Dynamische Symmetrien von Atomkernen an Unterschalenabschlüssen

In dieser Arbeit wurden die Einflüsse der Unterschalenabschlüsse bei Neutronenzahlen N=40 und N=56 auf die Kernstruktur der umliegenden Atomkerne untersucht. Der Schwerpunkt war hierbei der Kern 70Zn, der im Rahmen dieser Arbeit durch eine ganze Reihe von Experimenten untersucht wurde. Es wurde zunächst ein Photonenstreu-Experiment an der Universität Stuttgart durchgeführt, um die Lebensdauer des 2+2-Zustandes in 70Zn zu überprüfen. Des Weiteren wurde 70Zn mit monoenergetischen Neutronen an der University of Kentucky untersucht. Diese Messung konnte viele entscheidende Korrekturen im tiefenergetischen Termschema von 70Zn anbringen und zeigt generelle Probleme bei den bekannten experimentellen Daten der Zink-Isotope auf. Weiterhin wurden an der Yale University mit der Methode transienter Magnetfelder magnetische Momente kurzlebiger Zustände in 70Zn vermessen. Als Konsequenz dieser Resultate wurde in dieser Arbeit gezeigt, dass der Kern 70Zn durch einen F-Spin-symmetrischen IBM-2 -Hamiltonian in der dynamischen Symmetrie U(5) beschrieben werden kann. Es wurde eine neue Deutung für das ungewöhnliche energetische Verhalten der Zustände 0+2 und 2+3 gegeben. Für den Zustand 2+3 wurde dabei das Zerfallsverhalten als Signatur der Proton-Neutron gemischt-symmetrischen Anregung 2+1,ms gedeutet. Weiterhin wurden Kandidaten für gemischt-symmetrische Zustände höherer Phononenordnung vorgestellt. Hier konnten Effekte von starken Zustandsmischungen nachgewiesen werden. Das ungewöhnliche Verhalten der 2+1,ms-Zustände in den gerade-gerade Zink-Isotopen wurde als Brechung der F-Spin-Symmetrie beim Übergang in ein Isospin-symmetrisches System gedeutet. Es wurden ebenfalls Experimente mit radioaktiven Ionen-Strahlen der Kerne 88Kr und 92Kr vorgestellt um den aktuellen Stand der Entwicklung dieser Technik aufzuzeigen. Es wurde gezeigt, welche Aufgaben angegangen werden müssen, um in Zukunft die Spektroskopie gemischt-symmetrischer Anregungen mit radioaktiven Ionen-Strahlen möglich zu machen

Monitoring of Natura 2000 sites using hyperspectral remote sensing : quality assessment of field and airborne data for Ginkelse & Ederheide and Wekeromse Zand

In 2007, an airborne imaging spectroscopy campaign was organized in the frame of the HABISTAT project. Airborne data with the AHS sensor were acquired in the Netherlands and Belgium. One test site in Belgium was recorded, the Kalmthoutse Heide and one in the Netherlands: the Edese and Ginkelse Heide and the Wekeromse Zand. This report describes the quality assessment of the field and airborne data for the Edese and Ginkelse Heide and the Wekeromse Zand site. The results for the Kalmthoutse Heide will be presented in a separate report (INBO, 2008)

Land cover maps for environmental modeling at multiple scales

As described in the ECOCHANGE proposal, Task01.02.02 “Map production and aggregation”, two major products are generated within this WP. Firstly, land cover maps at high spatial resolutions will be produced for the European Union and for the reference years of 1960, 1990 and 2000. Secondly, thematic and spatial aggregated products will be derived at coarser spatial resolutions in order to synthesize the fragmentation and variability within coarser cells for biodiversity assessment and modelling. The name of the official deliverable is D01.02.01 “Land cover maps for environmental modelling at multiple scales” and includes this report, the digital land cover products and an interactive website to view the data at all thematic and spatial scales

Object identification and characterization with hyperspectral imagery to identify structure and function of Natura 2000 habitats

Habitat monitoring of designated areas under the EU Habitats Directive requires every 6 years information on area, range, structure and function for the protected (Annex I) habitat types. First results from studies on heathland areas in Belgium and the Netherlands show that hyperspectral imagery can be an important source of information to assist the evaluation of the habitat conservation status. Hyperspectral imagery can provide continuous maps of habitat quality indicators (e.g., life forms or structure types, management activities, grass, shrub and tree encroachment) at the pixel level. At the same time, terrain managers, nature conservation agencies and national authorities responsible for the reporting to the EU are not directly interested in pixels, but rather in information at the level of vegetation patches, groups of patches or the protected site as a whole. Such local level information is needed for management purposes, e.g., exact location of patches of habitat types and the sizes and quality of these patches within a protected site. Site complexity determines not only the classification success of remote sensing imagery, but influences also the results of aggregation of information from the pixel to the site level. For all these reasons, it is important to identify and characterize the vegetation patches. This paper focuses on the use of segmentation techniques to identify relevant vegetation patches in combination with spectral mixture analysis of hyperspectral imagery from the Airborne Hyperspectral Scanner (AHS). Comparison with traditional vegetation maps shows that the habitat or vegetation patches can be identified by segmentation of hyperspectral imagery. This paper shows that spectral mixture analysis in combination with segmentation techniques on hyperspectral imagery can provide useful information on processes such as grass encroachment that determine the conservation status of Natura 2000 heathland areas to a large extent. A limitation is that both advanced remote sensing approaches and traditional field based vegetation surveys seem to cause over and underestimations of grass encroachment for specific categories, but the first provides a better basis for monitoring if specific species are not directly considered

Sequential Estimation of Multivariate Factor Stochastic Volatility Models

We provide a simple method to estimate the parameters of multivariate stochastic volatility models with latent factor structures. These models are very useful as they alleviate the standard curse of dimensionality, allowing the number of parameters to increase only linearly with the number of the return series. Although theoretically very appealing, these models have only found limited practical application due to huge computational burdens. Our estimation method is simple in implementation as it consists of two steps: first, we estimate the loadings and the unconditional variances by maximum likelihood, and then we use the efficient method of moments to estimate the parameters of the stochastic volatility structure with GARCH as an auxiliary model. In a comprehensive Monte Carlo study we show the good performance of our method to estimate the parameters of interest accurately. The simulation study and an application to real vectors of daily returns of dimensions up to 148 show the method's computation advantage over the existing estimation procedures

Comprehensive test of nuclear level density models

For the last two decades, experimental information on nuclear level densities for about 60 different nuclei has been obtained on the basis of the Oslo method. While each of these measurements has been typically compared to one or a few level density models, a global study including all the measurements has been missing. The present study provides a systematic comparison between Oslo data and six global level density models for 42 nuclei for which $s$-wave resonance spacings are also available. We apply a coherent normalization procedure to the Oslo data for each of the six different models, all being treated on the same footing. Our quantitative analysis shows that the constant-temperature model presents the best global description of the Oslo data, closely followed by the mean-field plus combinatorial model and Hartree-Fock plus statistical model. Their accuracies are quite similar, so that it remains difficult to clearly favour one of these models. When considering energies above the threshold where the experimental level scheme is complete, all the six models are shown to lead to rather similar accuracies with respect to Oslo data. The recently proposed shape method can, in principle, improve the situation since it provides an absolute estimate of the excitation-energy dependence of the measured level densities. We show for the specific case of $^{112}$Cd that the shape method could exclude the Hartree-Fock plus statistical model. Such an analysis remains to be performed for the bulk of data for which the shape method can be applied to the Oslo measurements before drawing conclusions on the general quality of a given nuclear level density model.Comment: 11 pages, 7 figures, published in PR