[en] The confinement scenario in N = 2 supersymmetric gauge theory at the monopole point is reviewed. Basic features of this U (1) confinement are contrasted with those expected in QCD. In particular, extra states in the hadron spectrum and nonlinear Regge trajectories are discussed. Then another confinement scenario arising on Higgs branches of the theory with fundamental matter is also reviewed. Peculiar properties of the Abrikosov-Nielsen-Olesen string on the Higgs branch lead to a new confining regime with the logarithmic suppression of the linear rising potential. Motivations for a search for tensionless strings are proposed

[en] Short communication

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No abstract available

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[en] In analogy with well-known intermediate-valent Tm-Te-Se alloys, Sm_1-xLa_xS, with x = (0.10, 0.25, 0.35), and Sm_1-yTm_yS, with y = (0.10, 0.15), have also turned out as excitonic insulators under high pressure and low temperatures. The condensation of excitons results from strong Coulomb attraction between 4f holes and 5d conduction electrons, which is enhanced by external hydrostatic pressure. By hybridization in the intermediate-valent ground state, a narrow 4f band forms and lends the holes a high effective mass. Thus, the mobility of the excitons is reduced, and low temperature prevents their thermal dissociation. A sufficient exciton density triggers a Bose condensation. In the cryogenic range, the electrical resistivity of the pressurized samples indicates a gap of meV magnitude, corresponding to the activation energy of the excitons. Further pressure being applied closes the gap continuously, since more and more valence electrons pass into the conduction band and screen the Coulomb interaction. Finally, the integer-valent metallic phase is reached. (orig.)

[en] Thermal expansion of intermediate valence compound Sm_0.9La_0.1S has been measured under high pressure up to 2.1 GPa in the temperature range, 4.2≤T≤300 K. It is found that the thermal expansion shows a smooth variation below 0.5 GPa but an anomalously large expansion, i.e., a large negative thermal expansion coefficient is observed at low temperature above 0.5 GPa. These results are related to the pressure-induced metal-insulator transition. The negative anomaly in the thermal expansion coefficient is suggested to be due to the negative Grueneisen parameter of the energy gap

[en] Brillouin scattering on surface acoustic waves is a very powerful tool to determine the elastic constants of intermediate valent crystals, since the method is non-destructive and no mechanical contact is needed. A strong evidence for intermediate valence is a negative value of Poisson's ratio, which describes the behavior of the volume under uniaxial pressure. SmS by itself makes a semiconductor-metal transition at a pressure of more than 6.5 kbar. When substituting the divalent Sm by a trivalent cation, like Y, La or Tm, SmS can become - depending on the doping concentration - intermediate valent without any applied, external pressure. In this work, we will present measurements of the velocities of the surface acoustic waves and the calculation of the elastic constants of La- and Tm-doped SmS compounds. We found a clear dependence of Poisson's ratio on the doping concentration and on the valence of the materials. Furthermore, we will discuss the mechanism leading to intermediate valence when substituting Sm. Besides the internal, chemical pressure, which is produced by the built in trivalent cations with their smaller ionic radii, we have clear evidence, that the free electrons in the 5d band, induced by the substituting atoms, also play an important role in making doped SmS intermediate valent. (orig.)

[en] The motivation of this research is to understand the flow behavior through a 90° T- type bifurcation, which connects a Francis turbine and the storage pump of a ternary unit, under different operating conditions (namely turbine, pump and hydraulic short-circuit operation). As a first step a CFD optimization process to define the hydraulic geometry of the bifurcation was performed. The CFD results show the complexity of the flow through the bifurcation, especially under hydraulic short-circuit operation. Therefore, it was decided to perform experimental investigations in addition to the CFD analysis, in order to get a better understanding of the flow. The aim of these studies was to investigate the flow development upstream and downstream the bifurcation, the estimation of the bifurcation loss coefficients and also to provide comprehensive data of the flow behavior for the whole operating range of the machine. In order to evaluate the development of the velocity field Stereo Particle Image Velocimetry (S-PIV) measurements at different sections upstream and downstream of the bifurcation on the main penstock and Laser Doppler Anemometrie (LDA) measurements at bifurcation inlet were performed. This paper presents the CFD results obtained for the final design for different operating conditions, the model test procedures and the model test results with special attention to: 1) The bifurcation head loss coefficients, and their extrapolation to prototype conditions, 2) S-PIV and LDA measurements. Additionally, criteria to define the minimal uniformity conditions for the velocity profiles entering the turbine are evaluated. Finally, based on the gathered flow information a better understanding to define the preferred location of a bifurcation is gained and can be applied to future projects

[en] Coated conductors are becoming more and more applicable. The temperature range below the critical value (T_c) or below the critical current (I_c) is well characterized. But for applications such as fault current limiters, which take advantage of the superconducting-to-normal transition, characterization beyond the superconducting regime is mandatory. Therefore, this work studies the thermodynamic behaviour of a coated conductor immersed in boiling liquid nitrogen which is driven by a sinusoidal over-current of up to more than five times I_c. The temperature of the coated conductor exceeds 720 K without any significant degradation. To validate this current-induced high-temperature region, the resistance of the composite tape is measured from T_c to 600 K. A thermodynamic and electrical model is conceptualized for calculating the temperature, developing as a function of time during over-currents. The calculated temperature fits well with the measured temperature