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The influence of hydrostatic pressure up to P=1.05 GPa on resistivity, excess conductivity σ ′ (T ) and pseudogap ∆ * (T ) is investigated in slightly doped single crystals of Y Ba2Cu3O 7−δ (Tc(P = 0) ≈49.2 K and δ ≈ 0.5). The critical temperature Tc is found to increase with increasing pressure at a rate dTc/dP = +5.1 KGP a −1 , while ρ(300) K decreases at a rate dlnρ/dP = (−19±0.2)% GP a −1 . Near Tc, independently on pressure, the σ ′ (T ) is well described by the Aslamasov-Larkin and HikamiLarkin fluctuation theories, demonstrating a 3D-2D crossover with increase of temperature. The crossover temperature T0 determines the coherence length along the c-axis ξc(0) ≃ (3.43 ± 0.01)Å at P=0, which is found to decrease with increasing P. At the same time, ∆ * and the BCS ratio 2∆ * /kB Tc both increase with increasing hydrostatic pressure at a rate dln∆ * /dP ≈ 0.36 GP a −1 , implying an increase of the coupling strength with increasing P. At low temperatures below Tpair, the shape of the ∆ * (T ) curve is found to be almost independent on pressure. At high temperatures, the shape of the ∆ * (T ) curve changes noticeably with increasing P, suggesting a strong influence of pressure on the lattice dynamics. This unusual behavior is observed for the first time.

The effects of praseodymium doping on the excess conductivity σ′(T) and pseudogap (PG) Δ*(T) in Y1–xPrxBa2Cu3O7–δ single crystals with a change in the Pr concentration from x = 0 to x = 0.43 are presented. It is found that as x increases the resistance of the samples increases, whereas the critical temperature Tc drops. At the same time the shape of the ρ(T) curves changes from metallic (x ≤ 0.34) to one that is typical for weakly doped YBa2Cu3O7–δ single crystals with a characteristic thermally activated deflection (x > 0.34). Regardless of the value of x, close to Tc, σ′(T) is well described by the Aslamazov-Larkin and Maki-Thompson theories, demonstrating a 3D-2D crossover with increasing temperature. The crossover temperature T0 makes it possible to determine the coherence length along the c axis, ξc(0). At x = 0, Δ*(T) displays a maximum at Tpair ≈ 110 К that is typical for YBCO films. As x increases the maximum at Tpair is washed out, but a pronounced maximum Δ*(T) in the high temperature region appears, followed by a linear section with a positive slope. Such a dependence Δ*(T) is normal for magnetic superconductors and is, most likely, caused by the influence of the intrinsic magnetic moment of Pr (μPr ≈ 4μB).

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The problem of monolithic behavior of a metal pipe and fiberglass safety cage has been considered in the article. The prestressed case does not only decrease the deformability of a pipe on-load but it also protects metal from corrosion. The ability to withstand the arising stresses has been investigated for both strip fiberglass reinforcement and the whole construction. It has been shown that the deformability of fiberglass depends on the kind of binder. The maximum strength value has been obtained while gluing glass fibers with butvar-phenolic glue. The calculated rupture strength coefficient of strip fiberglass reinforcement and the analysis of monolithic behaviour of metal and reinforcement proved the precondition as to the plasticity of a developed material. The process of force transmission between a steel pipe and fiberglass at ductile stage has been analyzed in the article. While forecasting the work of a pipe on-load, it is necessary to take into account nonlinearity of metal-fiberglass pipe properties.