Strong 3D correlations in vortex system of Bi2212:Pb

The experimental study of magnetic flux penetration under crossed magnetic fields in Bi2212:Pb single crystal performed by magnetooptic technique (MO) reveals remarkable field penetration pattern alteration (flux configuration change) and superconducting current anisotropy enhancement by the in-plane field. The anisotropy increases with the temperature rise up to $T_m = 54 \pm 2 K$. At $T = T_m$ an abrupt change in the flux behavior is found; the correlation between the in-plane magnetic field and the out-of-plane magnetic flux penetration disappears. No correlation is observed for $T > T_m$. The transition temperature $T_m$ does not depend on the magnetic field strength. The observed flux penetration anisotropy is considered as an evidence of a strong 3D - correlation between pancake vortices in different CuO planes at $T < T_m$. This enables understanding of a remarkable pinning observed in Bi2212:Pb at low temperatures.Comment: 8 pages, 9 figure

Vortex Collisions: Crossing or Recombination?

We investigate the collision of two vortex lines moving with viscous dynamics and driven towards each other by an applied current. Using London theory in the approach phase we observe a non-trivial vortex conformation producing anti-parallel segments; their attractive interaction triggers a violent collision. The collision region is analyzed using the time-dependent Ginzburg-Landau equation. While we find vortices will always recombine through exchange of segments, a crossing channel appears naturally through a double collision process.Comment: 4 pages, 3 figure

Improvement of continuous calibration based on temperature oscillation and application to biochemical reaction calorimetry

This paper describes an improvement of a method for continuous calibration of the global heat transfer coeff., recently described in literature [A. Tietze, Moglichkeiten und Grenzen der Temperaturschwingungskalorimetrie, Doctoral Thesis, Technishe Universitat Berlin, 1998; Chem. Eng. Sci. 51 (1996) 3131; Chem. Ing. Tech. 68 (1996) 97]. The continuous calibration method is based on induced sinusoidal jacket temp. oscillations, allowing the uncoupling of the chem. heat prodn. from the heat transfer parameters during the reaction. A math. computation procedure based on two-anchors, before and after the reaction, has been developed which gives better results as compared to the one reported in literature, using one-anchor only, either before or after the reaction. The applicability of this method to biotechnol. has been explored with respect to different culture parameters, which affect the global heat transfer coeff., i.e. stirring speed, reactive vol., and medium viscosity. This oscillating reaction calorimetry method (ORC) has been successfully applied to a fed-batch culture of Saccharomyces cerevisiae with a non-linear increase of reactive vol. [on SciFinder (R)