Nonlinear effects at high flux-flow electric fields.

Ohm's law with the linear relation between resistive voltage and electric current is strictly valid only in the limit of infinitesimally small voltages. On the other hand, at finite electric voltages nonlinearities in the electric resistance can develop due to the energy picked up by the charge carriers in the electric field. This can lead to important effects both in the case of semiconductors and of superconductors, where the energy rise of the charge carriers or the quasiparticles can become relatively large.

Flux-flow resistivity anisotropy in the instability regime of the a-b plane of epitaxial superconducting YBa2Cu3O7-delta thin films.

Measurements of the nonlinear flux-flow resistivity rho and the critical vortex velocity vphi* at high voltage bias close to the instability regime predicted by Larkin and Ovchinnikov (Z. Eksp. Teor.

[Antimicrobial resistance in Streptococcus pneumoniae in Beijing and molecular typing of penicillin-resistant strains].

Objective: To investigate antimicrobial resistance of Streptococcus pneumoniae in Beijing and molecular epidemiology of penicillin-resistant pneumococci strains.

Methods: The resistance to beta-lactam and non-beta-lactam antibiotics of 244 nasopharyngeal isolates of Streptococcus pneumoniae collected from September to November 1997 in 8 day-care centers in Beijing was studied by Etest and agar dilution method. Serotyping was done by "capsular swelling" technique.

Spatially Resolved Observation of Static Magnetic Flux States in YBa2Cu3O7-dgr Grain Boundary Josephson Junctions.

With low-temperature scanning electron microscopy, the magnetic flux states in high critical temperature Josephson junctions have been imaged. The experiments were performed with YBa(2)Cu(3)O(7-delta) thin-film grain boundary Josephson junctions fabricated on [001] tilt SrTiO(3) bicrystals. For applied magnetic fields parallel to the grain boundary plane, which correspond to local maxima of the magnetic field dependence of the critical current, the images clearly show the corresponding magnetic flux states in the grain boundary junction.