The lightest neutralino annihilates into vector-like leptons or quarks which cascade decay through intermediate Higgs bosons. Due to the long decay chains, the gamma ray spectrum is much softer than naively expected and peaks at GeV energies. The model predicts correlated diboson and dijet signatures to be tested at the LHC.Comment: 8 pages, 8 figures; v2: focus on gamma ray excess, matches published versio

Adhesion Properties of Hydrogen on Sb(111) Probed by Helium Atom Scattering

We have carried out a series of helium atom scattering measurements in order to characterise the adsorption properties of hydrogen on antimony(111). Molecular hydrogen does not adsorb at temperatures above 110 K in contrast to pre-dissociated atomic hydrogen. Depending on the substrate temperature, two different adlayer phases of atomic hydrogen on Sb(111) occur. At low substrate temperatures ($110~$K), the deposited hydrogen layer does not show any ordering while we observe a perfectly ordered $(1\times 1)$ H/Sb(111) structure for deposition at room temperature. Furthermore, the amorphous hydrogen layer deposited at low temperature forms an ordered overlayer upon heating the crystal to room temperature. Hydrogen starts to desorb at $T_m = 430~$K which corresponds to a desorption energy of $E_{des}=(1.33\pm0.06)~$eV. Using measurements of the helium reflectivity during hydrogen exposure at different surface temperatures, we conclude that the initial sticking coefficient of atomic hydrogen on Sb(111) decreases with increasing surface temperature. Furthermore, the scattering cross section for the diffuse scattering of helium from hydrogen on Sb(111) is determined as \Sigma = (12 \pm 1)~\mbox{\AA}^{2}.Comment: 7 pages, 5 figure

Photoinduced molecule formation of spatially separated atoms on helium nanodroplets

Besides the use as cold matrix for spectroscopic studies, superfluid helium droplets have served as a cold environment for the synthesis of molecules and clusters. Since vibrational frequencies of molecules in helium droplets exhibit almost no shift compared to the free molecule values, one could assume the solvated particles move frictionless and undergo a reaction as soon as their paths cross. There have been a few unexplained observations that seemed to indicate cases of two species on one droplet not forming bonds but remaining isolated. In this work, we performed a systematic study of helium droplets doped with one rubidium and one strontium atom showing that besides a reaction to RbSr, there is a probability of finding separated Rb and Sr atoms on one droplet that only react after electronic excitation. Our results further indicate that ground-state Sr atoms can reside at the surface as well as inside the droplet