Search for Cooper-pair Fluctuations in Severely Underdoped YBCO Films

The preformed-pairs theory of pseudogap physics in high-$T_C$ superconductors predicts a nonanalytic $T$-dependence for the $ab$-plane superfluid fraction, $\rho_S$, at low temperatures in underdoped cuprates. We report high-precision measurements of $\rho_S(T)$ on severely underdoped YBa$_2$Cu$_3$O$_{6+x}$ and Y$_{0.8}$Ca$_{0.2}$Ba$_2$Cu$_3$O$_{6+x}$ films. At low $T$, $\rho_S$ looks more like $1 - T^2$ than $1 - T^{3/2}$, in disagreement with theory.Comment: 3 pages, 2 figure

The influrence of an optical receiving system on statistical characteristics of a lidar signal

The effects connected with correlation of direct and backward waves propagating through the same randomly inhomogeneous media can be observed along the path with refection in a turbulent atmosphere. In particular, the mean intensity of the reflected wave can increase in comparison with the wave propagating in the forward direction at a doubled distance; the intensity fluctuations can become stronger. These effects depend on the strength of optical turbulence, as well as on the diffraction sizes of the exit apertures of the source and the reflector. However, the focusing of radiation reflected with a receiving telescope leads, in some cases, to the fact that the dependence of amplification effects on the parameters becomes essentially different. This should be taken into account when alayzing the lidar signals. The effect of backscattering amplification and amplification of the intensity fluctuations is discussed

Correlation between superfluid density and Tc of underdoped YBa2Cu3O6+x near the superconductor-insulator transition

We report measurements of the ab-plane superfluid density Ns (magnetic penetration depth, \lambda) of severely underdoped films of YBa2Cu3O6+x, with Tc's from 6 to 50 K. Tc is not proportional to Ns(0); instead, we find Tc ~ Ns^{1/2.3 +/- 0.4}. At the lowest dopings, Tc is as much as 5 times larger than the upper limit set by the KTB transition temperature of individual CuO2 bilayers.Comment: 4 pages, 2 figures, Submitted to Phys. Rev. Let

Research of the plastic deformation localization of bimetal

The aim of this contribution was to study the localization of the plastic deformation of bimetal based on a low-carbon steel A 283 Grade C and austenitic stainless steel 301 AISI. The images of the localized zone plastic deformation upon the uniaxial tension have been obtained with using digital image correlation method (DIC). The stress-strain curves are found to show all the plastic flow stages: yield plateau, linear and parabolic work hardening stages and the prefracture stage would occur for the respective values of the exponent from the Ludwik-Holomon equation. The main parameters of plastic flow localization at various stages of the deformation hardening have been determined in bimetal

Zirconium Alloy Mechanical State and its Evolution during Deformation

  &nbsp

Research of the plastic deformation localization of bimetal

The aim of this contribution was to study the localization of the plastic deformation of bimetal based on a low-carbon steel A 283 Grade C and austenitic stainless steel 301 AISI. The images of the localized zone plastic deformation upon the uniaxial tension have been obtained with using digital image correlation method (DIC). The stress-strain curves are found to show all the plastic flow stages: yield plateau, linear and parabolic work hardening stages and the prefracture stage would occur for the respective values of the exponent from the Ludwik-Holomon equation. The main parameters of plastic flow localization at various stages of the deformation hardening have been determined in bimetal

Crystal structure and oxygen content of the double perovskites GdBaCo 2-xFexO6-δ

The iron solubility limit, x, in GdBaCo2-xFexO 6-δ determined by means of X-ray diffraction was found to be close to 0.65 in air. The crystal structure changes of the double perovskites GdBaCo2-xFexO6-δ (x=0-0.6) were studied by means of in situ X-ray diffraction in temperature range from 25 to 900 °C in air. The oxygen content, 6-δ, was determined for these double perovskites in air as a function of temperature by means of thermogravimetric technique in range 25≤T, °C≤ 1100. The Pmmm-P4/mmm structure transition was found to occur in GdBaCo2-xFexO 6-δ (0≤x≤0.4) with increasing temperature. This transition is observed at the same temperature for the compositions with 0≤x≤0.1 while the transition temperature reaches maximum for x=0.2 and that decreases linearly with further iron increase. The double perovskite GdBaCo1.4Fe0.6O6-δ was shown to have the tetragonal P4/mmm structure at room temperature. The P4/mmm-Pmmm structure transition occurs at temperature as low as 170 °C for this double perovskite while reverse one is already observed at 290 °C in air. The Pmmm-P4/mmm structure transition was found to be strongly related to the oxygen content for the undoped and slightly doped (x≤0.2) double perovskites while there is no such relation for the double perovskites enriched by iron (x≥0.2). © 2012 Elsevier Inc. All rights reserved

New Evidence for Supernarrow Dibaryons Production in pd Interactions

The analysis of new experimental data, obtained at the Proton Linear Accelerator of INR, with the aim to search for supernarrow dibaryons in the $pd\to ppX_1$ and $pd\to pdX_2$ reactions is presented. Narrow peaks with an experimental width of 5 MeV at masses of 1904$\pm 2$, 1926$\pm 2$, and 1942$\pm 2$ MeV have been observed in missing mass $M_{pX_1}$ spectra. In the missing mass $M_{X_1}$ spectra, the peaks at $M_{X_1}=966\pm 2$, 986$\pm 2$, and 1003$\pm 2$ MeV have been found. The analysis of the data obtained leads to the conclusion that the observed peaks in $M_{pX_1}$ spectra are most likely supernarrow dibaryons, the decay of which into two nucleons is forbidden by the Pauli exclusion principle. An alternative interpretation of the spectra by assuming a decay of the supernarrow dibaryons in "exotic baryon states" with masses $M_{X_1}$ is discussed.Comment: 17 pages, 6 figures. Considerably expanded version accepted for publication in Eur. Phys. J. A; a discussion, 4 figures and several references have been added, the title has been change

Transition from columnar to point pinning in coated conductors: critical currents, that are independent of magnetic field direction

We identify a phase transition in the vortex system of a high-temperature superconductor with nano-columnar stacks of precipitates as strong vortex pinning centers. Above a particular, temperature-dependent field $B_X(T)$ the vortex response is no longer determined by the nano-columns, and is instead determined by point-like pinning. This phase transition leads to the change in the measured critical current density as a function of angle between the applied magnetic field and the nano-columns. Below the unbinding, there is a strong maximum in $J_C$ when field is aligned parallel to the columns. Above the unbinding, there is a minimum for this orientation.Comment: Formatted for AP