Kinetik des Abbaues von 1,4-Polybutadien durch Olefin-Metathese

Ohne Zusammenfassung     

Resolution enhancement in a light-sheet-based microscope (SPIM)

Light-sheet-based microscopy [single-plane illumination microscope (SPIM)] performs very well at low numerical apertures. It complements conventional (FM), confocal (CFM), and two-photon fluorescence microscopy (2hnu-FM) currently used in modern life sciences. Lateral and axial SPIM point spread function (PSF) extents are measured by using fluorescent beads to determine the 3D resolution. The results are compared with values derived from an analytical theory and numerical simulations. The discrepancies are found to be less than 5%. The axial extent of a SPIM-PSF (10x/0.3 W) is approximately 5.7 microm. This value is almost a factor of 2 smaller than in CFM, more than 2.5 times smaller than in FM, and more than three times smaller than in 2hnu-FM. SPIM outperforms 2hnu-FM and FM, while CFM has a better axial resolution at NAs above 0.8.     

Revisiting the global electroweak fit of the Standard Model and beyond with Gfitter

The global fit of the Standard Model to electroweak precision data, routinely performed by the LEP electroweak working group and others, demonstrated impressively the predictive power of electroweak unification and quantum loop corrections. We have revisited this fit in view of (i) the development of the new generic fitting package, Gfitter, allowing for flexible and efficient model testing in high-energy physics, (ii) the insertion of constraints from direct Higgs searches at LEP and the Tevatron, and (iii) a more thorough statistical interpretation of the results. Gfitter is a modular fitting toolkit, which features predictive theoretical models as independent plug-ins, and a statistical analysis of the fit results using toy Monte Carlo techniques. The state-of-the-art electroweak Standard Model is fully implemented, as well as generic extensions to it. Theoretical uncertainties are explicitly included in the fit through scale parameters varying within given error ranges. This paper introduces the Gfitter project, and presents state-of-the-art results for the global electroweak fit in the Standard Model (SM), and for a model with an extended Higgs sector (2HDM). Numerical and graphical results for fits with and without including the constraints from the direct Higgs searches at LEP and Tevatron are given. Perspectives for future colliders are analysed and discussed. In the SM fit including the direct Higgs searches, we find M _H =116.4_−1.3^+18.3 GeV, and the 2σ and 3σ allowed regions [114,145] GeV and [[113,168] and [180,225]] GeV, respectively. For the strong coupling strength at fourth perturbative order we obtain α _S (M _Z ²)=0.1193_−0.0027^+0.0028(exp )±0.0001 (theo). Finally, for the mass of the top quark, excluding the direct measurements, we find m _t =178.2_−4.2^+9.8 GeV. In the 2HDM we exclude a charged-Higgs mass below 240 GeV at 95% confidence level. This limit increases towards larger tan β, e.g., is excluded for tan β=70.     

Evidence for multiphonon giant resonances in electromagnetic fission of 238U

Differential cross sections for electromagnetic fission of 238U projectiles (500 MeV/u) in C, Sn, and Pb targets are measured and analyzed in terms of single- and multiphonon giant resonance excitations as doorway states to fission. A novel experimental method exploits the linear relationship between neutron multiplicity and the primary 238U excitation energy. Multiphonon states contribute up to 20% of the cross section; a component at high excitation energies is indicated that may arise from three-phonon dipole and two-phonon GDR x GQRiv giant resonance excitations.     

Optical levitation of absorbing particles with a nominally Gaussian laser beam

We use a Gaussian laser beam to study the levitation of absorbing Mie particles. Several metal oxide particles are stably levitated, and their movement over time is recorded. Our studies show that the position of each particle is highly dependent on the other particles' locations. The observations are explained by the phenomenon of thermal creep. The increased local pressure that is due to a temperature gradient along the particle's surface induces levitation. The particles rest close to minima in the intensity distribution near the optical axis. An experiment is suggested that can be used to locate these minima in a laser beam.     

The PbPb collision

The reaction ²⁰⁸Pb on ²⁰⁸Pb was studied at bombarding energies of 7.0 and 7.57 MeV/u. One-particle inclusive measurements using a large-area position-sensitive ionisation chamber delivered the kinetic energy, charge and scattering angle of the reaction products. A precise calibration of the stopping power for very heavy ions in the detector gas was performed. The measured Wilczynski diagrams show, for increasing loss of kinetic energy, an increase of the mean scattering angle. It is attributed to the dominance of the repulsive Coulomb forces with respect to the attractive nuclear forces. The element distribution for the ²⁰⁸Pb on ²³⁸U reaction at 7.5 MeV/u was also measured and compared to the PbPb and UU reactions. Fission probabilities are derived as a function of charge and total kinetic energy loss. The most striking result is seen in the σ_z² versus TKEL correlation: the average rate of energy loss per nucleon exchange is abnormally large. It is shown that this behaviour is associated with the double magic closed shell character of the colliding nuclei. Nuclear structure information is extracted through a simple parametrisation.     

Nebenreaktionen bei der Umsetzung von Trimethylsilylazid mit Trimethylphosphit und Trisdimethylaminophosphin

Side Reactions upon Interaction of Trimethylsilyl Azide with Trimethylphosphite and Trisdimethylaminophosphine Trisdimethylaminophosphine reacts with trimethylsilyl azide with evolution of nitrogen and formation of N-trimethylsilyl-iminophosphoric acid hexamethyltriamide, (Me₂N)₃ · P ? N? SiMe₃. The diphosphazene (Me₂N)₃P ? N? P(NMe₂)₂ ? N? SiMe₃ is formed in a side reaction with concomitant elimination of dimethylamino trimethylsilane. The reaction of trimethylsilyl azide with trimethylphosphite affords, besides the expected N-trimethylsilyliminophosphorus trimethylester, (MeO)₃P ? N? SiMe₃, the isomeric N-trimethylsilyl-N-methyl-aminophosphoric dimethylester, (MeO₂)P(O)? N(Me)SiMe₃.