From modula to oberon

The programming language Oberon is the result of a concentrated effort to increase the power of Modula-2 and simultaneously to reduce its complexity. Several features were eliminated, and a few were added in order to increase the expressive power and flexibility of the language. This paper describes and motivates the changes. The language is defined in a concise report¹.     

Reconstruction of the lateral ligaments of the ankle using a regional periosteal flap

We have treated 94 patients with chronic instability of the lateral side of the ankle by reconstruction of the ligaments with local periosteal tissue. We reviewed 90 cases after a mean follow-up of 2.8 years (2 to 9) using a questionnaire, clinical examination and radiography. The results on a 100-point ankle score indicated that 81% had a good or excellent result. The periosteal flap-replacement technique allows anatomical reconstruction and does not sacrifice other ligaments or tendons in the foot.     

Vortex dynamics in Bi2Sr2CaCu2O8-thin films in the presence of columnar defects

With heavy ion irradiation we create continous amorphous columnar defects in Bi₂Sr₂CaCu₂O₈-thin films. With regard to a reliable comparison of irradiation effects three of four identical striplines on the same samples were exposed to different irradiation procedures. We performed irradiations as well parallel as under different angles with respect to the film -axis. Beside an enlarged normal state resistivity after irradiation the films suffer a T_c-reduction proportional to the volume of the damaged material. The activation energy ascertained from resistive transitions shows best enhancement for magnetic field values close to the matching field. Measurements of the transport critical current density, the activation energy and the irreversibility field in different field orientations show no anisotropic flux pinning due to the induced columnar defects. This can be explained by the two dimensional behaviour of the Bi₂Sr₂CaCu₂O₈-thin films.     

Kinetic Monte Carlo (KMC) simulation of fission product silver transport through TRISO fuel particle

A mesoscale kinetic Monte Carlo (KMC) model developed to investigate the diffusion of silver through the pyrolytic carbon and silicon carbide containment layers of a TRISO fuel particle is described. The release of radioactive silver from TRISO particles has been studied for nearly three decades, yet the mechanisms governing silver transport are not fully understood. This model atomically resolves Ag, but provides a mesoscale medium of carbon and silicon carbide, which can include a variety of defects including grain boundaries, reflective interfaces, cracks, and radiation-induced cavities that can either accelerate silver diffusion or slow diffusion by acting as traps for silver. The key input parameters to the model (diffusion coefficients, trap binding energies, interface characteristics) are determined from available experimental data, or parametrically varied, until more precise values become available from lower length scale modeling or experiment. The predicted results, in terms of the time/temperature dependence of silver release during post-irradiation annealing and the variability of silver release from particle to particle have been compared to available experimental data from the German HTR Fuel Program (Gontard and Nabielek [1]) and Minato and co-workers (Minato et al. [2]).     

Stability radii for positive linear time-invariant systems on time scales

We deal with dynamic equations on time scales, where we characterize the positivity of a system. Uniform exponential stability of a system is determined by the spectrum of its matrix. We investigate the corresponding stability radii with respect to structured perturbations and show that, for positive systems, the complex and the real stability radius coincide.     

Incoherent Beam Combining of Continuous-Wave and Pulsed Yb-Doped Fiber Amplifiers

We review the technique of incoherent beam combining and show experimentally the combination of four continuous wave fiber amplifiers to an average power of 2 kW and four pulsed 2 ns fiber amplifiers to an average power of 187 W (pulse energy 3.7 mJ) using binary dielectric gratings. The scaling potential and limitations are discussed in detail.