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We demonstrate experimentally a setup with which a two-dimensional picture can be transmitted from one plane to another at a signal request of the latter plane and the original picture continues to propagate unhindered along its original direction to the next stage. The setup makes use of photorefractive four-wave mixing and the self-pumped phase conjugation for its operation. Some means for increasing the contrast of the final transmitted image have been discussed.

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We have measured the resistive transition of molecular beam epitaxy prepared Bi 2 Sr 2 CaCu 2 O 8+x thin films in the presence of perpendicular low magnetic fields H (0 Oe < H < 1100 Oe) for different values of the bias current density J (10 2 A cm −2 < J < 10 5 A cm −2 ). The experimental data show two distinct dissipative behaviours. In the low-current region (J < 10 3 A cm −2 ) the electrical resistivity ρ is independent on J , changing only with H , while in the high-current region (J > 10 4 A cm −2 ) ρ is independent of both the bias current and the magnetic field. The result is considered in terms of thermally activated flux flow-flux creep-steady flux flow crossovers. The role of the statistical distribution of the pinning energy in the vortex dynamics is discussed.