Local structure of nanopowders of refractory nitrides used to increase the critical current of high-temperature superconductors
The effect of dispersivity on the local-structure features in ZrN nanocrystals has been investigated by X-ray absorption (EXAFS) spectroscopy. The Debye-Waller factors and bond lengths have been determined for Zr-N and Zr-Zr coordination spheres. It is found that a decrease in the nanoparticle size leads to an increase in the static Debye-Waller factor for the Zr-Zr bond. The scale of changes is comparable with the increase in the Debye-Waller factor upon heating from 15 to 77 K.
Physicochemical methods of enhancing the performance of high-Tc superconductors
Experimental data are summarized on the optimization of the performance of YBa2 Cu3O7–x, Bi2Sr2CaCu2OP8+δ, and (Bi,Pb)2Sr2Ca2Cu3O10 +δhigh–Tc ceramics by producing structural defects via irradiation or doping with metals and different inorganic compounds. A classification of additions is proposed according to their interaction with the superconductors. For additions having an advantageous effect on the superconducting and mechanical properties of the high–Tc materials, the optimum concentration and size ranges are indicated.
Observations of nearshore infragravity waves: Seaward and shoreward propagating components
[1] The variation of seaward and shoreward infragravity energy fluxes across the shoaling and surf zones of a gently sloping sandy beach is estimated from field observations and related to forcing by groups of sea and swell, dissipation, and shoreline reflection. Data from collocated pressure and velocity sensors deployed between 1 and 6 m water depth are combined, using the assumption of cross-shore propagation, to decompose the infragravity wave field into shoreward and seaward propagating components. Seaward of the surf zone, shoreward propagating infragravity waves are amplified by nonlinear interactions with groups of sea and swell, and the shoreward infragravity energy flux increases in the onshore direction. In the surf zone, nonlinear phase coupling between infragravity waves and groups of sea and swell decreases, as does the shoreward infragravity energy flux, consistent with the cessation of nonlinear forcing and the increased importance of infragravity wave dissipation. Seaward propagating infragravity waves are not phase coupled to incident wave groups, and their energy levels suggest strong infragravity wave reflection near the shoreline. The cross-shore variation of the seaward energy flux is weaker than that of the shoreward flux, resulting in cross-shore variation of the squared infragravity reflection coefficient (ratio of seaward to shoreward energy flux) between about 0.4 and 1.5.