Micromagnetic dissipation, dispersion, and mode conversion in thin permalloy platelets

Micron-sized ferromagnetic Permalloy disks exhibiting an in-plane ferromagnetic vortex structure are excited by a fast rise time perpendicular magnetic field pulse and their modal structure is analyzed. We find azimuthal and axial modes. By a Fourier filtering technique we can separate and analyze the time dependence of individual modes. Analysis of the experimental data demonstrates that the azimuthal modes damp more quickly than the axial modes. We interpret these results as mode conversion from low-frequency azimuthal modes to the fundamental mode which is higher in frequency, i.e., mode-mode coupling in a system with a single Landau-Lifshitz-Gilbert phenomenological damping constant alpha.     

4,5-Dihydro-1H-azepine aus aktivierten Cyclobutenen und 1,3-Dipolen

Cycloaddition of diphenylnitrile ylide to dicyanocyclobutene and of a mesoionic oxazolium-5-olate to isopropylidenecyclobutenone yields dihydroazepine derivatives by cleavage of the strained internal σ-bonds in the primarily formed bicyclic adducts.     

Calculation of the dielectric function for highly excited polar semiconductors

The optical dielectric function of an electron-hole plasma in highly excited polar semiconductors with a direct band gap is calculated by solving a Bethe-Salpeter equation for the polarization function. The screening of the Coulomb potential is treated in a damped phonon-plasmon-pole approximation. We include the complex dynamical self-energy corrections as well as electron-hole correlations.Project of the Sonderforschungsbereich Frankfurt/Darmstadt, financed by special funds of the Deutsche Forschungsgemeinschaft     

Quantum mechanical theory of fluctuations and relaxation in semiconductor lasers

Pumping, spontaneous emission and electron-electron scattering lead to relaxation terms in the mean equations of motion for the electron system. These terms are derived from a quantum mechanical basis by second order perturbation theory and by appropriate reservoir averaging. If the electron distribution is not too strongly degenerate, then a relaxation time approximation can be derived. The quantum mechanical Langevin method is used to include noise. The correlation functions of all fluctuation operators are calculated. From the knowledge of the equations of motion and of the correlation functions it is possible to calculate the noise properties of the laser light and of the junction current, as will be shown in other publications.     

A calculation of the odd parity spectrum of16O and40Ca from the interaction between nucleons: Method and first results

In the framework of an exact many-body theory based on the formalism of Green's functions, we rederive an eigenvalue equation capable of describing single particle excitations of a Fermi system. The effective two-particle interaction entering this equation is extracted free of all adjustable parameters from a very simple nucleon-nucleon interaction by solving the corresponding integral equation for nuclear matter and using a local density approximation. We apply our method for describing those states of the doubly magic nuclei¹⁶O and⁴⁰Ca which probably can be understood as one-particle-one-hole excitations from the ground state, i.e. low-lying negative parity levels, and — in view of the simplicity of the interaction assumed — find reasonably good aggreement with experimental evidence.     

Multibody elastic contact analysis by quadratic programming

A quadratic programming method for contact problems is extended to a general problem involving contact ofn elastic bodies. Sharp results of quadratic programming theory provide an equivalence between the originaln-body contact problem and the simplex algorithm used to solve the quadratic programming problem. Two multibody examples are solved to illustrate the technique.     

Uran

Ohne Zusammenfassung