Dependence of critical current density on microstructure and processing of high-Tc superconductors

Microstructural origins for reduced weak-link behavior in high-J_c melt-processed YBCO, spray pyrolyzed thick films of Tl-1223, metallic precursor Y-124 polycrystalline powder-in-tube (PIT) wires and PIT Bi-2212/2223 are discussed. Since the materials studied are the highest J_c, polycrystalline, high-T_c superconductors fabricated worldwide, the results provide important guidelines for further improvements in superconducting properties, thereby enabling practical applications of these materials. It is found that strongly linked current flow within domains of melt-processed 123 occurs effectively through a single crystal path. In c-axis oriented, polycrystalline Tl-1223 thick films, local in-plane texture has been found to play a crucial role in the reduced weak-link behavior. Formation of “colonies” of grains with a common c-axis and modest in-plane misorientation was observed. Furthermore, a colony boundary in general has a varying misorientation along the boundary. Large regions comprised primarily of low angle boundaries were observed. Percolative transport through a network of such small angle boundaries appears to provide the nonweak-linked current path. Although powder-in-tube BSCCO 2212 and 2223 also appear to have a “colony” microstructure, there are some important differences. Colonies in BSCCO consist of stacks of grains with similar c-axis orientation in contrast to colonies in Tl-1223 films where few grains are stacked on top of one another. Furthermore, most grains within a colony in BSCCO have the same lateral dimensions as that of the colony, resulting largely largely in “twist” boundaries. Further microstructural characterization of high-J_c PIT 2212 and 2223 is currently underway. In the case of Y-124 wires, weak macroscopic in-plane texture is found. Additional measurements are underway to determine if a sharper, local in-plane texture also exists. It is found that in three of the four types of superconductors studied, reduced weak-link behavior can be ascribed to some degree of biaxial alignment between grains, either on a “local” or a “global” scale.     

Polymerization characteristics of a dye of anthraquinone

A technical dye of the anthraquinone type was analyzed by GPC, mass spectroscopy, and elemental analysis. Along with the polymerizable component, N-[4-amino-3-methoxyanthraquinonyl-(1)] methacrylamide (I), it contained a saturated admixture, N-[4-amino-3-methoxyanthraquinonyl-(1)]-2-chloro-2-methylpropionamide (II). The homopolymerization of I was carried out, and admixture II was isolated and characterized. The copolymerization of the dye with styrene and methyl methacrylate was verified, and the retardation effect of II on the polymerization of these monomers was evaluated.     

Quantitative comparison between full-spectrum and filter-based imaging in hyperspectral fluorescence microscopy

We implement a filterless illumination scheme on a hyperspectral fluorescence microscope to achieve full-range spectral imaging. The microscope employs polarisation filtering, spatial filtering and spectral unmixing filtering to replace the role of traditional filters. Quantitative comparisons between full-spectrum and filter-based microscopy are provided in the context of signal dynamic range and accuracy of measured fluorophores' emission spectra. To show potential applications, a five-colour cell immunofluorescence imaging experiment is theoretically simulated. Simulation results indicate that the use of proposed full-spectrum imaging technique may result in three times improvement in signal dynamic range compared to that can be achieved in the filter-based imaging.     

Artificial in-plane ordering of textured YBa2Cu3O7?x films deposited on polycrystalline yttria-stabilized zirconia substrates

Anisotropie surface texturing of the polycrystalline yttria-stabilized zirconia substrates, prior to YBa₂Cu₃O_7–x film deposition, is shown to promote in-plane (basal plane) ordering of the film growth in addition to thec-axis texturing. TheJ _c 's of the films in the weak-link-dominated low-field regime are enhanced considerably, and this result is attributed to the reduction of weak links resulting from a reduction in the number of in-plane large-angle grain boundaries.The authors acknowledge the support and encouragement of V. G. Keramidas and P. L. Key. This work was supported by the Electric Power Research Institute (Contract No. RP 7911-13).     

Compound prism design principles, I

Prisms have been needlessly neglected as components used in modern optical design. In optical throughput, stray light, flexibility, and in their ability to be used in direct-view geometry, they excel over gratings. Here we show that even their well-known weak dispersion relative to gratings has been overrated by designing doublet and double Amici direct-vision compound prisms that have 14° and 23° of dispersion across the visible spectrum, equivalent to 800 and 1300 lines/mm gratings. By taking advantage of the multiple degrees of freedom available in a compound prism design, we also show prisms whose angular dispersion shows improved linearity in wavelength. In order to achieve these designs, we exploit the well-behaved nature of prism design space to write customized algorithms that optimize directly in the nonlinear design space. Using these algorithms, we showcase a number of prism designs that illustrate a performance and flexibility that goes beyond what has often been considered possible with prisms.     

Compound prism design principles, III: linear-in-wavenumber and optical coherence tomography prisms

We extend the work of the first two papers in this series [Appl. Opt. 50, 4998-5011 (2011), Appl. Opt. 50, 5012-5022 (2011)] to design compound prisms for linear-in-wavenumber dispersion, especially for application in spectral domain optical coherence tomography (OCT). These dispersive prism designs are believed to be the first to meet the requirements of high resolution OCT systems in direct-view geometry, where they can be used to shrink system size, to improve light throughput, to reduce stray light, and to reduce errors resulting from interpolating between wavelength- and wavenumber-sampled domains. We show prism designs that can be used for thermal sources or for wideband superluminescent diodes centered around wavelengths 850, 900, 1300, and 1375 nm.     

Electrical properties of 1,4-cis-polybutadiene

This paper contains results on electrical conduction in 1,4-cis-polybutadiene. Measurements were performed for thin films of thickness from 1 to 10 um with gold and aluminium electrodes. Study was made in the temperature range from 15 to 325 K for two types of polybutadienes: (1) containing 100% of cis form, from Aldrich; (2) containing 96% of cis form, from Philips Petroleum Co. It was found that direct conduction is determined by the Poole-Frenkel effect with some hopping and the Schottky effect. Evaluation of activation energies gave results from 0.3 to 0.36 eV. © 1997 John Wiley & Sons, Ltd.     

Kerr modulators based on polymer-dispersed liquid crystal complexes

We have demonstrated a possibility to design light modulator based on Kerr effect using borate La₂CaB₁₀O₁₉ (LCBO) nanocrystallites incorporated into two different polymer-dispersed liquid crystal composites (PDLC). For this reason we have used different amount of the LCBO nanocrystallites to find the optimal conditions for the Kerr modulators. It was established that for the both PDLC systems the borate nanocrystals may be used for effective operation by elecrooptical susceptibilities varying the content of the nanocrystals. At the same time the frequency shift of the Kerr coefficient seems to be sensitive only for the LCBO nanocrystals content about 5% by weight. The maximal value of the Kerr coefficients were varied within the 4 × 10⁻⁹ to 6 × 10⁻¹⁰ m V^−2.