Refine
Document Type
- Article (8)
Has Fulltext
- yes (8)
Is part of the Bibliography
- no (8)
Keywords
- Accelerators & Beams (1)
- Accelerators & storage rings (1)
- Atomic & molecular beams (1)
- Atomic, Molecular & Optical (1)
- Beam loss (1)
- Biochemistry (1)
- Charge-transfer collisions (1)
- Circular accelerators (1)
- Direct reactions (1)
- Electronic transitions (1)
- Grünlandgesellschaften (1)
- Hafenlohr-Tal (1)
- Landwirtschaftliche Nutzung (1)
- Low & intermediate-energy accelerators (1)
- Nuclear reactions (1)
- Nuclear structure & decays (1)
- Nucleon induced nuclear reactions (1)
- Photon counting (1)
- Proteins (1)
- Shell model (1)
- Spectroscopic factors & electromagnetic moments (1)
- x-ray techniques (1)
Institute
Quasifree one-proton knockout reactions have been employed in inverse kinematics for a systematic study of the structure of stable and exotic oxygen isotopes at the R3B/LAND setup with incident beam energies in the range of 300–450 MeV/u. The oxygen isotopic chain offers a large variation of separation energies that allows for a quantitative understanding of single-particle strength with changing isospin asymmetry. Quasifree knockout reactions provide a complementary approach to intermediate-energy one-nucleon removal reactions. Inclusive cross sections for quasifree knockout reactions of the type AO(p,2p)A−1N have been determined and compared to calculations based on the eikonal reaction theory. The reduction factors for the single-particle strength with respect to the independent-particle model were obtained and compared to state-of-the-art ab initio predictions. The results do not show any significant dependence on proton-neutron asymmetry.
The nucleosynthesis of elements beyond iron is dominated by neutron captures in the s and r processes. However, 32 stable, proton-rich isotopes cannot be formed during those processes, because they are shielded from the s-process flow and r-process β-decay chains. These nuclei are attributed to the p and rp process.
For all those processes, current research in nuclear astrophysics addresses the need for more precise reaction data involving radioactive isotopes. Depending on the particular reaction, direct or inverse kinematics, forward or time-reversed direction are investigated to determine or at least to constrain the desired reaction cross sections.
The Facility for Antiproton and Ion Research (FAIR) will offer unique, unprecedented opportunities to investigate many of the important reactions. The high yield of radioactive isotopes, even far away from the valley of stability, allows the investigation of isotopes involved in processes as exotic as the r or rp processes.
The neutron-unbound isotope 13Be has been studied in several experiments using different reactions, different projectile energies, and different experimental setups. There is, however, no real consensus in the interpretation of the data, in particular concerning the structure of the low-lying excited states. Gathering new experimental information, which may reveal the 13Be structure, is a challenge, particularly in light of its bridging role between 12Be, where the N = 8 neutron shell breaks down, and the Borromean halo nucleus 14Be. The purpose of the present study is to investigate the role of bound excited states in the reaction product 12Be after proton knockout from 14B, by measuring coincidences between 12Be, neutrons, and γ rays originating from de-excitation of states fed by neutron decay of 13Be. The 13Be isotopes were produced in proton knockout from a 400 MeV/nucleon 14B beam impinging on a CH2 target. The 12 Be-n relative-energy spectrum d σ /d Ef n was obtained from coincidences between 12Be(g.s.) and a neutron, and also as threefold coincidences by adding γ rays, from the de-excitation of excited states in 12Be. Neutron decay from the first 5/2+ state in 13Be to the 2+ state in 12Be at 2.11 MeV is confirmed. An energy independence of the proton-knockout mechanism is found from a comparison with data taken with a 35 MeV/nucleon 14B beam. A low-lying p-wave resonance in 13Be(1/2−) is confirmed by comparing proton- and neutron-knockout data from 14B and 14Be.
The Coulomb Dissociation (CD) cross sections of the stable isotopes 92,94,100Mo and of the unstable isotope 93Mo were measured at the LAND/R3B setup at GSI Helmholtzzentrum für Schwerionenforschung in Darmstadt, Germany. Experimental data on these isotopes may help to explain the problem of the underproduction of 92,94Mo and 96,98Ru in the models of p-process nucleosynthesis. The CD cross sections obtained for the stable Mo isotopes are in good agreement with experiments performed with real photons, thus validating the method of Coulomb Dissociation. The result for the reaction 93Mo(γ,n) is especially important since the corresponding cross section has not been measured before. A preliminary integral Coulomb Dissociation cross section of the 94Mo(γ,n) reaction is presented. Further analysis will complete the experimental database for the (γ,n) production chain of the p-isotopes of molybdenum.
Die durch ein kleinräumiges Standorts- und Gesellschaftsmosaik ausgezeichnete Grünlandvegetation des Hafenlohrtals (Spessart) wurde mittels pflanzensoziologischer Vegetationsaufnahmen untersucht, wobei der Schwerpunkt auf der Betrachtung der maßgeblich differenzierend wirkenden Standortsfaktoren lag. Als dominierend erweist sich die Nutzung, durch die auch bei unterschiedlichen edaphischen Voraussetzungen sehr ähnliche Pflanzengesellschaften entstehen. Die regelmäßig gemähten Flächen des unteren Talabschnitts bedeckt ein Arrhenatheretum elatioris, extensiv beweidete oder gemähte Flächen werden im gesamten Talprofil vorwiegend von einer Festuca rubra-Agrostis capillaris-Gesellschaft besiedelt; dieselbe Gesellschaft findet sich auch auf den jüngeren Brachen der Hänge. Jüngere Talgrundbrachen tragen meist Polygonum bistorta-Talwiesen, ältere dagegen großflächig Phalaridetum und Staudenfluren, unter anderem eine für den Spessart in dieser Form noch nicht erwähnte Lysimachia vulgaris-Staudengesellschaft.
Floristische und räumliche Vegetationsveränderungen wurden für den Zeitraum 1984-1992 betrachtet. Die Entwicklung wird maßgeblich durch das Brachfallen vorher gemähter und im Talgrund ehemals als "Wässerwiesen" angelegter Flächen bestimmt, wodurch es besonders im Talgrund zu einer Bodenvernässung und damit zur weiteren Ausbreitung des Phalaridetum kommt.
Protective ant-plant mutualisms that are exploited by non-defending parasitic ants represent prominent model systems for ecology and evolutionary biology. The mutualist Pseudomyrmex ferrugineus is an obligate plant-ant and fully depends on acacias for nesting space and food. The parasite Pseudomyrmex gracilis facultatively nests on acacias and uses host-derived food rewards but also external food sources. Integrative analyses of genetic microsatellite data, cuticular hydrocarbons and behavioral assays showed that an individual acacia might be inhabited by the workers of several P. gracilis queens, whereas one P. ferrugineus colony monopolizes one or more host trees. Despite these differences in social organization, neither of the species exhibited aggressive behavior among conspecific workers sharing a tree regardless of their relatedness. This lack of aggression corresponds to the high similarity of cuticular hydrocarbon profiles among ants living on the same tree. Host sharing by unrelated colonies, or the presence of several queens in a single colony are discussed as strategies by which parasite colonies could achieve the observed social organization. We argue that in ecological terms, the non-aggressive behavior of non-sibling P. gracilis workers — regardless of the route to achieve this social structure — enables this species to efficiently occupy and exploit a host plant. By contrast, single large and long-lived colonies of the mutualist P. ferrugineus monopolize individual host plants and defend them aggressively against invaders from other trees. Our findings highlight the necessity for using several methods in combination to fully understand how differing life history strategies affect social organization in ants.
The access to information on the dynamic behaviour of large proteins is usually hindered as spectroscopic methods require the site-specific attachment of biophysical probes. A powerful emerging tool to tackle this issue is amber codon suppression. Till date, its application on large and complex multidomain proteins of MDa size has not been reported. Herein, we systematically investigate the feasibility to introduce different non-canonical amino acids into a 540 kDa homodimeric fatty acid synthase type I by genetic code expansion with subsequent fluorescent labelling. Our approach relies on a microplate-based reporter assay of low complexity using a GFP fusion protein to quickly screen for sufficient suppression conditions. Once identified, these findings were successfully utilized to upscale both the expression scale and the protein size to full-length constructs. These fluorescently labelled samples of fatty acid synthase were subjected to initial biophysical experiments, including HPLC analysis, activity assays and fluorescence spectroscopy. Successful introduction of such probes into a molecular machine such as fatty acid synthases may pave the way to understand the conformational variability, which is a primary intrinsic property required for efficient interplay of all catalytic functionalities, and to engineer them.
The electron-capture process was studied for Xe54+ colliding with H2 molecules at the internal gas target of the Experimental Storage Ring (ESR) at GSI, Darmstadt. Cross-section values for electron capture into excited projectile states were deduced from the observed emission cross section of Lyman radiation, being emitted by the hydrogenlike ions subsequent to the capture of a target electron. The ion beam energy range was varied between 5.5 and 30.9 MeV/u by applying the deceleration mode of the ESR. Thus, electron-capture data were recorded at the intermediate and, in particular, the low-collision-energy regime, well below the beam energy necessary to produce bare xenon ions. The obtained data are found to be in reasonable qualitative agreement with theoretical approaches, while a commonly applied empirical formula significantly overestimates the experimental findings.