Processing and characterisation of long-length silver/bismuth-2223 tape for electric power applications
The potential of high temperature superconductivity (HTS) to raise efficiencies in electric power utilisation is dependent on the availability of HTS materials in a form which can be engineered into devices. This paper reviews a program of continuous process and product improvement which has enabled tape with lengths up to 1000 m and appropriate engineering properties to be reproducibly processed using the powder-in-tube technique. Underpinning this development of a large scale process capability, tape development on a small scale was necessary in the areas of innovative tape design, metal forming optimisation and heat treatment. In addition, techniques for the characterisation of long lengths of tape were developed. These techniques included the modelling of the effect of the self-field generated by the tape under test at 77 K to enable zero field Ic data to be determined.
Uranium doping of silver sheathed bismuth-strontium-calcium-copper-oxide superconducting tapes for increased critical current density through enhanced flux pinning
A combination of uranium doping with thermal neutron irradiation has been well demonstrated to be one of the most effective means to introduce pinning centres in (Bi,Pb) 2 Sr 2 Ca 2 Cu 3 O x /Ag tapes (Bi-2223/Ag). A substantial improvement in flux pinning and reduction of anisotropy in uranium doped Bi-2223/Ag tapes has been achieved due to thermal neutron irradiation. However, the radioactivity of the silver sheath is too high for practical application of this technique. This work aimed at minimising the detrimental effects of doping to allow for later irradiation and fission to create columnar defects for strong flux pinning. A number of uranium containing compounds, U 3 O 8 , U(Ca,Sr) 2 O 5 , and U(Ca,Sr) 3 O 6 have been identified in the U-Bi-Sr-Ca-Cu-O system. These equilibrium compounds have been synthesised and added to Bi-2223/Ag composite tapes in progressively greater amounts. The effects on the transport critical current density of Bi-2223/Ag of doping with a variety of uranium compounds up to 2 at% was determined. The compatibility and interaction between uranium compounds and the Bi-2223 matrix was systematically studied under various thermal processing conditions. Bi-2223/Ag doped with compounds using compositions closer to the equilibrium composition was shown to have superior superconducting properties to that doped with uranium oxide compounds. The effects of chemical degradation by uranium compound dopants via strontium and calcium removal from the Bi-2223 structure have been indirectly determined by critical current density (J c ) measurements. Losses in J c can be minimised by stabilising uranium into appropriate compounds.
The Arab Spring: The End of Postcolonialism
* Introduction: The Arab Spring: The End of Postcoloniality * 1. Decentering the World: How the Arab Spring Unfolded * 2. Towards Liberation Geography * 3. A New Language of Revolt * 4. Discovering a New World * 5. From the Green Movement to the Jasmine Revolutions * 6. The center cannot hold * 7. The End of Postcolonialism * 8. Race, Gender, and Class in Transnational Revolutions * 9. Libya: The Crucible * 10. Delayed Defiance * Conclusion. The People Demand the Overthrow of the Regime