[en] In this thesis the cosmological constant is investigated from two points of view. First, we study the influence of a time-dependent cosmological constant on the late-time expansion of the universe. Thereby, we consider several combinations of scaling laws motivated by renormalisation group running and different choices for the interpretation of the renormalisation scale. Apart from well known solutions like de Sitter final states we also observe the appearance of future singularities. As the second topic we explore vacuum energy in the context of discrete extra dimensions, and we calculate the Casimir energy density as a contribution to the cosmological constant. The results are applied in a deconstruction scenario, where we propose a method to determine the zero-point energy of quantum fields in four dimensions. In a related way we find a lower bound on the size of a discrete gravitational extra dimension, and finally we discuss the graviton and fermion mass spectra in a scenario, where the extra dimensions form a discrete curved disk. (orig.)

[en] EDDA is an internal experiment at the Cooler Synchrotron COSY of the Forschungszentrum Juelich. The detector is specialized for a detailed study of the elastic proton-proton-scattering and consists of two concentric scintillator hodoscopes of cylindrical symmetry, covering an angular range of 30 ≤θ_cm≤90 in the center of mass system. The reaction vertex and the scattering angle are reconstructed from the points of incidence through the two layers of the detector. The EDDA-Experiment measures angular distributions and excitation functions of five observables of the elastic proton-proton scattering in the energy range 500 MeV≤Tp_≤2500 MeV with focus on polarization observables. The first phase was devoted to the measurement of the unpolarized differential cross section dσ/dΩ, the second phase consisted of the measurement of the analyzing power A_N. Both are finished and first results have been published. This work deals with the third phase of the EDDA-experiment: the determination of the three spin correlation coeffcients A_SS, A_NN and A_SL, which were measured during three successive beam-times in November/December 1999, May/June 2000 and November/December 2000. For the measurements of the spin observables, a polarized atomic beam target was used with a typical target thickness of 1.8.10¹¹ cm-2 and effective polarizations between 60% and 70%. Some development during the different beam-times resulted in a polarized COSY-beam with up to 65% polarization at highest energies with 4.10⁹ stored protons. These numbers convert into luminosities of 9.0.10²⁶ cm^-2s^-1; they were insufficient to perform measurements only during beam acceleration, as it was done for dσ/dΩ and A_N to obtain data with sufficient statistics needed for high internal consistency. To accumulate statistics at higher energies, data acquisition for A_SS, A_NN and A_SL during beam acceleration (approx. 2 mio. events) was combined with measurements at some fixed energies. The spin correlation coeffcients are determined with a method developed within this work using count rate asymmetries. The systematic error of this method is smaller than 1.7%. The uncertainty of the determination of the beam- and targetpolarizations by normalizing count rate asymmetries to the analyzing power measured by the EDDA-Experiment in phase two is smaller than 4.1% on an absolute scale. The results of the EDDA-Experiment are in good agreement with the existing data. They expand the world data base, especially for ASS. The solutions of phase shift analyses not containing the EDDA data show significant systematic deviations where the data base is poor, especially for the observable ASS at higher energies

[en] To diagnose osteoporosis, a method has been developed and tested to determine the density and thickness of the finger bone. The main topic of the investigation was to find out which measuring equipment and apparative adjustments give the most reliable results. Besides influences of the time constants of the related ratemeters, systematic deviations were determined by using digital ratemeters. (ORU/LH)

[en] In a 6D model, where the extra dimensions form a discretised curved disk, we investigate the mass spectra and profiles of gravitons and Dirac fermions. The discretisation is performed in detail leading to a star-like geometry. In addition, we use the curvature of the disk to obtain the mass scales of this model in a more flexible way. We also discuss some applications of this setup like generating small fermion masses. (orig.)

[en] Six fuel pins with SNR-300, Mark-Ia fuel in finned tubes with 6 mm outer tube diameter were irradiated in the BR-2 reactor in Mol, Belgium. These pins were irradiated up to 90 MWd/kgHM in the MOL-7D experiment. For three of the six pins destructive examinations were performed in addition to the non-destructive ones. The results of all examinations are presented in this report. They include the fission gas analysis, burnup analysis and ceramography

[en] We establish an indirect link between relic neutrinos and the dark energy sector which originates from the vacuum energy contributions of the neutrino quantum fields. Via renormalization group effects they induce a running of the cosmological constant with time which dynamically influences the evolution of the cosmic neutrino background. We demonstrate that the resulting reduction of the relic neutrino abundance allows to largely evade current cosmological neutrino mass bounds and discuss how the scenario might be probed by the help of future large scale structure surveys and Planck data. (orig.)

[en] In the frame of the capsule group 6d three mixed carbide pins (pellet-density 92% T.D.) with a big radial gap (250 μm) were irradiated in the thermal neutron flux of FR 2. The cladding material consisted of the austenitic steel No. 1.4988. The exposure time in the reactor was up to 680 days, the burnup was 7.4 at %. The pins were instrumented on their surface with 6 thermocouples each. During irradiation in the NaK capsule no bigger irregularities in temperature readings were found. During dismantling in Karlsruhe Hot Cells the capsules it was found that all 3 pins showed cracks on their clads. The profilometry of the pins showed diameter increases from 4.5 to 6.0%. The carburization of the cladding proved the same tolerable magnitude as found for pins irradiated with moderate rod powers (Tsub(clad) <= 600⁰C). Comparing ceramography with that of other pins of the same capsule group (KfK 2577) no bigger differences in structure were found. (orig.)

No abstract available

[en] The irradiation experiment Mol-8C has been conceived to measure in pile the fission gas pressure built up. Furtheron, the influence of fabrication porosity (constant smear density) on pin behaviour for two different rod powers should be tested. The first objective was full comprehended. The second point could not be interpreted because of mechanical interaction. Pin No. 9 with zones of changing porosity (88 - 91 - 95% TD) was examined for radial porosity redistribution. The radial porosity redistributions were recalculated by the improved oxide-pin-program SATURN-3. Furtheron, the diameter increase of the claddings were recalculated and compured by SATURN-3. (orig.)

No abstract available