The Baldwin-effect in Wolf-Rayet stars

This thesis investigates the Baldwin-effect in Wolf-Rayet (WR) stars. The Baldwin-effect is a correlation with negative slope between the equivalent width of spectral emission lines and the monochromatic luminosity of the underlying continuum at the line wavelength. This effect has been known to exist in spectra of Active Galactic Nuclei and WR stars. The Baldwin effect in WR stars may function as a distance estimator, as it may provide a method to derive the stellar luminosity directly from the spectrum. Distances of WR stars are hard to derive. These stars lose matter in the form of a strong stellar wind, which hides the underlying star from view. The dense stellar wind is the reason that absolute visual magnitudes of WR stars do not correlate well with the star's temperature or intrinsic colours. Therefore, the derivation of the distance of a WR star through observational properties is not an easy task to perform. The research of this thesis confirms previous thoughts that the Baldwin effect in WR stars is mainly caused by differences in radius among stars, reflecting differences in wind density. Furthermore, it is found that the spread in the equivalent width-luminosity relations is caused by diffences in mass-loss rate and terminal wind velocity among stars and, to a lesser extend, differences in stellar temperature. This theoretical explanation of the Baldwin-effect is done by comparing simple semi-analytical expressions with the results of model stellar atmosphere calculations. For the application of the Baldwin-effect to estimate WR star distances, it is found that a reasonably accurate estimate of the mass-loss rate is required. However, the derived mass-loss rates of WR stars generally depend on an assumed distance of the star. Therefore it is tried to combine several mass-loss studies and find typical values of the mass-loss rate as function of stellar subtype. After adopting a value of the mass-loss rate for its spectral subtype, the distance of the star can be estimated through the Baldwin-effect. The performance of the Baldwin-effect as a distance estimator is tested by concentrating at WR stars with well known distances, such as those in the Large Magellanic Cloud or WR stars that are a member of an open star cluster or OB association. It is concluded that estimating WR star distances by means of this method does give a reasonable indication of the stellar distance, but often not better than existing methods

Comparative genomic profiling of Dutch clinical Bordetella pertussis isolates using DNA microarrays: Identification of genes absent from epidemic strains

Contains fulltext : 72769.pdf (publisher's version ) (Open Access)14 p

Correction: Comparative genomic profiling of Dutch clinical Bordetella pertussis isolates using DNA microarrays: identification of genes absent from epidemic strains

<p><b>Copyright information:</b></p><p>Taken from "Comparative genomic profiling of Dutch clinical isolates using DNA microarrays: Identification of genes absent from epidemic strains"</p><p>http://www.biomedcentral.com/1471-2164/9/311</p><p>BMC Genomics 2008;9():311-311.</p><p>Published online 30 Jun 2008</p><p>PMCID:PMC2481270.</p><p></p

Comparison of high-and low-let radiation-induced dna double-strand break processing in living cells

High-linear-energy-transfer (LET) radiation is more lethal than similar doses of low-LET radiation types, probably a result of the condensed energy deposition pattern of high-LET radiation. Here, we compare high-LET α-particle to low-LET X-ray irradiation and monitor double-strand break (DSB) processing. Live-cell microscopy was used to monitor DNA double-strand breaks (DSBs), marked by p53-binding protein 1 (53BP1). In addition, the accumulation of the endogenous 53BP1 and replication protein A (RPA) DSB processing proteins was analyzed by immunofluorescence. In contrast to α-particle-induced 53BP1 foci, X-ray-induced foci were resolved quickly and more dynamically as they showed an increase in 53BP1 protein accumulation and size. In addition, the number of individual 53BP1 and RPA foci was higher after X-ray irradiation, while focus intensity was higher after α-particle irradiation. Interestingly, 53BP1 foci induced by α-particles contained multiple RPA foci, suggesting multiple individual resection events, which was not observed after X-ray irradiation. We conclude that high-LET α-particles cause closely interspaced DSBs leading to high local concentrations of repair proteins. Our results point toward a change in DNA damage processing toward DNA end-resection and homologous recombination, possibly due to the depletion of soluble protein in the nucleoplasm. The combination of closely interspaced DSBs and perturbed DNA damage processing could be an explanation for the increased relative biological effectiveness (RBE) of high-LET α-particles compared to X-ray irradiation

The FDR4ATMOS Project

The FDR4ATMOS project has two main tasks. The focus of task A is to update the SCIAMACHY processing chain for better Ozone total columns. After the full re-processing of the SCIAMACHY mission with processor versions 9 (Level 1) and version 7 (Level 2), the comparison with ground-based data showed that the total Ozone column showed a downward trend of nearly 2% from the beginning of the time series to its end. This trend is an artefact and is likely caused by changes made to the calibration algorithms in the Level 1 processor (the DOAS retrieval algorithm for Ozone was not changed). The most likely reason are changes in the degradation correction that lead to subtle changes in the spectral structures that in the retrieval are interpreted as an atmospheric signature. In task A we will update the Level 0-1 processor with the final aim of a mission re-processing. The second task in the FDR4ATMOS project is to develop a cross-instrument Level 1 product for GOME-1 and SCIAMACHY for the UV, VIS and NIR spectral range with a focus on the spectral windows used for O3, SO2, NO2 total column retrieval and the determination of cloud properties. Contrary to other projects, FDR4ATMOS does not aim to build a harmonised time series on Level 2 products but on Level 1 products, i.e. radiances and reflectances. The GOME-1 and SCIAMACHY instrument together span 17 years of spectrally highly resolved data. The goal of the FDR4ATMOS project is to generate harmonised data sets that allow the user to use it directly in long term trend analysis, independent of the instrument. Since this was never done for highly resolved spectrometers, new methods have to be developed that e.g. take into account the different observation geometries and observation times of the instrument without impacting the spectral structures that are used for the retrieval of the atmospheric species. The resulting algorithms and the processor should also be as generic as possible to be able to transfer the methodology easily to other instruments (e.g. GOME-2, Sentinel-5p) for a future extension of the time series. The FDR4ATMOS started in October 2019 and is currently in phase 1. We will present the goals of the project and first results

Uptake and subcellular distribution of radiolabeled polymersomes for radiotherapy

Polymersomes have the potential to be applied in targeted alpha radionuclide therapy, while in addition preventing release of recoiling daughter isotopes. In this study, we investigated the cellular uptake, post uptake processing and intracellular localization of polymersomes. Methods: High-content microscopy was used to validate polymersome uptake kinetics. Confocal (live cell) microscopy was used to elucidate the uptake mechanism and DNA damage induction. Intracellular distribution of polymersomes in 3-D was determined using super-resolution microscopy. Results: We found that altering polymersome size and concentration affects the initial uptake and overall uptake capacity; uptake efficiency and eventual plateau levels varied between cell lines;

HSF2BP Interacts with a Conserved Domain of BRCA2 and Is Required for Mouse Spermatogenesis

The tumor suppressor BRCA2 is essential for homologous recombination (HR), replication fork stability, and DNA interstrand crosslink repair in vertebrates. We identify HSF2BP, a protein previously described as testis specific and not characterized functionally, as an interactor of BRCA2 in mouse embryonic stem cells, where the 2 proteins form a constitutive complex. HSF2BP is transcribed in all cultured human cancer cell lines tested and elevated in some tumor samples. Inactivation of the mouse Hsf2bp gene results in male infertility due to a severe HR defect during spermatogenesis. The BRCA2-HSF2BP interaction is highly evolutionarily conserved and maps to armadillo repeats in HSF2BP and a 68-amino acid region between the BRC repeats and the DNA binding domain of human BRCA2 (Gly2270-Thr2337) encoded by exons 12 and 13. This region of BRCA2 does not harbor known cancer-associated missense mutations and may be involved in the reproductive rather than the tumor-suppressing function of BRCA2. BRCA2 is a key homologous recombination mediator in vertebrates. Brandsma et al. show that it directly interacts with a testis-expressed protein, HSF2BP, and that male mice deficient for HSF2BP are infertile due to a meiotic recombination defect. They also find that HSF2BP contributes to DNA repair in mouse embryonic stem cells

Glyoxal tropospheric column retrievals from TROPOMI – multi-satellite intercomparison and ground-based validation

We present the first global glyoxal (CHOCHO) tropospheric column product derived from the TROPOspheric Monitoring Instrument (TROPOMI) on board the Sentinel-5 Precursor satellite. Atmospheric glyoxal results from the oxidation of other non-methane volatile organic compounds (NMVOCs) and from direct emissions caused by combustion processes. Therefore, this product is a useful indicator of VOC emissions. It is generated with an improved version of the BIRA-IASB scientific retrieval algorithm relying on the differential optical absorption spectroscopy (DOAS) approach. Among the algorithmic updates, the DOAS fit now includes corrections to mitigate the impact of spectral misfits caused by scene brightness inhomogeneity and strong NO2 absorption. The product comes along with a full error characterization, which allows for providing random and systematic error estimates for every observation. Systematic errors are typically in the range of 1 ×10^14–3 ×10^14 molec. cm−2 (∼30 %–70 % in emission regimes) and originate mostly from a priori data uncertainties and spectral interferences with other absorbing species. The latter may be at the origin, at least partly, of an enhanced glyoxal signal over equatorial oceans, and further investigation is needed to mitigate them. Random errors are large ( molec. cm−2) but can be reduced by averaging observations in space and/or time. Benefiting from a high signal-to-noise ratio and a large number of small-size observations, TROPOMI provides glyoxal tropospheric column fields with an unprecedented level of detail. Using the same retrieval algorithmic baseline, glyoxal column data sets are also generated from the Ozone Monitoring Instrument (OMI) on Aura and from the Global Ozone Monitoring Experiment-2 (GOME-2) on board Metop-A and Metop-B. Those four data sets are intercompared over large-scale regions worldwide and show a high level of consistency. The satellite glyoxal columns are also compared to glyoxal columns retrieved from ground-based Multi-AXis DOAS (MAX-DOAS) instruments at nine stations in Asia and Europe. In general, the satellite and MAX-DOAS instruments provide consistent glyoxal columns both in terms of absolute values and variability. Correlation coefficients between TROPOMI and MAX-DOAS glyoxal columns range between 0.61 and 0.87. The correlation is only poorer at one mid-latitude station, where satellite data appear to be biased low during wintertime. The mean absolute glyoxal columns from satellite and MAX-DOAS generally agree well for low/moderate columns with differences of less than 1×10^14 molec. cm−2. A larger bias is identified at two sites where the MAX-DOAS columns are very large. Despite this systematic bias, the consistency of the satellite and MAX-DOAS glyoxal seasonal variability is high

Guide-free Cas9 from pathogenic Campylobacter jejuni bacteria causes severe damage to DNA

CRISPR-Cas9 systems are enriched in human pathogenic bacteria and have been linked to cytotoxicity by an unknown mechanism. Here, we show that upon infection of human cells, Campylobacter jejuni secretes its Cas9 (CjeCas9) nuclease into their cytoplasm. Next, a native nuclear localization signal enables CjeCas9 nuclear entry, where it catalyzes metal-dependent nonspecific DNA cleavage leading to cell death. Compared to CjeCas9, native Cas9 of Streptococcus pyogenes (SpyCas9) is more suitable for guide-dependent editing. However, in human cells, native SpyCas9 may still cause some DNA damage, most likely because of its ssDNA cleavage activity. This side effect can be completely prevented by saturation of SpyCas9 with an appropriate guide RNA, which is only partially effective for CjeCas9. We conclude that CjeCas9 plays an active role in attacking human cells rather than in viral defense. Moreover, these unique catalytic features may therefore make CjeCas9 less suitable for genome editing applications

A new algorithm to retrieve SO2 layer height from UV backscattered measurements: Application to OMI and TROPOMI and comparison with other satellite datasets

info:eu-repo/semantics/nonPublishe