Relativistic quantum dynamics in strong fields: Photon emission from heavy, few-electron ions

Recent progress in the study of the photon emission from highly-charged heavy ions is reviewed. These investigations show that high-$Z$ ions provide a unique tool for improving the understanding of the electron-electron and electron-photon interaction in the presence of strong fields. Apart from the bound-state transitions, which are accurately described in the framework of Quantum Electrodynamics, much information has been obtained also from the radiative capture of (quasi-) free electrons by high-$Z$ ions. Many features in the observed spectra hereby confirm the inherently relativistic behavior of even the simplest compound quantum systems in Nature.Comment: Version 18/11/0

Forward K+ production in subthreshold pA collisions at 1.0 GeV

K+ meson production in pA (A = C, Cu, Au) collisions has been studied using the ANKE spectrometer at an internal target position of the COSY-Juelich accelerator. The complete momentum spectrum of kaons emitted at forward angles, theta < 12 degrees, has been measured for a beam energy of T(p)=1.0 GeV, far below the free NN threshold of 1.58 GeV. The spectrum does not follow a thermal distribution at low kaon momenta and the larger momenta reflect a high degree of collectivity in the target nucleus.Comment: 4 pages, 3 figure

Gregor Lang-Wojtasik (2008): Schule in der Weltgesellschaft – Herausforderungen und Perspektiven einer Schultheorie jenseits der Moderne. Weinheim, München: Juventa 2008, 240 S. [Rezension]

Rezension zu: Gregor Lang-Wojtasik (2008): Schule in der Weltgesellschaft – Herausforderungen und Perspektiven einer Schultheorie jenseits der Moderne. Weinheim, München: Juventa 2008, 240 S., ISBN 978-3-7799-1267-

Processing of triplex-directed psoralen DNA interstrand crosslinks by recombination mechanisms

Gene targeting via homologous recombination (HR) is an important application in biotechnology and medicine. However, in mammalian cells HR is much less efficient than random integration. Triplex-forming oligonucleotides (TFOs) linked to DNA damaging agents (e.g. psoralen) can stimulate HR, providing the potential to improve gene therapy applications. To elucidate factors affecting TFO-directed psoralen interstrand crosslink (ICL)-induced recombination, we constructed a series of plasmids with duplicated supF reporter genes, each containing an inactivating deletion, to measure HR frequencies in mammalian cells. Our results indicated that TFO-directed ICL-induced recombination frequencies were higher in the plasmids with larger distances between duplicated supF genes than with a smaller separation distance. However, the position of the ICL relative to the reporter genes did not affect HR frequencies. Recombination spectra were altered by the distance between supF copies. Although single-strand annealing (SSA) recombinants were predominant in all plasmid substrates, the plasmid with the shortest interval (60 bp) revealed a significant proportion of gene conversions (GCs). GCs occurred exclusively in the gene containing the shortest deletion, regardless of the distance between supF genes, ICL position or deletion orientation. Our analyses indicated that SSA is the predominant mechanism of ICL processing of these substrates in mammalian cells

Also at National Accelerator Centre, Faure, South Africa On leave from ICUF

Abstract A stack of annular detectors made of high-purity germanium was developed. The detectors are position sensitive with radial structures. The first one (&quot;Quirl&quot;) is double-sided position sensitive defining 40 000 pixels, the following three (E1, E2 and E3) have 32 wedges each. The Quirl acts as tracker while the other three act as calorimeter. The stack was successfully operated in meson production reactions close to threshold

Chemical–Genetic Profiling of Imidazo[1,2-a]pyridines and -Pyrimidines Reveals Target Pathways Conserved between Yeast and Human Cells

Small molecules have been shown to be potent and selective probes to understand cell physiology. Here, we show that imidazo[1,2-a]pyridines and imidazo[1,2-a]pyrimidines compose a class of compounds that target essential, conserved cellular processes. Using validated chemogenomic assays in Saccharomyces cerevisiae, we discovered that two closely related compounds, an imidazo[1,2-a]pyridine and -pyrimidine that differ by a single atom, have distinctly different mechanisms of action in vivo. 2-phenyl-3-nitroso-imidazo[1,2-a]pyridine was toxic to yeast strains with defects in electron transport and mitochondrial functions and caused mitochondrial fragmentation, suggesting that compound 13 acts by disrupting mitochondria. By contrast, 2-phenyl-3-nitroso-imidazo[1,2-a]pyrimidine acted as a DNA poison, causing damage to the nuclear DNA and inducing mutagenesis. We compared compound 15 to known chemotherapeutics and found resistance required intact DNA repair pathways. Thus, subtle changes in the structure of imidazo-pyridines and -pyrimidines dramatically alter both the intracellular targeting of these compounds and their effects in vivo. Of particular interest, these different modes of action were evident in experiments on human cells, suggesting that chemical–genetic profiles obtained in yeast are recapitulated in cultured cells, indicating that our observations in yeast can: (1) be leveraged to determine mechanism of action in mammalian cells and (2) suggest novel structure–activity relationships

Current Wildland Fire Patterns and Challenges in Europe: A Synthesis of National Perspectives

Changes in climate, land use, and land management impact the occurrence and severity of wildland fires in many parts of the world. This is particularly evident in Europe, where ongoing changes in land use have strongly modified fire patterns over the last decades. Although satellite data by the European Forest Fire Information System provide large-scale wildland fire statistics across European countries, there is still a crucial need to collect and summarize in-depth local analysis and understanding of the wildland fire condition and associated challenges across Europe. This article aims to provide a general overview of the current wildland fire patterns and challenges as perceived by national representatives, supplemented by national fire statistics (2009–2018) across Europe. For each of the 31 countries included, we present a perspective authored by scientists or practitioners from each respective country, representing a wide range of disciplines and cultural backgrounds. The authors were selected from members of the COST Action “Fire and the Earth System: Science & Society” funded by the European Commission with the aim to share knowledge and improve communication about wildland fire. Where relevant, a brief overview of key studies, particular wildland fire challenges a country is facing, and an overview of notable recent fire events are also presented. Key perceived challenges included (1) the lack of consistent and detailed records for wildland fire events, within and across countries, (2) an increase in wildland fires that pose a risk to properties and human life due to high population densities and sprawl into forested regions, and (3) the view that, irrespective of changes in management, climate change is likely to increase the frequency and impact of wildland fires in the coming decades. Addressing challenge (1) will not only be valuable in advancing national and pan-European wildland fire management strategies, but also in evaluating perceptions (2) and (3) against more robust quantitative evidence

Development of double-sided microstructured Si(Li) detectors

A new technique for manufacturing double-sided structured Si(Li) detectors has been established. The position-sensitive structure on the implanted p(+)-contact can be made smaller than 100 mum by photolithography followed by plasma etching of grooves to separate the position elements. By modifying this technique position-sensitive structures on a thin (similar to30 mum) Li-diffused contact were created. Areas of 50 mm x 50 mm were divided into 50 or 100 strips with a pitch of 1 mm or 500 mum, respectively. The strips were separated by similar to35-mum-deep and similar to50-mum-wide grooves. Measurements of the electrical resistance of the grooves and reverse current of the strips are presented. Charge splitting on the adjacent strips shows practically no charge loss through the groove. Small pixel effects are demonstrated on a Li-diffused contact (100 strips with the pitch of 500 mum) and on the first double-sided Si(Li) detector (50 x 50 strips with a pitch of 1 mm). By measuring the relative time distribution of the signal from both contacts it is possible to obtain some three-dimensional imaging capability