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Optimally doped ceramic superconductors (cuprates, pnictides, etc.) exhibit transition temperatures [T.sub.c] much larger than strongly coupled metallic superconductors like Pb ([T.sub.c] = 7.2 K, [E.sub.g]/k[T.sub.c] = 4.5) and exhibit many universal features that appear to contradict the Bardeen, Cooper, and Schrieffer theory of superconductivity based on attractive electron-phonon pairing interactions. These complex materials are strongly disordered and contain several competing nanophases that cannot be described effectively by parameterized Hamiltonian models, yet their phase diagrams also exhibit many universal features in both the normal and superconductive states. Here we review the rapidly growing body of experimental results that suggest that these anomalously universal features are the result of marginal stabilities of the ceramic electronic and lattice structures. These dual marginal stabilities favor both electronic percolation of a dopant network and rigidity percolation of the deformed lattice network. This 'double percolation' model has previously explained many features of the normal-state transport properties of these materials and is the only theory that has successfully predicted strict lowest upper bounds for [T.sub.c] in the cuprate and pnictide families. Here it is extended to include Coulomb correlations and percolative band narrowing, as well as an angular energy gap equation, which rationalizes angularly averaged gap/[T.sub.c] ratios, and shows that these are similar to those of conventional strongly coupled superconductors. percolation | theory doi/ 10.1073/pnas.0913002107

The stress analysis of High Temperature Superconducting (HTS) magnet for a 600 kJ superconducting magnetic energy storage (SMES) is discussed. Findings reveal that the HTS magnets are stable in radii stress and hoop stress.

The bending of High Temperature Superconducting (HTS) power cables and the force exerted by the bending process on the HTS tapes is examined. Findings reveal that it is possible to reduce the mechanical stress in the HTS tape by increasing the tape thickness as the friction force acting on an HTS tape is dependent on the width of the tape.

The study explains the effects of the bending and torsion strains on the values of the critical current in various YBCO coated conductors. The bend of the coil is shown to be extremely sensitive to the sample-tape thickness, as well as the sample-tape width.

The study investigates the dependence of the AC losses on the tensile stress in various conductors that are coated with high temperature superconductor (HTS) and have various magnetic substrates. The characteristics are found to depend on the recovery of critical current after the release of the stress.

Various tests and experiments are conducted to analyze and measure the axial compressive fatigue observed in the epoxy impregnated BSCCO coils. These coils are shown to exhibit very high critical current retention and mechanical stability at low values of stress.

Several tests are conducted to analyze the effects of Dy211 content on the bending mechanical properties of the Dy123 bulks at the room temperature. The analysis reveals that the average value of the Young's modulus increases with an increase in the Dy211 content.

The analysis describes the various electrochemical and thermal properties of Bi2223 and other high temperature superconductor (HTS) tapes. The results demonstrate that an increase in the tensile loads in the tape direction increases the value of the critical current of these tapes.

The study investigates the peculiarities of high-pressure oxygenation of the melt-textured Y[Ba.sub.2][Cu.sub.3][O.sub.x]-based thin-walled ceramics (MT-YBCO). The analysis shows that these ceramics acquire a higher microhardness after oxygenation.

The lattice defects and residual strain in layered perovskite [La.sub.2]Cu[O.sub.4+[delta]] (LCO) thin films, which are grown on LaSrAl[O.sub.4] and SrTi[O.sub.4] substrates, are investigated by using transmission electron microscopy and electron energy loss spectroscopy. The analysis has shown that the strain in LCO films on both the types of substrates are largely relaxed by the formation of misfit dislocation cores, although the small lattice mismatch is accommodated by elastic strain in the LCO film on the LaSrAl[O.sub.4] (LSAO) substrate.

This paper gives closed-form equations for the intermodulation and third harmonic signals generated in a nonlinear transmission line with distributed quadratic nonlinearities in the conductor and dielectric. Although the formulation developed is general, it is intended to be used in planar devices combining high-temperature superconductor (HTS) and oxide ferroelectrics. The analysis in this paper shows that the intermodulation and third harmonic signals produced by an HTS tend to cancel those of a ferroelectric, and that full cancellation is theoretically possible. This opens the way for using HTS/ferroelectric multilayers, not (only) for their tunable or phase-shifting properties, but for highly linear spurious-free planar HTS devices. Index Terms--Ferroelectric, high-temperature superconductor (HTS), intermodulation distortion (IMD), nonlinear transmission line (NLTL), nonlinearities, superconductor.

The tests of the Toroidal Field Model Coil (TFMC) are completed in the TOSKA facility of Forschungszentrun Karlsruhe. The TFMC isolated strand is characterized at different applied uniaxial strain, and preliminary results indicate a stronger reduction of carrying capacity compared to the extrapolation from summers scaling used in the analysis.

The support structure of the TF coils is designed to withstand the larger electromagnetic force on the basis of the stress analyses. The maximum displacement and the Tresca stress of the TF coil are evaluated in the cas4e of the plasma disruption at the end of plasma current flat-top.

The HFML has developed a design for a 30 T resistive insert to combine with an 11 T superconducting outsert to a 40+ T hybrid magnet. Design tools from NHMFL in Tallahassee FL are used to optimize the magnetic field, staying well within limits of available conductor ultimate tensile strength.

The study is conducted on mechanical performance of HTS coils with epoxy impregnation. The experimental results of repetitive hoop stress tests are discussed.

A cryogen-free 19 T superconducting magnet with a 52-mm room temperature bore is developed. The mechanical properties are investigated for oxide superconducting Bi-2223 tapes.

Two 15 m long longitudinal MAG welds along the shrinking cylinder, manufactured from AISI 316 LN stainless steel plates, close the cold mass and are submitted to tensile stress. The results of this study are meant to prove the robustness and reliability of the design at the working temperature of the magnets.

The study is conducted on the shear/compressive strength of GFRP under mixed load condition at low temperature. A new criterion for the shear/compressive static and fatigue failure is discussed.

The three directional strain states under applied tensile stress for various composite superconductors are analyzed using Finite Element Method (FEM). The experimental method and results are described.

The deformation and fracture behavior is studied in Sm123 bulk superconductors by comprehensive loading at room temperature. The effects of specimen length on the compressive mechanical properties are discussed.

Fracture toughness of SmBaCuO bulk superconductors is investigated by Vickers hardness test at cryogenic temperatures. The experimental procedure and test results are described.

Manufacturing techniques suitable for fabricating low AC loss high-temperature superconductor (HTS) coils are necessary to realize high-efficiency power equipment. A low mechanical loss, 30 a, 90 mH HTS coil is fabricated by winding with stainless-steel tape and employing epoxy impregnation.

Two superconducting closed coils are fabricated and the joint resistance of the coils by a field decay technique at 77 K is evaluated. (Bi, Pb)(sub 2)Sr2Ca2Cu3O(sub x)/Ag tape is wound in the form of double-pancake coils, and the ends of the tape are joined to each other by a resistive-joint method.

The degradation of critical currents I(sub c) owing to transversal-compressive force to bismuth tapes is presented and compressive force perpendicular to the Bi-2223 tape surface is applied to measure dependence of I(sub c) and n-values on the force. The result shows that the decreasing of the I(Sub c) is large when the damaged area on the compressed tape is small.

A study is conducted to examine the mechanical properties of the Gd123 single grain bulk superconductor at low temperature, bending test. The bending fracture strength at LNT scattered from 83 to 120 MPa is higher than that at RT, from 62 to 86 MPa.

Discussing the tensile strengths of bulk superconductors with and without resin impregnation is measured using a tensile testing machine is studied. It shows that the resin impregnation combined with the wrapping of carbon fiber fabric is effective in improving the mechanical properties of bulk superconductors is presented.